| Oil well acidification is one of the important measures to improve the productivity of oilfield reservoirs,but the acidification process will result in corrosion of metal pipes,which will cause huge economic losses and considerable safety risks.Adding corrosion inhibitor to acids is a very convenient and efficient method to inhibit the corrosion of metal materials by acids.Therefore,the development of new and more effective corrosion inhibitors has been focus on by researchers.The new heterocyclic quaternary ammoniums with more conjugatedπelectrons and double quaternary ammonium ions are designed as corrosion inhibitors,i.e4,4-ethylene-1,2-diylbis[1-（1-naphthylmethyl）pyridinium]dichloride（dNP）,1-（1-naphthylmethyl）-2-[（2-（1-naphthylmethyl）pyridium-4-yl）vinyl]quinolinium di-chloride（NQNP）,4,4’-[1,4-Phenylenebis（ethylene-2,1-diyl）]bis[1-（1-naphthylmethyl）pyridinium]dichloride（dNP-TP）.The results of quantum chemical calculations and molecular dynamics（MD）simulation showed that dNP、NQNP and dNP-TP present lower total energy（TE）,smaller energy gap（ΔE）,bigger number of transferred electron（ΔN）and larger adsorption energies,which indicated that dNP,NQNP and dNP-TP could display more effective corrosion inhibitions potentially.The appropriate route to synthesize dNP,NQNP and dNP-TP was obtained by quantum chemical calculations.Therefore,dNP,NQNP and dNP-TP were synthesized by the condensation of 1-naphthylmethyl-4-methyl pyridinium with 1-naphthylmethyl-4-formyl pyridinium,1-naphthylmethyl-2-methylquinolinium with 1-naphthyl methyl-4-formyl pyridinium and 1-naphthylmethyl-4-methyl pyridinium with terephthaldehyde.The yields of dNP,NQNP and dNP-TP were 34.57%、30.53%and16.71%,respectively.The results of the static weight loss showed that the corrosion rates of N80 steel in 15%hydrochloric acid at 90℃were 3.36 g.m-2.h-1、4.11 g.m-2.h-1and 11.9 g.m-2.h-1respectively for inhibitors of NQNP,dNP and dNP-TP at 0.06%concentration.The adsorption of NQNP,dNP and dNP-TP on the surface of N80 steel obeyed the Langmuir adsorption isotherm.The standard free energies of the adsorption(Δ？)showed that the adsorption of NQNP and dNP on the surface of N80 steel were chemisorption,and adsorption of dNP-TP was both physisorption and chemisorption.The results from polarization curve showed that NQNP,dNP and dNP-TP in 15%hydrochloric acid medium could inhibit the anodic dissolution reaction and the cathodic hydrogen evolution reaction simultaneously,which indicated that NQNP,dNP and dNP-TP were all mixed type inhibitors.The results of AC impedance showed that the value of charge transfer resistance(Rct)were 2383Ω·cm-2、2359Ω·cm-2and 2101Ω·cm-2for NQNP,dNP and dNP-TP,respectively when the concentrations of were 0.5%in 15%hydrochloric acid.Scanning electron microscopy（SEM）of N80 steel showed that the surface of N80 steel from 15%hydrochloric acid without corrosion inhibitor is seriously corroded,and there are a large number of rough cracks and pits.The surfaces of N80steel from 15%hydrochloric acid with NQNP,dNP and dNP-TP were smooth.The energy dispersive spectrometer（EDS）of N80 steel showed that the contents of nitrogen element,chlorine element and carbon element increased obviously,which indicated that NQNP,dNP and dNP-TP were adsorbed onto the surface and inhibited corrosion.The results of corrosion inhibition of NQNP,dNP and dNP-TP calculated from quantum chemical calculations and molecular dynamics simulation are in good agreements with the results from experimentation.Therefore,corrosion inhibition and synthetic routes of designed inhibitors are investigated by quantum chemical calculations and molecular dynamics simulation before experimental investigation,then appropriate inhibitors could be selected and their corrosion inhibition are investigated in laboratory.Thus,the work task in experimental investigation could be reduced and the efficiency of developing new inhibitors could be improved. |
