Method for synthesizing surfactant by alkylating sodium lignin sulfonate

The invention discloses a method for synthesizing a surfactant by alkylating sodium lignin sulfonate. The method includes the following steps that the sodium lignin sulfonate with the molecular weight over 1.5w is selected as a raw material; the sodium lignin sulfonate and purified water are mixed and added with saccharifying enzymes, after uniform dissolution, the solution is treated for 30-40 min at the temperature of 30 DEG C under ultrasonic waves, solvent is removed through ultrasonic liquid reduced pressure distillation, and residues are dried in vacuum at the constant temperature of 60 DEG C for 24 h to obtain a brown solid namely activated sodium lignin sulfonate; the activated sodium lignin sulfonate reacts through a conventional method under the protection of nitrogen with 1-bromododecane as an alkylating reagent and pyridine as a catalyst to prepare the alkylated sodium lignin sulfonate. The saccharifying enzymes and the ultrasonic waves have a coalitive synergism function, compared with modification only through the ultrasonic waves, the reaction time of the method is further shortened, and the obtained alkylated sodium lignin sulfonate is high in capacity for promoting decrease of surface tension and has high market potential.