Flow diagram of the Spheripol polypropylene process

Mitsui developed an analogue suspension process using their own catalyst system. The process differs from the Spheripol process in a way that a pre-polymerisation takes place in a CSTR in connection with a washing step. Two autoclave reactors are used in series the heat is dissipated to the reactors by evaporating liquid propylene. The suspension is then forwarded to a heated and agitated evaporation reactor in which polypropylene is removed from the polymer and returned to the production process, similar to the Spheripol process. The two processes thus only differ with respect to the reactors and catalysts used, allowing a common consideration of the data for emission and consumption values. 

The Borstar PP process is based on the Borstar PE process described in Section 3.2.3.3. When homopol5miers and random copol5miers are produced, the reactor configuration consists of a propylene bulk loop reactor and a fluidised bed gas phase reactor operated in series. During heterophasic copolymer production, the polymer from the first gas phase reactor is transferred into a second smaller gas phase reactor where the mbbery copolymer is made. 

The catalyst is continuously pre-pol5mierised before entering the main loop reactor, which is designed for supercritical conditions and typically operated in the temperature range of 80 to 100 °C and 5 to 6 MPa pressure with propylene as the diluent (bulk pol5mierisation). The slurry from the loop reactor is fed directly into the gas phase reactor without any flash separation step. The gas phase reactor is t5q)ically operated at 80 to 100 °C and 2.2 to 3 MPa. 

The powder withdrawn fi om the gas phase reactor is separated from the associated gas and purged with nitrogen to remove residual hydrocarbon before it is transferred to extrusion. The recovered gas is compressed and returned to the gas phase reactor. Because most of the propylene from the loop reactor is consumed in the gas phase reactor, the recycle stream to the loop reactor is very small. 

A second gas phase reactor is used to produce the rubber phase of a heterophasic copolymer. The powder is withdrawn, purged with nitrogen and sent to extrusion like in the homopolymer case. The gas associated with the powder is recovered and recycled back to the gas phase reactor. 

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Figure 3.14 Flow diagram of the Spheripol polypropylene process [15, IJIImann, 2001]...

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