This paper provides an overview of work on an integrated biorefinery concept for the conversion of Sugar Beet Pulp (SBP) into a range of value-added product streams. Over 8 million tonnes of sugar beet are grown annually in the UK. SBP is the main by-product of sugar beet processing which is currently dried and sold as a low value animal feed. SBP is a rich source of carbohydrates mainly in the form of cellulose and pectin; the major components being D-glucose (25%, Glu), L-arabinose (21%, Ara), D-galacturonic acid (20%, GalAc), D-galactose (6%, Gal). The challenge for integrated biorefinery design is to ensure complete utilization of the SBP substrate. In this work we will demonstrate new processes for SBP fractionation, recovery/purification of the released monosaccharides and biosynthetic routes to bioethanol and a range of aminopolyols. SBP fractionation was carried out by steam explosion yielding soluble pectin and insoluble cellulose fractions. The cellulosic fraction can be enzymatically hydrolysed to Glu and used for yeast-based bioethanol production at close to theoretical yield. The pectin fraction can then be either fully hydrolysed using physico-chemical methods or selectively hydrolysed using novel arabinases and galacturonases, yielding Ara-rich and GalAc-rich streams. In order to implement and scale-up the physico-chemical route we have established a continuous process for monomer fractionation based upon Centrifugal Partition Chromatography (CPC). This yields suitably pure and enriched Ara and GalAc fractions for subsequent conversion. To implement the selective enzymatic route we have established a continuous, two-step, enzyme-membrane reactor cascade that also yields Ara-rich and GalAc-rich streams suitable for subsequent conversion. Finally, biosynthetic routes for the production of aminopolyols from Ara and GalAc have been established based on the use of evolved transketolase (TK) and omega-transaminase (TAm) enzymes in engineered host organisms such as E. coli. The synthetic products have application for the production of pharmaceutical intermediates or can be polymerised to form biological polymers. Current work is modelling the various process routes to establish the most economically viable route and quantify key Life Cycle Analysis (LCA) metrics.

Integrated biorefinery concept for conversion of sugar beet pulp into fuels and value-added chemicals

256th National Meeting (2018)

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