Synthesis And Property Study Of Catalytic Materials For Alkylation Of Aromatic Hydrocarbons

With the increase of the more requirement for new polyester material-PEN, it is necessary to reduce the production cost of PEN by one-step preparation of its monomer-2,6-dimethylnaphthalene(2,6-DMN). The development of the catalytic materials with high selectivity and high activity is the core technology for one-step synthesis process of 2,6-DMN.The HZSM-12 zeolite and series of chloroaluminate ion liquid catalytic materials with high selectivity for 2,6-DMN and high reaction activity were prepared for alkylation of naphthalene(NAPH) with methanol(ME) and transalkytion of 2-methylnaphthalene(2-MN) with 1,2,4,5- tetramethylbenzene (TeMB) to synthesize 2,6-DMN by design, synthesis and modification of catalytic properties for high selectivity and environmental friendly catalytic materials. The structure and acidity for two kinds of catalytic materials were analyzed and characterized by means of XRD, FT-IR, SEM, N₂ adsorption, ²⁷A1NMR, NH3-TPD, Py-IR and CH3CN-IR. The effects of synthesis conditions for HZSM-12 zeolite and chloroaluminate ion liquids on their structure, acidity and catalytic properties were investigated.On the continuous fixed-bed catalytic reaction equipment, the suitable reaction conditions such as temperature of 350℃, pressure of 4 MPa, weight hourly space veolicity (WHSV) of 3h^-1 and NAPH/ME/1,2,4- trimethylbenzene (TMB) ratio of 1/2/10 were achieved for alkylation of NAPH with ME to synthesize 2,6-DMN over HZSM-12 zeolite,In the bath kettle reactor, the suitable reaction conditions such as temperature of 20℃, 2-MN/TeMB ratio of 1.0, reaction time of 8 h and addition amount of catalyst of 32 wt.% were obtained for transalkylation of 2-MN with TeMB to synthesize 2,6-DMN over ion liquids.The surface acidity and pore structure of HZSM-12 zeolite were modified by ion exchange, isomorphous substitution, chemical and steamed dealumination and base desilication technologies. Compared to Mg²⁺ ion exchange modification, the catalytic activity (conversion of NAPH),selectivity of 2,6-DMN and ratio of 2,6-/2,7-DMN for HZSM-12 zeolite modified by La³⁺ ion exchange get higher and respectively reach to 46.4%, 30.0% and 2.0 at 5 h. HZSM-12 zeolite modified by isomorphous substitution of gallium benefits for the rise of catalytic activity (conversion of NAPH), selectivity of 2,6-DMN and ratio of 2,6- /2,7-DMN because of larger pore volume, lower acid strength and new Lewis acid site. Compared to the dealumination modification by HCl, citric acid and steam, the catalytic activity, selectivity of 2,6-DMN and ratio of 2,6- /2,7-DMN were improved and respectively reach to 40.2%, 29.3% at 5 h for HZSM-12 modified by the sulfosalicylic acid dealumination. The base desilication modification may form micro-mesopore structure in HZSM-12 zeolite to reduce its acid strength and get rise of the catalytic activity, selectivity of 2,6-DMN and ratio of 2,6-/2,7-DMN, respectively this is 55.0%, 30.6% and 2.0 at 5 h. It is a kind of effective modification method of zeolites.The ion liquid catalytic materials, such as 1-alkyl-3-methylimidazolium aluminum chloride([C_nmim]Cl-xAlCl₃),N-alkylpyrodium aluminum chloride ([C_nPy]Cl-xAlCl₃) and Et₃NHCl-xAlCl₃ were prepared. It was showed from results of catalytic transalkylation of 2-MN & TeMB to synthesize 2,6-DMN that the alkylation reaction progress and the isomerization of 2,6-DMN could be controlled, and selectivity of 2,6-DMN get rise via adjusting the structure of cations, acid strength and changing reaction conditions.When [C₄Py]Cl-xAlCl₃ was used for catalyst, the highest selectivity of 2,6-DMN and ratio of 2,6- /2,7-DMN were obtained and respectively reached to 80.5% and 4.1, and conversion of 2-MN was 22.7%. The highest conversion of 2-MN and yield of 2,6-DMN were achieved and respectively reached to 48.7% and 18.5%, but ratio of 2,6- /2,7-DMN only was 2.3 by using Et₃NHCl-xAlCl₃ as catalyst. The conversion of 2-MN, selectivity of 2,6-DMN, ratio of 2,6-/2,7-DMN respectively were 30.9%, 68.2% and 3.7 in catalytic transalkylation over[C₄mim]Cl-xAlCl₃.The reaction activity basically keep unchange and the selectivity of 2,6-DMN slightly decreased by using mixed methylnaphthalene instead of pure 2-MN as material of transalkylation.It was found that moisture in the system of reaction is main reason that leads to deactivation of ionic liquids in cycle utilization. The reaction mechanism of transalkylation reaction of 2-MN with TeMB catalyzed by chloroaluminate ionic liquids has been proposed.