Interactions of Carbonaceous Materials with CO2 and Water for Repairing Global Carbon Cycle

Wei-Yin Chen

Department of Chemical EngineeringSeptember 11, 2015

See also: AIChE Journal. 60(3), 1054-1065 (2014)

www.see.uwa.edu.au/research/soil-biology 1

Outline Background and objective in broad sense since 2007 Synthesis of concepts and hypotheses Experimental results

• Role of sonication

• Roles of thermal and photochemical treatments

• Role of CO2

Technological benefits Development plan Conclusions

www.abc.net.au/science/articles/2009/03/04/2507238.htm 2

Renewable Energy & Climate Change Group, 2007- Over 200 participants around the world for the activities described below New courses on alternative energy and environment in the US and abroad Handbook of Climate Change Mitigation, 4 vol., 2254 p, 54 chapters, Springer, 2012,

http://www.springer.com/engineering/energy+technology/book/978-1-4419-7992-6 International workshops, short courses, outreach to K12 students & citizens Mitigating carbon emissions by examining CO2 / carbon interactions that have

fundamental significance in several technological areas community gasifiers in MS, Mekong, Yangtze, and Niger Deltas CO2 capture by nano, carbon-based adsorbents carbon activation

Evaline Tsai - Intel scholar

Anna Hailey- Goldwater scholar

Objective in Broad Sense

To explore transformative routes of CO2 fixations on different types of carbons as many

• CO2 capture processes, and

• CO2 utilization processes, including new cradle-to-cradle routes for CO2 reuse,

involve CO2 fixations on carbon as the first step in the process.

4

Two Routes of Special Interests

• Photochemical route

• Need to bring CO2 to high energy levels; i.e., to create a cradle-to-cradle carbon cycle

• Solar energy is renewable

• Demonstrated photochemical CO2 fixation on carbon

• Ultrasonic route

• Demonstrated mineral leaching

• Demonstrated water splitting

• Demonstrated graphite oxide exfoliation5

Initial Results Led to the Current Focuses

• to develop a char-pretreatment process prior to gasification

• to develop advanced sorbents based on functionalized nanographene oxide for CO2 capture

• to develop a carbon-activation process

oregonstate.edu/orb/terms?title=b

6

Synthesis of Concepts• CO2 fixation on the edge of aromatic carbons

• Reductive photocatalytic carboxylation of edge carbons of polycyclic aromatic hydrocarbons

• Ultrasound-induced reactions such as mineral removal, water splitting and exfoliation of graphite oxide

• H2O as a hydrogen donor

• Carbon swelling by polar solvents

• Supercritical (SC) CO2 treatment followed by rapid expansion

• Biochar’s unique physical and chemical structure• Functionalization of epoxy, carboxyl and hydrooxyl groups of

graphene oxide with amines

7

Reactivity of Aromatic Carbons – Kolbe-Schmitt Reaction (1860)

The heats of decarboxylation of a few reported carboxylic acids, 24 to 29 kJ per mol of CO2, are well within the range of current sorbent regeneration processes by using amines.

Our Postulation:Carboxylation of edge carbons of PAHs is an effective CO2 capture route.

8

Reactivity of Aromatic Carbons – Reductive Photocarboxylation

Chateauneuf et al. (2002) used supercritical CO2 in their reductive photo-carboxylation experiments, and discover the near complete conversion and the following mechanism:

2

2 2

*

Pr

hPAH PAH DMA PAH CO

PAH CO i OH H PAH CO

where DMA denotes N,N-dimethylaniline (an electron donor) and iPrOH 2-propanol (a hydrogen donor), respectively.

Our Postulations:Reductive photo-carboxylation of edge carbons of PAHs be considered as a mean to enhance the hydrogen

content, thus the energy content, of the reactant,

capture CO2.9

Dihydrocarboxylic acid, I, is the major product only when a hydrogen donor such as 2-

propanol is present (Chateaunef et al., 2002).

Ultrasound-Induced Exfoliation of Graphene and Graphene Oxide (GO)

Chars derived from coals and biomass and petroleum coke have graphitic and GO clusters in their structures.

Our postulations:• Ultrasound exfoliates the graphitic and GO clusters in chars into single-layered

graphene and GO platelets, and therefore facilitate the reactivity of edge carbons of these platelets.

• It is also known that ultrasound splits water; the impacts of the proton and hydroxyl radicals after water splitting on the char during treatment cannot be predicted.

• Ultrasound treatment removes minerals as leaching minerals from carbonaceous materials is a known technology.

Pioneering work of ultrasonic conversion of graphite oxide to graphene oxide:Stankovich, et al., Graphene-based composite materials. Nature. 2006, 442, 282-286.

10

Coal Swelling by Polar Solvents Attacks of nucleophilic solvents breaks the hydrogen bonds,

catalyzes the tautomerization, weakens cross covalent linkages in the carbon structure, and swells the coal matrix.

Gasification of type I and type III particles (Wall et al., 2002):

Our Postulations:Treatment of carbons with CO2 and H2O can• swell the carbon,• increase the internal surface area, and,• increase the reactivity of carbon.

www.growingnewlife.com/index.php?p=1_12_Benefits-of-Biochar 11

Fluid Properties at Supercritical (SC) State Fluid under SC condition has both gas and

liquid properties Density increases rapidly near the critical point

(c.p.)

Surface tension decreases dramatically near c.p.

Diffusivity increases dramatically near the c.p.

These properties facilitate fluid penetration, gas/solid reaction and extraction such as the ammonia fiber explosion (AFEX) process of biomass (Dale et al.)

Our Postulation:Rapid expansion from high pressure

treatment of carbon with CO2 and H2O disrupts carbon structure and enhances the reactivity.

12http://www.treepower.org/biochar/main.html

Rationale of Our Study of (Biochar+CO2+H2O)

Our postulations:• Photochemical treatment of biochar with CO2 and H2O leads to reductive

carboxylation (i.e., reductive CO2 fixation) such as that mentioned by Chateauneuf, et al. (2002) (see an earlier slide).

• Treatment by supercritical CO2 is expected to enhance the effects. • Ultrasound exfoliates graphite and graphene oxide clusters, and removes

minerals.

• Biochar contains stacks of graphene and GO layers (Hammes and Schmidt, 2009),

• Biochar contains TiO2, which enhances the photocatalytic reactions,

• Water and/or ethanol could serve as hydrogen donors.

13

Biochar Production and Treatment Conditions

Biochar Production

• sorghum

• 75 and 106 µm

• heated in He with 5 ºC/min heating ramp to 550 ºC followed by a 10 min holding time

Ultrasound and photochemical Treatment

• 3 to 6 gm biochar + H2O + saturated CO2

• 65 ºC, 1 atm

• 3 min, 12 min, 5 h

14

Treatment of Biochar with (CO2+H2O) under Magnetic Stirring

• Notable weight loss during both treatments,

• Loss of mineral matters, Si, Na, K

• Gain of hydrogen during photochemical treatment,

• Increases in both C/O and H/O ratios during photochemical treatment,

• Near 20% increase in heating value,

• 19-fold increase in internal surface area.

15

3 gm biochar + H2O + saturated CO2

1 atm, 5 h Moisturea 6.95 7.2 - 5.66 -

Asha 29.46 19.2 -43.0% 22.56 -33.0%

Fixed Carbona 46.42 57.73 8.1% 55.53 4.1%

Volatilesa 17.28 15.87 -20.1% 16.25 -18.1%

Carbona 55.35 64.85 1.9% 62.4 -1.9%

Hydrogena 1.895 1.84 -16.0% 2.71 24.0%

Nitrogena 0.595 0.62 -9.3% 0.81 18.0%

Oxygena (by difference)

12.62 13.41 -0.1% 11.52 -0.3%

Sulfura 0.08 0.08 -13.0% < 0.05 >-45%

Organicsa 70.54 80.8 -0.1% 77.44 -2.2%Overall Weight Change (dried)

- - -13.0% - -12.0%

Atomic C/O ratio

5.85 6.45 10.3% 7.22 23.5%

Atomic H/O ratio

2.40 2.20 -8.6% 3.76 56.7%

BET Surface Area (m2/g)

12.9 252.2 1855.0% 256.6 1889.1%

Heating Value (kcal/g)

4.83 5.63 16.6% 5.76 19.3%

K, % of total

samplea 5.75 0.914 -91.0% 0.779 -92.0%

Na, wt ppma 603 <445 > -58% <411 > -61%

Si, % of total

samplea8.71 4.65 -70.0% 4.34 -57.0%

ANALYSIS\ SAMPLES

Change during

treatment (wt%)

Change during

treatment (wt%)

Raw Biochar (wt)

Thermally Treated

wt%

Photochemically Treated

(wt%)

Treatment of Biochar with (CO2+H2O) under Ultrasound

• Both treatments result in high

• Weight loss,• Losses of minerals

detrimental to power generation,

• Gain in hydrogen,• Increase in carbon

content, 13%,• Increases in C/O and H/O

ratios,• Increase in heating value,

50%!

• The 11-fold increases in internal surface area are lower than those from stirred treatments w/o ultrasound – due to exfoliation of GO?

• Technological applications – to be discussed later.

16

Moisturea 6.95 2.16 - 2.36 -

Asha 29.46 11.4 -70.2% 11.8 -68.0%

Fixed Carbona 46.42 70 16.1% 70.7 21.8%

Volatilesa 17.28 16.5 -26.4% 15.1 -30.1%

Carbona 55.35 81.2 13.0% 80.1 15.8%

Hydrogena 1.895 2.68 8.9% 2.66 12.3%

Nitrogena 0.595 0.68 -12.0% 0.62 -17.0%

Oxygena (by difference)

12.62 3.98 -1.2% 4.76 -1.1%

Sulfura 0.08 0.06 -42.2% 0.06 -40.0%

Organicsa 70.54 88.6 -1.6% 88.2 0.0%

Overall Weight Change , %

- - -23.0% - -20.0%

Atomic C/O ratio

5.85 27.20 365.2% 22.44 283.7%

Atomic H/O ratio

2.40 10.77 348.4% 8.94 272.2%

BET Surface Area (m2/g)

12.91 151.41 1072.8% 171.74 1230.3%

Heating Value (kcal/g)

4.83 7.26 50.3% 7.18 48.7%

K, % of total

samplea 5.75 0.51 -97.4% 0.55 -97.0%

Na, w ppma 603 456 -77.5% <809 >58.5%

Si, % of total

samplea8.71 3.92 -86.6% 4.27 -76.2%

ANALYSIS\SAMPLES

Change during

treatment (wt%)

Change during

treatment (wt%)

Raw Biochar (wt%)

Thermally Treated (wt%)

Photochemically Treated wt%

Treatment of Biochar with H2O Only (no CO2) under Ultrasound

• Observed benefits in heating value, 40%, is between the thermal and ultrasound treatments with CO2,

• Remarkable photo-hydrogenation, 27.7%, of char by water is achieved,

• Photo-irradiation enhances hydrogenation, and ultrasound enhances carbon fixation.

• Limited increase in surface areas,

• Roles of CO2 are definite.

17

Moisturea 6.95 3.77 - 3.63 -

Asha 29.46 12.4 -65.5% 13.1 -63.5%

Fixed Carbona 46.42 61.4 8.6% 53.6 -5.3%

Volatilesa 17.28 22.4 6.3% 29.7 41.0%

Carbona 55.35

75 11.1% 71.4 5.8%

Hydrogena 1.895 2.54 9.9% 2.95 27.7%

Nitrogena 0.595 0.67 -7.7% 0.76 4.7%

Oxygena (by difference)

12.62 9.39 -0.6% 11.8 -0.4%

Sulfura 0.08 0.05 -48.8% 0.05 -48.8%

Organicsa 70.54 87.6 0.9% 86.9 0.5%

Overall Weight Change

- - -18.0% - -18.0%

Atomic C/O ratio

5.85 10.65 82.1% 8.07 38.0%

Atomic H/O ratio

2.40 4.33 80.1% 4.00 66.5%

BET Surface Area (m2/g)

12.9 45.12 249.8% 76.94 496.4%

Heating Value (kcal/g)

4.83 6.76 40.0% 6.5 34.6%

K, % of total

samplea 5.75 1.01 -93.9% 1.02 -93.9%

Na, w ppma 603 <851 >-54.3% <684 >58.6% Si, % of total

samplea8.71 3.7 >-85.3% 3.45 >-78.1%

ANALYSIS\SAMPLES

Change during

treatment (wt%)

Change during

treatment (wt%)

Raw Biochar (wt%)

Thermally Treated (wt%)

Photochemically Treated wt%

FTIR Spectra of Raw and Treated Biochar with CO2 (under Magnetic Stirring)

Carboxylation (CO2 fixation) is evident.

Reactions between Treated and Raw Biochars – mostly Implied by FTIR Spectra

• Kolbe-Schmitt Reaction (Carboxylation)

• Reductive photocarboxylation, Chateauneuf, et al. (2002)

• Breakage of Ester (Hydrolysis)

• Breakage of Ether

• Radical Ion Formation

• Dissolution of Salts

2RO CO ROCOO

19

2RCOOM H O RCOOH M OH

Effects of Ultrasound Power on Biochar’s Heating Value

• Short ultrasound treatment time, e.g., 3 min, results in a 19% increase in heating value.

• Energy consumed by the sonicator in 3 min is 0.84 kcal/g, which is a major fraction of the increase in heating value of the biochar, 0.91 kcal/g.

• But a major portion of the ultrasonic energy is dissipated into the environment, not by the solution in the flask.

• Ultrasonic energy can be most efficiently used by directly inserting a high powered ultrasonic horn in the solution in the treatment reactor.

20

Positive Technological Implications

Gasification – energy efficiency, CO2 utilization, less operational problems

CO2 Capture by char and functionalized nanographenes adsorbents

21

The Pretreatment Creates a “Cradle-to-Cradle” Carbon Cycle!

In a co-generation process where 20% of energy input comes from char, treatment results in• 13% gain in carbon and therefore 2.6% carbon recycle - the addition of a pretreatment

unit renders it possible to recycle about 2.6% of burned carbon fixed in the char.• Assuming char’s heating value increases by 50% and 20% of such increase is

used in the pretreatment process, the energy output from combustion of char will be 1.40 times of the original char. For a co-generation power plant that uses only 20% char as fuel source (with the rest of the energy source comes from coal or biomass), the overall energy output from char will increase to 28% (20%×1.40), resulting in a net gain of 8% in the total output. This is not considered an incremental improvement for power plants. 22

co-gasification withthe following benefits

1. higher energy output,2. higher gasification rate,3. less operational issues

Untreated biochar, 0.2 units

Coal, or biomass0.8 units of carbon

CO2,1 unit

Recycled carbonas CO2, 0.026 units

Ultrasonic or photopretreatment at

50oC - 100oC1- 100 atm

water water released to soil as nutrient

Biochar, Functionalized Nanographene or Graphene Oxide (GO) for CO2 Capture

• Biochar’s carbon content increases by 13% during ultrasound treatment suggesting the possible new route for CO2 capture.

• Graphene oxides (GO), clamped on fumed SiO2, will be an effective building block for CO2-capture adsorbents that can sustain the harsh operating conditions.

• Examples are given in the next few slides.

Functionalized GO

(1) oxidation of graphite to graphite oxide, (Park and Ruoff, 2012),(2) exfoliation of graphite oxide by ultrasound, (Park and Ruoff, 2012),(3) functionalization by amine, see next few slides.

23

Functionalized Nanographene or Graphene Oxide (GO) for CO2 Adsorption

Two routes that are considered for grafting tetraethylenepentamine (TEPA) on the two major oxygen functional groups on GO: carboxylic acids and epoxides. The functionalized GO can then be used as CO2-capture adsorbents. Published work also demonstrated that GO sheets can be clamped to silicon oxide substrate by strong van der Waals force (due to its thin nature); thus, amine functionalized GO-SiO2 beads could serve as a strong CO2-capture adsorbent that sustains harsh environments. GO has a C:O ratio between 2.1 and 2.9, implying the abundance of oxygen functional groups. It should be mentioned that other polyethyleneimines (PEI), and hyper-branched amines can serve the same purpose and produce high CO2 capture capacity.

24

O

HOC

O

OH

N-hydroxysuccinimideEDC

O C O4OH

C

O

NH

2

OH

heat

+ H2N

HN

NH

HN

NH2

NHNH

NHNH2

HN NH

NHNH

NH2

OH

C

O

NH

OH

NH2NH2

HN NH2 NH2

NH

OO

NH

OO

N

OO

N

OO

Other Reactions for CO2 Adsorption by Polycyclic Aromatic Hydrocarbons (PAH)

The versatile roles of NGO and PAH in the development of CO2–capture adsorbents. Chemical, photochemical and photocatalytic reactions of GO and PAH lead to either CO2 capture or a family of functionalized chemicals that can serve as CO2–capture adsorbents.

TiO2-graphene hybrid under UV excitation (Park and Ruoff, 2012).

25

Char as a Possible Source of Graphene Oxide (GO)

Production of single-sheet GO from chars of biomass, coal and petroleum coke. Ultrasound exfoliates graphite clusters (flat sheets in the figure) and graphene oxide clusters (wavy sheets) in chars into single-sheet platelets. Chars derived from relatively low temperatures with a small amount of O2 should produce more GO sheets than graphite sheets, but the optimal processing conditions for different feedstocks are not well studied. The resultant GO platelets will be useful building blocks for functionalization followed by CO2 adsorption.

26

Current Focus on CO2 Capture Sorbent Development in Our Lab

27

graphite has an interlayer spacing of 0.335 nm

exfoliation

graphite oxide has an interlayer spacing about 0.7 nm. It contains contains three major oxygen functional groups: epoxides, phenolics and carboxylic acids

oxidationby modifiedHummers'method

single-layer graphene oxide (GO) platelets. Nano-sized GO contains a rich population of oxygen functional groups that have emerged as the building blocks for many technologies

ultrasonicationH2SO4NaNO3KMnO4

tetraethoxysilane (TEOS)

Production of Adsorbent Base

Production of Graphene Oxide (GO)

sol-gel method

H2O and NaOH

highly porous silica (705 m2/gm) dioxide, SiO2 with basic surface

H2N

HN

NH

HN

NH2

tetraethylenepentamine (TEPA)

functionalization with activation agentsN-hydroxysuccinimide and EDC (1-ethyl-3-(3-dimethylaminopropyl)carbodiimide))

hydroxyl groups on GO are coverted to carboxyl groups

functionalized GO on SiO2

O

C

C

O

OH

OHO

1. orthoester formation2. Claisen thermolysis3. ester hydrolysis

Functionalization

CO2 Capture and Desorption

O C O6

OH

C

O

NH

Cheat

NHNH

NHNH2

HN NH

NHNH

NH2

OH

C

O

NH

C

NH2NH2

HN

NH2 NH2

NH

OO

NH

OO

N

OO

N

OO

NH3

ONH

NH

NH

NH

NH2

O

NH

NH2

NH2

O

O

N

OO

COOH

O

OHOOC

COOH

COOHHOOC

graphene oxide (GO) of nano size clampedon the internal and external surfaces of porous SiO2

Functionalization

Possible Incorporation of the New Concepts in Integrated Gasification Combined Cycle (IGCC)

www.cef-environmental.co.uk/BioChar.htm28

gas and liquid fuels

oxide

graphene

liquid

CO2

CO2

treated char + CO2

H2O for soil amendment

H2O

hot

steam

H2O

air

compressed air

air

oxygen

compressed

H2 CO2

H2

CO2

used adsorbent

char

adsorbed

(batch)

coalbiomasspet. coke

char

gasifier

gas clean up devices

water-shift

CO2

adsorption/ desorption

pyrolysis,partial

oxidation

functionalization

soil amendmentand carbon sequestration in soil

combustor

gas turbine

air separation

unit

air

power generator

heat recovery steam generator

steam turbine power generator

pretreatment

char

compressor

amine

biomass, coal

syngas

syngas cooling& Hg removal

char conversion to

graphene oxide process

ultrasound

sonication or solar Irradiation

hot water

Development Pathways in 3 Years

Pretreatment for Gasification

• effects of P, T, composition, and pH on phase diagram of CO2 / H2O system

• high pressure reactor for sonicated and photo-irradiated treatments

• process parameters: T, P, t, particle size, ultrasound and photo-irradiation power, feedstock (char derived from coal, biomass and petroleum coke),

• pilot-scale tests

• techno-economic analysis

Adsorbent for CO2 Capture

• CO2 Capture by Amine-Functionalized Nanographene Oxides (NGO)

• Photochemical and Ultrasonic Capture of CO2

• CO2 Capture by Phenolic Compounds through Kolbe-Schmidt or Chateauneuf Reactions

• CO2 Capture by Nanographenes derived from Biomass

• Molecular Simulation of Advanced Sorbents for CO2 Capture

• Technological Integration 29

Conclusions• The photocatalytic and

sonochemical reactions of CO2 on the surfaces of carbon are potentially fruitful areas for advanced technologies.

• The two proposed concepts (gasification & CO2 capture) appear promising, but the effects of parameters have to be investigated in the near future.

www.anzbiochar.org/ http://well95490.org/projects/local-food/biochar_grow_soil/ 30

AcknowledgmentsStudents

Mr. Eneruvie OkinedoMr. James Corbett Senter

Mr. Alec MatteiMr. Connor W. Redwine

Ms. Maha YusufMr. W. Richard Meredith

Mr. Will AbbeyMr. Ryan SmithMr. Josh Warren

UM Office of ResearchDr. Alice ClarkMr. Jason Hale

Dr. Walter ChamblissMr. Ken SleeperMs. Allyson Best

CollaboratorsSouthern ResearchSouthern Company

Univ of AkronWorley Parsons Group

Zhejiang UnivNREL

Energy CommercializationWestern Kentucky Univ

National Pingtung Univ of Sci. & Tech.

31

Previous FundingDoENSF

US Small Business Admin.

Comments and questions?

Wei-Yin ChenProfessorChemical EngineeringUniversity of Mississippi(662) 915-5651cmchengs@olemiss.edu www.engineering.olemiss.edu/~cmchengs/

www.charcoalremedies.com/charcoaltimes/0512/biochar_revolution

32

Treatment of Biochar with (CO2+H2O) under 3 min Ultrasound

• The increase in heating value is caused by both loss of minerals and carbon attachment.

33

Moisturea 6.95 4.07 -

Asha 29.46 24.40 -25.8%

Carbona 55.35 65.44 5.9%

Hydrogena 1.91 1.84 -13.7%

Nitrogena 0.59 0.61 -7.4%

Oxygena (by difference)

12.62 7.62 -45.9%

Sulfura 0.08 0.09 0.8%

Organicsa 70.54 75.6 -4.0%Overall Weight Change (dried)

- - -10.4%

Atomic C/O ratio

5.85 11.45 95.8%

Atomic H/O ratio

2.42 3.86 59.5%

BET Surface Area (m2/g)

12.9 118.9 821.7%

Heating Value (kcal/g)

4.83 5.74 18.8%

K, % of total

samplea 5.75 1.26 -83.74%

Na, wt ppma 603 734 -9.67%Si, % of total

samplea8.71 8.90 -24.17%

ANALYSIS\ SAMPLES

Raw Biochar (wt)

Ultrasound Treated 3-min

(wt%)

Difference (wt%)

A Recent Emphasis on Gasification Advancement

NETL and EPRI have been developing an efficient gasification technology for low rank coals that uses liquid CO2 as the fuel-carrier for gasification because the liquid CO2, in comparison with water, has

• lower heat of vaporization, • viscosity • surface tension.

The IGCC (integrated gasification combined cycle) plant thermal efficiency improvement on gasifier with liquid-CO2 slurry is about 2.8%.

• Pretreatment of char with CO2 and H2O under ultrasound and/or photo-irradiation provide an even higher synergism for such gasification process since the liquid CO2 and H2O are available in plant.

34

A Recent Emphasis on Gasification Advancement

NETL and EPRI have been developing an efficient gasification technology for low rank coals that uses liquid CO2 as the fuel-carrier for gasification because the liquid CO2, in comparison with water, has

• lower heat of vaporization, • viscosity • surface tension.

The IGCC (integrated gasification combined cycle) plant thermal efficiency improvement on gasifier with liquid-CO2 slurry is about 2.8%.

• Pretreatment of char with CO2 and H2O under ultrasound and/or photo-irradiation provide an even higher synergism for such gasification process since the liquid CO2 and H2O are available in plant.

35

Benefits of (Biochar+CO2+H2O) Pretreatment under Sonication to Power Generation

Liquid CO2 at high P is available in power plants, which can be brought to supercritical state easily since the critical temperature of CO2 is only 31.2 ºC.

Residual heat is also available in power plants.

The observed pretreatment benefits are expected to be higher at gasification pressure, e.g., 20 atm; our experiments were conducted at 1 atm.

The pretreatment concept is expected to

• enhance the thermal efficiency (heating value) and power generation rate (more porous nature),

• exhibit less operational issues such as fouling and slagging (removal of detrimental minerals),

• offer a new CO2 utilization route (CO2 used in treatment and gasification),

• offer a waste (biochar) utilization route.

36

Key Results of Current Study

• Pretreatment of biochar with CO2 and H2O under ultrasound and photochemical treatment prior to gasification• Removal of minerals that cause slagging and fouling in power generation

• Increase in heating value (50%) of biochar

• Increase in hydrogen (9%) content of biochar

• Increase in carbon (13%) content of biochar – CO2 utilization through fixation, and CO2 capture (how was such high level of capture achieved?)

• Exfoliation of graphite oxides in forming single-layer graphene oxide (GO)

• CO2 capture by biochar and functionalized nanographene oxides (NGO) adsorbents• Oxidized polycyclic aromatic hydrocarbons (PAH) and NGO are susceptible to

amine functionalization and then CO2 capture

• Ultrasound can be adopted in producing graphene oxide (GO) from biochar

37

Graphite Oxide vs Graphene Oxide (GO) for CO2 Adsorption

Zhao et al. (Applied Surface Science, 2012, 258, 4301) showed 53.6 CO2 loading per gram of graphite oxide impregnated with EDA under PCO2 = 0.15 atm and 30 ºC. However, in their work,1. The more reactive single sheets GO was

not used,2. no activation agent was used to enhance

the functionalization,3. hydroxyl groups on GO were not

functionalized for CO2 capture.

38

Indeed, our recent data reveal that single-sheet GO without amine functionalization has a CO2 capture capacity, 49.43 g CO2/g GO, comparable to that of impregnated graphite oxide, and functionalized GO with activation agent should show better results.

CO2 Adsorption by Graphene Oxide Framework (GOF)

Burress et al. (2010) showed a) boronic ester and b) GOF formation. Idealized graphene oxide framework (GOF) materials proposed in this study are formed of layers of graphene oxide connected by benzene diboronic acid pillars. The resultant GOF can be oxidized and then grafted with an amine (just like functionalization of GO mentioned in the last slide but with an amine of smaller size, such as ethylenediamine, or EDA) that serves as a potentially potent CO2-chemisorption adsorbent. 39

CO2 Adsorption by Graphene Oxide Framework (GOF) Burress et al. 2010

This GOF (not amine functionalized) showed a ~3 wt% CO2 capture capacity at 310 K when the CO2 pressure is about 0.15 bar (Burress et al. 2010). The capture capacity increases to 12 wt% when the partial pressure increases to 4 bar.

Functionalized GOF is expected to have even higher CO2 capture capacity.40

Characteristics of Carbon-Based Adsorbents

• Nanocarbons have large surface area for CO2 capture and functionalization. Procedures for manipulating and functionalizing nanocarbons (such as CNT, GO and GOF) have been well-established. But CO2 capture on theses carbon materials has not been systematically investigated.

• Adsorbents have lower heat capacity than those of liquid solvents – desorption process requires lower sensible heat than liquid solvents.

• Heat of decarboxylation, 24 to 29 kJ per mol of CO2, is comparable to those amine-based sorbent regeneration processes.

• Amine-functionalization is a highly desirable step in increasing the CO2/H2 selectivity for pre-combustion CO2 capture.

• Nano-grahene oxide platelets can be clamped on SiO2 with strong adhesion force, fumed SiO2 is a strong adsorbent base for harsh capture conditions.

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Characteristics of Carbon-Based Adsorbents

• Nanocarbons have large surface area for CO2 capture and functionalization. Procedures for manipulating and functionalizing nanocarbons (such as graphene, CNT, GO and GOF) have been well-established. But CO2 capture on these carbon materials has not been systematically investigated.

• Adsorbents have lower heat capacity than those of liquid solvents – regeneration of adsorbents requires lower sensible heat than liquid solvents.

• Heat of decarboxylation, 24 to 29 kJ per mol of CO2, is comparable to those of amine-based sorbent regeneration processes.

• Amine-functionalization is a highly desirable step in increasing the CO2/H2 selectivity for pre-combustion CO2 capture.

• Nano-grahene oxide platelets can be clamped on SiO2 with strong adhesion force; SiO2 is a strong adsorbent base ideal for harsh capture conditions.

Graphene Oxide (GO)

Graphene/carbon nanotube (CNT) hybrid (CEP, January, 2013)

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