Reductive catalytic fractionation of lignocellulosic biomass- new approaches and chemical insights to process debottlenecking
Author(s)
Rinken, Raul
Type
Thesis
Abstract
Over recent years, Reductive Catalytic Fractionation (RCF) has given traction as a potential method for lignocellulosic biomass valorisation. Based on the active stabilisation of reactive lignin intermediates, the process produces a carbohydrate-rich pulp and lignin oil- a mixture of lignin-derived monophenols, oligomers, polymers, and carbohydrate derivatives. For the RCF process industrial implementation, homogeneous monophenol streams and the faith of oligomeric and polymeric lignin fractions are among the key factors. Following this reasoning, the current thesis aims to provide new chemical insights into the polymeric lignin fractions and introduce new approaches to steer the RCF lignin oil composition. Accordingly, a solvent fractionation strategy is first developed to produce distinctive lignin oil fractions, enabling deconvoluting analytical data. As a result, new non-native reduced β-O-4 linkages are discovered, demonstrating an additional lignin stabilisation mechanism that also incorporates polymeric lignin moieties. Deconvoluting the spectral data showed that the carbohydrates in lignin oil are oligoxylan alcohols. Additionally, a new Structural Index metric is introduced to assess the chemical nature of oligomeric and polymeric lignin with a simple GPC/UV-VIS analysis. To steer the process outcomes, mechanocatalytic pretreatments are introduced prior to the RCF. It is discovered that adding acetic acid to ball-milling before the RCF process increases monophenol yields and carbohydrate retention in pulp. In addition, a semi-batch RCF strategy is introduced with incremental temperature increases. It is demonstrated that process conditions have an immense effect on monophenols distribution, and at low temperatures, lignin can be partially extracted with complete carbohydrate retention in pulp. In a broader context, the current thesis provides new insights into the chemical nature of lignin-derived oligomers and polymers, which can open new avenues for these lignin fractions' modification and utilisation. Additionally, the introduced RCF approaches provide new ways to steer the process outcomes, creating further options in the process design considerations.
Version
Open Access
Date Issued
2024-04-12
Date Awarded
2025-05-01
Copyright Statement
Attribution-NonCommercial 4.0 International Licence (CC BY-NC)
License URL
Advisor
Rinaldi, Roberto
Sponsor
Engineering and Physical Sciences Research Council
Grant Number
EP/R513052/1
Publisher Department
Department of Chemical Engineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)