The Preparation Of Catalysts And Research Of Kinetics For Carbon Disulfide Hydrolysis Under Moderate Temperature

Carbon disulfide (CS₂), which widely exist in gas-produced from coal or oiland nature gas, is a poison to many catalysts used in synthesis processes. So itneeds to be removed finely from gas. The removal of CS₂ under moderatetemperature with technic and energy match has gotten the attention ofresearchers. The researches on removing carbon disulfide have begun over theworld, but the few researches focus on the moderate temperature and theinfluence of CO atmosphere on CS₂ hydrolysis.This paper, according to technological reguirment in the project ofNational Basic Research Program '973', researched and developed a kindof catalyst for carbon disulfide hydrolysis under CO atmosphere, thencarried out research on carbon disulfide hydrolysis kinetics. The CS₂hydrolysis catalysts usingγ-alumina as the support were prepared byadding K₂O with the alkaline catalysis property, and rare earth metal oxidewith the property of restraining carbon deposition. Chose some bettercatalysts in the evaluation of N₂ then evaluated them under CO atmosphere. The CS₂ hydrolysis activity over prepared catalysts wastested in a fixed bed reactor, and surface properties for catalyst wascharacterized using the technique such as TPD, FTIR, XRD, XPS, BET.The appraisal results of CS₂ hydrolysis activity, which was obtained underCS₂ concentration of 200mgS/m³, temperature of 300℃, space velocity of 10000h^-1, showed that the CS₂ hydrolysis conversion approach to a stability valve overprepared cataststs after 12 hours. CS₂ hydrolysis conversion over catalystloading K₂O was the largestest among catalyst only loading single activecomponent; and that of catalyst loading ZrO₂-K₂O was the largest amongcatalyst loading varied componments. But CS₂ hydrolysis over all catalystsdecreased under high CO concentration of 35%. The CS₂ hydrolysis conversionover La₂O₃-ZrO₂-K₂O is considered to be the highest among all catalysts.Withthe decrease of CO concentration in gas,the drop in CS₂ hydrolysis conversionover all series of catalyst prepared got small and had difference in COatmosphere. In comprison with N₂ atmosphere, the CS₂ hydrolysis is lower. Theone reason for the declined maybe caused by the COS formed in the reaction ofCO and H₂S, which lead to the intermediate product COS increased, andrestrained the CS₂ hydrolysis; another reason maybe caused by the carbonformed from the disproportion of CO. The alkali metal oxide K₂O and transitionmetal oxide ZrO₂ can improve the conversion of CS₂. The rare earth metal oxidecan decrease the influencing of CO on the CS₂ hydrolysis over catalyst.The CO₂-TPD results show that the adding active components can improveThe amount of basic center on catalyst loaded K₂O is as times as that ofγ-Al₂O₃,and that of catalyst loaded La₂O₃-ZrO₂-K₂O is 20 times. The loading activecomponents can increase the intensity of basic center. But with the increasing of active components, the intensity of basic center was reduced.The CO-TPD results show that CO can be adsorbed by catalysts, and theamount of CO adsorbed decreased with the rise of adsorption temperature. Theadding active components can decrease the CO adsorption,and catalyst addedLa₂O₃,ZrO₂,K₂O,CO adsorption was the lowest. The XPS results about freshand reaction catalyst in CO atmosphere indicated that CO adsorbed on catalystchanged into graphite carbon, then formed graphite carbon can lead to catalystpoison.BET results show that adding active components will lead to surface areadrop. In CO atmosphere, the surface area of catalyst after reaction had a slightdecline.Carbon deposition mechanism in CO atmosphere over catalyst is acidcatalysis reaction.The decrease of surface acid center on catalyst will be mainmethod to reatrain poison of catalyst by carbon deposition.Because La₂O₃,ZrO₂,K₂O are alkila mental oxide, loading these components can decreasesurface acidity and increase surface basicity. By suitable combination of thesecomponents, proper strength of alkila center can be obtained. The carbondeposition on catalyst can restrain, and the activity of CS₂ hydrolysis increase.The research results about reaction kinetics for CS₂ hydrolysis showed thatCS₂ is first, H₂O is zero. The equation about reaction kinetics for CS₂ hydrolysisfollows as:γ_CS2=-dx/(d(W/F_CD2,0)=211.7P_(CS2)exp(-12042/8.314T)And the CS₂ reaction mechanism is that CS₂ adsorbs upon basic sites form an activated intermediate; adsorbed CS₂ reacts with adsorbed H₂O. Adsorption rateof CS₂ influence the rate of CS₂ hydrolysis.The adsorption rate of H₂O is veryfast.The influence of different concentration of CO and H₂ on the CS₂ hydrolysisconversion were studied under temperature of 300℃,the CS₂ concentration of300mgS/m³, veolicity of 60000h^-1, the mesh of catalyst of 60～80 mesh. Theresults showed that CS₂ hydrolysis conversion increased with the increase ofconcentration of H₂, this maybe caused by the reaction between H₂ and CS₂. Theconversion CS₂ hydrolysis was decreased with the increase of the concentractionof CO.