Research Articles (Chemical Engineering)

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The applicability of nanofiltration for the treatment and reuse of textile reactive dye effluent
(Water Research Commission, 2015) Chollom, M. N.; Rathilal, S.; Pillay, V. L.; Alfa, Dorcas
The main aim of the study was to test the feasibility of using nanofiltration (NF) processes for the treatment of reactive dyebath effluents from the textile industry, in order to recover the water and chemicals (salts) for reuse purposes. The study of the reusability of nanofiltered water for dyeing has been given little or no attention. About 30% of reactive dyes remain unfixed on fibres; the unfixed dyes are responsible for the colouration in effluents. Membrane processes were employed to treat reactive dye-bath effluents to recover the salts and water. Investigations were conducted firstly with ultrafiltration (UF) used as a pretreatment for NF. Secondly, evaluations were performed for 2 types of NF membranes (SR90 and NF90), in terms of quality of permeate produced and fluxes achieved for 2 different samples of effluent. The effect of cleaning on membrane performance was assessed. A reusability test was carried out on both permeate samples for dyeing light and dark shade recipes. The use of UF as pre-treatment to NF resulted in rejection of colloidal substances > 90% and a 15% flux improvement. Permeate from NF90 had a conductivity of 76 µS/cm and total organic carbon (TOC) of 20 mg/ℓ, as compared to SR90 which had a conductivity of 8.3 mS/cm and a TOC of 58 mg/ℓ. Light shade from NF90 gave satisfactory results on dyeing, with no colour difference. However a variation in colour was noticed when the medium sample was used to dye the light shade. Both NF permeates gave satisfactory results when used to dye the dark shades. Permeate from NF90 was within the accepted range for reuse, while permeate from SR90 had a higher salt recovery. Chemical cleaning resulted in 80% flux recovery. From the reusability test it was concluded that permeate from NF90 met the reuse criteria for feed water to the dye bath.
The application of activated carbon for the adsorption and elution of platinum group metals from dilute cyanide leach solutions
(Southern African Institute of Mining and Metallurgy, 2013) Snyders, C. A.; Mpinga, C. N.; Bradshaw, S. M.; Akdogan, G.; Eksteen, J. J.
ENGLISH ABSTRACT: The research presented in this paper investigated the practical aspects of the recovery of platinum group metals (PGMs) from a dilute cyanide leach solution containing base metals, in a manner similar to that used for gold extraction in a typical CIP process, and focuses on both the adsorption and elution stages. The carrierphase extraction of precious metals using activated carbon offers significant advantages over other processes in terms of simplicity, the high pre-concentration factor, rapid phase separation, and relatively low capital and operating costs. As a sorbent, activated carbon is still by far the most important material because of its large surface area, high adsorption capacity, porous structure, negligible environmental toxicity, low cost, and high purity standards. Adsorption tests were conducted on a pregnant alkaline leach solution (0.15 ppm Pt, 0.38 ppm Pd, 0.1 ppm Au) resulting from cyanide extraction performed in column leach tests. The initial adsorption rates of Pt, Pd, and Au were very fast and recoveries of these three metals were approximately 90 per cent after 2 hours, and 100 per cent for Pt, 97.4 per cent for Pd, and 99.9 per cent for Au after 72 hours. The parameters that influence the extraction of PGMs and Au were examined to assess their relative importance during the adsorption process in order to provide the basis for process optimization. The concentration of thiocyanate was not identified as significant factor for PGMs adsorption, while Ni concentration was the most significant extraction process parameter. Base metal cyanide complexes adsorb and compete with the PGM complexes for sites on activated carbon, and while copper adsorption can be minimized by adjusting the residence time, Ni adsorbs at approximately the same rate as the PGMs, influencing the loading capacity and adsorption kinetics of the PGMs. The feasibility of eluting platinum and palladium cyanide complexes from activated carbon using an analogue of the AARL process was investigated. Platinum and palladium elute from activated carbon almost to completion in 4 to 5 bed volumes at 80°C, while the elution of gold at this temperature is slow, with a significant amount of gold still to be eluted after 16 bed volumes. The equilibrium loading of gold is exothermic in nature (Fleming and Nicol, 1984) which will result in an increase in gold elution kinetics with an increase in temperature at similar pre-treatment conditions. A similar result was found for the elution of Pt and Pd. Cyanide pre-treatment was found to have a significant influence on PGM elution. Higher cyanide concentration in the pre-treatment step results in more efficient elution up to a point, and results suggest the possibility of an optimum cyanide concentration, beyond which elution efficiency starts decreasing due to increased ionic strength.
Application of membrane technology in a base metal refinery
(Southern African Institute of Mining and Metallurgy, 2013) Nel, D. W.; Van der Gryp, P.; Neomagus, H. W. J. P.; Bessarabov, D. G.
Nanofiltration (NF) has attracted much attention over the past few years due to the reduced energy consumption compared to reverse osmosis (RO) and better separation performance compared to ultrafiltration (UF). Although research has been done in the area of NF of nickel ions, sodium ions, and acid separation, not much attention has been given to the separation of high nickel concentrations from sulphuric acid streams. The use of NF for the separation of nickel and acid from a spent nickel electrolyte is an innovative process alternative for future industrial application within a base metal refinery. In this study, the separation performance of a composite polyamide NF membrane on a spent nickel electrolyte was investigated by varying the sodium sulphate concentration in the feed (50–150 g/l ), the trans-membrane pressure (35-55 bar), and cross-flow velocity (1.5-3.5 m/s), and measuring quantities such as total permeate flux, acid rejection, nickel rejection, and sodium rejection. The nickel and acid concentration in the feed were kept constant with variations between 40-60 g/l and 25-40 g/l respectively, while the temperature of the experiments was kept constant at 50˚C. The membrane was found to be very selective for nickel ions, with the rejection of nickel ions varying between 54.4% and 98.2%. The rejection of acid ions varied between -5.9% and 21.8%. The rejection of sodium ions varied between 16.6% and 72.4% at a cross-flow velocity of 2.5 m/s and sodium sulphate concentration of 50 g/l in the feed solution. An increase in trans-membrane pressure increased the rejection of nickel, sodium, and acid ions, while an increase in sodium sulphate concentration decreased the rejection of nickel and acid ions. The total permeate flux was found to increase with an increase in trans-membrane pressure and decrease with an increase in sodium sulphate concentration. The cross-flow velocity had an insignificant effect on the total permeate flux and the rejection of nickel, sodium and acid ions.
Applications of microwave heating in mineral processing
(Academy of Science of South Africa, 1999) Bradshaw, S. M.
Many minerals are effective absorbers of microwave energy, whereas in general gangue materials are not. This suggests applying microwave heating to mineral processing to effect selective heating of mineral phases. Many mineral processing applications have been tested only on a laboratory scale; the engineering realities of large-scale operations have largely been overlooked. Of particular concern are the modest power outputs of industrial magnetrons relative to the power requirements in mineral processing operations, the high capital cost of microwave equipment and the poor penetration depth of microwaves. Review of these applications, and comparison with guidelines developed for successful microwave technology transfer, suggests that niche areas for microwave heating are in the processing of low-throughput concentrates, especially where volumetric heating leads to enhanced rates of energy transfer. The use of combined heating sources should be investigated.
Canary in the coliform mine : exploring the industrial application limits of a microbial respiration alarm system
(Public Library of Science, 2021-03-04) Stone, Wendy; Louw, Tobi M.; Booysen, Marthinus J.; Wolfaardt, Gideon M.; Zhang, Dawei
Fundamental ecological principles of ecosystem-level respiration are extensively applied in greenhouse gas and elemental cycle studies. A laboratory system termed CEMS (Carbon Dioxide Evolution Measurement System), developed to explore microbial biofilm growth and metabolic responses, was evaluated as an early-warning system for microbial disturbances in industrial settings: in (a) potable water system contamination, and (b) bioreactor inhibition. Respiration was detected as CO₂ production, rather than O₂ consumption, including aerobic and anaerobic metabolism. Design, thresholds, and benefits of the remote CO₂ monitoring technology were described. Headspace CO₂ correlated with contamination levels, as well as chemical (R² > 0.83–0.96) and microbiological water quality indicators (R² > 0.78–0.88). Detection thresholds were limiting factors in monitoring drinking water to national and inter- national standards (0 CFU/100 mL fecal coliforms) in both open- (>1500 CFU/mL) and closed-loop CO₂ measuring regimes (>100 CFU/100 mL). However, closed-loop detection thresholds allow for the detection of significant contamination events, and monitoring less stringent systems such as irrigation water (<100 CFU/mL). Whole-system respiration was effectively harnessed as an early-warning system in bioreactor performance monitoring. Models were used to deconvolute biological CO₂ fluctuations from chemical CO₂ dynamics, to optimize this real-time, sustainable, low-waste technology, facilitating timeous responses to biological disturbances in bioreactors.
CFD modelling of global mixing parameters in a Peirce-Smith converter with comparison to physical modelling
(Berkeley Electronic Press, 2011) Chibwe, Deside K.; Akdogan, Guven; Aldrich, Chris; Eric, Rauf H.
The flow pattern and mixing in an industrial Peirce-Smith converter (PSC) has been experimentally and numerically studied using cold model simulations. The effects of air volumetric flow rate and presence of overlaying slag phase on matte on the flow structure and mixing were investigated. The 2-D and 3-D simulations of the three phase system were carried out using volume of fluid (VOF) and realizable k - ɛ turbulence model to account for the multiphase and turbulence nature of the flow respectively. These models were implemented using commercial Computational Fluid Dynamics (CFD) numerical code FLUENT. The cold model for physical simulations was a 1:5 horizontal cylindrical container made of Perspex with seven tuyeres on one side of the cylinder typifying a Peirce-Smith converter. Compressed air was blown into the cylinder through the tuyeres, simulating air or oxygen enriched air injection into the PSC. The matte and slag phases were simulated with water and kerosene respectively in this study. The influence of varying blowing conditions and simulated slag quantities on the bulk mixing was studied with five different air volumetric flow rates and five levels of simulated slag thickness. Mixing time results were evaluated in terms of total specific mixing power and two mixing time correlations were proposed for estimating mixing times in the model of PSC for low slag and high slag volumes. Both numerical and experimental simulations were in good agreement to predict the variation characteristics of the system in relation to global flow field variables set up in the converter through mathematical calculation of relevant integrated quantities of turbulence, Volume Fraction (VF) and velocity magnitudes. The findings revealed that both air volumetric flow rate and presence of the overlaying slag layer have profound effects on the mixing efficiency of the converter
Characterization of precipitate formed during the removal of iron and precious metals from sulphate leach solutions
(The Southern African Institute of Mining and Metallurgy, 2017-08) Coetzee, R.; Dorfling, C.; Bradshaw, S. M.
ENGLISH ABSTRACT: Nickel sulphate leach solutions produced in the first leaching stage of base metal refineries contain impurities such as iron as well as precious metals (Rh, Ru, and Ir). Iron precipitation results in sludge formation, which needs to be controlled for efficient operation of downstream nickel recovery processes. Recovery of precious metals from the leach solution is also desired. This study aimed to evaluate the characteristics of the precipitate produced from a nickel sulphate leach solution containing 62.5–89.3 g/L Ni, 2.5 – 3.57 g/L Fe, and 10 mg/L of each of Rh, Ru, and Ir. Seeded precipitation from ferric-containing solutions resulted in precipitates with a d₅₀ particle size of 100.6 μm, which was two orders of magnitude larger than the reference goethite seed d₅₀particle size of 1.3 μm. The particle size distributions of the precipitates formed from ferrous solutions were similar to that of the reference goethite seed. The precipitates formed from ferrous-containing solutions at pH 2.5 and at pH 4 had increased micropore areas (72.8 m²/g and 87.1 m²/g, respectively) and decreased external specific surface areas (53.4 m²/g and 49.0 m²/g, respectively) compared to the goethite reference material (micropore surface area of 66.2 m2/g and external surface area of 64.8 m²/g). For ferric-containing solutions at pH 2.5, a decline in specific surface area from 131.0 m2/g to between 82.0 m²/g and 100.6 m²/g was caused by aggregation and molecular growth inside micropores. Instantaneous iron precipitation from ferric solutions at pH 4 resulted in an increased Brunauer-Emmett-Teller (BET) surface area of 156.5 m²/g due to poor ordering of crystal structure and a more amorphous surface structure. Iron oxide phases present in the precipitates had elemental compositions similar to ferrihydrite and schwertmannite. Sulphate inclusion was more prominent during the rapid precipitation from ferric solutions than during precipitation from ferrous solutions. The precipitate formed at pH 2.5 was overall more crystalline than the precipitate formed at pH 4.0; nickel entrainment also increased with an increase in pH. Rhodium- and rutheniumcontaining species were finely dispersed throughout the iron phases in the precipitates. Iridium precipitated primarily without the inclusion of iron or other precious metals; particles consisting of iridium (50–80 wt%), chloride, and oxygen were formed.
Comparison of constitutive and inducible β-fructofuranosidase production by recombinant Pichia pastoris in fed-batch culture using defined and semi-defined media
(Elsevier, 2016) Anane, Emmanuel; Van Rensburg, Eugene; Gorgens, Johann F.
ENGLISH ABSTRACT: Short-chain fructooligosaccharides produced from sucrose by transfructosylation using β-fructofuranosidase (FFase), an industrially important enzyme, finds application in pre-biotics, 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.
Cyanobacterial growth in minimally amended anaerobic digestion effluent and flue-gas
(MDPI, 2019) Beyl, Talita; Louw, Tobias M.; Pott, Robert W. M.
ENGLISH ABSTRACT: Anaerobic digestion (AD) is an important industrial process, particularly in a biorefinery approach. The liquid effluent and carbon dioxide in the off-gas, can be used to produce high-value products through the cultivation of cyanobacteria. Growth on AD effluent is often limited due to substrate limitation or inhibitory compounds. This study demonstrates the successful cultivation of Synechococcus on minimally amended AD effluent, supplemented with MgSO4 and diluted with seawater. An 8 L airlift reactor illustrated growth in a pilot scale setup. Higher biomass yields were observed for cyanobacteria grown in diluted AD effluent compared to minimal medium, with 60% total nitrogen removal in the effluent. It was demonstrated that controlling the pH, increasing dissolved salt concentrations and adding MgSO4 to the effluent allowed for the successful cultivation of the cyanobacterium, circumventing the addition of clean water for effluent dilution. This could ultimately increase the feasibility of anaerobic digestion-microalgae integrated biorefineries.
Desorption of isobutyl acetate into air as a low-cost alternative system for the measurement of liquid phase mass transfer coefficients
(AIDIC, 2018) Lamprecht, Johannes H.; Burger, Andries J.
ENGLISH ABSTRACT: A study was conducted in enhancing the measurement of volumetric liquid phase mass transfer coefficients (K˪a) in packed columns, by re-considering the application of conventional desorption and absorption of oxygen and carbon dioxide. The cost-effectiveness of this well-established system is hampered by reagent costs, in the form of oxygen and nitrogen, as well as plant footprint requirements. Therefore, aqueous desorption of isobutyl acetate into air (ADIBAA) is proposed as alternative to the conventional system. This ADIBAA-method utilises continuous dosing of isobutyl acetate with on-line ultraviolet quantification. This decreases reagent costs as only the desorbed component is dosed, thereby limiting related losses. Additional benefits of the newly proposed ADIBAA-method include minimal environmental impact and short experimental evaluation times, in the order of 20-30 min. The ADIBAA-method was experimentally verified in a 400 mm ID column with a 1.1 m bed height. FlexiRings® sizes 1.5” and 2”, and Intalox® Ultra™ size A, were evaluated over liquid loadings ranging from 6 to 96 m³.m².h¹and vapour flow factors between 0.6 and 2 kg.m-ͦ ·⁵.s-¹. Liquid phase mass transfer coefficients (K˪a) ranging from 0.0032 to 0.168 s-¹ and 0.004 to 0.02 s-¹ were measured for the 1.5” and 2” FlexiRings®, respectively. This is in agreement with the literature, with deviations limited to ca 10%. The liquid phase mass transfer coefficient evaluations of the Intalox® Ultra™ size A, yielded K˪a values ranging from 0.00482 to 0.0242 s-¹. These results confirm the manufacturer statement that modern Intalox® Ultra™ packing provides similar mass transfer efficiency to smaller, and therefore higher apparent interfacial area packing from the second and third generations. This implies comparative mass transfer efficiencies between Intalox® Ultra™ A and 1” FlexiRings®, while providing decreased pressure drop and increased hydraulic capacity.
Development of fuzzy rule-based systems for industrial flotation plants by use of inductive techniques and genetic algorithms
(Southern African Institute of Mining and Metallurgy, 2000) Aldrich, C.; Schmitz, G. P. J.; Gouws, F. S.
Control of flotation processes is mostly managed by plant operators, who assess the performance of the plant based on their own experience and other heuristic rules. These rules tend to be subjective or ill-defined, since most of them are concerned with the structure of the flotation froth, such as colour, bubble size and shape distributions, froth mobility and froth stability. These phenomena are very difficult to quantify objectively, and inexperience on the part of the operators, human error, etc., can lead to significant inefficiencies in plant operation. In this paper the development of a fuzzy system to support the control decisions of plant operators is described, which leads to significantly smoother control action and more stable plant operation than could be obtained with crisp sets of rules or manual control strategies.
The effect of fluid properties and packing size on the hydrodynamics of packed columns
(AIDIC, 2018) Minne, Ulrich L.; Burger, Andries J.; Schwarz, Cara E.
ENGLISH ABSTRACT: The effect of fluid physical properties on the hydrodynamic behaviour in a packed column with 1.5” and 2.5” fourth generation random packing was investigated by measuring the pressure drop and liquid hold-up. Experimental data for combinations of four liquids and two gases were measured for both packings in a pilot plant setup with a column inside diameter of 393 mm and a packed bed height of 3 m. Liquid superficial flow rates in the range of 6 – 122 (m³/h)/m² and gas rates up to the flooding point were considered. The results provide significant extended information on how fluid properties affect the hydrodynamic behaviour in randomly packed columns. As expected, larger packing pieces enable higher hydrodynamic throughputs. However, the choice of packing size remains a balance between improved capacity (larger packing) and improved separation efficiency (smaller packing).
Empirical and economic modelling of winery and effluent parameters
(WineLand Publications, 2004-12) Sheridan, Craig M.; Bauer, Florian; Lorenzen, Leon
INTRODUCTION: Wine production in South Africa is strongly delocalised, with numerous small-to-medium sized producers situated in several regions within the Western Cape. The production process generally follows traditional methodologies. New technologies have resulted in important changes in winemaking over the last few decades. Whilst adapting to these technological changes, producers also have to respond to increased pressure from consumers regarding the quality of the product and the environmental consequences of winemaking, especially with regard to water usage and chemical pollution.
Enhancing the functional properties of acetylated hemicellulose films for active food packaging using acetylated nanocellulose reinforcement and polycaprolactone coating
(Elsevier, 2020-02) Mugwagwa, Lindleen R.; Chimphango, Annie F. A.
Acetylated hemicellulose (AH)-nanocellulose (ACNC) films coated with polycaprolactone (PCL) films, were evaluated as active packaging for aqueous, alcoholic, fatty and acidic food. The effects of nanocellulose loading (0–50 %), degree of acetylation (DS) (0–2.34) and polycaprolactone coating (0.3 g/mL) on hydrophobicity and solubility of AH films in food simulants, were investigated. In addition, AH-CNC/PCL films were doped with polyphenols and their antioxidant release (temperature 5 °C–40 °C, time - 48 h) into food simulants was evaluated experimentally and by modelling (Migratest software). Increasing ACNC DS and loading, combined with a PCL coating increased films’ hydrophobicity (24.59° to 82.48°) and reduced film solubility in all the simulants (∼82.8 %). The release of polyphenols by the films was highest and best predicted using Migratest software for the fatty food simulant. Therefore, these films can be used as active packaging for fatty foods. Furthermore, Migratest modelling can be used to predict film performance during film design.
Estimation of the maximum end buffer impact force for a given level of reliability
(South African Institution of Civil Engineering, 2012-04) Haas, T. N.; Maincon, P.; Dunaiski, P. E.
ENGLISH ABSTRACT: The first paper in this set of two, titled The effect of parameters on the end buffer impact force history of the crane (see page 55), examined the effect of a change in the magnitude of the parameter on the end buffer impact force history. This paper investigates to what degree a change in the magnitude of the parameter alters the impact force history. This was accomplished through a sensitivity analysis performed by individually varying the magnitude of the parameter in the FE model. For each case individual maximum impact forces were obtained. The maximum impact force could not simply be selected by choosing the greatest value from the sensitivity study. A constraint optimisation technique for a given level of reliability (β) using the FE simulation data was used to determine the maximum impact force. A comparison between the constraint optimisation and codified results showed that SABS 0160-1989 underestimates the impact force by 18%, while SANS 10160-2010 substantially overestimates the impact force by 64% for a level of reliability of β = 3. If the relevant clauses of SANS 10160-6 that pertain to end stop design are used in their present form, this will result in a conservative design, whereas SABS 0160 has a probability of 2.3% of being exceeded.
Ethanol production potential from AFEX™ and steam-exploded sugarcane residues for sugarcane biorefineries
(BioMed Central, 2018-05-04) Mokomele, Thapelo; Da Costa Sousa, Leonardo; Balan, Venkatesh; Van Rensburg, Eugene; Dale, Bruce E.; Görgens, Johann F.
Background: Expanding biofuel markets are challenged by the need to meet future biofuel demands and mitigate greenhouse gas emissions, while using domestically available feedstock sustainably. In the context of the sugar industry, exploiting under-utilized cane leaf matter (CLM) in addition to surplus sugarcane bagasse as supplementary feedstock for second-generation ethanol production has the potential to improve bioenergy yields per unit land. In this study, the ethanol yields and processing bottlenecks of ammonia fibre expansion (AFEX™) and steam explosion (StEx) as adopted technologies for pretreating sugarcane bagasse and CLM were experimentally measured and compared for the first time. Results: Ethanol yields between 249 and 256 kg Mg−1 raw dry biomass (RDM) were obtained with AFEX™-pretreated sugarcane bagasse and CLM after high solids loading enzymatic hydrolysis and fermentation. In contrast, StEx-pretreated sugarcane bagasse and CLM resulted in substantially lower ethanol yields that ranged between 162 and 203 kg Mg−1 RDM. The ethanol yields from StEx-treated sugarcane residues were limited by the aggregated effect of sugar degradation during pretreatment, enzyme inhibition during enzymatic hydrolysis and microbial inhibition of S. cerevisiae 424A (LNH-ST) during fermentation. However, relatively high enzyme dosages (> 20 mg g−1 glucan) were required irrespective of pretreatment method to reach 75% carbohydrate conversion, even when optimal combinations of Cellic ® CTec3, Cellic ® HTec3 and Pectinex Ultra-SP were used. Ethanol yields per hectare sugarcane cultivation area were estimated at 4496 and 3416 L ha−1 for biorefineries using AFEX™- or StEx-treated sugarcane residues, respectively. Conclusions: AFEX™ proved to be a more effective pretreatment method for sugarcane residues relative to StEx due to the higher fermentable sugar recovery and enzymatic hydrolysate fermentability after high solids loading enzymatic hydrolysis and fermentation by S. cerevisiae 424A (LNH-ST). The identification of auxiliary enzyme activities, adequate process integration and the use of robust xylose-fermenting ethanologens were identified as opportunities to further improve ethanol yields from AFEX™- and StEx-treated sugarcane residues.
Expanding the semantic range to enable meaningful real-world application in chemical engineering
(HESA, 2019) Dorfling, C.; Wolff, K.; Akdogan, G.
ENGLISH ABSTRACT: Legitimation Code Theory has proven to be useful in analysing the relationship between theory and practice. Semantic gravity can be used to illustrate teaching and learning processes that move between different levels of abstraction and context-dependency. Effective engineering education entails moving both up and down the semantic range in a way that enables students to apply concepts to contextual practices. However, students seldom engage at the strongest level of semantic gravity. This study investigated the contextualisation of theory in a chemical engineering programme through industrial site visits. Final-year chemical engineering students participated in a voluntary field trip to visit industrial sites. Data obtained through written surveys showed that visits allowed participants to develop a better appreciation for the relevance of taught material to industrial applications and to better understand relationships between different modules and problem solving. Site visits were found to be an effective way of expanding the semantic range.
Frequency sensitive mechanism in low-intensity ultrasound enhanced bioeffects
(Public Library of Science, 2017) Miller, April D.; Chama, Abdoulkadri; Louw, Tobias M.; Subramanian, Anuradha; Viljoen, Hendrik J.
This study presents two novel theoretical models to elucidate frequency sensitive nuclear mechanisms in low-intensity ultrasound enhanced bioeffects. In contrast to the typical 1.5 MHz pulsed ultrasound regime, our group previously experimentally confirmed that ultrasound stimulation of anchored chondrocytes at resonant frequency maximized gene expression of load inducible genes which are regulatory markers for cellular response to external stimuli. However, ERK phosphorylation displayed no frequency dependency, suggesting that the biochemical mechanisms involved in enhanced gene expression is downstream of ERK phosphorylation. To elucidate such underlying mechanisms, this study presents a theoretical model of an anchored cell, representing an in vitro chondrocyte, in an ultrasound field. The model results showed that the mechanical energy storage is maximized at the chondrocyte’s resonant frequency and the energy density in the nucleus is almost twice as high as in the cytoplasm. Next, a mechanochemical model was developed to link the mechanical stimulation of ultrasound and the increased mechanical energy density in the nucleus to the downstream targets of the ERK pathway. This study showed for the first time that ultrasound stimulation induces frequency dependent gene expression as a result of altered rates of transcription factors binding to chromatin.
Hydrodynamics of a packed column operated under supercritical conditions
(AIDIC, 2018) Franken, Hendrik H.; Knoetze, Johannes H.; Schwarz, Cara E.
ENGLISH ABSTRACT: There is a lack of hydrodynamic data under supercritical conditions, in particular in systems that attempt to isolate hydrodynamics from mass transfer. This paper presents hydrodynamic data focusing on the characterization of flooding. Two different flooding phenomena are identified using the column overheads, pressure drop and liquid hold-up of the system. It is further noted that the saturated fluid properties of density and dynamic viscosity play a significant role in flooding. A density difference of less than 250 kg/m3 between phases and a decrease in liquid viscosity causes a shift from classical gas-liquid flooding to behaviour more analogous to that of liquid-liquid extraction columns.
Impact of cultivar selection and process optimization on ethanol yield from different varieties of sugarcane
(BioMed Central, 2014-04) Benjamin, Yuda; Garcia-Aparicio, Maria. P.; Gorgens, Johann. F.
Background: The development of ‘energycane’ varieties of sugarcane is underway, targeting the use of both sugar juice and bagasse for ethanol production. The current study evaluated a selection of such ‘energycane’ cultivars for the combined ethanol yields from juice and bagasse, by optimization of dilute acid pretreatment optimization of bagasse for sugar yields. Method: A central composite design under response surface methodology was used to investigate the effects of dilute acid pretreatment parameters followed by enzymatic hydrolysis on the combined sugar yield of bagasse samples. The pressed slurry generated from optimum pretreatment conditions (maximum combined sugar yield) was used as the substrate during batch and fed-batch simultaneous saccharification and fermentation (SSF) processes at different solid loadings and enzyme dosages, aiming to reach an ethanol concentration of at least 40 g/L. Results: Significant variations were observed in sugar yields (xylose, glucose and combined sugar yield) from pretreatment-hydrolysis of bagasse from different cultivars of sugarcane. Up to 33% difference in combined sugar yield between best performing varieties and industrial bagasse was observed at optimal pretreatment-hydrolysis conditions. Significant improvement in overall ethanol yield after SSF of the pretreated bagasse was also observed from the best performing varieties (84.5 to 85.6%) compared to industrial bagasse (74.5%). The ethanol concentration showed inverse correlation with lignin content and the ratio of xylose to arabinose, but it showed positive correlation with glucose yield from pretreatment-hydrolysis. The overall assessment of the cultivars showed greater improvement in the final ethanol concentration (26.9 to 33.9%) and combined ethanol yields per hectare (83 to 94%) for the best performing varieties with respect to industrial sugarcane. Conclusions: These results suggest that the selection of sugarcane variety to optimize ethanol production from bagasse can be achieved without adversely affecting juice ethanol and cane yield, thus maintaining first generation ethanol production levels while maximizing second generation ethanol production.

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