The effect of chemical treatment on adsorption of natural gas by multi-walled carbon nanotubes: Sorption equilibria and thermodynamic studies

Abstract

In this study, adsorption of methane as the main constituent of natural gas was firstly studied on the pristine multi-walled carbon nanotubes (MWCNTs) and then purification and chemical treatments of MWCNTs was performed to enhance the natural gas adsorption capacity. MWCNTs were chemically treated using different methods in this research. The results revealed that chemical treatment of the MWCNTs in presence of H2SO4/HNO3 acidic mixture in 3:1 volume ratio, enhanced considerably natural gas adsorption capacity (an optimal up to 45 mmol/g) at temperature of 298.15 K and the pressure of 50 bar compared to the pristine MWCNTs (about 27 mmol/g) at the same operating conditions. This effect can be attributed to the opening of the nanotubes caps with a major alteration in its structural properties due to chemical treatment. The experimental data of adsorption were almost equally well described by Langmuir, Freundlich and Sips equations to determine the model isotherms. The best fit was obtained by the Sips model isotherm with the r-squared value near to unity. Furthermore, using the experimental data obtained in different temperatures the isosteric heat of natural gas adsorption onto pristine MWCNTs was also calculated in the interested range of pressures and temperatures using the thermodynamic-based Clausius-Clapeyron equation from the Sips isotherm model. The results revealed an energetically heterogeneous surface of MWCNTs in natural gas adsorption. Also the natural gas adsorption process was kinetically studied through pseudo-second order and intra-particle diffusion models which indicated the intra-particular diffusion is rate limiting step in adsorption of methane on MWCNTs

Fabrication, Purification and Characterization of Carbon Nanotubes: Arc-Discharge in Liquid Media (ADLM)

“…CNTs are attracted significant attention because of their unique physical and mechanical properties. These properties have been the engines of the rapid development in scientific studies in numerous applications such as in fuel cell and electrocatalyst, nanobiosensors, gas adsorptions and membrane separation [82][83][84][85][86][87][88].…”

CO2 reforming of CH4 over M(Ca, Ba, Sr)xLa1-xNiO3 perovskites used as coke resistant catalyst precursor

“…Natural gas could play a significant role as a carbon source for the world's supply of fuel and fuel-based chemicals in this century [1][2][3]. Methane is the main component of natural gas and almost all the transformation routes of this hydrocarbon involve its conversion into syngas (mixture of H2 and CO and some CO2) [3][4]. As seen in the literature [5], syngas is a key intermediate in the chemical industry and is produced from methane by steam reforming, dry reforming, autothermal reforming or partial oxidation.…”

Activated nanocarbons produced by microwave-assisted hydrothermal carbonization of Amazonian fruit waste for methane storage

“…This new ambitious value was only reached by a metal organic framework, HKUST-1, prepared recently in monolith form exhibiting a density of 1.06 g.cm -3 (Tian et al 2017) and a CH 4 uptake of 259 V/V. Activated carbons (ACs) with microporous structures constitute an important category of potential adsorbents for natural gas storage [6] . Properties of activated carbon required for natural gas adsorption includes: high micropores volume, high packing density, high adsorption desorption rate, high working capacity (difference between the maximal adsorption pressure to 0.1 MPa) [7], less susceptible to temperatures changes during adsorption and desorption and chemical stability [8].…”