Biocatalysis immobilization approaches

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. 

In Part I a selection of the types of membrane reactor is presented, together with chapters on the integration of membrane reactors with current industrial processes. To summarize, in Chapter 1 (Calabro) membrane bioreactors are described from an engineering point of view, together with a straightforward description and simulation, with a simple mathematical approach, of the most important configurations and processes in which they are involved. Basic principles of bioconversion, bioreactors and biocatalysis with immobilized biocatalysts are also presented. For all the cited systems the most significant parameters are defined in order to estimate their performances. The best approaches for the preparation of... 

Another category of enzymatic transformations in multiphase systems is enzymes immobilized on the reactor wall as presented in Table 10.4. Enzymes are advantageously used in immobilized form because this strategy allows for increased volumetric productivity and improves stability. Continuous mode of operation is employed in these systems. The approaches commonly used for immobilization in conventional multiphase biocatalysis can also be employed in microreactors such as covalent methods, cross-linked enzyme aggregates (CLEA), and adsorption methods. The experimental setups can either be chip-type reactors with activated charmel surface walls where enzyme binds, or enzyme immobilized monolith reactors, where a support is packed inside a capillary tube. 

The immobilization of enzymes in ionogels has been found to be an efficient approach to achieve higher activities in biocatalysis. The first example, reported by Liu et al, demonstrated that the activity of horseradish peroxidase (HRP) was about 30-fold greater when it was immobilized in an ionogel rather than in silica without IL and proved an excellent thermal stability [60]. Recently, ILs have also been used as sustainable media in bioelectrochemistry [61]. 

Biocatalytic processes have become very important in the chemical industry [1-4], Of particular importance is one property of enz3unes— their stereoselectivity—which enables either of the two enanhomers to be reacted or formed preferentially in chemical reactions with chiral or prochiral compounds. Thus, resolution of racemic mixtures and more importantly the direct synthesis of enantiomerically pure products can be achieved without the need to protect group chemistry. Biocatalytic reactions are usually carried out under mild conditions, thus avoiding xmwanted side reactions [5,6]. Particularly in combination with enz)me immobilization, which enables easy workup of the product and reusability of the catalyst, biocatalysis is a promising approach in green chemistry. Moreover, the availability of protein engineering techniques also makes evolved or tailor-made biocatalysts more suitable for meeting the requirements of industrial applications. 

Traditional techniques such as physical adsorption and covalent linkage onto solid supports, entrapment in polymer matrices, and microencapsulation have long been used for immobilizing such enzymes as lipases, proteases, hydantoinases, acylases, amidases, oxidases, isomerases, lyases, and transferases [12-18]. Encapsulation and adsorption have also proved their utility in the immobilization of bacterial, fungal, animal, and plant cells [12-21]. However, as biocatalysis applications have grown, so the drawbacks and limitations of traditional approaches have become increasingly evident. The forefront issues now facing bioimmobilization are indicated in Table 1. 

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