Download Chemistry of Gasworks

Chemistry of Gas Works Contaminants
Judith Nathanail,
Land Quality Management Ltd
[email protected]
© Land Quality Management 2013
1
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Gas Works Contaminants
•Ammonia liquors •Elemental
sulphur,
•Coal tar
sulphate,
•Spent oxide
thiocyanate,
•PAHs
•
Metals
•Free cyanide,
•
Acidic soils.
•complex cyanide
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Chemistry of Gas Works
Contaminants
• Follow the molecules and substances from
coal via gas works process and into waste
stream
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Coal
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•
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•
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readily combustible
more than 50% by weight of
carbon.
Comprises carbon, volatiles
and moisture
other constituents include,
nitrogen, ash, and sulphur.
hydrocarbons are fused
aromatic ring compounds,
each containing a vast number
of rings and aliphatic chains
(eg decane) and rings (eg
cyclohexane)
•
Chemical formula of coal C135H96O9NS
CH0.73O0.08N0.01S0.01
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http://www.tutorvista.com/content/chemistry/chemistry-i/coal-petroleum/coal.php#destructive-distillation-of-coal
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s te
a
W
/
ts
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od
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p
by
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Solid
Retort
Solid
Gas
• Heat coal in a closed
vessel (no O2) “a retort”,
• Drives off volatiles
• (including water)
• Thermal decomposition
(not combustion)
• Gases go up feed pipes
Gas
• methane, hydrocarbons,
hydrogen, carbon
monoxide, carbon dioxide,
nitrogen, HCN, NH3
• Coke in retort
• almost pure C
© Land Quality Management 2013
http://www.nationalgasmuseum.org.uk/index.asp?page=history-02
Tar
Ammonia
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Coke removed
and quenched
Liquors
produced
Remaining gases within
Coke condense and some dissolve
http://en.wikipedia.org/wiki/History_of_manufactured_gas
Tar
Ammonia
Gasworkers withdrawing a completed charge of coke.
Instant flame; quench water became ammoniacal toxic liqour
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Hydraulic main
•
•
Hydraulic main.
•
gas bubbles through liquid
Tar and ammonia condenses
and mixes with water
Hydraulic Main
Ascension Pipes
Retort
Gases condense and some
dissolve
© Land Quality Management 2013
Tar Ammonia
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Condenser
• Further cools down gas and
•
condense water vapour and
liquifiable hydrocarbons,
Volatiles condense into a dark
amber liquid called 'liquor',
• drained off from the condensers
into a tar pit or 'well'.
• What is coal tar?
Gases condense and some
dissolve
Tar
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Ammonia
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Coal Tar
• Viscous liquid
• mixture
• Phenols - C6 H5 OH
• alcohol (OH) groups
OH
attached to benzene rings:
• PAHs - fused aromatic
rings
• heterocyclic compound
• a cyclic compound that has
atoms of at least two
different elements as
members of its ring
(e.g. C + N)
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Pyridine
C5H5N
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Ammonia washer
• Gas is bubbled up through water which
•
absorbs the ammonia in the gas.
'ammoniacal liquor' is drained off, often
into the same pit as the tar (where it
floats on top of the tar).
• At larger works -
this was followed by
Livsey washer
• What is Ammoniacal liquour?
•
NH3 and NH4+
Tar
liquid with ammonia dissolved in it
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Ammoniacal liquor
• solution of
• ammonia,
• ammonium compounds
• phenols
• sulphur compounds…
• N and S – from coal
• C135H96O9NS
© Land Quality Management 2013
http://marysgasbook.blogspot.co.uk/2009/08/waht-to-dowith-waste-ammoniacal-liquor.html
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Ammonia
• NH3
• soluble in water (at lower
temperatures)
• NH4+
• NH3 and
NH4+ both
present in water
• distinctive odor
• Ammonia generated with
gas as ammonia vapours,
then condensed to
ammonia liqour
5 electrons in outer shell
Look at periodic table to show
why 1N bonds with 3H
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The Periodic Table
I
II
III
IV
V
VI VII
H
0
He
Li Be
B
C
N
O
F
Ne
Al
Si
P
S
Cl Ar
Transition elements
Na Mg
K
Ca Sc Ti
Rb Sr
Y
V
Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr
Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te
Cs Ba
Hf Ta W Re Os Ir
Fr Ra
Rf Db Sg Bh Hs Mt
I
Xe
Pt Au Hg Tl Pb Bi Po At Rn
La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
Ac Th Pa
© Land Quality Management 2013
U Np Pu Am Cm Bk Cf Es Fm Md No Lr
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Ammonia
Tar
Tar Well
• Gravity separation
• Lighter ammoniacal
liqour floats on top
• Decanted
liquor
removed from upper
layer
• Heavier coal tar
sinks to base
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Gas scrubber
• Transfer particulate matter from gas to sorbants
• Remaining ammonia and some H2S and HCN
were removed by scrubbing gas with water or
weak ammoniacal liquor
• H2S Hydrogen sulphide – stink bombs
• HCN Hydrogen cyanide (aka Prussic Acid) - a
systemic chemical asphyxiant
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Purifier
•
•
remove remaining impurities – mainly sulphides and cyanogens
Early works – SO2 passed over 'slaked lime', (Calcium hydroxide,
Ca(OH)2).
• Produces foul lime – mixture of slaked lime and calcium
compounds containing sulphur or cyanide
• Calcium thiocyanate Ca (SCN)2
• Calcium ferrocyanide Ca2 Fe(N)6.12H2O
• Calcium thiocarbonate
•
Later works – Iron oxides eg bog ore (peat with a lot of iron oxide)
•
•
Iron sulphides
Complex cyanides
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Cyanide
• A compound which
contains cyano group
• C triple-bonded to N
• cyanide ion (CN-)
• Free cyanide
• Complex cyanide
• Cyanide is toxic because
it binds with iron in body
– impedes respiration
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Free cyanide
•
Cyanide anion itself
•
hydrogen cyanide, HCN,
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•
© Land Quality Management 2013
gaseous
aqueous
produced by the combustion
of certain materials under
oxygen-deficient conditions
Used as chemical weapon in
WW1 but replaced by Chlorine
Very reactive
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Free cyanide - toxicity
• In body CN- binds to
•
•
haemoglobin (Hb) in
red blood cells.
From there it is taken
to the body's tissues
where it binds to an
enzyme called
cytochrome oxidase
Stops cells from being
able to use oxygen
Come back to this after discussing ligands
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Complex cyanide
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CN- ion forms ligands with Fe
(and other TMs eg Fe, Cu, Ni,
Pb, Cd)
Forms ferrocyanides and
ferricyanates
Complex cyanide less toxic
than free cyanide
Complexes may dissociate to
release free cyanide
in acid conditions
in UV to form CN- and so HCN
•
•
Look at ligand slide
May persist for 100s of years
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Jargon buster
What is a Ligand?
Ligand = negative ion or
neutral molecule which
can form a complex with
a central metal cation
Complex = ligand plus cation
Look at
periodic table
to show TMs
TM metals can accept extra electrons
© Land Quality Management 2013
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The Periodic Table
I
II
III
IV
V
VI VII
H
0
He
Li Be
B
C
N
O
F
Ne
Al
Si
P
S
Cl Ar
Transition elements
Na Mg
K
Ca Sc Ti
Rb Sr
Y
V
Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr
Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te
Cs Ba
Hf Ta W Re Os Ir
Fr Ra
Rf Db Sg Bh Hs Mt
I
Xe
Pt Au Hg Tl Pb Bi Po At Rn
La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
Ac Th Pa
© Land Quality Management 2013
U Np Pu Am Cm Bk Cf Es Fm Md No Lr
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Thiocyanate
(IUPAC = cyanosulfanide)
•
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Cyanide ion combined with sulfur
•
produced by the reaction of elemental sulfur or thiosulphate with
cyanide
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anion [SCN]−.
8 CN− + S8 → 8 SCN−
CN− + S2O32− → SCN− + SO32−
Does dissociate under weak acidic conditions
but has similar complexing properties to cyanide
approximately 7 times less toxic than hydrogen cyanide
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Jargon buster
The prefix thio-,
Sulphate
•
an oxygen atom in the
compound has been replaced
by a sulfur atom
•
•
Thiosulphate
Thiocyanate
Thiosulphate
Cyanate
ThioCyanate
•
Thiocarbonate e.g.
• CSO22-
Carbonate
CS3-xOx2- (x = 0, 1, or 2).
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Distribution/storage
http://iangrey.org/2008/06/03/lifes-a-gas/
Gas meter – Fakenham Gas Works
http://en.wikipedia.org/wiki/History_of_manufactured_gas
Tar
Gas continues to drop particles from tar fog/mist into water beneath
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Sulphur
• From S in coal
• Sulphur dioxide
• Hydrogen sulphide
• Sulphuric acid
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Metals often found on gas works sites
Metals
I
II
Mg
III
IV
V
VI VII
0
Transition elements
V
Cr Mn Fe Co Ni Cu Zn
Mo
As
Cd
Hg
Pb
U
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Metals
• Metal oxides = catalysts
• Trace elements in bog ore – hydrated ferric oxide mixed
•
•
•
with peat
Spent oxide
Foul lime
Lead in paint and as caulking for gas holders and
pipework
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Gas Works Contaminants
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From Coal
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Ammonia liquors
Ash and clinker (metals and
unburned coke or coal)
Coal tar
spent oxide
free cyanide, complex cyanide
elemental sulphur, sulphate,
thiocyanate
Metals
acidic soils
PAHs
BTEX
© Land Quality Management 2013
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Purification processes
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spent oxide
free cyanide, complex cyanide
elemental sulphur, sulphate,
thiocyanate
metals
acidic soils
Coal Tar processing
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PAHs
BTEX
metals
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Aspire
LQM Office
Land Quality Management Ltd.
The Sir Colin Campbell Building
University of Nottingham Innovation Park
Triumph Road
Nottingham NG7 2TU
Tel: +44 (0)115 7484080
Fax: +44 (0)115 7484083
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[email protected]
© Land Quality Management 2013
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Bus Station (2 mins from
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Road
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