Determination of external surface areas of zeolites

The external surface areas of NaA, CaA, H mordenite, NaX, and NaY zeolites were determined from the amounts of nitrogen adsorbed at 77 K on zeolites, after their internal pores had been filled previously with water, ethane, propane, butane, or 2,2-dimethylpropane by adsorption. The amount of nitrogen adsorbed was measured with a temperature-compensated tensimeter having symmetrical design. When the change in the pressure due to the adsorption of nitrogen on the zeolite previously filled with a filling substance stopped in a short while, the linear BET plot was obtained and the monolayer volume of nitrogen adsorbed on the external surface of zeolite was evaluated from the BET plot (the filled-pore method). When the pressure due to the adsorption of nitrogen on the zeolite changed slowly, the monolayer volume of nitrogen adsorbed on the external surface was evaluated from the amount of nitrogen adsorbed rapidly on the zeolite (the adsorption kinetic method).