Life cycle assessment of gasoline blending options

A life cycle assessment has been done to compare the potential environmental impacts of various gasoline blends that meet octane and vapor pressure specifications. The main blending components of alkylate, cracked gasoline, and reformate have different octane and vapor pressure values as well as different potential environmental impacts. Because the octane and vapor pressure values are nonlinearly related to impacts, the results of this study show that some blends are better for the environment than others. To determine blending component compositions, simulations of a reformer were done at various operating conditions. The reformate products of these simulations had a wide range of octane values and potential environmental impacts. Results of the study indicate that for low-octane gasoline (95 Research Octane Number), lower reformer temperatures and pressures generally decrease the potential environmental impacts. However, different results are obtained for high-octane gasoline (98 RON), where increasing reformer temperatures and pressures increase the reformate octane values faster than the potential environmental impacts. The higher octane values for reformate allow blends to have less reformate, and therefore high-octane gasoline can have lower potential environmental impacts when the reformer is operated at higher temperatures and pressures. In the blends studied, reformate and cracked gasoline have the highest total impacts, of which photochemical ozone creation is the largest contributor (assuming all impact categories are equally weighted). Alkylate has a much lower total potential environmental impact but does have higher impact values for human toxicity by ingestion, aquatic toxicity, terrestrial toxicity, and acidification. Therefore, depending on environmental priorities, different gasoline blends and operating conditions should be chosen to meet octane and vapor pressure specifications.