In situ measurement of gas adsorption processes using Flux Response Technology

Abstract

Flux Response Technology (FRT) is being developed as a powerful in situ perturbation technique to facilitate detailed characterisation of heterogeneous catalysts. FRT works by measuring minuscule changes in flowrate between two gas streams for potentially any gaseous process involving a change in volume (dV /dt). FRT functions analogous to an electrical Wheatstone bridge assembly whereby gas molecules represent electrons and flow capillaries represent resistors. A perturbation of pressure, temperature, but particularly of concentration causes an imbalance in the system, which is measured directly by a very sensitive differential pressure transducer (DPT). It is demonstrated how FRT can provide a simple, inexpensive, highly accurate means of quantifying the acidic sites of zeolites using ammonia ad/desorption as well as determining the dynamically available surface areas of catalysts using nitrogen adsorption at liquid nitrogen temperature. Temperature programmed experiments (temperature perturbations) can also be employed with FRT to rapidly compare catalyst activity directly (for catalyst development but also for quality control) without the need for much calibration.

Using temporal analysis of products and flux response technology to determine diffusion coefficients in catalytic monoliths

“…In previous studies, the versatility of the FRT method in measuring adsorption, reaction and desorption in situ in the reactor has been reported (Buffham et al, 2000;Palmer et al, 2011;Richardson et al, 2004). By applying the Zero Length Column (ZLC) method to analyse the desorption curves generated by the FRT system, the correct representation of the rate of diffusion within the washcoat is calculated.…”

“…The FRT method functions in a way that is analogous to an electrical Wheatstone bridge assembly whereby gas molecules represent electrons and flow capillaries represent resistors (Palmer et al, 2011). The technique is based on capillary viscometry and can be used to measure minuscule changes in flow rates between two gas streams for potentially any gaseous process involving a change in volume (dV/dt) (Buffham et al, 1986 and2002;Russell et al, 1986;Mason et al, 1998).…”

Flux response technology applied in zero length column diffusivity measurements

“…The purpose of this paper is to measure propane diffusivity in the washcoat of monolith samples using Flux Response Technology (FRT) and to show that this method can be used to compare and contrast with other micro and macroporous techniques in one experiment by analysing the adsorption and desorption transients in the FRT profile. In previous studies (Buffham et al 2000;Richardson et al 2004;Palmer et al 2011), we have shown the versatility of the FRT method in measuring adsorption, reaction and desorption in situ in the reactor. By applying the Zero Length Column (ZLC) method to analyse the sorption curves generated by the FRT system, the rate of diffusion in the washcoat is calculated.…”

“…The technique is based on capillary viscometry and can be used to measure minuscule changes in flowrate between two gas streams for potentially any gaseous process involving a change in molar hold-up (δN/δt) (Buffham et al 1986a(Buffham et al , 1986bMason 1998;Russell et al 2002Russell et al , 2003Palmer et al 2011). FRT functions analogous to an electrical Wheatstone bridge assembly whereby gas molecules represent electrons and flow capillaries represent resistors.…”

Flux Response Technology (FRT) Applied in Zero Length Column Diffusivity and Adsorption Measurements

“…The zeolites in question have been well characterised making use of both, XRD and solid state NMR to validate the non-existence of extra-framework Al which would compromise the accuracy of the FRT measurements (Palmer et al 2011). The textural characterisation of the zeolite samples was carried out using a Micromeritics Tristar 3000 Surface Analyser with the data shown in Table 1.…”