PORE STRUCTURE CHARACTERIZATION OF PILLARED CLAYS USING A MODIFIED MPMETHOD

The data of nitrogen adsorption on pillared clays (PILC) are converted to comparison plots (t-plots) to derive their pore size distribution (PSD). As in the MP method, the surface area of a group of pores havin g similar pore sizes is calculated from the slopes of tangent lines at two succeeding points on a comparison plot. By the modified MP method in this work, the tangent line is extrapolated to the adsorption axis on the t-plot, and the difference between intercepts is used to obtai n the volume of the group of pores. From the information of surface ar ea and pore volume, the average width of the pore group can be calcula ted and hence the PSDs of PILCs are obtained by carrying out such calc ulation procedures from high to low t. With this method, PSDs of sever al pillared clays are calculated over a wide pore size range, from mic ropores to mesopores. It is found that the modified MP method could re sult in the underestimation of the width of ultramicropores due to the enhancement in adsorption energy in these pores. Nevertheless, the me thod can be very useful in calculating the surface area and pore volum e, as well as a mean width of these pores. For super-micropores and me sopores, pore size can also be underestimated, due to deviation of the pore shape from a slit. The principles of the improved MP method, as well as problems associated with it are thoroughly discussed in this p aper. In general, this modified method provides practically meaningful results which are consistent with the pore dimension obtained from po wder X-ray diffraction measurements, but involves no complicated theor etical treatment or assumptions.