Study On Alkylation Of Isobutane And Butene Catalyzed By Modified Beta Zeolite And MAS-7 Mesoporous Molecular Sieve

Alkylated gasoline prepared by alkylation reaction of isobutane and butene as an excellent gasoline blending component has the advantages of high octane number,low vapor pressure,no sulfur,aromatics,etc.Alkylated gasoline occupies an increasing proportion in the fuel market.At present,the catalysts used in the industrial production of alkylated gasoline is mainly traditional concentrated sulfuric acid,which is followed by hydrofluoric acid catalyst.Both have good catalytic effects and but have many negative effects,such as large acid consumption,equipment corrosion,treatment difficulty of waste acid and environment pollution,etc.Aiming at resloving these shortcomings of liquid acids,we have designed and synthesized several solid acids to catalyze the alkylation reaction of isobutane and butene,which are mainly divided into three parts:Using beta zeolite（SiO₂/Al₂O₃=25）as the original catalyst,the micro-mesoporous beta zeolite was prepared by means of alkaline solution desilication.After replacing the cations into hydrogen proton,trifluorotrichloroethane was used as the solvent and nitrogen was used as the shielding gas.By combining different mass fractions of trifluoromethanesulfonic acid（Tf OH）with the hydroxyl groups on the surface of the zeolite through the esterification reaction,the modified catalysts Tf OH/B-Hbeta with different Tf OH loading were obtained.Using powder X-ray diffraction analysis（XRD）,X-ray fluorescence spectroscopy（XRF）,N₂ adsorption and desorption isotherm,infrared spectroscopy（FT-IR）,ammonia temperature program desorption（NH₃-TPD）,pyridine infrared analysis,scanning electron microscopy（SEM）and other characterization methods,the catalyst was characterized.The catalyst was used to catalyze the alkylation of isobutane with 2-butene,and the optimal reaction conditions were optimized.The loading of trifluoromethanesulfonic acid is 20 wt%（relative to the micro mesoporous beta zeolite）,the reaction temperature is 80°C,the reaction pressure is 2.5 MPa,and the space velocity of the olefin feedstock is 0.8 h^-1.The olefin conversion rate is 99.5%,and the C8 selectivity reaches 69.3%under this condition.The catalyst has higher catalytic activity and has a longer lifespan than the original beta zeolite.The mesoporous molecular sieve MAS-7 containing heteroatom Al was synthesized in situ,using traditional hydrothermal synthesis method.By using sodium metaaluminate as the aluminum source,fumed silica as the silicon source,and tetraethylammonium hydroxide as the template,appropriate amount of sodium hydroxide and water were added the solution to first prepare beta zeolite precursor according to a certain ratio,and then a certain amount of precursor was mixed with the hydrochloric acid solution of P123 mesoporous template to obtain mesoporous molecular sieve MAS-7 containing heteroatom aluminum after hydrothermal conditions crystallization,Finally,Tf OH was loaded on the MAS-7 mesoporous molecular sieve in the same way as above-mentioned.The catalyst Tf OH/MAS-7 was synthesized.By using powder X-ray diffraction analysis（XRD）,X-ray fluorescence spectroscopy（XRF）,N₂ adsorption and desorption isotherm,infrared spectroscopy（FT-IR）,ammonia temperature program desorption（NH₃-TPD）,pyridine infrared analysis,and transmission electron microscopy（TEM）,the catalyst was characterized.The optimal reaction conditions was optimized:the loading of Tf OH 25 wt%,the optimal reaction temperature 80℃,the reaction pressure 3 MPa,and the mass space velocity of olefin0.5 h^-1.The olefin conversion rate is 99.9%,and the C8 selectivity reaches 69.6%under this condition.The catalyst has higher catalytic activity and longer lifespan Compared to Tf OH/B-Hbeta catalyst.The mesoporous molecular sieve MAS-7 containing heteroatom aluminum was used as the carrier to support the different mass of phosphotungstic acid to catalyze the alkylation reaction of isobutane and 2-butene.The different mass fractions of phosphotungstic acid were impregnated into the mesoporous molecular sieve MAS-7,and the catalyst HPW/MAS-7 was subjected to powder X-ray diffraction analysis（XRD）,X-ray fluorescence spectroscopy（XRF）,infrared spectroscopy（FT-IR）,N₂ adsorption and desorption isotherm,pyridine infrared analysis,transmission electron microscopy（TEM）and other characterization methods.The reaction conditions are optimized:the optimal loading of phosphotungstic acid 30 wt%,the optimal reaction temperature 70℃,the reaction pressure 3.0 MPa,the mass space velocity of olefin 0.6 h^-1.the olefin conversion rate is 99.9%,and the C8 selectivity reaches 72.8%under this condition.The catalyst has higher C8 selectivity compared to Tf OH/MAS-7 catalystThree different molecular sieve catalysts with mesoporous pore structure are designed in this paper.They are Tf OH/B-Hbeta,Tf OH/MAS-7 and HPW/MAS-7.Three kinds of catalysts have high catalytic performance,and the preparation process is simple,environmentally friendly and pollution-free.It provides an idea for the preparation of macroporous acid molecular sieve catalyst to improve the activity and life for the alkylation reaction of isobutane and butene.