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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

Perspectives on CO2 Utilization

Eric J. Beckman,

Mascaro Sustainability Initiative

University of Pittsburgh

climate change the wedge concept

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

can utilization of co 2 deal with a reasonable fraction of a wedge
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

so does that mean that research into co 2 utilization is futile
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
so does that mean that research into co 2 utilization is futile1
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.
the chemical industry energy
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.

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.

diphenyl carbonate the conventional way
Diphenyl Carbonate, the conventional way.

DPC used in generation of bisphenol A polycarbonate.

+ salt

asahi diphenyl carbonate process fukuoka et al green chem 2003 5 497
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?

routes to diphenyl carbonate
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?

another interesting target isocyanates
Another Interesting Target: Isocyanates

Fast becoming one

of the leading

applications for


isocyanates using co 2
Isocyanates Using CO2

MeGhee, et al.;

O-sulfobenzoic acid anhydride, POCl3, P4O10

Horvath, et al;

Mitsunobu reagents;

azodicarboxylate &

triphenyl phosphine,


Possible to recycle drying agents; Mitsunobu residue is

likely not re-usable


Isocyanates via CO2: One route

Recycle of base and trifluoroacetic anhydride crucial.

replacing cl 2 phosgene dpc isocyanates
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?

Copolymerization of Cyclic Ethers and Carbon Dioxide: First Reports [Inoue, et al., J. Polym. Sci. – Polym Lett. (1969), 7, 287]


catalyst employed,

pressure of 60

bar for best


Most recent work

focuses on

cyclohexene oxide

as co-monomer

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!
what characteristics do we need in co 2 oxirane copolymers
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.

copolymerizing oxiranes and co 2 potential environmental benefits
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?
milestones porphyrins as catalysts
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]


and propylene oxide


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,


Soluble complexes; crystal structure

shows four-coordinate monomers

with highly distorted tetrahedral

geometry around Zn


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


One of our attempts: Sterically-hindered aluminum catalysts for polyol development

Several choices for R2

R1 = i-Pr


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




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


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]


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


Recent results: PO-CO2 alternating copolymers no longer a problem

High activity


Mw’s 20 – 40k

Tacticity control

Eg., Coates & colleagues, J. Polym. Sci. (2006),

44, 5182-5191

co 2 oxirane copolymers status
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?
polyesters from co 2 and olefins
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.
a competing route lee alper macromolecules 2004 37 2417
A Competing Route: Lee & Alper, Macromolecules (2004), 37, 2417

Mw’s in 3k to

19k range;

overall polymer

yield up to 50%;

cobalt catalysts


What about Carboxylic Acids?

Aromatic Acids:

Process energy of

19 GJ/ton; Dunn & Savage; Green Chem (2003); 5, 649


Or one could start with benzene

Either strategy requires formation of aromatic acid

using CO2 as raw material

aromatic acids using co 2 previous work
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.
does order of addition of lewis acid and aromatic matter
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

T = 80C;

P = 7 MPa

T = 18 hr

Incub. = 1 hr


ZnBr2, ZnO

give no



Incubation effects…

If we incubate AlCl3 with CO2….

If we incubate AlCl3 with toluene….


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


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.


Typically, yield approaches 90%

Addition of

quinoxaline, 1:1

with AlCl3,

improves yield to


Without real

turnover, this process

can’t move forward

T = 353 K, P = 6.9 MPa, AlCl3

aromatic acids
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.
co 2 as a raw material
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


and what about methanol
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?
methane reforming and co 2
Methane reforming and CO2
  • Steam reforming:
    • CH4 + H2O  CO + 3H2, ΔH298 = 206 kJ/mol
  • CO2 reforming
    • CH4 + CO2  2CO + 2H2, ΔH298 = 247 kJ/mol
  • Issues with coking (carbon formation), significant work on catalyst design…many more publications on this process than on other CO2 utilization schemes.
and then there s photosynthesis
And then there’s 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.
  • 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.