Estudos em adsorção de gás natural: armazenamento, transporte e purificação

Abstract

The use of vessels filled with activated carbon to store and transport natural gas (NG) at moderate pressures (about 3.5 MPa) and ambient temperature (about 298 K) has been studied as a potential alternative to compressed natural gas storage at high pressures (ca. 20 MPa). The present study provides an experimental investigation of charge and discharge cycles of natural gas in a prototype storage vessel filled with activated carbon and analyses the effect of the gas composition on the adsorption capacity. The adsorption properties were evaluated by measuring isotherms for each component of NG in a magnetic suspension balance and compared with the isotherms measured in a storage vessel using NG. The selectivities of the main constituents of natural gas in relation to methane were determined and the influence of the pressure on the selectivity was also observed. Although NG is composed mainly of methane (ca. 90% vol.), our experimental results indicate that the preferential adsorption of the heavier hydrocarbons and CO2 should be properly taken into account for the evaluation of the behavior of adsorbed natural gas systems along several charge and discharge cycles. In an another context, the separation of CO2 from CO2-CH4 mixtures is an important issue in natural gas and biogas purification/upgrading for energy generation applications and it was also studied in this work. Thus, co-adsorption data of the binary mixture CO2/CH4 on activated carbon at 293 K was obtained by the volumetricchromatographic method and it was compared with the IAST (Ideal Adsorbed Solution Theory) and the Extended Langmuir (EL) predictions. Preferential adsorption of CO2 was observed for the CO2 mixture composition more than around 20%. The accuracy of predictions was less than desirable to an application engineer.