Silicalite-1修饰的HY型分子筛及其对纤维素水解的催化性能

采用silicalite-1对HY型分子筛进行修饰,得到具有核壳结构的复合分子筛HY/silicalite-1。通过X射线衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)、N2的吸附-脱附及吡啶吸附红外(Py-FTIR)等手段对不同晶化时间合成的HY/silicalite-1复合分子筛进行了表征,研究了复合分子筛对纤维素水解的催化性能。结果表明,晶化时间直接影响复合分子筛的晶体生长规律和两组分的相对含量,最佳晶化时间为16-24 h,所得到的复合分子筛外貌呈核壳结构,silicalite-1附晶生长在HY型分子筛的表面;随着晶化时间的延长,复合分子筛的表面由胶浊状变为光滑,最终变为鳞片状;其B酸量先减少后增加,而L酸量则先增加后减少。其中,晶化时间为24 h的HY/silicalite-1复合分子筛B酸量最大,L酸量最小,对纤维素水解反应具有良好的催化性能,葡萄糖收率由HY型分子筛催化获得的28.0%大幅提高至45.8%。     

Formation of furans upon electron-beam heating of cellulose

Similarity between cotton cellulose and sulfate and sulfite pine celluloses in degradation during electron-beam distillation has been shown. The yield of the distillate liquid slightly depends on the type of cellulose and makes up ∼60 wt %. The product liquid contains organic compounds with molecular masses of 32 to 128, of which furfural and its derivatives prevail. Electron-beam distillation can be used as an effective method for the manufacturing of furfural and other furan derivatives from cellulose (along with the traditional pentosan conversion processes). It has been shown that grinding and preheating of cellulose lead to an increase in the proportion of furfural and other furans in the condensates.     

Enzymatic hydrolysis of cellulose hydrates

We prepared two cellulose hydrates, Na-cellulose IV and cellulose II hydrate, along with their respective anhydrous forms, cellulose II and II′, from microcrystalline cellulose. X-ray diffractometry analysis showed that the structure of the hydrophobic stacking sheet was conserved in the samples, but the distance between the sheets was in the order: cellulose II hydrate > Na-cellulose IV > cellulose II and II′. The hydrates exhibited an expanded structure compared with the anhydrous form from the incorporation of hydrate water, and cellulose II hydrate contained more hydrate water than Na-cellulose IV. Enzymatic hydrolysis of the samples was carried out at 37 °C using solutions comprising a mixture of cellulase and β-glucosidase. The hydrates were hydrolyzed more efficiently than the anhydrous forms, and cellulose II hydrate showed a more efficient hydrolysis than Na-cellulose IV. This result also agrees well with the enzymatic adsorption properties of each sample, where the samples that adsorbed the greater amount of enzyme showed a higher degradability. The results obtained in this study provide useful knowledge on controlling the biodegradability of cellulose by converting its structure.     

Enzymatic kinetic of cellulose hydrolysis

The ethanol effect on the Trichoderma reesei cellulases was studied to quantify and clarify this inhibition type. To determine inhibition parameters of crude cellulase and purified exoglucanase Cel7A, integrated Michaelis-Menten equations were used assuming the presence of two inhibitors: cellobiose as the reaction product and ethanol as a possible bioproduct of cellulose fermentation. It was found that hydrolysis of cellulose by crude enzyme follows a model that considers noncompetitive inhibition by ethanol, whereas Cel7A is very slightly competitively inhibited. Crude cellulase is much more inhibited (K _iul=K _icl=151.9 mM) than exoglucanase Cel7A (K _icl=1.6 × 10¹⁵ mM). Also, calculated inhibition constants showed that cellobiose inhibition is more potent than ethanol inhibition both for the crude enzyme as well as exoglucanase Cel7A.     

The conversion of furans into phosphinines

The [4+2] cycloadducts between furan compounds and a methylenechlorophosphane pentacarbonyltungsten complex are converted into the corresponding 2-hydroxy- or 2-bromophosphinine complexes by treatment with BBr(3) and triethylamine. The X-ray crystal structure of the parent 2-phosphaphenol complex shows that the hydroxy substituent is coplanar with the ring and that the conjugation between the π lone pair of electrons on the oxygen atom and the ring leads to lengthening of the P-C(OH) bond. This complex is methylated at the phosphorus atom by methyl iodide with disruption of the ring aromaticity. The complex is further silylated, acylated, and triflated at the oxygen atom with retention of the aromatic structure, and decomplexation by 1,2-bis(diphenylphosphino)propane (DPPE) leads to the free parent 2-phosphaphenol. The comparison of the X-ray crystallographic structural analysis of the 2-bromophosphinine complex with an earlier structure of the analogous 2-chlorophosphinine complex suggests that 2-bromo species is a better ligand than 2-chlorophosphinine. When the [4+2] adducts are treated with BBr(3) and water, a 2-hydroxy-3-bromo-1,2,3,6-tetrahydrophosphinine derivative is obtained, which yields a seven-membered 2,1-phosphaoxepin when treated with an amine.     

Catalytic enantioselective Diels-Alder reactions of furans and 1,1,1-trifluoroethyl acrylate

Catalytic enantioselective Diels-Alder reactions of furans and 1,1,1-trifluoroethyl acrylate in the presence of oxazaborolidium catalysts 2 or 3 provide 7-oxabicyclo[2.2.1]hept-5-enes with high endo-selectivity and excellent enantioselectivity.     

Enzymatic hydrolysis of mannoglucans obtained from cellulose

Conclusions The mannoglucans obtained by the reduction of ketocelluloses are easily cleaved by cellulase preparations, in which connection, depending on the activity ratio of the exo and endo enzymes in the cellulase complex, the predominant hydrolysis products are either monosaccharides (glucose and mannose) or oligosaccharides, in which the residues of these sugars are connected by -(1 4) linkages.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2622–2625, November, 1979.     

Catalytic conversion of cellulose into 5-hydroxymethylfurfural in high yields via a two-step process

As a key renewable chemical for plastics and fine chemicals, the preparation of 5-hydroxymethylfurfural (5-HMF) from biomass is an important research topic. Cellulose, although abundant in nature, is difficult to convert to 5-HMF in good yields due to its recalcitrant and heterogeneous nature. In this work, we show an efficient two-step process for converting microcrystalline cellulose into 5-HMF with ionic liquids under mild conditions. In the first step, high glucose yields of above 80% could be obtained from the cellulose hydrolysis by a strong acidic cation exchange resin in 1-ethyl-3-methyl imidazolium chloride ([EMIM][Cl]) with gradual addition of water. In the second step, the resin was separated from the reaction mixture and CrCl₃ was added which lead to a 5-HMF yield of 73% based on cellulose substrate. The strategy can allow practical conversion of biomass into bio-derived products.     

微波辐射下氯化锌催化纤维素转化为呋喃类物质的研究

以氯化锌作为溶剂和催化剂,利用微波辅助氯化锌降解纤维素,致使纤维素直接转化为5-羟甲基糠醛(5-HMF)和1-(2-呋喃基)-2-羟基-乙酮两种呋喃类物质。通过考察反应温度、反应时间、氯化锌用量、纤维素加入量、微波功率和加热方式等因素对其摩尔产率影响可知,在140 mL质量分数为69%的ZnCl₂溶液中,纤维素用量为1 g,反应温度为135 ℃,反应时间为5 min,微波功率为500 W时,5-羟甲基糠醛的摩尔产率达到19.4%,微波功率为600 W时,1-(2-呋喃基)-2-羟基-乙酮的摩尔产率达到12.0%。     

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     

Direct conversion of macrocyclic furans into macrocyclic isothiazoles

The first calixhetarenes with more than one heteroatom in the constituent rings are prepared in one step by treatment of calix[4]furan 1a and calix[6]furan 1b with ethyl carbamate, thionyl chloride and pyridine to give 2, 3, 4 and 5, 6, 7 respectively; these products have been characterised by X-ray crystallography which reveals that in 2 all eight heteroatoms lie on one face of the macrocyle.     

Model-based fed-batch for high-solids enzymatic cellulose hydrolysis

While many kinetic models have been developed for the enzymatic hydrolysis of cellulose, few have been extensively applied for process design, optimization, or control. High-solids operation of the enzymatic hydrolysis of lignocellulose is motivated by both its operation decreasing capital costs and increasing product concentration and hence separation costs. This work utilizes both insights obtained from experimental work and kinetic modeling to develop an optimization strategy for cellulose saccharification at insoluble solids levels greater than 15% (w/w), where mixing in stirred tank reactors (STRs) becomes problematic. A previously developed model for batch enzymatic hydrolysis of cellulose was modified to consider the effects of feeding in the context of fed-batch operation. By solving the set of model differential equations, a feeding profile was developed to maintain the insoluble solids concentration at a constant or manageable level throughout the course of the reaction. Using this approach, a stream of relatively concentrated solids (and cellulase enzymes) can be used to increase the final sugar concentration within the reactor without requiring the high initial levels of insoluble solids that would be required if the operation were performed in batch mode. Experimental application in bench-scale STRs using a feed stream of dilute acid-pretreated corn stover solids and cellulase enzymes resulted in similar cellulose conversion profiles to those achieved in batch shake-flask reactors where temperature control issues are mitigated. Final cellulose conversions reached approximately 80% of theoretical for fed-batch STRs fed to reach a cumulative solids level of 25% (w/w) initial insoluble solids.     

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.     

Kinetics of the hydrolysis of mixed cellulose derivatives

By acetylating weakly substituted Na and H carboxymethylcelluloses and methylcellulose we have synthesized acetone-soluble highly substituted mixed derivatives of cellulose — acetocarboxymethylcellulose and acetomethylcellulose. Water-soluble products have been obtained from these esters by subsequent deep hydrolysis. The kinetics of the hydrolysis of the acetyl groups in the mixed derivatives obtained have been studied. Rate constants of the hydrolysis reactions have been calculated. The influence of the substituted groups on the acetylation and hydrolysis reactions has been determined.Tashkent Institute of Chemical Technology. Translated from Khimiya Prirodnykh Soedinenii, Vol. 33, No. 1, pp. 102–106, January–February, 1997.     

Fast preparation of nanocrystalline cellulose by microwave-assisted hydrolysis

In this work we report on the procedure for fast and controlled preparation of nanocrystalline cellulose (NCC) from commercially available microcrystalline cellulose using microwave-assisted hydrolysis. By varying the sulfuric acid concentration and hydrolysis temperature, an average hydrodynamic diameter of NCC between 126 and 1,310 nm with corresponding yields between 16 and 82 %, respectively, was obtained in a very short reaction time of 10 min. An additional advantage of the described procedure is its high reproducibility and ability to fine-tune the average NCC particle size by adjusting the reaction conditions, i.e., the sulfuric acid concentration and/or reaction temperature.     

Acid hydrolysis of cellulose in zinc chloride solution

Applied Biochemistry and Biotechnology - The efficient conversion of cellulosic materials to ethanol has been hindered by the low yield of sugars, the high energy consumption in pretreatment...     

Interfacial properties of cellulose nanoparticles obtained from acid and enzymatic hydrolysis of cellulose

Rod-shaped cellulose nanocrystals obtained by acid hydrolysis of eucalyptus fibers (CNCa) presented high aspect ratio (estimated length and width of 180 and 5 nm, respectively) and zeta potential of ?(17 ± 1) mV at pH 6. This typical morphology of cellulose nanocrystals was in contrast to nanoparticles obtained upon enzymatic hydrolysis of bacterial cellulose (CNCe), which were asymmetric and irregular due to surface-bound cellulases and presented a distinctive surface roughness. Interestingly, CNCe also displayed axial grooves, to yield a C-shape cross section that has not been reported before. The effect of the characteristic shape and surface chemistry of CNCa and of grooved CNCe was studied at oil/water interfaces and solid surfaces. Emulsions (20 % v/v oil) prepared with the CNCa were more stable than those prepared with CNCe, owing to their characteristic shape and surface chemistry. Hydrophilic (silica surfaces cationized by pre-adsorbed polycation) and hydrophobic (polystyrene films) solid surfaces were used as substrates for the adsorption of CNCe and CNCa for each type of surface. The ellipsometric data and AFM images indicated larger affinity of CNCe than CNCa for the hydrophobic surface. On the other hand, CNCa formed homogeneous monolayer on hydrophilic surfaces, whereas CNCe formed discontinuous films. Sequential adsorption behavior of CNCa on CNCe layers (or vice versa) suggested that the interaction between them is controlled by the orientation of enzymes bound to CNCe.