Design of bio-oil additives using mathematical optimisation tools considering blend functionality and sustainability aspects

Abstract

In this work, a computer-aided molecular design based technique has been developed to upgrade bio-oil properties via solvent addition by targeting both functionality and sustainability targets. The direct application of bio-oils as a fuel is often constrained by their inferior properties such as high water content, high viscosity, low heating values, low miscibility, and storage instability as compared to conventional fuels. One promising method to upgrade bio-oil is the use of solvents as additives to generate a solvent–oil blend capable of meeting both its fuel functionality and sustainability targets in health, safety, and environmental aspects from production to point of application. Suitable solvents were formulated using computer-aided molecular design (CAMD) techniques by solving a two-stage multi-objective optimisation problem based on the defined targets. In the first stage, an optimisation model for solvent–oil blend functionality was constructed to optimise solvent functionality. In the second stage, a fuzzy optimisation approach aimed to optimise environmental, health, and safety (EHS) aspects via an index-based method. By implementing a max–min aggregation approach, an optimised solution has been generated by determining trade-off points that allowed significant EHS improvements at minimal expense of blend functionality. Lastly, the optimal solvent–oil blend was evaluated against conventional diesel in terms of carbon savings. This allowed the quantification of environmental savings through utilising biofuels while ensuring minimal compromise on fuel performance. Altogether, this approach has enabled the identification of feasible solvents for bio-oil upgrade and design of blends for application while allowing multi-objective optimisation of EHS targets.