Recovery , enzyme process design

The economic feasibility of enzymatic production of biodiesel depends on a series of factors. These factors mainly include (1) the raw material costs such as the prices of oil feedstock, alcohol and enzyme (2) the process parameters, such as oil-to-biodiesel conversion ratio, retention time for transesterification, biodiesel recovery yield, lipase life time, and solvent loss (if used) (3) process design regarding water recycle and heat integration and (IV) by-product credit. It has been found that lipase cost contributes a great part of the total production cost. 

As may be expected, criteria for the study of pseudo irreversible inhibitors are very similar to those for both affinity labels and mechanism-based inhibitors. However, because of the inherent reversibility of pseudoirrevers-ible inhibitors, it may be more difficult to obtain structural evidence for the covalent enzyme inhibitor adduct. Further, determination of the rate of reactivation and characterization of the products of the recovery process will also be of major importance in designating an inhibitor as pseudoirreversible. 

A constant final concentration in the retentate loop can be maintained by bleeding out a small fraction, either out of the system or to some other location in the process. This operation is described as a batch feed and bleed and is commonly used in the processing of many high value biotechnology products such as batch fermentations to recover vitamins, enzymes and common antibiotics.The CFF system will require larger surface area since the system must be designed at the flux obtained at the final concentration factor (e.g., 20 for 95% recovery). 

Subsequent studies (6) produced a mathematical model of the process which defined the importance of tube diameter on pressure drop. The design flow in a channel was found to be proportional to the 2.0 to 2.5 power of the tube diameter. Thus, a prototype utilizing 1 1/4-inch diameter tubes was constructed and operated stably at 85% juice yields with much lower pressure drops (250-350 psi). This same study (6) also addressed optimization of viscosity reduction of the puree and membrane flux utilizing commercial liquefaction enzymes. Viscosity reduction was readily obtained with even small amounts of liquefaction enzymes, and further increases in enzyme concentration did not appreciably affect viscosity reduction. However, steady state flux was proportional to the level of enzyme used up to 0.044%. Membrane flux correlated very well, as expected (3), with reduction of total pectin. It was evident that enzyme pretreatment should be further developed with the goal of enhancing flux rather than reducing viscosity, especially since increased tube diameter could be used to overcome pressure drops imparted by the viscosity of the retentate at high juice recoveries. 

The purpose of the recovery process, often referred to as the downstream process, is to separate the enzyme from the biomass and to produce a solution that contains the enzymes in a desired purity to be used for formulation of the final enzyme product. The production volumes and costs of enzyme products can be compared to fine chemicals, and thus the recovery processes need to be designed to handle large volumes in a fast and cost-effective way. 

The main factors influencing the design of the enzyme recovery process are as follows ... 

Most enzymes for detergent formulations, which are produced by genetically modified microorganisms, are monocomponents, that is, only one enzyme protein contributes to the overall activity. In a few cases, like cellulases, the enzyme product can be a multicomponent mixture of several enzyme proteins. In these cases, the recovery process must be designed to ensure that the ratio between the enzyme proteins important for the application is maintained throughout the recovery process. 

The properties of the enzyme have an impact on the design of the conditions for the recovery process, especially characteristics like temperature and pH stability, solubility of the enzyme protein, and hydrophobicity. The enzyme activity as a function of pH and temperature also influences the choice of process conditions. When processing (e.g., proteases), it can be advantageous to select process conditions where the enzyme has a low activity, to avoid self-digestion (auto proteolysis) of the enzyme. 

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