(582aq) Acid Catalyst Coupling with Ionic Liquids  to Catalyse  C4 Alkylation Process Synergistically | AIChE

(582aq) Acid Catalyst Coupling with Ionic Liquids  to Catalyse  C4 Alkylation Process Synergistically

Authors 

Tang, S. Sr. - Presenter, Sichuan University
Zhang, T., Sichuan University
Jing, K., Sichuan University
Zhang, S., Sichuan University
Zhang, Y., Sichuan University
Li, H., Sichuan University
Zhou, F., Sichuan University
Li, Y., Sichuan University
Hu, J., Sichuan University
Acidic ionic liquid was used to intensify C4 alkylation process catalysed by mineral acid or solid acid. When acidic ILs coupled with triflic acid to instead of the pure acid as catalyst, better conversion (>95%), C8-alkylates selectivity (>70%) and trimethylpentane/dimethylhexane selectivity (TMP/DMH > 7) were achieved[1]. The catalyst stability also increased by more than 30%.

Addition a little ILs (<0.1, molar fraction) in H2SO4 resulted in a sharp decrease in the density. The length of alkyl chain and the anion types showed a significant impact on the density. In the molar fraction of ILs <0.1, the ILs concentration also has a strong impact on the surface tensions of the ILs/H2SO4 mixture. The viscosities of IL/acid binary mixtures decreased drastically with the increasing temperature and decreasing IL-content. The Hammett acidity functions (H0) of binary mixtures of TfOH or H2SO4 and ionic liquids (ILs), namely, [Bmim][HSO4], [Bmim][TfO] and [Bmim][TFA], were measured by the 13CNMR method. The results show that the H0 values of the mixtures can be effectively controlled by tailoring the structure of the IL or tuning the amount of IL added to the system. For the system of IL/TfOH, the -H0 values of the binary mixtures decrease with the increasing amount of IL. At xIL<0.05, the addition of ILs just brought a very small decrease on the acidity of the catalyst [Bmim][HSO4]/TfOH and [Bmim][TfO]/TfOH (-H0>13.0). With the increasing of IL mole fraction from 0.05 to 0.20, the acidity -H0 of binary mixtures decreased sharply from13.0 to 8.0. However, for the binary mixture of [Bmim][TFA]/TfOH, the addition of [Bmim][TFA] brought an obvious decrease of the acidity. For the system of IL/H2SO4, the descending order of the -H0 values of the binary mixtures as the increasing concentration of IL follows: [Bmim][TFA] >[Bmim] [HSO4] > [Bmim][TfO] [2]. The solubility of isobutane in [BMIm]-[PF6], [BMIm][BF4], and [BMIm][Tf2N] were in the sequence: [BMIm][Tf2N] > [BMIm][PF6] > [BMIm][BF4]. The solubility parameters (δ) were used to qualitatively explain these differences[3]. These results show that addition of ILs in mineral acid has significant impact on the acidity, viscosity, density, surface tension and isobutane solubility, so has an improvement on the mass transfer and local I/O ratio, then leads to an intensification on the C4alkylation process.

Immobilizing 3-sulfobutyl-1-(3-propyltriethoxysilane)imidazolium hydrogen sulfate on MCM-22 displays relatively superior adsorption ability in tuning the ratio of paraffin/olefin (the adsorbed ratio of ethane/ethylene increased over 30%)[4]. 1-butyl-3-(triethoxysilylpropyl)imidazolium hydrogen sulfate (i.e., [BTPIm][HSO4]) was grafted onto the MCM-36 zeolite for the regulation of its adsorption properties towards isobutane and 1-butene. Results demonstrated that the interaction between isobutane and MCM-36-IL was enhanced and the interaction between 1-butene and MCM-36-IL was reduced. As a result, a tunable adsorption ratio of isobutane/1-butene on MCM-36 was achieved. The adsorption/desorption behaviors of 2,2,4-trimethylpentane on MCM-36 or ionic liquid immobilized MCM-36 were studies systematically by an intelligent gravimetric analyzer (IGA). The results show that a decease adsorption capacity of 2,2,4-trimethylpentane was obtained after grafting [BTPIm][HSO4]. The ionic liquid immobilization led to a low isosteric adsorption heat. It indicate that a weaken interaction between adsorbate and adsorbent was obtained by the grafting of ionic liquid. The kinetics research results show that the adsorption/desorption process was limited by the surface adsorption step. The ionic liquid loading are helpful to improve the desorption of 2,2,4-TMP from the reaction surface. It is also found that the ionic liquid immobilization improves the uniformity of adsorption energy on catalyst surface, weakens the interaction between 2,2,4-TMP and MCM-36. Meanwhile, it reduces the adsorption rate and promotes the timely desorption of 2,2,4-trimethylpentane, indicating the ionic liquid loading is an effective method to improve the stability of solid acid catalyst. These results show that grafting IL on solid acid provides a way to change the relative adsorption capacity of reactants and then the local I/O ratio can be tuned, so the improvement of the solid acid catalyst should be expected.

References

[1] Shengwei Tang, Aaron M. Scurto, Bala Subramaniam. Improved 1-butene/isobutane alkylation with acidic ionic liquids and tunable acid/ionic liquid mixtures [J]. Journal of Catalysis. 2009, 268:243-250.

[2]Shuai Zhang, Tao Zhang, and Shengwei Tang. Determination of the Hammett Acidity Functions of Triflic Acid/Ionic Liquid Binary Mixtures by the 13C NMR-Probe Method. Journal of Chemical & Engineering Data. 2016, 61(6):2088-2097

[3] Yuan Zhang, Tao Zhang, Panxue Gan, Hongxia Li, Ming Zhang, Keting Jin, and Shengwei Tang. Solubility of Isobutane in Ionic Liquids [BMIm][PF6], [BMIm][BF4], and [BMIm][Tf2N] [J]. Journal of Chemical & Engineering Data. 2015, 60(6):1706-1714

 [4] Keting Jin , Tao Zhang , Junyi Ji , Ming Zhang , Yuan Zhang , and Shengwei Tang. Functionalization of MCM-22 by Dual Acidic Ionic Liquid and Its Paraffin Absorption Modulation Properties[J]. Ind. Eng. Chem. Res., 2015, 54 (1), pp 164–170

[5]Hongxia Li, Tao Zhang, Shaojun Yuan, Shengwei Tang, MCM-36 Zeolites Tailored with Acidic Ionic Liquid to Regulate Adsorption Properties of Isobutane and 1-Butene[J]. Chinese Journal of Chemical Engineering. 2016,24(12):1703-1711.

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