Biocatalytic recovery

Straightforward. We have therefore employed XAD-4 to combine biocatalytic synthesis with simultaneous product extraction. The system (Figure 15.8) comprises a continuously stirred tank reactor, a starting material feed pump, a product recovery loop with a (semi-) fluidized bed of XAD-4, and a pump to circulate the entire reaction mixture through the loop." ° Preliminary studies indicated that XAD-4 had no detrimental effects on E. coli JMlOl (pHBP461), hence, separation of biomass and reaction liquid prior to catechol extraction was not required. The biocatalytic reaction was carried out at very low concentrations of the toxic substrate and product. This was achieved by feeding the substrate at a rate lower than the potential bioconversion rate in the reactor. 

Figure 15.9 shows that this approach worked quite nicely the substrate was added to a total concentration of 2.5 g/L, but neither substrate nor product accumulated in the bioreactor medium. Without a product recovery loop the product concentration (3-phenylcatechol) did not exceed 0.4 g/L, because of biocatalyst deactivation (results not shown). With the loop, 2-phenylphenol and 3-phenylcatechol concentrations remained below 0.1 g/L. Therefore, cell viability and biocatalytic activity were maintained, as indicated by the constantly low dissolved oxygen tension in the aerated reactor. As a result product yields (based on the 3-phenylcatechol eluted from the product sink) increased by one order of magnitude." ... 

The use of enzymes as biocatalysts for the synthesis of water-soluble conducting polymers is simple, environmentally benign, and gives yields of over 90% due to the high efficiency of the enzyme catalyst. Since the use of an enzyme solution does not allow the recovery and reuse of the expensive enzyme, well-established strategies of enzyme immobilization onto solid supports have been applied to HRP [22-30]. A recent work reported an alternative method that allows the recycle and reuse of HRP in the biocatalytic synthesis of ICPs. The method is based on the use of a biphasic catalytic system in which the enzyme is encapsulated by simple solubilization into an IL. The main strategy consisted of encapsulating the HRP in room-temperature IPs insoluble in water, and the other components of the reaction... 

Recovery of aroma compounds from diluted aqueous streams (we are excluding from this discussion the recovery of aromas from vapour streams) may be of industrial interest under different circumstances recovery of complex aroma profiles and/or target aroma compounds from active biocatalytic processes recovery of complex aroma profiles and/or target aroma compounds from natural extracts and industrial process water (or effluent) streams. 

The integration of two unit operations lies at the heart of process engineering. More often in bioprocesses it is the integration of product formation with the following recovery steps that is critical.5 In the specific case of biocatalytic processes the product recovery is also critical, but in this chapter the focus will be on the integration of the surrounding chemical steps with the biocatalysis. 

The above-mentioned processes employ isolated enzymes - penicillin G acy-lase and thermolysin - and the key to their success was an efficient production of the enzyme. As with chemical catalysts, another key to success in biocatalytic processes is an effective method for immobilisation, providing for efficient recovery and re-use. 

Enzyme immobilization has several benefits, including enzyme recovery and reuse. The abilitiy to recycle enzyme-catalysts so they may be reused hundreds of times is critical to achieve economically viable biocatalytic processes. Furthermore, by their immobilization, en2yme thermal and chemical stability as well as catalytic activity can be greatly improved. Numerous enzymes are available commercially in their immobilized form (e.g. Novozym 435, immobilized CALB). Not surprisingly, many immobilization methods have been devised 71-74). The following account provides several good examples these are also summarized in Table 1. 

Tlie factors determining the industrial and economic feasibility of biocatalytic processes are depicted in Figirre 8.2, showing the key aspects of the syntlietic process (and its economics), biocatalyst selection and characterization, biocatalyst engineering, its application in industrial use, and product recovery. 

Biocatalytic processes for the manufactming of complex or sensitive molecules require highly selective sepai ation and purification methods. Tlie in situ separation of inhibitory or toxic byproducts or the shifting of unfavourable equilibria aie additional aims of bioprocess conhol technologies. In situ product removal advances both the conhol of biocatalytic processes and the recovery of target molecules. 

Biocatalytic desulfurization of diesel fuel Sulfur recovery using oxygen-enriched air California smog control Zero emissions from a THF plant Volatile organic compound (VOC) abatement—thermal incineration, catalytic incineration, or adsorption, for ozone control... 

At present microbial sulfur oxidation reactions are certainly feasible on a preparative scale, but poor recoveries of the water-soluble products from the considerable amounts of biomass (a normal consequence of using whole cells as the biocatalyst) have to be taken into account. Whether the use of isolated oxidases will be an advantage [1199], future investigations will tell. For biocatalytic sulfur oxidation using peroxidase reactions, see Sect. 2.3.3. 

Enantioenriched a-substituted carboxylic acids have been prepared using the growing cell system of Nocardia diaphanozonaria JCM3208. Racemic 2-aryl and 2-aryloxypropanoic acid could be deracemized leading to the recovery of the (R)-enantiomer in high yield (>50%) and 69% ee (Scheme 4.44). A new biocatalytic... 

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