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Equipment scaling leads to reduced production efficiency in a wide range of industrial applications worldwide. Various antiscaling agents are currently commonly used to mitigate this problem. However, irrespective of their long and successful application in water treatment technologies, little is known about the mechanisms of scale inhibition, particularly the localization of scale inhibitors on scale deposits. The lack of such knowledge is a limiting factor in the development of applications for antiscalants. Meanwhile, fluorescent fragments integrated into scale inhibitor molecules have provided a successful solution to the problem. The focus of this study is, therefore, on the synthesis and investigation of a novel fluorescent antiscalant: (2-(6-morpholino-1,3-dioxo-1H-benzo[de]isoquinolin-2(3H)yl)ethylazanediyl)bis(methylenephosphonic acid) (ADMP-F) which is an analog of the commercial antiscalant: aminotris(methylenephosphonic acid) (ATMP). ADMP-F has been found to effectively control the precipitation of CaCO3 and CaSO4 in solution and is a promising tracer for organophosphonate scale inhibitors. ADMP-F was compared with two other fluorescent antiscalants—polyacrylate (PAA-F1) and bisphosphonate (HEDP-F)—and was found to be highly effective: PAA-F1 > ADMP-F >> HEDP-F (CaCO3) and PAA-F1 > ADMP-F > HEDP-F (CaSO4·2H2O). The visualization of the antiscalants on the deposits provides unique information on their location and reveals differences in the “antiscalant-deposit” interactions for scale inhibitors of different natures. For these reasons, a number of important refinements to the mechanisms of scale inhibition are proposed.

Phosphonates have found broad commercial applications as scale inhibitors in reverse osmosis facilities, boilers, heat exchangers, evaporation plants, and oilfields. Irrespective of their long-term use, there is a cogent need to detect phosphonates in aqueous solution “online” to control their actual concentration in industrial water treatment. Towards this goal, a novel fluorescent-labeled monomer M containing a triamine subunit and 1,8-naphthalimide with an allyl group has been synthesized and found to exhibit a selective fluorescence enhancement with phosphonates in the presence of other anions. The absorption and fluorescence properties of M as well as its effective stability constants with various phosphonates have been studied in a wide pH range. M has been implemented in the synthesis of cryopolymers, which can detect phosphonates in aqueous solution. The presented results provide an important contribution to the future design of fluorescent polymer probes for antiscalants.

Knowledge of the scaling mechanism makes it possible to develop effective means to control scaling and improve the membrane performance, increasing the recovery. This paper presents new approaches to the study of the mechanism of scaling in the presence of polymeric inhibitors (antiscalants); the adsorption of antiscalant molecules on the crystal and membrane surfaces has been investigated. The relations of the antiscalant adsorption rates to the antiscalant dose and the calcium carbonate scaling rate have been revealed. For the first time, the inhibition process was “visualized” by using a fluorescent antiscalant containing a fluorescent moiety—a copolymer of N-allyl-4-methoxy-1,8-naphthalamide and acrylic acid (PAA-F1). The examination of the surfaces of crystals and membranes by scanning electron and fluorescence microscopy showed new unexpected results: the antiscalant is adsorbed on the membrane surface and on the surface of calcite crystals formed. Fluorescence turned out to be more intense and noticeable on the surface of crystal faces than inside the crystal. During the nucleation phase, the “dark” part of the crystal lattice is formed and then begins to be covered with a “luminous” layer of the fluorescent antiscalant, which blocks further crystal growth. During experiments with antiscalant solutions in distilled water, the antiscalant was found to be adsorbed on the membrane surface in the absence of calcium ions. In experiments in which the antiscalant was added into the original tap water, it was adsorbed on the surface of the resulting crystals, not on the membrane. The visualization of the crystal growth inhibition process opens up new possibilities for studying the mechanism of scaling and developing of new technologies to control scaling.

Novel naphthalimide-functionalized bisphosphonates with different spacer length have been designed and synthesized. The spectroscopic properties, dissociation constants and complexation behavior with calcium(II) have been studied in aqueous solution. It has been shown that the length of the spacer has a dramatic effect on the fluorescence, Ca2+ binding properties and solubility of Ca2+ complexes in aqueous solution. New fluorescent bisphosphonates have been found to provide a perfect contrasting of inorganic industrial fouling (barite) and human tissue calcification (hydroxyapatite). The affinity of the fluorescent bisphosphonates for the bone matrix in the presence of human fibroblast cells has been tested in vitro with hydroxyapatite crystals imitated the human bone. Microscopic fluorescence analysis has demonstrated that fluorescent bisphosphonates are able to bind efficiently and selectively to the hydroxyapatite in the presence of human fibroblast cells.

The two fluorescent monomers N-allyl-4-methoxy-1,8-naphtalimide (F1) and N-allyl-2-(6-hydroxy-3-oxo-3H-xanthen-9-yl)benzamide (N-allylamidefluorescein, F2) have been synthesized and then conjugated to either polyacrylate (PAA) or to a co-polymer of fumaric and acrylic acids (MA-AA) to give four novel fluorescent-tagged antiscalants: nonbiodegradable PAA-F1, PAA-F2 and biodegradable MA-AA-F1, MA-AA-F2. All four reagents demonstrate the fluorescence intensity suitable for inhibitors monitoring with a detection limit within 0.40 mg dm−3. A good linear relationship between antiscalant fluorescent intensity and its dosage is detected. PAA-F1, PAA-F2, MA-AA-F1, and MA-AA-F2 can be used for corresponding scale inhibitor content on-line measurement. For some antiscalants, the fluorescence is found to be dependent on the background heavy metal ions normally present in the cooling water. This effect is explained by the corresponding complexes formation. PAA-F1, PAA-F2, MA-AA-F1, and MA-AA-F2 revealed a good antiscaling activity toward CaCO3 and CaSO4 deposition, comparable with that one of commercial polyacrylates. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45017.