The Hydrophobic Modification Of The β-CD-based Cationic Flocculant And Its Application In Pirnting And Dyeing Wastewater Decolorization

The dye is one of the main reasons that maked the dyeing and printing wastewater highchromaticity, high biotoxicity, high difficulty to deal with. The chromaticity is one of themain control indexes of printing and dyeing wastewater and the decolorization has becomethe primary problem to solve in the field of dyeing and printing wastewater treatment.Flocculence is the most commonly used method in the printing and dyeing wastewatertreatment now. Designing and synthesising new flocculants for color removal and researchingthe mechanism of the decolorization are the hotspot in the field of flocculated decolorization.β-cyclodextrin is a derivative from starches, has many advantages such as eco-friendly,renewable, biodegradable, relative cheap, wider range of source owing to its special chemicalstructure. Moreover, the molecular weight of β-cyclodextrin is low, the structure is definitedand it is easy to gain the procudt with high branching degree by homogeneous chemicalreactions. Therefore, the modified products from β-CD have more potential to be new, safe,economic, efficient and practical flocculants for decoloration.In this papepr, the solubilization effect of β-CD on hydrophobic monomer styrene (St)was studied by the means of phase solubility. Then without any other auxiliaries, aβ-cyclodextrin (β-CD) based cationic flocculant with improved hydrophobicity (P(β-CD-MAH-co-AETAC-co-St)) was synthesized by means of aqueous solution polymerization, inwhich the ammonium persulfate (APS) and sodium bisulfite (SBS) were used as the initiatorsand the derivative of β-CD (β-CD-MAH), acryloyloxyethyl trimethyl ammonium chloride(AETAC) and styrene (St) were used as monomers. The chemical structure and morphologyof P(β-CD-MAH-co-AETAC-co-St) was characterized by means of FT-IR,1H-NMR and13C-NMR, SEM photos. The production rate, cationic degree and intrinsic viscosity,dissolution time, solution surface tension of the copolymer that was prepared under thecondition of different mass ratio of the monmers (β-CD-MAH/AETAC/St) was measured.Moreover, the performances of the flocculanted decolorization and the interaction betweenthe dyestuff and the flocculant members were studied in detail when use the β-CD basedcationic flocculant. Besides, the flocculating mechanism was analyzed.The results showed that when the concentration of β-CD solution was20g/L, thesolubility of St was twenty-six times than that in water. And the chemical structure ofP(β-CD-MAH-co-AETAC-co-St) was achieved, the successfully prepared was proved. When the mass ratio of the monmers (β-CD-MAH/AETAC/St) was65/30/5, the production rate,cationic degree and intrinsic viscosity of the prepared flocculant were all high and thehydrophobicity was relatively strong. The cationic degree and the hydrophobicity, the dosageof the flocculant, pH values and salty concentration of the dye solution, the structure of thedyestuff would affect the flocculated decolorization performance of the flocculant.The β-cyclodextrin-based cationic flocculation agent P(β-CD-MAH-co-AETAC) wasprepared when the mass ratio of the monmers (β-CD-MAH/AETACt) was70/30while thehydrophobization β-cyclodextrin-based cationic flocculation agent P(β-CD-MAH-co-AETAC-co-St) was prepared when the mass ratio of the monmers (β-CD-MAH/AETAC/St)was65/30/5. The yield, cationic degree and intrinsic viscosity of the both were approximated,but the hydrophobicity of the latter was stronger. The flocculated decolorization performanceof P(β-CD-MAH-co-AETAC-co-St) was better when use them to deal with50mL dyesolutions of the reactive brilliant blue KN-R、reactive brilliant orange K-GN and reactivebrilliant purple BRN and the concentration is100mg/L. The best dosage of the flocculantrespectively ruedced from380,360,240mg/L to320,300,190mg/L. The best dosage offlocculant reduced and the range that acted out higher decolorization rete widen. P(β-CD-MAH-co-AETAC-co-St) showed better alkali and salt resistance in the performance offlocculanted decolorization. P(β-CD-MAH-co-AETAC-co-St) had faster decolorization speedfor the dye solutions, especially for reactive brilliant blue KN–R dye solution whose settingtime reduced from420min to50min. For the given flocculant-dye solutions, the interactionsbetween flocculant molecular and dyestuff molecular existed relatively notable hydrophobicinteraction which had a significant contribution to the flocculated decolorization.Keeping the content of hydrophobic monomer5wt%unchanged, changing the ratio ofβ-CD-MAH and AETAC, prepared a series of different cationic degrees of P(β-CD-MAH-co-AETAC-co-St).The cationic degree respectively was11.5,14.7,19.5,23.9,28.3%when themass ratio of the monmers (β-CD-MAH/AETAC) was65/30,60/35,55/40,50/45,45/50inturn. The results of flocculated decolorization showed that the cationic degree of flocculantwas higher, the hydrophilcity was stronger, the less dosage of it was used when reached thehighest decolorization rate.The product of cationic degree reciprocal and the best dosage offlocculant was a constant, the best dosage of the floucculant was up to the cationic degree.For the given flocculant and dye solutions system, the flocculating mechanism of using thehydrophobiza-tion β-CD-based cationic flocculation agent P(β-CD-MAH-co-AETAC-co-St)to deal with the dye solution is coordination of hydrophobic interaction and electrostaticneutralization, but the electrostatic neutralization played the leading role. The flocculant withlower cationic degree had higher decolorization rate under the condition of the same alkalinepH and salt concentration of dye solution, that showed better alkali and salt resistance.