Mathematical modeling and analysis of the flocculation process in chambers in series

In this study, the flocculation process in continuous systems with chambers in series was analyzed using the classical kinetic model of aggregation and break-up proposed by Argaman and Kaufman, which incorporates two main parameters: K (a) and K (b). Typical values for these parameters were used, i. e., K (a) = 3.68 x 10(-5)-1.83 x 10(-4) and K (b) = 1.83 x 10(-7)-2.30 x 10(-7) s(-1). The analysis consisted of performing simulations of system behavior under different operating conditions, including variations in the number of chambers used and the utilization of fixed or scaled velocity gradients in the units. The response variable analyzed in all simulations was the total retention time necessary to achieve a given flocculation efficiency, which was determined by means of conventional solution methods of nonlinear algebraic equations, corresponding to the material balances on the system. Values for the number of chambers ranging from 1 to 5, velocity gradients of 20-60 s(-1) and flocculation efficiencies of 50-90 % were adopted.

Electrochemical kinetic study of surface layer growth on natural pyrite in acid medium

This paper presents electrochemical experiments on natural pyrite that combine potentiostatic and voltammetric techniques. X-ray microanalysis is used as an auxiliary technique. The layer growth on pyrite surface is conducted in a wide range of pH and potential range: 3.4 <= pH <= 5.9 with E = 0.80 V (versus SHE), and 0.80 V <= E <= 1.00 V with pH 4.5 (versus SHE) in acetic acid-acetate buffer. This work is unique for two reasons: (1) phenomenological model about layer growth is applied and mathematical-physic consistence is verified and (2) Meyer's hypotheses of chemical mechanism are used to explain kinetic parameters of the phenomenological model. (c) 2005 Elsevier B.V. All rights reserved.

The kinetic of mullite crystallization: Effect of water content

The kinetic of mullite crystallization from sol–gel method, with different water content, was investigated under non-isothermal conditions using DTA. The sols were obtained from Al(NO3)3.9H2O (ANN) and Si(OC2H5)4 (TEOS) mixtures by varying the water–alcohol content of the system. The crystalline phase changes were verified by X-ray diffraction (XRD). For a sample prepared using ethanol-based alkoxide solution (M0), only Al-poor mullite (p-mullite) crystallizes at 1000 °C; for the one synthesized with low water concentration (M6) Al-rich mullite (r-mullite) and spinel crystallize together; and for a sample prepared using a water-based alkoxide solution only spinel is formed. Thus, the variation of water contents during the synthesis caused great variations in the course of mullitization process. The average value of the apparent activation energy determined for p-mullite, r-mullite and spinel phase crystallization were found to be E = (899 ± 61) kJ mol−1, E = (1015 ± 272) kJ mol−1 and E = (980 ± 196) kJ mol−1, respectively. These results showed that sample M(0) was a monophasic gel, where aluminum and silicon atoms are mixed at a molecular level while sample M(100) was a diphasic gel, where silicon and aluminum atoms are distributed in a nanometric level. The fast reaction between TEOS and water molecules is responsible for this great difference in the sample's homogeneity. The kinetic model of the crystallization process was determined using Malek's procedure. It was established that the crystallization of p-mullite, r-mullite and spinel phase can be described by Šesták–Berggren autocatalytic model.

Avaliação da remoção de sulfametoxazol, diclofenaco e 17β-estradiol em água por meio de processo oxidativo com cloro

Pós-graduação em Engenharia Civil - FEIS

Jogo digital e analogias: uma proposta para o ensino de Cinética Química

Pós-graduação em Educação para a Ciência - FC

Emprego de carvão ativado e resinas de troca ionica na remoção de substâncias orgânicas contaminantes do alcool etílico

This work had with objective to characterize and evaluate the performance of the combined system, involving activated charcoal and ionic exchange resins in the removal of substances organic contaminating of the ethyl alcohol from the fermentation of the cassava starch. To testing was used ethyl alcohol PA 96 oGL, conductivity of 0.90 μS/cm at 25 oC, acidity of 60 mg/L and Barbet test of 43 minutes at 15 oC. The contaminated alcohol was composed of ethyl alcohol additive of higher alcohols, organic acids, ester, diol, aldehydes, ketone and ether. Contaminated alcohol was added 2% activated charcoal and after the adsorption isotherm in ionic exchange resins was tested. The adsorption with activated charcoal was performed in a Water Bath at 30 oC for one hour and a half and shaking. Already adsorption ionic exchange columns occurred at room temperature on columns of 93,4 cm in filling height and diameter of 2.29 cm, for flows of 180 mL/min and 90 mL/min. Samples were collected in the tests with charcoal and with each one of the resins and the following analyses were performed: conductivity, acidity and Barbet test. The medium values for conductivity, acidity and Barbet test after the adsorption in charcoal and cation and anion resins were respectively: conductivity was 240; 354 and 465 μS/cm to 25 oC; acidity of 1.081; 1.103 and 1.062 mg/L and the Barbet test was 21; 20 and 9 minutes to 15 oC. It was observed that the addition of 2% of activated charcoal and the permanence in the columns of adsorption was not sufficient to remove the organic substances contaminating of the ethyl alcohol.

O tratamento probabilístico da teoria cinética de colisões em livros de química brasileiros para o ensino médio

This paper presents and discusses an analysis of the approaches and the didactic treatment of the kinetic model of collision between particles in chemical reaction (collision theory model) presented by brazilian chemistry textbooks for the medium level. Our starting point at this search was the correct and scientific model for this theory which is based on random events, but most of all the books investigated does not consider this fact like an important and very precious didactic aspect. We utilized in the investigation the writing discoursive analysis technique.

Influência da geometria e da temperatura na cinética de secagem de tomate (Lycopersicum esculentum)

O tomate é um fruto muito perecível por causa do seu conteúdo de umidade. A secagem é uma das práticas industriais mais utilizadas em alimentos para manter a qualidade do produto final. A pesquisa foi desenvolvida para estudo dos parâmetros de secagem de tomate (Lycopersicon esculentum Mill), cv Carmen, com relação ao tipo de corte (meio e um quarto) e à temperatura de processo (60 e 70 ºC), bem como à escolha do tempo de secagem para a obtenção de um produto com umidade de 45% (base úmida). As cinéticas de secagem foram determinadas experimentalmente por convecção forçada e ajustadas ao modelo de Page. Os resultados obtidos mostraram que a geometria de corte influenciou na taxa de secagem e no tempo de desidratação. Os tomates cortados em quatro partes e desidratados a 70 ºC alcançaram umidade de 45% em menor tempo (10 horas), quando comparados aos tomates com o corte em metades. O modelo de Page forneceu bom ajuste nas cinéticas de secagem

Thermal stability of the martensitic transformation of Cu-Al-Ni-Mn-Ti

The development of new shape memory alloys with high martensitic transformation temperature increases the potential for applications. The development and use of these new alloys depends on the stability of the structure during cycling at high temperatures. If it is possible to guarantee that on alloys keeps the structure during cycling, then the alloy can be used because of the shape memory properties. The aim of this work is to obtain a kinetic model of the forward and backward martensitic transformation of two Cu-Al-Ni-Mn-Ti alloys. Differential scanning calorimetry has been performed in order to establish the kinetic stability of the martensite and the beta transformation. (c) 2006 Elsevier B.V. All rights reserved.

MECHANISM OF ACTION OF COBALT IONS ON RAT OSSEOUS PLATE ALKALINE-PHOSPHATASE

Polidocanol-solubilized osseous plate alkaline phosphatase was modulated by cobalt ions in a similar way as by magnesium ions. For concentrations up to 1 mu M, the Chelex-treated enzyme was stimulated by cobalt ions, showing K-d = 6.0 mu M, V = 977.5 U/mg, and site-site interactions (n = 2.5). Cobalt-enzyme was highly unstable at 37 degrees C, following a biphasic inactivation process with inactivation constants of about 0.0625 and 0.0015 min(-1). Cobalt ions stimulated the enzyme synergistically in the presence of magnesium ions (K-d = 5.0 mu M; V = 883.0 U/mg) or in the presence of zinc ions (K-d = 75.0 mu M; V = 1102 U/mg). A steady-state kinetic model for the modulation of enzyme activity by cobalt ions is proposed.

Enzymatic Logic Gates with Noise-Reducing Sigmoid Response

Biochemical computing is an emerging field of unconventional computing that attempts to process information with biomolecules and biological objects using digital logic. In this work we survey filtering in general, in biochemical computing, and summarize the experimental realization of an and logic gate with sigmoid response in one of the inputs. The logic gate is realized with electrode-immobilized glucose-6-phosphate dehydrogenase enzyme that catalyzes a reaction corresponding to the Boolean and functions. A kinetic model is also developed and used to evaluate the extent to which the performance of the experimentally realized logic gate is close to optimal.

Caracterização da fertilidade do solo da composição mineral de espécies arbóreas de restinga do litoral paulista

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Mineralização do soro ácido de leite em função do pH do solo

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Determinação de parâmetros cinéticos para decomposição térmica de resinas utilizadas em revestimentos

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Síntese, caracterização, estudo termoanalítico e cinético do 2-metoxibenzalpiruvato de 'MN', 'FE', 'CO', 'NI', 'CU', e 'ZN', no estado sólido

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)