Optimization Of The Hexafluoropropylene Rectification Process

Preparation, development and application of hexafluoropropylene(HFP) were discussed in the thesis. The importance of product quality was emphasized. High purity HFP was required in the processes of production of fluorine polymer, fluororubber, fluorinated fine chemicals, etc. Therefore, optimization of rectification technology of HFP was proposed, through analyses of various purification technology in the literature.The optimization was done over five tower rectification process for HFP production according to physical and chemical properties of components which were generated through reaction. The main process was as follows: the unreacted TFE was recovered from the top of T-1 tower and was recycled to the pyrolytizer; left TFE was recovered from T-2 tower again; 99.99% high purity HFP was collected from the top of T-3 tower; left HFP was recovered from T-4 tower once more; the collected C-C₄F₈ from the top of T-5 tower could either be used as a product or recycled into the pyrolytizer as a diluent. Bottoms could either be sent directly or put into the cylinder for residual treatment.The optimization of operation conditions for HFP production was done based on above process. According to the feed rates of every tower and boiling points of components in different pressure, pressurized rectification was confirmed through study on separation difficulty of components and operation stability at different tower pressure. At the same tower pressure, operation temperature of every tower was confirmed through study on its various components at tower tops at different temperature. Optimum reflux ratio of every tower was confirmed through study on the relationship between recover capacity and quantity of reflux at the same tower pressure and temperature. The conditions were optimized and validated by practical operation of the production plant.The specifications of the fractionating towers were as follows:T-1 tower: Pressure: ～ 1. 3 MPa, temperature at top of the tower: -10±1℃; suitable raflux ratio: fifteen;T-2 tower: Pressure: ～ 1. 0 MPa, temperature at top of the tower: 5±1℃; suitable raflux ratio: eighty;T-3 tower: Pressure: ～0.75 MPa, temperature at top of the tower: 27±1℃; suitable raflux ratio: thirteen;T-4 tower: Pressure: ～0.55 MPa, temperature at top of the tower: 20±1℃; suitable raflux ratio: eighty;T-5 tower: Pressure: ～0.35 MPa, temperature at top of the tower: 17±1℃; suitable raflux ratio:six;Meanwhile, the number of theoretical plates, and reflux ratio of rectification tower was confirmed. The tower diameter, tower height and location of feed plate of rectification tower were calculated.The product purity was raised to 99.99% from 99.90% through optimization of operation conditions and theoretical research.