The effect of ethylene oxide groups in alkyl ethoxy carboxylates on its scale inhibition performance

• We study the effects of EO number on the scale inhibition performance of AEC.
• The scale inhibition performance of AEC actually depends on EO number.
• The scale inhibition performance of AEC decreases with increasing EO number.
• The corrosion inhibition of AEC shows a critical threshold regarding concentration.
• The corrosion inhibition is actually determined by EO number of AEC.

To study the effects of ethylene oxide (EO) number in alkyl ethoxy carboxylates (AEC) on scale inhibition, ten AEC compounds are prepared. The effect of EO number on the scale inhibition against CaCO3, CaSO4 and Ca3(PO4)2 scales and effects of the operating conditions on scale inhibition against CaCO3 are investigated by static test. The effect of EO number on the corrosion inhibition is measured by the weight loss of rotating hung steel slices. The influence of AEC on formation of CaCO3, CaSO4 and Ca3(PO4)2 is investigated using scanning electronic microscopy (SEM). The results indicate that the scale inhibition of AEC depends actually on EO number, the scale inhibition against CaCO3 and Ca3(PO4)2 scales decreases with increasing EO number. The ability of the inhibitors to tolerate high alkalinity and high hardness reduces with increasing EO number. AEC-3, AEC-4 and AEC-5 have good performance with scale inhibition more than 80% at the pH, concentration of calcium carbonate and temperature ranges of 7.0–9.0, 250–750 mg/L and 50–80 °C, respectively. Morphologies of the scales are highly modified in the presence of AEC. The corrosion inhibition of AEC shows a significant critical threshold regarding the concentration of AEC, the corrosion inhibition increases with increasing EO number.