Chapter 5 - Industrial scale lignin recovery from pulping liquors

Abstract

There is estimated an annually about 70 million tons of lignin from Kraft pulping mills and about one million lignosulfonates are produced in the world. Only about 60 kilo tons of Kraft lignin per year are commercialized in the United States. Recovery boilers produce a surplus of energy because of increasing pulp production. The capacity of recovery boiler becomes a bottleneck and the recovery and valorization of lignin from black liquor starts to draw much more attentions. Commercial technical lignin such as indulin is recovered from black liquor of softwood Kraft pulping process by using CO2 precipitation. The recovery efficiency can be significantly improved by careful control of the washing steps (LignoBoostTM), and the odor of lignin can be minimized by prior oxidization (LignoForceTM). The traditional batch or semibatch precipitation process can also be replaced by a continuous process (SLRPTM). The industrial processes of lignin and lignosulfonate recovery from pulping liquors are reviewed in this chapter.