IL28902A - Oxidation of soluble sulfide compounds - Google Patents

Description

. l'DJllLUl ■■■ fnU -Tlin *! HI PATENT ATTORNEYS · D'DIDD 1 D T 11) DR. REINHOLD COHN (Π3 "flinJ DR. MICHAEL COHN ] Π 3 1 H J * ISRAEL SHACHTER B.Sc. .0.3 File CI 27422 PATENTS AND DESIGNS ORDINANCE SPECIFICATION Oxidation of soluble sulfide compounds mo*oa T»a io niaiain Tixan I/We UNIVERSAL OIL PRODUCTS COMPARY, a corporation duly organized under the laws of the State of Delaware, U.S.A., of 30 Algonquin fioad, Des Plaines, Illinois, U.S.A. do hereby declare the nature of this invention and in what manner the same is to he performed, to he particularly described and ascertained in and hy the following statement :- The subject of the present invention is a process for the catalytic conversion of a soluble sulfide compound to a higher oxidation state such as elemental sulfur, sulfite, bisulfite, dithionate, thiosulfate, sulfate, or the like. More specifically, the present invention relates to a catalytic process which utilizes controlled amounts of oxygen in conjunction with a solid . metallic sulfide catalyst to effect a transformation in the oxidation level of a soluble sulfide compound.

In one important aspect, the invention concerns a process for the production of elemental sulfur from a solution containing a sulfide compound; in another important aspect it encompasses treatment of a solution of a sulfide compound, such as a waste stream produced during chemical processing, in order to lower its biological oxygen demand so that it ca be safely disposed of in streams and rivers.

As part of the price that has to be paid for a modern industrial society, large quantities of solutions of sulfide compounds which are produced from various industrial sources, must be disposed of. In particular, aqueous solutions containing hydrogen sulfide are. an undesired side-product of many economically significant industrial processes in the chemical, petroleum, and steel industries. For instance, in the petroleum industry large quantities of solutions of sulfide compounds are produced by such processes as hydrorefining, hydrocracking, reforming and the like. In fact, a common feature of all . of these processes is that they operate on a petroleum., fraction, a shale oil, a coal tar oil, and the like, , which invariably contain at least trace quantities of organic sulfur compounds. During the course of these processes, these organic sulfur compounds are generally converted into hydrogen sulfide and corresponding hydrocarbons. The resultant hydrogen sulfide is then typically removed from the process by absorption ii a suitable solution. In large measure, these solutions are aqueous alkaline solutions, and their disposal presents a proble because of their potential biological oxygen demand which is a consequence of the presence of sulfide ion. In a' case of particular interest (hydrorefini g of petroleum distillates) large quantities of ammonia and hydrogen sulfide are produced, and these are generally absorbed in an aqueous solution which is withdrawn from the process. Similarly, the sweetening treatment of natural gas with a suitable scrubbing fluid, such as monoethanolamine, also results, in a sulfide solution.

The. sulfide compound in these solutions is generally present as a salt of a strong base, such as ammonium sulfide, sodium sulfide, potassium sulfide, and the like, which may be ionized to various degrees.

Moreover, the sulfide compound may be present in the same kind of polar association which characterizes, for instance, solutions of hydrogen sulfide in diethanolamine.

In this respect, it should he remembered that hydrogen sulfide because of its polar nature is soluble in aqueous solution to some degree even in the absence of an appropriate solubility-increasing agent* For example, at 200C. and 1 atmosphere absolute pressure, about 2,5 ml* of hydrogen sulfide (vapor) will dissolve in 1 ml. of water.

Quite understandably, in recent years attention has been focused upon means of converting these sulfide compounds into forms that have less demand for oxygen and, if possible, into a form that has substantial economic value. One example of such means is the "dr box" process (Encyclopedia Kirk Othmer, First Edition, Vol. 13, p. 394) for removing hydrogen sulfide from coke-oven gases and other industrial gases, wherein the process gas is passed over iron oxide with excess air to allow formation of ferric sulfide and a subsequent reoxidation of the sulfide to iron oxide and sulfur* This simple operation provides for complete removal of any hydrogen sulfide in the process gas.

A method has now been found for converting these sulfide compounds, either into valuable elemental sulfur* if desired, or, alternatively, into sulfr compounds of reduced oxygen demand suitable for discharge into rivers and streams (if sulfur production is not economically feasible).

Accordingly, it is a urpose of this invention to provide a process or the production of elemental sulfur from a solution of a sulfide compound. A concomitant object is to provide a process for reducing the biological oxygen demand of an aqueous solutionjof a sulfide compound. Another object is to provide a process for purifying sulfide-containing waste streams so that they may be reused if desired. Still another general object is to control or prevent water polution by chemical, petroleum, and like industries.

Accordingly, the present invention provides a process for oxidizing a soluble sulfide compound which comprises contacting a solution of said sulfide compound with an oxygen-containing gas in the presence of a solid catalyst selected from the group consisting of the sulfides of nickel, iron, and cobalt and mixtures thereof.

In a preferred embodiment of the invention an aqueous ammoniacal solution of hydrogen sulfide, is oxidized by contacting the same with an oxygen-containing gas in the presence of a solid catalyst comprising nickel sulfide composited with alumina.

One feature of the present invention that is particularly advantageous is that it is a liquid phase operation. This allows operation on the streams generally available from industrial processes of the type previously mentioned. Moreover, this feature facilitates recovery of sulfur, if such is desired.

As pointed out hereinbefore, the solution to be charged to the process of the present invention contains a sulfide compound. This solution may be derived from any industrial operation such as chemical plants, sewage treatment plants, and the like. The solvent employed may be water, alcohol, or another suitable organic solvent. The solution is typically an aqueous solution and as such is commonly referred to as "waste water".

In some cases, it is desired to convert the sulfide compound contained in this waste water to the corresponding sulfite, thiosulfate, sulfate, dithionate, etc. which are in a highly oxidized state and thus have less demand for oxygen. On the other, it may be desired to convert the sulfide to elemental sulfur. In either case, the present invention can effect the desired transformation. Furthermore, the sulfide compound is generally present in small concentrations -- for example, less than $ by weight of the solution — although the present invention works equally well with a solution having a high concentration of sulfide. In addition, the solution typically contains other components which enhance the solubility of the sulfide in the solution — examples of these are: ammonia; metal salts of weak acids,^s¾cFf as sodium carbonate, sodium phosphate and the like; organic bases such as methyl amine, ethyl amine, ethanol amine, propanolamine, and the like; and others well known to the art. As previously noted, a particularly important class of solutions comprises ammoniacal aqueous solutions of hydrogen sulfide.

Another essential reactant for the present invention is oxygen. This may be present in any suitable form, either by itself or mixed with other gases, or in any suitable amount. In the embodiment of the present invention in which it is desired to produce elemental sulfur, oxygen is preferably utilized in approximately the stoichiometric amount needed to effect this transformation that is to say from about 0.2$ to about 1 mole of oxygen for every mole of sulfide. Alternatively, when it is desired to minimize the oxygen demand of the solution in order to allow its discharge into streams, then oxygen is preferably present in an amount in excess of the stoichiometric amount to convert sulfide to sulfate that is to say an amount greater than about 2.0 moles of oxygen per mole of sulfide.

Another advantageous feature of the present invention is the utilization of the catalyst in solid form. This enables operation without the catalyst recovery problem that generally attends operation with a soluble catalyst.

As indicated above, the present process is effected in the presence of an insoluble metallic sulfide„ The metal is selected from the group consisting of nickel, cobalt, and iron, with nickel-being preferred; moreover, mixtures of these sulfides can be employed.

Although it is possible to practice the present invention with a catalytic bed of the solid metallic sulfide as such, it is preferred that the metallic sulfide be composited with a suitable carrier material.

Examples of suitable carriers are: charcoals, such as wood charcoal, bone charcoal, or the like, which may be activated prior to' use; alumina; silica; zirconia; kieselguhr; bauxite; carbons; and other natural or synthetic highly porous inorganic carrier material.

The preferred carrier materials are alumina and activated charcoal. Thus, nickel sulfide composited with alumina or with activated charcoal represent particularly preferred catalysts.

Any suitable means of compositing the metallic sulfide with the carrier material may be used, including impregnating the latter by immersing it in a solution of a soluble salt of the desired metallic component, thereafter washing and drying it. The metallic component can then be converted to the sulfide by treatment with hydrogen sulfide, preferably at room temperature alternatively, the salt form may be converted to the sulfide during the initial part of the processing cycle. In some cases, it may be advantageous to calcine the impregnated carrier material prior to sulfiding it.

In general, when the metallic sulfide is composited with a carrier material, the amount by weight of the metal component, calculated as the sulfide, may range up to 600 or more of the total composite. However, it is generally preferred to operate in the range of about 10% to about .0 by weight of the total composite .

The process of the present invention can be carried out in any suitable manner, i.e., either in a batch or a continuous operation. A particularly preferred procedure involves a fixed bed system in which the catalyst is disposed in an oxidation zone.

The sulfide-containing solution is then passed there-thru in either upward or downward flow and the oxygen is passed thereto in either countercurrent or concurrent flow.

When the process of the present invention is operated to produce substantial yields of elemental sulfur, the sulfur may be separated from the effluent from the oxidation zone in any suitable manner such as filtration, centrifugation, settling, or by any other means known to the art for removing solid particles from a liquid. If desired, the effluent from the oxidation zone may be passed to a sulfur settler which may be maintained at a sufficiently elevated temperature (n.b. sulfur melts at about 112PC. ) so that the sulfur agglomerates and is then removed by simply drawing off a separate immiscible liquid sulfur phase.

In some situations , it may be desirable to operate the present invention in a multistage manner in order to effect complete conversion of the sulfide. For example, it may be desirable to operate the first stage in a manner' designed to effect production of sulfur, with the effluent from the first stage, after sulfur separation, being subjected to a second stage designed to oxidize the remaining sulfide to sulfate, thereby allowing the discharge of this effluent into streams and rivers. Moreover, it is to be recognized that in some cases the substantially sulfide-free effluent from the process of :the present invention may be recycled to the industrial process from which it came for further use therein.

The process of the present invention is effected at any suitable temperature which may range from ambient up to about 200°C. or more. When the process is operated to produce elemental sulfur it is preferred to operate in the range of about 0°C. to about 100°C. On the other hand, when the process is operated to produce sulfate, it is preferred to operate in a range of about 100°C. to about 200°C.

The pressure employed can be any pressure which maintains the sulfide solution in the liquid phase. In general it is preferred to operate at superatmospheric pressures, and a pressure from about 1.7 to about 10.2 atmospheres, gauge, is particularly suitable.

Liquid hourly space velocity (LHSV — defined as the volume of sulfide solution charged per hour divided by the total space volume of catalyst within the oxidation zone) preferably is in the .range of about 0„ to about Ι Ο.

The catalytic bed employed. in the present invention may be discarded if it becomes clogged with adsorbed elemental sulfur or may be regenerated by any of the methods known to the art. Examples of suitable methods are: burning at elevated temperature with oxygen followed by reduction in hydrogen; heating the bed in an inert atmosphere to the vaporization temperature of sulfur and then stripping the sulfur with an inert gas, using a desorbing fluid to remove the sulfur.

The following Examples are given to illustrate further the novelty, mode of operature, and utility of the present invention. It is not intended to limit the present invention to the flow scheme, process conditions and type of catalysts employed therein, since these are intended to be illustrative rather than restrictive.

EXAMPLE I An alumina carrier material was manufactured by passing droplets of an alumina hydrosol into an oil bath by means of a nozzle or rotating disk. After conventional agingp drying and calcining treatments, the carrier material was impregnated with a solution of a nickel nitrate solution in an amount which resulted in a final composite having 20% by weight nickel. After drying, the impregnated carrier material was heated for two hours in a stream of air at about 1 _7°0β to decompose the nitrate. Subsequently, the resultant composite was sulfided by passing a stream of HgS over it at room temperature. 100 cc, of the resultant catalyst were placed in a reaction zone. An aqueous feed stream, containing lo£>7% by weight of ammonia and 2,35 by weight sulfide, and oxygen in a ratio οί-.0„5 moles of oxygen per mole of sulfide,, were then passed into contact with the catalyst in the reaction zone,, The zone was maintained at an inlet pressure of about 3» atmospheres, gauge throughout the run. The charge rate was held at approxi-matsly^OO ml per hour for the duration of the run, thereby setting the LHSV at about 1.0. The run was continued for a period of 20 hours „ The run was divided into a series of four line-out periods and test periods designed to study the rate of oxidation as a function of reactio temperature. Results were as follows: Table I Selectivity, Test No. , Temp. °C. ; . (2) 1 35 81+ . 95 2 60 8 93 3 90 8 77 k 125 75 68 (1) Based upon sulfide content of aqueous feed stream (2) Wt. % elemental sulfur based upon total converted sulfide These results show the capability of the nickel sulfide catalyst to effect the desired transformation of sulfide to higher oxidation levels. In particular, these results manifest the fact that the nickel sulfide catalyst can, by appropriate selection of reaction conditions, be made to produce a product rich in elemental sulfur.

EXAMPLE II An alumina carrier material, manufactured as described in Example I, was impregnated with a cobalt nitrate solution to produce a final composite having 0$ by weight cobalt. The resultant composite was dried at a temperature of 100°C. Thereafter, it was immersed in a solution of sodium carbonate. Subsequently, it was washed with water, dried at 95°C and finally, sulfided by passing hydrogen sulfide over it at room temperature.

The resultant cobalt sulfide-alumina catalyst was subjected to an evaluation test identical to that . delineated in Example I. Results for the run, reported on the same basis as given in Example I, were as follows Table II % Conversion Selectivity Test No. Temp. °C. of Sulfide . . 1 35 65 6 2 60 71 79 3 90 75 73 . 12 68 59 These results indicate that cobalt sulfide is capable of effecting the desired transformation, but under these conditions does not perform as well as the preferred nickel sulfide.

EXAMPLE III An alumina carrier material, manufactured as described in Example I, was impregnated with a ferric nitrate solution to produce a final composite having 10$ by weigh -iron i The resultant composite was then dried at 100° C. A. stream of gaseous ammonia was then passed over the composite. Thereafter, the composite was washed, dried and sulfided in the same manner as described in Example II..

The resultant catalyst was subjected to an evaluation test identical with that described in Example Results of the test, on the same basis as before, were as follows: Table III Conversion Selectivity Test No. Temp., °C. of Sulfide % 1 35 79 82 2 60 . 79 82 3 90 81 82 I. 125 73 70 , These results, consequently, show that iron sulfide on alumina is effective for the desired reaction. However, this catalyst at these conditions is not as effective as the preferred nickel sulfide catalyst of Example I.

EXAMPLE IV A commercially available charcoal (i.e. known as Nuchar WA) was impregnated with a solution of nickel nitrate to produce a final catalytic composite having 63$ b weight nickel (based upon weight of charcoal support). After drying, the resultant composite was contacted with a stream of gaseous ammonia and then heated to 95>°C to drive off excess ammonia. Thereafter, the catalyst was washed with water, dried and sulfided at room temperature.

The resultant catalytic composite was then subjected to an evaluation test identical to that reported in Example I. Results of the test were as follows: Table IV · % Conversion Selectivity Temp., °C. of Sulfide % 1 . 35 93 98 2 60 93 96 3 90 92 93 12 85 89 These results exhibit the singular selectivity of nickel sulfide for the production of elemental sulfur and demonstrate a sustained activity for this catalyst in the oxidation of sulfide, EXAMPLE , V This Example concerns the embodiment in which the process of the present invention is utilized to effect oxidation of the sulfide to levels beyond the elemental state such that the demand for additional oxyge is minimized and the resultant stream may be safely discharged into rivers and lakes. This is especially useful in cases where the amount of sulfide in the solution is too low for economical recovery of elemental sulfur.

The nickel sulfi de-charcoal catalyst utilized was identical to that reported in' Example IV. As before, 100 cc. of this catalyst were placed in an oxidation zone. A solution containing 1.67 weight sulfide and 2. 35$ weight ammonia was then charged to the zone in admixture with an amount of air so that the mole ratio of oxygen to sulfide was about 3· 5» pressure of 6.8 atmospheres, gauge, was utilized in order to keep the solution in the liquid phase. Furthermore, the charging rate was such that the LHSV was 1.0.

The test was conducted over a 12-hour period divided into line-out periods and test periods. Results of the run were as follows: Table V Duration % Conversion of S to Test No. Hours Temp., °C. Sulfate Form (1) 1 3 125 97 2 2 150 100 3 2 1^0 97 (1) Weight % S in effluent in sulfate form.

Accordingly, this example clearly manifests the ability of the present invention to produce an effluent stream having substantially no intrinsic demand for oxygen and, thus, suitable for discharge into rivers, streams, and lakes.

Claims (3)

1. HAVIHG HOW particularly described and ascertained the natur our said invention and in what manner the same is to be performed, declare that what we claim is 1. A process for oxidizing a soluble sulfide compound which comprises contacting a solution of said sulfide compound with an oxygen-containing gas in the presence of a solid catalyst selected from the group consisting of tho sulfides of nickel, iron, and. cobalt and 'mixture s the reof .

2. , The process of Claim 1 further characterized in that said solution is an aqueous alkaline solution of the sulfide compound., 3» The process of Claim 2 further characterized. in that said, solution is an aqueous ammoniacal solution of hydrogen sulfide, i. The process of any of the Claims 1 to 3 further characterized in that saidAmetallic sulfide is supported on a carrier material.. 5. The. process of Claim l\. further characterized in that .said carrier material is alumina. 6. The process of Claim l. further characterized in that. said carrier material is activated charcoal. 7« The process of Claim 5 further characterized in that said solid catalyst comprises nickel sulfide composited with alumina. 8. ' The process of Claim 6 further characterized in that said solid catalyst comprises nickel sulfide composited with activated charcoal.' 9. The process of. any of the claims 1 to · 8 further characterized in that the contact is effected at a temperature within the range from 0° to 200° C. and at a pressure at which the solution is maintained in liquid phase. 10o The process of any of the claims 1 to 9, further characterized in that oxygen is contacted with, the solution in an amount within the range from 0.25 to 1 mol per mol of sulfide in the solution," and- the sulfide is oxidized substantially to elemental sulfur. 11. The process of claim 10, further characterized by effecting the contact at a temperature within the. range from 0° to 100°C. 12. The process of any of the claims 1 to 9 further characterized in that oxygen is contacted with the solution in an amount greater than 2 mols per mol of sulfide in the solution, ■ and the sulfide is oxidized substantially to sulfate form. 1

3. The process of claim 12, further characterized by effecting the contact at a temperature within the range from 100° to 200°C. ll. The process for oxidizing a soluble sulfide compound, substantially as hereinbefore described. Dated this 6th day of November, 1967