Synthesis And Performance Evaluation Of Amphoteric Imidazoline As Corrosion Inhibitor

Naphthenic acid is produced more than 30000t per year in China as a by-product in petrochemical industry. There are many things for us to do with it for such resource had not been made good use of, and it is very valuable to research naphthenic amphoteric imidazoline as a corrosion inhibitor.In this paper, two kinds of amphoteric imidazolines are synthesised by these reactions: One is imidazoline and sodium monochloroacetate; the other one is imidazoline and acrylic acid. This kind of imidazoline was synthesised by olic acid and diethylenetriamine (DETA). By the way, several factors that have important effect on the products have been researched, and the optimum reaction conditions have been obtained as follows:The optimum conditions of the reaction between imidazoline and sodium chloroacetic are: Reactants's molar ratio is n(imidazoline): n(sodium chloroacetic)=1:4; Reaction temperature is 80℃-90℃; pH8-10; reaction time is about 4h-13h,which is due to the ratio of reactant to water.The optimum conditions of the reaction between imidazoline and actylic acid are: Reactants's molar ratio is n(imidazoline): n(actylic acid)=l:4; Reaction temperature is 110℃-140℃; Reaction time is about 2h. Aqua NaOH was added as the same molar as actylic acid in the end.Amphoteric imidazoline acetic (MC) has a better inhibition efficiency than the other one in a senior corrsion test and its anticorrosion ability has been tested by weight loss method, and the results are as follows:Rotary coupon corrosion test is used in circulating cooling water, whose condensing multiple k=1.5. The corrosion inhibition efficiency is 99.5%, and the corrosion rate of carbon iron is 0.0033 mm/a when the concentration of MC is 20mg/L. The faster the water is running, the higher the corrosidon inhibition efficiency is. MC cooperated with Zn⁺ or with HEDP can keep dot corrosion away and can make the corrosion rates below 0.076mm/a. Weight loss method is carried out in simulated oilfield water. The anticorrosion efficiency is 94.7% and corrosion rate is 0.029mm/a when adding MC of 50mg/L, but it could not keep away dot corrosion because of scale. Adding 100mg/L MC and 20mg/L HEDP can inhibit scale completely, and the corrosion inhibition efficiency is 96.2%,the corrosion rate is 0.021mm/a; Using H₂SO₄ or other acid to keep the water's pH at 6 and adding MC of 60mg/L can inhibit scale completely, and the corrosion inhibition efficiency is 99.3%,the corrosion rate is 0.011mm/a.Weight loss method is carried out in HCl-H₂S water. In such corrosive water of (1000mg/L) HCl-(100mg/L) H₂S, adding MC of no less than 80 mg/L, the corrosion inhibition efficiency is 96.0%, and the corrosion rate is 3.3mm/a, for when MC reaches full adsorption on iron surface. Adding MC and using organic amine to keep the corrosive water's pH at 7 can low down the corrosion rate to 0.032mm/a, and get the anticorrosion efficency of 99.96%. The corrosion rate of iron increases as the H₂S's concentration increasing in the rang of 100mg/L-500mg/L. Adding MC can lower the corrosion rate of iron less than 0.125mm/a if H₂S's concentration is no more than 200mg/L.