Integrated Recycling of Polylactide using Biomass into Renewable Fuels: A Combined Experimental and Computational Design Approach

Abstract

Across the globe, the consumption of plastics and fuels rises steadily. Conventionally, both products are fossil-based and have a negative impact on the environment, particularly plastic pollution and CO2 emissions. This work explores the recycling of bio-based polylactide (PLA) into renewable fuels as a strategy to mitigate both issues. To develop an efficient recycling strategy and guide process development toward the most promising pathway, we propose a systematic, three-step screening approach that combines depolymerization experiments with computational methods to estimate fuel properties, production cost, and material efficiency across alternative production routes. First, the robust, non-toxic bisguanidine TMG2e as well as a zinc bisguanidine catalyst are evaluated for PLA alcoholysis using 15 different alcohols. Applying our predictive models, we rank each alkyl lactate as potential fuel blend candidate based on its estimated fuel properties. In the final step, we analyze the most promising candidates using reaction network flux analysis (RFNA) to gain insight into the economic costs and environmental impact of their production, considering biomass-alcohols as co-reactants in the alcoholysis step. As result of this screening approach, which is general and not limited only to the selection of fuel candidates, methyl and ethyl lactate are identified as the most promising alkyl lactates. Both candidates exhibit comparable properties and a similar catalytic efficiency in the depolymerization step. However, the whole production process of methyl lactate outperforms that of ethyl lactate when methanol is produced from CO₂ and hydrogen, whereas ethyl lactate becomes favorable when ethanol originates from biomass. We thus outline a new sustainable value chain starting from PLA plastic waste and biomass to sustainable fuel candidates.