Synthesis Of HPMA-AEO-n Polymer Scale Inhibitor And Study On Its Performance Against Calcium Carbonate Scale

Polymer scale inhibitors have been widely used to reduce the loss caused by mineral scaling in circulating cooling water systems.In this paper,Fatty alcohol polyoxyethylene ether?AEO-9,AEO-10,AEO-15 and AEO-20?and maleic anhydride?MA?are used to prepare monomers MA-AEO-n by esterification reaction.Then,the four polymers HPMA-AEO-n are synthesized by free radical polymerization with MA and MA-AEO-n as monomers,hydrogen peroxide?H₂O₂?as initiator,and ammonium ferric sulfate?NH₄Fe?SO₄?₂·12H₂O?as catalyst.The optimal synthesis conditions are?studied by orthogonal experiment method?:the molar ratio of MA to MA-AEO-n is 6:1 for HPMA-AEO-9,11:1 for HPMA-AEO-10 and HPMA-AEO-15,and 12:1 for HPMA-AEO-20;the dose of initiator and catalyst are 7.5 mol%and 0.04 mol%of total monomer,respectively;the reaction temperature is 95°C and the reaction time is 2 h.The structure and molecular weight distribution of HPMA-AEO-n are characterized using FT-IR,¹H NMR and GPC techniques.The effects of dosage,Ca²⁺concentration,temperature,inhibition time,pH,and the ratio of EO:carboxyl on CaCO₃ scale are studied by static experiments.The effect of HPMA-AEO-n on the relative super-saturation of CaCO₃ solution is investigated using conductivity method.CaCO₃ deposits and morphology in the presence of HPMA-AEO-n are analyzed using SEM and XRD.The CaCO₃ scaling process with dosing of HPMA-AEO-9 is investigated under dynamic tests and compared with HPMA.The results shown that:the scale inhibition efficiency of HPMA-AEO against CaCO₃can reached at 98%with dosing of 8 mg/L,HPMA-AEO-n has excellent ability to inhibit calcium carbonate scale with the Ca²⁺concentration being less than 900 mg/L,the temperature range is 40-90°C,and the pH range is 7.0-9.0;the effect of temperature and Ca²⁺concentration on the performance of HPMA-AEO-n decreases with the increase of the ratio of EO:carboxyl,and the impact of the pH on scale inhibition performance increases with the increase the ratio of EO:carboxyl;HPMA-AEO-n can maintain stable and high scale inhibition performance during long-term operation;HPMA-AEO-n has good calcium dissolution ability,alkali resistance and temperature resistance while compared with the commonly used commercial scale inhibitors HPMA,PAA and HEDP;the impact of HPMA-AEO-n on the critical super-saturation value?S_r?of CaCO₃ solution is less than that of HPMA and this influence decreases with increasing the ratio of EO:carboxyl,implying the binding effect of EO group on Ca²⁺ions?weak interaction?has a significant contribution to the performance of HPMA-AEO-n against CaCO₃ scale;compared with HPMA,HPMA-AEO-9 can inhibit the formation of crystal nuclei in the calcium carbonate nucleation stage,and interrupt the normal growth of crystals and reduce the formation of large particles in the scale growth stage,thus reducing the growth rate of fouling and the influence of calcium carbonate on the heat exchange efficiency of stainless steel pipe.HPMA-AEO-n exhibits an obvious“threshold effect”in preventing CaCO₃ scale.HPMA-AEO-n inhibition against CaCO₃ scale is due to chelation and lattice distortion.HPMA-AEO-n can bind Ca²⁺ions and form complexes with the excellent solubility,thereby reducing the effective super-saturation during precipitation.Furthermore,when HPMA-AEO-n adsorbs on the surface of calcium carbonate crystal,the presence of dodecyl in the AEO group might greatly affect the growth of calcium carbonate crystals and this effect will be far greater than that caused by HPMA molecule itself...