Preparation of a phosphorous-free terpolymer as a decalcifying agent for removing calcium from crude oil

A novel phosphorous-free terpolymer, used as a decalcifying agent for removing calcium from crude oil, was prepared through a free-radical polymerization reaction of acrylic acid (AA), allylpolyethoxy amino carboxylate (APEA), and 2-hydroxyethyl acrylate (HEA) in water with ammonium persulfate as initiator. The structure of the synthesized AA–APEA–HEA terpolymer was characterized by Fourier transform infrared spectrometry and 1H nuclear magnetic resonance (1H-NMR). AA–APEA–HEA was used to remove calcium from Luning pipeline crude oil. The effects of several factors, such as molar ratio, dosage, and reaction temperature on calcium removal efficiencies from crude oil were evaluated. The results indicated that the removal of calcium from crude oil using AA–APEA–HEA was far more efficient than that using AA–APEA, PAA, HPMA, and PESA under the same conditions. The optimum conditions for calcium removal from crude oils were as follows: (a) molar ratio of AA–APEA–HEA, 2 : 1 : 0.5; (b) dosage of AA–APEA–HEA, 100 ppm; (c) reaction temperature, 100 °C. Under these conditions, the removal efficiency of calcium from Luning pipeline crude oils was approximately 98.63%. Furthermore, the proposed decalcification mechanism suggests surface complexation and chelation between the carboxylic (–COO−) and amino (–NH2) functional groups and Ca2+, with the polyethylene glycol segments increasing its solubility in water and the lipophilic ester groups increasing its affinity to oil.