Water-soluble low molecular weight polymers are known to affect the crystal habit of scale-forming minerals and their rates of deposition. Poly(acrylic acid) (PAA) and poly(maleic acid) are commonly used to control scale formation in sugar mill evaporators. Calcium oxalate (both mono-and dihydrate) forms the bulk of the hard intractable scale found in Australian sugar mills, causing efficiency losses of significant economic importance. In this work, the formation of calcium oxalate monohydrate in a synthetic juice solution was investigated in the presence of PAAs of varying molecular weights and end-group functionality and a strong dependency on both of these factors was observed. Terminal functionality was controlled using three chain-transfer agents (CTA): thioethanol, thioglycolic acid, and dodecanthiol. Effectiveness of inhibition varied with CTA in the order thioethanol ϳ thioglycolic acid Ͼ dodecanthiol for all molecular weights. This suggests that polymer end groups play a role in scale inhibition. The polymers that were prepared with dodecanthiol accelerated rather than inhibited calcium oxalate formation, implying a different mode of action on calcium oxalate crystallization. Consistent with previous reports for other scales, the calcium oxalate inhibition tests show optimum effectiveness for PAAs of molecular weight 2000 -4000.

Rapid flocculation and sedimentation of suspended particles in primary cane sugar juice is achieved using a high molecular weight anionic polymer flocculant. This work reports on efforts to enhance the performance of an anionic flocculant by the addition of cationic polymers. Homopolymers of poly(trimethylammonium ethyl methacrylate chloride) (TMAEMAC) and cationic copolymers of poly(trimethylammonium ethyl acrylate chloride) (TMAEAC) and acrylamide were synthesized and their performance, to enhance the flocculation and sedimentation of cane sugar juice particles, was evaluated by turbidity and settling rate measurements. The charge-patch mechanism best explains the performance of the homopolymers, whereas the action of the copolymers is attributed to the bridging mechanism. The results of this work indicate that the copolymers are more effective than the homopolymers to aid flocculation and sedimentation of the cane sugar juice particles, and that the best-performing polymers are those that act by the bridging mechanism. Addition of increased amounts of anionic flocculant did not confer an improvement, suggesting that the cationic bridging flocculant targets a different population of particles that is largely responsible for the residual turbidity.

Two lipophilic tetradentate ligands, 5,5'-di-t-butyl-and 5,5'-dihe~yl-2,2~-bipyrirnidine, were prepared via either Ullmann or nickel(0)-promoted reactions in low but useful yields. Approaches towards the synthesis of lipophilic ligands based on 2,2'-biimidazole, namely 4,4',5,5'tetrabutyl-2,2'-biimidazole (from decane-4,5-dione) and various 4,4',5,5'-tetra(ary1amino)-2,2'-biimidazoles (from 4,4',5,5'-tetrabromo-2,2'-biimidazole and arylamines), and a 2,2'bibenzimidazole, 5,5',6,6'-tetra(octyloxy)-2$-bibenzimidazole (from N, N1-bis[4,5-di(octyloxy)-2-nitrophenylloxamide), were uniformly unsuccessful for preparing the 2,2'-biheteroaryl compounds.