Study On Mechanism Of Hydrogen Production By Supercritical Water Gasification Of Oily Sludge Under Alkaline Catalysis

The hydrogen production by supercritical water gasification technology is an emerging treatment technology that realizes the reduction,harmlessness,and resource utilization of oily sludge.The improvement of gasification efficiency is the key to the development of this technology.In this study,the research on the mechanism of hydrogen production by supercritical water gasification of oily sludge under alkaline catalytic conditions was carried out from both experimental and theoretical aspects,which provided experimental and theoretical basis for improving hydrogen gasification efficiency by supercritical water gasification of oily sludge.First of all,the experimental scheme was designed,and the batch-type supercritical water gasification reaction experimental platform was built independently.Secondly,a basic catalyst optimization experiment was carried out by comparing and analyzing the effects of catalyst type,concentration,and residence time on the yield and gasification efficiency of hydrogen and other gases.Thirdly,the effects of different reaction conditions,such as temperature and residence time,on the gas yield and gasification efficiency,the composition distribution of liquid products and the changes of various functional groups in solid and liquid products were compared and analyzed.Finally,through the establishment of a reaction kinetic model,the mechanism of supercritical water gasification of oily sludge under alkaline catalysis was analyzed by combining with the experimental results and the transition state theory.The results of experimental and theoretical analyses showed that:1.under the experimental reaction conditions of this study,K₂CO₃was the optimum catalyst.Under the action of K₂CO₃,the H₂yield increased by 89.5%,CO₂yield increased by48.5%,CH₄yield increased by 31.3%,the gasification efficiency（GE）increased by 42.5%,the carbon gasification efficiency（CGE）increased by 38.0%and the hydrogen gasification efficiency（HGE）increased by 41.8%.2.Under the action of K₂CO₃,C-C gradually broke and formed short-chain small molecule compounds,and the content of reconstituted components of n-alkanes in the liquid phase products kept decreasing and the content of light components kept increasing.3.Under the action of K₂CO₃,all kinds of organic compounds in the solid phase products were cracked to different degrees,and C≡C-H,C-H,=C-H and C-O were less stable,and such functional groups were the main targets of supercritical water-catalyzed gasification cracking of oil-bearing sludge.4.A reaction kinetic model was established and the activation energy of the reaction under the action of K₂CO₃was calculated to be reduced from 60.747 k J/mol to 49.296 k J/mol by combining with the experimental results.5.Combined with the transition state theory,the effects of kinetic parameters and the reasons for the reduction of activation energy of the catalyst were analysed from a microscopic perspective.Under the action of K₂CO₃,the activation entropy and activation enthalpy of the reaction were reduced,which in turn reduced the activation energy of the reaction and improved the efficiency of the reaction.