Lignin is the only sustainable aromatic resource in nature, its utilization has attracted much attention worldwide. Oxidation is one of the promising strategies that can convert lignin to a range of ...value-added platform chemicals. Lignin oxidation is generally carried out in a liquid phase with employed catalytic systems and oxidants, and this process is largely influenced by operation conditions, catalyst types, presence of oxidant, and solvent species. The inter-unit linkages in lignin can be selectively oxidized with the assistance of designed catalytic systems, facilitating the formation of aromatics (phenolic aldehydes, ketones, and acids), benzoquinones, and aliphatic (di)carboxylic acids. This work aims to provide a comprehensive review on traditional and advanced lignin oxidation concerning various catalytic systems for different terminal products. Deficiency in current lignin oxidation is also mentioned which indicates the direction of further lignin oxidative valorization.
•Innovative presentation on traditional lignin oxidation including bleaching, structural identification and wet air oxidation.•Comprehensive review on advanced lignin oxidation for platform chemicals based on different catalytic oxidation mechanisms.•State-of-the-art discussion on selective oxidation of α-OH and further conversion of oxidized lignin.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•Aromatic units and side-chain linkages within lignin were analyzed by 2D HSQC NMR.•Relevance between lignin structure and pyrolysis behaviors was explored by Py–GC/MS.•Selectivities of phenols ...derived from AOL vs. SAL reached 86.73% vs. 87.37%.•More β-O-4′ linkages led to the easier pyrolysis conversion and less demethoxylation.
In this study, the Fourier transform infrared (FTIR) spectrometry and the 13C–1H correlation two-dimensional (2D) heteronuclear single-quantum coherence (HSQC) nuclear magnetic resonance (NMR) were introduced to determine the chemical structure of soda alkali lignin (SAL) and Alcell organosolv lignin (AOL), and the relevance between chemical structure and pyrolysis behaviors was evaluated by thermogravimetric analysis (TGA) and pyrolysis–gas chromatography/mass spectrometry (Py–GC/MS). Results showed that the two lignin samples had similar functional groups and S/G ratio, excepting side-chain linkages. SAL was mainly cross-linked by β-β′ linkages, while the main linkage within AOL was β-O-4′. This difference proposed that AOL had the worse thermal stability and was easier to be pyrolyzed to phenols than SAL. Herein, the pyrolysis transformation of SAL was always promoted by the increased temperature, whereas the generated phenols from AOL would be redecomposed at high pyrolysis temperature (800°C). Moreover, the priority of demethoxylation occurring in SAL pyrolysis was higher than that in AOL pyrolysis. Further analysis on the types of phenols suggested that the formation of syringyl phenols benefitted from the increasing temperature. However, the formation of p-hydroxyphenyl phenols was inhibited as temperature increased, and the highest selectivity of guaiacyl phenols was obtained at 600°C. The reveal of the relevance between lignin chemical structure and pyrolysis behaviors is meaningful for the efficient thermal conversion of lignin to phenol compounds.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
•Ex-situ catalytic fast pyrolysis (CFP) was studied in a two-stage bench scale device.•Ex-situ and in-situ CFP gave a similar carbon yield of aromatics+olefins.•Ex-situ CFP produced significantly ...more olefins than in-situ CFP.•High pyrolysis temperature generated significantly less coke.•High catalysis temperature led to a boost in ethylene and benzene selectivities.
Ex-situ and in-situ catalytic fast pyrolysis (CFP) of biomass over HZSM-5 were compared in a two-stage fluidized-bed/fixed-bed combination reactor. Ex-situ CFP gave a similar carbon yield of aromatics+olefins (∼20%) with in-situ CFP but produced much more olefins (10.3% vs. 5.8%) and less char+coke (42.7% vs. 48.4%). The effects of weight hourly space velocity (WHSV), carrier gas flow rate, pyrolysis temperature and catalysis temperature on product distribution in ex-situ CFP were further studied. The maximum carbon yield of aromatics+olefins (21.7%) was obtained at pyrolysis temperature of 550°C and catalysis temperature of 600°C with the highest carrier gas flow rate (1.2L/min) and WHSV of 1.33h−1. Obviously less coke was generated at higher pyrolysis temperature. When catalysis temperature increased to 700°C, ethylene and benzene carbon selectivities boosted to 79.4% and 60.5%, respectively.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Plastic waste remains a global challenge due to the massive amounts being produced without satisfactory treatment technologies for recycling and upcycling. Photocatalytic processes are emerging as ...green and promising approaches to upcycle plastics into value‐added products under mild conditions using sunlight as the energy source. In this review, the recent advances in plastic conversion through photocatalysis have been comprehensively summarized. Special emphasis is placed on the photocatalytic mechanism and the selective CC and CH bond transformations of plastics to access fuels, chemicals, and materials. Finally, the challenges and the perspectives on establishing a new paradigm toward a sustainable and circular plastic economy are also put forward.
Photocatalysis is a promising technology to upgrade plastic wastes into value‐added products under mild conditions using sunlight as the energy source. This review summarizes the state‐of‐the‐art advances on the photocatalytic transformation of plastics into valuable fuels, chemicals, and materials, which sheds light on the establishment of a new paradigm toward a sustainable and circular plastic economy.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Fast pyrolysis of corncob with and without catalyst was investigated in a fluidized bed to determine the effects of pyrolysis parameters (temperature, gas flow rate, static bed height and particle ...size) and a HZSM-5 zeolite catalyst on the product yields and the qualities of the liquid products. The result showed that the optimal conditions for liquid yield (56.8%) were a pyrolysis temperature of 550
°C, gas flow rate of 3.4
L/min, static bed height of 10
cm and particle size of 1.0–2.0
mm. The presence of the catalyst increased the yields of non-condensable gas, water and coke, while decreased the liquid and char yields. The elemental analysis showed that more than 25% decrease in oxygen content of the collected liquid in the second condenser with HZSM-5 was observed compared with that without catalyst. The H/C, O/C molar ratios and the higher heating value of the oil fraction in the collected liquid with the catalyst were 1.511, 0.149 and 34.6 MJ/kg, respectively. It was indicated that the collected liquid in the second condenser had high qualities and might be used as transport oil.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Coke deposition on the zeolite catalysts in the conversion of furan (a main intermediate of biomass fast pyrolysis) is of serious concern for catalyst deactivation and product distribution. It is ...important to find out the nature and composition of coke on the spent ZSM-5 catalyst to study the coke-depositing behaviors. In this work, spent ZSM-5 catalysts obtained from furan catalytic conversion for chemicals at different reaction times and pyrolysis temperatures were characterized. The spent catalysts were first treated with hydrofluoric acid, and then the organics were extracted with CH2Cl2. The characterization of the origin coke and the treated insoluble coke were analyzed by the combination of some analytical techniques, including Fourier transform infrared spectroscopy (FTIR), high-performance liquid chromatography (HPLC), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and thermogravimetric analysis (TGA). The extracted organics were analyzed by HPLC to determine the chemical composition of the soluble coke. The results show that coke formation mainly involves condensation and rearrangement steps at a low reaction temperature (<200 °C). Coke components are polyaromatics, which formed by hydrogen transfer in addition to condensation and rearrangement steps at high temperatures (>200 °C). In the FTIR analysis, high aromaticity of coke species was obtained with increasing temperature, which indicates that the pyrolysis temperature plays a dominant role in the coke formation. TGA reveals that high temperature favors the formation of hard coke. The results enhance the understanding of coke formation and adjusting mechanism in biomass catalytic pyrolysis process.
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IJS, KILJ, NUK, PNG, UL, UM
•Catalytic pyrolysis of rice stalk was conducted in a new fluidized bed reactor.•Mesoporous or macroporous catalysts mixed with microporous catalyst were used.•The maximum hydrocarbon yield was ...obtained with 10% Gamma-Al2O3/90% LOSA-1.•The yield was boosted by 39.8% compared to that obtained with pure LOSA-1 catalyst.
Zeolite catalysts with micropores present good catalytic characteristics in biomass catalytic pyrolysis process. However, large-molecule oxygenates produced from pyrolysis cannot enter their pores and would form coke on their surfaces, which decreases hydrocarbon yield and deactivates catalyst rapidly. This paper proposed adding some mesoporous and macroporous catalysts (Gamma-Al2O3, CaO and MCM-41) in the microporous catalyst (LOSA-1) for biomass catalytic pyrolysis. The added catalysts were used to crack the large-molecule oxygenates into small-molecule oxygenates, while LOSA-1 was used to convert these small-molecule oxygenates into olefins and aromatics. The results show that all the additives in LOSA-1 enhanced hydrocarbon yield obviously. The maximum aromatic+olefin yield of 25.3% obtained with 10% Gamma-Al2O3/90% LOSA-1, which was boosted by 39.8% compared to that obtained with pure LOSA-1. Besides, all the additives in LOSA-1 improved the selectivities of low-carbon components in olefins and aromatics significantly.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The problem of stochastic stabilization for a class of hybrid dynamical systems with time‐varying delays is investigated by adaptive control approach. An adaptive controller is designed to stabilize ...the hybrid systems, and a sufficient criterion for exponential stabilization is derived based on certain conditions. The time‐varying delay observations on the states of noise are made and the least upper bound of time‐varying delays is also obtained. Finally, a numerical example is presented to demonstrate the effectiveness of the proposed new techniques.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Fast pyrolysis of lignocellulosic biomass produces a renewable liquid fuel called pyrolysis oil that is the cheapest liquid fuel produced from biomass today. Here we show that pyrolysis oils can be ...converted into industrial commodity chemical feedstocks using an integrated catalytic approach that combines hydroprocessing with zeolite catalysis. The hydroprocessing increases the intrinsic hydrogen content of the pyrolysis oil, producing polyols and alcohols. The zeolite catalyst then converts these hydrogenated products into light olefins and aromatic hydrocarbons in a yield as much as three times higher than that produced with the pure pyrolysis oil. The yield of aromatic hydrocarbons and light olefins from the biomass conversion over zeolite is proportional to the intrinsic amount of hydrogen added to the biomass feedstock during hydroprocessing. The total product yield can be adjusted depending on market values of the chemical feedstocks and the relative prices of the hydrogen and biomass.
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BFBNIB, NMLJ, NUK, PNG, SAZU, UL, UM, UPUK
•Controlling the oxygen release was proposed in chemical looping gasification.•The phase transfer of iron oxide was identified in the experiment.•A self-designed thermogravimetric fixed-bed reactor ...was constructed.
Establishing a direct relationship between the mass change of iron-based oxygen carrier and gas production is crucial for the efficient operation and the control of the lattice oxygen release in biomass chemical looping gasification. In this study, a thermogravimetric fixed-bed reactor was designed to achieve the simultaneous measurement of the mass change and gas composition in the reduction of the oxygen carrier. Three oxygen carriers of pure iron (III) oxide, natural hematite, and red mud were used as candidates. The phase transfer of the oxygen carrier along with the biomass pyrolysis/gasification was studied. The mass loss rates and the gas composition were matched by three significant phase transition stages. The phase transitions from Fe2O3 to Fe3O4, Fe3O4 to FeO, and FeO to Fe occurred when CO appeared, CO/CO2 = 0.97, and CO/CO2 = 2.61, respectively. The extent of oxygen carrier reduction was 28.61% of pure iron (III) oxide, whereas the oxygen carrier reduction molar ratio was 74.50% of red mud. X-ray diffraction (XRD) spectrums showed the oxygen carrier was reduced to the metallic iron phase. Sintering and agglomeration were found in the reacted oxygen carriers of the scanning electron microscope (SEM) images.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
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