Regulation Of Crystal Transformation Process For Manganese Oxide And Its Catalytic Depolymerization Of Calcium Lignosulfonate

At present,the conversion of biomass to produce high value-added chemicals has been widely concerned by researchers.Lignosulfonate contains a large amount of aromatic hydrocarbon structure,due to its complex and stable chemical structure,it is not easy to efficiently convert and use.By selecting a suitable catalyst,the lignosulfonate is hydrothermally depolymerized to obtain a small molecule phenolic compound.This article mainly used amphoteric metal oxide Mn O₂as a catalyst.Manganese dioxides of different crystalline structures??,?,?,??were mainly prepared by hydrothermal synthesis.Studied the synthesis conditions to regulate the crystalline structures of manganese dioxide such as:hydrothermal temperature,hydrothermal time,n(Mn²⁺)/n?Mn O₄^-?,anion,p H value,solvent and introduced different kinds of additives,etc.The XRD,SEM,FT-IR and XPS characterization methods were used to analyze the crystal composition and morphology of oxides.Selected calcium lignosulfonate as the target depolymerization substance and examined hydrothermal depolymerization conditions?hydrothermal temperature,hydrothermal time,m?Mn O₂?/m?CLS?mass ratio?and different crystalline structures of manganese dioxide for hydrothermal depolymerization impact.The GC-MS,FT-IR,and XPS characterization methods were used to analyze solid residue and the distribution of liquid products after hydrothermal depolymerization.The main findings of this paper are as follows:?1?The effect of hydrothermal preparation conditions on the crystalline structure and grain size of manganese dioxide was studied.It was an?-type stable phase in the range of 100-140?and a?-type stable phase in the range of 160-180?.The crystalline structure has no effect,and it is related to the size of the crystal grains;as the value of n(Mn²⁺)/n?Mn O₄^-?increased,the crystalline structure of the product changes from?-type to?-type;Cl^-and NO₃^-had no effect on the crystalline structure,while CO₃^2-and CH₃COO^-affect the crystal structure,and the oxides are in the?and?forms,respectively;Small molecular alcohols?such as ethanol and ethylene glycol?are added to the reaction solvent,so that the sample changes from Mn O₂to Mn OOH;The p H value is suitable for the synthesis of Mn O₂under acidic conditions and amorphous Mn O₂under alkaline conditions.?2?Under the same hydrothermal conditions,the effects of introduced different types of additives such as surfactants,salts,and small molecule organic compounds on the crystalline structure,grain size and morphological growth of oxides.Among surfactants,the order of effect on product size is:SDBS>CTAB>BS-12>TWEEN-20;in different salts,the order of effect on product size is:Na Cl>Na Br>NH₄Cl>KCl>CH₃COONa;In different small molecule organics,the order of effect on product size is:EDTA>urea>tartaric acid>oxalic acid>glucose>citric acid.?3?Used manganese dioxide with different crystalline structures of?,?,?and?as catalysts,in 240?,4 h and ethanol-water?65 vol.%ethanol?co-solvent,lignosulfonate depolymerization conversion rate can reach 82-85%,?-Mn O₂depolymerization rate 84.55%.The liquid product mainly contains phenols,esters,alcohols and other small molecule compounds,of which the selectivity of phenolic compounds is the highest,up to 77.78%.Through liquid phase product distribution studies,it is speculated that the main reaction pathways that may occur during hydrothermal depolymerization include dealkylation,decarboxylation,and demethoxy reactions.