Ni基催化剂上木质素模型化合物苯基苯乙醚C-O键的加氢裂解

研究了Ni基催化剂上木质素模型化合物苯基苯乙醚中C-O-C键加氢裂解性能.结果表明,Ni/C催化剂显示出优异的加氢裂解能力,苯基苯乙醚的转化率达到99%以上.Ni/C催化剂的还原方法对裂解选择性有重要影响;氢气还原制备的Ni/C-H催化剂上,C-O-C键裂解选择性为85%.Ru/C和Pd/C催化剂上裂解选择性分别为40%和69%.采用碳热还原方法制备的Ni/C-C催化剂,可以实现高选择性加氢和裂解,C-O-C键裂解选择性达到99%以上,其中芳烃化合物收率为44%.这可能与镍组分和载体碳之间的相互作用有关.     

Thermal degradation behaviour of isotactic polypropylene blended with lignin

The influence of lignin on the thermal degradation of isotactic polypropylene, investigated by thermogravimetric analysis, is reported in this article. Polypropylene blends containing 5 and 15 wt% of lignin were prepared by mixing the components in a screw mixer. An increase in the thermal degradation temperature of the blends was observed as a function of lignin content, in both oxidative and non-oxidative conditions. The increase is noticeably marked for the experiments carried out in air atmosphere, where the interactions between the polypropylene and the lignin lead to the formation of a protective surface able to reduce the oxygen diffusion towards the polymer bulk. Morphological analyses were carried out with optical and electronic microscopy, to evaluate the degree of dispersion of the lignin in the polypropylene matrix. X-ray techniques were employed to study the influence of lignin on the structure of the blended polypropylene.     

球型木质素碳化树脂的制备及性能研究

利用酸法制浆的木质素磺酸盐废液合成的球形木质素阳离子交换树脂，直接制备水质素碳化树脂；考察了碳化条件，运用电子显微镜、热重分析、Ｘ射线衍射等仪器对木质素碳化树脂的结构、碳化失重、孔结构、比表面和吸附量等性能进行了研究。研究结果表明：氯化锌法制备球状木质素碳化树脂的最优工艺条件为，碳化时间０．５ｈ、碳化温度４００℃、活化时间１ｈ、活化温度５００℃。碳化树脂的比表面为 ３８２．３ｍ２／ｇ，亚甲基兰吸附量为 １３２．６ｍｇ／ｇ。球形木质素碳化树脂具有丰富的孔结构，物理化学性能良好。     

1064 nm dispersive multichannel Raman spectroscopy for the analysis of plant lignin

The mixed phenylpropanoid polymer lignin is one of the most abundant biopolymers on the planet and is used in the paper, pulp and biorenewable industries. For many downstream applications, the lignin monomeric composition is required, but traditional methods for performing this analysis do not necessarily represent the lignin composition as it existed in the plant. Herein, it is shown that Raman spectroscopy can be used to measure the lignin monomer composition. The use of 1064 nm excitation is needed for lignin analyses since high fluorescence backgrounds are measured at wavelengths as long as 785 nm. The instrument used for these measurements is a 1064 nm dispersive multichannel Raman spectrometer that is suitable for applications outside of the laboratory, for example in-field or in-line analyses and using remote sensing fiber optics. This spectrometer has the capability of acquiring toluene/acetonitrile spectra with 800 cm⁻¹ spectral coverage, 6.5 cm⁻¹ spectral resolution and 54 S/N ratio in 10 s using 280 mW incident laser powers. The 1135–1350 cm⁻¹ and 1560–1650 cm⁻¹ regions of the lignin spectrum can be used to distinguish among the three primary model lignin monomers: coumaric, ferulic and sinapic acids. Mixtures of the three model monomers and first derivative spectra or partial least squares analysis of the phenyl ring breathing modes around 1600 cm⁻¹ are used to determine sugarcane lignin monomer composition. Lignin extracted from sugarcane is shown to have a predominant dimethoxylated and monomethoxylated phenylpropanoid content with a lesser amount of non-methoxylated phenol, which is consistent with sugarcane's classification as a non-woody angiosperm. The location of the phenyl ring breathing mode peaks do not shift in ethanol, methanol, isopropanol, 1,4 dioxane or acetone.     

Blind image analysis for the compositional and structural characterization of plant cell walls

A new image analysis strategy is introduced to determine the composition and the structural characteristics of plant cell walls by combining Raman microspectroscopy and unsupervised data mining methods. The proposed method consists of three main steps: spectral preprocessing, spatial clustering of the image and finally estimation of spectral profiles of pure components and their weights. Point spectra of Raman maps of cell walls were preprocessed to remove noise and fluorescence contributions and compressed with PCA. Processed spectra were then subjected to k-means clustering to identify spatial segregations in the images. Cell wall images were reconstructed with cluster identities and each cluster was represented by the average spectrum of all the pixels in the cluster. Pure components spectra were estimated by spectral entropy minimization criteria with simulated annealing optimization. Two pure spectral estimates that represent lignin and carbohydrates were recovered and their spatial distributions were calculated. Our approach partitioned the cell walls into many sublayers, based on their composition, thus enabling composition analysis at subcellular levels. It also overcame the well known problem that native lignin spectra in lignocellulosics have high spectral overlap with contributions from cellulose and hemicelluloses, thus opening up new avenues for microanalyses of monolignol composition of native lignin and carbohydrates without chemical or mechanical extraction of the cell wall materials.     

Structural changes in switchgrass lignin and hemicelluloses during pretreatments by NMR analysis

Switchgrass is currently being developed as a sustainable bio-energy crop due to its broad adaptability, high mass yield and low agricultural input. Its current conversion to biofuels is detrimentally impacted by its native recalcitrance which is typically addressed using chemical and/or biological pretreatments. In this study, extractives free switchgrass was pretreated with steam, dilute H₂SO₄ and lime at 160 °C for 1 h. The degradation and impact of pretreatment was estimated semi-quantitatively by ¹³C–¹H HSQC (heteronuclear single quantum coherence) NMR analysis of ball milled untreated and pretreated switchgrass samples in perdeuterated pyridinium chloride–DMSO-d₆ solvent system. As a result of steam pretreatment the resulting switchgrass was depleted of xylan and a slight degradation of lignin were observed. This was confirmed by the relative decrease of cross peak intensity for β-aryl ether, phenylcoumaran, resinol and dibenzodioxocin units. Significant structural changes observed due to the lime pretreatment of switchgrass was deacetylation/dissolution of hemicellulose and the extent of delignification was less however, a preferential removal p-hydroxy of benzoyl ester, ferulate and coumarate type linkages were notified from the HSQC studies. Finally the most significant degradation resulted in acid pretreatment involving ∼90% loss of hemicellulose and a substantial degradation of various lignin sub-units. These results are further supported by the composition analysis of the respective switchgrass samples.     

丹参木质素及其单体含量的测定

本文建立了一种准确、快速的检测丹参中木质素及其单体含量的方法.采用Klason法和紫外分光光度法分别对丹参根和茎中酸不溶性木质素(Klason木质素)和酸溶性木质素含量进行了测定;运用硫代酸解法并结合气相色谱-质谱法(GC-MS)分别对丹参根和茎中各木质素单体组成进行了分析.结果显示,总木质素在丹参根和茎中的含量分别为...     

Steric effects of bulky tethered arylpiperazines on the reactivity of Co-Schiff base oxidation catalysts—a synthetic and computational study

New C2-symmetric and C2-asymmetric Co-Schiff base catalysts tethered to arylpiperazine units were synthesized and used to oxidize phenolic lignin models to para-benzoquinones. Synthetic approaches to these catalysts were optimized to include fewer steps and broaden the types of catalyst structures available. In contrast to conventional Co-Schiff base catalysts, these systems induce phenolic oxidation in the absence of an external axial base, simplifying the process. Asymmetric catalysts bearing a phenylethylene or diphenylmethyl piperazine substituent display the highest catalytic activity observed to date for the conversion of S-models to 2,6-dimethoxybenzoquinone (DMBQ). Computational analysis shows that more reactive catalysts populate conformations that favor oxidation in preference to non-productive decomposition routes. This balance between catalyst reactivity and catalyst deactivation is optimized by inclusion of sufficient steric bulk around the periphery of the Schiff base ligand, reducing catalyst deactivation and allowing oxidations to proceed in the absence of an added axial ligand.     

一种测定纸制品中可迁移性荧光增白剂含量的双波长紫外光谱方法

在现行GB/T 27741—2011的“可迁移性荧光增白剂的定量测定—紫外分光光度法”对纸制品进行萃取时,其中的残余木素会部分析出,对可迁移性荧光增白剂含量的光谱检测造成了干扰。据此,提出了一种双波长(305和348 nm)光谱的改进方法,旨在消除析出木素的干扰。它是基于可迁移性荧光增白剂在348 nm波长处有最大吸收,并且析出木素和荧光增白剂分别在波长305和348 nm的吸光度比值确定,因此可通过双波长光谱法扣除析出木素在348 nm处对荧光增白剂吸光度检测的干扰,从而实现对可迁移性荧光增白剂的准确定量检测。结果表明：双波长光谱法可有效地减少析出木素对可迁移性荧光增白剂吸光度检测的干扰,使定量检测的结果更为可观。方法的重复性检测的相对标准偏差为2.17%;定量检测限为16.9 mg·kg-1;回收率在98%～104%之间。与现行可迁移性荧光增白剂的定量测定的平行标准—液相色谱法相比,由于本方法具有简便、仪器及操作维护费用低等优点,因此更适合生产过程的产品质量控制和市售点对纸制品中可迁移性荧光增白剂含量的快速分析。     

近红外光谱技术检测植物木质素纤维素研究进展

近红外光谱技术可用来检测植物木质素、纤维素及半纤维素含量,与传统的湿化学方法相比具有快速、操作简单、准确、无损等优点,是一种新型的测定方法,近年来在检测木本植物及草本植物木质纤维素组成成分中被广泛应用。综述了国内外利用近红外光谱技术快速检测木本植物(用作造纸原料的木材、竹材以及潜在的可用作生物质能源的木材)及草本植物(饲草及草类能源植物)木质素、纤维素、半纤维素含量的研究进展,并从样品前处理、光谱预处理及波长选取方法、化学计量学方法三个方面对利用近红外光谱技术快速检测植物木质素、纤维素方法研究上的进展进行了总结,并结合国内木材、牧草及能源草行业发展现状提出了四点展望: 建立适用性更强的模型;建立全面的草产品品质指标近红外光谱数据库;建立能源植物能用品质指标相关模型并对建模方法进行进一步的探索和完善;推动应用近红外光谱技术检测植物木质纤维素的方法从实验阶段走向实际应用。随着对近红外光谱检测植物木质纤维素方法的不断成熟和完善,它必将对造纸、饲草及能源草行业的发展产生巨大的推动作用。