The Mechanism Of Lignin Cellulose Thermal Conversion And Adsorption And Separation Of Pyrolytic Gases CO₂ And H₂ By Molecular Simulation

Biomass,as one of the renewable energy,has played an important role in solving energy and environment issues.Not only can the bio-oil derived from pyrolysis be the alternative fuel,but also it can product life and chemical outcomes due to it is the carbon based organics.However,the inner mechanisms of lignin cellulose conversion are not known to all of us.In present work,the quantum calculation methods were employed to further investigate pyrolytic processes of cellulose and lignin plus the effects of metal ions in cellulose pyrolysis and the mechanism of conversion of cellulose in supercritical water.At last,based on the new 2D material,phosphorene,the derived gases CO₂,CH₄ and H₂ were studied.Specifically,the adsorption and separation of CO₂ from CO₂/CH₄ gas mixture.The main results are as follows:?1?The mechanism of initial processes of cellulose pyrolysis.The model compound cellobiose was adopted to study ten reaction pathways of cellulose pyrolysis.Results indicate that H⁺ plays a pivotal role in breaking the cellulose chain during the primary pyrolytic processes.The concerted mechanism is the main way to product levoglucosan and cellulose chain with levoglucosan end at initial stage of cellulose pyrolysis.When pyrolytic temperature increases,the reaction pathways of generating HAA are another routes to cut down the chains.The parallel competing pathways happen between producing HAA and LG were interpreted in pathway 1 and 8 successfully.Moreover,the mechanism of depolymerization at high temperature are also described.Hydrolysis reaction is rare during the initial processes of cellulose pyrolysis.?2?The mechanisms of generating main small weight molecules during cellulose pyrolysis.The ?-D-glucopyrnose was selected as model compound and two reaction series were studied including 7 reaction pathways.The first reaction series unveils the reaction processes related to chain end of cellulose and the second series describes the reactions inner cellulose chain.The calculation results explain the experimental phenomenon that the proportion of HAA is larger than other small weight outcomes.And generating of furfural is difficult than that of 5-HMF,due to the high energy barrier.In addition,other small weight molecules like acetol,formaldehyde,formic acid,acetic acid,glyoxal,H₂O and CO have higher energy barrier than that of HAA,which indicate that HAA is the main product among generated small weight molecule during cellulose pyrolysis.Understanding these reaction processes contributes to the whole pyrolytic processes of cellulose,and supplies to guide the real industry.?3?The mechanism of lignin pyrolysis was investigated by using lignin model compound.Five possible pyrolytic pathways of guaiacol were proposed with an emphasis on the reactivity of the methoxy group.According to the calculation results,the five reaction pathways were ranked as Path 3,Path 1,Path 4,Path 2,Path 5,in descending order of reactivity.Kinetic analyses results of the three demethoxylation reaction pathways?Path 2,Path 3,Path 4?indicate that coupling a hydrogen radical to the carbon atom to which the methoxyl group bond can effectively lower the reaction energy barrier that existed in the process of demethoxylation.Pathway 5 demonstrates the possible formation mechanism of o-quinonemethide which is the key polymerization intermediate during lignin pyrolysis process.?4?A local pyrolytic model was brought up to understand better the pyrolysis mechanism of cellulose with alkalis metal,8 reaction pathways of ?-D-glucopyranose were investigated.According to calculation results,the formation of levoglucosan was restrained remarkably by adding alkalis mental ions,which indicated the validity of the local pyrolytic model and also demonstrated that it was indeed suitable to describe the process of levoglucosan formation through concerted mechanism.On the other hand,the yields of other small molecules were enhanced with K⁺ and Na⁺.All results above were consisted with related experimental conclusions.So the local pyrolytic model is an appropriate tool to study the effect of catalyst and a feasible way to search a new high-efficiency catalyst on the biomass pyrolysis in the future.?5?The mechanisms of glucose decomposition in supercritical water by 8 proposed reaction pathways to explore the formation mechanism of some main outcomes?levoglucosan,5-hydroxymethylfurfural,hydroxylacetaldehyde,erythrose,glyceraldehyde and fructose?.In addition,seven potential dehydration ways in glucose were investigated with and without the assistance of water molecule.All dehydration reactions are accelerated when water molecules take part in the reaction,because it can effectively lower the energy barrier of dehydration reaction by forming a six-ring transion state.In supercritical water surrounding with assistant of water molecule,pathways 3 and 4 are preferred routes of glucose conversion to hydroxylacetaldehyde and erythrose with the lowest energy barrier of 127.55kJ/mol.While a higher energy barrier?163.35kJ/mol?is required to form glyceraldehyde and fructose in pathways 5 and 6.Levoglucosan and 5-hydroxymethylfurfural are hard to generate during this chemical processes because of their higher energy barrier without water participating in.It seems like that water molecule acts as a magic catalyst that can transfer hydrogen atom in dehydrations,keto-enol tautomerization and structure rearrangement,which reducing the distance of hydrogen atom moving,result in reducing these reactions energy barriers dramatically.The computational results open a window to produce hydroxylacetaldehyde and erythrose in theory.Moreover,it sheds some light on the various proportions of different products in conversion of glucose in supercritical water,as well as suggesting concrete reaction pathways to form these main products,contributing to the elaboration of the mechanism of glucose conversion and cellulose decomposition from a molecule level.?6?Performance of phosphorene-based material in biomass derived CO₂ and CH₄ adsorption and separation from natural gas by using Density Function Theory calculation and Grand Canonical Monte Carlo?GCMC?simulations.DFT calculation results show that the CO₂ has higher adsorption energy than that of CH₄,which implies that they are more easily adsorbed to the phosphorene surface than CH₄.Detailed MC simulation reveal that the phosphorene has a high performance in separating CO₂ from nature gas and achieves the highest gas selectivity.It is suggested that the phosphorene is a promising candidate for natural gas purification and possessing practical potential applications in gas adsorption.Porous phosphorene is builted and is used in hydrogen separation from gas mixture by employing first-principles calculations.Calculation results indicate that the self-passivated defect in phosphorene is inert to the gas mixture containing N₂,CO,CO₂,H₂ O,and CH₄ molecules,and the porous phosphorene performs high selectivity for hydrogen over other gas molecules compared with previous graphene and silicenebased membranes.Our results unveil the great potential of porous phosphorene as a promising membrane in gas purification.