نشریه شیمی و مهندسی شیمی ایران
سال سی‌ام شماره 3 (پیاپی 62، پاییز 1390)

In this paper a new graphical method is presented for analysis of the time of fouling formation of heat exchanger networks. By using this method more opportunity of fouling formation are given for streams that have a high fouling formation rate, and the number of cleaning process of heat exchanger will decrease in a specified period of time. In fact high fouling formation rate streams are replaced with low fouling formation rate streams among different heat exchangers so that more fouling formation opportunity may be given for HEN. Therefore the high fouling formation streams should pass from the path that the low fouling formation rate stream previously has passed, and inversely. Therefore the HEN cleaning time decreases in fixed time period and the high fouling formation streams should pass from the path that the low fouling formation rate stream previously has passed, and inversely. As a result, second stream with high fouling formation rate mixes with residues of primary stream (low fouling formation rate stream). Therefore we should consider to adoption and conformability of streams structures (for prevention of streams destruction) and thermal considerations (for desirable heat transfer). Outlet temperatures of hot and cold streams should state in predefined temperatures. This method can be applied in plants that fouling and its related cost are undesirable (e. g. dairy industry).

In unit operation processes; the control of feed size entering to equipments is essential in the optimization of overall operation performance which is usually accomplished by classifiers. In commercial scale unites, a considerable amount of classifier feed bypasses to the underflow non-selectively; especially in the cut sizes less than 45microns. This leads to deteriorate the process performance of the unite operation plant. In the present research, operation of a reflux classifier in the cut size of about 45microns was evaluated. The imperfection coefficient of classification in the all experiments were about 0.3 or less and the bypass of particles finer than 25 microns to underflow was between 8 to 13% which indicates a high performance of the reflux classifier in the size separation having cut size of 45 microns. It was found that fluidization water flow rate has a significant effect to bypass of particles; but excess of fluidization water flow rate caused mixing and in the vertical section that deranges sedimentation procedure leading to non-selective transport of fine particles to underflow. In order to evaluate mixing phenomenon in the vicinity of underflow valve, a Mixing Index was defined. If the defined index equals to unit, indicates to a non-mixing in the region of underflow. The higher index value than unite, indicates to more intense mixing in the vicinity of underflow valve resulting in disordering sedimentation of particles.

Fuel cells will be one of the most important resources of energy in the future They use pure hydrogen, and natural gas as a feed. Converting chemical energy to electrical energy in fuel cells is a direct process without any environmental pollution. Thus the study and modeling of various hydrogen production and purification processes is necessary. Up to day, natural gas steam reforming is one of the most important chemical processes for hydrogen production. It should be mentioned that hydrogen is obtained from a produced synthesis gas (product of methane steam reforming process). A lot of researches have also done work on a direct production of pure hydrogen using various membranes. Previous studies have shown that using Pd-Ag membrane is only permeable for hydrogen is the best choice for pure hydrogen production. Thus, in the present study the modeling of natural gas steam reforming in the Pd-Ag membrane reactor has been done. Effect of some variables such as pressure, temperature, steam to methane ratio in the feed, membrane thickness and flow pattern of reactants and sweep gas on the methane conversion, hydrogen production and produced hydrogen-to-carbon monoxide ratio have been investigated and optimum operating conditions have been determined qualitatively. The proposed model has been evaluated by some data that obtained from an experimental study. The results of the proposed model have a good consistency with the results of experimental study.

Because of the importance of diffusion coefficient and its high application in mass transfer calculations, many correlations have been proposed in order to predict it in various systems. In this paper, one of the most simple, general and applicable correlation to estimate diffusivity in liquid systems, Siddiqi-Lucas correlation, selected and its accuracy and capability in calculation of diffusivity of various liquid systems have been investigated. Results indicate that average absolute errors of this correlation in diffusivity prediction are 25.1% and 20.8% in hydrocarbon mixtures and aqueous solutions, respectively. Also, the calculations show that average absolute error for alcoholic solutions is 44.8% and more than 30% of calculated diffusion coefficients in these systems have an error of more than 60% while the in non-alcohols solutions average error is 18.9% and less than 2% of results have an error of more than 60%. Because of the weakness of this correlation in the prediction of diffusion coefficients in systems including alcoholic solvents, and the results of previous studies, literatures which depict higher prediction errors using most relations for alcoholic solutions with respect to non-alcoholic solutions, and since, there is not a particular relation for these systems, a new correlation in the form of Siddiqi-Lucas relation proposed to calculate diffusivity in alcoholic systems. Using this relation, the average error decreased from 44.8% to 28.5% and the results percentage with error more than 70% decreased from 24 to zero. For more verification, the results of proposed relation compared with Wilk-Chang results, Tyn-Calus and Hayduk-Minhas correlations, and the results indicated a good improvement in calculated coefficients and the higher accuracy of the proposed relation which makes its usage reasonable and necessary.

The purpose of the present study was investigation of effect petroleum contaminants and surfactants on hydrodynamics and oxygen transfer as important parameters for treatment of crude contaminated wastewaters. Gas hold-up (εg), bubble size distribution and oxygen transfer coefficient (kLa) were evaluated for petroleum contaminants (C13 and C16) in water at concentrations of 0.1 and 0.5 vol.% over the range of superficial gas velocity (ug) of 1.18-23.52×10-3 m/s in bubble column reactor. A type of anionic surfactant (SDS) was utilized in the experiments for studying of surfactants on wastewater parameters. The bubble size distribution becomes bimodal with increasing of gas velocity and gas hold-up, mass transfer coefficient and Sauter mean diameter is increased. The petroleum contaminants and surfactants lead to delayed regime transition from the homogeneous to heterogeneous by decreased surface tension and by the coalescence inhibition, and also, Sauter mean diameter is decreased in the presence of petroleum contaminants. These changes increased in the presence of surfactants. Also, petroleum contaminants enhanced mass transfer coefficient and gas hold-up, especially at higher superficial gas velocity. Increasing of mass transfer and hold-up were more at higher concentrations of contaminants. Also, presence of surfactants on bubble surfaces, decreases oxygen transfer due to the enhanced mass transfer resistance. Empirical correlations were proposed for evaluating gas hold-up and mass transfer coefficient as a function of superficial gas velocity and interfacial surface tension.

In this research, the new microbial Bacillus licheniformisstrain ACO4 is used to produce a bioemulsifier. Based onlaboratorystudiesperformed, this bioemulsifier has a high emulsification capacity for the formation of the Iranian Nowruzheavy oil in water emulsion. This strain was able to reduce the viscosity of the emulsion from 10000 cP to 830 cP at pilot scale. This emulsion was stable for 72 h under the optimum conditions of temperature, water content and emulsifier concentration. The emulsion and heavy oil were passed through the pilot pipeline and the amount of sediment was observed and compared. The substantial stability of the oil in water emulsion allows the heavy oil to be transported practically over long distances or remain stationary for a considerable period of time prior to utilization.

Valerian plant contains more than 150 components with physiological activity. Valerenic acid was pointed as a measure for Valeriana Officinalis type. Optimization of extraction was determined by percent of valerenic acid in dried extract and also the total percent of dried extract. There were set four variables of mesh size, type of solvent, temperature and time. There was found that a mesh size of 60 with ethanol 70% (by volume) as solvent at boiling point and for 4h optimized the extraction. The percent of extracted valerenic acid was 0.3 by weight (recommended in pharmacopoeia).

In this study, the effect of Kraft lignin was investigated on the short term water absorption as well as mechanical properties in wood flour-polypropylene composites. Kraft lignin was extracted from black liquor by acidic method and mixed with the wood flour with ratio of 0, 2, 5 and 10 percent (based on wood flour dry weight) by solvent mixing method. The composites were manufactured by hot press method after mixing of the wood flour, the lignin, the polypropylene as well as the MAPP (0 and 2%) in internal mixer. The physical and mechanical properties of prepared samples were determined according to standard test methods. The results showed that the lignin improved physical and mechanical properties of the composites and it can be used as co-compatibilizer of MAPP in the wood plastic composites. The bending test results showed that in absence of MAPP, the composites with 10% lignin exhibited the highest flexural modulus and flexural strength. However at presence of MAPP, the composites with 5% lignin exhibited the highest flexural modulus and flexural strength. In absence and presence of MAPP, the composites with 10% lignin exhibited the lowest water absorption and the highest impact strength.

In this research the effect of three non-ionic surfactants named PEG-1000, KELA-2 and KECA-20 at four levels of 1, 2, 3 and 4 % on CMP pulping of Eucalyptus Camaldulensis, oxidative bleaching of selected pulps and strength of handsheet papers were investigated.The resulting pulps with higher screen yield and lower reject from application of each surfactant as well as the reference CMP pulps (without surfactant) were selected and bleached in two stages with H2O2. The pulping results showed that application of KECA-20 at the level of 1% increased accepted yield by about 2.5%. KECA-20 (1%) and PEG-1000 (4%) at the level of 1% lowered the consumption of bleaching agents and increased brightness and decreased opacity and yellowness of pulp. In addition, application of surfactants increased strength of handsheet papers compared to the paper obtained from the reference CMP pulp.

Photolysis of a homogeneous solutions of several of α–aryl carboxylic acids in presence of hydrogen peroxide and manganese tetrakis(2,6-dichloro)porphyrin chloride,(MnTDCPPCl), as catalyst have been studied. All of carbonyl products obtained was characterized by GC-MS and TLC with different yields.

In this research, by using the PASS Software, probability anti-acetylcholinesterase propertiec of two hundred and twenty-five phosphoramide molecules was predicted and then of among them of ten molecules with highest probability anti-acetylcholinesterase with general formula: [NH(CH3)]P(O)[SCH3][OCH3] (44), [N(CH3)2]P(S)[OCH3)[OCH3] (46), [NH(CH3)]P(O)[SCH2CH3] [OCH2CH3] (47), [N(CH3)2]P(O)[CN]2 (93),[2,4,5-Cl3-C6H2O]P(O)[OCH3][N(CH3)2] (99), [2,4,5-Cl3-C6H2O]P(O)[OCH2CH3][N(CH3)2] (103), [p-Cl-C6H4O]2P(O)[N(CH3)2] (178), [p-CH3-C6H4O]2P(O) [N(CH3)2] (179), [C6H5O]2P(O)[N(CH3)](183), [p-CH3C6H4O]P(O)[F][N(CH3)2] (217) was selected. After synthesis, purification and characterization of target compounds was performed by using the technique of IR, GC-Mass, X-Ray and 1H, 13C, 19F, 31P NMR spectroscopy. The lipophilicity parameter and the inhibitory potential for the target compounds was determined by the shake flask and the Ellman method respectively. The structure-activity relationships of the target compounds show that the log P parameter has more correlation with IC50 than the electronic and the stric parameters.