Process modelling and economic evaluation of biopropane production from aqueous butyric acid feedstock

Catalytic hydrothermal decarboxylation of biomass-derived butyric acid can produce renewable biopropane as a direct drop-in replacement fuel for liquefied petroleum gases. In this present study, experimental results from a batch reactor have been used to develop a hypothetical continuous process to deliver 20,000 tonnes/year of biopropane, as base-case capacity, from 10 wt% aqueous butyric acid. A combination of process synthesis and ASPEN Hysys simulation have been used to formulate a process flowsheet, after equipment selection. The flowsheet has been used to carry out economic analyses, which show that the minimum selling price of biopropane is $2.51/kg without selling the CO2 co-product. However, with the incorporation of existing UK renewable energy incentives, the minimum selling price can reduce to $0.98/kg, which is cheaper than the current $1.25/kg selling price for fossil liquefied petroleum gases. Sensitivity analysis based on raw material costs and production capacities show profound influence on the minimum selling price, with strong potentials to making biopropane competitive without incentivisation, whereas the influence of selling CO2 is marginal. While this biopropane technology appears promising, it still requires more detailed technical and process data, life-cycle analysis and detail economic costings and testing at a pilot-scale prior to commercial exploitation.