M. Di Serio

Lactose hydrolysis by immobilized β-galactosidase: the effect of the supports and the kinetics

Abstract The kinetic behaviour of β-galactosidase from Kluyveromices marxianus (Saccharomyces) lactis, immobilized on different oxides supports, such as alumina, silica, and silicated alumina has been studied. We observed a strong dependence of the immobilized enzyme activities on the chemical nature and physical structure of the supports. In particular, when the particle sizes of the supports are increased, the enzymatic activity strongly decreases. The hydrolysis of lactose, promoted by the mentioned enzyme immobilized on small commercial silica spheres, has been studied in different operative conditions, by changing: feed rate, reagent and products concentration and temperature, while pH has been kept constant (7.0). A depressing effect originated by both the reaction products, has been observed. Therefore, a kinetic model based on the Michaelis–Menten mechanism, in which the depressing effects of both the hydrolysis products (galactose and glucose) are also considered, have been developed and the related parameters determined.

Kinetic and catalytic aspects in the hydrogen peroxide production via anthraquinone

The kinetic and catalytic aspects involved in the hydrogen peroxide production via anthraquinone (method all-tetra) have been examined considering three of the four main production steps, i.e., hydrogenation of 2-ethyltetrahydroanthraquinone catalyzed by palladium-supported catalysts, oxidation of the product obtained in the first step, and reconversion of the deteriorated molecules for the regeneration of active quinones. For each reaction considered, a mechanism and a kinetic law are suggested with the numerical values of the related parameters.

Catalytic alkylation of phenol with methanol: factors influencing activities and selectivities: II. Effect of intracrystalline diffusion and shape selectivity on H-ZSM5 zeolite

Abstract Six samples of H-ZSM5 zeolites, differing in the size of crystallites and acidity, have been tested as catalysts in the alkylation of phenol with methanol. We observed that the size of crystallites strongly influences activity, even for very small crystallites (220–280A), by the intervention of intracrystalline diffusion. Kinetic runs have been performed on the most active catalyst. A moderate shape selectivity has been observed only in the formation of p-methylanisole and xylenols. Catalyst deactivation occurs through two mechanisms which are independent of the contact time, the first evolving exponentially and the second linearly. The interpretation of this behaviour and of related consequences on the reaction is discussed in the paper together with the reaction path model, the mechanism and the kinetics.

Preparation and properties of new acid catalysts obtained by grafting alkoxides and derivatives on the most common supports note I — grafting aluminium and zirconium alkoxides and related sulphates on silica

Abstract In this paper we will show that it is possible to modify the acid properties of a surface, rich of hydroxyl groups by grafting in suitable conditions metal alkoxides, such as aluminium and zirconium alkoxide. Depending on the amount of metal alkoxide it is possible to obtain, after steaming of the surface and calcination, different coverage degree up to the monolayer. Iteration of the grafting technique gives a multilayer, completely modifying the orginal surface. Grafting aluminium and zirconium alkoxides pre-treated in homogeneous phase with pure sulphuric acid leads to catalysts with very strong acid sites on the surface. The acidic properties of the catalysts obtained by grafting aluminium and zirconium alkoxides and their sulphate derivatives on silica have been characterized by different techniques such as: potentiometric titrations, Temperature Programmed Desorption of organic bases and differential calorimetry to evaluate the density of the active sites and their strength. Prepared catalysts were proven in test reactions such as methanol dehydration and hydrocarbon isomerization and cracking. We have shown that sulphated catalysts have very strong acid sites of both the Bronsted and Lewis type, able to promote hydrocarbon isomerization and cracking at the relatively low temperature of 250°C.

Double bond oxidative cleavage of monoenic fatty chains

Abstract A two steps process for the production of azelaic acid and pelargonic acid or alternatively of ω-hydroxynonanoic and pelargonic acid, starting from respectively oleic acid and oleyl alcohol has been studied. In the first step, the monoenic reagent reacts with hydrogen peroxide, in the presence of pertungstic acid, as catalyst, to give the corresponding diol (hydroxylation of the double bond). In the second step, the reaction mixture obtained in the first step containing the formed diol and the exhausted catalyst, was additioned of cobalt acetate and reacted with molecular oxygen (oxidative cleavage of vicinal diols). As the first step has largely been studied in the literature, the study of the nature of the catalytic site and of the catalytic mechanism of the second step of the process is the main subject of this work with the objective of identifying, for this step, an independent and reusable catalyst. In particular, we focused our attention on the diol deriving from oleyl alcohol, because reagents and products are more easily separated and analyzed. The study of the mentioned reactions is complicated by the presence of respectively two or three phases in the reactor. The “in-situ” formed catalyst, active in the second reaction step, seems to be a lacunary poly-oxometalate in which cobalt, sequestered by the tungstate anion groups and accessible to the reagent, is the active component. This has been shown by polarographic analyses of the catalyst solution before and after the reaction, and is also confirmed by the observation that cobalt, sequestered by EDTA, in the absence of tungstic acid is active, too.

Mass transfer and kinetics in ehtoxylation spray tower loop reactors

A mathematical model has been developed for describing the behaviour of the spray tower loop reactors. Th reactors are characterised by the fact that mass transfer and reaction occurs independently in two distinct zone of the reactor. The model has been used for simulating the performance of a pilot plant both by assuming liquid drops internally stagnant and turbulent. The last assumption gives the better results.

Oxidative dehydrogenation of ethanol to acetaldehyde on V2O5/TiO2-SiO2 catalysts obtained by grafting vanadium and titanium alkoxides on silica

Abstract Oxidative dehydrogenation of ethanol to acetaldehyde has been performed on vanadium based catalysts prepared by grafting on titania–silica supports with different procedures. A comparison of the performances of the prepared catalysts in terms of activity and selectivity has been made. Grafting technique gives place to well dispersed catalysts that resulted more selective than catalysts prepared by impregnation. In particular, very selective catalysts have been obtained by grafting vanadium–titanium bimetallic alkoxides directly on silica support. The effect of both the preparation methods and the used supports on the catalytic performances have been studied and an attempt to correlate the observed properties with the obtained results has been made.

Oxidative dehydrogenation of propane using V2O5/TiO2/SiO2 catalysts prepared by grafting titanium and vanadium alkoxides on silica

Abstract The oxidative dehydrogenation (ODH) of propane have been studied on three different vanadium oxide catalysts, containing comparable amounts of vanadium. All the proven catalysts have been prepared by grafting but following different procedures. One has been prepared by grafting vanadyl tri-isopropoxide, dissolved in n -hexane on a support of silica coated with a multi-layer of TiO 2 . The support has been prepared by grafting in three different steps titanium alkoxide on silica. Another catalyst has been prepared by partially hydrolysing vanadyl tri-isopropoxide, dissolved in isopropanol, before grafting the obtained product on the same support. The third catalyst has been prepared by reacting partially hydrolysed vanadyl tri-isopropoxide with titanium alkoxide in isopropanol and anchoring then the reaction product, a vanadium–titanium bimetallic alkoxide, directly on silica. The first and second catalysts have similar activities and selectivities, while the third catalyst is less active but more selective than the other two ones. A kinetic approach has been made and a pseudo-first order kinetic law has been used to interpret the results. All the observed catalytic phenomena have been interpreted also with the aid of the several used characterisation techniques.

Hydrogenation of the aromatic rings of 2-ethylanthraquinone on palladium catalyst

Abstract Hydrogenation of anthraquinones at the oxygen is a key step in the industrial production of hydrogen peroxide. The reaction is very fast in the presence of palladium supported catalysts. However, these catalysts also promote the hydrogenation of the aromatic rings of the anthraquinone molecules giving place to substances not participating in the formation of hydrogen peroxide and causing a loss of active quinone. 2-ethylanthraquinone can also give tautomerization to oxanthrone and derivatives with a further loss of active quinone. The kinetics of the hydrogenation of the aromatic rings of 2-ethylanthraquinone are studied. A dual site reaction mechanism well explains the experimental findings. On the basis of this mechanism, kinetic expressions have been developed and the kinetic parameters determined. The contribution of tautomerization to the kinetic pattern has also been ascertained.

Preparation and properties of new acid catalysts obtained by grafting alkoxides and derivatives on the most common supports. Part III : grafting titanium alkoxides and sulphate derivatives on silica

Abstract Some catalysts have been prepared by grafting different amounts of titanium isopropoxide dissolved in toluene on a silica support and by steaming and calcinating the products obtained. A catalyst has been prepared also by first treating with pure sulphuric acid titanium isopropoxide, grafting the titanium alkoxide sulphate on silica and again by steaming and calcinating the product obtained. All the catalysts prepared have been characterized using different techniques such as: electrochemical potentiometric titrations to evaluate the PZC (point of zero charge), the hydroxyl densities and the surface dissociation equilibrium constants; TGA (thermal gravimetric analyses) to evaluate the hydroxyl densities; TPD (thermal programmed desorption) of organic bases such as pyridine and lutidine; and XPS (X-ray photoemission spectroscopy). All catalysts have also been tested by determining the performances in three different reactions: dehydration of methanol, epoxidation of cyclooctene with cumene hydroperoxide and isomerization of 1-butene to 2-butene. The behaviour of the catalysts prepared shows that grafting titanium on silica strongly modifies the original surface and the catalysts obtained with the mentioned grafting techniques are different from those obtained by impregnation and coprecipitation.