Green synthesis of vanillin: Pervaporation and dialysis for process intensification in a membrane reactor

In the present work, two different membrane processes (pervaporation and dialysis) are compared in view of their utilization in a membrane reactor, where vanillin, which is probably the most important aroma of the food industry, is synthesized in a green and sustainable way. The utilized precursor (ferulic acid, which is possibly a natural product from agricultural wastes) is partially oxidized (photocatalytically or biologically) and the product is continuously recovered from the reacting solution by the membrane process to avoid its degradation. It is observed that pervaporation is much more selective towards vanillin than dialysis, but the permeate flux of dialysis is much higher. Furthermore, dialysis can work also at lower temperatures and can be used to continuously restore the consumed substrate into the reacting mixture. A mathematical model of the integrated process (reaction combined with membrane separation) reproduces quite satisfactorily the experimental results and can be used for the analysis and the design of the process

Visible Light Induced Oxidation of Trans-ferulic Acid by TiO2 Photocatalysis

The oxidation of trans-ferulic acid (C 10H 10O 4) in aqueous TiO 2 dispersion occurs via the formation of a charge-transfer complex on the TiO 2 surface that is able to absorb visible light (\u3bb 65 400 nm). The main product is CO 2, whereas secondary oxidation products are organic species such as vanillin, caffeic acid, homovanillic acid, and vanillylmandelic acid. Oxidation through the formation of a charge-transfer complex occurs only in the presence of specific TiO 2 samples. Experiments in the absence of oxygen, in the presence of bromate ions and by using a phosphate-modified TiO 2, have been carried out for investigating the reaction mechanism. In order to study the interaction between trans-ferulic acid and TiO 2 surface and to characterize the charge-transfer complex, UV-Vis diffuse reflectance and FT-IR spectroscopies have been used. FT-IR characterization of TiO 2 samples in contact with the aqueous trans-ferulic acid solution indicates that the charge-transfer complex formation occurs via adsorption of bidentate ferulate species

Modeling the drug release from hydrogel-based matrices

In this work the behavior of hydrogel-based matrices, the most widespread systems for oral controlled release of pharmaceuticals, has been mathematically described. In addition, the calculations of the model have been validated against a rich set of experimental data obtained working with tablets made of hydroxypropyl methylcellulose (a hydrogel) and theophylline (a model drug). The model takes into account water uptake, hydrogel swelling, drug release, and polymer erosion. The model was obtained as an improvement of a previous code, describing the diffusion in concentrated systems, and obtaining the erosion front (which is a moving boundary) from the polymer mass balance (in this way, the number of fitting parameters was also reduced by one). The proposed model was found able to describe all the observed phenomena, and then it can be considered a tool with predictive capabilities, useful in design and testing of new dosage systems based on hydrogels

Intensification of Water Detoxification by Integrating Photocatalysis and Pervaporation

Many studies have been made on the possibility of increasing the efficiency of the photocatalytic detoxification of water streams, since for several practical applications the need for increasing the yield of the process is important. In the present work, the integration of photocatalysis with a membrane separation process is studied in order to analyze the possibility of enhancing the efficiency. It is experimentally shown that for the integrated process, the rate of disappearance of a model pollutant (4-chlorophenol) is highly improved. Then it is demonstrated that this \u201cprocess intensification\u201d takes place through synergetic mechanisms that are identified, discussed, and optimized

Optimization of the thickness of a photocatalytic film on the basis of the effectiveness factor

In a supported ‘‘thick’’ photocatalytic film, internal diffusion of the reactant and transport of the photons might hinder the reactivity of the material and limit the obtainable rate of removal of the organic pollutant substrate. The effectiveness factor of the photocatalytic film is the index of the extent of the limitation. Two dimensionless parameters affect the effectiveness factor: the optical thickness and the ratio, alpha, of the characteristic time of diffusion with respect to the characteristic time of reaction. The analysis demonstrates that the process is controlled by the diffusion of the substrate when the parameter alpha is high and it is controlled by the transport of the photons when the optical thickness is high. It is also shown that different results are obtained if the film is illuminated from the fluid–film interface (PF) or from the glass–film interface (CF). In PF the observed rate of degradation increases with the film thickness, but no further enhancement of the rate of degradation is obtained when the thickness exceeds the depth where a substantial depletion of the photons or of the substrate takes place. In CF the rate of degradation reaches a maximum at an optimal thickness. Finally, a new simple procedure to estimate the parameters and then to predict the best thickness is illustrated

A Rational Approach to the Design of Photocatalytic Reactors

A model to assess the performances of an annular photocatalytic reactor has been developed by investigating different operational conditions through an analysis based on the proper dimensionless parameters (namely, the optical thickness, the Thiele modulus and two among the well-known Damkohler and Peclet numbers, which are properly redefined). Different dependences of the reaction kinetics on the local rate of radiant energy absorption are also considered. Because the progress of the reaction is affected by the radiation field, all these parameters are dependent on the catalyst concentration and then indirectly on the catalyst load. The conditions under which an optimal value for the catalyst concentration may exist are determined, thus contributing to provide insight to one aspect that is quite controversial in the literature

Study and optimization of an annular photocatalytic slurry reactor

The experimental results obtained for the photocatalytic degradation of a model organic dye in an annular slurry reactor are analyzed with the aid of a mathematical model. The model is used also to study the effects on the performances of many operative conditions: flow rate, photocatalyst concentration, power of the lamp, size of the photocatalytic particles, dimensions of the reactor. The investigation demonstrates that the rate of the process is often limited by the radiant energy transfer and that some simple rules can be followed in order to optimize different yields and the observed rate of reaction