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Characterization of Advanced Materials for Gas Storage


Gas Storage

Materials for gas storage have been studied for decades, but recent interest in sequestration of greenhouse gasses and fuel storage has made this one of the fastest growing areas of material science. Activated carbons from various sources are the traditional materials for gas and vapor sequestration; however, there has been significant activity in the field of metal organic frameworks (MOF) for this application. As candidate materials are developed it is necessary to evaluate their effectiveness for the target application. Gas sorption analysis has been and still is widely used for evaluating these materials.

CO2 Sequestration

With concerns over global warming, the removal and storage of carbon dioxide from the air is a topic receiving significant attention. Novel materials are continuously being synthesized to improve the efficiency of CO2 removal from power plant stacks and other sources of this greenhouse gas. Determination of the pore volume and pore size is routinely performed with nitrogen adsorption at 77K, argon adsorption at 87K, or carbon dioxide adsorption at 273K. The latter is the preferred method for pore size analysis of carbons, however, low pressure analyzers can only detect pores in the micropore region (<2nm). Use of a high pressure gas sorption analyzer, like the iSorbHP allows CO2 isotherms to be acquired at 273K up to the saturation pressure of CO2 (~35bar), enabling the characterization of both micro- and mesopores.


Relevant Tech Notes:

#40 - Application of QSDFT (quenched solid density functional theory) - a novel density functional theory for an accurate pore size analysis of disordered porous carbons.

#52 - Adsorptives for Physisorption Experiments: Selection and their Properties.

#53 - Application of Quenched Solid Density Functional Theory (QSDFT) for Pore Size Analysis of Cylindrical and Spherical Pore Carbons.


Quantachrome Instruments for CO2 adsorption are the iSorbHP, Quadrasorb evo, NOVA and Autosorb iQ,

    Gas Storage | Standards


    Fuel Storage

    The quest for alternate fuel sources has led to the need for safe and efficient methods of storage. Adsorption onto the surface and into the pores of highly porous materials can enhance the capacity of a fuel storage vessel without resorting to extremely high and dangerous pressures. Studying the pore volume and surface area of these materials by low-pressure gas adsorption can give valuable information as to the viability of candidate materials. High-pressure gas adsorption using the actual fuel (H2 or CH4) can yield reliable data regarding the storage capacity of these materials. The high-pressure capability of the iSorb HP along with built-in functions for calculating the storage capacity from the adsorption data, make it a valuable tool for identifying materials for fuel storage.


    Quantachrome Instruments for pore size analysis are Quadrasorb evo and Autosorb iQ,
    Quantachrome Instrument for high-pressure and supercritical analysis is the iSorb HP.
    		 

    Another approach to the storage of hydrogen is to form a hydride with the adsorbent. This can significantly increase the capacity of hydrogen stored at a given pressure. In studying hydride formers for fuel storage applications two characteristics are important:
    1) the absolute storage capacity and
    2) the rate at which the hydride is formed and decomposed.

    This second characteristic will determine if a candidate material can be charged in a reasonable time and if it can deliver the fuel at a high enough rate to be practical. The iSorb HP with the solid-gas process kinetics (SGPK) option is ideally suited for these measurements. The large expansion volume of the SGPK option allows for near isobaric kinetics measurements necessary to characterize the rates at which the fuel can be stored and released.


    Quantachrome Instrument for hydride formation / decomposition analysis is the iSorb HP
 

Separation of gasses such as carbon dioxide from nitrogen or methane from carbon dioxide requires a material which preferentially adsorbs one gas over the other(s) present in the mixture. In screening candidate materials for this application the determination of the isosteric heat of adsorption of the component gasses on the candidate material is an excellent indication of the viability of the material for separation. This can be done at near atmospheric pressures or above using a gas sorption instrument and taking measurements at multiple temperatures. Although it is possible to determine the heat of adsorption from only two isotherms at two different temperatures, much better results are obtained using three or more temperatures. Use of cryogens limits the number of temperatures to the boiling point of the cryogens used. Using a circulating bath allows multiple temperatures, but in many cases the adsorption at the higher temperatures of the circulating bath is too low to get accurate data. Using the cryogen-free CryoCooler with either an Autosorb iQ or iSorb HP multiple data points can be obtained and accurate, reliable heats of adsorption determined.

Quantachrome Instruments for determining heats of adsorption using the CryoCooler are the iSorbHP and the Autosorb iQ