Original scientific paper Gas hold-up in a three-phase reciprocating plate column

Abstract: The influence of the geometry of a reciprocating plate column (diameter), superficial gas velocity, vibration intensity and content of the solid phase in the column on the gas hold-up in a three phase column (G–L–S) were investigated in this study. For comparison, the gas hold-up was also analyzed in a gas–liquid system (G–L) in the same type of column. Good agreement between the experimentally determined values of the gas hold-up and those calculated on the basis of the derived correlation for the G–L and G–L–S system was obtained

Conversion of sulphur compounds into light gas oil: I. Kinetics of the conversion of model compounds

The problem of sulfur compounds conversion, particularly heterocyclic compounds, from the middle fraction of crude oil (light gas oil) was analyzed and will be published in several articles in the Chemical Industry Journal. Published data in the literature, covering the conversion of tiophene, benzothiophene and dibenzothiophene are presented in the first paper of this series with the goal of comparing and critically analyzing their usage for reactor calculation

Antifreeze life cycle assessment (LCA)

Antifreeze based on ethylene glycol is a commonly used commercial product The classification of ethylene glycol as a toxic material increased the disposal costs for used antifreeze and life cycle assessment became a necessity. Life Cycle Assessment (LCA) considers the identification and quantification of raw materials and energy inputs and waste outputs during the whole life cycle of the analyzed product. The objectives of LCA are the evaluation of impacts on the environment and improvements of processes in order to reduce and/or eliminate waste. LCA is conducted through a mathematical model derived from mass and energy balances of all the processes included in the life cycle. In all energy processes the part of energy that can be transformed into some other kind of energy is called exergy. The concept of exergy considers the quality of different types of energy and the quality of different materials. It is also a connection between energy and mass transformations. The whole life cycle can be described by the value of the total loss of exergy. The physical meaning of this value is the loss of material and energy that can be used. The results of LCA are very useful for the analyzed products and processes and for the determined conditions under which the analysis was conducted. The results of this study indicate that recycling is the most satisfactory solution for the treatment of used antifreeze regarding material and energy consumption but the re-use of antifreeze should not be neglected as a solution

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Continuous sunflower oil methanolysis over quicklime in a packed-bed tubular reactor

The continuous sunflower oil methanolysis catalyzed by quicklime in a packed-bed tubular reactor of 60 cm height was studied at 60 °C using methanol-to-oil molar ratios from 6:1 to 18:1 and weight hourly space velocities from 0.188 to 0.376 (kg/kgcat h). The main goal was to establish the effect of the process variables on the fatty acid methyl esters (FAME) synthesis. A full factorial design was used to evaluate the significance of the three process factors (methanol-to-oil molar ratio, flow rate of the reactants and bed height) statistically. Moreover, the recently reported kinetic model of methanolysis was used to describe variations of FAME and triacylglycerols (TAG) concentrations along the reactor length. The kinetic model predicted the axial concentration profiles of TAG and FAME in the reactor with acceptable accuracy. A high FAME content (98.5%) could be achieved at the two thirds of the bed of quicklime bits without loss of catalytic activity within 30 h of continuous operation

Biodiesel production by enzyme-catalyzed transesterification

The principles and kinetics of biodiesel production from vegetable oils using lipase-catalyzed transesterification are reviewed. The most important operating factors affecting the reaction and the yield of alkyl esters, such as: the type and form of lipase, the type of alcohol, the presence of organic solvents, the content of water in the oil, temperature and the presence of glycerol are discussed. In order to estimate the prospects of lipase-catalyzed transesterification for industrial application, the factors which influence the kinetics of chemically-catalysed transesterification are also considered. The advantages of lipase-catalyzed transesterification compared to the chemically-catalysed reaction, are pointed out. The cost of down-processing and ecological problems are significantly reduced by applying lipases. It was also emphasized that lipase-catalysed transesterification should be greatly improved in order to make it commercially applicable. The further optimization of lipase-catalyzed transesterification should include studies on the development of new reactor systems with immobilized biocatalysts and the addition of alcohol in several portions, and the use of extra cellular lipases tolerant to organic solvents, intracellular lipases (i.e. whole microbial cells) and genetically-modified microorganisms ("intelligent" yeasts)

Alumina/silica aerogel with zinc chloride as an alkylation catalyst

The alumina/silica with zinc chloride aerogel alkylation catalyst was obtained using a one step sol-gel synthesis, and subsequent drying with supercritical carbon dioxide. The aerogel catalyst activity was found to be higher compared to the corresponding xerogel catalyst, as a result of the higher aerogel surface area, total pore volume and favourable pore size distribution. Mixed AlOSi bonds were present in both gel catalyst types. Activation by thermal treatment in air was needed prior to catalytic alkylation, due to the presence of residual organic groups on the aerogel surface. The optimal activation temperature was found to be in the range 185225°C, while higher temperatures resulted in the removal of zinc chloride from the surface of the aerogel catalyst with a consequential decrease in the catalytic activity. On varying the zinc chloride content, the catalytic activity of the aerogel catalyst exhibited a maximum. High zinc chloride contents decreased the catalytic activity of the aerogel catalyst as the result of the pores of the catalyst being plugged with this compound, and the separation of the alumina/silica support into Al-rich and Si-rich phases. The surface area, total pore volume, pore size distribution and zinc chloride content had a similar influence on the activity of the aerogel catalyst as was the case of xerogel catalyst and supported zinc chloride catalysts

Kinetics of sunflower oil methanolysis catalyzed by calcium oxide

The methanolysis of sunflower oil was studied in the presence of CaO previously calcined at various temperatures and the optimal temperature for CaO calcination was determined. The sigmoidal process kinetics was explained by the initial triglyceride (TG) mass transfer controlled region, followed by the chemical reaction controlled region in the latter reaction period. The TG mass transfer limitation was due to the small available active specific catalyst surface, which was mainly covered by adsorbed molecules of methanol. In the later phase, the adsorbed methanol concentration decreased, causing the increase of both the available active specific catalyst surface and the TG mass transfer rate, and the chemical reaction rate become smaller than the TG mass transfer rate

Kinetic Modeling of Sunflower Oil Methanolysis Catalyzed by Calcium-Based Catalysts

The kinetic model originally developed for quicklime-catalyzed methanolysis of sunflower oil was tested for another three calcium-based catalysts, namely, neat CaO, Ca(OH)2, and CaO·ZnO. This model includes the changing reaction mechanism and the triacylglycerol (TAG) mass transfer. The applicability and generalization capability of this model for heterogeneous methanolysis reaction catalyzed by calcium-based catalysts was evaluated. As indicated by the high coefficient of determination and the relatively small mean relative percentage deviation, the model was a reliable predictor of the time variation of TAG conversion degree in the sunflower oil methanolysis over all four calcium-based catalysts within the ranges of the reaction conditions applied. This model is recommended in general for describing the kinetics of sunflower oil methanolysis over calcium-based catalysts.The kinetic model originally developed for quicklime-catalyzed methanolysis of sunflower oil was tested for another three calcium-based catalysts, namely, neat CaO, Ca(OH)2, and CaO·ZnO. This model includes the changing reaction mechanism and the triacylglycerol (TAG) mass transfer. The applicability and generalization capability of this model for heterogeneous methanolysis reaction catalyzed by calcium-based catalysts was evaluated. As indicated by the high coefficient of determination and the relatively small mean relative percentage deviation, the model was a reliable predictor of the time variation of TAG conversion degree in the sunflower oil methanolysis over all four calcium-based catalysts within the ranges of the reaction conditions applied. This model is recommended in general for describing the kinetics of sunflower oil methanolysis over calcium-based catalysts

Kinetics of sunflower oil methanolysis at low temperatures

The kinetics of the sunflower oil methanolysis process was studied at lower temperatures (10-30 °C). The sigmoidal kinetics of the process was explained by the mass transfer controlled region in the initial heterogenous regime, followed by the chemical reaction controlled region in the pseudo-homogenous regime. A simple kinetic model, which did not require complex computation of the kinetic constants, was used for simulation of the TG conversion and the FAME formation in the latter regime: the fast irreversible second-order reaction was followed by the slow reversible second-order reaction close to the completion of the methanolysis reaction. The mass transfer was related to the drop size of the dispersed (methanol) phase, which reduced rapidly with the progress of the methanolysis reaction. This was attributed to the formation of the emulsifying agents stabilizing the emulsion of methanol drops into the oil