Economic and environmental assessment of high-temperature water as a medium for terephthalic acid synthesis

Abstract

Large-scale chemical processes to produce terephthalic acid typically use acetic acid as the reaction medium. Recent research has demonstrated the technical feasibility of synthesizing terephthalic acid in high-temperature water (HTW), a medium widely perceived as environmentally benign. We have developed an economic and environmental assessment of an HTW-based terephthalic acid synthesis process to determine whether such a process is economically competitive with and, in fact, more environmentally benign than the current process. We simulated four variations of an HTW-based process and calculated the energy requirements and the capital investment for each of these variations. A US Department of Energy report contained the corresponding energy consumption data for an acetic-acid-based process. The capital investment and energy requirement for an acetic-acid-based process were $250 × 10⁶ and 19 MJ kg⁻¹ terephthalic acid, respectively. The capital cost for an HTW-based process operating at 300 °C and 150 bar was $280 × 10⁶; the energy intensity for this process was 17 MJ kg⁻¹ terephthalic acid. Given the approximately 20% uncertainty typically associated with capital investment estimates, the capital costs of these two processes are approximately equal. Moreover, adoption of HTW would likely reduce methyl bromide emissions from terephthalic acid synthesis plants. With a capital investment equivalent to the current process and reduced energy and pollutant intensities, HTW shows economic and environmental promise as a replacement for acetic acid in terephthalic acid synthesis.