Chemical processes, definition

The selectivity, conversion, and product yield of chemical reactions along with the power inputs, basically determine the practical availability of a chemical process. Definitions of these parameters may be found in [1-6],... 

No single method or algorithm of optimization exists that can be apphed efficiently to all problems. The method chosen for any particular case will depend primarily on (I) the character of the objective function, (2) the nature of the constraints, and (3) the number of independent and dependent variables. Table 8-6 summarizes the six general steps for the analysis and solution of optimization problems (Edgar and Himmelblau, Optimization of Chemical Processes, McGraw-HiU, New York, 1988). You do not have to follow the cited order exac tly, but vou should cover all of the steps eventually. Shortcuts in the procedure are allowable, and the easy steps can be performed first. Steps I, 2, and 3 deal with the mathematical definition of the problem ideutificatiou of variables and specification of the objective function and statement of the constraints. If the process to be optimized is very complex, it may be necessaiy to reformulate the problem so that it can be solved with reasonable effort. Later in this section, we discuss the development of mathematical models for the process and the objec tive function (the economic model). 

Classification is by definition used preponderantly in the treatment of raw materials. However, these raw materials find their way into chemical processing per se and thus become of interest to the chemical engineer, particularly when the products to be treated reaci better when of a defined cleanliness, size, gravity, or moisture content. 

What do we mean when we speak of an inherently safer chemical process Inherent has been defined as existing in something as a permanent and inseparable element, quality, or attribute (American College Dictionary, 1967). A chemical manufacturing process is inherently safer if it reduces or eliminates the hazards associated with materials and operations used in the process, and this reduction or elimination is permanent and inseparable. To appreciate this definition fully, it is essential to understand the precise meaning of the word hazard. A hazard is defined as a physical or chemical characteristic that has the potential for causing harm to people, the environment, or property (adapted from CCPS, 1992). The key to this definition is that the hazard is intrinsic to the material, or to its conditions of storage or use. Some specific examples of hazards include ... 

Process definition and design criteria Process and equipment design Company memory (management information) Documentation of risk management decisions Protective systems Normal and upset conditions Chemical and occupational health hazards... 

A single, all-embracing definition of human error is difficult to achieve. For the engineer, the worker in a system such as a chemical process plant may be... 

The Center for Chemical Process Safety s projects fall into a number of general topic areas that comprise a comprehensive program. These topic areas include identification of hazards and analysis of risks, prevention and mitigation of the hazards identified, and better definition of areas affected by a release of hazardous materials. This book is the latest in the series dealing with hazard identification and risk analysis. 

Mixing of fluids is necessary in many chemical processes. It may include mixing of liquid vith liquid, gas with liquid, or solids with liquid. Agitation of these fluid masses does not necessarily imply any significant amount of actual intimate and homogeneous distribution of the fluids or particles, and for this reason mixing requires a definition of degree and/or purpose to properly define the desired state of the system. 

The thermal decomposition of a solid, which necessarily (on the above definition) incorporates a chemical step, is sometimes associated with the physical transformations to which passing reference was made above melting, sublimation, and recrystallization. Aspects of the relationships between physical transitions and decomposition reactions of solids are discussed in a book by Budnikov and Ginstling [1]. Since, in general, phase changes exert significant influence upon concurrent or subsequent chemical processes, it is appropriate to preface the main survey of the latter phenomena with a brief account of those features of melting, sublimation, and recrystallization which are relevant to the consideration of thermal decomposition reactions. 

The definition of the chemical processing industries (CPI) used in this table is the one used by Data Resources and Chemical Engineering in compiling their statistics on these industries. For several of the industries listed, only a part is considered to be in the CPI and data are presented for this part only. A list of the Standard Industrial Classification codes used to define the CPI for this table is given in Appendix C. 

Homogeneous catalysts are very often known as examples of single-site catalysts characterized by complete structural definition and (presumably) complete knowledge of the chemical processes occurring at their catalytic centers. It is a matter of fact that the homogeneous catalysts are molecular complexes constituted by an active core containing a single active atom (of-... 

Stankiewicz and Moulijn extend the definition of process intensification from size reduction of apparatus to dramatic improvements in key features of chemical processing [25]. Substantial decreases in the following process-engineering properties are listed ... 

In order to exemplify the potential of micro-channel reactors for thermal control, consider the oxidation of citraconic anhydride, which, for a specific catalyst material, has a pseudo-homogeneous reaction rate of 1.62 s at a temperature of 300 °C, corresponding to a reaction time-scale of 0.61 s. In a micro channel of 300 pm diameter filled with a mixture composed of N2/02/anhydride (79.9 20 0.1), the characteristic time-scale for heat exchange is 1.4 lO" s. In spite of an adiabatic temperature rise of 60 K related to such a reaction, the temperature increases by less than 0.5 K in the micro channel. Examples such as this show that micro reactors allow one to define temperature conditions very precisely due to fast removal and, in the case of endothermic reactions, addition of heat. On the one hand, this results in an increase in process safety, as discussed above. On the other hand, it allows a better definition of reaction conditions than with macroscopic equipment, thus allowing for a higher selectivity in chemical processes. 

Keeping in mind the controversial discussion on new physics in micro reactors [198], we certainly have to be at least as careful when introducing or claiming essentially novel chemical processes. A thorough scientific consideration is required for an exact definition and differentiation here that is beyond the scope of this book. So far, no deep-rooted scientific work has been published analyzing the origin of the novelty of chemistry under micro-channel processing conditions. 

To give a thorough, rational review of the field of chemical micro-process technology itself, one ideally would like to follow a deductive analysis route, pursuing a bottom-up approach. First, one may provide a definition of micro reactors, then search for the impacts on the engineering of chemical processes, and try to propose routes for exploitation, i.e. applications. Alternatively, for a less comprehensive, but more in-depth description, one could use a top-dovm approach starting with a selected application and try to design an ideal micro reactor for this. 

A common definition of green chemistry, which clearly encompasses considerable chemical engineering as well, is the design, development and implementation of chemical processes and products to reduce or eliminate substances hazardous to human health and the environment, (P. T. Anastas and J. Warner, Green Chemistry Theory and Practice, Oxford University Press, Oxford, 1998). A more recent article expands this definition to twelve principles (M. Poliakoff, J. M. Fitzpatrick, T.R. Farren and P.T. Anastas, Science, 297, 807-810 (2002). 

Safety, hazard, and risk are frequently-used terms in chemical process safety. Their definitions are... 

Develop a definition for a major incident, and compare it to CCPS s definition. See CCPS, Plant Guidelines for Technical Management of Chemical Process Safety (1992), p. 236. 

The modeling of the plant, the chemical processes, and the production plan can be performed entirely in a graphical manner using three editors, the recipe editor, the plant editor and the production plan editor. A fourth editor is available for the definition and update of a physical properties library. The physical properties library is required to parameterize the models of the plant and of the recipes for the calculation of state changes during the processing steps in simulation. 

Process Knowledge and Documentation—The main features here are process definition and design criteria, process and equipment design, company memory (management information), documentation of risk management decisions, protective systems, normal and upset con-dtions, and chemical and occupational health hazards. 

Definition of Terms The following are terms necessary to characterize fires and explosions (Crowl and Louvar, Chemical Process Safety Fundamentals with Applications, 2d ed. Prentice-Hall, Upper Saddle River, N.J., 2002, pp. 227-229). 

Having set the fundamental definitions in the field of safety research, this Section discusses how the determination of safety indicators developed over time, and why it is still possible for accidents to happen in the chemical process industry. 

The number of Sis, present in today s chemical process industry is overwhelming as discussed by Tixier (Tixier et al., 2002). These indicators are categorized in several ways in literature, for example pro-active versus reactive indicators. Many of these categories are not unambiguous. Some authors, like Kletz (Kletz, 1998) define proactive as prior to the operational phase of an installation while other authors, like Rasmussen et al. (Rasmussen et al., 2000), define pro-active as prior to an accident. In this thesis two categories of indicators are used, i.e. pro-active and reactive indicators. Here the definition of Rasmussen (Rasmussen et al., 2000) is adopted, who defined pro-active indicators as indicators before an accident and reactive indicators as indicators after an accident. Moreover, the pro-active indicators are divided into predictive and monitoring indicators. The monitoring indicators use actual events as a measure for the likelihood, while the predictive indicators predict the likelihood. 

CSB searched over 40 data sources for incidents that met its definition of a reactive incident (Section 2.1). The data search focused on recent incidents (since 1980) where the primary cause was related to chemical reactivity however, the 1980 cutoff is not intended to diminish the important lessons learned from prior incidents. The search covered both chemical manufacturing (i.e., raw material storage, chemical processing, and product storage) and other industrial activities involving bulk chemicals, such as... 

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