A novel pore structure tortuosity concept based on nitrogen sorption hysteresis data

A corrugated pore structure model (CPSM-nitrogen)(9) was employed to define a novel pore structure tortuosity concept. An empirical correlation is pro posed for the prediction of tortuosity factors tau (CPSM) as follows: tau ( CPSM) = 1 + A[(D-max,D-eff - D-min,D-eff)/D-mean](N-S - 2)(a). Constants A and a are adjustable parameters. The second factor reflects the influence o f the intrinsic pore size distribution, and the third expresses the contrib ution of the nominal pore length parameter Ns. The latter is, by definition , the number of pore segments forming a single corrugated pore of the CPSM pore configuration model and represents the frequency of pore cross section variation per unit length along a characteristic catalyst pellet dimension . The determination of Ns and (D-max,D-eff - D-min,D-eff)/D-mean is accompl ished by fitting the CPSM model over the pertinent nitrogen sorption hyster esis data. Coefficients A and a were found to be A = 0.69 and a = 0.58 by a pplying the empirical correlation for two specified materials of known tort uosity. The tortuosity factors for an anodic aluminum oxide membrane, MCM-4 1 materials, dried lignite, a porous glass, and several HDS catalysts were predicted to be 2.60, 1.12-1.13, 1.33-2.79, 6.60, and 2.75-10.07, respectiv ely. Such values approximate the literature data. Mercury porosimetry runs on the HDS catalysts showed a proportional increase in mercury entrapment w ith an increase in the corresponding tau (CPSM) values. The tortuosity fact or of lignite increases proportionally with the pore volume evolution. Furt her testing of the proposed correlation requires a rigorous analysis of dif fusion phenomena, based on the CPSM pore structure configuration, combined with effective diffusivity measurements.