Study On Sulfur Tolerance Of Nickel Metal Catalysts In Aromatic Hydrogenation

The sulfur tolerance of nickel metal catalysts in aromatic hydrogenation has been studied systematically on the base of nickel active unit in this paper. The catalytic activities of Ni/Al2O3 were investigated by the probe reaction of hydrogenation of toluene using thiophene as poison in fixed-bed continuous-flow micro-reaction equipment. And it is studied deeply on the influences of the catalyst's performance on aromatic hydrogenation and the sulfur resisted by different preparation .methods, promoters, content of active parts, assistant catalyst , supports' acidity or alkalescence and reaction conditions. The catalysts' surface characteristic and configuration and activity center were discussed by means of XRD, TPR, BET, DSC, XPS, PY-IR, COIR. The results indicated that the factors discussed above have certain effects on Ni/Al2O3. At the same time, the industrial appliedstudies on Ni/Al2O3 were carried out with 200 and 260 solvent oil. The industrial test results showed these catalysts with high aromatic hydrogenation and high sulfur tolerance can produce low aromatic environmental solvent oil with good quality under abirritant conditions.Firstly, a series of Ni/Al2O3 catalysts were prepared by different methods. Resistance of these nickel metal catalysts to sulfur poison has been investigated by performing hydrogenation of toluene. It showed that obvious effects on hydrogenation activity and sulfur resisted lie in granularity of NiO crystalline and state of Ni in Ni/Al2O3 catalyst. The catalyst prepared by impregnant method was the best. The difference of catalytic activities obviously displayed on the interaction between Ni and A12O3 carrier. The results also indicated that calcined temperature had the same important roles in nickel metal catalyst. The high calcined temperature enhanced the interaction between NiO and Al2O3, and it isfavored to form NiAl2O4, which has no hydrogenation activity and sulfur resisted. While the low calcined temperature, the decompound and reduction of Ni has decreased. The best preparation conditions of the catalyst were to have it calcined at 450 C and reducted at 460~480 C.Secondly, systematic studies on the effects of catalysts property by assistant catalysts were carried out by adding Mg and Ti and earth to Ni/Al2O3 catalyst. It showed that catalytic activities increased with Mg or Ti. Among these promoters, the catalyst containing Mg was the best. The action of Mg promoter on catalyst has been discussed by means of XPS, BET. The results showed that Mg favored the sulfur resisted, which could enlarge the active surface area and increase the electronic cloud density of the nickel atom, and so could make catalysts life long.Finally, the catalyst performance modified by carrier was discussed. A series of Nickel catalysts which have been characterized by pyridine-adsorbed and CO-adsorbed infrared spectra supported by Y -Al2O3, SiO2-Al2O3, Sep and Y-type Zeolite have been prepared. Resistance of these nickel catalysts to sulfur poison has been investigated by reaction of hydrogenation for toluene. The existence of electron-dificiency Ni species was confirmed and correlated to acidity of catalysts and catalytic behaviors. It was found that the stronger the acidity, the higher the electron deficiency, the better the sulfur resistance. Acidity characterization indicated that Bronsted acid sites of the catalyst favored the sulfur resistance but Lewis acid sites did not.The effects of reaction conditions on catalysts performance were investigated by industrial test. The results showed increasing pressure and temperature and decreasing the LHSV were better for catalyst in aromatic hydrogenation and sulfur tolerance. The best handling conditions for Ni/Al2O3 were at 1.0MPa, 190-220 C, LHSV 1.0h-1.