Conserving Energy And Fresh Water

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.

Left: Energy consumption by US manufacturing sectors, 2006 (Source: manufacturing Energy Consumption Survey). Right: Water consumption by Texas manufacturing sectors, 2008 (Source: Texas Water Development Board).

CHEMICAL INDUSTRY SUSTAINABILITY

The US chemical industry is a cornerstone of American manufacturing, and the scale of chemical production is immense. The chemical industry produces commodities (large-volume, low-cost basic organic building blocks, such as ethylene, methanol, etc., as well as inorganics such as ammonia...

GLOBAL

FOOD SECURITY

In the 20th century, the invention of the Haber-Bosch process for converting atmospheric nitrogen into ammonia, together with the Green Revolution that dramatically improved agricultural yields, eliminated natural limits on bioavailable nitrogen and enabled an expansion...

INTEGRATING PHYSICAL AND SOCIAL SCIENCE

Replacement of conventional technologies by more sustainable versions is by no means automatic or rapid. New approaches must be cost-competitive; in manufacturing, this often means considering large existing capital investments, as well as supply risks. Changing or uncertain regulatory...

REDUCING DEPENDENCE ON CRITICAL METALS AND MINERALS

The precious metals (Ru, Rh, Pd, Os, Ir, Pt) make highly effective catalysts in a wide range of chemical reactions, due to their readiness to change oxidation states and their reluctance to form recalcitrant oxides. Unfortunately, they are also some of the least abundant elements in the Earth’s...

USING RENEWABLE RAW MATERIALS

The vast majority of synthetic carbon-based materials are currently made from a handful of petroleum-derived building blocks, including ethylene, propylene, butenes, benzene, toluene, xylene and methanol. These components are converted, using chemistry, into polymers...

REDUCING RISK THROUGHOUT THE SUPPLY CHAIN

Reduced risk of exposure and minimal environmental toxicity are important dimensions of sustainable chemistry. Cradle-to-grave life cycle assessments and fate and transport studies must be employed to quantify potential emissions of chemicals at different life cycle stages...

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