نشریه شیمی و مهندسی شیمی ایران
سال سی و نهم شماره 4 (پیاپی 98، زمستان 1399)

The hydrate formation has been investigated due to its application in recent years. Researchers study applications of hydrate such as gas storage, transportation, and gas mixture sequestration. Several studies have been carried out for clathrate hydrate formation due to their unique applications. In this work, the effects of zinc oxide and ferric oxide Nanoparticles on hydrate formation conditions were investigated. It has been shown that Nanoparticle has a promotion effect on hydrate formation conditions so kinetic and induction time are changed in the presence of these Nanoparticles. In the present study, the new data of carbon dioxide hydrate formation conditions were obtained in the presence of ferric oxide and zinc oxide Nanoparticles. The gas consumption versus time in the hydrate formation process in the presence of ferric oxide and zinc oxide are calculated and compared with those values are obtained by pure water. The results showed that the presence of these Nanofluids in carbon dioxide hydrates led to enhance the storage capacity by about ten percent in some cases and cause the intensification of the hydrate formation rate. Moreover, in the presence of these Nanofluids, at injection gas pressure of thirty-seven bar, the time of termination of hydrate formation decreases about ten times in compared with pure water at the same conditions; However, at twenty-eight bars, this time reduction is about twenty-two percent concerning pure water.

In this study, MCM-41, SBA-15, and that modified nanoporous materials were used for absorption of Pb2+ and Cd2+ ions from water. Nano-porous materials properties are characterized by XRD, BET, SEM, and FT-IR, and also, Pb2+ and Cd2+ ions concentration measurements by AAS. According to BET analysis for SBA-15 and NH2- MCM-41 samples, the shape of both sample isotherm is IV type. In this study, the parameters of adsorbent amount, pH changes, and absorption time were investigated. The results show Pb2+ absorption efficiency is more than Cd2+ absorption by synthesized samples. Also, the presence of the amine group in the structure increases the absorption efficiency. Repeatability of absorption by both samples was performed in four steps and the results show that absorption does not change much, which confirms the repeatability of adsorbents. Also, The X-ray diffraction pattern of the SBA-15 sample shows that the structure is retained after the absorption process.

In this research, the kinetics of removal of acidic blue 206, an acidic dye, from aqueous solution by multi-wall carbon nanotube at optimized pH of 6.5 and 298K has been investigated. Six kinetics models contain pseudo-first-order, pseudo-second-order, intra-particle, Elovich, Bingham, and modified Freundlich model used. Kinetic data were fitted by these six models using linear and nonlinear regression. The results showed that the pseudo-second-order model was best fitted in both linear and nonlinear regression methods. The rate-determining step was the surface adsorption. The calculated qe at pseudo-first-order and pseudo-second-order models, (73mg/g and 75mg/g, respectively) are near the experimental value (99 mg/g). The order of compatibility of data with other models at nonlinear regression is pseudo-first order> Bingham> modified Freundlich> Elovich> intra-particle diffusion models. For leaner regression the order of compatibility of data are Bingham> elovich> modified freundlich> intra-particle diffusion> pseudo-first-order models. The calculated Arrhenius activation energy was -61.63kJ/mol. The negative activation energy, Ea, means that there is no barrier energy on surface adsorption and the adsorption is exothermic.

In this work, a new sulfamic acid-based catalyst that could be used in the solid phase was synthesized using chlorosulfonic acid and methylene dianiline in a simple manner. The structure of the catalyst was characterized, and then it was used as a catalyst in the synthesis of biologically active xanthene derivatives to the evaluation of its efficiency. The mentioned catalyst showed better catalytic activity than the other reported ones from the points of simple using at solid phase and being free of environmental pollutant halogens. The results verified its capability for improving the reactions, which usually need an acidic catalyst to perform. Finally, bis(xanthenes) are synthesized using this catalyst for the first time in good yields. The structures of the new compounds were verified using FT-IR, H-NMR, and C-NMR spectroscopies.

A green and effective method for the synthesis of benzylidene malononitrile derivatives via condensation of different aldehyde and malononitrile in the presence of Acetoguanamine supported on CoFe2O4 magnetic nanoparticles coated by silica gel as a new catalyst at room temperature with ethanol and water solvent was reported. The simple separation of products from the reaction mixture, the improvement of product yields, the short reaction time, and the use of solvents that have relatively less environmental pollution, the easy reaction method, the recoverable and reusable catalysts are the advantages of this method. The 6-methyl-1,3,5-triazine-2,4-diamine supported on CoFe2O4 magnetic nanoparticles coated by silica gel could be recycled five times without significant loss of its catalytic activity. All products were characterized by spectral data and by comparison with authentic samples reported in the literature.

Copper acetylide was reacted with isothiocyanates and aziridines to form 1,4-thiomorpholine derivatives. Reaction outcome depends highly on the reaction conditions and the particular solvent employed. Optimum conditions are developed using copper triflate in DMSOat70 ˚C. Both the alkyl- and aryl- substituted aziridines and terminal alkynes were tolerated. Variation on isothiocyanates structure did not affect the reaction efficiency in an appreciable manner.Oxirane derivatives exhibited lower reactivity than that aziridines. Alkyl aziridines afforded terminal-attacked products while phenyl aziridines gave benzylic-attacked products.Aziridines derived from cyclopentene did not participate in this transformation.

In this work, tannic acid and aliginic acid as highly efficient catalysts were applied for the one-pot multicomponent synthesis of  9- Aryl-1,8-dioxo-octahydro- xanthene, 14-Aryl-14H- dibenzo[a,j] xanthene, 9,9- dimethyl-12-Aryl-8,9,10,12,tetrahydro-benzo[a]xanthene derivatives under the neutral and solvent-free conditions. These natural biopolymeric heterogeneous catalysts encompass advantages such as they are cheap and biodegradable and the protocols avoid using the expensive catalyst and toxic solvent. We believe that this methodology is simple, high yielding an efficient, time-saving, and environmentally friendly. In addition, this method is superior to reported methods in the literature, for the synthesis of various xanthene derivatives.

Formation of macrocycle from non-cyclic precursors is inherently difficult. In this research, to minimizing of this problem, two methods, crab-like, and template-directed synthesis were run together simultaneously, to afford new eleven aza macrocycles (AM1-11) based on 2,4,6-triaryl pyridine in high yields. The AM1-11 were synthesized by the reaction of diamine compounds (1-11) with 2,6-bis(3-(2-chloroacetamido)phenyl)-4-(phenyl)pyridine (BCP) as a crab-like reagent, in the presence of K2CO3/KI (template reagent). BCP was obtained from the reaction of 2,6-Bis(3-aminophenyl)-4-(phenyl)pyridine (BAP) and chloro acetylchloride at room temperature. Also, BAP was synthesized by using 3-nitro acetophenone and bezaldehyde in the manner of modified Chichibabin reaction and then the reduction of the product by Zn/NH4Cl. The structures of macrocycles were confirmed by IR, 1H NMR, 13C NMR, and Mass spectroscopies.

The purpose of this study is to report the quantum chemical study of enantioselectivity of a-cyclodextrin (a-CD) and g -cyclodextrin (g -CD) towards baclofen enantiomers. In this regard, host-guest interactions of a -CD and g -CD with baclofen enantiomers were simulated using DFT (B3LYP/6-31G(d)) method with water as solvent. The Natural Bond Orbital (NBO) for the direction and magnitude of charge transfer interactions was calculated. Furthermore, the Quantum Theory of Atoms in Molecules (QTAIM) was employed to indicate the existence and the relative strength of the intermolecular bonds. The investigations revealed that the interaction energies of R-baclofen with a-CD and g -CD were more negative than those of S ones. The interaction energies of a- and g -CD with baclofen enantiomers with the NBO indicate the most significant charge transfer occurs for the O atom lone pair of CDs to the O-H anti bond of the baclofen also interactions between baclofen and other atoms of CDs is slight. The QTAIM results show the non-covalent interactions of the baclofen with CDs with electrostatic effects. The overall theoretical data corroborate with experimental results.

Today, climate change caused by the emission of greenhouse gasses is one of the most important environmental challenges facing humankind. In this work, using density functional theory calculations, the probable reaction mechanisms for the reduction of CO2 by H2 molecule were investigated over a Ni atom incorporated nitrogen-doped graphene. Our results indicated that the Ni atom can be efficiently adsorbed over the monovacancy site in the nitrogen-doped graphene. According to the obtained results, the catalytic activity of the mentioned surface is mainly originated from the strong hybridization between the σ orbital of the hydrogen molecule and 3d orbitals of nickel. The activation energies indicated that for the reduction of CO2, the formation of carboxylate is energetically more favorable than that of the formate intermediate.

Hydrogen sulfide is a poisonous and lethal gas for living creatures that is produced industrially/naturally on large scale on the globe. The current route to eliminate this plentiful/perilous hazardous material is Claus industrial process that converts H2S into sulfur, generates SOx/NOx harmful by-products and ignores/oxidizes the H2 fuel stored in this chemical. Photocatalytic degradation/transformation of H2S to hydrogen clean fuel and valuable sulfur element is a modern and green as well as alternative strategy for the current Claus approach, which can be effectually employed in the conversion of H2S noxious pollutant into H2+S. To this end, the design and synthesis of effective, eco-friendly, low-price photocatalyst materials are highly in demand. Herein, through a facile hydrothermal route, an n-type mesoporous sulfide semiconducting material with strong ability of photons absorption in the UV-Vis. the spectral region was synthesized and successfully applied for the photo splitting reaction of the alkaline H2S-containing medium to generate H2 fuel and S element. Furthermore, the photo-transformation phenomenon was interpreted from a mechanistic standpoint and the energy diagram revealed that the photocatalyst material synthesized here, viz. bismuth sulfide had a suitable band structure to reduce proton and oxidize bisulfide anion, which could eventually evolve hydrogen gas and produce the sulfur product.

In this research Dispersive Liquid-Liquid Microextraction (DLLME) coupled with microvolume UV–Vis spectrophotometry has been used for the sensitive determination of tetryl. The method is based on the conversion of tetryl to anionic form in the alkaline medium and its extraction into CCL4 using Aliquat 336. In this method, there is no need to use extraction solvent because Aliquots 336, in addition to the formation of counter ions for the formation of ion-pair with anionic form of tetryl also acts as a disperser agent. In this method, the calibration graph was linear over the range of 10-700 ng/mL with a limit of detection of 2.1 ng/mL. The proposed method was successfully applied to the determination of tetryl in water and soil samples.

A new, sensitive, simple, and rapid fluorometric method was developed for the direct determination of carvedilol in real samples. The method was based on the inhibition of the fluorescence resonance energy transfer (FRET) process between terbium (III)-1, 10-phenanthroline (Tb-phen) complex, and silver nanoparticles (AgNPs). For this purpose, the quenching effect of AgNPs in the concentration range of 0.9×10-12 – 5.4 ×10-11 M was investigated on the Tb-phen complex fluorescence intensity in the excitation and emission wavelengths of 300 and 500 nm, respectively. The results showed that the amount of AgNPs quenching, as a result of FRET process, is very high and there is a good linear relationship between the quenched fluorescence intensity and AgNPs concentration. The quenching probably occurs when the Tb-phen complex is attached to the AgNPs by electrostatic force and long-range dipole-dipole interaction between the excited donor (Tb-phen complex) and ground-state acceptor molecules (AgNPs). Upon the addition of carvedilol, the quenched fluorescence of Tb-phen complex was gradually recovered by carvedilol via its strong adsorption on the surface of AgNPs and removal of Tb-phen complex from the AgNPs surface (turn off/on process). Under the optimum conditions, a linear relationship was obtained between the enhanced fluorescence intensity and the carvedilol concentration in the range of (5-1000)×10-8 M with the detection limit of 2.0×10-8 M. The proposed method was successfully applied to determine carvedilol in the spiked normal serum samples and analytical recoveries from treated serum samples were in the range of 92.5–103% and relative standard deviation (RSD%) were 0.14-1.15.

In this study, a selective and sensitive ion-selective liquid membrane electrode based on 2-benzamidopropanoic acid to the determination of chromium (III) was prepared. This electrode exhibits a Nernstian response for chromium (III) ions over a concentration range (0.3´10-1 to 1.0´10-5 mol/L) with a slope of 22.3 mV per decade. The limit of detection of the electrode was 8.0×10-6 mol/L. The sensor has a relatively fast response time (<10 s) and a useful working pH range of 3.5–8.0. Interference of some cations was also evaluated. The practical utility of the chromium (III) ion sensor has been demonstrated by using it as an indicator electrode in the potentiometric titration of chromium (III) with EDTA and for direct determination of chromium (III) in tea and cacao powder samples. Finally, the effect of ionic liquid of 1-Methyl-3-Pentylimidazolium bromide as an ionic additive was investigated.

Novel separation methods that are necessary for the purification of biomolecules and carboxylic acids at industries, are expanding. Therefore, these methods should be fast, selective, and easy to scale up. The aqueous two-phase system is an effective separation procedure for the purification of materials. The purification of biomolecules and carboxylic acids is extremely selective by this method and also, the separation process is conducted in one step. This research aimed to investigate the effects of molecular weight of polyethylene glycol, pH, salt concentration, and salt type in polymer/salt aqueous two-phase systems. In this research, purification of malic acid in aqueous two-phase systems containing polyethylene glycol 4000 and 8000 g/mol, different concentration sodium di hydrogen phosphate, diammonium hydrogen phosphate, and di potassium hydrogen phosphate were studied. After investigating the effective factors, the best operation conditions for malic acid extraction was obtained in a system composed of  PEG4000, 0.25 (w/w) sodium di hydrogen phosphate at pH=5. The purification parameters such as partition coefficient of malic acid and yield were achieved 0.85 and 80%, respectively.

Novel separation procedures that are essential for the purification of biomolecules in biotechnology industries, are developing. Hence, these methods should be rapid, selective, and easy to scale up. The aqueous two-phase system is an efficient method for the purification of materials. The purpose of the present work was to investigate the various parameters such as temperature, pH, salt concentration, and salt type in the polymer/salt system. In this research, purification of malic acid in the aqueous two-phase system which is containing polyethylene glycol 4000 g/mol and three variant salt (dipotassium hydrogen phosphate, diammonium hydrogen phosphate, and disodium hydrogen phosphate) were studied. According to the results, the optimum D and Y%  for extraction of malic acid was identified 0.85 and 80%, under these conditions, including 25% (w/w) disodium hydrogen phosphate at T=25°C and pH=5, respectively.

In this study, a model is presented using the black box neural network technique. In this model, the effects of four basic parameters, including temperature, voltage consumption, flow rate, and feed concentration on salt separation percentage from salty water, have been investigated. With the help of trial and error, the training method, transfer function, and the optimal number of neurons on each layer are selected to provide the best network performance. Multi-layer neural network, backpropagation, and Levenberg-Marquardt algorithm are utilized as the optimum options. In this study, 135 data were used, allocating 60% of them (81 data) to network training, 20% (27 data) to training data evaluation, and the remaining 20% (27 data) to assess the network generalizability as test data. Finally, a comparison of the model results with independent laboratory data indicates that the optimal network arrangement is 4:5:8:1, and the model with an error of less than 1% can predict the process behavior.

The desulfurization process is always one of the sensitive and important processes in the oil and gas industry. The presence of sulfur in hydrocarbon streams, in addition to the process problems it causes in refining sections, can produce hazardous gases and acid rain if found in fuel products. The oxidative desulfurization process is one of the new desulfurization methods to produce sulfur-free fuels. This process has some advantages over the hydrodesulfurization process such as not consuming valuable hydrogen, mild operating conditions, and simple elimination of sulfur-containing aromatic compounds. Despite the advantages of oxidative desulfurization, this process also faces challenges. One of the most important problems in this process is the waste treatment process, especially the mixture of sulfone compounds obtained from the process. In this study, various processes such as hydrodesulfurization, coking, gasification, and hydrocarbon recovery were studied to solve the problem of sulfone waste disposal. Also, a comparison has been done between the available technologies in terms of the requirement for new investment, the possibility of integration with refining units, and the level of maturity of the technology.

The emission of greenhouse gases, especially aromatic compounds, is a major challenge in the gas industry. In the dehydration process, glycol solvents are used to eliminate water content from the natural gas stream. Farashband gas processing plant consists of six dehydration units that operate by application of stripping gas injection. In this study, the application of Drizo process instead of the conventional process for solvent regeneration is investigated and in order to reduce the BTEX emission and decrease the solvent cost, the use of BTEX absorbed components from the gas stream as a regenerative solvent is suggested. Achieved results indicated that the application of Drizo process decreases the harmful environmental effects and improves the main operating parameters such as dewpoint of dry natural gas, glycol loss, and glycol purity. Also, according to simulation results, by application of Drizo process, the dewpoint of dry natural gas in the summer operating condition reduces from -25 ℃  to -29 ℃  and the glycol loss decreases from 3 kg/h to 2.5 kg/h.

In this study, we perform experimental and analytical investigations of corrosion effects on heat transfer in a kettle heat exchanger. In this heat exchanger, the oil is flown inside the tube and the water is flown inside the shell, which is their duty to convert water to superheat steam. First, the causes of corrosion in the heat exchanger are analyzed using optical and electronic microscopes and also metallographic experiments, that tube sintered ferrite, and perlite structure and grain size does not change in the surface crust boundary which illustrates the basic metal does not trigger the reaction. XRD and XRF experiments on the results of sediments in the external scale of silicate, calcium, and phosphorus tubes show that because of poor heat transfer, the feed water quality, the concentration of oxygen cells is made in that case sub-sediment corrosion which is the subset of SCC corrosion. This phenomenon reduces the outside of the tube thickness from 2.11 mm to 1.44 mm. Corrosion deposits in the outside surface of the tube cause a reduction in the heat transfer rate, which results in a hot spot, increasing tube oxidation intensity and corrosion. This issue exactly matches with a gradual reduction in the output heat exchanger vapor pressure during operation which is determined experimentally. MATLAB software coding is the relationship between sediment mass and sediment heat resistance. The results illustrate that by passing time, the sediment mass and sediment heat and at the end of this instance are matched with experimental results.

In this research, upgrading of cyclohexanone as a representative of lignin-derived bio-oil via hydrotreating process catalyzed by Pt/γ-Al2O3 in a fixed-bed tubular reactor is investigated at 573-673 K, 14 bar and space velocity of 3–120 (g of cyclohexanone)/(g of catalyst × h). In order to determine the reaction network and kinetic, the cyclohexanone conversion and products selectivity are evaluated. Data collected at the low conversion of cyclohexanone which quantitatively represents initial product distribution consists of hydrogenation, hydrodeoxygenation, dehydration, and condensation. The highest apparent activation energy is related to the condensation reaction in which the dehydration reaction resulting in phenol formation is assumed to be 17 kJ/mol. Rate constants of formation for the main products decrease as follows: phenol >  2-cyclohexylidenecyclohexan-1-one > 2-methylphenol > cyclohexylbenzene > cyclohexane > biphenyl > 2-cyclohexen-1-one > 2-cyclohexylcyclohexan-1-one > 2-phenylphenol > cyclohexene > 2-cyclohexylphenol.

Hydrogen production from biomass gasification via steam reforming can be introduced as one of the most attractive methods for overcoming energy challenges. In this study, the gasification of bagasse process in the presence of steam performed in fixed bed reactor under 850˚C and atmospheric pressure has been conducted in two stages of noncatalytic and catalytic. To evaluate the effect of active metal particles size, Ni12%-Fe6%/γ-Al2O3 bimetallic nanocatalysts were prepared through microemulsion and impregnation methods. The chemical and physical properties of the nanocatalysts were characterized by TPR, XRD, TEM, and BET techniques. The microemulsion technique especially at the lowest Water/Surfactant (W/S) ratio caused synthesis of the active metal average particle size and increased dispersion on the support. Using the microemulsion technique especially at lower W/S increased the hydrogen yields by a factor of 2.8. Also, Ni-Fe/γ-Al2O3 catalyst promoted by 1 percentage of ruthenium, increased the hydrogen yields by a factor of 3.8 compared to the noncatalytic process.

Polycarboxylic acid is one of the largest bioplastics consumed in the world and has a wide range of applications in the medical and industrial sectors and has many interesting properties such as biodegradability, biocompatibility, high strength, and more. Poly-lactic acid, as a renewable and stable source, has a high potential for reducing oil dependence for economic and environmental development. Based on the molecular weight of the polylactic acid, it is divided into two groups: low molecular weight and high molecular weight. The physical and structural properties of the molecular chains of polymers are influenced by the molecular weight of the polymers. Therefore, by changing the size of the molecule, the properties of the polymer also change. The melting point, strength, and other physical properties of the polymer also depend on the size and dimensions of the molecule (polymeric chain length). In this study, the effect of the degree of polymerization on the physical and thermodynamic properties of biocompatible and biodegradable polylactic acid polymers was investigated using molecular dynamics simulation technique at ambient temperature and pressure. And parameters such as solubility, density, free volume, etc. were calculated and the results of the simulation were compared with the available experimental data and were well-matched with each other. The results also show that the increase in the degree of polymerization reduces the solubility parameter and does not show any significant changes in the PLA solubility parameter after 30 degrees of polymerization, and the amount of FFV does not change much and is close to 18.2%.

Nowadays, the use of polymers is enhancing day by day. Through to not biodegradability in nature, they accumulate and contaminate the environment. One of the recent methods to solve this issue is using biodegradable polymers. Low-density polyethylene was chosen as a symbol and its film was prepared by an extruder in the lab. Starch, Oxo material, polylactic acid, and their mixture were used as biodegradable material and their influence on the physical and mechanical properties of low-density polyethylene were studied. Results indicated that using starch resulted in a significant decrease of mechanical properties for the low-density polyethylene, while Oxo material and polylactic acid caused a low change in the mechanical properties.

In the present study the mechanical and biodegradability properties of Low-Density Polyethylene (LDPE)/propolis blended films were investigated. For this purpose, crude propolis was powdered and was added to the polymer matrix at different percentages of propolis to LDPE (0, 5, 10, 15, and 20 by weight percentages). The films were prepared by the extrusion method. The characterizations of the obtained films were determined by using mechanical (tensile) and biodegradability in soil tests. The study of the microscopic structures of the films was performed using Field Emission Scanning Electron Microscopy (FESEM). FESEM images showed that the surface of the films containing propolis was swollen in the island form as compared to the control and this property expands with the increase in the amount of propolis in the polymer matrix. The mechanical properties of films showed that the addition of propolis to LDPE film reduced the tensile strength and also reduced the relative elongation of the films from 16.5262 and 1%, respectively, for film control to 9.7794 and 0.840% for LDPE film containing 20% propolis. The biodegradability results of these films showed that after 150 days of film placement in the soil, the biodegradability process in the films containing propolis was more rapid than the control. The percentage of soil biodegradability in the film containing 20 percentages of propolis was the highest and reached 5.2 percent. Also, the mechanical properties of the films after 150 days of soil biodegradability also decreased for each film containing propolis than before.