METHOD FOR PROCESSING STRAW

Abstract

Described herein is a method for processing straw into an intermediate straw product. The method comprises: (a) treating straw with an alkaline solution having a p H of between about 10 and about 14, at a temperature of between about 20° C. and about 80° C., for a period of between about 6 hours and about 30 hours; (b) separating excess alkaline solution and the treated straw from each other; and (c) maintaining the treated straw in an anaerobic environment at a temperature of between about 30° C. and about 45° C., for a period of between about 6 hours and about 30 hours to produce an intermediate straw product. Also described is an intermediate product produced by the method; a method for extracting lignin from straw; lignin thereby produced; a method for extracting cellulose fibres from straw to produce paper pulp; cellulose fibres and paper pulp thereby produced; a method for producing a paper pulp product or a paper product; a product thereby produced; and a container and apparatus for processing straw according to the methods described.

Claims

1. A method for processing straw into an intermediate straw product, the method comprising: (a) treating straw with an alkaline solution having a pH of between about 10 and about 14, at a temperature of between about 20° C. and about 80° C., for a period of between about 6 hours and about 30 hours; (b) separating excess alkaline solution and the treated straw from each other; and (c) maintaining the treated straw in an anaerobic environment at a temperature of between about 30° C. and about 45° C., for a period of between about 6 hours and about 30 hours to produce an intermediate straw product.

2. A method according to claim 1, wherein the intermediate straw product can be further processed and/or refined into cellulose fibres useful for paper production.

3-10. (canceled)

11. A method according to claim 1, wherein before step (c) the method comprises removing air to produce an anaerobic environment.

12-13. (canceled)

14. A method for extracting cellulose fibres from straw to produce paper pulp, the method comprising: (i) processing straw into an intermediate straw product according to a method of claim 1; and (ii) further processing the intermediate straw product into paper pulp.

15. A method according to claim 14, which comprises, (d) mixing the intermediate straw product with water and pulping the straw and water mixture; (e) processing the pulped straw to obtain cellulose fibres from the straw; and (f) obtaining the pulp.

16-17. (canceled)

18. A method according to claim 15, wherein step (e) comprises one or more of the following sub-steps: (e1) filtering the pulped straw through a filter to extract cellulose fibres from the straw; (e2) refining the filtered pulp straw in a refiner to extract further cellulose fibres from the straw; (e3) screening the refined pulp to separate lignin and/or ash from the cellulose fibres; (e4) washing the screened pulp with water to separate more lignin and/or ash; and (e5) returning liquid from step (e2) for re-use in a method according to any preceding claim.

19. A method according to claim 15, wherein step (e) may comprise processing the pulped straw by de-flaking.

20. A method according to claim 14, which comprises recovering lignin that has been separated from the cellulose fibres.

21. A method according to claim 1, wherein the alkaline solution comprises caustic soda.

22. A method according to claim 1, wherein the alkaline solution comprises sodium carbonate, potassium hydroxide or potassium carbonate.

23. A method according to claim 1, wherein the pH at step (a) is about 14.

24. A method according to claim 1, wherein the temperature at step (a) is about 80° C.

25. A method according to claim 1, wherein the time period at step (a) is about 12 hours.

26. A method according to claim 1, wherein step (a) comprises one or more of the following sub-steps: (a1) placing the straw in a first container; (a2) mixing water and an alkali in a second container to produce an alkaline solution having a pH of between about 10 and about 14; (a3) heating the solution in the second container to a temperature of between about 20° C. and about 80° C.; (a4) transferring the heated solution from the second container to the first container; (a5) leaving the solution in the first container with the straw for a time period of between about 6 and about 30 hours at a temperature of between about 20° C. and about 80° C. during which time period some of the solution is absorbed by the straw; and (a6) transferring the remaining solution in the first container to the second container.

27. (canceled)

28. A method according to claim 1, wherein the temperature at step (c) is about 35° C.

29. A method according to claim 1, wherein the time period at step (c) is about 12 hours.

30. A method according to claim 1, wherein the straw is placed in a holder prior to step (a).

31. A method according to claim 30, wherein the holder is arranged to be movable between a plurality of positions to allow for the straw to be immersed in the alkaline solution, and then transferred to a pulper tank.

32-38. (canceled)

39. A container for processing straw according to a method of claim 1.

40. A container according to claim 39, wherein the container comprises (i) an inlet for introducing alkaline solution into the container, (ii) a first outlet for removing excess alkaline solution from the container, (iii) a second outlet for removing air from the container, and (iv) a heater for heating alkaline solution in the container.

41-49. (canceled)

Description

DETAILED DESCRIPTION

[0092] Embodiments of the invention will now be described solely by way of example and with reference to the accompanying Figure which shows apparatus for carrying out the process of the present invention.

[0093] Within this specification, the term “about” means plus or minus 20%, more preferably plus or minus 10%, even more preferably plus or minus 5%, most preferably plus or minus 2%.

[0094] Within this specification, the term “straw” means any cellulose-containing plant material capable of being used for producing paper pulp, preferably which is “straw-like”.

[0095] Preferably, the term “straw” means the stalks of cellulose-containing plants, for example cereal plants, capable of being used for producing paper pulp.

[0096] Specific examples of the term “straw” include wheat, barley, oats, rye, rice, hay.

[0097] With reference to FIG. 1, there is shown apparatus 2 for carrying out a process for extracting cellulose fibres from straw 4 to produce paper pulp. The process comprises the following steps:

[0098] (a) immersing the straw 4 in a first tank 6 in an alkaline solution having a pH of 10-14 and a temperature of 20-80° C. for a period of 6-30 hours;

[0099] (b) removing excess alkaline solution;

[0100] (c) removing air from the first tank 6 to provide an anaerobic environment in the first tank 6 and maintaining a temperature of 30-45° C. in the first tank 6 for a time period of 6-30 hours to produce an intermediate straw product;

[0101] (d) transferring the intermediate straw product from the first tank 6 to a pulper tank 10 and mixing water with the intermediate straw product in the pulper tank 10 and pulping the straw and water mixture;

[0102] (e) processing the pulped straw to obtain cellulose fibres from the straw; and

[0103] (f) obtaining the pulp.

[0104] In preferred embodiments, alkaline solution is added to the container during step (a) to maintain the level of alkaline solution at a predetermined level.

[0105] Step (e) may comprise the following sub-steps: [0106] (e1) filtering the pulped straw through a filter 12 to obtain cellulose fibres from the straw; [0107] (e2) refining the filtered straw in a refiner 14 to cause the cellulose fibres in the pulp to separate from each other and thereby obtain further cellulose fibres from the straw; [0108] (e3) screening the refined pulp to separate lignin and ash from the cellulose fibres; [0109] (e4) washing the screened pulp with water to separate more lignin and ash; and [0110] (e5) returning liquid from step (e2) for re-use in the process.

[0111] Alternatively, or in addition, step (e), for example step (e2), may be one in which the pulped straw is processed by de-flaking.

[0112] Step (a) may comprise the following sub-steps: [0113] (a1) placing the straw in the first tank 6; [0114] (a2) mixing water and an alkaline in a second tank 8 to produce an alkaline solution having the pH of 10-14; [0115] (a3) heating the solution in the second tank 8 to 20-80° C.; [0116] (a4) transferring the heated solution from the second tank 8 to the first tank 6; [0117] (a5) leaving the solution in the first tank 6 in contact with the straw for a time period of 6-30 hours at a temperature of 20-80° C. during which time period some of the solution is absorbed by the straw; and [0118] (a6) transferring the remaining solution in the first tank 6 to the second tank 8.

[0119] The water for mixing with the straw at step (e) is provided from a water tank 16.

[0120] The liquid in the first tank 6 is heated by a heater 18.

[0121] The liquid in the second tank 8 may be heated by a heater (not shown) before being transferred to the first tank 6.

[0122] The pulper tank 10 has a frusto-conical bottom portion 20 in which some ash/sand is removed.

[0123] The pulped straw is pumped by a pump 22 to the refiner 14. Paper pulp exits the refiner 14 via an outlet 24. Liquid pumps 26, 28, 30 are provided as shown and in contact with the filter 12 in which the lignin is separated. A vacuum pump 29 provides the required anaerobic conditions in the first tank 6 for the step (c) of the process.

[0124] The process described above with reference to the apparatus 2 is conducted such that the alkali is caustic soda (sodium hydroxide), the pH at step (a2) is 14, the temperature at step (a3) is 80° C., the time period at step (a5) is 12 hours, and the temperature at step (a5) is 80° C.

[0125] The step (a5) in the process is conducted with repeated checking intervals for initial time period. This initial checking is for checking the level of the liquid in the first tank 6 to ensure that the straw 4 stays covered. This is necessary because the straw 4 absorbs liquid. The initial checking is also for checking the pH of the liquid in the first tank 6. The checking intervals are every 30 minutes, with the initial time period being the first 4 hours.

[0126] Step (a6) is such that the transferred liquid is substantially all of the liquid which has not been absorbed by the straw 4. This transferred liquid is approximately 70% of the initially provided liquid. Approximately 30% of the initially provided liquid will have been absorbed by the straw. This transferred liquid is approximately 70% of the initially provided liquid. Approximately 30% of the initially provided liquid will have been absorbed by the straw.

[0127] The temperature at step (c) is 35° C., and the time period at step (c) is 12 hours.

[0128] The pulping at step (d) is for a time period of 10-20 minutes, and more preferably is 15 minutes.

[0129] The filtering at step (e1) is through a mesh filter. The mesh filter is a 6 mm mesh filter.

[0130] The filtered pulp at step (e2) is at a pH of 9-10. The filtered pulp at step (e2) is refined with a refiner 14 which is a double-disc refiner 14.

[0131] The straw 4 is placed in a holder 30 prior to step (a1). The holder 30 is a cage having mesh sides 32. The holder 30 has a solid lid 34 as shown.

[0132] The apparatus 2 includes a transport framework 36. The transport frame work 36 is shown schematically as having an upright 38 and a horizontal top rail 40. A transfer arrangement 42 is able to transfer the holder 30 when it has been loaded with the straw 4 to the first tank 6 as shown, and then to the second tank 8. When the holder 30 is above the second tank 8, its lid 34 is removed as shown in order to tip the straw 4 with its water content into the pulper tank 10. The transfer arrangement 42 thus enables the holder 30 to be movable between a plurality of positions to allow for the straw filling, the immersion in the first tank 6, the removal from the first tank 6, and the transfer to the pulper tank 10.

[0133] The pulper tank 10 acts as an extraction tank. The pulper tank 10 has a pulper (not shown) for pulping the straw and water mixture. The pulper may act as a mixture device. The pulper may be such that it uses a blade for effecting the pulping/mixing.

[0134] A filter (not shown) in the bottom portion 20 of the third tank 10 filters the pulped straw. Known pulpers used in the paper industry are able to be used to effect the required pulping, mixing and filtering.

[0135] As shown in FIG. 1, the pH control for the first tank 6 is controlled by a pH controller 44. The heater 18 connects to a radiator 46 inside the first tank 6. The pH control for this second tank 8 is controlled by a pH controller 48.

[0136] The process of the present invention is advantageous in that the lignin can be physically separated from the water using the filter 12, which may be a filter press. The cellulose fibres are extracted at low temperatures, and without using any pressure. Still further, as can be seen from FIG. 1, the first tank 6, the second tank 8 and the pulper tank 10 are connected by conduits so that the liquid can be re-circulated. The liquid containing the lignin is usually black but once the liquid has been filtered, the liquid can be re-circulated in the illustrated closed loop conduit system. The colour of the water is brown when the lignin has been removed. In comparison with known processes, the process of the present invention may take more time; however, it is more economical because it uses low temperatures and does not require pressure. Also, advantageously, the separated lignin can be recovered more easily than in known processes and then used for making lignin-based and/or containing products, for example as a filler in certain plastics.

[0137] Step (a) may be conducted solely in the first tank 6. Thus the first tank 6 may be used for preparing the alkaline solution, and then subsequently adding the straw. In this case, the immersion of the straw should be such as to ensure that alkaline solution is not lost from the first tank 6 whilst the holder 30 with the straw 4 is lowered into the first tank 6.

[0138] The various tanks, containers and holders employed in the apparatus 2 are preferably made of stainless steel but they may be made of other suitable and appropriate materials if desired. The pulp obtained from the outlet 24 may be further processed using existing known technologies prior to being used as pulp for the production of the paper products. Alternatively, the pulp direct from the outlet 24 can be used for the production of the paper products. The pulp may be used in the paper industry other than for producing newspapers so that, for example, the pulp may be used for providing paper tissues, paper hand towels, toilet rolls, cardboard, cardboard packaging and other paper articles.

[0139] It should be understood that various changes and modifications to the presently preferred embodiments described herein will be apparent to those skilled in the art. Such changes and modifications can be made without departing from the spirit and scope of the present invention and without diminishing its attendant advantages. It is therefore intended that such changes and modifications are covered by the appended claims.