Combining thermal model and kinetics: Implications in dynamic simulation of anaerobic digesters.

In this study, ADM1-based kinetics were combined with a thermal model that accounts for various heat transfers inside and through the reactor's boundaries. Computing the energy of bioreactions based on kinetic rates prevented an overestimation of approximately 20% in the heat demand of the heat exchanger, compared to calculations using feedstock degradation heat. This also improved the representation of the digester's thermal and reactional inertia. Simulations across different climates demonstrated the necessity to tailor digester construction. In the North West United Kingdom, biogas auto-consumption was 23% higher than that of the same reactor in South West France. Enhancing the thermal insulation of the digester reduced heat losses by 37% in the United Kingdom. Therefore, coupling the kinetic and thermal models expands the insights that can be extracted from simulations, which can be valuable in optimizing the operation and design of biogas digesters.

Fixed-bed adsorption of toluene on high silica zeolites: experiments and mathematical modelling using LDF approximation and a multisite model.

The adsorption of toluene (TOL) as a target volatile organic compound has been studied experimentally and modelled on various hydrophobic zeolites: Faujasite (FAU), ZSM-5 (Z) and Mordenite (MOR). The influence of the nature of the compensating cation (H+ or Na+) has also been investigated for ZSM-5 zeolite, which is known to possess three kinds of adsorption sites (sinusoidal channels, straight channels and intersections). Type I isotherms observed on FAU, Na-Z and MOR fitted well with the Langmuir model. A deviation from a type I isotherm was observed for H-Z, because of the structure of this zeolite. The Successive Langmuir Model was more successful to fit the 'bump' of the experimental curve than the Double Langmuir. Classical shapes were found for MOR, FAU and Na-Z breakthrough curves that were fitted with good accuracy using the Linear Driving Force (LDF) approximation. In the case of H-Z, a change of profile was observed during the dynamic adsorption and the differences seen between the Na-Z and H-Z behaviours were explained by the strong interactions between Na+ and adsorbed TOL at the intersection sites. The Na+ cations prevented reorientation of TOL molecules at the intersection and thereby avoided the filling of the sinusoidal channel segments. Thus, a specific model was developed for fitting the breakthrough curve of H-Z. The model developed took into account these two types of adsorption sites with the overall uptake for each site being given by an LDF approximation.

Measurement and modelling of adsorption equilibrium, adsorption kinetics and breakthrough curve of toluene at very low concentrations on to activated carbon.

Indoor air pollution, characterized by many pollutants at very low concentrations, is nowadays known as a worrying problem for human health. Among physical treatments, adsorption is a widely used process, since porous materials offer high capacity for volatile organic chemicals. However, there are few studies in the literature that deal with adsorption as an indoor air pollution treatment. The aim of this study was to investigate the adsorption of toluene on to activated carbon at characteristic indoor air concentrations. Firstly, global kinetic parameters were determined by fitting Thomas's model to experimental data obtained with batch experiments. Then, these kinetic parameters led to the determination of Henry's coefficient, which was checked with experimental data of the adsorption isotherm. Secondly, we simulated a breakthrough curve made at an inlet concentration 10 times higher than the indoor air level. Even if the kinetic parameters in this experiment are different from those in batch experiments, it can be emphasized that the Henry coefficient stays the same.