Chemistry of Organosolv Delignification, 1992 Solvent Pulping Symposium Proceedings

Organosolv pulping is attracting increased attention, as a result of its potential suitability for economically adding incremental pulp production capacity, and possible environmental advantages. As yet, however, relatively little research has been done on its fundamental aspects. The purpose of this review is to facilitate further work by summarizing available information on the likely delignification mechanisms operative in major acidic and alkaline organosolv pulping systems. Acidic systems are emphasized, the rationale being that they differ more from conventional processes than do other organosolv processes. Some important reactions in alkaline systems are nevertheless also reviewed It is concluded that the cleavage of ether linkages is of major importance. Under acidic conditions this is particulary true for *SYMBOL*-ethers, but *SYMBOL*-ether cleavage also plays a role, especially in hardwood pulping. In alkaline systems, the cleavage of *SYMBOL*-ethers is more important. Lignin condensation, a potential limiting factor, can occur in several ways, usually involving reactive carbocation or quinone methide intermediates. Hardwoods are delignified more readily than softwoods, primarily as a result of differences in *SYMBOL*-ether reactivity, *SYMBOL*-ether concentration, lignin content and propensity to undergo condensation reactions.