Process Simulation and Economic Evaluation of the [bmim][FeCl₄] Ionic Liquid for H₂S Direct Conversion to Elemental...

The urgent demand for cleaner industrial gas treatment and sustainable sulfur recovery has intensified the search for alternatives to conventional high-temperature processes. In this work, the ionic liquid transition metal (ILTM) process using [bmim]-[FeCl₄] was designed and simulated in Aspen Plus (v14), while the conventional Claus process was modeled in Aspen HYSYS (v14). [bmim]-[FeCl₄] was defined as a pseudocomponent, with thermophysical properties estimated using COSMO-RS and the Valderrama-Robles method. A refinery off-gas containing 91.4 mol % H₂S served as the feed basis. Technical performance was assessed through mass and energy balances and sulfur recovery efficiency, while economic performance was evaluated in Aspen Process Economic Analyzer (APEA). Technically, the ILTM achieved a sulfur recovery efficiency of 99.68% under milder conditions. Its simplified single-stage absorption regeneration cycle eliminates catalytic reactors and high-temperature units, reducing the process complexity and energy demand. Economically, ILTM lowered capital expenditure (CAPEX) by 43.96% and operating expenditure (OPEX) by 38%, resulting in a total annualized cost (TAC) 42% lower than that of the conventional process. Overall, the [bmim]-[FeCl₄]-based ILTM technology represents a promising low-carbon alternative to the Claus process, exhibiting zero direct CO₂ emissions compared with approximately 0.78 t of CO₂/t of S generated in the conventional process. However, further analysis is needed to reduce the ionic liquid cost and validate large-scale operation through pilot-scale studies.