Review of Isobutane Alkylation Technology Using Ionic Liquid-Based Catalysts—Where Do We Stand?

Abstract

Conventional strong liquid acids such as H 2 SO 4 and HF are used for the majority of current commercial isobutane alkylation processes to produce motor fuel alkylates, but these acids can have significant safety and sustainability concerns. Ionic liquid (IL) catalyst technologies offer potential advantages over current processes due to the negligible vapor pressure and molecularly tunable properties that can optimize both the chemistry and engineering for alkylate production. In this review, IL-based catalysts used in isobutane alkylation are reviewed. ILs are categorized and discussed by type: (1) metal-based Lewis acidic ILs, (2) metal-based Bronsted−Lewis acidic ILs, (3) nonmetal-based Bronsted acidic ILs, and (4) immobilized/supported ILs. A critical perspective on the use of these ILs in alkylation is presented, focusing on the effect of speciation and physicochemical properties on chemical reaction. Further, a summary of IL speciation is provided and examples of how the tunability of ILs can be used to overcome current limitations in alkylation chemistry. The reaction conditions and performance (e.g., conversion, C 8 selectivity, and trimethylpentane:dimethylhexane ratio) of literature reports are summarized. A comparison of IL-based catalysts with the incumbent H 2 SO 4 process and the new ISOALKY Chevron process are also discussed. Gaps in the literature (e.g., mass transfer rates, material compatibilities, and phase equilibrium) associated with IL-based alkylation technology and our perspectives on solving the relevant issues in this field are summarized.

H2SO4‐catalyzed isobutane alkylation under low temperatures promoted by long‐alkyl‐chain surfactant additives

“…The isobutane alkylation (C 4 alkylation) with C3 ~ C5 olefins is an important industrial process for the production of the alkylate as an ideal blending component for motor gasoline, due to the dramatic advantages, including no aromatics, free sulfur‐containing components, negligible vapor pressure, high‐octane number, and full combustion 1–3 . Among the alkylate components, TMPs are the most desirable targets with RON more than 100.…”

Effects of deep eutectic solvents on H2SO4‐catalyzed alkylation: Combining experiment and molecular dynamics simulation

“…The alkylate, produced by isobutane alkylation (C4 alkylation) with C3–C5 olefins using strong acid as catalyst, is an ideal blending component of the gasoline pool, owing to the numerous advantages, such as high research octane number (RON), low vapor pressure, free of sulfur, absence of aromatics and alkenes compounds 1–4 . The commercial alkylation process usually uses liquid acid as catalyst, including concentrated sulfuric acid (H 2 SO 4 ) and hydrofluoric acid (HF) 5,6 .…”

Target high‐efficiency ionic liquids to promote H2SO4‐catalyzed C4 alkylation by machine learning

“…The alkylation between isobutane and C3–C5 olefins (C4 alkylation) under strong acidic condition is a very important industrial process to produce the alkylate, an ultraclean‐fuel component for motor gasoline produced in the refinery with high research octane number (RON), low vapor pressure, and no content of aromatics and sulfur components 1 . Current industrial alkylation processes usually use liquid mineral acids as catalysts, either hydrofluoric acid (HF) or concentrated sulfuric acid (H 2 SO 4 ).…”

“…Room‐temperature ILs, a kind of salts composed solely of ions with melting points typically lower than 100°C at the ambient temperature, exhibit advantageous properties, including low volatility, high stability, adjustable acidity, high tunability, and strong amphiphilicity. Recently, ILs have attracted much attention as the promising additives for H 2 SO 4 alkylation 1,10,11 . It is well‐accepted that the interfacial properties of H 2 SO 4 alkylation, such as interfacial thickness, interfacial ratio of isobutane to olefins (I/O ratio), and interfacial diffusion of isobutane, play a decisive role in the alkylate quality 6 .…”