Approximate solution of the autocatalytic hydrolysis of cellulose

Depolymerization of cellulose in homogeneous acidic medium is analyzed on the basis of autocatalytic model of hydrolysis with a positive feedback of acid production from the degraded biopolymer. The normalized number of scissions per cellulose chain, S(t)/n° = 1 − C(t)/C₀, follows a sigmoid behavior with reaction time t, and the cellulose concentration C(t) decreases exponentially with a linear and cubic time dependence, C(t) = C₀exp[−at − bt ³], where a and b are model parameters easier determined from data analysis.     

Hydrolysis of Cellobiose in Dilute Sulpuric Acid and Under Hydrothermal Conditions

The sulfuric acid hydrolysis rate of cellobiose between pH 2 and 3 is directly proportional to the acid concentration. In good agreement with other authors, an activation energy of 133 kJ/Mol was found under these acidic conditions. The relation of the reaction rate constants for the glucose formation and glucose degradation (k₁/k₂) shows, in contrast to the hydrolysis of cellulose, little dependence on the temperature. Hydroxymethylfurfural, and to a lesser extent furfural, are glucose degradation products, which are also consumed but at a lower reaction rate than glucose. At pH values between 3 and 4.7 (pure water) strong deviations of the hydrolysis rates were observed. The formation of organic acids decreases the pH but has no influence on the reaction rate. This fact indicates that hydrothermolysis follows a reaction mechanism different from that of acidic hydrolysis.     

Hydrolytic Methods for the Quantification of Fructose Equivalents in Herbaceous Biomass

A low, but significant, fraction of the carbohydrate portion of herbaceous biomass may be composed of fructose/fructosyl-containing components (“fructose equivalents”); such carbohydrates include sucrose, fructooligosaccharides, and fructans. Standard methods used for the quantification of structural-carbohydrate-derived neutral monosaccharide equivalents in biomass are not particularly well suited for the quantification of fructose equivalents due to the inherent instability of fructose in conditions commonly used for hemicellulose/cellulose hydrolysis (>80% degradation of fructose standards treated at 4% sulfuric acid, 121°C, 1 h). Alternative time, temperature, and acid concentration combinations for fructan hydrolysis were considered using model fructans (inulin, β-2,1, and levan, β-2,6) and a grass seed straw (tall fescue, Festuca arundinacea) as representative feedstocks. The instability of fructose, relative to glucose and xylose, at higher acid/temperature combinations is demonstrated, all rates of fructose degradation being acid and temperature dependent. Fructans are shown to be completely hydrolyzed at acid concentrations well below that used for the structural carbohydrates, as low as 0.2%, at 121°C for 1 h. Lower temperatures are also shown to be effective, with corresponding adjustments in acid concentration and time. Thus, fructans can be effectively hydrolyzed under conditions where fructose degradation is maintained below 10%. Hydrolysis of the β-2,1 fructans at temperatures ≥50°C, at all conditions consistent with complete hydrolysis, appears to generate difructose dianhydrides. These same compounds were not detected upon hydrolysis of levan, sucrose, or straw components. It is suggested that fructan hydrolysis conditions be chosen such that hydrolysis goes to completion; fructose degradation is minimized, and difructose dianhydride production is accounted for.     

On the kinetics of cellulose degradation: looking beyond the pseudo zero order rate equation

The kinetics of cellulose degradation was analysed by means of a two-stage model, characterised by an autoretardant and autocatalytic regime, later tempered by the consumption of glycosidic bonds in the amorphous regions. The proposed model explains the effects on the kinetic equations of different modes of ageing (acid hydrolysis, ageing in ventilated oven or sealed vessels), initial oxidation of cellulose and experimental procedures (with or without reduction of oxidised groups). The autoretardant branch can be analysed in a quantitative way, while the integration of the non-linear autocatalytic branch is allowed in some cases, characterised by the decrease of pH and/or emission of acid volatile organic compounds (VOCs). Most of the controversial results of the literature can be easily explained, but the proposed model offers also a guide for further studies on the kinetics of cellulose degradation.     

苯环5位取代磺酰脲类化合物的水解动力学及三维定量构效关系初步研究

研究了除草活性较好的9个新型苯环5位取代的磺酰脲类化合物(A~I)分别在酸性、中性及碱性水溶液中的水解情况.采用HPLC-MS对水解产物进行分离鉴定,推测了水解产物的结构及水解路径.采用比较分子力场(Co MFA)方法,对化合物的结构与水解半衰期之间的关系进行了三维定量构效关系(3D-QSAR)研究.结果表明,苯环5位取代的苯磺酰脲类化合物的水解遵循一级动力学反应,容易发生酸性条件下的水解,水解反应第一步主要为酸催化下磺酰脲桥的断裂,形成5位取代的苯磺酰胺和氨基杂环.苯环5位取代的苯磺酰胺进一步发生5位酰胺基的水解,最后得到化合物c(6-氨基糖精)和d(糖精).苯环5位经修饰改造后,在相同条件下,其水解速度明显高于改造前的母体化合物单嘧磺酯和甲磺隆.苯环5位为酰胺基取代的化合物的水解速度随酰胺基上烷基碳原子数的增加及烷基体积的增大而降低.经计算所得的Co MFA模型能够对该系列化合物的水解半衰期进行较好的预测.     

Isolation of a novel,crystalline cellulose material from the spent liquor of cellulose nanocrystals (CNCs)

We have modified the standard sulphuric acid hydrolysis method for the production of cellulose nanocrystals (CNCs) to successfully isolate a novel, highly crystalline cellulose material from the spent liquor of CNCs. The novel material has a cellulose II crystal structure that is distinctly different from the cellulose I crystal structure of CNCs. The modified method uses a shorter time for the hydrolysis, followed by maintaining a high residual acid concentration for the separation of the spent liquor and CNCs, and by adding the spent liquor to water. The modified method offers an opportunity to concurrently produce CNCs in up to ~40 % yield and the novel, highly crystalline, sulphated cellulose II in ~15 % yield in separate and pure forms from sulphuric acid hydrolysis of a commercial northern bleached softwood kraft pulp. It can potentially reduce the production cost of CNCs, allow easier downstream processing of CNCs and recovery of sulphuric acid, and generate a new cellulose bio-material for product development.     

Production of 2,3- butanediol from pretreated corn cob byKlebsiella oxytoca in the presence of fungal cellulase

A simple and effective method of treatment of lignocellulosic material was used for the preparation of corn cob for the production of 2,3-butanediol byKlebsiella oxytoca ATCC 8724 in a simultaneous saccharification and fermentation process. During the treatment, lignin, and alkaline extractives were solubilized and separated from cellulose and hemicellulose fractions by dilute ammonia (10%) steeping. Hemicellulose was then hydrolyzed by dilute hydrochloric acid (1%, wJv) hydrolysis at 100°C at atmospheric pressure and separated from cellulose fraction. The remaining solid, with 90% of cellulose, was then used as the substrate. A butanediol concentration of 25 g/L and an ethanol concentration of 7 g/L were produced byK. oxytoca from 80 g/L of corn cob cellulose with a cellulase dosage of 8.5 IFPU/g corn cob cellulose after 72 h of SSF. With only dilute acid hydrolysis, a butanediol production rate of 0.21 g/L/h was obtained that is much lower than the case in which corn cob was treated with ammonia steeping prior to acid hydrolysis. The butanediol production rate for the latter was 0.36 g/L/h.     

Use of Cellulase Inhibitors to Produce Cellobiose

The economics driving biorefinery development requires high value-added products such as cellobiose for financial feasibility. This research describes a simple technology for increasing cellobiose yields during lignocellulosic hydrolysis. The yield of cellobiose produced during cellulose hydrolysis was maximized by modification of reaction conditions. The addition of an inhibitor from the group that includes glucose oxidase, gluconolactone, and gluconic acid during cellulase hydrolysis of cellulose increased the amount of cellobiose produced. The optimal conditions for cellobiose production were determined for four factors; reaction time, cellulase concentration, cellulose concentration, and inhibitor concentration using a Box-Behnken experimental design. Gluconolactone in the cellulase system resulted in the greatest production of cellobiose (31.2%) from cellulose. The yield of cellobiose was 23.7% with glucose oxidase, similar to 21.9% with gluconic acid.     

N-methyl-2-pyrrolidonium-based Brönsted-Lewis acidic ionic liquids as catalysts for the hydrolysis of cellulose

We experimentally studied the catalytic performances of a series of Br?nsted-Lewis acidic N-methyl-2-pyrrolidonium metal chlorides([Hnmp]Cl/MCl_x, where M=Fe, Zn, Al, or Cu) for the hydrolysis of microcrystalline cellulose(MCC) and cotton to produce reducing sugar. A variety of factors, such as temperature, time, ionic liquid(IL) species, IL dosage, and the concentration of the metal chloride were investigated. [Hnmp]Cl/FeCl_3 presented the best hydrolysis performance, affording a 98.8% yield of total reducing sugar from MCC(1 h, 100 °C, 0.1 g MCC, 0.2 g acidic IL, 2.0 g [Bmim]Cl as solvent), which is better than or comparable to results previously obtained with other –SO_3H functionalized acidic ILs. The hydrolysis performances of [Hnmp]Cl/MClx were rationalized using density functional theory calculations, which indicated that interactions between the metal chlorides and the cellulose, including charge-transfer interactions are important in the hydrolysis of cellulose and degradation of glucose. This work shows that Br?nsted-Lewis acidic ILs are potential catalysts for the hydrolysis of cellulose to produce sugar.     

The Challenging Measurement of Protein in Complex Biomass-Derived Samples

Measurement of the protein content in samples from production of lignocellulosic bioethanol is an important tool when studying the adsorption of cellulases. Several methods have been used for this, and after reviewing the literature, we concluded that one of the most promising assays for simple and fast protein measurement on this type of samples was the ninhydrin assay. This method has also been used widely for this purpose, but with two different methods for protein hydrolysis prior to the assay—alkaline or acidic hydrolysis. In samples containing glucose or ethanol, there was significant interference from these compounds when using acid hydrolysis, which was not the case when using the alkaline hydrolysis. We evaluated the interference from glucose, cellulose, xylose, xylan, lignin and ethanol on protein determination of BSA, Accellerase® 1500 and Cellic® CTec2. The experiments demonstrated that the presence of cellulose, lignin and glucose (above 50 g/kg) could significantly affect the results of the assay. Comparison of analyses performed with the ninhydrin assay and with a CN analyser revealed that there was good agreement between these two analytical methods, but care has to be taken when applying the ninhydrin assay. If used correctly, the ninhydrin assay can be used as a fast method to evaluate the adsorption of cellulases to lignin.     

A study of anhydrocelluloses--is a cellulose structure with residues in a 1C4-conformation more prone to hydrolysis?

A study of the effect of introduction of 3,6-anhydroglucose residues in the cellulose structure on glycoside hydrolysis rate was performed. A cellotetrose with an 3,6-anhydroglucose as the third residue was synthesised. Acidic hydrolysis of this tetrasaccharide showed that hydrolysis of the 3,6-anhydro-β-D-glucoside linkage was 31.400 times faster than hydrolysis of cellobiose. A series of different 3,6-anhydrocelluloses with different degree of substitution were prepared by tosylation of cellulose with varying amounts of tosyl chloride in dimethylacetamide and subsequent treatment with sodium hydroxide. Anhydrocelluloses with degrees of substitution of 0.02, 0.07, 0.31 and 0.74 were obtained. The anhydrocelluloses were subjected to acidic hydrolysis in 2.0 M aqueous HCl and the rate of hydrolysis monitored by ion chromatography analysis of the amount of glucose and/or cellobiose formed. All 3,6-anhydrocelluloses hydrolyzed with a faster rate than cellulose, but the anhydrocellulose with a low degree of substitution (ds = 0.07) hydrolyzed fastest which was 90 times faster than cellulose.     

秸秆纤维素的一步快速提取和水解

研究了秸秆纤维素的一步快速提取方法, 在醋酸和硝酸溶液体系中, 选择10种不同的反应条件, 进行了提取条件优选, 然后对提取的纤维素样品分别进行了水解. 结果发现, 纤维素提取的最佳条件为120 ℃, 固液比为1∶25, 在体积分数为80%的醋酸和10%的硝酸混合溶液中反应20 min, 纤维素的产率为38%. 纤维素样品的水解实验发现, 在最佳条件下提取样品的葡萄糖含量都大于90%, 水解率达到94%. 13C NMR和FTIR分析结果表明, 纤维素的分子结构未被破坏, 但纤维素Ⅰβ含量较高, 木质素和半纤维素的去除率都很高, 表明此方法是比较理想的制备高纯度纤维素的方法.     

Crystallite structure of cellulose

The crystallite structure of cellulose has been elucidated through analyses of the degradations of model compounds by gel-permeation chromatography. These compounds include single crystals of cellulose triacetate, regenerated cellulose from single crystals, precipitated celluloses from solutions, and commercial regenerated cellulose. The corresponding distribution profiles are found to follow the Keller transformation, which is a characteristic behavior of the folded crystals of synthetic polymers. It is also found that the leveling-off DP of cellulose is a first-order approximation of the corresponding fold length. A detailed folding chain model for the regenerated cellulose was constructed, and the various aspects of the structure are discussed. The kinetic data and the degradation products of native celluloses were also analyzed and found to obey the ruling of the chain fold model but not the conventional fringe-micellar model. In addition, an iodine-staining experiment pinpoints a minimum of 1.5% of true amorphous material; this is in quantitative agreement with the conformation analysis for the six-fold helical β-loop bonds. It is therefore suggested that the same chain-fold conformation is applicable to the native polymer. The hydrolysis of cellulose is found to be composed of a triple mode of degradation, i.e., a first-order random scission at the folds, a zero-order peeling reaction at the ends of the crystallites, and a first-order random scission on the lateral surfaces of the cellulose.     

A preliminary spectroscopic investigation on the molecular interaction of metal-diphenylthiocarbazone complex with cellulose biopolymer and its application

Biopolymer adsorbents are versatile in their application for removal of heavy metals. The present work is focused towards the preliminary study of the interaction of diphenylthiocarbazone (DTZ) complex of chromium(VI) in acidic medium with cellulose biopolymer. Chromium-DTZ complex could be quantitatively adsorbed on a cellulose column in the pH range 1.0-2.5 and the effect of various experimental parameters such as stability of the column and the complex, column breakthrough volume, and interfering ions have been studied in detail. The probable mechanism of adsorption of complex on the cellulose biopolymer was corroborated using Fourier transform infra-red spectroscopy (FT-IR), scanning electron microscopy (SEM), energy dispersive X-ray (EDX) and solid state 13C nuclear magnetic resonance techniques (CP-MAS). The pores formed due to the hydrogen bond between the cellulose layers and then the ensuing occupation of the complex between these layers and on the surface of the biopolymer layer through electrostatic attractive force and Π interaction of aromatic ring with cellulose are expected to play a vital role in the interaction. The cellulose column could be regenerated using environmentally benign polyethylene glycol-400 (PEG-400) in acidic medium. The cellulose biosorbent has been successfully tested to study the removal of chromium as its dithizone complex from synthetic and real waste water samples.     

Xylan hydrolysis in zinc chloride solution

Xylan is the major component of hemicellulose, which consists of up to one-third of the lignocellulosic biomass. When the zinc chloride solution was used as a pretreatment agent to facilitate cellulose hydrolysis, hemicellulose was hydrolyzed during the pretreatment stage. In this study, xylan was used as a model to study the hydrolysis of hemicellulose in zinc chloride solution. The degradation of xylose that is released from xylan was reduced by the formation of zinc-xylose complex. The xylose yield was >90% (w/w) at 70°C. The yield and rate of hydrolysis were a function of temperature and the concentration of zinc chloride. The ratio of zinc chloride can be decreased from 9 to 1.3 (w/w). At this ratio, 76% of xylose yield was obtained. When wheat straw was pretreated with a concentrated zinc chloride solution, the hemicellulose hydrolysate contained only xylose and trace amounts of arabinose and oligosaccharides. With this approach, the hemicellulose hydrolysate can be separated from cellulose residue, which would be hydrolyzed subsequently to glucose by acid or enzymes to produce glucose. This production scheme provided a method to produce glucose and xylose in different streams, which can be fermented in separated fermenters.     

Preparation and characterization of cellulose nanofibers from partly mercerized cotton by mixed acid hydrolysis

Cellulose nanofibers with a diameter of 70 nm and lengths of approximately 400 nm were fabricated from partly mercerized cotton fibers by acid hydrolysis. Morphological evolution of the hydrolyzed cotton fibers was investigated by powder X-ray diffraction, Fourier transform infrared analysis and field emission scanning electron microscopy. The XRD results show that the cellulose I was partially transformed into cellulose II by treatment with 15 % NaOH at 150° for 3 h. The crystallinity of this partially mercerized sample was lower than the samples that were converted completely to cellulose II by higher concentrations of NaOH. The intensities of all of the diffraction peaks were noticeably increased with increased hydrolysis time. Fourier transform infrared results revealed that the chemical composition of the remaining nanofibers of cellulose I and II had no observable change after acidic hydrolysis, and there was no difference between the hydrolysis rates for cellulose I or II. The formation of cellulose nanofibers involves three stages: net-like microfibril formation, then short microfibrils and finally nanofibers.     

Dilute-acid hydrolysis of sugarcane bagasse at varying conditions

Sugarcane bagasse, a byproduct of the cane sugar industry, is an abundant source of hemicellulose that could be hydrolyzed to yield a fermentation feedstock for the production of fuel ethanol and chemicals. The effects of sulfuric acid concentration, temperature, time, and dry matter concentration on hemicellulose hydrolysis were studied with a 20-L batch hydrolysis reactor using a statistical experimental design. Even at less severe conditions considerable amounts (>29%) of the hemicellulose fraction could be extracted. The percentage of soluble oligosaccharides becomes very low in experiments with high yields in monosaccharides, which indicates that the cellulose fraction is only slightly affected. For the sugar yields, acid concentration appears to be the most important parameter, while for the formation of sugar degradation products, temperature shows the highest impact. It could be demonstrated that the dry matter concentration in the reaction slurry has a negative effect on the xylose yield that can be compensated by higher concentrations of sulfuric acid owing to a positive interaction between acid concentration and dry matter contents.     

Morphological evolution of curauá fibers under acid hydrolysis

Cellulose whiskers were obtained by means of sulfuric acid hydrolysis of curauá fibers. Before hydrolysis, the natural fibers were treated with an alkaline solution to remove the non-cellulosic content. Fiber degradation evolution and cellulose whisker formation were analyzed by structural and morphological analysis. The original fiber structure underwent a fragmentation mechanism after being exposed for 3?min to sulfuric acid. Cellulose whiskers were lixiviated from the fiber surface after 10?min of hydrolysis, developing two scenarios: one where the whiskers became unattached from the original fiber, and the other which remained attached. The cellulose whiskers presented a needle-like geometry with an approximate diameter of 11?nm and average length of 185?nm, after 30?min of acid hydrolysis. Based on microscopic characterization, a schematic representation of the morphological evolution of the cellulose fibers submitted to acid hydrolysis is proposed.     

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.     

Effect of inhibitors released during steam-explosion pretreatment of barley straw on enzymatic hydrolysis

The influence of the liquid fraction (prehydrolysate) generated during steam-explosion pretreatment (210°C, 15 min) of barley straw on the enzymatic hydrolysis was determined. Prehydrolysate was analyzed for degradation compounds and sugars' content and used as a medium for enzymatic hydrolysis tests after pH adjusting to 4.8. Our results show that the presence of the compounds contained in the prehydrolysate strongly affects the hydrolysis step (a 25% decrease in cellulose conversion compared with control). Sugars are shown to be more potent inhibitors of enzymatic hydrolysis than degradation products.