Ultrasound technology and molecular sieves improve the thermodynamically controlled esterification of butyric acid mediated by immobilized lipase from Rhizomucor miehei

Abstract

In this research, the effects of ultrasound stirring and the addition of molecular sieves on esterification reactions between butyric acid and several alcohols catalyzed by immobilized lipase from Rhizomucor miehei (Lipozyme RM-IM) were studied. Among the tested alcohols, 1-propanol and isobutanol allowed the highest activities, whereas Lipozyme RM-IM showed poor activities for esterification using secondary and tertiary alcohols. Different solvents were also tested and n-hexane was selected because of its reaction effects, besides being cheaper, available at low boiling point, and ease of recovery. Using the preselected alcohol and solvent, other reaction parameters (butyric acid concentration, temperature, substrate molar rate, and biocatalyst content) were studied to optimize the reaction conditions. Optimal conditions were acid concentration, 0.7 M; substrate molar ratio, 1 : 1 alcohol-acid; temperature 45 C; biocatalyst content, 14% (by substrate mass). Under these conditions, it was possible to obtain a yield of 86% of butyl butyrate in 2.5 h. When molecular sieves (90 mg mmol À1 butytic acid) were added to the reaction, the observed yield increased to 96%. The biocatalyst was used in 5 successive reaction cycles keeping 100% of its initial activity. The overall process productivity was improved 2-fold when compared to the traditional mechanical agitation, showing that ultrasound is a promising technology for application in biocatalysis.

Evaluation of reaction parameters and kinetic modelling for Novozym 435 catalysed synthesis of isoamyl butyrate

“…The test showed that the enzyme was stable in isoamyl alcohol confirming the fact that Novozym 435 was inhibited and not denatured at higher concentrations of isoamyl alcohol. In this study use of molecular sieves assisted in preventing accretion of water, hence averting hydrolysis and giving higher initial rates . Also, it has been observed that molecular sieves not only adsorb water formed in situ but also a small amount of acid as well .…”

“…Kinetic energy of molecules rises with temperature and provides numerous collisions with the enzyme to enhance the rate of reaction . At higher temperatures, most of the interactions driving esterification and equilibrium processes, like miscibility, partitioning of substrates between the micro‐interface of enzyme–water, dissociation of acid as well as binding of substrate and interactions, are intensified . Moreover, the diffusion of components also increases at higher temperature due to the reduction in viscosity.…”

“…Along with ester, water is a major by‐product of the esterification reaction. Although water is a crucial element for maintaining enzymatic functional activity, an excess of water in the enzymatic process not only reduces the rate of forward reaction, but also introduces high conformational flexibility that diminishes its catalytic activity . Thus, molecular sieves are recommended to prevent the undesired hydrolysis of ester and enzyme deactivation.…”

“…Although water is a crucial element for maintaining enzymatic functional activity, an excess of water in the enzymatic process not only reduces the rate of forward reaction, but also introduces high conformational flexibility that diminishes its catalytic activity. 10 Thus, molecular sieves are recommended to prevent the undesired hydrolysis of ester and enzyme deactivation. The work on lipase catalysed synthesis of isoamyl butyrate in the presence and absence of solvent system, has been reported by various researchers.…”

Production and optimization of isopropyl palmitate via biocatalytic route using home‐made enzymatic catalysts

“…Lipases (EC 3.1.1.3) are an important group of biocatalysts used in many biotechnological applications, such as in the synthesis of biopolymers, biodiesel, biolubricants, pharmaceuticals, agrochemicals, compounds used in the cosmetics industry, among others . These enzymes are able to catalyze distinct reactions, such as hydrolysis, esterification and transesterification, presenting enormous versatility in different types of organic synthesis, exhibiting high specificity and selectivity . In esterification reactions, for example, depending on the alcohol or carboxylic acid chain length, ester molecules exhibiting distinct properties are produced and can be employed for different purposes, such as emulsifiers, lubricants, flavor or cosmetic compounds …”