José M. Gómez

Enzymatic synthesis of short-chain esters in n-hexane and supercritical carbon dioxide: Effect of the acid chain length

Enzymatic synthesis is the preferred way to produce so‐called “natural products.” Hydrolases have been used for short‐chain ester synthesis. These esters present a pleasant flavor and they have a lot of applications in different industries. Novozym 435 from Candida antarctica (EC 3.1.1.3, triacylglycerol lipase) was used for hexyl ester synthesis in n‐hexane and supercritical carbon dioxide (SCCO2). Direct esterification provided higher yields than transesterification for the synthesis of esters. Several carboxylic acids of different chain lengths were tested for the esterification reactions: acetic, propionic, butyric, caproic and caprylic acids. The reactions were carried out at 40°C and the amount of enzyme used was 13.8 g/mol alcohol. Substrates were added at equimolar concentrations, with sufficient stirring to avoid external diffusion control. Different substrate concentrations up to 1.5 M were used. The working pressure was 14 MPa in the case of SCCO2 and atmospheric pressure in the case of organic solvent. The results in both solvents show that the reaction rate increases with the chain length of the acid, but the final yields were similar. However, some of the reactions prove to be faster in SCCO2, except for hexyl acetate and propionate synthesis, in which acetic and propionic acid presented a lower solubility in SCCO2 due to its high polarity. Moreover, an acetic acid concentration of 1.5 M brought about a strong inhibition of the enzyme activity.

Adsorption of trypsin on commercial silica gel

The immobilization of trypsin onto various commercial silica gels was studied. Silica gels were used directly and characterized by mercuric porosimetry. Agitation rates (100–740 rpm) and particles size (35–75 to 250–500 μm) of silica gels did not affect the trypsin immobilization capacity. The pore size (3 to 15 nm) is a limiting factor of the trypsin adsorption onto the mesopores structure of silica gels. The adsorption of trypsin was determined as a function of their initial concentration and multilayer formed at high trypsin concentration.

18-P-11 - Dibenzothiophene adsorption over zeolites with faujasite structure

Publisher Summary This chapter presents the adsorption of dibenzothiophene (DBT) over FAU zeolites exchanged with alkali cations. Cristallinity, exchange level, and basic properties of different adsorbents used have been determined. The influence of silicon/aluminum (Si/Al) molar ratio and type of cation exchanged in the zeolite as well as the presence of toluene in feedstock mixture on DBT adsorption capacity and selectivity of adsorbent has also been determined. Thermogravimetric analysis show a stronger DBT adsorption over X zeolites.

Estimation of Adsorption Parameters from Temperature-programmed Desorption Thermograms: Application to the Adsorption of Carbon Dioxide onto Alumina

In this work, a model is proposed for estimating the desorption activation energy from a TPD thermogram. The model considers the effects of diffusional resistance, the reactor cell volume, the sample weight and the carrier gas flow rate. The adsorption and desorption rate constants are estimated using theoretical expressions deduced from statistical thermodynamics, assuming first-order desorption kinetics. This model has been applied to the CO2/activated alumina system. The TPD thermogram has been obtained with a commercial apparatus, and the distribution of the desorption activation energy has been analyzed. A sensitivity analysis has been performed to determine the importance of different phenomena which can alter the position of the TPD peaks (re-adsorption, diffusional resistance, volume of sample cell). An experimental study of the effect of diffusional resistance has also been performed, comparing the TPD thermograms obtained with powdered and pelletized alumina. The experimental results have been compared with the model predictions.