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In this paper, the retarding effect of a green additive, citric acid, towards calcium carbonate scale deposition is studied. Scale formation is one of the most common causes of malfunctions in process equipment. This is the reason it is crucial to retard scale precipitation, that is, in order to reduce economic damages. With this additive in the solution, experimental runs have been carried out in supersaturation conditions in terms of concentration of calcium carbonate at equilibrium, with a supersaturation ratio ranging from 16 to 280, at 25°C. Three different concentrations of citric acid have been investigated (0.520 × 10−3, 1.041 × 10−3 and 1.561 × 10−3 M) in a laboratory scale plant. Comparing results obtained in terms of induction time with previous experimental runs, performed without additives, citric acid has shown its significant capacity to retard calcium carbonate precipitation, by increasing induction time values. This behaviour is enhanced by raising the additive concentration in solution up to a specific threshold value, beyond which no benefit in terms of calcium scale inhibition is gained. Furthermore, interfacial tension has been computed without and with citric acid at 0.520 × 10−3 and 1.041 × 10−3 M, as a function of the different concentration amounts investigated. The values obtained are in good agreement with data reported in the literature.

The chemical effect of hydrodynamic cavitation (HC) in a Venturi reactor from both the theoretical and the experimental point of view is dealt. A mathematical model is presented to simulate the global production of hydroxyl radicals; it is based on a set of ordinary differential equations that account for the hydrodynamics, mass diffusion, heat exchange, and chemical reactions inside the bubbles. Experimentally, the degradation of p-nitrophenol (initial concentration 0.15 g dm−3) has been conducted in a lab scale Venturi reactor at inlet pressure ranging from 0.2 to 0.6 MPa and has been used to estimate the hydroxyl radical production. The optimum configuration, suggested by numerical simulations, has been experimentally confirmed. Thanks to the empirical validation, this novel modeling approach can be considered as a theoretical tool to identify the best configuration of HC operating parameters. © 2014 American Institute of Chemical Engineers AIChE J, 60: 2566–2572, 2014

The comprehension of the mechanisms of nucleation and growth that regulate the gypsum (calcium sulfate dihydrate) precipitation is fundamental to prevent scaling problems. The present paper reports measurements of the induction period for gypsum nucleation when citric acid is added in solution as an additive to retard scale formation. The supersaturation ratio was varied in the interval 2.3-6.0, the concentration of citric acid ranged from 0.01 to 0.30 g/L, while in all experiments the temperature was fixed to 25°C. The induction period values were compared to those previously obtained, by using the same experimental technique, in the absence of foreign ions in the mother liquor, showing that the citric acid has a strong retarding effect towards gypsum nucleation. La comprehension des mecanismes de nucleation et de croissance qui regulent la precipitation de gypse (dihydrate de sulfate de calcium) est fondamentale pour empecher les problemes d'encrassement. On presente dans cet article des mesures de la periode d'induction pour la nucleation de gypse lorsque de l'acide citrique est ajoute a la solution comme additif pour retarder la formation de tartre. On a fait varier le taux de sursaturation dans l'intervalle de 2,3-6,0, la concentration d'acide citrique entre 0,01 et 0,30 g/L, tandis que dans toutes les experiences la temperature a ete fixee a 25 °C. Les valeurs de periode d'induction sont comparees a celles obtenues anterieurement, avec la meme technique experimentale, en l'absence d'ions etrangers dans l'eau-mere, montrant que l'acide citrique exerce un fort effet de retardement dans la nucleation du gypse.