WO2012059643A2

WO2012059643A2 - Method for fractionating of lignocellulosic material and novel ionic liquids therefor

Info

Publication number: WO2012059643A2
Application number: PCT/FI2011/050959
Authority: WO
Inventors: Pasi Virtanen; Ikenna Anugwom; Jyri-Pekka Mikkola; Päivi MÄKI-ARVELA
Original assignee: Åbo Akademi
Priority date: 2010-11-01
Filing date: 2011-11-01
Publication date: 2012-05-10
Also published as: WO2012059643A3; FI20106142A0

Abstract

The present invention is directed to a method for fractionating lignocellulosic material and its constituents. In particular, the method according to the present invention concerns dissolution of lignocellulosic material into a switchable ionic liquid (SIL) and further processing of the dissolved constituents. Additionally the present invention concerns novel switchable ionic liquids prepared from a mixture of an amidine or a guanidine and an OH-containing compound, which OH-containing compound can be a liquid or solid compound with multiple hydroxyl groups or a hydroxy alkyl ammonium compound or an amino alkyl sulfonic acid. Amidine or guanidine and the above specified OH-containing compound are bubbled with an acid gas to switch the molecular solution to an ionic liquid. These novel ionic liquids are suitable to be used in the above mentioned fractionation process.

Description

METHOD FOR FRACTIONATING OF LIGNOCELLULOSIC MATERIAL AND NOVEL IONIC LIQUIDS THEREFOR

Technical field

Background of the invention

Wood is a renewable source for cellulose, lignin, hemicelluloses, extractives and polysaccharides. Wood is composed of low molecular weight substances and macromolecular substances, which are the main components accounting for about 90 to 99 % of the wood material. About three quarters of the macromolecular substances consists of polysaccharides, primarily of cellulose and hemicellulose. Lignin fills the spaces in the cell wall between cellulose, hemicellulose and pectin components.

Lignin confers mechanical strength to the cell wall. Pulping is a process to convert wood or lignocellulosic nonwood material, like straws, grasses and canes, to separated pulp fibers to be used for example in papermaking. The lignocellulosic material can be pulped mechanically or chemically. Chemical pulping encompasses many different processes, from strongly alkaline (Kraft) to strongly acidic. The basic principle in chemical pulping is the fiber liberation by dissolving enough lignin from the wood to free the fibers without mechanical action or with only a small amount of it. The dominant chemical pulping process is Kraft pulping. In a typical Kraft process, wood chips are fed into a digester capable of withstanding high pressures and operating either batch wise or in a continuous manner. The chips are impregnated with cooking liquors conventionally consisting of warm black and white liquor, wherein the white liquor is a mixture of sodium hydroxide and sodium sulfide. Typically delignification requires several hours at 130-180°C. The cooked wood chips are discharged out of the digester and washed, screened and in most cases also bleached before utilizing the fibers as a raw material in e.g. paper mill.

Ionic liquids are salts composed solely of ions. The properties of ionic liquids can be tailored by tuning the pairing and structure of cations and anions. Ionic liquids find a variety of industrial applications in several fields like chemical industry, cellulose processing, gas handling and gas treatment, solar thermal energy, food and

bioproducts, waste recycling, batteries, high purity organometallics and as dispersants. One of the most common applications of ionic liquids has been their use as chemical solvents. Typically they exhibit very low vapor pressures and are thus considered as green solvents. However the toxicity, biodegradation, bio-accumulation, safety, health and environmental impact data of the conventional ionic liquids have been very limited. Additionally extreme cost, separation issues and high viscosities have been challenges relating to conventional ionic liquids. Recycling of ionic liquids typically requires extensive washing with water or organic solvents creating large amounts of wastes and VOCs (Volatile Organic Compounds). Majority of ionic liquid

applications ignore product separation and purification. However in order to fulfill the requirements of today and to obtain a full process it is necessary to solve the problems associated with separation and reuse, because energy consumption as well as losses and pollution are strongly related to these factors. Switchable or reversible ionic liquids disclosed e.g. in US Patent Application

2008/0058549 provide a method of separating a solute (i.e. a dissolved compound) from a solution by switching the physical properties of the solvent of the system. According to one embodiment of that method the solvent can be reversibly and readily switched between nonionic liquid and ionic liquid forms by applying or removing C0₂, SO₂ ,CS₂ or COS. The nonionic liquid mixture includes an amidine or guanidine or both, and water, alcohol, or a combination thereof. With these reversible ionic liquids, the separation and purification problems of conventional ionic liquids have been overcome. Furthermore the switching between the molecular and ionic form can be performed under mild conditions and preferably with mild reagents. By this "on and off chemistry synergy of reaction and purification can be achieved; which both are ecological and economical. The interest on using ionic liquids for dissolving cellulose, lignin and wood has increased recently and the state of the art relating to this is summarized in a review article of Maki-Arvela, P., Anugwom, I., Virtanen, P., Sjoholm R., Mikkola, J. -P., Dissolution of lignocellulosic materials and its constituents using ionic liquids - A review, Ind. Crops and Prod., 2010, 32, 175-201.

Kilpelainen et al. disclose in their article "Dissolution of Wood in Ionic Liquids", J. Agric. Food Chem. 2007, 55, 9142-9148, that imidazolium-based ionic liquids can be used to dissolve both hardwoods and softwoods. The problems associated with the prior art pulping processes can be solved or at least the environmental aspects can be now remarkably improved without compromising the economical competitiveness of the process. In the fractionation or dissolution method according to the present invention lower temperatures can be used when compared e.g. to Kraft pulping. Additionally corrosive chemicals like H₂S and NaS0₃ are not used at all and typically no hydrogen sulfide or sulfur oxides are formed as byproducts.

One further advantage of the present method is that both hardwood and softwood components can be dissolved and fractionated efficiently with the swithcable ionic liquids. Although, it has been very challenging to dissolve hardwood with traditional ionic liquids, there are some examples in the prior art. Moreover, no examples of dissolving birch (Betula) were found.

Additionally both dried and moist (native) wood chips components can be dissolved as well with the fractionating method according to the present invention. Further, it has been shown that the dissolved wood chips can have the size corresponding to today's industrial wood chip size. In prior art trials with ionic liquids the size of the chips has been smaller. Improved recyclability and reusability achieved by the switching concept, makes the process economically and ecologically very efficient and competitive. With the current Kraft pulping system the hemicelluloses are degraded and thus remain unutilized. The present method enables the recovery of the hemicelluloses as well.

The novel ionic liquids according to the present invention prepared from a mixture of an amidine or a guanidine and an OH-containing compound, which is selected from a group consisting of a liquid or solid compound with multiple hydroxyl groups or a hydroxy alkyl ammonium compound or an amino alkyl sulfonic acid, which amidine or guanidine and above specified OH-containing compound are then bubbled with an acid gas to switch the molecular solution to ionic liquid. These ionic liquids according to the present invention have several benefits as they are reusable or recyclable, easy to manufacture (gas bubbling) and moisture-resistant. Additionally these novel ionic liquids have quite a high decomposition temperature (about 100°C or more), at least when compared to some prior art ionic liquids. Conventional ionic liquids can although have even higher decomposition temperatures. From the environmental point of view it is of great advantage in the manufacture of these novel SILs to be able to utilize acid gases or their mixtures (industrial flue gases) as well as other suitable compounds that, in fact, at least partly compose of chemicals present in the nature (e.g. alcohols, carboxylic acids etc.) and are thus biodegradable and non-toxic. The ionic liquids according to the present invention are especially suitable for the fractionation process of the invention as a selective dissolution of the lignocellulosic material is obtained and the different fractions of the lignocellulosic material can be separated and thus utilized. The non dissolved fractions can also be better utilized in the traditional pulping industry and also as new products. Brief description of the figures

Fig. 1 A schematic illustration of the process scheme and its variables according to the present invention. Fig. 2A A bar chart showing the results obtained from acid methanolysis test for native spruce as well as for SIL#3 treated spruce and

Fig. 2B a bar chart showing the results obtained from acid methanolysis test for native birch as well as for SIL#3 treated birch.

FIG. 3 ¹ H NMR spectra of a neat sample of DBU/glycerol (3: 1) (A) and of

DBU/glycerol (3: 1)/C0₂ (B).

FIG. 4 ¹³C NMR spectra of a neat sample of DBU/glycerol (3: 1) (A) and of

DBU/glycerol (3: 1)/C0₂ (B).

FIG. 5 shows the numbering of carbon atoms in DBU.

FIG. 6 FT-IR of (a) DBU, (b) glycerol and (c) DBU/glycerol mixture after bubbling with C0₂ until there was no increase in weight.

FIG. 7 A bar chart showing the results obtained from acid methanolysis test for the recovered material from the spent SIL (DBU/glycerol/C0₂).

FIG. 8 A bar chart showing the results obtained from acid methanolysis test for native spruce and SIL # 21 treated spruce.

Description of the invention

The method for fractionating lignocellulosic material and its constituents with structure preserving manner according to the present invention is described in more detail with reference to the enclosed figure 1.

The present fractionation method starts from the preparation of a switchable ionic liquid (SIL) i.e. from the switching reaction wherein the molecular reactants are switched into an ionic form (top of Fig. 1; in the left hand side). In the context of this applica- tion switchability means that the molecular compounds defined below can be switched into ionic liquid and vice versa. The first process stage i.e. the switching operation (from molecular to ionic) is performed by bubbling acid gas or a mixture of acid gases in the mixture of an amidine or a guanidine and an OH-containing compound. In other words either amidine or guanidine is mixed with the OH-containing compound and that mixture is bubbled with the acid gas or with the mixture of acid gases. Amidine is a compound containing a carboxamidine or carboximidamide (IUPAC name) group. Guanidine is otherwise similar compound, but the central carbon atom is bonded to three nitrogen atoms. The OH-containing compound used in the method according to the present invention can be an alcohol. Examples of suitable alcohols to be used in the fractionation process according to the present invention are hexanol, butanol and 2-amino ethanol. These SILs are known from the prior art.

When preparing the novel switchable ionic liquids according to the present invention, which can also be utilized in the fractionation process according to the invention, the OH-containing compound is selected from the group consisting of a compound containing at least two OH-groups (e.g. diethanolamine (DEA), glycerol, xylitol or sorbi- tol), a hydroxy alkyl ammonium compound (e.g. choline chloride) and an amino alkyl sulfonic acid (e.g. taurine). The OH-containing compound containing at least two OH- groups is more specifically defined in the chemical equation 1 below. amidine or guanidine + R₁-(R₂-OH)_x + acid gas— > SIL wherein

x > 2, typically 2-6 (liquid or solid compounds containing multiple OH- groups)

Ri = hydrogen or alkyl or alkenyl or alkynyl or aryl or silyl or siloxyl; may be branched or cyclic and may be substituted or unsubstituted

R₂ = C, CH, CH₂

Amidine can be for example l,8-diazabicyclo-[5.4.0]-undec-7-ene (DBU) and guanidine can be e.g. 2-butyl-l,l,3,3-tetramethyl guanidine (BTMG).

For these novel SILs the structures with various stoichiometric, depending on the ratio of the reactants and reactivity of the OH-groups, can be estimated with NMR.

The table 1 gives indirect evidence of the formation of ionic liquid, since e.g. DBU is miscible with dichloromethane but glycerol is not miscible. However, the reacted form is again miscible with dichloromethane. If there were un-reacted glycerol in the mixture, it should form separate phase when dichloromethane is added. Table 1. Miscibility test results

V: miscible, x: immiscible, *: formation of white crystals

Other indirect evidence is that when Nile-red, a common dye, is added to the mixture of e.g. DBU and glycerol it dyes the solution red, because it is soluble to non-polar solvents. However, when C0₂ is bubbled throw the solution the red colour disappears, since Nile-red is not soluble in highly polar (ionic) solvents.

Regarding the fractionation process according to the present invention, both the switchable ionic liquids of the prior art and the novel ones according to the above description are suitable. The switching back operation i.e. reverse switching (from ionic to molecular) will be discussed later.

In the switching operation from molecular to ionic, any suitable acid gas or mixtures thereof (e.g. carbon dioxide and/or sulphur dioxide) can be used in the bubbling of the mixture of an amidine and an OH-containing compound. The acid gas may also be a mixture from industrial operation, e.g. flue gas containing C0₂ and/or S0₂. The acid gas may also contain e.g. S0₃, H₂S, CS₂ and/or HCl, to mention a few common possibilities. The prepared SIL is then pumped to the dissolution tank, wherein the dissolution of the lignocellulosic material i.e. the dissolution reaction is to be performed. Subsequently the lignocellulosic material is added into the dissolution tank (top of Fig. 1; in the middle).

According to the present invention any lignocellulosic material can be dissolved and thus fractionated by the method, e.g. wood; both hardwood and softwood. As an example birch, pine and spruce can be mentioned as well as eucalyptus. Also other types of lignocellulosic feedstrocks can be used, e.g. switch-grass, other grasses or any other lignin and cellulose containing material. The lignocellulosic material can be native (wet) or dried. Typically wood is used in the form of chips, no milling is needed. The dissolution time naturally depends on the size of the particles of the lignocellulosic material, in principal so that smaller particles are dissolved faster. Thus, it is also within the scope of the invention to use wood e.g. in the form of sawdust.

It is possible to use stirring in the dissolution step if needed. Also, circulation of the ionic liquid through the chips can be applied in order to enhance the dissolution process.

The dissolution temperature can vary. It can typically vary from the room temperature (20°C) to 150°C, depending on the ionic liquid used and also on other process variables. The preferable dissolution temperature is from 50°C to 120°C. Person skilled in the art can easily optimize the dissolution temperature.

The pressure used in the dissolution operation varies normally from atmospheric to about 60 bar, but it can also be higher. The preferable dissolution pressure is between atmospheric and 5 bar. The dissolution time can vary from minutes to several days depending on the lignocellulosic material and the SIL in question and on the dissolution conditions, like temperature and pressure. Also the target of the dissolution or fractionation process affects the dissolution time, meaning that depending on what fractions of the lignocellulosic material or of its constituents are intended to be utilized i.e. to get dissolved, the required dissolution time is different. The skilled person can optimize the dissolution conditions based on the above defined facts and on his knowledge. After dissolution is completed i.e. the dissolution is as complete as needed, the undissolved material is separated typically by filtration. The undissolved material is called herewith as "Products [1]" and comprises at least cellulose. Typically also some lignin is present in "Products [1]". The composition of "Products [1]" depends on the ligno- cellulosic material and SIL used, as well as on the dissolution time and temperature.

The liquid phase can either be reused in the following dissolution operation (see Fig. 1, line "Reuse of SIL") or directed to a switching process (follow line "Liquid phase" to vessel "Switching reaction: From ionic liquid to molecular"). According to the present invention the switchable ionic liquids can be directly reused in the preceding dissolution reaction several times if desired, e.g. at least three times. As the dissolution ability or capacity of the ionic liquid decreases remarkably it is directed to the reverse switching operation. On the other hand, the SIL can be directly after the first dissolution reaction, switched back into its molecular form and re-used by that way. This reverse switching is performed by bubbling inert gas like nitrogen (N₂) through the liquid phase or by applying heat or vacuum on it (bottom of Fig. 1, on the right hand side). During this reverse switching step the ionic form of the dissolving agent i.e. SIL is switched back to the molecular forms of the compounds and evaporating products such as volatile extractives like terpenes ("Products [2]") can be collected. Acid gas (see line "Recycling of CO₂/SO₂", which are shown as examples) can be recycled to a new switching reaction i.e. from molecular to ionic liquid.

According to one embodiment of the present invention, after the molecular form of the reactants is obtained, an anti solvent is added into the solution to precipitate the dis- solved component(s). This is shown in figure 1, in the middle thereof. For example ethanol or acetone can be used as an anti-solvent. The precipitation of hemicelluloses, its degradation products (sugars) and lignin as well as of non- volatile extractives typically occurs immediately after addition of the anti solvent. The precipitated solids or "Products [3]" are recovered e.g. by filtration or any other suitable phase separation process. This process step is shown at the bottom of Fig.1 in the middle thereof, as "Phase separation". The used anti solvent(s) can be recovered and separated from the molecular liquids e.g. by evaporation (in Fig. 1 left hand side: Evaporation/recovery of anti solvent). The recovered anti-solvent can also be reused. After phase separation the molecular compounds of the SIL are switched to ionic liquid as was described above and the process starts from the beginning.

According to another embodiment of the present invention, no anti- solvent is needed for the precipitation of the dissolved compounds as the switching reaction itself induces the precipitation. The precipitated compound(s) are separated e.g. by filtration and the molecular liquids are recovered (in Fig 1. straight line from reverse switching reaction to filtration). According to still another embodiment, after separation of the undissolved material e.g. by filtration (Products [1]) from the dissolving media (i.e. SIL) acid gas is bubbled through the solution and this will induce precipitation. Thus, instead of adding anti solvent, acid gas is added and used for precipitation. In the following the present invention will be illustrated with reference to the non- limiting examples.

Examples The switchable ionic liquids used in the examples were all basically and technically prepared in a similar manner, only the starting compounds were altered. In the SIL preparation step, the molecular form of the used constituents is switched to ionic liquid by the aid of acid gas. The basic principle of the preparation step or switching reaction is described below. A few of these kinds of ionic liquids are known from the US Patent publication US2008/058549. Preparation of the switchable ionic liquid (SIL); switching reaction:

The first process stage i.e. the switching operation (from molecular to ionic) is performed by bubbling acid gas or a mixture of acid gases in the mixture of an amidine or a guanidine and an OH-containing compound. The OH-containing compound used in the fractionation process according to the present invention can be an alcohol or a compound containing at least two OH-groups (e.g. glycerol, xylitol or sorbitol) or a hydroxy alkyl ammonium compound (e.g. choline chloride) or an amino alkyl sulfonic acid (e.g. taurine). The OH-containing compound containing at least two OH-groups is more specifically defined in the chemical equation 1 below. amidine or guanidine + R₁-(R₂-OH)_x + acid gas— > SIL (1) wherein

x > 2, typically 2-6; (liquid or solid compound containing multiple OH- groups)

Ri = hydrogen or alkyl or alkenyl or alkynyl or aryl or silyl or siloxyl; may be branched or cyclic and may be substituted or unsubstituted R₂ = C, CH, CH₂

DBU (l,8-diazobicyclo-[5.4.0]-undec-7-ene) has been used as an amidine in most of the prepared example SILs. BTMG (2-butyl-l,l,3,3-tetramethylguanidine) is one possible example of a guanidine. The use of any other suitable amidine or guanidine is also within the scope of the present invention. Examples of liquid or solid compounds containing multiple OH-groups tested are

DEA (diethanolamine), glycerol, sorbitol, propylene glycol, ethylene glycol and xylitol. Choline chloride was tested as a hydroxy alkyl ammonium compound and taurine as an amino alkyl sulfonic acid. For example hexanol and butanol were tested as alcohols. In table 1 these all are captioned as "OH-containing compound".

In the examples carbon dioxide (C0₂) or sulphur dioxide (S0₂) was used as an acidic gas. Nevertheless, any acid gas (enlisted in prior patent publications like US 2008/0058549 Al) can in principle be used although C02 and S02 are the preferred ones.

The SILs prepared are listed in table 2.

Table 2. List of synthesized SILs

SIL# Amidine/ OH-containing Molar ratio* Acid Novel SIL

Guanidine compound gas eq. (1)

SIL#1 DBU DEA 2:1 so₂ x(l)

SIL#2 DBU DEA 2:1 C0₂ x(l)

SIL#3 DBU glycerol 3:1 C0₂ x(l)

SIL#4 DBU glycerol 3:1 so₂ x(l)

SIL#5 DBU choline chloride (s) 1:1 C0₂ x

SIL#6 DBU sorbitol (s) 1:6 C0₂ x(l)

SIL#7 DBU xylitol (s) 1:5 C0₂ x(l)

SIL#8 DBU taurine (s) 1:1 C0₂ X

SIL#9 DBU ethylene glycol 2:1 C0₂ x(l)

SIL#10 DBU propylene glycol 2:1 C0₂ x(l)

SIL#11 DBU 2-amino ethanol 1:1 C0₂ -

SIL#12 DBU hexanol 1:1 C0₂ -

SIL#13 DBU butanol 1:1 C0₂ -

SIL#14 DBU hexanol 1:1 so₂ -

SIL#15 DBU butanol 1:1 so₂ -

SIL#16 BTMG hexanol 1:1 C0₂ -

SIL#17 BTMG glycerol 3:1 C0₂ x(l)

SIL#18 DBU 2-amino ethanol 1:1 so₂ -

SIL#19 DBU ethylene glycol 2:1 so₂ x(l)

SIL #20 DBU propylene glycol 2:1 so₂ x(l)

SIL#21 TMG glycerol 3:1 C0₂ x(l)

SIL #22 TMG DEA 2:1 C0₂ x(l)

SIL #23 DBU 1 ,4-butanediol 2:1 C0₂ x(l)

SIL #24 DBU phenol 1:1 C0₂ - (s) solid compound

* Molar ratio; Amidine : OH-cont. comp.

x SIL according to the present invention

x (1) = SIL according to the present invention and according to equation (1)

= SIL according to the prior art

DBU = l,8-diazobicyclo-[5.4.0]-undec-7-ene

BTMG = 2-butyl- 1 , 1 ,3,3-tetramethylguanidine

TMG = 1, 1, 3, 3 - tetramethylguanidine

DEA = diethanolamine

Lignocellulosic material

Both softwood and hardwood were used in the dissolution tests, i.e. spruce (Norway spruce), pine and birch (Betula) chips. The used chips were approximately 30 mm x 30 mm in size. In order to investigate the effect of the moisture content of the wood chips on dissolution ability/capability, both dried and wet (native) chips were tested. The moisture content of the wet spruce chips was about 56 wt-% and of the wet birch chips about 32 wt-%. One test was made with grass (common reed, Phragmites austra- lis). The grass was used as native - no drying before testing.

Dissolution conditions

In order to find out the optimal dissolution conditions several trials were performed by varying e.g. the SIL to wood ratio and dissolution time. Additionally the effect of stirring was tested; with or without stirring. The dissolution temperature is in principal dependent on the ionic liquid in question, but also the effect of the temperature was tested with some samples.

Examples 1- 4: Effect of the SIL to wood ratio

The effect of SIL to wood ratio on dissolution capacity was tested with four different ratios, 10: 1, 5: 1, 3: 1 and 2: 1. The ionic liquid used in this test was obtained by the preparation method described above using DBU, glycerol and carbon dioxide (SIL #3). The dissolution temperature was 100°C and the dissolution time was 24 hours. The dissolved material was birch. No stirring was used. The results are shown in table

3. Table 3. Effect of the SIL to wood ratio on dissolution capacity

Conclusion: no considerable difference was observed between the different SIL to wood ratios during the dissolution time of 24 hours with this specific ionic liquid.

Examples 5-9: Effect of dissolution time

The effect of dissolution time on the weight reduction of the lignocellulosic material was investigated by using DBU/Glycerol/C0₂ (SIL #3) as an ionic liquid. The dissolution temperature was 100°C and SIL to wood ratio was 25: 1. No stirring was used during dissolution of the birch chips. The weight reduction of the lignocellulosic material was measured after 4, 8, 18, 24 and 120 hours of dissolution and the results are shown in table 4.

Table 4. Dissolution time

Conclusion: already within the first 4 hours considerable weight reduction has been achieved. The optimization of the dissolution time depends on several factors and has to be done case by case. The dissolution time can vary from few hours to several days. The preferable dissolution time is from 4 to 24 hours, more preferably from 8 to 16 hours.

Examples 10-25 : Effect of the moisture content of the lignocellulosic material

The effect of the moisture content of the lignocellulosic material on the dissolution capacity was tested for both birch (hardwood) and spruce (softwood), with and with- out stirring, at dissolution temperature of 100°C and for two different switchable ionic liquids, namely glycerol/DBU/C0₂ (SIL #3) and glycerol/DBU/S0₂ (SIL #4). The used SIL-to-wood ratio was 25: 1. The results are shown in tables 5 and 6. In the tables the results are calculated from the dry mass of the wood. Table 5. Test results for birch

Table 6. Test results for spruce

Conclusion: Similar dissolution is obtained with wet and dried wood chips. This is a great advantage compared to conventional (i.e. not switchable, e.g. imidazolium, pyri- dinium, phosphonium, ammonium based IL's) ionic liquids, which are very sensitive to moisture. It is very beneficial that no additional drying step for the lignocellulosic material is needed before dissolution.

Examples 26 - 35 : Dissolving ability of different SILs

Different switchable ionic liquids were tested for their dissolving ability. The dissolving tests were performed at a temperature of 80°C, except for choline chloride based ionic liquid the temperature was higher i.e. 150°C . The dried wood chips (approx- imately 30 mm x 30 mm in size), either birch or spruce, were allowed to dissolve for 5 days, without stirring. The used SIL-to-wood ratio was 25: 1. Weight reduction of the lignocellulosic material was determined. The ionic liquids tested can be seen from the tables 2 and 7. Table 7. Test results for different SILs

* see the text, 150 C

Conclusion: These experiments show that higher dissolution is achieved with S0₂ - based SILs. This is probably due to the higher acidity of S0₂. For SIL #5 the dissolu- tion temperature has to be higher, thus it is not as such comparable with the other SILs tested.

Examples 36 - 45; Re-usability of different SILs

The dissolution efficiency and especially the re-usability of different SILs was tested in the following manner. The lignocellulosic material was added to the dissolution vessel containing the SIL at atmospheric pressure and at 80°C; both native and dried samples were tested. The dissolution was allowed to proceed for five days without stirring. The used SIL to wood ratio was 10: 1. After the dissolution period of five days, the lignocellulosic material i.e. birch chips were separated by filtration and washed with water and vacuum dried over night at about 20 mbar, the weight loss was recorded. For the wet samples the moisture content of the native wood was added to the weight loss recorded after drying. The same SIL was used in the preceding dissolution of "fresh" lignocellulosic material (either native or dried). This dissolution- washing cycle was repeated three times.

Table 8. Re-usability of SILs tested for birch

Example no. 36 37 38 39 40 41 42 43 44 45

SIL # #2 #3 #4 #6 #] 14

Wet/dry dry wet dry wet dry wet dry wet dry wet

Weight reduction (%)

I cycle 6 9 6 9 9 7 16 7 4 3

II cycle 5 8 5 8 10 7 13 5 3 3

III cycle 6 6 6 5 10 5 11 6 4 3 Conclusion: According to the tests performed it seems that the switchable ionic liquids are applicable at least for three subsequent dissolving operations/cycles without a need for any switching operation there between.

Examples 46 - 77; Acid methanolysis - gas chromatography (GO

Hardwood and softwood, both native and dry, chips were allowed to dissolve in SIL for five days with and without stirring at normal pressure. Dissolution temperatures of 80°C and 100°C were used. The used SIL-to-wood ratio was 10: 1. The results are shown in tables 9-12. The testing procedures are described below. The obtained values depict sugar content reduction in undissolved wood. The sugars originate from hemi- celluloses.

Determination of cellulose content

The carbohydrates contents were determined by acid hydrolysis (cellulose), in which 0.075 ml of 72% H₂SO₄ was added to about 1 mg of wood sample in a test tube and kept at room temperature for about 120 min. The secondary hydrolysis was conducted on the sample by Autoclaving at 125°C during 90 min. 1-2 droplets of bromocresol green indicator were added and the hydrolysate was neutralized by addition of BaC0₃. Internal standard (250mg of sorbitol in 50 ml water); 1 ml of the internal standard was added. 1 ml of hydrolysate and 1ml of acetone was taken and evaporated to dryness. Thereafter the sample was silylated (for silylation the following chemicals were used: 150 μΐ HMDS (hexamethyldisilazane), 70 μΐ TMCS (trimethylchlorosilane) and 100 μΐ of pyridine) and the solution was allowed to stand overnight and analyzed by gas chromatography (GC).

Determination of hemicelluloses

Acid methanolysis of the wood sample was performed as follows to analyze the hemi- celluloses and pectin: 2 ml of 2 M HCl in dry methanol was added to about 1-2 mg of wood sample, and heated at 105°C during 5 hours. The excess of acid was then neutralized with pyridine. 1 ml of an internal standard (0.1 mg/ml sorbitol) was added to the solution, thereafter it was dried under nitrogen and silylated as described above, and the sample is then analyzed by gas chromatography (GC) as described in the next section.

GC analysis for the carbohydrates

For GC analysis, about 2 μΐ of the silylated sample was injected through a split injector (260°C, split ratio 1:5) into capillary column coated with dimethyl polysiloxane (HP-1, Hewlett Packard). The column length, internal diameter and film thickness were 30 m, 320 μιη and 0.17 μιη, respectively. The following temperature program was applied: 100-4°C/min- 175°C followed by 175-12°C/min- 290°C. The detector (FID) temperature was 290°C. Hydrogen was used as carrier gas. The different peaks were identified by GC-MS. The following analytical grade sugars or their acids were identified: arabinose, rhamnose, xylose, galactose, glucose, mannose, glucuronic acid and galacturonic acid. For the calculation of the concentrations from peak area, calibrations were made for each sugar unit comprising the hemicelluloses. The calibration factors were determined for each series of analyses by performing the methanolysis or hydrolysis, silylation and GC analysis on two parallel samples containing equal amounts of 0.1 mg, of the above mention sugars and their derivatives. The calibration factors were determined by the ratio of the total area of the different sugar unit peaks to the area of the sorbitol peak. The calibration factor for 4-O-methylglucoronic acid was assumed to be equal to the calibration factor of glucuronic acid.

Table 9. Results of the acid methanolysis tests for birch and with SIL #3

ND = not determined Table 10. Results of the acid methanolysis tests for birch and with SIL #4

Table 11. Results of the acid methanolysis tests for spruce and with SIL #1

Table 12. Results of the acid methanolysis tests for spruce and with SIL #2

Example no. 70 71 72 73 74 75 76 77

SIL # #2 #2 #2 #2

Wet/dry dry wet dry wet

Temperature (°C) 80 80 100 100

Stirring: yes/no yes no yes no yes no yes no

Hemicellulose content

in wood (mg/g)

- at the beginning 200 200 200 200 200 200 200 200

- after 5 days ND 192 ND 180 170 184 ND 188 In figures 2A and 2B the sugar content of the untreated and treated birch and spruce is shown in more detail. The dried wood chips were allowed to dissolve for five days at 100°C without stirring in switchable ionic liquid of DBU, glycerol and S0₂ (i.e. SIL #3). The SIL-to-wood ratio used was 10: 1.

Examples 78 - 87; Dissolution tests for pine with different switchable ionic liquids

The dried pine chips were allowed to dissolve in different ionic liquids for three days and also for a longer period of five days without stirring. The SIL-to-wood ratio in these tests was 25: 1. The results are shown in table 13.

Table 13. Dissolution test results for pine

Example 88; Characterisation of the DBU/Glycerol/C0₂ system (SIL #3) by ^lH and ¹³C NMR spectroscopy and IR

NMR spectra were taken on neat samples of DBU/Glycerol (3: 1) i.e. SIL #3 before and after addition of C0₂. Due to the high viscosity of the SILs at room temperature the NMR spectra were recorded at 60°C to minimise signal broadening. 1H as well as quantitative 13 C NMR spectra was recorded. The spectra of the samples are shown in Figs. 3 and 4. Spectra were taken at 60 °C using external DMSO-dg as a reference. In order to assign the signals and to confirm the structures, different 2D NMR techniques were also utilised.

The ¹H NMR spectral data is shown in Table 14 and the ¹³C NMR spectral data is shown in Table 15. Most of the signals in the ¹H NMR spectra were broad and complex and no detailed spectral analysis was performed. However, the assignments of 1H 13

and C NMR signals were performed using standard 2D correlation NMR spectroscopy-

Table 14. 1H NMR shifts and signal assignments in spectra of DBU:Glycerol (3: 1) and DBU/Glycerol (3: 1)/C0₂. Shifts are referred to external DMSO (δ = 2.50 ppm)

The numbering of carbon atoms in DBU is shown in Figure 5.

Table 15. 13 C NMR shifts and signal assignments in spectra of DBU:Glycerol (3: 1) and DBU:Glycerol (3: 1):C0₂. Shifts are referred to external DMSO (δ = 39.50 ppm)

) The numbering of carbon atoms in DBU is shown in Figure 5. Approximate values measured by quant. ¹³C NMR.

The formation of the ionic liquid resulted in quite small signal shifts in the 1H NMR spectrum. The addition of C0₂ resulted in broadening of the signals. This was most marked in the signals of the protons of glycerol and the acidic proton of the protonated DBU. Moreover, the signal of the latter was shifted downfield by ca. 1.4 ppm, indicating an increase of acidity.

IR analysis:

Figure 6 shows an FT-IR of (a) DBU, (b) Glycerol and (c) DBU/glycerol mixture after bubbling C0₂ until there were no increases in weight. The IR spectrum of

DBU/glycerol/C0₂ showed evidence of N-H bands at 3223 and 3084 cm^"1 and evidence of the broad band of the free OH in glycerol at 3328 cm^"1, thereby confirming that DBU is protonated and the alcohol is deprotonated. The 1800-1450 cm^"1 spectral region [Fig. 6(b)] is dominated by the strong signal at 1641 cm^"1 assigned to proto- nated C=N, 1313 cm^"1 assigned to the C-Ν,1157,1112, assigned to C-0 and C-O-C bands respectively.

Example 89; Analysis of the recovered material from the spent ionic liquid (SIL#3)

Figure 7 shows the results of the acid methanolysis analysis done on the recovered material from the spent SIL (DBU/glycerol/CC^) i.e. SIL #3. Birch was allowed to dissolve for 5 days in SIL#3 at 100°C under normal pressure without stirring. The analysis shows that the material main component was hemicelluloses, which was about 35wt- % of the recovered material. From the figure it can be seen that the wood was hardwood because of high xylose content, which was about 70 wt- % of the hemicelluloses.

Example 90; Acid methanolysis test of spruce with SIL #21

Figure 8 shows results from the hemicelluloses analysis for treated spruce using SIL #21 for 3 days at 100°C with stirring. The weight reduction was 48 wt-%.

Claims

1. A method for fractionating of a lignocellulosic material and its constituents, which method comprises the steps of

a) preparing of a switchable ionic liquid (a SIL) by a switching reaction in which molecular starting compounds are switched to ionic liquid with the aid of an at least one acid gas, and thereafter

b) contacting said lignocellulosic material with said switchable ionic liquid and

c) allowing said lignocellulosic material to dissolve in said switchable ionic liquid for a dissolution time (t) to obtain a solid phase containing undissolved material and a liquid phase containing dissolved material, and then d) separating off said undissolved material to obtain "Products [1]" for further processing,

e) performing a reverse switching reaction to said liquid phase to switch said switchable ionic liquid into a molecular solution of said starting compounds containing said dissolved material; and to collect "Products [2]" f) adding of an anti-solvent into said molecular solution to precipitate said dissolved material

g) performing a phase separation to separate said precipitated material to collect "Products [3]" and to obtain a second liquid phase containing said anti-solvent and said molecular solution without dissolved material h) performing a liquid/liquid separation to said second liquid phase to recover said anti-solvent and said molecular starting compounds.

2. Method for fractionating according to claim 1, wherein said switchable ionic liquid is prepared by said switching reaction in which a mixture of an amidine or a guanidine and an OH-containing compound is bubbled with said at least one acid gas.

3. Method for fractionating according to claim 2, wherein said amidine is 1,8- diazabicyclo-[5.4.0]-undec-7-ene (DBU).

4. Method for fractionating according to claim 2, wherein said guanidine is 2- butyl-l,l,3,3-tetramethyl guanidine (BTMG).

Method for fractionating according to any of claims 2 to 4, wherein said OH- containing compound is an alcohol.

Method for fractionating according to any of claims 2 to 4, wherein said OH- containing compound is selected from the group consisting of a compound containing at least two OH-groups, a hydroxy alkyl ammonium compound and an amino alkyl sulfonic acid.

Method for fractionating according to claim 6, wherein said compound containing at least two OH-groups is defined as

Ri-(R₂-OH)_x

wherein

x > 2, preferably 2-6

Ri= hydrogen or alkyl or alkenyl or alkynyl or aryl or silyl or siloxyl; may be branched or cyclic and may be substituted or unsubstituted R₂= C, CH, CH₂

Method for fractionating according to any of the preceding claims, wherein after separating off said undissolved material said switchable ionic liquid is reused in the subsequent dissolution operation.

Method for fractionating according to any of the preceding claims, wherein said reverse switching reaction is performed by bubbling an inert gas through said liquid phase or by applying heat or vacuum on it.

10. Switchable ionic liquid obtained by bubbling at least one acid gas in a mixture of an amidine or a guanidine and an OH-containing compound selected from the group consisting of a compound containing at least two OH-groups, a hydroxy alkyl ammonium compound and an amino alkyl sulfonic acid.

11. Switchable ionic liquid according to claim 10, wherein said compound containing at least two OH-groups is defined as

R_!-(R₂-OH)_x

wherein

x > 2, preferably 2-6

Ri= hydrogen or alkyl or alkenyl or alkynyl or aryl or silyl or siloxyl; may be branched or cyclic and may be substituted or unsubstituted R₂= C, CH, CH₂.

12. Switchable ionic liquid according to claim 11, wherein said compound containing at least two OH-groups is selected from the group consisting of dietha- nolamine (DEA), glycerol, sorbitol, xylitol, ethylene glycol and propylene glycol.

13. Switchable ionic liquid according to any of claims 10 - 12, wherein said ami- dine is l,8-diazabicyclo-[5.4.0]-undec-7-ene (DBU).

Switchable ionic liquid according to any of claims 10 - 12, wherein said gua- nidine is 2-butyl-l, l,3,3-tetramethyl guanidine (BTMG).

Switchable ionic liquid according to any of claims 10 - 14, wherein said acid gas is carbon dioxide or sulphur dioxide or a mixture thereof or a flue gas con taining C0₂ and/or S0₂.