A process for purifying xylosugars of pre-hydrolysis liquor from kraft-based dissolving pulp production process

Jiachuan Chen,Guihua Yang,Feng Xu,Jiran Dong,Ming He,Pedram Fatehi

doi:10.1186/s13068-018-1336-0

Abstract

BackgroundIn the kraft-based dissolving pulp production process, pre-hydrolysis liquor (PHL) is produced, which contains hemicelluloses, lignin, furfural and acetic acid. PHL is currently burned in the recovery boiler of the kraft pulping process, but it can be utilized for the generation of high-valued products, such as xylitol and xylanase, via fermentation processes. However, some PHL constituents, e.g., furfural and lignin, are contaminants for fermentation processes and they must be eliminated for production of value-added products.ResultsIn this work, a process is introduced for removing contaminants of PHL. Ca(OH)2 treatment is the first step of this process, which removed 41.2% of lignin and negligible amount of sugars. In this step, a notable increase in the concentration of acetic acid was achieved (ranging from 6.2 to 11.7 g/L). In the second step, the implementation of adsorption using activated carbon (AC) at 1 wt% dosage led to additional 32% lignin and 5.9% xylosugar removals. In addition, laccase assisted activated carbon treatment led to further removal of lignin via accelerating lignin polymerization and adsorption on AC (i.e., removal from PHL). Overall, 90.7% of lignin, 100% of furfural, 5.7% of xylose, and 12% of xylan were removed from PHL, while the concentration of acetic acid became twofolds in the PHL.ConclusionsThis study reports an attractive process for purifying sugars and acetic acid of PHL. This process may be implemented for producing sugar-based value-added products from PHL. It also discusses the mechanism of Ca(OH)2 treatment, AC adsorption and laccase assisted activated carbon treatment for lignin removal.

Highlights

In the kraft-based dissolving pulp production process, pre-hydrolysis liquor (PHL) is produced, which contains hemicelluloses, lignin, furfural and acetic acid
It was reported that calcium could generate complexes with lignin, which implied that the complexation between lignin of PHL and dissolved calcium ions might have contributed to the removal of lignin [15]
The adsorption of lignin onto the Ca(OH)2 particles might have contributed to the lignin removal from PHL [3, 15]

Summary

Introduction

In the kraft-based dissolving pulp production process, pre-hydrolysis liquor (PHL) is produced, which contains hemicelluloses, lignin, furfural and acetic acid. PHL is currently burned in the recovery boiler of the kraft pulping process, but it can be utilized for the generation of high-valued products, such as xylitol and xylanase, via fermentation processes. Some PHL constituents, e.g., furfural and lignin, are contaminants for fermentation processes and they must be eliminated for production of value-added products. In the hydrolysis stage of kraft-based dissolving pulp process, most of the hemicellulose and part of lignin are dissolved into liquor that is called pre-hydrolysis liquor (PHL). PHL is considered a waste liquor and mixed with black liquor for combustion in the recovery boiler of the kraft process [1, 2]. The complexity of solvent recovery, the high operational costs and technical issues constrained the commercialization of this technology [1].

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