ASSESSMENT OF NOVEL POLY(ACRYLIC ACID) SPECIES FOR CALCIUM OXALATE SCALE INHIBITION

Calcium oxalate scale is a major cause of fouling in sugar mill evaporators and among the most difficult scale to remove. Low molecular weight poly(acrylic acid) and poly(maleic acid) are commonly used for scale inhibition, but there has been little work on optimising these polymers for maximum performance for calcium oxalate scale. Acrylic acid was polymerised using various concentrations of an initiator and a range of chain transfer agents (CTA). The function of the CTA was to control the molecular weight of the product and to introduce specific functional groups (viz. –OH, –COOH, or –C12H25) to the end of the polymers produced. The synthesised poly(acrylic acids) were evaluated for their ability to inhibit calcium oxalate crystal formation in a synthetic juice solution. A number of products terminated with –OH and –COOH groups showed a marked improvement over common commercial scale inhibitors. Others, terminated with –C12H25 groups, gave enhanced formation of calcium oxalate crystals, suggesting it may be possible to precipitate out calcium oxalate scale in earlier evaporator vessels where it may be much easier to remove by chemical means. These results indicate a significant difference in inhibition behaviour for different chain transfer agents independent of the molecular weight, suggesting for the first time, that polymer end-groups may participate in scale inhibition.