L aboratory of P hysical and A nalytical C hemistry KULeuven Department of Chemistry Laboratory for...

L aboratory of P hysical and A nalytical C hemistry

KULeuven

Department of Chemistry

Laboratory for Physical and Analytical Chemistry (LPAC)

Celestijnenlaan 200 F

3001 Leuven

Belgium

Tel: 0032 16 32 7376

Fax: 0032 16 32 7992

www.chem.kuleuven.be/research/LPAC/index.htm

General MeetingLeuven, 23/11/2005

Frank De Smedt

Hans Vankerckhoven

Prof. C. Vinckier

WP 1.4. : O3 generation testbed


O3 generatorbox nr 1

Storage tank

Water jet (Venturi-system)

FRONT VIEW

External control of O3 boxes by means of CL software MAXO

Boxnr 2

Water pump (stainless steel)

O3 generation testbed: 2 modules


MODULE 1:

• Two ozone generation boxes, designed by

Copperline and constructed by CL and Seaking

• Air inlet and introduction into the Venturi injector

MODULE 2:

• Venturi injector (mixing of gas and water)

• Water pump (external water loop)

• Storage tank (designed and constructed by Copperline and

Seaking)

see 2nd Technical meeting (Offenburg) + Report W.P. 1.3

WP 1.4. : O3 generation testbed


OUTLINE

HISTORY

AIR TIGHTNESS

OZONE GAS CONCENTRATION [O3]gas

Pure O2

N2/O2 (air)

Note: target = air as feed gas[O3]gas ≥ 10 g/m3 (0.5 % v/v)

W.P. 1.4: O3 generation testbed


HISTORY



CONSTRUCTION: Copperline (ETR) and Seaking

INSTALLATION: beginning of july 2005 at LPAC

(see Minutes of the installation)

LEAKS ! (new type of cover needed)

suggestion for a smaller air corridor

(because of extreme low [O3]gas)

ADAPTATIONS: new cover was constructed and installed

at 2nd Technical meeting (CL-Seaking)

further adaptations to the cover by LPAC

(reinforcement + screws)



Smaller air corridor(from 2.2 to 0.4 liter)

Additional reinforcement


AIRTIGHTNESS




PUMP

VENTURI

WATER

AIRWATER / AIR

PRESSURE METER

FLOW REGULATOR AND METER

FLOW REGULATOR

exhaust

Flow meter

O3 Box

1

2

CHECKING THE AIR TIGHTNESS by

→ air suction (Venturi system)

→ pressure (Mass Flow Controller)

O2

FC

Ventinghood

O3 Box

Flowmeter



Air tightness of the O3 Boxes with Qwater = 3 l/min and 8 turns of the Venturi regulator. Qair measured by the Schlumberger Flow meter.

Qair (Schlumberger) Relative decrease dm3/hr %

blank 174.97 ± 1.74 Box 1, valve open 175.14 ± 0.82 Box 1, valve closed 103.52 ± 1.15 40.9 Box 2, valve open 153.40 ± 2.71 Box 2, valve closed 74.26 ± 2.00 51.6

RESULTS AND DISCUSSION

Airsuction

Air tightness of O3 Box 2 and Box 1 + 2 as a function of QO2 (Brooks F.C.). Gas flow measured by the Schlumberger flow meter.

QO2 (F.C.) QO2 (Schlumberger) Relative loss

dm3/hr dm3/hr % Box 2

60 60.76 ± 0.36 Test (before O3 Box) 60 57.74 ± 0.28 3.8 30 28.15 ± 0.21 6.2 10 9.00 ± 0.36 10.0 60 53.53 ± 0.28 10.78 80 71.30 ± 0.49 10.88

100 89.87 ± 0.25 10.13 120 106.77 ± 0.87 11.03 140 124.66 ± 1.26 10.96

Box 1 + 2 60 58.06 ± 0. 10 Test (before O3 Box) 60 35.83 ± 0.76 40.3

Airpressure


OZONE

PRODUCTION




O3 BOXES CL

Upper part Upper part

MODULE 1

MODULE 2

MODULE 3

PATT-devices:6 per Box

(2 per Module)

Box 1: Module 1 to 3Box 2: Module 4 to 6



Upper part of the O3 Box:

Power supply

Air corridor

Gas inlet Gas outlet

: PATT-module

PROTOTYPE 1

Upper part of the O3 Box:

Power supply

Air corridor

Gas inlet Gas outlet: PATT-module

PROTOTYPE 2



O2

FC

Ventinghood

O3 Box

O3

sensor

Pure O2 as feed gas

Measurement of: [O3]gas , current I (mA)

Variables: QO2 (FC: 0 – 60 dm3/hr)n° of ModulesPower setting (% P)



Pure O2

Gas inlet Gasoutlet

: PATT-module

Air corridorO--O

O--OO--O O--OO--O

O--O O--O

O--O

O--O

O--O : O2 molecule : discharge

Reaction Rate constant k units R1 O2 + ε → ε + O + O (1) cm3s-1 R2 O + O2 + O2 → O 3 + O2 6.401 10-35 exp(663/T) cm6s-1 R3 O + O2 + O3 → O 3 + O3 1.45 10-34 exp(663/T) cm6s-1 R4 O + O3 → O 2 + O2 1.9 10-11 exp(-2300/T) cm3s-1 R5 O3 + ε → ε + O + O 2 (2) cm3s-1 R6 O3 + wall → 1.5 O 2 + wall (3) s-1 R7 O + O + O2 → O 2 + O2



Pure O2 , Box 2, 1 Module activatedMeasurement of: [O3]gas , current I (mA)Variables: Power setting (% P)

0

1

2

3

4

5

6

7

0 20 40 60 80 100 120

% P

[O3]gas

g/m3

[O3]gas (g/Nm3) as a function of the % P of Module 4 (O3 Box 2) at QO2 = 60 l/hr. Gas temperature Tgas = (30 ± 1)°C.

Linear between 15 and 75 % P, small decrease at % P > 75



0

100

200

300

400

500

600

0 20 40 60 80 100 120

% P

I(mA)

Pure O2 , Box 2, 1 Module activated

I (mA) as a function of the % P of Module 4 (O3 Box 2) at QO2 = 60 l/hr. Gas temperature Tgas = (30 ± 1)°C.

Same trend as with [O3]gas

y = 0.0107x - 0.0031

R2 = 0.9879

0

1

2

3

4

5

6

0 100 200 300 400 500 600

I (mA)

[O3]gas

g/m3

[O3]gas as a function of I (mA) of Module 4 (O3 Box 2) at QO2 = 60 l/hr. Gas temperature Tgas = (30 ± 1)°C.

Linear relationship between [O3]gas and I



0

1

2

3

4

5

6

0 15 30 45 60 75 90 105 120 135 150

time (minutes)

[O3]gas

g/m3 25 % P

50 % P

85 % P

100% P


Time dependence of O3 buildup

First buildup isalways slower

Temperature-effect ?

0

1

2

3

4

5

6

7

0 100 200 300 400 500 600

time (minutes)

[O3]gas

g/m3

10 % P85 % P

75 % P




Reproducibility (from day-to-day) Very reproducible ozone production

0

1

2

3

4

5

6

7

0 20 40 60 80 100

% P

[O3]gas

g/m3

19/10/200520/10/200521/10/200524/10/200528/10/2005

0

1

2

3

4

5

6

7

0 100 200 300 400 500 600

I (mA)

[O3]gas

g/m3

19/10/200520/10/200521/10/200524/10/200528/10/2005



Pure O2 , Box 2, 3 Modules activatedVariables: n° of Modules, position, Power setting (% P)

15.4

12

8

15.4

10.7 10.55 10.6

15.3

0

2

4

6

8

10

12

14

16

18

75

+7

5+

75

50

+5

0+

50

25

+2

5+

25

10

0+

10

0+

10

0

75

+2

5+

25

25

+2

5+

75

25

+7

5+

25

75

+7

5+

75

[O3]gas

g/m3

Device 4 + 5 + 6 exp

device 4 + 5 + 6 calculated

iModule

gas

n

ifinalgas OO

1

3,3 Cumulative O3 production (n = 3) Position in air corridor of no importance



Pure O2 , Box 2, 3 Modules activatedVariables: QO2

Exponential dependence of the O3 concentration on QO2

Reproducibility !

0

10

20

30

40

50

60

0 50 100 150 200 250 300 350 400 450 500 550 600

QO2 (l/hr)

[O3]gas

g/m3

24/10/200525/10/200528/10/20054/11/200510/11/2005

5

48.7



Pure O2 , Box 2, 3 Modules activatedVariables: QO2

Linear dependency of the O3 concentration on I(but different from 1 Module at constant QO2)

0

10

20

30

40

50

60

1350 1400 1450 1500 1550 1600 1650

total current I (mA)

[O3]gas

g/m3

25/10/2005

28/10/2005

4/11/2005

10/11/2005



Pure O2 , Box 2, 3 Modules activatedCapacity of the ozone generator a.f.o. QO2 (3 Modules at 75% P)

exponential increase of the O3 capacity a.f.o. QO2

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

0 50 100 150 200 250 300 350 400 450 500 550 600

QO2 (l/hr)

O3 capac.g/hr

24/10/2005

25/10/200528/10/2005

4/11/200510/11/2005

Capacity = [O3]gas x QO2



Pure O2 , Box 1+2, 6 Modules activatedVariables: n° of Modules and QO2

iModule

gas

n

ifinalgas OO

1

3,3

Cumulative O3 production apparently does not hold for more than 4 Modules (air tightness problem Box 1?)

65.8

46.7

29.6

0

10

20

30

40

50

60

70

0 10 20 30 40 50 60 70

QO2 (l/hr)

[O3]gas

g/m3

Modules 4+5+6

Modules1+2+3+4+5+6

47.3

30.3

14.9

66 g/m3 O3 ~ 3 % v/v O3



SUMMARY (pure O2)

[O3]gas is linearly dependent on the power setting (15 - 75 % P)

higher % P (> 75) result is equal or slightly lower [O3]gas

the same dependence on % P is observed for I and AD-I’s

[O3]gas is linearly dependent on I: I ↑ [O3]gas ↑

O3 production is reproducible from day to day & from Module to Module

the ozone production is cumulative when multiple Modules are used for

n = 3, but not for n = 6 (Modules in two separate Boxes)

[O3]gas is depending on QO2: QO2 ↓ [O3]gas ↑ (n = 3 and n = 6), again

this production is reproducible from day to day

QO2 ↓ I ↓ [O3]gas ↑



N2 / O2 as feed gas: “air”

N2

78.084 %

Ar0.934 %

O2

20.947 %

CO2

0.033 %

Composition of air :



N2 / O2

Gas inlet Gasoutlet

: PATT-module

Air corridorN--N

O--ON--N N--NO--O

N--N N--N

O--O

N--N

O--O : O2 moleculeN--N : N2 molecule : discharge

32,arg

232 NONONONNN OOedisch

More details in the LPAC-report



N2 / O2 as feed gas

Measurement of: [O3]gas , current I (mA)

Variables: QO2 (FC: 0 – 60 dm3/hr)n° of ModulesPower setting (% P)composition feed gas (N2 / O2)

O2

FC

Ventinghood

O3 Box

O3

sensor

N2



N2 / O2 as feed gasVariables: n° of Modules, composition feed gas (N2/O2)

0

5

10

15

20

25

0 10 20 30 40 50 60 70 80 90 100

% O2 (versus N2) (total = 100)

[O3]gas

g/m3

25/10/2005

26/10/2005

28/10/2005

31/10/2005 (Module 4)

[O3]gas as a function of the composition of the feed gas (O2/N2) at 75% P (Modules 4+5+6 of Box 2 and Module 4). Total gas flow = 60 l/hr.

Addition of N2 : Beneficial between 60/40 & 80/20. Identical behavior for 1 or 3 Modules (Box 2).



0

200

400

600

800

1000

1200

1400

1600

1800

2000

0 20 40 60 80 100% O2 (versus N2) (total = 100)

totalcurrent I

(mA)

25/10/2005

26/10/2005

28/10/2005

0

10

20

30

40

50

60

70

80

90

100

0 20 40 60 80 100

% O2 (versus N2) (total = 100)

AD-i

25/10/2005

26/10/2005

28/10/2005

N2 / O2 as feed gas

Addition of N2 : Modules behave differently then in the absence of N2.

0

100

200

300

400

500

600

700

0 100 200 300 400 500 600

time (minutes)

ImA

Module 4

Module 5

Module 6

100/0

60/40

80/20

90/10



N2 / O2 as feed gas (versus pure O2): effect of the gas flow

Effect of the gas flow Q : [O3]gas ↓ as Q ↑ (for both) O3 generator capacity ↓ as Q ↓ (more pronounced with pure O2)

0

5

10

15

20

25

30

0 50 100 150 200 250 300

QO2 (lhr)

[O3]gas

g/m3

14/11/2005 21/79

10/11/2005 pure O2

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

0 50 100 150 200 250 300

QO2 (lhr)

O3 capac.

g/hr

14/11/2005 21/79

10/11/2005 pure O2



N2 / O2 as feed gas: is the increased O3 gas concentration in the presence of N2 an artefact or real ??

0

1

2

3

4

5

6

0 50 100 150 200 250 300

time (minutes)

[O3]liq

mg/l

15.0 g/Nm3 O3

100/0pH 4.86

19.4 g/Nm3 O3

80/20pH 2.54

15.1 g/Nm3 O3

100/0pH 2.50

no O3

[O3]liq follows [O3]gas (in accordance with Henry’s Law)

Increase ozone production is real ! = N2-effect

Effect on pH and conductivity when N2 is present



N2 / O2 as feed gas: effect on pH

Sharp decrease of pH and sharp increase of the

conductivity when N2 is present !

+ Ultraviolet absorption observed

0

1

2

3

4

5

6

0 100 200 300 400

time (minutes)

pH

O3

100/0

O3

80/20

O3

100/0

O2 bubbling



N2 / O2 as feed gas: UV-absorption

Ultraviolet absorption observed at 208 nm, even after

degassing

presence of HNO3

O3-free MilliQ-water after ozonation with N2 presence



N2O5(g) + H2O(g) → HNO 3 + HNO3 N2O5(g) + 2 H2O(g) → HNO 3 + HNO3 + H2O(g)

N2 / O2 as feed gas:

32,arg

232 NONONONNN OOedisch

NOx is obviously being produced as a by-product

In the presence of water (thus also in the feed gas): formation of acidic acid: corrosion problems possible !!

→ Effect of the presence of N2 during ozone production on pH, conductivity and the UV-absorbance at 208 nm→ Indication that HNO3 is introduced in the water (acidification)

W.P. 1.4 : O3 generation testbed


General conclusions

Design needs to be improved ! [O3]gas much higher with smaller air corridorStill some leaks in the Box coverMultiple Boxes ? (parallel or in series ?)

Ozone gas concentration / productionWith pure O2: → [O3]gas ~ current I (1 versus 3 Modules)

→ “cumulative” effect of multiple Modules→ [O3]gas ~ 1/ gas flow Q→ capacity O3 generator exponentially

increases as Q increases→ good reproducibility→ position Modules in air corridor of no

importance



General conclusions

Ozone gas concentration / production

With N2 / O2: → addition N2 not detrimental (40 – 20 %)

→ [O3]gas ~ current I (different behavior)

→ [O3]gas ~ 1/ gas flow Q

→ capacity O3 generator exponentially

increases as Q increases (less than

pure O2)

→ good reproducibility

→ NOx are formed as by-product

→ HNO3 is formed when water is present

(= acidification + possible corrosion)


future

* Gas flow path (smaller ?)

* (better) Air tightness & safety aspects

* Geometry of the ozone producing section

* Number of PATT-modules (more in 1 Box ?)

* Electronics of the PATT-modules (delay effects in

the ozone production + faster programming of the

modules)

* Introduction system (see report on Storage tank)

* Compactness of the Box (more compact)

more experiments: O2 + H2O and air as feed gas


L aboratory of P hysical and A nalytical C hemistry KULeuven Department of Chemistry Laboratory for...

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