Simulation and Feasibility Assessment of Normal Butane Substitution for LPG Feed in the Alkylation Unit

Document Type : Research Article

Authors

Chemical Engineering Department, University of Sistan and Baluchestan, Zahedan, Iran.

Abstract

The strategic demand for propylene in the market leads to the conventional LPG feedstock is now redirected, with the C₃ fraction sent to the Propylene Recovery Unit (PRU). This operational adjustment left the alkylation unit primarily reliant on C₄ feed, prompting a comprehensive investigation of alternative feed scenarios to optimize product yield and process economics. In this study, steady-state process simulations were performed using Aspen HYSYS to evaluate the feasibility of replacing the LPG feed with surplus normal butane in the unit. Three scenarios were investigated: (i) baseline operation with standard LPG feed, (ii) replacement of the propane fraction with normal butane, and (iii) replacement of the isobutane fraction with normal butane. The simulation results demonstrated that the substitution of normal butane for propane in the LPG feed is technically feasible, achieving a net alkylate yield of 15.48 ton/h with product quality comparable to industrial benchmarks. However, replacing isobutane with normal butane resulted in a drastic drop in alkylate production, with net output falling to 4.72 ton/h, rendering this scenario economically unviable. Validation against plant process flow diagrams (PFDs) confirmed the simulation’s reliability within acceptable error margins. The findings also highlight the importance of effective feedstock management in alkylation units while partial replacement of LPG with normal butane can optimize resource utilization and meet operational demands, the critical role of isobutane in achieving high alkylate yield and purity must be preserved. The study offers practical implications for the strategic adaptation of Iranian refineries facing changing feedstock availability and market priorities.

Keywords

References

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Chemical Process Design
Volume 5, Issue 2
December 2026
Pages 77-88

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