Kinetic Models of Batch Sorption in a Limited Volume

Russian Journal of Physical Chemistry A - The batch sorption kinetics described by a nonlinear equation with a variable equilibrium parameter for the interface was considered. It was shown that a...     

A Pseudo-Second Order Kinetic Equation for Sorption Processes

Russian Journal of Physical Chemistry A - The problem of substantiating a pseudo-second order equation in the kinetics of sorption processes is considered. A simple way is presented of transforming...     

Studies on Batch Sorption Methodologies: Eu Sorption onto Kivetty Granite

Six different methodological features of the batch sorption experiment were investigated using ¹⁵²Eu, Kivetty granite, saline water with initial pH of 8.5, 9 and 10, [Eu]tot=5·10^-7M, S:L = 1:20, pre-washing of granite, occasional shaking, centrifugation, wall sorption correction with separate tubes. This gave final Rd= 8.3±2.1, 7.3±2.6 and 8.6±3.7m³/kg at 6 months for each pH, respectively. Then [Eu]tot and S:L were varied, filtration was compared with centrifugation, separate tubes for wall sorption was compared with wall desorption, pre-washing of granite was compared with no washing and two shaking methods were compared. Two of the investigated methodological features gave too large apparent Rd due to: 1) filter sorption, and 2) low radiotracer concentration, leading to detection problems.     

溶液间歇结晶动力学模型的新型算法

针对溶液间歇结晶过程, 基于粒数衡算理论和ΔL定律, 借助分段归纳的研究方法, 建立了晶体粒度分布函数各阶矩量的关联式. 利用此关联式, 对文献模型中晶体粒度分布函数的二阶矩量进行替换, 并结合计算机程序设计, 可直接拟合得到结晶体系的成核和生长动力学参数, 从而为结晶动力学模型的求解建立了一种新型算法. 通过对文献报道的硝酸钾水溶液和混二甲苯溶液两组结晶数据的模拟计算, 结果发现, 运用该算法求取的结晶成核和生长动力学参数均与传统的矩量变换法的计算结果相近, 但新建算法无需预知结晶体系的总传热系数.     

A New Kinetic Model for Water Sorption Isotherms of Cellulosic Materials

Summary: Some natural fibres like flax, hemp and others show excellent mechanical properties which make them a promising choice for the reinforcement of polymers. For natural fibre reinforced composites, hydrophilicity is a problem with respect to dimensional changes, fibre to matrix adhesion and long term stability. The interaction of differently prepared and modified fibres with water vapour has been investigated by dynamic vapour sorption. It has been found that the sorption and desorption kinetics of cellulosic fibres can be excellently fitted by assuming two parallel, independent first order processes. This empirical model, defined here as the “Parallel Exponential Kinetics” model (PEK-model), reveals two distinct mechanisms with slow and fast exchange of water vapour respectively, related to different sorption sites. The specific sorption mechanisms are represented by individual sorption-desorption isotherms as components of the total isotherms. The results suggest a relation to the differing types of amorphous regions in the fibres and/or to the different states of “bound” or “free” water, discussed for hydrophilic materials. The PEK-model proved to be consistently applicable for sorption and desorption over the whole humidity range, and also for all tested cellulose fibres. It is especially useful for a clearer distinction of different fibre types or modifications and can be successfully used for an extended fibre characterization.     

Single-Microparticle Injection and Microabsorptiometry: Direct Analysis of Sorption Processes

Sorption processes of methylene blue in a single silica gel microparticle in an aqueous solution was kinetically analyzed by a new technique combined with the microcapillary injection/manipulation and microabsorptiometry of the single particle. The observed sorption rates were analyzed in terms of the solute concentration in water and the particle size. The sorption processes were governed by diffusion of the solute in the particle. Copyright 2000 Academic Press.     

Using Kinetic Modeling and Experimental Data to Evaluate Mechanisms in PET-RAFT

Reversible deactivation radical polymerization (RDRP) techniques have become important tools for polymer chemists because they control the structure and are tolerant to functionality. Photoinduced polymerizations have seen a growing interest due to their mild conditions, as well as spatial and temporal control over the polymerization. Among these techniques, photoinduced electron/energy transfer reversible addition–fragmentation chain transfer polymerization (PET-RAFT) is one of the most widely investigated. While PET-RAFT is seen as an increasingly useful tool, there is still much to understand about the mechanism of this process. In particular, there are ongoing questions regarding the kinetic contribution of electron versus energy transfer. In order to better understand the mechanism, this work aims to use kinetic modeling along with experimental data to help determine the likelihood of the proposed mechanisms for the PET-RAFT process using the trithiocarbonate-mediated polymerization of methyl acrylate with fac-tris[2-phenylpyridinato-C²,N]iridium(III) as a photocatalyst. Simulation data show that electron transfer without a corresponding reduction pathway cannot explain the experimental kinetics, while energy transfer offers a good fit to experimental data. © 2019 Wiley Periodicals, Inc. J. Polym. Sci. 2020 , 58, 139–144     

Calculation of Kinetic Parameters for Crystallization Processes

In this work, kinetic data of crystallization processes have been determined by measurement of the intensities of reflection of X-ray diffraction spectra and modeled using the Avrami-Eroféev and Jander expressions. We have created a simple Microsoft Excel spreadsheet that allows students to calculate the kinetic data. Students will be able to calculate the kinetic parameters of any crystallization process, for example, hydrothermal crystallization of catalytic materials like zeolites. The possibility of using the spreadsheet with different models or expressions and discriminating among them is also validated by comparing the model results with experimental data (differential thermal analyses, DTA) from papers available in the recent literature.     

Sorption of Bisphenol A as Model for Sorption Ability of Organoclays

The arrangement of bisphenol A molecules into organoclays and their interactions with the intercalated surfactant were studied. The organoclays were prepared via solid-state intercalation of four cationic surfactants, such as dodecyltrimethyl-, tetradecyltrimethyl-, hexadecyltrimethyl-, and didodecyldimethyl-ammonium, as bromide salts, at different loading levels into the interlayers of two natural clays. The natural clays, the prepared organoclays, and the spent organoclays were characterized by X-ray powder diffraction, infrared spectroscopy, and scanning electron microscopy. X-ray powder diffraction measurements showed successive interlayer expansions of the d₀₀₁ basal spacing due to the intercalation of the cationic surfactants and the bisphenol A sorption. The increased d₀₀₁ basal spacing of the organoclays after bisphenol A sorption indicates that the molecules are integrated between the alkyl chains of the surfactant in the organoclays interlayers. Infrared spectroscopy was employed to probe the intercalation of the cationic surfactants and the sorbed bisphenol A. New characteristic bands attributed to the bisphenol A phenol rings appear in the range 1518–1613 cm⁻¹ on the infrared spectra of the spent organoclays, proving the presence of bisphenol A in the hydrophobic interlayers. Scanning electron microscopy of the organoclays before and after BPA sorption shows that their morphology becomes fluffy and that the presence of the organic molecules expands the clay structure.     

CSTR和批式反应器中酶法拆分萘普生的比较

比较了批式反应器和连续流动搅拌反应器中酶动力学拆分萘普生的不同之处。从宏观反应器平衡角度,推导出了在ＣＳＴＲ中不同于在批式反应器中的酶立体选择性,产物对映体过量值和反应转化率的定量关系式,并通过脂肪酶催化的萘一甲酯的不对称水解反应得到了证实。     

Investigating Cu(0)‐Mediated Polymerizations: New Kinetic Insights Based on a Comparison of Kinetic Modeling with Experimental Data

A kinetic model is developed mimicking experimental results obtained via detailed kinetic investigation of Cu⁰‐mediated LRP processes of butyl acrylate in variable solvents at 50 °C. In all polymerizations, a pronounced offset in the $\overline {M} _{{\rm n}} $ versus conversion profile is observed. The kinetic modeling predicts that conventional FRP is responsible for a high molecular weight fraction of terminated polymer. The initial $\overline {M} _{{\rm n}} $ offset is congruent with a relatively slow establishment of the controlling equilibrium. Kinetic modeling and experiments demonstrate that the conversion versus time data cannot be adequately described by a first‐order kinetic analysis. For selected rate coefficients (k_a, k_d, and k_{dis_cu}) a range is assigned, which affords a well controlled polymerization.

     

Kinetic Study of the Thermopolymerization of Furfuryl Methacrylate in Bulk by Mathematical Modeling. Part A: Simulation of Experimental Data and Sensitivity Analysis of Kinetic Parameters

Mathematical modeling of the thermopolymerization of FM and CMFMA was carried out using a cross‐linked kinetic model proposed for the photo‐initiated polymerization of acryl‐furanic compounds. In this model, the photochemical initiation step was substituted by a thermal one and it was assumed that the constant of radical termination was time‐dependent, which allowed the gel effect (Trommsdorff) at high monomer conversion to be simulated. Optimization of all kinetic constants was achieved and the results of simulation suitably fitted the experimental data of the monomer conversion. The contribution of each step in the mechanism and its dependence on the experimental conditions were estimated by a sensitivity analysis technique.

     

Experimental studies of the Progressing Batch Reactor

The data obtained in the single reactor experiments has shown the use of 1/2-in. chips to produce results that are reliable and repeatable. These data are not sensitive to variations in wood chip packing or prehydrolysis procedures. The latter is important since multireactor studies will try various prehydrolysis strategies while investigating the operational characteristics of a multireactor system. The possible importance of hydrodynamics within the wood chip bed was demonstrated by the data from the 1/4- and 1/8-in. chip experiments. The importance of shrinking wood chip bed was demonstrated by the reactor’s inferior performance in the upflow versus the downflow mode. A hydrodynamic study should be undertaken to investigate these phenomena. This study can proceed concurrently with work on a tworeactor system that can give a preliminary glimpse at the operation and benefits of a multireactor system.     

Residue Desulfurization: A Kinetic Model Approach

In the refining of petroleum residue, sulfur removal is an important objective to produce low sulfur fuel oil and to obtain a suitable feed for residue catalytic cracking. The increasing severity of sulfur specifications for fuels implies the optimization of heavy residue processes, which in turn requires improving knowledge on reaction mechanism. The goal of this study is to contribute to a better understanding of the reactions in the process desulfurization section and to develop a kinetic model. To carry out this, hydrotreatment pilot tests were performed on demetallized residues. The products were investigated using SEC, ¹³C NMR, liquid chromatography and elemental analyses.     

Isoconversional Kinetic Analysis of Thermally Stimulated Processes in Polymers

Summary: Isoconversional kinetic analysis involves evaluating a dependence of the effective activation energy on conversion or temperature and using this dependence for making kinetic predictions and for exploring the mechanisms of thermally stimulated processes. The paper discusses major results obtained by the authors in the area of the isoconversional analysis of polymer kinetics over the past decade. It provides a brief introduction to isoconversional methods and surveys the impact made by isoconversional analysis in several application areas that include kinetic predictions, thermal degradation, crosslinking (curing), glass transition, and glass and melt crystallization. It is concluded that isoconversional analysis has been used broadly and fruitfully because it presents a fortunate compromise between the single‐step Arrhenius kinetic treatments and the prevalent occurrence of processes whose kinetics are multi‐step and/or non‐Arrhenius.

An isoconversional method applies the Arrhenius equation to a narrow temperature region, ΔT related to a given extent of conversion.     

高岭土吸附稀土元素的实验研究

为更好了解粘土矿物对稀土元素(REE)的吸附及其控制因素,进行了不同溶液介质条件(平衡时间、REE含量、pH＝3～6.5) 1 g·L-1高岭土对REE吸附的系列实验.结果表明: 稀土在较短时间内(24 h)吸附/解吸过程达到平衡;Langmuir吸附等温线能模拟REE在高岭土上的吸附,总的趋势是REE含量越高,分馏越不明显;此外,pH对REE吸附和分馏有很大影响,REE分配系数随pH值增加而增加,且在pH近中性时,出现了明显的重稀土比轻稀土更多的被吸附.