Measurement method for finding gas adsorption equilibrium isotherms by employing a gas chromatograph and using its integrator in a new way
2005 (English)In: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 76, no 4, 044102- p.Article in journal (Refereed) Published
A method for measuring the adsorption ability of zeolites has been developed. The adsorption can be accurately measured over a wide range of pressures and temperatures. The range usually covered is partial pressures ranging from 0.2 to 20 bar (a) and temperatures from 10 to 50 degrees C. However, it may be extended to 0.1-25 bar (a) and -40-80 degrees C. When a partial pressure below 2 bar (a) is to be used, the gas is diluted with helium. The method is built around a gas chromatograph (GC) equipped with a thermal conductivity detector (TCD) and having a programming and peak integrating unit. It also has an option using liquid nitrogen to allow work below ambient temperature. The GC has been modified with two special columns to be used alternately for purging with helium and as test chamber for the measurements. It is also equipped with a separate external flow and pressure-handling unit. The GC is used, not as a chromatograph, but instead to integrate suitably interrupted breakthrough curves. The primary measured data are evaluated using a program written in BASIC, which separates the part of the primary measured results that originates from the adsorption from the part that is induced by the measuring equipment. Using a calibration file that can easily be updated from within the program, this separation has achieved a high degree of accuracy. Using the adsorption data from these measurements, Langmuir-type isotherm equations are fitted, which accurately represent the adsorption of the tested gas both with respect to pressure and to temperature. It has been found that adsorption data measured in this way can achieve a standard deviation between measured and calculated data that typically varies around 1% over the whole measured range. In order to do this, however, in the case of nitrogen adsorption the sum of two Langmuir isotherms has to be used. This is not needed with oxygen or argon adsorption.
Place, publisher, year, edition, pages
2005. Vol. 76, no 4, 044102- p.
IdentifiersURN: urn:nbn:se:kth:diva-14677DOI: 10.1063/1.1889468ISI: 000228362200029ScopusID: 2-s2.0-17644396327OAI: oai:DiVA.org:kth-14677DiVA: diva2:332718
QC 20100525 201202142010-08-052010-08-052012-02-14Bibliographically approved