Process for producing purified BIO based aromatics

Abstract

The invention relates to a process for the preparation of purified (D)(M)PA, the process comprising first reacting a cycloadduct according to structure I with R1 = H or CH3; R2 = H or CH3; R3 = COOH; R4 = COOH; or R3 and R4 are an anhydride bridge COOOC; with an acidic mixture comprising a first acid and an activating agent to obtain the aromatic product according to formula II, with R1 = H or CH3; R2 = H or CH3; R3 = COOH; R4 = COOH; or R3 and R4 are an anhydride bridge COOOC; while removing during the reaction a by-product formed due to the reaction between structure I and the activating agent.

Description

[0001] PROCESS FOR PRODUCING PURIFIED BIO BASED AROMATICS

[0002] Field of the invention

[0003] The present invention relates to a process for the preparation of purified bio-based aromatics, in particularly variants of phthalic anhydride, denoted as (D)(M)PA. In addition, the invention relates to the product (D)(M)PA with a certain purity. The invention also relates to the use of (D)(M)PA in several applications.

[0004] Background of the invention

[0005] Worldwide there is a growing demand for sustainability, expressed in the use of renewable feedstock and the reduction of the CO2-footprint. As a result, there is an increasing need for sustainable processes for the production of aromatic molecules (e.g. phthalic anhydride derivatives, benzene-tricarboxylic acids etc.). Biomass, which is renewable and CO2-neutral, appears to offer a good opportunity as an aromatic source.

[0006] Aromatic building blocks such as phthalic anhydride (PA) are key ingredients in for example coatings. They provide important properties such as hardness to coatings. Today, aromatics are produced almost exclusively from fossil raw materials. Moreover, in some coatings, such as alkyd coatings, aromatic di-acids were the only ingredient for which there was no sustainable alternative available. This alternative now becomes available in the form of bioaromatics, opening the way towards fully biobased alkyd coatings.

[0007] The production and application of biobased 3-methylphthalic anhydride (bio-MPA) to be used in coatings has been successfully developed, assessed and demonstrated, as renewable alternative for fossil-based phthalic anhydride (PA). For example, in EP-A-4041705, is the preparation of an aromatic product described from a cycloadduct comprising a 7-oxabicyclo[2.2.1 ]hept-2-ene core structure or from an intermediate, possibly ring-opened compound formed in this process. The starting material for this process are C5 or C6 sugars from biomass comprising (hemi-)cellulose, like glucose, xylose, mannose and arabinose. These sugars offer more potential as a source for renewable aromatics. Said sugars can easily be converted to 2,5-bis(hydroxymethyl)furan, 5-(hydroxymethyl)furfural, 5- methoxymethylfurfural, 5-chloromethylfurfural, 2,5-dimethylfuran, furfural, furfuryl alcohol, 2-methylfuran or furan. Said compounds were showing promising opportunities for a sustainable process to synthesize aromatic compounds. For instance, the furan core of the compounds is able to react as a diene in a Diels- Alder reaction with dienophiles. The cycloadduct formed during said reaction can undergo a ring-opening and be carried on in further processing to yield aromatic products.

[0008] Another example of a successful synthesis of phthalic anhydride is published in Green Chemistry, 2014, 16, 167-175. It describes the production of phthalic anhydride by reacting furan with maleic anhydride followed by a second reaction with mixed-sulfonic carboxylic anhydrides in excess methanesulfonic acid. A downside to the disclosed process is that methanesulfonic acid is used in a large access (10 molar equivalents), is expensive, and very difficult to recover and recycle, meaning that achieving significant production scale with this process is unlikely. Furthermore, the phthalic anhydride must be extracted with large volumes of toluene or the addition of water for quenching the reaction, destroying the anhydride formed in said process.

[0009] In WO-A-2010012442 a process is described wherein via a ring-opening process 3-methylphthalic anhydride is synthesized using sulfuric acid and sulfolane as co-solvent. One of the disadvantages of the process according to WO-A-2010012442 is that yields are generally poor.

[0010] EP-A-3844165 discloses a process of preparing aromatic compounds from bio-based furanic compounds. The process is an improved bio-based route from furanic compounds to phthalic anhydride compounds by reacting furfuryl alcohol (i.e. 2-hydroxymethylfuran) or an analogue thereof having a nucleophilic atom on the 2-methyl, with a dienophile comprising an a,[3-unsaturated carbonyl comprising an a'-leaving group. The invention further involves preparation of phthalic anhydride compounds, phthalic acid compounds and reduction products of the intermediate phthalide compounds. Although the formation of structures was confirmed, no yields and purity was noted.

[0011] The documents that are discussed above disclose processes that are complicated to implement on pilot plant scale or even larger. Production routes are inefficient or expensive. The batch experiments have limited potential to produce the millions of tons of aromatics required each year by industry. Accordingly, there is a demand for an optimized process to manufacture high quality bio-MPA that can be implemented more easily at large scale. There is furthermore a demand for a process to purify the high quality bio-MPA to contain less by-products of low quality. There is also a demand for a variety of purities of bio-MPA to fit the requirements of the applications it is used for.

[0012] Summary of the invention

[0013] It is an objective of the invention to address one or more of the disadvantages faced in the prior art. It is another objective of the invention to provide an alternative to the lab scale processes that are less suited for scaling up the production of bio-MPA. Further objectives include avoiding the formation of unwanted by-products. A particular objective is to provide an efficient and low- cost process for the production of bio-MPA with certain purities. Another objective of the invention is that bio-MPA can be produced in standard and / or widely available chemical manufacturing equipment. A further objective is that bio-MPA can be produced at milder, more sustainable conditions.

[0014] Accordingly, the present invention relates to a process for the preparation of purified (D)(M)PA, the process comprising first reacting a cycloadduct according to structure I with Ri = H or CH3; R2 = H or CH3; R3 = COOH; R4 = COOH; or R3 and R4 are an anhydride bridge COOOC; with an acidic mixture comprising an acid and an activating agent to obtain the aromatic product according to formula II, with Ri = H or CH3; R2 = H or CH3; R3 = COOH; R4 = COOH; or R3 and R4 are an anhydride bridge COOOC; while removing during the reaction at least a byproduct and / or a product formed due to the reaction between structure I and the activating agent.

[0015] Furthermore, the present invention relates to a product comprising (D)(M)PA, being bio-based 3-methylphthalic anhydride (3-MPA) or acid (3-MPAc) and / or 3,6-dimethylphthalic anhydride (DMPA) or acid (DMPAc) and / or biobased phthalic anhydride (PA) or acid (PAc), with a purity of at least 97.0%.

[0016] The present invention also relates to the use of such product as one of the ingredients in a resin, and / or a polyol and / or a pigment and / or an ester product.

[0017] Detailed description of the invention

[0018] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0019] The term “(D)(M)PA” or “bio-MPA” or “bio MPA” as used herein, includes but is not limited to the group consisting of 3-methylphthalic anhydride (3-MPA) (CAS 4792-30-7) with R1 = CH3, R2 = H, (or R1 = H and R2= CH3) and R3and R4are an anhydride bridge COOOC: 3-methylphthalic acid (3-MPAc) (CAS 37102- 74-2) with R1 = CH3, R2 = H, (or R1 = H and R2 = CH3) and R3 and R4 are COOH; 3,6-dimethylphthalic acid (DMPAc) (CAS 944-38-7) with Ri= CH3, R2 = CH3 and R3 and R4 are COOH; and 3,6-dimethylphthalic anhydride (DMPA) (CAS 5463- 50-3) with RI =CH3, R2 = CH3; and R3 and R4 are an anhydride bridge COOOC; phthalic anhydride (PA) with R1 = H, R2 = H, and R3 and R4 are an anhydride bridge COOOC; phthalic acid (PAc) with R1 = H, R2 = H, and R3 and R4 are COOH. In a typical embodiment no chemical compound can be produced in an entirely pure form due to inherent chemical equilibria and / or unavoidable environmental factors. For example, MPA (anhydride) is prone to spontaneous hydrolysis when exposed to atmospheric moisture, resulting in the formation of trace amounts of the corresponding acid. Conversely, during the drying or processing of the diacid form (MPAc), partial dehydration may occur, yielding small quantities of the anhydride (MPA). These phenomena are driven by fundamental chemical reactivity under ambient conditions. As a result, such impurities are generally limited to less than 3%, preferably below 2%, more preferably below 1 %, ensuring that the overall chemical behaviour of the compound remains consistent with its intended use.

[0020] The term "cycloadduct" as used in this disclosure, includes but is not limited to adducts starting from maleic anhydride, such as furan-maleic anhydride adduct (CAS 5426-09-5), including all its stereoisomers; 2-methylfuran-maleic anhydride adduct (CAS 62653-25-2), including all its stereoisomers; and 2,5- dimethylfuran-maleic anhydride adduct (CAS 77880-59-2), including all its stereoisomers.

[0021] The innovative process of the invention relates to a more commercially viable process for the preparation of purified (D)(M)PA, which stands for biobased 3-methylphthalic anhydride (3-MPA) or acid (3-MPAc) and / or 3,6- dimethylphthalic anhydride (DMPA) or acid (DMPAc) and / or biobased phthalic anhydride (PA) or acid (PAc). Although the formation of (D)(M)PA has been described in the prior art, one of the major drawbacks is that those processes are not suitable to produce (D)(M)PA in commercially attractive amounts and with a purity that it can replace certain fossil-based compounds in a variety of applications. Another drawback of the formation of (D)(M)PA as described in the prior art is that it cannot be easily produced in standard and / or widely available chemical manufacturing equipment.

[0022] When the cycloadduct starting from maleic anhydride, according to structure I with Ri = H or CH3; R2 = H or CH3; R3 = COOH; R4 = COOH; or R3 and R4 are an anhydride bridge COOOC; is being contacted with an acidic mixture comprising a first acid and an activating agent, an aromatic product can be obtained according to formula II, with the R-groups as defined above. We now found that if, during the reaction, at least one of the by-products formed and / or one of the products formed due to the reaction between structure I and the activating agent is being removed, that the purity of the end-product increases drastically, to a level that it might be directly applied in all sorts of applications after isolation of the product.

[0023] The activating agent is typically selected from a group consisting of acylating agent, triflating agent, sulfonating agent, carbamylating agent, carbonylating agent. Preferably an acylating agent consisting of acetyl chloride, propionic anhydride, butyric anhydride, isobutyric anhydride, trimethylacetic anhydride, mixed anhydrides and combinations thereof is used. In said mixed anhydrides the groups adjacent to the acyl groups are different C1 -C20 alkyl groups to one another.

[0024] The bridging oxygen will typically form a bond during the ring-opening process with a part of the activating agent. Without wishing to be bound to theory, the inventors believe that as such, the presence of the activating agent encourages fast ring-opening which limits the otherwise occurring unwanted retro-Diels-Alder reaction. The activating agent is therefore believed to contribute to the ring-opening at the bridged oxygen of the cycloadduct, such that said ringopening is the main reaction.

[0025] Contacting the cycloadduct according to formula I with the acid mixture, preferably at low temperature, more preferably at temperatures in the range of from -10°C up to 20°C, even more preferably in the range of from -5°C up to 10°C, most preferably in the range -2°C up to 5 °C, typically provides a ring-opened product. In said ring-opened product, the bond between the oxygen and at least one of the carbon atoms binding R1 and R2 is broken, comprising a ring-opened cyclohexene product. The aromatized product with formula II is generally formed from the ring-opened cyclohexene product by elimination OAct group or groups as ActOH. This formation of the aromatized product with formula II takes preferably place at higher temperature than the initial reaction of the cycloadduct addition to the acid mixture, namely at a temperature in the range of from 40°C up to 70°C, more preferably in the range of from 45°C up to 55°C.

[0026] By the above-described bond formation wherein a part of the activating group forms a bond with the bridging oxygen, another part of the activating group typically leaves the activating agent (OACt). Thus, for instance, if the activating group comprises a symmetrical anhydride (i.e. a non-mixed anhydride), a corresponding acid with respect to the part of the activating agent that forms a bond with the bridging oxygen is also formed. More specifically, if the activating agent comprises acetic acid anhydride, the oxygen is acylated and acetic acid is formed.

[0027] Advantageously, the activating agent that is being used is acetic anhydride. Acetic anhydride reacts with the cycloadduct to form (D)(M)PA and as the by-product of the activating agent acetic acid is formed. The advantage in the process of this invention is that the formed acetic acid can be easily removed from the reactor by applying a separation technique that is readily available.

[0028] It is thus preferred to remove the by-product using distillation, more preferably evaporative distillation, even more preferably evaporative distillation at a reduced pressure, even more preferably evaporative distillation at a pressure below 100 mbar. The exact applied pressure or vacuum is dependent on the reaction temperature and the type of molecule that needs to be removed from the reaction mixture. If acetic acid is the by-product that has to be removed, normally a reduced pressure will suffice.

[0029] The activating agent is preferably mixed with the first acid before contact with the cycloadduct. This typically results in an acidic mixture that is essentially free of water. In a typical embodiment, the acidic mixture is kept at a temperature of 0 to 80 °C before contact with the cycloadduct. Contacting the cycloadduct with the acid mixture can be carried out at a temperature ranging from -10 to 20°C, preferably in the range of -5°C to 10°C. It is believed that in a cooler acidic mixture, for instance a mixture below 10 °C, the unwanted retro Diels-Alder reaction is hindered and competes less with the ring-opening process upon contact with the cycloadduct. In other words, the equilibrium of the Diels-Alder reaction is hindered and competes less with the ring-opening upon contact with the cycloadduct. The elimination reaction is preferably executed at elevated temperature to speed up the process. A balance was found between the speed of reaction, conversion of the starting materials into the products and the purity of the final product or products. Advantageously, the reaction temperature is in the range of from 40°C up to 70°C, more preferably in the range of from 45°C up to 55°C. The reaction itself can be either executed in the same vessel in which the mixing and contacting takes place, or the mixture is transferred to a next vessel, for the benefit of faster overall processing and better temperature control.

[0030] In case evaporative distillation is the preferred method for removing byproducts during reaction, the distillation takes preferably place at around the same temperatures as the reaction temperatures. Preferably, the evaporative distillation temperature is in the range of from 40°C up to 70°C, more preferably in the range of from 45°C up to 55°C.

[0031] Alternatively, or at the same time, it is possible to remove the obtained aromatic product according to formula II from the reactor during the reaction. The aromatic product represented by formula II might be extracted from the reactor during the reaction as soon as product crystallization begins. This presents a favourable embodiment that facilitates the transition to a continuous process, thereby allowing for significantly expedited bio aromatic product downstream processing. This can also prevent or limit the accumulation of impurities in the product due to the decreased residence time of the product into the reaction medium. Currently, the process of the invention is a (fed-)batchwise process. Once the reaction has finished due to conversion of the starting materials to the end product, the obtained aromatic product according to formula II is maintained in solution in the reactor and subsequently isolated in an isolation zone, preferably isolated via filtration and more preferably washed with (fresh, deionized) water or with a solvent, comprising a weak acid. Preferably, the weak acid is one or more of acetic acid, formic acid, benzoic acid, oxalic acid, ethyl acetate and / or sulphurous acid, more preferably acetic acid, formic acid or ethyl acetate and / or sulphurous acid, even more preferably acetic acid.

[0032] In the preferred case that the activating agent that is being used is acetic anhydride, acetic acid is formed as by-product. The formed acetic acid can be removed from the reactor by for example evaporative distillation and easily collected. Preferably, acetic acid is recovered and at least partly used to wash the obtained aromatic product according to formula II.

[0033] Advantageously, washing of the obtained aromatic product according to formula II is performed at a temperature below 30°C, more preferably below 20°C. The cooler the temperature washing takes place, the better results are obtained in terms of yield, and this is due to the solubility of the (di)(M)PA in the (fresh) water or solvent. On the other hand, the washing liquid must remain liquid, so the melting temperature of the washing liquid is the minimum washing temperature of the product.

[0034] Advantageously, the solvent comprises a weak acid, more preferably acetic acid, even more preferably the solvent is a pure technical grade acetic acid (97%), most preferably the solvent is the obtained by-product formed due to the reaction between structure I and the activating agent. In the preferred case that the activating agent that is being used is acetic anhydride as by-product acetic acid is formed. The washing step with the solvent is intended to remove any impurities present in the product. These impurities can be for example sulphur, and other impurities like polymers and humins. The addition of extra water might be done for the formation of the acidic form, for example 3-methylphthalic acid.

[0035] Once the product according to formula II has been washed it might be that the purity is still not sufficient for certain applications. In that case further purification steps are required. It is then preferred that after washing the obtained aromatic product according to formula II is subjected to re-crystallization by cooling or evaporative crystallization in a solvent, comprising one or more of water, ethyl acetate, t-butyl acetate, butyl acetate, n-propyl acetate, isopropyl acetate, ethylene glycol, dimethyl propylene urea, diethylene glycol, butyl ether, propionic acid, methyl isobutyl ketone, isoamyl alcohol, 2-ethylhexanol, butanol, more preferably water, ethyl acetate, t-butyl acetate, butyl acetate, n-propyl acetate, isopropyl acetate, more preferably water and / or ethyl acetate.

[0036] Advantageously, the solvent for recrystallization has a temperature above 50°C, more preferably above 60°C, more preferably above 80°C, even more preferably above 90°C. If warm water is being used for recrystallization, hydrated (D)(M)PA is formed. If ethyl acetate is used for recrystallization, a temperature above 60°C but not more than 80 °C is preferred for safety purpose. The crystals form again by cooling to below 20°C, preferably below 10°C, more preferably below 0°C, as the solubility is high at high T and lower at low T.

[0037] If even further purification is required, there is still the option to distil the product. This is however not preferred as it is impractical on a larger scale and it might be costly.

[0038] In the context of the present invention, the starting material, the cycloadduct according to structure I is typically derived from a Diels-Alder reaction of biomass-derived furanics with a dienophile. A diene can contain a furanic core structure based on the formula and is typically substituted on the positioned herein numbered as 2, 3, 4, and / or 5 by one or more alkyl chains, heteroatoms and / or halogens. Said diene, when used in a Diels-Alder reaction, can provide a cycloadduct comprising a 7- oxabicyclo[2.2.1 ]hept-2-ene core structure based on formula A:

[0039] In the present invention, the cycloadduct may undergo a ring-opening at the bond between the bridged oxygen and the carbon at positions 2 and / or 5 when contacted with the acidic mixture.

[0040] In an alternative embodiment, when the intermediate compounds are provided, they are typically present in a mixture which comprises said intermediates together with the acidic mixture comprising the first acid and the activating agent. This mixture may be the result of the ring-opening. The ring opening reaction and the elimination of the OAct group can be either executed in the same vessel without full removal of the acidic mixture in which the mixing and contacting takes place, or the elimination of the OAct group can be carried out independently from the ring opening reaction. In the latter case, the mixture is transferred to a next vessel, preferably containing around 0.5 equivalent of activating agent and around 0.1 equivalent of the acid. This is advantageous, for the benefit of better temperature control (no exotherms are observed), resulting into greater conversion with less or even no polymers (byproducts) formation.

[0041] The ring opening reaction relates to contacting the cycloadduct according to formula I with an acidic mixture comprising the first acid and the activating agent to obtain the intermediate compound Examples of first acids that are suitable for this reaction include organic acids like triflic acid, p-toluenesulfonic acid (pTSA), methanesulfonic acid (MSA), trifluoroacetic acid (TFA) and the like. Examples of first acids furthermore include inorganic acids such as sulfuric acid (H2SO4), tetrafluoroboric acid (HBF4), gaseous HCI and the like. Gaseous acids and acid in solution (such as HBF4) are, for practical reasons, not the most desirable. Sulfuric acid is particularly preferred since it is neither gaseous nor dissolved and it is cost-efficient. Moreover, good yields were obtained with sulfuric acid. Thus, advantageously, the first acid is sulfuric acid, more preferably sulfuric acid with a concentration of at least 80%, even more preferably technical grade sulfuric acid with a concentration of 97%.

[0042] Solid acids may also be applied and may particularly be suitable for a continuous reaction wherein the reaction is carried out in a tube / column reactor.

[0043] Examples of solid acids include acidic ion exchange resin (e.g. Amberlyst™) and / or tetrafluoroethylene-based fluoropolymer-copolymer (e.g. Nation™). The tube / column reactor may be equipped with a fixed acidic bed comprising the first acid. However, if step a) is carried out continuous in a reactor such as a continuous stirred tank reactor (CSTR), liquid acids such as sulfuric acid are preferred.

[0044] The amount of the first acid should not be too high in order to prevent side reactions such as the retro-Diels Alder reaction. However, it should neither be too low to prevent a slow or incomplete ring-opening reaction. As such, the amount of sulfuric acid is in the range of from 0.1 up to 2 equivalent by weight to the molecule I, preferably in the range of from 0.5 up to 1 equivalent by weight to the molecule I. Naturally, during the progression of the ring-opening reaction the molar ratio may change and with the molar ratio in the previous sentence is meant the molar ratio at the moment the first acid and the cycloadduct are first contacted (e.g. mixed or introduced in a reaction container).

[0045] The amount of activating agent should also not be too high in order to prevent side reactions. However, it should neither be too low to prevent a slow or incomplete ring opening reaction. Advantageously, the amount of activating agent is in the range of from 0.5 up to 4 equivalent by weight to the molecule I, preferably in the range of from 1 up to 3 equivalent by weight to the molecule I. Naturally, during the progression of the ring-opening reaction the molar ratio may change and with the molar ratio in the previous sentence is meant the molar ratio at the moment the activating agent and the cycloadduct are first contacted.

[0046] The present invention is also directed to a product comprising (D)(M)PA with a purity of at least 97.0%. For many applications, this purity is required. However, it is still not commercially available, at this purity and at higher quantities, and that might be one of the reasons that the substitution of fossil based aromatic compounds in many applications is delayed, or simply impossible. Even higher purities can be obtained, preferably the purity of (D)(M)PA is at least 98%, preferably at least 99%, more preferably at least 99.5%.

[0047] Advantageously, the product comprises less than 1500 ppm sulphur, more preferably less than 700 ppm sulphur, even more preferably less than 500 ppm sulphur, and most preferably equal or less than 150 ppm sulphur, even most ideally less than 50 ppm sulphur.

[0048] Preferably, the product comprises 3-methylphthalic anhydride and / or 3- methylphthalic acid. These relatively new molecules find a broad range of applications. Furthermore, the starting materials are more easily and commercially available, as the starting material is 2-methyl furan. Also from a biobased perspective 3-methylphthalic anhydride and / or 3-methylphthalic acid are preferred, as 2-methyl furan is produced or isolated from non-edible sugars (hemicellulose). For the other molecules the starting materials are edible sugars. 3-methylphthalic anhydride and / or 3-methylphthalic acid are also more attractive from a commercial point of view. Besides sulphur as contaminant, the product preferably comprises up to 1 wt% acetic acid and / or acetyl acetate and / or water. Some of these contaminants are the remains of the production of (D)(M)PA.

[0049] The purity of the product might be determined by techniques known by the skilled person. These techniques include quantitative titration with H-NMR, GC and / or HPLC usually coupled with mass spectrometry, UV and IR spectroscopy to determine the structure profile under different wavelengths of light (to measure conjugated bonds, functional groups etc) and / or ICP to determine the amount of inorganics, such as sulphur.

[0050] Aromatic type anhydrides or aromatic type di-acids are often used in the industry as ingredient in formulations to create consumer products that possess a certain level of required hardness, toughness, resistance, etcetera. These levels are not easily achieved by using non-aromatic types of ingredients. A workhorse petrochemical product that is often used in the industry is phthalic anhydride (PA) but also iso-phthalic acid and variations thereof are being used widely. At this moment very few bio-based options for aromatic type anhydrides or aromatic type di-acids are available. Because of a trend towards more sustainable products, and a lack of bio-based alternatives, the (D)(M)PA products as described in this document are of high interest to the market.

[0051] The present invention is therefore also directed to a use of the product comprising (D)(M)PA, being bio-based 3-methylphthalic anhydride (3-MPA) or acid (3-MPAc) and / or 3,6-dimethylphthalic anhydride (DMPA) or acid (DMPAc) and / or biobased phthalic anhydride (PA) or acid (PAc) with a purity of at least 97.0%, as one of the ingredients in a resin, and / or a polyol and / or a pigment and / or an ester product.

[0052] (D)(M)PA and more specifically 3-MPA has been evaluated and tested as ingredient in various end-product applications. For example, 3-MPA has been evaluated as part of an alkyd resin that was used to formulate various types of alkyd coatings. Advantageously, the resin is an alkyd resin, a polyester resin and / or an epoxy resin. To prepare the formulation, the specific properties of 3- MPA were taken into account, amongst others molecular weight and melting point. The alkyd resins in which 3-MPA was used, were both solvent borne as well as water based alkyd resin formulations. These resins were subsequently used to formulate coatings. In all cases, the physical coating properties were tested against coating formulations based on more traditional petrochemical based ingredients, such as PA. The physical coating properties that included 3- MPA showed most of the time equal, or in some cases even a better performance, compared to alkyd resins based on more traditional petrochemical based ingredients.

[0053] (D)(M)PA and more specifically 3-MPA have also been tested and evaluated as an ingredient in plasticizers, pigments, polyols (that ultimately were used in polyurethane or polyisocyanurate foams), epoxy resins (used for adhesives and composite materials). In all of these cases interesting physical properties have been observed.

[0054] Advantageously, the polyol prepared with (D)(M)PA and more specifically 3-MPA, is part of a polyurethane or a polyisocyanurate formulation.

[0055] Advantageously, the pigment prepared with (D)(M)PA and more specifically 3-MPA, is part of a is part of colourant and / or of ink formulations.

[0056] In another aspect of the invention, the ester product prepared with (D)(M)PA and more specifically 3-MPA, is part of a plasticizer formulation and / or part of a lubricant and / or a grease formulation.

[0057] As a conclusion, (D)(M)PA and more specifically 3-MPA, are very suitable bio-based replacement products for petrochemical aromatic type anhydrides or aromatic type di-acids that are widely used in industry. Uses of the before mentioned compositions are preferably in coatings, paints, insulating foams, adhesives, composites and powder coatings.

[0058] The following, non-limiting examples are provided to illustrate the invention.

[0059] Examples

[0060] Experiments were conducted to demonstrate if by distillation I stripping of volatiles (in this case acetic acid), the recovery of 3-methylphthalic anhydride and / or 3-methylphthalic acid could be improved.

[0061] Example 1 : experiment according to the prior art (no distillation)

[0062] In a 250 ml reactor, a mixture of acetic anhydride (94.9 ml) and sulfuric acid (9.2 ml) was cooled to 0°C. The Diels Alder adduct formed between 2 methylfuran and maleic anhydride (59.9 grams) was added over a period of 30 minutes, maintaining an internal temperature of less than 10°C. In the following step the mixture was heated to 65°C and held for 4 hours. The mixture was then cooled to 20°C and the formed solid was isolated by filtration.

[0063] The total mass of solid was 47.3 gram (the % of 3-methylphthalic acid crude was 78.1 % so 37.0 grams). 6.1 gram of 3-methylphthalic acid remained in the reaction media uncrystallized. 30g of the isolated of 3-methylphthalic acid was then washed with acetic acid (56 grams). After drying, the solid 3-methylphthalic acid appeared to have a light brown color (13.3 grams, overall yield about 39%, considering reaction AND washing) with a measured purity of 97.9%.

[0064] Example 2: applying distillation (stripping) after completion of the reaction

[0065] In 250 ml reactor, a mixture of acetic anhydride (118.6 ml) and sulfuric acid (11.5 ml) was cooled to 0°C. The Diels Alder adduct formed between 2 methylfuran and maleic anhydride (74.7 grams) was added over a period of 30 minutes, maintaining an internal temperature of less than 10°C. In the following step the mixture was heated to 65°C and held at that temperature for 4 hours. At the end of the reaction, distillation (stripping) was conducted by applying a 76- mbar vacuum for 1 hour. An amount of 20.9 gram of distillate was recovered (corresponding to circa 30% of the theoretical recoverable mass, equivalents of acetic anhydride inserted at the beginning of the reaction), with a composition of around 70 wt% being acetic acid and around 10 wt% acetic anhydride. The mixture was cooled to 20°C and the formed solid was isolated by filtration.

[0066] The mass of solid was 78.9 grams (3-methylphthalic acid crude in total solid was 57.9% so 45.7 gram), whilst 4.9 gram 3-methylphthalic acid remained in the reaction mixture uncrystallized (4.3%). The overall chemical yield was similar to the previous experiment (NMR titration 75.2%). An amount of 30.0 gram of isolated product was washed with acetic acid (47 gram). After drying, this yielded 3-methylphthalic acid as a yellowish solid (9.4 grams, 37% considering reaction AND washing) with a measured purity of 96.5%.

[0067] This experiment proved to reduce the losses in the filtrate before the washing (7.2% vs 11 .4% in experiment 1 ), yet after the washing recovery results were worse than according to experiment 1 . Example 3: applying distillation (stripping) during the reaction at 65°C (according to the invention)

[0068] In a 250 ml reactor, a mixture of acetic anhydride (118.6 ml) and sulfuric acid (11.5 ml) was cooled to 0°C. The Diels Alder adduct formed between 2 methylfuran and maleic anhydride (75.2 gram) was added over a period of 30 minutes, maintaining an internal temperature of less than 10°C. The mixture was heated to 65°C and held for 4 hours. Immediately after the beginning of the reaction, distillation (stripping) was conducted by applying a 76-mbar vacuum. An amount of 21 .5 gram of distillate was recovered, with a composition of around 70 wt% being acetic acid and around 10 wt% acetic anhydride. The mixture was then cooled to 20°C and the formed solid was isolated by filtration.

[0069] The mass of solid was 63.7 gram (3-methylphthalic acid crude % is 76.2 corresponding to 48.5 gram), whilst 5.6 gram remained in the reaction mixture (4.5%). The overall chemical yield was similar to the previous experiment (NMR titration 80%). An amount of 30.0 gram of isolated product was then washed with acetic acid (47 gram). After drying, the yielded 3-methylphthalic acid was a yellowish solid (18 gram, boosting overall yield to 56% considering reaction AND washing) with a measured purity of 97.2%.

[0070] This experiment improved purity and reduced the losses in the filtrate before the washing and doubled the washing recovery respect to experiment 2. Distillation during reaction has a positive impact.

[0071] Example 4: applying distillation (stripping) during the reaction at 50°C (according to the invention)

[0072] In a 250 ml reactor, a mixture of acetic anhydride (118.6 ml) and sulfuric acid (11.5 ml) was cooled to 0°C. The Diels Alder adduct formed between 2 methylfuran and maleic anhydride (75.1 gram) was added over a period of 30 minutes, maintaining an internal temperature of less than 10°C. The mixture was heated to 50°C and held for 4 hours. Immediately after the beginning of the reaction, distillation (stripping) was triggered by applying a 38-mbar vacuum. An amount of 20.5 gram of distillate was recovered, with a composition of around 70 wt% being acetic acid and around 10 wt% acetic anhydride. We observed that 3- methylphthalic acid crystals were already formed before the beginning of the cooling procedure during continuous distillation. The mixture was then cooled to 20°C and the solid was isolated by filtration.

[0073] The mass of solid was 51.3 gram (3-methylphthalic acid crude % is 86.1 corresponding to 44.2 gram), whilst 5.6 gram remained in the reaction mixture (4.0%). The overall chemical yield was slightly less than to the previous experiment (NMR titration 74%), most likely due to a lower reaction kinetics at the lower temperature. An amount of 30.0 gram of isolated product was then washed with acetic acid (47 gram). After drying, the yielded 3-methylphthalic acid was an off-white solid (20.8 gram, with an overall yield similar to experiment 3 including reaction and washing) with a measured purity of 99.5%.

[0074] This experiment improved purity and reduced the losses in the filtrate before the washing step and doubled the washing recovery with respect to experiment 2. Distillation during reaction at lower temperature might have a less positive impact than 65°C (considering same reaction time) but it improves significantly the 3-methylphthalic acid purity to 99.5%.

[0075] In the below tables the experiments and results are summarized.

[0076] Table 1 : Summary of the experimental conditions Table 2: 3-MPA analysis after washing with acetic acid

[0077] Table 3: Impact of acetic acid distillation during reaction

[0078] Furthermore, the impact of the purity of the 3-MPA on the appearance of the solid material was studied. An important difference on coloration of 3-MPA was observed as effect of the reaction conditions. The solid 3-MPA of trial 1 was a brownish sticky solid, and the solid 3-MPA of trials 2 and 3 was less brownish. The resulting solid 3-MPA of trial 4 was even light brown and the material itself was more crystalline than the other 3 trials. In conclusion from the above presented results one can say that distillation of acetic acid during the reaction has a positive effect on the quality of the 3-MPA produced. The effect is even higher when the temperature of the aromatization reaction is lowered to 50°C. Further research might be required to further optimize the process condition to optimize the yield of 3-MPA, although the yield was already good, and the quality was much higher with a putity of 99.5% and a slightly colored crystalline product.

Claims

CLAIMS1. Process for the preparation of purified (D)(M)PA, the process comprising first reacting a cycloadduct according to structure Iwith Ri = H or CH3; R2 = H or CH3; R3 = COOH; R4 = COOH; or R3 and R4 are an anhydride bridge COOOC; with an acidic mixture comprising a first acid and an activating agent to obtain the aromatic product according to formula II,with Ri = H or CH3; R2 = H or CH3; R3 = COOH; R4 = COOH; or R3 and R4 are an anhydride bridge COOOC; while removing during the reaction at least a by-product and / or a product formed due to the reaction between structure I and the activating agent.

2. Process according to claim 1 , wherein the activating agent is acetic anhydride and the by-product formed of the activating agent is acetic acid.

3. Process according to claim 1 or 2, wherein the by-product is removed using distillation, preferably evaporative distillation, more preferably evaporative distillation at a reduced pressure, even more preferably evaporative distillation at a pressure below 100 mbar.

4. Process according to any of the previous claims, wherein the reaction temperature is in the range of from 40°C up to 70°C, more preferably in the range of from 45°C up to 55°C.

5. Process according to claim 4, wherein the evaporative distillation temperature is in the range of from 40°C up to 70°C, more preferably in the range of from 45°C up to 55°C.

6. Process according to any of the previous claims, wherein the obtained aromatic product according to formula II is removed from the reactor during the reaction.

7. Process according to any of the previous claims, wherein the obtained aromatic product according to formula II is isolated via filtration and washed with (fresh) water or with a solvent, comprising a weak acid.

8. Process according to claims 2 to 7, wherein acetic acid is recovered and at least partly used to wash the obtained aromatic product according to formula II.

9. Process according to claims 7 or 8, wherein after washing the obtained aromatic product according to formula II is subjected to re-crystallization by cooling or evaporative crystallization in a solvent, comprising one or more of water, ethyl acetate, t-butyl acetate, butyl acetate, n-propyl acetate, isopropyl acetate, ethylene glycol, dimethyl propylene urea, diethylene glycol, butyl ether, propionic acid, methyl isobutyl ketone, isoamyl alcohol, 2-ethylhexanol, butanol, preferably water, ethyl acetate, t-butyl acetate, butyl acetate, n-propyl acetate, isopropyl acetate, more preferably water and / or ethyl acetate.

10. Process according to claims 7 or 8, wherein washing is performed at a temperature below 30°C, preferably below 20°C, more preferably below 10°C.

11. Process according to claims 7 to 10, wherein the solvent comprises a weak acid, preferably acetic acid, more preferably the solvent is a pure technical gradeacetic acid (97%), even more preferably the solvent is the obtained by-product formed due to the reaction between structure I and the activating agent.

12. Process according to claim 9, wherein the solvent has a temperature above 50°C, preferably above 60°C, more preferably above 80°C.

13. Process according to any of the previous claims, wherein the first acid is sulfuric acid, preferably sulfuric acid with a concentration of at least 80%, more preferably technical grade sulfuric acid with a concentration of 97%.

14. Process according to any of the previous claims, wherein the amount of the first acid is in the range of from 0.1 up to 2 equivalent by weight to the molecule I, preferably in the range of from 0.5 up to 1 equivalent by weight to the molecule I.

15. Process according to any of the previous claims, wherein the amount of activating agent is in the range of from 0.5 up to 4 equivalent by weight to the molecule I, preferably in the range of from 1 up to 3 equivalent by weight to the molecule I, more preferably in the range of from 1 up to 2 equivalent by weight to the molecule I.

16. A product comprising (D)(M)PA, being bio-based 3-methylphthalic anhydride (3-MPA) or acid (3-MPAc) and / or 3,6-dimethylphthalic anhydride (DMPA) or acid (DMPAc) and / or biobased phthalic anhydride (PA) or acid (PAc), with a purity of at least 97.0%.

17. Product according to claim 16, wherein the purity of (D)(M)PA is at least 98%, preferably at least 99%, more preferably at least 99.5%.

18. Product according to claims 16 and 17, wherein the product comprises less than 1500 ppm sulphur, preferably less than 700 ppm sulphur, more preferably less than 500 ppm sulphur, even more preferably less than 150 ppm sulphur.

19. Product according to claims 16 to 18, wherein the product comprises 3- methylphthalic anhydride and / or 3-methylphthalic acid.

20. Product according to claims 16 to 19, wherein the product comprises up to 1 wt% acetic acid and / or acetyl acetate and / or water.

21. Use of the product according to claims 16 to 20, as one of the ingredients in a resin, and / or a polyol and / or a pigment and / or an ester product.

22. Use according to claim 21 , wherein the resin is an alkyd resin, a polyester resin and / or an epoxy resin.

23. Use according to claim 21 , wherein the polyol is part of a polyurethane or a polyisocyanurate formulation.

24. Use according to claim 21 , wherein the pigment is part of colourant and / or of ink formulations.

25. Use according to claim 21 , wherein the ester product is part of a plasticizer formulation and / or part of a lubricant and / or a grease formulation.

26. Use according to claim 21 to 25 in coatings, paints, insulating foams, adhesives, composites and powder coatings.

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