JP2019529306A - Method and apparatus for removing organic sulfur compounds from hydrogen enriched gas - Google Patents

Abstract

The present invention relates to a method for separating sulfur from a hydrogen enriched gas containing a carbon disulfide compound and oxygen, wherein the carbon disulfide compound is converted to hydrogen sulfide using a catalyst, and a noble metal catalyst is used as the catalyst. . When a noble metal catalyst is used, oxygen can be converted into water simultaneously with the reduction of the carbon disulfide compound. Furthermore, oxygen reduction can provide the energy necessary to heat the catalyst. The invention also relates to an apparatus for carrying out the corresponding method. [Selection] Figure 1

Description

  The present invention is in the field of industrial gas desulfurization, and more particularly relates to a novel process and its use for removing carbon sulfide from coke oven gas using a noble metal catalyst.

  Coke oven gas is generated in the coke oven during the dry distillation of bituminous coal. The coke oven gas typically contains about 55 wt% hydrogen, 25 wt% methane, 10 wt% nitrogen, and 5 wt% carbon monoxide as the main components. For this reason, coke oven gas is in principle suitable as a synthesis gas for chemical reactions. Because coal contains a certain proportion of sulfur, coal coking forms inter alia carbonyl sulfide and carbon disulfide, which act as catalyst poisons in subsequent reactions, for example, before further utilization of coke oven gas. Need to be removed. Without removal of sulfur compounds, these catalysts require frequent cleaning or even replacement, which is costly and complex and is undesirable due to equipment downtime.

  One way to release unwanted carbon sulfide from coke oven gas is to subject it to catalytic hydrogenation and to convert sulfur compounds to hydrogen sulfide. This gas is likewise undesirable, but it is easy to scrape with an aqueous alkaline solution, such as an ammonia solution.

  Many methods for hydrogenating sulfur compounds are already known from the prior art. Thus, for example, DE 15 45 470 (Pichler) describes carbon sulfide in coke oven gas in a two-step process in the presence of a cobalt-molybdenum, nickel-molybdenum or nickel-cobalt-molybdenum catalyst. A method has been proposed in which hydrogen sulfide is obtained to obtain hydrogen sulfide, which can then be removed from the gas mixture using conventional methods. The reaction temperature in the examples is higher than 550 ° C.

  A similar method is known from German Offenlegungsschrift 26 47 690 (Parsons). This is obtained using hydrogenated sulfur-containing carbon compounds in the presence of catalysts based on cobalt, molybdenum, iron, chromium, vanadium, thorium, nickel, tungsten and / or uranium and using alkali metal hydroxide solutions. It is proposed to remove the hydrogen sulfide with an extraction tower. The specific catalyst proposed here is a sulfide of the above metals. However, the disadvantage is that, for the purposes of the process specified in DE 2647690, the catalyst also requires a minimum temperature of 260 ° C. and the hydrogenation is preferably a significantly higher temperature, In some cases, it must be performed at a temperature exceeding 400 ° C. This is undesirable not only for reasons of energy consumption, but also because the gas composition also changes at these temperatures, i.e. methanation has already taken place.

  DE 102013009885 describes a process for removing sulfur compounds from a coke oven gas in which a cobalt sulfide-molybdenum catalyst is to be used to convert the sulfur compounds to hydrogen sulfide. is doing. These are catalysts mainly composed of molybdenum sulfide and containing cobalt in the sulfide form as cocatalyst. The use of such a catalyst made it possible to lower the operating temperature in desulfurization to a temperature in the range of 240 ° C. to 260 ° C. with the further advantage of suppressing methane formation.

  One problem in desulfurization, particularly when carried out at high temperatures, is that of industrial gases, particularly coke oven gases that contain not only sulfur compounds but also a certain proportion of oxygen. When heating a hydrogen-containing gas in the presence of oxygen, an uncontrolled explosion gas reaction can occur, which can damage the processing plant for coke oven gas. Therefore, the gas sent to desulfurization should be as free of oxygen as possible before being fed to the desulfurization unit. However, the removal of oxygen from gas mixtures such as coke oven gas is technically relatively complex and therefore expensive. Thus, a significant proportion of coke oven gas is currently subjected to heat recovery (ie, incineration), which causes harmful emissions due to sulfur content.

  The catalyst described in DE 102013009885 significantly reduces the reaction temperature for sulfur compounds compared to, for example, the catalyst known from DE 1545470. It is already possible. However, since the energy required to heat the gas mixture to the reaction temperature of the catalyst accounts for a significant proportion of the cost for desulfurization, it is from industrial gases that guarantee sufficient desulfurization at low temperatures such as 200 ° C. A catalyst for the reduction of sulfur compounds is required.

German Offenlegungsschrift 10 201 11053353 discloses a method for the reductive conversion of sulfur-containing hydrocarbons, such as thiophene, CH ₃ SH, and 2- and 3-methylthiophene to hydrogen sulfide using a noble metal catalyst. This conversion can be carried out in the presence of oxygen gas. The catalyst used is, for example, a platinum / ruthenium catalyst on a cerium oxide / aluminum oxide / lanthanum oxide support. However, in this known method, the hydrogen-enriched gas contains neither COS nor CS ₂ .

US 2002/0121093 discloses the conversion of COS to H ₂ S using a catalyst such as Pt on Al ₂ O ₃ , for example. However, this document does not relate to the reduction of organic sulfur compounds but to the hydrolysis of COS to react COS with water to obtain CO ₂ and H ₂ S. Therefore, the organic sulfur compound COS is oxidized without being reduced. Since the reaction has an overall uniform electron balance based on the organic sulfur compound, the overall reaction is not reduction.

US Pat. No. 4,981,661 similarly discloses a method for converting organic sulfur compounds such as COS and CS ₂ to H ₂ S and CO ₂ in combination with water. However, this method does not include reducing a hydrogen-enriched gas containing a proportion of organic sulfur compounds and oxygen with a noble metal catalyst. Furthermore, the method is divided into two steps, the first step comprising removing oxygen from the gas mixture. In this step, for example, a Co—Mo catalyst is used. For Pt-based catalysts, this publication states that they have oxidative properties and thus lead to the oxidation of H ₂ S present in combination with oxygen to SO ₂ . This results in the formation of sulfur, which can lead to equipment clogging through secondary reactions with residual H ₂ S.

JP 59-232175 describes the treatment of coke oven gas containing dienes, oxygen, olefins and sulfur compounds as impurities. Such coke oven gas is reduced in the presence of a palladium-based catalyst on an Al ₂ O ₃ support, yielding H ₂ S that can subsequently be absorbed on an adsorbent such as ZnO. This publication does not list COS and CS ₂ among the sulfur compounds. Furthermore, in the examples, the composition has a very low sulfur content of 0.01% H ₂ S, so that the treatment here does not take place in the crude coke oven gas, but rather a treatment not reported in this document. It must be assumed that the process has been performed.

German Patent Application Publication No. 1545470 German Patent Application No. 2647690 German Patent Application Publication No. 102013009885 German Patent Application Publication No. 1020111053353 US Patent Application Publication No. 2002/0121093 US Pat. No. 4,981,661 JP 59-232175 A

  Thus, the present invention reduces the cost of removal of elemental oxygen in industrial gases, and at the same time ideally at a relatively low temperature compared to the prior art, carbon sulfide present in the gas and also sulfurized. The aim is to propose a method that ensures an ideal quantitative conversion of any organosulfur compounds present in hydrogen (for example thiophene or mercaptans). A further object of the invention is to propose a method that requires as little energy as possible to heat the gas mixture for desulfurization.

Accordingly, the present invention is a method for removing sulfur from a hydrogen enriched gas comprising an organic sulfur compound and optionally oxygen, the organic sulfur compound being converted to hydrogen sulfide under the action of a catalyst. Wherein the catalyst used is a noble metal catalyst and the hydrogen-enriched gas comprises at least one compound selected from the group comprising COS and CS ₂ .

A reactor 2 containing a noble metal catalyst, a hydrogen-rich gas supply unit 1, a gas discharge unit 3 from the reactor, and an apparatus 4 for removing hydrogen sulfide from a gas arranged downstream of the reactor It is a figure which shows the embodiment of this invention. FIG. 3 shows a further embodiment of the invention comprising a reactor 6 for the reduction of an organic sulfur compound to obtain hydrogen sulfide arranged downstream of the reactor 2, which contains a catalyst based on noble metals.

  In the context of the present invention, “noble metal” is to be understood as meaning a metal having a positive standard potential (in an aqueous solution of pH 7) of at least 0.45 V with respect to the hydrogen electrode, and in the context of the present invention preferably , Gold, platinum, iridium, palladium, osmium, silver, ruthenium and rhodium, particularly preferably palladium, platinum and rhodium, with palladium and platinum being most preferred. The noble metal may consist of one of the listed metals or may be a mixture of listed metals.

  In the context of the present invention, “hydrogen-enriched gas” is to be understood as meaning a gas having a minimum content of hydrogen of 20%, preferably at least 40% by volume, particularly preferably at least 45% by volume. Coke oven gas generally has a hydrogen content of 60-65% by volume and is therefore a particularly suitable hydrogen-enriched gas in the context of the present invention.

  In the context of the present invention, “organic sulfur compounds” are to be understood as meaning compounds which contain sulfur and carbon atoms, but which may also contain other heteroatoms or hydrogen atoms.

  The noble metal catalyst is preferably in a form bound to a solid support material. Suitable support materials include aluminum oxide or ceramics, which are also used in particular as support materials for conventional automobile catalysts. Suitable aluminum oxides are those with a particularly high internal surface area.

  The listed types of aluminum oxide supports are well known from the prior art. Thus, for example, EP 1 385 786 and EP 1 385 787 (Axens) grind hydrargillite-type aluminum oxide and use an aqueous solution of aluminum nitrate and formic acid at 200 ° C. for 6 hours. It describes a method for producing an aluminum oxide carrier that is hydrothermally treated and calcined at 400 ° C to 1300 ° C. The carrier material is subsequently extruded and then ready to be loaded. As far as the nature and production of the catalyst support are concerned, the two listed documents are hereby incorporated by reference.

  Although there are no standards related to the shape of the support material, suitable shapes include spheres that can be used in the form of dump beds in the reactor, and honeycombs that ensure a relatively large surface area of the catalyst.

  In conventional applications of the listed catalysts, such as hydrogenation reactions, carbon monoxide acts as a catalyst poison. However, in the work underlying the present invention, it was surprisingly found that noble metal catalysts can be used in hydrogen-enriched gas mixtures without observing a significant loss of catalyst effectiveness. . It has further been found that in the context of the work performed, it is also possible to supply the catalyst with an oxygen-containing gas mixture without observing a dangerous mixture of oxygen and hydrogen in the product. Instead, it was observed that oxygen reacts with hydrogen to form water under the action of a catalyst, so that the gas mixture discharged from the catalyst-containing reactor has a negligible proportion of oxygen (<0.01% by volume). ) Only included.

  The catalytic reaction of oxygen and hydrogen further has the advantage that the catalyst and gas mixture are heated by waste heat from the explosive gas reaction, so that once the optimum operating temperature is reached, no external heating of the catalyst is required. There is. Further, the hot off-gas may be utilized using a heat exchanger to heat the gas feed to the catalyst-containing reactor, thus providing further energy savings. Accordingly, the hydrogen-enriched gas in the present invention preferably contains a certain proportion of oxygen.

  Hydrogen-enriched gases contemplated in the context of the present invention include, for example, steel mill gas and are reducing gas or synthesis gas, but a particularly suitable gas is coke oven gas. Furthermore, the gas suitably contains a hydrocarbon component in a proportion of 50% by volume or less, preferably 40% by volume or less, most preferably 30% by volume or less.

As specified, the hydrogen-enriched gas further contains an organic sulfur compound. Possible organic sulfur compounds are in particular carbonyl sulfide (COS) and carbon disulfide (CS ₂ ), but also aromatic sulfur compounds such as thiophene or aliphatic sulfur compounds such as mercaptans. The typical content of carbonyl sulfide can range from 1 to 100 ppm, in particular from 10 to 50 ppm. A typical content of carbonyl disulfide can be a content of 10 to 200 ppm, in particular 5 to 100 ppm. A typical total content of organic sulfur compounds in the hydrogen-enriched gas can be a content of 20 to 300 mg / Nm3, in particular 20 to 200 mg / Nm3.

  The hydrogen-enriched gas preferably further contains oxygen. A typical oxygen content can range from 0.2 to 3.0% by volume, in particular from 0.4 to 1.5% by volume.

  As noted above, certain catalysts function without limitation in a gas atmosphere containing a substantial proportion of carbon monoxide. Therefore, it is preferable that the hydrogen-enriched gas contains carbon monoxide in an amount of 1 to 20% by volume, particularly 1 to 10% by volume.

  The coke oven gas used in the method according to the present invention is preferably generated by dry pyrolysis of bituminous coal, comprising a gas mixture containing hydrogen, methane, nitrogen and carbon monoxide as main components and carbon sulfide as secondary components. obtain. In the dry distillation / pyrolysis of bituminous coal performed at 900 ° C. to 1400 ° C., volatile components of the coal are liberated, and porous coke containing essentially only carbon is formed. The crude gas is subsequently fractionated into tar, sulfuric acid, ammonia, naphthalene, benzene and coke oven gas by fractional condensation.

  As specified above, the noble metal catalyst reductively converts oxygen present in the gas mixture to water. Therefore, in the context of the process according to the invention, it is preferred if the oxygen present in the gas is converted into water simultaneously with the reduction of the organic sulfur compound. When the oxygen present in the gas is substantially, ie to the extent of at least 80% by volume, preferably at least 90% by volume, particularly preferably at least 95% by volume, based on the total volume of oxygen in the gas mixture, It is particularly preferred that it is converted to water simultaneously with the reduction of the organic sulfur compound.

  On the other hand, in the context of the present invention, before removing a part or a substantial part of oxygen (ie at least 70% by volume based on the total volume of oxygen in the gas mixture) from the gas mixture or reducing the organic sulfur compound. Conversion to water with hydrogen is not excluded.

  Suitably, the catalytic conversion of the organic sulfur compound is carried out at a temperature of at least 150 ° C, preferably at least 200 ° C. On the other hand, it is preferred in the context of the present invention that the catalytic conversion of the organic sulfur compound takes place at 270 ° C. or lower, preferably 250 ° C. or lower, particularly preferably 230 ° C. or lower. The temperature range for the catalytic conversion of organosulfur compounds which has proven particularly suitable is in the range from 200 ° C. to 250 ° C., in particular from 200 ° C. to 230 ° C.

  Catalytic conversion can be further carried out in the range of 1-15 bar, ie either at atmospheric or superatmospheric pressure. One embodiment wherein the pressure is in the range of about 1.2 to about 5 bar is preferred.

  As indicated above, thermal energy is released during the reaction of oxygen and hydrogen in the gas mixture. Thus, it is possible and preferred to adjust the amount of oxygen in the hydrogen-enriched gas so that the energy released from the reaction is sufficient to maintain the temperature at the desired level. For this purpose, the amount of oxygen in the reaction mixture can be increased, for example by adding oxygen, if it is advantageous.

  Depending on the gas flow rate, the catalyst design and its configuration, the reaction between the catalyst and the organosulfur compound in the hydrogen-enriched gas can be incomplete, so that the gas resulting from the reaction is significantly adversely affected by further use of the gas. Having an organic sulfur compound content. Therefore, it may be preferred to arrange the stage where the organic sulfur compound still present in the gas mixture is converted into hydrogen sulfide using a catalyst that is not based on a noble metal, downstream of the catalytic conversion. For this conversion, for example, a known cobalt-molybdenum catalyst or nickel-molybdenum catalyst in which the metal is present in the form of sulfides can be used.

Catalytic conversion converts organic sulfur components present in the hydrogen-enriched gas to hydrogen sulfide (H ₂ S). The content of hydrogen sulfide is typically in the range of 50 to 300 ppm. The presence of H ₂ S is not as desirable as the presence of carbon sulfide, but in contrast to the latter, hydrogen sulfide can be removed relatively easily and especially by scrubbing quantitatively. Therefore, it is preferred to place a stage downstream of the catalytic process that involves removing hydrogen sulfide from the gas mixture by absorption in a basic medium. This can be achieved, for example, by an absorption tower in which the gas is passed and treated, for example countercurrently, with an aqueous base solution such as aqueous sodium hydroxide or ammonia. However, other devices suitable for gas purification are also conceivable, for example a venturi scrubber. In the case of small amounts of hydrogen sulfide, this may be adsorbed on the solid material, for example in the form of zinc oxide. H ₂ S can be released from it again in the regeneration phase.

  Hydrogen sulfide removed via scrubbing or absorption can then be converted to elemental sulfur by a conventional Claus process.

  In a further aspect, the present invention relates to an apparatus for carrying out the above-described method, which comprises a hydrogen-enriched gas supply 1, a reactor 2 containing a noble metal catalyst, a gas discharge 3 from the reactor, And a device 4 for removing hydrogen sulfide from the gas connected downstream of the gas discharge from the reactor.

  The reactor is preferably a fixed bed reactor in which the catalyst is present in discrete dump beds or in the form of small pieces as a hard packing. Because dump beds are more prone to channel formation and thus non-uniform flow profiles, embodiments in which the catalyst is disposed as a packing in the reactor are preferred. A further advantage of the catalyst in the form of a packing is a low pressure drop.

The advantage of hydrogenation in a fixed bed reactor is that high space-time yields can be achieved, so that the process according to the invention has a high GHSV value of about 5000 to about 30000 h ⁻¹ , preferably about 10000 to about 20000 h ^−1. But it can be implemented. A further advantage is that the hydrogen discharge gas is preferably introduced at the bottom of the reactor, flows through the catalyst bed, undergoes hydrogenation, and again exits in product form from the top of the reactor, so that product discharge No special means are needed.

  The described apparatus is preferably implemented as apparatus 4 for removing hydrogen sulfide from a gas as a gas scrub using a liquid basic medium or as an adsorption stage for hydrogen sulfide using a solid adsorption medium. Further configured to be.

  Alternatively or in addition, the described apparatus preferably comprises a non-noble metal based catalyst for the reduction of organosulfur compounds to obtain hydrogen sulfide connected downstream of the reactor 2 containing the noble metal catalyst. It may be further configured to include a reactor 6 for

  It has been specified above that for optimal conversion to hydrogen sulfide, the reduction of the organic sulfur compound requires a certain temperature, for example at least 150 ° C. Therefore, in order to ensure the conversion of the organic sulfur compound as complete as possible to hydrogen sulfide from the beginning, the device according to the invention comprises a heat exchanger 5 connected upstream of the supply 1 of hydrogen-enriched gas. The case is preferred.

  In order to monitor the temperature in the reactor 2, the device according to the invention can further comprise a temperature measuring device capable of measuring the temperature. In order to be able to control the temperature by the amount of oxygen in the hydrogen-enriched gas, the supply 1 for hydrogen-enriched gas can be connected to a controllable supply device for oxygen, said device being It is preferably controlled by a control loop connected to the temperature measuring device.

  Furthermore, the heat exchanger can be configured such that the gas discharged via the gas discharge section 3 from the reactor can be used to heat the gas supplied to the reactor.

In a further aspect, the present invention relates to the use of a noble metal catalyst for simultaneous hydrogenation of organic sulfur compounds and oxygen in a hydrogen enriched gas to obtain hydrogen sulfide and water, wherein the hydrogen enriched gas is , comprising at least one compound selected from the group comprising COS and CS _2. The above description applies equally to the preferred embodiments of the noble metal catalyst and the hydrogen-enriched gas.

  The essential advantage of the process according to the invention is that the content of organic sulfur compounds is reduced from about 50 to 300 ppm to a content of residual organic sulfur compounds of less than 1 to 5 ppm, preferably about 1 to 2 ppm, while at the same time in the gas. It is possible to reduce the oxygen ratio to a level where there is no problem. A further preferred embodiment is that the catalyst also hydrogenates or oxidizes unsaturated hydrocarbons that may be present in the coke oven gas, thereby avoiding coking in downstream units (catalysts).

DESCRIPTION OF SYMBOLS 1 Supply part of hydrogen rich gas 2 Reactor 3 Gas discharge part 4 Apparatus for removing hydrogen sulfide 5 Heat exchanger 6 Reactor for reduction of organic sulfur compound

Claims (9)

A method for removing sulfur from a hydrogen-enriched gas containing a proportion of organic sulfur compounds and oxygen, wherein a catalytic process for reducing the organic sulfur compounds to hydrogen sulfide is carried out, the catalyst used being a noble metal a catalyst, the hydrogen-enriched gas is characterized in that it comprises at least one compound selected from the group comprising COS and CS _2, method.   2. Process according to claim 1, characterized in that the catalyst used is a palladium and / or platinum catalyst, preferably on a solid support material.   The method according to claim 1 or 2, characterized in that the gas used in the method is coke oven gas.   The method according to claim 1, wherein the oxygen present in the gas is converted into water simultaneously with the reduction of the organic sulfur compound.   The stage located downstream of the catalytic process is carried out as a stage where hydrogen sulfide is removed from the gas mixture by absorption in a basic medium or as an adsorption stage for hydrogen sulfide using a solid adsorption medium The method according to claim 1, characterized in that   2. The step disposed downstream of the catalytic process is a step in which organic sulfur compounds still present in the gas mixture are converted to hydrogen sulfide with a noble metal-based catalyst. The method as described in any one of -5.   The process according to claim 6, characterized in that the noble metal-based catalyst is a cobalt sulfide-molybdenum catalyst or a nickel-molybdenum catalyst.   8. A process according to any one of the preceding claims, characterized in that the hydrogen-enriched gas is heated for the catalytic process to a temperature of at least 150 <0> C, preferably from 200 <0> C to 250 <0> C. Use of a noble metal catalyst for simultaneously hydrogenating an organic sulfur compound and oxygen in a hydrogen enriched gas to obtain hydrogen sulfide and water, wherein the hydrogen enriched gas is selected from the group consisting of COS and CS ₂ Use comprising at least one compound.

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