Investigations on Selectivity of Gas-Liquid Reactions in Capillaries

Biocatalysis offers a broad spectrum of possible ecological and economic advantages over conventional chemical catalysis processes, e.g., lower energy consumption and high enantio selectivity. The focus of this work is on gas-liquid reactions. These are of great importance in the chemical and biochemical industry and subject of current research since they are often limited by mass transfer or show low selectivity. Different suitable biocatalytically gas-liquid reaction systems were tested in capillary reactor designs in order to obtain information about the interaction between reaction and fluid mechanics. Furthermore, an optical measuring method was established. The experiments were performed in batch mode in a glass beaker with a flow cuvette for UV/Vis measurement of product concentration.     

Molecular Aspects of Catalytic Reactivity. Application of EPR Spectroscopy to Stuies of the Mechanism of Heterogeneous Catalytic Reactions

The basic objective of mechanistic studies of real catalytic processes is to dissect the course of the reaction into individual steps; ascertain their sequence; and determine the stoichiometry, structure, and electronic states of active sites and intermediates. The electron paramagnetic resonance (EPR) technique is at present widely used to explore many of these principal aspects of heterogeneous catalysis and surface chemistry. The extreme sensitivity compared to the usual spectroscopic methods is perhaps its most acknowledged advantage and makes EPR best suited to investigate and characterize low-abundance active sites and intermediates appearing during catalytic reaction. Additional information can be drawn from the theoretical analysis of the experimental spin Hamiltonian parameters within the ligand field and from angular overlap or Newman's superposition models as well as by more sophisticated quantum chemical calculations. The purpose of this paper is to show how catalysis benefits from EPR spectroscopy and to identify the issues and areas explored by this method. A comprehensive literature review is not attempted in this article; instead, attention is directed toward application of EPR for elucidation of the molecular reaction mechanism that can provide a scientific background for understanding many fundamental aspects of catalytic activity. The major events of mechanistic studies which involve the identification of active sites, activation of reagents, and determination of the reaction pathways are illustrated by selected examples and discussed. An approach that is complementary to mechanistic catalytic test studies is also presented. It consists of spectroscopic investigations of a set of partial reactions, driven by external creation of the supposed active sites and intermediates, with the aim of reproducing and verifying the feasibility of the postulated catalytic cycle. Moreover, to assure some consistency of the subject, basic characteristics of EPR spectroscopy related to surface studies and chemical theories of reactivity are concisely reviewed.     

Molecular Aspects of Catalytic Reactivity. Application of EPR Spectroscopy to Stuies of the Mechanism of Heterogeneous Catalytic Reactions

The basic objective of mechanistic studies of real catalytic processes is to dissect the course of the reaction into individual steps; ascertain their sequence; and determine the stoichiometry, structure, and electronic states of active sites and intermediates. The electron paramagnetic resonance (EPR) technique is at present widely used to explore many of these principal aspects of heterogeneous catalysis and surface chemistry. The extreme sensitivity compared to the usual spectroscopic methods is perhaps its most acknowledged advantage and makes EPR best suited to investigate and characterize low-abundance active sites and intermediates appearing during catalytic reaction. Additional information can be drawn from the theoretical analysis of the experimental spin Hamiltonian parameters within the ligand field and from angular overlap or Newman's superposition models as well as by more sophisticated quantum chemical calculations. The purpose of this paper is to show how catalysis benefits from EPR spectroscopy and to identify the issues and areas explored by this method. A comprehensive literature review is not attempted in this article; instead, attention is directed toward application of EPR for elucidation of the molecular reaction mechanism that can provide a scientific background for understanding many fundamental aspects of catalytic activity. The major events of mechanistic studies which involve the identification of active sites, activation of reagents, and determination of the reaction pathways are illustrated by selected examples and discussed. An approach that is complementary to mechanistic catalytic test studies is also presented. It consists of spectroscopic investigations of a set of partial reactions, driven by external creation of the supposed active sites and intermediates, with the aim of reproducing and verifying the feasibility of the postulated catalytic cycle. Moreover, to assure some consistency of the subject, basic characteristics of EPR spectroscopy related to surface studies and chemical theories of reactivity are concisely reviewed.     

Digital Image Processing of Gas-Liquid Reactions in Coiled Capillaries

In the course of the investigation of biocatalytic gas-liquid reactions with color change in straight and coiled capillaries, a non-invasive evaluation method is needed to determine reaction progress and selectivity. Correlations between hydrodynamics, mass transfer phenomena, and reaction kinetics are in the focus of our work. For this purpose, it is necessary to investigate the flow and evaluate the reaction progress without disturbing the flow. Digital image processing (DIP) is presented as a suitable optical evaluation method for reactions with color change in capillary reactor designs. The developed DIP program is independent from the capillary reactor design, applicable to differently colored systems, and can analyze up to three different species simultaneously.     

Experimental Evidence of Gas-Liquid Boundary Controlled Reactions in UV-Ozone Systems

Oxalic acid is chosen as a model compound to study the UV + O₃ reactions in an heterogeneous continuous gas sparging reactor. Oxalic acid has the advantage of not reacting significantly with ozone alone, and when oxidized with O₃ + UV radiation, the reaction is of the single-step type : HOOC-COOH + O₃ (UV) = 2 CO₂ + H₂O + O₂. The reactions are of zero order as long as no additional alkalinity is introduced into the system. Evidence is that the photolysis of ozone is produced in the gas phase and that the reaction occurs in the gas-liquid boundary layer.     

Oscillations in Catalytic Reactions

This paper deals with the status of knowledge concerning open catalytic reaction systems which, though exposed to constant conditions, exhibit sustained oscillatory states. Such behavior arouses interest because, aside from the practical aspects and matters of fundamental importance, it has a battling quality - it usually defles physical explantion offered in the total absence of a mathematical analysis, and hence its occurrence is not easily anticipated     

精馏过程中气-液比条件的工程意义

精馏生产技术的关键是确保过程中气-液比如何接近最优条件,通过各技术参数和气-液比之间的关系,研究了如何判断气-液比条件,如何调节气-液比条件的方法和技术措施。     

Oscillations in Catalytic Reactions

Abstract

This paper deals with the status of knowledge concerning open catalytic reaction systems which, though exposed to constant conditions, exhibit sustained oscillatory states. Such behavior arouses interest because, aside from the practical aspects and matters of fundamental importance, it has a battling quality – it usually defles physical explantion offered in the total absence of a mathematical analysis, and hence its occurrence is not easily anticipated     

超临界流体中的催化反应

介绍超临界流体中的固体催化反应、酶催化反应、均相催化反应及催化加氢反应。     

Unsteady-State Performance of Heterogeneous Catalytic Reactions

The opinion that performance of continuous catalytic processes under invariable conditions is highly efficient has gained great popularity, especially among chemical engineers. However, very often the optimal conditions of the process can be achieved with the so-called unsteady-state operation. The steady-state condition thus appears to be a particular case of the variety of unsteady-state conditions which can be obtained, e.g., by changing the reaction conditions. Unsteady-state operation opens up wide possibilities to form the profiles of the catalyst states, concentrations, and temperatures in reactors, thus providing more favorable conditions for the process performance.     

Unsteady-State Performance of Heterogeneous Catalytic Reactions

The opinion that performance of continuous catalytic processes under invariable conditions is highly efficient has gained great popularity, especially among chemical engineers. However, very often the optimal conditions of the process can be achieved with the so-called unsteady-state operation. The steady-state condition thus appears to be a particular case of the variety of unsteady-state conditions which can be obtained, e.g., by changing the reaction conditions. Unsteady-state operation opens up wide possibilities to form the profiles of the catalyst states, concentrations, and temperatures in reactors, thus providing more favorable conditions for the process performance.     

Catalytic Aspects of Synthetic Fuels from Coal

It is appropriate that this symposium honoring Dr. Henry H. Storch should focus on catalysis, a field in which he made so many contributions and in which he published widely, most recently posthumously in the comprehensive review with Wu [1]. One of Dr. Storch's greater contribution was in attracting to the Bureau of Mines and training highly competent scientists and engineers who still constitute a research resource of great present national value and who, in a real sense, are continuing his research efforts.     

Intraparticle Diffusion in Multicomponent Catalytic Reactions

Catalytic processes on solid catalysts dominate among large-scale operations in chemical and petrochemical industry.     

Intraparticle Diffusion in Multicomponent Catalytic Reactions

Catalytic processes on solid catalysts dominate among large-scale operations in chemical and petrochemical industry.     

Improved Donors for the Separation of the Boron Isotopes by Gas-Liquid Exchange Reactions

Abstract

Chemical exchange between gaseous boron trifluoride (BF₃) and the liquid BF₃·dimethyl ether complex has been used extensively for the commercial fractionation of boron isotopes. Several compounds never before studied as donors in the isotope exchange reaction were examined to determine if they were viable replacements for the dimethyl ether system. For the first time, ketones were studied as donors in the boron isotope exchange reaction. The ketones examined were acetone, methyl isobutyl ketone, and diisobutyl ketone. The ideal single stage separation factors, α, measured for these ketones were between 1.038 and 1.043 at 30°C. The observed separation factor for a fourth donor system, nitromethane, was 1.067 at 30°C, well above that predicted by theory or observed for any known BF₃/donor system. For each of the systems studied, the separation factors were greater than the value of α = 1.027 reported for the dimethyl ether/BF₃ system at 30°C. In view of the experimentally observed separation factors, these donor systems are potential replacements for dimethyl ether in large-scale boron isotope fractionation schemes. It is concluded that plant size could be significantly reduced by using any of these donors rather than dimethyl ether.

     

催化精馏技术在酯化反应中的应用

催化精馏技术应用于酯化反应体系,提高了反应的转化率,原材料利用率和产品收率。与传统工艺相比,具有生产流程简单、能耗低,设备投资和操作费用低、无环境污染等优点。催化精馏技术应用于酯化行业生产,对提高酯化行业的技术水平和经济效益具有积极意义。     

超临界流体在催化反应中的应用

综述了超临界流体在酶催化、多相催化、均相催化等催化反应中的应用。指出了超临界流体作为催化反应介质在基础研究和应用研究方面的课题方向。     

Chemical Engineering Aspects of Dyeing Processes

Abstract

First, existing research on diffusion of disperse, reactive, and ionic dyes in polymers and correlation of the rate of dyeing to the operating variables in the dyebath is reviewed. Second, to discuss the kinetic aspects of various dyeing processes, the dyeing of textiles is classified into two categories: adsorptive and reactive dyeings, and these two dyeing processes are modeled in terms of diffusion of dyes in polymers accompanied by some physicochemical interaction with the polymer substrates. The process of adsorptive dyeing was formulated on the basis of a dual-mode sorption and mobility model where the porelike region was conveniently invoked. The calculated profiles of the concentration of immobilized dye are similar to the measurments of dye distribution curves by means of film-roll, microdensitometric, and microspectrophotometric techniques. The outline of formulation of the process of dyeing with reative dyes (i.e., reactive dyeing) is given on the basis of diffusion of dye within the fiber accompanied by a fixation reaction incorporating hydrolysis of dye species. It is concluded from numerical analysis that the lower the bath ratio, the less the decrease of the final fixation due to hydrolysis of the dye and the less the influence of mixing in the dyebath on the fixation. When the fixation reaction is slow, the final futation is almost independent of the bath ratio and the degree of mixing.     

Engineering Aspects of Selective Hydrocarbon Oxidation

This review represents an attempt to offer a comprehensive critical collection of information concerning chemical reaction engineering of selective hydrocarbon catalyric oxidation. Many excellent reviews are available in which the fundamental and industrialaspects of hetarogreous selective oxidation of hydrocarbons are presented and discussed[1-11]