The rate inhibiting effect of water as a product on reactions catalysed by cation exchange resins : formation of mesityl oxide from acetone as a case study

It is known that when water is a product in reactions catalysed by cation exchange resins, it inhibits the reaction rate much more than predicted by the reverse reaction or dilution effects. In this work the inhibiting effect is ascribed to the preferential association of the catalytically active sites with water. In the derivation of the kinetic model, a Freundlich type adsorption isotherm was used to quantify the number of sites occupied by water. This is combined with a power law expression for the reaction rate. The resultant expression can accurately predict the reaction rate for various initial concentrations of water and mesityl oxide. Even when water was initially added to the reaction mixture, this model still gave an absolute average error of 6.5% compared to a 54.6% error when the same approach was followed but with the more popular Langmuir isotherm to describe site deactivation. The kinetic expression previously proposed for this reaction system by Klein and Banchero also failed when water was added to the reaction mixture and gave an average error of 71.1%. The procedure used to derive the model is therefore suggested for all cation exchange catalysed reactions where water is one of the products.Dissertation (MSc)--University of Pretoria, 2005.Chemical Engineeringunrestricte

Effect of fines content on bubble properties in a two-dimensional fluidized bed by digital image analysis

The effect of fines content in fluid catalytic cracking (FCC) catalyst on bubble properties was investigated by considering two catalyst batches. One contained fewer fines and had a Sauter mean diameter of 83 μm while the other had a higher fines content with a 74 μm mean diameter. The hydrodynamics were analyzed in a two-dimensional fluidized bed with superficial gas velocities in the bubbling regime. Photos of the bed were analysed by isolating bubble images, after which colour images were converted to binary images by using MATLAB® software. These binary images were used to determine properties such as equivalent bubble diameter, gas fraction, circularity and bubble hold-up in the bed as function of superficial gas velocity and fines content. The results showed that bubble diameter increases with gas velocity for both catalyst batches. A smaller bubble size was observed at all except the highest superficial velocities for the catalyst batch with the higher fines content. However, the high fines content catalyst had a higher gas fraction than the low fines content batch at all gas velocities. This average value was the same regardless of gas velocity, while an increase in superficial velocity resulted in an increase in gas fraction for the lower fines content catalyst. The bubble hold-up for the catalyst batch with the lower fines content was also higher than that of the high fines content catalyst. For both batches an increase in bubble hold-up with velocity was observed. Similar circularity values for both catalyst types were calculated at all superficial velocities.http://www.saiche.co.za/article.aspam2013ai201

Axial variation of wetting efficiency and liquid-solid mass transfer in long trickle bed columns

The wetting efficiency and solid liquid mass transfer coefficient was measured separately and simultaneously using the electrochemical cell technique while varying the superficial liquid velocity and hydrodynamic state of the column by using different pre-wetting procedures. The wetting efficiency in columns with an aspect ratio - distance from distributor divided by column diameter – of up to 33, decreased with distance from the distributor regardless of the hydrodynamic state of the column. Although the solid liquid mass transfer coefficient also decreased with an increase in axial position, this decrease was much more significant where the pre-wetting procedure that resulted in a lower overall wetting efficiency was used. When a pre-wetting procedure that resulted in a higher average wetting efficiency was used, the liquid solid mass transfer coefficient was much less dependent on liquid velocity and only a relatively small decrease with axial position was observed. The results highlight the difference in surface renewal processes that is possible between columns operated at the same conditions but under different hydrodynamic states and emphasise the importance of hydrodynamic multiplicity when liquid redistribution is considered.http: pubs.acs.org/IECRhb201

Deep eutectic solvents for solid pesticide dosage forms

Deep eutectic solvents aid the formulation of solid pesticide dosage forms for water-insoluble actives. This was demonstrated by encapsulating Amitraz powder in a low-melting matrix based on the eutectic mixture of urea (32 wt%) and 1,3-dimethylurea. Dissolution in water of melt-cast discs, containing 20 wt% active, led to the rapid release of Amitraz in a finely dispersed form. The order of magnitude reduction in particle size, after dissolution, is ascribed to the solubilization of Amitraz in the hot deep eutectic solvent and its subsequent precipitation as a separate phase on crystallization of the matrix.The Institute of Applied Materials, University of Pretoriahttp://www.nature.com/srepam2021Chemical Engineerin

Breakdown mechanisms of oil-in-water emulsions stabilised with Pluronic F127 and co-surfactants

Please read abstract in the article.The University of Pretoria and the Institute of Applied Materials for a stipend to AK, the Council for Scientific and Industrial Research (CSIR) for allowing access to the surface tension instrument and to BASF for donation of the Pluronic F127 block copolymer.http://www.elsevier.com/locate/colsurfa2021-01-20hj2019Chemical Engineerin

Kinetic model for the dimerisation of 1-hexene over a solid phosphoric acid catalyst

Batch kinetic experiments at 150 °C, 200 °C and 250 °C showed that the reaction can be modeled with a three step sequential reaction scheme. This involves firstly linear isomerisation of 1-hexene followed by skeletal isomerisation and finally dimerisation and cracking. The first and last steps in the sequence are modeled as reversible reactions. When first order reaction kinetics is assumed for each of the reactions, the model gave a very good representation of the experimental data. In order to test the validity of the series pathway hypothesis, the reaction was repeated with a skeletal hexene isomer – 2,3-dimethyl-2-butene (DMB) – as reactant. Although the rate and equilibrium constants for the third reaction step as obtained from the 1-hexene conversion data gave a good prediction of the DMB conversion at 200 °C and 250 °C, it failed to predict the reaction rate at 150 °C. This suggests that a different reaction pathway – where linear hexene isomers are directly converted to dimer product – becomes more significant at lower temperatures. The relatively high activation energy of the linear to skeletal hexene reaction may be to blame for this observation. However, this needs to be confirmed be further experimental work. The same equilibrium conversions of both 1-hexene and DMB were observed at all three temperatures investigated—suggesting that the equilibrium conversion is independent of the type of hexene isomer in the reaction mixture

Extruded cellulose/ionic liquid carbon scaffolds

Monolithic carbon scaffolds were obtained by pyrolysis of regenerated cellulose. First, microcrystalline cellulose was compounded, at a 1:1 mass ratio, with 1-ethyl-3-methylimidazolium acetate, choline chloride or a mixture of the two ionic liquids. Test bars were extrusion-molded and the ionic liquid removed by leaching with water. The porous cellulose bars were carbonized at 800 °C in a nitrogen atmosphere. The Raman ID/IG peak intensity ratios ranged from 0.74 to unity confirming the formation of amorphous carbon. Scanning electron microscopy revealed a highly porous structure consisting of both micro- and nanopores.https://aip.scitation.org/journal/apcpm2021Chemical Engineerin

Estimating binary liquid composition from density and refractive index measurements : a comprehensive review of mixing rules

A comprehensive review of refractive index mixing rules of binary solutions is presented. All published mixing rules, with the exception of the Wiener mixing rule, can be reformulated into expressions with a linear dependence in either mole- or volume-fractions. Comparison of the predictive performance of both types of linear mixture models show that mixture models which are linear in volume fractions fail to represent real data trends. Mixture refractive index data reveal that both positive and negative deviations from linear behaviour in this property with volume fraction can occur, explaining the inability of linear models in volume fraction to be generally applicable. Improved data fits are possible with the modified Eykman and the power mean mixing rules, provided that in both cases the adjustable constant can be tuned for each binary system of interest. Only the Lorentz-Lorenz molar refraction mixing rule that is linear in mole fraction provides excellent data fits for all the systems investigated, allowing for prediction of composition of solutions from combined density and refractive index measurements. The aforementioned conclusions are derived from extensive experimental data of binary systems consisting of n-alkanes (C12 to C32) and different organic solvents, ultimately providing a tool to determine liquid composition from refractive index measurements.The Deutsche Forschungsgemeinschaft (DFG)http://www.elsevier.com/locate/molliq2022-03-17hj2021UP Centre for Sustainable Malaria Control (UP CSMC

Dextrin nanocomposites as matrices for solid dosage forms

Safe application of water-insoluble acaricides requires fast release from solid dosage systems into aquatic environments. Dextrin is a water-soluble form of partially hydrolyzed starch, which may be used as matrix material for these systems if retrogradation can be inhibited by the inclusion of nanofillers. Several glycerol-plasticized thermoplastic dextrin-based nanocomposites were prepared with a twin-screw extrusion-compounding process. The nanofillers included a layered double hydroxide (LDH), cellulose nanofibers (CNF), and stearic acid. The time-dependent retrogradation of the compounds was monitored by X-ray diffraction (XRD) and dynamic mechanical thermal analysis (DMA). XRD showed that composite samples that included stearic acid in the formulation led to the formation of an amylose-lipid complex and a stable crystallinity during aging. The most promising nanocomposite included both stearic acid and CNF. It was selected as the carrier material for the water-insoluble acaricide Amitraz. Fast release rates were observed for composites containing 5, 10, and 20% (w/w) of the pesticide. A significant reduction in the particle size of the released Amitraz powder was observed, which is ascribed to the high-temperature compounding procedure.PAMSA and the Department of Science and Innovationhttps://pubs.acs.org/journal/aamickhj2021Chemical EngineeringConsumer ScienceFood Scienc

Mosquito repellent thermal stability, permeability and air volatility

Please read abstract in the article.The Deutsche Forschungsgemeinschaft (DFG) (Grant AN 212/22-1).https://onlinelibrary.wiley.com/journal/152649982021-03-01hj2020Chemical EngineeringChemistryUP Centre for Sustainable Malaria Control (UP CSMC