The past decades have seen increasing interest in developing pyrolysis pathways to produce biofuels and bio-based chemicals from lignocellulosic biomass. Pyrolysis is a key stage in other ...thermochemical conversion processes, such as combustion and gasification. Understanding the reaction mechanisms of biomass pyrolysis will facilitate the process optimization and reactor design of commercial-scale biorefineries. However, the multiscale complexity of the biomass structures and reactions involved in pyrolysis make it challenging to elucidate the mechanism. This article provides a broad review of the state-of-art biomass pyrolysis research. Considering the complexity of the biomass structure, the pyrolysis characteristics of its three major individual components (cellulose, hemicellulose and lignin) are discussed in detail. Recently developed experimental technologies, such as Py-GC–MS/FID, TG-MS/TG-FTIR, in situ spectroscopy, 2D-PCIS, isotopic labeling method, in situ EPR and PIMS have been employed for biomass pyrolysis research, including online monitoring of the evolution of key intermediate products and the qualitative and quantitative measurement of the pyrolysis products. Based on experimental results, many macroscopic kinetic modeling methods with comprehensive mechanism schemes, such as the distributed activation energy model (DAEM), isoconversional method, detailed lumped kinetic model, kinetic Monte Carlo model, have been developed to simulate the mass loss behavior during biomass pyrolysis and to predict the resulting product distribution. Combined with molecular simulations of the elemental reaction routes, an in-depth understanding of the biomass pyrolysis mechanism may be obtained. Aiming to further improve the quality of pyrolysis products, the effects of various catalytic methods and feedstock pretreatment technologies on the pyrolysis behavior are also reviewed. At last, a brief conclusion for the challenge and perspectives of biomass pyrolysis is provided.
In order to study the fracture mechanism of rock materials containing weak layers and holes, the rock-like specimens with holes and cracks were made by using cement mortar, and the numerical ...simulation was carried out based on the statistical damage theory. Then the damage constitutive equation is deduced based on the acoustic emission results of numerical simulation. Finally, the failure mechanism of “through layer” and “along layer” crack propagation modes were discussed. Results show that: The failure mode of rock-like specimens includes tensile cracks (T), shear cracks (S) and remote cracks (R). The pre-existing crack angle changes the failure mode of the rock-like specimens. The stress–strain curves of rock-like specimens are divided into three stages: linear elastic deformation, nonlinear deformation and residual deformation. The numerical model is established based on the statistical damage theory, and the numerical results are similar to the test results. Based on the acoustic emission results of numerical simulation, the damage constitutive equation is derived, which can characterize the damage process of rock-like specimens under different conditions. The damage evolution is divided into four stages: linear elastic deformation stage, crack initiation stage, crack acceleration stage and steady development stage, and the damage factor ranges from 0.72 to 0.87. The mechanism of “through layer” and “along layer” crack propagation modes are discussed and we consider that the tensile strength and inclination angle of weak layers are the key influencing factors.
Pyrolysis has created many (and will open more) possibilities for high-value utilization of biomass. To obtain the optimal amount of desired pyrolysis products, especially high-quality bio-oil, a ...great deal of effort has been conducted in both academia in the past few decades, to clarify fundamental mechanisms of biomass pyrolysis and design efficient relevant technical processes. This paper comprehensively reviews recent advances in both fundamental studies and technology applications of biomass pyrolysis. First, pyrolysis mechanisms of real biomass and its major components, the reactor-scale simulation of biomass pyrolysis, and applications of pyrolysis products are discussed. Then, according to the requirements imposed to improve the physicochemical properties of respective pyrolysis products, relevant optimization and regulation methods for biomass pyrolysis process are reviewed. Previous research has indicated that biomass copyrolysis with other feedstock can not only enhance physicochemical properties of pyrolysis products but also effectively realize recycling of wastes. Thus, an in-depth discussion of recent advances in biomass copyrolysis with four different feedstocks (i.e., coal, plastics, tires, and sludge) is covered in this Review. As an indispensable component of general biomass pyrolysis, recent activities of catalytic biomass pyrolysis are also summarized, including new catalytic pyrolysis processes such as catalytic hydropyrolysis and catalytic copyrolysis. Besides, two novel heating approaches (microwave heating and solar heating) for biomass pyrolysis are described, and their features are compared with the conventional heating method. Finally, this Review is concluded with perspectives for future directions of biomass pyrolysis.
The pyrolysis characteristics of three main components (hemicellulose, cellulose and lignin) of biomass were investigated using, respectively, a thermogravimetric analyzer (TGA) with differential ...scanning calorimetry (DSC) detector and a pack bed. The releasing of main gas products from biomass pyrolysis in TGA was on-line measured using Fourier transform infrared (FTIR) spectroscopy. In thermal analysis, the pyrolysis of hemicellulose and cellulose occurred quickly, with the weight loss of hemicellulose mainly happened at 220–315
°C and that of cellulose at 315–400
°C. However, lignin was more difficult to decompose, as its weight loss happened in a wide temperature range (from 160 to 900
°C) and the generated solid residue was very high (∼40
wt.%). From the viewpoint of energy consumption in the course of pyrolysis, cellulose behaved differently from hemicellulose and lignin; the pyrolysis of the former was endothermic while that of the latter was exothermic. The main gas products from pyrolyzing the three components were similar, including CO
2, CO, CH
4 and some organics. The releasing behaviors of H
2 and the total gas yield were measured using Micro-GC when pyrolyzing the three components in a packed bed. It was observed that hemicellulose had higher CO
2 yield, cellulose generated higher CO yield, and lignin owned higher H
2 and CH
4 yield. A better understanding to the gas products releasing from biomass pyrolysis could be achieved based on this in-depth investigation on three main biomass components.
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•Catalytic pyrolysis of waste plastics produces H2 and carbon nanotubes (CNTs).•Ni-Fe catalysts and different alumina supports have been investigated.•H2& CNTs production is highly ...dependent on catalyst type and process parameters.•Bimetallic Ni-Fe/γ-Al2O3 produced 31.8mmol H2/gplastic and 287mgg−1plastic CNTs.
The use of Ni-Fe catalysts for the catalytic pyrolysis of real-world waste plastics to produce hydrogen and high value carbon nanotubes (CNT), and the influence of catalyst composition and support materials has been investigated. Experiments were conducted in a two stage fixed bed reactor, where plastics were pyrolysed in the first stage followed by reaction of the evolved volatiles over the catalyst in the second stage. Different catalyst temperatures (700, 800, 900°C) and steam to plastic ratios (0, 0.3, 1, 2.6) were explored to optimize the product hydrogen and the yield of carbon nanotubes deposited on the catalyst. The results showed that the growth of carbon nanotubes and hydrogen were highly dependent on the catalyst type and the operational parameters. Fe/γ-Al2O3 produced the highest hydrogen yield (22.9mmol H2/gplastic) and carbon nanotubes yield (195mgg−1plastic) among the monometallic catalysts, followed by Fe/α-Al2O3, Ni/γ-Al2O3 and Ni/α-Al2O3. The bimetallic Ni-Fe catalyst showed higher catalytic activity in relation to H2 yield than the monometallic Ni or Fe catalysts because of the optimum interaction between metal and support. Further investigation of the influence of steam input and catalyst temperature on product yields found that the optimum simultaneous production of CNTs (287mgg−1plastic) and hydrogen production (31.8mmol H2/gplastic) were obtained at 800°C in the absence of steam and in the presence of the bimetallic Ni-Fe/γ-Al2O3 catalyst.
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•Plasma reforming of naphthalene as a tar surrogate was carried out using a gliding arc.•Adding steam enhanced the conversion of tar and energy efficiency of the process.•The presence ...of OH radicals enhanced the conversion of naphthalene.•Introducing steam reduced the formation of by-products.•The optimal S/C ratio of 2 was found to achieve the highest process performance.
The contamination of producer gas with tars from biomass gasification remains a significant challenge in the bioenergy industry and a critical barrier, limiting the commercial applications of biomass gasification. Non-thermal and non-equilibrium plasma offers an unconventional and emerging technology for the effective reduction of problematic tars from gasification. In this study, we investigated plasma reforming of naphthalene as a two-ring tar model compound using a gliding arc discharge (GAD) reactor with/without steam. The influence on the plasma conversion of naphthalene based on the inlet naphthalene concentration, discharge power and steam-to-carbon ratio was examined to understand the effects of these operating parameters on the destruction of tar, gas selectivity/yield and energy efficiency. Adding H2O in the plasma process generates oxidative OH radicals, creating additional reaction routes for the step-wised oxidation of naphthalene and its fragments towards the CO, CO2 and water. The optimum ratio (2.0) of steam-to-carbon was identified to achieve the highest naphthalene conversion (84.8%), C2H2 yield (33.0%), total gas yield (72.2%) and energy efficiency (5.7 g/kWh). The effect of the amount of steam on the plasma reduction of tars was dependent on the balance between two opposite effects due to the presence of steam: positive effect of OH radicals and the negative effect of electron attachment on water molecules. Introducing an appropriate amount of steam to the plasma reduction of naphthalene also substantially minimized the formation of by-products and enhanced the carbon balance. Plausible reaction mechanisms for the plasma decomposition of naphthalene were proposed through a comprehensive analysis of gaseous and condensable products combined with plasma spectroscopic diagnostics.
Recognizing that bioenergy with carbon capture and storage (BECCS) may still take years to mature, this study focuses on another photosynthesis-based, negative-carbon technology that is readier to ...implement in China: biomass intermediate pyrolysis poly-generation (BIPP). Here we find that a BIPP system can be profitable without subsidies, while its national deployment could contribute to a 61% reduction of carbon emissions per unit of gross domestic product in 2030 compared to 2005 and result additionally in a reduction in air pollutant emissions. With 73% of national crop residues used between 2020 and 2030, the cumulative greenhouse gas (GHG) reduction could reach up to 8620 Mt CO
-eq by 2050, contributing 13-31% of the global GHG emission reduction goal for BECCS, and nearly 4555 Mt more than that projected for BECCS alone in China. Thus, China's BIPP deployment could have an important influence on achieving both national and global GHG emissions reduction targets.
Owing to intrinsic structural limitations, it is difficult to control the pore structure of biomass to synthesize hierarchical porous carbons (HPCs) to achieve high supercapacitor performance. As an ...inevitable by-product of the thermochemical conversion of biomass, wood tar exhibits good thermoplasticity and high-carbon content, and can be used as an alternative carbon source for biomass to prepare HPCs. To improve the utilization of wood tar, a facile synthetic route is proposed for preparing HPCs, based on a natural biological template method coupled with KOH activation. The HPCs possess favorable features in terms of high solid-carbon yield, high oxygen content (~9 at%), large specific surface areas (626.43–2489.62 m2 g−1), and an interconnected hierarchical porous structure, which greatly improved wettability and synergistically enable the construction of high-performance supercapacitors in aqueous and organic systems. The optimized HPC electrode exhibits a specific capacitance of 338.5 F g−1 in a 6 M KOH electrolyte, and the constructed symmetric supercapacitors deliver high energy densities up to 9.9 Wh kg−1 and 33.87 Wh kg−1 in aqueous and organic electrolytes, respectively. This study provides an effective route for the utilization of wood tar and crab shell waste.
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•Hierarchical porous carbons were synthesized from biomass waste wood tar.•Crab shell template improves the carbon yield and regulates the pore structure.•The effects of pore structure and oxygen-containing groups were investigated.•High capacitance and superior energy density were reached.
•Volatiles-interaction affected the yield and composition distribution of bio-oil.•Gas yield increased but liquid yield decreased after volatiles-interaction.•CH4 increased above 600 °C in the ...presence of lignin volatiles.•Hemicellulose volatiles increased decomposition of cellulose volatiles.•Cellulose-derived sugars was promoted by hemicellulose or lignin volatiles.
Secondary reactions, including those caused by the interaction of volatiles, are unavoidable during biomass pyrolysis. This study investigated the interactions of the volatiles from cellulose, hemicellulose, and lignin in a two-stage fixed bed reactor without a pre-mixed feedstock. The yield distribution of the products and gases, and the composition of liquids were all affected by the interaction of the volatiles. The interactions increased the gas yield but inhibited the liquid yield. However, when temperature increased, the interactions weakened in the presence of cellulose but increased when hemicellulose and lignin were used. Independent of feedstock, the interactions also generated CO2 and H2 at 400–700 °C and inhibited the generation of CH4 and phenols below 500 °C and 400–700 °C, respectively. However, several feedstock-dependent interactions were also observed: 1) CH4 generation increased at temperatures above 600 °C in the presence of lignin volatiles; 2) both hemicellulose and lignin volatiles resulted in significant amounts of cellulose-derived sugars at temperatures above 500 °C; and 3) hemicellulose volatiles increased decomposition of cellulose volatiles, while the latter inhibited the decomposition of lignin volatiles, when the temperature was below 500 °C.
•The broken of OH bond and CO bond in primary alcohol groups occurs preferentially.•Until 230°C, hydroxyl removal and generation of micropore are due to dehydration.•Formation of carboxyl or ...conjugated ketone and reconstruction of pore occur followed.•Hydrophobicity may have a highly linear correlation with hydroxyl and micropore.
The evolution of physicochemical structure of two stalks during torrefaction and its correlation with the hydrophobicity were investigated. Two-dimensional perturbation correlation infrared spectroscopy was used to study the evolution of functional groups. The pore structure of torrefied stalks was analyzed based on the isothermal adsorption of N2 and CO2. During torrefaction, the removal of hydroxyl groups on the holocellulose resulted in dehydration and formation of carboxyl and conjugated ketone. The breaking of OH bond and CO bond in primary alcohol groups occurs preferentially for cotton stalk and corn stalk, respectively. Due to the modification of structure, the macropores diminished while more micropores formed. Equilibrium moisture content decreased significantly when torrefaction temperature increased, suggesting that hydrophobicity is improved by torrefaction. Meanwhile, the removal of hydroxyl and the formation of micropores had highly linear correlation with the formation of hydrophobicity. The result will be beneficial for better understanding of the mechanism of torrefaction and formation of hydrophobicity.
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