Carboxymethylation of dextran in aqueous alcohol as the first step of the preparation of derivatized dextrans

Carboxymethyldextrans (CMD) with a degree of substitution of carboxymethyl groups DS > 0.9 are precursors for the synthesis of derivatized dextrans termed CMDBS, which present heparin-like biological properties. Syntheses of CMD in water/organic solvent mixtures using monochloroacetic acid (MCA) and strong alkaline conditions allowed to obtain highly substituted CMD with good reproducibility and high yields. The influences of, respectively, individual concentrations of reactants, composition and temperature of reaction medium, and allowed reaction time have been examined. The most favorable conditions for dextran carboxymethylation were obtained with 3.8 M NaOH and a [MCA]/[dextran] ratio of 2.5, allowed to react at 60°C for 90 min, in a reaction medium consisting of a tert-butanol/water (alternatively isopropanol/water) 85 : 15 (v/v) mixture. A DS of about 1.0 was obtained in one step, as compared to a DS less than 0.6 when using aqueous conditions. Improvements on overall CMD substitution levels (up to DS of 1.47) were achieved by merely repeating the reaction i. e. using the CMD products of the first reaction as substrate in the second.     

Kinetics and thermal characterization of thermoset cure

The differential scanning calorimeter (Perkin-Elmer DSC-1) is used to characterize the cure of a general-purpose polyester during isothermal and scanning experiments. The technique is based on a new proposed model for the kinetics of isothermal cure. The model yields results which are in good agreement with experimental isothermal rate of reaction and integral heat of reaction data. It also gives some information about the residual reactivity of the sample after an isothermal cure experiment. With the aid of the proposed kinetic model, it is possible to obtain integral heats of reaction and rates of heat generation at different temperatures during a scanning experiment. The difference between the rate of heat input to the sample and the heat of reaction at any instant during scanning may be used to calculate the specific heat of the sample at the same instant. Specific heat data show two maxima during each scanning experiment. These maxima may be associated with transitions occurring during cure in the melt and rubbery states.     

Kinetics modelling of Fischer-Tropsch synthesis over an industrial Fe-Cu-K catalyst

The kinetic experiments of Fischer-Tropsch synthesis (FTS) over an industrial Fe-Cu-K catalyst are carried out in a micro-fixed-bed reactor under the conditions as follows: temperature of 493-542 K, pressure of 10.9-30.9 bar, H₂/CO feed ratio of 0.98-2.99, and space velocity of 4000-10?000 h⁻¹. The effects of secondary reactions of olefins are investigated by co-feeding C₂H₄ and C₃H₆. A detailed kinetics model taking into account the increasingly proven evidence of the olefin re-adsorption mechanism is then proposed. In this model, different sites are assumed for FTS reactions and water gas shift (WGS) reaction, respectively. Rate expressions for FTS reactions are based on the carbide polymerisation mechanism, in which olefin re-adsorption is considered to be a reverse step of olefin desorption reaction. Rate expression for WGS reaction is based on the formate mechanism. An integral reactor model considering both FTS and WGS kinetics is used to describe the reaction system, and the simultaneous estimation of kinetic parameters is conducted with non-linear regression procedure. The optimal model shows that the rate determining steps in FTS reactions proceed via the desorption of hydrocarbon products and the adsorption of CO and the slowest step in WGS reaction is the desorption of gaseous carbon dioxide via formate intermediate species. The activation energies of FTS reactions and WGS reaction are in good agreement with literature values.     

Extension and evaluation of the integral model for transient pyrolysis of charring materials

In most numerical simulations of fire growth and fire spread, pyrolysis models are required to calculate the reaction of the solid material to an incident heat flux. Important results of the pyrolysis model are the mass release rate of combustible pyrolysis gases and the surface temperature. In this paper an integral model is evaluated for the prediction of pyrolysis of charring materials. An existing integral model is extended with a finite and semi‐infinite cooling state. In this state both char and virgin material are present but the pyrolysis reactions have been interrupted due to insufficient heat supply. The results show that such a cooling state can occur in flame spread calculations. Simulations with the integral model are further compared with the results of a moving grid model, which has the same physical basis. Unlike the integral model, the moving grid model does not require any assumption for the temperature profile in the solid. The influence of the quadratic assumed temperature profile in the integral model on the accuracy of the predictions of the mass release rate of pyrolysis gases is evaluated for several cases. It is shown that the integral model has problems with sudden variations of the external heat flux. Copyright © 2005 John Wiley & Sons, Ltd.     

On facilitated computation of mesoscopic behavior of reaction‐diffusion systems

Various cellular and subcellular biological systems occur in the conditions where both reactions and diffusion take place. Since the concentration of species varies spatially, application of reaction‐diffusion master equation has served as an effective method to handle these complicated systems; yet solving these equation incurs a large CPU time penalty. Counter to the traditional technique of generating many sample paths, this article introduces a method which combines Grima's effective rate equation approach (Grima, J Chem Phys. 2010;133:3) with a linear operator formalism for diffusion to capture averaged species behaviors. The formulation also shows correct results at various choices of compartment sizes, which have been found to be an important factor that can affect accuracy of the final predictions (Erban, Chapman, Phys Biol. 2009;6:4). It is shown that the method presented allows the computation of the mesoscopic average of reaction‐diffusion systems at considerably accelerated rates (exceeding a thousand fold) over those based on sample path averages. © 2017 American Institute of Chemical Engineers AIChE J, 63: 5258–5266, 2017     

Monitoring the reaction progress of a high‐performance phenylethynyl‐terminated poly(etherimide). Part I: Cure kinetics modeling

The cure kinetics of a phenylethynyl‐terminated poly(etherimide) are examined via differential scanning calorimetry (DSC) measurements. Isothermal holds at temperatures ranging from 325°C to 360°C provided the necessary information to develop reaction kinetics models using both first‐order reaction kinetics and combination reaction kinetics. The first‐order reaction kinetics model works well for quick estimates of degree of cure versus time over the experimental temperature range. However, significantly more accurate predictions of degree of cure versus time were provided by the combination reaction kinetics model. The lack of accuracy in the first order model is due to the fact that the reaction cannot be described by a simple order. The experimental procedures followed to obtain the cure kinetics data and the construction of the models from this data are described; the predictions of these models are compared with the experimental results.     

Kinetic modeling of non-hydrocarbon/nitric oxide interactions in a flow reactor above 1,400K

The reduction of nitric oxide by reaction with non-hydrocarbon fuels under reducing conditions at comparatively higher temperature has been studied with a detailed chemical kinetic model. The reaction mechanism consists of 337 elementary reactions between 65 chemical species based on the newest rate coefficients. The experimental data were adopted from previous work. Analyses by comparing existing experimental data with the modeling predictions of this kinetic mechanism indicate that, at comparatively high temperature, apart from the reaction path NO→HNO→NH→N₂, NO+N→N₂ is also prominent. In the presence of CO, NO is partly converted to N by reaction with CO. Based on present model, the reduction of NO at high temperature, which was usually underestimated by previous work, can be improved to some extent. This work was presented at the 7 ^th China-Korea Workshop on Clean Energy Technology held at Taiyuan, Shanxi, China, June 26–28, 2008.     

Étude de l'hydrogénation sélective du cyclopentadiène sur l'aérogel Cu/Al2O3 fluidisé

This work was conducted to evaluate the use of Cu/Al₂O₃ aerogel for the selective hydrogenation of the cyclopentadiene. Aerogel particles belonging to the C group of Geldart's classification, fluidize via a discrete clustering process above a minimum superficial velocity of 0.04 m/s. A kinetic study of the cyclopentadiène hydrogenation was performed on an integral reactor. The kinetic data suggest that the rate model can be represented by an equation corresponding to the Rideal—Eley mechanism. The reaction between gaseous hydrogen and the cyclopentadiène adsorbed on the catalyst surface is, in this mechanism, the controlling step. Because of the low activity of the catalyst, several reactor models (homogeneous and heterogeneous) were able to describe the experimental conversion rates observed in a small pilot fluidized bed reactor. However, the single phase plug flow model, which conforms more to the pseudo-homogeneous behaviour of the bed, was the most appropriate based on statistical discrimination.     

Analysis of a carbon membrane reactor: from atomistic simulations of single-file diffusion to reactor design

We study the dehydrogenation of iso-butane in a membrane reactor with carbon membranes; these are molecular sieves with pores of molecular dimensions. To provide information on the transport laws of the various components, for reactor design purposes, we studied the separation in a membrane module either by maintaining the shell-side under lower pressure (or under vacuum) or by sweeping it with an inert diluent stream. The purpose of this work is to derive multi-component flux expressions for single-file diffusion in these two modes of separation, using molecular mechanics calculations of the thermodynamics of molecular adsorption into, diffusion within and desorption from the pores, and apply them for reactor design. In the process we calibrate these expressions with integral measurements of separation in a membrane module. Good predictions of reactor performance are obtained for a reaction coupled with separation by sweeping the hydrogen with nitrogen but poor predictions were achieved for a reaction coupled with vacuum-driven separation. Reactor performance in the former mode is better due to excellent transport selectivity, which we attribute to mutual blocking of counter-diffusion by nitrogen and hydrocarbons.     

Autothermal reforming of methane on rhodium catalysts: Microkinetic analysis for model reduction

Methane autothermal reforming has been studied using comprehensive, detailed microkinetic mechanisms, and a hierarchically reduced rate expression has been derived without apriori assumptions. The microkinetic mechanism is adapted from literature and has been validated with reported experimental results. Rate determining steps are elicited by reaction path analysis, partial equilibrium analysis and sensitivity analysis. Results show that methane activation occurs via dissociative adsorption to pyrolysis, while oxidation of the carbon occurs by O(s). Further, the mechanism is reduced through information obtained from the reaction path analysis, which is further substantiated by principal component analysis. A 33% reduction from the full microkinetic mechanism is obtained. One-step rate equation is further derived from the reduced microkinetic mechanism. The results show that this rate equation accurately predicts conversions as well as outlet mole fraction for a wide range of inlet compositions.     

甲醇制烯烃反应动力学

在固定床等温积分反应器内进行了甲醇制烯烃反应动力学研究,借助集总动力学的概念,充分考虑到水和积炭对反应过程的影响,得到甲醇制烯烃反应动力学模型方程.采用Runge-Kutta法求解动力学微分方程,并优化动力学参数,最终得到了可计算各集总组分反应速率的总动力学方程.然后根据乙烯、丙烯、丁烯相互之间的比值随温度的变化规律,分别计算出乙烯、丙烯、丁烯在任一条件下的反应速率方程.通过统计检验及计算值与实验值的比较,结果较为满意.     

FUNDAMENTAL MODEL OF TRANSPORT AND REACTION IN A CYLINDRICAL CATALYST PORE

The kinetic theory of gases is used to arrive at integral equations which govern free molecular flow and heterogeneous kinetics in a single, cylindrical, isothermal, uniform catalytic pore. The formulation is in terms of reactant fluxes to the catalytic surface and overall or reactive sticking factors. Focus is on simple m-th order reactions which depend on the surface concentration of a single species. Effectiveness factors for the pore, as well as reactant flux profiles obtained using this fundamental model, are compared to conventional continuum diffusion-reaction model predictions of effectiveness factors and reactant concentration profiles. There are distinct differences between the predictions of the two models for moderate to high sticking factors (0·1 to 1). For very small sticking factors, as commonly found in practical catalytic reaction systems, predictions of both models are essentially the same. The widely used continuum diffusion-reaction method provides good predictions of effectiveness factors and reactant concentration profiles, although it is not rigorous in its treatment of species transport.     

基于模糊HSE评价的多目标反应路径综合方法

为在过程早期获取HSE综合性质优良的反应路径,提出了基于模糊HSE评价的多目标反应路径综合方法。全面考虑HSE因素,形成了HSE指标结构,通过设定指标的隶属度函数,建立模糊推理系统,应用层次分析法（analytic hierarchy process,AHP）确定指标的权重因子,形成了模糊HSE评价方法。基于模糊HSE评价体系,建立以安全、环境和健康为目标函数的多目标优化模型,求解得到优良的反应路径组合。应用于萘甲胺反应路径综合实例,定量得到了反应路径及其HSE目标函数值,为过程早期的路径优选提供定量数据。     

Berries and Their Polyphenols as a Potential Therapy for Coronary Microvascular Dysfunction: A Mini-Review

Ischemia with no obstructive coronary artery disease (INOCA) is a common diagnosis with a higher prevalence in women compared to men. Despite the absence of obstructive coronary artery disease and no structural heart disease, INOCA is associated with major adverse cardiovascular outcomes as well a significant contributor to angina and related disability. A major feature of INOCA is coronary microvascular dysfunction (CMD), which can be detected by non-invasive imaging and invasive coronary physiology assessments in humans. CMD is associated with epicardial endothelial-dependent and -independent dysfunction, diffuse atherosclerosis, and left-ventricular hypertrophy, all of which lead to insufficient blood flow to the myocardium. Inflammatory and oxidative stress signaling, upregulation of the renin-angiotensin-aldosterone system and adrenergic receptor signaling are major drivers of CMD. Treatment of CMD centers around addressing cardiovascular risk factors; however, there are limited treatment options for those who do not respond to traditional anti-anginal therapies. In this review, we highlight the ability of berry-derived polyphenols to modulate those pathways. The evidence supports the need for future clinical trials to investigate the effectiveness of berries and their polyphenols in the treatment of CMD in INOCA patients.     

Thin film flow over structured packings at moderate Reynolds numbers

A model describing the dynamic evolution of waves on laminar falling wavy films at low to moderate Reynolds numbers (Re<30) over corrugated surfaces is presented. This model is based on the integral balance method, which is used to simplify the analysis by assuming a parabolic velocity profile within the bulk of the film. The predictions of this model are compared to those obtained from a computational fluid dynamics (CFD) code for which no assumptions regarding the film velocity profile are made. The film evolution profiles, obtained via numerical solution of the model equations, are used to calculate the ratio of film interfacial area to that of the substrate. The model predicts suppression of wave growth on a corrugated surface. The model is also used to predict the effect of packing geometry on the flow characteristics, which may improve packing design. Solutions obtained for Re∼200 using the CFD code demonstrate the degree of fluid accumulation within the ‘valleys’ of the structured substrate wherein re-circulation occurs.     

SUPERCRITICAL AND SUB-CRITICAL FLUID SOLVENT EFFECTS ON A DIELS-ALDER REACTION

The effect of pressure on the measured bimolecular rate constant of the Diels-Alder reaction between maleic anhydride and isoprene was investigated in supercritical CO₂ and sub-critical propane. The reaction was carried out at 35°C in CO₂ and 80°C in propane. Measured bimolecular rate constants are also compared to predictions from the thermodynamic pressure effect using transilion state theory and the Peng-Robinson equation of state. The rate constants in supercritical C0₂ agreed closely with the thermodynamic pressure effect predictions over the entire pressure range. Furthermore, the mole fraction based rate constants were found to vary linearly with the density of the solution. The rate constants in the sub-critical propane solvent significantly diverged from the thermodynamic pressure effect predictions and were found to deviate from this linear density dependence at the lower pressures studied. The results are interpreted in the context of local reactant concentrations about the reacting maleic anhydride and solvent-solute and cosolvent-solute interactions.     

The effects of non-continuum hydrodynamics on the Brownian coagulation of aerosol particles

Most theoretical predictions of the rate of Brownian-induced coagulation have considered the continuum hydrodynamic resistance of the suspending gas or liquid as well as van der Waals and/or electrostatic forces. However, the mean-free path of the gas is comparable with the length scale at which van der Waals forces become important during the collision of two Brownian aerosol particles. We predict the initial rate of coagulation in a monodisperse aerosol driven by Brownian motion in the presence of van der Waals forces and non-continuum lubrication forces when the Knudsen number (ratio of the mean-free path to the particle radius) is small but non-zero. A comparison with experiments demonstrates the accuracy of the predictions and the importance of accounting for non-continuum effects to provide quantitative predictions of coagulation rates.     

Mechanical behavior of closed cell plastic foams used as cushioning materials

Two methods for the prediction of force–deformation curves of closed cell plastic foams at any strain rate from a limited number of experiments are described. These methods are based on the “modified Boltzman integral model” and on the “reference model.” Both methods use constitutive equations and experimentally determined parameters. The modified Botlzman integral model uses data obtained in a limited number of stress–relaxation experiments while the reference model uses a very limited number of stress–relaxation and one force–deformation curve data. Both models predict well the force–deformation curves, the reference model providing somewhat better predictions.     

Kinetic study of the direct causticization reaction involving titanates and titanium dioxide

The solid state reaction between titanium dioxide and sodium carbonate forming sodium titanates was investigated. Reactions between sodium carbonate and titanium dioxide and/or sodium tri-titanate play a key role in the direct causticization of kraft black liquor. Experiments were carried out in a microdifferential reactor made of quartz glass at varying temperatures up to a maximum of 880 °C. Kinetic data were obtained by measuring the release of carbon dioxide. The physical and chemical properties of the reactants and products were analysed in order to obtain a maximum understanding of the reaction path. Scanning electron microscopy (SEM) and the specific surface area of the reactants and products were applied for morphology determination. X-Ray diffraction (XRD) was employed to characterize the phase composition of the product. The results showed that 100% conversion can be obtained at temperatures above 830 °C. Different kinetic models were taken into consideration, such as the Jander and Valensi-Carter models for diffusion-controlled reaction rates and the phase-boundary model for first-order reaction kinetics. One model was based on the theory that the kinetics can be described by the phase-boundary theory at the beginning of the reaction but, as the reaction proceeds, the rate becomes diffusion controlled. This model gave a good fit to the experimental data collected at 840 °C. However, this model did not work as well at high temperature (880 °C) or at lower temperatures as at 840 °C. This was explained by the fact that the reaction path is different at these temperatures, i.e. other reaction products are involved.     

基于1-甲基-2,4-苯二脲路径的尿素法合成甲苯-2,4-二氨基甲酸甲酯反应研究

采用尿素法合成甲苯-2,4-二氨基甲酸甲酯(TDC)是一条绿色的工艺路线.其反应路径之一是以1-甲基-2,4-苯二脲(TBU)为中间产物,即2,4-二氨基甲苯(TDA)与尿素反应生成TBU,TBU再与甲醇反应得到TDC.首先对该路径进行了热力学分析,然后分别对两步反应进行了研究.对于TBU合成反应,适宜溶剂和催化剂分别为环丁砜(CBS)和乙酸锌;适宜反应条件为:反应温度130℃,反应时间7 h,n(TDA):n(Zn(OAc)2):n(Urea):n(CBS)=1:0.05:3.5:10.此时TDA转化率为54.3%,TBU选择性为73.3%.对于TDC合成反应,基于液相色谱-质谱和气相色谱分析结果,确定了反应组分.适宜的反应条件为:反应温度140℃,反应时间5 h,反应压力1.1 MPa,甲醇与TBU摩尔比为110:1.在该反应条件下,TBU转化率为100%,TDC选择性为60.4%.