Investigations to intensified hydrogen production via sorption enhanced water gas shift reaction

Abstract

Sorption enhanced water gas shift (SEWGS) reaction for the equilibrium enhanced hydrogen production is investigated using lithium orthosilicate (Li4SiO4) sorbents mixed with 1 wt% Pt/Al2O3 catalysts. The Li4SiO4 sorbents, synthesized using novel surfactant-mediated method, are characterized by ultra-fast CO2 capture rates with CO2 absorption capacity in the range of 319–333 mgCO2·g−s1. The thermogravimetric analysis results show ∼ 26 wt% of the carbonation sites are participating in the fast CO2 absorption (∼ 298 mgCO2·g−s1·min−1). The use of these sorbents with 1 wt% Pt/Al2O3 catalysts in the water gas shift reaction show a 103% increase in the hydrogen yield compared to the equilibrium concentration at 600◦C. The Li4SiO4 sorbent-catalyst combination show a shift in the equilibrium by preventing the reverse reaction in the temperature range of 600–650◦C. The SEWGS experiments show that the CO2 absorption capacities, and consequently the hydrogen yields, are affected by the diffusional resistance across Li2CO3 and Li2SiO3 product domains in the sorbent. The Li4SiO4 conversion rates during the SEWGS reaction are measured by sampling at different points in the SEWGS reaction and subsequent Rietveld analysis of the XRD patterns. The XRD results suggest the decrease in CO2 absorption rates as a result of the formation of additional Li2CO3 and Li2SiO3 fractions with decreasing Li4SiO4 phase in this nano-structured composite.