(533b) Plastic Pyrolysis Gas Purification and Polymorph Control of Metal Carbonate Using Captured CO2 By Deep Eutectic Solvents

Due to the recent exponential increase production of plastic waste, the need for its treatment has become crucial. Pyrolysis technology, which pyrolyzes plastic waste to generate useful materials through it, is currently gaining a lot of attention. By definition, pyrolysis is the thermal decomposition of a material in an oxygen-free condition. In pyrolysis, the plastic waste feedstock is introduced into a reactor at 450–600 ℃ to produce a vapor which consists of condensable and non-condensable fractions. After condensation, the condensed vapor which is known as pyrolysis oil can be used as an auxiliary fuel and a chemical raw material. However, non-condensing vapor is a mixture of gases containing large amounts of CO₂, H₂, CH_4, and C₂H₄ approximately 15%, 49%, 22%, and 14%, respectively. It is generally used as a fuel for pyrolysis that produces heat. Non-condensing gas contains about 15% of CO_2, it reduces calorific value and utilization. To increase the calorific value and efficiency of utilization, it is necessary to remove CO₂ from non-condensing gas. To do so, the carbon capture, and utilization (CCU) technology that presents several available processes for use can be applied. Mineral carbonation, among CCU technologies, can sequester CO₂ on a large scale; does not require additional energy consumption because no catalyst is required for metal carbonate formation, and the generated carbonate can be reused or sold, finally improving the economy of the process.

Deep eutectic solvents (DESs), eutectic mixtures of two or more components by hydrogen bond, have been identified as a novel class of Ionic liquids(ILs). DESs are synthesized by mixing a hydrogen bond acceptor (HBA) and a hydrogen bond donor (HBD) and have similar properties and characteristics as ILs, such as existing as a liquid below 100℃. However, DESs have a high viscosity disadvantage via hydrogen bonding, which causes the gas mass transfer problem. To enhance the gas mass transfer of DESs, H₂O is added to compensate for the high viscosity of DESs. H₂O can serve as a lubricant with very low friction while in liquid absorption using DESs. Furthermore, the ILs-H₂O system has also been used to create a shape-specific and shape-controlled synthesis of nanoparticles.

Throughout this study, DESs were synthesized by mixing CO₂-active site-containing HBD such as monoethanolamine and used HBA such as choline chloride, and tetrabutylammonium bromide. Then to compensate for the high viscosity of DESs, H₂O was added and CO₂ contained in the non-condensing gas was removed by the synthesized DESs-H₂O system. Following that, mineral carbonation, among CCU technologies, was applied to utilize the absorbed CO₂ without additional energy. In the mineral carbonation process, the CO₂ in CO₂-saturated DESs reacted with calcium ions, and then the absorbed CO₂ and calcium ions are converted into calcium carbonate. Furthermore, the Fourier transform infrared spectroscopy (FT-IR) and ¹H nuclear magnetic resonance (NMR) analyses were conducted for the investigated samples to analyze the absorption mechanism between CO₂ and DESs, and to compare changes in the DES properties depending on the water contents. In addition, the crystallographic properties of the calcium carbonate were investigated using X-ray diffraction (XRD) analysis. FT-IR analysis was used to validate the non-crystallographic properties of the calcium carbonate which is are not detected via XRD analysis. Finally, scanning electron microscopy (SEM) was used to verify the crystal shapes of the product and support XRD and FT-IR results.