Experimental Study And Degradation Analysis Of CO₂ Absorbent

Chemical absorption method is the most mature technology for capturing CO₂ in the coal-fired flue gas,but this method could lead to corrosion,foaming,solvent degradation and other issues.In this paper,ethanol?MEA?and N-?2-hydroxyethyl?ethylenediamine?AEEA?were selected for studying the possible degradation mechanism of alcohol amine in the process of CO₂ capture.Firstly,the relationship between cyclic absorption and desroption performance and degradation of AEEA and MEA were studied.Then AEEA-based mixture absorbents with diethanolamine?DEA?,piperazine?PZ?and N-methyldiethanolamine?MDEA?were compared to select 3 solvents with the best absorption effect,and the relationship between cyclic performance and degradation of the 3 solvents were studied.Besides,the thermol and oxidation degradation of AEEA and MEA were studied by high pressure reactor.The adsorption and desorption properties of MEA and AEEA with 10%mass fraction were studied under the conditions of absorption temperature of 40?and desorption temperature of 120?.The results show that AEEA 6 cycles of absorption load and absorption rate are better than that of MEA,AEEA 6 cycles of regeneration temperatures are lower than MEA's,and AEEA cyclic regeneration rate and regeneration rate are lower than MEA.In the third cycle of the experiment,AEEA produced N-?2-hydroxyethyl?-diethylene triamine,and MEA produced AEEA,and these two degradation products can increase the reabsorption load.DEA,PZ,MDEA with the mass fraction ratio of 20:1,20:3,and 20:5 were added respectly into AEEA solution to make up 9 mixted solvents.The absorption load,absorption rate,desorption rate and regeneration rate of these 9 solvents were compared.The results show that 3 solvents with the best initial absorption effect are 20:5 AEEA+PZ>20:1 AEEA+DEA>20:3 AEEA+MDEA.And their first desorption performance show that 20:5 AEEA and PZ complex solution is the best CO₂ absorbent.The results of studying the relationship between cyclic absorption and desroption performance and degradation of 20:5 AEEA+PZ,20:1 AEEA+DEA and 20:3 AEEA+MDEA show that the initial absorption load of all the mixed amine solutions is the largest,and all mixed solvents can degrade to 1-?2-hydroxyethyl?-2-imidazolidinone?HEIA?and2,5-dipiperidone,which are harmful to cyclic absorption.But they can also degrade to favorable products.20:5 AEEA+PZ mixed solution can degrade to N-?2-hydroxyethyl?diethylenetriamine;20:1 AEEA+DEA solution can degrade to PZ;and 20:3 AEEA+MDEA solution can degrade to DEA,which can continue degrading to PZ.After 6 cycles of experiments,the degradation degree of AEEA-based three complex solutions and AEEA monoamine solution is:20:1 AEEA+DEA>AEEA>20:3 AEEA+MDEA>20:5 AEEEA+PZ.In the thermal degradation experiment,250 mL MEA solution with mass fraction of 30%was forced to degrade for 10 day at 2.0 MPa by using high pressure reactor.The experimental results show that the increase of CO₂ loads?0.45 molCO₂/mol amine?and temperature can increase the thermal degradation rate and degradation products rate of MEA.The iron ions have no effect on the degradation rate of MEA,and play no role in the MEA thermal degradation process.The main products of pure thermal degradation are ethylene glycol and ammonia.Products of thermal degradation with CO₂ load?0.45 molCO₂/mol amine?are mainly 2-oxazolidinone?OZD?,HEIA,AEEA.Oxidation degradation experiment of 250 mL 30%MEA solution were studied on the basis of thermal degradation experiment at 120?and 2.0 MPa.Results show that without CO₂ load oxidation productions of MEA are mainly ammonia,N-?2-hydroxyethyl?formamide?HEF?,N-?2-hydroxyethyl?acetamide?HEA?,N-(2?2-hydroxyethyl?oxalamide?BHEOX?,1-?2-hydroxyethyl?piperazin?HEPO?;MEA loaded with CO₂?0.45 molCO₂/mol amine?,a new degradation OZD appears,which can increase the production rate of NH₃,HEA and HEPO.Iron ions can increase the six kinds of degradation products.