Engineering, chemical

Chemical engineering involves the application of chemistry, physics, and engineering to the design and operation of plants for the production of materials that undergo chemical changes during their manufacture (22). Such materials include various chemicals, such as paints, lubricants, fertilizers, pharmaceuticals and cosmetics, petroleum products, foods, metals, plastics, ceramics, and glass. 

In these and other industries, chemical engineers are responsible for creating systems for producing large quantities of materials that chemists make in small quantities in the laboratory. Ghemical engineers select appropriate processes and arrange them in proper sequence to produce the desired product. These include  

Mass transfer processes such as absorption, humidification, and drying. 

The complex field of photochemical engineering is governed by the reaction system, the lamp technology and by chemical engineering (see Fig. 3-3). Suitable photoreactor concepts can only be obtained by an appropriate combination of these three aspects. Nevertheless, many commercially available photoreactor systems are still based on empirical developments coupled with successive improvements, and on the expertise of the manufacturers. 

Particular problems of photochemical engineering are related to the scaling-up of photoreactors. This is mainly due to problems of lamp technology related to the variations of the radiant exitance M with the increase of the lamp s geometry and electrical input power. Thus, to carry out a reasonable scaling-up and optimization of photoreactors the radiant exitance M or the radiant density (expressed as the ratio of radiant power P to the arc length I of the lamp in W cm , see Tab. 4-1) of the lamps used must be fixed (Braun et al., 1993 a). This, however, is a challenge for the manufacture of lamps. 

Classical chemical reaction engineering provides mathematical concepts to describe the ideal (and real) mass balances and reaction kinetics of commonly used reactor types that include discontinuous batch, mixed flow, plug flow, batch recirculation systems and staged or cascade reactor configurations (Levenspiel, 1996). Mixed flow reactors are sometimes referred to as continuously stirred tank reactors (CSTRs). The different reactor types are shown schematically in Fig. 8-1. All these reactor types and configurations are amenable to photochemical reaction engineering. 

Many commercial photochemical reactor systems make use of the batch recirculation mode for the treatment of highly contaminated wastewaters of limited volume. On the other hand, cascades of photoreactor modules (in serial or parallel mode) allow the gradual treatment of contaminated water streams with a very high photon flow Op in total. Hence, there exist powerful photochemical waste- 

Levenspid earlier presented, in 1972, a qualitative discussion about the product distribution related to photochemical reactions comparing batch and batch recirculation photochemical reactors. The essentials of this discussion can be transferred to photo-initiated AOPs (at least to the H2O2-UV process), which at low concentrations of a pollutant M ([M] 100 mg L ) usually follow an overall first order reaction kinetics (Bolton et al, 1996). 

Benefits of large scale production are unusually high in the case of continuous flow chemical plants. When the size of a plant doubles, the unit cost of product approaches 0.5. This poses a difficult economic problem. While it is tempting to overbuild a new plant in anticipation of increased product demand in the future, this may prove disastrous if increased demand falls short of expectations due to unexpected competition, or emergence of a better product or process. Two design problems follow. The first involves the possibility of replacing a batch type process by a continuous flow 1) )6, while the second involves improvement of atypical unit process. 

Some of the concepts introduced in this text are complex and usually require an entire course and its prerequisites to appreciate fully. You must be willing, therefore, to set aside questions about the basis for certain material or the origins of certain equations or relationships. We will, however, attempt to provide at least a heuristic description of the material s origin and point to where in the chemical engineering curriculum the material is discussed in more detail. 

Finally, in this text we attempt to appeal to a variety of learning and thinking styles. We appreciate that not all students prefer to think globally, reason deductively, or perceive visually. In each of the exercise sets we have attempted to invoke different styles of learning to make learning chemical engineering as inclusive as possible. 

Synthetic rubber. Elastic materials, such as automobile tires and drive belts, are an integral part of everyday life. The annual production of rubber in 1983 was twenty-two billion pounds. Remarkably, this industry was developed in only two years, just in time to replace shortages of natural rubber during World War II. 

Antibiotics. In 1918 an influenza epidemic killed twenty million people worldwide, one-half million in the United States alone. Venereal diseases were incurable. Until the 1950s polio crippled millions. Discovering medicines was only part of the solution. After it was observed that a mold inhibited bacterial growth in a Petri dish, chemical engineering developed the technology to ultimately produce millions of pounds per year of penicillin. Chemical engineering made possible the mass production of medicines and the subsequent availability to people worldwide. 

Polymers. Plastics - such as PVC, nylon, polystyrene, and polyethylene - are the predominant materials for consumer products. Plastics have replaced wood, metal, and glass in many applications because of their superior strength/weight ratio, chemical resistance, and mechanical properties. 

---

This chapter presents a general method for estimating nonidealities in a vapor mixture containing any number of components this method is based on the virial equation of state for ordinary substances and on the chemical theory for strongly associating species such as carboxylic acids. The method is limited to moderate pressures, as commonly encountered in typical chemical engineering equipment, and should only be used for conditions remote from the critical of the mixture. 

Figure 1.2 Process design starts with the reactor. The reactor design dictates the separation and recycle problem. (From Smith and Linnhoff, Trans. IChemE, ChERD, 66 195, 1988 reproduced by permission of the Institution of Chemical Engineers.)...

Figure 3.8 Separation of a minimum boiling azeotrope by pressure change. (From Holland, Gallun, and Lockett, Chemical Engineering, March 23, 1981, 88 185-200 reproduced by permission.)...

Figure S.19 The approach based on optimization of a reducible structure starts with the most general configuration and simplifies. (From Eliceche and Sargent, IChemE Symp. Series No. 61 1, 1981 reproduced by permission of the Institution of Chemical Engineers...

Perry, R. H., Chemical Engineers Handbook, 6th ed., McGraw-Hill, New York, 1984. 

Figure 11.1 An inertial collector. (Reproduced with permission from Stenhouse, "Pollution Control, in Teja, Chemical Engineering and the Environment, Blackwell Scientific Publications, Oxford, UK, 1981.)...

---