TY - JOUR
T1 - Effect of pH on dicarboxylic acids extraction by amine-based extractants
AU - Canari, Riki
AU - Eyal, Aharon M.
PY - 2003/4/2
Y1 - 2003/4/2
N2 - The work presented here studies the effect of pH on the extraction of malic, maleic, and glutaric acids by Primene JMT, tris(2-ethylhexyl)amine, and tri-n-octylamine and the IR and NMR spectra of the formed organic phases. Three categories were found: (1) In the first case, the extractant is a weaker base than both anions of the acid, i.e., pHhn < pka1 < pKa2. The undissociated acid is the dominant species in the organic phase. Extraction is mainly due to H-bonding or solvation interactions and shows a drop-off at pH≈pKa1. (2) For systems in which pKa1 < pHhn < pKa2, at acid-to-amine molar ratios greater than 1, undissociated acid is above-stoichiometrically extracted, R3NH+⋯AH-⋯HAH in addition to ion-paired acid. As the pH is increased, the undissociated acid is neutralized first. Thus, the extraction curve shows a drop-off at pH ν pKa1. At stoichiometric loading, the monovalent ion pair, R3NH+⋯AH-, becomes the dominant species. Upon further pH elevation, the protonated amine R3NH+ is the neutralized acid. (3) In systems where pKa1 < pKa2 < pHhn, the divalent ion pair R3NH+⋯A2-⋯+ HNR3 is formed. Thus, the extraction curve shows an additional drop-off at pH ≈ pKa2.
AB - The work presented here studies the effect of pH on the extraction of malic, maleic, and glutaric acids by Primene JMT, tris(2-ethylhexyl)amine, and tri-n-octylamine and the IR and NMR spectra of the formed organic phases. Three categories were found: (1) In the first case, the extractant is a weaker base than both anions of the acid, i.e., pHhn < pka1 < pKa2. The undissociated acid is the dominant species in the organic phase. Extraction is mainly due to H-bonding or solvation interactions and shows a drop-off at pH≈pKa1. (2) For systems in which pKa1 < pHhn < pKa2, at acid-to-amine molar ratios greater than 1, undissociated acid is above-stoichiometrically extracted, R3NH+⋯AH-⋯HAH in addition to ion-paired acid. As the pH is increased, the undissociated acid is neutralized first. Thus, the extraction curve shows a drop-off at pH ν pKa1. At stoichiometric loading, the monovalent ion pair, R3NH+⋯AH-, becomes the dominant species. Upon further pH elevation, the protonated amine R3NH+ is the neutralized acid. (3) In systems where pKa1 < pKa2 < pHhn, the divalent ion pair R3NH+⋯A2-⋯+ HNR3 is formed. Thus, the extraction curve shows an additional drop-off at pH ≈ pKa2.
UR - http://www.scopus.com/inward/record.url?scp=0037414158&partnerID=8YFLogxK
U2 - 10.1021/ie010579p
DO - 10.1021/ie010579p
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AN - SCOPUS:0037414158
SN - 0888-5885
VL - 42
SP - 1293
EP - 1300
JO - Industrial and Engineering Chemistry Research
JF - Industrial and Engineering Chemistry Research
IS - 7
ER -