| CO is present in a large portion of off-gas of yellow phosphorus. COS is a harmful gas which can affect the Cl (one carbon) chemical industry. If yellow phosphorus tail gas can be used as raw material gas to synthesize chemically product, removal of COS are needed. According to the characteristics of yellow phosphrus tail gas, the COS and product of H2S can be removed simultaneously by catalytic hydrolysis method.A novel type of metal oxide/active carbon catalysts was prepared by sol-gel method for the hydrolysis of carbonyl sulfide.The kinds of activated carbon were studied and the physical and chemical characteration over activated carbon surface and the porous of carrier which influence to COS hydrolysis were also examined.The influences of the activitation process on the drying temperature, the calcination temperature, additives and the basic density were thoroughly investigated. At the same time, the methods of regeneration was systemetally proposed.According to the complexity and particularity of yellow phosphorous tail gas, the influence factors of COS hydrolysis kinetics were analyzed, such as COS concentration, the gas hourly space velocity(GHSV), reaction temperature, relative humidity, O2 concentration and CO concentration. The surface of catalysts was characterized from point of view of its chemistry (Boehm titration). The products were characterized by using SEM, XRD and XPS. Reaction mechanism of COS hydrolysis was also proposed.The activities test results showed the coconut-activitated carbon loading 2.5-5% Fe2O3 and n(Fe):n(Cu)=10 after calcinations at 500℃and dried at 170℃have superior activity and the activities of COS hydrolysis reduced with the increasing of O2 concentration. The effect of CO concentration was not strong when the catalyst was dried at 160～170℃.The catalytic activities results showed that the activities increasing with the basic intensity over coal-based activated carbon, and the activity follows the order KOH> Na2CO3> NaHCO3.Meanwhile, addition of Cu and Ce can enhance the activities of COS hydrolysis and Fe-Cu-Ce/AC gave a higher stability. The regeneration results showed that water-washing can flush away part of the dissolved sulfur-containing compound on the surface of the catalyst, however, it simultaneously caused the loss of a considerable amount of basic groups, consequently, resulting in the decrease of the catalyst.Thermal regeneration by 99.99% N2 could remove the most sulfates at 250～300℃, only leaving a very small amount of element sulfur on the catalysts surface. The Fe-Cu/AC catalysts could be regenerated by thermal N2 several times, showing good regeneration performance and greatly decreasing the cost in industrial production. The XPS results showed the product of H2S might be absorbed by the interaction with metal compounds and O2 to form the sulfate (171.28eV) and element sulfur (164.44 eV), which contribute to catalysts poisoning.The kinetics of hydrolysis COS was studied.The results showed that the external diffusion was main control process when GHSV is below 5000h-1.While, the internal diffusion can be neglected above 8000h-1. The reaction kinetics was expressed as follows: The increasing reaction temperature was benifical to COS hydrolysis and the apparent reaction activation energies of COS over active carbon was 3.67kJ.mol-1 and pre-exponential factor wasA=2.27x104min-1. Based on the XPS, XRD and SEM result and some literatures, the reaction mechanism of COS hydrolysis was proposed and it was that COS adsorbs on basic sites to form an activated intermediate and COS reacts directly with adsorbed H2O. The rate of COS adsoption was effect to the rate of COS hydrolysis because of H2O adsorbtion very strongly, which was the controlling step of COS hydrolysis.
|
PDF Full Text Request