Search

Experimental determination of the separate effects of palm oil and methanol concentrations on the rate of their enzymatic transesterification was used to propose suitable mechanismic steps and to test the generated kinetic model. The reaction took place in n -hexane organic medium and the lipase used was from Mucor miehei . At a constant methanol concentration of 300 mol m −3 , it was found that, initially as the palm oil concentration increased, the initial reaction rate increased. However, the initial rate dropped sharply at substrate concentrations larger than 1250 mol m −3 . Similar behaviour was observed for methanol concentration effect, where at a constant substrate concentration of 1000 mol m −3 , the initial rate of reaction dropped at methanol concentrations larger than 3000 mol m −3 . Ping Pong Bi Bi mechanism with inhibition by both reactants was adopted as it best explains the experimental findings. A mathematical model was developed from a proposed kinetic mechanism and was used to identify the regions where the effect of inhibition by both substrates arised. The proposed model equation is essential for predicting the rate of methanolysis of palm oil in a batch or a continuous reactor and for determining the optimal conditions for biodiesel production.

Biodiesel, defined as monoalkyl fatty acid ester (preferentially methyl and ethyl esters), represents a promising alternative fuel for use in compression-ignition (diesel) engines. Biodiesel fuel comes from renewable sources as it is plant- not petroleum-derived and as such it is biodegradable and less toxic. In addition, relative to conventional diesel, its combustion products have reduced levels of particulates, carbon oxides, sulphur oxides and, under some conditions, nitrogen oxides. Enzymatic production of biodiesel has been proposed to overcome the drawbacks of the conventional chemically catalyzed processes. The main obstacle facing full exploitation of the enzyme, lipase, potential is its cost. Therefore, reuse of lipase is essential from the economic point of view, which can be achieved by using the lipase in immobilized form. In addition, immobilized lipase displays improved stability and activity. Common immobilization techniques include attachment to solid supports and entrapment within the matrix of a polymer. This article presents a comparison between conventional processes and enzymatic processes and different possible feedstocks for biodiesel production. In addition, possible ways to overcome the problems facing the use of lipase are described. © 2007 Society of Chemical Industry and John Wiley & Sons, Ltd

The hydrolysis of oil by lipase takes place at the interface between the oil and the aqueous solution containing the enzyme. For such systems, interfacial area between the oil phase and the aqueous phase influences the rate of hydrolysis. In this study, to enhance the hydrolysis rates of lipids, ultrasonication instead of mechanical agitation was used for interfacial area generation. By ultrasonication, larger interfacial area with much narrower distribution of oil droplet diameter could be produced as compared to by mechanical agitation. Experiments carried out to assess the hydrolysis rate of lipids showed that it was significantly enhanced by ultrasonic emulsification and the interfacial area saturation with enzyme was also not observed due to large interfacial area generated.

The kinetics of the production of biodiesel by esterification of butyric acid with methanol, catalysed by lipase from Mucor miehei, was studied in two types of systems, namely, n-hexane microaqueous and biphasic (n-hexane/water) containing different amounts of water. The experimental results were fit to a Ping-Pong mechanism and the constants found in the rate expression were determined. The results have shown that in a microaqueous media, butyric acid does not inhibit the reaction in the range of initial concentrations considered. The effect of water content on the initial rate of reaction and conversion were illustrated. It was shown that the initial rate of reaction increased as the initial water content increased up to 25% (v/v). However, the conversion was found to be higher at low initial water concentrations.

All the kinetic studies, found in the literature, on the production of biodiesel (fatty acids methyl esters) considered the esterifications of free fatty acids rather than the transesterification of the vegetable oil itself. The main industrial interest, however, is for the production of biodiesel with the triglyceride (oil) being the substrate. A mathematical model taking into account the mechanism of the methanolysis reaction starting from the vegetable oil as substrate, rather than the free fatty acids, has been developed. From the proposed model equation, the regions where the effect of alcohol inhibition fades, at different substrate concentrations, were identified. The proposed model equation can be used to predict the rate of methanolysis of vegetable oils in a batch or a continuous reactor and to determine the optimal conditions for biodiesel production. Copyright © 2005 Society of Chemical Industry

Mushtak T. Al-Atabi and S. B ChinDepartment of Mechanical Engineering, University of SheffieldSheffield, UKSulaiman Al-ZuhairSchool of Chemical Engineering, Faculty of Engineering,The University of Nottingham Malaysia CampusSemenyih, MalaysiaXiao Yu LuoDepartment of Mathematics, University of GlasgowGlasgow, UKFlow in a circular pipe fitted with segmental baffles may be treated as a shell-without-tube system. Its pressure drop has been calculated by adapting the Kerncorrelation [1] for pressure drop in the shell side of shell-and-tube heat exchang-ers. The Kern correlation is essentially based on the Hagen–Poiseuille equationfor laminar flow, but flow visualization results presented here show that enhancedmixing and turbulence-like flow may be present at Reynolds numbers (based onthe pipe diameter) as low as 50. A mathematical model, accounting for the ef-fects of geometry of the baffle configurations, has been developed to predict thepressure drop in circular pipe fitted with segmental baffles. The model was solvedalgebraically for flow in pipe with three baffle arrangements and the results werevalidated by experimental data. The pressure drops thus calculated showed betteragreement with experimental results than those predicted by the modified Kernmodel for Reynolds number in the range of 50–600.* * *Nomenclature

A mathematical model to predict the hydrolysis rate of oils by lipase, from a proposed kinetic mechanism of the reaction is derived. The model predicts interfacial saturation at high enzyme concentration. It is used to determine, under different operating conditions, the critical enzyme concentration, i.e., the enzyme concentration at which the interface between the oil and the aqueous phase containing the enzyme is saturated. To verify the model predictions, experimental results of the hydrolysis of palm oil and sunflower oil are used. The model predictions closely agree with the experimental results for sun flower oil. The sensitivity of the model predictions to the values of the kinetic parameters is also investigated.

An unsteady-state kinetic model has been proposed for the hydrolysis of palm oil by lipase in a stirred batch bioreactor. The hydrolysis model was derived from a reaction mechanism and simplified for conditions of low enzyme concentration. From it, the regions where the quasi-steady-state assumption for the intermediates is applicable is identified and verified experimentally. The experimental results showed that the hydrolysis of palm oil by lipase in a well-stirred reactor has a short induction time for the penetration of enzyme at the interface and for the formation of the enzyme–substrate complex. This indicates that the quasi-steady-state assumption for the intermediates is applicable under the operating conditions used in this study. It is also shown that increasing the agitation speed results in reduced induction time.

Oil–water dispersions have many important applications in the chemical and oleochemical industries. A measure of the specific interfacial area of the dispersed phase provides a direct indication of the quality of the dispersion. In this study, the specific interfacial area for the palm oil–water system was determined using a microscopic technique. The effects of oil volume fraction, agitation speed and temperature on the specific interfacial area have been determined experimentally and an empirical correlation to predict the total specific interfacial area under different operating conditions is proposed. This correlation can be used in the design of reaction and non-reaction systems using palm oil–water dispersions. Copyright © 2004 Society of Chemical Industry

A liquid–liquid separation model (LLSM) has been utilised to describe the clear palm oil separation from the crude palm oil mixture, which is a process that involves disengagement of oil droplets from an oil–water emulsion. The LLSM is used to determine the design parameters of industrial scale settlers and the results compared with that of the conventional solid–liquid settling model (SLSM) using three different industrial scale settlers as the basis of comparison. The LLSM predictions were much more accurate than the SLSM. This justifies the use of the LLSM instead of the conventional SLSM in determining the optimal design parameters and the optimal operating conditions of industrial settlers.

The sequential addition of the enzymes, laccase for lignin degrading, followed by xylanase for hemicelluloses hydrolysis, then cellulase for cellulose hydrolysis, was compared to the synergistic action of using the three enzymes together. It was shown that the reducing sugars yield increased from 5.6% using cellulase only to 45.6% by pretreatment with laccase and xylanase, prior to the enzymatic hydrolysis. A higher conversion of 60% was achieved by using the three enzymes together for the same incubation period. The proposed synergistic enzymes approach is a simpler and less energy intensive alternative compared to the conventional lignocelluloses pretreatment techniques.

The kinetics of the enzymic hydrolysis of palm oil using lipase in a batch reactor has been investigated. The lipase enzyme used was not ester bond position selective and its activity at the interface was higher compared to that in the bulk. A mathematical model taking into account the mechanism of the hydrolysis reaction and the effect of interfacial area between the oil phase and the aqueous phase containing the enzyme was developed. A correlation between the interfacial area and the operating conditions including agitation speed and oil volume fraction was established experimentally. The kinetic parameters were estimated by fitting the data to the model and comparing with previously reported values. The kinetic model represented the experimental data accurately.

Various methods have been proposed to monitor and determine microalgae lipid content accumulation, but they are indirect, time consuming, require sample preparations, and costly treatment steps. In this work, a novel electrical based technique, utilizing the impedance measurements to quantify the microalgae lipid accumulations. The lipid content estimation is an important element in the development of continuous non-invasive monitoring systems. The proposed technique correlates the lipid content to the change property in the measured impedance phase. A capacitor is used to host the microalgae suspension and is probed to the Gamry impedance analyzer tool, which records the impedance phase change versus frequency variations for various lipid accumulation. The relationship between lipid content and phase measurements is used to predict the unknown lipid content for microalgae.

Most conventional techniques for the determination of microalgae lipid content are time consuming and in most cases are indirect and require excessive sample preparations. This work presents a new technique that utilizes radio frequency (RF) for rapid lipid quantification, without the need for sample preparation. Tests showed that a shift in the resonance frequency of a RF open-ended coaxial resonator and a gradual increase in its resonance magnitude may occur as the lipids content of microalgae cells increases. These response parameters can be then calibrated against actual cellular lipid contents and used for rapid determination of the cellular lipids. The average duration of lipid quantification using the proposed technique was of about 1 minute, which is significantly less than all other conventional techniques, and was achieved without the need for any time consuming treatment steps.

Biodiesel production from microalgae lipids showed to be the promise approach for alternative fuels. However, this is not yet commercialized. In the present study, the efficient production of biodiesel from Nannochlorpsis sp. grown locally was confirmed. Novozyme®435 and supercritical carbon dioxide were used as reaction catalyst and reaction medium, respectively, and the results were compared to lamb fat. In addition, the microalgae biomass production was studied extensively. It was found that Nannochlorpsis sp. can accumulate lipids by nitrogen starvation reaching 29 % with 21.06 mg L-1d-1 lipid productivity when grown in nitrogen sufficient medium. The enzymatic production in supercritical carbon dioxide was efficient with 55 % ester yield higher than lamb meat fat.

This paper discusses the apparent viscosity of crude palm oil, using rotary viscometer, under different boundary conditions. It was experimentally shown that the apparent viscosity of palm oil drops with increasing of the shear rate and the temperature. However, the effect of temperature on the viscosity tends to fade at temperatures beyond 80 oC. A correlation between the apparent viscosity of crude palm oil and the operating conditions was developed. This correlation can be used in design of crude palm oil settlers and in determining the optimum operating conditions.Key Words: Crude palm oil, apparent viscosity, shear rate, modelling, separation&nbsp

High quality transformer oil is required to increase the reliability and the life time of the transformer. This oil carries information about the operating condition of the transformer. Therefore, the transformer oil properties should be monitored in order to give early warnings and maintain the transformers efficiency. When the oil quality is decreased, it should be either changed or regenerated. Transformer oil regeneration is carried out using adsorption on Activated Carbon (AC) produced from waste date-pits. After adsorption, drop in density, viscosity, neutralization index and metallic contents were observed, whereas adsorption resulted in an increase in interfacial area. The properties of the regenerated oil after adsorption was found to approach the acceptable standards, which clearly demonstrate the potential of using locally made AC from waste date-pits as an adsorption agent for transformer oil regeneration.

Biodiesel is considered a promising replacement to petroleum-derived diesel. Using oils extracted from agricultural crops competes with their use as food and cannot realistically satisfy the global demand of diesel-fuel requirements. On the other hand, microalgae, which have a much higher oil yield per hectare, compared to oil crops, appear to be a source that has the potential to completely replace fossil diesel. Microalgae oil extraction is a major step in the overall biodiesel production process. Recently, supercritical carbon dioxide (SC-CO2) has been proposed to replace conventional solvent extraction techniques because it is nontoxic, nonhazardous, chemically stable, and inexpensive. It uses environmentally acceptable solvent, which can easily be separated from the products. In addition, the use of SC-CO2 as a reaction media has also been proposed to eliminate the inhibition limitations that encounter biodiesel production reaction using immobilized enzyme as a catalyst. Furthermore, using SC-CO2 allows easy separation of the product. In this paper, conventional biodiesel production with first generation feedstock, using chemical catalysts and solvent-extraction, is compared to new technologies with an emphasis on using microalgae, immobilized lipase, and SC-CO2 as an extraction solvent and reaction media.

This chapter discusses the enzymatic production of biodiesel using lipase enzyme as a biocatalyst. It starts by highlighting the advantages and limitations of the enzymatic approach and includes a review on the effects of the source of lipase, type and quality of feedstock, type of acyl acceptor and temperature. The chapter then discusses importance of using the lipase in immobilized form and different immobilization techniques. A kinetic model that is developed from the mechanismic steps of enzymatic transesterification of triglyceride is also presented. The chapter concludes with an exploration of the future advances in enzymatic biodiesel production.

Experiments were carried out to evaluate the batch adsorption of COD from petroleum refinery wastewater on a locally prepared date-pit activated carbon (DP-AC), and its adsorption effectiveness was compared to that of commercially available BDH activated carbon (BDH-AC). Adsorption equilibrium and kinetic data were determined for both adsorbents and fitted to several adsorption isotherm and kinetics models, respectively. The Langmuir monolayer isotherm fitted well the equilibrium data of COD on both adsorbents; whereas, the kinetics data were best fitted by the pseudo-second order model. Modeling of the controlling mechanisms indicated that both intrinsic kinetics and mass transfer contributed to controlling the adsorption process. Mass transfer seemed to be the dominant mechanism at low COD content, while intrinsic kinetics dominates at high concentrations. In general, the adsorption effectiveness of locally prepared DP-AC was proven to be comparable to that of BDH-AC. Therefore, DP-AC can be utilized as an effective and less expensive adsorbent for the reduction of COD in refinery wastewater.

A kinetic model is devised, from the reaction mechanism steps, to predict the rate of reducing sugar production by hydrolysis of two types of cellulose, namely, amorphous carboxymethylcellulose (CMC) and highly crystalline wood shavings, using Aspergillus niger cellulase. Experimental results in a stirred batch reactor at 40 degrees C show that the production of reducing sugar reduced at much shorter times for wood shavings in comparison to CMC at the same initial substrate concentration. The experimental results are used to determine the kinetic parameters of the model equations. The significance of crystallinity was determined using inert fraction coefficient, which is assumed to be constant and equals 0.05 and 0.98 for CMC and wood shavings, respectively. It is shown there is a good agreement between the experimental results and proposed kinetic model predictions. The effect of the inert fraction coefficient on the production of reducing sugar by the enzymatic hydrolysis of cellulose is also determined. It is found that the cellulase used extracted from A. niger is much more sensitive towards the substrate structure in comparison to that extracted from Trichoderma reesei.

Hydrolysis of two types of cellulose, namely, totally amorphous Carboxymethyl-cellulose (CMC) and highly crystalline wood shavings, by Aspergillus niger cel-lulase was studied in a stirred batch reactor at 50 o C. Two kinetic models weredevised to predict the rate of reducing sugar production assuming competitive andnon-competitive product inhibition of the enzyme. The applicability of the modelswas tested by comparing experimental results with those predicted by the models.Both models followed the experimental data fairly well, giving standard deviationof 13.3 and 7.9 for the competitive and the non-competitive inhibition models, re-spectively. However the non-competitive inhibition model showed more realisticbehaviour than the non-competitive model and represented better the experimentaldata. The significance of crystallinity was determined by comparing the produc-tion of reducing sugar from wood shavings to the production from CMC. At sameinitial substrate concentration, it was found that the production of reducing sugarceased at much shorter times for wood shavings in comparison to that for CMC.KEYWORDS: cellulose, cellulase, product inhibition, enzymatic hydrolysis

Kinetics of production of biodiesel by enzymatic methanolysis of vegetable oils using lipase has been investigated. A mathematical model taking into account the mechanism of the methanolysis reaction starting from the vegetable oil as substrate, rather than the free fatty acids, has been developed. The kinetic parameters were estimated by fitting the experimental data of the enzymatic reaction of sunflower oil by two types of lipases, namely, Rhizomucor miehei lipase (RM) immobilized on ion-exchange resins and Thermomyces lanuginosa lipase (TL) immobilized on silica gel. There was a good agreement between the experimental results of the initial rate of reaction and those predicted by the proposed model equations, for both enzymes. From the proposed model equations, the regions where the effect of alcohol inhibition fades, at different substrate concentrations, were identified. The proposed model equation can be used to predict the rate of methanolysis of vegetable oils in a batch or a continuous reactor and to determine the optimal conditions for biodiesel production.

With the inevitable depletion of the nonrenewable resources of fossil fuels and due to their favorable environmental features, biofuels promise to be the preferred fuels of tomorrow. They can displace petroleum fuels and, in many countries, reduce the dependence on imported fuel. Biofuels, derived from biomass conversion, such as biodiesel, bioethanol, biohydrogen, and biogas, are sustainable and renewable sources of energy, which are also considered CO2 neutral. In addition, burning biofuels results in reduced levels of particulates, carbon oxides and sulfur oxides, emissions compared to fissile fuels. To respond to the increased demand for biofuels, advanced biochemical processes using enzymes are being developed, which are gaining increased global attention. Research in this field aims at improving efficiency, and reducing negative environmental impacts, of production processes, in addition to enhancing the quality of the produced biofuels. Enzymes have been employed to overcome the drawbacks associated with the use of conventional chemical catalysts. For example, biodiesel production by enzymatic catalyzed processes is less energy intensive and more environmental friendly compared to its production by conventional alkaline catalyzed processes. In addition, the biocatalyst allows using unrefined feedstock, including waste oil, readily without the need to separate the free fatty acids that may be present in large amounts in the feedstock. Another example is the use of enzymes for the hydrolysis of cellulose to produce fermentable sugars for bioethanol production. The utility cost of enzymatic hydrolysis is much lower compared to the alternative methods of acidic hydrolysis because it is carried out at mild conditions and does not require subsequent treatment step. There are several obstacles, however, facing the use of enzymes as catalysts for biofuels production, most importantly is their high costs. Therefore, repeated use of the enzymes is essential from the economic point of view, which can be achieved by using them in immobilized form. In a continuous process using immobilized enzyme, the operational stability, the exhaustion of enzyme activity, and inhibition by reactants and/or products play vital roles. The use of membrane bioreactors for the enzymatic processing is increasingly becoming more attractive, as such systems allow continuous separation of products and prevent enzyme inhibition. Research attention is also focused on genetic engineering in enzymes production. Recently, genes of various enzymes have successfully been cloned, and more genes are promised to be cloned rapidly in the coming years. The use of recombinant DNA technology to produce large quantities of recombinant enzymes will help lower the enzymes costs. In addition, protein engineering will help to create novel enzyme proteins that are more resistant and highly thermo-stable. The introduction of a new generation of cheap enzymes, with enhanced activities and resilience, should change the economic balance in favor of enzyme use. It gives me great pleasure to present to you this special issue. The issue covers both basic and applied aspects of using enzymes in the production of various types of biofuels. Articles published present different aspects of current and potential involvement of enzymes in biofuel production.

This paper presents a general and a simplified method for deliverability calculations of gas wells, which among other advantages, eliminates the need for conventional multipoint tests. The analytical solution to the diffusivity equation for real gas flow under stabilized or pseudo-steadystate flow conditions and a wide range of rock and fluid properties are used to generate an empirical correlation for calculating gas well deliverability. The rock, fluid and system properties, used in developing previous correlations found in literature, were limited to reservoir pressure, reservoir temperature, gas specific gravity, reservoir permeability, wellbore radius, well drainage area, and shape factor. Additional key properties such as reservoir porosity, net formation thickness and skin factor are included in this work to develop a more general dimensionless Inflow Performance Relationship (IPR). It is found that the general correlation, developed is this study, presents the observed field data much closer than previous ones found in the literature. In addition, based on the larger data set, an empirical relation to predict future deliverability from current flow test data is also developed. The two modified and general relations developed in this work provide a simple procedure for gas deliverability calculations which greatly simplifies the conventional deliverability testing methods. The required data can be obtained from a build-up test, or a single-point flow test, instead of an elaborate multipoint flow test. Further, the broad range of practically all rock and fluid properties used in developing the modified dimensionless IPR curves should cover the majority of the field situations generally encountered. The use of the modified dimensionless IPR curves, the pseudo-pressure formulation and the sensitivity analysis indicate a generality of the approach presented in this paper, irrespective of the gas reservoir system under study.

It is generally accepted that the use of iPad enhances students’ engagement in the classroom. However, assessing the benefits of using iPad in teaching laboratory sessions have seen less attention, due to the hands-on nature of these courses. To do this assessment, iPad was applied in teaching two pilot sessions of the General Chemistry Lab, and students’ evaluation was compared to that of other students in sections taught by conventional teaching techniques. The evaluation was based on the students’ assessment of their achievements in meeting the main course outcomes, which indicated that the students in the classes taught using iPad showed more satisfaction with the course, and believed that they have better achieved the outcomes of the course compared to the conventional classes. Furthermore, the comparison process included the overall students’ quantitative performance, which showed insignificant difference between the two classes, with slightly better performance of students in normal classes in quizzes, whereas final exam marks were almost the same for both the iPad piloted students and conventional class students. The differences in quizzes results were attributed to the normal variation in the students’ academic merits. In addition, the piloted students were asked about their experience of using iPad in class and their satisfaction by using different iPad Apps. The feedback was collected and analysed, and the results showed that the students generally enjoyed using iPad in the class and appreciated all Apps.