Sieve Type Research Articles

AVALIAÇÃO DE PROGÊNIES DE CAFEEIROS OBTIDAS DO CRUZAMENTO ENTRE CATUAÍ E HÍBRIDO DE TIMOR

A partir da década de 70, com a entrada da ferrugem no Brasil, uma das linhas de pesquisa que tem recebido mais atenção nos programas de melhoramento do cafeeiro é a resistência à ferrugem, devido aos prejuízos causados por esta doença nas lavouras cafeeiras. Entretanto, para se obter uma cultivar é preciso que a mesma tenha uma boa adaptabilidade e estabilidade fenotípica em vários locais para produtividade e outras características de interesse. A avaliação de progênies em vários locais é uma etapa importante na fase final de um programa de melhoramento. O objetivo desse trabalho foi avaliar o comportamento de progênies oriundas do cruzamento de ‘Catuaí’ x Híbrido de Timor, em dois locais no que se refere às características de produção, aspectos vegetativos e peneira dos grãos. Os experimentos foram instalados em dezembro de 1999, no Campus da Universidade Federal de Lavras e em propriedade particular, em Campos Altos –MG. O delineamento experimental utilizado foi blocos casualizados, com três repetições e parcelas constituídas por seis plantas. O espaçamento adotado em ambos os locais foi 3,5 x 1,0 m. Avaliaram-se 23 progênies mais a cultivar Catuaí Vermelho IAC 15 nos anos safra 2003/2004, 2004/2005, 2005/2006 e 2006/2007. Analisou-se produção, vigor e classificação dos grãos por peneira. Os resultados indicam que as progênies de cafeeiro exibem variação para vigor, produção e classificação por tipo de peneira nos dois locais de cultivo sendo que as progênies H 337-13-3-1, H 419-8-13-3 e H 514-7-16-3 apresentaram bom comportamento nos dois locais de cultivo.

An improved and rapid 5A molecular sieve method for gas chromatography isotope ratio mass spectrometry of n-alkanes (C 8–C 30+)

The accurate analysis of stable carbon isotope ratios of individual n-alkanes in petroleum by gas chromatography isotope ratio mass spectrometry (GC–irMS) requires that the n-alkanes be separated from branched/cyclic hydrocarbons. Conventional separation methods include urea adduction or separation using different types of molecular sieves (5A, ZSM5). Although the molecular sieves procedures are well established, they generally require the use of hydrofluoric (HF) acid, a potentially hazardous material, to digest and release compounds trapped within the sieve. In this study, a simplified 5A method that avoids the use of HF acid has been developed to isolate n-alkanes ranging from n-C 8 to at least n-C 30 from a saturated petroleum hydrocarbon fraction. 12% cyclohexane in n-pentane was found to be a sufficient solvent in extracting most of the n-alkanes (>90%) in the n-C 8 to n-C 30 range from the sieve. The new 5A sieve procedure is a rapid and safer method for extracting n-alkanes from petroleum to yield fractions amenable for routine GC–irMS.

Fabrication of functionally graded 3A/5A zeolites by electrophoretic deposition

Functionally graded zeolites of molecular sieve type 3A and 5A are deposited by electrophoretic deposition (EPD) from acetone suspension with 8% volume concentration of n-butylamine as particle charging agent. The EPD characteristics of both 3A and 5A suspensions are studied. Functionally graded zeolite 3A/5A deposits are obtained at 200 V DC. Energy dispersive X-ray dispersion (EDX) analysis results confirm the graded structure. The deposited zeolites are also analysed by scanning electron microscopy (SEM). The factors influencing the deposition process are discussed.

Different effects of silane and carboxyled polypropylene on crystal morphology of polypropylene/molecular sieves type 5A composites

AbstractThe silane KH‐550 and carboxyled polypropylene (EPP) were used as compatibilizers in this study. The effect of them on crystalline morphology of polypropylene/molecular sieves type 5A (PP/5A) composites was investigated. IR illustrated that 5A interacts with EPP by forming molecule interaction or hydrogen bonds, but interacts with silane by covalent bonds. Polarized optical microscopy (POM) and X‐ray diffraction (XRD) revealed that a suitable amount of silane can promote β‐crystal formation in PP, and the average size of spherulites in the PP/5A/silane is smaller than that of PP. EPP interacts with 5A by molecule interaction and cocrystallizes with PP, leading to the crystal morphology of PP/5A/EPP resembles to that of pure PP. Significant difference was detected in the effect of the two compatibilizers, which attributed to the different compatibility mechanisms. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007

Reinigung im Mähdrescher durch Kreisschwinger

Steadily increasing throughputs in modern combine harvesters require new ideas for developing combine cleaning units. One possibility for increasing the throughput of the cleaning unit is to use a vertical circularly oscillating sieve. Many tests were carried out to optimize its amplitude and frequency, airflow direction, sieve inclination, sieve opening and sieve type. This article shows some examples of the test results.

Compatibilization of polypropylene/molecular sieves type 13X based on carboxyled polypropylene

AbstractMolecular sieves type 13X (13X) was selected as a filler of polypropylene (PP). The effect of carboxyled polypropylene (EPP) on mechanical properties, melting behavior, morphology and rheology behavior of PP/13X composites was studied. Mechanical properties tests showed that when 4% EPP added, the impact strength and tensile strength increased 65.6 and 4.6% than PP/13X composites, respectively. It was suggested that the EPP activated the heterogeneous nucleation centers on the filler surface, and made 13X dispersed in PP matrix homogeneously by POM. SEM illustrated that EPP improved the adhesion and the compatibility between 13X and PP. Flow tests indicated that the EPP played the role of lubricant in PP/13X. All the investigations showed EPP was a true coupling agent for PP/13X composites. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007

On zeros of cubic L-functions

In this paper we obtain a zero density theroem for Hecke L-functions associated to cubic characters by Heath-Brown's large sieve type inequality. Using Patterson's result on cubic Gauss sums we also have the moments estimate for corresponding L-functions. Distribution of class numbers of a family of degree 6 fields over Q is obtained as an application of the main results.

Large Sieve Inequality with Quadratic Amplitudes

In this paper, we develop a large sieve type inequality with quadratic amplitude. We use the double large sieve to establish non-trivial bounds.

Characterization and activity of Mo supported catalysts for diesel deep hydrodesulphurization

Various highly dispersed Mo supported catalysts with various carriers were prepared for deep hydrodesulphurization of diesel. The carriers included a high surface area and large pore volume γ-Al 2O 3, two types of meso-microporous composite molecular sieves prepared by incipient-wetness impregnation method. A new mesoporous MoSiO x catalyst synthesized with in situ composite method was also studied. The hydrodesulphurization experiments were carried out in a micro-reactor over different catalysts including Mo supported series and a commercial catalyst. Spectroscopic techniques (FT-IR and UV–vis DRS) were utilized to determine the structure of MoO x species. The catalyst characterizations of BET, XRD, FT-IR, UV–vis DRS and FTIR pyridine adsorption indicated that the existences of metal active component of Mo in the catalysts were highly dispersed nano MoO 3 clusters and the Mo series catalysts had high surface areas and plenty of large pores which were propitious to the diffusions of reactant and product molecules. Cat NiMo exhibited the highest B/ L acidity ratio and higher total concentration of Brønsted acid sites and Lewis acid sites, and its HDS activity also gave the highest in this study to produce a sulphur-free diesel, which was verified by the sulphur content in products analyzed by GC–MS methods.

Passive Flux Samplers to measure Nitrous Oxide and Methane Emissions from Agricultural Sources, Part 2: Desorption Improvements

In the first part of this research work, it was shown that it was feasible to adsorb nitrous oxide (N2O) and methane (CH4) on to molecular sieves loaded into standard stainless-steel gas sampling tubes. Of three types of sieve examined, zeolite 5A molecular sieve gave the best performance. A thermal desorption procedure was used to recover the gas adsorbed. However, the average efficiency for desorption of N2O and CH4 was respectively 59% and 6% for zeolite 5A molecular sieve. The objective of the present study was to develop a complete desorption procedure for N2O and CH4 absorbed on zeolite 5A molecular sieve. The parameters investigated were: desorption gas flow rate, desorption duration and temperature. The complete procedure includes a two-stage desorption using in first stage a flow rate of 21 ml min−1 and 40 min purge period. A flow rate of 64 ml min−1 and 15 min purge period was used for the second stage. In this study, five temperatures were investigated (50, 100, 150, 200 and 250 °C). The N2O desorption efficiency was not significantly influenced by the temperature. A temperature of 100 °C was recommended for a desorption efficiency of N2O ranged from 75% to 94%, with an average of 88%. For CH4, the second stage desorbs almost the same amount as does the first stage and the desorption temperature has significant effect. Together, the two stages allowed recovery of up to 51% of the total amount of CH4 absorbed.

Comparative studies of Zr-based MCM-41 and MCM-48 mesoporous molecular sieves: Synthesis and physicochemical properties

Two surfactant-templated synthetic routes are developed for the preparation of new types of mesoporous molecular sieves, Zr-MCM-41 and Zr-MCM-48, using different Si sources but keeping the same zirconium precursor (zirconium- n-propoxide). When fumed silica was used as Si precursor, a Zr-MCM-48 material of cubic structure was formed with a surface area of 654.8 m 2/g and an unimodal pore diameter distribution. It shows low stability: after calcination at 600 °C, the ordered structure was transformed into a relatively disordered worm-like mesostructure with many defects and silanol groups. The use of tetraethyl orthosilicate as Si source led to the formation of a Zr-MCM-41 mesoporous solid, which had good thermal stability and a highly ordered hexagonal arrangement, with a surface area 677.9 m 2/g and an uniform pore diameter distribution. Fourier transform infrared (FT-IR) characterization and 29Si NMR analysis confirm that zirconium ions indeed incorporated into the framework of the solid. The in situ FT-IR spectroscopy of pyridine adsorption reveals that both, Lewis and Brönsted acid sites, were formed on the surface of these mesoporous materials. The strength and number of the Brönsted acid sites of the Zr-MCM-48 solid were greater than those of the Zr-MCM-41, due to a lower degree of condensation reaction during the synthesis that led to more structural defects in the framework and more silanol groups stretching from the solid surface.

Sorption properties for different types of molecular sieve and their influence on optimum dehumidification performance of desiccant wheels

The sorption property data for different types of molecular sieves (synthetic zeolites) are presented in equation form. The variation of the isosteric heat of sorption with water loading is derived using Othmer’s method. It is found that heat of sorption can be up to 50% greater than the latent heat of vaporization. Heat of sorption data, together with equilibrium isotherms are curve fitted and are incorporated into a numerical model of the nonlinear heat and mass transfer processes that occur in desiccant wheels. Using the numerical model, the influence of different assumptions for heat of sorption and equilibrium equation of molecular sieve on predicted optimum performance of rotary dehumidifier is evaluated.

Low temperature oxidative template removal from SBA-15 using MnO4−solution and carbon replication of the mesoporous silica product

We report a new method of low temperature removal of template from SBA-15 by KMnO4 chemical oxidation. Using this silica as template, mesoporous carbon with thick pore walls and relatively small mesopores can be cast. The results from XRD and nitrogen sorption show that the silica obtained after surfactant removal has high surface area, high pore volume and good structural ordering. The obtained carbon replica also shows good structural ordering as reflected from XRD and TEM characterizations. EDX analysis shows that no residue of potassium and manganese in the carbon sample can be detected, indicating the complete removal of such species during the washing step. Interestingly, the analysis of the micropore volume based on the DFT method shows that these carbon replicas have a large fraction of micropores with respect to the total pore volume. These micropore rich carbon materials could be candidates as molecular sieve type adsorbents and catalyst supports.

The role of MCM-41 composition in the creation of basicity by alkali metal impregnation

Three types of mesoporous molecular sieves (silicate MCM-41, niobosilicate NbMCM-41, and aluminosilicate AlMCM-41) were impregnated with alkali metal acetates. The textural stability of the samples was estimated on the basis of XRD measurements and nitrogen adsorption/desorption methods. The acidic–basic properties of the obtained materials were tested in the cyclization of acetonylacetone and studied by FTIR spectroscopy after adsorption of methylacetylene (propyne) and pyridine. Two types of chemical reactions between mesoporous matrix and alkali metal salt/oxide were observed: the reaction between alkali metal salt and silica/silicate and the reaction between basic oxide and silanol groups or Na + cations. In the first one the alkali metal silicate formation decreases from Li to Cs species and leads to the destruction of the material. The second reaction places alkali metal cations in extra framework positions, which increases from Li to Cs species and is only observed in the case of AlMCM-41 and NbMCM-41 materials. As a result of the second reaction Lewis acidity is generated. The average effect of these two interactions leads to the volcanic curve for basicity of M/AlMCM-41 and M/NbMCM-41 with the maximum for K-samples. In contrast, basicity of M/MCM-41 systematically increases from Li to Cs form since the second type of interaction does not occur for these samples.

An Improvement of a Large Sieve Inequality in High Dimensions

In this paper, we present an improvement of a large sieve type inequality in high dimensions and discuss its implications on a related problem.

Effects of channel structure and acidity of molecular sieves in hydroisomerization of n-octane over bi-functional catalysts

SAPO-5, −11, −31, −41, −34, ZSM-5, −22 and −23 were synthesized by using the hydrothermal method and characterized by various methods such as XRD, SEM, XRF and TPD of NH3. They are representative of large-pore, medium-pore, small-pore, weak acid, strong acid, monodimensional channel and zigzag channel type of molecular sieves. Effects of pore size, the number of acid sites over medium-pore SAPOs, acid strength and shape of medium-pore channel on hydroisomerization of n-octane were examined over Pt-loaded corresponding molecular sieves. These results indicate that the selectivity to isomerization in hydroisomerization of n-octane is highly influenced by channel structure in molecular sieves and the conversion activity of n-octane is dependent on acidity of molecular sieves. Monodimensional medium-pore molecular sieves are ideal catalytic materials for higher isomerization selectivity in hydroisomerization of n-octane regardless of acid strength, such as SAPO-11, −31, −41, ZSM-22 and −23.

Aluminum chloride grafted mesoporous molecular sieves as alkylation catalysts

The aim of this work is to study the influence of different mesoporous molecular sieves (MMSs) type and the effect of pore diameter on MMSs silica grafted aluminum chloride catalysts and their activity in benzene alkylation by 1-dodecene. Four samples (two hexagonal and two wormhole like structures with different pore diameters) were prepared by post-synthesis grafting reaction in moisture free conditions (Schlenk technique). The physico-chemical properties were monitored by N 2 adsorption, XRD, atomic adsorption, 29Si and 27Al MAS NMR. Acidity data were obtained by TPD of ammonia, and FTIR of adsorbed pyridine. The alkylation of benzene is carried out in a Schlenk tube under dry conditions at room temperature. The products were analyzed by GC-MS. Grafting aluminum chloride on MMSs increases the yield of monoalkylated products.

Magma mixing recorded in intermediate rocks associated with high-Mg andesites from the Setouchi volcanic belt, Japan: implications for Archean TTG formation

Calc-alkaline intermediate rocks are spatially and temporally associated with high-Mg andesites (HMAs, Mg#>60) in Middle Miocene Setouchi volcanic belt. The calc-alkaline rocks are characterized by higher Mg# (strongly calc-alkaline trend) than ordinary calc-alkaline rocks at equivalent silica contents. Phenocrysts in the intermediate rocks have petrographical features such as: (1) coexisting reversely and normally zoned orthopyroxene phenocrysts in single rock; (2) sieve type plagioclase in which cores are mantled by higher An%, melt inclusion-rich zone; and (3) reversely zoned amphibole phenocrysts with opacite cores. In addition, mingling textures and magmatic inclusions were observed in some rocks. These petrographic features and the mineral chemistry indicate that magma mixing was the most important process in producing the strongly calc-alkaline rocks. The core composition of normally zoned orthopyroxene phenocrysts and the mantle composition of reversely zoned orthopyroxene phenocrysts have relatively high Mg# (85–90) in maximum. Although basaltic and high-Mg andesitic magmas are candidate as possible mafic end-member magmas, basaltic magma is excluded in terms of phenocryst assemblage and bulk composition. HMA magmas are suitable mafic end-member magmas that precipitated high Mg# (∼90) orthopyroxene, whereas andesitic to dacitic magma are suitable felsic end-members. In contrast, it is difficult to produce the strongly calc-alkaline trend through fractional crystallization from a HMA magma, because it would require removal of plagioclase together with mafic minerals from the early stage of crystallization, whereas the precipitation of plagiolase is suppressed due to the high water content of HMA magmas. These results imply that Archean Mg#-rich TTGs (>45–55), which are an analog of the strongly calc-alkaline rocks in terms of chemistry and magma genesis, can be derived from magma mixing in which a HMA magma is the mafic end-member magma, rather than by fractional crystallization from a HMA magma.

Characterization of metal-containing molecular sieves and their catalytic properties in the selective oxidation of cyclohexane

Three types of metal-containing molecular sieves with AFI, AEL and CHA structures (Me=Co, Mn, Cr and V) were synthesized hydrothermally and characterized by XRD, XRF, TG, TPR, NH 3-TPD and FT-IR. It was revealed that metals were incorporated into the framework of molecular sieves and induced the presence of charge centers. Both cobalt and manganese in the framework of AlPO-5, AlPO-11 and SAPO-34 were not reducible before the structure collapse. The redox behaviours of these catalysts in cyclohexane oxidation at 403 K using O 2 as oxidant were examined. CoAPO-11 exhibited best activity and good selectivities for the monofunctional oxidation products (88.5%). Cyclohexanol was the major product over most catalysts, whereas for Cr-containing molecular sieves, high selectivity of cyclohexanone was observed. Investigation of reaction mechanism based on CoAPO-11 and CrAPO-5 catalysts indicated that the decomposition of cyclohexyl hydroperoxide (CHHP), the intermediate in cyclohexane oxidation, followed the pathway: cyclohexanone ← CHHP → cyclohexanol → cyclohexanone.

Separation of Ethanol–Water Mixtures Using Molecular Sieves and Biobased Adsorbents

The potential use of new biobased adsorbents and different types of molecular sieve was assessed in the separation of the ethanol–water azeotrope. Molecular sieves of type 3A, type 4A, and type 5A and biobased adsorbents such as natural corncobs, natural and activated palm stone and oak, were used in this study. Each of these adsorbents was packed in a column, which was surrounded by a heating jacket. The jacket temperature was maintained constant in an attempt to maintain the packed-column at constant temperature. The water concentration in the feed solution was varied from 5% to 12% (weight basis). Although the initial concentration of ethanol in the flask was constant at the beginning of the experiment, it varied with time due to boiling. The breakthrough curves of water sorption on these adsorbents at different water contents showed that among the molecular sieves examined, type 3A molecular sieves gave the best separation of the ethanol–water system and among biobased adsorbents examined, natural palm stone was the best. The Guggenheim, Anderson, and De Boer (GAB) model at different water contents represented the isotherms for water sorption on molecular sieves and biobased adsorbents. In addition, the surface area of adsorbents and maximum water uptake were calculated. Type 3A molecular sieves were determined to have the largest surface area and the highest value of water uptake compared with the other two types of molecular sieve. However, for the biobased adsorbents, activated palm stone was found to have the largest surface area and the highest value of water uptake compared to the other biobased adsorbents. It was found that upon activation, the adsorption capacity of biobased adsorbents was not enhanced. On the contrary, the activation gave negative results on some occasions.