(273d) Potential for Using High Temperature Membranes in the Sulphur Trioxide Decomposition Stage of a Thermochemical Cycle

A sulphuric acid thermal decomposition step is used as part of a number of potentially viable thermochemical cycles, notably the hybrid sulphur (HyS) and sulphur iodine (SI) cycles. Sulphuric acid first decomposes to sulphur trioxide, followed by decomposition to sulphur dioxide. Sulphur trioxide decomposition to sulphur dioxide exhibits poor yield in the temperature range accessible by conventional heat sources.

It is proposed that the sulphur dioxide yield from the sulphuric acid thermal decomposition process could be increased by the use of a membrane oxygen separation step. This would allow a broader range of heat sources to be used, as well as increasing the yield where a higher temperature heat source, e.g. solar energy, is used. Modelling work is presented which shows the potential yield improvements.

This work investigates the suitability of existing dense ion-conducting membranes for this process. A bespoke quartz membrane holder and associated apparatus have been designed to allow oxygen permeation through yttria stabilised zirconia membranes to be measured at temperatures ≤1200K. The membrane can be exposed to mixtures of helium, oxygen and sulphur dioxide and the voltage applied across the membrane electrodes can be varied.

Initial data obtained using helium-oxygen feed mixtures is presented, followed by data obtained using helium-oxygen-sulphur dioxide feed mixtures. The results of XRD analysis of the exposed membranes are also provided.