Adsorption Characteristics of Carbon Dioxide Gas on a Solid Acid

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Adsorption Characteristics of Carbon Dioxide Gas on Solid Acid Derivative of #-Cyclodextrin Tianxiang Guo, Alemayehu H. Bedane, Yuanfeng Pan, Babak Shirani, Huining Xiao, and Mladen Eic Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.6b03167 • Publication Date (Web): 27 Feb 2017 Downloaded from http://pubs.acs.org on February 28, 2017

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Adsorption Characteristics of Carbon Dioxide Gas on Solid Acid Derivative of β-Cyclodextrin Tianxiang Guo †, Alemayehu H. Bedane‡, Yuanfeng Pan§, Babak Shirani‡, Huining Xiao‡*, Mladen Eić‡ †

School of Environmental Science and Engineering, North China Electric Power University, Baoding 071003, China

‡

Department of Chemical Engineering, University of New Brunswick, Fredericton, NB, E3B 5A3, Canada

§

School of Chemistry and Chemical Engineering, Guangxi University, Nanning 530004, China

Keywords: CO2 adsorption; β-cyclodextrin; adsorption capacity; selectivity; sulfonic group ABSTRACT: A solid acid derivative of β-cyclodextrin was synthesized as an adsorbent for CO2 capture. The adsorption characteristics, such as adsorption capacity, selectivity and uptake rate under different temperatures and gas pressures were analyzed. The results from SEM, EDX, BET, FTIR and TGA indicated that the dehydration and grafting of sulfonic groups changed the structure of β-cyclodextrin aggregates into a relatively homogeneous porous structure with a concave-convex surface. Meanwhile, the specific BET surface area and pore volume of the solid acid derivative were increased by 40 and 37 times compared to β-cyclodextrin aggregates. Thereby, the performance of solid acid derivative of β-cyclodextrin toward CO2 sorption was significantly enhanced, in which CO2 adsorption capacity at 3.5bar was increased to 1.78 mmol/g and the selectivity of CO2 over N2, O2 and CH4 at 298K reached 7. Interestingly, there was no


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adsorption of nitrogen on as-prepared solid acid derivative at 77K based on BET sorption. Lowering temperature is disadvantageous for N2 adsorption but helpful to promote CO2 capture so that the high selectivity of CO2 to N2 sorption can be achieved.

■ INTRODUCTION Global warming resulted from the emission of greenhouse gases has received much attention recently. The increase of worldwide CO2 emissions is commonly considered as one of the important causes. Various CO2 capture technologies such as chemical absorption, adsorption and membrane have been exploited to reduce CO2 emissions.1 However, the conventional absorption processes such as alkanolamine aqueous solutions still possess some drawbacks, e.g., high equipment corrosion rate, high energy consumption in regeneration; whereas the membrane technologies have not yet been matured for disposing a huge amount of flue gas due to the existence of significant mass transfer limitations. As a result, adsorption processes are well received as the effective approaches to overcome these inherent problems using some highefficient adsorbents, such as activated carbon2-7, zeolite molecular sieve8-12 and various other silicate materials13-21. Current research of carbonaceous adsorbent for CO2 separation mainly focuses on how to improve the adsorption capacity and selectivity via two ways: (1) to improve surface area and pore structure of the adsorbents either using different precursors or fabricating different structures such as ordered mesoporous carbon22, single-wall CNT23, multi-walled CNT24,25, graphene26and other polymer materials27,28; (2) to increase alkalinity by chemical modification on the surface with some alkali substance(e.g., NaOH29, KOH30,31, -NH232-34). To date, cyclodextrin applications have been mainly intended for the entrapment of small molecules,


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stabilization of reactive intermediates, catalysis through encapsulation and as potential molecular transport and drug delivery device.35-40 The investigations of CO2 encapsulation and complexation with cyclodextrins have indicated that β-cyclodextrin could form cyclodextrin based nanosponges with inclusion of CO241,42, whereas, not form “cyclodextrin-gas” clathrates with CO2 by crystallization from water solution of β-cyclodextrin43. And a supra-molecular system of aniline encapsulated into β-cyclodextrin cavity was studied to achieve a high amine efficiency of 0.85 mol CO2/mol(N) with dry carbon dioxide gas.44 Meanwhile, some microporous carbon materials derived from β-cyclodextrin were synthesized by a method of solvothermal carbonization with p-toluene sulfonic acid monohydrate and dichlorobenzene, achieving a capacity of CO2 adsorption up to 12.7 wt% at 273 K and 1.0 bar with obtained high specific surface area between 600 and 700 m2/g45 and a significant amount up to 0.35 mmol/g of CO2 adsorption from dry air containing 400 ppm CO2.46 However, the literatures related to CO2 capture of solid adsorbent derived from β-cyclodextrin through acid treatment47 for gaseous phase catalytic synthesis and the reduction of CO2 emission are very limited48. Moreover, those derivatives were restricted in their application due to the use of expensive and poisonous chemicals, e.g., aniline and p-toluene sulfonic acid monohydrate. Thereby, it is necessary to synthesize environmental friendly adsorbent based on β-cyclodextrin for CO2 capture by a simplified method with less use of those poisonous chemicals. In this work, β-cyclodextrin was used to synthesize an environmental friendly solid acid adsorbent in the presence of concentrated sulfuric acid at 413K for CO2 capture. The synthesis temperature is lower than that of conventional activated carbon; and the adsorbent owns high practicality to achieve commercialization. The resulting adsorbent was characterized with scanning electron microscopy(SEM)-energy dispersive X-ray spectroscopy (EDX), Brunauer-


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Emmett-Teller (BET) sorption, Fourier Transform Infrared spectroscopy(FTIR) and thermogravimetric analysis(TGA). Then its adsorption performances related to CO2 adsorption capacity and the selectivity of CO2 over N2, O2 and CH4 under different temperatures and gas pressures were experimentally investigated mainly using an intelligent gravimetric analyzer (IGA). ■ EXPERIMENTAL SECTION Materials. β-cyclodextrin (β-CD) powder (98% purity) was purchased from Sigma-Aldrich Co. LLC(Missouri, USA). Sulfuric acid (98% wt) as a main modified agent came from Products Chemiques ACP Chemicals Inc(Quebec, Canada). Ethanol (anhydrous) from the Industrial & Beverage Alcohol Division of GreenField Ethanol Inc (Ontario, Canada) was used to incude the precipitation of the solid acid derivative of β-cyclodextrin. Methylene dichloride mould agent was obtained from Electrical Manufacturing and Distributors Inc (Texas, USA). All these chemicals were used as received without further purification. Synthesis of solid acid derivative. Solid acid derivative was prepared by adding βcyclodextrin (1g) into a flask(100ml) containing 20ml of sulfuric acid (98%wt), followed by stirring until the β-cyclodextrin was completely dissolved. The solution was kept at 413K for 5 hrs, then precipitated with 50ml of ethanol. The precipitate was treated by washing with distilled water and ethanol, followed by impregnation in methylene dichloride and ultrasonic treatment for 15 min. The final product was obtained after filtering and drying under vacuum overnight. Characterization. The surface morphologies of solid acid derivative and β-cyclodextrin were examined by means of a scanning electron microscope (SEM, JEOL JSM6400, Tokyo, Japan) configured with a Noran energy dispersive X-ray analyzer (EDX system). The samples were fixed on a brass stub using double-sided tape and made electrically conductive by coating in


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vacuum with thin layer of carbon. The photographs were taken with a Pentax (model MZ-10) camera at an excitation voltage of 10 kV. And surface element composition of the adsorbents was evaluated by EDX system. Meanwhile, the spectra of solid acid derivative and βcyclodextrin were also recorded using spectrum 100 FTIR spectroscopy (Perkin Elmer & PIKE Technologies, USA) associated with diffuse reflectance accessory (DiffusIR™, PIKE Technologies, USA). Spectra acquisitions were performed in powder samples with the application of 30 scans at a resolution of 4 cm-1 over wave-number range of 4000-400 cm-1. The surface area and pore volume of solid acid derivative were determined by the BET method using BELSORP-max specific surface area & pore size distribution analyzer (MicrotracBEL Corp., Japan) in STD mode (p/p0=10-4 - 0.99). Then, thermal degradation behaviors of solid acid derivative and β-cyclodextrin were studied by means of thermogravimetric analysis (TGA). Experiments were performed in a thermal gravimetric analyzer (Q600 SDT, TA Instrument, USA) under flowing air using a heating ramp of 10 K/min up to 850K. From the TGA derivative curves, the peaks at different temperatures corresponded to the dehydration, oxidation and decomposition of the adsorbents. CO2 Adsorption/Desorption Isotherms. CO2 adsorption/desorption experiments were mainly performed at least three times for each sample using a gravimetric-IGA system (IGA-003, Hiden Isochema Ltd, Japan) at the temperatures of 298K/403K and pressure up to 3.5 bar, and also checked by volumetric method using BELSORP-max analyzer with 0-1 bar pressure range at 293K. The capacities of CO2 captured by the adsorbent (50-200 mg for testing) were obtained during every pressure step at different temperatures under a CO2 flow of 100ml/min. Meanwhile, the differential isosteric heat of CO2 adsorption, was calculated according to Clausius-Clapeyron


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equation (Eq.1) and the CO2 uptake rate was obtained from Eq.2, accompanying the selectivity expressed by molar ratio of adsorbed carbon dioxide to other gases (Eq.3).

(

Ri +1 =

∂ ln( p/p0 ) q )qCΟ = st 2 2 RT ∂T

( qi +1 − qi )

∆p ( 2t i +1 − 2ti ) p − p i +1 i ×

2

S=

(1)

(i =0,1,2,3, ▪▪▪)

(2)

2

qCΟ2

(3)

q N 2 / O2 / CH 4

where qst -isosteric heat of adsorption, J/mol; qCΟ2 -adsorbed amount of CO2 at certain pressure, mmol/g(adsorbent); p-gas pressure, bar; p0 -referred pressure, bar; T-adsorption temperature, K; R-universal gas constant, 8.314 J/K/mol; R i +1 -the gas uptake rate at i+1 gas pressure step; qi +1 ,

qi -gas adsorbed amount before and after i+1 gas pressure step; ti , t i +1 - starting time of CO2 2

adsorption and the time for adsorbed amount up to

qi +1 + qi at i+1 gas pressure step; pi , pi +1 2 2

initial pressure of CO2 adsorption and the pressure for adsorbed amount up to

qi +1 + qi at i+1 2

gas pressure step; ∆p -0.1bar; S-selectivity of carbon dioxide to other gases; qN 2 / O2 / CH 4 -the adsorbed amount of nitrogen, oxygen and methane, mmol/g(adsorbent) at certain pressure.

■ RESULTS AND DISCUSSION


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Adsorbent characteristics. The tests of SEM and BET of β-cyclodextrin aggregates and solid acid derivative were conducted to study surface morphology and pore structures; and the results are shown in Figure 1 and Table 1, respectively.

Table 1. BET test results of the adsorbents Sample

Specific surface area, m2/g

Pore volume, cm3/g

Mean pore size, nm

β-cyclodextrin aggregates

5.34

1.03×10-2

34

Solid acid derivative

211.10

3.82×10-1

7

As can be seen, β-cyclodextrin aggregates owned a heterogeneous blocky surface structure(Figure 1(a): scale bar-5µm and (b): scale bar-2µm), and exhibited only 5.34 m2/g of specific surface area and 1.03×10-2 cm3/g of pore volume with a mean pore size of 34 nm. In contrast, the solid acid derivative obtained after the modification by concentrated sulfuric acid, had a concave-convex surface and relatively homogeneous porous structure observed from its SEM images (Figure 1(c): scale bar-5µm and (d): scale bar-2µm), meaning it might have higher specific BET surface area and pore volume. Table 1 shows that the solid acid adsorbent exhibited 211.10 m2/g of specific surface area and 3.82×10-1 cm3/g of pore volume, which were 40 and 37 times higher than native β-cyclodextrin aggregates. Meanwhile, the mean pore size of solid acid derivative decreased into 7nm. The higher specific surface area and pore volume with decreased mean pore size of solid acid derivative, compared with β-cyclodextrin aggregates, indicated that the treatment with concentrated sulfuric acid led to the formation of porous structure of the derivative.


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Figure 1. The SEM images of the adsorbents-SEM-5µm-β-cyclodextrin aggregates(a), 2µm-βcyclodextrin aggregates(b),SEM-5µm-solid acid derivative(c), SEM-2µm-solid acid derivative(d)

Meanwhile, those functional groups on the surface of solid acid derivative were demonstrated by the results from EDX and FTIR spectra of β-cyclodextrin aggregates and solid acid derivative presented in Figure 2. Compared to β-cyclodextrin aggregates (Figure 2(a)), an obvious decrease of the oxygen content of solid acid derivative (Figure 2(b)) indicated a dehydration phenomenon existing during the acid treatment49. The dehydration phenomenon led to a decrease of the intensities of the FT-IR peaks (Figure 2(c)) between 3350 and 3450 cm-1 due to O-H stretching vibration. Meanwhile, a new peak of sulfur element appearing in the EDX spectrum of solid acid derivative accompanied by adsorption peak change between 1200 and 1300 cm-1 in the FTIR spectrum of solid acid derivative due to SO2 stretching vibration, demonstrated some amount of sulfonic groups (-SO3H) were successfully grafted on the surface of solid acid derivative50-52. In addition, the intensities of the peaks at 1158 cm-1 due to the C–O stretching vibration and


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between 1000 and 1100 cm-1 due to the C–O–C blending vibration were also obviously decreased so that the structure of as-prepared sample was considered as a mixture of sulfonated glucose and sulfonated cycodextrin. Some cavities of the cyclodextrin possibly disappeared due to the breaking of the glucosidic bond. Meanwhile, the decrease of the intensities of the peaks between 2800 and 2950 cm-1 due to C-H stretching vibration, the appearance of a new peak at 1701 cm-1 due to the C=O stretching vibration and an intensity increase of the peak between 1500 and 1650 cm-1 due to the ring vibration or C=C stretching vibration meant that partial carbonation of β-cyclodextrin aggregates happened in dehydration process with concentrated sulfuric acid. Therefore, the obtained solid acid derivative was considered as a polymer with the function groups of sulfonated glucose, sulfonated cycodextrin and carbon ring, which were mainly linked by ether linkage. The dehydration and crosslinking functions formed a number of smaller pores and led to higher pore volume compared with β-cyclodextrin aggregates. The grafting of sulfonic groups (-SO3H) created the concave-convex surface and resulted in the increase of specific surface area in conjunction with two functions above.

(a)

(b)

(c)

Figure 2. EDX/ FTIR spectra of β-cyclodextrin aggregates and solid acid derivative EDX image of β-cyclodextrin aggregates(a), EDX image-solid acid derivative(b), FTIR spectra of β-cyclodextrin aggregates and solid acid derivative(c)


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Subsequently, it is necessary to check the effects of dehydration and grafted sulfonic groups on the thermal stability of solid acid derivative. Figure 3 presents the TGA test results of solid acid derivative and β-cyclodextrins. For the both tested samples, there were two peaks related to their dehydration and thermal decomposition appeared in their differential weight curves under flowing air. As the first peak, β-cyclodextrin aggregates exhibited a 13.4% weight loss of its water content below 390K accompanying a maximum rate of weight loss (0.38%/K) at 357K and near 10 mol/mol(β-cyclodextrin) water contained in tested sample, similar with the previous report53. Then it began to decompose at 492K after a stable stage without weight loss between 390 and 491K. A rapid thermal decomposition near 610K might result from the release of oxygenated compounds and led to the second perk with a maximum rate of weight loss(3.02%/K) at 589K, followed by a relatively slow decomposition rate due to the carbonization of some amount of β-cyclodextrin aggregates after 610K, formed the residual at 850K54.

Figure 3. TGA tests of solid acid derivative (a) and β-cyclodextrin aggregates (b)


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Contrastively, solid acid derivative had a different trend of weight loss from β-cyclodextrin aggregates with increasing temperature. For dehydration as the first perk shown in its differential weight curve, it exhibited a lower water-adsorbing capacity (ca.5.9%) with the maximum rate of weight loss (0.066%/K) at 359K. Although the derivative was still relatively stable below 491K, a slight weight loss occurred due to the stronger interaction between water and solid acid derivative possibly caused by those hydrophilic groups such as -SO3H grafted on the surface of solid acid derivative. The stronger interaction possibly led to a simultaneous appearance of dehydration and thermal decomposition in the subsequent heating process, accompanying a slow thermal decomposition before 700K. The thermal decomposition was attributed to the release of surface groups from the surface of solid acid derivative. Furthermore, the temperature of 443K with minimum rate of weight loss (0.016%/K) was considered to be the initial decomposition temperature of solid acid derivative. After a slow thermal decomposition, a rapid thermal decomposition with a maximum rate of weight loss (1.02%/K) at 789K as the second perk happened after 700K due to the release of oxygenated compounds from ring structure in an oxidizing atmosphere, leading to the complete decomposition of solid acid derivative at 830K. The solid acid derivative exhibited improved thermal stability between 550K and 700K.

CO2 adsorption capacity. The CO2 adsorption on solid acid derivative was measured within the CO2 pressure range 0-3.5bar at 298 and 403K, and the results are shown in Figure 4. As seen from Figure 4(a), the capacity of CO2 adsorption on solid acid derivative increased with an increase of CO2 pressure, but decreased with a rise of temperature. For instance, the capacity of CO2 adsorption was 1.2mmol/g at 298K and 1bar, and then increased to 1.71mmol/g with increasing CO2 pressure to 3 bar but declined to 0.27mmol/g with increasing temperature to 403K. The downward trend of CO2 adsorption capacity with the increase of adsorption


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temperature indicated that CO2 adsorption on solid acid derivative is an exothermic process and decreasing the temperature is beneficial to improve the capacity of CO2 adsorption. In comparison with the trace amount of CO2 adsorption on β-cyclodextrin aggregates shown in Figure 4(b) (e.g. 0.04mmol/g at 1bar and 293K), CO2 adsorption capacities on solid acid derivative at low temperatures and 1bar (e.g. 0.76mmol/g measured by volume method at 293K) were at least 19 times higher than β-cyclodextrin aggregates and close to those of other polysaccharide base adsorbent reported elsewhere

12,13

, such as fiber-APS(mesoporous

silica/cellulose acetate hollow fibers with 3-aminopropyltrimethoxysilane) and fiber-PEI(hollow fibers infused with poly(ethyleneimine)). It was identified that the performance of CO2 adsorption were significantly improved by the modification of β-cyclodextrin aggregates with concentrated sulfuric acid.

Figure 4. Capacity changes of CO2 adsorption on solid acid derivative at different temperatures with gravimetric-IGA system (a) (a-adsorption at 298K;b-adsorption at 403K;c-Langmuir model with adjusted R-squared value of 0.994; d-Langmuir model with adjusted R-squared value of 0.997); on different samples at 293K with BELSORP-max analyzer(b) (e-adsorption on solid acid derivative; f-desorption from solid acid derivative; g-adsorption on β-cyclodextrin aggregate; h-desorption from β-cyclodextrin aggregate)


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Thermodynamic analysis. Curve fitting (c and d in Figure 4(a)) showed that CO2 profiles complied well with Langmuir model under CO2 pressure below 3 bar regardless of the temperature was 298K or 403K, indicating that CO2 capture under low CO2 pressure could be considered as a monolayer adsorption process. According to the calculated results from Eq.1, Figure 5 shows that the isosteric heat of CO2 adsorption on solid acid derivative changed in the range from 23.5 to 24.8 kJ/mol with the error range of ±0.5kJ at 0.2 mmol of adsorbed CO2, implying that CO2 adsorption on solid acid derivative was not only a physical adsorption process. And the declining tendency of isosteric heat with an increase of the amount of CO2 adsorbed indicated that the interaction between CO2 adsorbed in subsequent steps and the functional groups on the surface of solid acid derivative became weaker with the increase of equilibrium pressure. The formation of hysteresis loop with an inconsistent phenomenon between the adsorption and desorption profiles just as shown in Figure 4(b) might be attributed to short pace time at certain pressure. The short pace time led that the equilibrium status of CO2 adsorption between gas phase and the adsorbent surface was not completely achieved at certain pressure

so

that

obtained

adsorbed

amount

of

CO2

was

lower

than

the

equilibrated adsorption capacity with increasing pressure in adsorption processes and higher than the equilibrated adsorption capacity as CO2 pressure decreased in desorption processes.


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Figure 5. Isosteric heat of CO2 adsorption

Carbon dioxide uptake rate. Figure 6 presents the apparent change of CO2 uptake rate obtained based on Eq.2 via pressure and temperature under the pressure derive force of 0.1bar. At a certain temperature, the uptake rate of CO2 could be considered as a power function of CO2 pressure. With increasing CO2 pressure from 0.1 to 3.5 bar, it decreased from 7.97 to 0.19 µmol/min at 298K and dropped from 4.41×10-2 to 6.30×10-3 µmol/min at 403K. The declining tendency of CO2 uptake rate with increasing pressure was attributed to the dependence of the on both pressure difference (P-P*) and the rate constant of CO2 adsorption which is related to the amount of CO2 adsorbed in previous adsorption step. Using the same pressure difference (P-P*) of 0.1bar as an example, the uptake rate of CO2 at 3.5bar was lower than that at 0.1bar. This is attributed to the steric effect of CO2 adsorbed in previous adsorption step, which weakened the interactions between CO2 molecules in subsequent adsorption step and grafted groups on the surface of solid acid derivative with an increase of CO2 adsorbed amount, accompanied by increasing gas pressure. The weak interaction resulted in the lowering of rate constant of CO2


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adsorption so that the declining of CO2 uptake rate with increasing pressure was observed. Meanwhile, at a given CO2 pressure, the apparent uptake rate of CO2 declined with the increase of adsorption temperature. For instance, it decreased to 4.41×10-2 µmol/min from 7.97µmol/min at 0.1bar and dropped from 0.19µmol/min to 6.30×10-3 µmol/min at 3.5 bar with increasing temperature from 298K to 403K, accompanying a change by two orders of magnitude. The decrease tendency of CO2 uptake rate with increasing temperature was caused by an exothermic effect during CO2 adsorption. The exothermic effect resulted in a higher promotion of desorption rate than adsorption rate with increasing temperature so that the apparent uptake rate of CO2 declined.

Figure 6. Uptake rate of carbon dioxide at 298K(a); 403K(b)

Selectivity of carbon dioxide. The selectivity of CO2 adsorption is significantly important for solid acid derivative in its application for gaseous phase catalytic synthesis and gas adsorption. Therefore, the adsorptions of N2, O2 and CH4 were also tested in this work and the results are shown in Figure 7. Figure 7(a) shows that all the adsorption capacities related to N2, O2 and CH4 increased with the increase of gas pressure just like CO2. Thereof, the amount of CH4 adsorbed


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was the highest, followed by O2 and N2, as a case of the adsorption amounts of 0.49mmol/g for CH4, 0.21mmol/g for O2 and 0.13mmol/g for N2 at 3 bar and 298K.

Figure 7. Adsorption selectivity of carbon dioxide-the amounts of N2, O2 and CH4 adsorbed on solid acid derivative at 298K(a) (a-nitrogen; b-oxygen; c-methane); adsorption selectivity of carbon dioxide at 298K(b) (d-CO2 to N2; e-CO2 to O2;f-CO2 to CH4)

According to Eq.3, the molar ratio of CO2 to N2 changed in the range from 8.9 to 15.1, followed by the molar ratio of CO2 to O2 and CO2 to CH4 declining from 19.7 to 7.8 and 8.9 to 3.4, respectively, with the increase of gas pressure from 0.3 to 3.5bar (Figure 7(b)), indicating that the adsorbent had high adsorption selectivity of CO2 over N2, O2 and CH4 at low pressure. In consideration of flue gas components (15% of CO2, 78% of N2 and 7% of O2), the selectivity of CO2 to N2 calculated according to the IAST method36, 37 (selectivity = amount of CO2 adsorbed at 0.15 bar/ amount of N2 adsorbed at 0.78 bar×0.78/0.15) was 24.8; and the selectivity of CO2 to O2 was 16.1 based on the similar equation. The results demonstrated that the solid acid derivative was suitable for CO2 separation from flue gas. It is worth mentioning that the adsorbent exhibited an interesting characteristics of gas adsorption. There was no adsorption of N2 at 77K for as-


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prepared solid acid derivative. The CO2 uptake capacity of the derivative as adsorbent was increased with decreasing the temperature; but meanwhile its N2 uptake capacity was decreased with lowering the temperature. As a result, the high adsorption selectivity of CO2 to N2 could be obtained at a relatively low temperature.

■ CONCLUSION A solid acid adsorbent based on β-cyclodextrin aggregates was successfully prepared for CO2 capture. The adsorption properties were investigated at different temperatures and gas pressures. In addition, the surface characteristics of the adsorbent were revealed with the analysis from SEM, EDX, BET, FTIR and TGA. The capacity of CO2 adsorption on solid acid derivative increased with increasing pressure, but decreased with the increase of temperature, which was up to 1.71mmol/g at 298K and 3bar. The adsorption isotherm of CO2 profiles complied with Langmuir model, accompanying exothermic process. In comparison with β -cyclodextrin aggregatezs, solid acid derivative had a higher capacity of CO2 adsorption at low temperature and better selectivity of CO2 over N2, O2 and CH4 at low pressure.

■ AUTHOR INFORMATION Corresponding author: *E-mail: [email protected]/[email protected], Tel: 1-506-453-3532

Notes The authors declare no competing financial interest. ■ ACKNOWLEDGMENTS


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The research is supported by the Fundamental Research Funds for the Central Universities in China, the Science & Technology Planning Project of Hebei (No.15273706D), CSC and NSF China (Grant #: 51379077 and # 21466005) and NSERC Canada.

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Captions Figure 1. The SEM images of the adsorbents Figure 2. EDX/ FTIR spectra of β-cyclodextrin aggregates and solid acid derivative Figure 3. TGA tests of solid acid derivative and β-cyclodextrin aggregates Figure 4. Capacity changes of CO2 adsorption on solid acid derivative at different temperatures Figure 5. Isosteric heat of CO2 adsorption Figure 6. Uptake rate of carbon dioxide Figure 7. Adsorption selectivity of carbon dioxide Table 1. BET test results of the adsorbents


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Adsorption Characteristics of Carbon Dioxide Gas on a Solid Acid

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