Retrofit Design of a De-Isobutanizer Column via Vapor Recompression: Techno-Economic and CO2 Emission Analysis

Isobutane is a key feedstock for alkylate production. For separating an equimolar isobutane/n-butane mixture with 2 mol% ethane, two conventional designs are reported in the literature: a single water-cooled condenser (SC) and a dual condenser system with refrigeration (DC). This study proposes two vapor recompression retrofit configurations, SC-VR and SC-PHVR (with preheating), to improve energy efficiency and enable electrification. Economic and environmental performance were evaluated using total annualized cost (TAC) and CO2 emissions. Compared with SC and DC schemes, SC-VR reduces CO2 emissions by 49 and 52%, while SC-PHVR delivers higher reductions of 64 and 66%. A sensitivity analysis of electricity prices across 3-, 5-, and 10-year payback periods indicates the most favorable performance at 10 years. At 16.67 USD/GJ, SC-PHVR lowers TAC by 22 and 25%; in contrast, SC-VR provides marginal savings. At 24.03 USD/GJ, SC-VR is not economically competitive, whereas SC-PHVR continues to outperform the conventional cases, with TAC reductions of 8% and 4%. Both retrofit options significantly reduce emissions, with SC-PHVR offering the best economic performance. Finally, the proposed configurations enable the complete electrification of the de-isobutanizer system, eliminating reliance on fossil-based thermal utilities, which allows the use of renewable sources in line with the decarbonization efforts.