Preparation Of Mg-based Solid Base Oxides And Its Catalytic Depolymerization Performance Of Calcium Lignosulfonate For The Production Of Phenolic Compounds

A method named the production of phenolic compounds from depolymerizing calcium lignosulfonate（CLS）under the catalytic action of solid base in the hydrothermal system was proposed,which opened up a new way to realize the resource and high value utilization of CLS.In this paper,hydrotalcite-like precursors were used to optimize the synthesis process parameters by orthogonal experiments,and binary and ternary Mg-based solid base oxides were obtained after the calcination process,which were used to study the hydrothermal depolymerization of CLS.X-ray diffraction analysis,scanning electron microscope,N₂physical adsorption and desorption curve and temperature-programmed desorption of CO₂were used to characterize the crystal phase,morphology and alkalinity of the hydrotalcite precursor and solid alkali oxide,and finally the catalytic performance of their depolymerization of CLS was evaluated,besides,the solid residues,water residues and liquid phase products produced after the reaction were analyzed by infrared spectroscopy（FT-IR）and gas-mass spectrometry（GC-MS）.After that,the Mg-based solid base oxides were regenerated,and then the reaction paths of their depolymerization were inferred from the distribution patterns of a series of solid base oxides of NiMg Fe solid base metal oxides（NiMg FeO_x）on their liquid-phase products.The experimental results are as follows:（1）The process parameters for the preparation of precursors of binary Mg-based solid alkali oxides were determined by orthogonal experiments.The effect of MgAlsolid alkali oxide precursors（Mg Al-LDHs）preparation conditions was p H value>n（Mg）/n（Al）>crystallization temperature>crystallization time.The conditions were as follows:Mg Al-LDHs synthesized at p H=12,n（Mg）/n（Al）=3,crystallization temperature was 180℃,and crystallization time was 24 h were complete and belonged to the hexagonal crystal system,its sizes was 140-230 nm.The effect of the preparation conditions of Mg Fe solid alkali oxide precursors（Mg Fe-LDHs）was p H value>n（Mg）/n（Fe）>crystallization temperature>crystallization time,the crystalline precursors of Mg Fe-LDHs at p H=10,n（Mg）/n（Fe）=3,crystallization temperature 180℃,crystallization time 24 h were complete and also belonged to the hexagonal crystal system with sizes of 190-370 nm.The effect of preparation conditions of Mg Co solid alkali oxide precursors（Mg Co-LDHs）was p H value>crystallization temperature>n（Mg）/n（Co）>crystallization time,the process parameters of Mg Co-LDHs were p H=10,crystallization temperature 180℃,crystallization time 24 h,n（Mg）/n（Co）=3,Mg Co-LDHs was regular in shape,with circular lamellar structure and 500-600 nm in size.（2）MgAl solid base oxide（MgAlO_x）,Mg Fe solid base oxide（Mg FeO_x）and Mg Co solid base oxide（Mg CoO_x）were used for the depolymerization of CLS under the conditions of m（catalyst）:m（CLS）=1:2,ethanol-water solvent mixture（ethanol content of 65vol.%）,depolymerization temperature of 270℃,and depolymerization time of 4 h.Compared with no catalyst added,and the yields of phenolic compounds were increased by 4.27%,16.14%,and3.82%,respectively,which indicating that the addition of Mg-based solid base oxide to the system was beneficial to CLS depolymerization,besides,the water phase residue decreased from 39.91%to 9.24%when MgAlO_x was added.（3）Fixing the n(M²⁺)/n(M³⁺)molar ratio unchanged,doping Ni into M²⁺to prepare composite ternary Mg-based solid base oxides,the NiMg Co composite solid base oxide（25%-NiMg CoO_x）with 25%Ni content was determined as a reference,and subsequently the NiMgAlcomposite solid base oxide（NiMgAlO_x）,NiMg Fe composite solid base oxide（NiMg FeO_x）and NiMg CoO_x were used for the depolymerization of CLS,and the yield of phenolic compounds was increased,esceptically with the highest yield of 59.59%for phenolic compounds catalyzed by NiMg FeO_x,it is possible that the metal active center synergizes with the basic center led to an increase in yield.（4）The 25%-NiMg CoO_x was calcined at 600℃ for 6 h for cyclic regeneration experiments.XRD and XPS showed that the crystalline phase structure and valence state of Mg-solid base oxide remained unchanged,and the catalytic activity was still maintained,indicating the good stability of the Mg-based solid base oxide.（5）MgO,NiO,Fe₂O₃,Mg FeO_x,Ni FeO_x and NiMg FeO_x samples were prepared by hydrothermal synthesis and analyzed for crystalline phase and structural characterization,and their catalytic depolymerization properties of CLS were evaluated in the hydrothermal reaction system.In the catalytic depolymerization of CLS by NiMg FeO_x,compared with binary Mg FeO_x and Ni FeO_x,the yields of phenolic compounds were all increased to 59.59%,while the alkalinity of MgO and NiO were different,indicating that there was a synergistic catalytic effect between the metal active center and the solid base center,the reaction path may be that the metal active center and the basic center in the solid base oxide attack the phenolic hydroxyl group in CLS,and the electron transfer occurred after the phenol anion become the phenol anion,which led to unstable chemical bonds and broken,thereby forming phenolic compounds.