Comparative techno-economic analysis of single-step and two-step biodiesel production with supercritical methanol based on process simulation

[Display omitted] •Industrial scale capacities simulated with process design software Aspen Plus 8.8.•Supercritical process is a techno-economically viable solution for UCO processing.•Two-step process has lower investment and costs per unit of biodiesel produced.•Higher energy cost of the two-step process is compensated by higher yields. Two alternative processes for biodiesel production from used/waste cooking oil, the single-step supercritical transesterification and the two-step process consisting of oil hydrolysis and subsequent supercritical methyl esterification, were designed and simulated using the Aspen Plus 8.8 software and assessed from a techno-economic point of view. Detailed operating conditions, material and energy flows, and equipment designs were provided for biodiesel plants with 15,000t and 30,000t annual inlet capacities. Results revealed that both technologies offer a techno-economically viable solution for biodiesel production from low quality feedstocks such as used cooking oil. The two-step process requires milder operating conditions, lower investment and overall production costs per unit of biodiesel produced, however, it has higher process energy requirements. Total capital investments for a 15,000t capacity plant which applies the single- or the two-step process were estimated as 6.1 million EUR or 5.8 million EUR, respectively, whereas the production cost of biodiesel are estimated as 0.824EUR/kg and 0.786EUR/kg for the single- and two-step processes, respectively (at used cooking oil price of 0.500EUR/kg). Higher plant capacities have lower production and capital costs per unit of biodiesel output. Supercritical transesterification should lead to a clean, flexible and modular method to process used cooking oil for the production of a more valuable product.