Pure Water is an essential part of creating chemical reagents, microbiological buffers and media that are consistently pure. It is also an excellent source of water for glassware washing, and as feed water for laboratory equipment such as autoclaves, laboratory dishwashers, and water baths. It is also a recommended source of pretreated water for your Type 1 ultrapure systems.
TYPE 3 (RO / DEIONIZED) WATER Purification – Evoqua Labostar
How does reverse osmosis work?
A solution with a high salt concentration is separated by a semi permeable membrane from a solution with a low salt concentration. In normal osmosis, the water from the side with less salt will begin permeating the membrane into the more concentrated solution. In reverse osmosis, pressure is supplied that exceeds the osmotic pressure of the higher concentrated solution to force water in the reverse direction. Clean water starts to permeate through the membrane.
This water contains approximately 98% less salt than the inlet water. This technology will also remove > 99 % of particles and bacteria.
The production rate of an RO system depends on the water temperature. Our specifications are given at a water temperature of 15°C. Each °C of temperature variation creates a water production shift of 3 %! Most manufacturers use 25°C to rate their performance, however, with our systems, you can be assured that your water production is in the right range even if the temperature falls below 25°C.
How does deionization works?
When inorganic salts dissolve in water they disassociate into positively charged cations and negatively charged anions. Common table salt, sodium chloride (NaCl), disassociates to form positively charged sodium and negatively charged
chloride. (NaCl (solid) + H2O Na+ + Cl- + H2O) These and other unwanted ions may be removed by ion exchange.
Ion exchange is the reversible exchange of unwanted ions for wanted ions between a solid and liquid phase. In most ultrapure or reagent grade water applications, the solid materials are ion exchange resins made of styrene-divinylbenzene copolymers. Strong acid cation exchange resin is used to exchange cations such as sodium. Strong base anion resin is used to remove anions such as chloride. Ion exchange resins are typically produced as small bead shaped materials exhibiting a gel or porous appearance. The styrenedivinylbenzene copolymer resins contain multiple sulfonic groups or sites for cation exchange and quaternary amine groups for anion exchange throughout the resin structure.
Liquid will pass over and through the resin bead. Since the exchange sites are distributed throughout the structure of the resin bead, there is high surface area availability for efficiention exchange. The ion exchange sites on the resin structure have an affinity toward ions based on molecular weight and valence or charge. Monovalent ions of higher molecular weight are held more strongly to the resin exchange site. Divalent or multivalent ions are held more strongly than lower charge ions.
Cation exchange resins used for ultrapure water are provided in the hydrogen (RH+) form and anion resins are provided in the hydroxide form (ROH-). As water containing sodium chloride passes through and around the cation and anion resins, sodium is exchanged for hydrogen and chlorides are exchanged for hydroxide ions. This can be illustrated for the individual resins as:
Cation = RH+ + Na+ + Cl- <> RNa+ + H+ + Cl-
Anion = ROH- + Na+ + Cl- <> RCl- + Na+ + OH-
Note that the above reactions are illustrated as reversible. Concentrated acid can be used to regenerate exhausted cation resin and concentrated caustic can be used to regenerate anion resin. In practice, the cation resin is placed in front of the anion resin in a two bed system. This would eliminate the sodium (most) prior to the anion exchange reaction. The hydrogen and hydroxide ions then combine to form water molecules. Thus, the reaction becomes:
RH+ + Na+ + Cl- <> RNa+ + H+ + Cl- <> + ROH- RCl- + H+ + OH- H2O
The most efficient way to apply cation and anion resins for high purity water applications is to proportionally mix the two
resins together into a single bed. Since cation resins have a higher capacity per unit volume than anion resins, the pro-
portions are typically about 40 % cation and 60 % anion by volume. Mixing the resins basically creates many two-bed sys-tems inside one bed of resin and allows for virtually complete removal of ions. Mixed bed resins can produce water puri-
ties of 18.2 MΩ-cm (0.055 μS/cm) at 25°C. Two-bed systems may struggle to reach 10 MΩ-cm due to competing ions
|ISO 3696 Water Specifications |
|||Type 3 (RO) water|
|Resistivity (megohm-cm compensated to 25°C)||0.25|
|Absorbance at 254 nm/cm optical path (A.U.)||N.S.|
|Dry residue after evaportating on heating at 110°C™||<2.0
Laboratory, medical and industrial applications all need pure water in various qualities and quantities.
- Feed for laboratory ultrapure
- General chemistry
- Laboratory washing machines
- Water for autoclaves and
- buffer preparation