(BAT) Reference Document for the Production of Chlor-alkali ...

Chapter 2
The main characteristics of the three electrolysis techniques processes are presented in Table
2.1.
Table 2.1: Main characteristics of the different electrolysis techniques processes
Criterion Mercury Diaphragm Membrane
Anode
RuO2 + TiO2 coating on
Ti substrate
RuO2 + TiO2 + SnO2
coating on Ti substrate
RuO2 + IrO2 + TiO2
coating on Ti substrate
Nickel coated with high
Cathode Mercury on steel
Steel (or steel coated with
activated nickel)
Asbestos, polymer-
area nickel-based or
noble metal-based
coatings
Separator None
modified asbestos, or nonasbestos
diaphragm
Ion-exchange membrane
Cell voltage 3.15 – 4.80 V 2.90 – 3.60 V 2.35 – 4.00 V
Current density 2.2 – 14.5 kA/m 2
0.8 – 2.7 kA/m 2
1.0 – 6.5 kA/m 2
Inlet:
Inlet:
Temperature
Inlet: 50 – 75 °C
Outlet: 80 – 90 °C
Outlet:
{Please TWG provide
Outlet:
{Please TWG provide
information.}
information.}
pH 2 – 5 2.5 – 3.5 2 – 4
Cathode
product
Sodium amalgam (Na-
Hgx)
10 – 12 wt-% NaOH and H2
30 – 33 wt-% NaOH and
H2
Decomposer
product
50 wt-% NaOH and H2 No decomposer needed No decomposer needed
Evaporator
product
No evaporation needed 50 wt-% NaOH
NaCl: ~ 10 000 mg/kg
50 wt-% NaOH
Quality of
caustic soda
(50 wt-%
NaOH)
NaCl: ~ 50 mg/kg
NaClO3: ~ 5 mg/kg
Hg: ~ 0.1 mg/kg
(15 000 – 17 000 mg/kg
before concentration)
NaClO3: ~ 1000 mg/kg
(400 –500 mg/kg before
concentration)
NaCl: ~ 50 mg/kg
NaClO3: Q 10 – 50 mg/kg
Chlorine
quality
O2: 0.1 – 0.3 vol-%
H2: 0.1 – 0.5 vol-%
N2: 0.2 – 0.5 vol-%
O2: 0.5 – 2.0 vol-%
H2: 0.1 – 0.5 vol-%
N2: 1.0 – 3.0 vol-%
O2: 0.5 – 2.0 vol-%
H2: 0.03 – 0.3 vol-%
Low total energy
Advantages
50 wt-% high-purity
caustic directly from
cell, high-purity chlorine
and hydrogen, simple
brine purification
Low quality requirements
of brine, low electrical
energy consumption
High steam consumption
consumption, low
investment and
operating costs, no use
of mercury or asbestos,
high-purity caustic,
further improvements
expected
Disadvantages
Use of mercury,
expensive cell operation,
costly environmental
protection, large floor
space
for caustic concentration in
expensive multi-effect
evaporators, low-purity
caustic, low chlorine
quality, some cells are
operated with asbestos
diaphragms
High-purity brine
required, low chlorine
quality, high cost of
membranes
Caustic quality
High,