Handbook of Membrane Reactors

Reactor Types and Industrial Applications

Angelo Basile

• Publisher: Woodhead Publishing
• Year: 2013
• Print ISBN: 9780857094155
• eBook ISBN: 9780857097347
• Topic: Technology & Engineering
• Subtopic: Chemical & Biochemical Engineering
• Index: Technology & Engineering

Membrane reactors are increasingly replacing conventional separation, process and conversion technologies across a wide range of applications. Exploiting advanced membrane materials, they offer enhanced efficiency, are very adaptable and have great economic potential. There has therefore been increasing interest in membrane reactors from both the scientific and industrial communities, stimulating research and development. The two volumes of the Handbook of membrane reactors draw on this research to provide an authoritative review of this important field.Volume 2 reviews reactor types and industrial applications, beginning in part one with a discussion of selected types of membrane reactor and integration of the technology with industrial processes. Part two goes on to explore the use of membrane reactors in chemical and large-scale hydrogen production from fossil fuels. Electrochemical devices and transport applications of membrane reactors are the focus of part three, before part four considers the use of membrane reactors in environmental engineering, biotechnology and medicine. Finally, the book concludes with a discussion of the economic aspects of membrane reactors.With its distinguished editor and international team of expert contributors, the two volumes of the Handbook of membrane reactors provide an authoritative guide for membrane reactor researchers and materials scientists, chemical and biochemical manufacturers, industrial separations and process engineers, and academics in this field. - Discusses integration of membrane technology with industrial processes - Explores the use of membrane reactors in chemical and large-scale hydrogen production from fossil fuels - Considers electrochemical devices and transport applications of membrane reactors

Part I

Selected types of membrane reactor and integration with industrial processes

1

Engineering aspects of membrane bioreactors

V. Calabrò, University of Calabria, Italy

Abstract:

This chapter describes membrane bioreactors from an engineering point of view. A membrane bioreactor can be defined as a unit operation or a piece of chemical equipment that combines a biocatalyst-filled reaction chamber with a membrane system for the purposes of adding reactants or removing products from a reaction. The basic principles of bioconversion, bioreactors and biocatalysis are introduced, together with a description of the most important biocatalyst immobilization techniques. The mass transfer phenomena involved in membrane systems are discussed along with some representative configurations of membrane bioreactors, whose behaviour can be described using a simple mathematical approach. For all the aforementioned systems the most significant parameters have been defined to estimate the system performance.

Key words

membrane bioreactors

biocatalysis

process modelling

biocatalyst kinetics

1.1 Introduction

A bioreactor is a device within which biocatalysts, usually enzymes or living cells, carry out biochemical transformations. A bioreactor is frequently called a fermenter whether the transformation is carried out by living cells or in vivo cellular components, that is, enzymes. A membrane bioreactor can be defined as a unit operation or a piece of chemical equipment that combines a bioreactor with a membrane system. An enzyme membrane reactor is a membrane bioreactor in which the biocatalyst is an enzyme. In a membrane bioreactor, the membrane can be used for different tasks:

• separation,

• selective extraction of reactants,

• retention of the biocatalyst,

• distribution/dosing of a reactant and

• biocatalyst support (often combined with distribution of reactants).

Consequently, membrane bioreactors are an example of the combination of two unit operations in one step; for example, membrane filtration with the chemical reaction. In a typical membrane bioreactor, as well as acting as a support for the biocatalyst, the membrane can be a very effective separation system for undesirable reactions or products. The removal of a reaction product from the reaction environment can be easily achieved thanks to the membrane selective permeability, and this is of great advantage in thermodynamically unfavourable conditions, such as reversible reactions or product-inhibited enzyme reactions. A very interesting example of a membrane bioreactor is the combination of a membrane process, such as micro-filtration or ultrafiltration (UF), with a suspended growth bioreactor. Such a set up is now widely used for municipal and industrial wastewater treatment, with some plants capable of treating waste from populations of up to 80 000 people (Judd, 2006).

Over the last few decades membrane science and technology have offered a great contribution to the development of biotechnology and, more specifically, to the engineering of enzyme bioreactors. Membranes have been extensively used to support biocatalyst immobilization with the aim of creating workable membrane bioreactors (Atkinson, 1974; Belfort, 1989; Cheryan and Mehaia, 1986; Giorno et al., 2003; Iorio et al., 1994; Messing, 1975). Different membrane configurations and membrane bioreactors have been proposed in recent years for this purpose and have been widely discussed by several authors (Calabrò et al., 2008) and the optimization of novel immobilization techniques certainly improves biocatalyst behaviour, thus leading to the development of very effective bioreactors. Synthetic membranes, for example, have been well-assessed as supports for the immobilization of biological catalysts under milder conditions, compared to those that exist when biocatalysts are chemically bound to a membrane. A synthetic membrane, with a suitable molecular weight cut-off (MWCO), somehow artificially replicates the functions of a cell membrane ensuring the protection of a purified enzyme against contaminants and inhibitors.

Biocatalysts are not always immobilized on membranes in bioreactors, though. As enzymes are macromolecules and often differ greatly in size from reactants they can be separated by size exclusion membrane filtration with ultra- or nano-filtration. This is used on an industrial scale in one type of enzyme membrane reactor for the production of enantiopure amino acids by kinetic racemic resolution of chemically derived racemic amino acids. The most prominent example is the production of L-methionine on a scale of 400 t/y (Liese et al., 2006). The advantage of this method over immobilization of the catalyst is that the enzymes are not altered in activity or selectivity as they remain solubilized. This principle can be applied to all macromolecular catalysts which can be separated from the other reactants by means of filtration. So far, only enzymes have been used to a significant extent.

The aim of this chapter is to give a detailed overview of the characterization of biocatalysts and the development of membrane bioreactors, in particular, the main aspects of biocatalyst kinetics and their immobilization/ entrapment, either within the porous membrane structure, or on its surface. Transport models that can help to predict the behaviour of membrane bioreactors, as well as the most relevant theoretical models and operating parameters, are presented below. This data is then analysed in order to ascertain how to improve effectiveness and productivity of the membrane bioreactors. Some relevant fields of application are also discussed in order to show the potential of such systems.

1.1.1 Basic principles of bioconversion

Bioprocess plants which use microorganisms and/or enzymes, such as fermentation plants, have many characteristics similar to those of chemical plants. Therefore, an engineering approach to the design and operation of various plants which involve biological systems would be valuable, provided the differences in the physical properties of some materials are taken into account.

Bioprocesses involve many reactions, both chemical and biochemical. In order to design a successful reactor, it is essential to understand how the composition of reactants and products and their utilization and production rates change under var...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Contributor contact details
• Woodhead Publishing Series in Energy
• Foreword
• Preface
• Part I: Selected types of membrane reactor and integration with industrial processes
• Part II: Membrane reactors in chemical and large-scale hydrogen production from fossil fuels
• Part III: Electrochemical devices and transport applications of membrane reactors
• Part IV: Membrane reactors in environmental engineering, biotechnology and medicine
• Index