Selective Catalytic Synthesis Of P-cresol By Alkylation Of Phenol With Methanol Over Modified Zeolites

Para-cresol（p-cresol）as an important chemical synthesis intermediate is widely used in the synthesis of drugs,herbicides,antioxidants,pesticides and dyes.The industrial production of p-cresol usually adopts toluene sulfonation alkali fusion method and toluene chlorination hydrolysis method,but in those processes,serious environmental pollution problem is always happened due to using a large number of strong acid or strong base liquid catalyst.Using phenol and methanol as the reactants and MCM-22 as catalyst to produce p-cresol has the advantages of mild conditions and less environmental pollution.In this dissertation,the modified microporous MCM-22 catalyst was prepared by ammonium fluosilicate（dealuminization）and chemical liquid phase deposition（aluminium coating）methods then study its catalytic performance on alkylation reaction of phenol and methanol.All the catalysts were characterized by XRD,SEM,BET,²⁷Al MAS NMR,NH₃-TPD,Py-IR,1,3,5-TIPB cracking and xylene isomerization reaction as probe reaction to reveal their catalytic nature in the reaction.The HMCM-22 zeolite was modified by using series of concentration of solution of ammonium fluosilicate,named（X）FS/HMCM-22 catalyst,and then used for alkylation reaction of phenol with methanol.The results showed that ammonium fluosilicate can removal the non-framework aluminum,thus reducing the surface acidic,improve the selectivity of p-cresol.When the content of ammonium fluosilicate increased from 0 g to 0.07 g,the conversion of phenol decreased from32.8%to 22.2%,and the p-cresol selectivity increased from 33.9%to 44.3%.Continue to increase the content of ammonium fluosilicate,the selectivity of p-cresol had no obvious change.Finally,using 0.07FS-HMCM-22 as the best catalyst,the process conditions were optimized,and the results showed that the optimum reaction conditions were 325°C,WHSV=2.0 h^-1and 1.3 g catalyst dosage.The SiO₂/MCM-22 catalysts with different SiO₂loading were prepared by liquid phase deposition using ethyl orthosilicate as precursor and ethanol as solvent.Those catalysts were then used for the alkylation reaction of phenol with methanol,and the results showed that with increasing of SiO₂content from 0 wt%to 1 wt%,the conversion of phenol decreased from 23.3%to 16.1%,the selectivity of p-cresol increased from 39.6%to 47.3%.The selectivity of p-cresol did not change significantly with continue increase of SiO₂loading.This is because SiO₂passivates the acid site on the surface of zeolite,modifies the size of the orifice,and then improves the selectivity of p-cresol.The 1%SiO₂/MCM-22 catalyst with the best catalytic performance was used to study the optimum reaction conditions.The results show that 325°C,WHSV=2.0 h^-1and 1.3 g catalyst dosage are the optimum reaction conditions for the alkylation reaction of phenol and methanol to produce p-cresol.