Abstract
Trialkyl-2,3-dihydroxypropylammonium chloride salts have been investigated as liquid eutectic-forming salts for the extraction of phenol from aromatic-rich model oil (toluene), demonstrating how the increased partitioning of phenol from oil-phases can be combined with reduced co-miscibility of the salt with aromatic hydrocarbons through the introduction of the dihydroxypropyl-function.
Highlights
Phenols are used on a megatonne scale worldwide as major chemical feedstocks for the production of phenolic and synthetic resins, caprolactam and bisphenol A, alkylphenols, and adipic acid [1,2]
They showed that the addition of organic tetraalkylammonium salts to phenol-containing hexane and toluene model oil feeds generated eutectic liquids that contained around 1:1–1:2 salt:phenol molar ratios that separate from the non-polar carrier hydrocarbon
It is necessary to promote phenol–salt association, while, at the same time, restricting co-miscibility of the resultant DES with aromatic-rich feeds in order to obtain good selective phenol extraction. We speculated whether these two competing challenges could be reconciled by introducing both lipophilic (N-alkyl) and lipophobic groups into the organic salt eutectic former, and here we report on the successful demonstration of the validity of this design strategy using trialkyl-2,3-dihydroxypropylammonium chloride salts (Figure 1) in order to extract phenol from hexane and toluene as models for aliphatic and aromatic oils
Summary
Phenols are used on a megatonne scale worldwide as major chemical feedstocks for the production of phenolic and synthetic resins, caprolactam and bisphenol A, alkylphenols, and adipic acid [1,2]. The concept that the formation of a polar eutectic liquid between phenol and an organic salt could be used to drive the non-aqueous extraction of phenol from oil was first described by Wu, Marsh, and co-workers [7,8]. They showed that the addition of organic tetraalkylammonium salts to phenol-containing hexane and toluene model oil feeds generated eutectic liquids that contained around 1:1–1:2 salt:phenol molar ratios that separate from the non-polar carrier hydrocarbon. And key to this approach, is the ability to use an organic ether as an antisolvent to precipitate the organic salt component of the formed eutectic liquid, facilitating the separation and recovery of the phenols without generating the contaminated aqueous waste streams that are associated with conventional alkali/acid extraction/neutralisation pathways
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