Regulation of Dioxins in Combustion Processes

Melissa Dettmann

CBE 555

March 15, 2010

What are Dioxins?

• In total, 75 and 135 congeners of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) respectively

• Only 10 PCDFs and 7 PCDDs are “toxic”• Nomenclature: 2,3,7,8-TCDD =

2,3,7,8-Tetrachlorinated dibenzo-p-dioxin

Health effects of dioxins (at levels of 1-5000 μg kg-1)

• Cause a fatal wasting disease in animals (die within 2-6 weeks)

• Damages to thymus gland (causes changes in cell immunity), liver, kidney, and digestive tract

• Miscarriage, sterility, birth defects• Cancer, most potent cancer promoter

known, some evidence of tumor initiation• Chloracne (persistent skin eruptions)

Dioxins and the Aryl hydrocarbon (AH) Receptor

• AH receptor binds to contaminants, stimulates production of cytochrome P-450 enzymes to de-toxify the body

• 2,3,7,8-TCDD binds extremely tightly to the Ah receptor, causing continuous production of P-450 enzymes that degrade other chemicals– Intermediates are frequently mutagens

• Activates genes that regulate the growth and division of cells

Toxicity of dioxins• Travis and Nixon (1992), “2,3,7,8-TCDD, the

most potent chemical toxin ever evaluated by the EPA”– One millionth of one gram will kill a guinea pig

• Estimates:– EPA’s virtually safe dose: 0.006 pg TEQ kg-1day-1 – WHO’s Tolerable Daily Intake: 10 pg TEQ

kg-1day-1

– Average U.S. daily intake: 1.8 pg TEQ kg-1day-1

• Inclusion of dioxin on 2006 EPA MSAT list

dioxins and furans

tetrachlorodibenzofuran

tetrachlorodibenzo-p-dioxin

pentachlorodibenzofuran

pentachlorodibenzo-p-dioxin

hexachlorodibenzo-p-dioxin

hexachlorodibenzofuran

heptachlorodibenzofuran

heptachlorodibenzo-p-dioxin

octachlorodibenzofuran

octachlorodibenzo-p-dioxin

1,2,3,4,7,8-hexachlorodibenzofuran

1,2,3,6,7,8-hexachlorodibenzofuran

1,2,3,4,6,7,8-heptachlorodibenzo-p-dioxin

1,2,3,4,6,7,8-heptachlorodibenzofuran

1,2,3,4,7,8,9-heptachlorodibenzofuran

1,2,3,4,7,8-hexachlorodibenzo-p-dioxin

1,2,3,4,7,8-hexachlorodibenzofuran

1,2,3,6,7,8-hexachlorodibenzo-p-dioxin

1,2,3,7,8,9-hexachlorodibenzo-p-dioxin

1,2,3,7,8,9-hexachlorodibenzofuran

1,2,3,7,8-pentachlorodibenzo-p-dioxin

1,2,3,7,8-pentachlorodibenzofuran

2,3,4,6,7,8-hexachlorodibenzofuran

2,3,4,7,8-pentachlorodibenzofuran

2,3,7,8-tetrachlorodibenzofuran

2,3,7,8-tetrachlorodibenzo-p-dioxin

2,3,4,6,7,8-hexachlorodibenzofuran

Dioxins in the Food Chain

Quantifying the Toxicity• Toxic Equivalent Factor (TEF): weighing

factors for dioxin compounds

i

ii concTEFTEQ

Formation Mechanisms

Role of catalyst in precursor formation

Inventory of Dioxin Emissions- 1985

Inventory of Dioxin Emissions- 1997

Inventory of Dioxin Emissions- 2000

Consideration 1: Regulations for some industries have proven to be

effective

0.1

1.0

10.0

100.0

1000.0

10000.0

Muncipalwaste

combustion

Medicalwaste

incineration

Cementkims

burninghazardous

waste

Bleachedchemicalwood pulpand paper

mills

1987 (g TEQ)

2000 (g TEQ)

Consideration 2: Relatively few methods exist for measuring

dioxins from industrial sources

• Method TO-9A (ambient air)

• Method 0023A (industrial stacks)

Consideration 3: How to interpret the results of the tests

• How to handle non-detection? EPA detection limit is 50 pg!!!

• Pg/bhp-hr vs. pg/m3

0

20

40

60

80

100

120

TE

Q E

mis

sio

ns

of

PC

DD

/Fs

ND = 0, pg/dscm

ND = DLWHO 1998, pg/dscm

ND = 0, pg/bhp*hr

ND = DLWHO 1998, pg/bhp*hr

0

2

4

Detection Limit (pg/sample)

Fre

quen

cy

14121086420

16

14

12

10

8

6

4

2

0

Case study: Diesel Engines

• Questions: – 1. Should dioxins be regulated in diesel

engine emissions?– 2. What is the effect of a Copper Zeolite SCR

have on dioxin formation?

The case against copper

• Copper has been shown to catalyze PCDD/F formation

• Studies by Heeb et al. showed that copper “induced intense PCDD/F formation”

Rebuttal

• PCDD/Fs formation and destruction are equilibrium process– Some studies have actually seen a reduction

in PCDD/F emissions in the presence of copper

• Criticisms of Heeb’s study– Used copper fuel additives, NOT copper

zeolite SCR– Unrealistically high levels of chlorine doping =

100 ppm

Why the need for Selective Catalytic Reduction (SCR)?

• EPA has issued increasingly stringent NOx and PM regulations for diesel engines

• SCR = aftertreatment component that catalyzes the decomposition of NOx

• 2010, Tier 4 EPA regulations are “aftertreatment-forcing”

Typical 2010 Architecture

4 NH3 + 4 NO + O2 4 N2 + 6 H2O (1)4 NH3 + 2 NO + 2 NO2 4 N2 + 6 H2O (2)

Advantages of Copper zeolite

Arguments against PCDD/F Formation in Copper Zeolite SCRs

• Size-exclusion argument

• Destructive pathways– Presence of NH3, SO2

Dioxin formation conditions: Industrial Incinerators

Dioxin formation conditions: Diesel engine with fuel additives

Dioxin formation conditions: Diesel engine with copper zeolite SCR

Recent Comparisons of TEQ Emissions (linear scale)

Recent Comparisons of TEQ Emissions (logarithmic scale)

References

• Travis, C. C.; Nixon, A.G. Human exposure to dioxin. The Royal Society of Chemistry. 1996. • EPA. Final rule: Control of hazardous air pollutants from mobile sources. EPA-420-F-07-017.• Harrison, N. Ch. 8: Environmental organic contaminants in food. Food Chemical Safety, Vol. 1. Foods

Standards Agency. • EPA. An inventory of sources and environmental releases of dioxin-like compounds in the United States for

the years 1987, 1995, and 2000. 2006, EPA/600/P-03/002F• Mayer, A.; Heeb, N.; Czerwinski, J.; Wyser, M. Secondary emissions from catalytic active particle filter

systems. SAE, 2003, 2003-01-0291.• Stanmore, B.R. The formation of dioxins in combustion systems. Combust. Flame 2004, 136, 398-427.• Altarawneh, M.; Dlugorgorski, B. Z.; Kennedy, E.M.; Mackie, J.C. Mechanisms for formation, chlorination,

dechlorination and destruction of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs). Prog. Energy Combust. Sci. 2009, 35, 398-427.

• Lomnicki, S.; Dellinger, B. Formation of PCDD/F from the pyrolysis of 2-chlorophenol on the surface of dispersed copper oxide particles. Proc. Combust. Inst. 2002, 29, 2463-2468.

• Lomnicki, S.; Dellinger, B. A Detailed Mechanism of the Surface-Mediated Formation of PCDD/F from the oxidation of 2-chlorophenol on a CuO/Silica Surface. J. Phys. Chem. A. 2003, 107, 4387-4395.

• EPA. Method 0023A: Sampling method for polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofuran emissions from stationary sources. 1996.

• Coordinating Research Council. Phase 1 of the Advanced Collaborative Emissions Study, 2009.• Ura, J. A., Girard, J., Cavataio, G., Montreuil, C., Lambert, C. (2009). Cold start performance and enhanced

thermal durability of vanadium SCR catalysts, SAE Paper 2009-01-0625. • Heeb, N.V., Ulrich, A., Emmenegger, L., Czerwinski, J., Mayer, A., Wyser, M. (2005). Secondary emissions

risk assessment of diesel particulate traps for heavy duty applications, SAE Paper SIAT 2005-ABS-165.• EPA (1999). Compendium Method TO-9A: Determination of Polychlorinated, Polybrominated, and

Brominated/ Chlorinated Dibenzo-p-Dioxins and Dibenzofurans in Ambient Air. Excerpt from the Comendium of Methods for the Determination of Toxic Organic Compounds in Ambient Air. EPA 1625/R-96/010b.

• Liu, Z.G., Swor, T.A., Schauer, J.J., Debilzen, J.A., Severance, C.L. (2008). A source dilution sampling system for characterization of engine emissions under transient or steady-state operation, Aerosol Science and Technology 42 (4), pp. 270-280.

EPA Regulations