Direct contact enzyme reactors

The first step for the design of an EMR is to select the type of reactor. Extractive membrane reactors are desirable when one of the substrates or products is poorly soluble in aqueous solution or when an undesirable by-product has to be separated, as the membrane acts as a solvent extraction step [99]. Immobilized enzyme reactors are usually applied with materials that enable enhancement of enzymatic stability or preserve enzyme from deactivation by a direct contact with an organic solvent [99]. Finally, direct-contact membrane reactors are the most versatile alternative in processes with soluble compounds. 

In this class of reactors, substrates are fed to the region of the system that contains the enzyme, ensuring a direct contact between them and immediate enzymatic action. The separation of the biocatalyst can be performed in the same reactor or by coupling an external membrane unit. 

Although some efforts are being made to develop EMRs based on the immobilization of peroxidases onto the membrane [106, 112], the most applied configurations correspond to the use of direct contact reactors for wastewater treatment, with SBP and MnP applied to effluents containing both phenols [74] and dyes [8, 85]. Some attempts were made to apply an EMR for the synthesis of oxindole from indole by CPO [86]. However, the reactor was only stable for a short period (10 residence times). Afterward, the polymerization of oxindole yielded a solid substance, which blocked the membrane, causing enzyme deactivation and the reduction of the total turnover numbers compared to those obtained in batch assays. 

The patent described a method for the removal of thiophenic compounds from fossil fuels, in which the reacting media might contain organic solvents. Additionally, the biocatalyst may be contacted with the fuel directly either as free enzyme or in its immobilized form. The process could, therefore, be performed either in a batch reactor or in a semi-continuous or continuous manner. Further, it may be performed either as a stand... 

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