A fully-continuous flow synthesis method of glyphosate using a fully-continuous flow synthesis system, the fully-continuous flow synthesis system comprising a first pump, a second pump, a micromixer, a first microchannel reactor, a second microchannel reactor, a third microchannel reactor, a fourth microchannel reactor, a first tubular reactor, a second tubular reactor, a third tubular reactor, a first back pressure valve, a second back pressure valve, a first reaction vessel, a second reaction vessel, a third reaction vessel, a fourth reaction vessel, a fifth reaction vessel, a sixth reaction vessel, a first continuous crystallizer, a second continuous crystallizer, and a third continuous crystallizer;
- and the fully-continuous synthesis method comprising:
- (1) dissolving paraformaldehyde in a first solvent to obtain a first reactant liquid;
- mixing the first reactant liquid with a second reactant liquid in the micromixer, followed by depolymerization in the first tubular reactor to obtain a depolymerization product, wherein the second reactant liquid is a first base or a solution of the first base in a second solvent;
- feeding the depolymerization product to the first reaction vessel;
- feeding, by a dual-screw feeder with a weighing function, glycine solid under a positive pressure created by a nitrogen atmosphere to the first reaction vessel followed by addition reaction under stirring to generate a first reaction mixture which contains N, N-dihydroxymethylglycine, wherein a sedimentation rate of the glycine solid is adjusted by controlling a stirring rate of the first reaction vessel to be identical to a downward flow rate of the depolymerization product;
- transporting the first reaction mixture from an outlet at a bottom of the first reaction vessel to a bottom of the second reaction vessel under the action of gravity, wherein the bottom of the first reaction vessel is located above the bottom of the second reaction vessel;
- (2) quantitatively transferring, by a first pump, the N, N-dihydroxymethylglycine-containing reaction mixture from a top of the second reaction vessel to the first microchannel reactor;
- transporting, by a second pump, a part of a phosphite ester to the first microchannel reactor;
- mixing the N, N-dihydroxymethylglycine-containing reaction mixture with the phosphite ester in the first microchannel reactor followed by esterification in the second microchannel reactor and the third microchannel reactor, so as to obtain a preliminarily-esterified product, wherein a second base is introduced into the second microchannel reactor, and the second base is the same as the first base;
- and another part of the phosphite ester is introduced into the third microchannel reactor;
- transporting the preliminarily-esterified product to the second tubular reactor for continuous esterification reaction to ensure complete conversion, so as to obtain a completely-esterified product;
- and
- (3) transporting the completely-esterified product to pass through the first back pressure valve to enter the fourth microchannel reactor followed by cooling;
- introducing an acid from a middle of the fourth microchannel reactor followed by neutralization reaction to obtain a second reaction mixture;
- transporting the second reaction mixture to the third tubular reactor, and heating the second reaction mixture to a preset temperature for hydrolysis reaction to obtain a third reaction mixture;
- transporting the third reaction mixture to the third reaction vessel through the second back pressure valve for desolventization to remove solvents, so as to obtain a desolvated product;
- transporting the desolvated product sequentially to the fourth reaction vessel and the fifth reaction vessel for complete hydrolysis to obtain a fourth reaction mixture, wherein temperatures of the fourth reaction vessel and the fifth reaction vessel are elevated to continuously remove water and promote hydrolysis;
- transporting the fourth reaction mixture to the sixth reaction vessel followed by pH adjustment with a third base in a liquid state and sequential transportation to a first continuous crystallizer, a second continuous crystallizer and a third continuous crystallizer for gradient cooling crystallization to a crude glyphosate product;
- and subjecting the crude glyphosate product to filtration and drying to produce a glyphosate finished product with a purity greater than 99% and a total yield greater than 88% calculated based on glycine.