Abstract :
[en] Nowadays, in order to limit the global warming, CO2 emissions have to be drastically reduced. A first way is to use CO2 as a renewable C1 feedstock that could be industrially valorized to produce added value chemicals such as urea, methanol, salicylic acid and cyclic carbonates. Among those compounds, cyclic carbonates are used in a wide range of applications: electrolytes for Li-ion batteries, solvent, intermediates in pharmaceutical and cosmetic industries and also monomers of non-isocyanates polyurethanes (niPU). A second approach, in order to reduce the household energetic consumption and save energy, is insulating using polyurethane (PU) materials. In fact, in comparison with glass wool, rock wool, wood and hemp, PU is one of the most efficient materials for thermal insulation as it exhibits very low thermal conductivity values. But because of the high toxicity of the isocyanate monomer, a new alternative routine using the copolymerization of cyclic carbonates with diamines to produce niPU is a promising solution.
In this work, different types of heterogeneous catalysts have been synthesized toward a cyclocarbonation reaction between CO2 in a supercritical state (scCO2) and an epoxidized source (polyethylene glycol diglycidylether (PEG-500), for 4h at 80°C and 100 bar of pressure). First, optimal organic salt-based catalysts were chosen for this reaction: tetrabutylammonium iodide (TBAI) and tetrabutylammonium bromide (TBABr). These catalysts were immobilized onto a silica-based support by condensation reaction between silane and surficial silanol groups (R2). The best support was identified being EH-5 fumed silica (from CAB-O-SIL) because of its large specific area and its higher mesoporous to microporous volume ratio. Afterwards, it has been demonstrated that better grafting percentages as well as a better conversions could be obtained if the quaternization (R1) step is performed before the grafting step (R2). Then, it has been shown that - surprisingly ! - the best candidate (FIGURE 1 : IC3Q-EH-5) gives better conversions than the corresponding homogeneous catalyst ! This phenomenon has been explained through an epoxy-ring-opening activator effect thanks to the surficial silanol groups. Finally, the up-scaling of the IC3Q-EH-5 from 5g to 60g was successfully performed, as well as the use of a fluorinated alcohol co-catalyst, which allows reducing the operation conditions from 100 bar to 55 bar and from 240 min. to 150 min.
Characterizations were made by liquid 1H NMR for cyclocarbonation yield, by solid 29Si NMR for organic-to-inorganic bonds description, by TG-DSC-MS for grafting efficiency and catalyst description and by nitrogen adsorption/desorption for support description. Kinetic studies of cyclocarbonation with or without a co-catalyst were further performed by in situ Raman spectroscopy.
