Sustainable Approach for Paraffin Wax Removal Using CO2 Switchable Solvents

In this work, a sustainable approach for paraffin wax removal by using CO2 switchable-hydrophilicity solvents (SHSs) is developed, where paraffin wax exhibits better solubility in SHSs and can be simply separated by introducing CO2. Here, SHSs exhibit an excellent dissolving capacity for paraffin wax, especially, N,N-dimethylcyclohexylamine (DMCHA). All SHSs can effectively dissolve paraffin wax at a dissolution rate > 0.03 g/min. The detection using differential scanning calorimetry and the rheology behavior demonstrated that the decreased viscosity, melting points, and wax appearance temperature of paraffin wax in SHSs (especially in DMCHA) are lower than in traditional solvents, such as kerosene and petroleum ether, which contributes to improvement in the paraffin wax removal. Furthermore, the polarizing microscope images of paraffin wax reveal that the changed properties of paraffin wax in SHS are attributed to the dispersion of needle-shaped wax crystals in solvent. Interestingly, the paraffin wax is separated from SHS by introducing CO2, and the SHS is recovered under N2 at 65 °C after separating paraffin wax. Here, the recovery of paraffin wax can be improved by increasing water content, temperature, and aeration rate. Based on the molecular dynamics simulation, it is revealed that paraffin wax containing hydrocarbons (the main component of wax) with different alkane carbon numbers exhibits good dissolution behavior in DMCHA. After introducing CO2, the separation of paraffin wax is caused by the transformation from the hydrophobic state to the hydrophilic state of DMCHA.