The Research On Appilcation Of Aqueous Tertiary Amines And Derivative Solutions In CO₂ Capture

Post combustion CO₂ capture?PCC?is one of the most viable techonolgy to reduce greenhouse gas emission in the short and medium term.However,large scale and affordable CO₂ capture is currently limited by absorbents with somewhat non-optimised chemical and physical properties.Tertiary amines are thermodynamically efficient CO₂ capture absorbents but unfortunately suffer from low CO₂ absorption rates requiring larger absorption equipment compared to faster reacting absorbents.This work fouces on tertiary amines and their derivatives to explore next generation absorbents with high CO₂ absorption rate and desorption efficiency,reducing the energy penality for PCC.?1?Since the structure of tertiary amines varies a lot,their CO₂ capture performance differs from each other.This work tries to find monotertiary amine with high reactivity in CO₂absorption.The relationship between the structure of various commercial tertiary amines including N-methyldiethanole amine,triethanolamine,diethylethanolamine,etc.,and their activities in terms of CO₂ abosrption kinetic constant,equilibrium CO₂ solubility,pKa and heat of CO₂ absorption was revealed to provide guidelines for the beneficial structure feature.For example,the electronic donating group like ethyl group can improve tertiary amine reactivity with CO₂ while the additional hydroxythyl group or the short distantce between hydroxythyl group and amino group reduce tertiary amine performance in CO₂ absorption.?2?Some tertiary amines were chosen based on the relationship between molecular structure and activities in CO₂ absorption for modeling study.Experimental data for the equilibrium system were acquired to systematically study three important factors in terms of temperature,amine concentration and CO₂ partial pressure.For the equilibrium amine-CO₂-H₂O ternary system,this work established different thermodynamic moels i.e.Kent-Eisenberg,Modified Kent-Eisenberg,Correction factor and activity coefficient models to correlate and analysis experimental data.Various equations according to chemical reaction,phase behaviour and mass balance in CO₂ absorption were established to describe the system mathematically.The activity coefficient model was suitable for different amine systems to provide most accurate prediction.It could also make reasonable extrapolation outside the experimental conditions.?3?In order to improve the molecular efficiency of tertiary amine,this work screened three symmetrical tertiary diamines,N,N,N',N'-tetramethyl-1,2-ethanediamine,N,N,N',N'-tetramethyl-1,3-propanediamine and N,N,N',N'-tetramethyl-1,4-butanediamine for application in PCC.A competition relationship between two amino functional groups was found during the acidification of amine solutions and CO₂ absorption.Tertiary diamine showed similar CO₂absorption performance as monoamine when the competition was obvious.This intramolecular effect could be reduced via molecular modification which enabled diamine to show higher molecular efficiency than monoamine.Results proved that diamine had great advantageous in carbon capture.?4?Tertiary amine is limited to the low CO₂ absopriotn rate due to the reaction mechanism.Diamnes with one tertiary amino group and one primary amine group and tunable molecular structure are proposed to contribute favorably to improve absorbent performance and robustness for CO₂ capture.In this work,N,N-dimethyl-1,2-ethanediamine N,N-dimethyl-1,3-propanediamine,4-amino-1-methylpiperidine and 4-amino-1-propylpiperidine were investigated to reveal the impact of chain length,linear and cyclic structure on absorbent performance.The results here in terms of the observed CO₂ absorption rate,equilibrium CO₂ solubility,CO₂ desorption rate,CO₂ desorption rate and cyclic capacity affirmed that the appropriate distribution of amino functional groups and introduction of cyclic structure strongly improve the general performance of the absorbents evaluated here.?5?The use of formulated CO₂ capture absorbents incorporating simple aliphatic amines and diamines as promoters in tertiary amine solutions have been suggested and evaluated.The overall CO₂ absorption properties i.e.absorption rate,equilibrium CO₂ solubility,desorption rate and cyclic capacity are typically evaluated as well as the chemical contribution of the promoter to the underlying speciation in the solutions are addressed here.Results showed that the new proposed formulated absorbent with 4-amino-1-methylpiperidine and diethylethanolamine has comparable CO₂ absorption rate,high equilibrium CO₂ solubility and especially superior desorption efficiency,indicating a lower energy penalty.The formulated solutions show great potential to be a promising absorbent in PCC.