Results 1 - 10 of 90
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[en] A chemical-mathematic model and experimental method based on the acid base balances is developed for the analysis of metallic ions, isolated or in mixtures. The theoretical titling curves, including chelones-forming agents and metallo-chromic indicator were worked on a personal computer. This chelometric method was applied to the quantitative determination of copper, zinc and lead ions in alloys
[en] This study describes the validation of a multi-residue method for the determination of most used organo chlorine, organophosphorus and organonitrogen pesticides in cabbage in the Cundinamarca Department (Colombia). The extraction process includes blending of small sample quantity with ethyl acetate in presence of Na2SO4 and NaHCO3, filtration and concentration. The clean up steps include GPC and mini-column chromatography using silica gel. Final determination was carried out by gas chromatography with: pulsed splitless injection, HP-5 capillary column, and a parallel detection system with micro electron capture detection (μ - ECD) and Nitrogen-Phosphorus Detection (NPD). The methodology is specific, selective, accurate and robust. Recovery values of majority of pesticides were in the range 70-120% at spiking levels ranging 0.05-10.73 mg/kg. Limits of detection were less than 0.10 mg/kg for most of the studied compounds. The distribution of the analyses in the laboratory sample was evaluated and it was found its homogeneity. The evaluation of pesticide residues was made in a specific area of municipality of Madrid-Cundinamarca, (Colombia). No residues of the studied analyses were founded
[en] Different methods for micropore volume calculation in carbonaceous material s were studied. it was investigated a method which approximates the micropore volume calculated from high pressure methane adsorption isotherms by means of low pressure adsorption isotherms (N2 and CO2). the best fit was achieved for the Dubinin-Astakhov equation for carbon dioxide isotherms, CO2 at 273 K
[en] A new method for the interpretation of complex mechanisms is proposed. This method is used in the simulation of the Gyorgyi-Field (GF) mechanism of the Belousov-Zhabotinski (BZ) reaction. The method is based on the mass action law and on the independence and coexistence of the elemental step principles. It reproduces the oscillatory behavior of the intermediaries of reaction
[en] The changes of the surface acid groups of an activated commercial carbon after placing it under oxidation treatment with nitric acid are studied. The time used was in the range 1.5 and 9 hours, the concentrations range was from 4 to 7 molL-1. The study included the determination of immersion enthalpy. Boehm's type titrations, FTIR, and pH at the point of zero charge, pHpzc. It was found that total acid groups are in a range from 0.207 mmolg-1 to 1.247 mmolg-1, and that they are proportional to the immersion enthalpy in NaOH that are between 40 and 54Jg-1. The pHpzc decreases with the oxidation treatment and have values between 8.3 and 4.3
[en] A high volatile bituminous coal from the Department of Cundinamarca (Colombia), was liquefied in the presence of a polymetallic catalyst in a 500 mL batch reactor at 370, 410 and 450 celsius degrade under hydrogen atmosphere, using tetralin as hydrogen donor solvent and residence time of 1 h. When the catalyst was used and the temperature increased, the coal conversion and the oil yield increased too. The maximum oil yield obtained was 67% at 450 celsius degrade.
[en] The chemical speciation in soils that had been treated with sewage sludge was determined to find out what had occurred to the heavy metals present. This was done nine weeks after sludge application. An incubation assay was realized using 2.5 % w/w sludge level; this is equivalent to 81.5 ton of sludge per hectare. Pots filled with sludge-soil mixture were placed in a greenhouse at temperature between 17 and 25 Celsius degrade, humidity at field capacity distributed in accordance with a random experimental design with four replicates and seven treatments. It was found that the concentration of Cd, Cu, Mn, Pb, and Zn was lower than the limits established by the environmental protection agency (EPA) for soil usage. Also, the organic carbon content, the available nitrogen and phosphorus were in the normal concentration range reported for organic fertilizers. The sludge addition to the soil gave significant increase of the fraction of Cd bounded to organic material as compared with the exchangeable fraction and the fraction bounded to iron-manganese oxides. Cooper showed more affinity for the fraction of iron-manganese oxides. Lead gave a fraction bounded to organic material that was absent in the witness samples. Zinc had a bigger proportion in the fraction associated with iron manganese oxides. Manganese as compared with the other metals showed the biggest unchangeable fraction
[en] NiO and CuO based oxygen carriers (OCs) supported on Al2O3 prepared by impregnation were selected for its evaluation in a continuous pilot plant of 500 Wth of two interconnected fluidized beds, where both methane and syngas were used as fuel gas. In addition, the effect of possible impurities in the fuel gas such as sulphur compounds and other hydrocarbons in the combustion efficiency of the process and the behaviour of the OCs were studied. Based on these results, it can be concluded that both OCs are suitable for a chemical looping combustion (CLC) process with methane, syngas and methane with impurities such as light hydrocarbons or sulphur.
[en] We report the preparation of an activated carbon obtained by impregnation of mineral carbon samples with phosphoric acid solution (50%). the obtained material, exhibits a superficial area of 586 m2.g-1 and a total pore volume of 0,37 cm3g-1. with respect to the chemical properties, the activated carbon shows an increased number of acidic sites (0,92 meq g-1) compared to basic sites (0,63 meq g-1) which yields a material with almost neutral characteristics (pHpzc: 7,4). At a pH: 4.0 the amount of pb2+ absorbed and the immersion enthalpy values for the activated carbon reached maxim with values of 15.7 mg-1 y 27,6 Jg-1 respectively. it was established that similar behavior occurs for the two properties, absorption and immersion enthalpy, as a function of pH. in addition, a second order function that relates the adsorption constant and immersion enthalpy, and the adsorption constant and ph of the solution are presented
[en] In a commercial activated carbon the total amounts of basic and acidic sites were determined. The values are 0.45 and 0.55 meqg-1. The immersion enthalpies in 0.1 NaOH and in 0.1 N HCl were -15.26 Jg-1 and -36.63 Jg-1 respectively and he zero charge point, PCZ, at 8.9 pH. These results show the character basic of the solid. The adsorption isotherm at 298 K of the activated carbon in Pb+2 solutions was determined. The adsorption capacity is around 40 mg g-1 for the maximum adsorption. Immersion enthalpies of activated carbon in aqueous solutions of Pb+2 in concentrations in the range from 10 to 120 mg L-1 were measured. The values obtained are in the range from 5.12 to 48.7 Jg-1. The activated carbon surface was studied using scanning electronic microscopy before and after the adsorption of Pb+2 which allows to observe the position of the metal on the solid