Studies On The Oxidative Dehydrogenation Of Cyclohexane And The Alkylation Of Phenol With Methanol Via A Fixed-bed Reactor

1. Studies on the oxidative dehydrogenation of cyclohexaneCatalytic selective oxidative dehydrogenation (ODH) ofcyclohexane has been the subject of many studies due to the importanceof refining and reforming processes in the petroleum industry. So far, thecatalyst used in the cyclohexane ODH is mainly the one taking noblemetal such as platinum or palladium as main active component, itsshortcoming is costly and that the requirement of the impurity content isharsh in raw materials.Herein, based on the viewpoint that the reactants could be cheaplyobtained and the reaction procedures were simple,Cu-Ca-hydroxyphosphates (CCHP) and MnO_x have been investigated ascatalysts for the vapor phase ODH of cyclohexane at atmosphericpressure via a fixed-bed reactor. It was found that catalysts only exhibiteddeeply oxidative dehydrogenation activity rather than oxidativeperformance. The catalyst CCHP was proved to be good stability inactivity in the investigative temperature range. It was worthy to mentionthat, after this catalyst was treated with tetraethyl orthosilicate (TEOS),its catalytic activity was significantly improved, its reason might be thatthe catalyst CCHP becomes more hydrophobicity after it was treated withTEOS. Besides, the catalyst MnO_x were found to have a good catalyticactivity of the ODH of cyclohexane when it either activated with H₂ or O₂.In addition, the temperature played an important role in the activity of MnO_x.2. Studies on the alkylation of phenol with methanolThe methylation of phenol with methanol over a series of HZSM-5zeolites with different Si/Al ratios was investigated. Reaction conditionssuch as the catalyst SiO₂/Al₂O₃, temperature, the reactant mole ratio, feedflow rate had significant influences on the reaction. The results revealedthat the various physical and chemical properties of HZSM-5, includingthe specific surface area, microporous volume and acid strengthsincreased with Si/Al ratios of HZMS-5. HZSM-5 with various Si/Alratios all exhibited good initial activity, and the higher Si/Al molar ratioof HZSM-5 is, the better activity and stability It may be interpreted thatthe catalyst described above with larger micro specific surface area andpore size could facilitate the mass transfer and didn't coke easily thanksto the strong acidic sites and lower acid density. And we found that theactivity of catalysts increased with temperature and reached theiroptimum activities until the molar ratio of methanol/phenol was 5, whilethe value of WHSV was between 1.50-2.00 h^-1.In order to discuss the law of phenol alkylation over HZSM-5zeolites, the effect of the acid sites on the internal and external surfaces ofHZSM-5 and modification of zeolite with oxide on the alkylation ofphenol with methanol was also studied. A series of catalysts such asMgO/HZSM-5 and P₂O₅/HZSM-5 were prepared by co-impregnationmethod. In our study, it was observed that aid-base characteristics ofmodified oxides was important to the reactivity of zeolites, the C-alkylation activity of catalysts declined without exception whenHZSM-5 were modified with MgO or P₂O₅ and decreased gradually witha concomitant increase of the oxide loading too. In addition, moderateimpregnation of zeolites with H₃PO₄ solution could distinctly improve theselectivity for p-cresol, but the modification of catalysts with MgO didn't.Finally, the activity of HZSM-5 zeolite obviously drops when it treatedwith tetraethyl orthosilicate (TEOS), indicated that the acid sites locatedin the external surfaces of HZSM-5 played some role in the reaction.