US3253055A - Isomerization and cracking of paraffinic hydrocarbons - Google Patents

Description

United States Patent 3,253,055 ISOMERIZA'HUN AND CRACKING 0F PARAFFTNIC HYDRGCARBGNS Anthony George Goble and John Vincent Fletcher, Sunhury-on-Thames, England, assignors to The British Petroleum Company Limited, London, England, a British joint-stock corporation No Drawing. Filed July 3, 1962, Ser. No. 207,387 Claims priority, application Great Britain, July 4, 1961, 24,095/61 7 Claims. (Cl. 260-68355) This invention relates to the hydrocatalytic conversion of parafiin hydrocarbons, by isomerization and cracking.

The conversion of hydrocarbons to lower boiling products by hydrocatalytic cracking has been proposed. When applied to higher-boiling petroleum hydrocarbons it provides, for example, a method of producing additional quantities of high volatility material boiling in the gasoline range. It is also desirable in many instances that these lower-boiling products should be iso-parafiinic in character, since isoparaffins have higher octane numbers and lower sensitivities than the corresponding normal paraffins. A process which combines both cracking and isomerization in a single stage is, therefore, useful.

Copending US. patent application S.N. 135,425, filed September 1, 1961, and now abandoned, which discloses a process for the isomerization of C and higher parafiin hydrocarbons boiling in the gasoline boiling range comprising contacting the parafiin hydrocarbons in the presence of hydrogen at a temperature below 400 F. (204 C.) with a catalyst prepared by contacting alumina with a compound of general formula (where X and Y may be the same or different and selected from H, Cl, Br, F, or SCl, or where X and Y together may be 0 or S) under non-reducing conditions and at a temperature such that chlorine is taken up by the alumina without the production of free aluminum chloride.

It has now been found that the catalyst described above can be used in a process which combines isomerization and cracking. According to the present invention, therefore, a process for the hydrocatalytic conversion of hydrocarbons comprises contacting the hydrocarbons with a catalyst prepared as described above in the presence of hydrogen and at an elevated temperature such that isomerization and cracking ocurs and recovering a product containing isomerized hydrocarbons boiling below the initial boiling point of the feedstock.

The feedback need not consist entirely of parafiin hydrocarbons but particularly preferred feedstocks consist predominantly of parafiin hydrocarbons and they may contain at least 90% wt. of paraffin hydrocarbons. if necessary non-paraffin hydrocarbons in the feedstock may be removed by a preliminary selective treatment, for example fractionation, solvent extraction or so-called molecular sieving. Since the lowest boiling hydrocarbons do not exist in isomeric forms, the preferred lowest boil ing constituents in the feedstock are C hydrocarbons. The preferred upper limit is C hydrocarbons, although higher boiling materials may be treated if desired. Thus a suitable feedstock is one boiling outside the gasoline boiling range (i.e. containing C or higher hydrocarbons) which can be isomerized and cracked to give a gasoline containing a high proportion of iso-parafiins.

The feedstock should have a low water content, for

3,253,055 Patented May 24, 1966 example less than 10 p.p.m. since water tends to hydrolyze the chlorine in the catalyst. It also has desirably a low content of sulphur and aromatic hydrocarbons for example less than 0.01% wt. of sulphur and less than 0.5% Wt., preferably less than 0.1% wt. of aromatic hydrocarbons.

The amount of cracking will depend on the nature of the feedstock and the type of product desired but it is desirably at least 5 wt. of lower boiling products and preferably at least 10%. Conversions of 25% wt. or more may be obtained if desired, the upper limit being determined by practical considerations such as coke formation and on-stream time before catalyst regeneration or placement is necessary. As compared with the process, such as that described in the hereinbefore mentioned U.S. patent application Ser. No. 135,425, in which isomerization is the principal reaction and cracking is kept to a minimum, the process conditions of the present invention will be more severe. For any given feedstock, increase in severity may be achieved by increasing the temperature, decreasing the space velocity or decreasing the pressure. Another method of promoting cracking and also of maintaining the activity of the catalyst is by maintaining a concentration of hydrogen chloride in the reaction zone. Methods of maintaining such a concentration are given below. The higher boiling feedstocks will in general require more severe conditions to obtain an equivalent degree of cracking. Isomerization will be favored by lower temperatures, lower space velocities and increased pressure.

Optimum conditions for any given degree of cracking with any given feedstock can readily be determined by simple experiments and may be selected from within the following ranges Temperature, C 150400, preferably 205- 350 C. Pressure, p.s.i.g Atmospheric to 2000,

preferably to 500. Liquid space velocity,

v./v./hr. ODS-10.0, preferably 0.2-5. Hydrogen: hydrocarbon ratio 0.01-20:1, preferably 1.5

If desired hydrogen chloride or a compound producing hydrogen chloride may be added to the reaction zone, either by direct injection or by addition to the feedstock or hydrogen-containing gas. Examples of suitable materials for addition are hydrochloric acid gas, carbon tetrachloride or other chlorine derivatives of lower boiling hydrocarbons. The amount of material added may be from 0.01 to 5% by weight of feedstock, preferably O.l2% wt.

Preferably the catalyst contains less than 25% wt. of a metal or metal compound having hydrogenating activity selected from Groups Vla or VIII of the Periodic Table. The metal may be present as such or as a compound, for example the oxide. The preferred metal is a platinum group metal which may be present in an amount from 0.01 to 5% wt. and preferably 0.1 to 2% wt. The preferred platinum group metals are platinum and palladium.

The method of preparing catalysts for use in the process of the present invention is described and claimed in copending US. patent application Ser. No. 135,426, filed September 1, 1961. i

A particular feature of the catalyst preparation is the use of the specific compounds of the general formula indicated, these compounds giving a specific form of chlorination which produces active catalysts.

The following examples of compounds giving active and inactive catalysts respectively illustrate the specific nature of the compounds used.

Compounds giving active catalysts:

Carbon tetrachloride (CCl Chloroform (CHCl Methylene chloride (CH CI Dichlorodifiuoromethane (CCl F Trichlorobromomethane (CCl Br) Thiocarbonyltetrachloride (CCl SCl) Compounds giving inactive catalysts:

Hydrogen chloride (HCl) Chlorine (C1 Methyl chloride (CH3C1) Acetyl chloride (CH COCl) Dichloroethane (CH ClCH Cl) Tetrachloroethane (CHCl CHCl Tetrachloroethylene (CCIFCCI In the case of compounds containing elements other than chlorine, carbon and hydrogen, the treatment may add the other elements to the catalyst in addition to the chlorine. For example treatment with dichlorodifluoromethane results in the uptake of both chlorine and fluorine onto the catalyst. It has been found, however, that catalysts so prepared are still active and they may have, in addition, other properties resulting from the addition of the other elements. In has also been found that small amounts of halogens (including chlorine) which may be present in the alumina prior to the chlorination treatment of the present invention do not affect the activity of the catalysts for isomerizaion and cracking although this halogen does not contribute in any way to the isomerization activity. Thus, the alumina used may already contain up to 1% wt. of chlorine and/or fluorine, as when, for example, the metal material which is chlorinated by the process of the present invention is a catalyst normally used for the reforming of gasoline boiling range hydrocarbons. The preferred compounds giving active catalysts are carbon tetrachloride, chloroform and methylene chloride.

The compounds covered by the general formula in which X and Y together are or S are phosgene and thiophosgene.

Any convenient form of alumina may be used which contains hydrogen. This is a characteristic of activated aluminas which, although predominantly alumina, do contain a small amount of hydrogen, usually less than 1% wt. This hydrogen is generally considered to be in the form of surface hydroxyl groups, and it is believed that the chlorine compound reacts with the surface hydroxyl groups to form the active catalyst sites. Water is, in fact, a product of the reaction, but not all the hydrogen is removed and the treated catalyst still contains a measurable quantity of hydrogen. The amount of chlorine added to the catalyst is preferably within the range 1 to 15% Wt., the precise amount being dependent on the surface area as measured by low temperature nitrogen absorption. It has been found that for maximum amount of chlorine which can be added without the formation of free aluminium chloride is related to the surface area and is about 3.0-3.5x g./m. Maximum chlorination is preferred, but lower amounts of chlorine still give active catalysts and a suitable range is, therefore, from 2.0X10- to 3.5 lO- g./m.

Any of the forms of alumina suitable as a base for reforming catalysts may be used, but a particularly preferred form is one derived from an alumina hydrate precursor in which the trihydrate predominates. One containing a major proportion of B-alumina trihydrate is particularly suitable. A convenient method of preparing the alumina is by hydrolysis of an aluminium alcoholate, for example aluminium isopropoxide, in an inert hydrocarbon solvent, for example, benzene. Other things being equal, the greater the amount of chlorine taken up by the alumina, the greater is the activity of the catalyst and since, as stated above, the maximum amount of chlorine which can be added is related to the surface area, it is desirable that the alumina should have a high surface area, for example more than 250 m. /g. and preferably more than 300 m. g.

If desired there may be admixed with the alumina a minor proportion of one or more other refractory oxides selected from Groups II to V of the Periodic Table. Thus the alumina may contain up to 50% wt. of, for example, silica, titania, beryllia, zirconia or magnesia.

The hydrogenating metal is desirably incorporated with the alumina prior to the treatment with the chlorine. When using a platinum group metal it is also desirable that it should be finely dispersed as small crystallites on the alumina, suitable criteria for the size of the crystallites being that they are not detectable by X-ray diffraction and that on treatment of the platinum group metal-alumina composite with benzene at 250 C. they have a measurable. chemisorption, preferably not less than 0.1 molecule of benzene absorbed/atom of platinum and not less than 0.03 molecule of benzene absorbed/atom of palladium. Details of the benzene chemisorption technique have been published in Actes du Deuxieme Congres International de Catalyse, Paris, 1960, vol. 2, page 1851.

A convenient method of obtaining the platinum group metal in the required state of sub-division is to add a solution of a platinum group metal compound to a hydrogel of the alumina and to precipitate the platinum group metal as a sulphide, for example by treatment with hydrogen sulphide. The treatment of the platinum group metal-alumina composite with the chlorine compound is preferably given with the platinum group metal in a reduced state, and this can conveniently be achieved by pre-treating the composite with hydrogen. When a platinum group metal-alumina composite is treated with a chlorine compound according to the present invention it is believed that a portion of the chlorine taken up is associated with the platinum group metal as an active complex.

The non-reducing conditions used for the chlorination may be either inert or oxidizing conditions, the latter being preferred. A convenient method of contacting the alumina is to pass a gaseous stream of the chlorine compound over the alumina either alone or, preferably, in a non-reducing carrier gas. Examples of suitable carrier gases are nitrogen, air or oxygen.

Non-reducing conditions are essential, since reducing conditions tend to convert the chlorine compound to hy drogen chloride, which gives an inactive catalyst. The

temperature for the chlorination may be from 300-1 When treating platinum group metal-alumina composites the temperature is preferably 300700 F. (149-37l C.), platinum-on-alumina composites being more particularly treated at 450600 F. (232316 C.) and palladiumalumina composites at SOD-650 F. (260343 C.). The

chlorination reaction is exothermic and the temperatures specified are the initial temperatures used.

The rate of addition of the chlorine compound is preferably as low as practicable to ensure uniform chlorination and to avoid a rapid increase of temperature as a result of the exothermic reaction. Preferably the addition rate does not exceed 1.3% wt. of chlorine compound by weight of catalyst per minute. If a carrier gas is used the rate of flow is preferably at least 200 volumes/ volume of catalyst/hour and a convenient range is 200-1000 v./v./hr. The pressure used is conveniently atmospheric. The active catalyst is susceptible to hydrolysis in the presence of water and should, therefore, be stored under anhydrous conditions. Similarly the materials used in the catalyst preparation should also be free from water.

The invention is illustrated by the following examples.

Example 1 N-hexane was passed, together with hydrogen, at a hydrogenzhydrocarbon mole ratio of 6.2: 1, atmospheric pressure and a gas space velocity of 220 v./v./hr. (equivalent to a liquid space velocity of 0.1 v./v./hr.) over a platinum-alurnina-chlorine catalyst.

and it was prepared by contacting 150 ml. of a platinumon-alumina catalyst, containing 0.58% wt. platinum and 0.81% wt. chlorine, with 30 ml. of dry carbon tetrachloride at a reaction temperature of 300 C. The treatment time was 30 minutes, during which a nitrogen flow (200 m1./min.) was maintained to remove the products of the reaction.

The product yields obtained under steady state conditions at various temperatures are given below:

Temperature, C 83 120 168 208 300 Hydrocracked Products C1-C percent wt 3. 3 24. 2 99. 1 Isomerized Product i-Ce 31. 5 49. 7 71. 7 61. 9 0.9 Unconverted 11-0 68.5 50.3 25.0 13.9

As can be seen, sustained hydrocracking becomes significant at a temperature of about 170 C. and is virtually complete by 300 C.

Typical GLC analyses of the hydrocracked products obtained at temperatures of 180 C. and 268 C. are given below and show the high percentage of isobutane and N-heptane was passed together with hydrogen over a platinum-alumina-chlorine catalyst. The process conditions used were:

Catalyst mi; 75

Feedstock, n-heptane percent 99 Pressure p.s.i.g. 100 Space velocity v./v./hr. 2.0

Hydrogen:n-heptane mole ratio 5:1

1 Hole purity.

The temperature was varied during the course of the run as indicated below and the catalyst used was similar to that used in Example 1.

During a two-hour period /2-12 /2 hours on stream) at a temperature of 175 C. 205 gm. of n-heptane were processed and 189 gm. of liquid product were obtained (liquid recovered 92%). The full product analysis (obtained by GLC) is given below. Product analysis (total):

C percent wt 3 5.9 i-C 1 12.9 n-C 1 0.1 i-C 2 10.3 11-C5 2 1.2 i-C 3 9.0 I l-c5 3 Di-methyl-C 1 1.8 Methyl-C 26.4 11-0 21.3 Conversion to C; isomers percent 38.2 Conversion to hydrocracked products percent" 40.5 Selectivity for hydrocracking, Yield of C to 0 Yield of C to C percent 85.5

i/n ratio 100.

n/n ratio 8.6.

3 i/n ratio 7.5.

Results obtained during the course of the run at other temperatures show that variation in temperature brings about a change in the ratio of hydrocracking to isomerization. Below are given analytical data for the liquid products obtained from the n-heptane feedstock at various process temperatures. The other reaction conditions were as described above.

Temperature, C 150 Hours on Stream 4-6 68 15y -17% 19%2l% Liquid Product, percent wt.:

i-C 6.0 5. 1 9. 7 17. 2 1 -0 neg. neg. 0.1 0.1 1-O 2. 5 2. 9 4. 7 6. 4 11-0 neg. 0. 1 0. 2 0.4 i-C 1. 8 1. 9 4.3 6.3 n-O neg. neg. 0. 1 0. 3 Di: ethyl 0 11.1 10. 3 11. 7 11.1 Methyl C6"--- 35. 6 33. 5 33. 5 30. 8 n-C 43.0 46. 2 35.8 27. 4 Hydroeracked Products, percent Wt 10.3 10. 0 19. 0 30. 7 Isomerised Products, percent wt. 46. 7 43.8 45.2 41. 9 Unconverted Feed, percent wt. 43. 0 46. 2 35. 8 27. 4

Example 3 Using the same catalyst as in Example 2, a n-parafiin extract of a gas oil (n-C to n-C ca. 90% pure) was processed under the following conditions:

0 Pressure, p.s.i.g 100 Temperature, C. 285 Space velocity, v./v./hr 2.0 Hydrogen gas rate s.c.f./bbl 6000 During a two hour period (30 /232 /2 hours on stream) 233 gm. of feed were processed and 219 gm. of liquid product collected (liquid recovered 94% The full product analysis (obtained by GLC) is given below:

Product analysis, percent wt.: Trace i-Cg 8.2 n-C 5 0.4 C -C 3.0 C and above 24.5 Conversion to hydrocracked products percent 75.5 Selectivity for hydrocracking, Yield of C -C Yield of C -C percent 96.5

1 i u 3.5 a i /n 5.9. a i /n 12.0. 4 i/n 10.6. B i/n 20.5.

We claim:

1. A process for the hydrocatalytic conversion of paraffin hydrocarbons comprising contacting a feedstock containing a major proportion of parafiin hydrocarbons having from 11-20 carbon atoms in the presence of hydrogen and at an elevated temperature in the range of 205 to 400 C. such that isomerization and cracking occurs, with a catalyst prepared by contacting alumina with a compound of general formula A where X is selected from the class consisting of H, Cl, Br, F and 8G1 and Y is selected from the class consisting of H, Cl, Br, F and SCI, in the absence of free hydrogen and at a temperature in the range of 149-593 C. such that chlorine is taken up 'by the alumina without the production of free aluminum chloride, said catalyst containing from 2.0 lO to 3.5 X 10 g. of chlorine/sq. meter of surface area, and recovering a product containing isomerized hydrocarbons boiling below the initial boiling point of the feedstock.

2. A process as claimed in claim 1 wherein the feedstock contains at least 90% by weight of paraffin hydrocarbons. I

3. A process as claimed in claim 1 wherein the pressure is from atmospheric to 2000 p.s.i.g., the liquid space velocity from 0.05 to 10 v./v./hr. and the hydrogenzhydrocarbon mole ratio from 0.01 to 1.

4. A process as claimed in claim 3 wherein the pressure is from to 500 p.s.i.g., the liquid space velocity from 0.2 to 5 v./v./hr. and the hydrogemhydrocarbon mole ratio from 1.511 to 15:1.

5. A process as claimed in claim 1 wherein the catalyst contains up to 25% Wt. of a metal having hydrogenating activity selected from Groups VIa and VIII of the Periodic Table.

6. A process as claimed in claim 5 wherein the catalyst contains from 0.01 to 5% wt. of a platinum group metal.

7. A process vfor the hydrocatalytic conversion of paraffin hydrocarbons comprising contacting a feedstock containing a major proportion of parafiin hydrocarbons having from 11-20 carbon atoms in the presence of hydrogen and at an elevated temperature in the range of 205 to 400 C. such that isomerization and cracking occurs, with a catalyst prepared by contacting alumina with a compound of general formula Where X and Y together form a divalent radical selected from the class consisting of O and S, in the absence of free hydrogen and at a temperature in the range of 149- 593 C. such that chlorine is taken up by the alumina Without the production of free aluminum chloride, said catalyst containing from 2.0 10 to 3.5 l0 g. of chlorine/sq. meter or surface area and recovering a product containing isomerized hydrocarbons boiling below the initial boiling point of the feedstock.

References Cited by the Examiner UNITED STATES PATENTS 2,642,384 6/1953 Cox 208--139 2,698,829 1/ 1955 Haensel 260-68365 2,798,105 7/1957 Heinemann et al. 260--683.65 2,908,735 10/1959 Haensel 260683.68 2,944,097 7/ 1960 Starnes et al 260-68368 2,966,528 12/1960 Haensel 260683.65

DELBERT E. GANTZ, Primary Examiner.

ALPHONSO D. SULLIVAN, Examiner.

Claims (1)

1. A PROCESS FOR THE HYDROCATALYTIC CONVERSION OF PARAFFIN HYDROCARBONS COMPRISING CONTACTING A FEEDSTOCK CONTAINING A MAJOR PROPORTION OF PARAFFIN HYDROCARBONS HAVING FROM 11-20 CARBON ATOMS IN THE PRESENCE OF HYDROGEN AND AT AN ELEVATED TEMPERATURE IN THE RANGE OF 205 TO 400* C. SUCH THAT ISOMERIZATION AND CRACKING OCCURS, WITH A CATALYST PREPARED BY CONTACTING ALUMINA WITH A COMPOUND OF GENERAL FORMULA