Physicochemical properties of bio-oil obtained from fast pyrolysis of rice husk were studied in the present work.Molecular distillation was used to separate the crude bio-oil into three fractions viz.light fraction,middle fraction and heavy fraction.Their chemical composition was analyzed by gas chromatograph and mass spectrometer（GC-MS）.The thermal behavior,including evaporation and decomposition,was investigated using thermogravimetric analyzer coupled with Fourier transform infrared spectrometer（TG-FTIR）.The product distribution was significantly affected by contents of cellulose,hemicellulose and lignin.The bio-oil yield was 46.36%（by mass） and the yield of gaseous products was 27%（by mass）.The chemicals in the bio-oil included acids,aldehydes,ketones,alcohols,phenols,sugars,etc.The light fraction was mainly composed of acids and compounds with lower boiling point temperature,the middle and heavy fractions were consisted of phenols and levoglucosan.The thermal stability of the bio-oil was determined by the interactions and intersolubility of compounds.It was found that the thermal stability of bio-oil was better than the light fraction,but worse than the middle and heavy fractions.
The structure of milled wood lignin（MWL）, isolated via the Bjrkman procedure, was studied by means of 1H NMR spectroscopy and Fourier transform infrared spectroscopy, and then its pyrolytic product distribution was investigated on a pyrolysis device. MWL obtained from Manchurian Ash（MA） contained more methoxyl and free phenolic hydroxyl groups per C9 unit than MWL from Mongolian Pine（MP） due to the existence of both guaiacyl and syringyl units, which have a major influence on the pyrolysis behavior of lignin. The results of pyrolysis show that MWL from MA generated a higher yield of bio-oil, mainly composed of phenols, guaiacols, syringols and catechols, and a less yield of char, in addition to the gaseous products CO, CO2, methane and methanol, compared with MWL from MP. Guaiacol and syringol were the typical products from G-lignin and S-lignin, probably attributed to the easier cleavage of the aryl-alkyl linkage in the side chain compared with the C―OCH3 bond in the benzene ring. The degradation of MWL from MP was dominated by the demethylation reaction and the cleavage of aliphatic ―CH2OH at the γ-position, followed by the cracking of the Cα―Cβ and C4―Cα bonds.
GUO Xiu-juan WANG Shu-rong WANG Kai-ge LUO Zhong-yang
