Probing sub-5 Ångstrom micropores in carbon for precise light olefin/paraffin separation

Abstract

Olefin/paraffin separation is an important but challenging and energy-intensive process in petrochemical industry. The realization of carbons with size-exclusion capability is highly desirable but rarely reported. Herein, we report polydopamine-derived carbons (PDA-Cx, where x refers to the pyrolysis temperature) with tailorable sub-5 Å micropore orifices together with larger microvoids by one-step pyrolysis. The sub-5 Å micropore orifices centered at 4.1–4.3 Å in PDA-C800 and 3.7–4.0 Å in PDA-C900 allow the entry of olefins while entirely excluding their paraffin counterparts, performing a precise cut-off to discriminate olefin/paraffin with sub-angstrom discrepancy. The larger voids enable high C2H4 and C3H6 capacities of 2.25 and 1.98 mmol g−1 under ambient conditions, respectively. Breakthrough experiments confirm that a one-step adsorption-desorption process can obtain high-purity olefins. Inelastic neutron scattering further reveals the host–guest interaction of adsorbed C2H4 and C3H6 molecules in PDA-Cx. This study opens an avenue to exploit the sub-5 Å micropores in carbon and their desirable size-exclusion effect.

pH‐Regulated Refinement of Pore Size in Carbon Spheres for Size‐Sieving of Gaseous C8, C6 and C3 Hydrocarbon Pairs

“…When decreasing the pH further to 1.0, C‐HC‐1 showed complete size‐exclusion of C 3 H 8 from C 3 H 6 with the superior separation factor of 22.0, implying that its pore size almost lies between the kinetic diameters of C 3 H 6 (4.7 Å) and C 3 H 8 (4.9 Å) with a variation of 0.2 Å (Figure 5c). The remarkable separation factor of C‐HC‐1 (22.0) can be comparable with reported state‐of‐the‐art carbonaceous materials, including PDA‐C800 (34.7), [2c] CDMOF‐2‐700 (14.5) [41] and SCMS‐0.2‐800 (30.5), [42] though a moderate amounts of crystalline solids have ever been reported for size‐sieving C 3 H 6 /C 3 H 8 pair, as shown in Table S5. The C 3 H 6 uptake of C‐HC‐1 could reach up to 75.6 mg g −1 at 1.0 bar and 298 K. Above results demonstrate that the fine‐tuning ultramicropore size of C‐HC‐ x , along with the advantageous narrow PSD, enable molecular sieving of industrial important C 8 , C 6 and C 3 hydrocarbon pairs.…”

Construction of Boron‐ and Nitrogen‐Enriched Nanoporous π‐Conjugated Networks Towards Enhanced Hydrogen Activation

“…To understand the ultramicroporous feature of the material, taking BN-NCN-750 as an example, CO 2 was used as the probe molecule to study the porosity information below 0.7 nm. [49] The CO 2 adsorption/desorption isotherms of BN-NCN-750 was collected at 195 K (Figure S9). The surface area of BN-NCN-750 was calculated to be 1502 m 2 g À 1 , and according to the pore size distribution curve obtained via the Horvath-Kawazoe (H-K) method, ultra-micropores in the range of 3.2-10.5 Å existed in the scaffolds.…”

“…Among them, BN‐NCN‐650 contained the highest total pore volume (0.34 cm 3 g −1 ), with 67 % being contributed by the micropores (Table S4). To understand the ultra‐microporous feature of the material, taking BN‐NCN‐750 as an example, CO 2 was used as the probe molecule to study the porosity information below 0.7 nm [49] . The CO 2 adsorption/desorption isotherms of BN‐NCN‐750 was collected at 195 K (Figure S9).…”

Sub-nm Pore Size of Phenylethynyl End-Capped Imide Oligomer-Derived Carbon for Molecular Sorption and Separation

“…Carbon molecular sieves (CMSs) have attracted much attention in recent years due to their great potential in the development of next-generation separation technologies for gases and liquids, which account for 10–15% of the global energy consumption. − Specifically, membrane-based separations can lead to an order of magnitude improvement in energy efficiency compared to conventional thermal-based processes. − Molecular sieving separation enabled by CMSs is controlled via thermodynamic partitioning and diffusion kinetics, which provides opportunities for complementary molecular diffusion and sorption selectivity through CMS engineering, such as developing uniform pore channels and heteroatom doping of the carbon framework . However, fabrication of ordered sub-nm porous structures in carbonaceous materials remains challenging, as uncontrollable defect formation that occurs during the carbonization step can cause a broad pore size distribution (PSD) below 1 nm …”