NiY分子筛表面酸性影响其选择性吸附脱硫性能的机理研究

采用原位红外光谱技术,以噻吩、环己烯和苯为模型探针分子,分别考察单一烃分子在NiY分子筛上的吸附与反应行为以及噻吩与烯烃、芳烃间的竞争吸附和催化反应行为。单一探针分子吸附研究发现,NiY分子筛中与Ni物种相关的Lewis(L)酸位是噻吩的选择性吸附活性位;噻吩和环己烯在NiY分子筛中Brnsted(B)酸位上发生的质子化和低聚反应明显弱于HY分子筛。双探针分子竞争吸附研究发现,环己烯二聚体在NiY中强B酸位上的强化学吸附与噻吩存在显著的竞争吸附行为。另外,苯和噻吩在NiY上的竞争吸附现象在373K时明显减弱。由此,在选择性吸附脱硫过程中,减少吸附剂表面B酸中心可降低烯烃对噻吩的竞争吸附,另外适当提高吸附体系的温度可以有效避免芳烃对噻吩的竞争吸附。     

Effect of pretreatment of molasses and posttreatment of fermented broth in industrial production of ethanol

The aim of preclarification is to minimize sludge going to yeast separators. This purpose is partially fulfilled. However, it has been measured during the plant trial runs that preclarification does not noticeably improve fermentation. The aim of postclarification is to minimize sludge going to distillation. This purpose is well served as noted from the fact that cycle run of distillation columns using postclarification is three times longer (9–12 mo) as compared to the normal one (3–4 mo).     

Possibilities of determination of alteration degree of rocks by thermogravimetry

Rhyolite-rhyodacite tuff samples were analysed by X-ray powder diffraction, ICP-OES and thermogravimetric (TG) methods to determine mineral and major element composition as well as different types of bound water, respectively. Similarly to CIA values, some TG parameters (H₂O[I] — water released up to ca. 200–220°C; H₂O[III] — water loss above 500–550°C and H₂O[I+III]) show positive correlation to the amount of secondary minerals. Moreover, these parameters are in close positive correlation to CIA values. Our results suggest that TG determination of different types of bound water may serve as a useful tool for estimation and characterisation of alteration degree of rocks.     

Optimization of the Hydrolysis of Freshwater Polysaccharides

Abstract

Three techniques of acid hydrolysis are verified for their ability to efficiently hydrolyse freshwater polysaccharides. Polysaccharides isolated from two eutrophic lakes were hydrolysed rapidly as compared to model or marine polysaccharides. No single technique is 100% satisfactory for all polysaccharides (i.e. complete hydrolysis with no degradation). Hydrolysis by 0.1 M HCl appeared to give the best results while acceptable results were also obtained for 1.2 M H₂SO₄. The results suggest that it is prudent to hydrolyse freshwater polysaccharides under the least drastic conditions and for as short of a time as possible in order to minimize decomposition of the sample, (esp. uronic acids). Interferences due to humic acid; did not appear to increase as a function of hydrolysis time.     

Synthesis of a Pair of Derivatives of N-Methylpyrrole Polyamide

A pair of derivatives of tetrameric N-methylpyrrole polyamide were synthesized in order to develop a new method for the study of interaction of the polyamide derivatives with DNA. Indole acetic acid and nicotinic acid were introduced to the polyamide in the synthesized compound, which showed an expected red shift in the UV spectrum. These compounds may function as a potential tool in the detection of the polyamide binding to DNA.     

Study of the solid-state hydrolysis of chitosan in presence of HCl

Chemical depolymerization of chitosan was obtained in the solid state by means of gaseous HCl. This new method allowed us to simultaneously form the hydrochloric salt and saturate the hydration water with acid. The depolymerization was carried out by keeping the product at a given temperature for the desired time. The measurements of the molecular weight distributions demonstrated the ability to control the reaction and produce oligomers with chosen dimensions. This solid-state hydrolysis favors the presence of a four-fold distribution that can be related to the original morphology and crystallinity of the initial material. The effects of the hydrolysis on the crystallinity, the crystalline structure, and the supramolecular order of the obtained chitosans were also studied. Finally, the washing of the hydrolyzed products in concentrated alkaline or acidic media allowed us to eliminate the lowest DPs and thus to narrow the molecular weight distribution. In this case, the crystallinity was also increased up to values beyond 70%. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3181–3191, 1997     

Multi-instrumental analysis of asphalts of archaeological interest

Use was made of thermal and other techniques to characterise three native asphalt samples. The purpose was to support archaeological investigations reconstructing their thermal history and composition. The first sample (from a Roman quarry in central Italy) proved to have 37% impurities, no sign of oxidation or degradation and to have never been heated to above 100°C. The second sample (from a Roman ship sunk south of France) was pure, but partially oxidised, with a saturated fraction in its structure. Analyses of the latter sample, obtained from the eye of a Thracian bronze head, revealed that the asphalt had been heated to over 100°C and then mixed with natural wax.     

Acid hydrolysis of carboxymethylcellulose of low degree of substitution

Cotton cellulose was swollen in a sodium hydroxide solution and carboxymethylated by a two-bath method for different periods of time for each process. The kinetics of acid hydrolysis and the crystallinity of the swollen and carboxymethylated samples were measured. The proportion of broken bonds, rate constants for hydrolysis, and permeability of cellulose to hydrolyzing agents were calculated. The susceptibility of glycosidic linkages to acid hydrolysis was improved by carboxymethylation more than by swelling in alkali. The increased accessibility of carboxymethylcellulose to acid was regarded as a consequence of increased intra-and intercrystalline swelling and of the glycosidic bonds' weakness caused by the electron-attracting carboxymethyl group on the C-6 position.     

Some recent studies of the mechanisms of dehydration reactions of solids

Thermal Analysis, the central topic of this conference, is a technique that is widely used for the measurement of reaction rates and from which deductions can be made concerning the identity of the bond redistribution steps contributing to the chemical change being investigated. The mechanistic insights obtained from such studies enable us to identify the factors that determine reactivity and to understand theoretically the controls operating in chemical reactions. The present article points out, however, that kinetic data alone do not usually provide sufficient information to enable detailed identification of the sequence of steps through which reactants are converted into products.This review discusses recent research concerned with characterizing mechanisms within a group of solid state processes that has been the subject of extensive kinetic investigations (including thermal analyses): the dehydrations of crystalline hydrates. Conclusions from previous studies of reactions of this type have contributed extensively to the more general understanding of solid-state reactions. Here we discuss some mechanistic conclusions from a number of recent studies in the field and emphasize the value of complementing rate measurements with other relevant observations, including microscopic examinations of the textural modifications that accompany chemical changes.The sincere thanks of the author to all his collaborators cited in the reference list and to M. E. Brady for his helpful contributions during the preparation of this review.     

ESR study of the effect of fluorinated alcohols on magnetic resonance parameters of spin-adducts of phosphoryl radicals with products of cycloaddition of substituted nitriloxides to C60

Regioselectivity of the addition of phosphoryl radicals to the products of cycloaddition of substituted nitriloxides to fullerene C₆₀ was studied by ESR spectroscopy. The effect of fluorine-containing alcohols on the magnetic resonance parameters of the isomers of spinadducts of phosphoryl radicals located at different distances from the five-membered heterocycle was studied. Complexation of the obtained isomeric spin-adducts with (CF₃(₃COH leads to a 3 to 5 G increase in the constant of hyperfine interaction with the phosphorus nucleus, which makes it possible to observe additional lines in the ESR spectrum. Deceased. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1808–1811, September, 1999.     

Characterization of the barrier properties of composites of HDPE and purified cellulose fibers

The present work presents and discusses the interrelation between composition, morphology, thermal history, mechanical and barrier properties to oxygen and limonene of composites of HDPE/MA-PE/cellulose fibers of significant interest in, among others, food packaging applications. From the overall results, it was observed that increasing the loading of purified alpha-cellulose fibers in the polyethylene matrix beyond 10 wt.% led to a decrease in the permeability coefficient of d-limonene, effect which was found to be primarily related to a decrease in the overall solubility of this strongly plasticizing aroma component. On the other hand, the oxygen permeability was found to decrease to a significant extend with increasing fiber content beyond 5 wt.%, but this effect was more strongly ascribed to a significant decrease in the diffusion coefficient. Therefore, the fibers are thought to generate a more tortuous path for the non-interacting gas molecules to travel across the composites thickness, even when tested at high relative humidity conditions. Optimum fiber loading levels in terms of overall property balance were found to be around 20 wt.%.     

Application of a dynamic method of minimisation in the study of reaction surfaces

This paper describes the application of Snyman's dynamic minimisation method to a fitted potential surface of H₃. Comparisons are made with conventional algorithms. A method is described to extend Snyman's method so that it will find only a particular kind of stationary point. It is emphasized that this method enables saddle points to be found without having to resort to approaches based on trial and error.     

两种含杂环的氨基萘醌化合物的合成

以2,3-二氯-1,4-萘醌为主要原料,分别与吗啡啉和糠胺在一定条件下反应生成2种含杂环的氨基萘醌类化合物。2,3-二氯-1,4-萘醌与吗啡啉及2,3-二氯-1,4-萘醌与糠胺物质的量比均为1∶2,反应温度为60℃,溶剂为乙醇。2,3-二氯-1,4-萘醌与吗啡啉反应时间为1 h,产物2-氯-3-吗啡啉基萘-1,4-二酮(a)收率为93.5%;2,3-二氯-1,4-萘醌与糠胺反应时间为4 h,产物N~2,N~3-二(2-呋喃甲基)-1,4-二((2-呋喃甲基)亚胺)-1,4-二氢化萘-2,3-二氯化铵(d)收率为46.7%。对产物进行IR、Uv、MS和H-NMR等分析表征。     

Estimation of Sorption Parameters of Solids by Means of Derivatograph Q

Derivatograph Q-1500D was completed with a partial vapour pressure control unit in order to study the sorption phenomena. The proposed arrangement allows to perform time consuming experiments at ambient atmospheric pressure in the temperature range 10–200°C.This revised version was published online in November 2005 with corrections to the Cover Date.     

Non-isothermal kinetic of oxidation of tungsten carbide

Tungsten carbide, WC, has shown dissimilar thermal behavior when it is heated on changeable heating rate and flow of oxidant atmosphere. The oxidation of WC to WO₃ tends to be in a single and slow kinetic step on slow heating rate and/or low flux of air. Kinetic parameters, on non-isothermal condition, could be evaluated to the oxidation of WC to heating rate below 15°C min⁻¹ or low flow of air (10 mL min⁻¹). The reaction is governed by nucleation and growth at 5 to 10°C min⁻¹ then the tendency is to be autocatalytic, JMA and SB, respectively.     

The effect of structural characteristics of porous hydrophobized electrodes on selectivity of electrolysis of organic substances

A theoretical study of the effect of the electrode structure on the electrosynthesis in hydrophobized electrodes (HPE) for a case of further electrochemical conversion of the target product is performed by the example of nitromethane electroreduction to methyl hydroxylamine followed by its reduction to methylamine. The effect of the electrode structure on the selectivity of electrosynthesis in HPE was shown to be related to the effective diffusivity and conductivity.     

Efficient quantification of the importance of contacts for the dynamical stability of proteins

Understanding the stability of the native state and the dynamics of a protein is of great importance for all areas of biomolecular design. The efficient estimation of the influence of individual contacts between amino acids in a protein structure is a first step in the reengineering of a particular protein for technological or pharmacological purposes. At the same time, the functional annotation of molecular evolution can be facilitated by such insight. Here, we use a recently suggested, information theoretical measure in biomolecular design - the Kullback-Leibler-divergence - to quantify and therefore rank residue-residue contacts within proteins according to their overall contribution to the molecular mechanics. We implement this protocol on the basis of a reduced molecular model, which allows us to use a well-known lemma of linear algebra to speed up the computation. The increase in computational performance is around 10(1)- to 10(4)-fold. We applied the method to two proteins to illustrate the protocol and its results. We found that our method can reliably identify key residues in the molecular mechanics and the protein fold in comparison to well-known properties in the serine protease inhibitor. We found significant correlations to experimental results, e.g., dissociation constants and Φ values.     

Dechlorination of contaminated sediments of Ionian Sea

Natural dredged sediments contaminated by PCBs from the heavy industrialized harbor of Taranto (S. Italy) on the Ionian Sea, previously dechlorinated by mechanical activation in different ball mills (SPEX and AGO-2), together with synthetic mixtures emulating the contaminated sediments, were submitted to thermogravimetric and calorimetric measurements as well as to X-ray powder diffraction in order to clarify the dechlorination reaction mechanism. Both major sediment components, i.e., carbonates and clay minerals, were found to be affected by the mechanical activation. As trace pollutants like PCBs are concentrated in clays, the mechanical activation of sediments increases the release of pollutants yielding a more active decontamination. DSC results were less informative as calorimetric peaks from different thermal events were found to overlap.     

Thermal explosion of nitrophenates of transition metals

The thermal decomposition studies on nitrophenates of copper, nickel and cobalt have been undertaken,-t curves show dehydration of these compounds at lower temperatures whereas dehydration cum decomposition seem to occur at higher temperatures leading to oxidative combustion of aromatic part. NO₂ gas is evolved during decomposition which seems to be responsible for oxidative reactions leading to detonation. The explosion temperature and velocity of detonation have been found to be linearly related with the number of nitro groups. The mechanism of thermal explosion has also been discussed.Thanks are due to Prof. S. Giri for providing laboratory facilities; and Aeronautics R&D Board, Ministry of Defence for financial assistance. Authors are also grateful to Shri I. P. S. Kapoor for helpful discussions.