Abstracts of Paper's Published in 2010


In the following:

  1. M.S. Mahmudp, T. Safinski, M. Nelson, H.S. Sidhu and A.A. Adesina. Kinetic Analysis of Oleic Acid Esterification Using Lipase as Catalyst in a Microaqueous Environment, Industrial & Engineering Chemistry Research 49(3), 1071-1078. 2010. (2010 ERA A)

    The DOI (Digital Object Identifier) link for this article is http://dx.doi.org/10.1021/ie900704n.

  2. S.D. Watt, H.S. Sidhu, M.I. Nelson and A.K. Ray. Analysis of a model for ethanol production through continuous fermentation: ethanol productivity. International Journal of Chemical Reactor Engineering 8, A52, 2010. (2010 ERA B)

    This paper is available at http://www.bepress.com/ijcre/vol8/A52.

  3. T. Luangwilai, H.S. Sidhu, M.I. Nelson and X.D. Chen. Modelling air flow and ambient temperature effects on the biological self-heating of compost piles. Asia-Pacific Journal of Chemical Engineering, 5(4), 609-618, 2010. (2010 ERA B)

    The DOI (Digital Object Identifier) link for this article is http://dx.doi.org/10.1002/apj.438.

  4. A.H. Msmalip and M.I. Nelson. A model for incomplete mixing in a bioreactor. In Proceedings of the 38th Australasian Chemical Engineering Conference, CHEMECA 2010, (on CDROM), Engineers Australia, 2010. ISBN 978-085-825-9713.
  5. R. van Bentump, M.I. Nelson, X.D. Chen and G. O'Brien. The pH profile of the human stomach. In Proceedings of the 38th Australasian Chemical Engineering Conference, CHEMECA 2010, (on CDROM), Engineers Australia, 2010. ISBN 978-085-825-9713.
  6. T. Luangwilaip, H.S. Sidhu, M.I. Nelson and X.D. Chen. Using Singularity Theory to Analyse a Spatially Uniform Model of Self-Heating in Compost Piles. East-West Journal of Mathematics, Contributions in Mathematics and Applications III: 328-343, 2010. (2010 ERA C).
  7. T. Luangwilaip, H.S. Sidhu, M.I. Nelson and X.D. Chen. The Semenov Formulation of the Biological Self-Heating Process in Compost Piles. In P.~Howlett, M.~Nelson, and A.~J. Roberts, editors, Proceedings of the 9th Biennial Engineering Mathematics and Applications Conference, EMAC-2009, volume~51 of ANZIAM J., pages C425--C445, Jun 2010. http://journal.austms.org.au/ojs/index.php/ANZIAMJ/article/view/2439 [June 29, 2010].

Kinetic Analysis of Oleic Acid Esterification Using Lipase as Catalyst in a Microaqueous Environment

Abstract

This paper reports the lipase-catalyzed esterification of oleic acid (with ethanol) in a batch reactor at temperatures between 298 to 338 K using a wide range of the reactant ratio, β (0<β<2). All kinetics runs were performed under conditions of negligible transport limitations. The sigmoidal behaviour evidenced from the initial rate - substrate concentration curve suggests the allosteric nature of the acrylic-supported Aspergillus lipase, and hence, the data were described by a non-Michaelis Menten kinetic model. The associated oleic acid binding coefficient and ethanol inhibition constant were obtained as 2.382 mmol/L and 1.643 mmol/L respectively. The allosteric effect was attributed to conformational change in the enzyme site occasioned by the presence of trace amounts of water formed within the first few minutes of the reaction. Indeed, the transient water concentration profile at different β values revealed an initial overshoot in water concentration before the relaxation to final equilibrium value after about 6 hours. The appearance of the initial overshoot increased with decreasing β. The water concentration history is symptomatic of two 1st order interacting processes containing a linear generative term for water (input) consistent with the two-enzyme state concerted symmetry proposition for nonlinear feedback autoregulatory behaviour. The rate-temperature envelope showed a maximum at about 318 K suggesting protein denaturation above this temperature. Even so, a fit of the raw data obtained between 298 to 318 K gave an activation energy of 22.4 kJ/mol typical of many enzymatic reactions. FTIR spectra of the catalysts displayed peaks at wave-numbers 1723.23 /cm and 1666.12 /cm assigned to COO- and NH2+ groups respectively for both fresh and used specimens. BET measurements, however, revealed a significant drop in surface area between fresh (165 m2/g) and used (5-20 m2/g) catalysts. This was attributed to pore blockage of the immobilised enzyme by the relatively large oleic-acyl-lipase complex left after the reaction.

M.S. Mahmudp, T. Safinski, M. Nelson, H.S. Sidhu and A.A. Adesina. Kinetic Analysis of Oleic Acid Esterification Using Lipase as Catalyst in a Microaqueous Environment, Industrial & Engineering Chemistry Research 49(3), 1071-1078. 2010.

The DOI (Digital Object Identifier) link for this article is http://dx.doi.org/10.1021/ie900704n.


Analysis of a model for ethanol production through continuous fermentation: ethanol productivity

Abstract

We investigate a model for the production of ethanol through continuous fermentation using Saccharomyces cerevisiae in a single reactor and cascades of up to five reactors. Using path-following methods we investigate how the ethanol productivity varies with the residence time in each reactor of the cascade. With a substrate feed concentration of 160 g/l we find the optimal productivity is 3.80 g/l/h, 5.08 g/l/h, and 5.18 g/l/h in a single reactor, a double reactor cascade and a triple reactor cascade respectively. For the case of a cascade containing reactors of equal size we investigate reactor configurations of up to five reactors and find that the maximum productivity is obtained in a cascade containing three reactors.

S.D. Watt, H.S. Sidhu, M.I. Nelson and A.K. Ray. Analysis of a model for ethanol production through continuous fermentation: ethanol productivity. International Journal of Chemical Reactor Engineering 8, A52, 2010.

This paper is available at http://www.bepress.com/ijcre/vol8/A52.


Modelling air flow and ambient temperature effects on the biological self-heating of compost piles

Abstract

Keywords: air-flow; ambient temperature; combustion; composting; non-linear dynamics; self-heating .

We formulate and investigate a one-dimensional model for self-heating in compost piles. The self-heating occurs through a combination of biological and chemical mechanisms. Biological heat generation is known to be present in most industrial processes handling large volumes of bulk organic materials. The heat release rate due to biological activity is modelled by a function which at sufficiently low temperatures is a monotonic increasing function of temperature. At higher temperatures, it is a monotonic decreasing function of temperature. This functionality represents the fact that micro-organisms die or become dormant at high temperature. The heat release due to oxidation reaction is modelled by Arrhenius kinetics. The model consists of mass balance equations for oxygen and energy. Steady-state temperature diagrams are determined as a function of the size of the compost pile and the flow rate of air through the pile. We show that there is a range of flow rates for which elevated temperatures, including the possibility of spontaneous ignition, occur within the pile. We also investigate the effects of variations in the ambient temperature

T. Luangwilai, H.S. Sidhu, M.I. Nelson and X.D. Chen. Modelling air flow and ambient temperature effects on the biological self-heating of compost piles. Asia-Pacific Journal of Chemical Engineering, 5(4), 609-618, 22010.

The DOI (Digital Object Identifier) link for this article is http://dx.doi.org/10.1002/apj.438.


A model for incomplete mixing in a bioreactor

Abstract

In many models for biological processes it is assumed that the reactor contents are well mixed. This assumption may be good if the reactor is small but for a large reactor this assumption is not so good. Here we analyse a model for a bioreactor with imperfect mixing. We use a two parameter mixing model in which the reactor is split into two compartments: a large compartment and a small compartment, with mixing between the two compartments. In each compartment there are two equations: one for the concentration of substrate and one for the concentration of microorganisms. The interaction between the substrate and biomass is governed by Monod growth kinetics. We investigate how the effluent concentration leaving the reactor depends upon the degree of mixing in the reactor (δ) and the size of the small compartment (ε). The model has two limits. When delta is equal to zero there is no mixing between the compartments and when delta is equal to infinity we have perfect mixing. When delta is equal to zero the effluent concentration is higher than when delta is equal to infinity. It might be expected that as the value of delta increases from the zero the effluent concentration decreases. However, for small values of delta the effluent concentration actually increases. Therefore an important conclusion from this work is that a very small amount of mixing is actually worse than no mixing.

A.H. Msmalip and M.I. Nelson. A model for incomplete mixing in a bioreactor. In Proceedings of the 38th Australasian Chemical Engineering Conference, CHEMECA 2010, (on CDROM), Engineers Australia, 2010. ISBN 978-085-825-9713.


The pH profile of the human stomach

Abstract

Following ingestion of a food substance, the pH within the human stomach changes. Initially it increases to accomodate the activities of the salivary amylase and gastric lipase. After digestion takes place, the pH of the stomach falls back to its original value due to continuous secretion of the acidic gastric juices. The time variation of the pH is known as the pH profile of the stomach and this can be a very strong indicator of human health and nutrition. Small changes in the pH profile can affect the disintegration of coating materials and capsules, the interaction of drugs with gastric secretions, drug absorption and dosage performance. We model the change in pH under ideal reactor conditions, in which a non-homogeneous food source, composed of a mixture of unreacted acid and base molecules, is mixed with gastric secretions of the stomach. Through a graphical comparison, we show that the pH model closely resembles trends observed from experimental data.

R. van Bentump, M.I. Nelson, X.D. Chen and G. O'Brien. The pH profile of the human stomach. In Proceedings of the 38th Australasian Chemical Engineering Conference, CHEMECA 2010, (on CDROM), Engineers Australia, 2010. ISBN 978-085-825-9713.


Using Singularity Theory to Analyse a Spatially Uniform Model of Self-Heating in Compost Piles

Abstract

Fires at industrial comp osting facilities, such as those storing indus- trial waste products like municipal solid waste (MSW) and landfills, are fairly common. In most cases these are manageable and such incidents are not destructive enough to attract attention b eyond these facilities. However, over the years there have b een a few notable devastating fires at such facilities.

In each of these industrial processes (e.g. comp osting) there is an inherent increase in temp erature as a consequence of the biological activity. Indeed such a temperature increase is one of the goals of the composting waste. Elevated temp eratures of the order of 70 - 90 degrees Celsius have been documented within a few months (or even a few days) of forming the comp ost pile. Although the basic theory of spontaneous combustion relating to organic materials is well understood, there has been very little work undertaken with regard to the mechanism for fires involving biological self-heating.

In this work we formulate and investigate a uniformly distributed mathematical model (based up on Semenov's theory ) for the thermal response of cellulosic materials in compost pile. The model consists of mass balance equations for oxygen and energy equations. The model incorporates the heat release due to biological activity within the pile. Biological heat generation is known to be present in most industrial processes handling large volumes of bulk organic materials. We utilize dynamical systems theory, in particular singularity theory, to investigate the generic properties of the model, as well as to determine the critical sizes of the compost piles under various conditions.

Keywords: bifurcation analysis, biological heating, composting, self-heating, semenov model, singularity theory.

T. Luangwilaip, H.S. Sidhu, M.I. Nelson and X.D. Chen. Using Singularity Theory to Analyse a Spatially Uniform Model of Self-Heating in Compost Piles. East-West Journal of Mathematics, Contributions in Mathematics and Applications III: 328-343, 2010.


The Semenov Formulation of the Biological Self-Heating Process in Compost Piles

Abstract

We formulate and investigate a uniformly distributed mathematical model (based upon Semenov's theory for thermal explosions) for the thermal response of cellulosic materials in compost piles. The model consists of a mass balance equation for oxygen, a heat balance equation, and incorporates the heat release due to biological activity within the pile. Biological heat generation is known to be present in most industrial processes handling large volumes of bulk organic materials. We utilise singularity theory to investigate the generic properties of the model, as well as to determine the locus of different singularities, namely the cusp, isola and double limit point. Singularity theory provides a useful tool to systematically analyse this system. We investigate the conditions where biological activity results in the initiation of an elevated temperature branch within the compost pile.

T. Luangwilaip, H.S. Sidhu, M.I. Nelson and X.D. Chen. The Semenov Formulation of the Biological Self-Heating Process in Compost Piles. In P.~Howlett, M.~Nelson, and A.~J. Roberts, editors, Proceedings of the 9th Biennial Engineering Mathematics and Applications Conference, EMAC-2009, volume~51 of ANZIAM J., pages C425--C445, jun 2010. http://journal.austms.org.au/ojs/index.php/ANZIAMJ/article/view/2439 [June 29, 2010].


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