Synthesis And Application Of Modified Bis-quaternary Ammonium Salt In Oilfield Wastewater Treatment

SRB, TGB and other microbes in oilfield reinjection water could cause corrosion of injection equipments and pipelines. However, the microbes would contain genes conferring resistance on biocide, resulting in increasing in MIC of common biocide and treatment costs and even that the treated water couldn't meet the criteria. Aiming at solving this problem, one novel biocide, the modified bis-quaternary ammonium salt MHTD was synthesized by using epichlorohydrin (ECH), N,N-dimethyl dodecyl amine (DMA 12) and metronidazole (MDZ) as raw materials. In this paper, the synthesis process conditions, bactericidal properties, corrosion inhibition, surface activity of MHTD were studied, as well as compatibility with other wastewater treatment agents. The results show that:It took three steps to synthesis MHTD. First, DMA 12 combined with hydrogen chloride to form N, N-dimethyl dodecyl amine hydrochloride (DMAH). Second, DMAH reacted with ECH to produce the intermediate product of CHAC (N-(3-chloro-2-hydroxypropyl)-N, N-dimethyl dodecyl ammonium chloride). At last, MHTD was obtained from the reaction of CHAC and MDZ. The yield of CHAC could reach the best of 93.5% in the conditions of reaction temperature at 40℃and the molar ratio of reactants n(DMAH): n(DMA12):n(ECH) at 1:0.15:1.10. The best yield of MHTD reached 82.4% in acetonitrile with the conditions of the reaction temperature at 80℃, the molar ratio of reactants n(MDZ):n(CHAC) at 1.2:1 and reaction time of 12 h. The product structure of MHTD was detected by IR spectrum and melting point apparatus, the result was coined with the primary design.The results of the bactericidal properties study show that: the bactericidal rate is increasing with the concentration of MHTD; the bactericidal rates could reach 99.99% and 99.14% to SRB and TGB respectively when the concentration of MHTD is 30 mg/L, which meet to the water injection requirements and 63% and 99% more than 1227 at the same concentration; MHTD had a bactericidal rate up to 100% to SRB and TGB in the concentration of 40 mg/L. The bactericidal rate of MHTD to SRB and TGB maintained above 90% within the contacting time of bacterium and drug at 48 h. MHTD is perfectly adapted to oilfield wastewater with salinity from 1×104 mg/L to 1×105 mg/L, temperature of 30℃to 60℃and pH of 5.5 to 8.5. Furthermore, it has good compatibility with the corrosion inhibitor and scale inhibitor applying in oilfield.The corrosion inhibition of MHTD was evaluated by the static hanging experiments and potentiodynamic electrochemical test. The results demonstrate that MHTD with the concentration of 50 mg/L has corrosion rates of 77.2% and 71.2% respectively to A3 steel in 8.68×104 mg/L salinity simulated salt water. The CMC and ys(CMC) of MHTD are 0.77 mmol/L and 34.14 mN/m respectively.