Enhancing sustainability in bagasse pulping: Hexenuronic acid removal and membrane-based chemical recovery

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School of Chemical Engineering | Master's thesis

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Date

2025-11-24

Department

Major/Subject

Biomass Refining

Mcode

Degree programme

Master's Programme in Chemical, Biochemical and Materials Engineering
Kemian-, bio- ja materiaalitekniikan maisteriohjelma
Magisterprogrammet i kemi-, bio- och materialteknik

Language

en

Pages

56

Series

Abstract

This study focused on two significant challenges in sustainable bagasse pulping: high chlorine dioxide (ClO2) consumption during bleaching and inefficient chemical recovery from silica-rich spent liquor. To address this, a combined approach of acid pretreatment (A-stage) to remove hexenuronic acid (HexA) from bagasse, and ultrafiltration (UF) for soda liquor fractionation was systematically explored. In the bleaching trials, the conventional ECF sequence D0–Ep–D1 was compared with a modified A/D0–Ep–D1 sequence. The A-stage effectively hydrolyzed 49% of the initial HexA (reducing it from 14.4 to 7.4 μmol/g), resulting in a 25% reduction in ClO2 demand when active chlorine charge applied on pulp. Although with saving of ClO2 demand, the A-stage sequence led to about 5% lower final ISO brightness (75% vs 80%) and a 21% decrease in viscosity (685 vs 874 ml/g) when comparing to the ECF sequence D0–Ep–D1, indicating a trade-off between chemical savings and pulp quality. Concurrently, ultrafiltration (UF) of spent liquor with a 0.5 kDa-sized membrane effectively fractioned the stream: the retentate was enriched in high-molecular-weight lignin (Mw = 980 g/mol), while the permeate contained recoverable low-molecular-weight hydroxy acids (HAs, e.g., lactic acid, GISA, XISA) with over 60% recovery rate. Furthermore, NMR spectroscopy revealed that hemicelluloses existed possibly in the form of lignin-carbohydrate complexes (LCCs) in the retentate. Overall, UF enables promise of converting soda spent liquor into sources of lignin, HAs, and residual alkali, providing a potential alternative to traditional recovery boilers for small-scale mills utilizing non-wood feedstocks.

Description

Supervisor

Dou, Jinze

Thesis advisor

Le, Huy Quang
Munib, Wajeeha

Keywords

bagasse, bleaching, chlorine dioxide, hexenuronic acid, recovery, ultrafiltration

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Permanent link to this item

https://urn.fi/URN:NBN:fi:aalto-202512179389

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[dipl] Kemian tekniikan korkeakoulu / CHEM