Effect of casting conditions on the performance of porous cellulose acetate membranes in reverse osmosis

Several sets of porous cellulose acetate membranes were made using the same casting solution composition and gelation conditions but varying the casting solution temperature and solvent evaporation conditions. The films were tested in reverse osmosis experiments at 250 psig using aqueous feed solutions containing 3500 ppm NaCl. The results show that the product rate obtained at a given level of solute separation is independent of evaporation time in the range tested and, for a given casting solution composition, the temperature of the casting solution and conditions of solvent evaporation during film formation together constitute an important interconnected variable governing the porous structure of the resulting membranes. These results offer a new approach to the problem of developing more productive reverse osmosis membranes and have led to a new class of porous cellulose acetate membranes capable of giving product rates 100% to 150% higher than those of the best membranes reported, at any given level of solute separation under the experimental conditions used. These results are of practical importance in low-pressure reverse osmosis applications.     

Effect of boron nitride addition on some properties of aluminosilicate refractories

Conclusions An addition of 10–60 wt.% of boron nitride significantly alters the thermal conductivity, thermal expansion, and the elastic modulus of aluminosilicate refractories.As the boron nitride content is increased from 1–60% the strength of specimens heated in a nitrogen atmosphere with an oxygen content of 0.02% decreases.During cyclic heat treatment in an oxidizing atmosphere between 900 and 20°C additional bonds develop between the particles of the aluminosilicate and the oxygen-free additive. As a result the strength of the specimen increases.The thermal shock resistance of the specimens increases with an increase in the amount of boron nitride addition. Specimens with 40–50% boron nitride addition are in practice insensitive to temperature drops in the range 20–2400°C.Aluminosilicate refractories with the addition of 30–40 wt.% of boron nitride can be used as lining material in high temperature systems with brief nonsteady or cyclic work schedules.Translated from Ogneupory, No. 4, pp. 36–39, April, 1968.     

HYDRODYNAMIC MODELLING IN AN AIR-LIFT LOOP REACTOR

A simple hydrodynamic model is proposed for use in the design, scale-up and characterization of external loop air-lift reactors. The approach is based upon a momentum balance for the flow loop coupled with a drift-flux equation for the reactor riser and establishes a rational basis for a predictive model relating gas throughput to induced liquid flow and gas hold-up in a range of air-lift reactors. The effective resistance of the reactor, k, defined in terms of the total loss coefficients of the reactor and the aerated height of the two-phase riser, was identified to allow for the quantification of the influence of reactor design on the hydrodynamic variables. An extensive body of data for the air-water system, collected on two reactors with active volumes of 0·055 m³ and 0·3 m³, is presented and used, in conjunction with literature data encompassing a wide range of reactor geometries and flow conditions, to define a unique relationship between flow behaviour and reactor configuration. The model, which accounts for the prevailing flow regime in the reactor, provides a direct method of predicting hydrodynamic behaviour in relatively non-viscous systems.     

Liquid Immiscibility in the Systems X2O-MO-B2O3-SiO2 (X=Na, K; M=Mg, Ca, Ba) and Na2O-MgO-BaO-B2O3-SiO2

The limits of miscibility at 650°C were determined for compositions with the mole ratio SiO₂/B₂O₃=1.07 in the systems X₂O-MO-B₂O₃-SiO₂ (X = Na,K; M = Mg,Ca,Ba) and Na₂O-MgO-BaO-B₂O₃-SiO₂. The form of the miscibility gaps in the quaternary systems is similar to that previously described for the system Na₂O-ZnO-B₂O₃-SiO₂. The topography of miscibility gaps in systems of this type is discussed in detail. The extent of the miscibility gap is correlated with the polarizing power of each cation, X and M (Na > K and Zn ≅ Mg > Ca > Ba) both among the seven quaternary systems and within the single five-component system examined. The possibility of using empirical correlations observed among the quaternary systems to predict the behavior of other compositions, or of more complex systems, is explored.     

Boundary layer model for char combustion and gasification

A non-steady boundary layer model is developed for numerical simulation of combustion and gasification of a single shrinking char particle. The model considers mass and energy conservation coupled with heterogeneous char reactions producing CO and homogeneous oxidation of CO to CO₂ in the boundary layer surrounding the char particle. Mass conservation includes accumulation, molecular diffusion, Stefan flow and generation by chemical reaction. Energy conservation includes radiation transfer at the particle surface and heat accumulation within the particle. Simulation results predict experimentally measured conversion and temperature profiles of a burning Spherocarb particle in a laminar flow reactor. Effects of bulk oxygen concentration and particle size on the combustion process are addressed. Predicted particle temperature is significantly affected by boundary layer combustion of CO to CO₂. With increasing particle size, char gasification to char combustion ratio increases, resulting in decreasing particle temperature and increasing peak boundary layer temperature.     

HEC influence on cement hydration measured by conductometry

Cellulose ethers are of universal use in factory-made mortars, though their influences on mortar properties at a molecular scale are poorly understood. Recent studies dealt with the influence of hydroxyethylmethyl cellulose (HEMC) and hydroxypropylmethyl cellulose (HPMC) molecular parameters on cement hydration. It was concluded that the degree of substitution is the most relevant factor on cement hydration kinetics, contrary to the molecular weight. Nevertheless, the major role played by the substitution degree has not been verified for other types of cellulose ethers such as hydroxyethyl cellulose (HEC), which generally possesses a higher hydration retarding capacity compared to HPMC and HEMC. In this frame, a study of the impact of HEC molecular parameters on cement hydration was performed. A negligible influence of the molecular weight was observed. Moreover, the results emphasize that the hydroxyethyl group content mainly determines the delay of cement hydration.     

Super-resolution: a comprehensive survey

Super-resolution, the process of obtaining one or more high-resolution images from one or more low-resolution observations, has been a very attractive research topic over the last two decades. It has found practical applications in many real-world problems in different fields, from satellite and aerial imaging to medical image processing, to facial image analysis, text image analysis, sign and number plates reading, and biometrics recognition, to name a few. This has resulted in many research papers, each developing a new super-resolution algorithm for a specific purpose. The current comprehensive survey provides an overview of most of these published works by grouping them in a broad taxonomy. For each of the groups in the taxonomy, the basic concepts of the algorithms are first explained and then the paths through which each of these groups have evolved are given in detail, by mentioning the contributions of different authors to the basic concepts of each group. Furthermore, common issues in super-resolution algorithms, such as imaging models and registration algorithms, optimization of the cost functions employed, dealing with color information, improvement factors, assessment of super-resolution algorithms, and the most commonly employed databases are discussed.     

The influence of water vapour on the transformation of γ calcium sulphate anhydrite to β anhydrite

The isothermal kinetics of the transformation of γ calcium sulphate anhydrite to β anhydrite have been determined. All the curves obtained have a sigmoidal form. We have also observed an influence of the water vapour pressure on the rate of formation of β anhydrite. On each plot of rate vs. water vapour pressure one observes a maximum whose position shifts to lower values of water vapour pressure when the temperature decreases. The formation of β anhydrite a low temperatures may be explained by the geometry of the water vapour pressure-temperature diagram of the hydrated forms of calcium sulphate, and by the “mineralizing” action of water vapour at or close to saturation.     

Hyper-Spherical Search (HSS) algorithm: a novel meta-heuristic algorithm to optimize nonlinear functions

This paper proposes a novel optimization algorithm called Hyper-Spherical Search (HSS) algorithm. Like other evolutionary algorithms, the proposed algorithm starts with an initial population. Population individuals are of two types: particles and hyper-sphere centers that all together form particle sets. Searching the hyper-sphere inner space made by the hyper-sphere center and its particle is the basis of the proposed evolutionary algorithm. The HSS algorithm hopefully converges to a state at which there exists only one hyper-sphere center, and its particles are at the same position and have the same cost function value as the hyper-sphere center. Applying the proposed algorithm to some benchmark cost functions shows its ability in dealing with different types of optimization problems. The proposed method is compared with the genetic algorithm (GA), particle swarm optimization (PSO) and harmony search algorithm (HSA). The results show that the HSS algorithm has faster convergence and results in better solutions than GA, PSO and HSA.     

Selektivhydrierung von Fettstoffen mit metallorganischen Mischkatalysatoren nach Ziegler-Sloan-Lapporte IV: Isomerenverteilung während der Hydrierung mehrfach ungesättigter Fettsäuremethylester

Selective Hydrogenation of Fats and Derivatives Using Ziegler-Type Organometallic Catalysts IV: Distribution of Isomers during Hydrogenation of Polyunsaturated Fatty Acid Methylesters Hydrogenation of methyl linoleate using a Ziegler-type catalyst, containing nickel stearate and triethyl aluminium, proceeds mainly without previous conjugation or trans-isomerization. Both olefinic double bonds are hydrogenated with equal probability. As long as the reaction mixture contains double unsaturated esters, these compounds are inhibiting hydrogenation and isomerization of single unsaturated esters. During hydrogenation of methyl linolenate there is only less selectivity to formation of methyl linoleate. Intermediate product is a mixture of single and double unsaturated fatty acid methylesters. In the latter compounds after consumption of triple unsaturated esters both double bonds are separated by two or more methylene groups. Polyenic compounds with 1,4-position of olefinic double bonds are preferably hydrogenated than polyenic compounds with greater distance between the double bonds.