Polyphospate-based industrial cooling water treatment
Condensed phosphates were first used in cooling water applications in the early 19030's. Extensive use was found for these polyphosphates because of their ability to control calcium carbonate scaling at threshold or substoichiometric dosages. Later, their ability to control the corrosion of steel in open recirculating cooling water systems and once through cooling water systems demonstrated the versatility of this class of compounds. The use of polyphosphates began to give way to the acid chromate programs as the primary corrosion inhibitor for mild steel in open recirculating systems in the early 1960's. This preference for chromate and chromate-zinc programs was still quite prevalent in the early 1970's. The cause for this change stems from the one major disadvantage of polyphosphate treatments -hydrolytic instability which produces orthophosphate. The orthophosphate anion forms insoluble scales with all bivalent cations, the most important of which are calcium, magnesium and iron. These scales can foul heat transfer surfaces and reduce dramatically heat transfer efficiency of process heat exchangers. In addition to providing fouling problems, the orthophosphate anion fails to provide the positive effects of condensed phosphates. Orthophosphate does not show a threshold effect and is not as effective in corrosion prevention of steel as condensed phosphates. The Clean Water Act of 1972 began a level of environmental awareness that was not seen before. One of the outcalls of this movement was the identification of hexavalent chromium (chromates) as toxicity to aquatic life because of its low LD50. Chromates were also identified as potential carcinogens. Efforts to remove the chromate ion from cooling tower blowdown were hampered by the need to label any sludge from the waste treatment facility as hazardous. The need for a non chromate cooling water treatment that could provide the same or better performance as the acid-chromate-zinc treatments became a top priority for industry. This dissertation in the form of US Patent 4,172,032 describes the development of such a cooling water treatment. It also describes the discovery of an optimum molecular weight of polyphosphate as the most critical factor in determining the performance of these programs. The synthesis of spire (4,4) nonanes was done in the period of 1966 to 1970. This work was completed but not defended before a Dissertation Defense Committee. It is included in Appendix A of this document in the interest of completeness.
George Thomas Farley,
"Polyphospate-based industrial cooling water treatment"
Dissertations and Master's Theses (Campus Access).