Spray Reactor for Terephthalic Acid Production (Case Study)

Spray reactor, a type of jet loop reactor, has been employed industrially for the alkoxylation of aliphatic alcohols. In laboratory-scale studies, this reactor has been shown to perform well for the liquid-phase oxidation of p -xylene ( p X). In the spray reactor process, the reaction mixture containing p -xylene and the dissolved catalyst are dispersed as fine droplets by a nozzle into a continuous vapor phase containing the oxidant (O 2 ) to produce high-purity terephthalic acid (TPA) with less than 25 ppm 4-carboxybenzaldehyde (4-CBA) in the solid TPA product. The dramatic improvement in TPA product quality during spray reactor operation is attributed to the alleviation of interphase gas–liquid mass transfer limitations and reduced back-mixing, both of which enhance the oxidation rates. Cooling provided by partial evaporation of the acetic acid solvent maintains stable reaction in the droplet microreactors, preventing thermal runaway. Economic analyses and life-cycle assessments of a simulated 0.5 million MT/annum plant show that the spray process reduces capital and operating costs by approximately 50% and 15%, respectively, and also lowers adverse environmental impacts (such as global warming, acidification, and VOC emissions), compared with the MC process. These benefits of the spray process stem from the avoidance of the hydrogenation step required in the conventional process for purifying the crude TPA. The spray process is also demonstrated for making 2,5-furandicarboxylic acid (FDCA) in high yields from 5-hydroxymethylfurfural (HMF).