The ChlorAlkali Industry

1
The Chlor-Alkali Industry

• NaOH (Caustic Soda)
• Chlorine
• Na2CO3 (Soda Ash)

2
Downs Cell Production of Cl2 (g) and Na (l)
Look up pictures of this on the web! Search for
Downs Cell Production of Sodium.
3
NaOH Cl2 Na2CO3
NaCl
Commodity 1994 1995 1996
NaOH 25.1 22.8 23.6 Cl2 24.4 24.8
25.2 Na2CO3 20.6 22.3 22.3 billions of
pounds - CEN, June 23, 1997, pg. 42.
4
Historical Background
Discovery of Chlorine - C.W. Scheele - 1774 4
HCl (aq) MnO2 (s) 2 Cl2 MnCl2 (aq) H2O (l)
Scheele also discovered the bleaching
properties of Cl2 and this lead to a textile
market demand for Cl2 and NaOH. This also meant
that an economically viable method for producing
HCl had to be developed.
5
LeBlanc Process
NaCl H2SO4 (conc.) NaHSO4 HCl NaHSO4
NaCl Na2SO4 HCl 4 HCl (aq) MnO2 (s) 2
Cl2 MnCl2 (aq) H2O (l)
Na2SO4 Glass or Na2SO4 C
CaCO3 Na2CO3 CaSO4 Na2CO3 Ca(OH)2 2
NaOH CaCO3
6
Where did the raw materials for this process come
from?
S or Fe2S3 O2 SO2
SO3 H2SO4 NaCl - Mined or extracted as brine
solution. CaCO3 - Mined as limestone. CaCO3
CaO Ca(OH)2
H2O
D
Lime Slaked Lime
7
Weldon Process (1866)
The LeBlanc process produced MnCl2 which
was wasted. The Weldon Process improved on this
by recycling the MnCl2.
Deacon Process (1868)
CuCl2 on Bricks
4 HCl (aq) O2 (g) 2 Cl2 2 H2O (l)
440oC
A very small amount of Cl2 is still produced by a
modified version of this process wherein
a fluidized bed of a mixture of Pr2O3, Nd2O3,
and CuCl2 is used as a catalyst at 400oC.
8
Electrolytic Processes
Cruickshank (1800) - Described electrolysis
of brine. Faraday (1834) - Put forward the Laws
of Elec- trolysis. First Commercial Brine
Electrolysis Plant (1891) - A discontinuous or
batch process. First Continuous Process
Electrolysis Plant (1893) Brine is constantly
added and NaOH and Cl2 are continuously removed.
9
Electrolysis Reactions Anode - 2 Cl- Cl2 (g)
2 e- Cathode - Na e- Na 2 Na
2 H2O 2 NaOH H2 (g)
Side Reactions 2 NaOH Cl2 NaCl
NaOCl H2O 2 OH- Cl2 2 OCl- H2 4 OH-
O2 (g) 2 H2O 4 e-
10
Commercial Production
( - )
( )
Power Supply
Carbon
Carbon
Cathode
Anode
H2
Cl2
NaCl (aq)
Diaphragm Cell
Porous Diaphragm (Teflon Mesh)
NaOH (aq)
Net Flow
11

11 NaOH (aq) 16 NaCl (aq)
Diaphragm Cell
50 NaOH (aq) 1 NaCl (aq)
Steam Evaporator
Acceptable purity for most industrial
applications. The product is typically NOT
purified further due to the expense of the energy
required to continue evaporation. It is cheaper
to transport the solution.
12
Mercury Cathode Cell
Na e- Na (metal) Na Hg Hg/Na
Amalgam Hg/Na Amalgam H2O NaOH (aq)
H2 (g) Hg (l)
Carbon Anode ()
Cl2
Brine
Hg
Hg/Na
Hg Cathode (-)
13
Production of Na2CO3 Mined as Trona (Sodium
Sesquicarbonate) 2 (Na2CO3 NaHCO3 2
H2O) 3 Na2CO3 CO2 5 H2O
D
Solvay (Ammonia-Soda) Process
2 NaCl CaCO3 Na2CO3 CaCl2
This is the overall process but the
actual process is more complicated.
14
NH3 H2O CO2 NH4HCO3 NH4HCO3 NaCl
NaHCO3 NH4Cl
2 NaHCO3 Na2CO3 CO2 H2O 150oC
1100oC
CaCO3 CaO CO2 Lime Kiln
CaO H2O Ca(OH)2 2 NH4Cl Ca(OH)2 2
NH3 CaCl2 2 H2O
15
Chapter 11Alkaline Earth ElementsGroup 2

• Density m.p. I.E.
• Be He 2s2 hcp 1.85 g/mL 1287 899
• Mg Ne 3s2 hcp 1.74 g/mL 649 737
• Ca Ar 4s2 fcc 1.55 g/mL 839 590
• Sr Kr 5s2 fcc 2.63 g/mL 768 549
• Ba Xe 6s2 bcc 3.62 g/mL 727 503
• Ra Rn 7s2 5.5 g/mL (700) 509

16
Comparison of Group 1 andGroup 2 Properties
Group 1 m.p. m.p. Group 2 Metal oC oC Metal
Li 181 1287 Be Na 98 649 Mg K 63 839 Ca
Rb 39 768 Sr Cs 28.5 727 Ba
17
Comparison of Group 1 andGroup 2 Properties
Group 1 1st 2nd 1st 2nd Group 2 Metal I.E. I.E. I
.E. I.E. Metal
Li 520 7296 899 1757 Be Na
496 4563 737 1450 Mg K 419 3069
590 1145 Ca Rb 403 2650
549 1064 Sr Cs 376 2420 503 965 Ba
18
Comparison of Group 1 andGroup 2 Properties
Group 1 Hydration Hydration Group 2 Metal
Ion Energy Energy Metal Ion
Li - 544 - 2494 Be2 Na - 435 -
1921 Mg2 K - 352 - 1577 Ca2 Rb - 326 -
1443 Sr2 Cs - 293 - 1305 Ba2
19
Summary of Property Comparisons
1. Melting points and boiling points of Group 2
metals are higher than the corresponding Group 1
metals. 2. Except for Be, the Group 2 elements
form predom- inently ionic compounds. 3. The
1st ionization energies of the Group 2
elements are higher but the 2nd ionization
energies are lower than those of the
corresponding Group 1 metals.
20
Summary of Property Comparisons
4. Be compounds are much more covalent than
Li compounds
Ionic Charge-to- Example Radius Mass Ratio
Li 0.60 Å 1.7 LiCl (Ionic) Be2 0.31 Å
6.5 BeCl2 (Polymeric)
Cl Cl Cl Cl Be Be Be Cl Cl Cl Cl
21
Summary of Property Comparisons
5. Be2 ions in aqueous solution are acidic but
Mg2 ions are neutral.
d
d
H H Be2 O O
H H
d -
d -
Be(H2O)42 H2O Be(H2O)3OH2 H2O
22
Summary of Property Comparisons
6. Group 2 metals are monatomic in the gas
phase while Group 1 metals are diatomic.
2s
2s
2s
2s
Li Be
Non-Bonding
23
Occurrence of the Metals
Abundance by Mass Be 2.0 ppm Mg
276 40 ppm Ca 466 60 ppm Sr
384 ppm Ba 390 ppm Ra 1.3
x 10-6 ppm
24
Extraction of Metals
Electrolysis Aqueous solutions can be
electrolyzed using a mercury cathode but the
metals are difficult to remove from the amalgam.
MCl2 (l) M (l) Cl2 (g) NaCl
Strontium and Barium tend to form
colloidal dispersions.
25
Extraction of Metals
Magnesium - Pidgeon Process
CaCO3 MgCO3 CaO MgO Mg
Ca2SiO3 Fe
D
Fe/Si
Dow Sea Water Process
Ca(OH)2 (aq) MgCl2 (aq) Mg(OH)2 (s)
CaCl2 (aq)
26
Extraction of Metals
Dow Sea Water Process (Continued)
Mg(OH)2 (s) HCl (aq) MgCl2
Electrolysis
MgCl2 (l) Mg (l) Cl2 (g)