Pilot plant evaluation of advanced vs. conventional scale inhibitors for RO desalination

doi:10.1016/0011-9164(95)00072-0

Desalination

Volume 103, Issue 3, December 1995, Pages 189-198

https://doi.org/10.1016/0011-9164(95)00072-0 Get rights and content

Abstract

An advanced anti-scalant, consisting of a polyacrylate and hydroxyethylidene diphosphonate (HEDP), was tested against the conventional H₂SO₄ and sodium hexa-meta-phosphate (SHMP) inhibitors in a pilot plant which had parallel RO units. The two units were fitted with identical brackish hollow fine fiber (HFF) permeators arranged in a two-stage mode which received the same brackish feed water, and were operated at the same feed pressure (27.6 bar/400 psig) and product water recovery (70%). Unit #1 was treated 9 ppm of as-received advanced anti-scalant, and unit #2 was treated with 6 ppm of SHMP and about 130 ppm of 98% H₂SO₄. The pilot plant trial lasted for 3,000 h. The techno-economic evaluation of the two scale control treatments was carried out in terms of pumping energy, the anti-scalants consumed, and the quality and total output of the product water produced in 3,000 h. The pumping energy and scale control treatment costs (as $/m³ of water produced) were same for the two treatments; but in terms of salt rejection, product TDS and output, performance of the advanced anti-scalant was inferior; after 3,000 h the salt rejection of unit #1 (which operated on the advanced anti-scalant) was about 81% vs. 94% for unit #2 (H₂SO₄+SHMP). Similarly, in 3,000 h unit #1 produced 20% less water of unacceptable quality (620 ppm) whereas unit #2 produced more water of excellent quality (180 ppm), providing a clear testimony to the superior performance of the conventional H₂SO₄+SHMP treatment over the advanced anti-scalant.

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Usually, inlet feed water must pass through a residence time of 15 min in the RO chamber during which pure water (70%) and concentrated reject brine (30%) are produced. Antiscalant study was carried out at 40 °C in the presence of a supersaturated solution containing three times the concentrations of Ca2+ and SO42− ions (using CaCl2 and Na2SO4) found in the reject brine of a local RO plant [57]. In the presence of 1–5 ppm antiscalants (12, 14, and 15), the 15-min residence time must be negotiated to mitigate the scale formation.
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Synthesis and application of alternate cyclopolymers of β-diallylaminoethyliminodiacetic acid with maleic acid and sulfur dioxide
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Bis-cationic monomer β-diallylaminoethyliminodiacetic acid dihydrochloride (I) underwent alternate cyclocopolymerizations with SO₂ and maleic acid to give poly(bis-zwitterion) (PBZ) (± ±) II, and III, respectively. The PBZs contained the chelating motifs of [NH⁺(CH₂)₂NH⁺(CH₂CO₂⁻)₂] embedded in the pyrrolidine ring of each repeating unit. Both the PBZs were water-insoluble, however they became water-soluble with assistance from salts like NaCl. PBZs II and III, having the point of zero charge at pH 2.4, became water soluble outside the pH-windows of 0.81–4.46 and 1.49–3.35, respectively, whereby the electroneutral pH-responsive polymers become charge-imbalanced. The ‘apparent’ pK_as of the protonated amine centers in II were found to be 5.18 and 9.92. As an antiscalant, PBZ III (2.5 ppm) demonstrated inhibition of CaSO₄ scale formation with 99% efficacy for over 180 min, while at 1.5 ppm inhibition efficiency was found to be 98% for 50 min. PBZ II at concentrations of 20 and 10 ppm demonstrated CaCO₃ scale inhibition of 98% for over 240 min and 95% for over 90 min, respectively. A synergistic mixture of III (20 ppm) and KI (400 ppm) arrested corrosion of mild steel in 1 M HCl with a remarkable efficacy of 98% for 24 h at 60 ^οC.
Synthesis and application of a poly(bis-zwitterion) containing chelating motifs of N-(2-aminoethyl)iminodiacetic acid
2020, European Polymer Journal
A bis-cationic (+ +) diallyl monomer [(H₂C=CHCH₂)₂NH⁺(CH₂)₂NH⁺(CH₂CO₂H)₂ •2Cl⁻] (I) was prepared by a one-pot, two-step reaction of 2-bromoethylamine hydrobromide, ethyl bromoacetate and diallylamine to generate [(H₂C = CHCH₂)₂N(CH₂)₂N(CH₂CO₂Et)₂] followed by ester hydrolysis. I underwent cyclopolymerization to afford a unique poly(bis-zwitterion) (PBZ) (± ±) II, containing repeating unit embedded with chelating motifs of N-(2-aminoethyl)iminodiacetic acid in bis-zwitterionic form NH⁺(CH₂)₂NH⁺(CH₂CO₂^–)₂. Electroneutral II was found to be water-insoluble, while salts like NaCl imparted water-solubility. The polymer was soluble outside a pH window of 1.5–3.5 owing to the equilibration of pH-responsive II to charge-imbalanced polymer chain. The ‘apparent’ pK_as of the two NH⁺ centers were determined to be 5.89 and 10.57. At 2.5 ppm concentration, antiscalant PBZ II imparted 100% inhibition of CaSO₄ scale formation for 30 min from its supersaturated solution, while at 20ppm concentration aided by KI, it demonstrated an outstanding synergistic 99% inhibition of mild steel corrosion in 1 M HCl.
Synthesis of unexplored aminophosphonic acid and evaluation as scale inhibitor for industrial water applications
2018, Journal of Water Process Engineering
Citation Excerpt :
The modified Gambier extract also showed a high efficiency, of 92% at 300 ppm, but information on the effectiveness of calcium sulphate inhibition is not indicated. As described in previous work [40], inorganic scale inhibitors have a number of drawbacks, such as thermal instability, they are only effective up to 80 °C, hydrolysis up to orthophosphates, with the formation of insoluble calcium salts at low efficiency for CaSO4. By introducing productive horizons with fresh water, SHMP activates the development of sulphate-reducing bacteria.
A new aminophosphonic acid was synthesized by condensation of 4,4'-(propane-2,2-diylbis(4,1-phenylene)bis(oxy)dianiline), phosphorous acid and formaldehyde, according to the Moedritzer-Irani reaction. The structure of the inhibitor was analyzed by ¹H and ³¹P NMR, FT-IR, mass spectrometry and thermogravimetry.
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Consequently, the new aminophosphonic acid described here can be used as a potential scale inhibitor.
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The cyclotetrapolymerization of four diallylamine salt monomers, containing chelating motifs of aminocarboxylate, aminophosphonate, aminosulfonate and primary amine at the terminal of an alkyl chain (CH₂)₁₂, has led to the synthesis of a tetrapolymer in excellent yield. A copolymer of methacrylate having acetyl acetate pendant has also been synthesized. The two polymers in aqueous solution is found to form gel because of covalent crosslinking via formation of imine bond by condensation of –NH₂ groups of the tetrapolymer with the acetoacetate groups of the polymethacrylate copolymer. This is the first example of a cyclopolymer immobilized by covalent crosslinking with a polymethacrylate. The hydrogel, embedded with chelating motifs of aminoalkyl-carboxylate, phosphonate and sulfonate as well as imine motifs, demonstrated remarkable efficacies for the removal of Hg(II) ions at ppb levels. A 50 mg-dose of the hydrogel immersed in aqueous medium (20 mL) could reduce the concentration of Hg(II) from 200 and 500 ppb to 0.20 and 0.17 ppb, respectively, within 30 min. The hydrogel has also been shown to be remarkably effective in the removal of several toxic and priority metal pollutants from the matrix of an industrial wastewater.

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