Separation process electrification and site-wide integration for energy and carbon efficiency in sulfuric acid alkylation

Motivated by comprehensive energy and sensitivity analyses of the existing sulfuric acid-catalyzed alkylation (SACA) process, this study presents an electrified low-temperature distillation system featuring site-wide process integration. The new design enhances separation efficiency, substantially decreases high-temperature steam usage, and alleviates refrigeration requirements in the reaction section, leading to deep reductions in both total energy consumption and associated carbon emissions. Response surface methodology and a Bayesian optimization algorithm employing Tree-structured Parzen Estimator (TPE) sampling are used to evaluate the influence of deisobutanizer operating parameters on the total annualized cost (TAC). Multi-objective optimization using the NSGA-II algorithm is performed to trade off TAC and carbon emissions. During both single- and multi-objective optimization, heat exchanger network reconfiguration and energy analyses are performed concurrently. Single-objective optimization reduces the TAC to 5.40 million $/year, representing a 36.9% decrease relative to the base SACA process. Multi-objective optimization can reduce the TAC by 36.8% and CO2 emissions by 46.8% simultaneously. Energy analysis indicates that the optimized process uses low-grade heat (factory waste heat/solar hot water) for the deisobutanizer reboiler, resulting in a high-temperature steam energy consumption (SEC) reduction of 11,454 kW, an approximately 83.5% decrease relative to the base SACA process. Process integration retrofit for low-temperature distillation reduces additional cooling water consumption by 175 t/h with a 10 °C temperature difference and electricity consumption by 233 kW.