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Perspectives on CO 2 Utilization

Perspectives on CO 2 Utilization. Eric J. Beckman, Mascaro Sustainability Initiative University of Pittsburgh. Phil asked me to provide a “big picture” of the situation. First, can CO 2 utilization significantly help with our climate problems…. Climate Change: The Wedge Concept.

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Perspectives on CO 2 Utilization

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  1. Perspectives on CO2 Utilization Eric J. Beckman, Mascaro Sustainability Initiative University of Pittsburgh

  2. Phil asked me to provide a “big picture” of the situation

  3. First, can CO2 utilization significantly help with our climate problems… Climate Change: The Wedge Concept From Socolow & Pacala, Science (2004), 305 (5686), 968-972; Data from Climate Mitigation Institute @ Princeton University

  4. Wedge Concept & Climate Change

  5. Where are we headed?

  6. The wedge concept

  7. Cutting Greenhouse Emissions using Current Technology…..

  8. Carbon Emissions by Sector

  9. Can utilization of CO2 deal with a reasonable fraction of a “wedge”? • If we were to convert all of the worlds ~ 33 x 106 ton methanol capacity* to a CO2 basis, and if the H2 needed for such a process could be produced in a CO2-free manner….we could account for ~ 4% of a wedge. • So, it would appear that utilization of CO2 for products is not going to make an impact in reducing atmospheric carbon…. *Methanol Institute

  10. So, does that mean that research into CO2 utilization is futile? • Can we use CO2 as a raw material to create high value products? • CO2 is relatively low cost (value may be negative, depending upon various trading credit schemes). • CO2 is a renewable raw material

  11. So, does that mean that research into CO2 utilization is futile? • Can we use CO2 as a raw material to reduce energy use? • Generate needed materials using less energy? • Create new materials that displace currently used analogs with high energy densities? • Create components that lower energy use of systems that they are part of? • Look for materials with relatively long lifetimes. • Where use of CO2 reduces energy consumption, make sure that other sustainability metrics don’t move the wrong way.

  12. The Chemical Industry & Energy • Ethylene: ~ 26 GJ/ton • Chlorine: ~ 20 GJ/ton • Ammonia: ~ 36 GJ/ton • These numbers, coupled with the scale of production of each, make these three excellent targets for substitution.

  13. Cl2 as a Target ~ 45 million tons of Cl2 produced worldwide. Generation of Cl2 consumes 1-2% of world’s electricity. ~ 33% of Cl2 goes into PVC, rising amounts go to phosgene, and subsequently urethanes and polycarbonates.

  14. Diphenyl Carbonate, the conventional way. DPC used in generation of bisphenol A polycarbonate. + salt

  15. Asahi Diphenyl Carbonate Process:Fukuoka, et al., Green Chem (2003), 5, 497 Competition from routes using CO. Need to include the energy intensity of ethylene, then credit for production of EG (assume recycle of methanol and phenol). Which route is more sustainable?

  16. Routes to Diphenyl Carbonate • Li, et al., Chemistry Letters (2006), 35(7), 784-785: • Direct synthesis of DPC from phenoxide, CO2, and CCl4 using ZnCl4 as catalyst; trichloromethyl cation said to participate in the reaction. Will drop in BPA-PC demand for more sustainable solutions render this work unnecessary?

  17. Another Interesting Target: Isocyanates Fast becoming one of the leading applications for chlorine

  18. Isocyanates Using CO2 MeGhee, et al.; O-sulfobenzoic acid anhydride, POCl3, P4O10 Horvath, et al; Mitsunobu reagents; azodicarboxylate & triphenyl phosphine, -78C Possible to recycle drying agents; Mitsunobu residue is likely not re-usable

  19. Isocyanates via CO2: One route Recycle of base and trifluoroacetic anhydride crucial.

  20. Replacing Cl2 (phosgene): DPC & Isocyanates • DPC process (Asahi) successful – LCA/LCI study has not been published. • Isocyanate route using CO2 a lab result only – recycle of reagents critical for future use. • Cl2 remains an excellent target – high energy, hazardous byproducts, safety issues. Can a CO2-based material replace PVC?

  21. Copolymerization of Cyclic Ethers and Carbon Dioxide: First Reports [Inoue, et al., J. Polym. Sci. – Polym Lett. (1969), 7, 287] ZnEt2-H20 catalyst employed, pressure of 60 bar for best results Most recent work focuses on cyclohexene oxide as co-monomer

  22. This work involves generation of “new” materials: What characteristics do we need in CO2/oxirane copolymers • For use in medicine (EO): • Carbonate as minor component • Blocky and random copolymers • Functionality • For use as polyols (PO): • High % Carbonate – alternating • Low molecular weight (< 5000) = chain transfer • MWD’s less than 2.0 • Functionality!

  23. What Characteristics Do We Need in CO2/Oxirane Copolymers • TPE’s? • Blocky copolymers • Tacticity in “hard segment” • Micro phase separation • Degradable Surfactants (EO & PO): • MWD’s should be less than 2.0 • Chain transfer crucial! • % carbonate ~ 30% (water solubility!) • EO critical comonomer Unfortunately, CHO is simply not interesting from a product perspective.

  24. Copolymerizing oxiranes and CO2:Potential environmental benefits • Energy intensity of ethylene • Energy intensity of propylene oxide (~ 14.0 GJ/ton) • PO process exhibits environmental flaws • Can we achieve properties while using less of the oxirane than at present? • What is the energy intensity of CO2? It is assumed that capture of CO2 from power plants leads to efficiency loss of 20 to 35%. Other sources of CO2?

  25. Milestones: Porphyrins as Catalysts * Living polymerization, MWD less than 1.2; * Reaction time 12-26 days; * 20 – 35% carbonate * PC produced as well [Aida & Inoue (1982), Macromolecules 15, 682] Alumino-porphyrin and propylene oxide

  26. Milestones: Soluble “Single-Site” Zinc Catalysts for Cyclohexene Oxide/CO2 Copolymerizations R = Ph, i-Pr, t-Bu; R’ = H [Darensbourg & Holtcamp, (1995), Macromolecules 28, 7577 Darensbourg, et al. (1999), J. Am. Chem. Soc. 121, 107] Soluble complexes; crystal structure shows four-coordinate monomers with highly distorted tetrahedral geometry around Zn

  27. Milestones: Soluble “Single-Site” Zinc Catalysts for Cyclohexene Oxide/CO2 Copolymerizations * Very high yields; over 1100 g polymer/g zinc after 144 hours * Methyl substituent allows for highest yields by factor of 2+ * Rate highest at temperatures >/= 80C * Yield increases with increasing CO2 pressure Very effective with cyclohexene oxide; propylene oxide produces primarily propylene carbonate

  28. One of our attempts: Sterically-hindered aluminum catalysts for polyol development Several choices for R2 R1 = i-Pr

  29. Mw vs. conversion, CHO; iC3H7O-Al[O-C(C6H5)3]2 in the absence (1) and presence of alcohol (2); 24 hr; 55oC 1 2

  30. Use of Iso-propanol as chain transfer agent with sterically hindered Al catalysts, CHO. No success with PO. 5 - diphenyl methyl; 6 – di-isobutyl, methoxy phenyl; 7 – fenchyl; 8 – fenchyl + 2 moles ether

  31. Milestones: Beta-Diimine Zinc Complex for Copolymerization of Cyclohexene Oxide and CO2 * High TOF (~ 200 hr-1) at low T’s (20 – 50C) * Low PDI (~ 1.1) * 95%+ carbonate [Coates & colleagues (1998) J. Am. Chem. Soc. 120, 11018]

  32. Solutions for the Propylene Oxide (propylene carbonate) Problem: P ~ 100 - 500 psi; T = 298K TOF’s up to 200 PPC:PC of 0.25 to 13. Allen, et al., JACS 2002, 124, 14284 Review: Coates & colleagues, Angew. Chemie (2004), 43, 6618

  33. Recent results: PO-CO2 alternating copolymers no longer a problem High activity Regioregularity Mw’s 20 – 40k Tacticity control Eg., Coates & colleagues, J. Polym. Sci. (2006), 44, 5182-5191

  34. CO2-oxirane copolymers: Status • One can make alternating copolymers of propylene oxide and CO2, narrow MWD’s, reasonable rates (other oxiranes as well – CHO, EO, etc). • Displacement of oxiranes could result in life cycle energy savings provided that CO2 obtained in a low energy manner • At this point, no LCA/LCI studies have been done on the materials – are they greener? • Applications for new materials not entirely clear at present – numerous possible applications. Physical properties?

  35. Polyesters from CO2 and olefins? • Soga and colleagues (1977); Yokoyama, et al. (J. Appl. Poly. Sci. (2003): copolymerization of ethyl vinyl ether & CO2 w/wout Lewis acids. • Low molecular weights (< 1000); yields up to ~ 3%, high CO2 incorporation. • Thought to proceed via lactone intermediate, cleavage of C-O bond produces polyether-ketone. • Energy intensity of aliphatic polyesters derived from corn is significant.

  36. A Competing Route: Lee & Alper, Macromolecules (2004), 37, 2417 Mw’s in 3k to 19k range; overall polymer yield up to 50%; cobalt catalysts

  37. What about Carboxylic Acids? Aromatic Acids: Process energy of 19 GJ/ton; Dunn & Savage; Green Chem (2003); 5, 649

  38. Or one could start with benzene Either strategy requires formation of aromatic acid using CO2 as raw material

  39. Aromatic Acids using CO2: Previous Work • Friedel and Crafts [Compt. Rendu. 1878]; low yields of benzoic acid as CO2 is bubbled through benzene/AlCl3 • Morgan [Chem & Industr, 1931]; benzoic acid using CO2 and anhydrous AlCl3 • Calfee & Deex [US Patent 3,138,626 1964]; addition of aluminum powder gives yields of toluic acid up to 60% from toluene, AlCl3 and CO2 at 80C • Olah and coworkers, [J. Am. Chem. Soc. 2002]; benzoic acid from benzene and CO2, with AlCl3 yields ~ 90% at 80C; Al powder used to drive reaction to higher yields; other Lewis acids completely ineffective.

  40. Does order of addition of Lewis acid and aromatic matter? • Pernecker & Kennedy [Polym Bull. 1994]; Lewis acid plus CO2 forms product; initial incubation of monomer and Lewis acid allows polymerization in CO2 • Our work: mix CO2 and Lewis acid, let stand for x minutes; then add toluene

  41. T = 80C; P = 7 MPa T = 18 hr Incub. = 1 hr MgBr2, ZnBr2, ZnO give no product

  42. Incubation effects… If we incubate AlCl3 with CO2…. If we incubate AlCl3 with toluene….

  43. Olah and colleagues calculate that CO2:AlCl3 complexes are 20-30 kcal/mole more stable than aromatic:AlCl3 complexes.

  44. Toluene and CO2 form two phases at 80C and 1000 psi. Lower phase is 60 mole % toluene Why is incubation effective? Or…the effects due to incubation could simply be due to heterogeneous surface reactions on the Lewis acid.

  45. Typically, yield approaches 90% Addition of quinoxaline, 1:1 with AlCl3, improves yield to 250% Without real turnover, this process can’t move forward T = 353 K, P = 6.9 MPa, AlCl3

  46. Aromatic acids • Suzuki, et al., Chem. Lett. (2002), 1, 102; use of AlBr3 to generate aromatic acids from naphthalene & anthracene in CO2. • Tokuda, et al: electrolysis using sacrificial anode (Mg or Al); J. Nat. Gas Chem. (2006), 15, 275. • Nemoto, et al., Chem. Lett. (2006), 35, 820; Lewis acids + chlorotrimethyl silane. • So far, CO2-based routes use more energy (including embedded energy) and reagents that are less green than what is used currently.

  47. CO2 as a Raw Material • Formic acid, dimethylformamide [Jessop & Noyori, Leitner group] from CO2 and H2. Commercial process relies on low-cost methanol generated from syngas. For CO2 to be able to complete, we need a green & inexpensive source of H2. Methanol from syngas; syngas from methane

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