Farm to furan derivatives : Fractionation of agricultural residues and transformation of sugars to chemical building blocks

Sammanfattning: The transition of industrial production from petrochemistry to a more sustainable economy requires the use of carbon neutral, renewable feedstock, which does not compete with food and feed supplies – by-products of farming and agro-food industry offer this possibility. With a limited range of low-value applications today coupled with the need for maximal utilisation of resources, the by-products of farming can be repurposed as feedstock for biorefineries. The challenge, however, is to develop sustainable and scalable processes and systems whose benefits must outweigh the costs of implementation. The research performed within the framework of this thesis involves investigations on fractionation of the complex agriculture residual biomass into different streams for further valorisation, and transformation of sugar and sugar derived furan to valuable building blocks for chemicals and materials. Sugar beet pulp and wheat bran are amongst the main agricultural residues in Sweden, generated as by-products of manufacture of sugar and wheat flour, respectively. Fractionation of beet pulp by a three-stage process comprising treatment with weak mineral acid, pectinases and cellulases, resulted in streams enriched in arabinose, galacturonic acid and glucose, respectively. A preliminary techno-economic assessment of the process together with conceptual valorisation of the sugars to arabitol, mucic acid and levulinic acid, respectively, revealed potential viability. In the case of wheat bran, a sequential fractionation involving starch- and protein hydrolysis, steam explosion for hemicellulose breakdown, hydrotropic extraction for release of lignin, and cellulose hydrolysis was tested to release separate streams originating from the different components of bran.Levulinic acid (LA) is a five-carbon bifunctional chemical with ketone and carboxylic acid originating from C6 sugars in the biomass via 5-hydroxymethylfurfural (5-HMF). LA was directly produced with >70% yield from high concentrations of fructose and glucose, respectively, by heterogeneous catalytic dehydration using a strong cation exchange resin in the presence of salt. The study showed that the salts enhanced the rate of dehydration in the order of Cl->CO32->SO42-. Carboligation of 5-HMF, using whole cells of Escherichia coli bearing recombinant benzaldehyde lyase, led to a rapid formation of the C12 product, 5,5’-bis(hydroxymethyl)furoin (DHMF) at high yields. DHMF was further converted in situ by subsequent oxidation to 5,5’-bis(hydroxymethyl)furil (BHMF). The reaction performed in a fed-batch mode resulted in 53 g/L of DHMF in 5 hours by feeding 20 g/L 5-HMF every hour. The products were analysed for their potential as crosslinkers in coatings by reaction with adipic acid hydrazide to form hydrazones. The thesis lays ground for further optimisation, scale up, techno-economic and life cycle assessments of biomass fractionation and production of building blocks for a low carbon economy.

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