Preparation Of Novel Catalysts For Liquid Phase Hydrogenation Of Benzene And Their Application In Hydrogenated Debenzolization Of 6～# Solvent Oil

Hydrogenation of benzene to cyclohexane, an important chemicalengineering raw material and an excellent solvent, has been known to be animportant industrial process. In recent years, there is an increasing demandfor benzene reduction in petroleum product, and especially in gasoline,diesel and solvent oil because benzene, as a carcinogen, seriously harms thehealth of human beings. The most frequent benzene elimination route is bycatalytic hydrogenation. In industry, benzene hydrogenation can be carriedout in gas phase or liquid phase. Compared with gas phase hydrogenation,liquid phase hydrogenation has the advantages of lower reactiontemperature, lower investment and ease in reaction temperature control, butit requires higher hydrogen pressure and has lower conversion. So,preparation and development of efficient liquid phase benzenehydrogenation catalysts is an important means to overcome thedisadvantages in the present liquid phase benzene hydrogenation. Further, elimination of benzene in the solvent oil by hydrogenation under mildreaction conditions is also the key to the production of high-quality solventoil, but so far little work is reported in this aspect. Based on this, in thispaper, the main work was focused on preparation and development ofnovel hydrogenation catalysts and their application in elimination ofbenzene in 6^# solvent oil by hydrogenation.1. Hydrogenation of benzene over metal complexes encapsulatedin molecular sieves1) MSalen/Y(M=Ni, Pd and Ru) and RuL/Y(L=phenanthroline(phen),2,2'-bipyridyl(bipy) and N,N'-ethylenebis(salicylidene-aminato)(Salen)were prepared by flexible ligand method and characterized by XRD,N₂-adsorption, FTIR, DRS and DTA. The catalytic results show that theproperties of metal ions and ligands have great influence on the catalytichydrogenation activity of the prepared catalysts. Among the selected threemetal ions, RuSalen/Y has much higher catalytic activity than NiSalen/Yand PdSalen/Y. RuL/Y with different ligands exhibit different catalyticperformance in benzene hydrogenation, indicating that the ligands withdifferent properties and structures can greatly change the catalytichydrogenation performance of the prepared catalysts. The catalytichydrogenation activity of Ru(Salen)/Y is much higher than that ofRu(phen)₃/Y and Ru(bipy)₃/Y.2) Three types of Schiff-bases, Salen, Salpn(N,N'-bis(salicylidene) propane-1,3-diamine) and Salicyhexen(N,N'-bis(salicylidene)-1,2-cyclohexanediamine) with different size were used as ligands forpreparation of Ru(Schiff-base)/Y. The results of XRD, N₂-adsorption,FT-IR, DRS, DTA and catalytic reaction show that Schiff-base ligands inthe prepared catalyst change the electronic state of central metal atom, thusmake the catalyst to form transition coordinative state with reactionsubstrate more easily. Compared with Ru/Y prepared by ion-exchangemethod, the catalytic activities of Ru(Schiff-base)/Y increased significantlyin benzene hydrogenation. The geometry size of different Schiff-baseligands has strong influence on the catalytic performance of the preparedcatalysts and with the increase of the ligands in the size, the activity of thecorresponding Ru(schiff-base)/Y catalyst decreases.3) Ruthenium(5,5'-X₂-Salen) complexes, where Salen=N,N'-ethenebis(salicydene-aminato) and X=H, Cl, Br or (OCH₃), wereencapsulated in the cavities of zeolite by flexible ligand method andcharacterized by XRD, ICP, N₂-adsorption, FTIR, UV-vis, DTA andcatalytic hydrogenation reaction. It is found that substitution of thearomatic hydrogen atoms of the Salen ligand by different groups not onlycan modify the electronic and spectra properties of the encapsulatedcomplex, but also has great influence on the catalytic hydrogenationperformance of the prepared catalysts. The benzene hydrogenation catalyticactivities of the prepared encapsulated catalysts with electron-withdrawing group like -Cl, -Br or electron-donating group like -OCH₃ are lower thanthat of the un-substituted encapsulated catalyst. The prepared catalysts arestable in benzene hydrogenation and can be reused.4) A series of Ru(â…¢) tetrahydro-Schiff base complexes (denoted asRu(H₄Schiff base) with Schiff base=Salen, Salpn and Salicyhexen) wereencapsulated in the supercages of zeolite Y by flexible ligand method. Theprepared catalysts were characterized by XRD, UV-vis, FTIR, ICP, as wellas N₂-adsorption techniques. It is shown that upon encapsulation in zeoliteY, Ru(â…¢) tetrahydro-Schiff base complexes exhibited higher activity forthe liquid phase hydrogenation of benzene than the correspondingRu(â…¢)-Schiff base complexes. This indicates that hydrogenation of theC=N bond of the Schiff base ligands led to a modification of thecoordination environment of the central Ru(â…¢) cations. The stability of theprepared catalysts has also been confirmed against leaching of the complexmolecule from the zeolite cavities, as revealed by the result that no loss ofcatalytic activity was observed within three successive runs withregeneration. In addition, the reaction temperature and H₂ pressure on thehydrogenation performance of Ru(H₄Salen)/Y were also investigated.2. Hydrogenation of benzene in model reactant and 6^# solvent oilover molecular sieves supported metal catalysts1) A series of Ru, Pd and Pt catalysts supported on HY, HUSY, and Hβwere prepared, and their liquid phase catalytic hydrogenation performance was investigated for 0.06% benzene/hexane model reactant at reactiontemperature of 313K and total pressure of 1.0MPa. The results show thatsupport, metal and reaction conditions have great influence on the catalyticperformance of the prepared supported catalysts; different metals supportedon USY exhibit different hydrogenation activity, and the hydrogenationactivity for unit mass Ru is comparable with metal Pt; the hydrogenationactivity for Ru catalysts supported on different zeolites decreases in theorder of Ru/HY＞Ru/HUSY＞Ru/Hbeta. The optimum hydrogenationactivity can reach at 313K and 1.0MPa H₂ reaction condition.2) A series of Ru catalysts supported on Si-MCM-41, Al-MCM-41(1)(n(Si)/n(Al)=15), Al-MCM-41(2)(n(Si)/n(Al)=10), as well as H-MCM-41(N) and H-MCM-41(H) from ion-exchanged Si-MCM-41 with thesolution of NH₄NO₃ or HAc in ethanol were prepared and characterized byN₂-adsorption, XRD and H₂-TPR techniques. The liquid phasehydrogenation reaction of benzene on these catalysts was studied by amodel reactant containing 0.5% (mass fraction) benzene in cyclohexane at298K and 3.0MPa. It is indicated the dispersed state, reducibility andcatalytic activity of supported Ru depended on the n(Si)/n(Al), surfacecomposition and acidic nature of supports. The results of the benzeneconversion as a function of reaction time show that the catalytic reactionfollow a first-order kinetic equation. The reaction rate is in order ofRu/Al-MCM-41(2)＜Ru/Al-MCM-41(1)＜Ru/Si-MCM-41＜Ru/H-MCM -41(H)＜Ru/H-MCM-41(N). The Si-MCM-41 with very high surface areaallows for better dispersion of the Ru particles, and the Ru/Si-MCM-41shows higher activity as compared to the Ru/Al-MCM-41. The acidity ofH-MCM-41 results in the improvement of catalytic activity, which isattributed to alternative pathway induced by spillover hydrogen in themetal-acid interfacial region.3) Y/MCM-41 and USY/MCM-41 composites were prepared byin-situ synthesis method and ion-exchange method respectively and theirtextural and structural characteristics were studied by variousphysicochemical means. The two kinds of composites were used assupports for preparation of Ru supported catalyst and their catalyticperformance of the prepared catalysts in liquid benzene hydrogenationwere investigated. The catalytic results showed that Ru supported onY/MCM-41 or USY/MCM-41 composite has higher catalytic activity thanon single phase support and their activities are related to the weight ratio ofY to MCM-14 or USY to MCM-41 in the composites, in which Rusupported on USY/MC-41with a HUSY/MCM-41 weight ratio of 1exhibits the highest activity.4) The low-temperature catalytic hydrogenation for benzene in modelreactant and 6^# solvent oil over Ru(HUSY/MCM-41)(1:1), Ru/H-MCM-41(N), Ru/HUSY and the mechanical mixture of Ru/HUSY with differentmolecular sieve promoters were investigated. It is found that the catalytic hydrogenation rate for model reactant over various catalysts is in the orderof Ru/(HUSY/MCM-41)(1:1)＞Ru/Si-MCM-41(N)＞Ru/HUSY, whilefor 6^# solvent oil is in the order of Ru/HUSY＞Ru/(HUSY/MCM-41)(1:1)＞Ru/Si-MCM-41(N). The different catalytic activities of variouscatalysts for two reactants are due to the presence of small quantity sulfurcompounds in the 6^# solvent oil, while various catalysts have differentsulfur resistance. The sulfur resistance of the catalysts is related to theacidity of the support and the good sulfur resistance for Ru/USY isattributed to the stronger acidity of HUSY. Both the hydrogenationbehavior and the sulfur resistance of Ru/HUSY for 6^# solvent oil, can begreatly improved by addition of H-type molecular sieves (HY, HUSY andHeBeta) promoters to it. The hydrogenation activity and sulfur resistance ofRu/HUSY increased with the increase of promoter amount and keptconstant until weight ratio of HUSY to Ru/USY reached 5. In addition, thepromoters of NaUSY and NaY could also improve the sulfur resistance ofRu/USY due to their adsorption to sulfur compounds.