Chemical processes for the production of polypropylene

For the purposes of this work, the mass process called Spheripol will be explained:

• The Spheripol process is continuous and is based on a superactive catalyst (Ti/MgCl2), an alkylaluminum, an electron donor).
• There are two reactors in series:

The first one to work in mass and the second one in gas phase.
The first reactor is of the loop type, in which catalyst and monomer are circulated at high speed so that they remain suspended in the diluent.
The diluent is actually the liquid propylene itself, which, given the operating conditions, facilitates the evacuation of the heat generated by the reaction and at the same time increases the performance of the catalytic system. In this loop reactor, the reaction mixture flows driven by an axial pump (no external agitation is required); it reaches high velocity which prevents polymer deposition on the reactor walls; the heat transfer area per unit volume is higher than in a stirred reactor, which allows better temperature control and higher productivity. The residence time in the reactor can be altered by varying the recirculation rate.

Propylene, which can be diluted with propane (up to 40%), is fed to the reactor in the presence of catalyst and hydrogen. The reaction temperature is between 65 and 80 Cº, and the pressure is 33 atm. The reaction mixture circulates rapidly and contains up to 50% solids.

• Polymer and unreacted monomer are separated in a flash tank at 16 atm. The monomer is recirculated to the reactor, and excess propane is removed.
• In the second reactor, the gas phase, the polymer produced in the loop reactor is incorporated. In this phase, copolymers with special characteristics are prepared by adding a co-monomer (e.g. ethylene) in addition to the monomer.
• Polymer particles and water vapor enter the fluidized bed reactor to deactivate the catalyst. Drying is carried out with nitrogen. The polymer is obtained in the form of spherical particles with a diameter between 1.5 and 2 mm and a narrow size distribution. Productivity is of the order of 20 kg / g supported catalyst (1000 kg / g Ti). The isotacticity index is 97%.
• The molecular weight is controlled by addition of hydrogen during the reaction, and also by using organometallic compounds derived from zinc or cadmium.