Synthesis of unexplored aminophosphonic acid and evaluation as scale inhibitor for industrial water applications

Abstract

A new aminophosphonic acid was synthesized by condensation of 4,4'-(propane-2,2-diylbis(4,1-phenylene)bis(oxy)dianiline), phosphorous acid and formaldehyde, according to the Moedritzer-Irani reaction. The structure of the inhibitor was analyzed by 1H and 31P NMR, FT-IR, mass spectrometry and thermogravimetry.The new inhibitor presented high efficiency in a static condition on the model imitating water composition with respect to CaCO3 and CaSO4 deposits. The crystal formation of CaCO3 and CaSO4 was investigated by scanning electronic microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). The inhibitor obviously affected the procedure of crystal growth. The morphology of the CaCO3 crystals, in the absence of inhibitor, showed a predominant content of rhombohedral crystals (calcite), whereas in the presence of inhibitor we could observe a mixture of calcite with acicular crystals (aragonite) and a small content of spherical crystals (vaterite). Concerning CaSO4 crystals, thin needles with a smooth surface were observed in the absence of the inhibitor, which became thicker with many crystal defects in the presence of the inhibitor.Consequently, the new aminophosphonic acid described here can be used as a potential scale inhibitor.