سال:1391 | دوره: | شماره: |تعداد مقالات:15

Effective methodologies for efficient preparation of semicarbazones from aldehydes or ketones via milling and the subsequent regeneration of the parent carbonyls by gaseous nitrogen dioxide are described under solid-solid and gas-solid reaction conditions, respectively. These methods are fast, simple and environmentally benign which do not require the use of any auxiliaries such as catalysts or solid supports in their procedures.

In this research, the selective oxidation of benzene to maleic anhydride (MAN) in a fixed-bed reactor was studied. The gas phase catalytic oxidation of benzene was carried out in a laboratory scale fixed bed reactor on the catalysts, which were prepared having two different compositions on silica gel. The effects of temperature, flow rates of benzene and air, and catalyst type on the reaction selectivity were investigated at normal atmospheric pressure. The experiments were performed at the temperature range of 300oC to 375oC, the space-time (W/FB0) range was from 1*106 to 2.5*106 g.sec/mole, and the air/ benzene weight ratio changes were between 16-51.Experimental results show that the maximum conversion is obtained at 375oC, at the space-time 1.33*106 g.s/mol and at the benzene/air mol ratio 41.36 by using first catalyst. According to the experimental results, a difference between catalyst 1 and 2, it could not be seen. MAN conversion was observed for both catalysts and both catalysts are suitable for oxidation of benzene to MAN in a fixed bed reactor.

A method to quick detect concentration of lecithin in eggs, namely microwave digestion spectrophotometry, was established in this research. The homogenate of eggs was treated with absolute ethanol to eliminate phosphate protein in eggs which could possibly affect concentration of lecithin examined. A sample then received a new way of pre-treatment, called microwave digestion, before UV-Vis spectrometry was applied to examine the concentration of phosphate at 400nm. The linear equation was A=0.08628X (mg), the corresponding coefficient of correlation was 0.9998, the detection limit of phosphorous was 0.2mg (n=11). The content of lecithin in eggs was then obtained. According to the result, the recovery of 90% was secured; therefore the conclusion of high degree of accuracy was reached.

Oxidation of Methyl Orange (MO) solution in potassium peroxydisulfate (KPS) homogeneous reaction system without UV irradiation was investigated. The result shows that decolorization of MO increases as the dosage of K2S2O8 increases. The kinetic results demonstrate that the decolorization reaction is a pseudo first-order reaction when the concentration of MO is below 10 mg/L and Langmuir-Hinshewood kinetic model (L-H) can well described it, the value of Ea is 19.5 kJ/mol. The decolorization efficiency is low when the pH value is low (£2). Result of CODCr shows MO can be effectively mineralized with KPS direct oxidation. The knowledge on the kinetics of the system and influence of some parameters on the system possesses both practical and theoretical values.

This work deals with the calculation of Franck-Condon factors using Hua potential function for the first time. The advantages of this function have been mentioned, and the numerical methods are used to obtain Franck-Condon factors for the following band systems:Li2: (B1IIU-X1S+g), (A1S+u - X1S+g)CN: (A2II-X1S+), (B2S+ - X2S+)N2: (A3S+u - X1S+g), (B3IIg-A3S+u), (a1IIg-X1S+g), (C3IIu- B3IIg), (C3IIu- X1S+g)CO: (a1II-X1S)Agreement between the values of this work and those obtained from other works is quite good that verifies the reliability of the present calculations

Polycrystalline MFI zeolite membranes were prepared on a-alumina tubular support by hydrothermal treatments at 413 K. The synthesized zeolite membranes were characterized by XRD, SEM and single gas permeation. The influence of hydrothermal treatment steps and the calcination time on the zeolite layer formation were investigated. MFI zeolite membrane prepared by four subsequent hydrothermal treatments and calcined at 673K for 30 h had optimum quality from morphological and crystalline point of view. The grown MFI zeolite layer was uniform with about 20 mm thickness and well-intergrown zeolite crystals.

This paper refers to an experiment of SO2 absorption to the three different sorbents: calcium-oxide (CaO), calcium-carbonate (CaCO3) and dolomite (CaMg (CO3)2). In the reactor under the condition of oxidation atmosphere with the mass of sorbent (sample) of 100 g with fractional composition of 500-700mm, the gas temperature varied from 200°C and 400°C. The examinations indicated that the highest degree of sorbent utilization of 14% was determined for dolomite (CaMg (CO3)2) and the binding degree of SO2 from 65-80% and the lowest for calcium oxide (CaO) of 4% and the binding degree of SO2 from 34-60% at the reaction temperature of 200°C. When the reaction temperature is 400°C the degree of sorbent utilization is a bit lower. The achieved results indicate the injection capability of powdered sorbents CaMg (CO3)2, CaCO3 and CaO in the areas of lower temperatures as it is the convective part of the boiler or furnace flue of the thermo power plant.

This paper deals with the extraction of L-Theanine containing Aliquat 336 as a carrier and cyclohexane as solvent across bulk liquid membrane. The optimum operation condition are as follows: extraction time of 150 min, initial concentration of theanine in the feed phase is 1.8 g/L, the carrier concentration is 0.5 M, the ion of the receiving phase is 0.2 M NaCl of Na2HPO4-NaH2PO4 buffer solution. A mathematical model of transport process was deduced, the forward interfacial reaction rate constants and the backward interfacial reaction rate constants between the feed phase and the membrane phase, the receiving phase and the membrane phase were taken into account in the model equations. Using the experimental results, several parameters of the proposed model have been achieved by a nonlinear fitting method.

Recovery of metabolites from fermentation broth by solvent extraction can be used to optimize fermentation processes. End-product reutilization, low product concentration, large volumes of fermentation broth and the requirements for large bioreactors, in addition to the high cost largely contributed to the decline in fermentative 2, 3-butanediol production. Extraction can successfully be used for in-situ alcohol recovery in 2, 3-butanediol fermentations to increase the substrate conversion. In the present work organic extraction of 2, 3-butanediol produced by Klebsiella pneumoniae fermentation was studied to detect solvent effect on 2, 3-butanediol production and determination of efficient volume of solvent. The aim of this research was liquid-liquid extractive fermentation systems evaluation as an alternative to overcome the end product effect and to increase of 2, 3-butanediol production by K. pneumoniae because conventional fermentative production of 2, 3-butanediol by K. pneumoniae has the disadvantage of product reutilization by the organism. The highest 2, 3-butanediol production (23.01 g/L) achieved when 20% oleyl alcohol was used.

Effect of temperature on hydrodynamics of bubbling gas-solid fluidized beds was investigated. Experiments were carried out in the range of 25-600ºC and different superficial gas velocities in the range of 0.17-0.78 m/s with sand particles. Time-position trajectory of particles was obtained by radioactive particle tracking technique. These data were used for determination of mean velocities of upward-moving (including bubble wake and ascending clusters) and downward-moving (descending clusters) particles. It was found that the upward velocity increases by increasing temperature up to 300oC, however, it decreases by further increase in temperature. Due to the wall effect, there is no significant change in the mean velocity of downward-moving clusters. The change in hydrodynamic parameters with temperature can be a consequence of changing physical properties of the bed which have been represented by Reynolds number in this study.

Various scaling methods such as relative viscosity, Peclet and Reynolds scaling were used to find the best scaling law. Scaling and modeling of the flow curves of various model emulsions consist of Tragacanth Gum (TG) (0.5, 1 % wt), Oleic acid (5, 10% v/v) and WPI (2, 4 % wt) were investigated and the best models were selected. As these emulsions are non-Newtonian, they do not obey the usual, simple scaling laws. When the apparent viscosity is reduced to relative viscosity of the medium at zero shear rate, a distinct reduced flow curve is obtained, regardless of TG, oleic acid and WPI concentrations. This will lead to a technique of simplifying complex non-Newtonian flow curves and therefore predicting the rheological flow curves and fluid mechanics when different modifiers are added to food emulsions. The flow behavior of all samples was successfully modeled with Cross, power law and Ellis models and power law model was found as the better model to describe the flow behavior of dispersions. Results showed that both G' and G'' increased with TG, oleic acid and WPI concentrations with pronounce effect of TG content.

The substances responsible for saffron’s characteristic quality are crocins, picrocrocin, and safranal. The drying process is critical to the saffron quality as measured by levels of secondary metabolites, crocin (color and anti-tumor properties), picrocrocin (taste), and safranal (aroma). Four different dehydration methods were evaluated: Iranian traditional method (room temperature); dehydration with electrical oven at different temperatures; and dehydration with microwave at different powers. The results showed that the highest coloring strength was obtained when saffron treated at higher temperatures and lower times. Also the higher amount of safranal (aroma) and crocin (color) was obtained at high temperature. There was not significant difference between the amounts of picrocrocin at different temperatures in all drying methods. Between these methods, drying with microwave at 1000 W and drying at room temperature obtained the highest the lowest results respectively.

The mixing behavior of the gas-liquid phase in three loop bioreactors was investigated. A gas-induced External Airlift Loop Bioreactor (EALB), a forced-liquid Vertical Tubular Loop Bioreactor (VTLB) and a forced-liquid Horizontal Tubular Loop Bioreactor (HTLB) were used for mixing studies as well as biomass production from natural gas. The effect of design parameters, riser to down comer cross sectional area ratio (Ar/Ad), height to diameter ratio (H/D), length to diameter ratio (L/D) and volume of gas-liquid separator (S); as well as operational parameters, i.e. superficial gas velocity (UsG) and superficial liquid velocity (UsL) on mixing time were studied. It was found that liquid circulation (pumping) had an important effect on mixing time. VTLB, because of providing an effective countercurrent flow between gas and liquid streams, demonstrated the best mixing time performance. HTLB, as the second, provides a moderated mixing time output. EALB, since circulates no forced liquid, presents less mixing ability (gas moves liquid). It was observed from experimental results that mostly superficial gas velocity has an obvious effect on EALB. Accordance to mixing time data, a region that was independent on bioreactor type was explored that happened in high gas superficial velocity. In that zone, mixing time was not reliant on bioreactor variety and varies with the variation of operational and design parameters only. Some empirical correlations for mixing time in terms of Ar/Ad, H/D, L/D, UsG, UsL and volume of gas-liquid separator were obtained and expressed separately which can be used for design and scale up. The best biomass production occurred in the VTLB for gas mixture of 40% methane and 60% air.

The snake venom´s thrombin-like enzymescomprise a number of serine proteases, which are functionally and structurally related to thrombin. Purification and partial characterization of a thrombin-like enzyme from the venom of the Iranian snake, Agkistrodon halys, was the aim of this study. Purification was carried out by a combination of variety of chromatographic methods that included: gel filtration on Sephadex G-50, ion-exchange chromatography on DEAE-Sepharose and HPLC with a C18 column. A trial for the purification of protease resulted in an enzyme with specific activity of 721.2 (mmol/min/mg), which was purified by 72.1 fold. The purified thrombin-like enzyme designated AH144 was found to have a molecular weight of approximately 30.5 kDa. This thrombin-like enzyme had the highest activity at 37oC and pH 7.5. Enzyme activity increased as its concentration increased, and the purified enzyme did not have any effect on casein. AH144 demonstrated clotting and proteolytic activities in the presence of the human plasma and the synthetic substrate (BApNA), respectively. Data emphasized the possibility of AH144 for quantitative determination of fibrinogen.

Finding repetitive subsequences in genome is a challengeable problem in bioinformatics research area. A lot of approaches have been proposed to solve the problem, which could be divided to library base and de novo methods. The library base methods use predetermined repetitive genome’s subsequences, where library-less methods attempt to discover repetitive subsequences by analytical approaches. In this article we propose novel de novo methodology which stands on theory of pattern recognition’s science. Our methodology by using Support Vector Machine (SVM) classification and clustering methods could extract exact and Solo LTR-retrotransposons. This methodology issued to show complexity efficiency and applicability of the pattern recognition theories in bioinformatics and biomathematics research areas. We demonstrate applicability of our methodology by comparing its results with other well-known de novo method. Both applications return classes of discovered repetitive subsequences, were their results when had applied on show more that 90 percents similarities.