FIELD OF THE INVENTION

The present invention relates to a method for the production of liquefied cellulose-containing material, such as liquefied wood, wherein the liquefied product is suitable for use as fuel for combustion engines.

BACKGROUND

Procedures for the liquefaction of wood under the conditions that cause the depolymerisation of the natural polymers in wood, such as cellulose, hemicellulose and lignin are known. See, e.g., Slovenian patent applications: SI 21884: Liquefaction of wood with the use of the microwaves as a energy source. SI 21883: A method for the liquefaction of wood and wood wastes with polyols and acids. SI 21882: A method for the synthesis of the polyester based on the liquefied wood for the polyurethane foam production. SI 22448: Preparation and utilization of the liquefied wood for the production of the heating energy. SI 21884 describes the fast liquefaction of wood but due to the utilization of the microwaves it is too energy demanding. SI 21883 describes different procedures for the liquefaction of wood but these have yields of less than 64% and a reaction time 3 hours and more. SI 22448 describes the use of the liquefied wood for the production of the heating energy but does not mention the use as fuel for combustion engines .

Jasiukaityte et al . (2010, Lignin behavior during wood liquefaction - Characterization by quantitative ³¹ P, C NMR and size-exclusion chromatography, Catalysis Today, 156: 23-30) describe a method of liquefaction of wood, which method employs a solvent mixture including a large amount of glycerol. The liquefied composition so obtained shows unsatisfactory mechanical properties.

WO 2010/069582, WO 2009/115075, WO 2008/105618 and Zhu et al . (2006, Dissolution of cellulose with ionic liquids and its application: a mini -review. Green Chem, 8:325-327) describe various methods for the liquefaction of cellulose-containing solids. The resulting liquids, however, are not equally suitable for use as a fuel for combustion engines, specifically in Diesel engines, as compared with the biofuels of the current invention.

SUMMARY OF THE INVENTION

The inventors of the present invention have found that the prior art bio-fuels from the liquefaction of wood, e.g., the bio-fuels obtained by the method of Jasiukaityte et al . (ibid.) , are not ideal when used as fuel for combustion engines, because the resulting products have, e.g., a relatively high viscosity. The inventors have found that the high viscosity is a disadvantageous property, which renders the liquefied wood compositions unsuitable for most modern combustion engines .

The present invention is based on the unexpected finding that a fuel composition particularly suitable for use for combustion engines, such as Diesel engines, can be obtained from natural resources by liquefaction of cellulose-containing particles in a specific mixture of diethylene glycol, glycerol and p-toluenesulfonic acid, said mixture including a relatively large amount of diethylene glycol .

This sets the present invention apart from the methods of Jasiukaityte et al . (ijbid.), which uses relatively large amounts of glycerol.

Unlike many other methods of producing bio- fuel from natural starting materials (e.g., the method described in WO 2008/105618) , the inventive method does not include a fermentiation step.

The present invention thus relates to a method for the production of a liquid fuel from a cellulose- containing solid starting material, said method comprising contacting said solid starting material with a mixture comprising diethylene glycol, glycerol and p- toluenesulfonic acid (PTSA) , wherein ratio of diethylene glycol to glycerol in said mixture is from 1:1 to 20:1 by weight .

In preferred embodiments of the invention the ratio of diethylene glycol to glycerol in said mixture is from 1:1 to 15:1, even more preferred 1:1 to 10:1 by weight.

In other preferred embodiments of the invention the ratio of diethylene glycol to glycerol in said mixture is from 2:1 to 20:1, or from 2:1 to 15:1, even more preferred from 2:1 to 10:1 by weight.

The inventors have found that such relative amounts of diethylene glycol and glycerol yield bio- fuels having a viscosity which is particularly suitable for the use of the fuel for combustion engines, such as Diesel engines.

In a preferred embodiment of the invention the amount of PTSA in the mixture is from 0.5 %wt (% weight) to 10 %wt, more preferably 1 to 8 %wt , more preferably 2 to 5 %wt, more preferably 2 to 4 %wt, of the sum of weights of diethylene glycol and glycerol in the mixture. Without wishing to be bound by theory, PTSA serves as a catalyst for the dissolution of cellulose, hence, as a chemical enhancer of the dissolution process.

Fuel products of the present invention preferably have a viscosity at 20°C of between 0.5 and 10 Pa.s, more preferably of between 1 to 8 Pa.s, most preferably of 1.5 to 5 Pa.s. In another embodiment of the invention, the fuel products have a viscosity at 120°C of between 10-400 mPa.s, more preferably 20-200 mPa.s, most preferably 40- 150 mPa.s.

In a further embodiment of the invention the ratio of the weight of the cellulose-containing starting material to the sum of weights of diethylene glycol and glycerol is from 1:0.5 to 1:10, or 1:1 to 1:10, more preferably 1:1 to 1:6, most preferably 1:2 to 1:4 by weight .

In a further embodiment of the invention said solid starting material comprises at least one component selected from the group consisting of lignocellulosic material, wood, wood sawdust, wood chips, straw, hay, plant fibers, cellulose fibers, cotton fibers, bagasse, and waste materials from a lignin, a tannin or a furfural alcohol production process. A preferred starting material is lignocellulosic material, such as wood chips or wood sawdust .

In preferred starting materials of the present invention more than 90 %wt, preferably more than 95 %wt, most preferred more than 99 %wt of the particles have a particle size of less than 10 mm, 5 mm, 4 mm, or most preferred less than 2 mm. The particle size shall be understood as being the distance along the longest dimension of the particle.

In one embodiment the solid starting material comprises or consists of milled wood. Accordingly, the method may comprise a step of grinding the starting material to a suitable particle size of the invention, prior to the step of contacting the starting material with the mixture comprising diethylene glycol and glycerol .

In one embodiment of the invention said contacting is at a temperature of above 80°C, preferably at 80- 350°C, 100-250°C, 130-190°C, most preferred 150-180°C. A higher reaction temperature results in faster dissolution of the cellulose-containing starting material. Using the appropriate reaction temperature is advantageous to obtain a useful product. With too low reaction temperature, the reaction may not proceed at the appropriate reaction rate. With too high a temperature the reaction product may become a glue- like or rubberlike substance.

In a further preferred embodiment, the contacting is at atmospheric pressure. In other preferred embodiments the contacting is at 50-1000 kPa (0.5-10 bar), 100-500 kPa (1-5 bar) , most preferably at 100-200 kPa (1-2 bar) .

In a further embodiment of the invention said contacting is for a time period of between 0.5 and 10 hours, more preferably 0.8-7 hours, or 1-5 hours, most preferred 1.5 to 2 hours.

In a further embodiment of the invention, during said contacting step, said solid starting material and said mixture are blended with a blending device, such as a mixer.

In a further embodiment of the invention the method further comprises a filtration step for removing particles larger than 1, 2, 4, 8, or 16 μνη from said fuel after said contacting step.

Preferably, the methods of the invention do not include a fermentation step. Accordingly, preferred products of the invention comprise less than 10 %wt, or 1 %wt, or 0.1 %wt ethanol, or most preferred no ethanol (or no detectable amounts of ethanol) .

The invention also relates to a method for the liquefaction of cellulose-containing starting material of the above defined kind.

In accordance with another embodiment the invention relates to a method of dissolution of cellulose of the above defined kind.

In yet another embodiment the invention relates to the use of a mixture comprising diethylene glycol and glycerol for the liquefaction of cellulose-containing solid material.

The invention further relates to the use of the products obtained by methods of the current invention as fuel for a combustion engine.

The invention also relates to a liquid fuel produced by a method of the invention.

DETAILED DESCRIPTION OF THE INVENTION

"Cellulose", in accordance with the present invention, shall be understood to relate to an organic compound with the formula (C _G H ₁₀ 05) _n , in particular to a polysaccharide consisting of a linear chain of a plurality (e.g., more than 100, or more than 1000) 3(1→4) linked D-glucose units.

A "combustion engine", according to the present invention, is any type of engine using the oxidation of fuel as the source of energy. Combustion engines of the invention may be internal combustion engines or external combustion engines. An internal combustion engine is an engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber to produce the thermal/mechanical energy. An external combustion engine is a heat engine where an (internal) working fluid is heated by combustion of an external source, through the engine wall or through a heat exchanger. The fluid then, by expanding and acting on the mechanism of the engine, produces mechanical energy. Preferred internal combustion engines are two-stroke cycle engines, four- stroke cycle engines, Diesel engines, Atkinson cycle engines, Wankel engines, Brayton cycle engines, gas turbines, jet engines (including turbojet, turbofan, ramjet, Rocket) . Preferred external combustion engines are organic Rankine cycle engines, steam engines, Stirling engines. Particularly preferred engines in the context of the present invention are Diesel engines. Further preferred engines are turbine engines.

"Diethylene glycol" shall be understood as being the chemi having the following structure:

"Fuel", according to the present invention, shall be understood as being any material that stores chemical energy which can later be converted to thermal energy to perform mechanical work in a controlled manner.

"Glycerol", accoding to the invention, shall be understood to be the chemical entity having the following structure :

"Liquefaction", according to the present invention, shall be understood as being the process of dissolving a solid material in a liquid material, the solvent.

"P-toluenesulfonic acid" (4 -methylbenzenesulfonic acid, PTSA) , according to the invention, shall be understood to be the chemical entity having the following structure :

"Fermentation", within the context of the present invention, shall be understood as being the process of converting sugars, such as mono-saccharides or disaccharides, into ethanol by the action of microorganisms, e.g., yeast.

The method for the liquefaction of solid renewable resources, according to the invention, utilizes wood, sawdust or other cellulose-containing materials, e.g., cellulose, cotton, waste materials from lignin, tannin or furfural alcohol -production processes.

The present invention uses a mixture of the diethylene glycol and glycerol, preferably in a ratio that yields a product with appropriate viscosity and particle size. Preferably, the particle size of the particles in the resulting fuel is below 2 μπι.

An advantageous property of the methods of the invention is that by changing the ratio between the diethylene glycol and glycerol, the viscosity of the liquefied solid material can be adjusted to be suitable for use as a fuel in specific combustion engines.

The production of liquefied cellulose-containing material preferably takes place in an inert reaction vessel, preferably with the aid of a mixer.

The invention thus relates to a chemical reaction process of the liquefaction of renewable resources to the product with particles size of preferably less than 2 μχα and a viscosity, adopted for the use as a fuel for combustion engines. The invention uses a mixture of the diethylene glycol and glycerol for the liquefaction of renewable resources in a ratio that gives a product with a viscosity and a particle size according to the demands for combustion engine fuels. The viscosity variation can be achieved by changing the ratio between the diethylene glycol and glycerol . With higher loading of diethylene glycol the viscosity is reduced. Such products can then be used as a fuel in the piston engines and internal combustion turbine engines. The liquefied products with higher viscosity (higher loading of glycerol in production formulation) can be used as a fuel in external combustion engines, e.g., in engines with higher tolerance to low fuel quality.

The invention relates to a process for the liquefaction of wood, wood wastes and similar materials in a mixture of diethylene glycol and glycerin in a ratio that enables the production of a liquid fuel product with viscosity and particles size according to the demands for fuels for combustion engines. The fuel product of the invention is for the replacement of materials produced from crude oil . An important property of the fuel product of the invention is a high energy value fuel for combustion engines. The product reduces the carbon dioxide emission from fossil fuels.

The invention presents a chemical reaction process of liquefaction of renewable resources. The liquefaction reaction takes place at elevated temperatures and in the presence of a mixture of diethylene glycol and glycerol . 3 %wt of p-toluenesulfonic acid (relative to the total diethylene glycol and glycerol content) is added. The reaction preferably takes place at temperatures between 150°C and 180°C in a closed reactor vessel made from inert materials, preferably with internal mixing and preferably also with attached condenser for the waste vapor removal . Renewable resources usable according to the invention are wood, wood wastes and or similar materials, such as cellulose, cotton, waste materials from the production of lignin, tannin and furfural alcohol .

Before the liquefaction reaction, the solid materials are preferably milled to particles of less than, e.g., 10 mm or 5 mm in size (i.e., largest dimension of the particle) . Smaller particles give higher yields in a shorter reaction time. All ingredients are put into the reactor. The mixture is preferably mixing and heated to temperatures between 150°C and 180°C. The volatile side products of the reaction can be collected by using a condenser. Side products are water, small amounts of acetic acid and furfural. The reaction preferably takes 1.5 to 2 hours. Particles larger than 2 μτη can optionally be removed by filtration.

The invention relates to a method for the liquefaction of solid renewable resources, such as wood, sawdust, cellulose, cotton, waste materials after production of lignin, tannin and furfural alcohol. The invention lies in the use of a mixture of the diethylene glycol and glycerol in a ratio that yields a product with appropriate viscosity and particle size, e.g., below 2 μιτι, for use as a fuel in combustion engines. The product can be used as the sole liquid fuel for combustion engines, as a replacement for fuels otherwise produced from crude oils, or it can be used in admixture with such fuels produced from crude oils or mineral oils.

The invention is now described with reference to the following examples that shall not be construed as limiting the scope invention.

EXAMPLE 1

1000 ml reaction vessel with attached mixer and condenser is charged with 100 g of the milled wood, 300 g of a mixture of diethylene glycol : glycerol at a 1:1 ratio by weight. 9 g of p- toluenesulfonic acid is also added. The mixture is heated to 160°C to 180°C under the constant stirring. After 2 hours the product is cooled to room temperature and viscosity and particles size determined. Viscosity at 20°C is 4.3 Pa . s and at 120°C is 130 mPa.s. The particle size is below 2 μπι.

EXAMPLE 2 1000 ml reaction vessel with attached mixer and condenser is charged with 100 g of the milled wood, 300 g of a mixture of diethylene glycol : glycerol at a ratio of 4:1 by weight. 9 g of p- toluenesulfonic acid is also added. The mixture is heated to 160 °C to 180 °C under the constant stirring. After 2 hours the product is cooled to room temperature and viscosity and particles size determined. Viscosity at 20°C is 2.3 Pa.s and at 120°C is 75 mPa . s . The particles size is below 2 μχη.

EXAMPLE 3

1000 ml reaction vessel with attached mixer and condenser is charged with 100 g of the milled wood, 300 g of the mixture diethylene glycol : glycerol at a ratio of 9:1 by weight. 9 g of p- toluenesulfonic acid is also added. The mixture is heated to 160°C to 180°C under the constant stirring. After 2 hours the product is cooled to room temperature and viscosity and particles size determined. Viscosity at 20°C is 1.8 Pa.s and at 120°C is 65 mPa.s. The particles size is below 2 μτ ^η .

EXAMPLE 4

Liquefied wood was prepared substantially as in Example 1, but the weight proportions of diethylene glycol and glycerol were stepwise varied from 100 %wt glycerol to 100 %wt diethylene glycol. The following viscosities of the resulting fuel were obtained (20°C) :

60:40 6.2 Pa.s

50 : 50 4.2 Pa.s

40 : 60 3.9 Pa.s

30 :70 2.7 Pa . s

20 :80 2.1 Pa.s

10 :90 1.9 Pa.s

100%wt DEG 1.8 Pa . s

For comparison, the viscosity of glycerol at 20°C was determined to be 1.4 Pa.s and the viscosity of diethylene glycol was 0.036 Pa.s.