Influence of Temperature, Initial Reactant Ratio, and Catalyst Type and Concentration on a More Sustainable Synthesis of Pentyl Propanoate in a BSTR

Abstract

This work presents an investigation into a solvent-free esterification reaction of pentan-1-ol with propanoic acid to produce pentyl propanoate using a batch stirred-tank reactor (BSTR). The overall objective is to achieve a more sustainable and efficient reactive process. The individual effects of key variables – temperature, initial reagent ratio, and catalyst concentration – were evaluated using Lipozyme435 and compared against Amberlyst-15. Experimental data were correlated with two kinetic models: (a) a second-order reversible rate law, and (b) a Bi–Bi Ping Pong model incorporating dual-substrate inhibition, as well as an enzymatic mechanism induced by temperature and carboxylic acid concentration. The modeling reveals certain novel characteristics, which are discussed and lead to a positive evaluation. The results demonstrate a high pentyl ester conversion of 75–80% using Lipozyme435, when a stoichiometric molar ratio of alcohol/acid of 1 is used. However, under these conditions, enzyme deactivation occurred at temperatures ≥70 °C. When the alcohol/acid molar ratio was increased to 2, no loss of enzymatic activity was observed, even at the maximum tested temperature of 80 °C. Furthermore, the biocatalyst systematically developed Amberlyst-15 in reaction rate under similar conditions. Finally, reaction energy determined via a mini-scale procedure in a high-resolution calorimeter revealed an exothermic reaction enthalpy of −5.6 kJ/mol of ester produced. These findings provide a comprehensive kinetic and thermodynamic framework for improving ester synthesis under sustainable conditions.