Field of the invention

The present invention relates to a process for the isolation of levulinic acid from a composition comprising levulinic acid and optionally a compound having a boiling temperature of less than 245°C, and to the use of reactive distillation step for the isolation of levulinic acid from a composition comprising levulinic acid and optionally a compound having a boiling temperature of less than 245°C.

Background of the invention

Levulinic acid is a starting molecule for the synthesis of commercially important compounds. For example, levulinic acid can be used to produce levulinic acid esters, which can be used as fuel additives or as plasticisers and solvents and can be prepared from levulinic acid. Examples of levulinic acid esters are ethyl levulinate and (other) levulinate.

Commercially, levulinic acid is made from furfuryl alcohol. When levulinic acid is produced from furfuryl alcohol, it can be isolated e.g. by distillation.

It is also possible to produce levulinic acid by acid hydrolysis of biomass, although this has not been commercially practiced. In addition to levulinic acid, biomass hydrolysates usually also contain low-boiling compounds such as formic acid, acetic acid, and proprionic acid.

The inventors have surprisingly found that when such biomass hydrolysate is subjected to distillation in order to separate the levulinic acid from the biomass hydrolysate, the levulinic acid yield is unsatisfactory. The inventors have tried hard to increase the yield of levulinic acid in the distillate, because low yields of levulinic acid after the distillation would mean that the yield, and therefore the economics of the production of levulinic acid, and its derivatives, would also be poor.

The isolation of angelica lactone from a composition comprising levulinic acid using distillation is described in DE745313. DE745313 describes that when a composition containing levulinic acid and an organic or inorganic acid is subjected to distillation at a temperature of greater than 100°C, angelica lactone is formed. DE745313 discloses that angelica lactone can be isolated as a distillate further comprising water.

Summary of the invention

The invention provides a process for the isolation of levulinic acid from a composition comprising levulinic acid and optionally a compound having a boiling temperature of less than 245°C said process comprising: subjecting said composition to distillation and recovering a distillation residue comprising at least 1 wt% angelica lactone; subjecting said distillation residue to a hydration reaction under conditions of temperature and time and in the presence of water and optionally an acid catalyst to produce levulinic acid or to increase the amount of levulinic acid in said distillation residue; and optionally recovering said levulinic acid. The process is suitable for isolating preparing levulinic acid from compositions made by acid hydrolysis of a lignocellulosic biomass, and also from compositions be made by acid hydrolysis of sugar such as glucose and fructose. The invention also provides the use of reactive distillation for the isolation of levulinic acid from a composition comprising levulinic acid and optionally a compound having a boiling temperature of less than 245°C.

Detailed description of the invention

In a first aspect, the invention provides a process for the isolation of levulinic acid from a composition comprising levulinic acid and optionally a compound having a boiling temperature of less than 245°C said process comprising:

subjecting said composition to distillation and recovering a distillation residue comprising at least 1 wt% angelica lactone;

subjecting said distillation residue to a hydration reaction under conditions of temperature and time and in the presence of water and optionally an acid catalyst to produce levulinic acid or to increase the amount of levulinic acid in said distillation residue; and optionally recovering said levulinic acid.

The inventors have realized that levulinic acid can be efficiently isolated from a biomass or C6 sugars hydrolysate by recovering a distillation residue comprising at least 1 wt% angelica lactone. The inventors also surprisingly found that when a biomass or C6 sugars hydrolysate is subjected to distillation in order to isolate levulinic acid, angelica lactone is formed during the distillation, and have used this phenomenon to efficiently isolate levulinic acid. The process of the invention is particularly advantageous when carried out as a batch process.

The boiling temperature is measured at standard conditions, namely at 1 atmosphere, or 760.00 mm Hg. At this pressure, the boiling temperature of pure water is 100°C, and the boiling point of levulinic acid is 245°C.

The distillation preferably comprises reactive distillation. The distillation is preferably done under reactive conditions such that levulinic acid may be converted to angelica lactone. The distillation temperature is preferably 80°C or more, more preferably between 120 and 150°C. The pressure is preferably 10 mbar or higher. Such pressures and temperatures 120-150°C may result in a distillation residue having at least 1 wt% angelica lactone.

Preferably, during said distillation levulinic acid goes into the gas phase, where reactive distillation to angelica lactone may take place, which may be recovered as a distillation residue.

The compound having a boiling temperature of less than 245°C preferably has a boiling temperature of at least 90°C.

The composition may comprise formic acid, acetic acid, furfural, and/or propionic acid. That is, the compound having a boiling point of less than 245°C may comprise formic acid, acetic acid, furfural, and/or propionic acid (i.e. may comprise each one of these compounds or a combination of two or more of these compounds).

The composition may comprise a biomass hydrolysate or C6 sugars acid hydrolysate. Acid hydrolysis of biomass may not only result in formation of levulinic acid, but usually also results in the formation of formic acid, boiling temperature 100°C. Often a range of other low boiling compounds are produced such as acetic acid, furfural, and proprionic acid, all having a boiling temperature of 90°C or higher, but lower than the boiling temperature of levulinic acid.

The biomass may be or may be derived from grass, cereal, starch, algae, tree bark, hay, straw, leaves, paper pulp, paper sludge, or dung. Paper pulp, or simply pulp, is a lignocellulosic fibrous material prepared by chemically or mechanically separating cellulose from wood, fibre crops or waste paper. Pulp is rich in cellulose and other carbohydrates. Paper sludge, or simply sludge, is a lignocellulosic fibrous containing cellulose fibres too short for usage in the paper industry. The biomass may comprise lignocellulosic biomass. Lignocellulosic biomass typically has a fibrous nature and comprises a bran fraction that contains the majority of lignocellulosic (bran) fibers. As an example, corn fiber is a heterogeneous complex of carbohydrate polymers and lignin. It is primarily composed of the outer kernel covering or seed pericarp, along with 10-25% adherent starch. Carbohydrate analyses of corn fiber vary considerably according to the source of the material. The lignocellulosic biomass may comprise hemicellulose.

In one embodiment, the composition is a biomass hydrolysate made by acid hydrolysis of lignocellulosic biomass.

In another embodiment, the composition is a made by acid hydrolysis of C6 sugars, particularly of fructose or glucose or mixtures thereof. Sucrose (C12H22O11) can be broken down into one molecule of glucose (C ₆ H ₁₂ 0 ₆ ) plus one molecule of fructose (also C ₆ H ₁₂ 0 ₆ , an isomer of glucose), in a weakly acidic environment by a process called inversion. Fructose can also be made by enzymatic isomerization of glucose. Sucrose is commonly produced from biomass such as beet, corn and cane.

The conditions for the acid hydrolysis of biomass or C6 sugars are such it results in the formation of at least levulinic acid and optionally a compound having a boiling temperature of less than 245°C and preferably also of tar and/or humins. Suitable acids include sulphuric acid, hydrochloric acid, and phosphoric acid. A preferred acid is sulphuric acid, preferably diluted sulphuric acid, for example at a concentration between 1 .5 - 3%. The temperature in the acid hydrolysis may depend on the source of carbohydrates, and may range between 150-250°C, preferably between 170-240°C, more preferably between 190-230°C, even more preferably between 200 and 220°C. The acid hydrolysis may comprise one, two, or more stages. The pressure may also depend on the source of carbohydrates, as well as on the temperature, and may be anywhere between 1 and 50 bar, preferably between 5 and 40 bar, even more preferably between 10 and 30 bar. Suitable reactors include plugflow reactors, backmix reactors, and CSTR reactors. Different reactors for different stages may be used.

The distillation residue may comprise levulinic acid, i.e. it may be a mixture comprising at least 1 wt% angelica lactone and levulinic acid.

The composition may comprise an aqueous liquid (e.g. solution or suspension).

The composition may also comprise an organic liquid, such as e.g. an organic phase obtained by solvent-solvent extraction. Liquid-liquid extraction is a process for separating components (the solutes) of a liquid (the feed) by contact with a second liquid phase (the solvent). The two liquids must not be completely mutually miscible. The process takes advantage of differences in the chemical properties of the feed components, such as differences in polarity and hydrophobic/hydrophilic character to separate them (T.C. Frank, L.Dahuron, B.S. Holden, W.D. Prince, A.F. Seibert, L.C. Wilson, Liquid-liquid extraction and other liquid- liquid operations and equipment in Perry's Chemical Engineering Handbook, 8th Edition, Section 15). Two streams result from the liquid-liquid extraction process: the extract, which is the solvent rich solution containing the desired extracted solute, and the raffinate, the residual feed solution containing little solute. Solvent extraction commonly (but not necessarily) takes place with an aqueous solution as one liquid and an organic solvent or mixture of solvents as the other. Numerous solvents with various properties are used in solvent extraction (Y.Marcus, Principles of Solubility and Solutions, in J. Rydberg, M. Cox, C. Musicas, G.R. Chopin (Editors), Solvent Extraction Principles and Practice, 2nd Edition, Chapter 2, Marcel Dekker Inc., New York). Extraction capacity of a solvent can be adjusted by changing process parameters like temperature or pH.

Before subjecting the composition to the distillation to produce the distillation residue, the composition may undergo one or more additional steps, preferably non- chemical steps. Examples of such steps include concentration, e.g. by flashing, solvent-solvent extraction, solid/liquid separation. A combination of two or more of these steps is also possible. Suitable solid-liquid separation techniques include filtration and centrifugation.

A flashing step may combine cooling of a biomass hydrolysate after acid hydrolysis and concentration of such biomass.

The amount of angelica lactone on the residue is at least 1 wt% relative to the total weight of the residue. Preferably the amount is at least 2%, at least 5%, at least 10%, more preferably at least 15%, at least 20%, more preferably at least 30%, at least 40%, even more preferably at least 50%, at least 60%, even more preferably at least 70%, at least 80%, or at least 90%, even more preferably at least 95 wt%.

The composition comprising levulinic acid and optionally a compound having a boiling point of less than 245°C may further comprise humins, tar, and/or char.

Tar and char represent organic material which is insoluble in water, which is dark in colour and which tends to become viscous and very dark to almost black when concentrated. Tar can be formed during heating of organic material, for example by pyrolysis, but is also formed when carbohydrates are subjected to acid hydrolysis, particularly when done at high temperatures. Char usually refers to solid material, for example the remains of solid biomass that has been incompletely combusted, such as charcoal if wood is incompletely burned. Tar usually refers (viscous) liquid, e.g. derived from the destructive distillation of organic matter.

Humins may also be produced by acid hydrolysis of carbohydrates. Yang and Sen (Chem. Sus. Chem. 2010, vol. 3, 597-603) report the formation of humins during production of fuels from carbohydrates such as fructose. They speculate that the humins are formed by acid-catalysed dehydration. According to US7,896,944 the molecular weight of humins ranges from 2.5 to 300 kDa.

In the context of the invention, "char" is understood to include "tar"

The presence of tar is undesired, amongst other reasons because it may stick to the wall of a reactor. It may also cause problems in a distillation. If a distillation process consists of more than one unit, which is often the case, any char present in the feed of a distillation char may accumulate in later distillation units and will be even more viscous and darkly-coloured, and will also be more concentrated in the bottom, because products exit the "train" via the top sections.

In a further aspect the invention provides a composition comprising at least 1 wt% angelica lactone obtainable by the process of the invention. This composition can be advantageously used to produce levulinic acid.

The temperature and the reaction time in the hydration reaction are not critical. For example, the temperature may range between 0 and 200°C, preferably between 20 and 150°C, more preferably between 40 and 120°C. The reaction time may be between 1 minute and 100 hours. The temperature must not be too high so as to avoid degradation of levulinic acid. Shorter reaction times are advantageous due to plant throughput, but longer reaction times are also possible, since the reaction will usually proceed towards production of levulinic acid.

The hydration reaction is done in the presence of water. Water may be added to the reaction, for example added separately, or may be added together with a catalyst.

The hydration reaction preferably comprises an acid catalyst, preferably a solid acid catalyst. A catalyst may be added to the reaction, or it may already be present. For example, any (mineral) acid in the distillation residue, for example from a biomass hydrolysate, may advantageously act as an acid catalyst. During the hydration reaction levulinic acid is produced, or, if already present, the amount of levulinic acid is increased.

Preferably the levulinic acid concentration at the end of the reaction is at least 1 .5 times higher than the levulinic acid concentration prior to the reaction, preferably this factor is at least 2 times, more preferably at least 3 times.

Prior to the hydration reaction, the recovered distillation residue may undergo one or more additional steps, preferably non-chemical steps. Examples of such steps include concentration, e.g. by flashing, solvent-solvent extraction, solid/liquid separation, and/or distillation. A combination of two or more of these steps is also possible.

In an embodiment the invention includes a process for the isolation of levulinic acid from a composition comprising levulinic acid and optionally a compound having a boiling temperature of less than 245°C, said process comprising;

optionally subjecting said composition to a solid-liquid separation to yield a solid fraction and a liquid fraction and collecting said liquid fraction;

optionally subjecting said composition or said liquid fraction to solvent-solvent extraction by adding a solvent, preferably MTHF to yield an organic phase comprising at least some of the levulinic acid and optionally at least some of the compound having a boiling temperature of less than 245°C, and an aqueous phase, and recovering the organic phase;

subjecting said composition or said liquid fraction or said organic phase to a first distillation to yield a first residue comprising at least 1 wt% angelica lactone, and a first distillate, and recovering said first residue;

optionally subjecting said first distillation residue to a second distillation to yield a second distillate comprising angelica lactone and optionally levulinic acid, and a second distillation residue, and recovering said second distillate;

subjecting said recovered first residue or said recovered second distillate to a hydration reaction under conditions of temperature and time and in the presence of water and optionally an acid catalyst to produce levulinic acid or to increase the amount of levulinic acid in said distillation residue; and

optionally isolating the levulinic acid.

In another embodiment the invention also includes a process for the isolation of levulinic acid from a biomass hydrolysate, said process comprising; optionally subjecting said biomass hydrolysate to a solid-liquid separation to yield a solid fraction and a liquid fraction and collecting said liquid fraction;

optionally subjecting said biomass hydrolysate or said liquid fraction to solvent- solvent extraction by adding a solvent, preferably MTHF to yield an organic phase comprising at least some of the levulinic acid and optionally at least some of the compound having a boiling temperature of less than 245°C, and an aqueous phase, and recovering the organic phase;

subjecting said biomass hydrolysate or said liquid fraction or said organic phase to a first distillation to yield a first residue comprising at least 1 wt% angelica lactone, and a first distillate, and recovering said first residue;

optionally subjecting said first distillation residue to a second distillation to yield a second distillate comprising angelica lactone and optionally levulinic acid, and a second distillation residue, and recovering said second distillate;

subjecting said recovered first residue or said recovered second distillate to a hydration reaction under conditions of temperature and time and in the presence of water and optionally an acid catalyst to produce levulinic acid or to increase the amount of levulinic acid in said distillation residue; and

optionally isolating the levulinic acid.

The invention further provides the use of reactive distillation step for the isolation of levulinic acid from a composition comprising levulinic acid and optionally a compound having a boiling temperature of less than 245°C.

EXAMPLES

All compounds were analysed by GC.

LA, levulinic acid

LA, angelica lactone

FA, formic acid

MTHF, methyl tetrahydrofuran Example 1

100g wood chips were impregnated for 90 minutes. After impregnation, the temperature was raised to the hydrolysis temperature and the slurry was hydrolyzed in the presence of approximately 5 wt% hydrosulphuric acid without stirring. After solid- liquid fractionation the liquid fraction of the resulting biomass hydrolysate was analyzed. The analysis results and the hydrolysis conditions are stated in Table 1.

Table 1

^* concentration on total mass (liquor + wood)

Example 2

The reaction suspension of Example 1 is cooled via evaporation of the liquid reaction product. The resulting vapor is condensed resulting in an aqueous solution of approximately 1 wt% formic acid, 0.02 wt% acetic acid and 0.02 wt% levulinic acid.

Example 3

A biomass hydrolysate was enriched with pure levulinic acid to a levulinic acid concentration of 9.07 wt%, and with formic acid to a formic acid concentration of 1 .89 wt%, in order to simulate the flash step in Example 2. A total of 2.1 kg enriched biomass hydrolysate was extracted 5 times with each time 1 .7kg of fresh methyltetrahydrofuran at 60°C. After the fifth extraction 99.1 wt% of the levulinic acid and 98.8 wt% of the formic acid present in the reaction solution could be collected in the organic layer.

Example 4

Nine kg of the collected organic layer form the extraction described above was batch wise distilled. The initial concentrations were: levulinic acid, 1.74wt%; formic acid, 0.33 wt%; acetic acid, 0.1 wt%. The organic phase was distilled to remove the extraction solvent with a falling film evaporator in a 3m BX column with a diameter of 7cm at 500mbar with a reflux ratio of 2. Eight kg of distillate was collected containing MTHF and water, and trace levels of formic acid, acetic acid and levulinic acid (all below 100 ppm). One kg of distillation residue was found to contain 92 wt% of the levulinic acid feed, and 100 wt% of the formic acid feed, respectively.

Example 5

The residue of the distillation of Example 4 is subjected to a further distillation to remove any low boiling compounds, the decreasing the pressure from 500mbar to 20mbar and increasing the temperature from 125°C to 175°C. The first fraction contains (nearly) pure methyltetrahydrofuran. The second fraction contains 75 wt% methyltetrahydrofuran and 20 wt% formic acid. The third fraction (bottom temp, 142°C) contains 20 wt% methyltetrahydrofuran, 65 wt% formic acid and 8 wt% acetic acid. No fraction can be isolated containing any detectable amounts of levulinic acid. Instead, the distillation residue is rich in levulinic acid and angelica lactone, and contains no detectable amounts of formic acid or acetic acid.

Example 6

A residue of a distillation as described in Example 5 which is rich in angelica lactone and levulinic acid is subjected to a further distillation to remove any high boiling substances such as humins. This distillation yields a distillate containing angelica lactone and levulinic acid, and contains no detectable amounts of other compounds.

Example 7

A distillation residue according to Example 5 was distilled. Two distillate fractions were recovered both containing (nearly) pure angelica lactone. Of the feed to the distillation, 5 wt% ended up as the residue. The amount of angelica lactone in the collected distillates corresponded to 95 mol% relative to the amount of the levulinic acid present in the feed.

Example 8

A solution of levulinic acid (88.5 wt%), alpha-angelica lactone (8.35 wt%), beta- angelica lactone (0.14 wt%) and water (3 wt%) was heated to 60°C. After 40h the solution contained 1 .2 wt% alpha-angelica lactone, 0.26 wt% beta-angelica lactone, and 96.1 wt% levulinic acid After 100h the solution contained 0.4 wt% alpha-angelica lactone, 0.17 wt% beta-angelica lactone, and 97.0 wt% levulinic acid.

Example 9

A solution of 49.1 wt% levulinic acid, 41 .1 wt% alpha-angelica lactone, 0.84 wt% beta-angelica lactone, and 8.9 wt% water was heated to 60°C. After 20h the solution contained 0.16 wt% alpha-angelica lactone, 0.01 wt% beta-angelica lactone, and 99.8 wt% levulinic acid.

Example 10

A solution of 88.5 wt% levulinic acid, 8.35 wt% alpha-angelica lactone, 0.14 wt% beta-angelica lactone, and 10.45 wt% water, and a solid acidic catalyst (DOWEX® 50, 0.1 mol%) was heated to 60°C . After 1 .5h the solution contained 0.1 wt% alpha angelica lactone, less than 0.1 wt% beta-angelica lactone, and 99.8 wt% levulinic acid.

Example 11

A solution of alpha-angelica lactone (84.3 wt%), beta-angelica lactone (0.31 wt%) and water (15.4 wt%) and a solid acidic catalyst (DOWEX® 50, 0.1 mol%) was heated to 60°C. After 1 .5h the solution contained alpha-angelica lactone (45.6 wt%), beta-angelica lactone (less than 0.1 wt%) and levulinic acid (39.3 wt%). After 3h the solution contained alpha-angelica lactone (0.6 wt%), beta-angelica lactone (less than 0.1 wt%), and levulinic acid (99.4 wt%).