Influence of degassing temperature on the performance of carbon molecular sieves for separations involving O2, N2, CO2, and CH4

The effect of thermal pretreatment on the diffusion Of O-2, N-2, CO2, and CH4 at 298 K in the commercial carbon molecular sieve Takeda 3A was studied. The results indicate that pore mouth barrier controls nitrogen transport. For oxygen and carbon dioxide, however, two mechanisms are present. Pore mouth barrier control determines the transport at lower temperature degassing, and micropore diffusion is present with a high temperature degassing. When the degassing temperature is increased, the adsorption as a function of contact time is almost constant for O-2 and CO2, is almost null for CH4, and increases significantly for N-2 between 373 and 653 K. The rates of diffusion also increase with increasing degassing temperature, but more appreciably for N-2, which results in a significant decrease in selectivity for O-2/N-2 and CO2/N-2 separations. These separations are therefore more efficient for Takeda 3A if it is only subjected to temperatures lower than 373 K. On the other hand, for CO2/CH4, the separation is more efficient if the Takeda 3A sample is first submitted to a degassing temperature around 673 K.