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

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. © 2015 Elsevier B.V. All rights reserved.

In this paper ten alkyl ethoxy carboxylateses are prepared by the way of carboxyl methlation. The molar ratio of AEO:sodium chloroacetate:NaOH is controlled at 1:1.05:1.1. The reaction temperature is controlled in the range of 45–55 °C. The experiments are focused on the effects of ethoxy (EO) number of AEC on the scale inhibition against CaCO3, CaSO4 and Ca3(SO4)2. The effects of EO number on the Fig. 13. Influence of EO number on the corrosion inhibition efficiency with the same molar concentration of AEC (inhibitor: 6 × 10−5 mol/L). corrosion inhibition of AEC are studied. The effects of the operating conditions on the scale inhibition against CaCO3 and the influence of AEC on the morphology of CaCO3, CaSO4 and Ca3(SO4)2 scales are also investigated. The main results can be summarized as following: (a) For the same molecular structure, the scale inhibition performance of AEC against CaCO3 scale depends actually on the EO number, and the scale inhibition performance decreases with increasing EO number. AEC-3, AEC-4, AEC-5, AEC-7, AEC-9, AEC-10 and AEC-11 can be used significantly to inhibit the formation of CaCO3 scale. The scale inhibition performance of AEC against CaSO4 is related to EO number, AEC-4 and AEC-5 are good inhibitors against CaSO4 scale. The scale inhibition performance of AEC against Ca3(SO4)2 decreases with increasing EO number, AEC-3, AEC-4 and AEC-5 show good performance in inhibition of Ca3(PO4)2 scale. (b) The variation of the inhibition performance of AEC against CaCO3 scale may mainly be attributed to the adsorption of carboxylic ion of AEC on the crystal surface, which causes crystal distortion, and the distortion decreases with increasing EO number. AEC may also inhibit crystal growth through coordination or chelation with lattice cations. The crystal structure of CaCO3, CaSO4 and Ca3(SO4)2 scales is highly modified in the presence of AEC. (c) The influence of pH on the inhibition performance of AEC is more obvious than that of temperature, the pH affects only on some compounds of AEC, but the effect of temperature increases with increasing EO number at low temperature. For AEC-3, AEC-4, AEC-5 and AEC-7, when pH ≤ 9.0, ηCaCO3 ≥ 85%; as 9.0 ≤ pH ≤ 10.0, 85% ≥ ηCaCO3 ≥ 50%. For AEC-3, AEC-4 and AEC-5, as the concentration of CaCO3 is less than 750 mg/L, ηCaCO3 ≥ 80%. Therefore, AEC-3, AEC-4 and AEC-5 can be used in high alkalinity and high hardness water. (d) The corrosion inhibition of AEC shows a significant critical threshold characteristic. The corrosion inhibition increases with increasing EO number of AEC regardless under the same concentration or the same molar concentration. The corrosion inhibition of AEC depends actually on EO number of AEC.