Chemical industry: Trapping of acetylene contaminants
Separation of trace acetylene from ethylene in ultramicroporous metal-
organic frameworks

Date:
August 27, 2020
Source:
Wiley
Summary:
Ethylene, a key feedstock in the chemical industry, often
includes traces of acetylene contaminants, which need to be
removed. Researchers describe a robust and regenerable porous
metal-organic framework that captures acetylene with extraordinary
efficiency and selectively. Its synergistic combination of
tailor-made pore sizes and chemical docking sites makes the material
especially efficient, the study says.



FULL STORY ========================================================================== Ethylene, a key feedstock in the chemical industry, often includes
traces of acetylene contaminants, which need to be removed. In the
journal Angewandte Chemie, researchers describe a robust and regenerable
porous metal-organic framework that captures acetylene with extraordinary efficiency and selectively. Its synergistic combination of tailor-made
pore sizes and chemical docking sites makes the material especially
efficient, the study says.


========================================================================== Ethylene is the most important chemical precursor for ethanol and
polyethylene and is mainly produced by steam cracking. Although the
ethylene fraction is usually very pure (more than 99%), remaining traces
of acetylene contaminants can destroy the catalysts used in downstream processes.

As ethylene and acetylene are very similar and only differ in the amount
of hydrogen atoms -- ethylene has four hydrogen atoms bound to two carbon atoms, acetylene has two -- the separation of both gases is elaborate
and difficult.

The current industrial processes rely on distillation, which consumes
a huge amount of energy.

However, hydrocarbon compounds bind to porous substances called
metal-organic frameworks (MOFs). MOFs are made of metal ions and
organic ligands and contain pores and chemical docking sites that can be designed to capture specific molecules from a stream of gas at ambient conditions. However, for the separation of ethylene and acetylene,
the industry demands robust, regenerable, highly selective, and cheap materials, which have not been found so far.

Dan Zhao and his colleagues at the National University of Singapore
have now developed a MOF specific for acetylene capture that may meet
the demands of extraordinary selectivity and robustness. The scientists
focused on an established MOF with nickel sites, but they "opened" up
these nickel sites for the binding of more molecules by activating them
and exposing them to the pores so that they were able to bind two guest molecules at once.

In addition, the scientists adjusted the pore sizes of the MOF to allow
entry only for very small gas molecules, and filled the pore walls with chemical groups that would attract acetylene over ethylene through their stronger electrostatic and chemical interactions.

Thus, combining small pore sizes with the open nickel sites and sites
for preferential acetylene binding, the scientists have created a Ni-MOF
called Ni (3)(pzdc)(2)(7Hade)(2) that is extraordinarily selective,
robust, stable, and can be regenerated. According to the study, the
Ni-MOF purified the ethylene stream by a factor of a thousand and kept the selectivity high across a range of pressures and regeneration cycles. In addition, the Ni-MOF can be prepared in a standard hydrothermal procedure,
the scientists say.

The authors point out that the synergy of pore geometry and size,
combined with chemical interactions, can be further enhanced and may lead
to even more effective separations. This is interesting for industrial application.


========================================================================== Story Source: Materials provided by Wiley. Note: Content may be edited
for style and length.


========================================================================== Journal Reference:
1. Zhaoqiang Zhang, Shing Bo Peh, Yuxiang Wang, Chengjun Kang,
Weidong Fan,
Dan Zhao. Efficient Trapping of Trace Acetylene from Ethylene in
an Ultramicroporous Metal‐Organic Framework via Synergistic
Effect of High‐Density Open Metal Sites and Electronegative
Sites. Angewandte Chemie International Edition, 2020; DOI:
10.1002/anie.202009446 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/08/200827105917.htm

--- up 3 days, 6 hours, 50 minutes
* Origin: -=> Castle Rock BBS <=- Now Husky HPT Powered! (1337:3/111)