Sorption-enhanced Fischer-Tropsch synthesis – Effect of water removal

Abstract

The Sorption-Enhanced Fischer-Tropsch synthesis (SEFTS), with water removal by means of a solid sorbent, has been demonstrated for the first time experimentally. Commercial water sorbents (Zeolites type 13X and 4 A) were thoroughly characterized to determine water sorption capacity at relevant temperatures (100–250°C) as well as multicycle stability after 100 cycles at 210°C. The adsorption capacity of both zeolties decreased with increasing temperature. The adsorption capacity of 4 A remained almost constant after 100 adsorption/desorption cycles, while 13X lost almost 50% of its capacity. Post characterization of the 13X sample showed distorted crystallinity after 100 cycles which explains the drop in stability. The SEFTS experiments were performed as a cyclic operation, first FT reaction and then water sorbent regeneration, at 210 °C and 5 bar. The system with zeolites showed 10% higher CO conversion after 65 hours on stream compared to the system without any sorbents. The selectivities to C5+ was higher for the system with sorbents compared to the system without zeolites. A much steeper deactivation curve was also observed for the system without zeolites at steady state conditions. This might be due to the fact that zeolites adsorbs the water and remove it from the catalyst active centers, thus increase catalyst stability by preventing the catalyst re-oxidation. Overall, this work opens an opportunity for enhancing the catalyst activity in FTS by in situ water sorption.