Synthesis Of Sodium Fatty Alcohol Ether Carboxylate And Its Calcium Scale Inhibition Mechanism Research

The scale inhibitor is a chemical agent that prevents the precipitation and accumulation of fouling in the water treatment process.It is mainly used in pharmaceutical plants,refineries,food processing and thermal power plants.At present,most of the research on scale inhibitors depends on experiments,which requires a lot of manpower,material and financial resources.Due to the complex physical and chemical processes involved,there is no unified understanding of the scale inhibition mechanism in the academic community.In this paper,experiments and molecular dynamics（MD）simulation methods were used to explore the variation of the performance of fatty alcohol ether carboxylate（AEC）calcium scale inhibition with the number of EO in AEC molecules from macro and micro perspectives.The mechanism of AEC calcium scale inhibition provides theoretical guidance for the synthesis of new green scale inhibitors.Ten fatty alcohol ether carboxylates（AEC）were synthesized by using fatty alcohol polyoxyethylene ether（AEO-n,n=3,4,5,7,9,10,11,12,15,20）,sodium chloroacetate and sodium hydroxide as raw materials and ethanol as solvent.FT-IR and ¹H NMR were used to characterize AEC.Through static scale inhibition experiments,it was found that the inhibition effect of EO number on calcium scale（Ca CO₃,Ca SO₄and Ca₃（PO₄）₂）in AEC molecules decreased with the increase of EO number,and its inhibition effect on Ca CO₃was the best,followed by Ca SO₄and Ca₃（PO₄）₂.The corrosion inhibition performance of EO number in AEC molecule on carbon steel was enhanced with the increase of EO number.The interaction between AEC and calcite,anhydrite and hydroxyapatite crystal plane in aqueous solution was studied by molecular dynamics（MD）simulation.The calculation results are as follows:the binding energy of AEC molecules to the three calcium scale compounds Ca CO₃is the largest,followed by Ca SO₄,and Ca₃（PO₄）₂is the smallest.The degree of bending and folding of the carbon chain increases with the increase of EO number.The results show that the oxygen atom on the carboxyl group in AEC forms an intramolecular hydrogen bond with the hydrogen atom on the carbon chain,which further hinders the adsorption of the carboxyl group on the active growth point of calcium scale,resulting in lattice distortion.The analysis of the interaction and radial distribution function of the system shows that the adsorption type of AEC and three calcium scale compounds is mainly ionic bond,and the proportion of non-bond interaction increases with the increase of EO number.Finally,the interaction between AEC and Fe crystal plane was simulated.The analysis of the interaction and radial distribution function of the system shows that the O atom in the EO group forms a coordination adsorption with the Fe crystal plane,and the carboxylic acid group in the molecule forms a negative feedback adsorption with the Fe crystal plane.The synergistic effect between the groups enables the AEC molecule to spontaneously adsorb on the Fe crystal plane in a parallel state,reducing the contact area between the metal and the water molecule,thereby improving the corrosion of the metal.From the strength of AEC and Fe crystal plane,the coordination bond of（1 1 0）crystal plane is stronger than that of（0 0 1）crystal plane,and the former is easier to combine with Fe crystal plane.In summary,the scale and corrosion inhibition mechanism of scale and corrosion inhibitor AEC was systematically studied in this paper.The interaction between AEC and calcite,anhydrite,hydroxyapatite and iron crystal plane in water environment was explored from macro and micro perspectives.The simulation results were consistent with the results of static scale inhibition experiments.