Selection of optimal feed flow sequence for a multiple effect evaporator system

A nonlinear model is developed for a SEFFFE system employed for concentrating weak black liquor in an Indian Kraft Paper Mill. The system incorporates different operating strategies such as condensate-, feed- and product-flashing, and steam- and feed-splitting. This model is capable of simulating a MEE system by accounting variations in τ, U, Q_loss, physico-thermal properties of the liquor, F and operating strategies.The developed model is used to analyze six different F including backward as well as mixed flow sequences. For these F, the effects of variations of input parameters, T₀ and F, on output parameters such as SC and SE have been studied to select the optimal F for the complete range of operating parameters. Thus, this model is used as a screening tool for the selection of an optimal F amongst the different F.An advantage of the present model is that a F is represented using an input Boolean matrix and to change the F this input matrix needs to be changed rather than modifying the complete set of model equations for each F. It is found that for the SEFFFE system, backward feed flow sequence is the best as far as SE is concerned.     

E.p.r. study of molecular phases in coal

E.p.r. spectra from coals of various carbon content are reported. The e.p.r. signal from coals in a vacuum consists of two lines with different widths. The results are interpreted using the Larsen-Kovac structural model (Am. Chem. Soc. Div. Fuel Chem. Preprints 1977, 22, 181). The paramagnetic centres, disposed in the macromolecular phase, give a narrow line whereas the spins of the molecular phase are responsible for the broad line. These results provide a good interpretation of the changes in e.p.r. signal-shape under the influence of various organic solvents observed by Yokokawa (Fuel 1968, 47, 273; Fuel 1969, 48, 29).     

Synthesis and characterization of whitlockite from sea urchin skeleton and investigation of antibacterial activity

In the present study, undoped whitlockite and ZnO doped-Whitlockite, which is the second most abundant inorganic material in bone structure, were synthesized from sea urchin skeleton. The obtained bioceramic materials were characterized by XRD, FT-IR, and SEM and their antibacterial activities were determined using the inhibition zone diameters of Escherichia coli and Pseudomonas aeruginosa as gram negative bacteria and Staphylococcus aureus as gram positive bacterium after 24 h incubation. The characterization studies showed that nano size homogenous biocereamic whitlockite (Ca_2.86Mg_0.14(PO₄)₂) was synthesized from the sea urchin skeleton. After dopping process, the main structure of the whitlockite keeps stable, showing a dopping concentration-independent character. On the other hand, the peaks belonging to ZnO were started to seen in the XRD pattern with increasing the level of ZnO-concentration (after 7 %). All experimental results point out that the obtained whitlockites are viable nominate candidates for bioceramic materials and the results of antibacterial sensitivity prove the inhibitory effect towards Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus for ZnO-doped-whitlockite.     

Fluorescence probe for microenvironments: On the fluorescence properties of p-N,N-dialkylaminobenzylidenemalononitrile in polymer matrices

The effect of an alkyl group (R) in a series of poly(alkylmethacrylate) and poly(alkylacrylate) polymers on the fluorescence properties of p-N,N-dialkylaminobenzylidenemalononitrile derivative, 1, has been studied. The fluorescence emission maximum shifts to the blue and the fluorescence quantum yield decreases as the chain length of R increases. These results are interpreted in terms of a model which assumes that the location of 1 is dependent on R and the change in quantum yield reflects the difference in free volume or polymer chain flexibility in various locations in these polymers.     

Feasibility study on sharpening metal-bond metal diamond grinding tool by microwave-induced electric discharge machining

Microwave-induced electric discharge machining (MV-EDM) is an emerging machining method that can be applied to fine machining of metal materials. A feasibility analysis of the application of MV-EDM to sharpen diamond grinding tools was conducted in this study. A multiphysical simulation model for sharpening using MV-EDM was established, and MV-EDM sharpening experiments and measurements were performed to verify the accuracy of the simulation model. It was found that MV-EDM can effectively improve the protrusion height h_p and does not result in severe graphitization of diamond grains under appropriate conditions. Under the conditions of a microwave power of 1 kW and a gap scale d of 0.1 mm, the h_p of the diamond grain increased to 91 μm with a complete diamond crystal shape and slight graphitization. In addition, it was discovered that the gap scale d and initial protrusion height h₀ had a significant effect on the protrusion height h_p and the graphitization of the diamond grains. After verification, the accuracy of the simulation model for calculating the protrusion height of diamond grains was controlled within a range of ±15 μm. The results of this study provide a theoretical basis for the industrial application of MV-EDM to sharpening.     

Syntheses of siloxane-grafted aromatic polymers and the application to pervaporation membrane

The syntheses of siloxane-grafted poly(amide-imide) and polyamide were carried out by a macromonomer method, in order to develop a highly permeable and durable membrane material for pervaporation. A novel compound, 3,5-bis(4-aminophenoxy)benzyloxypropyl-terminated polydimethylsiloxane (BAPB-PDMS), was synthesized as a macromonomer. BAPB-PDMSs with different PDMS segment lengths were prepared by hydrosilylation of 3,5-bis(4-nitrophenoxy)benzyl allyl ether with hydrosilyl-terminated PDMS using Pt catalyst, followed by hydrogenation reduction of the terminal dinitro groups. The polycondensations of BAPB-PDMSs with trimellitic anhydride chloride and terephthaloyl chloride yielded the desired siloxane-grafted poly(amide-imide) (PAI-g-PDMS) and polyamide (PA-g-PDMS) copolymers, respectively. The copolymer membranes were prepared by solvent-casting method, and the gas permeability and pervaporation property of these membranes were evaluated. As the solubility of the copolymers depended on the main chain structure, PA-g-PDMS membrane was insoluble in any solvents after it was dried in vacuo. The gas permeability coefficients of these copolymer membranes were increased as increase of PDMS segment length, and these values of PAI-g-PDMS were higher than those of PA-g-PDMS containing the same PDMS segment length. From the results of pervaporations of the dilute aqueous solutions of organic solvents, it was found that PA-g-PDMS exhibited the excellent permselectivity toward several organic solvents, such as alcohols, acetone, tetrahydrofuran, chloroform, dichloromethane and benzene with a high and stable permeation. Furthermore, it was confirmed that the removal of tetrahydrofuran from its dilute aqueous solution was efficiently achieved by the pervaporation using PA-g-PDMS membrane.     

The effect of diffusivity on gas-liquid mass transfer in stirred vessels. Experiments at atmospheric and elevated pressures

Mass transfer has been studied in gas-liquid stirred vessels with horizontal interfaces which appeared to the eye to be completely smooth. Special attention has been paid to the influence of the coefficient of molecular diffusion. The results are compared with those published before. The simplifying assumptions of identical hydrodynamical conditions at the same stirrer speed in one particular geometry, which have been made in some previous investigations, is shown to be wrong and may lead to incorrect conclusions on the influence of the diffusion coefficient. For the gas phase the mass transfer can be described by the penetration theory (Higbie, R., 1935, Trans. Am. Inst. Chem. Engrs35, 36–60) or surface renewal model (Danckwerts, P. V., 1951, Ind. Engng Chem.43, 1460–1467). With the use of a dimensionless equation, Sh, Re and Sc numbers, all data, even experiments carried out at elevated pressures, could be well correlated. For the liquid phase the results indicate that the mass transfer cannot be described by a simple model. The King model (King, C.J., 1976, Ind. Engng Chem. Fundam.5, 1–8), a combination of molecular and eddy diffusivity, is able to explain qualitatively the observed phenomena and the literature data.     

Mathematical modeling of mass transfer in multicomponent gas mixture across the synthesized composite polymeric membrane

This study presents a new mathematical model to investigate the ternary gas mixture permeation across a synthesized composite PDMS/PA membrane. A novel algorithm is introduced for direct determination of diffusion coefficients. It pertains to study gas permeation through concentration dependent systems and comparing with traditional time lag method confirms the precision of this approach. Feature is that this method does not require physical properties of the membrane. Accordingly, it can be used as a general comprehensive model. In addition, molecular pair and molecular trio interactions were taken into account and in order to investigate the deviation of gas mixture from ideality, fugacities were calculated. The results showed that permeabilites of H₂ and CH₄ increase with increasing feed temperature and fugacity, while that of C₃H₈ decreases. Moreover, increasing C₃H₈ concentration improved permeation properties of all components. The results demonstrated that considering the concentration dependent system (CDS) leads to the small deviation of about less than 10%, while the deviation of 50–100% by the concentration independent system (CIS) was acquired. Additionally the results indicated that permeability of the lighter gases is specially affected by diffusivity, while solubility is dominant on permeability of the heavier gases.     

A facile galvanostatic method for the synthesis of quinoxalinediones

Electrochemical oxidation of catechols (1a-d) has been studied in the presence of N,N-dimethylethylendiamine (3) as a nucleophile in aqueous solutions, using cyclic voltammetry, constant-current coulometry and controlled-potential coulometry. The results indicate that the quinones derived from catechols (2a-d) participate in Michael addition reactions with N,N′-dimethylethylendiamine (3) via the ECECE mechanism to form the corresponding quinoxalinedione derivatives (6a-c).     

The log-normal size distribution theory of brownian aerosol coagulation for the entire particle size range: part II—analytical solution using Dahneke’s coagulation kernel

In this study an analytical solution of the Brownian coagulation equation utilizing the method given in Park et al. [(1999) J. Aerosol Sci. 30, 3–16] but using a more detailed coagulation coefficient instead of the simple approach—the harmonic mean—Park et al. [(1999) J. Aerosol Sci. 30, 3–16] is derived. Comparisons are made with the analytical solution given in Park et al. [(1999) J. Aerosol Sci. 30, 3–16], with a method of moments model, with a log-normal reference model as well as with a sectional model (Landgrebe and Pratsinis, (1990) J. Colloid Interface Sci. 139, 63–86).In order to make a fair comparison between the models, all of them should use the same coagulation coefficients except Park et al. [(1999) J. Aerosol Sci. 30, 3–16] which is already fixed to the harmonic mean method. The most frequently used coagulation coefficients to describe the process of Brownian coagulation in the entire size regime (Fuchs, Dahneke, harmonic mean) were compared and a universal enhancement function to the near-continuum coagulation kernel is given. Furthermore, Fuchs’ coagulation kernel is reviewed and modified for the use with different sized particles. It was shown that Dahneke’s coagulation kernel is very close to those of Fuchs and Wright with a relative error of less than 1%. Based on this finding, Dahneke’s coagulation kernel is used in the models developed as well as during the comparison.In order to develop fast and easy-to-use coagulation models we used the moment method assuming a log-normal size distribution function [Lee et al., (1997), J. Colloid Interface Sci. 188, 486–492]. In the first step the integrals over the particle size distribution are solved analytically and DGEAR (IMSL, 1980) is used to solve for the time dependence. In the second step we solved also the time dependence of the parameters of the size distribution analytically. The models developed are compared over a wide parameter range with a reference model based on the moment method of log-normal size distribution functions as well as a sectional reference model. For a worst case, the moment method shows a relative error of less than 4% for the number concentration; the mean geometric standard deviation and the volume square concentration and for the geometric standard deviation the relative error is less than 8% in the self-preserving state. The analytical solution developed shows a maximum relative error of less than 10% if the dimensionless time is limited to K_coN₀t=1.     

Colorimetric sensing of metal ions by bis(spiropyran) podands: Towards naked-eye detection of alkaline earth metal ions

In order to develop a selective and sensitive colorimetric sensor for metal ions, a series of oligoether-linked bis(spiropyran) podands were prepared and their ability to colorimetrically sense alkaline earth metal ions was investigated. UV–vis absorption and ¹H NMR spectroscopic studies showed that the podands isomerized from the colorless spiropyran form to the colored merocyanine form upon complexation with alkaline earth metal ions, whereas spectral changes were not visible in the presence of alkali metal ions. Podands of spiropyran subunits linked by a spacer of a 3-oxapentan-1,5-dioxy group, i.e. X-BSP-1 (X = MeO, tBu, iPr, H, Cl, Br), exhibited high selectivity to Ca²⁺. Introduction of an electron-donating group to the 5-position of each indoline ring of the podand gave rise to an increase in affinity to alkaline earth metal ions, enhancing the sensitivity. The absorption maximum of the colored metal–X-BSP-1 complex varied over a range of ca. 30 nm, from reddish purple to bluish purple. Clear discrimination of the Ca²⁺ complex from that of Mg²⁺ was possible using the naked eye. These results indicate the potential application of the X-BSP-1 podands as a colorimetric sensor for Ca²⁺.     

Novel hexanuclear and octanuclear zinc alkyl cages derived from a bis-oxamidate ligand

1 and 2 were prepared by coordination self-assembly from reacting N,N′-bis(3,5-di-tert-buthyl-2-phenol)oxamide (L-H₄) with ZnEt₂ in toluene and THF, respectively. The molecular X-ray structures show 1 as an octanuclear Zn₈ cage and 2 as a hexanuclear Zn₆ cage. The nuclearity of these cages is driven by the solvent, in fact 1 gives 2 upon addition of THF. Good polymer conversions for the ROP of rac-lactide were achieved by using 1 and 2 with alcohols as co-catalysts.     

Efficient combination of ionic liquids and microwave irradiation as a green protocol for polycondensation of 4-(3-hydroxynaphthalene)-1,2,4-triazolidine-3,5-dione with diisocyanates

In this investigation, a novel urazole containing 3-hydroxynaphthalene group, 4-(3-hydroxynaphthalene)-1,2,4-triazolidine-3,5-dione (3HNTD) was synthesized in six steps starting from 3-hydroxy-2-naphthalene carboxylic acid. The reaction of 3HNTD with n-propylisocyanate was performed in N,N-dimethylacetamide solution at different molar ratios, and the resulting monosubstituted as well as disubstituted urea derivatives were obtained in high yields and were used as model compounds for polymerization studies. An efficient, fast and easy method for the preparation of new soluble poly(urea-urethane)s (PUU)s containing heterocyclic and chromophoric moieties from 3HNTD and various diisocyanates are employed using room temperature ionic liquids and molten tetrabutylammonium bromide under microwave irradiation as well as conventional heating. The polymerization reactions occurred rapidly under microwave and produced a series of PUUs with good yields and moderate inherent viscosities of 0.21-0.46 dL/g. All of the new PUUs showed good solubility and were readily dissolved in organic solvents.     

Improved photovoltaic performances of Ru (II) complex sensitized DSSCs by co-sensitization of carbazole based chromophores

Herein, we report photovoltaic performance studies of three carbazole based dyes (N_1–3) derived from (Z)-3-(9-hexyl-9H-carbazol-3-yl)-2-(thiophen-2-yl)acrylonitrile scaffold as effective co-sensitizers in Ru (II) complex, i.e. NCSU-10 sensitized DSSCs. From the results it is evident that, the device fabricated using co-sensitizer N₃ with 0.2 mM of NCSU-10 exhibited improved photon conversion efficiency (PCE) of 8.73% with J_SC of 19.87 mA·cm^− 2, V_OC of 0.655 V and FF of 67.0%, while N₁ displayed PCE of 8.29% with J_SC of 19.75 mA·cm^− 2, V_OC of 0.671 V and FF of 62.6%, whereas NCSU-10 (0.2 mM) alone displayed PCE of 8.25% with J_SC of 20.41 mA·cm^− 2, V_OC of 0.667 V and FF of 60.6%. However, their EIS studies confirm that, N₁, showing higher V_OC is efficient in suppressing the undesired charge recombination in DSSCs through enhanced surface coverage on TiO₂ and thereby resulting in longer electron lifetime than that of NCSU-10 dye alone. Here, the higher PCE of N₃ can be attributed to its improved light harvesting efficiency, which is due to the presence of highly electron withdrawing barbituric acid in its structure. Conclusively, the results showcase the potential of simple carbazole based dyes as co-sensitizers in improving efficiency of DSSCs.     

Electrochemistry of polyhalogenated organic compounds—II. Electrochemical reduction of 2,2,2-trichloro-1-phenylethyl derivatives

The electroreduction of 2,2,2-trichloro-1-phenylethyl derivatives (VIII) in aqueous dmf yields β,β-dichlorostyrene (VII) and/or the corresponding 2,2-dichloro-1-phenylethyl derivatives (IX). For the set of compounds thus far investigated there is a strong dependence of the product distribution as well as the polarographic half-wave potentials, on the nature of the substituent adjacent to the trichloromethyl group. These relationships are discussed in terms of a reduction mechanism which shifts from a carbanion model to a concerted elimination depending on an increase in leaving group tendency of this substituent.     

Construction of three Cd(II) coordination polymers based on extended pyridyl-tetrazolyl-bifunctional ligands: Structures and luminescent properties

Reactions of Cd(II) with three new pyridyl-tetrazole-bifunctional ligands, 3-(4-(1H-tetrazol-5-yl)phenyl)pyridine (HL¹), 4-(3-(1H-tetrazol-5-yl)phenyl)pyridine (HL²), and 3-(3-(1H-tetrazol-5-yl)phenyl)pyridine (HL³) resulted in three Cd(II) coordination polymers (CPs), namely, [CdL¹₂]_n (1), [CdL²₂]_n (2), and [CdL³₂(H₂O)]_n (3). Although the geometry of L¹ and L² is quite different, the coordination modes of Cd(II) ion and ligand, as well as the SBUs in compounds 1 and 2 are quite similar, thus give rise to 3D frameworks with same (3,6)-connected ant topology. Compound 3 is a 3D framework composed of 1D helical chains and features as (3,5)-connected tcj topology. The results showed that the topologies are largely dependent on the coordination angle between two coordination groups. The thermal stabilities and luminescent properties of compounds 1–3 have also been studied.     

Synthesis,structures, and magnetic properties of tetranuclear nickel and cobalt complexes with 2-mercaptobenzoxazole

The synthesis and magnetic properties of two tetranuclear Ni complex Ni₄(L)₄(CH₃CN)₄(OCH₃)₄ 1 and Co complex Co₄(L)₄(CH₃CN)₄(OCH₃)₄ 2 (HL = 2-mercaptobenzoxazole) are reported. The X-ray structures reveal that 1 and 2 are isostructural with [Ni₄O₄] 1 and [Co₄O₄] 2 cubane-like cores. Analysis of the temperature dependent magnetic measurements data shows that both complexes are paramagnetic with weak antiferromagnetic coupling. One-J model and two-J model are both applied to fit the experimental magnetic data of 1 and the results indicate the exchange coupling between the type A Ni(II) ions affected by NCS three atoms bridge in 2-mercaptobenzoxazole ligand.     

The crystal structures of three azonaphtharylamide pigments

The single crystal X-ray structures of three structurally related azonaphtharylamide pigments are reported. Two azo pigments derived from 4-amino-3-nitrotoluene as diazo component (1a and b) crystallize in the centrosymmetric space group P2₁/c while the third (1c), an analogue of 1b but derived from 2,5-dichloroaniline as diazo component, crystallizes in the chiral space group P2₁2₁2₁. The compounds adopt the ketohydrazone tautomeric forms with intramolecular, but no intermolecular, hydrogen bonding. The application performance of the products is discussed in relation to the molecular and crystal structures. X-ray powder diffraction, supported by FTIR spectroscopic and DSC analysis, demonstrate that pigment 1a shows polymorphism. The application performances of the two polymorphs of this pigment are compared.     

Coordination assembly of helicate and mesocate with two-armed carbohydrozine ligand: Synthesis,structure and fluorescence

Two-armed carbohydrozine ligand, H₂L¹ and its cobalt(III) and zinc(II) complexes (1 and 2) have been synthesized and characterized by single-crystal X-ray diffraction analysis. In the solid state, compound 1 has double-strand helicate structure involving ligand that twists to the central metal ions. Abundant π…π stacking interaction extended in the crystallographic bc plane. However, compound 2 has mesocate structure with a side-by-side arrangement of two ligands. The structure of zinc(II) compound 2 can be described as plane-symmetry one with symmetry plane perpendicular to the metal linker. The π…π stacking interaction existed in the crystallographic ac plane of compound 2. Weak intermolecular interactions play dominant roles in shaping the extended two-dimensional structures for all the molecules in the solid state. In solution, zinc(II) compound 2 exhibited strong ligand-based π*–π fluorescent emissions that can be tuned by the attached proton, a potential proton probe model.     

Mechanistic study of electrochemical oxidation of o-dihydroxybenzenes in the presence of 4-hydroxy-1-methyl-2(1H)-quinolone: Application to the electrochemical synthesis

Electrochemical oxidation of o-dihydroxybenzenes (1a and 1b) has been studied in the presence of 4-hydroxy-1-methyl-2(1H)-quinolone (3) as a nucleophile in aqueous solution using cyclic voltammetry and controlled-potential coulometry. The results indicate that the o-quinones derived from o-dihydroxybenzenes (1a and 1b) participate in 1,4-(michael) addition reactions with 3 to form the corresponding new o-dihydroxybenzene derivatives (6a and 6b). We propose a mechanism for the electrode process. The efficient electrochemical synthesis of 6a and 6b has been successfully performed at carbon rod electrodes in an undivided cell in good yield and purity. The products have been characterized after purification by IR, ¹H NMR, ¹³C NMR and MS.