WO2000013786A1 - Device with plasma from mobile electric discharges and its applications to convert carbon matter - Google Patents

Abstract

A process and system for using plasma from mobile electric discharges for conversion of a carbon substance. The process and system (R) use plasma from mobile electric discharges (7) for conversion of carbon substances, such as light hydrocarbons, heavy hydrocarbons or residues from refining these, CO2 or CO into products such as gases containing CO and/or H2 and/or C2H4 and C2H 2 and/or liquid carbon fuels. The conversions are based on oxidation and/or cracking of the matter in the presence of water vapor and of gas such as CO2, O2, N2, H2, alone or mixed. The system generates a non-equilibrium plasma by very rapidly stretching the discharges (7) established between at least one fixed electrode (r, s, t) and at least one mobile electrode (d). The non-equilibrium plasma sweeps the gas passing through the reactor in order to stimulate chemical conversions. The flow of the matter activated by the plasma entering through (k) may pass through one or more discharge stages (d1, d2, d3, d4) and may be brought into contact with a metal or ceramic body placed near the discharges before exiting through (1). This body becomes active in the presence of the catalytic species originating from the plasma and thus participates in the continuation of the conversion.

Description

TITLE: DEVICE WITH PLASMA FROM MOBILE ELECTRIC DISCHARGES AND ITS APPLICATIONS TO CONVERT CARBON MATTER

BACKGROUND OF THE INVENTION

1 Field of the Invention

The invention relates generally to the conversion of carbon substances and more particularly to the use of fixed and mobile electrodes to stretch discharges and create an off equihbnum plasma for stimulating conversion reactions

2 Description of Related Art

The production of synthesis gas starting from light hydrocarbons (HCs) is a very well-known and very important stage, especially for upgrading natural gases and biogases (mixtures with mainly almost equal contents of methane and carbon dioxide) onginating from anaerobic fermentation of an organic substance The chemical upgrading of enormous natural gas (NG) resources may happen to be a much more attractive way than its total combustion limited to direct recovery of energy in ovens, boilers or turbines Situations also occur in which NGs with high HC content are released into the atmosphere without any recovery of energy, examples of this are found in the oilfield flares which burn a so-called "associated" hydrocarbon gas or the emissions of biogas Any emission of a uselessly burned (and especially not burned) HC contnbutes heavily to air pollution The process most often used now to produce synthesis gas, catalytic steam reforming (or "steam reforming") encounters major problems In principle, it needs only high temperature (thermodynamic reason) and high pressure (kinetic reason). However, in practice, despite the know-how for the production of SG according to this process, mastering the combination of composition, pressure and temperature is difficult, even impossible without resorting to catalysts In order to reform NG with steam, usually a catalyst is used presence of a solid substance in highly dispersed and active form (with a specific surface area of at least approximately one hundred square meters per gram) for temperatures which can be reached without too many problems The traditional steam reforming technology uses ovens in which several hundred fragile metal pipes are located (filled with a catalyst and with a length which may attain several tens of meters), heated externally to the NG Hence, the large quantities of carbon dioxide onginating from the combustion are ejected into the atmosphere by these ovens with a very poor thermal yield Moreover, this technology is tied to very high pressure losses The temperature which can be withstood by the oven pipes prevents also a decrease in CO, content in the SG itself (C0₂ is a hindrance product onginating from a parasite reaction at too low a temperature) Other problems are tied to catalyst poisoning by sulfur and/or nitrogen, aging the catalysts, the necessary excess of steam and/or the formation of soot (which blocks the entire tubular system at macroscopic scale and, above all, the microscopic pores of the catalyst) These problems are observed mostly at the time of steam reforming of heavier HCs (heavier than methane) which are more fragile and, therefore, more coking

Dry reforming of HCs with carbon dioxide is not yet used lndustnally, since it requires the presence of catalysts capable of withstanding high temperatures in a highly coking medium Research is still actively pursued, since this reforming would have important applications to produce a CO nch SG, for example for "oxo" syntheses, starting from NGs (or biogases) with high CO, content and, for this reason, considered less valuable Partial oxidation (reaction 6 or 6a) is sometimes achieved industnally but it requires always special care to prevent explosion of a reactor when the 0,/NG ratio is exceeded We will see that this nsk disappears in the presence of our mobile electnc discharges always present in the reactive medium

SUMMARY OF THE INVENTION

Broadly speaking, the invention compnses a method and system for converting carbon substances in plasma-chemical reactors based on mobile electric discharges The discharges cause high activation of the medium by unusual species (with respect to the traditional conditions of conversions) onginating from the matter in which these discharges develop Thus, electrons, atoms, ions and molecular radicals such as H, OH, O, 0₂, H⁺, 0⁺, 0₂ ⁺ 0₂ , H0₂, CH₃, CH₂, CH, C₂ and many others are detected Most of these species may exist in their electronic or vibratory excited states with a rather long lifetime They are also known to be extremely chemically active

In one embodiment, a device compnses one or more fixed electrodes and one or more mobile electrodes Discharges established between the fixed electrodes and the mobile electrodes generate an off equihbnum plasma by very rapidly stretching the discharges between the electrodes and thereby causing the off equihbnum plasma to sweep the gas passing through the reactor in order to stimulate chemical conversions The flow of the matter activated by the plasma may be brought into contact with a metal or ceramic body placed near discharges This body becomes active in the presence of the catalytic species onginating from the plasma and thus participates in the continuation of the conversion

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and advantages of the invention will become apparent upon reading the following detailed description and upon reference to the accompanying drawings in which

Fig 1 is an illustration of a toothed mobile electrode used in one embodiment

Fig 2 is an illustration of a multiple-stage reactor using mobile disk electrodes Fig 3 is an illustration of a mobile electrode composing a circular brush

Fig 4a is an illustration of an embodiment using an inductor to alter the phase of the terminal voltage with respect to the discharge current and voltage

Fig 4b is a graph of the terminal voltage, discharge current and discharge voltage for the embodiment illustrated in Fig 4a While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example m the drawings and will herein be described in detail It should be understood, however, that the drawing and detailed description thereto are not intended to limit the invention to the particular form disclosed, but on the contrary, the mtention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the present invention as defined by the appended claims

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The system descnbed herein proposes a device with high voltage mobile discharges, as well as its application for the conversion of hydrocarbons and/or carbon dioxide and/or carbon monoxide

We propose first an endothermic process with upgrading conversion of light hydrocarbons (HCs) aided by a specific plasma generated in a device with mobile electric discharges in the presence of carbon dioxide C0₂ or steam or of an H₂0/C0₂ mixture. We can also add to the HC load an amount of oxygen (either pure or contained in the air or in any mixture) in order to obtain partial oxidation of the feed. The processes are illustrated by the conversion of natural gas (NG) containing mostly methane, but also some ethane, propane and butanes. The process can thus be applied to any pure HC, such as CH₄, C₂H₆, C₃H₈ or C₄H₁₀, as well as to their mixtures of natural or industrial origin. In the presence of steam, we convert CH₄ (and other light HCs) into "synthesis gas" (SG) consisting mostly of hydrogen and of carbon monoxide CO and also of other valuable products, such as ethylene C₂H₄ and acetylene

C₂H₂, without using traditional catalysts. The process is based mainly on steam reforming reactions, such as:

CH₄ + H₂O_vap → CO + 3 H₂ (1)

knowing that the heavier hydrocarbons C_nH_m will undergo similar steam reforming:

C_nH_m + n H₂O_vap → n CO + (n +^m/₂) H₂. (la)

We observe, at the same time, methane cracking according to the following reactions:

2 CH₄ → C₂H₄ + 2 H₂ (2)

2 CH₄ → C₂H₂ + 3 H₂ (2a)

H₄ → C + 2 H₂ (2b)

and similar cracking of heavier HCs yielding acetylene, ethylene, propylene C₃H₆ and other unsaturated olefϊnic and/or acetylenic HCs. Also, part of the CO produced undergoes a slightly exothermal conversion called "water shift":

CO + H₂O_vap → C0₂ + H₂. (3)

Thus, at the time of said steam reforming of a NG or of another HC mixture, we produce a SG containing all these gases produced by reaction (1) through (3), in unusual ratios with respect to the conventional methods of production of a "classic" SG. We propose then "dry" reforming of the NG (or of another HC mixture) with carbon dioxide according to the following reaction:

CH₄ + C0₂ → 2 CO + 2 H₂ (4)

knowing that other C_nH_m hydrocarbons react in a similar manner:

C_nH_m + n CO, → 2n CO + ^m/₂ H, (4a) and that said conversion is accompanied by cracking reactions, such as (2), (2a) and (2b). At the same time, we also observe a conversion called "inverse water shift":

C0₂ + H, → CO + H₂O_vap (5)

following the appearance of the hydrogen (reactions 4 and 4a) in the mixture containing C0₂ which has not yet reacted. Thus, at the time of said dry reforming of a NG or of another HC mixture or even of a biogas (mixture of CH₄ with C0₂) we produce a SG containing all the above-mentioned molecules.

Obviously, we can mix the two oxidizers, H₂0 and C0₂ in any ratios and make them react with a NG or another mixture of HCs, in order to perform a "mixed" conversion based simultaneously on the previously mentioned reactions, each of these reactions being weighted according to the specification of the product desired and as a function of the load to be converted.

Reaction (4) or (4a) of the "dry" reforming can also be considered as an upgrading conversion of C0₂, a gas suspected of causing the greenhouse effect; of course, that will depend on the main objective of the industrial operation considered.

In the presence of elemental oxygen, we observe weakly exothermal reactions of partial oxidation of the methane and or of its paraffinic homologues:

C_nH_2n+2 + 7₂ 0₂ → n CO + (n+ 1 ) H₂, (6a)

as well as methane dimerization:

2 CH₄ + '/_ 0₂ → C₂H₆ + H₂O_vap. (7)

Partial oxidation of very heavy HCs can also be carried out in order to convert them to lighter liquid hydrocarbons. Therefore, this would consist of slightly oxidizing cracking with high added value.

In the presence of mobile electric discharges, we observe also all the other conversions described by equations (1) through (7) and also a complete parasite combustion and highly exothermal reaction:

CH₄ + 2 0₂ → CO, + 2 H₂O_vap. (8)

However, this reaction is minor, since its products are to a large extent consumed by profitable reactions (1) or (la) and (4) or (4a) or neutral reactions (3) and/or (5). Nothing prevents partial oxidation (6) or (6a) in the presence of steam and/or carbon dioxide already present in the feed or added, in order to proceed with a 0₂/H₂0 or 0₂/CO, or even 0₂/H₂0/C0₂ hybrid conversion, so as to obtain a SG with a special composition or to upgrade a particular feed of HCs. Other applications are noted when the values of the oxidizer/HC ratios are extreme This is the case of a NG or of another HC mixture without oxidizer or, on the contrary, of CO or C0₂, in the absence of an "organic" reactant such as CH₄, NG or other HC mixture In these cases, we aim at

The special conversions described by reactions (2), (2a), (2b) and similar reactions with partial crackmg of a NG or of an HC, possibly diluted in a neutral gas or in the hydrogen, to obtain one or more products among those written on the right side of reactions (2), (2a), (2b) and similar reactions,

The "water shift" descnbed by reaction (3) in order to obtain hydrogen starting from carbon monoxide, • The "inverse water shift" (5) to convert carbon dioxide to carbon monoxide

All the above-mentioned conversions are performed in plasma-chemical reactors based on mobile electπc discharges, called GhdArc-II, which are the subject of this application These discharges cause high activation of the medium by unusual species (with respect to the traditional conditions of conversions) onginating from the matter in which these discharges develop Thus, electrons, as well as atoms, ions and molecular radicals are detected, such as H, OH, O, 0₂, H⁺, 0⁺, 0₂ ⁺, 0₂ , H0₂, CH₃, CH₂, CH, C₂ and many others Most of these species may exist in their electronic or vibratory excited states with a rather long lifetime They are also known to be extremely chemically active

HC conversion according to endothermic reactions (1) through (2b) and (4) through (5) would require a supply of preferably "clean" energy, not connected with any external combustion which is not economic and is highly polluting The best way to help these reactions would be to have electnc arcs and/or discharges directly in the medium to be converted, imposing permanent distribution of energy in the larger volume to be treated The transfer of energy of electnc ongin to the gas mixture would occur by direct transfer of the energy to the molecules This would entail excitation, lonization and dissociation phenomena and also Joule effect, considering the mixture partially ionized as a gaseous electnc conductor The gas mixture having become a conductor after lonization (itself due to dielectπc breakdown, hence to pre-ionization) between electrodes brought to different potentials, would be considered as an electπc resistance and, at the same time, as a sort of electrolyte in gaseous phase the plasma

The weakly exothermic reactions (3) and (6) to (7) develop better at higher temperatures because of a merely kinetic reason The presence of a traditional catalyst or of catalytic species in homogeneous phase helps greatly in this type of reactions Such species are obviously present in a plasma Plasma is defined as a state of matter and, therefore, cannot be taken as a cπteπon of similaπty for different, previously known processes There is a multitude of plasmas and several ways whereby to obtain each of these plasmas By definition, plasma is a gaseous medium in which particles are partially oxidized In most plasmas, the main physical macroscopic quantity - temperature - is the same for all the components this is thermodynamic equihbnum These conditions can be easily obtained it is sufficient to supply much energy, such as in the case of plasma torches ("plasmatrons") in which plasma is produced by a very high current electnc arc There are other devices capable of generating this state, such as induction or radiofrequency (RF) torches in which the gas medium becomes resonant with a very high frequency electromagnetic field These plasmas are called "thermal plasmas" It is obvious that a thermal plasma will modify the chemistry of a gas mixture by destroying almost all the molecules, especially the fragile ones, such as HCs The fragments which meet at the end of the process, after a sudden drop in temperature produced by quenching without recovery of energy, ongrnate from partial recombination phenomena producing simple molecules. This chemistry offers mediocre prospects; it is energy costly and presents problems connected with the high temperature, such as the resistance of the materials.

Chemists prefer plasmas which do not respect the thermodynamic equilibrium conditions. For example, it is sufficient to act on the free electrons. It is also possible to act on the rotation or vibration properties of certain molecules. In terms of energy, that breaks again the balance of energy exchange between the plasma and the medium surrounding it. This state is called "out of thermodynamic equilibrium" or simply "non-equilibrium". These plasmas are sometimes called "low temperature" plasmas, although the concept of temperature can no longer be used! There are several methods for generating these plasmas: microwaves, electron beams, flame fronts, etc. However, at industrial scale, the generators of such transposable plasmas are rare and fit only a well-defined application. This is the reason why these plasmas are not used much in chemistry.

Furthermore, when a plasma is prepared or its existence is ended, the equilibrium is broken. These transitory states are in fact non-equilibrium plasmas and last only a few milliseconds. A type of plasma already makes use of this phenomenon, the plasma from gliding electric arcs "GlidArc-I" (see further on). Apart from the numerous geometric possibilities of such a plasma generator and, very globally, the parameters on which a chemist can act are: pressure, temperature, gas speed, current intensity, voltage and electric frequency. Such a number of parameters exceeds the conventional reasoning capabilities of the expert. For each application, real know-how and inventive activity are necessary to attain results in which the objectives are economic feasibility and respect of ecological principles. GlidArc-I already enabled a chemist to envision the distribution of an energy supply directly in the gas mixture, without, for example, resorting to catalysts. A chemist could also distribute the energy directly rather than in thermal form or in chemical form. He could also intervene on the flow still charged with active species from the arc or discharge zone to have these substances react with the feed to be converted or reconverted in a post-plasma zone. Nevertheless, some difficulties were determined in the last few years, hence our research to bypass them. Thus, we have succeeded in perfecting a totally new device with mobile arcs, GlidArc-II.

Various electric plasma devices have already been tested as source of an "active" energy. Our bibliographic search concerning the last three decades provides few published or patented results concerning the conversion of hydrocarbons assisted by plasma (outside of our own work). The main cause of these problems is connected to the presence of oxygen (elementary oxygen or oxygen deriving from dissociation of the H₂0 and or C0₂ molecules) attacking the conventional tungsten or graphite electrodes of traditional plasma devices. However, we will report these attempts at using different plasma generators. Systematically, both the basis and the reaction process are different from ours; there is only one common point: the use of the very broad term "plasma" or the possibility of handling the same hydrocarbon molecules.

K. KARL et al. [Verfahren zur Herstellung eines wasserstoffreichen Gases aud Kohlen-wasserstoffen, CH 378 296 (1957)] propose stem reforming of hydrocarbons under 66.7 kPa to 0.3 MPa pressure in a "silent" discharge characterized by a very intense 0.3 to 0.5 MV/m electric field. This source of plasma has been known for a century; it is totally different from that which is the subject of this application.

R.J. HEASON presented in 1964 his doctorate thesis concerning pyrolysis of methane as well as the reaction of CH₄ with steam in an arc plasma (700 A, 20 V) in argon. These results were published in manuscript form ["Investigation of methane and methane-stem reactions in an argon plasma", Dissertation, Ohio State Univ., Columbus]. This is a "thermal" plasma and a device consuming a large quantity of argon (2 moles Ar for 1 mole CH₄). CH. LEIGH and E.A. DANCY ["Study on natural gas reforming by plasma arc", Proc. of the Int. Round

Table on Study and Appl. of Transport Phenomena in Thermal Plasmas, contnbution I 5, Odeillo, 1975, 11 pp.] heated a mixture of C0₂/CH₄ ~ 1 in a jet of argon plasma at the outlet of a traditional arc plasmatron The temperature of the jet was approximately 10 kK. The argon flow was in the same order of magnitude as that of the mixture to be treated. These researchers observed a conversion of 11 to 74% carbon to H₂, CO, C₂H₄ and C₂H₆ (without ever detecting C₂H₂ or H₂0 in the products!?). No application was possible because of the high consumption of electnc energy (70% of this energy went to the water cooling the plasmatron) as well as the use of the noble gas

P. CAPEZZUTO et al. ["The oxidation of methane with carbon dioxide, water vapor and oxygen in radio- frequency discharges at moderate pressures", 3rd Int Symp. on Plasma Chemistry, Limoges, 1976, contnbution G.5.11, 7 pp.] also studied partial oxidation of methane separately mixed with C0₂ or with 0₂ or with H₂0 with oxιdιzer/CH₄ ratios = 1. The 35 MHz radiofrequency (RF) plasma reactors needed an additional argon flow and could operate only at low pressures around 2.7 kPa. For the total input gas flow rate of 3 to 36 l(n)/mιn (the "n" indicating the gas volume at normal condition of 0°C and 1 atm) the energy density at the range of 1 to 12 kWh/m³(n) was very big. No industnal application was possible because of the high consumption of electnc energy and of noble gas (in addition to complexity of electnc supply and the need to work under vacuum) The mechanical setup constraints, the low energy yield and the insufficient unit powers of the RF plasma sources cause the use of this method to be poorly adapted from the economic point of view to conversions of large volumes of gas. Nevertheless, it is of mterest to note that, in any case, the authors observe an almost total conversion of the methane and the appearance of the following products • mainly H₂, CO, C₂H₂ with presence of C₂H₄ (< 5%) and of C₂H₆ (< 1 %) for the C0₂/CH₄ system, the same as those above but with some traces of C0₂ for the H₂0/CH₄ system. A patent of S. SANTEN et al. ["Thermal reforming of gaseous hydrocarbon" GB-A-2172011 (1986)] claims the use of a plasma generator to heat reagents (a gaseous hydrocarbon, some water vapor and possibly some coal), entirely or partially, up to a temperature exceeding 1200°C. At such temperatures, these inventors expect favorable conditions to handle their process merely thermally, without the use of catalysts. The temperatures reached in the reactor and the thermal manner of the reforming (claimed and even emphasized in the patent title) therefore indicate treatment of hydrocarbons under thermodynamic equilibrium The process is based on a direct arc plasma generator (two annular electrodes) or transferred arc plasma generator, which are very traditional devices that have been known for nearly a century! L. KERKER wrote in general on production tests of synthesis gas at Huls [Herstellung von Reduktionsgas oder Synthesegas mit Lichtbogenplasmaverfahren", Elektro-warme international B, Industnelle Elektrowarme, vol 45 (3-4), 155-61 (1987)]. The illustrations mdicate a very powerful (1 through 9 MW) traditional tubular arc reactor used at this plant since 1939 to produce acetylene This time, a natural gas steam reforming project is involved, to produce 99.9% pure hydrogen at a very competitive cost with respect to electrolysis (but still more expensive than for hydrogen from traditional steam reforming or partial oxidation methods)

We have also worked since 1986 on the conversion of NGs in thermal plasma reactors These simple or transferred arc plasma torches make it possible to obtain small volume plasmas at very high temperatures (T > 10 kK) Although these devices represent potential sources of active species, they are nevertheless poorly suitable for chemical applications requiring much lower temperatures, in order not to demolish the hydrocarbon molecules to soot) and mostly larger volumes, filled with plasma, in order to act intimately on the entire fluid to be treated The plasma torch technology, for example well established in the area of projection of solids, was found then to be at the same time very expensive and very difficult to implement for chemical processes. However, we have obtained improvements in the area of thermal plasmas in the case of conversion of methane m a specifically controlled electnc arc, see P. JORGENSEN et al., "Process for the Production of Reactive Gases Rich in Hydrogen and Carbon Oxide in an Electnc Post- Arc, BF 2593493 (1986). However, the structure of the device utilized at the time did not make it possible to use steam as reagent, nor to work without consuming the argon necessary to form a first pilot arc. Later we used almost the same arc with very high current (20 - 150 A) to study ethane oxidation, see K. MEGUERNES et al., "Oxidation of ethane C₂H₆ by C0₂ or 0₂ in an electnc arc", J. High Temp Chem Process , vol 1(3), p 71-76

(1992), without much improvement in the consumption of electnc energy and of argon It is m order to correct these problems that we studied pure methane reforming by carbon dioxide in an electro-reactor which had just been mvented by our team, see H LESUEUR et al., Low Temperature Plasma Generation Device by Formation of Sliding Electnc Discharges, BF 2639172 (1988). It consisted of three fixed electrodes between which gliding arcs developed; the plasma medium thus obtained was greatly out of thermodynamic equihbnum and contained numerous excited species which made it highly reactive. This plasma device is currently known under the name of GhdArc-I. Our first tests for the production of synthesis gas starting from a CH₄ + C0₂ mixture directly mjected into this new type of plasma (without any cooling nor plasma-forming argon) were reported by H. LESUEUR et al., "Production of synthesis gas (CO + H₂) starting from the oxidation of CH₄ by C0₂ in an electro-reactor with gliding discharges", Physics Colloquium, Supplement to the Journal of Physics, vol. 51 (18), p. C5-49 - C5-56 (1990) We then made a more systematic comparison of methane reforming with carbon dioxide m a transferred arc and in GhdArc-I, to show the great supenonty of the gliding arc reactors, see K. MEGUERNES et al , "Oxidation of CH₄ by C0₂ m an electnc arc and in a cool discharge", 11th Int Symp. on Plasma Chem , Loughborough (England), 1993, vol. 2, p. 710-715. Lastly, a complete article on the conversion of CH₄ by C0₂ was published by H. LESUEUR et al , "Electncally assisted partial oxidation of methane", Int J Hydrogen Energy, vol 19(2), p. 139-144 (1994). This methane reforming by CO, shows a very interesting way of upgrading some gases with large contents of carbon dioxide. However, the products from our reactor had a limited H₂/CO molar ratio, between 0 5 and 0.8, almost in agreement with reaction (4). Therefore, this gas composition was totally unsuitable for the Fischer-Tropsch (FT, synthesis of hydrocarbon synthetic fuels, "syncrude") or a similar technology for the production of methanol The two processes require a synthesis gas with a H₂/CO ratio close to 2 We then discovered that GhdArc-I is very well suited for a supply of steam as sole plasma-forming medium The tests on overheating water vapor by this device were performed at on a laboratory scale and at atmosphenc pressure. This reactor was supplied with very humid water vapor at 105°C No detenoration of the plasma generator supplied with water vapor was detected after lengthy experiments. The water vapor, thus overheated at atmosphenc pressure and chemically activated by the presence of H, O, OH and other metastable species may be of interest for drymg or for chemical conversions, see P CZERNICHOWSKI and A CZERNICHOWSKI, Gliding electnc arcs to overheat water vapor, 9th Colloquium Umversite-Industπe "Technical techniques and drying quality", Bordeaux-Talence, 1994, p Bl-1 - Bl-7

It is at this stage that we thought that traditional steam reforming of pure methane could be improved in the presence of gliding electnc discharges which provide the reactional medium at the same time with an easily controlled enthalpy and very reactive species These special discharges and arcs may thus play a catalyst role in homogeneous phase, see A. CZERNICHOWSKI et al., "Assistance device and process by plasma in non-catalytic steam cracking of hydrocarbon and halogen-organic compounds", BF 2724806 (1994)

The decomposition of CH₄ m the presence of overheated water vapor m a simple GhdArc-I reactor has actually given large quantities (m terms of percentages by volume) of H₂ (up to 66%) and CO (up to 15%). In all cases, we had H₂/CO molar ratios exceedmg a value of 4 and even up to 5 8¹ Moreover, the energy cost (EC) to be borne in order to produce 1 m³(n) of said SG was rather high and another negative pomt appeared- too large a quantity of unconverted methane remamed m the product

Therefore, we had a new idea, which is the subject of this application: to apply at the same time H₂0 and 0₂ mixed, so as to perform, at the same time, dunng one operation in the new reactor with mobile discharges, a conversion of certain HC by endothermic steam reforming (reactions 1 or la) and partial oxidation with oxygen (reactions 6 or 6a), which would both contnbute part of the energy necessary for the endothermic steam reforming Part of the oxygen would be consumed by reaction (8), apparently parasitic (but highly exothermic), on the other hand, the CO, produced by this reaction could contnbute to lower the H₂/CO ratio via reaction (5). This makes it possible to obtain a synthesis gas with an H,/CO ratio for further use of the SG, for example a FT process. This objective was achieved and, in addition, we were surpnsed by the appearance of other feed conversion products following reactions (2) through (2b). C₂H₄ and C₂H, in relatively high contents Therefore, these unsaturated products can supply an additional value to this HC conversion process, assisted by the mobile electnc discharges. For example, mixed with the synthesis gas, these unsaturated molecules facilitate the construction of hydrocarbon chains at the time of the FT synthesis, see A.L. LAPIDUS et al., Hydrocarbon Syntheses from acetylene-containing gases, Khim. Tverd. Topi (Moscow), No. 6, p. 3-17 (1996). Thus, formed simultaneously with CO and H₂, dunng the conversion of hydrocarbons in GhdArc-II, these unsaturated molecules can contnbute to direct application of an improved synthesis of liquid hydrocarbons

A similar approach of 0₂ H₂0 NG reforming is known in the industry under the name of "Auto-Thermal Reforming" (or the "auto-thermal process"), but this mixed process is ob gatonly coupled with post-treatment of the gases leaving the partial combustion zone by means of a traditional catalyst, see T.S CHRISTENSEN and LI PRIMDAHL, "Improve syngas production using autothermal reformmg", Hydrocarbon Processmg, vol 73(3), p 39- 46 (1994). A very sophisticated thermal burner is at the core of the process, since all the safety of the operations on the oxygen and HC mixtures at explosion limit depend on proper operation of said burner Moreover, the high presence of unsaturated HC was not observed there We previously mentioned the possibility of converting CO mto H₂ or, inversely, H₂ mto CO via the so- called "shift" reactions (3) and (5). This makes it possible to prepare mixtures with the desired composition of synthesis gas for a particular application However, in industnal practice, these reactions require a separate reactor, presence of catalysts and present all the problems of complexity, poisoning and agmg of the catalytic load, etc. In order to explam the observed phenomenon of too high an H,/CO ratio m our pure methane steam cracking tests assisted by GhdArc-I plasma, we performed a senes of tests, see A CZERNICHOWSKI and K MEGUERNES,

"Electncally assisted water shift reaction", 12th Int. Symp. on Plasma Chem , Minneapolis, Minnesota, 1995, vol. 2, p 729-33. By injecting a mixture of carbon monoxide with steam m GhdArc-I, we clearly observed reaction (3), and this without the least presence of traditional catalyst Therefore, it is the plasma itself that catalyzed this shift, converting CO into H₂' The same shift can be obtamed, m a yet much more advantageous manner, in the GhdArc-II device, (see further on). Moreover, injecting the CO, + H, mixtures m the GhdArc-II reactor with mobile discharges, we performed the mverse shift reaction (5) which can serve as a new process for the production of CO from carbon dioxide

We have already implemented an idea, see P CZERNICHOWSKI, A CZERNICHOWSKI, Conversion of hydrocarbons assisted by gliding electric arcs m the presence of steam and/or carbon dioxide, BF 2758317 (1997), which consists of applying H₂0 and/or C0₂ and/or a mixture of H₂0/C0₂ (m vanable composition, as needed) in order to attain the following m an unproved GhdArc-I reactor conversion of some HC by steam reformmg (reaction 1 or la),

HC reformmg with carbon dioxide (reaction 4 or 4a), one smgle simultaneous HC conversion operation by steam reforming accompamed by reforming with carbon dioxide, m the presence of the mverse shift of part of the hydrogen (reaction 5)

Thus, we were able to obtain a synthesis gas having an H₂/CO molar ratio desirable for further utilization of this synthesis gas, for example via a FT process We were also surpnsed by the appearance of other conversion products of the load C₂H₄, C₂H₂ and C₃H₆, in relatively high percentages These unsaturated products can also contnbute additional value to the hydrocarbon conversion processes assisted by electnc arcs The GhdArc-I reactor was divided mto two compartments by a diaphragm to remforce recirculation of the reagents m the arc compartment and to produce maturation in the other empty compartment where the reactions generated m the arc zone can be terminated The two parts of the GhdArc-I reactor communicated by means of a very large hole allowing the reagents and the active species to penetrate the maturation post-plasma zone

The beneficial effect for a plasma-chemical conversion of "cold" electnc discharges (we also call these "arcs" for currents greater than 5A) was then demonstrated in the GhdArc-I generator of non-equihbnum plasma

(previously mentioned) to treat high volumes of gas circulating at very high speed m the vicinity of a system of stationary electrodes The gas must move m the vicinity of the stationary electrodes m order to dnve the bases of the discharges at a local 10 m/s minimum speed Hence, only a small part of the volume of the gas to be processed was coming m contact with the active species produced m the discharge The yield from the operation suffered from this It was also observed that it is very difficult to develop more than 5 kW per pair of electrodes Consequently, in order to process a large volume of gas, it would be necessary to arrange in battery a large number of modules, each accompamed by a gas acceleration system m the vicinity of the electrodes, which would make the facility very complex Takmg these problems mto account, we visualized a new device, descnbed herembelow, with electπc discharges gliding on mobile electrodes

PLASMA DEVICE

The new device, named GhdArc-II, is based on electπc discharges which explode on at least two electrodes, of which at least one is mobile The electrodes are arranged so as to form a mobile structure which can be divergent, but this arrangement is only optional The gas circulates almost mdependently with respect to the structure of the electrodes, for example along one of the electrodes, or perpendicular to the movement of the mobile electrode, or also otherwise The gas flow can also participate m the displacement of the roots of the discharge which, for example, moves rapidly along one of the electrodes The electrodes involved are anywhere at a minimum distance, regardless of their geometnc arrangement That is where electnc breakdown occurs, if the voltage applied to the electrodes exceeds the dielectnc breakdown Immediately after this breakdown, a small volume of plasma, formed between the electrodes, is dnven by the movement of one electrode with respect to the other This dnving is possibly aided by a gas flow The displacement speed of the discharge depends mostly on the mechamcal displacement speed of one (or two) electrode(s) The column of plasma begms to stretch and, at the same time, the voltage at the electrodes mcreases Dunng this initial phase, the discharge is near thermodynamic equihbnum, 1 e at each point of the plasma, the temperature of the electrons T_e is near the temperature of the gas T₀ This regime is caused by the high frequency of collisions between electrons and molecules, as well as by the electnc power supplied per unit of length of the discharge, this bemg sufficient to compensate for the radial losses due to thermal conduction This equihbnum phase continues as the discharge continues to lengthen, until the moment at which the current attains its maximum value Starting from this moment, the dissipated electnc power decreases, while the losses by thermal conduction continue to increase Then the discharge enters its thermal non-equihbnum phase and a major drop m the gas temperature T₀ is observed Instead, the temperature of the electrons is still very high Due to the drop of the gas temperature T₀, the heat losses decrease, the length of the off equihbnum plasma can then continue to grow until the moment at which the heat losses become greater than the power available in the discharge which dies down A new discharge is established between the two electrodes and the cycle starts again

The second phase of the life of the discharge, that of thermal and electnc non-equihbnum dunng which up to 80% of the energy is mjected, is of special mterest in order to stimulate a chemical reaction The active discharges, thus created m the GhdArc-II device, can sweep almost the entire gas flow without the need for accelerating this gas flow in the vicinity of the electrodes The displacement speed of the mobile discharge is then mdependent of the flow-rate and speed of the gas

It will be possible to use the new GhdArc-II reactors for handling large volumes of gas in systems with multiple stages, without the need for compressmg these gases between the stages or pushmg/pullmg them by compressors and/or pumps cooperatmg with nozzles between the acceleration stages The gases can be treated in the developed GhdArc-II structures, supplied simultaneously in a single reactor containing a certain number of concomitant and successive discharges between electrodes These electrodes move rapidly with respect to each other, so as to stretch each discharge until the passage to its phase of thermal non-equilibrium, followed by extmction and re-ignition between the nearby electrodes Stretching of the discharges, which has become mdependent of the flow rate and, especially of the displacement speed of the gas (speed which can be low at the time of passage into the zone activated by the discharges), makes it possible to ensure that almost all the gas effluent is submitted to the electrons, ions, radicals and other particles excited by the discharge This makes it possible to attain the chemical effect desired After rapid diffusion and aerodynamic turbulence, these active species, which have a relatively long lifetime, succeed m scattermg even m this space which is not touched by the discharges These phenomena contribute also to the extraordinary activity of these mobile discharges

The following descnption will help to better understand the method of operation and the scope of this application Figure 1 represents a method of execution of the device according to one embodiment A high voltage and low intensity (a few Amperes) discharge is established between end 2 of a stationary electrode 1 and a pomt 4' of a second electrode 3 The voltage applied between electrodes 1 and 3 is that of the secondary 6" of the transformer (voltage amplifier) 6 whose primary 6' is connected at 8 with the network The base of discharge

4' is separated at very high speed from end 2 of electrode 1 , so as to rapidly stretch the discharge and displace the mobile discharge base 4" This rapid displacement is obtamed, for example, by rotating electrode 3 around axis 5

The discharge 7 is thus stretched over a great length and sweeps the peripheral zone of mobile electrode 3 When the cunent has reached its maximum value, the power begins to decrease and the discharge enters its thermal non- equilibrium phase When the length of the discharge contmues to grow and the sinusoidal voltage at secondary 6" of transformer 6 decreases, the discharge dies down; then it is pruned aga between the stationary electrode 1 and the 4' part nearest electrode 3; then the cycle begins again. As an example, we observed that, on a circular electrode 3 with 140 mm diameter rotatmg at a speed between 50 and 1000 rad/s, that the zone affected by the diffused discharge may extend on more than 2 rad between points 4' and 4". We have also remarked that it is not necessary that the mobile electrode be toothed, as shown m Fig. 1. In fact, small surface irregulanties are sufficient for the discharge base to be "hooked" and moved with the disk at high speed The gas to be processed no longer has to be used to drive the discharge, as it did in the case of the precedmg GlidArc-I Therefore, it is possible to fill with gas the annular space of the reactor included between the turning disk and the reactor wall and then process a certain volume of gas for a definite period of time, or introduce a desired continuous gas flow in the reactor.

Figure 2 shows the diagram of a reactor with 4 identical stages Of course, this is only an example and it does not limit the execution of a future industnal size reactor. Each stage includes a disk d and 3 stationary electrodes offset by 120°, identified as r, s and t, each electrode bemg connected to a three-phase transformer phase, the disk bemg connected to the neutral pomt of the transformer This turning disk may also be connected to the ground, which eliminates the problem of electπc insulation of this movmg part. The gas is introduced, for example, m k in the lower part of the reactor and extracted in /. Several gas inputs and outlets can be arranged m the same reactor The rotating motion of the mobile electrode can be provided by an electnc motor or a compressed gas motor, or even by the gas to be processed The turning electrode may consist of a stack of identical disks d] through d4, be a conductor brush (see Fig. 3) or even be hehcoidal m shape. It is understood that these representations are given only as examples and that other methods of execution may be proposed, particularly 6- or 12-phase electncal supplies. The mtenor part of the body of the reactor can be srmply cyhndncal or equipped with baffles in order to guide the gas flow, for example, vortically. Likewise, each tummg electrode can be equipped with blades which can very thoroughly stir the gas to be processed. In the case of treatment of a gas loaded with solid or liquid particles or of a particularly chemically aggressive gas, it is possible to observe some wear of the fixed electrodes which, m contrast to the turning electrodes, are permanently exposed to the action of the discharge Therefore, it may be advantageous to equip each fixed electrode with a nozzle through which to run a protective gas Another solution consists of applymg stationary electrodes with an elongated shape which allows the discharge bases to move rapidly on these electrodes Although it is still possible, it is not necessary to resort to a coolmg system for the stationary electrodes, since the intensities used are limited and, as a rule, are lower than 10 A. As an example, the power developed m a three-phase system can reach 3 x l0 A x 2 kV = 60 kW per stage, which makes it possible, with a stack of 4 stages as shown m Fig. 2, to develop 240 kW on a reactor with 0 3 m diameter and 0 5 m height, so m a volume of the inner chamber of approximately 0.03 m³ for a 0.2 m turning electrode diameter

It is possible to make good use of a stabilization inductor L per phase between the transformer and each stationary electrode. The discharge voltage U_a and the current I_a are thus out of phase with respect to the voltage at the transformer terminal U„ as shown m Fig 4a and 4b Thus, the possibility exists of supplymg the discharge, after the voltage at the transformer terminals has passed through its maximum and is real canceled by the energy accumulated m the mductor Then, when the discharge dies down, full empty voltage of the transformer is available at the terminals of the electrodes Several gas conversion tests were performed in an experimental GhdArc-II reactor previously shown schematically on Fig 2, Its construction, but hereby limited, is as follows The reactor consists of four steel or nickel toothed or smooth disks, with 140 mm diameter, and twelve fixed electrodes Said electrodes, also made of steel oi nickel (shaped as curved knives) are placed symmetncally (each one offset 120°), three per stage, around disks d mounted on the same in fast rotation At each stage of the reactor, each one of the three fixed electrodes is linked to one of the phases of a three-phase 8 7 kV transformer (voltage between 50 Hz phases), the disk is connected to the neutral pomt of the transformer There are four identical transformers, one per disk (stage) All the mobile and fixed electrodes are placed inside a ceramic tube (possibly lmed on the mside with refractory wadding), with 203 mm inside diameter and 265 mm length The tube is closed on each side by refractory plate covers These plates accommodate the fastening and dnving system of the shaft by means of a small electπc motor, the refractory glass windows, the mput and outlet of the gas to be treated and some probes (pressure, temperature) No part of the reactor is cooled by forced means The reactor is leakproof and makes it possible to obtain, m its tntenor, pressures rangmg from 0 1 to 6 bars The electnc power of the reactor is regulated by activating one, two or three fixed electrodes per stage (each injecting the 0 12 A limited current) We can also activate one, two, three or four stages of the reactor The maximum electric power of the reactor is 3 kW However, it is quite possible to use higher power for industnal activities

The reactor is supplied by controlled flows (by mass flow meters) of gas taken from cylmders The reactor supply m compound initially liquid at ambient or higher temperature (for example, a heavy hydrocarbon or water) may also be provided by a dosmg pump The constant flow of said liquid, controlled by a valve and a flow meter, can thus be evaporated m an oven, to be then mjected mto the reactor, whether or not bemg previously mixed with another process fluid The incoming fluids are mixed far from the injection spray tip, m the injection tip itself or in its vicinity They can be preheated together or separately by means of a temperature controlled resistance oven This last method would be preferable for an industrial reactor, m order to prevent an early 0₂ + HC combustion at the time of preheating Another subject of this application consists of dividing a GhdArc-II mobile discharge reactor in some compartments By addmg (for certain tests) a more or less perforated separation, for example m the form of gnllwork, we thus create a compartment of mobile electnc discharges close to another compartment C, empty oi partially filled with solid matter, see Fig 2 We thermally msulate the entire reactor (for example, by usmg refractory felt) to save energy inside the reactor and have the temperature of the walls of two zones, that of the mobile and immobile electrodes as well as that of the optional solid load, nse as high as possible Therefore, some molecules generated m the plasma zones and penetrating the other zone can be modified m the compartment without discharges, called "post-plasma" The solid matter which may be filling the post-plasma zone may act as a contact on which we facilitate reactional exchanges between the species from the plasma zone This matter is not necessanly known as a catalyst, but may become so m contact with the species from the plasma zone Besides, the solid matter inserted in the post-plasma zone (m most cases, we use Nickel metal chips) has a geometric surface area of a few square decimeters, which is less by a few orders of magnitude than the surface area of a traditional catalyst' The perforated partition between the zones then provides a passage for the reagents (partially consumed) and for active "long-living" species produced by the excitation of the gases by the mobile discharges The Nickel or other electnc conductor stationary and mobile electrodes can also contribute by their surface area to the plasma, m an almost catalytic post- treatment of the gases, vapors or liquids introduced m the reactor In the post-plasma zone and on the surface of the electrodes, the conversion is thus likely to be completed m the presence of said solid matter and m an environment where the temperature is naturally lower than the "temperature" in the plasma zone The bnght zone of mobile electnc discharges (as well as other elements of the reactor) can be observed through wmdows m order to make certain of the proper operation of the reactor and to determine the temperature of the walls of the two compartments Important mformation may also be deduced from the plasma emission spectrum Physics provides us with mformation on these atomic and molecular species, such as H^*, OH^*, 0₂ ^*, C0₂ ^*, CO^*, H₂ ^*, H₃ ^* (and many others) which have a sufficiently long life time to travel relatively long distances m the gas flow, even at atmosphenc pressure or at higher pressure This phenomenon is very important for the conversion of HCs known for their fragility In fact, the action of a non-equihbnum plasma, such as the mobile discharge plasma combmed with the post-plasma zone, enables us to perform "gentle" transformations m this type of reactor with one or more post-plasma compartments There, very active and metastable species (hence, having catalytic properties) make it possible to reform these HCs originating from violent reactions m the plasma zone, through deactivation on other molecules directly m the gas phase or indirectly on the surface of some electrodes or on a solid matter inserted m the post- plasma zone It is also possible to extend the conversion of the reagents A multiple stage reactor may contam several post-plasma compartments located downstream from each or some plasma zones, so that the products of conversion by plasma may be transported there by the gas stream passmg through the reactor towards its exit

At the time of the tests, a pressure gauge shows the pressure mside the reactor, this pressure is established and controlled by a manual valve placed at the reactor exit The products leavmg the reactor are first cooled in an air- heat exchanger When they leave the exchanger, the gases and vapors are directed to a tee-piece which serves to send them either to analysis or to the exhaust chimney We gather and weigh the liquids leavmg the reactor, by condensation at 0°C We gather also the dry gas products for chromatographic analyses To this effect, we first send all the products to a chrmney, then, when we estimate that the reactor is operating at the desired way, we send the outgomg products towards analysis The liquids deposit m a cooled flask and in an absorbent matter, then the dry gases are sucked mto a syringe

Some chemical analyses are performed, usmg traditional gas chromatography methods We use three chromatographs, each intended for mdividual dry gases CO, C0₂, N₂, O, and CH₄ for the first, hydrogen alone for the second and all hydrocarbons for the third The water vapor stream which may exit together with some products is calculated from the material balances or quantified by cold trapping of a known volume of exiting gases

EXPERIMENTAL RESULTS Numerous feasibility tests of the natural gas (NG) reformmg process were performed in the new GhdArc-II reactor We present only the most significant tests The composition (by % volume) of the NG onginating from a commercial cylinder was 98 7% CH₄, 0 57% C₂H₆, 0 07% C₃H₈, 0 67% C₄H,₀ and 0 01 % C₅₊ The overall NG conversion ratio is limited in almost all the tests m order to better study the mdividual conversion phenomena of each of the components This conversion can obviously be much higher, for example after mcrease of the specific energy mjected mto the reagents Dry Conversion with Carbon Dioxide Table 1 summarizes tests 2 through 9f on NG reformmg with CO, alone under atmosphenc pressure. The reactor was not thermally msulated (hence the high losses of energy). The stationary and mobile electrodes are made of stainless steel; no post-plasma compartments. The temperature of the incoming gases was always equal to 22°C This table (as well as the followmg tables) is divided horizontally mto three parts. The first part shows the nature and quantity of the fluids mjected mto the reactor, the specific energy (SE) mjected mto the plasma (the real electnc power of GhdArc-II related to the normal hourly flow of all the incoming gases and vapors, as well as the temperature of the fluid leavmg the reactor, which is equal to the temperature read inside the last plasma compartment (but not m contact with the mobile discharges). The second part of each table shows the volumes (m standard liters) of dry products of the process leavmg the reactor after mjection of 1 kWh of electnc energy in the GhdArc-II plasma under experimental conditions. Thus, these values mdicate an actual energy cost (EC) m electncity of the process at laboratory scale. This section shows also the energy cost of a unit mass of CO (other products considered "free") or of unit volume of synthesis gas (other products also considered "free") with a given H₂/CO ratio. The third part of each table shows the other results of calculations based on the experimental data: the overall rate of conversion of carbon of HC ongm and possibly of CO, ongm, the conversion rates of different hydrocarbons present in the NG, as well as the relative conversion selectivities of carbon present m the HC and possibly of C0₂ ongm towards vanous products. The matenal balances were facilitated by the absence of coke, soot, tar or other pyrolytic compounds m our products (within limits not to exceed 1% expressed m mass of converted carbon). Table 1

Companson of our present results of NG conversion with C0₂ with our old results obtained m a GlidArc-I (see Table 2 of BF 2758317) confirms the supenonty of the new GhdArc-II device. This companson is illustrated in Table la Table la

The energy costs for the production of 1 kg of CO or 1 m³(n) of SG are thus respectively 2.2 or 1.5 higher usmg GhdArc-I with respect to the new test m GhdArc-II, with incoming cold gas and the more advantageous SE Best performances are also observed now regardmg the quantities of exiting acetylene

We emphasize also that we performed "dry" reformmg of ethane, propane and butanes present m the NG (used as reagent). After precise balances and analyses (see Table 1), we determined that the conversion of these HC heavier than methane is more advanced, despite very high excess of methane m the studied NG. This mdicates agam that the reformmg process with C0₂ of hydrocarbons heavier than methane would be easier.

The dry reformmg process assisted by mobile discharges can then be applied, regardless of which natural gas (or other mixture of hydrocarbons) is to be converted. For example, we are thinking of the different biogases or certain gas resources like mixtures of hydrocarbons and carbon dioxide. These gases can thus be upgraded without costly extraction of C0₂. Moreover, when a "clean" energy source (solar, hydraulic, nuclear, etc.) or "free" energy source (exhaust gas from thermal engmes, etc.) is available, we will be able thus to recycle the carbon dioxide, now a major problem.

Steam Reformmg

Table 2 summarizes tests 31 through 34 of natural gas steam reformmg. This time, the NG earned by the steam, enters preheated at a higher temperature than before. The conversion took place under atmosphenc pressure. The stationary and mobile electrodes are made of stainless steel; no post-plasma compartments.

Table 2

Companson of our present results of NG steam reformmg with our old results obtained from experiments conducted m the GhdArc-I reactor (see BF 2758317) confirms also the definite supenonty of the new GhdArc-II device descπbed herernabove Table 2a illustrates these differences and recalls the conditions of the comparative tests

Table 2a

We now obtain much more acetylene 22 l(n)/kWh mstead of 9 6 l(n) kWh before We will point out that the temperature of the reaction (or, rather, that of the mteπor of the GhdArc-II reactor) is much lower' Therefore, it appears that the hydrocarbon load placed mto closer and more prolonged contact with the zone of mobile discharges dispersmg the energy along the passage of the reagents is much more efficient than the gliding arcs of GlidArc-I injecting only a portion of the energy mto the gas We emphasize also that we perform steam reformmg of ethane, propane and butanes present m the natural gas On the basis of our chemical analyses and our balances of matenal entering and leavmg the GhdArc-II reactor, we determine that the conversions of HCs heavier than methane are much more distmct than that of methane This mdicates to us that, thanks to this steam reformmg process of hydrocarbon feeds containing mcreasmgly heavy hydrocarbons, their conversion is achieved mcreasmgly more easily, and this with the same specific energy applied to the entering feed The steam reforming process assisted by mobile discharges may then be applied to any natural gas (or other mixture of hydrocarbons) to be converted

Mixed Steam and Carbon Dioxide Reformmg

Table 3 summarizes tests 11 through 15 of NG reformmg with an H,0/CO, mixture The three reagents are mjected at 22°C and then H₂0 is in fog form The conversion takes place under atmosphenc pressure The reactor was not thermally msulated, hence the high energy losses The stationary and mobile electrodes are made of stainless steel, no post-plasma compartments

Table 3

We previously demonstrated the feasibility of a HC conversion process (without the use of traditional catalysts) assisted by ghdmg arcs plasma (GhdArc-I) m sunultaneous presence of carbon dioxide and steam (BF 2758317). The companson of our present results from this mixed NG reformmg with our previous results mdicates also the definite supenonty of the new GhdArc-II device. Table 3 a illustrates these differences and recalls some comparative test conditions

Table 3a

Agam we note a broad range of ratios of two oxidizers which can be used Although our examples are given for H₂0/C0₂ values between 0 25 and 1 1, the fact of bemg able to use only one oxidizer (see Table 1 and Table 2) enables us to expand this ratio for values between 0 and infinity Thus, all the H,0/C0₂/NG feeds can be converted m GhdArc-II reactors without prior separation of the components

We note the absence of soot, cokes or other products which would be undesirable at the time of the conversion of heavy hydrocarbons, such as the butanes present m considerable quantity m the NG On the other hand, the mcreasmg fragility of mcreasmgly heavy HCs is a "plus" for our process from the pomt of view of energy cost for the production of CO as well as for other valuable unsaturated products. This is a strong pomt of our process with respect to traditional processes which are confronted with problems of deposition of cokes and tars, especially m the presence of hydrocarbons heavier than methane Lastly we point out the considerable quantities (but at adjustable ratio) of unsaturated HCs in our products from conversion assisted by GlidArc-II plasma. They are of additional value as final commercial product (acetylene) or as raw material for other organic syntheses.

Mixed Steam and Oxygen Reforming Table 4 summarizes tests 41 through 47 on NG reforming simultaneously with an H,0/0₂ mixture. The question was: is it possible to steam reform a NG with a small amount of oxygen to improve the energy cost and to approach the H₂/CO ratio of 2? The three reagents are injected through the same nozzle at temperature over 100°C (except for test 45), in order to evaporate water. The conversion takes place under atmospheric pressure. The reactor is not thermally insulated; hence, the high losses of energy. The stationary and mobile electrodes are made of stainless steel: no post-plasma compartments.

The results of this set of tests show that it is possible to oxidize the hydrocarbon feed in deficit, the 0₂/HC molar ratio being between 0.06 and 0.38. Another positive point which could lead to choose the use of steam beside the oxygen is that it is possible to create a relatively large quantity of ethylene and acetylene in the SG (see tests 41, 42 and 44). Comparing tests 31 and 45, 32 and 44 or 33 and 43, we see that a limited addition of H,0 makes it possible to lower the EC; we thus demonstrate that it is possible to add a well proportioned quantity of oxygen to achieve a particular objective. We note that the overall rate of NG conversion (at this time limited in our tests) can be brought to 100% by increasing the power of the reactor and/or reducing the NG flow entering the reactor (this again increases the SE). We add also that, by analyzing individually the conversion rates of each HC, we determine that the heavier HCs react more easily. Our partial oxidation and steam reforming process assisted by mobile discharges could thus be applied, regardless of the HC content of a NG (or other mixture of hydrocarbons) to be converted.

Table 4

At the time of a short senes of preliminary limited power tests, we replaced all the electrodes of GhdArc-II

(made of stainless steel) with those made of Nickel metal Without changing the body of the reactor, we replaced also two sections of the reactor with two inserts (with 19 cm diameter and 5 cm thickness) containing Ni chips

(disconnected from the power supply) Thus, the gas first came m contact with the mobile discharges between the Ni electrodes (first stage), then it passed through the chip zone to take agam the second discharge zone followed by a second Ni chip zone The internal walls of the reactor were lmed with a double layer of refractory felt m order to reduce the thermal losses of the device and to operate at the highest possible temperature Other inert bodies, such as large fragments of ceramic bnck or copper chips could also be placed mstead of Ni chips for some comparative tests

The presence of apparently inert matter m the post-discharge section considerably modified the nature and quantity of the products from the conversion Acting on the nature of the solid matter placed m contact with a gas flow onginating from electric treatment in the plasma zone of mobile electnc discharges, we can obtain more or less unsaturated hydrocarbons, almost block the production of hydrogen and acetylene on large fragments of copper metal, regulate the H,/CO ratio, etc This is a very strong effect of the matter inserted m the post-plasma zone on the chemical composition of the products'

Partial Oxidation m Air, m Oxygen-Ennched Air or m Pure Oxygen

Table 5 summarizes 51 through 59 NG reformmg tests m a NG/N₂/0₂ system, without any water vapor added Whenever we used the term "added" we emphasize the external provenance of this reagent which may appear m any case (but m a very small quantity) as product of the (5), (7) and/or (8) reactions The partial oxidation of a NG with oxygen-ennched air (for example, of membrane provenance) is much less expensive and less dangerous than oxidation with pure oxygen of cryogenic ongm The reagents are mjected through the same nozzle at 28°C The conversion takes place under atmosphenc pressure The reactor is thermally msulated by refractory waddmg to reduce the large losses of energy (except for test 51) The stationary and mobile electrodes are made of stainless steel, no post-plasma compartments

Table 5

All the results of this seπes of tests show us that it is preferable to convert a NG when the mtenor of the reactor attams the highest possible temperature. Despite the presence of a large mtrogen ballast (between 46 and 59% vol. m the entermg flow), we can mamtam, thanks to the energy and the active species present m the plasma, a reactional environment favoring the evolution of the HC partial oxidation reactions. This is seen at the level of very high temperatures m the reactor. This senes of tests shows then the feasibility of partial oxidation of the HCs also with atmosphenc air This oxidation can also be earned out with very high oxygen deficit, but it is possible only m the presence of mobile electnc discharges; otherwise, the purely auto-thermal process stops very soon (the chemical inertia of the reactor is very small).

A large ballast (up to 40% by volume) of C0₂ present m some NGs which we have also simulated and tested, does not prevent a proper development of the conversion of these NGs mto SG This ballast can be comparable to the inert nitrogen ballast, although a fraction of C0₂ may participate actively, via reactions (4), (4a) and (5), m the production of CO, which mcreases the content of valuable product. For a pressure higher than 2 bars (test 58a) and other parameters significantly near those of test 58, we observe all the slightly improved performances (from 10 to 30%). However, when the pressure is agam increased to 6 bars at the time of preliminary tests, we observe an increasing amount of soot, especially for 0₂ NG ratios < 0.5

The results of this senes of tests teach us that it is preferable to convert a NG when the 0₂ NG ratio reaches a value slightly exceedmg 0.5. At this level, we obtam very good results with total conversion of carbon and oxygen, particularly under pressures over 1 bar and when the mtenor walls of the reactor attam a temperature near 1100°C

Under these conditions, we can also approach a desired H,/CO ratio of 2.

Now we consider the limit of 6 bars as the maximum with which our device operates in stable fashion

Besides, we aim at developing partial oxidation of HC under relatively low pressures for specific applications, such as chemical conversion of gas associated with oil (otherwise burned m flares at almost atmospheric pressure), of biogases produced m low pressure digesters, of hydrocarbon permeates originating from membrane separation, etc Our process at relatively low pressure thus makes it possible to avoid high energy consumption compressors and facilities at high degree of techmcity connected with the traditional high pressure technology of the catalytic auto-thermal process.

Companson of our present results with the results obtained from the literature mdicates the supenonty of the new GhdArc-II device (descnbed heremabove) with respect to a traditional 0₂/HC burner used m an auto-thermal process. For reference, we take the details published by the Haldor Topsoe company (Denmark) m the article by CHRISTENSEN and PRIMDAHL previously mentioned. Although the mformation is not complete, we can establish some balances of matenal of the mdustnal process us g only the chemical energy of more or less exothermic reactions (6) through (8) Without any mformation on the NG treated, we consider it comparable to pure methane Table 5a summarizes the data (marked HT) taken from this article

Another companson is made with respect to very complete data published m November 1995 by S.C NIRULA m "Synthesis Gas, Report No. 148A", SRI International, Menlo Park, California. MRULA's report provides some information on the volume of the mdustnal reactor (94 m³), the flow rate of entermg gases (200,000 m³(n)/h) and outlet temperature (1350°C). The data and balances (recalculated by us) are also inserted m Table 5a under a SRI reference

Table 5 a

First of all, we note that these are fhermo-catalytic processes under high pressure The HCs, confronted with a relatively oxygen-nch flame (theoretically, one should stop at 0₂ HC ~ 0.5) at over 2000°C, are consumed preferentially towards C0₂ and H₂0, accordmg to reaction (8) rather than (7), leavmg large quantities of unconsumed HCs (especially methane, the chemically sturdiest). It is only m the presence of a large mass of a fragile catalyst that the conversion of the HCs is completed accordmg to the endothermic reforming reactions (1) or (la) and (4) or (4a) on a catalytic bed exposed to very high temperatures (1100-1400°C). This catalyst and its support should then present very high resistance and very good stability under severe conditions

In no mdustnal example or pilot test do CHRISTENSEN and PRIMDAHL mention the 0,/C ratio lower than 0.54 and the H,0/C ratio lower than 0 58. Instead, on the contrary, they emphasize the need for addmg at least these quantities of oxygen and water vapor m order to ensure proper operation of their burner, requiring also special recirculation. We, mstead, can reduce these ratios respectively to 0 06 and zero (tests without water vapor), since we have another adjustment button: the very active energy of mobile electπc discharges added to the very sub- stoichiometπc flame! Therefore, we demonstrate, for the first time, the feasibility of a new NG conversion assisted by mobile discharge plasma m the presence of oxygen or of oxygen-ennched air, or of atmosphenc air with possible addition of steam. This process is illustrated in Tables 4 and 5 through the conversion of a model NG m a new GhdArc-II reactor m which the plasma zone (with all the electrodes) is brought to a temperature not over 1150°C. Another post-plasma zone communicates directly with that of the plasma. This post-plasma zone, at a temperature lower than 1100°C can be partially filled with a solid metal or ceramic matter which, m contact with a flow of products of treatment of the hydrocarbon feed with plasma, becomes active and participates m a total or almost total conversion of the HCs mto SG with more or less co-generated ethylene and acetylene. In the presence of oxygen and, possibly, of the steam added, we can thus convert all the HCs, such as CH₄, C₂H₆, C₃H₈ and C₄H,₀ mto synthesis gas and also, partially, mto valuable products: C₂H₄ and C₂H₂, without usmg traditional catalysts.

A broad range of ratios of the two oxidizers (0₂ and H₂0) with respect to the NGs may be used. Our examples are given for 0₂/NG values between 0 06 and 0.97 and H₂0/HC between 0 and 2 5, but it is evident that we can further expand at will these two terminals from zero to infinity, smce our mobile discharges can be generated m pure water vapor as well as m pure oxygen. Thus, all the H₂0/0₂/NG mixtures can be converted m the reactor descnbed herem Accordmg to need, we can in this manner obtain synthesis gas with an H₂/CO ratio near 2 for the

FT synthesis of synthetic oil, or of methanol, or a highly hydrogen-nch synthesis gas for the synthesis of ammonia, or yet a gas highly nch m CO for Syntheses called "oxo" ..., without bemg limited to these examples. As previously, we note the total or almost total absence of soot, coke or other undesirable products at the time of the NG conversion

We pomt out also the presence of considerable (but adjustable m content) quantities of unsaturated hydrocarbons C₂H₄ and C₂H₂ in our conversion products. These are of additional value, smce, mixed with the synthesis gas, they facilitate construction of hydrocarbon chains at the time of the FT synthesis. Thus, formed at the same time as CO and H₂ dunng the conversion of hydrocarbons m mobile discharges, these unsaturated molecules will contnbute to the direct application of an improved FT synthesis of liquid hydrocarbons

In most of the tests involving 0₂ or C0₂, we determine a conversion of the initial ethane which is considerably less than that of methane, propane and butanes. In some tests, we even have more ethane leavmg than entermg, hence a negative conversion or rather a synthesis of ethane. This effect, apparently strange, nevertheless confirms the feasibility of the methane dimenzation reaction (7) by a radical process mvolvmg probably two CH₃ fragments formed after gentle oxidation by the oxygen (excited?) onginating from 0₂, introduced as plasma-forming gas or by a radical denvmg from plasmatic dissociation of C0₂. This production of ethane starting from methane is very visible m the presence of certain bodies inserted m the post-plasma zone

Production of Hydrogen, Acetylene and Ethylene Starting from Hydrocarbons

The partial pyrolysis of methane yields a considerable quantity of Hydrogen at largely lower price than that of water electrolysis, smce the previously mentioned reaction (2a) shows a standard enthalpy (at 1 ami and 298 K) of 125.5 kJ/mol H₂, while, for the electrolysis, this enthalpy is 285.8 kJ/mol H₂ In the case of Pyrolysis, at the same time other highly valuable products are recovered, such as acetylene and, m smaller amount, ethylene, m accordance with reaction (2)

However, the pyrolysis of methane earned out m the thermal plasmas of arcs or of traditional plasma torches causes almost total destruction of the methane, in accordance with reaction (2b) expected for complete thermodynamic equilibrium. Our thermodynamic calculations for 1 4 atm, applied to partial equilibrium (barring the appearance of graphite) nevertheless mdicate the possibility of running the reactional path (2a). For that, the required conditions are as follows: raismg the temperature to approximately 1700 - 2300 K and quickly quench the system, bπngmg it down to temperatures around 700 K m order to protect the fragile acetylene (or ethylene) molecule. Thus, the production of soot via reaction (2b) is prevented

Table 6 presents confirmation of these assumptions Our tests under atmosphenc pressure and at limited power are very encouragmg The same NG, diluted by hydrogen (m order to prevent cokmg) is mtroduced, under control, mto the GhdArc-II reactor The reactor is not thermally msulated and the gases enter at ambient temperature, hence the large losses of energy The stationary and mobile electrodes are made of stamless steel; no post-plasma compartments

The matenal balance still mdicates the presence of soot which we must find m the products. In fact, m a filter at the outlet of the reactor, we collect a small amount of very fine, dry soot, with nanometnc granulation and high resistance to thermal graphitization which appears only at the end of very long heating at 2800 °C

Table 6

The selectivities of NG pyrolysis towards acetylene, ethylene and soot mdicate that reaction (2b) of the complete pyrolysis is m the minonty. This is surpnsmg at this low level (~ 300°C) of average temperatures of the outgomg gases. In fact, the methane entermg the active discharge is treated at certainly much higher "temperature" (smce this concept is reserved for the complete thermodynamic equihbnum), but the products of this plasma pyrolysis are soon abandoned at relatively low temperature, smce the mobile discharge is no longer present

Our tests reopen a very important technology method (forgotten, however, smce it mvolves acetylene produced from calcium carbide). In fact, acetylene was a good base for the syntheses of vanous final or intermediate products. Moreover, the extraordinary quality of the other product, soot, leads us to believe m a future renewal of the method mentioned

Upgradmg Conversion of Heavy Hydrocarbons Fuel production discards a "bottom of the barrel" consisting of a very heavy residue. This black and viscous residue, resulting from the extraction of light products from the crude, is a very hydrogen-poor hydrocarbon In order to convert it mto gasolme or other valuable liquid products, it would be necessary to restore the equihbnum of its molecular deficit either by adding hydrogen or by removmg carbon, both operations bemg difficult and very expensive due to the excessive content of metals, sulfur and mtrogen These elements, present m the crude m relatively small quantity, have ended by concentration (despite subsequent punfications) m this last product of the all refining operations

Facmg the scarce external outlets for heavy fuels, but also the mcreasmg ratio of heavy oils m proven reserves, the Refiner must then m the end mcreasmgly resort to so-called conversion units This conversion of refinery residues (or, possibly, of very heavy primary feeds) mto gasoline or diesel oil, although very expensive, has regamed the mterest of the oil companies It would also offer commercial compensations deeper conversion of residues m gasolme and other valuable liquids The most effective technological solution is to be chosen Liquid HC

(naphtha, diesel oil) bemg by far the most desirable, this is the reason why the processmg techniques which lead to obtaining maximum yields of these products are preferred by Refiners

The sulfur and metal contents m the residues may attam very high values, makmg it much more difficult to treat and upgrade the products The metals (V, Na) are undesirable poisons for the traditional hydro-treatment catalysts and render the hydrogen processes inoperative

In the "bottom of the barrel", we find a C/H ~ 1 atomic ratio In order to upgrade this residue, several methods are possible, depending on the agents which are gomg to allow attack of the molecules and/or segregation m cuts

• The most brutal agent seems naturally to be oxygen partial oxidation may lead to total destruction of the carbon skeletons, gasification is almost complete, although with the formation of fatty soots for which it is necessary to find an upgrading method Nevertheless, we prefer "gentle" plasma oxidation leadmg to a large portion of liquid fraction lighter than the processed feed

In order to improve the C/H ratio of the residue, obviously, hydrogen can be added However, m addition to the high cost, this requires highly pure hydrogen, without CO, which is poison for the catalysts Moreover, it is almost impossible to hydrogenate and to hydrocrack directly a heavy residue, due to the presence of high concentrations of metals, sulfur and mtrogen compounds poisonmg the catalyst

It is also possible to imagme attacking the heavy load with these two reagents at the same time, l e by water at high temperature Steam-gasification is then obtained, leadmg to the production of gas highly πch m hydrogen Nevertheless, we advocate a "gentle" steam-gasification assisted by electnc discharge plasma, leadmg to a large portion of liquid fraction lighter than the processed feed

Lastly, we will mention steam cracking of heavy feeds at very high temperature for the production of a gaseous phase containing hydrogen, acetylene, ethylene, olefins and aromatic di-olefins But we prefer to recover also liquids via our process assisted by electnc discharges

Several preliminary tests were performed m the reactor m vertical position by introducing fogs of heavy

HCs These fogs ongmated from preheating (up to 370°C) of liquid hydrocarbons (such as gasoil or n-C₁₆) driven with a process gas (dosed by flow meter) by means of a dosing pump through a tubular oven heated by electnc resistance The liquid would evaporate partially m the oven, thus forming a mixture of gas/vapors/droplets which entered through the upper part of the reactor to undergo four stages of the mobile discharge Part of the liquid would be thrown on the inner walls of the reactor by centntugal force from rotation of the central disks dnving the rotation of the gas (and of the fog) filling the reactor A liquid film thus would flow slowly on the walls while bemg m contact with the post-discharge gas containing multiple active radicals The products of the conversion exited through the lower part of the reactor where they were separated m a trap at 0°C mto liquids and gas/vapors for qualitative and quantitative analysis For the liquids, we use gas chromatography (a FID detector and a column capable of properly separating the hydrocarbons from C₅ to C₂₀)

Tests with pure n-C,₆ (Hexadecane or otherwise Cetane) simulating a heavy feed were performed m the presence of vanous plasma-forming gases: H₂ and/or N₂, N₂/H₂0, N₂/0₂, CH₄/ N₂/0₂ or C0₂/N₂/0₂ m different proportions. The presence of oxygen seemed puzzlmg, but we envisioned a process m which part of the heavy hydrocarbons (considered a waste to be upgraded) would be converted in place mto Hydrogen used to hydrogenate the other part of the load. Therefore, it was not a total gasification of heavy hydrocarbons that was sought, but, rather, a conversion to less heavy HCs We applied different pressures (between 1 and 3 bars), different proportions of gases m the mixtures, high mput temperature, etc. Thus, the n-C,₆ flow rate would vary between 0.16 and 0.50 kg/h, the flow rate of the incoming plasma-forming gas between 1 4 and 2.4 m³(n)/h, the electnc power of the reactor between 0.7 and 2.0 kW. The most important vanable of this set was found to be the plasma-forming gas. It should be noted that, regardless of which plasma-forming gas, the same type of "useful" light product is always observed m the liquid recovered: the alpha-olefins centered on C_π (between C₆ and C₁₅).

• Six tests were performed with Hydrogen We thus demonstrated that GhdArc-II can operate with this gas at pressure up to 3 bars. The quantity of the "light" liquid fraction m the liquid product existing was less than 5%. At the same time, we observed very pronounced gasification up to 50%

(mamly towards acetylene and ethylene). The mcrease of the mput temperature of the feed and of the gas (for almost equal specific energies and pressures) would seem to play a positive role from the pomt of view of the mam objective

One test was performed for 2 bars with Nitrogen We first demonstrated that GhdArc-II can operate with this gas at high pressure (3 bars) and that this Nitrogen plasma yields less fraction C_{6 15}, less HC gas (especially CH₄) and more soot m the gas (grayish smoke) and m the reactor

(deposit).

Seven previous tests were performed with H, + N, mixtures for pressures between 2 and 3 bars

However, the most important vanable was the concentration of Hydrogen (from 100% to 0%). For similar conditions, it is possible to see that the mcrease m H, content causes the overall yield of the

C_{6 15} liquid product to nse and that the mcrease of the mjection temperature of the feed for a low

H, content does not yield the result desired (the result is better at a lower temperature with the availability of a 90% H₂ plasma- forming gas). The quantity of the liquid fraction concerning C₆ „ m the liquid product exiting was always less than 5% We observed less pronounced gasification of the feed when the H₂ content is reduced It would appear that transfer of N₂ excitation towards

H₂ or NH radicals plays a positive role The role of the hydrogen plasma at low temperature seems to be limited, perhaps when an additional medium intervenes in the system This analysis seems to be remforced by our experiments conducted as a function of the gas volume and of the nature of the gas in which the role of the hydrogen plasma alone m the conversion phenomenon seems to remam relatively low The first conclusions which we draw from this are that the hydrogen plasma (at low temperature) hardly acts on liquid HCs (fine droplets) and that the experimented reduction conditions do not appear to be very favorable towards obtaimng major conversion of heavy HCs mto light liquid fractions We note a high presence of acetylene and of alpha-olefins. It is, therefore, imperative to explore other plasma-formmg gases as follows • A test with an N, + H₂Q mixture (very moist Nitrogen) was performed for 2 bars. We demonstrate first that GhdArc-II can operate with this mixture, which possibly opens a new approach for partial steam crackmg of heavy HCs at relatively low temperature and at low pressure. The test yields better conversion mto useful liquids (6% mstead of 1.3% m dry Nitrogen)

Let us say immediately that a presence of Oxygen pertains only to the initial gases entermg the reactor; m the plasma zone, a controlled oxidation occurs, which definitely produces: H₂, CO, C0₂ and H₂0 as final products of the radical reactions m which H, OH, CH₃, CH₂, CH and other radicals intervene Such reactions, m the presence of small amounts of oxygen, can be performed on a large scale only m the presence of a catalyst m homogeneous phase: the GhdArc-II plasma

Therefore, this would be an incomplete and "gentle" combustion which stops m a crackmg phase of the heavy HCs, m the presence of a hydrogenating (H,) or functionahzing agent (OH or CO, knowing that alcohols and ketones could be considered as fuels) Sixteen tests were performed for plasma-formmg gases (impovenshed air) containing 3.3 to 15% 0₂ (thus still m the presence of

Nitrogen) and CH₄ or C0₂. Another test with C0₂ is mcluded m this senes, smce it is known that this gas is easily decomposed m a plasma mto CO and very active Oxygen in statu nascendt. The pressures vary from 1 6 to 2.3 bars We demonstrate that GhdArc-II can also function as an electro-activator of a partial oxidation, m absolute safety (not the least accident dunng all the experimentation)! At the same time, we observe very pronounced gasification of the load mto CO and C0₂, as well as mto HC gas - but this is a pnce to pay to prevent consumption of the Hydrogen onginating externally. This conversion mto CO and CO, supplies heat which, m principle, will cause low consumption of electnc energy m a process m which GhdArc-II will serve only to mamtam this crackmg oxidation

In conclusion, the experiments conducted m the same conditions of pressure and temperature, although with plasma-formmg gases consisting of different CH₄ + air, C0₂ + air or N₂ + 0₂ mixtures, all yielded better results than the experiments in "Hydrogen" medium. We observed very few aromatic compounds m the liquid products and practically no CH₄ m the gaseous products (basically ethylene and acetylene for the HCs). By this method, we obtam m the liquid products up to 54% compounds between C₆ and C₁₅ with very pronounced maxima near C₁₀ - C_n

CO + H,0 <-> CO, + H₂ (Simple and Inverse) Shift

Table 7 shows the feasibility of these two reactions m the GhdArc-II reactor without the presence of a catalyst Our tests took place at atmospheric pressure and at limited power The reactor was not thermally msulated The stationary and mobile electrodes are made of stamless steel, no post-plasma compartments

Thus, we demonstrate the feasibility of either non-catalytic conversion operation assisted by GlidArc-II plasma. Thereby, we open a new method of conversion of the carbon matter which can be applied to improve the composition of synthesis gases, pyrolytic gases or gases originating from gasification of waste and various industrial releases, knowing that these gases contain poisoning molecules for catalysts. Therefore, conversion of these gases into a SG of the required quality for the FT process opens the industrial possibility of conversion of waste into very pure synthetic fuel.

It is obvious that the direct or inverse shift assisted by the discharges generated in GlidArc-II can also serve for the production of Hydrogen starting from CO or of CO starting from Hydrogen.

Other Remarks and Conclusions Our experiments have demonstrated the feasibility of a new process for the production of gases rich in hydrogen and carbon oxide, containing also very large quantities of C₂H₄ and C₂H₂. The process consists of producing these gases by means of the mobile electric discharges which strike directly in the light or heavy hydrocarbons mixed with water vapor and/or with carbon dioxide and/or with oxygen in any proportions. This causes oxidation and/or partial cracking of these hydrocarbons, avoiding the problems of the existing processes. The reagents, partially converted in a mobile discharge compartment, can then penetrate another post-plasma compartment near the direct reaction zone (plasma zone). There, in the presence of still active species, produced in the discharges and carried by the gas leaving the discharge zone, this gas undergoes an additional conversion at a slightly lower temperature than that present in the direct reaction zone.

The subject of this application is then a process which makes oxidation and partial cracking of hydrocarbons possible, in the active presence of water vapor and/or of carbon dioxide and/or of oxygen, without need for the intervention of other reagents or catalysts, as well as without the formation of soot, coke or tar which would hinder the proper operation of the reactor. The tests demonstrate clearly the feasibility of steam reforming, "dry" reforming with carbon dioxide, simultaneous reforming with an H,0/CO, mixture or partial oxidation with oxygen, all accompanied by hydrocarbon non-catalytic cracking. This partial oxidation and steam reforming are also accompanied by reforming with carbon dioxide (if it is already present in the NG or is created by the over-oxidation parasite reactions). Comparing Tables 1 through 6, we see that it is possible to oxidize or pyrolyze totally or partially a NG with reagents and/or diluent gases such as O,, C0₂, H,0, N, and H,. These conversions take place in a very broad range of concentrations, with or without the presence of metal or ceramic matter initially non-catalytic in the zone near the mobile discharge The result of this is the production of a synthesis gas or of Hydrogen more or less accompanied by ethylene and acetylene without (or nearly without) soot A free choice of the solid matter placed m contact with the post-plasma flow and a free choice of its temperature offer vast possibilities of onenting the composition of the product accordmg to need, dependmg on the composition of the hydrocarbon feed, the availability of oxygen, etc Thus, injecting more or less electnc energy directly mto the discharges (see the SE values), we can convert more or less HC For example, we can opt for a natural gas, seeded with hydrogen and carbon monoxide, for better combustion in piston engines or for transporting it through a traditional gas pipeline, to a civilized location where the CO and/or the H₂ would be extracted for a more sophisticated use We can also convert the entire hydrocarbon feed and then send to a FT synthesis of a synthetic liquid HC Everything mdicates that a combination of the auto-thermal process with mobile electnc discharges provides a new approach to products of greater mterest (presence of ethylene and acetylene), obtained starting from light or heavy HC feeds, partially oxidized by oxygen or by 0₂-eππched air or by atmosphenc air, all under low pressure of less than 6 bars

On a more technical level, the amazing ease of operation of the reactor and of its assembly, without detenoration of electrodes, electrode holders, zone separators and all the reactor walls must be emphasized, smce all these components are subjected to the action of mcommg reagents and outgomg products This is explamed by the moderate temperature of the assembly (< 1150°C) and by a very short contact time of the roots of the discharges with the stationary or mobile electrodes, even made of steel and even not cooled We add that we never changed the steel or Ni electrodes or the Ni chips m the post-plasma zone, they underwent severe temperature and pressure conditions, they have "seen" the HCs, the 0₂, the H₂0 and other gases and vapors, they have worked covered by a layer of soot at the time of some tests with very weak oxidizer HC, they have been exposed then to an air or pure oxygen or CO, plasma , it is clear that their activity does not depend on pre-treatment They become active whenever they are exposed to the residual flow of species from the plasma zone

Other positive points may also be mentioned for future practical application

• The energy cost of treatment of the gaseous or liquid matter m G dArc-II reactors does not appear to be high

• We note the absence of any catalyst except that generated spontaneously by the electπc discharge in the gas phase or on the suiface of initially inert bodies placed in contact with the gas flow leaving the mobile discharge

The necessary reagents are extremely simple water and/or C0₂ and/or 0₂ • The unit is very compact and, therefore, can be transported and installed near the storage, emission or extraction site of the products to be treated (for example, offshore oil platforms to convert associated gases)

The process does not depend on the chemical, composition or punty of the gases or liquids to be treated • With the exception of the use of atmosphenc or enriched air and of conversion of NG initially nch m C0₂ and/or N₂, the products exiting, after condensation of the water vapor, mclude very little

C0₂ and no other foreign ballast mcreasmg their volume, which makes the conversion and/or recyclmg operations easier

The GhdArc-II reactors have no thermal inertia and, therefore, can respond very quickly to control signals • Extrapolation to large volumes will be easy.

Even with a non-optimized reactor, a great part of the initial molecules is converted into synthesis gas and into unsaturated hydrocarbons. This conversion is greatly improved by a subsequent passage of the reagents in the zone of discharges stratified in several zones. It will certainly be possible to improve these results by increasing the power of the reactor. Since the GlidArc-II does not require any cooling, it can accept a gas arriving from high preheating, such as solar heat, which should reduce the electric demand of the process. It will then be possible to present our electrolysis in gaseous phase as a "cold" electric discharge developing in a hot gas.

While the present invention has been described with reference to particular embodiments, it will be understood that the embodiments are illustrated and that the invention scope is not so limited. Any variations, modifications, additions and improvements to the embodiments described are possible. These variations, modifications, additions and improvements may fall within the scope of the invention as detailed within the following claims.

Claims

WHAT IS CLAIMED IS:

1 A process compnsmg providmg one or more repetitive discharges between two or more electrodes, wherem at least one of said two or more electrodes is mobile, movmg said at least one mobile electrode to stretch said discharges and place said discharges off thermal equihbnum, and subjecting a flow of carbon substance to said discharges to promote chemical conversion of said carbon substance

2 The process of claim 1 wherem subjecting said flow of carbon substance to said discharges is performed at a pressure of between 0 1 and 6 bars and at a maximum temperature of 1150┬░C

3 The process of claim 1 wherem said carbon substance compnses heavy hydrocarbons and wherem said conversion compnses at least partial crackmg of said heavy hydrocarbons mto lighter carbon compounds

4 The process of claim 1 wherem said carbon substance compnses heavy hydrocarbons and wherem said conversion compnses at least partial oxidation of said heavy hydrocarbons mto lighter carbon compounds

5 The process of claim 1 further compnsmg combmmg said carbon substance with an oxidizer, wherem said chemical conversion compnses reformmg said carbon substance mto a synthesis gas contammg hydrogen H₂, carbon monoxide CO, and unsaturated hydrocarbons

6 The process of claim 1 wherem said carbon substance compnses carbon dioxide C0₂, wherem the process further compnses combmmg said carbon substance with a hydrogen-containmg substance, wherem said chemical conversion produces carbon monoxide CO

7 The process of claim 1 wherem said chemical conversion produces less than 5% soot or coke, expressed m mass of carbon converted

8 The process of claim 1 wherem said carbon substance compnses saturated hydrocarbons, and wherem said chemical conversion is achieved by pyrolysis of said hydrocarbons

9 The process of claim 8 wherem said chemical conversion mcludes pyrolysis of one or more additional substances selected from the group consisting of unsaturated hydrocarbons, soot, and hydrogen H₂ , wherem said one or more additional substances are generated by said pyrolysis

10 The process of claim 1 wherem said chemical conversion is earned out m the presence of a metal or ceramic body located near said discharges, said body havmg a temperature of less than or equal to 1150┬░C, wherem said body catalyzes said chemical conversion

11. A device for conversion of carbon substances comprising: a plasma compartment configured to allow gasses to pass therethrough; and an arc structure located within said plasma compartment, wherein said arc structure includes a first electrode and a second electrode which is movable with respect to said first electrode, wherein an electrical discharge between said first and second electrodes creates an off-equilibrium plasma.

12. The device of claim 11 wherein said second electrode is selected from the group consistmg of: a toothed disk; a disk having a smooth edge; and a disk having a brush around its circumference.

13. The device of claim 11 further comprising an electric generator coupled to said first and second electrodes.

14. The device of claim 13 wherein said generator comprises a multi-phase generator and wherein one pole of said generator is coupled to said first electrode and a neutral point of said generator is coupled to said second electrode.

15. The device of claim 13 wherein said generator comprises a plurality of monophase generators and wherein one pole of each of said plurality of monophase generators is coupled to said first electrode and another pole of each of said plurality of monophase generators is coupled to said second electrode.

16. The device of claim 11 further comprising a solid material located in close proximity to said electrodes.

17. The device of claim 11 further comprising a maturation compartment in fluid communication with said plasma compartment, wherein gasses pass through said plasma compartment and into said maturation compartment.

18. The device of claim 17 further comprising a solid material located within said maturation compartment.

19. A method comprising: providing a reactor having an arc compartment, said arc compartment having two or more electrodes wherein at least one of said the electrodes is mobile; introducing a mixture in gaseous form into said arc compartment, wherein said mixture comprises a carbon-containing substance; providing one or more electrical discharges between said mobile electrode and another of said electrodes to create an off-equilibrium plasma; and submitting said mixture to said off-equilibrium plasma to convert at least a portion of said mixture into a synthesis gas.