Eric J. Beckman,

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Perspectives on CO2 Utilization

• Eric J. Beckman,
• Mascaro Sustainability Initiative
• University of Pittsburgh

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Phil asked me to provide a big picture of the
situation
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Climate Change The Wedge Concept
First, can CO2 utilization significantly
help with our climate problems

• From Socolow Pacala, Science (2004), 305
  (5686), 968-972
• Data from Climate Mitigation Institute _at_
  Princeton University

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Wedge Concept Climate Change
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Where are we headed?
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The wedge concept
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Cutting Greenhouse Emissions using Current
Technology..
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Carbon Emissions by Sector
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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
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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

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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 dont move
  the wrong way.

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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.

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Cl2 as a Target
45 million tons of Cl2 produced worldwide.
Generation of Cl2 consumes 1-2 of worlds
electricity. 33 of Cl2 goes into PVC, rising
amounts go to phosgene, and subsequently
urethanes and polycarbonates.
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Diphenyl Carbonate, the conventional way.
DPC used in generation of bisphenol A
polycarbonate.
salt
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Asahi Diphenyl Carbonate ProcessFukuoka, et
al., Green Chem (2003), 5, 497
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?
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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?
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Another Interesting Target Isocyanates
Fast becoming one of the leading applications
for chlorine
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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
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Isocyanates via CO2 One route
Recycle of base and trifluoroacetic anhydride
crucial.
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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?

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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
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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 (lt 5000) chain transfer
• MWDs less than 2.0
• Functionality!

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What Characteristics Do We Need in CO2/Oxirane
Copolymers

• TPEs?
• Blocky copolymers
• Tacticity in hard segment
• Micro phase separation
• Degradable Surfactants (EO PO)
• MWDs 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.
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Copolymerizing oxiranes and CO2Potential
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?

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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
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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
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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 gt/ 80C Yield
increases with increasing CO2 pressure
Very effective with cyclohexene oxide
propylene oxide produces primarily propylene
carbonate
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One of our attempts Sterically-hindered aluminum
catalysts for polyol development
R1 i-Pr
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Mw vs. conversion, CHO iC3H7O-AlO-C(C6H5)32 in
the absence (1) and presence of alcohol (2) 24
hr 55oC
     
1
2
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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
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Milestones Beta-Diimine Zinc Complex for
Copolymerization of Cyclohexene Oxide and CO2
High TOF ( 200 hr-1) at low Ts (20
50C) Low PDI ( 1.1) 95 carbonate
Coates colleagues (1998) J. Am. Chem. Soc.
120, 11018
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Solutions for the Propylene Oxide (propylene
carbonate) Problem
P 100 - 500 psi T 298K TOFs up to
200 PPCPC of 0.25 to 13.
Allen, et al., JACS 2002, 124, 14284
Review Coates colleagues, Angew. Chemie
(2004), 43, 6618
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Recent results PO-CO2 alternating copolymers no
longer a problem
High activity Regioregularity Mws 20
40k Tacticity control
Eg., Coates colleagues, J. Polym. Sci.
(2006), 44, 5182-5191
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CO2-oxirane copolymers Status

• One can make alternating copolymers of propylene
  oxide and CO2, narrow MWDs, 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?

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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 (lt 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.

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A Competing Route Lee Alper, Macromolecules
(2004), 37, 2417
Mws in 3k to 19k range overall polymer yield up
to 50 cobalt catalysts
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What about Carboxylic Acids?
Aromatic Acids Process energy of 19 GJ/ton Dunn
Savage Green Chem (2003) 5, 649
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Or one could start with benzene
Either strategy requires formation of aromatic
acid using CO2 as raw material
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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.

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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

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Lewis Acid Mmol used yield o/m/p Toluic acid Other products
AlCl3 5.37 80 5/2/93
Al(acac)3 4.51 65 Acylated product
NaAlCl4 4.66 60 2/-/98
TiCl4 3.34 71 5/5/90
Ti(OEt)4 5.22 25 No Carboxylated product
Zn(OTf)2 5.10 30 4/1/95
Zn(OAc)2 5.62 55 4/2/94
CuBr2 4.91 50 7/2/91
SnCl4 5.00 81 5/4/91
MoCl5 4.42 76 8/4/88
T 80C P 7 MPa T 18 hr Incub. 1 hr
MgBr2, ZnBr2, ZnO give no product
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Incubation effects
If we incubate AlCl3 with CO2.
Incubation time Yield
30 minutes 30
1 hour 80
If we incubate AlCl3 with toluene.
Incubation time Yield
1 hour 28
5 hours 15
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Olah and colleagues calculate that CO2AlCl3
complexes are 20-30 kcal/mole more stable than
aromaticAlCl3 complexes.
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Why is incubation effective?
Orthe effects due to incubation could simply
be due to heterogeneous surface reactions on the
Lewis acid.
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Typically, yield approaches 90
Addition of quinoxaline, 11 with
AlCl3, improves yield to 250
Without real turnover, this process cant move
forward
T 353 K, P 6.9 MPa, AlCl3
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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.

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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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And what about methanol.

• In general, reduction of CO2 to provide valuable
  feedstocks depends on a viable source (non-fossil
  fuel, economic, OK via LCA/LCI) of H2.
• H2 derived using nuclear power? From biomass?

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Methane reforming and CO2

• Steam reforming
• CH4 H2O ? CO 3H2, ?H298 206 kJ/mol
• CO2 reforming
• CH4 CO2 ? 2CO 2H2, ?H298 247 kJ/mol
• Issues with coking (carbon formation),
  significant work on catalyst designmany more
  publications on this process than on other CO2
  utilization schemes.

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And then theres photosynthesis

• Use of naturally occurring materials in long-life
  applications employs CO2 as a raw material.
• Using nature to better design such materials
  may be the most viable means of CO2 utilization.

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Summary

• CO2 utilization via synthetic chemistry will not
  significantly affect atmospheric carbon loads
• CO2 can be used to make carbonates, isocyanates,
  acids
• It is not clear that current CO2-based routes to
  these products are more economical sustainable
  than conventional routes.
• Replacing raw materials with high embedded energy
  by CO2 an interesting future target.
• Most viable area for future work may be CO2
  reforming synthetic biology, although a
  sustainable source of H2 could change the
  equation significantly.