Efficient Capture Of SO₂ By Porous Chitin Microspheres Supported With Deep Eutectic Solvent

Sulfur dioxide(SO2)is one of the main atmospheric pollutants emitted by industrial sources.Direct emissions not only cause serious ecological damage such as ozone holes and acid rain,but also pose a threat to human health.Furthermore,SO2 is also an important chemical raw material.It can not only be used to produce sulfurcontaining compounds such as sulfuric acid,sulfur trioxide,and sulfite,but also for food additives such as bleach,reducing agents,and preservatives.Therefore,being able to efficiently and reversibly capture SO2 gas and recycle it can bring huge environmental and economic benefits.The traditional process methods for capturing SO2 mainly include wet desulfurization,dry desulfurization,and semi dry desulfurization,which may encounter problems such as high cost,low efficiency,difficult recovery and secondary pollution to some extent.In recent years,a large number of new adsorption materials have been developed,such as ionic liquids(ILs)with high atomic utilization and designable structures,Deep eutectic solvents(DESs),solid adsorption materials such as carbon based,zeolite,MOFs with low energy consumption and pollution,and membrane separation technology with simple installation and easy operation.DESs are considered promising absorbents for SO2 capture due to their designable structure and environmentally friendly properties.However,like ILs,the high viscosity of most DESs to some extent limits their application in the SO2 separation industry.In order to eliminate the impact of high viscosity on material adsorption and improve the capture efficiency of SO2,we consider dispersing and loading DESs onto porous materials to fully expand them to reduce the viscosity effect during the elimination of adsorption.Chitin nanofiber carbon microspheres(NCMs),a porous nanofiber carbon material obtained from biomass pyrolysis and carbonization,have a wide range of raw materials,low prices,and simple preparation,making it an ideal carrier material.The extensive pore structure of NCMs not only provides a large number of loading sites for Deep eutectic solvents,but also forms a retention effect on gas molecules,enabling them to adsorb SO2 more efficiently.This article combines the advantages of solid adsorbents and DESs to develop a new type of composite adsorption material.Porous biomass carbon material is selected as the carrier,and alkaline groups that can strongly interact with SO2 are loaded onto the porous carbon material through physical loading to prepare a composite adsorption material for SO2 capture research.Exploring the microstructure of materials using micro electron microscopy,determining the structure of materials using nuclear magnetic resonance hydrogen spectroscopy and infrared spectroscopy,characterizing the pore structure and specific surface area of materials using gas adsorption instruments,and exploring the thermal stability and actual load situation of materials using thermogravimetric analysis.Exploring the capture performance and selectivity of SO2 through dual reactor absorption and penetration devices.The specific research is as follows:Porous nanofiber carbon microspheres were prepared using chitin and applied for the first time in loaded 1-ethyl-3-methylimidazole chloride+imidazole type Deep eutectic solvents.Thus,a new type of composite adsorption material(NCMs-DESs)with a three-dimensional porous structure and a large specific surface area was formed.DESs are uniformly adsorbed on the carbon surface of chitin nanofibers,with strong loading capacity,low viscosity,and good stability.Using NCMs-DESs to capture SO2,the results showed that while retaining the excellent adsorption performance and cycling effect of DESs,NCMs-DESs eliminated the influence of viscosity and improved adsorption capacity and rate to a certain extent.At 25℃ and 1 kPa,the adsorption capacity of NCMs-5DESs for pure SO2 is as high as 14.66 mol/kg,which remains at 2.89 mol/kg even under low content SO2(1700 ppm)mixed gas,higher than most solid adsorbents reported in literature.The high adsorption capacity of NCMs-DESs is due to the porous structure of NCMs and the multiple interactions between DESs and SO2.Cl-in DESs has strong electron donating ability and weak alkalinity,and can interact with SO2 through electron deficiency and Lewis acidity.At the same time,there is also an H-bond interaction between DESs and SO2,which increases the adsorption stability of SO2.In addition,NCM-DESs absorbents exhibit excelient reversibility and seiectivity for SO2 adsorption.By constructing an adsorption model,we further explored the adsorption mechanism of NCM-DESs materials.Based on the fitting results,we found that the adsorption of SO2 by NCMDESs materials belongs to the process of simultaneous physical and chemical adsorption at multiple sites,with strong adsorption,high adsorption efficiency,and high degree of regeneration.It is an ideal adsorption material.Therefore,NCM-DESs adsorption materials may be the most promising candidate for capturing polluting gas SO2 due to their high selectivity,high cycling,and high stability.