Methods and systems for recovering sulfur dioxide from a Claus unit process emissions stream are provided. The method comprises the steps of generating a process emissions stream from a thermal oxidizer or other combustion device, introducing the emissions stream to an SO.sub.2 removal system, introducing the SO.sub.2 rich stream from the SO.sub.2 removal system to a CO.sub.2 removal system, and introducing an enriched SO.sub.2 stream back to the Claus unit. The SO.sub.2 removal system can include one or more SO.sub.2 selective membranes. The CO.sub.2 removal system can include one or more CO.sub.2 selective membranes.

Methods and systems for recovering sulfur dioxide from a Claus unit process emissions stream are provided. The method comprises the steps of generating a process emissions stream from a thermal oxidizer or other combustion device, introducing the emissions stream to an SO.sub.2 removal system, introducing the SO.sub.2 rich stream from the SO.sub.2 removal system to a CO.sub.2 removal system, and introducing an enriched SO.sub.2 stream back to the Claus unit. The SO.sub.2 removal system can include one or more SO.sub.2 selective membranes. The CO.sub.2 removal system can include one or more CO.sub.2 selective membranes.

A process for producing sulfuric acid and cement clinker may use calcium sulfate that is formed as a solid by-product and separated off in phosphoric acid production in a reaction of raw phosphate with sulfuric acid to form phosphoric acid. The process comprises treating calcium sulfate separated from the phosphoric acid with an acid to obtain a suspension comprising purified calcium sulfate, separating the purified calcium sulfate in solid form from the liquid phase of the suspension, mixing the purified calcium sulfate with admixtures and reducing agents to obtain a raw meal mixture for cement clinker production, burning the raw meal mixture to obtain the cement clinker, with formation of sulfur dioxide as offgas, and subjecting the sulfur dioxide formed to offgas purification and feeding the sulfur dioxide as raw material to sulfuric acid production to produce the sulfuric acid. The sulfuric acid produced may be used as starting material in phosphoric acid production.

A process for producing sulfuric acid and cement clinker may use calcium sulfate that is formed as a solid by-product and separated off in phosphoric acid production in a reaction of raw phosphate with sulfuric acid to form phosphoric acid. The process comprises treating calcium sulfate separated from the phosphoric acid with an acid to obtain a suspension comprising purified calcium sulfate, separating the purified calcium sulfate in solid form from the liquid phase of the suspension, mixing the purified calcium sulfate with admixtures and reducing agents to obtain a raw meal mixture for cement clinker production, burning the raw meal mixture to obtain the cement clinker, with formation of sulfur dioxide as offgas, and subjecting the sulfur dioxide formed to offgas purification and feeding the sulfur dioxide as raw material to sulfuric acid production to produce the sulfuric acid. The sulfuric acid produced may be used as starting material in phosphoric acid production.

A method for cleaning an off-gas from viscose production, essentially containing H.sub.2S and CS.sub.2, comprises passing the gas through a catalytic reactor containing a direct oxidation type catalyst, such as V.sub.2O.sub.5 on silica, to convert H.sub.2S in the gas to elemental sulfur, SO.sub.2 or mixtures thereof, either via the oxygen present in the gas or via oxygen added to the gas stream. Elemental sulfur and SO.sub.2 are removed from the effluent gas from the catalytic reactor, and the unconverted CS.sub.2 is recycled to the viscose production process.

A method for cleaning an off-gas from viscose production, essentially containing H.sub.2S and CS.sub.2, comprises passing the gas through a catalytic reactor containing a direct oxidation type catalyst, such as V.sub.2O.sub.5 on silica, to convert H.sub.2S in the gas to elemental sulfur, SO.sub.2 or mixtures thereof, either via the oxygen present in the gas or via oxygen added to the gas stream. Elemental sulfur and SO.sub.2 are removed from the effluent gas from the catalytic reactor, and the unconverted CS.sub.2 is recycled to the viscose production process.

A composite material is used for desulfurization. The composite material contains activated carbon, alkali metal oxides, silicon oxides, iron oxides, and rare earth element oxides. The weight ratio among the activated carbon, iron oxides and rare earth element oxides is 100:(0.5-5):(1-10). The composite material, used as a sulfur adsorbent, has a higher sulfur breakthrough capacity and desulfurization rate.

A molecular sieve complex contains an oxide of aluminum, an oxide of an alkaline earth metal and a rare earth-modified molecular sieve. The rare earth-modified molecular sieve is a molecular sieve doped by a rare earth element. The percentage of the pore volume occupied by pores of 3 nm or less to the total pore volume in the molecular sieve complex is greater than or equal to 63.5%. The content of the rare earth element and the contents of the oxide of aluminum, the oxide of the alkaline earth metal and the molecular sieve satisfy a certain relationship. The composite material contains a molecular sieve complex and an auxiliary agent loaded on the molecular sieve complex, and the composite material may be applied to flue gas adsorption and desulfurization.

Provided is a sulfur dioxide mixture that hardly corrodes metals. A sulfur dioxide mixture contains sulfur dioxide and water. The sulfur dioxide mixture is filled in a filling container in such a manner that a gas phase and a liquid phase exist, and the moisture concentration of the gas phase is from 0.005 mole ppm to less than 5,000 mole ppm.

Provided is a sulfur dioxide mixture that hardly corrodes metals. A sulfur dioxide mixture contains sulfur dioxide and water. The sulfur dioxide mixture is filled in a filling container in such a manner that a gas phase and a liquid phase exist, and the moisture concentration of the gas phase is from 0.005 mole ppm to less than 5,000 mole ppm.