Many processes producing chlorinated aliphatic compounds would produce little or no PCDD/PCDF (recent measurements of perchloroethylene gave results below detection limits). However, if residues from processes such as the production of EDC (see above) or other mixed residues are used as a feedstock there may be formation and releases of PCDD/PCDF.
At one time in the UK residues from EDC production were fed to an oxychlorinator to produce per- and trichloroethylene (solvents). This process produced significant quantities of PCDD/F in the residue streams (350-630 g TEQ in the residues from the production of 130,000 tons of tri- and perchloroethylene produced approximately 4,000 μg I-TEQ/t of product – Dyke et al. 1997). The handling and fate of these residues will determine actual releases to the environment. An emission factor for the residues cannot be given. When these production residues occur within chemical production processes and are being recycled into the process, e.g., oxychlorination process, they will show up in the residues from oxychlorination.
Chlorinated Inorganic Chemicals
Chlorine is used in the synthesis of inorganics where it remains in the final product (NaOCl, ClO2, FeCl3, AlCl3, ZnCl2, etc.) or is simply used in the process (TiO2, Si) (SC BAT/BEP 2004). The inorganic chemical manufacturing process of anhydrous magnesium chloride (MgCl2), an intermediate in the manufacture of metallic magnesium is addressed in source group 2. The other process that involves chlorine is the manufacture of titanium dioxide (TiO2).
There are two processes to manufacture TiO2: the chlorine process and the sulphate process. The sulphate process generates much more wastes than the chlorine process and thus, is less common. The chlorine process has grown in use over the past thirty years as a result of its relative compactness, recycling of process materials, better product properties, and considerably lower generation of waste. TiO2 is produced from ores, such as rutile or ilmenite, which is chlorinated at high temperatures to produce titanium tetrachloride (TiCl4), a stable, distillable liquid. TiCl4 is purified and oxidized with oxygen, liberating chlorine, which is recycled into the process. Optimal operating temperature is above 600°C (SC BAT/BEP 2004).
The presence of coke, chlorine, metals, and elevated temperature may give rise to formation of PCDD/PCDF analogous to their formation in oxychlorination. PCDD/PCDF, if formed, partition into solid residues (streams containing residual coke).
7 c Petroleum Industry
Crude oil is a mixture of many different hydrocarbons and small amounts of impurities. The composition of crude oil can vary significantly depending on its source. Petroleum refineries are a complex system of multiple operations and the operations used at a given refinery depend upon the properties of the crude oil to be refined and the desired products.
Within the petroleum refining industry, as potential source for PCDD/PCDF re-generation of the catalyst used during catalytic cracking of the larger hydrocarbon molecules into smaller, lighter molecules has been identified (Beard et al. 1993).
Feedstock to catalytic reforming processes is usually low octane naphtha. Catalytic hydroreforming uses platinum-based catalysts. In the continuous process, aged catalyst is continuously removed from the bottom of the reactor and sent to a regenerator where the carbon is burned from the catalyst with hot air/steam. Trace quantities of a promoter, normally organochlorines, such as tri- or perchloroethylene, are added to retain catalytic activity. Moisture is removed and the regenerated catalyst is returned to the first reformer bed. In the cyclic or semi-regenerative units, the regeneration of the catalyst is discontinuous as well as the resulting emissions. In this process, PCDD/PCDF have been detected.
PCDD/PCDF may be emitted to air or captured in scrubbing systems and transferred to effluents. Ultimate releases will depend on the pollution controls and handling of residues.
To assess emissions from flaring, the emission factor for category 3c Landfil/Biogas combustion can be applied.
PCDD/PCDF emission factors for one source class are listed in Table X. Detailed information on how these emission factors have been derived can be found in Annex 49.6
USEPA 2001 Database of Sources of Environmental Releases of Dioxin-Like Compounds (EPA/600/C-01/012 proposes an emission factor of 0.011 ng TEQ/kg processed for petroleum refining catalyst regeneration.
Activity rates may be obtained from various sources, in particular:
Owners/operators of the relevant facilities (by questionnaires);
State, provincial, national and/or international agencies that gather centralized statistical information.
Data quality rating is provided for the default emission factors