Silica-Supported Immobilized Amine for CO2 Capture Processes: Molecular Insight by In Situ Infrared Spectroscopy

C H A P T E R

7 Silica-Supported Immobilized Amine for CO2 Capture Processes: Molecular Insight by In Situ Infrared Spectroscopy Yuxin Zhai*, Hailiang Jin* and Steven S.C. Chuang Department of Polymer Science, The University of Akron, Akron, OH, United States

7.1 INTRODUCTION The relations between synthesis approaches and the resultant structures as well as connections between material structures and their functions have been a common theme in materials chemistry. Many studies on these relations/connections are aimed at tailoring SiO2 structures and at functionalizing SiO2 surfaces for a wide range of applications in many areas: sorbents, catalysts, fillers, and binders, etc. For CO2 capture applications, SiO2 possesses a few attractive features: (1) syntheses from low-cost precursors, shown in Fig. 7.1A, (2) large pores to facilitate adsorption/desorption, (3) high surface area for supporting or grafting amine, (4) easy palletization, and (5) excellent stability.1 5 These attributes have promoted extensive research on the use of SiO2 as a support to immobilize

amines for thermal swing CO2 capture processes (Figs. 7.2 and 7.4). This chapter will begin with an overview on global CO2 emission, introduce the process for treating flue gas from a coal-fired power plant, that is, a major CO2 source; discuss the use of solid sorbents, especially SiO2-supported amines for CO2 capture; and lastly examine the nature of sites on SiO2-supported amine for CO2 capture by infrared (IR) spectroscopy, illustrated in Fig. 7.1B. IR spectroscopy provides the direct information on the structure of SiO2, immobilized amine on SiO2, and its adsorbed CO2. In situ IR, which allows investigation of bond formation/breaking steps on SiO2-immobilized amine during the CO2 capture process, serves as an excellent method for determining the specific structures of CO2 adsorption sites and its relation to CO2 binding

*Y.Z. and H.J. contributed equally to this work.

Chemistry of Silica and Zeolite-Based Materials DOI: https://doi.org/10.1016/B978-0-12-817813-3.00007-9

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FIGURE 7.1 Synthesis of amine-functionalized SiO2 sorbents and corresponding infrared (IR) spectra: (A) porous SiO2, SiO2-based amine sorbent [tetraethylenepentamine (TEPA)/SiO2], and adsorbed CO2 on amines; (B) IR absorbance spectra of SiO2, TEPA/SiO2, and adsorbed CO2 on TEPA/SiO2 at 25 C. Absorbance spectra were obtained by log(I0/I), where I0 is the single beam spectrum of the atmosphere. The measurement of SiO2, TEPA/SiO2, and adsorbed CO2 on TEPA/SiO2 were described elsewhere.1

energy as well as diffusion of CO2 in SiO2-supported amine at a molecular level. Molecular insights of the CO2 capture process by SiO2immobilized amines provide a scientific basis for design and fabrication of sorbent pellet at millimeter and adsorber at meter scale, as illustrated in Fig. 7.2.

7.1.1 Global Carbon Dioxide Emission Carbon dioxide (CO2), a major greenhouse gas, has increased its atmospheric concentration over 20% since 1980. Many catastrophic weather events have been attributed to greenhouse effects. Emission of greenhouse gas,

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FIGURE 7.2 The hierarchical structure of CO2 capture processes from the molecular level to pilot scale. Inset: fluidized bed, fixed bed, rotating bed, and monolith.

especially CO2, from developing countries, in Fig. 7.3A is expected to continue to rise at a rate of approximately 3 ppm/year because of the demand for low-cost electricity from coal.7 The cost of electricity from coal-fired power plants has been significantly lower than renewable sources because its impacts on human health and environments were not taken into account.8,9 CO2 emission from coal and natural gas power plants could remain at a level of 40% of global CO2 emission for many decades in Fig. 7.3B.10

In addition to CO2 emission from stationary power plants, CO2 emission from transportation constitutes one-quarter of the total emission in Fig. 7.3B, from which CO2 capture is technically feasible. Electrification of vehicles will allow shifting CO2 emission from transportation to stationary fossil fuel power plants. Thus one intermediate approach for mitigating CO2 emission prior to the successful development of low-cost renewable energy is the capture of CO2 from the electric power sector, especially from the coal-fired power plant.

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FIGURE 7.3 (A) CO2 emission by country, 1990 2016.; (B) CO2 emissions by sectors, 2016. *Per capita CO2 emission was calculated by dividing the total CO2 emission of a country by its population. Source: (A) Data from Emissions Database for Global Atmospheric Research (EDGAR); (B) data from International Energy Agency (IEA).

7.1.2 Postcombustion CO2 Capture Technology CO2 capture from coal-fired power plants can be achieved technically by three pathways: precombustion capture, in which carbon is removed from the fuel before combustion; oxy-combustion, in which the fuel is burned in an oxygen stream without nitrogen; and postcombustion capture, in which CO2 is separated from flue gas.11 Postcombustion capture can be directly attached to the existing power plants, shown in Fig. 7.4, which illustrates the incorporation of a postcombustion CO2 capture

process into the flue gas stream of coal-/natural gas-fired power plants.12 The flue gas generated by the boiler in the coal-fired power plant proceeds through the following gastreatment processes before entering the CO2 adsorber: (1) selective catalytic reduction system which removes the NOx content (DeNOx); (2) electrostatic precipitator for dust elimination; and (3) flue gas desulfurization (FGD) to remove SO2. The composition of flue gas in the stream, listed in Table 7.1, shows that typical conversion efficiency of DeNOx and FGD is around 90% 95%, reducing NOx from 0.3% to 70 ppm and SO2 from 2000 to 45 ppm.12 Dilute concentrations of SO2 and NOx, could still impact the efficiency of CO2 capture processes because these species bind with amine sorbents stronger than CO2. It is instructive to point out each of these flue gas treatment processes add a significant cost to the cost of electricity generation from coal. Many coal-fired power plants around the globe emit flue gas directly to the atmosphere without flue gas treatments. The purity of CO2 produced from capture processes must exceed 99% for sequestration and other applications.13 CO2 was required to be compressed into a supercritical phase for transportation by pipeline or ship and stored into depleting oil fields in order to perform CO2 sequestration as well as oil recovery. Low purity CO2 requires a significantly higher pressure (i.e., energy) than high purity CO2 for compressing into a supercritical phase.14,15 A core principle employed for postcombustion CO2 capture is thermal swing adsorption (TSA) for separation of CO2 from flue gas. A typical TSA process involves either a solvent or a solid sorbent for CO2 adsorption at low temperature and CO2 desorption at high temperature. Considering MEA (monoethanolamine) as an example, as shown in Scheme 7.1,16 18 CO2 reacts with the primary amine to form a zwitterion intermediate, which is deprotonated to a neighboring amine

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FIGURE 7.4 Potential incorporation of a postcombustion CO2 capture process into an existing coal-fired power plant.

TABLE 7.1 Normal Flue-Gas Composition From Pulverized Coal Boiler After Pollution Controls.12 Coal (Illinois No. 6)

Flue Gas Components After Combustion (vol%)

After NOx Control (vol%)

After PMa and Hg Control (vol%)

After SOx Control (vol%)

Component

Content (wt%)

Components

(1)

(2)

(3)

(4)

Moisture

11

CO2

15.8

15.9

15.9

15.9

Carbon

64

N2 1 Ar

80.8

81.1

81.1

81.3

Hydrogen

4.5

O2

2.8

2.8

2.8

2.8

Nitrogen

1.2

NOx

0.3

74 ppmv

74 ppmv

B80 ppmv

Chlorine

0.3

SOx

0.21

0.21

0.21

B45 ppmv

Sulfur

2.5

Moisture

8.7

8.7

8.7

17.0

Oxygen

6.9

Ash

9.7

PM

7100 ppmw

7100 ppmw

B9 ppmw

B9 ppmw

Mercury

0.15 ppm (dry)

Hg

12 ppbw

12 ppbw

B1.2 ppbw

B1.2 ppbw

a

PM is the abbreviation of particulate matter.

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SCHEME 7.1 Reaction pathway of CO2 adsorption/desorption on primary amine from MEA and secondary amine from SiO2-immobilized tetraethylenepentamine (TEPA).

to form a carbamate, followed by the hydrolysis of carbamate to bicarbonate in an aqueous environment. The forward step is exothermic; the reversed step is endothermic. MEA is typically employed in a 30 wt% MEA aqueous solution to facilitate heat transfer and to maintain a low viscosity for pumping CO2-rich MEA from the CO2 adsorber to the stripper where CO2 desorbed into a high purity stream, regenerating MEA for further CO2 capture.19 Both aqueous amine (i.e., MEA) and SiO2immobilized amine [tetraethylenepentamine (TEPA)/SiO2] possess metal-organic framework (MOF) amine functional groups which proceed through the same pathway in CO2 adsorption/ desorption. Because of solvation with H2O and high mobility in the aqueous phase, aqueous MEA has a higher CO2 binding energy than TEPA/SiO2. On the contrary, geometric constraints of amine functional group on TEPA/ SiO2 could result in a low CO2 binding energy.1,2,20 Alternatively, given the same CO2 capture and the same amine structure, it requires higher thermal energy for regeneration of aqueous amine sorbent than that of solid immobilized sorbents. This is one reason why SiO2-immobilized amines hold a great promise for large-scale CO2 capture process.

The adsorption step is carried out in an adsorber at 50 C 60 C, removing CO2 from flue gas, as illustrated in Fig. 7.4. Adsorption is an exothermic process that leads to temperature rise in the adsorber. Thus it is desirable to keep the flue gas and adsorber at low temperatures for CO2 adsorption. Desorption in a desorber (i.e., stripper) above 100 C regenerates the solvent, producing high purity CO2.21 The MEA TSA process has been practiced for many decades in natural gas and chemical industry. Technical report from DOE has shown that incorporation of the MEA process into a coal-fired power plant, which captured 90% of generated CO2, will increase the cost of electricity by 6.92 cent/kWh.19 This drastic increase in the cost of electricity is unbearable in the current global economy. TSA is a preferable choice because of its ability to process a large gas flow in a short period of time. Solid sorbents hold a great promise for reducing both capital and operating cost of a TSA CO2 capture process.22,23 The use of solid sorbent eliminates corrosion to equipment, provides a gas-solid environment for rapid adsorption kinetics, and allows finetuning energy for thermal regeneration.1 3,20 Comparison of a number of solid sorbents in

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OH/H2OS

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FIGURE 7.5 Sorbent characteristics: CO2 capture capacity, adsorption/desorption temperature, adsorption kinetics, and the effect of water vapor.24,25

CO2 captures capacity, adsorption kinetics, the range of operating temperature, and the impact of water vapor in Fig. 7.5 which reveals that immobilized amine sorbent holds a great promise for further development. Zeolite and carbon lack selectivity for CO2 adsorption. Their CO2 capture capacities are severely impaired by water vapor in the flue gas stream. Calcium oxide and hydrotalcite operate at a high temperature, that is, 300 C 650 C and 200 C 520 C, respectively. Hightemperature operation requires the use of expensive equipment and sophisticated thermal management. Amine-based sorbents (i.e., impregnated and grafted amine sorbents) possess a reasonably high CO2 capture, fast adsorption kinetic, and minimization of equipment corrosion.1 3,20,24,25 In addition, amine-

based sorbents can be regenerated at a low cost because adsorbed CO2 on these sorbents desorbs at 80 C 130 C, which are in the temperature range of low-quality steam and waste heat, a by-product of coal-fired power plants.1,2,20

7.2 SIO2 AND ITS SURFACE OH/H2OS 7.2.1 Properties of SiO2 Solid amine sorbent is an amine-containing porous solid material in which amine functional group is dispersed either physically or chemically grafted on the surface of pores of the materials such as SiO2 (illustrated in Fig. 7.1A),

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porous carbons, MOF, and polymeric materials. Because of its low manufacturing cost, controllable pore structure, and high thermal stability, SiO2 has been a preferable choice for serving as a support for immobilized amines. SiO2, a polymorphous material, can be formed or prepared from a wide range of precursors. Synthetic amorphous SiO2 can be produced from precipitation, hydrolysis of sol-gel precursors, and high-temperature combustion synthesis.26 The Sto¨ber process is a widely used method to prepare SiO2 spheres due to its ability to control particle size, particle size distribution, and morphology by changing the reaction parameters. The process involves hydrolysis of a SiO2 precursor in the mixture of an alcoholic solvent with either acidic or basic catalyst.27,28 Silica alkoxides, such as tetraethylorthosilicate or sodium silicate (Na2SiO3) can act as SiO2 precursors.27,29 The synthesis process can be further modified with surfactant templates and pH value to produce a porous structure, illustrated in Fig. 7.1A.30 The larger pore size of SBA-15 (diameter at around 6 nm, comparing to the 0.5 1.2 nm of MCM-41) allows accommodation of high loading of functional molecules and facilitates the diffusion of adsorbing molecules.31 Porous structures of SiO2 expand its uses in many applications: adsorption, catalyst support, wastewater treatment, indoor air cleaning, and drug delivery carriers.32 MOF has been explored as a sorbent for CO2 capture because of its unique network structure with high porosity and surface area.33 The amount of physisorbed CO2 can reach 40 mmol/g under 50 bar.34 However, physisorption process lacks selectivity for applications in CO2 capture and separation. The addition of amine functional group into the MOF network (i.e., amine-functionalized MOF) allowed CO2 to be chemisorbed on the amine site on which mechanism of adsorption resembles that of SiO2-supported amine. Amine-functionalized MOF gives the same level of CO2 capture capacity as SiO2-

Amine-functionalized supported amine.35 MOF did not provide any advantage other than SiO2-supported amine for CO2 capture. The surface of all oxide materials, including SiO2, contains both a cation and an oxygen anion with an unsaturated coordination. These unsaturated coordinated ions are reactive toward H2O, dissociating H2O and then producing OH group on the surface, illustrated in Fig. 7.6.36 Adsorbed H2O, which interacts with surface OH through hydrogen bonding, can be removed by heating treatment, a dehydration process. The amount of H2O uptake by porous SiO2 is determined by the following: (1) surface defects, structures, and contaminants which affect their acidity/basicity; and (2) the size and distribution of pores which govern capillary condensation of H2O vapor.37 Adsorbed water will undoubtfully influence how a molecule such as polyethyleneimine (PEI) and TEPA (the widely used amine molecules for CO2 capture research) physically interacts with the pore surface and how an amine-containing molecule can be chemically grafted on the pore surface.20,38 The performance of many sorbents, including immobilized amine sorbents, is greatly influenced by the amount of water present in the preparation process. The structure of adsorbed water can be examined by their IR spectra in Fig. 7.6 which provides IR spectra of adsorbed H2O on an amorphous SiO2 (Rhodia, surface area 5 160 m2/g, prepared by precipitation) during a dehydration process. It is instructive to compare IR of adsorbed H2O and liquid H2O to shed light on the nature of hydrogen bond on the Si-OH and in adsorbed water. Liquid H2O gives a broad and intense band in 3000 3600 cm21 which is a result of hydrogen bonding, illustrated in Fig. 7.6. The broadness of this O H stretching band partially covers the O H’s asymmetric vibration at 3756 cm21 and completely covers its symmetric vibration at 3657 cm21. The formation of hydrogen bonding led a downward shift of these two

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OH/H2OS

FIGURE 7.6 IR spectra of amorphous SiO2 (Rhodia, precipitated SiO2, surface area 160 m2/g) during heat treatment by TPD from 30 C 400 C. The structures of Si-OH H2O and H2O H2O hydrogen bonding are illustrated with the corresponding IR spectra. Inset: IR difference spectrum of desorbed H2O, taken from I150 C I30 C and I400 C I190 C in IR absorbance spectra.

stretching bands and an increase in their intensity with respect to that of bending vibration at 1595 cm21.1,39 Adsorbed water further expands the broadness of O H stretching vibrations and their intensity. The 5262 cm21 peak in the near IR region is a combination of the asymmetric stretch and bending of the water molecule. The broadness of this peak also reflects the influence of hydrogen bonding on the O H asymmetric stretch. It is interesting to note that that adsorbed water, shown in the negative bands in I150 C I30 C in Fig. 7.6, exhibited a significantly weaker intensity in bending vibration than liquid water, which suggested this water on the SiO2 surface is strongly adsorbed on the surface OH groups of SiO2 through hydrogen bonding. Much of these water molecules remained

on the SiO2 surface at 190 C as evidenced by the similar in IR spectra at 150 C and 190 C. Desorption of the majority of adsorbed water desorbed at 400 C, allowed the free OH to emerge. Further heating above 400 C would result in an irreversible removal of neighboring OH and the formation of the surface Si O Si bond (i.e., a hydrophobic surface) which exhibits low water uptake capability.36,40 The shape of a sharp free OH at 3737 cm21 indicates that this OH is not hydrogen-bonded with other neighboring polar species including those other OH groups. The negative difference spectrum (I400 C I190 C) for those adsorbed water desorbed in 190 C 400 C gave a band at 3525 cm21, a lower wavenumber than those of water desorbed in 30 C 150 C, showing that

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the stronger the hydrogen bonding associated with adsorbed water; the lower the wavenumber for its OH stretching. The wavenumber (i.e., frequency) of O H stretching could serve as an index of the strength of hydrogen bond.

7.2.2 SiO2-Supported Immobilized Amine Sorbents Based on the method of functionalization (Fig. 7.7), solid amine sorbents could be categorized into four classes: (1) class I, impregnated amine sorbents; (2) class II, grafted amine sorbents; (3) class III, in situ polymerized amine sorbents; and (4) class IV, hybrid amine sorbent prepared by impregnating amines on grafted amine sorbents.41 44

The most commonly used amine molecules for class I sorbents are TEPA and PEI, which contain both primary and secondary amine sites for CO2 adsorption. Impregnated amine (i.e., TEPA and PEI) molecules are immobilized on the SiO2 surface through hydrogen bonding interactions between amine groups and hydroxide groups on the SiO2 support surface, as illustrated in the inset in Fig. 7.7A. This hydrogen bonding interaction diminished the IR intensity of OH at 3737 cm21 and broadened the NH2 peak toward a lower wavenumber. Typical class I sorbent is composed of more than one monolayer of amine molecules. Subsequent impregnated molecules are packed on the top of a monolayer of amine molecules of which amine function groups form hydrogen bond inter or intramolecularly,

FIGURE 7.7 Classification of SiO2-immobilized amine sorbents (A) Class I sorbent: Impregnated amine sorbent with low amine loading (B) Class I sorbent: Double impregnated sorbent with high amine loading, (C) Class II sorbent: grafted amine, (D) Class III sorbent: polymerized amine, and (E) Class IV sorbent: hybrid amine sorbent. Source: Adapted from Yu, J.; Zhai, Y.; Chuang, S. S. C., Water Enhancement in CO2 Capture by Amines: An Insight Into CO2 -H2O Interactions on Amine Films and Sorbents. Ind. Eng. Chem. Res. 2018, 57 (11), 4052 4062.

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FIGURE 7.8 (A) IR spectra of absorbed benzene (C6H6) on SiO2 and the TEPA/SiO2 sorbents after exposing to Ar/ C6H6 flow. (B) Integrated absorbance profiles for regeneration of Si-OH groups during removal of benzene from SiO2 and TEPA/SiO2 sorbent. The initial slopes were calculated from estimated linear regions of the profiles. Source: Adapted from Wilfong, W. C.; Chuang, S. S. C., Probing the Adsorption/Desorption of CO2 on Amine Sorbents by Transient Infrared Studies of Adsorbed CO2 and C6H6, Industr. Eng. Chem. Res. 2014, 53 (11), 4224 4231.

illustrated in Fig. 7.9B. Class I sorbents give CO2 capture capacity in the range of 0.5 6.2 mmol/g for 10 15 vol% CO2 stream and 0.2 3.6 mmol/g for 400 ppm CO2 flow.21,45 47 High CO2 capture of class I sorbent is a result of its high amine loading. One distinct advantage of using high capacity sorbent is a reduction of the amount of sorbent used for the CO2 capture process. However, the amine-amine hydrogen bonding from packed amine molecules could slow down the CO2 diffusion process, increasing the time needed for CO2 adsorption and desorption steps in a CO2 capture cycle.1

7.2.3 Probing CO2 Diffusion by the Kinetics of Benzene Adsorption/ Desorption Kinetics of CO2 diffusion and adsorption/ desorption step can be decoupled by in situ IR study using benzene as a probing molecule.48

Benzene, a hydrophobic molecule, is able to interact with isolated Si-OH on the SiO2 surface. This interaction is manifested by a decrease in Si-OH intensity upon benzene adsorption, as shown in Fig. 7.8A. The slow response in the intensity of Si-OH from amine-impregnated SiO2 (TEPA/SiO2) during the desorption of benzene from the surface of SiO2, in Fig. 7.8B, indicates that amine molecules (i.e., TEPA), block the diffusion pathway of benzene.48 Thus one challenge of sorbent development is to design the structure of amine molecules to minimize the diffusion-limitations for adsorbing and desorbing CO2 in the pore of amine sorbents.

7.3 EFFECTS OF LIQUID H2O ON SORBENT STABILITY An attractive advantage of class I sorbent is its low manufacturing cost. However, the weak hydrogen bonding interaction between amine molecules and support materials could

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lead to the degradation of class I sorbent through amine leaching in a H2O-rich environment, that is, the immobilized amine will redissolve into water or other solvents, leading to the decreasing of amine loading. Thus condensation of steam or water vapor to liquid water should be avoided in adsorber and stripper when class I sorbent is in use. Class II sorbents in Fig. 7.7C have been prepared by impregnation of a reactive aminosilane onto a dry, pretreated SiO2 support. The silanization (i.e., grafting) reaction occurs between the aminosilane and the surface OH, forming the Si O Si bond, which links the aminosilane onto the SiO2 surface with a covalent bond. Strict control of the H2O content within the system is needed to avoid shifting from the grafting reaction to the hydrolysis of aminosilane, producing low-quality solid amine sorbents.44 This type of sorbent eliminates amine-leaching issues, because amine is covalently bonded to the SiO2 surface. However, class II sorbents suffer from a high manufacturing cost and low CO2 capture capacity, typically below 3.0 mmol CO2/g sorbent.49 Low CO2 capture capacity is a result of low amine loading because only one layer of amine functional groups is attached on the SiO2 surface. Thus high surface area SiO2 materials, especially mesoporous SiO2 including MCM-41 and SBA-15, have been used as a support for class II sorbents. Because of their limited pore diameter and the long pore length, CO2 adsorption/desorption processes on class II sorbent could be diffusion-limited.

7.4 THE MOLECULAR STRUCTURE OF SIO2-IMMOBILIZED AMINE SORBENTS BY VIBRATIONAL SPECTROSCOPY Comparison of IR spectra of SiO2-based class I and class II sorbents in Fig. 7.9 revealed a number of insights into the structure of these

sorbents at the molecular level. Both sorbents exhibited the IR characteristics of amine molecules: asymmetric and symmetric N H stretching bands at 3365 and 3298 cm21, respectively, and N H deformation band at 1600 cm21; the symmetric and asymmetric C 2 H stretching bands at 2939 and 2817 cm21, respectively, and C 2 H deformation band at 1456 cm21.1 3,20,44,48,51 The key difference is that class I sorbent gives broad amine bands at 3365 and 3298 cm21, whereas class II sorbent gives distinctive and sharp amine bands. The former is a result of hydrogen bonding between the amine and amine functional group, as illustrated in Fig. 7.7A, B, the latter shows little interaction between neighboring amine functional groups. Class I and II sorbents are in an amorphous form that exhibits similar IR features for Si-OH at 3737 cm21 and Si-O at 1096 cm21, but drastically different characteristics in DRIFTs (diffuse reflectance infrared Fourier transform spectroscopy) and transmission modes in Fig. 7.9A.5,52 In DRIFTs, IR radiation strikes the surface of fine particles with a diameter at a micron scale or less. Because of irregular surfaces of fined amine sorbent particles, the radiation is reflected in different and random directions, further striking on the neighboring particles, shown in Fig. 7.10A. The reflected lights, which are collected and directed to the IR detector, provide mainly the structure information of the molecular bonding located at the surface of the particles. In the transmission mode, the incident IR radiation passes through a sample to the detector where the transmitted IR intensity is measured. Thus there is no surprise at observing a prominent Si-O band at 1096 cm21 in the transmission IR since the IR beam passes through a thick layer of SiO2 with many Si-O bonds in the IR beam path. In contrast, this Si-O bond in the bulk of SiO2 is lacking while a prominent Si-OH at 3737 cm21 on the SiO2 surface is observed in

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FIGURE 7.9 (A) IR spectra of SiO2 and aminefunctionalized SiO2 illustrated with their TEM images. The spectra were obtained by DRIFTs (diffuse reflectance infrared Fourier transform spectroscopy) technique. A transmission IR spectrum of SiO2 is included for comparison.50 (B) Raman spectra of SiO2, TEPA, and TEPA/SiO2 sorbent with a laser source of 1060 nm.

DRIFTs results. Coupling DRIFTs with transmission IR allows elucidation of the molecular structure on the surface and in the bulk of the SiO2-immobilized amine sorbents. Raman spectroscopy is produced by scattered radiation from a chemical bond which exhibits changes in the polarizability during

its vibration. In contrast to many IR observable bands in SiO2 in Fig. 7.9A, amorphous SiO2 did not produce any Raman spectrum, as shown in Fig. 7.9B. Note that crystalline SiO2, such as quartz, cristobalite, and tridymite gives a number of intense Raman bands of Si-O in 200 600 cm21.53

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FIGURE 7.10 (A) IR DRIFT cell that is loaded with 45 mg of sorbents. (B) 2D waterfall IR spectra during CO2 adsorption/desorption cycle. Flowing 15 vol% of CO2 and 85 vol% of air at 100 cc/min for 10 min over the sorbents allowed the breakthrough curve to reach more than 98% of its final value. (C) IR difference spectra of strongly, weakly, and totally adsorbed CO2. The IR difference spectrum of weakly adsorbed CO2 was obtained by subtracting the spectrum of Ar purge from that of CO2 adsorption (ICO2 ads: IAr purge), and the IR spectrum of strongly adsorbed CO2 was obtained by subtracting the spectrum of pretreatment from that of Ar purge (IAr purge Ipret.). Source: Adapted from Zhai, Y.; Chuang, S. S. C., The Nature of Adsorbed Carbon Dioxide on Immobilized Amines During Carbon Dioxide Capture From Air and Simulated Flue Gas, Energy Technol. 2017, 5 (3), 510 519.

An in-depth understanding of the IR and Raman of SiO2 allowed us to elucidate the interaction between NH2/ NH of amine molecules and Si-OH on the SiO2 surface by examining the spectra of SiO2 and amine/SiO2 in Figs. 7.1B and 7.9A. Commonly used amines, TEPA and PEI (illustrated in Scheme 7.1 and Fig. 7.9) have very similar IR spectra,

exhibiting the bands at the same wavenumber with a slightly different intensity because they possess the same functional groups, but with different ratios. DRIFT spectra in Fig. 7.1B showed that the presence of an amine (TEPA) on SiO2 suppressed the intensity of isolated hydroxyl groups at 3737 cm21 and broadened the bands associated with hydrogen bonding

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7.5 CO2 ADSORPTION/DESORPTION ON SIO2-SUPPORTED AMINE-FUNCTIONALIZED SORBENTS

between hydroxyl groups centered at 3506 cm21 and NH2/NH at 3365/3298 cm21 in Fig. 7.9A. High amine density sorbent (i.e., class IV amine-coated pellets) shows a broader hydrogen bonding of NH. . .N in 21 3000 3500 cm and a higher ratio of amine at 3357 and 3290 cm21 to CH at 2939 and 2817 cm21 than sorbents with low amine density (i.e., class II and class I). The formation of hydrogen bonding between hydroxyl groups and amine groups2 4 also led to the suppression of NH2 intensity and enhancement of C H intensity at 3929 and 2817 cm21 in Raman in Fig. 7.9B. Further study is needed to interpret the origin of enhancement in Raman intensity. Thus the broadness and intensity of NH/NH2 and C H bands in IR and Raman can serve as an index to quantify the extent of hydrogen bonding interaction on SiO2-immobilized amine sorbents.

7.5 CO2 ADSORPTION/ DESORPTION ON SIO2-SUPPORTED AMINE-FUNCTIONALIZED SORBENTS The design of an effective SiO2-immobilized amine sorbent requires consideration of a number of characteristics: CO2 captures capacity, amine efficiency, adsorption temperature, desorption temperature, adsorption/desorption kinetics, sorbent stability, and manufacturing cost.2 Most sorbents reported in the literature are at an early stage in development, which usually only consider CO2 capture capacity and adsorption/desorption temperature. Sorbents with high CO2 capture capacity will allow the use of a low amount of sorbent materials to achieve the same level of CO2 capture; sorbents with high amine efficiency indicate each amine functional groups in the sorbent are effectively utilized in the CO2 capture. Sorbents that allow CO2 to desorb at low temperature will give low thermal

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regeneration energy, a key factor governing operating cost. Table 7.2 provides a brief summary of these characteristics for a few class I sorbents, which are composed of either a single type of amine or mixture of primary/secondary/tertiary amines. Intuitively, one would speculate that the CO2 capture capacity of an amine sorbent could increase by increasing (1) surface area of support and (2) high amine loading.58 The high surface area supports should allow spreading amine molecules on the surface of their pores, facilitating CO2 access to amine sites, thus giving high amine efficiency. In contrast, many immobilized amines on high surface area supports, that is, SBA-15, gave low amine efficiencies. Likewise, high surface area support did not lead to high CO2 capture capacity. TEPA-impregnated SBA-15, which has a 1099 m2/g surface area, represents the highest CO2 capture capacity of 4.6 mmol/g reported in the literature. Nevertheless, the sorbent prepared with amorphous SiO2 (160 m2/g), which has a 6.9-time lower surface area than SBA-15, shows a 3.3 mmol/g capture capacity. The PME-PEI (spell out PME) sample developed based on PME support with 570 m2/g surface area, performs a 4.6 mmol/g of capture capacity. These observations indicate that the effect of surface area and amine loadings to the capture capacity may not be as significant as expected. When the surface area of supports or amine loadings of sorbents reached a certain critical point, the capture capacity was no longer limited by the surface area.42,45 47 In general, increasing the amine loading on the support could enhance CO2 capture capacity but often leads to a reduction in amine efficiency.46,51 How amine molecules are packed on the surface of the pores should be more important than the surface area available for spreading amine molecules. One feasible approach to achieve high CO2 capture and high amine efficiency is the use of a support with a hierarchical

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7. SILICA-SUPPORTED IMMOBILIZED AMINE FOR CO2 CAPTURE PROCESSES: MOLECULAR INSIGHT

TABLE 7.2 Amine-Immobilized SiO2 Sorbents.

Amine/Support

Surface Area of Support (m2/g)

Amine Loading (mmol N/g)

Conc. CO2 Capture Capacity of CO2 (vol %) Tads ( C) (mmol/g)

PEI/MacS

261

10.13

15

40

3.84 (S)a

0.37

[10]

PEI/amorphous SiO2

160

5.8

100

40

2.0 (S)

0.34

[51]

Acrylamide/SiO2

337

1.7

5

30

0.8 (S)

0.48

[21]

6.2

85

40

2.8 (S)

0.45

[44]

7.8

10

35

1.2 (S)

0.15

[45]

0.31

[1]

PEI800/amorphous SiO2 TEPA/SiO2 gel TEAP/SiO2

380 160

9.2

15

50

15% with moist

2.86 (D)

b

Amine Efficiency (mol CO2/mol N) References

4.03 (D)

0.45

PEHA/KIT-6

857

12.6

100

105

4.48(S)

0.33

[54]

TEPA/(33%HPS/ 67%SBA-15)

8578

10.13

15

75

5.05 (S)

0.49

[55]

14.7

15

90

4.71 (S)

0.31

[56]

8.4

100

75

3.6 (S)

0.42

[46]

9.5

4.5 (S)

0.47

10.4

4.6 (S)

0.44

12.6

3.7 (S)

0.26

3.6 (S)

0.20

TEPA/SBA-15 TEPA /SBA-15

TEPA/SBA-15

1099

835

18.4

0.04

23

[57]

a

S indicates the CO2 capture capacity was measured based on static measurement. D indicates the CO2 capture capacity was measured based on dynamic measurement.

b

pore structure which not only increases the dispersion of amine sites but also provides a fast mass-transfer channel for the diffusion of CO2 into those channels inside the sorbent. CO2 capture capacities of the sorbents have been measured by static and dynamic approaches. The static approach produces an absorption isotherm by measuring the amount of CO2 adsorbed as a function of CO2 partial pressure in a static CO2 environment at a specific temperature. Dynamic measurement produces a breakthrough curve by exposure of the

sorbent to a step-switch of the flow from an intergas to CO2-containing gas, as shown on the left wall of Fig. 7.10B. Dynamic measurement also allows conducting in a TPD mode (temperature-programmed desorption). Dynamic measurement emulates the practical condition of adsorption and desorption, providing working CO2 capture capacity. It is expected that working capacity is usually lower than those measured by static measurement because diffusion and kinetics play a role under practical and working condition.

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7.6 DEGRADATION OF SOLID AMINE SORBENTS

Coupling the dynamic measurement with in situ infrared spectroscopic studies allows determination of the structure of adsorbed CO2 and its binding energy under working conditions. Fig. 7.10A illustrates the basic principles of the DRIFTS setup. Although the IR beam path of diffuse reflection is complex, the DRIFT technique is particularly amenable to producing high quality IR spectra of adsorbed CO2 on the fined particles of amine sorbents. Fig. 7.10B provides an overview of the dynamic measurement which involves a CO2 capture cycle: (1) pretreatment by TPD at 110 C to remove the preadsorbed CO2 and H2O, (2) CO2 adsorption with 15 v% CO2/Ar flowing at 35 C, (3) Ar purge by flowing Ar into the system at 35 C to remove the gas phase CO2 and weakly adsorbed CO2, and (4) regeneration of sorbent by TPD at 110 C to release the strongly adsorbed CO2.2 The IR spectra shown in Fig. 7.2B, C, obtained by (ICO2 ads: Ipret.), are difference spectra that exhibit all of the features of adsorbed CO2 (ammonium carbamate). Because of hydrogen bonding, ammonium ion gives a very broad band in 2400 3200 cm21 with negative C H bands in 2817 2939 cm21.2 Note that IR spectra of adsorbed CO2 on amine in Fig. 7.1B is ICO2 ads: Although the working capacity is determined in a fixed-bed mode at a mg scale, the experimental conditions emulate the flue gas flowing through sorbent particles in a vessel of adsorber. The breakthrough curve gives a value of adsorption half-time—a simple index of kinetics of diffusion and adsorption process. TPD provides the desorption peak temperature which can be translated to the binding energy of adsorbed CO2 and heat of adsorption. It is interesting to note that the adsorbed CO2 on a SiO2-based sorbent can be classified into weakly and strongly adsorbed CO2. The former can desorb during Ar purge; the latter only can desorb under heating.2 Fig. 7.10C showed weakly adsorbed CO2 (i.e., the fraction

137

of adsorbed CO2 removed at 35 C in Ar) and strongly adsorbed CO2 (i.e., the fraction of adsorbed CO2 removed at TPD). The weakly adsorbed CO2 consists of carbamic acid and ammonium carbamate which adsorbed on secondary amine. Ammonium carbamates on primary amine constitute the majority of strongly adsorbed species, which could be in the form of a network of hydrogen-bonded species, which may constitute a diffusion barrier. The sorbents with a high fraction of weakly adsorbed CO2 should be selected for a pressure-swing separation process; those with a high fraction of adsorbed CO2 are suitable for a temperature-swing separation process.

7.6 DEGRADATION OF SOLID AMINE SORBENTS One critical issue in the development of an effective regenerative sorbent is the durability of amine sites which have to maintain their structure under high-temperature regeneration condition in the presence of CO2, air, and steam.8,22,23,25 Many approaches have been developed to slow down the degradation of SiO2-supported amine sorbents in CO2 capture process, including (1) synthesizing the specific amine molecules, (2) adding stabilizer such as polyethylene glycol and crosslinker to stabilize amine sites, and (3) developing OH-abundant polymer support such as polyvinyl alcohol (PVA).5,59 The insight into the origin of inhibiting degradation can be obtained by infrared spectroscopic studies. Fig. 7.11 compares the evolution of adsorbed species during CO2 capture on PEI/SiO2 and PEI/PVA. The former showed a rapid formation of an amide at 1675 cm21; the latter showed a gradual formation of urea at 1600 cm21. The formation of these species consumed the amine sites for CO2 capture, leading to decreases in IR intensity of adsorbed CO2. The gradual decline in

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7. SILICA-SUPPORTED IMMOBILIZED AMINE FOR CO2 CAPTURE PROCESSES: MOLECULAR INSIGHT

FIGURE 7.11 3D color map of IR of adsorbed CO2 on PEI/SiO2 and PEI/PVA during CO2 capture/degradation cycles. Source: Adapted from Zhai, Y.; Chuang, S. S. C., Enhancing Degradation Resistance of Polyethylenimine for CO2 Capture With Cross-Linked Poly(vinyl alcohol). Ind. Eng. Chem. Res. 2017, 56 (46), 13766 13775.

IR profiles of adsorbed CO2 on PEI/PVA, in contrast to a rapid declining IR profile on PEI/ SiO2, showed that PVA plays a critical role in inhibiting degradation of amine sorbents. Further IR study revealed that PVA’s OH groups interacted mainly with the secondary amine ( NH) of branched PEI through a hydrogen bonding. This interaction avoids a direct exposure of NH to oxygen in the flue gas, inhibiting its oxidative degradation.51

7.7 CO2 CAPTURE PROCESS FOR SOLID AMINE SORBENTS Coal-fired power plants produced an enormous large volumetric flow rate of flue gas, that is, 42,500 m3/min at a 500 MW plant with a 10% 15% CO2.60 Thermal swing separation

process is one of very few processes that are capable of treating streams with large flow rates. Thermal swing CO2 capture processes can be operated in fixed beds, rotating bed, fluidized beds, and monolith modes which require amine sorbents to be fabricated in the form of pellets, particles, and monoliths, respectively, as illustrated in Fig. 7.2.61 SiO2supported immobilized amine provides a flexibility for sorbent fabrication because of SiO2 surface’s ability to adhere with various polymer binders. Fixed-bed mode has been widely used in the process industry, that is, adsorber for gas separation, a catalytic reactor, heat storage devices, and pebble bed heaters.61,62 Literally, the solid amine pellets with a size around 2 mm in diameter were packed inside a vessel, that is, an adsorber. One disadvantage of

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7.8 CONCLUSIONS

fixed-bed adsorber is its large pressure drop which requires the use of a high-power blower to push flue gas through the adsorbent bed. Another disadvantage is poor heat transfer in fixed-bed adsorber where the removal of heat during CO2 adsorption and for the addition of heat during CO2 desorption are hindered. Issues of heat transfer and large pressure drop can be overcome by the use of a fluidized-bed adsorber which employs sorbent particle with a typical diameter of 200 500 µm. Operation in a circulating fluidized-bed mode facilitates the diffusion and adsorption/desorption steps, and shortens the time needed for a CO2 capture cycle. Because of violent agitation during fluidization, the resistance of the sorbent particle to attrition is of concern.22,23 The rotating bed in CO2 capture process is operated with a packed bed of pellets, rotating inside a cylindrical vessel, shown in the inset of Fig. 7.2. The rotating bed is a hybrid of fixed bed and fluidized bed, which possesses unique advantages, that is, intensive mixing and fast mass transfer which eliminate heat transfer issue of a fixed-bed adsorber and eradicate the attrition issue of a fluidized-bed adsorber.61 Mechanical design of rotating bed and energy needed for pushing the rotation are key issues to be addressed. Monolithic adsorber with many parallel channels and high heat/mass transfer, illustrated in the inset of Fig. 7.2, could provide an excellent platform for addressing many critical issues encountered in conventional adsorbers. Amine sorbent particles are adhered on the monolithic structure. The monolithic structure can be made of metal which could facilitate the transfer of heat during adsorption and desorption steps. Further research in development of the CO2 capture process could be directed toward the design of monolith adsorbers.63

7.8 CONCLUSIONS Anthropogenic emissions of CO2 from coalfired power plants present a major threat to our living environment. CO2 capture is a strategy to mitigate the environmental impacts of CO2 before the successful development of costeffective non-CO2 emission energy generation technologies. SiO2-supported immobilized amines hold a great promise to serve as a sorbent for capturing CO2 from coal-fired power plants. SiO2 provides several attractive features for immobilizing amine molecules: low regeneration energy, low water retention, low manufacturing cost, and high specific surface area. This chapter provides a holistic view of the development of silica-immobilized sorbents for CO2 capture. Sorbent development requires considerations of many disciplines and subjects: chemical reactions and diffusion at the molecular level, fabrication of sorbent particles and pellets at meso scale, adsorber technology at macro level, and process optimization at scale-up level. This chapter discussed scientific and technical issues that need to be addressed at each level. Emphasis was placed on the use of infrared spectroscopy to investigate the structure of SiO2immobilized amine sorbents and diffusion of CO2 in adsorption/desorption steps. In situ infrared spectroscopy allows us to examine the nature of Si-OH on the surface of various types of SiO2 under a wide range of conditions. Hydrogen bonding between amine and amine functional groups as well as between amine and Si-OH is manifested by the broadness and intensity of NH/NH2 in IR and Raman spectra. Diffusion of CO2 in amine sorbent plays a significant role in controlling CO2 adsorption/desorption kinetics because the presence of amineamine and ammonium-carbamate hydrogen bonding network could hinder CO2 diffusion. In situ IR study of benzene probing allows quantification of the effect of diffusion on CO2 adsorption/desorption. The benzene probing can also

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7. SILICA-SUPPORTED IMMOBILIZED AMINE FOR CO2 CAPTURE PROCESSES: MOLECULAR INSIGHT

be employed to determine the effect of mass transfer in various adsorption/desorption processes using SiO2-based sorbents. This chapter highlights the significance of in situ IR studies—the ability to determine the structure of adsorbed species and sorbents under working conditions. In situ infrared spectroscopic methods are able to provide an insight of a silica-based CO2 capture process at the molecular level to guide its further development. The in situ IR methods, which have also been extensively used for studying the reaction mechanisms of catalysis and photocatalysis, can be further extended to mechanistic investigation of various sorbent and membrane separation processes.64

NOTES The authors declare no competing financial interests.

Acknowledgment This work was supported by the U.S. Department of Energy under grants DE-FE0013127, Ohio Coal Development Office under grants R-13 16, R-14-04, and R-15-08, and the University of Akron Faculty Initiation Fund.

References 1. Yu, J.; Zhai, Y.; Chuang, S. S. C. Water Enhancement in CO2 Capture by Amines: An Insight Into CO2 H2O Interactions on Amine Films and Sorbents. Ind. Eng. Chem. Res. 2018, 57 (11), 4052 4062. 2. Zhai, Y.; Chuang, S. S. C. The Nature of Adsorbed Carbon Dioxide on Immobilized Amines During Carbon Dioxide Capture From Air and Simulated Flue Gas. Energy Technol. 2017, 5 (3), 510 519. 3. Tumuluri, U.; Isenberg, M.; Tan, C.-S.; Chuang, S. S. C. In Situ Infrared Study of the Effect of Amine Density on the Nature of Adsorbed CO2 on Amine-Functionalized Solid Sorbents. Langmuir 2014, 30 (25), 7405 7413. 4. Hahn, M. W.; Jelic, J.; Berger, E.; Reuter, K.; Jentys, A.; Lercher, J. A. Role of Amine Functionality for CO2 Chemisorption on Silica. J. Phys. Chem. B 2016, 120 (8), 1988 1995.

5. Srikanth, C. S.; Chuang, S. S. Spectroscopic Investigation Into Oxidative Degradation of SilicaSupported Amine Sorbents for CO2 Capture. ChemSusChem. 2012, 5 (8), 1435 1442. 6. Srikanth, C. S.; Chuang, S. S. C. Infrared Study of Strongly and Weakly Adsorbed CO2 on Fresh and Oxidatively Degraded Amine Sorbents. J. Phys. Chem. C 2013, 117 (18), 9196 9205. 7. Kahn, B. Carbon Dioxide Is Rising at Record Rates. http://www.climatecentral.org/news/carbon-dioxiderecord-rates-21242 (accessed July 09, 2018). 8. Kresge, A. J. Proton NMR Chemical Shifts of Hydronium and Hydroxyl Ions. J. Chem. Phys. 1963, 39 (5), 1360 1361. 9. Stoyanov, E. S.; Stoyanova, I. V.; Reed, C. A. The Structure of the Hydrogen Ion (Haq1) in Water. J. Am. Chem. Soc. 2010, 132 (5), 1484 1485. 10. Min, K.; Choi, W.; Choi, M. Macroporous Silica With Thick Framework for Steam-Stable and HighPerformance Poly(ethyleneimine)/Silica CO2 Adsorbent. ChemSusChem. 2017, 10 (11), 2518 2526. 11. Figueroa, J. D.; Fout, T.; Plasynski, S.; McIlvried, H.; Srivastava, R. D. Advances in CO2 Capture Technology—The U.S. Department of Energy’s Carbon Sequestration Program. Int. J. Greenhouse Gas Control 2008, 2 (1), 9 20. 12. U. S. Department of Energy, N. E. T. L. Bench-Scale and Slipstream Development and Testing of PostCombustion Carbon Dioxide Capture and Separation Technology for Application to Existing Coal-Fired Power Plants, DE-FOA-0000403, 2011. 13. Naims, H. Economics of Carbon Dioxide Capture and Utilization—A Supply and Demand Perspective. Environ. Sci. Pollut. Res. 2016, 23 (22), 22226 22241. 14. Bossa, J.-B.; Borget, F.; Duvernay, F.; Theule´, P.; Chiavassa, T. Formation of Neutral Methylcarbamic Acid (CH3NHCOOH) and Methylammonium Methylcarbamate [CH3NH31][CH3NHCO22] at Low Temperature. J. Phys. Chem. A 2008, 112 (23), 5113 5120. 15. Cue´llar-Franca, R. M.; Azapagic, A. Carbon Capture, Storage and Utilisation Technologies: A Critical Analysis and Comparison of their Life Cycle Environmental Impacts. J. CO2 Utiliz. 2015, 9, 82 102. 16. Lv, B.; Guo, B.; Zhou, Z.; Jing, G. Mechanisms of CO2 Capture into Monoethanolamine Solution with Different CO2 Loading during the Absorption/ Desorption Processes. Environ. Sci. Technol. 2015, 49 (17), 10728 10735. 17. Sun, C.; Dutta, P. K. Infrared Spectroscopic Study of Reaction of Carbon Dioxide With Aqueous Monoethanolamine Solutions. Ind. Eng. Chem. Res. 2016, 55 (22), 6276 6283.

CHEMISTRY OF SILICA AND ZEOLITE-BASED MATERIALS

REFERENCES

18. Garcı´a-Abuı´n, A.; Go´mez-Dı´az, D.; Lo´pez, A. B.; Navaza, J. M.; Rumbo, A. NMR Characterization of Carbon Dioxide Chemical Absorption With Monoethanolamine, Diethanolamine, and Triethanolamine. Ind. Eng. Chem. Res. 2013, 52 (37), 13432 13438. 19. Massood Ramezan, T. J. S. Research and Development Solutions Carbon Dioxide Capture from Existing Coal-Fired Power Plants; U.S. Department of Energy National Energy Technology Laboratory, 2007. 20. Yu, J.; Chuang, S. S. C. The Structure of Adsorbed Species on Immobilized Amines in CO2 Capture: An In Situ IR Study. Energy Fuels 2016, 30 (9), 7579 7587. 21. Zhao, Y.; Shen, Y.; Bai, L.; Ni, S. Carbon Dioxide Adsorption on Polyacrylamide-Impregnated Silica Gel and Breakthrough Modeling. Appl. Surf. Sci. 2012, 261, 708 716. 22. Levenspiel, O. Chemical Reaction Engineering. Ind. Eng. Chem. Res. 1999, 38 (11), 4140 4143. 23. Kunii, D.; Levenspiel, O. Chapter 7 - Entrainment and Elutriation From Fluidized Beds. In Fluidization Engineering; Kunii, D., Levenspiel, O., Eds.; . 2nd ed. Butterworth-Heinemann: Boston, MA, 1991; pp 165 192. 24. Chen, C.; Kim, J.; Ahn, W.-S. CO2 Capture by AmineFunctionalized Nanoporous Materials: A Review. Korean J. Chem. Eng. 2014, 31 (11), 1919 1934. 25. Saifullah, B.; Hussein, M. Z. B. Inorganic nanolayers: structure, preparation, and biomedical applications. Int. J. Nanomed. 2015, 5609 5633 PubMed. 26. McLaughlin, J. K.; Chow, W. H.; Levy, L. S. Amorphous Silica: A Review of Health Effects From Inhalation Exposure with Particular Reference to Cancer. J. Toxicol. Environ. Health 1997, 50 (6), 553 566. 27. Son, W.-J.; Choi, J.-S.; Ahn, W.-S. Adsorptive Removal of Carbon Dioxide Using Polyethyleneimine-Loaded Mesoporous Silica Materials. Microporous Mesoporous Mater. 2008, 113 (1), 31 40. 28. Ji, P.; Zhang, J.; Chen, F.; Anpo, M. Ordered Mesoporous CeO2 Synthesized by Nanocasting From Cubic Ia3d Mesoporous MCM-48 Silica: Formation, Characterization and Photocatalytic Activity. J. Phys. Chem. C 2008, 112 (46), 17809 17813. 29. Yamashita, H.; Kawasaki, S.; Ichihashi, Y.; Harada, M.; Takeuchi, M.; Anpo, M.; Stewart, G.; Fox, M. A.; Louis, C.; Che, M. Characterization of Titanium 2 Silicon Binary Oxide Catalysts Prepared by the Sol 2 Gel Method and Their Photocatalytic Reactivity for the Liquid-Phase Oxidation of 1-Octanol. J. Phys. Chem. B 1998, 102 (30), 5870 5875. 30. Lehman, S. E.; Larsen, S. C. Zeolite and Mesoporous Silica Nanomaterials: Greener Syntheses,

31.

32.

33.

34.

35.

36.

37.

38.

39.

40.

41.

42.

141

Environmental Applications and Biological Toxicity. Environ. Sci. Nano 2014, 1 (3), 200 213. Alfonso, E. R.; Jean-Marc, C.; Chantal, L.; Yannick, P. Comparison Between SBA-15 and MCM-41 Structure on the Stability and the Selectivity of Basic Catalysts in Oligomerization of Glycerol. Curr. Org. Chem. 2012, 16 (23), 2774 2781. Hanrahan, J.P.; O’Mahony, T.F.; Tobin, J.M.; Hogan, J.J. Mesoporous Silica and their Applications. https:// www.sigmaaldrich.com/technical-documents/articles/ materials-science/renewable-alternative-energy/mesoporous-silica.html (accessed June 09, 2018). Martı´nez, F.; Sanz, R.; Orcajo, G.; Briones, D.; Ya´ngu¨ez, V. Amino-Impregnated MOF Materials for CO2 Capture at Post-Combustion Conditions. Chem. Eng. Sci. 2016, 142, 55 61. Llewellyn, P. L.; Bourrelly, S.; Serre, C.; Vimont, A.; Daturi, M.; Hamon, L.; De Weireld, G.; Chang, J.-S.; Hong, D.-Y.; Kyu Hwang, Y.; Hwa Jhung, S.; Fe´rey, G. High Uptakes of CO2 and CH4 in Mesoporous Metal— Organic Frameworks MIL-100 and MIL-101. Langmuir 2008, 24 (14), 7245 7250. Couck, S.; Denayer, J. F. M.; Baron, G. V.; Re´my, T.; Gascon, J.; Kapteijn, F. An Amine-Functionalized MIL53 Metal 2 Organic Framework With Large Separation Power for CO2 and CH4. J. Am. Chem. Soc. 2009, 131 (18), 6326 6327. Boehm, H. P. Infrared Spectroscopy in Surface Chemistry. Von M. L. Hair. Marcel Dekker Inc., New York 1967. XIII, 315 S., mehrere Abb. Angew. Chem. 1968, 80 (11), 451. Sneh, O.; Cameron, M. A.; George, S. M. Adsorption and Desorption Kinetics of H2O on a Fully Hydroxylated SiO2 Surface. Surface Science 1996, 364 (1), 61 78. Goeppert, A.; Czaun, M.; May, R. B.; Prakash, G. K. S.; Olah, G. A.; Narayanan, S. R. Carbon Dioxide Capture From the Air Using a Polyamine Based Regenerable Solid Adsorbent. J. Am. Chem. Soc. 2011, 133 (50), 20164 20167. Colthup, N. B.; Daly, L. H.; Wiberley, S. E. Introduction to Infrared and Raman Spectroscopy, 3rd ed.; Academic Press: New York, 1990. Alarcos, N.; Cohen, B.; Zio´łek, M.; Douhal, A. Photochemistry and Photophysics in Silica-Based Materials: Ultrafast and Single Molecule Spectroscopy Observation. Chem. Rev. 2017, 117 (22), 13639 13720. Kim, H. J.; Moon, J. H.; Park, J. W. A Hyperbranched Poly(ethyleneimine) Grown on Surfaces. J. Colloid Interface Sci. 2000, 227 (1), 247 249. Aquino, C. C.; Richner, G.; Chee Kimling, M.; Chen, D.; Puxty, G.; Feron, P. H. M.; Caruso, R. A. AmineFunctionalized Titania-based Porous Structures for

CHEMISTRY OF SILICA AND ZEOLITE-BASED MATERIALS

142

43.

44.

45.

46.

47.

48.

49.

50.

51.

52.

53.

7. SILICA-SUPPORTED IMMOBILIZED AMINE FOR CO2 CAPTURE PROCESSES: MOLECULAR INSIGHT

Carbon Dioxide Postcombustion Capture. J. Phys. Chem. C 2013, 117 (19), 9747 9757. Sanz, R.; Calleja, G.; Arencibia, A.; Sanz-Pe´rez, E. S. Development of High Efficiency Adsorbents for CO2 Capture Based on a Double-Functionalization Method of Grafting and Impregnation. J. Mater. Chem. A 2013, 1 (6), 1956. Wilfong, W. C.; Kail, B. W.; Jones, C. W.; Pacheco, C.; Gray, M. L. Spectroscopic Investigation of the Mechanisms Responsible for the Superior Stability of Hybrid Class 1/Class 2 CO2 Sorbents: A New Class 4 Category. ACS Appl. Mater. Interfaces 2016, 8 (20), 12780 12791. Xie, W.; Ji, X.; Fan, T.; Feng, X.; Lu, X. CO2 Uptake Behavior of Supported Tetraethylenepentamine Sorbents. Energy Fuels 2016, 30 (6), 5083 5091. Zhao, A.; Samanta, A.; Sarkar, P.; Gupta, R. Carbon Dioxide Adsorption on Amine-Impregnated Mesoporous SBA-15 Sorbents: Experimental and Kinetics Study. Ind. Eng. Chem. Res. 2013, 52 (19), 6480 6491. Irani, M.; Gasem, K. A. M.; Dutcher, B.; Fan, M. CO2 Capture Using Nanoporous TiO(OH)2/ Tetraethylenepentamine. Fuel 2016, 183, 601 608. Wilfong, W. C.; Chuang, S. S. C. Probing the Adsorption/Desorption of CO2 on Amine Sorbents by Transient Infrared Studies of Adsorbed CO2 and C6H6. Ind. Eng. Chem. Res. 2014, 53 (11), 4224 4231. Sayari, A.; Belmabkhout, Y. Stabilization of AmineContaining CO2 Adsorbents: Dramatic Effect of Water Vapor. J. Am. Chem. Soc. 2010, 132 (18), 6312 6314. Coblentz Society, Inc., Evaluated Infrared Reference Spectra. In NIST Chemistry WebBook, NIST Standard Reference Database Number 69; National Institute of Standards and Technology (retrieved October 20, 2018). Zhai, Y.; Chuang, S. S. C. Enhancing Degradation Resistance of Polyethylenimine for CO2 Capture With Cross-Linked Poly(vinyl alcohol). Ind. Eng. Chem. Res. 2017, 56 (46), 13766 13775. Jentys, A.; Pham, N. H.; Vinek, H. Nature of Hydroxy Groups in MCM-41. J. Chem. Soc. Faraday Trans. 1996, 92 (17), 3287 3291. Kingma, K. J.; Hemley, R. J. Raman Spectroscopic Study of Microcrystalline Silica. Am. Mineral. 1994, 79, 269 273.

54. Kishor, R.; Ghoshal, A. K. Amine-Modified Mesoporous Silica for CO2 Adsorption: The Role of Structural Parameters. Ind. Eng. Chem. Res. 2017, 56 (20), 6078 6087. 55. Zhao, P.; Zhang, G.; Sun, Y.; Xu, Y. CO2 Adsorption Behavior and Kinetics on AmineFunctionalized Composites Silica With Trimodal Nanoporous Structure. Energy Fuels 2017, 31 (11), 12508 12520. 56. Wang, W.; Motuzas, J.; Zhao, X. S.; Diniz da Costa, J. C. Improved CO2 Sorption in Freeze-Dried Amine Functionalized Mesoporous Silica Sorbent. Ind. Eng. Chem. Res. 2018, 57 (16), 5653 5660. 57. Kumar, A.; Madden, D. G.; Lusi, M.; Chen, K. J.; Daniels, E. A.; Curtin, T.; Perry, J. J. t; Zaworotko, M. J. Direct Air Capture of CO2 by Physisorbent Materials. Angew. Chem. Int. Ed. Engl. 2015, 54 (48), 14372 14377. 58. Yu, C.-H., A Review of CO2 Capture by Absorption and Adsorption. Aerosol Air Quality Res. 12, 2012, 745 769. 59. Didas, S. A.; Zhu, R.; Brunelli, N. A.; Sholl, D. S.; Jones, C. W. Thermal, Oxidative and CO2Induced Degradation of Primary Amines Used for CO2 Capture: Effect of Alkyl Linker on Stability. J. Phys. Chem. C 2014, 118 (23), 12302 12311. 60. Fout, T.; Zoelle, A.; Keairns, D.; Turner, M.; Woods, M.; Kuehn, N.; Shah, V.; Chou, V.; Pinkerton, L. Cost and Performance Baseline for Fossil Energy Plants Volume 1a: Bituminous Coal (PC) and Natural Gas to Electricity Revision 3; U.S. Department of Energy: 2015. 61. Meisen, A. Gas Purification, Arthur L. Kohl and Fred C. Riesenfeld, 4th Edition, 1985, 900 pages, Gulf Publishing Co. Book Division, Houston, Texas, USA. Can. J. Chem. Eng. 1988, 66 (3), 526 527. 62. Heggs, P. J. FIXED BEDS. http://www.thermopedia. com/content/765/ (accessed 09/15/2018). 63. Chen, C.; Yang, S.-T.; Ahn, W.-S.; Ryoo, R. AmineImpregnated Silica Monolith With a Hierarchical Pore Structure: Enhancement of CO2 Capture capacity. Chem. Commun. 2009, 24, 3627 3629. 64. Guzman, F.; Chuang, S. S. C. Tracing the Reaction Steps Involving Oxygen and IR Observable Species in Ethanol Photocatalytic Oxidation on TiO2. J. Am. Chem. Soc. 2010, 132 (5), 1502 1503.

CHEMISTRY OF SILICA AND ZEOLITE-BASED MATERIALS