Chem Oxidation
-
Upload
aghnia-qinthari-nabilah -
Category
Documents
-
view
221 -
download
0
Transcript of Chem Oxidation
-
7/29/2019 Chem Oxidation
1/37
The use of oxidizing agents without the need of
microorganisms for the reactions to proceed
oxidizing agents : O3, H2O2, Cl2 or HOCl or O2 etc
catalysts : pH , transition metals, light , ..etc
CHEMICAL OXIDATION
-
7/29/2019 Chem Oxidation
2/37
Types of oxidation Processes
1. Conventional oxidation processes
- Use common oxidizing agents such as ozone,
chlorine without production of highly reactive species
2. Oxidation processes carried out at high
temperature/ high pressure
- Produce highly reactive species, hydroxyl radicals
(HO)
-
7/29/2019 Chem Oxidation
3/37
3. Advanced oxidation processes (AOPs)
- Produce highly reactive species, hydroxyl radicals
(HO ) using oxidizing agents and catalysts
Oxidation rate observed
HO > O3 > H2O2 > HOCl > ClO2 > KMnO4 > Cl2 > O2
-
7/29/2019 Chem Oxidation
4/37
Application
o For nonbiodegradable , toxic organic compounds
o For compounds that inhibit microbial growth
o Effective for destruction of many inorganic compounds
o Elimination of odorous compounds e.g. H2S
-
7/29/2019 Chem Oxidation
5/37
Extent of degradation
1. Primary degradation
2. Acceptable degradation
3. Ultimate degradation (mineralization)
4. Unacceptable degradation (fusing)
- a destruction change in the parent compounds
- a structural change in the parent compounds to the extent
that toxicity is reduced
- conversation of organic carbon to inorganic carbon CO2
- a structural change in the parent compounds resulting inan increase in toxicity
-
7/29/2019 Chem Oxidation
6/37
Stoichiometry
Stoichiometric relationship between an oxidant and the
compoundsto be treated To estimate the required oxidant dosages for the
treatment
General approach
Express the half reaction for each oxidant in terms
of free reactive oxygen OExp. Oxygen , O2 2O
-
7/29/2019 Chem Oxidation
7/37
For convenient :
1. Use the electrochemical half-reaction (reduction reaction)
of the oxidant
2. Balance e- with half reaction of water (that gives O in this
approach)H2O O + 2 H
+ + 2 e- ( O = O2)
Exp. Ozone O3 + 2H+ + 2e- O2 + H2O
H2O O + 2 H+ + 2 e- (O = O2)
O3 O + O2
-
7/29/2019 Chem Oxidation
8/37
For ultimate conversion
CaHbOc + d O
a CO2 + (b/2) H2O
Balance equation using free reactive oxygen produced from
an oxidant
moles oxidant required for conversion of a mole of pollutant
Ex. The ultimate conversion of phenol using O3
C6H5OH + 14 O3 6 CO2 + 14 O2 + 3 H2O
-
7/29/2019 Chem Oxidation
9/37
Note : Wastewater contains a wild variety of compounds
Exp. For O3
O3 stoichiometric demand = (2/1)(48/32) COD
= 3 COD
Adapt free reactive oxygen approach to the surrogate COD
Oxidant demand = (2/n)(MW/32) COD
COD = Chemical oxygen demand (mg O/L)
MW = Molecular weight of oxidantn = mole O/mole oxidant
-
7/29/2019 Chem Oxidation
10/37
Exp. Estimate stoichiometric dosage of HClO needed
to treat an effluent having COD = 288 mg/L
HOCl + H+ + 2 e- Cl- + H2O
H2O O + 2 H+ + 2 e- (O = O2)
1. Mole of O per mole of HOCl
HOCl Cl- + O + H+
2. Oxidant demand
Oxidant demand = (2/n)(MW/32) COD
= (2/1) (52/32) (288)
= 936 mg/L
-
7/29/2019 Chem Oxidation
11/37
the stoichiometric requirement -- yield of free reactive oxygen
( e.g. Moles of O per kg oxidant)
Establish a Ranking of oxidants based on
- cost
- effectiveness of oxidant
Choose a suitable oxidant
How to choose an oxidant for treatment
-
7/29/2019 Chem Oxidation
12/37
Applicability
Apart from O2, most oxidants are expensive and not
competitive with biological treatment for high strength,
large-volume wastewater.
Coupling chemical oxidation and biological treatment
Chemical oxidation processes are designed for toxic,
inhibitory and refractory compounds
- to reduce toxicity
- to increase biodegradability of the parents compounds
at dosages far less than required for ultimate degradation
-
7/29/2019 Chem Oxidation
13/37
Oxidants
O2 (in wet air oxidation)
Ozone (O3)
Hydrogen peroxide (H2O2)
Fentons reagent (Fe(II)/ H2O2)
H2O2/UV
O3/H2O2Advanced Oxidation Processes (AOPs)
-
7/29/2019 Chem Oxidation
14/37
Ozone :
* powerful oxidant* unstable gas which decomposes to O2 at
normal temperature
* decomposition is accelerated by contact with
solid surfaces, chemical substances and by heat
* generated by electric discharge of air, O2
-
7/29/2019 Chem Oxidation
15/37
The corona discharge device can be fabricated and
configured in many different ways.
The primary feature is to generate a corona between
two electrode surfaces
air or oxygen pass between these electrodes
high-energy electrons bombard gas molecules
gas molecules are ionized forming a light emitting
gaseous plasma referred to as a corona
-
7/29/2019 Chem Oxidation
16/37
Reaction of ozone
O3 (aq) oxidized MAdded to water
O3 (g)
O3 (g)
M
OH
R
MS
OH -
Direct reaction
Indirect reaction
M : organic / inorganic molecule
S : scavenger : by-products
-
7/29/2019 Chem Oxidation
17/37
Direct reactions of ozone
Ozone can be electrophilic and nucleophilic
I . Reaction with organic compounds
Examples :
- oxidation of alcohols to aldehydes, organic acids
- substitution of an oxygen atom onto an aromatic ring
- clevage of carbon double bonds
II. Reactions with inorganic compounds
a. Oxidation of ammonia
4 O3 + NH3 NO3- + 4 O2 + H3O
+
-
7/29/2019 Chem Oxidation
18/37
b. Oxidation of iron and manganese
Fe 2+ (aq) 2 Fe3+
(aq) 2Fe(OH)3 (s)
O3 O2
Mn2+ (aq) Mn4+
(aq) MnO2 (s)
O3 O2
c. Oxidation of nitrite
NO2- + O3 NO3
- + O2
Indirect reactions of ozone
Free radicals reactions
Radicals produced will react with compounds in water
-
7/29/2019 Chem Oxidation
19/37
Phenol and aromatic hydrocarbon destruction
Color removal
Drinking water purification
Water bottling plants
Swimming pools
Laundry recycling
Applications
-
7/29/2019 Chem Oxidation
20/37
Hydrogen peroxide
- Colorless liquid at room temperature
- decomposes easily to give O2
- the decomposition is slow in dilute solutionor in pure solution well conserved in dark
Reactivity of H2O2 : 2 types
Direct or molecular reactivity
indirect or radical reactivity
-
7/29/2019 Chem Oxidation
21/37
As an oxidant , H2O2 can react with number of organic
and inorganic pollutants. Examples are shown below.
a) Treatment of sulfide , H2S
rapid oxidation : H2S + H2O2 S + 2H2O
b) Treatment of cyanides
H2O2 + CN- + H+ CNO- + H2O
c) Purification of iron and manganes containing groundwaterH2O2 + 2Fe
2+ + 2H+ 2Fe3+ + 2H2O
Fe(OH)3 (S)
I. Direct reaction
-
7/29/2019 Chem Oxidation
22/37
Limit : - oxidation by H2
O2
alone is not effective for high
concentration of certain contaminants
e.g. Highly chlorinated compounds
: - Low rate of reaction at reasonable [H2O2]
II. Direct reaction : Reaction of hydroxyl radicals formed in
H2O2 decomposition
-
7/29/2019 Chem Oxidation
23/37
Advanced Oxidation Processes (AOPs)
The advanced oxidation process can be used to
decompose many hazardous chemical compounds
to acceptable levels.
The term advanced oxidation processes refers
specifically to processes in which oxidation of organic
contaminants occurs primarily through reactions withhydroxyl radicals.
Source: http://www.spartanwatertreatment.com/advanced-oxidation-processes.html
-
7/29/2019 Chem Oxidation
24/37
The most widely applied AOPs are:
Peroxide/ultraviolet light (H2O2/UV),
Ozone/ultraviolet light (O3/UV),
Hydrogen peroxide/ozone (H2O2/O3)
Hydrogen peroxide/ozone/ultraviolet (H2O2/O3/UV)
-
7/29/2019 Chem Oxidation
25/37
H2O2/UV process
- Irradiation of UV light ( < 365 nm) can break H-O bond
chain reactions
Initiation : H2O2 + h 2 OHx = 18.6 L mol-1 cm-1
Propagation : H2O2 + 2 OHx H2O + HOOx
Termination : HOOx + HOOx H2O2 + O2
-
7/29/2019 Chem Oxidation
26/37
O3
/UV process
O3 decomposes to produce radicals at high pH values(photolysis).
Initiation : O3 + OH- OH2
+ O2 -
OH2 O2
- + H+
Propagation : O3 + O2 - 2O2 + OH
O3 + OH OH2
+ O2
Termination : OH2 + OH O2 + H2O
h
Source: http://www.spartanwatertreatment.com/advanced-oxidation-UV-Ozone.html
Radicals produced will react with compounds in water
-
7/29/2019 Chem Oxidation
27/37
Chlorine
Use in water and wastewater treatment e.g. Color removal
At room temperature, Cl2 can dissolved in water giving
HClO.
Cl2 + H2O HClO + Cl- + H+
HOCl + H2O ClO- + H3O+
ka = 1.6-3.2 x 10-8
Hypochlorous acid hypochlorite ion
-
7/29/2019 Chem Oxidation
28/37
Nature of species in water depends on pH
(HClO, ClO-, H2ClO+, Cl2O)
Cl2 and its derivatives can react with organic
Matters in water by :
- oxidation reaction
- addition / substitution reaction
==> results in formation of organochlorinated compounds
==> reduce the use of chlorine
-
7/29/2019 Chem Oxidation
29/37
Applications of chlorine
Treatment of CN-
- change CN- to CNO- and finally to N2
Reactions with NH3, NH4+
- result in formation of chloroamines (NH2Cl, NHCl2, NCl3)
- possible reactions leading to disappearance of
chloroamines :
4 NH2Cl + 3Cl2 + H2O N2 + N2O + 10HCl
2 NH2Cl + HClO N2 + H2O + 3HCl
NH2Cl + NHCl N2 + 3HCl
-
7/29/2019 Chem Oxidation
30/37
Overall reactions for total degradation of NH3
2 NH3 + 3 HOCl N2 + 3H2O + 3HCl
2 NH3 + 3 Cl2 N2 + 6H + 6Cl-
Molar ratio Cl2 : NH3 = 3 : 2Mass ratio Cl2 : NH3 = 7.6 : 1
CHLORINE DEMAND
amount of Cl2
used in reactions
= Cl2 added to water - total available residual
chlorine remaining at the end of the specific time (Cl2, HClO,
ClO-)
-
7/29/2019 Chem Oxidation
31/37
CHLORINE DEMAND
C
hlorine
residua
ls
Cl2 added (mg/L)
Zero demand residual
A
B
D
Chlorine demand
-
7/29/2019 Chem Oxidation
32/37
Point A : low chlorine residual
= > consumption of chlorine by reducing compounds
e.g. Fe
2+
, Mn
2+
, H2S and organic matters
Above point A : Formation of chlorinated org compounds
e.g. chloroamines
Point B : All compounds has been reacted
B D : some chlorinated org compounds are oxidized
(then chlorine residual is reduced to Cl-)
-
7/29/2019 Chem Oxidation
33/37
Point D : Breakpoint (most of chlorinated organic
Compounds are oxidized)
Beyond D : - presence of some resistant chlorinated
compounds
- all added chlorine residual is free
available chlorine (Cl2, HClO, ClO-)
-
7/29/2019 Chem Oxidation
34/37
-
7/29/2019 Chem Oxidation
35/37
Chemicals
Hypochlorites (salt of HClO)
- NaOCl, Ca(OCl)2
give OCl-
- use in small installation e.g. Swimming pools
Liquid chlorine- used in water treatment plant e.g. In US
ClO2 - prepared by following reactions
2 NaClO2 + Cl2 2ClO2 + 2NaCl
2 NaClO2 + 4HCl 4ClO2 + 5NaCl + 2H2O
-
7/29/2019 Chem Oxidation
36/37
CHOICE OF USAGE
- Sterilization of water
ClO2 is superior to chlorine in destruction of spores,
bacterias, virus and other pathogen organisms
- Industrial water treatment
- chlorine are more reactive than ClO2 and will react with
most organic compounds (ClO2 does not react with NH3 or
NH4+
)
-
7/29/2019 Chem Oxidation
37/37
http://www.iwawaterwiki.org/xwiki/bin/view/Articles/CHEMICALOXIDATIO
NAPPLICATIONSFORINDUSTRIALWASTEWATERS
http://www.lenntech.com/products/chemicals/water-treatment-chemicals.htm
http://openlearn.open.ac.uk/mod/oucontent/view.php?id=399252§ion=1.4.7
References
( 6 Feb 2011)