South African Journal of Chemical Engineering - Volume 24 Number 1, 2017

Analysis of purification of potassium nitrate with incorporation of single effect mechanical vapor compressor for solvent recovery was done. Analysis focused on the effect of concentration and temperature of mother liquor on the energy efficiency of the process and the amount of recovered solvent. Performance coefficient of mechanical vapor compressor ranged between 1.5 and 7.5 depending primarily on the temperature of mother liquor. It was found that with increase in temperature of mother liquor through pre-heating, the power of the compressor, compression ratio and amount of heat supplied to the evaporator decrease. For a 40% concentrated feed solution and mother liquor temperature above 80 °C, performance coefficient is higher than 4. It is therefore concluded that preheating mother liquor and reduction of the effect of concentration of both mother liquor and concentrated waste stream through other methods reduces the power consumption of purification process.

The amount of organic micro pollutants like antibiotics detected in effluents, lakes, rivers, hospital wastewater, sewage water and ground water. These antibiotics are affecting aquatic organisms. Common wastewater treatment plants are not built to remove these substances. Thus there is a need for new technologies. The present study focuses on the application of a promising technology, that is the use of advanced oxidation processes (AOPs), which works based on the intermediacy of hydroxyl and other radicals to oxidized non-biodegradable compounds. Hence, in the present study treatment of certain gemifloxacin commonly used in day-to-day life has been carried out. The combination of UV, UV/H₂O₂, Fenton, and UV/Fenton systems has been studied. Gemifloxacin concentration degradation, Chemical Oxygen Demand (COD) and Total Organic Carbon (TOC) are monitored. Among all the processes studied photo-Fenton process has been found to be the maximum removal of gemifloxacin (97%).

Whereas meeting product quantity and quality are prime intent in process optimization of materials manufacturing, the application of the more reliable full factorial experiment has not been well-explored in optimization studies of Carbon nanotubes (CNTs) synthesis. In this study, statistical full factorial design of experiment was explored in the parametric studies of CNTs synthesis via acetylene-chemical vapour deposition (CVD). Bimetallic (Fe-Co) catalyst supported on CaCO3 was employed for the synthesis of CNTs. The dependence of CNTs yield on the growth time (45/60 min), growth temperature (700/ 750 °C), acetylene flow rate (150/190 ml/min), and argon flow rate (230/290 ml/min) was investigated in the 24 factorial design of experiment. The growth temperature and acetylene flow rate were found to have the most significant effects on the yield of CNTs, and a maximum yield of 170% was obtained at growth conditions of 60 min, 700 °C, 190 ml/min acetylene flow rate, and 230 ml/min argon flow rate. Since acetylene undergoes polymerization or dissolution during non-catalyzed thermal decomposition, the significant effects of temperature and acetylene flow rate as illustrated by the factorial analysis suggests that the selective ability of the Fe-Co/CaCO₃ catalyst towards CNTs growth in the thermal decomposition of acetylene in CVD was mainly thermodynamics-controlled. Characterization of CNTs samples synthesized at different conditions shows that highest-yield conditions do not guarantee best quality properties.

Artificial neural network (ANN) and Response Surface Methodology based on a 2^5-1 fractional factorial design were used as tools for simulation and optimisation of the dissolution process for Azaraegbelu clay. A feedforward neural network model with Levenberge-Marquard back propagating training algorithm was adapted to predict the response (alumina yield). The studied input variables were temperature, stirring speed, clay to acid dosage, leaching time and leachant concentration. The raw clay was characterized for structure elucidation via FTIR, SEM and X-ray diffraction spectroscopic techniques and the result indicates that the clay is predominantly kaolinite. Leachant concentration and dosage ratio were found to be the most significant process parameter with p-value of 0.0001. The performance of the ANN and RSM model showed adequate prediction of the response, with AAD of 11.6% and 3.6%, and R² of 0.9733 and 0.9568, respectively. A non-dominated optimal response of 81.45% yield of alumina at 4.6 M sulphuric acid concentration, 214 min leaching time, 0.085 g/ml dosage and 214 rpm stirring speed was established as a viable route for reduced material and operating cost via RSM.

We demonstrated the formulation of wood plastic composite (WPC) materials with flexural strength of 13.69 ± 0.09 MPa for applications in outdoor fencing using municipal waste precursors like low density polyethylene (LDPE) plastics (54.0 wt. %), sawn wood dust with particle size between 64 and 500 mm derived from variable hardwood species (36.0 wt. %) and used automotive engine oil (10 wt. %). The WPC panels were prepared by precompounding, extruding at a screw auger torque of 79.8 Nm and pressing through a rectangular mould of dimension 132 mm × 37 mm × 5 mm at temperature 150 °C. The efficacy of black waste oil, as a coupling agent, was demonstrated by the absence of voids and pull-outs on microscopic examination using scanning electron microscopy. No hazardous substances were exhaled during thermo-gravimetric mass spectrometry analysis. The percentage crystallinity of the LDPE in the as-prepared material determined by differential scanning calorimetry was 11.3%.

Acid mine drainage (AMD) causes massive environmental concerns worldwide. It is highly acidic and contains high levels of heavy metals causing environmental damage. Conventional treatment methods may not be effective for AMD. The need for environmental remediation requires cost effective technologies for efficient removal of heavy metals. In this study, algae based systems were reviewed and analyzed to point out the potentials and gaps for future studies. Algae strains such as Spirulina sp., Chlorella, Scenedesmus, Cladophora, Oscillatoria, Anabaena, Phaeodactylum tricornutum have showed the capacity to remove a considerable volume of heavy metals from AMD. They act as “hyper-accumulators” and “hyper-adsorbents” with a high selectivity for different elements. In addition, they generate high alkalinity which is essential for precipitation of heavy metals during treatment. However, algae based methods of abating AMD are not the ultimate solution to the problem and there is room for more studies.

Using Time Domain Reflectometry (TDR), dielectric relaxation studies have been carried out on binary mixtures of amides (N-methylacetamide, N,N-dimethylacetamide) with alcohol (1-butanol, 1-pentanol, 1-hexanol, 1-heptanol, 1-octanol and 1-decanol) for various concentrations over the frequency range from 10 MHz to 10 GHz at 303 K. The Kirkwood correlation factor and excess dielectric constant properties were determined and discussed to yield information on the molecular interactions of the systems. The relaxation time is varies with the chain length of alcohols and substituted amides are observed. The Bruggeman plot shows a deviation from linearity. This deviation was attributed to some sort of molecular interaction which might place between the alcohols and substituted amides. The excess static permittivity and excess inverse relaxation time values vary from negative to positive for all the systems indicating the solute-solvent interaction to exist between alcohol and substituted amides for all the dynamics of the mixture.

Silica gel was functionalized with six different quaternary diammonium centres derived from ethylenediamine (EDA), tetramethylenediamine (TMDA), hexamethylenediamine (HMDA), 1,8-diaminooctane (OMDA), 1,10-diaminodecane (DMDA) and 1,12- diaminododecane (DDMDA) to produce Si-QUAT EDA, Si-QUAT TMDA, Si-QUAT HMDA, Si-QUAT OMDA, Si-QUAT DMDA and Si-QUAT DDMDA, respectively. The synthesized silica-based resins were characterized by means of FTIR, XPS, SEM, BET surface area, thermogravimetric analysis and elemental analysis. The materials were used to investigate the adsorption and separation of [RhCl₅(H₂O)]^2- and [IrCl₆]^2-. Batch studies (equilibrium and kinetic studies) were conducted to study the adsorption of [RhCl₅(H₂O)]^2- and [IrCl₆]^2- onto Si-QUAT EDA, Si-QUAT TMDA, Si-QUAT HMDA, Si-QUAT OMDA, Si-QUAT DMDA and Si-QUAT DDMDA using single metal aqueous solutions. The Freundlich isotherm confirmed multilayer adsorption and the Freundlich constant (kf) displayed the following ascending order; Si-QUAT EDA, Si-QUAT TMDA, Si-QUAT HMDA, Si-QUAT OMDA and Si- QUAT DMDA, and a decrease in kf for Si-QUAT DDMDA. Kinetic studies suggest a pseudo-first order kinetic model. Column studies were also conducted for a binary mixture of these metal ion chlorido species ([RhCl₅(H₂O)]^2- and [IrCl₆]^2-). The iridium loading capacities increased as the carbon spacer between the diammonium centres increased in the following order; Si-QUAT EDA, Si-QUAT TMDA, Si-QUAT HMDA, Si-QUAT OMDA and Si- QUAT DMDA (4.56 mg/g, 6.88 mg/g, 14.63 mg/g, 19.01 mg/g and 29.35 mg/g, respectively). It was observed that the iridium loading capacity of Si-QUAT DDMDA decreased to 8.90 mg/ g. This paper presents iridium-specific materials that could be applied in solutions of secondary PGMs sources containing rhodium and iridium as well as in feed solutions from ore processing.

Batch pyrolysis was a valuable process of assessing the potential of recovering and characterising products from hazardous waste materials. This research explored the pyrolysis of hydrocarbon-rich refinery residue, from crude oil processes, in a 1200 L electricallyheated batch retort. Furthermore, the off-gases produced were easily processed in compliance with existing regulatory emission standards. The methodology offers a novel, cost-effective and environmentally compliant method of assessing recovery potential of valuable products. The pyrolysis experiments yielded significant oil (70%) with high calorific value (40 MJ/kg), char (14%) with carbon content over 80% and non-condensable gas (6%) with significant calorific value (240 kJ/mol). The final gas stream was subjected to an oxidative clean-up process with continuous on-line monitoring demonstrating compliance with South African emission standards. The gas treatment was overall economically optimal as only a smaller portion of the original residue was subjected to emissioncontrolling steps.

Potassium amyl xanthate (PAX) and sodium isobutyl xanthate (SIBX) are commonly used collectors in both the bulk and selective froth flotation of sulfide ores. These thiol xanthate collectors are conventionally mixed together as well as with more selective thiol collectors such as dithiophosphates (DTP) and dithiocarbamates (DTC), in order to improve selectivity. With deteriorating nickel sulfide ores, more selective collectors and collector mixtures are desired for the efficient extraction of nickel. Thionocarbamates (TC) are another group of thiol collectors used for selective froth flotation of sulfide minerals. Thionocarbamates are especially used in the selective froth flotation of chalcopyrite over pyrite and galena, but little is known about its selectivity with regards to nickel. Thionocarbamates are also more stable over larger pH ranges in comparison to xanthates and they possess beneficial frothing properties. This study compared the effects of using potassium amyl xanthate (PAX), isopropyl ethyl thionocarbamate (IPETC), sodium isobutyl xanthate (SIBX) and their mixtures in the froth flotation of a pentlandite ore. In the mixtures of PAX or SIBX with IPETC, the xanthate accounted for 95.5 mol% and for the PAX and SIBX mixture a 50:50 mixture was used. This study showed that the highest cumulative nickel grades were obtained with PAX, SIBX and there mixture. The highest cumulative nickel recoveries were obtained with IPETC and its mixtures with PAX and SIBX (50e62%).

Biogas has been exploited as one of the alternative sources of renewable energy having the potential to replace fossil fuels. It contains impurities when raw, as it consists of 50e70% methane (CH₄), 30e50% carbon dioxide (CO₂) and trace gases such as hydrogen sulfide (H₂S). Chemical absorption is often a preferred purification technique in industrial applications because it has high efficiencies, removes H₂S completely, operates at low pressures, and has higher reaction rates. The focus of this study is on amines as they are widely used worldwide to purify biogas. A continuous system was used where 1 L digester was used for biogas production which was bubbled through an absorbent in 500 mL gas washing bottle. The gas exiting the absorption column was analyzed using Gas Chromatography. The methane yield obtained in this study was higher because MEA is a good absorbent. The biomethane potential was found to be 0.40 m³ CH₄/kg VS (volatile solids). An increase in concentration resulted in increased CO₂ absorption capacity and rate, an average of 76%, 78%, and 84% vol from an initial concentration of 52% vol were achieved for the respective concentrations. The CH4 content of the purified biogas improved with increasing temperature. The removal efficiency of carbon dioxide increased from 66% at room temperature to 77% at 40 °C. Temperature of the solvent increased the absorption capacity and carbon dioxide removal efficiency of the process.

This study evaluates the performance of two laboratory scale aerobic sequencing batch reactor operated under continuous low aeration and cyclic aeration scheme for the treatment of wastewater generated from a local brewery in Durban South Africa. The continuous low aeration scheme was intended to determine its effect on the performance of the reactor in terms of organic material removal compared to a typical cyclic aeration reactor for biological organic material removal. The performance of the two laboratory scale reactor was determined in terms of removals of chemical oxygen demand and biological oxygen demand. These two parameters were selected because they are priority pollutants and organic components in brewery wastewater. The experimental results demonstrated that reductions in chemical oxygen demand and biological oxygen demand in wastewater generated from the breweries can be successfully achieved using both aeration configurations. However, the treatment efficiencies in terms of the removal of chemical oxygen demand was consistently maintained above 90% and for biological oxygen demand it was observed to be above 80% with the reactor operated under the continuous low aeration scheme performing significantly better than the reactor operated under the cyclic aeration scheme.

Dry grinding of Class F fly ash (FA) was carried out using the planetary ball mill to obtain mechanically activated nanostructured FA particles. The resulting FA powders were characterized for (i) particle size: dynamic light scattering and sieve analyzer, (ii) specific surface area: BET-analyzer, (iii) structure: X-ray diffractometer, (iv) chemical composition: field emission scanning electron microscope with the electron diffraction spectrum analyzer and x-ray fluorescence analyzer, and (v) aggregation and shape of the particles: Fourier-transformed infra-red spectrometer and scanning electron microscope. A significant enhancement in surface and bulk properties of milled FA was obtained over fresh FA. The breakage parameters (i.e., the specific rate of breakage and primary breakage distribution function) of FA were determined by the direct experimental method using the narrowly-sized fraction of FA over the short grinding period under identical milling environment. A relatively simple back-calculation method was employed to determine above breakage parameters of FA also using time-variant milling data that were obtained after the grinding of distributed-sized FA feed. The parameters obtained from the direct experimental and back-calculation method yielded comparative milling simulation results with the acceptable accuracy.

Benzosulfonazole was evaluated for its corrosion inhibition effect on S40977 stainless steel in 3 M H₂SO₄ solution through potentiodynamic polarization, open circuit potential measurement, optical microscopy and IR spectroscopy. Results obtained showed the effective performance of the compound with values of 77.33%-88.32% inhibition efficiency, at 0.25% -1.25% inhibitor concentration from electrochemical analysis. Corrosion potential value decreased from -0.359 V to -0.306 V upon addition of the compound at 0.25% concentration, which decreased progressively to -0.278 at 1.25% concentration. Identified functional groups of alcohols, phenols, amines, amides, carboxylic acids, aliphatic amines, esters and ethers within the compound completely adsorbed onto the steel from analysis of the adsorption spectra while others decreased in intensity due to partial adsorption. Thermodynamic calculations showed the cationic adsorption to be through chemisorption mechanism according to Langmuir, Freundlich and Temkin adsorption isotherms. Microanalytical images showed a severely corroded morphology with corrosion pits in the absence of benzosulfonazole which contrast the images obtained with the inhibitor addition. The compound was determined to be mixed type inhibition.

Thermocatalytic Decomposition of Methane (TCD) is a completely green single step technology for producing hydrogen and carbon nanomaterials. This paper review about the research in laboratory-scale on TCD, specifically the recent advances like co-feeding effect and regeneration of catalyst for enhancing the productivity of the entire process. Although a remarkable success on the laboratory-scale has been fulfilled, TCD for free greenhouse gas (GHG) hydrogen production is still in its infancy. The necessity for commercialization of TCD is more than ever in the present-day condition of massive GHG emission. TCD generally studied over several types of catalysts, for example mono, bi, trimetallic, combination of metalemetal oxide, carbon and metal doped carbon catalysts. Catalyst Deactivation is the main problem found in TCD process. Regeneration of catalyst and co-feeding of methane with other hydrocarbon are the two main solutions placed helped in accordance to overcome deactivation problem. Higher amount of co-feed hydrocarbon in situ produce more amount of highly active carbon deposits which support further methane decomposition to produce extra hydrogen. The conversion rate of methane increases with increasing temperature and decreases with the flow rate in the co-feeding process in a comparable manner as observed in normal TCD. The presence of co-components in the post-reaction stream is an important challenge attempted in the co-feeding and regeneration.

The need to reduce carbon emissions has encouraged more research into use of biomass energy in place of coal. Biomass is carbon neutral; its use can therefore lower net emissions. Biomass can be upgraded to a fuel similar to coal by torrefaction. Different biomass have been torrefied but there is limited research in possible use of lignocellulose biomass from animal waste. This study aims to compare extent of energy densification of torrefied cow dung, corn cob and pine wood. They were dried, ground and sieved. Proximate and ultimate analysis was conducted. The samples were then torrefied at 200, 250 and 300 °C at 10 °C/min for 40 min. The resulting biochar were characterized using mass yield, higher heating value, energy yield and density. Biochar obtained at 250 °C were analyzed for elemental composition. Results were compared to Anglo bituminous coal and other torrefied biomass in literature. Corn cob and pine wood reached a maximum of 25.98 MJ/kg and 20.90 MJ/kg in heating value respectively whilst cow dung only increased to a maximum of 18.60 MJ/kg. Increase in heating value for corn cob was attributed to reduction in oxygen due to release of volatiles as well as water. This lowered the O/C ratio thereby densifying the fuel. The O/C and H/C ratio for corncob and wood moved towards that of bituminous coal unlike that of cow dung. Cow dung had a high inorganic composition so its heating value could not be upgraded as much as the other 2 biomass. Its use as a torrefaction raw material was therefore discouraged.

Traditional coal-to-liquid (CTL) plants are synonymous with the production of carbon dioxide. Coal may be gasified in the presence of steam and oxygen to produce gas comprising carbon dioxide (CO₂), carbon monoxide (CO), methane (CH₄), hydrogen (H₂) and steam (H₂O). The gases can be reacted to a myriad of chemicals and fuels via the Fischer-Tropsch (FT) reaction. However, excess carbon dioxide is generated via the Water-Gas-Shift reaction during preparation of CO:H₂ ratios for FT. Here, a process development is represented on a CHO phase diagram, where unique regions are identified for autothermal operations for coal conversion. Considerations are given to develop idealised processes for the production of liquid chemicals from coal which emit minimal process CO₂, require minimal energy input and do not require steam. This is achieved by co-feeding coal with methane and identifying endothermic-exothermic process pairs for methane-coal dry reforming. Furthermore, it is shown that a preferred method to produce liquid fuels from coal is by first creating dimethyl ether (DME) as an intermediate, followed by the dehydration of DME to liquid fuels (gasoline range). For this route, via DME, the CO₂ emission was found to be four times less than idealised CTL processes

The present work focuses on the synthesis of cobalt doped titania nano material assisted by 1,4-butane sultone anionic gemini surfactant: Co²⁺-TiO₂ (with surfactant). The synthesized nano catalysts were characterized by XRD, UVeVis DRS, XPS, SEM, FT-IR, HR-TEM and BET-surface area analysis. XRD and UV-DRS studies have indicated that all the catalysts synthesized were in anatase phase and red shift was observed with decrease in the band gap energy. XPS analysis of the catalysts has confirmed the presence of cobalt along with TiO₂. SEM analysis indicated change in morphology of the particles without any agglomeration. From FTIR studies frequency shift was observed for TiO₂ which was due to doping of cobalt into TiO₂ lattice. TEM images have shown reduced particle size of Co²⁺-TiO₂ (with surfactant). BET analysis confirmed increase in surface area of the catalyst. From BET analysis Pore volume and pore size was also analyzed. These results emphasize the important role played by the gemini surfactant on the structure and photocatalytic activity of the catalyst synthesized. The photocatalytic efficiency of the synthesized catalyst was investigated by degradation of Acid Red where degradation was completed within 30 min.

The extraction of vegetable oil from Jatropha from the Tanzanian variety with a fat content of 33.84 ± 2.58% and a moisture content of 5.4 ± 1.97%, was made using two methods: the traditional and the mechanical extraction method. The traditional consists in extracting the oil from the paste using boiling water as a solvent. While the mechanical consists of directly pressing the seeds of Jatropha using a ram press called Bielenberg press, to extract the oil contained in the seeds dried or heated before. The net yield of oil extraction by the traditional method was 22.02 ± 2.1%, with a oil cake percentage of 67.02 ± 3.3% and the ratio water/paste in mass adopted was 0.36. Mechanical extraction has an average raw yield of 26.15 ± 2.74%, with a recovery rate of 74.71%. After decanting for 10 days and filtration, the net yield was 15.39 ± 2.82% with a decantation and filtration rate of 58.67 ± 7.24%. The oil produced by traditional method has a water and volatile content of 1.01 ± 0.05% and a density of 0.884. The one produced by mechanical extraction has 0.19 ± 0.09% and a density of 0.891. The result of combustion test using two burners and one stove showed that the combustion rates were: 0.177 ± 0.034 g/min for the burner using one flame and 1.06 ± 0.04 g/min for the six flame burner and finally 3.07 ± 0, 4 g/min for the ten-flame stove. This tenflame stove allowed 3 L of water to be boiled at 100 °C for 32 min, although during combustion it was observed a release of black fumes which indicates incomplete combustion with Jatropha in this Stove. The cost of the liter of Jatropha oil obtained is higher compared to fossil fuels such as petroleum (500 FCFA per liter) and gas oil (624F CFA per liter). It would be possible to use vegetable oil from Jatropha as a cooking fuel.

Layered structure LiNi_0.45M_0.1Mn_0.45O₂ (M=Cu and Al) cathode materials for lithium-ion batteries are synthesized by sol-gel auto combustion method. The structural, morphological, electrical and magnetic properties are examined by X-ray diffraction (XRD), field effect scanning electron microscope FESEM, FT-IR, EIS and ESR. XRD data revealed the rhombohedral and α-NaFeO₂ structure with a space group R-3m. The electrical conductivity, dielectric constant, and dielectric loss are measured in the room temperature at a frequency ranging from 20 Hz to 1 MHz. The electrical conductivity of the compound is measured by AC impedance. An effective improvement in the electrical conductivity of order 5.42 × 10^-6 S/cm is observed for the copper doped LNMO compounds. ESR spectra is recorded at room temperature on a Bruker EMX model X-band spectrometer operating at a frequency of 9.50 GHz. The critical dopants of Cu, with minimum g-factor and maximum line-width (W) are observed.