capture of co2

Capture of CO2

Background and Future Prospects

Dr. I. M. MishraPt. G. B. Pant Chair Professor of Environmental Pollution Abatement,

Professor of Chemical Engineering and Dean Saharanpur Campus

Indian Institute of Technology, RoorkeeE-mail:- [email protected]

Planetary Constraints Availability of non renewable carbon-based fossil fuels-coal,

petroleum oils, natural gas

Accommodation of emissions/effluents/wastes - CO2 emissions (global warming); river/ground water/air pollution, etc.

The range of carbon-based fuels, the resource constraint is flexible. Emission constraint is inflexible

Which constraint will become active first?

Economic system can deal with resource constraint

Ostrich-like behaviour-no consequences: So

Emission constraint will “bite” before the Resource constraint

- whereabouts of carbon-based fuels is known: therefore not

much problem to biosphere

- scarcity of ‘supply’ can be coped with; scarcity of emission

capacity (carrying capacity) will have global impact:

hence economic devices need to be developed

‘Carbon –Trading’ is one such device, no guarantee of it to be

effective

Reduction of carbon intensity in diverse economies is a

engineering challenge

Global concentrations of GHG increased markedly as a result of

human activities.

In 2005, CO2 conc. >> the natural range over the last 650,000

years.

> 375ppm CO2 now ; GHG emission now >70% over that of

1970. India emits ~ 1.2 ton/person as against Qatar ~44.5

ton/person/year

Human Contribution to Climate Change

Atmospheric concentration of CO2 (solid blue line, right scale) and three principal ODS (dashed red line, left scale). The ODS are chlorofluorocarbons (CFCs) 11, 12, and 113 and were weighted based on their ozone-depleting potential). (World Resources Institute: World Resources 2002-2004, Earth trends Data, Washington,2003)

(IPCC Report, 2007)

Changes in temperature, sea level and northern hemisphere snow cover (IPCC Report, 2007)

Carbon Emission Per Capita and Per-unit GDP of Nations.(Sikdar, 2007)

The 12 Principles of Engineering for Sustainable Development

1. look beyond your own locality and the immediate future

2. innovate and be creative

3. seek a balanced solution

4. seek engagement from all stakeholders

5. make sure you know the needs and wants

6. plan and manage effectively

7. give sustainability the benefit of any doubt

8. if polluters must pollute. . . then they must pay as well

9. adopt a holistic, ‘cradle-to-crematorium’ approach

10. do things right, having decided on the right thing to do

11. beware cost reductions that masquerade as value engineering

12. practice what you preach.

Beyond Adaptation to Climate Change

Adaptation to climate change is necessary to address impacts

resulting from the warming which is already unavoidable due to

past emissions.

However: Adaptation alone cannot cope with all the projected

impacts of climate change

The costs of adaptation and impacts will increase as global

temperatures increase.

Making development more sustainable can enhance both

mitigative and adaptive capacity, and reduce emissions and

vulnerability to climate change

(Pachauri, R.K., Final presentation of IPCC Report, 2007)

UNEP,24th Sept., 2007

Global measures for Green House Gas Mitigation Worldwide agreement that, steps are necessary to contain rising CO2

levels.

Less agreement on how best to achieve this.

Only 55 countries including Russia have signed the Kyoto Protocol where industrial nations will be required to bring their emissions of GHG down by 5.2% to pre 1990 levels in the next 8 years.

US has not ratified Kyoto Protocol. Measures announced in US include:

* Release of vision 21 statement

*Release of carbon sequestration technology roadmap

*Funding of CO2 capture tech development

*Hydrogen fuelled car development

Key Technologies to Reduce EmissionsEnergy supply:

Efficiency; fuel switching; renewable (hydropower, solar, wind,

geothermal and bioenergy); combined heat and power; nuclear power;

early applications of CO2 capture and storage.

Transport :

More fuel efficient vehicles; hybrid vehicles; biofuels; modal shifts

from road transport to rail and public transport systems; cycling,

walking; land-use planning

Buildings :

Efficient lighting; efficient appliances and air-conditioning; improved

insulation; solar heating and cooling; alternatives for fluorinated gases

in insulation and appliances

Key Policies to Reduce Emissions

Appropriate incentives for Development of technologies Effective carbon price signal to create incentives to invest

in low-GHG products, technologies and processes Appropriate energy infrastructure investment decisions,

which have long term effects on emissions. Changes in lifestyle and behavior Patterns, especially in building, transport and industrial

sectors

(IPCC Report,2007)

Pathways towards Stabilization of CO2 LevelCharacteristics of Stabilization Scenarios

Stabilization level (ppm CO2-eq)

Global mean temp. increase at equilibrium (oC)

Year CO2 needs to peak

Year CO2 emissions back at 2000 level

Reduction in 2050 CO2 emissions compared to 2000

445-490 2.0-2.4 2000-2015 2000-2030 -85 to -50

490-535 2.4-2.8 2000-2020 2000-2040 -60 to -30

535-590 2.8-3.2 2010-2030 2020-2060 -30 to +5

590-710 3.2-4.0 2020-2060 2050-2100 +10 to +60

710-855 4.0-4.9 2050-2080 +25 to +85

855-1130 4.9-6.1 2060-2090 +90 to +140

Mitigation efforts over the next two to three decades will have a large impact on opportunities to achieve lower stabilization levels(IPCC Report,2007).

Typical Composition of Flue Gases

CO2 3-5% (NG fired)11-14% coal fired

Oxygen 12-15% (NG fired)3-4% coal fired

Water 4-5%

NOx 300-500 mg/Nm3

SOx 700-1200 mg/Nm3

SPM 130-150 mg/Nm3

Temperature 150 °C

Pressure atmospheric

Typical Flow 1.5 MMCM/hr for 210 MW plant

Operational Constraints under which CO2 recovery process must perform in Post Combustion CO2 Capture

Low Pressure

High temperature

Presence of oxygen

Presence of Sox, NOx

Presence of Water Vapour

Soot

Fly ash

SPM

Cost Associated with Implementation of CO2 Capture Technologies

Substantial cost factor is associated with implementation of CO2

capture technology in power generation This cost varies with plant type-greater for gas- fired plant than coal

fired plant. Cost of electricity generation estimated to be 40% higher if current

technology for CO2 capture used in power plants

Large scope for development of more efficient CO2 capture

technologies

CO2 capture options

Advantages and Disadvantages of capture options

CO2 Capture

Efficient CO2 removal processes from flue gas

CO2 concentration: 3-14%Capture important for

C1 feedstock into industrially useful compounds Reduction in GH effects.

Most widely used processes for CO2 capture are: Chemical absorption by solvents (aqueous amines or

amine based solvents to form carbamates)/New Solvents, Wet Absorption.

Adsorption by adsorbent using PSA/TSA./Dry Adsorption.

Membrane separation. Cryogenic separation.

Emerging Technologies1. Carbonate based system

K2CO3(K)/piperazine(Pz)/ (5 molar K/2.5 molar Pz), O2 is less soluble in K/Pz

2. Aqueous NH3

(Ammonium carbonate + CO2 + H2O Ammonium bicarbonate)

Flue gas to be cooled to 16-260C to reduce ammonia emission

chilled NH3 process

3. Membrane

Zeolite membrane

4. Adsorbents Supported Na2CO3, meso porous zeolites

5. Metal organic Framework (MoF)

6. Enzyme based system

CO2 Emissions from Fertilizer Industry

• Fertlizer industry consumes ~35% petroleum products; ~70% natural gas; ~3-4% coal and ~30% of fuel in utilities ofthat in the total industrial sector (2007).

• Average specific power consumption (SEC)/ ton of ammonia is ~ 50, 840, 210, 1490 kWh from NG, naphtha, fuel oil, coal as feed stock.

• Average SEC for ammonia to urea is ~ 55, 200, 80, 315 kWh/ton of urea for NG , Naphtha, fuel oil and coal

Urea demand ~35 M tons/yearPhosphate (P2O5) ~ 7 mt/yearCO2 emissions (t/t) for ammonia/urea production

Ammonia Urea

NG ~ 0.55 ~ 0.55

Naphtha ~ 1.10 ~ 0.95

Fuel Oil ~ 1.25 ~ 1.05

Coal ~ 4.4 ~ 2.95

CO2 capture schemes for fossil-fueled power plants

• In a global context, among all the industries emitting CO2, fossil-fueled power plants generate the largest amount of CO2 emission and that accounts for about 33–40 percent of the total (Carapellucci and Milazzo, 2003; Stewart and Hessami, 2005).

• CO2 needs to be separated and captured from the flue gases of such point sources before direct sequestration.

• For these power plants, CO2 separation and capture processes can be divided into several scenarios: post-combustion processes for a tradition coal-fired power plant,

• pre-combustion processes for gasification or reforming and oxy-fuel processes.

• Oxyfuel combustion is sometimes referred to as oxy-firing or oxy-combustion.

• Newly emerged technologies, such as chemical-looping combustion (CLC), significantly reduce the complexity of separating CO2 from a gas stream.

Supercritical & Ultra –Supercritical Technologies

Gas Turbine Combined Cycle

Integrated Gasification Combined Cycle

Oxy-fuel Combustion

Increasing Efficiency of old power plants by

Renovation & Modernization(R&M)

CATs Options

Variation of CO2 Emission with Technology

Efficiency (%) Technology Specific CO2 emission kg/KWh

46-58 NGCC 0.40-0.30

>50 IGCC + FC 0.65-0.60

45-49 IGCC 0.75-0.70

>41.5 USC 0.80-0.75

39.3-40.5 Supercritical 0.85-0.80

37.9-38.5 PC Subcritical 0.90-0.85

• First seperation of CO2 from NOx and SO2

• One way to do post-combustion capture is to use chemical absorption, such as monoethanolamine (MEA) absorption. This technique has been widely used in natural gas industry for over 60 years.

• Another advantage of this technique is it produces a relatively pure CO2 stream.

• Although the size and cost of the required absorber would be comparable to those of an SO2 scrubber, the absorber would consume one-quarter to one-third of the total steam produced by the plant, reducing its generating capacity by the same amount. Also the footprint of the host plant is increased by 60% (Elwell and Grant, 2006).

• An alternative post-combustion CO2 capture method is the use of membrane gas separation technologies.

Pulverized coal combustion CO2 separation and capture process.

Pre Combustion CO2 Capture: Gasification CO2 separation and capture process

• In this pre-combustion process, fuels are first converted into a mixture of CO2 and H2 through a reforming (natural gas) or gasification (coal) process and the subsequent shift-reaction. CO2 can be separated from the conversion product stream and H2 can then be burned in gas turbine or be used by fuel cell. Fig.3 shows this process flow (Feron and Hendriks, 2005).

• Gasification partially oxidizes coal to produce a gaseous fuel, which is essentially a hydrogen and carbon monoxide mixture. When syngas is used to fuel a plant similar to a traditional combined-cycle power plant, the process is referred to as integrated gasification combined-cycle (IGCC).

• Several methods can be used to capture CO2. The leading option for CO2 capture is an absorption process, in which the solvent can be a chemical one, such as MEA absorption process, or physical one, such as pressure swing adsorption (PSA).

• Physical absorption is a mature technology and has been used in the Great Plains Synfuels plant in North Dakota, U.S. for 20 years (Elwell and Grant, 2006).

Oxy-combustion CO2 separation and capture process.

Gasification CO2 separation and capture process.

In the oxy-firing process, pure O2 is separated from air and sent to energy conversion unit and combines with partially recycled flue gas of concentrated CO2 to keep the furnace temperature below the allowable point. The combustion takes place in an environment of O2/CO2 mixture. The resulting flue gas is high-purity CO2 stream(Feron and Hendriks, 2005).

The exhaust gas stream is free of nitrogen components.Particulates and sulfur compounds are first removed from the exhaust stream using widely adopted techniques. After SO2 removal, the exhaust gas stream is approximately 90%CO2 by volume on a dry basis.

Further separation of CO2 is not necessary. CO2 can then be compressed for storage or transportation.

The main advantage of this technology is the elimination of NOx control equipment and the CO2 separation step.

Oxy-combustion CO2 separation and capture process.

Chemical-looping combustion process

Chemical-looping combustion (CLC) is a novel process with inherent CO2 capture. It has also been called unmixed combustion since direct contact between fuel and combustion air is avoided. Instead, an oxygen carrier brings oxygen from air to fuel. Suitable oxygen carriers are small particles of metal oxide such as Fe2O3, NiO, CuO orMn2O3. A basic CLC system is shown in Fig.5 (Ryd´en and Lyngfelt, 2006).

CLC has several advantages compared with conventional combustion. The exhaust gas stream from air reactor is harmless, consisting mainly of N2. In a well-designed system, there should be no thermal formation of NOx sincethe regeneration of oxygen carrier takes place without flame and at moderate temperatures. The exhaust gas from the fuel reactor consists of CO2 and H2O. Separation of CO2 can be done by a condenser. This is the major advantage with CLC which avoids the huge energy penalty necessary in traditional amine scrubbing process to capture CO2.

Chemical-looping combustion process.

2 2 2O Me MeO

2 2

1 1 12 2

2 2 2n mC H n m MeO nCO mH O n m Me

Carbon fixation

Forestation.

Ocean fertilization.

Photosynthesis process.

2 2 6 12 6 26 6 ( ) ( .) 6 ( )CO H O l light heat C H O aq O g

In-situ CO2 capture.

2 3CaO CO CaCO

Hydrate-based separations.

Mineral carbonation, natural or biomimetic

One of the major CO2 fixation process in nature is the chemical

weathering of rocks, such as silicates, containing calcium or

magnesium. The silicate rocks could be turned into carbonates by

reacting with CO2 following this mechanism:

2 2 3 2, ,y x yxMg Ca Si O xCO x Mg Ca CO ySiO

Mineral carbonation results in the storage of CO2 in solid form as a

stable, environmentally benign mineral carbonate. The energy state

of mineral carbonate is 60 to 180 kJ/mol lower than CO2, which is

400 kJ/mol lower than carbon (Maroto-Valera et al., 2005).

• Carbon separation technical options Capture of CO2 contributes 75 percent to the overall CCS cost and CCS increases the electricity production cost

• by 50 percent (Feron and Hendriks, 2005).

• Although these numbers may vary with different CCS schemes, cutting• the capture cost is the most important issue for the CCS process to be acceptable to the

energy industry.

• There are many options for CO2 separation and capture, and these include• adsorption, absorption, membrane and biotechnology. The optimum CO2 capture

scheme could be determined by analyzing costs in the context of power generation.

• The absorption/stripping process, using amine solutions such as MEA, is a commercialized technology used in natural gas industry for 60 years and is regarded as the most mature process. The CO2 recovery rate is 98% for

• MEA (Yamasaki, 2003).

• The adsorption process is based on the same principle but using porous solid adsorbents such as zeolites and activated carbon, and chemical reactions between the adsorbent and CO2 may or may not occur during the separation process. Both pressure swing adsorption and temperature swing processes are widely used.

Amine absorption process

• Natural gas industry uses MEA to absorb CO2 from natural gas. There are commercial MEA absorption processes with which CO2 is removed from combustion flue gas stream.

• MEA reacts with CO2 in the gas stream to form MEA carbamate. The CO2-rich MEA solution is then sent to a stripper where it is reheated to release

• almost pure CO2. The MEA solution is then recycled to the absorber

• This process is generally uneconomic as it requires large equipment sizeand intensive energy input. It is widely known that the heat duty for solvent regeneration can constitute up to 70% of the total operating costs in a CO2 capture plant (Idem et al., 2006).

• Besides MEA, diethanolamine (DEA) and methyldiethanolamine (MDEA) are often used as absorbents.

• The proposed mechanism of reactions between CO2 and amines are shown in Fig.6. According to this mechanism, the majority of the CO2 captured will result in the formation of bicarbonate in the liquid amine capture system.

• In aqueous media, there is a requirement of 2 mol-amine/mol-CO2 for the formation of stable bicarbonate compounds resulting in the capture of CO2.

Proposed reaction sequence for the capture of carbon dioxide by liquid amine-based systems (Gray et al., 2005).

Mixed amines have been reported to maximize the desirable qualities of the individual amines.

The use of mixed amines is to have a solution consisting of tertiary and primary amines or tertiary plus secondary amines that retains much of the reactivity of primary amines or secondary amines at similar or reduced circulation rates but offers low regeneration costs similar to those of tertiary amines.

Ammonium absorption process

This process uses aqueous ammonia as CO2 sorbent with the capability of multi-component control. Flue gas needs to be pretreated by oxidizing SO2 and NO to SO3 and NO2, respectively. The flue gas then reacts with aqueous ammonia in a wet scrubber. The regeneration of ammonium requires heat input to thermally decompose ammonium bicarbonate and ammonium carbonate.They estimated that this process saves energy up to 60 percent compared to MEA process. The major by-products from this process include ammonium sulfate, ammonium nitrate, ammonium bicarbonate. Ammonium sulfate and ammonium nitrate are well-known fertilizers.

Dual-alkali absorption approach

2 3 2 3 4CO NaCl NH H O NaHCO NH Cl

4 3 2 222 2 2NH Cl Ca OH NH CaCl H O

3 2CaCO CaO CO

2 2 2 3 2 3

2 2 3 .

CO NaCL HOCH CH CH NH H O NaHCO

HOCH CH CH NH HCL

2 2 3 22 2 2NaCl CO CaO H O NaHCO CaCl

Molecular sieve adsorbent

This technology is believed to be cost-effective and can be adapted to a variety of carbon sequestration schemes (Stewart and Hessami, 2005). There were many research activities aiming to improve the CO2 adsorption by chemically treat the molecular sieve surface.

Adsorbents based on high surface area inorganic supports that incorporate basic organic groups, usually amines, are of particular interest. The interaction between the basic surface and acidic CO2 molecules is thought to result in the formation of surface ammonium carbamate under anhydrous conditions and in the form of ammonium bicarbonate and carbonate species in the presence of water.

Similar to amine absorption process, the CO2 adsorption capacity is0.5 mol CO2/mol surface-bound amine group without the presence of water.

Surface reactions of amine groups with CO2

“Molecular basket” adsorbent for CO2 separation

This adsorbent is based on mesoporous molecular sieve of MCM-41 impregnated with polyethylenimine (PEI). Fig.8 shows the structuresof MCM41 and PEI.

With the increase in PEI loading, the surface area, pore size and pore volume of the loaded MCM-41 decrease.

When the loading is higher than 30wt.%, the mesoporous pores began to be filled with PEI and the adsorbent shows a synergetic effect on the adsorptionof CO2 by PEI. At PEI loading of 50 wt.%, the highest CO2 adsorption capacity of 246 mg/g PEI is obtained, which is 30 times higher than that of MCM-41 and is about 23 times that of the pure PEI.

Chemical impregnation proved to be a better way to prepare the molecular basket. This study also shows that this molecular basket can selectively capture CO2 for the separation of CO2 from simulated flue gas, the separation of CO2 from natural gas-fired and coal-fired boiler flue gas

Structures of MCM-41 and PEI (Song, 2006).

“Molecular basket” concept for highly-selective high-capacity CO2 adsorbent (Song, 2006).

Adsorption by activated carbon

Anthracites are known to produce high surface area activated carbon.

The highest CO2 adsorption capacity was 65.7 mg CO2/g adsorbent for theanthracite activated at 800°C for 2 h with a surface area of 540 m2/g. The anthracite with the highest surface area of 1,071 m2/g only had a CO2 adsorption capacity of 40 mg CO2/g adsorbent. This could be explained by certain size pores being effective for CO2 adsorption. Also the NH3 treatment and PEI impregnation increased the CO2 capture capacity of the activated anthracites at higher temperature, due to the introduction of alkaline nitrogen groups on the surface.

2 3 2 2 3 2( ) ( ) ( )Li ZrO s CO Li CO s ZrO s

4 4 2 2 3 2 3Li SiO CO Li SiO Li CO

CO2 adsorbents based on lithium compounds

CO2 capture based on membrane separation

1. Polymeric membranes

2. Inorganic membranes

3. Carbon membranes

4. Alumina membranes

5. Silica membranes

6. Zeolite membranes

7. Facilitated transport membranes

8. Mixed-matrix and hybrid membranes

9. Facilitated transport membranes

Problems with Amines The uptake of water into the gas stream requires additional

drying process. The loss of volatile amines and the evaporation of water:

energy and cost intensive process. The desorption of CO2 by heating causes serious corrosion and

other operational difficulties with addition of costly zeolites ($80,000/ton)

SO2, even though present in small amount (500-2500 ppm) in the flue gas undergoes chemical reaction (irreversible) with amines and causes solvent degradation, so reduction in solvent’s capacity to capture CO2.

Therefore with sulfur bearing fossil fuels, an additional pre scrubbing of SO2 from the flue gas before using amine-based scrubbers is necessary.

Problems with Membranes

Although the membrane separation technology is immature compared with the other processes, the membrane separation process is considered to be one of the least energy-demanding processes if membranes that could withstand the process temperature and conditions are available.

Membranes that could withstand high temperatures in the order of 500–600 ◦C are rarely available. Also membranes such as microporous silica membranes, even if they could be processed with high CO2 separation factors at high temperature, will definitely allow higher permeance of lighter molecules such as hydrogen making selective separation of CO2 practically impossible from (for e.g.) membrane reactor environment where mostly H2 and CO2 are the conversion products.

Current commercially available solvents for CO2 capture systems (EPA, 2006)

Supplier solvent Solvent Loss,

kg/ton of CO2

Solvent cost, $/kg

Solvent Cost, $/ton

CO2

Steam, kg/kg Co2

Non Proprietary

MEA 1 to 3 1.25 1.20 to2.50 2.0

Fluor; US MEA + inhibitors

2.0 1.50 2.30 2.3

KS-1, MHI Hindered Amines

0.35 3.00 1.55 1.5

Problems with Lithium silicate based membranesLi4SiO4, has enhanced ability to absorb CO2 at high temperature. The absorption of CO2 took place because of a reaction to form lithium carbonate and a solid oxide. Theoretically this reaction, if proceeds to the end, should make SiO2 as in the reaction

Li4SiO4 + 2CO2→2Li2CO3 + SiO2. Hence, the material should be capable of absorbing

73.5% (by wt.) of CO2. However, in practice the solid product Li2SiO3, which is formed as the reaction product between 1 mol of Li4SiO4 and CO2 restricts the absorption. Hence the reaction proceeds according to the equation

Li4SiO4 +CO2→Li2CO3 +Li2SiO3. Consequently the total amount of CO2 absorbed is

limited to 36.7% (by wt.)Similarly, Li2ZrO3 membrane, salt hydrates etc. are

having the same problems as like this Li4SiO4 (Lithium arthosilicate) based membranes.

Ionic Liquid (ILs)

ILs have high CO2 solubility. The activity of H-2 in the imidazolium ring responsible for

high CO2 solubility. Higher selectivity for CO2 than CH4, so can be used for CO2

removal from natural gas. Both imidazolium and phosphonium cation based ILs can be

used. Several types of anions can be used. Amine based anions have superior sorption characteristics. Solid porous support enhances CO2 solubility as the bulk

liquid resistance gets decreased. Upto 50 mole% of CO2 can be absorbed by IL. With 1% water, equimolar absorption of CO2 can be obtained.

Ionic Liquid Properties

ILs can be tailored by choice of cation and anionProperties can be varied by choice of anion, cation and substituents

ILs have negligible vapor pressures (“green” potential)

No contamination of IL into gas streamNo loss of IL from evaporation

Good solvation propertiesHas been shown to dissolve polars, non-polars, organic, inorganic, aromatics

Thermally stable Reusable/recyclable

Ionic Liquid with SilicaResults of absorption of CO2 by [P(C4)4][b-Ala]-SiO2, [P(C4)4][Gly]-SiO2 and P(C4)4][Ala]-SiO2

Cycles of CO2 absorption of [P(C4)4][AA]-SiO2. □ =[P(C4)4][Gly]-SiO2, О =[P(C4)4][Ala]-SiO2, and =[P(C4)4][b-Ala]-SiO2.

Results of absorption of CO2 by [P(C4)4][b-Ala]-SiO2, [P(C4)4][Gly]-SiO2 and P(C4)4][Ala]-SiO2

The results suggests that CO2 absorption equilibrium can all be reached in less

than 100 min. The absorbed CO2 was released in a vacuum at room

temperature over several hours. Due to the large surface area of silica gel

(approximately 500 m2g-1), the absorption rate of CO2 was significantly increased.

Results of absorption of CO2 by [P(C4)4][Gly]-SiO2 with water (1% mass fraction)


Absorption of CO2 by using these ionic liquids with a small amount of water (1%, mass fraction) was found

The viscosity was low and the liquid was stirred with greater ease at the beginning of the absorption, but the viscosity gradually increased and finally became very high and the transparent liquid became cloudy.

[P(C4)4][Gly] with water can absorb almost 13 wt% of CO2, which is close to the theoretical absorption capacity (13.52%, based on a 1:1 mol ratio between the ionic liquid and CO2), in 200 mins.


If more water is added, the ionic liquid saturates with CO2 separates into a solid phase and a liquid phase.

The residue liquid finally obtained, after drying in vacuum at 353.15 K for 12 h, is more viscous than pure [P(C4)4][Gly].

Mechanisms of Absorption

In the first mechanism (Scheme 1), CO2 attacks the free electron pair of the N atom on the -NH2 group and forms a hydrogen bond OH···N with the NH2 group of another AA.

A second possibility is that one of the H atoms in the NH2 group is taken as a proton by the original CO2

- to form a new CO2H group (Scheme 2).

(Scheme 1) (Scheme 2).

Finally;

The rates of CO2 absorption of the supported ionic liquids were much higher than those of the viscous ionic liquids themselves.

The CO2 absorption of the ionic liquids supported on porous SiO2 is fast and reversible with a capacity of 1CO2/2 [P(C4)4][AA].

The proposed mechanism suggests that a CO2 molecule attacks the N atom of the NH2 group and results in -NHCO2 formation, during which one H atom leaves and forms a new CO2H with the NHCO2

- or the original CO2 in the amino acid anion.

The CO2H group formed a hydrogen bond with the electron pair of NH2 in another amino acid anion for which the N atom was inert to reaction with CO2.

In the presence of water (1%, mass), the [P(C4)4][AA] can absorb an equimolar amount of CO2 by a different mechanism.

For your Patience

capture of co2

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