The Relationship Between The Structure Of Quaternary Ammonium Salt Of N-heterocyclic Compounds And Corrosion Inhibition

The acidification of oil well is beneficial to the improvement of oil and gas recovery and is one of the effective measures to increase oil production.However,the use of acid solution will inevitably corrode underground metal equipment,causing frequent accidents and serious economic losses.Moreover,the corrosion of underground metal equipment will generate metal ions,which will cause new formation damage.Therefore,the addition of corrosion inhibitor with the advantages of low consumption,high eff-iciency and easy operation has become a widely accepted anticorrosion measure.The heterocyclic quaternary ammonium salts as corrosion inhibitors used in acidizing engineering are paid close attention because of its effective corrosion inhibition,high solubility and simple chemical synthesis.However,the relationship between the corrosion inhibition and structure of heterocyclic quaternary ammonium salts was not clear yet,which is not favorable for the design and development of new corrosion inhibitors.Therefore,the relationship between the structure of heterocyclic quaternary ammonium salt and its corrosion inhibition is investigated mainly in this paper.In this paper,pyridine or quinoline reacts with alkyl halides(or methanol)and eight heterocyclic quaternary ammonium salts were obtained,i.e.,1-methyl pyridine chloride(MP),1-ethyl pyridine bromide(EP),1-benzyl pyridine chloride(BP),1-naphthalene methyl pyridine chloride(NP),1-methyl quinoline chloride(MQ),1-ethyl quinoline bromide(EQ),1-benzyl quinoline chloride(BQ)and 1-naphthalene methyl quinoline chloride(NQ).The purity and structure of the heterocyclic quaternary ammonium salts were determined by potentiometric titration,NMR and elemental analysis.The corrosion inhibition of the heterocyclic quaternary ammonium salts was investigated by static weight loss method,adsorption behavior,polarization curve and electrochemical impedance spectroscopy(EIS),respectively.The relationship between corrosion inhibition and structure of heterocyclic quaternary ammonium salts was researched.The corrosion inhibition of the heterocyclic quaternary ammonium salts in 15 wt%HCl solution at 90? was investigated by static weight loss method.The results showed that corrosion inhibition increased with the change of hydrocarbyl chained in the nitrogen atom of pyridine(or quinolone),i.e.,EP<MP<BP<NP,and EQ<MQ<BQ<NQ.When the hydrocarbyl was same,the corrosion inhibition of heterocyclic quaternary ammonium salts increased from pyridine to quinolone,i.e.,MP<MQ,EP<EQ,BP<BQ and NP<NQ,respectively,which indicated that corrosion inhibition of quinoline quaternary ammonium salts were better than those of pyridine quaternary ammonium salts.The results implied that the heterocyclic quaternary ammonium salts with more conjugated ? electrons exhibit the more excellent corrosion inhibition in 15 wt%HCl solution.The adsorption behavior of the four heterocyclic quaternary ammonium salts of BP,NP,BQ and NQ with better corrosion inhibition were in good agreement with the Langmuir adsorption model,and the standard free energy of adsorption(AGads0)increased in the order,BP<BQ?NP<NQ,which indicate that the adsorption of the compounds of BP,NP,BQ and NQ on N80 steel were physical-chemical adsorption.The standard free energy of adsorption(?Gads0)of NQ was-35.16kJ·mol-1,which implied that the compound NQ is effectively adsorbed on the N80 steel because of more conjugated ? electrons contained in the NQ molecular,and exhibits the more excellent corrosion inhibition.The result of corrosion inhibition of NQ was in agreement with the results from static weight loss method.The adsorption behaviors of MP,EP,MQ,and EQ,which presented poor corrosion inhibition,did not meet the Langmuir adsorption model.The results of polarization curves showed that the corrosion inhibition of BP,NP,BQ and NQ was increased in the order,BP<BQ?NP<NQ,and they all were mixed-type inhibitors The results of EIS showed that he diameter of the impedance semicircles increased in the order,BP<BQ<NP<NQ,which indicated that the corrosion inhibition increased in the order,BP<BQ<NP<NQ.The results from static weight loss method,adsorption behavior,polarization curve and EIS indicated that heterocyclic quaternary ammonium salt with more conjugated ? electrons in the structure could be effectively adsorbed on the N80 steel surface and present better corrosion inhibition in 15 wt%HCl solution,which implied that corrosion inhibitors used in acidizing engineering should contain conjugated ? electrons as many as possible in molecular design and development of corrosion inhibitors.