Recovery of styrene from waste polystyrene

• US 5,672,794 A
• Filed: 08/29/1996
• Issued: 09/30/1997
• Est. Priority Date: 10/21/1993
• Status: Expired due to Fees

• Current Assignee: BASF AG (BASF SE)
• Original Assignee: BASF AG (BASF SE)
• Inventors: Northemann, Andreas
• Primary Examiner(s): Caldarola, Glenn A.
• Assistant Examiner(s): Yildirim, Bekir L.
• Application Number:
  US08/697,718
• Time in Patent Office: 397 Days
• Field of Search: 585/241, 585/240, 585/832, 585/242
• US Class Current: 585/241
• CPC Class Codes: C07C 15/46 Styrene; Ring-alkylated styrenes
• CPC Class Codes: C07C 2521/12 Silica and alumina
• CPC Class Codes: C07C 2521/14 Silica and magnesia
• CPC Class Codes: C07C 4/22 by depolymerisation to the original monomer, e.g. dicyclopentadiene to cyclopentadiene

Abstract

Monomeric styrene is recovered from plastics waste containing styrene polymers by thermal depolymerization by a process in which the waste is transported in liquid or solid form into a fluidized bed of a solid heat transfer agent and is cracked or depolymerized in an average residence time of less than 60 seconds and styrene is obtained from the gaseous crack products. Preferably, magnesium aluminum silicate is used as a heat transfer agent and C₁ -C₆ -hydrocarbons formed as byproducts in the depolymerization are used as operating gas for maintaining the fluidized bed and are circulated.

Claims

1. A process for recovering monomeric styrene from plastics waste containing styrene polymers by thermal depolymerization, wherein the waste in liquid or solid form is transported into a fluidized bed of magnesium aluminum silicate heated to 400°

-700°

C. and is cracked or depolymerized in an average residence time of less than 60 seconds and styrene is recovered from the gaseous crack products.

2. A process as claimed in claim 1, wherein C₁ -C₆ -hydrocarbons formed as byproducts in the depolymerization are circulated as operating gas for maintaining the fluidized bed.

3. A process as claimed in claim 1, wherein the condensation of the crack products is carried out in two or more stages, a first condensation stage at from 160°

-200°

C. and a second stage at up to 40°

C. being provided and styrene being obtained from the second condensation stage.

4. A process as claimed in claim 1, comprising a fluidization point of 0.02-0.07 m/s or a particle size of 300-500 μ

m.