Solid-gas biocatalysis in a biocatalytic membrane reactor

Solid-gas biocatalysis is a special type of reaction system that exploits the ability of some enzymes, being in the solid state, to catalyze reactions of substrates in the gas phase. This approach, has been proposed in the aim of developing new technologies for applications in production, waste treatment, biosensing and so on. Solid-gas biocatalysis respect to traditional solid-liquid biocatalysis has many advantages such as an higher thermostability of the dehydrated enzyme, absence of leakage, reduction of microbial contamination, improvements in mass transfer and product recovery. Several enzymes, such as lipases, esterases, cutinases, alcohol oxidases, alcohol dehydrogenases, that traditionally converts substrates in aqueous solutions has been tested in solid-gas systems showing significant activity. The objective of the work was to develop a biocatalytic membrane reactor for hydrolysis of substrates in gaseous streams. Lipase from candida rugosa (LCR) covalently immobilized onto functionalized polyvinylidene fluoride (PVDF) membrane was used as model enzyme and ethyl acetate as gaseous substrate. Process parameters such as reaction temperature and transmembrane pressure were optimized and under the selected condition (T: 50° C, TMP: 0.36 Bar and relative humidy: 55%) the amount of LCR immobilized on the membrane was varied between 13 and 72 µg/cm2. The ethyl acetate hydrolysis, which end up in ethanol and acetic acid production, was monitored following the ethanol production by gas chromatography analysis. In comparison with the free LRC the immobilized one showed an higher thermostability and productivity. The use of this strategy, in which the enzyme immobilized on membrane has been used to catalyze a reaction in gaseous phase, shows promise for extension to other enzymes and substrates of interest (e.g. carbonic anhydrase, nitrogenase).