Designing Of Mineralization Technologies Of CO₂ Capturing And Utilization For Systematic Manufacturing Of CaCO₃ Materials And Their Applications

Synthetic approaches enclosed within the current thesis are the proposed green routes for CO2 mineralization aimed at the production of CaCO3 materials of high values known as aragonite and vaterite.Given the challenges accounted for controlling the polymorphism of CaCO3 that initially resulted in a mixture of phases of the end product,techniques designed herein demonstrated high efficiency in selecting and stabilizing both the compositional phase and control of the crystal's properties.Besides,the techniques are eco-friendly to meet the demand for sustainable manufacturing because they could ensure the recyclability of the additives employed in the systems without leaving behind potential environmental wastes or by-products.As such,we first proposed a high-pressure solid-gas reaction technique to produce vaterite without adding water in the system(note that the system could not produce aragonite CaCO3 type).The system developed herein,was efficient to suppress the passivation phenomenon accounted for in the carbonation reaction to alter the surface reactivity of Ca(OH)2 reactant to achieve the incomplete carbonation.The study showed that urea via its melt would entrap the portlandite into a molten mass and produce tiny water to initiate the carbonation reaction.Thus,vaterite could be stabilized by an amine functional group of the melted urea while high-pressure CO2 inhibited the decomposition of urea besides being the reactant.This platform has many advantages to suppress industrial effluents generated from conventional aqueous synthetic methods,production of unstable phase vaterite,and reusability of the additives.Secondly,a strategy for CO2 capture into a solid material and its further utilization was proposed.Unlike the traditional ways of using absorbent solutions for CO2 capture which could result in solvent loss in solution,this work proposed a synthetic platform to capture CO2 into a solid CO2 storage material(CO2CSM)from ethylenediamine(EDA)and 1,4-butanediol(BDO)solutions.Experimental pathways and analytical data proved that the CO2CSM could capture and release enough CO2 when prepared under supercritical condition.Thus,it could be used efficiently to produce controlled CaCO3 materials,providing a selectivity of vaterite,aragonite,and calcite polymorphs of high purities.Also,the system provided an easy recycling way to continuously capture and store CO2 for further utilization.In the synthesis of CaCO3 products,a tiny amount of water added into the system of a mixture of CO2 storage material and Ca(OH)2 or CaO in a solid-solid type reaction could facilitate the dissociation and hydration of lime and CaO,respectively.This way,the precipitation of CaCO3 polymorphs could be directed at the organic functional matrix to enhance their control and stability,and therefore,aragonite,vaterite,and calcite could be obtained.Thirdly,a green-based CO2 responsive switchable solvent in the aqueous system was designed.The switchable solvent which normally is immiscible in water could then form a homogeneous mixture when exposed to CO2 by a formation of bicarbonate ions.The latter could be consumed upon the precipitation of CaCO3 allowing the deprotonation of the solvent to its hydrophobic nature.Thus,the system has merits of CO2 capture,easy solvent recovery,and the selectivity of the CaCO3 crystals.Thus,CaCO3 polymorph phases(aragonite and vaterite)were produced and could be tailored upon controlling the experimental conditions.The study revealed that the chemical functional groups of the switchable solvents could enhance the selectivity of a specific polymorph and prevent its rapid phase transformation to a more stable form.In this way,the phase transition is a slow-driven process to allow easy control and selection of a desired crystal's phase or size.Moreover,crystal morphology could also be tailored;as such,spherical and cone-like vaterite morphologies could be synthesized while long rod-like and short spindlelike aragonite particles were also obtained by this solvent-based system.Finally,we designed a simple procedure to regenerate CO2 responsive switchable solvent employed in the system.Finally,CaCO3 products(aragonite,vaterite,and calcite)obtained by the above routes,were investigated for possible alteration of additive sources for enhancing the properties of the polyethersulfone(PES)and polydimethylsiloxane(PDMS)membranes as well as lubricant oils.Results revealed that the CaCO3 vaterite powder prepared by the CO2 responsive switchable solvent approach improved the property of the PES membrane enhancing the wettability of the membrane.Not only,vaterite improved the hydrophilicity characteristic of the PES membrane,but also it positively influenced the tensile strength of the doped-membrane to withstand tension,a desired characteristic for manufacturing of small-sized membranes.The opposite observation was noticed for the PDMS hybrid membrane whereby the same vaterite particles increased the hydrophobic behavior of the blended membrane.For example,the additio On of vaterite content(4 wt.%)increased the tensile strength of the PDMS/CaCO3 and PES/CaCO3 from 6.865 to 11.278 MPa;and 1.961 to 3.923 MPa,respectively.Moreover,it was noticed that the applied aragonite and vaterite particles(obtained by synthetic systems introduced in the respective chapters 3 and 4)into lubrication of 500SN ester oil could result into a significant decrease of friction behavior of the tribopair(stainless-steel ball,Automatic four-ball tribological testing machine SGW-10A)of about 35 and 42%for aragonite,whereas vaterite attained 30 and 40%at 0.1 wt.%loading,respectively;which would have an economical and industrial significance for employing CaCO3 products as lubricant additives.