Preparation and Absorption Behaviors Study of Doped Li4SiO4 At Low CO2 Concentration

Preparation and Absorption Behaviors Study of Doped Li₄SiO₄ at Low CO₂ Concentration

Sai Zhang, Qi Zhang*,Qian Ye, Haiyan Wang, Zibin Zhu

Dept. of Chemical Engineering, East China University of Science and Technology, Shanghai 200237, China

Abstract

Different K-doped Li₄SiO₄ samples were prepared to improve the pure Li₄SiO₄ adsorbent's sorption/desorption properties in the critical SESMR practical conditions with low CO₂ partial pressure and steam atmosphere. The optimized sample was analyzed by sorption experiments and simulation with FactSage5.5 Software. The results show that the K-doped Li₄SiO₄ has a better CO₂ absorption ability than pure Li₄SiO₄ as the K can form a eutectic compound with Li₄SiO₄ which enhances the Li⁺ and O^2- ions diffusion and thus facilitating the CO₂ absorption ability of Li₄SiO₄. It is also found that steam not only enhances the Li⁺ mobility but also reacts with Li₄SiO₄, therefore increase the mass uptake of the adsorbent. In order to make the adsorbent more practical, sorption-desorption cycle processes were also carried out. The results show that the optimized Li₄SiO₄ has a lower desorption temperature and stable absorption ability.

Furthermore, the sorbents, Li₄SiO₄ and different K-doped Li₄SiO₄, were evaluated using a bench scale unit, of which the results can provide reference for the subsequent industrial design. Li₄SiO₄ and different K-doped Li₄SiO₄ were prepared by solid-state reaction method. The results was obtained from the studies of different Li₄SiO₄ samples in a fixed-bed reactor with 15%CO₂ and 85%N₂ at 575°æ. The pure Li₄SiO₄ showed a short breakthrough time, approximately 20 min, while modified Li₄SiO₄ samples presented a relative 20~40 min longer breakthrough time under same conditions. The results of the experiment indicate that doping K into Li₄SiO₄ can improve the adsorption capacity of the sorbents. Comparing with MgO-based K₂CO₃^[1] and hydrotalcites^[2] sorbents, which breakthrough time are no more than 40min and 13min, respectively, the relatively long breakthrough time of K-doped Li₄SiO₄ exhibits huge potential for industrial applications. K-Li₄SiO₄ with good performance at low CO₂ partial pressure can be applied into sorption enhanced steam methane reforming system, in which the CO₂ concentration can be also as low as 15%. Meanwhile, the regeneration period can be prolonged by doping appropriate amount K into Li4SiO4, which means cost for recycling can be reduced as a result. K-doped Li4SiO4 has a certain value in industrial application, both practicability and economically.

Key words: CO₂ acceptors, Lithium orthosilicate, on-line absorption behaviors

References

[1]Soo Chool Lee, Ho Jin Chae, et al. Development of Regenerable MgO-Based Sorbent Promoted with K2CO3 for CO2 Capture at Low Temperatures[J]. Environ.Sci. Technol, 2008, 42: 2736-2741

[2]Hendricus Th. J. Reijers, Sacha E. A.Valster-schiermeier, et al. Hydrotalcite as CO2 Sorbent for Sorption-Enhanced Steam Reforming of Methane[J]. Ind. Eng. Chem. Res, 2006, 45, 2522-2530