The principle objectives of this thesis are to determine which gases are evolved during alkaline hydrogen peroxide bleaching, and to develop techniques to measure these gases. Also, the relationship of the composition of the evolved gases from alkaline hydrogen peroxide bleaching of mechanical pulp to the reaction kinetics was elucidated. We have shown that the only gas being evolved into the bleaching headspace is oxygen; whereas, carbon dioxide is produced and fixed in solution as carbonate. / A new non-invasive technique for measuring the amount of oxygen evolved throughout the bleaching reaction was developed. This technique is able to be used in laboratory bleaching experiments that simulated most industrial parameters except consistency, which is limited to hand mixing at medium (10--12%) consistencies. With this method, we have shown that pulp washing, caustic charge and addition of chelating agent play key roles in the rates of oxygen evolution due to the decomposition of hydrogen peroxide. Better washing and higher chelating agent additions result in significant lowering of the rates of oxygen evolution. The rate of decomposition has been related to the dissociation of hydrogen peroxide which is dependent on pH. / The effect of transition metal ions on the kinetics of hydrogen peroxide decomposition during alkaline hydrogen peroxide bleaching of mechanical pulps was investigated. Iron, whether added or native to the pulp, did not contribute to the decomposition of hydrogen peroxide in the presence of lignin. Manganese is the main catalyst for peroxide decomposition, whether added or native to the pulp. The initial rate of oxygen evolution, in the presence of manganese, varies linearly with manganese concentration. Although alkali itself does decompose hydrogen peroxide, increased caustic charge results in an increase in the manganese induced decomposition rate. Kinetic equations are presented, which account for manganese concentration and caustic charge. The effect of DTPA on reducing the rate of hydrogen peroxide decomposition has been attributed to the chelation of manganese. / The relationship between hydrogen peroxide decomposition and the oxidation state of iron and manganese was determined visually. The effect of other bleaching additives on the catalyzed decomposition of hydrogen peroxide were also evaluated. Manganese is unreactive in the +II state, yet very reactive in the +III and +IV forms. Iron is not reactive in the presence of lignin. The presence of cellulose acts to prevent the formation of large low surface area precipitates of manganese III and IV. Manganese IV is the most likely reactive species in alkaline hydrogen peroxide bleaching. DTPA will bind Mn(II) but not the other oxidation states. The DTPA-manganese complex once formed is stable even after the pH is increased. / A new technique for the determination of carbon dioxide produced during hydrogen peroxide bleaching is presented. Carbon dioxide is produced during alkaline hydrogen peroxide bleaching, from reactions of hydrogen peroxide and lignin. The rate of carbon dioxide evolution varies linearly with lignin concentration. Kinetic equations are presented and rate constants have been calculated. The source of carbon dioxide is most likely decarboxylation of carboxylic acid groups formed in lignin by alkaline hydrogen peroxide oxidation.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.38250 |
| Date | January 2001 |
| Creators | Murphy, Craig E. |
| Contributors | van de Ven, T. G. M. (advisor), Heitner, Cyril (advisor) |
| 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 Chemistry.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 001873003, proquestno: NQ78743, Theses scanned by UMI/ProQuest. |
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