MIL-101(Cr) Polymeric Fiber Adsorbents for Sub-Ambient Post-Combustion CO₂ Capture

Abstract

In this work, the development of a new metal−organic framework (MOF) fiber adsorbent for application to sub-ambient CO 2 capture is discussed. MIL-101(Cr), a large pore (27 and 34 Å) MOF, provides unique advantages for this application as it has good water stability and high capacity for CO 2 at sub-ambient conditions. The synthesis of MIL-101(Cr) was scaled to ∼20-g scales to facilitate fiber spinning, and the fibers were successfully manufactured up to 50 wt % loading of the MOF at rates up to 25 m/min. A variety of dynamic adsorption experiments, including sub-ambient fixed bed breakthroughs, high and ambient pressure helium-sweep desorption, and preliminary single-bed PSA cycles, were performed to better understand the performance of these fiber adsorbents for application to sub-ambient CO 2 capture. Breakthrough and pseudoequilibrium capacities showed this promising fiber adsorbent retained its exceptionally high sub-ambient CO 2 capacity under realistic PSA conditions, while desorption experiments showed there was some promise for the collection of a high-purity vacuum product in real cycles. Preliminary single-bed PSA cycles showed some promise while also proving much work needs to be done with cycle design to reach the required performance for post-combustion CO 2 capture.

Support Pore Structure and Composition Strongly Influence the Direct Air Capture of CO2 on Supported Amines

“…As discussed in this article, observation of bicarbonate formation on solid-supported amines under humid CO 2 capture conditions is challenging with in situ FT-IR. Finally, this study evaluated powder materials, and any scalable, low pressure drop contactor design will need to incorporate such materials into alternate forms, such as fibers, monoliths, or other structures, which may result in deviations in amine-surface interactions from those found in powder studies. − …”

Elucidating Improvements to MIL‐101(Cr)’s Porosity and Particle Size Distributions based on Innovations and Fine‐Tuning in Synthesis Procedures

“…[ 66 ] On the other hand, HNO 3 ‐MIL‐101(Cr) has reaction mixtures with molar ratios of Cr:H 2 BDC:HNO 3 :H 2 O = 1:1:1:277 [ 12,69,73,88 ] or 1:1:1:265. [ 18,31,72 ] The reaction conditions for HCl‐MIL‐101(Cr) and HNO 3 ‐MIL‐101(Cr) bear close semblance to the HF‐based syntheses at 200–220 °C for 8, [ 12,17,18,55,62,70,72,74 ] 10, [ 59,65,82 ] 12, [ 57,60,64,66,71 ] or even 15 h. [ 68,81,86,87 ] Reports suggest that using HCl instead of HF reduces the MIL‐101(Cr) particle sizes (e.g., decreasing from 500–1500 to 200–1200 nm) [ 17 ] whereas replacing HF with HNO 3 seems to increase MIL‐101(Cr) crystallite sizes (e.g., increasing from 560–1100 to 720–1490 nm). [ 31,69 ] Specifically, by lowering the pH of the reaction mixture, HNO 3 reduces the crystal nucleation speeds to form larger crystallites.…”

“…Replacing HF with mineral acids that penetrate tissues less readily [16] is an alternative. MIL-101(Cr) syntheses using hydrochloric acid (HCl), [17,55,[57][58][59][60][61][62][63][64][65][66][67] nitric acid (HNO 3 ), [12,18,31,[68][69][70][71][72][73][74][75][76][77][78][79][80][81][82][83][84][85][86][87] and even sulfuric acid (H 2 SO 4 ) [12] as mineralizers have been reported. [11] Although HCl is a stronger acid than HNO 3 , H 2 SO 4 , and HF (Table 3), MIL-101(Cr) synthesized using HCl (denoted HCl-MIL-101(Cr)) in molar ratios such as 1 Cr:1 H 2 BDC:1 HCl:266 H 2 O remains highly crystalline.…”

A multifunctional rooftop unit for direct air capture

“…It has been widely used to evaluate the CO 2 absorption and desorption behavior of a sorbent. 50,51 The TGA and evolved gas analyses were performed using a TGA 5500 (TA Instruments) coupled with a quadrupole mass spectrometer with a Faraday detector (Cirrus 3, MKS Instruments). Samples between 3 and 7 mg were loaded into Pt pans and allowed to equilibrate at 30 °C.…”