Faculty of Engineering, Built Environment and Information Technology
School of Engineering
Department of Chemical Engineering
Selected Highlights from Research Findings
Nanotechnology is an enabling technology that, potentially, could lead to cost-effective and high-performance water treatment systems. It has the scope and performance potential to generate technically and environmentally appropriate solutions to water related problems over a wide spectrum. It has the potential for instant and continuous monitoring of water quality, but its biggest impact on the environment could be in pollution prevention through improved clean technologies for better conversion of materials and elimination of waste production. From an initial survey of nanotechnology developments in the water field and problems in the South African water industry, the following preliminary list of areas was compiled in which research on water-related nanotechnology could be initiated and existing South African efforts be coordinated to address South African problem areas. Three general areas have been identified: (i) water treatment technology including development of improved membranes and development of activated filter media, (ii) development of real-time diagnostic tools for water quality assessment, (iii) development of membrane-based wastewater treatment technology. The fact that these processes function on the nano level presents a significant opportunity for the early introduction of nanotechnology in water treatment. It should be relatively simple (compared to development of new generation nanotechnology processes) to employ nanotechnology for the modification and improvement of existing materials and equipment such as reverse osmosis and nanofiltration membranes, activated carbon, ion exchange resins, etc. to be used in existing processes. Challenges that need to be resolved before nanomaterials could be successfully used on a large scale in water treatment include safety evaluation, large scale production facilities, safe disposal of wastes and energy efficiency. These are major challenges that might cause major delays in the large scale application of nanotechnology in water treatment.
Contact person: Prof CF Schutte.
The aim of this project was to study the intercalation of fatty acids in hydrotalcite clays produced by a specific manufacturer. The Institute of Applied Materials has developed a facile surfactant-mediated method to intercalate aliphatic carboxylic acids into a commercial layered double hydroxide (LDH or Hydrotalcite). The reaction is conducted at elevated temperatures with the LDH powder as a suspension in a stearic acid oil-in-water emulsion. The acidic fatty acid, e.g. stearic acid, reacts with the basic carbonate anions, CO2 is released and the fatty acid is intercalated as a bilayer. High concentration anionic or nonionic surfactants, e.g. sodium dodecylsulfate or Tween 60 aid the intercalation process by emulsifying the molten acid and dispersing the hydrotalcite particles. X-ray diffraction, thermal analysis and infrared spectroscopy confirmed that a bilayer-intercalated hydrotalcite was formed and that the surfactant is not co-intercalated. The method is convenient, economical and environmentally friendly: It employs the readily available carbonate form as starting reagent; water is used as medium rather than organic solvents; low reaction temperatures suffice, i.e. calcinations of the clay are superfluous and there is no need for working under a CO2-free atmosphere.
Contact person: Prof WW Focke.
Steam boilers are used to generate steam in order to meet the heat requirements for cold process streams. The most common heat exchanger network layout usually assumes a parallel arrangement, for example each associated heat exchanger tends to be directly connected to the boiler. This observation suggests that the flow rate of steam needed for the system can be reduced, while maintaining the required heat, simply by changing the layout of the network. In order to achieve this objective in a systematic manner, we have developed a hybrid graphical and mathematical technique that can be applied to systems of this nature. Phase change of saturated steam to saturated liquid plays a vital role in determining the minimum flowrate of steam required as well as the resultant layout of the steam system network. In retrofit design, the technique promises to be powerful as a debottlenecking tool, whilst in grassroot design major capital cost savings could be realised with minimum effort. In order to assess the advantage of the developed hybrid technique, it has been successfully applied to a case study where steam savings of 30% were realized in comparison with traditional system layouts.
Contact person: Prof T Majozi.
Fin-gas CC has identified a market for pure, bottled carbon monoxide (CO) sold as a speciality gas. CO is a useful intermediate for producing other high-value speciality chemicals. The aim of the project was to show that a fluidized bed of carbon, operating at very low superficial gas velocities, with CO2 as feed, would be suitable to produce high-purity CO. A suitable fluidized bed gasifier was built, and CO with a purity of >99% was successfully produced at a temperature of 1000°C with a mass hourly space velocity of 0,13. This set of reaction conditions confirms the economic viability of using this process to produce high-purity CO commercially.
Contact person: Prof MD Heydenrych.
Solid dosage forms are popular systems to deliver pesticides to the site of application due to their ease of handling and safety in transportation. The challenge remains to rapidly release the active pesticide in water at the point of use. Urea-1,3 dimethyl urea eutectics were shown to retain the fast aqueous dissolution rate of urea, whilst providing a lower melting point solid into which lower melting point actives or temperature sensitive actives, may be successfully incorporated. A solid dosage form for AmitrazTM (N-methyl bis(2,4-xylyliminomethyl) methylamine) was developed for Bayer Agricultural Sciences and patented world-wide. This new technology provides an alternative, commercially viable release system for the agrochemical industry to deliver a range of pesticides into aqueous dip solutions.
Contact person: Prof WW Focke.
Monodispersed nanoparticulate clay fillers have been shown to greatly enhance the properties of plastics materials, including gas barrier properties, strength, dimensional stability, flame retardancy and UV stability. Most studies have focused on cationic smectite-based clays. Anionic clays such as the class of layered double hydroxides (LDH) may provide an alternative route. They have the general chemical formula with MII = Mg, Zn, Fe, Co, Ni, Cu and MIII = Al, Fe, Cr. The structure of these compounds consists of trioctahedral metal hydroxide sheets that alternate with interlayers containing anions and water. The brucite-like sheets have a net positive charge x per formula unit owing to isomorphic substitution of some of the divalent cations by trivalent ones. This net positive charge is balanced by an equal negative charge from the interlayer anions. Water molecules occupy the interlayer space. They are partially oriented owing to hydrogen bond interactions with the anions and the hydroxyl groups on the surface of the octahedral layers. Recently Chamotte Holdings, a local mining and chemicals- manufacturing company started up a local plant for the production of hydrotalcite with a novel and environment-friendly manufacturing process. It uses magnesium oxide as a starting material and can produce hydrotalcite, hydromagnesite and magnesium hydroxide as viable products. The primary market for the hydrotalcite is its use as a heat stabiliser in polyvinyl chloride (PVC). It promises to be an environmentally safer alternative than the toxic barium, cadmium and lead salts largely used in South Africa. As for the smectite clays, the LDHs can be intercalated by appropriate organic species and specifically long chain carboxylic acids and anionic surfactants such as sodium dodecyl sulphate (SDS). The distinctive properties of such modified layered double hydroxides permit a wide range of uses including polymer additives, precursors for catalysts and magnetic materials. Their generally non-toxic nature and membrane-like structure can be harnessed to protect, carry, deliver and controllably release pharmaceuticals or genes. Nanocomposites can be prepared by exfoliation within polymer matrices. The currently available intercalation procedures described suffer from some of the following problems: (i) Poorly crystallized products; (ii) contamination with other anions and solvents, and (iii) mixed phases containing one or more of the following: Precursor material owing to incomplete reaction or ion exchange and carbonate forms owing to reaction with CO2. Owing to the wide-ranging utility of LDH intercalates, it is of interest to develop environmentally friendly and energy efficient methods of intercalation that yield pure products. The Institute for Applied Materials (IAM) has recently developed environmentally friendly methods for intercalation of fatty acid anions and anionic surfactants into carbonate containing layered double hydroxides (hydrotalcite). In addition, a new process for intercalating cationic surfactants in local smectite clays was developed. This work is being funded by an IRDP grant from the NRF. This opens the way to tailoring the properties of locally produced hydrotalcite for a variety of applications. The successful production of nanoparticle clays could enable South Africa to produce its own products and reduce our dependence on imports. It could open lucrative new local and export markets to the South African mining and clay processing industry. Although the focus is initially on the plastics industry, there might be spin offs in other areas such as the pharmaceutical and cosmetic industries, which use similar products.
Contact person: Prof WW Focke.
The purpose of this project was to develop a reliable laboratory test, through which performance of open-gear lubricants can be determined under conditions as close as possible to those of the real system. The test method used was based on the standard FZG-test, where modifications were made to maintain a constant operating temperature by removal of heat generated due to friction. These modifications were made in such a way as to not compromise the equipment when a standard FZG test needs to be performed. By optimizing in-situ quantification of the performance of various lubricants in terms of their friction characteristics, their wear protection performance as well as their daily cost, an educated choice can be made to obtain the most cost effective gear lubricant and re-lubrication interval. Comparing in-situ results with a laboratory-based test method will enhance the accuracy of predictions, based on laboratory results. Reduction in lubricant usage based on reliable performance testing can be established by means of the test method and will also lead to fewer disposal problems and consequently to a decrease in environmental impact. Results will also provide an excellent means of quantifying the savings in frictional losses that can be achieved by using more efficient lubricants. Three primary tools were used to assess how well a lubricant performed under constant temperature conditions. The first was measurable gear wear, where the gears are weighed before the first load stage and then again after each subsequent load stage. This allowed for a gravimetric assessment of wear occurring during the test. The second tool was to make use of a measurement from which the amount of friction during operation can be inferred. As the circumferential speed of the gears is constant throughout the test, the electric motor that drives the gears draws current from a 3-phase power source that will vary the amount of current drawn in order to maintain the specified circumferential speed. This current was measured during the test. The third tool was to apply the conservation of heat principle to the test bed, which made it possible to determine the amount of heat generated through friction by measuring the flow rate and temperature difference of the cooling water circulated through the system to maintain a constant operating temperature. These three tools were used as performance indicators for five different lubricants representing the technologies currently in use on open gear drives. Although it was not the intention of the project to determine a specific best or worst performing lubricant, clear differences in the performance of the five lubricants tested, could be determined.
Contact person: Prof PL de Vaal.
In this project, methods to predict process behavior and applying these to fault detection and diagnosis were studied. These include kernel-based principal component analysis, and discriminate methods of analysis that can be used to extend on feature extraction methods by increasing the isolation between different faults. Data from a pilot scale distillation column were used to explore the performance of the techniques. Models were trained with normal and faulty operating data. They were tested with unseen and/or novel fault data. The techniques demonstrated very promising fault detection and diagnosis ability. This was mainly due to the ease of the training and the ability to relate the scores achieved back to the input data. The attributes of these multivariate statistical techniques were compared to the goals of statistical process control and the desirable attributes of fault detection and diagnosis systems. Linear and kernel discriminate analysis are proposed as fault diagnosis methods. Applications of these techniques are seemingly diverse, multidisciplinary and could have far-reaching consequences. They could be used from control of chemical processes, predicting how operating conditions in chemical reactors can be manipulated to produce products within a very tight specification range, to automotive applications where combustion emissions have to conform to strict environmental requirements. They can also be used in power distribution systems, where varying load requirements have to be met with available generation capacity. These are very topical indeed.
Contact person: Prof PL de Vaal.