Modeling & experimental studies on enhancement of H ₂ S conversion using catalytic membrane reactor for hydrogen production

Abstract Acidic gases such as H 2 S and CO 2 are generated in the refineries during coal gasification. These pollutant gases need to be treated before releasing to the atmosphere. Conventionally, H 2 S gas is treated by Claus process in which H 2 S is converted to elemental S and H 2 O, in presence of O 2 at ∼1,200 K. In the present energy scenarios, hydrogen has got importance as a source of clean fuel for industrial application. The H 2 S generated in the refineries can be a potential precursor of hydrogen. If this hydrogen can be obtained by thermal decomposition of H 2 S, that can increase the overall economic value of the H 2 S containing streams and the produced hydrogen can be used for hydrocracking and hydro-treating in refineries, as well as to synthesize value-added products for chemical industries. However, H 2 S thermal decomposition is an endothermic and equilibrium limited reaction (equilibrium conversion is only ∼15 % at 1,000 K), requiring a very high temperature (∼1,500 K) to achieve even a conversion of greater than 40 %. Packed Bed Catalytic Membrane Reactor (PBCMR) for thermal decomposition of H 2 S can be a potential technology augmentation and process intensification to increase this equilibrium conversion. In this work, modeling and experimental studies of H 2 S thermal decomposition using in-house designed & developed PBCMR have been carried out. The modeling studies were validated with experimental data. Clay-alumina ceramic tubular membrane (L: 250 mm; OD: 12 mm; thickness: 2 mm) was fabricated using extrusion process having an average membrane pore size of ∼1 μm and with a porosity of ∼20 %. Pt (2 %) coated alumina extrudes were used as catalyst to accelerate the reaction kinetics. Experimental studies showed that H 2 S to hydrogen conversion of ∼90 % is achieved using PBCMR at ∼1,523 K, compared to only ∼40 % conversion in a conventional packed bed tubular reactor (without membrane). Modelling studies were carried out to study the influence of operating parameters such as, reactor wall temperature, feed temperature, pressure and feed velocity. Studies showed that reactor wall temperature is having the most dominant effect on H 2 S conversion, which is confirmed by experimental findings. The studies offer useful insights into the application of PBCMR technology for management of waste gas stream containing H 2 S and recovery of hydrogen.