environmental and biological applications of (micro ...bonitz/si08/talks/august_7th/morning... ·...

Environmental and Biological Applications of (Micro)Plasmas

Kurt H. BeckerPolytechnic Institute of New York University, Brooklyn, NY, USA

Thanks to many collaborators:• Christos Christodoulatos• Agamemnon Koutsospyros• Shu-Min Yin• Abe Belkind• Jose Lopez• WeiDong Zhu • Nina Abramzon• Sophia Gershman• Oksana Mozgina• Erich Kunhardt

Research andTechnology Initiatives

Thanks to many sponsors:NSF, NASA, Ozonia, US Army, AFOSR, ONR, FCE

FROM: B.M. Penetrante and S.E. Schultheiss“Non-thermal Plasma Technologies for Pollution Control”Proc. NATO-ASI, Vol. 34, Plenum Press, New York (1993)

“Non-thermal plasmas have an enormous potential of becoming the leading technology for the remediation of environmental pollutants in the near future”

15 Years Later:Much of the “enormous potential” remains unrealized - why ???

What are the challenges, where are the opportunities ???

Environmental Applications:• Electrostatic Precipitators• Ozonizers (briefly)• VOC Destruction (in low-flow applications)• Preparation of fuel cell feed gas• Pulsed electrical discharges in liquids


Biological Applications:• Bio-decontamination• Biofilm inactivation• Bio-medical application

TO DATE:Only 2 commercial plasma-based technologies in the environmental field

I. Electrostatic Precipitators (using corona discharge plasmas):Removal of particulates from gas streams

• mature technology• large industrial scale• economical & efficient• reliable• little unknown science• some engineering issues


II. Ozonizers (using dielectric barrier discharge, DBD, plasmas):Generation of ozone (O3) for disinfection applications


Industrial Ozonizer

• mature technology• large industrial scale• fairly economical• fairly reliable• not efficient (< 20% O3)• some unknown science• engineering issues

Science Issues (correlation with O3 generation efficiency):• effect of feed gas mixture, pure O2 vs. air (O2/N2); exact N2 admixture• effect of HC contaminants• effect of electrical power coupling to DBD• plasma – surface processes• materials issues (exposed electrode, dielectric coating)• degree of DBD filamentation


Filamentary DBD and O3 Generation(complex interplay between plasma chemistry & discharge physics)

• low power, many weak filaments

• low O3 generation efficiency at low O3 background concentrations

• high O3 generation efficiency at high O3 background concentration

• high power, few strong filaments

• low O3 generation efficiency at high O3 background concentrations

• high O3 generation efficiency at low O3 background concentration


O3

• Adjust microdischarge (gap, coating)• Adjust fraction of total applied power (gap, capacitance)

Microdischarges get weaker

One Solution: Intelligent Gap System (IGS)

Strongmicrodischarges

High O3generation

Low O3 generation, but also much less O3 destruction

Optimize O3 outlet concentration at >20% and maintain over time


Ozone Generation in DBDs

State of the Art:

• Larger ozonizers can produce up to 100 kg of O3 per hour• O3 concentrations are typically 18 wt% in O2 and 6 wt% in air• Use of O2 requires <50 ppm HC contamination• Energy for 1 kg of O3 is 8 kWh for O2 and up to 20 kWh for air• Cost is about $2 per kg of O3

Future Prospects:

• Novel concepts (e.g. the IGS) can push max. O3 concentration to >20% • Advances in power semiconductors (improved gate turn-off thyristorsand insulated gate bipolar transistors which can switch 1 kA at 5 kV) willreduce size of ozonizers by eliminating the need for step-up transformers and allow use of more efficient excitation waveforms

• Use of homogeneous self-sustained volume discharges may lead tomore favorable plasma conditions for O3 generation


Application of Low-T Plasmas in ‘High Potential’ Area:Removal of VOCs, SOx, and NOx from Gaseous Streams

Low-T plasmas have been used in bench-scale applications to:• convert VOCs in gaseous waste streams• convert SOx and NOx in gaseous waste streams• use in high-flow and low-volume applications• convert contaminants in Diesel exhaust• prepare feed gas for fuel cell

Possible show-stoppers preventing industrial-scale applications :• by-product formation (characterization, control)• carbon closure (accounting for fate of all C atoms)• competing technologies (advanced oxidation techniques, catalysts, …)• energy efficiency• economics (cost of manufacture, cost of operation, …)


Capillary Plasma Electrode (CPE) Concept

dielectric(pulsed ) dc, ac, or rf voltage

metal

metaldielectric

Capillary Plasma Electrode (CPE) Realizations

Cylindrical Electrodes

(Longitudinal Flow)Solid Pin Electrodes

(Cross Flow)

Hollow Pin Electrodes

(Flow-Through)

Some Low-T Plasma Concepts Research andTechnology Initiatives

Exh

aust

Gas Preparation

VOCs in dry air50 – 1500 ppm(v)

Plasma Reactor

I-V, PowerMeasurement

influent effluent

Off-Line AnalysisCarbon Trap

Solvent ExtractionGC-MS

On-Line AnalysisFTIR Absorption

GC-FIDGC-MS (gas phase)

Experimental Setup

0

160

320

480

640

800

0.00 0.50 1.00 1.50 2.00 2.50 3.00 3.50

Specific Energy, J/cm3

Efflu

ent C

once

ntra

tion,

ppm

0

20

40

60

80

100

Rem

oval

Effi

cien

cy, %

Removal of n-Heptane in an Annular Plasma Reactor (residence time: 0.6 s; initial concentration: 700 ppm)

Removal of Toluene in an Annular Plasma Reactor (residence time: 0.6 s; initial concentration: 490 ppm)

0

100

200

300

400

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0


Efflu

ent C

once

ntra

tion,

ppm

0

20

40

60

80

100

Rem

oval

Effi

cien

cy, %

Destruction of Toluene in a Cross-Flow RectangularCapillary Plasma Reactor vs. Residence Time

(specific energy 1.5 J/cm3; initial concentration 490 ppm)

0.010.020.030.040.050.060.070.080.090.0

100.0110.0120.0130.0140.0150.0

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8

Residence Time, s

Efflu

ent C

once

ntra

tion,

ppm

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

90.0

100.0

Des

truc

tion

Effic

ienc

y, %

0 2 4 6 8 100

10

20

30

40

50

60

70

80

90

100

Des

truc

tion

Effic

ienc

y (%

)

Energy Density (J/cm3)

Initial contaminant concentration:

Benzene Destruction200 - 1200 ppm(v)

flow rate: 2 - 8 l/min; residence for maximum destruction efficiency

A-CPE Reactor

CF-CPE Reactor

Destruction Efficiency of 4 compounds with Different Ionization Energies vs. Specific Energy (Identical Conditions)

(shortest residence time for ~ 100% Xylene destruction)

20

30

40

50

60

70

80

90

100

0.5 1.0 1.5 2.0 2.5 3.0


Des

truc

tion

Effic

ienc

y, % IE = 8.77 eV

IE = 8.44 eV

IE = 8.83 eV

IE = 9.24 eV

Xylene

Ethylbenzene

Toluene

Benzene

Destruction Efficiency of the four BTEX Compounds vs. Degree of Substitution and Ionization Energy

XyleneEthylbenzeneTolueneBenzene

Destruction Efficiency

Degree of Substitution

Ionization Energy

Kinetic Model

• Basic assumptions– Plug flow conditions prevail throughout the reactor

(verified by Reynolds and Dispersion numbers)– The temperature remains constant, thus the density of the

gaseous influent and effluent streams remain constant

• Mass balance around the reactor

Co, C = influent, effluent contaminant concentrationE = contaminant degradation efficiencyES = energy density

C = Co exp (-kd ES); E = 1 – exp (-kd ES)


• 3 model compounds: toluene, ethylbenzene, and m-xylene

• Influent flowrate and contaminant concentration tightly controlled (i.e. approximately constant to within ±3%))

• Five sets of experiments at input power: 20, 30, 40, 50, and 75 W

• At each power setting influent stream the flow rate was varied in the range from 2.0 - 8.0 l/s

• Influent target compound concentration was constant at 265 ppm, 270 ppm, and 155 ppm for toluene, ethylbenzene, and m-xylene

• Effluent concentration is plotted vs. energy density

Kinetic StudiesResearch and

Technology Initiatives

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.40

50

100

150

200

250

300Ef

fluen

t Con

cent

ratio

n (C

), pp

m

Energy Density E, J/cm3

R2 = 0.953

C = 275.2 exp(-0.519 E)

Ethylbenzene Destruction


C-H

str.

Alk

anes

C-H

str.

Aro

mat

ic R

ing

Plasma OffPlasma On

-0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18

0.20

Abs

orba

nce

2700 2800 2900 3000 3100 3200 3300 Wavenumbers (cm-1)

C=C

Aro

mat

ic R

ing

Plasma OffPlasma On

-0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

0.10

0.11

0.12

0.13

0.14

0.15

Abs

orba

nce

1400 1450 1500 1550 1600 Wavenumbers (cm-1)

Destruction of Toluene – FTIR Spectra


FTIR Spectra of a Pure Air Plasma and a 750 ppm(v) Toluene in Air Plasma

Trace Concentrations of VOCs in Air Create a very Complex Plasma Chemistry


Low-T plasmas for Environmental Applications:• High Percentage of VOC Destruction in Low-Flow Applications• Reasonable Destruction Efficiency in High-Flow Applications• Extensive Characterization of By-Products• High Level of Carbon Closure

But: Challenges RemainScale-up to high gas flow is non-trivialCost and energy efficiency (vs. competing technologies)Materials for long-term, maintenance-free operationControl of by-product formationPoorly understood plasma chemistryCoupling of discharge physics to plasma chemistry

SUMMARY:Low-T plasmas can be used effectively for the treatment of gaseous waste streams containing VOCs in a bench-scale R&D environment

Large-scale industrial utilization is still some time away !

Solid Oxide Fuel Cell Chemistry

Low-T Plasmas for Fuel Cell Systems

300 kW Fuel Cell

2 m

Idea:Use low-T plasma to generatehydrocarbon feed gas for cell


Clean Fuel Cell Feed

DieselVaporization

Plasma ReactorDiesel CH4,H2, HCsR-S + H2 H2S + R

ZnO CartridgeZnO + H2S ZnS + H2O

Water/Steam

Conventional SOFC Process

Diesel SulfurRemoval

Pre-Reforming

CarbonateDFC/SOFC

Heat/WaterRecovery

SteamGenerationairsteam

Exhaust

PowerConditioning

AC Power

Two Catalytic Reactors

Low-T Plasma Alternative

H2


Various DBDs1. Surface DBDs (S-DBDs) using Microrods

High Voltage(~10-15 KHz)

Ground Wires

Dielectric

Plasma

Gas in Gas out10”

2. Parallel-Plate DBD (PP-DBD)

Top electrode removed


(1) Low & High Sulfur Fuel @ Steam/Fuel = 3

1614Higher Hydrocarbons2/01/0Ethane/Propane25Acetylene2930Ethene2323Hydrogen2827 % (v/v)Methane

High SulfurLow Sulfur

(2) Effect of Steam/Fuel Ratio for NATO 76 Diesel

141/05302327

MEDIUM (3:1)

1619Higher Hydrocarbons1/02/1Ethene/Propane44Acetylene3328Ethene2121Hydrogen2525 % (v/v)Methane

HIGH (8:1)LOW (2:1)

Good Stuff

Good Stuff

Not Bad

Not Bad

Work continues – at bench-scale R&D, no engineering realization yet

• Pulsed electrical discharges in water to develop a reactor and process for the in-situ,on-demand generation of oxidants (O, OH, H2O2, O3) for the disinfection of water

• Produce high concentrations of oxidants and UV with low power consumptionuse externally introduced oxygen bubbles in the water (bubbled water discharge)

Pulsed Electrical Discharges in Bubbled Water

Typical Reactor Set-up Bubble locations

Most efficient scenario is difficult to realize and stabilize in practice !!!

Bubble not touching electrodes:• High power required• Weak discharge, low efficiency• most bubbles

Bubble touching one electrode:• Medium power required• Stronger glow discharge, more efficient• some bubbles

Bubble touching both electrodes:• Low power required• Strong spark discharge, high efficiency• few bubbles


Hydrogen peroxide and ozone generation

O3


0 20 40 60 80 1000

5

10

15

20

25

30

Ar, 200 ml/min O2, 200 ml/min Air, 200 ml/min

H2O

2 con

cent

ratio

n, m

g/l

Time, min

Conditions:T = 25ºC; 200 ml of DI water; conductivity ~ 1.5mS/cm;

pH = 3 (H2SO4); [Fe2+] – 1.5 mmol/lvoltage 15 kV; pulse repetition rate 20 Hz; power consumption ~ 2 W

Production of H2O2 at low pH:more efficient

H2O2 production:

• is highest for air

• the same for Ar and O2

• has efficiency of ~ 3 mg/kWh


HMX degradation:optimization of process parameters

Conditions:T = 25ºC; 200 ml of HMX solution; conductivity – 1.38 mS/cm;voltage -15 kV; repetition rate – 20Hz; C0 of HMX – 4 mg/l; pH is varied: 5.5 and 3 (H2SO4); [Fe+2] – 1.5 mmol/l

Results:HMX degradation:

is much faster at low pHis faster in O2 than Ar

H2O2 is responsible for about 25% of HMX degradation

The remaining degradation is due to ozone and other radicals, UV

Octahydro-1,3,5,7-tetranitro 1,3,5,7-tetrazocine; high melting explosive (HMX)

NN

NN

O2N

NO2

NO2

O2N

0 20 40 60 80 100 1200.0

0.2

0.4

0.6

0.8

1.0

Ar, pH 5.5, no [Fe+2] O2, pH 5.5, no [Fe+2] Ar, pH 5.5, [Fe+2]=1.5mM/l O2, pH 5.5, [Fe+2]=1.5mM/l Ar, pH 3, [Fe+2]=1.5mM/l O2, pH 3, [Fe+2]=1.5mM/l

HM

X, C

/C0

Time, min

Technology InitiativesResearch and

0 20 40 60 80 100 1200.0

0.2

0.4

0.6

0.8

1.0

Power off

Ar, 200 ml/min O2, 200 ml/min

HM

X, C

/C0

Time, min

Under these conditions:

Reactions continue after discharge is turned off

HMX degradation rate is higher for O2 than Ar

O3 plays a role in the HMX decomposition

HMX decomposition at low pH with Fenton reagent


Conditions:pH = 3 (H SO )[Fe2+] – 1.5 mmol/l

2 4

HMX decomposition at low pH with Fenton reagent with and without the discharge

0 20 40 60 80 100 1200.0

0.2

0.4

0.6

0.8

1.0

Ar, pH 3, [Fe+2]=1.5mM/l + H2O2

Ar, pH 3, [Fe+2]=1.5mM/l O2, pH 3, [Fe+2]=1.5mM/l

HM

X, C

/C0

Time, min

Conditions:

pH = 3 (H2SO4)[Fe2+] = 1.5 mmol/l[H2O2] = 20 mg/l

Results:HMX degradation by H2O2 + Fenton reaction (black) and by discharge in water bubbled using Ar (red) and Oxygen (blue) + Fenton reaction

HMX degradation:H2O2 is responsible for about 25% of HMX degradationDischarge is essential for rapid degradationOzone and other radicals and UV contribute as well

Technology InitiativesResearch and

Discharge

SummaryResearch and


The discharge in gas bubbles in DI water is a DBD: a high current, pulsed, self-terminating microplasma

Fast space-charge propagation – streamerDBD discharge (SS electrodes are covered by a layer of water)Streamers in small bubbles and in large bubbles that occupy the space between the electrodes

Large bubbles are more effective for radical production and water treatmentRadicals (O, H, OH) and H2O2 and O3 are generated in-situ

No significant difference in H2O2 production for O2 and Ar, but more effective in air

HMX decomposition is not effective using only H2O2 and Fenton reaction

HMX decomposition is effective using a discharge in bubbled water at low pH and Fenton reaction

Degradation is due to O3, other radicals (O, OH) and/or UV (not clear yet)

Destruction of Bacteria

Known Facts:• Plasmas can inactivate (“kill”) individual microorganisms

(cells, bacteria, spores, viruses; E.coli, Anthrax, etc. …)• Both low-pressure and high-pressure plasmas “work”

(higher inactivation rates compared to conventional methods suchas EtO, dry heat, steam heat, etc. ..)

“Kill Agents”:• UV radiation• Reactive Radicals, Ions• Heat• Electric fields

“Kill Mechanisms”:• well understood at the cellular level• fairly well understood how low-pressure plasmas

induce cell death• less well understood for high-pressure plasma

??? Open Question (not really a plasma physics question) ???Role of synergistic effects of the various “kill agents”, i.e. effect of the of simultaneous or sequential action of more than one “kill agent” !!!


HV

Power Supply

Ground Plate

CapillaryPlate

Cold Plasma Jets

Sample Glass Plate

Gas Analyzer

DataAcquisition

Reactor Enclosure

Gas Mixing and Control

Carrier Gases

Ambient Gas

Experimental Setup for Spore Inactivation


0

1

2

200 250 300 350 400

Wavelength (nm)

Abs

orba

nce

After Plasma Treatment

Before Plasma Treatment

UV Absorption - A Qualitative Measure for Cell Destruction (Bacillus subtilis spores)


0 30 60 90 120 150 180 210 2401

10

100

1000

D-Value: 101 s

Num

ber o

f CFU

/ml

Plasma Exposure Time (s)

Bacillus subtilis Spore Destructionby a CPE Plasma (Air, 760 Torr)

0 20 40 60 80 100 1200

1x106

2x106

3x106

4x106

(Decimal Reduction Number)D-Value: 92 s

Num

ber o

f CFU

/ml

Plasma Exposure Time (s)

Bacillus stearothermophilusSpore Destruction by a CPE

Plasma (He, 760 Torr)

The Status in 2002

D-values of 10s of seconds

y = 0.0773e-2.5065x

R2 = 0.998

y = 0.1e-0.6941x

1.E-07

1.E-06

1.E-05

1.E-04

1.E-03

1.E-02

1.E-01

1.E+00

0 2 4 6 8 10 12

Treatment time, sec

CFU

3 mm10 mm

The Status in 2007


D-values of (much) less than 10s (with additives in the feed gas)

A biofilm is a highly structured community of bacteria with a complex structure that can

adhere to solid surfaces or interfaces.

• Biofilms can form when planktonic bacteria adhere to surfaces and begin to excrete exopolysaccharide that anchor them to the surface

• A biofilm may form on any surface exposed to bacteria and some water, but moisture is not always necessary

Low-T Plasmas and BiofilmsResearch and


• Biofilms can cause serious side effects associated with many illnesses and implants

• Biofilms impact on many industrial processes and have adverse effects on the environment

Biofilms Impact Many Aspects of Daily Life


Biofilms are not easy to Inactivate• Biofilms have different properties than planktonic cells • Biofilms are highly resistant to antibiotics, germicides,

and other conventional forms of inactivation– Concentrations of antibiotics required to destroy a biofilm

would probably kill the patient– Concentrations of germicides required to sanitize equipment is

usually environmentally detrimental.

!!! Most conventional inactivation approaches do not work well for biofilms !!!

!!! BUT: Plasma Works !!!


0 10 20 30 40 50 60103

104

105

106

Num

ber o

f CFU

/ml

Plasma Exposure Time (min)

Inactivation of Chromobacterium violaceumbiofilm-forming cells (4-day old bioflm)

Rapid 2-order-of-magnitude reduction

Slow 1-order-of-magnitude exponential reduction

(needs to be looked at further)


SUMMARY & OUTLOOKResearch and


• Electrostatic Precipitators & Ozone Generators are the only fullycommercialized plasma-based environmental technologies

• Plasma-initiated degradation of contaminants (VOCs, NOx, SOx) ingaseous waste streams has been demonstrated in the lab

• By-product characterization & control, carbon closure, and scale-up challenges remain obstacles to full commercialization

• Plasma-assisted generation of fuel cell feed gas mixtures and plasma-enabled degradation of biofilms are being studied in the lab

• Unresolved science issues remain before engineering realization

• Pulsed electrical discharges in water and aqueous solutions represent a promising approach to disinfection and decontamination of liquids

• Early-stage lab phase technology

• Non-thermal plasmas have yet not fulfilled their full potential asa key technology in the area of environmental applications

• Remaining science and/or serious engineering challenges haveslowed down the translation of lab achievements into viable technologies for large-scale industrial applications

Medical and Biomedical Applications

The Plasma Needle

Cleaning of Dental Cavities

Other Applications• Bio Decontamination• Sterilization of Medical Instruments and Wounds

!!! BIG ISSUE: PLASMAS AND HUMANS !!!


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