The Chemistry of CO 2. Walter E. Cleland, Jr. Ph.D. Department of Chemistry and Biochemistry 25 February 2008

Transcription

1 The Chemistry of CO 2 Walter E. Cleland, Jr. Ph.D. Department of Chemistry and Biochemistry 25 February 2008

2 Outline Introduction Physical Properties Uses Production, Recovery, Purification Chemical Properties

3 Oxides of Carbon Stable Oxides of Carbon CO C O CO 2 O C O C 3 O 2 C 12 O 9 O C C C O O O O O O O O O O

4 Selected Physical Properties of CO 2 Colorless, Odorless Gas Molecular Weight Mp Critical T Critical P Density of and C Relative density of and 21.1 o C (Air=1) Solubility in water at 25 o C Henry s Law constant Gº f (CO 2 (g)) Hº f (CO 2 (g)) Sº f (CO 2 (g)) Dissociation Energy (C-O) IR (gas) UV (gas) 44.01g/mol C (5.2 atm) C (subl) 31 C atm ( psi) Kg/m ppm (wt) 392 x 10-4 mol/l atm kj/mol kj/mol 3.02 J/mol K kj/mol 2349 cm -1 (Asym C=O), cm -1 (Sym C=O; Raman), 667 cm -1 (Bending) Å

5 Phase Diagram

6 Walsh Diagram

7 Industrial Uses of CO 2 Uses Based on Physical Properties (major) Refrigeration Cleaning fluid Air conditioning Solvent for Reactions Extractions Nanopartical production Food and Agro-chemical Applications Fumigant Additive to beverages Inert atmosphere Uses Based on Chemical Properties Production of Urea Production of Salicylic acid Inorganic carbonates and pigments Production of Propylene carbonate Neutralization of caustic waste water

8 Production Sources Ammonia/Hydrogen plants CH H 2 O CO H 2 Flue gases from combustion Fermentation C 6 H 12 O 6 2 C 2 H 5 OH + 2 CO 2 Lime-kiln operations CaCO 3 CaO + CO 2 Sodium phosphate manufacture 3 Na 2 CO H 3 PO 4 2 Na 3 PO CO H 2 O Natural CO 2 gas wells

9 Recovery by Reversible Absorption Sodium or Potassium Carbonate Process K 2 CO 3 (aq) + H 2 O(l) + CO 2 (g) KHCO 3 (aq) Girbotol Amine Process 2 HOCH 2 CH 2 NH 2 (aq) + H 2 O(l) + CO 2 (g) (HOCH 2 CH 2 NH 3 ) 2 CO 3 (aq)

10 Purification Permanganate Process 3 H 2 S + 2KMnO CO 2 3 S + 2 MnO KHCO H 2 O Dichromate Process 3 H 2 S + K 2 Cr 2 O 7 + H 2 O + 2 CO 2 3 S + 2 Cr(OH) KHCO 3

11 Chemical Properties General Reactivity Aqueous chemistry Reactions of Industrial Importance Biological Reactions Organic Reactions Coordination Chemistry Reactions incorporating CO 2 without Reduction Reactions with Reduction

12 General Reactivity Not very reactive at ordinary temperature ; nonreactive ; stable ; inert Many reactions of CO 2 are thermodynamically favorable, but kinetically slow Ex: M 2 SiO CO 2 2 MCO 3 + SiO 2

13 Aqueous Chemistry Species involved: CO 2, H 2 CO 3, HCO 3-, CO 3 2-, H +, OH -, [H 2 CO 3* ] = [CO 2 (aq)] + [H 2 CO 3 ] Equilibrium concentrations described completely by system of 5 equations CO 2 + H 2 O H 2 CO 3 K 1 = 1.67 x 10-3 H 2 CO * 3 H + + HCO - 3 K 2 = 4.47 x 10-7 H 2 CO 3 H + + HCO - 3 K a = 2.68 x 10-4 HCO - 3 H + + CO 2-3 K 3 =4.68 x H 2 O H + + OH - K w = 1.0 x C T = [H 2 CO 3* ] + [HCO 3- ] + [CO 2-3 ] Carbonates insoluble K sp (CaCO 3 ) = 2.8 x 10-9 ; K sp (MgCO 3 ) = 3.5 x 10-8

14 Slow Kinetics for Reactions of At ph < 8 CO 2 CO 2 + H 2 O H 2 CO 3 (slow) H 2 CO 3 + OH - HCO 3- (fast) At ph > 10 CO 2 + OH - HCO 3 - (slow) HCO 3- + OH - CO 3 2- (fast) At ph 8-10 both sets of equilibria are important.

15 Important Reactions of CO 2, At high temperature 2 C + O 2 2 CO C + O 2 CO 2 C + H 2 O CO + H 2 CO and O 2 Hº = kj/mol Hº = kj/mol Hº = kj/mol 2 CO C + CO 2 Hº = kj/mol CO 2 CO + 1/2 O 2 Also CO 2 + H 2 CO + H 2 O (reverse of water-gas shift rxn) CO NH 3 NH 4 O 2 CNH 2 NH 2 CONH 2 + H 2 O

16 Basic Organic Reactions

17 Coordination Chemistry CO 2 is a poor ligand A number of complexes and bonding modes known Important for activation of CO 2 in reduction reactions

18 Reactions of M-CO 2 With Protons or other electrophile M-CO 2 + 2H + + 2e - M-CO + H 2 O M-CO 2 + R + M-C(O)OR Hydride insertion M-H + CO 2 M-O 2 CH With External Phosphine M-CO 2 + PR 3 M-CO + O=PR 3 With Coordinated Isonitrile M(CNR)(CO 2 ) RNCO + M-CO

19 Biological Reactions Ubiquitous in Nature Animal metabolism C 6 H 6 O O 2 6 CO H 2 O + energy Photosynthesis is reverse of above reaction Numerous enzymes catalyze reactions of CO 2 Carbonic anhydrase (Zn 2+ ) - H 2 CO 3 CO 2 RuBisCO (Mg 2+ ) - carboxylation of ribose Carbon monoxide dehydrogenase (Ni,Fe) - CO 2 CO

20 Use of CO 2 as C 1 Feedstock Conversion reactions (CO 2 not reduced) Carboxylates, lactones RCOOR Carbamates, RR NCOOR Ureas, RR NCONRR Isocyanates, RNCO Carbonates, ROC(O)OR Reduction of CO 2 Formates, HCOO - Oxalates, - O 2 C-CO 2 - Formaldehyde, H 2 CO Carbon Monoxide, CO Methanol, CH 3 OH Methane, CH 4

21 Carboxylation Reactions C-C bond formation Direct carbonylation in ionic liquid from imidazoliumcarbonate N-C, O-C bond formation also known

22 Metal Salen complexes as catalysts Production of Polycarbonates from Epoxides and CO 2 Plastics from CO 2

23 CO 2 Hydrogenation to form Formic Acid

24 Production of Methanol CO + 2 H 2 CH 3 OH CO H 2 CH 3 OH Cu-Zn-O catalyst, ºC, 5-10 MPa Up to 30% CO 2 added to syngas feedstock significantly improves yield CO 2 + H 2 O CH 3 OH Cascade of enzymes CO 2 HCOO - (formate dehydrogenase) HCOO - CH 2 O (formaldehyde dehydrogenase) CH 2 O CH 3 OH (methanol dehydrogenase)

25 Photoelectrochemical Reduction In anhydrous,aprotic solvent, reduction potential of CO 2 to CO 2 - is -2.2V vs NHE! Large kinetic overvoltage Yield of photochemical conversion is low Proton assisted multielectron reductions more favorable CO 2 + 2H + + 2e - HCO 2 H CO H + + 6e - CH 3 OH + H 2 O -0.61V -0.38V

26 References Cotton,F.A.; Wilkinson, G.; Murillo,C.A.; Bochmann, M.; Advanced Inorganic Chemistry 6th ed.; Wiley-Interscience: New York, Greenwood, N.N.; Earnshaw, A.; Chemistry of the Elements; Pergamon: New York, Aresta, M. Carbon Dioxide Reduction and Uses as a Chemical Feedstock. In Activation of Small Molecules: Organometallic and Bioinorganic Perspectives; Tolman, W.B., Ed.; Wiley-VCH: Weinheim, Stumm, W.; Morgan, J.J.; Aquatic Chemistry: Chemical Equilibria and Rates in Natural Waters; Wiley: New York, Ballou, R.W. Carbon Dioxide. In Kirk-Othmer Encyclopedia of Chemical Technology; Wiley: New York, 2005; Vol. 4, pp Tommasi, I.; Sorrentino, F.; Utilization of 1,3-dialkylimidazolium-2-carboxylates as CO 2 -carriers in the presence of Na + and K + : Application in the Synthesis of Carboxylates, Monomethylcarbonate Anions and Halogen-free Ionic Liquids. Tetrahedron Letters 2005, 46, Darrensbourg, D.J.; Making Plastics from Carbon Dioxide: Salen Metal Complexes as Catalysts for the Production of Polycarbonates from Epoxides and CO 2. Chem. Rev. 2007, 107, Leitner, W. Carbon Dioxide as a Raw Material: The Synthesis of Formic Acid and Its Derivatives from CO 2. Angewante Chemie International Edition in English 1995, 34,