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In ethylene production, hydrocarbon feedstocks (such as ethane or naphtha) are heated in pyrolysis furnaces, separated into gaseous products, and then rapidly cooled, compressed, and purified into final products with the largest energy requirements required in the pyrolysis, refrigeration and rapid cooling (WEC, 1995). Lighter feedstocks such as ethane produce higher ethylene yields. More severe processing conditions (higher temperatures and pressures) used on heavier feedstocks require more energy to crack but also result in a more co-product yields (methane, butadienes, benzene, and toluene) (Phylipsen et al, 1998a). In the US, ethane remains the primary feedstock used in steam cracking, followed by propane, naphtha and gas oil. Chapter 3 describes energy use and energy intensity for ethylene manufacturing in more detail. Methanol is produced through the reaction of carbon monoxide and hydrogen, with the production of hydrogen being a significant energy use. Methanol demand has been driven up in recent years due to increasing demand for Methyl tertiair-butyl ether (MTBE) as a reformulated gasoline additive. Growth over the last decade has averaged 8.5% annually. However, MTBE-use in the U.S. will be phased out in the foreseeable future due to water pollution problems associated with MTBE-use. Estimated energy intensity for methanol (including feedstocks) is 38 GJ/tonne with most of the energy use being used for hydrogen production (Lipinsky and Ingham, 1994). 2.2 Industrial inorganic chemicals, not elsewhere classified (SIC 2819) Industrial inorganic chemicals not elsewhere classified accounted for the second largest share of carbon emissions within the US chemicals sector in 1994 (14%). This category includes a wide variety of inorganic chemicals including sulfuric and hydrochloric acid, potassium fertilizers (potash), alumina, and aluminum oxide. Hydrochloric acid and Potash are produced in bulk quantities and were among the top 40 chemicals produced in the US in 1994. 2.3 Plastic Materials and Resins (SIC 2821) While not as energy-intensive as the production of bulk chemicals, the production of plastic materials in SIC 2821 accounts for a significant share of carbon dioxide emissions (9% of chemical industry emissions in 1994) due to primarily the large volume of production. Some of the main plastic products include polyethylene, (low and high density), polypropylene, polystyrene, and polyvinyl chloride. Ethylene (within SIC 2869) is used as a primary feedstock for polyethylene manufacture. Estimates of per ton energy requirements for polymerization processes are shown in Table 3 below. Estimates from Worrell et al (1994a), except for polystyrene, likely reflect best practice levels for the US. Table 3. Energy Requirements for Plastics Production (GJ/tonne) Product Polyethylene (LDPE) Polypropylene Polystyrene Polyvinyl Chloride* Estimate 1* 9.3 10.5 9.3 11.6 Estimate 2* 1.6 1.2 11.3 9.9 *Estimate (1) is based on Lipinsky and Wesson (1995); Estimate 2 is based on Worrell et al. (1994a). Table 4 shows the production growth rates of high and low density polyethylene, polypropylene, polystyrene, and PVC over the last two decades. As table 4 shows, plastics production has grown rapidly at rates of over 3-8% since 1974, with particularly strong growth in PVC, polypropylene, and high-density polyethylene. Given the continued demand for plastics in a variety of end uses, we expect continued growth in this subsector. 4 1PDF Image | Energy use and energy intensity
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