Sodium carbonate pre-extraction of bamboo prior to soda-anthraquinone pulping

Abstract

A part of hemicelluloses is dissolved in black liquor during pulping process, which can be extracted prior to pulping, that would be used for producing biofuels, biopolymers, paper additives, and other chemicals in addition to pulp. However, the amount of hemicellulose extraction must be limited to maintain pulp yield and pulp quality. In this investigation, hemicelluloses were pre-extracted from bamboo with weak alkali (Na2CO3) and compared with hot water and dilute H2SO4 extraction prior to kraft, soda, and soda-anthraquinone (AQ) pulping. Bamboo chips were also pulped by the kraft process without pre-extraction. The biomass dissolution in weak alkaline pre-extraction was 11.1 %, which was 1.2 and 7.9 % lower than the hot water and dilute H2SO4 pre-extraction, respectively. In the alkaline pre-extraction process, 1.3 % lignin, 1.7 % acetic acid, and about 6.4 % sugars (on oven-dried mass of bamboo) were extracted. The soda-AQ process responded well in terms of pulp yield and pulp quality. Pulp yield after alkaline pre-extraction was higher and kappa number was lower than the hot water and dilute H2SO4 pre-extraction. Alkaline pre-extraction followed by kraft and soda-AQ pulping produced pulp with lower kappa number than non-extracted kraft pulp at almost similar pulp yield. This pulp showed better results in pre-bleaching with peroxyformic acid. Alkaline pre-extracted kraft and soda-AQ pulps had better tear index and slightly inferior tensile index than the non-extracted kraft pulp after D0EpD1 bleaching. Final brightness for soda-AQ and kraft pulp was 1.1 and 2.8 %, respectively, higher than the control pulp. Alkaline pre-extraction is a better option to integrate pulp mill with hemicellulose extraction and pulp production biorefinery.