Development of a sustainable process for the selective catalytic conversion of biogenic humin-model substrates and biomass-derived humins to carboxylic acids by the help of tailor-made polyoxometalate catalysts

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Humins are dark polymeric solids that occur inevitably in numerous processes where biomass is transformed to platform chemicals by acid catalysis. They are only soluble in strong bases and so far not suitable for large-scale applications. The detailed structure and formation mechanism are commonly not known, whereby the scientific investigations are restricted to the avoidance or minimization of humin formation in the designated process. Due to their kinetics this is mostly not possible.By the implementation of new chemical valorization pathways for humins that are formed during levulinic acid or HMF synthesis, more added value can be created from biomass conversion processes. Based on the first very promising preliminary work on catalytic oxidation of humins to low-molecular organic acids (formic acid, acetic acid) by the help of homogeneous polyoxometalate catalysts in aqueous media, it is the overall objective of the project to gain a fundamental understanding of these completely new low-temperature conversion of humins to carboxylic acids, especially in the light of a technical implementation by performing kinetic investigations.Therefore, investigations concerning the structure-activity relationships in humin model substrates will be carried out. Moreover, specific adjustment of catalyst properties and process conditions for the selective oxidation of model substrates with humin-type structural features allows for tuning of the product selectivity. Reaction kinetics and transport phenomena will be determined by performing kinetic investigations. Furthermore, mechanistic studies for the textural transferability of the findings with model substrates to real humins as well as recyclability studies of the used catalysts and investigations with respect to the product isolation will be carried out. Finally, the integration of all findings will result in a continuous miniplant operation.