Monoethanolamine (MEA) pulping of beech and spruce wood for production of dissolving pulp

Delignification with the use of monoethanolamine (MEA) is an innovative, environmentally friendly chemical pulping process that, in contrast to conventional pulping methods, works without the use of sulphur compounds. Of particular benefit is the simple MEA recovery by distillation, allowing black liquor combustion to be dispensed with and the dissolved lignin to be gained. The MEA process is suitable for pulping both hardwood (e.g. beech) and softwood (e.g. spruce). Compared with conventional processes, the MEA process has the advantage of achieving a high degree of delignification through an increase in temperature during pulping without any appreciable damage to the cellulose. When manufacturing dissolving pulps, however, this specific selectivity of MEA requires the removal of the hemicelluloses in an additional stage, preferably by acid prehydrolysis. The conditions of this prehydrolysis step must be selected specifically to be in keeping with the ultimate use of the dissolving pulp, as this stage involves the cellulose chains being chemically attacked. The residual lignin is removed after pulping in a sequence of different bleaching stages. Substituting MEA for the sodium hydroxide solution required as a bleaching alkali in the oxygen delignification stage proves to be especially beneficial, as in this case the COD after bleaching can be considerably reduced by treating the bleaching filtrate from this stage jointly with the effluents from the MEA pulping process.