Microwaves get the measure of catalysts

The petrochemical industry converts thousands of barrels of crude oil into hydrocarbon fuels and chemicals each day. To ensure the conversion is rapid and efficient, microporous materials known as acid zeolite catalysts are used to speed up the rate of chemical reactions. To maintain efficiency, the catalyst needs to be replaced when the pores get clogged by the accumulation of a non-volatile carbon-rich material, a process known as coking.  

Current techniques for measuring the extent of coking in acid zeolite catalysts are costly, difficult to use and require the destruction of samples. 

Now, Hamid Al-Megren and Mohammed Al-Kinany from KACST’s Petrochemical Research Institute in Riyadh, and co-workers from Oxford University, and Cardiff University, have developed a microwave-based technique for probing the inside of an acid zeolite catalyst. The new technique could detect the amount and chemical composition of cokes formed inside the pores of the catalyst, without ever needing to break open the catalyst. 

The new technique, known as microwave cavity perturbation analysis, uses around 2.45 gigahertz microwaves to interrogate catalyst samples. Microwaves are a highly penetrative form of electromagnetic radiation. Unlike most forms of electromagnetic radiation, such as ultraviolet or visible light, they can peer deep within the catalyst.

Microwaves are partially absorbed by water, oil and other dielectric materials, including coke formed inside the pores of acid zeolite catalysts. Therefore, by measuring the amount of microwaves being absorbed, it’s possible to determine the extent of coking within the pores of an acid zeolite catalyst.

The absorption efficiency, which is calculated as the dielectric loss value divided by the weight of coke, is reflective of the chemical composition of coke formed within the pores. The researchers have demonstrated that by burning off the coke within a catalyst sample at 1120 °C, as well as measuring the before and after treatment weight of the catalyst sample, one can work out the weight of coke — and, in turn, its chemical composition.

“Carbon formation and monitoring is crucial for the catalytic process and is also directly concerned with the safety of the plant,” says Al-Megren. “Our work provides a quick, easy, and accurate method for real-time monitoring of catalyst bed, which would be a step change for catalytic optimization and development.”

1. Liu, B., Slocombe, D. R., Wang, J., Aldawsari, A., Gonzalez-Cortes, S., et al. Microwaves effectively examine the extent and type of coking over acid zeolite catalysts. Nature Communications 8, 514 (2017).| article