At Fraunhofer ICT first promising plasticizer batch extraction test were performed on PVC dryblends and PVC sheets (mostly containing mainly DEHP) using the test batch extraction unit shown in Figure 1. The extraction achieved good yields > 70 %.
Figure 1: Batch extraction construction of plasticizers from PVC with scCO2
To develop a continuous extraction process, the maximum solubility of DEHP must be known as a function of temperature and pressure. In contrast to the batch extraction process in continuous process only short extraction times can be achieved, meaning that the amount of CO2 fed in that time must be able to extract the whole amount of DEHP from the PVC.
To determine the maximum solubility cloud point (CP) curve measurement were carried out at ICT with the view cell shown in Figure 2 on the left.
Figure 2: View cell for CP curve measurements (left) and CP-curve of 1wt% DEHP in scCO2 (right)
The measurements show that the solubility of DEHP in scCO2 is quite low at higher temperatures (Figure 2 (right)). As a consequence, a high CO2 flow rate in the continuous extraction process will be needed. Suitable co-solvent for scCO2 might increase solubility. Corresponding studies are currently carried out.