Enantiomers are chiral molecules (i.e. they are mirror-images of each other). They have identical physical properties except for the rotation of polarized light. However their chemical properties are different when reacting with other chiral molecules. The majority of biological processes involve the reaction of two or more chiral molecules. There is therefore a strong interest coming from the pharmaceutical, food and agricultural industry for the separation of enantiomers. / Separation methods such as chromatography exist but are generally expensive and limited in scale. Stereosynthesis often has prohibitive development and operating costs. / For 10 to 15% of known enantiomeric systems, a conglomerate is formed upon crystallization (each individual crystal contains only one type of enantiomer). / Crystallization is widely used as an inexpensive separation process which takes advantage of the difference in solubility of the compounds to be separated and yields very high purities in one separation stage. There is no difference in solubility between two enantiomers but in the special case of conglomerates, a difference in crystallization rate can be used as the driving force for the separation of the enantiomers. / In this project, the effects of the important parameters governing the crystallization of asparagine (ASN) were studied in order to develop a separation method based on crystallization. ASN is an amino acid having two enantiomers (L-ASN and D-ASN) and forming a conglomerate. The effects of mixing speed, crystallization temperature, initial supersaturation and seeds (amount, type and time of addition) on the crystallization rates were studied. The crystallization temperature was shown to have a negligible effect over the range studied. Increasing initial supersaturations had a strong accelerating effect on the crystallization. The addition of L-ASN seeds increased the crystallization rate of L-ASN without affecting that of D-ASN. The corresponding statement was true for D-ASN. Larger amounts of seeds and faster mixing increased crystallization rates. Separation methods were developed and 95.8-97.7% pure enantiomers with yields of 73.1% were obtained in a cyclic process. The growth and desupersaturation rates were also modeled.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.100356 |
| Date | January 2005 |
| Creators | Elgarhy, Karim. |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Department of Chemical Engineering.) |
| Rights | © Karim Elgarhy, 2005 |
| Relation | alephsysno: 002340128, proquestno: AAINR25138, Theses scanned by UMI/ProQuest. |
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