Weak Acid Cation Exchangers

The polycondensation exchangers can be prepared by the reaction of salicylic acid, or 1,3,5-resorcylic acid, with formaldehyde. In the former case, the addition of phenol is required because one ortho-position is not accessible to the aldehyde.

Several polymerization networks that contain -COOH groups are known. Some structures together with their preparative routes are illustrated in Figure 3. Only those with acrylic networks are commercially available.

Compared with the sulfonic group the -COOH group, has a much lower acidity and is fully ionized only in an alkaline medium as a salt form. The -COOH group also shows a very considerable preference for the H ion, unlike the -SO3H group. This situation leads to easy regeneration of the weak acid exchangers from salt form to H form using stoichiometric quantities of mineral acids. These exchangers can react only with bases, like NaOH, and alkaline salts; they show a strong preference for Ca and Mg cations. The 'salt-splitting' reactions do not take place in the case of the weak acid cation exchangers.

The acrylic-type exchangers have a higher acidity than the methacrylic ones and can be used for the treatment of hard water containing large quantities of bicarbonates. The methacrylic type is used for special applications, such as the purification of antibiotics, where a mild pH is required.

Solar Panel Basics

Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

Get My Free Ebook


Post a comment