Kinetics And Quantum Chemistry Studies On Isobutane Alkylation Catalyzed By Ionic Liquids

The alkylation reaction of isobutane with butenes can produce highquality gasoline.C4 alkylation reactions have been developed for many years,and novel catalysts ionic liquid catalyzed C4 alkylation reactions have also been extensively studied experimentally.Ionic liquids(IL)have many advantages over conservation alkylation catalysts(e.g.,H2SO4,HF).They are more modest and less corrosive.A few investigators have studied the reaction mechanism of C4 alkylation through computational chemistry approaches.However,most studies are based on HF or H2SO4 catalysts,and the macro and molecular dynamics of IL-catalyzed C4 alkylation have not been studied in depth.This work presents a kinetic and quantum chemical investigation for IL-catalyzed alkylation.The experimental methods and theoretical calculations were employed for this studyThe deuterated 2-butene was used to determine the alkylation reaction of isobutane and 2-butene in the composite ionic liquid([BMIm]Cl-AlCl3-CuCl,CIL).The alkylation reaction was investigated in a batch stirred reactor.The self-alkylation and the oligomerization of 2-butene are more likely to occur in the CIL.The key components of the alkylates,such as trimethylpentane(TMP),dimethylhexane(DMH),light ends(LE),and heavy ends(HE),were investigated at different reaction temperatures.The kinetics model with the primary and secondary reactions was established to predict the alkylation reaction.In order to test the reliability of the kinetics model,the solubility and diffusivity of isobutane in the CIL were measured.The isobutane alkylation under the industrial reaction conditions was also studied in a static mixer.Whether in the traditional batch reactor or the static mixer,the predicted data from the kinetics model are in good agreement with the experimental values.The obtained model is much more reliable to describe the alkylation reaction catalyzed by ionic liquids.By using deuterated 2-butene and on-line rapid analysis technology,the relationship between the isobutane-to-olefins ratio and the kinetic parameters was determined.In a scale-up reactor,we found that the ILs with a small amount of aromatics would exhibit excellent performances for the alkylation reaction.The behaviors of aromatics on the liquid-liquid interface and the alkylation performance of IL/benzene have been investigated by molecular dynamics simulations and experimental studies.Based on density profile,segment orientation,and self-diffusion coefficient,the main reason that benzene affects the IL alkylation performance was discussed.Although the amount of benzene was small,benzene would accumulate in the acid-hydrocarbon interfacial layer during the alkylation process.A little benzene was enough to change the strong acidity of chloroaluminate anions at the interface.The presence of benzene also provided a transport channel for reactants,increasing the concentration of isobutane at the interface.At the interface,the proper acidity and higher isobutane-to-olefin ratio significantly improved the IL alkylation performance.Effects of other aromatics on the C4 alkylation have also been studied,which further confirmed our findings in the IL/benzene alkylation reaction.Hopefully,these studies can provide useful information to the design of the ionic liquid catalysts and the optimization of the C4 alkylation process.When a small amount of benzene was introduced into the chloroaluminate ionic liquid(IL),the IL-alkylation can produce premium alkylation gasoline.In order to deepen our understanding of IL-alkylation in general,the electronic properties of [BMIm][AlCl4]/benzene/reactant system were analyzed by the ADCH charge analysis,DOS analysis,frontier molecular orbital analysis,non-covalent interactions(NCI),and energy decomposition analysis(EDA).ADCH analysis reveals that benzene could markedly affect the charge transfer of alkanes and chloroaluminate anions,which weakened the super-acidity of the IL.Frontier molecular orbital analysis shows that the IL system has a significant decrease of H-Lgap,and it increases the sensitivity of the reactants.The anchoring effect of [BMIm] cation was observed in the DOS spectra,which enhanced stabilization of the IL structure.NCI analysis shows that ?-H bonds could be formed between benzene and the IL.It is believed that better alkylation performance of IL/benzene system is due to these weak interactions.