US3714030A

US3714030A - Desulphurization and hydrogenation of aromatic-containing hydrocarbon fractions

Info

Publication number: US3714030A
Application number: US00089445A
Authority: US
Inventors: J Winsor; J Carruthers
Original assignee: Individual
Current assignee: Individual
Priority date: 1967-07-11
Filing date: 1970-11-13
Publication date: 1973-01-30
Anticipated expiration: 1990-01-30
Also published as: AT286476B; JPS4927170B1; GB1232393A; FR1573584A; NO122197B; BE717937A; NL6809780A; SE350981B

Abstract

A liquid phase process is disclosed in which an aromaticcontaining hydrocarbon fraction containing up to 50 ppm wt sulphur is desulphurized in the presence of only enough hydrogen to dissolve in the liquid feed-stock at the process conditions. The fraction is passed upwardly or downwardly through a bed of supported nickel catalyst which is preferably nickel sepiolite. This process may be preceded by conventional catalytic hydrodesulphurization and/or followed by hydrogenation, on one stage if the feedstock contains less than 30 percent wt aromatics and in two stages if the feedstock contains more than 30 percent wt aromatics.

Description

ilnited States Patent 1191 Winsor et al.

DESULPHURIZATION AND IIYDROGENATION OF AROMATIC- CONTAINING HYDROCARBON FRACTIONS Inventors: John Winsor, 5 8 Giffard Drive, Famborough; John Carruthers, 42 Sandalwood Avenue, Chertsey, both of England Filed: Nov. 13, 1970 Appl. N0.: 89,445

Related U.S. Application Data Continuation of Ser. No. 742,734, July 5, I968, abandoned.

Foreign Application Priority Data July ll, 1967 Great Britain ..3l,77l/67 U.S. Cl. ..208/2l0, 208/217, 260/667 Int. Cl ..Clg 23/02, C07c /l0 Field'of Search ..208/2l0, 209, 208 R, 212,213, 208/217, 244; 260/667 References Cited UNITED STATES PATENTS I 5/1966 Smith et al. 260/667 HYDROGEN Jan. 30, 1973 3,274,275 9/1966 Hutto et al. "260/667 3,3l8,965 5/1967 Hutto et al. ..260/667 FOREIGN PATENTS OR APPLICATIONS 1,098,698 l/l968 Great Britain ..260/667 57l,792 10/1958 Belgium ..208/2l0 Primary Examiner-Delbert E. Gantz Assistant Examiner-4L]. Crasanakis vAttorney-Morgan, Finnegan, Durham & Pine [57] ABSTRACT A liquid phase process is disclosed in which an aromatic-containing hydrocarbon fraction containing up to ppm wt sulphur is desulphurized in the presence of only enough hydrogen to dissolve in the liquid feedstock at the process conditions. The fraction is passed upwardly or downwardly through a bed of supported nickel catalyst which is preferably nickel sepiolitc.

This process may be preceded by conventional catalytic hydrodesulphurization and/or followed by hydrogenation, on one stage if the feedstock contains less than 30 percent wt aromatics and in two stages if the feedstock contains more than 30 percent wt aromatics.

16 Claims, 1 Drawing Figure PRODUCT I PATENTEDJAN30 Ian 3.714.030

HYDROGEN 2 FEED I PRODUCT I/WENTOES JOHN W/MS'OQ JOHN 64220771625 ATTORNEYS the lower boiling aromatics such as benzene and DESULPHURIZATION AND HYDROGENATION OF AROM ATlC-CONTAINING HYDROCARBON FRACTIONS CROSS-REFERENCE TO RELATED APPLICATION toluene, a very low content of sulfur is called for. Thus, it is desirable that fractions containing benzene required for hydrogenation to cyclohexane should have a very low sulphur content if the hydrogenation process employed uses a sulphur-sensitive catalyst such as nickel.

A low sulphur content may also be desirable in aromatic-containing hydrocarbon fractions which are to be subsequently processed over sulphur-sensitive catalysts such as elemental nickel.

It is also known that sulphur combines with nickel at moderate temperatures and pressures, and hence a process in which thearomatics are desulphurized over nickel is potentially feasible. However, it has been found that for such a process to be effective for long periods it has to be operated in the presence of hydrogen, although only a small amount may be required, particularly if the sulphur content of the feedstock is small. Thus, for a feedstock containing 20 ppm wt. sulphur the amount of hydrogen required is only 3.7 X 10"? liters at N.T.P. per liter of feedstock. The necessity for hydrogen to be present is believed to be due to the fact that the sulphur is present as organic sulphur compounds, and that as the sulphur is adsorbed, un-

saturated organic radicals are produced which tend to polymerize on the nickel surface and reduce its catalytic activity. If hydrogen is available these unsaturated radicals are hydrogenated to harmless saturated hydrocarbons. The need to have hydrogen present then introduces the risk of hydrogenation of the aromatic hydrocarbons, and the practical value of a desulphurization process using nickel thus turns on whether it is possible to find conditions in which desulphurization takes place without appreciable hydrogenation of the aromatic hydrocarbons. The hydrogen used should, of course, be sulphur-free. 1

The complete U.K. Pat. specification No. l,l4l,809 proposes one solution to the problem by claiming a process for the desulphurization of an aromatic-com taining hydrocarbon fraction containing 1-50 ppm wt. sulphur without appreciable hydrogenation of the aromatic hydrocarbons which comprises passing the fraction in the liquid or vapor phase, and in the presence of hydrogen, over supported nickel at an elevated temperature and pressure such that sulphur combines with the nickel but no substantial amount of hydrogen sulphide is produced, the equilibrium hydrogen partial pressure being greater than the minimum necessary to prevent catalyst de-activation but less than that at which up to 10 mol percent hydrogenation of the aromatic hydrocarbons occurs.

It has now beenfound that when operating in the liquid phase the quantity of hydrogen necessary can be simplythe amount which dissolves in the feedstock without there being any positive hydrogen partial pressure.

According to the present invention, therefore, a process for the desulphurization of an aromatic-containing hydrocarbon fraction containing up to 50 ppm 0 wt. of sulphur without appreciable hydrogenation of the aromatic hydrocarbons comprises passing the fraction in the liquid phase and in the presence of hydrogen upwardly or downwardly through a bed of supported nickel catalyst at an elevated temperature and pressure such that sulphur combines with the nickel but substantially no hydrogen sulphide is produced, the amount of hydrogen being not more than the maximum amount which would dissolve in the liquid fraction at the process temperature and pressure.

The aromatic-containing fraction need not consist wholly of aromatics, and in fact can contain any concentration of aromatics. Thus, for example, the feed stock may contain from to percent wt. of aromatics, for example, benzene, and the desulphurization may be preliminary to the hydrogenation of the aromatics to naphthenes. As a further example the feedstock may be a hydrocarbon distillate having up to 25 percent wt. aromatics, for example, a straight-run petroleum distillate boiling within the range 15-250 C. Such fractions are used for the production of SBP solvents, white spirits, and high quality kerosines, and may require de-aromatization in the presence of a sulphur-sensitive catalyst before they are suitable for such uses.

Preferred feedstocks, whether wholly or partly aromatic, are those boiling within the range l5-250 C. If the feedstock is not wholly aromatic the preferred other components are saturated hydrocarbons.

In a further aspect, the invention consists in a process in which an aromatic-containing hydrocarbon fraction is desulphuriaed by the above-mentioned process to produce a fraction containing up to 2 ppm wt. sulphur, and this fraction is hydrogenated in the presence of a supported nickel catalyst. Such hydrogenation may be carried out in one or more stages.

Although the present desulphurization process is capable of dealing with feedstocks containing up to 50 ppm wt. sulphur in any form, including thiophenic sulphur, the sulphur content is preferably not more than 10 ppm wt. Feedstocks containing higher amounts of sulphur than 50 ppm wt. can be subjected to any of the known catalytic hydrodesulphurization processes. Catalysts suitable for use in such processes may comprise one or more oxides or sulphides of elements of Groups Vla and Vlll of the Periodic Table on a support comprising one or more refractory oxides selected from oxides of elements of Groups ll to V of the Periodic Table, for example, cobalt oxide and molybdenum oxide on alumina. Typical reaction conditions in such known catalytic hydrodesulphurization processes are a temperature of 2045 10 C, a pressure of 50-1 ,500 psig, a space velocity (LHSV) of 0.1 to 20 v/v/hr and a hydrogen rate of ZOO-5,000 scf/brl. Such treatment serves to reduce the sulphur content to the desired level, or alternatively more than one stage of desulphurization over supported nickel according to the process previously described can be used. The present invention includes such catalytic hydrodesulphurization steps as are described above. If a preliminary hydrodesulphurization is carried out hydrogen sulphide produced must be removed before the feedstock is contacted with the supported nickel material in the subsequent desulphurization process, so that the desulphurization capacity of the nickel is not wasted on easily-removed sulphur. The majority of the hydrogen sulphide can be removed in the high pressure and low pressure separators which conventionally follow a catalytic hydrodesulphurization reactor. Alternatively, or in addition to such separators, hydrogen sulphide can be removed in any of the other known ways, for example, by stripping with inert gas, by washing with caustic soda, by adsorption on an adsorbent such as zinc oxide, clay, or molecular sieves, or by treatment with a solvent such as glycol-amine solution.

The hydrogenation stage or stages of the invention may use an aromatic feedstock containing up to 2 ppm wt. sulphur, although the desulphurization process is capable of producing a product containing less than 1 ppm wt. sulphur.

References to sulphur contents in the specification are to both combined and uncombined sulphur, but are expressed as the element.

Nickel is susceptible to de-activation by sulphur-containing materials, although it has a number of advantages over other substances used for the hydrogenation of aromatic hydrocarbons. The supported nickel catalysts used in the present processes may incorporate any of the known natural or synthetic support materials, such as the refractory oxides of elements of Groups II V of the Periodic Table, or kieselguhr, pumice or sepiolite. Sepiolite is the preferred material, and the preferred catalyst for both the adsorption desulphurization and hydrogenation processes of the invention is nickel on sepiolite prepared and activated according to the disclosure of British Patent No. 899652. It is not essential, however, that the same catalyst should be used in the desulphurization process as in any subsequent hydrogenation process.

Nickel on sepiolite prepared and activated according to the above-mentioned British Patent may contain from 1 to 50 percent wt. nickel (expressed as elemental nickel), and more particularly from 5 to 25 percent wt. Such a catalyst has a high nickel surface area, and has high activity and selectivity. It is capable of maintaining its hydrogenation activity in the hydrogenation stage or stages of the invention up to a sulphurmickel atomic ratio of 01:1, and its total sulphur capacity is much higher than this. We have found that sulphur sorption takes place at least up to 0.75:1 sulphurznickel atomic ratio. Since the sulphur capacity of the supported nickel material is high, and is known, it is possible to provide a sufficient amount to give an economic catalyst life. It has been found that a life in excess of 1 year can be obtained with nickel sepiolite using a feedstock containing 1.3 ppm wt. thiophenic sulphur.

The amount of hydrogen supplied should be controlled so that it is greater than the minimum necessary to prevent de-activation of the supported nickel. In addition, the extent of hydrogenation must be controlled, at least when the catalyst surface is fresh, so that an excessive temperature rise does not occur; the

hydrogenation of aromatics such as benzene being an exothermic reaction. Restriction of the amount of hydrogen supplied to that sufficient to saturate the liquid feedstock ensures that hydrogenation in the desulphurization stage occurs only to an acceptable extent, and hence that an excessive amount of heat is not evolved.

Saturation of the liquid feedstock with hydrogen, with substantially no free gaseous hydrogen present, and hence no hydrogen partial pressure, is accordingly of greatest value when the catalyst is fresh, i.e., unsulphided. However, although the same technique may be employed throughout the active life of the catalyst, the invention includes the method of operation of the desulphurization stage whereby when the nickel catalyst has become partly sulphided, and there is no risk of a temperature runaway, the amount of hydrogen supplied may be increased to a level at which a hydrogen partial vapor pressure exists. It should be emphasized that desulphurization according to the invention should always involve the use of the saturation technique when the catalyst is fresh.

When the nickel catalyst is fresh the inlet hydrogen to hydrocarbon ratio, based on total feed, should not exceed 0.3:1 molar. The nickel may be regarded as fresh when thesulphurmickel ratio at any point in the catalyst bed is less than 0.06:1 atomic. During use the inlet hydrogenzhydrocarbon ratio based on total feed should not at any time exceed 10:1 molar. Preferably, the inlet hydrogenzhydrocarbon ratio should be 0.001 to 02:1 molar.

The feedstock to the desulphurization stage may be in the vapor or liquid phase, depending on whether or not the nickel catalyst is sulphided, the criterion being the above sulphurznickel ratio of 0.06:1 atomic. When the catalyst is fresh the feedstock should be in the liquid phase, with upward or downward flow through the catalyst bed. As the catalyst becomes sulphided the feedstock may be maintained in the liquid phase as originally operated or, if the amount of hydrogen is increased to give a hydrogen partial pressure, the stage may be operated with the feedstock in the vapor phase, or still in the liquid phase. 1f the feedstock is highly aromatic and a mixed gas containing a relatively low proportion of hydrogen together with inert constituents is used, mixed phase operation is possible, since the inert gases will provide system pressure, and the extent of hydrogenation will be controlled by the small amount of hydrogen present.

The solubility of hydrogen in the feedstock will depend on the nature of the feedstock, the operating temperature, and the operating pressure, although it has been found in work done with single hydrocarbons at pressures up to 1,000 psig and temperatures up to about C, that the nature of the feedstock is of relatively little importance, i.e., that solubilities in aromatic and non-aromatic hydrocarbons are of the same order of magnitude. The operating temperature and pressure should be chosen from the ranges given below, and in the light of the known effects of these variables on the solubility of hydrogen in hydrocarbons, so as to provide the desired mode of operation.

Naphthenes can be supplied to the desulphurization stage if the aromatic content of the feedstock is high, i.e., greater than 15 percent wt. This is to avoid the rapid adsorption of hydrogen that would result from the hydrogenation of such an amount of aromatic hydrocarbons, which might cause a considerable variation in the concentration of hydrogen present and an excessive temperature rise. Naphthene addition may be by direct addition of suitable material or, more conveniently, by recycle of product from any subsequent hydrogenation stage or stages.

It has previously been shown that the temperature and pressure must be considered in relation to the hydrogemhyd'rocarbon ratio. in addition it is desirable to operate the desulphurization stage at a fairly high temperature, since the sulphur capacity and desulphurization activity of the supported nickel catalyst increase with temperature. In practice the upper limit of temperature is set by the onset of side-reactions such as cracking, isomerization, and possibly ring opening, the first of these being the most important. As the nickel becomes sulphided the operating temperature can be raised without by-product formation taking place. The space velocity of the stage will depend on the amount of sulphur present, andthe level to which it is to be reduced, but subject to these requirements it should be desirably as high as possible.

Having regard to the foregoing, the reaction conditions other than the hydrogemhydrocarbon ratio, may be selected from the following ranges:

(preferably 0.1 to 5) The temperature rises occurring must be within the range given. Thus the reactor exit temperature must not exceed the upper limit of the range and the inlet temperature must be above the lower limit. The upper limit will apply also to the increased temperature possible when the-nickel is partly sulphided.

The accompanying drawing illustrates, schematically, a possible mode of operation of the first (absorption desulphurization) stage of the invention.

In the drawing, a feedstock is pumped by pump 2 to a saturator 21.

Valves

15, 17, 18, 24, and 25 are closed Excess hydrogen leaves saturator 21 via

lines

22, 26, and 28.

Valves

23 and 27 are open, the latter acting as a pressure control valve, and the excess gas is vented off, desirably being used in the other stages of the invention. In the saturator 21 the feed is saturated with hydrogen, and the feed, containing dissolved hydrogen only, then leaves via lines 4 and 6 and open valve 5 to reactor 7, containing fresh catalyst. Liquid leaving reactor7 goes via

lines

8, 10, and 12, and open valve 11, to open valve 13, where it is flow-controlled out to the hydrogenation stage or stages via line 14, cooling taking place in condenser 9.

I When the activity of the catalyst has declined, more hydrogen is admitted to reactor 7 by closing

valves

5, 23, and 11, and opening

valves

15, 17, 18, 24, and 25. In this situation feedstock passes through saturator 21 and thence through valve 24 to reactor 7. Excess hydrogen is not bled off as before via valve 23, but passes with the feedstock into the reactor. Liquid leaving the reactor is cooled in condenser 9 as before, but instead of passing directly to product it enters a high pressure separator 16 via line 10 and valve 15. A secondary supply of hydrogen is supplied to separator 16 via valve 25 and valve 18 and

lines

20, 26, and 19 to maintain the system pressure. Excess gas is pressure-controlled out of the stage via valve 27. The liquid from separator 16 leaves via valve 17 and line 12 to flow control valve 13, and thence to product (i.e., to the hydrogenation stage or stages).

A fixed or fluidized catalyst bed may be used in the desulphurization stage. in the case of a fluidized catalyst, high liquid velocities may cause catalyst to be carried over with the product, in which case a settling tank will be necessary to separate the product and catalyst.

If the fraction containing up to 2 ppm wt. sulphur, obtained from the first stage, contains not more than 30 percent wt. aromatics it may be de-aromatized in one stage over a supported nickel catalyst. If, however, it contains more than this concentration of aromatic hydrocarbons, it should desirably be hydrogenated over supported nickel catalyst in two stages.

Accordingly, in a still further aspect, the invention consists ina process in which a hydrocarbon fraction containing more than 30 percent wt. aromatic hydrocarbons is desulphurized by the above-mentioned process to produce a fraction containing up to 2 ppm wt. sulphur, and this fraction is hydrogenated in two stages, both using supported nickel catalysts, in which not less than percent wt. and not more than 99 percent wt. of the aromatic hydrocarbons is hydrogenated in the first hydrogenation stage, with the hydrogenation reaction being substantially completed in the second hydrogenation stage, the temperature of the first hydrogenation stage being controlled by cooling, and the second hydrogenation stage being uncooled.

The first hydrogenation stage will be'designated the mainreactor stage, and the second hydrogenation stage will be designated the finishing reactor" stage.

The material entering the main reactor is preferably in mixed (gas/liquid) phase. It may be in mixed phase or in vapor phase on leaving the reactor, depending on the extent of hydrogenation taking place in the reactor, the extent of cooling, and thenature of the feedstock to the stage. The inlet material may possibly be in the vapor phase, but in this case as the outlet temperatures is fixed a large amount of recycle cooling would be necessary. Since the bulk of hydrogenation occurs in the first hydrogenation stage, i.e., the main reactor, the major part of the heat produced by the hydrogenation reaction is produced in this stage, and cooling in therefore necessary to control the stage temperature to within the desired limits. This cooling may be achieved either by liquid recycle or by the use of a cooled tubular reactor. Liquid may be conveniently recycled from the main reactor outlet or from the finishing reactor outlet. The use of liquid recycle means that the volume of material passing through the reactor is increased, and to achieve the same contact time the use of a larger reactor would be necessary. This can be avoided by using a cooled tubular reactor, with the catalyst in the tubes and a cooling agent being passed over them. In this way the temperature rise in the tubes is limited to the required range. In this type of reactor a higher average catalyst bed temperature can be attained for a given level of hydrogenation than is possible with an adiabatic reactor. Suitable cooling agents for the cooled tubular reactor are steam, water under pressure, gas, or indeed any substance which is thermally stable within the temperature range of the process. In such a system the limiting factor is the rate at which heat can be removed to keep the catalyst at a temperature within the acceptable range. If a cooled tubular reactor is used as the main hydrogenation reactor this stage is preferably in vapor phase throughout, since otherwise distribution difficulties may occur.

The most convenient recycle cooling medium is the hydrogenated feedstock and desirably this is, as far as is possible, in the liquid phase at the main reactor inlet, since the heat of vaporization will assist the cooling effect, and the minimum to achieve the necessary cooling can be recycled. This means that the total feed to the hydrogenation process enters the main reactor at as low a temperature as possible, provided that the temperature is high enough for the catalyst to be sufficiently active to give the required degree of hydrogenation. In order to achieve complete conversion in one stage it would be necessary to re strict the exit temperature to below 300 C, otherwise the hydrogenation reaction would not go to completion. In fact, the reaction temperature would have to be less than about 200 C, so that the hydrogen partial pressure would be at a suitable level in relation to the total pressure. Moreover, to obtain complete conversion and at the same time to maintain the temperature rise across the reactor at a suitable value would require recycle at a level which would unduly depress the hydrogen partial pressure. The alternatives of using a higher total pressure or a very large excess of hydrogen would be impracticable in a commercial process.

To obviate these difficulties, where a highly aromatic feedstock is to be hydrogenated, an uncooled finishing reactor is used in the process of the invention. From 90 to 99 percent wt, and preferably about 95 percent wt. hydrogenation of the aromatic hydrocarbons occurs in the main hydrogenation reactor, with the remainder of the conversion taking place in the finishing reactor. At these lower levels of conversion in the main reactor a higher main reactor exit temperature can be employed than if 100 percent conversion were attempted in the main reactor, while maintaining a satisfactory hydrogen partial pressure.

A higher hydrogen partial pressure is more easily maintained in the finishing reactor than in the main reactor, and completion of hydrogenation achieved without an unacceptable temperature rise, even though cooling is not employed in the finishing reactor. The finishing reactor can operate in mixed (gas/liquid) phase or vapor phase, and its outlet temperature can be, and preferably is, lower than the main reactor outlet temperature, since this is thermodynamically advantageous for high levels of conversion.

Desirably the flow of reactants in the main reactor is periodically reversed. This is because any sulphur not removed in the desulphurization stage would tend to deactivate the catalyst at the inlet side of the reactor, where the temperature, and thus the sulphur capacity of the catalyst, are lower than at the outlet. By flow reversal catalyst of higher sulphur capacity can be exposed to the material from the desulphurization stage with consequent extension of the main reactor catalyst life.

The hydrogen used in the process of the invention should be sulphur free. In can be commercially pure or it can be a mixed gas derived from a refinery process, such as steam reformer tail gas, also containing methane, or catalytic reformer off-gas. The use of catalytic reformer off-gas is preferred. Preferably the gas contains at least 50 mol. percent hydrogen, and more suitably to 99 mol. percent hydrogen. An advantage of the process is that hydrogen produced by steam reforming of natural gas or naphtha can be used without makeup gas compression.

In accordance with conventional practice gas can be recycled to the main reactor, and if a mixed gas is used, for example one containing methane, gas can be purged from the recycled gas stream, or not, as desired, or methane can be removed in the liquid leaving the high pressure separator. In the latter case optionally the product contained in the off-gas can be recovered, for example, by adsorption on activated charcoal or other suitable adsorbent.

The reaction conditions for the hydrogenation stages of a comprehensive process for the desulphurization and hydrogenation of aromatic hydrocarbon-containing feedstocks using a recycle cooled main reactor and an uncooled reactor, nickel on sepiolite being the catalyst in all stages, can be chosen from the following:

Main hydrogenation reactor Temperature 25 to 350C (preferably 122 to 570F (50 to Pressure 25 to 2000 psig (preferably 50 to 500 psig) Space velocity 0.01 to 10.0 v/v/hr (fresh feed) (preferably 0.5 to 5.0 v/v/hr) Product recycle ratio 0.1 to 10:1

(preferably 2.511 to 6:1)

Hydrogen recycle rate 50 to 5000 scf/brl (preferably 500 to 2000 scf/brl) The temperature rises occurring in each stage will be within the ranges given, the reactor exit temperatures not exceeding the upper limits of the ranges set out, and the inlet temperatures being above the lower limits.

The temperatures of the hydrogenation stage or stages may be increased during processing as necessary to allow for decreases in catalystactivity with time.

Where the desulphurized fraction from the first stage contains not more than 30 percent wt. aromatics, and is subsequently hydrogenated in one stage, the reaction conditions of the hydrogenation stage may be chosen from the ranges given above for the main reactor, except that the preferred range of product recycle ratio is from 1:1 to 6:1. Subject to this, the phase conditions of the material entering and leaving the hydrogenation stage, the amount of cooling required, and whether this is achieved by recycle or the use of a cooled reactor,

and whether or not hydrogen is recycled or onethrough operation is carried out, will depend on the aromatic content of the feedback to the stage.

The processes of the invention are capable of producing products having, in addition to sulphur levels of less than 1 ppm wt., aromatic contents of less than 2 ppm wt. from wholly aromatic feedstocks. Certain types of SBP solvents require aromatic contents of less than 30 ppm wt., and this can be achieved in a single hydrogenation stage with feedstocks containing up to 9 percent wt. aromatics. With kerosines, the initial aromatic content can be up to 25 percent wt., and reduction to an aromatic content of less than 1 percent wt. is easily possible.

References made in this specification to main hydrogenation reactors, and finishing reactors, or these terms suffixed by the word stage include the use of one or more reactors in any stage, or the use of one or more reactors containing more than one stage. It is only required that the catalysts of each stage should be specifically separate, and that independent control of the process parameters should be possible in each stage.

The invention is illustrated by the following examples.

EXAMPLE 1 Temperature C 204 Pressure psig 400 Space velocity (LHSV) v/v/hr 1.0 Make-up gas to saturator Under these conditions the sulphur content of the benzene was reduced to a very low level as follows:

Hours Sulphur Content on ppm wt. Stream Feed Product The benzene content of the blend did not alter in the process.

EXAMPLE 2 a. Desulphurization Over Nickel Benzene containing ca 5 per cent weight cyclohexane was desulphurized by processing it over nickel on sepiolite catalyst under the following liquid phase conditions, using the flow system described and illustrated: 5

Space velocity (LHSV) v/v/hr 1.0 Make-up gas to saturator H,

Pressure psig 200 lnlet temperature C 82 Outlet temperature C 207 Fresh feed space velocity v/v/hr 1.0

Product recycle space velocity v/v/hr 3.93 Total feed space velocity v/vlhr 4.93 Makeup gas Hydrogen Gas recycle rate on fresh feed scf/brl 5000 Gas recycle rate on total feed scf/brl 1000 H, partial pressure at psia 92 reactor outlet The hydrogenation activity of the catalyst declined very slowly as a result of a very low rate of sulphiding. The rate at which the operatingtemperature had to be raised to maintain hydrogenation at the required level was as follows:

Temperature Estimated Cyclohexane Content Catalyst Ratio of product HOS lnlet Outle SulphurzNickel C C Atomic wt.

If the same reate of deactivation were maintained the estimated catalyst life would be 5,500 hours, by which time the sulphurznickel ratio would be 0.021 1.

c. Finish Hydrogenation Stage The residual 3 to 5 per cent weight benzene was hydrogenated over nickel on sepiolite catalyst to yield high purity cyclohexane under the following conditions:

Pressure sig 200 Temperature F 208 Space velocity v/v/hr 1.0 Make-up gas Hydrogen Gas recycle rate scf/brl l Hydrogen: hydrocarbon ratio at reactor outlet molar 1:1 Hydrogen partial pressure at reactor outlet psia 108 Under these conditions the benzene content of the product was 1 to 2 ppm by weight. The run was in progress for 4,880 hours without any indication of a decline in the activity of the catalyst. The method of determining sulphur used was unable to detect any difference between the sulphur contents of feedstock and product. No estimation of catalyst life can be made, but from the data available it may be concluded that the catalyst would be active almost indefinitely.

The purity of the cyclohexane product was 99.78 per cent weight.

What is claimed is:

1. A process for the catalytic desulphurization of an aromatic-containing hydrocarbon fraction containing up to 50 ppm wt. sulphur without hydrogenation of more than mol percent of the aromatic hydrocarbons, which process comprises passing said fraction in the liquid phase with hydrogen through a bed of catalyst comprising nickel supported on sepiolite, at a temperature in the range 75 to 250 C., a pressure in the range 100 to 2,000 psig, a liquid hourly space velocity (LHSV) in the range 0.1 to 5 v/v/hr and an inlet hydrogenzhydrocarbon molar ratio in the range 0.001:l to 02:1, such that sulphur combines with the nickel but substantially no hydrogen sulphide is produced, the amount of hydrogen present being greater than the minimum necessary to prevent de-activation of the supported nickel catalyst but not more than the maximum amount that would dissolve in the liquid fraction at the process temperature and pressure.

2. A process as claimed in claim 1 in which the aromatic-containing hydrocarbon fraction contains from 95 to 100 percent wt. aromatics, and boils within the range -25 0 C, any other components present being saturated hydrocarbons.

3. A process as claimed in claim 1 in which the aromatic-containing hydrocarbon fraction is a straight-run distillate containing up to 25 percent wt. aromatics and boiling within the range 15-250 C.

4. A process as claimed in claim 1, in which the aromatic hydrocarbon-containing fraction containing up to 50 ppm wt. sulphur is desulphurized to produce a fraction containing up to 2 ppm wt. sulphur, and this fraction is then hydrogenated in at least one hydrogenation stage with a catalyst comprising nickel supported on sepiolite.

5. A process for the desulphurization of an aromaticcontaining hydrocarbon fraction containing more than ppm wt. sulphur without hydrogenation of more than 10 mol percent of the aromatic hydrocarbons which comprises first contacting the fraction in a hydrodesulphurization stage with one or more oxides or sulphides of elements of Groups Vla and VIII of the Periodic Table in the presence of hydrogen, to reduce the sulphur content of the feedstock to about 50 ppm wt. sulphur, removing the hydrogen sulphide formed, and the fraction from which the H 8 is removed being passed in the liquid phase with hydrogen through a bed of catalyst comprising nickel supported on sepiolite, at a temperature in the range 75 to 250 C., a pressure in the range 100 to 2,000 psig, a liquid hourly space velocity (LHSV) in the range 0.1 to 5 v/v/hr and an inlet hydrogenzhydrocarbon molar ratio in the range 0.001:l to 0221 such that the sulphur combines with the nickel but substantially no hydrogen sulphide is produced, the amount of hydrogen present being greater than the minimum necessary to prevent deactivation of the supported nickel catalyst but not more than the maximum amount that would dissolve in the liquid fraction at the process temperature and pressure.

6. A process as claimed in claim 1, in which the nickel on sepiolite catalyst used for the desulphurization and any subsequent hydrogenation stages contains from 1 to 50 percent wt. nickel.

7. A process as claimed in claim 6, in which the catalyst contains from 5 to 25 percent wt. nickel.

8. A process as claimed in claim 1, in which naphthenes are supplied to the desulphurization reaction when the aromatic content of the feedstock thereto is greater than 15 percent wt.

9. A process as claimed in claim 4, in which a hydrocarbon fraction containing more than 30 percent wt. aromatics is desulphurized to produce a fraction containing up to 2 ppm wt. sulphur and this latter fraction is hydrogenated in two stages, the first a main stage and the second a finishing stage, both of said stages using a catalyst comprising nickel supported on sepiolite, in which not less than percent wt. and not more than 99 percent wt. of the aromatic hydrocarbons is hydrogenated in the first hydrogenation stage, with the hydrogenation reaction being substantially completed in the second hydrogenation stage and in which the temperature of the first hydrogenation stage is controlled by cooling.

10. A process as claimed in claim 9, in which the reaction conditions for the first and second hydrogenation stages are selected from the following:

main hydrogenation reactor (first hydrogenation stage) 25 to 350C 25 to 2000 psig 0.01 to 10.0 v/v/hr Temperature Pressure Space velocity (fresh feed) Product recycle ratio 0.1 to 10:1 Hydrogen recycle rate on total feed 50 to 5000 scf/brl finishing reaction (second hydrogenation stage) 77 to 662F (25 to 350C 75 to 2000 psig 0.01 to 10.0 v/vlhr 100 to 5000 scf/brl.

Temperature Pressure Space velocity Hydrogen recycle rate 11. A process as claimed in claim 10, in which the reaction conditions for the first and second hydrogenation stages are selected from the following:

main hydrogenation reactor (first hydrogenation stage) Temperature 122 to 572F (50 to 300C) Pressure 50 to 500 psig Space velocity (fresh feed) 0.5 to 5.0 v/v/hr Product recycle ratio 2.521 to 6:1

Hydrogen recycle rate 12. A process as claimed in claim 9, in which the feedstock to the first hydrogenation stage is in mixed phase and the temperature of this stage is controlled by liquid recycle from the main reactor outlet or the finishing reactor outlet, and in which the finishing reactor outlet temperature is lower than the main reactor outlet temperature.

13. A process as claimed in claim 9, in which the flow of reactants in the main reactor is periodically reversed.

14. A process as claimed in claim 4, in which a hydrocarbon fraction containing not more than 30 percent wt. aromatics is desulphurized to produce a fraction containing up to 2 ppm wt. sulphur and this fraction is hydrogenated in one stage using conditions selected from the following:

Temperature C 25 to 350 Pressure psig 25 to 2000 Space velocity (LHSV) v/v/hr 0.01 to 10.0 Product recycle ratio 0.1 to :1 Hydrogen recycle rate on total feed scflbrl 50 to 5000.

15, A process as claimed in claim 14, in which the conditions are selected from the following:

Temperature C 50 to 300 Pressure psig 50 to 500 Space velocity (LHSV v/v/hr 0.5 to 5.0 Product recycle ratio lzl to 6:! Hydrogen recycle rate on total feed scf/brl 200 to 1000.

16. A process for the catalytic desulphurization of an aromatic-containing hydrocarbon fraction containing up to 50 ppm wt. sulphur without hydrogenation of more than 10 mol percent of the aromatic hydrocarbons, which process comprises passing said fraction in the liquid phase and with hydrogen through a bed of catalyst comprising nickel on a support, said support selected from the group consisting of Kieselguhr, pumice and sepiolite, at a temperature in the range to 250 C., a pressure in the range to 2,000 psig, a liquid hourly space velocity in the range 0.1 to 5 v/v/hr and an inlet hydrogen: hydrocarbon molar ratio in the range 0.001 :1 to 0211, such that sulphur combines with the nickel but substantially no hydrogen sulphide is produced, the amount of hydrogen present being greater than the minimum necessary to prevent de-activation of the supported nickel catalyst but not more than the maximum amount that would dissolve in the liquid fraction at the process temperature and pressure.

Claims

1. A process for the catalytic desulphurization of an aromatic-containing hydrocarbon fraction containing up to 50 ppm wt. sulphur without hydrogenation of more than 10 mol percent of the aromatic hydrocarbons, which process comprises passing said fraction in the liquid phase with hydrogen through a bed of catalyst comprising nickel supported on sepiolite, at a temperature in the range 75* to 250* C., a pressure in the range 100 to 2,000 psig, a liquid hourly space velocity (LHSV) in the range 0.1 to 5 v/v/hr and an inlet hydrogen:hydrocarbon molar ratio in the range 0.001:1 to 0.2:1, such that sulphur combines with the nickel but substantially no hydrogen sulphide is produced, the amount of hydrogen present being greater than the minimum necessary to prevent de-activation of the supported nickel catalyst but not more than the maximum Amount that would dissolve in the liquid fraction at the process temperature and pressure.

2. A process as claimed in claim 1 in which the aromatic-containing hydrocarbon fraction contains from 95 to 100 percent wt. aromatics, and boils within the range 15*-250* C, any other components present being saturated hydrocarbons.

3. A process as claimed in claim 1 in which the aromatic-containing hydrocarbon fraction is a straight-run distillate containing up to 25 percent wt. aromatics and boiling within the range 15*-250* C.

5. A process for the desulphurization of an aromatic-containing hydrocarbon fraction containing more than 20 ppm wt. sulphur without hydrogenation of more than 10 mol percent of the aromatic hydrocarbons which comprises first contacting the fraction in a hydrodesulphurization stage with one or more oxides or sulphides of elements of Groups VIa and VIII of the Periodic Table in the presence of hydrogen, to reduce the sulphur content of the feedstock to about 50 ppm wt. sulphur, removing the hydrogen sulphide formed, and the fraction from which the H2S is removed being passed in the liquid phase with hydrogen through a bed of catalyst comprising nickel supported on sepiolite, at a temperature in the range 75* to 250* C., a pressure in the range 100 to 2,000 psig, a liquid hourly space velocity (LHSV) in the range 0.1 to 5 v/v/hr and an inlet hydrogen:hydrocarbon molar ratio in the range 0.001:1 to 0.2:1 such that the sulphur combines with the nickel but substantially no hydrogen sulphide is produced, the amount of hydrogen present being greater than the minimum necessary to prevent deactivation of the supported nickel catalyst but not more than the maximum amount that would dissolve in the liquid fraction at the process temperature and pressure.

9. A process as claimed in claim 4, in which a hydrocarbon fraction containing more than 30 percent wt. aromatics is desulphurized to produce a fraction containing up to 2 ppm wt. sulphur and this latter fraction is hydrogenated in two stages, the first a main stage and the second a finishing stage, both of said stages using a catalyst comprising nickel supported on sepiolite, in which not less than 90 percent wt. and not more than 99 percent wt. of the aromatic hydrocarbons is hydrogenated in the first hydrogenation stage, with the hydrogenation reaction being substantially completed in the second hydrogenation stage and in which the temperature of the first hydrogenation stage is controlled by cooling.

10. A process as claimed in claim 9, in which the reaction conditions for the first and second hydrogenation stages are selected from the following: main hydrogenation reactor (first hydrogenation stage) Temperature 25 to 350*C Pressure 25 to 2000 psig Space velocity (fresh feed) 0.01 to 10.0 v/v/hr Product recycle ratio 0.1 to 10:1 Hydrogen recycle rate on total feed 50 to 5000 scf/brl finishing reaction (second hydrogenation stage) Temperature 77 to 662*F (25 to 350*C Pressure 75 to 2000 psig Space velocity 0.01 to 10.0 v/v/hr Hydrogen recycle rate 100 to 5000 scf/brl.

11. A process as claimed in claim 10, in which the reaction conditions for the first and second hydrogenation stages are selected from the following: main hydrogenation reactor (first hydrogenation stage) Temperature 122 to 572*F (50 to 300*C) Pressure 50 to 500 psig Space velocity (fresh feed) 0.5 to 5.0 v/v/hr Product recycle ratio 2.5:1 to 6:1 Hydrogen recycle rate on total feed 200 to 1000 scf/brl finishing reactor (second hydrogenation stage) Temperature 122 to 572*F (50 to 300*C) Pressure 50 to 500 psig Space velocity 0.5 to 5.0 v/v/hr Hydrogen recycle rate 500 to 2000 scf/brl.

12. A process as claimed in claim 9, in which the feedstock to the first hydrogenation stage is in mixed phase and the temperature of this stage is controlled by liquid recycle from the main reactor outlet or the finishing reactor outlet, and in which the finishing reactor outlet temperature is lower than the main reactor outlet temperature.

14. A process as claimed in claim 4, in which a hydrocarbon fraction containing not more than 30 percent wt. aromatics is desulphurized to produce a fraction containing up to 2 ppm wt. sulphur and this fraction is hydrogenated in one stage using conditions selected from the following: Temperature *C 25 to 350 Pressure psig 25 to 2000 Space velocity (LHSV) v/v/hr 0.01 to 10.0 Product recycle ratio 0.1 to 10:1 Hydrogen recycle rate on total feed scf/brl 50 to 5000.

15. A process as claimed in claim 14, in which the conditions are selected from the following: Temperature *C 50 to 300 Pressure psig 50 to 500 Space velocity (LHSV) v/v/hr 0.5 to 5.0 Product recycle ratio 1:1 to 6:1 Hydrogen recycle rate on total feed scf/brl 200 to 1000.