Search

In this study, two configurations of Temperature Swing Adsorption (TSA) were assessed with the aim of evaluating their efficacy on CO2 capture on commercial adsorbent zeolite 13X within a post-combustion scenario. A fixed bed setup was employed to measure breakthrough curves from the adsorption and desorption steps. Considering a dry desulfurized flue gas stream, breakthrough curves for CO2–N2 (15/75 % v/v) in Helium were performed at 25, 50 and 75 °C. The desorption step was carried out following two TSA regeneration strategies: a two-step desorption arrangement (configuration 1) consisting of a purging phase followed by a heating-purging phase, and a one-step desorption arrangement (configuration 2) involving only the heating-purging phase. Adsorption equilibrium isotherms were also obtained for pure CO2 (25, 50, 75, 100 and 125 °C) and N2 (25, 50 and 75 °C) on zeolite 13X in the range of 0–1 bar. Finally, a mathematical model considering mass and energy differential balances was used to predict the whole adsorption-desorption history. The results obtained on breakthrough curves showed that CO2 separation from N2 on zeolite 13X is accomplished by adsorption under the studied conditions with a marked selectivity for CO2. In regards to the desorption phase, configuration 1 may not be adequate for an integration of adsorption-desorption steps once only the purge phase duplicates the desorption time as compared to the adsorption stage. On the other hand, configuration 2 is more likely to synchronize the whole adsorption—desorption process since the regeneration time was significantly reduced by this strategy. However, configuration 1 managed to obtain full CO2 recovery with all the temperatures tested during the heating step, whereas configuration 2 reached recovery values around 92%. Moderate temperatures (e.g. 125–150 °C) are feasible to be used for configuration 2 regeneration strategy so as to avoid energy penalties. Simulations were able to reproduce well the experimental breakthrough curves, even though some discrepancies were observed in the desorption histories.

In view of the promising applicability of adsorption to the capture of CO2 from post-combustion gases, the use of mesoporous silica functionalized with 3-aminopropyltriethoxysilane (APTES) was studied as adsorbent in a fixed bed for CO2–N2 separation under thermal swings. Characterization of the adsorbent performed before and after functionalization indicated that amine grafting was successful. Additionally, CO2 adsorption on a magnetic suspension balance showed a significant increase in uptake of the APTES-functionalized sample over the support, mainly at low relative pressures. Relatively high values of adsorption enthalpy suggest the occurrence of chemical adsorption attributed to CO2 bonding with the amines. Breakthrough curves were measured for pure CO2, N2 and the CO2/N2 (15/75% v/v) mixture, which showed good agreement with respect to the uptake of the individual gases, as determined from gravimetric tests. Full CO2 desorption from the bed required a temperature rise, which suggests that these materials may be suitable for TSA cyclic processes. A temperature of 90 °C was enough for a complete regeneration of the adsorbent during the desorption phase under dynamic conditions. The material showed very stable behavior after 20 successive cycles.

Pure component adsorption equilibrium of CH4 and CO2 on activated carbon have been studied at three different temperatures, 298, 323, and 348 K within a pressure range of 10–2000 kPa. Binar...

The increasing worldwide demand for energy bound to a strong dependence of fossil fuels has considerably intensified the concentration of greenhouse gases in the atmosphere, reaching alarming levels. Among those gases, carbon dioxide is considered the main responsible for global warming due to its higher concentration. In order to mitigate the negative effects of global warming and to reduce emissions, many technologies have been developed in the last decades to separate and recover carbon dioxide (CO 2 ) at different capture scenarios. Adsorption processes rely on the use of highly porous solids such as activated carbons, which are either commercially. Pressure Swing Adsorption (PSA) is a cyclic adsorption process, which allows continuous separation of gas streams. PSA is performed by periodic changes of pressure aiming the optimization of contaminants removal and is considered viable for separation of CO 2 from flue gases containing about 5-15% v/v. To achieve a certain performance, a PSA process may consist of several steps, columns and cycle time. One of the most basic configurations comprises four steps: pressurization, feed, blowdown and purge. The performance of a PSA process is usually evaluated by the purity, recovery and productivity reached. This study presents experimental and simulated data obtained from a bench-scale PSA, with a maximum pressure of 6 bar for pressurization and feed steps and minimum of 1 bar for blowdown and purge steps. The unit was tested with a mixture containing 85% of N 2 and 15% of CO 2 (on a molar basis). Carbon dioxide and nitrogen breakthrough curves were obtained under typical conditions of post combustion capture. A mathematical-phenomenological model combining momentum, mass and heat balances and using the Linear Driving Force approach (LDF) for mass transport and Langmuir model for equilibrium was applied in this study to simulate the dynamic behavior of the process. The performance tests presented productivity of 15 mol h -1 kg-ads -1 and, according to the changes of step time, N 2 purity of 97.7%. The model predicted reasonably the breakthrough curves and temperature profiles, with more precision for the latter. The combination of the simulation tool with and experimental PSA unit is very valuable for a deeper understanding of the involved phenomena and helpful with the design of optimized and efficient CO 2 adsorption-based capture processes.