Improved pretreatments and fractionation of soft and hardwoods to access feedstock chemicals

Summary Description:

Whilst current approaches to the use of wood are highly optimised and integrated, novel technologies can be developed that further improve the efficiency of use of all the possible product streams. The current use of LIGNIN derived from wood is to burn it and this represents an inefficient use of this potentially valuable resource. It is desirable to convert wood into a set of product streams that can be used for several different applications.

One of these streams should be a high quality Lignin, whilst other streams should contain cellulose and hemicellulose-derived sugars. Current methods of isolating high quality lignin from (i) Sitka spruce and (ii) mixtures of soft and hardwoods can be improved. After isolation from the wood, it will be advantageous to purify (fractionate) the Lignin before attempts are made to convert it to feedstock chemicals. The proposed programme of work builds on these assumptions.

Project Outcomes:

Original project aims and objectives (or approved updated objectives), including reasons for amendments    

1. Develop improved pretreatments for sitka spruce processing that deliver high quality lignin and fermentable sugar product streams

2. To test fractionation protocols for lignin derived from (i) sitka spruce and (ii) mixtures of soft- and hardwoods

3. To optimise the production of aromatic monomers from the lignins delivered in Objective 2

4. To deliver a highly trained, interdisciplinary PhD-level individual with a broad overview of challenges and solutions relevant to Industrial Biotechnology and Forestry Science.

 

Overall progress towards meeting the aims and objectives of the project

Aims 1 and 4 were achieved in that the butanosolv processing of sitka spruce sawdust was explored and optimised in detail. Gerard Su submitted a PhD thesis and this has been examined and passed by external examination by the University of St Andrews.

Aim 2: Fraction of butanosolv lignin was attempted and has been studied by others in the Westwood lab. However, this did not become a major part of the PhD as these studies were replaced by detailed work on the sugar-containing components of the sitka spruce sawdust as well as monosaccharides obtained from alternative biomass sources (resulting from issues around supply of sawdust during the COVID 19 pandemic)

Aim 3: This was a very ambitious aim but significant attempts were made to produce aromatic monomers from oxidised sitka spruce lignin. Some novel insights were identified.

During the period of the PhD significant development in the literature on the development of lignin-derived materials occurred. This led to add-on studies on the development of methods to modify the sitka spruce starting lignin using a chemical reaction known as metathesis. Whilst the synthesis of final materials was not fully completed during this study, this methodology for lignin modification was demonstrated on sitka spruce lignin for the first time.

 

How have the results been used?

An optimised pretreatment for sitka spruce sawdust was developed. This is important as sitka spruce is arguably Scotland’s largest forestry asset.

This pretreatment method delivered:

(i) (almost) lignin-free cellulose that should be useful for enzyme-catalysed depolymerisation and fermentation

(ii) high quality lignin (a rare entity)

(iii) large amounts of modified monosaccharides.

During the optimisation, interesting questions were developed, and partially answered, on the reactivity of lignin with alcohols under acidic conditions. The monosaccharides from a variety of sources (including sitka spruce sawdust and rice husks) were purified. In one example, the purified monosaccharides were converted by another PhD student in the Westwood group to potential high added-value chemicals (fire follower molecules). A key reaction in this sequence was a highly selective Pd-catalysed oxidation. This reaction was studied further in the context of other possible sugar substrates.

There is significant interest in the use of modified lignin in materials applications. A first step towards the development of new lignin-based materials was made. This involved the development of a method to modify lignin using a metathesis reaction. Unfortunately, time ran out before it was possible to use this reaction to develop potential flame-retardant materials.

Meetings attended:

FALCON, 2021, online

IBioIC annual conferences and symposia 2022, 2023, 2024, Glasgow.

University of St Andrews, School of Chemistry symposium 2021, 2022, 2023.

SFT 40 years symposium, 2023, Stirling.

Scottish Science Advisory Council, 2023, online.

EUBCE, 2024, Marseille, France

 

Publications:

1. From Biomass to the Karrikins via Selective Catalytic Oxidation of Hemicellulose-Derived Butyl Xylosides and Glucosides, ejoc.202101308R2, Very Important Paper

First Author: Ganyuan Xiao

Co-Author: Gerard Su (provided data for Figures S31 and S32)

 

Poster Presentations:

1. Studies toward the depolymerisation of lignin^ox

Conference: EUBCE 2024, Marseille, France.

2. From Sitka spruce lignin to platform chemicals

Conference: IBioIC 2024, Glasgow, Scotland.

A large number of training events provided by IBioIC were attended.