Enhanced gas separation performance of 6FDA-DAM based mixed matrix membranes by incorporating MOF UiO-66 and its derivatives

Abstract

Functionalization and post-synthetic modification (PSM) of metal-organic frameworks (MOFs) are two important routes to obtain MOFs with full potential in mixed matrix membrane (MMM) fabrication. We synthesized UiO-66 and two derivatives UiO-66-NH 2 and UiO-66-NH-COCH 3 with less than 50 nm particle size. The CO 2 uptakes at 10 bar in the two functionalized UiO-66s were improved by 44% and 58%, respectively, with respect to the pristine solid. The MOF nanoparticles were incorporated into the highly permeable polymer 6FDA-DAM, making MMMs with 5-24 wt% particle loadings. All fillers and membranes were characterized accordingly, and their gas separation performances were evaluated by feeding CO 2 /CH 4 equimolar mixtures at 2 bar pressure difference at 35°C. CO 2 permeability (P CO2) of pristine 6FDA-DAM (P CO2 = 997 ± 48 Barrer, α CO2/CH4 = 29 ± 3) increased by 92% with 20 wt% UiO-66 loading, while maintaining the CO 2 /CH 4 selectivity. Improvements of 23% and 27% were observed for P CO2 with the same 20 wt% loading of UiO-66-NH 2 and UiO-66-NH-COCH 3 , respectively. The α CO2/CH4 was improved up to 16% using both functionalized UiO-66 type MOFs. The best separation performance in this work was obtained with 14 wt% UiO-66 MMM (P CO2 = 1912 ± 115 Barrer, α CO2/CH4 = 31 ± 1), 16 wt% UiO-66-NH 2 MMM (P CO2 = 1223 ± 23 Barrer, α CO2/CH4 = 30 ± 1) and 16 wt% UiO-66-NH-COCH 3 MMM (P CO2 = 1263 ± 42 Barrer, α CO2/CH4 = 33 ± 1) at 2 bar feed pressure difference. The measurement was also conducted with various binary compositions (CO 2 = 10-90%), both at low and high pressures up to 40 bar at 35°C, showing no pressure-related CO 2-induced plasticization. The atomistic modelling for the MOF/polymer interface was consistent with a moderate MOF surface coverage by 6FDA-DAM which did not play a detrimental role in the membrane performance. with improved permeation and selectivity have been described extensively, including the very promising approach of mixed matrix membranes (MMMs) [5]. MMM technology exploits the distinct and complementary properties of both polymer and inorganic materials with different physicochemical properties, selectivity and permeation flux for their selective separation. Various materials, generally porous, such as carbon molecular sieves (CMS) [6,7], zeolites and silicas [7,8], metal oxides [9], carbon nanotubes (CNTs) [10], metal organic frameworks (MOFs) [11-14], graphene [15,16], etc. have been embedded in continuous polymer

Hydrogen‐Bonded Polyimide/Metal‐Organic Framework Hybrid Membranes for Ultrafast Separations of Multiple Gas Pairs

“…In fact, literatures show that mixed gas permeation could yield relatively better performance than pure gas permeation at low feeding pressures . Experimental results were summarized in Figure , compared with literatures7c,12c,d,13,14,15b,16,25 (Tables S4–S6). As illustrated in Figure a–d, the introduction of MOFs increases the gas permeabilities (CO 2 and H 2 ) noticeably and an intrinsic selectivity is attained at a loading as high as 55 wt%.…”

“…More significantly, despite this potential, only a handful of MOF‐based hybrid membranes have performed at or beyond current Robeson upper bounds. Furthermore, the few successful cases, like CO 2 /CH 4 ,12c predominantly rely upon rigid PIMs7c,14a,15 or an aggressive thermal annealing process, adding complications which hinder practical applicability 14a. In addition, most hybrid membranes reported are limited in scope and highly optimized for a particular gas pair (e.g., CO 2 /CH 4 , C 2 , or C 3 ), thus lacking a more general approach to accommodate multicomponent gas mixture separations.…”

“…The surface area of these MOFs has been reported as high as 1135 g cm −3 ; incorporation of this MOF with amino moieties imparts preferential adsorption of particular gases to the membrane. Attempts using UiO‐66‐NH 2 to fabricate hybrid membranes were made previously,14a,16,19 however, these membranes suffered from above‐mentioned challenges of performance and durability. For instance, most of those reports used rigid PIMs 12d.…”

“…For instance, most of those reports used rigid PIMs 12d. 6FDA‐DAM was selected but involved aggressive heating treatment of 180 °C; polysulfone and ODPA‐DAM (ODPA = 4,4′‐oxidiphthalicanhydride) were used but the resultant membranes performed below the current Robeson upper bounds and were only specialized for CO 2 separations 19a,b. To overcome these challenges, we judiciously selected a carboxylic polyimide, so‐called 6FDA‐DAM:DABA (3:2) (6FDA = 4,4′‐ (hexafluoroisopropylidene)diphthalic anhydride; DAM = 2,4,6‐ trimethyl‐1,3‐diaminobenzene; DABA = 3,5‐diaminobenzoic acid) as the organic constituent as this polymer combines high permeability and selectivity with tunable chemical functionalities, i.e., hydrophilic carboxylic groups (Scheme S1 and Table S1, Supporting Information).…”

A Review on Computational Modeling Tools for MOF-Based Mixed Matrix Membranes

“…Molecular simulations demonstrated that CO 2 molecules generally tend to accumulate in the micro-voids at the MOF/polymer interface. Coronas's group [111] also combined experiments and molecular simulations to examine a 6FDA-DAM-based MMM with a different MOF filler, UiO-66, and reported enhanced gas separation performance of the MMM. Zhao et al [112] incorporated MOF nanosheets, NUS-8, into PIM-1 to prepare MMMs.…”