Introduction to Advanced Oxidation Processes (AOPs) and Photochemical Based AOPs

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Introduction to Advanced Oxidation Processes (AOPs) and

Photochemical Based AOPs

James Bolton (U of A, Edmonton, Canada) and

Thomas Oppenländer

Hochschule Furtwangen University, Germany Department of Process Engineering

Outline

Definitions

Survey: Advanced Oxidation Technologies The Hydroxyl Radical

AOT Mechanism

Basics of Photochemistry UV Treatment of NDMA

Development Status of Photochemical AOTs Organic Parameters of Water Analysis

Some important definitions

AOP: Advanced Oxidation Process AOT: Advanced Oxidation Technology UV: ultraviolet radiation

VUV: vacuum-UV radiation between 100

nm and 200 nm

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Advanced Oxidation Technologies (AOTs)

Usually involve the generation of hydroxyl radicals (•OH).

Called “Advanced” because the reactions are just highly accelerated oxidation reactions that occur when pollutants enter the environment.

The •OH radicals react with organic pollutants to initiate a series of oxidative degradation reactions.

The overall process often leads to mineralization (i.e., conversion to CO₂, H₂O and mineral acids) of the pollutants.

Photochemical Processes

Advanced Oxidation Processes and

Technologies:

AOPs AOTs Solar Processes TiO Photocatalysis2

Super Critical Water Oxidation

(SUWOX) Catalytic

Processes

Sonolysis Non-thermal

Plasma Techniques

γ-Radiolysis Electron Beam

Irradiation

X-Ray Irradiation Electrochemical

Processes

Survey of Advanced Oxidation Processes (AOPs)

Short Lived

Highly Reactive Powerful

Oxidant

Ubiquitous in Nature

Easy to Produce

Non-Selective Reagent

O H

• _ _

Electrophilic Character Kinetic Reaction

Control

The Hydroxyl Radical

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The Hydroxyl Radical

Reacts (usually with very high rate constants) by hydrogen abstraction (saturated aliphatics) addition to double bonds (unsaturated &

aromatics)

electron transfer (primarily with inorganics) radical-radical reactions (e.g., ^••••OH + HO2^••••) Molar absorption coefficients

εεεε230= 530 M^-1cm^-1; εεεε260= 370 M^-1cm^-1 pK_a= 11.9

E^o= 2.7 V (acid solution)

AOT mechanism

••••OH + CH₃OH ^••••CH₂OH + H₂O

• •OH radicals react with organic compounds by:

• hydrogen abstraction from aliphatic compounds

addition to unsaturated compounds

••••OH + CH₂= CH₂ ^••••CH₂CH₂OH

• This is followed by reaction with oxygen initiating a series of degradative oxidation reactions

Mechanism of methanol degradation

Other organics are more complex, but generally:

pollutant aldehydes carboxylic acids bicarbonate

••••OH + CH₃OH ^••••CH₂OH

O₂ O

HCH + HO₂^••••

••••OH/O₂

O CO₂ HCOH

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AOT mechanism: oxidation and mineralization

Photo- initiated

AOP

•OH

Mi H O2

Mi•

•O •2 M -O-Oi •

Hydrogen Abstraction Electrophilic Addition

II II

M -O-Oi II •II ^?

Mi ox

M2 ox

M1 ox

HO2•/O• H O /O

2

2 2 2

-

HCO3

- HO^-

HCO3•/CO •3 -

Mi

Peroxyl Radicals

M3 ox

Electron Transfer

Selective Oxidation

CO2

Tasks of AOTs for water and air treatment

Oxidation of undesirable organic water contaminants R-H R-H^ox

Mineralization of organic water contents R-CH₂-X CO₂ + H₂O + HX + ……

Detoxification and purification of Water and air

Basics of Photochemistry (1)

Photochemistry

Photophysics Photobiology

Photo- medicine

Absorption

Fluorescence Phosphorescence

Excited State Properties

Energy or Electron Transfer

Deactivation Mechanisms Formation of

Photoproducts Photochemical

Engineering

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Basics of Photochemistry (2)

Reaction System

Lamp Technology

Chemical Engineering

Photochemical Engineering Chemical Analysis

UV/VIS-Spectroscopy and Actinometry

Photoreactor Concepts

Basics of Photochemistry (3)

0 200 400 600 800 1000 1200

0 200 400 600 800 1000 Wavelengthλ/ nm

RadiantEnergyQλof NAPhotons/kJmol-1

E = p N hcA 0/λ

Basics of Photochemistry (4)

0 10 20 30 40 50 60 70

0 200 400 600 800 1000 1200 Wavelengthλ /nm

Near IR IR VIS = Light UV-A UV-B UV-C VUV X-ray γ-ray M M + e⁺ ^- Photoionization

Photoexcitation

M M^vib Vibrational Excitation M M*

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Basics of Photochemistry (5)

Incident Beam Reflection

Refraction Absorption

Formation of Photoproducts Transmitted Beam Scattering Transparent

Material

Luminescence

Basics of Photochemistry (6) Rate of a Photochemical Reaction

V R_C====GF^CΦΦΦΦ^C

G= incident photon flow (einstein s^-1) F_C= f(λλλλ)χχχχC= fraction of light absorbed by

component C Φ

Φ Φ

ΦC= quantum yield of component C V= volume (L)

Rate (R_C) of photochemical reaction of component C

Basics of Photochemistry (7): Definitions

Total fraction of light absorbed

Fraction absorbed by a single component i

Quantum Yield (ΦΦΦΦp)- defined as the number of moles of product formed or reactant removed (P) per mole of photons absorbed.

) 10 ( 1 )

(λλλλ ^A^λλλλ f ==== −−−− ⁻⁻⁻⁻

a c_i i εεεεi

χχχχ ====

absorbed )

(einsteins photons

of moles

generated of

moles

p

==== P ΦΦ ΦΦ

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Basics of Photochemistry (8):

Kinetic Regimes

If F_Cis near unity, the kinetics will be “zero-order”, that is R_Cwill be independent of c_C.

If FCis < 0.1, f(λλλλ) may be expanded in a Taylor Series so that R_Creduces to:

such that now the kinetics are “first-order”, that is,RCis proportional to cC.

l V c

R_C≈≈≈≈GΦΦΦΦ^Cln(10)εεεε_C _C

Treatment of NDMA

NDMA (N-nitrosodimethylamine) is a carcinogen that is often found in industrial effluents. It does not biodegrade, air strip or adsorb well to activated carbon. However, it does photolyze very efficiently.

NDMA absorbs only in the range 200–250 nm;

thus, a UV lamp with strong output in this region is essential for effective treatment.

(CH₃)₂NNO h

νννν

(CH₃)₂N• + NO

UV Treatment of NDMA: Degradation Curves at Different Concentrations

0.0001 0.001 0.01 0.1 1

0 2 4 6 8 10 12 14

time / min

concentration / mM

0.0 0.2 0.4 0.6 0.8 1.0

concentration / mM

k₁= 1.31 min^-1 k0= 0.164 mM min^-1

Question: Which degradation curve represents zero and which first order degradation kinetics?

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VUV Oxidation UV Oxidation Photocatalysis UV Disinfection

H O-VUV2 H O -UV O -UV O -H O -UV

2 2

3

3 2 2

TiO -UV/VIS H O -Fe /Fe -

UV/VIS (Photo- )

2

2 2

2+ 3+

Fenton

UV-C

Xe * Excimer Lamp(172 nm)

2 MP

Mercury Lamps

UV-A Lamps Solar UV/VIS

LP and MP Mercury Lamps

Research Industry Industry

Suprasil LP Hg Lamps (185 nm)

Hetero- geneous

Homo- geneous

Homogeneous Homogeneous Homogeneous

Development status of photochemical AOTs

VUV Oxidation UV Oxidation Photocatalysis UV Disinfection

H O-VUV2 H O -UV O -UV O -H O -UV

2 2

3

3 2 2

TiO -UV/VIS H O -Fe /Fe -

UV/VIS (Photo- )

2

2 2

2+ 3+

Fenton

UV-C

Xe * Excimer Lamp(172 nm)

2 MP

Mercury Lamps

UV-A Lamps Solar UV/VIS

LP and MP Mercury Lamps

Research Industry Industry

Suprasil LP Hg Lamps (185 nm)

Hetero- geneous

Homo- geneous

Homogeneous Homogeneous Homogeneous

Development status of photochemical AOTs

Organic Parameters of Water Analysis (1): Global Parameters

T C : T o t a l C a r b o n T I C : T o t a l I n o r g a n i c C a r b o n T O C : T o t a l O r g a n i c C a r b o n D O C : D i s s o l v e d O r g a n i c C a r b o n P O C : P a r t i c u l a t e O r g a n i c C a r b o n V O C : V o l a t i l e O r g a n i c C a r b o n

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Organic Parameters of Water Analysis (2):

Group Parameters and Lead Substances

TOX: Total Organic Halogen

DOX: Dissolved Organic Halogen AOX: Adsorbable Organic Halogen EOX: Extractable Organic Halogen POX: Purgable Organic Halogen

VOX: Volatile Organic Halogen

Lead Substrates NOM: Natural Organic Matter HC: Hydrocarbons

PAH: Polycyclic Aromatic HCs

Phenols

Chlorophenols

etc.

Hyperlinks >>>>

Measurement of TOC with a TOC analyzer with auto sampling unit

Combustion of the probe at a catalyst surface and quantification of CO₂

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Second Order Rate Constants of OH-Radical Reactions with different Substrates:

Typical elementary reaction Substrate + ・OH Product

Rate

(-substrate)

= - k

_{・OH, M}

[ ・ OH] [Substrate]

Examples of Second Order Rate Constants of OH- Radical Reactions with different Substrates:

rate = - k

・・・・OH, M

[

・・・・

OH] [Substrate]

Free Database:

http://kinetics.nist.gov/solution/

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… for example:

… results:

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Rationalization

O O O

H H H

O O

H O H H

HO₂• + CH2O Hydroperoxyl Radicals

and Formaldehyde

Medium Pressure Hg Lamp: Emission Spectrum

0,0 0,5 1,0 1,5 2,0

200 400 600 800 1000

Wavelengthλ/ nm SpectralIrradiance Eλ/Wm-2 nm-1

MP Mercury Lamp QC 1000 Enhanced

Emission (UV-C)

Low Pressure Hg Lamp: Emission Spectrum

0,0 0,2 0,4 0,6 0,8 1,0

200 400 600 800 1000 1200 LP Mercury Lamp

NNI 120/84 λ = 253.7 nm

0,0 0,2 0,4 0,6 0,8 1,0

200 400 600 800 1000 1200 λ = 253.7 nmLP Mercury Lamp

NN 50/81

Wavelength / nmλ Spectral Irradiance E, Relative Unitsλ

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Development of Modern Mercury-free Excilamps for

Water and Air Treatment and

Applications in Photochemical Technology

(Two Lectures)

Definition: Elementary Reaction

A reaction for which no reaction intermediates have been detected or need to be postulated in order to describe the chemical reaction on a molecular scale.

An elementary reaction is assumed to occur in a single step and to pass through a single transition

state.

Introduction to Advanced Oxidation Processes (AOPs) and Photochemical Based AOPs