The role of water on the equilibrium of esterification by immobilized lipase packed-bed column reactor
SummaryThe role of water on the continous synthesis of geranyl esters by immobilized lipase fromHumicola lanuginosa No. 3 was studied in a packed-bed column reactor (PBR) installed with a molecular sieve column for water extraction. The conversion degress by PBR were highly influenced by the water concentration throughout the reaction which acted as a determinant on the reaction equilibrium. Almost 100% conversion of geranyl laurate could be achieved under the optimum water-controlled conditions. The stability of the PBR system was for 35 days with the half-life of 38 days.
Optimized synthesis of (Z)-3-hexen-1-yl caproate using germinated rapeseed lipase in organic solvent
Abstract (Z)-3-hexen-1-yl esters are important green top-note components of food flavors and fragrances. Effects of various process conditions on (Z)-3-hexen-1-yl caproate synthesis employing germinated rapeseed lipase acetone powder in organic solvent were investigated. Rapeseed lipase catalyzed ester formation more efficiently with non-polar compared to polar solvents despite high enzyme stability in both types of solvents. Maximum ester yield (90%) was obtained when 0.125 M (Z)-3-hexen-1-ol and caproic acid were reacted at 25 °C for 48 h in the presence of 50 g/L enzyme in heptane. Enzyme showed little sensitivity towards a w with optimum yield at 0.45, while added water did not affect ester yield. Esterification reduced by increasing molecular sieves (>0.0125%, w/v). The highest yields of caproic acid were obtained with isoamyl alcohol (93%) followed by butanol and (Z)-3-hexen-1-o1 (88%) respectively reflecting the enzyme specificity for straight and branched chain alcohols. Secondary alcohols showed low reactivity, while tertiary alcohol had either very low reactivity or not esterified at all. A good relationship has been found between ester synthesis and the solvent polarity (log  P value); while no correlation for the effect of solvents on residual enzyme activity was observed. It may be concluded that germinated rapeseed lipase is a promising biocatalyst for the synthesis of valuable green flavor note compound. The enzyme also showed a wide range of temperature stability (5–50 °C).
Impact of Nuclear Data Uncertainties on Transmutation of Actinides in Accelerator-Driven Assemblies
Abstract The potential impact of nuclear data uncertainties on a large number of performance parameters of reactor cores dedicated to the transmutation of radioactive wastes is discussed. An uncertainty analysis has been performed based on sensitivity theory, which underlines the cross sections, the energy range, and the isotopes that are responsible for the most significant uncertainties. To provide guidelines on priorities for new evaluations or validation experiments, required accuracies on specific nuclear data have been derived, accounting for target accuracies on major design parameters. The required accuracies (mostly in the energy region below 20 MeV), in particular for minor actinide data, are of the same order of magnitude of the achieved accuracies on major actinides. Specific requirements also concern the improvement of minor actinide data related to decay heat and effective delayed-neutron fraction assessment.