Methanolysis of microbial polyester poly(3-hydroxybutyrate) catalyzed by Brønsted-Lewis acidic ionic liquids as a new method towards sustainable development

Abstract

Chemical recycling of bio-based polymer poly(3-hydroxybutyrate) (PHB) by methanolysis was discussed in detail from the perspective of biological refining. The results of methanolysis transformed PHB into ester monomer successfully by using some ionic liquids. PHB was depolymerized into methyl 3-hydroxybutyrare (M3HB) at lower degradation temperatures in the presence of Brønsted-Lewis acidic ionic liquid 1-(3-sulfonic acid)-propyl-3-methylimidazole ferric chloride ([MIMPS]FeCl4) as catalyst. Obtained M3HB from this reaction can be used in many areas, which is consistent with the principles of sustainable development. Then, the influences of reaction parameters on PHB methanolysis were investigated and the optimum conditions were obtained. Under the optimum conditions, the conversion of PHB and yield of M3HB was 98.5% and 87.4%, respectively. This catalyst could be recycled up to 6 times with no apparent decrease in catalytic activity. At the same time, the methanolysis mechanism of PHB is proposed through the experiments. In addition, kinetic study indicated that this reaction was pseudo-first-order reaction with activation energy of 24.74 kJ/mol.