Çetin Çakanyıldırım

The Production of NaBH4 from Its Elements by Mechano-chemical Reaction and Usage in Hydrogen Recycle

Abstract In this study, sodium borohydride (NaBH4) is synthesized from Na and MgH2 in the presence of B2O3 that behaves as a stickiness inhibitor and boron source. All experiments are performed under argon atmosphere via ball milling, without applying high temperature or pressure. An optimum synthesized parameter is searched with reaction time and stochiometric ratio. Mechano-chemical reactor working time is varied from 100 to 1,100 min, while stoichiometry of B2O3/Na ranges over 0.6–1.4, and MgH2 is used 30% in excess. FT-IR and XRD instruments are utilized to analyze the products. Additionally, hydrogen contents of the untreated products are measured with the inverse burette technique. Consequently, results show that long reaction times favor the yield. Moreover, equalizing the amounts of B2O3 and MgH2 can raise NaBH4 yield to 25% or more.

Conducting Composites and Blends of Polythiophene and Polyoxymethylene

Abstract Conductive polyoxymethylene/polythiophene (POM/PT) composites and PT/POM blends were prepared by in situ chemical polymerization using FeCl3 oxidant and mixing in solutions, respectively. It was found that the properties of the composites and blends were different from those of homopolymers and also from each other. Formation of polymer and composites was supported by FT-IR analyses. According to the results of thermal analyses (TGA), it was shown that polymers and composites have good thermal stability. The thermal degradation temperature of POM/PT composite containing 88% PT is higher than those of the other composites. The thermal degradation temperature of PT/POM blend containing 27% POM was described as higher than that of the other blends. The morphological structures of polymers and composites were studied by scanning electron microscopy (SEM). It was found that morphological structures of composites were smoother than that of PT. The crystal structures of polymers and composites were investigated by X-ray diffraction analysis. It was found that the crystal regions increased with increasing amount of POM in the composites and blends.

Oxidative desulfurization of Tufanbeyli coal by hydrogen peroxide solution

Abstract It is becoming popular to use fossil fuels efficiently since the necessary energy is mostly supplied from fossil fuels. Altough there are high lignite reservoirs, high sulfur content limits the efficient use of them. In this article, we aimed to convert combustible sulfur in coal to non-combustible sulfate form in the ash by oxidizing it with a hydrogen peroxide solution. The parameters affecting the sulfur conversion were determined to be: hydrogen peroxide concentration, reaction time, mean particle size at constant room temperature and shaking rate. The maximum desulfurization efficiency reached was 74% of the original combustible sulfur with 15% (w/w) hydrogen peroxide solution, 12 hours of reaction time, and 0.25 mm mean particle size.

The Processing of NaBH4 from Na2B4O7 by Mechano-chemical Synthesis and Its Catalytic Dehydrogenation

Abstract Sodium borohydride (NaBH4) is a specialty reducing agent used in fuel cell systems. Feasible NaBH4 production techniques are required to reduce the costs of NaBH4, making its usage attractive. At present, anhydrous borax (Na2B4O7) is a promising reactant in NaBH4 synthesis. However, further improvements to optimize the yield of the NaBH4 production process operating with MgH2 and Na2B4O7 in ball milling are necessary. In order to obtain optimum reaction conditions, experiments were performed under inert atmosphere. First, we attempted to compensate Na insufficiency with the addition of Na, NaH, and Na2CO3. Next, the reaction period and stoichiometric ratio of our experiments were studied with Na2B4O7 and MgH2. Reaction times were varied from 200 to 600 min, and regulated the excess MgH2 addition at 0, 10, 30, 50, and 70%. The synthesized products were characterized by FT-IR and XRD analysis and checked our results using iodimetry and dehydrogenation tests. We were able to achieve yield levels of approximately 84% of NaBH4 in certain purification processes with ethylene diamin after 400 min of reaction time and at excess MgH2 levels of 10% or more.

Decomposition of NaBH4 with self-regeneration of carbon supported CoCl2 catalyst

ABSTRACT In this study, economically favorable CoCl2 catalysts at four different amounts were supported on activated carbon (AC) for NaBH4 dehydrogenation. Supported catalyst could achieve hydrogen release for 2,060 cycles, which is equivalent to 103 days of uninterrupted operation. Slow and continuous hydrogen release was observed in all experiments. Even 1 g of NaBH4 can carry 1.2 L of hydrogen, and in hydrolysis process, it liberates 2.5 L of hydrogen that indicates the decomposition of water. EDX analysis and reverse burette measurements show that CoCl2 could be homogeneously distributed on and permanently joined to the support surface. Kinetic investigation of the dehydrogenation reaction fits zero order kinetics, and activation energy was calculated to be 48 kJ/mol.

Processing of Cer-Met Composite Material from Zn and B2O3

The properties of ceramic-metal (cermet) composites as tensile strength, hardness and resistance to corrosion are superior to individual ceramics and metals. Especially, high temperature mechanical property of a composite material and its stability are very important for specific usages. On the other hand, the use of a composite material is limited by inadequate mechanical properties at high temperatures, large thermal expansion and fast oxidation. Besides, thermal expansion obviously impairs thermal shock strength. In this study, a composite material with dimensional stability and high oxidation strength, which preserves main mechanical properties at high temperatures, was produced. Anhydrous boron oxide was chosen as reinforcement due to its light weight, high melting point, limited thermal expansion and fire retardant property. As a matrix, zinc was used owing to its low density, low melting point, low cost and high corrosion resistance. For this purpose, zinc and anhydrous boron oxide powders were mixed in an attritor at 600 rpm and sintered at temperatures determined from the TGA-DSC analyses. The obtained composites were characterized by mechanical, microstructural and thermal expansion tests.