A simplified model for biomass pyrolysis in a fluidized bed reactor

A reaction scheme of a set of three parallel reactions followed by a set of two parallel reactions has been used to describe the primary and secondary reactions of biomass pyrolysis in a fluidized bed reactor. A simple first-order kinetic approach has been applied to predict the product yields. The pyrolysis model detailed in this paper is actually a sub-model. The effects of operating parameters on biomass pyrolysis product yield were simulated. Results show that reaction temperature plays an important role in the yield of bio-oil. The model is robust and can predict good results in a gasification environment as well. Good agreement between predicted and published results was obtained.     

Theoretical and experimental studies of the effect of side reactions in copper deposition from dilute solutions on packed-bed electrodes

This paper analyses the effect of side reactions, such as the reduction of oxygen or Fe(III), on copper deposition from dilute acid sulfate solutions. Fundamental studies with a rotating disc electrode were performed to determine the potential regions where the reactions take place and also to calculate kinetic parameters under the conditions of the experiments. Applied studies carried out in a through-flow electrochemical reactor with a packed bed cathode formed by a stack of nets are reported. The experimental data are compared with theoretical results, according to the continuous model, to corroborate its reliability for the case of simultaneous electrochemical reactions. It was found that the agreement between the mathematical treatment and the experimental data is similar to the case of a single reaction in the electrode. Taking into account the side reactions, criteria for the selection of bed thickness parallel to the current flow are discussed.     

The electrochemical recovery of iron in a two-compartment batch electrochemical reactor

A model has been developed for a two-compartment batch electrochemical reactor in which simultaneous iron deposition and hydrogen evolution occur at the cathode, the anodic reaction being the production of hydrogen ions. The model incorporates ionic diffusivities through the diaphragm and a composite kinetic parameter for the cathodic reactions. In order to apply the model to data from a small batch reactor, the diffusivities have been obtained under conditions in which hydrogen alone is evolved at the cathode. The value of the kinetic parameter has been chosen to provide the best agreement between the model predictions and the experimental results. Satisfactory predictions of the current efficiency for iron deposition and the final concentrations in the reactor has been obtained, the largest discrepancies between predicted and actual concentrations being at high anolyte hydrogen ion concentrations. Reasons for these discrepancies are discussed.     

Selectivity and reactor analysis for parallel electrochemical reactions

A methodology is outlined for the analysis of multiple parallel electro-organic reactions of arbitrary, simple electrode kinetics on solid or porous electrodes, in the absence and in the presence of slow mass transport processes. The analysis is further used to predict the selectivity and rate of two model electrochemical reactors under potentiostatic, channel plug-flow or complete mixing. The product yield of both reactors depends strongly on the electrode potential, with reductions of low transfer coefficients favoured by positive, electrogenerative potentials. Channel flow reactors result in non-uniform rate, current and selectivity distributions and exhibit apparent limiting currents before the onset of slow mass transport. With multipath competing reactions or in the presence of slow external transport, both reactors are amenable to maximisation of desirable product yields.     

Pyrolysis kinetics of waste automobile lubricating oil

The kinetics of waste automobile lubricating oil have been studied experimentally and modeled mathematically. Experiments were carried out in the tubing bomb microreactor at a temperature of 420–440°C and reaction times of 5–50 min. Volatile pyrolysis products were identified and quantitatively determined by gas chromotography. A lump model of combined series and parallel reactions for oil formation is proposed. Conversion data fitted first order kinetics for C₅–C₁₁ and C₁₂–C₂₅. The kinetic parameters were determined by nonlinear least-squares regression of the experimental data. These calculated values of the product distribution were found to be in agreement with the experimental data.     

Experimental investigation and modeling of steam cracking of Fischer–Tropsch naphtha for light olefins

The characteristics of product distribution and the kinetic model for predicting the yields of the major products from steam cracking of Fischer–Tropsch (F–T) naphtha have been investigated in a pilot plant under various conditions. An analysis of the experimental data suggests that the naphtha produced via the low-temperature slurry-phase F–T process is an excellent feedstock for the production of light olefins, especially ethylene. For steam cracking of two F–T naphthas studied, ethylene is the primary product varying from 36.89 to 41.83 wt%, and the total yield of valuable light olefins (C₂H₄, C₃H₆ and 1,3-C₄H₆) is not less than 60.34 wt% under the conditions estimated. The experimental product distributions could be satisfactorily predicted by use of a detailed molecular reaction scheme which consists of a first-order primary reaction and 37 secondary reactions.     

The effect of time on stream and feed composition on the selectivity of a cobalt fischer—Tropsch catalyst

The Taylor–Wojciechowski formulation of Fischer Tropsch product distributions has been used to study the effect of time on stream and of feed composition on the parameters which arise in the T–W treatment. An experimental setup which allows the required evaluation of product yields is also described. The T–W formulation was found to give an excellent fit to data obtained using a cobalt-on-kieselguhr catalyst. Since the ratios of the various specific rates of parallel synthesis reactions were found to be different functions of the H₂/CO ratio in the reactor, we conclude that propagation, branching and termination reactions are not governed by the same kinetics.     

绝热加速量热无模型方法动力学预测

绝热加速量热主要采用基于单一实验数据的模型拟合方法进行动力学预测,难以应用于未知机理反应和复杂反应。为此,通过数值模拟方法在绝热条件下产生n级反应与Kamal自催化反应数据,采用Vyazovkin和Friedman等转化率方法进行动力学求解;然后在不同起始温度和等温条件下,采用无模型动力学参数进行绝热和等温动力学预测,并与模拟数据对比。结果表明,绝热加速量热采用Vyazovkin方法预测最大相对误差为39.9%,Friedman方法预测最大误差超100%,前者更适合进行预测;建议在预测温度±40℃范围内进行实验测量。这为未知化学物质和复杂反应热失控风险评估及化工事故模拟等提供了有效手段。     

Zur stromausbeute und kinetik elektrochemischer reaktionen bei hohen stromdichten unter stationären bedingungen

The investigation of the kinetics of electrochemical reactions at high current densities (20?300 A cm^?2) and high streaming velocities of the electrolyte, is difficult. Large ohmic drops occur which make the exact measurement of potential impossible. A method is reported for multiple electrodes in which the kinetic parameters are deduced, without measuring current-voltage curves, from the dependence of the current efficiency on total current density. The basis of the theory is discussed for a model system of two parallel Tafel type reactions. The anodic dissolution of iron with simultaneous oxygen evolution in KNO₃ and NaClO₃ solutions has been investigated experimentally.     

Kinetic modeling and optimization of the operating condition of MTO process on SAPO-34 catalyst

In this paper, a new kinetic model for methanol to olefin process (MTO) over SAPO-34 catalyst was developed based on data obtained from a micro catalytic reactor using appropriate reaction network. The reaction rate equation has been introduced with consideration of reaction mechanism and the parameters were optimized on the experimental data by genetic algorithm. Comparing the experimental and predicted data showed that the predicted values from the presented model are well fitted to the experimental data. Using this kinetic model, the effect of most important operating conditions such as temperature, pressure, inlet water to methanol molar ratio and methanol space–time on the product distribution, has been examined. Finally, the optimal operating conditions for maximum production of the ethylene and the propylene were introduced.     

石油馏份加氢精制的混合动力学模型

本文首先对加氢精制类二级反应动力学模型的研究做了简要的回顾,然后提出了一个混合反应动力学模型,可用以处理一级反应动力学模型及作者提出的类二级反应模型所不能处理的实验数据得到了较为满意的结果。编制了一个可同时用一级反应,类二级反应模型或本模型对数据进行处理并做出判断的电子计算机程序。     

Pyrolysis of Miscanthus Giganteus and wood pellets: TG-FTIR analysis and reaction kinetics

Characterisation of two biomass fuels (pelletised Miscanthus Giganteus and wood) was performed using thermogravimetric analysis with measurement of products by means of Fourier transform infrared spectroscopy (TG-FTIR). Three heating rate profiles were applied (10, 30 and 100 °C/min), with a final temperature of 900 °C. HCN and HNCO were found to be the major N-products, while the NH₃ fraction was detected to a minor extent. Kinetic parameters were obtained from the TG-FTIR results using a model based on parallel first-order reactions with a Gaussian distribution of activation energies. On the basis of the above kinetic analysis and product yields, input files for the functional group-devolatilisation, vaporisation, cross-linking biomass-pyrolysis model were prepared. The fit of model parameters to TG-FTIR product-evolution data was found to be generally good, but the model-predicted yields for some species did not fit experimental data at all heating rates. Further improvements in the model are needed to resolve above difficulty.     

Practical Considerations in Kinetic Resolution Reactions

This review provides a critical analysis of catalytic kinetic resolution reactions from a practical perspective, asking the question of when, if ever, is kinetic resolution the best option for the synthesis of an optically active target. A series of crucial conditions are identified, and it is postulated that if all of them are met, then indeed kinetic resolution can be highly practical. A variety of catalytic kinetic resolution processes are evaluated in the context of these criteria, with particular emphasis on catalyst availability, substrate scope, availability of the racemic substrate and of alternative methods for accessing enantiopure substrate or product, and key experimental considerations. It is found that several catalytic systems have been developed that offer almost unbeatable methods for the preparation of useful chiral building blocks.     

Electrosynthesis of dimethylsulfone from dimethylsulfoxide at a dimensionally stable anode

Galvanostatic electrochemical oxidation of dimethylsulphoxide (DMSO) to dimethylsulfone (DMSO₂) has been effected at a dimensionally stable anode (DSA) under different conditions of current density and reaction media, in both a batch and a flow reactor (membrane cell with an ion-exchange membrane between the two working electrodes) functioning in batch recirculation mode. Excellent yields of the sulfone have been obtained under both conditions. The product has been characterized by various physicochemical techniques. The operational conditions giving maximum yield of the product have been established. The electrochemical oxidation of DMSO has also been studied by cyclic voltammetry at a glassy carbon (GC) electrode. The mechanism of electrochemical oxidation and the advantages of the present methods over existing ones, are discussed.     

Numerical modelling of the electrochemical behaviour of 316L stainless steel based upon static and dynamic experimental microcapillary-based techniques

Microcapillary-based techniques allow the selection and interrogation of single metallurgical sites and are therefore becoming increasingly popular to investigate the electrochemical behaviour of metallic phases and non-metallic heterogeneities in alloys. This study has been carried out to assess the differences between current measurements made using a ‘closed’ microcapillary system (the electrochemical microcell technique) with current measurements derived from a flowing ‘open’ microcapillary droplet cell (the scanning droplet cell). The experimental results were compared with calculations derived from a model system adopting a finite element approach. The corrosion system consists of four parallel electrochemical reactions: three cathodic reactions (the oxygen reduction reaction, the hydrogen evolution reaction and water dissociation) and one anodic reaction (metal dissolution reaction). Comparative experimental results have shown there is a large discrepancy between the magnitudes of the cathodic current obtained by the two techniques. The results of this study allow an assessment of the parameters responsible for the mass transport and distribution of species in the closed and open systems. Critical parameters (for example, microcell crevice geometry, specimen surface-capillary gap distance, etc.) which lead to significant modifications of the curves were then identified using the numerical simulation.     

微孔无机膜反应器研究

主要介绍了无机膜在化学反应中的应用－－膜反应器研究，对膜反应器的特点、类型、应用、影响因素以及与其它反应器的比较进行了评述，并对其应用前景进行了展望。     

大庆常渣催化裂解反应动力学模型

An 8-lump kinetic model was proposed to predict the yields of propylene,ethylene and gasoline in the catalytic pyrolysis process of Daqing atmospheric residue.The model contains 21 kinetic parameters and one for catalyst deactivation.A series of experiments were carried out in a riser reactor over catalyst named LTB-2.The kinetic parameters were estimated by using sub-model method,and apparent activation energies were calculated according to the Arrhenius equation.The predicted yields coincided well with the experimental values.It shows that the kinetic parameters estimated by using the sub-model method were reliable.     

Kinetics of reactions involved in pyrolysis of cellulose I. The three reaction model

Kinetics of reactions involved in pyrolysis of cellulose has been modeled in terms of a three reaction model. In this model it is assumed that cellulose decomposes to tars, chars and gaseous products via three competitive first-order reactions. Arrhenius parameters have been obtained to describe the rate constants of these reactions. The three reaction model predicts the weight loss data reasonably well. Product yields of tars, chars and gases predicted by the three reaction model are compared over the temperature range 250 to 360°C. In this communication a technique for analyzing experimental data of a solid state reaction is presented.     

钛硅分子筛催化环已酮氨肟化反应动力学

An intrinsic kinetics of cyclohexanone ammoximation in the liquid phase over titanium silicate molecular sieves is investigated in an isothermal slurry reactor at different initial reactant concentrations, catalyst loading,and reaction temperature. The rate equations are developed by analyzing data of kinetic measurements. More than 10 side reactions were found. H202 decomposition reaction Inust be considered and other side reactions can be neglected in the kinetic modeling. The predicted values of reaction rates based on the kinetic models are almost consistent with experimental ones. The models have guidance to the selection of reactor types and they are useful to the design and operation of reactor used.