HIx system thermodynamic model for hydrogen production by the Sulfur–Iodine cycle

The HI_x ternary system (H₂O–HI–I₂) is the latent source of hydrogen for the Sulfur–Iodine thermo-chemical cycle. After analysis of the literature data and models, a homogeneous approach with the Peng–Robinson equation of state used for both the vapor and liquid phase fugacity calculations is proposed for the first time to describe the phase equilibrium of this system. The MHV2 mixing rule is used, with UNIQUAC activity coefficient model combined with of hydrogen iodide solvation by water. This approach is theoretically consistent for HI_x separation processes operating above HI critical temperature. Model estimation is done on selected literature vapor–liquid, liquid–liquid, vapor–liquid–liquid and solid–liquid equilibrium data for the ternary system and the three binaries subsystems. Validation is done on the remaining literature data. Results agree well with the published data, but more experimental effort is needed to improve modeling of the HI_x system.     

Diffusion Coefficient Measurements Under Reduced Gravity Conditions by Means of the Shear Cell Technique. The Impact of Free Surfaces

A recent computational methodology is applied here in order to analyze the impact of free surfaces on the measurement of the interdiffusion coefficients if shear cells are used. Calculations indicate that the above-mentioned impact depends on the intensity of the solutal Marangoni convection but mainly on the number of active Marangoni segments, that is to say, on the extent of the free surface considered. Bulk solutal convection due to reduced gravity levels is not relevant if the gravity vector acts orthogonally to the gradient of concentration.     

Bunsen section thermodynamic model for hydrogen production by the sulfur–iodine cycle

A model for the Bunsen section of the Sulfur–Iodine thermo-chemical cycle is proposed, where sulfur dioxide reacts with excess water and iodine to produce two demixing liquid aqueous phases (H₂SO₄ rich and HI rich) in equilibrium. Considering the mild temperature and pressure conditions, the UNIQUAC activity coefficient model combined with Engels' solvation model is used. The complete model is discussed, with HI solvation by water and by iodine as well as H₂SO₄ solvation by water, leading to a very high complexity with almost hundred parameters to be estimated from experimental data. Taking into account the water excess, a successful reduced model with only 15 parameters is proposed after defining new apparent species. Acids total dissociation and total H⁺ solvation by water are the main assumptions. Results show a good agreement with published experimental data between 25 °C and 120 °C.     

“Tropicalisation” of Feed-in Tariffs: A custom-made support scheme for hybrid PV/diesel systems in isolated regions

The interest and actions towards introducing renewables for off-grid regions has increased due to their ostensible cost-effectiveness, eco-friendliness and quality services provided. Nevertheless, in many isolated areas diesel generators appear as a common option, confirming that there is a need for financial support mechanisms that aid the introduction of renewables due to their higher initial investment costs.This paper proposes a so-called ‘tropicalisation’ of the Feed-in Tariff scheme to promote the introduction of hybrid systems in isolated communities based on the idea of awarding for each kWh produced by renewable energies a premium value during a guaranteed period of time. The proposed Renewable Energy Premium Tariff (RPT) scheme is an alternative mechanism to the usual initial investment donation for off-grid energy development projects by recognising the production of renewable electricity and opting for a long-term sustainability of the projects. Ecuador presents ideal conditions to study the introduction of such a ‘tropicalised’ scheme since a Feed-in Law including off-grid projects was established in 2002 and since there are governmental and local efforts for the introduction of renewable hybrids in isolated regions.Modelling of the introduction of photovoltaics (PVs) into diesel systems for several mini-grids located in isolated regions of Ecuador has been performed, and included a detailed financial analysis for optimisation of RPT values and a comparison with existing stand-alone diesel systems. The results show the cost-effectiveness of PV/diesel hybrids over diesel gensets, taking into account present and future diesel prices. To obtain long-term sustainability of the project, the RPT values are set at 0.70–1.20$ kWh covering the operability of the whole system for 20 years, where the renewable fraction should have the largest share in the hybrid system. The proposed mechanism is expected to aid the introduction of renewable technologies to bring solutions and sustainable energy options to final users of off-grid isolated regions.     

Improvement of epoxy thermosets using a thiol‐ene based polyester hyperbranched polymer as modifier

The anionic curing initiated by 1‐methyl imidazole of diglycidyl ether of bisphenol A with a hyperbranched polymer (HBP) containing long aliphatic chains in the structure were studied. The hydroxyl groups present as chain ends in the HBP structure played an important role in the curing kinetics, as demonstrated by differential scanning calorimetry, Fourier transform infrared spectroscopy and rheological studies. Properties such as shrinkage on curing and thermomechanical characteristics were also investigated. The structure of the HBP, which contains long aliphatic chains and reactive hydroxyl groups as chain ends, flexibilizes the network significantly, improving the impact resistance without notably affecting either the glass transition temperature or the microhardness of the modified thermosets. Copyright © 2012 Society of Chemical Industry     

Crosslinking of mixtures of diglycidylether of bisphenol‐A with 1,6‐dioxaspiro[4.4] nonan‐2,7‐dione initiated by tertiary amines: III. Effect of hydroxyl groups on network formation

BACKGROUND: Blends of epoxy resin oligomers, diglycidylether of bisphenol‐A (DGEBA), and a bislactone, 1,6‐dioxaspiro[4.4]nonan‐2,7‐dione (s(γBL)), were anionically copolymerized using two tertiary amines as anionic initiators. Their curing rheology and gelation behaviour were studied to provide a more comprehensive knowledge of the curing of these previously studied systems. RESULTS: The activation energy for gelation was found to be similar to that previously measured using differential scanning calorimetry and appeared to increase in the presence of the bislactone. The reaction rate during copolymerization of DGEBA with s(γBL) was slower than DGEBA homopolymerization alone because the alkoxide attack on the epoxide is faster than the reaction of the carboxylate ion and the epoxy group. The effect of the initiator type on the gel conversion was small and was presumably due to differences in the kinetic chain length caused by amine regeneration from the quaternary amine. For the same initiator and at a constant ratio of DGEBA/s(γBL), an increase in the hydroxyl concentration of the DGEBA oligomer raised the gel conversion. For a DGEBA oligomer with low hydroxyl levels, an increase in the concentration of s(γBL) increased the gel conversion; however, for a DGEBA oligomer with high hydroxyl levels, increasing s(γBL) concentration decreased the gel conversion. CONCLUSION: These results are interpreted in terms of the effect of initiation rate and chain transfer rate on the kinetic chain length. The glass transition temperature of the gel was found to be controlled by the fraction of the aliphatic s(γBL) and the amount of plasticizing sol in the matrix. Copyright © 2009 Society of Chemical Industry     

Gas pollutants removal in a single- and two-stage ejector-venturi scrubber

The absorption of SO₂ and NH₃ from the flue gas into NaOH and H₂SO₄ solutions, respectively has been studied using an industrial scale ejector–venturi scrubber. A statistical methodology is presented to characterise the performance of the scrubber by varying several factors such as gas pollutant concentration, air flowrate and absorbing solution flowrate. Some types of venturi tube constructions were assessed, including the use of a two-stage venturi tube.

The results showed a strong influence of the liquid scrubbing flowrate on pollutant removal efficiency. The initial pollutant concentration and the gas flowrate had a slight influence. The use of a two-stage venturi tube considerably improved the absorption efficiency, although it increased energy consumption.

The results of this study will be applicable to the optimal design of venturi-based absorbers for gaseous pollution control or chemical reactors.     

Low-intensity optical bistability in an active Fabry-Perot mirror induced by input-phase-insensitive parametric downconversion

A Fabry-Perot resonator filled with second-order nonlinear optical material is investigated. Attention is devoted to making the resonator act as a nonlinear mirror for ultralow-intensity light signals that can be switched by a control beam at the second-harmonic frequency. The interaction process is an input-phase-independent parametric downconversion. The theoretical problem is solved through implementation of a dummy variable method optimized for a parametric process. Efficient amplification and bistability of low-intensity signals have been found.