The Catalyst Review December 2024 - 12

Experimental Abstracts
A Microporous Multi-Cage Metal-Organic Framework for an
Effective One-Step Separation of Branched Alkanes Feeds
The petrochemical industry relies heavily on advanced separation methods
like adsorption and membrane technology to purify hydrocarbons, because
traditional separation techniques like distillation consume excessive
energy. This process is particularly important in gasoline production,
where the Research Octane Number (RON) must exceed 90 to ensure
proper engine performance. To achieve premium-grade gasoline with a
RON above 92, combinations of unique absorbent materials (zeolites and
MOF) must be used to categorize pentane and hexane molecules into three
groups: linear, mono- and di-branched isomers. However, no single
porous material has exhibited this separation on its own. Herein, the
authors report the design of a new multi-cage microporous Fe(III)-MOF
(MIP-214) illustrated in (Figure 1), capable of achieving this goal (Figure
1). Its flu-e topology incorporates an asymmetric heterofunctional ditopic
ligand, 4-pyrazole-carboxylic acid, and its unique pore structure (including
small tetrahedron, medium cube, and large rhombicuboctahedron cages
associated with square and triangle apertures) allows the diffusion of
all C5 and C6 isomers, but with distinct affinities according to their
shape and size.
Figure 1. Schematic illustration of the separation of
C5/C6 alkane isomers into fractions ofLRON and
HRON alkanes via: Left-Two-step(synergistic action)
separation with zeolite SA and MIL-160(AI). " 01 Right:
One-step separation using MIP-214.
The alkane isomer separation performance of MIP-214 was assessed using a
chromatographic technique through dynamic breakthrough experiments.
The separation of a quinary mixture of equimolar C6 isomers was first
investigated, followed by the separation of a septenary mixture of equimolar C5/C6 isomers (Figure 2). The C6 isomers
included di-branched alkanes:2, 2-dimethylbutane (22DMB; RON 94) and
2,3-dimethylbutane (23DMB; RON 105), mono-branched alkanes: 2-methylpentane
(2MP; RON 74.4), 3-methylpentane (3MP; RON 75.5) and i-pentane
(iC5; RON 93.5), and linear alkanes: n-hexane (nC6; RON 30) and n-pentane
(nC5; RON 61.7). MIP-214 was found to enable a separation according to the
degree of branching: linear (nC6) ~mono-branched (2MP, 3MP) ~
di-branched (22DMB, 23DMB). This separation sequence depicted in
(Figure 2a) is similar for most materials with channel-like pores mentioned
above. MIP-214 can even separate the two mono-branched isomers (2MP
and 3MP) of similar kinetic diameter (5 A). Furthermore, for an equimolar
mixture of all seven C5/ C6 isomers, the breakthrough times of the C6 isomers
follow the same sequence as in the separation of the quinary mixture
(Figures 3b, S17, S18). Remarkably, with an adsorption hierarchy of nC6 > nC5
2MP > 3MP > 23DMB r=f, iC522DMB, the high-octane di-branched 22DMB
and 23DMB, and mono-branched iC5 elute nearly together, much earlier
than the elution of the other four LRON components, leading to an ideal 92
RON productivity of 0.67.
Further calculations indicate the strongest affinities of MIP-214 towards nC6
and nC5, followed by those of the monobranched C6 isomers, and the
weakest adsorption affinities towards dibranched C6 isomers and
monobranched C5 isomer revealing the thermodynamic separation
mechanism. This outstanding performance of MIP-214 can be attributed to
its exceptional/unique ability to effectively separate High RON isomers, such
as 22DMB, 23DMB, and iC5, from Low RON isomers, specifically 3MP and
2MP. Zhou L, Brantuas P, Henriquegue A, et al. (2024). Angew. Chem. Int.
Ed., 63, e202320008, doi.org/10.1002/anie.202320008
12
The Catalyst Review
Figure 2. Separation of equimolar mixtures of
C6 isomers (a) and C5 and C6 isomers (b) by
fixed bed adsorption with MIP-214 at 373 K and a
total isomers pressure of 10 kPa. Breakthrough
data is plotted as the normalized molar fraction
of each isomer (left y-axis) and average realtime
RON (right y-axis) as a function of time.
December 2024
http://www.doi.org/10.1002/anie.202320008
The Catalyst Review December 2024

Table of Contents for the Digital Edition of The Catalyst Review December 2024
