Mannich Base Derivatives - A Novel Class of Corrosion Inhibitors for Cooling Water Systems

Abstract

Limited resources of good quality water and the stringent environmental regulations on disposal of water warrant the operation of the present day's cooling water treatment systems with the highest practically feasible cycle of concentration (COC). However, with increase in COC, all the inorganic and organic constituents of the recirculating water increase proportionally thereby augmenting the possibility of failure of the system due to corrosion, scaling and fouling. Environmental concerns on the use of heavy metal based corrosion inhibitors have called for an effective alternative approach that is environmentally safe as well as cost-effective. The present investigation is aimed at evaluating the suitability of some Mannich base derivatives, namely, 4-methyl-2-fonnyl-6-(piperidine-1-yl methyl) phenol (MFPP) and 4-methyl2-formyl-6-(molpholine-1-yl methyl) phenol (MFMP), synthesized in our laboratory, as corrosion inhibitors for cooling water treatment systems, under simulated laboratory conditions. Mild steel was used as the substrate material and the inhibition efficiency of MFPP and MFMP were assessed under varying conditions of temperature, pH and dissolved salts. Both compounds exhibit good inhibition towards the corrosion of mild steel under varying experimental conditions. The other interesting feature about these compounds is their ability to perform as a self-indicator in the cooling water system based on the existence of their chemical structure under acidic and alkaline conditions, respectively, exhibiting a colourless and fluorescent green colour. This inherent property of these compounds is very useful in continuous monitoring and control of cooing water systems. Besides it also helps in identifying critical conditions like tolerance level of the acid dosage, given to prevent scaling, which would otherwise cause excessive metal attack and ultimately lead to a premature failure of the system.