12.2.3.1 Origin and Isolation

Organosolv lignins are those derived from delignification processes using an organic solvent, frequently ethanol or methanol, and an acid catalyst (mineral or organic), leading to liberation of lignin from cellulosic fibers. High temperatures (approximately 195°C) and pressures (about 28 bars) lead to the cleavage of a- and b-ether linkages of lignin structure [66] and some linkages between lignin and other cell wall components. As for other pulping processes, hardwoods are more readily delignified than softwoods. At lab scale, the isolation is usually performed by acidification of resulting lignin solution and precipitation with water. The solids are recovered by centrifugation or filtration and dried [67]. At industrial scale, the liquor lignin is recovered by precipitation with an aqueous process stream, fol­lowed by filtration, washing and drying [68]. The yields reported are considerably high [67, 69, 70].