EP2029479A2

EP2029479A2 - Method for the catalytic oxidation of sulfide to sulfate

Info

Publication number: EP2029479A2
Application number: EP07729466A
Authority: EP
Inventors: Peter Ebbinghaus; Jochen Winkler; Wolfgang Schaffer; Jörg ERASSME
Original assignee: Sachtleben Chemie GmbH
Current assignee: Venator Germany GmbH
Priority date: 2006-05-24
Filing date: 2007-05-24
Publication date: 2009-03-04
Also published as: WO2007135184A3; BRPI0712503A2; WO2007135184A2; CN101495404B; CN101495404A

Abstract

The invention relates to a method for the catalytic oxidation of sulfide (S2-) to sulfate (SO42-), particularly alkali metal sulfides, alkaline earth metal sulfides, transition metal sulfides, and ammonium sulfide to the respective sulfates. Also disclosed is the use of said method for purifying waste water from the production of barium sulfate or paper.

Description

Process for the catalytic oxidation of sulphide to sulphate

The invention relates to a process for the catalytic oxidation of sulfide (S ^{2 "} ) to sulfate (SO ₄ ^2" ), in particular of alkali and alkaline earth metal sulfides and transition metal sulfides and ammonium sulfide to the corresponding sulfates.

The catalytic oxidation of sodium sulfide (Na ₂ S) to sodium sulfate (Na ₂ SO ₄ ) is an industrially relevant problem. Na ₂ S is used in many large-scale chemical processes in the form of aqueous solutions, for example, in the production of barium sulfate (BaSO ₄ ). These solutions are strongly basic and can be partially used, for example, for depilation of animal skins in the leather industry, but industrial production is higher than demand in other industries. A common disposal of the Na ₂ S solution is to put them with sulfuric acid (H ₂ SO _4), hydrogen sulfide gas (H ₂ S) and a sodium sulfate solution. The hydrogen sulfide gas is reacted with oxygen to sulfur dioxide (SO ₂ ) and subsequently processed to sulfuric acid (H ₂ SO ₄ ) on. In the reaction of hydrogen sulfide with sulfuric acid, however, also elemental sulfur is formed, which can possibly add to systems and thus represents a problem. In addition, due to the high toxicity of hydrogen sulfide, special safety precautions are essential; These plants are therefore subject to the accident ordinance in Germany.

For the oxidation of sulfide, a number of proposals are known from the prior art.

Thus, US-A-4855123 discloses the oxidation of sodium sulfide using unimpregnated carbon catalysts to polysulfide and sodium thiosulfate. However, a way to oxidize sodium sulfide to sodium sulfate is not demonstrated.

US-A-5207927 and US-A-5470486 disclose the selective oxidation of sodium sulfide to sodium sulfate using metal phthalocyanine compound impregnated carbon catalysts. This oxygen is in used overstoichiometric amounts. Disadvantages of this method, in addition to the high oxygen demand, the cost-intensive catalysts, since the impregnations tend to bleed and therefore the catalysts have only a low stability.

US-A-5338463 discloses the use of an insoluble copper compound coated carbon catalyst for the oxidation of sulfide to sulfate. Even such a coated catalyst is expensive, tends to bleed and therefore has only a low stability.

US-A-6017501 discloses a process for the oxidation of gaseous H ₂ S to sulfate by means of a carbon catalyst in a three-phase fixed bed Riemel reactor. The

The maximum solubility of H ₂ S in water is 0.1 mol / L, of which only 10 ^"13 mol / L of the dissolved H ₂ S are present as dissolved sulfide due to the low dissociation In contrast, Na ₂ S is present in concentrations of up to 3 mol / L prior to oxidation, with the salt being completely dissociated, a process for the oxidation of sulphide to sulphate, in which the

Sulfide in aqueous solution as a dissolved salt anion, does not disclose US-A-6017501.

Bal ^'zhinmaev et al. disclose in "Proceedings of 12th International Congress on Catalysis, Spain (2000)" a principled method for the oxidation of sodium sulfide (Na ₂ S) to sodium sulphate (Na ₂ SO ₄₎ using a carbon catalyst Sibunit. The catalyst screening experiments were carried out in a batch-operated pressure reactor (reactor volume 200 ml); For the investigation of mass and heat transport processes, a flow reactor (reactor volume 15 ml) made of Teflon was used. These apparatuses are not suitable for carrying out the catalytic oxidation of sulphide (S ^{2 "} ) to sulphate (SO ₄ ^2" ) on an industrial scale because the conversions and selectivities are insufficient and moreover because of the loss of unreacted Oxygen is too expensive. The object of the invention is to overcome the disadvantages of the prior art and to provide a method by which sulfide, which is present in aqueous solution as an anion of a salt, can be oxidized in the simplest and most cost-effective manner to sulfate. Further objects have been that this process is operated with a continuous reaction procedure, that it uses an unimpregnated catalyst, that it ensures an almost complete conversion of sulfide to sulfate with high selectivity and / or that losses of unreacted oxygen are avoided.

According to the invention, this problem is surprisingly solved by the features of the main claim. Preferred embodiments can be found in the subclaims.

In particular, it has surprisingly been found that almost complete conversion (> 99.5%) of sulfide is achieved at a selectivity of> 99.5% to sulfate already after the first pass through the reactor, when in the inventive process for the catalytic oxidation of sulfide to sulfate an aqueous solution of the sulfide in a three-phase reactor, in particular a fixed-bed Riesel reactor, using a carbon catalyst, in particular an unimpregnated porous carbon material, for example SIBUNIT-3, is oxidized with a superstoichiometric amount of oxygen to sulfate. The excess oxygen is returned.

The oxygen can be supplied as gaseous pure oxygen or technical oxygen or in a mixture with other gases, in particular as compressed air. According to the invention, the oxygen is preferably supplied in the form of technically pure oxygen. Since the oxidant oxygen is highly concentrated in this, the reactor can be made smaller than if compressed air were used. In addition, compressed air must be repeatedly supplied in larger quantities, since the present in the compressed air in a lower concentration of oxygen is consumed faster; This has a constant complex compression of the compressed air - A -

result. In addition, the nitrogen present as the main component in the compressed air occupies the catalyst surface and thus reduces its activity.

The preferred fixed-bed trickle reactor according to the invention is a three-phase reactor in which gaseous, liquid and solid phases are in contact with each other. It can be designed, for example, as a tube reactor filled with catalyst.

The fixed bed Rieselreaktor is used according to the invention, because it ensures ease of handling and scale transfer, high volumetric material conversion performance and safe retention of the catalyst. Due to the narrow residence time distribution and the pronounced substrate concentrate gradient above the reactor height, almost complete substance conversions can be achieved. In addition, this type of reactor causes only low operating costs.

A disadvantage of this type of reactor, however, are the poor heat transfer properties, which must be taken procedural measures to achieve optimal temperature distribution in the reactor. Thus, the temperature at the reactor inlet should not be too low to ensure a sufficient reaction rate. At the same time, it should not be too high at the reactor outlet to reduce by-product formation and catalyst aging.

The catalyst used according to the invention is preferably an unimpregnated porous carbon material, for example a catalyst of the SIBUNIT series, more preferably SIBUNIT-3. This catalyst has a high activity at high selectivity and high relative to the oxidation of sulfide to sulfate

Life. Structure and properties of this catalyst are in the

Patent Application DE-A-3912886, the disclosure of which is fully incorporated in this specification, and in Proceedings of 12th International Congress on Catalysis,

Spain (2000) / Bal ^' zhinmaev et al. ".

The subject of the present invention is in detail: a process for the catalytic oxidation of sulphide to sulphate;

a process for the catalytic oxidation of sulphide to sulphate by means of a gaseous oxidant;

a process for the catalytic oxidation of sulphide to sulphate, wherein the reaction in a three-phase reactor containing the catalyst, preferably in a

Catalyst-containing fixed-bed reactor, particularly preferably carried out in a catalyst-containing fixed bed Rieselreaktor;

a process for the catalytic oxidation of sulphide to sulphate, wherein both sulphide and sulphate are in aqueous solution;

a process for the catalytic oxidation of sulphide to sulphate, wherein the sulphide is in the form of a dissolved salt anion;

a process for the catalytic oxidation of sulphide to sulphate, wherein the sulphate is in the form of a dissolved salt anion;

a process for the catalytic oxidation of sulphide to sulphate, the process being operated in a continuous reaction mode;

a process for the catalytic oxidation of sulphide to sulphate using as catalyst a non-impregnated porous carbon material;

a process for the catalytic oxidation of sulphide to sulphate using as catalyst SIBUNIT-3;

a process for the catalytic oxidation of sulphide to sulphate, the conversion of sulphide being between 99 and 99.999%, preferably between 99.5 and 99.99%, with a selectivity between 99 and 99.999%, preferably between 99.5 and 99, 99%, to sulfate; a process for the catalytic oxidation of sulphide to sulphate, the sulphide being an alkali metal sulphide, preferably sodium and / or potassium sulphide;

a process for the catalytic oxidation of sulphide to sulphate, the sulphide being an alkaline earth sulphide, preferably magnesium and / or calcium sulphide;

a process for the catalytic oxidation of sulphide to sulphate, the sulphide being ammonium sulphide;

a process for the catalytic oxidation of sulphide to sulphate, wherein the sulphide is a transition metal sulphide;

a process for the catalytic oxidation of sulphide to sulphate, the concentration of the sulphide solution being between 0.1 and 3 mol / l, preferably between 0.3 and 2 mol / l, particularly preferably between 0.5 and 1.5 mol / l is;

a process for the catalytic oxidation of sulphide to sulphate, oxygen being used as the oxidant;

- A process for the catalytic oxidation of sulfide to sulfate, wherein the oxygen is supplied in gaseous form as technically pure oxygen;

a process for the catalytic oxidation of sulphide to sulphate, the oxygen being supplied in gaseous form in admixture with other gaseous constituents;

a process for the catalytic oxidation of sulphide to sulphate, the oxygen being supplied in the form of compressed air;

a process for the catalytic oxidation of sulphide to sulphate wherein the oxygen is substituted for sulphide in an over-stoichiometric ratio; a process for the catalytic oxidation of sulphide to sulphate, wherein the stoichiometric factor n (O ₂ ) / n (S ^{2 "} ) is between 1 and 10, preferably between 1, 5 and 8, more preferably between 2 and 6, with very particular preference between 3 and 5;

a process for the catalytic oxidation of sulphide to sulphate, wherein the unused oxygen is recycled to the process;

a process for the catalytic oxidation of sulphide to sulphate, the ratio between sulphate withdrawn from the process and recycled to the reactor being between 1: 2 and 1:20, preferably between 1: 5 and 1:15, more preferably between 1: 7 and 1: 12;

a process for the catalytic oxidation of sulphide to sulphate, the sulphate solution returned to the reactor being cooled and mixed with the sulphide solution to ensure high liquid loading and to minimize the adiabatic increase in temperature along the catalyst bed;

a process for the catalytic oxidation of sulphide to sulphate, the heat energy accumulating in the heat exchanger being used for further processes;

a process for the catalytic oxidation of sulphide to sulphate, the oxidation reaction being carried out in the temperature range from 90 to 170.degree. C., preferably in the temperature range from 105 to 155.degree. C., more preferably in the temperature range from 15 to 145.degree.

- A method for the catalytic oxidation of sulfide to sulfate, wherein the temperature at the reactor inlet between 90 to 150 ⁰ C, preferably between 100 to 140 ⁰ C, more preferably between 1 10 to 130 ⁰ C; - A process for the catalytic oxidation of sulfide to sulfate, wherein the temperature at the reactor outlet between 1 10 to 170 ° C, preferably between 120 to 160 ° C, more preferably between 130 to 150 ⁰ C;

a process for the catalytic oxidation of sulphide to sulphate, the pressure in the oxidation reaction being between 1 and 50 bar, preferably between 5 and 25 bar, more preferably between 12 and 18 bar;

the use of the process for the catalytic oxidation of sulphide to sulphate for the purification of sulphide contaminated effluents, preferably of effluents from barium sulphate and / or papermaking;

the use of the process for the catalytic oxidation of sulphide to sulphate for the production of sulphate, which can be used in production processes, preferably in the production of barium sulphate;

FIG. 1 shows, by way of example, the schematic structure of a plant for carrying out the process according to the invention for the catalytic oxidation of sulphide to sulphate without restricting the invention to this.

In this case, an aqueous sulfide solution 1 flows at the top of the reactor inlet 2 in the fixed-bed trickle reactor 3, where it is added via a spray nozzle 4 to the catalyst bed 5 of the reactor. The oxygen stream 6, which is also fed into the top of the reactor, is entrained by the sprayed sulphide solution.

The sulfide solution and the oxygen entrained in the liquid stream come into direct contact with the catalyst surface in direct current, at which the actual oxidation reaction takes place.

After passing through the catalyst, the liquid solution containing the dissolved sulfate leaves the reactor via the reactor outlet 7 at the lower end of the reactor. Since the oxidation of sulphide to sulphate is highly exothermic, the liquid stream becomes passed through a heat exchanger 8, in which the heat is dissipated via the cooling water stream 9/10 and made usable for other methods. After the heat exchanger, a small part of stream 1 1 of the sulfate solution is withdrawn and thus removed from the process cycle. This sulphate solution can be used again for further production processes, for example for the production of barium sulphate. The larger part stream 12 of the sulfate solution is combined with the sulfide solution stream 1 and fed back into the reactor via the feed. As a result, the undiluted sulfide solution stream is preheated and also diluted so that on the one hand at the reactor inlet the optimal temperature for the catalyst in the range of 90 to 170 ° C is reached in the oxidation reaction, on the other hand, is not exceeded at the reactor outlet. It can be maintained as a high liquid loading of the reactor without adding additional liquid, which unnecessarily dilute the deducted sodium sulfate solution. In addition, the pressure losses in the system are kept small.

The excess, not consumed in the reaction oxygen is separated below the catalyst bed by a gas / liquid separator from the liquid stream, removed from the reactor and fed again with newly supplied oxygen above the reactor. As a result, a complete oxygen conversion is achieved after several passes. In addition, this also keeps the pressure losses in the system small.

The following are exemplary associated operating parameters, without limiting the invention thereto:

Example 1 :

• Oxidizing agent: oxygen (100%, technical) • Pressure p = 15 bar

• Temperature at the reactor inlet T = 120 ° C

• Temperature at the reactor outlet T = 140 ° C

• V (Na ₂ S solution) = 50 L / h with recycling 1/9 • c (Na ₂ S) = 0.77 mol / L

Stoichiometric factor N (O ₂ ) / n (Na ₂ S) = 4

• conversion / selectivity:> 99.5% /> 99.5%

Comparative Example 1: reduced stoichiometric factor N (O ₂ ) / n (Na ₂ S) • Oxidizing agent: oxygen (100%, technical)

• pressure p = 15 bar

• Temperature at the reactor inlet T = 120 ° C

• Temperature at the reactor outlet T = 140 ° C

• V (Na ₂ S solution) = 50 L / h with recycle 1/9 • c (Na ₂ S) = 0.77 mol / L

Stoichiometric factor N (O ₂ ) / n (Na ₂ S) = 2

• conversion / selectivity:> 99.5% / approx. 60%

Comparative Example 2: reduced pressure

• Oxidizing agent: oxygen (100%, technical) • Pressure p = 10 bar

• Temperature at the reactor inlet T = 120 ° C

• Temperature at the reactor outlet T = 140 ⁰ C

• V (Na ₂ S solution) = 50 L / h with recycling 1/9

• c (Na ₂ S) = 0.77 mol / L • Stoichiometric factor N (O ₂ ) / n (Na ₂ S) = 2

• Revenue / selectivity:> 99.5% / approx. 65%

Comparative Example 3: reduced oxygen partial pressure

• oxidizer: oxygen (100%, technical) • pressure p = 10 bar

• Temperature at the reactor inlet T = 120 ⁰ C

• Temperature at the reactor outlet T = 140 ⁰ C

Stoichiometric factor N (O ₂ ) / n (Na ₂ S) = 2

• Revenue / selectivity: approx. 92% / approx. 17%

Example 1 clearly shows in comparison to Comparative Examples 1 to 3 that the choice of the correct operating parameters is decisive for the economical use of the method.

Claims

claims

1 . Process for the catalytic oxidation of sulfide to sulfate, characterized in that both sulfide and sulfate are present in aqueous solution as dissolved salt anions and the reaction in a three-phase reactor containing the catalyst, preferably in a fixed-bed reactor containing the catalyst, more preferably in a fixed bed Rieselreaktor containing the catalyst is carried out by means of a gaseous oxidizing agent.

2. The method according to claim 1, characterized in that the method is operated with continuous reaction procedure.

3. The method according to claim 1 or 2, characterized in that a non-impregnated porous carbon material is used as the catalyst.

4. The method according to at least one of claims 1 to 3, characterized in that is used as the catalyst SIBUNIT-3.

5. The method according to at least one of claims 1 to 4, characterized in that the conversion of sulfide between 99 and 99.999%, preferably between 99.5 and 99.99%, with a selectivity between 99 and 99.999%, preferably between 99, 5 and 99.99%, to sulfate.

6. The method according to at least one of claims 1 to 5, characterized in that it is an alkali sulfide, preferably sodium and / or potassium sulfide, is the sulfide.

7. The method according to at least one of claims 1 to 5, characterized in that it is an alkaline earth sulfide, preferably magnesium and / or calcium sulfide, is the sulfide.

8. The method according to at least one of claims 1 to 5, characterized in that it is the sulfide to ammonium sulfide.

9. The method according to at least one of claims 1 to 5, characterized in that it is the sulfide is a transition metal sulfide.

10. The method according to at least one of claims 1 to 9, characterized in that the concentration of the sulfide solution between 0.1 and 3 mol / L, preferably between 0.3 and 2 mol / L, more preferably between 0.5 and 1, 5 mol / L.

1 1. Method according to at least one of claims 1 to 10, characterized in that oxygen serves as the oxidizing agent.

12. The method according to at least one of claims 1 to 1 1, characterized in that the oxygen is supplied in gaseous form as technically pure oxygen.

13. The method according to at least one of claims 1 to 1 1, characterized in that the oxygen is supplied in gaseous form in mixture with other gaseous components.

14. The method according to at least one of claims 1 to 1 1 or 13, characterized in that the oxygen is supplied in the form of compressed air.

15. The method according to at least one of claims 1 to 14, characterized in that the oxygen is used against sulfide in a superstoichiometric ratio.

16. The method according to at least one of claims 1 to 15, characterized in that the stoichiometric factor n (O ₂₎ / n (S ^{2 ")} is between 1 and 10, preferably between 1, 5 and 8, more preferably 2 to 6 , most preferably between 3 and 5.

17. The method according to at least one of claims 1 to 16, characterized in that the unused oxygen is supplied to the process again.

18. The method according to at least one of claims 1 to 17, characterized in that the ratio between withdrawn from the process and the recycled into the reactor sulfate between 1: 2 and 1: 20, preferably between 1: 5 and 1: 15, especially preferably between 1: 7 and 1: 12.

19. The method according to at least one of claims 1 to 18, characterized in that the recirculated to the reactor sulfate solution is passed through a heat exchanger.

20. The method according to at least one of claims 1 to 19, characterized in that the heat energy accumulating in the heat exchanger is used for further methods.

21. Method according to one or more of claims 1 to 20, characterized in that the oxidation reaction in the temperature range of 90 to 170 ⁰ C, preferably in the temperature range of 105 to 155 ° C, more preferably in the temperature range of 1 15 to 145 ° C.

22. The method according to at least one of claims 1 to 21, characterized in that the temperature at the reactor inlet between 90 to 150 ° C, preferably between 100 to 140 ⁰ C, more preferably between 1 10 to 13O ⁰ C.

23. The method according to at least one of claims 1 to 22, characterized in that the temperature at the reactor outlet between 1 10 to 170 ° C, preferably between 120 to 160 ⁰ C, more preferably between 130 to 15O ⁰ C.

24. The method according to at least one of claims 1 to 23, characterized in that the pressure in the oxidation reaction between 1 and 50 bar, preferably between 5 and 25 bar, more preferably between 12 and 18 bar.

25. Use of a method according to at least one of claims 1 to 24 for the purification of sulphide contaminated wastewaters, preferably of effluents from barium sulphate or papermaking.

26. Use of a method according to any one of claims 1 to 24 for the recovery of sulfate, which can be used in manufacturing processes, preferably in the production of barium sulfate.