Interactions between Char and CO 2 - to Create a Cradle-to-Cradle Carbon Cycle, and, - to Develop Advanced Sorbents for Carbon Capture Wei-Yin Chen Nosa O. Egiebor Daniell L. Mattern University of Mississippi See also: AIChE Journal. 60(3), 1054-1065 (2014). www.see.uwa.edu.au/research/soil-biology 1
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Interactions between Char and CO 2 - to Create a Cradle-to-Cradle Carbon Cycle, and, - to Develop Advanced Sorbents for Carbon Capture Wei-Yin Chen Nosa.
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Interactions between Char and CO2
- to Create a Cradle-to-Cradle Carbon Cycle, and,- to Develop Advanced Sorbents for Carbon Capture
• 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
6
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.
7
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.
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
9
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.
10
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 CO2.11
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 radical 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.
12
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.
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.
Gasification – energy efficiency, CO2 utilization, less operational problems
CO2 Capture by char and functionalized nanographenes adsorbents
24
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.
25
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.
26
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. 27
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.
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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.
29
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
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.
30
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. 31
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.32
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).
33
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.
34
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.
Current Focus on CO2 Capture Sorbent Development in Our Lab
36
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