CO2-Selective Capture from Light Hydrocarbon Mixtures by Metal-Organic Frameworks: A Review

Abstract

CO2 represents a typical impurity in light hydrocarbon feedstocks, which affects the quality of subsequent chemical products. Owing to their highly similar nature, industrial separation requires large amounts of energy. Adsorptive gas separation based on porous materials is considered an efficient alternative, as it can offer faster kinetics, higher selectivity, long-term stability and more energy-efficient regeneration. For the adsorption separation method, preferential CO2 capture from gas mixtures in one step is more energy-efficient for direct purification than light hydrocarbons, saving about 40% energy by eliminating energy-intensive post-regeneration processes such as countercurrent vacuum blowdown. Therefore, CO2-selective adsorbents are more sought-after than light hydrocarbon-selective adsorbents. Metal-organic frameworks (MOFs) have been demonstrated as outstanding physisorbents for CO2 capture due to their configurable channels for CO2 recognition, structural flexibility and large specific surface area. Many highly selective CO2 adsorption behaviors of MOFs have been reportedly achieved by precise modulation of pore size, pore chemistry or structural flexibility. In this review, we discuss the emerging development of MOFs for CO2-selective capture from different light hydrocarbon mixtures. The challenges of CO2 recognition and the strategies employed to achieve CO2 selectivity over light hydrocarbon mixtures by MOFs are summarized. In addition, the current challenges and prospects in the field of MOFs for CO2 capture are discussed and elaborated.

Turning Normal to Abnormal: Reversing CO2/C2‐Hydrocarbon Selectivity in HKUST‐1

“…The uptake ratios (UR) at 1 bar for CO 2 /C 2 H 6 , CO 2 /C 2 H 4 , CO 2 /C 2 H 2 , and CO 2 /CH 4 are 41, 15.5, 4, and 50, respectively, which outperform many materials previously recognized for their CO 2 preference over hydrocarbons ( Table 1 ; Figures S3,S4, Supporting Information). [ 4 ] Ideal Adsorbed Solution Theory (IAST) calculations revealed that FS‐CuBTC UM exhibits superb CO 2 over hydrocarbon selectivities at 1 bar and 298 K as shown in Table 1, Tables S3,S4, Figures S9–S16 (Supporting Information). Interestingly, a striking improvement in CO 2 over C 2 H 6 selectivity was observed in FS‐CuBTC UM ( S UR = 41 and S IAST(50:50) = 4416) at 298 K and 1 bar, surpassing the performance of benchmark materials, MUF‐16 (15.6 and 600), [ 15 ] and [Zn(odip) 0.5 (bpe) 0.5 ] (4.3 and 27.9).…”

“…Metal–organic frameworks (MOFs) have been extensively studied in this regard, demonstrating selective adsorption of hydrocarbons over CO 2 “normal selectivity” using mechanisms like acid–base interactions, hydrogen bonds, functional groups, and open metal sites. [ 4 ] However, the rapid filling of the material by the dominant hydrocarbon component leads to time lags and necessitates two energy‐intensive steps: adsorption followed by desorption.…”

Series of Cadmium-Organic Frameworks Based on Mixed Flexible and Rigid Ligands: Single-Crystal-to-Single-Crystal Transformations, Sorption, and Luminescence Properties

“…At the same time, compound 1 demonstrated extremely low C 2 H 6 uptake in the studied pressure range and therefore remarkable selectivity for C 2 H 4 /C 2 H 6 and C 2 H 2 /C 2 H 6 mixtures (see Table S4 for comparison with the most representative MOFs). Moreover, the C 2 H 6 uptake is even significantly lower than the CO 2 uptake, which is interesting for light hydrocarbon purification from carbon dioxide contaminants . Taking into account also the observed step adsorption (so-called “gate-opening effect”), high efficient separations of gas flows can be reached on both compounds 1 and 2 due to differences in gate-opening pressures.…”

“…Moreover, the C 2 H 6 uptake is even significantly lower than the CO 2 uptake, which is interesting for light hydrocarbon purification from carbon dioxide contaminants. 18 Taking into account also the observed step adsorption (so-called "gate-opening effect"), high efficient separations of gas flows 19 can be reached on both compounds 1 and 2 due to differences in gate-opening pressures.…”