US2315662A - Treatment of hydrocarbons - Google Patents

Description

Patented Apr. 6, 1943 2,315,662 TREATMENT OF HYDROCNS Walter A. Schulze, Armas A. Ruoho, and Gra E. Short, Bartlesville, kla., assignors to Phillips Petroleum aware Company, a corporation oi Del No Drawing. Application June 7, 19M, Serial No. 397,134

Claims. (Cl. Hit- 23) This invention relates to a process for removing carbonyl sulfide from hydrocarbon fluids, and to a specific reagent therefor. More specifically, this invention relates to the treatment of hydrocarbons, including the so-called normally gaseous hydrocarbons, from any source for the selective removal of carbonyl sulfide associated with said hydrocarbons.

Hydrocarbon fluids such as those obtained from crud petroleum oils and other sources usually contain varying amounts of deleterious suliur compounds as impurities. The kinds and amounts of sulfur compounds occurring in any hydrocarbon fluid vary with thesource material and with the method of manufacturing and processingpsaid fluid, For example, thermal cracking-operations have a tendency to convert hydrogen sulfide and open-chain sulfur compounds into cyclic compounds and to cause the combination of hydrogen sulfide with carbon compounds to form organic sulfur compounds includins carbon sulfides.

Many of the sulfur compounds present in hydrocarbon fluids are detrimental to the processing or marketing of said fluids or of products derivable therefrom. Thus, there are conventional methods for removing hydrogen sulfide from hydro carbon fluids and for converting mercaptans to less obnoxious form. Further, there are means known to the art for extracting mercaptans as such. However, carbonyl sulfide, a sulfur compound occurring in the lower-boiling products fromthe thermal processing of hydrocarbon oils does not belong in the classifications mentioned,

and being relatively inert is not satisfactorily removed by conventional treating processes em ployed 'bythe industry for the removal of hydro- 'ge'nsuliide, mercaptans, and the like.

Carbonyl sulfide is presumably formed by reaction of hydrogen sulfide with oxides of carbon under the conditions of heat and pressure and exposed metal surfaces encountered in thermal processes such as cracking and reforming operations. The pure compound has a boiling point slightly lower than that of propane, although we have found its apparent boiling point is somewhat higher in hydrocarbon mixtures. Thus, the fractionation-of cracking still gases to segregate a propane butanefraction willresult in the inclusion of Substantiallyall the carbonyl sulfide present within-thatfraction. Likewise a butane and heavier fraction containing only minor percentages of' propane may contain appreciable amounts of carbonyl sulfide.

The ncce'ssityi'or selectively removing carbonyl short. For example,

sulfide arises when a hydrocarbon fluid, e. 8., a Ca fraction from refinery gases is to be substantially completely .desulfurlzed prior to processing to effect polymerization, alkylation or the like. Liquefied refinery gases containing butane and/or propane as produced for consumption as fuel have been found to contain carbonyl sulfide even after conventional methods of desulf urization, such liquefied gases are more commonly called liquefied petroleum gas or LPG. This invention provides a more complete desulfurization of such hydrocar bons after conventional methods for the removal of hydrogensulflde and mercaptan have been applied.

Carbonyl sulfide is relatively stable toward acidic reagents, and is only slowly afi'ected by strongly alkaline treating reagents such as solutions of caustic soda and the like. The slow reaction with alkaline reagents is apparently based on the hydrolysis of the compound to form hydrogen sulfide which reacts with the alkaline me dium. In view of the relatively slow rate of the hydrolysis reaction, incomplete removal or carbonyl sulfide results in a continuous-type treating system wherein the time of intimate contact of hydrocarbon with treating reagent is relatively in washing a propanebutane mixture with a solution of caustic soda to remove hydrogen sulfid we have found that with caustic solutions of ordinary strength. say 10 to 20 per cent by weight of sodium hydroxide. only 20 to 30 per cent 0! the carbonyl sulfide is hydrolyzed and extracted even when mind-stage contacting is employed.

We have now discovered a method of treatment and a type of reagent which efl'ecta the complete removal of carbonyl sulfide from hydrocarbon fluids oi the type described. By the conditions of our process, a rapid reaction occurs involving the carbonyl sulfide which. is converted to a form in soluble in the hydrocarbon fluid and thus easily and completely removed from the purified fluid. The reagent we prefer to use is a solid contact type reagent comprising an adsorbent carrier im pregnated with active chemical ingredients.

An object of this invention is to provide for the and/or mercaptans may be freed of carbonyl sulfide remaining therein after said conventional treatment. Other objects will be apparent .from the following detailed disclosure.

We have found that while carbonyl sulfide is rather non-reactive toward acidic as well as strongly alkaline treating solutions, the reaction to form hydrogen sulfide and carbonic acid Carbonyl hydrogen carbonic suliide sulfide acid can be .promoted by the proper conditions and brought to completion in the presence'of the reagents disclosed herein. For this purpose we employ an alkaline solution and/or suspension of a cadmium compound. The cadmium compound and the alkaline medium bring about the reaction of both products of the hydrolysis of carbonyl sulfide, formingcadmium sulfide and a salt of carbonic acid.

Solutions of soluble cadmium salts either inorganic or organic, such as the chloride, acetate, sulfate, etc., are used to advantage, as well as suspensions of insoluble cadmium compounds such as the'hydroxide, oxide, carbonate, etc. Ordinarily, except in the case of ammonia complexes, the soluble salts are converted more or less completely to the hydroxide by action of the alkaline medium.

We have found that by the use of our solidtype reagent a more complete removal of carbonyl sulfide is obtained than by the use of aqueous solutions of the reagents disclosed herein in the absence of adsorbent carriers. This effect is due in part to the great amount of reagent which is exposed to the hydrocarbon fluid on the surfaces of the adsorbent carriers.

Then, too, there are no emulsion difllculties such as are encountered when aqueous alkaline solutions are mixed with hydrocarbon fluids. Of course, water must always be present on the carrier in appreciable quantities to permit the hydrolysis reaction to proceed. This essential water may be added through the use of aqueous solutions, or otherwise added to the carrier as will be hereinafter more fully shown. In some instances, the stream of hydrocarbon fiuid being treated may be supplied with a small quantity of water to prevent desiccation of the solid reagent.

water A further advantage of our process of treat- I ing with a solid reagent is that we may obtain long contact time of hydrocarbon with the reagent and thus promote complete removal of carbonyl sulfide. Within our preferred range of treating rates, about 0.5 to 5 liquid volumes per hour per volume of reagent, the contact time ranges from about 12 minutes to two hours. This range is in contrast to contact times of ordinarily less than three minutes in processes utilizing aqueous reagent solutions to treat hydrocarbons, and is partly responsible for the eiliciency of our process.

In addition to the above-named advantages, our method of treating provides true countercurrent contact of hydrocarbons with the solid reagent. Thus, the reagent is spent in the direction of hydrocarbon flow while the section of the reagent bed adjacent to the hydrocarbon exit port is least spent and is most effective for the removal of the lowest concentrations of carbonyl sulfide.

Since the cadmium compounds described herein will react preferentially with hydrogen sulfide and/or mercaptans, we prefer to operate our processes to treat only hydrocarbon fluids which have undergone treatments designed to remove these types of sulfur compounds. Treatment by known methods to remove hydrogen sulfide and/or mercaptans may be given to the fluid containing carbonyl sulfide immediately prior to passage over the reagent herein disclosed or at any time previous thereto. Or the conventional desulfurizing treatment or treatments may be made on a crude material which is subsequently fractionated to give the hydrocarbon fraction in question, or on charge stocks to conversion processes which produce the low-boiling hydrocarbons. Any suitable methods known to the art may be used for preliminary removal of hydrogen sulfide and/or mercaptans; such methods include coppersweetening, treatment with bauxite, fractionation and removal by chemicals. Of course, if hydrogen sulfide, for instance, is not present in appreciable quantities in the hydrocarbons, treatment for hydrogen sulfide removal is not necessary. In other words, any type of treatment may be relied on which will insure that the material processed for the removal of carbonyl sulfide in accordance with this invention be essentially free from hydrogen sulfide and mercaptans. Our purpose is to avoid an uneconomic spending of our reagent which would prevent complete removal of carbonyl sulfide and add greatly to the operating costs. Hydrogen sulfide and mercaptans are ordinarily present in hydrocarbon fluids in far greater concentrations than carbonyl sulfide and may be more economically removed by processes featuring regeneration of the treating solutions. Thus our reagent could react only with minor traces of hydrogen sulfide and/or mercaptans remaining in hydrocarbon fluids after treatment by conventional processes.

The reagent may be prepared by impregnating iullers earth or other clay-type minerals, synthetic aluminas or various adsorbent carriers with a solution of a cadmium salt in alkaline media. Alternately, neutral cadmium salt solutions may be added to the adsorbent, and converted to alkaline suspensions of the hydroxide or other basic salts by subsequent addition of a dilute alkaline solution. Cadmium salts form a soluble complex with ammonia, and impregnation may be accomplished with a suitable ammoniacal cadmium salt solution. If the excess of ammonia is later driven off, an alkaline suspension of cadmium hydroxide will remain on the adsorbent. In some cases it may be desirable first to spray the adsorbent with a suitable alkaline solution and then to add a solid cadmium compound such as cadmium hydroxide in finely divided form to the still-damp adsorbent.

It is necessary to maintain an aqueous solution phase on the surface of the adsorbent material throughout the period of use of the above described reagents. Thus the use of dry metal salts is not contemplated in our process. It is also necessary to have a pH in the adsorbed solution of above about 8 and preferably nearer 12 or above to promote the reaction of carbonyl sulfide with the reagent solution and to secure satisfactory results in the use of said reagents.

The preferred range of pH in which optimum results are obtained is between about 8 and l4.v

The necessary alkalinity may be obtained by the use of alkali metal or ammonium hydroxides or in some cases with alkaline earth metal hydroxides.

The amount of cadmium saltto be added will depend on the solubility of the salt in the chosen alkaline medium and/or on the adsorptive capacity of the carrier. In general, weights of cadmium compound in the range of 1 to per cent of the reagent weight are sufficient and avoid mechanical losses from the surface of the adsorbent material. The water content of the reagent preferably ranges from about 5 to 25 per cent, although somewhat lower concentrations may sometimes be used while the upper limit of water content depends to a large extent on the adsorptive capacity of the carrier.

The following examples will serve to illustrate methods of preparing and using satisfactory reagents according to our process. Numerous modifications of the reagent preparations will be obvious to those skilled in the art, and therefore are within the scope of our invention.

Example I Eight to twenty mesh fullers earth was impregnated with an ammoniacal solution of cadmium sulfate to produce a reagent containing 3 per cent by weight of the cadmium salt.

A liquid propane-butane mixture substantially free of hydrogen sulfide and mercaptans was passed over the reagent at low flow rates at about 75 F., and given a water wash' for the removal of ammonia during the early stages of treatment. The untreated hydrocarbon contained 0.005 per cent by weight of carbonyl sulflde, while the treated hydrocarbon contained less than 0.0001 per cent of the impurity. Satisfactory removal of carbonyl sulfide was obtained until the cadmium salt had been almost completely converted to the sulfide.

Example II Fuller's earth was impregnated with cadmium acetate solution in an amount equivalent to 3 per cent by weight of the earth. Following this impregnation, a volume of 5 per cent sodium hydroxide solution in excess of that suificient to convert the cadmium acetate to the hydroxide was sprayed onto the earth. The pH of the adsorbed aqueous phase was above 12.

A liquid propane-butane mixture which had been treated to remove hydrogen sulfide and mercaptans and which contained 0.005 per cent by weight of carbonyl sulfide was passed in liquid phase over this reagent at flow rates of about one volume per hour per volume of reagent. The treated hydrocarbon mixture contained less than 0.0001 per cent by weight of carbonyl sulfide.

We claim:

l. A process for the removal of carbonyl sulfide from hydrocarbon fluids essentially free of hydrogen sulfide and mercaptans comprising the step of contacting said hydrocarbon fluid with a solid reagent comprising an adsorbent carrier impregnated with an aqueous solution of a soluble cadmium salt, the impregnating solution having a pH between the 2. A process for the removal of carbonyl sulfide from hydrocarbon fluids essentially fre of hydrogen sulfide and mercaptans comprising the step of contacting said hydrocarbon fluid with a solid reagent comprising an adsorbent carrier impregnated with an aqueous ammoniacal solution of a soluble cadmium salt to the extent of from approximately 1 to 10 percent of the cadmium salt, the impregnating solution having a pH between the limits of approximately 8 to 14.

3. A process for the removal of carbonyl sulfide from hydrocarbon fluids essentially free of hydrogen sulfide and mercaptans comprising the step of contacting said hydrocarbon fluid with a solid reagent comprising an adsorbent carrier impregnated with an aqueous solution of a soluble cadmium salt to the extent of from approximately 1 to 10 percent of the cadmium salt, and treated with a caustic alkali solution having a, pH between the limits of approximately 8 to 14.

4. A process for the removal of carbonyl sulfide from hydrocarbon liquids essentially free of hydrogensulflde and mercaptans comprising the step of contacting said hydrocarbon liquids with a solid reagent at a liquid flow rate of from approximately 0.5 to 5.0 liquid volumes per volume of reagent per hour, the solid reagent comprising an adsorbent carrier impregnated with an aqueous ammonlacal solution of a soluble cadmium salt to the extent of from approximately 1 to 10 percent of the cadmium salt, the impregnating solution having a pH between the limits of approximately 8 to 14.

5. A process for the removal of carbonyl suifide from hydrocarbon liquids essentially free of hydrogen sulfide and mercaptans comprising the step of contacting said hydrocarbon liquids with a solid reagent at a liquid flow rate of from apf proximately 0.5 to 5.0 liquid volumes per volume Our process is conveniently carried out at ordinary atmospheric temperatures between about 30 and 110 F. although slightly higher temperatures may be used if desired.

Pressures in our process are usually low superatmospheric pressures between 50 and 500 pounds gage. Operating pressures may depend upon the hydrocarbon being treated. Thus when treating butane or propane in liquid phase, sumcient pressure is used to avoid vaporization.

It is usually desirable to treat in liquid phase, since the volume of reagent required for nominal flow rates of from 0.5 to 5 volumes per hour per volume of reagent is not excessive. However, treating the normally gaseous hydrocarbons in vapor phase is satisfactory if provision is made in the size of the reagent bed to allow contact times corresponding to linear vapor velocities of under about five feet per minute.

of reagent per hour, the solid reagent comprising an adsorbent carrier impregnated with an aqueous solution of a soluble cadmium salt to the extent of from approximately 1 to 10 percent of the cadmium salt, and treated with a caustic alkali solution having a pH between the limits of approximately'il to 14.

6. A process for the removal of carbonyl sulfide from hydrocarbon vapors essentially free of hydrogen sulfide and mercaptans comprising the step of contacting said hydrocarbon vapors with a solid reagent at a linear vapor velocity of under approximately 5 feet per minute, the solid re agent comprising an adsorbent carrier impregnated with an aqueous ammoniacal solution of a cadmium salt to the extent of from approximately 1 to 10 percent of the cadmium salt, the impregnating solution having a pH between the limits of approximately 8 to 14.

7. A process for the removal of carbonyl sulfide from hydrocarbon vapors essentially free of hydrogen sulfide and mercaptans comprising the step of contacting said hydrocarbon vapors with a solid reagent at a linear vapor velocity of under approximately 5 feet per minute, the solid reagent comprising an adsorbent carrier impreglimits of approximately nated with an aqueous solution of a soluble cadmium salt to the extent of from approximately 1 to 10 percent of the cadmium salt, and treated with a caustic alkali solution having a pH between the limits of approximately 8 to 14.

8. A process for the removal of carbonyl sulflde from hydrocarbon liquids essentially free of hydrogen sulfide and mercaptans comprising the step of contacting the'said hydrocarbon liquids with a solid reagent comprising an adsorbent carrier at a liquid flow rate from approximately 0.5 to 5.0 liquid volumesper volume of reagent per hour, the adsorbent carrier impregnated with an aqueous solution of a soluble cadmium salt, the impregnating solution having a pH between the limits of approximately 8 to i4.

9. A process for the removal of carbonyl sultide from hydrocarbon vapors essentially free of hydrogen sulfide and mercaptans comprising the step of contacting the said hydrocarbon vapors with a solid reagent comprising an adsorbent carrier at a linear vapor velocity of under approximately 5 feet per minute, the adsorbent carrier impregnated with an aqueous solution of asoluble cadmium salt, the impregnating solution having a pH between the limits of approximately 8 to 14.

WALTER. A. SCHULZEL ARMAS A. RUOHO.

GRAHAM H. SHORT.