“a promoter-activator blend as absorbent for carbon dioxide capture”

Abstract

The present invention relates to an aqueous amine blend for capturing of carbon dioxide from flue gases. The absorbent of the present invention exhibits high equilibrium CO2 loading, low regeneration heat duty, high regeneration efficiency, high cyclic equilibrium CO2 loading, high cyclic capacity, high initial CO2 absorption and desorption rate and low toxicity. The absorbent comprises of a diamine and a tertiary amine. The diamine is Hexamethylenediamine (HMDA) that is present in an amount ranging from 0.05–0.20 mole fraction and the tertiary amine is 2-Dimethylaminoethanol (DMAE) that is present in an amount ranging from 0.80–0.95 mole fraction. The absorbent exhibits equilibrium carbon dioxide loading in a range of 0.7155–1.2174 mol CO2 / mol amine. Figure 1 on sheet no. 1 of the drawings may accompany the abstract when published.

Description

FIELD OF THE INVENTIONThe present invention relates to the field of capturing carbon dioxide from fluegases. More particularly, the present invention relates to a cost-effective and aneco-friendly aqueous amine blend that exhibits high equilibrium CO2 loading,low regeneration heat duty, high regeneration efficiency, high cyclicequilibrium CO2 loading, high cyclic capacity, high initial CO2 absorption anddesorption rate, and low toxicity.BACKGROUND OF THE INVENTIONCarbon dioxide (CO2) is captured from the exhaust of a combustion process byabsorbing it in a suitable solvent; this is called CO2 capture from flue gases. Theabsorbed CO2 is liberated from the solvent during regeneration, and this CO2 iscompressed for transportation and storage. In this process, CO2 is removedfrom the combustion reaction product stream called flue gases before emissionto the atmosphere. A wide range of technologies is available or underdevelopment to address the problem of CO2 separation from flue gases. The useof chemical solvents, such as Monoethanolamine (MEA), is the most matureand is widely deployed method of CO2 capture. Further, the literature alsoreported that Dimethylethanolamine (DMAE) also offered excellentabsorption and desorption rate, low regeneration energy demand, low heat ofCO2 absorption and low desorption enthalpy than conventional MEA. A largenumber of amines are available, but choosing an efficient amine blend thatperforms well in all aspects of CO2 absorption and desorption is not so easy.The screening of amine blends is very tough. It has been discovered that themany amine blends do not show good CO2 absorption and desorption results.The heat duty required to regenerate the CO2-saturated amine blend is high andlow regeneration efficiency was also discovered with most of the amine blends.High toxicity is the major concern for most of the amines. Hence, the selectionof an amine blend is a rigorous process, and it takes much time to performexperiments on the laboratory scale to achieve the best possible operatingconditions.US11224836 discloses about the methods and solvent compositions useful forcarbon capture. The solvents may include an aqueous mixture of 2-Amino-2-methylproponol, 2-Piperazine-1-ethylamine, Diethylenetriamine, 2-Methylamino-2-methyl-1-propanol, and potassium carbonate or potassiumcarbonate buffer salt. However, the methods and compositions disclosed in thecited document are time-consuming.US20230078337 discloses about the methods and compositions to capturecarbon dioxide from an exhaust stream of a hydrocarbon combustion emitter.The solvent comprises Diethylaminoethanol (DEAE), Hexamethylenediamine(HMDA), water, and Polyethylenimine (PEI). DEAE is present in molarconcentration ranging from 2.0 M to 4.0 M, HMDA is present in molarconcentration ranging from 0.1 M to 1.0 M, and PEI is present in molarconcentration ranging from 0.001 M to 0.5 M and the total molar concentrationof the solvent is in the range of 2.10 M to 5.5 M. However, the solvent disclosedin the cited document does not show good results in terms of equilibrium CO2loading, cyclic capacity and absorption-desorption rate.Ling et al., in Energy Fuels 2019, 33, 7614; doi:10.1021 / acs.energyfuels.9b01764 discloses the characterization andcorrelations of CO2 absorption performance in an aqueous amine blendedsolution of Monoethanolamine (MEA) and N, N-Dimethylethanolamine(DMEA) in a packed column. However, the accuracy of the volumetric overallmass transfer coefficient prediction of different solution systems in the packedcolumn needs further investigation and verification.Ji et al., in Applied Energy 225 (2018) 356-366; doi:10.1016 / j.apenergy.2018.04.108, discloses an integrated absorptionmineralization process for CO2 sequestration from flue gas that integratesamine scrubbing, CO2 mineralization and amine regeneration in a singleprocess. The technical feasibility of absorption-mineralization process and theassociated mechanism was investigated by adding CaO or fly ash into CO2-loaded amine solutions, including the five commonly used amines: MEA,Diethanolamine (DEA), Piperazine (PZ), and N-Methyldiethanolamine(MDEA). However, the leaching and accumulation of various metals from flyash may affect the CO2 absorption performance and are likely to require a newamine-CO2 contactor instead of a packing column. The dissolved metals leadto amine degradation.In view of the above, the existing state of the art has many limitations, such ascostly amines, which influence the overall CO2 capture cost, low CO2absorption, and desorption rate. Further, most of the widely employed aminesare highly toxic, which adversely harms the environment. Low equilibriumCO2 loading and low cyclic capacity of most of the previously reported aqueousamines or their various blends are major issues. High demand for solventregeneration heat and low solvent regeneration efficiency are the prime issuesof most of the amine blends.Therefore, there is a need to resolve the aforementioned challenges by exploringamine blends that would be capable of overcoming the challenges of lowequilibrium CO2 loading, low cyclic capacity, high regeneration heat dutydemand, low regeneration efficiency, and high toxicity.OBJECT OF THE INVENTIONThe main object of the present invention is to provide a promoter-activatorblend as absorbent for carbon dioxide capture from flue gases.Another object of the present invention is to provide a cost-effective, ecofriendly and least toxic absorbent for capturing carbon dioxide from flue gases.Yet another object of the present invention is to provide an absorbent thatresolves the issues of the low equilibrium CO2 loading and low cyclic capacityrelated to carbon dioxide capture.Yet another object of the present invention is to provide an absorbent thatexhibits low heat duty and high regeneration efficiency for capturing carbondioxide from flue gases.Still another object of the present invention is to provide an absorbentcomprising of a primary and a tertiary amine that reduces the overall cost of theamine blend.SUMMARY OF THE INVENTIONThe present invention relates to a promoter-activator blend as absorbent ofHexamethylenediamine (HMDA) and 2-Dimethylaminoethanol (DMAE) thatis prepared for carbon dioxide capture from flue gases. The absorbent exhibitsefficient heat duty, regeneration efficiency, cyclic equilibrium CO2 loading,cyclic capacity, CO2 absorption and desorption rate.In an embodiment, the present invention provides a promoter-activator blendas absorbent for carbon dioxide capture comprising of a plurality of aminesincluding a primary diamine that is Hexamethylenediamine (HMDA) in anamount ranging from 0.05-0.20 mole fraction and a tertiary amine that is 2-Dimethylaminoethanol (DMAE) in an amount ranging from 0.80-0.95 molefraction. Further, the absorbent is in the form of an aqueous binary amine blendin a concentration ranging from 1-3 mol / L.The present invention relates to the promoter-activator blend as absorbent forcapturing carbon dioxide emitted from various industries in the form of fluegas, emitted from coal-fired thermal power plants, cement industries, refineries,integrated steel industries, ethylene industries and CO2 emission from blastfurnaces.The above objects and advantages of the present invention will becomeapparent from the hereinafter set forth brief description of the drawings,detailed description of the invention, and claims appended herewith.BRIEF DESCRIPTION OF THE DRAWINGSAn understanding of the promoter-activator blend as absorbent for carbondioxide capture of the present invention may be obtained by reference to thefollowing drawings:Figure 1 is a schematic representation of the absorption setup employed toperform absorption experiments for the aqueous amine blend ofHMDA+DMAE for CO2 capture, according to an embodiment of the presentinvention.Figure 2 is a schematic representation of the desorption setup employed toevaluate the performance of the aqueous amine blend of HMDA+DMAE forCO2 capture, according to the present invention.Figure 3 is a graphical representation illustrating: the effect of temperature (T)on equilibrium CO2 loading (α) for C = 1, 2, and 3 mol / L at constant PCO2 =25.33 kPa and mHMDA = 0.20 in part (a); the effect of CO2 partial pressure (PCO2)on equilibrium CO2 loading (α) for C = 1, 2, and 3 mol / L at constant T =313.15 K and mHMDA = 0.20 in part (b); the effect of mole fraction of HMDA(mHMDA) on equilibrium CO2 loading (α) for C = 1, 2, and 3 mol / L at constantPCO2 = 20.27 kPa and T = 313.15 K in part (c); the effect of solutionconcentration (C) on equilibrium CO2 loading (α) for mHMDA = 0.05, 0.10, 0.15,0.20 at constant T = 313.15 K and PCO2 = 20.27 kPa in part (d); the effect ofCO2 loading time on equilibrium CO2 loading (α) for mHMDA = 0.05, 0.10, 0.15,and 0.20 at constant C = 1 mol / L, T = 313.15 K, and PCO2 = 20.27 kPa in part(e); and parity plot of experimental (αexSymbol) and calculated (αcal) CO2 loading forthe aqueous amine blend of HMDA+DMAE in part (f), according to thepresent invention.Figure 4 is a graphical representation illustrating cyclic equilibrium CO2loading (Δα) and cyclic capacity for 30 wt% MEA and for solutionconcentrations, i.e., C = 1, 2, and 3 mol / L at T = 313.15 K, PCOTwo = 25.33 kPa,and mHMDA = 0.20 for the aqueous amine blend of HMDA+DMAE for CO2capture, according to the present invention.Figure 5 is a graphical representation for the correlation between solutionconcentration and molar ratio of HMDA on heat duty illustrating: comparisonbetween the heat duty values for 30 wt% MEA and solution concentration, i.e.,C = 1, 2, and 3 mol / L for the aqueous amine blend of HMDA+DMAE forCO2 capture in part (a); and the effect of increasing the HMDA molar ratio inthe aqueous amine blend of HMDA+DMAE on heat duty at T = 313.15 K,PCOTwo = 25.33 kPa, and C = 3 mol / L in part (b), according to the presentinvention.Figure 6 is a graphical representation illustrating effect of increasing molar ratioof HMDA in the aqueous amine blend of HMDA+DMAE on the initialabsorption rate in part (a); and the effect of increasing molar ratio of HMDA inthe aqueous amine blend of HMDA+DMAE on the initial desorption rate inpart (b), according to the present invention.Figure 7 is a graphical representation illustrating the effect of solutionconcentration, i.e., C = 1, 2, and 3 mol / L on solution pH for CO2-unloaded,CO2-loaded, and CO2-regenerated aqueous amine blend of HMDA+DMAE atT = 313.15 K, PCOTwo = 25.33 kPa, and mHMDA = 0.20, according to the presentinvention.Figure 8(a) is a graphical representation of nuclear magnetic resonance (NMR)spectroscopic analysis of the CO2-unloaded sample for the aqueous amineblend of HMDA+DMAE for CO2 capture, according to the present invention.Figure 8(b) is a graphical representation of NMR spectroscopic analysis of theCO2-loaded sample for the aqueous amine blend of HMDA+DMAE for CO2capture, according to the present invention.Figure 8(c) is a graphical representation of NMR spectroscopic analysis of theCO2-regenerated sample for the aqueous amine blend of HMDA+DMAE forCO2 capture, according to the present invention.Figure 9 is a graphical representation illustrating FTIR investigation of speciespresent in CO2-unloaded, CO2-loaded and CO2-regenerated solutions of theaqueous amine blend of HMDA+DMAE for CO2 capture, according to thepresent invention.Figure 10 is a graphical representation illustrating toxicity assessment in termsof LD50 values for various conventional amines, according to the presentinvention.DETAILED DESCRIPTION OF THE INVENTIONThe present invention will now be described hereinafter with reference to theaccompanying drawings in which a preferred embodiment of the invention isshown. This invention may, however, be embodied in many different formsand should not be construed as being limited to the embodiment set forthherein. Rather, the embodiment is provided so that this disclosure will bethorough, and will fully convey the scope of the invention to those skilled inthe art.The present invention now will be described hereinafter with reference to thedetailed description, in which some, but not all embodiments of the inventionare indicated. Indeed, the invention may be embodied in many different formsand should not be construed as limited to the embodiments set forth herein;rather, these embodiments are provided so that this disclosure will satisfyapplicable legal requirements. Like numbers refer to like elements throughout.The present invention is described fully herein with non-limiting embodimentsand exemplary experimentation.The present invention provides a promoter-activator blend as absorbent forcarbon dioxide capture comprising of Hexamethylenediamine (HMDA) and 2-Dimethylaminoethanol (DMAE) for CO2 capture. The absorbent exhibits highequilibrium CO2 loading, low regeneration heat duty, high regenerationefficiency, high cyclic equilibrium CO2 loading, high cyclic capacity, highinitial CO2 absorption and desorption rate and low toxicity.In a preferred embodiment, the present invention provides a promoter-activatorblend as absorbent for carbon dioxide capture comprising of a plurality ofamine including a primary amine and a tertiary amine; wherein, said absorbentis in the form of an aqueous binary amine blend in a concentration rangingfrom 1-3 mol / L; said diamine is Hexamethylenediamine (HMDA) in anamount ranging from 0.05-0.20 mole fraction; said tertiary amine is 2-Dimethylaminoethanol (DMAE) in an amount ranging from 0.80-0.95 molefraction.Here, the absorbent exhibits equilibrium carbon dioxide loading of 1.2174 molCO2 / mol amine at a temperature of 298.15 K, CO2 partial pressure of 25.33kPa, mole fraction of HMDA of 0.20, and solution concentration of C of 1mol / L, exhibits absorption capacity in a range of 0.9647 to 2.7624 mol CO2 / Lsolution at a temperature ranging from 298.15-333.15 K, CO2 partial pressureranging from 10.13 to 25.33 kPa, mole fraction of HMDA ranging from 0.05 to0.20 and solution concentration ranging from 1 to 3 mol / L for absorption timeof 10 hours, exhibits carbon dioxide absorption rate ranging from 12 x 10-4 to26 x 10-4 mol CO2 / (L solution.min) and exhibits carbon dioxide desorption rateranging from 67 x 10-4 to 138 x 10-4 mol CO2 / (L solution.min).Further, the absorbent exhibits regeneration efficiency in range of 52.21-63.51% for solution concentration of 1-3 mol / L at a temperature of 313.15 K,CO2 partial pressure of 25.33 kPa, HMDA mole fraction of 0.20, regenerationtemperature of 393.15 K and pH of an aqueous amine blend regenerated aftercapturing carbon dioxide in a range of 9-11, exhibits cyclic capacity of 1.5951mol CO2 / L solution at concentration of 3 mol / L and cyclic equilibrium CO2loading ranging from 0.5317-0.6375 mol CO2 / mol amine for a concentrationranging from 1-3 mol / L at HMDA mole fraction value of 0.20, temperature of313.15 K, CO2 partial pressure of 25.33 kPa and regeneration temperature of393.15 K, exhibits heat duty of 357.11-131.24 kJ / mol CO2 for a solutionconcentration of 1-3 mol / L and exhibits heat duty in a range of 141.42-164.48kJ / mol CO2 on increasing molar ratio of HMDA at a concentration of HMDAranging from 0.5 mol / L to 2 mol / L in the aqueous binary amine blend in asolution concentration of 3 mol / L.In addition, the absorbent exhibits density of CO2-loaded samples in a range of1031.8 kg / m3 to 1093.2 kg / m3 with concentration of solution ranging from 1mol / L to 3 mol / L and exhibits pH in a range of 12.04-12.78 in CO2-unloadedsamples and pH in a range of 8.37-9.50 in CO2-loaded samples.Referring to Figure 1, a schematic representation of the absorption setupemployed to perform absorption experiments for the absorbent ofHMDA+DMAE for carbon dioxide capture, is depicted. The variouscomponents are as follows: CO2 gas cylinder (1); gas cylinder (2); pressureindicator (3); pressure regulator (4); control valve (5); digital mass flowcontroller (6); gas mixing chamber (7); gas mixing coils (8); T-joint (9); waterbath (10) with thermocouple; heating medium (11); agitator (12); gas disperser(13); bubble column reactor (14); thermometer (15); power indicator (16) ofwater bath; condenser (17); silica bed for moisture removal (18); portableinfrared CO2 gas analyzer (19); and outlet stream (20) is depicted.EXAMPLE 1For Experimental DetailsAqueous amine blend of Hexamethylenediamine (HMDA) and 2-Dimethylaminoethanol (DMAE)Hexamethylenediamine (HMDA) is a diamine that contains two primaryamino groups and two amino groups that are separated by six carbon atoms.When two amino groups go apart, a situation of decreasing electronic influencebetween the groups exists that causes an increase in CO2 absorption capacity.HMDA exhibits a high partial atomic charge on the nitrogen atom, whichmakes HMDA better than conventional amines. HMDA provides a high CO2absorption rate, high equilibrium CO2 loading, is miscible with water, possesseselevated boiling point, is less volatile, and is less corrosive than conventionalMonoethanolamine (MEA).2-Dimethylaminoethanol (DMAE) is a tertiary amine that contains two methylgroups attached to nitrogen atoms and one hydroxyethyl group. DMAE ischemically synthesized by the addition of an equal percentage of ethylene oxideand dimethylamine. High equilibrium CO2 loading, good degradationresistance, low viscosity, fabulous thermal stability, more pKa value, and leasttoxic behavior are the major advantages of DMAE.An aqueous amine blend of Hexamethylenediamine (HMDA) and 2-Dimethylaminoethanol (DMAE) was prepared for CO2 capture from fluegases. DMAE is feasible to be prepared from renewable energy resources(which is not possible in the case of most amines). Therefore, employingDMAE produced from such renewable resources is helpful in reducing theoverall cost of the process.The equilibrium CO2 loading of the aqueous amine blend is 1.2174 molCO2 / mol amine, which is much higher than conventional 30 wt% MEA andalso with most of the other amine blends previously reported. Speciationanalysis of the intermediate species formed in the CO2-unloaded, CO2-loaded,and CO2-regenerated aqueous amine blend samples was done by 13C NMR andFTIR techniques. Density estimation of different samples of HMDA+DMAEwas done in the chosen operating conditions. Heat duty, regenerationefficiency, cyclic equilibrium CO2 loading, cyclic capacity, initial CO2absorption and desorption rate estimation of the amine blend showedcommendable results as compared to 30 wt% traditional MEA. The toxicity ofaqueous amine blend is slightly toxic and is one of the novelties of the presentexperimental work since most of the reported amine blends are highly toxic,which leads to adverse environmental effects. The initial CO2 absorption anddesorption rates were examined to judge the performance of the aqueousHMDA+DMAE amine blend. On amine blending, the overall properties of theamine blend are enhanced and the individual disadvantages are balanced byanother amine. The performance of the aqueous amine blend ofHMDA+DMAE was checked by considering CO2 absorption and desorptionexperimental setups.Components of CO2 absorption experimental setupThe components that include nitrogen (N2) and carbon dioxide (CO2) cylinders,pressure indicator, regulators, control valves, digital mass flow controller, gasmixing chamber, gas mixing coils, T-joint, water bath with thermocouple,heating medium, agitator, gas disperser, bubble column reactor, thermometer,water bath's power indicator, condenser, silica gel bed, portable infrared CO2gas analyzer, were the essential auxiliaries involved in the CO2 absorptionsetup.Components of CO2 desorption experimental setupThe components that include three-necked round bottom flask, glass insulator,magnetic bead, condenser, oil bath, thermometer, thermocouple sensor, and anelectric hot plate with a magnetic stirrer were the major components of theregeneration setup. Further, the equilibrium CO2 loading for both CO2absorption and desorption investigation was estimated with the help of the'Chittick apparatus'.Processes and properties studiedEquilibrium CO2 loading, absorption capacity, cyclic equilibrium CO2 loading,cyclic capacity, heat duty, regeneration efficiency, initial CO2 absorption anddesorption rates, density estimation, pH effect, reaction mechanism, 13C NMRand FTIR characterization, and theoretical toxicity assessment were the majorexperimental outcomes.Description of CO2 absorption setupInitially, pure CO2 and N2 gas cylinders of 46.7 L volume and purity of 99.99% each were assisted in producing the simulated flue gas stream on thelaboratory scale. On the gas cylinders, pressure indicators and pressureregulators were made available to access the volume of gas available inside thecylinders and to turn the regulators completely on and off. The pressureregulators were helpful in extracting the gases from each of the cylinders thatwere routed through the control valve and then to the digitally controlled massflow controllers. The desired CO2 and N2 flow rates were achieved through thesupport of the digitally controlled mass flow controllers. The accuracy of thecontrollers was fabulous, and no variation in the total flow rate was seen. Everyexperiment was performed with a fixed flow rate of the total flue gas stream,and the stream acquired the specific mole percent of the CO2 gas for thedifferent experimental runs. The gases coming out from each cylinder weremixed adequately through a mixing chamber and further by helical mixingcoils. The outlet stream from the helical mixing coil exhibited a particular CO2mole percent in the flue gas, and the same was verified. As a result, the outletstream was sent through the portable infrared CO2 gas analyzer to checkwhether the theoretical volume percent of CO2 was actually displayed in theanalyzer or not. After the stream was passed to the analyzer and waited forsome time, the actual scenario emerged, and the theoretical volume percent ofCO2 based on specific CO2 partial pressure was attained, and the demonstrationby the analyzer indicated the preparation of flue gas that was ready to beemployed at the desired CO2 partial pressure.Further, the stream was passed through the gas dispenser, and the dispensercreated the wet gaseous mixture of CO2-based flue gas stream. The gaseousmixture leaving the dispenser was connected to the bubble column forabsorption. A digital water bath with high heating accuracy was utilized to heatthe water to provide the desired operating temperature. The water bathacquired the feature of a water shaker, and the shaking speed of the water bathwas controlled by a speed regulator to provide uniform water temperature. Athermometer was situated inside the water bath to double-check the water bathtemperature regularly, and no variation in the temperature was discovered. Theexperiments of CO2 absorption were conducted in the glass-based apparatus,i.e., borosilicate bubble column reactor (Length = 35.5 cm, Diameter = 3 cm,and Volume = 150 mL). Inside the bubble column reactor, a knowncomposition of the aqueous amine blend of HMDA+DMAE was poured. Theflue gas interacted with the aqueous amine blend inside the bubble columnreactor and gets absorbed with time in a semi-batch mode. The outlet stream ofthe bubble column reactor was condensed, and to remove moisture, the outletstream was attached to the bed of silica gel. Finally, the dried gas stream wasattached to the analyzer, and the analyzer provided the value of the CO2saturation level for the aqueous amine blend of HMDA+DMAE blend. Thecomplete pictorial representation of the CO2 absorption experimental setup isshown in Figure 1.CO2 absorption experimentsEach operating run set in the run sheet, as depicted in Table 1, was prepared insuch a way as to achieve a wide range of possible results. The results includeoptimum possible results amongst all the parameters for evaluation of theequilibrium CO2 loading for the aqueous amine blend of HMDA+DMAE. Thecomposition of CO2 in the flue gas stream was analyzed by a portable CO2 gasanalyzer and the composition was measured in volume %. A solution of 100mL of the aqueous amine blend of HMDA+DMAE was prepared by takingdouble distilled water for a specific operating condition. The prepared amineblend was filled within the bubble column reactor and dipped inside the waterbath. The digital water bath includes a collective assembly of an incubatorshaker, thermocouple, and heating indicator. All the essential components ofthe water bath aided to achieve the desired water bath temperature with acommendable accuracy of ±1 K. The accuracy of the water bath wascontinuously examined with an external thermometer located inside the waterbath having sub-divisions of 0.1 K. The flue gas stream with 240 mL / minuteof total constant gas flow rate was introduced to the amine blend to perform theabsorption experiments. The entire absorption experimental work wasperformed at one atmospheric pressure.The infrared-based portable CO2 gas analyzer examined the CO2 saturationlevel of the aqueous amine blend of HMDA+DMAE. The amount wasevaluated in volume percentage. The stream that left the bubble column reactorwas continuously monitored for a regular period of every 10 minutes. As CO2passes through the amine blend sample, it undergoes CO2 absorption andchemically reacts with the amine blend, thus known as 'CO2 loading'. Atcomplete CO2saturation, the pre-defined CO2 composition in the simulated fluegas is approximately equal to the outlet stream of the bubble column reactorpassing through silica gel, which is referred to as 'equilibrium CO2 loading'.When the aqueous amine blend solution of HMDA+DMAE was completelyCO2-saturated, the experiments were halted.The experimental equilibrium CO2 loading was calculated with the help of theChittick Apparatus. 1 mL of CO2-loaded amine sample at complete saturationwas titrated with the help of 1 molar stock solution of hydrochloric acid. Littledrops of indicator, i.e., methyl orange were added to the blend to ensure theend-point of the titration. The conversion of the yellowish to the pinkish-redcolor of the amine blend attained during titration showed that the titration wascompleted, and in that situation, the titration was then stopped. CO2-saturatedamine solutions were titrated thrice to assure accuracy, and the average valuewas finally considered. The amount of CO2 dissolved in the aqueous amineblend was proportional to the volume of water displaced while titrating thesolution. The volumetric approach helped in the determination of theequilibrium CO2 loading value.Operating conditions of CO2 absorption experimentsThe total flow rate of the simulated flue gas stream remained constant at 240mL / min during the entire experiment. As per the different CO2 partial pressure(PCOTwo) values (as depicted in Table 1), N2 gas with a flow rate ranging from180.0029 mL / min to 216.0059 mL / min and CO2 gas with a flow rate rangingfrom 23.9940 mL / min to 59.9970 mL / min was taken to prepare simulated fluegas inside the mixing chamber and then passed through the helical coil. TheCO2 absorption experiments were conducted at one atmospheric pressure.Equilibrium CO2 loading was the most significant aspect of CO2 absorptioninvestigation that depends upon five parameters such as temperature (T), CO2partial pressure (PCOTwo), mole fraction of activator, HMDA (mHMDA), solutionconcentration (C) and absorption time (θ). The ranges of the aforementionedoperating parameters that were considered are as follows: T = 298.15-333.15K; PCOTwo = 10.13-25.33 kPa; mHMDA = 0.05-0.20; C = 1-3 mol / L; and θ = 10hours (or complete saturation). Based on the operating parameters, differentrun sets were manually prepared, and was found that at T = 298.15 K, PCOTwo =25.33 kPa, mHMDA = 0.20, and C = 1 mol / L, the amine blend ofHMDA+DMAE yielded optimum equilibrium CO2 loading of 1.2174 molCO2 / mol amine. An uncertainty (i.e., error bar) of ±0.5 mL of waterdisplacement was observed during titration that led to the uncertainty of ±0.02mol CO2 / mol amine in the value of equilibrium CO2 loading. The equilibriumCO2 loading (α) and absorption capacity were calculated through the equation(1) and equation (2), respectively:Equationwhere α represents equilibrium CO2 loading and VCOTwo, Cblend, VCOTwo saturated, Tare the volume of CO2 gas released (L) from the amine solution, amine blendconcentration (mol / L), volume of CO2 saturated amine sample (L), and roomtemperature (°C).Description and operating conditions of CO2 desorption setupA regeneration reactor consists of a three-necked round bottom flask ofborosilicate that assisted in performing the overall desorption experiments. Theregeneration reactor with a volume capacity of 500 mL was charged with 60mL of the CO2-loaded aqueous amine blend of HMDA+DMAE from one ofthe necks, referred to as a sampling point. An analog thermometer was putinside the second neck of the desorption reactor to examine the temperature ofthe amine blend situated inside the regeneration reactor. The reactor's last neckwas connected with the condenser to condense the vapors of the amine blend.Digitally operated chilled water circulator (Company: Equitron Medica PrivateLimited, Mumbai, India; Model: #8502.ROT.000; Serial No.:8502.ROT.000.BAB.002034.AX; Temperature range: up to -10°C; Capacity: 4L; Watts: 400 W) was connected with the condenser that continuouslycirculated the chilled water through the condenser. Two of the reactor's neckswere closed with glass stoppers, and the third neck was linked to the condenserto ensure that no leakage occurred. The glass insulator was filled with a siliconoil bath for heating purposes, and the regeneration reactor containing theaqueous amine blend was dipped inside the oil bath. Silicon oil is highly viscous(viscosity = 300 centistokes) and colorless in nature that is heated up to 250°C.The entire glass insulator was placed on an electrically operated hot plate witha facility of magnetic stirring. The hot plate provided a continuous supply ofheat that heated the sample of the amine blend through silicon oil. Theregeneration reactor was filled with CO2-loaded HMDA+DMAE amine blend,and the oil bath was heated to 393.15 K (regeneration temperature). Athermocouple sensor dipped inside the oil bath measured the temperaturecorrectly. Maintaining the fixed oil bath temperature of 393.15 K was tough;slight fluctuations were seen in the temperature, and a deviation of ±5 K wasobserved, as indicated by the thermocouple.A magnetic bead situated inside the regeneration reactor was employed to mixthe amine sample uniformly at a stirring speed of 500 rpm. The water chillercirculated the cooling water to the condenser at a temperature of 288 K. Duringthe entire experiment, the condenser helped to prevent amine and watervaporization losses. The outlet stream of the condenser was routed to the bedof silica gel to remove the moisture. The amine blend temperature reachedthermal equilibrium with the oil bath in around 10-15 minutes. Afterequilibrium was achieved, at every 5 minute interval, the amine blend samplewas drawn out to estimate the equilibrium CO2 loading through the Chittickapparatus. The same process continued till the amine solvent showed arepetitive equilibrium CO2 loading.The complete diagrammatic representation of the desorption setup is shown inFigure 2. The cyclic equilibrium CO2 loading (Δα) and cyclic capacity (C.C)are two essential aspects of desorption study that are represented by equation(3) and equation (4).∆α = αThreeOneThree.OneFive K,TwoFive.ThreeThree kPa - αThreeεThree.OneFive K,TwoFive.ThreeThree kPa ; mol COTwo / mol amine ......... (3)C. C = ∆α. Cblend ; mol COTwo / L solution ........................ (4)EXAMPLE 2Equilibrium CO2 loading estimationExperimental outcomes of CO2 absorptionBefore conduction of the actual CO2 absorption experiments, validation of theexperimental setup with a benchmark solution of 30 wt% MEA was critical.Equilibrium CO2 loading, cyclic capacity, cyclic equilibrium CO2 loading, andinitial CO2 absorption rate were the main parameters for investigation of CO2absorption.Calculations for equilibrium CO2 loadingFor the aqueous amine blend of HMDA+DMAE, the equilibrium CO2 loading(α) was calculated with the help of Chittick apparatus through waterdisplacement method. Based on operating parameters (T, PCOTwo, mHMDA and C),a total of 40 experimental run sets were manually created to analyze the effectof all the parameters on equilibrium CO2 loading. At T = 298.15 K, PCOTwo =25.33 kPa, mHMDA = 0.20, and C = 1 mol / L, the amine blend ofHMDA+DMAE yielded optimum α = 1.2174 mol CO2 / mol amine. Theexperimental results were validated by an empirical modeling equation(equation 5) and a fabulous percentage average absolute relative deviation (%AARD) of 3.06 % was obtained.αcal = aOne + aTwoT + aThreeTTwo + aFourPCOTwo + aFivePCOTwo Two + aSixmHMDA + aSevenmHMDA Two + aEightC +aεCTwo ................................................ (5)where, αcal = Model calculated equilibrium CO2 loading; aOne to aε = Unknowncoefficient; T = Operating temperature; PCOTwo = CO2 partial pressure; andmHMDA = Mole fraction of HMDA.The above modeling equation (5) is only valid for T = 298.15-333.15 K, PCOTwo= 10.13-25.33 kPa, mHMDA = 0.05-0.20, and C = 1-3 mol / L. Table 2 showsthe values of unknown coefficients that were calculated through MicrosoftExcel solver.Percentage absolute relative deviation (% ARD) and % AARD were calculatedby equation (6) and equation (7).Equationwhere, N = Total number of experiments; αexSymbol = Experimental equilibriumCO2 loading.Table 1: Experimental equilibrium CO2 loading (αexp) and calculatedequilibrium CO2 loading (αcal) for the aqueous amine blend ofHMDA+DMAE under the specified operating condition at atmosphericpressureaNote: aStandard uncertainties u are u(T) = 1 K, u(PCOTwo) = 0.05 kPa, u(mHMDA)= 0.001, u(C) = 0.01 mol / L and u(α) = 0.02 mol COTwo / mol amine.As per equation (5), the unknown coefficients involved in the modelingequation were calculated by the Microsoft Excel solver with the help ofoperating conditions of parameters such as T, PCOTwo, mHMDA, C andαexSymbol as reported in Table 1. The equilibrium CO2 loading was calculated bymodel developed equation (5) after finding unknown coefficients, as reportedin Table 1 as αcal. Further, the deviation between αexSymbol and αcal was calculatedas % ARD by equation (6) and % AARD by equation (7). The parity plot ofαexSymbol and αcal CO2 loading is shown in part (f) of Figure 3.Table 2: Values of the unknown coefficients involved in the empiricalmodeling associated with the experimental data setsAbsorption capacityThe absorption capacity of aqueous amine blend was calculated by equation (2)and it was calculated for 40 experimental run set as represented in Table 1. Theabsorption capacity was calculated for operating condition: T = 298.15-333.15K, PCOTwo = 10.13-25.33 kPa, mHMDA = 0.05-0.20, C = 1-3 mol / L and absorptiontime of 10 hours. It was found that the absorption capacity of aqueous amineblend of HMDA+DMAE was lying in the range of 0.9647 to 2.7624 molCO2 / L.EXAMPLE 3Effect of operating parameter on equilibrium CO2 loadingThe effect of various operating parameters such as temperature (T), partialpressure of CO2 (PCOTwo), mole fraction of HMDA (mHMDA), concentration ofsolution concentration (C) and operating time on equilibrium CO2 loading areas follows:Effect of temperature on equilibrium CO2 loadingTo judge the effect of T on α value, the experiments were performed at atemperature (T) ranging from 298.15 to 333.15 K, where CO2 partial pressureand mole fraction of HMDA remained constant, i.e., 25.33 kPa and 0.20. Theeffect of temperature was analyzed for the aforementioned operating conditionsfor different solution concentrations, i.e., C = 1, 2, and 3 mol / L. Part (a) inFigure 3 represents the relationship between the T and α. The α value was highat low temperature, and further started to decrease with increasing temperature.Therefore, minimum and maximum equilibrium CO2 loading for C = 1, 2, and3 mol / L was attained at T = 333.15 K and 298.15 K. The main reason for thescenario is stated by Le-Chatelier's principle. The principle dictates that as thetemperature rises, the gas-liquid equilibrium shifts in the backward direction;therefore, the solubility of a gas in the aqueous amine blend is highest at thelowest temperature and vice-versa. Another important reason is that desorptiondominates over absorption at high temperatures because the CO2 gas moleculestry to escape from the aqueous amine blend, which reduces the equilibrium CO2loading. Therefore, high α value was obtained at low temperatures and viceversa.Effect of partial pressure of CO2 on equilibrium CO2 loadingTo check the effect of partial pressure of CO2, the experiments were done at aconstant T and mHMDA of 313.15 K and 0.20. The variation of PCOTwo was in therange of 10.13 to 25.33 kPa for different solution concentrations, i.e., C = 1, 2,and 3 mol / L. Part (b) of Figure 3 represents the relationship between CO2partial pressure and equilibrium CO2 loading. On raising the value of PCOTwo thevalue of α also increased in the PCOTwo range, i.e., from 10.13 to 25.33 kPa. Therelationship between PCOTwo and α was followed by all different solutionconcentrations, i.e., C = 1, 2, and 3 mol / L. Henry's law states that the solubilityof any gas in a liquid is directly proportional to the partial pressure of the gas.Therefore, on raising PCOTwo value, the driving force increases, which alsoincreases interfacial mass transfer, leading to the dissolution of more CO2molecules available in the amine blend of HMDA+DMAE. Based on α valuedata, as presented in Table 1 and part (b) of Figure 3, the aqueous amine blendperfectly obeys Henry's law.Effect of mole fraction of HMDA on equilibrium CO2 loadingThe effect of raising the activator's mole fraction (i.e., HMDA) in the aqueousamine blend of HMDA+DMAE on the α value was evaluated. To judge theeffect of mHMDA on the α value, the experiments were conducted at a constantPCOTwo and T, i.e., 20.27 kPa and 313.15 K. The value of mHMDA varied from 0.05to 0.20, and the effect on α value was observed for various solutionconcentrations, i.e., C = 1, 2, and 3 mol / L. Part (c) of Figure 3 represents therelationship between the mole fraction of HMDA and equilibrium CO2 loading.The primary and secondary amines are categorized as activators and arecapable of attaining the highest theoretical α value of 0.5 mol CO2 / mol amine.Likewise, the tertiary amines are known as promoters that are capable ofachieving the maximum theoretical α value of 1 mol CO2 / mol amine. As aresult, blending the high kinetics HMDA with the low kinetics DMAE wasfruitful in achieving high equilibrium CO2 loading, enhanced absorption rate,fabulous degradation resistance, and so on. Therefore, the effect of theactivator's mole fraction (HMDA) on the promoter (DMAE) was analyzed inthe above-mentioned operating conditions. On enhancing mHMDA value from0.05 to 0.20, α value also enhanced accordingly. The minimum and maximumα value was attained at PCOTwo = 20.27 kPa and T = 313.15 K on varying mHMDAfrom 0.05 to 0.20, for every C = 1, 2, and 3 mol / L. HMDA is a diamine withtwo primary amino groups present in its chemical structure and the nitrogenatom in HMDA possess a high partial atomic charge that led to high reactivitytowards CO2 as compared with most conventional amines. Therefore,enhancement of mHMDA in the aqueous amine blend of HMDA+DMAE alsoenhances the α value that was also validated by the actual experimental runs.Increase in the value of mHMDA, the value of α also increases, but at the sametime, the ∆Habs value also increases, which is not fruitful. As a result, the rangeof mHMDA was varied from 0.05 to 0.20, and a further increase in the value ofmHMDA will impart an enormous hike in overall ∆Habs value of the aqueousamine blend of HMDA+DMAE.Effect of solution concentration on equilibrium CO2 loadingThe effect of increasing the solution concentration on α value of the aqueousamine blend of HMDA+DMAE has been studied. Choosing the appropriateconcentration of the solution to attain the maximum α value was essential. Toexamine the effect of solution concentration, the experiments were conductedat constant T of 313.15 K and PCOTwo of 20.27 kPa. The solution concentration ofthe aqueous amine blend was changed from 1 to 3 mol / L and the effect on theα value was determined for various mole fractions of HMDA, i.e., mHMDA =0.05, 0.10, 0.15, and 0.20. Part (d) of Figure 3 signifies the establishedcorrelation between the solution concentration and equilibrium CO2 loading.When concentration varied from 1 to 3 mol / L for every definite value ofmHMDA, the value of α decreased accordingly. Based on the above statement,the general trend for α value with respect to concentration is as follows: 1mol / L > 2 mol / L > 3 mol / L. The main reason is that on increasing thesolution concentration, the steric hindrance of the solution increased, whichacts as a barrier for converting carbamate into bicarbonate in the gas-liquidreaction that finally decreased the equilibrium CO2 loading. Another majorreason is based on Le-Chatelier's principle that inferred that as the solutionconcentration of the amine increases, the reacting amine molecules also getenhanced; however, simultaneously, the amine to CO2 ratio also rises thatresults in the decrease of α value. Finally, the maximum α value is attained atthe lower value of concentration and vice-versa. Therefore, the experimentalinvestigation (as depicted by Serial No. 09 of Table 1) for the aqueous amineblend of HMDA+DMAE determined αmaximum = 1.2174 mol CO2 / mol aminethat was attained at T = 298.15 K, PCOTwo = 25.33 kPa, mHMDA = 0.20, and C = 1mol / L.Effect of operating time on equilibrium CO2 loadingAbsorption time signifies the duration of the CO2 absorption within the amineblend. Absorption time is the reaction time of any amine blend at which thesolution becomes CO2-loaded. Based on the reactivity of amine, different amineblends possess different equilibrium absorption times to attain CO2 loading atequilibrium conditions. At the start of the experiments, the CO2 absorption ratewas fast, and after sometimes, the absorption rate was reduced as timeproceeded. The main reason for the scenario is that in the beginning, the amineblend solution tended to absorb more CO2 gas. When the amine blend solutionis about to attain CO2-saturation, the further addition of CO2 in the solutiondoes not impart much effect on CO2 loading, and the same scenario aroused atmaximum operating time. To examine the effect of absorption time on α valuefor the amine blend, the experiments were performed at constant T of 313.15 Kand PCOTwo of 20.27 kPa. C = 1 mol / L was selected to examine the absorptiontime effect for different mole fractions of HMDA, i.e., mHMDA = 0.05, 0.10,0.15, and 0.20. Part (e) of Figure 3 shows the influence of CO2 loading time onequilibrium CO2 loading. All experiments of the aqueous amine blend wereconducted for 10 hours of absorption time. The experimental results show thatup to 300 minutes of absorption time, the CO2 absorption rate was very fast,and enhanced CO2 loading in the amine blend was seen. Up to 300 minutes,the increment was approximately linear; however, after an absorption time of300 minutes, such increment of CO2 loading was drastically diminished. After500 minutes, a negligible increase in CO2 loading was seen and indicated thatthe aqueous amine blend of HMDA+DMAE was entirely CO2-saturated, andthe aqueous amine blend attained the scenario of equilibrium CO2 loading.EXAMPLE 4Cyclic equilibrium CO2 loading and cyclic capacityThe CO2-loaded aqueous amine blend of HMDA+DMAE was collected fromthe bubble column reactor for desorption experiments to check the performanceof the amine blend. In the industrial world, cyclic equilibrium CO2 loading andcyclic capacity are two critical parameters that are targeted for selecting thesuitable amine blend for CO2 capture from flue gases. The cyclic equilibriumCO2 loading (Δα) is defined as the difference between α values at a particulartemperature and the temperature at which the amine regeneration is conductedand PCOTwo remains constant throughout the process. Δα was estimated at twodifferent temperatures, i.e., T = 313.15 and 393.15 K at a constant PCOTwo = 25.33kPa. Similarly, the ability of amine to capture CO2 per mole amine per aminecycle through the CO2 capture unit is defined as the cyclic capacity (C.C).Initially, CO2-loaded samples with different solution concentrations, i.e., C =1, 2, and 3 mol / L, at constant mHMDA = 0.20 and PCOTwo = 25.33 kPa, weretargeted to investigate Δα and C.C of the aqueous amine blend. According tothe operating conditions, serial no. 07, 21, and 34 were selected, and theoperating conditions are represented in Table 1. A solution of 30 wt% MEAwas regenerated and was considered to evaluate the above-mentioned Δα andC.C to compare the experimental results. After desorption experiments wereconducted, the CO2-regenerated samples were taken off from the desorptionreactor and titrated thrice, and the average value was finally considered forfurther investigation. At T = 313.15 K and PCOTwo = 25.33 kPa, 30 wt% MEAsolution yielded α = 0.6313 mol CO2 / mol amine, Δα = 0.1972 mol CO2 / molamine and C.C = 0.986 mol CO2 / L solution. After 30 minutes of desorption,the amine blend solution led to the final CO2 loading of 0.5366, 0.3662, and0.3544 mol CO2 / mol amine, corresponding to serial no. 07 (C = 1 mol / L), 21(C = 2 mol / L), and 34 (C = 3 mol / L). The cyclic equilibrium CO2 loading andcyclic capacity of the aqueous amine blend of HMDA+DMAE are shown inFigure 4. The Δα value of solutions with concentration, i.e., C = 1 (serial no.07), 2 (serial no. 21), and 3 mol / L (serial no. 34), were 0.5862, 0.6375, and0.5317 mol CO2 / mol amine. The calculation shows that the cyclic capacity of3 mol / L solution was 1.5951 mol CO2 / L solution, which is 61.77 % greaterthan the 30 wt% benchmark MEA. The reason was due to the general trends ofCO2 cyclic capacity and based on amine classification, it is expressed as:Diamines > 3° amines > 2° amines > 1° amines. Therefore, HMDA is adiamine, and DMAE is 3° amines, so the aqueous amine blend ofHMDA+DMAE resulted in a high value of cyclic capacity. The result obtainedfor the cyclic capacity of the aqueous amine blend of HMDA+DMAE requiresa small size of the CO2 capture unit that needs a less solvent circulation rateand ultimately results in a reduction in the entire capital cost.EXAMPLE 5Heat duty and regeneration efficiencyFormula usedAccording to Figure 2, a hot plate heated the aqueous amine blend solutionexternally and served as a heating medium. Therefore, heat duty is defined asthe ratio of steady-state heat transfer from the silicon oil to the regenerationreactor to the amount of CO2 released from the CO2-saturated amine sample.Correlation by Fourier yielded heat transfer value that is expressed as:Equationwhere q is the steady state heat transfer (J / s); K denotes the thermalconductivity of the Pyrex glass material ( Wm-K); A represents the sphericalsurface area of the regeneration reactor normal to heat flow (m2); dT signifiesthe temperature difference between the oil bath and the amine blend solution(K); dx is the thickness of the regeneration reactor (m2). Specification for thechosen regeneration reactor are as follows: K = 1.14 Wm-K; A = 18.36 x 10-Fourm2; dT = 6 K; and dx = 1.8 x 10-Three m.The cyclic capacity of the aqueous amine blend is an essential parameter thatwas considered to calculate the amount of CO2 removed during theregeneration experiment and is estimated as follows:Equationwhere ∆α. Cblend represents the cyclic capacity of the amine blend (mol CO2 / Lsolution); V is the volume of the amine sample; t denotes the desorption time(sec). During desorption experiments, the aqueous amine blend sample showednearly constant equilibrium CO2 loading after 30 minutes of the experiment.According to equation (8) and equation (9), the overall formula for evaluatingheat duty is expressed as depicted in equation (10):EquationRegeneration efficiency (%) = ( Cyclic caSymbolacityAbsorSymboltion caSymbolacity) x 100 ......... (11)Experimental results of heat duty and regeneration efficiencyThe external heat needed to regenerate the CO2-loaded aqueous amine blendsolution is a critical aspect for the evaluation of the effectiveness of the aqueousamine blend; therefore, the external heat requirement during desorption isreferred to as heat duty. Heat duty data for 30 wt% MEA was 450 kJ / mol CO2,as per the previous investigation. Therefore, the heat duty data for MEA waschosen as a standard reference for further investigations. When CO2 getsabsorbed in the MEA solution, more stable carbamate is formed; therefore,while regeneration, high heat duty is required. When calculated by equation(8), the heat transfer value remained unchanged for the entire experimentalwork. Therefore, cyclic capacity became more prominent in determining heatduty, and the heat duty was inversely proportional to cyclic capacity.Experimental investigation on the cyclic capacity for the aqueous amine blendof HMDA+DMAE corresponding to solution concentration follows the trend:3 mol / L > 2 mol / L > 1 mol / L.The relationship between heat duty and different solution concentrations, i.e.,C = 1, 2, and 3 mol / L, along with conventional 30 wt% MEA, is shown in part(a) of Figure 5. The values of 357.11, 164.18, and 131.24 kJ / mol CO2 heat dutywere experimentally determined, corresponding to C = 1, 2, and 3 mol / L. Incomparison with 30 wt% of MEA, a reduction in heat duty of 20.64 %, 63.51%, and 70.83 % was achieved, corresponding to C = 1, 2, and 3 mol / L.Four different CO2 absorption experiments were done to judge the effect of themolar ratio of HMDA on heat duty. Operating conditions of such absorptionexperiments were as follows: Experiment 1st: 0.50 mol / L HMDA-2.50 mol / LDMAE (T = 313.15 K, PCOTwo = 25.33 kPa, mHMDA = 0.166, C = 3 mol / L, α =0.8784 mol CO2 / mol amine); Experiment 2nd: 1 mol / L HMDA-2 mol / LDMAE (T = 313.15 K, PCOTwo = 25.33 kPa, mHMDA = 0.333, C = 3 mol / L, α =0.9723 mol CO2 / mol amine); Experiment 3rd: 1.50 mol / L HMDA-1.50 mol / LDMAE (T = 313.15 K, PCOTwo = 25.33 kPa, mHMDA = 0.50, C = 3 mol / L, α =1.0456 mol CO2 / mol amine); and Experiment 4th: 2 mol / L HMDA-1 mol / LDMAE (T = 313.15 K, PCOTwo = 25.33 kPa, mHMDA = 0.667, C = 3 mol / L, α =1.1782 mol CO2 / mol amine). The effect of enhancement of the HMDA molarratio in the aqueous amine blend of HMDA+DMAE on heat duty is shown inpart (b) of Figure 5. On enhancing the amount of HMDA in an amine solution,the heat duty of regeneration also increased accordingly. When the HMDAmolar ratio was enhanced, the value of ∆Habs and HCOThree - ion formation alsoincreased; as a result, large heat was needed to regenerate the amine blends.The trend of effect of enhancing molar ratio of HMDA in the amine blend ofHMDA+DMAE on heat duty was as follows: 30 wt% MEA > 2 mol / LHMDA-1 mol / L DMAE > 1.50 mol / L HMDA-1.50 mol / L DMAE > 1mol / L HMDA-2 mol / L DMAE > 0.50 mol / L HMDA-2.50 mol / L DMAE.The regeneration efficiency for serial no. 07, 21, and 34 of Table 1 were foundto be 52.21, 63.51, and 60.47 %. The regeneration efficiency for 30 wt% MEAwas 31.23 %. According to the experimental data, the amine blend performedwell in terms of regeneration efficiency, which was approximately twice asefficient as 30 wt% MEA.EXAMPLE 6Initial CO2 absorption and desorption rateThe absorption rate directly impacts the absorption column size, and if theabsorption rate is fast, a smaller size of the absorption column is needed andvice-versa. The initial CO2 absorption rate was calculated for increase in theHMDA molar ratio in the amine blend of HMDA+DMAE, i.e., 0.5 mol / LHMDA-2.5 mol / L DMAE, 1 mol / L HMDA-2 mol / L DMAE, 1.5 mol / LHMDA-1.5 mol / L DMAE and 2 mol / L HMDA-1 mol / L DMAE and theexperiments were conducted at T = 313.15 K, PCOTwo = 25.33 kPa, and C = 3mol / L. The influence of increasing the molar ratio of HMDA on the initialabsorption rate was estimated according to the above-discussed operatingcondition and the same is shown in part (a) of Figure 6. The experimentalvalues of the CO2 absorption rate were compared with 30 wt% MEA solutionat the same operating parameters. The results show that on escalating theHMDA molar ratio in the aqueous amine blend of HMDA+DMAE, the CO2absorption rate was also increased.For 30 wt% MEA, the initial CO2 absorption rate was calculated as 16 x 10- 4mol CO2 / (L solution. min). In the sequence, the order of CO2 absorption ratefor the aqueous amine blend of HMDA+DMAE is as follows: 0.5 mol / LHMDA-2.5 mol / L DMAE < 1 mol / L HMDA-2 mol / L DMAE < 1.5 mol / LHMDA-1.5 mol / L DMAE < 2 mol / L HMDA-1 mol / L DMAE. When themolar ratio of HMDA to DMAE was 0.20, the absorption rate was slower than30 wt% MEA. In the case of 0.50 molar ratio, the rate of CO2 absorption of theaqueous amine blend was comparable with MEA, while in the rest of the cases,the absorption rate was faster than MEA. The main reason for this scenario wasdue to enhancing the HMDA molar ratio in the amine blend ofHMDA+DMAE which caused the higher CO2 gas molecule interactionbecause of the availability of two primary amino groups in the molecularstructure of HMDA. Solvents with high initial CO2 absorption rates werealways advantageous over other solvents in terms of an economic point of view.The initial CO2 absorption rate for 2 mol / L HMDA-1 mol / L DMAE was 26x 10- 4 mol CO2 / (L solution. min) that yielded a 62.5 % higher absorption ratethan 30 wt% MEA.Similarly, the CO2 desorption rates were also examined for the similarincreased composition of HMDA in the aqueous amine blend ofHMDA+DMAE. The CO2 absorption and desorption rates were two opposingprocesses. The relationship between different molar ratios of HMDA in theaqueous amine blend of HMDA+DMAE and 30 wt% MEA corresponding tothe initial desorption rate is shown in part (b) of Figure 6. The investigationrevealed that 30 wt% MEA exhibits a desorption rate of 96 x 10-4 mol CO2 / (Lsolution. min). The experimental trend of desorption rate on enhancing theHMDA molar ratio is as follows: 0.5 mol / L HMDA-2.5 mol / L DMAE > 1mol / L HMDA-2 mol / L DMAE > 1.5 mol / L HMDA-1.5 mol / L DMAE > 2mol / L HMDA-1 mol / L DMAE. When the molar ratios of HMDA to DMAEwere 0.20 and 0.5, the desorption rate was higher than 30 wt% MEA, and thedesorption rate was lower for the remaining cases. The experimentalinvestigation also revealed that results for the initial desorption rate wereincreased by decreasing the HMDA molar ratio in the amine blend from 2 to0.20. The main reason is that on enhancing the HMDA molar ratio in theamine blend, the concentration of DMAE gets reduced, which ultimatelyreduced the concentration of HCOThree - ions due to DMAE. When large moles ofHCOThree - ions are present in any amine blend system, enhancement of thedeprotonation of protonated amine (Amine - H+) becomes easy. Since thedecomposition efficiency of the HCOThree- ion is higher than that of carbamate ions.While reacting with the HCOThree- ions, the protonated amines form the carbonicacid (H2CO3) and further dissociate into CO2 and H2O, as depicted in equation(12) and equation (13).AmineH+ + HCOThree - <-> Amine + HTwoCOThree ........................... (12)HTwoCOThree <-> HTwoO + COTwo ....................................... (13)When protonated amines react with H2O, deprotonated amines were formed,however, the reaction path was very slow since the pH of H2O was lower thanHCOThree -AmineH+ + HTwoO <-> Amine + HThreeO+ ........................... (14)The initial CO2 desorption rate of 0.5 mol / L HMDA-2.5 mol / L DMAE was43.75 % higher than the benchmark 30 wt% MEA.EXAMPLE 7Density estimationThe density of the CO2-unloaded, CO2-loaded, and CO2-regenerated aqueousamine blend of HMDA+DMAE samples was measured through portabledensity meter DMATM 35 (Serial number: 82907440; Weight: 660 g; dimensions(L x W x H): 245 mm x 103 mm x 126 mm; accuracy: 0.001 g / cm3;reproducibility: 0.0007 g / cm3; measuring range: 0 g / cm3 to 3 g / cm3) that wasprocured by Anton Paar India Private Limited, Haryana, India.The density estimation for the CO2-unloaded, CO2-loaded, and CO2-regenerated aqueous amine blend samples was measured to judge the effect ofCO2 interaction with the aqueous amine blend of HMDA+DMAE. Referringto Table 1, serial no. 07, 09, 21, 34, and 40 were targeted to evaluate the densityof different amine blend samples. 13C NMR and FTIR characterization weredone for serial no. 07, maximum and minimum equilibrium CO2 loading wereprovided by serial no. 09 and serial no. 40, and the cyclic capacity (C.C) andcyclic equilibrium CO2 loading (∆α) were calculated by serial no. 07, 21, and34. Therefore, serial no. 07, 09, 21, 34, and 40 were chosen for densityestimation of CO2-unloaded, CO2-loaded, and CO2-regenerated amine blendsamples. Similarly, the influence of enhancement in the HMDA molar ratio inthe aqueous amine blend was judged for heat duty and regeneration efficiency.Therefore, Condition 1st: 0.5 mol / L HMDA-2.5 mol / L DMAE, Condition 2nd:1 mol / L HMDA-2 mol / L DMAE, Condition 3rd: 1.5 mol / L HMDA-1.5mol / L DMAE, and Condition 4th: 2 mol / L HMDA-1 mol / L DMAE werechosen for the density estimation. In the sequence, density for benchmark 30wt% MEA for CO2-unloaded, CO2-loaded, and CO2-regenerated was alsocalculated. The experimental density results for different runs are presented inTable 3.Based on the experimental density data for serial no. 07, 21, and 34, the densityfor all the CO2-unloaded amine blend samples was almost similar, and novariation in the density was observed. However, when CO2 was loaded in theamine sample, the density was increased as compared with CO2-unloadedsamples. According to the experimental investigation, the increment in densitywas also dependent upon the solution concentration, i.e., when the solutionconcentration increased from C = 1 mol / L to C = 3 mol / L, the density alsoenhanced correspondingly. On increasing the solution concentration, aminemolecules enhance, which increases the overall mass of the solution while thevolume remains unaffected; therefore, the solution density also increases. Onregenerating the solutions, the density of all the solutions decreased, and thedensity range of the solutions was almost similar; however, it was slightlyhigher than that of CO2-unloaded amine solutions. Similar tendencies of theresult were seen for all the experiments corresponding to the CO2-regeneratedamine samples. The main reason for this scenario is that when CO2 getsabsorbed in the amine sample, the mass of the solution increases, and the viceversa effect was encountered in the case of regeneration experiments, howeverthe volume change was negligible. Now, the reason for the higher value ofdensity for CO2-regenerated amine blends than CO2-loaded samples lies in thefact that while regenerating the solution, the liberation of the entire absorbedCO2 from the amine blend was impossible.Table 3: Density data for CO2-unloaded, CO2-loaded, and CO2-regenerateddifferent aqueous amine blend of HMDA+DMAE for CO2 captureEXAMPLE 8Effect of CO2 loading on pHThe nature of the amines is basic, and the basicity depends upon theconcentration of the aqueous solutions. Regarding CO2 capture behavior, pHis a critical factor to consider while judging the performance of any amine blendsolvent. Therefore, a considerable variation in the solution pH was observedwhen an aqueous amine blend of HMDA+DMAE interacted with the CO2.The change in pH value provides information about the level of CO2 loading inthe aqueous amine blend. Experimental results showed that CO2 loading wasinversely proportional to the solution pH. The entire family of amines possesspH values in the range of 11-12, and similar trends were observed for the CO2-unloaded amine samples, as listed in Table 1. Initially, pH of amine decreasedvery fast with time; however, as time proceeded, the pH-decreasing tendencyof the amine blend became sluggish because of the reduced CO2 loadingtendency of the aqueous amine blend. Firstly, the pH value of CO2-unloaded,CO2-loaded, and CO2-regenerated samples of 30 wt% MEA was measured,which yielded the pH values of 12.53, 8.50, and 10.21, respectively.The 40 experimental run sets were established, and the pH for CO2-unloaded,CO2-loaded, and pH values of a few CO2-regenerated samples were determined.Table 1 shows that the CO2-unloaded and CO2-loaded amine sample's pH lyingin the range of 12.04-12.78 and 8.37-9.50. The lowest value of pH for the CO2-loaded sample was 8.37, corresponding to serial no. 09 (T = 298.15 K, PCOTwo =25.33 kPa, mHMDA = 0.20, C = 1 mol / L and α = 1.2174 mol CO2 / mol amine).Likewise, the maximum pH value for the CO2-loaded amine blend sample was9.50, which was observed in serial no. 40 (T = 333.15 K, PCOTwo = 25.33 kPa,mHMDA = 0.20, and C = 3 mol / L, α = 0.7155 mol CO2 / mol amine). CO2-loadedamine blend samples in serial no. 07, 21, and 34 were regenerated, which ledto a final pH of 9.89, 10.51, and 10.54. The influence of solution concentrationon the pH value for CO2-unloaded, CO2-loaded, and CO2-regenerated amineblend samples is shown in Figure 7. When the concentration of the solutionincreased from 1 to 3 mol / L, the pH values for CO2-unloaded, CO2-loaded, andCO2-regenerated amine samples also increased accordingly. During CO2absorption experiments, carbamate, bicarbonate, and carbonate ions wereformed, resulting in a lowering of solution pH. When the CO2-loaded aqueousamine blend of HMDA+DMAE was heated, the bicarbonate and carbonateions dissociated during regeneration; thus, the captured CO2 in the amine blendwas liberated, and the solution tried to attain the original pH value that did nothappen so. Therefore, the pH of the CO2-regenerated samples was minutelylesser than that of CO2-unloaded amine blends because a percentage of CO2was still left over even after regenerating the solution. So, the experimentalresults show that the regenerated amine samples exhibit pH in a range of 9 to11.EXAMPLE 9Reaction mechanism of HMDA + DMAE + H2O + CO2When HMDA is blended with DMAE in the aqueous solution, an aqueousamine blend forms, and various sets of chemical reactions occur when thisblend physically reacts with CO2. These chemical reactions involve CO2solubility in the aqueous phase, H2O dissociation, HCOThree - and COThree Two- formation,and HMDA and DMAE intermediate reactions. Using 13C NMR and FTIRanalyses, ionic species available in the HMDA+DMAE amine blend system inCO2-unloaded, CO2-loaded, and CO2-regenerated samples were verified. Thefollowing are the complete sets of chemical reactions:Physical CO2 solubility:EquationDissociation of H2O molecule:EquationBicarbonate formation:EquationCarbonate formation:EquationHMDA intermediate reactions:HMDA + COTwoKFive <-> HMDA+COO- .......................... (20)HMDA + HMDA+COO- KSix <-> HMDA+ + HMDACOO- (Monocarbamateformation) ..................................................... (21)HMDAH+ + HTwoO KSeven <-> HMDA + HThreeO+ (Amine deprotonation) ............. (22)HMDACOO- + COTwo + HTwoOKEight <-> HThreeO+ + HMDA(COO-)Two (Bicarbamateformation) .............................................................. (23)HMDACOO- + HTwoOKε <-> HCOThree - + HMDA (Bicarbonate formation) ............. (24)HMDA + COTwo + HTwoOKOneZero <-> HCOThree - + HMDAH+ .................................. (25)DMAE intermediate reactions:DMAE + H+ KOneOne <-> DMAEH+ (Protonation of DMAE) ........................ (26)DMAE + COTwo + HTwoOKOneTwo <-> DMAEH+ + HCOThree - ................................. (27)Overall chemical reaction of the system2HMDA + 3DMAE + 4COTwo + 4HTwoOKOneThree <-> 3HCOThree - + COThree Two- + 2HMDAH+ +3DMAEH+ ........................................................................ (28)HCOTwo is the Henry's constant, equations 15 to equation 28 are the chemicalreactions of aqueous amine blend of HMDA+DMAE, K1 to K13 is chemicalreaction equilibrium.EXAMPLE 10Characterization techniques for the authentication of reaction mechanism13C NMR spectroscopyThe NMR experiments were performed with the OneBay NMR spectrometerinstrument. The instrument was designed by the company: BRUKER BioSpinINTERNATIONAL AG; Model specification: AVH D 500 AVANCE III HD500 MHz. The operating parameters were as follows: Operating spectralfrequency = 125.8131145 MHz; Time delay = 2 s; Spectral width = 29761.904Hz; Total no. of scans = 256; Acquisition time = 1.101 sThe spectral analysis of HMDA and DMAE species in the amine blendHMDA+DMAE was done by 13C NMR spectroscopy to validate theintermediate complexes formed while reacting with CO2, as discussed in thereaction mechanism. Referring to Table 1, serial no. 07 (T = 313.15 K, PCOTwo =25.33 kPa, mHMDA = 0.20, C = 1 mol / L, pHCOTwo-unloaded = 12.29, pHCOTwo-loaded= 8.50, and pHCOTwo-regener = 9.89) was selected to check the presence ofintermediate complexes in CO2-unloaded, CO2-loaded, and CO2-regeneratedamine blends.CO2-unloaded samplesFigure 8(a) represents the NMR spectroscopic analysis of the CO2-unloadedsample and the spectral peaks of DMAE were obtained at 44.32, 58.86, and59.74 ppm. The spectral peaks in the range of 44.32-59.74 ppm were due to theavailability of DMAE in the amine blend of HMDA+DMAE. As DMSO-d6was mixed with the amine samples to ensure signal locking, the peak of DMSOd6 was obtained at 39-41 ppm. Many spectral peaks of varying intensities ofHMDA were obtained at 25.90, 29.58, 30.36, 31.41, 31.58, 37.50, 37.67, 37.84,38.01, 38.18, 38.35, and 38.52 ppm. The presence of HMDA spectral peaks wasgenerally represented in the 25.90-38.52 ppm range for CO2-unloaded amineblends.CO2-loaded samplesWhen the CO2-absorption experiment was performed, CO2 chemically reactedwith the amine blend and formed carbamate (HTwoNCOO-), bicarbonate (HCOThree -),and carbonate (COThree Two-). The spectral peaks corresponding to HCOThree - and COThree Two-species were obtained at chemical shifts of 160.48 ppm. Figure 8(b) representsthe NMR spectroscopic spectral analysis of a CO2-loaded aqueous amine blend.The peak lying anywhere in the range of 160-168 ppm (except the carbonylregion) was mainly responsible because of the formation of HCOThree - and COThree Two-species. The peak present in the carbonyl region (i.e., C = O bond) in between163-165 ppm was mainly responsible for carbamate formation. One peak wasdiscovered at 164.55 ppm, indicating carbamate formation. The chemical shiftsof HMDAH+ and DMAEH+ were discovered in the zone of 25.04-38.49 ppmand 43.19-59.09 ppm. Compared with the CO2-unloaded sample, thefrequency of chemical shifts of HMDAH+ and DMAEH+ peaks shrinks slightly.The amine-CO2 product formation was the primary cause of spectral peakshrinkage in the CO2-loaded amine blend sample.CO2-regenerated samplesCO2 liberates during desorption experiments by dissociation of HCOThree- / COThree Two-species due to the supply of external heat to the regeneration reactor duringdesorption experiments. Figure 8(c) represents the NMR spectroscopic spectralanalysis of a CO2-regenerated aqueous amine blend. NMR spectra reveal thatthe peaks of HMDA and DMAE species were obtained at 25.25-38.64 ppmand 44.06-59.62 ppm range. The slight shrinkage in the chemical shifts due tothe amine-CO2 product, as observed in the CO2-loaded sample, again returnedthe near original values, as in the case of CO2-unloaded amine blend samples.NMR investigation of CO2-regenerated sample, carbamate and HCOThree - / COThree Two-species were still present at 164.37 ppm and 160.65 ppm. However,HCOThree - / COThree Two- species intensity was diminished as compared with the CO2-loadedamine sample. The availability of such species in the amine sample was reducedto a large extent (i.e., easily decomposable) due to heat supplied. At the sametime, the intensity of carbamate remained unaffected because thedecomposition of such species while regenerating it at 393.15 K waschallenging. The spectral peaks of DMSO-d6 remained unaffected in CO2-unloaded, CO2-loaded, and CO2-regenerated amine blends.Fourier transform infrared (FTIR) spectroscopyFTIR investigation of functional group and chemical bonding associated withCO2-unloaded, CO2-loaded, and CO2-regenerated amine blend solutions wasdone through the FTIR spectrophotometer instrument (Model: Nicolet iS5;Company: THERMO Electron Scientific Instruments LLC, USA). The KBrpellet sampling approach was employed to record infrared spectra in the 4000-400 cm-One region. The resolutions and number of scans chosen for the FTIRstudy were 4 cm-One and 32.Characteristic peaks due to HMDAThe characteristic peaks at 3416.02, 3424.51, and 3422.72 cm-One correspondingto CO2-unloaded, CO2-loaded, and CO2-regenerated amine blend samplessignify the presence of HMDA, as shown in Figure 9. The peaks appearedbecause of N-H stretching vibration within the HMDA molecules. However,due to the N-H bending of HMDA, the peaks lying at 1571.27, 1647.87, and1628.87 cm-One were also responsible for HMDA corresponding to CO2-unloaded, CO2-loaded, and CO2-regenerated amine blend samples. Vibrationdue to C-N stretching of HMDA was found at the characteristic peaks of1047.64, 1013.73, and 1023.81 cm-1, corresponding to the CO2-unloaded, CO2-loaded, and CO2-regenerated amine blend samples. The primary and secondaryamines also exhibit a broad N-H wag band, with characteristic peaks locatedbetween 665-910 cm-One. One peak at 820.39 cm-1 for the CO2-unloaded sample,two peaks at 837.28 and 696.75 cm-One for the CO2-loaded sample, and againtwo peaks at 837.25 and 696.14 cm-One for the CO2-regenerated samples wereobtained due to N-H wag of HMDA.Characteristic peaks due to DMAEIn the case of tertiary amines, N-H stretching and N-H wag vibrations wereabsent; therefore, only C-N stretching was found in DMAE. One characteristicpeak at 499.94 cm-One for CO2-unloaded, two peaks at 499.99 and 645.27 cm-1for CO2-loaded, and two peaks at 499.93 and 586.16 cm-One for CO2-regeneratedsamples were attained due to the DMAE availability in the aqueous amineblend. Similarly, peaks for all samples of the amine blend lying between thewavenumber of 2800-2950 cm-One and 1000-1250 cm-One were responsible for theC-N stretching of DMAE, as shown in Figure 9. Stretching vibration of C = Obond due to DMAE was found in the frequency range of 1380-1485 cm-One.Characteristic peaks due to other speciesCarbamate, carbonate, and bicarbonates were formed upon the successful CO2loading in the amine samples. NHTwo+ deformation was mainly responsible foramine protonation and carbonate species formation. The availability ofasymmetric carbonyl (-COO-) stretching vibration at characteristic peaks of1283.38, 1628.74, and 1697.79 cm-One for CO2-loaded and 1297.63, 1565.30, and1697.63 cm-One for CO2-regenerated amine blend samples was present due to theformation of carbamate. Interaction between the hydroxyl group of tertiaryamine and CO2 is responsible for the carbamate formation that was absent inthe CO2-unloaded samples. Carbamate peaks were still present in theregenerated amine blend samples due to the fact that such bonds were difficultto break when the heat was supplied during regeneration, performing at 393.15K.EXAMPLE 11Toxicity assessment for the aqueous amine blendThe amine losses from the industrial sectors form the degradation products thatreact in the environment and mix in soil, rivers, ponds, lakes, oceans, and otherwater bodies in the form of rain. The chemical consumption by rats that causes50 % fatality amongst the rats (LD50), was considered during the entire toxicityassessment. According to chemical hazardousness, Environmental ProtectionAgency (EPA) classified various chemicals into four main categories by LD50values. A higher LD50 value indicated that the amine is safe and vice-versa. Theamines lying in category 1st (LD50 ≤ 50) are highly toxic in nature; category 2nd(50 < LD50 ≤ 500) indicates the moderately toxic behavior of amines. Likewise,the amines that fall in category 3rd (500 < LD50 ≤ 5000) are slightly toxic, andfinally, amines in category 4th (LD50 > 5000) are safe.The toxicity of the aqueous amine blend of HMDA+DMAE was judged bycollecting data on the LD50 value from the material safety data sheet (MSDS).The LD50 values of conventional amines such as Methyldiethanolamine(MDEA), 2-Amino-2-methyl-1-propanol (AMP), DMAE, Piperazine (PZ),Diethanolamine (DEA), 2-(Diethylamino)ethanol (DEEA), HMDA, MEA, 2-(Butylamino) ethanol (BAE), and 3-Dimethylamino-1-propanol (3DMAP)were also targeted during toxicity assessment. The LD50 values of the chosentraditional amines range from 442 to 4680 mg / Kg. The highest and lowest LD50values among the selected amines were 4680 mg / Kg and 442 mg / Kg,corresponding to MDEA and 3DMAP. Various traditional amines, along withHMDA and DMAE with different LD50 values are shown in Figure 10.According to the MSDS, the widely employed traditional MEA possesses aLD50 value of 1089 mg / kg (Category 3rd; slightly toxic), and the LD50 values ofDMAE and HMDA were found as 2000 mg / Kg and 1160 mg / Kg. The LD50values of DMAE and HMDA were higher than MEA, indicating lesser toxicitythan MEA. According to EPA, none of the investigated amines were classifiedunder the first and fourth categories of toxicity, as per the entire investigation.Amongst all the amines, only 3DMAP showed moderately toxic behavior witha LD50 value of 442 mg / Kg. Likewise, AMP , PZ , DEA, DEEA, and BAEexhibit toxicity of 2900 mg / Kg, 1900 mg / Kg, 1600 mg / Kg, 1300 mg / Kg, and890 mg / Kg. The toxicity of DMAE and HMDA was lower than that ofconventional MEA, with slight toxic behavior that was a commendable factorfrom an environmental and human health point of view. Therefore, HMDAand DMAE are recommended for industrial purposes for CO2 capture from fluegases.Hence, the present invention is based on preparing a comination ofHMDA+DMAE and studying its performance by conducting CO2 absorptionand desorption investigations. Based on operating conditions, 40 experimentswere performed on the laboratory scale during CO2 absorption investigation.The equilibrium CO2 loading estimation was the prime objective during CO2absorption experiments. The experimental data were authenticated by thedeveloped modeling equation and % AARD was found to be 3.06 %. Thereaction mechanism of the aqueous amine blend with the CO2 was providedand the intermediate species formed during the chemical reaction wereauthenticated by 13C NMR and FTIR characterization. The major experimentaloutcomes were equilibrium CO2 loading, absorption capacity, cyclicequilibrium CO2 loading, cyclic capacity, heat duty, regeneration efficiency,density estimation, initial CO2 absorption and desorption rate and theoreticaltoxicity assessment.Therefore, the present invention provides a cost-effective and an eco-friendlyblend of Hexamethylenediamine (HMDA) and 2-Dimethylaminoethanol(DMAE) for capturing carbon dioxide, which exhibits high equilibrium CO2loading, low regeneration heat duty, high regeneration efficiency, high cyclicequilibrium CO2 loading, high cyclic capacity, high initial CO2 absorption anddesorption rate and low toxicity.Many modifications and other embodiments of the invention set forth hereinwill readily occur to one skilled in the art to which the invention pertain havingthe benefit of the teachings presented in the foregoing descriptions and theassociated drawings. Therefore, it is to be understood that the invention is notto be limited to the specific embodiments disclosed and that modifications andother embodiments are intended to be included within the scope of theappended claims. Although specific terms are employed herein, they are usedin a generic and descriptive sense only and not for purposes of limitation.

Claims

1. A promoter-activator blend as absorbent for carbon dioxide capture comprising of: a plurality of amines including a primary diamine and a tertiary amine; wherein, said absorbent is in the form of an aqueous binary amine blend in a concentration ranging from 1-3 mol / L; said primary diamine is Hexamethylenediamine (HMDA) in an amount ranging from 0.05-0.20 mole fraction; and said tertiary amine is 2-Dimethylaminoethanol (DMAE) in an amount ranging from 0.80-0.95 mole fraction.

2. The absorbent as claimed in claim 1, wherein said absorbent exhibits equilibrium carbon dioxide loading of 1.2174 mol CO2 / mol amine at a temperature of 298.15 K, CO2 partial pressure of 25.33 kPa, mole fraction of HMDA of 0.20, and solution concentration of 1 mol / L.

3. The absorbent as claimed in claim 1, wherein said absorbent exhibits absorption capacity in a range of 0.9647 to 2.7624 mol CO2 / L solution at a temperature ranging from 298.15-333.15 K, CO2 partial pressure ranging from 10.13 to 25.33 kPa, mole fraction of HMDA ranging from 0.05 to 0.20 and solution concentration ranging from 1 to 3 mol / L for absorption time of 10 hours.

4. The absorbent as claimed in claim 1, wherein said absorbent exhibits carbon dioxide absorption rate ranging from 12 x 10-4 to 26 x 10-4 mol CO2 / (L solution.min).

5. The absorbent as claimed in claim 1, wherein said absorbent exhibits carbon dioxide desorption rate ranging from 67 x 10-4 to 138 x 10-4 mol CO2 / (L solution.min).

6. The absorbent as claimed in claim 1, wherein said absorbent exhibits regeneration efficiency in a range of 52.21-63.51% for solution concentration of 1-3 mol / L at a temperature of 313.15 K, CO2 partial pressure of 25.33 kPa, HMDA mole fraction of 0.20, regeneration temperature of 393.15 K and pH of an aqueous amine blend regenerated after capturing carbon dioxide in a range of 9-11.

7. The absorbent as claimed in claim 1, wherein said absorbent exhibits cyclic capacity of 1.5951 mol CO2 / L solution at concentration of 3 mol / L and cyclic equilibrium CO2 loading ranging from 0.5317-0.6375 mol CO2 / mol amine for a concentration ranging from 1-3 mol / L at mole fraction of HMDA of 0.20, temperature of 313.15 K, CO2 partial pressure of 25.33 kPa and regeneration temperature of 393.15 K.

8. The absorbent as claimed in claim 1, wherein said absorbent exhibits heat duty of 357.11-131.24 kJ / mol CO2 for a solution concentration of 1-3 mol / L.

9. The absorbent as claimed in claim 1, wherein said absorbent exhibits heat duty in a range of 141.42-164.48 kJ / mol CO2 on increasing molar ratio of HMDA at a concentration of HMDA ranging from 0.5 mol / L to 2 mol / L in the aqueous binary amine blend in a solution concentration of 3 mol / L.

10. The absorbent as claimed in claim 1, wherein said absorbent exhibits density of CO2-loaded samples in a range of 1031.8 kg / m3 to 1093.2 kg / m3 with concentration of solution ranging from 1 mol / L to 3 mol / L.

11. The absorbent as claimed in claim 1, wherein said absorbent exhibits pH in a range of 12.04-12.78 in CO2-unloaded samples and pH in a range of 8.37-9.50 in CO2-loaded samples.