Investigations to convert CO2, NaCl and H2O into Na2CO3 and HCl by thermal solar energy with high solar efficiency

•Solar driven conversion of CO2 to Na2CO3.•Concentrated HClaq by MgCl2/MgO modified ammonia soda process.•Chemical storage of thermal solar energy with high efficiency.

Exhaust CO2, NaCl and H2O can be converted to Na2CO3 and HCl by the MgCl2/MgO modified ammonia soda process at a maximum temperature of 525 °C. Such a temperature is easily reached by solar troughs. Subsequently this process stores thermal solar energy as chemical energy and concomitantly CO2 can be removed from the environment. The process has been investigated theoretically and experimentally to further enhance its solar efficiency. It is shown theoretically that Mg-compounds are unique for this process and that the MgCl2/MgO modification is optimal. Experiments demonstrate that by splitting the main reaction of this process into two steps the solar efficiency can be enhanced to 21.5% and very highly concentrated HClaq can be obtained. The yield of the main chemical reaction exceeds 95% at 525 °C. Suggestions are given for an improved thermal solar trough system to perform the main chemical reaction.

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