Long-Term Effect of Steam Exposure on CO₂ Capture Performance of Amine-Grafted Silica

This study investigates the hydrothermal stability of triamine-grafted CO₂ adsorbent based on a commercial-grade silica (CARiACT, P10). Grafting was conducted in dry and wet conditions at 85 °C. At optimum grafting conditions using 0.2 cm³ water and 1.5 cm³ aminosilane per gram of silica, the highest CO₂ uptake of 1.93 mmol/g at 50 °C was obtained. This material was exposed to steam at 120 °C for up to 360 h. It was observed that increasing the duration of steam exposure from 3 to 24 h reduced adsorption uptake at 25 °C by 56%. However, the CO₂ uptake reduction was much less severe at higher adsorption temperatures, reaching 21% at 50 °C and only 4% at 75 °C. Conducting steam treatment for 360 h reduced adsorption uptake at 25, 50, and 75 °C by 83, 61, and 26%, respectively. For this extreme steaming experiment, the decrease in CO₂ uptake at all adsorption temperatures was attributed to the reduction of the sorbent average pore width, increasing diffusional mass transfer resistance. The results revealed that steam exposure did not reduce the amine loading or deactivate the amine groups; however, increasing exposure time decreased the average pore width, until partial collapse of material structure. Nevertheless, the large average pore width (21 nm) of the P10 silica led to higher hydrothermal stability of the amine-grafted sorbent compared to those with ordered pore structure supports, such as SBA-15 silica

Adsorption and Desorption of Mixtures of Organic Vapors on Beaded Activated Carbon

In this study, adsorption and desorption of mixtures of organic compounds commonly emitted from automotive painting operations were experimentally studied. A mixture of two alkanes and a mixture of eight organic compounds were adsorbed onto beaded activated carbon (BAC) and then thermally desorbed under nitrogen. Following both adsorption and regeneration, samples of the BAC were chemically extracted. Gas chromatography–mass spectrometry (GC-MS) was used to quantify the compounds in the adsorption and desorption gas streams and in the BAC extracts. In general, for both adsorbate mixtures, competitive adsorption resulted in displacing low boiling point compounds by high boiling point compounds during adsorption. In addition to boiling point, adsorbate structure and functionality affected adsorption dynamics. High boiling point compounds such as <i>n</i>-decane and 2,2-dimethylpropylbenzene were not completely desorbed after three hours regeneration at 288 °C indicating that these two compounds contributed to heel accumulation on the BAC. Additional compounds not present in the mixtures were detected in the extract of regenerated BAC possibly due to decomposition or other reactions during regeneration. Closure analysis based on breakthrough curves, solvent extraction of BAC and mass balance on the reactor provided consistent results of the amount of adsorbates on the BAC after adsorption and/or regeneration

Two-Dimensional Modeling of Volatile Organic Compounds Adsorption onto Beaded Activated Carbon

A two-dimensional heterogeneous computational fluid dynamics model was developed and validated to study the mass, heat, and momentum transport in a fixed-bed cylindrical adsorber during the adsorption of volatile organic compounds (VOCs) from a gas stream onto a fixed bed of beaded activated carbon (BAC). Experimental validation tests revealed that the model predicted the breakthrough curves for the studied VOCs (acetone, benzene, toluene, and 1,2,4-trimethylbenzene) as well as the pressure drop and temperature during benzene adsorption with a mean relative absolute error of 2.6, 11.8, and 0.8%, respectively. Effects of varying adsorption process variables such as carrier gas temperature, superficial velocity, VOC loading, particle size, and channelling were investigated. The results obtained from this study are encouraging because they show that the model was able to accurately simulate the transport processes in an adsorber and can potentially be used for enhancing absorber design and operation