DE2546353A1 - METHOD OF REMOVING SULFUR OXIDES FROM GAS MIXTURES - Google Patents

Description

METALLGESELLSCHAFT Frankfurt / Main, October 14, 1975 Aktiengesellschaft -Wgn / HSz-Nr. 7651 LT

Process for removing sulfur oxides from gas mixtures

The invention relates to a method for removing sulfur oxides from a gas mixture by passing over a carbonaceous, large surface area adsorbent «, to be treated Gas mixtures can e.g. exhaust gases from the combustion of liquid or solid fuels or exhaust gases from sulfuric acid production or ore roasting, but the process is not limited to this.

Numerous methods for removing sulfur oxides from flue gases are known. They sometimes work as an absorption process with liquid, mostly weakly alkaline detergents, or with solid oxidic substances, mostly base anhydrides, or with solid compounds of basic oxides with the anhydrides of weak acids, e.g. NagOAlgO, other processes work again on the path of adsorption at., high surface area materials are to be z _o B, become known in recent times procedures by which sO ₂ can be removed with molecular sieves of gases (Chem, Eng. 80 (1973) 18, p 62/63, and U.S. Patent 3 829 560).

It is also known for the adsorptive removal of sulfur oxides to use activated carbon from gases. A method described in DT-AS 1 942 519 is based on sulfur oxides to bind to activated carbon impregnated with vanadium oxide and the loaded adsorbent with carbon monoxide or hydrogen regenerate as desorption gases so that sulfur dioxide is removed from the desorption gas.

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The object of the invention is to create a method of the type mentioned at the beginning which enables a high loading of the adsorption device and at the same time works in a cost-effective manner. This object is achieved in that the gas mixture containing oxygen and water vapor at least corresponding to a dew point of 35 ° C and a maximum corresponding to 90% relative saturation, at temperatures between 20 and 120 ⁰ C on the with oxides of cobalt, nickel, molybdenum, or Tungsten or mixtures of these oxides impregnated adsorbent is passed until the adsorbent contains 5 to 80 wt.% Sulfuric acid, and that the sulfur compounds for regenerating the adsorbent at temperatures between 150 and 450 ⁰ C with a hydrogenating gas are desorbed gas mixture to be treated ensures that the adsorbent is not _{loaded with SO 2} but with sulfuric acid. The absorption capacity of the adsorbent is thereby increased quite considerably, at least by a factor of 10, compared to processes which use the sulfur oxides in gaseous form, ie. completely or largely dry, adsorb »

The desorption of the adsorbed sulfuric acid with a hydrogenation gas runs without loss of catalyst material, whereas thermal regeneration, for example, consumes carbon the reaction equation

2H ₂ SO ₄ + C- * 2H ₂ O + CO ₂ + 2SO ₂

would result «, In the method according to the invention, on the other hand only an equivalent proportion of the hydrogenation gas is consumed

Due to the desorption with a hydrogenation gas belonging to the process according to the invention, H ₂ SO ₄ and possibly still remaining S0 _{2 are} partially hydrogenated up to H ₂ S. The oxides of cobalt, nickel, molybdenum or tungsten with which the adsorbent is impregnated * act as the catalyze desired hydrogenation

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rending substances. The desorption gas thus contains the sulfur compounds as a mixture of SOpAnd HpS that is easy to elemental sulfur can be implemented.

Activated charcoal or activated coke are particularly suitable as adsorbents. The adsorbent may be up to 10% of its own weight with the above-mentioned metal oxides as the hydrogenation catalysts impregnated be "Mixtures of these catalysts may yield a composition that the molar ratio CoO or NiO to Mo ₂ O- * and WPO, sth 1: 1.5 corresponds.

As a reducing gas for the desorption of the sulfur compounds For example, hydrogen, carbon monoxide or the cheaper natural gas can be used or gases that contain these: Components predominantly included.

The desorption gas mixture formed during the regeneration of the adsorbent is expediently passed over a large-area substance which catalyzes the Claus reaction and elemental sulfur is separated off. The Claus reaction (2H ₂ S + SO ₂ -) 3S + 2H ₂ O) can be carried out in a manner known per se over aluminum oxide catalysts or activated carbon. The elemental sulfur formed is a very desirable end product of gas desulfurization. It is expedient to use _a s d by the Claus reaction of the sulfur compounds at least predominantly freed hydrogenating gas for the desorption of the adsorbent again.

In a further embodiment of the invention, the desorption with the hydrogenating gas can be carried out in such a way that the desorption gas already has approximately the stoichiometric composition of 2 mol H ₂ S and "T mol SO _{2 of} the Claus reaction»

Both the adsorbent and the catalyst for the Claus reaction can be used not only in the fixed bed, but also in the moving or fluidized bed can be applied.

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A circuit example for the method according to the invention is explained below with the aid of the drawing.

A gas mixture containing SC ^ is supplied in line 1, which is approximately up to 90 % saturated with water vapor. The water vapor content in the gas mixture should be at least a dew point of 35 ⁰ C, preferably correspond to from about 45 ⁰ C _f. In addition, so much oxygen in the gas is present in that order that the SO can be reacted ₂ to SO quantitatively _e The gas mixture in line 1 is mixed with temperatures of 20 to 120 ⁰ C, preferably 50 to 100 ⁰ C, through a reactor 2 which contains a carbonaceous, large-surface adsorbent such as activated carbon. This adsorbent is impregnated with Co, Ni, Mo and / or W oxides. _{The SO 2} withdrawn from the moist gas mixture is bound to this adsorbent as H ₂ SO ^. To improve the catalytic effect of the adsorbent can also the H ₂ SO, formation accelerating, per se known substances, such as metal oxides (see _o the German Patents 1,176,101, 1 I76 621 and 1767 and DT-AS 1,227,434 ). The purified gas leaves the reactor through line 3 *

Once the adsorbent in reactor 2 sulfuric acid an amount of at least 5 wt.%, Preferably at least 20 wt% _o, of the unloaded adsorbent has recorded is the reactor to regeneration switched "In this time, a second, not shown, the reactor can take over the adsorption «For regeneration, a hydrogenating gas, for example a hydrogen-rich gas or methane, is passed through a line 4 into the reactor 2 and through the adsorbent to desorb the sulfuric acid and at the same time convert it to a mixture of S0 ₂ and H ₂ S. Is desorbed at temperatures in the range of 150 to 450 ⁰ C, preferably in the range of 200 to

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-ιτ-

The desorbed gas leaves the reactor 2 via line 5, _# cooled in heat exchanger 6 and passed into the reactor 7 in the reactor 7 "contains, for example, activated carbon or alumina, is performed at temperatures about in the range of 120 to 14O ° C by the Claus Reaction formed sulfur deposited · The residual gas, which mainly consists of hydrogenation gas, is _{returned to the reactor through line 8 f,} fan 9 and heater 10. Fresh hydrogenation gas to replace the amount used is fed in through line 11. As soon as the regeneration of the adsorbent in the reactor 2 has ended, it can be put back into operation _{for S0 2 removal.}

The sulfur separated in the reactor 7 is after one or more regeneration cycles by inert gas, e.g. nitrogen, discharged, which comes from the line 12 and has been passed through a gas heater 13. By the heated inert gas the sulfur is melted out in the reactor 7; the sulfur-containing inert gas is in line 14 to the sulfur condenser 15 led. The inert gas, largely freed from sulfur again, is passed through line 16, fan 17 and line returned for reuse, fresh inert gas comes from line 19 if necessary. The sulfur which has condensed out is withdrawn through line 20.

example

In a procedure according to the drawing, flue gas is treated with 0.2 vol. SO ₂ , 11 vol.% CO ₂ , 3 vol. # O ₂ and 33 vol.% Steam. The water vapor content corresponds to a relative saturation of 70 %.

The flue gas is passed through a fixed bed of granular activated carbon in the reactor 2 ^{at a temperature of 80 ° C. with a residence time of 5 seconds.} The activated carbon is impregnated with cobalt molybdenum oxide; the amount of impregnation, expressed as Co and Mo metal, is 2.9% by weight of the activated carbon. Co and Mo are present in the stoichiometric ratio of the compound Co ₂ (MoO ^) -z . On this adsorbent, 98 % of the SO _{2 is converted} into H ₂ SOr and bound in this form.

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After a running time of 35 hours, the adsorbent is _{loaded with 30% by weight of H 2} SO ^ and the S0 ₂ conversion has fallen below 98%. The ^ SO ^ loading corresponds to an S0 ₂ uptake of 196 g / kg adsorbent. The reactor 2 is then switched to regeneration and technically pure hydrogen at a temperature of 370 ° C. is passed through it. The adsorbent is heated to temperatures of 120 to 140 ° C. In reactor 2, the desorption of SO ₂ and then the formation of H ₂ S begins. Both gases partially react with the formation of sulfur. However, most of the sulfur is formed in reactor 7 on an aluminum oxide catalyst arranged in a fixed bed at a temperature of 120 to 140.degree. This sulfur is removed from the reactor 7 again after 3 regeneration cycles with nitrogen at a temperature of 300 ° C.

In a desorption in the reactor 2 low C0 ₂ amounts were detected in the desorption gas only at the beginning of the regeneration, but obviously came from the. ^ Flue gas and were also adsorbed. When the adsorbent was further heated by the hot hydrogen, no new formation of CO _{2 was} observed. A consumption of activated carbon through reaction of the carbon with the sulfuric acid could not be determined.

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Claims (9)

Claims 1) A method for removing sulfur oxides from a gas mixture by passing over a carbon-containing, large-surface adsorbent, characterized in that the gas mixture, which contains oxygen and water vapor at least corresponding to a dew point of 35 ° C and at most a relative saturation of about 90 % , at temperatures between 20 and 120 ⁰ C over the with oxides of cobalt, nickel, molybdenum or tungsten or mixtures of these oxides impregnated adsorbent is passed until the adsorbent contains 5 to 80 wt.% sulfuric acid, and that the sulfur compounds to regenerate the adsorbent Temperatures between 150 and 450 ° C are desorbed with a hydrogenating gas. 2) Method according to claim 1, characterized in that the desorption gas mixture passed over a large surface area, the Claus reaction catalyzing substance and elemental sulfur is deposited. 3) Method according to claim 2, characterized in that the elemental sulfur deposited by the CLaus reaction is desorbed by heating in the inert gas stream and obtained by condensation. 4) Method according to claim 1 or one of the following, characterized in that the hydrogenating gas from the Claus reaction is passed back to desorb the sulfur compounds and regenerate the adsorbent. 709820/0843 ORIGINAL INSPECTED 5) Method according to claim 1 or one of the following, characterized in that the gas mixture containing sulfur oxides, water vapor and oxygen is passed at temperatures of 50 to 100 ° C over the adsorbent. 6) Method according to claim 1 or one of the following, characterized in that the adsorbent is regenerated at temperatures between 200 and 400 ⁰ C by desorption of the sulfur compounds. 7) Method according to claim 1, characterized in that the gas mixture containing sulfur oxides and oxygen contains water vapor corresponding to a dew point of over 45 ^° C. 8) Method according to claim 1 or one of the following, characterized in that the oxygen content of the gas containing sulfur oxides and water vapor is sufficient for the quantitative oxidation of SOp to SO *. 9) Method according to claim 1 or one of the following, characterized in that the adsorbent is regenerated when its sulfuric acid loading is at least 20 Gevr.% Of the unloaded adsorbent. 709820/0843