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[Display omitted] • Characterization of the enzyme preparation Ecopulp® TX-800 A. • Immobilization of Ecopulp® TX-800 A on uncoated metallic hollow spheres. • Combination of covalent bonds and cross-linking of enzymes by glutaraldehyde (GDA). • Improvement of long-term stability (reduction of thermal ageing) of the xylanases. • Successful use in differential circulation reactor for hydrolysis of xylan. The increasing demand for and the necessity of using sustainable resources require the further development of alternative technologies. The project "CrossCat - Symbiosis of bio- & chemo-catalysts for the sustainable conversion of hemicelluloses" deals with the utilization of the hemicellulose fraction, especially xylan. In an example process for combining of biological and chemical catalysts in a one-pot process, xylan shall first be hydrolyzed to xylose and then hydrogenated to xylitol. To make this possible, suitable immobilization of the xylanases is required. For this purpose, the xylanases were immobilized covalently using glutaraldehyde (GDA) on various carrier materials with and without surface functionalization and activation. Immobilization on uncoated stainless steel hollow spheres with simultaneous covalent binding to the surface and cross-linking of the enzymes was most suitable for later use. The produced immobilizates showed an increased long-term stability (57 % residual activity after 24 h) compared to free enzymes (8 %) and could be used for several days (4–6 d) for the hydrolysis of xylan to xylose. [ABSTRACT FROM AUTHOR]

[Display omitted] • Novel one-pot process for conversion of xylan to xylitol. • Successful combination of xylanase mixtures and Ru/C catalyst. • Experimental studies on multi-step process. • Xylitol production of up to 80 % yield. A novel hybrid process for the conversion of xylan via hydrolytic hydrogenation achieved a xylitol yield of up to 65 %. As part of this study, the hypothesis of decreased product (xylose) inhibition of enzymes during xylan hydrolysis due to rapid conversion of xylose to xylitol was investigated experimentally. We found that xylose inhibition can play an important part in the reaction kinetics of xylan hydrolysis with commercially available enzymes. For example, at 10 wt.-% xylose concentration, the activity of enzymes dropped by ca. 80 %. In contrast, the final desired product xylitol showed only a slight inhibitory effect of about 20 % activity loss of the enzymes. The one-pot process of hydrolytic hydrogenation requires enzyme stability at higher-than-optimal temperatures and pressures, to ensure their activity at harsher process conditions needed for the chemo-catalytic hydrogenation. Therefore enzyme activity was tested at elevated temperatures and pressures. The tests were carried out with two enzyme mixtures (Ecopulp TX-800 A and Alkozym CPX). Both showed no activity loss over 60 min exposure time at pressures of up to 40 bar. However, their thermal resistance differs strongly, with Alkozym already deactivating at 50 °C, while Ecopulp remained mostly active at up to 80 °C. The novel sequential process (4 consecutive steps) achieved a xylitol yield of up to 65 % with almost 80 % xylan conversion. Our findings show both limitations and potential benefits of hybrid processes which try to exploit both biological and chemical catalysis. This type of combined catalysis for reaction cascades could further accelerate the ongoing research in process development for catalytic biorefineries. [ABSTRACT FROM AUTHOR]