OVERVIEW

Many chemical industry practices are highly energy- and water-intensive. For example, the Haber-Bosch process (described above), which produces 500 million tons of ammonia-based fertilizer annually, consumes 1-2 % of the entire world energy supply. Light olefins (ethylene and propylene) are versatile chemical building blocks and are produced in very large quantities (ca. 150 million tons/a). The main process is thermal (steam) cracking of hydrocarbons, conducted at ca. 900 °C. In 2000, this accounted for about 3 x 1018 J of primary energy use, or about 20 % of all the energy consumed by the global chemical industry, and nearly 200 million tons of CO2 emissions - about 30% of all CO2 emissions by the chemical industry. Some of this energy use is thermodynamically unavoidable, since chemical reactions that are thermodynamically unfavorable require energy input to proceed. However, innovative design of catalysts and reactors can result in huge energy savings. Separations are another energy-intensive component of the chemical and related industries. These essential purification steps generally account for 40 - 70% of plant operating costs. A large part of this cost is energy, which is required to drive thermodynamically unfavorable “un-mixing”. Energy consumption depends sensitively on how the separation devices are configured: sub-optimal sequences can result in energy penalties of 50% or more. The design of optimal separation systems with appropriate heat integration can lead to very large energy savings. Likewise, the chemical industry is a large user of freshwater; in regions where the chemical industry is concentrated, such as Texas, its fraction of industrial state freshwater use is ca. 45%. Process optimization to minimize the use of freshwater is another critical sustainability issue.