The development of a commercial production process for p-menthane-3,8-diol
- Authors: Rust, Nico
- Date: 2009
- Subjects: Insect pests -- Control , Repellents
- Language: English
- Type: Thesis , Doctoral , DTech
- Identifier: vital:10427 , http://hdl.handle.net/10948/d1018273
- Description: The synthesis of p-menthane-3,8-diol via the acid-catalyzed cyclization of citronellal in a dilute aqueous sulphuric acid medium was investigated using conventional batch and continuous systems in order to develop a commercial production process for said p-menthane-3,8-diol (PMD). The batch studies conducted during the first part of this study showed that the formation of PMD from citronellal occurs via an intra-molecular Prins reaction that results in the formation of both the desired PMD product, as well as the partially hydrated isopulegol. It was shown that the formationof the by- product, PMD-acetal, results from the reaction between an intermediate, 5-methyl-2- isopropylcyclohexanol, and the citronellal starting material, and not from the reaction between PMD and citronellal as previously reported. Kinetic studies confirmed the existence of a complicated kinetic model. The formation of PMD from citronellal displayed typical pseudo first order kinetics up to conversions of 70 after which the kinetic model becomes complicated as the result of the establishment of quasi equilibrium reactions between PMD and isopulegol (dehydration of PMD and hydration of isopulegol) and between PMD the PMD-acetal, both systems being acid catalysed. The PMD-acetal formation reaction appears to be second order with respect to PMD. Scale-up studies of the batch process to 30L and 50L scales showed that it would be extremely difficult to limit the level of PMD-acetal formation below the desired level of 1 percent, even if citronellal conversions are restricted to about 50 percent. During studies conducted on a commercially availablemicro-structured organic synthesis plant (OSP) it was shown that it is possible to perform the PMD reaction as a continuous process. The results obtained showed that the use of a micro-mixer such as the caterpillar micro-mixer did not provide enough residence time in order for desirable conversions (- 40 percent) to be obtained. By combining themicro-mixer with delay-loops of different thicknesses and lengths, and using increasing reaction temperatures, it was shown that the conversion of citronellal could be improved to some extent, but compared poorly to the expected conversions for a well-stirred batch reactor. By packing selected delay loops with inert SiC particles, improved mass transfer was observed between the organic and aqueous phases as reflected in the increased conversion of citronellal. Using the observations that were made during the use of the OSP, a continuous-flow, tubular reactor system was designed and constructed. Advanced statistical techniques were used to investigate the effect of variables such as temperature, acid concentration, reactor length, flow rate and the organic to aqueous ratio on the rate and selectivity of the reaction. Mathematical models were derived for citronellal conversion, yield of PMD and yield of PMD- acetals, and used to predict the concentrations of citronellal, PMD and PMD-acetals at set experimental conditions. The results obtained showed that it was possible to obtain a product which approached desired specifications.Downstream processing of the PMD reaction mixture as it exits the reactor requires phase separation and neutralization of the acid catalyst solution, followed by further work-up to recover unreacted starting material and intermediates for recycle back to the synthesis reactor, followed by purification of crude PMD to the desired specification. The study showed that neutralization, prior or after phase separation, does not affect the selectivity of the PMD to such a great extent, but does influence the relative conversion due to extended contact of the catalyst with the organic phase after the reaction is terminated. Recovery of unreacted citronellal and isopulegol could be achieved by a simple vacuum evaporation step, which may either be carried out in a batch manner using traditional distillation equipment, or in a continuous process using wiped-film (short path) techniques. It was also shown that selective crystallization of PMD from the crude product mixture by addition of a solvent, such as heptanes or hexane proved to be the best way of achieving the desired product specification.
- Full Text:
- Date Issued: 2009
- Authors: Rust, Nico
- Date: 2009
- Subjects: Insect pests -- Control , Repellents
- Language: English
- Type: Thesis , Doctoral , DTech
- Identifier: vital:10427 , http://hdl.handle.net/10948/d1018273
- Description: The synthesis of p-menthane-3,8-diol via the acid-catalyzed cyclization of citronellal in a dilute aqueous sulphuric acid medium was investigated using conventional batch and continuous systems in order to develop a commercial production process for said p-menthane-3,8-diol (PMD). The batch studies conducted during the first part of this study showed that the formation of PMD from citronellal occurs via an intra-molecular Prins reaction that results in the formation of both the desired PMD product, as well as the partially hydrated isopulegol. It was shown that the formationof the by- product, PMD-acetal, results from the reaction between an intermediate, 5-methyl-2- isopropylcyclohexanol, and the citronellal starting material, and not from the reaction between PMD and citronellal as previously reported. Kinetic studies confirmed the existence of a complicated kinetic model. The formation of PMD from citronellal displayed typical pseudo first order kinetics up to conversions of 70 after which the kinetic model becomes complicated as the result of the establishment of quasi equilibrium reactions between PMD and isopulegol (dehydration of PMD and hydration of isopulegol) and between PMD the PMD-acetal, both systems being acid catalysed. The PMD-acetal formation reaction appears to be second order with respect to PMD. Scale-up studies of the batch process to 30L and 50L scales showed that it would be extremely difficult to limit the level of PMD-acetal formation below the desired level of 1 percent, even if citronellal conversions are restricted to about 50 percent. During studies conducted on a commercially availablemicro-structured organic synthesis plant (OSP) it was shown that it is possible to perform the PMD reaction as a continuous process. The results obtained showed that the use of a micro-mixer such as the caterpillar micro-mixer did not provide enough residence time in order for desirable conversions (- 40 percent) to be obtained. By combining themicro-mixer with delay-loops of different thicknesses and lengths, and using increasing reaction temperatures, it was shown that the conversion of citronellal could be improved to some extent, but compared poorly to the expected conversions for a well-stirred batch reactor. By packing selected delay loops with inert SiC particles, improved mass transfer was observed between the organic and aqueous phases as reflected in the increased conversion of citronellal. Using the observations that were made during the use of the OSP, a continuous-flow, tubular reactor system was designed and constructed. Advanced statistical techniques were used to investigate the effect of variables such as temperature, acid concentration, reactor length, flow rate and the organic to aqueous ratio on the rate and selectivity of the reaction. Mathematical models were derived for citronellal conversion, yield of PMD and yield of PMD- acetals, and used to predict the concentrations of citronellal, PMD and PMD-acetals at set experimental conditions. The results obtained showed that it was possible to obtain a product which approached desired specifications.Downstream processing of the PMD reaction mixture as it exits the reactor requires phase separation and neutralization of the acid catalyst solution, followed by further work-up to recover unreacted starting material and intermediates for recycle back to the synthesis reactor, followed by purification of crude PMD to the desired specification. The study showed that neutralization, prior or after phase separation, does not affect the selectivity of the PMD to such a great extent, but does influence the relative conversion due to extended contact of the catalyst with the organic phase after the reaction is terminated. Recovery of unreacted citronellal and isopulegol could be achieved by a simple vacuum evaporation step, which may either be carried out in a batch manner using traditional distillation equipment, or in a continuous process using wiped-film (short path) techniques. It was also shown that selective crystallization of PMD from the crude product mixture by addition of a solvent, such as heptanes or hexane proved to be the best way of achieving the desired product specification.
- Full Text:
- Date Issued: 2009
Identifying the need for the development of an instrument to determine senior phase teachers' science-assessment competence
- Authors: Lombard, Elsa Helena
- Date: 2002
- Subjects: Science -- Ability testing -- South Africa , Science -- Study and teaching -- South Africa -- Port Elizabeth -- Evaluation , Educational tests and measurements -- South Africa , Competency-based education -- South Africa
- Language: English
- Type: Thesis , Masters , MTech
- Identifier: vital:10786 , http://hdl.handle.net/10948/100 , Science -- Ability testing -- South Africa , Science -- Study and teaching -- South Africa -- Port Elizabeth -- Evaluation , Educational tests and measurements -- South Africa , Competency-based education -- South Africa
- Description: The focus of this study is the competences expected of teachers in the senior phase to assess the Natural Sciences learning area. In order to be in line with the new developments, the South African science teacher will need relevant assessment training in order to utilise appropriate techniques that are in line with the new educational philosophy. The question arises: What competences do teachers need for assessing science in the senior phase? An ethnographic case study was implemented as research methodology in the descriptive research paradigm. The investigation comprised observing the classroom practices of a sample of three senior phase science teachers in two primary schools and in one secondary school in the Port Elizabeth region. The data obtained from the observations were triangulated with related artefacts produced by both the teachers and the learners in each case. In order to establish these expected competences a document analysis was done from a selection of South African documents. The descriptions of the real life assessment practices of the sample of science teachers were then compared with the competences expected by the South African education system. The comparison between the real-life assessment practices and the expected practices concurred with Shepard’s (2000, p.12) belief that the abilities needed to implement classroom assessment “are daunting”. The classroom-based assessment practices of the sample of teachers revealed a variety of assessment beliefs, practices and competence. The needs of these teachers are so diversified and intense that individualised professional development is needed if sustained implementation of the new curriculum and accompanying assessment competences is to be facilitated. The research established the need to develop an instrument that the science teachers can use to assess their own competence. There should be training modules drawn up in line with this instrument. Teachers should be able to choose the professional development modules that would address their own unique needs
- Full Text:
- Date Issued: 2002
- Authors: Lombard, Elsa Helena
- Date: 2002
- Subjects: Science -- Ability testing -- South Africa , Science -- Study and teaching -- South Africa -- Port Elizabeth -- Evaluation , Educational tests and measurements -- South Africa , Competency-based education -- South Africa
- Language: English
- Type: Thesis , Masters , MTech
- Identifier: vital:10786 , http://hdl.handle.net/10948/100 , Science -- Ability testing -- South Africa , Science -- Study and teaching -- South Africa -- Port Elizabeth -- Evaluation , Educational tests and measurements -- South Africa , Competency-based education -- South Africa
- Description: The focus of this study is the competences expected of teachers in the senior phase to assess the Natural Sciences learning area. In order to be in line with the new developments, the South African science teacher will need relevant assessment training in order to utilise appropriate techniques that are in line with the new educational philosophy. The question arises: What competences do teachers need for assessing science in the senior phase? An ethnographic case study was implemented as research methodology in the descriptive research paradigm. The investigation comprised observing the classroom practices of a sample of three senior phase science teachers in two primary schools and in one secondary school in the Port Elizabeth region. The data obtained from the observations were triangulated with related artefacts produced by both the teachers and the learners in each case. In order to establish these expected competences a document analysis was done from a selection of South African documents. The descriptions of the real life assessment practices of the sample of science teachers were then compared with the competences expected by the South African education system. The comparison between the real-life assessment practices and the expected practices concurred with Shepard’s (2000, p.12) belief that the abilities needed to implement classroom assessment “are daunting”. The classroom-based assessment practices of the sample of teachers revealed a variety of assessment beliefs, practices and competence. The needs of these teachers are so diversified and intense that individualised professional development is needed if sustained implementation of the new curriculum and accompanying assessment competences is to be facilitated. The research established the need to develop an instrument that the science teachers can use to assess their own competence. There should be training modules drawn up in line with this instrument. Teachers should be able to choose the professional development modules that would address their own unique needs
- Full Text:
- Date Issued: 2002
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