Chemical engineering is the branch of engineering that applies scientific and mathematical principles to design and develop processes by which available chemicals can be converted into a variety of useful products. A person who practices chemical engineering is called a chemical engineer. Those chemical engineers involved in the design and maintenance of large-scale manufacturing processes are known as process engineers.
Chemical engineering is applicable to a wide range of technologies, including the production of energy, materials, electronics, and pharmaceuticals, the processing of food, and environmental protection and remediation. Development of the high-quality materials and large-scale processes characteristic of industrialized economies is a feat of chemical engineering.
As ecological sustainability takes on ever greater significance in the twenty-first century, there is likely to be a sustained demand for chemical engineers to collaborate with ecologists, mechanical engineers, and others in planning eco-industrial projects. Such projects would integrate several different industrial and biological processes into synergistic complexes to produce materials and products needed by human society.
In 1824, French physicist Sadi Carnot, in his On the Motive Power of Fire, was the first to study the thermodynamics of combustion reactions in steam engines. In the 1850s, German physicist Rudolf Clausius began to apply the principles developed by Carnot to chemicals systems at the atomic to molecular scale. During the years 1873 to 1876, at Yale University, American mathematical physicist Josiah Willard Gibbs, the first to be awarded a Ph.D. in engineering in the U.S., in a series of three papers, developed a mathematical-based, graphical methodology, for the study of chemical systems using the thermodynamics of Clausius. In 1882, German physicist Hermann von Helmholtz, published a founding thermodynamics paper, similar to Gibbs, but with more of an electro-chemical basis, in which he showed that measure of chemical affinity, such as the “force” of chemical reactions is determined by the measure of the free energy of the reaction process. Following these early developments, the new science of chemical engineering began to develop. The following timeline shows some of the key steps in the development of the science of chemical engineering:
Chemical engineering is applied in the manufacture of wide variety of products. The chemical industry proper manufactures inorganic and organic industrial chemicals, ceramics, fuels and petrochemicals, agrochemicals (fertilizers, insecticides, herbicides), plastics and elastomers, oleochemicals, explosives, fragrances and flavors, additives, dietary supplements, and pharmaceuticals. Closely allied or overlapping disciplines include wood processing, food processing, environmental technology, and the engineering of petroleum, glass, paints and other coatings, inks, sealants, and adhesives.
To show the difference between laboratory chemistry and industrial chemical engineering, consider a simple one-step reaction between two reagents R1 and R2 to give a product P and waste W. The reaction may be represented R1 + R2 = P + W. A solvent S and possibly a catalyst C may be required, and it may need to be heated to speed the reaction.
A specific example would be the synthesis of aspirin by the reaction of salicylic acid (R1) with acetic anhydride (R2) in solvent water (S) and in the presence of catalyst phosphoric acid (C). Aspirin is the product P, and acetic acid (W) is also formed.
In the laboratory, 5 grams of R1 (a solid) are added to 120 ml of water in a flask. 5 ml of R2 (a liquid) are added plus 0.5 ml of phosphoric acid solution, and the flask is heated in a water bath. The contents are agitated by swirling the flask or with a laboratory stirrer and heated under reflux for about an hour.
The material is allowed to cool down and crystals of aspirin are formed, which may be filtered off, and perhaps recrystallized. A good yield would be 5 to 6 grams. The remaining solution is poured down the sink.
Now consider an industrial process in which grams are replaced by tons.
Firstly suitable storage (say, for two weeks of production) must be provided for the raw materials. In this case, R1 is a solid and would be put in a storage silo; R2 is a corrosive liquid, combustible and sensitive to water, so would need a closed tank of resistant material. A means of transport to the reactor must be provided, such as a screw conveyor for the solid R1 and a pump and pipes for liquid R2. Chemical engineers would calculate the sizes and power requirements and specify suitable materials. Similar arrangements must be made for the solvent S and the catalyst C. In this case, water is the solvent, but ordinary tap water would not be good enough, so there will be a separate process to clean the water.
The reactor0 now contains 120 tons of water and the other ingredients, so it cannot be swirled. An agitator must be designed and its power consumption calculated to give the necessary mixing. Heating and cooling are considered free in the laboratory, but not in industry. The chemical engineers must first calculate the amount of heat to be added and removed, then design suitable methods to do this, perhaps by passing steam through an outer jacket of the vessel to heat. They will probably decide to pump the reacted mixture to another vessel with a cooler, then to a filter. The solid will then go to further equipment to dissolve, crystallize and filter again, giving perhaps 5.5 tons of aspirin, which will be dried and placed in suitable storage, which must also be designed. (The drying process uses significant amounts of energy.)
However, there is about 125 tons of waste which cannot be just poured down the drain. It will contain some unreacted R1 and about 3 tons of W, which must be recovered and recycled. (In this case, W can be converted to R2 in another reactor.) The catalyst may be recovered, or made harmless by a chemical reaction before disposal. Thus there will be another set of equipment to save the cost of wasting chemicals and to protect the environment. Solvents other than water are generally recycled by distillation, but water is also re-used and recycled as far as economically feasible.
What has been described is a batch process. It will probably be modified to operate continuously, particularly if large amounts of the product are required. Efforts will be made to reduce the amount of energy used and to minimize waste.
Chemical engineers aim for the most economical process. This means that the entire production chain must be planned and controlled for costs. A chemical engineer can both simplify and complicate "showcase" reactions for an economic advantage. Using a higher pressure or temperature makes several reactions easier; ammonia, for example, is simply produced from its component elements in a high-pressure reactor. On the other hand, reactions with a low yield can be recycled continuously, which would be complex, arduous work if done by hand in the laboratory. It is not unusual to build 6-step, or even 12-step evaporators to reuse the vaporization energy for an economic advantage. In contrast, laboratory chemists evaporate samples in a single step.
The individual processes used by chemical engineers (for example, distillation or filtration) are called unit operations and consist of chemical reaction, mass-, heat-, and momentum-transfer operations. Unit operations are grouped together in various configurations for the purpose of chemical synthesis and/or chemical separation. Some processes are a combination of intertwined transport and separation unit operations, (e.g. reactive distillation).
Three primary physical laws underlying chemical engineering design are conservation of mass, conservation of momentum and conservation of energy. The movement of mass and energy around a chemical process are evaluated using mass balances and energy balances which apply these laws to whole plants, unit operations or discrete parts of equipment. In doing so, chemical engineers use principles of thermodynamics, reaction kinetics and transport phenomena. The task of performing these balances is now aided by process simulators, which are complex software models that can solve mass and energy balances and usually have built-in modules to simulate a variety of common unit operations.
The modern discipline of chemical engineering encompasses much more than just process engineering. Chemical engineers are now engaged in the development and production of a diverse range of products, as well as in commodity and specialty chemicals. These products include high performance materials needed for aerospace, automotive, biomedical, electronic, environmental, and space and military applications. Examples include ultra-strong fibers, fabrics, adhesives and composites for vehicles, bio-compatible materials for implants and prosthetics, gels for medical applications, pharmaceuticals, and films with special dielectric, optical, or spectroscopic properties for opto-electronic devices. Additionally, chemical engineering is often intertwined with biology and biomedical engineering. Many chemical engineers work on biological projects such as understanding biopolymers (proteins) and mapping the human genome.
All links retrieved February 8, 2017.
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