Photoionization Time-of-flight mass spectrometry (PIMS) is a valuable analytical technique for process analysis, since it enables an online measurement with high temporal resolution. In addition, ionization with photons is a soft method enabling a molecular characterization producing a very low amount of fragments. High selectivity and sensitivity especially for aromatic species can be provided as well.

The Fischer-Tropsch synthesis, this year celebrating its hundred year anniversary of development, is a catalytic reaction to produce synthetic fuels, aliphatic hydrocarbons, olefins and waxes from synthesis gas (mixture of carbon monoxide and hydrogen). Since synthesis gas can be generated from biomass, and recent developments allow using carbon dioxide instead of CO as well, it has gained new interest with respect to greenhouse gas reduction. 

In a study supported by Reacnostics Hamburg and Christian-Albrechts-University Kiel a compact profile FT reactor equipped with a combination of an iron catalyst for the FT synthesis and a zeolite catalyst for conversion of aliphatic into aromatic compounds was taken for a proof-of-concept study. The reactor allows sampling within the catalyst with the sampling location moving through the catalyst bed. The evolving products were analyzed in real time with PIMS and an addtionally coupled fast gas chromatograph. Various aliphatic and aromatic product molecules such as propene, butene, benzene, toluene and alkylated naphthalenes could be monitored during one complete movement of the sampling probe through the whole catalyst bed. The onset of catalytic activation and the transition point for intensified production of aromatic compounds were made visible. The fast gas chromatography allowed for distinction between isobaric compounds exhibiting the same molecular mass, such as the aliphatic hydrocarbon nonane and the aromatic naphthalene, which are not distinguishable by the mass spectrometer, thereby enhancing the detection space.

With the online process analysis capabilities successfully demonstrated, the analytical technique could be used to investigate further parameters of the process, such as different carbon monoxide to hydrogen ratios, other catalysts, and varied dimensions of the catalysts. Furthermore, other caltalytic processes such as methanol synthesis and its subsequent conversion to olefins and fuels could be monitored as well.