Use of antiscalants for mitigation of silica (SiO2) fouling and deposition: fundamentals and applications in desalination systems

Colloidal silica (SiO2) is perhaps the most undesirable inorganic deposit formed in process industrial waters, either in bulk or on surfaces, such as membrane heat exchangers or pipelines. Conventional mineral scale inhibitors do not inhibit its formation. Chemical cleaning is difficult and not free from hazards. Research on silica scale formation and prevention is on-going and has led to various chemical approaches. This paper is focused on silica formation, deposition and its inhibition in desalination applications by following designed chemical approaches. More specifically, benchtop screening tests on various silica inhibition chemistries are reported, with emphasis on additives with dendrimeric or polymeric structure and backbone. The inhibition performance of Starburst® polyaminoamide (PAMAM) dendrimers of generations 0.5, 1, 1.5, 2, and 2.5 are investigated in detail. Experimental results show that inhibition efficiency largely depends on structural features of PAMAM’s such as generation number and nature of the end groups, as well as dosage levels. Poly(2-ethyl-2-oxazoline) polymers of a variety of molecular weights are also investigated as potential SiO2 inhibitors. The general scope of silica formation and inhibition in waters relevant to desalination systems is also discussed.

The purpose of this work is to identify and exploit novel dendrimer chemistries as effective SiO2 scale growth inhibitors in process waters. The principle findings are summarized as follows: (1) PAMAM dendrimers are effective inhibitors of SiO2 scale growth. (2) Their structure (generation number and nature of end groups) affects inhibitory activity in a profound way. (3) The NH2-terminated dendrimers, PAMAM 1 and 2 are much more effective SiO2 scale growth inhibitors. The optimum dosage is 40 ppm. (4) PAMAM 1 and 2 dendrimers also form SiO2PAMAM composite precipitates after prolonged periods. These composites have been Acknowledgments The Department of Chemistry, University of Crete for financial support and Professor Petros G. Koutsoukos, University of Patras, Department of Chemical Engineering for experimental assistance and useful discussions.