Charles G. Hill

Kinetics and mechanisms of reactions catalysed by immobilized lipases

This review focuses on the kinetics and mechanisms of reactions catalysed by immobilized lipases. The effects of pH, temperature, and various substances on the catalytic properties of immobilized lipases and on the processes by which they are deactivated are reviewed and discussed.

Use of Candida rugosa lipase immobilized in a spiral wound membrane reactor for the hydrolysis of milkfat

Lipase from C. rugosa was immobilized by adsorption on flat sheets made of microporous polypropylene and placed into a reactor in a spiral wound (axial-annular flow) configuration. Equations based on a Ping Pong Bi Bi kinetic mechanism are used to model the effect of the water content of the feed emulsion on the rate of hydrolysis of milkfat triglycerides. The kinetic data are consistent with a mechanism which assumes that deacylation of the enzyme is the rate-limiting step of the hydrolysis reaction. The optimum pH for hydrolysis is ca. 7.0. Operation of the reactor yielded relatively high conversions at short space times, thus indicating that this type of reactor is an interesting option for use on an industrial scale for the production of lipolysed butteroil.

Acidic properties of molybdena-alumina for different extents of reduction: Infrared and gravimetric studies of adsorbed pyridine

Abstract Infrared spectroscopy and thermogravimetric studies of adsorbed pyridine, combined with volumetric reduction/oxidation measurements, were used to investigate the acidic properties of molybdena-alumina samples reduced to different extents in hydrogen at 670 K. Pyridine was adsorbed at 420 K and studied after evacuation at progressively higher temperatures ranging from 370 to 670 K. The average molybdenum oxidation state was varied from +6 to +4.7, as monitored by measuring the consumption of hydrogen and the formation of water during reduction and the consumption of oxygen during reoxidation. Infrared spectra of adsorbed pyridine showed the presence of Bronsted acid sites and two types of Lewis acid sites on oxidized molybdena-alumina. The number of Bronsted acid sites increased at low extents of reduction (e.g., an average Mo oxidation state of +5.6) and decreased to zero with further reduction. The Lewis acidity also passed through a maximum with extent of reduction but was not eliminated with reduction. These results are explained by the accepted model for molybdena-alumina in which the surface of alumina is populated with small molybdena clusters. It is proposed that the electronegativity of alumina is altered in the vicinity of these molybdena clusters, thereby altering the acidic properties.

Raman spectroscopy of iron molybdate catalyst systems:: Part I. Preparation of unsupported catalysts

Abstract Iron molybdates (mixed oxides of iron and molybdenum) are used to effect the partial oxidation of methanol to formaldehyde. In the present work, Raman spectroscopy was used to characterize supported mixed iron/molybdenum oxide catalysts. These supported catalysts were prepared by impregnation of silica and alumina with solutions of ferric nitrate and ammonium molybdate. The Raman spectroscopic studies were employed to obtain information about the influence of variations in the preparation protocol on the properties of the final catalysts. The spectra were indicative of surface enrichment of one species [(MoO3 or Fe2(MoO4)3)] and also provided evidence for catalyst-support interactions.

Immobilization of pregastric esterases in a hollow fiber reactor for continuous production of lipolysed butteroil

Lingual Upases from calf, lamb and goal were semi-purified by cold storage and microfiltralion, and subsequently immobilized by physical adsorption on hollow fibers fabricated of microporous polypropylene. The immobilized lipases were employed in a hollow fiber membrane reactor to effect the continuous hydrolysis of a butterfat fraction that remains liquid at 18°C. The goat lipase showed higher lipolytic activity than the other two, but all three enzymes had good selectivilies for short-chain fatty acids. No deactivalion was observed for any of the immobilized enzymes during 5 d of continuous operation. A process based on this technology offers a number of advantages for the commercial production of lipolysed butteroil.

Raman spectroscopy of iron molybdate catalyst systems: Part III. IN SITU studies of supported and bulk catalysts under reaction and redox conditions

Abstract Raman spectra of both supported and unsupported Fe/Mo/O catalysts of the type used for the partial oxidation of methanol to formaldehyde were obtained while this reaction was proceeding over the catalyst surface. No changes in band locations or relative peak intensities associated with these mixed metal oxides were detected in the presence of reactant and product species. Moreover, no spectral features which could be attributed to adsorbed species could be detected under reaction conditions. Band intensities in the Raman spectra were related to the extent to which the catalysts were reduced; fully oxidized catalysts were stronger Raman scatterers than partially reduced catalysts. Although differences in color were noted between fresh and used catalysts, the Raman and Mossbauer spectra of these catalysts were identical. Calcination of used catalysts in an oxygen environment at 500 °C was sufficient to restore partially reduced catalysts to their original fully oxidized states.

Lipase‐catalyzed interesterification (acidolysis) of corn oil and conjugated linoleic acid in organic solvents

Abstract Lipase mediated interesterification of acylglycerols from corn oil with conjugated linoleic acid (CLA) was studied in several organic solvents. Two commercially available lipases, IM‐60 from Mucor miehei and Chirazyme L‐2 from Candida antarctica brought about greatest extents of interesterification. Hexane was the best solvent from the standpoint of both maximizing the reaction rate and the extent of interesterification.

Raman studies of aldol condensation reactions on sodium hydroxide-treated silica gel

Adsorbed species from the reaction of acetaldehyde on NaOH-treated silica gel were studied using Raman spectroscopy. Catalytic activity for acetaldehyde condensation reactions increased with coverage of Na+ ions. At room temperature and an acetaldehyde vapor pressure of 300 Torr, the Raman spectrum of acetaldehyde adsorbed on NaOH-treated silica gel is characteristic of adsorbed acetaldehyde and 6-hydroxy-2,4-dimethyl-1,3-dioxane. The latter compound is a trimer of acetaldehyde from the base-catalyzed condensation of the monomer. At lower pressures the above dioxane decomposes and chemisorbed acetaldol is the dominant surface species. At elevated temperatures, Raman bands of crotonaldehyde, which is produced by the dehydration of adsorbed species, appear in spectra of the acetaldehyde reaction system. The reactions of crotonaldehyde on the catalyst surface are similar to those of acetaldehyde. Two condensation products result from the reactions of crotonaldehyde with adsorbed acetaldol and with adsorbed acetaldehyde. When acetaldehyde is adsorbed in the presence of pyridine, the rate of the condensation reaction is not significantly affected. In the presence of formic acid the catalytic activity for aldol condensation reactions is destroyed.

Deactivation of nickel methanation catalysts induced by the decomposition of iron carbonyl: I. Deactivation via pore-mouth blocking

The deactivation of alumina-supported nickel methanation catalysts due to decomposition of Fe(CO)5 was studied using both reaction kinetics measurements and in situ Mossbauer spectroscopy. Iron carbonyl, enriched in 57Fe for Mossbauer spectroscopy studies, was produced in situ and entrained with the carbon monoxide feed to a methanation reactor operating at temperatures of 620–650 K and H2CO ratios near 7. This incorporation of Fe into the nickel catalyst via the decomposition of Fe(CO)5 resulted in significant catalyst deactivation as well as changes in the parameters of a power law rate expression describing the methanation kinetics. With increasing amounts of Fe deposited on the catalyst, the kinetic parameters were shifted toward those of iron catalysts. These iron-induced phenomena are due to (1) pore-mouth blocking of the Al2O3 micropore structure by iron particles formed during the diffusion-limited decomposition of Fe(CO)5, and (2) interactions between iron and nickel in the macropores of the support. Specifically, the loss of catalyst activity is primarily caused by pore-mouth blocking, while shifts in kinetic parameters are the consequence of both pore-mouth blocking and interactions between iron and nickel. The majority of the iron deposited under methanation reaction conditions has been identified as χ-carbide (Hagg carbide) using Mossbauer spectroscopy at liquid helium temperature.

Rapid solvent-free esterification of conjugated linoleic acid and glycerol in a packed bed reactor containing an immobilized lipase

The product distribution for the polyesterification reactions between glycerol and conjugated linoleic acid (CLA) is primarily determined by the molar ratio of these species in the feed stream. The presence of excess glycerol serves to drive the initial esterification reaction to the right by forming a second phase which dissolves the water produced by the esterification reaction, thereby removing if from the fatty acid/acylglycerol phase. By appropriate manipulation of the fluid residence time, the reaction temperature, and the initial ratio of reactants, one can control the relative proportions of the mono-, di- and tri-acylglycerols in the effluent stream. At the reactor outlet, one observes excellent spontaneous separation of the glycerol and fatty acid/acylglycerol phases.