The Protonation of Polyacrylate in Seawater. Analysis of Concentration Effects

Abstract

The protonation of polyacrylate (PAA, MW 2 kDa) was studied potentiometrically at 25 degrees C, in mixed electrolyte aqueous solution simulating the composition of seawater, in the salinity range 30 < or = S < or = 40. The salt composition of different solutions was varied in order to study its effect on apparent protonation constants. Results were analysed using two fairly different approaches: by simple regression analysis on a combination of concentration parameters and salinity, and by canonical correlation analysis. Unexpectedly we found that variations on protonation constants, due to the different relative component concentrations, are fairly low, revealing a sort of buffering capacity of seawater respect to protonation properties of polyacrylate (and likely for other HMW and LMW polycarboxylates). The intrinsic protonation constant of polyacrylate 2 kDa at 25 degrees C and 35 salinity is log K(H*) = log K(int) = 4.399 +/- 0.004. The use of different pH scales and standard seawater compositions is also discussed.

Calcium sulfate precipitation in the presence of water-soluble polymers

“…It has been suggested that larger number of functional groups of negatively charged species increases the polar attraction between the adsorbate and the positive sites at the solution interface [29]. The proton dissociation constant, log K, for polyacrylates is in the order of 4.4 [30]. The presence of hydrophobic aromatic nucleus on the molecule may change the mode of adsorption and the respective efficiency.…”

Contrasting Behaviors between Gypsum and Silica Scaling in the Presence of Antiscalants during Membrane Distillation

“…We first compared the efficiencies of antiscalant candidates with varied electric charges in retarding mineral precipitation in static experiments (i.e., without membranes) at pH of 6.50 ± 0.05. At this pH, PAA molecules with a p K a value of 4.4 are negatively charged due to the deprotonation of carboxyl groups, whereas PEI molecules with a p K a value of 7.1 displayed cationic nature that resulted from the protonation of amino groups . In contrast, PEG molecules possess near-neutral electric charge at the solution pH of our study. , For gypsum scaling, the change of soluble scaling precursors (i.e., Ca 2+ and SO 4 2– ions) was monitored by measuring the solution conductivity.…”

Wetting, Scaling, and Fouling in Membrane Distillation: State-of-the-Art Insights on Fundamental Mechanisms and Mitigation Strategies

“…The two major mechanisms that are likely responsible for scaling inhibition are (1) the formation of soluble complexes in the bulk solution, which decreases the SI by reducing availability of the “free” ions for precipitation, and (2) the direct adsorption onto the nuclei surface, which retards the mineral growth. , Antiscalants that are widely used in industry are weak acids such as phosphonate derivatives and polymeric molecules anchored with carboxylic groups. Under near-neutral conditions of desalination, such antiscalants are partially or fully deprotonated, exposing negative active sites that are able to form complexes with multivalent cations in the solution. − For example, poly­(acrylate acid) (PAA), a carboxylic derivative polymer with p K a of 4.4, is highly deprotonated at approximately the pH of 7 and may strongly chelate with Ca 2+ to reduce its activity for precipitating with CO 3 2– or SO 4 2– to form calcite or gypsum. , However, this complex formation mechanism is challenged by the fact that the antiscalants can be highly effective at a very low concentrationmuch lower than the concentration of Ca 2+ stoichiometrically. , …”

“…Under near-neutral conditions of desalination, such antiscalants are partially or fully deprotonated, exposing negative active sites that are able to form complexes with multivalent cations in the solution. 136−139 For example, poly(acrylate acid) (PAA), a carboxylic derivative polymer with pK a of 4.4, 140 is highly deprotonated at approximately the pH of 7 and may strongly chelate with Ca 2+ to reduce its activity for precipitating with CO 3 2− or SO 4 2− to form calcite or gypsum. 141,142 However, this complex formation mechanism is challenged by the fact that the antiscalants can be highly effective at a very low concen-trationmuch lower than the concentration of Ca 2+ stoichiometrically.…”