Optimization of CO_2 adsorption capacity and cyclical adsorption/desorption on tetraethylenepentamine-supported surface-modified hydrotalcite

The objective of this research was to investigate CO2adsorption capacity of tetraethylenepentamine-functionalized basic-modified calcined hydrotalcite（TEPA/b-c HT）sorbents at atmospheric pressure formed under varying TEPA loading levels,temperatures,sorbent weight to total gaseous flow rate（W/F）ratios and CO2concentrations in the influent gas.The TEPA/b-c HT sorbents were characterized by means of X-ray diffraction（XRD）,Fourier transform infrared spectrometry（FT–IR）,thermal gravimetric analysis（TGA）,Brunauer–Emmet–Teller（BET）analysis of nitrogen（N2）adsorption/desorption and carbon–hydrogen–nitrogen（CHN）elemental analysis.Moreover,a full 2~4factorial design with three central points at a 95%confidence interval was used to screen important factor（s）on the CO2adsorption capacity.It revealed that85.0%variation in the capacity came from the influence of four main factors and the15.0%one was from their interactions.A face-centered central composite design response surface method（FCCCD–RSM）was then employed to optimize the condition,the maximal capacity of 5.5–6.1 mmol/g was achieved when operating with a TEPA loading level of 39%–49%（W/W）,temperature of 76–90℃,W/F ratio of 1.7–2.60（g·sec）/cm^3and CO2concentration of 27%–41%（V/V）.The model fitted sufficiently the experimental data with an error range of±1.5%.From cyclical adsorption/desorption and selectivity at the optimal condition,the 40%TEPA/b-c HT still expressed its effective performance after eight cycles.

CO_2 capture performance of bi-functional activated bleaching earth modified with basic-alcoholic solution and functionalization with monoethanolamine: isotherms, kinetics and thermodynamics

CO2 capture performance of bifunctional activated bleaching earth （ABE） was investigated at atmospheric pressure. The sorbents were characterized by means of X-ray diffraction （XRD）, Brunauer-Emmett-Teller （BET）, Caron-Hydrogen-Nitrogen analysis （CHN）, Fourier transform infrared （FT-IR） and thermal gravimetric analysis （TGA）. The CO2 capacity was enhanced uia basic-modification and monoethanolamine （MEA） loading of the ABE sorbent to obtain a bifunctional surface property. Here, basic-modified calcined ABE with a 30 wt.% MEA loading （SAB-30） showed the highest CO2 capture capacity, but this was decreased with excess MEA loading （〉 30 wt.%）. At a 10% （V/V） initial CO2 concentration feed, the maximum capacity of SAB-30 increased from 2.71 mmol/g at 30~C {without adding moisture to the feed） to 3.3 mmol/g at 50℃ when adding 10% （V/V） moisture to the feed. Increasing the moisture concentration further reduced the maximum CO2 capacity due to the blocking effect of the excess moisture on the sorbent surface. However, SAB-30 could completely capture COg even in a 100% （V/V） initial CO2 concentration feed. A maximum CO2 capacity of 5.7 mmol/g for SAB-30 was achieved at 30℃. Varying the ratio of sorbent weight to total flow rate of the gas stream had no discernible effect on the equilibrium CO2 capture capacity. Avrami＇s equation and Toth＇s isotherm model provided a good fitting for the data and suggested the presence of more than one reaction pathway in the CO2 capture process and the heterogeneous adsorption surface of SAB-30. Thermodynamics studies revealed that CO2 capture on the bifunctional SAB-30 is feasible, spontaneous and exothermic in nature.