Kinetic and Equilibrium Study of the Adsorption of CO2 in Ultramicropores of Resorcinol-Formaldehyde Aerogels Obtained in Acidic and Basic Medium

Abstract

In this work, aerogels were prepared using resorcinol-formaldehyde as a precursor in two synthetic routes, one basic and one acidic, to perform the adsorption of CO 2 at 0 • C and atmospheric pressure. Aerogels were Characterization by N 2 and CO 2 Physisorption, Raman Spectroscopy, Scanning Electron Microscopy, and Infrared Spectroscopy. In general, was found that aerogels have a polymeric, disordered, three-dimensional structure and have a microporous surface. Langmuir, Freundlich, Sips and Toth equilibrium models present a good data fit of CO 2 adsorption at relative pressure ranging between 1 × 10 −4 and 3 × 10 −2 . The diffusion intra-particle kinetic model explains the setps of this process; the Elovich model also showed a good fit, therefore, there are an energetic heterogeneity of the CO 2 superficial adsorption sites. The aerogel carbonized in basic medium at 1050 • C (ACB 1050) material was the best adsorbent of this pollutant, reaching an adsorption capacity of 6.43 mmol g −1 .Achieving economic and favorable separation of CO 2 from gas mixtures represents one of the main technological and environmental problems facing our society today [10]. The most studied post-combustion technology is chemical adsorption. Monoethanol amine (MEA) has been the chemical most used for this purpose. Alternative solvents, such as piperazine and ammonia, have also been proposed to achieve this objective [6]. The advantage of this method is the low partial pressure that is used because the CO 2 molecules are easily absorbed over liquids in flue gas streams [11]. The disadvantage is that the use of amine alkoxysilanes is very expensive [12], and the method requires high regeneration energy due to the large emission of combustion gases and the costs of repairing the process equipment [4]. Other common methods to achieve CO 2 sequestration include separation in membranes, cryogenic and biological methods, and physical adsorption [13].Capture and storage technology has been considered the best option to reduce carbon dioxide emissions from large sources, and particularly adsorption is considered a promising process to separate gas mixtures [14]. This process is inexpensive, requires less regeneration energy, is easy to handle, has fast kinetics, and has a high capacity of CO 2 adsorption and selectivity [4]. The adsorbents provide a high surface area, which is a fundamental parameter in this process. Among the different adsorbents, 13X zeolite has been investigated to adsorb CO 2 by oscillating the pressure [6]. It is generally recognized that CO 2 is physically adsorbed to activated carbon, mainly by condensation or liquefaction in pores with widths that are less than 1 nm [15]. The adsorption of this greenhouse gas in nanopore materials has also been investigated in zeolites exchanged with alkali metals, amino-modified and modified alkaline, mesoporous silicas, microporous polymers, carbons, and metalorganic structures [10]. It has also been established that the chemical properties of activated carbon play a relevant role in...

Valorization of spent disposable wooden chopstick as the CO2 adsorbent for a CO2/H2 mixed gas purification

“…The Freundlich model explains a multilayer adsorption of adsorbates on the heterogeneous surface of adsorbents 46 . The adsorption energy is initially high and exponentially decreases as the degree of occupied sites increases 47 , 48 . Both nonlinear- and linearized forms of the Freundlich model are given in Table 1 .…”

Electrospun Composites Made of Reduced Graphene Oxide and Polyacrylonitrile-Based Activated Carbon Nanofibers (rGO/ACNF) for Enhanced CO2 Adsorption

“…It can be seen that all samples under investigation exhibit two characteristic peaks at 1368 cm −1 and 1612 cm −1 , which represent the D-band and G-band of graphitic materials, respectively. The presence of D-band in all samples indicates the presence of defective or disordered carbon structures [37], whilst the existence of G-band is attributed to the ordered graphitic structures with sp 2− hybridized carbon atoms [26]. The only significant different observed in Raman spectra before and after activation is the higher Raman intensity and more amorphous structure exhibited by the samples before activation.…”

“…Therefore, if the representation of t/q t versus time can be well fitted to a straight line, then it can be said that adsorption of CO 2 obeys the pseudo-second order model. This pseudo-second order model explains relatively strong interactions, chemical interactions, between the gas molecules and the adsorbent, therefore the process would be represented by a chemisorption as the rate controlling step [37]. Both k 1 and k 2 values can be obtained from the slopes of the corresponding fitted straight lines.…”

The Importance of Precursors and Modification Groups of Aerogels in CO2 Capture

“…Organic aerogels can be made from Resorcinol/Formaldehyde (RF) [ 53 , 54 , 55 , 56 ], 2,4-dihydroxybenzoic acid (DHBA)/F [ 57 ], Phenol/Formaldehyde (P/F), Melamine/F (MF) [ 58 ], Polyurethane-Dichloromethane [ 59 ], Cresol/Formaldehyde (CF) [ 60 ], RF/CTAB [ 55 ], Pararosaniline base (PAB) and 1,3,5-triformylbenzene (TFB), Phloroglucinol-formaldehyde (FPOL) [ 61 ], Phloroglucinol-terephthalaldehyde (TPOL) [ 61 ], Poly(vinyl alcohol) PVA aerogels [ 62 ], Carbon nanotubes (CNT) [ 63 ], and Graphene [ 64 , 65 , 66 , 67 , 68 , 69 , 70 ]. Different catalysts are usually used to prepare RF aerogel [ 71 ].…”