FIBRES

Abstract

A process (1, 2) for processing feedstock containing cotton fibres and PET fibres, the process (1, 2) comprises: i. heating a suspension of feedstock containing cotton fibres and PET fibres in water at a temperature above 180° C. to produce a mixture comprising char; ii. removing the water from the mixture comprising char; iii. adding a base to the mixture comprising char to produce a terephthalate salt in a liquid phase; iv. removing the char from the liquid phase to produce dried char; v. acidifying the liquid phase to produce terephthalic acid.

Claims

1. A process for processing feedstock containing cotton fibres and PET fibres, the process comprising: i. heating a suspension of feedstock containing cotton fibres and PET fibres in water at a temperature above 180° C. to produce a mixture comprising char; ii. removing the water from the mixture comprising char; iii. adding a base to the mixture comprising char to produce a terephthalate salt in a liquid phase; iv. removing the char from the liquid phase to produce dried char; v. acidifying the liquid phase to produce terephthalic acid.

2. A process according to claim 1, further comprising shredding the feedstock prior to Step i.

3. A process according to claim 1, wherein the ratio of water to feedstock is between 4:1 to 8:1 (w/w).

4. A process according to claim 1, wherein Step i. comprises heating a suspension of feedstock containing cotton fibres and PET fibres in water at a temperature of between 180 to 240° C.

5. A process according to claim 1, wherein Step i. further comprises heating a suspension of feedstock containing cotton fibres and PET fibres in water under a pressure of greater than 2.0×10.sup.6 Pa (20 bar).

6. A process according to claim 2, wherein Step ii. Comprises removing the water from the mixture comprising char via filtration.

7. A process according to claim 1, further comprising recovering ethylene glycol from the water removed in Step ii. of the process.

8. A process according to claim 1, wherein Step iii. comprises adding a base comprising ammonia and/or ammonium hydroxide to the mixture comprising char to produce diammonium terephthalate in a liquid phase.

9. A process according to claim 8, wherein Step iii. is performed at a temperature, e.g. between 0 to 40° C.

10. A process according to claim 1, wherein Step iv. comprises filtering the char from the liquid phase and further comprises drying the filtered char to produce a solid fuel.

11. (canceled)

12. A process according to claim 1, further comprising forming pellets and/or briquettes from the char to form a solid fuel.

13. A process according to claim 1, further comprising Step vi. purifying the liquid phase by contacting the liquid phase with one or more of activated carbon or clay.

14. A process according to claim 12, wherein Step vi. is performed after Step iii. and before Step v.

15. A process according to claim 12, comprising subsequently removing the activated carbon and/or clay by filtration.

16. (canceled)

17. A process according to claim 1, wherein the pure terephthalic acid is collected via filtration.

18. A process according to claim 1, further comprising Step vii. torrefaction of the mixture comprising char.

19. A process according to claim 18, wherein Step vii. is performed after Step ii. and before Step iii. of the process.

20. A process according to claim 18, wherein Step vii. is performed at a temperature between 200 to 280° C.

21. A process according to claim 18, wherein Step vii. is performed for less than one hour.

22. Terephthalic acid produced from the process of claim 1.

Description

[0064] Embodiments of the invention will now be described by way of example only with reference to the accompanying drawings in which:

[0065] FIG. 1 is process for producing solid fuel and terephthalic acid from fabric waste containing cotton fibres and PET fibres, according to a first embodiment of the invention; and

[0066] FIG. 2 is process for producing solid fuel and terephthalic acid from fabric waste containing cotton fibres and PET fibres, according to a second embodiment of the invention.

[0067] Referring now to FIG. 1, there is shown a process 1 for producing solid fuel, e.g. bio-coal, and terephthalic acid from fabric waste containing cotton fibres and PET fibres, according to a first embodiment of the invention. The process 1 comprises six steps.

[0068] In Step 1 of the process, the feedstock is shredded into the smallest pieces possible, e.g. using a shredder. The feedstock is a mixture of cotton and PET (polyethylene terephthalate) fibres.

[0069] In Step 2, the shredded feedstock is converted into char. The shredded feedstock is added to a reactor and mixed with a suitable amount of water in a ratio of between 4:1 to 8:1 volume to weight of water to shredded feedstock. The shredded feedstock and water mixture is then subjected to an elevated temperature. The reaction conditions are 200 to 220° C. for 4 hours at 23 bar. In use, the reactor is a sealed vessel. A suitable reactor for use in this step is that described in EP2719748 B1 or EP2366757 E1.

[0070] After this step, the char may additionally contain monomers of the PET polymer, e.g. terephthalic acid and/or ethylene glycol.

[0071] In Step 3, the char is dewatered, i.e. the water is removed from the char. This may be performed using via filtration using a screen with a rinse. However, this step may also be performed using another suitable solid-liquid separation process such as centrifugation.

[0072] The dewatering step may be a multistep process, e.g. filtering and subsequent centrifugation.

[0073] Advantageously, the process water removed from the char may optionally be reused in Step 2 of the process to add to more feedstock and heat in the reactor.

[0074] In embodiments of the process, ethylene glycol (originating from the PET fibres) may be recovered from the water phase. Advantageously, terephthalic acid is poorly soluble in water, and therefore remains associated with the char solid phase.

[0075] In Step 4, a base, e.g. ammonia, is added to the dewatered char. This may be performed at room temperature. In embodiments wherein the base is ammonia, the ammonia may be added to the char as ammonium hydroxide. This step results in solid char and a liquid phase containing di-ammonium terephthalate.

[0076] In Step 5a, the solid char is separated from the liquid phase, for example, using a filter press. The solid char is dried. In embodiments, the solid char may be pelletised or used to form briquettes for use as a fuel.

[0077] In Step 5b, the liquid phase is then purified. In addition to crude terephthalic acid in the form of di-ammonium terephthalate, the liquid phase may further contain dyes and other water-soluble organic molecules. In this embodiment, purification comprises contacting the liquid phase with activated carbon and/or clay (e.g. bentonites and/or acid activated clay) to remove said dyes and other water-soluble organic molecules. The activated carbon and/or clay is removed, e.g. via filtration, to provide a clear filtrate containing di-ammonium terephthalate.

[0078] Advantageously, the activated carbon and/or the clay may be regenerated for re-use in the process.

[0079] In Step 6, the pH of the clear filtrate containing di-ammonium terephthalic acid is reduced using concentrated hydrochloric acid to pH 5. In this step, the crude di-ammonium terephthalate precipitates out to form pure terephthalic acid in greater than or equal to 99.9% purity. This may be collected via filtration.

[0080] The waste effluent is preferably recycled.

[0081] Referring now to FIG. 2, there is shown a process 2 according to a second embodiment of the invention. The process 2 comprises many similar steps to the process 1 shown in FIG. 1. Only the differences will be further described.

[0082] Steps 1 to 3 of the process are performed in a like-manner to that described previously for the process 1.

[0083] The process 2 comprises an additional step, Step 7, which is performed after Step 3. In Step 7, the char from Step 3 undergoes a torrefaction process. This is performed at 240° C. for 30 minutes.

[0084] Advantageously, energy from the steam produced in the torrefaction process may be recovered. More advantageously, the torrefaction process removes humic acid from the cotton component of the feedstock.

[0085] The torrefied char produced in Step 7 is then used in Steps 4 to 6, which are performed in a like-manner to that described previously for the process 1.

[0086] In this embodiment, Step 5 involves the use of activated carbon only, rather than using clay.

[0087] The invention will now be further described with reference to the following non-limiting Examples.

EXAMPLE 1 USING PROCESS 1 OF THE INVENTION

[0088] The feedstock comprised a 70:30 ratio of cotton to PET fabric. The feedstock was shredded into pieces having an average length of 15 mm. The shredded feedstock (6g) was added to a reactor with a capacity of 55 mL. Water (36 mL) was added to the reactor in a 6:1 mass ratio of water to feedstock. The mixture was heated for 4 hours at 220° C. to produce a char mixture in water. The mixture was cooled to room temperature and the water was removed using a screen. Ammonium hydroxide (25%) was added to the filtered char mixture. The solid char was removed from the liquid phase via filtration. The solid char was pelletised to produce fuel having an energy value of 19 MJ/kg. The yield of pelletised char was 50% on a dry basis.

[0089] Activated carbon and clay were contacted with the liquid phase. Once the liquid phase had turned colourless, the activated carbon and clay were removed via filtration. The resulting clear filtrate was acidified to pH 5 using HCl (12M). The precipitate was removed via filtration to produce terephthalic acid with a purity of 99.9% in a yield of 60%.

EXAMPLE 2 USING PROCESS 2 OF THE INVENTION

[0090] The feedstock comprised a 70:30 ratio of cotton to PET fabric. The feedstock was shredded into pieces having an average length of 15 mm. The shredded feedstock (6g) was added to a reactor with a capacity of 55 mL. Water (36 mL) was added to the reactor in a 6:1 mass ratio of water to feedstock. The mixture was heated for 4 hours at 220° C. to produce a char mixture in water. The mixture was cooled to room temperature and the water was removed using screen. The char mixture underwent a torrefaction process at 240° C. for 30 minutes. Ammonium hydroxide (25%) was added to the filtered char mixture. The solid char was removed from the liquid phase via filtration. The solid char was pelletised to produce fuel having an energy value of 25 MJ/kg. The yield of pelletised char was 40% on a dry basis.

[0091] Activated carbon was added to the liquid phase. Once the liquid phase had turned colourless, the activated carbon and clay were removed via filtration. The resulting clear filtrate was acidified to pH 5 using HCl (12M). The precipitate was removed via filtration to produce terephthalic acid with a purity of 99.9% in an 89% yield.

[0092] It is shown that, although the yield of pelletised char in Example 2 is 20% lower than the yield of pelletised char in Example 1, the calorific value of the char in Example 2 is 30% higher than that produced in Example 1. Therefore, the solid char of Example 2 is a more valuable product.

[0093] It is thought that the torrefaction step removes the water from the char mixture to reduce the amount of water from 40 w/w % in the char mixture to 10 w/w % in the char prior to pelletising.

[0094] Additionally, torrefaction of the char mixture in Example 2 appears to at least partially remove the colour of the char mixture. This further aids removal of, for example, humic acid, dyes and other organic compounds in the process.

[0095] It will be appreciated by those skilled in the art that several variations to the aforementioned embodiments are envisaged without departing from the scope of the invention.

[0096] It will also be appreciated by those skilled in the art that any number of combinations of the aforementioned features and/or those shown in the appended drawings provide clear advantages over the prior art and are therefore within the scope of the invention described herein.