Department of Chemical Engineering

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Department Process Engineering now has a new name, and will be known from March 2023, as Department of Chemical Engineering.

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Browsing Department of Chemical Engineering by browse.metadata.advisor "Callanan, L. H."

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    Biodiesel analytical development and characterisation.
    (Stellenbosch : University of Stellenbosch, 2010-03) Prah, Ebenezer; Callanan, L. H.; Lorenzen, L.; University of Stellenbosch. Faculty of Engineering. Dept. of Process Engineering.
    ENGLISH ABSTRACT: Development of analytical methods to characterise biodiesel has become central to the overall success of the marketing of biodiesel fuel. In this regard, different bodies including the American Society for Testing and Materials (ASTM) and the European normalization (EN) have come up with various methods to determine important biodiesel parameters such as total glycerol, methanol and the fatty acid methyl esters (FAMEs), etc. Various studies have been conducted on the parameters mentioned above using a variety of instrumentation and sample preparations. The best methods reported are those that have been adopted by both the ASTM and EN standards. The purpose of this study was to develop alternative analytical methods to both the recommended ASTM and EN methods and, in some cases, to make modifications to both standards (ASTM D 6571 and EN 14214) and methods to determine total and bound glycerol, the ester content and also methanol content in biodiesel. Moreover, water washing after transesterification and the effect this practice has on biodiesel cold flow properties such as kinematic viscosity, cloud and pour point and density were evaluated. The possibility of using the iodine value to predict the feedstock source of an unknown biodiesel was also investigated. Six different vegetable oil samples were transesterified with methanol and used for this study. The six samples used were palm, crown, sunflower, waste vegetable oil (wvo), peanut and rapeseed biodiesel. Quantitative results indicated that the use of programmable temperature volatilisation (PTV) for total glycerol did not produce the required repeatability of between 1-4% relative standard deviation(RSD) for total glycerol analyses in biodiesel with precision of 25%, 86%, 25% and 56% for free glycerol (FG), monoglycerides (MG), diglycerides (DG), and triglycerides (TG) respectively. The standard requires a relative standard of between 1-4% As an alternative to the method using gas chromatography, normal phase high performance chromatography (HPLC) with binary gradient elution was used to determine the bound glycerol content. This method proved accurate and repeatable with RSD % of 0.33, 1.12, and 1.2 for TG, DG and MG respectively. Following the EN14103 protocol (European standard ester determination), the Zebron ZBWAX column which is comparable to the specification recommended by EN14103 but afforded the determination of ester content from the esters of myristic acid (C14:0) to behenic acid (C22:0) with reproducibility with RSD % of 6.81, 1.91, 7.27, 0.64, 1.18, 1.55, 6.03, 1.96, and 5.21 for methyl esters of myristic, palmitic, stearic, oleic, linoleic, linolenic, arachidoic, gadoleic and behenic acid respectively. Solid phase micro extraction (SPME) using GC-MS was developed as an alternative to both the EN14110 and ASTM D93 protocols for determining the methanol content in biodiesel. For this method, polyethylene glycol fibre (PEG) was used together with a deuterated methanol internal standard and a DB-FFAP (60m×0.25um×0.25um) column. Less volume of sample was required as compared to the EN14214 method. This method was found to be sensitive, accurate and repeatable with a RSD % of 4.82. The Iodine number of biodiesel decrease compared to their corresponding feed stock and therefore predicting the feed stock of an unknown biodiesel was going to be difficult .Results from this study indicated that it is not possible to predict the feed stock source of an unknown biodiesel from its iodine value. The effect of water washing after phase separation on biodiesel cold flow properties such as kinematic viscosity, density, cloud and pour point depended on the type of biodiesel produced. We observed that water washing after transesterification caused an increase in all the cold flow properties of sunflower biodiesel, whereas only the densities and kinematic viscosities increased in the case of palm and waste vegetable oil biodiesel. The cloud and pour point of the latter two diesel samples remained unchanged after water washing. Thus, the effect of water washing on biodiesel cold flow depended on the type of biodiesel. Blending a highly saturated biodiesel (fewer numbers of double bonds) with a less saturated biodiesel (higher number of double bonds) resulted in an improvement of both the pour and cloud points of the resultant biodiesel blend.
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    Carbon dioxide reaction in aqueous amine solutions
    (Stellenbosch : Stellenbosch University, 2012-03) Machinga, Phineas; Callanan, L. H.; Knoetze, J. H.; Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering.
    ENGLISH ABSTRACT: See item for full text
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    Catalytic distillation : design and application of a catalytic distillation column
    (Stellenbosch : University of Stellenbosch, 2005-12) Nieuwoudt, Josias Jakobus (Jako); Callanan, L. H.; Moller, K. P.; University of Stellenbosch. Faculty of Engineering. Dept. of Process Engineering.; University of Cape Town. Faculty of Engineering. Dept. of Chemical Engineering. Catalysis Research Unit.
    Catalytic Distillation (CD) is a hybrid technology that utilizes the dynamics of si- multaneous reaction and separation in a single process unit to achieve a more compact, economical, efficient and optimized process design when compared to the traditional multi-unit designs. The project goal (and key question) is (how) to design a cost-effective, simple and accurate laboratory-scale continuous CD system that will sufficiently and accurately supply useful data for model validation. The system to be investigated is the continuous hydrogenation of an a-olefin C6 (1-hexene) feed stream to the corresponding alkane (n-hexane) product with simultaneous reactant/product separation. Hypothetically, a system can be constructured to determine whether hydrogenation will benefit from the heat and mass transfer integration observed under CD conditions in terms of energy usage, temperature control and the catalyst's surface hydrogen concentration. System convergence with commercial distillation simulation packages ...
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    Development and evaluation of an alkane bioconversion process using genetically modified Escherichia coli
    (Stellenbosch : Stellenbosch University, 2014-04) Roux, Philipp Francois; Clarke, K. G.; Callanan, L. H.; Smit, M. S.; Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering.
    ENGLISH ABSTRACT: Alkanes can be used as an inexpensive feedstock to produce more valuable alcohols. The biotransformation of alkanes to alcohols provides an alternative to conventional chemical procedures. The scope of this research was to develop a process utilising a biocatalyst to catalyse the oxidation of an alkane to its corresponding alcohol on a larger scale than had been reported on in previous research. The research utilised a recombinant E. coli BL21(DE3) cell, containing the CYP153A6 operon in pET 28 vector, as the biocatalyst. The CYP153A6 enzyme catalyses the oxidation of octane to 1-octanol. The principle objective of the research was to determine the amount of 1-octanol that can be produced by a system utilising this strain of recombinant E. coli as a biocatalyst on a three orders of magnitude larger scale than what had previously been reported on for this reaction system. An additional objective was to model the 1-octanol production performance in the bioreactor. Bioconversion batch reactions, with excess octane used as a substrate, were conducted in 30ml McCartney bottles and in a 7.5L BioFlo 110 Modular Benchtop Fermentor (New Brunswick). The McCartney bottles were not equipped to actively control process conditions.The bioreactor was equipped to control process conditions such as temperature, pH and dissolved oxygen concentration. Experiments in the bioreactor were therefore described as being performed under controlled conditions. The procedures used to grow, maintain and harvest the biocatalyst cells were based on those developed by the Department of Microbial, Biochemical and Food Biotechnology at the University of the Free State. The product and substrate concentrations were determined through gas chromatography (GC) analysis. The McCartney bottle bioconversion reactions, with a 1.33ml reaction volume, produced 1.88 mg 1-octanol per gram of dry cell weight per hour. The bioreactor under controlled conditions, with a 2L reaction volume, produced 14.89 mg 1-octanol per gram of dry cell weight per hour. The formation of a secondary product, octanoic acid, was observed for the bioreactor under controlled conditions experiment at a production of 1.12 mg per gram of dry cell weight per hour. The McCartney bottle experiments did not produce any by-products. The 1-octanol production performance in the bioreactor experiments was empirically modelled. The empirical rate law was based on the form of the Monod equation, with the addition of a product inhibition term. The model achieved an average Root Mean Square Error of less than 5% when compared to experimental data, and was therefore concluded to be accurate within the range of experimental data and conditions tested for. The principal finding of the research is that the cells produced an order of magnitude more product in the bioreactor than in the McCartney bottles. The literature on this reaction system, however, reports only on smaller scale research than that performed in the bioreactor. The improved production results in the bioreactor therefore give the first insight into the potential that this technology has for being scaled up. Of equal significance is the finding that a secondary product developed during the biotransformations performed in the bioreactor. This refutes the assumption that the biocatalyst cells are unable to catalyse any secondary reactions. This aspect of the cells’ performance must be addressed before the biocatalyst cell strain can be considered to be a viable option for utilisation in large-scale processes.
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    Establishing a pilot plant facility for post combustion carbon dioxide capture studies
    (Stellenbosch : Stellenbosch University, 2013-03) Kritzinger, Liaan Rudolf; Knoetze, J. H.; Callanan, L. H.; Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering.
    ENGLISH ABSTRACT: Carbon dioxide (CO2) is seen as one of the main contributors to global warming. The use of fossil fuels for power production leads to large quantities of carbon dioxide being released into the atmosphere. The released CO2 can, however, be captured by retrofitting capture units downstream from the power plant called Post Combustion Carbon Dioxide Capturing. Post combustion CO2 capture can involve the reactive absorption of CO2 from the power plant flue gas steam. Reactive solvents, such as monoethanolamine (MEA), are used for capturing the CO2 and the solvent is regenerated in a desorber unit where the addition of heat drives the reverse reaction, releasing the captured CO2. However, the large energy requirement for solvent regeneration reduces the viability of employing CO2 capture on an industrial scale. This study focused on establishing a facility for CO2 capture studies – the main aim being the construction and validation of the results produced by the pilot plant facility. A secondary aim of this study was developing an Aspen Plus® Simulation method that would simplify simulating the complex CO2 capture process. Results from the simulation were to be compared to that of the pilot plant experiments. A pilot plant facility with a closed gas system, allowing gas recycling from both the absorber and the stripping columns, was set up. The absorber column (internal diameter = 0.2 m) was set up to allow one to obtain information regarding gas- and liquid temperatures and compositions at various column heights. Online gas analysers are used for analysing the gas composition at various locations in the absorber column. The pilot plant was initially commissioned with 20 weight % MEA in aqueous solution; however the main validation experiments were conducted with 30 weight % MEA in aqueous solution. 30 weight % MEA (aq) is generally used as the reference solvent for pilot plant studies. Pilot plant results with regards to the carbon dioxide concentration profiles for the absorber column as well as the regeneration energy requirement and capture rates compared well to literature data. The Aspen Plus® simulation was also set up and validated using published pilot plant data. The comparison of the pilot plant results from this study, to the results from the Aspen Plus® Simulation, showed good agreement between the two. The Aspen Plus® Simulation could further be used to validate pilot plant data that has been gathered outside the range of reported CO2 capture efficiencies. The Aspen Plus®model was evaluated at liquid-to-gas ratios of 1.7 and regeneration energies matching the pilot plant results. It was found that the model under predicts the capture efficiency of CO2 with an average of 4.0%. The model was corrected for this error at liquid-to-gas ratios of 2 and the fit of the model to pilot plant results improved considerably (R2-value = 0.965). Pilot plant repeatability was investigated with both 20 weight %- and 30 weight % MEA in aqueous solution. Temperature- and gas concentration profiles from the absorber column showed good repeatability. The maximum deviation of the regeneration energy and the capture efficiency from the calculation means were ±0.72% and ±1.40% respectively. The aims of this study have been met by establishing, and validating the results of a pilot plant facility for carbon dioxide capture studies. It has been shown that the pilot plant produces repeatable results. Results from the Aspen Plus® Simulation were validated and also match results from the established pilot plant setup. The simulation may prove to provide valuable information regarding the optimal operating conditions for the pilot plant and may aid in performing a full parametric study on the CO2 capture process.
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    Hydroxylation of 2-methylnaphthalene to 2-methylnaphthoquinone over TI-substituted catalysis
    (Stellenbosch : University of Stellenbosch, 2010-12) Rose, Jamey; Callanan, L. H.; University of Stellenbosch. Faculty of Engineering. Dept. of Process Engineering.
    ENGLISH ABSTRACT: Partially oxygenated aromatic compounds, e.g. quinones, hydroquinones and cresols, play a vital role in the fine chemical industry and were initially prepared by stoichiometric oxidation processes that produce toxic products that are hazardous towards the environment. As a result, it was important to investigate environmentally friendly processes for the hydroxylation of aromatic compounds. This resulted in newer methods using Ti-substituted microporous zeolites as catalysts with hydrogen peroxide as oxidant in the presence of a solvent. However, the methods were found to be ineffective for large, bulky substrates due to the small pore structure. This led to using Ti-mesoporous materials as catalysts but suffered from two drawbacks; the hydrophilic nature and low hydrothermal stability of the catalyst structure. Ti-microporous and Ti-mesoporous materials acting as catalysts for the oxidation of bulky substrates achieved environmentally friendly processes but obtained low conversions and quinone yields. Therefore, the challenge has been to develop a process that is environmentally friendly, achieves high conversions, where the catalyst acts truly heterogeneous and obtains high quinone yields for the hydroxylation of bulky substrates. Recently, micropores/mesopores catalysts incorporating advantages of both micropores and mesopores materials were synthesised and seemed promising for the hydroxylation of bulky substrates. This study focuses on synthesising and evaluating the feasibility of various Ti-substituted catalysts for improving the hydroxylation of the bulky substrate, 2-methylnaphthalene (2MN) with hydrogen peroxide as oxidant in the presence of a solvent, acetonitrile. The oxidation of 2MN produces 2-methyl-1,4-naphthoquinone (2MNQ). 2MNQ is also known as menadione or Vitamin K3 and acts as a blood coagulating agent. The catalysts synthesised for this study were mesoporous catalysts, Ti- MCM-41 and Ti-MMM-2 and microporous/mesoporous catalysts, Ti-MMM-2(P123) and a highly ordered mesoporous material. The main objective of this study was to design an efficient process that is environmentally friendly and achieves high 2MN conversions and 2MNQ yields. This was achieved by evaluating the various catalysts synthesised, reaction conditions, testing if the catalyst was truly heterogeneous and identifying the products formed from the process. The designed process was proved to be environmentally friendly because the system did not produce products that were harmful towards the environment. The products identified in this study were 2MNQ, 2-methyl-1-naphthol, 2-naphthaldehyde, 3-ethoxy-4-methoxybenzaldehyde and menadione epoxide. An investigation was conducted to determine which catalyst synthesised favoured this process by quantifying the effect reaction conditions have on the various catalysts. The reaction conditions were defined in terms of the hydrogen peroxide volume, catalyst amount, solvent volume, substrate amount, reaction time and reaction temperature. The desired catalyst for this study obtained the highest 2MN conversions in comparison with the other catalysts and favoured the formation of 2MNQ. The catalyst achieving the highest conversions and favouring 2MNQ in most cases for this investigation was the highly ordered mesoporous material. Improving operating conditions to obtain high 2MNQ yields for the oxidation of 2MN to 2MNQ over the highly ordered mesoporous material was determined by varying the reaction conditions with the one factor at a time approach and a factorial design. The one factor at a time approach showed that best 2MNQ yields were obtained at 1 g substrate when investigating a change in substrate amount between 0.5 g and 2 g. Best 2MNQ yields were obtained at 10 ml solvent when investigating a change of solvent volume between 5 ml and 20 ml. The 2MNQ yield increased with increasing the catalyst amount (50 mg to 200 mg), hydrogen peroxide volume (1 ml to 6 ml) and increasing the reaction times (2 hour to 6 hours) at reaction temperatures, 120°C and 150°C. The yield decreased with increasing the reaction time (2 hours to 6 hours) at reaction temperature, 180°C. A preliminary 2 level factorial design was prepared to observe if there were any important interactions affecting the 2MNQ yield. The results from the factorial design indicated that the hydrogen peroxide volume had the most influence on the 2MNQ yield followed by the reaction time-reaction temperature interaction and reaction temperature. From the factorial design, the yield increased by increasing the hydrogen peroxide volume and reaction temperature whilst decreasing the reaction temperature-reaction time interaction. The highest 2MNQ yields and 2MN conversions obtained for the hydroxylation of 2MN to 2MNQ over the highly ordered mesoporous material in this study were in the ranges 48-50 % and 97-99 %, respectively. This study indicates that the process system, reaction conditions and catalyst type have an impact on the products formed, 2MN conversion, 2MNQ selectivity and 2MNQ yield. The highly ordered mesoporous material was found to be truly heterogeneous because no leaching occurred and the catalyst could be recycled without losing its catalytic activity and selectivity for at least two catalyst cycles. It can be concluded that the highly ordered mesoporous material is therefore a promising catalyst for the selective oxidation of bulky substrates with aqueous H2O2 because it produces an environmentally friendly process, achieves high conversions, obtains high quinone yields and the catalyst truly acts heterogeneous.
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    Hydroxylation of aromatic compounds over zeolites
    (Stellenbosch : University of Stellenbosch, 2009-03) Gqogqa, Pumeza; Callanan, L. H.; University of Stellenbosch. Faculty of Engineering. Dept. of Process Engineering.
    Aromatic precursor compounds are derivatives that play an important role in biosystems and are useful in the production of fine chemicals. This work focuses on the catalytic synthesis of 2-methyl-1, 4-naphthoquinone and cresols (para- and ortho) using aqueous hydrogen peroxide as an oxidant in liquidphase oxidation of 2-methylnaphthalene and toluene over titanium-substituted zeolite TS-1 or Ti-MCM-41. Catalysts synthesised in this work were calcined at 550°C, extensively characterised using techniques such as X-ray Fluorescence for determining the catalyst chemical composition; BET for surface area, pore size and micropore volume; Powder X-ray diffraction for determining their crystallinity and phase purity and SEM was used to investigate the catalyst morphologies. The BET surface areas for Ti-MCM-41 showed a surface area of 1025 m2/g, and a 0.575 cm3/g micropore volume. However, zeolite TS-1 showed a BET surface area of 439 m2/g and a 0.174 cm3/g micropore volume. The initial experiments on 2-methylnaphthalene hydroxylation were performed using the normal batch method. After a series of batch runs, without any success as no products were generated as confirmed by GC, a second experimental tool was proposed. This technique made use of the reflux system at reaction conditions similar to that of the batch system. After performing several experimental runs and optimising the system to various reactor operating conditions and without any products formed, the thought of continuing using the reflux was put on hold. Due to this, a third procedure was brought into perspective. This process made use of PTFE lined Parr autoclave. The reactor operating conditions were changed in order to suit the specifications and requirements of the autoclave. This process yielded promising results and the formation of 2-MNQ was realised. There was a drawback when using an autoclave as only one data point was obtained, at the end of each run. Therefore, it was not possible to investigate reaction kinetics in terms of time. Addition of aqueous hydrogen peroxide (30 wt-%) solution in the feed was done in one lot at the beginning of each reaction in all oxidation reactions, to a reactor containing 2-methylnaphthalene and the catalyst in an appropriate solvent of choice (methanol, acetonitrile, 2-propanol, 1-propanol, 1-pentanol, and butanol), with sample withdrawal done over a period of 6 hours (excluding catalytic experiments done with a Parr autoclave as sampling was impossible). As expected, 2-methylnaphthalene oxidation reactions with medium pore zeolite TS-1 yielded no formation of 2-methyl-1, 4-naphthoquinone using various types of solvents, with a batch reactor, reflux system, or a Parr PTFE autoclave. This was attributed to the fact that 2-methylnaphthalene is a large compound and hinders diffusion into zeolite channels. With the use of an autoclave, Ti-MCM-41 catalysed reactions showed that the choice of a solvent and reaction temperature strongly affect 2- methylnaphthalene conversion and product selectivity. This was proven after comparing a series of different solvents (such as methanol, isopropanol, npropanol, isobutanol, n-pentanol and acetonitrile) at different temperatures. Only reactions using acetonitrile as a solvent showed 2-MNQ. Formation of 2- MNQ, indicating that acetonitrile is an appropriate choice of solvent for this system. The highest 2-methylnaphthalene conversion (92%) was achieved at 120 ˚C, with a relative product selectivity of 51.4 %. Temperature showed a major effect on 2-MN conversion as at lower reaction temperature 100˚C, the relative product selectivity (72%) seems to enhance; however, the drawback is the fact that lower 2-methylnaphthalene conversions (18%) are attained. Another important point to note is the fact that using an autoclave (with acetonitrile as a solvent), 2-methyl-1-naphthol was generated as a co-product. In conclusion, it has been shown that the hydroxylation of different aromatic compounds over zeolites conducted in this study generated interesting findings. In 2-MN hydroxylation over Ti-MCM-41 as a catalyst, only acetonitrile is an appropriate choice of solvent using an autoclave. In addition, zeolite TS-1 is not a suitable catalyst for 2-MN hydroxylation reactions. It is ideal to optimise an autoclave in order to investigate reaction kinetics and optimum selectivity. Toluene hydroxylation reactions yielded para and ortho-cresol as expected with either water or acetonitrile as a solvent. No meta-cresol was formed. The kinetic model fitted generated a good fit with water as a solvent or excess toluene, with acetonitrile as a solvent generating a reasonable fit.
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    Oxidant concentration effects in the hydroxylation of phenol over titanium-based zeolites Al-free Ti-Beta and TS-1
    (Stellenbosch : University of Stellenbosch, 2006-03) Burton, Robert M; Callanan, L. H.; University of Stellenbosch. Faculty of Engineering. Dept. of Process Engineering.
    This work focuses on the effects of hydrogen peroxide concentration on the catalytic activity and product selectivity in the liquid-phase hydroxylation of phenol over titanium-substituted zeolites Al-free Ti-Beta and TS-1 in water and methanol solvents. Hydroquinone is typically the desired product, and these solvents employed have previously been shown to be of importance in controlling the selectivity of this reaction. Different volumetric quantities of an aqueous 30 wt-% peroxide solution were added to either water or methanol solutions containing the catalyst and phenol substrate, and the reaction monitored by withdrawing samples over a period of 6-8 hours. For Al-free Ti-Beta catalysed reactions, the peroxide concentration affects the selectivity and activity differently in water and methanol solvents. Using methanol solvent, the selectivity to hydroquinone formation is dominant for all peroxide concentrations (p/o-ratio > 1), and favoured by higher initial peroxide concentrations (> 1.27 vol-%), where p/o-ratios of up to can be reached; in water solvent, increasing the peroxide concentration above this level results in almost unchanging selectivity (p/o-ratio of ca. 0.35). For lower peroxide concentrations in water, the p/o-ratio increases slightly, but never exceeds the statistical distribution of ca. 0.5. Using water as a solvent, higher phenol conversion is obtained as the initial peroxide concentration increases; in methanol the phenol conversion is largely independent of peroxide concentration. As expected for the smaller pore TS-1, higher hydroquinone selectivity is obtained in methanol than for Al-free Ti-Beta, which is consistent with shape-selectivity effects enhanced by the use of this protic solvent. Interestingly, with TS-1 the p/o-ratio is higher at lower phenol conversions, and specifically when the initial peroxide concentration is low (p/o-ratio exceeding 3 were obtained at low phenol conversion), and decreases to a near constant value at higher conversions regardless of the starting peroxide concentration. Thus, low peroxide concentrations favour hydroquinone formation when TS-1 is used as the catalyst. Comparing the performance of the two catalysts using methanol solvent, the phenol conversion on TS-1 is more significantly influenced by higher hydrogen peroxide concentrations than Al-free Ti-Beta. However, with higher initial concentrations the unselective phenol conversion to tars is more severe since the hydroquinone selectivity is not higher at these high peroxide concentrations. The increased tar formation, expressed as tar deposition on the catalyst or as the tar formation rate constant, confirms that the greater amount of free-peroxide present is mainly responsible for the non-selective conversion of phenol. Kinetic modelling of the reaction data with an overall second-order kinetic model gave a good fit in both solvents, and the phenol rate constant is independent of changing hydrogen peroxide concentration for the hydroxylation over Al-free Ti-Beta using water as the solvent (kPhenol = 1.93 x 10-9 dm3/mmol.m2.s). This constant value suggests that the model developed to represent the experimental data is accurate. For TS-1 in methanol solvent the rate constant is also independent of peroxide concentration (kPhenol = 1.36 x 10-8 dm3/mmol.m2.s). The effect of the method of peroxide addition was also investigated by adding discrete amounts over a period of 4.5 hours, and was seen to improve hydroquinone selectivity for reaction on both catalysts, and most significantly for Al-free Ti-Beta in methanol solvent. With TS-1, the mode of peroxide addition had little influence on phenol conversion, but the initial selectivity to hydroquinone was ca. 1.6 times higher than for an equivalent single-portion addition (at a similar phenol conversion). Discrete peroxide addition for hydroxylation in methanol over Al-free Ti-Beta gave greatly improved hydroquinone selectivities compared to the equivalent single-dose addition. Compared to TS-1, the initial selectivity was not as high (p/o-ratios of 0.86 and 1.40 respectively at 10 mol-% phenol conversion), but this can be explained on the basis of geometric limitations in the micropores of TS-1 favouring hydroquinone formation. The final selectivity, however, is marginally higher (using the same mode of peroxide addition, and at the same phenol conversion). Discrete peroxide addition has an additional benefit in that it also reduces the quantity of free-peroxide available for product over-oxidation, and consequently reduces the amount of tars formed. Thus, the interaction of the effects of peroxide concentration and the solvent composition and polarity on the product selectivity and degree of tar formation is important. Particularly with TS-1, lower peroxide concentrations in bulk methanol solvent are highly beneficial for hydroquinone formation, because of the implicit geometric constraints in the micropores, the lower water concentration, and the decreased tar formation associated with high methanol concentrations. This could have significant reactor design implications, as the results obtained here suggest that the reaction should be terminated after approximately 30 minutes to maximise hydroquinone production (under the conditions evaluated in these experiments), even though the corresponding phenol conversions are low (ca. 10 mol-%). The higher hydroquinone selectivities reached at low phenol conversions for the discrete peroxide addition experiments also confirm this. Practically, to enhance the hydroquinone selectivity for reaction over TS-1, the initial phenol-peroxide molar ratio should be ca. 10, methanol should constitute not less than 90 vol-% of the reaction volume, and the peroxide should be added in discrete amounts. For reaction over Al-free Ti-Beta, methanol solvent also enhances the hydroquinone formation as expected. At low phenol conversions (ca. 10 mol-%) hydroquinone is still the preferred product, although in contrast to TS-1 the selectivity increases with phenol conversion, and is higher with higher initial peroxide concentrations. Under the best conditions evaluated here for optimal hydroquinone formation, the initial phenol-peroxide molar ratio should be ca. 2.5, with methanol making up at least 90 vol-% of the total volume. Discrete peroxide addition in methanol solvent for the Al-free Ti-Beta catalysed hydroxylation gives excellent improvements in hydroquinone selectivity (2.5 times higher than water solvent), and the addition in more discrete portions might further improve hydroquinone formation, and should therefore be examined.
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    Process optimization for partial oxidation of bacterial sludge in a sonochemical reactor
    (Stellenbosch : Stellenbosch University, 2014-04) Beyers, Analene; Callanan, L. H.; Aldrich, C.; Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering.
    ENGLISH ABSTRACT: It was found that bacterial sludge from anaerobic water treatment systems is produced internationally at a rate of 60 grams per person per day and the accumulation of the potentially hazardous by-product has become of increasing concern. The produced bacterial sludge is frequently pumped into dams, dried out and used as agricultural fertilizer. This bacterial sludge is expected to have a relatively high heating value and as such, has the potential to produce energy from the biomass. It is, therefore, advisable to utilize this energy potential as an alternative to conventional sludge disposal. This project aimed to improve the yield of syngas by optimizing the reactor design to partially oxidize bacterial sludge using a sonochemical reactor that is operated at bulk atmospheric conditions. The effect of different conditions was investigated and the optimum settings for syngas production were found by investigating temperature, pressure and the effect of the amplitude of operation that regulates the energy input by the ultrasonic equipment. The optimum conditions were used to investigate the kinetics involved in this process as well as to determine the energy consumption by the process. It was also required to study the feasibility of partially oxidizing bacterial sludge using a sonochemical reactor instead of conventional steam gasification and also as an alternative means of sludge disposal. By eliminating this pollutant source, the future environmental threat posed by an increasing population size will be minimized and energy will be utilized from a thus-far wasted energy source. The syngas that is produced is used as a green alternative to fossil fuels in the Gas-to-Liquids (GTL) process to produce liquids fuels. A thus-far wasted energy source will be consumed and fossil fuels can be saved in the process. It was found that the maximum hydrogen mole percentage produced is 0.141 mole % of the vapour phase with the maximum carbon monoxide mole percentage in the vapour phase at 1.896 mole %. This shows an improvement on work conducted by Beyers (2011) of 59 % for hydrogen, 92% for carbon monoxide and a reduction of 49 % for carbon dioxide. A kinetic study of the process indicated that the rate equations that describe the hydrogen and carbon monoxide production are zero order and, therefore, independent of initial concentration of the sludge. The rate constants were 0.0146 (mol % hydrogen/s) and 0.0183 (mol % hydrogen/s) for hydrogen and carbon monoxide, respectively. It was found that the most severe change to the higher heating value of the feed was a mere 0.27 mJ/kg from an original value of 9.81 mJ/kg. This therefore confirms that the reaction has not proceeded to completion. The statistical model predicted a maximum value for hydrogen production at 0.151 mole % in the product gas, 0.01 mole % from the measured maximum. It was also found that hydrogen is produced during the sonolysis of distilled water and that this confirms that the hydrogen production during partial oxidation of the sludge sample comes mainly from the water present in the sludge. The hydrogen produced when only using water, was found to be 0.127 mole % and when using the active sludge, the value was 0.116 mole % hydrogen in the vapour phase. The thermal decomposition of calcium carbonate in the lime that is used to treat the pH of the unit where the sludge originates from, followed by the formation of carbon monoxide during the Boudouard reaction, led to an increased amount of carbon monoxide present in the product gas. Ultrasonic intensity is defined as the amount of energy that is transferred to the sample per cubic meter of the internal surface area of the reactor vessel. It was found that the intensity that was delivered to the reactant was lower than expected as the reactor was operating at an efficiency of only 36%. The design intensity was 1.44 W/m2 and the actual delivered intensity was 0.52 W/m2. Based on a maximum yield of 0.00012 Nm3/kg, the cost of syngas production under the conditions described by this study, would amount to R 19.98/Nm3. This cost only implicates the operational expenses and does not take further downstream processing and initial capital investment repayments into account. Conventional steam gasification at a yield of 0.67 Nm3/kg has an operational syngas production cost of R 1.48/Nm3. This process was therefore found to not be economically feasible as the cost of utilizing ultrasound as opposed to normal steam gasification is more than ten times more expensive. It was concluded that the process was successfully optimized by the redesigning of the reactor and that carbon dioxide production was limited by excluding oxygen from the feed gas. It was also concluded that the sonolysis of water and the thermal decomposition of calcium carbonate, followed by the conversion of carbon dioxide to carbon monoxide, supplements the syngas production under the current operational conditions. Based on the production of no methane during the course of this study, the sonochemical process can be tied into the GTL process after the steam reforming unit. Due to the relatively high carbon dioxide content, the process will need to join the main feed gas stream that is fed into the carbon dioxide removal unit before it enters the GTL process to correct the desired feed gas ratio. Based on the very low syngas yields, the low hydrogen to carbon monoxide ratio in comparison to the required ratio of 2 as well as the high energy intensity required for this process, it can be concluded that the partial oxidation of biomass sludge in a sonochemical reactor is not feasible as an alternative technology to conventional steam gasification. The operating costs of the sonochemical unit would be nearly ten times that of steam gasification and is therefore concluded to not be a competitive technology to conventional steam gasification. It is recommended that the reactor design is reinvestigated to improve the delivered ultrasound intensity as well as the surface area where the ultrasonic waves are intensified. This would eliminate dead-zones. It was also recommended that the argon gas is continuously bubbled through the reactant mixture during experiments to eliminate the degassing effect caused when the ultrasound is initially emitted. The gas outlet of the process can then be connected to an online gas chromatograph (GC) with a thermal conductivity detector (TCD) and flame ionization detector (FID) methanizer in series as the TCD does not destroy the sample and this setup would improve the analytical process. The production of carbon monoxide from lime as well as the production of hydrogen from water during sonolysis needs to be investigated. The effect of radicals can also be studied by the addition of a radical scavenger to the process. It is recommended that the experimental design is reinvestigated and a design that will deliver similar information utilizing fewer data points should be chosen. Based on this model as well as further kinetic testing, it is recommended that a complete ASPEN model is developed to simulate the energy requirements to tie the ultrasonic process into the commercial plant. Based on this model, a complete feasibility study can then be conducted to determine the capital costs involved, the operating costs, the repayment period as well as taking the current costs of sludge disposal into account.
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    Reactive absorption kinetics of CO2 in alcoholic solutions of MEA: fundamental knowledge for determining effective interfacial mass transfer area
    (Stellenbosch : Stellenbosch University, 2014-04) Du Preez, Louis Jacobus; Knoetze, J. H.; Callanan, L. H.; Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering.
    ENGLISH ABSTRACT: The reactive absorption rate of CO2 into non-aqueous solvents containing the primary amine, mono-ethanolamine (MEA) is recognised as a suitable method for measuring the effective interfacial mass transfer area of separation column internals such as random and structured packing. Currently, this method is used under conditions where the concentration of MEA in the liquid film is unaffected by the reaction and the liquid phase reaction is, therefore, assumed to obey pseudo first order kinetics with respect to CO2. Under pseudo first order conditions, the effect of surface depletion and renewal rates are not accounted for. Previous research indicated that the effective area available for mass transfer is also dependent upon the rate of surface renewal achieved within the liquid film. In order to study the effect of surface depletion and renewal rates on the effective area, a method utilising a fast reaction with appreciable depletion of the liquid phase reagent is required. The homogeneous liquid phase reaction kinetics of CO2 with MEA n-Propanol as alcoholic solvent was investigated in this study. A novel, in-situ Fourier Transform Infra-Red (FTIR) method of analysis was developed to collect real time concentration data from reaction initiation to equilibrium. The reaction was studied in a semi-batch reactor set-up at ambient conditions (T = 25°C, 30°C and 35°C, P = 1 atm (abs)). The concentration ranges investigated were [MEA]:[CO2] = 5:1 and 10:1. The concentration range investigated represents conditions of significant MEA conversion. The reaction kinetic study confirmed the findings of previous research that the reaction of CO2 with MEA is best described by the zwitterion reactive intermediate reaction mechanism. Power rate law and pseudo steady state hypothesis kinetic models (proposed in literature) were found to be insufficient at describing the reaction kinetics accurately. Two fundamentally derived rate expressions (based on the zwitterion reaction mechanism) provided a good quality model fit of the experimental data for the conditions investigated. The rate constants of the full fundamental model were independent of concentration and showed an Arrhenius temperature dependence. The shortened fundamental model rate constants showed a possible concentration dependence, which raises doubt about its applicability. The specific absorption rates (mol/m2.s) of CO2 into solutions of MEA/n-Propanol (0.2 M and 0.08 M, T = 25°C and 30°C, P = ±103 kPa) were investigated on a wetted wall experimental setup. The experimental conditions were designed for a fast reaction in the liquid film to occur with a degree of depletion of MEA in the liquid film. Both interfacial depletion and renewal of MEA may be considered to occur. The gas phase resistance to mass transfer was determined to be negligible. An increase in liquid turbulence caused an increase in the specific absorption rate of CO2 which indicated that an increase in liquid turbulence causes an increase in effective mass transfer area. Image analysis of the wetted wall gas-liquid interface confirmed the increase in wave motion on the surface with an increase in liquid turbulence. The increase in wave motion causes an increase in both interfacial and effective area. A numerical solution strategy based on a concentration diffusion equation incorporating the fundamentally derived rate expressions of this study is proposed for calculating the effective area under conditions where surface depletion and renewal rates are significant. It is recommended that the reaction kinetics of CO2 with MEA in solvents of varying liquid properties is determined and the numerical technique proposed in this study used to calculate effective area from absorption rates into these liquids. From the absorption data an effective area correlation as a function of liquid properties may be derived in future.
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    The selective oxidation of methane and propene over α-Bi2Mo3O12
    (Stellenbosch : University of Stellenbosch, 2007-03) Nel, Jacobus; Callanan, L. H.; University of Stellenbosch. Faculty of Engineering. Dept. of Process Engineering.
    The catalytic selective oxidation of hydrocarbon molecules is the process where a selectively oxidized intermediate molecule is formed instead of the thermodynamically favoured total oxidation products, in the presence of a suitable catalyst. Examples are the selective oxidation of methane to synthesis gas at moderate temperatures, for which a catalyst is still needed and the selective oxidation of propene to acrolein over α-Bi2Mo3O12. The selective oxidation of propene over α-Bi2Mo3O12 occurs via a Mars-van Krevelen mechanism where the bulk oxygen in the catalyst is inserted into the propene molecule and leaves as part of the product, while being replaced with gaseous oxygen. From an economic perspective there is a need to produce synthesis gas from methane at low temperatures. It was seen in the literature that α-Bi2Mo3O12 is a mixed metal oxide that might be capable of achieving this. The feasibility of the selective oxidation of methane to synthesis gas with α-Bi2Mo3O12 was therefore investigated. However, it was found that the selective oxidation of methane over α-Bi2Mo3O12 is not feasible at moderate temperatures. To circumvent the problem of producing synthesis gas at low temperatures a membrane reactor was suggested that might be able to produce synthesis gas at moderate temperatures with conventional selective methane oxidation catalysts that thermodynamically favours carbon dioxide formation at low temperatures. No time on-stream experiments had been done previously for the selective oxidation of ...
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    Selective oxidation of propene to acrolein on α-Bi₂Mo₃O₁₂ nano-particles
    (Stellenbosch : University of Stellenbosch, 2005-03) Van Vuuren, Peter; Callanan, L. H.; University of Stellenbosch. Faculty of Engineering. Dept. of Process Engineering.
    Although selective oxidation catalysts are widely used and extensively studied for their industrial and academic value, their complex mechanisms are, to a large extent, still unclear. The field of so-called allylic (amm)oxidations reactions was chosen for further investigation, in particular the simplistic selective oxidation of propene to acrolein over an α-Bi2Mo3O12 catalyst. One of the most important approaches in selective oxidation is to try to correlate the physicochemical properties of catalysts with their catalytic performance (activity and selectivity). The most interesting, and seemingly most widely invoked parameter, is lattice oxygen mobility. The problem, however, is the difficulty encountered in measuring oxygen mobility. It is hypothesised that the depth of oxygen utilisation and lattice oxygen mobility of bismuth molybdate during the partial oxidation of propene to acrolein may be determined by measuring the rate of acrolein formation and lattice oxygen usage over a range of discrete particle sizes that could be synthesised using reverse micelle technology. Catalyst Preparation A preliminary investigation into the reverse micelle technique showed that discrete nanosized particles could be synthesised, but that there was no size control over the outcome and that, in most cases there were some degree of particle agglomeration. It was also found that nanorod formation occurred due to adsorbtion of surfactant. More in-depth investigation had to be done in order to achieve particle size control and the liberation of the calcined α-Bi2Mo3O12 catalyst particles required for kinetic experiments. Simple precipitation methods, the catalyst calcination step, and the formation and stability of reverse micelles were investigated. A simple precipitation method to prepare α-Bi2Mo3O12, suitable to be integrated into the reverse micelle technique was found by buffering the mixture of bismuth nitrate and ammonium molybdate solutions with an excess of molybdate. This prevented the pH from decreasing below a critical value of 1.3 (at which β-Bi2Mo2O9 forms as an impurity). The excess molybdenum caused the formation of MoO3 in the calcined product, which was selectively and successfully removed using a warm ammonium wash followed by a water rinse and a recalcination step. XRD of a temperature range calcination shows that the calcination starts at temperatures as low as 200°C and almost complete calcination of the catalyst at 280°C. DSC analyses show a 47.15 J/g crystal formation peak only at 351°C. The Mo18O56(H2O)8 4- anion or its double, Mo36O112(H2O)16 8-, is responsible for the formation of α-Bi2Mo3O12 in the precipitation calcination reaction. Reverse micelles were investigated using a Malvern Zetasizer and showed a complex dynamic system in which the reverse micelle sizes and size distributions change over time as a function of surfactant and aqueous concentrations, the salt used and aqueous phase salinity. Although much was accomplished in this study, more investigations into the constituent steps of the reverse micelle technique are needed to develop a method to synthesise the range of discrete catalyst particle sizes required for kinetic studies. Kinetic Studies For the purpose of kinetic experiments a metal reactor was found to be superior to that of a glass reactor. The reactor rig was adequate for these kinetic studies but do not meet the requirements for detailed reaction order experiments. The analysing apparatus could not measure CO2 formation accurately and it had to be calculated using a carbon balance. Only the model proposed by Keulks and Krenzke [1980a] was able to describe the kinetic result, but the model parameter describing the oxidative state of the catalyst surface could not be calculated due to the lack compatibility between published data. Values were awarded to this parameter so to give an Arrhenius plot which corresponded to published data. The parameter describing the oxidative state vs. temperature took on a function that was consistant with the reasoning of Keulks and Krenzke [1980a]. Comprehensive preliminary kinetic studies are needed, both in catalyst reduction and reoxidation, in order to determine the reaction conditions, explore more advanced kinetic models and investigate model parameters that are theoretically and/or empirically obtainable and quantifiable.
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    Synthesis of mixed metal oxides for use as selective oxidation catalysts
    (Stellenbosch : University of Stellenbosch, 2007-03) Motshweni, Jim Sipho; Callanan, L. H.; University of Stellenbosch. Faculty of Engineering. Dept. of Process Engineering.
    The synthesis of mixed metal oxides, specifically the need and ability to successfully and accurately control the particle size, their stability and the reactivity of these nanoparticles is required, so as to allow the attachment of catalyst nanoparticle to the surface of a substrate or to other particles without leading to coalescence of the catalyst particle and hence to loss of their size induced properties. However, the synthesis of mixed metal oxides is a complex problem. Though various methods of preparing these types of oxides have been reported and applied, such methods they rarely produced pure forms and have often been recorded as having been contaminated with other phases. Often the particle sizes are too large in the micrometer range, and the size distribution is overly wide. Moreover, even if particles of nanometer size are formed, they tend to aggregate or agglomerate. In the current research, microemulsions were used to synthesize the nanoparticles. Such microemulsion consists of water droplets encapsulated by surfactant molecules in a pool of oil, comprising: water in oil (w/o) or reverse micelles. Reverse micelles in the nanometer size range are thermodynamically stable and optically transparent in the solution. They are believed to be highly dynamic structures whose components rearrange themselves over time and space through interaction or collision, coalescing and redispersing. However, the advantage of this method over using the standard method is that the particle size can largely be controlled, and a narrow size distribution obtained. The aim of the research was to investigate the feasibility of using the reverse micelle technique for the synthesis of mixed metal oxides - specifically α-bismuth molybdate (α- Bi2Mo3O12) with a controlled and desirable particle size and a narrow size distribution...