Enhanced CO2/CH4 separation performance of BTDA-TDI/MDI (P84) copolyimide mixed-matrix membranes by incorporating submicrometer-sized [Ni3(HCOO)6] framework crystals

doi:10.1016/j.jngse.2019.103123

Journal of Natural Gas Science and Engineering

Volume 75, March 2020, 103123

https://doi.org/10.1016/j.jngse.2019.103123 Get rights and content

Highlights

•
[Ni₃(HCOO)₆] frameworks were incorporated into P84 matrix to separate CO₂/CH₄.
•
Defect-free MMMs were prepared and characterized at 7 wt% and 15 wt% loadings.
•
CO₂/CH₄ separation performance was obviously enhanced for the defect-free MMMs.
•
The pore blockage of [Ni₃(HCOO)₆] frameworks was profitable for gas separation.

Abstract

The incorporation of metal-organic frameworks (MOFs) into mixed-matrix membranes (MMMs) is gaining widespread attention because of the combined advantages of easy processability and superior separation performance. In this paper, submicrometer-sized [Ni₃(HCOO)₆] frameworks were incorporated into BTDA-TDI/MDI (P84) matrix as filler material to separate CO₂ from CH₄. When the loadings of [Ni₃(HCOO)₆] frameworks in MMMs were 7 and 15 wt%, obvious enhancements in gas separation properties were obtained. Especially at the loading of 15 wt%, CO₂ permeability and the CO₂/CH₄ selectivity increased 76% (from 0.72 Barrer to 1.26 Barrer) and 52% (from 44 to 67), respectively, compared with the pristine P84 membrane. The partial pore blockage was found by the high-pressure gravimetric adsorption measurements and it was deemed to be profitable to separate CO₂/CH₄. In order to better understand the gas separation behavior, the characterizations of [Ni₃(HCOO)₆] frameworks (XRD, SEM, Ar adsorption-desorption, CO₂ and CH₄ adsorption, ATR-FTIR, TGA) and P84/[Ni₃(HCOO)₆] MMMs (SEM, ATR-FTIR, XRD, TGA, stress–strain tests) were performed.

Graphical abstract

Section snippets

Author contributions section

Lujie Sheng: Conceptualization, Methodology, Formal analysis, Investigation, Writing-Original draft preparation, Ya Guo: Methodology, Investigation, Formal analysis, Dan Zhao: Writing – Review & Editing, Founding acquisition, Jizhong Ren: Supervision, Writing – Review & Editing, Shudong Wang: Supervision, Maicun Deng: Supervision.

Materials

Commercial co-polyimide P84 (Fig. 1) powders were dried in a vacuum oven over night. N-Methyl pyrrolidone (NMP) was provided by Sinopharm Chemical Reagent Co. Ltd. Pure CH₄ and CO₂ were supported by Dalian gases company. Nickel (II) nitrate hexahydrate [Ni(NO₃)₂·6H₂O, 98%], nickel (II) acetate tetrahydrate [Ni(CH₃COO)₂]·4H₂O, 98%], formic acid (HCOOH, 98%), methanol (CH₃OH, 99%), and ethanol (CH₃CH₂OH, 99.7%) were supplied by Sinopharm Chemical Reagent Co. Ltd., Shanghai, China. All chemicals

Characterization of the as-synthesized [Ni₃(HCOO)₆] frameworks

Fig. 2a shows the XRD pattern of the as-synthesized [Ni₃(HCOO)₆] sample. The XRD peak positions agree well with reported ones (Wang et al., 2007), confirming the successful synthesis of the specific MOF structure. Fig. 2b indicates the SEM image of the [Ni₃(HCOO)₆] sample. The crystals are approximately sphere-like particles with an average diameter of about 400 nm. Argon adsorption-desorption isotherms confirm the microporous characteristic of the [Ni₃(HCOO)₆] sample (Fig. 2c). The BET surface

Conclusions

Submicrometer-sized [Ni₃(HCOO)₆] framework crystals, which have uniform ultra-micropore with micropore size of 0.46 nm, were synthesized by solvothermal method. They were incorporated into P84 matrix successfully for the first time, resulting in P84/[Ni₃(HCOO)₆] MMMs with good potential to separate CO₂ from CH₄. Detect-free MMMs were obtained when the [Ni₃(HCOO)₆] loadings were not more than 15 wt% and their gas separation performance was obviously enhanced. When the loading increased to

Acknowledgments

This work was supported by the National Natural Science Foundation of China (21908215) and the Strategy High Technology Innovation Fund, CAS (CXJJ-19-B06).