Encyclopedia of Environmental Science and Engineering, Volume I and II

886 PCBs AND ASSOCIATED AROMATICS

TABLE 20

PCDFs in new and used commercial PCB mixtures

Polychloro dibenzo furans

PCB Cl^4 Cl^5 Cl^6 Total

New:

Aroclors 1254, 1260(5 1) ———0.05

Clophen A-60(2) 1.4 5.0 2.2 8.4

Phenoclor DP-6(2) 0.7 10.0 2.9 13.6

T 1242(5 5) 2.3 2.2 — 4.5

T 1248(5 5) 0.5 2.3 — 2.8

T 1254(5 5) 0.1 3.6 1.9 5.6

T 1260(5 5) 0.8 0.9 0.5 2.2

Kanechlor 300(5 5) 6.7 1.6 — 8.3

Kanechlor 400(5 5) 12.2 10.4 0.9 23.8

Kanechlor 500(5 5) 1.7 1.1 3.1 6.1

Kanechlor 600(5 5) 0.2 0.5 0.4 1.1

Used:

T 1248(5 5) 5.8 5.6 0.7 12.4

Aroclor 1254(5 1) — — — 0.55

Aroclor 1260(5 1) ———1.1

Yusho Oil (KC-400) 520 1330 810 2680

TABLE 21

Chlorobenzene pyrolysis

Chlorobenzene pyrolysis

PCBz studied Process Product Yield Ref.

Mixture of tri-/tetra- Pyrolysis PCDD, PCDF, PCB, 2,000 ppm 156

CBz; PC 5 Bz in air higher chlorinated

benzenes, Cl-phenols

Monochlorobenzene Pyrolysis Mono- and di-Cl- 50 ppm 96

in N 2 biphenyl

Monochlorobenzene Pyrolysis di-Cl-biphenyl 10% 157

A second simplification can sometimes be made in good

approximation when one or more reactions occur much faster

than other reactions in the system. Under these conditions,

partial-equilibrium is assumed. This allows the expressions

which describe forward and backward reactions to be equated.

Further simplifications can be made using sensitivity analysis

of solution variables in which numerical solutions are derived

for small changes in input variables to determine the magni-

tude of induced change. When reactions or species are found

which have little overall effect, the equilibrium equations and

terms which involve the species can be dropped and the con-

servation equations are thereby simplified.

A reaction mechanism for the formation of dioxins has

been suggested by Altwicker et al. (1990):

Precursor (g)  Precursor (ads) → PCDD (ads)

PCDD (ads) → PCDD (g)

PCDD (ads) → non-toxic product

PCDD (ads) → non-toxic decompo-

sition product.

In generalized terms, formation and destruction can also

occur by a mechanism such as the following:

Polychlorinated phenol → polychlorinated phenoxy

radical

↓

polychlorinated

2-phenoxyphenols

(pre-dioxins)

↓

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