Optimization of the separation of sulfur hexafluoride and nitrogen by selective adsorption using monte carlo simulations

We present molecular simulations to find the optimal conditions for the separation by adsorption of SF₆ from a gaseous mixture with N₂, a mixture of key interest in electrical applications. The effect of pore size, pressure, and mixture compositions on the selective adsorption of SF₆ was investigated by using Grand Canonical Monte Carlo simulations with simple fluid models and a simplified model of MCM‐41. Simulations performed with multisite fluid models confirm that general trends are predicted using simple models, including a maximum in SF₆ selectivity for pore diameters around 1.1 nm. Simulations were also performed using two atomistic models of zeolite‐templated carbon (ZTC), FAU‐ZTC, and EMT‐ZTC, materials with average pore sizes close to 1.1 nm, obtaining high selectivities for both materials. Selectivities for FAU‐ZTC are approximately four times higher than the best materials published for this mixture separation, opening excellent opportunities to use it for recovering SF₆ from SF₆/N₂ mixtures. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

Nonisothermal crystallization behavior of a biodegradable segmented copolymer constituted by glycolide and trimethylene carbonate units

Nonisothermal crystallization of a segmented copolymer constituted by glycolide and trimethylene carbonate units was studied from both the melt and the glass state by optical microscopy, differential scanning calorimetry and time‐resolved X‐ray diffraction techniques. Positive spherulites with a fibrilar appearance were always obtained and corresponded to the crystallization of the polyglycolide hard segments. A single crystallization regime and the kinetic parameters were inferred from optical microscopy data on crystallizations performed at different cooling/heating rates. The parameters were in good agreement with values previously deduced from isothermal experiments. Isoconversional data of melt and glass nonisothermal crystallizations were combined to obtain the Lauritzen and Hoffman parameters from calorimetric data. Results revealed again the existence of a single crystallization regime with a secondary nucleation constant close to that deduced from isothermal DSC experiments. Morphological changes occurring during the hot and cold crystallization were evaluated by time‐resolved SAXS/WAXD experiments employing synchrotron radiation. Measurements showed that significant differences on the lamellar thicknesses exist depending on the crystallization process. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Phytal: A Candidate Sex Pheromone Component of the Moroccan Locust Dociostaurus maroccanus

Outbreaks of locusts cause enormous economic losses to agriculture in many countries. To develop environmentally friendly strategies for their control, much research has been focused on the factors that influence locust biology, particularly infochemical‐mediated interactions. We present herein the identification and synthesis of both Z and E isomers of phytal (3,7,11,15‐tetramethylhexadec‐2‐enal, 1 ), which are involved in chemical communication and behaviour of the Moroccan locust, Dociostaurus maroccanus, a serious agricultural pest. The compound was identified by comparison of its chromatographic and spectrometric features and microchemical reactions with those of a synthetic sample. The natural compound was shown to have the R,R configuration by chiral HPLC analysis, and its structure is unique as an insect pheromone component. Both isomers of phytal are produced by sexually mature adult males and elicit electroantennographic responses in antennae of both sexes. In two‐choice olfactometer bioassays, males and females significantly preferred the stream enriched with racemic phytal to the control. In contrast, hydrogenated phytal was behaviourally inert. Both isomers of phytal are specific to D. maroccanus as they are absent in the closely related, habitat‐sharing species Dociostaurus jagoi and Calliptamus wattenwylianus. Legs and wings are the main release sites of the compound: approximately 90 % of that emitted by living individuals. In biosynthetic studies, phytal appears to proceed from oxidation of phytol ( 2 ) after injection of deuterated phytol into the abdomen of the insect or after administration in the diet. Our results demonstrate that phytal is a candidate sex pheromone component of the Moroccan locust; it is produced by mature males, and might be eavesdropped upon by conspecific males.     

Atomistic modeling of the effects of dose and implant temperature on dopant diffusion and amorphization in Si

We discuss atomistic simulations of ion implantation and annealing of Si over a wide range of ion dose and substrate temperatures. The DADOS Monte Carlo model has been extended to include the formation of amorphous regions, and this allows simulations of dopant diffusion at high doses. As the dose of ions increases, the amorphous regions formed by cascades eventually overlap, and a continuous amorphous layer is formed. In that case, most of the excess interstitials generated by the implantation are swept to the surface as the amorphous layer regrows, and do not diffuse in the crystalline region. This process reduces the amount of transient enhanced diffusion (TED) during annealing. This model also reproduces the dynamic annealing during high temperature implants. In this case, the local amorphous regions regrow as the implant proceeds, without the formation of a continuous amorphous layer. For sufficiently high temperatures, each cascade is annealed out independently; interstitials and vacancies can escape from the cascade and thus increase dopant diffusion.     

Characterization of pili nut (Canarium ovatum) oil: Fatty acid and triacylglycerol composition and physicochemical properties

The fatty acid and triacylglycerol composition of pili nut (Canarium ovatum) oil and fractions were analyzed by gas chromatography and reversed-phase high-performance liquid chromatography, respectively. The oil obtained by solvent extraction was low in polyunsaturated fatty acids and high in saturates. The polyunsaturated fatty acid (18∶2 and 18∶3) contents were less than 11%, whereas palmitic (16∶0) and stearic acid (18∶0) were 33.3 and 10.9%, respectively. The saturated fatty acid level of the low-melting fraction oil was reduced from 44.4 to 35.5% and the total unsaturated fatty acid levels were increased from 55.6 to 65% by fractional crystallization. Triacylglycerol analysis showed that the high-melting fraction (HM) from pili nut oil consisted of POP, POS, and SOS+SSO (P=palmitic acid, O=oleic acid, and S=stearic acid) in the proportion of 48.6, 38.8, and 8.7%, respectively. The physicochemical properties of the HM fraction were studied using differential scanning calorimetry and pulsed nuclear magnetic resonance. The results showed that the melting range and solid fat content of the HM fraction were very similar to those isolated from cocoa butter and olive oil. The content of POP played an important role in determining the melting range of the HM fraction. It is suggested that this HM fraction may have applications as a cocoa butter substitute in confectionery products.     

Improved Toughness of Polylactide by Binary Blends with Polycarbonate with Glycidyl and Maleic Anhydride-Based Compatibilizers

This work reports on the development of polylactide (PLA) and polycarbonate (PC) blends with different compatibilizers with enhanced toughness. Since both polymers are immiscible, two types of compatibilizers are tested: petrochemical-based copolymers Xibond 160 and Xibond 920 with maleic anhydride and epoxy groups, respectively, and natural-based compatibilizers with the same functionalities, namely maleinized linseed oil (MLO) and, epoxidized linseed oil (ELO). Mechanical, thermal, and morphological characterization shows better properties for the PLA/PC (80/20 wt%) blends with chemically modified natural oils (ELO and MLO). The addition of 5 phr (parts per hundred resin) of MLO gives the maximum values for impact strength and elongation at break. Moreover, the glass transition temperature (T_g) slightly decreases with the addition of natural compatibilizers, thus showing some plasticization effect. Petroleum-derived compatibilizers give interesting results regarding tensile strength and stiffness without plasticization. PLA/PC blends show higher thermal stability than neat PLA, regardless of the compatibilizer used, since PC is much more thermally stable than PLA. The obtained results indicate that both petroleum-based and natural-derived compatibilizers positively contribute to enhance the properties of the binary PLA/PC blends. Nevertheless, the results with MLO suggest this is an interesting biobased solution to provide increased toughness to PLA/PC blends.     

Stabilization of soil by means alternative alkali-activated cement prepared with spent FCC catalyst

Alkali-activated cements are widely studied as alternative and sustainable binder in soil stabilization. In this research work, a mold was designed and constructed, which allowed small cubic specimens to be made (40 × 40 × 40 mm³). With the newly designed mold, cubic samples of soil stabilized with portland cement (OPC) and alternative AAC (based on spent fluid catalytic cracking catalyst FCC) were prepared from which compressive strength was obtained. Cylindrical specimens were also prepared using the same binders as in the previous case to obtain their compressive strength. The results obtained in both cases were compared. Greater resistances for cubic samples were achieved. The cubic specimens were selected for being better in terms of standard deviation of compressive strength for AAC stabilized soil. The obtained compressive strength and standard deviation results were compared between the soil specimens stabilized with different stabilizers cured at 7, 14, 28, and 90 days. The method allows small-sized cubic specimens to be prepared. It improves ergonomics. It also facilitates a large number of specimens being obtained with a small amount of sample. Soil stabilized with AAC yielded higher compressive strength after 90 days compared to that with OPC.     

Gemeinsame kondensation von harnstoff,melamin und formaldehyd. I. Einfluß der reaktionsparameter

The dependance of the simultaneous polycondensation of urea, melamine, and formaldehyde on reaction conditions was studied using chromatographic and spectroscopic methods. The results indicate an increase in the reactivity between urea and formaldehyde and also between melamine and formaldehyde with increasing acidity. A. controllable reaction involving simultaneously urea, melamine, and formaldehyde was possible only in neutral and basic media. An increasing proportion of urea in the reaction mixture increases the degree of polycondensation. A comparison of the three-component-resin with the UF-and MF-resins gives information pertaining to the formation of cocondensats consisting of urea and melamine. Acetone dilutability and turbidimetric measurements are in agreement with the results of chromatographic and spectroscopic methods.     

Nutritive value of chicken and potato mixtures for infant and preschool children feeding

Two chicken/potato protein mixtures (50:50 and 60:40) were prepared for use in formulas of high nutritive value and low cost for the diet of undernourished children and those with lactose intolerance. The proximate analysis and amino acid content of the raw materials and mixtures were determined and the chemical score (CS) was calculated. The proximate analysis and amino acid content of a commercial soybean formula were used as reference. The protein quality of the mixtures was evaluated by protein efficiency ratio (PER) and digestibility measurements. The protein content of cooked chicken and potato on a dry basis was 889 and 70 g kg^?1 respectively and the carbohydrate content of potato was 762 g kg^?1. Tryptophan was the limiting amino acid in chicken for infants according to the 1985 FAO pattern (CS = 76), but not for preschool children. Valine was limiting in potato for both infants and preschool children (CS = 56 and 88 respectively). Tryptophan was limiting in both 50:50 and 60:40 mixtures for infants; also the PER was higher in the 60:40 mixture and not significantly different from the control (casein), but both were different from the 50:50 mixture. Since both chicken and potato are available even for low‐income people, a formula prepared in the 60:40 ratio is of potential benefit for infants or preschool children who have lactose intolerance, mainly in developing countries. Copyright © 2003 Society of Chemical Industry