Improvements In Or Relating To Plastic Recycling

Abstract

A method to dissolve a polymer in a solvent in a process for the removal of additives in plastics, in which the polymer and solvent are combined in a reactor vessel having a stack of perforated discs which are oscillated. The linear motion of the stack speeds up dissolution time to minutes rather than hours and the required polymer to solvent ratio can be increased to 0.3 to 10% wt addition. The reactor vessel can be heated with pressure remaining at atmospheric. The method lends itself to commercial scale processing with reactor vessels of 1,000 litres and greater.

We claim: 
     
         1 . A method to dissolve at least one polymer in at least one solvent in a process for the removal of additives in plastics, comprising the steps:
 (a) introducing at least one polymer to at least one solvent in a reactor vessel to create a mixture;   (b) operating a mixing device within the reactor vessel for a first time duration;   characterised in that, the mixing device comprises: a plurality of discs aligned parallel to each other in a stacked arrangement; each disc extending over a majority of the cross-sectional area of the reactor vessel and including a plurality of perforations to allow the mixture to flow from a first end of the reactor vessel to a second end of the reactor vessel, through the discs; one or more supports to hold the discs in position; and the one or more supports connected to a linear motion generator so that the discs are moved to oscillate at a first frequency and first amplitude, the linear motion dissolving at least a portion of the polymer in the solvent in the first time duration.   
     
     
         2 . A method according to  claim 1  wherein the first time duration is less than an hour. 
     
     
         3 . A method according to  claim 2  wherein the first time duration is less than 30 minutes. 
     
     
         4 . A method according to  claim 3  wherein the first time duration is less than 15 minutes. 
     
     
         5 . A method according to  claim 1  wherein the at least one polymer is in the range of 0.1% to 30% wt addition to the at least one solvent. 
     
     
         6 . A method according to  claim 5  wherein the at least one polymer is in the range of 0.3% to 10% wt addition to the at least one solvent. 
     
     
         7 . A method according to  claim 1  wherein the reactor vessel has a volume of 1,000 litres or greater. 
     
     
         8 . A method according to  claim 1  wherein the first frequency is in the range 1 to 15 Hz. 
     
     
         9 . A method according to  claim 1  wherein the first amplitude is in the range 40 to 1000 mm. 
     
     
         10 . (canceled) 
     
     
         11 . (canceled) 
     
     
         12 . A method according to  claim 1  wherein the method includes heating the mixture to a first temperature, wherein the first temperature is between room temperature and the at least one solvent boiling point. 
     
     
         13 . (canceled) 
     
     
         14 . (canceled) 
     
     
         15 . A method according to  claim 12  wherein the first temperature is in the range of 80° C. to 120° . 
     
     
         16 . A method according to  claim 12  wherein the first temperature is above 120° C. 
     
     
         17 . A method according to  claim 1  wherein the at least one polymer is one or more polyolefins. 
     
     
         18 . A method according to  claim 17  wherein the at least one polymer is polyethylene (PE). 
     
     
         19 . A method according to  claim 17  wherein the at least one polymer is polypropylene (PP). 
     
     
         20 . A method according to  claim 19  wherein the at least one polymer is mixed PE/PP recyclate. 
     
     
         21 . A method according to  claim 1  wherein the method includes a first step in which a mixed plastic feedstock is mechanically separated to remove contaminants. 
     
     
         22 . A method according to  claim 1  wherein the at least one solvent is selected from a group comprising: butylal, xylene, toluene and ethyl benzene. 
     
     
         23 . A method according to  claim 1  wherein the plurality of discs are aligned parallel to each other in a vertical stack, with the mixture flowing vertically in the reactor vessel through the discs, and the discs are moved up and down at the first frequency and the first amplitude. 
     
     
         24 . A method according to  claims 1  wherein the plurality of discs are aligned parallel to each other in a horizontally stacked arrangement, with the mixture flowing along the reactor vessel through the discs, and the discs are moved back and forth at the first frequency and the first amplitude.