Synthesis And Corrosion Inhibition Of Mannich Bases Corrosion Inhibitors For Acidification

In the process of oil field exploitation,oil well acidification is one of the important measures to improve oil recovery.Acidification can dissolve the cements and blockages,which could avoid damages to reservoir in the process of drilling,completion and exploitation and transform the low-permeability layer.However,acidification can also bring serious corrosion to metallic pipeline,resulting in significant economic losses.In order to diminish or resist the corrosion,the application of corrosion inhibitor in acidizing fluid is the most economic and effective measure.Mannich bases are extensively used as acidifying corrosion inhibitor,which present environmentally friendly,inexpensive,and soluble in hydrochloric acid.Five Mannich base inhibitors,3-diethylamino-1-phenylpropan-1-one（DPO）,3-benzylamino-1-phenylpropan-1-one（BPO）,3-cyclohexylamino-1-phenylpropan-1-one（CPO）,3-p-toluidino-1-phenylpropan-1-one（TPO）and 3-phenylamino-1-phenyl-propan-1-one（PPO）were prepared by Mannich reaction or amine exchange reaction of Mannich base with primary amine.The structures of the inhibitors were identified by titrimetric analysis,elemental analysis,FT-IR and NMR.The corrosion inhibition of the Mannich bases as inhibitors to N80 steel in 15%hydrochloric acid and soil acid（12%hydrochloric acid and 3%hydrofluoric acid）were investigated by static gravimetric measurement.The results showed that corrosion inhibition of the inhibitors could be arranged（in order of increasing corrosion inhibition）as DPO<BPO<CPO<TPO<PPO.From BPO,CPO,TPO and PPO,the minimum concentrations of the inhibitors required in 15%hydrochloric acid are 6.99mmol·L^-1（0.16wt.%）,4.66mmol·L^-1（0.10wt.%）,4.66mmol·L^-1（0.10wt.%）and 2.33mmol·L^-1（0.05wt.%）,respectively,at which the corrosion inhibition of the inhibitors satisfy the first grade specification in SY/T5405-1996.The PPO presents an effective corrosion inhibition,and the corrosion inhibition of DPO can’t satisfy the specification at the experimental concentration.The adsorption processes of the five Mannich bases on the N80 steel surface were further studied and obeyed the Langmuir adsorption isotherm.From DPO,BPO,CPO,TPO to PPO,the standard free energy of adsorption of five inhibitors were-30.07kJ·mol^-1,-41.11kJ·mol^-1,-43.76kJ·mol^-1,-44.56kJ·mol^-11 and-48.07kJ·mol^-1,respectively,which indicated that the adsorption process of the five inhibitors are spontaneous on N80 steel surface and the order（in increasing adsorbability）is as DPO<BPO<CPO<TPO<PPO.The adsorption processes were combination of physisorption and chemisorption for DPO and chemisorption for BPO,CPO,TPO and PPO.The corrosion inhibition and mechanism of the inhibitors were further investigated by Polarization Curves and Electrochemical Impedance Spectroscopy（EIS）.The results from the polarization curves indicated that the five inhibitors were mixed-type inhibitors,in which BPO and CPO mainly retarded the cathodic corrosion.Surface analysis was carried out by SEM technique.The results from electrochemical method and SEM technique are consistent with that from static gravimetric measurement,in which the corrosion inhibition of the inhibitors could be ordered（increasing corrosion inhibition）as DPO<BPO<CPO<TPO<PPO.The corrosion inhibition of the inhibitors is dependent on the structures of the inhibitors.Because of the conjugative effect between phenyl and amino group,PPO and TPO present more effective corrosion inhibition than CPO,BPO and DPO with the electron-donating induction effect between alkyl groups and amino groups.Compared with PPO,the methyl（withoutπelectron or lone-pair electron）in TPO could not be adsorbed effectively on steel surface by chemisorption,which influences the chemisorption and the corrosion inhibition of TPO.For DPO,BPO and CPO molecules,the difference of alkyl groups（with different induction effect and spatial effect）linked to amino groups result in the difference of adsorption process and corrosion inhibition.