Improve in CO2 and CH4 Adsorption Capacity on Carbon Microfibers Synthesized by Electrospinning of PAN

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.

Effect of Calcination Temperature and Chemical Composition of PAN-Derived Carbon Microfibers on N2, CO2, and CH4 Adsorption

“…The carbonization at 600 • C (CMF-600) and 700 • C (CMF-700) of the PANMFs led to: (i) increments in the signals between 1480-1630 cm −1 (-C=C,~1574 cm −1 and -C=N, 1590 cm −1 ), although as the calcination temperature increased there was a trending shift towards the formation of -C=C bonds and a decrease in -C=N bonds, which is consistent with the XPS results reported in Ojeda et al [13], showing that the amount of carbon increases as the amount of nitrogen decreases (Figure 1B); (ii) an increment in the signal between 1180-1420 cm −1 , although the signal for -C-H (1360 cm −1 ) disappeared and the signal for -C-C bonds is shifted to a single center located at~1240 cm −1 . This corroborates that dehydrogenation had occurred, and adjacent polymer chains were joined by C-C bonds, resulting in longer carbon sheets, which is the objective of the 90 min carbonization process [17]. Nevertheless, when PANMFs were carbonized at 800 • C (CMF-800), both signals decreased because, at this temperature, the material had reached a higher carbon content and had significantly decreased in nitrogen compared to the CMF-600 and CMF-700 samples, which was confirmed by XRD and Raman analysis, as described in the following sections.…”

“…Polyacrylonitrile microfibers (PANMFs) were synthesized using polyacrylonitrile (PAN) and N, N-Dimethylmethanamide (DMF) with a concentration of 10%, as described elsewhere [ 16 , 17 ]. Briefly, the electrospinning apparatus was set at: (i) flow rate of 1.0 mL/h, (ii) voltage of 15 kV and (iii) distance between the tip of the syringe and the collector of 10 cm.…”

“…Briefly, the electrospinning apparatus was set at: (i) flow rate of 1.0 mL/h, (ii) voltage of 15 kV and (iii) distance between the tip of the syringe and the collector of 10 cm. The PANMFs obtained were carbonized at 600, 700 and 800 • C (all previously stabilized at 280 • C for 0.5 h in air atmosphere) for 1.5 h in nitrogen atmosphere [17]. The samples were labelled as: PAN (precursor polymer without any treatment), PANMFs (polyacrylonitrile microfibers), PANMF-E280 (polyacrylonitrile microfibers stabilized at 280 • C), CMF-600 (polyacrylonitrile microfibers stabilized at 280 • C and carbonized at 600 • C), CMF-700 (polyacrylonitrile microfibers stabilized at 280 • C and carbonized at 700 • C), and CMF-800 (polyacrylonitrile microfibers stabilized at 280 • C and carbonized at 800 • C).…”

Isosteric Enthalpy Behavior of CO2 Adsorption on Micro-Mesoporous Materials: Carbon Microfibers (CMFs), SBA-15, and Amine-Functionalized SBA-15

“…The electrospinning apparatus was set at (i) flow rate of 1.0 mL/h, (ii) voltage of 15 kV and (iii) distance between the tip of the syringe and the collector of 10 cm. Then, the carbon microfibers were obtained by a calcination process that involved two phases: (i) Stabilization at 553 K (air atmosphere) for 30 min and (ii) carbonized at 1223 K (nitrogen atmosphere) for 90 min [21].…”

Importance of Pore Structure and Surface Chemistry in Carbon Dioxide Adsorption on Electrospun Carbon Nanofibers

“…(16,19) Although the effect of the carbonization temperature of carbon nanofibers has been discussed in some studies, the activation process after carbonization was not conducted in these studies. (20) Therefore, in this study, we prepared activated PAN carbon nanofibers by electrospinning followed by stabilization, carbonization, and activation, and we focused on the effect of the carbonization temperature on the properties and CO 2 adsorption performance of the samples. PAN was selected as the carbon precursor because it is one of the most widely used polymers for preparing carbon fibers and has a high nitrogen content and excellent thermal and mechanical properties.…”