Molecular Simulation And Experimental Study Of Cellulose/polyethylene Co-gasification For Hydrogen Production Based On Calcium Looping Cycle

Calcium cycle enhanced biomass steam gasification for hydrogen production technology uses calcium-based absorbent to capture CO₂ in situ,which Not only contributes to the production of H2 with high concentration and high yield but also achieves negative carbon emissions through CO₂ enrichment,which has broad prospects in the utilization of renewable clean energy and environmental protection.However,the high-temperature sintering of calcium-based absorbent makes its CO₂ cycling performance decline rapidly,inhibits the balance of chemical reaction,and leads to the reduction of hydrogen gasification effect.At the same time,the gasification reaction rate was low only with calcium absorbent.Therefore,improving the cyclic stability and CO₂ trapping activity of calcium-based materials and selecting appropriate catalysts to enhance the reaction rate of hydrogen production by gasification are the keys to improving the performance of hydrogen production by calciumcycling enhanced biomass steam gasification.In addition,the characteristics of high O content and low H content of biomass lead to low H2 yield from gasification,while coke and tar yields are high.Adding waste plastics to biomass can not only significantly improve the steam gasification characteristics of biomass but also solve the environmental problems caused by waste plastics.To solve the above problems,a series of Ni-CaO-Ca12Al14O33 and Ni-CaO-MgO composites were prepared by using industrial solid waste--calcium carbide slag as calcium base absorber,Ni as the catalyst,Ca12Al14O33 and MgO as inert supports.The catalytic hydrogen production performance,CO₂ capture capacity and cycle stability of Ni-CaOCai2Al14O33 and Ni-CaO-MgO were studied and compared in macroscopic experiments.The effects of polyethene blending on the sorption enhanced steam gasification of cellulose were studied with cellulose and polyethene as biomass and waste plastics.DFT calculation revealed part of the mechanism of absorption and enhancement of steam gasification for hydrogen production by Ni-CaO bi-functional materials and the reason for higher cycle stability of NiCaO-Ca12Al14O33.At the same time,the co-pyrolysis and pyrolysis mechanisms of cellulose/polyethene were studied based on molecular simulation（DFT and Reax FF）.The improvement mechanism of cellulose pyrolysis products by polyethene blending was revealed,which laid an important theoretical foundation for further research on the gasification mechanism.Using DFT calculation and the ReaxFF MD method,the co-pyrolysis mechanism of biomass and waste plastics was studied at the micro-level with cellulose and polyethene as the typical representatives.The yield and structure changes of main components during cellulose/polyethene co-pyrolysis were summarized and analyzed by ReaxFF MD simulation.DFT transition state analysis was used to calculate the energy barrier of pyrolysis oil and gas products generated by co-pyrolysis and self-pyrolysis of cellulose,and the mechanism of polyethene improving the quality of pyrolysis oil and gas products during co-pyrolysis was determined.It is found that ·H and hydrocarbon free radicals generated from polyethene pyrolysis can interact with alcohol groups and furan generated from cellulose pyrolysis to produce long-chain alcohols and furan alcohols,which is beneficial to improve the quality of pyrolysis oil.The large amount of ·H free radicals produced by polyethene can also combine with ·CH3 free radicals to significantly increase the production of hydrocarbon gases.Polyethene plays a key role in improving the quality of pyrolysis oil and gas products.Ni-CaO-Ca₁₂Al₁₄O₃₃ and Ni-CaO-MgO bifunctional materials were prepared by a wet mixing method for hydrogen production from cellulose/polyethene co-gasification.The effect of polyethene on co-gasification products was determined.The cyclic CO₂ capture performance of Ni-CaO-Ca₁₂Al₁₄O₃₃ and Ni-CaO-MgO in 20 calcium cycles and the catalytic activity and stability of absorption enhanced cellulose/polyethene co-gasification for hydrogen production were studied.The effect of inert carrier type on product yield and concentration was evaluated.The separation density,differential electron density and adsorption energy of NiCaO/Ca12Al14O33 and Ni-CaO-MgO were analyzed and compared by DFT calculation.which revealed the reason for higher cycle stability of Ni-CaO-Ca₁₂Al₁₄O₃₃ at the micro-level.The results show that the carbon capture capacity of Ni-CaO90-（Ca12Al14O33）10 after 20 cycles of calcium is 1.32 times that of Ni-CaO75-MgO25,and the H2 yield and concentration after 20 cycles of gasification/calcination are 2.6 times and 1.4 times that of Ni-CaO75-MgO25,respectively.At the same time,the lower adsorption energy（-13.13 eV）,more new chemical bonds and lower overlapping electronic state energy region（-0.26 to 0.04 eV）in DFT calculation indicate that Ca12Al14O33 can inhibit the sintering and deformation of Ni-CaO materials more effectively.Ni-CaO90-（Ca12Al14O33）10 has better CO₂ capture ability,hydrogen production performance and cycle stability.Sorption enhanced water-gas shift reaction is one of the most important reactions in the absorption enhanced biomass/waste plastic steam co-gasification system for hydrogen production.To fully study the reaction mechanism of the entire gasification system,the mechanism of sorption enhanced water-gas shift reaction on the Ni-CaO surface was firstly studied by DFT calculation.The effect of Ni on the surface stability and catalytic performance of Ni-CaO was studied.The adsorption energies of the reactants,intermediates and products involved in the reaction were calculated,and the optimal configuration for the transition state search of the subsequent reaction was determined.The energy barriers of different reaction paths were compared utilizing transition state calculation,and the best reaction paths on The Surface of Ni-CaO were revealed.The results show that the formation energy,state density and differential electron density all confirm that the addition of Ni makes the Ni-CaO model have higher catalytic activity.Ni reduces the surface adsorption energy of H2O*（-1.30 eV）and CO*（0.68 eV）,which contributes to the adsorption of reactants and promotes the sorption enhanced water-gas shift reaction.Ni increases the adsorption energy of H2*on the surface（0.05 eV）and promotes the release of H2.At the same time,the Surface of Ni-CaO still retains effective CO₂ capture ability.Sorption enhanced water-gas shift reaction on Ni-CaO surface is easier to follow the redox mechanism.