Tributyl Citrate: Citric Acid and Butanol Esterified in a Hot Pressure Coil at 175 °C (Bruins, Pfizer, US 2,766,273)

Boiled for hours with butanol and acid, citric acid darkens and turns partly to aconitic acid. Bruins pumped the mixture under pressure through a thin hot coil for under a minute, then flashed the water off, three times over. Result: tributyl citrate of high quality, very light in colour, with no measurable aconitic acid. Source: Bruins and Canapary, US 2,766,273 (Chas. Pfizer, 1956), Example I. Picture drawn by Youblob.