Analysis of design variables for water-gas-shift reactors by model-based optimization

This work analyzes the water-gas-shift reactor design as component of the CO clean-up system of the ethanol processor for H₂ production applied to PEM fuel cells. The WGS reactor constitutes the element of greater volume of the processor motivating its optimization. A model-based reactor optimization for different reactor configurations permits to obtain both designs for reducing volumes and optimal operating conditions. The heterogeneous model used allows computing the optimal reactor length and diameter, and the optimal catalyst particle diameter. The model computes the constraints required for catalyst, such as maximum and minimum operation temperature. The volume is sensitive to the CO outlet concentration. According to the required CO conversion it is necessary more than one reactor unit for the case study analyzed. When considering the insulating material, there exists an optimal thickness that affects the final volume and the design variables. These results are useful for estimating the minimum and relative sizes that allows conventional reactor technology.     

Supported Faceted Gold Nanoparticles with Tunable Surface Plasmon Resonance for NIR‐SERS

A novel dry plasma methodology for fabricating directly stabilized substrate‐supported gold nanoparticle (NP) ensembles for near infrared surface enhanced Raman scattering (NIR SERS) is presented. This maskless stepwise growth exploits Au‐sulfide seeds by plasma sulfidization of gold nuclei to produce highly faceted Au NPs with a multiple plasmon resonance that can be tuned from the visible to the near infrared, down to 1400 nm. The role of Au sulfidization in modifying the dynamics of Au NPs and of the corresponding plasmon resonance is discussed. The tunability of the plasmon resonance in a broad range is shown and the effectiveness as substrates for NIR SERS is demonstrated. The SERS response is investigated by using different laser sources operating both in the visible and in the NIR. SERS mapping of the SERS enhancement factor is carried out in order to evaluate their effectiveness, stability, and reproducibility as NIR SERS substrates, also in comparison with gold NPs fabricated by conventional sputtering and with the state‐of‐the‐art in the current literature.     

Spectrokinetic Analysis of the NOx Storage Over a Pt–Ba/Al2O3 Lean NOx Trap Catalyst

In this work the kinetics of the (reactive) lean accumulation phase of the NO_x storage-reduction process is described through a detailed kinetic model, involving both the gas-phase molecules and the adsorbed species. Kinetic data have been collected following a novel approach based on simultaneous operando spectroscopic measurements and on-line pulse reactor effluent analysis. To our knowledge, this is the first time the temporal evolutions of the concentration of both the surface and the gas species are used jointly to describe the kinetic of a transient catalytic process.     

Effect of municipal solid waste compost and sewage sludge use on wheat (Triticum durum): growth,heavy metal accumulation,and antioxidant activity

BACKGROUND: Inappropriate utilisation of biosolids may adversely impact agrosystem productivity. Here, we address the response of wheat (Triticum durum) to different doses (0, 40, 100, 200 and 300 t ha^?1) of either municipal solid waste (MSW) compost or sewage sludge in a greenhouse pot experiment. Plant growth, heavy metal uptake, and antioxidant activity were considered. RESULTS: Biomass production of treated plants was significantly enhanced at 40 t ha^?1 and 100 t ha^?1 of MSW compost (+48% and +78% relative to the control, respectively). At the same doses of sewage sludge, the increase was only 18%. Higher doses of both biosolids restricted significantly the plant growth, in concomitance with the significant accumulation of heavy metals (Ni²⁺, Pb²⁺, Cu²⁺ and Zn²⁺), especially in leaves. Leaf activities of antioxidant enzymes (ascorbate peroxidase, glutathione reductase, catalase and superoxide dismutase) were unchanged at 40 t ha^?1 MSW compost or sewage sludge, but were significantly stimulated at higher doses (200–300 t ha^?1), together with higher leaf concentration of reduced glutathione. CONCLUSION: This preliminary study suggests that a MSW supply at moderate doses (100 t ha^?1) could be highly beneficial for wheat productivity. Copyright © 2010 Society of Chemical Industry     

Energy efficiency analysis of an integrated glycerin processor for PEM fuel cells: Comparison with an ethanol-based system

The aim of this work is to analyze energetically the use of glycerin as the primary hydrogen source to operate a proton exchange membrane fuel cell. A glycerin processor system based on its steam reforming is described departing from a previous process model developed for ethanol processing. Since about 10% w/w of glycerin is produced as a byproduct when vegetable oils are converted into biodiesel, and due to the later is increasing its production abruptly, a large glycerin excess is expected to oversaturate the market. The reformed stream contains mainly H₂ but also CO, CO₂, H₂O and CH₄. As CO is a poison for PEM fuel cell type, a stream purification step is previously required. The purification subsystem consists of two water gas shift reactors and a CO preferential oxidation reactor to reduce the CO levels below 10 ppm. The reforming process is governed by endothermic reactions, requiring thus energy to proceed. Depending on the system operation point, the energy requirements can be fulfilled by burning an extra glycerin amount (to be determined), which is the minimal that meets the energy requirements. In addition a self-sufficient operation region can be distinguished. In this context, the water/glycerin molar ratio, the glycerin steam reformer temperature, the system pressure, and the extra glycerin amount to be burned (if necessary) are the main decision variables subject to analysis. Process variables are calculated simultaneously, updating the composite curves at each iteration to obtain the best possible energy integration of the process. The highest net system efficiency value computed is 38.56% based on the lower heating value, and 34.71% based on the higher heating value. These efficiency values correspond to a pressure of 2 atm, a water/glycerin molar ratio of 5, a glycerin steam reformer temperature of 953 K, and an extra glycerin amount burned of 0.27 mol h⁻¹. Based on the main process variables, suitable system operation zones are identified. As in practice, most PEM fuel cells operate at 3 atm, optimal variable values obtained at this condition are also reported. Finally, some results and aspects on the system performance of both glycerin and ethanol processors operated at 3 atm are compared and discussed.     

Biochemical composition of two red seaweed species grown on the Brazilian coast

BACKGROUND: Algae species have been used as an important source of food because they are highly nutritive considering their vitamin, protein, mineral, fiber, essential fatty acid and carbohydrate contents. However, a large number of seaweeds have been poorly studied, especially Brazilian species. Two red macroalgae species from the Brazilian coast (Plocamium brasiliense and Ochtodes secundiramea) were assessed with respect to their total lipid, fatty acid, total nitrogen, protein, amino acid and total carbohydrate contents. RESULTS: The total lipid contents (dry weight) were 36.3 and 35.4 g kg^?1; fatty acid contents were 9.3 and 12.1 g kg^?1; total nitrogen contents were 37.4 and 24.9 g kg^?1; protein contents were 157.2 and 101.0 g kg^?1; amino acid contents were 127.5 and 91.4 g kg^?1; and total carbohydrate contents were 520.3 and 450.7 g kg^?1 for P. brasiliense and O. secundiramea, respectively. CONCLUSION: Considering these compositions, both algae species were determined to have sources of protein, essential amino acids and carbohydrates similar to the edible seaweeds Laminaria japonica and Palmaria palmata. Copyright © 2011 Society of Chemical Industry