WO1999009092A1

WO1999009092A1 - The reprocessing of polymeric products

Info

Publication number: WO1999009092A1
Application number: PCT/US1998/017383
Authority: WO
Inventors: Pieter Johannes Van Den Heever
Original assignee: Edsview Belleggings (Proprietary) Limited; Handelman, Joseph, H.
Priority date: 1997-08-21
Filing date: 1998-08-21
Publication date: 1999-02-25
Also published as: AU9293498A

Abstract

A process for reprocessing polymeric products, for example, used rubber tyres or PVC-coated metal products, includes contacting the polymeric product with at least one vegetable oil such as sunflower seed oil. The vegetable oil in contact with the polymeric product is subjected to an elevated temperature, for example, 60 - 150 °C, for a sufficient time to liquify the polymer. The liquified polymer is then separated from the metals and canvas/belting products in the polymeric product in order to recover the polymer and the metals and canvas/belting products. The vegetable oil optionally contains an organic acid such as acetic acid to enhance or assist with the rate at which reprocessing takes place.

Description

THE REPROCESSING OF POLYMERIC PRODUCTS

THIS INVENTION relates to the reprocessing of polymeric products.

According to the invention, there is provided a process for reprocessing a polymeric product, the process including contacting the polymeric product with at least one vegetable oil; and subjecting the vegetable oil in contact with the polymeric product to an elevated temperature for a sufficient time to liquify the polymer.

The vegetable oil may be sunflower seed oil. The sunflower seed oil may include used sunflower seed oil .

Optionally, an additive such as an organic acid is added to the vegetable oil to enhance or assist with the rate at which reprocessing takes place.

Typically, a mixture is formed of the organic acid and the vegetable oil, the mixture containing 5 - 15% m/m organic acid, for example, 10% m/m organic acid.

The organic acid may be acetic acid, for example, in the form of commercial vinegar (5% m/m aqueous solution of acetic acid) .

The contacting of the polymeric product with the vegetable oil may take place in a metal vessel. Typically, the metal is of sufficient thickness to withstand a pressure of 2 bar. The metal may be of stainless steel, mild steel, aluminium, or other metal having low adhesion for the reprocessed polymer.

The temperature at which the process is carried out may be about 60 - 150°C, typically, about 110°C. The optimum reaction temperature and the optimum period of heating can be determined by experimentation, taking into account the particular polymer and the vegetable oil . Typically, the optimum period of heating in the case of used rubber tyres is about 50 min . and, in the case of PVC-coated cable, is about 15 min.

Typically, the process is carried out at an elevated pressure, for example, 0.5 bar.

The process may be heated from an external heat source such as steam condensing or thermal fluid circulating in a jacket or heating coil, an electrical or gas heating element, pumping energy, or other suitable indirect heating method.

The polymeric product may be based on a natural or a synthetic polymer. The polymer may be an elastomer such as a natural or a synthetic rubber. In this case, the polymeric product is typically a used tyre or any used rubber product . The polymer may also be a polymer such as PVC and, in this case, the polymeric product is typically a PVC-coated metal product, for example, scrap copper cable or electrical wiring.

Typically, a portion of the oil used in the reprocessing of the polymer is recovered for re-use. The percentage of the oil which is recovered from the process after the polymer has been reprocessed is in the range S0% - 99% of the quantity of oil originally used , preferably 80% - 98%, more preferably 95%. According to another aspect of the invention, there is provided a process for recovering the constituents of a rubber tyre casing, the process including contacting the tyre casing with at least one vegetable oil at an elevated temperature; and liquifying the rubber constituent of the tyre through the contact with the vegetable oil, thereby releasing the steel and/or canvas constituents of the tyre from the tyre casing.

The process may be carried out at an elevated pressure, for example, 0.5 bar.

The process may be carried out in a vessel in which the tyre(s) is submerged in the oil. The process may include macerating the tyre casing to expose a larger rubber surface area for contact with the oil.

The steel and/or the canvas may be separated from the liquified rubber for reprocessing separately.

The vegetable oil may be as described previously. Optionally, an organic acid as described previously is added to the vegetable oil to accelerate the liquifying process .

According to a another aspect of the invention, there is provided a process for recovering the constituents of a polymer-coated cable or electrical wiring, the process including contacting the polymer-coated cable or electrical wiring with at least one vegetable oil at an elevated temperature ; and liquifying the polymer constituent of the polymer-coated cable or electrical wiring through the contact with the vegetable oil, thereby releasing the metal constituent of the polymer-coated cable or electrical wiring from the polymer.

The process may be carried out at an elevated pressure, for example, 0.5 bar.

Optionally, an organic acid as described previously is added to the vegetable oil to accelerate the liquifying process.

The process may be carried out in a vessel in which the polymer-coated cable or electrical wiring is submerged in a vinegar/vegetable oil mixture, the vinegar/vegetable oil mixture being distilled off and out of the vessel for recycling, leaving the liquified polymer and the metal in the vessel. The liquified polymer may then be removed from the vessel and cooled to form a semi- solid polymeric product for re-use, the metal being recovered separately from the vessel for re-use.

The vegetable oil used in the process may be sunflower seed oil . The sunflower seed oil may include used sunflower oil.

The invention will now be described, by way of non-limiting example, with reference to the accompanying diagrammatic drawings.

In the drawings Figure 1 shows a schematic flow sheet of an installation for carrying out a process in accordance with the invention;

Figure 2 shows a process vessel forming part of the installation of Figure 1;

Figure 3 shows a cooler forming part of the installation of Figure 1; Figure 4 shows a reticulation tank forming part of the installation of Figure 1 ; Figure 5 shows an air purifier forming part of the installation of Figure 1; and

Figure 6 shows a schematic flow sheet of another installation for carrying out a process in accordance with the invention.

With reference to Figures 1 to 5, reference numeral 10 generally indicates an installation for carrying out the process of the invention to reprocess polymeric products such as used rubber tyres or scrap PVC-coated copper cable.

The installation 10 includes a process tank or vessel 12 which is connected via line 14 to a cooler 16. The cooler 14 is connected via line 18 to a reticulation tank 20, and the reticulation tank 20 is connected via line 22 to an air purifier 24 which is open to atmosphere. The process vessel is also connected via line 28 to a drain tank 30 which has means (not shown) for discharging and recovering liquified polymer via a gate valve. The drain tank 30 is also connected via line 34 to the cooler 16 to permit any process vapour passing via line 28 into the drain tank 30 to be passed to the cooler 16.

With reference to Figure 2, the process tank or vessel 12 has a bottom 12.1 and a top 12.2. The process vessel 12 is provided with a bottom release valve 36 in line 28 and a top release valve 38 in line 14, a metal lid 40 for closing the vessel in use, a metal sieve 42 located inside the vessel adjacent the vessel bottom 12.1, a sieve handle 44 fast with the sieve 42, and heating means in the form of a gas burner 46 provided with a non-return valve 48. The process vessel 12 is also provided with heat and pressure gauges (not shown) and an air pressure line 50. The metal of the process vessel 12 is stainless steel of sufficient thickness to withstand a pressure of 2 bar. With reference to Figure 3, the cooler 16 is an water-filled vessel or tank having an inlet 16.1 and an outlet 16.2 and an internal pipe 16.3 which defines a labyrinthine path between the inlet and the outlet . The tank thereby serves to cool the vinegar/sunflower seed oil vapour mixture passing into the cooler via line 14 from the process vessel 12 by heat exchange with the water in the tank surrounding the pipe 16.3. The cooled process vapour passes out of the cooler to the reticulation tank via line 18.

With reference to Figure 4, the reticulation tank 20 has an inlet 20.1, a vapour outlet 20.2, a liquid outlet 20.3 provided with a valve 20.4, and a series of breaker plates 20.5 extending transversely across the tank. The cooled vapour from the cooler 16 passing into the tank 20 via the line 18 condenses during its passage through the tank across the breaker plates 20.5 and the condensate can be recovered via the liquid outlet 20.3 and valve 20.4. Any remaining vapour passes out of the tank 20 via the vapour outlet 20.2 and line 22. The breaker plates serve to break the flow of the vapour through the reticulation tank and to increase the surface area of the tank to enhance the rate of condensation.

With reference to Figure 5, the air purifier 24 is a tank having an inlet 24.1, an outlet 24.2 to atmosphere, and contains multiple layers of scrim wool material generally designated by reference numeral 24.3. The process vapour passing into the purifier via the line 22 from the reticulation tank 20 is filtered by passing through the layers of scrim wool material to permit the filtered vapour to be discharged to atmosphere via the outlet 24.2.

The air purifier also contains an outlet 24.4 and valve 24.5 for use when it is desired to recycle the process vapour instead of releasing it to atmosphere.

In operation, the polymeric product to be reprocessed is placed on the sieve 42 and the sieve is inserted into the open process vessel 12 by means of the sieve handle 44. The polymeric product is then submerged in a mixture containing 600 ml commercial vinegar and 8 ? sunflower seed oil (not shown) . The lid 40 is then placed on top of the process vessel to close it .

The process vessel 12 is heated by means of the gas burner 46 to a temperature of 80°C and air is passed into the vessel via line 50 to maintain an air pressure of 0.5 bar. Heating is continued at 80 °C for 7 - 50 minutes, depending on the particular polymeric product being reprocessed. The optimum period of heating can be determined by experimentation. The heated vinegar/sunflower seed oil mixture in the process vessel liquifies the polymer of the polymeric product and the liquified polymer passes through the sieve 42 to the bottom 12.1 of the process vessel 12. After the reaction is completed, the liquified polymer is drained out of the process vessel 12 via the bottom release valve 36 and line 28 into the drain tank 30. On cooling, the liquified polymer forms a semi-solid polymer product which can be reused.

The process vessel 12 is then cleaned by a cleaning process which includes increasing the temperature of the vessel to 150 °C and maintaining the temperature at 150°C for 5 minutes. At 150°C, the vinegar/sunflower seed oil mixture begins to boil and distil off via the top release valve 38 and line 14. The vinegar/sunflower seed oil vapour mixture which distils off via the top release valve 38 and line 14 is passed to the cooler 14 and after cooling the condensate is recovered via the liquid outlet 20.3 and valve 20.4 of the reticulation tank 20 and re- used .

The process of cleaning the process vessel 12 includes increasing the air pressure through line 50 in order to blow air through the process vessel.

The lid 40 is then opened and the non-polymeric constituents such as metal and canvas/belting in the sieve are recovered by removing the sieve 42 from the process vessel 12 by means of the sieve handle 44.

In a production run using 50kg scrap PVC-coated copper cable, 70 - 80% of the scrap was recovered as copper and other metals. In another production run using 50 kg of used rubber tyres, it was found that the optimum process temperature was 110 °C and the optimum period of heating was 50 minutes. In this case, 8 - 10% of metal and 3 - 10% of canvas/belting was recovered from the used rubber tyres.

With reference to Figure 6, reference numeral 110 generally indicates another installation for carrying out the process of the invention. The installation 110 includes a process vessel 112, a pump 114, pipe work 116, and heating means in the form of an indirect transfer heat exchanger 118.

In operation, the polymeric product such as used rubber tyres (not shown) are placed in the process vessel 112 and submerged in sunflower seed oil 120. The pump 114 is started and the oil is extracted out of the vessel 112 and re-circulated through the pipework 116 back into the vessel 112. Through this re-circulation action, the temperature inside the vessel 112 steadily increases. The temperature of the oil 120 can be increased further by heating the contents of the vessel 112 by the indirect heat exchanger 118 by means of condensing steam, thermal fluid or electricity. After a period of re-circulation e.g. maximum two hours, the oil reacts with the rubber causing the rubber to liquify and become soft and tacky and to sink to the bottom of the vessel 112. At this stage, any steel and/or canvas present in the rubber can be removed from the vessel and stored separately for reprocessing later.

The vessel 112 is then permitted to cool down and the oil 120 separates from the rubber such that the oil floats on top of the rubber. The oil 120 may now be decanted for re-use later while the tacky rubber may be stored in polypropylene drums (not shown) for later use. Additives such as chalk may be added to promote or assist with the solidification of the liquified rubber.

It is an advantage of the invention that waste rubber products such as used tyres, which pose both an environmental and a health risk, may be reprocessed into useful commodities as well as enabling the recovery of the steel and canvas from the tyres for separate reprocessing. Also, scrap PVC-coated cables and electrical wiring can be reprocessed into useful commodities as well as enabling the recovery of the metal constituents for separate reprocessing.

Claims

CLAIMS :

1. A process for reprocessing a polymeric product, the process including contacting the polymeric product with at least one vegetable oil ; and subjecting the vegetable oil in contact with the polymeric product to an elevated temperature for a sufficient time to liquify the polymer.

2. A process as claimed in Claim 1, in which the vegetable oil is sunflower seed oil.

3. A process as claimed in Claim 1 or Claim 2, in which the vegetable oil contains an organic acid to enhance or assist with the rate at which reprocessing takes place .

4. A process as claimed in Claim 3, in which the organic acid and the vegetable oil forms a mixture, the mixture containing 5 - 15% m/m organic acid.

5. A process as claimed in Claim 3 or Claim 4, in which the organic acid is acetic acid.

6. A process as claimed in any one of Claims 1 to 5 inclusive, in which the temperature at which the process is carried out is 60 - 150┬░C.

7. A process as claimed in Claim 6, in which the temperature is 110┬░C.

8. A process as claimed in any one of Claims 1 to 7 inclusive, in which the process is carried out at an elevated pressure.

9. A process as claimed in Claim 8, in which the pressure is 0.5 bar.

10. A process as claimed in any one of the preceding claims, in which the polymer is a natural or a synthetic rubber.

11. A process as claimed in any one of Claims 1 - 9 inclusive, in which the polymer is PVC.