Synthesis and Visualization of a Novel Fluorescent-Tagged Polymeric Antiscalant during Gypsum Crystallization in Combination with Bisphosphonate Fluorophore

Abstract

An attempt to reveal the mechanisms of scale inhibition with the use of two different fluorescent-tagged antiscalants at once is undertaken. To reach the goal, a novel 1,8-naphthalimide-tagged polyacrylate (PAA-F2) is synthesized and tested separately and jointly with 1,8-naphthalimide-tagged bisphosphonate (HEDP-F) as a gypsum scale inhibitor within the frames of NACE Standard TM0374-2007. Here, it is found that at a dosage of 10 mg·dm−3 it provides a much higher inhibition efficiency (96%) than HEDP-F (32%). A PAA-F2 and HEDP-F blend (1:1 mass) has an intermediate efficacy (66%) and exhibits no synergism relative to its individual components. The visualization of PAA-F2 revealed a paradoxical effect: an antiscalant causes modification of the CaSO4·2H2O crystals habit, but does not interact with them, forming particles of its own solid complex [Ca-PAA-F2]. This paradox is interpreted in terms of the “nano/microdust” concept, prioritizing the bulk heterogeneous nucleation step, while an ability of the scale inhibitor to block the nucleus growth at the next steps is proven to be of secondary importance. At the same time, HEDP-F does not change the gypsum crystals morphology, although this antiscalant is completely located on the surface of the scale phase. The PAA-F2 and HEDP-F blend revealed an accumulation of both antiscalants in their own [Ca-PAA-F2/Ca-HEDP-F] phase with some traces of HEDP-F and PAA-F2 on the CaSO4·2H2O crystals surface. Thus, the visualization of two different antiscalants separately and jointly applied to gypsum deposition demonstrates differences in phosphonic and polymeric inhibitors location, and a lack of causal relationship between antiscalant efficiency and scale particle habit modification. Finally, it is shown that the confocal microscopy of several fluorescent antiscalant blends is capable of providing unique information on their interrelationships during scale deposition.

Fluorescent‐tagged Antiscalants: A New Look at the Scale Inhibition Mechanism and Antiscalant Selection

“…Meanwhile, already the first communication on synthesis of the fluorescent‐tagged phosphonate scale inhibitor – 1‐hydroxy‐7‐(6‐methoxy‐1,3‐dioxo‐1H‐benzo[de]isoquinolin‐2(3H)‐yl)heptane1,1‐diyl‐di(phosphonic acid), (HEDP‐F) [16] and its visualization during gypsum scale formation, published in 2019, provided results, that exceeded all expectations. Five publications that report on both phosphonic (HEDP‐F; ADMP‐F) and polycarboxylic (PAA‐F1; PAA‐F2; PASP‐F; HBP‐AP) fluorescent antiscalants visualization microscopy during gypsum [16,18–21] and barite [17] scale formation were registered recently, Figure 1. Among these, HEDP‐F, PAA‐F1, PASP‐F, HBP‐AP exhibit the blue light emission (fluorescence band at 440÷465 nm), while PAA‐F2 reveals green fluorescence (fluorescence band at 505 nm).…”

“…Thus, in our reports [16,17,18,20] the original blue emission is changed for an artificial green pseudo‐color. However, in the present review, we tried to depict the fluorescence of antiscalants with colors close to their real ones, as it was done in [19] …”

“…Meanwhile, a significant progress both in scale inhibition mechanisms understanding and in critical assessment of antiscalant efficacy determination methods has become possible recently due to fluorescent‐tagged scale inhibitors [15] . Therefore, an objective of present review is to generalize the first results of antiscalant fluorescent microscopy visualization during scale deposition, published during 2019–2021 [16–21] . Our publication is an important supplement to the comprehensive overview of scale inhibition theory problems, to be published recently [4]…”

Green and High Effective Scale Inhibitor Based on Ring-Opening Graft Modification of Polyaspartic Acid

“…The reasons may be listed as follows. Firstly, the sparingly soluble salts, such as CaCO 3 , Ca 3 (PO 4 ) 2 , and gypsum, are crystallized on the nano/microdust impurities in the aqueous solution [30]. Those nano/microdusts are not uniform and consist of different ingredients.…”

“…The synergy of the introduced hydroxyl and carboxylic groups of PASP-ASP-MEA can enhance the blocking of the nano/microdust crystallization centers of CaCO3 and Ca3(PO4)2. Therefore, the rate of crystallization of CaCO3 and Ca3(PO4)2 decreased, which finally resulted in the smaller crystals [30][31][32]. The CaCO 3 and Ca 3 (PO 4 ) 2 scale deposits were observed by scanning electron microscope (SEM).…”