| Alkanolamine solutions are used as solvents in CO2 absorption,especially CO2 in biogas.However,up to now,traditional alkanolamine solution for absorbing CO2 have been proven high energy consumption in regenerating,serious corrosion on equipment and easy to degrade,etc.Thus,sustainable and practical solutions to overcome the problem of CO2 absorption efficiently are urgently required.In order to alleviate the negative effect of traditional alkanolamine solution,some new ideas-hypotheses on adjusting chemical structure were presented.Propyl diethanolamine(PDEA),a high performance amine solvent,was evaluated in CO2 absorption and regenerative performance with investigating corrosivity and thermodynamics in this thesis.Firstly,the PDEA synthetic conditions(reactant ratio,reaction temperature and reaction time)were optimized by orthogonal experiment.PDEA was synthesized through SN2 Hoffman alkylation reaction,with using propyl bromide and diethanolamine(DEA)as raw materials.The results derived from this study clearly demonstrated optimal conditional parameters were npropyl bromide/nDEA=0.2:0.1,nsodium carbonate/nDEA=0.09:0.1,79 ?(reaction temperature)and 8 h(reaction time).In addition,adding 2%Nal could improve 9.07%on conversion of product under the optimal conditions,which has a better catalysis on the reaction rate compared to PEG400.Secondly,the performance of PDEA during absorption and regenerative process on CO2 were also discussed mainly by chemical methods.According to bubble absorption experiment,PDEA/H2O could reach equilibrium in a shorter absorption time compared to MDEA/H2O under the same conditions.On the other hand,equilibrium absorption and removal rate of PDEA/H2O were higher than MDEA/H2O,with increased ratio of 15.9%,8.94%,respectively.Additionally,the results of regeneration experiment showed that degree of regeneration on CO2 was 55.4%higher than MDEA,with nearly two-time cycling net load of MDEA.It also showed that the absorption capacity of CO2 after the third regeneration was about 85%of the first regeneration,indicating that the regeneration performance was better and could be used repeatedly.Furthermore,conjugated acid dissociation constant(pKa)of PDEA,combining the formation regularity of ions in the reaction system,demonstrated that as loading of CO2 increased(pH value decreased),free amine(PDEA)concentration decreased with concentration of protonated amine(PDEAH+)and HCO3-increasing as well as CO32-concentration increased first and then decreased.Finally,corrosion regularity of carbon steel in various amine solvents were analyzed by gravity drop method.The results showed the corrosivity of various amine solvents differed and followed the sequence of Equilibrium amine solvent>Regenerated amine solvent>Original amine solvent.In particular,the corrosion rate of original PDEA solvent and regenerated PDEA solvent were lower than MDEA,while the corrosion rate of PDEA per unit CO2 absorption capacity was close to MDEA.After corrosion,the surface of carbon steel was filmed with a thick layer of corrosion product,which was speculated to be FeCO3 according to XRD analysis. |
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