US2558137A - Process for sulfur removal - Google Patents

Description

Patented June 26, 1951 PROCESS FOR SULFUR REMOVAL Harold J. Hepp, Bartlesville, kla., assignor to Phillips Petroleum Company, a corporation of Delaware No Drawing. Application December 29, 1947, Serial No. 794,437

2 Claims.

This invention relates to a process for sulfur removal. In one aspect this invention relates to the removal of sulfur-containing compounds present in refinery streams. In another aspect this invention relates to the removal of sulfur-containing materials present in olefin-containing hydrocarbon mixtures. In a more specific aspect this invention relates to the removal, catalytically, of sulfur compounds present in a normally gaseous hydrocarbon mixture containing olefins.

The presence of sulfur in various refinery streams is frequently difiicult to avoid because of the presence of sulfur-containing compounds in crude petroleum. The presence of sulfur-containing compounds in motor fuels is undesirable. Sulfur present in motor fuels in one form or another corrodes the metallic parts of internal combustion engines as a result of the action of acids formed by the sulfur-containing compounds during combustion. Also, sulfur compounds in a refinery stream exert deleterious effects on refinery processing equipment, including many catalysts. Sulfur in any form, present in motor fuel, adversely affects the TEL response of the motor fuel. The readiness of most sulfur materials to enter into complex reaction with many intermediate refinery products presents further problems in the processing of the petroleum. For such reasons as those above mentioned it is desirable to remove sulfur compounds contained in refinery streams as early as is possible in a given processing step.

Sulfur compounds present in crude petroleum or in distillates from the fractionation of crude petroleum or refined stocks therefrom, occur in major proportions as mercaptans or thiol type compounds, and hydrogen sulfide, and as such render the distillate corrosive, malodorous, or sour, and otherwise of considerably less value for incorporation in finished gasoline stocks. Hydrogen sulfide is relatively easily removed from refinery streams by extraction means, or a caustic alkali treatment, or the like. Extensive research and study have been devoted to the problem of removing such sulfur compounds contained in various refinery streams or converting them to relatively innocuous compounds. One of the methods employed, for example, is to treat the hydrocarbon distillate with so-called doctor solution which is a solution of lead oxide or litharge in an aqueous solution of sodium hydroxide. On mixing the hydrocarbon mixture containing sulfur compounds with this solution, lead mercaptides are formed. To this mixture is added a reagent adapted to form insoluble lead compounds and to convert the sulfur compounds to disulfides. This may be accomplished by the addition of finely divided sulfur which reacts with the lead mercaptides to form insoluble lead sulfide and the corresponding disulfides 'or thioether type compounds which are non-corrosive in nature and non-odorous. The conversion of the original sulfur-containing compounds to relatively innocuous compounds is referred to as sweetening, and comprises a means of rendering all sour hydrocarbon mixtures more useful for incorporation into a finished motor fuel. Another well-known method for sweetening sour hydrocarbon streams is the copper sweetening process which comprises bringing the hydrocarbon mixture containing sulfur compounds in contact with a bed of solid or a solution of cupric chloride. The sulfur-containing compounds are directly oxidized to disulfides in an oxidation-reduction reaction involving the reduction of cupric chloride to cuprous chloride and hydrochloric acid from which the cupric chloride is regenerated with oxygen.

The sweetening processes as above described and others referred to as such are so named because of the effect of the process on a sour hydrocarbon distillate. Any sweetening process herein referred to eifects a conversion of the sulfurcontaining compounds present in the hydrocarbon stream substantially completely to relatively innocuous compounds.

Since the advent of petroleum cracking, most refinery streams contain at least a small proportion of unsaturated or olefin hydrocarbons and usually contain olefins in a concentration varyin from about 1 to as high as about 40 mol per cent andin some instances higher. Many such refinery streams contain both olefins and sulfurcontaining compounds, and it is with such a refinery stream or hydrocarbon mixture that my invention is concerned.

An object of my invention is to provide a process for removing sulfur-containing compounds from hydrocarbon mixtures.

Another object is to provide a catalytic process for removing sulfur-containing compounds contained in normally gaseous olefin-containing hydrocarbon mixtures.

Still a further object is to provide a process for removing sulfur containing compounds present in normally gaseous olefin-containing hydrocarbon mixtures or refiery streams in the presence of a silica-alumina type catalyst.

Other objects and advantages of this invention will become more apparent to one skilled in the art from the accompanying disclosure.

The deleterious effects of sulfur compounds in normally gaseous hydrocarbon mixtures used in the manufacture of finished motor fuel products, are such as to necessitate their removal, or at least their chemical conversion to those compounds exerting no such harmful effects such as is the function of a sweetening process.

By employing my process, sulfur-containing compounds are converted to higher-boiling sulfur compounds instead of being retained in the hydrocarbon mixture as such are removed therefrom.

In one specific application my invention is concerned with the removal of sulfur compound present in normally gaseous olefin-containing mixtures by which it is to be understood is meant such refinery streams or hydrocarbon mixtures as comprise a mixture of propene and/or butenes with propane and/or butanes, in any proportions, and in any case containing relatively small concentrations of hydrocarbons boiling slightly above the range of the principal components thereof. For example, hydrocarbons containing from to 6 carbon atoms would comprise such hydrocarbons above the range of a propane-propene-butanebutene hydrocarbon mixture.

I have discovered that a normally gaseous hydrocarbon mixture containing olefins and sulfur compounds can be contacted with a silicaalumina type catalyst at conditions of temperature, pressure, and contact time such that a minor proportion of the said olefin is reacted concomitantly with a condensation of sulfur compounds with olefins to form high-boiling sulfur compounds. The sulfur compounds thus formed can be separated from the remaining normally gaseous olefin-containing mixture by any suitable means, preferably as a kettle product of fractionation. The lighter product of such a separation comprises substantially the initial mixture of normally gaseous hydrocarbons freed of a large portion of the sulfur contained initially, the portion usually removed approximating 85 to 90 per cent of the sulfur present in the normally gaseous stream initially.

Catalysts employed effectively and advantageously for use in this invention comprise silica combined with an oxide of a metal of Group IIIB or IVA of the periodic table, and may be referred to in general as silica-alumina type catalysts. As listed in Modern Inorganic Chemistry, by J. W. Mellor (Longmans, Green & Company (1939) revised and edited by G. D. Parkes) on page 118, Group IIIB consists of boron, aluminum, gallium, indium, and thallium, and Group IVA consists of titanium, zirconium, hafnium, and thorium. In general, these catalysts are prepared by first forming a hydrous silica gel from an alkali silicate and an acid, washing soluble material from the gel, treating or activating the gel with an aqueous solution of a suitable metal salt and subsequently washing and drying the treated material. In this catalyst comprising silica with a minor portion of alumina, said minor portion of alumina comprising less than 10 per cent and preferably in the range of 0.1 to 2 per cent by weight of the catalyst, is herein referred to as a silica-alumina catalyst and is the catalyst usually employed in the process of this invention, although it is to be understood that catalysts as described above can be utilized in carrying out the process of this invention.

In the use of silica-alumina type catalysts for polymerization of normally gaseous olefins it has been the practice to conduct the process to produce a certain desired amount of polymerization, and as the catalyst becomes progressively deactivated to increase progressively the reaction temperature, thereby maintaining a constant amount of conversion over a period of time. However, there is a more or less fixed maximum temperature, of about 550-650 F. above which it is not feasible to conduct the polymerization, and it is of great advantage therefore to start the use of a fresh silica-alumina type catalyst at as low a temperature as possible, so that there can be a greater temperature range through which the polymerization temperature may be raised, and therefore a longer catalyst life. Minimum temperatures, or lowest starting temperatures below which it is not feasible to conduct the polymerization are in the range of 200- 275 F. when polymerizing normally gaseous olefins on a commercial scale to produce polymer constituents for motor fuels. In such cases normally gaseous hydrocarbon mixtures containing as high as 40-50 mol per cent olefins are polymerized, converting as high as -80 per cent per pass of the total olefin charged. However, when conducting the desulfurization process of this invention, olefin conversions in the range of 5-25 per cent of the total olefins charged are sufiicient and conversions in the order of 5-15 per cent are preferable. Initial temperatures lower than said temperatures of 200-275 F. are therefore feasible when conducting the desulfurization process of this invention, such temperatures often comprising those in the range of l50-190 F. It is to be understood that although the process of this invention is usually conducted at temperature conditions such that low olefin conversions are effected, such conversion levels are not to be limiting thereby because the efficiency of the process of this invention is not impaired when higher temperatures are employed and consequent high olefin conversions are obtained.

In accordance with my process, at least a minor portion of the olefins in the normally However, catalysts of a very similar nature, but

differing among themselves as to one or more specific properties, may be prepared by using, instead of an aluminum salt, a hydrolyzable salt of a metal selected from Group IlIB or Group IVA and may be referred to in general as silicaalumina type catalysts. Whether prepared by this method, or by some modification thereof, the catalyst will contain a major portion of silica and a minor portion of metal oxide, in a combination which causes the resulting granular, dried material to have especially active catalytic properties for the process of my invention. The minor portion of metal oxide such as alumina will generally not be in excess of 10 per cent by weight and will often and preferably be between about 0.1 and 1.5 or 2 per cent by weight. The specific silica-alumina type gaseous olefin-containing mixture containing sulfur compounds, hereinafter referred to as charge stock, is converted to a higher boiling product. The reaction product comprises compounds having at least 6 carbon atoms per molecule, depending on the particular charge stock.

I have found that the olefin-sulfur compound condensation above described proceeds selectively at mild reaction conditions in the presence of a silica-alumina type catalyst to provide relatively high-boiling sulfur-containing products comprising at least per cent of thio-ether type compounds. About 10 per cent or less, and usually in the range of 3 to 5 per cent of the sulfur-containing condensate present in the product, comprises high-boiling mercaptans. The mechanism of the formation of these high-boiling mercaptans is not known but is thought to proceed through the initial formation of a thio-ether, formed by the interaction of an olefin with a sulfur-containing compound present in the charged stock, or by a reacted olefin of the reaction mixture with a sulfur compound present in the charge stock, in either case the thio-ether product splitting off a low-boiling olefin and the corresponding high-boiling mercaptan. However, the content of high-boiling mercaptans in the reaction product comprises usually a low proportion, and as such exerts no marked deleterious efiects such as those described and attributed hereinbefore to the presence of larger proportions of sulfur-containing compounds. Other sulfur-containing compounds may be present in the reaction product such as disulfides and. traces of polysulfides, although such sulfides comprise usually less than 1 per cent of the sulfur-containing compounds present in the reaction product. The total sulfur-containing condensate distills outside the distillation range of the unconverted charge, the products of this conversion usually boiling between 125-4'75 F.

The sulfur-containing by-product of my invention can be desulfurized by any of the various known desulfurization methods to produce a sufiiciently sulfur free stock for utilization in finished motor fuels. For example, the desulfurization or removal of organically combined sulfur contained in hydrocarbon mixtures, can be effected in the presence of a bauxite catalyst and in the vapor phase at temperatures in the range of 500-700 F. or higher.

The reactions in the process of this invention proceed to form, as by-products, sulfur compounds selectively in high yield under reaction conditions so mild as to react only a minor proportion of the olefin contained in the hydrocarbon mixture. I have operated my process treating a butane-butene-propane-propene stream containing butenes in the order of 15-40 per cent by weight and sulfur in the order of 0.01-0.05 weight per cent, in the presence of silica-alumina catalyst at conditions of temperature and pressure such that olefin conversions as low as 4 per cent were obtained. In other instances of such mild conditions of operation wherein low olefin conversions were efiected I have obtained a icy-product having a sulfur content as high as 2 per cent by weight. I have also operated my process wherein charge stocks having a sulfur content as high as 0.05 weight per cent were treated and conversions higher than those required for my process were effected; for example, a butane-butene propane-propene mixture containing sulfur in the order of 0.05 weight per cent and olefins in the order of 25-50 weight per cent were treated at conditions of temperature, pressure, and space velocity so as to obtain olefin per pass conversions in the order of 15-35 per cent of the total olefin charged, at moderate temperatures in the presence of a very active catalyst, and also at substantially maxium temperatures that would permit the reaction of olefins to chiefiy dimers when utilizing a nearly inactive or spent silica-alumina catalyst. When cperatingmy process under reaction conditions varying in temperature from mild temperatures in the range of 150-250 F. to maximum temperatures in the range of 550-650 F. the condensations of sulfur-containing compounds and olefins are consistently obtained in per pass yields approximating a 90 per cent conversion of the total sulfur initially present in the hydrocarbon mixture with substantially 90 per cent or more of "a sulfur content would the condensation product comprising a thioether type product.

In many cases it is preferable to retain a maximum olefin concentration in the particular normally gaseous olefin-containing stream being treated and in that regard the process of my invention is especially advantageous since the condensation progresses selectively and rapidly, at reaction conditions effecting very low olefin conversions as aforesaid.

In the practice of my invention a normally gaseous hydrocarbon mixture, containing olefins usually in the range of from 10 to 50 mol per cent and contaminated with sulfur compounds, in the order of 0.001 to 0.05 per cent by weight, is passed to an initial reaction zone containing a silicaalumina catalyst such as is described herein, at reaction conditions of temperature, pressure, and space velocity such that a minor amount of olefin or olefins, usually at least 4 per cent by weight is reacted. Usually such conditions comprise initial temperatures in the range of -220 F., a pressure in the range of 500-1500 p. s. i. and a space velocity in the order of 3 to 7 liquid volumes of charge stock per volume of granular catalyst per hour, depending upon the activity of the catalyst, the reactivity of the olefins, and upon the olefin conversion desired. The effluent of the reaction zone is passed to a separation means, preferably a fractionation system, wherein the products of condensation are separated from the efiiuent as a fractionation kettle product. The overhead product of the fractionation system comprises a normally gaseous olefin-containing hydrocarbon stream of substantially reduced content of sulfur-containing compounds. Often the concentration of sulfur compounds in the overhead product is sufficiently low as to be disregarded so far as further utilization of the overhead product is concerned. However, in some instances the sulfur concentrations exceed such limits, as for example, when the sulfur content thereof is in the range of 0.001 to 0.005 per cent by weight or higher. When the sulfur content of the said fractionator overhead product must be further reduced, the said product is passed to a second reaction zone containing silica-alumina catalyst at conditions of temperature, pressure, and space velocity similar to those aforedescribed in the initial reaction zone wherein reactions similar to those taking place in the initial reaction zone are effected. The efiiuent of the second reaction zone is passed to a fractionation system and the products of the reaction are separated as a fractionator kettle product as aforesaid and the overhead product of the fractionation comprises a substantially sulfur-free normally gaseous olefin-containing hydrocarbon mixture. Usually subsequent to passing the sulfur-containing normally gaseous olefin mixture to a second reaction zone and fractionating the efiluent of same as above described the sulfur content of the desulfurized mixture approximates 0.00005 to 00005 or lower depending upon the initial charge stock. When initially charging a stock having a sulfur content of 0.018 per cent for example, the fractionation overhead of the initial reaction zone effluent will have a sulfur content approximating 0.0018 per cent by weight. A sulfur content in the order of 0.0018 weight per cent is often considered to be excessively high and an overhead product having such in such instances necessarily be passed to a second reaction zone and subsequently fractionated as described hereinbefore. Subsequent to passing a stream such as aforesaid having a sulfur content approximat ing 0.0018 weight per cent to a second reaction zone as aforedescribed the overhead fractionation product of the ellluent thereof would have a sulfur content in the order of 0.00018 weight per cent. A sulfur content such as one in the range of 0.0001 to 0.0002 weight per cent of a normally gaseous olefin-containing hydrocarbon mixture can be disregarded in most instances and the hydrocarbon mixture can be considered to be substantially completely desulfurized; the olefin or olefins contained therein can then be converted at conditions of temperature, pressure and space velocity approximating those of this invention, aforesaid, in the presence of a silicaalumina type catalyst, to sulfur free hydrocarbons boiling in the motor fuel range.

Advantages of this invention are illustrated by the following example. The reactants, and their proportion, and other specific ingredients, are presented as being typical and should not be construed to limit the invention unduly.

Example A refinery propane propene butane butene stream containing 26 per cent by weight of olefins, and 0.009 per cent sulfur by weight is contacted in a first pass with a silica-alumina catalyst at a temperature of 250 F., a pressure of 1500 p. s. i. and at a space velocity of 6 liquid volumes of charge stock per volume catalyst per hour. Olefin reaction product is formed in the amount of 15.4 per cent by weight of the total olefin charged. The effluent of the first pass is fractionated to provide a residual olefin reaction kettle product containing 0.198 per cent sulfur by weight. The fractionator overhead product comprises a normally gaseous mixture containing 22 per cent olefins by weight. Sulfur present in the kettle product is 88 per cent by weight of that initially charged. The sulfur content of the fractionator overhead product is 0.0011 per cent by weight. The fractionator overhead product is passed to a second reactor containing silicaalumina catalyst, at the same conditions of temperature, pressure, and space velocity as those employed in the initial reactor, and the effluent fractionated. 83 per cent of the sulfur entering the second reactor is present in the fractionator kettle product and a normally gaseous overhead product containing 18.6 weight per cent olefin and 0.00018 weight per cent sulfur is obtained.

As will be evident to those skilled in the art, various modifications can be made or followed, in the light of the foregoing disclosure and discussion, without departing from the spirit or scope of the disclosure or from the scope of the claims.

I claim:

1. A process for the manufacture of sulfur-free hydrocarbons boiling in the motor fuel range, from a normally gaseous olefin-containing hydrocarbon mixture contaminated with sulfur compounds, comprising passing said hydrocarbon mixture as a liquid into a reaction zone containing a silica-alumina type catalyst, at a temperature in the range of 150 to 550 F., at a pressure in the range of 500 to 2000 p. s. i. g., at a space velocity in the range of l to 10 liquid volumes hydrocarbon mixture per catalyst volume per hour, and correlating said temperature, pressure, and space velocity conditions with the activity of said catalyst so as to react at least 4 and not more than 25 per cent of the total olefins initially pres-v ent in said hydrocarbon mixture with sulfur compounds to produce high-boiling sulfur compounds; said silica-alumina type catalyst comprising silica and alumina and prepared by first forming a hydrous gel by introduction of a sodium silicate solution into an excess of acid, water washing the resulting gel, partially drying the washed gel, activating same with an aqueous solution of an aluminum salt to form hydrous alumina adsorbed on said gel in such amount to produce a finished catalyst containing from 0.1 to 2 per cent alumina by weight on a dry basis. washing the activated gel and drying the washed activated gel to form hard glassy granules of finished catalyst; separating efiluents of said reaction zone into a fraction comprising sulfur compounds boiling in the range of to 475 F. and a desulfurized normally gaseous olefin-containing hydrocarbon fraction, converting olefins in'said desulfurized normally gaseous hydrocarbon mixture to sulfur-free hydrocarbons boiling in the motor fuel range by passing said desulfurized mixture in contact with a silica-alumina catalyst prepared as above described at a temperature in the range of from 250 to 650 F., and recovering sulfur-free normally liquid hydrocarbons so produced as a product of the process.

2. A process for removing sulfur compounds present in a normally gaseous olefin-containing hydrocarbon mixture, comprising passing said hydrocarbon mixture as a liquid into a reaction zone containing a silica-alumina type catalyst, at a temperature in the range of to 550 F., at a pressure in the range of 500 to 2000 p. s. i. g., at a space velocity in the range of 1 to 10 liquid volumes hydrocarbon mixture per catalyst volume per hour, and correlating said temperature, pressure, and space velocity conditions with the activity of said catalyst so as to react at least 4 and not more than 25 per cent of the total olefins initially present in said hydrocarbon mixture with said sulfur compounds to produce highboiling sulfur compounds; said silica-alumina type catalyst comprising silica and alumina and prepared by first forming a hydrous gel by introduction of a sodium silicate solution into an excess of acid, water washing the resulting gel, partially drying the washed gel, activating same with an aqueous solution of an aluminum salt to form hydrous alumina adsorbed on said gel in such amount to produce a finished catalyst containing from 0.1 to 2 per cent alumina by weight on a dry basis, washing the activated gel and drying the washed activated gel to form hard glassy granules of finished catalyst; separating effluents of said reaction zone into a fraction comprising sulfur compounds boiling in the range of 125 to 475 F. and a desulfurized normally gaseous olefin-containing hydrocarbon fraction, and recovering desulfurized normally gaseous hydrocarbons as a product of the process.

HAROLD J. HEPP.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,273,038 Houdry et a1 Feb. 17, 1942 2,310,630 Hancock Feb. 9, 1943 2,328,756 Thomas Sept, 7, 1943 2,366,453 Meadow Jan. 2, 1945 2,421,320 Ernest May 27, 1947 2,427,309 Schulze Sept. 9, 1947 Certificate of Correction Patent No. 2,558,137 June 26; 1951 HAROLD J. HEPP It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows:

Column 2, line 58, after compounds insert which; column 8, line 1, after with insert said and that the said Letters Patent should be read as corrected above, so that the same may conform to the record of the case in the Patent Oflice. Signed and sealed this 25th day of December, A. D. 1951.

THOMAS F. MURPHY,

7 Assistant Commissioner of Patents.

Claims (1)

1. A PROCESS FOR THE MANUFACTURE OF SULFUR-FREE HYDROCARBONS BOILING IN THE MOTOR FUEL RANGE, FROM A NORMALLY GASEOUS OLEFIN-CONTAINING HYDROCARBON MIXTURE CONTAMINATED WITH SULFUR COMPOUNDS, COMPRISING PASSING SAID HYDROCARBON MIXTURE AS A LIQUID INTO A REACTION ZONE CONTAINING A SILICA-ALUMINA TYPE CATALYST, AT A TEMPERATURE IN THE RANGE OF 150 TO 550 D.; AT A PRESSURE IN THE RANGE OF 500 TO 2000 P.S.I.G., AT A SPACE VELOCITY IN THE RANGE OF 1 TO 10 LIQUID VOLUMES HYDROCARBON MIXUTER PER CATALYST VOLUME PER HOURS, AND CORRELATING SAID TEMPERATURE, PRESSURE, AND SPACE VELOCITY CONDITIONS WITH THE ACTIVITY OF SAID CATALYST SO AS TO REACT AT LEAST 4 AND NOT MORE THAN 25 PER CENT OF THE TOTAL OLEFINS INITIALLY PRESENT IN SAID HYDROCARBON MIXTURE WITH SULFUR COMPOUNDS TO PRODUCE HIGH-BOILING SULFUR COMPOUNDS; SAID SILICA-ALUMINA TYPE CATALYST COMPRISING SILICA AND ALUMINA AND PREPARED BY FIRST FORMING A HYDROUS GEL BY INTRODUCTION OF A SODIUM SILICATE SOLUTION INTO AN EXCESS OF ACID, WATER WASHING THE RESULTING GEL, PARTIALLY DRYING THE WASHED GEL, ACTIVATING SAME WITH AN AQUEOUS SOLUTION OF AN ALUMINUM SALT TO FORM HYDROUS ALUMINA ADSORBED ON SAID GEL IN SUCH AMOUNT TO PRODUCE A FINISHED CATALYST CONTAINING FROM 0.1 TO 2 PER CENT ALUMINA BY WEIGHT ON A DRY BASIS, WASHING THE ACTIVATED GEL AND DRYING THE WASHED ACTIVATED GEL TO FORM HARD GLASSY GRANULES OF FINISHED CATALYST; SEPARATING EFFLUENTS OF SAID REACTION ZONE INTO A FRACTION COMPRISING SULFUR COMPOUNDS BOILING IN THE RANGE OF 125 TO 475 * F. AND A DESULFURIZED NORMALLY GASEOUS OLEFIN-CONTAINING HYDROCARBON FRACTION, CONVERTING OLEFINS IN SAID DESULFURIZED NORMALLY GASEOUS HYDROCARBON MIXTURE TO SULFUR-FREE HYDROCARBONS BOILING IN THE MOTOR FUEL RANGE BY PASSING SAID DESULFURIZED MIXTURE IN CONTACT WITH A SILICA-ALUMINA CATALYST PREPARED AS ABOVE DESCRIBED AT A TEMPERATURE IN THE RANGE OF FROM250 TO 650* F., AND RECOVERING SULFUR-FREE NORMALLY LIQUID HYDROCARBONS SO PRODUCED AS A PRODUCT OF THE PROCESS.