Synthesis of Siloxane Polyether Surfactants and Their Solubility in Supercritical CO2

Four siloxane polyether surfactants were synthesized from allyl bromide, polyethylene glycol methyl ether and heptamethyltrisiloxane (HMTS) to explore their solubility in CO2. The dissolving pressures of these surfactants were measured using a high-pressure view cell at 318-343 K to calculate their solubility in CO2. The results show that, the silicone-containing surfactants exhibit excellent solubility in CO2. The shorter the polyethylene glycol group, the better the solubility in CO2. Of the five compounds tested, HMTS showed the best solubility in CO2 which was around 2.4% as a mole percentage. The surfactants show much better solubility than the commonly used surfactants. Moreover, by investigating the effects of the pressure and temperature on the solubility, it was found that an increase in pressure benefits solubility of the compound in CO2, while an increase in temperature within the experimental range does the opposite. In addition, a linear correlation in the logarithmic values of the solubility data and the density of CO2 was found, which means the solubility follows density more directly and not the pressure.