Mads Mørk Jensen has conducted his Ph.D. thesis in BioValue’s project 6. Below is a short summary of his findings and information on the defense.


PhD title: Characterization of lignin and products from conversion of lignocellulose by hydrothermal liquefaction and other biorefinery technologies.

Today, chemicals are primarily derived from fossil carbon, and its environmental effects and depletion have generated research in finding sustainable alternatives to petrochemicals. Lignocellulosic byproducts are candidates for conversion into sustainable chemicals. Lignin is a phenolic polymer in lignocellulosic biomass and is an abundant renewable source of aromatics. Hydrothermal liquefaction (HTL) utilizes unique reaction conditions of superheated water for conversion of biomass. Alkaline HTL of lignin produces an aqueous product and a solid residue. The aqueous product is a complex mixture of monomeric and polymeric compounds, which can be used for further processing into e.g. materials. However, optimizing HTL is hindered by unresolved reaction pathways and limited characterization of lignin feedstock and products.

The experimental work reported in this thesis was aimed at providing detailed characterization of the chemical structures in all product fractions from alkaline HTL of lignin. Extensive qualitative and quantitative analyses of monomeric products were performed to provide additional information about lignin reactions and the potential value of this product fraction. Polymer products were qualitatively characterized in order to elucidate their structure and the reactions that result in their production.

The monomers represent up to 20% of the products, and here, the monomers from HTL of lignin were extensively quantified. Gas chromatography coupled to mass spectrometry (GC-MS) with trimethylsilyl derivatization was demonstrated as suitable for quantification of monomers in the product from lignin-rich feedstocks subjected to HTL. The product mixture was found to contain about 20 major monomer products and more than 100 minor monomer products.

Biomass needs pretreatment to expose the carbohydrates prior to conversion into bioethanol, and the bioethanol production produce a lignin-rich enzymatic hydrolysis residue (EnzHR). Increased severity of pretreatment results in changes of the chemical structure of lignin in the EnzHR. HTL was performed on EnzHR from biomass hydrothermally pretreated at two industrially relevant severity levels. It showed that both Miscanthus and wheat straw lignins were more effectively depolymerized by HTL, if the biomass was pretreated at a lower severity rather than a higher severity.

Most of the lignin HTL products are oligomers and polymers. Their structure and the reactions that result in their production are poorly understood. Characterization of these products was performed by analytical pyrolysis coupled to GC-MS. The results showed highly altered structures compared to the unconverted lignin. The observations indicate that the polymer products are not unconverted lignin; instead, a major contributor to production of polymers during HTL could be condensation reactions of aldehydes and phenols after initial depolymerization. The results showed that the repolymerization could potentially be reduced by performing HTL of lignin in the presence of protein, where ammonia from protein deplete aldehydes through reaction to imines.

This PhD project has provided increased knowledge about lignin HTL and about interdependency of lignocellulosic conversion processes, which makes this work especially relevant for evaluation of lignin valorization in combination with cellulose biorefining.

We hope that you will participate at Mads’ defense:

Time: Friday 13 April 2018 at 13.00

Place: Building 1514, room 213, Auditorium I, Department of Chemistry, Aarhus University, Langelandsgade 140, 8000 Aarhus C

Main supervisor: Associate Professor Marianne Glasius, iNANO and Department of Chemistry, Aarhus University

Contact information: Mads Mørk Jensen, e-mail: madsmj@chem.au.dk

Defense title: Characterization of lignin and products from conversion of lignocellulose by hydrothermal liquefaction and other biorefinery technologies