Nitrogen Sorption in a Transition Metal Complex Solution for N-2 Rejection from Methane

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Abstract

Nitrogen is a ubiquitous impurity in natural gas that has to be removed for the production of liquefied natural gas (LNG). The most widely used technology for N-2 rejection, cryogenic distillation, is a capital and energy intensive process. In this work, a nitrogen selective K[Ru-II (EDTA)] aqueous solution was prepared and tested for nitrogen sorption with the aim of reducing the N-2 rejection costs by using a continuous recirculation absorption process analogous to the acid gas removal process in LNG production. The overall equilibrium amount of N-2 sorption in the K[Ru-II(EDTA)] solution was obtained at 20 degrees C (0.075 mol N-2/L solution at 2860 kPa), 30 degrees C (0.061 mol N-2/L solution at 2873 kPa), and 40 degrees C (0.052 mol N-2/L solution at 3049 kPa) using a custom-built volumetric sorption measurement apparatus. The corresponding specific N-2 sorption amounts were 0.54 mol N-2/mol Ru at 20 degrees C and 2860 kPa; 0.43 mol N-2/mol Ru at 30 degrees C and 2873 kPa; and 0.34 mol N-2/mol Ru at 40 degrees C and 3049 kPa. These specific N-2 sorption amounts exhibited similar values to the specific loading of carbon dioxide in monoethanolamine (MEA) which is one of the most widely used chemicals for acid gas removal in LNG production industry. The heat of N-2 absorption in the K[Ru-II(EDTA)] solution was in the range of 30-60 kJ/mol N-2, suggesting the regeneration of the K[Ru-II(EDTA)] solution would require less energy than that required for CO2 scrubbing using MEA aqueous solution. The N-2/CH4 selectivity in the K[Ru-II(EDTA)] aqueous solution is in the range of 1.7 to 2.4 depending on the pressure of the gas, which is the highest N-2/CH4 selectivity known for a liquid based N-2 and CH4 separation system. The comparable specific N-2 sorption capacity to CO2-amine system and the high N-2/CH4 selectivity of the K[Ru-II(EDTA)] aqueous solution exhibit a great potential of the solution for nitrogen rejection from natural gas.

Original languageEnglish
Pages (from-to)13284-13293
Number of pages10
JournalINDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH
Volume58
Issue number29
DOIs
Publication statusPublished - 24 Jul 2019

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