(41e) Isobutane Alkylation with C4 Olefin Catalyzed By Combination of so3h-Functionalized Ionic Liquids and Sulfuric Acid

Isobutane Alkylation with C4 Olefin
Catalyzed by Combination of SO₃H-Functionalized Ionic Liquids and
Sulfuric Acid

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

Ionic liquids (ILs), also called room temperature ionic liquids (RTILs), are a
class of organic salts that are liquid at near room temperature. Recently, ILs
have attracted significant attention because of their unique properties, such
as negligible vapor pressure, high chemical, thermal, and photocatalytic
stability, nonflammability, and thus become good alternatives to traditional
liquid solvents and catalysts.¹ In particular, the ILs have been
widely investigated in
the C4 alkylation, because the alkylate,
produced by the C4 alkylation, a desirable blending component for high quality gasoline.² Currently, the alkylation processes for commercial
importance still
rely heavily on either
sulfuric or hydrofluoric acid as catalyst. However, the equipment corrosion, high
acid consumption, safety, and environmental issues related to the disposal of
spent acid are still challenges to overcome.³ To cope with these
problems, SO₃H-functionalized
ionic liquids (SFILs)
are regarded as a
promising candidate, playing a dual solvent-catalyst role in extensive
applications for considerable chemical processes due to their excellent
properties, including tunable acidity, high catalytic activity, and better
dissolving capacity for a wide range of organic and inorganic compounds.⁴Therefore, it is necessary to deeply investigate the
catalytic performances of SFILs as co-catalyst for the H₂SO₄
alkylation, especially the structure-property relationship.

In this work, the
SFILs with different alkyl chain length were investigated as co-catalyst mixed
with the concentrated H₂SO₄ for the isobutane alkylation.
The SFILs with longer alkyl chain show a better catalytic performance with the
C8 selectivity up to 75.73 and RON up to 95.66, respectively. The better
catalytic performance can be attributed to the better dispersion of isobutane
in the SFIL/H₂SO₄ system led by the SFILs with longer
alkyl chain, which is further correlated with the nanostructured-aggregation
feature of the longer alkyl chain confirmed by MD simulation, as shown in
Figure 1. In addition, the reusability of SFIL/H₂SO₄
mixture can reach up to 22 runs, outclassing the pure H₂SO₄,
which can be attributed to cationic clusters formed by the strong hydrogen
bonds between the sulfonic acid group and the H₂SO₄. The
fundemental understanding in this work can bring us important insights into the
physicochemical properties of the alylation process and provide a novel
approach to screen and design SFILs for isobutane alkylation.

Figure 1. Snapshots of the isobutane
dispersion behaviors in different simulation systems.

(a)    Pure H₂SO₄
(b) [MPSIm][HSO₄] (c) [EPSIm][HSO₄] (d) [BPSIm][HSO₄]
(e) [HPSIm][HSO₄] (f) [OPSIm][HSO₄]. Molecules in red
color represent isobutane, and molecules with the blue (N), grey (C), yellow
(S), and red (O) atoms stand for the cations of the SFILs. The concentrated H₂SO₄
and anions are removed.

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

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