Iranian Journal of Chemistry and Chemical Engineering
Volume:23 Issue: 2, Nov-Dec 2006

A study was made of the coking of a commercial fresh sulfide Ni-Mo/Al2O3 catalyst in a fixed-bed reactor. The catalyst was coked using different coke precursors in the gas oil under accelerated conditions at temperatures of 400 to 450°C to yield different deactivated catalysts containing 2-20 wt% C. Two cases were studied; crushed catalyst without diffusional resistance and extruded pellets with diffusional resistance. Physical properties and catalytic activities of the coked catalysts were measured using the thiophene sulfur removal in the gas oil. It is concluded that coking occurs by selective deactivation on hydrotreating catalyst and the experimental results of the catalyst activity under different operating conditions, obey a power law as a function of the coke cantent. In the pellet catalyst showed a lower rate of coking and deactivation in comparison to the catalyst without diffusional resistance. It is inferred that high level of coke content (higher than 12 wt% C) affects the tortusity factor of the catalyst,considerably. In the study of transient deactivation, initial activity of the catalyst was derived by a time variable function, then this equation was used in dynamic model of hydrodesulfurization reaction in a packed bed reactor to determine the activity change of the catalyst in the reactor during actual operational conditions.

: A mathematical model for the performance prediction of an industrial glass furnace with six ports on each side was developed. This model comprises of two main sub-models for the combustion chamber and glass-melting tank. The first sub-model consists of the models for the combustion and the heat transfer model including, radiation, convection and conduction. The fuel combustion in atmospheric pressure is assumed perfectly and without soot. Heat balance equations in the gas; glass and walls determine the rate of heat transfer to the glass surface. The second sub-model consists of the model for the batch melting. The temperature distribution in the glass tank is computed by using results of the combustion simulation and effective conduction coefficient of molten glass. The results of the combustion model can be used for the pollution prediction and optimization of the furnace parameters to decrease the gas pollutants in the furnace.

This article deals with the issues associated with developing a new design methodology for the nonlinear model-predictive control (MPC) of a chemical plant. A combination of multiple neural networks is selected and used to model a nonlinear multi-input multi-output (MIMO) process with time delays. An optimization procedure for a neural MPC algorithm based on this model is then developed. The proposed scheme has been tested on a model of an 18-plate multi-component distillation column. The algorithm provides excellent disturbance rejection for this process.

Resin Transfer Molding (RTM) is a composite manufacturing process. A preformed fiber is placed in a closed mold and a viscous resin is injected into the mold. In this paper, a model is developed to predict the flow pattern, extent of reaction and temperature change during filling and curing in a thin rectangular mold. A numerical simulation is presented to predict the free surface and its interactions with heat transfer and cure for flow of a shear-thinning resin through the preformed fiber. To verify the model, the temperature profiles for preformed fiber have been calculated, and compared with the experimental results of other researchers. The results showed that, to optimize better quality of production of composite materials, while considering the effect of curing on temperature distribution during the process, the heat dispersion term should not be neglected.

AbsA new, high yielding method for the preparation of vasicinone (7) is described. Reaction of 2-nitrobenzoic acid with N, N¢-carbonyldiimidazole followed by 2-pyrrolidinone gave 1-(2-nitrobenzoyl)pyrrolidine-2-one (3). Reduction of the latter with 10% Pd-C afforded deoxyvasicinone (4). Reaction of deoxyvasicinone (4) with bromine yielded monobromo-deoxyvasicinone (5). Exchange of bromine of 5 with acetoxy followed by hydrolysis gave vasicinone in high yield.

Microwave irradiation is used in the synthesis of four tricyclic chromanones 11-14. The chromanone 14 and 12 are selectively formed thermally and under microwave in the presence of polyphosphoric acid (PPA) from the same dicarboxylic acid 9, respectively. The crystal structures of the two diacids are also reported. The corresponding ortho and meta isomers of diacids crystallize in the space group Pbca of the orthorhombic system and C2/c of the monoclinic system respectively, with 8 and 4 molecules in the unit cells of dimensions a = 4.9955(1) Å and 4.8092(4) Å; b = 19.177(4) Å and 11.5609(1) Å; c = 25.885(5) Å and 21.247(2) Å; α = 90˚ and β = 91.214(3)˚ respectively. The structures have been refined to final values for the crystallographic R factors of 0.0401 and 0.0247, based on 2146 and 1030 observed independent reflections, respectively.

In this work, a more accurate prediction of liquid evaporation flux has been achieved. The statistical rate theory approach, which is recently introduced by Ward and Fang and exact estimation of vapor pressure in the layer adjacent to the liquid–vapor interface have been used for prediction of this flux. Firstly, the existence of an equilibrium layer adjacent to the liquid-vapor interface is considered and the vapor pressure in this layer and its thickness calculated. Subsequently, by using the Fick’s second law, an appropriate vapor pressure expression for the pressure of equilibrium layer is derived and by this expression and the statistical rate theory approach, evaporation flux is predicted more accurately than the previous work. Finally, some novel steady state evaporations are simulated and the effects of both liquid and vapor temperature and the effect of the length of the evaporation chamber on the evaporation flux are investigated.

Urease was immobilized on platinum electrode both by chemical binding and electropolymerization.The conductometric urea biosensor thus prepared showed a detection limit of 4.9×10-5 M and linear dynamic range from 4.9×10-5 to 5.8×10-3 M for urea concentration when the enzyme is covalently immobilized on Pt electrodes. Conductometric transducers respond to the changes in ionic strength thereby leading to uncontrolled inaccuracies. Such interferences were effectively suppressed by here the use of differential sensor pairs. It was shown that measurements in diluted fluids are possible with the use of a reference sensor having no immobilized enzyme. Specifically, the sensor constructed by covalent binding provided more reproducible responses than that prepared by electropolymerization. Namely the former preserved 80% of its initial activity over a period of 25 days. In order to provide more reproducibility, a method was developed for regeneration of the sensor surface so that, the renewed sensor would responded to urea almost as new.

The objectives of this investigation are the studies on the effect of copper ion on photolytic degradation of ethylenediaminetertraaceticacid (EDTA), the effect of EDTA on electrolytic recovery of copper as well as the introduction of a novel combined photolytic and electrolytic cell system for simultaneous recovery of copper and the degradation of EDTA. In this experimental study, a photolytic cell, an electrochemical system, and a combined photolytic -electrochemical (photoelectrolysis) system with and without an activated carbon cathode were used. Analysis was carried out using atomic absorption spectroscopy, and high performance liquid chromatography (HPLC). The results show that a single electrochemical cell can be used to recover copper (82.1% after 9 hours) without achieving complete mineralization of EDTA by anodic oxidation (49.9 % after 9 hours). On the other hand a single photolytic cell can achieve 99.9% degradation of EDTA after 9 hours at pH 3.5 but leaves copper in solution. However, a combined photoelectrolytic system using an activated carbon concentrator cathode achieves a rapid simultaneous degradation of EDTA and recovery of copper. The amount of degradation of EDTA was 99.9% while recovery of copper was 98.8% after 9 hours.

The presence of particles in liquid-solid fluidized beds enhances the bed heat transfer, because the movement of the particles leads to an increased turbulence in the system. Moreover, the violent movement of the particles has a positive effect on fouling of the heat transfer surface. The aim of this investigation was to perform systematic measurements of bed voidage and heat transfer coefficient for solid-liquid fluidization in a cylindrical tube and to study the effect of process parameters such as particle size and density, flow velocity, and liquid viscosity on these subjects. A large number of experiments were performed using different cylindrical and spherical particles fluidized in aqueous CMC solution with different concentrations. Using the experimental results, a new correlation for predicting heat transfer coefficient in non-Newtonian liquid-solid fluidized bed heat exchanger was introduced.

This paper presents a simple methodology for cost estimation of a near optimal heat exchanger network, which comprises mixed materials of construction. In traditional pinch technology and mathematical programming it is usually assumed that all heat exchangers in a network obey a single cost model. This implies that all heat exchangers in a network are of the same type and use the same materials of construction (an assumption that is unwarranted). The method introduced in this article enables the designer to decomposes the total cost of a heat exchanger into two elements, namely cost of the tubes and cost of the shell, thereby predict a more reliable cost for the network. By subsequent use of the binary variables and evaluation of the physical conditions of the streams, one can assign the streams to pass either through shell or tubes. Whereby, shell and tubes can be of different materials and therefore different cost models can be applied. Another advantage of the approach is that the pressure drop in each side of the exchanger (shell or tubes) can be assessed leading to more accurate evaluation of corresponding heat transfer coefficient for each individual stream. Finally an objective function (total cost) can be defined based on mixed materials of construction and different values of heat transfer coefficients. The proposed model has been utilized in three different case studies and the results are compared with those of a commercially available software (SUPERTARGET). The comparison shows reductions of more than 17% and 14% in total annual costs in the two cases, and 2.5% reduction in third, confirming the fact that more accurate evaluation of heat transfer coefficient for each individual stream can lead to better network design.

The recovery process of selenium from Iranian Sar-Cheshmeh copper anode slimes employing hydrometallurgical methods has been investigated. The copper anode slimes are made up of those components of the anodes, which are not soluble in the electrolyte. They contain varying quantities of precious metals like gold, silver, selenium and tellurium. They are being extracted as a by product in the copper production process. In this paper, some parameters affecting the leaching conditions of anode slimes in nitric acid are studied. Taguchi experimental design method is used to find out the effect of acid concentration, temperature and time. The statistical results of the experiments show that the above parameters are important in the leaching of -10 microns fraction. The optimum conditions determined are: T = 90º C, acidity = 4 M and the leaching time = 60 min. Under these conditions, 99 % of the selenium is leached out.

The high temperature oxidation behaviour of Nimonic-115 industrial alloy has been investigated in presence of NaNO3, Na2CO3 and Na2O2 at 850oC in flowing air. The oxidation kinetics and effect of salt deposition for the period of 48 h were studied. The scale morphologies were determined on the basis of X-ray diffraction analysis and Scanning electron microscopic techniques. It has been shown that the alloy corrodes at different rate in presence of different sodium salts although each salt contains the same amount of sodium equivalent to Na2O.

Lanthanide(III) chloro complexes of 4[N-(4’-hydroxy-3’-methoxybenzalidene) amino] antipyrine semicarbazone (HMBAAPS) (I) and 4[N-(3’,4’,5’-trimethoxybenzalidene) amino] antipyrine semicarbazone (TMBAAPS) (II) with the general composition LnCl3.2L (Ln = La, Pr, Nd, Sm, Gd, Tb, Dy or Ho; L = HMBAAPS or TMBAAPS) are reported. All the complexes were synthesized in ethanolic medium and refluxed the reaction mixture (1:2.2, M:L ratio). The yield percentage ranging from 78 – 82%. The complexes are non-ionic in nature. The infrared spectral studies reveal that both of the semicarbazones are tridentate (N,N,O) ligands. Magnetic spectral and thermal properties of the complexes have also been investigated. A coordination number nine is tentatively suggested in these complexes.

The present work describes the studies on the coordination behaviour of 4[N-(benzalidene) amino]antipyrine semicarbazone (BAAPS) (I), 4[N-(furfural)amino]antipyrine semicarbazone (FFAAPS) (II) and 4[N-(cinnamalidene)amino]antipyrine semicarbazone (CAAPS) (III) in presence of dimethyl sulfoxide (DMSO) or diphenyl sulfoxide (DPSO) towards Th4+ and UO22+ salts. All the complexes were isolated in non-aqueous solvents like ethanol or acetone. The mixed ligand complexes have the general composition ThX4(L)DPSO (X = Cl, Br, I, NCS or NO3), Th(ClO4)4(L)2DPSO (L = BAAPS or CAAPS), UO2X2(L)DMSO (X = Br, I, NCS, NO3 or CH3COO) and UO2(ClO4)2(L)2DMSO (L=FFAAPS or CAAPS). The analytical data include elemental analyses, molecular weight determination, conductivity, spectral and thermal studies. XRD-powder diffraction of two representative thorium(IV) complexes have also been reported.In these complexes, the primary ligands behave as neutral tridentate (N, N, O) ligand, while the secondary ligand (DMSO or DPSO) acts as unidentate oxygen donor. Thorium(IV) displays coordination number 6,7,8 or 12, while uranium(VI) ion displays coordination number 8, 9 or 10 depending on the nature of anionic ligand.