APPLICATION OF A SYSTEMATIC APPROACH FOR DETERMINING POSSIBLE REACTION MECHANISMS: METHANOL SYNTHESIS AND ANODIC OXIDATION OF ZINC

A systematic enumeration of possible reaction mechanisms consistent with a given set of chemical species and elementary steps is useful in guiding research in heterogeneous reaction systems which are encountered in catalysis and electrochemistry. In this paper, the synthesis of methanol by catalytic hydrogenation of carbon monoxide and the anoidic oxidation of zinc in alkaline solutions are presented as two examples of the usefulness of such an approach. The technique utilized to generate the reaction mechanisms is based upon combinatorial analysis, linear algebra and the principle of microscopic reversibility.

In the case of methanol synthesis, it is shown that in addition to the two currently proposed mechanisms, there exist two alternate reaction pathways each of which involves the hydrogenation of a formyl species to form a surface methoxide. One of these mechanisms has recently been proposed for a ZnO catalyst, however there remains an additional mechanism for consideration. For the case of anodic zinc oxidation, it is shown that mechanisms which involve cathodic elementary steps are also possible. To the authors knowledge, these mechanisms have not been previously discussed in the literature.     

气相直接法甲醇氧化羰化合成碳酸二甲酯催化剂的研究

采用气相直接法甲醇氧化羰化工艺路线合成碳酸二甲酯，以ＣｕＣｌ２为活性组分，用浸渍法制备催化剂。比较了活性炭等数种载体，并对载体进行表面改性，考察了催化剂制备过程中溶剂、助剂、同液比、浸渍浓度与次数、浸渍时间等因素对催化剂性能的影响     

A COMPARISON OF A NOVEL RECUPERATIVE CONFIGURATION AND CONVENTIONAL METHANOL SYNTHESIS REACTOR

Coupling energy-intensive endothermic reaction systems with suitable exothermic reactions improves the thermal efficiency of processes and reduces the capital cost of the reactors. In this study, a steady-state heterogeneous model for a novel thermally coupled reactor, containing methanol synthesis reactions and cyclohexane dehydrogenation, was developed. This heat exchanger reactor consists of two fixed beds separated by a wall, where heat is transferred across the surface of the tube from the exothermic into the endothermic side. The co-current mode is investigated, and the simulation results are compared with corresponding data for an industrial methanol fixed bed reactor operated at the same feed conditions. The results show that although methanol productivity in the thermally coupled reactor is not higher than that in the conventional methanol reactor, benzene is also produced as an additional valuable product in a favorable manner, and autothermality is achieved within the reactor. This novel configuration can increase the methanol synthesis temperature at the first part of the reactor for higher process rates and then reduce the temperature at the second part of reactor for increasing thermodynamic equilibrium; those are two key issues in methanol reactor configurations. The influence of inlet temperature, molar flow rate, and shell diameter of the endothermic stream on reactor behavior is investigated. The results suggest that coupling of these reactions in co-current mode could be feasible and beneficial. Experimental proof-of-concept is needed to establish the validity and safe operation of the novel reactor.     

STEADY STATE AND DYNAMIC MODELLING OF A PACKED BED REACTOR FOR THE PARTIAL OXIDATION OF METHANOL TO FORMALDEHYDE II. EXPERIMENTAL RESULTS COMPARED WITH MODEL PREDICTIONS

Heterogeneous and pseudohomogeneous two-dimensional models are compared to steady state and dynamic experimental data from a packed bed reactor for the partial oxidation of methanol to formaldehyde over an iron oxide-molybdenum oxide catalyst. Highly effective parameter estimation software was used to fit selected model parameters to large sets of experimental data so as to obtain small residuals. Heat transfer parameters which were successful in matching data from experiments without reaction were not capable of fitting data from experiments with reaction, and it was necessary to increase the radial heat transfer for higher temperatures or reaction rates. Axial composition profile data was represented by estimating the preexponential factors and activation energy in a half-order redox rate expression for methanol oxidation. After some decline in catalyst activity, a time-varying axial catalyst activity profile was determined from the data. A redox-type rate expression for the oxidation of formaldehyde to carbon monoxide was proposed to fit the data. The dynamics of the reactor temperature profile were accurately represented by the model. The heterogeneous and pseudohomogeneous models gave similar results in fitting experimental data, although the parameters determined for the two models were somewhat different.     

STEADY STATE AND DYNAMIC MODELLING OF A PACKED BED REACTOR FOR THE PARTIAL OXIDATION OF METHANOL TO FORMALDEHYDE I. MODEL DEVELOPMENT

Several levels of mathematical models involving one and two dimensions as well as single and multiple phases are used to predict the steady state and dynamic behavior of a packed bed reactor for the partial oxidation of methanol to formaldehyde. Parametric sensitivity is examined for several heat and mass transfer parameters, kinetic parameters, and operating conditions. Yield is compared for various models, and significant differences are observed between the one-dimensional and two-dimensional models. The dynamic behavior after step changes in the operating conditions is found to be qualitatively similar for different models.     

高级氧化技术去除水中双酚A研究进展

双酚A(BPA)是一种典型的内分泌干扰物,在环境水体中广泛存在,近年来其受到越来越多的关注。高级氧化技术(AOPs)是降解有机污染物的新技术,在水处理中有良好的应用前景。本文对几种较新的高级氧化技术处理BPA的基本原理和处理效果做了较为详细的阐述,并提出几点不足以及进一步可能的研究方向。     

新型炭阳极密度测量方法的开发与应用

针对成型预焙炭阳极密度测定方法中存在的问题，通过对国内厂家使用的密度测定方法的分析和研究，开发设计出了新型炭阳极密度测量装置，很好地解决了炭素行业中炭阳极密度测量的难题。     

聚乙烯编织袋防滑剂—A的合成及应用

聚乙烯编织袋防滑剂－ Ａ用于提高编织袋安全防滑等性能。分别对主要原料、合成树脂、增粘树脂进行了筛选,并对各种原料的配比、合成工艺条件进行了研究。应用试验表明：防滑性能提高３３％ ～３８ ％ ,热稳定性良好。     

A NEW APPROACH FOR THE CLASSIFICATION AND ENUMERATION OF UNIQUE REACTION ROUTES AND UNIQUE OVERALL REACTIONS IN MULTIPLE CHEMICAL REACTION SYSTEMS

The methodology of response reactions (RERs) introduced earlier from thermodynamic and kinetic considerations is used in this work to develop a new algorithm for the classification and enumeration of unique/direct reaction routes (RRs) and overall reactions (ORs). According to the RERs approach, a unique set of both RRs and ORs may be generated starting from any conceivable set of linearly independent RRs and ORs. In particular, the direct ORs may be most conveniently enumerated starting from the formula matrix of the terminal species (reactants and products), i.e., without any relation to the elementary reactions comprising the detailed mechanism. Depending on the type of ORs produced by the RRs one can distinguish between two distinct types of direct RRs. Namely, one option is to define a direct RR by specifying the intermediate species that need to be eliminated. This type of RR is referred to as Milner RRs. The other option is to require the direct RRs to produce RERs, thus resulting in RRs referred to as Happel-Sellers RRs.     

SEPARATION OF ETHYLBENZENE-XYLENES MIXTURES BY DISTILLATION: A POSSIBLE APPLICATION OF VAPOUR RECOMPRESSION CONCEPT

The application of direct vapour recompression to an existing plant, fractionating ethylbenzene-xylenes mixtures, has been studied.

The behaviour of the saturated liquid and vapour curves for ethylbenzene in the Temperature-Entropy diagram has been evaluated theoretically by means of well known equations of state. The most important operating parameters of the process (as functions of ΔT) in the reboiler-condenser have been obtained. The economic analysis performed indicates that for the case considered, the best value for ΔTis about 6°C, but only a small energy saving can be achieved.     

A REACTIVE DISTILLATION PROCESS FOR AN AZEOTROPIC REACTION SYSTEM: TRANSESTERIFICATION OF ETHYLENE CARBONATE WITH METHANOL

A reactive distillation process is proposed for manufacturing dimethyl carbonate (DMC) through the transesterification reaction of ethylene carbonate (EC) with methanol. Modeling and simulation of the reactive distillation column have been carried out to study the effects of operating conditions, such as the reflux ratio, the number of theoretical plates, the feed ratio, the top effluent, the liquid holdup, and the feed location, on EC conversion and product composition at the top of the reactive distillation column. The calculated results show that a complete EC conversion can be achieved. The model reliability is analyzed under different Murphree tray efficiencies, showing no considerable difference between the equilibrium and nonequilibrium models for this system. And the calculated results are verified by experimental data and commercial operation of a dimethyl carbonate plant of 10,000 tons per year.     

FORMATION OF BENZYLIC ALCOHOLS AND MESO-ALDEHYDES BY ONE-ELECTRON OXIDATION OF DMBA,A MODEL FOR THE FIRST METABOLIC STEP IN METHYLATED CARCINOGENIC HYDROCARBON ACTIVATION

The hypothesis that hydroxylation of the 7-methyl group is the first step in metabolic activation of 7,12-dimethylbenz[a]anthracene (DMBA) was advanced over three decades ago (1 Flesher, J. W. and Sydnor, K. L. 1971. Carcinogenicity of Derivatives of 7,12-Dimethylbenz[a]anthracene. Cancer Research, 31: 1951–1954. [PubMed], [Web of Science ®] , [Google Scholar], 2 Flesher, J. W. and Sydnor, K. L. 1973. Possible Role of 6-Hydroxymethylbenzo[a]pyrene as a Proximate Carcinogen of Benzo[a]pyrene and 6-Methylbenzo[a]pyrene. Int. J. Cancer, 11: 433–437.  [Google Scholar]). A considerable body of evidence supports the hypothesis (3 Flesher, J. W., Horn, J. and Lehner, A. F. 2002. The Meso-Region Theory of Aromatic Hydrocarbon Carcinogenesis. Polycyclic Aromatic Compounds, 22: 379–393. [Taylor & Francis Online], [Web of Science ®] , [Google Scholar]). A chemical model for the oxidative metabolism of DMBA may be useful in understanding the mechanism of metabolic activation of DMBA and other methylated carcinogenic hydrocarbons, particularly the first step. Here we show that a nonenzymatic one-electron oxidation pathway transforms DMBA to carcinogenic alcohol and meso-aldehyde metabolites. The results are consistent with the hypothesis that hydroxylation of the 7-methyl and/or 12-methyl groups is the first metabolic step in DMBA activation. The hypothesis predicts that hydroxylation of other meso-methyl-substituted hydrocarbons is the first essential step in the metabolic activation of methylated carcinogenic hydrocarbons.     

STEADY STATE SIMULATION OF A PACKED BED REACTOR FOR THE PARTIAL OXIDATION OF METHANOL TO FORMALDEHYDE. INFLUENCE OF DIFFUSIONAL PHENOMENA AND CATALYST ACTIVITY DISTRIBUTION WITHIN THE PELLETS

The scope of this work is to present a real case in which reactor performance predicted theoretically, avoiding the numerical integration within the particle, is compared with experimental findings. The influence of realistic catalytic activity distributions are also studied since minimum extra efforts are needed with the procedure presented in this contribution. The partial oxidation of methanol in a tubular catalytic reactor, studied by Windes et al. (1989), giving rise to formaldehyde and carbon monoxide as main reaction products, was used as example for the application of our procedure. Both, inter and intraparticle, diffusional limitations were taken into account. Experimental data and theoretical predictions along the reactor were compared in terms of outlet conversion and temperature profiles showing a fairly good agreement which gives support to the procedure developed in this contribution to predict reactor performance. Furthermore, the effect of different realistic activity distribution function was simulated and its influence on the reactor performance is shown. The obtained results are discussed and some interesting conclusions are withdrawn.     

URINARY 3-HYDROXYBENZO[A]PYRENE AS A BIOMARKER OF EXPOSURE TO POLYCYCLIC AROMATIC HYDROCARBONS: AN APPROACH FOR DETERMINING A BIOLOGICAL LIMIT VALUE

Atmospheric and biological monitoring was carried out on 38 people exposed to polycyclic aromatic hydrocarbons in different workplaces. The relationship between the atmospheric BaP and the 3-OHBaP urinary concentration peaks was determined. To avoid misinterpretation due to dermal exposure, only people with mainly respiratory exposure were chosen. The selection was carried out from observation of working conditions and from urinary data. For the limit value determination, BaP concentrations higher than 5,000 ng/m³ were discarded and the 3-OHBaP values were adjusted to a 8 h exposure time. A close relationship was observed between the two variables: n = 17, r = 0.89, p < .0001 (C 3-OHBaP = 0.001835*C BaP + 0.1729). To estimate the 3-OHBaP limit concentration, the French recommended value of 150 ng/m³ for atmospheric BaP was used. The corresponding 3-OHBaP was 0.45 nmol/mol creatinine. This value could be used as a sound basic element for determining a biological exposure index.