Inclusion of a pressurized acidolysis stage in chemical pulp bleaching

Abstract

Hardwood soda-AQ pulps are believed to be rich in benzyl sugar ethers (BSE) that can be partially cleaved by aqueous acidic treatments. The aim of this investigation was to evaluate the effect of acidolysis on final bleached brightness for kraft and soda-AQ (SAQ) hardwood pulps. The increase in final brightness due to acidolysis at 110 °C was twice as high for a eucalyptus SAQ pulp as compared to the kraft pulp. An oxygen delignified maple C-SAQ pulp (carbonate pre-treated SAQ) was acidolyzed at 120 °C and pH 2.6 for 30 min. When 1.60% ClO2 + 0.25% H2O2 on pulp was used in DEPD final bleaching of the control sample a brightness of 91.5% was achieved. When only 1.00% ClO2 + 0.25% H2O2 on pulp was used for the acidolyzed sample a brightness of 92.0% was attained. Analyses of the maple pulp after the acidolysis showed no major change in lignin content, brightness, or pulp yield. The minor changes suggest that a facile reaction such as benzyl ether cleavage was responsible for the improved bleachability. Preliminary research involving a lignin model compound and commercial birch xylan showed that lignin-carbohydrate condensation products were generated under SAQ cooking conditions. Furthermore, a fraction of these lignin-carbohydrate moieties were subsequently cleaved by acidolysis at pH 2.5 and 105 °C.

Highly Bleachable Wood Fibers Containing Less Condensed Lignin from Acid Hydrotropic Fractionation (AHF)

“…The low temperature and short fractionation times resulted in dissolved lignin with low degrees of condensation, especially with a flow-through configuration . Furthermore, acidic fractionation can hydrolyze lignin–carbohydrate complex (LCC) and prevent the formation of hexenuronic acid, , both of which improves the bleachability of the p -TsOH fractionated cellulosic water insoluble solids (WIS). In addition, AHF has the simplicity of valorizing all three major components, i.e., cellulose, lignin, and hemicellulloses, using hydrotrope p -TsOH alone and has several advantages: , (1) p -TsOH as a catalyst does not participate in reaction, unlike pulping chemicals in commercial wood pulping.…”