Emissions from Recycled Products

The emission of low molecular weight compounds from recycled HIPS has been investigated using microwave assisted extraction or headspace solid phase microextraction followed by GC/MS (32,33). 

Styrene was identified already in virgin HIPS, but the amount significantly decreases in reclaimed HIPS. In addition, benzaldehyde, n-methylbenzenaldehyde, and acetophenone were detected in recy- 

Volatile Compound Relative Abundance Virgin Recycled  

In general, the nature and the relative amount of the emitted compounds increase with higher temperature of exposure and reduced polymeric particle size (33). 

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Control technologies employed for the handling of air emissions normally include the capture and recycling or combustion of emissions from vents, product transfer points, storage tanks, and other handling equipment. Boilers, heaters, other combustion devices, cokers, and catalytic units may require paniculate matter controls. Use of a carbon monoxide boiler is normally a standard practice... 

Figure 3.1 identifies the major stages in a solvents life cycle production, transport, use, and disposal. Although there are many opportunities to recycle and reuse solvents they will eventually need to be disposed of as waste. As an example, consider a process which uses tetrahydrofuran (THF). A 1 kg reduction in the amount ofTHF would reduce the CO2 emissions from THF production by about 16kg [3], This reduction in CO2 emissions does not account for the savings in transportation or disposal of excess THF in a process. Therefore, reductions in solvent use by the pharmaceutical industry not only reduce the waste it produces as part of its processes but also the waste that would be generated from the manufacture of additional solvent. 

Modern industry practice can be extremely effective in limiting lead emissions from recycling facilities. Facility emissions have been a cause of historic concern, with speculation that increased use of lead-acid batteries in electric and/or hybrid electric vehicles might result in unacceptable levels of lead contamination. For example. Lave et al. [23] estimated that emissions to water and air associated with primary lead production, secondary lead production, and battery prodnction were 4, 2, and 1%, respectively, of the total amount of lead processed. In contrast, Socolow and Thomas [24] estimated that secondary smelting and refining were associated with system losses of up to only 0.01% of material processed. 

Assumes 100% of the purf ication purge stream (primarily C02, H2, CH4, and CO) is recycled tothe production step, where the purge stream is burned to generate heat forthe reforming process. There may be some additional purification emissions in other system configurations, but the total sum of emissions from the production and purification steps will remain the same. 

GHG emissions associated with the raw material are determined from the energy used to manufacture the plastic materials and the fuel used to transport them to the plant. The transportation and manufacture of the secondary packaging used to transport the primary raw materials and finished materials may also be considered. The embedded energy of the materials, if made from petroleum products, is also accounted for when it is used as a raw material (Keoleian and Spitzley, 1999 Spitzley et al., 1997). End-of-life emissions may also be included in LCA of milk packaging and include fhe energy used fo recycle the package or emissions in the form of CH4 from a landfill. 

Although photovoltaic conversion is nonpolluting, environmental, health, and safety aspects must be considered, especially with regard to harmful emission and waste products resulting from the production of the solar cell modules. It has been shown that, with proper encapsulation and a proactive recycling program, it should be possible to minimize environmental concerns. 

Another important factor that distinguishes this separation is that it is not environmentally or economically feasible to simply return a rejected stream to the environment, as in a typical aqueous RO process where the brine can be returned to the ocean. The federal regulations mandate that C02 emissions from refineries and chemical plants be reduced to low levels therefore, facilities can no longer afford to dispose of waste hydrocarbon streams in their flare systems. Pure streams from polyolefin reactors and vents from polymer-storage facilities, which were once flared, must be redirected to recovery systems. To reduce the economic penalty of environmental compliance, these paraffin and olefin mixtures must be recovered and recycled. In other words, two products must be made, a useful fuel and a useful chemical product, hence more process engineering is required in order to achieve such an objective. 

The use of ecologically harmless SCCO2 as solvent and substrate in chemical reactions is a particularly intriguing prospect. Increased governmental and environmental restrictions on solvent emission make this supercritical fluid more and more attractive as a reaction medium because it can be easily separated from the product and recycled more efficiently than conventional liquid solvents. The special properties (miscibility, transport properties, etc.) of sc CO2 require a development of suitably adjusted catalysts. A simple transformation of catalyst properties from conventional solvents to SCCO2 will mostly fail, and will not lead to higher catalytic efficiency. Supported catalysts could perhaps play a particular role in this field as the possibility of product extraction by depressurization of the supercritical phase and subsequent compression of the CO2 (solvent/substrate) should permit the development of a profitable continuous process. 

Waste arising from limited feedstock conversion can be minimized in the overall process by recycling unreacted feedstock from the reactor effluent back to the reactor feed. Benefits of such recycling include reduced raw material consumption and reduced waste disposal or emissions. The burdens of recycling such streams include the need for separation of feedstock from reaction products and any necessary compression or pumping of recycled streams. These benefits and burdens have both economic and environmental consequences, which must be identified and evaluated. 

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