Aspects of the surface and bulk nitration of cellulose in nitric acid,nitric acid/water,and nitric acid/dichloromethane mixes

Electron spectroscopy for chemical analysis (ESCA) has been employed to follow the surface nitration of cellulose papers in nitric acid–water and nitric acid–dichloromethane mixes with the aim of: elucidating the identity of the nitrating species in these mixes and from comparison of surface and bulk degree of substitution (DOS) further understanding on the role that morphology plays in the nitration of cellulose in these mixes. In nitric acid, nitric acid–water and nitric acid–dichloromethane mixes, surface nitration was observed to be slow (cf. to that reported in mixed acids) and the concentration of nitronium ion was observed to be low (cf. to mixed acids). On the basis of these observations and from the results of kinetic experiments, reported herein, it is proposed that the nitronium ion, NO₂⁺, is the important nitrating species of cellulose in these nitric acid mixes. Nitration in all but the most concentrated nitric acid–dichloromethane mixes produced equal surface and bulk DOS; however, nitration in pure nitric acid produced different surface and bulk DOS. The latter result implies that the heterogeneous nature of the nitration reaction can influence the DOS achieved.     

由邻硝基甲苯生产三硝基甲苯过程模拟

引　言目前 ,国内外生产三硝基甲苯大都采用甲苯三段硝化工艺 .混合硝基甲苯生产线是由甲苯硝化成一硝基甲苯 ,然后再将一硝基甲苯根据其异构体性质的不同分离成对位 (36 .1% )、邻位 (5 9.2 % )、间位硝基甲苯 (4.7% ) [1] 3种产品 .市场上对硝基甲苯的需求量远远大于邻、间硝基甲苯 ,在生产中占较大比例的邻硝基甲苯不能得到充分利用 ,如用其代替甲苯生产三硝基甲苯 ,可将三段硝化工艺减为二段 ,且邻硝基甲苯得到合理利用 .本文根据硝化与氧化反应动力学理论[2 ] 建立了用邻硝基甲苯生产三硝基甲苯的末段硝化过程的稳态模型 ,根据生产数据…     

Chemical celluloses derived from Pinus radiata wood pulps for nitrocellulose preparation

The nitration capabilities of a range of chemical celluloses, including some containing the cellulose-II polymorph, were examined. The cellulose samples, derived from Pinus radiata wood by bisulphite, prehydrolysis-kraft or kraft pulping, were compared with a commercial nitration-grade cellulose and two bleached cotton linters samples. All samples on nitration gave nitrocelluloses (degree of substitution ≈ 2–45) which had satisfactory stabilities and solubilities, with the exception of a P. radiata bisulphite cellulose which had a high pentosan value. The presence of cellulose-II in the samples was not an impediment to the nitration. High performance size exclusion chromatography of the nitrocelluloses showed that the molecular weight distributions of samples derived from the P. radiata celluloses were generally similar to that derived from a commercial nitration-grade cellulose.     

ENZYMATIC HYDROLYSIS OF CELLULOSE: DETERMINATION OF KINETIC PARAMETERS

The effects of cellulose substrate concentration, cellulase enzyme concentration, and product concentration on the kinetic parameters involved in the enzymatic hydrolysis of cellulose have been studied. The Michaelis constant showed a decreasing trend with a decreasing crystallinity of cellulose substrate while the maximum reaction rate showed an increasing trend. These kinetic parameters were found to be significantly larger when the enzyme concentration was increased. The adsorption kinetic parameters showed an increasing trend as the crystallinity is decreased. It was found that the optimal enzyme loading should be determined by the source, concentration, and crystallinity of cellulose substrate and the initial specific rate of cellulose hydrolysis which is, in large part, influenced by the degree of crystallinity of cellulose substrate. The inhibition constant for cellulase-by cellobiose and that for cellobiase were also determined. These kinetic parameters determined experimentally can be applied to kinetic modeling and simulation of cellulose hydrolysis.     

Empirical Kinetics Equation of the Synthesis of NTO in Nitric Acid

The influence of concentration of reactants (HNO₃ and TO) and reaction temperature on the rate of synthesis of NTO from TO in nitric acid solution was investigated by using an experimental kinetics model. An exponential kinetic equation was established by nitration of TO in 60.4–76.2 % HNO₃. Experimental data of the nitration of TO with 60.0–96.7 % HNO₃ were used to verify this model. Kinetic parameters such as apparent reaction orders of TO and HNO₃, activation energy and frequency factor for nitration of TO were determined. The values of nitration rate calculated were similar to those measured. This model can quantitatively and qualitatively describe the influence of concentration of reactants and reaction temperature on the rate of nitration TO. In addition, it was found that the kinetics model is potentially suitable for approximately predicting the rate of NTO synthesis from TO.     

Chemical reaction modeling of industrial scale nitrocellulose production for military applications

A model was developed to describe the nitration of cellulose in mixed acids used in the production of military grade nitrocellulose. Acid dissociation, swelling, diffusion, and chemical reaction were considered to model the nitration of industrially important cellulose materials for given reaction times and conditions. This model is supported by experimental work conducted to measure the dynamics of swelling and diffusion in wood pulp slivers, and the model was validated using the results of lab-scale nitration reactions. Microcomputed tomography was also used to perform a structural analysis of wood pulp slivers that were cut on industrial, rotary cutting machines to evaluate features that may influence the reactivity of these materials.     

Ru/CNT催化纤维二糖加氢制备山梨醇的机理及动力学

针对纤维素的转化,研究了以钌碳纳米管(Ru/CNT)为催化剂,纤维素模型分子纤维二糖催化加氢制备山梨醇的反应。通过对反应产物的分析,考察了纤维二糖转化生成山梨醇的反应机理,建立了纤维二糖催化加氢的动力学模型。并根据实验数据,拟合得到纤维二糖催化加氢反应各步的反应数率常数和表观活化能,其中,纤维二糖水解活化能为147.1 KJ·mol^-1;纤维二糖部分加氢活化能为73.8 KJ·mol^-1。纤维二糖催化加氢反应模型的建立,为纤维素资源的高效利用提供了重要的基础数据。     

E.s.c.a. studies of the nitration and denitration of cellulosic materials

The relative rates of the nitration and denitration of cellulose and cellulose nitrate, respectively (in the form of linters paper), have been monitored in the outermost few tens of Angstroms of the fibres using e.s.c.a. (X-ray photoelectron spectroscopy). Important conclusions are drawn on the equilibrium conditions at the surface and it has been shown that in mixed acid nitrations sulphate esters, (often thought to be a cause of instability in cellulose nitrates), are confined to the outermost few tens of Angstroms of the material. Comparison of the degree of substitution at the surface and that determined for the bulk by Kjeldahl methods provides a new insight into this complex problem.     

Intrinsically coloured polymers from cellulose carbanilates

The synthesis and characterization of intrinsically coloured polymers from cellulose tricarbanilates has been achieved. Data relating to the intermediate stages are given. Spectroscopy, thermal analysis and light fastness tests were used to establish some of the physical properties of the products. Information was obtained regarding the kinetics of nitration of cellulose tricarbanilate and the nature of the nitration process has been elucidated. Evidence is presented which indicates that the light fastness characteristics of coloured compounds are not necessarily governed by energy transfer phenomena since the system studied is known to exhibit efficient energy transfer yet the light fastness results are invariably poor. The thermal properties of the products are complex and best dealt with in context.     

A study of the low temperature nitration of cellulose in mixed acids

The low temperature surface and bulk nitration of cellulose has been investigated by electron spectroscopy for chemical analysis (ESCA), ¹³C-NMR and X-ray diffraction. Acid mix composition has been probed at room temperature and at low temperatures (0–20°C) by Raman spectroscopy. This multitechnique approach has been employed to elucidate the behavior of surface degree of substitution (DOS) with acid mix composition over a 40°C temperature range. The data obtained have prompted a reinterpretation of previously reported work. Surface “equilibrium DOS” is shown to be established within 1 s at all temperatures investigated. but, at lower temperatures (> 5°C) the surface DOS as monitored by ESCA is observed to “dip” after immersion times of t < 5 s. This change in DOS is correlated with major structural changes in the fiber as observed by SEM. At low temperatures, e.g., ?15°C, nitration is shown to be complete throughout the cellulose fiber after 10 h nitration. Solution state ¹³C-NMR is used to compare the nitrate ester substitution distribution in cellulose nitrates prepared from acid mixes of the same composition at different temperatures.     

Solvent extraction using dialysis through artificial phase boundaries

Several solvent extraction systems were studied using a cellulose dialysis membrane as an artificial phase boundary separating one solvent phase from the other. Solutes were allowed to come to extraction equilibrium by permeation through the membrane. The rate of permeation depended on the osmotic properties of the solute, such as the molecular size and the presence of colloidal species. The extraction equilibrium was established by the solvent-extraction properties of the solute in each system, and the equilibrium was approached through the cellulose membrane by a first-order kinetic process. The method appears to be useful for ‘packaging’ organic solvents in membrane containers to be used for extractions in which time is not a factor. In certain cases, equally well extracted solutes, such as zirconium and aluminium 8-hydroxyquinolates, can be separated because one solute exists as a partially colloidal material [Zr(IV)] and hence does not pass through the membrane rapidly.     

Macrokinetics of toluene nitration

Data are presented for the heterogeneous nitration of toluene in a miniature CFSTR using nitrating acid of initial composition 15 mol% HNO₃, 30 mole % H₂SO₄, 55 mole %H₂O under a range of operating conditions. The results are shown to be inconsistent with the simple kinetic model adopted by previous workers on this system and suggest that diffusion resistances may play a more important part in determining nitration rates in the two liquid phase region than has hitherto been supposed.     

一种新的绿色硝化技术

综述了近二十年关于臭氧介质二氧化氮硝化技术的研究成果 ,该技术的实验室探索性研究已证明其可用于几乎所有芳烃的环上硝化 ,是最有希望取代传统混酸硝化工艺的一种新技术 ,并且认为臭氧介质二氧化氮载体硝化是今后的发展方向 ,是该技术实现工业化的关键     

Study of the nitration of methyl cellulose

A two-step procedure for the preparation of methyl cellulose nitrate is described. The heterogeneity of the methylation step is reflected in the nonuniformity of the products obtained by nitration with either 98% nitric acid or a solution of 98% nitric acid in methylene chloride. On the basis of the experimental data it is calculated that methyl cellulose having a minimum degree of substitution of 1.8 is required for the preparation of a uniformly substituted methyl cellulose nitrate.     

Influence of electrolyte on electrical properties of thin cellulose acetate membranes

The electrical behavior of thin cellulose-2.5-acetate membranes for chemical semiconductor sensor applications was investigated. The influence of electrolyte on the electrical membrane properties was studied by means of electrochemical impedance spectroscopy. The polymeric membranes can be described using the electrical model of Cole and Cole. The membrane electrolyte distribution equilibria were investigated by means of an absorption–desorption method using conductivity measurements. The desorption kinetics for thin cellulose acetate membranes differ significantly from those of thicker cellulose acetate reverse osmosis membranes because here the rate of the ionic exchange at the membrane interface cannot be neglected. The experimentally determined distribution coefficients were used for the discussion of the electrolyte influence on the electrical membrane parameters. A functional dependence was found between the specific membrane resistance of cellulose acetate membranes and the ionic hydration enthalpy. The effect of electrolyte on the relative permittivity can be explained by a theoretical model. © 1994 John Wiley & Sons, Inc.     

Significance of the intrinsic viscosity ratio of unsubstituted and nitrated cellulose in different solvents

It has been studied the intrinsic viscosity ratios of cellulose solutions in different solvents and of the corresponding nitrates dissolved in aceton using cellulose samples from different origins and with different degrees of polymerization. The results demonstrate that with FeTNa and CdEn as solvents, molecular dispersed solutions are only produced with cellulose having a DP≤3000. FeTNa is limited to cotton cellulose only. Contrary to this, the intrinsic viscosity ratio [η]/[η] shows independence from the range of degree of polymerization and the origin of cellulose, confirming thus once more the polymeranalogous course of nitration. Its value referred to a degree of substitution S = 2.90±0.02, to absolute dry and pure cellulose and to standardized viscosity measurements amounts [η]_Ac/[η]_CuEn = 1.95±0.05. Determination of the intrinsic viscosity ratio permits, therefore, to obtain information in respect of the polymeranalogous and homogeneous character of the cellulose nitrate, and, in connection with determinations of yield of nitration, in respect of the purity of the corresponding unsubstituted cellulose. Basing on the constant value of the intrinsic viscosity ratio [η]_Ac/[η]_CuEn, and using the quotients [η]_FeTNa/[η]_CuEn and [η]_CdEn/[η]_CuEn, there has been derived the [η]-DP-relationships for unsubstituted cellulose in the respective solvents.     

Preparation and characterization of cellulose nitrate-acetate mixed ester fibers

Cellulose nitrate-acetate mixed esters (CNA) were synthesized by nitration of cellulose diacetate, using HNO₃/H₂SO₄ as nitration agent. The CNA structures were confirmed and analyzed by IR and ¹H NMR. A decrease in molecular weight and an increase in nitrate group content were observed with increasing H₂SO₄ ratio and reaction time. The highest degree of nitrate substitution, 9.2%, for CNA was achieved with the reaction time of 6h in concentrated HNO₃. Increasing HNO₃ ratio in nitration media resulted in more thermally stable CNA. CNA fibers were prepared by altering the polymer concentration from 15 to 30% in an 85:15 (w/w) acetone:water solvent. The electrospun CNA fibers were characterized by SEM to investigate the influence of different NO₂% on fiber formation, diameters and architectures.     

Evaluation of the accessibility of celluloses by the intrinsic viscosity ratio [η] acetone cell.nitr. / [gh] CuEn unsubst.cell.

Summary Standarization of the nitration procedure as well as of the conditions of viscosimetric measurements on cellulose nitrates and unsubstituted celluloses leads to a constant Intrinsic Viscosity Ratio [] _Acetone ^Cell.nitr. / [gh] _CuEn ^{Unsubst.cell.} = 1.95±0.05, independently from the range of DP. Since nitration under the standarized conditions occurs without degradation and delivers a reproducible constant degree of substitution of DS = 2.90±0.02, intrinsic viscosity ratios lower than 1.90 indicate a diminished accessibility of the respective cellulose. Determination of the intrinsic viscosity ratio reveals, therefore, the possibility to evaluate the accessibility of a cellulose sample.     

The significance of heating rate on char yield and char properties in the pyrolysis of cellulose

The carbonization of powdered cellulose was investigated in the temperature range 200–950°C by measuring weight loss, carbon and hydrogen content, BET-adsorption of nitrogen and carbon dioxide, mercury penetration and particle-size distribution. Evidence is presented in support of a kinetic model according to which cellulose decomposition is controlled by dehydration at low temperature and by cleavage/scission at high temperature. Increased char yield and lower $\text{O}\text{C}$ ratio at low heating rate, as well as kinetic investigations into the effect of potential catalysts, support this model. The difference in reaction mechanism according to the heating rate appeared to influence the char properties considerably. Yield in micropore volume and surface area of slowly carbonized cellulose is up to four times larger than that of rapidly heated cellulose. Mercury pore volume, density and particle diameter depend on the heating rate, also. By adsorption of various gases, differences in relative size of the pore openings of different chars can be discerned. Micropore volumes measured with carbon dioxide were as much as seventy times larger than the corresponding volume measured with nitrogen. Thus, it is possible to obtain chars with molecular sieve properties by simple pyrolysis heating schemes.     

纤维素亲和膜对木瓜蛋白酶的吸附特性

以纤维素滤纸膜为载体,染料汽巴蓝F3GA为配基,制备出一种新型亲和膜色谱介质。分别在277,298,310K的均衡实验条件下,批量法对木瓜蛋白酶进行等温吸附测定。所得的数据用准一级动力学模型和准二级动力学模型进行分析。结果表明:准二级动力学模型具有更好的相关性,纤维素染料亲和膜对木瓜蛋白酶的吸附符合Lang-muir吸附模型,在298K条件下吸附现象的热力学参数:ΔGΘ,ΔHΘ,ΔSΘ分别为-7.71kJ/mol,34.91kJ/mol和0.143kJ/(mol.K),染料纤维素亲和膜对木瓜蛋白酶的吸附是自发的,并且是吸热过程。