Design and control of an improved acrylic acid process

The acrylic acid (AA) process involves the partial oxidation of a flammable and explosive gas medium (propylene), so considerable attention is paid to the concentration of the reactants. Water and air is added to dilute the reactant and enhance the thermal stability of the reaction. Different compositions of water and air can lead to different methods to separate AA product. A modified AA process is developed based on the AA process proposed by Turton, and consists of a tubular reactor, an absorber and only two distillation columns, one of which is an azeotropic distillation column. This process is characterized by shortening and simplifying AA refining process so that equipment investment cost can be reduced. A plantwide control structure featured with cascade control provides effective control for the multiunit process and insures safe operation of the two distillation columns. Dynamic results also reveal that it is useful to apply temperature/temperature cascade control and composition/temperature cascade control to the distillation columns with maximum temperature limitations.