草酸电还原反应机理的研究

以硫酸钠溶液作底液,用快速循环伏安和电势阶跃法研究了草酸在铅电极上的电还原机理,测定了草酸电还原第一步反应的动力学参数,并根据循环伏安图比较相同条件下草酸,乙醛酸和乙醇酸的还原峰峰电势,推断出草酸还原的中间产物.研究结果表明,草酸电还原遵从不可逆2电子EE反应机理.     

Two-stage dilute-acid pretreatment of softwoods

Whole treechips obtained from softwood forest thinnings were pretreated via single-and two-stage dilute-sulfuric acid pretreatment. Whole-tree chips were impregnated with dilute sulfuric acid and steam treated in a 4-L steam explosion reactor. In single-stage pretreatment, wood chips were treated using a wide range of severity. In two-stage pretreatment, the first stage was carried out at low severity tomaximize hemicellulose recovery. Solubilized sugars were recovered from the first-stage prehydrolysate by washing with water. In the second stage, water-insoluble solids from first-stage prehydrolysate were impregnated with dilute sulfuric acid, then steam treated at more severe conditions to hydrolyze a portion of the remaining cellulose to glucose and to improve the enzyme digestibility. The total sugar yields obtained after enzymatic hydrolysis of two-stage dilute acid-pretreated samples were compared with sugar yields from single-stage pretreatment. The overall sugar yield from two-stage dilute-acid pretreatment was approx 10% higher, and the net enzyme requirement was reduced by about 50%. Simultaneous saccharification and fermentation using an adapted Saccharomyces cerevisiae yeast strain further improved cellulose conversion yield and lowered the enzyme requirement.     

Mercerization and acid hydrolysis of bacterial cellulose

Structural changes in never- dried, disintegrated bacteria l cellulose by treatment with aqueous NaOH were examined by electron microscopy, X-ray diffractometry and acid hydrolysis behaviour and compared with those of cotton cellulose. The microfibril kept its fibrillar morphology after treatment with NaOH solutions of less than 9% (w/w), but changed into irregular aggregates when treated with NaOH above 12% (w/w), corresponding to the crystal conversion to cellulose II. The crystallinity of the resulting cellulose II was very low after a brief alkali treatment, but was increased significantly by elongated treatment (up to 10 days). In contrast, cotton cellulose was converted to cellulose II of fairly high crystallinity by alkali treatment of as little as 3 min duration, and the crystallinity did not change with longer treatments. The leveling-off degree of polymerization (LODP) of bacterial cellulose was decreased from 150 to 50 by 18% (w/w) NaOH treatment, while that of cotton linter decreased from 260 to 70. These characteristic differences between cotton linter cellulose and bacterial cellulose can be ascribed to a basic difference in microfibrillar organization in these materials: the microfibrils in cotton cellulose are in close contact with neighbouring microfibrils having opposite polarity, and in bacterial cellulose are isolated from each other and require chain folding to form the antiparallel cellulose II crystal     

High Yielding Acid-Catalysed Hydrolysis of Cellulosic Polysaccharides and Native Biomass into Low Molecular Weight Sugars in Mixed Ionic Liquid Systems

Ionic media comprising 1-butyl-3-methylimidazolium chloride and the acidic deep eutectic solvent choline chloride/oxalic acid as co-solvent-catalyst, very efficiently convert various cellulosic substrates, including native cellulosic biomass, into water-soluble carbohydrates. The optimum reaction systems yield a narrow range of low molecular weight carbohydrates directly from cellulose, lignocellulose, or algal saccharides, in high yields and selectivities up to 98 %. Cellulose possesses significant potential as a renewable platform from which to generate large volumes of green replacements to many petrochemical products. Within this goal, the production of low molecular weight saccharides from cellulosic substances is the key to success. Native cellulose and lignocellulosic feedstocks are less accessible for such transformations and depolymerisation of polysaccharides remains a primary challenge to be overcome. In this study, we identify the catalytic activity associated with selected deep eutectic solvents that favours the hydrolysis of polysaccharides and develop reaction conditions to improve the outcomes of desirable low molecular weight sugars. We successfully apply the chemistry to raw bulk, non-pretreated cellulosic substances.     

Nanofibrillation of dried pulp in NaOH solutions using bead milling

The drying process in typical pulp production generates strong hydrogen bonding between cellulose microfibrils in refined cell walls and increases the difficulty in obtaining uniform cellulose nanofibers. To investigate the efficacy of alkaline treatment for cellulose nanofibrillation, this study applied a bead-milling method in NaOH solutions for the nanofibrillation of dried pulps. NaOH treatments loosened the hydrogen bonding between cellulose microfibrils in dried pulps and allowed preparation of cellulose nanofibers in 8 % NaOH with a width of approximately 12–20 nm and a cellulose I crystal form. Both the nanofiber suspensions prepared in 8 and 16 % (w/w) NaOH were formed into hydrogels by neutralization because of surface entanglement and/or interdigitation between the nanofibers. When the dried pulp was fibrillated in 16 % (w/w) NaOH, the sample after neutralization had a uniquely integrated continuous network. These results can be applied to the preparation of high-strength films and fibers with cellulose I crystal forms without prior dissolution of pulps.     

Optimization of oxalic acid pretreatment of moso bamboo for textile fiber using response surface methodology

In this article, samples of moso bamboo were pretreated with oxalic acid under various process conditions. Response surface methodology was applied to optimize the pretreatment conditions. A three-variable quadratic polynomial regression model was obtained to predict the cellulose content, lignin removal and hemicellulose solubilization. The reliability of the model was also evaluated by the key elements obtained from analysis of variance of the coefficients. The surface response plot and contour plot of the effects were studied to further examine the interactions of the three factors and determine the optimum levels of each factor. Finally, the optimized conditions for oxalic acid pretreatment were temperature 178.4 °C, 3.68 % oxalic acid and 28.4 min, respectively. The maximum predicted value of cellulose content in the residue fraction was 64.98 %, along with 79.43 % lignin removal and 96.71 % hemicellulose solubilization after the oxalic acid pretreatment.     

Furfural and 5-Hydroxymethylfurfural Production from Sugar Mixture Using Deep Eutectic Solvent/MIBK System

Choline chloride (ChCl) / glycolic acid (GA) deep eutectic solvent (DES) media with high water content but without any additional catalyst are introduced in furfural and 5-hydroxymethylfurfural (HMF) production. The effects of water content, reaction time, and reaction temperature are investigated with two feedstocks: a glucose/xylose mixture and birch sawdust. Based on the results, 10 equivalent quantities of water (32.9 wt.%) were revealed to be beneficial for conversions without rupturing the DES structure. The optimal reaction conditions were 160 °C and 10 minutes for the sugar mixture and 170 °C and 10 minutes for birch sawdust in a microwave reactor. High furfural yields were achieved, namely 62 % from the sugar mixture and 37.5 % from birch sawdust. HMF yields were low, but since the characterization of the solid residue of sawdust, after DES treatment, was revealed to contain only cellulose (49 %) and lignin (52 %), the treatment could be potentially utilized in a biorefinery concept where the main products are obtained from the cellulose fraction. Extraction of products into the organic phase (methyl isobutyl ketone, MIBK) during the reaction enabled the recycling of the DES phase, and yields remained high for three runs of recycling.     

食醋中C_1－C_8脂肪酸及乳酸的气相色谱分析

食醋中Ｃ１－Ｃ８脂肪酸和乳酸与适当过量的四甲基氢氧化铵作用生成季胺盐，用二甲基甲酰胺将其溶解，在室温下与过量溴乙烷完全反应而生成相应的乙酯。生成的乙酯在１０％丁二酸乙二醇聚酯（ＰＧＳ）柱上进行分离。用保留时间定性，用内标法定量。本法操作简便、快速，分离完全，对几种样品的测定结果较好     

The effect of glycolic acid monomer ratio on the emulsifying activity of PLGA in preparation of protein-loaded SLN

Our previous work demonstrated that lactic/glycolic acid copolymer (PLGA) was an efficient emulsifier for the primary w/o emulsion in the formulation of protein-loaded solid lipid nanoparticles (SLN) by w/o/w double emulsion-solvent evaporation technique. In this work, the effect of PLGA composition on the emulsifying activity was studied with PLGA of different lactic/glycolic acid ratios (90/10, 75/25, 50/50). The results demonstrated that the glycolic acid monomer ratio significantly affected the emulsifying activity of PLGA. Increasing the glycolic acid monomer ratio from 10% to 50% decreased the minimum PLGA content needed to produce stable w/o emulsions. With same PLGA contents, increase of the glycolic acid monomer ratio increased the stable time of the w/o emulsion, yielded smaller and narrower-distributed SLN, and enhanced the encapsulation efficiency and loading capacity.     

Determination of ionic metabolites from ethylene glycol in human blood by isotachophoresis

Conditions for isotachophoretic determination of anionic metabolites in blood from ethylene glycol in poisoned humans were established. Leading electrolytes with 5 mM chloride and and 2.5 gave good separation. Optimal separation was found with leading electrolytes at pH 2.5, and 10 mM acetic acid as terminating electrolyte. Separation and quantification of four out of six metabolites were possible. The four were glycolic acid, glyoxylic acid, oxalic acid and formic acid. Besides these compounds, citric acid, lactic acid, and alpha- and beta-hydroxybutyric acid were separated and quantified. The formation of mixed zones did not give any serious problems, although in samples with high amounts of glycolic acid we had to reduce the maximum injected amount from 3 to 1 microliter. This method might be valuable in further studies of the mechanism of ethylene glycol toxicity and as an important supplement in the diagnosis of late stages of ethylene glycol poisoning in which the glycol has been metabolized to glycolic acid.     

Glycine/Glycolic acid based copolymers

Glycine/glycolic acid based biodegradable copolymers have been prepared by ring-opening homopolymerization of morpholine-2,5-dione, and ring-opening copolymerization of morpholine-2,5-dione and glycolide. The homopolymerization of morpholine-2,5-dione was carried out in the melt at 200°C for 3 min using stannous octoate as an initiator, and continued at lower reaction temperatures (100–160°C) for 2–48 h. The highest yields (60%) and intrinsic viscosities ([η] = 0.50 dL/g; DMSO, 25°C) were obtained after 3 min reaction at 200°C and 17 h at 130°C using a molar ratio of monomer and initiator of 1000. The polymer prepared by homopolymerization of morpholine-2,5-dione was composed of alternating glycine and glycolic acid residues, and had a glass transition temperature of 67°C and a melting temperature of 199°C. Random copolymers of glycine and glycolic acid were synthesized by copolymerization of morpholine-2,5-dione and glycolide in the melt at 200°C, followed by 17 h reaction at 130°C using stannous octoate as an initiator. The morphology of the copolymers varied from semi-crystalline to amorphous, depending on the mole fraction of glycolic acid residues incorporated. © 1994 John Wiley & Sons, Inc.     

逐级提取-高效液相色谱法快速测定植物组织中8种有机酸

针对植物组织中草酸存在的不同形态,建立了水和稀盐酸作为提取介质的逐级提取方法,获得了水溶态和酸溶态草酸及乙醇酸、乙醛酸、酒石酸、苹果酸、乙酸、柠檬酸、琥珀酸等有机酸。采用Hypersil ODS (200 mm×4.6 mm, 5 μm)色谱柱,以5 mmol/L磷酸二氢钾水溶液(pH 2.8)作为流动相,在进样量5 μL、检测波长210 nm、柱温30 ℃的条件下,通过分时段控制流速实现了8种有机酸的快速分离,同时去除了盐酸对酸溶态草酸测定的干扰。本方法精确灵敏、回收率高、重复性好,可应用于实际样品的测定分析。     

A new method of ion chromatography technology for speedy determination and analysis in organic electrosynthesis of glyoxylic acid

Based on ion chromatography (IC) technology, we have developed a new method that combines ion chromatography with a conductivity detector to separate and determine the substances of glyoxal, glycolic acid, oxalic acid and glyoxylic acid. The ion chromatography was applied for the first time in quantitative determination of substances involved in electrosynthesis of glyoxylic acid. The method has been applied to separate and analyze simultaneously either glyoxylic acid and glyoxal in electroxidation of glyoxal, or glyoxylic acid and oxalic acid in electroreduction of oxalic acid. An aqueous Na2CO3-NaHCO3 or NaOH-Na2CO3 solution was confirmed to be the most desirable eluent. The experimental results demonstrated that the detection sensitivity is ahead of ppm grade, and the variation coefficients such as the retention time, the peak height and the peak area outperform 2%. All the recoveries of the detected substances are ranged between 97 and 103%. The method exhibits advantages of high selectivity, high sensitivity, speediness and simple apparatus requirement. Furthermore, simultaneous determination of a mixture of several substances can be achieved by the developed method, and even a neutral molecule of glyoxal can be also determined by choosing an appropriate composition and concentration of eluent.     

Effect of alkaline ultrasonic pretreatment on crystalline morphology and enzymatic hydrolysis of cellulose

In this study, ultrasound-assisted alkaline pretreatment is developed to evaluate the morphological and structural changes that occur during pretreatment of cellulose, and its effect on glucose production via enzymatic hydrolysis. The pretreated samples were characterized using scanning electron microscopy, infrared spectroscopy, and X-ray diffraction to understand the change in surface morphology, crystallinity and the fraction of cellulose Iβ and cellulose II. The combined pretreatment led to a great disruption of cellulose particles along with the formation of large pores and partial fibrillation. The effects of ultrasound irradiation time (2, 4 h), NaOH concentration (1–10 wt%), initial particle size (20–180 μm) and initial degree of polymerization (DP) of cellulose on structural changes and glucose yields were evaluated. The alkaline ultrasonic pretreatment resulted in a significant decrease in particle size of cellulose, besides significantly reducing the treatment time and NaOH concentration required to achieve a low crystallinity of cellulose. More than 2.5 times improvement in glucose yield was observed with 10 wt% NaOH and 4 h of sonication, compared to untreated samples. The glucose yields increased with increase in initial particle size of cellulose, while DP had no effect on glucose yields. The glucose yields exhibited an increasing tendency with increase in cellulose II fraction as a result of combined pretreatment.     

富含纤维素类农作物秆与丙烯酸接枝共聚制备高倍率吸水树脂

用棉花秆、麦秆和玉米秆等富含纤维素类农作物秆与丙烯酸接枝共聚制备了高倍率的吸水树脂. 研究了不同水质(去离子水、自来水及雨水)对接枝产物吸水性能的影响. 采用棉花秆、麦秆、玉米秆与丙烯酸的接枝产物对去离子水的吸水倍率分别为930, 790和630 g/g, 对自来水的吸水倍率分别为670, 350和250 g/g, 用玉米秆/地瓜淀粉混合物制备的接枝产物对雨水的吸水倍率为540 g/g. 为棉花秆、 麦秆及玉米秆等富含纤维素的农作物秆的深加工与应用开辟了一条途径.     

草酸淀粉酯制备及其性能研究

本文以草酸和玉米淀粉为原料,通过改变原料的摩尔比反应制备了不同取代度(0.1到0.9)的草酸淀粉酯,采用滴定法测定产物的取代度,利用红外光谱和核磁共振表征产物(取代度为0.41)的化学结构,产物中含有羰基的结果表明成功制备了草酸淀粉酯.详细考察了草酸淀粉酯的物理化学性质,利用粘度测定、热重分析、广角X衍射(WXRD)以及湿度吸收等研究不同取代度的草酸淀粉酯的分子量、热稳定性,结晶形态以及吸水性能.结果说明,与玉米淀粉相比,草酸淀粉酯的吸水率随着取代度的提高而增加,其分子量、热稳定性以及结晶性能则呈下降趋势.     

Gold- and gold-palladium/poly(1-vinylpyrrolidin-2-one) nanoclusters as quasi-homogeneous catalyst for aerobic oxidation of glycerol

Glycerol was oxidized catalytically under aerobic conditions in the presence of monometallic nanoclusters of gold on poly(1-vinylpyrrolidin-2-one) (PVP) to give hydroxymalonic acid (tartronic acid) as the major product, together with 2,3-dihydroxypropanoic acid (glyceric acid) and hydroxyacetic acid (glycolic acid) as minor products. In contrast, oxalic acid was selectively obtained when bimetallic Au-Pd:PVP nanoclusters were used as the catalyst.     

[2+2] Photodimerization of Stilbazoles Promoted by Oxalic Acid in Suspension

In this study, a very simple technique to perform efficiently photodimerization of some vinylpyridines is reported. By irradiating a stirred mixture of several stilbazoles with solid oxalic acid dihydrate dispersed in a nonpolar (i.e., cyclohexane) or moderately polar (benzene, dichloromethane, dioxane) solvent, the corresponding dimeric cyclobutane adducts were obtained in high yields and excellent regio- and stereoselectivities. The strategy could also be applied successfully to oily, waxy, or even insoluble stilbazoles. Moreover, the oxalic acid loading could be lowered to substoichiometric amounts. When further optimizations were needed, our strategy was found to be highly flexible to identify other oligocarboxylic acids as alternative additives to improve, or even overturn, the regioselectivity. Oxalic acid and other oligocarboxylic acids were found to be capable of orienting more than 50 stilbazoles toward photodimerization under these conditions.     

Mercerization of primary wall cellulose and its implication for the conversion of cellulose I→cellulose II

The mercerization of homogenized primary wall cellulose extracted fromsugar beet pulp was investigated by transmission electron microscopy (TEM),X-ray diffraction together with ¹³C CP-MAS NMR, and FT-IR spectroscopy.For samples resulting from acid extraction, mercerization began at 9% NaOH, whereasfor samples purified by alkaline treatment, the mercerization started at 10%NaOH. The change in morphology when going from cellulose I to cellulose II wasspectacular, as all the microfibrillar cellulose morphology disappeared duringthe treatment. This change in morphology was very drastic as soon as the NaOHconcentrations were increased beyond 8 and 9% for the acid and alkalinepreparedsamples, respectively. On the other hand, the conversion was found to be moreprogressive in terms of increasing NaOH concentration when the transformationwas analyzed by X-ray diffraction or spectroscopy. Our observations of themercerization of isolated cellulose microfibrils are consistent with theconceptof cellulose microfibrils made of parallel chains in cellulose I and crystalsofcellulose II consisting of antiparallel chains.     

Using a fully recyclable dicarboxylic acid for producing dispersible and thermally stable cellulose nanomaterials from different cellulosic sources

We fabricated cellulose nanocrystals (CNCs) and cellulose nanofibrils (CNFs) from different cellulose materials (bleached eucalyptus pulp (BEP), spruce dissolving pulp (SDP) and cotton based qualitative filter paper (QFP) using concentrated oxalic acid hydrolysis and subsequent mechanical fibrillation (for CNFs). The process was green as acid can be easily recovered, and the prepared cellulose nanomaterials were carboxylated and thermally stable. In detail, the CNC yield from the different materials was similar. After hydrolysis, the DP of the cellulose materials decreased substantially, whereas the mechanical fibrillation of the cellulosic solid residues (CSRs) did not dramatically reduce the DP of cellulose. CNCs with different aspect ratios were produced from different starting materials by oxalic acid hydrolysis. The CNCs and CNFs obtained from BEP and QFP possessed more uniform dimensions than those from SDP. On the other hand, CNFs derived from SDP presented the best suspension stability. FTIR analyses verified esterification of cellulose by oxalic acid hydrolysis. The results from both XRD and Raman spectroscopy indicated that whereas XRD crystallinity of CNCs from BEP and QFP did not change significantly, there was some change in Raman crystallinity of these samples. Raman spectra of SDP CNCs indicated that the acid hydrolysis preferably removed cellulose I portion of the samples and therefore the CNCs became cellulose II enriched. TGA revealed that the CNCs obtained from QFP exhibited higher thermal stability compared to those from BEP and SDP, and all the CNCs possessed better thermal stability than that of CNCs from sulfuric acid hydrolysis. The excellent properties of prepared cellulose nanomaterials will be conducive to their application in different fields.