Abstract:
A method for the separation of a mixture of polyvinyl chloride particles and polyethylene terephtalate particles comprising the steps of applying a solution composed of a low density solvent of polyvinyl chloride, water and sodium hydroxide to flakes of polyvinyl chloride and polyethylene terephtalate whereby the polyvinyl chloride absorbs the solvent contained in the solution, which changes the density of the polyvinyl chloride so that it is less than the density of the polyethylene terephtalate. The plastics may then be differential density separated by flotation or centrifugation and recovered.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a method for the separation of a mixture of plastics. More particularly, it is directed to a method for separating flakes of polyvinyl chloride (PVC) from flakes of polyethylene terephthalate (PET) by the application to the flakes of a solution composed of a low density solvent of PVC, water (H 2  O) and sodium hydroxide (NaOH). 
     For many years there has been the problem of separating different kinds of plastics which have been mixed together in a recycling situation. Usually, plastic bottles made of various types of plastics are brought to recycling stations where they are ground into flakes. Quite often, the bottles are not separated according to the plastic of which they are composed before they are ground into flakes. As a result of this practice, flakes of different plastics are randomly mixed together. The separation of these flakes becomes difficult when the physical properties of the plastics make separation by standard flotation and melting techniques impossible. Two such plastics with almost identical physical properties are PVC and PET. PVC and PET are the primary types of plastics used in the production of plastic bottles and other containers. It is important to recover these plastics by recycling in order to preserve the environment, conserve energy and reduce cost. 
     Previous prior art methods of separating a mixture of plastics can be found, for example, in U.S. Pat. Nos. 3,925,200; 3,926,790; 3,926,791; and 4,132,633. These prior art references disclose the general concept of separating a mixture of plastics by flotation after a conditioning agent has been added to the mixture. 
     The present invention provides for an improved method of separating particles or flakes of PVC from particles or flakes of PET. 
     SUMMARY OF THE INVENTION 
     The present invention relates to a method for the separation of a mixture of PVC and PET comprising the steps of applying a solution composed of a low density solvent of PVC, H 2  O and NaOH to flakes of PVC and PET whereby the PVC absorbs the low density solvent which changes the density of the PVC so that it is less than the density of the PET. The modified materials having different densities may then be separated by flotation or by centrifugation and the individual plastics recovered. 
     It is the primary object of the present invention to provide a method for the separation of a mixture of PVC and PET. 
     A further object of the present invention is to provide a method for the separation of a mixture of PVC and PET which can be accomplished easily and effectively. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention relates to a method for the separation of a mixture of plastics composed of particles or flakes of PVC and PET. 
     PVC and PET are difficult to separate because their physical properties are very similar. Their densities, 1.34 grams/cc for PET and 1.32 grams/cc for PVC, cause standard differential density separation to be impracticable. 
     According to the invention, a solution composed of a low density solvent of PVC which has a density of less than 0.95 grams/cc, H 2  O and NaOH is applied to the mixed particles or flakes of PVC and PET. Examples of low density solvents of PVC which have densities of less than 0.95 grams/cc are alcohols, ketones, esters and ethers. For the purpose of explanation, methyethyl ketone (MEK) will be used as the low density solvent. MEK has a density of 0.80 grams/cc. 
     the mixture of flakes of PVC and PET is present in a proportion of from about 1 to 3 parts by weight per 100 parts of the solution of MEK, H 2  O and NaOH. H 2  O is added to the MEK to suppress the tendency of PVC to dissolve, become tacky or to plate onto the PET in the presence of MEK. A small amount of NaOH can be added to the MEK and H 2  O in order to accelerate the separation process. 
     The PVC absorbs the MEK contained in the MEK, H 2  O and NaOH solution. As a result of the MEK absorption, the density of the PVC changes from its original density of 1.32 grams/cc to a significantly lower density. The PET retains its original density of 1.34 grams/cc during the process because it is insoluable in MEK. The newly lowered density of the PVC allows it to be differential density separated from the PET ether by flotation in a flotation cell or centrifugation. The plastics may then be recovered individually. 
     EXPERIMENTAL DATA 
     Test formulas, physical properties and comparative experimental data are set out below. 
     
         __________________________________________________________________________Trial  I    II  III IV  V   VI  VII  VIII                                    IX  X   XI   XII XIII__________________________________________________________________________MEK/   90** 90  90  85  80  70  25   90  90  95  90   90  90Water/ 10   10  10  15  20  30  75   9.6 9.6 4.8 9.6  9.6 9.6NaOH   0    0   0   0   0   0   0    .4  .4  .2  .4   .4  .4Temp °C.  23   32  42  23  23  23  26   41  63  61  62   62  50Mass   xx   xx  xx  .14 .14 .41 .43  .13 .09 .12 .13  .16 .10Color  white       white           white               white                   white                       white                           white                                white                                    white                                        white                                            clear                                                 white                                                     whiteThicknessTime (min)  1.34 Density Range (PVC) gr/cc                           Density Range1:00   &gt;1.05       &gt;1.16           &gt;1.16               &gt;1.16                   &gt;1.16                       &gt;1.16                           &gt;1.27                                &gt;1.16                                    &gt;1.05                                        &gt;1.05                                            &gt;1.05                                                 &gt;1.05                                                     &gt;1.052:00   &gt;1.05       &gt;1.05           &gt;1.05               &gt;1.16                   &gt;1.16                       &gt;1.16                           &gt;1.27                                &gt;1.05                                    &gt;1.05                                        &gt;1.05                                            &gt;1.05                                                 &gt;1.05                                                     s&gt;1.054:00   s&gt;1.05       &gt;1.05           &gt;1.05               &gt;1.05                   &gt;1.16                       &gt;1.16                           &gt;1.16                                &gt;1.05                                    &gt;1.05                                        &gt;1.01                                            &gt;1.05                                                 &gt;1.05                                                     &gt;1.016:00   s&gt;1.05       &gt;1.05           &gt;1.05           &gt;1.16                                &gt;1.05                                    &gt;1.01                                        &gt;.97                                            &gt;1.01                                                 &gt;1.01                                                     &gt;.978:00   &gt;1.01       &gt;1.05           &gt;1.05           &gt;1.16                                &gt;1.05                                    &gt;.97                                        &gt;.97                                            &gt;.97 &gt;.97                                                     &lt;.9710:00  &gt;1.01       &gt;1.05           &gt;1.05           &gt;1.16                                &gt;1.05                                    &gt;.97                                        &lt;.97                                            &lt;.97 &lt;.97                                                     &lt;.9712:00                                            .9714:0016:0018:00Mass   xx   xx  xx  .18 .13 .45 .52  .17 .12     .28  .36 .20% Gain xx   xx  xx  29  8   10  21   31  25      115  125 100Color  white       white           white               white                   white                       white                           white                                white                                    white                                        white                                            cldy. wht                                                 white                                                     whiteComments  not  not not not not not thick        broke    many                                                     not  sticky       sticky           sticky               sticky                   sticky                       sticky                           material     into     small                                                     tacky                                        pieces   pieces__________________________________________________________________________Trial  XIV XV   XVI  XVII XVIII                          XIX  XX   XXI  XXII XXIII                                                  XXIV                                                      XXV__________________________________________________________________________MEK/  90   90   90   30   30   30   30   30   30   30  30  30Water/ 9.6  9.6  9.6  67.2 67.2 67.2 67.2 67.2 67.2 67.2                                                  67.2                                                      67.2NaOH  .4   .4   .4   2.8  2.8  2.8  2.8  2.8  2.8  2.8 2.8 2.8Temp °C. 55   55   55   50   48   65   62   62   64   65  64  65Mass  .12  .59  .16  .16  .15  .17  1.00 .19  .54  .65 .15 .09Color white      white           white                clear                     clear                          clear                               clear                                    clear                                         white                                              white                                                  white                                                      whiteThickness                                     .019-.021                                              .027                                                  .027-                                                      .021                                                  .031Time (min) Density Range1:00  &gt;1.05      &gt;1.16           &gt;1.16                s&gt;1.16                     &gt;1.16                          s&gt;1.16                               &gt;1.16                                    &gt;1.16                                         &gt;1.16                                              &gt;1.16                                                  &gt;1.16                                                      &gt;1.052:00  &gt;1.05      &gt;1.16           &gt;1.05                &gt;1.05                     &gt;1.16                          &gt;1.05                               &gt;1.16                                    &gt;1.16                                         &gt;1.05                                              &gt;1.05                                                  &gt;1.05                                                      &gt;1.054:00  &gt;1.05      s&gt;1.16           &gt;1.05                &gt;1.05                     &gt;1.05                          s&gt;1.05                               &gt;1.05                                    &gt;1.05                                         &gt;1.05                                              &gt;1.05                                                  &gt;1.05                                                      &gt;1.056:00  s&gt; 1.05      &gt;1.05           &gt;1.05                &gt;1.01                     &gt;1.05                          &gt;1.01                               &gt;1.05                                    &gt;1.05                                         *&gt;1.01                                              &gt;1.05                                                  &gt;1.05                                                      &gt;1.018:00  &gt;1.01      &gt;1.05           s&gt;1.05                &gt;1.01                     &gt;1.01                          &gt;.97 s&gt;1.05                                    &gt;1.05                                         *&gt;.97                                              &gt;1.05                                                  &gt;1.01                                                      *&gt;1.0110:00 &gt;.97 &gt;1.05           &gt;1.01                &gt;.97 &gt;1.01                          &gt;.97 &gt;1.01                                    &gt;1.05                                         *&gt;.97                                              &gt;1.05                                                  *&gt;1.01                                                      *&gt;.9712:00 &gt;.97 &gt;1.05           &gt;1.01                &gt;.97 &gt;.97 &lt;.97 &gt;1.01                                    &gt;1.05                                         *=.97                                              &gt;1.01                                                  *&gt;1.01                                                      *&gt;.9714:00 s&gt;.97      &gt;1.05           s&gt;1.01                s&gt;.97                     s&gt;.97                          &lt;.97 &gt;1.01                                    &gt;1.05                                         *&lt;.97                                              *&gt;1.01                                                  *&gt;.97                                                      *&gt;.9716:00 &lt;.97 &gt;1.05           s&gt;1.01                s&gt;.97                     s&gt;.97                          xx   &gt;1.01                                    &gt;1.01     *&gt;.97                                                  *&gt;.97                                                      *&gt;.9718:00 &lt;.97 &gt;1.05           &gt;.97 &lt;.97 s&gt;.97                          xx   &gt;1.01                                    &gt;1.01     *&gt;.97                                                  *s&gt;.97                                                      *=.97Mass  .28  .96  .26  .31  .29  .35  1.43 .28  1.05 1.13                                                  .29 .17% Gain 133  63   63   94   93   106  43   47   94   74  93  89Color white      white           white                white                     white                          white                               white                                    white                                         white                                              white                                                  white                                                      whiteThickness                                     .01-.012                                              .025                                                  .018-                                                      .024                                                  .025Comments not  threaded                      threaded                                         Handle                                              Bottom                                                  Bottom                                                      Side tacky      part of                       section                                         of   of  of  Wall      the bottle                    of bottle Bottle                                                  Bottle                                                      Bottle__________________________________________________________________________Trail  XXVI XXVII           XXVIII                XXIX XXX  XXXI  XXXII                                     XXXIII                                          XXXIV                                               XXXV XXXVI__________________________________________________________________________MEK/   21   21  30   30   80   90    90   90   30   30   30Water/ 76   76  67.2 67.2 19.2 9.6   9.6  9.6  68.9 68.6 68.6NaOH   3    3   2.8  2.8  .8   .4    .4   .4   1.4  1.4  1.4Temp °C.  54   54  58   58   58   58    67   67   58   58   72Mass   .07  .07 .06  .06  .05  .055  .07  .09  .05  .06  .06Color  clear       white           clear                clear                     clear                          clear clear                                     clear                                          clr  clr  clrThickness  sphere       .026           sphere                .021 sphere                          sphere                                sphere                                     sphere                                          .019 .024 .022Time (min)  Density Range1:00   &gt;1.22       &gt;1.19           &gt;1.22                &gt;1.21                     &gt;1.19                          &gt; 1.22                                &gt;1.19                                     &gt;1.15                                          &gt;1.15                                               &gt;1.15                                                    &gt;1.152:00   &gt;1.22       &gt;1.15           s&gt;1.22                =1.19                     =1.19                          &gt;1.19 &gt;1.15                                     &gt;1.08                                          &gt;1.08                                               &gt;1.08                                                    &gt;1.084:00   &gt;1.22       &gt;1.08           &gt;1.19                &gt;1.08                     &gt;1.15                          &gt;1.15 &gt;1.08                                     &gt;1.02                                          &gt;1.02                                               &gt;1.08                                                    &gt;1.026:00   &gt;1.19       &gt;1.02           &gt;1.15                *&gt;1.02                     =1.15                          &gt;1.08 &gt;1.02                                     &gt;1.02                                          *&gt;.97                                               &gt;1.02                                                    *&gt;.978:00   &gt;1.19       &gt;1.02           &gt;1.15                *&gt;.97                     &gt;1.08                          &gt;1.08 &gt;1.02                                     =1.02                                          *&gt;.97                                               *&gt;1.02                                                    *&gt;.9710:00  &gt;1.19       &gt;1.02           &gt;1.08                *&gt;.97                     &gt;1.08                          &gt;1.08 &gt;.97 &gt;.97 *&gt;.97                                               *&gt;.97                                                    *&gt;.9712:00  &gt;1.19       &gt;1.02           &gt;1.08                *&gt;.97                     =1.08                          &gt;1.08 &gt;.97 &gt;.97 *&gt;.97                                               *&gt;.97                                                    *&gt;.9714:00  &gt;1.08       &gt;1.02           &gt;1.08                *&gt;.97                     &gt;1.02                          &gt;1.02 &gt;.97 &gt;.97 *&gt;.97                                               *&gt;.97                                                    *&gt;.9716:00  &gt;1.08       &gt;1.02           &gt;1.08                *&gt;.97                     &gt;1.02                          &gt;1.02 &gt;.97 &gt;.97 *&gt;.97                                               *&gt;.97                                                    *&gt;.9718:00  &gt;1.08       &gt;1.02           &gt;1.08                *&lt;.97                     &gt;1.02                          &gt;1.02 &gt;.97 =.97 *s&gt;.97                                               *&gt;.97                                                    *&gt;.97Mass   .09  .09 .09  .12  .06  .068  .11  .15  .09  .11  .11% Gain 29   29  50   100  20   24    57   66   80   83   83Color  cldy. wht       white           cldy. wht                cldy. wht                     cldy. wht                          cldy. wht                                cldy. wht                                     cldy. wht                                          cldy. wht                                               cldy.                                                    cldy. whtThickness  sphere       .031           sphere                .026 sphere                          sphere                                sphere                                     sphere                                          .027 .030 .030Comments  Resin       Side           Resin                Side pellet                          pellet                                pellet                                     pellet  Pellets       Wall           Pellet                Wall 2-phase__________________________________________________________________________Trial  XXXVII       XXXVIII            XXXIX                 XL   XLI  XLII XLIII                                     XLIV XLV  XLVI XLVII__________________________________________________________________________MEK/   30   30   30   90   30   30   90   90   30   90   90Water/ 65.8 65.8 65.8 9.4  64.4 64.4 9.2  9.2  63.0 9.0  9.0NaOH   4.2  4.2  4.2  6    5.6  5.6  .8   .8   7    1.0  1.0Temp °C.  69   50   35   58   58   63   62   62   58   60   60Mass   .04  .083 .075 .078 .099 .098 .09  .117 .093 .089 .089Color  clr  clear            clear                 clear                      clear                           clear                                clear                                     clear                                          clear                                               clear                                                    clearThickness  .019 .020 .022 .018 .022 .022 .020 sphere                                          .018 .018 sphereTime (min)  Density Range1:00   &gt;1.08        1.15            &gt;1.15                 &gt;1.08                      &gt;1.15                           =1.15                                s&gt;1.08                                     &gt;1.22                                          *&gt;1.08                                               &gt;1.02                                                    &gt;1.192:00   *&gt;1.02       &gt;1.08            &gt;1.08                 &gt;1.02                      &gt;1.08                           *&gt;1.08                                s&gt;1.02                                     =1.19                                          *&gt;1.02                                               &gt;.97 &gt;1.154:00   *&gt;.97       =1.08            &gt;1.08                 =1.02                      *&gt;1.02                           *&gt;1.02                                &gt;.97 &gt;1.08                                          *s&gt;1.02                                               &lt;.97 &gt;1.086:00   *&gt;.97       *&gt;1.02            &gt;1.02                 s&gt;.97                      *&gt;.97                           *&gt;.97                                =.97 &gt;1.08                                          *&gt;.97     &gt;1.088:00   *&gt;.97       *&gt;.97            &gt;1.02                 &lt;.97 *&gt;.97                           *s&gt;.97                                &gt;.97 s&gt;1.08                                          *=.97     &gt;1.0210:00  *&lt;.97       *&gt;.97            *s&gt;1.02   *&gt;.97                           *&gt;.97     &gt;1.02                                          *&lt;.97     &gt;1.0212:00       *&gt;.97            *=1.02    *&lt;.97          &gt;1.02          &gt;1.0214:00       *&lt;.97            *&gt;.97                    &gt;.97           &gt;.9716:00            *&gt;.97                    &gt;.97           &gt;.9718:00            *&gt;.97                    &gt;.97           &gt;.97Mass   .095 .157 .14  .182 .197 .21  .232 .181 .197 .198 .134% Gain 137  89   87   133  99   114  158  55   112  122  51Color  cldy. wht       cldy. wht            clr wht                 cldy. wht                      cldy. wht                           cldy. wht                                cldy. wht                                     cldy. wht                                          cldy. wht                                               cldy.                                                    cldy. whtThickness  .027 .025 .029 .026 .030 .027 .027 sphere                                          .026 .022 sphereComments                                  resin                                          side side resin                                     pellet                                          wall wall pellet__________________________________________________________________________                           Trial XLVIII                                      XLIX L    LI   LII__________________________________________________________________________                           MEK/  30   30   90   90   90                           Water/                                 61.6 61.6 8.8  8.8  8.8                           NaOH  8.4  8.4  1.2  1.2  1.2                           Temp °C.                                 55   55   55   55   45                           Mass  .162 .152 .167 .121 .108                           Color white                                      clear                                           white                                                clear                                                     clear                           Thickness                                 .125 .023 .125 .020 sphere                           Time (min)                                 Density Range                           1:00  &gt;1.19                                      *&gt;1.08                                           &gt;1.15                                                =1.08                                                     &gt;1.19                           2:00  *&gt;1.08                                      *=1.08                                           &gt;1.08                                                &gt;.97 &gt;1.12                           4:00  *&gt;1.08                                      *=1.02                                           &gt;1.02                                                &lt;.97 &gt;1.08                           6:00  *&gt;1.02                                      *&gt;.97                                           &gt;1.02     &gt;1.08                           8:00  *&gt;1.02                                      *&gt;.97                                           &gt; .97     &gt;1.08                           10:00 *&gt;1.02                                      *=.97                                           &gt;.97      &gt;1.02                           12:00 *&gt;1.02                                      *&lt;.97                                           &gt;.97      &gt;1.02                           14:00 *=1.02    &gt;.97      &gt;1.02                           16:00 *&gt;.97     s&gt;.97     &gt;1.02                           18:00 *&gt;.97     &lt;.97      s&gt;1.02                           Mass  .253 .284 .287 .202 .168                           % Gain                                 56   87   72   67   56                           Color white                                      cldy. wht                                           white                                                cldy.                                                     cldy. wht                           Thickness                                 .144 .034 .151 .34  sphere                           Comments                                 threaded                                      side threaded                                                side resin                                 top of                                      wall top of                                                wall pellet                                 bottle    bottle__________________________________________________________________________ **Percent by Weight *floates in upper phase 
    
    
    
     EXAMPLE I (TRIAL IX) 
     It has been found (see Trial IX) that the best conditions to arrive at a separation of particles or flakes of PET from PVC is by applying to the flakes a solution containing 90% MEK, 9.2% H 2  O and 0.8% NaOH at a temperature between 55° and 65° C. After approximately 5 minutes in the solution, the density of the PVC changes from its original density of 1.32 grams/cc to 0.97 grams/cc. The flakes of PVC can then be separated from the flakes of PET by either flotation or centrifugation. 
     EXAMPLE II (TRIAL XX) In order to reduce the amount of MEK used in the method, for cost saving reasons, a solution containing 30% MEK, 67.2% H 2  O and 2.8% NaOH is applied to the particles of flakes of PVC and PET at a temperature between 60° and 65° C. After approximately 10 minutes in the solution, the density of the PVC changes from 1.32 grams/cc to approximately 1.01 grams/cc. The flakes of the PVC can then be differential density separated from the flakes of PET by flotation or centrifugation. 
     The above detailed description of the present invention is given for explanatory purposes. It will be apparent to those skilled in the art that numerous changes and modifications can be made in the examples of the invention described above without departing from the scope of the invention. Accordingly, the whole of the foregoing description is to be construed in an illustrative and not in a limitative sense, the scope of the invention being defined solely by the appended claims.