Prefeasibility for Obtaining Isobutane and Propane Via Petroleum Extraction Gases in Colombia

Abstract

Isobutane and propane obtained from natural gas and liquefied petroleum gas (LPG) can be used to replace synthetic refrigerants, reducing emissions of ozone-depleting gases that generate global warming. For this reason, a simulation was carried out using Aspen HYSYS to corroborate that it is possible to obtain isobutane and propane at 99.5% purity. Properties of natural gas and LPG were analyzed with gas chromatography provided by Gas Natural Fenosa and Almagas, taking the lowest average of isobutane and propane data to determine the purity of each of the compounds to be obtained.  Using PUGH analysis, four methods were selected: direct, indirect, inorganic porous membranes, and fixed adsorption bed to analyze the separation of isobutane and propane at 99,5% purity with natural gas and LPG. Finally, the conceptual engineering of the separation was carried out with the simulation in Aspen HYSYS V 9.0, obtaining 99.5% propane, 49.62% isobutane, and 49.38% n-butane in purity, when using natural gas, which is composed of methane (CH4) in a volume of 84%, ethane (C2H6) at 3-8%, propane (C3H6) 1-2%, and butane (C4H10) less than 1%. Small amounts of heavier compounds such as hexane (C6H14), heptane (C7H16), and octane (C8H18) were also observed with a volume percentage lower than 1%. Additionally, some impurities were found in this gas such as carbon dioxide (CO2) with 1-2%, hydrogen sulfide (H2S) with less than 1%, and nitrogen (N2) with 1%, 99.9% propane, 1.98% isobutane, and 97.45% n-butane. LPG is composed of nitrogen (N2) at 0,05%, ethane (C2H6) at 2.07%, propane (C3H8) at 66.65%, isobutane (i-C4H10) at 16.46%, n-butane (n-C4H10) at 14.87%, and isopentane (i-C5H12).