Recent Advances in Carbon-Based Adsorbents for Adsorptive Separation of Light Hydrocarbons

Abstract

Light hydrocarbons (LHs) separation is an important process in petrochemical industry. The current separation technology predominantly relies on cryogenic distillation, which results in considerable energy consumption. Adsorptive separation using porous solids has received widespread attention due to its lower energy footprint and higher efficiency. Thus, tremendous efforts have been devoted to the design and synthesis of high-performance porous solids. Among them, porous carbons display exceptional stability, tunable pore structure, and surface chemistry and thus represent a class of novel adsorbents upon achieving the matched pore structures for LHs separations. In this review, the modulation strategies toward advanced carbon-based adsorbents for LHs separation are firstly reviewed. Then, the relationships between separation performances and key structural parameters of carbon adsorbents are discussed by exemplifying specific separation cases. The research findings on the control of the pore structures as well as the quantification of the adsorption sites are highlighted. Finally, the challenges of carbonaceous adsorbents facing for LHs separation are given, which would motivate us to rationally design more efficient absorbents and separation processes in future.

Figure 1

(a) The development of the field of “carbon materials” and “crystalline materials” on light hydrocarbons separation in the last two decades (web of science until March. 2022). (b) The research timeline on the development of porous carbons with defined pore structures.

Figure 2

Proposed mechanisms for the adsorptive separation of LHs. (a) Thermodynamic effect. (b) Kinetic effect. (c) Molecular sieving effect.

Figure 3

(a) The ultramicropore formation process for the starch-based carbon adsorbents (SC-M) by using the alkali metal ion-exchange method. (b) The schematic diagram of the microstructure. (c, d) Pore size distribution of SC-M [70]. (e) Synthesis schematic of starch-based carbon molecular sieve (SCMS) [71].

Figure 4

(a) Schematic illustration of the synthesis for the polymer nanoplates. (b) SEM image of FCP-1. (c) Pore size distribution. (d) Gas adsorption isotherms and (e) breakthrough profile of x/CH₄ (10/90 v/v, X = CO₂, C₂H₆, C₃H₈) of FCP-1-KC at 298 K and 1 bar [63]. (f) Schematic illustration of the synthesis process. (g) N₂ adsorption isotherms. (h) LHs adsorption isotherms. (i) IAST selectivity and (j) breakthrough simulation profile in an equimolar 6-component CH₄/C₂H₂/C₂H₄/C₂H₆/C₃H₆/C₃H₈ mixture [93].

Figure 5

(a) Schematic illustration of O and N interaction sites in porous carbon and (b) corresponding binding energy of C₂H₄/C₂H₆ with different interaction sites. (c) FTIR spectra of samples [30]. (d) Interaction between C₂H₄/C₂H₆ and the Csp² and N/O-Csp² single layers. (e) The interaction energy between C₂H₄/C₂H₆ and different pore sizes of Csp² and N/O-Csp² double carbon layer is referred to as that of the Csp², N/O-Csp² single carbon layers [98]. (f) Schematic structures and Schwarzite models of samples. (g) Adsorption isotherms of beta-ZTC at 303 K [96].

Figure 6

(a) Simplified chemical structure of cation exchange resin: monosulfonated polystyrene. (b) Pore size distribution. (c) The pressure drops of C₃H₆ (top) and C₃H₈ (middle) and the ratio of the two (bottom) during adsorption at different carbonization temperatures. (d) Time-resolved adsorption curve for CMS samples with different carbonization temperatures [117]. (e) Illustration of the proposed mechanism for C₃H₆/C₃H₈ separation in MC-wiggle. (f) Pore size distributions. (g) Time-resolved absorption curves for C₃H₆/C₃H₈ at 298 K [119].