Infrared spectroscopy and multivariate calibration to monitor stability quality parameters of biodiesel

This paper evaluates analytical methods based on near infrared (NIR) and middle infrared (MIR) spectroscopy and multivariate calibration to monitor the stability of biodiesel. There was a focus on three parameters: oxidative stability index, acid number and water content. Ethylic and methylic biodiesel from different feedstocks were used in experiments of accelerated aging, in order to take into account the wide variety of oilseeds and feedstocks available in Brazil. Partial least squares (PLS) and multiple linear regression (MLR) models were developed. Different pre-processing techniques and spectral variable/regions selection algorithms were evaluated. For MLR models, the successive projection algorithm (SPA) was employed. Interval PLS (iPLS) and selection of variables taking into account the significant regression coefficients were used for PLS models. Results showed that both near and middle infrared regions, and all variable selection methods tested were efficient for predicting these three important quality parameters of B100, the root mean squares error of prediction (RMSEP) values being comparable to the reproducibility of the corresponding standard method for each property investigated.     

Some Results on Stability of Retarded Functional Differential Equations Using Dichotomic Map Techniques

This paper deals with the study of the stability of nonautonomous retarded functional differential equations using the theory of dichotomic maps. After some preliminaries, we prove the theorems on simple and asymptotic stability. Some examples are given to illustrate the application of the method. Main results about asymptotic stability of the equation and of itsnonlinear generalization are established.     

Feedstock recycling of polyethylene over AlTUD-1 mesoporous catalyst

The catalytic degradation of high density polyethylene (HDPE) was investigated using AlTUD-1 as catalyst, a recently discovered mesoporous aluminosilicate. The catalytic activity of AlTUD-1 was evaluated by TGA measurements, using a polymer/catalyst ratio of 9:1. AlTUD-1 has a Brønsted acidic behaviour, three-dimensional (3D) connectivities and a pore diameters between 2 and 50 nm. Compared to HY zeolite, the large pore size of AlTUD-1 enhances a selective catalytic degradation of the polymer and prevents rapid deactivation. Moreover, the apparent activation energy of polymer cracking is much lower than with HY zeolite. For these reasons, AlTUD-1 is a potentially interesting catalyst for the catalytic cracking of plastic waste into liquid fuels.     

Lipase production byPenicillium restrictum in a bench-scale fermenter

A preliminary screening work selectedPenicillium restrictum as a promising micro-organism for lipase production. The physiological response of the fungus towards cell growth and enzyme production upon variable carbon and nitrogen nutrition, specific air flow rate (Qa) and agitation (N) was evaluated in a 5-L bench-scale fermenter. In optimized conditions for lipase production meat peptone at 2% (w/v) and olive oil at 1% (w/v) were used in a growth medium with a C/N ratio of 9.9. Higher C/N ratios favored cell growth in detriment of enzyme production. Low extracellular lipase activities were observed using glucose as carbon source suggesting glucose regulation. Final lipase accumulation of 13,000 U/L was obtained, using optimized specific air flow rate (Qa) of 0.5 wm and an impeller speed (N) of 200 rpm. Agitation showed to be an important parameter to ensure nutrient availability in a growth medium having olive oil as carbon source.     

Thermogravimetric investigations on the thermal degradation of bixin,derived from the seeds of annatto (<Emphasis Type=”Italic”>Bixa orellana L.</Emphasis>)

Conventional methods have been proposed to determine thermal properties of edible vegetable oils. The evaluation of the applicability of DSC and microwave oven (MO) methods to determine the specific heat capacities of the edible vegetable oils was performed. It was observed that the specific heat capacities of each edible oil increased as a function of the saturation of the fatty acids.     

Degradation of polyamide 11 in rotational moulding

The degradation of polyamide 11 (PA 11) was studied in samples rotationally moulded using a range of processing temperatures. The chemical changes occurring in the moulded material were assessed using FTIR, UV-vis spectroscopy, ¹H NMR spectroscopy, gas chromatography, rheometry and microscopy. The results showed that the degradation is complex and depends on the location of the material in the moulding. At the internal surface, the degradation is predominantly thermo-oxidative leading to the formation of carbon dioxide, carboxylic acids and conjugated unsaturated oligo-enimines (UV-vis-active chromophores). Away from the internal surface, the dominant process is through the recombination of broken chains and/or post-condensation reactions that increase the molecular weight without the formation of UV-vis-active chromophores. A degradation mechanism is proposed for PA 11 in rotational moulding.     

Global analysis of planar neural networks

In this paper, the global qualitative analysis of cubic dynamical systems is established. These systems are used as learning models of planar neural networks.     

Vapor pressure and intramolecular hydrogen bonding in fluorotelomer alcohols

Vapor pressure and aqueous solubility are important parameters used to estimate the potential for transport of chemical substances in the atmosphere. For fluorotelomer alcohols (FTOHs), currently under scrutiny by environmental scientists as potential precursors of persistent perfluorocarboxylates (PFCAs), vapor pressure is the more significant property since these compounds are only very sparingly soluble in water. We have measured the vapor pressures of a homologous series of fluorotelomer alcohols, F(CF2CF2)nCH2CH2OH (n = 2-5), in the temperature range 21-250 degrees C by three independent methods: (a) a method suitable for very low vapor pressures at ambient temperatures (gas-saturation method), (b) an improved boiling point method at controlled pressures (Scott method), and (c) a novel method, requiring milligram quantities of substance, based on gas-phase NMR, a technique largely unfamiliar to chemists and holding promise for studies of relevance to environmental chemistry. The concordant values obtained indicate that recently published vapor pressure data overestimate the vapor pressure at ambient temperature, and therefore the volatility, of this series of fluorinated compounds. It was suggested that substantial intramolecular -O-H...F- hydrogen bonding between the hydroxylic proton and the two fluorines next to the ethanol moiety was responsible for their putative high volatility. Therefore, we have used gas-phase NMR, gas-phase FTIR, 2D NMR heteronuclear Overhauser effect measurements, and high-level ab initio computations to investigate the intramolecular hydrogen bonding in fluorotelomer alcohols. Our studies unequivocally show that hydrogen bonding of this type is not significant and cannot contribute to and cause unusual volatility. The substantially lower vapor pressure at ambient temperatures than previously reported resulting from our work is important in developing a valid understanding of the environmental transport behavior of this class of compounds.     

Thermospray flame furnace-AAS determination of copper after on-line sorbent preconcentration using a system optimized by experimental designs.

The present paper describes the on-line coupling of a flow-injection system to a new technique, thermospray flame furnace-AAS (TS-FF-AAS), for the preconcentration and determination of copper in water samples. Copper was preconcentrated onto polyurethane foam (PUF) complexed with ammonium O,O-diethyldithiophosphate (DDTP), while elution was performed using 80% (v/v) ethanol. An experimental design for optimizing the copper preconcentration system was established using a full factorial (2(4)) design without replicates for screening and a Doehlert design for optimization, studying four variables: sample pH, ammonium O,O-diethyldithiophosphate (DDTP) concentration, presence of a coil and the sampling flow rate. The results obtained from the full factorial and based on a Pareto chart indicate that only the pH and the DDTP concentration, as well as their interaction, exert influence on the system within a 95% confidence level. The proposed method provided a preconcentration factor of 65 fold, thus notably improving the detectability of TS-FF-AAS. The detection limit was 0.22 microg/dm3 and the precision, expressed as the relative standard deviation (RSD) for eight independent determinations, was 2.7 and 1.1 for copper solutions containing 5 and 30 microg/dm3, respectively. The procedure was successfully applied for copper determination in water samples.     

Dominance Criteria for the Capacitated Warehouse Location Problem

The paper examines the capacitated warehouse location problem where fixed costs, generally relating to the installation of warehouses and variable costs, consisting mainly of transportation costs, are minimized. The minimization of each kind of cost drives the solution towards opposite directions with respect to the number of warehouses to be opened/closed. Therefore, dominance criteria between fixed and variable costs are examined. This leads to exact tests as well as greedy heuristics, the latter known in the literature as ADD/DROP techniques.