超临界二氧化碳中的甲苯选择性氧化反应

考察了甲苯选择性氧化反应中反应物及产物在超临界二氧化碳中的溶解性质。结果表明,甲苯在超临界二氧化碳中的溶解度较大,在反应条件下能与二氧化碳形成均相;苯甲醇、苯甲醛和苯甲酸在超临界二氧化碳中的溶解度随着物质极性的增强而降低。利用不同产物的溶解性差异,可实现超临界二氧化碳中甲苯的选择性氧化。同时考察了超临界二氧化碳中甲苯选择性氧化反应过程中,反应时间、反应压力、反应温度以及n(甲苯)/n(氧气)对反应选择性的影响。     

超临界流体萃取法分离B炸药中RDX的工艺研究

为解决废旧炸药的高效回收问题,采用超临界萃取技术(SCFE)对废旧B炸药中的TNT进行萃取,从而达到回收RDX的目的,并考察了不同压力和温度对回收效果的影响。结果表明,压力越高,超临界二氧化碳对B炸药中TNT的萃取效果越好,对RDX的回收效果越好,但压力过高时,RDX在超临界二氧化碳中的溶解不可忽视;温度越高,超临界二氧化碳对B炸药中TNT的萃取效果越好,RDX的回收效果越好。但是,过高的温度可能会导致TNT变质,影响RDX的回收效果。     

超临界CO2在PCDL中溶解扩散的分子动力学模拟

通过分子动力学模拟,研究了温度和压力的改变对超临界CO_2在聚碳酸酯二醇中的溶解和扩散行为的影响。结果表明,降低温度和升高压力有利于超临界CO_2的溶解;降低压力和升高温度有利于超临界CO_2的扩散。研究结果可以为相关发泡工艺参数的设置提供参考。     

过氯乙烯清漆超临界二氧化碳喷涂的研究

采用超临界二氧化碳替代涂料中的挥发性有机化合物达到保护环境的目的。以过氯乙烯清漆为原料,探究温度、压力、清漆质量分数(清漆质量占清漆与超临界二氧化碳混合物的质量比)和喷涂距离(基板和喷枪之间距离)对喷涂效果的影响。结果表明,清漆质量分数是高度显著性因素,随清漆质量分数的减少,喷涂液滴尺寸减小;压力是具有一定影响的因素,随着压力的升高,喷涂液滴尺寸减小;温度和喷涂距离对喷涂无显著影响。通过喷涂获得的涂膜可以通过国标实验。通过测量黏均分子质量与红外光谱分析表明,超临界二氧化碳不影响涂料中的成膜物质性质。     

利用超临界二氧化碳去除含氟聚合物中全氟辛酸铵的方法

<正>本发明公开了一种利用超临界二氧化碳去除含氟聚合物中全氟辛酸铵的方法,先采用超临界二氧化碳在设定的温度和压力下溶解并萃取含氟聚合物中的全氟辛酸铵,达到将全氟辛酸铵从含氟聚合物分离及去除的目的,然后降温减压,收集萃取釜中的产物。本发明整个过程仅使用少量的甲醇作为夹带     

超临界流体快速膨胀法制备超细阿昔洛韦粒子

以二氧化碳作为超临界溶剂,采用超临界溶液快速膨胀技术制备得到超细阿昔洛韦药物粒子,在一定的温度和压力情况下,测定了阿昔洛韦在超临界二氧化碳中的溶解度,考察了各种操作参数对药物粒子粒径的影响,研究了药物粒子粒径随各种操作参数的变化规律。结果表明:阿昔洛韦在超临界二氧化碳中的溶解度较小,在10-5~10-6之间(摩尔分率),溶解度随着温度和压力的升高而增大,不存在文献中所报道的反向区。同时实验结果表明:药物粒子粒径变化对预膨胀温度最敏感,粒径随预膨胀温度的升高而减小;一定范围内随收集距离的增大而增大;在萃取温度较低的情况下,粒子粒径基本随着萃取温度的升高而减小;随着萃取温度的升高,在相对较高预膨胀温度下,粒径随着萃取温度升高而增大。     

超临界流体特性及在有机溶剂中相行为研究

超临界流体具有许多独特的性质,如粘度、密度、扩散系数、溶剂化能力等性质随温度和压力变化十分敏感:粘度和扩散系数接近气体,而密度和溶剂化能力接近液体。本文通过实验首先进行了超临界二氧化碳与氟原子作用考察氟原子的引入对膨胀效果的影响、超临界二氧化碳与羰基作用,考察羰基对膨胀效果的影响、从而确定出最佳的共溶剂[1]。随后,使之与肉桂醛做一系列比例的膨胀对比实验。     

合成纤维的超临界二氧化碳染色

传统染色工艺使用大量的水,存在环境污染严重及资源消耗、浪费大的问题,有机溶剂作染色介质也存在生态、成本问题等,很难工业化应用。超临界二氧化碳流体染色作为一种新型染色技术越来越得到关注。本文介绍了超临界流体的性质及其染色工艺的特点,讨论了分散染料在超临界二氧化碳中的溶解和分散性,分析了三种合成纤维在超临界二氧化碳流体中染色研究现状、应用趋势和存在问题。     

液态和超临界态二氧化碳的非线性声学性质

根据美国国家标准局提供的二氧化碳在液态和超临界态下的声速、密度、比定压热容、膨胀系数等物理参数数据库中数据,计算了二氧化碳在液态和超临界状态下的声速压力系数、声速温度系数和非线性声参量几个非线性声学参数。分析归纳了液态二氧化碳和超临界二氧化碳的非线性声学特性,对比分析了液态二氧化碳、超临界二氧化碳和一般有机液的非线性声学特性。详细分析了二氧化碳在临界点附近的非线性声学特性。研究表明,液态二氧化碳表现出类似于一般液体在常温常压下的非线性声学特性;超临界二氧化碳的声速压力系数、声速温度系数和非线性声参量值可为正值或负值,其值随压力或温度的变化具有一定的规律性。压力越大温度越低,超临界二氧化碳的非线性声学特性越接近液态二氧化碳或一般液体。在临界点附近区域,3个参量值随压力或温度的变化出现正负最大值间的跳跃变化。     

超临界二氧化碳萃取器萃取分离香茅油

本文介绍了利用现有１５０Ｌ高压釜（压力２０ＭＰａ）改造的超临界二氧化碳萃取器萃取分离香茅油,探讨了压力、温度、时间对萃取分离效果的影响。结果表明,采用超临界二氧化碳萃取器萃取分离香茅油时应选择一个适宜的压力、温度和萃取时间,产品的色、香味、纯度均优于常规的减压蒸馏法。     

Some Effects of Elevated Temperatures on the Structure of Cellulose and its Transformation

In many commercial processes cellulose is exposed to elevated temperatures in the 100 to 200°C range. Though this range is below the glass transition temperature (Tg) of dry cellulose, in the presence of polar media Tg is depressed, and molecular mobility is sufficient to allow structural reorganization. In the present study, a number of regenerated celluloses, some amorphous and some semicrystalline, were heat treated at elevated temperatures in water under pressure, as well as in other polar media. Two groups of factors were found to influence the type and amount of structural change. The first were the characteristics of the cellulose, that is, the degree of polymerization (DP) and the structure of the cellulose prior to treatment. The other group were the nature of the medium and the time and temperature of the treatment. The amorphous high DP celluloses were found to aggregate as cellulose IV, with the time and temperature determining the extent of ordering rather than resulting in qualitative reorganization. The low DP celluloses, which were of low enough molecular weight to reduce the constraints on molecular mobility imposed by molecular entanglements, had a more diverse pattern of responses. At ambient temperatures the aggregation was into high crystallinity cellulose II; at intermediate temperatures, a variety of forms fitting into the category of cellulose IV were produced; and finally, at high enough temperatures, a cellulose I of very high crystallinity was produced in low yield.     

Effect of Cellulose Characteristic and Hydrolyze Conditions on Morphology and Size of Nanocrystal Cellulose Extracted from Wheat Straw

In this paper, preparation and characterization of cellulose and nanocrystalline celluloses (NCC) and the effect of cellulose characteristic and hydrolyze conditions on the morphology and size of the obtained NCC will be discussed. Two different celluloses were prepared by two procedures, A and B, then the cellulose obtained was hydrolyzed under the same conditions. The result showed that the morphology and size of the nanocrystals obtained are not only attributed to the cellulose sources, but also to the hydrolyze conditions.     

Graft copolymerization of vinyl monomers onto modified cotton. IX. Hydrogen peroxide–thiourea dioxide redox system induced grafting of 2-methyl-5-vinylpyridine onto oxidized celluloses

Cotton cellulose was independently oxidized with potassium periodate, potassium dichromate-sulfuric acid, and potassium dichromate–oxalic acid, and the resulting oxidized celluloses were further modified by treatment with chlorous acid or sodium borohydride. The various modified celluloses so obtained were grafted with 2-methyl-5-vinylpyridine using a thiourea–dioxide–H₂O₂ redox system. It was found that the initiation characteristics of the cellulose samples vary widely with the oxidizing agent used. Further modification of the oxidized celluloses by treating them with chlorous acid enhances considerably their susceptibility toward grafting. The opposite holds true when these oxidized celluloses were modified by sodium borohydride treatment. Excluding thiourea dioxide from the polymerization system offsets grafting onto cotton cellulose while considerable grafting takes place on the various oxidized celluloses and their further modified samples. The work was also extended to study the factors which affect the graft uptake, homopolymer formation, and total conversion. In addition, the reactions involved in initiation of grafting were elucidated.     

Enzymatic hydrolysis of celluloses obtained via the hydrothermal processing of Miscanthus and oat hulls

The enzymatic hydrolysis of celluloses obtained via the refinement of fibrous products after the hydro-thermobaric processing (with an explosion) of two types of feedstocks (Miscanthus and oat hulls) in a high-pressure reactor is studied. A multi-enzyme composition of such enzyme preparations as CelloLux-A, BrewZyme BGX, and Rapidase CR, is used as a catalyst. The celluloses obtained by refining fibrous products from the mentioned feedstocks at a pressure of 1.5 MPa are found to have close reactivities: the yield of reducing substances (RS) was 81% (relative to the substrate weight) and 87–91% (relative to the weight of hydrolyzable compounds). When the pressure of the hydro-thermobaric treatment processing of the feedstocks (Miscanthus) is raised from 1.5 to 2.5 MPa, the fermentability of celluloses diminishes: the RS yield was 53–57% (relative to the substrate weight) or 56–60% (relative to the weight of hydrolyzable compounds). The universality of the hydro-thermobaric processing of different non-wood feedstocks for the subsequent successive fermentolysis of substrates into RS solutions that predominantly contain cellulose is shown. The obtained glucose hydrolyzates are high-quality feedstocks for the biosynthesis not only of fuel alcohols, but also a wide spectrum of such microbiosynthesis products as aminoacids, organic acids, bacterial cellulose jelly films, and protein-vitamin concentrates.     

Effect of crystalline structure on the trapped radical spectra of irradiated cellulose

The effects of crystalline modification of cellulose and of water on the ESR spectra generated by the trapped free radicals in gamma-irradiated celluloses were investigated for cotton cellulose I, II, III, and IV, partially decrystallized cotton cellulose, ballmilled cotton cellulose, hydrocelluloses of cellulose III and IV, and ramie. On irradiation of the celluloses, free radicals were formed on the cellulose molecule, probably following dehydrogenation or chain cleavage. The free radicals located within the less ordered or amorphous regions of the cellulose reacted readily with water and were terminated. The radicals located within the more ordered regions of the celluloses could be made accessible to reaction with water by the interaction of the celluloses with solvents which caused dimensional changes in the cellulosic structure. In the highly ordered regions of the celluloses, even after long periods of time in solvents which caused large dimensional changes in the cellulosic structure, the trapped free radicals were not terminated by reaction with solvent or water. The ESR spectra of the irradiated, dried celluloses were determined at ?160°C, the single-line spectra recorded had line widths of about 18-24 gauss. On the absorption of water by the irradiated celluloses, the ESR spectra changed and were dependent on the crystalline structure of the irradiated celluloses. The effects of different arrangements of the irradiated celluloses, as shown by their trapped radical spectra, particularly after interaction with water, were discussed.     

Dyeing of chemically modified cellulose. IV. Dyeing of oxidized celluloses with some reactive and direct dyes

Oxidation of cotton cellulose with potassium periodate, potassium dichromate-sulfuric acid, and potassium dichromate-oxalic acid results in creation of variable amounts of acidic and reducing groups along the cellulose molecule, being dependent upon the type of oxidizing agent used. Such groups were found to have a profound effect on the acceptability of cellulose for reactive and direct dyes. The rate and extent of dye uptake for the oxidized celluloses were significantly lower than those of the unoxidized cellulose. While presence of the acidic groups in cellulose molecules induces a negative environment thereby making approach of the dye anions to the cellulose difficult, presence of the reducing groups lowers the magnitude of cellulose reactivity as well as decreasing its adsorptive power. Further modification of the oxidized celluloses via either borohydride or chlorous acid treatment brought about modified celluloses the dyeability of which confirms the inhibiting effect of the acidic and reducing groups of those oxidized celluloses on the rate and extent of dyeing with reactive and direct dyes.     

Cellulose membranes for reverse osmosis Part I. RO cellulose acetate membranes including a composite with polypropylene

With the aim of obtaining RO membranes for brackish water desalination from purified celluloses (cotton linters and bleached bagasse pulp), two reactions (heterogeneous and homogeneous) were applied for the synthesis of cellulose acetate (CA). The efficiency of the membranes was measured and compared with those prepared from purchased CA and prepared CA by acetylation of imported high-grade viscose wood pulp. The effect of blending CA with polypropylene (PP), on the efficiency of the prepared RO membranes was also studied. Results showed that the method of preparation of CA plays a profound effect on the salt rejection and water flux of the RO membranes. The efficiencies of RO membranes formed from heterogeneously acetylated celluloses are higher than those prepared from homogeneous ones. Blending the acetylated cellulose with 9% PP wastes improves the efficiency of membranes prepared from the homogeneously acetylated celluloses.     

Chemically modified celluloses. XII. Affinities of azoic coupling components for chemically modified celluloses

Three azoic coupling components were purified and applied at different concentrations on standard cellulose and a series of chemically modified celluloses, involving oxidation with potassium periodate and potassium dichromate, as well as further borohydride reduction or chlorous acid oxidation of the oxycelluloses. Thermodynamic affinities of the azoic coupling components for all the chemically modified celluloses were determined from the adsorption data. As shown in the earlier studies on the affinity of vat and direct dyes for chemically modified celluloses, the affinity of the azoic coupling components also decreased with increasing degree of oxidation and increased after the oxycelluloses were reduced with sodium borohydride, though not to the extent of that for standard cellulose.     

Modification of the fine structure of cellulose by halogen and heat treatments

Treatment of various celluloses such as cotton, sulphite, and sulphate pulp with bromine water brings about profound changes in the fine structure of the fiber. Depending on the conditions of the treatment and on the nature of the cellulose, increases or decreases in the accessibility of the cellulose are observed, indicating crystallization and decrystallization processes. In the case of bleached sulphate pulp, similarly to rayon previously studied, an initial decrystallization proceeds the crystallization step. These changes were determined by the IR method, which was correlated previously to the bromine accessibility method. They are accompanied by highly significant changes in moisture absorption. The crystallization proceeds according to first-order kinetics with respect to the concentration of the less-ordered regions (LOR) of the cellulose. The rates of crystallization for the various celluloses varied in a range of 4 orders of magnitude. The activation energies of the bromide induced crystallization were found for all celluloses to be in the range of 10–15 kcal/mol, as compared to 30–40 kcal/mol obtained upon crystallizing the same celluloses by heating in the temperature range of 180–200°C. These values correspond to those of solvent and thermal crystallizations of poly(ethylene terephthalate), indicating the similarity between the crystallization mechanisms of the two polymers.     

热熔压敏胶的粘接性能和流变行为的关系

研究了热熔压敏胶初粘性、剥离强度与流变学行为之间的关系。研究发现,用温度扫描方法得到的流变曲线与压敏胶主曲线较为一致,因此可以将其转化为不同弛豫时间下的流变行为。通过调整液体树脂含量,设计出一系列橡胶平台模量保持相对不变的同时,具有不同玻璃化温度的压敏胶配方,其中玻璃化温度相同的压敏胶配方,具有基本相同的环形初粘力和剥离强度。