Published on February 13, 2008
The Chlor-Alkali Industry: The Chlor-Alkali Industry NaOH (Caustic Soda) Chlorine Na2CO3 (Soda Ash) Slide2: Downs Cell Production of Cl2 (g) and Na (l): Look up pictures of this on the web! Search for “Downs Cell Production of Sodium”. Slide3: NaCl NaOH Cl2 Na2CO3 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 - C&EN, June 23, 1997, pg. 42. Historical Background: 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. Slide5: 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 Slide6: 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 Lime Slaked Lime D H2O Slide7: Weldon Process (1866): The LeBlanc process produced MnCl2 which was wasted. The Weldon Process improved on this by recycling the MnCl2. Deacon Process (1868): 4 HCl (aq) + O2 (g) 2 Cl2 + 2 H2O (l) CuCl2 on Bricks 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. Slide8: 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. Slide9: 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- Commercial Production: Commercial Production Diaphragm Cell ( - ) ( + ) Power Supply Anode Cathode Porous Diaphragm (Teflon Mesh) NaCl (aq) NaOH (aq) H2 Cl2 Net Flow Carbon Carbon Slide11: Diaphragm Cell 11% NaOH (aq) 16% NaCl (aq) Steam Evaporator 50% NaOH (aq) 1% NaCl (aq) 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. Slide12: Carbon Anode (+) Hg Cathode (-) Hg Hg/Na Cl2 Brine Mercury Cathode Cell Na+ + e- Na (metal) Na + Hg Hg/Na Amalgam Hg/Na Amalgam + H2O NaOH (aq) + H2 (g) + Hg (l) Slide13: 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. Slide14: NH3 + H2O + CO2 NH4HCO3 NH4HCO3 + NaCl NaHCO3 + NH4Cl 2 NaHCO3 Na2CO3 + CO2 + H2O 150oC CaCO3 CaO + CO2 Lime Kiln 1100oC CaO + H2O Ca(OH)2 2 NH4Cl + Ca(OH)2 2 NH3 + CaCl2 + 2 H2O Chapter 11Alkaline Earth ElementsGroup 2: Chapter 11 Alkaline Earth Elements Group 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 Comparison of Group 1 andGroup 2 Properties: Comparison of Group 1 and Group 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 Comparison of Group 1 andGroup 2 Properties: Comparison of Group 1 and Group 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 Comparison of Group 1 andGroup 2 Properties: Comparison of Group 1 and Group 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+ Summary of Property Comparisons: 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. Summary of Property Comparisons: 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 Summary of Property Comparisons: Summary of Property Comparisons 5. Be2+ ions in aqueous solution are acidic but Mg2+ ions are neutral. H H Be2+ :O: :O: H H d - d - d + d + [Be(H2O)4]2+ + H2O [Be(H2O)3OH]2+ + H2O Summary of Property Comparisons: Summary of Property Comparisons 6. Group 2 metals are monatomic in the gas phase while Group 1 metals are diatomic. Li Be 2s 2s 2s 2s Non-Bonding Occurrence of the Metals: 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 Extraction of Metals: 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. Extraction of Metals: Extraction of Metals Magnesium - Pidgeon Process [CaCO3• MgCO3] CaO • MgO Mg + Ca2SiO3 + Fe Dow Sea Water Process Ca(OH)2 (aq) + MgCl2 (aq) Mg(OH)2 (s) + CaCl2 (aq) D Fe/Si Extraction of Metals: Extraction of Metals Dow Sea Water Process (Continued) Mg(OH)2 (s) + HCl (aq) MgCl2 Electrolysis MgCl2 (l) Mg (l) + Cl2 (g)
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