Pulsing industrial chemical reactions

By Ian Page

From Nature 605 19 May 22 470.

Chemical reactions are often a mixture of potential parallel reactions, and potential serial reactions. Chemists play with temperature, flow rate, pressure, proportions etc. to persuade just the one reaction they want to happen.

One of the unwanted reactions can be the decomposition of the catalyst through sintering to form larger less reactive lumps, or the destruction of the active element of the catalyst.

Just to make it more complicated, reactions have a thermodynamic equilibrium- where they get given time to settle, and a kinetic profile, in which a variety of intermediate chemicals may appear and disappear over time.

A process called programmable heating and quenching, has been described.

This zaps the temperature of the catalyst (in this case carbon mesh, with other things embedded, up to temperatures such as 1000 degrees or more, in a tenth of a second, and then allows it to cool for the rest of a second then repeats.

For two commercial chemical reactions - the conversion of methane (natural gas) to ethene (for polyethylene and other volume chemicals), and the conversion of nitrogen to ammonia, this approach resulted in up to 80% saving in energy, increased lifetime for the catalyst, and a larger and more selective yield of the desired product

Even more interesting, the use of very high temperatures for very short times allowed the activation of the input molecules without expensive rare metals.

Rare metals are typically used because they form transient compounds with say nitrogen which then react further to form the output regenerating the metal and allowing the reaction to proceed with less temperature to activate it.

This Technique allows very high temperatures and thus doesn’t need the catalyst.

We have seen papers showing that pulsing the electrical input to batteries when charging improves life, and that pulsing the electrical input to fuel cells increases efficiency.

This approach to separating and preferring certain reactions and physical processes over others sounds like a very general concept