Method for the recovery of carboxylic acids

Abstract

The invention relates to a method for recovering at least one carboxylic acid. A first feedstock comprising at least one salt of a carboxylic acid and a second feedstock comprising at least one ammonium salt and / or comprising at least one acid are introduced in a vessel. Droplets are formed from the first feedstock and the second feedstock or from a mixture of the first feedstock 5 and the second feedstock. The droplets are heated to form vapors comprising at least one carboxylic acid. The residence time of the first feedstock and the second feedstock or of the mixture of the first feedstock and the second feedstock is controlled to be less than (2) minutes. Subsequently, the vapors are subjected to a condensation step to obtain a fraction comprising at least one carboxylic acid and optionally an ammonia fraction or an ammonia / water fraction.

Description

Method for the recovery of carboxylic acidsField of the invention

[0001] The present invention relates to a method for the recovery of carboxylic acids, in particular for the recovery of volatile fatty acids. Furthermore, the present invention relates to a method for the simultaneous recovery of carboxylic acids and ammonia, in particular for the simultaneous recovery of volatile fatty acids and ammonia.Background art

[0002] Carboxylic acids, and in particular volatile fatty acids (VFAs), are valuable renewable resources that can be used as building block for the production of, for example, paints, rubbers, plastics, synthetic fibers, textile finishes, pesticides, polymer emulsions, flavors, solvents for coating formulation, food supplements and many more. Carboxylic acids can be produced through anaerobic fermentation of mixed organic waste. However, as purification currently accounts for 40-50 % of the production cost, the production process is not profitable. The high costs are mainly due to the low VFA concentration obtained in the fermentation broth, typically 1 to 2 wt% and due to the presence of impurities.

[0003] Current proven technology based on a combination of liquid-liquid extraction and distillation has several drawbacks. Such technology is expensive and complex, energy inefficient, requires excessive use of acids and produces undesirable waste products. Another disadvantage of the liquid-liquid extraction process is that some solvents used for in-line recovery may be toxic and inhibitory to microorganisms.

[0004] Membrane-based technologies known in the art are susceptible to fouling and suffer from the same disadvantages as those mentioned above.

[0005] Other techniques such as adsorption, ion-exchange or gas stripping are investigated but suffer from different drawbacks that limit their use on industrial scale. Such techniques can be very sensitive to contaminants in the broth and consequently lose capacity (anions). In addition, such techniques are energy inefficient, have low recovery rates and produce significant waste streams.

[0006] Therefore, there is a need to provide an improved method to recover carboxylic acids.Summary of the invention

[0007] It is an object of the present invention to provide a method for the recovery of one or more carboxylic acids, in particularto provide a method forthe recovery of one or more volatile fatty acids, from a first feedstock comprising at least one salt of a carboxylic acid and a second feedstock comprising an ammonium salt and / or an inorganic acid.

[0008] It is another object of the present invention to provide a method for the recovery of one or more carboxylic acids, for example one or more VFA from complex mixtures such as fermentation broths.

[0009] It is a further object of the present invention to provide a method for the recovery of one or more carboxylic acids and more particularly for the recovery of one or more VFAs without the formation of unwanted or toxic by-products such as amides (which may be converted to toxic nitriles).

[0010] It is a further object of the present invention to provide a method for the simultaneous recovery of more carboxylic acids and ammonia, for example one or more VFAs and ammonia, for example from complex mixtures such as fermentation broths.

[0011] It is still a further object of the present invention to provide a method requiring lower energy consumption than methods known in the art.

[0012] According to a first aspect of the present invention a method for the recovery of at least one carboxylic acid is provided. The method comprises the steps ofproviding a first feedstock comprising at least one salt of a carboxylic acid having a pKa ranging between 3 and 6,providing a second feedstock comprising at least one ammonium salt and / or comprising at least one acid, preferably at least one inorganic acid,introducing the first feedstock and the second feedstock or a mixture of the first feedstock and the second feedstock into a vessel, forming droplets, for example droplets having a size ranging between 10 and 500 micrometer, from the first feedstock and the second feedstock or from the mixture of the first and the second feedstock and heating the droplets to a temperature higher than 80°C thereby allowing the first feedstock and the second feedstock to react thereby forming vapors comprising at least one carboxylic acid and water (and optionally ammonia) and a solid residue, whereby the residence time of the first feedstock and the second feedstock or the residence time of the mixture of the first and the second feedstock in the vessel is controlled to be less than 2 minutes;subjecting the vapors to a condensation step thereby obtaining a fraction comprising the at least one carboxylic acid.

[0013] The method according to the present inventions allows to recover one carboxylic acid or to recover a number of carboxylic acids, starting from a first feedstock comprising one or more salts of a carboxylic acid.

[0014] In preferred embodiments, the method according to the present invention allows to recover one VFA or to recover a number of VFAs, starting from a first feedstock comprising one or more salts of a VFA.

[0015] The droplets formed from the first feedstock and the second feedstock or from the mixture of the first feedstock and the second feedstock preferably have a size ranging between 10 and 500 micrometer.

[0016] In preferred embodiments, the first feedstock and the second feedstock or the mixture of the first feedstock and the second feedstock are atomized to form droplets. Such droplets typically have a size ranging between 10 and 150 micrometer, for example between 10 and 100 micrometer, such as 20 micrometer, 50 micrometer or 75 micrometer.In alternative embodiments, the first feedstock and the second feedstock or the mixture of the first feedstock and the second feedstock form droplets having a size ranging between 150 and 500 micrometer, for example droplets having a size of 200 micrometer, 250 micrometer, 300 micrometer or 400 micrometer

[0017] In a preferred method a gas is introduced in the vessel during the reaction of the first feedstock and the second feedstock. The gas can be introduced either continuously or periodically in the vessel during the reaction of the first feedstock and the second feedstock or can be introduced with a constant flow rate or a variable flow rate. Typical flow rates range between 500 and 100000 m3 / s or between 1000 and 50000 m3 / s, for example 5000 m3 / s, 10000 m3 / s or 20000 m3 / s. For medium size spray drying installations, the flow rate typically used for treating industrial chemicals ranges between 1000 and 10000 m3 / s. By introducing a gas in the vessel during the reaction of the first feedstock and the second feedstock, the heat transfer to and between the droplets is improved. This can significantly improve the reaction efficiency. The gas can also be referred to as a drying gas.

[0018] The gas comprises preferably a non-condensable gas. For the purpose of the present invention, a non-condensable gas is defined as a gas that is not condensing during the condensation step of the vapors generated during the reaction of the first feedstock and the second feedstock, i.e. under the conditions such as temperature and pressure of the condensation step of the vapors. Preferably, the non-condensable gas is an inert gas. Preferred non-condensable gases comprise nitrogen, helium, neon, argon or combinations thereof.

[0019] The first feedstock comprises at least one salt of a carboxylic acid. In particular embodiments the first feedstock comprises one salt of a carboxylic acid. In other embodiments the first feedstock comprises a number of salts of a carboxylic acid, for example 2, 3, 4, 5 or 6 salts of a carboxylic acid. In most embodiments, the first feedstock further contains water.

[0020] A carboxylic acid is defined as an organic compound characterized by the presence of a carboxyl group (-COOH). Carboxylic acids comprise for example monocarboxylic acids, dicarboxylic acids, aromatic carboxylic acids, hydroxy carboxylic acids and keto carboxylic acids. Examples of monocarboxylic acids comprise formic acids, acetic acid, propionic acid, butyric acid, valeric acid and caproic acid.Examples of dicarboxylic acids comprise malonic acid, succinic acid, glutaric acid and adipic acid. Examples of aromatic carboxylic acids comprise benzoic acid, salicylic acid, gallic acid and phthalic acid.Examples of hydroxy carboxylic acids comprise lactic acid, citric acid, tartaric acid, 3-hydroxypropanoic acid, 3-hydroxybutyric acid and glycolic acid.Examples of keto carboxylic acids comprise pyruvic acid, levulinic acid, acetoacetic acid and 2,2-dimethylpropanoic acid.

[0021] The minimum concentration of salts of carboxylic acids in the first feedstock is preferably at least 5 wt%, and more preferably at least 10 wt%, at least 20 wt% or at least 30wt%. In preferred embodiments, the concentration of salts of carboxylic acids is ranging between 30 and 40 wt%.

[0022] The concentration of a salt of a carboxylic acids is preferably lower than the solubility limit at boiling temperature of the salt of the carboxylic acid. More preferably, the concentration of a salt of a carboxylic acid is close to its solubility limit at boiling temperature.

[0023] In case the first feedstock comprises a plurality of salts of carboxylic acids, the concentration of salts of carboxylic acids refers to the total concentration of salts of carboxylic acids corresponding with the sum of the concentration of the different salts of carboxylic acid present in the first feedstock. Preferably, the concentration of each individual salt of a carboxylic acid does not exceed its solubility limit at boiling temperature.

[0024] In case the first feedstock comprises a plurality of salts of carboxylic acids, the concentration of salts of carboxylic acids is preferably lower than the solubility limit at boiling temperature of the salt of the carboxylic acid having the lowest solubility and more preferably close to the solubility limit at boiling temperature of the salt of the carboxylic acid having the lowest solubility.

[0025] In case the first feedstock comprises water, the water content ranges preferably between 25 and 75 wt%, for example between 30 and 70 wt% or between 40 and 60 wt%.

[0026] In preferred embodiments the first feedstock comprises at least one salt of a VFA. In particular embodiments the first feedstock comprises one salt of a VFA. In other embodiment, the first feedstock comprises a number of salts of a VFA, for example 2, 3, 4, 5 or 6 salts of a VFA. In most embodiments, the first feedstock further contains water.

[0027] A VFA is defined as a linear short-chain aliphatic mono-carboxylic acid having 1 to 7 carbon atoms. VFAs may have a straight of branched-chain. These acids are termed "volatile" because they can readily evaporate at room temperature and are commonly found in fermentation processes, such as anaerobic digestion. Examples of VFAs comprise formic acid, acetic acid, propionic acid, butyric acid, isobutyric acid, 2-methylbutyric acid, valeric acid, isovaleric acid, , hexanoic acid (caproic acid) and heptanoic acid (enanthic acid). Examples of salts of VFAs present in the first feedstock comprise formates such sodium formate, potassium formate, or calcium formate; acetates such as sodium acetate, potassium acetate or calcium acetate; propionates such a sodium propionate, potassium propionate or calcium propionate or butyrates such as sodium butyrates, potassium propionate or calcium propionate. It is clear that the first feedstock may comprise more than one salt of a VFA, for example salts of formats and salts of acetates or salts of acetates and salts of propionates.

[0028] The minimum concentration of salts of VFAs in the first feedstock is preferably at least 5 wt% and more preferably at least 10 wt%, at least 20 wt% or at least 30 wt %. Preferably, the concentration of salts of VFAs is ranging between 30 and 40 wt%.

[0029] The concentration of a salt of a VFA is preferably lower than the solubility limit at boiling temperature of the salt of a VFA. More preferably, the concentration of a salt of a VFA is close to its solubility limit at boiling temperature.

[0030] In case the first feedstock comprises a plurality of salts of VFAs, the concentration of salts of VFAs refers to the total concentration of salts of VFAs corresponding with the sum of the concentration of the different salts of VFAs present in the first feedstock. Preferably, the concentration of each individual salt of a VFA does not exceed its solubility limit at boiling temperature.

[0031] In case the first feedstock comprises a plurality of salts of VFAs, the concentration of salts of VFAs is preferably lower than the solubility limit at boiling temperature of the salt of the VFA having the lowest solubility and more preferably close to the solubility limit at boiling temperature of the salt of the VFA having the lowest solubility.

[0032] The first feedstock comprises for example sodium formate, sodium acetate, sodium propionate and / or sodium butyrate.

[0033] In case the first feedstock comprising at least one salt of a VFA also comprises water, the water content ranges preferably between 25 and 75 wt%, for example between 30 and 70 wt% or between 40 and 60 wt%.

[0034] As mentioned above, the first feedstock comprises at least one salt of a carboxylic acid having a pKa ranging between 3 and 6, for example at least one salt of a VFA. The first feedstock may further comprise additional compounds (impurities) such as (residual) carbohydrates, proteins, lipids, polysaccharides, peptides, nucleic acids, ammonia, phosphates, nitrates, chlorides, potassium, sodium, ammonium, trace metals and suspended matter.

[0035] The first feedstock comprises for example a fermentation broth or is derived from a fermentation broth. A fermentation broth is a mixture produced during a fermentation process. A fermentation broth typically comprises a significant portion of fatty acids in the non-volatile salt form. Utilizing a fermentation broth or a derivative of a fermentation broth ensures a renewable and sustainable source of raw materials. The integration of fermentation broth in the method according to the present invention streamlines the production pipeline by leveraging existing biotechnological processes, potentially lowering operational costs and enhancing overall efficiency.

[0036] The fermentation broth may comprise a concentrated fermentation broth, i.e. a fermentation broth having a minimum concentration of salts of carboxylic acids, for example salts of VFAs of 20 wt% and more preferably having a minimum concentration of salts of carboxylic acids of 30 wt%, for example a concentration of salts of carboxylic acids ranging between 30 and 40 wt%. Such concentrated fermentation broth can for example be obtained by advanced evaporation techniques such as mechanical vapor recompression, thermal vapor recompression, multiple effect evaporation, falling film evaporation or combinations thereof.

[0037] The second feedstock comprises at least one ammonium salt, at least one acid, or a combination of at least one ammonium salt and at least one acid. In particular embodiments, the second feedstock comprises one ammonium salt or one acid or a combination of one ammonium salt and one acid. In other embodiments the second feedstock comprises a number of ammonium salt, for example 2, 3, 4 or 5 ammonium salts, the second feedstock comprises a number of acids, for example 2, 3, 4 or 5 acids or the second feedstock comprises a number of ammonium salts and a number of acids, for example 2, 3, 4 or 5 ammonium salts and 2, 3, 4 or 5 acids.

[0038] Ammonium salts are compounds comprising an ammonium cation (NH4+) and an anion such as a chloride, nitrate, sulfate, carbonate, bicarbonate or phosphate.

[0039] An acid is defined as a substance that can donate a proton (H+ion) (Bransted-Lowry definition) or accept an electron pair (Lewis definition). The acid may comprise an organic acid or an inorganic acid. In preferred embodiments the acid comprises an inorganic acid.

[0040] An organic acid is an acid that contains carbon and typically has a carboxyl (-COOH) functional group, such as acetic acid (CH3COOH) and citric acid (C6H8O7).

[0041] An inorganic acid, also known as a mineral acid, is an acid that does not contain carbonhydrogen (C-H) bonds in its molecular structure. These acids typically dissociate in water to release hydrogen ions (H+), making the solution acidic. Examples of inorganic acids comprise HCI, HNO3, FhPC and H2SO4.

[0042] The minimum concentration of ammonium salts or acids is preferably at least 5 wt%, and more preferably at least 10 wt%, at least 20 wt% or at least 30wt%. In preferred embodiments, the concentration of salts of ammonium salts or acids is ranging between 30 and 40 wt%.

[0043] The concentration of an ammonium salt is preferably lower than the solubility limit at boiling temperature of the ammonium salt. More preferably the concentration of an ammonium salt is close to its solubility limit at boiling temperature.

[0044] In case the first feedstock comprises a plurality of ammonium salts and / or a plurality of acids, the concentration of ammonium salts and the concentration of acids refers to the total concentration of ammonium salts or the total concentration of acids, corresponding respectively with the sum of the concentration of the ammonium salts and with the sum of the concentration of acids. Preferably, the concentration of each individual ammonium salt does not exceed its solubility limit at boiling temperature.

[0045] In case the second feedstock comprises water, the water content ranges preferably between 25 and 75 wt%, for example between 30 and 70 wt% or between 40 and 60 wt%.

[0046] The second feedstock, in particular a feedstock comprising at least one ammonium salt may comprise a waste stream for example from a gas scrubber, for example a gas scrubber of exhaust animal stable, the liquid fraction of animal manure or any other organic or inorganic source. Such waste stream is for example first subjected to a pretreatment, for example to a coagulation and / or sedimentation step, a filtration step, a centrifugation step or a combination thereof.

[0047] The second feedstock, in particular a second feedstock comprising at least one ammonium salt may comprise a concentrated ammonium waste stream, i.e. a stream comprising a minimum concentration of ammonium salts of 10 wt% or at least 20 wt%, for example a concentration of ammonium salts ranging between 40 and 50 wt%. The concentration of an ammonium salt is preferably lower than the solubility limit at boiling temperature of the ammonium salt. More preferably the concentration of an ammonium salt is close to its solubility limit at boiling temperature.

[0048] Such a concentrated ammonium waste stream can for example be obtained by advanced evaporation techniques such as mechanical vapor recompression, thermal vapor recompression, multiple effect evaporation, falling film evaporation or combinations thereof.

[0049] A typical second feedstock, for example obtained through acid scrubbing of exhaust air originating from animal stables comprises 5-15 wt% ammonium sulfate, 0.1-0.5 wt suspended solids, 0.5-2 wt% organic matter: 0.5-2 wt%. The residual H2SO4concentration of such second feedstock is typically lower than 1 wt%. Such feedstock can either be used directly or can be concentrated, preferably to a concentration of ammonium salts higher than 10 wt% or higher than 20 w t%, before being introduced in the vessel. In particular embodiments the second feedstock is concentrated to a concentration of ammonium salts of 30, 40 or 50 wt% . Alternatively or additionally, such second feedstock can be enriched with a (waste) stream comprising an acid, for example a strong inorganic acid. A waste stream typically comprises between 5 and 10 wt% inorganic acid (for example HCI). Such waste stream results for example from metal cleaning process. Preferably, such stream does not comprise toxic compounds (volatile or nonvolatile) such as heavy metals, organic chlorines, pesticides and radioactive substances.

[0050] Some preferred first and second feedstock for methods according to the present invention are specified below:In a first method the first feedstock comprises one or more salts of a carboxylic acid and the second feedstock comprises at least one acid, preferably at least one inorganic acid.In a second method the first feedstock comprises one or more salts of a VFA and the second feedstock comprises a least one acid, preferably at least one inorganic acid.In a third method the first feedstock comprises one or more salts of a carboxylic acid and the second feedstock comprises at least one ammonium salt.In a fourth method the first feedstock comprises one or more salts of a VFA and the second feedstock comprises at least one ammonium salt.In a fifth method the first feedstock comprises one or more salts of a carboxylic acid and the second feedstock comprises at least one ammonium salt and at least one acid, preferably at least one inorganic acid.In a sixth method the first feedstock comprises one or more salts of a VFA and the second feedstock comprises at least one ammonium salt and at least one acid, preferably at least one inorganic acid.

[0051] According to the method of the present invention the first feedstock and the second feedstock or the mixture of the first and the second feedstock are introduced into a vessel or reactor. For the purpose of the present invention the terms vessel and reactor are used interchangeably. The vessel may have any shape. The vessel comprises for example a cylindrical structure promoting an efficient vertical airflow.

[0052] A vessel with a conical top and / or bottom design, for example a cylindrical structure with a conical top and / or bottom design, can be preferred to influence and effective solid particle separation from the vapors. Furthermore, the vessel can be equipped with one or more distributors to maintain consistent temperature throughout the chamber.

[0053] In preferred embodiments, the vessel can be equipped with one or more integrated cyclone separators and / or one or more bag filters to ensure efficient separation of solid particles from the vapors.

[0054] The vessel can be provided with means to create mechanical agitation, for example a rotor comprising one or more blades.

[0055] Furthermore, the vessel can be provided with means for heating. Any type of heating element can be considered. In particular embodiments heat can be provided by the wall of the vessel. Alternatively or additionally, heat is provided by the introduction of a gas, for example a noncondensable gas. Careful management of the vessel dimensions and thus residence time is needed to ensure thorough reactions and vaporization without overheating the material and preventing issues like sticking or degradation. Preferably, the design mitigates the risk of condensation by proper insulation.

[0056] A typical medium sized vessel used for spray drying has a cylindrical chamber having a diameter ranging between 2.5 and 3.5 m, a height ranging between 3 and 5 m, a conical bottom height ranging between 1 and 2 mm, resulting in a total height ranging between 4 and 7m. Such vessel has a volume ranging between 20 and 50 m3.

[0057] It is clear that other vessels, for examples vessel having another volume and / or shape can be considered as well.

[0058] The pressure in the vessel typically ranges between 0.001 and 1 atm. In particular embodiments the pressure in the vessel ranges between 0.1 atm and 1 atm.

[0059] According to the method of the present invention, droplets of the first feedstock and the second feedstock or of the mixture of the first feedstock and the second feedstock are formed during their introduction or shortly after their introduction in the vessel. The droplets typically have a size ranging between 10 and 500 micrometer. In particular embodiments, the droplets have a size ranging between 50 and 150 micrometer.

[0060] In case of more viscous feedstocks the droplets may have a size ranging between 100 and 300 micrometer.

[0061] Suitable devices to form droplets having a diameter ranging between 10 and 500 micrometer comprise nozzles, pressure nozzles, two-fluid nozzles, mechanical dispersers, rotary (centrifugal) atomizers and ultrasonic atomizers.

[0062] In preferred embodiments, the first feedstock and the second feedstock or the mixture of the first and the second feedstock are atomized during their introduction or shortly after their introduction in the vessel. In case of atomization, the droplets typically have a size ranging between 10 and 100 micrometer, for example 20, 30 or 50 micrometer.

[0063] Suitable atomizers comprise two-fluid atomizers, rotary atomizers and ultrasonic atomizers.

[0064] Droplet size can be measured by inline laser beam diffraction spectroscopy or by digital imaging.

[0065] According to the method of the present invention, the droplets are heated or dried. For the purpose of the present invention the terms heating and drying are used interchangeably. According to the present invention the droplets are heated to a temperature higher than 80 °C, higher than 100 °C or higher than 150 °C. In preferred embodiments the droplets are heated to a temperature ranging between 150 and 300 °C, for example to a temperature ranging between 170 and 250 °C, for example 180 °C, 190 °C, 200 °C, 210 °C, 220 °C or 230°C. The temperature may depend on the composition of the first feedstock and the second feedstock. For example, in the case the first feedstock comprises acetate / acetic acid the droplets are preferably heated to a temperature ranging between 170 and 180 °C.

[0066] To heat or dry the droplets any technique known in the art that allows the heating or drying of the droplets can be considered.

[0067] In preferred embodiments of the present invention a gas, for example a non-condensable gas, is introduced to heat the droplets and / or to improve the heat transfer to and between droplets.

[0068] Preferred techniques comprise spray drying or flash drying. In case of spray drying the droplets typically have a size ranging between 50 and 150 micrometer, for example 70, 100 or 120 micrometer. In case of flash drying the droplets typically have a size ranging between 100 and 300 micrometer, for example 120, 150, 170, 200 or 220 micrometer.Another preferred technique comprises Agitated Thin Film Drying (ATFD). In case of ATFD a feedstock or mixture of feedstock is introduced in a vessel thereby forming droplets. The feedstock or mixture is then distributed as a continuous, thin layer across a surface, for example the heated surface of the vessel by mechanical agitation. The mechanical agitation is for example caused by a rotor equipped with blades. While the thin layer is continuously agitated, volatile components evaporate under controlled temperature and pressure conditions. The temperature is preferably higher than 80 °C and the pressure preferably ranges between 1 and 10 mbar. Vapors are removed and preferably condensed. The dried solids are discharged continuously or intermittently from the vessel, for example from the lower section of the vessel.

[0069] According to the method of the present invention, the residence time (actual residence time) of the first feedstock and the second feedstock or the residence time of the mixture of the first andthe second feedstock in the vessel is controlled to be less than 2 minutes, for example less than 1 minute, less than 30 seconds, or less than 15 seconds.

[0070] The residence time of a material in a system is defined as the (average) time a material spends within the system, for example within a vessel, before exiting. It represents the characteristic duration that a material remains in a given environment.

[0071] In case a gas, for example a non-condensable gas is introduced in the system, the residence time T is defined asVT~ QwithV: the volume of the vessel (in m3); andQ: the flow rate of the incoming gas (in m3 / hour)

[0072] In case the flow rate of the incoming gas and the outgoing gas is different the residence time T is defined asVmax(Q[ni Qout)withQin: the flow rate of the incoming gas (in m3 / hour);Qout: the flow rate of the outgoing gas (in m3 / hour); andmax(Qin, Qout) the maximum value between Qin and Qout.

[0073] According to the method of the present invention, the (actual) residence time of the first feedstock and the second feedstock or the residence time of the mixture of the first feedstock and the second feedstock is controlled to be less than 2 minutes, for example to be less than 1 minute or to be less than 30 seconds.

[0074] The required residence time for a given method, depends among other things on the required amount of residual carboxylic acids in the solid residue after reaction. The required amount of residual carboxylic acids in the solid residue after reaction is preferably less than 5 wt%, more preferably less than 2 wt%.

[0075] The residence time of the first feedstock and the second feedstock or of the mixture of the first feedstock and the second feedstock can be controlled in different ways, for example by altering one or more of the following process parameters:the inlet temperature of the heat source, usually the inlet temperature of the gas, preferably of the (inert) non-condensable gas, introduced in the vessel. The higher the inlet temperature, the shorter the required residence time.the outlet temperature of the heat source, usually the outlet temperature of the gas, preferably of an (inert) non-condensable gas, introduced in the vessel. The higher the outlet temperature, the shorter the required residence time. This outlet temperature is among others dependent on the required amount of residual carboxylic acids in the solid residue,which is preferably less than 5 wt%, more preferably less than 2 wt%. Preferably the temperature is lower than 120 °C to avoid the formation of byproducts. It is clear that the temperature should be lower than the decomposition temperature of the carboxylic acids to be vaporized at given pressure.the water content of the first and second feedstock. The lower the water content, the shorter the residence time. As specified above, the water content is preferably ranging between 25 and 75 wt%.the amount of vapors in the gas introduced in the vessel, usually an (inert) non-condensable gas. The higher this amount of vapors in the gas, the longer the residence time. Vapors can consist out of carboxylic acids and humidity in case the gas is recycled or out of humidity in case the gas is not recycled and air is used.the droplet size. The smaller the droplet size, the shorter the residence time. The optimal droplet size depends mainly among others on the feed injection method. Atomized feedstocks have a droplet size typically between 50 and 100 micrometer and dry faster, reducing residence time. High viscous slurries as feedstock have a droplet size typically ranging between 100 and 300 micrometer and require longer residence time to dry. the velocity of the gas, preferably (inert) non-condensable gas introduced in the vessel, depending largely on the applied feed injection method: (0.5-40 m / s) and turbulence. The higher the drying gas velocity and / or the more turbulence, the shorter the required residence time.the flow rate of the incoming first feedstock, the flow rate of the incoming second feedstock, or the flow rate of the mixture of the first feedstock and the second feedstock. The higher such flow rates, the higher the required residence time

[0076] By introducing the first feedstock and the second feedstock or the mixture of the first feedstock and the second feedstock in the vessel, by forming droplets of the first feedstock and the second feedstock or of the mixture of the first feedstock and the second feedstock to obtain droplets having the specified droplet size, by heating the first feedstock and the second feedstock or the mixture of the first feedstock and the second feedstock to the specified temperatures while controlling the residence time of the first feedstock and the second feedstock or the mixture of the first feedstock and the second feedstock, the first feedstock and the second feedstock are reacting to form vapors and a solid residue while avoiding that undesirable components such as amides are formed.

[0077] According to the method of the present invention, the vapors that are formed during the reaction are subjected to a condensation step to obtain a fraction comprising at least one carboxylic acid, for example comprising at least one volatile fatty acid. The condensation step results in at least one fraction comprising one carboxylic acid or a number of carboxylic acids, for example one VFA or a number of VFAs.

[0078] In preferred embodiments, the vapors formed during the reaction are subjected to one or more condensation steps to obtain a number of fractions whereby each fraction comprises a carboxylic acid. In particular embodiments, the vapors formed during the reaction are subjected to one or more condensations steps to obtain a number of fractions whereby each fraction comprises a VFA. The condensation step or condensation steps result for example in a fraction comprising formic acid, a fraction comprising acetic acid, a fraction comprising acetic acid, a fraction comprising butyric acid, a fraction comprising isobutyric acid, a fraction comprising valeric acid, a fraction comprising isovaleric acid, a fraction comprising 2-methylbutyric acid, a fraction comprising hexanoic acid and / or a fraction comprising heptanoic acid.

[0079] It is clear that the condensation step may result in other fractions, for example a fraction comprising water and / or a fraction comprising ammonia.

[0080] In preferred embodiments, the vapors are subjected to a condensation step by direction the vapors through a distillation column, for example through a fractionated distillation column. The vapors can be directed though one distillation column or through a number of distillation columns, for example through one fractionated distillation column or through a number of fractionated distillation columns.

[0081] It can be preferred that the vapors formed during the reaction are first directed to a scrubber or a condenser-scrubber before being subjected to the condensation step in order to separate the non-condensable gas from gases that will condense during the condensation step.The scrubber may comprise a wet scrubber, a dry scrubbers or an electrostatic scrubber.

[0082] In a preferred method first the vapors formed during the reaction are directed to a scrubber or condenser scrubber and the outlet of the scrubber or condenser-scrubber is subsequently directed through one or more distillation columns, for example through two coupled fractionated distillation columns. In a particular embodiment the liquid effluent exiting the scrubber or condenserscrubber enters a first distillation column, for example in the middle of a first distillation column equipped with 25 to 35 theoretical plates, a partial condenser and a reboiler and is split in a bottom fraction yielding one or more carboxylic acids, for example one or more VFA, with a purity of at least 97 wt% and a top fraction comprising water and ammonia. The top fraction can then be directed to a second distillation column, for example in the middle of a second distillation column equipped with 8 to 12 theoretical plates and a total condenser. The bottom fraction of the second distillation column yields water with a purity of at least 99.9 wt% and the top fraction yields an ammonia-water mixture having between 20 and 30 wt% ammonia.

[0083] The method according to the present invention may further comprise the step of recovering one or more compounds from the solid residue.

[0084] Compounds can be recovered from the solid residue by any technique known in the art. Preferred techniques to recover one or more compounds from the solid residue comprise leaching,dissolution, filtration, solid / liquid extraction, crystallisation, evaporation, washing and any combination thereof.

[0085] Compounds that can be recovered comprise for example an organic residue, organic or inorganic nitrogen, phosphor compounds, struvite, metal ions such as potassium, calcium or metal salts. Such compounds can for example be used as fertilizer.

[0086] According to a second aspect of the present invention a method for the simultaneous recovery of at least one carboxylic acid and ammonia is provided. The method comprises the steps ofproviding a first feedstock comprising at least one salt of a carboxylic acid having a pKa ranging between 3 and 6, the first feedstock has preferably a water content ranging between 25 and 75 wt % and a total content of salts of carboxylic acids of at least 5 wt%, providing a second feedstock comprising at least one ammonium salt and optionally comprising at least one acid, preferably an inorganic acid, the second feedstock has preferably a water content ranging between 25 and 75 wt% and a total content of ammonium salts of at least 10 wt%,introducing the first feedstock and the second feedstock or a mixture of the first feedstock and the second feedstock into a vessel, forming droplets, for example droplets having a size ranging between 10 and 500 micrometer, from the first feedstock and the second feedstock or from the mixture of the first and the second feedstock and heating the droplets to a temperature higher than 80 °C, allowing the first feedstock and the second feedstock to react thereby forming vapors comprising at least one carboxylic acid and ammonia, preferably comprising at least one carboxylic acid, ammonia and water, and a solid residue, whereby the residence time of the first feedstock and the second feedstock or the residence time of the mixture of the first and the second feedstock in the vessel is controlled to be less than 2 minutes;subjecting the vapors to a condensation step thereby obtaining a fraction comprising the at least one carboxylic acid and a fraction comprising ammonia.

[0087] In preferred method the droplets formed from the first feedstock and the second feedstock or the droplets formed from the mixture of the first and the second feedstock are heated to a temperature ranging between 150 °C and 300 °C, for example to a temperature ranging between 170 and 250 °C, for example 180 °C, 190 °C, 200 °C, 210 °C, 220 °C or 230°C.

[0088] The method according to the present inventions allows to recover simultaneously one carboxylic acid and ammonia or to recover a number of carboxylic acids and ammonia. In the former case the first feedstock comprises one salt of a carboxylic acid, in the latter case the first feedstock comprises a number of salts of carboxylic acid.

[0089] In preferred embodiments, the method according to the present invention allows to recover one VFA and ammonia or to recover a number of VFAs. starting from a first feedstock comprisingone or more salts of a VFA. In the former case the first feedstock comprise one salt of a VFA, in the latter case the first feedstock comprises a number of salts of a VFA.

[0090] The droplets of the first and second feedstock or of the mixture of the first and second feedstock have preferably a size ranging between 10 and 500 micrometer.

[0091] In preferred embodiments, the first feedstock and the second feedstock or the mixture of the first feedstock and the second feedstock are atomized to form droplets. Such droplets typically have a size ranging between 10 and 150 micrometer, for example between 10 and 100 micrometer, such as 20 micrometer, 50 micrometer or 75 micrometer.In alternative embodiments, the first feedstock and the second feedstock or the mixture of the first feedstock and the second feedstock form droplets having a size ranging between 150 and 500 micrometer, for example droplets having a size of 200 micrometer, 250 micrometer, 300 micrometer or 400 micrometer

[0092] In a preferred method a gas is introduced in the vessel during the reaction of the first feedstock and the second feedstock. The gas can be introduced either continuously or periodically in the vessel during the reaction of the first feedstock and the second feedstock or can be introduced with a constant flow rate or a variable flow rate. Typical flow rates range between 500 and 100000 m3 / s. Typical flow rates used for medium sized spray drying installations range between 1000 and 10000 m3 / s. By introducing a gas in the vessel during the reaction of the first feedstock and the second feedstock, the heat transfer to and between the droplets is improved. This can significantly improve the reaction efficiency. The gas can also be referred to as a drying gas. Also in case of Agitated Thin Film Drying, it might be advantageous to introduce a gas in the vessel.

[0093] The gas comprises preferably a non-condensable gas. For the purpose of the present invention, a non-condensable gas is defined as a gas that is not condensing during the condensation step of the vapors generated during the reaction of the first feedstock and the second feedstock, i.e. under the conditions such as temperature and pressure of the condensation step of the vapors. Preferably, the non-condensable gas is an inert gas. Preferred non-condensable gases comprise nitrogen, helium, neon, argon or combinations thereof.

[0094] As first feedstock any feedstock as described can be considered.

[0095] The content of carbonate and / or bicarbonate salts in the first feedstock used in a method for the simultaneous recovery of at least one carboxylic acid and ammonia is preferably limited. The content of carbonate and / or bicarbonate salts is typically expressed as the content of example CaCOs Preferably, the content of CaCOs is preferably lower than 250 ppm.The concentration of carbonate and / or bicarbonate salts is preferably limited to minimize CO2 contamination in particular in the top product originating from the condensation step in the NH3 / water stream as ammonium may react with carbon alkalinity to generate NH3 and CO2. This also results in less ammonium being available for converting carboxylic acid salts to carboxylic acid. A possible indication of a high carbonate and / or bicarbonate content is a pH higher than 9. Carbonalkalinity can be measured by analytical methods known in the art and can be lowered to a value less than 250 ppm by adjusting the pH of the feedstock to a value less than 9 but preferably higher than 7 by adding a mineral acid and / or by introducing the feedstock in a degassing vessel, prior to reacting with the second feedstock.

[0096] The second feedstock comprises at least one ammonium salt and optionally at least one acid, preferably an inorganic acid.

[0097] As defined above, ammonium salts are compounds comprising an ammonium cation (NH4+) and an anion such as a chloride, nitrate, sulfate, carbonate, bicarbonate or phosphate.

[0098] Any acid as described above can be considered.

[0099] A particularly preferred second feedstock comprising at least one ammonium salt comprises a waste stream for example from a gas scrubber, for example a gas scrubber of exhaust animal stable, the liquid fraction of animal manure or any other organic or inorganic source. Such waste stream is for example first subjected to a pretreatment, for example to a coagulation and / or sedimentation step, a filtration step, a centrifugation step or a combination thereof.

[0100] The second feedstock comprising at least one ammonium salt may comprise a concentrated ammonium waste stream, i.e. a stream comprising a minimum concentration of ammonium salts of 10 wt%, for example a concentration of ammonium salts ranging between 30 and 50 wt% or between 40 and 50 wt%. Such a concentrated ammonium waste stream can for example be obtained by advanced evaporation techniques such as mechanical vapor recompression, thermal vapor recompression, multiple effect evaporation, falling film evaporation or combinations thereof.

[0101] The vessel used in a method for the simultaneous recovery of at least one carboxylic acid and ammonia can be any vessel as described above.

[0102] The pressure in the vessel typically ranges between 0.001 and 1 atm. In particular embodiments the pressure in the vessel ranges between 0.1 atm and 1 atm.

[0103] According to the method for the simultaneous recovery of at least one carboxylic acid and ammonia according to the present invention, droplets of the first feedstock and the second feedstock or of the mixture of the first feedstock and the second feedstock are formed during their introduction or shortly after their introduction in the vessel. The droplets typically have a size ranging between 10 and 500 micrometer. More preferably, the droplets have a size ranging between 50 and 150 micrometer.

[0104] In case of more viscous feedstocks the droplets may have a size ranging between 100 and 300 micrometer.

[0105] Suitable devices to form droplets having a diameter ranging between 10 and 500 micrometer comprise nozzles, pressure nozzles, two-fluid nozzles, mechanical dispersers, rotary (centrifugal) atomizers and ultrasonic atomizers.

[0106] In preferred embodiments, the first feedstock and the second feedstock or the mixture of the first and the second feedstock are atomized during their introduction or shortly after their introduction in the vessel. In case of atomization, the droplets typically have a size ranging between 10 and 100 micrometer, for example 20, 30 or 50 micrometer.

[0107] Suitable atomizers comprise two-fluid atomizers, rotary atomizers and ultrasonic atomizers.

[0108] Droplet size can be measured by inline laser beam diffraction spectroscopy or by digital imaging.

[0109] According to the method of the present invention, the droplets are heated or dried. For the purpose of the present invention the terms heating and drying are used interchangeably. According to the present invention the droplets are heated to a temperature higher than 80°C. In particular embodiment the droplets are heated to a temperature ranging between 150 and 300 °C, for example to a temperature ranging between 170 and 250 °C, for example 180 °C, 190 °C, 200 °C, 210 °C, 220 °C or 230°C. The temperature may depend on the composition of the first feedstock and the second feedstock. For example, in the case the first feedstock comprises acetate / acetic acid the droplets are preferably heated to a temperature ranging between 170 and 180 °C.

[0110] To heat or dry the droplets any technique known in the art that allows the heating or drying of the droplets can be considered.

[0111] In preferred embodiments of the present invention a gas, for example a non-condensable gas, is introduced to heat the droplets and / or to improve the heat transfer to and between droplets.

[0112] Preferred techniques comprise spray drying or flash drying. In case of spray drying the droplets typically have a size ranging between 50 and 150 micrometer, for example 70, 100 or 120 micrometer. In case of flash drying the droplets typically have a size ranging between 100 and 300 micrometer, for example 120, 150, 170, 200 or 220 micrometer.

[0113] Another preferred technique comprises Agitated Thin Film Drying (ATFD). In case of ATFD a feedstock or mixture of feedstock is introduced in a vessel thereby forming droplets. The feedstock or mixture is then distributed as a continuous, thin layer across a surface, for example the heated surface of the vessel by mechanical agitation. The mechanical agitation is for example caused by a rotor equipped with blades. While the thin layer is continuously agitated, volatile components evaporate under controlled temperature and pressure conditions. The temperature is preferably higher than 80 °C and the pressure preferably ranges between 1 and 10 mbar. Vapors are removed and preferably condensed. The dried solids are discharged continuously or intermittently from the vessel, for example from the lower section of the vessel.

[0114] According to the method for the simultaneous recovery of at least one carboxylic acid and ammonia according to the present invention, the residence time (actual residence time) of the first feedstock and the second feedstock or the residence time of the mixture of the first and the secondfeedstock in the vessel is controlled to be less than 2 minutes, for example less than 1 minute, less than 30 seconds, or less than 15 seconds.

[0115] The residence time of a material in a system is defined above.

[0116] The residence time of the first feedstock and the second feedstock or of the mixture of the first feedstock and the second feedstock can be controlled in different ways as described above.

[0117] By introducing the first feedstock and the second feedstock or the mixture of the first feedstock and the second feedstock in the vessel, by forming droplet of the first feedstock and the second feedstock or of the mixture of the first feedstock and the second feedstock to obtain droplets having the specified droplet size, by heating the first feedstock and the second feedstock or the mixture of the first feedstock and the second feedstock to the specified temperatures while controlling the residence time of the first feedstock and the second feedstock or the mixture of the first feedstock and the second feedstock, the first feedstock and the second feedstock are reacting to form vapors and a solid residue while avoiding that undesirable components such as amides are formed.

[0118] The condensation step of a method for the simultaneous recovery of at least one carboxylic acid and ammonia and in particular for the simultaneous recovery of at least one VFA and ammonia may comprise any condensation step as described above.

[0119] The recovering of one or more compounds from the solid residue in a method for the simultaneous recovery of at least one carboxylic acid and ammonia and in particular for the simultaneous recovery of at least one VFA and ammonia may comprise any technique as described above.Brief description of the drawings

[0120] The present invention will be discussed in more detail below, with reference to the attached drawings, in which:Figure 1 to Figure 3 show schematic illustrations of methods according to the present invention;Figure 4a to Figure 4d show the influence on the recovery rate of the inlet feed concentration C, the inlet temperature Tin of the non-condensable gas, the outlet temperature Tout of the non-condensable gas and the airflow rate of the non-condensable gas.Description of embodiments

[0121] The present invention will be described with respect to particular embodiments and with reference to certain drawings but the invention is not limited thereto but only by the claims. Thedrawings are only schematic and are non-limiting. The size of some of the elements in the drawing may be exaggerated and not drawn on scale for illustrative purposes. The dimensions and the relative dimensions do not correspond to actual reductions to practice of the invention.

[0122] When referring to the endpoints of a range, the endpoints values of the range are included.

[0123] When describing the invention, the terms used are construed in accordance with the following definitions, unless indicated otherwise.

[0124] The term ‘and / or’ when listing two or more items, means that any one of the listed items can be employed by itself or that any combination of two or more of the listed items can be employed.

[0125] Figure 1 represents a schematic illustration of a method according to the present invention. A first feedstock (feedstock 1) and a second feedstock (feedstock 2) are introduced in a vessel (a reactor) while forming droplets having a droplet size ranging between 10 and 500 micrometer, more preferably to form droplets having a droplet size ranging between 50 and 300 micrometer, for example 100 micrometer.The first feedstock comprises for example at least 10 wt% sodium acetate.The second feedstock comprises for example at least 10 wt% ammonium sulfate.[00126JA non-condensable gas such as nitrogen, air, helium, neon, argon or combinations thereof can be introduced in the vessel (not shown). By introducing a non-condensable gas the heat transfer to and between the droplets is improved. This may considerably improve the reaction efficiency.

[0127] The droplets are heated to a temperature ranging between 150 and 300 °C, for example to a temperature of 180 °C.

[0128] The first feedstock and the second feedstock are reacting and form vapors and a solid residue (solids).

[0129] The residence time of the first feedstock and the second feedstock in the vessel is controlled to be less than 2 minutes, for example to be less than 30 seconds.

[0130] The vapors are subjected to one or more condensation steps resulting in a gas fraction and an ammonia-water-carboxylic acid fraction. The ammonia-water-carboxylic acid fraction may further result in one or more carboxylic acid fractions or in a fraction comprising a mixture of carboxylic acids (CA), an ammonia fraction and a water fraction.

[0131] Figure 2 is a schematic illustration of an alternative method according to the present invention. A first feedstock (feedstock 1) and a second feedstock (feedstock 2) are introduced in a reactor (1) while being atomized to form droplets having a droplet size ranging between 10 and 500 micrometer, more preferably to form droplets having a droplet size ranging between 50 and 300 micrometer.A non-condensable gas such as nitrogen, oxygen, air, helium, neon, argon or combinations is introduced in the vessel (not shown).

[0132] The droplets are heated to a temperature ranging between 150 and 300 °C, for example 180 °C.

[0133] The first feedstock and the second feedstock are reacting and form vapors (3) and a solid residue (solids (2)).

[0134] The residence time of the first feedstock and the second feedstock in the vessel is controlled to be less than 2 minutes, for example to be less than 30 seconds.

[0135] The vapors are directed to a scrubber or scrubber condenser (4) to recover the noncondensable gas.

[0136] After being directed to a scrubber or scrubber condenser the vapors are direct over a column (5) to separate VFAs and vapors (6) which may subsequently be directed to a column (8) and a condenser (9) to recover water and ammonia.

[0137] Figure 3 is a further illustration of a method according to the present invention. A first feedstock (feedstock 1) and a second feedstock (feedstock 2) are introduced in a vessel (reactor) while forming droplets for example droplets having a size of 150 micrometer. The first feedstock (feedstock 1) comprises at least one salt of a carboxylic acid, for example one salt of a VFA. The second feedstock (feedstock 2) comprises at least one inorganic acid and / or an ammonium salt. Possibly, a non-condensable gas is introduced in the reactor (not shown). In the reactor, the first feedstock and the second feedstock are heated (dried) using a batch drying process at a pressure ranging between 0.05 and 1 atm, preferably at a pressure of 0.1 atm, and at temperature ranging between 110 °C and 180 °C, preferably at a temperature between 120 and 140 °C or in a continuous drying process, equipped with a condenser and buffer vessel (not shown).During the heating (drying) process, the first and the second feedstock react to form vapors and a solid residue. The vapors comprise carboxylic acid vapors and optionally NH3 vapors. Subsequently, the vapors are, or in case of buffering, the liquid is purified using a batch distillation process to obtain different fraction of carboxylic acids (CA1 , CA2) and a water or ammonia-water fraction. The distillation comprises for example two successive distillations using a column with 25-35 real plates followed by a condensation step using a partial condenser with reflux. The method according to the present invention allows to obtain carboxylic acid fractions having a purity ranging between 80 and 99.5 wt% and an ammonia-water fraction in the range of 20 to 30 wt%Example 1, example according to a preferred embodiment

[0138] A first influent (mix A) was prepared by mixing equal volumes of a first feedstock comprising a solution containing 221.5 g / L of sodium acetate, equal to 16.2 wt% VFA with a second feedstock comprising a solution containing 178.5 g / L ammonium sulphate, equal to 2.4 wt% ammonium. This resulted in a total dry matter content of 20 wt%, referred to as concentration C.

[0139] A second influent (mix B) was prepared by mixing equal volumes of a first feedstock comprising a solution containing 332.3 g / L of sodium acetate, equal to 24.3 wt% VFA with a second feedstock comprising a solution containing 267.8 g / L ammonium sulphate, equal to 3.6 wt% ammonium. This resulted in a total dry matter content of 30 wt%, referred to as concentration C.

[0140] The first influent and the second influent were atomized in a laboratory set-up spray dryer, model B-290 Mini Spray Dryer supplied by Buchi having a typical residence time of approximately 3-5 seconds.

[0141] The inlet temperature of the drying gas (Tin), the outlet temperature of the drying gas (Tout), the flow rate of the drying gas (Qasp), and the flow rate of the nebulizer gas (Qspr) were varied according to a 27-4fractionated factorial design in order to evaluate the recovery rate of acetate (wt%) and the amount of acetamide byproduct in the effluent, expressed as wt%. The parameter settings, the amount of acetamide byproduct in the effluent, the recovery rate and the particle size are specified in Table 1. All experiments were done under atmospheric pressure.Table 1 : parameter settings according to a 27-4fractionated factorial designAmount Recovery Droplet Sample Mix Tin Tout Qasp Qspr acetamide rate size run (°C) (°C) (m3 / h) (L / h) (wt%) (wt%) (pm) 1 A 160 70 25 1000 0 97,4 35 2 A 180 70 20 1000 0 98,1 50 3 A 160 95 25 500 0 98,4 40 4 A 180 95 20 500 0 98,3 50 5 B 160 70 20 500 0.05 94,6 20 6 B 180 70 25 500 0.05 95,4 20 7 B 160 84 20 1000 0 95,0 2096,0 158 B 180 95 25 1000 0

[0142] All samples had a recovery rate between 95wt% and 98wt%. As shown in Figure 4, the recovery rate was positively influenced by a decreasing inlet feed concentration (C ) (Figure 4a), an increasing inlet temperature Tin of the non-condensable gas (drying gas) (Figure 4b), an increasing outlet temperature Tout of the non-condensable gas (drying gas) (Figure 4c) and an increasing flow rate of the non-condensable gas (drying gas) (Figure 4d) and a decreasing droplet size (not shown). The flowrate of the nebulizer had no significant effect.

[0143] 0nly samples 5 and 6, having a high amount of dry matter and a low outlet temperature (Tout) of the non-condensable gas (drying gas), showed a small amount of acetamide (0.05 wt%)Example 2, comparative example (not according to the present invention)

[0144] An influent comprising a synthetic feedstock mix comprising 400 g sodium acetate, a stoichiometric amount of 322.6 g ammonium sulphate and 700 mL of water (= 49.2 wt% water) was inserted in a pilot set-up of a conical vacuum batch reactor dryer with a working volume of approximately 3L, supplied by Lehmann Industrie.

[0145] The applied pressure was kept at 75 mbar and the heating oil temperature was set to an initial temperature of 90 °C and was gradually increased until 175 °C. the temperature was then kept constant until the distillate flow stopped after 3 hours. According to literature this is a typicaldrying time for such a set-up. The distillate was collected and the concentration of sodium acetate and acetamide were measured with Ion Chromatography (IC) and High-Performance Liquid Chromatography (HPLC)

[0146] The distillate contained a total of 285.1 g sodium acetate. The amount of acetamide in the distillate amounted to 3.61 g or 1.25 wt% of the total amount recovered.

[0147] 71.3 wt% of the original amount of sodium acetate was recovered in the distillate. As shown by the experiments a substantial amount of sodium acetate as not recovered and a the formation of amide byproducts was substantial.Example 3, example according to a preferred embodiment

[0148] An influent was prepared by combining a first feedstock comprising an aqueous solution of calcium lactate having a pH of 7.0 with a second feedstock comprising a 10 wt% sulfuric acid solution. The second feedstock was added to the first feedstock until the pH of the resulting solution, hereinafter referred to as the influent, reached 2.2. Following addition of the second feedstock, the concentration of lactic acid in the influent was measured by ion chromatography and determined to be 162.8 g / L.

[0149] The influent was, after removing solid deposits by sedimentation, subjected to an Agitated Thin Film Drying (ATFD) process. The influent was introduced in a conical vessel. In the vessel mechanical agitation is caused by a rotor. Atomization is obtained by using the internal rotating mechanical disperser at a rotating speed of 250 rpm.

[0150] By mechanical agitation, the material is conveyed and sprayed against the heated inner wall of the conical vessel, thereby forming a thin film. Upon contact with the heated wall, volatile components evaporate and are withdrawn through a vapor outlet to a condenser maOintained at 25 °C. The condenser is provided with a receiving vessel and is further connected downstream to a cold trap containing liquid nitrogen. The dried material descends to the bottom of the vessel and is recovered in the form of a powder.

[0151] Optionally, a non-condensing (heated) gas can be applied to increase evaporation efficiency (while minimizing condensation, dehydration, oxidation and polymerization of the lactic acid).

[0152] The internal pressure in the vessel, having a volume of 100 ml, was kept at 0.005 bar and the temperature of the vessel wall was kept at 180 °C.

[0153] After 40,0 ml of influent was added to the vessel, the condensed vapors in the receiving vessel were added to the condensed vapors collected in the cold trap and the volume was found to be 35,0 ml. The concentration of lactic acid in condensed vapors was found to be 176,7 g / L

[0154] The recovery rate of lactic acid was determined by multiplying the volume of condensed vapors by the concentration of lactic acid in the condensed vapors to obtain the amount of lactic acid recovered, and dividing this value by the product of (i) the volume of influent introduced into the first vessel and (ii) the concentration of lactic acid in the influent and was found to be 95.0%.

Claims

-22-Claims1. A method for the recovery of at least one carboxylic acid, the method comprising the steps ofproviding a first feedstock comprising at least one salt of a carboxylic acid having a pKa ranging between 3 and 6,providing a second feedstock comprising at least one ammonium salt and / or comprising at least one acid,introducing the first feedstock and the second feedstock or a mixture of the first feedstock and the second feedstock into a vessel, forming droplets from the first feedstock and the second feedstock or from the mixture of the first and the second feedstock and heating the droplets to a temperature higher than 80 °C, allowing the first feedstock and the second feedstock to react thereby forming vapors comprising at least one carboxylic acid and water (and optionally ammonia) and a solid residue, whereby the residence time of the first feedstock and the second feedstock or the residence time of the mixture of the first and the second feedstock in the vessel is controlled to be less than 2 minutes;subjecting the vapors to a condensation step thereby obtaining a fraction comprising the at least one carboxylic acid.

2. The method according to claim 1 , wherein the droplets have a size ranging between 10 and 500 micrometer.

3. The method according to claim 1 or claim 2, wherein the droplets of the first feedstock and the second feedstock or from the mixture of the first feedstock and the second feedstock are formed by atomization.

4. The method according to any one of the preceding claims, wherein a gas is introduced in the vessel during the reaction of the first feedstock and the second feedstock.

5. The method according to claim 4, wherein the gas comprises a non-condensable gas, with a non-condensable gas being defined as a gas that is not condensing during the condensation step.

6. The method according to any one of the preceding claims, wherein the salt of a carboxylic acid comprises a salt of a volatile fatty acid and the at least one carboxylic acid comprises a volatile fatty acid.

7. The method according to any one of the preceding claims, wherein the acid of the second feedstock comprises an inorganic acid.

8. The method according to any one of the preceding claims, wherein the vapors are subjected to a condensation step by directing the vapors through a distillation column, preferably a fractionated distillation column.

9. The method according to any one of the preceding claims, wherein the vapors are directed to a scrubber or a scrubber-condenser to separate the non-condensable gas before being subjected to the condensation step.

10. The method according to any one of the preceding claims, wherein the first feedstock comprises a fermentation broth or is derived from a fermentation broth.

11. The method according to any one of the preceding claims, wherein the method further comprises the step ofrecovering one or more compounds from the solid residue.

12. A method for the simultaneous recovery of at least one carboxylic acid and ammonia, the method comprising the steps ofproviding a first feedstock comprising at least one salt of a carboxylic acid having a pKa ranging between 3 and 6, the first feedstock having a water content ranging between 25 % and 75 wt% and a total content of salts of carboxylic acids of at least 5 wt%, providing a second feedstock comprising at least one ammonium salt and optionally comprising at least one inorganic acid, the second feedstock having a water content ranging between 25 and 75 wt% and a total content of ammonium salts of at least 10 wt%, introducing the first feedstock and the second feedstock or a mixture of the first feedstock and the second feedstock into a vessel, atomizing the first feedstock and the second feedstock or the mixture of the first and the second feedstock to form droplets and heating the droplets to a temperature higher than 80 °C thereby allowing the first feedstock and the second feedstock to react thereby forming vapors comprising at least one carboxylic acid and water (and optionally ammonia) and a solid residue, whereby the residence time of the first feedstock and the second feedstock or the residence time of the mixture of the first and the second feedstock in the vessel is controlled to be less than 2 minutes; subjecting the vapors to a condensation step thereby obtaining a fraction comprising the at least one carboxylic acid and a fraction comprising ammonia.

13. The method according to claim 12, wherein the first feedstock has a total content of carbonate and / or bicarbonate salts expressed as total content CaCOs lower than 250 ppm.

14. The method according to claim 12 or claim 13, wherein a non-condensable gas is introduced in the vessel during the reaction of the first feedstock and the second feedstock, the non- condensable gas being a gas that is not condensing during the condensation step..

15. The method according to any one of claims 12 to 14, wherein the salt of a carboxylic acid comprises a salt of a volatile fatty acid and the at least one carboxylic acid comprises a volatile fatty acid.

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