US2889264A - Hydrocarbon conversion process - Google Patents

Description

June 2, 1959 B. SPURLOCK ,889,

HYDROCARBON CONVERSION PROCESS Filed Dec. 27. 1954 TO H23 V 27 RECO ERY 2a WATER E /9 i HYDROCARBON PRODUCT INVENYTOR BURWELL URLOCK I V [ATTORNEYS United States HYDROCARBON CONVERSION PROCESS Application December 27, 1954, Serial No. 477,736

1 (Ilaim. (Cl. 208-89) This invention relates to a hydrocarbon conversion process, and it is particularly directed to an improvement in processes wherein petroleum naphthas and similar heavy stocks are catalytically converted in the presence of added hydrogen.

It is known that the quality of naphtha fractions of either straight run or cracked origin can be improved by reacting the feed with added hydrogen at elevated temperatures and at superatmospheric pressures in the presence of a hydro-genation-dehydrogenation catalyst, such operations being variously referred to as hydroforrning, hydrofining, hydrocracking, hydrodesulfurizing and the like. In most of these operations the feed is supplied to the catalyst-containing reaction zone at temperatures above about 600 F. (usually in the range of from 650 to 950 F.), and it is a general practice to obtain such temperatures by passing the feed, along with added hydrogen, through a heat exchanger provided with a large number of tubes of small diameter. It has been found, however, that as temperatures above about 550 F. are reached many naphtha feeds tend to form deposits on the walls of these tubes and thus decrease the efliciency of the unit, the problem becoming so severe in some instances as to plug the tubes altogether. While it is known that this difficulty can be avoided in some measure with straight run naphtha stocks by a pretreatment wherein an inert gas is passed through the stock to strip off the free oxygen content, this method is not effective with cracked naphthas of either thermal or catalytic origin except in the possible instance of nitrogen-free stocks.

It is an object of this invention to provide a method whereby naphtha feed stocks of either straight run or cracked origin can be heated in a heat exchanger unit to temperatures above about 550 F., along with added hydrogen if desired, without depositing out any appreciable amount of solids on the tube walls of said unit. A further object is to provide a method of this character which can be practiced in a simple and inexpensive fashion and which does not alter the characteristics of the feed insofar as concerns the employment thereof in a subsequent catalytic hydrogenation treatment conducted at temperatures above 600 F. The nature of still other objects of this invention will be apparent from an examination of the descriptive portion to follow.

The present invention is based on the discovery that the foregoing objects can readily be achieved by a method wherein the naphtha feed stock to be catalytically hydrogenated at temperatures above 600 F., and which manifests deposit-forming characteristics in a heat exchanger at said temperatures, is subjected to a pretreatment step in which the stock is brought into contact, along with added hydrogen, with a hydrogenation-dehydrogenation catalyst at temperatures above about 300 F. but below those at which any substantial amount of solids deposition occurs, and preferably between about 300 and 475 F. It has been found that while little measurable reaction takes place in the first, or low-temperature, catalytic stage, as evidenced by the fact that there is little apparent rise atent G in the temperature of the feed mixture passing through the catalyst and little net consumption of hydrogen under the reaction conditions employed, nevertheless the feed stock is evidently modified in some fashion since its deposit-forming characteristics, when thereafter heated to temperatures above about 550 F. in a heat exchanger unit preparatory to being passed through the second catalytic hydrogenation stage (where the reaction becomes strongly exothemic), are greatly reduced.

In carrying out the process of this invention, beneficial results can be obtained by utilizing as feed any one of a variety of hydrocarbon stocks, and particularly those which are of such a character that they are susceptible of being upgraded by a catalytic hydrogenation treatment at temperatures above about 600 F. Suitable feeds of this type are those which boil at least in part Within the gasoline range, as, for example, the various coker distillates, straight run naphthas and those recovered from various catalytic or thermal cracking operations. Representative feed materials of this character boil over a range of from about to 450 F., good results also being obtained with various fractions of said materials, e.g., a fraction boiling between about 330 and 440 F. and obtained by a distilling off of the lower boiling components from a naphtha recovered in an operation involving the thermal cracking of a heavily naphthenic residual stock of California origin.

As indicated above, little reaction from the quantitative standpoint takes place in the first, or low-temperature, catalytic hydrogenation zone wherein the feed is admitted at from about 300 to 475 F. Accordingly, little added hydrogen need be combined with the feed stream to this zone and good results have been obtained with amounts as low as about 0.01 mole H per mole of feed. On the other hand, since a larger amount of hydrogen than this is required in the succeeding, high-temperature hydrogenation treatment, it is preferable from an operating standpoint that the feed stream to said first zone contain a substantial proportion (at least 50%) of the hydrogen required in the next catalytic hydrogenation stage, which normally ranges from about 0.5 to 10 moles H per mole of feed.

While the space rate at which the hydrogen-containing feed stream is passed through the low-temperature catalyst zone is not critical and can be varied within relatively Wide limits, as from about 0.1 to 30 v./v./hr. (volumes of total feed, calculated as liquid, per superficial volume of catalyst, per hour), it is preferable to employ a space rate of from about 1 to 6 v./ v./ hr.

In carrying out the process of this invention, any of the conventional hydrogenation-dehydrogenation catalysts can be employed. Such materials, referred to herein for convenience as hydrogenation catalysts, include various oxides or sulfides of groups VI and Vii metals, including oxides and sulfides of molybdenum, tungsten, vanadium, chromium and the like, as well as metals like iron, nickel and cobalt or their oxides, preferably deposited on a porous carrier such as activated alumina, silica gel, a silica-alumina material, or the like. These catalysts are suitable for employment in the first, or low-temperature, catalytic hydrogenation step of the present invention, as Well as for the second, or high-temperature hydrogenation step, the particular catalyst chosen for the latter treatment being selected With a View of tr e desired result there to be achieved.

Particularly good results have been obtained with catalysts made up of molybdenum oxide, or a combination of molybdenum and cobalt oxides or other compound of these metals, deposited on an activated alumina carrier, such catalysts being preferred for use in both the lowas well as the high-temperature hydrogenation zones.

The process of the present invention can be illustrated in one embodiment thereof by reference to the appended drawing wherein the figure represents a flow diagram of a process for the catalytic hydrogenation of a representative hydrocarbon feed.

In the drawing, a naphtha fraction boiling between about 330 and 440 F. and obtained by distillation of a naphtha stock recovered from an operation involving the thermal cracking of a naphthenic residual stock of California origin, is introduced at a pressure of about 800 p.s.i.g. through line to which hydrogen is supplied through line 11 in an amount equivalent to approximately 3 moles per mole of hydrocarbon feed. The resulting mixture is then passed through a heat exchanger 12 where the temperature of the mixture is raised to approximately 450 F., it being observed that substantially no deposition of solids on the heat exchanger tubes occurs at this temperature, though solids deposition is heavy when, in a companion operation, the temperature of the mixture is raised to 600 F. From the heat exchanger 12 the mixture is passed at a rate of 4.2 v./v./hr. through a catalyst in a reaction vessel 13, the catalyst being made up of a mixture of molybdenum and cobalt oxides (9% Mo, 3% Co, as metals) deposited on alumina. The eifiuent from reaction chamber 13, at a temperature of approximately 450 F., is passed via line 14through heat exchanger 16 where the temperature of the mixture is raised to 650 F. It is observed that even under these conditions hydrogen-containing feed stream, as pretreated by passage of the catalyst in reactor 13, caused little if any deposition of solids on the tube walls of heat exchanger 16. From heat exchanger 16 the heated and now vaporous mixture of hydrogen and hydrocarbon is passed through the catalyst in reaction vessel 17 at a rate of 2 v./v./hr., the catalyst in said chamber being the same as in chamber 13. The efiiuent from reactor chamber 17, at a temperature of approximately 800 F., is admixed with water supplied through line 19, with the resulting mixture then being passed through a condenser 20 and into a gas-liquid separating vessel 21. From the latter vessel the uncondeused gaseous portion of the effluent from reactor 17, largely comprised of hydrogen gas, is returned through line 22 to the incoming hydrogen line 11, with a portion of the hydrogen being returned via line to line 14, if desired, by suitable adjustment of the valves 29 and 30. An aqueous layer is discharged as waste from the bottom of vessel 21 through line 23, while the liquid hydrocarbon layer is removed through line 24 to a desulfurizing column 25 provided with a re boiler 26. From the column 25, an overhead gaseous stream containing large amounts of hydrogen sulfide is taken through line 27, while the desired hydrogenated hydrocarbon product stream is recovered as bottoms through line 28. While the latter product can be used without additional treatment, it is well adapted to be employed as the feed to a reforming unit incorporating a platforming or other catalyst having reforming characteristics.

In a subsequent operation conducted in the same general fashion as described in the preceding paragraph, there is employed as feed a naphtha fraction boiling between about 322 and 425 F., as recovered from an operation involving the catalytic cracking of a gas oil produced by the vacuum distillation of a California crude residual stock. In this case, the conditions of operation are the same as those described above except that here the temperature of the hydrogen-hydrocarbon feed stream in reactor 13 is 350 F., it again being observed that with this pretreatment the amount of solids deposited in the subsequently encountered heat exchanger 16 is reduced to negligible proportions. On the other hand, relatively large amounts of deposits are formed in this exchanger when the pretreatment step in vessel 13 is omitted.

I claim:

In a method for the catalytic hydrogenation of a petroleum naphtha stock having deposit-forming characteristics when brought to a temperature above 550 F. in a heat exchanger, the steps comprising heating said stock to a temperature between about 300 and 475 F.; passing the resulting heated stock, along with from about 0.01 to 10 moles of hydrogen per mole of naphtha stock, through a hydrogenation catalyst comprising cobalt oxide and molybdenum oxide on an alumina-containing support in a first reaction zone; heating the efduent from said zone to a temperature of at least 550 F. in a heat exchanger; passing the heated naptha effiuent from the heat exchanger, along with from about 0.5 to 10 moles of hydrogen per mole of naphtha, through a hydrogenation catalyst in a second reaction zone; separating the elliuent from the second reaction zone into a gaseous phase rich in hydrogen, which is recycled through at least the second reaction zone, and a liquid phase; and recovering the desired hydrogenation products from the liquid phase; said process being characterized by a substantial absence of solids deposition in the heat exchanger by the efliuent from the first reaction zone.

References Cited in the file of this patent UNITED STATES PATENTS 1,908,286 Dorrer May 9, 1933 2,222,128 Wagner Nov. 19, 1940 2,542,471 Brandon Feb. 20, 1951 2,573,149 Kassel Oct. 30, 1951 2,694,671 Baumgarten Nov. 16, 1954 2,717,230 Murray et al. Sept. 6, 1955 2,739,927 Doumani Mar. 27, 1956 FOREIGN PATENTS 424,748 Great Britain Feb. 27, 1955

Images