South African Journal of Chemical Engineering - latest Issue
Volume 22, Issue 1, 2016
Citrus aurantium leaves extracts as a sustainable corrosion inhibitor of mild steel in sulfuric acidSource: South African Journal of Chemical Engineering 22, pp 1 –5 (2016) http://dx.doi.org/10.1016/j.sajce.2016.07.002More Less
Corrosion inhibition of mild steel in 1 M H2SO4 was investigated in absence and presence of Citrus aurantium leaves extracts as a friendly inhibitor. The effect of temperature, time, and inhibitor concentration were studied using weight loss technique. The result obtained revealed that Citrus aurantium leaves extracts act as an inhibitor for mild steel in H2SO4 and reduces the corrosion rate. The inhibition efficiency was found to increases with increase in inhibitor concentration whereas the temperature shows otherwise. Higher inhibition efficiency was 89% at 40 °C and 10 ml/l inhibitor concentration. The adsorption of Citrus aurantium leaves extracts was found to follow Langmuir adsorption isotherm model. The values of the free energy of adsorption was around -20 kJ/mol, which is indicative of physical adsorption between charged molecules and a charged metal. Quantum chemical calculations were also used as a theoretical support to the experimental results. Finally the scanning electron microscope and Fourier transform infrared spectroscopy were evaluated to examine surface morphology and molecular structure of inhibitor respectively.
Source: South African Journal of Chemical Engineering 22, pp 6 –16 (2016) http://dx.doi.org/10.1016/j.sajce.2016.07.001More Less
Artificial Neural Network (ANN)-Genetic Algorithm (GA) interface and Response Surface Methodology (RSM) have been compared as tools for simulation and optimization of gmelina seed oil extraction process. A multi-layer feed-forward Levenberg Marquardt backpropagation algorithm was incorporated for developing a predictive model which was optimized using GA. Design Expert simulation and optimization tools were also incorporated for a detailed simulation and optimization of the same process using Response surface methodology (RSM). It was found that oil yield increased with rise in temperature, time and volume of solvent but decreased with increase in seed particle size. The maximum oil yield obtained using the numerical optimization techniques show that 49.2% were predicted by the RSM at the optimum conditions of; 60 °C temperature, extraction time 60 min, 150 mm seed particle size, 150 ml solvent volume and 49.8% by ANN-GA at extraction temperature 40 °C, extraction time 40 min, 200 mm seed particle size, 100 ml solvent volume, respectively. The prediction accuracy of both models were more than 95%. Models validation experiments indicate that the predicted and the actual were in close agreement. The extract was analyzed to examine its physico-chemical properties (acid value, iodine value, peroxide value, viscosity, saponification value, moisture and ash content, refractive index, smoke, flash and fire points and specific gravity) and structural elucidation by standard methods and instrumental techniques. Results revealed that the oil is non-drying and edible. Desaturation of the oil further reveal its potential in alkyd resin synthesis.
Comparison of constitutive and inducible β-fructofuranosidase production by recombinant Pichia pastoris in fed-batch culture using defined and semi-defined mediaSource: South African Journal of Chemical Engineering 22, pp 17 –22 (2016) http://dx.doi.org/10.1016/j.sajce.2016.10.001More Less
Short-chain fructooligosaccharides produced from sucrose by transfructosylation using β-fructofuranosidase (FFase), an industrially important enzyme, finds application in prebiotics, sweeteners and confectionary products. Using recombinant Pichia pastoris, the influence of replacing the commonly-used Invitrogen® medium with a semi-defined medium for FFase production under the control of the glyceraldehyde-3-phosphate dehydrogenase (GAP) and alcohol oxidase (AOX) promoters was investigated. Replacing the trace metals (PTM1) solution with yeast extract resulted in a 54.3% decrease in FFase volumetric activity under control of the AOX promoter, suggesting a distinct requirement for trace metals for recombinant protein synthesis during methanol induction, given that the biomass yield on methanol decreased by only 10%. The same medium adjustment had no effect on enzyme production under GAP promoter control, although AOX promoter control resulted in double the FFase volumetric activity compared to glycerol-fed cultures. Decreasing basal salts by half did not affect the cultures, but alleviated precipitation during sterilisation. Optimisation of the glycerol feed rate and dissolved oxygen tension in DO-stat fed-batch fermentations using the semi-defined medium resulted in 17% increase in volutmetric activity of FFase expressed under the GAP promoter. This study highlighted the influence of carbon source and trace metals on heterologous protein production by P. pastoris using constitutive and inducible promoters.