WATER TREATMENT of 6.0-7.5 must now operate at higher pH ranges to help mitigate the rate of mild steel corrosion , typically 8.0-9.2 . This has a significant impact upon
CaCO 3 saturation and the potential for scale formation and requires the use of polymers and / or phosphonates for
CaCO 3 control . From a polymer standpoint ,
CaCO 3 control does not require the development of new technologies . At a low Langelier saturation index ( LSI ) of < 2.0 and calcite saturation of < 125x , low (< 3,000 Da ) MW polyacrylic acids and / or HEDP phosphonate can be used . At high (> 2.0-3.0 ) LSI and calcite saturation of < 225x , polymaleic acid and / or PBTC phosphonate are effective choices .
The real issue is that polycarboxylates are extremely poor to ineffective for the stabilisation of
Ca 3
( PO 4
) 2 and zinc . This is important for two reasons . Phosphates and zinc must be stabilised in cooling recirculating waters in order to be available as mild steel corrosion inhibitors . In addition , bulk water precipitation of Ca 3
( PO 4
) 2 forms mineral scale , while bulk water precipitation of zinc forms a deposit .
Essentially , the industry solved the issue of removing Cr 6 + but did not have in place a polymer technology to manage all of the resulting problems . However , technology was soon developed to address these issues in the form of sulfonated polymers .
2-acrylamido-2-methylpropane sulfonic acid ( AMPS *) copolymers were first developed in the mid-1960s and have been refined ever since . They are highly effective scale inhibitors for water treatment applications . Acrylic acid : AMPS copolymers are now industry standard for the effective stabilisation of Ca 3
( PO 4
) 2 and transition metals like zinc .
Building a new polymer
Radical Polymers , a division of MFG Chemical , has sought to develop an optimised copolymer incorporating the learnings from previous work in the industry . The obvious thread here is the use of the common polymer
Figure 3 - Calcium phosphate stabilisation with polymers of < 5,000 ( top ), 5,000-10,000 ( middle ) & > 10,000 Da ( bottom )
functional groups of carboxylates , sulfonates and non-ionics or hydrophobics .
Specifically , polycarboxylates provide good functionality for metal carbonate and metal sulfate scales and effective functionality for inorganic solids control . The addition of sulfonate functional groups added a dimension of efficacy for the stabilisation of phosphate and transition metals .
AMPS is the primary building block for most widely commercialised sulfonated copolymers used today . Typical ratios are either 60:40 or
75:25 acrylic acid : AMPS with MWs of 12,000-15,000 or 4,500 respectively . These materials can be enhanced in one way or another by using either hydrophobic monomers or other sulfonate types , such as sodium styrene sulfonate .
In this work , we examined several critical factors such as the percentage of sulfonated monomer , polymer MW , the use of a functional polymerisation aid ( FPA ) and the incorporation of one of three distinct hydrophobic monomers . We judged the impact of these changes by looking at Ca 3
( PO 4
) 2 stabilisation .
MAY / JUN 2024 SPECCHEMONLINE . COM
59