WO2009153399A1

WO2009153399A1 - Method of treating cellulose-containing material

Info

Publication number: WO2009153399A1
Application number: PCT/FI2009/050521
Authority: WO
Inventors: Olli Aaltonen; Pekka Savolahti
Original assignee: Valtion Teknillinen Tutkimuskeskus
Priority date: 2008-06-16
Filing date: 2009-06-16
Publication date: 2009-12-23
Also published as: FI20085593A0; FI20085593L

Abstract

Method of treating an starting material which comprises cellulose, the uses of the method and an apparatus which is suitable for the implementation of the method. In the method, an aqueous starting material is treated with electricity, in which case, according to the present invention, the state of organisation of the initial cellulosic material is selectively changed by directing electric energy at the cellulose, the amount of which energy is sufficient to break the hydrogen bonds between the polymer chains of the cellulose. Hydrolytic chemicals are not needed in the solutions, nor is it necessary to use a high temperature or an elevated pressure. After the treatment and depending on whether the degree of organisation of the cellulose is increased or decreased, it is possible to use the cellulosic material in applications that utilise the fibrous structure of cellulose or, correspondingly, in applications in which decomposition products of cellulose are recovered.

Description

Method of treating cellulose-containing material

The present invention relates to a method according to the preamble of Claim 1 of treating a starting material which contains cellulose.

According to a method of this kind, the aqueous starting material is treated with electricity in order to modify its degree of organisation.

Furthermore, the present invention relates to use of that method in the utilisation of cellulose contained in a starting material, and as a pretreatment step of a process which aims at recovering the decomposition products of cellulose.

The present invention also relates to an apparatus according to Claim 26.

Decreasing the crystallinity of cellulose and other opening up of the structure of cellulose is a significant part of all cellulose utilisation processes, in which chemical derivatives are produced from cellulose (for instance carboxy-methyl cellulose and cellulose acetate) or sugar, by applying enzymatic hydrolysis.

All modern methods of activating cellulose (mercerization, steam explosion, fractionating acid hydrolysis etc.) are expensive and they waste energy. Also, many of these methods are flawed by by-product flows which result from using lye and mineral acids. For instance, the affordability of second generation bioethanol production mainly depends on the efficiency of the pretreatment method which is used to "open up" the structure of the cellulose. To date, no satisfactory solution exists. An efficient pretreatment is also a prerequisite for the affordability of a bio-refinery chain which advances along the so-called sugar route.

On the other hand, increasing the crystallinity and other state of organisation of the cellulose is desirable, for instance in cases where the aim is to increase the strength of the fibres or the fibrils. High state of organisation of cellulose is also desirable in the manufacture of micro- or nano-scale cellulose-based products. The application of an electric current in the treatment of cellulose-bearing material is already known. SU Patent Publication 1 504 249 describes a solution in which the lignin percentage of the cellulosic raw material is reduced by directing a 50-100 V direct-current voltage at the raw material. During the treatment, the raw material is kept in acidic water, into which 2-8 % of hydrogen peroxide is added in order to raise the efficiency of the removal of lignin. The acid used is sulphuric acid or, alternatively, acetic acid. After the treatment, the raw material is reported to be easily hydrolyzed, which means it can be utilised in enzymatic production of sugar.

In the solution according to the above-mentioned SU patent, the starting material is primarily modified by the influence of the chemicals in the aqueous phase, which influence is enhanced by an electric current. A treatment such as this is non-specific and the hydrogen peroxide, which is dissolved in water, and the sulphuric acid break down both the lignin and the cellulose.

It is an aim of the present invention to provide a solution with which it is possible to affect the degree of organisation of the cellulose share of fibrous raw material, without weakening the fibre matrix.

It is another aim of the present invention to provide a method with which it is possible to open up the fibrous structure and to modify the crystallinity of cellulose, depending on the need for further treatment in each case.

The present invention is based on the idea that the state of organisation of the cellulosic starting material is selectively modified by directing electric energy at the cellulose of the starting material, for instance with the help of an electric field or with an electric current, in which case the amount of the energy that is brought to the starting material is equivalent to or greater than the bond energy of the hydrogen bonds. The degree of organisation of the cellulose depends, among other things, on the hydrogen bonds between the anhydroglucose chains, and by means of directing at the material an amount of external energy which is equivalent to the bond energy of the hydrogen bonds it is possible to separate the chains from each other. Following that, the material can be allowed to reorganise, in which case the degree of organisation of the cellulose exceeds the degree of organisation of the original material. Alternatively, it is possible to prevent such reorganisation, for instance by introducing, between the chains, materials which prevent the formation of new hydrogen bonds.

The method is put into practice in a liquid phase that does not comprise chemicals which essentially break down or oxidise the fibrous structure of the starting material. Instead, the liquid phase primarily comprises, besides water or another corresponding polar solvent, only ions with which the progress of the electric current in the cellulose is enhanced.

After the treatment and depending on whether the treatment is meant to increase or to decrease the organisation of the material, it is possible to use the cellulosic material for applications in which the fibrous structure of the cellulose is utilised or, correspondingly, for applications in which the decomposition products of cellulose are recovered.

The method is carried out in an apparatus which comprises a treatment unit, in which it is possible to direct at the material an electric or magnetic field in order to selectively change the degree of organisation of the cellulose, and which apparatus is connected to the source of the cellulose-bearing material.

More specifically, the method according to the present invention is mainly characterized by what is stated in the characterization part of Claim 1.

The uses according to the present invention are characterized by what is stated in Claim 18 and Claim 21 , respectively.

The apparatus according to the present invention is, in turn, characterized by what is stated in the characterization part of Claim 26.

Considerable advantages are obtained by means of the present invention. Thus, this solution renders unnecessary not only traditional hydrolytic chemicals, such as strong lye or mineral acids, but also high temperatures or elevated pressures. For instance, the formation of toxic by-products which are typical of steam explosions and which are detrimental to further processing, are avoided in the present method.

In the described method, the energy which is needed for breaking the internal bonds of the cellulose is introduced in the form of electrical energy, which can be generated for instance with the help of a magnetic field. Both the generation of a magnetic field and the electric current losses generate heat, all of which can be used for heating this treatment process and the process flows integrated into it.

Besides being applicable for activating crystalline cellulose and the opening up of that crystalline cellulose for further chemical processing, the method according to the present invention may be applied to the controlled production of fibrils possessing a high state of organisation.

In the following, the present invention will be examined more closely with the aid of a detailed description.

The accompanying figure is a graphical presentation of the crystallinity of the samples described in Table 1.

As described above, the purpose of the present solution is to pre-tailor cellulosic or a cellulose-bearing fibrous starting material. Examples of such materials are mechanical, chemi-mechanical and chemical cellulosic pulp, partly defibred paper furnish and untreated paper furnish, such as wood, cotton, straw or grass, and combinations and mixtures of all of the abovementioned materials. The starting material may comprise, besides cellulose, also typical components of lignocellulose, lignin, hemicellulose, fats, resin, pectin and inorganic compounds, such as metallic salts.

In the present invention, cellulose is treated in order to selectively modify, i.e. change, its degree of organisation. Here, "selective modification" means that other parts of the fibre matrix are not essentially broken down, i.e. the polymeric chains are not significantly degraded and side chains are not removed.

Electric energy is brought to the cellulose with the help of an electric field, an electric current or a combination of these. It is possible to generate electrical energy such as this in the starting material, for instance by directing a variable magnetic field at it or by exposing it to a voltage passing between two electrodes.

Alternatively, it is possible to carry the cellulose through an electric field or a variable magnetic field. This variable magnetic field induces local electric eddy currents in the cellulosic slush.

Generally, the frequency of the magnetic field may vary between for instance 0.01-100 MHz, especially approximately 0.1-10 MHz. In the example below, the frequency varies between approximately 0.2 and approximately 1.5 MHz. The strength of the magnetic field is for instance approximately 10-20,000 gauss. In the case where an electric voltage is directed at the material, the voltage can generally vary in the range of 1-10.000 V, especially it is approximately 10-1,000 V, most suitably approximately 15-500 V. The current density, again, is approximately 0.01-100 A/dm², most suitably approximately 0.1- 10 A/dm².

The amount of electric energy which is introduced to the cellulose is at least 1 kcal/mole, typically approximately 5-100 kcal/mole, per each anhydroglucose unit.

By the influence of both the electric field and the ions carrying the current which move by force of the field, the weak hydrogen bonds, which maintain the crystal structure of the cellulose, break, the structure of the cellulose opens up and the cellulose molecules are settled in a less organised state.

According to one embodiment of the present invention, because the cellulose molecules recrystallize easily when the hydrogen bonds are regenerated, the state of the cellulose, being more opened up, is stabilized when chemical compounds or agents from the aqueous phase, which agents prevent the cellulose from recrystallizing, are introduced into the positions of the hydrogen bonds. Examples of such agents and compounds are carbohydrate oligomers, sugars, organic acids and, in general, decomposition products of carbohydrates. These are generated for instance in the further processing of cellulose, from which they are recirculated. In the treated cellulosic material their amount can be approximately 0.01-20 %, especially approximately 0.1-10 %, of the total weight of the material.

The starting material is aqueous, which means in practice that its water content is approximately 5-99 weight-%, preferably approximately 10-95 weight-%, of the total weight of the starting material. According to the present invention, it is thus possible to treat both an aqueous slurry and a fairly dry material which comprises sufficient moisture to render it possible to induce electric energy in it with the help of either an electric field or a magnetic field or a combination of these.

Most suitably, the aqueous phase of the starting material comprises ions which enhance the electrical conductivity but which starting material is preferably at least essentially free from oxidizing chemicals, such as strong acids, alkalis or oxidizing agents, for example ozone or chlorine chemicals.

The pH of the liquid phase is typically neutral, slightly acidic or slightly alkaline. In practice, the pH of the solution is approximately 4-12, especially approximately 5-10. The treatment is carried out usually at room temperature, but generally it is possible to implement that treatment at a temperature of approximately 5-95 ⁰C. As mentioned above, the treatment generally increases the temperature of the intermediate agent and the cellulosic material at least slightly, for instance by at least approximately 5 ⁰C. The temperature increase can be exploited in the further processing of the material, for instance in hydrolysis and fermentation.

The surrounding atmosphere can be inert (for instance helium or nitrogen) or oxygenous (for instance air). Generally, it is possible to carry out the treatment in an open vessel, in which case the pressure is the same as the surrounding pressure, but it is also possible to implement the treatment at a pressure of approximately 1-25 bar (abs.). The treatment time can vary within a wide range, depending on the raw material, the treatment conditions and the purpose of the treatment , from seconds to a few days (0.1 s to 48 h). However, preferably the treatment time is approximately 1 second to 30 minutes.

On the basis of what is presented above, according to a first embodiment of the present invention, intermolecular hydrogen bonds, which disrupt the chemical and physical processing of the cellulose, are broken by exposing the cellulose, in an aqueous environment and, if needed, in the presence of ions, to an electric current which is induced by a magnetic field.

It is possible to put into practice this embodiment for instance by treating crystalline cellulose in water, into which, if needed, current-carrying ions in the form of salts have been added. Examples of these salts are inorganic and organic salts of alkali metal ions or alkali earth metal ions, such as chlorides, sulphates, carbonates, oxalates of sodium, potassium, calcium and magnesium, and salts of uronic acid and galacturonic acid, and acetates. Generally, the amount of added salts is large enough to render the conductivity of the water at least approximately 30 mS/cm, most suitably approximately 100-10,000 mS/cm, especially approximately 150-5000 mS/cm, at room temperature.

The present method can be applied for instance as a pretreatment stage of a process, the purpose of which is to recover decomposition products of cellulose. In this case, the degree of crystallization of cellulose is first selectively decreased, after which the cellulose is brought for further treatment in order to recover the chemicals. In a further treatment such as this, carbohydrate oligomers, sugars or organic acids or alcohols are recovered from the cellulose or formed of its decomposition products.

In the further treatment, the material which is generated in the process described above can be brought into mechanical, chemical or enzymatic treatment or a combination of these, especially it can be introduced into the processes of hydrolyzation, fermentation or oxidization or a combination of these, which is optionally combined either with the preceding or following mechanical treatments.

The material to be recovered is brought for instance into a second treatment in order to increase the yield of carbohydrates, chemicals or lignin. By continuing the hydrolysis of polysaccharides and oligosaccharides it is possible to increase the yield of monosaccharides. Monosaccharides, in particular pentoses and hexoses, such as xylose and glucose and galactose, are suitable for the production of ethanol by means of fermentation. It is possible to use and to combine different treatments and stages of fermentation. According to one embodiment, cellulose (and hemicelluloses) is converted into ethanol by using a separate hydrolysis and fermentation process (SHF) or a simultaneous hydrolysis and fermentation process (SSF). The latter solution can be carried out as a simultaneous saccharification and hemicellulose fermentation (SSHF or SSCF - Simultaneous Saccharification and CoFermentation).

It is possible to apply these solutions to the production of any chemical. Examples of such chemicals are ethanol, lactic acid, saccharic acids, acetic acid and similar products which are generated by fermentation.

According to another embodiment of the present invention, the number of hydrogen bonds is increased, i.e. the degree of organisation of cellulose is increased.

Thus, it is possible to use the present method for recovering cellulose and cellulose-based products, in which case the degree of crystallization is first selectively increased, after which the cellulose is separated from the starting material and recovered at least mainly as a crystalline product. Interesting products are microfibrils and nano-scale products.

The present invention also relates to an apparatus for implementing the method described above. An apparatus such as this comprises a unit for the treatment of cellulosic material, in which unit it is possible to direct at the material an electric field or a magnetic field and which unit has an input side and an output side, an inlet pipe which is connected to the source of the cellulosic material and which is also connected to the input side of the treatment unit, with the purpose of feeding the cellulosic material into the treatment unit; and an outlet pipe which is connected to the output side of the treatment unit, with the purpose of removing the material which is coming from the treatment unit; and a current source which is connected to the treatment unit, in which case in the treatment unit, there is a pair of electrodes, or a winding, with the purpose of generating an electric or a magnetic field in the treatment unit, which electrodes or winding are connected to the source of an electric current. The outlet pipe is most suitably connected to the process in which the cellulosic material is further treated. The reject from the pretreatment forms the feed of this main process, into which it is possible to add, depending on each process, chemicals/enzymes/micro-organisms or from which it is possible to separate and recover the cellulosic material.

Preferably, the treatment unit comprises a flow-through space, with the help of which the apparatus continuously generates cellulose which has a modified state of organisation and which is suitable for further treatment.

The following non-limiting examples illustrate the present invention.

Example 1

Salt solutions comprising 1, 5, 10 and 20 weight-% of NaCl were prepared, and a solution comprising 10 weight-% of NaCl and 10 weight-% of Na-salt of galacturonic acid. 15 ml of each salt solution were put into separate test-tubes, and 1.5 g of microcrystalline cellulose was mixed in each tube.

The solutions were allowed to stand for 24 hours to ensure that the solution had totally penetrated into the cellulose and was totally mixed with it and, after that, tests were run in which the slush formed of the salt solution and the cellulose was placed in the test-tube inside a coil which generated a magnetic field. The frequency of the magnetic field was varied between 0.2-1.5 MHz, and the treatment time and the power were varied, too.

After the test run, an XRF analysis was run and the crystallinity index (Index of Order) of each sample was determined.

In the cellulose slush, no changes arising from the electromagnetic treatment were observed. As a result of the treatment, the temperature of the cellulose slush increased by approximately 5 ⁰C. TABLE 1

Samples tested Na salt of galacturonic At the At the acid beginning end

1% 5% 10% 20%

Sample MCC, g NaCl, g NaCl, g NaCl, g NaCl, g 20 %, g t, min U, Vac I, A T, kHz U, Vac I, A

SS-I 1.5 15.1 - - - 30 16 8 189 16 8

SS-4 1.5 15.1 - - - 30 35 2.0 303 35 1.8

SS-7 1.5 15.0 _ 30 36 2.2 758 33 1.9

SS-Il 1.5 15.1 - - - 30 37 1.6 1440 36 1.0

SS-2 1.5 - 15.3 - - 30 12 6 184 14 6

SS-5 1.5 - 15.1 - - 30 35 2.0 303 35 1.8

SS-8 1.5 - 15.1 - - 30 33 2.0 759 33 1.9

SS-12 1.5 15.1 - - 30 36 1.3 1419 36 1.0

SS-3 1.5 - - 14.1 - 30 14 6 186 14 6 O

SS-6 1.5 - - 15.0 - 30 35 2.1 302 36 1.8

SS-9 1.5 - - 15.1 - 30 •"1 O

JJ 2.1 759 JJ 1.9

SS-13 1.5 - 15.1 - 30 35 1.4 1470 35 1.0

SS-14 1.5 - - - 15.2 30 35 1.3 1410 35 1.0

SS-16 1.5 - - - 7.0 8.1 30 32 1.4 1540 32 1.0

SS-IO 1.5 - 15.0 - - - 0 blank sample

SS-15 1.5 - - - 15.0 - 0 blank sample

SS-17 1.5 - - - 7.0 8.1 0 blank sample

The results reveal that the IO of the cellulose changes as a function of both the salt content and the frequency of the alternating current. In these test runs (i.e. with this test apparatus and with these parameters) the IO increases, i.e. the crystallinity seems to increase as a function of the frequency. Under these test conditions, the changes in the salt content resulted in a greater change in the 10, but it is essential that the treatment using different frequencies, too, had an effect on the 10.

It is obvious that the electromagnetic treatment has a clear effect on the material.

Example 2

Salt solutions comprising 0.1, 0.5, and 1.0 weight-% of NaCl were prepared. 0.5 weight-% of xylan was added to each of the salt solutions. From each salt solution, 10 ml was transferred into bags made of polyolefin plastic film, and 1 g of dry, powdery microcrystalline cellulose was added into each bag. One bag at a time is placed in the 5 mm wide air space of an electromagnet that has the shape of a cut toroid which is made of transformer core metal. An alternating voltage, the strength of which is adjusted in the range of 0-75 V, was led to the coil of the electromagnet.

The frequency of the alternating voltage is varied within wide limits by using an oscillation generator and, depending on the frequency range, also one or two interstage amplifiers, and an output amplifier, which feeds the voltage to the coil of the electromagnet. The oscillation frequency of the electric current is varied in the range of 25— 120 kHz and in the range of approximately 1-35 MHz. In the coil of the electromagnet, the current intensities varies between 0.1-17 amperes. The arrangement that was formed of the oscillator, the amplifier and the coil of the electromagnet could be tuned over several frequencies. The resonant frequencies and the waveforms of the electromagnetic field were determined by means of a detector circuit and an oscilloscope which was attached to that circuit.

Each cellulose batch, which had been electromagnetically treated, was moved to a sample holder and pressed to at least approximately a standard water content. The state of organisation of each cellulose batch is measured by using X-ray diffraction (XRD). It is stated that the state of organisation of the cellulose decreased in those experiments in which the electromagnetic load had been tuned and had directed a desired electromagnetic oscillation at the cellulose sample. The changes in the state of organisation of the cellulose were found to be within the range of 0.2-0.5 IO units.

Claims

1. A method of treating a starting material which contains cellulose, according to which method an aqueous material is treated with electricity, characterized in that the state of organisation of the cellulose in the starting material is modified by selectively directing at the cellulose electric energy, the amount of which is sufficient to break the hydrogen bonds between the polymer chains of the cellulose.

2. The method according to Claim 1, characterized in that the electric energy is brought to the cellulose with the help of an electric field, electric current or a combination of these.

3. A method according to Claim 1 or 2, characterized in that the aqueous phase of the starting material comprises current-carrying ions.

4. A method according to Claim 1 or 2, characterized in that the electric energy is generated in the starting material by directing at it a variable magnetic field or by exposing it to a voltage between electrodes.

5. The method according to Claim 4, characterized in that electric eddy currents are generated in the starting material.

6. A method according to any of Claims 1-5, characterized in that hydrogen bonds between the cellulose chains are broken with the help of an electric field.

7. The method according to Claim 6, characterized in that, in order to prevent recrystallization of the cellulose, chemical compounds or agents are brought from the aqueous phase to the positions of the hydrogen bonds.

8. The method according to Claim 7, characterized in that carbohydrate oligomers, sugars or organic acids, or similar decomposition products of carbohydrates, are brought to the sites of the hydrogen bonds.

9. The method according to Claim 8, characterized in that the decomposition products of carbohydrates are brought to the cellulose from the further treatment, from which treatment they are recirculated.

10. A method according to any of the preceding claims, characterized in that the amount of electric energy which is introduced into the cellulose is at least approximately 1 kcal/mole, preferably at least 5 kcal/mole, per each anhydroglucose unit.

11. A method according to any of the preceding claims, characterized in that the aqueous phase of the starting material is at least essentially free from oxidizing chemicals.

12. A method according to any of the preceding claims, characterized in that the moisture content of the starting material is approximately 5-99 weight-%, preferably approximately 10-95 weight-%, of the total weight of the starting material.

13. A method according to any of the preceding claims, characterized in that the initial cellulosic material comprises, besides cellulose, also lignin and/or hemicellulose.

14. The method according to Claim 13, characterized in that the initial cellulosic material is mechanical, chemi-mechanical or chemical cellulosic pulp, wood, straw or grass, or a combination of these.

15. A method according to any of the preceding claims, characterized in that the structure of the polymer chains of the starting material is not essentially broken down.

16. A method according to any of the preceding claims, characteri zed in that the cellulose is allowed to recrystallize after the electrical treatment.

17. A method according to any of Claims 1-16, characterized by directing at the cellulose

- a magnetic field, the frequency of which is approximately 0.1-10 MHz and the strength of which is approximately 10-20,000 gauss; or

- an electric voltage, which is approximately 10-1,000 V; or - an electric current, the density of which is approximately 0.1-10 A/dm².

18. Use of a method according to any of Claims 1-15 or 17, as a pre-treatment stage of a process, the purpose of which is to recover the decomposition products of cellulose.

19. The use according to Claim 18, characterized in that the degree of crystallization of the cellulose is first selectively decreased, after which the cellulose is brought to further treatment, with the purpose of recovering the glucose.

20. use according to Claim 18 or 19, characterized in that hydrocarbon oligomers, sugars or organic acids or alcohols are recovered from the cellulose, or are formed of the decomposition products of cellulose.

21. A use of a method according to any of Claims 1-6 or 10-17, as a pretreatment stage of a process, with the purpose of recovering the cellulose.

22. The use according to Claim 21, characterized in that the degree of crystallization of the cellulose is first selectively increased, after which the cellulose is separated from the starting material and recovered at least mainly as a crystalline product.

23. The use according to Claim 22, c h a r a c t e r i z e d in that cellulose products which have a higher degree of organisation than the starting material are recovered.

24. A cellulosic material, which has a lowered crystallinity, characterized in that the material is produced according to any of Claims 1-5 or 17 and which comprises, besides cellulose, at least to a certain degree hydrocarbon oligomers, sugars or organic acids, or similar decomposition products of carbohydrates which have been separately added.

25. A cellulosic material which has an increased degree of crystallinity characterized in that the material is produced according to any of Claims 1-5, 10- 16, 17 or 20-22.

26. An apparatus for the treatment of an starting material which comprises cellulose, c h a r a c t e r i z e d in that the apparatus comprises

- a unit for treatment of cellulosic material, in which unit it is possible to direct at the material an electric or a magnetic field and which unit has an input side and an output side;

- an inlet pipe which is connected to the source of the cellulosic material and also connected, in order to feed the cellulosic material into the treatment unit, to the input side of the treatment unit;

- an outlet pipe which is connected to the output side of the treatment unit, in order to remove the material which is generated in the treatment unit; and

- a source of an electric current which is connected to the treatment unit, in which case in the treatment unit there is a pair of electrodes or a winding with the purpose of generating an electric or a magnetic field in the treatment unit.

27. The apparatus according to Claim 26, c h a r a c t e r i z e d in that the treatment unit comprises a flow-through space, with the help of which the apparatus continuously generates cellulose which has a modified state of organisation and which is suitable for further treatment.