Optimal design and control of Eastman organic wastewater treatment process

The Eastman process discharges a wastewater stream with high organic contents. Its chemical oxygen demand (COD) and flowrate are up to 60,000 mg/L and 1011 kg/h, respectively. The ecological environment will be polluted severely in case of an inappropriate disposal of this wastewater. This paper proposes a novel “waste control by waste” strategy to dispose of such a wastewater with a combination of modeling and experiment methods. First, several possible schemes are simulated and evaluated with Aspen Plus software. One scheme that employs internally synthesized 2,2,4-trimethyl-1,3-pentanediol di-isobutyrate (TXIB) to extract organics is chosen because it can alleviate the recovery problems of solvent. The simulation of this scheme shows a mass fraction increase of water in disposed wastewater from 96.941% to 98.572%. Second, experiments concerning extraction and reaction are performed to obtain the requisite parameters for simulation. The optimum operating conditions for extraction column are obtained: room temperature and pressure, the number of trays is 8, the flowrate of extractant is 350 kg/h. The optimum operating conditions for esterification reaction are obtained: reaction time is 3.5 h, catalyst concentration is 8% and reaction temperature is 130 °C. Finally, the importance of each variable in the wastewater treatment process is evaluated based on complex network theory, and two variables comprised of recycle extractant flow and reactor temperature are selected accordingly. One control scheme is proposed based on selected key variables after its anti-disturbance ability is verified with Aspen Dynamics software.