The interplay between cationic polyethyleneimine and anionic polyelectrolytes for the control of silica scale formation in process waters

• A. Spinthaki, A. Stathoulopoulou and K. D. Demadis

Engineering, Growth and Design Laboratory, Department of Chemistry, University of Crete, Voutes Campus, Crete, GR-71003, Greece

Abstract: Stabilization of mono- and disilicic acids is accomplished by using a cationic polymeric chemical additive, polyethyleneimine (PEI), in supersaturated silica solutions (the starting solution contained 500 ppm/8.3 mM sodium orthosilicate, Na2SiO3·5H2O, expressed as SiO2) at pH = 7. The PEI polymeric system contains an excess of amine groups (~25% primary amines, ~50% secondary amines and ~25% tertiary amines) that become protonated at circumneutral pH, hence charging the molecules positively. PEI was found to be efficient as a silica scale inhibitor only at the low dosage of 10 ppm. Its inhibitory activity was found to drop as its concentration increased. It was hypothesized that PEI is entrapped into the colloidal silica matrix and deactivated. Thus, one way to maintain its activity was to create blends of PEI and anionic polymers. Anionic polyelectrolytes that were tested included polyacrylic acid (PAA), phosphonated polyacrylic acid (PAA(PO3H2)2), carboxymethylinulin (CMI), poly(acrylamide-co-acrylic acid) (PAM-co-AA), phosphonomethylated chitosan (PCH) are also studied for their silica scale inhibition efficiency. It is observed that the silica inhibitory activity of PEI was improved upon its combination with anionic polyelectrolytes.

Keywords: silicic acid stabilization, water systems, inhibitors, polyethyleneimine, PEI, scale, silica deposits, water treatment

Int. J. Corros. Scale Inhib., 2015, 4, no. 2, 125-138 PDF (845 K)
doi: 10.17675/2305-6894-2015-4-2-125-138

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