Optimization of the loading patterns of silica gels for o‐xylene recovery by vacuum swing adsorption

Abstract

The key step for the adsorption-desorption engineering process is the reversible in-situ desorption of the adsorbent without VOCs (volatile organic compounds) accumulation. Our previous results show that the mesoporous silica gel performs well in adsorbing and desorbing the VOCs due to their capillary condensation in the mesopores. However, the microporous silica performs better in adsorbing though poorer in desorbing VOCs because of the direct interaction between VOCs molecules and the adsorbent wall in the micropores. Herein, the adsorption and desorption of o-xylene on two silica gels (SG) with different pore size distribution by vacuum swing adsorption (VSA) has been systematically studied. The equilibrium adsorption and desorption experiments of two kinds of silica gels at different loading heights in fixed bed show that the concentration front of o-xylene in microporous SG disperses slowly. However, the concentration front of o-xylene in mesoporous SG is significantly dispersed. To improve the overall efficiency of adsorptiondesorption, the mesoporous and microporous SGs are loaded together in the fixed bed. It was found that the increase in the microporous SG loading percentage facilitated the adsorption capacity but deteriorated its desorption efficiency, while the opposite occurs to the mesoporous SG. After optimization, it was observed that minimal energy consumption (1.295 kWh/m 3 VOCs gas) was used when the adsorption column is loaded with 60% SG B at the inlet and 40% of the SG A at the outlet end for o-xylene vapour adsorption. This finding will be useful for designing adsorbent loading in the adsorption column.

Green synthesis of silica gel adsorbents: microwave boosts silanol groups for improved moisture uptake

“…Silanol groups, characterized by the Si-OH functional group, play a crucial role in water molecule binding and therefore, influence the material's moisture adsorption capacity. The observed increase in peak area directly translates to more available silanol sites for moisture uptake, explaining the enhanced adsorption capacity with longer irradiation times (Alsaman et al, 2022) , (Li et al, 2020).…”

Design and Synthesis of a Water-Resistant Mesoporous Silica Gel for the VOC Adsorption–Desorption Treatment

“…Different kinds of adsorbents have been used in the adsorption–desorption process, such as activated carbons, silica gels, resins, molecular sieves, etc. Silica gel, as a widely used adsorbent and dehydration desiccant, is used in the process of industrial VOC treatment because of its flame retardancy, easy regeneration, low cost, and broad resource of raw materials. , However, due to the presence of a large number of hydroxyl groups on the surface of silica gel, the adsorption of VOCs will be highly influenced by the existence of water vapor. The water will not only produce competitive adsorption with adsorption VOCs, resulting in the reduction of silica gel adsorption capacity .…”