Design criteria chemicals

Chemical Rockets/Propellant Hazards, Vol I, General Safety Engineering Design Criteria, Chemical Propulsion Information Agency Publication 194, Johns Hopkins Applied Physics Laboratory, Laurel, MD (1971). 

In the introduction to this chapter it has been already pointed out that for the design of chemical process equipment rules of thumb exist. Upon closer examination, these rules provide conditions which unconsciously accept partial similarity. Actually, one cannot expect that complicated processes of fluid dynamics occurring during mass and heat transfer can be adequately described by criterions such as power per unit of volume, P/V, for mixing vessels and superficial gas velocity, v = q/S, for bubble columns. 

Although much is understood about the hazard of various substances, chemists frequently neglect toxicity as a design criterion when they are evaluating the performance of a chemical substance. Because hazardous materials are so routinely used in the laboratory, hazard becomes a trivial matter. Hazard should be explicitly considered and minimized during chemical design. 

Designing chemicals that are less toxic is one of the principles of green chemistry and the focus of this chapter is to present an expansion of this principle into a comprehensive approach for designing safer chemicals that can be used in the classroom. The same tools of chemistry used to examine structure, kinetics, dynamics and mechanisms that have revolutionized the electronics, transportation, and communication industries can also be used to design minimal hazard into chemical products. Minimized hazard needs to be understood as a performance criterion in the design of safer chemicals. The existence of hazard should be recognized as a design flaw. 

Anastas, N.T. and Warner, J.C. (2005) The incorporation of hazard reduction as a chemical design criterion in green chemistry, Chem. Health Saf, 12(2) 9-13. 

Green Chemistry, defined as the design of chemical products and processes that reduce or eliminate the use and generation of hazardous substances (5), has been referred to as pollution prevention at the molecular level. This emerging area recognizes fiiat during the design phase of any chemical synthesis, product, or process, minimized hazard must be viewed as a performance criterion. Moreover, hazard must also be viewed as a physical/chemical property that is possible to manipulate and control at die molecular level. 

The chemical and pharmaceutical industries use a good deal of piping, often for the transport of aggressive fluids. The design criterion in these circumstances is usually resistance to corrosion or solvation of the pipe wall. These industries will accept high materials cost, for instance stainless steel is commonly used. Plastic materials are therefore used when they have appropriate chemical resistance or perhaps temperature tolerance. Reinforced-plastic pipes in particular are also used in the chemicals sector. 

A central criterion for the design of chemically cross-linked systems is the polymerization rate, and this rate correlates directly to the setting time. A fast-curing material is highly desirable in clinics, as it would reduce the working time of the surgeon and the risk of developing infections in the defect. In addition, system viscosity increases... 

In this paper I have attempted to demonstrate a method for the development of hyperbolic rate models that are adequate for the design of chemical reactors. The method is rapid and overcomes most of the problems that historically have hampered the development of such models for complex reactions. I have shown that the quality of fit of a model to error-containing data is a poor criterion for model discrimination, and that several models may predict almost equally well. This, of course, has been known for a long time, but it has not been widely recognized that the model that fits the data least well may be the best model, and that the converse also may be true. In the final analysis... 

Five of the criteria are normally considered when any air pollution monitor is designed however, the fifth criterion—portability—is essential in a personal monitor. Obviously, this requirement has an impact on the other criteria because it establishes a challenge for achieving specificity for a chemical or suite of chemicals, for low detection limits for adequate determination of the concentration and exposure, and for units that are not cost-prohibitive. Sensitivity of current personal monitors is less than that for stationary monitoring techniques. Thus, entirely new approaches appear to be necessary for detection of a contaminant in a personal monitor. 

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