Regulation On Preparation Process Of Iron Based Hydrotalcites Solid Alkali Oxides And Its Catalytic Performance For The Depolymerization Of Calcium Lignosulfonate

In recent years,the production of high value-added chemicals and fuels derived from biomass resources has attracted widespread attention.The conversion of biomass into chemicals through depolymerization is the main method for high value-added utilization of biomass resources.Energy crisis and environmental pollution can be alleviated by the utilization of biomass resources,which has great importances on the sustainable development of Chinese economy.At present,most of the biomass resources are mainly concentrated on cellulose and hemicellulose which are easy to be used.Lignin,due to its complex chemical structure and strong stability,cannot be converted to high value-added chemicals and fuels.It is possible that lignin can be selectively break the chemical bonds through catalytic depolymerization to produce phenolic chemicals.Therefore,the most important problem is to select the appropriate catalytic system for lignin depolymerization.In this research,catalytic depolumerization of calcium lignosulfonate by solid base oxides derived from sub-micron sized LDHs through introducing hydroxyl compounds were proposed.The effects of hydroxyl compounds on the growth of LDHs were studied.The crystal phase,morphology,functional groups and pore structure of hydrotalcites（NiMgFe）and solid base oxides（NiMgFeO_x）were characterized by XRD,SEM-EDX,FT-IR,FAAS and BET.The depolymerization of calcium lignosulfonate by NiMgFeO_x was evaluated in a hydrothermal reaction system（ethanol-water as solvent）.Optimizing the reaction parameters to explore the distribution law of gas,liquid and solid phase.The composition of liquid products was analyzed by GC-MS and GPC to study the selectivity of liquid products.The spent solid base oxides can be regenerated through oxidization to recycle.The results are as follows:（1）By optimizing the preparation process of LDHs precursor,the optimal conditions of NiMgFe-LDHs were determined as follows:pH=10,180℃,24 h,n（Ni+Mg）/n（Fe）=4,and n（Ni）/n（Mg）had little effect on the crystalline of LDHs.（2）Different hydroxyl compounds（such as ethanol,ethylene glycol and glycerol）were added to regulate the growth process of LDHs.Among them,the particle size of LDHs can be regulated by the addition of ethanol under the optimum conditions（pH=10,180℃,24 h,n（Ni+Mg）/n（Fe）=4,15 vol.%ethanol）.The average grain size of NiMgFe-LDHs was about150 nm),and the dispersion was better.（3）The growth kinetics curves of NiMgFe-LDHs were"S"growth.The nucleation and growth rate can be accelerated by increased temperature,ion ratio and the addition of hydroxyl compound.The apparent activation energy of nucleation is E_n=11.85 kJ·mol^-1 and the apparent activation energy of growth is E_g=65.58 kJ·mol^-1.Among them,the addition of ethanol can not only increase the crystal nucleation and growth rate,but also improve the dispersion.（4）600℃ was the optimal calcination temperature and the solid base oxides had better dispersibility and regular flake structure as compared with the samples without the addition of hydroxyl compounds.SEM-EDX and BET results showed that the active metals uniformly distributed with the surface area of 81.72 m²·g^-1,average pore size of 17.94 nm and pore volume of 0.73 m³·g^-1（NiMgFeO_x-ET）.（5）Calcium lignosulfonate was hydrothermal depolymerized by solid base oxides with different metal compositions and n（Ni）/n（Mg）.Among them,NiMgFeO_x with n（Ni）/n（Mg）/n（Fe）=1:3:1 showed the best catalytic activity.The liquid yield was 75.8%and the residue yield（including unreacted calcium lignosulfonate and coke）was 19.7%with about4.5%gas（main product was CO₂）under 270℃,4 h and ethanol-water（65 vol.%ethanol）as solvents.The composition of liquid products was analyzed by GC-MS.The main products were phenolics（including phenol,guaiacol,syringol）with the selectivity of 78.7%.（6）The solid base oxides were regenerated through oxidation,after 4 cycles,the liquid yield was still over 70%,and the crystalline phase and composition remained basically unchanged,which confirmed that the solid base oxides had better catalytic activity and stability.