US3655621A - Adding mercaptan sulfur to a selective hydrogenation process - Google Patents

Abstract

A PROCESS FOR REDUCING THE SULFRUIC ACID REQUIREMENTS OF A C4 HYDROCARBON-CONTAINING ALKYLATION FEED COMPRISES SELECTIVELY HYDROGENATING ACID POLYMERIZABLE MATERIALS SELECTED FROM THE GROUP CONSISTING OF BUTADIENE, ETHYL ACETYLENE, AND MIXTURES THEREOF TO BUTYLENE IN A C4 HYDROCARBON-CONTAINING STREAM IN THE PRESENCE OF A PRESULFIDED HIGH NICKEL CONTENT CATALYST AND HYDROGEN IN THE VAPOR STATE AT ABOUT 300-500*F. AND IN THE PRESENCE OF AT LEAST ABOUT 1 GRAIN OF MERCAPTAN PER 100S.C.F. OF THE STREAM AND IN THE SUBSTANTIAL ABSENCE OF SULFURBEARING NICKEL CATALYST POISONS.

Description

APril 1972 A. s. KASPERIK ErAL 3,655,621

ADDING MERCAPTAN SULFUR TO A SELECTIVE HYDROGENATION PROCESS Filed March 23, 1970 m5 EE INVENTORS v AROHIBALD S. KASPERIK HERBERT A. FUCHS MM ATTORNEYS United States Patent 3,655,621 ADDING MERCAPTAN SULFUR TO A SELECTIVE HYDROGENATION PROCESS Archibald S. Kasperik, Palos Verdes Estates, Calif., and Herbert A. Fuchs, El Dorado, Ark, assignors to Signal Oil and Gas Company, Los Angeles, Calif. Continuation-impart of application Ser. No. 739,904, June 14, 1968, which is a continuation of application Ser. No. 490,518, Sept. 27, 1965. This application Mar. 23, 1970, Ser. No. 21,621

Int. Cl. C07c 11/08; Cg 23/02 US. Cl. 260-677 H 12 Claims ABSTRACT OF THE DISCLOSURE RELATED APPLICATIONS This application is a continuation in part application of SN. 739,904, filed June 14, 1968, for Selective Hydrogenation, which was a continuation application of SN. 490,518, filed Sept. 27, 1965. Both of these parent applications are now abandoned.

The present invention generally relates to an improved process of selective hydrogenation and more particularly relates to an improved process for selectively hydrogenating acid polymerizable material comprising butadienes and ethyl acetylene in a C hydrocarbon-containing petroleum stream.

In certain modern petroleum refining processes, selected C hydrocarbon-containing streams are passed into alkylation units for conversion of unsaturates into high octane components. However, certain difliculties have historically been associated with such alkylation processes. In this regard, thermal cracking processes and fluid coking processes conventionally employed for the production of various cuts (boiling ranges) of hydrocarbons normally produce streams which contain significant concentrations of butadienes and ethyl acetylene, along with isobutane, butylene, propylene and the like. When such a stream is passed to a conventional alkylation unit employing sulfuric acid, the butadienes and acetylene interfere with the alkylation by polymerizing and consuming substantial quantities of the sulfuric acid.

Accordingly, in order to avoid a heavy expenditure of sulfuric acid in the alkylation process, certain techniques have been developed for pretreating the fluid stream which is the alkylation feed, so as to remove butadienes and ethyl acetylene. Thus, for example, one conventional technique comprises selectively extracting the butadienes from the alkylation feed. However, such a procedure is relatively expensive and time consuming. It would be highly desirable to provide a simple, rapid and inexpensive process of selectively removing butadienes and also ethyl acetylene from alkylation feed streams. Preferably, such process should convert the butadienes and ethyl acetylene to products which improve the quality of the alkylation feed streams and that of the product stream from the alkylation unit. Obviously, the process should not result in impairment of other components of the alkylation feed stream.

Accordingly, it is a principal object of the present invention to provide an improved process for selectively treating butadienes and ethyl acetylene in a C hydrocarbon-containing stream so as to reduce the sulfuric acid requirement of the stream during subsequent alkylation thereof.

It is also an object of the present invention to provide an improved process for converting butadienes and ethyl acetylene to products which consume lowered amounts of sulfuric acid in an alkylation process.

It is a further object of the present invention to provide a process for selectively converting butadienes and ethyl acetylene in a C hydrocarbon-containing stream to mono-olefins without conversion of other C, hydrocarbons in the stream.

It is a still further object of the present invention to provide an inexpensive, rapid and efiicient process for selectively treating butadienes and ethyl acetylene in an alkylation feed stream, which process is capable of being carried out continuously and inexpensively over a long period of time.

The foregoing and other objects are accomplished by the present invention which comprises a process for selectively hydrogenating acid polymerizable material selected from the group consisting of butadienes, ethyl acetylene and mixtures thereof to mono-olefins in a C hydrocarbon-containing stream. The stream also contains mercaptan sulfur in a controlled concentration but is essentially free of inorganic sulfur-bearing catalyst poison material, including carbonyl sulfide and hydrogen sulfide. A presulfided nickel base catalyst containing a high concentration of nickel sulfide is utilized to effect hydrogenation of the butadienes (and ethylacetylene, if present) to mnon-olefins, even in the presence of a relatively low concentration of hydrogen. In the process, the catalyst comprising nickel deposited on alumina or other suitable refractory base in an about optimal concentration, for example about 20% to 30% nickel, by weight, is first reduced (from the oxidized state) and sulfided with hydrogen and hydrogen sulfide or another inorganic sulfur-bearing catalyst poison material. The hydrogen converts the catalyst to an active form. The hydrogen sulfide reduces the overall activity of the catalyst for hydrogenation to a minimum level, while increasing the selectivity thereof. The catalyst is then equilibrated with mercaptans in the feed stream, "whereupon the overall activity of the catalyst is adjusted to a satisfactory level while the hydrogenation selectivity of the catalyst is maintained at a high level so that the catalyst is only capable of effecting hydrogenation of easily hydrogenatable butadienes and ethyl actylene and does not result in hydrogenation of butylene, propylene and the like under the processing conditions. After equilibration of the catalyst with the mercaptans, such mercaptans, such mercaptans block a change in activity and selectivity of the catalyst during conversion of the butadienes and ethyl acetylenes. The conversion is carried out in a fixed bed with hydrogen and the C hydrocarbon-containing feed stream in the vapor state at any suitable temperature and pressure. The desired conversion is effected by a single pass of the stream through the bed of catalyst. The stream can then be passed to an alkylation zone and can be alkylated with maximum efficiency and with minimum consumption of sulfuric acid during the alkylation.

As a specific example, a catalyst in a 3504 pound amount and comprising 23%, by weight, of nickel (in oxide form) deposited on an alumina base is presulfided and reduced in a fixed bed reactor zone by passing a sour gas comprising hydrogen and hydrogen sulfide through the catalyst at a rate of 720 to 1200 m.s.c.f.d. The sour gas comprises 32.2 vol. percent hydrogen, 1.6 vol. percent H 8, the remainder comprising methane. The catalyst is converted from the inactive oxidized state to the active reduced state and simultaneously presulfided to nickel sulfide of minimal overall activity and high hydrogenation selectivity during passage of the sour gas through the catalyst bed while heating the catalyst at the rate of about 150 F. per hour. When the bed temperature reaches about 400 F., the sour gas flow rate is increased to about 14401680 m.s.c.f.d. and is maintained at that rate until a positive test for hydrogen sulfide is attained on the effiuent passing from the bed, i.e. in about six hours. The bed temperature is then raised to 500 F. and held until a positive hydrogen sulfide test is again attained, i.e. in about four additional hours. The presulfiding is thereupon completed, after which the catalyst is cooled to 400 F.450 F. During the presulfiding, the gas pressure in the system is about 100 p.s.i. After the presulfiding the sour gas inflow is stopped and the pressure is allowed to drop to the 10 p.s.i.g. level whereby most of the sulfur-containing sour gas is removed from the system.

Pure or substantially pure hydrogen flow into the bed is then started to sweep out the remaining sour gas, after which the C hydrocarbon-containing stream is passed to the catalyst bed, along with hydrogen, and the system pressure is raised to 100 p.s.i.g. In the feed stream the butadiene concentration is about 1 percent, by volume, and the ethyl acetylene concentration is about 0.08 percent, by volume. The stream contains mixed C hydrocarbons, mainly butylenes, with about percent propylene. The hydrogen addition is controlled so as to constitute one mole of hydrogen for each mole of acid polymerizable material, i.e. butadiene and ethyl acetylene, in the C hydrocarbon stream, plus 3 mole percent excess of hydrogen, based on the total feed in the reactor eflluent gas. This amounts to a hydrogen addition of about 70-100 s.c.f. per barrel of the C hydrocarbon feed stream. The hydrogen is preferably pure. However, hydrogen of, for example, 80%-90% purity can also be used, with appropriate changes in gas fiow rate, etc., and providing that such gas does not contain more than a small amount of H 5, preferably less than about 15 p.p.m. The inlet temperature to the reactor zone is adjusted to 400 F. The C hydrocarbon-containing exit stream from the reactor zone is tested for butadiene content. The temperature of the incoming C hydrocarbon stream is then adjusted so as to maintain the butadiene content of the exit stream at less than about 0.10%. The ultimate temperature attained in the reactor bed in the particular run is 450 F. The run is continued for 6 months, with the product stream consistently showing a nil concentration of ethyl acetylene and less than about 0.10% butadiene. The product stream is suitable for alkylation with minimal sulfuric acid consumption.

Further objects and advantages of the present invention will be apparent from a study of the following detailed description and the accompanying drawings of which:

The single figure is a schematic flow diagram of a typical system utilized for the hydrogenation of butadiene and ethyl acetylene to mono-olefins in a C hydrocarbon-containing stream.

Now referring more particularly to the single figure of the accomanying drawings, a schematic flow diagram is illustrated showing a typical arrangement of components and steps for the present process. Typical C hydrocarbon alkylation feed is treated by the present process. Such feed usually comprises mainly mono-olefins, such as butylenes, but also may contain normal butane, isobutane, propane and a propylene content usually of not more than about 20% by volume. The stream also contains an appreciable quantity of butadienes, for example up to about 3%, by weight, and may contain a small (e.g. 0.08%) concentration of ethyl acetylene. It will be understood that higher concentrations of butadienes and/ or ethylene acetylene are contemplated, although they are rarely encountered. The stream further contains a con centration of mercaptans of not less tan one grain per 100 s.c.f., desirably at least about 5 grains per 100 s.c.f. feed. Ordinarily, the mercaptan content does not exceed about 100 grains per 100 s.c.f. and consequently a practical range of mercaptan in the feed stream is from about 5 to about 100 grains of mercaptan per 100 s.c.f., and preferably about 30-35 grains per 100 s.c.f. The sulfurbearing catalyst poison content, e.g. the combined carbonyl sulfide and hydrogen sulfide content, of the stream is preferably nil and in any event is kept less than five grains per 100 s.c.f. Usually it is not more than about 100 ppm.

The described feed stream is passed through an entry line 10 in which are disposed a pump 12 and valve 14, and into a heat exchanger 16 in indirect heat exchange with the efiluent from a hydrogenation reactor 18 operating within the temperature range of from about 300 F. to about 550 F. Higher and lower reactor temperatures are contemplated, although unusul and unnecessary. Substantially pure hydrogen containing no appreciable concentration of inorganic sulfur-bearing nickel catalyst poison passes into the heat exchanger 16 via entry line 20, valve 22 and line 10, mixing with the feed stream. Such hydrogen is preferably pure, but can be impure, as for example %-95% concentration, but kept essentially free of impurities (except mercaptan) which poison the catalyst. Thus, the sulfur-bearing nickel catalyst poison content, e.g. H 8 and COS, of the H stream is kept low, well below one grain per s.c.f. and preferably close to nil.

In the heat exchanger 16, the feed stream and hydrogen are heated to, for example, about 175 F. The temperature, of course, can vary considerably, depending upon the size of the heat exchanger, the temperature of the eflluent from the reactor, etc. The feed stream and hydrogen pass through the heat exchanger 16 at any suitable flow rate, for example about 1,000 barrels per day, under any suitable pressure from ambient to about to 200 p.s.i. for example about 170 p.s.i.g., then pass therefrom through lines 24 and 27 and into and through a steam vaporizer 28, thereafter passing to a heater 30 via line 32. In the steam vaporizer 28 and heater 30, the latter of which may be gas fired or the like, as by fuel fed through line 34 and valve 36, the feed stream and hydrogen are raised in temperature to the desired reaction temperature, i.e. from about 350 F. to about 550 F., for example about 400 F. Usually the steam vaporizer is bypassed after start-up of the conversion reaction.

The feed stream and hydrogen are then passed through line 38 into the top of the reactor 18 which carries a fixed bed of the catalyst. The reactor operates at a catalyst bed temperature of about 350550 F. or the like and under any suitable pressure from ambient to about 200 p.s.i.g., for example with an inlet pressure of about p.s.i.g. and an outlet pressure of about 150 p.s.i.g. During start-up of the reactor, the catalyst bed temperature is increased at the rate of about 150 F. per hour to reaction temperature, utilizing preheated feed and/or hydrogen. Once the conversion reaction occurs, the feed and hydrogen flow rates and preheating steps control the reactor bed temperature within the desired range. It will be understood that the reactor 18, steam vaporizer 28, heat exchanger 16, heater 30 and associated lines, pumps and valves, and all equipment to be described and as illustrated in the accompanying figure can be of conventional size, shape and construction. It will be further understood that alternative arrangements of equipment can be made without departing from the spirit and scope of the invention.

The reactor 18 contains a fixed bed of a suitable high nicked content catalyst on an inert base. The nickel content should be at least about 18 percent and preferably 20-23 percent, and such catalyst is supported on an inert base, such as alumina, silica, or silica-alumina. The nickel catalyst has been placed in the reduced state prior to use, in order to activate it, and has been presulfided substantially completely to nickel sulfide. The nickel content of the catalyst should be at least about 18 percent, by weight, since lower concentrations severely limit the amount of inorganic sulfur-containing catalyst poison which can be tolerated in the feed stream. Preferably, such poison is nil. However, most alkylation feed streams contain sufiicient concentrations of such poisons to render the catalyst inactive within a relatively short period of time if the nickel content is not at least about 18 percent by weight, and preferably near 23 percent by weight or above. The catalyst is preferably in fine granular form of such size in the fixed bed that the C hydrocarboncontaining alkylation feed stream and hydrogen can readily pass down therethrough in intimate contact therewith.

In a typical presulfiding operation, the catalyst is disposed as a fixed bed in the reactor 18, and sour gas containing hydrogen and hydrogen sulfide in any suitable concentration, for example, about 10-40 vol. percent hydrogen and about l-l vol. percent hydrogen sulfide, in methane or the like is passed into the reactor 18 at a suitable pressure, e.g. 100 p.s.i.g., via line 20 valve 22, line 10, heat exchanger 16, lines 24 and 27, steam vaporizer 28, line 32, heater 30 and line 38 at any suitable temperature, e.g. 150 F. It will be understood that hydrogen sulfide in the absence of hydrogen is eifective for presulfiding, and also is effective for reduction and presulfiding at about 400 F. Accordingly, hydrogen-free hy drogen sulfide-containing gas can be used, if desired, for this operation, so also can other inorganic sulfur-bearing nickel catalyst poisons such as COS.

The temperature of the sour gas is increased at a suitable rate of, for example, about 150 F. per hour. The catalyst is heated via the sour gas at about the same rate. The sour gas flow rate is initially about 500-1200 m.s.c.f.d., but is usually increased to about 1400-1700 m.s.c.f.d. when the bed temperature reaches about 400 F. The bed usually is then maintained at about 400 F. until hydrogen sulfide is detected in the reactor efiluent. This usually occurs in about -7 hours. Thereafter, the bed is raised to final temperature, about 500-550 F. and held at that temperature until a positive hydrogen sulfide test is again attained, usually in about 3-5 additional hours. The bed temperature in each instance is controlled by heating the sour gas to the desired temperature. It will be understood that presulfiding and reducing can also be accomplished with hydrogen sulfide or hydrogen sulfide and hydrogen utilizing comparable time-temperature sequences.

The purpose of the presulfiding is to decrease to a minimum the overall activity of the reduced catalyst While maximizing the selectivity of the catalyst for hydrogenating easily hydrogenatable butadienes and ethyl acetylene (without hydrogenating mono-olefins in the feed stream). However, after the presulfiding it is necessary to maintain the overall activity of the catalyst sufiiciently to allow the reaction to proceed relatively rapidly. This is accomplished in accordance with the invention, by equilibrating the presulfided catalyst with at least 1 grain of mercaptan sulfur per 100 s.c.f. of feed and preferably 30-35 grains per 100 s.c.f. of feed during the conversion of the butadienes and ethyl acetylene. The particular concentration of mercaptan sulfur will vary with the feed. Ordinarily, 1-5 grains of mercaptan sulfur per 100 s.c.f. is sufficient.

Sufficient activity of the catalyst is restored during partial strip-off of hydrogen sulfide therefrom prior to full equilibration with the mercaptan sulfur to allow the hydrogenation reaction to pnoceed with sufficient rapidity. The equilibration occurs upon passage of the described mercaptan-bearing feed and hydrogen through the reactor bed at reaction temperature over a period of several hours to a day or so, depending on the reactor temperature, etc. Moreover, after equilibration is established, the mercaptan sulfur blocks further removal of the hydrogen sulfide from the catalyst so that the high hydrogenation selectivity is retained along with satisfactory catalyst activity. Since the mercaptan sulfur does not react with the catalyst, an equilibrium continues substantially throughout the process.

It is necessary to avoid having more than, at most, 1 grain per s.c.f. of feed and preferably not more than a few parts per million of inorganic sulfur-bearing catalyst poison such as hydrogen sulfide in the feed stream, since higher concentrations will resulfide the catalyst sufficiently to reduce its activity to about the low presulfided level, essentially hindering the speed and efficiency of the hydrogenation reaction at the desired reaction temperature. It will be understood that it is preferred that no or essentially no hydrogen sulfide and other inorganic sulfur-bearing poisons be present in the feed stream.

Upon completion of the presulfiding operation, the catalyst is allowed to cool to about 400 'F. and the sour gas is shut off at valve 22. The system pressure is allowed to drop to a low level, e.g. l0 p.s.i.g., after which the system is swept free of hydrogen sulfide by passage of hydrogen therethrough for a few minutes. The system pressure is then gradually built up to, for example, 100 p.s.i.g. and the feed stream is passed to the reactor bed, along with hydrogen, as previously described.

In the reactor 18 during the desired conversion reaction of 350 F.550 F. or the like, the acid polymerimble material comprising the butadienes and/ or the ethyl acetylene are substantially completely hydnogenated to the corresponding butylenes without significant hydrogenation of the monoolefins in the feed stream. In this regard, the particular process conditions, including the temperature and fiow rate, are adjusted so that the concentration of the butadienes and the ethyl acetylene in the reactor efiluent is maintained at below about 2 parts per 1000 and preferably at not more than about 0.10%. One pass of the feed stream in vapor form down through the reactor bed is sufiicient to accomplish the desired con'version.

After continuous operation of the conversion (selective hydrogenation) for a period of 6 months or so, a sufficient amount of carbonaceous deposit builds upon the catalyst to require a higher operating temperature within the described range. Shortly thereafter, the catalyst required regeneration, as by conventional steam/air treatment. For example, in catalyst regeneration steam can be passed through the purged system at 400-600 pounds per hour. The catalyst bed temperature is increased at about F. per hour to 700 F.-750 F. When oil-free effiuent is obtained, 1-5 volume percent air is added to the steam with temperature control of the bed below 900 F. When the CO content of the efiluent decreases to below 2%, the reactor is cooled with steam to below 400 F.

In a typical run, a feed stream having the composition shown in Table II was fed to the reactor as depicted in the drawing and described above at a liquid hourly space velocity of 2.387. The reactor temperature was recorded as 391" F. at the reactor inlet and 414 F. at the reactor outlet. The pressure within the reactor was p.s.i.g. The catalyst was 22 percent nickel on alumina and the catalyst had been run approximately lfive months. The analysis of the reactor efiluent and off gas is shown in Tables HI and IV respectively. It can thus be seen that in actual operation our process reduces the diolefin (acid polymerizable material) content to acceptable levels, i.e. from 1.26% to 0.07% while the desirable olefin content was increased from 40.9 percent to 43.1 percent. From the data shown below it is also apparent that the reaction conditions of our process are not such as to result in the conversion of mercaptan sulfur to hydrogen sulfide.

7 TABLE 11 Feed rate: 1162 bbls./day

Analysis: H 5: 2.4 grains/100 s.c.f. Total mercaptan sulfur: 77.6 grains/100 s.c.f. Methane (CH 0.1% (liq. vol percent) Ethane (C H 0.2%

Propane (C H 17.8%

Propylene (C H 10.0%

Isobutane (C H 13.0%

N-butane (C H 16.7%

Butylene 0,11 40.9%

Butadiene (C H 1.26%

TABLE III Analysis: H 5: .4 grains/ 100 s.c.f. Total mercaptan sulfur: 34.7 grains/100 s.c.f. Methane: .1% Ethane: .1% Propane: 16.6% Propylene: 9.5% Iso butane: 13.2% N-butane: 17.2% Butylene: 43.1% Butadiene: 0.07%

TABLE V Off gas rate: 201 m.s.c.f. per day Analysis: H 8: 0.5 grains/100 s.c.f. Total mercaptan sulfur: none Hydrogen: 64.7% (molal percent) Nitrogen+inerts: 0.3% Methane: 3.7% Ethane: 0.3% Propane: 10.4% Propylene: 7.6% Iso-butane: 2.7% N-butane: 2.5% Butylenes: 7.8%

TABLE V (Feed gas to reactor) Feed rate: 119 -rn.s.c.f. per day H 8: none Hydrogen: 96.9 mol percent Nitrogen-kinertsz 0.3% Methane: 2.8%

Off gas: 201 m.s.c.f. per day Accordingly, a simple, inexpensive and efficient process is provided for removing butadienes and ethyl acetylene from mono-olefin-containing alkylation feed streams by substantially and selectively hydrogenating only the butadienes and ethyl acetylene to mono-olefins. The treated feed is superior alkylation feed, being capable of being alkylated with minimal consumption of sulfuric acid. The conversion reaction can be carried out continuously over long periods of time without requiring regenenation of the catalyst or frequent variation of control conditions. The reaction occurs at moderate temperature and pressure, utilizing a high nickel content presulfided catalyst having high selectivity for hydrogenation of the unsaturated hydrocarbons, namely, butadienes and ethyl acetylcues in the feed stream. Such selectivity is maintained in the presence of effective concentrations of mercaptans and in the substantial absence of inorganic sulfur-bearing nickel catalyst poisons such as hydrogen sulfide. The process does not require complicated equipment nor extensive maintenance. Accordingly, it is very economical to operate. Other advantages are as set forth in the foregoing specification.

Various modifications, alterations, changes and additions can be made in the present process, its steps and parameters and in the equipment required for carrying out such steps. All modifications, alterations, changes and additions as are within the scope of the appended claims form a part of the present invention.

We claim as our invention:

1. A process for selectively hydrogenating a C hydrocarbon-containing alkylation feed to substantially remove therefrom acid polymerizable materials selected from the group consisting of butadiene, ethyl acetylene, and mixtures thereof and thereby reduce the alkylation process sulfuric acid requirements, which comprises the steps of:

(a) selectively hydrogenating said acid polymerizable material to butylene in a C hydrocarbon-containing stream in a reaction zone in the substantial absence of hydrogenation of mono-olefins in said stream by contacting said stream and hydrogen in the vapor state at about 300 -F.-550 F. and up to about 200 p.s.i.g. with presulfided high nickel content catalyst supported on a refractory base in the substantial absence of inorganic sulfur-bearing nickel catalyst poisons;

(b) equilibrating said catalyst by adding mercaptan sulfur to an amount of from about 5 grains to about grains of mercaptan sulfur per 100 s.c.f. of said stream in the substantial absence of conversion of said mercaptan sulfur to inorganic sulfur-bearing nickel catalyst poisons;

(c) continuing said contacting until the content of said acid polymerizable material in said stream is substantially reduced; and

(d) thereafter recovering the effluent from said zone for alkylation with reduced consumption of sulfuric acid.

2. The process of claim 1 wherein said nickel catalyst has a nickel sulfide content of at least about 18 percent, by weight, and wherein the total concentration of said inorganic sulfur-bearing nickel catalyst poison, including hydrogen sulfide, in said reaction zone is maintained below one grain per 100 s.c.f. of said stream.

3. The process of claim 2 wherein said mercaptan sulfur content is between about 30 grains and about 50 grains per 100 s.c.f. of said stream, wherein said nicked sulfide content of said actalyst is between about 18 and about 23 percent, by weight, and wherein the hydrogen mole concentration in said reaction zone is at least about 3 mole percent in excess of the mole concentration of said acid polymerizable material in said reaction zone.

4. The process of claim 3 wherein said selective hydrogenation is effected in the gaseous state under elevated pressure at a temperature of between about 400 F. and about 550 F.

5. The process of claim 4 wherein the total of the hydrogen sulfide content f0 said stream and said hydrogen is substantially nil, and wherein the mercaptan concentration in said reaction zone is maintained at between about 5 and about 35 grains per 100 s.c.f. of said stream.

6. The process of claim 3 wherein said selective hydrogenation is carried out continuously over an extended period of time, the total concentration of said acid polymerizable material in the effluent from said reaction zone being maintained at not more than about two parts per thousand.

7. The process in accordance with claim 6 wherein the total concentration of said acid polymerizable material in said effluent does not exceed about 50 parts per million.

8. The process of claim 3 wherein said catalyst is substantially completely presulfided, prior to said selective hydrogenation, by contacting said catalyst at least about 400 F. with inorganic sulfur-bearing catalyst poison, and wherein the presulfiding temperature is subsequently increased to about 550 F. while maintaining said contact with said poison until said presulfiding is substantially completed.

9. The process of claim 8 wherein said presulfiding is carried out utilizing hydrogen sulfide as said catalyst poison, wherein said catalyst is concomitantly reduced from an oxidized state by contact with hydrogen, wherein during said presulfiding said catalyst is heated at a rate of not more than about F. per hour to about 400 F.

and maintained at said temperature until hydrogen sulfide is present in the efiluent therefrom, wherein said catalyst is subsequently heated from said about 400 F. level to about 550 F. at the rate of not more than about 150 F. per hour in the presence of said hydrogen and hydrogen sulfide and maintained at said latter temperature until hydrogen sulfide is again detected in the efiluent therefrom, and wherein said catalyst is subsequently cooled to about 300 F.-400 -F., whereupon said selective hydrogenation is initiated.

10. The process of claim 9 wherein said process is carried out continuously by periodically discontinuing said selective hydrogenating, and regenerating said catalyst, and thereupon repeating said presulfiding and subsequent selective hydrogenating.

11. A process for reducing the sulfuric acid requirement of C hydrocarbon-containing alkylation feed, which process comprises:

(a) selectively hydrogenating acid polymerizable material selected from the group consisting of butadiene, ethyl acetylene, and mixtures thereof to butylene in a C hydrocarbon-containing stream in a reaction zone in the substantial absence of hydrogenation of mono-olefins in said stream by contacting said stream and hydrogen in the vapor state at about 300 F.- 550 F. and up to about 200 p.s.i.g. with presulfided high nickel content catalyst disposed on a refractory base in the substantial absence of inorganic sulfurbearing nickel catalyst poisons and in the presence of mercaptan sulfur added to an amount of from about 5 grains to about 100 grains per 100 s.c.f. of said stream and in the substantial absence of conversion of said mercaptan sulfur to inorganic sulfur-bearing nickel catalyst poisons;

(b) continuing said contacting until the content of said acid polymerizable material in said stream is substantially reduced; and

(c) thereafter recovering the efiluent from said zone for alkylation with reduced consumption of sulfuric acid.

12. A process for improving the quality of C hydrocarbon-containing alkylation feed by reducing the sulfuric acid requirement for said feed, which process comprises:

(a) periodically presulfiding a metal catalyst on a refractory base, the metal of said catalyst consisting essentially of nickel in a concentration of between about 18 percent and about 23 percent, by weight, of said catalyst, and said refractory comprising material selected from the group consisting of alumina, silica and mixtures thereof, said presulfiding being effected by disposing said catalyst as a fixed bed and heating the same at a rate not in excess of about 150 F. per hour to a temperature of about 400 F. in the presence of hydrogen sulfide and hydrogen;

(b) maintaining said catalyst at about 400 F. until the efiluent therefrom contains unreacted hydrogen sulfide;

(c) thereafter raising the temperature of said catalyst at a rate not in excess of about 150 F. per hour up to about 550 F. in the presence of said hydrogen sulfide and maintaining said latter temperature until hydrogen sulfide is present in the eflluent therefrom;

(d) thereafter cooling said catalyst slowly to at least about 350 F., and then sweeping said hydrogen sulfide from contact with said catalyst;

(e) introducing a C hydrocarbon-containing stream and hydrogen, both of which are substantially free of inorganic sulfur-bearing poisons, including carbonyl sulfide and hydrogen sulfide, into contact with said catalyst in the presence of mercaptan sulfur added to an amount of from about 5 grains to about grains per 100 s.c.f. of said stream in the substantial absenec of conversion of said mercaptan sulfur to inorganic sulfur-bearing nickel catalyst poisons, said stream including acid polymerizable material selected from the group consisting of butadiene and ethyl acetylene;

(f) continuously selectively hydrogenating in the vapor phase said acid polymerizable material over an extended period of time in the presence of said mercaptans, catalyst and hydrogen, while maintaining said hydrogen in a concentration of about three mole percent in excess of the mole concentration of said acid polymerizable material;

(g) maintaining the temperature during said selective hydrogenation at between about 300 F. and about 550 F. and the pressure between about 100 and about 200 p.s.i.g.;

(h) recovering efiluent from said selective hydrogenation substantially free of said acid polymerizable material;

(i) passing said efiluent to a recovery zone and at least periodically separately recovering therefrom improved C hydrocarbon-containing alkylation feed having a reduced sulfuric acid requirement during subsequent alkylation;

(j) periodically discontinuing said selective hydrogenating and regenerating said catalyst; and

(k) thereupon repeating said presulfiding and subsequent selective hydrogenating.

References Cited UNITED STATES PATENTS 2,511,453 6/1950 Barry 260-677 3,152,193 10/19-64 [Fleming et a1 260677 3,268,608 8/1966 DeKOsset 260683.9

3,301,913 l/ 1967 Holmes et a1 260-677 HERBERT LEVINE, Primary Examiner US. Cl. X.R. 260-68361

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