Submission : 13874
Thesis proposal CSC 2015
Title:
How to obtain universal solvents from supercritical CO2 ?
Thesis supervisor:
Jean-Daniel MARTY and Mathias DESTARAC
E-mail address:
[email protected]
PhD School name:
Physics, Chemistry & Material Sciences (SDM)
Research Laboratory:
IMRCP, UMR 5623
Laboratory website:
http://imrcp.ups-tlse.fr
Scientific domain:
%scientific_domain
Subject short description:
Emulsions and microemulsions are involved in a wide variety of chemical and
industrial processes. They are isotropic mixtures of oil, water and surfactant.
However, the use of organic solvent within the oil phase is required in many
processes such as the synthesis of nano-sized materials with a good size and
dispersity control (which is crucial for their applications in catalysis, electronics,
miniaturization, ceramics…). The hazards of such solvents (e.g. toxicity and
flammability) have driven the search for greener solvents. The most useful
alternatives to traditional solvents are sc-CO2, ionic liquids and water.[1]
Supercritical carbon dioxide is of special interest because of its low cost and its
moderate critical conditions (Tc=31ºC, Pc=7.38 MPa, ρc=0.468 g.cm-3). CO2 is
environmentally benign and biocompatible solvent, nontoxic, cheap, abundant,
volatile, inert, non-flammable and recyclable. Moreover sc-CO2 is one of the few
solvents not regulated as a volatile organic solvent and compound by the U.S.
Environmental Protection Agency. Hence, use of sc-CO2 as green solvent has
recently been identified as one of the three key developments in green
chemistry.[2] Nevertheless, despite numerous attractive features and widespread
applications, sc-CO2 is generally a poor solvent: only relatively non-polar low
molecular weight compounds and a few fluorinated or silicone polymers exhibit a
significant solubility in sc-CO2. The low solubility of most hydrophilic compounds
and polymers in sc-CO2 rules out many potential applications. Therefore, the
combination of the two most abundant and inexpensive solvents on the earth, CO2
and water as environmentally benign, non-toxic and non-flammable fluids to form
emulsion/microemulsion systems, offers new possibilities in waste minimization for
the replacement of organic solvents. Whereas water and carbon dioxide exhibit a
weak mutual solubility (depending on pressure and temperature: the solubility of
water in CO2 at 50°C and 20 MPa is about 1 mol%), water-in-sc-CO2 (W/sc-CO2) or
sc-CO2-in-water (sc-CO2/W) emulsions or microemulsions, formed by the addition
of surfactants, can function as a “universal” solvent medium by solubilizing high
concentrations of polar, ionic and nonpolar molecules within the dispersed and
continuous phases.[3] Due to their tuneable nature, these systems have been
applied in numerous fields including chemical processing, pharmaceuticals,
microelectronics, for solubilization and separations, organometallic catalysis and
synthesis of polymer colloids and inorganic nanoparticles.3-6 Thus, the
overarching goal of this project is to replace organic solvents in
emulsion/microemulsion processes by scCO2 to obtain a useful “universal” solvent
to be used in a wide range of industrial processes.
As mentioned above, this necessitates having access to surfactants. However,
surfactants for sc-CO2 usually find a limited use in industrial chemical processes
because of their high price and sometimes inadequate toxicological profile (e.g.
perfluorooctanoic acid). In addition, large surfactant molecules such as
amphiphilic block copolymers offer better anchoring and steric stabilisation at
interfaces than low molar mass candidates. There is consequently a substantial
need for developing cheap, stable and environmentally friendly polymeric
surfactants for water/sc-CO2 emulsions. Moreover, despite the huge amount of
work in the last decade, tedious conditions of temperature or pressure are still
required to obtain emulsions/microemulsions systems and to use them as
nanoreactors. This is mainly due to the lack of suitable surfactants with enhanced
sc-CO2 solubility at conditions of low temperature and pressure.
In this context, we propose a modular synthetic platform of CO2-philic
macromolecular surfactants based on vinyl acetate (VAc), a hydrocarbon-based
cheap, non-toxic and industrially available monomer.[4-7]
Our first objective is to design new surfactants with enhanced solubility at low
temperature and low pressure. The CO2-philic part of these polymers will consist
of entirely fluorine-free vinyl ester copolymers, such as poly(vinyl acetate-co-vinyl
pivalate). Our research will focus on minimizing the reduction in CO2-solubility
caused by the addition of CO2-phobic segments, while maintaining the ability of
the surfactants to stabilize polar solutes. To accomplish this we will investigate the
effects of block length and chemical composition, as well as the effect of replacing
a block structure with a gradient structure with gradual change in composition and
CO2-philicity as a function of chain length.
Our second objective will then be to study the stabilization of water droplets within
sc-CO2 in presence of the aforementioned surfactants (mainly control of size and
stability). For this, a microfluidic approach using microreactors working under
pressure and temperature will be envisaged in order to enhance the screening of
the studied conditions.[8] Preliminary results have already been obtained in the
stabilization of water droplets within scCO2 without surfactant where the size of
the water droplet was determined by the size of the microreactor channel. We
intend to precisely control the size of water droplet, an important condition for
many applications of this universal solvent. This approach combined with in-situ
Raman spectroscopy will allow to study the structure and dynamics of molecules at
the w/sc-CO2 interface and potentially observe the diffusion of reactants between
stabilised droplets. The knowledge acquired from this project will pave the way for
the preparation of stable w/sc-CO2 emulsions with great promise for the
development of green chemical processes in diverse fields of organic, inorganic
and polymer chemistry.
References :
1. P. G. Jessop, Green Chemistry, 2011, 13, 1391-1398.
2. R. Noyori, Chemical Communications, 2005, 1807-1811.
3. K. P. Johnston, G. B. Jacobson, C. T. Lee, C. Meredith, S. R. P. Da Rocha, M. Z.
Yates, J. DeGrazia and T. W. Randolph, "Microemulsions, Emulsions, and Latexes
in Supercritical Fluids", Wiley-VCH, Weinheim, 1999.
4. E. Girard, T. Tassaing, C. Ladavière, J.-D. Marty and M. Destarac,
Macromolecules, 2012, 45, 9674-9681.
5. E. Girard, T. Tassaing, S. v. Camy, J.-S. p. Condoret, J.-D. Marty and M.
Destarac, Journal of the American Chemical Society, 2012, 134, 11920-11923.
6. E. Girard, T. Tassaing, J.-D. Marty and M. Destarac, Polymer Chemistry, 2011, 2,
2222-2230.
7. E. Girard, X. Liu, J.-D. Marty, M. Destarac Polymer Chemistry, 2014, 5,
1013-1022.
8. S. Marre, C. Aymonier, P. Subra and E. Mignard, Appl. Phys. Lett., 2009, 95, 1.
Two major publications in the domain of PhD:
1. ‘Enhancement of poly(vinyl ester) solubility in supercritical CO2 by partial
fluorination: the key role of polymer-polymer interactions.’E. Girard, T. Tassaing,
S. Camy, J.-S. Condoret, J.-D. Marty,* M. Destarac* J. Am. Chem. Soc, 2012, 134,
11920-11923.
2. ‘RAFT/MADIX (co)polymerization of vinyl trifluoroacetate: a means to many
ends’ E.Girard, X. Liu, J.-D. Marty,* M. Destarac* Polymer Chemistry, 2014, 5,
1013-1022.
Keywords: Supercritical CO2, RAFT, Microfluidic, emulsions, polymers
Expected collaboration in China:
First name and family name of the laboratory director:
Monique MAUZAC
Address of the laboratory director:
Université Paul Sabatier 31062 Toulouse Cedex 09
Signature and stamp of the laboratory director:
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