Cleaning chemistry and cleaning physics A3P Seminar Brussels, Belgium November 2009 Dusko Filipovic Borer Chemie AG

Agenda • Cleaning chemistry - Water • Cleaning physics - Heat absorption - Phase changes - Surface tension • Cleaning mechanisms

Water: a cleaning instrument? • Chemical properties

- Dipole character - Water hardness - pH-value

Chemical properties • Dipole character two opposite electrically-charged sides, dipole-molecule: two poles; centre of gravity of the negative charges does not coincide with the centre of gravity of the positive charges. Reason: molecule is angled.

H δ+

O δH

Dipole - character is the reason for the properties of water.

Chemical properties • Water hardness - Presence of Ca2+ and Mg2+

– they can engage in reactions that leave insoluble mineral deposits. – These deposits can make hard water unsuitable for many uses. – Scale formation and excessive soap consumption are the main concerns with hardness.

Chemical properties • Water hardness (cont.) - Mineral deposits are formed by ionic reactions resulting in the formation of an insoluble precipitate. - For example, when hard water is heated, Ca2+ ions react with bicarbonate (HCO3-) ions to form insoluble calcium carbonate (CaCO3), as shown in:

Chemical properties • Water hardness (cont.) - This precipitate, known as scale, coats the vessels in which the water is heated, producing the mineral deposits on your cooking dishes. - In small quantities, these deposits are not harmful, but they may be frustrating to try to clean. - As these deposits build up, however, they reduce the efficiency of heat transfer, so food may not cook as evenly or quickly in pans with large scale deposits.

Chemical properties • Water hardness (cont.) - More serious is the situation in which industrialsized water boilers become coated with scale: the cost in heat-transfer efficiency can have a dramatic effect on your power bill! - Furthermore, scale can accumulate on the inside of appliances, such as dishwashers, and pipes. As scale builds up, water flow is impeded, and hence appliance parts and pipes must be replaced more often than if Ca2+ and Mg2+ ions were not present in the water.

Chemical properties • Water hardness – softening of hard water - For large-scale municipal operations, a process known as the "lime-soda process" is used to remove Ca2+ and Mg2+ from the water supply. - Ion-exchange reactions, which result in the formation of an insoluble precipitate, are the basis of this process. - The water is treated with a combination of slaked lime, Ca(OH)2, and soda ash, Na2CO3. Calcium precipitates as CaCO3, and magnesium precipitates as Mg(OH)2.

Chemical properties • Water hardness – softening of hard water (cont.) - These solids can be collected, thus removing the scale-forming cations from the water supply. - To see this process in more detail, let us consider the reaction for the precipitation of Mg(OH)2. - Consultation of the solubility guidelines in the experiment reveals that the Ca(OH)2 of slaked lime is moderately soluble in water. - Hence, it can dissociate in water to give one Ca2+ ion and two OH- ions for each unit of Ca(OH)2 that dissolves. The OH- ions react with Mg2+ ions in the water to form the insoluble precipitate.

Chemical properties • Water hardness – softening of hard water (cont.) - The Ca2+ ions are unaffected by this reaction, and so we do not include them in the net ionic reaction. They are removed by the separate reaction with CO32- ions from the soda ash:

- Household water softeners typically use a different process, known as ion exchange.

Chemical properties • Water hardness – softening of hard water (cont.) - Ion-exchange devices consist of a bed of plastic (polymer) beads covalently bound to anion groups, such as -COO-. - The negative charge of these anions is balanced by Na+ cations attached to them. When water containing Ca2+ and Mg2+ is passed through the ion exchanger, the Ca2+ and Mg2+ ions are more attracted to the anion groups than the Na+ ions. - Hence, they replace the Na+ ions on the beads, and so the Na+ ions (which do not form scale) go into the water in their place.

Chemical properties • Water hardness – temper / hardness grade Conversion of Ca-ions and Mg-ions into CaO „in former times“: Example: in Germany 1°dH (1 degree of German hardness)

10mg CaO in 1L water

7,19mg Ca 2+ and 4,34mg Mg 2+ „today“: indication in mmol Ca- respectively Mg-ions/L

Chemical properties • Classification of the hardness grades: e.g. in Germany „in former times“:

„today“:

•very soft: 0-4

•Hardness level 1:

•soft: 4-8

0 – 1,3mmol/L

•middlehard: 8-12

•Hardness level 2:

•quite hard: 12-18

1,3mmol/L-2,5mmol/L

•hard: 18-30 •very hard: > 30

•Hardness level 3: 2,5-3,8mmolL •Hardness level 4: > 3,8mmol/L

Chemical properties • Water hardness and the importance for the cleaning chemistry Ions of „hard water“ (Ca 2+ , Mg 2+ ) could influence the surfactant effect negatively detergents containing surfactants are in „soft water“ more effective than in „hard water“

formulated cleaners consist of substances, that cover Ca 2+ bzw. Mg 2+ -Ions as a complex to achieve the best possible effectiveness (e.g. MGDA, EDTA, NTA, Polyphosphate)

pH-value • The pH-change of aqueous solutions could be used for cleaning effectiveness the solubility of residues on surfaces could be improved as:

1. Some acidic residues are more soluble in alkaline solutions. 2. Some alkaline residues are more soluble in acidic solutions.

E.g.: Surface-oxides (e.g. Fe2O3) are cleaned with acidic solutions (z.B. H3PO4).

Physical properties • Heat absorption • Phase changes • Surface tension

Heat absorption • Heat properties of water make it useful for transporting heat. • High specific heat (capacity) • It takes a lot of heat to increase the temperature of a fixed weight of water. • This water with the “stored heat” can be transported elsewhere, and the “stored heat” can be used in cleaning operations.

Phase changes • From gas to liquid, liquid to gas, solid to liquid or liquid to solid. • Liquid to gas: evaporation or boiling (100 °C at atmosph. pressure. • Water has a high specific heat, the amount of heat required to vaporize is high, it is stored in the steam. • Steam can be transported to another location and be used for sanitation.

Surface tension – – – –

Wetting properties of water Unit: dynes/cm Pure water: 70 dynes/cm By adding a surfactant to the water, the surface tension is lowered, the wetting ability increased. – By adding a typical surfactant to the water, you will lower the s.t. to at about 30-45 dynes/cm. – S.t., especially with the addition of a surfactant, is vitally important in the wetting of surfaces in cleaning operations.

Water qualities • Tap water: meets only drinking water standards and there are no restrictions on water hardness. Some companies use it as a initial rinse or initial cleaning step. • Purified water: purified by ion-exchange, reverse osmosis or distillation and tested to meet certain standards of the USP. Used for manufacturing many pharmac. products exept those that are injectables.Microbial count of