RESUMO

The membranes' role is of supreme importance in the separation of compounds under different phases of matter. The topic addressed here is based on the use of membranes on the gases separation, specifically the advantages of mixed-matrix membranes (MMMs) when using carbon nanotubes as fillers to separate carbon dioxide (CO2) from other carrier gas. MMMs consist of a polymer support with additive fillers to improve their efficiency by increasing both selectivity and permeability. The most promising fillers in the MMM development are nanostructured molecules. Due to the good prospects of carbon nanotubes (CNTs) as MMM fillers, this article aims to concentrate the advances and developments of CNT-MMM to separate gases, such as CO2. The influence of functionalized CNT or mixtures of CNT with additional materials such as zeolites, hydrogel and, graphene sheets on membranes performance is highlighted in the present work.

RESUMO

Physical adsorption on activated carbons has shown to be a very attractive methodology for CO2 separation from flue gas streams and biogas. In this context, the goal of this work was to prepare granular activated carbons intended for CO2 adsorption from an abundant and low-cost biomass residue (coconut shell) by using practical and cost-effective procedures. By the first time, parameters involved in chemical activation with dehydrating agents (H3PO4 or ZnCl2) and/or physical activation with CO2 were systematically screened in depth in order to obtain materials with improved performance for CO2 adsorption on a volume basis. Compared with the commonly used mass basis, the data expressed on a volume basis are very important for industrial applications because they permit to estimate the efficiency of a fixed bed adsorption column. The work permitted to prepare granular activated carbons with a blend of relatively high gravimetric CO2 uptake and bulk density, so that high volumetric CO2 uptakes were attained. The highest values were 2.67 and 1.17 mmol/cm3 for CO2 pressures of 1.0 and 0.15 bar, respectively. It is remarkable that the obtained results were similar to those reported by other authors for carbons chemically activated with KOH, the activation methodology that has been widely claimed as the one that produce ACs with the best performances for CO2 adsorption, but which involves severe restrictions. Therefore, the present work can be considered a very important step in paving the way toward making CO2 adsorption an each time more interesting technology to reduce the emissions of anthropogenic greenhouse gases.

RESUMO

CO2 separation from natural gas is considered to be a crucial strategy to mitigate global warming problems, meet product specification, pipeline specs and other application specific requirements. Silica xerogels (SX) are considered to be potential materials for CO2 capture due to their high specific surface area. Thus, a series of silica xerogels functionalized with imidazolium, phosphonium, ammonium and pyridinium-based room-temperature ionic liquids (RTILs) were synthesized. The synthesized silica xerogels were characterized by NMR, helium pycnometry, DTA-TG, BET, SEM and TEM. CO2 sorption, reusability and CO2/CH4 selectivity were assessed by the pressure-decay technique. Silica xerogels containing IL demonstrated advantages compared to RTILs used as separation solvents in CO2 capture processes including higher CO2 sorption capacity and faster sorption/desorption. Using fluorinated anion for functionalization of silica xerogels leads to a higher affinity for CO2 over CH4. The best performance was obtained by SX- [bmim] [TF2N] (223.4 mg CO2/g mg/g at 298.15 K and 20 bar). Moreover, SX- [bmim] [TF2N] showed higher CO2 sorption capacity as compared to other reported sorbents. CO2 sorption and CO2/CH4 selectivity results were submitted to an analysis of variance and the means compared using Tukey's test (5%).

Assuntos

Líquidos Iônicos , Dióxido de Silício , Ânions , Dióxido de Carbono , Cátions

RESUMO

Physical immobilization of ionic liquids (ILs) in solid materials appears as an interesting strategy for the development of new sorbents for CO2 separation from natural gas. In this work the effect of physical immobilization of two ionic liquids with different anions (bmim[Cl] and bmim[OAc]) on two mesoporous supports (commercial silica SBA-15 and silica extracted from rice husk) was evaluated for CO2 separation from natural gas by experimental determination of CO2 sorption, CO2/CH4 selectivity and sorption kinetics. Results showed that the pure supports present the greatest CO2 sorption capacity when compared to immobilized ILs. However, CO2 removal efficiency improves considerably in the CO2/CH4 mixture when ILs are immobilized in these supports. The best selectivity results were obtained for supports immobilized with the IL bmim[Cl] and values increased for SIL-Cl by 37% and SBA-Cl 51% when compared with their respective supports. The contribution of SIL-Cl (3.03 ± 0.12) to separation performance (CO2/CH4) is similar to SBA-Cl (3.29 ± 0.39). ILs supported also presented fast sorption kinetics when compared to pure ILs thus being an interesting alternative in the search for highly efficient and low-cost separation processes.