Method for preparing and detoxifying using liquid rinsing medium

Abstract

The present invention concerns a method for processing and detoxification of a material, especially a thermoplastic material, and for removal of contaminants or impurities from this material, wherein the material is heated under vacuum in at least one receiving tank, mixed and possibly comminuted, and wherein a rinsing medium is introduced into the receiving tank beneath the material level, conducted through at least a partial region of the material, and the rinsing medium enriched or saturated with contaminants is brought out from the receiving tank once more. According to the invention, the quantity of rinsing medium introduced into the receiving tank is less than 0.1 liter per hour per kilogram of material or material throughput per hour, while at the same time the vacuum in the receiving tank is kept constantly below 100 mbar.

Claims

1. A method for processing and detoxification of a thermoplastic material, and for removal of contaminants or impurities from the material, wherein the material is heated under vacuum in at least one receiving tank, mixed and comminuted, and wherein a liquid rinsing medium is introduced into the receiving tank comprising the material from only beneath the material level, conducted through at least a partial region of the material, the liquid rinsing medium evaporates after being conducted through at least the partial region of the material, and the evaporated liquid rinsing medium enriched or saturated with contaminants is brought out from the receiving tank, wherein the quantity of rinsing medium introduced into the receiving tank is less than 0.1 liter per hour per kilogram of polymer material throughput per hour, while at the same time the vacuum in the receiving tank is kept constantly below 100 mbar.

2. The method according to claim 1, characterized in that the vacuum is held permanently below 50 mbar.

3. The method according to claim 1, wherein the liquid rising medium includes water.

4. The method according to claim 1, wherein the liquid rinsing medium is polar or apolar.

5. The method according to claim 1, wherein the liquid rinsing medium is heated before entering the receiving tank.

6. The method according to claim 1, wherein the liquid rinsing medium enters the receiving tank or strikes the material being cleaned with a velocity of at least 1 m/min.

7. The method according to claim 1, wherein the quantity of liquid rinsing medium entering the receiving tank prior to the evaporation is in the range of 0.0001 to 0.08 liters per hour per kilogram of material throughput per hour.

8. The method according to claim 1, wherein the throughput, or the adding of the material and the liquid rinsing medium to the receiving tank and the removal therefrom, is continuous.

9. The method according to claim 1, wherein the liquid rinsing medium is introduced through the bottom surface of the receiving tank.

10. The method according to claim 1, wherein the liquid rinsing medium is introduced by at least one nozzle.

11. The method according to claim 1, wherein the processing, the detoxification or the removal of contaminants or impurities occurs at a temperature above the glass transition temperature and below the melting range of the material.

12. The method according to claim 1, wherein at least one other receiving tank is added upstream or downstream from the receiving tank, and the material runs through the receiving tanks in succession, the method further comprising: heating the material under vacuum in the other receiving tank, mixing the material in the other receiving tank, and optionally comminuting the material in the other receiving tank; and introducing an additional rinsing medium into the other receiving tank beneath a level of the material in the other receiving tank, conducting the additional rinsing medium through at least a partial region of the material in the other receiving tank, and bringing out the rinsing medium, enriched or saturated with contaminants, from the other receiving tank.

13. The method according to claim 12, wherein one or more pretreatment tanks switched in parallel are further provided, wherein the receiving tank is a main treatment tank connected to the pretreatment tanks, the method further comprising: heating the material under vacuum in the pretreatment tanks, mixing the material in the pretreatment tanks, and optionally comminuting the material in the pretreatment tanks; and introducing an additional rinsing medium into the pretreatment tanks beneath a level of the material in the pretreatment tanks, conducting the additional rinsing medium through at least a partial region of the material in the pretreatment tanks, and bringing out the rinsing medium, enriched or saturated with contaminants, from the pretreatment tanks.

14. The method according to claim 1, wherein the quantity of the rinsing medium introduced into the receiving tank is selected from the group consisting of: in the range of 0.0001 to 0.08 liters, and between 0.003 and 0.05 liters, per hour per kilogram of material throughput per hour.

15. The method according to claim 1, wherein the vacuum is held permanently between 10 and 20 mbar.

16. The method according to claim 1, wherein the vacuum is held permanently under 2 mbar.

17. The method according to claim 1, wherein the quantity of liquid rinsing medium entering the receiving tank prior to the evaporation is in the range of between 0.003 and 0.05 liters per hour per kilogram of material throughput per hour.

18. The method according to claim 1, wherein the processing, the detoxification or the removal of contaminants or impurities occurs at a temperature at which the material exists in a softened state.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Especially preferred devices in which the following process examples were also carried out are presented in the drawings.

(2) FIG. 1 shows a single-stage device

(3) FIG. 2 shows a two-stage device with a pretreatment tank

(4) FIG. 3 shows a two-stage device with two pretreatment tanks

(5) FIG. 4 shows the average limonene content as a result of the experiment.

DETAILED DESCRIPTION

(6) FIG. 1 shows a single-stage device whose design is borrowed from a Vacurema Basic layout, with the difference that a feed opening 2 for the rinsing medium has been fashioned. The device consists of a receiving tank or vacuum reactor or cutter-compactor 1, which can be evacuated with a vacuum pump, being connected in the lowermost region to a single-worm extruder 4. The contaminated flakes being recycled arrive by a vacuum sluice 6 from above in the receiving tank 1, are heated, softened, but not melted by a mixing and agitating element 3 driven in rotation on a vertical axis, constantly moved, mixed and comminuted. At the same time, a scouring gas is introduced from below through a feeding opening 2 located in the bottom, conducted through the material or the mixing vortex, and taken out once more at the top through the suction opening 7. Thus, the method of the invention takes place in the receiving tank 1, achieving a decontamination, with simultaneous drying, crystallization, and raising of the intrinsic viscosity. After an appropriate dwell time, the material is force fed into the intake zone of the extruder 4 while maintaining the vacuum, where it is melted, and then filtered and further processed.

(7) FIG. 2 shows a layout whose design is borrowed from a Vacurema Advanced layout. Here, there are two receiving tanks 1, 1configured the same as the tank in FIG. 1or an evacuable pretreatment tank 1 is connected upstream from the evacuable main treatment tank 1, in which the raw material being cleaned and recycled is first introduced and treated by the method of the invention. After an appropriate dwell time, the material is taken from the pretreatment tank 1 by a noncompressing exit worm 5 under vacuum to the main treatment tank 1, where it again undergoes the processing of the invention, especially under altered conditions yet still conforming to the invention, and it is then finished similarly to FIG. 1.

(8) FIG. 3 shows a layout whose design is borrowed from a Vacurema Prime layout. Here, there are three receiving tanks 1, 1configured the same as the tank in FIG. 1namely, an evacuable main treatment tank and two pretreatment tanks 1 connected upstream from the main treatment tank. The two pretreatment tanks 1 are switched in parallel with each other and are operated alongside each other or alternating and discontinuously in batch operation and the alternately and thus continuously charge the downstream main treatment tank 1. All three tanks 1, 1 are configured or provided with a feeding opening 2 for the rinsing medium so that the method of the invention can be carried out in each of the tanks 1, 1, possibly with different parameters.

(9) Alternatively, it can be provided that no scouring gas is introduced or can be introduced in the pretreatment tanks 1 of FIGS. 2 and 3 and that they are operated in traditional manner. In the main treatment tank 1, however, the introducing of the scouring gas according to the method of the invention occurs in every case.

(10) The following process examples were carried out with the devices described here.

Example 1

(11) Cleaning of HD-PE Milk Bottles in a Single-Stage Process Vacurema Basic

(12) The following effects were achieved in the processing of HD-PE flakes from milk bottles that were first washed in a conventional washing plant with an adapted single-stage Vacurema Basic layout:

(13) If one has, for example, an operating point of T.sub.polymer=115 C., pressure p in the tank=10 mbar, dwell time=60 min and a cleaning efficiency of around 92.3% for certain marker chemicals like toluene or chloroform, the cleaning efficiency is increased to 98.2% when a rinsing medium, namely, 0.003 liters of water per hour per kg of material per hour is introduced (the material throughput was around 300 to 350 kg of PH per hour), which evaporates in the tank. The vacuum is reduced to around 20 to 25 mbar in this process, but it is still adequate.

Example 2

(14) Cleaning of HD-PE Milk Bottles in a Two-Stage Process Vacurema Advanced

(15) HD-PE milk bottles that were first washed in a conventional washing plant are processed in an adapted Vacurema Advanced System (FIG. 2) and freed from toxins that had diffused into them. The device consists of a pretreatment tank 1 and a downstream connected main treatment tank 1. Both tanks 1, 1 are operated under a vacuum and can be subjected to scouring gas.

(16) In the pretreatment tank 1, the rough cleaned and ground-up HD-PE flakes in the cold, dry state are continuously introduced (material throughput 1000 kg/h) in small batches through a sluice 6. Under continual stirring, the flakes are mechanically heated under vacuum. The temperature is held below or near the Vicat temperature in order to prevent a sticking or agglomeration of the flakes. The flakes behave as a fluid in the pretreatment tank 1 and move through the tank under continual agitation, the mean dwell time being 50 minutes, and a temperature of around 90 to 115 C. is achieved in the lower region of the tank. At the same time, a vacuum of around 1 to 30 mbar is maintained. Under optimal conditions, especially minimal residual moisture etc., the vacuum can at times drop even below 1 mbar.

(17) Now, the goal in this first tank 1 is to remove the toxins having diffused into the flakes at least from the regions of the flakes near the surface.

(18) For this purpose, a quantity of around 0.01 to 0.03 liters of water per hour per kg of material per hour is sprayed in with a flow rate of around 2 m/min by a needle nozzle 2 in the lower region of the tank, which evaporates at once and is carried by the moving material in the counterflow principle. The suctioning off point is located in the roof of the tank. The evaporation of the water in the tank results in a sharp rise in volume. The vacuum is reduced to around 10 to 30 mbar.

(19) The material is then taken to the main treatment tank 1 by sluices or conveyor means 5. Here, a further treatment occurs under different conditions.

(20) In detail, the following conditions occur in the two tanks:

(21) Pretreatment tank:
T.sub.material=101 C.
p=29 mbar

(22) rinsing medium: water in a quantity of 0.021/h per material throughput in kg/h

(23) flow velocity: around 2 m/min

(24) Main treatment tank (reactor):
T.sub.material=123 C.
p=3 mbar
rinsing medium: air in a quantity of 0.0033 Nm.sup.3 per material throughput in kg/h, corresponding for a material throughput of 1000 kg of PE per hour to a quantity of 3.36 Nm.sup.3 of scouring air per hour or 1650 m.sup.3/h under the aforementioned conditions.

(25) flow velocity: around 2 m/min

(26) The cleaning effect for certain marker chemicals such as toluene and chlorobenzene increases thanks to the method of the invention for toluene from 94.5% (without rinsing medium) to 99.8% and for chlorobenzene from 93.7% to 99.8%.

Example 3

(27) Air-Water Comparison

(28) Here, the air in the main treatment tank 1 in example 2 was replaced by water as the rinsing medium, whereupon the conditions in the main treatment tank 1 changed as follows:

(29) Main treatment tank (reactor):
T.sub.material=124 C.
p=5 mbar

(30) rinsing medium: water in a quantity of 0.0032 l/h per material throughput in kg/h, corresponding to around 1.800 m.sup.3 of steam per hour per material throughput in kh/h under the aforementioned conditions

(31) flow velocity: around 2 m/min

(32) It was no longer possible to detect the chemicals toluene and chlorobenzene in the material. They had fallen below the limits of detection.

Example 4

(33) Cleaning of Polypropylene Bottles

(34) The PP bottles were treated similar to example 2 under the following conditions:

(35) Pretreatment tank:
T.sub.material=122 C.
p=35 mbar
rinsing medium: water in a quantity of 0.028 l/h per material throughput in kg/h, corresponding to around 2.640 m.sup.3 of steam per hour per material throughput in kh/h under the aforementioned conditions

(36) flow velocity: around 2 m/min

(37) Main treatment tank (reactor):
T.sub.material=135 C.
p=3 mbar
rinsing medium: water in a quantity of 0.0012 l/h per material throughput in kg/h, corresponding to around 1.900 m.sup.3 of steam per hour per material throughput in kh/h under the aforementioned conditions (=1900 m.sup.3 of steam per hour per 1000 kg of PP/h)

(38) flow velocity: around 2 m/min

(39) The limonene content was analyzed before and after the cleaning step. The initial values in the uncleaned PP flakes were in the range of around 32544 to 46800 detector counts of a headspace detection system. Without the use of rinsing agents, a detection of around 5200 to 8900 counts was found. With the use of rinsing agents according to the invention, the values in the treated material were reduced to 1250 to 1500 counts.

Example 5

(40) Cleaning of HD-PE Milk Bottles

(41) The method was carried out according to example 2, but with a dwell time of 60 minutes in both the pretreatment and the main treatment tanks. HD-PE flakes contaminated with limonene were used. In a long-term experiment, 3000 samples were taken continuously in order to monitor the course of the decontamination.

(42) At first (up to sample 200), the flakes were treated without rinsing agents, only under vacuum, whereupon the average limonene content receded to around 1.2 ppm and fluctuated there.

(43) After this, with otherwise unchanged conditions, rinsing agents were added, namely, by a combined use of water in the pretreatment tank 1 and air in the main treatment tank 2. From sample 200 onward, the rinsing agents were added to both tanks, under the following conditions:

(44) Pretreatment tank:
T.sub.material=104 C.
p=22 mbar
rinsing medium: water in a quantity of 0.045 l/h per material throughput in kg/h corresponding for a material throughput of around 1000 kg of PE per hour to a quantity of around 43 m.sup.3/min of scouring gas (steam) under the aforementioned conditions.

(45) flow velocity: around 2 m/min

(46) Main treatment tank (reactor):
T.sub.material=121 C.
p=5 mbar
rinsing medium: air in a quantity of 2.3 m.sup.3 hour per material throughput in kg/h under the aforementioned conditions, corresponding for a throughput of 1000 kg of PE per hour to a quantity of 2300 m.sup.3 of scouring air per hour under the aforementioned conditions (around 7.86 Nm.sup.3/h).

(47) flow velocity: around 2 m/min

(48) The average limonene content as a result receded to around 0.25 ppm and fluctuated there. The course of the experiment can be seen from FIG. 4.