Cleaner production of purified terephthalic and isophthalic acids through exergy analysis

The purified terephthalic and isophthalic acids production process was improved through the exergy analysis approach demonstrated in this work. The overall exergy losses and low-exergy-efficient units were first identified and presented using visualised exergetic flowsheets. Recommendations were then proposed to reduce losses based on the main cause(s) of irreversibility. Three out of the five constituent blocks contained the highest exergy losses. The oxidation block was the main player where it was suggested that using several reactors in series with gradually decreasing temperatures could lower losses. The product refining block had the second-largest irreversibilities, where improving coolers' performances were recommended. The crude terephthalic acid crystallisation block was the third-largest loss producer, where isothermal and isobaric mixing in the solvent dehydrator was suggested to reduce losses. The approach used in this work can be adapted to improve the energy footprint of other chemical processes.