METHOD FOR REMOVING FOREIGN MATERIALS FROM THE SURFACE OF AN ARTICLE

Abstract

The present invention relates to a method for removing a foreign material from the surface of an article comprising the following steps: i) providing an article having a surface covered at least partly with a foreign material; ii) contacting the article provided in step i) with a cleaning medium being an acid having a pKa in the range from −10 to 7 having a minimum concentration of 1 wt.-% and with a carrier medium having a density different from the density of the cleaning medium to obtain a mixture comprising the foreign material solved and/or dispersed in the cleaning medium, the carrier medium and the article free from the foreign material; iii) allowing the mixture obtained in step ii) to separate to obtain a heterophasic emulsion comprising at least a first phase comprising the carrier medium and the article free from the foreign material and a second phase comprising the cleaning medium and the foreign material solved and/or dispersed therein; iv) separating the phases obtained in step iii); and v) separating the article free from the foreign material from the carrier medium. Furthermore, the present invention relates to an installation for carrying out the inventive process.

Claims

1. A method for removing a foreign material from the surface of an article comprising the following steps: i) providing an article having a surface covered at least partly with a foreign material; ii) contacting the article provided in step i) with a cleaning medium being an acid having a pKa in the range from −10 to 7 having a minimum concentration of 1 wt.-% and with a carrier medium having a density different from the density of the cleaning medium to obtain a mixture comprising the foreign material solved and/or dispersed in the cleaning medium, the carrier medium and the article free from the foreign material; iii) allowing the mixture obtained in step ii) to separate, to obtain a heterophasic emulsion comprising at least a first phase comprising the carrier medium and the article free from the foreign material and a second phase comprising the cleaning medium and the foreign material solved and/or dispersed therein; iv) separating the phases obtained in step iii); and v) separating the article free from the foreign material from the carrier medium.

2. The method according to claim 1, wherein the article in step ii) is first contacted with the cleaning medium and afterwards with the carrier medium.

3. The method according to claim 1, wherein the article in step ii) is contacted simultaneously with the cleaning medium and the carrier medium.

4. The method according to claim 2, wherein the mixture comprising the cleaning medium and the article is subjected to sheer forces induced by mechanical mixing, preferably by agitation, pump-around loop, mechanical grinding, extrusion, addition of abrasive agents and/or is treated with ultrasound before contacting the mixture with the carrier medium.

5. The method according to claim 3, wherein the mixture comprising cleaning medium, carrier medium and the article is subjected to sheer forces induced by a mechanical mixing and/or is treated with ultrasound before step iii); and/or an agent for breaking the emulsion is added before or during step iv); and/or the density of the carrier medium is lower than the density of the cleaning medium.

6. The method according to claim 1, wherein the foreign material is selected from the group consisting of ink, labels, paper, paper board, card board, mono- or multilayer films, organic coatings, inorganic coatings, preferably vapour deposed metallic materials and non-metallic materials or aluminium, pigments, adhesives, glues, metals, organic waste, non-organic waste, odorous materials and mixtures thereof.

7. The method according to claim 1, wherein the cleaning medium is an acid selected from the group consisting of oleum, sulphuric acid, phosphoric acid, nitric acid, hydrochloric acid, hydrofluoric acid, boric acid, adipic acid, formic acid, acetic acid, and mixtures thereof; and/or the carrier medium is an oil.

8. The method according to claim 1, wherein at least a part of the surface of the article comprises a polymer; or at least a part of the surface of the article comprises a material selected from the group consisting of glass, ceramics, steel and mixtures thereof; and/or the article originates from post-consumer waste or post-industrial waste, post-commercial waste.

9. The method according to claim 1, wherein the density difference between the carrier medium and the cleaning medium is at least 550 kg/m.sup.3, preferably is in the range from 500 to 1800 and more preferably is in the range from 650 to 1000 kg/m.sup.3.

10. The method according to claim 1, wherein the cleaning medium is an acid having a concentration in the range from 10 to 100 wt.-%; and/or a pKa in the range from −5 to 5; and/or a minimum concentration of 10 wt.-%.

11. The method according to claim 1, wherein the cleaning medium is consisting of sulphuric acid having a concentration of 94 to 100 wt.-%.

12. The method according to claim 1, wherein the method comprises an additional step vi) of rinsing residual foreign material residues and/or degradation products thereof from the article, which is carried out after step v).

13. The method according to claim 1, wherein the method is conducted continuously and the carrier medium obtained after separation step (v) is reintroduced into the process in step (ii); and/or the cleaning medium obtained after step (iv) is reintroduced into the process in step (ii).

14. The method according to claim 1, wherein step v) is carried out by a solid liquid separation process; and/or the article is not decomposed or attacked during any of steps i) to vi).

15. An installation for carrying out the method according to claim 1, wherein said installation comprises at least a mixer for cleaning medium, carrier medium and article to be cleaned (2), a device for density separation of the cleaning medium and carrier medium (3), a drying device (5), a filtering device (6) and a device for separating cleaning medium and carrier medium (8).

16. The method according to claim 2, wherein the article in step ii) is first contacted with the cleaning medium until the foreign material is completely solved or dispersed in the cleaning medium.

17. The method according to claim 5, wherein sheer forces are induced by mechanical mixing selected from the group consisting of pump-around loop, mechanical grinding, extrusion, and addition of abrasive agents.

18. The method according to claim 7, wherein the carrier medium is an oil selected from the group consisting of mineral oil, silicon oil, vegetable oil and mixtures thereof and more preferably is mineral oil or is an organic solvent, preferably cyclohexane.

19. The method according to claim 8, wherein the surface of the article consists of a polymer selected from the group consisting of polyolefins, polyvinyl chloride, polyethylene terephthalate, polyamides, and mixtures thereof.

20. The method according to claim 14, wherein solid liquid separation process in step v) is selected from the group consisting of filtration, sieving, centrifugation, preferably by using a hydrocyclone and combinations thereof.

Description

[0079] Apparatus

[0080] The present invention relates also to an installation for carrying out the method according to the invention, wherein said installation comprises at least a mixer for cleaning medium, carrier medium and article to be cleaned (2) a device for density separation (3), a drying device (5), a filtering device (6) and a device for separating cleaning medium and carrier medium (8).

[0081] FIGS. 1 to 4 are illustrating the process and the installation according to the present invention, but are in no way to be regarded as limiting.

[0082] FIG. 1 shows a preferred embodiment of the process according to the present invention. The article to be cleaned (11) (e.g. pellets or flakes) is added together with the cleaning medium (12) in a mixer (2) to remove the foreign material from the article (11). The carrier medium (10) is put in a different mixer (1) and is subsequently added under mixing into the mixer (2) containing the cleaning medium with the dissolved foreign material (16) and the article (11). After a certain period of time mixing is stopped and time is given for separating the carrier medium including the cleaned article and the cleaning medium including the foreign material (16). The separation can take place in mixer (2) or in a separate device (3), preferably by the different density of the cleaning medium and the carrier medium. After the separation the carrier medium containing the cleaned article may be transferred to a filtering and washing device (4) and the cleaning medium containing the foreign material (16) may be transferred to a filtering device (6). The article from (4) free from foreign material (16) may be rinsed with water (9) in the filtering and washing device (4) and subsequently the washing water and the carrier medium may be transferred, optionally together with the cleaning medium from filtering device (6), into a container for neutralization (7). The remaining article containing washing water, but free from foreign material may be transferred to a drying device (5) where the cleaned article (15) may be separated from the washing water, which is removed as condensate (14). The filtrates from (4) and (6), which contain the dilute cleaning and carrier medium are collected in container (7). In this container (7) the mixture is treated with a base (13), preferably calcium hydroxide or aqueous ammonia, thereby neutralizing acid components. Subsequently the neutralized mixture containing neutralized carrier medium and water may be transferred to a container (8) for separating cleaning medium and carrier medium. The separation can also be performed in container (7). The waste water (17) is removed from the process and the carried medium may be transferred for re-use to mixer (1).

[0083] FIG. 2 illustrates another preferred embodiment of the process according to the present invention, which is in particular suited for the situation where the cleaning medium, which is used in far higher quantities than required for chemical and physical chemical reasons, is highly reactive, expensive and difficult to recover. In said embodiment a stable emulsion of the cleaning medium and the carrier medium is formed in an emulsifier (19). The achieved dilution of the cleaning medium allows to moderate the cleaning rate and renders the process, in many instances, more controllable and more efficient.

[0084] According to said embodiment the emulsion will have a perceived density which is proportional to the quantity and density of the individual medium components. The emulsion will have at most 3 phases once the cleaning has been completed. [0085] 1) A light solid phase under the upper surface of the emulsion, the solid particles having a density lower than that of the emulsion; [0086] 2) a heavy solid phase at the lower surface of the emulsion, where the solid particles have a density which is higher than that of the emulsion; and [0087] 3) a continuous emulsion phase.

[0088] In a first step according to said embodiment of the present invention carrier medium (10) and cleaning medium (12) are put in a device for emulsification (19). The article to be cleaned (11) is put together with the emulsion of the carrier medium (10) and cleaning medium (12) in mixer (2). After a certain period of time mixing is stopped and time is given for separating the carrier medium including the cleaned article and the cleaning medium including the foreign material (16). The separation can take place in mixer (2) or in a separate device (3a), preferably by the different density of the solid articles versus the apparent density of the emulsion as described above. After the separation in device (3a) the cleaned article is transferred together with some emulsion (=parts of the carrier and cleaning medium) into a second device for separation (3b). Water is added to device (3b) causing the emulsion to separate into a carrier phase which contains the cleaned article. The second solid phase containing the foreign and the remaining liquid phase (=mainly carrier medium) from device (3a) is transferred into a third separating device (3c). After separation of the phases in device (3b) the upper phase containing the carrier medium and the cleaned article may be transferred to filtering and washing device (4) and the lower phase may be transferred to the third separating device (3c). In the filtering and washing device (4) the article (15) free from foreign material (16) may be rinsed with water (9) and subsequently parts of the washing water and the carrier medium may be transferred into separating device (3c). The remaining washing water containing the article (15) free from foreign material (16) may be transferred to a drying device (5) where the cleaned article (15) may be separated from the washing water, which is removed as condensate (14).

[0089] After separating the phases in separating device (3c) the upper phase (=recycled carrier medium (18)) may be transferred for re-use to emulsifier (19). The lower phase containing the remaining dilute cleaning solution and the foreign material (16) are transferred into a container for neutralization and a base (13) may be added. The neutralized mixture is transferred from container (7) into a filtration device (6) and foreign material (16) and waste water (17) are separated.

[0090] The embodiment of the process according to the present invention illustrated in FIG. 3 is very similar to that according to FIG. 2. The article to be cleaned (11) is also mixed together with an emulsion made of the carrier medium and the cleaning medium, but after the mixing step the emulsion containing the solid constituents (=foreign material and article to be cleaned) is first filtered. The solid filter cake, containing parts of the emulsion as residual moisture as well as the foreign material and cleaned article, may be transferred to a separating device (3) in which the emulsion is broken. The density of the heavier medium phase containing the diluted cleaning medium, can be adjusted by addition of an appropriate material (in the case of sulphuric acid as cleaning agent that would be water). The foreign material with a density higher than the dilute cleaning medium is transferred to a separator (8). The filtrate from filtering device (6) and the lower phase from device (3) may be transferred to a separator (8) and further processed as already described above. The upper phase from device (3) may be transferred to a filtering and washing device (4) and be further processed as described for the embodiments according to FIG. 2.

[0091] FIG. 4 illustrates still a further preferred embodiment of the process according to the present invention. The difference to the embodiment illustrated in FIG. 3 is that the filtrate from the filtering device (6a) is transferred directly in a container for neutralization (7). The lower phase from separating device (3) and filtering and washing device (4) may also be transferred to container (7). After neutralisation with a base (13) the carrier medium and the neutralised cleaning medium may be separated in separator (8). The recycled carrier medium may be transferred for re-use to emulsifying device (19) and the foreign material (16) may be separated from waste water in a filtering device (6b).

LIST OF REFERENCE SIGNS

[0092] (1): Mixer for carrier medium [0093] (2): Mixer for cleaning medium, carrier medium and article to be cleaned [0094] (3): Device for density separation [0095] (4): Filtering and washing device [0096] (5): Drying device [0097] (6): Filtering device [0098] (7): Container for neutralization [0099] (8): Separator for cleaning medium and carrier medium [0100] (9): Water [0101] (10): Carrier medium [0102] (11): Article to be cleaned [0103] (12): Cleaning medium [0104] (13): Base [0105] (14): Condensate [0106] (15): Cleaned article [0107] (16): Foreign material [0108] (17): Waste Water [0109] (18): Recycled carrier medium [0110] (19): Device for emulsification of carrier medium and cleaning medium

[0111] The invention will now be described with reference to the following non-limiting examples.

[0112] Experimental Part

[0113] A. Materials Used

[0114] LDPE-Bags

[0115] LDPE-bags imprinted with blue, green and red ink and paper labels fixed with glue, commercially available from Borealis (see FIG. 5).

[0116] H.sub.2SO.sub.4

[0117] H.sub.2SO.sub.4 (96%, commercially available from Sigma Aldrich Corporation), H.sub.2SO.sub.4 having a lower concentration was obtained by dilution with distilled water.

[0118] Mineral Oil

[0119] The oil used for the testing was a mineral oil, commercially named Finavestan A360B, supplied by Total Belgium (density at 15° C.=870 kg/m.sup.3).

[0120] B. Deinking Trials

[0121] LDPE-bags as described above printed with ink were cryo-milled and treated with a mixture of mineral oil and sulphuric acid at different concentrations and different ratios oil to acid. The desired volume of sulphuric acid was added to a vial with a magnetic stirrer that contained the cryo-milled sample. The remaining missing volume of oil was added on top and the vial was shaken for a couple of seconds. Tests were performed with different oil to acid ratio and with two concentrations of sulphuric acid (96% and 70%). In these tests, 0.5 g of cryo-milled LDPE bags, 2.5, 5, 7.5 and 9 mL of acid and 7.5, 5, 2.5 and 1 mL of oil were used. All tests were made at room temperature and the results are summarized in below Table 1.

TABLE-US-00001 TABLE 1 Summary of deinking and separation of LDPE bags in oil-acid mixture. Conc. H.sub.2SO.sub.4 Ratio Test [%] oil:H.sub.2SO.sub.4 Visual evaluation 1 96 75:25 All inks removed 2 96 50:50 All inks removed 3 96 25:75 All inks removed 4 96 10:90 All inks removed 5 70 75:25 Green ink not fully removed 6 70 50:50 Green ink not fully removed 7 70 25:75 Green ink not fully removed 8 70 10:90 Green ink not fully removed

[0122] The visual observation showed a complete deinking of the LDPE bags in the case of use of 96% sulphuric acid. In the 70% sulphuric acid trials, the green ink is not fully removed. In both cases (96% and 70%), the sample is in the oil phase (FIGS. 6a and 6b).

[0123] The same procedure was applied for the trials summarized in Table 2. The oil: acid ratio was kept constant, but acids with different concentration were used. 0.5 g of cryo-milled LDPE bags, 1 mL of sulphuric acid and 9 mL of mineral oil were used and all tests were made at room temperature.

TABLE-US-00002 TABLE 2 Summary of deinking and separation of LDPE bags in oil-acid mixture. Conc. Time to H.sub.2SO.sub.4 Ratio settle Test [%] oil:H.sub.2SO.sub.4 [min] Visual evaluation 9 96 90:10 30 All inks removed 10 90 90:10 30 All inks removed 11 70 90:10 15 Green ink not fully removed 12 50 90:10 4 No inks removed

[0124] The visual evaluation of these tests gave similar results than the previous one in terms of ink removal. Lowering the sulphuric acid concentration reduces the effectiveness of deinking. On the other hand, the more diluted is the solution, the faster it settles (see FIG. 7).

[0125] Further tests were made in order to investigate the reuse of the acid and its effectiveness on deinking. For these tests, the oil to acid ratio of 25:75 and a concentration of 96% sulphuric acid were used. 0.5 g of cryo-milled LDPE bags, 7.5 mL of acid and 2.5 mL of oil were used. All tests were made at room temperature. After a couple of minutes, the acid portion is taken out and added to a new vial containing inked cryo-milled LDPE bags and 2.5 mL of oil. This step is repeated after an additional time.

TABLE-US-00003 TABLE 3 Summary of tests on the reuse of sulphuric acid for deinking. Conc. H.sub.2SO.sub.4 Ratio Test Reuse [%] oil:H.sub.2SO.sub.4 Visual evaluation 13 0 96 25:75 All inks removed H.sub.2SO.sub.4 light red 14 1 96 25:75 All inks removed H.sub.2SO.sub.4 red 15 2 96 25:75 All inks removed H.sub.2SO.sub.4 dark red

[0126] The reuse of the sulphuric acid proved to be efficient, and the separation of the cryo-milled sample does not take any longer from test 13 to test 15 (see FIG. 8).

[0127] Additional tests were performed, substituting the oil as carrier phase by cyclohexane, an organic solvent. These tests have been carried out following the procedure previously described for Table 1. The results are shown in Table 4 and FIGS. 9 and 10.

TABLE-US-00004 TABLE 4 Summary of tests with H.sub.2SO.sub.4-cyclohexane mixtures. Conc. Time to H.sub.2SO.sub.4 Ratio settle Test [%] cyclohexane:H.sub.2SO.sub.4 [s] Visual evaluation 16 96 75:25 <1 All inks removed 17 96 50:50 <1 All inks removed 18 96 25:75 <1 All inks removed 19 96 10:90 <1 All inks removed 20 70 75:25 <1 Green ink not fully removed 21 70 50:50 <1 Green ink not fully removed 22 70 25:75 <1 Green ink not fully removed 23 70 10:90 <1 Green ink not fully removed Plastic agglomerates

[0128] A fast, quasi-instantaneous, separation between the two phases is observed. All inks are removed as seen previously with the 96% sulphuric acid, whereas the green ink is not fully removed for the 70% sulphuric acid as cleaning medium.