Magnesium bi:sulphite boiling acid prodn. for pulping cellulose - using sulphur di:oxide from thermal decomposition of one fraction to increase acidity

摘要

Prodn. of strengthened boiling acid for pulping cellulose with Mg(HSO3)2 from waste gases contg. SO2 from combustion plants, esp. lye burners, involves introducing an absorbent suspension into the gas stream, so that Mg-(HSO3)2 is produced in the first scrubbing stage from Mg-SO3 obtd. from MgO and SO2 in subsequent scrubbing stages. The novel is that part of the Mg(HSO3)2 soln. produced, contg. residual MgSO3, is decomposed thermally to SO2 and MgSO3 and the SO2 formed is contacted with another pt. of the soln., so that the residual MgSO3 in the soln. is converted to Mg(HSO3)2 and also free SO2 passes into soln., whilst the MgSO3 formed is recycled to the absorber. The process avoids the need to use additional gases with a high SO2 content from a roasting process and increases the utilisation of SO2.