Preparation method for quaternary ammonium salt dimeric surfactant containing hydroxyl group and application of quaternary ammonium salt dimeric surfactant containing hydroxyl group in tertiary oil recovery

The invention discloses a preparation method for a quaternary ammonium salt dimeric surfactant containing a hydroxyl group and application of the quaternary ammonium salt dimeric surfactant containing the hydroxyl group in tertiary oil recovery. The preparation method comprises the following steps: mixing alkyl tertiary amine with chloropropylene oxide according to a mol ratio of 2-3: 1 and carrying out stirring at 60 to 100 DEG C for 4 to 6 h with water as a solvent so as to obtain a crude quaternary ammonium salt dimeric surfactant containing a hydroxyl group; and subjecting the crude quaternary ammonium salt dimeric surfactant to recrystallization with a solvent and then carrying out drying so as to obtain the purified quaternary ammonium salt dimeric surfactant containing the hydroxyl group. The quaternary ammonium salt dimeric surfactant containing the hydroxyl group has good oil-water interfacial activity and can be applied to improvement of petroleum recovery efficiency. According to the invention, a one-step synthesis process is employed, so production cost is low; the prepared quaternary ammonium salt dimeric surfactant containing the hydroxyl group has better water-solubility compared with common quaternary ammonium salt dimeric surfactants and is applicable to oil recovery under the condition of great inorganic salt concentration; and through combined usage of the prepared quaternary ammonium salt dimeric surfactant with an amphoteric ionic surfactant, petroleum recovery efficiency can be improved.