RELATED APPLICATIONS

This application is a § 371 national stage of PCT International Application No. PCT/EP2019/069230, filed Jul. 17, 2019, claiming priority of European Patent Application No. 18382538.9, filed Jul. 18, 2018, the contents of each of which are hereby incorporated by reference into this application.

FIELD OF THE INVENTION

The present invention relates to the area of purification or extraction of levulinic acid. More specifically, the present invention relates to a process for the purification of levulinic acid, an aqueous solution comprising levulinic acid and a process for the production of levulinic acid.

BACKGROUND

Levulinic acid is a starting molecule for the synthesis of esters known as fuel additive and is known to be useful as a plasticizer and as a solvent. Moreover, levulinic acid can be used to synthesize methyl tetrahydrofuran (MTHF). Other applications of levulinic acid are for example the synthesis of delta-amino levulinic acid used as herbicide and pesticide, diphenolic acid used to synthesize polycarbonates and succinic acid used to make polyesters. Levulinic acid can also be used to produce gamma valerolactone (5-methylbutyrolactone), which in turn can be used for production of adipic acid (1,6-hexanedioic acid). Additionally, levulinic acid is an intermediate in the production of liquid fuels from biomass.

The production of levulinic acid from lignocellulosic biomass has been disclosed in numerous documents such as U.S. Pat. No. 6,054,611A, WO2014087016A1, WO2014037560A1, and WO2015007602A1.

Lignocellulose contains cellulosic-polymers bound together by lignin. When subjected to an acid treatment, lignocellulose splits into lignin and cellulosic components. These cellulosic components can then be hydrolyzed to their constituent pentose and hexose monomers. The pentose monomers, upon further acid treatment, can degrade to furfural, and the hexose monomers can degrade to hydroxymethylfurfural (HMF) which can further degrade in the presence of acid to levulinic acid (LEVA) and formic acid (FA).

Great purification and separation effort is needed in order to remove unwanted components and side products, as tar or humins, from the reaction mixture in order to obtain levulinic acid. For example, U.S. Pat. No. 6,054,611A discloses the purification of levulinic acid from an aqueous biomass hydrolysate by distillation followed by vacuum distillation and optionally, recrystallization. Also, several documents such as WO2014087016A1, WO2014037560A1 and WO2015007602A1 describe purification methods involving a solvent-extraction step that yields to an organic phase comprising levulinic acid that can be further purified. For example Patent Application No. WO2014087016A1 suggests recovering the levulinic acid and/or the formic acid from the organic phase by distillation. Patent Application No. WO2014037560A1 suggests subjecting said organic phase to nanofiltration, and optionally to a further distillation step. Also, Patent Application No. WO2015007602A1 describes a process for the isolation of levulinic acid from an organic solution that comprises a step of washing said organic solution with an alkaline aqueous stream to yield a washed organic solution and subject said washed organic solution to a distillation.

Nevertheless, methods for producing, purify, extract, isolate or concentrate levulinic acid that include a solvent-extraction step to yield an organic phase comprising levulinic acid, as those disclosed above, have issues related to the cost associated to high organic solvent usage. Additionally, humins and other impurities present in the organic phase can create problems in subsequent purification steps, particularly if a distillation is required, and lead to high amounts of impurities and lower concentration in the products.

Therefore, there is a clear need for new methods of producing, purifying, extracting, isolating or concentrating levulinic acid with high yield, low impurities and high concentration of the products and reduced cost.

BRIEF DESCRIPTION OF THE INVENTION

The authors of the present invention have developed a new process for the purification of levulinic acid, an aqueous solution comprising levulinic acid and a process for the production of levulinic acid.

The inventors have observed that the yield of levulinic acid and its purity is insufficient when a levulinic acid containing stream is just subjected to an organic extraction. In particular it has been surprisingly found that by performing a double extraction (an organic extraction followed by an aqueous extraction) the process of the present invention significantly improves the yield of the levulinic acid (purity over 95%) as compared to having no double extraction (purity below 85 wt %). Additionally, the products obtained by a double extraction are colorless as opposed to those obtained after a single extraction which has a yellow, reddish or brownish color indicative of the presence of humins or other residues. Thus, a double extraction significantly reduces the presence of impurities in the final products of the process of the present invention.

If further purification is performed on said aqueous solution, the additional purification steps are simplified and for example no viscous residues are generated during distillation.

In addition, since the process of the present invention is simple and inexpensive, it can be applied for large-scale purification and/or production of levulinic acid.

Therefore, a first aspect of the invention is directed to a process for the purification of levulinic acid, comprising:i) providing an aqueous solution comprising levulinic acid;ii) subjecting the aqueous solution of step (i) to an organic extraction to yield an organic solution and an aqueous solution;iii) subjecting the organic solution obtained in the previous step to an aqueous extraction to yield an aqueous solution, comprising levulinic acid, and an organic solution; andiv) subjecting the aqueous solution comprising levulinic acid obtained in step (iii) to a membrane separation to yield an aqueous solution, comprising levulinic acid, and a residue.

In a second disclosure, the present invention is directed to an aqueous solution comprising levulinic acid obtainable by a process comprising:i) providing an aqueous solution comprising levulinic acid;ii) subjecting the aqueous solution of step (i) to an organic extraction to yield an organic solution and an aqueous solution; andiii) subjecting the organic solution obtained in the previous step to an aqueous extraction to yield an aqueous solution comprising levulinic acid and an organic solution;

wherein said aqueous solution comprising levulinic acid obtained in step (iii) comprises:between 0.01 and 27 wt % of levulinic acid; andbetween 0.01 and 13.5 wt % of formic acid.

In a second aspect, the present invention is directed to a process for the production of levulinic acid from pulped lignocellulosic biomass comprising the following steps:i. providing pulped lignocellulosic biomass;ii. optionally subjecting the pulped lignocellulosic biomass of step (i) to a pre-hydrolysis to obtain a pre-hydrolyzed pulped lignocellulosic biomass;iii. subjecting the pulped lignocellulosic biomass provided in step (i) or the pre-hydrolyzed pulped lignocellulosic biomass obtained in step (ii) to an hydrolysis in the presence of an acid and under conditions of temperature, time, and acid concentration to yield an aqueous slurry comprising levulinic acid;iv. subjecting the aqueous slurry obtained in step (iii) comprising levulinic acid to a solid-liquid separation yielding to an aqueous solution comprising levulinic acid and a solid;v. subjecting the aqueous solution obtained in step (iv) to an organic extraction to yield an organic solution and an aqueous solution;vi. subjecting the organic solution obtained in the previous step to an aqueous extraction to yield an aqueous solution, comprising levulinic acid, and an organic solution;vii. subjecting the aqueous solution comprising levulinic acid obtained in step (vi) to a membrane separation to yield an aqueous solution comprising levulinic acid, and a residue; andviii. optionally, subjecting the aqueous solution comprising levulinic acid obtained in the previous step to at least one further purification to yield an aqueous solution comprising levulinic acid.

