ROLE OF WATER IN THE KINETIC MODELING OF METHANOL TRANSFORMATION INTO HYDROCARBONS ON HZSM-5 ZEOLITE

The attenuating effect of reaction-medium water (feed and/or reaction product) on the kinetics of the steps of methanol transformation into hydrocarbons on a HZSM-5 zeolite catalyst was studied by means of a kinetic model. In this model, the effect of water was quantified in all the steps of the kinetic scheme by means of a kinetic parameter, which is constant with temperature under the conditions of the MTG process. At low temperature, under conditions in which only methanol dehydration occurs, the kinetics of this reaction is attenuated by the presence of water, and the coefficient that quantifies the attenuation decreases as temperature is increased. In addition to considering the effect of water content in the reaction medium, another innovation of the kinetic model proposed, compared to those proposed in the literature consisting of lumps, is the fact that the higher reactivity of dimethyl ether over methanol is taken into account. A step of cracking of gasoline lump hydrocarbons to produce light olefins (ethene and propene) was also taken into account. The kinetic model proposed was verified by using the results obtained in an integral isothermal fixed bed reactor, in the 573-723 K range, for an ample range of space time values. The results revealed that the effect of water is due to its adsorption on the active sites by competition with the intermediate compounds of the kinetic scheme.     

Removal of diazinon by various advanced oxidation processes

Diazinon is a widely used organophosphorus insecticide that is an important pollutant in aquatic environments. The chemical removal of diazinon has been studied using UV radiation, ozone, Fenton's reagent, UV radiation plus hydrogen peroxide, ozone plus hydrogen peroxide and photo‐Fenton as oxidation processes. In the photodegradation process the observed quantum yields had values ranging between 2.42 × 10^?2 and 6.36 × 10^?2 mol E^?1. Similarly, the ozonation reaction gave values for the rate constant ranging between 0.100 and 0.193 min^?1. In the combined systems UV/H₂O₂ and O₃/H₂O₂ the partial contributions to the global oxidation reaction of the direct and radical pathways were deduced. In the Fenton's reagent and photo‐Fenton systems, the mechanism of reaction has been partially discussed, and the predominant role of the radical pathway pointed out. Additionally, the rate constant for the reaction between diazinon and the hydroxyl radicals was determined, with the value 8.4 × 10⁹ L mol^?1 s^?1 obtained. A comparison of the different oxidation systems tested under the same operating conditions revealed that UV radiation alone had a moderate oxidation efficiency, which is enhanced in the case of ozone, while the most efficient oxidant is the photo‐Fenton system. Copyright © 2007 Society of Chemical Industry     

Undesired components in the transformation of biomass pyrolysis oil into hydrocarbons on an HZSM‐5 zeolite catalyst

The results of the catalytic transformation on HZSM‐5 zeolite of mixtures of components of biomass pyrolysis oil in the 673–723 K temperature range are evidence of the need for previously separating certain components (aldehydes, oxyphenols and furfural) that undergo severe thermal degradation by forming carbonaceous deposits at the reactor inlet ducts and on the catalyst itself. The deactivation of the catalyst is a consequence of the deposition of two different types of coke: one of catalytic origin (similar to that generated in the transformation of methanol and bioethanol) and the other of thermal origin, which is produced by the aforementioned degradation. The remaining oxygenate components react to each other with synergistic effect, which means that their reactivity is higher than that of the pure components. The results show that the aqueous fraction of biomass pyrolysis oil may be transformed into hydrocarbons on acid catalysts similarly to the more familiar transformation of methanol and bioethanol. Copyright © 2005 Society of Chemical Industry     

Range-Doppler image processing in linear FMCW radar and FPGA based real-time implementation

The paper introduces an FPGA based signal processing system to perform Range-Doppler processing in real-time for Linear FMCW （frequency Modulated Continuous Wave） radar systems. Novel design architecture in FPGA is proposed and experimental results indicate that the design can verify the correct operation of the processing flow. The Ping-Pang architecture in FPGA saves the resources in chip and the system has been designed so as to allow future addition of complex target detection algorithms.     

Removal of Methylene Blue from aqueous solutions using as biosorbent Sargassum muticum: an invasive macroalga in Europe

Methylene Blue adsorption on Sargassum muticum, an invasive macroalga in Europe, has been investigated using visible absorption spectroscopy. Different pre‐treatments, protonation and chemical cross‐linking with CaCl₂ or H₂CO, have been tested in order to improve the stability as well as the adsorption capacity of the algal biomass. The equilibrium binding has been described in terms of Langmuir or Freundlich isotherms depending on the algal pre‐treatment; from the maximum adsorption capacity values, an estimation of the algal specific surface area was made. Moreover, it has been found that adsorption kinetics can be described according to the first order Lagergren model, from which the rate constant and the adsorption capacity were determined. Finally, simple empirical equations were obtained to evaluate the amount of Methylene Blue removed at any initial concentration and reaction time. The results obtained have shown that this type of material has a high adsorption capacity for Methylene Blue dye, this feature together with the short times needed to reach the equilibrium suggest that Sargassum muticum can be used as a low‐cost biosorbent in wastewater treatments. Copyright © 2004 Society of Chemical Industry     

Enhancement of the solid-liquid extraction of sucrose from sugar beet (Beta vulgaris) by pulsed electric fields

A systematic study of the impact of pulsed electric fields (PEF) parameters (1–7 kV/cm, 5–40 pulses, specific energy of 0.006–0.19 kJ/kg per pulse, pulse frequency of 1–10 Hz, pulse width of 2–5 μs, square and exponential decay pulses) on the kinetics of the sucrose extraction from sugar beet at different temperatures (20–70 °C) has been carried out in this investigation. The efficiency of the solid-liquid extraction was independent of the frequency, as well as of the pulse width, and the pulse shape at 7 kV/cm, and it was influenced by the electric field strength applied and by the temperature of the extracting medium. Sucrose yield increased with both field strength, time of extraction, and temperature. The effect of the field strength was higher the lower the temperature. The application of 20 pulses at 7 kV/cm (3.9 kJ/kg) increased the maximum yield by 7 and 1.6 times, compared to non-PEF-treated samples, at 20 and 40 °C, respectively. A mathematical expression was generated, which enabled to evaluate the influence of the electric field strength (from 0 to 7 kV/cm) and temperature (from 20 to 70 °C) on the sucrose extraction efficiency and the extracting time in a solid-liquid PEF-assisted sucrose extraction process. Based on this equation, for 80%-sucrose extraction in 60 min, the temperature could be reduced from 70 °C to 40 °C, when 20 pulses of 7 kV/cm were applied.     

The impact of fuzziness in social choice paradoxes

Since Arrow’s main theorem showed the impossibility of a rational procedure in group decision making, many variations in restrictions and objectives have been introduced in order to find out the limits of such a negative result. But so far all those results are often presented as a proof of the great expected difficulties we always shall find pursuing a joint group decision from different individual opinions, if we pursue rational and ethical procedures. In this paper we shall review some of the alternative approaches fuzzy sets theory allows, showing among other things that the main assumption of Arrow’s model, not being made explicit in his famous theorem, was its underlying binary logic (a crisp definition is implied in preferences, consistency, liberty, equality, consensus and every concept or piece of information). Moreover, we shall also point out that focusing the problem on the choice issue can be also misleading, at least when dealing with human behaviour.