Dynamic column breakthrough measurements of nitrogen, methane and their mixtures for increased liquefied natural gas production efficiency


P. Hofman1, T. Rufford1, G. Watson1 and E. May1

1Centre for Energy, The University of Western Australia, Crawley WA, Australia

Keywords: gas processing
property: adsorption
material: methane, nitrogen

The production of LNG requires stringent pre-processing of the natural gas before liquefaction. Usually, however, nitrogen is carried through the cooling and liquefaction stages of the LNG production and it remains in the end-flash vapour in equilibrium with the LNG. This end-flash vapour must then be disposed of, which often can require the use of expensive cryogenic distillation towers. A proposed technology for the more effective removal of N2 and CO2 from natural gas is cryogenic pressure-swing adsorption (CPSA) using novel nanopore materials. By using the low temperatures readily available in an LNG plant and adsorbents with optimal pore sizes for this separation it may be possible to design a CPSA process that is competitive with cryogenic distillation. To design such a CPSA process an accurate knowledge of the adsorbent material’s equilibrium capacity and kinetic selectivity for each component gas is critical. While there are several adsorption measurement techniques capable of determining equilibrium capacity and kinetic selectivity, we have constructed dynamic column breakthrough (DCB) method to provide results most relevant to potential gas processes. The novel DCB apparatus constructed in this work is capable of measuring equilibrium adsorption capacity and the kinetics of adsorption at temperatures between 190 K and 298 K and pressures to 1 MPa. The system is entirely automated and consists of several high-precision mass flow controllers located upstream of a column packed with the adsorbent under study. Downstream of the column a mass flow meter and residual gas analyser allow the effluent flow rate and composition to be measured. We will present results for several adsorbents including natural zeolites and carbon adsorbents, and demonstrate how the dynamic data can be used extract the key equilibrium and kinetic adsorption parameters needed to design potential CPSA processes.


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