A novel process for CO₂ capture by using sodium metaborate. Part I: effects of calcination

This paper presents a comprehensive study on the carbonation of sodium metaborate (NaBO₂) and the synthesis of high added value chemicals via NaBO₂ and carbon dioxide (CO₂). Carbon dioxide (CO₂) is a greenhouse gas and NaBO₂ is a by-product of sodium borohydride (NaBH₄) hydrolysis reaction to produce H₂. Therefore their transformation into commercial chemicals is quite important in order to provide a mutual benefit to global warming issue and hydrogen economy. In the presented study, reaction parameters such as hydration factor, furnace type, calcination temperature, and environment are investigated at different levels and optimized. The effects of those key parameters on CO₂ fixation yield are discussed. It is found that 400 °C is a key temperature for dehydration and reaction steps. Both dehydrated NaBO₂ is obtained and maximum carbonation conversion is reached at 400 °C. Moreover, at relatively low temperatures (below 400 °C), a new reaction pathway is proposed and proved by thermodynamic calculations. Structural properties of NaBO₂ are exhibited differences regard to thermal exposure and the conversion is strictly related to the structural properties.