RECYCLING PROCESS

Abstract

The present invention provides a process for separating cellulose from a feedstock, comprising the steps of: a) wetting the cellulose with a first solvent system to form wet cellulose; b) contacting the wet cellulose with a second solvent system to form a mixture; c) maintaining the mixture at a first temperature for a first period of time; d) maintaining the mixture at a second temperature for a second period of time to dissolve the cellulose; and e) removing the first and second solvent system containing the dissolved cellulose.

Claims

1. A process for separating cellulose from a feedstock, comprising the steps of: a) wetting the cellulose with a first solvent system to form wet cellulose; b) contacting the wet cellulose with a second solvent system to form a mixture; c) maintaining the mixture at a first temperature for a first period of time; d) maintaining the mixture at a second temperature for a second period of time to dissolve the cellulose; and e) removing the first and second solvent system containing the dissolved cellulose.

2. The process according to claim 1 further comprising e steps of separating polyester from the feedstock.

3. The process according to claim 2 wherein the steps for separating polyester from the feedstock precede the steps for separating cellulose from the feedstock.

4. The process according to claim 2 wherein the polyester comprises polyglycolic acid, polylactic acid, polycaprolactone, polyethylene adipate, polyhydroxyalkanoate, polyethylene terephthalate, polybutylene terephthalate, polytrimethylene terephthalate, polyethylene naphthalate, or combinations of two or more thereof.

5. (canceled)

6. The process according to claim 1 further comprising the steps of dissolving and removing dye stuffs or impurities from the feedstock.

7. The process according to claim 1 further comprising step f), wherein the cellulose is recovered from the first and second solvent systems.

8. The process according to claim 1 wherein he feedstock comprises textiles or fabrics.

9. The process according to claim 1 wherein the cellulose is present in the mixture in an amount of from 0.1% to 20% by weight of the mixture.

10. The process according to claim 1 wherein the first solvent system comprises an amide.

11. The process according to claim 1 wherein the first solvent system is present in the mixture in an amount of from 1% to 50% by weight of the mixture.

12. The process according to claim 1 wherein the second solvent system comprises an ionic liquid comprising an acid and a base.

13. The process according to claim 12 wherein the base has an aqueous pK.sub.a of at least 12.

14. The process according to claim 12 wherein the base comprises one or more nitrogen-containing functional groups.

15. The process according to claim 12 wherein the base comprises guanidine or a guanidine derivative.

16. The process according to claim 12 wherein the acid comprises a carboxylic acid of general formula RCOOH, wherein R is an optionally substituted hydrocarbyl group.

17. The process according to claim 16 wherein the optionally substituted hydrocarbyl group comprises between one and eight carbon atoms.

18. The process according to claim 12 wherein the acid comprises acetic acid.

19. The process according to claim 12 wherein the ionic liquid comprises one or more of 1,1,3,3-tetramethylguanidinium acetate 1,1,3,3-tetramethylguanidinium propionate; 1,2,3,3-pentamethylguanidiniumacetate; 1,1,2,3,3-pentamethylguanidinium propionate; 1,2-dimethyl-5,6-dihydro-4H-pyrimidinium acetate; 1,2-dimethyl-5,6-dihydro-4H-pyrimidinium propionate; 1,5-diazabicyclo[4.3.0]non-5-enium acetate; 1,5-diazabicyclo[4.3.0]non-5-enium propionate; 1,5,7-triazabicyclo[4.4.0]dec-5-enium acetate; and 1,5,7-triazabicyclo[4.4.0]dec-5-enium propionate.

20. The process according to claim 12 wherein the base is present in the ionic liquid in an amount greater than that of the acid.

21. The process according to claim 12 wherein the base is present in the ionic liquid in an amount of from 40 mol % to 80 mol %.

22. The process according to claim 12 wherein the acid is present in the ionic liquid in an amount of from about 20 mol % to about 60 mol %.

23. The process according to claim 1 wherein the temperature is greater than the second temperature.

24. The process according to claim 1 wherein the first temperature is in the range of from about 70° C. to about 120° C.

25. The process according to claim 1 wherein the second temperature is in the range of from about 20° C. to about 75° C.

26. The process according to claim 1 wherein the mixture is comprises no more than 4 wt % of water.

27. (canceled)

28. A process for separating polyester and cellulose from a feedstock using a solvent system comprising a cyclic urea and an ionic liquid, comprising a carboxylic acid and an optionally substituted guanidine.

29. (canceled)

30. process according to claim 1 wherein the first solvent system comprises a cyclic amide.

31. The process according to claim 1 wherein the solvent system comprises 1,3-dimethyl-2-imidazoladmone.

32. The process according to claim 14 wherein the one or more nitrogen-containing functional groups are selected from amine groups, imine groups, and/or amidine groups.

33. The process according to claim 12 wherein the base comprises 1,1,3,3-tetramethylguanidine.

Description

[0084] The invention will now be more particularly described with reference to the following examples and figures, in which;

[0085] FIG. 1 illustrates how the wt % of dissolved cellulose varies with the wt % of DMI in the mixture, and the ratio of acid:base in the IL.

EXAMPLE 1

[0086] Roughly chopped Post-Consumer Cotton (PCC) sheets, 7.5 g, was heated in a large excess of DMI at 110° C. for 1-2 hours. The excess DMI was removed and the DMI retention of the fabric was calculated to be 2.7 times its mass. In a separate vessel, TMGA (60:40 mol ratio TMG:Acetate) was prepared and kept hot at 110° C. To account for the total DMI in the system 30 g of extra DMI was added to the wet textile, to bring the final DMI wt % in the solution to 20 wt % and the cotton concentration to 5 wt %. The hot IL solution was transferred from its vessel into the vessel containing the wet textile with DMI and stirring was started with an overhead stirrer and standard impeller. Mixing of the fabric in the solvent was good, with all the fabric being “moved” around the flasks in a circular motion by the impeller whilst a strong vortex was seen. Within 20 minutes the fabric was fully homogenised in the solvent, at the “mash” undissolved stage at the high temperature. After 1 hour of cooling to room temperature without stirring, a clear and viscous solution was formed.

Comparative Example A

[0087] A solution of TMGA (60:40 mol ratio TMG:Acetate) and DMI was made up and stirred at 110° C. with an overhead stirrer on the lowest RPM speed. After 15 minutes of reaction and temperature equilibration, roughly chopped PCC was added to make a final solution of containing 20 wt % DMI and 5 wt % PCC. After ca. 40 minutes the mixture was observed to reach the point where the fabric was swelled and dispersed in the solvent. Upon cooling, the viscosity increased rapidly, and the bulk solution turned clearer, but there was still significant undissolved cotton in the solution. The solution was re-heated to 110° C. and stirred at a higher RPM for ca. 20 minutes. Upon cooling to room temperature, there were still pieces of undissolved cotton and the solution was not entirely clear, but very slightly opaque.

[0088] This comparative example demonstrates the importance of firstly wetting the cellulose with a first solvent system to form wet cellulose, before contacting the wet cellulose with a second solvent system. This systematic process allows for the cellulose to be fully dissolved.

Example 2

[0089] FIG. 1 shows what effect changing the wt % of DMI in the mixture, and the ratio of acid:base in the IL, has on the wt % of dissolved cellulose in the mixture.

[0090] The cotton and solvent mixtures were heated to 80° C. overnight and subsequently cooled to room temperature. The cellulose saturation limit (the maximum wt % of dissolved cellulose in the mixture) was determined when the solutions were cloudy, turbid or had undissolved fibres still present.

[0091] As demonstrated in FIG. 1, for the conditions as described, it was found that the wt % of dissolved cellulose peaks at around 55:45 60:40 mol % [TMGH]:[OAc] and 20-30 wt % DMI. This gave a maximum of 7.5 wt % PCC being dissolved.

[0092] Surprisingly, it was found that mixtures containing 50:50 mol % [TMGH]:[OAc] dissolved slightly less PCC (with a maximum of 5 wt %) compared to those using an excess of TMG. On the other hand, an excess of OAc (i.e. 45:55 mol % [TMGH]:[OAc]) prevented cellulose dissolution from happening.

[0093] At compositions with a greater than 70:30 mol % of [TMGH]:[OAc] it was found that cellulose dissolution ability decreases. Mixtures containing 80:20 mol % [TMGH]:[OAc] dissolved only a maximum of 2.5 wt % PCC, and mixtures containing 90:10 mol % [TMGH]:[OAc] were unable to dissolve any cellulose.

[0094] FIG. 1 also shows the effect of changing the wt % of the first solvent system (in this case, DMI) in the mixture on the wt % of dissolved cellulose in the mixture.

[0095] As can be seen in the figure, in the range of 0-10 wt % DMI the mixture can dissolve only a maximum of 5 wt % cellulose. The most cellulose (up to 7.5 wt %) can be dissolved in the range of 10-30 wt % DMI. This decreases at values of DMI greater than 30 wt %, and dramatically decreases at values of DMI greater than 40 wt %. It was found that no cellulose can dissolve in mixtures where DMI is present in an amount greater than 60 wt %.

Example 3

[0096] Table 1 shows whether or not samples of cellulose dissolved at different ratios of [TMGH]:[OAc], different wt % of DMI and different first temperatures. The ratios in the table relate to the ratio of [TMGH]:[OAc]. A cross indicates that the sample dissolved.

TABLE-US-00001 TABLE 1 % First Temperature = 110° C. First Temperature = 80° C. DMI 50:50 60:40 50:50 60:40 0 X X X 10 X X 20 X X X 30 X X X 40 X X

[0097] As can be seen from the table, cellulose is able to dissolve in mixtures of both 50:50 and 60:40 [TMGH]:[OAc] between 0-40 wt % DMI and with a first temperature of 110° C. However, with a first temperature of 80° C., none of the cellulose samples in the 50:50 mixtures were able to dissolve. On the other hand, the mixtures comprising 60:40 [TMGH]:[OAc] alongside 0-30 wt % DMI were able to dissolve cellulose.

[0098] This further demonstrates that those mixtures comprising an excess of TMGH performed better than those comprising a stoichiometric amount of TMGH and OAc.

Example 4

[0099] A range of DMI compositions (0-40 wt % of the mixture) and two ratios of [TMGH]:[OAc] in the ionic liquid (50:50 and 60:40) were used to demonstrate the effect on the second temperature and second period of time. 2.5 wt % and 5 wt % of PCC were used, and the results outlined in Tables 2 and 3. In all cases the first temperature was 110° C. The word “part” indicates that the mixture was mostly clear, but with some trapped fibres/cotton pieces, or not quite clear.

TABLE-US-00002 TABLE 2 50:50 [TMGH]:[OAC] 60:40 [TMGH]:[OAC] 2.5 Min. Average Average Min. Average Average wt % First Second Second First Second Second PCC Period Period of Tem- Period Period of Tem- DMI/ of Time Time perature of Time Time perature wt % (min) (min:sec) (° C.) (min) (min:sec) (° C.) 0 60  9:58 49 10 3:05 75 10 10  7:53 53 10 3:44 69.4 20 15 11:01 46 10 4:08 62.4 30 15 16:47 37 15 7:16 49 40 60 Overnight RT 15 27:48  RT (Part)

TABLE-US-00003 TABLE 3 50:50 [TMGH]:[OAc] 60:40 [TMGH]:[OAc] 5.0 Min. Average Average Min. Average Average wt % First Second Second First Second Second PCC Period Period of Tem- Period Period of Tem- DMI/ of Time Time perature of Time Time perature wt % (min) (min:sec) (° C) (min) (min:sec) (° C.) 0 60 21:06 32.6 30 6:33 62 (Part) (Part) 10 10 11:56 45.3 10 5:19 65 20 30 20:46 37.8 10 6:37 60 30 240 Overnight RT 45 19:14  33 40 60 1 + day RT 30 1 + hours RT (Part) (Part) (Part) (Part)

[0100] As can be seen from the tables, the second period of time is considerably quicker for 60:40 [TMGH]:[OAc] mixtures compared to 50:50 [TMGH]:[OAc] mixtures. Therefore, it is clear that cellulose is able to dissolve quicker in mixtures with a stoichiometric excess of TMGH.

[0101] Furthermore, 60:40 [TMGH]:[OAc] mixtures generally dissolve cellulose at a higher second temperature than 50:50 [TMGH]:[OAc] mixtures, and therefore requires less of a decrease in temperature from the first temperature. The lower decrease in temperature is advantageously energy saving.