Search

The effects of Mn/Na2WO4, Li, and CaO loading on the monoclinic Sm2O3 catalyst were investigated for the oxidative coupling of methane using O2 or N2O as an oxidant. The catalysts were prepared by ...

Effect of calcination temperature on Ni/MgAl 2 O 4 catalyst was investigated in order to evaluate changes on structural and catalytic properties for catalytic partial oxidation of methane. The catalysts were calcined at different temperatures after impregnation of nickel salt solution on MgAl 2 O 4 support. The prepared catalysts showed nearly 89% CH 4 conversion and 99% H 2 selectivity under the flow of 157,000 (l kg −1 h −1 ) with the ratio of CH 4 /air = 0.44 at 1 atm and 800 °C. However, turnover frequency values of the catalysts were between 8.2 and 42.3 s −1 and increased according to Ni particle size. Lewis basicity/acidity ratio increased from 2.14 to 4.46 with increasing calcination temperature. It was found that coking rate on the catalysts depends on Ni particle size and surface basicity/acidity. The experimental results showed that calcination temperature and time have a significant influence on both structural and catalytic properties of the catalysts that show strong metal oxide support interaction. It could be claimed that high calcination temperatures could be beneficial to obtain highly active, selective and stable Ni/MgAl 2 O 4 catalysts, which possess strong metal oxide support interaction, by maintaining Ni dispersion high after reduction, increasing surface basicity and enhancing the stability of Ni particles against sintering.

SmxCa0.2−xCe0.8Oy materials are synthesized by changing mol ratios of the composition as x = 0, 0.05, 0.1, 0.15 and 0.2, respectively, with a fast and facile cellulose templating method for the first time. Microstructures of the calcined and sintered samples are characterized by XRD and SEM-EDX. Density measurements are actualized by using Archimedes method. The electrical conductivity of the samples is obtained from two-probe impedance spectroscopy. Maximum solubility limit of CaO in CeO2 is found to be 9.4 mol% from the XRD results. Incorporation of CaO slightly increases the sinterability of the samples. It is observed that Sm+3 expands the CeO2 lattice more than Ca+2. 10 mol% CaO incorporated sample show the highest total conductivity with the value of 0.032 S cm−1 at 800 °C. Obtained results show that Sm0.1Ca0.1Ce0.8Oy can be an excellent candidate for intermediate temperature solid oxide fuel cell applications due to its lower cost and higher performance compared to Sm0.2Ce0.8Oy at 800 °C. Additionally, cellulose templating method can be used as an effective method in order to prepare mixed oxide structures since the performances of the samples are higher than the samples which are prepared by more complex or costly hydrothermal and co-precipitation methods in literature.

The catalytic partial oxidation of methane (CPOM) was studied on Ni based catalysts. Catalysts were prepared by wet impregnation method and characterized by using AAS, BET, XRD, HRTEM, TPR, TPO, Raman Spectroscopy and TPSR techniques. The prepared catalysts showed nearly 95% CH4 conversion and nearly 96% H2 selectivity under the flow of 157,500 (L kg−1 h−1) with the ratio of CH4/O2 = 2 by using air as an oxidant at 1 atm and 800 °C. Support basicity greatly influenced the H2/CO ratio and carbon deposition. It was found that the lowest carbon deposition occurred on Ni impregnated MgO catalyst. Considering the results, it was found that Ni/MgO catalyst with 10% Ni content would be the best catalyst amongst Ni/Al2O3, Ni/MgO/Al2O3, Ni/MgAl2O4 and Ni/Sorbacid for the CPOM only under more reductive conditions. Under optimum conditions, Ni/MgO showed poor performance and therefore Ni/Sorbacid would be the ideal catalyst because of its greater carbon resistance than the other catalysts.

The paper is concerned with the formation of Layer-by-Layer (LbL) self-assembly of highly charged polyvinyl sulfate potassium salt (PVS) and polyallylamine hydrochloride (PAH) on Nafion membrane to obtain the multilayered composite membranes with both high proton conductivity and methanol blocking properties. Also, the influences of the salt addition to the polyelectrolyte solutions on membrane selectivity (proton conductivity/methanol permeability) are discussed in terms of controlled layer thickness and charge density. The deposition of the self-assembly of PAH/PVS is confirmed by SEM analysis and it is observed that the polyelectrolyte layers growth on each side of Nafion membrane regularly. (PAH/PVS) 10 –Na + and (PAH/PVS) 10 –H + with 1.0 M NaCl provide 55.1 and 43.0% reduction in lower methanol permittivity in comparison to pristine Nafion, respectively, while the proton conductivities are 12.4 and 78.3 mS cm −1 . Promisingly, it is found that the membrane selectivity values ( Φ ) of all multilayered composite membranes in H + form are much higher than those of Na + form and perfluorosulfonated ionomers reported in the literature. These encouraging results indicate that composite membranes having both superior proton conductivity and improved methanol barrier properties can be prepared from highly charged polyelectrolytes including salt for fuel cell applications.

A series of highly proton conductive electrolyte membranes with improved methanol barrier properties are prepared from polyallylamine hydrochloride (PAH) and polystyrene sulfonic acid (PSS) including salt by Layer-by-Layer (LbL) method. The effects of added salt type (NaCl, MgCl 2 ) and salt concentration (1.0 M, 0.1 M) on proton conductivity ( σ ) and methanol barrier properties of the LbL self-assembled composite membranes are discussed in terms of controlled layer thickness and charge density. Furthermore, the influences of ion type in the multilayered composite membranes are studied in conjunction with physicochemical and thermal properties. The deposition of the self-assembly of PAH/PSS film on Nafion is followed by UV–Vis spectroscopy and it is observed that the polyelectrolyte layers growth on both sides of Nafion membrane regularly. (PAH/PSS) 5 –Na + and (PAH/PSS) 5 –H + with 1.0 M NaCl exhibits 49.6 and 27.8% reduction in lower methanol permittivity in comparison with the pristine Nafion ® 117, respectively, while the proton conductivities are 12.97 and 74.69 mS cm −1 . Promisingly, it is found that the membrane selectivity values ( Φ ) of all multilayered membranes in H + form are much higher than that of salt form (Na + and Mg 2+ ) and perfluorosulfonated ionomers reported in the literature. Also, we find out that the use of polyelectrolytes with high charge density causes a further improvement in proton conductivity and methanol barrier properties simultaneously. These encouraging results indicate that upon a suitable choice of LbL deposition conditions, composite membranes exhibiting both high proton conductivity and improved methanol barrier properties can be tailored for fuel cells.

Poly(acrylic acid-co-methacrylamide), P(AA-co-MAAm), and poly(acrylic acid), PAA, gels were prepared and the use of these gels in the non-competitive removal of Pb2+, Cu2+, and Cd2+ ions from aqueous solutions was investigated at room temperature. Characterization of the polymers was performed by FTIR spectroscopy both before and after adsorption of metal ions on P(AA-co-MAAM) or PAA. The equilibrium swelling values (ESVs) of both polymers were determined by gravimetric method. During the adsorption of metal ions on both polymers, residual metal ion concentration in the solution (by atomic absorption spectrophotometer (AAS)) and the solution pH were measured. The kinetics of the adsorption process was determined from the experimental results. Pseudo-first and second-order plots and the correlation coefficients showed that the kinetics of non-competitive adsorption of Pb2+, Cu2+, and Cd2+ ions on P(AA-co-MAAM) or PAA is correlated best with pseudo-second-order process. While the removal order in the non-competitive adsorption of heavy metal ions on PAA was Pb2+ (2.60 mmol g−1) > Cu2+ (1.04 mmol g−1) > Cd2+ (0.88 mmol g−1), it was in the order of Pb2+ (1.85 mmol g−1) > Cd2+ (0.70 mmol g−1) > Cu2+ (0.64 mmol g−1) for P(AA-co-MAAM) copolymer. The introduction of MAAm into PAA decreased the metal ion removal capacity of copolymer for Pb2+ and Cu2+ ions considerably, but it did not significantly affect that for Cd2+ ion. Copyright © 2008 John Wiley & Sons, Ltd.

The paper is concerned with the deposition of self-assembled polyelectrolyte multilayer on Nafion membrane by layer-by-layer (LbL) technique with lowered methanol cross-over for direct methanol fuel cell (DMFC) applications. The formation of self-assembled multilayered film on Nafion was characterized by UV–vis spectroscopy and it was found that the polyelectrolyte layers growth on the Nafion surface regularly. Furthermore, the proton conductivity and methanol cross-over measurements were carried out for characterization of the LbL self-assembled composite membranes. The results showed that the concentration and pH of the polyelectrolytes significantly affect the proton conductivity and methanol barrier properties of the composite membranes. 10−1 monomol polyelectrolyte concentration and pH 1.8 was found to be optimum deposition conditions considering proton conductivity and methanol permeation properties of the LbL self-assembled composite membranes. The methanol permeability of the 10 bi-layers of PAH1.8/PSS1.8 deposited LbL self-assembly composite membrane was significantly suppressed and found to be 4.41 × 10−7 cm2/s while the proton conductivity value is in acceptable range for fuel cell applications.

A series of sulfonated homo- and random co-polyimides (co-SPI) based on 2,4-diaminobenzenesulfonic acid (2,4-DABS) and 2,5-diaminobenzenesulfonic acid (2,5-DABS) has been synthesized via conventional two-step polyimidization method. 2,4-DABS and 2,5-DABS were used as sulfonated diamine compounds, 4,4′-oxydianiline (ODA) and 4,4′-diaminodiphenyl sulfone (DDS) were used as non-sulfonated diamine compounds. Mixtures of sulfonated and non-sulfonated diamine compounds were reacted with benzophenonetetracarboxylic dianhydride (BTDA) to obtain co-SPI membranes. Molar ratios of sulfonated to non-sulfonated diamine were systematically varied to produce copolymers of controlled compositions. The co-SPIs were evaluated for thermal oxidative stability, ion exchange capacity (IEC), water uptake, proton conductivity, solubility, and hydrolytic stability. Proton conductivity and hydrolytic stability of the co-SPIs were compared with the fully aromatic polyimide, homo-SPIs (BTDA/2,4-DABS and BTDA/2,5-DABS). Regarding thermogravimetric analysis (TGA) analysis, it is concluded that desulfonation temperature in the range of 200–350°C suggests high stability of sulfonic acid groups. co-SPIs with 40 mol% of 2,4-DABS showed similar or higher proton conductivity than Nafion® 117 in water. Proton conductivity values of the co-SPIs were mainly a function of IEC and water uptake. Consequently, the optimum concentration of 2,4-DABS was found to be in the range of 30–40 mol% from the viewpoint of proton conductivity, IEC, and hydrolytic stability. Copyright © 2008 John Wiley & Sons, Ltd.

A series of random sulfonated copolyimides containing aliphatic linkages (co-SPIAs) with controlled degrees of sulfonic acid groups were synthesized via a conventional two-step polyimidization method. 2,4-Diaminobenzene sulfonic acid (2,4-DABS) and 1,6-diaminohexane (DAH) were used as sulfonated aromatic diamine and nonsulfonated aliphatic diamine compounds, respectively. Mixtures of diamine compounds were reacted with benzophenonetetracarboxylic dianhydride (BTDA) to obtain the co-SPIAs. The molar ratios of DAH/2,4-DABS were systematically varied to produce copolymers with controlled compositions that contained up to 70 mol % sulfonic acid moieties. The co-SPIAs were evaluated for thermal oxidative stability, ion-exchange capacity (IEC), water uptake, proton conductivity, solubility, and hydrolytic stability. The proton conductivity and hydrolytic stability of the co-SPIAs were compared with the fully aromatic polyimide, sulfonated homo-polyimide (homo-SPI) (BTDA/2,4-DABS). From thermogravimetric analysis, we observed desulfonation temperatures in the range 200–350°C, which suggested a high stability of the sulfonic acid groups. The co-SPIAs with 40–70 mol % 2,4-DABS showed higher proton conductivity than Nafion 117 in water. The proton conductivity values of the co-SPIAs were mainly a function of IEC and water uptake. Furthermore, the hydrolytic stability of the 2,4-DABS-based sulfonated polyimide membranes were improved by the introduction of the nonsulfonated diamine with aliphatic linkages. The optimum concentration of 2,4-DABS was found to be around 40 mol % from the viewpoint of proton conductivity, IEC, and hydrolytic stability. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Asphaltenes are a major concern in production operations, due to their role in conversion of vacuum residues by processes such as coking, catalytic cracking and hydroconversion. Six Turkish asphaltenes were characterized by elemental content, proton NMR, carbon NMR, GPC, DSC. Differential scanning calorimetry (DSC) provides parameters for comparing the glass transition temperatures, endothermic behavior of asphaltene and a hypothetical melting temperature of the asphaltenes which is within the range of the pyrolysis temperature of asphaltenes. The glass transition temperatures points (Tg) of asphaltenes were determined using DSC. Hypothetical melting point temperature (Tm) of the asphaltenes was also calculated. Among all the asphaltenes tested, Bati Raman showed much higher glass transition temperatures than the others. � 2007 Elsevier Ltd. All rights reserved.

The cement has to be ground fine enough and have the optimum particle size distribution (PSD) to meet the requirements such as strength properties and setting times in current standards. As it takes quite a long time to determine especially the late strength, grinding has to be based on the cement fineness and the PSD. In this study, the effects of fatty acids were investigated on the PSD of Portland cement. Experimental results showed that the fineness of the cement was decreased for that replaced with 0.025 wt.% lauric acid (LA), myristic acid (MA) and sunflower oil acid (SO), then increased for the other additions. The fineness measurements revealed that the cement grains aggregated for an amount of 0.025 % (w) during the grinding. Also, when the PSD of the ground cement is examined, the relationship between the saturated and the unsaturated components is evident that milling the cement clinker together with 0.1% (w) LA and 0.1 wt. % MA gave the finer cement from that with 0.1 wt.% SO.

Oksuzomer, Faruk/0000-0003-0827-8667; Koc, Serkan Naci/0000-0003-4472-4337 WOS: 000242522000015 LaAlO3 powders are prepared by sol-gel method. The effect of preparation conditions on morphological properties and crystal formations are investigated. iso-Propanol/tert-butanol and ethyl acetoacetate/ethylene glycol monomethylether are used solvents and complexing agents, respectively. Samples are dried with conventional and freeze-drying methods and calcined between 600 and 1000 degrees C. TGA, DTA, XRD, SEM and TEM methods are used for characterization. It is observed that freeze-dried sample prepared with tert-butanol has the lowest LaAlO3 formation temperature and uniform rhombohedral crystals. But conventionally dried sample, prepared with iso-propanol has smallest agglomerates at 1000 degrees C and does not show clear crystallization temperature in DTA analysis. The XRD peaks of LaAlO3 crystal are observed at 600 degrees C for all samples prepared by various sol-gel conditions. (C) 2006 Elsevier Ltd. All rights reserved.

Dimer acid-based polyamides were synthesized by condensation polymerization in the absence and presence of monofunctional reactants. Acetic acid, oleic acid and propyl amine were used as monofunctional reactants. The influences of the equivalent percentage (E%) and type of monofunctional reactant on the physical properties of dimer acid-based polyamides such as glass transition temperature (Tg), melting point (Tm), heat of fusion (ΔH), degree of polymerization (DP), number average molecular weight (Mn), and kinematic viscosity were investigated. The molecular weight and viscosity of dimer acid-based polyamides decreased with the increase in equivalent percentage of monofunctional reactant. Differential scanning calorimetry (DSC) studies showed that acetic acid and propyl amine had higher effect on the thermal properties of polyamides than that of oleic acid. In the case of polyamides prepared in the presence of acetic acid, the values of Tg, Tm, and ΔH of the polyamides increased remarkably with the increase in acetic acid content. On the contrary, propyl amine had a decreasing effect on the values of Tg, Tm, and ΔH of the polyamides. Incorporation of oleic acid into the polymer structure had no significant effect on the values of Tg and Tm of the dimer acid-based polyamides. Copyright © 2006 John Wiley & Sons, Ltd.

In cement industry, a great energy consumption has been observed during grinding of clinker. To reduce this consumption, some waste products have been used as grinding aids. In this investigation, the effects of sunflower oil (SO), oleic acid (OA), stearic acid (SA), myristic acid (MA) and lauric acid (LA) on the fineness and strength of the cement have been examined. These aids were added into clinker in certain ratios based on the cement clinker weight and the grinding has been done for a definite time at the same condition. All of the fatty acids used increased the fineness as compared with the cement without the grinding additives. SO and OA decreased the strength significantly, LA decreased it to a lesser extent and SA increased it definitely according to the common cement. But MA did not alter the strength of the cement as much as SA. In addition, the covering of the balls influences the grinding of cement clinker unfavourably.

{gamma}-Lithium aluminate was prepared by sol-gel method using lithium methoxide and aluminum-sec-butoxide precursors in i-propanol, n- and tert-butanol. Clear gels could be obtained due to the addition of ethylacetoacetate and the dried solids were calcined at 550 and 900 deg. C. The resulting solids were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), thermo-gravimetric analysis/differential thermal analysis (TGA/DTA). {gamma}-Lithium aluminate with the highest purity was obtained with t-butanol solvent and LiAl{sub 5}O{sub 8} was the second major phase.

Acrylic acid (AA) was grafted to cellulose by using ceric ammonium nitrate (CAN) initiator in aqueous nitric acid solution at 30, 50, 70, and 907C during reaction periods of 30 to 180 minutes. About 45% of the AA was polymerized at 907C after 180 minutes. The grafted polymer and homopolymer were isolated by acetone from the reaction mixture, dried, and subjected to Soxhlet extraction with dioxane to separate the homopolymer, poly(acrylic acid), from the graft copolymer. The water absorption capacities and grafting values of grafted cellulose were also determined. The maximum grafting yield was obtained at 307C. It was also observed that polyacrylic acid-grafted cellulose produced at 307C had the highest water retention capacity. The time depen- dence of AA conversion allowed calculation of first-order reaction rate constants. These rate constants were then used to determine apparent activation energies. q 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 929-934, 1997

Currently, the sulfur level in diesels is limited to 10 and 15 ppm in Europe and USA respectively, since the organosulfur compounds available in fuels emit corrosive SO2 gases into atmosphere during combustion, thus leading to acid rain. A lot of processes such as hydrodesulfurization (HDS), oxidative desulfurization (ODS) etc. have been used to reduce sulfur level in fuels and ODS, which is alternative to conventional HDS, is much more efficient in removing benzothiophene (BT), dibenzothiophene (DBT) and their alkyl derivatives as compared with HDS and more economical. One of very powerful oxidation systems used in ODS is H2O2-formic acid and removal of alkyl-substituted derivatives of T, BT and DBT with this oxidation system is easier than that with H2O2-phosphotungstic acid catalyst system due to the steric hindrance of alkyl groups adjacent to sulfur atom because phosphotungstic acid is a bulky catalyst. In this work, oxidative desulfurization reactions of the model compounds, thiophene (T), 2-methylthiophene (2-MT) and 2,5-dimethylthiophene (2,5-DMT), which have the lowest reactivity in ODS, on sonication at low H2O2 (O)/F (formic acid)/S (organosulfur solution) volume ratios were carried out sequentially in the presence of tetrabutylammonium bromide (TBAB) as phase transfer catalyst at 30 and 40 °C. First, the solution of the relevant model sulfur compound in n-heptane was put into a steel batch reactor and later, reactions were performed by adding mixture of 35% H2O2, formic acid and TBAB onto the organic phase. After each reaction cycle, the aqueous phase was removed by a separation funnel and the oxidative desulfurization reaction of the remaining treated organic phase was repeated three or four times with reuse of the same amounts of fresh hydrogen peroxide, formic acid and TBAB as in the first reactions at 30 and 40 °C for 15 min. After every reaction cycle, the sulfur compounds in heptane were analyzed by using GC with Sulfur Chemiluminescence Detector. Afterwards, the oxidative desulfurization reactions of the model sulfur compounds in heptane were performed for only one cycle in sonoreactor with total amount of oxidation reagents H2O2, formic acid and the same amount of TBAB used in the former multi-cycle reactions at 30 and 40 °C for 15 and 60 min. It was observed that the total conversions of model sulfur compounds obtained from multicycle reactions were higher than its conversions obtained from single-cycle reactions with total amount of oxidation reagents used in the multicycle reaction. The same method was also applied to diesel fuel sample and it was shown that high sulfur removal is reached.