Abstract
Low solubility of terephthalic acid in common solvents makes its industrial production very difficult and not environmentally benign. Ionic liquids are known for their extraordinary solvent properties, with capability to dissolve a wide variety of materials, from common solvents to cellulose, opening new possibilities to find more suitable solvents for terephthalic acid. This work presents studies on the solubility of terephthalic acid in ionic liquids, and demonstrates that terephthalic acid is soluble in ionic liquids, such as 1-ethyl-3-methylimidazolium diethylphosphate, 1-butyl-3-methylimidazolium acetate, and dialkylimidazolium chlorides up to four times higher than in DMSO. Additionally, the temperature effect and correlation of ionic liquid structure with solubility efficiency are discussed.
Highlights
Purified terephthalic acid (PTA) is a white, crystalline solid with negligible vapor pressure under standard conditions [1]
Solubility studies were conducted at temperatures between 25 and 100 ◦ C and the obtained results are summarized in Table 2 in order of decreasing solubility
Solubility measurements: A total of 1 g of ionic liquid was placed in the round bottom flask and PTA was added in small portions (0.01 g)
Summary
Purified terephthalic acid (PTA) is a white, crystalline solid with negligible vapor pressure under standard conditions [1]. Most PTA is consumed in polyester production, including polyester fiber and film, and polyethylene terephthalate (PET) resin. PTA is produced by the catalytic liquid-phase oxidation of p-xylene in acetic acid, in the presence of air, using a manganese or cobalt acetate catalyst. In 2011, global PTA capacity reached 28.8 million tons, with China being the main world producer [2]. Terephthalic acid is poorly soluble in organic solvents (Table 1) [1,3]. Among all tested solvents the best solubility of PTA was observed in DMSO (20 g of PTA per 100 g DMSO at 25 ◦ C). The solubility of PTA in organic solvents is low and slowly increases with increasing temperature
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