Catalysis of Organic..

42Monolithic BioreactorMenten equation, the observed reaction rate was calculated assuming a mass transferlimited regime in the substrate concentration range 0.1-0.2 g/l.Activity [10 -4 mmol/l*s]654321Figure 5. Effect ofstirrer rate on trypsinactivity in the hydrolysisof BAEE at under themass transfer limitedconditions at 308 K.00 50 100 150Stirrer rate [rpm]From these results, the effective mass transfer coefficient k s [s -1 ] can becalculated and was found to vary from 8*10 -6 m/s (10 rpm) to 1.2*10 -5 m/s (40 rpm).Around 100 rpm, the system enters the kinetically limited regime (Ca=0.05). Theseresults show that immobilized trypsin is very active and useful for determining masstransfer rates for liquid solid systems.In summary, it can be concluded that the monolithic stirrer reactor is aconvenient reactor type both for the laboratory and the production plant. It is userfriendlyand can be used to compare different catalysts in the kinetically limitedregime or hydrodynamic behavior in the mass transfer controlled regime. Stirrers ormonolith samples can be easily exchanged and reloaded to suit the desired enzymeand/or reaction conditions.Experimental SectionSucrose-based carbon carriers were prepared following the method of (7). Monolithswere coated with a 65% sucrose solution in water, followed by horizontal drying andcarbonization for two hours at 823 K in a horizontal furnace under H 2 . Polyfurfurylalcohol (PFA) based carbon coatings were prepared (8) by coating with PFAsolution. Carbonization was performed in a horizontal furnace at 823 K under Ar for2 h. Carbon nanofibers (CNFs) were prepared by washcoating the monolithicsupports with a silica layer (9). Ni was deposited on the support by homogeneousdeposition precipitation at 353 K from a 0.5 M aqueous urea solution (10). Afterreduction under H 2 for 1 h at 823 K, carbon nanofibers were grown at 823 K undermethane and H 2 in N 2 . Polyethylenimine-functionalized supports were prepared (11)via a direct coupling through (3-glycidoxypropyl)trimethoxysilane (GPTMS). Themonoliths were washcoated with a colloidal silica layer, followed by reaction atroom temperature for 24 h in a 5wt% solution of silane in toluene, containing 0.1%v/v triethylamine. The polymer was attached from a 10 wt% PEI solution in water(pH 10) under ambient conditions for 24 h. Chitosan coatings were applied by