7.4.3 Chemicals and fertilizers
The chemical industry is highly diverse, with thousands of companies producing tens of thousands of products in quantities varying from a few kilograms to thousand of tonnes. Because of this complexity, reliable data on GHG emissions is not available (Worrell et al., 2000a). The majority of the CO2-eq direct emissions from the chemical industry are in the form of CO2, the largest sources being the production of ethylene and other petrochemicals, ammonia for nitrogen-based fertilizers, and chlorine. These emissions are from both energy use and from venting and incineration of byproducts. In addition, some chemical processes create other GHGs as byproducts, for example N2O from adipic acid, nitric acid and caprolactam manufacture; HFC-23 from HCFC-22 manufacture; and very small amounts of CH4 from the manufacture of silicon carbide and some petrochemicals. Pharmaceutical manufacture uses relatively little energy, most of which is used in the buildings that house industrial facilities (Galitsky and Worrell, 2004).
The chemical industry makes use of many of the sector-wide technologies described in Section 7.3. Much of the petro-chemical industry is co-located with petroleum refining, creating many opportunities for process integration and cogeneration of heat and electricity. Both industries make use of the energy in byproducts that would otherwise be vented or flared, contributing to GHG emissions. Galitsky and Worrell (2004) identify separations, chemical synthesis and process heating as the major energy consumers in the chemical industry, and list examples of technology advances that could reduce energy consumption in each area, for example improved membranes for separations, more selective catalysts for synthesis and greater process integration to reduce process heating requirements. Longer-term, biological processing offers the potential of lower energy routes to chemical products (See Section 7.12.1).