One-step synthesis of 2-pentanone from ethanol over K-Pd/MnOx-ZrO2-ZnO catalyst

A highly active and selective K-Pd/MnOx-ZrO2-ZnO catalyst for the one-step synthesis of 2-pentanone from ethanol is described. The possible reaction pathways for ethanol reaction over K-Pd/MnOx-ZrO2-ZnO catalyst were investigated by means of TPSR, CO2- and NH3-TPD techniques. The reactions were performed in a fixed bed continuous flow reactor. Complete conversion with high selectivity for 2-pentanone, was observed under 370 similar to 390degreesC, 2 similar to 4 MPa, GHSV = 8000 similar to 10,000 h(-1) and LHSV < 1.25 h(-1) conditions. Ethanol reactions over K-Pd/MnOx-ZrO2-ZnO catalyst showed that the catalyst could catalyze dehydrogenation. aldol. dehydration and hydrogenation reactions. Both acidic and basic properties are found on the surface of K-Pd/MnOx-ZrO2-ZnO catalyst, whose multifunctionality with the combination of basic, acid and metal sites may be responsible for the efficiency of the K-PdMnOx-ZrO2-ZnO catalyst. (C) 2004 Elsevier B.V. All rights reserved.

Butene catalytic cracking to propene and ethene over potassium modified ZSM-5 catalysts

Catalytic cracking of butene over potassium modified ZSM-5 catalysts was carried out in a fixed-bed microreactor. By increasing the K loading on the ZSM-5, butene conversion and ethene selectivity decreased almost linearly, while propene selectivity increased first, then passed through a maximum (about 50% selectivity) with the addition of ca. 0.7-1.0% K, and then decreased slowly with further increasing of the K loading. The reaction conditions were 620 degrees C, WHSV 3.5 h(-1), 0.1 MPa 1-butene partial pressure and 1 h of time on stream. Both by potassium modification of the ZSM-5 zeolite and by N(2) addition in the butene feed could enhance the selectivity towards propene effectively, but the catalyst stability did not show any improvement. On the other hand, addition of water to the butene feed could not only increase the butene conversion, but also improve the stability of the 0.7%K/ZSM-5 catalyst due to the effective removal of the coke formed, as demonstrated by the TPO spectra. XRD results indicated that the ZSM-5 structure of the 0.07% K/ZSM-5 catalyst was not destroyed even under this serious condition of adding water at 620 degrees C.

Gas phase catalytic partial oxidation of toluene in a microchannel reactor

Gas phase partial oxidation of toluene over V/Ti oxide catalysts has been successfully performed in a microchannel reactor, which provides very good mass and heat transfer conditions. With the elimination of hot spots, which are known as the most negative factors for partial oxidation of hydrocarbons, steady and uniform reaction conditions can be achieved in the catalyst bed by using, the microreactor. Since the best performance of the catalysts might be exploited, the selectivity of partial oxidation products of toluene has remarkably increased compared to the traditional packed fixed-bed reactor, even without the bother of modifying the catalysts, diluting the reactants or catalysts with inert contents to avoid hot spots or improve the diffusion and mixing. Furthermore, in virtue of its inherent safety features, when using pure oxygen as oxidant, the reactions were handled safety within the explosion limits in the microreactor. With TiO2 carried V2O5 as catalysts, the total selectivity of benzaldehyde and benzoic acid reaches around 60%, and the toluene conversion is about 10%. The conversion can go up without violent decline of selectivity, unlike most fixed bed reactors. Space time yield of 3.12 kg h(-1) L-1 calculated on the basis of the channel volume has been achieved. The influence of operating conditions has been investigated in detail in the microreactor. (c) 2005 Elsevier B.V. All rights reserved.

New route for light olefins production from chloromethane over HSAPO-34 molecular sieve

HSAPO-34 molecular sieve was employed in chloromethane conversion and showed high performance in activity and selectivity in production of light olefins. Our detailed IR investigation allowed the identification of the active sites and the adsorbed species and demonstrated that the conversion started from 350 degrees C with alkoxy group as the intermediate. The fixed-bed catalytic testing evidenced that in the range of 350-500 degrees C, 70-80% of chloromethane was transferred to ethylene, propylene and butenes. Increasing reaction temperature favors the conversion and enhances the yield of lighter olefins. A very important reversible phenomenon, the breaking of Al-O-P bonds upon adsorption of HCl, a main product of reaction to generate a large amount of P-OH groups and the recovery of Al-O-P upon removal of HCI was revealed. (c) 2005 Elsevier B.V. All rights reserved.

Adsorption Characteristics of Reactive Dyes in Columns of Activated Carbon

Abstract: Adsorption behaviour of reactive dyes in fixed-bed adsorber was evaluated in this work. The characteristics of mass transfer zone (MTZ), where adsorption in column occurs, were affected by carbon bed depth and influent dye concentration. The working lifetime (t(x)) of MTZ, the height of mass transfer zone (HMTZ), the rate of mass transfer zone (RMTZ), and the column capacity at exhaustion (q(column)) were estimated for the removal of remazol reactive yellow and remazol reactive black by carbon adsorber. The results showed that column capacity calculated at 90% of column exhaustion was lower than carbon capacity obtained from equilibrium studies. This indicated that the capacity of activated carbon was not fully utilized in the fixed-bed adsorber. The bed-depth service time model (BDST) was applied for analysis of reactive yellow adsorption in the column. The adsorption capacity of reactive yellow calculated at 50% breakthrough point (No) was found to be 0.1 kg kg(-1) and this value is equivalent to about 14% of the available carbon capacity. The results of this study indicated the applicability of fixed-bed adsorber for removing remazol reactive yellow from solution. (C) 2008 Elsevier B.V. All rights reserved.

Limiting withdrawal rate and maximum film thickness during dip-coating of titania sols onto a Si substrate

The article highlights new insights into production of thin titania films widely used as catalyst support in many modern reactors including capillary microreactors, microstructured fixed-bed reactors and falling film microreactors. Dip-coating of a Mania sol onto a Si substrate has been studied in the range of the sol viscosities of 1.5-2.5 mPa s and the sol withdrawal rates of 0.2-18 mm/s. Different viscosities of sols were created by addition of desired amounts of nitric acid to the synthesis mixture of titanium isopropoxide and Plutonic F127 in ethanol which allowed to control the rate of the condensation reactions. Uniform inesoporous titania coatings were obtained at the solvent withdrawal rates below 10 mm/s at sol viscosities in the range from 1.6 mPa s to 2.5 mPa s. There exists a limiting withdrawal rate corresponding to a capillary number of ca. 0.01 beyond which uniform titania films cannot be obtained. Below the limiting withdrawal rate, the coating thickness is a power function of the sol viscosity and withdrawal rate, both with an exponent of 2/3. The limiting withdrawal rate increases as the solvent evaporation rate increases and it decreases as the sol viscosity increases. Crown Copyright (C) 2011 Published by Elsevier B.V. All rights reserved.

Preferential CO oxidation over a copper-cerium oxide catalyst in a microchannel reactor

The activity of a 5-wt% Cu/CeO2-x catalyst during preferential CO oxidation in hydrogen-rich gas mixtures was studied in a microchannel reactor. The CO concentration dropped from 1 vol.% to 10 ppm at a selectivity of 60%, at a temperature of 190 degrees C, and a weight hour space velocity (WHSV) of 55,000 cm(3) g(-1) h(-1). Both the CO concentration and the temperature increased when the WHSV was increased from 50,000 to 500,000 cm(3) g(-1) h(-1). An increase of the O-2 concentration from a 1.2 to 3 fold excess reduced the CO concentration to 10 ppm in a broad temperature interval of 50 degrees C at WHSVs up to 275,000 cm(3) g(-1) h(-1). The preferential CO oxidation could be carried out at higher flow rates and at higher selectivities in the microchannel reactor compared to a fixed-bed flow reactor. (C) 2008 Elsevier B.V. All rights reserved.

Effect of precursor on the performance of alumina for the dehydration of methanol to dimethyl ether

Dimethyl ether (DME) is amongst one of the most promising alternative, renewable and clean fuels being considered as a future energy carrier. In this study, the comparative catalytic performance of γ-Al2O3 prepared from two common precursors (aluminum nitrate (AN) and aluminum chloride (AC)) is presented. The impact of calcination temperature was evaluated in order to optimize both the precursor and pre-treatment conditions for the production of DME from methanol in a fixed bed reactor. The catalysts were characterized by TGA, XRD, BET and TPD-pyridine. Under reaction conditions where the temperature ranged from 180 °C to 300 °C with a WHSV = 12.1 h−1 it was found that all the catalysts prepared from AN(η-Al2O3) showed higher activity, at all calcination temperatures, than those prepared from AC(γ-Al2O3). In this study the optimum catalyst was produced from AN and calcined at 550 °C. This catalyst showed a high degree of stability and had double the activity of the commercial γ-Al2O3 or 87% of the activity of commercial ZSM-5(80) at 250 °C.

Microwave-assisted Cu-catalyzed Ullmann ether synthesis in a continuous-flow milli-plant

The combination of milli-scale processing and microwave heating has been investigated for the Cu-catalyzed Ullmann etherification in fine-chemical synthesis, providing improved catalytic activity and selective catalyst heating. Wall-coated and fixed-bed milli-reactors were designed and applied in the Cu-catalyzed Ullmann-type CO coupling of phenol and 4-chloropyridine. In a batch reactor the results show clearly increased yields for the microwave heated process at low microwave powers, whereas high powers and catalyst loadings reduced the benefits of microwave heating. Slightly higher yields were found in the Cu/ZnO wall-coated as compared to the Cu/TiO fixed-bed flow-reactor. The benefit here is that the reaction occurs at the surface of the metal nanoparticles confined within a support film making the nano-copper equally accessible. Catalyst deactivation was mainly caused by Cu oxidation and coke formation; however, at longer process times leaching played a significant role. Catalyst activity could partially be recovered by removal of deposited by-product by means of calcination. After 6h on-stream the reactor productivities were 28.3 and 55.1kgprod/(mR3h) for the fresh Cu/ZnO wall-coated and Cu/TiO fixed-bed reactor, respectively. Comparison of single- and multimode microwaves showed a threefold yield increase for single-mode microwaves. Control of nanoparticles size and loading allows to avoid high temperatures in a single-mode microwave field and provides a novel solution to a major problem for combining metal catalysis and microwave heating. Catalyst stability appeared to be more important and provided twofold yield increase for the CuZn/TiO catalyst as compared to the Cu/TiO catalyst due to stabilized copper by preferential oxidation of the zinc. For this catalyst a threefold yield increase was observed in single-mode microwaves which, to the best of our knowledge, led to a not yet reported productivity of 172kgprod/(mR3h) for the microwave and flow Ullmann CO coupling. © 2012 Elsevier B.V.

Reactive dye adsorption onto a novel mesoporous carbon

A new mesoporous carbon (MCSG60) was developed using an inexpensive commercial mesoporous silica gel as a template and sucrose as the carbon source. The surface area, porosity and density of the carbon were determined. The material possesses a high specific surface area and pore volume accessible for most typical aqueous pollutants. The adsorbent material was tested in a batch dye adsorption system. The behaviour of three reactive dyes adsorbed onto MCSG60 was evaluated (Naphthol Blue Black, NBB; Reactive Black 5, RB5; and Remazol Brilliant Blue R, RBBR). The maximum adsorption capacities obtained for the dyes were: 270. mg/g for NBB; 270. mg/g for RB5; and 280. mg/g for RBBR. Kinetic studies indicated that the adsorption process onto the mesoporous carbon was rapid and that equilibrium was reached in less than 1. h for all the dye systems investigated. Further batch experiments showed MCSG60 successfully adsorbed the dyes over a wide pH range and at low adsorbate concentration. The adsorption potential of MCSG60 for dye removal was further evaluated using a fixed-bed adsorption column. © 2013 Elsevier B.V.

Aqueous phase reforming of xylitol over Pt-Re bimetallic catalyst: Effect of the Re addition

The aqueous phase reforming (APR) of xylitol was studied in a continuous fixed bed reactor over three catalysts: Pt/Al2O3, Pt/TiO2 and Pt-Re/TiO2. The data obtained in the case of the monometallic Pt catalysts was compared to the bimetallic Pt-Re sample. The effect of Re addition on the catalyst stability, activity, product formation and selectivity toward hydrogen and alkanes was studied. The bimetallic catalyst demonstrated a higher selectivity to alkanes compared to the monometallic samples. The monometallic catalyst was more selective toward hydrogen formation. A plausible reaction scheme explaining differences in selectivity toward hydrogen and alkanes was proposed and discussed.

Mercury (II) removal from aqueous solutions by microporous materials

O Mercúrio é um dos metais pesados mais tóxicos existentes no meio ambiente, é persistente e caracteriza-se por bioamplificar e bioacumular ao longo da cadeia trófica. A poluição com mercúrio é um problema à escala global devido à combinação de emissões naturais e emissões antropogénicas, o que obriga a políticas ambientais mais restritivas sobre a descarga de metais pesados. Consequentemente o desenvolvimento de novos e eficientes materiais e de novas tecnologias para remover mercúrio de efluentes é necessário e urgente. Neste contexto, alguns materiais microporosos provenientes de duas famílias, titanossilicatos e zirconossilicatos, foram investigados com o objectivo de avaliar a sua capacidade para remover iões Hg2+ de soluções aquosas. De um modo geral, quase todos os materiais estudados apresentaram elevadas percentagens de remoção, confirmando que são bons permutadores iónicos e que têm capacidade para serem utilizados como agentes descontaminantes. O titanossilicato ETS-4 foi o material mais estudado devido à sua elevada eficiência de remoção (>98%), aliada à pequena quantidade de massa necessária para atingir essa elevada percentagem de remoção. Com apenas 4 mg⋅dm-3 de ETS-4 foi possível tratar uma solução com uma concentração igual ao valor máximo admissível para descargas de efluentes em cursos de água (50 μg⋅dm-3) e obter água com qualidade para consumo humano (<1.0 μg⋅dm-3), de acordo com a legislação Portuguesa (DL 236/98). Tal como para outros adsorbentes, a capacidade de remoção de Hg2+ do ETS- 4 depende de várias condições experimentais, tais como o tempo de contacto, a massa, a concentração inicial de mercúrio, o pH e a temperatura. Do ponto de vista industrial as condições óptimas para a aplicação do ETS-4 são bastante atractivas, uma vez que não requerem grandes quantidades de material e o tratamento da solução pode ser feito à temperatura ambiente. A aplicação do ETS-4 torna-se ainda mais interessante no caso de efluentes hospitalares, de processos de electro-deposição com níquel, metalúrgica, extracção de minérios, especialmente ouro, e indústrias de fabrico de cloro e soda cáustica, uma vez que estes efluentes apresentam valores de pH semelhantes ao valor de pH óptimo para a aplicação do ETS-4. A cinética do processo de troca iónica é bem descrita pelo modelo Nernst-Planck, enquanto que os dados de equilíbrio são bem ajustados pelas isotérmicas de Langmuir e de Freundlich. Os parâmetros termodinâmicos, ΔG° and ΔH° indicam que a remoção de Hg2+ pelo ETS-4 é um processo espontâneo e exotérmico. A elevada eficiência do ETS-4 é confirmada pelos valores da capacidade de remoção de outros materiais para os iões Hg2+, descritos na literatura. A utilização de coluna de ETS-4 preparada no nosso laboratório, para a remoção em contínuo de Hg2+ confirma que este material apresenta um grande potencial para ser utilizado no tratamento de águas. ABSTRACT: Mercury is one of the most toxic heavy metals, exhibiting a persistent character in the environment and biota as well as bioamplification and bioaccumulation along the food chain. Natural inputs combined with the global anthropogenic sources make mercury pollution a planetary-scale problem, and strict environmental policies on metal discharges have been enforced. The development of efficient new materials and clean-up technologies for removing mercury from effluents is, thus, timely. In this context, in my study, several microporous materials from two families, titanosilicates and zirconosilicates were investigated in order to assess their Hg2+ sorption capacity and removal efficiency, under different operating conditions. In general, almost all microporous materials studied exhibited high removal efficiencies, confirming that they are good ion exchangers and have potential to be used as Hg2+ decontaminant agents. Titanosilicate ETS-4 was the material most studied here, by its highest removal efficiency (>98%) and lowest mass necessary to attain it. Moreover, according with the Portuguese legislation (DL 236/98) it is possible to attain drinking water quality (i.e. [Hg2+]< 1.0 μg⋅dm-3) by treating a solution with a Hg2+ concentration equal to the maximum value admissible for effluents discharges into water bodies (50 μg⋅dm-3), using only 4 mg⋅dm-3 of ETS-4. Even in the presence of major freshwater cations, ETS-4 removal efficiency remains high. Like for other adsorbents, the sorption capacity of ETS-4 for Hg2+ ions is strongly dependent on the operating conditions, such as contact time, mass, initial Hg2+ concentration and solution pH and, to a lesser extent, temperature. The optimum operating conditions found for ETS-4 are very attractive from the industrial point of view because the application of ETS-4 for the treatment of wastewater and/or industrial effluents will not require larges amounts of adsorbent, neither energy supply for temperature adjustments becoming the removal process economically competitive. These conditions become even more interesting in the case of medical institutions liquid, nickel electroplating process, copper smelter, gold ore tailings and chlor-alkali effluents, since no significant pH adjustments to the effluent are necessary. The ion exchange kinetics of Hg2+ uptake is successfully described by the Nernst-Planck based model, while the ion exchange equilibrium is well fitted by both Langmuir and Freundlich isotherms. Moreover, the feasibility of the removal process was confirmed by the thermodynamic parameters (ΔG° and ΔH°) which indicate that the Hg2+ sorption by ETS-4 is spontaneous and exothermic. The higher efficiency of ETS-4 for Hg2+ ions is corroborate by the values reported in literature for the sorption capacity of other adsorbents for Hg2+ ions. The use of an ETS-4 fixed-bed ion exchange column, manufactured in our laboratory, in the continuous removal of Hg2+ ions from solutions confirms that this titanosilicate has potential to be used in industrial water treatment.

Aplicação de cortiça em dois tipos de reatores para tratamento de água

A qualidade da água degradou-se de forma relevante nas últimas décadas e os processos de sorção têm vindo a ser investigados como métodos promissores para o tratamento de águas contaminadas. Neste trabalho avaliou-se a capacidade de dois tipos de cortiça para a remoção de diversos contaminantes, em reatores de vaso fechado e de leito fixo. Os ensaios realizados em reatores de vaso fechado permitiram (i) avaliar o efeito do pH e da granulometria na eficiência dos sorventes na remoção de mercúrio e (ii) avaliar a afinidade dos sorventes para outros contaminantes, nomeadamente arsénio, cádmio, níquel e chumbo. Estruturalmente as duas cortiças estudadas aparentam ser semelhantes, com uma pequena diferença de comportamento ácido-base e não apresentam diferenças estatisticamente significativas na remoção de mercúrio. Os resultados obtidos permitiram constatar que o processo de remoção é independente do pH, tendo-se obtido percentagens de remoção da ordem dos 80% e de concentrações de mercúrio na cortiça na ordem dos 117 μg/g. As cortiças estudadas revelaram-se menos eficazes no tratamento de água com os restantes contaminantes, atingindo percentagens de remoção máximas de 0% para As, 11% para Cd, 35% para Ni e 69% para Pb. Os ensaios em leito fixo, mesmo sem terem sido otimizados, revelam que é possível obter uma eficácia de remoção de mercúrio superior a 90% nas primeiras 40 horas de trabalho, sendo a concentração de mercúrio no leito de 680 μg/g. Relativamente aos mecanismos de sorção, os resultados experimentais indicam que estes são possivelmente de natureza química e que as interações eletrostáticas têm pouca importância.

Catálise de hydrocraking baseado em zeólitos

Trabalho Final de Mestrado para obtenção do grau de Mestre em Engenharia Química

Selective N-monomethylation of aniline over Zn1-xNixFe2O4 (x=0, 0.2, 0.5, 0.8 and 1) type systems

The reaction of aniline with methanol was carried out over Zn1-xNixFe2O4 (x= 0, 0.2, 0.5, 0.8 and 1) type systems in a fixed-bed down-flow reactor. It was observed that systems possessing low ``x'' values are highly selective and active for mono N-alkylation of aniline leading to N-methyl aniline. Selectivity for N-methyl aniline over ZnFe2O4 was more than 99% under the optimized reaction conditions. Even at methanol to aniline molar ratio of 2, the yield of N-methyl aniline was nearly 55.5%, whereas its yield exceeded 67% at the molar ratio of 7. The Lewis acid sites of the catalysts are mainly responsible for the good catalytic performance. Cation distribution in the spinel lattice influences their acido-basic properties, and hence, these factors have been considered as helpful to evaluate the activity and stability of the systems.