Cellulose stabilization during alkaline pulping for the production of high-purity dissolving-grade pulp

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Journal ISSN

Volume Title

School of Chemical Engineering |

Authors

Date

2012

Department

Puunjalostustekniikan laitos

Major/Subject

Paperi- ja painatustekniikka

Mcode

Puu-21

Degree programme

Language

en

Pages

62 s. + liitt. 14

Series

Abstract

In view of the increasing competition between forest companies all over the world, it becomes essential to transform even the very small element of the wood into a high value-added product. The hot water extraction is a good way to extract hemicelluloses from wood, to recover them easily and to convert them in by-products. The wood residue after the extraction, composed mostly of cellulose and lignin, can be further subjected to pulping and then potentially used as dissolving pulp. However, the crucial point is the amount of reducing end group after this pre-treatment under severe extraction conditions, which leads to further cellulose depolymerization during subsequent alkaline pulping. Thus, stabilization of cellulose is required by using some additives during pulping. In this study, the performance of two different additives, sodium borohydride and anthraquinone monosulfonate, was investigated during soda-anthraquinone (SAQ) pulping of pre-extracted birch wood chips. These chips had been pre-treated over a wide range of extraction intensities. Stabilization was carried out in-situ by the addition of the stabilizing agents to the soda-anthraquinone pulping liquor. Pulp analysis (Kappa number, intrinsic viscosity, residual alkali) were performed and the chemical composition was determined to characterize the obtained pulps. Based on the results, addition of sodium borohydride (BH) gave the highest yields, the lowest ratios reject/pulp as well as the lowest Kappa numbers. However, this additive gave also the lowest viscosities. The chemical composition revealed that BH enhances cellulose content and hence leads to cellulose stabilization. Xylans content were also found to be improved by using the two additives. Effects of two different H-factors and two soda (NaOH) charges were further investigated on one selected pre-treated wood sample. The results showed that optimization in terms of energy and chemicals may be possible.

Description

Supervisor

Sixta, Herbert

Thesis advisor

Borrega, Marc

Keywords

anthraquinone monosulfonate, cellulose, hot water extraction, sodium borohydride, stabilization, soda-anthraquinone pulping

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Permanent link to this item

https://urn.fi/URN:NBN:fi:aalto-202108318744

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