The selective dechlorination of poly-chlorophenols
- Authors: Thomas, Maxwell Paul
- Date: 2009
- Subjects: Sewage -- Purification -- Chlorination , Pesticides -- Toxicology , Chlorine -- Toxicology
- Language: English
- Type: Thesis , Doctoral , DTech
- Identifier: vital:10391 , http://hdl.handle.net/10948/1124 , Sewage -- Purification -- Chlorination , Pesticides -- Toxicology , Chlorine -- Toxicology
- Description: Liquid phase catalytic hydrodechlorinations can provide a convenient and environmentally friendly method for treating organic chlorinated compounds in waste streams generated during the manufacturing of agrochemicals. During such treatment hydrochloric acid is generated as a by-product, which can be easily neutralized employing a base to yield an inorganic salt. This work describes the results obtained during the liquid phase hydrodechlorination of 2,6-dichlorophenol (2,6-DCP) and 2,4,6-trichlorophenol (2,4,6-TCP). The hydrodechlorination of these chlorinated phenolic compounds in a mixture of methanol and water was investigated using supported and unsupported palladium catalysts to yield lower chlorinated phenols or phenol. Various parameters were investigated such as catalyst concentration, ammonium formate concentration, effect of base addition and effect of temperature. During this study two methods of hydrodechlorination were also investigated such as hydride-transfer hydrogenolysis, using ammonium formate, and hydrogenolysis, using dihydrogen. These methods offer a mild treatment in terms of the reaction temperature with temperatures used below 800C. A comparison of the palladium catalyst systems using these methods also showed that Pd/C produced the best results in terms of the hydrodechlorination rate and the selectivity towards phenol. When the ammonium formate method was used, complete hydrodechlorination of both substrates was achieved in 1h of reaction time at a selectivity of 100 percent towards phenol. A comparison of the method using dihydrogen and Pd/C showed that the reaction rate and the selectivity towards phenol during the hydrodechlorination of 2,6-DCP were 87.92 percent and 93.30 percent. Similarly, the reaction rate and selectivity during 2,4,6- TCP hydrodechlorination were 63.77 percent and 70.57 percent. These results were achieved in a reaction time of 3 hours. A high catalyst loading increases the reaction rate at the expense of selectivity, due to the formation of cyclohexanone, formed during further hydrogenation of phenol. The formation of cyclohexanone was limited at high temperatures (ca. 800C) with none detected during the hydrodechlorination of 2,6-DCP and 0.19 percent during the hydrodechlorination of 2,4,6-TCP. Evaluation of the hydrodechlorination parameters showed that the catalytic efficiency of the Pd/C catalysts was inhibited as the reaction proceeded due to the formation of HCl as by-product. A significant increase in the reaction rate was achieved when the reaction was performed in the presence of an inorganic base, which neutralized HCl.
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- Date Issued: 2009
The development of a model for the assessment of the subject entrepreneurship and business management at the N4 level using an outcomes based education approach
- Authors: Olivier, Marina
- Date: 2002
- Subjects: Curriculum-based assessment -- South Africa , Competency-based education
- Language: English
- Type: Thesis , Masters , MTech
- Identifier: vital:10781 , http://hdl.handle.net/10948/86 , Curriculum-based assessment -- South Africa , Competency-based education
- Description: The focus of this study is on assessment in an Outcomes Based Education environment. The question arises as to how assessment of Entrepreneurship and Business Management-N4 can be changed to suit an Outcomes Based Education approach. Action research was used as the research methodology and the findings were reported as case studies. A sample of three colleges in the Eastern Cape was chosen to take part in the study. Only two modules of the Entrepreneurship and Business Management-N4 syllabus were adapted to suit an Outcomes Based Education approach, as the students still had to write the normal external examination at the end of the semester as required by the Department of Education. In the first two cycles the participants implemented Outcomes Based Education in the classroom using only the resources available at the college for the old education system. During the third cycle the researcher implemented Outcomes Based Education in the classroom under the same circumstances, but with the advantage that the researcher benefited from the reflections of the first two cycles. In order for assessment to meet the requirements of an Outcomes Based Education approach, it was necessary to change teaching practices as well. Important aspects such as group work, new assessment methods, the role of resource materials and the training of lecturers were included in the study. At the end of the third cycle a model for the assessment of Entrepreneurship and Business Management-N4 was developed. Recommendations on aspects such as students, lecturers, resources and assessment were made.
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- Date Issued: 2002