EP4638408A1

EP4638408A1 - Fermentative production of dicarboxylic acids

Info

Publication number: EP4638408A1
Application number: EP23836501.9A
Authority: EP
Inventors: Luigi Capuzzi; Maria Grazia CAPRARO; Marco Cotti Comettini; Francesca Digioia; Antonio Verdoliva
Original assignee: Novamont SpA
Current assignee: Novamont SpA
Priority date: 2022-12-22
Filing date: 2023-12-20
Publication date: 2025-10-29
Also published as: CN120418222A; IT202200026568A1; WO2024133542A1

Abstract

The present invention relates to a process for obtaining saturated C12-C24 dicarboxylic acids from a fermentation product and a saturated C12-C24 dicarboxylic acid composition suitable for use in polymerisation. Said process comprises the steps of (a) separating at least a portion of the fermentation by-products and/or the residual fermentation substrate from an aqueous mixture comprising unsaturated C12-C24 dicarboxylic acids or derivatives thereof, and (b) subjecting said unsaturated C12-C24 dicarboxylic acids or derivatives thereof to hydrogenation.

Description

FERMENTATIVE PRODUCTION OF DICARBOXYLIC ACIDS

This application relates to a process for the purification of long-chain dicarboxylic acids, produced by fermentation from raw materials of renewable origin such as monocarboxylic acids or their derivatives, comprising a hydrogenation step. The composition of the dicarboxylic acids obtained by this process is particularly suitable for use in the synthesis of polymers, particularly polyesters.

Long-chain dicarboxylic acids (those with 12 carbon atoms or more in the meaning of the present invention) have a wide range of applications as chemical intermediates in polymer production processes and in sectors as diverse as cosmetics, pharmaceuticals and detergents. For example, dodecanedioic acid (C12) is used for the synthesis of polyesters, polyamides and polyurethanes, which in turn find applications in fibres, films, resins, plasticisers, synthetic lubricants, coatings and adhesives. However, their production by chemical means is technically difficult, environmentally unsustainable and economically expensive.

Over the past 20 years, research has therefore turned its attention to the production of dicarboxylic acids by means of biotechnological processes mediated by microorganisms capable of using fatty acids or their derivatives as substrates, with the aim of achieving sustainable and low-cost processes.

For example, application WO 2019/030652 describes the development of a strain of Candida maltosa through genetic modification to inhibit dissipative fatty acid metabolism and favour the metabolic pathway of co-oxidation, resulting in conversion to long-chain dicarboxylic acids. Patent EP 2 191 003 B 1 describes instead a process for obtaining dicarboxylic acids of different chain lengths by the fermentation of monounsaturated fatty acids or their esters, followed by a ruthenium- and/or rhenium-catalysed cross-metathesis reaction in solvents such as dichloromethane or toluene. The document states that the resulting unsaturated metathesis product may possibly be subjected to a “conventional” hydrogenation process to obtain saturated dicarboxylic acids.

However, the processes for obtaining dicarboxylic acids from the corresponding fermentation broths that contain impurities, residual monoacids and unsaturations in particular, making them suitable for e.g. application as monomers in polymerisation, are still problematic.

Typically, the fermentation broth (or culture broth) containing di carboxylates is acidified to obtain dicarboxylic acids, which are then separated using a membrane and/or undergo extraction with organic solvents at elevated temperatures, such as in the process described in patent application US 20015/025259 for the production of dicarboxylic acids. Nevertheless, from experience with the production of lower-chain dicarboxylic acids, such as adipic acid from muconic acid, it is known that reduction of the unsaturated content by catalytic hydrogenation has critical problems in relation to the impurities that result from the fermentation processes. In particular, the presence of salts can interfere with the stability of catalysts and it is difficult to achieve good performance under scalable conditions (e.g. low temperature and pressure, and environmentally friendly solvents), (Capelli S. et al., Applied Catalysis B: Environmental 218 (2017) 220-229).

The applicant has now developed a process that solves the problems outlined above by subjecting long-chain unsaturated dicarboxylic acids or their derivatives to hydrogenation after a preliminary purification step that at least partly separates out the fermentation by-products and any residual substrate from the fermentation broth. In addition, the process is particularly versatile and can be carried out in solution in either water or organic solvent, with the advantage in each case that it is possible to conduct the hydrogenation step in the same medium as the previous purification step.

In said preliminary purification step the residual substrate can be advantageously removed from the fermentation product comprising dicarboxylates through at least one ultrafiltration operation carried out at pH >8, after at least partial acidification of the dicarboxylates. This leads to a significant simplification of the subsequent operations.

It is therefore one object of the present invention to provide a process for obtaining saturated C12-C24 dicarboxylic acids from an aqueous mixture comprising unsaturated C12-C24 dicarboxylic acids or their derivatives, fermentation by-products and any residual substrate, comprising the steps of:

(a) separating at least some of the fermentation by-products and/or of the residual fermentation substrate from said unsaturated C12-C24 dicarboxylic acids or their derivatives by subjecting said aqueous mixture to one or more purification operations selected from centrifugation, settling or filtration;

(b) subjecting said unsaturated C12-C24 dicarboxylic acids or their derivatives to hydrogenation.

Said process is particularly suitable for obtaining saturated C16-C18 dicarboxylic acids from a mixture comprising unsaturated acids.

The process according to the invention will be described in more detail below.

Unless otherwise specified, the terms "monocarboxylic acids" and "dicarboxylic acids" refer to monocarboxylic acids having a carbon chain of from C12 to C24, their derivatives or mixtures, and dicarboxylic acids having a carbon chain of from C12 to C24, their derivatives or mixtures, respectively. These acids are preferably aliphatic.

The starting material for the process is an aqueous mixture comprising unsaturated C12-C24 dicarboxylic acids or their derivatives, fermentation by-products and any residual fermentation substrate.

Said aqueous mixture is obtained as a fermentation broth by subjecting a substrate comprising unsaturated C12-C24 monocarboxylic acids or their derivatives, preferably of renewable origin, to fermentation by means of a microorganism capable of oxidising monocarboxylic acids to dicarboxylic acids.

According to a preferred aspect, this substrate comprises, or is predominantly composed of, unsaturated C12-C24 monocarboxylic acids.

Said unsaturated monocarboxylic acids may be monounsaturated or polyunsaturated and may be used in the form of mixtures of acids of different chain lengths and unsaturation. Monounsaturated monocarboxylic acids are preferred. Acids having chain lengths from C16 to C22 are particularly preferred.

Examples of unsaturated monocarboxylic acids are: 9-tetradecenoic (myristoleic), 9-hexadecenoic (palmitoleic), 9-octadecenoic (oleic), 12-hydroxy-9-octadecenoic (ricinoleic), 9-eicosenoic (gadoleic), 13-docosenoic (erucic), 15-tetracosenoic (nervonic), 9,12- octadecadienoic (linoleic), and 9,12,15-octadecatrienoic or 6,9,12-octadecatrienoic (linolenic) acids.

Monocarboxylic acids obtained from vegetable oil, or from a mixture of vegetable oils, for example by hydrolysis, are preferred. By vegetable oils are meant either the unmodified pressed product or an oil that has undergone chemical or chemical-physical modifications such as purification treatments or enzyme enrichment or hydrogenation, for example oils which have been selectively hydrogenated to increase the monounsaturated fatty acids content. Examples of vegetable oils are thistle oil, soybean oil, olive oil, castor oil, sunflower oil, peanut oil, maize oil, palm oil, safflower oil, jatropha oil, cuphea oil, oils from Brassicaceae such as Crambe abyssinica. Brassica carinala. Brassica napus (rapeseed), Lesquerella, and other oils with a high content of monounsaturated acids.

The use of monocarboxylic acids from sunflower oil, thistle oil, safflower oil, palm oil, oils from Brassicaceae, preferably with a high monounsaturated acid content, as the fermentation substrate is preferred. Particularly preferred is the use of mixtures of monocarboxylic acids from the hydrolysis of sunflower oil, thistle oil, safflower oil, Crambe abyssinica, Brassica carinala. Brassica napus (rapeseed) with a high monounsaturated acid content. Even more preferred is the use of mixtures of monocarboxylic acids from one or more oils with a high oleic acid content and/or high erucic acid content. The said mixtures may contain geometric or positional isomers of the said monocarboxylic acids, which can derive from the chemical or chemi cal -physical modification of polyunsaturated acids. An example of isomer of oleic acid is 12-octadecenoic acid.

One example of a particularly preferred mixture comprises at least 70% oleic acid (preferably 80-90% by weight), up to 20% linoleic acid (preferably 4-12% by weight), up to 5% stearic acid (preferably 1.5-4% by weight) and up to 6% palmitic acid (preferably 2-5% by weight).

In the meaning of the present invention, a "derivative" of a carboxylic acid means, for example, a carboxylic acid whose carboxylic group forms an ester bond, e.g. by reaction with an alcohol. Said derivative may be of natural or synthetic origin.

Preferably, said derivatives are esters of unsaturated carboxylic acids with monoalcohols and/or polyalcohols.

In the case of ester-type derivatives, the carboxyl group may be linked to monoalcohols or polyalcohols. Preferred monoalcohols include C1-C9 alkyl groups; more preferred are methyl, ethyl, propyl and butyl alcohols. An example of a preferred polyalcohol is glycerol.

Methyl and ethyl esters of unsaturated carboxylic acids are particularly advantageous as starting material for this process, particularly those obtained by the transesterification of methanol and ethanol with the triglycerides present in the oils mentioned above.

Esters of carboxylic acids with polyhydric alcohols are for example monoglycerides, diglycerides and triglycerides of carboxylic acids, preferably the triglycerides present in the oils mentioned above.

The use of methyl and ethyl esters as fermentation substrates, in particular those obtained by the trans-esterification of methanol and ethanol with the triglycerides present in the oils mentioned above is advantageous.

According to a preferred aspect, said fermentation substrate is in a liquid state at fermentation temperature (e.g. 25-35°C).

According to one aspect, this substrate comprises monocarboxylic acids in aqueous solution in dissociated form, e.g. due to the addition of a base.

According to one aspect, said substrate has a suitable saturated, monounsaturated and polyunsaturated monocarboxylic acid composition. For example, the content of saturated monocarboxylic acids relative to the total weight of monocarboxylic acids is preferably less than 25%, more preferably less than 15%, even more preferably less than 10%, by weight. Preferably, with respect to the total weight of monocarboxylic acids, the monounsaturated monocarboxylic acid content is more than 20%, more preferably more than 55%, even more preferably more than 70% by weight. A monounsaturated monocarboxylic acid content of 80% or more is particularly preferred.

Compared to the total weight of monocarboxylic acids, the polyunsaturated monocarboxylic acid content is preferably less than 30%, more preferably less than 10%, by weight.

The microorganisms used for preparation of the starting material according to the process according to the present invention are capable of oxidising monocarboxylic acids to dicarboxylic acids; they may be bacterial or fungal in nature and optionally genetically modified.

Examples are microorganisms belonging to the genuses Yarrowia, Candida, Rhodotorula, Rhodosporidium, Cryptococcus, Trichosporon or Lipomyces.

Yeasts of the Candida genus, preferably Candida maltosa or Candida tropicalis, or Yarrowia are preferred. Yeasts of the Candida maltosa species are particularly preferred.

Production of the starting material for this process by fermentation takes place according to known techniques; it may be conducted as a batch, fed batch or continuously. For example, it is carried out in a sterile environment, controlling temperature and pH, and monitoring and adjusting the dosage of nutrients and compounds required by the microorganism (e.g. 02, source of carbon) and the removal of potential excess by-products (e.g. CO2).

Appropriate culture media for the micro-organism used and the stage the micro-organism is at (e.g. stage of cell growth or development and/or stage of production of dicarboxylic acids) are used.

The components of the culture medium, which include sugars, protein hydrolysates, proteins, amino acids, organic acids, vitamins, minerals, yeast extracts and trace elements are typically added in excess of the micro-organism's actual needs and, therefore, are not fully utilised and remain in the broth at the end of fermentation in the form of impurities.

With regard to possible other components of the culture medium, the medium generally contains salts, essential minerals, urea and antifoaming agents. The culture medium may be prepared in any way known to those skilled in the art, for example by mixing all its components together or by pre-mixing all the components with the exclusion of glucose, urea and antifoaming agents and adding these later, either individually or already pre-mixed in turn. A commercially available culture medium may also be used as a starting point and its composition suitably modified at a later stage, for example when bringing the culture medium into contact with the micro-organism capable of oxidising monocarboxylic acids to dicarboxylic acids. During the dicarboxylic acid production stage, the substrate comprising monocarboxylic acids is advantageously fed either continuously or discontinuously, in a manner known to those skilled in the art. The latter are able to take the necessary steps to keep the fermentation substrate in a liquid state and facilitate dosing and access by the microorganism.

The fermentation broth fed to step a) of the process according to the invention is therefore an aqueous mixture comprising unsaturated C12-C24 dicarboxylic acids or their derivatives and any residual unsaturated monocarboxylic acids, preferably at least partly present as salts. The broth also comprises fermentation by-products, including residues of the culture medium and cells.

Said C12-C24 unsaturated dicarboxylic acids may be monounsaturated or polyunsaturated and may be present as mixtures of acids with different chain lengths and degrees of unsaturation. Monounsaturated dicarboxylic acids are preferred. Saturated dicarboxylic acids may also be present.

Examples of dicarboxylic acids are: dodecanedioic acid, tridecanedioic or brassylic acid, tetradecanedioic acid, tetradecendioic acid, hexadecanedioic acid, hexadecendioic acid, octadecanedioic acid, 9-octadecendioic acid, eicosendioic acid, 13-docosendioic acid, tetracosendioic acid, 9,12-octadecadiendioic acid, and 9,12,15-octadecatriendioic acid and 6,9,12-octadecatriendioic acid.

The aqueous mixture fed to step a) of the process advantageously comprises one or more unsaturated dicarboxylic acids selected from the group consisting of tetradecendioic acid, hexadecendioic acid, octadecendioic acid, eicosendioic acid, docosendioic acid, tetracosendioic acid, octadecadi endioic acid, octadecatriendioic acid and mixtures thereof. Mixtures with a predominance of C16-C18 dicarboxylic acids are preferred; mixtures with a predominance of octadecendioic acid are particularly preferred.

Depending on the type of microorganism selected, the fermentation broth has a dicarboxylic acid content preferably >20 g/L, more preferably >50 g/L, even more preferably >80g/L.

At the end of fermentation, the fermentation broth conveniently undergoes a process of deactivation of the micro-organism.

Deactivation may be performed using techniques known in the art, either chemical, mechanical or thermal, for example by pasteurisation. A particularly convenient way of performing deactivation is treatment at basic pH, for example at pH >9, preferably pH >10, even more preferably pH >11. The basic pH treatment can be conveniently conducted at room temperature, or preferably at a temperature >50°C, even more preferably at a temperature >75°C. The viscosity of the fermentation product subjected to step a) in the process according to the invention must be maintained at values below 1000 cST, preferably < 700 cST, even more preferably < 500 cST.

During said step a) at least some of the fermentation by-products and/or the residual fermentation substrate are separated from the unsaturated C12-C24 dicarboxylic acids or their derivatives by subjecting said aqueous mixture to one or more purification operations selected from, for example, centrifuging, settling or filtration. If two or more separation operations are performed, the order of these operations in time is not particularly limiting.

According to a preferred aspect of the process, said step a) comprises separating any residual C12-C24 monocarboxylic acids present in the form of salts from said aqueous mixture, for example at a pH >8, through at least one ultrafiltration operation. Said separation is advantageously performed according to the process described in patent EP 3 083 544 B 1. When this operation is performed, it is preferably followed by an acidification in order to recover the dicarboxylic acids in acid form.

Step a) in the process according to the invention preferably comprises a combination of different operations, selected for example from centrifuging, tangential filtration, crystallisation, precipitation or reactive crystallisation, solvent extraction, or treatment with activated carbon, ion exchange resin or molecular sieves.

The purpose of said operations is to remove at least some of any by-products and/or residual fermentation substrate from the fermentation product.

Such by-products or impurities comprise, for example, nitrogen compounds such as amino acids, oligopeptides, nucleic acids, and degradation products of both DNA and RNA. For the identification of impurities of a peptide nature, a direct infusion mass spectrometry method may be used for samples derived from the process of purification of dicarboxylic acids, using an LCQ-Fleet (Ion Trap) mass spectrometer. As far as the identification of nucleic acids is concerned, analyses using UV spectroscopy with scanning between 200-350 nm are suitable: nucleic acids in fact have a characteristic UV absorption spectrum with a maximum at 260 nm. A preferred method for removing residual impurities is crystallisation. This method may be effectively used for dicarboxylic acids in aqueous solution that are partly in the form of salts. A preferred method of conducting crystallisation is by evaporation followed by cooling of the concentrated solution.

Another preferred method for removing residual impurities is the extraction of dicarboxylic acids in acid form (e.g. obtained by titration with an acid) in organic solvent. In this case the dicarboxylic acids dissolved in said solvent may be further purified by one of the other methods listed above.

Said extraction in organic solvent is performed by addition of the solvent after separation of the dicarboxylic acids in acid form from the aqueous mixture, for example by precipitation and drying. Alternatively, solvent extraction may be performed by adding the solvent to the aqueous mixture; this second method is particularly advantageous since, in addition to allowing separation of the dicarboxylic acids in acid form at the same time as they form, it greatly simplifies purification operations.

According to a preferred embodiment, after step a) and before hydrogenation step b), the process according to the invention comprises the steps of: i) dissolving the C12-C24 dicarboxylic acids in a non-polar organic solvent and removing the insoluble fermentation by-products therein; and ii) optionally purifying the organic phase comprising C12-C24 dicarboxylic acids by means of one or more operations selected from ultrafiltration, nanofiltration, crystallisation, adsorption and passage over ion exchange resins.

One of the advantages of this embodiment lies in the possibility of carrying out hydrogenation step b) in the same medium as separation step a), i.e. in the presence of said non-polar organic solvent. The process is greatly simplified as no intermediate solvent removal and recovery operations are required.

Advantageously, one or more washings with water of the organic phase are performed during step ii).

Said non-polar organic solvent is appropriately selected according to the composition of the mixture, considering the solubility of the dicarboxylic acids present in it and is preferably an oxygenated non-polar organic solvent.

Examples of suitable non-polar organic solvents are ethers, esters, ketones; ethers being preferred. Solvents which do not react in the presence of molecular hydrogen (e.g. solvents other than olefins) are also preferred.

Said non-polar organic solvent is preferably selected from t-amyl methyl ether, t-butyl methyl ether, n-dibutyl ether, butyl acetate and methyl isobutyl ketone; t-amyl methyl ether, t-butyl methyl ether and/or n-dibutyl ether being preferred. Extraction in such solvents allows effective removal of the dicarboxylic acid(s) from the impurities, in particular the nitrogenous impurities which are insoluble therein, even at room temperature (ca. 25 °C) and in any event at temperatures of 50°C or below. N-dibutyl ether is a particularly preferred solvent for the separation of dicarboxylic acids having chain lengths of up to 16-18 carbon atoms and their mixtures, particularly when the solvent is added directly to the aqueous mixture. Its use results in a product with a nitrogen content (from elemental analysis) advantageously below 500 ppm, preferably below 100 ppm and most preferably below 50 ppm.

According to another preferred embodiment of the process, the hydrogenation in step b) is carried out on C12-C24 dicarboxylic acids in aqueous solution. In this case it is particularly advantageous to work on the dicarboxylic acids in at least partly dissociated form. For this purpose, a base may be added to the aqueous solution before or during the hydrogenation step. The purified product from step a) is then hydrogenated in step b) to convert the unsaturated dicarboxylic acids into saturated dicarboxylic acids.

The method chosen for conducting the hydrogenation reaction must take into account the characteristics of the purified product from step a), e.g. the presence of the dicarboxylic acids in dissociated form in aqueous solution, or the presence of the dicarboxylic acids in undissociated form in solvent.

Nevertheless, the operation is carried out by catalytic hydrogenation, with equipment and technology similar to those used in the vegetable and animal oils and fats industry.

Hydrogenation may be performed in continuous or batch, stirred or fixed-bed, reactors in the presence of both heterogeneous and homogeneous catalysts.

The catalysts may be metal-based, e.g. Pt, Pd, Rh, Ru, Ni. In the case of heterogeneous catalysis, they may be supported on inert materials such as alumina or activated carbon.

The reaction conditions depend on the method chosen and the composition of dicarboxylic acids being treated.

In any event, hydrogenation step b) is preferably carried out at temperatures from 70°C to 160°C, more preferably from 80°C to 150°C.

When operating in an aqueous environment, a temperature of 80°C to 150°C is preferably maintained, with pressures above atmospheric pressure, preferably 5 to 40 bar, more preferably between 10 and 30 bar.

When working in the presence of solvent a temperature of 70 to 110°C is preferred, with pressures of 1 to 5 bar; for example, when working with dibutyl ether, temperatures between 80°C and 100°C at atmospheric pressure are preferred.

According to a preferred aspect, after step b) the process according to the invention comprises one or more operations for recovering any solvent and/or further reducing the impurities content, selected for example from the group consisting of crystallising, centrifuging, filtration, treatment with activated carbons, treatment with ion exchange resins, treatment with molecular sieves, evaporation and drying (e.g. spray drying, fluidised bed drying and direct contact drying).

According to one aspect of the process, the dicarboxylic acids are present in aqueous solution in dissociated form. In this case the dicarboxylic acids can be recovered by the addition of acids, preferably strong acids such as HC1 or H2SO4. This operation may conveniently be carried out by reactive crystallisation, which allows the size of the crystals produced to be controlled and a further stage of removal of residual impurities to be achieved. This crystallisation may be followed by one or more washing operations to facilitate the removal of salts.

The dicarboxylic acids obtained are then separated from the aqueous phase by filtration, e.g. through a belt filter.

At the end of the process the separated solid can be dried with a process typical for the industry, for example, using a fluidised bed or spray dryer.

According to another aspect of the process, the dicarboxylic acids are dissolved in organic solvent. In this case the dicarboxylic acids can be recovered by solvent crystallisation, followed by separation of the dicarboxylic acids in solid form and appropriate recovery of the solvent, which is advantageously reused.

For example, when step a) of the process comprises an ultrafiltration operation performed at a pH >8, the composition of the saturated C12-C24 aliphatic dicarboxylic acids obtained at the end of the process according to the invention advantageously has a monounsaturated carboxylic acid content of less than 0.5% by weight, preferably less than 0.2%, more preferably less than 0.1% and even more preferably less than 0.05% by weight. Furthermore, the nitrogen content of the composition obtained by the present process, in particular by performing at least one nonpolar solvent extraction in step a) of the process, is advantageously less than 500 ppm, preferably less than 100 ppm and more preferably less than 50 ppm.

Also said composition advantageously has a content of saturated aliphatic dicarboxylic acids having a number of carbon atoms one unit less than the monocarboxylic acids fed to fermentation (namely for example Cl 5, Cl 7 and C19 acids in a composition of Cl 6, Cl 8 and C20 acids, i.e. one-carbon shorter saturated aliphatic dicarboxylic acids), which can be obtained as fermentation by-product and would be difficult to separate from the main components of the fermentation broth, in an amount that is less than 500 ppm, preferably less than 450 ppm, more preferably 350 ppm and even more preferably from 1 ppm to 200 ppm. More preferably, the content of said saturated aliphatic dicarboxylic acids having a number of carbon atoms one unit less is individually less than 150 ppm. This makes the composition particularly suitable for use as a monomer in polymerisation reactions, e.g. in the synthesis of polyesters, polyamides and polyurethanes.

In particular, said composition is useful for the synthesis of polyesters from diacid-diols. A nitrogen impurity content of less than 500 ppm, preferably less than 100 ppm and more preferably less than 50 ppm, e.g. 1 ppm to 50 ppm, does not interfere with the activity of the polymerisation catalysts typically employed, such as organometallic tin compounds (e.g. stannoic acid derivatives), Titanium compounds (e.g. ortho-butyl titanate), Aluminium compounds (e.g. Al-triisopropyl), Antimony and Zinc and Zirconium compounds and mixtures thereof.

Thus, a saturated C12-C24 dicarboxylic acid composition having a nitrogen impurity content of less than 500 ppm, a saturated monocarboxylic acid content of preferably less than 0.5% by weight and a one-carbon shorter saturated aliphatic dicarboxylic acid content with respect to the main components (for example odd-numbered dicarboxylic acids such as C15, C17 or C19) of preferably less than 500 ppm, the use of said composition in the synthesis of polymers, preferably polyesters, polyamides and polyurethanes, and in particular polyesters from diacid- diols obtained therefrom, also constitute objects of the present invention.

The invention also relates to use of the dicarboxylic acid composition obtained by the process described above in polymerisation, in particular for the synthesis of polyesters, polyamides and polyurethanes.

Preferred uses are for the synthesis of diacid-diol-type polyesters or for the synthesis of polyesters-polyols for use in the preparation of polyurethanes.

According to one aspect, the composition according to the invention comprises at least one saturated dicarboxylic acid having 18 carbon atoms, in an amount advantageously from 40 to 99% by weight, and at least one saturated C16 dicarboxylic acid, in an amount advantageously from 1 to 60% by weight. Said composition is obtained, for example, by subjecting a mixture of dicarboxylic acids obtained by the fermentation of a mixture of monocarboxylic acids from vegetable oils such as sunflower oil, thistle oil or palm oil to the process according to the invention.

While the presence of different co-monomers typically influences the properties of the copolyesters obtained (for example by causing a decrease in temperature resistance), it has been unexpectedly observed that a composition with octadecanedioic acid and hexadecanedioic acid makes it possible to obtain co-polyesters with substantially unchanged properties as compared to the corresponding polyesters in which the aliphatic dicarboxylic component consists of octadecanedioic acid alone or hexadecanedioic acid alone, particularly when present in the above-mentioned amounts. Consequently, its use in polymerisation has the advantage of not initially requiring time-consuming steps to obtain high-purity dicarboxylic acids.

Said composition therefore makes it possible to obtain new co-polyesters from diacid-diols in which the dicarboxylic component mainly consists of 1,18-octadecanedioic acid and 1,16- hexadecanedioic acid as co-monomer. These polyesters have thermal properties and, in particular, a melting temperature and crystallisation temperature that make them suitable for use in all the main transformation processes (e.g. film-forming, thermoforming, injection moulding, extrusion coating) and in particular for the preparation of thermoformed articles and films for food packaging.

A further object of the present invention is therefore the use in polymerisation of said aliphatic dicarboxylic acid composition comprising a saturated Cl 6 dicarboxylic acid in an amount from 1% to 60% by weight, preferably 2-40%, more preferably 5-15% by weight, and a saturated Cl 8 dicarboxylic acid from 40 to 99% by weight, preferably 60-98%, more preferably 85-95% by weight, in which the saturated monocarboxylic acid content is preferably less than 0.5% by weight, more preferably less than 0.2%, more preferably less than 0.1% and even more preferably less than 0.05% by weight. Advantageously, compositions having a nitrogen content of less than 500 ppm, preferably less than 100 ppm and more preferably less than 50 ppm, and/or saturated aliphatic dicarboxylic acids having an odd number of carbon atoms (namely for example Cl 5, C17 and Cl 9) in an amount of less than 450 ppm, more preferably less than 350 ppm and even more preferably from 1 ppm to 200 ppm, are used. More preferably, the content of said saturated aliphatic dicarboxylic acids having an odd number of carbon atoms is individually less than 150 ppm.

Finally, the invention relates to the polyester (co-polyester) from diacid-diols obtained from one of the compositions described above, the dicarboxylic component of which therefore comprises units derived from said compositions.

According to one aspect, said diacid-diol polyesters according to the invention are aliphatic, i.e. their dicarboxylic component consists of units derived from aliphatic dicarboxylic acids or their C1-C24 alkyl esters.

According to another aspect, said diacid-diol polyesters according to the invention are aliphatic- aromatic, i.e. the dicarboxylic component comprises units derived from aromatic dicarboxylic acids or their Cl -C24 alkyl esters in addition to units derived from aliphatic dicarboxylic acids or their C1-C24 alkyl esters.

According to one preferred aspect, said diacid-diol polyester comprises:

(a) a dicarboxylic component comprising: (al) 0-80% in moles, relative to the total moles of the dicarboxylic component, of units derived from at least one aromatic dicarboxylic acid, and

(a2) 20-100% in moles, relative to the total moles of the dicarboxylic component, of units derived from the aliphatic dicarboxylic acid composition according to the invention described above, preferably obtained by the process according to the invention, and

(b) a diol component, preferably selected from saturated aliphatic diols.

The aromatic dicarboxylic acids of component (al) are preferably selected from aromatic dicarboxylic acids of the phthalic acid type, preferably terephthalic acid or isophthalic acid, more preferably terephthalic acid and heterocyclic dicarboxylic aromatic compounds, preferably 2 ,5-furandicarboxylic acid, 2,4-furandicarboxylic acid, 2,3-furandicarboxylic acid, 3,4- furandicarboxylic acid, more preferably 2,5-furandicarboxylic acid, their esters, salts and mixtures thereof.

Polyesters in which said component (al) comprises units deriving from mixtures comprising at least two aromatic dicarboxylic acids, in turn comprising, in relation to the total aromatic dicarboxylic acids content:

- 1-99% in moles of terephthalic acid, its esters or salts,

- 99-1% in moles of 2,5-furandicarboxylic acid, its esters or salts, are preferred.

The aliphatic dicarboxylic acids of component (a2) are preferably selected from Ci2-C₂₄, preferably C₁₄-C₂2, more preferably C16-C20, aliphatic dicarboxylic acids, their C C₂₄, preferably C₄-C₄, alkyl esters, their salts and mixtures thereof. The aliphatic dicarboxylic acids are preferably saturated. They are advantageously selected from dodecanedioic acid, brassylic acid, tetradecanedioic acid, hexadecanedioic acid, octadecanedioic acid, docosanedioic acid and their Ci-24 aliphatic esters. According to a preferred aspect, said dicarboxylic component (a2) mainly consists of 1,18-octadecanedioic acid and 1,16-hexadecanedioic acid as co-monomer.

According to one embodiment of the present invention, the aliphatic dicarboxylic acids (a2) further comprise units derived from one or more C4-C11 dicarboxylic acids, their esters with Ci- C24, preferably Ci- C₄, alcohols and mixtures thereof; for example, said C4-C11 acids are selected from succinic acid, adipic acid, azelaic acid, sebacic acid and mixtures thereof.

Unsaturated aliphatic dicarboxylic acids may be present in quantities advantageously lower than 5 per cent in moles of aliphatic dicarboxylic units. They are preferably selected from hexadecendioic acid, octadecendioic acid and their mixtures. With regard to diol component (b), this preferably comprises one or more diols selected from 1,2-ethanediol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,5 -pentanediol, 1,6- hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,11 -undecanediol, 1,12-dodecanediol, 1,13 -tridecanediol, 1,4-cyclohexanedimethanol, neopentylglycol, 2-methyl-l,3-propanediol, dianhydrosorbitol, dianhydromannitol, dianhydroiditol, cyclohexanediol, cyclohexanmethanediol, dialkylene glycols and polyalkylene glycols with molecular weights of 100-4000 such as polyethylene glycol, polypropylene glycol and mixtures thereof. Preferably, the diol component comprises at least 50% in moles of one or more diols selected from 1,2-ethanediol, 1,3-propanediol, 1,4-butanediol. More preferably, the diol component comprises, or consists of, 1,4-butanediol.

Unsaturated aliphatic diols may be present (preferably in amounts of 0 to 5% in moles of component b), for example those selected from cis 2-buten-l,4-diol, trans 2-buten-l,4-diol, 2- butyn-l,4-diol, cis 2-penten-l,5-diol, trans 2-penten-l,5-diol, 2-pentyn-l,5-diol, cis 2- hexen-l,6-diol, trans 2-hexen-l,6-diol, 2-hexyn-l,6-diol, cis 3-hexen-l,6-diol, trans 3-hexen- 1,6-diol, 3-hexyn-l,6-diol.

The polyester according to the present invention may also advantageously comprise repeating units derived from at least one hydroxy acid in an amount of between 0 and 30%, preferably between 0 and 25%, more preferably between 1 and 15%, even more preferably less than 10% in moles with respect to the total moles of the dicarboxylic component. Examples of convenient hydroxy acids are glycolic acid, hydroxybutyric acid, hydroxycaproic acid, hydroxyvaleric acid, 7-hydroxyheptanoic acid, 8-hydroxycaproic acid, 9-hydroxynonanoic acid, lactic acid or lactide. The hydroxy acids may be inserted into the chain as such or as prepolymers/oligomers, or may also be first reacted with diacids or diols.

Long molecules with two functional groups, including those with non-terminal functional groups, may also be added in quantities not exceeding 10% in moles in relation to the total moles of the dicarboxylic component. Examples are dimer acids, ricinoleic acid and acids with epoxy functional groups, and also polyoxyethylenes with molecular weights between 200 and 10000.

Diamines, amino acids, and amino-alcohols may also be present in percentages of up to 30 per cent in moles with respect to the total moles of the dicarboxylic component.

In the process of preparation of polyester according to the present invention, one or more polyfunctional molecules may also be advantageously added in amounts of up to 3%, preferably between 0.1 and 1% in moles in relation to the total moles of the dicarboxylic component, in order to obtain branched products. Examples of these molecules are glycerol, pentaerythritol, trimethylolpropane, citric acid, dipentaerythritol, monoanhydrosorbitol, monohydromannitol, acid triglycerides, poly glycerols, etc.

The molecular weight Mn of said polyester is preferably > 15000, more preferably > 20000. As for the poly dispersity index of the molecular weights, Mw/Mn, this is preferably between 1.5 and 10, more preferably between 1.6 and 5, and even more preferably between 1.8 and 4.

The molecular weights Mn and Mw may be measured by Gel Permeation Chromatography (GPC). The determination can be conducted with the chromatographic system held at 40°C using a set of two columns in series (particle diameter 5 pm and 3 pm with mixed porosity), a refractive index detector, chloroform as eluent (flow rate 0.5 ml/min) and using polystyrene as the reference standard.

The Melt Flow Rate (MFR) of the polyester is preferably between 500 and lg/10 min, more preferably between 100 and 3g/10 min, even more preferably between 15 and 3g/10 min (measured at 190°C/2.16 kg according to ISO 1133-1 “Plastics - determination of the melt mass-flow rate (MFR) and melt volume flow rate (MVR) of thermoplastics - Part 1 : Standard method”).

According to the present application rheological properties are measured on a dried sample, that is one having a water content of less than 300 ppm, for example by drying for 1 hour at 90°C in a ventilated oven.

The terminal acid groups content of said aliphatic and/or aliphatic-aromatic polyester is preferably less than 100 meq/kg, preferably less than 60 meq/kg and even more preferably less than 40 meq/kg.

The terminal acid groups content may be measured as follows: 1 ,5-3g of the polyester is placed in a 100 ml conical flask together with 60ml of chloroform. After complete dissolution of the polyester, 25ml of 2-propanol is added and, immediately before analysis, 1ml of deionised water. The resulting solution is titrated with a previously standardised solution of NaOH in ethanol. An appropriate indicator, such as a glass electrode for acid-base titrations in nonaqueous solvents, is used to determine the equivalence point of the titration. The terminal acid groups content is calculated on the basis of the consumption of NaOH solution in ethanol according to the following equation:

[(Veq - 7b)-T]-1000

Terminal acid groups content (meq/kg polymer) = - - - in which:

Veq = ml of NaOH solution in ethanol at the equivalence point of the sample titration; Vb = ml of NaOH solution in ethanol required to achieve pH = 9.5 during the blank titration;

T = concentration of NaOH solution in ethanol expressed in moles/litre;

P = weight of sample in grams.

Preferably, said polyester has an inherent viscosity of more than 0.3 dl/g, preferably between 0.3 and 2 dl/g, more preferably between 0.4 and 1.4 dl/g (measured with an Ubbelohde viscometer for solutions in CHCh at a concentration of 0.2 g/dl at 25 °C).

The polyesters according to the invention are extremely suitable for use, alone or in blends with other polymers, in many practical applications for the manufacture of products such as films, fibres, non-wovens, foils, and moulded, thermoformed, blown, foamed and laminated articles, also using the extrusion coating technique.

The diacid-diol type polyesters according to the invention are advantageously used in mixtures with one or more natural or synthetic polymers other than diacid-diol type polyesters, also obtained by reactive extrusion processes.

Said polyesters and/or said mixture according to the invention are preferably biodegradable according to EN 13432.

With regard to mixtures with other polymers, biodegradable polyesters of the diacid-diol, hydroxyacid or polyester-ether type are preferred.

With regard to these biodegradable polyesters of the diacid-diol type, they may be either aliphatic or aliphatic-aromatic.

Preferably, the mixtures of polyesters with biodegradable aliphatic and aliphatic-aromatic diacid diol polyesters obtained by the process according to the present invention are characterised by a biodegradable polyesters content that varies in the range from 1 to 99% w/w, more preferably between 5 and 95% w/w, with respect to the sum of the weights of the polyesters obtained by the process according to the present invention and the latter respectively. It is also possible to mix the polyesters according to the invention with more than one biodegradable polyester of the diacid-diol type. Particularly preferred are both binary and ternary mixtures of the polyesters obtained by the process according to the present invention with said biodegradable diacid-diol polyesters.

Of the preferred biodegradable hydroxyacid polyesters, those preferred are poly L lactic acid, poly D lactic acid and poly D-L lactic acid stereo complex, poly-s-caprolactone, polyhydroxybutyrate, polyhydroxybutyrate-valerate, polyhydroxybutyrate-propanoate polyhydroxybutyrate-hexanoate, polyhydroxybutyrate-decanoate, polyhydroxybutyrate- dodecanoate, polyhydroxybutyrate-hexadecanoate, polyhydroxybutyrate-octadecanoate, poly- 3-hydroxybutyrate-4-hydroxybutyrate.

Preferably, mixtures of the polyesters according to the present invention with the biodegradable hydroxyacid polyesters described above are characterised by a content of said biodegradable polyesters in the range from 1 to 99% w/w, more preferably between 5 and 95% w/w, with respect to the sum of the weights of the polyesters obtained by the process according to the present invention and the latter respectively.

The polyesters obtained by the process according to the present invention may also be used in mixtures with polymers of natural origin such as starch, cellulose, chitin, chitosan, alginates, proteins such as gluten, zein, casein, collagen, gelatin, natural gums, rosinic acid and its derivatives, lignins as such, or purified, hydrolysed, basified, etc., lignins or their derivatives. The starches and celluloses may be modified, and these include, for example, starch or cellulose esters with a degree of substitution between 0.2 and 2.5, hydroxypropylated starches, starches modified with fatty chains, and cellophane. Mixtures with starch are particularly preferred. The starch may also be used in both unstructured and gelatinised form or as a filler. The starch may be the continuous or the dispersed phase, or it may be in co-continuous form. In the case of dispersed starch, the starch is preferably in sub-micron form and more preferably of less than 0.5 pm mean diameter.

Preferably, the blends of the polyesters according to the present invention with the polymers of natural origin described above are characterised by a content of said polymers of natural origin in the range from 1 to 99% w/w, more preferably from 5 to 95% w/w and more preferably from 10 to 40% w/w with respect to the sum of the weights of the polyesters obtained by the process according to the present invention and the latter, respectively.

In a further aspect, the present invention relates to a product comprising at least one polyester according to the invention or a mixture according to the invention. Said product is suitable in a variety of applications. Examples of products comprising at least one polyester according to the present invention include the following:

- films, optionally mono- or bi-layer, either single- or multi-layer with other polymer materials, with application for example as stretch films for foodstuffs, for baling in agriculture and for waste wrapping, or as mulching film in agriculture;

- bags and liners for organic collection such as food waste and grass cuttings;

- thermoformed items, both single and multilayer, also suitable for contact with food, such as plates, cups, rigid containers, beverage capsules, lids, food packaging such as containers for milk, yoghurt, meat and beverages, food containers that can be heated in conventional or microwave ovens;

- coatings obtained using the extrusion coating technique;

- multilayer laminates with layers of paper, plastics, aluminium, metallised films;

- expanded or expandable granules for the production of formed parts by sintering;

- expanded and semi-expanded products including expanded blocks made from pre-expanded particles;

- expanded sheets, thermoformed expanded sheets, containers made from them for food packaging;

- containers in general for fruit and vegetables;

- composites with gelatinised, de-structured and/or complexed starch, natural starch, flours, other materials of natural, vegetable or inorganic origin as fillers; and

- fibres, microfibres, composite fibres, fibres with different cross-sections, from round to rnulti- lobed, staple fibres, woven and non-woven or spunbonded or thermo-bonded fabrics for health, hygiene, agriculture and clothing.

The process according to the invention will now be described according to non-limiting examples.

EXAMPLES

Example 1

An aqueous mixture comprising unsaturated C12-C24 dicarboxylic acids was obtained by fermentation using a strain of Candida maltosa genetically modified for inactivation of the function of the CAT (Carnitine Acetyl-Transferase) gene by deletion of both alleles of the gene according to the method described in WO 2019/030652. A mixture of monocarboxylic acids with a high oleic acid content (Oleic acid 18: 1, min 70%; Linoleic acid 18:2, max 20%; saturated C18 and lower acids, max 12%) has been used as fermentation substrate.

The mixture obtained after fermentation was analysed to quantify the individual monocarboxylic and dicarboxylic acids by reversed-phase liquid chromatography (HPLC- CAD) using the following operating conditions:

• Column: Gemini NX C18 (150 x 3.0mm), Phenom enex

• Injection volume: lOpl

• Injection and column temperature: 40°C

• CAD temperature: 35°C

• Buffer A: MetOH (LC-MS grade) 60%, H2O (LC-MS grade) 40%, Formic acid 0.1%. • Buffer B: ACN (LC-MS grade)

• Run (38 minutes):

The quantification was carried out using an external standard.

The mixture had a dicarboxylic acid content of 76.4 g/L, of which unsaturated 86%, and a monocarboxylic acid content of less than 10 g/L.

Step a)

An aliquot of fermentation broth containing C16-C18 dicarboxylic acids in a concentration of about 76 g/1 was subjected to deactivation treatment (pasteurisation) at a temperature of 50°C and a pH of 12 using KOH for about 30 minutes. The broth was subsequently centrifuged in order to remove solid residues and to obtain a solution containing dicarboxylic acids (and residual monocarboxylic acids) in dissociated form.

Said solution was subjected to tangential ultrafiltration with a 10 kDa regenerated cellulose membrane to remove the monocarboxylic acids present in the retentate. The permeate was then titrated with sulphuric acid to pH 2 to precipitate out the dicarboxylic acids in acid form. The filtered solid was washed with acidified water to remove any impurities present.

The washed solid was then redissolved by titration with a solution of KOH and the salt solution obtained, with a concentration of 50 g/1, subsequently underwent a second tangential filtration treatment on a 1 kDa teflon membrane. The solution obtained had an unsaturated dicarboxylic acid content (predominantly C18:2 + C18: l) of approximately 86.8% and a saturated dicarboxylic acid content (predominantly C16:0 + C18:0) of approximately 13.2% (from qualitative HPLC-CAD analysis). The residual monocarboxylic acid content was less than 0.5%. Kjeldahl analysis found a nitrogen content of 0.01%.

The solution so obtained was partly acidified by the addition of sulphuric acid (stoichiometrically approximately 30% in relation to the dicarboxylic acids present).

The resulting solution was concentrated to 160 g/L by evaporation and then subjected to crystallisation by controlled cooling to 12°C.

The crystals formed were separated out by filtration, washed with water and redissolved with a KOH solution in water to a pH of 10.5 and a concentration of 30 g/L.

Step b)

The aqueous solution thus purified, comprising dicarboxylic acids in their salt form, was transferred to a trickle bed reactor operating continuously in the presence of 0.5% Pd/C. The reaction was conducted at a temperature of 150°C, using an H2 pressure of 20 bar, until complete conversion of the unsaturated groups.

The hydrogenated solution was then acidified by the addition of 5M sulphuric acid under controlled conditions (pH 3, 50°C) to precipitate out crystals of saturated dicarboxylic acids. The resulting suspension was filtered and washed with water on a belt filter, obtaining saturated dicarboxylic acids which were then dried in an oven at 50°C.

The resulting product had a monoacid content of less than 0.1% w/w and an unsaturated species content of less than 0.1% w/w, making it suitable for application in polymer synthesis.

The dicarboxylic acids composition was confirmed by qualitative CG/FID analysis and was found to be 11.4% w/w C16:0 and 86.2% w/w C18:0. Dicarboxylic acids with numbers of carbon atoms other than 16 and 18 were present in an amount of approximately 2%. After the samples had been methylated with BF3MeOH, the analysis was carried out using a Thermo gas chromatograph equipped with an on-column injector, an FID detector and a Restek Rt 2560 100m x 0.25 mm x 0.20 mm column.

Elemental analysis revealed a nitrogen content < 30 ppm.

Example 2

An aqueous mixture comprising unsaturated C12-C24 dicarboxylic acids was obtained as in Example 1.

An aliquot of the fermentation broth was extracted and analysed for quantification of the individual monocarboxylic and dicarboxylic acids, indicating a palmitic and linoleic monocarboxylic acids content of < 2g/L; oleic, stearic and dicarboxylic C16 and Cl 8:2 acids contents of < lOg/L, < 2g/L and > 5g/L; C18:0 > 2g/L; C18: l > 50g/L.

Step b) An aliquot of fermentation broth containing C16-C18 dicarboxylic acids in a concentration of about 78g/l was subjected to deactivation treatment (pasteurisation) at a temperature of 50°C and a pH of 12 using KOH for about 30 minutes. The broth was subsequently centrifuged to remove solid residues and to obtain a solution containing dicarboxylic acids (and residual monocarboxylic acids) in dissociated form.

This solution was subjected to tangential filtration with a 10 kDa regenerated cellulose membrane to remove the monocarboxylic acids present in the retentate. The permeate thus obtained was subjected to a second tangential filtration step on a 1 kDa PES membrane in order to reduce the content of impurities present. It was then concentrated to bring the content of total dicarboxylic acids to a value of about 40 g/L. The resulting solution had an unsaturated dicarboxylic acid content (C18:2 + C18: 1) of about 89.8% and a saturated dicarboxylic acid content (C16:0 + C18:0) of about 10.2% (from qualitative GC/FID analysis).

An aliquot of this permeate was then titrated to pH 2 with sulphuric acid at a temperature of 50°C to precipitate the dicarboxylic acids in acid form. Subsequently, a volume of solvent (n- Dibutyl ether) was added such that the total concentration of dicarboxylic acids in the organic phase was 70-80 g/L.

When the temperature of the solvent reached 45°C, the system was shaken vigorously to promote mixing of the phases. After 5 to 10 minutes, shaking was stopped and phase separation was awaited.

The organic phase was removed and stored in a reactor pre-heated to a temperature of 50°C pending the decol ourisati on phase on activated charcoal, which was conducted by feeding the organic phase continuously into a jacketed glass column containing charcoal in granular form. On exiting the decolourisation column the dicarboxylic acids were analysed by qualitative GC/FID analysis, which yielded the following results: an unsaturated dicarboxylic acid content (C18:l+C18:2) of 92.7% and a saturated dicarboxylic acid content (C16:0+C18:0) of 7.3%. After methylation of the samples with BF3MeOH, the analysis was performed using a gas chromatograph equipped with an on-column injector, an FID detector and a Restek Rt 2560 100m x 0.25 mm x 0.20 mm column.

The nitrogen content determined by elemental analysis on the solid product was 30mg/kg.

The decolourised organic solution was diluted with the solvent to a concentration of 10 g/L.

Step b)

The organic solution thus purified and diluted, comprising dicarboxylic acids in their acid form, was transferred into a trickle bed reactor operating continuously in the presence of 0.5% Pd/C. The reaction was conducted at a temperature of 100°C, in the presence of a flow of 200 NL/h of H₂, resulting in complete conversion of the unsaturated groups.

The hydrogenated solution was then transferred into suitable containers and allowed to cool to a temperature of 20°C to promote the precipitation of saturated dicarboxylic acid crystals.

The suspension so obtained was filtered and washed with solvent using Buchner-type funnels. Saturated dicarboxylic acids of high purity (>99%) were obtained, and these were dried first under a hood and then in an oven at 50°C.

The product obtained had a monoacid and unsaturated species content of less than 0.1%, making it suitable for application in polymer synthesis. In addition, LC-MS analysis revealed the presence of molecular species with a mass compatible with saturated dicarboxylic acids having an odd number of carbon atoms (Cl 5, C 17 and Cl 9).

The composition of saturated C16 and Cl 8 dicarboxylic acids obtained by quantitative UHPLC-CAD analysis was 7.5±0.1% and 91.5±0.5%, respectively.

Elemental analysis revealed a nitrogen content of < 30 ppm.

Claims

1. Process for obtaining saturated C12-C24 dicarboxylic acids from an aqueous mixture comprising unsaturated C12-C24 dicarboxylic acids or derivatives thereof, fermentation by-products and any residual substrate, comprising the steps of:

(a) separating out at least some of the fermentation by-products and/or the residual fermentation substrate from said unsaturated C12-C24 dicarboxylic acids or their derivatives by subjecting said aqueous mixture to one or more purification operations selected from centrifuging, settling or filtration;

2. Process according to claim 1 wherein said step a) comprises the operations of bringing said aqueous mixture to a pH >8 and separating out any residual C12-C24 monocarboxylic acids, in the form of salts, by at least one ultrafiltration operation.

3. Process according to any of claims 1-2 comprising, after step a) and before step b), the steps of: i) dissolving the C12-C24 dicarboxylic acids in a non-polar organic solvent and removing the fermentation by-products insoluble in it; ii) optionally purifying the organic phase comprising C12-C24 dicarboxylic acids by means of one or more operations selected from ultrafiltration, nanofiltration, crystallisation, adsorption and passage over ion exchange resins.

4. Process according to claim 3 wherein hydrogenation step b) is carried out in the presence of said non-polar organic solvent.

5. Process according to any of claims 3 and 4 wherein said non-polar organic solvent is selected from t-amyl methyl ether, t-butyl methyl ether, n-dibutyl ether, butyl acetate, methyl isobutyl ketone.

6. Process according to any of claims 1-2 wherein the hydrogenation in step b) is carried out on C12-C24 dicarboxylic acids in at least partially dissociated form in aqueous solution.

7. Process according to any of claims 1-6 wherein hydrogenation step b) is carried out at temperatures of from 70°C to 160°C, preferably 80°C to 150°C.

8. Process according to any of claims 1-7 comprising, after step b), one or more operations for recovering any solvent and/or reducing the impurities content, selected from the group consisting of crystallisation, filtration, evaporation, spray drying, fluidised bed drying and direct contact drying.

9. Process according to any of claims 1-8 wherein said aqueous mixture comprising unsaturated C12-C24 dicarboxylic acids or derivatives thereof is obtained by fermentation in the presence of a microorganism belonging to the genuses Yarrowia, Candida, Rhodotorula, Rhodosporidium, Cryptococcus, Trichosporon or Lipomyces and preferably belonging to the genus Candida or Yarrowia.

10. Process according to any of claims 1-9 for obtaining saturated C16-C18 dicarboxylic acids from an aqueous mixture comprising unsaturated C16-C18 dicarboxylic acids or derivatives thereof.

11. Composition of saturated C12-C24 dicarboxylic acids obtained by the process according to one or more of claims 1-10.

12. Composition of saturated aliphatic C12-C24 dicarboxylic acids having a nitrogen impurity content of less than 500 ppm, a saturated monocarboxylic acid content of preferably less than 0.5% by weight and a one-carbon shorter saturated aliphatic dicarboxylic acid content preferably less than 500 ppm.

13. Use of a composition according to any of claims 11-12 in polymerisation, preferably for the synthesis of polyesters, polyamides and polyurethanes.

14. Diacid-diol polyester whose dicarboxylic component comprises units derived from a composition according to claim 11 or claim 12.

15. Article including the diacid-diol polyester according to claim 14.