Hydrothermal Conversion Of Lignin For Phenolic Compounds

Presently, fossil fuels such as coal, oil and gas is more and more shortage, seeking a renewable, cheap, abundant reserves and alternative resources receive widespread attention. In order to solve this problem, alkali lignin were obtained from black liquor of pulping and papermaking process by acid precipitation. The structure of lignin was identified and finally takes it into high value-added chemicals (phenol chemicals) using hydrothermal conversion technology (subcritical and supercritical conditions).The results shown that the conversion yields and the content of phenolic compounds were strongly associated with the conversion temperature and the ethanol volume-%, whereas residence time in the autoclave only had a slight influence. It was determined that from the optimal hydrothermal conditions (30 min,310℃,25% ethanol), the major constituent was quantitative with the following individual chemicals and associated yields (mg liquid side-stream/g lignin):phenol (4.25 mg/g), 4-methylguaiacol (2.93 mg/g),3,5-dimethoxyacetophenone (0.78 mg/g),1,2, 4-trimethoxybenzene (2.47 mg/g), and 2,6-dihydroxy-4-methoxyacetophenone (2.47 mg/g). The highest yield of guaiacol (11.87 mg/g) and 2,6-dimethoxyphenol (12.17 mg/g) were obtained at a reaction temperature of 310℃ over 60 min in pure water.In order to compare the potential of alkali lignin (AL) conversion in the under supercritical conditions, the experiment introduced the corn cob hydrolysis of residual lignin (XRL) and corn stalk residue of hydrolysis lignin (ERL) conversion performance. Lignin was first isolated and characterized by elemental analysis, Fourier infrared spectrum quantitative phosphorus spectrum (FT-IR), nuclear magnetic resonance (31P-NMR). The analysis results show that the AL has the lowest conversion performance because of the cooking and separation process. Results indicated three phenylpropanoid monomers from lignin greatly decided on its hydrothermal conversion products. The proportions of phenolic compounds from AL were had a high proportion of guaiacyl (G) and syringyl (S), a low proportion of hydroxyphenyl (H). XRL was a promising candidate for H-type products (such as phenol,4-ethylphenol), while more S-type products (such as 2,6-dimethoxyphenol) can be obtained from AL with a higher content of S phenolic units. Under the reaction temperature of 375℃, and the residence time has more significant effect on the conversion yield and the products yield. The highest amount of total phenolic compounds was measured to be from XRL at 375℃ after 30 min. On the transformation performance, the activity of AL is lowest; the total phenol content (< 9%mass ratio of the original lignin) is less than the XRL and ERL their can produce up to 14%. Under the optimal condition of AL, the highest yield of guaiacol and 2,6-dimethoxyphenol can reach 14.34 and 15.67 mg/g. Among the products of XRL, the highest yield of phenol and 4-ethylphenol can obtain 28.94 mg/g and 36.21 mg/g.