Trapping of acetylene

August 27, 2020

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.
About the Author

Dr. Dan Zhao is an Associate Professor in the Department of Chemical and Biomolecular Engineering at the National University of Singapore. His research focuses on the molecular-level design and synthesis of advanced porous materials and hybrid membranes, and their applications in clean energy and environmentally sustainable areas such as storage, separation, and sensing.


Related Molecules Articles from Brightsurf:

Finally, a way to see molecules 'wobble'
Researchers at the University of Rochester and the Fresnel Institute in France have found a way to visualize those molecules in even greater detail, showing their position and orientation in 3D, and even how they wobble and oscillate.

Water molecules are gold for nanocatalysis
Nanocatalysts made of gold nanoparticles dispersed on metal oxides are very promising for the industrial, selective oxidation of compounds, including alcohols, into valuable chemicals.

Water molecules dance in three
An international team of scientists has been able to shed new light on the properties of water at the molecular level.

How molecules self-assemble into superstructures
Most technical functional units are built bit by bit according to a well-designed construction plan.

Breaking down stubborn molecules
Seawater is more than just saltwater. The ocean is a veritable soup of chemicals.

Shaping the rings of molecules
Canadian chemists discover a natural process to control the shape of 'macrocycles,' molecules of large rings of atoms, for use in pharmaceuticals and electronics.

The mysterious movement of water molecules
Water is all around us and essential for life. Nevertheless, research into its behaviour at the atomic level -- above all how it interacts with surfaces -- is thin on the ground.

Spectroscopy: A fine sense for molecules
Scientists at the Laboratory for Attosecond Physics have developed a unique laser technology for the analysis of the molecular composition of biological samples.

Looking at the good vibes of molecules
Label-free dynamic detection of biomolecules is a major challenge in live-cell microscopy.

Colliding molecules and antiparticles
A study by Marcos Barp and Felipe Arretche from Brazil published in EPJ D shows a model of the interaction between positrons and simple molecules that is in good agreement with experimental results.

Read More: Molecules News and Molecules Current Events is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to