Improved relationships between kinetic parameters associated with biomass pyrolysis or combustion.

Improved relationships between the kinetic parameters (pre-exponential factor and kinetic energy) associated with biomass pyrolysis or combustion processes are proposed. These relationships rely on observations of the mass and mass rate curves and on the experimental data through computations performed on the kinetic model which describes the mass evolution of each pseudo-component of the biomass during its thermal degradation. These relationships improve the so-called kinetic compensation effect. They are here implemented as part of the Extended Independent Parallel Reaction (EIPR) model.

Modeling SOx trapping on a copper-doped CuO/SBA-15 sorbent material.

A mixture of SO2 and air was continuously injected in a fixed bed reactor containing a CuO/SBA-15 sorbent material and submitted to an isothermal temperature between 325 and 400 °C. The SO2 emissions were measured at the exit of the reactor. Different isothermal temperatures, different injected SO2 concentrations and different sorbent masses, all representative of industrial conditions, were tested. The purpose of the paper was to propose efficient global models which simulate the breakthrough curves whatever the experimental conditions. A simplified model was first considered assuming that the oxidation and trapping processes can occur on each copper site. The values of the four kinetic parameters which are involved were determined solving this model using Scilab software and an optimization routine. Because this model failed to reproduce in a satisfying way the breakthrough curves for different sorbent masses, a second model was introduced which involves surface and bulk trapping sites and six kinetic parameters. The breakthrough curves simulated with this second model following the same resolution techniques were in better agreement with the experimental ones, whatever the experimental conditions. For comparison, a simulation of the breakthrough curves returned by a model with bulk diffusion was presented.

Combustion of hydrolysis lignin in a drop tube furnace and subsequent gaseous and particulate emissions.

The aim of the study was to analyze the combustion of hydrolysis lignin in industrial plants which use pulverized combustible and which are characterized by very high heating rates (up to 105 K/min). Pulverized samples of hydrolysis lignin and of spruce bark or spruce trunk for comparison were injected in a drop tube furnace under an oxidative flow (synthetic air) and under an isothermal temperature (between 800 and 1200 °C) in the reaction zone. The gaseous and particulate emissions were analyzed. Ash was collected at the bottom of the drop tube furnace and analyzed. The fly ash were collected in an electrical low-pressure impactor and analyzed. Whatever the sample, the number of particles PM2.5 was sensitive to the temperature and a minimum was observed which is reached at 900 °C for hydrolysis lignin and spruce bark and at 1100 °C for spruce trunk.

Thermal degradations of wood biofuels, coals and hydrolysis lignin from the Russian Federation: Experiments and modeling.

The thermal degradation of wood biofuels (spruce, pine), of coals from different fields of the Russian Federation and of hydrolysis lignin is investigated using a thermogravimetric analyzer under different heating conditions and under non-oxidative or oxidative atmospheres. The samples are indeed submitted to a linear temperature ramp of 10K/min or to a temperature ramp of 200K/min up to a residence temperature between 250 and 450°C where they are maintained during 4h (isothermal conditions). The values of the kinetic parameters are determined for these different samples in both thermal conditions, either using the differential isoconversional method or by means of an Extended Independent Parallel Reaction (EIPR) model. The values of the kinetic parameters obtained with this EIPR model for spruce trunk are also compared with that of its main constituents (hemicellulose, cellulose and lignin).

Asymptotic analysis of the Poisson-Boltzmann equation in biological membrane channels.

The Poisson-Boltzmann equation has been increasingly used for the description of biomolecular systems in order to derive their electrostatic properties. We here consider a domain consisting of two living cells which communicate through a system of proteins which assemble at specific membrane areas building microchannels called gap junctions. We describe the asymptotic behavior of the solution of the Poisson-Boltzmann equation posed in this domain. Using Γ-convergence tools, we derive some electrostatic properties of the biological membrane with respect to a vanishing parameter which is simultaneously associated to the membrane thinness, to the diameter of the gap junction microchannels and to the Debye length parameter which characterizes the spatial scale electrostatic interactions between particles within the gap junctions.