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The radiation field in an annular photocatalytic reactor is simulated using a Monte Carlo method (MC) for two TiO 2 suspensions in water. Simulations are performed by using both the spectral distribution and the wavelength-averaged scattering and absorption coefficients. The Henyey-Greenstein phase function is adopted to represent forward, isotropic, and backward scattering modes. It is assumed that the UV lamp reflects the backscattered photons by the slurred medium. Photoabsorption rates using MC simulations and spectral distribution of the optical coefficients agree closely with experimental observations from a macroscopic balance. It is found that the scattering mode of the probability density function is not a critical factor for a consistent representation of the radiation field. MC simulation for the optimal catalyst concentration reveals that the maximum LVREA is reached at a concentration of 0.14 g L -1 for TiO 2 Degussa P25. From this concentration, the apparent optical thickness is determined to be 2.8476 which is in agreement with the optimal one previously reported. This concentration is comparable to that determined experimentally for phenol photocatalytic degradation.

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Photocatalytic conversion of a model pollutant (methylene blue) is studied in a novel Photo-CREC reactor unit. The experiments developed allow us to investigate the suitability of an heterogeneous reaction model which accounts for the concentrations of the model pollutant both in the bulk and on the mesh-TiO 2 . In addition, a photochemical-thermodynamic efficiency factor (PTEF) is further examined, with the help of the enthalpy of • OH formation from water and oxygen and based on the analysis in the light energy absorbed by the mesh. The resulting PTEF is a dimensionless parameter and has to be calculated at high enough model pollutant concentrations, that is, at conditions where zero-order reactions prevail. The PTEF values found in the Photo-CREC unit with the incorporated recent technical improvements are in the 0.0182 level, and this represents quantum yields of 6.31% of the so-called ideal efficiency.

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A thermodynamic equilibrium model based on evaluations involving C, H, and O element balances and various product species up to C 6 hydrocarbons is reported in this study. This model establishes the effects of biomass composition, temperature, and steam on the various gas product molar fractions. On this basis, most significant parameters determining the chemical interconversions and distribution of chemical species are identified. On the basis of the proposed equilibrium model and using glucose as a model biomass species [C 6 H 12 O 6 ], an optimum gasification temperature close to 800 °C and a steam/biomass ratio between 0.5 and 0.7 g/g is established. This study has the special value of comparing thermodynamic equilibrium predictions with experimental data obtained in a CREC riser simulator using a fluidizable Ni-Al 2 O 3 catalyst. Results are relevant for scaled-up gasifiers. They show that for reaction times longer than 30 s chemical species are essentially equilibrated and that the proposed model does provide adequate description of various product fractions. Data obtained also demonstrate the shortcomings of equilibrium models for gasifiers with reaction times shorter than 10 s and the need for nonequilibrium models to describe gasifier performance at such conditions.

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OH • radicals react in photocatalytic reactors via adsorbed species on the catalytic surface through complex reaction mechanisms leading to complete mineralization of organic molecules. Our research group has recently contributed with kinetic modeling of the photocatalytic network using a parallel-series reaction network. This kinetic approach helps toward the assessment of the photocatalytic thermodynamic efficiency factors (PTEF) and quantum yields (QY). Efficiency calculations consider stoichiometric relationships involving observable chemical species and OH • groups. These stoichiometric equations set the OH • requirements for reaching a particular intermediate species and for the complete mineralization of them. On this basis, the PTEF and QY factors for phenol photoconversion point toward a high degree of photon utilization as in the case of Photo-CREC units and, as a result, confirm the value of photocatalysis for the conversion of organic pollutants in water.