Method and system for cleaning and upgrading post-consumer and/or post-industrial polyvinylbutyral

Abstract

A method and a PVB cleaning and/or upgrading system for cleaning and upgrading post-consumer and/or post-industrial polyvinyl butyral is provided. The system includes an extraction station for extraction with liquid or supercritical carbon dioxide. The extraction station comprises a sealable container with means for introducing pressurized liquid carbon dioxide into the container and means for stirring PVB material. The station further includes transfer means for transferring the pressurized liquid carbon dioxide containing extracted plasticizer and/or contaminants from the container to a distillation unit. The distillation unit separates extracted plasticizer and/or contaminants from the carbon dioxide, by evaporation of the liquefied CO2. The system further includes pressurizing means, such as a compressor, for pressurizing and liquefying of the CO2 evaporated in the distillation unit.

Claims

1. A method for cleaning and/or upgrading post-consumer and post-industrial polyvinyl butyral, in particular PVB material having served as interlayer in laminated glass products, wherein the PVB material is provided in flakes, said method comprising the following steps: a) extraction of the PVB flakes in a stepwise manner to reduce or eliminate the content of plasticizers and/or contaminants such as TEG-EH, 2-butoxy-ethanol, butyric acid, and/or butyric aldehyde present in the PVB flakes subjecting the PVB flakes to extraction with pressurized liquid carbon dioxide at a pressure of between 30 and 70 bars, preferably between 40 and 60 bars, and at a temperature between 20 C. to +30 C., and b) Optionally repeating the extraction step a) at least once more.

2. The method according to claim 1, wherein the extraction step a) is carried out for 1-15 minutes.

3. The method according to claim 1, wherein the method further comprises a step prior to the step a) of applying a vacuum of 0.001-0.5 bars absolute or below, which is maintained for a period of about 15 seconds to 2 minutes.

4. The method according to claim 1, further comprising varying the pressure during of CO2 during at least one of the extraction steps, by changing the pressure of CO2 with at least +/0.1 bars-5 bars, during at least one of the extraction steps.

5. The method according to claim 1, wherein the PVB flakes has an average size in which the average length and/or average width is 4-50 mm, such as such as 5-35 mm.

6. The method according to claim 1, wherein the extraction step is repeated at least two times, such as repeated at least 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 times or even more times.

7. The method according to claim 6, wherein the liquid carbon dioxide phase is discharged to a distillation vessel from which purified CO2 is recovered and subsequently recycled into the extraction unit.

8. The method according to claim 1, wherein, the extraction step or steps are carried out in pressure tight rotatable drum, a sealed stirred container, or where the PVB material is stirred by means of the CO2 flow into the sealed container, such as stirring induced by the CO2 flow and/or a fluidized bed within a sealed container.

9. The method according to claim 1, further comprising the further step c) in which the PVB material washed with water adjusted to alkaline pH of at least pH above 8.

10. The method according to claim 9, wherein the alkaline washing step d) is performed prior to and/or subsequent to the CO2- extraction step.

11. The method according to claim 9, wherein the water is adjusted to alkaline pH by adding an inorganic or organic alkaline hydroxide, selected from sodium hydroxide, potassium hydroxide, calcium hydroxide, sodium carbonate, potassium carbonate, ammonia or organic or inorganic amines, and/or mixtures thereof.

12. The method according to claim 1, wherein a drying step is performed after the alkaline washing step or steps.

13. A PVB product obtainable by the method according to claim 1.

14. A PVB cleaning and/or upgrading system for cleaning and upgrading system post-consumer and/or post-industrial polyvinyl butyral, in particular, PVB material having served as interlayer in laminated glass products, wherein the system comprises an extraction station for extraction with liquid or supercritical carbon dioxide having a sealable container with means for introducing pressurized liquid carbon dioxide into the container, such as by the sealable container being a rotating drum, in particular, a drum rotating about a horizontal or inclined axis, or by stirring, such as by mechanical stirring means or stirring caused by the flow of liquid carbon dioxide from the pressurized liquid carbon dioxide introduction means, transfer means for transferring the pressurized liquid carbon dioxide containing extracted plasticizer and/or contaminants from the container to a distillation unit, a distillation unit for separating extracted plasticizer and/or contaminants from the carbon dioxide, by evaporation of the liquefied CO2, and pumping means for pressurizing and liquefying of the CO2 evaporated in the distillation unit, and recirculation means for recirculating the liquefied and pressurized CO2 to the sealable container.

15. The PVB cleaning and/or upgrading system according to claim 14, further comprising alkaline washing fluid addition means for adding alkaline washing fluid to the pressurized container or to a separate washing means.

Description

BRIEF DESCRIPTION

(1) Some of the embodiments will be described in detail, with references to the following figures, wherein like designations denote like members, wherein:

(2) FIG. 1 illustrates a stepwise diagram of variants of the upgrading procedure including stepwise CO2 extraction according to embodiments of the present invention;

(3) FIG. 2 illustrates an alternative stepwise diagram of variants of the upgrading procedure including stepwise CO2 extraction according to embodiments of the present invention;

(4) FIG. 3 shows a diagram illustrating a preferred layout of the CO2 extraction equipment according to embodiments of the present invention, and

(5) FIG. 4 illustrates the equipment used for alkaline washing.

DETAILED DESCRIPTION

(6) FIG. 1 is a schematic drawing of a treatment sequence for PVB.

(7) Step 1 denotes optional initial pre-treatment steps where PVB material is subjected to mechanical treatment and optionally optically controlled treatment which may be required as the case may be. This pre-treatment may, in particular, comprise separation of PVB from particulate matter including, among others, in particular glass, metal, colored PVB. This separation process may be automated or manual as provided at the production facility and may comprise magnetic means, optical recognition, digital image processing systems etc.

(8) Step 2 denotes washing with alkaline water as described above. Step 3 denotes a drying step. Step 4 denotes grinding or milling to reduce PVB size to flakes of a size as also outlined above. Step 5 denotes CO2 extraction of low molecular weight components in one or more substeps. Step 6 denotes the optional final preparation of PVB dispersions or other intermediate products such as pellets or powder or raw material for extrusion.

(9) FIG. 2 is a schematic drawing of an alternative procedure step sequence of the treatment steps of embodiments of the invention. In this procedure, The CO2 extraction step 5 is performed prior to the alkaline washing step 2, or as shown in FIG. 2, the alkaline washing step 2 may be omitted. One advantage is that drying step 3 may (also) be omitted.

(10) Different alternative sequences are conceivable. For example, the grinding step 4 may be performed after the CO2 extraction step(s). In that case, the PVB flakes are considerably more brittle and easier to mill. On the other hand, small flake size pf the PVB flakes within the above described range is advantageous for the alkaline washing step and/or CO2 extraction as they balance the possibility to bend the flakes during mechanical action and provide particles that are small enough to provide particulate material which is easily handled in conventional production equipment, e.g. conveyors, pipes etc.

(11) In commercial practice, the most cost-efficient solution will be used. In particular, there is an incentive to omit the water washing step as this also avoids the energy-intensive drying step. Further omitting the alkaline washing step and further avoids disposal of water borne residues from the alkaline washing step to the public drains and/or local water treatment or at least pre-treatment of the waste water fraction in order to allow the production site to discharge waste water to the public waste sewage collection and/or treatment systems. The alkaline washing step is for example avoided when relatively pure fractions of PVB are treated, e.g. virgin PVB that originates from cut-away surplus PVB from products during manufacturing thereof, e.g. along the edges of a newly produced laminated glass product.

(12) This embodiment is preceded by one or more initial pre-treatment steps. The pre-treatment steps may comprise one or more of the following steps: Separating PVB interlayers from glass layers in laminated glass, e.g. car windshields or architectural glass or glass used for production of furniture. Milling to reduce particle size of the PVB fraction and/or the glass fraction, sorting, e.g. sorting metallic fractions, such as aluminium metallic pieces, or sorting undesired coloured PVB material from desired uncoloured PVB material, and/or removal of undesired components, such as separation of the glass fraction from the valuable PVB fraction.

(13) These separations milling and/or sorting steps may be carried out in a known system as discussed in WO2008/000273 A, which is incorporated herein by reference.

(14) A preferred equipment for performing the above-mentioned separation, milling and/or sorting step(s) as well as the alkaline washing step or steps are preferably carried out in a sorting and washing system as shown in FIG. 4, and as is disclosed in WO2008/000273 A. The system comprises four main components: a first process chamber 8, a second process chamber 9, an approximately horizontal washing drum 10 and an upwards inclining screw conveyor 11. Comminute laminated glass produced by a not shown previous process is fed to a funnel or inlet 12 in the facility in chamber 8. Glass and other particles are separated off in chamber 9. The drum 10 and the screw conveyor 11, after which cleaned PVB film pieces are discharged, possibly together with some process water at the outlet. In principle, the four main process steps may be described as coarse comminution of the material in chamber 8, finer comminution of material and separating off heavy particles in chamber 9. Subsequently, the PVB material in the form of PVB flakes or pieces are washed in drum 10 in alkaline water at pH of 11-14 as described above by adding an alkaline washing solution to the drum 10 through not shown inlet means. The alkaline washing solution is discussed above. After the washing step in drum 10, the PVB flakes are flushing with water, e.g. in the specially designed screw conveyor 11.

(15) The screw conveyor 11 may transfer the PVB flakes into a not illustrated drying unit. Drying may e.g. be provided in an air-drying unit.

(16) The method for the processing of PVB using pressurized CO2 extraction may use supercritical or liquid CO2 in the CO2 extraction step(s). Suitable suitable equipment may be used as described below.

(17) The inventors have found that liquid CO2 between 20 to +30 C. and applied at a pressure of 30-70 bars or preferably 40-60 bars while subjecting to mechanical action is highly useful, efficient and, in particular, cost-effective.

(18) From the washing station or from drying or from intermediate storage after drying, the PVB flakes are subjected to extraction with CO2. A sealable container 13 is provided with stirring means such as a rotating mixer or as shown in FIG. 3 a rotating drum 14. PVB flakes are loaded into the rotating drum, e.g. after being bagged in large textile bags.

(19) The sealable container 13 is sealed and a vacuum is optionally applied as discussed above.

(20) Then pressurized CO2 is supplied to the sealed container 13 through supply pipe 17a from a first CO2 storage 15, which stores recycled CO2. Alternatively, or in combination therewith, CO2 may be supplied from a second CO2 storage or supply 16, e.g. to replenish CO2 that escapes the system with product streams.

(21) The drum 14 is rotated during extraction, and after a time period described above, the liquid CO2, is extracted from the sealed container 13 and transferred to the distillation unit 18.

(22) The liquid CO2 now contains extracted plasticizer, other extracted components, e.g. colorants, and/or degradation products or polluting components etc. from the PVB flakes, such as butyric acid or butyric aldehyde.

(23) The liquid CO2 fraction is subjected to distillation in the distillation unit 18 as described above.

(24) The liquid CO2 is vaporized in the distillation unit 18 and the gaseous CO2 is withdrawn from the distillation unit through a gas outlet 19. The liquid fraction is withdrawn from the distillation unit 18 via a liquid outlet 20.

(25) The liquid fraction may be blown out from the distillation unit 18 to a liquid storage container (not shown) as discussed above.

(26) The gaseous CO2 is then compressed in a compressor 21 to increase the pressure and condense the gaseous CO2 into a liquid.

(27) The compression increases the temperature of the liquid CO2. Thus, the compressed liquid CO2 is supplied to a heater 22, e.g. a heating coil, in the sealable container 13. Similarly, Liquid CO2, which exits the compressor 21 is supplied to a second heater 23, which is provided in the distillation unit 18.

(28) The liquid CO2 from the compressor 21, from the first 22 and/or second 23 heaters is then directed to the first CO2 storage for intermediate storage.

(29) If necessary, the liquid CO2 is cooled in a cooling unit 24 before feeding into to the first CO2 storage container 15.

EXAMPLES

Example 1

(30) 50 kg PVB flakes (or an alternative weight as indicated in table 1 below) having an average length and average width of approx. 10 mm are placed in textile bags each comprising 10 kilos of PVB flakes. The bags are sealed and placed in a 200 l pressure tight rotating drum extraction machine, marketed as SiOx P35 provided by SiOx in Sweden. Initially, the rotating drum chamber is evacuated to a pressure of approx. 0.1 bars (absolute) for a period of minimum 30 seconds in order to remove any atmospheric air in the system and to extract and remove volatile compounds such as butoxy ethanol from the PVB flakes.

(31) Prior to CO2-extraction the PVB flakes were subjected to an alkaline washing step in a process equipment as described in WO2008/000273 A. The alkaline washing step is carried out using wash water to which sodium hydroxide was added to obtain a pH of 11-14. In all the examples, a pH concentration of NAOH is adjusted to 11.30.1 was used as a washing solution. During CO2 extraction the PVB flakes are treated with approx. 80 liter/70 kg of liquid CO2. The temperature is maintained at 20 C. and the pressure is maintained at 55 bars above atmospheric pressure. The extraction step is carried out for 5 minutes/300 seconds.

(32) The liquid CO2 is then discharged into a distillation vessel from which pure CO2 is recovered into a CO2 storage vessel using a compressor and a cooler, whereas extracted plasticizer is retained in the distillation vessel. From time to time, the plasticizer can be blown out from the distillation vessel from the distillation vessel using the CO2 pressure inside the distillation vessel. The blown-out fraction is then weighed. The main component of the extracted fraction is plasticizer(s).

(33) The CO2 extraction step is repeated 3, 6 or 12 times as indicated in table each example below (washprogram/e.g. 3300 s).

(34) Table 1 below summarizes the results obtained with varying repetitions of a standardized CO2 extraction step which is set to 300 seconds (5 minutes). In all examples post-consumer PVB windshield interlayers were processed.

(35) TABLE-US-00001 TABLE 1 Wash Difference in program weight before Moisture Moisture (Number, and after before after Batch duration of extraction extraction extraction number cycles) Weight with CO.sub.2 with CO.sub.2 with CO.sub.2 #3 3 300 s 60 kg 4.60% 1.61% 1.41% #4 6 300 s 12 kg 9.29% 1.61% 1.44% #8 3 300 s 50 kg 5.83% 1.61% 1.40% #39 3 300 s 50 kg 3.47% 2.64% 1.13% #56 3 300 s 50 kg 3.58% 2.64% 1.66% #76 12 300 s 50 kg 12.29% 1.59% 1.29% #82 12 300 s 50 kg 9.27% 1.59%

(36) About 50% or more removal of the total plasticizer content is obtained in all examples. The treated PVB flakes are non-tacky, easily dispersible, easily grindable and non-smelling.

(37) With a ratio of 6 kg CO2/1 kg PVB using 3 cleaning cycles, the extraction level of approximately 50% by weight reduction of the content of plasticizer is achieved.

Example 2

(38) This example is carried out to check the evaporation of CO2 from the extracted PVB flakes and determine the best possible time at which the weight after extraction can be determined. Samples of extracted batches #3 (1001.5 g) and #82 (1002.2 g) of example 1 were each placed in a container. The moisture content is determined before the extraction and a day after the CO2 extraction (see table 1).

(39) The weight of the PVB sample+filter is noted in table 2.

(40) TABLE-US-00002 TABLE 2 Time Weight (g)- Weight (g)- (minutes) sample #3 sample #82 0 1009.9 1007.7 5 1007.2 993.7 15 1001.7 976.9 30 992.8 961.9 45 987.8 951.4 60 981.4 944.2 90 973.7 933.4 120 967.9 926.0 After 1 day 955.4 908.6

(41) This example shows that CO2 is present in the flakes after extraction with CO2. This CO2 and diffuses into the surrounding air for at least a few hours. Thus, in order to determine the most precise extent of extraction of plasticizer, it is preferable to wait for at least one day before determining the weight of the PVB flakes after the CO2 extraction program.

Example 3

(42) Flakes of PVB obtained from a specific constant source were extracted in a process using 3300 second extraction cycles as described in example 1. (Batch #1-#3; Batch #5-#37, Batch #53-#54).

(43) We have weighed these flakes before extraction, 1867 kg, after and the washed/extracted flakes after two days, 1754 kg. The difference in weight between untreated and washed with an extraction program of 3300 s is 113 kg less. This is 6.04% by weight less.

Example 4

(44) Example 2 was repeated with the exception that the extraction with CO2 was carried out in 12300 seconds cycles. PVB is flakes of same origin (Batch #71-#87)

(45) We have weighted the PVB flakes before treatment, 900 kg, and after two days subsequent to CO2 extraction, 790 kg. The difference in weight between untreated and treated flakes with an extraction program of 12300 s is 110 kg less. This is 12.22% by weight less than before extraction.

(46) The weight of the extracted plasticizer withdrawn from the distillation column after treatment of batches #71-#87 is 46 kg.

Example 5

(47) A sample of batch #4 as mentioned above in table 1 was evaluated manually prior to treatment. The sample was dirty and was clearly covered with algae and colorations that indicated other microbial growth. The entire sample had a very clear smell of butyric acid. The residual glass content in batch #4 was determined to 4.5% by weight.

(48) The content of glass residues in the batch was determined by burning of a pooled sample of smaller samples taken evenly throughout the batch. The pooled sample was weighed and the PVB was burned off by means of a gas flame using a conventional Bunsen burner. The glass residues were weighed.

(49) Samples of batch #4 were taken after above mentioned CO2 extraction procedure. The content of potential contaminants butyric acid (CAS: 107-92-6), 2-butoxy ethanol (CAS: 111-76-2) and butylated hydroxytoluene (BHT; CAS: 128-137-0), an anti-oxidant used in PVB, was analyzed by means of gas chromatography in the approved laboratory CENTEXBEL, in Belgium.

(50) The amount of butyric acid, butoxy ethanol and BHT was determined to the following amount (in % by weight):

(51) Butyric acid: N/D (below detection level)

(52) Butxy ethanol: 0.0024% BHT: 0.08%

(53) The detection level is 0.001%.

(54) Although the invention has been illustrated and described in greater detail with reference to the preferred exemplary embodiment, the invention is not limited to the examples disclosed, and further variations can be inferred by a person skilled in the art, without departing from the scope of protection of the invention.

(55) For the sake of clarity, it is to be understood that the use of a or an throughout this application does not exclude a plurality, and comprising does not exclude other steps or elements.