What question did this study set out to answer?

The aim is to simulate and analyze a two-stage catalytic process for biodiesel production using high-FFA waste cooking oil.

June 21, 2026Open Access

Steady-state simulation and energy analysis of a two-stage heterogeneous catalytic process for biodiesel production from high-FFA waste cooking oil using Aspen HYSYS

Key Points

The aim is to simulate and analyze a two-stage catalytic process for biodiesel production using high-FFA waste cooking oil.
Used Aspen HYSYS for steady-state process simulation
Applied SHER for esterification and CaO for transesterification
Conducted sensitivity analysis on reaction temperature and methanol-to-oil ratio.
Esterification stage achieved 98.7% FFA conversion at 61 °C and MTO 12:1–13:1
Transesterification stage achieved 99.9% triglyceride conversion at optimal temperature of 62–65 °C
Specific energy consumption reduced from 3.08 to 1.66 MJ/kg with heat integration, significantly lower than industrial benchmarks.

Abstract

Abstract The widespread use of homogeneous alkaline catalysts for biodiesel production is fundamentally incompatible with high free fatty acid (FFA) feedstocks such as waste cooking oil (WCO), owing to saponification side reactions that reduce yield and complicate product separation. This study presents a steady-state process simulation of a two-stage heterogeneous catalytic biodiesel production process developed in Aspen HYSYS v15, employing a Sulphonated Hypercrosslinked Exchange Resin (SHER) for acid-catalysed esterification and waste mussel shell-derived calcium oxide (CaO) for base-catalysed transesterification, processing a high-FFA WCO feedstock (15 wt% FFA, 85 wt% triglycerides) at 100 kg/h. The Non-Random Two-Liquid (NRTL) thermodynamic package was applied alongside experimentally validated LHHW and pseudo-first-order kinetic parameters. Systematic sensitivity analysis of reaction temperature and methanol-to-oil (MTO) ratio was conducted for both stages. The esterification stage achieved a maximum FFA conversion of 98.7% at 61 °C and MTO 12:1–13:1, reducing FFA content to 0.49 wt% and protecting the downstream CaO catalyst from deactivation. The transesterification stage achieved 99.9% triglyceride conversion within the optimal thermal window of 62–65 °C at MTO 12:1–15:1. The final FAME product purity of 99.9 wt% substantially exceeds the EN 14214 minimum of 96.5 wt%. Flash heater duty was found to increase linearly with MTO ratio, establishing a quantifiable energy–conversion trade-off unique to heterogeneous systems. Heat integration reduced specific energy consumption from 3.08 to 2.68 MJ/kg (13% improvement) and further to 1.66 MJ/kg at the optimal MTO ratio—compared favourably against industrial benchmarks of 6.30 MJ/kg. These results establish transparent operating windows for decentralised, community-scale biodiesel production from high-FFA waste feedstocks.

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