Hydrolysis of lignocellulosic biomass is a crucial step for the production of sugars and biobased platform chemicals. Pretreatment experiments in a semi-continuous plant with diluted sulphuric acid ...as catalyst were carried out to measure the time-dependent formation of sugars (glucose, xylose, mannose), furfurals, and organic acids (acetic, formic, and levulinic acid) at different hydrolysis temperatures (180, 200, 220 °C) of one representative of each basic type of lignocellulose: hardwood, softwood, and grass. The addition of the acid catalyst is followed by a sharp increase in the sugar concentration. Xylose and mannose were mainly formed in the initial stages of the process, while glucose was released slowly. Increasing the reaction temperature had a positive effect on the formation of furfurals and organic acids, especially on hydroxymehtylfurfural (HMF) and levulinic acid, regardless of biomass type. In addition, large amounts of formic acid were released during the hydrolysis of miscanthus grass. Structural changes in the solid residue show a complete hydrolysis of hemicellulose at 180 °C and of cellulose at 200 °C after around 120 min reaction time. The results obtained in this study can be used for the optimisation of the hydrolysis conditions and reactor design to maximise the yields of desired products, which might be sugars or furfurals.
•Pyrolysis of beech wood particles in a bubbling fluidized bed was investigated.•Effect of beech wood particle shape on their pyrolysis conversion was studied.•A high-precision scale was used to ...measure the beech wood mass evolution.•Pyrolysis time is proportional to the particles heat transfer characteristic length.•A simple shrinking model proposed can properly predict the effect of particle shape.
The effect of biomass particle shape on the conversion of beech wood during pyrolysis in a bubbling fluidized bed (BFB) was experimentally quantified. A lab-scale BFB installed on a high-precision scale was used to characterize the mass loss of the biomass particles immersed in the bed. The scale could monitor the mass loss of the beech wood particles while moving freely inside the bed, which was operated at 2.5 times the minimum fluidization velocity of the bed material employed. The tests were performed at 500 and 600 °C using beech wood particles of the same mass, but different in shape. All particles used were cylindrical in shape, with the same mass, and differing in their aspect ratio, analyzing particles from typical biomass chips to standard biomass pellets. The experimental results indicate that the velocity of pyrolysis for the different particles is proportional to the characteristic heat transfer length of the particles, with pyrolysis times ranging from 27 to 53 s for a bed temperature of 600 °C and from 43 to 85 s for a bed temperature of 500 °C. The minimum pyrolysis time was obtained for particles with a diameter of 20 mm and a length of 2 mm pyrolyzing in a bed at 600 °C, whereas the maximum pyrolysis time corresponds to particles of 10 mm in diameter and 8 mm in length converting in a bed at 500 °C. Estimations of the conversion time obtained from a Shrinking Unreacted Particle Model (SUPM), assuming a constant density and reducing volume of biomass during conversion, and a Uniform Conversion Model (UCM), considering uniform volume and decreasing density of biomass along the conversion process, were compared to experimental measurements of the conversion time. Qualitative agreement was found between the experimental values and the predictions of the conversion time from the simplified models, obtaining in all cases conversion times proportional to the characteristic length of heat transfer of each particle shape.
•Thermogravimetry coupled with Fourier transform infrared analysis was applied.•Estimation of kinetic parameters of beech wood by three model-free methods.•K-K method was used to predict the peak ...locations of three main components.•The gases evolved were identified by the spectra.•The heating rate had little influence on the produced composition.
Pyrolysis of beech wood (Fagus sylvatica) was investigated based on thermogravimetric analysis coupled with Fourier transform infrared spectrometry analysis at heating rates from 20K/min to 60K/min. The various activation energies were estimated at different conversions by three model-free methods and were in the range of 146.84–174.44kJ/mol. The peak locations of three main components (hemicellulose, cellulose and lignin) were predicted more exactly by the K-K method. The absorbance spectra corresponding to the three peak locations were basically the same at different heating rates, indicating that the heating rate had little influence on the produced composition. During the whole pyrolysis process, the evolution of gas components (CO, CO2, methane, methanol and formaldehyde) was consistent with the trend of derivative thermogravimetric curves, and possible formation pathways of main gases were tentatively presented. The amount of these five components produced in the order of most to least produced was formaldehyde>CO2 or methanol>methane>CO. In particular, the amount of formaldehyde was almost triple the amount of methanol and ten times the amount of methane at the maximum peak.
•A new apparatus enabling coupled convective and radiative heating is built.•Glowing and flaming autoignition of 5 and 15 mm wood is experientially studied.•A new glowing ignition temperature ...correlation is proposed.•Da and heat loss ratio are indictors of flaming ignition in gas and solid phases.•An ignitibility map identifying ignition and nonignition regimes is drawn.
Autoignition of solid fuels driven by coupled convective and radiative heating is frequently encountered in fires, whereas its controlling mechanism is rarely revealed. To challenge this issue, autoignition tests of 5 and 15 mm thick cylindrical wood samples were conducted using a newly developed apparatus enabling coupled convective and radiative heating. The total heat flux imposed on wood was maintained at 25 kW/m2, while the fractions of the two heating components changed as the airflow velocity and temperature varied in the ranges of 0–1.51 m/s and 298–473.3 K. Glowing ignition occurred in all scenarios except for one case due to enhanced heat loss and declined radiative heating. Flaming ignition was observed in all conditions except for 298 K airflow temperature. Four stages were identified during flaming combustion: a preheating and deformation stage, a glowing combustion stage, a coupled glowing and flaming combustion stage, and an extinction stage. Compared to 5 mm samples, the surface temperature rise of 15 mm wood was significantly delayed due to its thermally thick nature. By fitting experimental data, a new formula was proposed to correlate glowing ignition temperature with radiative heat flux, airflow velocity, and airflow temperature. Both glowing and flaming ignition times were affected by airflow and radiative heating in a complex manner, and their values to the power of −0.5 approximately linearly depended on radiative heat flux. Damköhler number and nondimensional heat loss ratio were employed to quantitively analyze the flaming ignition propensity. Meanwhile, an ignitability trend map identifying the flaming and non-flaming ignition regimes was drawn.
•Bio-oils from beech wood by hydrothermal liquefaction and fast pyrolysis.•Physical and chemical properties of bio-oils are presented.•Bio-oils generally have a high acidity, iodine values and ...residual carbon.•Hydrothermal bio-oil has a high viscosity and low volatility.
There are many different ways to convert biomass into liquid fuels, mostly referred to as bio-oils. This paper presents the analysis of bio-oils produced by hydrothermal liquefaction and fast pyrolysis of beech wood. Both processes have a wide panel of parameters that can be optimised influencing the oil quality. Results of the analysis show that both oils have high acidities. Iodine values indicate a high degree of unsaturations. These two qualities seem to be inversely proportional in the case of pyrolysis oils. In the case of hydrothermal conversion, additives to adjust the pH such as sodium hydroxide increase oil yields, lower its viscosity but do little to further improve the quality of the oils. For pyrolysis oils, increasing the severity does reduce acidity but at the expense of more unsaturations and a loss in yield. The results show that without extensive upgrading or refining, commercial fuel standards cannot be met. Specific norms and standards are being elaborated for pyrolysis used in specific installations. This paper shows how detailed analysis can help to optimise process parameters with an objective that goes beyond the mass or energy yield.
•A new hybrid PSO-GA algorithm is proposed to gain advantages of PSO and GA.•Genetic evolution is incorporated into PSO to increase its population diversity.•TGA results of two pseudo solids and ...beech wood are analyzed.•Convergency efficiency and accuracy are both improved in PSO-GA.•Compensation effect is found in parameterizing pyrolysis model of wood.
A hybrid optimization algorithm, combining both Particle Swarm Optimization (PSO) and Genetic Algorithm (GA), is proposed to gain the favorable features of each individual algorithm when determining the pyrolysis kinetics of biomass. High convergence efficiency and the capability of avoiding being trapped in local optimal solution are primarily associated with PSO and GA, respectively. Gene operations in GA, including selection, crossover and mutation, are partially incorporated into PSO to increase the population diversity. Pyrolysis of beech wood was experimentally studied at three heating rates, and a numerical solver was established to simulate the pyrolysis details. In order to demonstrate the improved performance of PSO-GA, two pyrolysis models with given reaction schemes and kinetic parameters were adopted to create the acritical thermogravimetric analysis (TGA) curves. Then the kinetics was estimated using PSO-GA and individual GA and PSO. Subsequently, the experimental data were analyzed with the same manner. The results show that PSO-GA has the highest possibility of obtaining desired outcomes followed by PSO and then GA. With fixed population size, PSO-GA converges to a lower fitness function value, corresponding to higher accuracy. The attained kinetics of wood falls into the reported ranges in the literature. In some scenarios, the optimized results of hemicellulose and lignin contradict with the existing conclusions even though the global curves match the experimental measurements well. This implies the general concept of the pyrolysis process should also be given adequate consideration to avoid potential compensation effect when encountering complex issues.
•Compensation effect is minimized using Gauss multi-peak fitting method.•Ea of cellulose and hemicellulose vary in range of 140–220 kJ mol−1.•Ea of lignin varies in range of 30–200 kJ mol−1.•Linear ...dependency of lnA on Ea also exists for high-order reactions.•High-order reaction is more suitable for lignin pyrolysis.
Compensation effect is an unsolved issue when determining pyrolysis kinetics of biomass using inverse modelling and optimization algorithms, implying no unique solution can be obtained. To address this problem, a new method coupling Gauss multi-peak fitting method, Kissinger method, a numerical model, and Shuffled Complex Evolution (SCE) optimization algorithm is proposed to extract kinetics from microscale thermogravimetric analysis (TGA) experiments and avoid attainment of unreasonable good-fit solutions. TGA tests of beech wood at nitrogen atmosphere were conducted at three heating rates. Gauss multi-peak fitting method was employed to separate the overlapped peaks in TGA curves and identify the contribution of each elemental component reaction. The kinetics of individual reactions were estimated by Kissinger method to provide an initial solution for SCE optimization. Then, narrow initial search ranges were determined to further refine the kinetics by SCE. By compiling previous data in literature and our optimization results, it was found compensation effect exists for individual basic components, hemicellulose, cellulose and lignin, following a linear correlation between lnA andEa, and among multiple components. Pyrolysis of hemicellulose can be modelled by either first-order or high-order reactions, while cellulose pyrolysis is more likely a first-order reaction. Nevertheless, the long tail in DTG curves associated with decomposition of lignin can only be captured by a high-order reaction. Although the Kissinger solution of lignin cannot be used in selecting an appropriate search range for SCE optimization, the narrow search ranges of the remaining kinetic parameters can ensure the accuracy and convergency efficiency of optimization.
•Char was obtained during solar pyrolysis at various temperatures and heating rates.•“Solar chars” up to 2000°C and up to 450°C/s have been produced.•Temperature and heating rate jointly affected ...char yield, structure and reactivity.•Reactivity evolution with temperature and heating rate were related to structure.
Char samples were produced from pyrolysis in a lab-scale solar reactor. The pyrolysis of beech wood was carried out at temperatures ranging from 600 to 2000°C, with heating rates from 5 to 450°C/s. CHNS, scanning electron microscopy analysis, X-ray diffractometry, Brunauer–Emmett–Teller adsorption were employed to investigate the effect of temperature and heating rate on char composition and structure. The results indicated that char structure was more and more ordered with temperature increase and heating rate decrease (higher than 50°C/s). The surface area and pore volume firstly increased with temperature and reached maximum at 1200°C then reduced significantly at 2000°C. Besides, they firstly increased with heating rate and then decreased slightly at heating rate of 450°C/s when final temperature was no lower than 1200°C. Char reactivity measured by TGA analysis was found to correlate with the evolution of char surface area and pore volume with temperature and heating rate.
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•Heat treatment led to structural changes in wood cell wall compounds.•Structural changes didn’t affect the elastic modulus but decreased the creep modulus at treating temperature ...higher than 160 °C.•At treating temperature of 160 °C, an improved creep performance.•At relative humidity of 90%, heat treatment led to an improvement in creep behavior.
In this study, wood was heat treated at temperatures of 160, 175 and 190 °C and creep behavior of modified wood at various moisture contents was assessed. Fourier-transform infrared spectroscopy (FTIR) was conducted to find a relation between creep behavior and structural changes, aiming to develop their applications for constructionpurposes. FTIR results showed fundamental structural changes: removal of extractives, hemicelluloses and amorphous parts of cellulose and partial degradation of lignin. Creep results showed that unlike elastic short-term modulus, creep modulus decreased at treating temperature higher than 160 °C. Treated samples at 160 °C had an improved creep performance in moist conditions, attributable to lower degradation of cell wall components and to the lower hygroscopicity.
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