No abstract

No abstract

Volatile C6- and C9-aldehydes and alcohols are widely used as food flavors to reconstitute the "fresh green" odor of fruits and vegetables lost during processing. To meet the high demand for natural flavors, an efficient, cheap, and versatile biocatalytic process was developed to produce C6-aldehydes on a large scale. Vegetable oils were converted by soybean lipoxygenase and recombinant hydroperoxide lyase into hexanal and (2E)- or (3Z)-hexenal. In contrast to plant extracts, generally used as enzyme sources, high molar conversions were obtained with recombinant hydroperoxide lyase (50% for hexanal and 26% for hexenal formation), and no side products were formed. Furthermore, recombinant hydroperoxide lyase lacks isomerase activity, allowing production of (3Z)-hexenal, which could not be obtained in previously described processes. Recombinant hydroperoxide lyase is stable and can be stored at 4 degrees C for 1 month without significant loss of activity.

No abstract

ooo9-2509/92 s5.cIo+o.m Printed in Great Britain. 01992FWgMlOIlRessLM A catalytically active membrane reactor for fast, exothemic, heterogeneously catalysed reactions AbstractA membrane reactor with separated feed of reactants is demonstrated as a promising contactor type when dealing with heterogeneously catalysed, very fast and exothermic gas phase reactions. Due to the separation of reactants a good control of the system is obtained, because process variables can be varied independently from each other. Transport of reactants is the rate governing process and because this is only slightly temperature dependent a thermal runaway will not occur. When dealing with e.g. combustion processes no explosive mixtures will build up and safety is increased.Based on the dusty-gas model, the concentration profiles of zomponents inside the membrane can be calculated together with the fluxes. However this is a calculation time consuming process and not necessary in all cases. In absence of a pressure drop and no slip of reactants to the opposite side a linearisation is possible leading to a simplified expression for the interfacial flux of a reactant and a criterion to evaluate the possibility of slip of reactants. Using the oxidation of carbon monoxide cata.lysed by platinum as a model reaction this approximation was experimentally verified by comparison of measured fluxes with the calculated results. Apart hrn flux measurements exploratory overall conversion measurements were carried out with the membrane reactor module in order to demonstrate its operation performance. From these studies it was concluded that conversion levels up to 90% carbon monoxide could easily be achieved. I. IntroductionRecently in our laboratory a catalytically active membrane reactor with separated feed of reactants was studied by Sloot with an extremely fast reversible reaction (Sloot et al., 1990). In this reactor the reactants were separated by a catalytically active membrane and owing to transport in the pores inside the membrane reaction proceeds. On studying the well-known Claus reaction. this principle was demonstrated to be very useful when dealing with reactions requiring strict stoechiometric feed of reactants. From numerical simulations Sloot showed that applying a pressure difference over the membrane, favours the tluxes while the products can be directed preferentially to one side of the membrane. Zaspalis (199la, 1991b) also used a catalytically active membrane in the NOx-reduction and methanol dehydrogenation reactions. He discussed different types of operation (e.g. premixed and separated feed) with respect to the influence on selectivity. Separated feed of reactants to the reactor offers advantages with respect to safety in case mixing of reactants is restricted to explosion boundaries. A second advantage is an improved controllability, because all process variables can be varied independently from each other. As the rate governing process is the tranport of reactants, thermal runaway will not occur when dealing with exothermal re...