The health risks associated with certain chemical agents and the need for their disposal pushes research towards new efficient and environmentally sustainable processing strategies. Enzymatic reactions owing to their specificity, efficiency and low energy consumption are the more promising candidates to reach this goal. Membrane processes and in particular, biocatalytic membrane reactors (BMR), have the potential to play a significant role in preventing pollution allowing process intensification by integrating biocatalysis and separation in a single unit. Enzymatic catalysis besides conventional media, can be also conducted with reactants present in the gas phase. This approach named solid-gas biocatalysis with respect to traditional solid-liquid biocatalysis has many advantages such as higher thermostability of the dehydrated enzyme, absence of leakage, reduction of microbial contamination, improvements in mass transfer. In addition, solid-gas systems offer very high production rates for minimal plant sizes, allow important reduction of treated volumes and permit simplified downstream processes. Therefore, it appears as a promising technology for new cleaner processes development. The aim of the present work was to study enzyme immobilization conditions to develop a solid-gas BMR, able to work in continuous. As model reaction has been selected the hydrolysis of ethyl acetate (eq. 1) and as model enzyme lipase from candida rugosa (LCR) immobilized on functionalized polyvinylidene fluoride (PVDF) membranes. CH3COOCH2CH3(g) + H2O(g) CH3CH2OH(g) + CH3COOH(g) (eq. 1) The enzyme microenvironment is a crucial factor, which can affect enzyme efficiency. To investigate this aspect, the LCR was immobilized by means of three different methods. In the first method, the negatively charged LCR was immobilized in a no covalent way (by both adsorption and ionic interaction) on PVDF membrane functionalized with positively charged amino. In the second method, aldehyde groups were introduced on PVDF and LCR was immobilized by covalent bond. In the third method, LCR was immobilized employing as carrier polyacrylamide (PAAm) microgels synthesized in the desired size range and purpose-functionalized. In the developed BMR process, parameters such as amount of immobilized LCR, flow rate of ethyl acetate and water were investigated. Results demonstrate that the dehydrated-immobilized LCR has higher thermostability when compared with the free-hydrated one. In fact, during experiments carried out at temperature of 50°C the dehydrated LCR showed biocatalytic activity and long-term stability (at least 3 months) whereas the hydrated one resulted completely inactive. In the BMR, the best performance in terms of specific activity were obtained feeding 0.3 mL h-1 of water and 1.3 mL h-1 of ethyl acetate, for the membrane containing 84 µg cm-2 of LCR immobilized by the microgels assistance.
Biocatalytic membrane reactor for organic compounds treatment in gas phase
Giuseppe Vitola;Rosalinda Mazzei;Giuseppe Barbieri;Teresa Poerio;Enrica Fontananova;Lidietta Giorno
2018
Abstract
The health risks associated with certain chemical agents and the need for their disposal pushes research towards new efficient and environmentally sustainable processing strategies. Enzymatic reactions owing to their specificity, efficiency and low energy consumption are the more promising candidates to reach this goal. Membrane processes and in particular, biocatalytic membrane reactors (BMR), have the potential to play a significant role in preventing pollution allowing process intensification by integrating biocatalysis and separation in a single unit. Enzymatic catalysis besides conventional media, can be also conducted with reactants present in the gas phase. This approach named solid-gas biocatalysis with respect to traditional solid-liquid biocatalysis has many advantages such as higher thermostability of the dehydrated enzyme, absence of leakage, reduction of microbial contamination, improvements in mass transfer. In addition, solid-gas systems offer very high production rates for minimal plant sizes, allow important reduction of treated volumes and permit simplified downstream processes. Therefore, it appears as a promising technology for new cleaner processes development. The aim of the present work was to study enzyme immobilization conditions to develop a solid-gas BMR, able to work in continuous. As model reaction has been selected the hydrolysis of ethyl acetate (eq. 1) and as model enzyme lipase from candida rugosa (LCR) immobilized on functionalized polyvinylidene fluoride (PVDF) membranes. CH3COOCH2CH3(g) + H2O(g) CH3CH2OH(g) + CH3COOH(g) (eq. 1) The enzyme microenvironment is a crucial factor, which can affect enzyme efficiency. To investigate this aspect, the LCR was immobilized by means of three different methods. In the first method, the negatively charged LCR was immobilized in a no covalent way (by both adsorption and ionic interaction) on PVDF membrane functionalized with positively charged amino. In the second method, aldehyde groups were introduced on PVDF and LCR was immobilized by covalent bond. In the third method, LCR was immobilized employing as carrier polyacrylamide (PAAm) microgels synthesized in the desired size range and purpose-functionalized. In the developed BMR process, parameters such as amount of immobilized LCR, flow rate of ethyl acetate and water were investigated. Results demonstrate that the dehydrated-immobilized LCR has higher thermostability when compared with the free-hydrated one. In fact, during experiments carried out at temperature of 50°C the dehydrated LCR showed biocatalytic activity and long-term stability (at least 3 months) whereas the hydrated one resulted completely inactive. In the BMR, the best performance in terms of specific activity were obtained feeding 0.3 mL h-1 of water and 1.3 mL h-1 of ethyl acetate, for the membrane containing 84 µg cm-2 of LCR immobilized by the microgels assistance.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
