Process for depolymerizing polyalkylene terephthalates in mixtures with lower-melting polyolefins

A process for depolymerizing at least one polymer P1, wherein the at least one polymer P1 comprises n1 interlinked repeating units of the following structural formula (I):

• wherein a is an integer for which 2≤a≤6,
• wherein b is an integer for which 2≤b≤6,
• wherein c is an integer for which 0≤c≤10,
• wherein n1 is an integer ≥50,
• wherein the n1 interlinked repeating units of structural formula (I) encompassed by the polymer P1 are the same or different,
• and wherein the n1 interlinked repeating units of structural formula (I) are interlinked within the polymer P1 in such a way that the bond of the one repeating unit of structural formula (I) labelled “(i)” is linked to the bond of the adjacent repeating unit of the structural formula (I) labelled “(ii)”,
• comprising the following steps:
• (a) adding a first portion PG1 of at least one glycol compound G having structural formula (V):
• HO—(CH2)d—[O—(CH2)e]f—OH,
• wherein d is an integer for which 2≤d≤6,
• wherein e is an integer for which 2≤e≤6,
• wherein f is an integer for which 0≤f≤10,
• to give a mixture M1 comprising
• the at least one polymer P1,
• a melt of at least one polyolefin PO having a lower melting temperature TPO than the melting temperature TP1 of the at least one polymer P1,
• and at least partly reacting the glycol compound G with at least a portion of the polymers P1 in the mixture M1 to give at least one cleavage product P2,
• wherein the cleavage product P2 has the structural formula (II):
• wherein aII is an integer for which 2≤aII≤6,
• wherein bII is an integer for which 2≤bII≤6,
• wherein cII is an integer for which 0≤cII≤10,
• wherein n2 is an integer for which 2≤n2≤48,
• wherein units W2 are interlinked within the cleavage product P2, and each unit W2 conforms to the structure in the parentheses indexed with “n2” in structural formula (II), and the units W2 are identical or different within the cleavage product P2,
• where RII1 is selected from the group consisting of —H, and —(CH2)a♥—[O—(CH2)b♥]c♥—OH, and
• wherein a♥ is an integer for which 2≤a♥≤6,
• wherein b♥ is an integer for which 2≤b♥≤6,
• wherein c♥ is an integer for which 0≤c♥≤10,
• where RII2 is selected from the group consisting of —H, —OH, a radical of the structural formula (IV):
• and wherein step (a) is conducted at a temperature Ta above the melting temperature TPO of the at least one polyolefin PO,
• so as to obtain a mixture M2 comprising:
• at least one cleavage product P2,
• a melt of the at least one polyolefin PO,
• and wherein the molar amount of all cleavage products P2 in the mixture M2 is greater than the molar amount of all cleavage products P2 in the mixture M1 used in step (a);
• (b) cooling the mixture M2 to a temperature Tb below the melting temperature TPO of the at least one polyolefin PO,
• wherein, during and/or after the cooling of the mixture M2 to the temperature Tb, a second portion PG2 of at least one glycol compound G of the structural formula (V) is added to the mixture M2, so as to obtain a mixture M3 comprising:
• at least one cleavage product P2,
• the at least one polyolefin PO in the solid state,
• at least one glycol compound G,
• (c) at least partly reacting the glycol compound G with at least a portion of the cleavage products P2 in the mixture M3 to give at least one compound of structural formula (III):
• wherein R1 and R2 are independently selected from the group consisting of —H, and —(CH2)p—[O—(CH2)q]r—OH,
• wherein p is an integer for which 2≤p≤6,
• wherein q is an integer for which 2≤q≤6,
• wherein is an integer for which 0≤r≤10,
• wherein the reaction in step (c) is conducted at a temperature Tc below the melting temperature TPO of the at least one polyolefin PO, which affords a mixture M4 comprising
• the at least one polyolefin PO in the solid state,
• at least one compound of structural formula (III),
• wherein the molar amount of all compounds of structural formula (III) in M4 is greater than the molar amount of all compounds of structural formula (III) in the mixture M1 used in step (a),
• (d) at least partly separating the solid polyolefin PO from the mixture M4.