Synthesis Of Diquaternary Ammonium Salts And The Experimental And Theoretical Study On Inhibition Performance

Acidizing is a common stimulation technique in oil and gas industry to improve productivity.Generally,12～28 % hydrochloric acid is injected down to the wells to etch the formation rock and to improve the permeability of reservoir.In the process,the highly concentrated acid may corrode the tubing and casing equipment then cause financial losses and safety problem.Therefore,the addition of efficient inhibitor in acidizing fluid is absolutely essential to reduce the aggressive attack of acid on metal surfaces.Inhibitors for acidizing application should maintain high inhibition efficiency in strong acidic medium and at high temperature,and have good solubility with the fluid system.As an emerging inhibitor type,diquaternary ammonium salts have the properties of multiple adsorption center,good solubility,hypotoxicity,stability in high temperature,for which become the research hotspots of acidizing corrosion inhibitors field.In this paper,based on 9-methyl-2,3-dihydro-1H-cyclopenta[b]quinoline,three diquaternary ammonium salts(DQD-n,where n represents the C atom number in dibromohydrocarbon)were synthesized with 1,4-dibromobutane,1,6-dibromohexane and 1,8-dibromooctane by quaternization reaction.These diquaternary ammonium salts with different spacer lengths were used to explore the influence of chain length on the corrosion inhibition performance of diquaternary ammonium salts.The corrosion inhibition performances of the three diquaternary ammonium salts on N80 steel sheet in 15wt% hydrochloric acid was evaluated by means of static weight loss experiment,electrochemical test and surface morphology analysis.On the other hand,quantum chemistry calculations and molecular dynamics simulation were used to explore the influence of the spacer length on the reactivity and adsorption behavior of the diquaternary ammonium salts molecule.The experimental results show that the three diquaternary ammonium salts are all mixed corrosion inhibitors mainly to inhibit the cathodic reaction,and as the length of the spacer increases,the corrosion inhibition performance increases.And the corrosion inhibition efficiency order from high to low is DQD8>DQD6>DQD4.The calculation results of quantum chemistry show that the three diquaternary ammonium salts mainly rely on the quinoline ring part of the head group to adsorb on the iron surface,and the longer the spacer chain,the higher the reactivity of the molecule and the easier it is to interact with the metallic surface.The results of molecular dynamics calculations show that the three corrosion inhibitors are adsorbed on the metal surface in parallel through the head groups of quinoline derivatives.The spacer part has a certain hindering effect on the both-side adsorption of the head groups,and this hindering effect decreases with the increase of the length of the spacer chain.Then,based on 1,8-dibromooctane,two kinds of diquaternary ammonium salts with different head group structures were synthesized with pyridine and quinoline.Similarly,static weight loss method,electrochemical test,surface topography analysis,quantum chemical calculation,molecular dynamics simulation and other methods were used to perform inhibition efficiency evaluation and theoretical calculation of the two diquaternary ammonium salts.The influence of different head group structures on the corrosion inhibition performance of the diquaternary ammonium salts was studied with the addition date of 1,8-diquinoline bromide derivative quaternary ammonium salt.The results of weight loss method and electrochemical test show that the order of the corrosion inhibition performance of the three different head groups of diquaternary ammonium salt is DQD8>DQ8>DB8.And the three corrosion inhibitors are all mixed type corrosion inhibitors mainly to inhibit the cathodic reaction.As the ring number of the head groups increases,the corrosion inhibition performance will increase accordingly.The results of quantum chemistry calculations show that the two kinds of diquaternary ammonium salts mainly rely on the aromatic ring structure of the head group to participate in the adsorption.DB8 can only perform physical adsorption,and DQ8 has much more electron donating capacity than QB8,which can simultaneously perform physical and chemical adsorption.The MD results show that the larger the part of the diquaternary ammonium salt head group that can participate in the adsorption,the stronger the adsorption on the metallic surface,and the stronger the corrosion inhibition ability。...