Abstract
Carbon microfibers (CMF) has been used as an adsorbent material for CO2 and CH4 capture. The gas adsorption capacity depends on the chemical and morphological structure of CMF. The CMF physicochemical properties change according to the applied stabilization and carbonization temperatures. With the aim of studying the effect of stabilization temperature on the structural properties of the carbon microfibers and their CO2 and CH4 adsorption capacity, four different stabilization temperatures (250, 270, 280, and 300 °C) were explored, maintaining a constant carbonization temperature (900 °C). In materials stabilized at 250 and 270 °C, the cyclization was incomplete, in that, the nitrile groups (triple-bond structure, e.g., C≡N) were not converted to a double-bond structure (e.g., C=N), to form a six-membered cyclic pyridine ring, as a consequence the material stabilized at 300 °C resulting in fragile microfibers; therefore, the most appropriate stabilization temperature was 280 °C. Finally, to corroborate that the specific surface area (microporosity) is not the determining factor that influences the adsorption capacity of the materials, carbonization of polyacrylonitrile microfibers (PANMFs) at five different temperatures (600, 700, 800, 900, and 1000 °C) is carried, maintaining a constant temperature of 280 °C for the stabilization process. As a result, the CMF chemical composition directly affects the CO2 and CH4 adsorption capacity, even more directly than the specific surface area. Thus, the chemical variety can be useful to develop carbon microfibers with a high adsorption capacity and selectivity in materials with a low specific surface area. The amount adsorbed at 25 °C and 1.0 bar oscillate between 2.0 and 2.9 mmol/g adsorbent for CO2 and between 0.8 and 2.0 mmol/g adsorbent for CH4, depending on the calcination treatment applicated; these values are comparable with other material adsorbents of greenhouse gases.
Highlights
In the last few years, carbon dioxide (CO2 ) and methane (CH4 ) emissions have become the most important greenhouse gases with the largest impact on climate change [1]
The results suggest that changes in microporosity and chemical composition affect both the CO2 and CH4 adsorption capacity of Carbon microfibers (CMF)
polyacrylonitrile microfibers (PANMFs) were synthesized using a concentration of 10% (w/w) of PAN, the electrospinning apparatus was set at a flow rate of 0.5 mL/h, a voltage of 15 kV, and 10 cm distance between the tip of the syringe and the collector
Summary
In the last few years, carbon dioxide (CO2 ) and methane (CH4 ) emissions have become the most important greenhouse gases with the largest impact on climate change [1]. Fibers 2019, 7, 81 for greenhouse gases capture is adsorption at mild conditions, because the adsorbents materials are modifiable, reusable, and adsorption is a low energetic process [2,3,4]. Some materials have been tested as adsorbents for greenhouse gases, for example, zeolites [5,6], alumina [7], mesoporous silica [8,9,10,11], and porous carbons (graphite, carbon nanotubes, and carbon fibers) [3,12,13,14,15].
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