Both these trials were successful in showing that the supercritical extraction method could possibly achieve greater separations than drying alone.Ī design of experiments (DOE) was conducted on the supercritical extraction process. For reference, the viscosity at the thermodynamic limit was 5103 cP. These trials, as well as all other trials, were conducted using mixtures at the determined thermodynamic limit, or 1:8 heptane:PDMS by mass. The trials yielded a viscosity of 76 cP, respectively. Two trials were run at 1300 psi and 40☌, with 1 and 2 cycles. Initial trials were run using the isobaric system constructed in Gavett to determine if the thermodynamic limit could be broken. Red arrows indicate the interface between the two phases. Sample inside supercritical dryer exhibiting phase separation. An image of the setup is shown below:įigure 11. The slide was then placed on a pre-heated hot plate. This equation describes a diffusion-limited process and does not account for thermodynamic effects, which are described in Equation 2.Įquation 1 (left): The relation between drying rate versus the diffusion coefficient ( D), film thickness ( □ (t)), solvent concentration ( C).Įquation 2 (right): Thermodynamic expression for evaporation showing the relation between drying rate, liquid/vapor mole fractions ( x i/y i), activity coefficient ( γ i), component partial pressure ( P i), and pressure ( P).Ī small amount of sample was placed on a glass slide using a syringe and then a doctor blade, which is used to create a sample of a given thickness, was passed over it as shown in Figure 5. The concentration of heptane in the environment is negligible, so the term C ∞(t) may be set equal to zero. Equation 1 shows the relation between drying rate (on the left side of the equation) and the diffusion coefficient, film thickness, solvent concentration in the film, and solvent concentration in the surrounding environment. The evaporation process was believed to be diffusion-limited, so thin films were chosen to maximize solvent removal. It was hypothesized that the heptane could be evaporated in an efficient manner by casting it on a thin film and applying heat.
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