Diffusion Coefficient of Ethylene in NMP Using Pressure Decay Method: Experimental and Modelling Study

The pressure decay of ethylene due to diffusion into the stagnant liquid of N-methyl-2-pyrrolidone (NMP) is evaluated at temperatures of 278.15, 298.15, and 328.15 K, and at three initial pressures of about 0.6, 0.8, and 1.1 MPa. Then, an available graphical method named the initial model is implemented to calculate the diffusion coefficient. Some corrections on the initial model are applied as follows: 1) in the infinite series of the solution to Fick’s second law, more terms are considered. 2) the equilibrium pressure is considered a tuning parameter to eliminate the requirement for an inaccurate experimental measurement. The proposed model is proven to be more reliable and valid for a whole range of pressure decay data including the early times. Due to the large differences between the results of the initial and the proposed models, the Wilke-Chang relation is considered a basis for comparison. This comparative study shows that the results of the Wilke-Chang relation are more compatible with the proposed model.