342 / 2018-07-31 11:00:56

Analysis and Comparison of Pyrolytic Lignin from Crude Bio-Oils and Products from Pyrolysis of Model Compounds

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In this work,fast pyrolysis bio-oil derived from three kinds of lignocellulosic biomass (Rice Straw; Cotton Stem; Walnut Shell) were used to obtain three PL samples (simplified as RS-PL, CS-PL, WS-PL) as fine homogeneous powder by precipitation method. Besides, aromatic monomers (guaiacol, eugenol, vanillin) and acetic acid were mixed together as model compounds of bio-oil vapour for fast pyrolysis at 550℃ to simulate the actual pyrolysis condition so that the formation of pyrolytic lignin can be studied. The products were collected as model compounds’ pyrolysis sample (M-PL). Then three types of techniques were performed to analyse and compare all samples. Similar spectra or chromatograms of three PL samples indicated a lot of compounds in pyrolytic lignin were the same. With HPLC/QTOF-MS test, molecular formula and possible structure of the common components of the three PL samples were confirmed. Comparing with M-PL, we found the compounds with molecular weight lower than 250 matched well according to extra ion chromatogram (XIC). Since the GPC results showed that three PL samples had two obvious peaks with the bigger one at about Mp=450 and the smaller one at about Mp=190, and M-PL had only one peak at almost the same place with the smaller ones, we inferred that low-molecular part (mainly aromatic monomers and dimers) of pyrolytic lignin may mainly come from recombination of aromatic monomers and higher-molecular part of it were primarily lignin fragments derivations. In addition, HSQC spectra demonstrated that aromatic regions from three PL samples and M-PL were quite similar and the C-O or C-C regions were overlapped in some degree. As more correlation signals appeared in three PL samples, it was clear that pyrolytic lignin had more complicated linkage among aromatic rings which probably derived from lignin fragments directly, such as ester bond, and aromatic monomers’ recombination reaction only form simple linkage like ether bond, Caromatics-Caromatics bond and so on.