In this study, heat treatment was carried out in a relatively low temperature (230 degrees C). Mass loss kinetics was studied using equipment, specially conceived to measure sample's mass during the ...thermal treatment. Laboratory experiments were performed for heating rates of 1 degrees C min(-1). Mathematical model for kinetics of pyrolysis process was used and validated. During the pyrolysis of dry wood samples under inert atmosphere, measurements of temperature distribution and dynamic weight loss were performed. Five different wood species Fagus sylvatica (Beech), Populus nigra (Poplar), Fraxinus excelsior (Ash), Pinus sylvestris (Pine) and Abies pectinata (Silver Fir) were investigated. The unsteady-state mathematical model equations were solved numerically using the commercial package Femlab 2.0. A detailed discussion of the computational model and the solution algorithm is given. The validity of different model assumptions was analyzed. Experimental results were compared with those calculated by the model. Acceptable agreement was achieved.
Last decades, wood was promoted as building material. Wood heat treatment by mild pyrolysis has been reported to improve biological durability and dimensional stability of the material and ...constitutes an attractive `` non biocidal `` alternative to classical preservation treatments. Previous studies have shown that conferred properties strongly depend on the heat treatment intensity. A quality control marker based on mass loss has been developed. For several years, the increased development of Tunisian wood industry provides a significant capacity of wood production and transformation. Forests in Tunisia consist essentially of coniferous species Aleppo pine (Pinus halepensis), Radiata pine (Pinus radiata), Maritime pine (Pinus pinaster), Stone pine (Pinus pinea), characterised by a weak natural durability. Improved durability and fungal resistance should allow the use of Tunisian species in the wood industry. Import limitation of European species and the use of local species allow the conservation of economic value added in the country and improve the economic balance. For this reason, several Tunisian softwood species (Aleppo pine, Radiata pine and Maritime pine) have been heat-treated under vacuum atmosphere at 230 degrees C to obtain a thermal degradation with mass losses of approximately 8, 10 and 12%. The oven device allows recording the dynamic Mass Loss (ML) during the treatment and following the thermodegradation kinetic. The chemical composition of the studied wood samples was determined before and after heat treatment. For each wood species and treatment intensity, wood chemical and mechanical analyses were performed by measuring O/C ratio, bending and hardness tests. Afterward, tests of decay resistance were performed according to the EN 113 Standard, with different fungal attacks (Poria Placenta, Coriolus Versicolor) at 22 degrees C and 70% of humidity for 16 weeks. Results were related to the mass loss. Furthermore, intensity of thermal degradation was evaluated by TD-GC-MS. Treated and untreated wood samples were maintained during 15 minutes at 230 degrees C under nitrogen in the thermodesorption tube in order to analyse and compare resulting from the wood thermodegradation volatile compounds.
Wood heat treatment is an attractive alternative to improve decay resistance of wood species with low natural durability. However, this improvement of durability is realized at the expense of the ...mechanical resistance. Decay resistance and mechanical properties are strongly correlated to thermal degradation of wood cells wall components. Mass loss resulting from this degradation is a good indicator of treatment intensity and final treated wood properties. However, the introduction of a fast and accurate system for measuring this mass loss on an industrial scale is very difficult. Nowadays, many studies are conducted on the determination of control parameters which could be correlated with the treatment conditions and final heat treated wood quality such as decay resistance. The aim of this study is to investigate the relations between kinetics of temperature used during thermal treatment process representing heat treatment intensity, mass losses due to thermal degradation and conferred properties to heat treated wood. It might appear that relative area of treatment temperature curves is a good indicator of treatment intensity. Heat treatment with different treatment conditions (temperature-time) have been performed under vacuum, on four wood species (one hardwood and three softwoods) in order to obtain thermal degradation mass loses of 8, 10 and 12%. For each experiment, relative areas corresponding to temperature kinetics, mass loss, decay resistance and mechanical properties have been determined. Results highlight the statement that the temperature curves' area constitutes a good indicator in the prediction of needed treatment intensity, to obtain required wood durability and mechanical properties such as bending resistance and Brinell hardness.
Torrefaction is a thermal treatment step in a temperature range of 210–240 °C, which aims to improve the dimensional stability and durability of wood. The mass loss kinetics for torrefaction of wood ...samples was studied using equipment specially conceived to measure mass losses during thermal treatment. Laboratory experiments were performed under nitrogen for heating rates of 0.1, 0.25, 1, and 2 °C min
−1
. A mathematical model for the kinetics of the thermodegradation process was used and validated. Measurements of temperature distribution and anhydrous mass loss were performed on dry sample of poplar wood during torrefaction in an inert atmosphere for different temperatures. The mathematical formulation describing the simultaneous heat and mass transfers requires coupled nonlinear partial differential equations. These unsteady-state mathematical model equations were solved numerically by the commercial package FEMLAB for the temperature under different treatment conditions. A detailed discussion of the computational model and the solution algorithm is given below. Once the validity of different assumptions of the model had been analyzed, the experimental results were compared with those calculated by the model. Acceptable agreement was achieved.
Low-cost materials containing carboxyl groups have been synthesized by grafting succinic anhydride onto sawdust and cotton fibers. These materials were used after activation with NaHCO
3
for the ...removal of Cu
2+
from water. Removal of copper was carried out at different concentrations in a discontinuous reactor and in a continuous adsorption column. The adsorption of Cu
2+
obeys to the Langmuir isotherm law and the values determined for the separation factor show that the system adsorbent/adsorbed substance is favorable to the adsorption process. Copper desorption and adsorbent regeneration can be achieved with diluted acid.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, GIS, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
A new model for the prediction of particle dispersion in homogeneous isotropic stationary turbulence, based on an autoregressive moving average (ARMA) process, is presented in order to predict the ...fluctuating component of the fluid velocity along a heavy particle path. This model accounts for the crossing trajectory effect in that the transverse fluid velocity correlation is perfectly consistent with the negative loop correlation derived by Wang and Stock (1993). The particle turbulent intensity is shown to be increased compared to predictions based on exponential correlations. Possible consequences of the finite particle Reynolds number are also investigated, showing that the anisotropy of the motion of heavy particles is increased by nonlinear drag effects. In case of zero mean drift velocity, significant effects of nonlinear drag may also appear.
Low-cost materials containing carboxyl groups have been synthesized by grafting succinic anhydride onto sawdust and cotton fibers. These materials were used after activation with NaHCO... for the ...removal of ... from water. Removal of copper was carried out at different concentrations in a discontinuous reactor and in a continuous adsorption column. The adsorption of ... obeys to the Langmuir isotherm law and the values determined for the separation factor show that the system adsorbent/adsorbed substance is favorable to the adsorption process. Copper desorption and adsorbent regeneration can be achieved with diluted acid. (ProQuest: ... denotes formulae/symbols omitted.)
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, GIS, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
This study is devoted to a chemical reaction, carried out in a gaseous phase under isothermal conditions and without internal convective flow. Traditionally, in the mass-balance equations, the ...transport of reactants and products in a porous catalyst is introduced by the diffusion phenomenon in gaseous phase. The reaction rate then is written as a function of the reactant's and product's concentrations in gaseous phase G.F. Froment, K.B. Bischoff, Chemical Reactor Analysis and Design, Wiley, New York, 1979. However, in stationary conditions and with the hypothesis of the thermodynamic equilibrium between the gaseous and the adsorbed phase, the existence of a concentration gradient in the gaseous phase brings about a concentration gradient in the adsorbed phase. The diffusion process occurring in the adsorbed phase is usually neglected in the traditional modeling. The present work aims to investigate the influence of the considered diffusion processes on the evaluation of the performance of the catalyzed chemical reaction. The analysis is based on the study of a simple chemical reaction and consecutive reactions. The study shows that the flux of consumed reactant, evaluated by a traditional way could be different from the flux obtained with the diffusion in the adsorbed phase. Also, in these conditions the kinetic parameters obtained by the traditional modeling of the experimental results do not represent then the real kinetic parameters.
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