Iranian Journal of Chemistry and Chemical Engineering
Year:2007 | Volume:26 | Issue:4|Papers Count:16

The enzymatic hydrolysis of meso-1, 7-diacetoxy-2,6-dimethylheptane 5, prepared from 2,6-dimethylhepta-1,6-diene 6, gave the (2S,6R)-7-acetoxy-2,6-dimethyl-1-heptanol 1, which was transformed to the (2R,6R)-2,6,10-trimethyl-1-undecanol 7. In this manner, the C14 side chain of a-Tocopherol was synthesized from 2,6-dimethylhepta-1,6-diene 6 in only 5 steps.

Different samples have been prepared from different products in Chadormalu iron ore concentrator plant: Low intensity magnetite separators concentrate (magnetite concentrate), reverse flotation tail (final hematite concentrate), flotation concentrate (apatite concentrate), final tail (L.I.M.S. tail+reverse flotation concentrate+ apatite flotation tail). The samples were used for rare earth elements (REEs) distribution and origin studies. The assay of REEs was determined by ICP-MS spectrometry. The amount of total (light and heavy) REEs were 9631, 291, 199, 2236 ppm and the distributions were 19.3, 3.6, 10.1, 67 % in flotation concentrate (apatite concentrate), reverse flotation tail (hematite concentrate), magnetite concentrate and total tail respectively. About 19.3 % of total REEs were distributed in apatite concentrate with an assay of 9631 ppm. Therefore, further studies have been conducted on this product. According to the Xray studies the minerals of fluorapatite, ankerite and calcite are the main mineral phases in apatite concentrate which the apatite is dominant among them. The scanning electron microscopy studies were shown that the high amount of REEs distributed on fluorapatite mineral. The results have clearly shown that the apatite concentrate that is a by product of iron dressing in Chadormalu plant, with a low economical value and left without any further treatment, can be used as a significant source of REEs. According to this characterization studies, the recovery of a mixed rare earth oxide from fluorapatite is possible either with the treatment of liquors from the total dissolution of the ore in nitric acid or with the proposed treatment of the phosphogypsum by-product from the conventional sulphuric acid route and the recovery of rare earth oxides from phosphoric acid sludges that the detailed flowsheet needs further extraction work.

Crown ethers 12-crown-4 (12C4), benzo-15-crown-5 (B15C5), 18-crown-6 (18C6), nitrobenzo-18-crown-6 (NB18C6) dibenzo-18-crown-6 (DB18C6) and dicyclohexyl-18-crown-6 (DC18C6), dissolved in dichloromethane, are able to form oxonium-ion complexes in contact with aqueous sulfuric and hydrochloric acid solutions. This ability allows the transfer of Cr (VI) ox anions from the acid media, through an organic liquid membrane, into a distilled water receiving phase. Among the studied crown ethers, DC18C6 shows the highest transport efficiency. The effect of parameters influencing the process such as the crown ether concentration in the membrane, types of the organic diluent's, acid concentration in the feed phase and time is investigated and discussed. Four replicate experiments show that an average of 95.6 (±1.3)% of the initial chromium in the source phase (10-3 M Cr (VI), 6 M H2SO 10 ml) is extracted into the distilled water (10 ml) through the membrane (DC18C6 0.05 M in CH2Cl2, 20 ml) after 8 h. The corresponding result, under similar conditions, in the presence of hydrochloric acid solution (4 M) was found to be 95.0 (±1.2)%. The selectivity of the process was assessed by performing the competitive transport experiments on a solution containing Cr (VI), Ni (II), Co (II), Pb (II), Mn (II), Zn (II) and Fe (III) ions. The method was used for the recovery of chromium from two real samples provided by chromium-electroplating industries.

A Multi-objective optimization procedure has been developed to determine some kinetic parameters of free radical polymerization of vinyl acetate based on genetic algorithm. For this purpose, mathematical modeling of free radical polymerization of vinyl acetate is carried out first and then selected kinetic parameters are optimized by minimizing objective functions defined from comparing experimental data and mathematical modeling outcomes. A ranking procedure is applied to classification of solutions, and a Pareto optimal set filter is used to preserve the non-dominated solutions on the basis of Pareto optimality definition. Results show by this optimization technique, kinetic parameters are calculated in reasonable time and computational costs near the global optimum without scalarization of objective functions into a single objective function.

In this work the likelihood of asphaltene deposition problems during dynamic displacement of oil by natural gas in unconsolidated porous media is experimentally inspected. The two different rock materials, limestone and sandstone, are used as a representative of porous media. Dynamic flow experiments indicate that the increase of natural gas injection increases asphaltene deposition in the unconsolidated matrix. The results of the study show that increase in asphaltene deposition leads to pore plugging, porosity reduction and absolute permeability damage. Irreducible water measurements showed that natural gas-induced asphaltenes change the rock wet ability to oil-wet.

The recovery and removal of the most organic acids in liquid solutions is usually treated with fixed-bed adsorption processes. Among many adsorbents, Granular Activated Carbon (GAC) is used to remove organic pollutants such as Benzoic Acid (BA) from wastewaters conventionally. In this research, adsorption isotherm curves of BA onto GAC at varying temperatures 25-60 oC are developed and the amounts of BA concentration in feed fluid and on the adsorbent are obtained. The results show that Radke and Prausnitz (Ra-Pr) model among five applicable isotherm models has best fitting with experimental data. In this paper, for the first time, a new model for temperature effect on isotherm curve of BA is investigated. This model could predict isotherm curves in accordance to the isotherm curve in reference temperature with absolute relative error (ARE) less than 1.2%. Thus Temperature Effect Term (T.E.T) model is able to predict isotherm curves only by using experimental data in one temperature successfully. Furthermore T.E.T and Ra-Pr models jointly, could predict the every isotherm curve only with experimental data in three equilibrium points in one temperature with low error. In this case, the average A.R.E% in comparison with experimental data is less than 1.4%.

Microwave-assisted three component cyclocondensation reactions of aldehydes, amides and dienophiles in the presence of acetic anhydride and para-toluenesulfonic acid as a catalyst to afford the highly substituted cyclohexene derivatives, in relatively good yields after several minutes are reported.

-2, 5, 10, 13-Tetraazatricyclo [12,2,2,26,9] icosa-1 (16), 6,8,14,17,19-hexene-3,4,11,12-tetraone tetraoxime (1a) and 2,5,11,14-tetraazatricyclo [13,3,1,16,10] icosa-1 (19), 6,8,10 (20), 15,17-hexaene-3,4,12,13-tetraonetetraoxime (1b) were obtained from condensation of 1,4- and 1,3-phenylendiamine with dichloroglyoxime, respectively. The reaction of 1,2-phenylendiamine with dichloroglyoxime resulted in the production of (2Z,3Z)-1,4-dihydroquinoxaline-2,3-dione dioxime (2). The x-ray structure determination of compound 2 shows the piprazine ring is rather planar relative to the fused aromatic ring. The results show that a resonance occurs between the aromatic ring and the C=N bond, through N4 and N3 atoms of the molecule. The results from x-ray data indicated that the molecules 2 could exist as a dimmer by intermolecular hydrogen bonding between NH and OH groups.

In this work, we have calculated the Joule-Thomson inversion curve of two important associating fluids, namely water and methanol, from the SAFT equation of state. Comparisons with the available experimental data, for water and methanol indicate that this molecular based equation of state gives good prediction of the low temperature branch; but, unfortunately, due to lack of isenthalpic data for high-pressure-high- temperature gas condensate for water and methanol, the reliability of model predictions could not be completely verified. We have also reported the influence of the molecular dipole moment and the segment number on the Joule-Thomson inversion curve.

Urinary 1-hydroxypyrene is frequently used as a major metabolite and biological indicator of the overall exposure to polycyclic aromatic hydrocarbons. In this study, solid phase extraction was appropriately conditioned with regard to sample pH, sample concentration, loading flow rate, elution solvent, washing solvent, sample volume and sorbent mass. Octadecyl silica cartridge (C18) was used as solid phase adsorbent and showed to be an efficient phase in simplifying sample preparation for1-hydroxypyrene. Methanol extracted analyte from spiked urine gave a clean sample for reverse-phase HPLC-florescence. In the developed solid phase extraction conditions (sample pH: 5, sample concentration: 10 mg/l, washing solvent: distilled water, eluent: methanol, sample volume: 200 ml sample flow rate: 10 ml/min), the extraction recovery exceeded 99.96%, achieving detection limit of 0.02 mg/l. The extraction factors (sample pH, sample concentration, washing solvent, eluent, sample volume and sample flow rate), were evaluated statistically and also the procedure was validated with three different pools of spiked urine samples at low, medium, and high sample concentrations and showed a good reproducibility over six consecutive days as well as six within-day experiments. All coefficients of variations were less than 3.1%. Finally, urinary 1-hydroxypyrene of industrially exposed workers was also measured, using the appropriate conditions obtained in this study, in which, the amount of the compound of interest in the total exposed subjects was significantly higher than those of non-exposed.

A simple, rapid and economic procedure was presented to remove lead(II) from aqueous solution under the optimized conditions. It is based on the sorption of Pb2+ ions from aqueous solutions onto limestone fines (LS), which is an inexpensive and widespread over the globe, followed by flotation with oleic acid (HOL) surfactant. The different parameters (namely: solution pH, sorbent, surfactant and lead concentrations, shaking times, ionic strength, temperature and the presence of foreign ions) influencing the sorptive-flotation process were examined. Nearly, 99% of Pb2+ ions were removed from aqueous solutions at pH 7 after shaking for 5 min and at room temperature (~25 oC). The procedure was successfully applied to recover lead(II) spiked to some natural water samples. A mechanism for sorption and flotation is suggested.

Silica sulfuric acid is found to catalyze efficiently the condensation of  o-phenylenediamines with various linear and cyclic ketones to afford the corresponding 1,5-benzodiazepines in quantitative yields under solvent-free conditions at room temperature.

In this paper, polyacrylamide/chromium acetate gel polymer system was prepared as water shut-off system to control water production in one of the Iranian oil reservoirs condition. Effect of various parameters such as temperature (90 oC) and water formation from view point of salinity and divalent cations, was evaluated on the gelation kinetic and gel strength using bottle testing method. The results showed that the increase of temperature caused a decrease in the gelation time. Also, presence of divalent cations in formation water, decreased gelation time and by precipitation could cause instability in gel structure.

The solvent extraction of gallium from a concentrated Jajarm Bayer process liquor containing 164.90 g/l of Na2O, 86.70 g/l of Al2O3 and 106.02 ppm of gallium was investigated using 10 vol.% Kelex100, a 7-alkyl substituted-8 hydroxyquinoline as an extractant, 10 vol.% etanol as a modifier and kerosene as a diluent. At (vo: va= 1.0:1.0) organic to aqueous phase ratio and at room temperature, 93.39% of gallium was recovered in 60 minutes. Back extraction studies of the loaded organic phase were carried out using hydrochloric acid, sulfuric acid and sodium hydroxide. Scrubbing of aluminium co-extracted into the organic phase was carried out with 5.0 M HCl and subsequently stripping of gallium was carried out with 1.5 M HCl. The final strip liquor was found to contain 490 ppm of gallium along with 141.73 ppm of aluminium.

A chromium electroplating bath with the ability to produce homogenous mist was used to evaluate parameters influencing hexavalent chromium (Cr+6) mist sampling methods. The results of 48 Cr+6 mist samples collected using the U.S. National Institute for Occupational Safety and Health method 7600 showed that Cr+6 concentration was higher: (1) For sampling by closed-face filter cassettes than for sampling by open-face filter cassettes (P<0.001); (2) for samples collected at 35 cm above the electroplating solution surface than for samples collected at 50 cm (P<0.001); (3) for sampling duration of 30 minutes than for sampling duration of 180 minutes (P<0.001); and, (4) for samples extracted immediately after sampling than for samples with delayed extraction (24 hours after sampling) (P<0.001). It is concluded that the accuracy of Cr+6 mist sampling in electroplating shops will be enhanced when: (1) closed-face filter cassette is used to prevent liquid splash contamination; (2) the recommended sampling height is 35 cm above the solution surface; (3) the sampling duration is short-approximately 30 minutes; and, (4) the extraction of the Cr+6 sample is performed as soon as the sampling is completed.

The structure of the nonaaquayttrium (III) bromate, [Y(H2O)9] (BrO3)3, at low temperature (100 K) has been studied by means of single-crystal X-ray diffraction. Crystallography shows a hexagonal unit cell, space group P63/mmc (No. 194) with Z=2, a=b=11.7104(11) A3,  c=6.6259 (5) A and V=786.90 (12) A3 at 100 K. The hydrated trivalent yttrium (III) ion forms a tricapped trigonal prism, in which the yttrium(III) ion is surrounded by six equidistant water molecules in the prism and three more distant water molecules in capping positions with M-O bond distances of 2.370 (2) and 2.446 (3) A, respectively. Relatively strong hydrogen bonds (2.818 and 2.851 A) from water molecules to the bromate ions stabilize the trigonal prism around the yttrium (III) ions.