Research On A Novel CO₂ Mineralization Process Integrated With A Thermochemical Cycle For H₂O Splitting

The anthropogenic emission of CO₂,mainly induced by excess fossil fuel consumption,contributes significantly to global warming and climate change.Various methods of CO₂ reduction have been developed.To provide a solution to the drawbacks of Carbon capture and storage（CCS）,CO₂ mineralization is developed,which has the ability to safely and permanently store CO₂ if successfully implemented.However,despite the intrinsic advantages,CO₂ mineralization processes using natural magnesium silicates are still confronted by high energy consumption and poor economic aspects.A novel CO₂ mineralization process integrated with the sulfur-iodine thermochemical cycle for H₂O splitting is developed by Zhejiang university.The CO₂ mineralization process is innovatively introduced to take the place of the electroosmosis and distillation steps of the HI solution in a conventional SI cycle.As a result,CO₂ is fixed by magnesium silicate minerals while H₂O is split to produce the ideal clean hydrogen energy.Experiment and simulation are both conducted to study the novel process.A fixed bed experimental system is used to study the hydrolyzation of MgI₂ and the carbonation of Mg（OH）₂.The technical feasibility and energy economy of the novel process are investigated.Results show that the vaporization of MgI₂ solution results in the crystallization of magnesium iodide hydrate,which then dehydrates and releases HI when the temperature is increased.The complete hydrolyzation of MgI₂ products Mg₂（OH）₃I and HI.There is an upper bond of hydrolyzation rate found to be 75%.The addition of vapor during hydrolyzation reaction can reduce the temperature requirement of reaching max hydrolyzation rate.The carbonation of Mg（OH）₂ at 100℃and 1 bar results in a carbonation conversion rate of 26.9%,which is much more reactive than the（Finnish）serpentinite-based hydroxide used by Fagerlund.The large difference in reactivity may be explained by the different surface areas and pore volumes.A process simulation for the whole system is developed.The effects of different design parameters on the thermal efficiency are studied,including Bunsen reaction products,hydrolyzation rate of MgI₂and carbonation rate of Mg（OH）₂.Results show that the main heat consuming step is the vaporization of H₂O and I₂ in MgI₂ solution.Thermal efficiency can be effectively improved by change the operation conditions of Bunsen reaction to increase the value of HI/（HI+H₂O+I₂）in HI_x phase.The maximum thermal efficiency calculated among these simulation cases is 47.6%when waste heat recovery is considered.A modified calculation for net energy requirement per kg CO₂ fixed is carried out so that a comparison and evaluation of the energy efficiency between different CO₂ mineralization processes can be made.The optimal result among these simulation cases is 1.4 MJ per kg CO₂ fixed.The energy requirement of this novel process is superior to that of discussed processes using magnesium silicate minerals.Considering the energy for capture by this chilled ammonia process,the total energy requirement for the process in this paper is 3.45 MJ per kg CO₂ fixed.