NL2009377C2

NL2009377C2 - Ester formation.

Info

Publication number: NL2009377C2
Application number: NL2009377A
Authority: NL
Inventors: Pez Garz N Camilo Sixto L; Adrianus Johannes Jozef Straathof
Original assignee: Univ Delft Tech
Priority date: 2012-08-28
Filing date: 2012-08-28
Publication date: 2014-03-03
Also published as: WO2014035240A1; WO2014035240A4

Abstract

The present invention is in the field of a process for producing an ester, such as a biobased ester, from an aqueous biomass comprising solution, batch wise or continuously, wherein use of raw material is limited and if possible re-used. The present invention is in the field of green technology.

Description

Ester Formation

DESCRIPTION

FIELD OF THE INVENTION

The present invention is in the field of a process 5 for producing an ester, such as a sustainable ester, from an aqueous solution comprising a carbohydrate, batch wise or continuously, wherein use of raw material is limited and if possible re-used. The present invention is in the field of green technology.

10 BACKGROUND OF THE INVENTION

Dimethyl carbonate (DMC) is a liquid organic compound with the formula OC(OCH3)2. As it is colourless and flammable it has to be handled with care. It can be used as a methylating agent, but many of these reactions require a high 15 pressure, such as higher than about 1000 kPa. Further, despite its much lower toxicity and its biodegradability it is not used very much as it is a relatively weak methylating agent compared to e.g. typically used reagents. It is noted that as a consequence production and application of dimethyl carbonate 20 is limited in volume. Use is considered to be limited to gas-liquid interaction.

Many compounds, such as those originating from natural sources such as sugar and cellulose, may be used as a starting point for forming further molecules. These compounds 25 may be considered as chemical building blocks. Such compounds are a potential "carbon-neutral" feedstock for fuels and chemicals. An example is hydroxymethylfurfural (HMF), or 5-(Hydroxymethyl)furfural. Recently, an enzyme from Cupriavidus basilensis (HMF14) was used to convert HMF to FDCA using 30 molecular oxygen. Also Pseudomonas putida can convert HMF to FDCA. Such bioconversion is typically effected in water, at ambient temperature and pressure.

HMF is typically produced from sugars, such as through dehydration of fructose. HMF is also naturally 35 generated in sugar-containing food during heat-treatments and it is formed in the Maillard reaction. HMF can be converted to 2,5-dimethylfuran (DMF), which is a liquid biofuel. HMF can be converted into 2,5-furandicarboxylic acid (FDCA) by oxidation. It is noted that dehydration processes using 2 hydroxymethylfurfural (HMF) as intermediate are generally non-selective, not cost effective and there is no industrially viable oxidation technology that can operate in concert with the necessary dehydration processes.1 5 Several dicarboxylic acids are of industrial relevance, and so are their esters. FDCA and its esters are valuable sources in production of polyesters. FDCA can be used as an important renewable resource e.g. to substitute terephthalic acid (PTA) and to form polymers. There are 10 various further derivatives of FDCA. FDCA undergoes reactions typical for carboxylic acids. FDCA has also been applied in pharmacology.

Other dicarboxylic acids are considered important platform chemicals such as fumaric, malic, itaconic and succinic acid. 15 Due to their chemical functionality, succinic acid can be further transformed into different chemical derivatives and into polymers. Succinic acid undergoes reactions typical for carboxylic acids. The uses of succinic acid are broad in the chemical industry. Many microorganisms are able to convert 20 carbohydrates to succinic acid. Recently, engineered

Corynebacterium glutamicum strains, for example, have been used to produce succinic acid in high yields and concentrations .

Succinic acid and its esters, e.g. dimethyl 25 succinate, can be used in the production of valuable polyesters such as poly(butylene succinate) (PBS). PBS is a fully biodegradable polymer with good thermal stability and processing ability. Other poly(homo- and copolyesters) can be produced by condensation of succinic acid diesters with diols. 30 Applications and market, for those polymers have been increasing in the latest years.

The market size for sustainable esters is still relatively small (about 0.1 million tonnes) at a selling price range of a few dollar per kilogram. Higher production cost of these 35 esters compared with e.g. petrochemical-based esters has hampered the commercialization, therefore there is a need to reduce production cost of esters, to increase ester biosynthesis capability, to broaden a utilizable substrate range, and to produce novel polymers.

3

The production of several carboxylates has been hampered by its recovery and purification. Conventional methods, e.g. precipitation, consume substantial amounts of chemicals and produce stoichiometric waste, therefore are 5 considered polluting processes. Alternatives have been described elsewhere. Various patents recite a process in which a carboxylic acid (namely lactic and succinic acid) or a carboxylate is extracted by an amine-based extractant, or adsorbed by a basic sorbent. Regeneration of the auxiliary 10 phase is performed using ammonia or a low molecular weight amine (trimethylamine) which forms an ammonium carboxylate salt that can be decomposed thermally if required, yielding a desired carboxylic acid. The extraction/sorption stage is greatly hindered by the solution pH and the basicity of the 15 ion exchanger. In the case of succinic acid, at neutral pH a mixture of carboxylic acid and its monovalent salt is obtained, which is unwanted. The process needs improvement in order to enhance e.g. stability of the ammonium carboxylate salt and to reduce the amount of sorbed salt by e.g. carbon 20 dioxide acidification. So e.g. succinic acid recovery at neutral pH is not provided and further at the best a mixture of salts is produced.

Some other (succinic acid) purification processes are energy demanding, can create corrosion problems, and have mass 25 and heat transfer problems.

Production of esters from carboxylates will require its purification and acidification preceding ester formation by conventional esterification reaction.

In some publications concepts of acidification and salt-to-30 acid conversion are misconceived, such as that ion-exchange based process does not require acidification and effectively acidification takes place by exchanged hydrogen ions from the resin.

Further a process for production of especially 35 diethyl succinate from succinate salts and ethanol using sulphuric acid for acidification is recited. The process intends to avoid acid purification prior to an esterification step. The advantages are limited to that aspect and to the purity of the obtained ester. On the down side mineral acid is 4 consumed and waste salts are produced. The process can not be integrated further.

Also production of alkyl esters from several solid metal carboxylates e.g. via conventional esterification using 5 carbonic acid is recited. Reaction conditions however are harsh (P = 20-60 bar and T = 175 °C). Disadvantages are a relative low yield, consumption of methanol, formation of byproducts and low selectivity, amongst others.

Some organic processes relate to phase transfer 10 catalysis (PTC). In a regular application, catalytic amounts of phase transfer agents are used which in principle facilitate interphase transfer of species, making reactions between reagents in two immiscible phases possible. PTC can be used in both liquid-liquid and solid-liquid systems. PTC 15 typically involves a series of equilibrium and mass-transfer steps, beside main reactions. Conversion efficiencies are typically limited, e.g. due to low activity of catalysts. In general, the recovery of chemicals (catalysts) is at least difficult. Typically PTC is combined with other enhancement 20 techniques to overcome disadvantages, albeit these are not explored in detail yet, despite promising chances (see e.g.

S.D. Nalk and L.K. Doraiswamy, AIChE Journal, March 1998, Vol. 44, No. 3 pp.612-646).

Some further articles describe the application of PTC 25 to the production of esters. Moreover a process for production of methyl esters from carboxylic acids or salts using dimethyl carbonate in the presence of a strong base homogeneous catalyst (1,8-Diazabicycloundec-7-ene known as DBU, 1,4-diazabicyclo[2.2.2]octane known as DABCO, 1,5,7-30 Triazabicyclo[4.4.0]dec-5-ene knows as TBD or 4-

Dimethylaminopyridine known as DMAP) under microwave irradiation is described. Despite a focus on fine chemicals, it covers a wide range of carboxylates. Furthermore, it shows feasibility of using a base as a catalyst for the alkylation 35 reaction. However chemicals are not recovered, nor can biobased processes be integrated.

In a similar context, it is recited the use of anion exchange resins for O-alkylation of carboxylate ions. Anions (substrates) tested were alkyl and aryl mono carboxylates. As 5 alkylating agents, strong alkyl- and aryl- halides (mostly bromides) were used. It recites a purely synthetic strategy, without much further details. As a disadvantage the process is not cost effective and not green.

5 The present invention therefore relates to a process for obtaining a reaction product, suitable for use as a biobased chemical building block, which overcomes one or more of the above disadvantages, such as minimizing chemical consumption, using renewable material, providing a highly pure 10 compound, being non-toxic, at low (energy) costs, without jeopardizing functionality and advantages.

SUMMARY OF THE INVENTION

The present invention relates in a first aspect to a green process minimizing use of chemicals and energy for 15 producing a carboxylate ester, such as a biobased ester, from a renewable resource according to claim 1. Therein the dialkyl carbonate and specifically DMC is considered as a green methylating agent.

Therein consumption of chemicals such as inorganic 20 acids and bases, and associated production of inorganic waste salt are prevented, contrary to conventional methods that produce up to 1 kg salt per kg ester.

The present process can start with a bio-based production (fermentative or enzymatic) of a carboxylate. Such 25 is carried out while controlling the pH at neutral values (4-10) using e.g. an inorganic base. Thereafter the carboxylate may be captured using an anion exchange sorption step which may liberate the inorganic base above.

In an example a bicarbonate or carbonate base is also 30 an inorganic carbon source for a microorganism. As a key step thereinvthe (sorbed) carboxylate is transformed in an ester derivative with a dialkyl carbonate, such as DMC, and preferably with simultaneous regeneration of an anion exchanger, for example into the (bi)carbonate form. Optionally 35 an ester produced can be purified with ease and refined by e.g. conventional means.

It is noted that use of DMC in synthesis of fine chemicals is known to some extent. Therein it is purely used as a reagent and no integration with (product) recovery 6 occurs. In addition, when DMC is used as methylating agent in organic chemistry applications carbon dioxide and methanol are released and are not used in the (subsequent) process. In the present process, on the contrary, such inorganic carbon will 5 remain attached to a support such as a resin and is (re-)used in e.g. the fermentation as inorganic carbon source. Even further, a support such as an anion exchange resin has not been used previously as a catalyst. Most often strong organic bases are used (DBU, TBD) which are expensive and difficult to 10 recover after reaction.

Ester derivatives of target carboxylates have not been previously synthetized by alkylation using dialkyl carbonate; especially esters of succinate and FDCA have not been synthesized before using DMC. Mild conditions, such as 15 neutral pH, relatively low temperature and low pressure would be beneficial and are provided by the present process. In addition, the present integrated process and regeneration of e.g. a (strong) anion exchange resin is not known. The present level of integration comprising e.g. an anion exchanger as a 20 core of a downstream process is novel. In the present direct downstream catalysis chemicals and auxiliary phases are seized to a maximum, e.g. an ion exchanger is used as a sorbent and catalyst and the alkylating agent as reagent and regenerant. Furthermore, the way of supplying (re-using) required 25 inorganic carbon in bio-based production, e.g. fermentation, by integrating both bio-based production and sorption processes is also novel.

It is noted that to obtain methyl esters, methanol is obviously cheaper than dimethyl carbonate. However, when using 30 methanol, water needs to be evaporated from the carboxylate salt, and the carboxylate needs to be acidified with an inorganic acid, producing stoichiometric amounts of waste salts. This is not the case for e.g. dimethyl carbonate.

The present process is more efficient and largely 35 integrated. It uses less materials, energy and equipment and it produces less or no waste (salts).

After thorough scientific research, in particular relating to recovery of carboxylates, such as succinate and 2,5-furandicarboxylate, and synthesis of diesters thereof, 7 inventors have arrived at the present process. Equilibrium studies (e.g. Ion exchange isotherms) and column dynamics (sorption breakthrough profiles) have been carried out for the above mentioned carboxylates using several ion exchange 5 resins. As a result, static and dynamic sorption capacities as well as selectivities and affinities have been determined.

With respect to the synthesis of diesters by alkylation, experiments were carried out to establish a basic understanding about the reaction stoichiometry since the 10 present reaction has not been reported before to the knowledge of inventors. Also influence of water and temperature on reaction kinetics was quantified. In addition, resin stability was tested after several sorption-reaction cycles. Also an impact of e.g. resin functional group (basicity) on the 15 present integrated process was studied.

Thereby the present invention provides a solution to one or more of the above mentioned problems.

Advantages of the present description are detailed throughout the description.

20 DETAILED DESCRIPTION OF THE INVENTION

The present invention relates in a first aspect to a green process minimizing use of chemicals and energy for producing a carboxylate ester, such as a biobased ester, from a renewable resource comprising the steps: 25 providing a water soluble carboxylate, providing a transfer agent, removing water, and providing a di-alkyl carbonate, reacting the carboxylate, transfer agent and di-alkyl 30 carbonate thereby forming a di-alkyl ester of the carboxylate, and a carbonate, substantially in absence of water.

In the present process the carboxylate is water soluble, as e.g. it is produced in an aqueous solution, such as a broth, it is e.g. transferred in an aqueous solution, and 35 typically an acidic form of the carboxylate can only be obtained at relative low pH, such as pH = 2, which is cumbersome. In an aspect the water soluble carboxylate allows for a high degree of integration of process steps.

8

The present transfer agent performs a catalytic action, and may perform further actions, such as sorption, as in e.g. an anion exchanger. Therewith the transfer agent supports an envisaged reaction.

5 Preferably the present process relates to liquid- liquid and solid-liquid phase transfer catalysis, such as with an alkyl carbonate organic phase aqueous solution and a carboxylate-laden solid support, such as an anion exchanger.

The present di-alkyl carbonate may have two alkyls 10 being the same or being different.

The present reaction provides optimal results in absence of water. Thereto water is removed to a large extent, such as 95% or more, preferably 99% or more, even more preferably 99.5% or more, such as 99.9% or more. Thereto a 15 solid support, such as an exchanger, is dried, such as with an alcohol, such as with methanol produced in the present process .

The present process provides e.g. high yields, minimised waste production, advanced integration, at low 20 (energy) costs.

In an example of the present process the transfer agent is a positively charged transfer agent, preferably comprising a nitrogen atom, such as a quaternary nitrogen atom, a guanidine, a quaternary onium, N,-N-dimethylformamide, 25 N-methyl-2-pyrrolidone, tetra methyl urea, an anion exchange resin, such as Dowex MSA, wherein the transfer agent preferably is supported on a solid or diluted in a suited liquid phase, such as on a porous material, a polymer structure, silica, functionalized material, and combinations 30 thereof. It has been found that these transfer agents perform best e.g. in terms of yields, waste, etc.

In an example of the present process the carboxylate is produced by biotransformation, such as microbial or enzymatic transformation, or a combination thereof, such as by 35 conversion by a microorganism from a broth, such as with C.

glutamicum or P. putida, preferably conversion in an aqueous medium, wherein a pH of the medium is from 4-10, preferably from 5-9, more preferably from 6-8. Therewith high yields are 9 obtained. Further a high degree of integration with such transformation may be obtained.

In an example of the present process the carboxylate is a mono-, di- or tri- carboxylate, preferably selected from 5 acetate, acrylate, adipate, benzoate, butyrate, FDCA, fumarate, 3-hydroxybutyrate, 3-hydroxypropionate, itaconate, lactate, malate, pimelate, propionate, succinate, and combinations thereof.

In an example, using DMC, methyl acetate, methyl 10 acrylate, dimethyl adipate, dimethyl benzoate, methyl butyrate, dimethyl FDCA, dimethyl fumarate, methyl 3-hydroxybutyrate, methyl 3-hydroxypropionate, dimethyl itaconate, D- or L-methyl lactate, dimethyl malate, dimethyl pimelate, methyl propionate, dimethyl succinate, and 15 combinations thereof are formed. Also using diethyl carbonate, ethyl acetate, ethyl acrylate, diethyl adipate, diethyl benzoate, ethyl butyrate, diethyl FDCA, diethyl fumarate, ethyl 3-hydroxybutyrate, ethyl 3-hydroxypropionate, diethyl itaconate, D- or L-ethyl lactate, diethyl malate, diethyl 20 pimelate, ethyl propionate, diethyl succinate, and combinations thereof are formed. The above esters relate to readily available carboxylates, which can be formed relatively easy with the carbonates, providing the advantages of the invention.

25 In an example of the present process the ester is a mono-, di- or tri ester, preferably a diester in its final form.

In an example of the present process the di-alkyl carbonate comprises an alkyl selected from the group of C1-C12, 30 preferably Ci-Cé, such as methyl, ethyl, propyl, butyl, isopropyl, pentyl and hexyl, C1-C12 cyclic carbonates, preferably ethylene, propylene and butylene, and combinations thereof.

The di-alkyl carbonate may comprise cyclic compounds with linked alkyl chains such as ethylene carbonate (the carbonate 35 of ethylene glycol). Especially the smaller alkyls perform well, such as methyl and ethyl.

In an example of the present process the water soluble carboxylate comprises one or more of Na+, NH4+, K+,

Mg2+, Ca2+, and combinations thereof.

10

In an example of the present process the carboxylate is sorbed by an anion exchanger from an aqueous solution, i.e. fermentation broth with or without previous purification. In a general example, the carboxylate is sorbed in a fixed bed 5 operation after protein and cell removal performed by conventional means such as filtration operations. In a particular example, the carboxylate is sorbed in expanded bed mode without the need of protein or cell removal. In a particular instance of such example, both processes, i.e.

10 biotransformation and sorption, are integrated and occur simultaneously.

In an example of the present process the water soluble carboxylate is sorbed by an anion exchanger, wherein the anion exchanger comprises the transfer agent, wherein the 15 transfer agent comprises a (bi)carbonate species, thereby forming an aqueous (bi) carbonate salt, and a complex of the carboxylate and transfer agent, wherein the (bi)carbonate salt solution is preferably recovered to be used in the production of the carboxylate. An 20 advantage thereof is reduction of waste.

In an example of the present process the resin is dried, such as by desiccation, by heating, or by washing using a suitable drying solvent, preferably an alcohol, such as ethanol or methanol, and thereafter the di-alkyl carbonate is 25 provided to the resin in order to form the ester, preferably provided as a liquid, wherein the carbonate is preferably provided to the transfer agent.

In an example of the present process the ester is 30 formed at a temperature of 20-140 °C, preferably 25-120 °C, at a pressure of 80-900 kPa, such as at 90-500 kPa, preferably at or near ambient conditions. Such will e.g. depend on whether the reaction is carried out in a Liquid-Solid or Gas-Solid mode. L-S modes typically require pressures above 101 kPa to 35 keep e.g. DMC in a liquid state. Such temperatures and pressures are relatively mild.

In an example of the present process the ester is purified without much trouble, such as by distillation, crystallisation, or combination thereof.

11

In an example of the present process the carboxylate is purified.

In an example of the present process the reacting is carried out as a solid-liquid, gas-solid or liquid-liquid 5 reaction, preferably as a solid-liquid reaction.

The one or more of the above examples and embodiments may be combined, falling within the scope of the invention.

EXAMPLES

The invention is further detailed by the 10 accompanying figures, which are exemplary and explanatory of nature and are not limiting the scope of the invention. To the person skilled in the art it may be clear that many variants, being obvious or not, may be conceivable falling within the scope of protection, defined by the present 15 claims.

Example 1: Conversion of aqueous carboxylate, such as succinate- or FDCA- dianion into its respective dimethyl esters without isolating succinate or FDCA.

It is observed that microbial or enzymatic 20 production of carboxylic acids is usually more efficient at neutral pH than at low pH, as uncharged carboxylic acids may be toxic or inhibiting.

FDCA is so acidic that its production from HMF will yield its corresponding anion unless the pH is 2 or 25 lower. That pH is not feasible with typical microorganisms. Succinic acid has been produced from glucose at pH down to 3, but this is at the expense of the performance of the microorganisms used. In order to control the pH close to neutral values in state of the art processes, a 30 neutralizing base is added during fermentation/enzymatic conversion, and carboxylate anions are obtained. Further, during downstream processing, an inorganic acid is added to recover the carboxylic acid. This leads to stoichiometric inorganic salt production, usually gypsum. In some cases 35 such salt can be used, for example as fertilizer, and in some other cases bipolar electro-dialysis is used to split the salt into acids and bases that can be reused. However, these methods have limitations and drawbacks. Consequently, recovery of succinate or FDCA requires acidification and 12 crystallization, and yields stoichiometric amounts of waste inorganic salt. This hampers the economic and ecologie sustainability of a such processes.

For the above mentioned dicarboxylic acids, the 5 present process can be combined with fermentation and/or biotransformation at neutral pH (5-9) and it avoids acidification and crystallization. As an advantage it generates an inorganic base to be used in controlling e.g. fermentation pH.

10 The present process provides an advantageous bio based ester production process from succinate or FDCA produced from renewable resources. Such sequence of operations is schematically presented as a flow diagram in Fig. 1.

15 Referring to Fig. 1, renewable resources, such as glucose or HMF, are converted by a specific biological agent to for example succinate or FDCA disodium salts (Na2A) in a bioreactor 101, cells can be removed in 102 and recycled back to 101. In certain embodiments cell removal 20 operation 102 can be avoided, such scenario is included into the proposed invention. The disodium salt is sent to a column operation 103 packed with a suitable anion exchanger in a (bi) carbonate form, thus releasing (bi) carbonate base as the carboxylate sorption takes place. Succinate or FDCA 25 anions remain bound to the anion exchanger. The generated base is recycled to the bioreactor 101 for pH control. In the case of succinate production, certain bacteria may also consume part of the carbonate since inorganic carbon is required, therefore minimizing chemical consumption.

30 Previous to the ester production, water is removed from the carboxylate-laden anion exchanger (Q2A ) in 104. Ester production is carried out in 105 by O-alkylation using dimethyl carbonate (DMC), a cheap green solvent and reagent, in liquid or gas state. The reaction directly 35 yields the diester of the respective carboxylate (DMA), i.e. dimethyl succinate or dimethyl 2,5-furandicarboxylate, without any monomethyl ester. As ester formation takes place, regeneration of the anion exchanger to a (bi) carbonate form is achieved. In certain reaction 13 conditions, methanol can be produced as a reaction byproduct .

DMC may need to be removed in 106 from the regenerated anion exchanger if reaction is carried out in 5 liquid-solid conditions. The regenerated anion exchanger (Q2C03 , QHC03 ) can be reused in 103 in a subsequent sorption cycle. Operations 103, 104, 105 and 106 can be performed in the same process unit and therefore such operation mode is within the scope of this invention. The raw DMA stream, 10 composed mainly of diester, methanol and DMC, from unit 105 is purified easily by conventional means, e.g. distillation, in 106 and pure diester is obtained. For the case of FDCA, dimethyl 2,5-furandicarboxylate is a preferred monomer for esterification with ethylene glycol 15 towards PET-compatible polymers.

In a broader process embodiment, DMA can be polymerized in 108. Methanol produced as by-product can be recovered from the purification unit 107 and the polymerization process 108 and recycled to dimethyl 20 carbonate synthesis 109.

Example 2: Conversion of succinic acid.

Succinic acid sorption from aqueous solutions.

In the described process scheme, sorption is carried out using carbonate or bicarbonate counter-ions.

25 The anion exchange reactions are: Q2C03 + Na2Succ<—±Q2Succ + Na2C03 2QHC03 + Na2Succ < Q2Succ + 2NaHC03

Therein Q is a transfer agent and Q species are supported in the resin. The equilibrium characteristics of these reactions are not known and they have not been 30 described in literature. Thus, succinate sorption isotherms were determined for both possible counter-ions.

It is noted that reaction characteristics of alkylation of e.g. sorbed carboxylates using dialkyl carbonates in general and DMC in particular have been topic 35 of present studies.

14

Experimental

In a column operation, 80 mL of Dowex MSA resin (Dow chemical, strong anion exchange resin, macroporous structure, type I, Cl" form) was transformed to the required 5 forms (OH", HC03~ and C032") . The resin bed was washed with deionized water (10 bed volumes), then converted to the hydroxide form by eluting chloride ion with 10 bed volumes of 1M NaOH solution. Superficial velocities were maintained close to 1 m/h according to supplier specifications. Given 10 the column geometry, a flow rate of 8 mL/min was required.

After conversion to OH- form, the column was washed until a pH close to neutrality (7-7.5). The column suffered a volume expansion of approximately 18%.

The resin in the OH- form was further converted to 15 bicarbonate and carbonate forms. Elution using 1 M

solutions of sodium bicarbonate and sodium carbonate were used. Bed expansions for these forms were 4.6 and 11.2%, respectively. The column was subsequently washed with deionized water until pH near to neutral.

20 Batch sorption experiments were performed in scintillation vials using a 1:10 (w:v) phase ratio for four hours. Neutral succinate solutions were used. Agitation and temperature were controlled to 120 rpm and 25°C. Succinate concentrations were determined by HPLC using a Waters HPLC 25 system comprising a Bio-Rad Aminex HPX-87H column (7.8 x 300 mm). Phosphoric acid was used as an eluent. Quantification was done by UV detection at 210 nm using an external standard.

Results 30 The succinate sorption equilibrium distribution dependence for the tested counter-ions is shown in Fig. 2 (Succinate loading (g/g dry resin) versus total succinate (g/1). As expected, succinate sorption equilibrium is favoured by bicarbonate and carbonate counter-ions. The 35 saturation capacities are 0.18 and 0.22 g/g dry resin, respectively. Affinities are greater as well. Thereby, a column sorption operation based on either of these exchanger counter-ions will perform better than chloride-based operations (mainly narrower mass transfer zone, 15 improving operating column capacity).

The equilibrium pH corresponding to the sorption isotherms was determined for each counter-ion (Fig. 3, equilibrium pH versus total succinate (g/1)). The observed 5 trends were expected, although the pH values for carbonate indicate some dissociation to bicarbonate species.

Study of reaction characteristics.

Succinate ester production via O-alkylation using DMC has not been described in previous literature. It is 10 known that DMC has tuneable active centres which reactivity depends on the temperature, being 120°C a regular temperature for methylation. In the presence of water, the expected stoichiometry is as follows: 2CH3OCOOCH3 + Q2Succ + 2H20 -+ 2QHC03 + H3CSuccCH3 + 2CH3OH 2CH3OCOOCH3 + Q2Succ + H20 -+ Q2C03 + H3CSuccCH3 + 2CH3OH + C02 2CH3OCOOCH3 + Q2Succ -+ Q2C03 + H3CSuccCH3 15 In all reactions, dimethyl succinate (DMS) is formed from sorbed succinate anions. In the first two reactions, methanol is produced as by-product and can be recycled for the synthesis of DMC, therefore meeting most of the green chemistry requirements. Water in excess will 20 promote DMC hydrolysis side-reaction.

Experimental

In a typical run, 1.5 g of oven-dried succinate loaded resin (0.24 g succinate/g total dry resin) was loaded on a catalyst addition device held within the 25 autoclave reactor. In the vessel, 30 g of DMC were added.

The vessel was then purged 10 times with nitrogen in order to achieve an inert atmosphere. The reactor was then heated up to 120°C and the temperature maintained constant throughout the reaction. Agitation was controlled at 750 30 rpm. Once the reactor has attained stable conditions, succinate-laden resin was released and O-alkylation reaction started. Sampling was performed regularly to establish reaction kinetics. After eight hours the reactor was cooled down to room temperature and vented, and final 35 concentrations of DMS, methanol and water were determined. DMS identity was confirmed by GC-MS. DMS and methanol were 16 quantified using a Agilent gas chromatography system comprising a HP-INNOWax PEG capillary column (60m x 0.25mm, 0.15 pm film). Detection was done using an FID detector, helium was used as a carrier gas. Identity of the compounds 5 was confirmed by gas chromatography- quadrupole mass spectrometry.

In order to discern in which form (type of counter-ion) the resin would be after reaction, the resin was eluted and the effluent pH checked. The reacted resin 10 was washed three times with methanol and water and 2 mL of resin were eluted in a column using a solution of 20 g/L of sodium nitrate at 0.5 mL/min.

Results

During the reaction, an increase in the reactor 15 pressure was noticed. This might indicate that low vapour pressure substances are generated during the reaction. It was noticed that after eight hours the reaction was reaching stable pressure.

Fig. 4 shows the DMS yield reaction (time (h)) 20 profile, defined as mole of DMC produced by mole of succinate sorbed. After 2 h, 0.87 mole DMS/mole succinate was produced. Final reaction yield achieved was 0.93 mole DMS/mole succinate. The methanol produced exceeded (1.6 times higher) the stoichiometric amount expected. DMC 25 hydrolysis might be occurring.

After reaction, the washed resin was eluted with sodium nitrate. During elution, the pH of the effluent was kept between 9.1 and 8.2. This might be a clear indication that the resin was mainly in the bicarbonate form after 30 reaction.

Conclusion

Using DMC, sodium succinate was converted into 94% dimethyl succinate without further optimization. Sodium bicarbonate or carbonate formed is a useful co-product, 35 particularly in the present process.

Example 3: FDCA case comparison.

Anion exchange resins can be used in the carbonate or bicarbonate form. If FDCA is produced as sodium dianion, the following exchange will occur.

17 —>

Na2FDCA (aq) + Q+2C032' (resin) i— Na2C03 (aq) + Q+2FDCA2' (resin)

Na2FDCA (aq) + 2Q+HC03' (resin) 2NaHC03 (aq) + Q+2FDCA2‘ (resin)

It has been found that other anions present in biotransformation broth will elute early, and may be 5 recycled to e.g. the biotransformation with the liberated

Na2C03. The carbonate is preferably the base for controlling the biotransformation pH.

Experiments with succinate have shown that succinate binding much stronger than carbonate or 10 bicarbonate binding, thus allowing efficient anion exchange in a column mode.

So far, the resin drying step has been done by simple desiccation, though other options are open, such as use of an alcohol, such as the methanol produced.

15 In an example the dried, FDCA-loaded resin is in an example heated in the presence of dimethyl carbonate to obtain dimethyl FDCA: 2CH3OCOOCH3 + QZFDCA + 2HzO -» 2QHC03 + H3CFDCACH3 + 2CH3OH 2CH3OCOOCH3 + QZFDCA + HzO -+ Q2C03 + H3CFDCACH3 + 2CH3OH + C02 2CH3OCOOCH3 + q2fdca -+ q2co3 + h3cfdcach3

It has been found that the monomethyl ester cannot 20 desorb from the resin because there are no free cations, and therefore it is not found in the dimethyl carbonate solution. Distillation of excess DMC is easy whereas distillation also allows removal of methanol (if hydrolysis occurs due to traces of water) and purification of dimethyl 25 furandicarboxylate.

Fig. 5 presents a comparison of waste production according to known reaction stoichiometries. Therein Na2C03, HMF, 02, H2SO4 and glycol are added, whereas C02, aq, Na2S04, H20 and PET are removed, in comparison to the present 30 addition of HMF, 02, CO and glycol, whereas C02, H20 and PET are removed.

In an example, per kg FDCA the proposed method does not produce any waste according to the reaction stoichiometry as currently known. In contrast, the default 35 method that we want to replace produces 0.91 kg sodium sulphate waste per kg FDCA (Fig.5). Moreover, the present 18 process saves 0.20 $ on chemicals according to the overall process stoichiometry (Fig. 6). This is considered substantial.

Fig. 6 presents a comparison of main chemicals 5 costs according to known reaction stoichiometries. Therein Na2C03, HMF, 02/ H2SO4 and glycol are added, whereas C02, aq, Na2S04, H20 and PET are removed, in comparison to the present addition of HMF, 02, CO and glycol, whereas C02, H20 and PET are removed.

10 Only for the differences between the processes, costs are indicated, in $/kg FDCA. Assuming that renewable CO can be used, it is assumed that the extra C02 produced in the proposed case does not lead to emission costs.

FIGURES

15 The invention although described in detailed explanatory context may be best understood in conjunction with the accompanying figures.

Fig. 1 shows details of a schematic sequence of operations for dimethyl succinate production.

20 Fig. 2 presents succinate sorption equilibrium distribution dependence (isotherms) for the tested counterions .

Fig 3. shows equilibrium pH corresponding to the sorption isotherms for succinate determined for each 25 counter ion.

Fig. 4 shows the DMS yield reaction profile, defined as mole of DMC produced by mole of succinate sorbed.

Fig. 5 presents a comparison of waste production 30 according to known reaction stoichiometries for FDCA.

Fig. 6 presents a comparison of main chemicals costs according to known reaction stoichiometries for FDCA.

Claims

A green process for minimizing the use of chemicals and energy to produce a carboxylate ester, such as a biobased ester, from a renewable source, comprising the steps of: providing a water-soluble carboxylate of a transfer agent, removal of water, and provision of a di-alkyl carbonate, reaction of the carboxylate, transfer agent and di-alkyl carbonate to form a di-alkyl ester of the carboxylate and a carbonate, substantially in the absence of water .

2. A method according to claim 1, wherein the transfer agent is a positively charged transfer agent, preferably comprising a nitrogen atom, such as a quaternary nitrogen atom, a guanidine, a quaternary onium, N, -N-dimethylformamide, N-methyl-2- purrolidone, tetramethylurea, an anion exchange resin, the transfer agent preferably being supported on a solid or diluted in a suitable liquid phase, such as on a porous material, a polymer structure, silica, functionalized material, and combinations thereof.

3. Method according to at least one of the preceding claims, wherein the carboxylate is produced by biotransformation, such as by conversion of a microorganism from a culture, such as with C. gultamicum or P. putida, preferably conversion in an aqueous medium wherein a pH of the medium is from 4-10, preferably 5-9, more preferably 6-8.

The method according to at least one of the preceding claims, wherein the carboxylate is a mono-, di- or tri-carboxylate, preferably selected from acetate, acrylate, adipate, benzoate, butyrate, FDCA, fumarate, 3-hydroxy-butyrate , 3-hydroxypropionate, itaconate, lactate, malate, pi-melate, propionate, succinate, and combinations thereof.

A method according to at least one of the preceding claims, wherein ester is a mono, di or tri ester, preferably an ester in its final form.

A method according to at least one of the preceding claims, wherein the di-alkyl carbonate comprises an alkyl selected from the group of C 1 -C 12, preferably C 1 -C 6, such as methyl, ethyl, propyl, butyl, iso-propyl, pentyl and hexyl, C 1 -C 12 cyclic carbonates, preferably ethylene, propylene and butylene, and combinations thereof.

The method of at least one of the preceding claims, wherein the water-soluble carboxylate comprises one or more of Na +, NH 4 +, K +, Mg 2+, Ca 2+, and combinations thereof.

8. A method according to at least one of the preceding claims, wherein the water-soluble carboxylate is sorbed by an anion exchanger, wherein the anion exchanger comprises the transfer agent wherein the transfer agent comprises a (bi) carbonate species, whereby an aqueous (bi) carbonate salt is formed, and a complex of the carboxylate and transfer agent, wherein the (bi) carbonate salt solution is preferably recovered for use in the production of the carboxylate.

9. A method according to claim 8, wherein the resin is dried, such as by drying, heating, or by washing with a suitable drying agent, preferably alcohol, such as ethanol or methanol, and after which the di-alkyl carbonate is provided to the resin to to form an ester, preferably provided as a liquid, the carbonate preferably being provided to the transfer agent 30.

The method according to claims 8 or 9, wherein the ester is formed at a temperature of 20-140 ° C, preferably 25-120 ° C, at a pressure of 80-900 kPa, preferably at or near ambient conditions.

The method of at least one of the preceding claims, wherein the ester is purified, such as by distillation, crystallization, or a combination thereof.

The method according to at least one of the preceding claims, wherein the carboxylate is purified.

A method according to at least one of the preceding claims, wherein the reaction is carried out as a solid-liquid, gas-solid or liquid-liquid reaction, preferably as a solid-liquid reaction.