Synthesis of a new polyunsaturated cationic crosslinker by a new micro‐polycondensation reaction as a critical modifier of polycationic flocculant for purifying dyeing wastewater

Abstract BACKGROUND This work explored a complete evolutionary process, from discovering a new reaction and synthesizing a new crosslinker intermediate, to product application in the purification of dyeing wastewater. RESULTS A new micro‐polycondensation reaction between propylacryloyloxypropyldimethylamine and epichlorohydrin was first observed, forming a new polyunsaturated cationic crosslinker (poly (2‐hydroxypropylacryloyloxypropyldimethylammonium chloride) (PHPAC), abbreviating HPAC unit as the repeating unit); meanwhile, this new PHPAC crosslinker was just a critical modifier of a polycationic flocculant. When the thimbleful of PHPAC crosslinkers containing only 0.2% molar percentage of HPAC units were incorporated into a polycationic skeleton of poly (acryloyloxyethyltrimethylammonium chloride) (PDAC), the application properties of the obtained modified product (known as SC‐PDAC) were greatly improved compared to the unmodified product of PDAC. The cost for preparing the modified product of SC‐PDAC was hardly increased because the quantity of HPAC modifier used was minimal. The multi‐dimension flocculation interactions of SC‐PDAC with the anionic dyes allowed the SC‐PDAC to realize a more efficient purification of dyeing wastewater than the unmodified PDAC. The obtained SC‐PDAC could remove 99.10% of the dyes Reactive Scarlet 3BS and 96.69% of the dyes Methyl Blue when used for purifying the dyeing wastewater. In real engineering applications, the further complex interactions of SC‐PDAC with certain inorganic flocculants and coagulant aids would allow the flocs to be quickly formed, condensed, and aggregated, so as to realize a fast purification of dyeing wastewater within 10 s. The successful implementation of a simulation amplification experiment for treating a 4.0 L dye solution further confirmed that the SC‐PDAC had good potential to be applied in real water treatment engineering. CONCLUSIONS Therefore, as expected, it could be regarded as an economic and facile modification way to obtain the efficient organic cationic flocculant by selecting the PHPAC crosslinker as a critical modifier. © 2021 Society of Chemical Industry (SCI).