Precise parameter estimation for chemical batch reactions in heterogeneous medium

A sequential experimental strategy for precise parameter estimation has been used in the case of liquid-liquid dispersions in batch-stirred tank reactors where slow chemical reactions take place. The mathematical model for a batch reaction in a stirred tank reactor is formulated as a system of non-linear differential equations standing for the mass balance of each component. Physical kinetic parameters and chemical kinetic parameters which arise from this model are estimated simultaneously. The estimation problem is posed as a weighted least squares problem and solved by using a standard Levenberg-Marquardt algorithm. In this work, we intend to show how it is possible to develop efficient experimental design strategies that lead to an accurate estimation of the parameters involved in phenomenological models and most particularly in kinetic models. Three design criteria for designing the experiments have been employed in order to increase the precision on the parameter estimates of the model. A standard non-linear sequential quadratic programming method ensures the determination of the operating conditions which define the experimental design. The well-known alkaline hydrolysis of esters in aqueous phase has been treated as a numerical application example.     

Solitary traveling waves in a heterogeneous medium with a chemical reaction

A correct method for constructing autowave solutions is proposed for single-temperature models of unsteady processes in a dissipative medium with Arrhenius type chemical reactions. It is based on extending the temperature range to 0 K and using the Kolmogorov-Petrovskii-Piskunov approach. Solutions that are not inconsistent with the Nernst theorem are selected from the obtained finite spectrum of autowave solutions. For a quasihomogeneous model of gas filtration in a dissipative heterogeneous medium with a single irreversible chemical reaction, such an autowave solution is unique. A nondimensional parameter is found whose critical value for the selected Zel’dovich number defines the existence condition for this self-similar solution. A criterion is obtained for the initial temperature range in which the chemical transformations in the reaction are negligibly small for autowave processes. Translated fromFizika Goreniya i Vzryva, Vol. 34, No. 3, pp. 29–36, May–June 1998.     

Fluorination in gaseous phase of carbon tetrachloride on aluminium fluoride catalyst: Kinetics and chemical mechanism

The fluorination in gaseous phase of carbon tetrachloride has been investigated on aluminium fluoride with the aim of defining the mechanism of the reaction on this catalyst. The reactor and the operating conditions, were chosen in such a way as to isolate the effects of diffusion analysing the single reaction steps. While for the process in liquid phase the kinetics appears to be controlled by the formation of activated complexes between carbon tetrachloride and the catalytic support, the selective adsorption of HF on the catalyst is more probably the controlling step when the reaction is carried out in gaseous phase.     

Partial oxidation of methane to methanol-comparison of heterogeneous catalyst and homogeneous gas phase reactions

Potential catalysts for the partial oxidation of methane to methanol have been synthesised and tested in high pressure annular reactors. Uranium oxide and molybdenum oxide catalysts and iron sodalite catalyst have been tested under the conditions reported in the patents and under conditions which allow comparison with reactions carried out in the gas phase. None of the catalysts tested showed an improvement on the gas phase results. It was found that the oxidative nature of the metal oxide catalysts is an inherent feature which reduces the selectivity to methanol.     

Flow reversal of reaction mixture in a fixed catalyst bed - a way to increase the efficiency of chemical processes

Various methods for increasing the efficiency of heterogeneous catalytic processes carried out in the forced unsteady-state regime are discussed. Increase in the efficiency may be caused by the influence of reaction medium on the catalyst and by the dynamic properties of the converter. Unsteady-state conditions can be created, e.g. when the direction of the reaction mixture flow is periodically reversed. In this case, temperature and concentration fields are formed in the catalyst fixed bed which are close to theoretical optimum values for a number of processes of great practical importance. Experimental data are reported which prove the efficiency of process performance (SO₂ oxidation on vanadium catalysts) in unsteady-state conditions.     

Ion exchange membranes and separation processes with chemical reactions

Recent research trends in the development of ion exchange membranes and their use in separation processes with chemical reactions are reviewed. Emphasis in research on the ion exchange membrane is trending toward analysis of micro-structure of the membranes and to development of new functionalized ion exchange membranes in response to industrial requirements. Separation processes with chemical reactions are discussed according to the following classifications: (1) double decomposition of electrolytes; (2) production of acid and base by bipolar ion exchange membrane processes; (3) separators for electrolysis; (4) separators for batteries; (5) use as solid polyelectrolytes; (6) active transport through ion exchange membranes; (7) acceleration of chemical reactions by ion exchange membranes; (8) carrier transport in ion exchange membranes; (9) transducers for electrical signals from chemical reactions; and (10) modified electrodes.     

负载金作为非均相催化剂催化选择性液相加氢反应的研究进展(英文)

The great potential of gold catalysts for chemical conversions in both industrial and environmental concerns has attracted increasing interest in many fields of research. Gold nanoparticles supported by metal oxides with high surface area have been recognized as highly efficient and effective green heterogeneous catalyst even at room temperature under normal reaction conditions, in gas and liquid phase reactions. In the present review, we dis-cuss the recent development of heterogeneous, supported monometal ic gold catalysts for organic transforma-tions emphasizing mainly liquid phase hydrogenation reactions. Discussions on the catalytic synthesis procedures and the promoting effect of other noble metals are omitted since they are already worked out. Appli-cations of heterogeneous, supported monometal ic catalysts for chemoselective hydrogenations in liquid phase are studied including potential articles during the period 2000–2013.     

Recent development of supported monometallic gold as heterogeneous catalyst for selective liquid phase hydrogenation reactions

The great potential of gold catalysts for chemical conversions in both industrial and environmental concerns has attracted increasing interest in many fields of research. Gold nanoparticles supported b...     

One-dimensional heterogeneous model of a Fischer-Tropsch synthesis reactor with a fixed catalyst bed in the isothermal granules approximation

A one-dimensional heterogeneous model has been developed for a cat6alytic fixed-bed Fischer-Tropsch (FT) synthesis reactor in the isothermal granules approximation. The FT process has been simulated for a laboratory-scale reactor. The effects of the linear gas velocity and of the inner diameter of the reactor on the thermal stability of the process are considered. The size of the reactor is limited by the possibility of a “thermal explosion” occurring in the frontal layer of the catalyst. Raising the linear gas velocity enhances heat transfer, thereby reducing the overheating of the catalyst bed. The synthesis of solid hydrocarbons can be conducted in reactors no larger than 18 mm in diameter. According to calculations, the maximum temperature drop in a 3-, 4-, and 6-m-long reactor is 4.7, 4.2, and 3.6°C, respectively. The corresponding CO conversion is 35.0, 34.4, and 33.9%, respectively. For producing liquid hydrocarbons in a high-performance reactor, it is necessary to decrease its inner diameter to 12 mm. In this case, the maximum temperature drop at a reactor length of 3, 4, and 6 m is 9.6, 8.7, and 7.6°C, and the CO conversion is 78.0, 77.4, and 76.7%, respectively. The mathematical model devised here provides means to estimate the necessary design parameters of the reactor and the appropriate FT synthesis conditions for producing liquid or solid hydrocarbons.     

Standing waves of gaseous chemical reactions in inert porous media

Standing waves of gaseous, exothermic, chemical reactions in inert porous media are investigated in the two-temperature and one-temperature approximations. A semiinfinite reaction zone method is developed to solve the problem analytically. It is shown that the wave solutions obtained by this method form a large set. Traditional solutions with strong heat transfer at the end of the wave make up but a small fraction of this set.LENIIKhIMMASh, St. Petersburg 193167. Translated from Fizika Goreniya i Vzryva, Vol. 30, No. 4, pp. 11–20, July–August, 1994.     

纳米金在若干化学反应中的催化应用

高度分散的纳米金催化剂作为一个新兴的研究领域,对许多化学反应具有优良的活性。本文概括地介绍了近期发表的关于金负载催化剂成功地用于催化CO氧化、环己烷氧化制环己酮、催化氧化甲醛,、二醇氧化制内酯反应、丙烯直接环氧化、苯甲醇氧化制苯甲醛和氮氧化物还原等反应的例子。     

Catalyzing the carbonylation of methanol using a heterogeneous vapor phase catalyst

Nickel supported on activated carbon has been shown to be active for the carbonylation of methanol. Methyl acetate was the major and primary product; acetic acid was formed as a minor product. The greatest yield of methyl acetate was approximately 0.21 at a reaction temperature of approximately 225°C. The effect of reduction temperature and nickel loading on the performance of catalyst is reported. The catalyst was mostly stable at temperatures near 225°C but deactivated irreversibly at elevated temperature. The results are consistent with a competitive reaction between the nickel catalyst and the activated carbon support, to produce an inactive nickel carbide product.     

General mathematical models of transport processes with and without chemical reactions

Based on the surface renewal and penetration concept, a number of fairly general mathematical models for transport systems without chemical reaction or heat generation and transport systems with zero and first order reactions have been developed. Solutions of the governing transport equations are presented for cases in which the number of capacitors of the multiple capacitance age distribution is finite or infinite. Some of their limiting solutions are reduced to those proposed by the previous investigators.     

反应精馏过程模拟研究进展

对均相反应精馏和非均相催化精馏过程的各种模拟计算方法进行了评述，分析了各种算法的优缺点和适用范围，指明了目前研究中存在的不足和今后的发展方向。     

Metathesis of methyl oleate with a homogeneous and a heterogeneous catalyst

The cometathesis reaction of methyl oleate (MO) with unsaturated dicarboxylic acid esters has been studied using either a homogeneous catalyst system (WCl₆-Me₄Sn) or a heterogeneous catalyst system (Re₂O₃-Al₂O₃-Me₄Sn). In the presence of the homogeneous catalyst, dimethyl-3-hexenedioate (DMHD) reacted with MO to give cometathesis products in 47% yield with a distribution of products that agreed with the theoretical equilibrium composition. When dipropyl-4-octenedioate (DPOD) was used, however, the yield of cometathesis products was less than 1%. The lower reactivity of DPOD might be due to the formation of a stable complex of DPOD with the catalyst. The cometathesis reaction of MO and DMHD was also catalyzed by the heterogeneous catalyst. However, the reaction rate decreased significantly and the distribution of products did not attain the theoretical. Similar results were obtained in the cometathesis reaction of MO and DPOD catalyzed by the heterogeneous catalyst. These results suggest that MO and DMHD are preferentially adsorbed onto the surface of this catalyst according to their polarity, and that the molar ratio of MO and DMHD at the catalytic site was different from that in the reaction medium.     

Liquid-liquid-solid reactions: esterification of phenol with benzoyl chloride using a polymer-supported phase transfer catalyst

The reaction of phenol in alkaline solution and benzoyl chloride dissolved in toluene with a polymer-supported tri-n-butylphosphonium ion as phase transfer catalyst has been carried out in a slurry reactor. Mass transfer effects have been analysed with the standard theory of porous catalysts. The intrinsic reaction rate constant and diffusion coefficients within the porous polymer particle are estimated. The rate-limiting step has been identified.