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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.

Process for the preparation of vanillin from a mixed m-cresol/p-cresol stream

Buddoo, Subash January 2002 (has links)
The Vanillin project was undertaken by AECI as it was believed that with the raw materials available from SASOL i.e. cresols, it would be possible to develop a process that would be globally competitive. A process for preparing both vanillin and ethyl vanillin was developed by AECI’s Research and Development Department using a mixed m- and p-cresol stream as feed. The displacement of bromide by methoxide is very successful when using a dimethyl formamide (DMF)/alcohol solvent system and excellent conversions (>95%) and selectivities (>95%) may be obtained. However, the use of DMF, which poses a serious chronic health risk, is unacceptable in this process since the products are intended for use as food and flavouring chemicals. In view of the above the main objectives of this study were: · To find a suitable alternative solvent system, which could produce comparable results while still being economically viable; · To develop an appropriate experimental protocol in the laboratory based on the alternative solvent system; · To determine the important reaction variables by conducting statistically designed experiments; · To optimise the reaction to produce a reproducible and robust experimental protocol; and · To test the reaction thoroughly at bench-scale level and to obtain experimental data for scale-up to pilot plant The most promising alternative solvent system was a methanol/methyl acetate mixture, which produced satisfactory results in the preliminary assessment (conversion of 98.3% and selectivity of 92.0%). DMA and acetonitrile also produced promising results but were not considered for further investigation because of toxicity and cost issues. A set of statistically designed experiments was carried out on the methanol/methyl acetate solvent system where four variables were tested i.e., substrate concentration, temperature, catalyst loading, and methanol to methyl acetate volume ratio. The experimentally determined response surface model showed that the most important variable was catalyst loading (63.2%) for conversion. With respect to selectivity, the most important variables were catalyst loading (31.9%) and methanol to methyl acetate ratio (33.1%). The optimum reaction conditions were as follows: · Temperature: 120°C · Methanol:methyl acetate: 15:1 vol/vol · Catalyst loading: 8 mol % to substrate · Substrate concentration: 22 %m/m on solvent · Catalyst: Copper(I) bromide · Sodium Equivalents: 2.7 wrt substrate · Time: 3 hours The optimum conditions were tested for reproducibility in a 1 Labmax pressure reactor. Replicated reactions, two at a 10% and two at a 20% substrate concentration gave conversions and selectivities all greater than 90%. Although the reaction mixture was a slurry at these concentrations, the reactions were very fast and virtually complete within the first hour (~95% conversion). Initial scale-up studies were conducted in an 8 Parr reactor where five reactions were carried out using the optimum conditions described above. The conversion of substrate and vanillin selectivity was consistently high and compared favourably to the Labmax reactions. The average conversion was 97.3% (96.3 to 98.5%) at an average selectivity of 98.2% (97.4 to 99.1%). A study of the reaction kinetics confirmed that the reaction was first order with respect to the substrate as a plot of substrate concentration versus reaction rate gave a straight line. The rate constant was calculated as 1.1096 k(h-1). The reaction mechanism proposed for the copper assisted nucleophilic aromatic substitution involves the formation of an adduct between sodium methoxide, methyl acetate and copper(I) bromide. The formation of a transient intermediate with the substrate allows intramolecular delivery of the methoxide ion to the aryl moiety through a CuI – CuIII type cycle.

The use and performance of recycling polypropylene in lead-acid battery cases

Rust, Nico January 2004 (has links)
Polypropylene has proven to be the ideal material for the outer shell of the lead acid batteries. Due to its mold-ability and inert properties the material provides a capsule for the functioning components of the lead acid battery and can withstand a variety conditions encountered during its application, such as impact shock resistance, high and low temperatures and acid resistance. Polypropylene has however become of great concern with regards to environmental pollution since it is generally resistant to normal conditions of degradation and can only be properly disposed of by incineration. This factor has encouraged the industry to find ways to regenerate spent polypropylene. A good example of such a process is the recycling of lead acid batteries. This allows not only for the regeneration of lead, but also for the recycling of polypropylene in the manufacturing of battery cases. There are some cost advantages in using recycled polypropylene. However it does have its disadvantages in that the material does start to deteriorate after multiple processes. A common practice amongst battery manufacturers is to add virgin polypropylene to the recycled material in order to ensure performance consistency. The comparative study investigated the use of various ratios of virgin and recycled PP in the manufacturing of lead acid battery cases and their influence on the physical properties and performance of the final material. The degradation of PP was also investigated as the material was subjected to multiple manufacturing processes where the influence of stabilizers was further considered. A common technique of PP analysis such as MFI was shown to be an effective technique to maintain good quality control. The study further showed that it is important that the material grade of PP used in the manufacturing of the battery case and lid is compatible in order to allow for effective heating sealing of the two components. Polypropylene has a waxy surface finish and it is generally difficult to label or write on. Labels tend to fall off in application and make it difficult to maintain a track record of the manufactured batteries with time. This study showed successfully that a laser activated dye can be added to the PP without influencing its color or its performance. This allows for successful labeling of battery cases by various bar coding writers that can trace the battery through its manufacturing process. Lead acid batteries are often operated outside the specified temperature range that is determined by battery manufacturers resulting in premature failure. These failures can occur within the warranty period of the battery and result in illicit claims since the monitoring of the batteries in its application was not possible. A suitable temperature monitoring device was designed that would be incorporated into the vent cap or lid of the battery case. The device contained temperature sensitive indicators that would undergo a permanent color change at specified temperatures thereby giving the battery manufacturer an indication as to the maximum temperature the battery was exposed to.

Electrochemical investigation of valve regulated lead acid batteries

Ferg, Ernst Eduard January 2004 (has links)
One of the technical advances made by the lead-acid battery industry in the field of portable power supply was the development of the valve regulated lead-acid battery (VRLA). This battery reduced the necessity for periodic servicing in terms of having to replenish the cells with distilled water. Further, this new type of battery can now be installed near sensitive electronic equipment without the danger of acid spill or dangerous fumes being emitted. In addition, longer service performance is achieved in terms of life cycle capacity, when compared to the conventional flooded type batteries. However, the new type of battery requires the manufacturing of high precision electrodes and components with low tolerances for error. In order for the manufacturers to produce such a premium product, a thorough understanding of the electrochemistry of the inner components is necessary. None of the South African lead-acid battery manufacturers are currently making VRLA batteries to supply a very competitive global market, where a large range of sizes and capabilities are available. In order to introduce the VRLA battery into such a competing market in South Africa, a niche area for its application was identified in order to establish the viability of manufacturing such a battery locally. This is done by integrating the VRLA concept into an existing battery, such as the miners cap lamp (MCL) battery. Its application is specific with well-defined performance criteria in a relatively large consumable market in the South African mining industry. The study looked at various components within a local manufacturing environment that required a better understanding and modification of the processes to build VRLA MCL batteries. This included a detailed study of the manufacturing processes of the positive electrode. The study involved the investigation of the types of grid alloys used, the type of electrode design, such as tubular or flat plate, the addition of redlead to the paste mixing process and subjecting the batteries to accelerated life cycle testing. A better understanding of the oxygen recombination cycle was also performed in order to evaluate the correct use of certain design criteria in the manufacturing process. This included the study of the pressure release valve and the type of positive electrode used. The study also looked at developing an inexpensive analytical technique to evaluate the porosity of cured and formed electrodes using a glycerol displacement method. The monitoring of the state of health (SoH) of VRLA batteries on a continuous basis is an important parameter in unique applications such as remote power supply. A device was developed to monitor the SoH of VRLA batteries on a continuous basis. The working principle of the device was tested on a MCL VRLA battery. With the development of other types of VRLA batteries for specific applications such as in stand-by power supplies, the monitoring device would then be integrated in the battery design.

Comparison of two granulation processes with the view to reduce manufacturing cost

Maclean, Aldritt Allister January 2004 (has links)
Aspen Pharmacare, one of the leading pharmaceutical manufacturers in South Africa has embarked on a programme of improving the production processes currently employed at their Port Elizabeth site. With the introduction of new technology at the site and the move towards globalization, it became imperative that Aspen remain competitive in the market. The product of interest in this research, Degoran Plus tablets, is one of the company’s leading brand sellers. Upon investigation, it became apparent that this product created opportunity for process improvement using the new technology. The manufacture of Degoran Plus entails granulation, compression and coating of the product. Most opportunity for improvement was possible in the granulation stage because of the laborious nature of the present process. Degoran Plus tablets had a history of analytical failures, especially with regard to the dissolution rate of the final product, as well as other quality related issues. The product was not considered to be a “through-runner”, which resulted in bad production output, due to continual repeats of not only analysis but also reworks in production. A strategic decision was taken to manufacture Degoran Plus using the Collette Gral granulator as the equipment offered superior mixing capability when compared to the Bear planetary granulator. It was assumed that the granulation process would result in more uniform distribution of the actives. Upon producing a better granule, a final product of superior quality would be attained. The validation protocol stipulates that three samples be taken and tested from the powder mix. Nine samples taken from granulated bulk are treated in the same manner. The validation protocol further stipulates that the first three batches manufactured utilise the new process, and tested according to the protocol. The results obtained from the analysis are evaluated statistically and a conclusion and recommendation were derived based on the evaluation.

Evaluation and optimization of selected methods of arsenic removal from industrial effluent

Rubidge, Gletwyn Robert January 2004 (has links)
This research was directed at reducing arsenic levels in the effluents generated at the Canelands facility that manufactures monosodium methyl arsenate. Two effluent streams containing arsenic have to be considered, a raw water stream that is treated on site and a brine stream that is disposed of by sea outfall. Removal of arsenate from aqueous media by coagulation was investigated and models were developed describing selected variables that influence the removal of the arsenate. Three coagulant systems were investigated, namely aluminium(III) coagulation, iron(III) coagulation and binary mixtures of aluminium(III) and iron(III). Researchers have studied individual aluminium (III) sulphate and iron(III) chloride coagulation. No detailed research and modelling had, however, been carried out on the use of binary mixtures of aluminium (III) sulphate and iron (III) chloride coagulation of aqueous arsenate, nor had individual aluminium(III) sulphate and iron(III) chloride coagulation of arsenate been modelled at relatively high arsenate concentrations. The models that were generated were validated statistically and experimentally. The variables investigated in the aluminium(III) model included initial arsenate concentration, pH, polymeric flocculent concentration, aluminium(III) concentration and settling time. The variables modelled in the iron(III) coagulation were initial arsenate concentration, pH, polymeric flocculent concentration, and iron(III) to arsenic mole ratio. The modelling of the binary coagulant system included initial arsenate concentration, pH, iron (III) concentration, aluminium(III) concentration, and flocculent concentration as variables. The most efficient arsenic removal by coagulation was iron(III), followed by the binary mixture of aluminium(III) and iron(III) and the weakest coagulant was aluminium(III) sulphate. Scale-up coagulations performed on real raw water samples at a 50 litre volume showed that iron(III) was the most efficient coagulant (on a molar basis) followed closely by the binary mixture, while aluminium(III) coagulation was considerably weaker. The residual arsenic levels of the iron(III) and the binary coagulation systems met the effluent discharge criteria, but the aluminium coagulation system did not. Leaching tests showed that the iron(III) sludge was the most stable followed by the sludge of the binary mixture and the aluminium(III)-based sludge leached arsenic most readily. Settling rate studies showed that the flocs of the iron(III) coagulations settled the fastest, followed by binary mixture flocs and the aluminium flocs settled the slowest. The flocs of the binary mixture had the lowest volume, followed by the iron(III) flocs, while the aluminium(III) flocs were the most voluminous. Based on current operations of the raw water treatment plant the aluminium(III)-based coagulation is the most cost efficient. Given a relative costing of 1.00 for the aluminium(III) coagulation, the iron(III) chloride-based coagulation would be 2.67 times more expensive and the equimolar binary mixed aluminium(III)/iron(III) system would be 1.84 times the cost of aluminium(III) coagulation.

To investigate the effect of a change in hard gelatin capsule supplier on a phenytoin sodium capsule formulation

Marx, Amor January 2004 (has links)
Stability studies were undertaken at ambient (25ºC/60%RH) and accelerated conditions (40ºC/75%RH) to determine the effect of changing of hard gelatin capsule supplier on a phenytoin sodium (100 mg) capsule formulation. Three hard gelatin capsule suppliers: RP Scherer (Supplier A), Capsugel (supplier B) and Associated Caps (Supplier C) were used in the study. Capsules were analyzed just after filling of the capsules (T0), after 1 month (T1), after 2 months (T2) and after 3 months (T3) after being stored in securitainers under the above-mentioned conditions. The moisture content of the empty shells as well as the capsule contents were analysed at each time-point. The capsule disintegration time was recorded at each time point. Multi-point dissolution testing was performed at each time point to determine the release of the active substance in each case. Based on the achieved results, the best capsule shell supplier was recommended, and other suggestions were made to improve the capsule formulation.

Preparation and characterisation of nanocomposites of biomass and montmorillonite clay for use as biofuels

Nyamutswa, Lavern Tendayi January 2014 (has links)
The aim of the study was to prepare composites of clay and biomass which burn longer than unmodified biomass. Montmorillonite clay was converted to mono-ionic clay by ion exchange with sodium using sodium chloride solution. The mono-ionic clay was organically modified with an organic surfactant, methyl triphenyl phosphonium bromide. Nanocomposites were then prepared by combining the modified forms of the clay with sawdust. The three forms of clay used for the formation of composites were unmodified montmorillonite, mono-ionic montmorillonite and organically modified montmorillonite. The solution blending method was used to make the nanocomposites. FT-IR and XRD analysis showed that organic surfactant increases the interlayer space of the clay since it is bulkier than the inorganic cations that are naturally present in the interlayer space of montmorillonite. The combination of clay and sawdust resulted in the formation of exfoliated nanocomposites as shown by the absence of peaks in the low 2 theta angle in the x-ray diffraction data of the nanocomposite. The nanocomposite which was made from sawdust and 1% organically modified clay showed the best results in terms of burning time and thermal stability, as well as giving a calorific value closest to unmodified sawdust and the least amount of residue.

Ethanol production from lignocellulosic sugarcane leaves and tops

Dodo, Charlie Marembu January 2014 (has links)
Various methods for the production of bioethanol using different feedstocks have been researched on. In most work on bioethanol synthesis from sugar cane, tops and leaves have been regarded as waste and generally removed and thrown away. In this work, lignocellulosic sugarcane leaves and tops were not discarded but instead used as biomass to evaluate their hydrolyzate content. The leaves and tops were hydrolysed using different methods, namely concentrated acid, dilute acid pre-treatment with subsequent enzyme hydrolysis and compared with a combination of oxidative alkali pretreatment and enzyme hydrolysis. Subsequent fermentation of the hydrolyzates into bioethanol was done using the yeast saccharomyces cerevisae. Acid hydrolysis has the problem of producing inhibitors, which have to be removed and this was done using overliming with calcium hydroxide and compared to sodium hydroxide neutralization. Oxidative alkali pre-treatment with enzyme hydrolysis gave the highest yields of fermentable sugars of 38% (g/g) using 7% (v/v) peroxide pre-treated biomass than 36% (g/g) for 5% (v/v) with the least inhibitors. Concentrated and dilute acid hydrolysis each gave yields of25% (g/g) and 22% (g/g) yields respectively although for acid a neutralization step was necessary and resulted in dilution. Alkaline neutralization of acid hydrolyzates using sodium hydroxide resulted in less dilution and loss of fermentable sugars as compared to overliming. Higher yields of bioethanol, 13.7 (g/l) were obtained from enzyme hydrolyzates than 6.9 (g/l) bioethanol from dilute acid hydrolyzates. There was more bioethanol yield 13.7 (g/l) after 72h of fermentation with the yeast than 7.0 (g/l) bioethanol after 24h. However, the longer fermentation period diminishes the value of the increase in yield by lowering the efficiency of the process.

Ni(II) and Pb(II) dithiocarbamate complexes as precursors for the synthesis of HDA-capped NiS and PbS nanoparticles

Chintso, Thobani January 2015 (has links)
Ni(II) and Pb(II) dithiocarbamate complexes were synthesized and characterized by elemental analysis, UV-Vis, FTIR and TGA and some of the Ni(II) complexes and one Pb(II) were further analyzed by 1H-NMR and 13C-NMR spectroscopy. Generally all the dithiocarbamate ligands are soluble in water while the complexes were soluble mostly in solvents such as chloroform, toluene, DMSO and DCM. Based on the elemental analysis, the dithiocarbamate complexes are formulated as four coordinate (tetrahedral or square planar) compounds. However, the FTIR showed that each of the dithiocarbamate ligands acted as bidentate ligand through two sulfur atoms. The TGA of the most complexes showed one major decomposition step to give respective metal sulfide above 200 oC. In this research project, dithiocarbamate complexes were used as single source precursor for the synthesis of metal sulfide nanoparticles. We studied the optical and structural properties of metal sulfide nanoparticles using UV-Vis, photoluminescence (PL), powder X-ray diffraction (XRD), energy dispersive X-ray (EDX), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The absorption spectra of the metal sulfide nanoparticles are blue shifted in respect to bulk material and they also showed broad emission. The XRD of the NiS nanoparticles were indexed to the cubic and rhombohedral phase, with crystallite sizes of 15 - 18 nm. The XRD of PbS nanoparticles were indexed to the face centered cubic and cubic rock salts, with the crystallite sizes 12 - 18 nm. The TEM images of the metal sulfide nanoparticles showed particles with spherical and rectangular shapes with crystallite sizes 4 - 35 nm.

Vapour phase dehydrogenation of cyclohexane on microstructured reactors

Mpuhlu, Batsho January 2012 (has links)
The work that is described in this thesis forms part of the research and development projects at InnoVenton: NMMU Institute of Chemical Technology in collaboration with Sasol Technologies. The broader view of the project was testing on the so-called “Small Production Platforms” (SPP’s). In particular the main aim of this study was to investigate the effect of micro-structuring on the heterogeneous catalysed, vapour-phase oxidative dehydrogenation of cyclohexane in the presence of air. Ground work studies were done to provide a proper comparison of the micro-structured reactor with a traditional fixed-bed reactor. These included evaluation of a proper vanadium pyrophosphate catalyst for the reaction, testing of reaction parameters for the oxidative dehydrogenation reaction on a fixed-bed reactor and lastly comparing the performance of the micro-structured reactor to that of the fixed-bed reactor Various vanadium pyrophosphate catalysts that were tested for activity included: bulk (VO)2P2O7, bulk (VO)2P2O7 promoted with Fe, (VO)2P2O7 supported on -Al2O3 and Fe promoted (VO)2P2O7 supported on -Al2O3. These catalysts showed significant differences in TOF, however it was not conclusive from the results whether these differences may be traced to increased activity for dehydrogenation for different catalysts since all reactions were run under conditions of oxygen deficiency. It is, however, clear that Fe promotion significantly increase activity, irrespective of the relative degrees of oxidative dehydrogenation and normal dehydrogenation. The Fe promoted catalyst was further tested for long term stability in-view of using it as the catalyst in the micro-structured reactor. These studies showed the catalyst to have a high degree of stability with minimal structural changes under the reaction conditions used. Various response surface models describing the variation in each of the cyclohexane conversion, cyclohexene selectivity, and benzene selectivity, respectively when changing reaction condition, were derived by means of multiple regression. To obtain some idea of the degree and nature of the normal dehydrogenation reaction, the amount of deficit oxygen was estimated from the measured results for cyclohexane conversion and cyclohexene and benzene selectivities. These estimated values were also modelled as described above. The regression models were used to interpret specific trends in the responses for the oxidative dehydrogenation of cyclohexane and account for the oxygen deficit in the system. The performance of a fixed bed tubular reactor (FBR) and micro-structured sandwich reactor (MSSR) were compared over an Fe promoted vanadium pyrophosphate. Reactor performance was evaluated by varying specific reaction conditions (temperature and space velocity). Subsequently the turn-over frequencies, conversion and selectivities from the two reactors were compared. The conversion achieved in the micro-structured reactor was observed to be significantly higher than that achieved in the fixed-bed reactor at all reaction parameters. This is despite the fact that the total amount of catalyst in the micro-structured reactor is approximately 5 times less than that used in the fixed bed reactor. In addition, the contact time (1/MHSV) in the micro-structured reactor is also significantly shorter than in the fixed-bed reactor.

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