Study On Capturing Acid Gas By Phase Change In Organic System

The large emission of CO₂ and SO₂ from coal-fired is a serious threat to the survival and development of human beings,It is urgent to solve the problem that how to reduce the emission of acid gas.Although conventional removal of CO₂ and SO₂has been applied in industry,requires significant energy use for regeneration of the absorbent.The CO₂ phase-change absorption was investigated to reduce energy consumption of regeneration.In this system,the homogeneous solvent is separated into a CO₂-rich phase and a CO₂-lean phase after CO₂ loading,and only the CO₂-rich phase needs to be heated for regeneration.While,the CO₂-lean phase can be used directly for the reuse.It's obvious that lower energy required because of only the product being heated.The liquid-liquid phase-change absorption is mostly concentrated on lipophilic amine aqueous,a sort of CO₂ absorbent in nonaqueous system was developed to achieve liquid-liquid phase-change absorption.Based on the similarity structure and property of CO₂ and SO₂,we succesfully developed DMI/organic solvent as SO₂ absorbent,which can achieve liquid-solid phase-change absorption.We also found some ILs for SO₂ capture exhibit liquid-solid phase-change behavior.They showed excellent performance for SO₂ capture due to the excellent properties of ILs and the characteristics of phase change absorption to reduce the energy consumption of desorption.The main research contents of this paper include the following three aspects:?1?A class of CO₂ absorbent was selected in organic solvent with high boiling point and low viscosity.The D230/DEGDME system showed excellent liquid-lolid phase-change performance.The FTIR results showed that there is no effect on the structure of product in different solvent.Combined with ¹³C NMR,it was further proved that D230-carbamate formed with equimolar CO₂ absorption.In this system,the capacity of CO₂ absorption decreases with the increase of temperature.The quantitative results of NMR show that the content of carbamate in the lower phase is close to 90%,which is an excellent phase change absorption system.The capacity of CO₂ in the five-cycle absorption experiment remains basically unchanged and has a very stable absorption performance.?2?In this work,the DMI with weak N atom as absorbent in organic solvents,which was developed to liquid-solid phase-change capture of SO₂.The FTIR and XRD results demonstrated that there is no effect on the structure of product in different solvents.The in-situ FTIR results indicated that SO₂ firstly reacted with DMI to form a charge-transfer complex,which is very unstable in the air.It can easily absorb water and convert to pyrosulfite.The GC and mass balance results showed that more than 90%SO₂ loaded are enriched in solid phase.A crystal of?C₅H₉N₂?₂S₂O₆was prepared by the recrystallization of the absorption product powder in methanol solution.The residual DMI and SO₂ in the filtrate would convert to sulfate crystal of?C₅H₉N₂?₂SO₄ after several days.TG-DSC analysis showed that it was difficult to regenerate DMI by the traditional heating method.But?C₅H₉N₂?₂S₂O₅ can replace SO₂ as a sulfur source to synthesize chemical products with high added value.?3?Liquid-solid phase-change behavior of aqueous PSP-based ILs were developed for SO₂ capture.The experimental result indicated that the type of anion has no effect on composition and structure of the absorption product.The in-situ FTIR results indicated that SO₂ reacted with PSP ILs to form a charge-transfer complex without water.In the presence of water,there is only[PSP]⁺[HSO₃]^-/neutral organic acids without[PSPH₂][SO₃]formed.The mechanism of SO₂ absorption was proposed by in-situ FTIR and¹H NMR.Interestingly,with the p Ka value of anions increasing,its absorption capability of SO₂ can be improved significantly.In addition,the capacity of SO₂ absorption decreases with the increase of temperature.A TG-DSC experiment shows that it can be effectively regenerated by conventional heating.What's more,the capacity of SO₂ absorption keep stability with no obvious loss after five recycles,showing highly reversible and effective,which is considered to be a promising absorption system.