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Synthesis of carbon material from low-cost and sustainable precursors has been intensively explored in recent years. In this study, a nitrogen (N)-enriched hydrochar was developed via a facile one-step hydrothermal carbonization (HTC) of corn stalk (CS) with liquid digestate (LD) of food waste. The LD substituted water and functioned as the N precursor during HTC. The physicochemical properties of hydrochar derived at different HTC temperatures (180-300 °C) were examined and the reaction mechanism was investigated. Intermolecular dehydration and condensation were the primary reactions in the HTC process of CS without LD. The CS-chars maintained the original structure and morphology of the raw corn stalk. The ammonia and inorganic salts in LD promoted the lignin removal, and accelerated the cleavage of the glycosidic linkages of the polysaccharide and hydrogen bonds of cellulose. Benefited from the ammonia and metals in the LD, the recalcitrance structure of the corn stalk was disrupted during the co-HTC even at a low temperature of 220 °C. Moreover, carbon spheres were observed in the LDCS-chars, indicating the LDCS-chars were resulted from sequential hydrolysis, dehydration and condensation during co-HTC reactions. Reactions between N compounds in the LD and derivatives from CS contributed to N doping. The N content of LDCS-chars achieved 4.95% at 260 °C and 83.94% of the N was presented as pyridinic-N. Co-hydrothermal treatment of CS and LD not only enhanced the characteristics of hydrochar, but also recovered two-thirds of ammoniacal N from the digestate to reduce greenhouse gas emission.

Melamine-urea-formaldehyde impregnated bond paper (MUF) is widely used as panel coating and decorative raw paper. Inappropriate treatment of MUF may lead to environmental pollution. In this study, routine MUF and MUF treated with additional titanium (MUF-T) were subjected to fast pyrolysis, and the product properties at different temperatures were investigated. The pyrolysis temperature was selected considering the reaction stages determined by Gaussian curve-fitting on thermogravimetric analysis curves. It was found that the presence of additional titanium changed the decomposition order of the organic components at 220 °C. Urea-formaldehyde in MUF could be decomposed at 220 °C, which had little effect on other components (melamine and cellulose). However, in terms of MUF-T, the decomposition temperature of urea-formaldehyde was postponed to 244 °C, which means that the pyrolysis strategy needs to choose a temperature higher than 244 °C. The volatiles in MUF-T are more easily converted to bio-gas or bio-oil than those in MUF. However, only CH

The enhancement of methane (CH4) production by metal addition during anaerobic digestion (AD) of organic waste has drawn much attention in recent years. In this study, four different forms of manganese (Mn, MnO, Mn2O3, and MnO2) were applied at the beginning of AD to investigate their effects on CH4 production. Results suggested that both Mn and the three manganese oxides accelerated CH4 generation. Mn and MnO showed thehigheset carbon conversion rates (about 67%) but the Mn group generated more CH4 (330 mL g−1 VS) than MnO. Moreover, the duration of lag phases for CH4 production was in the following order: MnO

Fast pyrolysis is one of the most promising ways for municipal sewage sludge (MSS) treatment and can generate bio-char as an important and beneficial product. The structure of bio-char determines its further utilization. Co-pyrolysis of MSS and wooden waste (WW) was carried out at 800 °C for bio-char preparation with different wet MSS/ WW mixing ratios. Both physical and chemical structural characteristics of the bio-chars were analyzed to reveal the evolution of bio-char structure during the co-pyrolysis. Results showed that the inherent moisture of MSS had gasification effect on the structure of bio-char generated from both MSS itself and WW. With the increase of WW content, the BET surface area of bio-chars increased from 68.49 cm 2 g −1 to 119.52 cm 2 g −1 due to the high surface area of WW-char (150.59 cm 2 g −1 ). But the average pore sizes of all mixed samples were smaller than 10 nm, which indicated that the MSS-char particles would block the WW-char particles. According to the Raman spectra and XRD results, the inherent moisture was beneficial for the formation of functional groups (mainly carbonyl group) on the bio-char surface. However, the excess moisture led to the additional carbonaceous component consumption and decreased the Raman intensity.

Microplastics have received considerable attention in recent years. Understanding the aging mechanism of plastics in different environments (land, fresh water, estuary, and ocean) is critical to control the microplastic formation. Therefore, the aging process of plastics, including polyethylene (PE) and polypropylene (PP), in different environments was simulated by analyzing their physical and chemical structures by using the Raman spectroscopy, scanning electron microscopy, and Fourier transform infrared spectroscopy techniques. After 23 weeks, micro-scale microplastics (size less than 100 μm) could be extracted from the plastic surface through smashing waves in all fresh water and seawater samples. However, complete fragmentation was observed only in the case of thin-film plastics (TFPs, thickness of approximately 10 μm). This phenomenon indicated that TFPs disintegrated to microplastics more easily in the water system than on land, and the water flow notably affected the production of micro-scale particles. Furthermore, ultraviolet radiation affected the chemical structure of plastics through a two-stage process in all environments. In the initial stage, chemical aging occurred in the amorphous regions of both PE and PP, leading to the generation of newly functional groups such as C=O at 1717 cm-1, and a reduced contact angle. In the later stage, PE exhibited additional crystals and increased contact angles, whereas PP demonstrated the tendency of producing oxygen-containing functional groups that could reduce the crystallinity. In addition, several inorganic salts (such as sulfate and phosphorus) in seawater likely combined with C-H-type stretches, thereby promoting the chemical aging of plastics.

The management of digestate from food waste (DFW) has become a big challenge for anaerobic digestion (AD) plants. It is crucial to understand the characteristics of DFW for its beneficial utilization. This study investigated the long-term characteristics of DFW from an industrial-scale AD plant in China for 16 months. The result showed that the characteristics of the DFW were relatively stable. The DFW contained considerable amounts of organic matter (23-40% of lignin and 12-26% of protein) and abundant nutrients (N, P, and K), with high concentrations of metals (e.g., 55.17 mg g-1 and 15.55 mg g-1 of Ca and Fe) and sulfur (1.40%) on a dry basis. Based on the results, pyrolysis and composting were evaluated as optional conversion ways of DFW. The pyrolysis temperature range of 500 °C to 600 °C was recommended for producing biochar. In this temperature range, the Brunauer-Emmett-Teller surface area of the produced biochar is over 120 m2 g-1. The composting offered the best potential for recovering the nutrients from DFW, but the high ammonia gas content (6970 ppm) should be paid attention to during composting.

The management of digestate from food waste (DFW) has become a worldwide challenge. Pyrolysis is a promising technology to generate biochar from the DFW. However, unlike other biomass, DFW usually has high salt and moisture content, which affects the properties of biochar generated from pyrolysis. The characteristics of biochar derived from DFW with different MCs (5%, 20%, 40%, and 60%) were investigated in the present study. It was found that more micropore and mesopore structures were generated in the biochar with the increase of MC from 5% to 60%, resulting in the Brunauer-Emmett-Teller surface area of the biochar increased from 89.23 m

Mineral carbonation using alkaline industrial solid wastes is a promising CO2 sequestration technology. In this work, the effects of temperature, CO2 content, steam content, and reaction time on CO2 sequestration at atmospheric pressure were studied by the direct gas–solid carbonation of circulating fluid bed fly ash in a thermogravimetric analyzer and a fixed bed reactor system. Results indicate that increasing the temperature and the content of CO2 and H2O(g) can improve the CO2 sequestration efficiency of the circulating fluid bed fly ash. However, the effect of CO2 content is not as significant as that of temperature and H2O(g). The maximum CO2 sequestration capacity of 60 g CO2/kg fly ash with a maximum sequestration efficiency of 28.74% was achieved at 600 °C with 20% H2O(g) addition. The Brunauer–Emmett–Teller surface area and the pore volume decreased with the increase in average pore size after carbonation, due to the formation of a dense carbonate protective layer and pore blockage. With steam addition, the surface area and the pore volume increase, which contributes to the conversion of CaO to CaCO3. The production of Ca(OH)2 or transient Ca(OH)2 and the enhancement of CO2 molecular mobility account for the promotion of steam in the carbonation process. The promotion mechanism of steam in different stages of reaction and temperature were explored in detail. Given the rich reserves of fly ash in China, it shows a good application prospect to use the Chinese fly ash as a mineral carbonation feedstock, which may not only reduces CO2 emission, but also stabilizes the wastes.

Hydrothermal treatments (HTT) at moderate temperatures (120–200 °C) were investigated in this study for the management and valorization of food waste digestate (DFW). The dehydration was the main reaction in HTT at a temperature lower than 180 °C. After HTT, the hydrophobicity and dewaterability of DFW were improved significantly, which resulted in a 69% and 37% reduction in the digestate cake volume and solid residue mass, respectively. During HTT, the organic matter and carbon were mostly solubilized from solid to liquid, while the multivalent metals were concentrated in the solid residue. The more stable characteristics of the digestate cake after HTT eliminated its environmental risk. The accumulation of organic carbon and a reasonable ammonia nitrogen concentration in the HTT liquid increased the biochemical methane potential from 147 to 245 mL CH4/g TCOD, which demonstrated the feasibility of recovering energy from the HTT liquid.

This work aimed to evaluate the detailed chemical structures of the asphaltenes in the tetrahydrofuran-microwave-extracted portions from two Chinese coals, namely, Shenfu and Zhundong coal (SF, ZD) and to clarify their characteristics on chemical composition at molecular level. Based on the analyses of diffuse reflectance Fourier transform infrared spectroscopy (DRIFT) and Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR MS), the detailed chemical structure of a series of basic and non-basic nitrogen- and oxygen-containing class species in the asphaltenes were clarified. The results revealed that condensed nitrogen-containing alkylaromatic structures with amidogens (1–3) were the main structure units in N 4 O y (y = 0–2) class species due to the high double bond equivalent (DBE) values for both the asphaltene from SF (A SF ) and the asphaltene from ZD (A ZD ). Acidic O 2 –O 7 class species with two or three aromatic rings were the main structure units, among which O 4 and O 2 class species had the highest relative abundances (RAs) in A SF and A ZD , respectively. Acidic oxygen-containing components in A ZD had narrower range of DBE and carbon number and mainly consisted of aromatic structure units with two rings. On the contrary, the average DBE values of O 4 –O 7 class species in A SF had positive relationship with oxygen atom number which could be attributed to the introduction of phenol groups. The results provided more detailed information on the structural characteristics of polar and aromatic-rich components of mobile phase in coal.

The existence form and structure properties of mobile phase (MP) in low-rank coals (LRCs) can significantly influence the initial stage of thermal conversion. In the present work, three Chinese LRCs, namely, Shenfu, Zhundong and Hongshaquan, were extracted with tetrahydrofuran using the microwave-assisted heating. The tetrahydrofuran-microwave-extracted (TME) portion as the representative of MP was further separated to four fractions defined as oil, resin, asphaltene and preasphaltene, respectively. Diffuse reflectance Fourier transform-infrared spectroscopy (DRIFT), gas chromatography/mass spectrometer (GC/MS), matrix-assisted laser desorption ionization time-of-flight mass spectrometer (MALDI-TOF-MS) and X-ray photoelectron spectroscopy (XPS) were used to comprehensively investigate the molecular characteristics of the derived materials. The results indicated that the studied TME portions were mainly consisted of asphaltenes and rich in highly branched aliphatic hydrocarbons due to the relatively low CH 2 /CH 3 and H ar /H al ratios. Para -alkyl substituted aromatic structures with 1–2 rings were the main aromatic structures in the TME portions. C O bonds were the main oxygen-containing structures in the TME portions and could be more likely seen in aliphatic compounds. Combining the MALDI-TOF-MS and DRIFT analyses, the ratio of aliphatic side chains and aromatic hydrogens (3000–2800 cm −1 /900–700 cm −1 , I 2 ) derived from IR spectra seemed to be a suitable parameter for assessing the average molecular weight (AMW) of the specific fraction in TME portion of LRCs when the ratio of C O/C O was at very low level. The results made a further explanation for the detailed chemical structure of mobile phase in coal and could be helpful for studying the formation mechanism of volatiles during pyrolysis process.

During chemical looping process, the presence of H2O has great effect on oxygen transfer and hydrogen generation process, thus making the reaction become more complicated. In this study, Fe2O3 was chosen as the original oxygen carrier and its oxygen carrying capacity and reactivity under different H2O/CO molar ratios were systematically investigated. The chemical compositions of reacted iron-based oxides were measured by Mossbauer spectroscopy. According to Mossbauer spectroscopy results and product gas analysis, the paper gave further insight into the impact of H2O on oxygen carrying property and catalyzed effect of iron-based oxides. The results indicated that: (i) The oxygen carrying capacity of Fe2O3 decreased from 45.93% to 11.33% (the theoretical maximum to be 100%) when the H2O/CO ratio varied from 0:1 to 2:1. (ii) The maximum CO2 conversion rate, which reflects the reduction reactivity, was closely related to H2O/CO ratio and achieved the maximum (4.83%/min) at a H2O/CO ratio of 1:1. (iii) The presence of H2O could promote the reduction process of Fe2O3 to generate Fe3O4. (iv) Both Fe3O4 and FeO which existed as reduction states of iron oxides had ability to promote the water-gas shift reaction during oxygen transfer process.

A series of Fe-modified Ni/Al2O3 (FNA) catalysts with different Fe/Ni ratios (Fe/Ni = 0.5, 2, 3) was investigated during steam reforming of toluene as a model compound of biomass tar. The percentages of hydrogen in the product gas reached about 65% over prepared catalysts. The addition of Fe remarkably increased the toluene conversion and reduced the amount of coke. According to X-ray photoelectron spectrometer and pulse injection experiments, the addition of Fe increased the amount of lattice oxygen and adsorbed oxygen on the surface of FNA. The Fe in alloy was easily oxidized to FeOx by steam. The lattice oxygen in FeOx could oxidize the carbon deposited or intermediates on adjacent Ni atoms to produce CO. Meanwhile, the more adsorbed oxygen promoted the further reaction with the intermediates during the steam reforming of toluene. Both the adsorbed oxygen and lattice oxygen from the addition of Fe played important roles in the steam reforming of toluene. For the two types of cokes (amorphous/paraffinic and graphitic/filamentous), the formation of graphitic/filamentous carbon was remarkably suppressed due to the oxidization property of oxygen species from the addition of Fe.

Using Fe2O3, Fe2O3/Al2O3, and Fe2O3–NiO/Al2O3 as oxygen carriers (OCs) on chemical looping combustion with CO was investigated in this study. All the modified iron-based OCs were prepared by sol–gel method, and the samples were characterized by X-ray diffraction (XRD), N2 adsorption/desorption, and scanning electron microscope/energy dispersive X-ray spectroscopy. The temperature-programmed reduction showed that loading on Al2O3 will promote the reduction of Fe2O3 to Fe3O4, but further reduction will be inhibited, and the addition of NiO can effectively reduce this inhibition. Thermogravimetric analysis also revealed that NiO addition can improve the maximum reaction rate of iron-based OCs in the oxidation stage. Mixing with NiO will also decrease the oxygen capacity of iron-based OCs. The XRD data of the reduced samples showed that both Al2O3 and NiO have an isomorphous replacement effect on Fe3O4. The isomorphous replacement effect of NiO is much stronger than that of Al2O3. Thus, NiO introduction can effectively inhibit the formation of FeAl2O4 and promote the further reduction of Fe-oxides to Fe. However, Ni2 + will replace part of the Fe2 + in Fe3O4 to form NiFe2O4 and slightly decrease the oxygen capacity of iron-based OCs.

Oxygen carrier is one of the key roles in the chemical looping process. Thermogravimetric analysis results showed that, among the four metal oxides (Fe2O3, CuO, NiO, and CaSO4), Fe2O3 possessed the best regenerative capacity although its crystal cell would shrink after one redox reaction. It was found that loading of Fe2O3 on Al2O3 could effectively inhibit its crystal cell shrinking and increase Brunauer–Emmett–Teller (BET) surface of particles up to a certain value. Further study showed that BET surface of the particles had a positive relationship with their redox reactivity. When the BET surface area increased by five times, the maximum reaction rate improved about 13% (reduction stage) and 37% (oxidation stage). Fe2O3/Al2O3 oxygen carrier prepared by the sol-gel process contained a new crystal structure, Al3Fe5O12, which could improve the recycle stability of the oxygen carrier. The modified oxygen carrier with Fe/Al2O3 molar ratio 2:1 kept the best regeneration capacity of about 97% after fiv...

CaO plays multiple roles in the in-situ gasification process of coal to produce hydrogen-rich gas. It is well known as a sorbent for CO 2 capture, and as a catalyst to decompose tars and promote water–gas shift (WGS) reaction as well. It is very important to understand interactions between adsorption process and catalytic effect of CaO. In the current work, firstly, the carbonation degree of CaO and its reaction kinetics were studied at different CO 2 partial pressures via thermogravimetric analyzer. Then the catalytic activity of calcium-based materials (CaO/CaCO 3 ) at different carbonation degrees in the steam reforming of phenol (used as a model compound of tar) and WGS reaction were investigated, respectively. It showed that the catalytic activities of calcium-based materials for both reactions reduced with the increase of carbonation degree. On one hand, specified surface area had strong relationship with the catalytic activity of the materials for both reactions. On the other hand, the catalytic activity of calcium-based material in WGS reaction decreased due to CaCO 3 formation. However, CaCO 3 showed an obvious catalytic effect on phenol steam reforming. At last, performance of CaO for phenol steam reforming and WGS reaction were studied synchronously at different carbonation degrees. The results revealed that the phenol steam reforming and WGS reaction catalyzed by calcium-based materials were competitive with each other, and the presence of phenol strongly inhibited the conversion of CO in WGS reaction.

The synergistic effect of Ca(OH)2 prepared by the wet-mixing method on lignite steam gasification process at different temperatures (700–900 °C) was analyzed in a spout-fluid bed reactor. Firstly, to avoid disturbance of volatile and tar, active carbon was used as a model compound. On the one hand, Ca(OH)2 effectively catalyzed the water-gas shift (WGS) reaction to improve H2 concentration, but the performance was weaker at higher temperature due to the enhancement of boudouard reaction and the weakening of WGS reaction. On the other hand, it was found that the (CO+2CO2)/H2 ratio of syngas produced at 700 °C in the presence of Ca(OH)2 was 0.82, which was much lower than that of the other cases, owning to the absorption of CO2. The synergistic effect was observed at this temperature, for the adsorption of CO2 altered equilibrium of the WGS reaction and further improved H2 concentration. Then two kinds of Chinese lignite (HLH and XM) were selected to further study the performance of Ca(OH)2 on optimizing the lignite steam gasification process. In the presence of Ca(OH)2, tar and char yields greatly reduced at the same reaction temperature, whereas the gas yields significantly increased. As a catalyst, Ca(OH)2 can not only promote solid–gas reaction to decrease char yield, but also accelerate tar decomposition to reduce its yield in syngas. Based on GC–MS data, it can be deduced that Ca(OH)2 has different catalytic activity on the steam reforming of tar with different molecular structures. Contrast to Class 4, tars of aliphatic hydrocarbons, Class 2 and Class 5 were clearly catalytic reformed. Hydrogen-rich gas can be produced at 800 °C and 900 °C owning to the catalytic effect of Ca(OH)2, but the highest H2 concentration was found at 700 °C due to the additional effect of CO2 absorption, which was supported by the results of thermogravity experiments.

This study aims to investigate the interaction and kinetic behavior of CO 2 gasification of coal, biomass and their blends by thermogravimetry analysis (TG). The gas products evolved from gasification were measured online with Fourier Transform Infrared Spectroscopy (FTIR) coupled with TG. Firstly, TG experiments indicated that interaction between the coals and biomasses mainly occurred during co-gasification process. The most significant synergistic interaction occurred for LN with SD at the blending mass ratio 4:1. Furthermore, thermal kinetic analysis indicated that the activation energy involved in co-gasification decreased as the SD content increased until the blending ratio of SD with coal reached 4:1. The rise of the frequency factor indicated that the increase of SD content favored their synergistic interaction. Finally, FTIR analysis of co-gasification of SD with LN indicated that except for CO, most gases including CH 3 COOH, C 6 H 5 OH, H 2 O, etc., were detected at around 50–700 °C.

The non-isothermal thermogravimetric method (TGA) was applied to different chars produced from lignite (LN), sawdust (SD) and their blends at the different mass ratios in order to investigate their thermal reactivity under steam atmosphere. Through TGA analysis, it was determined that the most prominent interaction between sawdust and lignite occurred at the mass ratio of sawdust/lignite as 1:4, but with further dose of more sawdust into its blends with lignite, the positive interaction deteriorated due to the agglomeration and deactivation of the alkali mineral involved in sawdust at high steam gasification temperature. Through systematic comparison, it could be observed that the random pore model was the most suitable among the three gas-solid reaction models adopted in this research. Finally, rational kinetic parameters were reached from these gas-solid reaction models, which provided a basis for design and operation of the realistic system of co-gasification of lignite and sawdust in this research.