The present invention relates to a process for obtaining compounds that are useful for the production of biofuels, in particular glycerine, alone or mixed with propylene glycol, wherein said process comprises the solution of cellulose in an ionic liquid and the subsequent hydrogenation of said solution.

Ionic liquids are known in literature for being optimum solvents of cellulose, obtaining a quantity of dissolved cellulose even higher than 20% by weight without there being any degradation of the cellulose structure (Y. Cao et al . , Room temperature ionic liquids: a new and versatile platform for cellulose processing Chemical Engineering Journal 147, 2009, 13- 21) .

In recent years, greater attention is being paid towards technologies aimed at producing fuels deriving from alternative renewable energy sources, such as, for example, vegetable oils, animal fats, biomasses, algae, due to both a greater awareness with respect to environmental problems caused by emissions produced by the combustion of fuels deriving from fossil energy sources, such as, for example, coal, petroleum, natural gas, and also as a result of the increased cost in petroleum itself.

The use of biodiesel and hydrotreated vegetable oils (HVO) has therefore started, as such, or in a mixture with gasoil, to add aliquots of fuels coming from sources different from fossil sources, in compliance with new Community regulations on fuels (use of aliquots of fuels of a biological origin (so-called "GREEN" components) within quantities of fuels of a fossil origin) . Biodiesel generally comprises a mixture of fatty acid alkyl esters, in particular mixtures of fatty acid methyl esters (FAME) and can be produced starting from raw materials of a natural origin containing triglycerides (generally triesters of glycerine with long-alkyl-chain fatty acids) . Said raw materials as such, or the triglycerides obtained after subjecting said raw materials to separation, are subjected to a transesterification process in the presence of an alcohol, in particular methanol, and a catalyst, so as to obtain FAMEs. The use of said FAMEs, however, as such or in a mixture with gasoil, creates some problems relating to stability and oxidation. Furthermore, during their synthesis, there is the formation, as by-product, of glycerine (about 10% by weight) .

An important aspect for developing the production process and use of biodiesel is therefore the use of glycerine for obtaining further aliquots of green fuels .

In this respect, among the known uses of glycerine, there is that of reacting it, through an etherification reaction, with olefins to give the corresponding ethers, which can be used as oxygenated components for gasoline and diesel. The olefin mainly used and object of numerous patents, is isobutene. The reaction with isobutene leads to the formation of tert-butyl ethers of glycerine, of which the most interesting is di-tert- butyl ether. In said ethers, however, the biological component is a strict minority, as they are composed of two, or rather three, molecules of isobutene per molecule of glycerine: their contribution in reaching the aliquot of a biological origin is consequently not sufficiently high.

A method has therefore been conceived for obtaining glycerine, alone or in a mixture with propylene glycol ( 1 , 2-propanediol ) , starting from a natural compound such as cellulose. Said compounds can then be used as starting compounds in a method for obtaining fuel components, in particular diesel or gasolines deriving from renewable sources.

This method therefore has the advantage of obtaining glycerine, alone or mixed with propylene glycol, starting from biodegradable compounds with a high availability and at low costs, preferably deriving from waste matrices.

Processes are known in the art for the degradation of cellulose, for example by means of hydrolysis.

International patent application WO2009/030949 in the name of The Queen's University of Belfast describes a hydrolysis process of cellulose for obtaining monosaccharides, disaccharides or oligosaccharides, which comprises the dissolution of cellulose in an ionic liquid, followed by hydrolysis to glucose in an acid environment.

In this case therefore, only a mixture of sugars is obtained, as, in the absence of hydrogen, hydrogenolysis products such as glycols cannot be obtained .

International patent application WO 2012/035160 in the name of Bioecon International Holding N.V. describes the use of ionic liquids for dissolving cellulose, but not lignin, starting from a lignocellulosic composite material. It should be pointed out, however, that the compounds used in this patent application as ionic liquids are not actually ionic liquids, but inorganic salts, which are liquid at a temperature lower than 80°C. See, for example, the molten salt hydrates mentioned therein.

The difference between molten salts and ionic liquids is treated in P. Wasserscheid, T. Welton (eds.) "Ionic Liquids in Synthesis" (2003) Wiley-VCH, page 41, where it can be read that ionic liquids are characterized by organic cations whereas molten salts are characterized by inorganic cations.

The Applicants of the present invention have therefore found a process for obtaining glycerine, alone or mixed with propylene glycol, comprising a dissolution step of the cellulose in an ionic liquid and a hydrogenation step of said cellulose.

Optionally, before the hydrogenation step of the cellulose, a hydrolysis step of the cellulose to glucose can be present (step a')), which is effected in an aqueous environment, preferably in an acid aqueous environment .

A first aspect of the invention therefore relates to a process for the production of glycerine, alone or in a mixture with propylene glycol, which comprises the following steps:

a) dissolving a cellulose in an organic ionic liquid; b) subjecting the solution obtained in step a) to a catalytic hydrogenation reaction.

Optionally, before the catalytic hydrogenation, the cellulose can be hydrolyzed to glucose in an aqueous environment, preferably an acid aqueous environment (step a' ) ) ·

The organic ionic liquid used in the present invention is selected from salts of tetra- alkylammonium, tetra-alkylphosphonium, trialkyl- sulfonium, pyridinium, imidazolium, guanidinium, cholinium, preferably having the following general formulae :

R

-N-

R

tetra-alkylammonium salts [ I ]

R

-P-

R

tetra-alkylphosphonium salts (II);

R ¹

R ² -S ⁺ X

R ³

trialkyl-sulfonium salts (III);

pyridinium salts (IV);

imidazolium salts (V) ; wherein R is hydrogen or a linear or branched alkyl group, preferably having a number of carbon atoms ranging from 1 to 12, or an alkoxyalkyl group -(CH ₂ ) _n OH with n preferably ranging from 2 to 8, or a substituted amine group having formula

Yi

/

N

\

Y ₂

- wherein Yi and Y ₂ are independently selected from each other from hydrogen, methyl or ethyl; and

wherein R ² , R ³ and R ⁴ are linear or branched alkyl groups, preferably having a number of carbon atoms ranging from 1 to 12, more preferably from 1 to 8 carbon atoms or hydrogen, and

wherein X is an anion, preferably selected from halide, phosphate, hexafluorophosphate, hexafluoroantimonate, trifluoromethanesulfonate, tetrafluoroborate, trifluoroacetate, bistrifluoromethylsulfonylimidium and acetate, and even more preferably X is selected from chloride, hexafluorophosphate, trifluoromethylsulfonate and phosphate .

According to a preferred aspect of the invention, for processes at a moderate temperature, i.e. at a temperature lower than 50°C, X is acetate.

Saturated cations, without double bonds, or with a double bond in the molecule, are particularly preferred as cations.

Guanidinium salt having general formula (VI) is among the preferred salts:

guanidinium salts (VI);

wherein R ¹ , R ² , R ³ , R ⁴ , R ⁵ , R ⁶ are independently selected from each other from linear or branched alkyl groups, preferably with a number of carbon atoms ranging from 1 to 12, more preferably from 1 to 8 carbon atoms; or they are hydrogen; and

wherein X is preferably selected from halide, hexafluorophosphate and trifluoromethanesulfonate .

If the ionic liquid is selected from cholinium salts, salts having general formula (VII) are preferred :

cholinium salts (VII) wherein R , R and R are independently selected from each other from linear or branched alkyl groups, preferably with a number of carbon atoms ranging from 1 to 12 and even more preferably from 1 to 8 carbon atoms; or they are hydrogen; and

wherein X is preferably selected from halide, hexafluorophosphate and trifluoromethanesulfonate .

According to a preferred aspect, the cholinium salts can be used as such or in a mixture with other compounds, such as oxalic and/or citric acid, in order to further lower its melting point.

If oxalic acid and/or citric acid are added to the cholinium salts, the molar ratio between oxalic acid and/or citric acid and cholinium salt preferably ranges from 0.1:1 e 10:1.

According to a preferred aspect of the present invention, in step a) the dissolution of the cellulose can be facilitated by heating the cellulose-ionic liquid mixture to temperatures ranging from 20 to 150°C, preferably for a period of time ranging from 0.1 to 10 hours.

After the dissolving step of the cellulose in the ionic liquid, the solution obtained in step a) is subjected to a catalytic hydrogenation reaction.

According to a preferred aspect, among the catalysts that can be used for the catalytic hydrogenation, a nickel-based catalyst supported on tungsten carbide in an autoclave, is particularly preferred, according to what is described by N. Ji, T. Zhang et al . in Angew. Chem. Int. Ed., 2008, 47, 8510- 13, or a metal of group VIII B supported on SBA-15, according to what is described by M. Zheng, A. Wang, T. Zhang, in ChemSusChem, 2010, 3, 63-66, or a ruthenium- based catalyst supported on WO ₃ according to what is described in Z. Thai, J. Zhang, T. Zhang in Chem. Commun. 2012, 48, 7052-5.

The catalysts indicated above are preferably used at a temperature ranging from 150°C to 300°C, preferably from 220°C to 280°C, and even more preferably at 245°C.

The catalysts indicated above are preferably used at a hydrogen pressure ranging from 10 bar (1 MPa) to 80 bar (8 MPa), preferably ranging from 20 bar (2 MPa) to 65 bar (6.5 MPa) and even more preferably at a pressure of 60 bar (6 MPa) of hydrogen.

According to an even more preferred embodiment, a nickel-based catalyst is used, supported on tungsten carbide in an autoclave, at 245°C and 60 bar of hydrogen .

At the end of the catalytic hydrogenation step, glycerine is obtained, alone or in a mixture with propylene glycol in variable ratios with respect to one another, depending on the catalyst used and process conditions adopted, whereas the ionic liquid can be separated and re-used for a subsequent hydrogenation reaction of cellulose.

Operating under the hydrogen pressure conditions and hydrogenation temperature described hereunder, a more forced hydrogenation of cellulose is avoided, giving lighter products such as, for example, light alcohols (ethanol, methanol) or paraffins.

Before the catalytic hydrogenation step, a hydrolysis step in an aqueous environment of the cellulose, can be optionally carried out, preferably in an acid aqueous environment (step a' ) ) ·

In said optional step, water is added to the solution obtained in the previous step a) , in a weight ratio preferably ranging from 0.1 to 1 and from 10 to 1 with respect to the quantity of cellulose dissolved in the ionic liquid.

According to a preferred aspect, the addition of water is effected in fractionated portions, dividing the quantity of water added into at least three fractions.

An aqueous solution of glucose is thus obtained. In order to facilitate the hydrolysis of the cellulose to glucose, the water added can preferably contain a certain quantity of strong mineral acid, such as, for example, sulfuric acid, perchloric acid, hydrochloric acid, trifluoromethanesulfonic acid, methanesulfonic acid and preferably sulfuric acid, wherein the mineral acid is used in a weight ratio preferably ranging from 1 to 30%, and even more preferably ranging from 1 to 10% by weight with respect to the quantity of cellulose dissolved in the ionic liquid .

According to a preferred aspect of the present invention, the mixture consisting of water and ionic liquid in which the cellulose is dissolved is then heated to a temperature ranging from 50 to 150°C, preferably for a period of time ranging from 1 to 10 hours. As resulting from the reaction, the cellulose is hydrolyzed to glucose dissolved in the aqueous phase. At the end of the reaction, the ionic liquid and an aqueous solution of glucose is therefore obtained.

If the ionic liquid and aqueous solution are not miscible, the two steps can be separated physically, using a common liquid-liquid separator, such as, for example, a separator funnel or, in the case of an industrial process, a florentine separator, and the ionic liquid can be re-used, whereas the aqueous glucose solution can be subjected to evaporation. The glucose can then be subjected to the catalytic hydrogenation of step b) to preferably obtain two molecules of glycerine or one of glycerine and one of propylene glycol, wherein the hydrogenation reaction is preferably carried out within a temperature ranging from 220°C to 280°C, and a hydrogen pressure ranging from 2 MPa to 6.5 MPa. The preferred reaction conditions are 245°C and 6 MPa of hydrogen.

If the ionic liquid is miscible with water, the mixture can be subjected to distillation to remove the water and obtain a solution of glucose in the ionic liquid, which can be hydrogenated according to what is described as for the previous case.

According to a preferred aspect of the present invention, the reaction mixture, comprising glycerine, alone or in a mixture with propylene glycol, is subjected to a further separation step c) , preferably by means of physical separation methods, more preferably distillation, in order to obtain glycerine, alone or in a mixture with propylene glycol in purified form, to be used for the production of biocomponents useful for the production of biofuels.

According to a preferred aspect, the glycerine, alone or in a mixture with propylene glycol, obtained according to the process of the invention, is used in an integrated process which allows fuel components to be prepared, in particular diesel or gasolines, starting from glycerine.

The above integrated process allows various types of fuel components to be contemporaneously obtained, whose proportion can be varied depending on market demands and requirements. In particular, said integrated process comprises:

(A) a transformation of glycerine to an alkoxy- propanediol having formula RO-CH ₂ -CHOH-CH ₂ OH, wherein R is a linear or branched Ci-Cs alkyl;

(B) a transformation of glycerine to 1,2- propanediol CH ₃ -CHOH-CH ₂ OH;

(C) dehydration of the 1 , 2-propanediol obtained in (B) to propionic aldehyde;

(D) reaction of part of the propionic aldehyde obtained in (C) with the alkoxy-propanediol having formula RO-CH ₂ -CHOH-CH ₂ OH obtained in (A) to give an acetal having formula a) :

wherein R is a linear or branched Ci-Cs alkyl;

(E) transformation of part of the propionic aldehyde obtained in (C) to propionate having formula CH ₃ -CH ₂ -COOR' , wherein R' is a linear or branched Ci-Cs alkyl .

According to said process, the propionic aldehyde obtained from the transformation (C) is partly fed to the transformation (D) and for the remaining part fed to the transformation (E) : the quantities fed to the two transformations can be calibrated as desired, depending on the final component, propionate or acetal (a) , to be obtained in a larger quantity, depending on market requirements.

According to a further preferred aspect of the present invention, the cellulose to be used as raw material in the process of the invention for obtaining glycerine, alone or in a mixture with propylene glycol, can be obtained from waste-paper or scraps of paper mills .

In this way, there are further advantages, such as for example, the availability of the raw material itself. Waste-paper or scraps of paper mills, in fact, represent a source of supply which is always available and does not depend on the season. This problem has been encountered in the production of biofuels starting from waste from agricultural processing (for example, common reed, corn cuttings), also entailing considerable costs for the storage of said material. Furthermore, said waste from agricultural processing, due to its high water content, requires a drying treatment which necessarily creates further costs. This problem, on the other hand, does not apply to waste- paper or scraps of paper mills, which have a much lower water content, consequently not requiring drying treatment in order to be preserved.

A further advantage lies in the fact that the supply of paper, in particular deriving from scraps of paper mills, is provided free of charge by the paper mills themselves, and consequently the supply of raw material corresponds to a cost which is potentially equal to zero.

Finally, as this is a material that has already been used, said paper does not involve direct cultivation and consequently does not enter into competition with human nutrition.

Secondly, the biocomponents for gasolines or gasoil obtained starting from glycerine and/or propylene glycol obtained with the process of the invention, have advantageous characteristics such as a high octane number (or cetane number) , a high calorific value, complete miscibility with the hydrocarbon phase and an extremely low affinity with the aqueous phase. Furthermore they are not hygroscopic. There is consequently a reduction in problems linked to the miscibility and corrosion of the engine parts due to the presence of traces of water.

The present invention will now be described, for illustrative and non-limiting purposes, with particular reference to some specific embodiment examples, but it should be understood that variations and/or modifications can be applied by skilled persons in the field, all included in the relative protection scope, as defined by the enclosed claims.

EXAMPLES

Example 1

100 g of paper consisting of pure cellulose, were dissolved in 500 g of N, N, N' , N' tetrahexyl, N", N"dimethyl guanidinium chloride, by heating until reaching a temperature of 100°C, thus obtaining a limpid solution. A catalyst consisting of Ruthenium on tungsten oxide (2.4% Ru by weight), prepared according to what is described in Z. Thai, J. Zhang, T. Zhang in Chem. Commun., 2012, 48, 7052-54, Table 1, compound 4, was charged into a fixed-bed reactor. The reactor was heated until reaching a temperature of 245°C and the solution of cellulose in ionic liquid was fed with hydrogen at 6 MPa, in a ratio of 10 moles of hydrogen per mole of glucose contained in the cellulose. The samples were collected, from which the products obtained were subsequently distilled at a reduced pressure equal to 1 Pa (the ionic liquid has a practically zero vapour pressure) , obtaining a conversion of the cellulose equal to 90%, with a molar selectivity to glycerine of 52%, 1,2 propanediol 47% and 1% of ethylene glycol. The products of interest, i.e. glycerine and/or propylene glycol, were separated by fractionated distillation and sent to the production of biofuels.

Example 2

50 g of paper consisting of pure cellulose, were dissolved in 500 g of 1 butyl chloride, 3 methyl imidazole chloride, heating to a temperature of 100°C for an hour. A limpid solution of cellulose in the ionic liquid was obtained, which was introduced into an autoclave; as the ionic liquid was at an almost zero vapour pressure, no pressure increase was observed in the autoclave. Said limpid solution was heated to 150°C and 100 g of an aqueous solution at 5% of sulfuric acid were added in four equal fractions. At the end of the addition, the whole mixture was kept under stirring conditions for a further four hours under the same temperature conditions. At this point, after cooling, the yield to reducing sugars (glucose + fructose) was determined by means of HPLC, which proved to be equal to 75%. The sugars thus obtained were separated by dissolution in distilled water and subsequent crystallization.

The mixture of glucose and fructose (75% molar glucose + 25% molar fructose) is dissolved in 1 methyl, 3 butyl imidazole tetrafluoroborate, obtaining a solution at 10% by weight.

A commercial catalyst consisting of Pt/C at 5% by weight (Sigma Aldrich) , was added to this solution, in a quantity of 2% by weight with respect to the weight of glucose and fructose. This suspension was introduced into an autoclave and was heated to 120°C, feeding hydrogen for a period of 6 hours. Total molar ratio ¾/ sugars 10/1.

After this period, the autoclave was cooled and the reaction products were analyzed by gas chromatography: the conversion of sugars proved to be complete. The distribution of the products (% moles) proved to be the following: ethylene glycol 37.7%, propylene glycol 55.8%, glycerine 4.7%, mannitol + sorbitol 1.2%.