Study of rice husk ash derived MCM-41-type materials on pore expansion, Al incorporation, PEI impregnation, and CO2 adsorption

Abstract

Conventional MCM-41 (M41), silica-pure pore-expanded MCM-41 (PM41), and Al-containing pore-expanded MCM-41 (PM41Ax) were synthesized from rice husk ash and tested as polyethyleneimine (PEI) supports for CO 2 capture. Samples were characterized by small-angle X-ray diffraction, X-ray fluorescence spectroscopy, scanning electron microscopy, Fourier transform infrared spectroscopy, granulometric analysis, and nitrogen adsorption techniques. The PEI loading rate and CO 2 adsorption-desorption performance were determined via thermogravimetric analysis. The effects of pore expansion, heteroatom Al incorporation, PEI loading rate, and Si/Al ratio on CO 2 adsorption performance were examined. For the first time, the amount of PEI impregnated in PM41 was increased beyond 55 wt%, and the low-Si/Al-ratio PM41Ax support was used to load PEI in a novel procedure. Results show that at the same PEI loading rate, PM41 is always superior to M41 regarding adsorption capacity and adsorption rate. For a PEI loading rate >50 wt%, the superiority is amplified, reaching 15.9% and 21.3%, respectively. The use of the high-Al-containing PM41Ax support further increases adsorption capacity and adsorption rate by 13.4% and 9.6%, respectively. The presented reaction has a hybrid adsorption characteristic that includes both chemisorption and physisorption. Avrami’s fractional-order kinetic model describes the adsorption best. Over the entire time scale, the adsorption rate is determined by several kinetic diffusion-controlled processes. The intraparticle diffusion and equilibrium adsorption are two predominant rate-limiting steps, and their control ranges change with temperature. After five cycles of adsorption and desorption, the desorption ratio was as high as 99%, and the working capacity still retained 96.5% of the original capacity. In addition, the presence of water vapor increased the adsorption capacity of the adsorbents presented in this study. These advantages make them successful iin capturing CO 2 in the post-combustion scenario.

Evaluating solid sorbents for CO2 capture: linking material properties and process efficiency via adsorption performance

“…Alongside surface area and pore morphology, surface chemistry can strongly influence CO 2 adsorption capacity, interaction strength, and selectivity. Examples of rational tuning of surfaces include enhancing hydrophobicity (Piscopo and Loebbecke, 2020;Sáenz Cavazos et al, 2021) and amine-functionalization (Vilarrasa-García et al, 2015;Ünveren et al, 2017;Zhang and Du, 2022). The dispersive and specific chemical contributions to surface energy, and by extension a metric of hydrophobicity, can be determined by conducting liquid contact angle (Kozbial et al, 2014) or inverse gas chromatography measurements (Hamieh et al, 2020) using several fluid probes with different chemistries.…”

“…Starting with CO 2 adsorption capacity, the adsorbent surface area and pore morphology parameters typically affect material suitability in CO 2 capture applications. For free-standing physiand chemi-sorbents, these properties can directly influence CO 2 uptake by increasing the number of available sites for CO 2 to interact with (Alazmi et al, 2018;Akpasi and Isa, 2022); while for amine-functionalized chemisorbents, the degree of amine grafting or impregnation, and the subsequent accessibility of these amines strongly depends on the support's morphology (Franchi et al, 2005;Vilarrasa-García et al, 2015;Zhang and Du, 2022). Aside from CO 2 adsorption capacity, the rate at which the CO 2 molecules diffuse through solid sorbents and adsorb on active sites is important to determine process parameters like cycle time and overall process productivity (Wu et al, 2022).…”

Impregnation of Fe³⁺ into MCM-41 Pores: Effect of Fe³⁺ Concentration on the Weight Percent of Fe-Frameworks and Fe-Non-Frameworks

“…In general, silica precursors such as tetraethyl orthosilicate (TEOS) [5][6][7] and sodium silicate [8][9][10][11] are used in the synthesis of MCM-41, which is relatively expensive. Iron ore tailing [12][13], siliceous sugar industry waste [14], silicon carbide sludge and granite sludge [15], bentonite [16] and rice husk ash [17][18][19] have all been investigated for use as a silica precursor in the manufacture of MCM-41 to minimize production costs. Rice husk ash (RH) is the most potent natural substance because it contains SiO 2 at concentrations of over 90% [20][21][22].…”