(37d) Influence of Dissolved Carbon Dioxide on the Viscosity of Di-Isodecyl Phthalate

Introduction

It is well established carbon dioxide dissolves readily in most organic liquids under pressure and leading to a large reduction in viscosity. The extent of the viscosity reduction appears to depend greatly on the initial viscosity of the liquid and previous studies have focused mostly on relatively-low-viscosity liquids [1-4].In this work, we have studied the viscosity of di-isodecyl phthalate (DIDP) under addition of carbon dioxide. The results show a viscosity reduction of up to 98%.

Experimental

Measurements were carried out in a bespoke apparatus comprising a vibrating-wire viscometer and a vibrating-tube densimeter connected in a loop together with a recirculation pump. Fluids (DIDP and carbon dioxide) were injected quantitatively into the loop from high-pressure syringe pumps to create mixtures of known composition at pressures above the bubble curve where they forma single homogenous liquid phase. The circulation pump was used to homogenize the liquid prior to the measurements. The viscosity and density were measured at temperatures of 313, 343 and 373 K with pressures up to 80 MPa.

Results and Discussion

Figure 1a shows the viscosity of the mixture T = 343 K as a function of the mole fraction x_CO2 of dissolved carbon dioxide. The figure also shows the viscosity of pure DIDP [5] and pure CO₂[6] as end points. As the mole fraction of dissolved CO₂ increases from zero to approximately 80 mol%, the viscosity reduces by more than 90%. Figure 1b shows the densities of the mixtures under the same conditions. At a pressure of 80 MPa, dissolution of CO₂ is seen to slowly increase the density, while at 40 MPa, there is almost no change up to a mole fraction of 0.8, after which a reduction to the density of pure CO₂ is observed. These results demonstrate that the reduction in viscosity is not simply a reflection of density changes.

We also explore the applicability of a recently-developed model for mixture viscosity based on the residual entropy [7] and will present a comparison with this model for the present binary mixture.

References

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