(685f) CO2 - Ionic Liquids Synergies: Reactive Capture and Conversion of CO2 to Chemicals

CO₂ - Ionic Liquids synergies:
Reactive capture and conversion of CO₂ to chemicals

Valerie Eta^a, Pasi Virtanen^a, Ikenna Anugwom^a,
Päivi Mäki-Arvela^a, Jyri-Pekka Mikkola^a,b

^aLaboratory
of Industrial Chemistry and Reaction Engineering, Process Chemistry Centre, Åbo
Akademi University, Biskopsgatan 8, 20500 Turku/Åbo, Finland.

^bTechnical Chemistry, Department of Chemistry, Chemical ? Biological
Center, Umeå University, SE-90187 Umeå.

Novel
technologies based on the utilization of abundant and non-toxic carbon dioxide
(CO₂) for the synthesis of materials and chemicals may significantly
contribute towards the development of sustainable industrial practices.
Naturally, myriad substances are synthesized from CO₂ and consumed by
humans. The conversion of CO₂ to fuels and chemicals is an attractive method of utilizing
CO₂ from the viewpoint of green chemistry and sustainable
development. The use of CO₂ in the synthesis of chemicals such as
dimethyl carbonate (DMC) or switchable ionic liquids (SILs) constitutes an environmentally
attractive alternative to hazardous and toxic reagent, and resulting in waste
minimisation. DMC exhibits versatile physical and chemical properties,
such as low toxicity and excellent biodegradability and thus, is an
environmentally benign building block for other chemicals.

In the present study, i) DMC was
synthesised from CO₂ and methanol, and ii) CO₂ was used
as feedstock for the synthesis of switchable ionic liquids (SILs) where the
entire ?COO? moiety is maintained.

The direct synthesis of DMC
from methanol and CO₂ is characterized by low yields due to the
reaction equilibrium and the thermodynamic limitations (= +26.3 kJ/mol). Alkoxide ionic liquids possessing
alkylimidazolium and benzalalkonium cations were prepared, characterised and
tested together with ZrO₂-MgO catalyst for the synthesis of DMC from methanol and CO₂. By using the novel ionic liquid as additives, ca 12 % conversion of methanol, and 90 %
selectivity to DMC was obtained at 120 °C and 7.5 MPa [1]. The water
abstracting potential of the ionic liquids influenced the conversion of
methanol and the selectivity to DMC. The alkoxide ionic liquids were recovered
and reused in DMC synthesis without loss in activity and selectivity.

Switchable ionic
liquids are compounds which can be switched from molecular compounds to ionic
liquid by bubbling acid gas, such as CO₂, through the liquid. The
formed ionic liquid can be switched back to molecular building blocks - and CO₂
will be released - by bubbling an inert gas, such as N₂, through the
liquid or applying vacuum. Novel SILs containing
1,8-diazabicyclo-[5.4.0]-undec-7-ene (DBU), glycerol and CO₂ were
synthesized, characterized and tested for the selective fractionation of
lignocellulosic materials. The structures of the synthesized SILs were
confirmed by NMR and FTIR.  The results
showed that carbonate containing ionic liquid was thermally stable up to
120 °C and was capable of selectively
fractionate birch chips at 100 °C in a batch reactor (Fig. 1). FTIR
spectra indicated that DBU was protonated via formation of N?H and C=NH+
bands. Furthermore, deprotonation of
glycerol was confirmed by FTIR. NMR spectra of the SIL showed the formation of glyceryl carbonate [2]. As such, the challenges associated with
the use of ionic liquid, such as the high costs and the risk assessment of the
complete life cycle of ionic liquids could be minimized by using cheap and less
toxic SILs.

Figure 1. Photograph
of untreated (left) and SIL treated birch chip. Treatment conditions: T = 100 ^oC,
t = 120 h.

References

       
[1]       
Eta
V., Mäki-Arvela P., Salminen E., Salmi T., Murzin D., Mikkola J-P.; Catal Lett
(2011) 141:1254?1261

       
[2]       
Anugwom I., Mäki-Arvela P., Virtanen P., Willför S., Damlin P., Hedenström M., Mikkola J-P.; Affiliation
Information

1.       
Laboratory of Analytical Chemistry,Åbo Akademi
University,Process Chemistry Centre, Åbo-Turku, Finland

       
[3]       
Holzforschung, (2012) in press, DOI:
10.1515/hf-2011-0226