Preliminary study of needles-to-plate plasma dedicated

to the drug residues treatment

Olivier AUBRY*, Hervé RABAT, Yasmine BALOUL, Dunpin HONG GREMI, UMR7344 CNRS / Université d’Orléans, France

Abstract

The degradation of pharmaceutical compounds in aqueous solutions using a dielectric barrier discharge reactor in needles-to-plate configurations at atmospheric pressure where the discharges are

produced above the liquid is studied.This work has been performed in two steps in various operating conditions (applied high-voltage, gas flow…) for: i) characterization of the discharges by Optical

Emission Spectroscopy and imaging ICCD and, ii) paracetamol solutions treatments by plasma.

*olivier.aubry@univ-orleans.fr

Experimental set-up

.

Exposure time = 200 µs

ICCD and OES results in single needle configuration

Two discharge regimes are studied: spark and streamer.

The two discharge types are generated in function of the

high-voltage applied.

The objective is to characterize the discharge and to

obtain information on the behavior of the discharge in

function of the injected gas and applied HV on the

produced species in the discharge and plasma

temperatures.

Treatments of a 20 mg/L paracetamol solution

The reactor used to treat drug residues is similar to the single

needle reactor, except that there are 9 needles.

In this configuration, first results in spark regime showed that a

lot of water vapor is produced leading to instabilities of the

discharges due to the water condensation on the reactor wall.

So, the plasma treatments has been performed in the streamer

regime.

This preliminary study allowed us to obtain a better understanding of the needles-to-plate discharge applied to the treatment of drug residues in a liquid. On the single needle-to-plate discharge,

optical emission spectroscopy proved the presence of OH radical, one of among oxidative species, which highly depends on the operating conditions (Applied high-voltage, inlet gas mixture…).

A Multiple needles-to-plate discharges reactor has been implemented to remove paracetamol in a aqueous solution. In air, a conversion rate of 81% has been obtained. We showed the role of

oxidative conditions in our plasma reactor.

The perspectives of this work are:

Identification and quantification of the generated by-products and the chemical pathways leading to their formation

Identification and characterization of the oxidative species responsible of the pollutant degradation.

Evaluation of the energy yield by products, and temperatures by OES simulation in function of the operating conditions.

Acknowledgements

The authors thank Sotheara CHUON for the SPECAIR simulations and Région Centre-Val de Loire for their financial support in frame of TREMEMAP project.

Conclusions and perspectives

Single needle discharge

Exposure time = 200 µs

Effects of the inlet gas on paracetamol degradation

The concentration of paracetamol in the liquid is measured by UV absorption spectroscopy

Absorption wavelength of paracetamol = 243.9 nm

Two configurations of needles-to-plate discharges are studied

- A single needle-to-plate reactor ICCD imaging and OES experiments to study the behavior

of the discharge in spark and in streamer regimes

- A 9 needles-to-plate reactor chemical treatment of drug residues

For each reactor,

Inner diameter of the needles : 0.4 mm

A copper plate as lower electrode and an epoxy plate as a dielectric

High Voltage supply: square voltage powered by a high voltage amplifier (Trek

20/20C).driven by a TTI function generator

Applied High Voltage, Upp = 8 - 14 kV

Frequency : 100 Hz - 2 kHz

Gap between the tip of the needles and the surface of the liquid ; 0 - 10 mm

In spark regime, the peaks current number is higher and there are more intense. leading

to a rise of OH production. This result shows that the spark regime could be used for a

better oxidation of the paracetamol solution.

SPECAIR® simulation of emission spectra give us information on rotational temperature:

in spark regime, Trot = 2800 K

in streamer regime, Trot = 450 K

First results on paracetamol solution treatment

show that:

• In air, the paracetamol is possible. A conversion

rate close to 81% is obtained after 1h of plasma

treatment (Upp= 13.6 kV, 500Hz). A pseudo-1st

order reaction is obtained: k = 2.7 10-2 min-1

• Without air, no degradation. Ar plasma in contact

with water is not efficient to treat drug residue

• As expected, oxidizing species formed in the

gas (such as OH, O3 or O) are necessary to

convert the pollutant

• In the outlet gas, O3 and CO2 (due to the

pollutant degradation) are observed by FTIR

spectroscopy

Multiple needles discharges reactor

Spark discharge

Air flow - Upp=14 kV - f=2kHz

streamer discharge

Air flow – Upp =8 kV - f=2kHz

In argon, paracetamol is not converted In air, paracetamol is converted and by-products

are generated identification of these products

is undertaken

4 m

m

needle

liquid

4 m

m

needle

liquid

Optical Emission Spectroscopy

ICCD imaging

Voltage and current waveforms

0 min

15 min

30 min

45 min

60 min

0 min

15 min

30 min

45 min

60 min

-50

-40

-30

-20

-10

0

10

20

30

40

50

-8

-6

-4

-2

0

2

4

6

8

0 0.5 1 1.5 2

curr

en

t (m

A)

volt

age

(kV

)

time (ms)

voltage (kV)current (mA)

-50

-40

-30

-20

-10

0

10

20

30

40

50

-8

-6

-4

-2

0

2

4

6

8

0 0.5 1 1.5 2

curr

en

t (m

A)

volt

age

(kV

)

time (ms)

voltage (kV)current (mA)

More current peaks

are produced in Ar flow

in argon in air

Effects of the inlet gas on Voltage and current waveforms

Ar and O2+N2 mixtures are injected in the needles

paracetamol

By-products

in argon in air

-50

-40

-30

-20

-10

0

10

20

30

40

50

-8

-6

-4

-2

0

2

4

6

8

0 0.1 0.2 0.3 0.4 0.5

cuu

ren

t (m

A)

volt

age

(kV

)

time (ms)

voltage (kV)current (mA)

paracetamol

4.0 105

3.5 105

3.0 105

2.5 105

2.0 105

1.5 105

1.0 105

0.5 105

0.0 105

Inte

nsity

(u.a

.)

293 298 303 308 313 318

Wavelength (nm)

4.0 105

3.5 105

3.0 105

2.5 105

2.0 105

1.5 105

1.0 105

0.5 104

0.0 104

Inte

nsity

(u.a

.)

293 298 303 308 313 318

Wavelength (nm)

-200

-150

-100

-50

0

50

100

150

200

-8

-6

-4

-2

0

2

4

6

8

0 0.1 0.2 0.3 0.4 0.5

curr

en

t (m

A)

volt

age

(kV

)

time (ms)

voltage (kV)current (mA)

0

0.5

1

1.5

2

2.5

3

3.5

0

20

40

60

80

100

0 15 30 45 60

Ln

[pa

race

tam

ol]

co

nve

rsio

n r

ate

(%

)

time (min)

conversion rate (%)

Ln[paracetamol]