Development And Verification Of A Model To Describe An Immobilized Glucose Isomerase Packed Bed Bioreactor

Biochemical Engineering Journal 40 (2008) 328–336

Development and verification of a model to describe an immobilized glucose isomerase packed bed bioreactor
Rajab Khalilpour, Reza Roostaazad ∗
Department of Chemical and Petroleum Engineering, Sharif University of Technology, Azadi Avenue, Tehran, Iran Received 10 May 2006; received in revised form 6 January 2008; accepted 7 January 2008Abstract In this paper, the performance of immobilized packed bed glucose isomerase enzyme was mathematically modeled. A modified Michaelis–Menten type relation was used to describe the enzyme kinetics. Mass transfer inside the biocatalyst particle and through the bed column was analyzed simultaneously. Using measured data, physicochemical properties including diffusivity, viscosity and density ofsugar solutions were correlated with its concentrations and were used to provide precision in solving the set of model equations. Model equations were solved using the Runge–Kutta and Gauss–Seidel algorithms and finite difference numerical method in MATLAB environment. Model output was used to demonstrate the effect of parameters such as velocity and bulk substrate concentration on the concentrationprofile within the biocatalyst particle, effectiveness factor and bulk substrate concentration along the bed. Model predictions were further validated against experimental data collected from a lab scale isomerization bioreactor. Measurements of the overall bioreactor conversion at various substrate concentrations were shown to lie within 5% of the values as put forth by the model. Usingexperimental data, a criteria was proposed to maximize the isomerization conversion from the immobilized bioreactor. © 2008 Published by Elsevier B.V.
Keywords: Glucose; Fructose; Glucose isomerase; Packed bed; Bioreactor; Immobilized enzyme; HFS

1. Introduction In many applications including those motivated by diabetes disease, it is desired to convert glucose into its isomeric form fructose. In termsof sweetness, fructose is about 1.8 times sweeter than glucose. There has thus been high interest in conversion of glucose into fructose. The acidic starch hydrolysis process that leads to a glucose (dextrose) syrupy product, dates back to 1811, the time at which a pronounced shortage of sweeteners arose in Europe. In World War II and because of acid shortages, the enzymatic hydrolysis version ofthat process was developed. Until the late 1950’s, an enzyme which could use glucose as its substrate and convert it into fructose had not been discovered. In 1957 Marshall and Kooi [1] discovered an enzyme named xylose isomerase in bacteria that could isomerize glucose to fructose (Fig. 1). Today this enzyme is called glucose isomerase and its systematic name is d-xylose ketol-isomerase (EC5.3.1.5).

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Corresponding author. Tel.: +98 9121507158; fax: +98 21 66022853. E-mail address: roosta@sharif.edu (R. Roostaazad).

Later in 1967 Takasaki [2] introduced a commercial method for converting dextrose (glucose syrup) to high fructose syrup (HFS). This process used soluble enzyme and was carried out in a batch-wise operation. Introduction of HFS to the world sweetener market providedincentives to develop other new methods for producing sweeteners. In 1974, the first immobilized form of glucose isomerase was introduced [3–7]. Since that time several reactor designs have been applied in various modes of operation for this conversion process [8,9]. In this spectrum, one could point out a number of reactor choices such as batch packed bed reactors, continuous stirred tank reactors(CSTR), continuous stirred tank/membrane reactors, recycled reactors and tubular reactors with enzymatically active walls [10]. However, after 30 years of experience, industry has accepted packed bed columns to be the most appropriate. Today packed bed reactors (PBR) are widely used in this industry, hence the problems of modeling and design of immobilized enzyme PBR have received considerable...