| Catechol alkylation is an industrially important reaction since 4-tert-butylcatechol(4-TBC) and its derivatives are used as raw materials for the synthesis of several polymerization inhibitors, dye developers, Pharmaceuticals, and agricultural chemicals. Commercial alkylation of aromatics is carried out via electrophilic substitution, where the metal halides A1Cl3, FeCl3 and ZnCl2 are the most commonly used catalysts. The use of those catalysts gives rise to many problems concerning handling, safety, corrosion, and waste disposal. In this paper, therefore, we try to develop some better catalysts to catalyze the alkylation of catechol to prepare 4-TBC.Quinoline-phosphato-molybdate and H P zeolite appear to be more efficient catalysts for the selective formation of 4-TBC in catechol alkylation with t-butyl alcohol than other catalysts studied in this work. Using ICP, IR, XRD, SEM, TPD, etc, the effects of structure and acidity changes of them on the reaction are studied. The conclusions from the present results can be summarized as given below.The alkylation of catechol with t-butyl alcohol over acid catalysts produces 4-TBC, 3-TBC(3-t-butylcatechol) and DTBC(3,5-di-t-butylcatechol).Compared with ZrSO4, Strong Acid Cation-Exchange Resin, Solid Super Acid Fe2O3/SO42-, quinoline-phosphato-molybdate has the better catalytic activity on the alkylation of catechol with t-butyl alcohol. When the amount of catalyst(based on catechol) is 5%(weight), the molar ratio of catechol and t-butyl alcohol is 1/2, reaction temperature is 130C and reaction time is 2h, the conversion of catechol and the selectivity of 4-TBC reach 79.5% and 87.8%, respectively. The optimized condition of preparing catalyst is that the content of sulfuric acid is 1.00mol/L, and the content of quinoline is 20%(weight). IR and ICP characterized the acid properties and structure of the catalyst.The effect of H P zeolite on the t-butylation of catechol was compared to that of H P /Al2O3 and HY zeolite. The results show that the catalytic activity is corresponding with the number of acid sites. The catechol conversion over H P and H P /Al2O3 zeolites are 35% and 67%, respectively, even though they have the same SiO2/Al2O3 ratio. Although the conversion over H β is less than that over HY, its high 4-TBC selectivity can overcome this weak point. Since we thought that selectivity is a more important factor than the conversion on the catalyst for the production of fine chemical, H P /Al2O3 is mainly investigated in this study.Catechol conversion is very sensitive to the number of acid sites. Selectivity of 3-TBC and DTBC are sensitive to the strength of acid sites, however, 4-TBC selectivity is not. The 4-TBC selectivity is not changed significantly by acid properties, indicating that 4-TBC formation is mainly controlled by zeolite pores. DTBC and 3-TBC are formed on the external surface of zeolite because they are too large to penetrate into the zeolite channels. 3-TBC formation favors weak acid sites, and DTBC formation favors strong acid sites.Catalytic activity of Hβ /Al2O3 with five different SiO2/Al2O3 ratio were compared. The catechol conversion and DTBC selectivity decrease slowly through decreases in the framework Al content, while 3-TBC selectivity is contrary.The catalytic activities of H β zeolites modified by cation-exchanging with Li, Mg, Co, La and oxide soaking were discussed in this paper. The surface acidity and structure of different modification zeolites have been investigated by using NH3-TPD and XRD.The process conditions of alkylation of catechol with t-butyl alcohol at atmospheric pressure using the fixed-bed vertical flow reactor and interrupted-stirring reactor have been optimumed respectively. Using interrupted-stirring reactor, when reaction temperature is 140~150℃,the molar ratio of catechol and t-butyl alcohol is 0.67,the conversion of catechol over La2O3-Hβ zeolite reaches 83% and the selectivity of 4-TBC is 98%. In addition, using the fixed-bed reactor, when reaction temperature is 120℃,WHSV is 2h-1,and the molar ratio of catech... |
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