Porous carbon screening for benzene sorption

Abstract

Benzene is one of the aromatic hydrocarbons that are co‐absorbed with the acid gases during amine scrubbing and are carried over to the catalytic reactors in the sulfur recovery unit where they crack and deactivate the catalyst. As a solution, adsorption of benzene using porous adsorbents is being considered as a suitable process for removal. The present work considers carbon based porous adsorbents as potential adsorbents and attempts to screen the large pool of adsorbents. Preliminary screening was made using information in open literature and structural characteristics, before the adsorbents were subjected to gas phase benzene adsorption. The pool of porous carbons screened included highly acidic sulfonated carbons, ordered mesoporous carbons (OMCs) and various commercial activated carbons (ACs). Among the pool of porous carbons, mesoporous carbon identified as AC1, was found to possess the highest adsorption capacity for benzene with heat of adsorption capacity of 20–32 KJ/mol. It was found that it is possible to regenerate the benzene adsorption capacity of AC1 and a benzene adsorption capacity of about 14 mmol/g for the mesoporous carbon was found to be far superior to the adsorption capacities reported in literature. © 2018 American Institute of Chemical Engineers Environ Prog, 38: S93–S99, 2019

Comparative Study of Toluene and Hexane Adsorption on Activated Carbons From Gas and Liquid Phase. Enthalpy and Isotherms

“…As for the mixtures, the above was confirmed, since by adding 0.3 mol of toluene to hexane the enthalpy increased considerably (it doubled for CS and increased 1.5 times for CST), this increase was due to the fact that by immersing the solids in the two compounds, by orientation (Webster et al, 1998) and affinity (Rehman et al, 2019;Rubahamya et al, 2019) there was probably a higher entry of toluene molecules than hexane into the porous structure and since there were more interactions with C 7 H 8 [London forces (Mantri et al, 2017), ππ interactions (Rehman et al, 2019;Rubahamya et al, 2019)] than with C 6 H 14 (London forces; Mantri et al, 2017) more energy was released in the process becoming more exothermic; however, as the concentration of toluene increased, the enthalpy of immersion decreased, this inversely proportional relationship occurred because as the amount of toluene increased, there was greater displacement of hexane molecules, which implied a higher energy consumption since this process was endothermic (Unnikrishnan and Srinivas, 2016), which is reflected in a decrease in the enthalpy of the mixture when it was compared to H i for pure toluene.…”

“…Regarding to the samples, Figure 12 shows the immersion enthalpies of pure solvents and toluene-hexane mixtures in function of the molar fraction of toluene and the total acidity and basicity of samples. It can be seen that the immersion enthalpies increased with basicity and decrease with the total acidity of the samples, this occurred because according to other investigations the electron density of the adsorbent depended on its type of surface chemistry: electron withdrawing groups (like oxygen surface groups) reduced the adsorptive potential of the material whereas donating functional groups favored the electron density and then the adsorptive potential of the carbonaceous solid Montes-Morán et al, 2012;Rubahamya et al, 2019). This is why enthalpies for CS were lower than for CST, since CS contained higher concentration of acidic oxygen groups, which reduced the electron density and the potential adsorptive of activated carbon, as well as the adsorption affinity by ππ interactions (Goto et al, 2015), generating less adsorbate-adsorbent interaction, mainly with toluene; the opposite occurred with CST since when it was subjected to high temperature, electron withdrawing groups were removed and at the same time the concentration of aromatic rings in the solid structure was intensified (Contescu et al, 2018), increasing its electron density and therefore, the intensity of the interaction adsorbent-adsorbate was higher.…”

“…This showed the region of the mixtures (center of the figure, dark green square) and the edges where the pure solvents were. For the pure solvents, the intensity of the interaction was greater with toluene than hexane (it increased 2.5 times for CS and it doubled for CST); this occurred because both showed London dispersion interactions, which were originated between an adjacent pair of atoms or molecules when they were in close proximity and they were attractive forces between non-polar organic molecules (Mantri et al, 2017), such as hexane and toluene; but toluene, in addition to causing this type of forces, generated π-π interactions between its aromatic ring and the delocalized π electrons of the graphene layers of the activated carbon (Rehman et al, 2019;Rubahamya et al, 2019). Besides, the methyl group of toluene is an electron-donating group which also contributed to increasing the electronic density of the ring (Bazzini and Wermuth, 2015) and then, the interaction with the πē of the graphitic surface of the porous solid.…”

“…Regarding to the samples, electron density of the adsorbent depended on its type of surface chemistry: electron withdrawing groups (like oxygen surface groups) reduced the adsorptive potential of the material whereas donating functional groups favored the electron density and then the adsorptive potential of the carbonaceous solid (Montes-Morán et al, 2012;Rubahamya et al, 2019). This is why enthalpies for CS were lower than for CST, since CS contained higher concentration of acidic oxygen groups, which reduced the electron density and the potential adsorptive of activated carbon, as well as the adsorption 2 | Parameters obtained from the fit to the Langmuir and Freundlich models for the liquid phase adsorption isotherms of toluene/hexane on CS and CST.…”

Adsorbent screening for airborne BTEX analysis and removal

“…In this regard, several materials differing in structure, porosity and surface chemistry have been lately investigated. Among these materials, carbon-based materials have been addressed as VOC/BTEX adsorbents including activated carbons [15], [16], ordered mesoporous carbons [17] or carbon nanotubes [18]. However, graphitised carbon blacks, typically employed for sampling [19] and gas analysis [20] applications, have been scarcely evaluated in terms of adsorption capacity.…”