Development of heterogeneous catalysts for butyl butyrate production

Butyl butyrate is an environmentally friendly biofuel component that can be produced through the esterification of butyric acid with n-butanol, both of which are obtainable from waste products with a two-step fermentation process. To catalyse the production of butyl butyrate, heterogeneous solid acid catalysts were developed by sulfonation of char obtained from the carbonisation of Miscanthus x giganteus and solid residues derived from the fermentation of brown bin waste (digestate). In the case of Miscanthus derived material, prior to sulfonation, part of the char underwent chemical activation with the purpose of increasing the surface area of the char (from 6.4 to 571 m²·g-1 after chemical activation at 500°C). The catalysts possessing the highest surface area and acid density were shown to have the highest catalytic activity and thus performed better giving competitive results to Amberlyst 15 and H2SO4 (96 % yield), after 24 hours reaction. Activated Miscanthus based catalysts and Brown bin waste digestate based catalysts exhibited a superior catalytic activity after usage, and also a better reusability. Realistic kinetic parameters were formulated for the optimum char based solid acid catalyst using two power law models. A one-step synthesis process of butyl butyrate from butyric acid through hydrogenation and esterification has also been investigated. This process has the potential to replace currently used esterification processes in which both butyric acid and butanol are used. This study focused on the development and characterization of suitable catalysts and on the enhancement of the reaction conditions such as temperature and H2 pressure.