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SN Applied Sciences

, 1:1031 | Cite as

CO2 adsorption in hydrochar produced from waste biomass

  • Helida M. C. FagnaniEmail author
  • Cleiser T. P. da Silva
  • Murilo M. Pereira
  • Andrelson W. Rinaldi
  • Pedro A. Arroyo
  • Maria A. S. D. de Barros
Research Article
  • 30 Downloads
Part of the following topical collections:
  1. Earth and Environmental Sciences: Environment, Energy and Engineering Strategies for Sustainability (E3S)

Abstract

Sugar and ethanol plants produce a large amount of sugarcane bagasse. Such biomass can be the raw material for the production of an adsorbent to uptake CO2. Thus, this work aimed to evaluate the hydrocarbonization of sugarcane bagasse and to study its use as a CO2 adsorbent from a simulated flue gas. The temperature of the hydrothermal carbonization (HC) was set at 220 °C, while the operating time ranged from 12 to 48 h. Through the SEM–EDS analysis, the 48-h sample (HC48) was selected for chemical activation with KOH, resulting in activated hydrochar (AHC). The CO2 and N2 simple adsorption isotherms were obtained at 50, 70 and 80 °C. The results have shown a higher adsorption at a temperature of 50 °C for both gases. Activated hydrochar clearly preferred CO2 instead of N2 at 100 kPa as the maximum adsorption was 1.99 and 0.207 mmol g−1, respectively. The highest selectivity of CO2/N2 was 12–50 °C, according to the “Ideal adsorbed solution theory” model. Therefore, AHC is clearly an eco-friendly adsorbent that can be used to minimize the resulting release of climate-damaging CO2 from flue gas to atmosphere.

Keywords

CO2 adsorption Purification of the flue gas Hydrochar from sugarcane bagasse Biomass residue for gas purification 

1 Introduction

Large-scale ethyl alcohol production promoted the development of renewable energies related to the wastes of the sugarcane industry. This sector generates a huge amount of bagasse that is already used in heat and energy generation [1], in paper and pulp industries and in biochemical industries [2]. Bagasse can also be used as feedstock for the construction sector, animal food and furfural [2]. Other uses include bioelectricity and second-generation ethanol [2]. Nevertheless, bagasse production is much higher than its consumption, which justifies the research and development of new applications for it.

The Brazilian industrial scenario is based on boilers, which use air as a source of oxygen for burning and releasing of flue gas at atmospheric pressure, which is composed of N2 (85%) and CO2 (15%) [3]. As CO2 is a well-known greenhouse gas, its liberation into the environment should be avoided.

A promising technology used for the treatment of flue gas is adsorption. The removal efficiency through this process takes into account the physicochemical properties of each adsorbate. The nitrogen molecule has a kinetic diameter of 0.364 nm, while the carbon dioxide molecule is a fraction smaller (0.330 nm) [4]. Despite the similarities between both kinetic diameters, which would promote similar diffusion characteristics into adsorbent pores, the adsorption process can be influenced by the difference in the electronic property of each component. Note that the N2 and CO2 molecules have linear geometries but N2 has a very short triple-bond nonpolar character, whereas CO2 has a linear geometry, nonpolar character, but, polar bonds. In addition, CO2 also contains a large quadrupole moment that is capable of inducing specific interactions such as hydrogen bonding [4]. Such characteristics may strongly influence the adsorption process of such gases.

CO2 released to the atmosphere from industrial processes may be minimized through adsorption. Adsorbents for such purpose include activated carbons, zeolites, MOFs and mesoporous silica. Activated carbons may be synthesized through a wide range of raw materials, including the ones from vegetal sources such as biomass wastes [5]. Spite biomass wastes have low costs, and some drawbacks are already present such as relatively low selectivity in operation. To overcome them, carbonization should be considered as a promising CO2 adsorbent after some chemical modification that may provide higher alkalinity [6].

The bagasse is composed by cellulose fibers, lignin and hemicellulose [1]. With its lignocellulosic structure being constituted by macropores (diameter > 50 nm) [7], the sugarcane bagasse is considered as an excellent raw material for carbon.

Carbons may be obtained by pyrolysis or hydrothermal carbonation (HCT). The former occurs at high temperatures and forms the bio-oil linker, whereas the latter is carried out at lower temperatures and requires water as the solvent, which is compatible with eco-friendly routes [5]. The HCT process occurs in mild conditions (150–250 °C) and provides low CO2 emissions [8, 9]. It is influenced not only by temperature and reaction time, but also by its raw material as well as to the ratio between biomass and water that is placed in the reactor [10].

Temperature is by far the most important parameter in the HTC process because it is related directly to the biomass conversion into products in the solid, liquid and gas phases [5, 8]. As temperature is inversely proportional to the solid production, the range of different liquid and gaseous products intensifies with higher temperatures. Generally, the solid product is dominant in the temperature ranges of 150–220 °C [8, 10]. Naturally, the influence of reaction time should not be neglected; it defines the composition of the product as well as the total biomass conversion until a certain period. After that, the time has no impact on the process [10]. The products differ in short and long times of reaction and in high and low temperatures; so these two parameters should be investigated simultaneously.

Unfortunately, hydrochar has a low surface area [11], a characteristic that is not desired for adsorption purposes. The correction of this deficiency can be made by the hydrochar activation [7, 12]. As a consequence of this activation, the lignocellulosic biomass is activated as well, resulting in the formation of highly porous activated carbons, which are necessary for CO2 removal from combustion processes [13].

The activation can be physically or chemically performed. The chemical activation always happens when the carbon is impregnated or mixed with a chemical activating agent [14], and subjected to a thermal treatment in an inert atmosphere (usually helium or argon gas). Among the activation agents, KOH promotes the formation of samples with high superficial areas with narrow pore distribution [11] and a larger number of functional groups [15]. Such features favor the attraction of CO2 by the material at a sub-atmospheric pressure [16].

Adsorption in porous solids has been proposed as a viable alternative for the treatment of the flue gas [17, 18, 19]. However, in order to improve the efficiency of the adsorption process, the adsorbent should have not only a high adsorption capacity, but also a high selectivity [20] in addition to being easily regenerated [21]. The regeneration degree of the adsorbent can be determined by calculating its isosteric heat of adsorption [17].

Therefore, the present work aims to evaluate the HCT process of agro-industrial residue as a carbon source and to study its use as a CO2 adsorbent. Due to the vast sugarcane industry in Brazil, bagasse was chosen as the raw material for carbonization purposes. Single gas adsorption of CO2 and N2 was carried out at different temperatures (50, 70 and 80 °C) and pressures up to 100 kPa. The simulated flue gas was investigated through the ideal adsorbed solution theory (IAST) [22]. CO2/N2 selectivity was predicted, while the isosteric heat of adsorption was calculated by the Clausius–Clapeyron method.

2 Materials and methods

2.1 Bagasse collect and storage

Sugarcane bagasse was kindly donated by an alcohol plant located in the northern region of Paraná, Brazil. As soon as the bagasse was collected, it was dried up in an oven at 50 °C for 2 days and sieved with a particle size of less than 0.841 mm. The sample was then stored in the absence of light and moisture.

2.2 Synthesis and characterization of hydrochars

The HTC reactions occurred in Teflon® reactors, externally coated by 30-mL stainless steel cylinders. In each reactor, 0.500 g of sugarcane bagasse was added to 20 mL of deionized water. The system was heated at a rate of 10 °C min−1 up to 220 °C, and kept constant at this temperature for 12, 24, 36 and 48 h to produce the samples HC12, HC24, HC36 and HC48, respectively. After cooling back to room temperature, the hydrochar samples were filtered, and oven dried at 105 °C for 5 h. The hydrochar synthesis was carried out in duplicates.

An energy dispersive X-ray spectrometer (EDS) was used for qualitative analysis, along with the scanning electron microscopy (SEM) in all hydrochar samples. The solid was gold sputter coating in the Quorum metallizer, model Q150RES. Subsequently, the samples were observed in the Zeiss model EVO/MAI 15.

The hydrochar with the highest carbon concentration was submitted to activation and underwent textural characterization and infrared spectroscopy analysis by attenuated total reflectance (ATR–FTIR). ATR–FTIR analysis was carried out in the Varian 700 FTIR spectrometer with a germanium crystal in the range of 4000–700 cm−1 with a resolution of 2 cm−1. The textural characterization was performed using Micromeritics equipment, model ASAP 2020. First, a vacuum pre-treatment of 10−3 kPa was done for 4 h at a temperature of 300 °C. Secondly, the sample was exposed to N2 adsorption/desorption. Measurements were performed at 77 K.

2.3 Activation of hydrochar

The activation of the selected sample was based on the methodology described elsewhere [15]. Two grams of the selected hydrochar sample were added to 250 mL of a 40 g L−1 KOH solution. The suspension was stirred for 10 min on a magnetic stirrer, heated to 150 °C, and maintained at this temperature until the volume was reduced to 10 mL. Then, a reactor was used with an argon flow rate of 500 mL min−1, and the system was heated at a rate of 25 °C min−1 up to 800 °C and kept at this temperature for 45 min. After being cooled down to room temperature, the activated hydrochar (AHC) sample was washed three times with 200 mL of deionized water and finally, oven dried for 12 h at a temperature of 120 °C.

The AHC sample was also analyzed by textural characterization (nitrogen adsorption/desorption isotherm) and ATR–FTIR analysis.

2.4 Adsorption in the activated hydrochar

The AHC sample was used in single adsorption of CO2 (purity 99.99%) and N2 (purity 99.999%). As the usual temperature of flue gas is around 50 °C [16], adsorption isotherms were obtained at 50, 70 and 80 °C. The latter two temperatures were investigated to predict a breakdown in the downstream cooling system. Temperatures higher than 80 °C were not presented herein because preliminary results indicated a negligible adsorption capacity of both gases. Micromeritics brand ASAP 2020 equipment was used to carry low partial pressure (up to 100 kPa) isotherms. The experimental procedure followed the manual instructions of the equipment. Temperature accuracy was ± 0.1 °C. A brief description includes sample treatment and the gas adsorption. Firstly, sampling was performed under a vacuum of 10−3 kPa for 4 h at 300 °C. At this point, the treated sample was exposed to a stream of CO2 or N2 gas with a pressure ranging from 0.1 to 100 kPa (P0) to perform the adsorption isotherm. The adsorption models of Langmuir (Eq. 1) [23] and Sips (Eq. 2) [24] were used to represent experimental data.
$$q_{\text{eq}} = \frac{{q_{\hbox{max} } \cdot b \cdot P}}{1 + b \cdot P}$$
(1)
$$q_{\text{eq}} = \frac{{q_{\hbox{max} } \cdot \left( {b \cdot P} \right)^{1/n} }}{{1 + \left( {b \cdot P} \right)^{1/n} }}$$
(2)
where \(q_{\text{eq}}\) is the amount adsorbed; \(q_{\hbox{max} }\) is the saturation capacity; \(P\) is the gas phase pressure; \(b\) is a constant, and \(n\) is a parameter representing the system heterogeneity.
The CO2 selectivity of the CO2/N2 binary mixture is presented in Eq. 3 [17] where \(x\) refers to the molar fraction in the adsorbed phase, and \(y\) refers to the molar fraction in the gas phase. The value of \(x\) was estimated by the ideal adsorbed solution theory (IAST), which developed by Myers and Prausnitz [22], is widely accepted [25].
$$S_{1/2} = \frac{{x_{1} /x_{2} }}{{y_{1} /y_{2} }}.$$
(3)

2.5 Isosteric heat of adsorption

In order to calculate the isosteric heat of adsorption, a Clausius–Clapeyron method [26] was used, with an adsorbed amount of isotherms obtained at low pressures, as represented in Eq. 4:
$$Q_{\text{ST}} = - R\left[ {\frac{{\partial \left( {\ln P} \right)}}{{\partial \left( {\frac{1}{T}} \right)}}} \right]_{{n_{\text{a}} }}$$
(4)
where \(n_{\text{a}}\) is the specific amount adsorbed at a pressure \(P\) (bar) and temperature \(T\) (K). A plot of \(\ln P\) against \(1 \cdot T^{ - 1}\) gives a straight line whose slope represents \(Q_{\text{ST}} /R\), in which \(Q_{\text{ST}}\) is the isosteric heat of adsorption (J mol−1) and R is a gas constant (J mol−1 K−1). For the calculation of the isosteric heat, different amounts of adsorbed CO2 and N2 were used in the AHC, in the range of zero to the highest adsorption capacity for each gas in the three temperatures investigated [27].

3 Results and discussion

3.1 Activated hydrochar production

As hydrocarbonization proceeds, hydrogen and oxygen compounds are released to the aqueous environment, while the solid phase becomes richer in carbon [11], which consequently explains the decreasing content of hydrogen and oxygen as the hydrocarbonization continues (Fig. 1) [1]. In conclusion, time is extremely important in the hydrochar synthesis; hence, the hydrochar of 48 h (HC48) had the highest amount of carbon (70.94%) and lower yield mass (40.13%), which are close to the previously reported results [28].
Fig. 1

Energy dispersive X-ray spectrometer

As expected, scanning electron microscopy (SEM) was able to provide clear distinction in the original biomass when compared to the hydrochar samples, as shown in Fig. 2. As samples are coated whit a thin layer of gold, the micropores are not visible in the SEM images. However, adsorption/desorption isotherms of N2 demonstrates that the AHC sample has microporous characteristics. It also highlights the presence of microspheres or irregular particles, which is a consequence of the low hydrocarbonization temperature [29] that is associated with a range of distinct functional groups such as carbonyl, hydroxyl, carboxylic, ester, and quinone [9]. These structures are more often present in higher running times of hydrocarbonization [1]. This is exemplified by the hydrochar sample obtained at 48 h (HC48) (Fig. 2e), where more disruption of the cellulose molecules in the raw biomass material had probably occurred.
Fig. 2

Scanning electron spectroscopy: a in sugarcane bagasse; and hydrochars of: b 12 h; c 24 h; d 36 h; e 48 h

According to the EDS and SEM analysis, the HC48 was chosen as the best sample to be activated and used in adsorption. The mass yield of the activation was 17.23%, in other words, the total mass yield of the hydrochar production and activation process was 6.91%.

Following this, HC48 and its activated form, AHC, were submitted to characterization. The adsorption/desorption N2 isotherm at 77 K of both samples is shown in Fig. 3. The pore distribution is shown in Fig. 4. The adsorption/desorption isotherm of HC48 (Fig. 3a) is classified as type IV, which is a characteristic of mesoporous materials [30]. As expected, the pore distribution of HC48, as shown in Fig. 4a, has a wide range of large pore diameters, with an average pore diameter of 28.3 nm as estimated by the Barrett–Joyner–Halenda (BJH) method. Nevertheless, the AHC isotherm (Fig. 3b) is classified as type I(b), which indicates that the material has a pore size distribution in the range of larger micropores and possibly narrow mesopores, which can be observed in the pore distribution (Fig. 4b). Pores measuring below 1.0 nm and pores between 1.0 and 4.0 nm can be observed. This fact is in agreement with results already reported by [31, 32]. The specific surface area calculated by the BET method of HC48 and AHC samples is 13 m2 g−1 and 2080 m2 g−1, respectively. The HC48 pore volume is 0.0941 cm3 g−1, in which only 0.0101 cm3 g−1 is of micropores, whereas for the AHC, the volume of micropores is 1.246 cm3 g−1 of the total of 1.316 cm3 g−1. Due to the significant increase in the specific surface area and microporosity, the AHC may be successfully used in adsorption.
Fig. 3

Isotherms of adsorption/desorption of N2 of a HC48; b AHC

Fig. 4

Pore size distribution of: a HC48; b AHC

According to the ATR–FTIR analysis of the HC48 and AHC, as shown in Fig. 5, the characteristic bands of sugarcane bagasse, such as cellulose (900 cm−1 deformation of C–H), hemicellulose (1163 cm−1 C–O–C vibration) and lignin (region of 1000–1500 cm−1) [9], are observed in the HC48 sample, although they are not seen in the AHC sample. There was disruption of the remaining structures during activation for the formation of pores, also reported in the spectrum [12]. Moreover, there was the detection of more intense bands in the region of 1800–2800 cm−1 in HC48, suggesting the break of chemical bonds during the activation process. This fact occurs mainly due to the rupture of the spherical morphology present in the HC48 [9]. However, the bands 2920 cm−1 and 2830 cm−1 are present in both HC48 and AHC and are attributed to the C–H vibration elongation of carboxylic acids [12, 33]. Yet, the band at 1640 cm−1 in HC48 is related to the elongation vibration of the C=O in the carbonyl [12]; this band decreased in intensity and suffered displacement in AHC. The 1026 cm−1 band seen in the AHC sample is attributed to elongation of the C–O–C bonds, which may be present in esters [33] and had its intensity increased after activation. Finally, samples of HC48 and AHC contain a band between 3000 and 3600 cm−1 bands, which are attributed to the O–H stretching vibrations in hydroxyl or carboxylic groups [34, 35], are also seen in the KOH spectrum [36]. Such group allows the adsorption of acidic compounds in the material such as CO2. Moreover, AHC has a high surface area with pronounced microporosity and narrow mesopores. These features may also contribute to CO2 adsorption [16].
Fig. 5

ATR–FTIR of HC48 and AHC

3.2 Gas adsorption and selectivity

The adsorption isotherms are presented in Fig. 6. In analyzing those isotherms, it comes to the conclusion that at the lowest temperature of 50 °C, it had the highest amount of adsorption over the whole pressure range. In this way, agreeing with previous works where physisorption is the predominant mechanism in gas adsorption [16].
Fig. 6

Adsorption isotherms at different temperatures of: a CO2; b N2

The adsorption of CO2 in the AHC was higher than N2. At the conditions of 50 °C and 100 kPa, the adsorption capacity was 1.99 mmol g−1 and 0.207 mmol g−1 of CO2 and N2, respectively. Discrepancies in the adsorption capacity are a consequence of the differences in physicochemical properties of the gaseous phase. Indeed, the quadrupole moment of CO2 is responsible for the electrostatic interactions of such molecules with the basic Lewis sites present on the AHC surface (mainly OH). On the other hand, the nonpolar nitrogen molecule is less attracted to the superficial groups of activated hydrochar.

By means of the monocomponent adsorption isotherms at the three different temperatures investigated herein, the isosteric adsorption heat (QST) was calculated. Results are present in Fig. 7. The equilibrium amount varied from 0.04 up to 0.80 mmol g−1 for CO2, whereas values between 0.004 and 0.088 mmol g−1 were observed for N2. It is seen that the QST value decreases with increasing uptake amount, which may be related to the heterogeneity of adsorption sites (based on the theory of the Langmuir isotherm model). In addition, at the beginning of the adsorption, there are a large number of vacant pores on the surface of the AHC. So the CO2 and N2 molecules interact directly with the adsorbent surface through van der Waals forces. As the pores are filled, the van der Waals force decreases. As a consequence, the isosteric adsorption heat reduces [27]. The mean value of QST for was between 38 and 39 kJ mol−1 for CO2, which is in agreement with previous results [3, 35]. QST values in the range of 30–31 kJ mol−1 were estimated for N2 molecules. In both the cases, the exothermic behavior of the physisorption process was verified [37]. The higher the value of QST, the stronger is the interaction between the gas and the AHC. Therefore, the isosteric adsorption heat shows the selectivity CO2 > N2. In fact, this result was already expected due to the physicochemical characteristics of the adsorbates previously mentioned in characterized AHC.
Fig. 7

Isosteric adsorption heat of CO2 and N2 in AHC

The isosteric adsorption heat values estimated in this paper were slightly higher than those already reported [3] for CO2 and N2 adsorbed in activated carbon. However, the values are still low, suggesting that a physical adsorption occurs [38], in order to allow the adsorbent to regenerate [21].

To predict the adsorption equilibrium behavior of the gases over a wide temperature and pressure range, the Langmuir and Sips adsorption models were used (Fig. 8). The parameter adjustments to the experimental data are in Table 1 for Langmuir and Table 2 for Sips models. Although the Langmuir model was the one with the highest R2 and the lowest \(\chi^{2}\) for the adsorption of CO2, the Sips model was the best fit for N2 adsorption data in AHC. The N2 adsorption isotherm at 80 °C was poorly represented by both models, due to its low adsorption capacity.
Fig. 8

Adjustment of the Langmuir and Sips models at the temperatures of 50, 70 and 80 °C for the gas: a CO2; b N2

Table 1

Parameters obtained for the adjustment of the Langmuir model in the adsorption of CO2 and N2 at different temperatures

Gas

Temp. (°C)

\(q_{\hbox{max} } \left( {{\text{mmol}} \cdot {\text{g}}^{ - 1} } \right)\)

\(b \left( {{\text{kPa}}^{ - 1} } \right) \left( {10^{ - 4} } \right)\)

\(R^{2}\)

\(\chi^{2}\) \(\left( {10^{ - 6} } \right)\)

CO2

50

9.146 ± 0.9760

26.46 ± 3.393

0.9970

1220

 

70

6.944 ± 0.7900

20.22 ± 2.659

0.9981

309.8

 

80

5.829 ± 0.9029

15.77 ± 2.742

0.9977

165.0

N2

50

1.483 ± 0.1097

15.85 ± 1.315

0.9995

2.467

 

70

1.384 ± 0.4885

10.27 ± 3.917

0.9944

9.752

 

80

0.2855 ± 0.09146

36.34 ± 14.76

0.9590

28.55

Table 2

Parameters obtained for the adjustment of the Sips model in the adsorption of CO2 and N2 at different temperatures

Gas

Temp. (°C)

\(q_{\hbox{max} } \left( {{\text{mmol}} \cdot {\text{g}}^{ - 1} } \right)\)

\(b \left( {{\text{kPa}}^{ - 1} } \right) \left( {10^{ - 3} } \right)\)

\(n\)

\(R^{2}\)

\(\chi^{2}\) \(\left( {10^{ - 6} } \right)\)

CO2

50

3.133 ± 0.5243

12.71 ± 3.334

0.7721 ± 0.08213

0.9873

5200

 

70

2.108 ± 0.4449

10.68 ± 3.211

0.7336 ± 0.08168

0.9875

2010

 

80

1.445 ± 0.3342

10.42 ± 3.441

0.7403 ± 0.08768

0.9857

1040

N2

50

0.8250 ± 0.09429

3.535 ± 0.5610

0.9233 ± 0.01924

0.9996

1.761

 

70

0.4746 ± 0.05529

4.641 ± 0.6721

0.7997 ± 0.01962

0.9994

1.046

 

80

0.2897 ± 0.1516

4.942 ± 3.084

0.7660 ± 0.08523

0.9880

8.388

IAST methodology was used to predict the selectivity of CO2/N2 for the flue gas (15/85 vol%) at steady temperatures, along with pressure ranging from 0 to 100 kPa. Results are shown in Fig. 9. The CO2 isotherms were adjusted to the Langmuir model, whereas N2 used the Sips model.
Fig. 9

CO2/N2 selectivity for the combustion gas calculated by IAST at the different test temperatures

In all temperatures, the CO2/N2 selectivity was higher at low pressures and decreased to a close constant selectivity of 12 from 40 up to 100 kPa. At low pressures, the competition to adsorption sites is negligible. In this case, AHC strongly prefers CO2 molecule due to the quadrupole–dipole interaction between gas–solid. This fact can also be related to isosteric adsorption heat (Fig. 7). In such condition, heat reaches higher values for both gases. From 40 to 100 kPa, at 70 and 80 °C, selectivity remains in the ratio of 12 molecules of CO2 to 1 molecule of N2. That is, after filling the first adsorbent sites, the uptake amount of CO2 gas decreases relative to the uptake amount of N2 gas. With increasing pressure, N2 molecules are pushed to the adsorption sites. Thus, the chemical structure of the molecule has minor influence in the equilibrium of adsorption. This fact is also observed in the isosteric adsorption heat (Fig. 7). The CO2 isosteric heat decreases as the adsorption occurs, whereas the N2 remains almost constant. At 50 °C, the selectivity increases slowly, but the average is also close to 12 molecules of CO2 to 1 molecule of N2. Results reported in the literature of CO2/N2 selectivity of the flue gas in carbon are presented in Table 3.
Table 3

CO2/N2 selectivity of the flue gas found in the literature

Adsorbent

Temp. (°C)

Pressure (kPa)

CO2 uptake (mmol g−1)

Selectivity

References

Activated carbon honeycomb monolith

26

100

2.5

6.5

[3]

Activated hydrochar of sawdust

25

100

4.8

5.4

[32]

Nanostructured templated carbon by tuning surface area and nitrogen doping

25

101.3

4.0

6.1

[39]

Ordered mesoporous carbon

25

100

3.0

10

[21]

Activated microporous carbon compartments

25

100

3.5

16

[19]

Magnetic activated lignin from eucalyptus and spruce

50

100

4.0

3.2

[40]

Carbon monoliths

47

105

3.0

12

[18]

Palm kernel shell-based activated carbon

25

101.3

2.1

7.0

[27]

Nitrogen-doped biocarbons derived from rotten strawberries

25

100

4.3

16

[41]

Activated hydrochar of sugarcane bagasse

50

100

2.0

12

This paper

The major advantage of the hydrochar here investigated is higher when compared to many other activated carbons and hydrochars (Table 3) or as large as Querejeta et al. [18]. Therefore, hydrochars from sugarcane bagasse are a promising adsorbent for CO2 removal, specifically, when it comes to the purification of the flue gas.

4 Conclusions

In this paper, activated hydrochar was obtained from sugarcane bagasse through an eco-friendly route. The best HC sample was obtained after 48 h. Its activated sample (AHC) generated a microporous material with high specific surface area and important alkaline superficial groups such as hydroxide, responsible for the retention of the acid gas CO2.

Physisorption seems to be the preferred removal mechanism with the lowest temperature of 50 °C. The isosteric adsorption heat of CO2 was 77.10 kJ mol−1 and N2 of 30.89 kJ mol−1. These values are in agreement with such mechanism. AHC has much more affinity to CO2 than to N2, and the CO2/N2 selectivity was estimated at 12 according to the IAST model.

According to results presented herein, AHC is a proven CO2 adsorbent that can be efficiently used to minimize the greenhouse effects.

Notes

Compliance with ethical standards

Conflict of interest

On behalf of all authors, the corresponding author states that there is no conflict of interest.

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Copyright information

© Springer Nature Switzerland AG 2019

Authors and Affiliations

  1. 1.Department of Chemical EngineeringState University of MaringáMaringáBrazil
  2. 2.Laboratory of Materials Chemistry and Sensors - LMSenState University of MaringáMaringáBrazil
  3. 3.University of Technology of Paraná – UTFPRApucaranaBrazil

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