Chemical Engineering

Summary

Chemical engineering, sometimes also called processing engineering, is the field of engineering that studies the conversion of raw chemicals into useful products by means of chemical transformation. Chemical engineering applies engineering concepts to design, construction, operation, and improvement of processes that create products from chemicals. For example, chemical engineering converts petroleum into products such as gasoline, lubricants, petrochemicals, solvents, plastics, processed food, electronic components, pharmaceuticals, agricultural chemicals, paints, and inks. Chemical engineering relies on all the technologies used in chemical and related industries, including distillation, chemical kinetics, mass transport and transfer, heat transfer, control instrumentation, and other unit operations, as well as economics and communications.

Definition and Basic Principles

Chemical engineering is the discipline that studies chemical reactions used to manufacture useful products, which appear in almost everything people have and use. Chemical engineering also is involved with reduction and removal of waste, improvement of air and water quality, and production of new sources of energy. It is also the responsibility of chemical engineering to ensure the safety of all involved through design, training, and operating procedures.

The dividing line between chemistry and chemical engineering is hazy and there is much overlap. Primarily chemistry discovers and develops new reactions, new chemicals, and new analytical tools. It is the role of chemical engineering to take these discoveries and use them to evaluate the economic possibilities of a new product or a new process for making an existing product. Chemical engineers determine what processes or unit operation are needed to carry out the reactions required to produce, recover, refine, and store a particular chemical. In the case of a new process, chemical engineers consider what other products could be made using the process. They also examine what products newly discovered chemicals can be used to make.

The largest field of chemical engineering applications is the petroleum and petrochemical industries. Crude oil, if merely distilled, would yield less than 35 percent gasoline. Through reactions such a catalytic cracking and platforming, these yields have come to approach 90 percent. Other treatments produce other fuels, lubricants, and waxes. The lighter components of crude oil became the raw materials used to make most of the plastics, fibers, solvents, synthetic rubber, paper, antifreeze, pharmaceutical drugs, agricultural chemicals, and paints that are seen in people's daily lives.

Background and History

Modern chemical engineering started in Germany with the availability of coal tar, a by-product of metallurgical coke. German chemists in the late nineteenth century used these tars to make aniline dyes and pharmaceuticals, most famously aspirin. Large-scale production meant that organic chemists needed help from engineers, usually mechanical, who designed and built the larger units needed. It became a tradition in Germany to pair a chemist with a mechanical engineer who would work together on this type of operation.

Americans first trained engineers in the chemical sciences to improve their understanding of chemical processes. In 1891, the Massachusetts Institute of Technology (MIT) became the first school to offer a degree in chemical engineering. By 1904, the first handbook of chemical engineering, an encyclopedia of useful physical, chemical, and thermodynamic properties of chemicals and other information needed for design work, was published. A desire among professionals to share ideas, discoveries, and other useful information led to the founding in 1908 of the American Institute of Chemical Engineering.

World War I increased demand for military chemicals and the fuel needed for a mechanized war. Previously, chemicals had been developed in batches, but the petroleum industry converted to using continuous operations to raise the production rate. Soon the industry was developing systems to control production, first by empirical methods and then by scientific and mathematical techniques.

How It Works

The design, construction, and operation of chemical engineering projects are commonly divided into various unit operations. These unit operations, singly or in combination, require a basic knowledge and understanding of many scientific, mathematical, and economic principles.

Mathematics drives all aspects of chemical engineering. Calculations of material and energy balances are needed to deal with any operation in which chemical reactions are carried out. Kinetics, the study dealing with reaction rates, involves calculus, differential equations, and matrix algebra, which is needed to determine how chemical reactions proceed and what products are made and in what ratios. Control system design additionally requires the understanding of statistics and vector and non-linear system analysis. Computer mathematics including numerical analysis is also needed for control and other applications.

Chemistry, especially organic and physical, is the basis of all chemical processes. A full understanding of organic chemistry is essential in the fields of petroleum, petrochemicals, pharmaceuticals, and agricultural chemicals. A great deal of progress was made in the field of organic chemistry beginning in the 1880s. Physical chemistry is the foundation of understanding how materials behave with respect to motion and heat flow. The study of how gases and liquids are affected by heat, pressure, and flows is needed for the unit operations of mass transfer, heat transfer, and distillation.

Distillation, in which more volatile components are separated from less volatile materials, requires knowledge of individual physical and thermodynamic properties and how these interact with one another in mixtures. For example, materials with different boiling points sometimes form a constant-boiling mixture, or azeotrope, which cannot be further refined by simple distillation. A well-known example of this is ethyl alcohol and water. Although ethyl alcohol boils at 78 degrees Celsius as compared with 100 degree Celsius for water, a mixture of ethyl alcohol and water that contains 96 percent (by weight) or 190-proof ethyl alcohol is a constant-boiling mixture. Further concentration is not possible without extraordinary means.

Inorganic chemistry deals with noncarbon chemistry and is often considered basic as it is taught in high school and the first year of college. Many of the chemical industries do make inorganic chemicals and products such as ammonia, caustic, chlorine, oxygen, salts, cement, glass, sulfur, carbon black, pigments, fertilizers, and sulfuric, hydrochloric, and nitric acids. Catalysts are inorganic materials that influence organic reactions, and understanding them is very important. The effectiveness of any catalyst is determined by its chemical composition and physical properties such as surface area, pore size, and hardness.

Analytical chemistry was once strictly a batch process, in which a sample would be collected and taken to a laboratory for analysis. However, modern processes continually analyze material during various stages of manufacture, using chromatography, mass spectroscopy, color, index of refraction, and other techniques.

The disciplines of mechanical, electrical, and electronic engineering are needed by the chemical engineer to be able to consider process design, materials of construction, corrosion, and electrical systems for the motors and heaters. Electronic engineering is basic knowledge needed for control systems and computer uses.

Safety engineering is the study of all aspects of design and operation to find potential hazards to health and physical damage and how to correct them. This work begins at the start of any project. Not only must each and every part of a process be examined but also each chemical involved must be checked for hazards, either by itself or in combinations with other chemicals and materials in which it will come in contact. Safety engineering also is a part of operator training and the writing of operating procedures used for the proposed operation.

Communication is key to all progress. Chemical engineers must be able to interact with others; no idea—whether for a new process or product or an improvement in an existing operation—can be implemented unless others are convinced of its value and are willing to invest in it. Coherent and easily understood reports and presentations are as important as any other part of a project. Operating procedures must be reviewed with the operation personnel to ensure that they are understood and can be followed.

Economics is the driving force behind all design, construction, and operations. The chemical engineer must be conversant in finance, banking, accounting, and worldwide business practices. Cost estimates, operating balances to determine actual costs, market forces, and financing are a necessary part of the work of any chemical engineer.

Applications and Products

Chemical engineering is involved in every step in bringing a process from the laboratory to full-scale production. This involves determining methods to make the process continuous, safe, environmentally compatible, and economically sound. During these steps, chemical engineers determine the methods and procedures needed for a full-scale plant. Mathematical modeling is used to test various steps in the process, controls, waste treatment, environmental concerns, and economic feasibility.

Acetonitrile Process. The acetonitrile process demonstrates how these disciplines combine to produce a process. Acetonitrile is a chemical used as a solvent and an intermediate for agricultural chemicals. The chemistry of this process involves reacting acetic acid and ammonia to make acetonitrile and water. The reaction between these raw materials is carried out over a catalyst at 400 degrees Celsius. The reaction takes place in tubes loaded with a catalyst of phosphoric acid deposited on an alumina ceramic support, which allows the reaction to take place at high rates. The reaction tubes are located in a gas-fired furnace designed to provide even temperatures throughout the length of the tubes. The exiting gases are cooled and condensed by scrubbing with water. This mixture enters a train of distillation columns, which first removes a constant-boiling mixture of the acetonitrile along with some water. In another distillation column, an azeotroping agent is used to produce an overhead mixture that when condensed, produces two layers with all the water in one layer. The water layer is removed, and the other layer is recycled. The base material leaving the distillation column contains the water-free acetonitrile, which is then redistilled to produce the finished product, which is ready to package and ship.

Such a process involves chemical engineers in the design and assembly of all the equipment needed for the process: the furnace, reactor tubes, distillation columns, tanks, pumps, heat exchangers, and piping. The chemical engineers also create the controls, operating procedures, hazardous material data sheets, and startup and shut-down instructions, and provide operator training. Once the plant is running, the role of the chemical engineer becomes operating and improving the unit.

Petroleum and Petrochemical Applications. Chemical engineering is used in the petroleum and petrochemical industries. At first, all petroleum products were produced by simple batch distillations of crude oil. Chemical engineering developed continuous distillation processes that permitted marked increases in refinery production rates. Then high-temperature cracking methods permitted the conversion of high-boiling petroleum fractions (end products of refining) to useful products such as more gasoline. This was followed by the use of catalytic cracking that improved the gasoline output even more.

Distillation can take many forms in addition to simple atmospheric distillation. Chemical engineers can determine the need to use pressure distillation for the purification of components that are normally gases. Vacuum distillation may be useful if there are high-boiling components, which are sensitive to the elevated temperatures required for normal distillation. With the need for aviation gasoline and other high-octane fuels, chemical engineering developed such methods as platforming, which uses the addition of a platinum catalyst to speed up certain reactions, to convert lower-boiling petroleum components into high-octane additives.

Petrochemical industries convert surplus liquefiable gases into solvents, plastics, synthetic rubber, adhesives, coatings, paints, inks, intermediates for agricultural chemicals, food additives, and many more items.

Inorganics.Sulfuric acid is typical of a major inorganic product that requires the type of process improvement that is provided by chemical engineering. Sulfuric acid is a high-volume, low-profit-margin material that has been in production for more than a hundred years. The chemistry is well known. Sulfur is vaporized, mixed with air, and passed over a catalyst to make sulfur trioxide, which is then adsorbed into water to make sulfuric acid. Chemical engineers look for better catalysts and seek to improve the purity of raw materials and increase control over temperature, flows, safety, and environmental concerns.

Biological Applications. The ancient biological process of fermentation is best known for its role in producing alcoholic beverages and breads. Although many people do not realize that fermentation is a chemical reaction, it is much the same as other organic reactions. The biological component is a microorganism that acts as the catalyst. Biochemical engineering products created using fermentation include acetone and butyl acetate, chemicals that were in critical demand by the aviation industry during World War I.

Biochemical engineering also made antibiotics available on a large scale. In the 1920s, Sir Alexander Fleming discovered the antibiotic properties of penicillin, which was produced in laboratory flasks, a few grams at a time. During World War II, the need for penicillin increased, and chemical engineers developed a large-scale process for producing penicillin from corn. This process was adapted to produce other antibiotics, and chemical engineering processes were developed for the manufacture of many synthetic drugs. Genetic modifications are being developed that are expected to produce the drugs of the future.

Fibers. In 1905, the first synthetic fiber, reconstituted cellulose, commonly known as rayon, was developed. The second synthetic fiber, cellulose acetate, which was developed in 1924, is still manufactured in large amounts for use in cigarette filters. The first fully synthetic fiber was nylon, a commonly used polyamide, followed by polyesters. Chemically treated cotton, known as permanent press, is another product of chemical engineering. In addition to fibers, the textile industry uses lubricants, dyes, pigments, coatings, and inks, all derived by chemical processes.

Plastics. The first thermoplastic, a material that could be reheated and molded, were the cellulosics that are used to make large signs, toys, automobile parts, and other objects that can be easily fabricated. Acrylic polymers such as methyl methacrylate are formed into optically clear sheeting and used as a nonshattering replacement for plate glass and for eyeglass and camera lenses. Polyethylene, developed during World War II as a superior coating for the wiring needed in radar, is still used as an insulator. The most common use for polyethylene and polypropylene is as the thin film used in plastic bags. Molded items such as bottles, containers, kitchen items, and packaging are manufactured from these polymers as well as polyesters, nylon, polyvinyl chloride (PVC), polystyrene, Teflon, and polycarbonates. The manufacture of all these plastics was developed through chemical engineering and depends on it for operation and improvement.

Refrigerants. The first refrigerants were sulfur dioxide and ammonia. These substances were rather hazardous, so a new range of refrigerants was developed. These refrigerants, commonly known as Freon, are halogenated hydrocarbons that can be tailored to the needs of the application. Home air-conditioning, automotive air-conditioning, and industrial applications are examples of these uses.

Nuclear Energy. The nuclear energy industry requires many solvents and reaction agents for the separation and purification of the fuel used in the reactors. Special coatings and other materials used in the vicinity of intense radiation were developed by the chemical industry. Recovery of the spent nuclear fuel requires specially developed techniques, again requiring solvents and reactions.

Coatings. A typical example of corrosion is the rusting of iron. Corrosion causes the loss of equipment as well as physical and health hazards not only in the chemical industry but also in almost every aspect of modern life. Corrosion is avoided through metal alloys such as stainless steel and protective coatings. These coatings can be tailored to protective needs inside and outside of a product.

Water Treatment. Raw water, especially for industrial purposes, requires processing to remove suspended solids and soluble organics as well as inorganic ions such as sodium, calcium, iron, chlorides, sulfates and nitrates. Chemical engineering is used to design and manufacture the ion-exchange resins, coagulants, and adsorbents needed, as well as the procedures for use and regeneration of ion-removal systems.

Waste Treatment. Many chemical processes produce by-products or waste that may be hazardous to the environment and represent uncaptured value. The role of process improvement engineers is to first find ways to reduce waste and failing that, to develop methods to convert these wastes into nonhazardous materials that will not harm the environment.

Agricultural Applications. Agricultural chemicals such as insecticides, herbicides, fungicides, fertilizers, seed coatings, animal feed additives, and medicines such as hormones and antibiotics all are produced by chemical means. Other chemicals are used in the preparation of products for harvesting and transporting to market.

Food Processing. The manufacture of food stuffs such as dairy products, breakfast foods, soups, bread, canned goods, frozen foods, and other processed foods, as well as meats, fruits, and vegetables, use engineering operations such as heat transfer to heat or cool.

Careers and Course Work

A bachelor's degree in chemical engineering takes four to five years of study. Course work includes a great deal of chemistry, including organic, physical, and analytic chemistry; chemical engineering courses; and mechanical, electrical, and civil engineering courses. Advanced mathematics courses are also required. Courses in English, economics, history, and public speaking will also help further the career of a chemical engineer.

A bachelor's degree is generally sufficient for an entry-level position at most industrial companies. Many universities offer engineering degree programs in which students take classes one semester and work at a chemical plant the next semester, repeating this pattern until graduation. This enables students to pay for their education and to gain relevant work experience, as well as to make contacts within the industry.

A master's degree in chemical or computer engineering or a master's of business administration degree will help advance a career in chemical engineering. A doctorate is required for those seeking jobs in colleges and universities.

In 2020 the US Bureau of Labor Statistics reported 26,300 jobs for chemical engineers in the United States. This was expected to increase by 2,400 positions over the next decade or at about an average pace.

Social Context and Future Prospects

Many of the major issues that face society, particularly those concerning the supply of energy and water, the environment, and climate change, require immediate and continuing action from scientists such as chemists and chemical engineers. In the future, chemical engineers will likely be in greater demand in fields employing emerging technologies, such as nanotechnology, biotechnology, and alternative energies.

Energy. The predominant sources of energy are coal, liquid petroleum, and natural gas. Coal use produces air pollutants such as sulfur dioxide, nitrogen oxides, mercury, and more carbon dioxide per British thermal unit of energy generated than any of the other energy sources. Liquid petroleum and natural gas also produce carbon dioxide and other air pollutants. Problems regarding the limited supply of all three sources of energy are causing worldwide economic and political disruptions. Chemical engineering may be able to provide economical answers in that it can create clean oil and gas from coal and oil shale, produce better biofuels from nonfood agricultural crops, and develop materials to make solar energy, wind energy, and hydrogen fuel cells practical.

The Environment. Both air and water pollution are affected by chemicals that are the result of manufacturing, handling, and disposing of materials such as solvents, insecticides, herbicides, and fertilizers. Chemical engineering has reduced factory emissions through the development of water-based coatings. In addition, new methods of converting solid wastes into usable fuels will help the environment and provide new fuel sources.

Water Access. The supply of fresh water for personal and agricultural use is already limited and will become more so as the world population grows. Two methods for recovering fresh water are distillation and reverse osmosis. To become practical, distillation systems must use better materials to prevent corrosion. Chemical engineers are likely to develop new alloys and ways to manufacture them, as well as better heat-recovery methods to reduce cost and lower carbon dioxide emissions. Although the long-range effect of increased concentrations of carbon dioxide on the climate may not be known for sure, chemical engineers are striving to develop methods to control and reduce these emissions.

Reverse osmosis uses membranes that allow water to pass through but not soluble salts. Chemical engineers are working on improved membrane materials that will allow higher pressures to improve efficiency and membrane life.

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