Used 4,500 TPY Fumaric Acid Plant. In once-through-operation, refined molten maleic anhydride is dissolved in fresh process water to form 40% solution of maleic acid. The acid solution is then fed,simultaneously with catalyst and process air, to a reaction vessel which contains a preheated heel from the previous batch. The product fumaric acid solids are separated from the water solution in centrifuge. The plant contains facilities for bagging, drumming, car or truck loading of the solids product.