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Article

Waste Biomass Based Carbon Aerogels Prepared by Hydrothermal-carbonization and Their Ethanol Cracking Performance for H2 Production

by
Jialin Zhang
1,
Song Hu
1,2,
Yong Ding
3,
Rui Huang
2,
Qiangqiang Ren
1,*,
Sheng Su
1,2,
Yi Wang
1,2,
Long Jiang
1,2,
Jun Xu
1,2 and
Jun Xiang
1,2
1
State Key Laboratory of Coal Combustion, School of Energy and Power Engineering, Huazhong University of Science and Technology, Wuhan 430074, China
2
China-EU Institute for Clean and Renewable Energy, Huazhong University of Science and Technology, Wuhan 430074, China
3
China Energy Jiangxi New Energy Industry Company Ltd., Nanchang 330000, China
*
Author to whom correspondence should be addressed.
Processes 2023, 11(3), 892; https://doi.org/10.3390/pr11030892
Submission received: 28 February 2023 / Revised: 11 March 2023 / Accepted: 14 March 2023 / Published: 16 March 2023
(This article belongs to the Section Environmental and Green Processes)
Browse Figures
Versions Notes

Abstract

:
Biomass occupies a significant proportion of municipal solid waste. For the high-value processing of waste biomass, a hydrothermal-carbonization method was chosen because of the advantages of effective and mild conditions. Four typical types of waste biomass (banana peel, mangosteen peel, orange peel, and pomelo peel) were used in this work to prepare high-value carbon aerogels (CA) via hydrothermal-carbonization treatment for cracking ethanol. Four kinds of CA all had good performances in the ethanol cracking reaction and improved the yield of H2 from 21 wt% to about 40 wt%. The banana peel-based carbon aerogel (BPCA) showed the best performance in the reaction; it cracked ethanol and obtained 41.86 wt% of H2. The mechanism of ethanol cracking by CA was revealed: On one hand, the self-cracking of ethanol was improved due to the extension of residence time, which benefited from the abundant pores in CA. On the other hand, the heterogeneous reaction occurred on the surface of CA where the inorganic components, mainly Ca, Mg, and K, can promote the bond-breaking and reorganization in ethanol. The CO2 in byproducts was also fixed by Ca and Mg, improving the positive cracking reaction.

1. Introduction

The generation of municipal solid waste (MSW) is closely related to different factors, such as industrial and economic development [1]. About 60% of municipal solid waste is organic waste biomass, including food residue, leaves, fruit peels, and manure [2]. Landfilling for waste biomass is preferred in many municipalities globally, which leads to the pollution of landfill gases and leachate, as it is difficult to deal with high-moisture waste biomass [3]. Thus, there is an urgent need for efficient and high-value treatment of urban waste biomass [4,5,6,7].
Hydrothermal treatment, using water as the reaction medium, is a series of chemical reactions such as hydrolysis and hydrothermal decomposition of organic substances under suitable temperature and pressure conditions in a hydrothermal environment to convert large molecules into small monomers, as well as carbon substances [8]. The conditions for hydrothermal treatment are generally mild, with common hydrothermal reactions occurring at temperatures of 180–250 °C and pressures of 2–10 MPa [9], which favor obtaining the solid parts of hydrothermal products [10]. On account of the lower energy consumption, 180 °C was chosen for this work. Due to the advantages of a wide range of raw materials, lower energy consumption, higher reaction efficiency, environmental friendliness, and easy solid–liquid separation [11,12,13,14], hydrothermal-carbonization can be beneficial for the treatment of materials with high moisture contents, so it can be relatively effective for the high-value treatment of waste biomass [15,16]. Aside from chemical methods, one of the methods that has been widely used in the preparation of carbon aerogels [17], hydrothermal-carbonization treatment is obviously more suitable for waste biomass treatment.
Hydrochar is the major product of hydrothermal treatment, accounting for about 40 wt% of the product [18], which facilitates the high-value treatment of waste biomass. Hydrochar is still an amorphous carbonaceous material rich in oxygen and carbon with low qulity. To improve the performance of hydrochar, further treatment has been carried out. After freeze-drying and carbonization, which further carbonize the hydrochar in order to improve the pore structures at relatively higher temperatures [17], a high-quality carbon aerogel (CA) is obtained. CA, a porous carbon material prepared from biomass via hydrothermal-carbonization, has already been used in multiple areas, especially in the fields of absorption [19], water processing [20], electrochemistry [21], catalysis [22], and hydrogen production [23]. However, it is less used for ethanol cracking reactions. Based on its wide field of application, CA illustrates a good prospect for usage in ethanol cracking reactions.
Thus, in this work, four typical waste biomasses (banana peel, mangosteen peel, orange peel, and pomelo peel) were used to prepare CAs by the hydrothermal-carbonization method, and their ethanol cracking performance for H2 production were studied. The ethanol cracking mechanism of CA prepared from waste biomasses was also revealed.

2. Experiments and Analysis Methods

2.1. Materials

In this work, four typical waste peels were obtained from a local supermarket in Wuhan, Hubei Province, China. To exclude the influence of different biomass production regions on moisture content, dry basis samples were chosen. According to the national standard (GBT 28731-2012), they were washed to remove impurities before being dried at 105 °C for 24 h and ground to 60 mesh. The results of the proximate and ultimate analyses are shown in Table 1. From the table, it can be seen that every waste biomass sample has high content of volatile and fixed carbon. These characteristics can profit from the formation of porous carbon materials [24]. Banana peel (BP) has the highest ash content of 12.34 wt%, about four times more than other biomass, which means that BP contains more inorganic components [25]. The ultimate analysis shows that the waste biomasses selected in this work have more C and O content, with less N and S. Compared with the references [26,27,28,29], all waste biomass samples used in this work are representative. It is known to us that most biomasses are consisted of lignin, cellulose, and hemicellulose. They play an important role in determining the properties of biomass, and also affect the hydrothermal-carbonization process of waste biomass. However, their influence on the application of hydrothermal-carbonization products is not clear. We plan to explore this in the future.

2.2. Preparation of Hydrothermal Carbon Aerogel

First, different waste biomass peels were washed with deionized water to remove impurities on the surface, then cut into small pieces with dimensions of approximately 2 × 2 × 1 cm3. The high-pressure stainless-stain hydrothermal autoclave with teflon liner was used for the hydrothermal-carbonization treatment of waste biomass peels. The autoclave was sealed in the oven at 180 °C for 8 h with no extra pressure demanded. Then, the corresponding waste biomass hydrogels were washed several times with deionized water and prepared by freeze-drying at −40 °C for 24 h. The obtained waste biomass aerogels were put into a tubular furnace for the carbonization process at a temperature of 700 °C and held for 30 min. Finally, the carbonization products were naturally cooled down to room temperature to obtain banana peel carbon aerogels (BPCA), mangosteen peel carbon aerogels (MPCA), orange peel carbon aerogels (OPCA), and pomelo peel carbon aerogel (PPCA), respectively.

2.3. Evaluation of Ethanol Cracking Performances

Waste biomass-based carbon aerogels prepared by hydrothermal-carbonization were used in the ethanol cracking reaction. The experiments were implemented in a fixed bed microreactor under atmospheric pressure, as shown in Figure 1. In order to reveal the effect of carbon aerogels prepared from different waste biomasses, experiments using the same temperature and reaction time were carried out. A reaction temperature of 700 °C and a reaction time of 30 min were chosen in this work [30]. The ethanol cracking reaction was carried out under a pure N2 atmosphere. After the N2 flow was stable, the ethanol (Sinopharm Chemical Reagent, analytical reagent) was continuously injected into an evaporator, which was kept at 250 °C, and then carried by N2 gas to the reaction bed. The flow rate of N2 and the injection rate of ethanol were 98.91 mL/min and 29 μL/min, respectively. The gas products were collected by gas collection bags for further study.
Hydrogen yields and proportions of different gases are calculated as Equation (1) and Equation (2), respectively. To ensure the reliability of the results, repeated and blank tests were carried out.
Y i e l d H 2 % = n H H 2 n H E t h a n o l × 100 %
P r o p o r t i o n   o f   g a s e s % = A g a s e s 100 % − A N 2 × 100 %
where n ( H ) H 2 (mol) represents the moles of H atoms converted to H2, and n ( H ) E t h a n o l (mol) represents the moles of H atoms in ethanol in Equation (1). A g a s e s indicates the amount of different gas products and A N 2 indicates the amount of nitrogen in the gas collection bags.

2.4. Characterization of Carbon Aerogels and Gas Productions

Four kinds of biomass were analyzed by proximate and ultimate analyses. CAs prepared from different types of waste biomass were analyzed by Fourier Transform Infrared spectroscopy (FT-IR), Raman Spectra, N2 Adsorption-desorption Analyzer, and X-Ray Fluorescence (XRF). The gas product of ethanol cracking reaction with different CAs was collected and analyzed by Gas Chromatography (GC).
Proximate Analyzer (Thermostep, ELTRA) and Elemental Analyzer (EA3000, Euro Vector) were used to carry out the proximate and ultimate analyses of feedstocks and CAs, respectively. All analyses were repeated twice, and the average value was taken as the result. The chemical structures of waste biomass CAs were analyzed by FT-IR (Nicolet iS50, Thermo Scientific, Waltham, MA, USA) and Raman (DXR2, Thermo Scientific, Waltham, MA, USA). Before the experiments, the waste biomass based CAs were mixed with KBr in a mass ratio of 1:100 (waste biomass based CAs:KBr) and fully grounded; then, the mixtures were pressured into thin slices for the test. Raman with a laser of 532 nm was used to reveal the carbon skeleton structure of waste biomass CAs. The pore structures were analyzed by an N2 adsorption–desorption analyzer (BK100A, JWGB) at 77 K, and the specific surface area was calculated using the Beunauer–Emmett–Teller (BET) method and the Barret–Joyner–Halenda (BJH) method. Analysis of the inorganic elemental composition of samples was conducted using a microfocus X-ray Fluorescence Spectrometer (M4 TORNADO, BRUKER). The yield of H2 and the proportions of different gases in the products of the ethanol cracking reaction were measured by GC (TRACE 1300, Thermo Scientific, Waltham, MA, USA) using a TCD detector.

3. Results and Discussion

3.1. Ethanol Cracking Performance of CAs Prepared from Different Waste Biomasses

The yield of H2 and the proportion of every gas product with CAs prepared from different waste biomass are shown in Figure 2, which indicates the ethanol cracking performance of these CAs. From Figure 2a, it can be seen that waste biomass CAs are capable of improving ethanol cracking. Compared to the blank experiment, the yield of H2 significantly increases. The yield of H2 in the blank experiment is 20.47 wt%, and with CAs prepared from different waste biomass, the H2 yield is promoted to around 30 wt% to 40 wt%, which increases by at least 13.27 wt%. Among the tested CAs, BPCA shows the best performance, with a hydrogen yield of 41.86 wt%. The increment of the H2 yield indicates that CAs prepared from waste biomass can improve the ethanol cracking reaction, which is an effective method for H2 production. The blank experiment also indicates that ethanol can self-crack at a temperature of 700 °C, which demonstrates that a homogeneous reaction could occur. Under the same condition of the blank experiment, H2 production is thus improved. Therefore, it can be inferred that during ethanol cracking with CAs, both homogeneous and heterogeneous reactions occurred. The specific analysis will be shown later in this work.
Figure 2b shows the proportion of the gas products of the ethanol cracking reaction with CAs prepared from different waste biomass. The compositions of the gas products are slightly different. When ethanol is self-cracked, hydrogen, methane, carbon monoxide, and hydrocarbons present in the product, as well as very small amounts of carbon dioxide. With BPCA, MPCA, and OPCA, the proportion of CO2 significantly increases, and CO is almost non-existent. Ethanol cracking with MPCA produces the most CH4, and the highest production rate of CO2 is related to OPCA. However, in contrast to these three carbon aerogels, PPCA only increases the H2 content in ethanol cracking products, and there is no conversion of CO to CO2. Compared to other CAs, BPCA apparently shows the best selectivity. In order to illustrate the different compositions of the gas products, the O content of CAs prepared from different waste biomass is analyzed. The O content of PPCA is 0.31 wt%, while those of BPCA, MPCA, and OPCA were 17.56 wt%, 7.02 wt%, and 9.17 wt%, respectively. It can be seen that the O content in PPCA is the lowest. During the ethanol cracking process, the presence of O atoms can oxidize CO to produce CO2. Thus, it can be inferred that the difference in the composition of every reaction with different CAs may result in a different O content in every waste biomass CA.

3.2. Structures of CAs Prepared from Different Waste Biomasses

3.2.1. Chemical Structure of Different CAs Prepared from Different Waste Biomasses

The chemical structure of CAs prepared from different waste biomasses can be described by the functional group and carbon skeleton, which would be discussed below. Figure 3 shows the results of the FT-IR analysis. It can be seen that all 4 kinds of CAs have 3 obvious peaks, situated at around 600–650 cm−1 and 1100–1150 cm−1. According to the reference [31], the peaks centered at 1130 cm−1, 1132 cm−1, 1132 cm−1, and 1121 cm−1 are mainly due to symmetric C-O stretching, which is frequently found in lignocellulose. The other two peaks, located in the range of 600–650 cm−1, are related to the aromatic rings [32]. There are also small peaks between 800–900 cm−1 in the spectrums of BPCA and OPCA, which should correspond to C-H bending (aromatic CH out-of-plane deformation) [33]. However, the intensities of these two peaks are relatively weak; thus, we mainly focused on the other three characteristic peaks for further analysis.
In accordance with existing study [34], oxygen-containing functional groups in of carbon materials have high catalytic activity for certain reactions. Combined with Figure 2, the presence of oxygen-containing functional groups in CAs plays a relatively important role in the ethanol cracking reaction, and allows the production of H2 to be promoted. In Figure 3, it can also be seen that the intensity of the OPCA characteristic peak is higher than those of other CAs, which indicates that there are relatively more corresponding functional groups in OPCA. More functional groups indicate that there are more active sites for ethanol cracking [35]. However, the reaction with OPCA does not have the highest H2 yield. Thus, there are other factors that affect H2 production. To further analyze the other factors that affected ethanol cracking, more analyses results are analyzed below.
The carbon skeleton structures of CAs prepared from different waste biomasses were analyzed by Raman spectra. The amorphous degree of carbon can also be displayed by Raman spectra. Figure 4 shows the first-order Raman (800–1800 cm−1) spectrums of the CAs prepared from waste biomasses. It clearly shows that the Raman spectrums mainly consist of two characteristic peaks, namely, the D’ band and the G’ band. The two bands are located at about 1340 cm−1 and 1580 cm−1, respectively [36]. The D’ band corresponds to the disordered amorphous carbon structure, while the ordered graphite-like structure corresponds to the G’ band [37]. The Raman spectrums of the four CAs are relatively similar, as shown in Figure 4. This indicates that the CAs still contain significantly disordered amorphous carbon structures despite the presence of partially ordered graphite-type structures [38]. However, in the spectra of BPCA and PPCA, the two bands’ intensities are relatively similar. Compared to the other two CAs, the contents of amorphous carbon in BPCA and PPCA are relatively high. Therefore, in order to deeply analyze the carbon skeleton structure of carbon aerogels, the first-order Raman spectrums were resolved and analyzed by the ten-peaks method [39].
The key band area ratios (AD/AG, AD/A(VR + VL + GR), and AS/AG), which are shown in Figure 5, can be used to reflect the concentration of a large aromatic rings system (≥6 rings), the ratio of a large to small aromatic rings system, and the formation/decomposition of alkyl-aryl C-C bonds, respectively [40]. It can be seen in the figure that the key band ratios of AS/AG are relatively similar between the four biomasses, meaning that the concentrations of alkyl-aryl C-C bonds are similar in the four different CAs. It can also be easily observed from the figure that the concentration of large aromatic rings is at its highest in PPCA and lowest in BPCA, which indicates that BPCA has more disordered amorphous carbon structures. Combined with Figure 2a, this may explain the higher H2 yield in the ethanol cracking reaction with BPCA.

3.2.2. Pore Structures of Different CAs Prepared from Different Waste Biomasses

The pore structures of CAs prepared from different waste biomasses were analyzed via the N2 Adsorption–Desorption method. The results are shown in Table 2. The specific surface area was calculated using the Beunauer–Emmett–Teller (BET) method. In addition, the Barrett–Joyner–Halenda (BJH) method was used to calculate the pore size distributions. The isotherm curves and pore size distribution curves of CAs prepared from different types of waste biomass are shown in Figure 6. The N2 sorption isotherm curves of the different waste biomasses are shown in Figure 6a. Type IV sorption isotherm curves are displayed according to IUPAC classification. Hysteresis loops can be observed at the isotherm curves of all samples, which indicates the existence of abundant micro- and mesopores in CAs. From Figure 6b, the pore size distribution of CAs can be observed. Pore sizes ranging from 2 to 3 nm mainly appeared in the CAs, which is beneficial for the absorption of ethanol molecules. From the table above, it can be seen that hydrothermal-carbonization can convert waste biomass into porous carbon materials. Compared to other CAs in the published references [17,41], other carbon aerogels’ specific surface areas are in the range of 150–500 m2/g. The specific surface areas of four kinds of typical waste biomass in this work are also within this range. The specific surface area of BPCA is the smallest, but has the largest pore volume and average pore diameter. The feedstock itself has a more loose and porous structure, which is the reason for the difference in specific surface area between the four materials. From the reference [42], it is known that the influence of pore structures and their distribution regarding ethanol cracking performance are mainly reflected in the adsorption, cracking efficiency, and diffusion. When the specific surface area, pore volume, and average pore diameter increase, not only does the adsorption capacity increase but promotes the active sites in CAs.
However, in this work, the specific surface area of BPCA is the lowest, while the H2 yield in the ethanol cracking reaction with BPCA is the highest, as seen in Figure 2a. The pore volume and average pore diameter of BPCA are the largest. Combined with the lower specific surface area, this means that the pores in BPCA are fewer and larger than those in other CAs. The performance of BPCA does not fit the regular pattern in the reference, which indicates that there are other factors affecting the H2 yield in the ethanol cracking reaction. Thus, further analysis of the inorganic components of CAs is carried out.

3.3. Inorganic Components of CAs Prepared from Different Waste Biomasses

In order to further reveal the effect of CA on H2 production from ethanol cracking, the ash content was calculated. Furthermore, XRF analysis was used to measure the inorganic element content in the ash of CAs. The inorganic element content results are calculated by Equation (3), given below. The results are presented in Table 3.
Inorganic   element   content   ( wt % ) = Ash   content   ( wt % ) × XRF   results   ( wt % )
Ash content was considered to be the ratio of the original CAs sample’s mass to the mass of the sample after calcination in a muffle furnace. BPCA has the highest ash content, 9.67 wt%. The ash content reflects the inorganic matter content of CAs, indicating that there is a higher inorganic matter content in BPCA. Combined with the H2 yield in Figure 2a, it can be found that as the ash content becomes greater, the yield of H2 increases. Therefore, the performance that inorganic elements have more significant effects on ethanol cracking needs to be further studied.
XRF was thus used to determine the specific element that existed in CA ash. From the table, it can be seen that the ashes of CAs contain four main inorganic components, namely, Mg, Cl, K, and Ca. K and Ca occupy the majority of inorganic components in CAs. Meanwhile, the content of Cl in BPCA is significantly higher than that in other CAs.
The alkali metals and alkaline earth metals (AAEMs), including K, Ca, and Mg, can enhance the breakage and reorganization of atoms, but also promote the thermal decomposition of heavier aromatics [43,44]. This can explain the increment in H2 yield due to the reaction with CAs. The more AAEMs there are inside the CAs, the higher the H2 yields. From the reference [45], it is known that K most significantly induces the production of low-molecular-weight species and char. It also tends to promote the decarbonylation reaction and increase the yield of H2, CO, and CO2. Furthermore, the Mg and Ca content may cause this difference by reducing the byproducts of CO2. They act as immobilizers of CO2, and the cracking reaction proceeds positively when the by-products are reduced, resulting in increased H2 production. It is also beneficial to carbon fixation, which makes it more convenient for the further treatment of carbon oxides.
In Table 3, it can be found that PPCA has the highest K absolute content, while the Ca and Mg absolute contents are the highest in OPCA. However, as shown Figure 2a, the H2 yields of the reaction with PPCA and OPCA are both lower than that of BPCA. This phenomenon also indicates that in the case of ethanol cracking, the addition of CA affects H2 production in multiple ways. The specific mechanism is revealed below.

3.4. Mechanism of Ethanol Cracking Performance for H2 Production with CAs Prepared from Different Waste Biomasses

From the above analysis, the mechanism of ethanol cracking performance of CAs prepared from waste biomass via hydrothermal-carbonization is shown in Figure 7.
According to the available study [46], during hydrothermal-carbonization, biomass undergoes complex reactions to produce solid–liquid–gas products. The formation of porous materials is facilitated by the generation of gas products in the decarboxylation reaction [47], while the polymerization of carbon chains and aromatization form hydrogels [48]. This contributes to the waste biomass being converted to a high-value porous carbon material, which is sometimes also classified as ‘biochar’ [46] or ‘hydrogel’ [49].
In the ethanol cracking reaction, the contribution of CA to H2 production is reflected in two aspects. For the homogeneous phase occurring in the ethanol cracking reaction, the longer the residence time, the more ethanol is cracked [50,51]. CA increases the residence time of ethanol gas in the reactor due to its characteristic of relatively high specific surface area; thus, the H2 yield is increased. On the other hand, the heterogeneous reaction occurs on the surface of CA. Ethanol is adsorbed on the CA surface by the pores of CA by means of physical adsorption. After the hydrothermal and carbonization treatment, the inorganic components, mainly AAEMs, may be exposed. The bond-breaking and reorganization in ethanol are promoted [43,44], thus increasing the H2 yield, which has already been discussed in detail in Section 3.3. At the same time, the inorganic components also fix the CO2 in the products and improve the positive cracking reaction. The CA itself also has a certain promotion effect due to its functional groups being retained during hydrothermal-carbonization treatment and the aromatic ring system. Most reserved functional groups contain O atoms, which oxidize CO in the by-products of ethanol cracking. The CO is eventually converted into CO2, and then captured by inorganic components in CA. The production of H2 is thus further improved.

4. Conclusions

Waste biomass-based carbon aerogels prepared by hydrothermal-carbonization and their ethanol cracking performance for H2 production were studied. The main conclusions are as follows. The CAs prepared from waste biomass via hydrothermal-carbonization were able to increase the H2 yield from 20.47 wt% to at least 33.71 wt%. BPCA showed the best performance, catalyzing the ethanol cracking reaction to obtain 41.86 wt% of H2. The main mechanism of ethanol cracking performance with CA prepared from waste biomass was revealed. For the homogeneous phase appearing in the ethanol cracking reaction, CA increases the residence time of ethanol gas in the reactor due to its characteristic of relatively high specific surface area; thus, the H2 yield is increased. On the other hand, heterogeneous reactions occur on the surface of CA where the ethanol molecules are adsorbed on account of the physical adsorption. The inorganic components, mainly K, Ca, and Mg, on the surface promote bond-breaking and reorganization. At the same time, Ca and Mg also capture the CO2 in the products and improve the positive cracking reaction for H2 production.

Author Contributions

Conceptualization, Q.R. and J.Z.; validation, Y.D., S.S. and Y.W.; formal analysis, J.Z. and Q.R.; investigation, J.Z.; resources, J.Z. and R.H.; data curation, J.Z.; writing—original draft preparation, J.Z.; writing—review and editing, S.H., Y.D., R.H., Q.R., S.S., Y.W., L.J., J.X. (Jun Xu) and J.X. (Jun Xiang); visualization, J.Z.; supervision, S.H. and J.X. (Jun Xiang); project administration, S.H. and J.X. (Jun Xiang); funding acquisition, S.H. All authors have read and agreed to the published version of the manuscript.

Funding

This research was financially supported by Strategic International Scientific and Technological Innovation Cooperation Special Funds of National Key R&D Program of China (2018YFE0127500), and National Natural Science Foundation of China (NSFC) (52076097).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The data presented in this study are available upon request from the corresponding author. The data are not publicly available due to the presence of data that forms part of an ongoing study.

Acknowledgments

The assistance from the Analytical and Testing Center of Huazhong University of Science and Technology is highly acknowledged. Additionally, thanks are given to the facility support of Equipment Center in State Key Laboratory of Coal Combustion, Huazhong University of Science and Technology.

Conflicts of Interest

The authors declare no conflict of interest.

Nomenclature

AAsh
ADThe peak area of the D band
AGThe peak area of the G band
A(VR + VL + GR)The peak area of the VR, VL, and GR band
A(gases)Amount of gases
A(N2)Amount of N2
AAEMsAlkali metals and alkaline earth metals
BETBeunauer–Emmett–Teller
BJHBarret–Joyner–Halenda
BPBanana peel
BPCABanana peel carbon aerogel
CACarbon aerogel
FCFixed carbon
FT-IRFourier transform infrared spectroscopy
IUPACInternational Union of Pure and Applied Chemistry
MMoisture
MPMangosteen peel
MPCAMangosteen peel carbon aerogel
MSWMunicipal solid waste
n ( H ) H 2 The moles of H atoms
n H E t h a n o l The moles of H atoms in ethanol
OPOrange peel
OPCAOrange peel carbon aerogel
PPPomelo peel
GCGas chromatography
PPCAPomelo peel carbon aerogel
VMVolatile matters
XRFX-ray fluorescence spectrometer

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Figure 1. The cracking performance evaluation system for ethanol cracking reaction with CAs.
Figure 1. The cracking performance evaluation system for ethanol cracking reaction with CAs.
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Figure 2. The yields of H2 (a) and gas products proportions (b) with CAs prepared from different waste biomass.
Figure 2. The yields of H2 (a) and gas products proportions (b) with CAs prepared from different waste biomass.
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Figure 3. FT-IR spectrums of CAs prepared from different waste biomasses.
Figure 3. FT-IR spectrums of CAs prepared from different waste biomasses.
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Figure 4. Raman spectrums of CAs prepared from different waste biomasses.
Figure 4. Raman spectrums of CAs prepared from different waste biomasses.
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Figure 5. Analysis of Raman band area ratios of CAs prepared from different waste biomasses.
Figure 5. Analysis of Raman band area ratios of CAs prepared from different waste biomasses.
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Figure 6. Isotherm curves (a) and pore size distribution curves (b) of CAs prepared from different waste biomasses.
Figure 6. Isotherm curves (a) and pore size distribution curves (b) of CAs prepared from different waste biomasses.
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Figure 7. Mechanism of ethanol cracking for H2 production with CAs prepared from waste biomasses.
Figure 7. Mechanism of ethanol cracking for H2 production with CAs prepared from waste biomasses.
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Table
Table 1. Proximate and ultimate analysis results of four waste biomasses.
Table 1. Proximate and ultimate analysis results of four waste biomasses.
FeedstockProximate Analysis
(Dry Basis, wt%)		Ultimate Analysis
(Dry Basis, wt%)
M aV bFC cA dCHNSO e
Banana peel1.2664.9521.4612.3442.515.101.690.0237.08
Mangosteen peel0.9763.7332.532.7851.814.950.500.0538.95
Orange peel3.6675.2717.733.3544.785.400.980.0341.81
Pomelo peel5.4774.4616.463.6140.52 5.51 0.81 0.06 44.02
a Moisture. b Volatile matters. c Fixed carbon. d Ash. e By difference.
Table
Table 2. Pore structures of CAs prepared from different waste biomasses.
Table 2. Pore structures of CAs prepared from different waste biomasses.
SampleSpecific Surface Area (m2/g)Pore Volume (cm3/g)Average Pore Diameter (nm)
BPCA246.800.243.91
MPCA294.940.202.72
OPCA329.330.222.67
PPCA309.840.192.50
Table
Table 3. Ash content and inorganic element content of CAs prepared from different waste biomasses.
Table 3. Ash content and inorganic element content of CAs prepared from different waste biomasses.
SampleAsh Content (wt%)Inorganic Element Content (wt%)
MgClKCaOther
BPCA9.670.010.684.913.880.19
MPCA3.860.130.072.770.650.23
OPCA4.430.33-0.543.210.35
PPCA9.420.170.106.422.320.41
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Zhang, J.; Hu, S.; Ding, Y.; Huang, R.; Ren, Q.; Su, S.; Wang, Y.; Jiang, L.; Xu, J.; Xiang, J. Waste Biomass Based Carbon Aerogels Prepared by Hydrothermal-carbonization and Their Ethanol Cracking Performance for H2 Production. Processes 2023, 11, 892. https://doi.org/10.3390/pr11030892

AMA Style

Zhang J, Hu S, Ding Y, Huang R, Ren Q, Su S, Wang Y, Jiang L, Xu J, Xiang J. Waste Biomass Based Carbon Aerogels Prepared by Hydrothermal-carbonization and Their Ethanol Cracking Performance for H2 Production. Processes. 2023; 11(3):892. https://doi.org/10.3390/pr11030892

Chicago/Turabian Style

Zhang, Jialin, Song Hu, Yong Ding, Rui Huang, Qiangqiang Ren, Sheng Su, Yi Wang, Long Jiang, Jun Xu, and Jun Xiang. 2023. "Waste Biomass Based Carbon Aerogels Prepared by Hydrothermal-carbonization and Their Ethanol Cracking Performance for H2 Production" Processes 11, no. 3: 892. https://doi.org/10.3390/pr11030892

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