Kinetics of salt formation using terephthalic acid and n-methyl-2-pyrrolidinone

Abstract

Terephthalic acid (TA) is used as a raw material for producing polyesters. As the global demand for polyesters increases at a rate of 7% per year on average for the last few years and next 10-year forecast, the demand of TA also increases. The global production exceeded 27 million tons for the year 2003, and will be in excess of 30 million tons for the year 2004. Therefore improving the production or purification process for terephthalic acid becomes more and more important. A new purification method using N-methyl-2-pyrrolidinone (NMP) as solvent was recently developed. In this process, the salt complex consisting of TA and NMP was formed to exclude the impurities. The research topic of this thesis was to characterize the salt formation rate and develop possible explanations for salt formation kinetics. Gas Chromatography was used to determine the percentage of salt in the salt formation samples as prepared by varying mixing times, temperatures and loadings. The TA-salt transition (salt formation) was found to behave as first-order solid-solid phase transition with a temperature range where both phases coexist. The salt formation rate was explained using the combination of reaction rate and salt formation possibility.