Synthesis And Inhibition Performance Of Novel Dissymmetric Bisquaternary Ammonium Salt

Imidazoline inhibitor is a kind of inhibitor with excellent inhibition performance due to its unique molecular structure. Imidazoline and its derivatives are widely used in industrial application. Bisquaternary ammonium has been used as corrosion inhibitor in recent years. Due to its low toxicity,good surface activity and good water solubility, bisquaternary ammonium is a promising corrosion inhibitor. In consideration of designing inhibitor molecule, a compound is synthesized by combining bisquaternary ammonium structure with imidazoline. The compound is a kind of dissymmetric bisquaternary ammonium which may have multi-adsorption centers, good water solubility, good surface properties and excellent corrosion inhibition performance.Based on the above consideration, four series of novel dissymmetric bisquaternary ammonium which were named DBALⅠ, DBALⅡ, DBALⅢand DBAO were systhesized in this paper. The structures of intermediates and final products were identified by IR spectra, UV spectra and NMR spectra. The inhibition effect of four novel dissymmetric bisquaternary ammonium for Q235 steel in 1 mol/L HCl solution were investigated using weight loss, polarization curve, electrochemical impedance spectroscopy (EIS) and surface morphology methods.The results of weight loss method showed that four dissymmetric bisquaternary ammonium had excellent inhibition efficiency for Q235 steel in 1 mol/L HCl. The inhibition efficiency increased with increasing the concentration of inhibitor, but when inhibitor concentration was above 200 mg/L, the effect of inhibitor concentration on inhibition efficiency was small. The inhibition efficiency increased gradually in the temperature range of 25-55℃, and the inhibition efficiencies of four inhibitors were more than 96% when the concentration of inhibitor reached 200 mg/L at 55℃. The differences of inhibition efficiency between DBAO and DBALⅠwere very little, and the inhibition efficiencies of three dissymmetric bisquaternary ammonium tested by weight loss method decreased in the following order: DBALⅠ>DBALⅡ>DBALⅢ, which indicated that inhibition efficiency increased with the increase of carbon chain lenghth of alkyl group. The results of polarization curve revealed that both cathodic and anodic processes were obviously suppressed in the presence of dissymmetric bisquaternary ammonium. After adding inhibitor, the corrosion potential shifted slightly toward more negative potential, the corrosion current density decreased remarkably, four dissymmetric bisquaternary ammonium were mix-type inhibitors which mainly inhibited cathodic process.The results of electrochemical impedance spectroscopy (EIS) also showed that four dissymmetric bisquaternary ammonium were excellent inhibitors for Q235 steel in 1 mol/L HCl solution. The charge transfer resistance increased in the presence of inhibitor, which indicated the formation of a protective layer on the Q235 steel surface by the adsorption of inhibitor molecules. The film formed on Q235 steel growed firstly then decayed, in the presence of 200 mg/L inhibitor, the inhibition efficiency of inhibitor DBAO and DBALⅠachieved maximum at 168 h and 192 h respectively.The results of surface morphology suggested that the Q235 steel surface was strongly damaged in the absence of inhibitor, while the Q235 steel surface exposed to various concentrations of inhibitor was free from local corrosion, scratches polished with emery paper were seen on the Q235 steel surface, which indicated inhibitor molecules were adsorbed on Q235 steel surface forming a film, which prevented the Q235 steel from corrosion.