Abstract
We present adsorption and desorption isotherms of methane, ethane, propane, n-butane and iso-butane as well as carbon dioxide for two shales and isolated kerogens determined by a gravimetric method. The sorption measurements of two shales were performed at three different temperatures, 308.15, 323.15, and 338.15 K. For the isolated kerogens, the measurements were conducted at 338.15 K. Methane and ethane sorption isotherms were measured to 35 bar. Carbon dioxide sorption isotherms were studied to 30 bar. Due to the low vapor pressure at room temperature, the sorption isotherms of propane, n-butane and iso-butane were measured to 8, 2, and 2 bar, respectively. The adsorptions of propane, n-butane, and iso-butane were much higher than methane at the highest pressures where the measurements were conducted. The adsorption of n-butane was 10 times higher than methane by mole at 2 bar, followed by iso-butane and propane. Our data show significant adsorption hysteresis in ethane, propane, n-butane and iso-butane. The most pronounced hysteresis was found in n-butane and iso-butane. Significant hysteresis is attributed to the reversible structural changes of kerogens. Dissolution of adsorbates into organic matter may also affect the hysteresis. This is the first report of propane and butane sorption isotherms in shales.
Highlights
Natural gas, the cleanest fossil fuel and the premium fuel of the twenty-first century, is desirable for various uses
The outcrop shale sample contains over 50 wt% total organic matter, and the reservoir shale has around 3.6 wt% total organic matter which is typical in many shale formations
We investigated the sorption isotherms of methane, ethane and carbon dioxide in the two shale samples to 35, 35, and 30 bar, respectively, at three different temperatures, 308.15, 323.15, and 338.15 K
Summary
The cleanest fossil fuel and the premium fuel of the twenty-first century, is desirable for various uses. Current limitation is storage of natural gas in heavy cylinders in vehicles New materials such as flexible metal-organic frameworks with higher adsorption capacity may enhance the use of natural gas in vehicles drastically. The important feature of shale is the nanoscale size of pores, in both organic and inorganic matters. There are two common methods to measure gas adsorption, gravimetric and volumetric/manometric[5,6,7,8,9,10,11,12,13,14]. Gravimetric methods use high-resolution balances to directly measure the weight change of samples due to sorption. The volumetric/manometric methods are based on Boyle’s law In this investigation, the Rubotherm Sorption System was used to measure sorption isotherms of various light hydrocarbons and carbon dioxide in shales and isolated kerogens. The outcrop shale sample contains over 50 wt% total organic matter, and the reservoir shale has around 3.6 wt% total organic matter which is typical in many shale formations
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