Synthesis And Characterization Of Lignin ?-O-4 Dimer Model Compound And Its Application Inmechanism Study Of Alkali Lignin Catalytic Conversion

As a highly abundant natural polymer,the biosynthesis of lignin and its chemical mechanical properties,have attracted significant attention for decades.In the study of the structure of lignin,lignin model compounds may be used as a reference,and plays an important role?Meanwhile the ?-O-4 bond is the most abundant in lignin structure,so the study of ?-O-4 type lignin model compound plays a significant role in the study the structure of lignin and the reaction mechanism in a certain reaction.In this study a ?-O-4 type lignin model dimmers,guaiacyl glycerol-?-uaiacol ether,was synthesized and characterized by NMR,and analyze the pyrolysis pathways of guaiacyl glycerol-?-guaiacyl ether was analyzed by Py-GC/MS.The mechanism of the catalytic conversion of alkali lignin was investigated through the catalytic conversion of guaiacyl glycerol-?-guaiacyl ether.The depolymerization of guaiacyl glycerol-?-guaiacyl ether was studied under subcritical conditions and the results shows that the yield of guaiacol increased when the temperature is below 220? and get to the top up to 21.75 mg at 220?.However the yield of guaiacol began to decline when the temperature got higher,as the methoxy of guaiacol fracture into catechol.It indicates that the main reaction of guaiacyl glycerol-?-guaiacyl ether is the ?-O-4 ether bond cleavage under subcritical conditions.The pyrolysis behavior of guaiacyl glycerol-?-guaiacyl ether was investigated with the Py-GC/MS.The results showed that guaiacol was the major products of C?-O homolysis at low temperatures.C?-O homolysis and C?-O concerted decomposition occurred at moderate temperatures,producing 2-hydroxybenzaldehyde,2-methoxybenzaldehyde,guaiacol,and phenolic compounds.At high temperatures,the products were obtained from secondary thermal cracking of the C?-O homolysis and C?-O concerted decomposition products,which generated a large number of small molecule products that increased the complexity of the pyrolytic products.The results of Pt/Cu/Al2O3 catalytic guaiacyl glycerol-?-guaiacol ether conversion experiments shows that the main product is guaiacol and just a little other products were produced which indicate that the main reaction is the C?-O cleavage in the Pt/Cu/Al2O3 catalytic conversion experiments.The reaction conditions especially the reaction temperature and time has a significant impact on the lignin conversion and the yield of the products in the process of Pt/Cu/Al2O3 catalytic conversion of alkali lignin.The conversion rate is the highest at 240? and reaction time 2 h.meanwhile the main product of phenol reach the highest yield,phenol(6.72 mg/g),guaiacol(15.72 mg/g),3-methoxy catechol(10.11 mg/g)and 2,6-dimethoxy phenol(17.09 mg/g)respectively.While the yield of phenol get to highest up to 7.26 mg/g at 260?,residence time of 2 h.It can reduce the alkali lignin transition temperature under the Pt/Cu/Al2O3 bimetallic catalyst exist which realize the lignin degrades at lower temperatures converted to phenolic compounds.The main catalytic conversion products of alkali Lignin by Pt/Cu/Al2O3 were guaiacol and 2,6-dimethoxy phenol which has the mechanism with the catalytic conversion of guaiacyl glycerol-?-guaiacol ether by Pt/Cu/Al2O3.