Porous liquids allow for efficient gas separation

Date:
August 12, 2020
Source:
Karlsruher Institut fu"r Technologie (KIT)
Summary:
Scientists have developed 'porous liquids': Nanoparticles, that are
able to separate gas molecules of different sizes from each other,
float - finely distributed - in a solvent. The porous liquids may
be processed into membranes that efficiently separate propene from
gaseous mixtures.

This could replace the energy-intensive distillation that has been
the common procedure up to now.



FULL STORY ========================================================================== Jointly with cooperation partners, a researcher of Karlsruhe Institute
of Technology (KIT) has developed "porous liquids": Nanoparticles, that
are able to separate gas molecules of different sizes from each other,
float -- finely distributed -- in a solvent. This is because the particles
have empty pores, through whose openings only molecules of a certain size
can penetrate. These porous liquids may be used directly or processed into membranes that efficiently separate propene from gaseous mixtures. Propen,
in turn, is employed as the starting material for propylene, a widely used plastic material. This could replace the energy-intensive distillation
that has been the common procedure up to now.


========================================================================== Propene, also known as propylene, is one of the most important raw
materials for the chemical industry, of which around 100 million
tons are used up worldwide every year. Polypropylene, a real "mass
plastic," produced from propene is mainly used for packaging, but also
in industries such as construction and automotive. Propene is mainly
obtained by processing crude oil or natural gas. In this process, it is separated from other gases by distillation and then purified. "In the
technical literature, it is assumed that gas separation in petrochemistry
using membranes would only cost one fifth of the energy required for distillation. In view of the required high quantities of propene, this
means that the release of huge amounts of the greenhouse gas CO2 can be avoided," says Junior Research Group Leader Dr.

Alexander Knebel from the KIT Institute of Functional Interfaces who
conducted research at Leibniz Universita"t Hannover and in Saudi Arabia
until 2019.

The chemist is a major contributor to a research project that, for the
first time, raises interest in the petrochemical industry as regards
the use of membranes for the separation of propene. Knebel's cooperation partners were scientists from Leibniz Universita"t Hannover, King Abdullah University of Science and Technology and the Deutsches Institut fu"r Kautschuktechnologie.

Metal-organic framework distributed in a liquid for the first time The researchers started their work with the solid material ZIF-67 (zeolitic imidazole framework) whose atoms form a metal-organic framework with
0.34 nanometer-wide pore openings. In doing so, they systematically
modified the surface of ZIF-67 nanoparticles. "This enabled us to finely disperse a metal- organic framework in liquids such as cyclohexane,
cyclooctane or mesitylene," says Knebel joyfully. Scientists call the
resulting dispersion "porous liquid." Gaseous propene needs much longer
to pass through a column filled with the porous liquid than methane,
for example. This is because propene is retained, as it were, in the
pores of the nanoparticles, while the smaller methane molecules smoothly
pass through. "We want to exploit this property of the dispersion in
the future to produce liquid separation membranes," states Knebel.

Yet, porous liquids can also be used to produce solid separation
membranes with particularly advantageous properties. The researchers
produced membranes from a plastic material and the chemically modified
ZIF-67. They succeeded in increasing the proportion of modified ZIF-67 in
the membrane to 47.5 percent without making it mechanically unstable. When
the scientists passed a gas mixture consisting of equal parts of propene
and propane over two membranes arranged in series, they obtained propene
with a purity of at least 99.9 percent, even though the two gas molecules differ in size by not more than 0.2 nanometers.

Besides its separation efficiency, the quantity of a gas mixture that
can be passed through in a certain time is decisive for the practical
use of such a membrane. This flow rate was at least three times higher
with the new membranes than with previous materials. With the separation
values achieved, Knebel is convinced that it would pay off for the petrochemical industry for the first time to use membranes instead of conventional distillation processes for gas separation.

It is crucial for the performance of the membranes that as many
metal-organic particles as possible can be distributed uniformly in
the plastic and that the pores in the nanoparticles are not clogged by
solvents during membrane production, i.e. remain empty, so to speak. "We
were able to achieve both goals because we did not directly incorporate
solid particles into the membrane, but instead proceeded via the porous
liquids even though this looks like a detour," explains Knebel.


========================================================================== Story Source: Materials provided by
Karlsruher_Institut_fu"r_Technologie_(KIT). Note: Content may be edited
for style and length.


========================================================================== Journal Reference:
1. Alexander Knebel, Anastasiya Bavykina, Shuvo Jit Datta, Lion
Sundermann,
Luis Garzon-Tovar, Yury Lebedev, Sara Durini, Rafia Ahmad, Sergey M.

Kozlov, Genrikh Shterk, Madhavan Karunakaran, Ionela Daniela Carja,
Dino Simic, Irina Weilert, Manfred Klu"ppel, Ulrich Giese, Luigi
Cavallo, Magnus Rueping, Mohamed Eddaoudi, Ju"rgen Caro, Jorge
Gascon. Solution processable metal-organic frameworks for mixed
matrix membranes using porous liquids. Nature Materials, 2020;
DOI: 10.1038/s41563-020-0764-y ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/08/200812144054.htm

--- up 4 weeks, 1 hour, 55 minutes
* Origin: -=> Castle Rock BBS <=- Now Husky HPT Powered! (1337:3/111)