Processes for Control of Intended Chemical Reactions

Designing Processes for Control of Intended Chemical Reactions 

General Considerations The following should be taken into account whenever designing or operating a chemical process that involves intended chemical reactions (Hendershot 2002). CCPS (1999) also details many key issues and process safety practices to consider that are oriented toward the design and operation of batch reaction systems. 

Many possible abnormal situations can initiate a runaway reaction. These include 

23-15 For stable operation, all heat generated by an exothermic reaction is transferred to the surroundings, by whatever means (conduction, evaporation, etc.). 

23-16 For an exothermic reaction system with heat removal, e.g., to a vessel jacket and cooling coil, the limit of stable operation is reached as the reaction temperature increases to I m (temperature of no return), beyond which the rate of heat generation, which increases exponentially with increasing temperature, exceeds the capability of the system to remove the heat of reaction (see text). 

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Designing Processes for Control of Intended Chemical Reactions. . 23-26... 

These reviews can be either in addition to or combined with periodic process hazard analyses (PHAs) by using methods such as what-if analysis and HAZOP studies. The latter should consciously focus on identifying scenarios in which intended reactions could get out of control and unintended reactions could be initiated. One means of accomplishing this as part of a HAZOP study has been to include chemical reaction as one of the parameters to be investigated for each study node. Johnson and Unwin (2003) describe other PHA-related approaches for studying chemical reactivity hazards. 

S. A. Rice My answer to Prof. Manz is that, as I indicated in my presentation, both the Brumer-Shapiro and the Tannor-Rice control schemes have been verified experimentally. To date, control of the branching ratio in a chemical reaction, or of any other process, by use of temporally and spectrally shaped laser fields has not been experimentally demonstrated. However, since all of the control schemes are based on the fundamental principles of quantum mechanics, it would be very strange (and disturbing) if they were not to be verified. This statement is not intended either to demean the experimental difficulties that must be overcome before any verification can be achieved or to imply that verification is unnecessary. Even though the principles of the several proposed control schemes are not in question, the implementation of the analysis of any particular case involves approximations, for example, the neglect of the influence of some states of the molecule on the reaction. Moreover, for lack of sufficient information, our understanding of the robustness of the proposed control schemes to the inevitable uncertainties introduced by, for example, fluctuations in the laser field, is very limited. Certainly, experimental verification of the various control schemes in a variety of cases will be very valuable. 

To be able to understand how computational approaches can and should be used for electrochemical prediction we first of all need to have a correct description of the precise aims. We start from the very basic lithium-ion cell operation that ideally involves two well-defined and reversible reduction and oxidation redox) reactions - one at each electrode/electrolyte interface - coordinated with the outer transport of electrons and internal transport of lithium ions between the positive and negative electrodes. However, in practice many other chemical and physical phenomena take place simultaneously, such as anion diffusion in the electrolyte and additional redox processes at the interfaces due to reduction and/or oxidation of electrolyte components (Fig. 9.1). Control of these additional phenomena is crucial to ensure safe and stable ceU operation and to optimize the overall cell performance. In general, computations can thus be used (1) to predict wanted redox reactions, for example the reduction potential E ) of a film-forming additive intended for a protective solid electrolyte interface (SEI) and (2) to predict unwanted redox reactions, for example the oxidation potential (Eox) limit of electrolyte solvents or anions. As outlined above, the additional redox reactions involve components of the electrolyte, which thus is a prime aim of the modelling. The working agenda of different electrolyte materials in the cell -and often the unwanted reactions - are addressed to be able to mitigate the limitations posed in a rational way. 

Chemical reactors intended for use in different processes differ in size, geometry and design. Nevertheless, a number of common features allows to classify them in a systematic way [3], [4], [9]. Aspects such as, flow pattern of the reaction mixture, conditions of heat transfer in the reactor, mode of operation, variation in the process variables with time and constructional features, can be considered. This work deals with the classification according to the flow pattern of the reaction mixture, the conditions of heat transfer and the mode of operation. The main purpose is to show the utility of a Continuous Stirred Tank Reactor (CSTR) both from the point of view of control design and the study of nonlinear phenomena. 

To prepare hexaaluminates for ceramic applications a slightly different sol-gel process was proposed by Debsikbar.19 Ba-hexaaluminates were prepared via hydrolysis of Al di(isopropoxide) acetoacetic ester chelate and anhydrous Ba acetate obtained by reaction between BaC03 and glacial acetic acid. The substitution of Al(i-OC3H7)3 with the alkoxy ester was intended to control the chemical polymerization during gel formation. The reaction was performed in 1-butanol. The formation of the gel slowly occurred at room temperature in about 10 h. To obtain the final phase the gel precursor was dried at 70 °C for about 2 weeks, ground and calcined at 1200°C for 2 h. However no data on the morphology of the final materials were reported by the author. 

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