Non-nitrite and non-molybdate inhibitors for closed loop systems

Abstract

Methods and compositions for inhibiting corrosion in closed loop systems in which a heat transfer fluid is recirculated. A combination of a C6-C14 dicarboxylic acid and C6-C14 monocarboxylic acid is added to the recirculating fluid in a weight ratio of from 10:1 to 1:2.

What is claimed is: 
     
         1 . A method of treating a closed loop system in which a fluid is recirculated to inhibit corrosion, the method including:
 combining with the fluid a C6-C14 dicarboxylic acid and a C6-C14 monocarboxylic acid such that the dicarboxylic acid and monocarboxylic acid are present in the fluid in a weight ratio of from 10:1 to 1:2.   
     
     
         2 . The method according to  claim 1 , wherein the dicarboxylic acid and the monocarboxylic acid are present in the fluid in a weight ratio of from 3:1 to 1:1. 
     
     
         3 . The method according to  claim 1 , wherein the dicarboxylic acid and the monocarboxylic acid are present in the fluid in a weight ratio of from 2.5:1 to 1.5:1. 
     
     
         4 . The method according to  claim 1 , wherein the dicarboxylic acid includes a C8-C12 dicarboxylic acid, and the monocarboxylic acid includes a C8-C12 monocarboxylic acid. 
     
     
         5 . The method according to  claim 1 , wherein at least one of the dicarboxylic acid and monocarboxylic acid includes an aromatic group. 
     
     
         6 . The method of  claim 4 , wherein the dicarboxylic acid includes sebacic acid. 
     
     
         7 . The method of  claim 4 , wherein the dicarboxylic acid includes 2,6-napthalene dicarboxylic acid. 
     
     
         8 . The method of  claim 4 , wherein the monocarboxylic acid includes octanoic acid. 
     
     
         9 . The method of  claim 4 , wherein the monocarboxylic acid includes decanoic acid. 
     
     
         10 . The method of  claim 1 , wherein the dicarboxylic acid is combined with the fluid in an amount that is in a range of from 1 ppm to 5000 ppm. 
     
     
         11 . The method of  claim 1 , wherein the monocarboxylic acid is combined with the fluid in an amount that is in a range of from 10 ppm to 1000 ppm. 
     
     
         12 . The method of  claim 1 , further including combining solvent polymaleic acid (PMA-s) with the fluid. 
     
     
         13 . The method of  claim 12 , wherein the PMA-s and the dicarboxylic acid component are combined with the fluid in a weight ratio of from 1:4 to 1:100. 
     
     
         14 . The method of  claim 1 , further including combining an azole with the fluid. 
     
     
         15 . The method of  claim 1 , further including combining a buffer with the fluid. 
     
     
         16 . The method of  claim 1 , further including combining an inert chemical tracer with the fluid in a known ratio with the dicarboxylic acid and/or monocarboxylic acid. 
     
     
         17 . The method of  claim 1 , wherein the dicarboxylic acid and the monocarboxylic acid form a protective film on a metal surface of the closed loop system that is in contact with the fluid. 
     
     
         18 . A corrosion inhibitor composition comprising:
 (i) water and/or glycol;   (ii) a C6-C14 dicarboxylic acid;   (iii) a C6-C14 monocarboxylic acid; and   (iv) solvent polymaleic acid (PMA-s).   
     
     
         19 . The composition of  claim 18 , wherein the composition further includes an azole. 
     
     
         20 . The composition of  claim 18 , wherein the composition further includes a base and a buffer. 
     
     
         21 . The composition of  claim 18 , wherein the composition includes from 0.5 wt. % to 30 wt. % of the dicarboxylic acid and from 0.25 wt. % to 15 wt. % of the monocarboxylic acid. 
     
     
         22 . The composition of  claim 18 , wherein the composition includes from 0.05 wt. % to 3 wt. % of the PMA-s. 
     
     
         23 . The composition of  claim 18 , wherein the composition comprises less than 0.2 wt. % of nitrites and less than 0.2 wt. % of molybdates. 
     
     
         24 . The composition of  claim 18 , wherein the composition comprises less than 0.1 wt. % of nitrate, less than 0.1 wt. % of silica, and less than 0.1 wt. % of phosphorous. 
     
     
         25 . The composition of  claim 24 , wherein the composition is non-fouling. 
     
     
         26 . The composition of  claim 18 , wherein the composition is effective to from a protective film on metal surface in contact with a fluid independently of an amount of dissolved oxygen in the fluid.