Regeneration of supercritical carbon dioxide by membrane at near critical conditions

The separation of supercritical carbon dioxide from a mixture of carbon dioxide and caffeine with a membrane possessing nano-scale pore size was studied. The experimental data indicated that a 100% caffeine rejection could be obtained at the condition of 308 K and approximately 7.95 MPa which is near the critical point of carbon dioxide. Besides the caffeine rejection the highest carbon dioxide permeation flux also occurred at the same operating condition. The highest caffeine rejection and carbon dioxide permeation flux were caused by the presence of a large cluster size in the near critical region. Under this situation, caffeine clusters could not be allowed to enter into pores of the membrane. When the temperature and pressure are increased, both the caffeine rejection and carbon dioxide permeation flux would be reduced due to a reduction of cluster sizes.