Apparatus and method for efficient determination of equilibrium adsorption isotherms at low pressures

摘要

This invention provides an apparatus and method whereby variable amounts of adsorbent are dosed over a porous sample to measure the equilibrium amount adsorbed by a sample over more than two orders of magnitude in pressure. The apparatus fills a fixed volume to variable pressures of adsorbent and/or provides multiple doses of adsorbent from a fixed volume in order to change the amount of gas to which the sample is exposed. Thus, a sample is exposed to doses of adsorbent that span over an order of magnitude in amount.PPThe improved apparatus employs substantially larger capacity tubing and valves (diameters greater than 0.25 inch ID) than those that have been employed in prior apparatuses for the measurement of adsorption by porous solids. Further, the improved apparatus employs a vacuum system capable of substantially lower pressures than those conventionally employed for the measurement of adsorption by porous solids. These innovations allow for a sample to be evacuated efficiently to lower pressures than in prior apparatuses employed for the measurement of equilibrium adsorption by porous solids. PPThe amount adsorbed is measured after sufficient time is allowed for equilibrium to be achieved (as determined by the changes in adsorbent pressure with time). This time between equilibrium measurements varies throughout a series of measurements.PP The disclosed adsorption apparatus and method allow for variations in the amount of adsorbent exposed to the sample for variable periods of time. This enables more efficient measurement of adsorption on porous solids over more than two orders of magnitude in pressure.