Requirement of polysulphide for the reaction with methyl mercaptan

It has earlier been shown that polysulphide can be used to absorb the malod orous methyl mercaptan formed in kraft pulping. The reaction between methyl mercaptan and polysulphide is an equilibrium reaction, which means that so me unreacted polysulphide must be present in the final reaction solution in order to have a sufficient absorption of mercaptan in a scrubbing system. The amount of polysulphide needed, for the equilibrium state, in the elimin ation of methyl mercaptan in water solution was investigated. It was observ ed that an equilibrium state with low mercaptan content in the gas phase wa s reached when more than 3 molar units of polysulphide sulphur were charged per molar unit of methyl mercaptan. The consumption of polysulphide at the equilibrium state was however only 0.5 unit by unit of methyl mercaptan. T he required amount of unreacted polysulphide to reach the equilibrium state was thus at least 2.5 times of the amount of methyl mercaptan to be elimin ated. When that equilibrium state has been reached, a further increase in p olysulphide concentration only slightly improves the elimination of methyl mercaptan.