Improving the Carbon Capture Efficiency for Gas Power Plants

sustainability

Article Improving the Carbon Capture Efﬁciency for Gas Power Plants through Amine-Based Absorbents

Saman Hasan *, Abubakar Jibrin Abbas and Ghasem Ghavami Nasr

School of Science, Engineering and Environment, University of Salford, Manchester M5 4WT, UK; [email protected] (A.J.A.); [email protected] (G.G.N.) * Correspondence: [email protected] or [email protected]

Abstract: Environmental concern for our planet has changed signiﬁcantly over time due to climate change, caused by an increasing population and the subsequent demand for electricity, and thus increased power generation. Considering that natural gas is regarded as a promising fuel for such a purpose, the need to integrate carbon capture technologies in such plants is becoming a

necessity, if gas power plants are to be aligned with the reduction of CO2 in the atmosphere, through understanding the capturing efﬁcacy of different absorbents under different operating conditions. Therefore, this study provided for the ﬁrst time the comparison of available absorbents in relation

to amine solvents (MEA, DEA, and DEA) CO2 removal efﬁciency, cost, and recirculation rate to achieve Climate change action through caron capture without causing absorbent disintegration. The study analyzed Flue under different amine-based solvent solutions (monoethanolamine (MEA), diethanolamine (DEA), and methyldiethanolamine (MDEA)), in order to compare their potential for

CO2 reduction under different operating conditions and costs. This was simulated using ProMax 5.0 software modeled as a simple absorber tower to absorb CO2 from ﬂue gas. Furthermore, MEA, DEA, and MDEA adsorbents were used with a temperature of 38 ◦C and their concentration varied from 10 to 15%. Circulation rates of 200–300 m3/h were used for each concentration and solvent.

The ﬁndings deduced that MEA is a promising solvent compared to DEA and MDEA in terms of the highest CO2 captured; however, it is limited at the top outlet for clean ﬂue gas, which contained

Citation: Hasan, S.; Abbas, A.J.; Nasr, 3.6295% of CO2 and less than half a percent of DEA and MDEA, but this can be addressed either by 3 G.G. Improving the Carbon Capture increasing the concentration to 15% or increasing the MEA circulation rate to 300 m /h. Efﬁciency for Gas Power Plants through Amine-Based Absorbents. Keywords: process technology description of different amine solvents; amine-based chemical solvent Sustainability 2021, 13, 72. using monoethanolamine (MEA); degradation of MEA and other solvents; diethanolamine (DEA) https://dx.doi.org/10.3390/ solvent; methyldiethanolamine (MDEA) su13010072

Received: 23 October 2020 Accepted: 17 December 2020 1. Introduction Published: 23 December 2020 A considerable amount of attention has been focused on our planet due to the con- ceivable outcomes of climate change, which is a result of the energy generated from fossil Publisher’s Note: MDPI stays neu- tral with regard to jurisdictional claims fuel emissions and greenhouse gases such as CO2. Therefore, the number of CO2 capture in published maps and institutional technologies has increased significantly due to their flexibility and design, efficacious cost, affiliations. and proficient application [1,2]. In addition, flue gas is released into the environment from diverse industries, including power generation, the petrochemical industry, and refinery gases [3]. The definition of flue gas is a blend of combustion products, including carbon dioxide, particulates, water vapor, heavy metals, and acidic gases, generated from indirect Copyright: © 2020 by the authors. Li- (gasification and pyrolysis) intermediate synthesis gas or the oxidation of radial distribution censee MDPI, Basel, Switzerland. This functions (RDF) or generated directly (incineration) [4,5]. In this research, we will examine article is an open access article distributed which of the chemical solvents of monoethanolamine (MEA), diethanolamine (DEA), and under the terms and conditions of the methyldiethanolamine (MDEA) are best able to produce good, low-cost outcomes; low Creative Commons Attribution (CC BY) amine degradation; and losses to remove or capture CO2 from flue gases. Carbone dioxide license (https://creativecommons.org/ must be separated from the gases and other vapors by using absorption technology, which licenses/by/4.0/).

Sustainability 2021, 13, 72. https://dx.doi.org/10.3390/su13010072 https://www.mdpi.com/journal/sustainability Sustainability 2021, 13, 72 2 of 27

is used to remove carbon dioxide from flue gases by employing liquid solvents (e.g., MEA, MDEA, DEA, etc.) for this purpose. This was conducted in this study by a simulation program (ProMax) and there were two scenarios employed to compare amine solvents from previous study [6]. Currently, chemical solvents using absorption process consider use the technology of the post-combustion CO2 capture technologies, considered one of the best technology for capturing CO2, in addition to pre-combustion capture that has been used to remove CO2 and H2S from natural gas components in a refinery [5–7]. This study also presents trade-off option of CO2 capture versus amine recirculation required and cost for amine solvents (MEA, DEA, and MDEA). Therefore, the most significant problem which must be determined and considered is the percentage of oxygen in the flue gas, which is affected by caused degrade of the amine solvents. These solvents cause oxidative degradation and should prevent it and limit it to around 5 to 10 ppm [8]. Additionally, as a UK report, the highest emission came from power generation, which is shown in Table1. Therefore, choosing a power generation station represents the best source of CO2. The total emission of CO2 by power stations in the UK annually given in a British petroleum (BP) report is 65.2 million tons, which is a huge number, as shown in Table1[5].

Table 1. Greenhouse gas emissions in 1990–2018 in the UK on an annual basis (CO2 in million tons).

Years 1990 1995 2000 2005 2010 2015 2017 2018 Energy supply 242.1 210.3 204.0 219.1 197.3 137.6 106.0 98.3 from power 203.0 163.0 158.7 173.1 157.3 104.1 72.4 65.2 stations

2. Theory (Literature Review) 2.1. Background

There are two significant points that should be considered before capture CO2, which are (a) How to deal with the huge amount of carbon dioxide from fossil fuels formed during combustion; (b) How to grip impurities of the stream in flue gas. The impurities in flue gas may contain sulfur and nitrogen oxides, particulate matter, and water vapor. The combustion of the fuel source will produce various amounts of impurities and changes, depending upon the fuel source. It is crucial to know the fundamental mechanisms behind CO2 and to prevent impurities and the formation of impurities during the combustion of fossil fuel [9]. The common reactions taking place during combustion can be applied to any fuel for CO2 formation, as follows in Equations (1) and (2) [9]:

C + 0.5O2 → CO (1)

This is uncompleted combustion,

C + O2 → CO2 (2)

This is a complete combustion. It should be noted that, when using natural gas instead of coal, the emissions of carbon dioxide will be signiﬁcantly reduced and the coal will emit more nitrogen and sulfur dioxide because it will contain more impurities, rather than natural gas. Acid rain is caused by nitrogen and sulfur oxides, which are the main contributors to its formation. There is an advantage of employing some technologies for capturing CO2, such as oxy- combustion, chemical looping combustion, and pre-combustion, which is the creation of an environment for combustion without impurity precursors, such as H2, S, N, and N2. However, there are certain amounts of inherent nitrogen and sulfur in fuel, so complete Sustainability 2021, 13, 72 3 of 27

impurity removal is not possible, and it cannot be considered as a perfect fuel. In addition, this impurity of combustion depends on the process that is used to treat the fuel before use in burning. In common cases of CO2 capture, the impurities are removed from ﬂue gas before capture is applied. Finding ways to handle the large quantity of CO2 produced by burning fuel in power stations, whatever the source of fuel, is a big challenge [9]. In the different power plants in Hebei Province, China, as shown in Table2, the raw coal had a high emission value of about 900 to 1000 g per KW/h, which is double the amount of oil and gas that was emitted. Moreover, it needs excess oxygen more than other fuels to complete combustion, which is considered a challenge when using chemical solvents to capture CO2, increasing the degradation when amine solution is used [10,11]. However, the consumption of fuel per KW/h for oil and natural gas represents less than one third of the consumption of raw coal required to generate power. Currently, commercial CO2 capture systems have a maximum capacity of about 800 t/d CO2, which means that the capture process emits approximately ten times less than that in a power plant. Therefore, it is appropriate to begin discussing the various CO2 capture approaches and their associated technologies, such as post-combustion, pre-combustion, oxy combustion, and chemical looping combustion [7,9,10,12,13].

Table 2. The emission of ﬂue gases from different power plans in Hebei Province, China.

Fuel per SO CO NO Fuel PM 2 2 x CO Kilowatt- 2.5 Emission Emission Emission O % Type (mg/m3) Emission 2 Hour (mg/m3) (g) (mg/m3) 290–340 1800– Coal 20–30 50–200 900–1000 100–200 9 g 2000 1800– Oil 80–90 g 20–30 50–100 400–450 100–200 3.5 2000 Natural 1800– 70–80 g 5–20 35–50 400–450 100–150 3.5 gas 2000

On the other hand, rather than the amount of CO2 emitted into the atmosphere by many industries, the chemical and the physical properties of the CO2 should be studied to learn about it and how it behaves. Therefore, Table3 illustrates the physical and chemical properties of CO2 [14], and Table1 shows the properties of CO 2 that used in amine absorption come out from ProMax in AppendixA.

2.2. Process Technology Description of Different Amines Amine processing includes two major processes of absorption and separation. When the CO2 is absorbed by a lean amine aqueous solution solvent through an absorption process, the equipment used is called an absorber. In addition, the process in which the CO2 is separated from aqueous solution by applying heat is called a separation or regeneration process, and the equipment employed is called a regenerator or stripper [15]. Moreover, the treatment occurs at an absorber at high pressure and at a low temperature, while at the stripper, there is a low pressure and high temperature between 100 and 120 ◦C[13,16]. There are some arguments about the stripping temperature, which varies between 120 and 150 ◦C[8,17], 95 and 135 ◦C[18], and 120 and 140 ◦C[15]. Therefore, the system includes heat, a cooling source, and a compressor to raise the pressure of ﬂue gas before it enters the absorber. Furthermore, the system includes a pump to circulate the lean solution and rich amine [13,15,16]. In absorption, the following steps occur [19]:

(a) CO2 dissolves into the absorbent; (b) A low temperature is required to ensure a high rapport for the absorption of CO2; (c) The distribution of CO2 will occur between the gas–liquid interface and the bulk gas; (d) The CO2 will react with the amine in the solution. Sustainability 2021, 13, 72 4 of 27

Table 3. The physical and chemical properties of CO2.

Property Value and Unit Molecular weight 44.01 g/mol Critical density (ρc) 0.468 g/cm3 or 468 g/L or 468 kg/m Critical pressure (Pc) 72.85 atm (7383 kPa) Critical temperature (Tc) 31.04 ◦C Triple point pressure 5.185 bar Triple point at 5.1 atm (518 kPa) −56.5 ◦C Sublimation point at 1 atm (101.3 kPa) −78.5 ◦C Gas density at 0 ◦C and 1 atm (101.3 kPa) 1.976 g/L Liquid density at 0 ◦C and 1 atm (101.3 kPa) 928 g/L ◦ 25 C and 1 atm CO2 (101.3 kPa) 0.712 v/v Solid density 1560 g/L Speciﬁc volume at 1 atm and 21 ◦C 0.546 m3/kg Latent heat of vaporization at the triple point (−78.5 ◦C) At 0 ◦C 353.4 J/g 231.3 J/g ◦ Viscosity at 25 C and 1 atm CO2 (101.3 kPa) 0.015 cP (mPas) Solubility in water at 0 ◦C and 1 atm (101.3 kPa) ◦ 0.3346 g CO2/100 g-H2O or 1.713 mL 25 C and 1 atm (101.3 kPa) ◦ CO2/mL-H2O at 0 C 0.1449 g CO2/100 g-H2O or 0.759 mL CO2/mL-H2O at 25 ◦C Heat of formation at 25 ◦C, ∆H gas 0.1372−393.5 kJ/mol

The flue gas results from burning fossil fuel in power stations and represents approximately 3–20% of gas emitted. It is fed into an absorption column, needed to cool the temperature of flue gas to below 50 ◦C or about 47–50 ◦C, due to the high temperatures of the exhaust gas of power generations [17]. After the flue gas has been cooled by an exchanger, such as cooling water and a fan cooler, it will enter the absorption tower or so-called absorber column and pass through it from bottom to top, in which approximately 86–90 vol.% of the CO2 is absorbed by solvent [5,13,15,20] and amine absorbs the carbon dioxide at 40–75 ◦C[18]. In addition, the absorbent or solvent enters the column from the top side of the tower and moves down to the bottom. In the meantime, the flue gas which contains acid gas will react with the solvent and usually has a temperature of nearly 40 ◦C. Through this process, lean amine is converted into rich amine, which means that CO2 is absorbed by aqueous amine solution. Secondly, heat is released as a result of the absorbed CO2 and the temperature of the solvent is increased due to the exothermic reaction, which is a kind of reversible reaction. At the bottom of the absorber, the CO2-rich stream will be collected at a required level, to prevent untreated gas from escaping from the desorber tower and, for safety reasons, to prevent the stripper tower caps and trays from being damaged due to the high differential pressure between the regenerator and absorber. The purified gas emitted out into the atmosphere is washed by water at the top of the absorber to cool the top of the tower, prevent evaporation of the amine solution, and mitigate the loss of solvent [9,13,15,17]. Furthermore, the loading is varied from 0.1 to 0.45 mol CO2/mol amine, depending on the lean and rich solvent (generally, lean and rich solvent CO2 loading of 0.1-0.2 mol CO2/mol MEA and 0.4–0.5 mol CO2/mol MEA, respectively) and on several other factors, which are a. The increasing or decreasing amine flow rate; b. The increasing/decreasing concentration of amine, considering the factors of corrosion that are caused by amine and the amount of CO2 that will be absorbed; c. The loading is defined as the total amount of CO2 absorbed by amine and can be described as in Equations (3) and (4) [16,21]: Sustainability 2021, 13, x FOR PEER REVIEW 5 of 28

Sustainability 2021, 13, 72 5 of 27 Moles of all CO carrying species Loading = (3) Moles of all MEA carrying species Moles of all CO carrying species Loading = (3) Moles of++ all MEA+− carrying species = [MEA] [MEA ] [MEACOO ] Loading −− (4) [CO[MEA ]+[HCO] + [MEA ]+[CO+] + [2MEACOO ]+[ MEACOO−] ] Loading = 233 (4) −2 − [CO 2] + [HCO 3] + [CO 3 ] + [MEACOO The absorber column or tower includes trays and is different, depending on the solvent usedThe absorberfor the capturing column or pr towerocess includes [15]. Figure trays 1 and illustrates is different, the different depending types on the of solventamine aqueousused for solutions the capturing with process the number [15]. Figureof trays1 illustratesused in each the solvent different [15]. types of amine aqueous solutions with the number of trays used in each solvent [15].

FigureFigure 1. 1. NumberNumber of of trays trays required required for for CO CO22 absorptionabsorption in in an an amine’s amine’s aqueous aqueous solution. solution.

TheThe rich rich amine amine solution solution leaves via the bottombottom ofof thethe absorber,absorber, which which is is then then heated heated to ◦ toabout about 100 100 C°C across across the the amine–amine amine–amine exchanger exchanger (lean/rich(lean/rich amine heat exchanger). exchanger). It It is is fedfed to to the the top top side side of of a a stripping stripping column column or or re regenerator,generator, in in order order to to minimize minimize the the heating heating energyenergy cost cost of of the the rich rich solution, solution, which which is is requ requiredired before before it it enters enters the the stripper stripper to to avoid avoid widelywidely different different temperatures betweenbetween thethe solvent solvent and and regenerator. regenerator. The The ﬂow flow that that happens hap- pensbetween between the absorberthe absorber and stripperand stripper occurs occurs due todue the to different the different pressures pressures between between them, them,which which is quite is high,quite beinghigh, being about about 15–20 15–20 times greatertimes greater than the than regenerator the regenerator pressure pressure [21]. In the desorption column, the following occur [19]: [21]. In the desorption column, the following occur [19]: (a) To ensure a lower relationship for the absorption of CO2, the temperature be should (a) Tobe ensure high; a lower relationship for the absorption of CO2, the temperature be should be high; (b) To ensure that CO2 will be released, chemical equilibria should occur; (b)(c) ToThe ensure desorption that CO process2 will be is released, endothermic; chemical therefore, equilibria to maintain should theoccur; high temperature, (c) Theheat desorption must be applied process to is theendothermic; absorbent. therefore, to maintain the high temperature, heat must be applied to the absorbent. Where further heated, a supply at the bottom of the stripper is required to increase the temperatureWhere further to 120–140 heated,◦C a by supply using at a steamthe bottom reboiler of whichthe stripper is generated is required for this to increase purpose theor thetemperature power plant to 120–140 will become °C by exhausted. using a steam The operatingreboiler which pressure is generated for a stripper for this is nearly pur- pose1.5–2 or bar the and power it is formedplant will of abecome packed exhausted. column which The has operating a kettle reboilerpressure [ 5for,15 ,a21 stripper]. The rich is nearlysolution 1.5–2 or stablebar and product it is formed that formed of a packed in the absorbercolumn which and the has CO a2 kettle, which reboiler was absorbed [5,15,21]. by Thethe solvent,rich solution will be or recovered stable product at the regeneratorthat formed column; in the absorber then, CO and2 will the be CO released2, which from was the ◦ absorbedabsorbent by inside the solvent, the stripper will be at arecove high temperaturered at the regenerator of 100–120 column;C, due then, to the CO equilibrium2 will be releasedisotherm from and the loading absorbent (mole inside of CO the2/ molestrippe ofr amine)at a high transfer temperature from higherof 100–120 (rich °C, amine) due toto the lower equilibrium loading isotherm (lean amine and means loading amine (mole that of CO had2/mole taken of offamine) the CO transfer2); that from is why higher the solvent-recovering energy cost is high. The lean solution at the bottom of the regenerator Sustainability 2021, 13, x FOR PEER REVIEW 6 of 28

(rich amine) to lower loading (lean amine means amine that had taken off the CO2); that Sustainability 2021, 13, 72 6 of 27 is why the solvent-recovering energy cost is high. The lean solution at the bottom of the regenerator is circulated back to the absorption tower after passing through the heat ex- changeris circulated and cooler back to[13,15,16]. the absorption The gas tower consisting after passing of a mixture through of thewater heat vapor exchanger and CO and2 with some evaporated amine travels out of the top of the stripper and enters a cooler to cooler [13,15,16]. The gas consisting of a mixture of water vapor and CO2 with some coolevaporated it. Then, amineit is fed travels into a out flash of thedrum top and of the the stripper acid gas, and which enters is aCO cooler2 from to coolcondensate it. Then, 2 water,it is fed and into amine a ﬂash are drum physically and the separated, acid gas, which no matter is CO the2 from kind condensate of amine. water, Finally, and CO amineis compressedare physically and separated,transported no for matter sequestration. the kind Figure of amine. 2 shows Finally, a schematic CO2 is compressed diagram of the and amine-basedtransported chemical for sequestration. absorption Figure process2 shows [8,17]. a schematic diagram of the amine-based chemical absorption process [8,17].

Figure 2. Schematic diagram of the chemical absorption process used for capturing CO2 with solvent process regeneration. Figure 2. Schematic diagram of the chemical absorption process used for capturing CO2 with solvent process regeneration.

2.3.2.3. Amine-Based Amine-Based Chemical Chemical Solven Solventt Using Using Monoethanolamine Monoethanolamine (MEA) (MEA) AminesAmines are are officially ofﬁcially derivatives derivatives of ammonia, andand wherewhere oneone or or more more hydrogen hydrogen atoms at- omshave have been been displaced displaced by by an an organic organic substituent, substituent, suchsuch asas an alkyl group, group, these these amines amines calledcalled alkylamines alkylamines [22]. [22 ].MEA MEA is isone one of of the the most most important important absorption absorption liquids liquids and and is is the the leastleast expensive. expensive. It Itcan can be be produced produced in in larg largee quantities quantities from from ethylene ethylene oxide oxide and and ammonia ammonia reactions.reactions. The The Acid Acid Dissociation Dissociation Constant Constant (pKa) (pKa) is isclose close to to a aprimary primary amine. amine. Therefore, Therefore, it it hashas a avery very good good viscosity viscosity and and an an excellent excellent average average rate rate of of absorption absorption of of CO CO2, 2with, with an an over- over- averageaverage normalized normalized ability ability [19]. [19]. An amino groupgroup isis the the perfect perfect group group for for absorbing absorbing CO CO2 and2 andprovides provides enough enough alkalinity. alkalinity. It is It commonly is commonly dissolved dissolved so that so that CO 2COchemically2 chemically reacts reacts with withalkanolamines. alkanolamines. One One of the of most the most crucial crucial advantages advantages of alkanolamines of alkanolamines is that, is structurally, that, struc- at turally,least one at least hydroxyl one hydroxyl group is contained group is contained in them. Due in them. to this, Due it can to helpthis, toit raisecan help the solubilityto raise thein solubility aqueous solutionsin aqueous and solutions mitigate and the mitigate vapor pressure the vapor [10 pressure]. Monoethanolamine [10]. Monoethanola- (MEA) mineis considered (MEA) is oneconsidered of the mostone of general the most alkanolamine general alkanolamine groups and gr isoups widely and used. is widely It has used.been It used has been for over used 75 for years over to75 remove years to CO remove2 and CO H22S and from H natural2S from natural gas and gas ﬂue and gas flue [23 ]. gasDue [23]. to Due MEA to having MEA having a high-water a high-water solubility, solubility, high cyclic high capacity, cyclic capacity, and considerable and considera- kinetic blerates kinetic of absorption-stripping rates of absorption-stripping at a low CO at 2a concentration,low CO2 concentration, it is considered it is considered to be a standard to be a sorbentstandard [8 sorbent]. [8]. TheThe capacities capacities of of chemical chemical and and physical physical MEA MEA absorption absorption are are affected affected by by the the pressure, pressure, temperature,temperature, concentration concentration of of aqueous aqueous MEA, MEA, and and presence presence of of additional additional gases, gases, which which meansmeans impurities impurities [22]. [22 ].The The weight weight % % concentr concentrationation of of monoethanolamine monoethanolamine varies varies from from 15 15 toto 35%, 35%, depending depending on on the the process process and and 0.45 0.45 CO CO22 moles/molemoles/mole amine amine (324 (324 g g CO CO2/kg2/kg MEA), MEA), so the lean and rich amine solvent loading can vary from 0.242 to 0.484 CO2 moles/mole amine, respectively [2,9,22]. However, others have reported that monoethanolamine can remove around 90% and 30 wt.% MEA solution with optimum lean amine solvent loading Sustainability 2021, 13, x FOR PEER REVIEW 7 of 28

so the lean and rich amine solvent loading can vary from 0.242 to 0.484 CO2 moles/mole amine, respectively [2,9,22]. However, others have reported that monoethanolamine can remove around 90% and 30 wt.% MEA solution with optimum lean amine solvent loading Sustainability 2021, 13, 72 7 of 27 of nearly 0.32–0.33 mol CO2/mol MEA and a requirement of thermal energy of 3.45 GJ/ton CO2 [2]. Figure 3 [24] shows the chemical structure of primary amine and Table 4 illus- 2 tratesof nearly the typical 0.32–0.33 characteristics mol CO2/mol of MEAamine and solvents a requirement for MEA ofand thermal other amines energy ofused 3.45 for GJ/ton CO absorptionCO2 [2]. Figure [8,15,16,24,25].3[ 24] shows the chemical structure of primary amine and Table4 illustrates the typical characteristics of amine solvents for MEA and other amines used for CO2 absorption [8,15,16,24,25].

FigureFigure 3. 3. TheThe oxidation oxidation rate rate of of general general amines amines with with cycling cycling from from 55 55 to to 120 120 °C.◦C. There are two major amine technologies used to treat flue gas. Kerr-McGee/ABB Table 4. Typical characteristics of amine solvents employed for monoethanolamine (MEA) and other amines used for CO2 Lummus Crest was the first commercial technology, developed by Mitsubishi Heavy absorption. Industries with the Kansai Electric Power Company in the 1990s. This technology is Monoethanolamineoperated with Diethanolamine cogeneration Diglycolamine systems and boilers Methyldiethanolami that have a rangeDiisopropanolamin of fire fuels. The Amine (MEA)concentration of(DEA) aqueous amine solution(DGA) MEA is aboutne (MDEA) 15–20%. However,e in(DIPA) this process, Typical the flue gas should contain limited sulfur dioxide, as well as tolerate a reasonable amount Concentration of oxygen. Furthermore, in 1978, the first Kerr-McGee/ABB Lummus Crest technology 13–20 25–30 50–60 range in Trona (California) recovered CO2 from flue gas, with35–55 a production value20–40 of 800 t/day 15–25of CO . The most20–40 crucial advantages50–65 are the low amine losses, low heat required for recommended 2 regeneration, and low amine degradation due to the additives and inhibitors used in (wt.%) this technology [15]. Solvent loading 0.3 The second0.3–0.7 technology is the0.35 Fluor process, which 0.45 was developed by 0.45 Fluor Daniel (mole/mole) from Dow Chemical in 1989. Using a 30 wt.% of MEA solvent, the Kerr-McGee/ABB Heat of Lummus Crest process uses additives and inhibitors to prevent equipment corrosion and regeneration 2degradation. The Fluor1.5 Daniel process2 has mainly been1.3 used to remove exhaust 1.5 gases and (MJ/kg CO2) has been employed in more than 20 plants worldwide. For example, in Lubbock, Texas, the Chemical formula C2Hplant7NO has a capacityC4H11 rateNO2 of aboutC4 1200H11NO t/day2 of CO2C. This5H13NO technology2 can recoverC6H15NO between2 Boiling point (°C) 17185 and 95% of CO2269from flue gas, with221 the purity reaching 247 99.95% [15,19,21]. The 249 two most Molecular weight fundamental reactions of amines are shown in Equations (5) and (6) [22,26,27]: 61.08 105 105 119.16 133 (g/mol) RNH2+ CO2+ H2O ↔ RNH3+ HCO3 (5)

There are two major 2RNHamine 2technologies+ CO2 ↔ RNH used3+ toRNHCOO treat flue gas. Kerr-McGee/ABB (6) Lummus Crest was the first commercial technology, developed by Mitsubishi Heavy In- Finally, the temperature which causes the MEA to become exposed to thermal degra- dustries with the◦ Kansai Electric Power Company in the 1990s. This technology is oper- ateddation with is cogeneration 120 C and is systems considered and one boilers of the that main have drawbacks a range of in fire comparison fuels. The to concentra- oxidation, tionsoinhibitors of aqueous should amine be solution used to MEA avoid is it about [20]. 15–20%. However, in this process, the flue Sustainability 2021, 13, 72 8 of 27

Table 4. Typical characteristics of amine solvents employed for monoethanolamine (MEA) and other amines used for CO2 absorption.

Monoethanolamine Diethanolamine Diglycolamine Methyldiethanolamine Diisopropanolamine Amine (MEA) (DEA) (DGA) (MDEA) (DIPA) Typical Concentration 13–20 25–30 50–60 range 35–55 20–40 15–25 20–40 50–65 recommended (wt.%) Solvent loading 0.3 0.3–0.7 0.35 0.45 0.45 (mole/mole) Heat of regeneration 2 1.5 2 1.3 1.5 (MJ/kg CO2) Chemical C H NO C H NO C H NO C H NO C H NO formula 2 7 4 11 2 4 11 2 5 13 2 6 15 2 Boiling point 171 269 221 247 249 (◦C) Molecular 61.08 105 105 119.16 133 weight (g/mol)

2.4. Degradation of MEA and Other Solvents

The MEA degradation rate is nearly 1.5 kg/ton CO2 whatever the type of degradation [2,20]; therefore, degradation has several types, and two major types will now be discussed. A. Oxidative degradation Oxidation degradation occurs because of ﬂue gas containing oxygen in the absorber tower. Neither a high temperature nor CO2 is required for oxidative degradation. This is a major issue for capturing CO2 in the ﬂue gas, and the concentration of oxygen varies between 3 and 5% in the gas stream. It mainly occurs in the absorber, at 40–70 ◦C[8]. In addition, according to a study conducted at the University of Texas, the degradation can be controlled by the mass transfer of oxygen under industry conditions, where the degradation rate is nearly 0.29–0.73 kg of MEA/ton of CO2. Furthermore, loss of the solvent and the formation of heat-stable salts are also caused by oxidative degradation, and to prevent this, inhibitors are added to the system [21,23]. The products, such as aldehydes, organic acids, and ammonia, are formed by an oxidative degradation chain of amine solvent starting with MEA. In the second step, the acids are formed (heat-stable salts), leading to mitigation of the capacity rate of the absorption of CO2 by the solvent. These acids react with the absorbent MEA, leading to the production of amide compounds [8,23]. Table5 shows the oxidative degradation compounds formed from MEA [8,23].

Table 5. The formation of compounds from the oxidative degradation of MEA.

Solvent Compounds − − inorganic compounds (NH3, NO2 , NO3 ) − − − 2− Organic acids (HCOO , CH3COO , HOCH2COO , (C2O4) ) Amides (oxamides, HEF, formamides,) MEA cyclic compounds (HEPO-3, HEPO-2, HEI, HEP, DMPz) Aldehydes (CH3CHO, HOCH2CHO, CH2O) Amines (MAE, methylamines, BHEEDA, MEA-urea) Sustainability 2021, 13, x FOR PEER REVIEW 9 of 28 Sustainability Sustainability 2021 2021, 13, 13, x, FORx FOR PEER PEER REVIEW REVIEW 9 of9 of28 28

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Diethanolamine is formed by oxidizing primary and tertiary amines; however, a DiethanolamineDiethanolamine is isformed formed by by oxidizing oxidizing primary primary and and tertiary tertiary amines; amines; however, however, a a large amountDiethanolamine of diethanolamine is formed is by also oxidizing produced primary by oxidizing and tertiary MDEA, amines; as shown however, in Figure a large largelarge amountDiethanolamine amount of of diethanolamine diethanolamine is formed is by isalso also oxidizing produced produced primary by by oxidizing oxidizing and tertiaryMDEA, MDEA, amines;as as shown shown however, in in Figure Figure a 3 [19].amount of diethanolamine is also produced by oxidizing MDEA, as shown in Figure3[ 19]. 3 large[19].3 [19]. amount of diethanolamine is also produced by oxidizing MDEA, as shown in Figure B. B. Thermal degradation of MEA and other solventssolvents (polymerization(polymerization ofof Carbamate):Carbamate): B.3B. [19]. ThermalThermal degradation degradation of of MEA MEA and and other other so solventslvents (polymerization (polymerization of of Carbamate): Carbamate): PoldermanPolderman was was the the first ﬁrst person person to topropose propose the the mechanism mechanism of ofthe the polymerization polymerization of of B. PoldermanThermalPolderman degradation was was the the first first of person MEA person and to to propose other propose so thelvents the mechanism mechanism (polymerization of of the the polymerization ofpolymerization Carbamate): of of carbamatecarbamate of ofMEA MEA in in1955 1955 [28]. [28 ].The The polymerization polymerization of ofcarbamate carbamate occurs occurs in inthe the stripper stripper carbamatecarbamatePolderman of of MEA MEA was in in the1955 1955 first [28]. [28]. person The The polymerization topolymerization propose the ofmechanism of carbamate carbamate of occurs theoccurs polymerization in in the the stripper stripper of columncolumn at ata high a high temperature temperature and and over over a a long long period period of time [[21].21]. TheThe thermalthermal degradation degrada- columncarbamatecolumn at at a aofhigh high MEA temperature temperature in 1955 [28]. and and The over over polymerization a along long period period ofof of timecarbamate time [21]. [21]. The occursThe thermal thermal in the degrada- degrada-stripper tionincreases increases when when the the temperature temperature is increased is increased in the in stripperthe stripper column, column, where where the degradation the deg- tioncolumntion increases increases at a highwhen when temperature the the temperature temperature and over is isincreased increaseda long period in in the the of stripper strippertime [21]. column, column, The thermal where where thedegrada- the deg-◦ deg- radationrate of MEArate of or MEA any solventor any solvent will be 2.5–6%will be per2.5–6% week per at aweek temperature at a temperature of about 135of aboutC[16 ]. radationtionradation increases rate rate of ofwhen MEA MEA theor or anytemperature any solvent solvent will iswill increased be be 2.5–6% 2.5–6% in per the per weekstripper week at at acolumn, atemperature temperature where of theof about about deg- 135The °C polymerization[16]. The polymerization of carbamate of carbamate causes an increasedcauses an amineincreased solution amine viscosity, solution loss viscos- of car- 135radation135 °C °C [16]. [16]. rate The The of polymerization MEApolymerization or any solvent of of carbamate carbamate will be causes2.5–6% causes an per an increased increasedweek at aminea aminetemperature solution solution ofviscos- viscos- about ity,bon loss dioxide’s of carbon absorption dioxide’s capacity, absorption increased capacity, corrosion, increased and corrosion, foaming [and28]. Thefoaming mechanism [28]. ity,135ity, loss °Closs [16].of of carbon carbonThe polymerization dioxide’s dioxide’s absorption absorption of carbamate ca capacity,pacity, causes increased increased an increased corrosion, corrosion, amine and and solution foaming foaming viscos- [28]. [28]. Theof mechanism degradation of is degradation as follows. is as follows. Theity,The mechanism loss mechanism of carbon of of degradation dioxide’sdegradation absorption is isas as follows. follows. capacity, increased corrosion, and foaming [28]. First,First, the the reaction reaction occurs occurs at atthe the absorber absorber with with CO CO2, 2and, and CO CO2 associates2 associates with with MEA MEA to to TheFirst, mechanismFirst, the the reaction reaction of degradation occurs occurs at at theis the as absorber follows.absorber with with CO CO2, 2and, and CO CO2 associates2 associates with with MEA MEA to to formform carbamate carbamate of ofMEA, MEA, as asshown shown in inEquation Equation (7) (7) [28]: [28 ]: formform carbamateFirst, carbamate the reaction of of MEA, MEA, occurs as as shown shown at the in in absorberEquation Equation with(7) (7) [28]: CO[28]: 2 , and CO2 associates with MEA to form carbamate of MEA, as shown in Equation (7) [28]: (7)(7) (7)(7) (7) Then, at the stripper, the reaction is generally reversed; however, for some statuses, Then,Then,Then, at at the at the thestripper, stripper, stripper, the the thereaction reaction reaction is isgene is gene generallyrallyrally reversed; reversed; reversed; however, however, however, for for forsome some some statuses, statuses, statuses, 2-oxazolidone will form due to the cyclizing of MEA carbamate, and this reaction type is 2-oxazolidone2-oxazolidone2-oxazolidoneThen, at willthe will will stripper,form form form due due duethe to to reactionthe to the thecyclizing cyclizing cyclizing is gene of of rallyMEA of MEA MEA reversed; carbamate, carbamate, carbamate, however, and and and this this thisfor reaction reactionsome reaction statuses,type type type is is is also reversible, as shown in Equation (8) below [8]: also2-oxazolidonealsoalso reversible, reversible, reversible, aswill as shown as shown form shown indue in Equation in Equation to Equation the cyclizing (8) (8) (8)below below below of [8]: MEA[8]: [ 8]: carbamate, and this reaction type is also reversible, as shown in Equation (8) below [8]:

(8) (8)(8)(8) (8)

Furthermore, the 2-oxazolidone will react with one mole of monoethanolamine to Furthermore,Furthermore, the the 2-oxazolidone 2-oxazolidone will will react react with with one one mole mole of of monoethanolamine monoethanolamine to to form 1-(2-hydroxyethyl)-2-imidazolidoneFurthermore, the 2-oxazolidone will and react is referred with one to as mole HEIA. of monoethanolamine Equation (9) shows to formform 1-(2-hydroxyethyl)-2-imidazolidoneFurthermore, 1-(2-hydroxyethyl)-2-imidazolidone the 2-oxazolidone will and andreact is is referredwith referred one to tomole as as HEIA. HEIA.of monoethanolamine Equation Equation (9) (9) shows shows to theform reaction 1-(2-hydroxyethyl)-2-imidazolidone [29]: and is referred to as HEIA. Equation (9) shows theformthethe reaction reaction reaction1-(2-hydroxyethyl)-2-imidazolidone [29]: [29]: [29 ]: and is referred to as HEIA. Equation (9) shows the reaction [29]:

(9) (9)(9)(9) (9)

After that, the HEIA will react with water (hydrolyze) to form HEEDA, which is N- AfterAfter that, that, the the HEIA HEIA will will re reactact with with water water (hydrolyze) (hydrolyze) to to form form HEEDA, HEEDA, which which is isN- N- (2-hydroxyethyl)-ethylenediamine,After that, the HEIA will react as illustrated with water in (hydrolyze)Equation (10) to [28]: form HEEDA, which is (2-hydroxyethyl)-ethylenediamine,(2-hydroxyethyl)-ethylenediamine,After that, the HEIA will react as withas illustrated illustrated water (hydrolyze)in in Equation Equation to(10) (10) form [28]: [28]: HEEDA, which is N- N-(2-hydroxyethyl)-ethylenediamine, as illustrated in Equation (10) [28]: (2-hydroxyethyl)-ethylenediamine, as illustrated in Equation (10) [28]:

(10) (10)(10) (10)(10)

These four types (HEEDA, dihydroxy ethyl urea, 2-oxazolidone, and HEIA) of for- TheseThese four four types types (HEEDA, (HEEDA, dihydroxy dihydroxy ethyl ethyl urea, urea, 2-oxazolidone, 2-oxazolidone, and and HEIA) HEIA) of of for- for- mation are the major products of thermal degradation [29]. mationmationThese areThese are the fourthe four major major types types products products(HEEDA, (HEEDA, of of thermaldihydroxy dihydroxythermal degradation degradation ethyl ethyl urea, [29]. [29]. 2-oxazolidone, andand HEIA)HEIA) ofof forma- for- 2.5.mationtion Diethanolamine are are the the major major DEA products products Solvent of of thermal thermal degradation degradation [29 [29].]. 2.5.2.5. Diethanolamine Diethanolamine DEA DEA Solvent Solvent DEA is often used an abbreviation for diethanolamine, and it is an organic compo- 2.5. DEADiethanolamineDEA is isoften often used usedDEA an anSolvent abbreviation abbreviation for for diethanolamine, diethanolamine, and and it itis isan an organic organic compo- compo- nent that has both a Dialcohol and a secondary amine. In addition, a Dialcohol contains nentnent thatDEA that has hasis bothoften both a used aDialcohol Dialcohol an abbreviation and and a asecondary secondary for diethanolamine, amine. amine. In In addition, addition, and it ais aDialcohol anDialcohol organic contains containscompo- nent that has both a Dialcohol and a secondary amine. In addition, a Dialcohol contains Sustainability 2021, 13, x FOR PEER REVIEW 10 of 28

Sustainability 2021, 13, 72 two hydroxyl groups in its molecule [19,30]. Diethanolamine, like other alkanol amines,10 of 27 rules as a weak base [24]. DEA is an inexpensive solvent due to its wide use in many industries, and it is espe- 2.5.cially Diethanolamine used for removing DEA Solvent CO2 and H2S in natural gas that has rapidly reacted, where the selectivelyDEA is is often high used(between an abbreviation other and acid for diethanolamine, gases), and for andthe reversible it is an organic reaction component process thatat the has absorber both a column. Dialcohol Furthermore, and a secondary the operation amine. In conditions addition, can a Dialcohol be a low containsheat reaction two hydroxyl(around 70 groups kJ/mol in CO its2) molecule and low [pressure19,30]. Diethanolamine, [30]. One of the likemost other common alkanol disadvantages amines, rules is asthe a presence weak base of [SO24].2 and O2 in flue gas, causing solvent degradation (which should be less than DEA10 ppm). is an The inexpensive presence of solvent O2 in dueflue togas its causes wide the use oxidation in many of industries, DEA and and leads it to is especiallyincreased degradation used for removing [10]. The CO concentration2 and H2S in of natural diethanolamine gas that has vari rapidlyes, depending reacted, whereon the theamount selectively of CO is2 to high absorb. (between In approved other and industries, acid gases), the and concentration for the reversible has been reaction shown process to be atbetween the absorber 25 and column. 35% and Furthermore, lean amine (DEA) the operation loading conditions is set at 0.1 can mol be CO a low2/mol heat DEA reaction [30], (aroundwhereas 70the kJ/mol rich amine CO2 )of and diethanolamine low pressure loading [30]. One is of0.4 the mol most CO2 common/mol DEA, disadvantages as illustrated isin theFigure presence 4 [5]. of SO2 and O2 in ﬂue gas, causing solvent degradation (which should be less thanHowever, 10 ppm). the Themechanism presence of Odegradation2 in ﬂue gas of causes DEA theis a oxidation similar to of that DEA of and MEA leads [28]. to increasedConsequently, degradation the products [10]. The produced concentration after degradation of diethanolamine are Tris-hydroxyethyl varies, depending ethylene- on the amountdiamine ofcalled CO2 THEED,to absorb. Bis-hydroxyethyl In approved industries, piperazine the (bis-HEP), concentration MEA, has Bis-(hydroxyethyl) been shown to be betweenglycine (Bicine), 25 and 35%and polymers. and lean amine Polymers (DEA) are loadingproducts is produced set at 0.1 molwhen CO the2/mol DEA DEA molecule [30], whereasreacts with the THEED rich amine (ethylenediamines). of diethanolamine Furthe loadingrmore, is 0.4 the mol MEA CO 2product/mol DEA, is obtained as illustrated when inthe Figure DEA 4molecule[5]. degrades in the presence of oxygen [31].

Figure 4. The different types of amine with the capacity to absorb CO2. Figure 4. The different types of amine with the capacity to absorb CO2.

2.6. MethyldiethanolamineHowever, the mechanism MDEA of degradation of DEA is a similar to that of MEA [28]. Con- sequently,MEDA the is productsan abbreviation produced of afterN-methyldiet degradationhanol-amine are Tris-hydroxyethyl and the chemical ethylenediamine formula of calledit is C5H THEED,13NO2 [15]. Bis-hydroxyethyl MDEA is considered piperazine a chemical (bis-HEP), solvent, MEA, so Bis-(hydroxyethyl)the chemical solvents glycine have (Bicine),a characteristic and polymers. during the Polymers absorption are process, products which produced is that when the acid the DEAgas component molecule reactsin the withsolvent THEED is bonded (ethylenediamines). chemically [32]. Furthermore,The density of the MDEA MEA can product range is from obtained 1 to when1.149 at the a DEAtemperature molecule roughly degrades between in the 298 presence and 363.15 of oxygen K with [31 a]. concentration percentage between 23.8 and 60 wt.% [3]. MDEA can degrade at 119–129 °C [8]. Some of the advantages of 2.6. Methyldiethanolamine MDEA MDEA are the need for only a low energy for regeneration due to the acidic gas reaction havingMEDA a low is enthalpy an abbreviation and the of high N-methyldiethanol-amine capacity for the absorption and the of chemicalCO2 [10].formula In addition, of it isthe C solution5H13NO 2has[15 a]. lower MDEA vapor is considered pressure aand chemical corrosiveness, solvent, sowith the a chemicalgood chemical solvents and have ther- a characteristicmal stability. On during the theother absorption hand, there process, are so whichme drawbacks, is that the including acid gas componentthe slow reaction in the solventwith carbon is bonded dioxide chemically and low absorption [32]. The density capacity of when MDEA the can concentration range from of 1 carbon to 1.149 diox- at a temperature roughly between 298 and 363.15 K with a concentration percentage between ide is low [4]. ◦ 23.8 andMDEA 60 wt.%has several [3]. MDEA advantages can degrade which atmake 119–129 it a veryC[ 8popular]. Some solvent, of the advantages including the of MDEA are the need for only a low energy for regeneration due to the acidic gas reaction fact that it is less aggressive, requires a low heat for the reaction with CO2, is less corrosive, having a low enthalpy and the high capacity for the absorption of CO2 [10]. In addition, the solution has a lower vapor pressure and corrosiveness, with a good chemical and thermal stability. On the other hand, there are some drawbacks, including the slow reaction with Sustainability 2021, 13, 72 11 of 27

Sustainability 2021, 13, x FOR PEER REVIEW 11 of 28

carbon dioxide and low absorption capacity when the concentration of carbon dioxide is low [4]. can beMDEA used hasin higher several concentrations, advantages which has makelower it circulation a very popular rates, solvent, and is easier including to regener- the fact thatate [24]. it is less aggressive, requires a low heat for the reaction with CO2, is less corrosive, can be usedThe in major higher determinate concentrations, for the has operating lower circulation cost and rates,capital and cost is easieris the circulation to regenerate rate [24 of]. the solvent,The major which determinate is roughly for proportional the operating to the cost amount and capital of acid cost gas is to the be circulation removed. rateThe ofprocess the solvent, of gasification which isand roughly flue gas proportional treatment shown to the in amount Figure of5 is acid common gas to and, be removed. as in the TheMEA process process, of the gasiﬁcation lean MDEA and enters ﬂue the gas absorber treatment and shown reacts inwith Figure acid5 gas is commonto absorb and,some asof the in the CO MEA2 and process,H2S, whereas the lean bonding MDEA MDEA enters with the absorberH2S takes and place reacts quicker with than acid carbon gas to absorbdioxide. some At the of bottom the CO 2ofand the H absorber,2S, whereas the bondingrich stream MDEA is pre-heated with H2S and takes enters place the quicker strip- thanper/regenerator carbon dioxide. to regenerate At the bottomthe solvent of the by using absorber, the reboiler the rich to stream break isthe pre-heated bond of chem- and entersically reacted the stripper/regenerator substances. The component to regenerate of the acid solvent gas will by usingbe cooled the reboiler through to the break cooler the bondwhen ofexiting chemically the top reacted of the stripper substances. column The componentto condensate of acidout the gas water will be for cooled recycling through pur- theposes cooler [32]. when exiting the top of the stripper column to condensate out the water for recycling purposes [32].

Figure 5. A ﬂowsheetflowsheet of the typical methyldiethanolamine (MDEA)(MDEA) process.process. The degradation of MDEA will produce several products, which include dimers The degradation of MDEA will produce several products, which include dimers (degradation of DIPA-OX to diamines (“dimers”)), polymers (dimer reacts with a DIPA (degradation of DIPA-OX to diamines (“dimers”)), polymers (dimer reacts with a DIPA molecule), Monoisopropanolamine (MIPA) (occurs when oxygen reacts with a DIPA molecule), Monoisopropanolamine (MIPA) (occurs when oxygen reacts with a DIPA mol- molecule), Triisopropanolamine (TIPA) (produced when amine degrades in the presence ecule), Triisopropanolamine (TIPA) (produced when amine degrades in the presence of of oxygen in the ﬂue gases to produce simpler amines, whilst these simpler amines will oxygen in the flue gases to produce simpler amines, whilst these simpler amines will react react with other base amines to produce complex amines), and others, such as DIPA and with other base amines to produce complex amines), and others, such as DIPA and 1,1- 1,1-Dioxidetetrahydrothiophene (Sulfolane) [31]. Dioxidetetrahydrothiophene (Sulfolane) [31]. In 2008, Bedel assumed that there were several degradation pathways for MDEA, In 2008, Bedel assumed that there were several degradation pathways for MDEA, including hydrolysis, elimination reactions, disproportionation, and hemolytic splitting. including hydrolysis, elimination reactions, disproportionation, and hemolytic splitting. Amino acid hydrolysis occurs in extrapolated conditions of a stripper and at a high temperature,Amino which acid hydrolysis is a reasonable occurs reason in extrapolated for degradation conditions [28]. Underof a stripper normal and conditions at a high of tem- the regenerator,perature, which the commonis a reasonable pathway reason for thefor degradationdegradation of[28]. MDEA Under involves normal the conditions reaction ofof disproportionation,the regenerator, the common sometimes pathway referred for to the as alkanolaminedegradation of “scrambling”. MDEA involves Therefore, the reaction one moleculeof disproportionation, of dimethylethanolamine sometimes referred and triethanolamine to as alkanolamine is formed “scrambling”. by replacing theTherefore, methyl groupone molecule in the MDEA of dimethylethanolamine molecule with another and moleculetriethanolamine of the ethanol is formed group by [replacing8,28]. In thisthe methyl group in the MDEA molecule with another molecule of the ethanol group [8,28]. In this process, a methyl group can be replaced with a hydrogen to form DEA, and this reaction can continue for amine degradation by the polymerization of carbamate [8,15,19]. Sustainability 2021, 13, 72 12 of 27

process, a methyl group can be replaced with a hydrogen to form DEA, and this reaction can continue for amine degradation by the polymerization of carbamate [8,15,19].

2.7. Comparative Amines Solvent Table6 shows the comparatives of amine solvent, such as MEA, DEA, and MDEA as a rate, heat, and capacity of absorption, with the stability of solvent [19].

Table 6. Characterization properties of the solvents for popular amine solvents.

Rate of Absorption Stability of Heat of Absorbent Absorption Capacity CO2 Solvent Absorption Methyldiethanolamine Low High High Medium (MDEA) Diethanolamine Medium Medium Medium High (DEA) Monoethanolamine High Medium Low High (MEA)

3. Material and Method This section highlights the framework involves in specifying the variables for solving absorber column using Promax, which was developed using a typical composition of the Flue gas from gas-powered power plant plants as obtained in Table7.

Table 7. Flue gas feed compositions in mole%.

Compositions Mole Percent (%)

N2 77 CO2 21 H2O 1.99 O2 0.01

The Amine Sweetening Peng Robinson (PR) was employed as the most compatible thermodynamic equation to handle the components listed in Table7, when combined with Amine absorbent. The process was then followed by specifying the components in the Flue gas, followed by column convergence using MEA. This was then repeated at 300 m3/h as well as changing the absorbent type. The procedure shown in Figure6, was used to simulate amine solvents MEA, DEA, and MDEA, in order to capture the carbon dioxide from flue gas, utilizing amine concentrations of 10% and 15% for all solvents and circulation rates of 200 and 300 m3/h. In addition, the flue gas flow rate, compositions, temperature, and pressure of the flue gas and amine solvents was kept constant through all scenarios, having 20 trays and a 0.5 pressure drop from the bottom to top column. The flue gas that feed to the absorber had the following specifications: Temperature of ◦ 32 C; pressure of 30 bar; and CO2 representing 21% of the total components. Assumptions of steady state model whereby feed composition and materials flows re- mained the same during the convergence iterations were made, a 20 trays absorber column typical for Amine absorber columns. The limitation of this study is that it focused on typical natural gas-powered plant alone without consideration to fuel-switch between natural gas and other fuels such as Diesel etc., this was to ensure constant flue gas composition from the plant. Other limitations include steady-state analysis considered compared to the transient operations where plant start-up and shut-down generate different flue gas composition. Figure7 is a schematic diagram of the simple absorber tower used in an amine sweetening system. Sustainability 2021, 13, x FOR PEER REVIEW 13 of 28 Sustainability 2021, 13, 72 13 of 27

Figure 6. The ﬂowflow chart of a ProMax simulation.

TheTables flue7 and gas8 thatshow feed the to compositions the absorber of ha flued the gas following feed and aminespecifications: solvent, respectively,Temperature ofin 32 mole °C; percentage. pressure of 30 bar; and CO2 representing 21% of the total components. Assumptions of steady state model whereby feed composition and materials flows remainedTable 8. Amine-based the same during solution the solvents convergence in percent. iterations were made, a 20 trays absorber column typical for Amine absorber columns. The limitation of this study is that it focused on Composition of Amine Mole Percent (%) typical natural gas-powered plant alone without consideration to fuel-switch between naturalAmine gas (MEA, and other DEA fuels and MDEA) such as Diesel etc., this10 was to ensure constant 15flue gas com- H O 90 85 position from the plant.2 Other limitations include steady-state analysis considered compared to the transient operations where plant start-up and shut-down generate different flue gasWith composition. regard to the Figure amine-based 7 is a schemati solutionc diagram flow rate, of the two simple different absorber flow tower rates wereused inchosen, an amine which sweetening were 200 system. and 300 m3/h for each scenario. The first scenario was a 10% amine concentration of each amine solvent (MEA, DEA, and MDEA) with amine circulation rates of 200 and 300 cubic meters, and the second one was a 15% amine concentration with 200 and 300 m3/h. In this chapter, we will investigate the comparison of amine solvents (MEA, DEA, and MDEA) using the ProMax program. This program calculated and solved the process that occurred in the absorber tower and the outcome with an acceptable result. Sustainability 2021, 13, x FOR PEER REVIEW 14 of 28

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Figure 7. A schematic diagram of the simple absorber tower used in an amine sweetening system.

FigureThere 7. A are schematic two scenarios diagram for of the this simple process, absorber which tower was used conducted in an amine by simulations,sweetening system. and some constants did not change during all scenarios: 1. AbsorberTables 7 towerand 8 hadshow 20 the trays compositions with 29.5 andof flue 30 gas bar feed at the and top amine and bottomsolvent, of respec- the tively,tower in mole pressure; percentage. 2. The amine circulation temperature was 38 ◦C, with a pressure of 33 bar; 3. TableThe 8. flueAmine-based gas flow solution rate was solvents 76,000 in m 3percent./h and temperature were 32 ◦C, with a pressure of 30Composition bar. of Amine Mole Percent (%) AmineThe other (MEA, values DEA changed and MDEA) in the two scenarios:10 15 3 1. The amine circulationH2O rate was changed from 20090 to 300 m /h with a concentration85 of 10% for all flow rates, and 15%. With regard to the amine-based solution flow rate, two different flow rates were cho- 4.sen, Results which were 200 and 300 m3/h for each scenario. The first scenario was a 10% amine 4.1.concentration The First Scenario of each amine solvent (MEA, DEA, and MDEA) with amine circulation rates of 200The and first 300 scenario cubic meters, for amine and solvents the second MEA, one DEA, was a and 15% MDEA amine isconcentration a concentration with of 200 10%and of 300 each m3 solvent/h. In this with chapter, a change we inwill the investigat circulatione the each comparison time, that of which amine means solvents that (MEA, 200, 300DEA, m3/h and that MDEA) done byusing simulations the ProMax of ProMax program. were This conducted program withcalculated a value and of solved 200 and the 300process m3/h. that occurred in the absorber tower and the outcome with an acceptable result. There are two scenarios for this process, which was conducted by simulations, and 4.1.1. MEA with a Concentration of 10% some constants did not change during all scenarios: MEA with a Circulation Rate of 200 m3/h 1. Absorber tower had 20 trays with 29.5 and 30 bar at the top and bottom of the tower The whole process that was conducted by ProMax is shown in Figure8, demonstrating pressure; that the resulting products were clean flue gas and rich amine. 2. The amine circulation temperature was 38 °C, with a pressure of 33 bar; 3. The flue gas flow rate was 76,000 m3/h and temperature were 32 °C, with a pressure of 30 bar. The other values changed in the two scenarios: Sustainability 2021, 13, x FOR PEER REVIEW 15 of 28

1. The amine circulation rate was changed from 200 to 300 m3/h with a concentration of 10% for all flow rates, and 15%.

4. Results 4.1. The First Scenario The first scenario for amine solvents MEA, DEA, and MDEA is a concentration of 10% of each solvent with a change in the circulation each time, that which means that 200, 300 m3/h that done by simulations of ProMax were conducted with a value of 200 and 300 m3/h.

4.1.1. MEA with a Concentration of 10% MEA with a Circulation Rate of 200 m3/h

Sustainability 2021, 13, 72 The whole process that was conducted by ProMax is shown in Figure 8, demonstrat-15 of 27 ing that the resulting products were clean flue gas and rich amine.

FigureFigure 8. 8.Absorption Absorption process process using using MEA MEA solvent solven witht with a a 10% 10% concentration concentration and and 200 200 m m3/h3/h simulated simulated by by ProMax. ProMax. “*” “*” means means thethe results results that that come come out out from from bottom bottom and and top top of of absorber absorber are are mentioned mentioned in in the the Table Table9. 9.

3 Table 9. The A summary outcomeMEA with of the a absorber Circulation tower Rate results of 300 after m calculated/h by ProMax for amine (MEA, DEA, and MDEA) with an amine circulation rateThe from whole of 200process and 300 that m3 was/h and conducted with a concentration by ProMax of is 10%, shown and 15%in Figure for each 9, solvent.demonstrating that the resulting products were clean flue gas and rich amine. Amine Con. wt.% 10% 15% Amine Outcome from MEA DEA MDEA MEA DEA MDEA Feed Absorber Tower

CO2% in clean flue gas 3.6295 8.1355 8.4559 0.0000032862 5.5612 8.2545 3 200 m /h N2% in clean flue gas 95.466 91.29 91.278 99.782 93.911 91.51 Temp. of bottom 84.551 75.133 73.127 100.75 83.177 75.639 absorber (◦C) 2.9564 × CO % in clean flue gas 0.0038358 3.7518 6.9516 × 10−7 0.00036247 4.305 2 10−6 300 m3/h N2% in clean flue gas 99.768 99.768 96.01 99.782 99.782 95.468 Temp. of bottom 78.95 77.21 69.249 83.495 80.638 69.137 absorber (◦C)

MEA with a Circulation Rate of 300 m3/h The whole process that was conducted by ProMax is shown in Figure9, demonstrating that the resulting products were clean ﬂue gas and rich amine. Sustainability 2021, 13, x FOR PEER REVIEW 16 of 28 Sustainability 2021, 13, 72 16 of 27 Sustainability 2021, 13, x FOR PEER REVIEW 16 of 28

FigureFigure 9. Absorption 9. Absorption process process using using MEA MEA solvent solvent with with a a 10% 10% concentration concentration andand 300300 mm33/h simulated simulated by by ProMax. ProMax. Figure 9. Absorption process using MEA solvent with a 10% concentration and 300 m3/h simulated by ProMax. 4.1.2. DEA with a Concentration of 10% 4.1.2. DEA with a Concentration of 10% DEA4.1.2. with DEA a withCirculation a Concentration Rate of 200 of m10%3/h DEA with a Circulation Rate of 200 m3/h DEAUsing with DEAa Circulation solvent Ratewith ofa circulation200 m3/h rate of 200 m3/h and 10% concentration pro- Using DEA solvent with a circulation rate of 200 m3/h and 10% concentration pro- ducedUsing the results DEA shownsolvent in with Figure a circulation 10. rate of 200 m3/h and 10% concentration producedduced the the results results shown shown in in Figure Figure 10 10..

Figure 10. Absorption process using DEA solvent with a 10% concentration and 200 m3/h simulated by ProMax. FigureFigure 10. Absorption 10. Absorption process process using using DEA DEA solvent solven witht with a 10% a 10% concentration concentration and and 200 200 m m3/h3/h simulated by by ProMax. ProMax.

Sustainability 2021, 13, x FOR PEER REVIEW 17 of 28 Sustainability Sustainability2021 2021, 13,, 13 72, x FOR PEER REVIEW 17 of17 27of 28

DEADEA with with a Circulationa Circulation Rate Rate of of 300 300 m 3m/h3/h DEA with a Circulation Rate of 300 m3/h UsingUsing DEA DEA solvent solvent with with a circulationa circulation rate rate of of 300 300 m 3m/h3/h and and 10% 10% concentration concentration pro- pro- 3 ducedduced theUsing the results results DEA shown solventshown in in Figurewith Figure a 11circulation 11.. rate of 300 m /h and 10% concentration produced the results shown in Figure 11.

FigureFigure 11. 11.Absorption Absorption process process using using DEA DEA solvent solven witht with a 10% a 10% concentration concentration and and 300 300 m3 m/h3/h simulated simulated by by ProMax. ProMax. Figure 11. Absorption process using DEA solvent with a 10% concentration and 300 m3/h simulated by ProMax. 4.1.3. MDEA with a Concentration of 10% 4.1.3.4.1.3. MDEA MDEA with with a Concentrationa Concentration of of 10% 10% MDEA with a Circulation Rate of 200 m3/h MDEAMDEA with with a Circulationa Circulation Rate Rate of of 200 200 m 3m/h3/h Using MDEA solvent with a circulation rate of 200 m3/h and 10% concentration pro- Using MDEA solvent with a circulation rate of 200 m33/h and 10% concentration ducedUsing the results MDEA shown solvent in withFigure a circulation12. rate of 200 m /h and 10% concentration pro- producedduced the the results results shown shown in in Figure Figure 12. 12 .

Figure 12. Absorption process using MDEA solvent with a 10% concentration and 200 m3/h simulated by ProMax. FigureFigure 12. 12.Absorption Absorption process process using using MDEA MDEA solvent solven witht with a 10% a 10% concentration concentration and and 200 200 m3 /hm3/h simulated simulated by by ProMax. ProMax. SustainabilitySustainability2021, 13 2021, 72, 13, x FOR PEER REVIEW 1818 ofof 28 27

MDEA with a Circulation Rate of 300 m3/h MDEA with a Circulation Rate of 300 m3/h 3 UsingUsing MDEA MDEA solvent solvent with with aa circulationcirculation rate rate of of 300 300 m3 m/h and/h and10% 10%concentration concentration pro- producedduced thethe results shown shown in in Figure Figure 13. 13 .

FigureFigure 13. MDEA 13. MDEA solvent solvent with with a circulation a circulation rate rate of 500of 500 m3 m/h3/h and and 10% 10% concentration concentration simulated by by ProMax. ProMax.

4.2. Second Scenario 4.2. Second Scenario The second scenario for amine solvents MEA, DEA, and MDEA is was a concentra- tionThe of second 10% of scenario each solvent for amine with a solvents change the MEA, circulation DEA, and each MDEA time, that is was which a concentration means that of 10%simulations of each were solvent conducted with a by change ProMax the at circulation 200 and, 300 each m3/h time, that done that whichby simulations means thatof simulationsProMax. were conducted by ProMax at 200 and, 300 m3/h that done by simulations of ProMax. 4.2.1. MEA with a Concentration of 15% 4.2.1.MEA MEA with with a Circulation a Concentration Rate of of 200 15% m3/h 3 MEA withUsing a Circulation MEA solvent Rate with of 200 a circulation m /h rate of 200 m3/h and 15% concentration pro- Sustainability 2021, 13, x FOR PEER REVIEW 3 19 of 28 ducedUsing the MEA results solvent shown with in Figure a circulation 14. rate of 200 m /h and 15% concentration produced the results shown in Figure 14.

Figure 14. MEA solvent with a circulation rate of 300 m3/h and 15% concentration simulated by ProMax. Figure 14. MEA solvent with a circulation rate of 300 m3/h and 15% concentration simulated by ProMax. MEA with a Circulation Rate of 300 m3/h Using MEA solvent with a circulation rate of 300 m3/h and 15% concentration produced the results shown in Figure 15.

Figure 15. MEA solvent with a circulation rate of 300 m3/h and 15% concentration simulated by ProMax.

4.2.2. DEA with a Concentration of 15% DEA with a Circulation Rate of 200 m3/h Using DEA solvent with a circulation rate of 200 m3/h and 15% concentration produced the results shown in Figure 16. Sustainability 2021, 13, x FOR PEER REVIEW 19 of 28

Sustainability 2021, 13, 72 19 of 27 Figure 14. MEA solvent with a circulation rate of 300 m3/h and 15% concentration simulated by ProMax.

MEAMEA with with a Circulationa Circulation Rate Rate of of 300 300 m 3m/h3/h UsingUsing MEA MEA solvent solvent with with a circulationa circulation rate rate of of 300 300 m 3m/h3/h and and 15% 15% concentration concentration pro- pro- ducedduced the the results results shown shown in in Figure Figure 15 .15.

FigureFigure 15. 15.MEA MEA solvent solvent with with a circulation a circulation rate rate of 300of 300 m3 m/h3/h and and 15% 15% concentration concentration simulated simulated by by ProMax. ProMax.

4.2.2. DEA with a Concentration of 15% 4.2.2. DEA with a Concentration of 15% DEA with a Circulation Rate of 200 m3/h DEA with a Circulation Rate of 200 m3/h Using DEA solvent with a circulation rate of 200 m3/h and 15% concentration pro- 3 Sustainability 2021, 13, x FOR PEER REVIEWducedUsing the DEA results solvent shown with in Figure a circulation 16. rate of 200 m /h and 15% concentration20 pro- of 28 duced the results shown in Figure 16.

3 FigureFigure 16. 16.DEA DEA solvent solvent with with a circulationa circulation rate rate of of 200 200 m m/h3/h and and 15% 15% concentration concentration simulated simulated by by ProMax. ProMax.

DEA with a Circulation Rate of 300 m3/h Using DEA solvent with a circulation rate of 300 m3/h and 15% concentration produced the results shown in Figure 17.

Figure 17. DEA solvent with a circulation rate of 300 m3/h and 15% concentration simulated by ProMax.

4.2.3. MDEA with a Concentration of 15% MDEA with a Circulation Rate of 200 m3/h Using MDEA solvent with a circulation rate of 200 m3/h and 15% concentration produced the results show in Figure 18. Sustainability 2021, 13, x FOR PEER REVIEW 20 of 28

Sustainability 2021, 13, 72 20 of 27 Figure 16. DEA solvent with a circulation rate of 200 m3/h and 15% concentration simulated by ProMax.

3 DEADEA with with a a Circulation Circulation Rate Rate of of 300 300 m m/h3/h Using DEA solvent with a circulation rate of 300 m3/h and 15% concentration pro- Using DEA solvent with a circulation rate of 300 m3/h and 15% concentration produced the results shown in Figure 17. duced the results shown in Figure 17.

FigureFigure 17. 17.DEA DEA solvent solvent with with a a circulation circulation rate rate of of 300 300 m m3/h3/h andand 15%15%concentration concentrationsimulated simulatedby byProMax. ProMax.

4.2.3. MDEA with a Concentration of 15% 4.2.3. MDEA with a Concentration of 15% MDEA with a Circulation Rate of 200 m3/h MDEA with a Circulation Rate of 200 m3/h Using MDEA solvent with a circulation rate of 200 m3/h and 15% concentration pro- Using MDEA solvent with a circulation rate of 200 m3/h and 15% concentration Sustainability 2021, 13, x FOR PEER REVIEWduced the results show in Figure 18. 21 of 28 produced the results show in Figure 18.

FigureFigure 18. 18.MDEA MDEA solvent solvent with with a a circulation circulation rate rate of of 200 200 m m3/h3/h andand 15%15% concentrationconcentration simulatedsimulatedby byProMax. ProMax.

MDEA with a Circulation Rate of 300 m3/h Using MDEA solvent with a circulation rate of 300 m3/h and 15% concentration produced the results shown in Figure 19.

Figure 19. MDEA solvent with a circulation rate of 300 m3/h and 15% concentration simulated by ProMax.

A summary of the results obtained from simulations of ProMax was compiled from Figures 8–19 and is shown in Table 9, demonstrating that the MEA solvent is the best solvent in comparison to DEA and MDEA, whilst MDEA is the worst one.

Sustainability 2021, 13, x FOR PEER REVIEW 21 of 28

Sustainability 2021, 13, 72 21 of 27 Figure 18. MDEA solvent with a circulation rate of 200 m3/h and 15% concentration simulated by ProMax.

MDEAMDEA with with a Circulation a Circulation Rate Rate of 300of 300 m3 m/h3/h UsingUsing MDEA MDEA solvent solvent with with a a circulation circulation rate rate ofof 300300 m3/h/h and and 15% 15% concentration concentration pro- producedduced the the results results shown shown in in Figure Figure 19.19.

FigureFigure 19. 19.MDEA MDEA solvent solvent with with a circulation a circulation rate rate of 300 of 300 m3/h m3 and/h and 15% 15% concentration concentration simulated simulated by by ProMax. ProMax.

A summaryA summary of theof the results results obtained obtained from from simulations simulations of ProMaxof ProMax was was compiled compiled from from FiguresFigures8–19 8–19 and and is shownis shown in Tablein Table9, demonstrating 9, demonstrating that that the MEAthe MEA solvent solvent is the is bestthe best solventsolvent in comparisonin comparison to DEAto DEA and and MDEA, MDEA, whilst whilst MDEA MDEA is theis the worst worst one. one. From the aforementioned results presented in Table9, when using the 200 m 3/h

circulation rate with 10% concentration of amine, the CO2 % from clean flue gas is 3.6295% for MEA, while that for DEA is 8.1355%. Additionally, that of MDEA is the highest percent, with a value of 8.4559%. Furthermore, at 15%, with the same flow rate mentioned above, DEA and MDEA have the highest percentage values of 5.5612% and 8.2545%, respectively, whilst MEA has a value of 3.2862 × 10−6%. These mean that the concentration is directly proportional to the flow rate and inversely proportional to CO2 in the clean flue gas. 3 However, at 200m /h with 10% concentration, the CO2 in the clean flue gas for MEA is 2.9564 × 10−6%, while for DEA and MDEA is 0.0038358% and 3.7518%, respectively. At 15% concentration of amine with a circulation rate of 300m3/h, the percentage of CO2 in the clean flue gas for MEA, DEA, and MDEA is 6.9516 × 10−7%, 0.00036247%, and 4.305%. It has been noted that the percentage of CO2 in the clean flue gas for MEA and DEA decreased, while for MDEA, at 15% with 300 m3/h circulation rate increased. This is because MDEA has different operating condition and it works efficiently from 50 to 60 bars. Another reason is that at this flow (300 m3/h) of circulation rate is critical flow and the mass transfer in this flow is false for MDEA. That is the reason why CO2 % in clean gas flue increased rather than to decreased. As shown in Table4 the typical concentration should the MDEA be work is 35–55%. Therefore, considering these results, MEA is the best amongst them. Figures 20 and 21 illustrate the CO2 percent in clean flow gas at 200 and 300 m3/h for MEA, DEA and MDEA at 10 and 15% concentration of amines. Sustainability 2021, 13, x FOR PEER REVIEW 22 of 28

Table 9. The A summary outcome of the absorber tower results after calculated by ProMax for amine (MEA, DEA, and MDEA) with an amine circulation rate from of 200 and 300 m3/h and with a concentration of 10%, and 15% for each solvent.

Amine Con. wt.% 10% 15% Amine Outcome from Absorber Tower MEA DEA MDEA MEA DEA MDEA Feed CO2% in clean flue gas 3.6295 8.1355 8.4559 0.0000032862 5.5612 8.2545 200 m3/h N2% in clean flue gas 95.466 91.29 91.278 99.782 93.911 91.51 Temp. of bottom absorber (°C) 84.551 75.133 73.127 100.75 83.177 75.639 CO2% in clean flue gas 2.9564 × 10−6 0.0038358 3.7518 6.9516 × 10−7 0.00036247 4.305 300 m3/h N2% in clean flue gas 99.768 99.768 96.01 99.782 99.782 95.468 Temp. of bottom absorber (°C) 78.95 77.21 69.249 83.495 80.638 69.137

From the aforementioned results presented in Table 9, when using the 200 m3/h circulation rate with 10% concentration of amine, the CO2 % from clean flue gas is 3.6295% for MEA, while that for DEA is 8.1355%. Additionally, that of MDEA is the highest percent, with a value of 8.4559%. Furthermore, at 15%, with the same flow rate mentioned above, DEA and MDEA have the highest percentage values of 5.5612% and 8.2545%, respectively, whilst MEA has a value of 3.2862 × 10−6%. These mean that the concentration is directly proportional to the flow rate and inversely proportional to CO2 in the clean flue gas. However, at 200m3/h with 10% concentration, the CO2 in the clean flue gas for MEA is 2.9564 × 10−6%, while for DEA and MDEA is 0.0038358% and 3.7518%, respectively. At 15% concentration of amine with a circulation rate of 300m3/h, the percentage of CO2 in the clean flue gas for MEA, DEA, and MDEA is 6.9516 × 10−7%, 0.00036247%, and 4.305%. It has been noted that the percentage of CO2 in the clean flue gas for MEA and DEA decreased, while for MDEA, at 15% with 300 m3/h circulation rate increased. This is because MDEA has different operating condition and it works efficiently from 50 to 60 bars. An- other reason is that at this flow (300 m3/h) of circulation rate is critical flow and the mass transfer in this flow is false for MDEA. That is the reason why CO2 % in clean gas flue increased rather than to decreased. As shown in Table 4 the typical concentration should the MDEA be work is 35–55%. Therefore, considering these results, MEA is the best Sustainability 2021, 13, 72 22 of 27 amongst them. Figures 20 and 21 illustrate the CO2 percent in clean flow gas at 200 and 300 m3/h for MEA, DEA and MDEA at 10 and 15% concentration of amines.

Amine recirculastion rate of 200m3/hr

9 8.4559 8.1355 8.2545 8

6 5.5612

4 3.6295

% CO2 IN CLEAN FLUE GAS 2

1 3.29E-06 0 Amine concentration 10% Amine concentration 15% AMINE CONCENTRATION

Sustainability 2021, 13, x FOR PEER REVIEW 23 of 28 MEA DEA MDEA

3 Figure 20. The CO2% in clean ﬂue gas with concentration of amine solvents (MEA, DEA, and MDEA) at 200 m /h. Figure 20. The CO2% in clean flue gas with concentration of amine solvents (MEA, DEA, and MDEA) at 200 m3/h.

Amine recirculation rate of 300m3/hr 5.00 4.50 4.305 4.00 3.7518 3.50 3.00 2.50 2.00 6.95E-07 1.50 2.96E-06 0.0038358 0.00036247 %CO2 IN CLEAN FLUE GAS 1.00 0.50 0.00 MEA DEA MDEA AMINE CONCENTRATION

Amine concentration 10% Amine concentration 15%

Figure 21. The CO2% in clean flue gas with concentration of amine solvents (MEA, DEA, and MDEA) at 300 m3/h. Figure 21. The CO2% in clean ﬂue gas with concentration of amine solvents (MEA, DEA, and MDEA) at 300 m /h. 4.3. The Cost of Amine 4.3. TheTo find Cost out of Amine which solvent costs the least, each one’s price was estimated by performing a Tocalculation. ﬁnd out which The result solvent shows costs thethat least, the MEA each one’sis the price best wassolvent. estimated The prices by performing were as follows:a calculation. The result shows that the MEA is the best solvent. The prices were as follows: (a) GBP 1121/ton for monoethanolamine (MEA) [33]; (b) DEA GBP 1039/ton [33]; (c) MDEA unknown? (d) To calculate the price, there should be a specific gravity for amine to convert the cubic meters to tons, as shown in Equations (11) and (12); (e) Specific gravity of MEA = 1.01531, density = 1015.31 kg/m3 = 1.01531 t/m3 (ProMax program):

Total MEA ton = Amine feed × Amine concentration% × Density (ton/m3) = ton (11)

Total cost = Total MEA ton × GBP/ton = GBP (12) Therefore, by using Equations (11) and (12), the cost was calculated and is shown for MEA in Table 10 and for DEA in Table 11.

Table 10. The total weight of amine (MEA) in tons, with the total cost in GBP.

MEA Solution m3/h 10% = Net MEA Tons from Solution Total Cost GBP (GBP 1121/ton) 200 20.3062 22,763.25 300 30.4593 34,144.88

(a) Specific gravity of DEA = 1.04359, density = 1043.59 kg/m3 = 1.04359 t/m3 (ProMax program). Sustainability 2021, 13, 72 23 of 27

(a) GBP 1121/ton for monoethanolamine (MEA) [33]; (b) DEA GBP 1039/ton [33]; (c) MDEA unknown? (d) To calculate the price, there should be a speciﬁc gravity for amine to convert the cubic meters to tons, as shown in Equations (11) and (12); (e) Speciﬁc gravity of MEA = 1.01531, density = 1015.31 kg/m3 = 1.01531 t/m3 (Pro- Max program):

Total MEA ton = Amine feed × Amine concentration% × Density (ton/m3) = ton (11)

Total cost = Total MEA ton × GBP/ton = GBP (12) Therefore, by using Equations (11) and (12), the cost was calculated and is shown for MEA in Table 10 and for DEA in Table 11.

Table 10. The total weight of amine (MEA) in tons, with the total cost in GBP.

10% = Net MEA Tons from Total Cost GBP MEA Solution m3/h Solution (GBP 1121/ton) 200 20.3062 22,763.25 300 30.4593 34,144.88

Table 11. The total weight of DEA in ton with total cost in GBP.

10% = Net DEA Tons from Total Cost GBP DEA Solution m3/h Solution (GBP 1039/ton) 200 20.8718 21,685.8002 300 31.3077 32,528.7003

(a) Speciﬁc gravity of DEA = 1.04359, density = 1043.59 kg/m3 = 1.04359 t/m3 (Pro- Max program).

The capital cost for CO2 capture facility is USD 223 million and capture cost (USD/tonne CO2) ranges between USD $36–70 for MEA for a typical gas-powered power plant inte- grated with Carbon capture using MEA shown in Table 12[19,34].

Table 12. The cost of MEA for one a real company for post capture of CO2.

Study [19,34] Industrial source Combined stack gas CO2 capture technology PCC MEA CO2 capture efﬁciency (%) 90 CO2 captured (Mt CO2/y) 1.04 Project life (years) 20 Currency US Cost year 2007 External power plant or fuel Natural gas Capital cost for capture facility (millionUSD) 223 Capture cost (USD/tonne CO2 avoided) 36–70

5. Conclusions From the present study, the following conclusions can be drawn: 1. From the results of Table9, it can be concluded that • At 10% concentration and feed of 200 m3/h of amine solvents, the outcome obtained cannot be chosen for capture because the CO2% in ﬂue gas for each Sustainability 2021, 13, 72 24 of 27

MEA, DEA and MDEA are 3.6295%, 8.1355%, and 8.4559%, respectively, and these values are not enough. With these percentages obtained my target was not achieved neither of other of other researchers because to use capture process there should be clear from CO2% in clean flue gas as aforementioned is not acceptable (the percentage of carbon dioxide) as sustainable for power plants, even the temperature at the bottom of the absorber is quite good but the purity of nitrogen is not qualified to be utilized to other purposes such as food processes. • MEA produces a good outcome at 200 m3/h with a 15% concentration in comparison to DEA and MDEA, with their values being 3.2862 × 10−6, 5.5612, and 8.2545, respectively, but the temperature of the rich amine is still high, so it is recommended that cooling is induced by increasing the flow rate or decreasing the concentration of amine; • Likewise, the MEA has perfect significant results at a 300 m3/h amine circulation rate at a 10% concentration, reducing the temperature to 78.95 ◦C, whereas the temperature was 100.75 ◦C at 15%. A good result of 77.21 ◦C was obtained for 0.0038358% of CO2 in the top outlet of the tower and 99.768% nitrogen for both MEA and DEA and 96.01% for MDEA, with 3.7518% CO2 in clean flue gas, which is still high, however, the other significant advantages of capturing CO2 is that the gained nitrogen, with a purity 99.68%, can be used for other purposes; • For MDEA, the bad result means that the operating condition needs to be changed, which changes the pressure to 50 or 60 bar. This will produce good results but will be costly. 2. Based on the results in Tables 10 and 11, the following comparison can be drawn: • For MEA at 200 and 300 m3/h, the total weight in tons was equal to 20.3062 and 30.4593, with a total cost of GBP 22,763.25 and 34,144.88, respectively; • for DEA at 200 and 300 m3/h, the total weight in tons was equal to 20.8718 and 31.3077, with a total cost of GBP 21,685.8002 and 32,528.7003, respectively. 3. Finally, from the results of the comparison, MEA was proven to be the best solvent investigated in this study, rather than DEA and MDEA; however, the DEA was slightly cheaper than MEA, but the result was an enormously different comparison with MEA.

Author Contributions: S.H. conducted the study simulation and data analysis, A.J.A. supervised the overall research, contributed to paper development and editing, G.G.N. conducted review and made changes to the manuscript. All authors have read and agreed to the published version of the manuscript. Funding: This research was fully funded by CNOOC Iraq Limited. Conﬂicts of Interest: The authors declare no conﬂict of interest.

Abbreviations BP British Petroleum IPCC Intergovernmental on climate change CCS Carbon capture and storage CO2 Carbon dioxide COS Carbonyl sulﬁde SO2 Sulfur dioxide NOX Nitrogen oxides (x = 1, 2, 3) O2 Oxygen N2 Nitrogen H2O Water or (vapor water) Sustainability 2021, 13, 72 25 of 27

H2S Hydrogen sulﬁde PM Particulate matter RDF Radial distribution functions MEA Monoethanolamine DEA Diethanolamine DGA Diglycolamine MDEA Methyldiethanolamine DIPA Diisopropanolamine TIPA Triisopropanolamine Gt Gigatons Mt Million tons MPa Megapascal (unit of pressure) Ppm Part per million PCC Post-combustion capture

Appendix A pKa: This is one method that can be used to indicate the strength of acid. pKa = −log10Ka means pKa is a negative logarithm of the Ka value. In addition, a higher pKa value indicates a weaker acid, and a lower value of pKa means a stronger acid, and the latter means that the acid is fully dissociated in water. Dimers: A structure implicates two similar or identical units. These units may be associated by noncovalent forces or covalent bonding [31]. Rich amine: An amine solution that has held or absorbed the acid gas CO2 from the ﬂue gas during the absorption process. Lean amine: An amine solution that does not contain any acid gas CO2 and this means that, before the absorption processes, the amine undergoes the regeneration process, which removes all acid gas, producing a lean amine.

Table 1. The properties of CO2 that used in amine absorption come out from ProMax simulation program.

Properties Units Vapor Temperature ◦C 32 Pressure barg 30 Mole fraction vapor % 100 Mole fraction light liquid % 0 Mole fraction heavy liquid % 0 Molecular weight Kg/kmol 44.0095 Mass density Kg/m3 65.0285 Molar flow Kmol/h 2272.24 Mass flow Kg/h 100,000 Vapor volumetric flow m3/h 1537.79 Liquid volumetric flow m3/h 1537.79 Normal vapor volumetric flow Nm3/h 50,929.8 Std vapor volumetric flow m3/h 53726.7 Std liquid volumetric flow m3/h 121.773 Compressibility 0.827261 Specific gravity 1.51953 API gravity Enthalpy KJ/h −8.96706 × 108 Mass enthalpy kJ/kg −8967.06 Mass Cp kJ/(kg ◦C) 1.08707 Ideal gas Cp, Cv ratio 1.28541 Dynamic viscosity cP 0.0166239 Kinematic viscosity cSt 0.25564 Thermal conductivity W/(m ◦C) 0.0198344 Surface tension dyn/cm Net ideal gas heating value MJ/m3 0 Net liquid heating value MJ/kg −0.17659 Gross ideal gas heating value MJ/m3 0 Gross heating value MJ/kg 0.17659 Sustainability 2021, 13, 72 26 of 27

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