WO2010149339A1

WO2010149339A1 - Process for the preparation of hydrocarbons

Info

Publication number: WO2010149339A1
Application number: PCT/EP2010/003755
Authority: WO
Inventors: Poul Erik Højlund NIELSEN; Finn Joensen; Esben Lauge Sørensen
Original assignee: Haldor Topsoe A/S
Priority date: 2009-06-26
Filing date: 2010-06-22
Publication date: 2010-12-29

Abstract

The application relates to a process for preparation of hydrocarbons from a synthesis gas, in particular a synthesis gas obtained from gasification of a solid biomass. The synthesis gas comprises carbon monoxide, hydrogen and more than 20 mole % of inert gases and methane. The process comprises catalyticall the synthesis gas to an oxygenate mixture comprising methanol, dimethyl ether and/or higher alcohols; withdrawing the entire mixture and transferring said entire mixture to a catalytic oxygenate conversion step; catalytically converting methanol, dimethyl ether and/or higher alcohols to obtain a liquid phase comprising hydrocarbons and a gaseous phase comprising inert gases and methane; generating power from said inert gases and methane; pocessing said liquid phase comprising hydrocarbons into gasoline.

Description

Title: Process for the Preparation of Hydrocarbons

The invention relates to a process for the preparation of hydrocarbons from solid and liquid fuels. In particular, the invention relates to the preparation of hydrocarbons useful as gasoline compounds from synthesis gas obtained from solid fuel gasification.

The synthetic gasoline process is known to take place in two steps: the conversion of synthesis gas to oxygenates and the conversion of oxygenates to gasoline hydrocarbon product. These process steps may either be integrated, producing an oxygenate intermediate, e.g. methanol or methanol dimethyl ether mixtures, which along with unconverted syn- thesis gas is passed in its entirety to a subsequent step for conversion into gasoline or the process may be conducted in two separate steps with intermediate separation of oxygenates, e.g. methanol or raw methanol.

Useful oxygenates include methanol, dimethyl ether and higher alcohols and ethers thereof, but also oxygenates like ketones, aldehydes and other oxygenates may be applied.

In either case conversion of synthesis gas to oxygenates involves heat development in that both the conversion of synthesis gas to oxygenate and the further conversion of oxygenate to gasoline product are exothermic processes.

The production of gasoline by the integrated process scheme is discussed in US patent No. 4481305. Hydrocarbons and especially as gasoline are prepared by catalytic conversion in two subsequent reactors of a synthesis gas containing hydrogen and carbon oxides and having a mole ratio CO/H2 above 1 and when the conversion commences a mole ratio CO/CO₂ of 5 to 20. Synthesis gas is converted with high ef- ficiency in a first step into an oxygenate intermediate comprising predominantly dimethyl ether (DME) said mixture being converted in a second step into gasoline essentially according to the net reaction scheme

3H₂ + 3CO -> CH₃OCH₃ + CO₂ + Heat (1)

CH₃OCH₃ -> 2/n (CH₂) _n + H₂O + Heat (2)

(CH₂) n represents the wide range of hydrocarbons produced in the gasoline synthesis step. After separation of the hy- drocarbon product, unconverted synthesis gas comprising hydrogen and carbon oxides is recycled to the oxygenate synthesis step after CO₂ is at least partly removed, e.g. in a CO₂ wash.

Synthesis gas can be obtained in a variety of manners, for instance by reforming of natural gas or methane or by pre- reforming of higher hydrocarbons to methane, which can be subsequently converted to synthesis gas. Synthesis gas is then converted to gasoline hydrocarbon products.

US patent no. 5177114 discloses a process whereby natural gas is converted to synthesis gas, which in turn is converted to liquid hydrocarbon compounds. The liquid hydrocarbon compounds are removed to leave a residual qas stream containing unreacted hydrogen, carbon monoxide and natural gas components. The residual gas stream can be further treated. Combustion of solid renewable fuels such as biomass is associated with difficulty. Gasification of solid fuels provides a means of obtaining a gaseous fuel that is cleaner when burnt, as compared to direct combustion of the solid fuel. However, the synthesis gas produced by gasification of solid fuel contains a significant amount of undesirable elements which must be removed prior to the synthesis of the hydrocarbon gasoline products.

The general objective of the invention is to provide an improved process scheme for the preparation of valuable hydrocarbons, boiling in the gasoline range, from carbon monoxide rich synthesis gas, by an intermediate oxygenate syn- thesis and a gasoline synthesis, whereby inerts and methane present in the process gas do not require removal, but can be converted to valuable power and/or heat.

Recycle of unconverted synthesis gas to the oxygenate syn- thesis is optional and removal of carbon dioxide from the intermediate oxygenate synthesis product upstream the gasoline synthesis is not required.

It is a further objective of the invention to provide a process for the production of hydrocarbons boiling in the gasoline range and the co-production of power utilising the heating value provided by the gaseous phase (tail gas) resulting from the gasoline synthesis.

These and other objectives of the invention are addressed by a process for the preparation of hydrocarbons from a synthesis gas obtained from a solid fuel, the synthesis gas comprising carbon monoxide, hydrogen and more than 20 mole % of inert gases and methane by

(a) catalytically converting carbon monoxide and hydrogen comprised in the synthesis gas to an oxygenate mixture com- prising methanol, dimethyl ether and/or higher alcohols in the presence of the inert gases and methane,

(b) withdrawing from step (a) the entire oxygenate mixture comprising methanol, dimethyl ether and/or higher alcohols, including inerts and methane and transferring the entire oxygenate mixture including inert gases and methane to a catalytic oxygenate conversion step,

(c) catalytically converting methanol, dimethyl ether and/or higher alcohols comprised in the oxygenate mixture to obtain a liquid phase comprising hydrocarbons and a gaseous phase comprising inert gases and methane,

(d) transferring the gaseous phase comprising inert gases and methane to a power generation unit for generation of electrical energy and/or heat, and

(e) transferring the liquid phase comprising hydrocarbons for further processing to gasoline.

The following embodiments can be combined with each other in any order:

In an embodiment of the invention the synthesis gas is produced by air-blown gasification of a solid fuel.

In another embodiment of the invention the solid fuel is composed of biomass, bituminous coal, lignite or petroleum coke. In another embodiment the solid fuel is a mixture of bituminous coal, lignite or petroleum coke and biomass.

In an embodiment of the invention the inert gases in the synthesis gas comprise nitrogen, N2 and argon, Ar.

In an embodiment of the invention the catalytic conversion to the oxygenate mixture in step (a) is carried out in the presence of a catalyst selected from the group consisting of oxides of Cu, Zn, Al and their mixtures, and combined with a solid acid.

In an embodiment of the invention the catalytic conversion of methanol, dimethyl ether and/or higher alcohols com- prised in the oxygenate mixture to the liquid phase comprising hydrocarbons in step (c) is carried out in the presence of a zeolite catalyst.

In another embodiment of the invention the liquid compris- ing hydrocarbons comprises C2-C10 hydrocarbons.

In an embodiment of the invention, the synthesis gas additionally comprises carbon dioxide. Carbon dioxide can be present in amounts of at least 5 vol. %. Typically carbon dioxide is present in amounts of 5 to 15 vol. %.

In an embodiment of the invention, the synthesis gas has a molecular molar ratio between hydrogen and carbon monoxide of less than 1.5 and a molar ratio between carbon monoxide and carbon dioxide of less than 10.

In a preferable embodiment of the invention, the synthesis gas has a molecular molar ratio between hydrogen and carbon monoxide of approximately 1 and a molar ratio between car- bon monoxide and carbon dioxide of approximately 1 to 4 , thereby providing optimal conditions for gasoline synthesis .

The process of the invention is particularly suitable for small plants since recycle of unconverted synthesis gas is optional, thereby maintaining a relatively simple process. Furthermore air can be used directly to gasify solid fuel instead of oxygen, leading to production of gasoline hydrocarbon products and an unconverted synthesis gas which in- eludes nitrogen, other inerts and carbon dioxide which are suitable for the co-production of power. The inventive process can accommodate the presence of methane, which is transferred with the inerts, carbon dioxide and nitrogen for production of power.

Synthesis gas being useful for the invention is preferably adjusted to a H2/CO ratio of about 1, and is reacted ac- cording to reactions (3), (4) and (5) in presence of an oxygenate catalyst including the known methanol catalysts e.g. catalysts with copper, zinc and/or aluminium oxide or their mixtures combined with a dehydration catalyst com- prising a solid acid such as a zeolite, alumina or silica- alumina. The dehydration catalyst is useful for catalysing the dehydration of methanol to dimethyl ether (DME) according to reaction (5) .

CO + 2H₂ <→ CH₃OH (3)

CO + H₂O <→ CO₂ + H₂ (4) 2 CH₃OH <→ DME + H₂O (5)

The gasoline synthesis is performed at substantially the same pressure as employed in the oxygenate synthesis in the presence of a catalyst being active in the reaction of oxygenates to higher hydrocarbons, preferably C₅₊ hydrocarbons. A preferred catalyst for this reaction is the known zeolite H-ZSM-5.

The reaction of dimethyl ether to higher hydrocarbons is known to be strongly exothermic and needs either indirect cooling (e.g. boiling water or fluidised bed reactor) or dilution of the reacting gas (e.g. fixed-bed adiabatic re- actor) with an inert gas or the reaction product in order to control the reaction temperature.

It is a particular advantage of the process of the invention that it- r.^pn accept a relatively high content of inciL gases in the synthesis gas and even at moderate pressure provide a significant conversion of synthesis gas into gasoline. The inerts and methane, the inerts comprising ni- trogen, N₂ and argon, Ar, are carried through the entire gasoline synthesis steps and, eventually, end up in the gaseous stream (purge/tail gas stream) from the gasoline synthesis step subsequent to the product separation. The gaseous stream also contains significant amounts of carbon dioxide and also combustible components such as unconverted synthesis gas and light hydrocarbons and may as such be combusted with air to produce power and heat.

The synthesis gas is produced by air-blown gasification of a solid fuel. The air may, prior to being used in the gasification, be enriched in oxygen, e.g. through membranes or by other means. The solid fuel can be composed of biomass. It can also be composed of bituminous coal, lignite or pe- troleum coke. Furthermore, the solid fuel can be a mixture of bituminous coal, lignite or petroleum coke and biomass.

The synthesis gas obtained from air-blown gasification can comprise carbon monoxide, hydrogen and more than 30 mole % of inert gases such as nitrogen, and methane.

Gasoline is produced by feeding a syngas having a high inert level to an oxygenate reactor, preferably of the boiling-water type, charged with a catalyst system active in the conversion of synthesis gas into MeOH and DME according to the following reactions:

CO + 2H₂ <-> CH₃OH ( 3 )

CO- + U - / A \

\ -¹ /

2 CH₃OH <-> DME + H₂O ( 5 ) to produce an intermediate of MeOH and DME (2) which, together with unconverted synthesis gas, CO₂ and inerts is passed to the gasoline reactor.

Higher alcohols can be present and they are defined as being C2+ alcohols.

The oxygenate synthesis can be carried out at a temperature in the range of 200-300°C.

The oxygenate synthesis can be carried out at moderate pressures of approximately 4 MPs, but higher pressures of e.g. 8 to 12 MPa can be applied to increase the synthesis gas conversion and, in turn, the gasoline productivity.

The conversion of synthesis gas is also improved when higher alcohols and oxygenates are co-produced in the oxygenate synthesis. Suitable catalysts are alkali promoted oxides of copper, zinc, aluminium and/or their mixtures.

Suitable operation pressures are in the range of 2-20 MPa, preferably 4-8 MPa. Preferably, a boiling water reactor can be used to provide cooling of the exothermic oxygenate synthesis reaction.

The reaction effluent from the gasoline reactor contains hydrocarbons in the range from Cl to ClO, water and carbon dioxide and residual amounts of unconverted H₂, CO and inerts such as nitrogen and argon.

By cooling and condensation a liquid phase of water, a liquid phase of mixed gasoline and light petroleum gas (LPG) is obtained, referred to as raw gasoline, is separated from a gaseous phase containing inerts, light hydrocarbons such as methane, ethane, etc. and carbon dioxide originating from the synthesis gas and being formed in the upstream processes as described above. The raw gasoline may be further processed by conventional means to obtain a lower- boiling gasoline fraction and a fraction of LPG.

A part of the carbon dioxide containing gaseous phase can be recycled to the gasoline synthesis step for temperature control .

The process according to the invention does advantageously not require any separate upstream or intermediate carbon dioxide removal.

Still an advantage of the invention is that the amount of CO₂ being present in the synthesis gas feed stream and the amount of CO₂ being produced in the synthesis step may be recovered downstream the gasoline synthesis at essentially the synthesis pressure prevailing in the oxygenate synthesis step. This stream, apart from being rich in CO₂, contains inerts such as N₂ and Ar and also combustible compounds in appreciable amounts of unconverted H₂ and CO as well as uncondensed, primarily light, hydrocarbons and, therefore, represents a significant calorific value.

Therefore, the part of the C0₂-rich gaseous phase, which is not recycled to the gasoline synthesis, may advantageously be combusted thus providing source for producing power for instance electrical power. If recyle gas to the gasoline reactor is required, the amount of recycle gas is adjusted to provide an oxygenate (MeOH + DME) concentration inlet of the gasoline reactor between 2 and 10% by volume.

Conversion to power can be carried out by combustion with air in, e.g., a gas engine, gas turbine or steam boiler to produce electricity and heat.

One embodiment according to the invention is illustrated in figure 1. Gasoline is produced by feeding a syngas having a high inert level to an oxygenate reactor, preferably of the boiling-water type, charged with a catalyst system active in the conversion of synthesis gas into MeOH and DME ac- cording to the following reactions:

CO + 2H₂ <-> CH₃OH ( 3 )

CO + H₂O <-» CO₂ + H₂ ( 4 )

2 CH₃OH <-» DME + H₂O ( 5 )

to produce an intermediate of MeOH and DME which, together with unconverted synthesis gas, CO₂ and inerts is passed to the gasoline reactor in which MeOH and DME are converted into predominantly C3-C10 hydrocarbons and water.

By cooling and condensation is obtained a raw gasoline hydrocarbon phase and an aqueous phase. The gaseous phase, containing CO₂, inerts and combustible compounds such as hydrogen and carbon monoxide and additionally minor amouuL-s of light hydrocarbons like methane, ethane, etc. may thus may advantageously be combusted with air, e.g. in a gas en- gine, gas turbine or steam boiler to produce electricity and heat.

Fig. 1 shows an embodiment of the invention. A synthesis gas 1 as obtained by air-blown gasification of a solid fuel is fed to a boiling water oxygenate reactor at a pressure of 4 MPa to produce a reaction MeOH-containing and DME- containing mixture 2 at an exit temperature of 250°C. The effluent from the oxygenate reactor is passed to the gaso- line reactor where MeOH and DME are converted into a stream of C2-C10 hydrocarbons and water 3 and the resulting stream 3 is cooled to 5°C, causing the effluent (stream of C2-C10 hydrocarbons and water 3) to separate into a gaseous phase 4, a liquid phase 5 of raw gasoline and a liquid phase 6 of water. The gaseous phase 4 is combusted with air 7 in the combustor to generate heat and power.

Figure 2 represents a process layout similar to that shown in figure 1, the only exception being that a part of the gaseous phase resulting from the separation step is recycled to the gasoline reactor to dilute the oxygenate feed and thereby reduce the exothermicity of the feed gas. This will typically be required in process layouts where the gasoline synthesis takes place in an adiabatic reactor.

Referring now to Figure 2 a synthesis gas 1 as obtained by air-blown gasification of a solid fuel is fed to a boiling water oxygenate reactor at a pressure of 8 MPa to produce a reaction MeOH-containing and DME-containing mixture 2 at an reactor exit temperature of 250°C. The effluent from the oxygenate reactor is mixed with a recycle stream 4' to form stream 2' diluted with respect to MeOH and DME. Stream 2' is fed to the gasoline reactor where MeOH and DME are converted into C₂-CiO hydrocarbons and water and the resulting stream 3 is cooled to 5°C, causing the effluent to separate into a gaseous phase 4, a liquid phase 5 of raw gasoline and a liquid phase 6 of water. The part of the gaseous phase 4 which is not recycled to the gasoline reactor (4'') is combusted with air 7 in the combustor to generate heat and power.

EXAMPLES

Example 1

This example demonstrates the effect of conducting the process at a moderate pressure.

Referring now to Figure 1 and Table 1 a synthesis gas as obtained by air-blown gasification of a solid fuel and having the composition according to reference number 1 in Table 1 is fed to a boiling water oxygenate reactor at a pressure of 4 MPa to produce a reaction MeOH-containing and DME-containing mixture 2 at an exit temperature of 250°C. The effluent from the oxygenate reactor is passed to the gasoline reactor where MeOH and DME are converted into C2- ClO hydrocarbons and water and the resulting stream 3 is cooled to 5°C, causing the effluent to separate into a gaseous phase 4, a liquid phase 5 of raw gasoline and a liquid phase 6 of water. The gaseous phase 4 is combusted with air (7) in the combustor to generate heat and power. Table 1

Example 1 demonstrates that a synthesis gas containing more than one third by volume of inerts (nitrogen and methane) may be partly converted at a modest pressure such as 4 MPa to produce gasoline and leaving a tail gas (gaseous phase) that may be combusted to produce power and heat.

By the calorific values presented in Table 1 may be calculated a lower heating value efficiency of 36 %, based on the recovered gasoline product.

Example 2 This example demonstrates the effect of conducting the process at a higher pressure: Referring now to Figure 2 and Table 2 a synthesis gas 1 as obtained by air-blown gasification of a solid fuel and having the same composition as in example 1 (composition according to reference number 1 in Table 2) is fed to a boil -ing water oxygenate reactor at a pressure of 8 MPa to produce a reaction MeOH-containing and DME-containing mixture 2 at an reactor exit temperature of 250°C. The effluent from the oxygenate reactor is mixed with a recycle stream 4' (8072 NmVh) to form stream 2' diluted with respect to MeOH and DME. Stream 2' is fed to the gasoline reactor where MeOH and DME are converted into C2-C1₀ hydrocarbons and water and the resulting stream 3 is cooled to 5°C, causing the effluent to separate into a gaseous phase 4, a liquid phase 5 of raw gasoline and a liquid phase 6 of wa- ter. The part of the gaseous phase 4 which is not recycled to the gasoline reactor 4'' is combusted with air 7 in the combustor to generate heat and power.

Table 2

Example 2 demonstrates that, by increasing the synthesis pressure, the gasoline productivity may be substantially- increased reaching a lower heating value efficiency of 45%.

Claims

1. Process for the preparation of hydrocarbons from a synthesis gas obtained from a solid fuel, the synthesis gas comprising carbon monoxide, hydrogen and more than 20 mole % of inert gases and methane, by

(a) catalytically converting carbon monoxide and hydrogen comprised in the synthesis gas to an oxygenate mixture comprising methanol, dimethyl ether and/or higher alcohols in the presence of the inert gases and methane,

(c) catalytically converting methanol, dimethyl ether and/or higher alcohols comprised in the oxygenate mixture to obtain a liquid phase comprising hydrocarbons and a gaseous phase comprising inert gases and methane, (d) transferring the gaseous phase comprising inert gases and methane to a power generation unit for generation of electrical energy and/or heat, and

2. Process according to claim 1, wherein the synthesis gas is produced by air-blown gasification of a solid fuel.

3. Process according to claim 2, wherein the solid fuel is composed of biomass.

4. Process according to claim 2, wherein the solid fuel is bituminous coal, lignite or petroleum coke.

5. Process according to claim 2, wherein the solid fuel is a mixture of bituminous coal, lignite or petroleum coke and biomass.

6. Process according to claim 1, wherein the inert gases comprise nitrogen, N₂ and argon, Ar.

7. Process according to claim 1, wherein the catalytic conversion to the oxygenate mixture in step (a) is carried out in the presence of a catalyst selected from the group consisting of oxides of Cu, Zn, Al and their mixtures, and combined with a solid acid.

8. Process according to claim 1, wherein the catalytic conversion of methanol, dimethyl ether and/or higher alcohols comprised in the oxygenate mixture to the liquid phase comprising hydrocarbons in step (c) is carried out in the presence of a zeolite catalyst.

9. Process according to claim 1, wherein the liquid comprising hydrocarbons comprises C2-C10 hydrocarbons.

10. Process according to anyone of the previous claims, wherein the synthesis gas additionally comprises carbon dioxide .

11. Process according to anyone of the previous claims, wherein the synthesis gas has a molecular molar ratio between hydrogen and carbon monoxide of less than 1.5 and a molar ratio between carbon monoxide and carbon dioxide of less than 10.

12. Process according to anyone of the previous claims, wherein the synthesis gas has a molecular molar ratio between hydrogen and carbon monoxide of approximately 1 and a molar ratio between carbon monoxide and carbon dioxide of approximately 1 to 4.

13. Process according to anyone of the previous claims, wherein the synthesis gas additionally comprises at least 5 vol% carbon dioxide.