Timur Dogu

Effect of pH, flow rate and concentration on the sorption of Pb and Cd on montmorillonite : I. Experimental

Continuous column adsorption of lead (Pb) and cadmium (Cd) was studied using pH adjustment and calcium-saturated montmorillonite in a short stainless steel column. Changing either pH or flow rate, while keeping inlet concentration of the ions constant, led to considerable changes in effluent concentrations and breakthrough curves (BTCs). At low pH values (2–4), H+ ions competed strongly with lead and cadmium ions; at intermediate pH (4–6), ionic size played the major role in adsorption and ion exchange and at high pH (6–9) precipitation was the major process taking place especially for lead sorption. At low flow rates less than 0.5 cm3 min−1, sorption of both lead and cadmium increased due to the long retention time in the column. When both lead and cadmium ions were present in the feed, adsorption remained the same while that of cadmium decreased compared with single ion experiments. © 1999 Society of Chemical Industry

Etherification rates of 2‐methyl‐2‐butene and 2‐methyl‐1‐butene with ethanol for environmentally clean gasoline production

Etherification of C5 reactive olefins available in light fluidized catalytic cracking (FCC) gasoline is an attractive way to decrease the olefins and to increase the octane number. The reactivities of 2-methyl-1-butene (2M1B) and 2-methyl-2-butene (2M2B) in the etherification reaction with ethanol catalysed by a strongly acidic macroreticular resin catalyst were investigated in a temperature range of 333–360 K using a liquid phase differential flow reactor. In the presence of excess alcohol, the apparent reaction orders of etherification reactions of isoamylenes were found to be 0.93 and 0.69 with respect to 2M1B and 2M2B concentrations, respectively. 2M1B was shown to be more reactive than 2M2B and its activation energy is also lower in the etherification reaction. It was also shown that diffusion resistances, especially in the macropores of the catalyst, may play an important role on the observed rates. © 1999 Society of Chemical Industry

Mechanism of CVD of boron by hydrogen reduction of BCl3 in a dual impinging-jet reactor

Abstract Kinetics of boron deposition by hydrogen reduction of BCl 3 was investigated in a dual impinging-jet CVD reactor. Measurement of the effluent stream composition by an FT-IR allowed detailed analysis of the reaction kinetics. Formation of the intermediate BHCl 2 was found to take place both in the gas phase and also through a surface reaction involving three sites in the rate-determining step. Rate data obtained in a temperature range of 750–1350°C indicated a change of reaction mechanism at around 900°C. At higher temperatures decomposition of adsorbed BCl 3 to boron without the involvement of hydrogen should be considered. Decomposition or further reduction of the intermediate BHCl 2 may also be significant at high temperatures.

Conversion of Biodiesel By-Product Glycerol to Fuel Ethers over Different Solid Acid Catalysts

In this study, the etherification reaction of glycerol (G) with tert-butyl alcohol (TBA) was investigated for the production of high quality transportation fuel additives. The reaction was carried out in liquid phase, in a continuous flow reactor in the presence of various solid acid catalysts. Activities of acidic resin catalysts, such as Amberlyst-15 (A-15), Amberlyst-16 (A-16) and Amberlyst-35 (A-35), Nafion-SAC-13 and ?-alumina were compared. Significant increase in conversion was observed with an increase in temperature. Amberlyst 15 showed the highest activity at about 110°C, giving glycerol conversion values of about 0.5 at a space time of 18 g cm-3 s. However, A-16 gave higher di-ether selectivity values. Nafion-SAC-13 showed activity at higher temperatures, while the activity of ?-alumina was very low, even at 400°C.

Breakthrough Analysis OF H 2 S removal on CU-V-MO, CU-V, and CU-MO mixed oxides

Kinetic studies carried out for the sorption of H 2 S in the presence and absence of hydrogen on Cu-V-Mo, Cu-V, and Cu-Mo mixed oxides gave detailed information about the reaction sequences. Formation of SO 2 even in the presence of hydrogen at the initial stages of the sorption process showed the partial reduction of the metal oxides prior to the sulfidation step. A sorption experiment carried out with Cu-Mo mixed oxide gave incomplete sulfidation of molybdenum, whereas with Cu-V mixed oxide complete sulfidation was obtained. Predictions of the breakthrough curves by the deactivation model showed good agreement with the experimental results.

Analysis of diffusion and sorption of chlorinated hydrocarbons in soil by single-pellet moment technique.

The single-pellet moment technique was shown to be a powerful method for inuestigating the diffusion and adsorption of volatile hydrocarbons in the soil. The technique was used to evaluate effective diffusivities, adsorption equilibrium, and rate constants of chlorinated hydrocarbons (monochloroethane, 1,2-dichloroethane, 1,1,1trichloroethane, and 1,1,2-trichloroethane). Results obtained in a dry system showed that adsorption rate constants of all these hydrocarbons on the soil pellet used are of the same order of magnitude (4.4-8.0 cm 3 g -1 s -1 )

Diffusion Resistances and Contribution of Surface Diffusion in TAME and TAEE Production Using Amberlyst-15

Effective diffusivities and adsorption equilibrium constants of methanol, ethanol and 2-methyl-2-butene (2M2B), in Amberlyst 15, were evaluated from batch adsorption experiments. Moment expressions derived for different models involving diffusion resistances in the macropores and within the gel-like micrograins were used for the evaluation of effective diffusion coefficients. Contribution of surface diffusion to diffusion flux within the macropores was found to be quite significant. Also, it was found that diffusion resistance in liquid filled macropores was much more significant than diffusion resistance within the gel-like micrograins of Amberlyst 15., for methanol, ethanol and 2M2B.

Kinetics of trona sulfur dioxide reaction

Abstract One of the most efficient methods of desulfurization of flue gases involves the reaction of SO 2 with activated soda in a dry system. In this work, reactivities of activated soda produced from trona by direct calcination and by spray drying of trona solution were compared and a reaction mechanism was proposed. Due to the textural variations of the solid during the reaction and due to the increased significance of adsorption of SO 2 , at low temperatures, a two step reaction behavior was observed. Predictions from the deactivation model gave satisfactory agreement with the experimental data.

CVD of boron and dichloroborane formation in a hot-wire fiber growth reactor

Abstract Chemical vapor deposition (CVD) of boron by hydrogen reduction of BCl3 on a hot tungsten substrate was investigated in a parallel flow reactor. Effect of substrate temperature (1100–1250°C) on the relative rates of formation of BHCl2 and boron was observed by the on-line analysis of the reactor effluent stream composition using an FT-IR spectrophotometer. It was concluded that BHCl2 was majorly formed in the gas phase within the thermal boundary layer adjacent to the substrate with possible contribution of surface reactions at higher temperatures. Comparison of results obtained in the impinging jet and parallel flow reactors indicated the significance of diffusion resistance in the parallel flow system. Tubular flow reactor experiments indicated that BHCl2 formation reaction started at temperatures as low as 350°C and reached equilibrium in less than a second at temperatures over 420°C.

PERFORMANCE OF ACIDIC MCM-LIKE ALUMINOSILICATE CATALYSTS IN PYROLYSIS OF POLYPROPYLENE

Mesoporous aluminosilicate catalysts having different Al/Si ratios were synthesized following a hydrothermal synthesis route and using different aluminum sources, such as aluminum nitrate and aluminum isopropoxide. These mesoporous materials have high surface areas, in the range of 520–1001 m2/g, and exhibit Type IV nitrogen adsorption isotherms. EDS and 27Al MAS NMR results showed that aluminum was incorporated more effectively into the structure of the catalyst forming a tetrahedral framework when aluminum nitrate was used as the aluminum source. The activities of these catalysts in the polypropylene pyrolysis reaction were tested in a TGA apparatus. Results showed a marked reduction in the degradation temperature in the presence of aluminosilicate catalysts. The activation energy of degradation was 172 kJ/mole without any catalyst. However, using the mesoporous aluminosilicate catalysts synthesized by using aluminum nitrate as the aluminum source, activation energy of the degradation reaction decreased to values of about 24–28 kJ/mole.