Iranian Journal of Chemistry and Chemical Engineering
Volume:23 Issue: 1, Jan-Feb 2004

A spectrophotometric study concerning the interactoin between iodine and bromine with tetrabutylammonium iodide (TBAI), tetrabutyl- ammonium bromide (TBABr) and cryptand 222 (C222) has been performed in dichloromethane solution at 25°C. The results are indicative of the formation of TBA+X3- and C222X+X3- through equilibrium and formation of C222X+X- through nonequilibrium reactions. The stability constants of the equilibrium reactions were evaluated from the computer fitting of the absorbance-mole ratio data. It was found that iodine complexes were more stable than bromine ones. Comparision of the spectra of I2-TBAI with the I2-C222 mixtures indicates that the isosbestic points of the two systems are not identical. A similar behavior is observed for the corresponding bromine spectra. Comparision of the spectra of iodine complexes with those of bromine also indicates that in the spectra of iodine complexes 1) the wavelength of the isosbestic point is less than λmax of the free iodine and 2) addition of C222 or TBAI decreases the absorption intensity at λmax of iodine. However, in each case the reverse is observed for the spectra of bromine complexes. The possible reasons for the observed differences in various spectra are explained.

It has been proven that polyolefins specially low density polyethylene (LDPE), are resistant against degradation and microorganism attacks; Thus, one of the most important properties of industrial plastics, is their environmental biodegradability. Since plastics are being widely used in agriculture, horticulture and packaging, meeting this requirement becomes increasingly dificult (specially in IRAN as one of the biggest manufacturers of polyethylene materials).So, attention is focussed on production of biodegradable polyethylene. In this study, some different formulations based on starch and urea for making polyethylenes which are biodegradable in soil and moist media, have been investigated. The compounds produced are injection molded, and tested under natural conditions and their biodegradability has been studied. It has been thus possible to produce a biodegradable low-density polyethylene which is environmentally biodegradable material that is suitable for agriculture and packaging

This articles is comprised of two parts: a) an experimental investigation on the behavior of an acrylic gel under DC electric field and b) a physico - mathematical description. a) Gel rods made of poly [acrylamide-co-bisacrylamide] were partially hydrolyzed to different extents at pH 12 by teteramethylethylene diamine. Equlibrium properties of the resulting gels rods (water content, number of carboxyl groups and pore size) were determined. Gel rods were then placed in water parallel to planar platinum electrodes. Under the field strengths geater than 2 V/cm the gels gradually bend towards cathode and after reaching a maximum, they traverse a smooth reverse deformation, finally bending towards anode. The speed and extent of these deformations depend on the electric field strergth; length, diameter, charge density (extent of hydrolysis) of the gel rods; temperature, and the pH of the bathing medium. In all cases the bending behavior follows the relation for the tree – point mechanical bending of solid rods. Anodic swelling and bending towards cathode is attributed to the difference in the osmotic pressure between the anodic and the cathodic sides of the gel, while the reverse deformation and bending towards anode is assigned to the migration of H + ions from the anolyte into the gel and neutralization of COO¯ groups. b) Theoretical analysis: These attributes are quantitatively represented by a proper theoretical formulation based on Donnan and Flory-Huggins theories. The relation obtained for the osmotic pressure within the gels, in the absence of an electric field, is modified to include the ionic flux in response to concentration and electric field gradients. Considering the ionization of water and the network carboxyl groups, together with the principle of charge neutrality, and assuming Donnan equilibrium at the gel boundaries under the applied electric fields, the equations for ionic fluxes are derived and solved by Laplace transform. It is found that the concentration of cations decreases in the anodic side of the gel while it increases in the cathodic side, leading to an osmotic swelling gradient in the gel causing it to bend.

Leather manufacturing involves a crucial energy-intensive drying stage in the finishing process to remove its residual moisture. Determining drying characteristics of leather is vitally important so as to optimize the drying stage. This paper describes an analytical way for determination of the drying characteristics of leather. The model presented, is based on fundamental heat and mass transfer equations. Variations in temperature and moisture content distribution is solved numerically using the finite difference method. The effects of operation parameters, are examined using the model. The results of the parametric study provide a better understanding of the drying mechanisms and may lead to a series of recommendations for leather drying optimization. It opens the possibility for further investigations on description of relationships between model parameters and drying conditions.

Modeling and simulation of processing plants are widely used in industry. Construction of a mathematical model for a plant is a time-consuming and error-prone task. In light of extensive advancements in computer science (both hardware and software), computers are becoming a necessary instrument in industrial activities. Many software tools for modeling, simulation and optimization of processing plants have been developed. In this paper, a new tool, called “Modelsaz”, for the modeling of physical-chemical-biological processing systems is introduced. This software can automatically generate mathematical models of various processing plants in Mathematica™ compatible format, based on conservation principle. Lumped systems are the basic elements of processing plants. The dynamic lumped models of the plants are based on transient mass and energy balances of these basic elements. “Modelsaz” has been developed under Microsoft-Windows 2000 operating system using Microsoft Visual C++6 programming environment. The software uses object-oriented features and has a user-friendly graphical interface in order to facilitate the construction, modification and reusability of a processing system models.

The main object of this study was to compare the natural and synthetic(NaA and NaM) zeolites as absorbents in removing emulsified and dissolved traces of organic compounds, which appear in the wastewater of power plants, refinery and petrochemical complexes. The specific objectives of the work was: a) to select the best species that have the highest amount of absorption; b) to measure the rate of absorption of traces of organic compounds and emulsions on the natural and synthesized zeolites; c)to establish the absorption isotherms for the organics and emulsions with selected samples; d) to select readily available regenerants, and e) to examine the pH dependence of the process and to establish a simple and practical method to detect and to measure the pollutants after the treatment process. The BOD and COD of the treated and feedwaters were compared.

The interaction between benzo-15-crown-5 (B15C5), dibenzo-18-crown-6 (DB18C6), dibenzyl-daza-18crown-6 (DBzDA18C6), N-phenyl-aza-15-crown-5 (NPhA15C5) and dibenzopyridine-18-crown-6 (DBPy18C6) with π-acceptor 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) in chloroform solution was studied spectrophotometrically. The interaction of B15C5-DDQ and DB18C6-DDQ caused the formation of 1:1 charge transfer complexes through equilibrium reaction. The interaction of others caused the formation of 1:1 complexes in an equilibrium step and the conversion of the resulting adduct to D+DDQ- (D=NPhA15C5, DBPy18C6, DBzDA18C6) in a nonequilibrium step. The formation constant of DBzDA18C6 was evaluated by computer fitting of the absorbance mole ratio data. Other stability constants were evaluated through the Hildebrand method. It was found that the stabilities vary in the order: B15C5 < DB18C6 < DBPy18C6 < NPhA15C5 < DBzDA18C6. All of the resulting molecular complexes were isolated in crystalline form and characterized.

Magnesium is extracted with a chloroform solution of N-p-tolyl-2- thenohydroxamic acid (PTTHA) from aqueous solution of pH 9.5. Mg-PTTHA complex is colourless and the colour is developed by adding quinalizarin into the extract. lmax and e of the complex are 590nm and 2.8´103 Lmol -1cm-1respectively. Most common ions do not interfere in the determination of magnesium. The spectral characteristics of magnesium complexes with hydroxamic acids are recorded. Magnesium is also determined by AAS and the results are in agreement with those of spectrophotometric method. The method is applied to the determination of magnesium in standard alloy samples.

Hydrogen is an unusual substance in that its molecule exists in two forms, known as ortho and para, with markedly different properties. Energy level of the ortho molecule is higher than para, therefore, the latter is employed for industrial purposes. Consequently, for a high conversion of ortho to para hydrogen a catalyst reactor must be employed. Therefore, one of the main objectives of this work is to design a tubular reactor. To obtain this objective, one the parameters which should be considered is the proper selection of a catalyst that can in turn effect the price and the life of it. In this work and for an optimum of hydrogen feed and its liquefaction, the following parameters for the cryogenic apparatus in the Linde-Hampson cycle such as heat requirements, nitrogen needed for the cycle, specific capacity of refrigeration, compressor work and the cycle efficiency have been computed.

After designing and constructing a coalescence cell, drop/interface coalescence phenomenon was studied in the absence and presence of single surfactant.Two surface active agents of sodium dodecyl sulfate and 1-decanol were used. Distilled water was used as dispersed phase. Toluene, n-heptane and aqueous 60% (v/v) of glycerol were selected as continuous phases, separately. It was found that the coalescence time increased with both drop size and falling height. When the chemical system suffered from multi-step (partial) coalescence, number of coalescence steps decreased with either of these variables. Addition of a single ionic or nonionic surfactant made the drop size smaller, and hence caused the onset of partial coalescence. When the surfactant was soluble in the drop phase, it increased the time more effectively. Also, It was found that the viscosity of the continuous phase played an important role in drop-interface coalescence. Based on the experimental results, new correlations were proposed. Then, the results were compared with the other models by application of the existing condition.

Effects of binary mixtures of ionic/nonionic (sodium dodecyl sulfate/2-heptanol or 1-decanol) and nonionic/nonionic surfactants (2-heptnol/1-decanol) on drop/interface coalescence of water drops in a continuous n-heptane phase were examined. The drop size reduced appreciably and the multi-step coalescence was suppressed finally as the concentration of each of the constituting components of surfactant mixture was increased. The drop became more stable in comparison to single surfactant systems. It was concluded that the mixed surfactants were much more effective on coalescence time and drop lifetime than single surfactant, particularly when one of the components was soluble in the drop phase.

The stability constants of species present in the systems Ni(II)-pyridoxamine(pym)(A) and Ni(II)-pyridoxamine(pym)(A)-imidazole containing ligands(B) [B = imidazole(him), benzimidazole(bim), histamine(hist) and L-histidine(his)] have been determined pH-metrically using the MINIQUAD computer program. The existence of the species NiAH, NiA and NiA2 was proven for the Ni(II)-pym(A) system, whereas for the Ni(II)-pym(A)-B systems NiABH2, NiABH, NiAB and NiAB2 species were identified. The pym ligand(A) binds the metal ion via its phenolic oxygen and amino methyl nitrogen atoms in the NiAB and NiAB2 species, and the binding of ligand B in these complexes is similar to their binding in the respective binary species. The site of protonation in NiABH and NiABH2 species is explained. A more positive D log K values for NiAB compared to NiAB2 species is discussed. The computer simulated distribution of the complexes in solution has been evaluated. The mixed ligand pyridoxamine complex of Ni(II) with L-histidine was prepared and characterized by conventional methods.

The thermodynamic properties of fluids can be predicted using the global equations of state. Among these thermodynamic properties of fluids, we choose the densities of the liquid and vapor phases. This paper considers the application of the crossover model to the vapor-liquid rectilinear diameter of sulfurhexafluoride. We also present a comparison of the crossover model equation with the experimental data.

The equilibrium solubility data of CO2 in the various aqueous blends of triisopropanolamine (TIPA) + monoethanolamine (MEA) with the total alkanolamine concentration of 2 mole / dm3 were measured at the temperatures of 30, 40, 50, 60 and 70 oC and CO2 partial pressures below 100 kPa. The experiments were done in an atmospheric gas absorption system and the amount of absorbed CO2 was measured with acidification method and by a graduated burette. The results indicate that the increase in the CO2 partial pressure or the MEA ratio in the blended solvents increases the absorption capacity of the solutions and when the temperature is increased, the capacity decreases. Hence, one can use proper blends of TIPA+MEA to obtain acceptable absorption capacity and lower the regeneration cost and benefit from other useful properties of TIPA such as its low corrosivity and low degradation rate. Immersion corrosion tests carried out on stainless steel 304 coupons at 45 oC for 15 days in some blended solvents, in the presence or absence of dissolved CO2, showed no corrosion.

The one pot reaction of glyoxal and hydroxylamine hydrochloride in aqueous sodium hydroxide was found to be a safe and inexpensive method for the preparation of diaminoglyoxime. By increasing stoichiometric ratio of the hydroxylamine hydrochloride and decreasing the solvent volume, the product yield increased considerably (~ 70%).

The excellent performance of fluidized bed heat exchangers is due to the interaction between particles and heat transfer surface and to the mixing effects in the viscous sublayer. In this paper, the results of experimental investigations on heat transfer for a wide range of Newtonian and non-Newtonian (shear-thinning power law) fluids are presented. New design equations have been developed for the prediction of heat transfer coefficient. The predictions of these correlations and of numerous correlations recommended by other authors are compared with a large database compiled from the literature.

ژThe Taguchi design of experiments was used to test the relative importance of medium components and environmental factors on poly (β-hydroxybutyrate) (PHB) production by Ralstonia eutropha. The optimum condition was obtained as: fructose concentration, 15 g/L; C/N ratio, 7. 4; agitation speed 200 rpm; culture time, 40 h; temperature, 25 ° C; seed age, 15 h. At optimum condition the yield of PHB production was found to be 92. 36%.