Polymerisation unit and polymerisation process

Polymerisation unit for ionic polymerisation of a liquid monomer(s) containing reaction mixture, for example of isobutylene, comprising a polymerisation loop and a coolant loop and a heat exchanger reactor system (“HERS”) which is shared amongst the polymerisation loop and the coolant loop, wherein

• the polymerisation loop comprises a reaction mixture piping system connected to an inlet and an outlet of said HERS,
• the coolant loop comprises a coolant piping system connected to an inlet and an outlet of said HERS,
• the reaction mixture piping system comprises a circulating pump and the polymerisation loop comprises a polymer withdrawal system, characterised in that
• 1. the HERS comprises at least one section,
• 2. the said HERS' section(s) comprises “n” (n being an integer superior or equal to 1) parallelepipedic channel(s) for the reaction mixture and “n+1” passages for the coolant,
• 3. the flow paths of the reaction mixture in the “n” channel(s) of a section are unidirectionally parallel,
• 4. the flow paths of the coolant in the “n+1” passages of a section are unidirectionally parallel to the reaction mixture flow paths, and
• 5. the coolant is not in direct contact with the reaction mixture and wherein the coolant is an evaporative coolant and the coolant piping system comprises a coolant liquefaction system.