Molasses Purification and Valorisation : Towards a sustainable production of hydroxymethylfurfural

Abstract: The industrial transition from petrochemical-based to a more sustainable and circular economy requires the utilisation of renewable biobased raw materials that do not compete with other important industries, such as the food sector, preferably wastes or low value by-products. 5-hydroxymethylfurfural (HMF) is a versatile platform chemical that has great potential for utilisation in various sectors in a future bioeconomy, as it can be produced from sugars. In this thesis, sugar beet molasses was assessed for the production of HMF. This dark, highly viscous and impure by-product, but yet with a high content of sucrose, could first be hydrolysed using yeast into glucose and fructose, followed by a biphasic and acid-catalysed dehydration step to produce HMF. The challenge is to handle the impurities of the molasses and the by-products that are formed during the dehydration reaction. Hence, separation and purification processes are required. Initially, membrane filtration was tested and evaluated for the purification of molasses, and its impact on the hydrolysis and dehydration steps was determined. It was found that ultrafiltration of the molasses has a positive impact on the dehydration step with regards to increased conversion of fructose compared to crude molasses. Simultaneously, it also yielded in a higher product selectivity compared to the control sample consisting of a pure sucrose solution. This could possibly be due to the higher salt content in molasses compared to pure sucrose, which can aid the partitioning of HMF to the organic solvent. The reaction rate of the enzymatic hydrolysis was unfortunately not improved by membrane filtration. However, there is a significant difference in productivity between hydrolysis of sucrose in molasses compared to a pure sucrose solution. Results from this study revealed that viscosity, salt concentration and a synergistic effect of ions present in the molasses are the main reasons. Secondly, by-products from the dehydration step could be removed through adsorption using granular activated carbon in order to purify the HMF product. The HMF was thereafter recovered by an evaporation step. The organic solvent was condensed and could successfully be reused for either extracting more HMF from the aqueous phase to obtain more HMF and increase the overall process yield or being recycled for another dehydration reaction. The conclusion from this study is that it is possible to produce HMF from sugar beet molasses, but it requires additional separation and purification steps and further development to be efficient and economically competitive.