Bushra Al-Duri

Application of branched pore diffusion model in the adsorption of reactive dyes on activated carbon

Abstract In this work, the branched pore diffusion model (BPDM) was applied to the single component adsorption of three reactive dyes on activated carbon in a batch stirred vessel. Results are in terms of theoretical concentration decay curves, characterised by the non-linear combination of four mass transfer parameters namely the external mass transfer coefficient k f , the solid diffusivity D s , the micropore rate coefficient k b and the fraction micropores f . An ‘improved’ solution technique was presented where an optimising subroutine was employed to select ‘best’ combination of the mass transfer parameters. Compared to the existing methods, this yielded more accurate results over a longer period of adsorption and shorter computational time. Also, equilibrium was accurately described by the Fritz–Schlunder isotherm. Results showed that, over a wide range of system conditions, a single k f , k b and f value described each dye/carbon system; while D s increased with the initial solution concentration, C 0 . Furthermore, D s was mathematically related to the surface loading q s . This paper provides an in-sight into the relation between the sorbent surface, the solute properties and the adsorptive characterictics.

Modelling the extraction of essential oils with compressed carbon dioxide

Abstract Three models were used to describe the extraction of essential oils from oregano bracts using compressed carbon dioxide. They were developed on the basis of a plate-like geometry of the particles and were tested experimentally using various bract pre-treatments, pressures, temperatures and solvent flow rates. The two particle phase derived models applied, the Single Plate model (SP model) and the Simple Single Plate model (SSP model), differ only by the allowance or not for a film coefficient (kf) and have as the only adjustable parameter the matrix diffusivity (Dm). The third model, the Fluid Phase/Simple Single Plate model (FP/SSP model), considers both the particle mass balance and a detailed description of the fluid mass balance. In addition to the matrix diffusivity the FP/SSP model may require the adjustment of the fraction of oil leached by the solvent during the pressurisation procedure (f0). All models gave a good fit to the experimental data though the FP/SSP model gave the best fit. However, the matrix diffusivities found correlated very poorly with the estimated diffusivity of essential oils in carbon dioxide (D12), which indicates a complex intraparticle transport.

Esterification of oleic acid and ethanol in plug flow (packed bed) reactor under supercritical conditions: Investigation of kinetics

Abstract The present work provided the reaction kinetic data, required to predict the performance of packed-bed plug flow bioreactor operating under supercritical conditions. It investigated the kinetics of esterification of oleic acid and ethanol. Biocatalyst Lypozyme™ IM60, which is lipase from Rhizomucor miehei immobilised on Duolite (an ion exchange resin), was employed to synthesise ethyl oleate. Experimentally, esterification was carried out using a range of oleic acid- and ethanol concentrations, respectively. The effect of water concentration on the enzyme activity was also investigated. Analytically, the reaction mechanism was investigated by a series of kinetic analysis using the Direct Linear, the Primary and the Burke–Lineweaver (double reciprocal) plots. The reaction was modelled by the Henri–Michaelis–Menten equation and the reaction constants, namely Km and Vmax, were evaluated. It was found that the initial water concentration in the system effected the enzyme initial activity in a bell-like manner, giving an optimum (enzyme activity,and water concentration) value for each alcohol concentration. Furthermore, it was found that under higher alcohol concentrations, the reaction experienced substrate inhibition. The latter was identified to be competitive inhibition under moderate alcohol concentrations and non-competitive inhibitions under high alcohol concentrations. Hence, reaction inhibition constant value Ki was calculated.

Kinetic studies on immobilised lipase esterification of oleic acid and octanol

The present work investigates the reaction kinetics of immobilised lipase esterification of oleic acid and octanol, in a solvent-free system. Lipase from Rhizomucor miehei was immobilised on a hydrophobic support. The initial reaction rate was investigated as a function of octanol concentration and temperature, and the reaction kinetics were described in terms of the Michaelis-Menten mechanism. Evaluating K m , V max and k cat /K m as a function of temperature, it was found that K m was minimum and k cat /K m was maximum at 40°C while V max was maximum at 50°C. Furthermore, applying the Ping Pong Bi Bi mechanism yielded good results for this two-substrate system.

Efficient batch and continuous flow Suzuki cross-coupling reactions under mild conditions, catalysed by polyurea-encapsulated palladium (II) acetate and tetra-n-butylammonium salts

Suzuki cross-coupling reactions are effected in both conventional organic solvents, under continuous flow conditions at 70 degree C, and in batch mode in supercritical carbon dioxide (scCO2), at temperatures as low as 40 degrees C in the presence of palladium(II) acetate microencapsulated in polyurea [PdEnCat] and tetra-n-butylammonium salts.

Concentration-dependent surface diffusivity model (CDSDM): numerical development and application

Abstract In this paper, the film-solid diffusion model (FSDM) combined with a concentration-dependent surface diffusivity D s =D 0 exp {k(q/q sat )} was presented to describe the kinetics of adsorption of reactive dye from aqueous solution onto activated carbon in a batch reactor. A finite-difference scheme was employed to solve the partial differential equations which govern the entire adsorption process in the batch reactor and the resulting kinetic data was presented in terms of the concentration decay curve. It was found that, for the investigated adsorption system, one set of mass transfer parameters was adequate to describe the adsorption rate at different initial solute concentrations. Compared with the constant surface diffusivity model (CSDM), the concentration-dependent surface diffusivity model (CDSDM) yielded a steeper solid-phase concentration profile due to the concentration dependence of Ds. Parametric sensitivity analysis was also carried out in order to facilitate understanding of the effect of each parameter on the shape of the concentration decay curve.

A facile acidic choline chloride–p-TSA DES-catalysed dehydration of fructose to 5-hydroxymethylfurfural

The conversion of lignocellulosic biomass to biofuel precursors has recently been a focus of intensive research due to the essential role of biofuels as transport fuels in the future. Specifically, the conversion of fructose to 5-hydroxymethylfurfural (5HMF) has gained momentum, as 5HMF is a versatile bio-based platform molecule that leads to a plethora of high-value chemicals and biofuel molecules, such as DMF. Herein, we report the use of an environmentally friendly, Bronsted acidic, deep eutectic mixture consisting of choline chloride (ChCl) and p-TSA for the dehydration of fructose to 5HMF. Unlike previous systems, the use of ChCl–p-TSA plays a dual role, as both a hydrogen bond donor (HBD) and a catalyst for the dehydration reaction, thus obviating the addition of an external acid. The reaction was examined and optimised in a batch system, where it was found that fructose was readily dehydrated to 5HMF. The best reaction conditions, with the highest 5HMF yield of 90.7%, were obtained at a temperature of 80 °C using a DES molar mixing ratio of 1 : 1 ChCl : p-TSA and feed ratio of 2.5%, and with a reaction time of one hour.

Lipase-catalysed esterification of oleic acid and ethanol in a continuous packed bed reactor, using supercritical CO2 as solvent : approximation of system kinetics

This work investigated the immobilised lipase kinetics of esterification of oleic acid and ethanol. The reaction was conducted under supercritical conditions (13 × 106 Pa and 40 °C) using carbon dioxide as solvent in a continuous packed bed (plug flow) reactor. Biocatalyst LypozymeTM IM60, which is lipase from Rhizomucor miehei (EC.3.1.1.3), immobilised on Duolite (anionic exchange resin) was used as biocatalyst. Kinetically, with regard to oleic acid, the reaction was successfully modelled by the Michaelis–Menten mechanism. The reaction rate constants Km and Vmax were evaluated. Furthermore, it was found to undergo competitive inhibition by ethanol, and the inhibition constant Ki was evaluated. © 2000 Society of Chemical Industry

Modelling the disruption of essential oils glandular trichomes with compressed CO2

Abstract A theoretical model is proposed for the evaluation of the disruption efficiency of essential oils glandular trichomes (glands) with compressed CO 2 . The disruption of glands occurs during the fast decompression of the bed of herbaceous material. The glands are described as closed structures slightly permeable to CO 2 . When exposed to compressed CO 2 , the gas slowly penetrates the glands and dissolves in the intraglandular oil until the solubility limit is reached. During the fast decompression of the bed, the dissolved gas is desorbed from the oil phase and discharged to the bulk solvent. The inability of the glands to discharge the gas, at a rate dictated by the loss of solubility in the oil with the decompression of the bed, generates a pressure gradient across the glands that may lead to its rupture. In the present model, the excess pressure is described by an equation similar to Hagen–Poiseuilles formula for viscous flow due to a pressure gradient. The maximum pressure gradient across the glands during the fast decompression of the bed is then used to calculate the percentage of glands disrupted (efficiency of disruption) assuming a normal distribution of the bursting pressures of the glands. The model was applied to experimental results where the effects of pre- and post-expansion pressure, exposure time to pre-expansion pressure and the rate of decompression were investigated. Predictions of the model are also presented.

Predictive control of coal mills for improving supercritical power generation process dynamic responses

The paper is to study new control strategies for improvement of dynamic responses of a supercritical power generation process through an improved control to the associated fuel preparation performed by the coal milling process. Any control actions taking for the milling process will take a long time to show their influences onto the boiler, turbine and generator responses as the whole process experiences coal transmission, grinding, drying and blowing to the furnace. The control philosophy behind the work presented in the paper is to develop a control strategy to achieve prediction of the future demand for fuel input and implement control actions at the earliest possible time. The paper starts from description of the nonlinear mathematical model developed for the supercritical coal fired power plant and then moves onto control strategy development. Finally, the simulation study has been carried out to demonstrate the effect of the new predictive control.