Catalytic behavior of vanadium-containing mesoporous silicas in the oxidative dehydrogenation of propane

Three series of vanadium-containing silica catalysts (2–7.6 wt% V) have been prepared by varying the synthesis method. In all cases, conversion values in the oxidative dehydrogenation of propane increase with the temperature, vanadium loading and reducibility. For impregnated and anchored catalysts, a relationship between the selectivity towards propene and the effective acidity, as determined in the dehydration of 2-propanol, can be established. This revised version was published online in July 2006 with corrections to the Cover Date.     

Polymerisation of styrene using Y, USY and β zeolites as catalysts

The homopolymerisation of styrene is studied in the presence of Y, USY and beta zeolites. High molecular weight polymers, in the range 0.7 × 10⁶–1 × 10⁶, are obtained in good yields. The activity of zeolite beta is only slightly increased by calcination of the as-synthesised material, pointing to an important role of the zeolite outer surface. The influence of the catalyst acidity upon the polymer molecular weight is evaluated by the use of dealuminated zeolites. This revised version was published online in July 2006 with corrections to the Cover Date.     

In-situ Mössbauer spectroscopic study of the behaviour of tin(II) chloride during coal hydrogenation

In-situ Mössbauer spectroscopy has been used to study the catalytic role of SnCl₂ and its interaction with the IL6 coal during hydrogenation. The measurements have been recorded under three different atmospheres of nitrogen, hydrogen, and hydrogen in the presence of a heavy distillate solvent SRC-II. The study has shown that both tin and chlorine can enter the coal structure at an early stage of hydrogenation. The presence of chlorine has been shown to cause the cleavage of ether-oxygen linkages in the coal. Tin (II) sulphide is the predominant form of the catalyst after the hydrogenation and is the product of the scavenging of coal sulphur by tin. The study has also shown the formation of FeCl₂ · xH₂0 (x = 1, 2) as a result of the reaction between pyrrhotites (Fe_(1?x)S, formed by the decomposition of FeS₂) and hydrochloric acid in the nitrogen and the hydrogen atmospheres.     

Influence of Processing Parameters on the Sintering and Electrical Properties of Pb(Zn1/3Nb2/3)O3-Based Ceramics

Pb(Zn_1/3Nb_2/3)O₃-based ceramics have been prepared by two different processing methods: conventional (PZN-C) and reaction-sintering (PZN-RS). The conventionally prepared PZN-based ceramics densified at lower temperatures (950°C) than the reaction-sintered samples (1100°C), but the perovskite/pyrochlore ratio was always higher in PZN-RS. The presence of a substantial amount of pyrochlore phase in PZN-C ceramics caused a decrease in the electrical properties. The maximum dielectric constant values in PZN-C ceramics were 10%–15% lower than those of PZN-RS, despite a similar average grain size, 7 ± 0.2 μm. The temperature of the maximum of the dielectric constant ( T _max) was lower than that expected from the mixing rule because of the possible formation of Ba–Nb clusters. The higher chemical homogeneity in PZN-RS ceramics is the main reason for the higher dielectric constant, T _max and electromechanical response, as well as for the lower difference between T _max and the depolarization temperature ( T _d) and the lower diffusiveness parameter (δ).     

Synthesis of asymmetric diglycidyl ester compounds. Reaction with aromatic diamines

New diglycidyl esters coming from the corresponding diacids and epichlorohydrin were synthetized using a quaternary ammonium salt as a catalyst. The new asymmetric compounds were characterized by spectroscopic methods and employed as starting monomers in a crosslinking process. The course of the reactions was followed by IR spectroscopy. Some intermediate species were identified in the onset of the reactions by recording ¹³C-NMR spectra until the products became insoluble in the usual deuterated solvents. The thermal behaviour of these cured epoxy resins was also studied.     

DIMENSIONLESS CORRELATION FOR THE HEAT TRANSFER COEFFICIENT IN A BATCH-INDIRECT ROTARY DRIER

A batch-indirect rotary drier heated with steam was experimentally operated to obtain data of moisture content and temperature versus time for soy meal and fish meal. Operation conditions were as follow: steam pressure (1 to 4 bar), rotation speed (3.7 to 11.6 r.p.m.) and rate of vapor extraction (0.059 to 0.256 m/s).

From experimental data the effective heat transfer coefficient between the hot surface and the bed of solids was determined. These data were correlated by means of dimensional analysis as a function of the drying process variables. The equation obtained for the effective Nusselt number predicts adequately the effective heat transfer coefficient, for both substrates, in the range of the operating variables studied.     

A pipeline structure for the block QR update in digital signal processing

The Journal of Supercomputing - There exist problems in the field of digital signal processing, such as filtering of acoustic signals that require processing a large amount of data in real time....