Synthesis and catalytic performance of bimetallic NiMo- and NiW-ZSM-5/MCM-41 composites for production of liquid biofuels

This work presents a synthesis of bimetallic NiMo and NiW modified ZSM-5/MCM-41 composites and their heterogeneous catalytic conversion of crude palm oil( CPO) to biofuels. The ZSM-5/MCM-41 composites were synthesized through a self-assembly of cetyltrimethylammonium bromide( CTAB) surfactant with silica-alumina from ZSM-5 zeolite,prepared from natural kaolin by the hydrothermal technique. Subsequently,the synthesized composites were deposited with bimetallic NiMo and NiW by impregnation method. The obtained catalysts presented a micro-mesoporous structure,confirmed by XRD,SEM,TEM,EDX,NH_3-TPD,XRF and N_2 adsorption-desorption measurements. The results of CPO conversion demonstrate that the catalytic activity of the synthesized catalysts decreases in the series of NiMo-ZSM-5/MCM-41 NiW-ZSM-5/MCM-41 Ni-ZSM-5/MCM-41 Mo-ZSM-5/MCM-41 W-ZSM-5/MCM-41 NiMo-ZSM-5 NiW-ZSM-5 ZSM-5/MCM-41 ZSM-5 MCM-41. It was found that the bimetallic NiMo-and NiW-ZSM-5/MCM-41 catalysts give higher yields of liquid hydrocarbons than other catalysts at a given conversion. Types of hydrocarbon in liquid products,identified by simulated distillation gas chromatography-flame ionization detector( SimDis GC-FID),are gasoline( 150-200 ℃; C5-12),kerosene( 250-300 ℃; C5-20) and diesel( 350 ℃; C7-20).Moreover,the conversion of CPO to biofuel products using the NiMo-and NiW-ZSM-5/MCM-41 catalysts offers no statistically significant difference( P 0.05) at 95% confidence level,evaluated by SPSS analysis.     

Locally Factorisable Transformation Semigroups

A semigroup S is factorisable if S = GE = EG where G is a subgroup of S and E is the set of idempotents in S; and S is locally factorisable if eSe is factorisable for every e E. In this paper, we unify and extend results which characterise when certain transformation semigroups defined on a set are (locally) factorisable, and we consider the corresponding problem for the semigroup of linear transformations of a vector space.To Yupaporn Kemprasit, mentor of semigroup theorists in Thailand1991 Mathematics Subject Classification: 20M20The third section of this paper formed part of an MSc supervised by the first author. She greatly appreciates the help of her supervisor in this work; and the first two authors are grateful for the assistance of the third author in the preparation of this paper. The third author also acknowledges the generous support of Centro de Mathematica, Universidade do Minho, Portugal, during his visit in July–August 2000 when the paper was completed.     

Direct diagnosis of tuberculosis by computer assisted pattern recognition gas chromatographic analysis of sputum

Chemical detection of tuberculosis (TB) products in sputum was attempted by using gas chromatographic analysis in conjunction with different pattern recognition computer models. For the chromatographic separations, we used a 2 mm x 1.8 m packed column and a 0.25 mm x 30 m fused silica capillary column to analyse the methylated glycosides and fatty acid methyl ester derivatives. Three computer pattern recognition methods were applied: error score, TB score and discriminant analysis. These methods predicted the presence of active TB most often in sputa of active TB patients and less so in those from inactive, suspected and non-TB patients, in that order. Although the best true positive of 75% was obtained from the TB score method and best true negative of 98% from discriminant analysis, the accompanying false positive and false negative results (36% and 50%, respectively) were unacceptable. The use of capillary column or fatty acid methyl ester derivatives of the samples did not improve on the predictive values of chromatograms obtained from the packed column on trimethylsilylglycosidic derivatives. Additional work is needed before this method can have a direct clinical application.     

A microfluidic system for evaluation of antioxidant capacity based on a peroxyoxalate chemiluminescence assay

A microfluidic system incorporating chemiluminescence detection is reported as a new tool for measuring antioxidant capacity. The detection is based on a peroxyoxalate chemiluminescence (PO-CL) assay with 9,10-bis-(phenylethynyl)anthracene (BPEA) as the fluorescent probe and hydrogen peroxide as the oxidant. Antioxidant plugs injected into the hydrogen peroxide stream result in inhibition of the CL emission which can be quantified and correlated with antioxidant capacity. The PO-CL assay is performed in 800-μm-wide and 800-μm-deep microchannels on a poly(dimethylsiloxane) (PDMS) microchip. Controlled injection of the antioxidant plugs is performed through an injection valve. Of the plant-food based antioxidants tested, β-carotene was found to be the most efficient hydrogen peroxide scavenger (SA _HP of 3.27 × 10⁻³ μmol⁻¹ L), followed by α-tocopherol (SA _HP of 2.36 × 10⁻³ μmol⁻¹ L) and quercetin (SA _HP of 0.31 × 10⁻³ μmol⁻¹ L). Although the method is inherently simple and rapid, excellent analytical performance is afforded in terms of sensitivity, dynamic range, and precision, with RSD values typically below 1.5%. We expect our microfluidic devices to be used for in-the-field antioxidant capacity screening of plant-sourced food and pharmaceutical supplements. Figure Assembled PDMS microchip sandwiched between two glass plates with the top plate containing capillary reservoirs     

Importance of direction of vibration on the onset of Soret-driven convection under gravity or weightlessness

This paper considers the influence of the direction of vibration on the stability threshold of two-dimensional Soret-driven convection. The configuration is an infinite layer filled with a binary mixture, which can be heated from below or from above. The limiting case of high-frequency and small-amplitude vibration is considered for which the time-averaged formulation has been adopted. The linear stability analysis of the quasi-mechanical equilibrium shows that the problem depends on five non-dimensional parameters. These include the thermal Rayleigh number ( Ra_T), the vibrational parameter (R), the Prandtl number ( Pr), the Lewis number (Le), the separation ratio (S) and the orientation of vibration with respect to the horizontal heated plate (). For different sets of parameters, the bifurcation diagrams are plotted Ra_c = f (S) and k_c = g(S), which are the critical thermal Rayleigh and the critical wave numbers, respectively. Our results indicate that, relative to the classical case of static gravity, vibration may affect all regions in Ra_c-S stability diagram. In the case of mono-cellular convection, by using a regular perturbation method, a closed-form relation for the critical Rayleigh number is found. Several physical situations in the presence or in the absence of gravity (micro-gravity) are discussed.     

Use of unmodified silver nanoparticles (AgNPs) as colorimetric Hg(II) sensor: A new approach to sensitive and high sample throughput determination of Hg(II) under high influence of ionic suppression

Facile unmodified silver nanoparticles (AgNPs) as colorimetric sensor for determination of Hg(II) ions in aqueous samples were developed using UV-Vis spectrophotometry. Abrupt change in absorbance of the AgNPs was observed, which progressively decreased and slightly shifted to the blue wavelength as the concentration of Hg(II) increased. It appears that the AgNPs were oxidized by Hg(II), resulting in disintegration of the AgNPs and Hg(0). Deposition of Hg(0) on the surface of AgNPs also occurred, resulting in amalgam particles of mercury (Hg-Ag). Interestingly, the developed approach showed a significant enhancement in the Hg(II) analytical sensitivity when formic acid was doped onto the AgNPs, with the linearity range of 0.01–10 mg L^?1 (r² = 0.999) providing the quantitative detection limit of 0.007 mg L^?1 (3SD blank/slope of the calibration curve). Greater selectivity toward Hg(II) over other ions and colour dyes was also observed, likely a result of stabilization by polyvinylpyrrolidone (PVP), which kept the AgNPs well-stabilized and dispersed in the bulk aqueous environment making them resistant to ionic suppression. Under using a 96-well microplate and a smartphone equipped with homemade application as a colorimetric analyzer under controlled lighting, high sample throughput (128 sample h^?1, n = 4) was achieved, establishing its potential for practical analysis. The percentage recoveries of spiked aqueous samples obtained from the microplate-based system were in acceptable range, in agreement with the values obtained from the UV-Vis spectrophotometry-based system. The proposed colorimetric sensor has been shown to provide a rapid, simple, sensitive and selective detection of Hg(II) ions in various aqueous samples.     

Poly(m-ferrocenylaniline) modified carbon nanotubes-paste electrode encapsulated in nafion film for selective and sensitive determination of dopamine and uric acid in the presence of ascorbic acid

A nafion covered carbon nanotubes-paste electrode modified with poly(m-ferrocenylaniline), (Nf/p(FcAni)-CNTsPE), provides a novel voltammetric sensor for the selective determination of dopamine (DA) and uric acid (UA) in the presence of ascorbic acid (AA). We studied the electrochemical activity of Nf/p(FcAni)-CNTsPE toward DA, UA, and AA by differential pulse voltammetry (DPV). DA and UA anodic peaks appear at 0.30 and 0.45 V, respectively while an anodic peak for AA was not observed. DPV oxidation peak values are linearly dependent on DA concentration over the range 1–150 μM (r² = 0.992), and on UA concentration over the range 5–250 μM (r² = 0.997). DA and UA detection limits are estimated to be 0.21 and 0.58 μM, respectively. The modified electrode shows both good selectivity and reproducibility for the selective determination of DA and UA in real samples. Finally, the modified electrode was successfully applied for the determination of DA and UA in pharmaceutical or biological sample fluids.