DE2327616A1 - PROCESS FOR THE REDUCTION OF SULFUR DIOXIDE - Google Patents

Description

Sulfur dioxide (SO-) is found in many industrial gases that are emitted by plants, such as during the roasting, melting and sintering of sulfide ores such as chalcopyrite (CuFeS,) , iron pyrite (FeS ₂ ) or pyrrhotite (Fe ₇ Sg), or in gases from power plants that burn high-sulfur coal, or from other sulfur ores or other industrial processes that burn fuels containing sulfur , such as fuel oil, and from refineries. It can easily be seen that the emission of SO ₂ in these gases not only poses a health hazard by polluting the atmosphere, but also leads to a loss of valuable sulfur

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leads. One of the more difficult environmental problems facing industry is that of economically controlling _{these S0 2 emissions.} This problem is particularly critical in electrical equipment and non-ferrous power smelting industries which are large single point sources of emissions and which are responsible for the greater part of total SC ^ emissions.

Most of the development work on this problem has been directed towards the neutralization of the SO or its conversion to sulfuric acid. Although it has already been proposed _{to obtain elemental sulfur from gases containing SG 2} , very few industrially feasible processes for the reduction of sulfur dioxide to elemental sulfur have so far been developed. The reduction of sulfur dioxide has been studied extensively for many years and there are myriad references in the field. For example, the basic SOj reduction ϋίόη using a hydrocarbon reducing agent is described by Yushkevich et al. in the article in ZH.KHIM. PROM. No. 2, pp. 33-37 (1934) and discussed. In this article, the authors discuss in detail the various possible reaction products that can occur, such as carbon dioxide, water, hydrogen, carbon monoxide, hydrogen sulfide, carbonyl sulfide, carbon disulfide and sulfur, depending on the temperature, the flow rates of the reactants and the ratio of the reactants used - On the basis of the Yushkevich et al. The authors concluded that the reduction of SO ₂ with methane is best carried out at temperatures of 900 to 1000 ° C.

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At lower temperatures, i.e. H. at 800 ° C, report that Authors that significant amounts of unreacted methane in the product gas mixture remains. If the space velocity of the Reaction partners that enter into the reaction, reduced (i.e., the contact time is increased), larger processing facilities would of course have to be used for the same. Amount of gas can be used, which would increase the investment costs of an industrial plant.

In addition, U.S. Patents 2-270,427, 2,388,259, and 2-431,236 describe the reduction of sulfur dioxide with a reducing hydrocarbon gas such as methane, the sulfur being recovered in an essentially three-step reaction. In the first stage, the sulfur dioxide contained in the exhaust gases from smelting processes is reduced with ethane over a heat-resistant surface at temperatures of about 1200 to 132O ° C (2200 to 2400 ⁰ F). The main sulfur-containing by-products are carbonyl sulfide and hydrogen sulfide. The carbonyl sulfide is then reacted with further sulfur dioxide at temperatures of about 427 to 449 ° C (800 to 840 ° F) over a catalyst such as bauxite to form sulfur, and the hydrogen sulfide in the product stream is combined with additional amounts of sulfur dioxide at temperatures from about 210 to 232 ° C (410 to 450 ° F) in the presence of a catalyst such as bauxite to form sulfur according to the well-known Claus reaction.

In the USA patent 3 199 955 a similar system is used

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wrote that 3 catalyst converters used to convert the sulfur dioxide into elemental sulfur by reducing sulfur dioxide with a hydrocarbon reducing agent, such as methane, at temperatures on the order of 800 to 1000 C (1470 to 1830 ° F) in the presence of a catalyst, such as activated alumina, bauxite, calcium sulfide or quartz. This patent reports that about 40 to 60 percent of the inlet sulfur dioxide appears in the product gases from the first stage as elemental gaseous sulfur with the remainder being found as hydrogen sulfide, carbonyl sulfide, carbon disulfide and sulfur dioxide. The remaining two stages of the process described in this patent are essentially identical to the processing steps described in the above mentioned patents. The same authors use tedious steps to ensure that the temperature in the reduction zone remains below about 1000 ° C by using more than a single reactor, since a single reactor does not allow the temperature to be below the 1000 ° C desired keep. The authors envisage a second reactor, the gases from the first reactor going to the second, the temperatures being kept below 1000 ^° C. in this way according to the report.

As noted above, the greater problem with the methods described in these patents is the greater need Plant costs that have to be expended for the primary reaction stage and the intermediate reaction stage of a conversion of carbonyl sulfide and / or carbon disulfide in additional

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carry out common sulfur. Desirably, the reduction of sulfur dioxide with a hydrocarbon reducing agent should be carried out in as few parts of conventional equipment as possible and produce as few by-products as possible requiring further treatment or reaction. In addition, using the reduction of sulfur dioxide require a hydrocarbon reductant, which is at temperatures of 76o ° C and initiates it, and the control of the reached during the reduction of the maximum temperature, the use of particular catalytic materials, these high temperatures and sudden over extended periods Withstand increases in the reaction temperature without adversely affecting the activity of the catalyst. These high inlet temperatures also require additional considerations as to the type of equipment that can be used and the materials. Since the reduction is extremely exothermic, (corresponding to an adiabatic temperature rise in the reactor of about 200 to 750 F depending on the concentration of the SO ₂ "-containing gas) the known method brings an increase in costs for the heat exchange of the product gas with the feed gas to achieve the required This is not possible because of material problems in the heat exchanger. In standard heat exchangers, the upper limit of the heat exchanger temperature for _{gases containing SO 2 is} generally in the range of about 538 to 593 ° C (1000 to HOO ⁰ F) Processes requiring initiation temperatures of 76O ° C and above, one had to resort to either using heat exchangers of the pebble bed type or, instead, to using heat exchangers.

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additional heat from series-connected heaters or ovens.

It has now been found that the presence of a small amount of sulfur added to the reduction of a sulfur dioxide-containing gas with a hydrocarbon reducing agent lowers the temperature required to initiate the reduction. That is, in the presence of sulfur during the reaction, the temperatures normally required to initiate the reduction of sulfur dioxide with a hydrocarbon reducing agent such as methane will be from a temperature of about 760 to 900 ° C (1400 to 1650 ° C) ⁰ F) or higher to about 450 to 620 ° C (8Γ0 to 1150 ° F), preferably to about 510 to 59O ° C (950 to HOO ⁰ F). In addition to lowering the inlet temperature, it has been found that the presence of sulfur during the reduction, especially SO2-containing gases with a high sulfur dioxide concentration such as 50% or more, makes the action smoothly to completeness in an industrially acceptable manner and not one extremely fast reaction takes place once the inlet temperature is reached, whereby the chemical conversion of the SO would become faster and faster up to the point at which it violently decreases.

runs. By enabling, as stated above is to initiate or initiate the reduction at lower temperatures than before, can also be industrial attractive sulfur dioxide reduction processes carried out and can be applied using conventional heat exchangers and catalytic materials. .

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The amount of sulfur, expressed as S ", added to the reduction can be to initiate the reduction of sulfur dioxide To effect with a hydrocarbon reducing agent, can be in the range of about 0.05 to 3 ΜοΙ, -%, preferably from about 0.1 to 1.5 mole percent based on the feed gas. Although percentages higher than 3 mole percent are used you get no additional benefit with sulfur concentrations higher than those specified. Although the Sulfur in the form of sulfur-containing compounds such as carbonyl sulfide, carbon disulfide, hydrogen sulfide and the like, can be added, and these compounds have a beneficial effect on the initiation of the reduction, the sulfur becomes preferably added in the form of vaporized elemental sulfur, which is 'produced and more easily' recycled in the process can be. Instead, the added to the sulfur dioxide gas and / or the hydrocarbon reducing agent Sulfur can also be the product gas that comes out of the reactor. This product gas can contain elemental sulfur, hydrogen sulfide, contain unreacted sulfur dioxide and other gaseous sulfur compounds such as carbonyl sulfide and carbon disulfide. However, this is not the preferred method because of the larger volumes of process gas to be treated and plant requirements.

When operating the present process, the temperatures used in the reduction of sulfur dioxide-containing gas with a Hydrocarbon reducing agents and added sulfur can be applied in the range of about 454 to 1316 ° C (850 to

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240O ⁰ F), preferably from about 510 to 1093 ° C (950 to 2000 ° F). The reduction is preferably carried out in the presence of a catalyst. In a preferred embodiment of the present invention, a suitable catalytic material, preferably in the form of small spheres or stones, about 6 to 18 mm (1/4 to 3/4 inch) in diameter is used. Any of the known catalysts previously used for the reduction of sulfur dioxide, such as bauxite, alumina, silica, calcium sulfide, vanadium oxides, calcium aluminate, and combinations thereof, can be used. The normally gaseous hydrocarbons are preferred as hydrocarbon reducing agents and contain 1 to 4 carbon atoms. Examples of such reducing agents are natural gas, which is a mixture of methane, ethane, propane, butanes, pentanes, nitrogen and carbon dioxide, methane, ethane, propane and butanes. In addition, higher hydrocarbons can also be used if they are in the gaseous state under the reaction conditions. The choice of hydrocarbon is based on cost rather than technical considerations.

The sulfur dioxide that is reduced in the present process can be essentially pure or only a small percentage, as in an industrial exhaust gas in which the Sulfur dioxide content can vary from less than about 1% up to 100%, with the other components consisting essentially of oxygen, Nitrogen, carbon dioxide and water vapor exist. In general, the gases from melters contain about 2 to

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16% by volume sulfur dioxide, and these gases can be conveniently treated in the process of the present invention. However, emissions from operating chimney gases generally contain less than 1% by volume and more likely less than 1/2% by volume sulfur dioxide, and the processing of the sulfur dioxide from such chimney gases into elemental sulfur is considered uneconomical, unless the sulfur dioxide content is processed. There are a series of sulfur dioxide recovery processes in which the sulfur dioxide emissions are obtained in the form of a more concentrated gas of generally more than about 10% by volume of SO and with an SO ₂ concentration of up to 100% by volume on a dry basis. Typical of these recovery processes are the so-called "regenerative alkaline" processes, in which an alkaline agent, such as sodium sulfide, ammonium sulfite, metal carbonate or magnesium dioxide, strips the SO2 from the flue gas stream by combining it chemically with the sulfur dioxide. In a separate regeneration stage, the agent is regenerated again and a sulfur dioxide gas is obtained. Other processes are the so-called "regenerative solids absorption processes" in which a sulfur adsorber such as. Activated carbon or activated carbon that _{adsorbs SO 2} , whereupon the SO _{2 is} desorbed to deliver a S0 ₂ gas stream. There are also so-called "regenerative organic" processes which differ from the alkaline regenerative absorption processes in that an organic absorbent medium is used to absorb _{the SO 2.} The SO ₂ can then be removed from the organic solvent and processed in accordance with the present invention.

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As stated above, there is the reduction of sulfur dioxide with a hydrocarbon reducing agent at elevated temperatures between about 454 and 1316, preferably carried out between 510 and 1093 ° C. When using a catalyst contact times of about 0.1 to 7 seconds, preferably about 0.25 to 3.5 seconds can be used. at Contact times of less than 0.1 seconds, the conversion is incomplete, during contact times over 7 seconds no additional ■ Chen advantages arise, since equilibrium has already been reached. For contact times greater than 7 seconds, the diameter of the Reaction kettle too big to be practical.

The reduction of sulfur dioxide in the present process using a hydrocarbon reducing agent, preferably natural gas or methane, is carried out so that maximum conversion is obtained using an amount of reducing gas sufficient to convert the sulfur dioxide into elemental sulfur and hydrogen sulfide only with trace amounts of other sulfur-containing gases and preferably to a mol-f ratio of hydrogen sulfide to sulfur dioxide in the product gas stream of about 2: 1. The molar ratio of the reactants (sulfur dioxide: reducing gas) should be about 1 _r 33 and up to about 6.5: 1, depending on the reducing gas used. For example, when butane is used, the ratio of sulfur dioxide to butane is 4.5; 1 to 6.5: 1. When the reducing agent is natural gas or methane, the ratio of sulfur dioxide to reducing gas should be about 1.33: 1 to 2.0: 1, with that being particularly

309883/0939

preferred ratio of sulfur dioxide to reducing gas is 1.7 to 1.99: 1. Under the conditions described above at ratios below 1.33: 1 and above 2.0: 1, the desired molar ratio of H-S: SO- in the product gas becomes of 2: 1 not achieved. In addition, in circumstances below 1.33: 1 the product gas stream is unreacted !! contain ethane. Under these conditions one achieves a maximum conversion and thus maximum utilization of the hydrocarbon reducing agent , and there are only small amounts of unreacted carbon monoxide and hydrogen in the exhaust gases. In addition, only trace amounts are found in the product gas discovered by carbonyl sulfide and carbon disulfide, so that one only a single reduction vessel in front of the usual Claus reactor for converting the hydrogen sulfide into the product gases to use more sulfur by reaction with sulfur dioxide. The product gases leaving the reduction system flow through a sulfur condenser and then into a conventional Claus converter, in which the hydrogen sulfide, formed in the reduction reaction with residual sulfur dioxide in the product stream to form further quantities reacts with elemental sulfur. As stated above, a portion of the product gas stream can be added to the feed gas be returned to the reduction chamber to the additional To supply sulfur in it. Preferably, however, the sulfur that has condensed is evaporated and the desired amount then to the product feed stream for use in returned to the reduction reaction.

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The plant, which is used in the reduction of sulfur dioxide in the Methods used in accordance with the present invention can be conventional in nature such as those used for treatment of gases with catalytic material is used. Typical plants for the reduction of SOj are in those mentioned above ÜS patents 2 270 427, 2 388 259, 2 431 236, 3 199 955 and 3,653,833.

The following examples serve to further explain the Invention.

Examples 1 to 3

A number of experiments were carried out in a reaction vessel, lindem a sulfur dioxide-containing gas of different Sulfur dioxide concentrations with methane in the presence of a reducing catalyst made from calcium aluminate on an alumina support was set. The reaction vessel used was an adiabatic reactor with a fixed catalyst layer and with an inlet and outlet and can have facilities for introduction a portion of the feed gas in a central area of the reactor system, allowing better temperature control permitted during the reduction. The void in the catalyst layer was about 40%. Reference is made to the following Tables I, II, III and IV, which contain the essential information relating to the feed gas compositions, the reaction conditions such as contact times, residence times, reactor inlet and outlet temperatures and contain product gas compositions. the

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The amount of sulfur added to the reduction in Examples 1 and 3 is about 1 mol%, expressed as S _Q , which corresponds to an equilibrium mixture of elemental sulfur in the form of S 1, S- and Sg.

Loading JS Tabel I. Mole Example 3 A. .gas together-
settlement nitrogen Example 2 57.93 SO ₂ example 1 9.16 3O, 16 CH ₄ 57.93 4.66 8.28 H ₂ O 30.02 13.73 Sulfur as 8.28 - ^S 2 3, 73 - ^S 6 3.73 O, O2 - ■ - 0.02 O, O3 3.77 0.03 68.75 __

Reaction be 538 538 conditions Reactor inlet 952 663 temperature, ⁰ C Reactor outlet temperature, ° C actual Dwell time in the reactor to Time of 0.55 2, practically full constant methane exploitation in lake

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Table I (cont.)

C. Product gas ■■ ■ MoI Example 3 susan set
tongue example 1 Example 2 7.19 SO ₂ 7.34 2.66 - CH ₄ - .. O, OO67 53.43 H ₂ O 51.32 17.52 0.386 COS .0.397 0.039 3.302 CO 1.486 0, OO3 0.001 cs ₂ ■ 0 _Γ 001 0.020 11,337 H ₂ S 15.220 5 _f 431 3.545 H ₂ 1,772 0.084 26,326 CO ₂ 28.131 4,588 19.509 Sulfur ^C3i 21,374 4,383

Sulfur in the form of S ₂ , S _g and S _g at 538 ⁰ C in a Meng® of about 1 mol · - * as S «

Zuaeseaensetztmg de * Produktgasetrotnee in the reactor for
Timing of practically complete methane utilization,
d, ή, 0.55 (B «iapi« l 1), 2.5 (example 2) bsw _f 0.85 (example 3 |.

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CO O r » ρ ". , si r » in r- Ρ » r * r *. VO in ro • m m tn m tn in in O in in tn in in in tn O O O O. O O O O O O O O O O CD » O O O O σ O O O O O O O O O O O O O O O O α O O O O O O O O m O m O UI O in "« ■ in O tn O in O in cn O r-l - O * CM ro ro O* • * r m m VO VO r- r » Ο ' O* O" O* O* O' O ^# 3Qi8t3 / Q939 O' Ο O* ρ ' O* O*

Table IV

Example 3 (continued)

SO.

CH

H ₂ O COS · CO CS ₂ H ₂ SS ₂

S ₂

CO ₂

P.2

Part.ip.

O 80000 «.06 22.8036 21.34 O.090 O.005 0.824 1.271 4.930 O.092 6.293 0.000 0.000 0.000 828 O.SSOOO '7.26 aOOOO · 53.59 0.381 3.272 0.176 11.175 19.831 3.545 26.187 O.000 0.000 0.000 1O7C

“1.00000. 7.19

7.17 .0.0000 53.46 0.387 3,302 O.003 11,309 19,527 3,545 26,324 0.000 0.000 0.000 1070

O.0000 53.43 0.386 3,302 O.001 11,337 19,509 3,545 26,326 O.000 0.000 0.000 1O7Q

t £ 1,50000 7.19 O.0000 53.43 0.386 3.302 O.OOI 11,337 19,509 3,545 26,326 O.QOO 0,000 0,000

S 2.00000 7.19 O.0000 53.43 0.386 3.302 O.OOI 11.337 19.509 3.545 26.326 Ο, ΟΟΟ 0.000 0.000

In Example 1 the feed gas is a concentrated SO - containing one Gas containing 87.5% sulfur dioxide and 12.5% water to which methane is added by a molar ratio to get from sulfur dioxide to methane by 1.9 3: 1.

In Example 2, the feed gas has an S0 ₂ concentration of 10 mol .-%, and the molar ratio of SO ₂ to methane is 1.97: 1. Vie from the Ferten these tables it can be seen, the initiation of the reduction of starting Examples 1 and 2 at a temperature of 5 38 C, and the reactions were complete with actual residence times of 0.55 seconds and 2.5 seconds, respectively, as determined by the practically complete utilization of the methane. In Example 1, the reaction proceeded smoothly to completion within 0.55 seconds, and the product gas distribution is the thermodynamic equilibrium composition of the peactor outlet temperature of 952 ° C. It has also been found that a slight improvement in the utilization of methane, ie a reduced residual content of carbon monoxide and hydrogen, can be achieved by feeding some of the unheated reactants, ie sulfur dioxide and methane, into the catalyst layer at a central point. This reduces the reactor outlet temperature and shifts the equilibrium to lower carbon monoxide and hydrogen concentrations.

As stated above, Example 2 is similar to Example 1 except that the gas containing sulfur dioxide is approximately Contains 10 mol% sulfur dioxide and the actual residence

309883/0939

time for practically complete utilization of methane 2.5 seconds amounts to. The product composition is excellent, with the

en
Concentration ⁷ of CS ₂ , COS, H ₂ and CO are all negligible.

Example 3 demonstrates the benefits obtained from the presence of additional sulfur during the reduction. The inlet gas composition is essentially the same as in Example 1. Instead of a reactor inlet temperature of 538 ° C, the inlet temperature was increased to 732 ° C. In the absence of additional sulfur, it was found that it was necessary to increase the reactor inlet temperature to this level in order to initiate the reaction. Even at a temperature of 732 ° C the reactions started very slowly, with only 0.18 moles of methane being consumed in the first 0.5 seconds (Table IV) and with a contact time of about 0.8 seconds when the gas temperature was 828 ° C reached, the reaction proceeded to completion almost instantly, which characterizes a harsh abrupt reaction that led to the temperature rise in the reactor from 828 to 1070 ° C χι 0.05 seconds. If no sulfur was added and less concentrated gases containing sulfur dioxide were used, ie with an Sp ₂ content of about 1 to 16 mol%, the reduction was smoother than with more concentrated gases, but the required introduction temperature was of the order of magnitude from about 788 to 816 ° C.

The values in Tables II, III and IV show a profile of the relevant information regarding the residence time, temperatures, Product distribution and composition for each of the

3 09883/0939 ORSGiHAL

play I, 2 and 3. "

309883/0939

Claims (11)

Claims 1. Process for reducing sulfur dioxide to elemental Sulfur by reacting a gas containing sulfur dioxide with a hydrocarbon reducing agent at elevated temperatures Temperatures, characterized in that the initiation of the reduction reaction in the presence of additional Sulfur carries out. 2. The method according to claim 1, characterized in that the reduction in the presence of a catalyst, preferably an alumina-based catalyst or calcium aluminate. 3. The method according to claim 1 and 2, characterized in that the reduction at a temperature in the range from 450 to 1316 ° C. 4. The method according to claim 1 to 3, characterized in that an introduction temperature of 450 to 600 ° C is used. 5. The method according to claim 1 to 4, characterized in that the carbon reducing agent used is natural gas or a low molecular weight hydrocarbon with 1 to 4 carbon atoms, preferably methane is used. 6. The method according to claim 1 to 5, characterized in that 309883/0939 232761B one with a molar ratio of sulfur dioxide to hydrocarbon reducing agent works from about 1.33 - 6.5: 1. 7. The method according to claim 6, characterized in that one works with a molar ratio of sulfur dioxide to methane of 1.33 - 2.0: 1. 8. The method according to claim 6, dadurchgekennzelehnet that one works with a molar ratio of sulfur dioxide to natural gas of 1.33 - 2.0: 1. 9. The method according to claim 1 to 8, characterized in that the sulfur is in an amount of 0.05 to 3, preferably in an amount of 0.1 to 1.5 mol%, expressed as Sg, clogs. 10. The method according to claim 1 to 9, characterized in that one part of the feed mixture on a middle Introduces part of the catalyst layer. 11. The method according to claim 1 to 10, characterized in that the reduction is carried out at a temperature in the range from 510 to 1093.degree. 309883/0939