| 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 β-O-4 bond is the most abundant in lignin structure,so the study of β-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 β-O-4 type lignin model dimmers,guaiacyl glycerol-β-uaiacol ether,was synthesized and characterized by NMR,and analyze the pyrolysis pathways of guaiacyl glycerol-β-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-β-guaiacyl ether.The depolymerization of guaiacyl glycerol-β-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-β-guaiacyl ether is the β-O-4 ether bond cleavage under subcritical conditions.The pyrolysis behavior of guaiacyl glycerol-β-guaiacyl ether was investigated with the Py-GC/MS.The results showed that guaiacol was the major products of Cβ-O homolysis at low temperatures.Cβ-O homolysis and Cβ-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 Cβ-O homolysis and Cβ-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-β-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 Cβ-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-β-guaiacol ether by Pt/Cu/Al2O3. |
