Catalytic membrane reactors for SO3 decomposition in Iodine–Sulfur thermochemical cycle: A simulation study

Abstract

The possibility of applying a catalytic membrane reactor (CMR) to SO 3 decomposition in a low-temperature range was theoreticallyevaluated with the purpose of producing CO 2-free hydrogen inan Iodine-Sulfur thermochemical cycle.Aone-dimensional, isothermal and plug-flowmodelwas developed for a cocurrentmembrane reactor with selective permeation from the reactant stream to the permeate stream. Simulation results have revealedthat CMRs can greatly reduce the reaction temperature for SO 3 decomposition from the conventional 1,200-1,400 K to about 900 K.We predicted that porous inorganic membranes with a high O 2 permeabilityand with selectivitiesof more than 50 for O 2 /SO 3 and less than 10 for O 2 /SO 2 had the potential to effectively improve SO 3 conversion.CMRs were simulated to carry out SO 3 decomposition at different catalyst weights, reaction temperatures, and SO 3 feed flow rates as well as pressures in feed and permeate streams.SO 3 conversion at 900 Kwas increased to 0.93beyond the equilibrium conversion of 0.28due to a shift in thermodynamicequilibrium.

Evaluating the chemical stability of metal oxides in SO3 and applications of SiO2‐based membranes to O2/SO3 separation

“…5 In our previous work, we demonstrated a theoretical intermediate-temperature for SO 3 decomposition using a catalytic porous-membrane reactor. 9 The simulation indicated that a selective extraction of SO 2 and O 2 as a product from O 2 / SO 2 /SO 3 mixtures in a reaction stream via porous inorganic membranes would increase SO 3 conversion and significantly reduce the reaction temperature to 500°C-600°C.…”

“…The membrane provides selective removal of O 2 and SO 2 in parallel with a reversible reaction, which shifts the equilibrium toward the product side and thus results in a higher reaction conversion even at lower temperatures. 9 The simulation indicated that a selective extraction of SO 2 and O 2 as a product from O 2 / SO 2 /SO 3 mixtures in a reaction stream via porous inorganic membranes would increase SO 3 conversion and significantly reduce the reaction temperature to 500°C-600°C. In the early 2000s, the Oak Ridge National Laboratory attempted to apply porous inorganic membranes to SO 3 decomposition at lower temperatures.…”

SiC mesoporous membranes for sulfuric acid decomposition at high temperatures in the iodine–sulfur process

“…46 Therefore, the equilibrium of the reaction (R4) (SO 3 4 SO 2 + 0.5O 2 ) was forwarded to the product side by removing O 2 . In a comparison with a membrane without extraction, the membrane reactor with extraction achieved higher conversion at the same temperature of 600 C. The catalytic membrane reactor obtained conversion of 25% without extraction, which approximated the equilibrium (theoretical) conversion of SO 3 decomposition (eqn (4)) of 28% at 900 K. 3 Comparison with membrane without extraction, the conversion of H 2 SO 4 decomposition was increased to 45%, which was much higher at the same temperature of 600 C. Additionally, the H 2 SO 4 decomposition conversion remained constant at around 41% aer membrane exposure to H 2 SO 4 vapor for 10 h. Moreover, aer decomposition for 10 h, He permeance was approximately the same as that before the decomposition reaction, which indicated that the SiC particle layer (with SiO 2 -ZrO 2 ) had high hydrothermal and chemical stability under H 2 O and SO 3 . However, the separation properties of M4 membranes was still poor; the He/N 2 permeance ratio was 2.3 with N 2 permeance of 4.5 Â 10 À5 mol m À2 s À1 Pa À1 , since the SiC membrane was fabricated using SiC particles, and the gaps between particles were large enough to allow gas to pass through.…”

“…Over the past twenty years, the water-splitting iodine-sulfur (IS) process has been extensively investigated as a sustainable technology with a net production of H 2 and O 2 , at much lower temperatures compared with the direct thermal decomposition of water. [1][2][3][4][5][6] The IS process involves cyclic reactions such as the Bunsen reaction and the thermal decompositions of sulfuric acid at 850-950 C and hydroiodic acid at 450 C. In these cycles, the decomposition of sulfuric acid requires temperatures so high that the heat of solar or nuclear energy must be utilized. 3,[5][6][7] Net reaction: 9 nanoltration, 10 reverse osmosis, 11 and gas separation 12 consume the least amount of energy compared with other separation techniques.…”

“…Notably, we reported several classes of inorganic membrane materials/metal oxides employed in membrane reactors for O 2 /SO 3 separation. 3,5 SiO 2 membranes, due to their excellent thermal stability and high gas selectivity, 17,32 were rst used by our team for O 2 /SO 2 separation in 2015. 3 Bis(triethoxysilyl)ethane (BTESE)-derived membranes, particularly those fabricated under high temperatures, have demonstrated high oxidation resistance and exhibited an O 2 / SO 3 selectivity of 10 with an O 2 permeance of 2.5 Â 10 À8 mol m À2 s À1 Pa À1 .…”