Concentration Detection Of New Imidazoline Inhibitor And Research On The Growth And Decay Law Of Its Film Formed On Q235 Steel

There widely exits CO2 in oil gas exploring process, and steel is greatly corrupted in its dissolved water. Now, adding inhibitor is the mostly used method to prevent corrosion, which is economical and less influencing to production on oil field. Imidazoline inhibitor has excellent inhibitor efficiency, no special irritative smell, good heat stability, low toxicity and is widely used in protection of oil field pipe instrument. It is used to instruct sample adding quantity and adding time in local oil field and store inhibitor effectively concentration detection of new imidazoline inhibitor and research on the growth and decay law of its film formed on Q235 steel.New imidazoline inhibitor is synthesized according to high temperature and high pressure , high CO2 content , high Na+,Ca2+,Mg2+ inorganic salt ion content on local oil field. Structure characterization of imidazoline inhibitor is measured by IR, UV, 13CNMS, MS. Absorption on metal surface is strengthened and the protection of CO2 corrosion is more effective by the accessed sulfur atom. The following three questions are researched in this dissertation:A new ultraviolet spectrophotometer method has been developed for the hydrolysis of imidazoline inhibitor with temperature changing and the concept is put forward. The results show that the hydrolysis speed and ring-opening degree is greater as the temperature hoist. At 85℃, half of the imidazoline inhibitor has hydrolyzed; and it is more slowly at 25℃for there is absolutely no change at the beginning 4h. The best detection wavelength, time, temperature and other influence factor to concentration detection are researched, and the results show that the blank salt solution should be cooled to 25℃for it has UV absorption at high temperature; the organic compound, CO2 and Fe3+ have less influence on the detection. The wavelengths 205nm and 228nm were chosen as the optimal measurement wavelengths. Concentration was detected when the inhibitor was cooled to 25℃with 4 hours for its slow hydrolysis and low ring-opening degree during this period. This method was rapid, easily operated and good anti-jamming.The growth and decay law of film formed on Q235 steel are researched by the weight-loss, EIS and weak polarization tests. The results show that: at 85℃, the inhibitory efficiency is not increased all through with the increase of concentration but has a extremum concentration which is 40 mg·L-1 in this dissertation. EIS and weak polarization tests show that: At 85℃, the film of 40 mg·L-1 imidazoline inhibitor can form in 24h, has long life for 168h, and can be auto-repaired; the film of 20 mg·L-1 imidazoline inhibitor forms more lowly and can't be auto-repaired; the film of 60 mg·L-1 imidazoline inhibitor also can form in 24h, but obviously decay in 120h, has short life. At 25℃, the corrosion current density of Q235 steel in 40 mg·L-1 imidazoline inhibitor dropped, the charge transfer resistance is greatly higher , the film is more extend and tighten than at 85℃. It shows that on one hand corrosion is accelerated with the temperature hoist, on the other hand , imidazoline inhibitor has hydrolyzed seriously at high temperature which reduce the inhibitory efficiency. At 85℃, the film of 40 mg·L-1 non-mercapto imidazoline inhibitor forms more slowly, which is best in 48h. On that condition, an inductance arc appears at low frequency on the EIS fig of Q235 steel during the 72h-120h, which shows the desorption of inhibitor on electrode surface and on the contrary shows the mercapto group strengthened the absorption of imidazoline inhibitor.The stability of imidazoline inhibitor is researched also by the weight-loss, EIS and weak polarization tests. The film capability of 40 mg·L-1 imidazoline stored for 2 months and for 72h at 85℃is researched by EIS tests. The results show that: their film life and intensity are worse than the fresh imidazoline inhibitor, and the reason is hydrolyzed imidazoline has poor absorption capability. The UV spectra of imidazolin during the weight-loss tests are obtained by the ultraviolet spectrophotometer method. The results show that: the ring-opening degree and speed are different of different concentration of imidazoline inhibitor, the higher the concentration is ,the larger the ring-opening degree is , which make the difference of the molar absorption coefficientελ=228nm andελ=205nm. The UV spectra of imidazolin during the electrochemical tests are also obtained by the ultraviolet spectrophotometer method. The results show that: the trend of hydrolysis at 25℃is less than that at 85℃. The peak value atλ=228nm andλ=205nm during the electrochemical tests is different from that during the weight-loss tests , which are much larger and increases all along, it is deduced that the additional current changes the inhibitor and enhances the UV absorption at special wavelength.