Study On Synthesis And Production In Pilot Plant Scale Of Didodecylmethylcarboxybetaine

Alkali-surfactant-polymer (ASP) flooding is one of enhanced oil recovery techniques suitable for most of Chinese oilfields by which the recovery can be increased by 15-20% on the basis of water flooding. However, resent field experiments show that the use of alkali gives rise to some side effects, such as precipitation of the multivalent ions, erosion of rocks and materials, which more severely may results in destroying of oil wells. Thus alkali-free SP flooding becomes more attractive than ASP flooding in China. Unfortunately, surfactants effective in ASP flooding are usually ineffective in the absence of alkali and new surfactants need to be designed. It has been reported that didodecylmethylcarboxybetaine (diC₁₂B), synthesized by reacting tertiary amine with chloroactic acid in the presence of sodium hydroxide, is a good surfactant effective in alkali-free SP flooding. The conversion of the tertiary amine, however, is difficult to exceed 70%. This paper will focus on analyzing the reasons why the conversion of tertiary amine is so low and testing the measures which can be used to improve the recovery. After that production of diC₁₂B in pilot plant scale will be tested.To detect the conversion of tertiary amine new efficient methods to determine the amounts of both free tertiary amine and diC₁₂B was first developed. The results show that by controlling suitable end point the contents of free tertiary amine in synthesized product can be measured by direct titration with standard hydrochloric acid-in-isopropanol solution and on this basis the content of active matter can be determined by two-phase titration method. It is found that the hydrolysis of chloroactic acid is unavoidable at synthesizing temperature (ca.100°C) and the hydrolysis product, glycolic acid, and the residual chloroactic acid in reaction system can be quantitatively determined by HPLC. The results show that after 6 hours of reaction the chloroactic acid in reaction system exhausted, and only 70% of the total chloroactic acid was converted to target product, with the rest, approximately 27% of the total chloroactic acid, was hydrolyzed. The reaction system is not isotropic but a heterogeneous oil-water mixed system. Increasing stirring speed and adding emulsifies are found to be beneficial to the enhancement of conversion, but it is still difficult to made the total conversion to exceed 80%. Obviously the key to improve the conversion of the tertiary amine is to ensure sufficient chloroactic acid in the reaction system and prevent them from hydrolyzing. Increasing initial chloroactic acid/tertiary amine molar ratio can improve the conversion of tertiary amine, for example, by increasing the molar ratio to 1.8, a conversion of 86% can be achieved. This method, however, is not economically efficient. It is found that with an initial chloroactic acid /tertiary amine molar ration of 1.1, NaOH/ chloroactic acid molar ration of 1.1, by adding 20% extra chloroactic acid and corresponding NaOH after 6 hours of reaction at 100°C and continue to react for 4h, a total conversion of 85% can be achieved, while the total chloroactic acid/ /tertiary amine molar ratio is not beyond 1.3. The production tests in pilot plant scale were carried out using a reactor of approximately 0.5 M³. A conversion of 85.6% and 84.4% were achieved respectively in two tests, indicating that the technology and related reaction conditions in synthesizing diC₁₂B are stable and reliable. As a key surfactant, the diC₁₂B produced in the pilot plant scale production was formulated to an oil displacements agent used for SP flooding. With this formulation the lab examinations show that the Daqing crude oil/water interfacial tension can be reduced to an magnitude of 10-3 mN/m in a total surfactant concentration range of 0.01⁰.3%wt.% at 45°C without adding any alkaline chemicals or salts, and an average tertiary oil recovery, 17.8%, was achieved in oil displacement tests with natural cores.