Sugat Raymahasay

Studies on the hydrogenation of cinnamaldehyde over Pd/C catalysts†

The hydrogenation of cinnamaldehyde was investigated using a 5% Pd/C catalyst in a 250 cm3 stirred tank reactor and 500 cm3 autoclave. The experiments were carried out at 273–343 K and 0·1–1·1 MPa. Non-polar solvents, e.g. toluene, decane, methylcyclohexane, decalin, ether and heptane, and polar solvents such as methanol, ethanol, propan-1-o1, propan-2-ol, butan-1-ol and butan-2-ol were used to study the selectivity with respect to hydrocinnamaldehyde formation, the reaction kinetics and mass transfer. The additives, such as potassium acetate, ferrous chloride, ferrous sulphate and quinoline were incorporated into the catalyst in order to improve the catalyst selectivity, which was observed especially in the case of potassium acetate.

Production of β-D-glucosidase, endo-1,4-β-D-glucanase and D-xylanase from straw by Aspergillus fumigatus IMI 255091

Aspergillus fumigatus IMI 255091 has been found to grow well on ground straw as the principal substrate, Production of β - d -glucosidase ( β - d -glucoside glucohydrolase, EC 3.2.1.21), endo-1,4- β - d -glucanase [1,4-(1,3;1,4)- β - d -glucan 4-glucanohydrolase, EC 3.2.1.4] and d -xylanase (1,4- β - d -xylan xylanohydrolase, EC 3.2.1.8) was maximal within 7 days with 4% (w/v) straw. Comparisons were made with both a conventional agitated fermenter and an air-lift fermenter. The latter gave the highest yields. The β - d -glucosidase was partially purified by fractionation and its K m determined. This was found to differ from that of other β - d -glucosidases reported in the literature.

The cocurrent downflow contactor (CDC) reactor : chemically enhanced mass transfer & reaction studies for slurry & fixed bed catalytic hydrogenation

Abstract The CDC has been shown to be a mass transfer device of high efficiency (100% gas utilization, 97% approach to equilibrium) giving overall mass transfer coefficient (k L a) which are very high (0.2–1.5 s −1 for O 2 /H 2 O) and when used as a slurry reactor for the catalytic hydrogenation of various unsaturated compounds, the reactions were shown to be mostly surface reaction rate controlled. The larger values of k L a are due mainly to be high interfacial area generated (1000–6000 m 2 .m −3 fluid for 50% gas hold-up). These results, which were obtained using physical measurements have been confirmed using the SO 3 2− oxidation method. The CDC has been employed as a slurry reactor with and without added tangentail flow (swirl flow) for (i) itaconic acid hydrogenation (ii) rape seed oil hydrogenation and (iii) as a fixed bed reactor for itaconic acid and soybean oil hydrogenated using palladium and nickel catalysts. Due to the large values of k L a, all the reactions were operated under largely surface reaction controlled conditions and hydrogenation of triglycerides was observed to occur with greater selectivity than in stirred reactors. Use of swirl flow further enhanced mass transfer and reaction rate.

A comparison of triglyceride oil hydrogenation in a downflow bubble column using slurry and fixed bed catalysts

The hydrogenation of the triglyceride oil, soya bean oil, has been studied in the temperature range 130–160 °C and in the pressure range 100–600 kPa using (i) a 5% w/w Pd/C slurry catalyst and (ii) a 3% w/w Pd/Al2O3 Raschig ring catalyst in a cocurrent downflow contactor (CDC) reactor. Separate studies of residence time distribution (RTD) were carried out in a modified CDC device in order to determine dispersion numbers and dispersion coefficients. The RTD measurements indicated that the overall flow was a mixture of well-mixed and plug flow for the unpacked CDC, so that the entry section (0–30 cm from entrance) was perfectly mixed and the remainder of the column (30–130 cm) gave predominantly plug flow behaviour. The introduction of random packing in the form of 13 mm Raschig rings gave rise to increased back mixing in the lower part of the CDC and the overall dispersion number increased due to liquid and gas circulation around the packing elements. Kinetic studies revealed an initial rate reaction order of 1.24–1.26 with respect to hydrogen concentration both in slurry and fixed bed CDC reactors and is interpreted as a combination of a parallel pair of first and second order reactions during the initial stages of reaction. Mass transfer coefficients for gas absorption (kLa) and liquid–solid mass transport (ks) were determined for both types of reactor. The kLa values lay in the range 1.0–3.33 s−1 and the liquid–solid transport resistances (XLS) were all <1%, so that the reaction was almost totally surface reaction rate controlled. Apparent energy of activation measurements gave values of EA = 49 ± 6 kJ mol−1, which is strongly indicative of surface reaction rate control involving the hydrogenation of an olefinic double bond. The selectivity in respect of linolenate (three double bonds) removal and linoleate (two double bonds) retention was high with, for palladium, relatively low trans-isomer production (<30%). The overall selectivity was slightly, but significantly, better for the fixed bed CDC reactor and this is attributed to the greater degree of plug flow behaviour in the latter, despite the bed causing an increase in dispersion number. However, there is no reaction in the well-mixed section of the fixed bed CDC reactor as there is in the slurry CDC reactor and this is likely to improve selectivity in a consecutive reaction sequence. © 2000 Society of Chemical Industry

Inhibitor of β-d-glucosidase and endo-1,4-β-d-glucanase produced by Aspergillus fumigatus IMI 255091

Abstract Inconsistencies in assays of fermentation broths of Aspergillus fumigatus IMI 255091 were observed for endo-1,4-β- d -glucanase [1,4-(1,3;1,4)-β- d -glucan 4-glucanohydrolase, EC 3.2.1.4] and β- d -glucosidase (β- d -glucoside glucohydrolase, EC 3.2.1.21). Dilution of the original sample appeared to enhance activity. These enzymes were apparently not adsorbed by sintered microporous inorganic spheroids specially fabricated for protein adsorption. The adsorbents removed other proteins, including material shown to be of low molecular weight and assumed to be an inhibitor, permitting considerably enhanced activity.