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Use of H 2 O 2 in the Presence of a Catalyst as Bleaching Agent

Use of H 2 O 2 in the Presence of a Catalyst as Bleaching Agent. MELVINA CHENG (5) THEODORA LI (20) VIVIAN LI (21) RENA LI(22) CHERRY PO (28) . Aims. 1 . Find a detergent formulation that bleaches at room temperature

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Use of H 2 O 2 in the Presence of a Catalyst as Bleaching Agent

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  1. Use of H2O2 in the Presence of a Catalyst as Bleaching Agent MELVINA CHENG (5) THEODORA LI (20) VIVIAN LI (21) RENA LI(22) CHERRY PO (28)

  2. Aims 1. Find a detergent formulation that bleaches at room temperature 2. Find a suitable catalyst that promotes hydrogen peroxide bleaching at room temperature

  3. Principles of bleaching process Oxidative Reductive

  4. Oxidative bleaching process Hypochlorous acid (HOCl) in chlorine bleaches HOCl (aq) + D H+ (aq) + Cl- (aq) + DO Coloured Colourless

  5. Hydrogen peroxide (H2O2) in color-safe bleaches H2O2 (aq) + D  H2O (l) + DO Coloured Colourless

  6. Reductive bleaching process Sulphur dioxide (SO2) SO2 (aq)+ H2O (l)+ D → (SO4)2- (aq)+ (D - O ) Coloured Colourless

  7. Temperature-Dependent Oxidizing Power of H2O2 • Strong oxidizing agent  powerful bleaching agent. • Fairly stable, but decomposes into water and oxygen when heated above 80oC. 2H2O2 ž  2H2O + O2 + Energy • Rate of decomposition is dependent on • the temperature and concentration of the peroxide • the presence of impurities and stabilizers • Catalyst (e.g.MnO2) increases the rate of decomposition of hydrogen peroxide

  8. Substitutes of H2O2 in solid form • Sodium perborate (SPB) • Sodium percarbonate (Na2CO3·1.5H2O2) • liberates hydrogen peroxide when added to water. 2(2 Na2CO3 ·3 H2O2) → 2 Na2CO3 + 3 H2O2

  9. Surfactants Lower the surface tension of a liquid Lower the interfacial tension between 2 layers Act as detergents, wetting agents, emulsifies, foaming agents, dispersants

  10. Common surfactants used in detergents Linear Alkyl benzene sulfonates (LAS) Esterquats Ethoxylated fatty amines

  11. Structure of LAS

  12. Cleaning action of surfactants Surfactant molecules concentrate in surface layer of water Lower surface tension of water wetting agent

  13. Hydrocarbon tails are soluble in non-polar substances, e.g. oil. Hydrophilic heads are soluble in water.

  14. Water molecules attract hydrophilic heads and lift up grease.

  15. On stirring, hydrophilic heads repel each other. Emulsion formed.

  16. Tiny droplets can be washed away easily

  17. Environmental issues of detergents • soapy detergents (soaps) • soapless detergents (synthetic detergents • Detergents go to waste water systems, e.g. rivers and seas

  18. Detergents

  19. Biodegradable Detergents • Contain straight hydrocarbon chains • Broken down by bacteria in water • During the process, bacteria will use up dissolved oxygen in water • Water lives die

  20. NON-BIODEGRADABLE DETERGENTS used in the early 1950s contain branched hydrocarbon chains Unable to be broken down by bacteria Produce thick foam which will remain in rivers and seas for a long time →water pollution Prevent oxygen from dissolving in water →aquatic lives die

  21. Phosphate Additives Phosphorus (P) • Important in photosynthesis & all energy recovering processes in plants • One of the main nutrients in fertilizers • soften water • prevent formation of scum Example: sodium tripolyphosphate

  22. Impacts of adding phosphate additive to detergents Plant nutrients Causing rapid growth of algae in rivers and seas → red tides When the algae die and rot, they again use up dissolved oxygen in water. →Death of Aquatic lives

  23. Solutions Remove detergents and phosphates in sewage works →too costly!!! Better way: Use detergents without phosphates

  24. References • http://www.hindawi.com/journals/ijac/2009/404836.fig1.html • http://en.wikipedia.org/wiki/Hydrogen_peroxide#Decomposition

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