WO2009111836A1

WO2009111836A1 - A method for granulating cellulose fibres

Info

Publication number: WO2009111836A1
Application number: PCT/AU2009/000299
Authority: WO
Inventors: Martin Ernegg
Original assignee: Zeo Ip Pty Ltd
Priority date: 2008-03-14
Filing date: 2009-03-13
Publication date: 2009-09-17

Abstract

A method for granulating cellulose fibres from a solid-liquid mixture comprising water and cellulose fibres, the method comprising: a) separating the mixture into wet fibres and water; and b) forming the wet fibres into a plurality of wet granules; c) drying the granules.

Description

A METHOD FOR GRANULATING CELLULOSE FIBRES

Technical Field

The disclosure relates to a method for granulating cellulose fibres.

Background

The applicant has previously developed a process for producing moulded pieces out of cellulose fibres in which the specific gravity of the moulded pieces approaches that of pure cellulose, 1.5. The process involves finely chopping and grinding cellulose fibres in the presence of water into micro-fibres prior to forming a fibre-water mixture in which the cellulose fibre content is about 1-10% by weight. The process subsequently involves shaping and drying the mixture of cellulose fibres and water into the moulded pieces. Details of the process and the moulded pieces produced by the process are set out in United States Patent 6,379,594. It would be useful to be able to grind and chop the cellulose fibres into micro- fibres at one location and readily transport the micro- fibres to another location where they are used to form the moulded pieces . For example, one manufacturer may produce the micro-fibres for distribution to various other manufacturers to use in producing the moulded pieces at different sites. However, it is generally not economically viable to store or transport the cellulose micro-fibres when in the fibre- water mixture because: a) a wet mixture will biodegrade or otherwise deteriorate in storage unless it is treated before being stored, which is both difficult and costly; and b) transporting the fibre-water mixture requires the transportation of large volumes of water which has an unacceptable economic cost and environmental impact. Summary of the Disclosure

According to a first aspect of the present invention, there is provided a method for granulating cellulose fibres from a solid-liquid mixture comprising water and cellulose fibres, the method comprising:

(a) separating the mixture into wet fibres and water; and

(b) forming the wet fibres into a plurality of wet granules; (c) drying the granules.

Preferably, the mixture comprising water and cellulose fibres is prepared in accordance with the processes described in United States Patent 6,379,594, the contents of which are incorporated herein by reference . In an embodiment, the solid-liquid mixture to be granulated has a solids content of 1-30% by weight. In some methods, the solid-liquid mixture to be granulated may have a solids content of 1-6% by weight and in other methods may have a solids content of 7-30% by weight. The solids content of the mixture is at least mostly cellulose fibres and typically all cellulose fibres. However, the solid-liquid mixture may also comprise a pigment or other colorant which makes up a fraction of the solids content of the mixture. In an embodiment, the cellulose fibres in the mixture comprise cellulose micro-fibres. In this embodiment "micro-fibres" means fibres which are 0.1mm to 0.05mm in size.

In an embodiment, steps (a) and (b) occur simultaneously.

In another embodiment, step (a) occurs prior to step (b) .

The separation step may be a physical separation step. In an embodiment, the wet fibres have a solids content of 6-50% by weight, preferably 10-50% by weight, preferably 20-50% by weight, more preferably 30-40% by weight .

In an embodiment, the method also comprises the step of curling the cellulose fibres.

The step of curling the fibres may occur simultaneously with step (a) .

In an embodiment, step (a) comprises passing the mixture through a screw separator.

The screw separator may comprise a screw located in a cage . The screw may rotate inside the cage about its longitudinal axis.

In an embodiment, the mixture enters one end of the screw.

The water separated from the mixture in the screw separator may pass out through the cage.

The turning action of the screw of the screw separator may curl the cellulose fibres.

In an embodiment, step (b) also occurs whilst passing the mixture through the screw separator. The wet granules may be formed by the screw separator dewatering the mixture and preferably pass out of the end of the screw separator opposite to the end in which the mixture enters .

In another embodiment, step (b) occurs by using a granulator.

In another embodiment, step (a) comprises using centrifuge .

In another embodiment, step (a) comprises passing the mixture through a pressure filter, oscillating filter or any other suitable filter.

In another embodiment, step (a) comprises using capillary extraction.

In an embodiment, step (c) comprises heating the wet granules to no more than 220⁰C, preferably to a temperature of 14O⁰C to 160⁰C. Step (c) may also comprise extracting the evaporated water.

In another embodiment step (c) comprises using a swirl fluidizer to heat the granules and evaporate the water.

In an embodiment, steps (a) and (b) may occur prior to step (c) . In another embodiment, steps (a) , (b) and (c) occur simultaneously.

Steps (a) , (b) and (c) together may comprise spray drying the mixture to form dry granules comprising powder like particles. Any suitable spray drying process may be utilised and typically involves spraying the mixture through at least one nozzle.

In an embodiment, the mixture has a solids content of 1-20% by weight when fed into the spray dryer, preferably 1-6%. The dry fibres, after drying in the spray dryer may comprise the dried granules in the form of powder like particles.

The method may also comprise the step of (d) compressing the granules in larger granules. In an embodiment, step (d) comprises the step of pelletising the spray dried granules.

Any suitable pelletising process may be utilised and typically involves compacting multiple portions of the spray dried granules in dies . In an embodiment, the method may also comprise, prior to step (a) , heating the solid-liquid mixture, preferably to a temperature of approximately 160⁰C.

In an embodiment, the dried granules have a specific gravity of 0.2-1.0, preferably 0.2-0.7, most preferably 0.2-0.4.

The dried granules may have a water content of approximately 6-12% by weight.

According to a second aspect of the present invention, there is provided granules, produced according to the first aspect of the present invention.

According to a third aspect of the present invention, there is provided a method for forming an article from granules produced according to the first aspect of the present invention, the method for forming the article comprising the steps of:

(a) mixing the granules with water to form a solid-liquid mixture comprising cellulose fibres and water;

(b) shaping the mixture into the article_/ and

(c) hardening the article by drying.

In an embodiment, the method also comprises the step of leaving the granules to soak in the water, preferably for 1-12 hours, more preferably 3-6 hours.

In an embodiment, the method also comprises the step of adding pigments or other colorants to the solid- liquid mixture. Generally steps (b) and (c) are carried out in accordance with the steps of shaping and hardening the work piece (article) as described in United States Patent 6,379,594.

Detailed Description of Embodiments

A method of granulating cellulose fibres from a solid-liquid mixture of cellulose fibres and water has been developed by the applicant. By granulating the cellulose fibres, the fibres can be stored for long periods without risk of biodegradation or other deterioration and readily transported between a site where the cellulose fibres are prepared for use in forming an article and another site or sites where the articles are formed, without needing to also transport large volumes of water. Generally, the method involves the steps of separating the mixture into wet fibres and water and forming the wet fibres into a plurality of wet granules which are dried.

The solid-liquid mixture to be granulated has a solids content of 1-30% by weight. The majority of the solids content and typically all of the solids content in the mixture is cellulose fibres, which have been ground and/or chopped into micro-fibres (0.01-0.5mm in length) .

A fraction of the solids content in the mixture may be a pigment or other colorant .

The solid-liquid mixture to be granulated may be prepared by any suitable method for refining (ie. grinding and/or chopping) the cellulose fibres, such as LC/HC refining, ultra friction grinding, high pressure homogenizing, extruding, steam explosion, ultra sonic treatment, enzymatic fibre separation and chemical treatment for example. In a particular embodiment, the solid-liquid mixture is prepared in accordance with the processes described in US 6,379,594.

In one embodiment, the method of the present invention involves physically separating water out of the mixture comprising water and cellulose fibres by passing the mixture through a screw separator. The screw separator comprises a screw which rotates about its longitudinal axis and is located in a cage. The mixture enters one end of the screw separator and is passed through the screw separator by the rotation of the screw. As this occurs, water is removed from the mixture by passing through the cage. The dewatered mixture exits the other end of the screw as wet granules having a solids content of 10-50% by weight, preferably 20-50% by weight, more preferably 30- 40% by weight. The separated water may or may not be collected for recycling.

The action of the screw causes the cellulose fibres to be curled. Advantageously, this acts against the cellulose fibres from binding together. This is desirable because if the cellulose fibres bind together they form strong interlinking bonds which are difficult to break without re-grinding and/or re-chopping, thus making it difficult to later use the granules by re-mixing with water and shaping to form articles. In other embodiments, the mixture is first separated into wet fibres and water by centrifuge, capillary extraction or by passing the mixture through a pressure filter, oscillating filter or any other suitable filter. After this separation step, the wet granules are formed from the wet fibres using a granulator.

After the wet granules are formed, they are dried by heating the granules to a maximum temperature of 220⁰C, preferably to a temperature of 140⁰C to 160⁰C, to evaporate the remaining water. The produced granules having a specific gravity of 0.2-1.0, preferably 0.2-0.7, more preferably 0.2-0.4 and a water content of approximately 6-12% by weight.

In another variation, the method for granulating cellulose fibres comprises spray drying the mixture comprising water and cellulose fibres. Any suitable spray drying process may be utilised and typically involves spraying the mixture through at least one nozzle. The mixture has a solids content of 1-20% by weight when fed into the spray drier, preferably 1-6%, and is typically pre-heated to about 16O⁰C. The granules produced by the spray drying are a plurality of powder-like particles. The granules formed in the spray drying process may be subsequently pelletised to form larger granules (pellets) using any suitable pelletising process. Typically, this involves compacting multiple portions of the spray dried mixture in dies.. However, in a further variation the dried granules are not pelletised but are left in the form of the powder-like particles.

The granules which may be in the form of pellets or powder produced according to the above embodiments may be packaged and transported as desired. They may also be used subsequently in a method for forming an article. This method comprises firstly mixing the granules with water to form a solid-liquid mixture comprising cellulose fibres and water. The granules may be left to soak in the water for a period of time, preferably for 1-12 hours, more preferably 3-6 hours. This is to enable the cellulose fibres to completely distribute into the water. Pigments or other colorants may be added to the mixture comprising water and cellulose fibres.

Once the cellulose fibres have been adequately mixed into the water, the solid-liquid mixture can then be shaped into the article and hardened by drying. Generally, the steps of shaping and hardening the article are carried out in accordance with the steps of shaping and hardening the work pieces (articles) as described in United States Patent US6,379,594.

EXAMPLES

In the following Examples, compositional percentages are weight percentages unless otherwise specified.

Example 1

A mixture of cellulose fibres and water was prepared firstly by dissolving Amcor RCW80 recovered wastepaper (shown in Figure 1) in water at 25⁰C under stirring conditions of 30rpm for 10 minutes in a drum mixer (shown in Figure 2) . The cellulose concentration in the mixture was 15%. This mixture (pulp) was then refined in a HC Andritz 22" refiner (shown in Figure 3) in accordance with the methods described in US6379594. Refining was conducted for different periods of time to prepare different samples. Sample 1 (Sl) was prepared by refining the pulp for 30 minutes and Sample 2 (S2) was prepared by refining the pulp for 50 minutes. A photograph of S2 as a wet pulp is shown in Figure 4.

The viscosity, compositional and dimensional properties of the refined samples were ascertained by conventional methods and are set out in Table 1 below. Table 1 : Refined Sample Properties

Example 2

Sl was dewatered in a fan separator (shown in Figure 5) having a screen slot size of 0.1mm. The fibre content at the outlet of the fan separator was 36%. The stiff pulp from the outlet of the fan separator was then run through a fluid bed drier, specifically a Kason Double-Deck Circular Vibratory Fluid Bed Processor (shown in Figure 6) together with a second stream of Sl which was not dewatered (having a fibre concentration of 15%) . The batch running temperature during operation of the fluid bed drier was 160°. The granules produced by the fluid bed drier had a moisture content of 9% and are shown in Figure 7.

To demonstrate the workability of the dried Sl granules, they were then "regenerated" (rewetted) by mixing with water in a high friction mixer (shown in Figure 8) at 600rpm for 60 minutes to produce a fibre and water mixture having a fibre content of 15%. This mixture was then formed into a solid article in accordance with the processes described in US6379594. Various physical properties of this article produced from the regenerated Sl granules were compared to that of an article produced from the original as-formed Sl, set out in Table 2 below. Table 2

Although the article produced from the regenerated S2 granules had satisfactory properties for use as a structural material, it was noted that the elasticity (Young Modulus) of the regenerated Sl granules was less than that of the as-formed Sl. Without wishing to be bound by theory, it is believed that this was due to insufficient mixing of the dry granules with the water in the high friction mixer which does not sufficiently disentangle the fibres from the entanglement that occurs as they are formed into the dry granules .

It was also found that the specific gravity of the dried granules should preferably not exceed 0.4. Again without wishing to be bound by theory, it is believed that granules which are created with a high density have greater fibre entanglement and thus are more difficult to disentangle upon regeneration by mixing with water, thus making the mixing process longer and less, economical.

Example 3

S2 was dewatered using a fluid press to increase the fibre content to 48% prior to being dried using a Gea swirl fluidizer (shown in Figure 9) . The air inputted to the swirl fluidizer had a temperature of 160⁰C. Dried granules of fibres were produced by the swirl fluidizer having a moisture content of 10%, and are shown in Figure 10.

To demonstrate the workability of the dried S2 granules, they were then "regenerated" (rewetted) by mixing with water in a high friction mixer at 600rpm for 60 minutes to produce a fibre and water mixture having a fibre content of 15%. This mixture was then formed into a solid article in accordance with the processes described in US6379594. Various physical properties of this article produced from the regenerated S2 granules were compared to that of an article produced from the original as- formed S2, set out in Table 3 below.

Table 3

Although the article produced from the regenerated S2 granules had satisfactory properties for use as a structural material, it was noted that the elasticity (Young Modulus) of the regenerated S2 granules was less than that of the as-formed S2. Without wishing to be bound by theory, it is believed that this was due to insufficient mixing of the dry granules with the water in the high friction mixer which does not sufficiently disentangle the fibres from the entanglement that occurs as they are formed into the dry granules .

Example 4 S2 was first diluted by mixing in additional water to reduce the fibre content of the composition to 6% for suitable processing in a spray dryer. This watery composition of S2 was then pre-heated to 160⁰C prior to being spray dried by a Gea Mobile Mino Spray Dryer (shown in Figure 11) at a feed rate of 4L/hr to the nozzle and an atomization pressure of 1.6bar. The outlet temperature from the spray dryer was 95⁰C. Granules in the form of a dry powder (shown in Figure 12) were produced and were found to have a moisture content of 8%.

To demonstrate the workability of the dried S2 powder granules, they were then "regenerated" (rewetted) by mixing with water in a high friction mixer at 600rpm for 30 minutes to produce a fibre and water mixture having a fibre content of 15%. This mixture was then formed into a solid article in accordance with the processes described in US6379594. The E modulus (elasticity) and density of this article produced from the regenerated S2 granules was compared to that of an article produced from the original as-formed S2. It was found that the elasticity of the regenerated S2 granules was about the same as that of the as-formed S2. Without wishing to be bound by theory, it is believed that this was due to the very fine structure of the powder granules which enabled sufficient mixing with the water, even though the mixing time allowed was shorter than that provided in Examples 2 and 3.

Example 5

Cellulose fibre powder produced by spray drying S2 in accordance with Example 4 were pelletised using a

Hosokawa Bepex GCS 200/80 pelletizer (shown in Figure 13) . The pellets produced are shown in Figure 14. In the claims which follows and in the preceding description, except where the context requires otherwise due to express language or necessary implication, the word "comprise" or variations such as "comprises" or "comprising" is used in an inclusive sense, ie. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments .

It is to be understood that, if any prior art publication is referred to herein, such reference does not constitute an admission that the publication forms a part of the common general knowledge in the art, in Australia or any other country.

Claims

1. A method for granulating cellulose fibres from a solid- liquid mixture comprising water and cellulose fibres, the method comprising:

(d) separating the mixture into wet fibres and water; and

(e) forming the wet fibres into a plurality of wet granules; (f) drying the granules.

2. A method as claimed in claim 1, wherein the solid- liquid mixture to be granulated has a solids content of 1- 30% by weight.

3. A method as claimed in claim 1 or 2 , wherein the separation step is a physical separation step.

4. A method as claimed in any one of the preceding claims, wherein the wet fibres have a solids content of 6-50% by weight .

5. A method as claimed in any one of the preceding claims, wherein the method also comprises the step of curling the cellulose fibres.

6. A method as claimed in any one of the preceding claims, wherein step (a) comprises passing the mixture through a screw separator.

7. A method as claimed in any one of claims 1-5, wherein step (b) occurs by using a granulator.

8. A method as claimed in any one of claims 1-5 and 7, wherein step (a) comprises using centrifuge or passing the mixture through a pressure filter, oscillating filter or any other suitable filter or using capillary extraction.

9. A method as claimed in any one of the preceding claims, wherein, step (c) comprises heating the wet granules to no more than 220⁰C.

10. A method as claimed in any one of the preceding claims, wherein step (c) comprises using a swirl fluidizer to heat the granules and evaporate the water.

11. A method as claimed in any one of claims 1-3, wherein steps (a) , (b) and (c) together comprises spray drying the mixture to form dry granules comprising powder like particles.

12. A method as claimed in any one of the preceding claims, wherein the method also comprises the step of (d) compressing the granules into larger granules .

13. A method as claimed in claim 12, wherein step (d) comprises the step of pelletising the spray dried granules.

14. A method as claimed in any one of the preceding claims, wherein the method also comprises, prior to step (a) , heating the solid-liquid mixture.

15. A method as claimed in claim 14, wherein the solid- liquid mixture is heated prior to step (a) to a temperature of approximately 160⁰C.

16. A method as claimed in any one of the preceding claims, wherein the dried granules have a specific gravity of 0.2-1.0.

17. A method as claimed in any one of the preceding claims, wherein the dried granules have a specific gravity of 0.2-0.4.

18. A method as claimed in any one of the preceding claims, wherein the dried granules have a water content of approximately 6-12% by weight.

19. Granules, produced according to any one of the preceding claims.

20. A method for forming an article from granules produced according to any one of claims 1-18, the method for forming the article comprising the steps of:

(d) mixing the granules with water to form a solid-liquid mixture comprising cellulose fibres and water;

(e) shaping the mixture into the article; and (f) hardening the article by drying.

21. A method as claimed in claim 20, wherein the method also comprises the step of leaving the granules to soak in the water for 1-12 hours.

22. A method as claimed in claims 20 or 21, wherein the method also comprises the step of adding pigments or other colorants to the solid-liquid mixture.