Bruce D. Adkins

Comparison of nitrogen adsorption and mercury penetration results. I: Pore volume and surface area obtained for type IV isotherms

Mercury penetration pore volumes obtained for four materials (two silicas, alumina and zirconia) agreed closely with the “Gurvitsch Volume” obtained from nitrogen adsorption. The pore volume of the materials used in this study was found in a narrow range of pore sizes that are amenable to both mercury penetration and nitrogen adsorption measurements. The average crystallite sizes calculated from the BET surface area and from TEM measurements agreed closely except for the highest surface area (310 m2/g) material. The surface areas obtained from mercury penetration or the BET method agree closely for the two lower area materials but the mercury penetration is much higher than the nitrogen surface area for the two higher area materials.

Alumina supported molybdenum and tungsten oxide catalysts.: Surface area and pore size distribution from nitrogen adsorption and mercury penetration

Abstract Surface areas (BET) calculated from nitrogen sorption on aluminum oxide supports with varying MoO 3 and WO 3 loadings were consistently higher than surface areas calculated from mercury penetration data. Increasing the MoO 3 or WO 3 content from 0% to about 20% resulted in a gradual decrease in the surface areas calculated from mercury penetration even though the BET surface area remained constant. The mercury contact angles which provided agreement between BET and mercury penetration surface areas decreased with increasing molybdenum or tungsten oxide loading up to the concentration corresponding to about one monolayer coverage, and approached that of unsupported MoO 3 or WO 3 . The best agreement of data from the two techniques was obtained for samples with pores in the 100-200 A region.

Porosity by small-angle X-ray scattering (SAXS): comparison with results from mercury penetration and nitrogen adsorption☆

Abstract For several materials showing type-IV nitrogen adsorption behavior, the scatterer size distribution calculated from small-angle X-ray scattering (SAXS) data are shown to be consistent with pore size distributions (POSDS) calculated from nitrogen adsorption, over the range of pore radii from 2.0 to 20 nm. However, since neither pores nor particles are present as a dilute phase, it is not possible to assign unambiguously the SAXS distribution to either pores or particles.

Porosity of Silicas: Comparison of Nitrogen Adsorption and Mercury Penetration

Publisher Summary This chapter discusses the porosity of silicas: comparison of nitrogen adsorption and mercury penetration. Nitrogen adsorption and mercury penetration are two of the most common methods for obtaining information about the porosity of solids. Unfortunately, experimental realities limit the region where the two methods are both applicable to pore sizes of ca. 10–30 nm. Both nitrogen adsorption and mercury penetration provide a direct measure of pore size distribution and pore volume. However, these direct measures do not permit a determination of the morphology of the materials from pressure–volume relationships. Nitrogen adsorption–desorption isotherms were obtained with a Quantachrome Autosorb 6 instrument. Prior to analysis, samples were outgassed for several hours at about 10 -3 torr and 200°C. Surface areas are calculated from the linear form of the BET equation. The model utilized for pore size distribution calculations is a packed particle model, assuming each primary spherical particle is in contact with six neighboring spheres. Mercury penetration curves were generated from pressure–volume measurements from 0 to 60,000 psia using a Quantachrome Autoscan 60 instrument. The surface areas are calculated using the Rootare–Prenzlow equation.

Mechanism for coking of coal liquefaction catalysts involving basic nitrogen compounds, sodium and catalyst acid sites

A simple mechanistic model is presented to explain the deposition of sodium and coke on hydrotreating catalysts used in the Wilsonville, AL coal liquefaction pilot plant. The model incorporates data from four process configurations, two NiMo/Al2O3 catalysts, and two coal types. In this model, “coke” takes the form of basic nitrogen compounds which compete with sodium for acid sites on the catalyst surface. Elemental analyses of the spent catalysts allow calculation of average stoichiometries and approximate desorption rate constants for the basic nitrogen compounds, which are consistent with hydrotreater feed stream analyses and laboratory studies.

Thermal analysis of spent coal liquefaction catalysts

Abstract The accumulation of carbonaceous deposits (‘coke’) and metals on coal liquefaction catalysts causes substantial loss of catalytic activity and is a major concern during catalytic hydrotreating. A model has been developed to describe this accumulation as a function of process configuration for the operation of a pilot plant scale two-stage coal liquefaction system. Significant concentrations of carbon, nitrogen, iron, titanium, and sodium are observed. The work presented here investigates the effect of deposited metals and alkali on the combustion of coke from aged coal liquefaction catalyst samples.

Comparison of nitrogen adsorption and mercury penetration results. II: Pore size distributions calculated from type IV isotherm data

The pore distributions calculated from nitrogen desorption and from mercury penetration data are similar for the four materials utilized in this study. While there are small differences in the distributions calculated using different models (Cohan. Foster or Broekhoff-deBoer) with nitrogen adsorption or desorption isotherm data, all three show reasonable agreement with distributions calculated from mercury penetration data. Frequently practical catalysts have such a broad pore size distribution that neither method alone is adequate to measure the total pore size range. The present results suggest a direct comparison, without recourse to a scaling factor, is appropriate when comparing results from the two methods even though the pore size distribution maximum may vary by at least 50% depending upon the model chosen for the calculation. Better agreement may be obtained between the two experimental techniques by adjusting either the nitrogen adsorption data using a packed sphere model or the mercury penetration data by an earlier reported correction ratio. The difference between the two methods becomes less than 20% when a correction procedure is used; however, further studies are needed to define the range of material shaped that these procedures are applicable to.

Comparison of Nitrogen Adsorption and Mercury Penetration Results. Pore Size Distributions for a Series of Mo-A12O3 Catalysis with Increasing MoO3 Content

Scanning electron microscopic data, X-ray diffraction patterns and porosity measurements are consistent with a structure for an Mo-A12O3 catalyst series containing a single surface layer of Mo up to the point where the Mo loadings exceed the amount required for a monolayer. For greater Mo loadings than required for a monolayer, three dimensional orthorhombic MoO3 is also present. The cumulative pore volume, on an alumina basis, does not appear to be significantly altered by MoO3 loadings up to about 15 wt.%. The BET surface area, on an alumina basis, remains constant with Mo loading. However, the apparent surface area calculated from mercury penetration data decreases with Mo loading. For these materials with cylindrical pores, the Broekhoff-deBoer model for the calculation of pore size distributions produced closer agreement to the mercury penetration pore size distribution. This is in contrast to materials composed of nonporous spheres where the Broekhoff-deBoer model provided poorer agreement to mercury penetration results than either the Cohan or a packed sphere model. The results show that, within a factor of two the pore size distributions calculated from nitrogen adsorption and mercury penetration data are comparable.

SURFACE AREA OF CALCINED LIMESTONES OBTAINED BY NITROGEN ADSORPTION AND MERCURY PENETRATION MEASUREMENTS

ABSTRACT Two sets of limestones, one from Kentucky and one from Spain, have been used in a study to compare the surface areas from nitrogen adsorption and mercury penetration. As a first approximation for the higher area materials, the surface areas obtained by the two experimental methods are in reasonable agreement and either method could be employed. However, a consistent trend is established when the ratio of surface areas are considered for decreasing nitrogen. The mercury penetration area becomes increasingly greater than the nitrogen area as the nitrogen area becomes smaller.

Coal liquefaction catalysis: Metals deposition in the presence or absence of coal ash

Abstract Catalysts, aged in an ebullating bed reactor, have been characterized for carbon and metals deposition. It appears that the amount of carbon on the catalyst is more dependent upon the reactor temperature than on coal type; this carbon deposition attains a maximum value within the first few days of a run. Metals deposition does vary with coal. The presence of coal ash in a hydrotreater feed may significantly alter metals deposition. For iron, calcium and vanadium deposition is less when coal ash is present and the maximum content of these metals is attained at an earlier time on-stream when ash is present. Sodium, on the other hand, may be deposited to a much greater extent when coal ash is present. Titanium deposition appears to be independent of the coal ash concentration.