(671h) Modeling of Interfacial Behaviors of Isobutane Alkylation with 2-Butene Catalyzed By Sulfuric Acid/Brønsted Acidic Ionic Liquid

Modeling of Interfacial Behaviors of
Isobutane Alkylation with 2-butene Catalyzed by Sulfuric
Acid/Brønsted Acidic Ionic Liquid

Weizhong Zheng¹,
Piao Cao¹, Weizhen Sun¹,
and Ling Zhao¹

¹ State Key Laboratory of Chemical Engineering,
East China University of Science and Technology, 200237, Shanghai, China, wzzheng728@foxmail.com,
1621756797@qq.com, sunwz@ecust.edu.cn, zhaoling@ecust.edu.cn

The
alkylate produced by the alkylation of isobutane with C4 olefins is a desirable
blending component for high quality gasoline.¹ Although the
alkylation processes for commercial importance use either sulfuric or
hydrofluoric acid as catalyst, both of them suffer from fatal drawbacks.²
In recent years, ionic liquids (ILs) have drawn considerable attentions for
their applications in C4 alkylation owing to their chemical stability,
negligibly low vapor pressure, and Brønsted and Lewis acidity.³ As a
dual solvent-catalyst, Brønsted acidic ionic liquids (BILs) can enhance
obviously the catalytic activities of sulfuric acid, when used as a co-catalyst
with the sulfuric acid. The sulfonic acid functionalized BILs (SFILs) and
non-SFILs not only can improve the catalytic activities, but also can enhance
greatly the stability of the sulfuric acid.⁴ Actually, the BILs act
as a surfactant which can improve the acid/hydrocarbon interfacial properties
and further enhance the catalytic activities of sulfuric acid, because C4
alkylation catalyzed by sulfuric acid is a typical liquid/liquid interfacial
reaction. However, it is difficult to detect the interfacial properties using
experimental methods. Alternatively, the molecular dynamics simulation is
proved to be a proper tool to probe the interfacial behaviors involving the C4
alkylation.

The interfacial
properties between C4 hydrocarbons and the SFILs with different
alkyl chain length were modeled using molecular dynamic simulation. Compared to
the pure H₂SO₄ systems, BILs can enhance the dissolution
and diffusion of isobutane at interface, as shown in Figure 1. The SFILs with
longer alkyl chain show stronger density enrichment at interface and tend to
protrude more deeply into the reactant phase with their orientation
perpendicular to the interface, which is more beneficial to the dissolution of
isobutane. Compared
to the non-SFILs, the SFILs can facilitate a higher dissolution of isobutane
but inhibit its diffusion at interface. The good agreement between simulations
and experiments suggests that the solubility and diffusion of isobutane play a
synergized role in the quality of the alkylate. The fundemental understanding
in this work can provide a novel approach to screen and design SFILs for
isobutane alkylation.

Figure 1. Equilibrated snapshots of
MD simulation. (a) H₂SO₄, (b) [PMim][HSO₄],
(c) [BMim][HSO₄], (d) [HMim][HSO₄], (e) [OMim][HSO₄],
(f) [PSMim][HSO₄], (g) [HSMim][HSO₄], (h) [OSMim][HSO₄].
The sulfuric acid in the middle of the box is shown in the right side.

The financial support by the National
Natural Science Foundation of China (91434108) is gratefully acknowledged.

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