DE2305630A1 - PROCESS FOR OXIDATION OF HYDROGEN SULFUR - Google Patents

Description

The invention relates to a system for the recovery of sulfur products and for the manufacture of sodium polysulfide for use in the treatment of lignocellulosic materials and specifically an improved system for the recovery of sulfur in a form suitable for the production of sodium polysulfide by sulphide sulfur is in the form of hydrogen sulphide gas from one or more sources such as acidic Natural gas or from the circulatory system of a digestion recovery system, takes and oxidizes to a form of sulfur capable of forming sodium polysulfide, or another one containing sulfur Product converts.

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It Is: already a variety of different methods generally known in which _f is obtained sodium polysulfide, either as Hauptprodiakt or as a byproduct in smaller Meage "These methods are, for example, electrochemical Verfaferea * Bsäoxverfahren. and catalytic processes "

The üSÄ-Fatentschrift 3 249 522 describes the use of hydrogen sulphide gas as fuel in an electrochemical fuel cell * whereby the products are sulfur, sulphides, polysulphides UR & the generated electricity. The cathode is made of platinum-catalyzed carbon and the cathode is made of nickel-catalyzed carbon. Hydrogen sulfide is introduced into the anode chamber and oxygen is introduced into the cathode chamber, the electrolyte is alkaline Änod © and "the reduction of oxygen at the latkcäs

The US Pat Is. Bsi eimeu ® & ηζ & ΐί electrolytes Is the anodic® Oasldatlonsproxskt Ssskwefsl, where hydrogen gas is formed at the cathode »What the electrolyte is basic, - Is the anodic OxidatioasprosWith Pclfsulfldff where hydrogen gas is required at the cathode the application of electricity from a SeSsrnn source © »

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The catalytic oxidation of hydrogen sulfide in an alkaline Solution to form sulfur is described in U.S. Patent 3,471,254. The catalyst is a phthalocyanine complex, which is soluble in aqueous sulfide and insoluble in sulfide-free aqueous solutions, the catalyst as a sludge is recovered and recycled.

U.S. Patent 2,135,897 describes the air oxidation of calcium hydrogen sulfide, i.e. the reaction product of lime or calcium hydroxide and hydrogen sulfide, using a nickel sulfide catalyst to form polysulfides Thiosulfate and sulfate in the ratio of 74: 73: 17. To the crowd to increase polysulfide, 0.1 to 1.0% hydrogen sulfide gas is added to the air oxidizer to make up an excess to get hydrogen sulfide in the oxidation state.

In the processing of pulp, it is known that the use of sodium polysulphide (hereinafter referred to as polysulphide) in the boiling liquid increases the yield (see U.S. Patent 3,216,887 and the patents discussed therein and other publications). Different methods of extraction Polysulfide are discussed, such as the dissolving of sulfur in aqueous sodium hydroxide solution or aqueous sodium sulfide solution. The production of polysulphide by air oxidation of neutral sodium hydrogen sulphide is also discussed. the USA patent also contains the statement that white liquor or fresh liquor is strongly alkaline and that their sulphide is not

is easily oxidized by air. In addition, it is said in the USA patent that the oxidation of white liquor or fresh liquor

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not sodium polysulphide, but sodium thiosulphate. It is suggested to mix white liquor and black liquor and oxidize the sulfide to form polysulfide and thiosulfate. However, the values given in the US patent show that the amount of polysulfide formed, measured in grams per liter of Na2S2f, is less than the amount of thiosulfate, the latter being expressed as grams per liter of ^ 2S ₃ O ₃ .

Canadian patent 814 882 and the publications cited therein also describe the advantages of a pulp

preparation with polysulphide and especially an adsorption process for the production of polysulphide pulp eye, in which hydrogen sulphide gas on activated carbon in the presence of air or oxygen is adsorbed, whereby the hydrogen sulfide is oxidized to elemental sulfur, which is deposited on the coal. When the coal is saturated with sulfur, the sulfur is leached with an alkaline solution. You want the best results you get when you remove the hydrogen sulfide with water vapor before contact with the carbon saturates and the sulfur formed is removed by alkaline leaching to give some alkali to leave on the charcoal, which neutralizes the sulfuric acid formed during the reaction.

U.S. Patent 3,470,061 describes the formation of polysulfide using insoluble manganese oxide compounds which act as the oxidizing agent and which after use can be regenerated by heating in air to remove the manganese oxide

the
to bring the medium to the next higher oxidation level. These

the latter patent also discusses the disadvantages of the

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U.S. Patents 3,216,887, 3,210,235, and 2,944,928 Procedure.

In the field of catalysis it is known that certain finely divided Materials increase the reaction rate. For example, finely divided nickel and cobalt have been used as catalysts used in the hydrogenation of vegetable oils. Better results should be achieved when using thin films or flakes which remain more readily dispersed than fine powders (see, for example, U.S. Patent 1,083,930).

U.S. Patent 1,146,363 describes the use of coal in granulated form as a catalytic or cleaning agent, the coal being in a column or percolator in which liquid is passed through a layer of coal grains flows.

US Pat. No. 2,365,729 describes the oxidation of an acidic solution of iron (II) sulfate to iron (III) sulfate by granulated activated carbon containing absorbed oxygen or absorbed air is used as the catalyst. the Coal is suspended in the liquid and the oxidizer is bubbled through the suspension, or the oxidizer is diffused through the liquid with the help of a diffuser made of coal, or the liquid and the oxidizing agent are passed in cocurrent through a packed column.

The benefits of polysulfide treatment of lignocellulosic material are known. There is currently at least one paper mill that uses polysulfide pulp, with sulfur being converted to sodium sulfide

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is added to form polysulfide. The extra added one Sulfur is lost in the chemical recovery process. In the one paper mill that is known to use polysulphide pulp, the addition of 2.2% elemental sulfur improves the yield by 3 to 4%, both based on the dry weight the Holzschnitselo

One of the problems associated with the production and use of sodium polysulphide is based "on the fact that in the iron circulatory system of pulp preparation and extraction of pulp chemicals the sulphidity of the liquor in the circuit is in a constant state. the proseatsaty which is found by dividing the Na ^ S by Ha ₀ -S 4 HaOH ,, everything as Na ^ Of, and multiplying by 100) is gradually increased _s various potential problems arise , such as corrosion _t possible explosion as a result of contact of lard and water in the recovery boiler as well as possible pollution problems due to sulfur losses «►

According to the state of the art, attempts have been made in various ways Polysulfide made up of the various forms of sulfur found in the Pulp preparation and extraction cycles are available, to build. For example, the USÄ patent document deals with 3 2IO 235 part of the green liquor with the formation of hydrogen sulfide with carbon dioxide, the hydrogen sulfide subsequently being stripped and at a high temperature and in Presence of catalysts with the formation of elemental 'Sulfur is converted, jsron which part to the pulp preparation liquor added and some converted into sulfur dioxide "

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ORIGINAL INSPECTED

used in the oxidation of hydrogen sulfide will.

U.S. Patent 3,331,732 treats green liquor in a scrubber with flue gas, and then the resulting product treated in a stripper to form hydrogen sulfide gas which is then processed in a Claus reactor.

U.S. Patent 3,560,329 treats black liquor with disodium bicarbonate to form it prior to incineration in a furnace of hydrogen sulfide gas, which is then placed in a Claus reactor Formation of elemental sulfur is dealt with. By treating black liquor, its sulphidity is to be reduced to such an extent that that the sulphidity of the liquor to be burned in the furnace is reduced, whereby sulfur losses are reduced.

U.S. Patent 3,525,666 re-uses the sulfur content of black liquor to make white liquor for kraft paper processing by treating the black liquor with carbon dioxide to a pH below 11 using combustion gases containing at least 15% CO ₂ . Hydrogen sulfide gas is stripped off and oxidized to sulfur using a Claus reactor.

U.S. Patent 3,554,858 treats black liquor to an acidic pH to release hydrogen sulfide and precipitate the organic material, which is then separated to give a first mother liquor. A second Mother liquor is obtained after adding the melt to water, the two liquors are combined and made alkaline again,

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being a lime sludge and an aqueous sodium hydroxide solution form. Hydrogen sulfide is added to the hydroxide solution to form white liquor. For this, reference is made to the USA patent 3 594 125 pointed out.

The system of the present invention achieved because of its simplicity of effectiveness, the objectives of the prior art, but in a different T \ ^T else, and provides a versatility that is not possible according to the prior art. Most importantly, there is less investment in the main facility to achieve the same results while at the same time getting a reduction in airborne contaminants. .

According to the present invention, hydrogen sulfide gas, that is available from various sources, such as sour natural gas or from the recovery cycle of pulp processing at various points in this cycle, such as the digestion tank, the blow tank, the evaporator, the Extraction boiler or furnace, the tank for dissolving the melt, etc., is used as a source of sulphide sulfur, that by an improved process with the formation of sulfur in a suitable for the recovery of sodium polysulfide Form as can be oxidized as elemental sulfur or as other sulfur-containing products. Hydrogen sulfide can can also be formed by treating black liquor or green liquor, as described in the above patents or will be described below. Regardless of the source, hydrogen sulfide is the reducing agent. The oxidizing agent

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Is oxygen, air or a mixture of oxygen with other gases, and the oxidation-reduction reaction is in the presence carried out a contacogen and an aqueous medium. The aqueous medium can be acidic, neutral or alkaline. It the reducing agent can contain hydrogen sulfide, or the reducing agent can be introduced into the reaction zone as a gas mixture are introduced with the oxidizing agent.

The Contacogen, the opposite of the oxidizing agent and the reducing agent is chemically relatively inert, it probably has the function of removing electrons from those in contact with it Reducing agent molecules or ions to oxidizing agent molecules or ions in contact with it and thus the in the reaction trapped electron transfer accelerated. In contrast to known electrochemical systems such as For example, electrolysis or fuel cells in which the The anode and the cathode are separated from one another by barriers or membranes and in which the oxidation occurs on one electrode and the reduction takes place at the other electrode, the system according to the present invention closes adjacent oxidation and reduction reactions on the contacogen, which is an electronically conductive material and which the system requires not the use of membranes or barriers.

According to the present invention, a gas phase and a liquid phase become in simultaneous contact with the electronic conductive material and brought into contact with each other. At this point in the process, the gas phase comprises the oxidizing agent and optionally the reducing agent, i.e. the

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Include hydrogen sulfide gas. When the sulphurous water -,.; substance is not in the gas phase / is in the liquid phase. According to the present invention, this becomes electronic conductive material at the interface between the gas phase and the liquid phase arranged and at the same time in contact with held both phases.

An important aspect of the present invention is that the electronically conductive solid material is prevented from being in contact exclusively with the liquid phase. In In the same way, the electronically conductive solid material must not be in contact exclusively with the gaseous phase. When the term "flooded" is used in describing the present invention it means that the electronically conductive material is in exclusive contact either with the gas phase or with the liquid phase. When the electronically conductive material according to the present invention is flooded, the reaction between the oxidizing agent and the reducing agent interrupted for all practical purposes.

Catalysis and electrochemistry considerations can be found in may be applicable to some extent to the new discoveries of the present invention. For example, if that's electronically conductive material according to the present invention is regarded as an electrode, although it does not have connection wires connected for the supply to the removal of electric current both oxidation and reduction take place on the same "electrode" i.e. one part acts as both

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Anode and cathode, and both the oxidation product and the reduction product are connected to the same "electrode" educated. Although such a part could be characterized as a "mixed potential electrode", the kinetics of the system is after of the present invention is not sufficiently defined and does not give a complete explanation of the reaction mechanism. With regard to Due to the solid nature of the conductive material, elements of heterogeneous catalysis appear to be present in a similar way to be, since the effect of the present system is such that it significantly reduces the rate of reaction to that in The absence of the solid electronically conductive material increases. Identification by a term such as heterogeneous catalysis, however, does not provide a complete explanation or understanding of the mechanism of the reaction either.

Regardless of whether the explanation of the reaction mechanism is based on catalysis, electrochemistry or any Combinations thereof, the following general rules apply to the present invention:

a) The oxidizing agent and the reducing agent should be able to form an interface.

b) A flooding of the electronically or electrically conductive Materials should be avoided.

c) The oxidizing agent and the reducing agent should be in contact with each other and with the electronically or electrically conductive material.

The methods and system of the present invention encompass a fundamentally new concept and fundamental

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new way of working in the production of chemical materials, through a reduction-oxidation reaction from reactants. · one, the chemical elements of the desired product, but in a different valence level in the desired product Value level included. This new way of working closes the controlled contact of a gas or gas mixture and an aqueous liquid medium at an interface in place of an electronically or electrically conductive solid Materials a. This controlled contact is in opposition

set to mixing the reactants, such as bubbling in of gas into a liquid, for example with the help of a diffuser, and the reaction takes place at the point of contact between the gas phase, the aqueous medium and the electrically conductive solid material, for the sake of simplicity has been the following expression is used to identify the procedure and its essential elements.

The term "contacogen" means electronic or electrical conductive solid material, which forms the place of the interface contact for the gas phase and the liquid phase and that should be wetted by these two phases at the same time or be in contact with these two phases / around the desired Result in reaction.

Of particular interest is the fact that the present system provides unique advantages such that sulfur is present in a form which is easily converted to sodium polysulfide, easily and continuously produced at ambient temperatures although higher pressures and temperatures can also be used

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below the decomposition temperature of the reactants or Products can be used.

Accordingly, it is a primary object of the present invention to provide an improved system for the oxidation of hydrogen sulfide Get sulfur or polysulphide or other sulphurous products. Another goal is the production of polysulphide batch or on a continuous basis by a reaction in which the oxidizing agent is a gas and the reducing agent is an aqueous solution containing sulfide sulfur and wherein the oxidizing agent and the reducing agent are in Interface contact with each other and simultaneously in contact with be brought to a Contacogen.

Another goal is the recovery of polysulphide through a reaction that involves the oxidizing agent and hydrogen sulphide exist in a gaseous phase, the gaseous phase and aqueous medium in interfacial contact with one another and be brought into contact with a Contacogen at the same time. Yet another object of the present invention is a system for the recovery of polysulphide for use in pulping from lignocellulosic materials, wherein polysulphide is obtained from hydrogen sulphide, which is taken from the liquor cycle.

The reduction-oxidation system of the present invention includes the following reactions in the case of sodium sulfide:

oxidation
S ^e > S ° + 2e (1)

reduction
2H ₂ O 4 O ₂ + 4e> 4OH (2)

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together
2Na ₂ S + 2H ₂ O + O ₃ > 2 S + 4NaOH (3)

The elemental sulfur then combines with the sodium sulfide to form Na ₇ S, the latter being polysulfide in

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where the value for χ is above 1 and as high as 4.5 can. However, these materials can also react as follows ί

₂ S ₂ + 3O ₃ > 2Na ₂ S ₂ O ₃ (4)

2Na ₂ S + 2O ₂ + H ₂ O ^ Na ₂ S ₃ O ₃ + 2NaOH (5)

In the case of polysulfide, when used in treatment of lignocellulosic material it is desirable to reduce the amount of thiosulfate to a minimum and, if possible, to prevent its formation altogether. Because thiosulfate is not an effective chemical For pulp preparation in alkaline pulp production 1st, it represents an undesirable burden in the recovery system.

In the case of sodium hydrogen sulfide, which is produced by absorption of Hydrogen sulfide gas from the sources mentioned in an alkaline Solution can be obtained, the reactions are for example the following:

H ₂ S + ■ NaOH> NaHS + H ₃ O (6)

NaHS + O ₂ > 2S + 2NaOH "(7)

2H ₂ S + O ₂ * 2S + 2H ₂ O (8)

The essential components of the system according to the present, Invention are an oxidizing agent, a reducing agent, a aqueous medium and a contacogen. The oxidizing agent can

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be any gas that contains elemental oxygen, such as air-pure oxygen or mixtures of oxygen and small Amounts of chlorine and the like, although the amount of gases such as ozone should be limited if they attack the Contacogen or decompose. The reducing agent is hydrogen sulfide, the can be present either in the gas phase or dissolved in the aqueous medium, the aqueous medium also being ionically conductive Phase, although it is believed that the conductivity of this phase is not so important in the present invention Factor is like in an electrochemical fuel cell or in electrolysis systems. The gas phase and the reducing aqueous Medium are also characterized by the formation of an interface when the two are brought into contact with each other.

The contacogen or contact generating material of the present invention Invention is a solid that is essentially inert to the oxidizing agent, the reducing agent, the aqueous Medium and the products is in the sense that it does not combine chemically with them or react chemically with them. A material with a large surface area to weight ratio is preferred because it has greater interfacial contact results.

In order to initiate and control the reaction according to the present invention, the gas phase and the aqueous medium are in Brought into contact with each other and with the contacogen or contact-producing material and kept in this relationship. Since the Reaction zone a gas phase, a liquid phase and the Conta-

includes cogen, the contacogen must be in contact with the gas

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stand and be wetted by the liquid without being flooded by either of the two phases. If here the term When "wetted" is used it means that the contact angle or angle of contact between the contacogen and the liquid is small, such as less than about 90 °, and the X ^ ert approaches zero. When the contact angle is large, such as greater than about 90 °, and approaching 180 °, the liquid tends to move away from the surface of the contacogen withdrawn so that the surface of the contacogen is in effect essentially only in contact with the gas, i. from which gas is flooded. On the other hand, if the surface of the contacogen is slightly wetted by the liquid, i. with a contact angle close to zero between the contacogen surface and the liquid, the liquid tends to cover the surface of the contacogen, and then the surface stands of the contacogen essentially only comes into contact with the liquid, i.e. it is flooded by the liquid. A method of preventing the liquid from flooding is that of a treatment of the Contacogen called "wet proofing". These Method supplies the Contacogen with a smaller proportion of an inert substance that is not wetted by the liquid, i.e. a substance in which the contact angle or contact angle between this inert additive and liquid is greater than is about 90 °.

Typical of the electrically or electronically conductive materials, who act as contacogen or contact broker or contact

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generating material that can be used are carbon, activated carbon, platinum-coated asbestos, platinum-coated nikkei or platinized carbon or activated carbon containing inclusions such as nickel, iron, cobalt, silver, platinum, Palladium, manganese oxides (such as manganese dioxide), manganese sulfides, iron oxides or hydrated oxides, nickel oxide, Contains nickel sulfide, cobalt sulfide or mixtures thereof. Of the above materials, carbon and activated result Coal apparently performs best because of its relatively large surface area to weight ratio and because of its simplicity with which inclusions of metals and metal compounds can be introduced into the material, as well as because of the degree, in which coal can be finely divided. Also, this is a readily available material that can be obtained in a wide variety of particle sizes and surface areas. Coals from different sources often lead to different reaction rates. These variations can be easily determined by simple procedures. Typical of the coals useful in the present invention are Soot, furnace soot, sewer soot or types of coal or carbon obtained from various sources using known methods, such as wood, corn on the cob, beans, nutshells, bagasse, lignin, coal, tar, petroleum residues, bones, peat and others carbon-containing materials. The particle size can be from 9 m, u vary to relatively large particle sizes, such as 2.5 cm or more, and usually the carbon is used as a mixture of several Particle sizes supplied. The surface of the carbon

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2 Substance-containing material can be between 3 m / g and up to more

than 950 m / g as using gas absorption

the BET method.

The carbon or the charcoal can be in different physical Arrangements may be provided, such as a porous carbon plate or tube, which is made wet-proof, to prevent flooding to prevent, or as a mass of wetted carbon granules or such a carbon powder, that float on the surface of the reducing agent or as a layer of contacogen particles with a height greater than the capillary rising effect of the reducing agent, this being Contacogen layer in contact with the surface of the reducing agent stands, or as a mass of wetted carbon or coal granules or powders, which are packaged in a reaction vessel are provided.

Carbon or charcoal can be wettable as follows; made will:

Polytetrafluoroethylene (PTFE) in emulsion form is finely divided with Coal or finely divided carbon in an amount of 0.1 to 100%, based on the carbon or coal solids, mixed. The mixture is heated to add the vehicle and dispersant for removing the PTFE. Another wetting-proofing method is that finely divided coal or finely divided carbon is treated with 1 g of linear polyethylene per 10 g of carbon or charcoal. The polyethylene will dissolved in a ratio of 1 g of polyethylene per 100 g of hot toluene. and poured over the charcoal. After the treatment, the charcoal becomes

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heated to about 105 ° C to evaporate the toluene. The particles are not uniformly repellent; most of them are sufficiently repellent to last from a few hours to a few days to swim.

Using the method described above can be finely divided Coal or finely divided carbon also with polystyrene, Fluorocarbon resins, polyethylene emulsions, silicones or other hydrophobic materials by any suitable method that prevents encapsulation of hydrophobic materials, which are impermeable to the reactants or the products formed are made wetting-proof. Change Materials that can be used include polychlorotrifluoroethylene, prepolymerized silicone oils, and high vacuum silicone grease .

Another method is to sublimate a chlorinated paraxylylene in a vacuum chamber and deposit it of the vapors on materials such as finely divided carbon or porous sintered nickel, whereby a poly (chloro-p-xyIylene) forms what is known as "parylene".

In the case of materials such as finely divided platinum in one Asbestos base material, one achieves the wetting-proofing by using a 1% solution of polyethylene in toluene, wetting the asbestos base material with the solution, allowing it to run off of excess liquid and then drying in an oven to evaporate the toluene.

In another example, paraffin wax is used in a range of between 1/2 g and 2 g per 10 g of finely divided carbon

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Amount used. The paraffin is dissolved in a solvent such as hexane or toluene, the carbon is introduced into the mixture, heated, and the solvent is then evaporated. Also, cetyl alcohol may be used and applied in the same 7eise X ^A. Likewise, any paratoluenesulfonamide, polydichlorotrifluoroethylene, and octadecylamine can be used and applied by mixing with the carbon and heating the mixture, treating the material and causing it to adhere to the carbon. Each of the above materials work satisfactorily in the new system, as evidenced by the formation of crystalline sulfur or a yellow color characteristic of polysulfide.

The speed and / or effectiveness of the system of the present invention can be increased by the exclusion of inclusions and the like can be increased in the Contacogen. For example, inclusions of metals and metal compounds in the finely divided Carbon seem to increase the rate of reaction compared to that obtained when using the same Carbon without inclusions. The inclusions can be obtained as follows:

Cobalt sulfate was dissolved in water in a ratio of 0.5 g per 100 ml of water. Finely divided carbon was in one Amount of 10 g per 100 ml of solution added: The resulting mixture was heated to boiling and then in an oven at Dried at 110 ° C. The solid material was then washed with sodium hydroxide treated to precipitate an insoluble cobalt material, the solids were then filtered off and washed with 0.1 normal

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Washed sodium hydroxide. The carbon was then treated with a Sodium sulfide solution soaked for 4 hours, filtered and washed with hot Washed wet three times and then dried again at 110 ° C.

Manganese II nitrate was in a slightly acidic solution in one Amount ratio of 0.5 g per 1OO ml of water dissolved with 0.1 g of nitric acid had been acidified. The rest of the treatment was the same as described above in connection with cobalt sulfate.

The same procedure just described was used except that the inclusion of ferric sulfate that was dissolved in O, l-normal sulfuric acid.

Nickel sulfate, silver nitrate and chloroplatinic acid were each used individually to form inclusions in the manner described above.

It was observed that all such inclusions increase the reaction rate over that without inclusions. In the usual extraction of wood pulp, the liquor cycle includes a digestion tank, a Rias tank, a washer, an evaporator, a recovery cooker, a melting tank, a caustic tank, a clarifying tank and the sludge section between the clarifying tank and the caustic tank, such as a filter, kiln and lime slaking device although this arrangement can vary somewhat as is known in the art. Hydrogen sulfide comes from the digestion ^{tank, the T} ilastank, the evaporator, the recovery boiler and the melting tank and can be in aqueous alkali, such as

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for example sodium hydroxide, dissolved and then in the presence of a contacogen using air or oxygen as Oxidizing agents are oxidized, becoming an alkaline solution containing sodium polysulfide, hydrogen sulfide gas can also come from any of the methods described in the Connection with the prior art were discussed.

One of the preferred forms of this invention is to remove sulfur from the black liquor prior to the recovery cooker to avoid excessive sulfur losses. For example, it is known that losses in the recovery digester occur at a certain percentage of the throughput, the exact percentage being fairly constant for each digester. Thus, as the throughput is greater, the total sulfur loss also increases with the result that increased levels of supplement chemicals must be used to maintain constant conditions and, at the same time, there is an increase in odor nuisance and pollution problems. The other advantage of reducing the amount of sulfur contained in the outgoing to the recovery boiler material is that the suif idität the melt is reduced> da at levels of 60 to 80% suif the problems of corrosion and melting explosions idität grow \

In one embodiment is combustion gas _r CO ^ contains, used to convert an alkaline solution containing various sulfur compounds in a carbonated state, ie in acidic sodium carbonate and acidic Itfatriumsulfid, which can then be heated; ^ Sodium carbonate and

To yield hydrogen sulfide gas. The sodium carbonate can be found in the "purge tank" is fed while the hydrogen sulfide gas dissolved in aqueous sodium hydroxide solution and oxidized in the presence of a Contacogen to form 'sodium polysulfide will. In those cases where it is desired to recover elemental sulfur, the hydrogen sulfide gas is in dissolved in an aqueous medium at an acidic pH and then in the presence of a contacogen to form elemental Sulfur that is extracted is oxidized. Such a gas can be obtained from acidic natural gas or from a process stage in the pulp and paper industry, and in the latter case it is preferred that it comes from the treatment of the black liquor which leaves the digestion tank, but before the recovery boiler.

When black liquor is acidified to hydrogen sulfide gas produce, a significant part of this gas is released when the pH is lowered to 4. The rest consists of. Sodium thlosulfate and some insoluble sulfur materials, and by further lowering the pH, such as down to 3, the thiosulfate becomes elemental sulfur and Sulfur dioxide decomposes. The elemental sulfur can be extracted from the other solids with a water-insoluble solvent (Xylene or tributyl phosphate) and optionally added to the white liquor or to the digestion vessel. The sulfur dioxide can be returned to the untreated black liquor by heating the remainder after the elemental sulfur has been extracted. The rest of the heating stage can to the recovery cooker, after which the product is causticized or made alkaline.

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The acidification of the black liquor can be done with acetic acid or sulfuric acid or SOg gas or acid sodium sulfate. In each If it is desired to maintain reducing conditions in the black liquor (absence of air or oxygen), so as to prevent the loss of sodium sulfide. By this procedure, 50% or more of the sulfur is in the black liquor recoverable as hydrogen sulfide gas and elemental sulfur.

The second stage of acidification, which _{produces SO 2} and elemental sulfur, also gave a vanilla-like odor close to that

End of the stripping process. The SO2 can be fed back into the system be, as has already been said, by putting it in one aqueous alkaline medium and optionally in a furnace using methane, coal or wood waste or the like. and reduced while maintaining a reducing atmosphere.

The oxidation of the sulfide sulfur on the Contacogen can be in any one way of the different types of apparatus that are described in the publications cited above, as well as in other forms of apparatus capable of using the Contacogen effectively. The oxidation can also be carried out continuously, be carried out batchwise or semi-continuously.

Various methods can be used in the handling of H ₃ S-GaS, ie either the gas can be dissolved in water, an acidic or alkaline medium and then oxidized in the presence of a Contacogen, or the oxidizing gas, hydrogen sulfide gas and aqueous medium can be simultaneously in Contact with the Contacogen can be brought about, which is a simultaneous

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Dissolving and oxidizing causes. In one embodiment, both air (the oxidizer) and HS gas are introduced into a tower containing Contacogen which, as described, has been rendered wettable. The ratio of H ₂ S to air can be 150 to 500 ml of air to 50 to 80 ml of H ₃ S per minute. Both the air and the H ₂ S can flow in the same direction or in countercurrent to each other. The tower was packed with 31 g of wettable contacogen and 39 g of aqueous matron liquor at a concentration of 160 g per liter was added. In a typical experiment, both the H ₀ S and the air at the bottom of the tower were added. After a few hours of operation, analysis showed the presence of substantial amounts of sodium polysulphide, sodium sulphide and some sodium thiosulphate. The sodium hydroxide solution was not circulated.

In another example, water was circulated through a tower containing wettable contacogen at a rate of 80 to 85 ml per minute. A total of 300 ml of water was returned. Air was in counter-current direction to the ^one of water at a rate of 200 ml per minute, while hlndurchgefnhrt IT nit ₀ S in the same direction as the air a Genchwinciakoit of 2O nl per minute through console. The / ^ nlaae ran for 3 hours, during which the 8OO ml of water were extracted from the sulfur formed, which was not detectable in the solution as colloidal sulfur. No attempt was made to extract the sulfur formed from the "Contacoaen. Under rorücksinhtiauna the Γ, Μησο the ^ cit and the Tonnera-

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During the experiment (23 to 27 ° C), sulfur became more noticeable Identified yield.

In another tower, white liquor or fresh liquor from a pulp mill was used as the medium. The white liquor had an initial sulfide sulfur concentration of 6.71 g / l. The tower contained about 600 to 700 g of wettable contacogen. A mixture of air and K _? S was at the bottom of the tower at a rate of 1200 ml / min. with respect to air and from 160 to 170 ml / hin, with respect to HS. White liquor was passed down the column at a rate of 85 ml / min. circulates. The temperature at the caustic inlet was 59 ° C (138 ° F) and the temperature at the outlet was 64 ° C (148 ° F), indicating that a reaction was occurring. After 30 hours of operation, the circulated liquor was analyzed and found to contain 6.36 g / l sulphide sulfur and 9.47 g / l sulphide sulfur plus polysulphide sulfur. Thus 3.11 g / l of polysulfide sulfur were formed, indicating that the sulfide sulfur from the H _? S was converted to sulfur and then to sodium polysulfide. A parallel experiment was carried out under the same conditions but using non-wettable carbon of the same type and quality as the contacogen in the same amount

-en

carried out. The flow rate was maintained like the initial white liquor concentration, for 30 minutes of operation the white liquor had a concentration of 10.1 g / l sulphide sulfur, which indicated that H ₂ S had been dissolved, but a concentration of sulphide sulfur and polysulfide sulfur of 10.6 g / l. Only about 0.5 g / l sodium nolysulphide sulfur was

3098367 1,093

fei formed, indicating that little, if any, of the dissolved sulphide sulfur was converted from the H ₃ S to elemental sulfur and sodium polysulphide. A parallel experiment was carried out in the same manner as above, except that neither a contacogen nor carbon was used. After 30 minutes of operation, analysis of the white liquor showed 10.1 g / l sulfide sulfur and 10.5 g / l sulfide sulfur plus polysulfide sulfur. So there was little, if any, at all. Conversion of sulfide sulfur from the H ₃ S to elemental sulfur, indicating the small amount of sodium polysulfide sulfur found.

One apparatus that has been used successfully is a cross-flow gas scrubber, packed with a contacogen instead of saddles. The structure of the scrubber itself is common and includes a generally cylindrical shell with a gas inlet and gas outlet that are axially aligned with the shell. The liquid is inserted at right angles to the cylinder and flows across the path of gas flow. The liquid inlet is, like the outlet, tightly mounted on the cylinder so that a substantial escape of gas with the liquid is prevented will. The part of the cylinder through which liquid is introduced and removed is for the passage of the liquid perforated. According to the invention, the central section of the scrubber, that part in line with the fluid path, packed with wetting-resistant Contacogen, i.e. with granulated porous carbon that has been made resistant to wetting with polytetrafluoroethylene, as * described above. For the subject

309836/1093

it can be seen that the entire cylindrical shell or some of them can be packed with Contacogen as desired.

In operation, 1 _f 5 normal NaOH was _{saturated with H 3} S-GaS and treated in the cross-flow scrubber packed with wettable contacogen. The circulation rate was 400 ml / min. , and a total of 74.5 g Contacogen was used as the package. The oxidant was air introduced at the rate shown in the table below.

309836/1093

Tabel

O
(D
OO

Attempt ^ r.

Volume of car lye at the beginning, ml Volume of the lye at the end, ml of air, ml / min.
Temperature, C

Lauren analysis: 3 at the beginning of the experiment

as g / l S as g / l S as g / l

^{after 15}

^after

after 30

^Μ1η · ^;

after 45 "iin.:

Sum S * + S °

Thio as g / l SS ^e as g / ls S ° as g / l S

Sum S ^e + S ° yield

Prod. Speed gS ° / min. / ml C (IO)

Thio as g / l S

5- as g / 1S

S ° as g / l S

Sum S- + S °

Yield "

Prod. Speed gS ° / min. / ml C (IO "' ¹ )

Thio as g / l S

S "as g / l S

S ° as g / l S

Sum S "+ S °

yield

Prod. Speed gS ° / min. / ml C (IO ") 200 200 800 800

300 800

740 730

4750 6750

170 170

300 300

770 760

4750 6750 4750 6750 4750 6750

Room room 120 120 150 150 temp. temp.

2.56 - 1.28 ---- 43.36 43.04 44.00 43.34 44.00 43.76 46.80 46.64

44, PO 43, above 44.00 43.34 44.00 43.76 46.80 46.64

33.20 28.32 36.00 36.48 36.96 37.44 29.34 41.60 1/72 6.40 1.4 4 2.72 3.12 2.03 2.64 3.20

39.20 40.03 39.52 32.48 44.80 89.3 91.1 90.4 69.5 96.1

1.44
37744

35.92 34.72
82.8 80.6 85.1
2.01 4.74 4.27

3.06 9.24 6.17 7.80 9.47

28.56 24.32 34.08 33.28 32.72 33.36 36.00 36.48

6.64 9.28 1.44 5.6O 6.64 6.64 7.44 8.00

3 5.30 3 3.60 3 5.52 38.88 39.36 40.00 "43.44 44.48

73.5 78.0 30.7 83.7 89.4 91.5 92.7 95.4

2.46 3.43 2.14 8.26 9.81 9.83 11.0 11.8

- - - 0.32

24.88 21.60 31.52 31.52 28.64 27.44 32.32 31.52

10.00 - 5.44 6.88 10.00 3.56 10.96 13.44

36.96 38.40 38.40 33.00 43.28 44.96 33.9 87.6 87.8 86.9 92.5 96.4 5.36 6.78 9.89 8.45 10.8 13.2

Continuation of the table

after 60 min: thio as g / l S - 2.24 - 3.52 2.24

S- as g / l S 18.56 17.76 28.96 28.48 21.20 25.36 28.00 26.64

S ° as g / l S 11.84 14.24 6.88 9.60 13.60 13.92 14.24 18.08

Sum S = + S ° 30.40 32.00 35.84 38.08 34.80 39.28 42.24 44.72

Yield 67.8 74.4 81.5 86.9 79.1 90.0 90.2 96.0 Ber.Prod.speed. as

S ° / day / 28 1 Contacogen 19.7 23.8 45.8 63.9 90.9 92.6 94.5 120.7

al / min. Recycle rate at the scrubber 74.5 g Contacogen is used

If it is desired to keep the amount of sodium thiosulfate to a minimum, the media should be acidic, neutral or slightly alkaline in order to avoid those conditions which favor the known disproportionation reaction which in turn favors the formation of thiosulfate. Thiosulphate formation in strong !: alkaline media can also be avoided _{by controlling the ratio of air to H 2} S, ie to 45 to 65 liters of air per 22 liters of H _{3 S.} Above this ratio, the tendency to form thiosulphate is increased.

When IUS is present in acidic natural gas, it is preferred for safety reasons that the H ₂ S be stripped from the natural gas if it is to be mixed with the gaseous oxidizing agent, such as air or oxygen, prior to absorption in the media. It is possible and known to use air or oxygen in a proportion below the explosive limits, in which case the reaction may not be complete. In this case, the first medium can be transferred to a second reactor to complete the oxidation in the presence of a contacogen.

Another _{source of H 2} S is water in certain areas of the United States of America. In these zones, the amount of H ₂ S dissolved in the water known as drinking water is high enough to be detected by smell. According to the present invention, H ₂ S dissolved in such water is easily oxidized by oxidizing sulfide sulfur to elemental sulfur in the presence of a contacogen using air as an oxidizing agent. The educated elementary

309836/1093

Sulfur is then easily removed or deposited, whereby one a water that is otherwise drinkable and free of unpleasant things Odor is because it no longer contains the previously contained hydrogen sulfide gas. A simple facility to implement this method is a tower or column packed with Contacogen using a downward facing Flow of water and an upward flow of air.

In the pulp and paper field, one of the main advantages is the present invention the ease of conversion of sulfur-containing Compound in a form useful in treating lignocellulosic material. One of the additional Advantages is the reduction of the sulfur-containing compounds that go through the recovery cooker and the resulting from it Reducing the loss of such sulfur by-products. In addition, the liquidity of the melt is lower if that Method according to the invention is applied in comparison with the same process cycle without using the subject matter of the invention. This enables pulp production with higher SuIfiditat, if so desired, while at the same time the Sulphidity of the melt is maintained at an acceptable level.

The method of the present invention can also be used to remove hydrogen sulfide gas from acidic natural gas, using the methods described above with the advantage of converting noxious gas into sulfur or a sulfur compound that is used or further processed in other chemical processes in a known manner can be used to extract the sulfur, as has already been explained here. 309836/1093

Claims (1)

Claims \ ly Process for the oxidation of hydrogen sulfide gas with profit from tion of an oxidized sulfur product such as / elemental sulfur and polysulfides, from the sulfide sulfur, characterized in that nan an oxidizing agent, an aqueous medium and brings the hydrogen sulfide into contact with each other and with a Contacogen and the Contacogen at the same time in intimate> Contact with at least a portion of the oxidizing agent and at least a portion of the hydrogen sulfide in the aqueous Medium holds and thus at the same time the oxidizing agent on the Contacogen reduced and the hydrogen sulfide forming a oxidized form of sulfur that leads to the formation of sodium polysulfide or is suitable for recovery as elemental sulfur, oxidized. 2, method according to claim 1, characterized in that one aqueous medium used, which is on a neutral or acidic pH and formed by adding elemental sulfur and this elemental sulfur wins. 3, the method according to Ansoruch l, characterized in that one adverse medium used, which is an alkaline solution of sodium hydroxide, is sodium phosphate and / or sodium carbonate and in the sodium oolysulphide is formed. 4, method according to claim 1, characterized in that one aqueous medium used, the aqueous sodium hydroxide int and in deir. ! Sodium polysulphide is formed, 309836/1093 2305830 5. The method according to claim 1 to 4, characterized in that air is used as the oxidizing agent and this with the hydrogen sulfide mixed gas and the gases at least partially Dissolves in the aqueous medium. 6. The method according to claim 1 for the Gev / innung of chemicals from a sodium sulfide-containing liquor of a pulp-preparing process, in which this liquor is passed as black liquor to a recovery boiler, the melt formed thereby dissolved to form green liquor, the latter to form during the treatment white liquor or fresh liquor used by lignocellulosic material is causticized or made alkaline, the liquor in this process step contains at least sulfide sulfur in the form of sodium sulfide and hydrogen sulfide, and hydrogen sulfide gas is formed in the process step, at least a part of which is oxidized to sulfur in a form which at Combination with alkaline lye containing sodium hydroxide and sodium sulphide forms sodium polysulphide in this alkaline lye, characterized in that the oxidizing agent and the hydrogen sulphide gas dissolved in the aqueous medium are brought into contact with one another and with the Contaeogen, and s Even though the oxidizing agent and the hydrogen sulfide in an aqueous medium simultaneously keep in contact with the contacogen and thus simultaneously reduce the oxidizing agent and the sulfide sulfur with the formation of sulfur in a form that is suitable for the formation of sodium polysulfide * QxiöieEt * 7. The method according to claim 6, characterized geke ^ ßz ^ istoet »that one Aqueous medium used * the s4ch on an acidic »pH value and in which elemental sulfur is formed, and these elemental sulfur wins. 8. The method according to claim 6 and 7, characterized in that one Hydrogen sulfide obtained from black liquor is used. 9. The method according to claim 6 to 3, characterized in that _{hydrogen sulfide obtained by treating the black liquor with CO 2} -containing combustion gas is used. 10. The method according to claim 6 to 8, characterized in that the black liquor is acidified to a pH value of 4 with the release of hydrogen sulfide gas, then further acidified to a pH value of 3 or less and elemental sulfur precipitates and SO ₂ - Releases GaS. 11. The method according to claim 10, characterized in that the separating precipitated sulfur from the remaining solids in the mixture. 12. The method according to claim 6, characterized in that the sulfur suitable for the formation of sodium polysulphide in a Dissolves alkaline lye containing sodium sulfide. 13. The method according to claim 6 to 12, characterized in that one works continuously. 14. The method according to claim 1 to 13, characterized in that one a solid, finely divided porous material made resistant to wetting or repellent is used as a contacogen. 15. The method according to claim 14, characterized in that as finely divided material coal or carbon used by Treatment with a fluorinated polymer made wettable or repellent. 309 836/109 3 0RH3 & AL INSPB