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

Abstract

Solid deposits onto equipment surfaces represent a serious problem all over the world. Mitigation of this process is provided by chemical inhibitors. However, irrespective of successful antiscalant application, the mechanisms of scale inhibition are still not very clear. Thus, the present review summarizes recent advances in novel fluorescent‐tagged antiscalants (polyacarboxylates, phosphonates) application for scale inhibition mechanisms study. Some paradoxical effects, detected during gypsum and barite scale formation visualization are described and interpreted within the “nanodust” concept. It is demonstrated, that the solid nanoimpurities, naturally occurring in both industrial and deionized water samples, are definitely playing a key role in any crystal nucleation process. Such nanoimpurities are responsible for the bulk heterogeneous nucleation in a supersaturated salt solution. Scale inhibitor molecules block and isolate exactly these “nanodust” nucleation centers and therefore retards crystallization process on the whole. The advantages of fluorescent antiscalants to provide a new look at scale inhibition phenomenon and inhibition mechanisms are discussed. Among these, there is a possibility to distinguish particular scale inhibitors in their blends, and an opportunity to track an antiscalant location along the process of scale formation and deposition. Besides, a need of antiscalants testament procedure unification is considered, and a possible role of fluorescent reagents in such a procedure elaboration is indicated.

A Case Study of Calcium Carbonate Crystallization during Reverse Osmosis Water Desalination in Presence of Novel Fluorescent-Tagged Antiscalants

“…PAA-F1 covers the CaCO 3 surface completely and rather uniformly, while HEDP-F demonstrates a nonuniform location: some crystals of calcium carbonate appear to be completely uncovered, some are partly covered, while some are covered completely. The present study indicates, along with latest reports [27,31], that fluorescent-tagged scale inhibitors are capable to provide valuable information on the nature of scale inhibition.…”

Application and Visualization of Fluorescent-Tagged Antiscalants in Electrodialysis Processing of Aqueous Solutions Prone to Gypsum Scale Deposition

“…In this way, antiscalant was evidently disabled as the [Ca-HEDP-F] species before the nucleation of gypsum had started, but it still provided retardation of deposit formation. The same effect was observed during gypsum deposition in an RO facility in the presence of PAA-F1 (see [ 33 ] and references there). Besides, in a static experiment at ambient temperature (supersaturation is achieved by mixing Na 2 SO 4 and CaCl 2 solutions), we have detected a similar result: classical stick-like crystals of gypsum mixed with spherical [Ca-HEDP-F] particles.…”

“…Recently the situation has changed due to the possibility to track AS directly in any water treatment process using fluorescent-tagged scale inhibitors [ 32 , 33 , 34 ]. Indeed, our recent experiments with gypsum scale formation in a laboratory RO setup in the presence of fluorescent-tagged bisphosphonate 1-hydroxy-7-(6-methoxy-1,3-dioxo-1Hbenzo[de]isoquinolin-2(3H)-yl)heptane-1,1-diyl-bis(phosphonic acid), HEDP-F (H 4 hedp-F) [ 32 ] and of fluorescent 1,8-naphthalimide-tagged polyacrylate (PAA-F1) [ 33 ] revealed a paradoxical effect: an antiscalant does not show any kind of interaction with gypsum, but provides nevertheless retardation of the corresponding deposit formation.…”

“…However, when a mixture of Na 2 SO 4 and CaCl 2 solutions was heated at 70 °C for 24 hours according to NACE Standard TM0374-2007 and then cooled, the result was very different. We have observed [Ca-HEDP-F] particles inside the gypsum crystals and some traces of a HEDP-F molecular layer on the CaSO 4 ·2H 2 O crystal surface (see [ 33 ] and references there). This indicates that: (i) in particular cases [Ca-HEDP-F] particles are capable to act as crystallization centers of gypsum; and (ii) the mechanisms of scale inhibition may vary significantly depending on temperature, supersaturation degree, and antiscalant concentration, etc.…”

Review of Phosphorus-Based Polymers for Mineral Scale and Corrosion Control in Oilfield

“…Nanoimpurities' Role in Scale Formation/Inhibition More recently, a non-conventional inhibition mechanism in which scales are inhibited by heterogeneous formation on a "nanodust" particle surface, instead of ion pairs or clusters formed via homogeneous nucleation, was investigated [55]. Several fluorescent-tagged scale inhibitors were synthesized, which were able to provide visualization of the functionality of scale inhibitors during the formation of gypsum and some other scales [77][78][79].…”