Ammoxidation Of Ethane To Acetonitrile And Dehydration Of Ethanol To Ethylene Over Various Catalysts

There is considerable interest in converting light alkanes directly to highervalue organic chemica ls because of the low cost and abundance of the alkanes.Recently, more attention has been drawn on studying and developing of noveltechnical route for the use of ethane, such as the catalytic ammoxidation of ethaneto acetonitrile , which is ma inly stimula ted by the great success of acrylonitrileprocess via propane ammoxidation .Several catalyst systems, including Cr-Nb-Mo, Nb-Sb/Al2O3 and meta l ionsexcha nged zeolites, have found to be active for the ammoxidation of ethane.Among them, ion-excha nged Co-ZSM-5 zeolites exhibit better catalyticperforma nce. High-pressure-hydrotherma l excha nged method was carried out toprepare Sb2O3/ Co-ZSM-5 exhibit the best catalytic performa nce.In this work, further work was done in order to study the Sb2O3/ Co-ZSM-5,Various Sb2O3/Co-ZSM-5 zeolites with different Si/Al ratio and crysta l size were prepared and the catalytic performa nce of ethane ammoxidation was investigated.The physica l and chemica l natures of catalysts were characterized and studied byXRD, BET etc. techniques. The relationship between the structure properties of thecatalysts and the catalytic performa nce was built.1. Catalytic performance of ethane ammoxidation over Sb2O3/Co-ZSM-5 zeolitesVarious Sb2O3/Co-ZSM-5 zeolites with different Si/Al ratio and crysta l sizewere prepared by high-pressure-hydrothermal excha nged and mecha nical mixedmethod , the catalytic performa nce of ethane ammoxidation was investigated. Theactivities of Sb2O3/Co-ZSM-5 decrease with the increase of Si/Al ratio. The ma inreason is due to the fact that increasing Si/Al ratio can decrease the excha ngedamounts of Co ions, which are the ma in active centers for the ammoxidationreaction. Sb2O3/Co-ZSM-5 with sma ll crysta l size exhibits higher acetonitrileselectivity than the Sb2O3/Co-ZSM-5 with big crysta l size. The ma in reason is dueto the fact that Al in zeolites with different crysta l size has different distribution.In order to study the effect of Sb, Sb was introduced to the Co-ZSM-5 zeolitesby different kinds of method. Among them, Sb2O3/Co-ZSM-5 catalyst prepared bymecha nical mixed method exhibits the best catalytic performa nce. We think thereis interacting with Sb2O3 and Co-ZSM-5 at calcination , the effect is favorable toammoxidation reaction.Various factors, such as ion-excha nged temperatures, solution concentrationin the course of high-pressure-hydrothermal, can considerably influence thecatalytic performa nce of Sb2O3/Co-ZSM-5 zeolites for ethane ammoxidation. Characterization of the catalysts by XRD, ICP, N2 adsorption-desorption suggestthat the crysta lline level zeolites and Co content are related with the factors.2. Catalytic performance of ethane ammoxidation over modifiedSb2O3/Co-ZSM-5 zeolitesIn order to further enhance the catalytic performa nce of ethaneammoxidation over the catalysts Sb2O3/Co-ZSM-5, different kinds of meta l-ion ,oxides, P and B were introduced to the Sb2O3/Co-ZSM-5 zeolites by differentmethods and the catalytic performa nce of ethane ammoxidation wasinvestigated. Among them, Sb2O3/Fe-Co-ZSM-5 zeolites and Sb2O3/Ni-Co-ZSM-5 zeolites prepared by meta l-ion excha nged method enhance theselectivity to acetonitrile.Section 2: Dehydration of Ethanol to Ethylene overVarious CatalystsEthylene is an important materia l for the organic chemistry industry. Todaythe world production of ethylene is ma inly from naphtha cracking or cracking ofethane extracted from natural gas. Decreasing petroleum quantity anddevelopment of biological ethanol day by day, a conventiona l route of dehydrationof ethanol have attracted the attention of the entire world. Catalytic dehydration ofethanol into ethylene was always using Al2O3 and zeolites, in recent years, zeolitesare focous, because it requires lower temperature and higher WHSV.In this work, various zeolites were tested for dehydration of ethanol using fixed bed reactor.H-ZSM-5 zeolites exhibit the best catalytic performa nce.However, further work is required in order to study the influence of Si/Al ratio,reaction conditions etc on the catalytic performa nce. Besides, the catalyticperforma nce is still unsatisfied concerning future practical applica tion; therefore, itstill is a highly attractive and challenging research subject to search new catalyststhat have unique activity, selectivity for the dehydration of ethanol.1. Catalytic performance of dehydration of ethanol over H-ZSM-5Various zeolites such as H-ZSM-5, H-MCM-22, H-MCM-49, H-MCM-56, HMordenite,SAPO-11,AlPO were tested for dehydration of ethanol using fixed bedreactor. Among them, H-ZSM-5 zeolites exhibit the best catalytic performa nce. Atthe condition of reaction temperature 250℃, the flow rate of 95% ethanol0.02ml/min, dilution with He, ethanol conversion reached to 99.9%, ethyleneselectivity reached to 99.8%.Various factors, such as Si/Al ratio, reaction temperatures, space velocities(LHSV) and the concentration of feed liq uid, can considerably influence thecatalytic performa nce of dehydration of ethanol. The ethylene selectiveity decreaseand diethyl ether selectivity increase with the increase of Si/Al ratio, Si/Al ratioeffect the acid sites in zeolites, this is the ma in reason for changing the catalyticperforma nce of the catalysts. Besides, higher reaction temperature and lower spacevelocities are favorable to dehydration of ethanol into ethylene.2. Catalytic performance of dehydration of ethanol over modified HZSM-5 zeolitesVarious M-ZSM-5 (M=meta l ion) zeolites were prepared by ion-excha nge method and the catalytic performa nce of dehydration of ethanol was investigated.Among them, ion-excha nged Co-ZSM-5 zeolites exhibit the best catalyticperforma nce. Co contents in the Co-ZSM-5 zeolites can considerably influence thereaction performa nce of the catalysts. The characteriza tion of NH3-TPD suggestedthe Co contents in zeolites could affect the acid properties, suitable Co contents isneeded.Different kinds of oxides were introduced to the H-ZSM-5 zeolites and thecatalytic performa nce of dehydration of ethanol was investigated. Most of them,the activity of ethanol and ethylene selectivity was decreased. Dealuminza tion HZSM-5 zeolites were prepared by different methods, The characteriza tion of NH3-TPD suggested dealuminzation could affect the acid properties, but, the catalyticperforma nce has no significa nt difference.