Estudo dos fenômenos de transporte em cromatografia através da aplicação de modelos de rede e estocásticos

O estudo dos diferentes fenômenos de separação tem sido cada vez mais importante para os diferentes ramos da indústria e ciência. Devido à grande capacidade computacional atual, é possível modelar e analisar os fenômenos cromatográficos a nível microscópico. Os modelos de rede vêm sendo cada vez mais utilizados, para representar processos de separação por cromatografia, pois através destes pode-se representar os aspectos topológicos e morfológicos dos diferentes materiais adsorventes disponíveis no mercado. Neste trabalho visamos o desenvolvimento de um modelo de rede tridimensional para representação de uma coluna cromatográfica, a nível microscópico, onde serão modelados os fenômenos de adsorção, dessorção e dispersão axial através de um método estocástico. Também foram utilizadas diferentes abordagens com relação ao impedimento estérico Os resultados obtidos foram comparados a resultados experimentais. Depois é utilizado um modelo de rede bidimensional para representar um sistema de adsorção do tipo batelada, mantendo-se a modelagem dos fenômenos de adsorção e dessorção, e comparados a sistemas reais posteriormente. Em ambos os sistemas modelados foram analisada as constantes de equilíbrio, parâmetro fundamental nos sistemas de adsorção, e por fim foram obtidas e analisadas isotermas de adsorção. Foi possível concluir que, para os modelos de rede, os fenômenos de adsorção e dessorção bastam para obter perfis de saída similares aos vistos experimentalmente, e que o fenômeno da dispersão axial influência menos que os fenômenos cinéticos em questão

Recuperação do íon amônio gerado durante a evaporação de lixiviados de aterros utilizando resinas poliméricas de troca iônica

O lixiviado gerado em aterro sanitário possui substâncias de difícil degradação e amônia, que dificulta o tratamento biológico. O tratamento do lixiviado gerado em aterros sanitários requer uma série de processos de elevado custo e, outras técnicas de tratamento têm sido investigadas no intuito de reduzir custos e aumentar a eficiência do tratamento. A evaporação do lixiviado é uma técnica que aproveita o gás de aterro como fonte de calor, e é utilizada na redução do volume a tratar; porém as emissões atmosféricas geradas durante essa evaporação indicam a presença de amônia, o que pode causar impactos negativos em torno do aterro. Desta forma, é importante a realização de estudos que aprimorem esta técnica, para que a evaporação torne-se ambientalmente e economicamente viável. A amônia presente em amostras com pH em torno de 8,0 e temperatura em torno de 25C, está na forma de íon amônio, o que favorece ao processo de troca iônica. A troca iônica é um processo que tem sido estudado por muitos pesquisadores e consiste na troca de um ou mais constituintes de uma fase fluida para a superfície de uma fase sólida (resinas poliméricas). Este trabalho apresenta a eficiência de quatro tipos diferentes de resinas poliméricas: Amberlyst 15 Wet, Lewatit VPOC 1800, Dowex Mac-3 e Purolite MN250 na remoção e posterior, recuperação do íon amônio presente nos vapores condensados da evaporação de lixiviados. A princípio foi investigado a quantidade e o momento em que o amônio é lançado durante o processo de evaporação. Em seguida, caracterizaram-se as resinas quanto à eficiência de remoção, o tempo de contato e a quantidade ideal da resina. Estão apresentadas neste estudo as isotermas de adsorção de Langmuir, Freundlich e Temkin em diferentes temperaturas (298-318 K) e as condições ideais do processo. Os resultados apontaram duas resinas com eficiência de remoção, em torno de 40%, para concentrações acima de 1000 mg dm-3 de amônio, utilizando 0,5 g de resina e um tempo de contato de 20 minutos. Diferentes modelos cinéticos foram aplicados: Pseudo-Primeira Ordem, Pseudo-Segunda Ordem, difusão intrapartícula, Elovich e o modelo cinético de difusão externa e os resultados discutidos. Foi possível tratar Através da condensação dos vapores emitidos durante a evaporação do lixiviado, foi possível tratar foi possível obter uma recuperação em torno de 70% do íon amônio contido no vapor condensado proveniente da evaporação do lixiviado.

Preparo de óxidos de manganês em presença de biomassa e avaliação catalítica em reações de oxidação de hidrocarbonetos e remoção catalítica de SOx

Os riscos de poluição ao meio ambiente envolvendo petróleo envolvem, não só o seu transporte, como também seu refino. O prejuízo causado por um derramamento de petróleo vai além de danos à fauna e flora, pois envolvem também questões sociais. A emissão de óxidos de enxofre, denominadas SOx, durante o refino de petróleo através do craqueamento catalítico em leito fluidizado (FCC) também é uma das preocupações ambientais, já que esses óxidos estão relacionados com o a formação de chuva ácida e problemas respiratórios. Os hidrocarbonetos provenientes de um derramamento podem ser degradados em produtos menos agressivos ao meio ambiente, por oxidação química, por exemplo. Já as emissões de enxofre na unidade de FCC podem ser minimizadas por diversos processos, como por exemplo, o uso de aditivos nas unidades de FCC. Nesse trabalho óxidos de manganês dos tipos OMS-1 e OMS-2 foram sintetizados em presença e ausência de biomassa e óxidos OMS-2 foram dopados com os metais cobre, vanádio e ferro. Possíveis alterações em suas propriedades, suas atividades catalíticas em oxidação de hidrocarbonetos e em testes de captura de enxofre em condições de temperatura similares à unidade de FCC foram investigadas. Constatou-se uma diminuição na área superficial, tamanho e volume de poros nos óxidos sintetizados em presença de biomassa, através de uma análise de adsorção e dessorção de N2 (ASAP), porém seus difratogramas em uma análise de difração de raio X de pó (DRX) revelaram a obtenção de estruturas do criptomelano em todos os OMS-2. Os óxidos OMS-2 testados na oxidação do cicloexano, não sofreram modificações em sua estrutura após seu uso como catalisador, mas a presença da biomassa na síntese não aumentou sua atividade catalítica. Nos testes DeSOx, o óxido dopado com ferro apresentou o melhor desempenho e testes em ciclos mostraram ser possível sua reutilização

应用负载型纳米铁去除饮用水中砷的研究

砷是毒性最强的元素之一，水体中砷的污染己经引起人们广泛的关注。我国的新疆、内蒙、山西和台湾等省和地区地下水砷含量严重超标。全球共有5,000多万人遭受高砷饮用水的威胁，其中中国有1,500多万，是饮用水砷污染最严重的国家之一。WHO推荐饮用水砷的最高允许浓度从原来的50 µg•L-1已降至10 µg•L-1。更为严格的砷卫生标准的颁布，对作为饮用水源的地下水中的砷去除工艺提出了更高的要求。吸附法除砷比膜法、混凝法和离子交换法更安全、简便，是砷去除工艺中最有效的方法之一。 首先，本研究通过优化制备条件（包括炭种类的选择、炭的粒径大小、还原剂的浓度及滴定速率、反应温度、铁盐的种类及浓度、分散剂的比例及浓度），制备了负载型纳米铁。考虑到砷的去除效率、工程应用的可行性以及经济性，最优的制备条件如下：选用粒径为20~40目煤质炭，在室温、一定的分散剂比例及浓度，0.2 M KBH4滴速为20 d•min-1时所制备的Fe/炭为82.0 mg•g-1；纳米铁在活性炭孔内呈针状，其直径为30~500 nm，长度为1,000~2,000 nm。绝大多数的铁都负载到活性炭内部，这在处理水时铁不流失很重要。 其次，利用制备的负载型纳米铁作吸附载体，进行了饮用水中As(Ⅴ)的吸附去除实验。研究了该吸附剂对As(Ⅴ)的吸附等温线、动力学以及影响动力学的各种因素（包括As(Ⅴ)的不同初始浓度、吸附剂用量、pH值、共存离子和不同温度）、pH值、共存离子等环境条件对As(Ⅴ)去除的影响；以及吸附剂的再生及再生后的吸附效率等。研究发现在前12 h内吸附较快，72 h时达到了平衡。用Langmuir 吸附等温式估算出As(Ⅴ)的吸附量为12.0 mg•g-1。该吸附剂在pH 6.5， (25±2)℃， As(Ⅴ)初始浓度为2 mg•L-1，吸附剂用量为1.0 g•L-1时，As(Ⅴ)的去除率为75.2%；当把吸附剂的用量增加到1.5 g•L-1时，As(Ⅴ)的去除率可达99.9%以上。吸附剂可以用0.1M的NaOH浸泡12 h后即可再生，再生效率较高。常见的阴离子中PO43-、SiO32-对As(Ⅲ)的去除抑制较大，而SO42-、CO32-、C2O42-等离子对砷的去除影响较小。Fe2+对As(Ⅲ)的吸附抑制作用较大而其它阳离子影响不大。吸附剂可用0.1 M NaOH 有效再生，并且具有良好的机械性能。实验室初步实验数据表明，该吸附剂对饮用水除砷具有较好的应用前景。 第三，利用实验室制备的负载型纳米铁对饮用水中As(Ⅲ)的吸附去除也进行了研究。考察了吸附等温线、动力学以及影响动力学的各种因素、pH值、共存离子等环境条件对As(Ⅲ)去除的影响；以及吸附剂的再生及再生后的吸附效率等。研究发现，该吸附剂在pH 6.5， (25±2)℃， As(Ⅲ)初始浓度为2 mg•L-1，吸附剂用量为1.0 g•L-1时， 对As(Ⅲ)的去除率为99.8%；其吸附容量为1.996mg•g-1。吸附过程中部分As(Ⅲ)被氧化。与As(Ⅴ)的吸附相比，该吸附剂对As(Ⅲ)的效率比较高-而常见的其它除砷吸附剂如载铁纤维棉等，对As(Ⅴ)的效率比As(Ⅲ)高，为有效去除As(Ⅲ)，常常需要专门加上氧化这一过程。 最后，利用负载型纳米铁对饮用水中As(Ⅲ) 的氧化性能进行考察，发现该吸附剂不但能够有效吸附去除饮用水中的砷，而且还能把As(Ⅲ)有效地氧化为As(Ⅴ)。经过对吸附剂的构成组分分析发现，活性炭表面因富含多种官能团而对三价砷的氧化作用最大；其次是纳米铁也能把As(Ⅲ)氧化为As(Ⅴ)。

Interfacial activity of sec-nonylphenoxy acetic acid and kinetics of yttrium extraction

The interfacial behavior of sec-nonylphenoxy acetic acid (CA-100) at various diluents/(H, Na)Cl interfaces was examined using the Du Nouy ring method. Different adsorption isotherms such as the Gibbs and Szyszkowski were in good agreement with the experimental data. The values of interfacial excess at saturated interface increase in the following order: n-heptane > kerosene > cyclohexane > CCl4 > toluene > benzene > chloroform. The effects of temperature, acidity, and ionic strength of the aqueous phase on the interfacial activity of CA- 100 were also examined. The interfacial-activity data were used to discuss the mechanism and kinetics of yttrium (Y) extraction.

A Study of the Heterogenization of Heteropoly Acid (II)

The surface chemical species of surface-modified activated carbons and adsorption of 12-silicotungstic acid (SiW12) on them were studied It was found that these carbons have different adsorption isotherms and adsorptive force. The carbonyl groups on the s

EFFECT OF PH ON THE ELECTRON-TRANSFER OF CYTOCHROME-C ON A GOLD ELECTRODE MODIFIED WITH BIS(4-PYRIDYL)DISULPHIDE

The adsorption of bis(4-pyridyl)disulphide (PySSPy) and 4.4'-bipyridyl (PyPy) on a gold electrode was studied using cyclic voltammetry. The adsorption isotherms and equilibrium constants (1 X 10(6) mol-1 l for PyPy and 6 x 10(6) Mol-1 l for PySSPy) were determined. The effect of pH on the electrochemical behaviour of cytochrome c was studied on the PySSPy-modified gold electrode. The results show that cytochrome c can only transfer electrons on a deprotonated electrode surface. When the pH is decreased, the standard heterogeneous rate constant of cytochrome c on the modified gold electrode decreases and the electrochemical behaviour changes from a quasi-reversible to an irreversible process.

Investigation on the corrosion inhibitive effect of 2H-pyrazole-triazole derivatives in acidic solution

Four research methods, such as weight loss test, electrochemical techniques, adsorption isotherm, and quantum chemical calculation, were employed in this paper to study the inhibition efficiency (IE) and inhibition mechanism of three 2H-pyrazole-triazole derivatives, BHOT, FHOT, and CHOT in 1 M HCl solution for mild steel. Using the electrochemical technique, three inhibitors were proved to show a mixed-type character for mild steel by suppressing both anodic and cathodic reactions on the steel surface. The adsorption models of three compounds were established at different temperatures according to their adsorption isotherms. The results of the quantum chemical calculation method indicated that the adsorption sites of 2H-pyrazole-triazole derivatives were strongly centralized on benzene ring, triazole ring, or other substituents. All the results showed that the three derivatives were excellent inhibitors in I M HCl solution for mild steel.

Uniformly carbon-covered alumina and its surface characteristics

Uniformly carbon-covered alumina (CCA) was prepared via the carbonization of sucrose highly dispersed on the alumina surface. The CCA samples were characterized by XRD, XPS, DTA-TG, UV Raman, nitrogen adsorption experiments at 77 K, and rhodamine B (RB) adsorption in aqueous media. UV Raman spectra indicated that the carbon species formed were probably conjugated olefinic or polycyclic aromatic hydrocarbons, which can be considered molecular subunits of a graphitic plane. The N(2) adsorption isotherms, pore size distributions, and XPS results indicated that carbon was uniformly dispersed on the alumina surface in the as-prepared CCA. The carbon coverage and number of carbon layers in CCA could be controlled by the tuning of the sucrose content in the precursor and impregnation times. RB adsorption isotherms suggested that the monolayer adsorption capacity of RB on alumina increased drastically for the sample with uniformly dispersed carbon. The as-prepared CCA possessed the texture of alumina and the surface properties of carbon or both carbon and alumina depending on the carbon coverage.

Adsorción de fósforo en algunos suelos argentinos : 1-condiciones experimentales e isotermas de adsorción

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Ionic liquids as solvent and solvent additives for the synthesis of sol-gel materials

The ionic liquid (IL) 1-butyl-3-methylimidazolium chloride was used as a drying control chemical additive in the synthesis of silica sol-gel materials with and without methanol as a co-solvent. The resulting gels were characterized by using thermogravimetric analysis, differential scanning calorimetry, infrared spectroscopy and water sorption kinetics. Calcined gels were analyzed using scanning electron microscopy and nitrogen adsorption isotherms for surface area and pore volume determination. Non-calcined gels were monolithic and showed general cloudiness with lesser degrees observed at higher IL volumes. Calcinations resulted in the formation of powders with increased available surface area as the amount of IL volume was increased. This is consistent with an increase in respective pore volume but a general decrease in average pore size. The resulting materials exhibited conventional structural microdomains, in contrast to periodicity reported when other ionic liquids were used as templates.

Influence of preparation conditions on the characteristics of activated carbons produced in laboratory and pilot scale systems

The central theme of this investigation is to evaluate the feasibility of using bituminous coal as a precursor material for the production of chars and activated carbons using physical and chemical activation processes. The chemical activation process was accomplished by impregnating the raw materials with different dehydrating agents in different ratios and concentrations, prior to heat treatment (ZnCl2, KCl, KOH, NaOH and Fe2(SO4)3·xH2O). Steam activation of the precursor material was adopted for the preparation of activated carbon using physical activation technology. Different types of bituminous coal; namely, contaminated Columbian (contaminated with pet. coke), pure Columbian, Venezuelan and New Zealand bituminous coal were used in the production processes. BET surface area, micropore area, pore size distribution and total pore volume of the chars and activated carbons were determined from N2 adsorption/desorption isotherm, measured at 77 K. Charring conditions, charring temperature of 800 °C and charring time of 4 h, proved to be the optimum conditions for preparing chars. Contaminated Columbian were found to be the best precursor material for the production of char with reasonable physical characteristics (surface area = 138.1 m2 g-1 and total pore volume of 8.656 × 10-0.2 cm3 g-1). An improvement in the physical characteristics of the activated carbons was obtained upon the treatment of coal with dehydrating agents. Contaminated Columbian treated with 10 wt% ZnCl2 displayed the highest surface area and total pore volume (surface area = 231.5 m2 g-1 and total pore volume = 0.1227 cm3 g-1) with well-developed microporisity (micropore area = 92.3 m2 g-1). Venezuelan bituminous coal using the steam activation process was successful in producing activated carbon with superior physical characteristics (surface area = 863.50 m2 g-1, total pore volume = 0.469 cm3 g-1 and micropore surface area = 783.58 m2 g-1).

High capacity carbon based electrodes for lithium/oxygen batteries

Porous carbon aerogels are prepared by polycondensation of resorcinol (R) and formaldehyde (F)catalyzed by sodium carbonate (C) followed by carbonization of the resultant aerogels at 800? in an inert atmosphere. The porous texture of the carbons has been adjusted by the change of the molar ratio of resorcinol to catalyst (R/C) in the gel precursors in the range of 100 to 500. The porous structure of the aerogels and carbon aerogels are characterized by N2 adsorption-desorption measurements at 77 K. It is found that total pore volume and average pore diameter of the carbons increase with increase in the R/C ratio of the gel precursors.The prepared carbon aerogels are used as active materials in fabrication of composite carbon electrodes. The electrochemical performance of the electrodes has been tested by using them as cathodes in a Li/O2 cell. Through the galvanostatic charge/discharge measurements, it is found that with an increase of R/C ratio, the specific capacity of the Li/O2 cell fabricated from the carbon aerogels increases from 716 to 2077 charge/discharge cycles indicate that the carbon samples possess excellent stability on cycling.

Enhancement of the stability of microporous silica films in non-aqueous solvents at elevated temperature

The effect of Al incorporation and pH adjustment during hydrolysis of the silica precursor on the thermal and structural stability of ordered microporous silica films with a 2D structure is presented. The structural stability of the films was determined from a combination of LA XRD/TEM data with porosity data obtained from ethanol adsorption isotherms. Thermogravimetric analysis and MR data were used to determine the template removal and the thermal stability. Stability of aluminium incorporated silica films has further been examined in several organic solvents with different polarity. A solvent with a higher polarity interacts more strongly with the films; the long-order structure disappeared after exposure to polar solvents. After exposure to non-polar solvents, the pore size uniformity was retained after 48 h. The samples with an Al/Si ratio of 0.007 showed the smallest d-spacing shift after exposure to hexane. The stability was further tested in the hydrogenation of phenylacetylene performed in a batch reactor over 1 wt.% Pd/Si(Al)O-2/Si (Al/Si = 0.007) films at 30 degrees C and 10 bar H-2 with hexane as solvent. No deactivation was observed in two subsequent hydrogenation runs. (C) 2009 Elsevier Inc. All rights reserved.

Preliminary investigation of mixed adsorbents for the removal of copper and methylene blue from aqueous solutions

With most recent studies being focused on the development of
advanced chemical adsorbents, this paper investigates the possibility of
using two natural low-cost materials for selective adsorption. Multiadsorbent
systems containing tea waste and dolomite have been tested for
their effectiveness in the removal of copper and methylene blue from
aqueous solutions. The effects of contact time, solution pH and
adsorption isotherms on the sorption behaviour were investigated. The
Langmuir and Freundlich isotherms adequately described the adsorption of
copper ions and methylene blue by both materials in different systems.
The highest adsorption capacities for Cu and MB were calculated as 237.7
at pH 4.5 and 150.44 mg.g‒1 at pH 7 for DO and TW+DO respectively. Tea
waste (TW) and dolomite (DO) were characterized by Fourier transform
infrared spectroscopy, scanning electron microscopy and Energy dispersive
X-ray analysis. The removal of Cu and MB by dolomite was mainly via
surface complexation while physisorption was responsible for most of the
Cu and MB adsorption onto tea waste. Identifying the fundamental mechanisms and behaviour is key to the development of practical multi-adsorbent packed columns.