Ostwald ripening in porous materials

The process of coarsening of an ensemble of clusters is investigated for the case that elastic strains due to matrix - cluster interactions change the process qualitatively as compared with dependencies established theoretically first by Lifshitz and Slezov. Such a qualitatively different behavior occurs always when the energy of elastic deformation in cluster growth increases more rapidly than linear with the volume of a cluster. Analytic solutions, for limiting cases, as well as numerical solutions, for the general case of coarsening in an ensemble of pores with a given pore size distribution, are presented. Possible applications are discussed.

Validation of plant dynamic model by online and laboratory measurements – a tool to predict online COD loads out of production of mechanical printing papers

COD discharges out of processes have increased in line with elevating brightness demands for mechanical pulp and papers. The share of lignin-like substances in COD discharges is on average 75%. In this thesis, a plant dynamic model was created and validated as a means to predict COD loading and discharges out of a mill. The assays were carried out in one paper mill integrate producing mechanical printing papers. The objective in the modeling of plant dynamics was to predict day averages of COD load and discharges out of mills. This means that online data, like 1) the level of large storage towers of pulp and white water 2) pulp dosages, 3) production rates and 4) internal white water flows and discharges were used to create transients into the balances of solids and white water, referred to as “plant dynamics”. A conversion coefficient was verified between TOC and COD. The conversion coefficient was used for predicting the flows from TOC to COD to the waste water treatment plant. The COD load was modeled with similar uncertainty as in reference TOC sampling. The water balance of waste water treatment was validated by the reference concentration of COD. The difference of COD predictions against references was within the same deviation of TOC-predictions. The modeled yield losses and retention values of TOC in pulping and bleaching processes and the modeled fixing of colloidal TOC to solids between the pulping plant and the aeration basin in the waste water treatment plant were similar to references presented in literature. The valid water balances of the waste water treatment plant and the reduction model of lignin-like substances produced a valid prediction of COD discharges out of the mill. A 30% increase in the release of lignin-like substances in the form of production problems was observed in pulping and bleaching processes. The same increase was observed in COD discharges out of waste water treatment. In the prediction of annual COD discharge, it was noticed that the reduction of lignin has a wide deviation from year to year and from one mill to another. This made it difficult to compare the parameters of COD discharges validated in plant dynamic simulation with another mill producing mechanical printing papers. However, a trend of moving from unbleached towards high-brightness TMP in COD discharges was valid.

Reações de Diels-Alder entre compostos carbonílicos a,b-insaturados e ciclopentadieno

We review herewith the use of solids such as activated alumina and other modern Lewis acid catalysts, as well as the influence of different solvents, including water, on the title reactions, described in the last seven years.

Parâmetros e símbolos a serem utilizados em Ressonância Magnética Nuclear

NMR is now frequently the technique of choice for determination of chemical structure in solution. Its uses also span structure in solids and mobility at the molecular level in all phases. The research literature in the subject is vast and ever-increasing. Unfortunately, many articles do not contain sufficient information for experiments to be repeated elsewhere, and there are many variations in the usage of symbols for the same physical quantity. It is the aim of the present recommendations to provide simple check-lists that will enable such problems to be minimised in a way that is consistent with general IUPAC formulation. The area of medical NMR and imaging is not specifically addressed in these recommendations, which are principally aimed at mainstream use of NMR by chemists (of all sub-disciplines) and by many physicists, biologists, material scientists and geologists etc. working with NMR.

Glicídios no mel

A review about composition, origin and importance of carbohydrates in honey is presented. Fructose and glucose are the major carbohydrates, ranging from 65-85 % of the total soluble solids. Other minor carbohydrates, chiefly di- and trisaccharides, have been also identified. Fructose, glucose and sucrose are mainly originated from nectar. Oligosaccharides are mainly formed by trans-alpha-D-glucosylation reactions catalysed by honeybee alpha-D-glucosidase. The profile of carbohydrates can be useful for the identification of the brazilian region in which honey was produced and may also be useful for testing brazilian honey authenticity.

Propelente sólido compósito polibutadiênico: I- influência do agente de ligação

In the Brazilian Complete Spacial Mission, the research of Vehicle Satellite Launcher is important. The solid propellant composite used in this vehicle is made with ammonium perchlorate, aluminiun powder and hydroxy terminated polibutadiene resin. In the propellant the bonding agent has a function to promote the interaction between solids and polimeric matrix, improving mechanical properties as stress, strain, aging characteristics and moisture embrittlement. Due its importance in propellant, bonding agent is consider as industrial secret and the literature about it is generic, without greater informations.

Development of a Filter Aid Proportioning, Mixing, and Feeding System for a Polishing Filter

The purpose of this work was to study the characteristics of the most commonly used filter aid materials and their influences on the design of proportioning, mixing, and feeding system for polishing filter family. Based on the literature survey and hands-on experience a system was designed with defined equipment and capital and operating costs. The system was designed to serve precoating and bodyfeeding applications and is easily extended to be used in multiple filter processes. Also a test procedure was carried out where influences of flux and filter cloths to accumulated cake were studied. Filter aid is needed in challenging conditions to improve filtration efficiency and cleaning, and thus extend the operating life of the filter media. Filter aid preparation and feeding system was designed for the use of two different filter aids; precoat and bodyfeed. Precoating is used before the filtration step initiates. If the solids in the filterable solution have a tendency to clog the filter bag easily, precoat is used on the filter bag to obtain better filtration efficiency and quality. Diatomite or perlite is usually used as a precoating substance. The intention is to create a uniform cake to the overall surface of the filter cloth, with predetermined thickness, 2 – 5 mm. This ensures that the clogging of the filter cloth is reduced and the filtration efficiency is increased. Bodyfeed is used if the solids in the filterable solution have a tendency to form a sticky impermeable filter cake. The cake properties are enhanced by maintaining the permeability of the accumulating cake by using the filter aid substance as bodyfeed during the filtration process.

Catalisadores Ni/Al2O3 promovidos com molibdênio para a reação de reforma a vapor de metano

Mo-promoted Ni/Al2O3 catalysts for the methane steam reforming reaction were studied in this work. The Ni/Al2O3 catalysts were prepared by precipitation and molibdenum was added by impregnation up to 2%wt. The solids were tested using a micro-reactor under two H2Ov/C conditions and were characterized by ICP-OES, XRD, N2 adsoption, H2 chemisorption and TPR. NiO and NiAl2O4 phases were observed and the metallic area decreased with the increase of the Mo content. From the catalytic tests high stability was verified for H2Ov/C=4.0. On the other hand, only the catalyst containing 0,05% Mo stayed stable during 30 hours of the test at H2Ov/C=2.0.

Offdesign operation of kraft recovery boiler

A model to solve heat and mass balances during the offdesign load calculations was created. These equations are complex and nonlinear. The main new ideas used in the created offdesign model of a kraft recovery boiler are the use of heat flows as torn iteration variables instead of the current practice of using the mass flows, vectorizing equation solving, thus speeding up the process, using non dimensional variables for solving the multiple heat transfer surface problem and using a new procedure for calculating pressure losses. Recovery boiler heat and mass balances are reduced to vector form. It is shown that these vectorized equations can be solved virtually without iteration. The iteration speed is enhanced by the use of the derived method of calculating multiple heat transfer surfaces simultaneously. To achieve this quick convergence the heat flows were used as the torn iteration parameters. A new method to handle pressure loss calculations with linearization was presented. This method enabled less time to be spent calculating pressure losses. The derived vector representation of the steam generator was used to calculate offdesign operation parameters for a 3000 tds/d example recovery boiler. The model was used to study recovery boiler part load operation and the effect of the black liquor dry solids increase on recovery boiler dimensioning. Heat flows to surface elements for part load calculations can be closely approximated with a previously defined exponent function. The exponential method can be used for the prediction of fouling in kraft recovery boilers. For similar furnaces the firing of 80 % dry solids liquor produces lower hearth heat release rate than the 65 % dry solids liquor if we fire at constant steam flow. The furnace outlet temperatures show that capacity increase with firing rate increase produces higher loadings than capacity increase with dry solids increase. The economizers, boiler banks and furnaces can be dimensioned smaller if we increase the black liquor dry solids content. The main problem with increased black liquor dry solids content is the decrease in the heat available to superheat. Whenever possible the furnace exit temperature should be increased by decreasing the furnace height. The increase in the furnace exit temperature is usually opposed because of fear of increased corrosion.

Tratamento de efluente da indústria de processamento de coco utilizando eletroflotação

Electroflotation (EF) with aluminum electrodes was applied in the treatment of Brazilian industrial coconut wastewater. The results show that EF with polarity inversion is a very good treatment when compared to others. The removal of pollutants in the wastewater after EF with polarity inversion was 96.3% of oils and grease, 99% of color and 66% of total organic carbon. Also, metal concentrations, turbidity and total solids were reduced.

Síntese e caracterização de alfa-fosfato de zircônio(IV) contendo agregados de cobre metálico

The alpha-zirconium (IV) hydrogenphosphate (alpha-ZrP) has received great attention in the last years due to its properties like ion exchange, intercalation, ionic conductivity and catalytic activity. This work reports a method to produce metallic copper clusters on alpha-ZrP to be used as catalysts in petrochemical processes. It was found that the solids were non-crystalline regardless of the uptake of copper and the reduction. The specific surface area increased as a consequence of the increase of the interlayer distance to accept the copper ions between the layers. During the reduction, big clusters of copper (0,5-11µ) with different sizes and shapes were produced.

Preparação de eletrodos opticamente transparentes

A simple experiment for the preparation of transparent conducting glass electrodes by deposition of pure and fluorine doped SnO2 films is described. This procedure was tested in the undergraduate inorganic course at IQ-UNICAMP. The success in achieving a conducting layer was easily checked using the standard probes of a volt-ohm meter. The optical transmittance and thickness were studied by UV-vis spectrophotometry. To discuss the experimental results we place significant emphasis on molecular orbital and energy band model theories. The undergraduate students can also discuss the concepts related to the electronic properties of solids and to interesting new materials, such as transparent conducting films, which are the subject of significant current research and technological applications.

Interações hiperfinas em catalisadores metálicos

Heterogeneous catalysts are of fundamental importance in several modern chemical processes. The characterization of catalysts is an issue of very present interest as it can provide a better understanding of the fundamental aspects of the catalytic phenomena, thus helping in the development of more efficient catalysts. In order to extend and improve the characterization of catalysts, new and less conventional methods are being applied, such as nuclear spectroscopies. In this paper we focus on the application of angular correlation, with can be used to resolve different local environments of probe atoms in solids and can be applied, as shown here, in the characterization of heterogeneous catalysts. A brief theoretical introduction is given and experimental results related to catalytic systems of alumina and niobia-supported Pt-In and Pd-In catalysts are presented.

Geoquímica das águas da bacia hidrográfica do Rio Descoberto, Brasília/DF - Brasil

The objective of this paper is to investigate the physical and chemical quality of the water of the Descoberto River during the dry and rainy seasons by measuring pH, temperature, electric conductivity, total dissolved solids, turbidity, color, alkalinity and NO3-, SO4(2-), PO4(3-), NH4+, Cl- and HCO3-, and the elements Sr, Mo, Cd, Y, Ti, Ca, V, Mg, Fe, Si, Ni, Zr, Cu, Al, Cr, Mn, Ba, Co, Zn, P, Na and K. The results showed high concentrations in both seasons, with dilution along the course of the river, minimizing for a while problems that compromise the quality of the water of this source. However, a progressive deterioration can occur due to an increase in the discharge of pollutants, resulting from population growth, agricultural activities and other factors.