High pressure CO2 adsorption onto Malaysian Mukah-Balingian coals: Adsorption isotherms, thermodynamic and kinetic investigations

Adsorption of methane by modified-biochar aiming to improve the gaseous fuels storage/transport capacity: process evaluation and modeling

The CH4 storage by adsorption on activated carbons for natural gas handling has gained interest due to the appearance of lightweight materials with large surface areas and pore volumes. Consequently, kinetic parameters estimation of the adsorptive process can play a crucial role in understanding and scaling up the system. Concerning its versatility, banana peel (BP) is a biomass with potential for obtaining different products, such as biochar, a solid residue from the biomass' thermal decomposition of difficult disposal, where through an activation process, the material porous features are taken advantage to application as adsorbent of gaseous substances. This research reported data for the CH4 adsorption kinetic modeling by biochar from BP pyrolysis. The activated biochar textural characterization showed particles with fine mesoporous structure (pore diameter ranging between 29.39 and 55.62 Å). Adsorption kinetic analysis indicated that a modified pseudo-first-order model was the most suitable to represent the experimental data, with equilibrium adsorption of 28 mg g-1 for the samples activated with 20.0% vol wt.-1 of H3PO4 and pyrolysis at 500 °C. The equilibrium constant was consistent with the Freundlich isotherm model, suggesting a physisorption mechanism, and led to a non-ideal, reversible, and not limited to monolayer CH4 adsorption.

Upgrading recovered carbon black (rCB) from industrial-scale end-of-life tires (ELTs) pyrolysis to activated carbons: Material characterization and CO2 capture abilities

The current study presents for the first time how recovered carbon black (rCB) obtained directly from the industrial-scale end-of-life tires (ELTs) pyrolysis sector is applied as a precursor for activated carbons (ACs) with application in CO2 capture. The rCB shows better physical characteristics, including density and carbon structure, as well as chemical properties, such as a consistent composition and low impurity concentration, in comparison to the pyrolytic char. Potassium hydroxide and air in combination with heat treatment (500-900 °C) were applied as agents for the conventional chemical and physical activation of the material. The ACs were tested for their potential to capture CO2. Ultimate and proximate analysis, Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS), Raman spectroscopy, thermogravimetric analysis (TGA), and N2/CO2 gas adsorption/desorption isotherms were used as material characterization methods. Analysis revealed that KOH-activated carbon at 900 °C (AC-900K) exhibited the highest surface area and a pore volume that increased 6 and 3 times compared to pristine rCB. Moreover, the AC-900K possessed a well-developed dual porosity, corresponding to the 22% and 78% of micropore and mesopore volume, respectively. At 0 °C and 25 °C, AC-900K also showed a CO2 adsorption capacity equal to 30.90 cm3/g and 20.53 cm3/g at 1 bar, along with stable cyclic regeneration after 10 cycles. The high dependence of CO2 uptake on the micropore volume at width below 0.7-0.8 nm was identified. The selectivity towards CO2 in relation to N2 reached high values of 350.91 (CO2/N2 binary mixture) and 59.70 (15% CO2/85% N2).

Molecular Simulation of Thermodynamic Properties of CH4/CO2 Adsorption by Coal Molecules at Different Temperatures and Moisture Contents under Variable Pressure Conditions

In order to further elucidate the thermodynamic mechanism of CH4/CO2 adsorption by coal molecules, the adsorption behavior of a molecular model of coal (C206H128O36N2) at Wucaiwan, Zhundong was investigated by applying Materials Studio 2020 and Monte Carlo (GCMC) simulation methods, and the adsorption behavior of CH4 and CO2 was studied from the thermodynamic point of view under the conditions of different temperatures, pressures, and moisture contents. The results showed that at different temperatures or moisture contents, CH4 molecules had a low-density scattering distribution and CO2 molecules had a high-density polymerization distribution. Temperature and moisture content and adsorption constants a and b were negatively correlated. Under the same conditions, the relationship between single- and binary-component adsorption amounts was CO2 > CH4 and the relationship between heat of adsorption was CO2 > CH4. When adsorption potential energy or entropy of adsorption was the same, the adsorption capacity was CO2 > CH4. Temperatures and moisture contents were negatively correlated with the total adsorption capacity of CH4/CO2; pressure was positively correlated with the total adsorption capacity of CH4/CO2. The effect of temperature on the equivalent heat of adsorption was greater than that of pressure at different temperatures, and the entropy of adsorption was positively correlated between temperature and CH4/CO2, while the amount of adsorption was negatively correlated with the entropy of adsorption. The effect of moisture content on the equivalent heat of adsorption was greater than that of pressure at different moisture contents, and the entropy of adsorption was negatively correlated between moisture content and amount of adsorption. The adsorption entropy of CH4/CO2 was negatively correlated, and the adsorption amount was positively correlated to the adsorption entropy. At a temperature above 318 K or moisture content above 10%, the total CH4/CO2 adsorption decreased significantly and the CO2 adsorption decreased significantly. From a thermodynamic point of view, the presence of a large amount of H2O had a much greater effect on CO2 than on CH4, and an increase in temperature or moisture content was unfavorable for CO2 sequestration, CO2 stripping of CH4, and control of CH4 diffusion and desorption, whereas at low temperature, high pressure, and moisture content <1%, the effect of stripping, sequestration, and control was good.

Examination of the Factors Inhibiting CO2 Adsorption on Coal: A Case Study from Shallow-Depth Low-Rank Coal Seams

Understanding the inhibitory factors affecting the adsorption of CO2 on low-rank coal from shallow-depth coal seams is essential to identify potential coal seams for CO2 sequestration. The CO2 adsorption capacity of shallow-depth coals was measured at a low pressure on raw and dry coals. The samples were also prepared for organic analyses, scanning electron microscopy analyses, and low-temperature nitrogen adsorption analyses to evaluate the CO2 adsorption and identify the inhibitory factors. An investigation was conducted to determine how CO2 adsorption occurs on coal by fitting experimental data to adsorption isotherm models, followed by analyzing the results based on the statistical analysis. In addition, this study used Henry's law, surface potential, and Gibbs free energy to identify the adsorption inhibitor between CO2 and coal. The CO2 adsorption experiment was conducted on raw coal with a moisture content of 15.18-20.11% and dry coal with no moisture. The experimental data showed that the CO2 adsorption capacity in dry coal was 1.6-1.8 times greater than that in raw coal. A fitting graph between the adsorption data and the isotherm model indicated that CO2 adsorption on coal occurred on monolayers and multilayers under raw and dry conditions. Statistical evaluation of the adsorption isotherm models showed that the Langmuir and Freundlich models aligned more closely to the experimental data. According to this result, low-pressure adsorption of CO2 on coal occurred in monolayers and multilayers under raw and dry conditions. Coal containing a high huminite content had a higher potential for CO2 adsorption, and the drying increased the positive relationship. On the other hand, coal containing high inertinite content inhibited CO2 adsorption onto the coal, but the drying process did not adversely affect CO2 adsorption. Furthermore, coal with high moisture and inertinite content inhibited the affinity, accommodation, and spontaneous CO2 adsorption onto the coal. CO2 adsorption could lead to swelling, but moisture loss opened more sites and micropores, resulting in the swelling effect not closing all micropores in dry coal. Based on these results, coal seams with low moisture and inertinite content are the most promising for CO2 adsorption. Altogether, this study provides an understanding of the percentage of inhibitor factors that affects CO2 adsorption on low-rank coal from shallow depths, which may lead to different CO2 adsorption capacities.

Three-Dimensional Pore Structure Characterization of Bituminous Coal and Its Relationship with Adsorption Capacity

Bituminous coal reservoirs exhibit pronounced heterogeneity, which significantly impedes the production capacity of coalbed methane. Therefore, obtaining a thorough comprehension of the pore characteristics of bituminous coal reservoirs is essential for understanding the dynamic interaction between gas and coal, as well as ensuring the safety and efficiency of coal mine production. In this study, we conducted a comprehensive analysis of the pore structure and surface roughness of six bituminous coal samples (1.19% < Ro,max < 2.55%) using various atomic force microscopy (AFM) techniques. Firstly, we compared the microscopic morphology obtained through low-pressure nitrogen gas adsorption (LP-N2-GA) and AFM. It was observed that LP-N2-GA provides a comprehensive depiction of various pore structures, whereas AFM only allows the observation of V-shaped and wedge-shaped pores. Subsequently, the pore structure analysis of the coal samples was performed using Threshold and Chen's algorithms at ×200 and ×4000 magnifications. Our findings indicate that Chen's algorithm enables the observation of a greater number of pores compared to the Threshold algorithm. Moreover, the porosity obtained through the 3D algorithm is more accurate and closely aligns with the results from LP-N2-GA analysis. Regarding the effect of magnification, it was found that ×4000 magnification yielded a higher number of pores compared to ×200 magnification. The roughness values (Rq and Ra) obtained at ×200 magnification were 5-14 times greater than those at ×4000 magnification. Interestingly, despite the differences in magnification, the difference in porosity between ×200 and ×4000 was not significant. Furthermore, when comparing the results with the HP-CH4-GA experiment, it was observed that an increase in Ra and Rq values positively influenced gas adsorption, while an increase in Rsk and Rku values had an unfavorable effect on gas adsorption. This suggests that surface roughness plays a crucial role in gas adsorption behavior. Overall, the findings highlight the significant influence of different methods on the evaluation of pore structure. The 3D algorithm and ×4000 magnification provide a more accurate description of the pore structure. Additionally, the variation in 3D surface roughness was found to be related to coal rank and had a notable effect on gas adsorption.