(631g) Shape-Selective Adsorption Separation of C4 Olefins in Gallate-Based Metal-Organic Frameworks

Authors: 
Chen, J., Zhejiang University
Bao, Z., Zhejiang University
Wang, J., Zhejiang University
Zhang, Z., Zhejiang University
Yang, Q., Zhejiang University
Yang, Y., Zhejiang University
Su, B., Zhejiang University
Ren, Q., Zhejiang University

C4
olefins including 1,3-butadiene (C4H6), 1-butene (n-C4H8),
iso-butene (iso-C4H8), are widely used in the
production of synthetic rubbers and varieties of chemicals. C4
olefins are generally obtained from C4 hydrocarbon mixtures produced
in petrochemical plants. High-purity individual C4 olefin is critical
for its downstream processes. However, these C4 hydrocarbons have
similar molecular sizes, shapes and physical properties, such as close boiling
points and polarizability, making it difficult to separate. Currently,
industrial separation of C4 hydrocarbons is performed by extractive
distillations, which are energy-intensive and cost-inefficient. A promising
energy-efficient purification method is physisorption with porous materials
that can separate gas mixtures by distinguishing the differences in molecular
sizes, shapes, polarities, polarizabilities, coordination abilities, and so forth.
Metal-organic frameworks (MOFs), emerging as a new class of porous materials, have
showed great potential in adsorptive separation of C4 hydrocarbons.

Herein we report
gallate-based metal-organic frameworks, M-gallate (M=Mg, Co, Ni), realized
highly efficient separation of C4 olefins into individual components
by shape-size sieving (Scheme 1). Single-component adsorption isotherms of C4
olefins on Mg-gallate revealed that the uptake of C4H6 can
reach as high as 1.96 mmol/g (higher than DD3R of 0.83 mmol/g at 303 K and 1
bar), while the uptakes of n-C4H8 and iso-C4H8
were as low as 1.46 mmol/g and 0.13 mmol/g, respectively (Figure 1), affording high
selectivities of C4H6/n-C4H8,
C4H6/iso-C4H8 and n-
C4H8/iso-C4H8. DFT modelling
was performed to
gain a better insigh into the adsorption mechanism (Figure 2). Fixed bed
breakthrough experiments using a font-family:" times new roman>ternary C4
mixture was conducted to simulate the practical industrial separation processes
at 298 K and 1.01 bar on Mg-gallate (Figure 3). iso-C4H8 broke
through the bed of Mg-gallate almost immediately after feeding while n-C4H8 and C4H6 began to
breakthrough at approximately 20 min and 38 min. This work demonstrated that M-gallate
was one of top-performing MOF materials for adsorption separation of C4H6, n-C4H8 and iso-C4H8.

 

 

 

" times new roman>Scheme 1. Schematic
illustration of the adsorption separation of C4 olefins on M-gallate
(M=Mg, Co, Ni).

 

" times new roman>Figure 1. Adsorption
isotherms of C4H6(red), n-C4H8(blue),
iso-C4H8(dark green) on Mg-gallate at 298K.

 

" times new roman>Figure 2. The
adsorption binding sites of C4H6 in Mg-gallate calculated
by DFT method.

 

" times new roman>Figure 3. Ternary
mixture breakthrough curves on Mg-gallate for C4H6/n-C4H8/iso-C4H8/He
(20/10/10/60) at 298 K, with a flow rate of 0.5 mL/min.

 

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