US2770578A - Saturating of a hydrocarbon fraction with hydrogen and then hydrodesulfurizing said fraction - Google Patents

Description

United States Patent SATURATING or A HYDROCARBON FRACTION WITH HYDROGEN AND THEN HYDRODESUL- FURIZING SAID FRACTION Vladimir Haensel, Hinsdale, 111., assignor to Universal Oil Products Company, Des Plaines, 11]., a corporation of Delaware N0 Drawing. Application August 19, 1953, Serial No. 375,292

8 Claims. (Cl. 196-24) This invention relates to a process for treating unsaturated stocks and particularly to a method of preparing saturated and substantially sulfur-free charge stocks for other processes.

In one embodiment this invention relates to a process of preparing a saturated and substantially sulfur-free hydrocarbon fraction by first contacting an unsaturated and sulfur-containing hydrocarbon fraction in the presence of hydrogen with a hydrogenation catalyst selected from the group consisting of platinum and palladium and subsequently contacting the feed stock With a desulfurizing catalyst containing a group VI metal and a metal of the iron group of the periodic table.

It is a more specific embodiment of the present invention to prepare a saturated and substantially sulfur-free hydrocarbon fraction by contacting an unsaturated and sulfur-containing hydrocarbon fraction, in the presence of hydrogen, with a hydrogenating catalyst selected from the group consisting of platinum and palladium at a temperature of from about 200 F. to about 450 F. and subsequently contacting the fraction with a desulfurization catalyst containing a group VI metal and a metal of the iron group of the periodic table.

In a more specific embodiment the present invention relates to a method of preparing a saturated and substantially sulfur-free hydrocarbon fraction by contacting an unsaturated and sulfur-containing hydrocarbon fraction having a bromine number in excess of about 10, in the presence of hydrogen, with a hydrogenation catalyst selected from the group consisting of platinum and palladium at a temperature of from about 200 F. to about 450 F. and subsequently contacting the fraction with a desulfurizing catalyst containing cobalt and molybdenum.

In a still more specific embodiment the present invention relates to a process of preparing a saturated and substantially sulfur-free hydrocarbon fraction by contacting an unsaturated and sulfur-containing hydrocarbon, in the presence of hydrogen, with a catalyst comprising platinum at a temperature of from about 200 F. to about 450 F. and subsequently contacting the fraction with a catalyst containing cobalt and molybdenum at a temperature of from about 400 F. to about 750 F.

Since the use of cracking processes, both catalytic and thermal, has become so widespread, there has been an abundance of cracked stocks boiling in the gasoline range which may be used as motor fuel or may be further treated. Cracked stocks are characterized by some degree of unsaturation, those being severely cracked having a higher degree of unsaturation while those being more mildly cracked having a lower degree of unsaturation. Most thermally cracked stocks are more unsaturated than catalytically cracked stocks. As hereinbefore stated, all stocks produced by a cracking process do exhibit some degree of unsaturation and as a result, their character- 'istics as a motor fuel are different from straight run stocks which are saturated. Cracked stocks generally have a higher octane number and show better performance than straight run stocks, however, they are unstable in storage 'ice and tend to form sludges, gums and varnishes in use. The cracking process does not significantly diminish the sulfur content of a hydrocarbon fraction, in fact it very frequently will increase the sulfur content by concentrating sulfur bearing molecules due to yield losses. It is an object of this invention to treat sulfur-containing and unsaturated hydrocarbons, such as those obtained from a cracking process, to produce a stable, substantially sulfurfree fraction which may be used per se or more particularly may be used as a charge stock for other refining processes. A reforming process for example, greatly improves the characteristics of gasoline by dehydrogenating naphthenic hydrocarbons to form aromatic hydrocarbons, isomerizing straight chain hydrocarbons to form more highly branched hydrocarbons, dehydrocyclizing straight or slightly branched chain hydrocarbons to form aromatic hydrocarbons, selectively cracking heavier molecules to form lighter molecules, etc., as a result of which a motor fuel having extremely high octane number and desirable stability and other characteristics is formed. It is difficult to effect a reforming process on a highly unsaturated and sulfur-containing stock since, at reforming conditions, the unsaturated compounds in the feed stock tend to polymerize and form a highly carbonaceous substance called coke on the surface of the catalyst which results in the deactivation of the catalyst after a very short period of time. A high concentration of sulfur in the feed stock is generally harmful to reforming catalyst and may cause deactivation within a short period of time.

A highly aromatic feed stock may be extremely desirable as a charging stock to a solvent extraction process to remove the aromatics therefrom. A solvent extraction process for recovering aromatics is most successfully effected when the stock containing aromatics contains in addition to aromatics, saturated hydrocarbons exclusively, preferably paralfins. This is true since the order of solubility of hydrocarbon material in a solvent that is selective for aromatics is as follows: the least soluble material is the parafiinic material followed in order of increasing solubility by naphthenes, olefins, diolefins, acetylenes, sulfur bearing molecules, and aromatics. It may readily be seen, as hereinbefore stated, that a charge stock consisting entirely of parafiins and aromatics would represent the ideal charge stock for a solvent extraction process. The process of the present invention tends to make such an idealcharge stock out of a sulfur-containing and unsaturated feed.

The present process is particularly adapted for effecting the hydrogenation and desulfurization of a hydrocarbon fraction since it combines the use of two materials that are each particularly adapted to perform specific functions that are complementary to each other. Hydrogenating catalysts which may contain platinum and palladium, have been used as desulfurizing catalysts, however, platinum and palladium, although excellent hydrogenation catalysts, are sensitive to high concentrations of sulfur. When used at desulfurizing conditions, platinum or palladium catalysts will rapidly become deactivated and as a result of this deactivation, are not suitable for this use. On the other hand, there are sulfur resistant catalysts such as those resulting from combinations of group VI metalsand metals of the iron group, which are particularly suitable for desulfurization but which lack the extremely good hydrogenating characteristics of a platinum or palladium catalyst. As a result of these characteristics neither the platinum catalyst nor the combination desulfurizing catalyst is suitable for use with] an unsaturated and sulfur-containing feed stock because if the platinum catalyst is used alone it will effect the hydrogenation of the unsaturated compound but will become deactivated for essentially complete desulfurization upon exposure to high sulfur concentrations whereas if the group VI and iron group metal desulfurizing catalyst is used alone, its poor hydrogenating characteristics will allow polymerization of the unsaturated compounds and it will be deactivated by being covered bycarbonaceous deposits. The present process combines the desirable characteristics of these two catalysts in a combination process which first uses a hydrogenating catalyst to saturate the unsaturated compounds in the feed stock at a temperature which is too low to effect desulfurization and then to desulfurize the saturated, unpolymerizable stock that is produced. As a result of the low temperature hydrogenation the sulfur bearing molecules in the feed stock pass through the hydrogenation zone unaffected and the hydrogenating catalyst is not exposed to the harmful effects of hydrogen sulfide. The now saturated, sulfur-containing stock passes to a desulfurizing zone containing :a catalyst comprising a group V1 metal and a metal of the iron group, preferably cobalt and molybdenum which combination forms a highly sulfur resistant catalyst. In the desulfurizing catalyst zone the feed stock is subjected to tempenatures substantially higher than those in the hydrogenating zone for example, from about 400 F. to about 750 F. whereby desulfurization is effected and the harmful results of polymerization of unsaturated compounds are not experienced.

T he hydrogenation of unsaturated compounds is a highly exothermic reaction so that the charge stock, in assing through the hydrogenation zone, experiences a rise in temperature due to the heat of reaction. The temperature of the material passing from the hydrogenation zone will depend both on the amount of hydrogenation effected in the hydrogenation zone and the temperature of the feed to the hydrogenation zone. Therefore, a highly unsaturated feed stock will be charged to the hydrogenation zone at a lower temperature than a feed stock having a lesser degree of unsaturation when it is desired to have the effluent from the hydrogenation zone at a given temperature. Hydrogenation reactions may be effected at any temperature from room temperature to about 450 F., the upper limit being placed at about 450 F. since that is about the temperature at which desulfurization reactions are initiated. The process will generally be effected so that the temperature of the material entering into contact with the hydrogenation catalyst will be controlled by the temperature of the material flowing from the hydrogenation bed, that is, if the exit temperature increases the inlet temperature will be decreased.

As hereinbefore stated the treating reactions of the present invention are effected in the presence of hydrogen. The hydrogen used may be extremely pure or it may contain contaminants such as light hydrocarbon gases including methane, ethane, propane, etc. The hydrogen'used will generally be under superatmospheric pressure usually in the range of from about 100 p. s. i. to about 1000 p. s. i. or more. It is preferable to effect the hydrogenation and desulfurization reactions under high hydrogen pressure in that high pressure favors the hydrogenation reactions, however, an extremely high pressure is not required for simple'hydrogenation of unsaturated'compounds so the prohibitive costs of high pressure equipment'will generally result in a process using 7 moderate pressures of from about 100 p. s. i. to about 7009. s. i. Another limitationon the use of high pressure is that extremely high pressures may cause a certain amount of hydrogenation of aromatic compounds which a feedstock for an aromatic recovery process employing a selective solventsincethe'ultimate recovery of aromatic compounds would be diminished.

As hereinbefore stated the hydrogenation catalyst to be used by the present invention comprises platinum and/or palladium. It is preferred that the catalyst is in extended surface condition as when combined with a suitable carrying material such as silica, alumina, magnesia, zirconia, titania, activated carbon, or combinations of the above such as silica-alumina, silica-magnesia, silicaalumina-magnesia, silica-alumina-zirconia, etc. The carrying material may be synthetically prepared or it may be naturally occurring as in the case of bauxite, kieselguhr, mont'morillonite clay, etc. A particularly preferred hydrogenating catalyst contains platinum in an amount of from about 0.01 to about 1.0% by weight, and 0.1 to about 8% by weight of halogen, composited with alumina. The combined halogen is preferably chlorine or fluorine.

Sulfur resistant desulfurization catalysts, as hereinbefoie stated, may comprise group VI metals in combination with metals of the iron group. It is againpreferrecl that the desulfurizing catalyst is prepared in extended surface condition by being composited with a suitable supporting material which may be any of those hereinbe'fore cited. A particularly preferred desulfurization catalyst comprises a sulfided composite'of cobalt oxide-molybdenum oxide and alumina.

The process may be effected in any suitable equipment which may comprise two consecutive, adjacent beds of catalyst in one vessel, two catalyst beds in one vessel separated by an interheater, ortwo beds, one in each of two separate vessels separated by interheaters. Either the hydrogenation reactions or the desulfurization reactions or both may be eifected in multiple vessels in either series or parallel flow. It is preferred that the present process is effected in two vessels, one containing hydro genation catalyst and the other desulfurizing catalyst with a provision for interheat between. The only limitation on equipment is that the stock must contact the hydrogenation catalyst first and the desulfurizing catalyst second in the sequence of contacting zones.

A particularly suitable combination consists of the process of the present invention in combination with a reforming process. The process of the present invention is ideally suited to prepare a reforming stock and the reforming reactions result in a net production of hydrogen due to the dehydrogenation of naphthenic compounds to form aromatic compounds. The net production of hy 'drogen may be used as the hydrogen-containing gas of the present invention. It is not necessary that the hydrogen c'ontaini'ng gas used in the hydrogenating and desulfraction. The effluent from the desulfurizifig zone is subje'cte'dto a purification process whereby hydrogen sulfide is removed therefrom, by any suitable separation process including fractionation, adsorption, absorption, extraction, chemical combination, etc., and the resultant sulfur-free material is' passed to the reforming zone; The product from the reforming zone may be separated into a high octane, high quality gasoline and a gas consisting. essentially of hydrogen and normally gaseous hydrocarbons. At least a portion of the net gas make of the reformer is passed to the first hydrogenating zone to supply the required'hydroge'n. i As hereinb'efor'e stated when a charge stock having a high degree of unsaturat'i'on is to be treated it ispreferable that'the feed to'the hydrogenation reactofbe ata lower temperature than when a feed stock having a lowdegree of unsaturation is to be treated. For'example', the hydrogenation reaction may be effected at any temperature from room temperature to about 900 F., however, if the temperature increases, the equilibrium towards hydrogenation becomes less favorable. Since hydrogenation is an exothermic reaction the temperature of the material being hydrogenated increases as it passes through the reaction zone. A more unsaturated material experiences a greater increase in temperature and a less unsaturated material experiences a lesser rise in temperature. Again as hereinbefore stated, the desulfurization reactions wherein the sulfur contained in a sulfur bearing molecule is hydrogenated to form hydrogen sulfide leaving a residual hydrocarbon molecule, are initiated at temperatures in the range of 400 F. and proceed rapidly at about 600650 F. It may therefore be seen that it is desirable to operate the hydrogenation zone so that the outlet temperature from this zone is not in excess of about 650 F. It is therefore preferred that highly unsaturated feed stocks, say those having a bromine number in excess of 50 be charged to the hydrogenation zone at a temperature of from about 200 F. to about 350 F. wherein feed stocks having a bromine number in the range of from about to about 50 will be charged to the hydrogenation zone at temperatures in excess of 200 F., preferably in the range of from about 350 F. to about 450 F.

Following is one example of the process of the present invention. A mixture of straight run and catalytically cracked gasoline boiling from 175 F. to 400 F. and having a bromine number of 28 and a sulfur content of 0.5 by weight is commingled with hydrogen-containing gas obtained from a subsequent reforming process, heated to a temperature of 300 F. and the resultant hydrogencontain-stream under a pressure of 475 p. s. i. is passed into contact with a catalyst containing 0.3% platinum, 0.8% fluorine and alumina. As the stream passes through the hydrogenating catalyst bed the temperature rises to 350 F. due to the hydrogenation reactions effected in the hydrogenation zone. The stream is then heated to 600 F. and under substantially the same pressure (475 p. s. i.) is passed into contact with the catalyst comprising a sulfided composite of cobalt oxide, molybdenum oxide, and alumina. The efiluent from the desulfurizing zone is stripped of the hydrogen sulfide contained therein and the bottoms product from the stripper is a doctor sweet saturated gasoline boiling from 150 F. to 425 F. The stripper bottoms are subjected to a reforming operation, such as the well known platforming process de scribed in my U. S. Patent No. 2,479,110 to yield a stable, high octane gasoline and a hydrogen-containing gas, a portion of which is passed to the treating zone. The present example is intended to illustrate one embodiment of the present invention but not intended to limit the invention to the particular conditions or materials used.

As may be seen from the foregoing specification and example, the process of the present invention provides a means of treating a sulfur-containing, highly unsaturated hydrocarbon material to produce a stable, saturated substantially sulfur-free material without deactivating the treating catalyst either by sulfur deactivation or coke formation. When used in conjunction with a reforming process the present invention may be self sustaining with regard to hydrogen and economical with regard to heat.

I claim as my invention:

1. A process for refining an unsaturated sulfur-containing hydrocarbon distillate which comprises saturating unsaturated hydrocarbons in said distillate by subject ing the distillate to hydrogenation in the presence of a hydrogenating catalyst containing a member selected from the group consisting of platinum and palladium at below desulfurizing temperature and thereafter subjecting the thus saturated sulfur-containing distillate to desulfurization in the presence of a desulfurizing catalyst containing a group VI metal and a metal of the iron group of the periodic table.

2. The process of claim 1 further characterized in that said hydrogenating catalyst comprises platinum in a concentration of from about 0.01% to about 1% by weight, halogen in a concentration of from about 0.5% to about 8% by weight and alumina.

3. The process of claim 1 further characterized in that said desulfurizing catalyst comprises a sulfided composite of cobalt oxide, molybdenum oxide, and alumina.

4. The process of claim 1 further characterized in that said hydrogenating step is effected at a pressure of from about p. s. i. to about 1000 p. s. i.

5. The process of claim 1 further characterized in that said desul'furizing step is effected at a pressure of from about 100 p. s. i. to about 1000 p. s. i.

6. The process of claim 1 further characterized in that the hydrogenation is effected at a temperature of from about 200 to about 450 F. and the desulfurization at a temperature of from about 400 to about 750 F.

7. A process for refining an unsaturated sulfur-containing hydrocarbon distillate which comprises saturating unsaturated hydrocarbons in said distillate by subjecting the distillate to hydrogenation in the presence of a hydrogenating catalyst containing a member selected from the group consisting of platinum and palladium at below desulfurizing temperature and thereafter subjecting the thus saturated sulfur-containing distillate to desulfurization in the presence of a desulfurizing catalyst comprising cobalt and molybdenum.

8. The process of claim 7 further characterized in that the hydrogenation is effected at a temperature of from about 200 to about 450 F. and the desulfurization at a temperature of from about 400 to about 750 F.

References Cited in the file of this patent UNITED STATES PATENTS 2,116,061 Dorrer May 3, 1938 2,417,308 Lee Mar. 11, 1947 2,419,029 Oberfell Apr. 15, 1947 2,486,361 Nahin et al. Oct. 25, 1949 2,542,970 Jones Feb. 27, 1951 2,658,028 Haensel et al. Nov. 3, 1953

Claims (1)

1. A PROCESS FOR REFINING AN UNSATURATED SULFUR-CONTAINING HYDROCARBON DISTILLATE WHICH COMPRISES SATURATING UNSATURATED HYDROCARBONS IN SAID DISTILLATE BY SUBJECTING THE DISTILLATE TO HYDROGENATION IN THE PRESENCE OF A HYDROGENATING CATALYST CONTAINING A MEMBER SELECTED FROM THE GROUP CONSISTING OF PLATINUM AND PALLADIUM AT BELOW DESULFURIZING TEMPERATURE AND THEREAFTER SUBJECTING THE THUS SATURATED SULFUR-CONTAINING DISTILLATE TO DESULFURIZATION IN THE PRESENCE OF A DESULFURIZING CATALYST CONTAINING A GROUP VI METAL AND A METAL OF THE IRON GROUP OF THE PERIODIC TABLE.