Lipase-catalyzed esterification of stearic acid with ethanol, and hydrolysis of ethyl stearate, near the critical point in supercritical carbon dioxide

Optimization of the catalytic production of methyl stearate by applying response surface Box-Behnken design: an intensified green option for high-cetane biofuel manufacture

To enhance the efficiency of processes by decreasing the reaction severity and energy consumption, and reducing the equipment size, facilities' space and operation cost, process intensification is an increasingly used option in the chemical industry. Within this framework and in agreement with some of the green chemistry principles (design for energy efficiency and use of renewable feedstocks), this work deals with the implementation of high-shear mixing (HSM) to intensify the homogeneous esterification of stearic acid (SA) with methanol to methyl stearate, a high-cetane number alkyl ester suitable to be added into biofuel streams. The response surface Box-Behnken design (BBD) is applied to quantify the main effects and two-way interactions of four key input reaction factors: methanol : SA ratio (7-16 mol mol-1), catalyst mass (0.25-4.0 wt%), temperature (40-60 °C), time (1-12 min), and to approximate the optimal conditions on the intensified SA esterification. The statistical BBD results indicates that the four linear effects, two of the four possible quadratic effects (catalyst mass and temperature) and only one (catalyst mass-time) of the six existing two-way interactions are statistically relevant at the 95% confidence level. Catalyst mass is the most influencing factor in the reaction, followed by methanol : SA ratio, temperature, and time. The proposed second-order regression model predicts that the intensified esterification requires only 12 min to practically convert all SA (99% ± 6.8%) running the reaction at 12.4 methanol : SA ratio, 4 wt% catalyst mass, 60 °C and 500 rpm, a value experimentally validated (93.2% ± 0.7%). Under these conditions and with the assistance of HSM, the typical reaction length of conventional heterogeneous and homogeneous-phase esterification processes decreases from 5 to 117 and 35 to 90 times, respectively.

CO2 -Enabled Biomass Fractionation/Depolymerization: A Highly Versatile Pre-Step for Downstream Processing

Lignocellulosic biomass is inevitably subject to fractionation and depolymerization processes for enhanced selectivity toward specific products, in most cases prior to catalytic upgrading of the three main fractions-cellulose, hemicellulose, and lignin. Among the developed pretreatment techniques, CO₂ -assisted biomass processing exhibits some unique advantages such as the lowest critical temperature (31.0 °C) with moderate critical pressure, low cost, nontoxicity, nonflammability, ready availability, and the addition of acidity, alongside easy recovery by pressure release. This Review showcases progress in the study of sub- or supercritical CO₂ -mediated thermal processing of lignocellulosic biomass-the key pre-step for downstream conversion processes. The auxo-action of CO₂ in biomass pretreatment and fractionation, along with the involved variables, direct degradation of untreated biomass in CO₂ by gasification, pyrolysis, and liquefaction with relevant conversion mechanisms, and CO₂ -enabled depolymerization of lignocellulosic fractions with representative reaction pathways are summarized. Moreover, future prospects for the practical application of CO₂ -assisted up- and downstream biomass-to-bioproduct conversion are also briefly discussed.

Plant products for pharmacology: application of enzymes in their transformations

Different plant products have been subjected to detailed investigations due to their increasing importance for improving human health. Plants are sources of many groups of natural products, of which large number of new compounds has already displayed their high impact in human medicine. This review deals with the natural products which may be found dissolved in lipid phase (phytosterols, vitamins etc.). Often subsequent convenient transformation of natural products may further improve the pharmacological properties of new potential medicaments based on natural products. To respect basic principles of sustainable and green procedures, enzymes are often employed as efficient natural catalysts in such plant product transformations. Transformations of lipids and other natural products under the conditions of enzyme catalysis show increasing importance in environmentally safe and sustainable production of pharmacologically important compounds. In this review, attention is focused on lipases, efficient and convenient biocatalysts for the enantio- and regioselective formation / hydrolysis of ester bond in a wide variety of both natural and unnatural substrates, including plant products, eg. plant oils and other natural lipid phase compounds. The application of enzymes for preparation of acylglycerols and transformation of other natural products provides big advantage in comparison with employing of conventional chemical methods: Increased selectivity, higher product purity and quality, energy conservation, elimination of heavy metal catalysts, and sustainability of the employed processes, which are catalyzed by enzymes. Two general procedures are used in the transformation of lipid-like natural products: (a) Hydrolysis/alcoholysis of triacylglycerols and (b) esterification of glycerol. The reactions can be performed under conventional conditions or in supercritical fluids/ionic liquids. Enzyme-catalyzed reactions in supercritical fluids combine the advantages of biocatalysts (substrate specificity under mild reaction conditions) and supercritical fluids (high mass-transfer rate, easy separation of reaction products from the solvent, environmental benefits based on excluding organic solvents from the production process).