Pah

09/05/11 Kaushik K. Shandilya 1

Emissions from Fuel

Polycyclic Aromatic Hydro Carbons (PAH)

Kaushik K. Shandilya (M.E. III Sem)


What are PAH compounds?

• A class of Hydrocarbon

compounds

• Aromatic Hydrocarbons with more

than one benzene ring

• BP greater than or equal to 1000C

• Theoretically, millions of PAH

compounds could be formed

• Small portion of these compounds

have been identified as

carcinogenic

Benzo(k)fluoranthene Benzo(a)pyrene Dibenz(a,h)anthracene

Indeno(1,2,3-c,d)pyrene Benzo(g,h,i)perylene

Acenaphthene Fluorene

Fluoranthene Benz(a)anthracene

Benzo(b)fluoranthene

Phenanthrene

Anthracene Pyrene Chrysene

Naphthalene Acenaphthylene


Mechanism of Formation of PAH During Combustion

Majority of PAH in the environment are derived from reaction at high temperature during pyrolytic conditions during incomplete combustion

PyrolysisComplex organic molecules are partially cracked to

smaller unstable radicals and creates O2 deficient zone

PyrosynthesisThese fractions are unstable and partly combusted and

partly recombined to form stable PAH


CO- 11.4 %

H2 – 8.2 %

CH4 - 2 %

ORC – 0.5 %

O2 - 1.0 %

Coal firing System

Pyrolysis

During combustion, reduced environmental conditions are formed around the flame and unstable organic radicals are formed

CO- 18.2 %

H2 – 1.1 %

CH4 – 0.3 %

ORC – 6.0 %

O2 - 0 %

Automobiles

Reduced Conditions

Source: Diesel. Net


Pyrosynthesis

Source: H. Richter, J.B. Howard, Progress in Energy Combustion Science, Feb 2000

These fractions are unstable and partly combusted and partly recombined to form stable PAH


42%

20%

14%

13%

8% 3%

Vehicle

Aluminum

Residential

Coke

Power

Others

Source-1: Emission Inventory Program USEPA

Source-2: Bruce A. Benner, Environ. Sci. Technol. 1989, 23, 1269-1278

PAH Emissions by Category in

USA

Sources wise Emissions of PAH


Vapour Pressure of PAHs

0

2

4

6

8

10

12A

CY

AC

E

FL

U

AN

T

PH

E

FL

T

PY

R

BA

A

CR

Y

BB

F

BK

F

BA

P

IND

BD

A

Vap

ou

r P

ressu

re a

t 25 D

eg

C [

- L

og

(Vp

)]

0

1

2

3

4

5

6

7

No

. o

f R

ing

s

Vapour Pressure NO. Rings

Volatile Semi - Volatile

Source: US Department of Health and Human Services


% of Total PAH Associated with Particle

56

98

90

90

99

99

6.5

94

92

92 94 9

8

4.3

55

71

71

82 83

0.1

1

2.1 4.6

4.6

38

33

0102030405060708090

100

Nap

hFlu

r

Phen

Ant

hr

Flurn

th

Ben

z(a)

anth

% R

eta

ined

in

part

icle

ph

ase

40 Deg C

55 Deg C

85 Deg C

200 Deg C

Source: USPEA, Publications EPA-454/R-98-014


How to Capture PAH?

Particle Phase•Glass fiber filter

•Quartz filters

•Silver membrane

•Teflon filters (PTFE)

Vapour Phase•Activated Carbon

•XAD

•TENEX filters

•Polyurethane foam (PUF)


High Volume sampler for PAH

Size selective inlet (Separation of PM>10microns)

WINS Impactor (Separation of PM>2.5 and 10 microns)

Teflon filter (PTFE)(Collection of PM<2.5 microns)

PUF adsorbent (cartridge with ice jacket)(Collection of VOC)

Dry gas meter

Suction pump


PUF Holder

PUF Adsorbent


PUF Holder

Glass fiber filter

“PUF” holder


The PUF should be of the polyether type used for furniture upholstery, pillows, and mattresses.

The PUF cylinders (plugs) should be slightly larger in diameter than the internal diameter of the cartridge

Polyurethane Foam

PUF Adsorbent


“PUF” vrs “XAD Resin”

PUF XAD ResinCollection efficiency of NV-PAH >99 >99

Collection efficiency of V-PAH 90-100 97-100

Loss of V-PAH at 25 OC in 30 days 10-15 <5

Flow characteristics in HVS Unchanged -ve impact

Recovery More solvent Less solvent

Species collected other than PAH Pesticides, PCB, Dioxins

Poor collection

PUF is widely used for PAH samplingTechnical Assistance Document for Sampling and Analysis of Toxic Organic Compounds in Ambient Air, U. S. Environmental Protection Agency, EPA-600/4-83-027, June 1983.


Naphthalene, acenaphthylene, and acenaphthene possess relatively high vapor pressures

Collection efficiency less than 35%

Avoid PUF if…

PUF Adsorbent

XAD Resin is a suitable option


• Type of equipment WINS, DICHT, Cascade• Flow rate 0.5- 1 m3/min• Minimum air collection 300 m3 • Suction pump type Constant vol.

• Pore size for filter 0.25 µm (min)• Recommended particle range 0.45 - 10 µm• Filter type PTFE or GFA

Sampling Requirements for PAH analysis– (USEPA Recommendation)


PM (Size Selective Inlets)

• Inlet particle cut point 10 ± 0.5 µm• During wind tunnel tests

Collection of PM25 shall be less than 5% at 8 and 24KMPH wind speeds

• variation in sampling flow rate shall be less than 5%

• Filter media should collect more than 99% of 0.3 µm size

Certification of PM samplers– (USEPA Recommendation)


Selection of filters depends on

• Application (only PM, Ions, PAH, VOC, C)• Chemical stability• Storage and hygroscopic nature • Mechanical stability for the recommended flow

rate• Blank concentrations• Cost and availability

Selection of Filters for PM sampling


Types of Filters for “PM” sampling

Cellulose fiber Cellulose fiber (often called – Paper filters)

Cellulose Acetate Cellulose nitrate and mixer of esters (cellulose acetate)

Pure Quartz fiber Mat of Quartz fiber

Mixed Quartz Quartz + Borosilicate

Glass fiber Borosilicate glass fiber

Teflon coated glass fiber

Borosilicate glass fiber with a mat of Teflon

Teflon Carbon based material stretched between methyl pentane/propylene

Nylon Pure nylon


Sampling Errors and Uncertainties

• Baseline values of PAH in the filter

• Baseline values of PAH in the silicon oil used in WINS Impactor

• Loss of Filter weight during handling

• Uniformity in weighing conditions (pre-post sampling)

• Volatility of PAH during sampling, transportation and sample storage

(Effect of ambient temperature)

• Photolysis due to exposure to UV and incandescent light during

sampling and analysis


Loss of PAH during measurement

Baseline values in the filter and oil

Establishing blank tests and extraction with methanol before

sampling

Sampling Cold bath for PUF filter, minimum exposure to sunlight, add surrogate

standards

Storage of samples and

analysis

Storage in ice bath and

incandescent lighting in the lab


Recovery of PAH from Filter

56

50

74

70

94

91 9

7

0102030405060708090

100

Phen

Ant

hra

Flur

Pyren

e

Ben

z(a)

anth

Chr

y

Ben

z(a)

pyr

% R

eco

vere

d

•Surrogate standards are spiked on to quartz fiber filter

•Sampled with a high volume sampler in a controlled environment at 25C

•Spiked volume is about 10 times higher than ambient conc.

Source: James F, Galasyn, J. Air Pollution Control Association, Vol. 34, 1984


Photodecomposition of PAH

• PAH compounds are susceptible to

photodecomposition during sampling at

site and also at analytical table

• Major sources are sunlight and

fluorescent bulbs


Favourable region of light for decomposition of PAH is UV light ranging from 290 – 400nm

Favorable wavelengths for Photodecomposition of PAH

•Rate and extent widely varied in PAH degradation•Not easily correlated with molecular weight of PAH


36

.3

0.8

13

.6

34

.2

0.8

8

0.0

69

0.1

6

0

5

10

15

20

25

30

35

40

45

50

NA

P

AN

T

PH

E

FL

T

PY

R

BA

A

BA

P

Ha

lf lif

e (

T1

/2)

T1/2 (hr) Higher degradation in case of 6 to 8 ring compounds

More degradation with less ‘EC’ is present

Function of particle surface area

Photodecomposition of PAH

Source: Ingwen Chinm J. Environmental Pollution, 114, 2001


Reaction of PAH with Atmospheric pollutants

Pollutant Study Findings Ref

SO2

(Exposed to 10000 ug/m3 for 10 days)

No change in the concentration for 16 PAH

Butler, J.D, Atmos. Env. 15, 1981

Ozone

(Exposed to 2 PPM for 10 days)

Considerable degradation with half life ranging 0.1-0.6 h-1

Kataz, Envi. Sci. Technol. 9, 1977

NO2

Exposed to 3000 ug/m3 for 24 hours)

About 1% reduction and no change in lower ring compounds

Pitts et. al. Science, 202, 1978

General ambient concentrations of these pollutants are far less


Storage of samples and preservation

Filter cassettes

Filter holder and ice box


Analysis of samples

by High Performance

Liquid

Chromatography


Environment…-Not our bequeathal

property

-But borrowed from children


Thanks

Pah

Technology

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