Research On Alkylation Of 1-Dodecene With Benzene Catalyzed By Ionic Liquids

The 2-dodecylbenzene in linear alkylbenzene has become one of the important raw materials for the production of surfactants due to its good biodegradability.Chloaluminate ionic liquids have the characteristics of high activity at low temperature and high target product selectivity in the catalysts for the alkylation of benzene with 1-dodecene.Generally,ionic liquids first initiate 1-dodecene to generate carbon cations,and then react with benzene to produce linear alkylbenzenes（LAB）.The purpose of this thesis is to initiate benzene to generate phenyl carbocation through ionic liquids,and then react with1-dodecene to produce linear alkyl benzene with higher content of 2-LAB.Therefore,it is of great significance to research whether the ionic liquid can initiate the benzene ring to generate phenyl carbocation or not.In the experiment,chloroaluminate ionic liquid Et₃NHCl-xAlCl₃ was used as a catalyst for the alkylation reaction of benzene and 1-dodecene.The effects of different factors on the alkylation reaction system of benzene and 1-dodecene were systematically investigated.The factors examined included:ionic liquid composition,raw material addition sequence,Br?nsted acid/Lewis acid content of ionic liquid,molar ratio of aluminum trichloride to triethylamine hydrochloride,reaction temperature,reaction time,molar ratio of benzene to ionic liquid,and molar ratio of benzene to olefin.The optimal conditions were determined within the scope of the experimental investigation:the ionic liquid was Et₃NHCl-1.4AlCl₃,the reaction time and temperature were 10 min and 10°C respectively,the molar ratio of benzene to the ionic liquid was 20:1,and the molar ratio of benzene to 1-dodecene was 35:1.Under these optimal reaction conditions,the conversion of 1-dodecene reached 100%,the selectivity of mono-alkylbenzene reached99.89%,and the selectivity of 2-LAB reached 41.96%.NMR and in-situ IR were used to analyze the effects of chloroaluminate ionic liquids on aromatic hydrocarbons such as benzene rings.When deuterated dichloromethane was used as the field-locking solvent for NMR analysis,benzene and toluene were mixed with chloroaluminate ionic liquids,respectively.Under the catalysis of ionic liquids,benzene and toluene will react with deuterated dichloromethane,resulting in new chemical shifts in ¹³C-NMR and ¹H-NMR spectrum.In the ²⁷Al-NMR spectrum,the addition of benzene and deuterated dichloromethane will change the structure of the aluminum element in the ionic liquid,reduce the[Al₂Cl₇]ˉcontent and increasing the[AlCl₄]ˉcontent in the ionic liquid,thus resulting in the acid drop of the ionic liquid.When deuterated dichloromethane was not added to eliminate its interference on ¹³C-NMR analysis,benzene,toluene,and para-xylene were mixed with the ionic liquid respectively,there was no new chemical shift.When ethylbenzene was mixed with chloroaluminate ionic liquid,the carbon chemical shift of benzene ring in ethylbenzene changed.There was a new chemical shift in the polymerization of naphthalene mixed with ionic liquid.Through in-situ IR analysis online,it was found that the addition of ionic liquids caused the characteristic absorption peaks of the benzene ring corresponding to the C=C skeleton stretching vibration,C-H in-plane bending vibration,and C-H out-of-plane bending vibration to be red-shifted on the infrared spectrum.The energy required for benzene ring vibration was reduced,and the ionic liquid interacted with benzene to form a complex.Chloroaluminate ionic liquids cannot catalyze the benzene ring to generate phenyl carbocation when they catalyze the alkylation of benzene with 1-dodecene,but they can form complexes with benzene,thereby improving the selectivity of 2-LAB products.