Patent Application
20080023162
In one aspect of the invention there is provided a method for dissolving lignocellulosic material comprising mixing the lignocellulosic material with an ionic liquid solvent under microwave irradiation and/or under pressure in the substantial absence of water to completely dissolve the lignocellulosic material.
In a preferred embodiment microwave irradiation is applied to assist in dissolution.
It is also possible to apply pressure to assist in dissolution. The pressure is preferably below 2.0 MPa, more preferably below 1.0 MPa and most preferably between 0.2 MPa and 0.9 MPa.
The dissolution of the lignocellulosic material can be carried out at a temperature between 0° C. and 250° C., preferably at a temperature between 20° C. and 200° C. and more preferably at a temperature between 50° C. and 170° C., such as between 80° C. and 150° C. The heating can be carried out by microwave irradiation.
The solution is agitated until complete dissolution is obtained.
In the dissolution no auxiliary organic solvents or co-solvents, such as nitrogen-containing bases, e.g. pyridine disclosed in U.S. Pat. No. 1,943,176, are necessary. Preferably such solvents are omitted.
The ionic liquid solvent is molten at a temperature between −100° C. and 200° C., preferably at a temperature of below 170° C., and more preferably between −50° C. and 120° C.
The cation of the ionic liquid solvent in preferably a five- or six-membered heterocyclic ring optionally being fused with a benzene ring and comprising as heteroatoms one or more nitrogen, oxygen or sulfur atoms. The heterocyclic ring can be aromatic or saturated. The cation can be one of the following:
wherein R1 and R2 are independently a C1-C6 alkyl or C2-C6 alkoxyalkyl group, and R3, R4, R5, R6, R7, R8 and R9 are independently hydrogen, a C1-C6 alkyl, C2-C6 alkoxyalkyl or C1-C6 alkoxy group.
In the above formulae R1 and R2 are preferably both C1-C4 alkyl, and R3-R9, when present, are preferably hydrogen.
C1-C6 alkyl includes methyl, ethyl, propyl, iso-propyl, butyl, sec-butyl, tert-butyl, pentyl, the isomers of pentyl, hexyl and the isomers of hexyl.
C1-C6 alkoxy contains the above C1-C6 alkyl bonded to an oxygen atom.
C2-C6 alkoxyalkyl is an alkyl group substituted by an alkoxy group, the total number of carbon atoms being from two to six.
Preferred cations have following formulae:
wherein R1-R5 are as defined above.
An especially preferred cation is the imidazolium cation having the formula:
wherein R1-R5 are as defined above. In this formula R3-R5 are preferably each hydrogen and R1 and R2 are independently C1-C6 alkyl or C2-C6 alkoxyalkyl. More preferably one of R1 and R2 is methyl and the other is C1-C6 alkyl.
The anion of the ionic liquid solvent can be halogen such as chloride, bromide or iodide;
pseudohalogen such as thiocyanate or cyanate;
perchlorate;
C1-C6 carboxylate such as formate, acetate, propionate, butyrate, lactate, pyruvate, maleate, fumarate or oxalate;
nitrate;
C2-C6 carboxylate substituted by one or more halogen atoms such as trifluoroacetic acid;
C1-C6 alkyl sulfonate substituted by one or more halogen atoms such as trifluoromethane sulfonate (triflate);
tetrafluoroborate BF4−; or
phosphorus hexafluoride PF6−.
The above halogen substituents are preferably fluoro.
The anion of the ionic liquid solvent is preferably selected among those providing a hydrophilic ionic liquid solvent. Such anions include halogen, pseudohalogen or C1-C6 carboxylate. The halogen is preferably chloride, bromide or iodide, and the pseudohalogen is preferably thiocyanate or cyanate.
If the cation is a 1-(C1-C6-alkyl)-3-methyl-imidazolium, the anion is preferably a halogenid, especially chloride.
The melting point for the preferred ionic liquid solvent 1-butyl-3-methyl-imidazolium chloride (BMIMCI) is about 60° C.
The term “lignocellulosic material” as used in this specification means a natural material containing cellulose and lignin that has not been subjected to a pulping or defibering process. Thus, chemical and mechanical pulps and the like are not included in said term.
The lignocellulosic material is preferably native wood that has not been subjected to any chemical or mechanical pulping process. Besides wood also other native lignocellulosic materials can be used, such as straw.
The lignocellulosic material is prior to the dissolution reduced to a desired size and form, e.g. to small chips, and, if necessary, dried.
The phrase “in the substantial absence of water” means that not more than a few percent by weight water is present is the dissolution. Preferably, the water content is less that 1 percent by weight.
In another aspect of the invention there is provided a solution comprising dissolved lignocellulosic material in an ionic liquid solvent that is substantially free of water.
The ionic liquid solvent and the lignocellulosic material are as defined above.
The lignocellulosic material can be present in an amount of about 1% to 30% by weight of the solution. Preferably the amount is about 10% to 20%.
In a further aspect of the invention there is provided a method for separating cellulose from a lignocellulosic material comprising mixing the lignocellulosic material with an ionic liquid solvent under microwave irradiation and/or under pressure in the substantial absence of water to completely dissolve the lignocellulosic material, thereby obtaining a solution of the lignocellulosic material, and thereafter precipitating the cellulose by adding a non-solvent for the cellulose.
The ionic liquid solvent and the lignocellulosic material are as defined above.
According to an embodiment of this method the lignin is removed from said solution before precipitating the cellulose.
Said non-solvent is a liquid that is miscible with the ionic liquid solvent and includes water, an alcohol, a ketone, acetonitrile or an ether. The alcohol can for example be methanol or ethanol. The ketone can for example be acetone. The ether can for example be furan or dioxane. The non-solvent is preferably water, an alcohol or a ketone.
After the separation of the precipitated cellulose, the non-solvent can be separated from the ionic liquid solvent, for example by distilling or drying in case water is used as the non-solvent. Thereafter the ionic liquid solvent can be reused.
In a still further aspect of the invention there is provided a method for the delignification of a lignocellulosic material comprising mixing the lignocellulosic material with an ionic liquid solvent under microwave irradiation and/or under pressure in the substantial absence of water to completely dissolve the lignocellulosic material, thereby obtaining a solution of the lignocellulosic material, and thereafter subjecting the solution to extraction to separate lignin from the solution.
The ionic liquid solvent and the lignocellulosic material are as defined above.
The invention additionally provides a method for the separation of extractives or a component thereof from a lignocellulosic material comprising mixing the lignocellulosic material with an ionic liquid solvent under microwave irradiation and/or under pressure in the substantial absence of water to completely dissolve the lignocellulosic material, thereby obtaining a solution of the lignocellulosic material, and thereafter separating the extractives or a component thereof from said solution.
The ionic liquid solvent and the lignocellulosic material are as defined above.
Typical extractives to be separated by this method includes fats, fatty esters, terpenes and resin acids.
The extractives or a component thereof can be separated from the solution by extraction or by distillation.
As the present invention has made it possible to dissolve wood, straw etc. into an ionic liquid solvent, the basic consept of the invention can be applied e.g. for
The percentages in this specification refer to % by weight unless otherwise specified.
Dissolution of Plywood Sawdust
50 mg of plywood sawdust was mixed with an ionic liquid (BMIMCI, 5 g, melting point 60° C.) in 1% solution. The resulting mixture was heated by microwaves in a MW reactor designed for organic synthesis in 10 min sequences at temperatures ranging from 80 to 150° C. Partial dissolution could be detected.
The resulting solution after the experiment was partly cloudy. The cloudiness resulted from the adhesives present in the plywood.
Dissolution of Softwood
112 mg of small chips of Finnish softwood were mixed with an ionic liquid (BMIMCI, 5 g, melting point 60° C.). The resulting mixture was heated by microwaves in a MW reactor designed for organic synthesis in 10 min sequences at temperatures ranging from 80 to 150° C.
After 10 min at 80° C., the dissolution of the wood was visible. The outer layers of wood sticks became transparent and small fibers appeared on the surface of the sticks. The heating was continued in 10 min sequences at 100° C. for one hour. The wood sticks were gradually dissolved into solution. While decreasing in size, the sticks gradually lost their woodlike structure and became more like a bunch of fibers gradually dissolving into solution. After heating one hour at 150° C. even the still remaining small quantity of undissolved material was completely dissolved resulting in an amber coloured, transparent and viscous solution.
The ionic liquid having initial melting point at 60° C., remained as a viscous solution at room temperature.
Dissolution of Straw, 1% Solution
50 mg of straw was mixed with an ionic liquid (BMIMCI, 5 g, melting point 60° C.) in 1% solution. The resulting mixture was heated by microwaves in a MW reactor designed for organic synthesis for 10 minutes at 170° C. Full dissolution could be detected resulting in a darkish, amber coloured, transparent and viscous solution.
Dissolution of Straw, 2% Solution
100 mg of straw was mixed with an ionic liquid (BMIMCI, 5 g, melting point 60° C.) in 2% solution. The resulting mixture was heated by microwaves in a MW reactor designed for organic synthesis for 10 minutes at 170° C. Full dissolution could be detected resulting in a darkcoloured, transparent and viscous solution. The viscosity increased somewhat compared to 1% solution in example 3.
| Number | Date | Country | Kind |
|---|---|---|---|
| 20031156 | Aug 2003 | FI | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/FI04/00476 | 8/13/2004 | WO | 00 | 1/4/2007 |
