Synthesis of SBS thermoplastic block copolymers in cyclohexane in the presence of diethylether used as a structure modifier

Diethylether (DEE) was used as a structure modifier during the synthesis of linear styrene-butadiene block copolymers of poly A-block-polyB-block-polyA type (SBS). The microstructures of synthesized polymers were analyzed, and the effect of DEE on polymerization kinetics was studied. Addition of DEE at 2 wt% concentration results in the highest styrene polymerization rate, while addition at 6 wt% concentration gives the highest butadiene polymerization rate. The vinyl content of the polybutadiene portion increases from 14 to 47% with an increase in the DEE concentration from 500 ppm to 10 wt% while thetrans- l,4 andcis-1,4 isomers decrease. For SBS polymer synthesized via a sequential method, the addition of DEE as a structure modifier minimizes the crossover deficiency which would otherwise result in a skewed molecular weight distribution with a higher polydispersity. For SBS polymers made via a coupling method, the coupling efficiency appears to be constant in a range of DEE concentration from 500 ppm to 1 wt% before declining with a further increase in DEE.     

Theoretical Aspects Of The Kinetics Of Competitive First Reactions Of Ozone In The O3/H2O2 And O3/UV Oxidation Processes

Kinetics of competition between the ozone direct reaction with compounds in water, ozone-hydroperoxide ion reaction leading to free radicals in the O₃/H₂O₂ process, and the photolysis of ozone in the O₃/UV process are discussed in terms of diffusion and reaction times to establish conditions for these reactions to be competitive. Film theory and chemical kinetic concepts then are applied to estimate initial rates of ozone absorption and consumption, removal rates of compounds present in water, and the importance of the radical oxidation path versus direct ozone and/or photolysis reactions.     

Crystallization behavior of oxyethylene/oxybutylene diblock and triblock copolymers

The crystallization behavior of poly(oxyethylene)-b-poly(oxybutylene) block copolymers with different compositions, morphologies and architectures (E_mB_n diblock copolymers and E_mB_nE_m, B_nE_mB_n triblock copolymers) were investigated and the effect of volume fraction and architecture on the crystallization temperature (T_c) in non-isothermal crystallization was determined. It is found that the E_mB_n diblock copolymers having long E blocks exhibit similar crystallization temperatures, irrespective of volume fraction and morphology, but for the block copolymers with shorter E blocks the crystallization temperature increases with both the volume fraction, φ_E, and the length, m, of the E block. Some block copolymers with extremely low T_c, which fall into the temperature range normally associated with homogenous nucleation, were chosen for time-resolved small-angle X-ray scattering (SAXS) and isothermal crystallization kinetics experiments. The results show that breakout crystallization occurs in all these block copolymers. Therefore, unlike E_mB_n/B_h blends, there is no obvious relationship between T_c and crystallization behavior in neat block copolymers and homogeneous nucleation does not definitely lead to confined crystallization. The values of χ_c/χ_ODT for all the block copolymers with hex and bcc morphology were also calculated. It is found that all the block copolymers have χ_c/χ_ODT<3, in agreement with the previously reported critical value and consistent with their breakout crystallization behavior.     

A comparative study between chloride and calcined carbonate hydrotalcites as adsorbents for Cr(VI)

Hydrotalcite-type solids with different metal ions within the layers (M^II = Mg or Zn and M^III = Al and/or Fe) and carbonate or chloride between them have been synthesized. Chloride-LDHs and the solids obtained upon carbonate-LDHs calcination have been evaluated in the adsorptive removal of Cr(VI) from aqueous solutions. All the adsorption tests were carried out at 30 °C following two different stirring conditions: a) using a thermostatic bath with mechanical stirring at a speed of 52 rpm or b) in a sonicator bath under ultrasound waves. It was observed that no significant difference in the amount of adsorbed chromate is produced in both cases but the time spent to reach the equilibrium is much lower when the adsorbent/adsorbate mixture is submitted to ultrasounds. In all experiments L-type adsorption isotherms were obtained. The results show that chloride hydrotalcites are better adsorbents than calcined CO₃-hydrotalcites and in these last ones their adsorption capacity increases with increasing the surface area: MgAlFe > MgAl > MgFe > ZnAl.     

影响固态发酵速率的因素及其动力学

论述了固态发酵过程中基质的形态特性、基质含水量、通气速率与气体组成、发酵温度诸因素对发酵速率的影响；探讨了固态发酵过程动力学模型及其特征。     

The adsorption of dyes from aqueous solution using diatomite

Raw diatomite was calcined at 450 °C for dyes removal from aqueous solution. SEM and FTIR analysis show that the raw diatomite contains organic impurities, which are removed after the calcination. The impurities removal decreases the specific surface area and increases the average pore diameter of raw diatomite, while improves its adsorption capability of dyes. The adsorption isotherm and kinetics experiments of methylene blue onto calcined diatomite were then carried out to investigate the adsorption property. It shows that the adsorption capacity of methylene blue is about 50 mg/g. The adsorption isotherm was fitted by the Langmuir, Freundlich and Redlich-Peterson models, which reveals that the Redlich-Peterson isotherm is the best one. Two kinetic models, pseudo-first order and pseudo-second order, were rearranged for expediently investigating the adsortpion mechanisms. Fitting results show that the pseudo-first-order model is better in describing the adsorption process.     

C207甲醇合成铜基催化剂本征失活动力学

一、前言工业生产中广泛使用的甲醇合成铜基催化剂具有活性高、选择性好、起始活性温度低等优点。但铜基催化剂抗毒性能差,影响了它的使用寿命。铜基催化剂的主要毒物是原料气中所含的 H_2S。铜基催化剂 H_2S 中毒失活研究,国内未见报道,美国的 Wood 等和 Rdvodic 等作过一些研究。本文通过对国产 C207铜基催化剂硫化氢中毒失活动力学的研究,建立描述活性衰退过程的失活动力学方程,得到活性与硫化     

A SIMPLE METHOD FOR STUDYING THE KINETICS OF GAS-SOLID REACTIONS IN A FLUIDIZED BED REACTOR

A methodology for studying the kinetics of gas-solid reactions in a fluidized bed reactor is presented. This procedure is based on the analysis of the response of the system (flue gases) when batches of solids of different weight are added to the reactor. The method has been applied to the study of limestone particle calcination. The calcination rate constants obtained are in good agreement with those found in the literature. The method offers the advantage of simplicity and avoids the use of model assumptions or empirical correlations.     

Prediction of mean square radius of gyration of tree-like polymers by a general kinetic approach

This paper describes a kinetic method to predict the z-average molecular mean square radius of gyration of tree-like polymers formed by irreversible reactions, assuming Gaussian chains. It is based on the population balance equations for the two-sided molecular distributions of pendant chains associated with every chemically distinguishable kind of bonds. An automated method for the solution of those equations is valid both before as well as after gelation for complex kinetic schemes. Examples of its use are presented with polycondensation systems leading to hyperbranched polymers, the anionic polymerization of mono- and divinyl monomers and a radical polymerization with terminal branching and transfer to polymer.     

Optimal Operating Conditions For Lab-Scale Ozonation Reactors

A method for the assessment of the optimal operating conditions for a mechanically stirred gas–liquid reactor is presented. The method exploits both fluid dynamic and chemical information. First, the behavior of the specific stirring power as a function of the stirrer speed allows singling out the dispersion region, in which the most efficient gas–liquid mass transfer is achieved. Inside this region, the analysis of experimental data obtained when considering a chemical system reacting at moderate Hatta numbers (i.e., Ha < about 2) allows determination of the rate constants and the fluid dynamic parameters (i.e., the mass transfer coefficient in the absence of chemical reaction and the characteristic diffusion time).