1,3,5-三甲苯在沸石催化剂上的催化转化
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摘要
采用微型固定床催化反应装置,考察1,3,5-三甲苯(1,3,5-TMB)在丝光沸石(HMOR),HY,Hβ,HEU-1和HZSM-5这5种沸石催化剂上的催化转化率和产品分布。结合5种沸石的孔结构和酸性特征,探讨了沸石催化剂的结构、酸性与其催化活性、稳定性和产品分布之间的关系。结果表明,在沸石催化剂表面,1,3,5-TMB转化的主要反应是歧化和异构化反应,其相对量取决于沸石催化剂孔道的尺寸和可接近的表面酸性;其次是各烷基苯间的烷基转移或脱烷基反应。HY和Hβ沸石催化剂具有较大的三维孔道尺寸,因此反应活性和稳定性较高,反应以歧化反应为主;而在HEU-1和HZSM-5沸石催化剂上,因其孔道尺寸相对较小,所以转化率较低,且反应以异构化为主;另外沸石催化剂表面强酸中心的存在还会导致脱烷基反应的发生。
Different catalysts, i.e. HMOR, HY, Hβ, HEU-1 and HZSM-5 zeolites, were used to study the catalytic activity, products distribution and catalyst stability of 1,3,5-trimethylbenzene transformations reaction in a fixed-bed micro reactor. Based on the characterization results of the concentration and strength distribution of the acid sites, the relationship between the catalytic behavior and zeolite properties(i.e. pore structure and acidity) was investigated. The main reactions involved in 1,3,5-trimethylbenzene transformation are isomerization and disproportionation over zeolitic catalysts, and other possible side reactions are dealkylation of alkylbenzene and the transalkylation of xylene and tetramethylbenzene. Among the five zeolites, transformations of 1,3,5-TMB on HY and Hβ zeolites, which have 12-MR three dimensional large size pore structures, are mainly disproportionation reaction, and the catalysts show the highest catalytic activity and stability. Whereas the reactions on HEU-1 and HZSM-5 zeolites, which have smaller size pore channels, are mainly isomerization reactions with low conversion. The strong acidity on the surface of zeolites can result in dealkylation/cracking of intermediates.
Different catalysts, i.e. HMOR, HY, Hβ, HEU-1 and HZSM-5 zeolites, were used to study the catalytic activity, products distribution and catalyst stability of 1,3,5-trimethylbenzene transformations reaction in a fixed-bed micro reactor. Based on the characterization results of the concentration and strength distribution of the acid sites, the relationship between the catalytic behavior and zeolite properties(i.e. pore structure and acidity) was investigated. The main reactions involved in 1,3,5-trimethylbenzene transformation are isomerization and disproportionation over zeolitic catalysts, and other possible side reactions are dealkylation of alkylbenzene and the transalkylation of xylene and tetramethylbenzene. Among the five zeolites, transformations of 1,3,5-TMB on HY and Hβ zeolites, which have 12-MR three dimensional large size pore structures, are mainly disproportionation reaction, and the catalysts show the highest catalytic activity and stability. Whereas the reactions on HEU-1 and HZSM-5 zeolites, which have smaller size pore channels, are mainly isomerization reactions with low conversion. The strong acidity on the surface of zeolites can result in dealkylation/cracking of intermediates.
引文
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[3]R?GER H P,M?LLER K P,O’CONNOR C T.The transformation of 1,2,4-trimethylbenzene A probe reaction to monitor external surface modifications of HZSM-5[J].Microporous Materials,1997,8(3/4):151-157.
[4]AL-KHATTAF S,AKHTAR M N,ODEDAIRO T,et al.Catalytic transformation of methyl benzenes over zeolite catalysts[J].Applied Catalysis A General,2011,394(1/2):176-190.
[5]TUKUR N M,AL-KHATTAF S.Catalytic transformation of 1,3,5-trimethylbenzene over a USY zeolite catalyst[J].Energy&Fuels,2007,21(5):2499-2508.
[6]KIM G J,AHN W S.Direct synthesis and characterization of high-SiO2-content mordenites[J].Zeolites,1991,11(7):745-750.
[7]ZHU G,QIU S,YU J,et al.Synthesis and characterization of high-quality zeolite LTA and FAUsingle nanocrystals[J].Chemistry of Materials,1998,10(6):1483-1486.
[8]PEREZ-PARIENTE J,MARTENS J A,JACOBS P A.Crystallization mechanism of zeolite beta from(TEA)2O,Na2O and K2O containing aluminosilicate gels[J].Applied Catalysis,1987,31(1):35-64.
[9]RAO G N,JOSHI P N,KOTASTHANE A N,et al.Synthesis and characterization of high-silica EU-1[J].Zeolites,1989,9(6):483-490.
[10]ARGAUER R J,LANDOLT G R.Synthesis of zeolite ZSM-5:US 3702866[P].1972.
[11]MARTINS J,BIROT E,GUILLON E,et al.Sodium exchange over H-EU-1 zeolite Part II Catalytic properties[J].Microporous&Mesoporous Materials,2013,171(2):238-245.
[12]CHEN W H,TSAI T C,JONG S J,et al.Effects of surface modification on coking,deactivation and paraselectivity of H-ZSM-5 zeolites during ethylbenzene disproportionation[J].Journal of Molecular Catalysis AChemical,2002,181(1/2):41-55.
[13]PARK S H,RHEE H K.Shape selective conversion of1,2,4-trimethylbenzene over zeolite NU-87[J].Catalysis Today,2000,63(2/3/4):267-273.
[14]ALI S A,AITANI A M,ERCAN C,et al.Conversion of heavy reformate into xylenes over mordenite-based catalysts[J].Chemical Engineering Research&Design,2011,89(10):2125-2135.
[15]ALI S A,OGUNRONBI K E,AL-KHATTAF S S.Kinetics of dealkylation-transalkylation of C9alkyl-aromatics over zeolites of different structures[J].Chemical Engineering Research&Design,2013,91(12):2601-2616.