Principal flow scheme - solution polymerisation

The principle emission of VOC is from the finishing stage, but diffuse (fugitive) emissions can occur from all stages of the process. If applicable, hydrogenation would occur in a separate stage between polymerisation and blending. 

Solution processes often comprise an anionically catalysed polymerisation process. The catalyst is highly sensitive to the presence of polar impurities in the feedstream, particularly water. Therefore, it is essential that the solvent and monomers are free of such catalyst poisoning species. Even less sensitive catalysts, such as the Ziegler-Natta types, require a purification step on the feedstock prior to the reaction stage. 

Purification is generally operated in a continuous mode. Recycled and make-up solvent are passed through a bed containing molecular sieves. Alternatively, packed alumina columns or distillation columns may be used. 

Monomers are generally purified continuously to remove chain terminators such as water, oxygen, stabilisers like p-tert butyl catechol and polar compounds. This is generally done using alumina beds, or by using distillation columns. 

The polymerisation reaction is carried out in a batch or in a continuous mode depending on the specific process (details in Section 8.2). The reactor is charged with solvent and catalyst. Depending on the targeted polymer, monomers are added simultaneously or sequentially. Where a random copolymer is required, a structure modifier, usually an ether, is added. These chemicals have the additional benefit of increasing the amount of 1.2 polymerisation of the butadiene, i.e. they increase the vinyl content. 

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Figure 8.1. Principal flow scheme - solution polymerisation...

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