degradation of chloroethenes in aqueous solution by ultrasound - RUA

DEGRADATION OF CHLOROETHENES IN AQUEOUS SOLUTION BY ULTRASOUND

V. Sáez, M. D. Esclapez, P. Bonete, E. Marchante, J. González-García, D. Walton, O. Louisnard

11th Meeting of the European Society of Sonochemistry, Sonochemistry, June 11-5 , La Grande Motte, Motte, France

SONOCHEMICAL DEGRADATION OF HALOCOMPOUNDS AN OVERVIEW Chlorinated organocompounds are usually used as industrial solvents: CCl4, CHCl3, C2Cl4, C2HCl3 , among others, withspread environmental pollutants in the subsurface aquatic environment

harmful to human health and environment

Development of new technologies

which are difficult to treat by traditional technologies

- Air stripping - Incineration - Biodegradation - Oxidation with chemicals - Carbon adsorption


SONOCHEMICAL DEGRADATION OF HALOCOMPOUNDS AN OVERVIEW Development of new technologies (Advanced Oxidation Processes AOPs) Production of hydroxyl radical (OH·) as a primary oxidant: -Photochemical treatment (UV, UV/H2O2) -Ozonolysis -Fenton reaction Fe2+ + H2O2 Fe(OH)2+ + OH· Application of ultrasound field is a successful tecnology for environmental clean-up

Range of frequencies used 20-1000 kHz


SONOCHEMICAL DEGRADATION OF HALOCOMPOUNDS AN OVERVIEW Ultrasound field Physical effects (solution agitation) Cavitation

(highT,P ) Chemical effects (solvent sonolysis)

Pyrolytic degradation

Radicals generation

Pollutants oxidation

H 2O  → H• + OH• )))))

OH • + OH • → H 2 O 2 H• + O

2

→ HO

• 2


SONOCHEMICAL DEGRADATION OF HALOCOMPOUNDS AN OVERVIEW

Pyrolytic center ~ 5000 K 500 atm H2O(g) → OH• + H• S(g) → products OH• + S(g)→ products Interface T ~2000K OH• + S(aq) S(aq) → products S(aq) S(aq) → products 2OH• → H2O2 Bulk solution T ~300K OH• + S(aq) (aq) → products H2O2(aq) + S(aq) (aq) → products

During the cavitational collapse of single, isolated bubbles, extreme temperatures and pressures are achieved. The main chemical pathways for organic compound degradation include: - Hydroxyl chemical oxidation - Direct pyrolytic degradation -Supercritical water reactions: Water vapor splits during bubble cavitation to yield H· and OH· Several organic compounds have been degradated using an ultrasonic field: - Aromatic compounds (phenol, chlorophenols) - Organic dyes - Herbicides and pesticides - Aliphatic carboxilic acids - Surfactants


SONOCHEMICAL DEGRADATION OF HALOCOMPOUNDS OBJECTIVES Study of the degradation of chlorinated organic compounds in aqueous solution using a 20 and 850 kHz ultrasound field Cl

Cl

Cl

Cl

Degradation of perchloroethylene as a model molecule in aqueous solution

Abbreviation

Chemical name

Comercial name

Empirical formula

PCE

Tetrachloroethylene

perchloroethylene, perc, Ethylene tetrachloride, tetrachloroethene,

CCl2═CCl2


SONOCHEMICAL DEGRADATION OF HALOCOMPOUNDS RESULTS Property

Properties perchloroethylene

Molecular weight

165.83 g/mol

Melting point

-19ºC

Boiling point

121ºC

Density at 20ºC

1.6227g/mL

Solubility: Water at 25ºC Partition coefficients: Log Kow Log Koc

Excellent solvent

Applications 150mg/L

-Dry-cleaning industry -Metal cleaning -Vapor degreasing

Hazardous toxic compound 3.40 2.2-2.7

Vapour pressure at 25ºC

18.47mm Hg

Henry´s law constant at 25ºC

1.8 x 10-2 atm m3/mol

US EPA Persistent pollutant Table of physical and chemical properties of perchloroethylene


SONOCHEMICAL DEGRADATION OF HALOCOMPOUNDS EXPERIMENTAL PROCEDURE

- Perchloroethylene (Aldrich 99%) used as received. -Solutions were prepared with purified water obtained from a Milli-Q system, 18.2 MΩ cm and previously deoxygenated by bubbling argon before addition of pechloroethylene. - The solution was left stirring overnight. -Temperature was kept at 20 ±1 ºC with a refrigerated bath and circulator. -Ultrasonic irradiation was carried out at maximum volume (minimum headspace in the sonochemical reactor). -Samples were analyzed inmediately after collection


SONOCHEMICAL DEGRADATION OF HALOCOMPOUNDS RESULTS The degradation of perchloroethylene was studied by: Analysis of aqueous phase A) Following the chloride concentration formation in solution Chromatography

by Ion Exchange

B) Monitoring of PCE and byproducts by High Performance Liquid Chromatograph (HPLC) C) Detection and quantification of PCE and products from the degradation obtained at the end of each experiment was carried out using Purge and Trap Gas Chromatography Mass Spectrometry (PT-GC-MS) Analysis of gaseous phase A) Analysis CO/CO2 by Gas Cromatographic with TCD (GC-TCD) B) Anaysis of PCE and intermediates by Gas Cromatographic with FID (GC-FID)


SONOCHEMICAL DEGRADATION OF HALOCOMPOUNDS RESULTS Experimental set-up Sonoreactor ( Undatim) Frequency: 20kHz Maximum power output: 100W Hastelloy ultrasound horn: 3 cm diam. Cell dimensions: diameter 68mm depth 84mm Sonicated volume: 200cm3

(1) ultrasonic probe (2) transducer (3) gas passing (4) electrolyte (5) cooling jacket (6) Teflon adaptor (7) O-ring joints. 11th Meeting of the European Society of Sonochemistry, Sonochemistry, June 11-5 , La Grande Motte, Motte, France

SONOCHEMICAL DEGRADATION OF HALOCOMPOUNDS RESULTS Characterization of the sonoreactor, 20kHz, 100W Ultrasonic power input was measured using standard calorimetric procedures

10 -2

I/ W cm 8

6

Probe amplitude

Power dissipation in solution/ W

Acoustic intensity/ W cm-2

Power density/ W mL-l

20%

13

1.84

0.065

40%

24

3.39

0.120

60%

36

5.09

0.180

80%

45

6.36

0.225

100%

54

7.64

0.270

4

2

0 0

20

40

60

80

100

Amplitude/ %


SONOCHEMICAL DEGRADATION OF HALOCOMPOUNDS RESULTS Initial concentration of PCE 1.0

[PCE]/[PCE]0

PCE concentration/ ppm

120

100

Concentration decay is uneffected by initial concentration of PCE

0.8

80 0.6 60 0.4 40 0.2 20

0.0

0 0

50

100

150

200

250

300

insonation time/min

0

50

100

150

200

250

300

insonation time/min

● [PCE]0 = 14ppm ■ [PCE]0 = 64ppm ▲[PCE]0 = 100ppm 6.4 W cm-2 5h 20kHz 20ºC


Ultrasonic intensity

SONOCHEMICAL DEGRADATION OF HALOCOMPOUNDS RESULTS

1.0

[PCE]/[PCE]0

-2

1.84 W cm -2 3.39 W cm -2 5.09 W cm -2 6.36 W cm -2 7.64 W cm

0.8

The pH was found to decrease in all cases due to the HCl formation

0.6

0.4

I/ W cm-2

Yield of chloride formation/ %

1.84

24

3.39

29

5.09

30

6.36

25

7.64

21

0.2

0.0 0

50

100

150

200

250

300

insonation time/min

[PCE]0 ≈ 75ppm 20kHz 5h 20ºC


SONOCHEMICAL DEGRADATION OF HALOCOMPOUNDS RESULTS Ultrasonic intensity 0.0 -0.2

0.020

log(c(t)/c(0)

-0.4 -0.6

k/ min-1 0.016

-0.8

0.012

-1.0

1,84 W 3,39 W 5,09 W 6,36 W 7,64 W

-1.2 -1.4 -1.6 -1.8

-2

cm -2 cm -2 cm -2 cm -2 cm

0.008 0.004 0.000 0

1

2

3 I/ W cm

-2.0

4

5

-2

-2.2 0

50

100

150

200

250

300

350

t/ min

Experimental results show that sonochemical destruction of PCE follows pseudo first-order kinetics 11th Meeting of the European Society of Sonochemistry, Sonochemistry, June 11-5 , La Grande Motte, Motte, France

6

SONOCHEMICAL DEGRADATION OF HALOCOMPOUNDS RESULTS Main products from perchloroethylene sonochemical degradation: TCE Cl

Trans-DCE H

Cl

Cl

H

C2Cl3H

Products detected by P&T-GC-MS after 5h:

Cl

cis-DCE H

Cl

H

Cl

trans-C2Cl2H2

H

Cl

cis-C2Cl2H2

CHCl3 CCl4 Hexachloroethane Hexachlorobutadiene Hexachloropropene



45

70

80

50

[TCE],[DCE],[Cl-]/ ppm

50

80

[TCE],[DCE],[Cl-]/ ppm [PCE]/ ppm

[PCE]/ ppm

Ultrasonic intensity

45

70

40 60

40 60

35 50

30 25

40

20

30

35 50

30

40

25 20

30

15 20

Sonochemical treatment leads to TCE and DCE and chloride anions as major by-products

15 20

10 10

5

0 0

100

200

time/ min

1.84 W cm-2

0 300

10 10

5

0 0

100

200

time/ min

0 300

-■-■-▲-×-

[PCE] [TCE] [DCE] [Cl-]

3.39 W cm-2



Mechanism: Cl

Cl

Cl

Cl H

CHCl3

Cl

· ·

+ H + Cl Cl

Cl

Cl

Cl Cl

Cl

·

+ 2 Cl

· ·

Cl

Cl

+ Cl

Cl

Cl

))))))

))))))

C-C

·H

Cl

2

CCl2

Cl

+

Cl

· CCl

·Cl

3

+ ))))))

·Cl

C-Cl Cl

Cl

Cl Cl

·

+ CCl3

·

Cl

Cl

Cl

·Cl

+

+

Cl

·H

Cl

H

Cl

Cl

Cl

CCl4

))))))

x2

·

Cl

C-Cl

Cl

Cl

Cl Cl Cl

Cl

H Cl

+

·H

H

H

Cl

Cl


Experimental set-up 55


44

66 3 3 22

77 88

Sonoreactor Meinhardt Ultraschalltechnik, K80-5 Frequency: 850kHz Maximum power output: 140W Sonicated volume: 200cm3

1

1) Transducer, 2) bulk solution, 3) glass cell, 4) sample withdrawing system, 5) temperature probe, 6) lid, 7) inlet and outlet of the cooling jacket and 8) interface 11th Meeting of the European Society of Sonochemistry, Sonochemistry, June 11-5 , La Grande Motte, Motte, France

SONOCHEMICAL DEGRADATION OF HALOCOMPOUNDS RESULTS Characterization of the sonoreactor, 850kHz, 140W Ultrasonic power output was measured using standard calorimetric procedures 50

power output

40

30

20

10

0 0

1

2

3

4

5

Power input/ watts

W cm-2

W cm-3

2.2±0.2

0.11

0.01

4.7±0.1

0.24

0.02

17.2±0.9

0.88

0.07

37.9±4.4

1.93

0.15

amplitude


SONOCHEMICAL DEGRADATION OF HALOCOMPOUNDS RESULTS Effect of PCE concentration

80 150ppm perchloroethylene

60

150ppm PCE Saturation conditions!!

75ppm perchloroethylene

[Chloride]final/ ppm

100

40

80

60

38ppm perchloroethylene

20

40

20

0 0

1

2

3

4

5

insonation time/ hours

0 0

25

50

75

100

125

150

[PCE] initial/ ppm 100

yield

Chloride conc/ ppm

100

80

Initial Perchloroethylene concentration/ ppm 150 75 38

60

40

20

Yield of C l - formation/ % 58 73 91

0 0

25

50

75

100

125

150

p e rc h lo ro e th yle n e in itia l c o n c e n tra tio n / p p m


60

3 8 w att 1 7 w att

40

5 w a tt

20

2 w att

Yield of chloride formation / %

Chloride concentration/ ppm

SONOCHEMICAL DEGRADATION OF HALOCOMPOUNDS RESULTS Effect of ultrasound power

80 60 40 20 0 0

5

10

15

Power output / Wh

0 0

30

60

90

120

150

in s o n a tio n tim e / m in

Ultrasonic power / watts 38 17 5 2

Yield of Cl- formation/ % 70 62 50 26


SONOCHEMICAL DEGRADATION OF HALOCOMPOUNDS RESULTS Products from perchloroethylene sonochemical degradation at tracer level: CHCl3 H

CCl4 Cl

Cl

H

H

Cl Cl

Cl

Cl

Cl

Cl

Cl Cl Cl

Cl Cl

Cl Cl Cl

Mechanism?

Cl

Cl Cl Cl

Cl


SONOCHEMICAL DEGRADATION OF HALOCOMPOUNDS CONCLUSIONS Perchloroethylene sonochemical degradation can be carried out Different behaviour has been detected with the frequency Sonochemical degradation seems mainly to follow a pyrolytic radical mechanism Total degradation can not be stablished from the results coming from Cl- detection

Differences in the by-products obtained with different frequencies are still under study


ACKNOWLEDGEMENTS

Coventry University Generalidad Valenciana

Finantial Support Alicante University COST D32/004 (Electrochemistry with Ultrasound)


Thank you!
