Abstract: The present invention is a method to start-up a process to make expandable vinyl aromatic polymer pellets comprising, a) providing a pelletizer (S) containing means to introduce the molten vinyl aromatic polymer comprising the expandable agent and optionally additives, a die plate having a plurality of holes of small diameter, typically in the range 0.8 to 1.

Abstract: A method for producing non-expandable pellets can include introducing a vinyl aromatic polymer to a pelletizer (L). The pelletizer (L) can have a die plate having a holes of large diameter. During the start-up of the production of the non-expandable pellets, pellets can be produced in the pelletizer (L). When the polymer flow rate is in the operating range of the pelletizer (S), the introduction of the vinyl aromatic polymer can be switched from the pelletizer (L) to the pelletizer (S). The pelletizer (S) can be operated at conditions effective to produce the non-expandable pellets. The pelletizer (S) can have a die plate having holes of small diameter. The non-expandable pellets can be recovered from the pelletizer (S), and the pellets can be recovered from the pelletizer (L).

Abstract: A method for producing expandable pellets can include introducing a vinyl aromatic polymer and an expandable agent to a pelletizer (L). The pelletizer (L) can have a die plate having a holes of large diameter. During the start-up of the production of the expandable pellets, pellets can be produced in the pelletizer (L). When the polymer flow rate is in the operating range of the pelletizer (S), the introduction of the vinyl aromatic polymer and the expandable agent can be switched from the pelletizer (L) to the pelletizer (S). The pelletizer (S) can be operated at conditions effective to produce the expandable pellets. The pelletizer (S) can have a die plate having holes of small diameter. The expandable pellets can be recovered from the pelletizer (S), and the pellets can be recovered from the pelletizer (L).

Abstract: The present invention is a method to start-up a process to make expandable vinyl aromatic polymer pellets comprising, a) providing a pelletizer (S) containing means to introduce the molten vinyl aromatic polymer comprising the expandable agent and optionally additives, a die plate having a plurality of holes of small diameter, typically in the range 0.8 to 1.

Abstract: This process is intended to remove at least a part of the heat produced in at least one reaction and/or purification operation involving anhydrous HF, the cooling being performed by heat exchange with a cooling fluid circulating in a circuit which comprises at least one exchange zone (9; 10; 11) presenting a risk of leakage of HF into the cooling fluid. The fluid of this kind which is employed is an aqueous solution of at least one compound chosen from (a) strong bases, (b) the salts resulting from the combination of a strong base and of an organic or inorganic acid whose pKa is >3.5, (c) the salts of amphoteric oxides with bases, (d) compounds which, in contact with water, are converted into one of the abovementioned compounds; the said cooling fluid is circulated in a closed circuit, and the operation is carried out with a cooling fluid pressure which is lower than the pressure at which the reaction and/or the purification operation is conducted.