ZA200509836B - Process for improving the pour point of hydrocarbon charges resulting from the Fishcier-Tropsch process, using a catalyst based on ZBM-30 zeolite - Google Patents

Description

The present invention relates to a process for improving the pour point of hydrocarbon charges resulting from the Fischer-Tropsch process, in particular for converting, with a good yield, charges having high pour points to at least one fraction having a low pour point and a high viscosity index for the oil bases, by passing over a catalytic hydrodewaxing catalyst comprising at least one ZBM-30 zeolite (molecular sieve) synthesized in the presence of a particular structuring agent such as triethylenetetramine, at least one porous mineral matrix, at least one hydro- dehydrogenating element, preferably chosen from the elements of Group VIB and

Group VII of the periodic table.

Prior art

High-quality lubricants are of fundamental importance for the satisfactory operation of modern machinery, cars and lorries. However, the quantity of untreated paraffins originating directly from petroleum, and having suitable properties for constituting good lubricants is very small compared with the growing demand in this sector.

The treatment of heavy petroleum fractions with high linear or slightly branched paraffins contents is necessary in order to obtain high-grade base oils with the best possible yields, by an operation aimed at eliminating the linear or very slightly branched paraffins, from charges which will then be used as base oils or as kerosene or jet fuel.

In fact paraffins with a high molecular weight, which are linear or very slightly branched and which are present in oils or in the kerosene or jet fuel lead to high pour points and therefore to solidification phenomena for low-temperature uses. In order to reduce the pour points, these linear, unbranched or very slightly branched paraffins must be entirely or partially eliminated.

This operation can be carried out by extraction using solvents such as propane or methyl ethyl ketone, which is called propane or methyl ethyl ketone (MEK) dewaxing.

However, these techniques are expensive, lengthy and not always easy to implement.

Another means is selective cracking of the longest linear paraffin chains which leads to the formation of compounds with a lower molecular weight, some of which can be eliminated by distillation.

Given their form selectivity, zeolites are among the most widely-used catalysts. The idea underlying their use is that zeolitic structures exist, the pore openings of which are such that they allow the entry of the long linear or very slightly branched paraffins into their micropores, but exclude branched paraffins, naphthenes and aromatics. This phenomenon thus leads to a selective cracking of the linear or very slightly branched paraffins.

Catalysts based on zeolites having intermediate pore sizes such as ZSM-5, ZSM-11,

ZSM-12, ZSM-22, ZSM-23, ZSM-35 and ZSM-38 have been described for their use in these processes in particular in the patents US 3,894,938; US 4,176,050; US 4,181,598; US 4,222,855; US 4,229,282 and US 4,247,388.

Mixtures of zeolites with large pores and these zeolites with intermediate pores which can be used in a dewaxing process are described in Patent W002088279.

Moreover, it was found that processes using these zeolites (ZSM-5, ZSM-11,

ZSM-12, ZSM-22, ZSM-23, ZSM-35 and ZSM-38) make it possible to obtain oils by cracking of charges containing quantities of linear or very slightly branched paraffins of less than 50% by weight. However, for charges containing higher quantities of these compounds it transpired that their cracking leads to the formation of large quantities of products with lower molecular weights, such as butane, propane, ethane and methane, which considerably reduces the yield of sought products.

To overcome these drawbacks, the applicant concentrated his research efforts on the development of a process for improving the pour point of hydrocarbon charges resulting from the Fischer-Tropsch process using catalysts comprising at least one ZBM-30 zeolite, at least one hydro-dehydrogenating element, preferably chosen from the elements of Group VIB and Group VIII of the periodic table. The applicant then v £ discovered, surprisingly, that by using a catalyst comprising at least one ZBM-30 zeolite synthesized with a particular structuring agent such as triethylenetetramine it is possible to lower the pour point of the charge yet obtain a high viscosity index (VI) and maintain a good yield of desired products. Unexpectedly, in fact, the catalyst prepared with the

ZBM-30 zeolite synthesized in the presence of the triethylenetetramine structuring agent has a greater dewaxing activity and selectivity (pour point improvement) than the solids based on ZBM-30 that have been synthesized via other structuring agents and the zeolite-based catalytic formulae known from the prior art.

The present invention proposes a catalytic process for reducing the pour point based on such catalysts.

Object of the invention

More precisely the invention relates to a process for improving the pour point of a paraffinic charge produced by Fischer-Tropsch synthesis, in which the charge to be treated is brought into contact with a catalyst comprising at least one ZBM-30 zeolite synthesized with a particular structuring agent such as triethylenetetramine, at least one hydro-dehydrogenating element, preferably chosen from the elements of Group VIB and

Group VII of the periodic table, and at least one porous mineral matrix. This dewaxing process is carried out at a temperature between 200 and 450°C, a pressure between 0.1 and 25 MPa and an hourly space velocity between 0.05 and 30 h™', in the presence of hydrogen at a rate of 50 to 2000 normal litres of hydrogen per litre of charge (NI/1). ~The synthesis of the ZBM-30 zeolite is described in the patent EP-A-46504.

Unexpectedly, said catalyst has a greater dewaxing activity and selectivity (improvement of the pour point of charges resulting from the Fischer-Tropsch process) than the catalytic formulae based on zeolites (molecular sieve) known in the prior art.

Advantageously, this process makes it possible to convert a charge having a high pour point to a product having a lower pour point and makes it possible to obtain base oils having good low-temperature properties and a high viscosity index and gasoils of good quality.

The charges which can be treated according to the process of the invention are advantageously fractions having relatively high pour points, the value of which it is wished to reduce.

Typical charges which can be treated advantageously according to the invention generally have a pour point above 0°C. The products resulting from the treatment according to the process have pour points below 0°C and preferably below approximately -10°C.

The process according to the invention, under the conditions described above, allows, in particular, the production of products having a low pour point with good yields, and a high viscosity index in the case of the heaviest fractions which are treated with a view to producing oil bases.

Detailed description of the invention

The process according to the invention uses a catalyst which comprises at least one

ZBM-30 zeolite synthesized with a particular structuring agent such as triethylenetetramine, at least one hydro-dehydrogenating element, preferably chosen from the elements of Group VIB and Group VII of the periodic table and at least one porous mineral matrix.

The synthesis of the ZBM-30 zeolite is described in the patent EP-A-46504.

The ZBM-30 zeolite is synthesized according to the methods described in the patent

EP-A-46504 according to the procedure using the structuring agent triethylenetetramine.

The overall Si/Al ratio of the zeolites included in the composition of the catalysts according to the invention as well as the chemical composition of the samples are determined by X-ray fluorescence and atomic absorption.

The Si/Al ratios of the zeolites described above are those obtained on synthesis according to the procedures described in the various documents cited or obtained after post-synthesis dealumination treatments well known to a person skilled in the art, such as, non-exhaustively, hydrothermal treatments followed or not followed by acid attacks or direct acid attacks by solutions of mineral or organic acids.

The zeolites included in the composition of the catalysts of the process according to the invention can be calcined and exchanged by at least one treatment with a solution of at least one ammonium salt in order to obtain the ammonium form of the zeolites which, once calcined, leads to the hydrogen form of said zeolites.

The zeolites included in the composition of the catalyst of the process according to the invention are at least in part, preferably practically totally, in acid form, ie. in the hydrogen form (H*). The Na/T atomic ratio is generally below 10% and preferably below 5% and even more preferably below 1%.

Moreover, the catalyst contains at least one hydro-dehydrogenating element, preferably chosen from the elements of Group VIB and Group VIII (i.e. metal or compound) of the periodic table and at least one porous mineral matrix.

In the case where the element is at least one metal of Group VIII, preferably when it is at least one noble metal and advantageously a noble metal chosen from the group comprising platinum and palladium, it can be introduced onto the zeolites for example by dry impregnation, by ion exchange or any other process known to a person skilled in the art, or it can be introduced onto the matrix.

According to a first variant, prior to its shaping, the zeolite previously described is subjected to the application of at least one metal of Group VIII, preferably chosen from the group formed by platinum and palladium.

The zeolite is then shaped by any technique known to a person skilled in the art. It can in particular be mixed with a matrix, generally amorphous, for example a moist alumina gel powder. The mixture is then shaped, for example by extrusion through a die.

The shaping can be carried out with matrices other than alumina, for example magnesia, amorphous silica-aluminas, natural clays (kaolin, bentonite, sepiolite, attapulgite), silica, titanium oxide, boron oxide, zirconia, aluminium phosphates, titanium phosphates, zirconium phosphates, charcoal and their mixtures. It is preferable to use matrices containing alumina, in all its forms known to a person skilled in the art, and even more preferably aluminas, for example gamma-alumina. Techniques other than extrusion, such as pelletting and dragée production, can be used.

Mixtures of alumina and silica, and mixtures of alumina and silica-alumina, can also advantageously be used.

The catalysts obtained are shaped in the form of grains of various shapes and dimensions. They are generally used in the form of cylindrical or polylobate extrudates such as straight or twisted bilobates, trilobates, polylobates, but can optionally be produced and used in the form of crushed powders, tablets, rings, beads, coils.

After the shaping stage, the product obtained is subjected to a drying stage then to a calcination stage.

In the case where the hydrogenating metal belongs to Group Vill, and is preferably platinum and/or palladium, it can also and advantageously be applied to the support after the shaping of the zeolite which is free of metals, using any process known to a person skilled in the art and allowing the application of the metal to the molecular sieve.

In this case the support is obtained in a manner analogous to that described previously.

In the remainder of the text, the term support will be used to describe the zeolite (free of metals), plus the matrix after shaping, drying and calcination, for example as obtained previously.

In order to apply the metal to the zeolite, it is possible to use the cation exchange technique with competition where the competitor is preferably ammonium nitrate, the competition ratio being at least equal to approximately 20 and advantageously approximately 30 to 200. In the case of platinum or palladium, a tetramine complex of platinum or a tetramine complex of palladium is customarily used: these latter will then be applied practically totally to the zeolite. This cation exchange technique can also be used in order to apply the metal directly to the molecular sieve powder, before its optional mixing with a matrix.

The application of the metal (or metals) of Group VIII is generally followed by calcination under air or oxygen, usually between 300 and 600°C for 0.5 to 10 hours, preferably between 350°C and 550°C for 1 to 4 hours. This can then be followed by reduction under hydrogen, generally at a temperature between 300 and 600°C for 1 to 10 hours, preferably operating between 350 and 550°C for 2 to 5 hours.

It is also possible to apply the platinum and/or palladium no longer directly to the zeolite, but to the matrix (for example the aluminium binder) of the support, before or after the shaping stage, implementing an anion exchange with hexachloroplatinic acid, hexachloropalladic acid and/or palladium chloride in the presence of a competing agent, for example hydrochloric acid. Generally after the application of platinum and/or palladium, the catalyst is, as previously, subjected to calcination then reduced under hydrogen as indicated above.

The support of the catalytic dewaxing catalyst according to the present invention generally has the following contents of matrix and zeolites: - 5 to 95 wt.%, preferably 10 to 90 wt.%, more preferably from 15 to 85 wt.% and very preferably from 20 to 80 wt.% of ZBM-30 zeolite, - 5 to 95%, preferably from 10 to 90%, more preferably from 15 to 85% and very preferably from 20 to 80 wt.% of at least one amorphous or poorly crystallized oxide- type porous mineral matrix.

The noble metal(s) content thus optionally introduced, expressed as a wt.% relative to the total mass of the catalyst, is generally below 5%, preferably below 3%, even more preferably below 2% and generally below 1 wt.%.

In the case where the catalyst comprises a hydrogenating metal of Group VIil preferably a noble metal and advantageously platinum and/or palladium, the catalyst is generally reduced in the reactor in the presence of hydrogen and under conditions well known to a person skilled in the art.

In the case where the hydrogenating metal is not a noble metal, any elements of Group

VIB and of Group VII! introduced into the catalyst according to the invention can be present totally or partially in metal form and/or oxide and/or sulphide form.

Among the elements of Group VIB, molybdenum and tungsten are preferred.

The sources of elements of Group VIB which can be used are well known to a person skilled in the art. For example, among the sources of molybdenum and tungsten, it is possible to use oxides and hydroxides, molybdic and tungstic acids and their salts, in particular ammonium salts such as ammonium molybdate, ammonium heptamolybdate, ammonium tungstate, phosphomolybdic acid, phosphotungstic acid and their salts.

Preferably ammonium oxides and salts are used, such as ammonium molybdate, ammonium heptamolybdate and ammonium tungstate.

The dewaxing catalyst according to the present invention can contain a non-noble metal of Group VIII and preferably cobalt and nickel. Advantageously, the following combinations of the non-noble elements of Groups VI and VIII are used: nickel- molybdenum, cobalt-molybdenum, iron-molybdenum, iron-tungsten, nickel-tungsten, cobalt-tungsten, the preferred combinations are: nickel-molybdenum, nickel-tungsten. It is also possible to use combinations of three metals for example nickel-cobalt- molybdenum.

The sources of elements of Group VIII that can be used are well known to a person skilled in the art. For example, nitrates, sulphates, phosphates, halides will be used, for example chlorides, bromides and fluorides, carboxylates for example acetates and carbonates.

When the hydrogenating function is provided by a non-noble metal of Group Vill or a combination of a non-noble metal of Group Vill and a metal of Group VIB, - the composition of the support constituted by at least one matrix and zeolites described in the invention is the same as that described previously and,

- the content by weight of at least one element chosen from the non-noble elements of

Group VIB and Group VIII is between 0.1 and 60%, preferably between 1 and 50% and still more preferably between 2 and 40%.

Generally, in order to conclude the preparation of the catalyst, the moist solid is left to rest in a moist atmosphere at a temperature between 10 and 80°C, then the moist solid obtained is dried at a temperature between 60 and 150°C, and finally the solid obtained is calcined at a temperature between 150 and 800°C, generally between 250 and 600°C.

The catalysts of the present invention can optionally be subjected to a sulphurization treatment making it possible to convert, at least in part, the metallic species to sulphide before they are brought into contact with a charge to be treated. This activation treatment by sulphurizing is well known to a person skilled in the art and can be carried out by any method already described in the literature.

In the case of the non-noble metals, a standard sulphurizing treatment well known to a person skilled in the art consists of heating in the presence or under flow of a hydrogen/hydrogen sulphide mixture or also under pure hydrogen sulphide, at a temperature between 150 and 800°C, preferably between 250 and 600°C, generally in a crossed-bed reaction zone.

Charges

The hydrocarbon charges treated according to the process of the invention are charges produced by Fischer-Tropsch synthesis and advantageously fractions having relatively high pour points, whose value it is wished to reduce. :

In general, at least a proportion of the compounds having a boiling point higher than or equal to 340°C is treated according to the invention.

In the Fischer-Tropsch process, synthesis gas (CO+H,) is converted catalytically to oxidized products and to essentially linear hydrocarbons in gaseous, liquid or solid form.

These products are generally free from heteroatomic impurities such as sulphur,

nitrogen or metals. They also have little if any content of aromatics, naphthenes and more generally cyclic compounds especially in the case of cobalt catalysts. In contrast, they may have a content of oxidized products that is not negligible which, expressed as oxygen by weight, is generally below approximately 5 wt.% and also a content of unsaturated compounds (olefinic products in general) generally below 10 wt. %.

However, these products, mainly consisting of normal paraffins, cannot be used as they are, in particular because their low-temperature properties are rather incompatible with the customary uses of petroleum fractions. For example, the pour point of a linear hydrocarbon containing 20 carbon atoms per molecule (boiling point equal to approximately 340°C, i.e. often included in the middle distillate cut) is approximately +37°C, which makes its use impossible, as the specification is -15°C for gasoil. The hydrocarbons resulting from the Fischer-Tropsch process, mostly comprising n- paraffins, must be converted to higher-grade products such as gasoil and kerosene, which are obtained, for example, after catalytic reactions of hydroisomerization.

Typical charges which can be treated advantageously according to the invention generally have a pour point above 0°C. The products resulting from the treatment according to the process have pour points below 0°C and preferably below approximately -10°C.

In the hydrocarbon charge which comes into contact with the catalyst based on ZBM-30 (from which oils and possibly distillates of high quality can be obtained) preferably at least 50 wt.% of the charge has a boiling point of at least 340°C, and even more preferably at least 60 wt.% and better still at least 80 wt.% of the charge has a boiling point of at least 340°C, preferably above at least 370°C and even more preferably above at least 380°C. This does not mean, for example, that the boiling point is 380°C and more, but 380°C or more.

The charge therefore consists mainly of normal paraffins.

Generally, charges which are suitable for the objective oils have an initial boiling point above at least 340°C and better still above at least 370°C and better still above at least 380°C.

Use of the catalyst according to the invention under the conditions described below makes it possible, in particular, to produce products with a low pour point with good yields, and with a high viscosity index in the case of the heaviest fractions which are treated with the aim of producing base oils.

Operating conditions

The operating conditions under which the catalytic dewaxing process of the invention is carried out are the following: - the reaction temperature is between 200 and 450°C and preferably between 200 and 420°C, advantageously 250-410°C; - the pressure is between 0.1 and 25 MPa and preferably between approximately 1 and 20 MPa; - the hourly space velocity (HSV expressed as volume of charge injected per unit volume of catalyst per hour) is between approximately 0.05 and approximately 30 and preferably between approximately 0.1 and approximately 20 h'! and even more preferably between approximately 0.1 and approximately 10 ht.

The contact between the charge and the catalyst is carried out in the presence of hydrogen. The level of hydrogen used is expressed in litres of hydrogen per litre of charge and is between 50 and approximately 2000 litres of hydrogen per litre of charge and preferably between 100 and 1500 litres of hydrogen per litre of charge.

Embodiments

In a preferred first embodiment, the catalytic dewaxing process according to the invention can be preceded by a hydroisomerization-hydroconversion stage in the presence of a catalyst containing at least one noble metal applied to an amorphous acid support.

This hydroisomerization-hydroconversion stage is optionally preceded by a hydrorefining stage for removing the (oxidized) heteroatoms, and this hydrorefining stage can be followed by an intermediate separation.

The hydroisomerization-hydroconversion stage takes place in the presence of hydrogen and in the presence of a bifunctional catalyst comprising an amorphous acid support (preferably an amorphous silica-alumina) and a hydro-dehydrogenating metal function provided by at least one noble metal of Group VIII.

The support is called amorphous, i.e. having no molecular sieve, and in particular zeolite, as well as the catalyst. The amorphous acid support is advantageously an amorphous silica-alumina but other supports can be used. When it is a silica-alumina, the catalyst generally does not contain added halogen, other than that which could be introduced for the impregnation, of the noble metal for example. The silica-alumina can be obtained by any synthesis technique known to a person skilled in the art, such as the techniques of co-precipitation, co-gelation, etc.

During the hydroisomerization-hydroconversion stage, the molecules of the charge to be treated, for example n-paraffins, in the presence of a bifunctional catalyst, undergo an isomerization then optionally a hydrocracking in order to lead respectively to the formation of isoparaffins and lighter cracking products such as gasoils and kerosene.

The conversion of the products having boiling points above or equal to the initial boiling point of the charge, which is at least 340°C, or even 370°C or better still at least 380°C, to products with boiling points below the initial boiling temperature of the charge generally varies between 5 and 90%, preferably between 5 and 80% but is generally preferably below 80% and better still below 60%.

The characteristics of the hydroisomerization-hydroconversion catalyst are, in more detail:

The preferred support used for preparation of the catalyst for pretreatment by hydroisomerization-hydroconversion described within the scope of this patent is composed of silica SiO, and alumina ALOs. The silica content of the support, expressed as percentage by weight, is generally between 1 and 95%, advantageously between 5 and 95% and preferably between 10 and 80% and still more preferably between 20 and 70% and between 22 and 45%. This silica content is measured exactly using X-ray fluorescence.

For this particular type of reaction, the metal function is provided by a noble metal of

Group Vil of the periodic table of the elements and more particularly platinum and/or palladium.

The noble metal content, expressed as a wt.% of metal relative to the catalyst, is between 0.05 and 10 and more preferentially between 0.1 and 5.

The noble metal distribution represents the distribution of the metal inside the catalyst grain, the metal being able to be well or poorly dispersed. Thus, it is possible to obtain platinum which is poorly distributed (for example detected in a crown the thickness of which is clearly smaller than the grain radius) but well dispersed, i.e. all the platinum atoms situated in the crown, will be accessible to the reagents. In our case, the distribution of the platinum is good, i.e. the profile of the platinum, measured according to the Castaing microprobe process, has a distribution coefficient above 0.1 and preferably above 0.2.

The BET surface area of the support is between 100 m%g and 500 m*g and preferably between 250 m?/g and 450 m*/g and for the silica-alumina-based supports, still more preferably between 310 m*/g and 450 m*/g.

The preparation and shaping of the support, and in particular of the silica-alumina, are carried out by the usual methods well known to a person skilled in the art.

Advantageously, prior to the impregnation of the metal, the support can undergo a calcination such as for example a heat treatment at 300-750°C (600°C preferred) for 0.25-10 hours (2 hours preferred) under 0-30 vol.% of water vapour (for silica-alumina 7.5% preferred).

The noble metal salt is introduced by one of the usual methods used to apply the metal (preferably platinum and/or palladium, platinum being especially preferred) to the surface of a support. One of the preferred methods is dry impregnation, which consists of the introduction of the metal salt into a volume of solution which is equal to the pore volume of the mass of catalyst to be impregnated. Before the reduction operation, the catalyst can undergo calcination, for example a treatment under dry air at 300-750°C (520°C preferred) for 0.25-10 hours (2 hours preferred).

Before use in the hydroisomerization-conversion reaction, the metal contained in the catalyst must be reduced. One of the preferred methods for carrying out the metal reduction is treatment under hydrogen at a temperature between 150°C and 650°C and a total pressure between 0.1 and 25 MPa. For example a reduction consists of a 2-hour plateau at 150°C then a rise in temperature to 450°C at a rate of 1°C/minute then a 2- hour plateau at 450°C: throughout this reduction stage, the hydrogen flow rate is 1000 litres of hydrogen per litre of catalyst. It should also be noted that any ex situ reduction method is suitable.

The operating conditions under which the hydroisomerization-hydroconversion stage is carried out are described below.

Pressure will be maintained between 2 and 25 MPa and preferably 3 to 20 MPa and advantageously 2 to 18 MPa, the hourly space velocity will be between 0.1 h' and 10 h’ preferably between 0.2 and 10 h! and advantageously between 0.5 and 5.0 h'. The hydrogen level is between 100 and 2000 litres of hydrogen per litre of charge and preferentially between 150 and 1500 litres of hydrogen per litre of charge.

The temperature used in this stage is between 200 and 450°C and preferentially between 250 and 450°C, advantageously between 300 and 450°C, and still more advantageously above 340°C, for example between 320 and 450°C.

In the case where a hydrorefining stage precedes the hydroisomerization- hydroconversion stage, the two stages of hydrorefining and hydroisomerization- conversion can be carried out on two types of catalysts in (two or more) different reactors, and/or on at least two catalyst beds installed in the same reactor.

The use of the catalyst described above in the hydroisomerization-hydroconversion stage has the effect of increasing the isomerization rate of the heavy fraction (340°C+,

or 370°C+ and better still 380°C+) and reducing its pour point. More generally, it is found that the treatment of the hydroisomerization-hydroconversion stage then makes it possible to obtain better yields of dewaxed oil fraction which will be obtained in the catalytic dewaxing stage and to obtain the desired viscosimetric properties (viscosity and viscosity index VI).

In one embodiment variant, all of the effluent from the hydroisomerization-conversion stage can be treated in the dewaxing process according to the invention. This variant, with passage of all of the effluent from the hydroisomerization-hydroconversion stage through the stage of catalytic dewaxing, is economically beneficial, since a single distillation unit is used at the end of the process. Moreover, in the final distillation (after catalytic dewaxing or subsequent treatments) a very-low-temperature gasoil is obtained.

In another variant, the effluent from the hydroisomerization-hydroconversion stage can undergo separation of at least a proportion (and preferably of at least a major part) of light gases comprising hydrogen and optionally also hydrocarbon compounds with a maximum of 4 carbon atoms. The hydrogen can be separated beforehand.

Advantageously, in another embodiment variant, the effluent from the hydroisomerization-hydroconversion stage is distilled in order to separate the light gases and also separate at least one residue containing compounds having a boiling point above at least 340°C. This is preferably an atmospheric distillation.

Distillation can advantageously be carried out to obtain several fractions (gasoline, kerosene, gasoil for example), having a boiling point of at most 340°C and a fraction (called residue) having an initial boiling point above at least 340°C and better still above 350°C and preferably of at least 370°C or 380°C.

This fraction (residue) is then treated in the catalytic dewaxing stage, i.e. without undergoing vacuum distillation. But in another variant vacuum distillation can be used.

Generally, in this text the term "middle distillates" refers to the fraction or fractions with an initial boiling point of at least 150°C and final boiling point up to before the residue, i.e. generally up to 340°C, 350°C or preferably below 370°C or 380°C.

The effluent from the hydroisomerization-hydroconversion stage can undergo, before or after distillation, other treatments such as for example extraction of at least a proportion of the aromatic compounds. in general, at least a proportion of the effluent from the hydroisomerization- hydroconversion stage, said effluent optionally having undergone the separations and/or treatments described above, is then subjected to the catalytic dewaxing process according to the invention.

It should be noted that compounds boiling above at least 340°C are always subjected to the catalytic dewaxing.

The effluent leaving the catalytic hydrodewaxing process according to the invention is advantageously sent to the distillation line, which preferably combines atmospheric distillation and vacuum distillation, with the aim of separating the conversion products with a boiling point below 340°C and preferably below 370°C, (and in particular including those formed during the catalytic hydrodewaxing) stage, and of separating the fraction which constitutes the base oil and whose initial boiling point is above at least 340°C and preferably above or equal to 370°C.

Moreover, this vacuum distillation section makes it possible to separate the different grades of oil.

Preferably, before being distilled, the effluent leaving the catalytic hydrodewaxing process according to the invention is, at least partly and preferably in its entirety, sent over a hydrofinishing catalyst in the presence of hydrogen so as to effect deep hydrogenation of any aromatic compounds still present which impair the stability of the oils and distillates. However, the acidity of the catalyst must be weak enough not to lead to the formation of cracking product with a boiling point below 340°C so as not to degrade the final yields in particular of oils.

The catalyst used in this hydrofinishing stage contains at least one metal of Group VIII and/or at least one element of Group VIB of the periodic table. The strong metal functions: platinum and/or palladium, or nickel-tungsten and nickel-molybdenum combinations, will be advantageously used in order to carry out deep hydrogenation of the aromatics.

These metals are deposited and dispersed on an amorphous or crystalline oxide-type support, such as for example aluminas, silicas, and silica-aluminas.

The hydrofinishing (HDF) catalyst can also contain at least one element of Group VII A of the periodic table of the elements. Preferably these catalysts contain fluorine and/or chlorine.

The contents of metals by weight are between 10 and 30% in the case of the non-noble metals and below 2%, preferably between 0.1 and 1.5%, and still more preferably between 0.1 and 1.0% in the case of the noble metals.

The total halogen quantity is between 0.02 and 30 wt.%, advantageously between 0.01 and 15%, or even more advantageously between 0.01 and 10%, preferably between 0.01 and 5%.

Among the catalysts which can be used in this hydrofinishing stage, leading to excellent performance, and in particular for obtaining medicinal oils, there can be mentioned catalysts containing at least one noble metal of Group VIII (platinum and palladium for example) and at least one halogen (chlorine and/or fluorine), the combination of chlorine and fluorine being preferred.

The operating conditions under which the hydrofinishing stage optionally following the catalytic dewaxing process according to the invention is carried out are as follows: - the reaction temperature is between 180 and 400°C and preferably between 210 and 350°C, advantageously 230-320°C; - the pressure is between 0.1 and 25 MPa and preferably between 1.0 and 20 MPa; - the hourly space velocity (HSV expressed as volume of charge injected per unit volume of catalyst per hour) is between approximately 0.05 and approximately 100 and preferably between approximately 0.1 and approximately 30 hl.

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The contact between the charge and the catalyst is carried out in the presence of hydrogen. The amount of hydrogen used, expressed in litres of hydrogen per litre of ~ charge, is between 50 and approximately 2000 litres of hydrogen per litre of charge and preferably between 100 and 1500 litres of hydrogen per litre of charge.

Advantageously, the temperature of the hydrofinishing stage (HDF) is below the temperature of the catalytic hydrodewaxing (CHDW) stage. The difference Tcrow-THor is generally between 20 and 200°C, and preferably between 30 and 100°C. The effluent leaving HDF is then sent to the distillation line.

In the first preferred embodiment of the process according to the invention including a preliminary hydroconversion/hydroisomerization stage, the base oils obtained in a process such as described above have a pour point below -10°C, a VI above 95, preferably above 110 and still more preferably above 120, a viscosity of at least 3.0 cSt at 100°C, an ASTM colour below 1 and a UV stability such that the increase in the

ASTM colour is between 0 and 4 and preferably between 0.5 and 2.5.

Another advantage of this embodiment of the process according to the invention is that it is possible to achieve very low aromatics contents, below 2 wt.%, preferably 1 wt.% and better still below 0.05 wt.%) and even to go as far as the production of medicinal- grade white oils having aromatics contents below 0.01 wt.%. These oils have UV absorbance values at 275, 295 and 300 nanometres below 0.8, 0.4 and 0.3 respectively (ASTM process D2008) and a Saybolt colour between 0 and 30.

Particularly interestingly, therefore, the process according to the invention also makes it possible to obtain medicinal white oils. Medical white oils are mineral oils obtained by thorough refining of petroleum; their quality is subject to various regulations that are intended to guarantee their harmlessness for pharmaceutical applications, they are non- toxic and are characterized by their density and their viscosity. Medicinal white oils essentially comprise saturated hydrocarbons, they are chemically inert and their aromatic hydrocarbons content is low. Particular attention is given to the aromatic compounds and in particular to 6 polycyclic aromatic hydrocarbons (PAH) which are toxic and present at concentrations of one part per billion by weight of aromatic compounds in white oil. The total aromatics content can be monitored using the ASTM method D2008: this UV adsorption test at 275, 292 and 300 nanometres makes it possible to monitor an absorbance below 0.8, 0.4 and 0.3 respectively (i.e. the white oils have aromatics contents below 0.01 wt.%). These measurements are carried out with concentrations of 1 g of oil per litre, in a 1 cm cell. The white oils on the market vary in viscosity and according to the crude from which they were obtained, which can be paraffinic or naphthenic, and these two parameters will lead to differences both in the physicochemical properties of the white oils in question and in their chemical composition.

In a second preferred embodiment, the dewaxing process of the present invention is used advantageously in the following sequence of stages: - the charge to be treated is separated (D1) into at least one light fraction 3 with a boiling point below 380°C, and at least one heavy fraction 4 (residue), - said light fraction 3, hydrogenated if necessary in a hydrotreatment (HDT) stage, is subjected to hydroisomerization (HISM), - said heavy fraction 4 is subjected to a hydrocracking (HCK) stage in the presence of hydrogen, and is then subjected to distillation (D2) to produce at least one light fraction (13) and at least one heavy fraction (10), - the mixture resulting from hydroisomerization (HISM) is fractionated (D3) at the same time as at least a proportion of the light fraction 13 obtained from distillation D2 to obtain middle distillates having excellent low-temperature properties, and/or a high cetane number and/or reduced emission of pollutants, - the heavy fraction from D2 is subjected to a dewaxing (DWX) stage to obtain, after separation of the volatile products formed, an isomerized liquid product which can be used as a high-grade lubricant base,

and the dewaxing process is the process according to the invention.

This especially preferred form of sequence including the process according to the present invention is shown schematically by the diagram in Figure 1.

A liquid stream 1 consisting of a mixture of linear hydrocarbons from a Fischer-Tropsch synthesis process, also containing unsaturated products (linear olefins), in an amount up to 10 wt.%, preferably from 2 to 5 wt.%, and oxidized products (especially alcohols) in an amount up to 10 wt.%, preferably from 2 fo 7 wt.%, is separated in a distillation column D1 into a light fraction 3 with a boiling point below 380°C, preferably between 260 and 360°C and a heavy fraction 4, which constitutes the distillation residue. The distillation in D1 is preferably carried out in a single stage (flash) and can be followed by differential offtake of two fractions directly from the Fischer-Tropsch synthesis reactor.

Preferably, the mass ratio between the two fractions 3 and 4 is in the range from 0510 2.0, even more preferably from 0.8 to 1.5.

The light fraction 3 will be the feed for a hydroisomerization (HISM) unit. However, especially in the case where heteroatoms or unsaturated groups, and oxidized compounds in particular, are present and could constitute a problem for the proper functioning of the catalyst in this stage, said fraction 3 will preferably feed a hydrogenation (HDT) unit in which it comes into contact with hydrogen (line 2) in the presence of a suitable catalyst, under conditions such as to minimize or even eliminate the hydrocracking reaction.

The hydrogenation unit (HDT) can be operated according to the usual techniques and comprises preferentially a reactor under pressure containing a fixed bed of catalyst selected in order to meet the aforementioned specifications. Typical hydrogenation catalysts meeting the above specifications comprise a hydrogenating metal, such as nickel, platinum or palladium supported on an inert or acidic solid such as alumina, silica, silica-alumina, zeolite or molecular sieve. Occurrence of a hydroisomerization reaction and partial hydrocracking during hydrogenation is not excluded, but is generally limited to conversion of less than 15 wt.% of the total feed fraction. The small fraction of volatile compounds (150°C-) and water that may be formed, can optionally be separated by means of a distillation operation.

The light fraction, hydrogenated or not hydrogenated, in a second phase, is then subjected to a stage of hydroisomerization (HISM) by means of line 6, in which it will react, still in the presence of hydrogen, under the usual conditions making it possible to achieve deep isomerization and partial rupture of the linear hydrocarbon chains. The appropriate conditions for isomerization are extensively reported in the state of the art as well as an extensive list of suitable catalysts.

A portion normally less than 50%, preferably between 0 and 25%, of said light fraction can optionally be taken by means of line 7, before the isomerization stage and mixed again with said heavy fraction from line 4 to be sent to hydrocracking.

In said isomerization stage, typically the hydrocarbon mixture is supplemented with hydrogen (line 5) in an amount between 150 and 1500 normal litres per litre of liquid and passes over a fixed bed of a suitable catalyst, preferentially based on noble metal, at an hourly space velocity between 0.1 and 10 h”! and a temperature between 300 and 450°C and a pressure between 1 and 10 MPa.

The isomerized mixture is introduced via line 14 into a fractionating column D3 with the light fraction 13 from column D2 of distillation of the heavy fraction sent for hydrocracking. In accordance with the embodiment, a middie distillate is obtained at the outlet of column D3, and is optionally taken off at two different levels to separate the kerosene (line 17) from the gasoil (line 18), having excellent low-temperature properties, a high cetane number, preferably above 50 and reduced emission of pollutants.

Smaller amounts of low molecular weight products are aiso obtained at the outlet of the distillation and fractionating column D3, in particular, via line 15, a gaseous fraction C1-

C5, of relatively little significance, normally via line 16, a light hydrocarbon fraction, preferably having a boiling point below 150°C (naphtha).

According to a particularly advantageous aspect of this embodiment of the present invention, the amount of these volatile fractions is reduced significantly in comparison with the similar processes of the prior art, preferably to less than 20 wt.%, more preferably to less than 15 wt.% relative to the initial feed of line 1.

The fraction (line 4) of hydrocarbons with a high boiling point and low content of oxidized and unsaturated compounds is supplemented with the necessary amount of hydrogen (line 8) and provides the feed for a hydrocracking (HCK) unit, using one of the usual techniques. The product obtained will feed, via line 9, a device for distillation and fractionation, which operates in a preferred manner to obtain separation of the hydrocarbon mixture essentially into two fractions. A light fraction, having a boiling point below 380°C, preferably below 350°C and containing less than 10 wt.% of volatile compounds (150°C-), consisting of a product having a high concentration of iso- paraffins, which will feed, via line 13, the stage for fractionation of the light fraction isomerized in HISM. This combining of the two streams, which come from the stages carried out on the initial feed and under different, but complementary conditions, makes it possible advantageously to obtain kerosene and gasoil fractions with the excellent properties mentioned previously. In this case, a portion, preferably less than 50 wt.%, of the mixture obtained from distillation D2 is fed via line 19 to the inlet of the isomerization stage (HISM) for further enhancement of the grade and distribution of the isomerized fractions and for controlling the relative amount of gasoil and kerosene produced.

The residual fraction from distillation D2 consists of a mixture of high boiling point hydrocarbons surprisingly having a reduced content of waxes, relative to the products obtained with other catalysts of the prior art under similar conditions. Such a residue can also be used "as is" for special uses, but will preferably feed (line 10) a stage of catalytic dewaxing (DWX) prior to its use as lubricant base. According to a preferred embodiment, the latter is partly recycled to the hydrocracking stage (HCK) via line 12 in order to control the productivity of the process or vary the degree of isomerization according to the production requirements.

Said dewaxing stage (DWX) is carried out according to the process of the present invention in the presence of a catalyst suitable for the required objective. The partially isomerized mixture will further react in the presence of hydrogen and a suitable solid catalyst as described previously, under the conditions of the process according to the invention.

Advantageously, as the amounts of linear paraffins have been reduced, the dewaxing stage according to the process of the present embodiment can be carried out under particularly favourable conditions of contact time and yield of lubricant base.

At the end of this dewaxing stage, the volatile products formed are separated (generally less than 3 wt.%), and an isomerized liquid product is recovered (line 11), with excellent low-temperature properties and a high viscosity, having an initial boiling point above 350°C, preferably above 360°C and having an optimum composition for use as a high- grade lubricant base.

The examples given below illustrate the invention though without limiting its scope.

Example 1: Preparation of the dewaxing catalyst C1 according to the invention

Catalyst C1 contains a ZBM-30 zeolite. This catalyst is obtained in accordance with the procedure described below.

The ZBM-30 zeolite is synthesized according to BASF patent EP-A-46504 with the organic structuring agent triethylenetetramine.

The raw ZBM-30 zeolite as synthesized is subjected to a calcination at 550°C under a stream of dry air for 12 hours.

The H-ZBM-30 zeolite (acidic form) thus obtained has an Si/Al ratio of 45.

The zeolite is kneaded with a type SB3 alumina gel supplied by the company Condéa.

The kneaded paste is then extruded through a die with a diameter of 1.4 mm. The extrudates thus obtained are calcined at 500°C for 2 hours in air. The content by weight of H-ZBM-30 is 80 wt.%.

Then the support extrudates are subjected to a stage of dry impregnation with an aqueous solution of the platinum salt Pt(NH;)42+.20H-. The platinum content by weight in the catalyst C1 thus obtained is 0.52%.

Example 2: Preparation of a dewaxing catalyst C2 not according to the invention

Catalyst C2 contains a ZBM-30 zeolite. This catalyst is obtained in accordance with the procedure described below.

The ZBM-30 zeolite is synthesized according to BASF patent EP-A-46504 with the organic structuring agent hexamethylenediamine.

The raw ZBM-30 zeolite as synthesized is subjected to a calcination at 550°C under a stream of dry air for 12 hours.

The H-ZBM-30 zeolite (acidic form) thus obtained has a Si/Al ratio of 54.

The zeolite is kneaded with a type SB3 alumina gel supplied by the company Condéa.

The kneaded paste is then extruded through a die with a diameter of 1.4 mm. The extrudates thus obtained are calcined at 500°C for 2 hours in air. The content by weight of H-ZBM-30 is 80 wt.%.

Then the support extrudates are subjected to a stage of dry impregnation with an aqueous solution of the platinum salt Pt(NH;)42+ 20H-. The platinum content by weight in the catalyst C2 thus obtained is 0.53%.

Example 3: Use of catalysts C1 and C2 for improving the pour point of a charge resulting from the Fischer-Tropsch synthesis process

Catalysts C1 and C2, preparation of which is described in examples 1 and 2, are used for improving the pour point of a charge consisting of paraffins resulting from Fischer- Tropsch synthesis for the purpose of obtaining oils. With this aim and within the non-

exhaustive scope of this example, the Fischer-Tropsch paraffins obtained from the paraffin production unit are distilled to obtain a 370°C+ cut. The main characteristics of the charge thus obtained are as follows: initial point 356°C 5% point 370°C 10% point 383°C 30% point 399°C 50% point 424°C 80% point 509°C 90% point 568°C 95% point 631°C pour point + 83°C density (20/4) 0.789

The catalytic testing unit comprises a fixed-bed reactor, with ascending circulation of the charge ("up-flow"), in which 80 ml of catalyst C1 or C2 is placed. The catalyst is then subjected to an atmosphere of pure hydrogen at a pressure of 10 MPa to effect reduction of the platinum oxide to metallic platinum then the charge is finally injected.

The total pressure is 10 MPa, the hydrogen flow rate is 1000 litres of gaseous hydrogen per litre of charge injected, the hourly space velocity is 1.1 h'! and the reaction temperature is 340°C. After reaction, the effluents are fractionated into light products (P1-150°C gasoline), middle distillates (150-370°C) and residue (370°C).

The following table shows the yields for the various fractions and the characteristics of the oils obtained directly with the charge and with the effluents hydroisomerized on catalyst C1 (according to the invention) then dewaxed catalytically.

According to the Not according to

CEC CU ICR

Raw conversion to 63.9 64.1 row

Distribution by fractions

Oil grade (fraction 370°C+)

Fugen) [0 [9

ET I SO

It can be seen very clearly that the charge treated with the catalyst (C1) according to the invention leads to an oil fraction (370°C+) of better quality: lower pour point and higher viscosity index than the catalyst (C2) which is not according to the invention, for similar degrees of conversion of the charge to products having boiling points below 370°C.

Example 4: Preparation of a catalyst C3 for hydroisomerization pretreatment of the charge resulting from the FT process subjected to dewaxing

The catalyst for pretreatment by hydroconversion-hydroisomerization C3 is prepared from a silica-alumina support used in the form of extrudates. It contains 40 wt.% of silica

SiO, and 60 wt.% of alumina Al,O;. Before the noble metal is added, the silica-alumina has a surface area of 332 m?/g and its total pore volume is 0.82 ml/g.

Catalyst C3 is obtained after impregnation of the noble metal on the support. The platinum salt ClsH-Pt is dissolved in a volume of solution corresponding to the total pore volume to be impregnated. The solid is then calcined for 2 hours in air at 500°C. The platinum content is 0.48 wt.%. Measured on the catalyst, the BET surface area is equal to 310 mg. The dispersion of the platinum measured by H,/O; titration is 75%.

Example 5: Use of catalyst C1 (according to the invention) for improving the pour point of a paraffinic Fischer-Tropsch charge pretreated on catalyst C3 (for converting hydroisomerization)

The catalyst (C3), the preparation of which is described in Example 4, is used for the hydroisomerization of a charge of paraffins resulting from Fischer-Tropsch synthesis for the purpose of obtaining oils. The paraffinic charge used in this example is the same as that used and described in Example 3.

The catalytic testing unit comprises a fixed-bed reactor, with ascending circulation of the charge ("up-flow”), in which 80 ml of catalyst C3 is placed. The catalyst is then subjected to an atmosphere of pure hydrogen at a pressure of 10 MPa to effect reduction of the platinum oxide to metallic platinum then the charge is finally injected.

The total pressure is 10 MPa, the hydrogen flow rate is 1000 litres of gaseous hydrogen per litre of charge injected, the hourly space velocity is 1.0 h'! and the reaction temperature is 350°C. After reaction, the effluents are fractionated into light products (P1-150°C gasoline), middle distillates (150-370°C) and residue (370%°C).

The residue (370°C) is then dewaxed in a second reactor with ascending circulation of the charge ("up-flow"), in which 80 ml of catalyst C1 is placed. The catalyst is then subjected to an atmosphere of pure hydrogen at a pressure of 10 MPa to effect reduction of the platinum oxide to metallic platinum then the charge is finally injected.

The total pressure is 10 MPa, the hydrogen flow rate is 1000 litres of gaseous hydrogen per litre of charge injected, the hourly space velocity is 1.1 h! and the reaction temperature is 335°C. After reaction, the effluents are fractionated into light products (P1-150°C gasoline), middie distillates (150-370°C) and oil fraction (370°C).

The characteristics of the oil obtained are measured.

The following table shows the yields for the various fractions and the characteristics of the oils obtained directly with the charge and with the effluents pretreated on catalyst C3 then dewaxed on catalyst C1 according to the invention.

Hydroisomerized Effluent effluent hydroisomerized and dewaxed

EE

Raw conversion to 40.5 32.1

Esra I EA

Distribution by fractions

Oil grade (fraction 370°C+) *Yields in the catalytic dewaxing stage

It can be seen very clearly that treatment of the charge on the hydroisomerization- conversion pretreatment catalyst C3 followed by treatment on catalyst C1 (according to the invention) makes it possible to achieve pour points that are distinctly lower than those obtained with just the pretreatment catalyst (C3) or just the catalyst C1 (see the table in Example 3). On the other hand, we can also see that the use of a pretreatment stage, upstream from catalyst C1 according to the invention, makes it possible to obtain a yield of oil fraction 370°C+ having a pour point of -21°C at a yield of 40.4 wt.% whereas the catalyst C1 (according to the invention) used does not permit the production of an oil fraction with such a low pour point (it is only -9°C) and the yield of this oil fraction is lower 36.1% (cf. table in Example 3). Finally, the viscosity index and the VI of the oil fraction obtained with the pretreatment stage and catalyst C1 according to the invention are higher than in the absence of the pretreatment stage.

Claims (13)

1. Process for improving the pour point of a charge resulting from the Fischer-Tropsch process in which the charge to be treated is brought into contact with a catalyst containing at least one 7ZBM-30 zeolite synthesized in the presence Of triethylenetetramine, at least one hydro-dehydrogenating element and at least one porous mineral matrix.

2 Process according to claim 1 in which the hydro-dehydrogenating element is chosen from the elements of Group VIB and Group Vii of the periodic table.

3. Process according to claim 2 in which the hydro-dehydrogenating element of Group VIB is molybdenum and/or tungsten.

4. Process according to one of claims 2 to 3 in which the hydro-dehydrogenating element of Group Vil is a noble metal of Group VIII.

5 Process according to claim 4 in which the hydro-dehydrogenating element of Group VII is platinum and/or palladium.

6. Process according to one of claims 1 to 5 in which the charges treated have at least 50 vol.% of compounds boiling above 340°C.

7 Process according to one of claims 1 to 6 in which the operating conditions are as follows: - the reaction temperature is between 200 and 450°C, - the pressure is between 0.1 and 25 MPa. - the hourly space velocity (HSV expressed as volume of charge injected per unit volume of catalyst per hour) is between approximately 0.05 and approximately 30 hl.

8. Process according to one of claims 1 to 7 in which the charge undergoes a hydroisomerization-hydroconversion stage before it is treated.

9. Process according to claim 8 in which the effluent from the hydroisomerization- conversion stage is sent in its entirety to the dewaxing stage.

10. Process according to one of claims 8 and 9 in which the hydroisomerization- hydroconversion stage is preceded by a hydrorefining stage.

11. Process according to claim 10 in which the hydrorefining stage is followed by an intermediate separation.

12. Process according to one of claims 1 to 11 in which the effluent leaving the catalytic hydrodewaxing stage is sent at least partially over a hydrofinishing catalyst.

13. Process in which the following stages are carried out: - the charge to be treated is separated (D1) into at least one light fraction 3 with a boiling point below 380°C, and at least one heavy fraction 4 (residue), - said light fraction 3 optionally hydrogenated in a hydrotreatment (HDT) stage is subjected to hydroisomerization (HISM), - said heavy fraction 4 is subjected to a hydrocracking (HCK) stage in the presence of hydrogen, and is then subjected to distillation (D2) to produce at least one light fraction (13) and at least one heavy fraction (1 0), - the mixture resulting from hydroisomerization (HISM) is fractionated (D3) at the same time as at least a proportion of the light fraction 13 coming from distillation D2 to obtain middle distillates having excellent low-temperature properties, and/or a high cetane number and/or reduced emission of pollutants, . the heavy fraction leaving D2 is subjected to a dewaxing (DWX) stage to obtain, after separation of the volatile products formed, an isomerized liquid product which can be used as a high-grade lubricant base,