Structural Changes of Wheat Straw Lignin during Formic Acid Treatment

The aromatic nature of lignin makes it a potential renewable source of chemicals and other valuable products.Isolation of lignin from lignocellulosic biomass using organic solvents enables the production of high-purity lignin.The use of formic acid in the organosolv pulping and fractionation process has been widely studied.Characterization of lignin is necessary to achieve valueadded applications of lignin.To simplify the isolation of formic acid-treated lignin,herein,milled wheat straw lignin(MWSL) was employed as an archetype for characterization of the structural changes of lignin during formic acid treatment.The results showed that the MWSL was GSH-type(comprising p-hydroxyphenyl(H),guaiacyl(G),and syringyl(S) monolignols) and underwent structural changes during formic acid treatment.Lignin was esterified during the formic acid treatment.The content of alkyl hydroxyl groups in lignin decreased upon formic acid treatment,corresponding to an increase of the number of double bond equivalents(DBE).Lignin units with active reaction sites were liable to slight condensation,which resulted in a moderate increase of the molecular weight.The molecular weight distribution of formic acid-treated MWSL(FMWSL) was wider than that of the MWSL,although the molecular weight of both species did not differ significantly.The β-O-4 linkage in lignin was partially cleaved during formic acid treatment,resulting in the production of new phenolic structures.This improved the solubility of lignin in the cooking liquor and its reactivity for downstream applications.

TG-FTIR Study on the Pyrolysis Properties of Lignin from Different Kinds of Woody Biomass

Pyrolysis properties of lignin separated from four different kinds of wood(fir, larch, poplar, and eucalyptus) compared with commercial lignin were investigated using a thermogravimetric analyzer coupled to a Fouriertransform infrared spectrometer(TG-FTIR). Kinetic parameters of lignin thermal cracking reaction, such as activation energy and pre-exponential factor, were calculated using a three-dimensional diffusion model. The carbon residue rate and activation energy of softwood lignin were higher than those of hardwood lignin, showing that the decomposition of the former is relatively more difficult than that of the latter during pyrolysis. The distinct characteristic peaks of small-molecule gases and oxygenated chemicals such as ethers, phenols, acids, aldehydes, and alcohols were observed near the maximum weight loss rate by analyzing the 3D IR spectrum of the gas phase products. The formation routes of the main gaseous products were discussed, and the following order of releasing amounts was noted: CO_2>CH_4>H_2O>CO. It is believed that these results will provide valuable information for the thermo-chemical conversion process of lignin from the point of view of feedstock.

Preparation of Aminated Lignin through Etherification and Amination

A new method for the preparation of aminated lignin(AEL) through etherification and amination reaction was presented. Chlorine atoms were firstly introduced into lignin through its etherification with epichlorohydrin. Then, hydrophilic amine groups were grafted to the modified lignin structure through amination with ethylenediamine to obtain AEL. Subsequent acidification of AEL led to the ionized aminated lignin(IAEL). The results of our analyses showed that the nitrogen content of AEL was 6.9%. Foaming and emulsifying experiments indicated that AEL had better foamability and emulsifying properties than IAEL. Surface tension tests showed that AEL and IAEL had similar critical micelle concentration(CMC). However, IAEL had lower surface tension(36.33 mN/m) than AEL(42.89 mN/m) at CMC. These results demonstrate the promising applicability of AEL as an emulsifier and that of IAEL as feedstock in the production of detergent and dispersant.

Synthesis of Humin-based Carbon Quantum Dots and Luminescent Properties

The unique properties of carbon quantum dots(CQDs) make them promising materials in many fields. Herein, we present a facile method for the preparation of photo-luminescent CQDs using humins as the carbon precursor for the purpose of providing a high value-added solution for this "biomass conversion process waste". The structure of the CQDs was analyzed, and the effects of reaction temperature and time on the CQDs' fluorescence were investigated. The results showed that humins were effectively carbonized during the reaction. The fluorescence intensity of humin-based CQDs initially increased with reaction temperature and time, and subsequently decreased beyond 200℃ and 4 h. Polyaromatic structures and hydrophilic groups such as O—H, C—O, —COOH and C==O groups exist in the CQDs. The huminbased CQDs have the dimension of 3～7 nm with an average size of about 5.5 nm. The highest emission intensity of blue/cyan fluorescence light at 440 nm is achieved on the excitation with UV light at the wavelength of 330 nm.

刺槐对黄土高原林下草本植物及土壤性质的影响

外来物种刺槐(Robinia pseudoacacia)的引入会对林下草本植物、土壤性质及二者之间的相互关系产生一定影响,且这种影响可能与植被带有关。然而,在黄土高原较大面积范围内,关于刺槐对林下草本植物和土壤影响的研究依然很少。我们以黄土高原草原带、森林草原带和森林带作为研究区,选择了两种冠层植物类型:刺槐林分和相邻的原生植被。我们测定了5个叶片功能性状:叶片碳含量、叶片氮含量、叶片磷含量、比叶面积和叶组织密度,并计算了群落功能多样性、物种多样性和群落加权性状值。研究结果表明,(1)与原生植被相比,3个植被带内林下草本植物群落的叶氮、叶磷和比叶面积的群落加权性状值均显著提高,而叶碳和叶组织密度的群落加权性状值显著降低。(2)物种多样性、功能多样性和群落生物量在草原带内呈下降趋势,在森林带内呈上升趋势,在森林草原带内差异不显著。(3)与原生植被相比,土壤有机碳和土壤全氮仅在森林带内显著减少。(4)林下草本植物群落特性与土壤之间的关系是受刺槐和植被带所依赖的。总的来说,刺槐对林下草本植物和土壤性质的影响与植被带密切相关。该研究结果对黄土高原人工植被恢复与重建的规划具有重要指导意义。