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).     

Glyoxal Ozonation Process in Aqueous Solution

The process of ozonation of glyoxal in aqueous solution has been studied by following its chemical and kinetic evolution. Results show that the oxidative process leads to formation of carboxylic functions and carbon dioxide according to a constant selectivity ratio at varying conversion degree.. Comparison between the oxygen amounts of reaction products and the corresponding ozone consumptions reveals that molecular oxygen takes part in the reaction process. System behavior is explained on the basis of radical reaction mechanism.     

The role of temperature in copper electrocrystallization in ammonia-chloride solutions

This paper presents the analysis of temperature effect on the copper electrocrystallization process from the stainless steel/Cu(II)-Cu(I)-NH₄Cl-NH₃-H₂O system. Electrochemical techniques and scanning electron microscopy with energy dispersion spectroscopy were employed. An increment in temperature had a favorable effect in increasing the kinetic and nucleation parameters, favoring the copper reduction on the stainless steel substrate. From the chronoamperometric study, it was possible to find the transfer coefficient (α), which does not have a significant variation with temperature, and the exchange current density (i₀) for different temperatures, where a 50.63 kJ/mol value was estimated for the activation energy. The potentiostatic study suggested the presence of two processes involved: an electron transfer reaction and a 3D nucleation—growth process, under combined charge transfer and diffusion limitations. In addition, an important current contribution could be accounted for on the basis of the existence of a capacitive component in the system. This capacitive behavior was associated to the oxide layer (Cr₂O₃)-chloride interactions on the stainless steel surface. Current transients analyses at different potentials, based on the models of: Milchev (low overpotential), Scharifker-Mostany (SM) and Heermann-Tarallo (HT) (high overpotential) allowed to obtain the values of nucleation parameters, such as: the nucleation rate constant (A), the active nucleation sites number (N₀), the stationary nucleation rate (I_st = A × N₀) and the nuclei saturation number (N_s). Finally, the deposits obtained were analyzed by SEM, showing an acceptable correlation between the nucleation parameters and morphology of the deposits obtained. An increment in temperature favored the growth of the cluster before the coalescence occurred.     

A variable reaction order model for prediction of curing kinetics of thermosetting polymers

Based on the study of the curing reaction of an fluorinated aliphatic cyanate ester resin using an isothermal Differential Scanning Calorimetric (DSC) method, a new kinetics model with variable reaction order was proposed to describe the curing of thermosetting resins in both the chemical controlled and diffusion controlled regions. α-T_g relationship was used to calculate the diffusion controlled reaction rate constant during cure. Then the chemical and diffusion rate constants were combined in the Simon-Gillham equation to model the overall rate constant for the entire reaction. By using the overall rate constant combined with the variable reaction order, a simple model can be built up for prediction of curing kinetics of thermosetting polymer in both the chemical and the diffusion controlled regions. The new model is simple, easy to use and has very good agreement with the experimental results.     

Fatty acid esterification by reactive distillation: Part 2—kinetics-based design for sulphated zirconia catalysts

In a previous study on the basis of reaction equilibrium, it was demonstrated that the synthesis of fatty acids esters of heavy alcohols by catalytic reactive distillation (RD) is basically feasible. Presently, the analysis is expanded to the kinetics-based design applied to the synthesis of 2-ethylhexyl dodecanoate. Experimental data for a super-acidic sulphated zirconia catalyst are employed. It is shown that this catalyst is highly selective even for the high alcohol/acid ratios as prevail in a RD column. To avoid catalyst deactivation, liquid-liquid segregation into an organic and an aqueous phase must be prevented, and operating temperatures beyond must be chosen. A kinetic model based on liquid activities is proposed, with parameters determined from both kinetic and equilibrium measurements. A typical column design has 13 reactive stages with a catalyst loading of , temperature profile of 400-, and a space velocity of for 99.9% purity product ester. A modified Damköhler number is proposed.     

Development of a comprehensive free radical photopolymerization model incorporating heat and mass transfer effects in thick films

A comprehensive kinetic model describing photopolymerization is developed which allows variation of temperature, species concentrations, and light intensity through the thickness of a photopolymerized film. Heat and mass transfer effects are included, as is the generation of heat by both reaction and light absorption. In addition to initiation, propagation, and termination mechanisms, both primary radical termination and inhibition are incorporated into the model. The possible presence and diffusion of an inert solvent are also accounted for. Thus, the model is useful for examining complex polymerization kinetics and behavior in industrially and commercially important thick film photopolymerizations, such as the curing of contact lenses, dental restorative materials, photolithographic resists, and optoelectronic coatings. The comprehensive model is used to predict polymerization rate, temperature, and conversion profiles in a variety of systems. The effects of heat generation and the thermal boundary conditions are explored, with the result that heat generation in thick samples leads to greatly increased conversions approaching 100 percent. Increased temperature in these samples also may lead to the appearance of two rate maxima, with the first due to the temperature increase and the second caused by the autoacceleration process. The magnitude of the temperature increase, along with the resultant effects, is more pronounced in insulated systems.     

Intensification of nitrous acid oxidation

An alternative solution to the reduction of a discharge of residual nitric oxide and nitrogen dioxide into atmosphere has been proposed. Instead of using methane or ammonia for SCR or gas absorption into alkali solutions, which are the most popular treatment methods of tail gases, now the use of powerful oxidant—ozone capable of transforming nitrous acid and nitric oxides into nitrogen of the highest oxidation level—could be employed for this purpose. As the intensive oxidation and ozonation of nitrous acid is the heterogeneous gas-liquid process, the solubility of oxygen and ozone in HNO₂/HNO₃ aqueous solution was necessary to be determined. Variations of reaction rates depending on temperature, ozone dose and nitrous and nitric acid concentrations were studied experimentally. The kinetic model of the reactions, 2HNO₂+O₂→2HNO₃ and HNO₂+O₃→O₂+HNO₃, were proposed and the kinetic parameters (rate constants and activation energies) were estimated on the basis of experimental data in semi-batch laboratory gas-liquid contactor with the liquid phase drawn from an absorption column in the nitric acid plant. The determined kinetic parameters were then used in designing and modeling of the oxidation of nitrous acid using ozone-oxygen mixture in a continuous bubble column. The model consists of mass transfer kinetic equations and material balance equations for the gas and liquid phases. The co-current flow of gas and liquid phases and the complex kinetics of chemical reaction in the liquid phase were taken into account. The variation of the following process conditions, flow rate, compositions of the gas and liquid phases, temperature, and pressure in the bubble column of different diameters and heights, were studied in numerical solutions of the proposed model.