Process and apparatus for direct crystallization of polycondesates

A process for continuous production of partly crystalline polyethylene terephthalate homopolymer or copolymer pellet material, comprising the steps of:

• a) forming a melt of a polyethylene terephthalate homopolymer or copolymer into pellets by adding a liquid cooling medium, and cooling to an average pellet temperature within the range of temperature of crystallization of the polyethylene terephthalate homopolymer or copolymer, wherein cooling takes place before or during or after forming to pellets;
• b) separating the liquid cooling medium from the pellets in a first treatment space, wherein the pellets after exit from the first treatment space exhibit a pellet temperature (TGR) and a crystallinity of less than 10%;
• and
• c) crystallizing the pellets in a second treatment space, wherein in the second treatment space fixed bed conditions exist and the pellets are heated in the second treatment space by supply of energy from the exterior by a process gas, wherein the process gas has a gas temperature (TGas), which is higher than a sum of a pellet temperature (TGR) and a temperature increase (TKR) which occurs due to heat of crystallization released in the second treatment space, (i.e., TGas>(TGR+TKR)), and wherein the pellets at the exit from the second treatment space have an average temperature (TPH), which is 10 to 90° C. higher than the sum of the temperature of the pellets (TGR) and the temperature increase (TKR) which occurs due to heat of crystallization released in the second treatment space (i.e., (TGR+TKR+90° C.)≥TPH≥(TGR+TKR+10° C.)), and wherein a ratio X of a mass flows of gas (mG) and pellets (mP) (X=mG/mP) in the second treatment space is set such that 4° C.≤(TGas−TKR−TGR)*X≤400° C., wherein crystallizing the pellets in the second treatment space takes place in two or more stages, each stage of the two or more stages comprising feed devices and discharge devices, and wherein each stage is carried out with a ratio X of mass flows of gas (mG) and pellets (mP)(X=mG/mP) of less than 1.