Titanium Silicalite-1Catalyzed Propylene Epoxidation To Propylene Oxide In Fixed-bed Reactor

Propylene oxide is an important chemical raw material. Currently, propyleneoxide is mainly produced from chlorohydrin process and hydroperoxide process, butboth of these technologies have obvious disadvantages. The former process producesa large volume of waste water containing chlorine and solid waste, which is notenvironmentally friendly. The latter process is a complex process, and needs highpurity raw materials and large investments. Titanium silicalite-1(TS-1) catalyzedepoxidation of propylene with hydrogen peroxide to propylene oxide (HPPO process)is a simple and environmentally-friendly process, which has the advantages of mildconditions, high selectivity. This will be the main process for the production ofpropylene oxide.In this work, TS-1powder was hydrothermally synthesized, and then shaped toSiO2-supported TS-1catalyst for the epoxidation of liquid phase propylene in afixed-bed reactor. Firstly, the effects of reaction temperature, reaction pressure,methanol concentration and hydrogen peroxide concentration on the conversion,product selectivities and catalyst stabilities were investigated. Secondly, the catalystwas treated with base, deposited carbon, alkylation, etc, and the effects of themodification on the catalytic stabilities were also studied. Finally, the effects ofreaction temperature, methanol concentration and hydrogen peroxide concentrationon the deactivation were studied and a kinetic study of the catalyst decay for thisreaction was carried out.The experimental results showed that the catalytic stabilities were improved withincreasing the reaction temperature, reaction pressure, methanol concentration andselectivity of PO (SPO). However, the catalyst stability was not enhanced whencations in hydrogen peroxide were exchanged into hydrogen ion.The catalytic stability in the epoxidation of propylene was not improved throughthe modification. However, SPOin the initial reaction was remarkably affected. SPOover the catalyst treated by TPAOH and NH4AC was greatly increased, but wasalmost not changed when the catalyst was treated with inorganic alkali, lowconcentration deposition of carbon and steam. Instead, SPOover the catalyst treatedby triethanolamine, high concentration deposition of carbon and alkylation was decreased.In the deactivation reaction of propylene epoxidation, high reaction temperatureand methanol concentration or low H2O2concentration led to the slow deactivationrate. Kinetic study of TS-1/SiO2catalyst in the reaction showed that the deactivationreaction is a second order reaction, and then the kinetic equations of the catalystdecay were obtained.