The extraction of oils based on animal fat and vegetable oil from two types of spent bleaching earths, namely from the acidic sepiolite and the nonacidic palygorskite, was investigated by the Soxhlet method with hexane as a solvent. The yields of oil were independent of the feedstock, whereas a much lower oil yield was obtained with palygorskite exhibiting also a smaller surface area as compared to sepiolite which provided a higher yield. The glyceride compositions were very similar in bleached and extracted oils, while slightly lower melting and crystallization energies were determined by differential scanning calorimetry for the extracted oils bleached with acidic clay indicating minor hydrolysis of triglycerides.

A kinetic model was developed for racemic and enantioselective ethyl pyruvate hydrogenation based on selective and unselective reaction routes in the presence of a solid catalyst (Pt/Al2O3), a catalyst modifier (cinchonidine) and microwave irradiation. The temperature of the catalyst bed was estimated with the aid of a mathematical model for heat transfer in a packed bed as well as with energy balances for solid and liquid phases. The microwave reactor was modelled with mass and energy balances, which were decoupled, since the heat effect of the hydrogenation process was negligible compared to that of the microwave source. The Langmuir–Hinshelwood type of approach was used for the kinetic model, which was incorporated in a non-steady state plug flow reactor model. The proposed models described well the observed hydrogenation kinetics and the temperature behaviour of the microwave reactor.

The effect of acoustic irradiation has been studied in several hydrogenation reactions (1-phenyl-1,2-propanedione, ethyl-pyruvate and d-fructose hydrogenation) as well as in an esterification reaction over various heterogeneous catalysts. The reaction rate and selectivity were significantly improved under sonification in 1-phenyl-1,2-propanedione hydrogenation over Pt/SF (silica fiber) catalyst. Acoustic irradiation enhanced the reaction rate in esterification of propionic acid with ethyl alcohol over functionalized polymer fiber Smopex-101 catalyst compared to identical silent conditions. Furthermore, ultrasound remarkably suppressed catalyst deactivation in d-fructose hydrogenation over Raney-Ni catalyst. The spent catalysts used in the hydrogenation reactions either in presence or absence of acoustic irradiation were intensively studied by means of scanning electron microscopy (SEM) and transmission electron microscopy (TEM).

The enantioselective hydrogenation of 1-phenyl-1,2-propanedione was carried out over Pt/Al2O3, Pt/SiO2, Pt/SF (silica fiber), Pt/C catalysts modified with cinchonidine under ultrasonic irradiation. The initial rate, regioselectivity and enantioselectivity were investigated for different catalyst pretreatments, solvents and ultrasonic powers. The ultrasound effects were very catalyst dependent. The sonication significantly enhanced enantioselectivity and activity of the Pt/SF (silica fiber) catalyst. For the other Pt supported catalysts the reaction rate, enantioselectivity and regioselectivity increased moderately. The choice of solvent influenced the impact of ultrasound effect, namely in mesitylene, which has the lowest vapor pressure, the highest ultrasound enhancement was observed. The effect of sonication on catalysts surface was studied by transmission electron microscopy and scanning electron microscopy (SEM). No significant change in the metal particle size distribution due to sonication was observed. However, in the case of the Pt/SF catalyst, acoustic irradiation induced morphological changes on the catalyst particle surface (SEM), which might be the cause for enhancement of the initial reaction rate and enantioselectivity.

The effect of sonification on D-fructose hydrogenation over several heterogeneous catalysts was investigated. The reaction rate and selectivity were studied at different temperatures, pressures, and ultrasonic power inputs. The ultrasonic effects were clearly catalyst dependent. The sonification during the hydrogenation reaction significantly enhanced reaction rate over Cu/ SiO2. In the case of Raney-Ni, just moderate improvements of reaction rates were observed under ultrasound and a slight decrease of catalyst activity by sonification was obtained over Cu/ZnO/Al2O3. Although the choice of catalyst significantly influenced selectivity, no positive influence of acoustic irradiation on selectivity was achieved. The influence of pressure and temperature over Raney-Ni type catalyst was studied under sonification as well. High pressures and temperatures brought just moderate enhancements of reaction rates, while the variation of nominal ultrasonic power input significantly affected the catalyst activity. A catalyst deactivation study was conducted by recycling the catalyst. Acoustic irradiation significantly prevented catalyst deactivation compared to experiments in silent conditions. The effect of ultrasound on catalyst surface was confirmed by means of scanning electron microscopy (SEM).

Process intensification has become a very interesting approach, transforming current practices in chemical engineering and bringing forth new developments in equipment, processing techniques and operational methods. This development aims at more compact, safe, energy efficient and environmentally friendly process.Several unconventional processing techniques rely on alternative forms of energy. Chemistry under extreme and non-conventional conditions is an actively studied topic in applied research and industry. Alternatives to conventional synthetic procedures promise. enhancement of reaction rates, yields, selectivity and also bear promise of milder reaction conditions in chemical synthesis. During the last few decades, chemical application of ultrasound (US) and microwave (MW) irradiation has received a lot of attention and widespread research is going on in these areas. Significant enhancement of selectivities, rates and yields in chemical reactions has been achieved by means of US and MW irradiation. The popularity of US and MW irradiation as chemical laboratory techniques is rapidly growing. based on the number of publications, presentations and meetings. demonstrating their vast potential. Other less exploited methods are solar and plasma reactors. These, however, will not be touched in the present review, which focuses on the use of ultrasound and microwaves as sources of energy, mainly in catalytic applications. (C) 2004 Elsevier B.V. All rights reserved.

Esterification of propionic acid with ethyl alcohol over an ion-exchange resin catalyst was studied under microwave dielectric heating. Experiments were carried out in a single-mode microwave loop reactor, equipped with a heating band as well to directly compare the efficiency of the conventional convective/conductive heating and microwave dielectric heating. Series of kinetic experiments were carried out with both conventional and dielectric heating at the reaction temperature of 105°C and total pressure of 7bar. Different initial molar ratios of propionic acid-to-ethanol (from 1:2 to 2:1) were investigated. Initial molar ratios of acid-to-alcohol significantly affected the final yield of the desired product ethyl ester of propionic acid, ethyl propionate. The highest product yield was observed with equimolar initial ratio, compared to 1:2 and 2:1 initial molar ratios of acid-to-alcohol. However, the kinetics and equilibrium of this reaction were unaffected by the method of heating (microwave or conventional).

The effect of power ultrasound has been studied in the hydrogenation of 1-phenyl-1,2-propanedione (enantioselective hydrogenation) and linoleic acid (fat hardening). Furthermore the hydrogenation of d-xylose to xylitol and citral to citronellal and citronellol were studied under the influence of acoustic irradiation. We have investigated the effect of on-line acoustic irradiation of these heterogeneously catalysed liquid–gas–solid systems in which it was found to counter-effect catalyst deactivation, increase the reaction velocity and to enhance the selectivity of various heterogeneously catalysed reactions.