Electrochemical Synthesis of Ortho- and Para-Hydroxybenzoic Acids Using CO2: Experimental and Simulation-Based Optimization

The electrochemical conversion of CO2 into value-added aromatic carboxylic acids represents an emerging route for carbon utilization. This work investigates the regioselective electrochemical synthesis of ortho- and para-hydroxybenzoic acids (o-HBA and p-HBA) from CO2 using a stirred batch cell, supported by a phenomenological Aspen Plus (version 12) model to assess process-level behavior. Experiments conducted at −1.2 V vs. Ag/AgCl, 3 atm CO2, and 50 °C achieved yields of 58.4 ± 2.1% for o-HBA and 40.2 ± 1.6% for p-HBA, with a combined selectivity of 64.8%. Faradaic efficiencies were 76.2% (o-HBA) and 66.8% (p-HBA). A complete carbon balance, including dissolved inorganic carbon species, was established, demonstrating a single-pass CO2 conversion of 42.6% and an overall conversion of 74.8% when the recycle loop was considered. Aspen Plus simulations based on ELECNRTL(Electrolyte Non-Random Two-Liquid model) thermodynamics and RYield fitting reproduced qualitative trends but underpredicted yields (21% and 9% for o- and p-HBA, respectively), reflecting the limitations of non-kinetic modeling. Sensitivity analyses confirmed that both electrolysis temperature and electrolyte concentration substantially influence yields and purity. This work provides reproducible electrochemical data, process-level mass balances, and a validated phenomenological simulation framework for future scale-up studies.

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