Systems and methods for direct acidification and distillation for recovery of carboxylic acids

Abstract

A method of recovering carboxylic acids from solutions containing carboxylic acid salts includes contacting a feed solution including water and carboxylic acid salts with medium-chain fatty acids to form a mixture of water, carboxylic acids, medium-chain fatty acids and salts; separating the water and the carboxylic acids that have lower boiling point than the medium-fatty acids from the mixture to form a separated water and carboxylic acid stream and a separated medium-chain fatty acid salt stream; contacting at least a portion of the separated medium-chain fatty acid salt stream with water and carbon dioxide to form an aqueous phase including water, bicarbonates and / or carbonates, metal cations and dissolved medium-chain fatty acids and an organic stream including medium-chain fatty acids, water, carbon dioxide and heavy impurities.

Description

SYSTEMS AND METHODS FOR DIRECT ACIDIFICATION ANDDISTILLATION FOR RECOVERY OF CARBOXYLIC ACIDSCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of and priority to U.S. Application No. 63 / 654,444, filed on May 31, 2024, which is hereby incorporated by reference herein in its entirety.TECHNOLOGY

[0002] Provided herein are methods and systems for the recovery of carboxylic acids.BACKGROUND

[0003] Many fermentation processes are used in industry to produce organic acids, such as lactic acid, succinic acid, acetic acid, and butyric acid. In particular, mixed-culture acidogenic fermentation employs a naturally occurring consortium of microorganisms to produce carboxylic acids, specifically short-chain fatty acids (SCFAs) and medium-chain fatty acids (MCFAs). SCFAs include acetic, propionic, isobutyric and butyric acids, which can also be connoted by their carbon chain length: C2 (acetic), C3 (propionic), iC4 (isobutyric) and C4 (butyric), respectively. MCFAs include iso-valeric, valeric, caproic, heptanoic, octanoic and even nonanoic acids - iC5, C5, C6, C8, C9 acids, respectively. Although this type of non-sterile fermentation process is robust, the recovery of the carboxylic acids (the SCFAs and MCFAs) from the fermentation effluent has been a challenge.

[0004] Acidogenic fermentation is most efficient near neutral pH. Microbial activity and the efficiency of the fermentation process tends to drop as acids are produced because the produced acids cause the pH of the fermentation process to decrease. To minimize low-pH inhibition, many of these fermentations require that a buffering agent be added. Buffering agents serve to neutralize the acids, thereby mitigating the reduction in pH of the fermentation process. Such buffering agents include, for example, hydroxides, bicarbonates, or carbonates of calcium, potassium, sodium, and magnesium. The producedacids react with the buffering agent to produce fatty acid salts. The resulting product from the fermentation, therefore, is the salts of the acids rather than the acids themselves.

[0005] However, to recover the acids from the fermentation broth, the salts need to be acidified. Traditionally, mineral acids, such as sulfuric acid, hydrochloric acid, or phosphoric acid have been employed for acidification of the salts. However, the use of mineral salts as an acidification agent has several downsides. First, mineral acids are primarily sourced from petroleum processes, and as such are not considered to be green or sustainable. Further, the use of mineral salts generates the salts of the mineral acids as a byproduct. Huge amounts of these byproduct salts, such as calcium sulfate (gypsum), have been produced in years past in the production of carboxylic acids, such as lactic acid, which constitute a disposal issue and an environmental problem. Thus, long term continued use of mineral acids is not considered to be economical, green, or sustainable.

[0006] Some processes have been proposed that employ carbon dioxide (CO2) as the acidifying agent followed by or simultaneous with extraction with other compounds. Use of CO2 as an acidifying agent has the distinct advantage in that it is typically produced naturally from the fermentation itself. In addition, acidification with CO2 results in bicarbonate or carbonate salts. Unlike the salts of mineral acids, bicarbonate and carbonate salts can be recycled and re-used in the fermentation as a buffering agent. CO2 as a supercritical fluid, or just as a subcritical liquid or a gas, can also act as an extractant for the fatty acids, so advantageously, it is able to both acidify and extract at the same time. Later separation of the CO2 from the extracted compounds is also straightforward due to the high difference in the boiling point of CO2 and that of most molecules of interest, such as the carboxylic acids produced in fermentation.

[0007] A limitation of CO2 extraction is that it is efficient only with highly nonpolar molecules, such as MCFAs, but it is less effective for extracting SCFAs due to the lower non-polar nature of SCFAs. Although the CO2 can efficiently extract MCFAs, it may leave a large portion of the SCFAs behind. When SCFAs are desired to be extracted, it has been proposed to use other compounds such as esters, ketones, amines, and other known extractants of carboxylic acids, such as trioctylphosphine oxide (TOPO). Such extraneous extractants can be toxic or are non-environmentally friendly, therefore their use is less desirable than using materials produced in mixed-culture acidogenic fermentation.

[0008] It has been proposed that MCFAs, which are substantially water immiscible (i.e., they form a separate organic phase to the water or aqueous phase under certain conditions), be used to extract the SCFAs in the presence of CO2 as acidifying agent. Such an extraction process uses large quantities of MCFAs to extract the SCFAs, and although most of the MCFAs are recovered and recycled, such large streams increase capital and operating expenses. Further, the extraction efficiencies for the shortest SCFAs using MCFAs are still modest, with most of the acetic acid and a large portion of the propionic acid ending up unextracted in the raffinate. Acetic acid has very low extraction efficiencies <30%, and propionic acids extraction efficiencies are <90%. Additionally, such an extraction process may require a second extraction step to recover the MCFAs used as extractants in the first extraction step. In addition, to minimize the salts and water from being extracted into the MCFA extractant phase, large loadings of CO2 at high pressures are required, which further increases capital and operating costs. The final raffinate, which is typically recycled to fermentation, will contain a relatively large amount of unextracted acids, which causes inhibition in the fermentation, decreasing its efficiency.

[0009] It is desired to provide methods and systems for recovery of substantially all the acids exiting a fermentation (i.e., SCFAs and MCFAs), that also decreases the stream volumes, and increases the efficiency of CO2 usage in acidification and extraction, and therefore would have the potential to substantially decrease capital and operating expenses.SUMMARY

[0010] Provided herein are methods and systems for recovering carboxylic acids. The methods and systems disclosed herein may be applied to recover carboxylic acids from fermentation broths, such as fermentation broths produced from buffered or unbuffered acidogenic fermentation of organic materials. The methods and systems disclosed use or facilitate direct acidification of carboxylic acids via contact with medium-chain or long- chain fatty acids followed by distillation to fully remove the lighter carboxylic acids, then further, the regeneration and conversion of the resulting medium-chain or long-chain fatty acids salts back to medium-chain or long-chain fatty acids using carbon dioxide (CO2) in the presence of water to form carbonates and bicarbonates.

[0011] In a first aspect, provided herein is a method of recovering carboxylic acids, the method including: contacting a feed solution including water and carboxylic acid saltswith medium-chain fatty acids to form a mixture, thereby acidifying at least a portion of the carboxylic acid salts, the mixture including water, carboxylic acids, and medium-chain fatty acid salts; separating the mixture into a first stream and a second stream, the first stream including water and carboxylic acids that have a boiling point that is lower than a boiling point of the medium-chain fatty acids and the second stream including medium-chain fatty acid salts; and contacting at least a portion of the second stream with water and carbon dioxide to form an aqueous phase stream and an organic phase stream, the aqueous phase stream including water, bicarbonates and / or carbonates, metal cations, and dissolved medium-chain fatty acids, and the organic phase stream including medium-chain fatty acids, water, and carbon dioxide.

[0012] In some embodiments, the separating is performed using a distillation system. In some embodiments, the method includes hydrating the second stream with water to decrease viscosity of the second stream or to keep the second stream in a liquid state. In some embodiments, the contacting of at least a portion of the second stream with water and carbon dioxide is done at an operating pressure of greater than 200 psi. In some embodiments, the operating pressure ranges from 400 to 1500 psig, or from 600 to 1200 psig.

[0013] In some embodiments, the method includes contacting the aqueous phase stream with subcritical liquid carbon dioxide, subcritical gaseous carbon dioxide or supercritical carbon dioxide to recover medium-chain fatty acids dissolved in the aqueous phase stream. In some embodiments, the organic phase stream formed by the contacting of at least a portion of the second stream with water and carbon dioxide at high pressures is sent to a carbon dioxide separation unit to recover the carbon dioxide without decreasing the pressure down to atmospheric pressure. In some embodiments, the carbon dioxide separation unit is a flash vessel or a distillation column.

[0014] In some embodiments, the method includes separating and recovering carbon dioxide from the organic phase stream to form a carbon dioxide-free organic phase stream; and separating dissolved water from the carbon dioxide-free organic phase stream by heating and flashing or by distillation to form a water-free and carbon dioxide-free organic phase stream. In some embodiments, the water-free and carbon dioxide-free organic phase including medium-chain fatty acids undergoes purification to remove heavy impurities, thereby producing purified medium-chain fatty acids. In some embodiments, at least aportion of the organic phase stream formed by the contacting of at least a portion of the second stream with water and carbon dioxide, after separating and recovering the carbon dioxide, undergoes purification to remove heavy impurities, thereby producing purified medium-chain fatty acids. In some of these embodiments, the purification of the organic phase includes distillation, membrane filtration, or extraction.

[0015] In some embodiments, the purification is performed in a set of distillation columns including a first distillation column and a last distillation column, the mediumchain fatty acids are separated into a distillate of a first distillation column, and heavy impurities are removed through a bottoms of the last distillation column. In some embodiments, the set of distillation columns further includes one or more subsequent distillation columns between the first distillation column and the last distillation column, and carboxylic acids having boiling points higher than the boiling point of the mediumchain fatty acids are separated into one or more distillates of the one or more subsequent distillation columns. In some embodiments, separating the water and the carboxylic acids that have lower boiling point than the medium-chain fatty acids occur in separate distillation columns. In some embodiments, the carboxylic acids that have lower boiling point than the medium-chain fatty acids are sent to a set of distillation columns to fractionate them into individual carboxylic acids.

[0016] In some embodiments, separating the water and the carboxylic acids that have lower boiling point occurs in the same equipment. In some embodiments, the equipment includes an evaporator, a flash vessel, a distillation column, or combinations of any two or more thereof. In some embodiments, the evaporator includes a falling-film evaporator, a thin-film evaporator, a thin-film dryer, a wiped-film evaporator or combinations thereof.

[0017] In various embodiments, the contacting of at least a portion of the second stream with water and carbon dioxide and the subcritical liquid carbon dioxide, subcritical gaseous carbon dioxide, or supercritical carbon dioxide recovery of medium-chain fatty acids dissolved in the aqueous phase stream occur in the same contacting unit. In various embodiments, the contacting of at least a portion of the second stream with water and carbon dioxide and the subcritical liquid carbon dioxide, subcritical gaseous carbon dioxide or supercritical carbon dioxide recovery of medium-chain fatty acids dissolved in the aqueous phase stream occur in separate contacting units.

[0018] In some embodiments, the contacting units are liquid-liquid or gas-liquid extraction systems or both. In some embodiments, the contacting units are hollow-fiber membrane contactors or extraction columns or both. In some embodiments, the purification includes introducing an extraneous compound to act as an entrainer to allow more efficient removal of heavy impurities, while minimizing medium-chain fatty acid losses. In some embodiments, at least a portion of the organic stream formed by the contacting of at least a portion of the second stream with water and carbon dioxide, after separating and recovering the carbon dioxide, is recycled back to contact the feed solution and to provide at least a portion of the medium-chain fatty acids.

[0019] In various embodiments, at least a portion of the purified medium-chain fatty acids is recycled back to contact the feed solution and to provide at least a portion of the medium-chain fatty acids. In some of these embodiments, the purification with membrane filtration is done after the contacting of the feed solution with the recycled medium-chain fatty acids. In some embodiments, the feed solution is a concentrated and clean fermentation broth derived from fermentation of a biodegradable feedstock. In some of these embodiments, the aqueous phase formed by the contacting of at least a portion of the second stream with water and carbon dioxide, after separating and recovering free carbon dioxide, is sent to fermentation to act as a buffering agent.

[0020] In certain embodiments, the recovered carbon dioxide is recycled to contact at least a portion of the second stream and water. In some embodiments, carbon dioxide gas released during fermentation is recovered and used to contact at least a portion of the second stream and water.

[0021] In any of the previous embodiments, long-chain fatty acids are used instead of medium-chain fatty acids. In any of the previous embodiments, the medium-chain fatty acids include an individual medium-chain fatty acids or mixtures thereof. In any of the previous embodiments, the long-chain fatty acids include an individual long-chain fatty acid or mixtures thereof.

[0022] In another aspect, provided herein is a method of recovering carboxylic acids, the method including: contacting a feed solution including water and carboxylic acid salts with medium-chain fatty acids in a first contacting step to form a mixture including water, carboxylic acids, medium-chain fatty acids and salts; separating the mixture into aseparated water and carboxylic acid stream and a separated medium-chain fatty acid salt stream, wherein the carboxylic acids in the separated water and carboxylic acid stream have boiling point lower than the boiling point of the medium-chain fatty acids; contacting at least a portion of the separated medium-chain fatty acid salt stream with water and carbon dioxide in a second contacting step to form an aqueous phase stream and an organic phase stream; wherein the aqueous phase stream includes water, bicarbonates and / or carbonates, metal cations, and dissolved medium-chain fatty acids, and wherein the organic phase stream includes medium-chain fatty acids, carbon dioxide, water, and heavy impurities; and separating and recovering the carbon dioxide from the organic phase stream to form a recovered carbon dioxide stream and a carbon dioxide-free organic phase stream.

[0023] In certain embodiments, at least a portion of the recovered carbon dioxide stream is recycled to provide at least a portion of the carbon dioxide used in second contacting step. In some of these embodiments, at least a portion of the carbon dioxide-free organic stream including medium-chain fatty acids is recycled to provide at least a portion of the medium-chain fatty acids used in the first contacting step.

[0024] In another aspect, provided herein is a method including: a first contacting step including contacting carboxylic acid salts with medium-chain fatty acids to create a mixture including carboxylic acids and medium-chain fatty acid salts; a first separation step including separating the carboxylic acids from the mixture; and a second contacting step including contacting the remaining mixture with CO2, thereby producing an acidified mixture including medium-chain fatty acids.

[0025] In some embodiments, the method includes separating the medium-chain fatty acids from the acidified mixture. In some embodiments, the method includes recycling the medium-chain fatty acids for use in the first contacting step.BRIEF DESCRIPTION OF THE DRAWINGS

[0026] FIG. l is a process flow diagram of a system for the recovery of carboxylic acids according to an embodiment, including acidification and recovery of carboxylic acids by contact with medium- and / or long-chain fatty acids, and subsequent recovery of the medium- and / or long-chain fatty acids.

[0027] FIG. 2 is a process flow diagram of a system for the recovery of carboxylic acids according to an embodiment, wherein lighter acids are removed individually by a fractionation train and the MCFAs are also fractionated during purification.

[0028] FIG. 3 is a process flow diagram of a system for the recovery of carboxylic acids according to an embodiment including a lights separator or evaporator.

[0029] FIG. 4 is a process flow diagram of a system for the recovery of carboxylic acids according to an embodiment wherein separate contactors or extraction columns are used for the regeneration of the MCFA salts and for the extraction of MCFAs still solubilized in the water phase.

[0030] FIG. 5 is a process flow diagram of a system for the recovery of carboxylic acids according to an embodiment, wherein an inexpensive external heavy compound is used to aid the recovery of solubilized MCFAs in the water phase in the second extraction column or contactor and also to minimize MCFA losses during purification.

[0031] FIG. 6 is a process flow diagram of a system for the recovery of carboxylic acids according to an embodiment, wherein an inexpensive external heavy fatty acid is used as the main acidification agent.DESCRIPTION OF THE INVENTION

[0032] Various embodiments are described hereinafter. It should be noted that the specific embodiments are not intended as an exhaustive description or as a limitation to the broader aspects discussed herein. One aspect described in conjunction with a particular embodiment is not necessarily limited to that embodiment and can be practiced with any other embodiment s).

[0033] As utilized herein with respect to numerical ranges, the terms “approximately,” “about,” “primarily,” “substantially,” and similar terms will be understood by persons of ordinary skill in the art and will vary to some extent depending upon the context in which it is used. If there are uses of the terms that are not clear to persons of ordinary skill in the art, given the context in which it is used, the terms will be plus or minus 10% of the disclosed values. When “approximately,” “about,” “primarily,” “substantially,” and similar terms are applied to a feature (e.g., to describe its shape, size, orientation,direction, composition, etc.), these terms are meant to cover minor variations in structure or composition that may result from, for example, the manufacturing or assembly process and are intended to have a broad meaning in harmony with the common and accepted usage by those of ordinary skill in the art to which the subject matter of this disclosure pertains. Accordingly, these terms should be interpreted as indicating that insubstantial or inconsequential modifications or alterations of the subject matter described and claimed are considered to be within the scope of the disclosure as recited in the appended claims.

[0034] The use of the terms “a” and “an” and “the” and similar referents in the context of describing the elements (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the embodiments and does not pose a limitation on the scope of the claims unless otherwise stated. No language in the specification should be construed as indicating any non-claimed element as essential.

[0035] It should be understood that, although example implementations of embodiments of the disclosure are described herein, the systems and methods of this disclosure may be implemented using any number of techniques, whether currently known or not. The present disclosure should in no way be limited to the example implementations, drawings, and techniques illustrated below. Additionally, the drawings are not necessarily drawn to scale and may not illustrate obvious pieces of equipment such as certain flow controllers, pumps, compressors, valves, piping, and instrumentation. One of ordinary skill in the art would readily understand the difference between a general process flow diagram (PFD) as compared to the intricate and detailed aspects involved with an actual process. PFD(s) are described in general detail for brevity.

[0036] It is also noted that terms such as “process streams” or “streams” described herein need not be clean cut or pure. When referring to particular product streams herein, it should be understood that, although the primary product(s) may be described, otherproducts may exist in the product stream. Thus, there may be quantities of the other compounds in such streams and / or other impurities. For example, if referred as MCFAs, commonly C5-C9 acids are used, the bulk of the C5-C9 acids stream might comprise isovaleric, valeric, hexanoic, heptanoic, octanoic and nonanoic acid, individually or in combinations thereof, but it may also contain, in addition to some water, small quantities of lighter fatty acids (C1-C4), heavier acids (C10-C11), CO2, metal cations, and / or impurities. Similarly, if referred to SCFAs, commonly C2-C4 are used, the bulk of the C2-C4 acids stream might comprise, acetic, propionic and butyric acid, individually or in combination thereof, but it may also contain, in addition to some water, small quantities of the heavier fatty acids (C5-C9), but also formic acid (Cl), lactic acid, succinic acid, CO2, metal cations, and / or impurities.

[0037] Although traditionally, medium-chain fatty acids are acids with carbon numbers ranging from C6-C12, as used herein, medium-chain fatty acids (MCFAs) are individual or mixed fatty acids with carbon numbers ranging from C5-C9 (including the iso acids) or mixtures thereof, which may be typically produced in mixed-culture acidogenic fermentation. In the processes described, MCFAs are predominantly, but not necessarily limited to, C5-C8 fatty acids. It should be understood that small quantities of C9, CIO, Cl 1, and C12 fatty acids may or may not be present. The MCFAs might be straight-chain or branched, for example, iso-valeric and iso-caproic acids. On the other hand, short-chain fatty acids (SCFAs) are individual or mixtures of fatty acids with carbon numbers ranging from C2-C4, straight-chain or branched, for example, iso-butyric acid, or mixtures thereof. It should be understood that small quantities of the shortest volatile fatty acid, formic acid (Cl), and other acids such as lactic and succinic acid, may also be present. Finally, long- chain fatty acids (LCFAs), as used herein, are individual or mixed fatty acids with carbon numbers ranging from CIO and higher, which are not typically produced from mixed- culture acidogenic fermentation but are procured from natural oils, lipids and / or fats, such as, but not limited to, coconut oil, palm oil, palm kernel oil, soybean oil, sunflower oil. Furthermore, as used herein, the terms carboxylic acid salts, short-chain fatty acid salts, medium-chain fatty acid salts, and long-chain fatty acid salts should be understood as including the anions of the carboxylic acids, the anions of the short-chain fatty acids, and the anions of the long-chain fatty acids, respectively and the corresponding metal cations, such as, but not limited to, sodium, potassium, calcium, magnesium.

[0038] The terms “lighter” and “heavier” are used herein as a relative term when describing mixtures of carboxylic acids, which include fatty acids. In such usage, it should be understood that lighter carboxylic or fatty acids are shorter chain carboxylic or fatty acids present in the mixture and heavier carboxylic or fatty acids are longer chain carboxylic or fatty acids present in the mixture. These terms are distinct from short- and long-chain fatty acids, as they are relative to the contents of the mixture. For example, a mixture containing a mixture of fatty acids may be distilled and the “lighter” fatty acids collected at the top of the distillation column. Such lighter fatty acids are not necessarily short-chain fatty acids, but are instead a collection of the lighter fatty acids present in the initial mixture. The cut of lighter and heavier can be adjusted by changing the operating conditions of the corresponding equipment, for example by adjusting the operating temperature of a distillation column.

[0039] Embodiments disclosed herein may be described in a stepwise manner (e.g., describing process flow step-by-step), but the disclosure should in no manner be so limited. Although flow streams or products are often described as ‘sent’ from one location to another, the disclosure encompasses use of any and all aspects of fluid / product handling and transport (e.g., pumps, piping, vessels, etc.). Finally, although any process stream may be shown as directed to a particular destination (e.g., unit operation, vessel, system, etc.), the destination and handling of the process stream are not limited to such a depiction and it should be understood that intermediate handling or process steps may be carried out even though not explicitly mentioned or illustrated. Thus, a process stream may be sent to a flash column, a flash tank, a distillation column, combinations thereof, etc.

[0040] General Method of Carboxylic Acid Recovery Via Direct Acidification

[0041] Herein disclosed is a method for carboxylic acid recovery that uses direct acidification of a concentrated fermentation broth. In various embodiments, the method of carboxylic acid recovery includes: 1) contacting a fermentation broth containing carboxylic acid salts with an organic phase containing fatty acids, 2) recovering the carboxylic acids via a separation step. In some embodiments, the method also includes: 3) regeneration of the fatty acids by contact with CO2 and / or 4) recovery of fatty acids from an aqueous phase via contact with CO2. In some embodiments, the method also includes: 5) recycle of metal cations from the carboxylic acid salts to the fermentation to act as a buffer, and / or 6) recycle of CCh

[0042] In various embodiments, the carboxylic acid recovery method is performed without extraction of the carboxylic acids. In some embodiments, the carboxylic acid recovery method is performed without the addition of CO2. In some embodiments, CO2 is used to recover MCFAs and / or LCFAs that are used as acidifying agents, but is not used to acidify the fermentation broth. The fermentation broth may optionally comprise short-chain fatty acids (e.g., Cl, C2, C3, C4) (SCFAs). The acidifying agents are, preferably, mediumchain fatty acids (e.g., C5, C6, C7, C8, C9) (MCFAs), which are produced naturally in mixed-culture acidogenic fermentation and may also be part of the fermentation broth. The acidifying agents may also optionally comprise long-chain fatty acids (e.g., CIO, C12, C14, Cl 6) (LCFAs), such as those obtained naturally from natural oils, lipids, and / or fats. The concentrated fermentation broth is contacted with an acidifying agent, the acidifying agent including MCFAs, to form an acidified mixture. The MCFAs acidify at least a portion of the carboxylic acids contained in the fermentation broth. As a result, a portion or substantially all of the MCFAs are converted into MCFA salts. The carboxylic acids in the fermentation broth to be acidified and recovered may be the SCFAs or they may be other carboxylic acids, such as, but not limited to, lactic acid.

[0043] Relatively lighter carboxylic acids in the acidified mixture are recovered by distillation. The lighter carboxylic acids are captured from the top portion of the distillation column or equipment. Part or all of the resulting MCFA or LCFA salts are collected in a stream at the bottom of the distillation tower, which is substantially free of the lighter carboxylic acids (SCFAs and lighter MCFAs). The bottom stream then undergoes cation removal by contacting the stream in, for example, an extraction column with water in the presence of CO2. This causes bicarbonates and carbonates of the cations to form and acidifies the MCFA and LCFA salts, such that at least a portion of the cations / bicarbonates / carbonates move into the water phase, while the MCFAs or LCFAs mostly remain in the organic phase. The regenerated MCFAs or LCFAs leave the contactor as an organic phase, while the bicarbonates and metal cations (sodium, potassium, calcium, magnesium, etc.) are extracted by the water and leave with the aqueous phase.

[0044] The aqueous phase may still have MCFAs or LCFAs solubilized in it to a certain degree, typically close to the solubility of the MCFAs or LCFAs in water, which typically decreases as the size of the fatty acid increases (i.e., the solubility of longer chain fatty acids decreases as a function of chain length). Some embodiments of the presentdisclosure include a step to recover the MCFAs or LCFAs from the aqueous phase. In some embodiments, the MCFAs and LCFAs are extracted from the aqueous phase by contact with supercritical or subcritical liquid or gaseous CO2, or with another suitable water-insoluble extractant. The resulting raffinate will contain bicarbonates and carbonates and a very small amount of unextracted acids. In some embodiments, at least a portion of the raffinate is recycled to the fermentation as buffering agent to neutralize the acids produced in the fermentation, which assists with pH control of the fermentation.

[0045] In some embodiments, a least a portion of the regenerated MCFAs or LCFAs are purified to remove heavy impurities, which may include biopolymers, heavy oil and / or very long fatty acids. The purification of the MCFAs or LCFAs can take place by, for instance, distillation or by membrane filtration. Other methods may also be used. In various embodiments, at least a portion of the purified regenerated MCFAs or LCFAs are recycled to the first acidification step to be used again as acidification agents. In some embodiments, the purified regenerated MCFAs and LCFAs are mixed with unpurified regenerated MCFAs or LCFAs to form the recycle stream.

[0046] The methods disclosed herein produce a product stream comprising MCFAs. In some embodiments, the product stream includes purified MCFAs in excess of that required for the recycle stream. The product may include MCFAs fed to the system for use as an acidifying agent, MCFAs produced in the fermentation, or a combination thereof. The extraneous LCFAs, on the other hand, tend to be consumed due to operational losses and so may require a make-up.

[0047] In practice, and as described in greater detail below, the methods as disclosed herein show substantially full recovery of the acids without the need for a separate extraction step, thereby avoiding extraction inefficiencies. The disclosed methods and corresponding systems have the potential of substantially reducing capital and operating expenses when compared to other processes which employ extraction.

[0048] Various embodiments provide a multistep method for converting carboxylic acid salts in an aqueous phase to corresponding carboxylic acids by acidification of the carboxylic acid salts via contact with an acidic organic phase, recovery of the carboxylic acids from the aqueous phase, regeneration of the organic phase, and cleanup of the acidic organic phase. In some embodiments, the acidic organic phase contains MCFAs and / orLCFAs, which convert the carboxylic acid salts present in the aqueous phase into carboxylic acids. The recovery of the carboxylic acids is performed by a separation step, and may be carried out in a piece of separation equipment. In some embodiments, the recovery of the carboxylic acids is by distillation. The recovery of the carboxylic acids may be performed as a separate step, or may be simultaneous with the acidification of the carboxylic acid salts by contact with the acidic organic phase. In some embodiments, after the acidification of the carboxylic acids salts, the organic phase is regenerated by contact with CO2 and, optionally, water, which serves to regenerate the MCFA and / or LCFA salts present in the organic phase, and to form bicarbonates / carbonates from the metal anions present. The MCFAs and / or LCFAs present in the water phase (as solubilized acids and / or as salts) may be recovered from the aqueous phase by contacting it with subcritical liquid, gaseous or supercritical CO2. In some embodiments, at least a portion of the CO2 is recovered from the streams by flash tanks, distillation, or other suitable separation equipment.

[0049] In an embodiment, the method includes converting carboxylic acid salts exiting a fermentation into corresponding carboxylic acids by direct acidification with MCFAs or LCFAs, and the simultaneous or subsequent recovery of the carboxylic acids through distillation of the lighter carboxylic acids followed by regeneration or removal of the displaced metal cations (sodium, potassium, etc.) from the MCFA or LCFA stream by contacting this stream with carbon dioxide and water and further recovery of the MCFAs or LCFAs still present in the water phase using supercritical or subcritical liquid or gaseous CO2 extraction. The CO2 is further recovered at high-pressure using, for instance, distillation and lost CO2 is made-up as necessary.

[0050] Some embodiments have different distillation columns to recover and separate the lighter components, including water and the lighter carboxylic or fatty acids coming out as one stream or fractionated into individual acids. Other embodiments fully evaporate and remove all the lighter components, namely water and the lighter carboxylic or fatty acids, using a lights separator that can be a flash column, an evaporator or a distillation column before sending the lighter components to be fractionated in a series of distillation column or fractionation train. In some embodiments, the cation removal from the MCFA or LCFA salt stream with CO2 and water and the extraction of the remaining MCFAs from the water phase with supercritical or with subcritical liquid or gaseous CO2 occurs in the same column or in separate columns.

[0051] In general, the reactions that occur in the method are as follows:

[0052] 1. C A’(aq) + M+(aq)+ HF A(aq) - CA(aq) + HF A'(aq)+M+(aq)(acidification)A

[0053] 2. CA(aq) + HFA'(aq) + M+(aq) ~ > CA$ + H2O$ + HF AM (distillation)

[0054] 3. HF AM + H2O + CO2 - HF A + M+(aq)+ HCO3(aq) (HF A acidification)

[0055] Where:

[0056] CA' = Fermentation carboxylic acid anion

[0057] CA = Fermentation carboxylic acid

[0058] HFA = Heavy fatty acid, which can be MCFAs or LCFAs

[0059] HFA' = Heavy fatty acid anion, which can be MCFA anion or LCFA anion

[0060] M+= Metal cation (e.g., such as sodium, potassium)

[0061] HF AM = Salt of the heavy fatty acid (i.e., MCFA or LCFA) and metal

[0062] In equation 1, fermentation carboxylic acid (SCFAs and MCFAs produced by fermentation) anions (CA‘) and metal cations (M+), such as, but not limited to sodium and potassium, form the salts of these carboxylic or fatty acids, which enter the system with the conditioned and concentrated fermentation broth and are reacted with heavy fatty acids (HFA) (i.e., MCFAs or LCFAs used as acidification agents), which are in the acid form. The presence of free hydronium ions from HFA converts the CA' into carboxylic acid (CA). In equation 2, when heat is applied to the mixture, such as under evaporation or in distillation, the water and the lighter carboxylic acids (CA) will be selectively removed, leaving behind the heavier, less volatile HFA in the form of their anions, which comes together with the M+to form the salt of HFA and metal (HF AM). The presence of some residual free HF As in the HF AM composition results in the composition having a relatively low melting point, so it may remain liquid. A small amount of water, which may be added back, has also been found to cause these salts to remain liquid at even lower temperatures. Then, in equation 3, the HF AM is contacted with more water in the presence of high-pressure CO2. In contact with water, the HF AM ionizes back into HF A' and M+and the CO2 acidifies the HF A' back into HFA which phases out of the aqueous phase while the bicarbonates (HCO3 ) of M+remain or move into the aqueous stream.

[0063] Method and System for Recovery of Carboxylic Acids Via Direct Acidification

[0064] A first method and an associated system is illustrated in FIG. 1. In this method, a feed stream 100, a solution having a high-concentration of carboxylic acids, is provided to a recovery system. The feed stream 100 may be a fermentation broth, for example, a highly concentrated clean fermentation broth, which may be obtained, for example, from mixed-culture acidogenic fermentation. The fermentation feedstock may be any suitable feedstock, including but not limited to biodegradable or bio-sourced materials. A fermentation broth exiting a fermentation may contain desirable carboxylic acid salts, but will likely require further processing to be suitable for carboxylic acid recovery. The fermentation broth exiting the fermentation may be processed to remove solids and / or to concentrate the broth (i.e., remove water) (not shown in FIG.1). For example, the broth may be optionally processed to remove solids using liquid-solid separation equipment, such as, but not limited to, a centrifuge, a filter press, and / or one or more filters / screens to remove larger solid matter. The fermentation broth may be sent to clarification (or a clarifier) to produce a clean broth (e.g., clarified, solids / free, etc.). The clarification process may be, but is not limited to, micro- or ultra-filtration membranes, flocculation, coagulation, dissolved-air flotation, electrocoagulation, combinations thereof, and so forth. The cleaner effluent from clarification may optionally go through further cleaning with tighter membranes (e.g., nanofiltration) to clean proteins and other impurities from the cleaned broth, if desired.

[0065] The fermentation broth (either raw or cleaned) may be concentrated using reverse osmosis (RO), conventional electrodialysis (CED), electrodionization (EDI), evaporation (such as, but limited to, multiple-effect evaporator or mechanical-vapor recompression) or combinations thereof. Ammonia and solids may optionally be removed during concentration by, for example, evaporation, stripping, and filtration of the broth. The concentrated broth may be sent to a softener ion exchange bed (or the like) where impurities, including multi-valent cations such as magnesium, calcium, iron and others, which tend to form insoluble salts, may be removed if necessary. The softener bed may beregenerated with sodium or potassium chloride or hydrochloric acid producing a stream of these multi-valent cations chlorides (e.g., calcium, magnesium, iron chloride). This step may keep these ions from fouling the membranes. The impurity or ion (e.g., multi-valent- cation) free stream may then optionally pass through a degasifier (e.g., stripper, etc.) to remove gases, such as dissolved carbon dioxide. It may be desired to regenerate the softener ion exchange bed with hydrochloric acid to cause a drop in pH that allows carbon dioxide to be removed more easily; however, it is within the scope of the disclosure that degassing may occur prior to softening step.

[0066] The resulting broth from the cleaning and / or concentration steps may be a high-concentration clean broth, which contains the salts of carboxylic acids (i.e., short- and medium-chain fatty acids) produced in fermentation. The broth may have a water content ranging from 20% to 90% w / w, 30% to 70% w / w, or preferably 35% to 55% w / w, each expressed as weight of acids versus the weight of water in the broth. The high- concentration broth may undergo further filtration with membranes or normal filtration for a final polish, if needed.

[0067] The cleaning and concentration steps described above result in feed stream 100. The feed stream 100 contains salts of carboxylic acids with cations such as, but not limited to, sodium, potassium, calcium, magnesium and combinations thereof. The feed stream 100 is fed into an acidification vessel 101. The acidification vessel 101 may be a continuously stirred tank reactor (CSTR) or other suitable equipment. In the acidification vessel 101, the feed stream 100 is contacted with medium-chain fatty acids (MCFAs) 145 such as but not limited to, iso-valeric acid, valeric acid, caproic acid, heptanoic acid, caprylic acid or combination thereof. The MCFAs may be an individual MCFA (e.g., primarily iso-valeric acid, or primarily caproic acid) or may be a mixture of two or more MCFAs. At this stage, the carboxylic acid salts in the feed stream 100 are acidified, with the pH of the feed stream dropping below 6 or preferably below 5, or lower. Any present dissolved carbonates or bicarbonates in the feed stream 100 are converted to carbon dioxide and may be substantially removed at this stage and recovered if desired (not shown in FIG. 1). The resulting acidified mixture 102 contains the acidified carboxylic acids from the feed stream, MCFA salts, and water.

[0068] The acidified mixture 102 is sent to a water removal column 104 and excess water 105 in the acidified mixture 102 is removed. Before entering a water removal column104, the acidified mixture 102 may be passed through one or more optional heat exchanger 103 to be pre-heated before the water removal step. It should be noted that an azeotrope of water and carboxylic acids may form in the water removal column 104, precluding complete acid / water separation. Thus, to avoid the unnecessary loss of the carboxylic acids via the excess water stream 105, further separation of any acids carried in the excess water stream 105 may be necessary. Optionally, the excess water stream 105 (which may carry some amount of carboxylic acids) may be recycled upstream to the fermentation to replace some of the fermentation water input requirements, or it can also be recycled to before concentration of the fermentation broth which becomes high-concentration clean broth / feed stream 100.

[0069] The substantially water-free bottoms 106 from the water removal column 104 are sent to a light acid recovery column 107. In the light acid recovery column 107, lighter acids are recovered as a lighter acid product 108. The lighter acids are those that are lighter (and thus have a lower boiling point) than the MCFAs fed in the acidification vessel 101, including those in the feed stream 100 and those fed as an acidifying agent in the MCFA stream 145. The lighter acids of the lighter acid product 108 stream then are mostly short-chain fatty acids, such as but not limited to acetic, propionic and butyric acids. The lighter acids product 108 may be substantially pure lighter acids. The lighter acids product 108 may be 90 wt.%, 91 wt.%, 92 wt.%, 93 wt.%, 94 wt.%, 95 wt.%, 96 wt.%, 97 wt.%, 98 wt.%, 99 wt.%, 99.5 wt.%, or greater lighter acids. The lighter acids product 108 may be acetic, propionic, butyric, iso-butyric acids, or a mixture of any two or more thereof. The lighter acids product 108 is not limited to strictly short-chain fatty acids (C2-C4). In some embodiments, the lighter acids product 108 may include a small amount of valeric and / or iso-valeric acids.

[0070] The bottoms 109 of the light acid recovery column 107 includes MCFAs and MCFA salts with the cations from the salts in the original high-concentration clean broth / feed stream 100. The bottoms stream 109 leaves through the bottom of the light acid recovery column 107 as a mixture of free MCFAs and MCFA salts of the corresponding cations. Proper temperatures and vacuum level in the water removal column 104 and the light acid recovery column 107 are maintained to maximize the removal of water and lighter acids, respectively, while keeping most of the MCFAs at the bottoms 109. For example, the bottoms may contain substantially all of the MCFAs from the substantially water-freebottoms 106, or at least 99.5 wt.%, 99 wt.%, 98 wt.%, 97 wt.%, 95 wt.%, 92 wt.%, or 90 wt.% of the MCFAs from the substantially water-free bottoms 106. Heat energy from the bottoms stream 109 can optionally recovered by passing the stream through one or more heat exchangers 103, thereby pre-heating the acidified mixture 102 exiting the acidification vessel 101 and cooling the bottoms 109. Further trim cooling and heat recovery steps may be implemented as needed (not shown in FIG. 1).

[0071] As the MCFAs / MCFA salt mixture in the bottoms stream 109 cools, it becomes more viscous which can pose challenges for handling. If required, a relatively small amount of water (water stream 141) can be added to the mixture to reduce viscosity of the MCFAs / MCFA salt mixture. The salts of MCFAs (and long-chain fatty acids - LFCAs - for that matter), especially the potassium salts, exhibit this thickening at lower temperatures, and a small amount of water can hydrate the salts enough to allow them to thin out and even liquify from a solid state, which is a phenomenon we have innovatively discovered. The water may be added before or, more preferably and as shown in FIG. 1, after cooling. Addition of water is best performed after the temperature of the bottoms stream 109 has been decreased to below 100 °C but before temperature fully decreases to the target temperature going into liquid-liquid or gas-liquid contactor 111. The lower viscosity achieved by adding this small amount of water allows easier pumping and handling at the lower operating temperatures in contactor 111. The amount of water to be added to decrease viscosity can range from 1 to 20% w / w of the total mix (i.e., the total mass or mass flow rate of the bottoms stream 109 and the added water stream 141), 3 to 18% w / w of the total mix, or more preferably from 5 to 15% w / w of the total mix. At this stage, an optional bypass stream 142 may be taken from the lighter-acid lean MCFAs / MCFA salt (and optionally water) stream 143, where part of the stream 143 is directed back to the acidification vessel 101 to provide at least a portion of the MCFAs to act as an acidification agent.

[0072] After the optional bypass 142, the remaining MCFAs / MCFA salt stream 144, 143, or 109 is directed to a contactor 111 or other suitable extraction unit for MCFA acidification and extraction and cation removal. The contactor 111 for the acidification / extraction and cation removal may be a liquid-liquid or gas-liquid contactor, such as, but not limited to, an a hollow-fiber membrane contactor or an extraction column. The contactor 111 is operated at elevated pressures ranging from 200 to 1500 psi, 400 to1300 psi, or preferably from 600 to 1200 psi; therefore, the MCFA / salt stream 144, 143 or 109 is pumped to such elevated pressures using one or more pumps 110. In the contactor 111, the MCFA salts are contacted with subcritical liquid, gaseous or supercritical CO2 114, which is introduced at or near the bottom or the other side of the contactor 111 using CO2 pump 115. The CO2 converts the MCFA salts back into free MCFAs. A water stream 112, preferably substantially demineralized water or deionized water or distilled water, is introduced at or near the top of the contactor 111 and pumped to the proper elevated pressure using pump 113. As the MCFA salts are acidified and converted to free MCFAs in the organic phase, carbonates and bicarbonates, are formed. The bicarbonates and any carbonates and the cations move to the water / aqueous phase and so are removed from the organic phase. The amount of water 112 added is enough to ensure substantial extraction of the bicarbonates / carbonates and cations from the organic phase, and also to avoid precipitation of certain bicarbonates having relatively low solubility, such as sodium bicarbonate. In addition, in the lower section of the contactor 111, the rising CO2 contacts the water / aqueous phase and back extracts and recovers any MCFAs that might have dissolved into the water / aqueous phase in the upper section of the contactor 111 where the MCFAs in the organic phase are in contact with the water / aqueous phase. The water / aqueous phase stream 116 exits through the bottom of the contactor 111 carrying, as mentioned, the carbonates / bicarbonates, cations, and other water-soluble species. A substantial amount of CO2 is also carried in the water / aqueous phase stream 116 exiting the contactor 111. The water / aqueous phase stream 116 may be depressurized using a throttling valve 117 or a turbine or pressure exchanger device that can recover some of the energy from depressurization to be used in other devices.

[0073] A large portion of the dissolved CO2 in the water / aqueous phase stream 116 is flashed when the pressured is decreased to atmospheric and the now depressurized stream may be optionally sent to a CO2 recovery device 118. The CO2 recovery device 118 may be, but is not limited to, a flash vessel, a steam stripper, an air stripper, or a heated flash vessel. In CO2 recovery device 118, the flashed CO2 may be recovered. Bicarbonates may also be converted to carbonates, further recovering additional CO2. The recovered CO2 119 may be repressurized and recycled as CO2 make-up 126 to the contactor 111. The resulting carbonate-rich stream 120 (which will also include any unconverted bicarbonates) may be sent back to the fermentation to act as the buffering agent to control pH. An optional purge stream 121 may be taken from the carbonate-rich stream 120 to avoid accumulation ofspecies such as cations and other water-soluble species, leaving a reduced carbonate-rich stream 122. The carbonates and bicarbonates, when released into an acidogenic fermentation (not shown), act as buffering agents that neutralizes the carboxylic acids (SCFAs and MCFAs) as they are formed by the fermentation, thereby controlling the pH of the fermentation. The CO2 released during fermentation from the carbonates and bicarbonates when the carboxylic acids are neutralized, may be cleaned to remove other gases such as hydrogen sulfide, ammonia, and hydrogen, then pressurized to the proper pressure and recycled as CO2 make-up 126 to the contactor 111.

[0074] Turning now to the organic phase 123 exiting the contactor 111, the organic phase stream will be substantially free from salts including cations, and will contain dissolved CO2, free MCFAs and a small amount of water that is dissolved in the organic phase. This organic phase stream 123 is sent to a CO2 separation unit 124, which may be a distillation column or a flash vessel. The pressure in the separation unit 124 may be maintained to remove CO2 only by heat, or the pressure may be decreased slightly or fully to aid with the separation of the much more volatile CO2. The pressure may be maintained high to minimize losses of potential energy contained in the pressurized CO2 stream 125, which exits separation unit 124 and is recycled back to be re-pressurized using pump 115 to the proper pressure and fed to the contactor 111 as subcritical liquid, subcritical gaseous or supercritical CO2 stream 114 as useful in the contactor 111. Some make-up CO2 126 may be added to the system to replenish the CO2 that exits the contactor 111 as carbonates / bicarbonates and dissolved CO2 in the aqueous phase 116 and as unrecovered CO2 leaving with the bottoms stream 127 from CO2 separation unit 124. As previously mentioned, a portion or all of the CO2 make-up 126 can be recycled CO2 from fermentation. Another portion of the make-up CO2 may be recycled CO2 from the recovered CO2 stream 119 from the CO2 recovery device 118 and CO2 recovered (not shown in FIG. 1) from the CO2 released during acidification in the acidification vessel 101. Make-up CO2 can additionally or alternatively be obtained from one or more external CO2 external sources. These external sources may preferably include biogenically derived CO2 (e.g., CO2 from a brewery, or from a corn or sugarcane ethanol facility).

[0075] From the bottom of the CO2 separation unit 124, a substantially CCh-free (carbon dioxide-free) stream 127 is generated, primarily comprising free medium-chain fatty acids (MCFAs) and dissolved water. This stream is depressurized to atmosphericpressure via throttling valve 128, which may be replaced by a turbine or pressure-exchanger device to recover energy from the depressurization process. At least a portion of the depressurized MCFA / water stream 130 should undergo purification to eliminate heavy impurities. However, a portion of this stream can optionally be diverted into an MCFA bypass stream 129, which is recycled back to the acidification vessel 101 with minimal further processing. If the concentration of heavy impurities in the system exceeds the desired level, the volume of material directed through the bypass stream 129 can be reduced.

[0076] As previously mentioned, the depressurized MCFA / water stream 130 contains heavy impurities, which, if not removed, will accumulate within the system. To prevent this accumulation, at least a portion of the depressurized MCFA / water stream 130 must undergo purification to eliminate these undesirable species. The portion designated for purification may optionally be routed through a heat exchanger 131 to increase its temperature. In some embodiments, a steam stream 132 is utilized for this heating process, although alternative heating methods and integrations may also be employed. Additionally, or alternatively, the depressurized MCFA / water stream may be directed to an optional water separation unit 133, such as a flash vessel or distillation column, where at least a portion of the water is removed as a wastewater stream 134. It is possible that an azeotrope of water and carboxylic acids may form in this water separation unit 133; therefore, further separation of any acids in this wastewater stream 134 may be necessary to prevent the loss of carboxylic acids. Alternatively, or in addition, the wastewater stream 134 may be recycled upstream to the fermentation process (not shown) to replace a portion of the fermentation water input requirements, or it can be recycled to the fermentation broth before it is concentrated to produce the high-concentration clean broth / feed stream 100.

[0077] The substantially water-free stream 135 (or the MCFAs / water stream 130 if a dewatering step is not carried out) is then sent to a MCFA purification unit 136. The purification unit 136 may be, but it is not limited to, a distillation system, an extraction system, or a membrane filtration system. A distillation system, as illustrated in FIG. 1, would most typically use vacuum distillation to remove the purified MCFAs 137 through the top of the purification unit 136, while the heavy impurities 138 whose boiling point is higher than that of the MCFAs, are removed from the bottom portion of the purification unit 136. An extraction system may use an appropriate extractant to remove the heavyimpurities, such as, but not limited to, an ionic liquid that can selectively capture the MCFAs while leaving behind the heavy impurities. A membrane filtration system may use ultrafiltration or nanofiltration membranes with the proper molecular weight cut off, to be able to separate a pure MCFA stream 137 as the permeate, while the heavy impurities 138 are removed as retentate from the system. As noted previously, in some embodiments a portion of the MCFAs present in the system are introduced as part of the feed stream 100; therefore, to prevent accumulation of MCFAs in the system, a portion will need to be removed as an MCFA product stream 139. Thus at least a portion of the purified MCFA stream 137 is removed as product 139 for further separation of the individual MCFAs (e.g., valeric, caproic, heptanoic and caprylic acid). Most of the purified MCFAs in the purified MCFA stream 137, however, will be used as a MCFA recycle stream 140, so that the MCFA present can be used to repeat the acidification of the carboxylic acid salts in the feed stream 100. The MCFA recycle stream 140 may be optionally joined with bypass stream 129, or may be provided to the acidification vessel 101 without the bypass stream. Either the recycled purified MCFAs 140 or the combined streams 129 and 140, which form MCFA stream 145, are sent to the acidification vessel 101 to repeat the acidification step.

[0078] The method and system described above can be implemented to produce a lighter acids product 108 and a purified medium-chain fatty acid (MCFA) product 139. For the method or system utilizing a single column as a purification unit 136, as illustrated in FIG. 1, the overall recovery of carboxylic acids from the feed stream 100 ranges from approximately 75% to 99% on a weight basis, or from approximately 90% to 98% on a weight basis, with higher efficiency observed for shorter carboxylic acids (e.g., acetic acid) and lower efficiency observed for longer carboxylic acids (e.g., valeric) because the longer carboxylic acids experience more losses into various streams. Although not shown in FIG. 1, additional processing steps and equipment may be employed for further fractionation of the lighter acid product 108 and the MCFA product 137 139 into individual acids or other desired product profiles.

[0079] System and Method with Increased Number of Separation stages

[0080] A more versatile system, where individual acids can be recovered, may be achieved by increasing the number and / or size of the separation equipment used in the process. This approach is illustrated in FIG. 2, where, instead of utilizing a single column for the separation of lighter acids 108 (performed in purification unit / column 107) and asingle column for the purification of MCFAs 137 (column 136), which would require further separation and equipment for purification and separation of the lighter acids and MCFAs, multiple columns are employed to directly perform the purification and separation. FIG. 2 depicts a method and system analogous to those shown in FIG. 1, but includes additional unit operations and equipment to directly cause the fractionation of the product streams into individual acids. In the method illustrated in FIG. 2, the bottoms stream 206 from the water removal column 204 is processed through a series of separation or fractionation units 207, 247, and 250 to more thoroughly fractionate the lighter acids and MCFAs present in the bottoms stream 206. Most of the description provided for the embodiment in FIG. 1 also applies to the embodiment in FIG. 2, with each unit operation and stream numbered in the 100s in FIG. 1 corresponding to the 200s numbering in FIG. 2. In FIG. 2, the high-concentration clean broth for the feed stream 200 is obtained in the same manner as described for procuring the high-concentration clean broth for the feed stream 100 in FIG. 1.

[0081] The feed stream 200 contains salts of carboxylic acids with cations such as, but not limited to, sodium, potassium, calcium, magnesium, and combinations thereof. The feed stream 200 is introduced into an acidification vessel 201, which may be a continuously stirred tank reactor (CSTR), where it is contacted with medium-chain fatty acids (MCFAs) 245. These MCFAs can be individual acids such as iso-valeric acid, valeric acid, caproic acid, heptanoic acid, caprylic acid, or combinations thereof, thus optionally, a mixture of MCFAs may also be used as the acidifying agent. During this stage, the carboxylic acid salts in the feed stream 200 are acidified, resulting in a pH drop below 6, preferably below 5, or even lower. Any dissolved carbonates or bicarbonates present are converted to carbon dioxide and may substantially exit at this stage. The resulting acidified mixture 202 is then sent to a water removal column 204, producing a removed water stream 205. Before entering the water removal column, the acidified mixture 202 may optionally pass through one or more heat exchangers 203 for pre-heating. Due to the potential formation of an azeotrope of water and carboxylic acids in the water removal column 204, the removed water stream 205 may contain carboxylic acids and / or MCFAs. Additional separation steps and equipment may be necessary to prevent the loss of acids. Alternatively, the removed water stream 205 may be recycled upstream to the fermentation process to replace some of the fermentation water input requirements, or it can be recycled to join the fermentation broth before concentration to form the feed stream 200.

[0082] The substantially water-free bottoms 206 from this water removal column 204 are sent to a series of fractionation columns or a fractionation train to fractionate each of the lighter acids. The lighter acids are those which are lighter than the MCFAs fed into the acidification vessel 201 (primarily short-chain fatty acids, such as but not limited to, acetic, propionic and butyric acids, though it should be understood that some small amount of carryover of MCFAs such as valeric acid is also possible). The first acid fractionation column 207 in the train is operated to separate acetic acid (C2), which leaves through the first top stream 208 of the fractionation train. The first bottoms 246 of the fractionation train from the first acid fractionation column 207 are sent to the second acid fractionation column 247 in the fractionation train, which is operated to separate propionic acid (C3), which is produced as second top stream 248 of the fractionation train through the top. The second bottom stream 249 of the fractionation train from the second acid fractionation column 247 is sent to the third acid fractionation column 250 in the acid fractionation train, which separates isobutyric and butyric acid (iC4+C4) through the top 251 of column 250. As the prior acid fractionation columns can be operated to target specific acids, the overall separation is highly versatile for producing individual acids. The bottom stream 209 from column 250 is substantially free from the lighter acids. The bottom stream 209 is a mix of free MCFAs and MCFA salts with the cations from the salts in the original high- concentration clean broth / feed stream 200. Proper temperatures, refluxes, and vacuum level are maintained in the separation columns 204, 207, 247 and 250 to maximize the removal of water and each of lighter acids in each respective column, while keeping most or substantially all of the MCFAs at the bottoms of each separation column. Thus, the last bottoms stream 209 leaving the last column in the acid fractionation train is lighter-acid lean and contains primarily MCFAs and MCFA salts.

[0083] Additional columns may be added, depending on which acids are used as the main acidification agent. As an illustrative example, when iso-valeric and valeric acids (iC5 and C5) are used as the main acidification agent, the MCFAs in the system are a mixture of iC5 and C5 MCFAs. The system and method depicted in FIG. 2 also effectively fractionates the MCFAs in the system, thus the last bottoms stream 209 would contain substantially all iC5 and C5 MCFAs in this scenario. Thus, as the fermentation may produce some amount of iC5 and C5 MCFAs, these MCFAs will tend to concentrate in the system, especially when iC5 and C5 MCFA are also used as the acidification agents. However, the choice of iC5 and C5 is illustrative as other MCFAs can be chosen as themain acidification agent instead of iC5 and C5. For example, caproic acid (C6) may be chosen as the main acidification agent, in which case, iC5 and C5 produced in fermentation, would become part of the lighter acids because iC5 and C5 are lighter or more volatile than C6. In such a scenario, another acid fractionation column would be included in the acid fractionation train next to fractionation unit 250 to separate iC5 and C5 at the top and the final bottoms stream 209 exiting now from the additional separation column would be substantially free of iC5 and C5 MCFAs and other lighter acids. Similarly, if, for instance, caprylic acid (C8) is chosen as the main acidification, then all other acids lighter than C8 (i.e., C7 and lighter) would then be part of the lighter acids fractionated in the acid fractionation train and may require their own acid fractionation columns (or alternatively a single fractionation column could be used to separate C5-C7 acids from C8), thus ending up with a final bottoms stream 209 that is substantially free of any acid lighter than C8.

[0084] The final bottoms stream 209 may optionally be passed through one or more heat exchangers 203 to be cooled and to recover a portion of the heat energy of this stream. One option is to use the final bottoms stream 209 to pre-heat the acidified mixture stream 202 before it is fed to the water removal column 204, as shown in FIG. 2, though other energy integrations may also be implemented without departing from the spirit and scope of the invention. Further trim cooling may be implemented as needed (not shown in FIG. 2). As discussed in relation to FIG. 1, as the MCFAs / MCFA salt mix of the final bottoms stream 209 is cooled, it becomes more viscous and may become difficult to handle. A water stream 241 may be optionally added to thin the mixture, thus decreasing viscosity of the mixture. The water may be added before or, more preferably and as shown in FIG. 2, after cooling the final bottoms stream 209. It may be preferable to add the water after the temperature of the final bottoms stream 209 has been decreased to 100°C or less but before the temperature has been fully decreased to the target operating temperature of the upcoming contactor or extraction column 211. The lower viscosity achieved by adding the water allows easier pumping and handling at the lower operating temperatures suitable for the downstream contactor or extraction column 211. The amount of water to be added to decrease viscosity can range from 1 to 20% w / w of the total mix (i.e., the total mass or mass flow rate of the bottoms stream 209 and the added water stream 241) or preferably from 5 to 15% w / w of the total mix, forming a MCFAs / MCFA salt / water stream 243. Before the MCFAs / MCFA salt stream (209 or 243) is fed to the contactor, an optional bypass stream242 may be taken and directed to the acidification vessel 201 for the MCFAs present in the stream to act as an acidification agent for the carboxylic acids in the feed stream 200.

[0085] The remaining MCFAs / MCFA salt stream (244 243 or 209, depending on which optional steps are taken) is subjected to a MCFA acidification and extraction and cation removal step, which may be performed in liquid-liquid or gas-liquid contactor, such as, but not limited to, a hollow-fiber membrane contactor or an extraction column 211 (referred to as a contactor going forward). This contactor 211 operates at elevated pressures ranging from 200 to 1500 psi or preferably from 600 to 1200 psi; therefore, the MCFAs / MCFA salt stream (244, 243 or 209) is pumped to such elevated pressures using pump 210 and introduced into the contactor 211. A subcritical liquid, subcritical gaseous, or supercritical CO2 stream 214 is introduced at or near the bottom or on the other side of the contactor 211 away from the middle section where the MCFAs / MCFA salt stream is introduced using CO2 pump 215 to achieve the required pressure. In the contactor 211, the MCFA salts are converted back into free MCFAs by the subcritical liquid, subcritical gaseous, or supercritical CO2 214. A water stream 212 is pumped to the proper elevated pressure using pump 213, then introduced at or near the top or on the other side of the contactor 211 (i.e., opposite to where the CO2 214 is introduced). In some embodiments, the water stream 212 is substantially demineralized or deionized or distilled water. As the MCFA salts are acidified and converted to free MCFAs in the organic phase, carbonates, or more preferably bicarbonates, are formed with the freed salt cations. The bicarbonates and any carbonates and the cations move to the water phase and are thus removed from the organic phase. The amount of water provided to the contactor 211 should be sufficient to ensure substantial extraction of the carbonates / bicarbonates and cations, and should also avoid precipitation of certain bicarbonates that have relatively low solubility, such as sodium bicarbonate. In addition, in the lower section of the contactor 211, the rising CO2 contacts the water / aqueous phase and back extracts and recovers any MCFAs that might have dissolved into the water / aqueous phase in the upper section of the contactor 211 where the MCFAs in the organic phase are in contact with the water / aqueous phase. A water or aqueous phase stream 216 exits through the bottom of the contactor 211 carrying the carbonates / bicarbonates, cations and other water-soluble species. Some of the pressure work can be recovered from the water or aqueous phase stream 216 by depressurizing the stream using a throttling valve 217 or a turbine or pressure exchanger device, so that some of the energy from depressurization can be captured for use in other devices.

[0086] A large portion of the dissolved CO2 in the water or aqueous phase stream 216 is flashed when the pressure is decreased to atmospheric, and the now depressurized stream water / aqueous phase may be optionally sent to a CO2 recovery device 218. The CO2 recovery device may be, but is not limited to, a flash vessel, steam stripper, an air stripper, or a heated flash vessel, wherein flashed CO2 may be recovered. Bicarbonate in the water or aqueous phase stream 216 may be converted to carbonate in the CO2 recovery device 218, further recovering more CO2 for reuse / recy cling and reducing CO2 make-up requirements. The recovered CO2 219 may be repressurized and recycled to the contactor 211, for example. The CO2 recovery bottom stream 220 will contain the resulting carbonate (and any unconverted bicarbonate), and may be sent back to fermentation to act as the buffering agent to control pH. An optional carbonate purge stream 221 may be taken to avoid accumulation of species such as cations and other water-soluble species in the system. At the acidogenic fermentation (not shown in FIG. 2), CO2 from these carbonates and bicarbonates is released as this buffering agent neutralizes the carboxylic acids (SCFAs and MCFAs) as they are formed and pH is controlled. The resulting CO2 from the fermentation may be cleaned to remove other gases such as hydrogen sulfide, ammonia, and hydrogen, then pressurized to the proper pressure and recycled as at least a portion of the CO2 makeup 226 provided to the contactor 211.

[0087] Returning attention to the contactor 211, the organic phase stream 223 containing dissolved CO2, free MCFAs and a small amount of water exits the equipment at or near the top of the contactor. The organic phase stream will be substantially free from salts including cations. The organic phase stream 223 is sent to CO2 separation unit 224, which may be a distillation column or a flash vessel. The pressure in the CO2 separation unit 224 may be maintained to remove CO2 only by heat, or alternatively, the pressure of the stream may be reduced to aid with the separation of the much more volatile CO2. When the pressure is maintained high, losses of the potential energy contained in the pressurized CO2 stream 225 are minimized, but the overall recovery of the CO2 may be somewhat reduced. When the pressure is dropped, the potential energy of the pressure in the stream is difficult to effectively recover, but the overall CO2 recovery is enhanced. The recovered CO2 stream 225 exits the CO2 separation unit 224 and is recycled back to the contactor 211 as subcritical liquid, subcritical gaseous or supercritical CO2 stream 214 as useful in the unit. A pump 215 is used to bring the recovered CO2 stream up to the required pressure for use in the contactor 211.

[0088] A CO2 make-up stream 226 may be required to replenish lost CO2 from the system. For example, a portion of CO2 exits the contactor 211 as carbonates / bicarbonates and dissolved CO2 in the aqueous phase 216, and a portion of the CO2 in the CO2 separation unit 224 leaves with the bottoms stream 227. At least a portion of the CO2 make-up stream 226 can be provided by recycled CO2 from fermentation. The CO2 make-up stream 226 may also be provided by CO2 recycled from the recovered CO2 stream 219 from the CO2 recovery device 218 and CO2 recovered from the CO2 released during acidification in acidification vessel 201 (not shown in FIG. 2). Alternatively, or additionally, the CO2 make-up stream 226 may be provided by one or more external sources. In some embodiments, the externally-sourced CO2 is biogenically derived (e.g., CO2 from a brewery, or from a corn or sugarcane ethanol facility).

[0089] From the bottom of the CO2 separation unit 224, a substantially CCh-free MCFA / water stream 227, is produced, which contains mostly free MCFAs and dissolved water and, as mentioned, is substantially free of CO2. This stream is depressurized to atmospheric pressure using one or more energy recovery devices 228, which can include a throttling valve, a turbine, and / or a pressure-exchanger device to recover some of the energy from the depressurization of the stream. The MCFA / water stream 227 will carry heavy impurities which will accumulate in the system if not otherwise removed. To prevent a buildup of heavy impurities, at least a portion of the depressurized MCFA / water stream 227 should be purified. However, a portion of the depressurized MCFA / water stream 227 can optionally be split into an MCFA bypass stream 229, which may be recycled back to the acidification vessel 201 with minimal further processing. If the amount of heavy impurities in the system is higher than desired, the amount of material sent through the bypass stream 229 can be reduced.

[0090] At least a portion of the depressurized MCFA / water stream 227 must be purified to remove the heavy impurities to prevent accumulation of these undesirable species in the system. The portion of the depressurized MCFA / water stream 227 to be purified, (i.e., depressurized MCFA / water stream 230), may optionally first be directed through a heat exchanger 231 to heat up the depressurized MCFA / water stream 230. In some embodiments, a steam stream 232 is used to heat up the depressurized MCFA / water stream 230, but other heating methods and integrations may also be used. The depressurized MCFA / water stream may additionally or alternatively be sent to an optionalwater separation unit 233, which could be, but is not limited to, a flash vessel or a distillation column, where at least a portion of the water in the depressurized MCFA / water stream 230 is removed as a water stream 234. It is possible that an azeotrope of water and carboxylic acids may be formed in this water separation unit 234, so further separation of any acids in this water stream 234 may be optionally necessary. Alternatively, or additionally, to avoid the loss of acids, the water stream 234 may be recycled upstream to the fermentation to replace some of the fermentation water input requirements, or it can also be recycled to before concentration of the fermentation broth which becomes high- concentration clean broth 200. The substantially water-free stream 235 (or the MCFAs / water stream 230, if the optional flash is not performed) is then sent to a purification unit operation 236. Though shown as a single column where the MCFAs are fractionated, the MCFA purification may also be a fractionation train with several columns or other pieces of equipment. The purification unit 236 may be, but is not limited to, one or more distillation columns. In some embodiments, each MCFA may be individually fractionated, and each MCFA may be fractionated and produced as a product from an individual purification unit. In other embodiments only some of the MCFAs are individually fractionated, and a mixture of MFCAs is also produced. For example, in the illustration of FIG. 2, where the main acidification agent is a combination of iC5 and C5 MCFAs, the purification unit 236, which may be, but is not limited to, a distillation system, will separate purified iC5 and C5 237 through the top, while the bottom stream 252 is sent on to another separation unit 253. This separation unit 253 may be, but it is not limited to, a distillation system, an extraction system, a membrane filtration system. A distillation system, as illustrated in FIG. 2, would most typically use vacuum distillation to remove a purified caproic acid (C6) stream 254 through at the top of the vessel, while acids larger than or equal to heptanoic acid (C7) including any heavy impurities are removed through the bottom stream 238 of separation unit 253. An extraction system may use an appropriate extractant to remove the heavy impurities from the bottoms stream 238. A membrane filtration system may use ultrafiltration or nanofiltration membranes with the proper molecular weight cut off, to be able to separate a pure C6 stream 254 as the permeate, while the acids >C7 and heavy impurities 238 are removed as retentate from the system. Optionally, stream 238 may be sent to further purification, such as, but not limited to, distillation, extraction or membrane filtration to separate C7, C8 and any other MCFA that might be present, while the heavy impurities are removed and purged from the system.

[0091] Because some of the iC5 and C5 in stream 237 in the illustration of FIG. 2, are provided to the system with the feed stream 200, a portion of the iC5 and C5 acids will need to be output from the system as a product stream 239. A portion of the purified iC5 and C5 237 will be sent as product stream 239 for further separation of iC5 from C5, or as a final combined product to be packaged. Most of the purified iC5 and C5 stream 237, however, will be used as a recycle stream 240 and optionally joined with bypass stream 229. Either the recycled purified iC5 and C5 240 or both combined streams 229 and 240, which form stream 245, are sent to the acidification vessel 201 to repeat the acidification process on the carboxylic acids entering the acidification vessel with feed stream 200. As a summary, the intended products in this illustrative system are the C2, C3, iC4+C4 streams (208 248 251) and the purified iC5 and C5 stream 239 and C6 stream 254. Though not depicted in FIG. 2, depending on the composition of the acids in the system, additional separation steps and equipment may be used to produce longer MCFAs, such as C7 and C8 acids, as product streams.

[0092] Separation Method and System with a Dedicated Lights Separator

[0093] A third method and associated system are depicted in FIG. 3, the method and system being substantially similar to those depicted in FIG. 2 and as described above for the recovery of carboxylic acids from a solution containing carboxylic acids salts, such as those obtained from carboxylic acid fermentation. Most of the description above for the embodiment for FIG. 1 and FIG. 2 also applies to the embodiment in FIG. 3, with each unit operation and stream with 100s numbering in FIG.1 and 200s numbering in FIG. 2, corresponding to the 300s numbering in FIG. 3. However, the method and system depicted in FIG. 3 differs from those depicted in FIG. 2 in that they include a dedicated lights separator unit operation 358. Instead of sending the acidified mixture stream 202 directly to the water removal 204 and fractionation train (columns 207, 247 and 250) as depicted in FIG. 2, acidified mixture stream 302 in FIG. 3 is first heated by optionally passing through one or more heat exchangers 303 and then heated in one or more heat exchangers 356 heated with steam 357. In some embodiments, the first heat exchanger 303 and second heat exchanger 356 can be integrated into one heat exchanger. The acidified mixture stream 302 is then sent to a lights separator unit 358, which can be, but it is not limited to, a flash column, a distillation column, or an evaporator. In some embodiments, the lights separation unit 358 is an evaporator that is configured to handle viscous liquids or slurries (mix ofsolids and liquids) that are more difficult to handle during evaporation. Such an evaporator can be, but it is not limited to, a falling-film, a thin-film dryer, a thin-film evaporator or a wiped-film evaporator. These types of devices can handle less flowable, more viscous streams, which makes the method more advantageous because it allows for a lesser amount of MCFA or for heavier MCFAs, which tend to be more viscous, to be employed as acidifying agent 345 in the acidification vessel 301 and also avoids heavy viscous, contaminating and / or corrosion-causing impurities from entering the water removal unit 304 and fractionation train (307, 347 and 350). This may allow these units to be made of less- expensive materials of construction and / or with simpler operational configurations, thus saving on overall system costs. The lights separation unit 358 may be operated at temperatures and pressures (or at a vacuum) to evaporate most or substantially all the lighter components (water and lighter acids) in the acidified mixture stream 302 while striving to keep from evaporating heavier components or MCFAs, which are used for acidification in this stream.

[0094] In FIG. 3, the high-concentration clean broth feed stream 300 is procured or obtained in the same manner as described above for the description of FIG.1 for procuring the high-concentration clean broth for use as the feed stream 100. In the method depicted in FIG. 3, the main MCFA acidification agent is illustratively a mix of iso-valeric and valeric acids (iC5 and C5), which are produced by fermentation. Due to the additional separation step and equipment, such as the lights separation unit 358, a large portion of these acids are captured and recycled for reuse. Thus, in lights separation unit 358, a light acids stream 359 is obtained that contains substantially all components lighter than iC5 and C5 acids, these lighter components being evaporated or otherwise separated from the iC5 and C5 acids present in the acidified mixture stream 302. The lights stream is sent to water removal 304 and the following fractionation train (columns 307, 347 and 350) and separated, similar to the method and equipment described above for FIG. 2.

[0095] The light separator bottom stream 309 from lights separator 358 is substantially free from the components lighter than C5 and iC5. In some embodiments, the light separator bottom stream 309 contains less than 10 wt.% or less than 5 wt.% of components lighter than C5 and / or iC5. In some embodiments, the light separator bottom stream 309 contains less than 3 wt.%, or less than 2 wt.%, or less than 1 wt.% of components lighter than C5 and / or iC5. Again, the choice of iC5 and C5 is illustrative, asother MCFAs can be chosen as the main acidification agent instead of iC5 and C5, which should improve the separation in lights separator 358 if the molecular weight of the MCFAs increases and the separation train can be adjusted accordingly to handle other MCFAs. For example, caproic acid (C6) may be chosen as the main acidification agent, in which case, iC5 and C5 acids produced in fermentation would become part of the light acids stream 359, because iC5 and C5 are lighter and more volatile than C6. In such a scenario, the lights separator 358 would be operated by controlling feed rates, temperatures, and vacuum level to substantially evaporate all iC5 and C5 and lighter components and capture them as the light acids stream 359. Meanwhile, the separator bottoms 309 from the lights separator 358 would be substantially free of iC5 and C5 in addition to all the other lighter acids including water. The iC5 and C5 acids, along with all the lighter components in the light acids stream 359 are sent to water removal 304 and to the fractionation train (columns 307, 347 and 350). If desired, an additional column (not shown) may be positioned in the system next to the butyric acid separation column 350 to separate iC5 and C5 acids. Similarly, if, for instance, caprylic acid (C8) is chosen as the main acidification, then all other acids lighter than C8 (i.e., C7 and lighter) would then be part of the lighter components (acids and water), the light acids stream 359, removed in lights separator 358 and sent to water removal 304 and fractionated in the fractionation train and they may be further processed in their own fractionation columns, thus ending up with a bottoms stream 309 that is substantially free of any acid lighter than C8.

[0096] After the water removal 304 and the fractionation train (307, 347, 350 or other further columns if heavier acidification agents are used as exemplified above), the final bottoms stream 355 of the last distillation column in the train (350 in the illustration of FIG. 3 or other column not shown if heavier acidification agents are used), will contain the heavier MCFAs and other heavy components that evaporated in lights separator 358. These heavier MCFAs and other components will be primarily the main acidification agent, illustratively iC5 and C5 in FIG. 3. This final bottoms stream 355 can then be joined with either the substantially water free MCFA acidification agent 335 coming from the water separation unit 333 or with the CO2 free MCFA stream 330 from the CO2 separation unit 324 and then sent to MCFA purification steps. The MCFA purification steps may also be performed in a fractionation train, where some of, or optionally each of, the MCFAs are fractionated. In method and system depicted in FIG. 3, where the main acidification agent is illustratively iC5 and C5 acids, MCFA separation unit 336, which may be, but is notlimited to, a distillation system, will separate purified iC5 and C5 acids through the top to produce a purified C5 stream 337, and the MCFA bottom stream 352 is sent to another separation unit, secondary MCFA separation unit 353. Secondary MCFA separation unit 253 may be, but is not limited to, a distillation system, an extraction system, or a membrane filtration system. A distillation system, as is depicted in FIG. 3, may use vacuum distillation to remove purified caproic acid (C6) as a caproic acid stream 354 through the top of the distillation system, while acids larger than or equal to heptanoic acid (C7) and heavy impurities, whose boiling point is higher than C6, are removed through the bottoms of purification unit 353 as a heavy stream 338. Alternatively, an extraction system (not shown) may use an appropriate extractant to remove the heavy impurities and produce the desired MCFA streams. For example, a membrane filtration system may use ultrafiltration or nanofiltration membranes with the proper molecular weight cut off, to be able to separate the purified C6 stream 354 as the permeate, while the C7+ acids and heavy impurities 338 are removed as retentate from the system. Optionally, the heavy stream 338 containing C7+ and heavy impurities may be sent to further purification (not shown in FIG. 3), such as, but not limited to, distillation, extraction, or membrane filtration to separate C7, C8, and any other heavier acids that might be present, while the heavy impurities are removed and purged from the system.

[0097] Returning attention to the lights separator 358, the lights separator bottom stream 309 may be optionally cooled by passing through one or more heat exchangers 303 to exchange heat with acidified stream 302, which may require heating, thus allowing heat recovery. Further trim cooling may be implemented as needed (not shown in FIG. 3). As cooling occurs, the MCFAs / MCFA salt mix in the lights separator bottom stream 309 becomes more viscous, so a small amount of water 341 may be optionally added to thin the mixture and to decrease the viscosity. The salts of MCFAs (and even LFCAs for that matter), especially the potassium salts, exhibit this characteristic, where a small amount of water can hydrate the salts enough to allow them to thin out and even liquify from a solid state. The water may be added before or, as shown in FIG. 3, after cooling, although more likely it will be after temperature of the lights separator bottom stream 309 has been decreased to 100°C or less, but before temperature fully decreases to the target operating temperature going into the contactor unit 311. The lower viscosity achieved by adding this small amount of water allows easier pumping and handling at the lower operating temperatures used in the contactor unit 311. The amount of water to be added to decreaseviscosity can range from 1 to 20% w / w of the total mix (i.e., the total mass or mass flow rate of the bottoms stream 309 and the added water stream 341), or preferably from 5 to 15% w / w of the total mix.

[0098] Further cation removal and acidification of the MCFA salts in liquid-liquid contact 311, CO2 separation in CO2 separation unit 324, and the processing of the bottoms 327 from this unit 324, as well as the processing and recycle to fermentation of the aqueous phase exiting contactor 311, occurs in the same manner as described for FIG. 2 above, with each piece of equipment or stream labeled 3XX in FIG. 3 corresponding with each piece of equipment or stream labeled 2XX in FIG. 2, where XX is any two digit number.

[0099] Method and System Having Increased MCFA Extraction Control

[0100] A fourth method and associated system are depicted in FIG. 4. The fourth method and system are similar to those depicted in FIG. 1 and described above for the recovery of carboxylic acids from a solution containing carboxylic acids salts, such as those obtained from carboxylic acid fermentation. As such, the description of the method and system depicted in FIG. 1 is applied here as well with streams and equipment having 100’s numbering in FIG. 1 generally applying to the similar streams and equipment having 400’ s number in FIG. 4, but for the differences discussed below.

[0101] The method and system depicted in FIG 1 includes one contactor 111, which both acidifies the MCFAs while removing cations and extracts the MCFAs from the aqueous phase. The method and system depicted in FIG. 4 provides more control to this arrangement, performing separation of the acidification agent / cation removal from the MCFA extraction from the aqueous phase using two separate unit operations. The first separation is performed in a first column or contactor 411, which performs the acidification and cation removal, while a second column or contactor 450 performs the extraction of the MCFAs from the resulting aqueous phase raffinate 449 exiting the first column or contactor 411. Other than the details around the separation columns / contactors 111 in FIG. 1, which is separated into two units (411 and 450) in FIG. 4, the descriptions above for the embodiment for FIG. 1 also applies to the embodiment in FIG. 4, with each unit operation or stream labeled with 1XX numbering in FIG.1 corresponding to each unit operation or stream with 4XX numbering in FIG. 4, where XX is any two digit number.

[0102] In FIG. 4, the high-concentration clean broth for the feed stream 400 is procured or obtained in the same manner as described above for the description of FIG.1 for procuring the high-concentration clean broth for the feed stream 100. In FIG. 4, as described above for FIG. 1 with its corresponding 100s streams, the bottoms stream 409 from the lighter acids recovery column 407, which is mostly MCFA salts with their corresponding cations and free MCFAs, may optionally be cooled down by one or more heat exchangers 403. Further trim cooling may be implemented as needed (not shown in FIG. 4). Then optionally a small amount of water 441 is added, as described and in the amounts ranging from 1 to 20% w / w of the total mix (i.e., the total mass or mass flow rate of the bottoms stream 409 and the added water stream 441), 3 to 18% w / w of the total mix, or more preferably from 5 to 15% w / w of the mixture, to decrease viscosity and thin it out resulting in stream 443. This small amount of water 441 may be added before or, as shown in FIG. 4, after stream 409 has been cooled down or after it has been partially cooled down to below 100°C but before it is fully cooled down to the target operating temperature in contactor 411. Further, optionally a bypass 442 is diverted back to the acidification vessel 401 resulting in stream 444.

[0103] The remaining MCFAs / M FA salt stream (444, 443 or 409 depending on which optional steps are taken) is directed to a MCFA acidification and extraction and cation removal step. Though the equipment is referred to as a first contactor 411, this step may be performed in a liquid-liquid or gas-liquid contactor, such as, but not limited to, hollow-fiber membrane contactor or an extraction column. This first contactor 411 operates at elevated pressures ranging from 200 to 1500 psi or preferably from 600 to 1200 psi; therefore, the MCFAs / MCFA salt stream 444, 443 or 409 is pumped to such elevated pressures using one or more pumps 410. Subcritical gaseous, subcritical liquid or supercritical CO2447 is added to the pressurized stream 444 as the stream is fed to the contactor 411 or before the stream is fed. Alternatively, the subcritical liquid, subcritical gaseous or supercritical CO2447 may be added to the column without being mixed with the pressurized MCFA stream 444. Water 412 is introduced at the top of the first contactor 411 and pumped to the proper elevated pressure using one or more pumps 413. The water stream 412, as introduced at the top of the first contactor 411, may be substantially demineralized or deionized or distilled water. The MCFA salts present in the first contactor 411 are acidified by the carbonic acid formed and are converted back into free MCFAs. Carbonates and bicarbonates also form by this process. The carbonates and / or bicarbonatesand the displaced cations move to the water or aqueous phase within the first contactor 411, and thus they are removed from the organic phase. The amount of water needed should be enough to ensure substantial extraction of the carbonates / bicarbonates and cations, but also to avoid precipitation of certain bicarbonates with relatively low solubility such as sodium bicarbonate. The water or aqueous phase 449 exits through the bottom of the contactor 411 carrying, as mentioned, the carbonates / bicarbonates, the cations, and other water-soluble species. Some amount of solubilized MCFAs may also be present in the aqueous phase 449; therefore, this aqueous phase raffinate 449 is sent to a second contactor 450 for recovery of the MCFAs. In the second contactor 450, the MCFAs still present in the aqueous raffinate are extracted by subcritical liquid, subcritical gaseous or supercritical CO2 414, which is introduced at the bottom or the opposing side of the second contactor 450 from the aqueous phase feed 449 position using one or more CO2 pumps 415. The aqueous raffinate stream 416 leaving the second contactor 450 may be depressurized using a throttling valve 417 or a turbine or pressure exchanger device to recover some of the energy from depressurization for use in other devices or parts of the process.

[0104] When the raffinate stream is depressurized, a large portion of the dissolved CO2 is flashed. The now depressurized aqueous raffinate stream 416 may be optionally sent to a CO2 recovery unit 418, which may be, but is not limited to a flash vessel, a steam stripper, an air stripper, or a heated flash vessel. In the CO2 recovery unit 418, the flashed CO2 may be collected as a recovered CO2 stream. Bicarbonate present may be converted to carbonate, increasing the amount of CO2 recovered. The recovered CO2 419 may be repressurized and recycled to units 411 and 450 for reuse. The resulting carbonate stream 420 may be recycled to acidogenic fermentation to act as the buffering agent to control pH, though an optional purge 421 may be taken to avoid accumulation of species such as cations and other water-soluble species in the system. At the acidogenic fermentation (not shown in FIG. 4), CO2 from these carbonates and bicarbonates is released as this buffering agent neutralizes the carboxylic acids (SCFAs and MCFAs) as they are formed and pH is controlled. This resulting CO2 may be cleaned to remove other gases such as hydrogen sulfide, ammonia, and hydrogen, pressurized to the proper pressure, and recycled as CO2 make-up 426 to unit 411 and 450. Excess recovered CO2 may be optionally used for other purposes, such as carbon utilization (e.g., reacting it with H2 to produce other valuable products) or storage (i.e., sequestration) to improve the carbon intensity score of the process by decreasing greenhouse gas emissions.

[0105] The organic phase stream 423 exiting the first contactor 411 is combined with the organic phase stream 446 exiting second contactor 450, forming a combined organic phase stream containing dissolved CO2, free MCFAs, and a small amount of water that is dissolved in the organic phase. The combined organic phase stream is substantially free from salts including cations. The combined stream formed by streams 423 and 446 is sent to CO2 separation unit 424, which may be a distillation column or a flash vessel, though other appropriate equipment may be used as needed. The CO2 separation unit 424 may be operated at a pressure that is lower than the upstream process to aid with the separation of the much more volatile CO2. Alternatively, to minimize losses of potential energy contained in the pressurized CO2 stream 425, the pressure in the CO2 separation unit 424 may be maintained at elevated levels, such that the CO2 in the combined organic phase stream is removed mostly by heat. The recovered CO2425 exits separation unit 424 and can be directed to other portions of the process for reuse. For example, as illustrated in FIG. 4, a portion of the recovered CO2 425 forms a CO2 recycle stream 448 that is recycled back to be re-pressurized using one or more pumps 415 and the fed to the second contactor 450 as subcritical liquid, subcritical gaseous or supercritical CO2 stream 414 as required. A second portion of the recovered CO2 425 is sent as subcritical liquid, subcritical gaseous or supercritical CO2 stream 447 to the first contactor 411 as described above.

[0106] Make-up CO2 426 may be added to the system to replenish the CO2 that exits the second contactor 450 as carbonates / bicarbonates, as dissolved CO2 in the aqueous phase 416, and / or as unrecovered CO2 leaving with the bottoms stream 427 from CO2 separation unit 424. As already mentioned, part of the CO2 make-up 426 can be recycled CO2 extracted from the fermentation. CO2 419 from the CO2 recovery device 418 and CO2 recovered from the CO2 released during acidification in acidification vessel 401 (not shown in FIG. 4) and / or CO2 from any external sources may also be at least a portion of the CO2 make-up stream 426. In some embodiments, the CO2 is biogenically derived (e.g., CO2 from a brewery, or from a corn or sugarcane ethanol facility).

[0107] From the bottom of CO2 separation unit 424, a substantially CCh-free stream 427 emerges, which contains mostly free MCFAs and dissolved water. This stream is depressurized to atmospheric pressure using throttling valve 428 or an energy-recovery device to recover some of the energy from the depressurization. The depressurized MCFA / water stream can be split into an optional bypass 429, which directs the flow of thedepressurized MCFA / water stream back to the acidification vessel 401 and stream 430, which is sent downstream to MCFA purification as described above for the corresponding steps in the method and system depicted in FIG. 1. It is also important to note that if the aqueous raffinate 449 exiting contactor 411 has an acceptably low concentration of MCFAs, it may be decided to skip the second contactor 450, thus avoiding the need for the subcritical liquid, subcritical gaseous or supercritical CO2 extraction and saving significant energy costs.

[0108] Method and System with Improved Medium Chain Fatty Acid Recovery by Using a Heavy Compound as Entrainer

[0109] A fifth method and associated system is depicted in FIG. 5. The method and system are similar to those depicted in FIGS. 1-4 and described above for the recovery of carboxylic acids from a solution containing carboxylic acids salts, such as those obtained from carboxylic acid fermentation. As with previous methods and systems described herein, a fermentation broth is cleaned and provided to the system as a feed stream 500 then subjected to acidification and subsequent recovery and separation steps. The description of the steps and equipment of the previous figures applies to the method and system depicted in FIG. 5. Other than the addition of the heavy compound or substance 551 in FIG. 5 as will be described below, all the other description of all the unit operations and streams in FIGS. 1 and 4 apply directly to the embodiment in FIG. 5, with each unit operation and stream labeled with 1XX or 4XX numbering in FIGS. 1 and 4, respectively, corresponding to the same unit operations and streams having 5XX numbering in FIG. 5, where XX is any two-digit number.

[0110] The method and system depicted in FIG. 5 differs from those in FIG. 4 in that a heavy compound or substance 551 is added to the CO2 stream 548 before the CO2 is provided to the second contactor 550. The heavy compound aids the CO2 extraction of the MCFAs from the aqueous raffinate 549, with subcritical liquid, subcritical gaseous or supercritical CO2, in the second contactor 550 and reduces losses of MCFAs in the purification bottoms 538 during purification in the MCFA purification unit 536. The heavy compound may act as an entrainer, entraining heavy impurities in the stream and causing them to be caught in the bottoms of the purification equipment for removal from the system, while minimizing MCFA losses, which would occur in previous embodiments shown in FIGs. 1-4. This heavy compound or substance 551, which is added together with the CO2stream 548 and 526 entering the second contactor 550, should be highly insoluble in water so as to increase the efficiency of the recovery of the MCFAs from the aqueous raffinate 549 entering contactor 550, should have a high boiling point so as to remain in the bottoms 538 of the MCFA purification unit 536, and should preferably be low cost. In some embodiments, the heavy compound has a water solubility of 1 g / L, 0.5 g / L, or preferably below 0.1 g / L. In some embodiments, the heavy compound has a boiling point at atmospheric pressure of about 240°C, 250°C, 275°C, 300°C, 325°C, 350°C, 360°C or greater. The heavy compound may be exogenically sourced or endogenic to the method and system. Some example heavy compounds that are suitable for use include, but are not limited to, compounds that are less expensive than the MCFAs and whose losses are more affordable such as, but not limited to, heavy fatty acids with carbon chain-length larger than C8, such as, but not limited to, capric, lauric, myristic, palmitic, stearic acids, or other heavy triglyceride oils that have high boiling points and that are stable at high temperatures, such as, but not limited to, avocado oil.

[0111] Method and System With Heavier Acidification Agent

[0112] In all the above methods and system depicted in FIGS. 1-5, although not shown in the figures, external or extraneous or non-endogenous MCFAs (i.e., MCFAs not produced in the fermentation) ranging from valeric acid (C5) through nonanoic (C9) acids and / or LCFAs ranging from decanoic (CIO) acid (capric) or longer, such as, dodecanoic (C12) acid (lauric), tetradecanoic (C14) acid (myristic), hexadecanoic (C16) acid (palmitic) acid or octadecanoic (Cl 8) acid (stearic), may be used as acidification agents by adding them to acidification vessel (101, 201, 301, 401 or 501, respectively) to effect acidification and they may then be recovered as described in the embodiments in FIGS. 1-5. Optionally, the purification of external or extraneous or non-endogenous MCFAs or LCFAs (purification units 136, 236, 336, 436, 536 as described in FIGS. 1-5, respectively) may be the same membrane filtration unit employed upstream to polish the incoming feed stream (100, 200, 300, 400, 500 in FIGS. 1-5, respectively) by sending the depressurized MCFA or LCFA stream leaving the CO2 separation unit (124, 224, 324, 424, 524 in FIGS. 1-5, respectively) either before or after taking the bypass (streams 129, 229, 329, 429, 529 in FIGS. 1-5, respectively) to an acidification tank prior to the broth polishing membrane filtration unit (not shown in figures). The heavier fatty acids are more water insoluble thus potentially avoiding the need for subcritical liquid, subcritical gaseous or supercritical CO2extraction (bottom portion of contactor units 111, 211 and 311 and second contactor units 450 and 550). Some of the heavier acids are also less costly, and so may be economically preferable. With heavier fatty acids, the use of an appropriate separator or evaporation equipment that can handle viscous liquid or slurry streams, such as a thin-film dryer, a thin- film evaporator or a wiped-film evaporator, as described in FIG. 3, becomes more crucial but the method and associated system can be simplified as shown in FIG. 6.

[0113] The method and associated system depicted in FIG. 6 shows a method and system similar to those depicted in FIGS. 1 and 3 described above for the recovery of carboxylic acids from a solution containing carboxylic acids salts, such as those obtained from carboxylic acid fermentation. The method and associated system depicted in FIG. 6 differ from those in FIG. 3 in that FIG. 3 uses as an exemplary illustration an MCFA (e.g., C5 and iC5) as the main acidification agent, whereas FIG. 6 uses an inexpensive external or extraneous or non-endogenous heavy fatty acids (EHF A) as the main acidification agent. This EHFA is a single or mixture of fatty acids that are highly insoluble in water to below 1 g / L, 0.5 g / L, or preferably below 0.1 g / L. In some embodiments, the EHFA is obtained from natural oils, lipids or fats, such as, but not limited to, coconut oil, palm oil, palm kernel oil, soybean oil, sunflower oil. The EHFA can be, but is not limited to, an MCFA, such as caprylic acid (C8), or LCFAs, such as capric acid (CIO), lauric acid (C12), myristic acid (Cl 4), palmitic acid (Cl 6), stearic acid (Cl 8), or combinations thereof. Smaller acids, such as lauric or myristic acid, might be preferred because larger acids require a larger mass quantity as the amount of EHFAs required is dependent on meeting the molar stoichiometric amount of the acidification agent needed to fully acidify all the SCFA and MCFA salts entering with the feed stream 600. However, the use of EHFAs can result in reduction or removal of certain steps. For example, because the EHFA acting as acidification agent is highly water insoluble, the system and method depicted in FIG. 6, unlike the method and system depicted in FIG. 3 (and those depicted in FIGS.l, 2, 4 and 5, for that matter) does not require extraction of the EHFAs from the aqueous phase 616 exiting the fatty acid (FA) acidification / cation removal column 611. In addition, due to the low water solubility of the EHFAs, after separating the CO2 625 from the EHFAs 627 in CO2 separation unit 624, the EHFAs may be optionally bypassed as stream 629 and sent to the front-end acidification vessel 601 without first passing through a water removal step, such as depicted as 333 in FIG. 3 (or 133, 233, 433 and 533 in FIG. 1, 2, 4 and 5, respectively). Instead, the CCh-free EHFA stream 627 may be directly sent to purification 636. Optionally, the CO2-free EHFAstream 627 may be first heated up in heat exchanger 631 and before being sent to purification 636. Furthermore, the EHF As can potentially be acidified with CO2 at lower pressures (<500 psi) even at relatively high temperatures (as high as 90°C). The ability for the EHF As to be acidified at these higher temperatures is useful to maintain a low viscosity in the fatty acid (FA) acidification / cation removal column 611.

[0114] Another difference between the methods and systems depicted in FIG. 3 and FIG. 6 is that because the EHFA acidification agents is heavier than all the SCFAs and MCFAs entering the system as salts with the feed stream 600, all of the converted acids and water are the lighter components 659 removed in the lights separator 658. The lights separator 658, similar to the analogous unit depicted in FIG. 3 (358), may be though is not limited to, a flash column, a distillation column, or an evaporator. When an evaporator is used, the evaporator is preferably one that is configured or designed to efficiently handle viscous liquids or slurries (mix of solids and liquids), which are more difficult to handle during evaporation. An evaporator suitable for use as the lights separator 658 may be though is not limited to, a falling-film, a thin-film dryer, a thin-film evaporator, or a wiped- film evaporator suitably sized to handle the high viscosity in the acidified mixture stream 602. It is also noted that the fractionation train (z.e., units 607, 647, 650, 661, 664, 668, and 671) may also optionally include separation units 661, 664, 668 and 671 configured to fractionate MCFAs C5 and iC5, C6, C7, and C8, into separated MCFA stream 662 665 669 and 672, respectively. Each separation unit produces a bottom stream 660 663 667 and 670 containing the heavier fatty acids, which exit the separation units 650, 661, 664, 668 and 671, respectively, and are fed to the next separation unit in the train.

[0115] The last bottom stream 655 exiting from the last fractionation unit 671 will contain a small amount of heavies, including some EHF As that evaporated in unit 658, which can then be combined with the EHF As 635 from CO2 separation 624. The combined stream 635+655 can be sent to purification unit 636, which may include, but is not limited to, a distillation, extraction, or membrane filtration unit designed to separate any heavy impurities and purify the EHFA in the combined stream. Optionally, the purification unit 636 may be the same membrane filtration unit used upstream to polish an incoming high- concentration clean broth to generate the feed stream 600. This can be achieved by sending the depressurized EHFA stream 630 from the CO2 separation unit 624, after taking the bypass 629, to an acidification tank before the broth polishing membrane filtration unit. Ifno bypass is taken, the broth polishing membrane filtration unit may optionally be placed after the acidification vessel 601 and all of the depressurized EHF A stream 627 from the CO2 separation unit 624 is directly sent to the acidification vessel 601. Since the EHF A is an external or extraneous material not produced in the upstream fermentation, there will not be any excess that can be extracted as a product stream, as in FIG. 3 (339). Instead, an EHF A make-up 673 will be required, which may be added to the acidification vessel 601.

[0116] Other than these details, the description above for the method and system depicted in FIG. 3 also applies to the embodiment in FIG. 6. Each unit operation and stream numbered as 3XX in FIG. 3 corresponds to the unit operation and stream numbered 6XX in FIG. 6, where XX is any two-digit number. In FIG. 6, the high-concentration clean broth is procured and processed for the feed stream 600 in the same manner as described for the development of the feed stream 100 in FIG. 1.

[0117] Industrial Applicability

[0118] The methods and associated systems disclosed herein are suitable for processing solutions containing carboxylic acid salts, such as those derived from fermentations, to acidify the salts and recover useful carboxylic acids. The overall effectiveness of the methods and systems disclosed will vary based on the composition of the feedstock, the configuration and the operating temperatures and pressures of the system, and the composition of the acidifying agent. The overall effectiveness may also be impacted by which optional steps as described above for each of the methods and systems are taken and the use of certain additives.EXAMPLES

[0119] The following examples more specifically illustrate various steps of the general method described, starting with direct acidification of a concentrated and clean fermentation broth coming from a mixed-culture acidogenic fermentation, which contains salts of carboxylic acids or fatty acids followed then by distillation to recover the carboxylic acids. An MCFA is used as the main acidification agent. The distillation removes the water and then the lighter acids acid, leaving behind at the bottoms the salts of the MCFA (cations and anions of the MCFAs) and free MCFAs. This stream then undergoes acidification by carbonation in the presence of water to remove the carbonate / bicarbonates and cations, thus converting the MCFA salts back to MCFAs, followed by subcritical liquid or subcriticalgaseous CO2 extraction to recover MCFAs still present in the water containing carbonates / bicarbonate and cations. These examples should in no way be construed as limiting the scope of the present disclosure.

[0120] Example 1.

[0121] Direct acidification with MCFA

[0122] A mixed-culture acidogenic fermentation of glycerol, as the carbon source, with other nutrients to supply nitrogen, vitamins and other minerals, was performed. The pH was maintained near neutrality with sodium and potassium alkali as buffering agents, thus ending up mostly with sodium and potassium salts of the carboxylic acids. The resulting fermentation broth was clarified using a series of membrane filtration units to remove any cells and solids, and other precipitates, and the broth which contained the salts of the carboxylic acids produced in fermentation was then concentrated using reverse osmosis followed then by an evaporator to a concentration of 425 g of total carboxylic acids / L of total solution (at a density of about 1.25 kg / L, this would be close to 340 g of total carboxylic acids / kg of total solution). The resulting concentrated broth concentration in g / L with the profile distribution % of carboxylic acids (i.e., SCFAs - acetic (C2), propionic (C3), isobutyric (iC4), butyric (C4) and MCFAs - isovaleric (iC5), valeric (C5), caproic (C6), heptanoic (C7) and caprylic (C8)) can be seen in Table 1 as measured by GC- FID using a HP-FFAP column.Table 1. Concentration and profile of cleaned and concentrated fermentation broth

[0123] About 24 gallons (approximately 250 lbs.) of the high-concentration clean broth with an individual and total concentration and acid profile of SCFA and MCFA salts as shown in Table 1 was mixed in a mechanically stirred tank with 375 lbs. of an MCFA, namely valeric acid (C5), to act as the acidification agent. As it can be observed in Table 1, the acidogenic fermentation does produce C5 acid, which means that advantageously the method does not require any external or extraneous fatty acids for acidification. Uponadding the C5 acid, carbonates and bicarbonates still present in the concentrated broth were converted into CO2 and released, which was observed by bubbling (although some CO2 could still remain in the mixture because CO2 has some solubility in valeric acid). The released CO2 could be recovered but was not done in this example. The resulting acidified mix had the carboxylic acid content (g / kg) and acid profile (%) as measured by GC-FID with a HP-FFAP column, Karl Fischer (KF) water content (%) and sodium and potassium content (%) measured by ion chromatography shown in Table 2.Table 2. Acid profile and acid, water, sodium, and potassium content of acidified mixture

[0124] Example 2

[0125] Distillation for water removal and for recovering the lighter acids

[0126] The acidified mixture from Example 1 shown in Table 2 was then fed using pumps to a continuous distillation system to remove its close to 14% water content.Various flows in and out of the distillation (feed, distillate and bottoms) and within the distillation (i.e., reflux) were monitored using Coriolis flowmeters. This distillation system was operated under about 1 to 2 psia of vacuum at an average bottoms temperature of 214°F (ranging from 208 to 220°F) and an overhead temperature of 127°F (steady at 127°F throughout the run) with an average reflux ratio (L / D) of 0.43 (0.36 to 0.52 during the run). Under these conditions, during the first 16.5 hours of operation after the temperatures and pressures of the column stabilized, about 93% of the water entering with the acidified mixture feed was removed as per KF measurements, while 1.3% (±0.1% S.D.) of the acids that entered with the acidified mixture feed was lost to the water in the distillate with 50.1% (±0.9% S.D.) of those acids being the acidification agent (C5 acid) as per GC-FID (HP- FFAP column) measurements. These results can be improved with proper adjustment of thetemperatures and reflux ratio; however, it is expected that some acid would be removed regardless with the water because of the existence of azeotropes. Such water can be recycled back to fermentation or to broth evaporation to avoid the loss of these acids. The average mass closure for the acid for this distillation run in this water removal column was 93.5% (±2.8% S.D ).

[0127] The bottoms from the distillation run in the water removal column were then sent to a second distillation column for removal of the acidified lighter acids (i.e., C2-C4). The bottoms in this new distillation run were kept at an average 262 °F (260 to 263°F throughout the run), while the overhead temperature ran at an average of 160°F (ranging from 170 down to 142°F at the end). The system was kept under vacuum at 1 to 2 psia. The reflux ratio (L / D) average was 2.28 (ranging from 0.78 to 4.73 at the end of the run). The overall recovery of the C2-C4 lighter acids in the distillate or overheads of this distillation column was in average 80.4% (±2.9% S.D.), however, there was virtually complete recovery (>99%) of C2 and C3 acids, with only C4 acid not being fully recovered at an average recovery of only 39.8% (±8.2% S.D.). On the other hand, the loss of the MCFAs (i.e., C5 acidification agent and other heavier acids, such as C6) in the distillate was in average 2.0% (±1.3% S.D.) (from 3.84% improving down to 0.14% as adjustments were made) so most of the MCFAs remained in the bottoms as desired. The mass closure of the acids in this lighter acids removal column was in average 98.4% (±1.8% S.D.), while the overall sodium and potassium balance around both the water and lighter acids removal distillation columns showed that the cations remained, as expected, in the bottoms with a recovery of 93.4% (±13.1% S.D.) and 89.8% (±12.4%), respectively. All data above is reported for the first 16.5 hours of operations after the temperatures and pressures of the columns had stabilized. Table 4 shows the composition of the distillate in the lighter acids removal column as a function of time during the operation of the distillation column for the16.5 hour after temperature and pressure stabilization reported above and then for another12.5 hours (total 29 hours). It can be observed that as operators were able to better adjust the conditions (e.g., increase reflux), the amount of MCFAs (C5 and longer) loss to this distillate decreased over time, while desirably recovery of C4 increased. Although not done in this example, this distillate stream from the lighter acids removal column could then be sent to further fractionation by distillation if required to produce the individual final carboxylic acids products while any minor amounts of MCFAs would be recycled back to the acidification step.Table 4. Composition of distillate stream from lighter acids removal column over time.

[0128] Although there were inefficiencies in this distillation run (e.g., the low recovery of C4 acid and the loss of MCFAs in the distillate, which may be remediated and improved by further adjusting column temperatures, reflux ratio and other parameters), this example demonstrated the feasibility of recovering the lighter acids selectively by distillation after using MCFAs for acidification of fermentation broths.

[0129] Example 3

[0130] Regeneration of the resulting MCFAs salts with carbonation and CO2 extraction

[0131] The bottoms leaving the lighter acid removal column in Example 2 contained mostly the heavy acids (C5 and larger), a small amount of C2-C4 lighter acids (due to, as mentioned, correctable inefficiencies in the lighter acid removal column) and the metal cations, mostly sodium and potassium, that entered the system with the high-concentration clean broth. This stream needed to be regenerated by removing the cations and converting all the MCFAs salts into their corresponding acids so that the acidifying agent may be reused. This process was accomplished in this example by contacting the cation-laden bottoms streams leaving the lighter acid removal column in Example 2 with deionized water and high-pressure CCh in a liquid-liquid extraction column. The extraction column is a packed static extraction column about 30-ft in height with structured packing. Prior to sending the bottoms stream to the extraction column, the temperature of this stream, which was at about 262°F as it left the distillation column, needed to be decreased to ambienttemperature because CO2 infusion into both the water and the organic phase is more efficient at lower temperatures and because it is preferred to contact with water below water atmospheric boiling point. The cation-laden bottoms stream, however, tends to be more viscous and more difficult to handle (pump) at lower temperatures. In fact, depending on the amount of free MCFAs in the mix, they can solidify at lower temperatures; therefore, as the temperature was decreased, a small amount of deionized water (-10%) was added to this stream, which thinned out the stream allowing adequate pumping.

[0132] The hydrated thinner bottoms stream and high-pressure CO2 were introduced at the bottom of the liquid-liquid static (packed) extraction column operating at a pressure of 950 psig and ambient temperature, while deionized water was introduced at the top. The ratio of deionized water to the hydrated bottoms stream was on average 3.4. Such high deionized water flow was implemented to ensure that sodium bicarbonate did not precipitate, but optimization still needs to be performed to find the proper deionized-water- to-feed ratio, which is expected to not need to be that high, thus enabling collection of an aqueous raffinate that is smaller and more concentrated. The resulting raffinate from the first extraction column, which still has acids that solubilized in the aqueous phase, was then sent to a second liquid-liquid packed static extraction column, also about 30 ft in height with structured packing, operating at 850 psig, where for this example subcritical gaseous CO2 was used to extract the acids, particularly the MCFAs, which can more efficiently be extracted with CO2. The solvent (CO2)-to-feed ratio in this second liquid-liquid extraction column was an average of 0.27 (±0.06 S.D.), which is quite low due to operational limitations during the run. Typically, solvent-to-feed ratios range from 0.1 to 2.5. The two extract phases from both liquid-liquid extraction columns were consolidated and sent to a third distillation column, which operated at slightly lower pressure (<650 psi) than the liquid-liquid extraction columns to allow the removal of CO2 without having to completely depressurize the mix. The bottoms of this CO2 separator distillation column operated at an average temperature of 289°F and the overhead temperature at an average temperature of 60°F. The reflux ratio necessary for this column was very small at an average of 0.05 (±0.004 S.D.) because of the ease of separation of CO2 from the other components due to the large differences in boiling point. The recovered CO2 from the distillation was repressurized by pumping and recycled back to both extraction columns. An average 28.6% (±2.6% S.D.) of the CO2 was lost to bicarbonate formation and to venting of the differentstreams as they are depressurized to atmospheric pressure. Such CO2 loss can be recovered in a fully integrated system as described for the embodiments above.

[0133] The results from this example for the regeneration of the bottoms from the lighter acids distillation column in Example 3, which mostly contained the MCFAs salts (mostly C5) that were to be converted back into MCFAs by CO2, showed good efficiency in the removal of cations (sodium and potassium) with over 99.9% removal of sodium and over 99.7% removal of potassium as per the analysis with ion chromatography, showing almost full conversion of the MCFA salts to MCFAs. Table 5 shows a comparison of the bottoms of the lighter acids removal column in Example 2, which is the feed to the regeneration step in Example 3, and the bottoms of the CO2 separation column after the two liquid-liquid or gas-liquid extraction columns, which is the output of the regeneration step in Example 3. Table 5 shows substantial removal of sodium (Na+) and potassium (K+) cations.Table 5. Comparison of the bottoms of the lighter acids removal column and the bottoms of the CO2 removal column

[0134] The second liquid-liquid or gas-liquid extraction column performed extraction of the acids which were still solubilized in the aqueous raffinate leaving the first extraction column. Table 6 shows the acid concentration in the aqueous phase before and after the second liquid-liquid extraction column as measured by GC-FID (HP-FFAP column). The focus is on the MCFAs (>C5 acids), which would be the ones that areexpected to be in this stream, while the presence of a small amount of the short acids is an artifact of inefficient distillation upstream. The extraction of the MCFAs with subcritical gaseous CO2 is modest, estimated to be an average of 30.7% (±19.7% S.D.) of the total MCFAs entering this second extraction column, which was expected because of inefficiencies of the column itself, which does not have the necessary theoretical stages, and the very low CO2 solvent-to-feed ratio mentioned above. More efficient extraction columns, such as agitated extraction columns, instead of static columns as the ones used in this example, can achieve a larger number of stages, and a higher CO2 solvent-to-feed ratio is necessary for better extraction efficiencies.Table 6. Comparison of the acid profile and concentration of the aqueous raffinates from the first and second liquid-liquid extraction columns.

[0135] Part of the regenerated MCFAs should be sent to another separation system, such as a distillation column, to further purify the MCFAs and remove heavy impurities entering with the concentrated broth, prior to recycling the material to the front-end acidification step done in Example 1, however, such step was not performed in this example.

[0136] While certain embodiments have been illustrated and described, it should be understood that changes and modifications can be made therein in accordance with ordinary skill in the art without departing from the technology in its broader aspects as defined in the claims.

[0137] The embodiments, illustratively described herein may suitably be practiced in the absence of any element or elements, limitation or limitations, not specifically disclosed herein. Thus, for example, the terms “comprising,” “including,” “containing,” etc. shall be read expansively and without limitation. Additionally, the terms and expressions employed herein have been used as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the claimed technology. Additionally, the phrase “consisting essentially of’ will be understood to include those elements specifically recited and those additional elements that do not materially affect the basic and novel characteristics of the claimed technology. The phrase “consisting of’ excludes any element not specified.

[0138] The present disclosure is not to be limited in terms of the particular embodiments described in this application. Many modifications and variations can be made without departing from its spirit and scope, as will be apparent to those skilled in the art. Functionally equivalent methods and compositions within the scope of the disclosure, in addition to those enumerated herein, will be apparent to those skilled in the art from the foregoing descriptions. Such modifications and variations are intended to fall within the scope of the appended claims. The present disclosure is to be limited only by the terms of the appended claims, along with the full scope of equivalents to which such claims are entitled. It is to be understood that this disclosure is not limited to particular methods, reagents, compounds, compositions, or biological systems, which can of course vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting.

[0139] In addition, where features or aspects of the disclosure are described in terms of Markush groups, those skilled in the art will recognize that the disclosure is also thereby described in terms of any individual member or subgroup of members of the Markush group.

[0140] As will be understood by one skilled in the art, for any and all purposes, particularly in terms of providing a written description, all ranges disclosed herein also encompass any and all possible subranges and combinations of subranges thereof. Any listed range can be easily recognized as sufficiently describing and enabling the same rangebeing broken down into at least equal halves, thirds, quarters, fifths, tenths, etc. As a nonlimiting example, each range discussed herein can be readily broken down into a lower third, middle third and upper third, etc. As will also be understood by one skilled in the art all language such as “up to,” “at least,” “greater than,” “less than,” and the like, include the number recited and refer to ranges which can be subsequently broken down into subranges as discussed above. Finally, as will be understood by one skilled in the art, a range includes each individual member.

[0141] All publications, patent applications, issued patents, and other documents referred to in this specification are herein incorporated by reference as if each individual publication, patent application, issued patent, or other document was specifically and individually indicated to be incorporated by reference in its entirety. Definitions that are contained in text incorporated by reference are excluded to the extent that they contradict definitions in this disclosure.

[0142] Other embodiments are set forth in the following claims.

Claims

WHAT IS CLAIMED IS:

1. A method of recovering carboxylic acids, the method comprising: contacting a feed solution comprising water and carboxylic acid salts with mediumchain fatty acids to form a mixture, thereby acidifying at least a portion of the carboxylic acid salts, the mixture comprising water, carboxylic acids, and medium-chain fatty acid salts; separating the mixture into a first stream and a second stream, the first stream comprising water and carboxylic acids that have a boiling point that is lower than a boiling point of the medium-chain fatty acids and the second stream comprising medium-chain fatty acid salts; and contacting at least a portion of the second stream with water and carbon dioxide to form an aqueous phase stream and an organic phase stream, the aqueous phase stream comprising water, bicarbonates and / or carbonates, metal cations, and dissolved medium-chain fatty acids, and the organic phase stream comprising medium-chain fatty acids, water, and carbon dioxide.

2. The method of claim 1, wherein the separating is performed using a distillation system.

3. The method of claim 1 further comprising hydrating the second stream with water to decrease viscosity of the second stream or to keep the second stream in a liquid state.

4. The method of claim 1, wherein the contacting of at least a portion of the second stream with water and carbon dioxide is done at an operating pressure of greater than 200 psi.

5. The method of claim 4, wherein the operating pressure ranges from 600 to 1200 psi.

6. The method of claim 1 further comprising contacting the aqueous phase stream with subcritical liquid carbon dioxide, subcritical gaseous carbon dioxide or supercritical carbon dioxide to recover medium-chain fatty acids dissolved in the aqueous phase stream.

7. The method of claim 4, wherein the organic phase stream formed by the contacting of at least a portion of the second stream with water and carbon dioxide at high pressuresis sent to a carbon dioxide separation unit to recover the carbon dioxide without decreasing the pressure down to atmospheric pressure.

8. The method of claim 7, wherein the carbon dioxide separation unit is a flash vessel or a distillation column.

9. The method of claim 1 further comprising: separating and recovering carbon dioxide from the organic phase stream to form a carbon dioxide-free organic phase stream; and separating dissolved water from the carbon dioxide-free organic phase stream by heating and flashing or by distillation to form a water-free and carbon dioxide-free organic phase stream.

10. The method of claim 9, wherein the water-free and carbon dioxide-free organic phase comprising medium-chain fatty acids undergoes purification to remove heavy impurities, thereby producing purified medium-chain fatty acids.

11. The method of claim 1, wherein at least a portion of the organic phase stream formed by the contacting of at least a portion of the second stream with water and carbon dioxide, after separating and recovering the carbon dioxide, undergoes purification to remove heavy impurities, thereby producing purified medium-chain fatty acids.

12. The method of claim 10 or 11, wherein the purification of the organic phase comprises distillation, membrane filtration or extraction.

13. The method of claim 12, wherein the purification is performed in a set of distillation columns comprising a first distillation column and a last distillation column, the medium-chain fatty acids are separated into a distillate of a first distillation column, and heavy impurities are removed through a bottoms of the last distillation column.

14. The method of claim 13, wherein the set of distillation columns further comprises one or more subsequent distillation columns between the first distillation column and the last distillation column, and carboxylic acids having boiling points higher than the boiling point of the medium-chain fatty acids are separated into one or more distillates of the one or more subsequent distillation columns.

15. The method of claim 1, wherein separating the water and the carboxylic acids that have lower boiling point than the medium-chain fatty acids occur in separate distillation columns.

16. The method of claim 15, wherein the carboxylic acids that have lower boiling point than the medium-chain fatty acids are sent to a set of distillation columns to fractionate them into individual carboxylic acids.

17. The method of claim 1, wherein separating the water and the carboxylic acids that have lower boiling point occurs in the same equipment.

18. The method of claim 17, wherein the equipment comprises an evaporator, a flash vessel, a distillation column, or combinations of any two or more thereof.

19. The method of claim 18, wherein the evaporator comprises a falling-film evaporator, a thin-film evaporator, a thin-film dryer, a wiped-film evaporator or combinations thereof.

20. The method of claim 6, wherein the contacting of at least a portion of the second stream with water and carbon dioxide and the subcritical liquid carbon dioxide, subcritical gaseous carbon dioxide, or supercritical carbon dioxide recovery of medium-chain fatty acids dissolved in the aqueous phase stream occur in the same contacting unit.

21. The method of claim 6, wherein the contacting of at least a portion of the second stream with water and carbon dioxide and the subcritical liquid carbon dioxide, subcritical gaseous carbon dioxide or supercritical carbon dioxide recovery of medium-chain fatty acids dissolved in the aqueous phase stream occur in separate contacting units.

22. The method of claim 20 or 21 wherein the contacting units are liquid-liquid or gasliquid extraction systems or both.

23. The method of claim 20 or 21 wherein the contacting units are hollow-fiber membrane contactors or extraction columns or both.

24. The method of claim 10 or 11, wherein the purification comprises introducing an extraneous compound to act as an entrainer to allow more efficient removal of heavy impurities, while minimizing medium-chain fatty acid losses.

25. The method of claim 1, wherein at least a portion of the organic stream formed by the contacting of at least a portion of the second stream with water and carbon dioxide, after separating and recovering the carbon dioxide, is recycled back to contact the feed solution and to provide at least a portion of the medium-chain fatty acids.

26. The method of claim 10 or 11, wherein at least a portion of the purified medium-chain fatty acids is recycled back to contact the feed solution and to provide at least a portion of the medium-chain fatty acids.

27. The method of claim 26, wherein the purification with membrane filtration is done after the contacting of the feed solution with the recycled medium-chain fatty acids.

28. The method of claim 1, wherein the feed solution is a concentrated and clean fermentation broth derived from fermentation of a biodegradable feedstock.

29. The method of claim 28, wherein the aqueous phase formed by the contacting of at least a portion of the second stream with water and carbon dioxide, after separating and recovering free carbon dioxide, is sent to fermentation to act as a buffering agent.

30. The method of claim 7, 9, 10, 25 or 29, wherein the recovered carbon dioxide is recycled to contact at least a portion of the second stream and water.

31. The method of claim 30, wherein carbon dioxide gas released during fermentation is recovered and used to contact at least a portion of the second stream and water.

32. The method of any one of claims 1-31, wherein long-chain fatty acids are used instead of medium-chain fatty acids.

33. The method of any one of claims 1-32, wherein the medium-chain fatty acids comprise an individual medium-chain fatty acids or mixtures thereof.

34. The method of claim 33, wherein the long-chain fatty acids comprise an individual long-chain fatty acid or mixtures thereof.

35. A method of recovering carboxylic acids, the method comprising: contacting a feed solution comprising water and carboxylic acid salts with mediumchain fatty acids in a first contacting step to form a mixture comprising water, carboxylic acids, medium-chain fatty acids and salts;separating the mixture into a separated water and carboxylic acid stream and a separated medium-chain fatty acid salt stream, wherein the carboxylic acids in the separated water and carboxylic acid stream have boiling point lower than the boiling point of the medium-chain fatty acids; contacting at least a portion of the separated medium-chain fatty acid salt stream with water and carbon dioxide in a second contacting step to form an aqueous phase stream and an organic phase stream; wherein the aqueous phase stream comprises water, bicarbonates and / or carbonates, metal cations, and dissolved medium-chain fatty acids, and wherein the organic phase stream comprises medium-chain fatty acids, carbon dioxide, water, and heavy impurities; and separating and recovering the carbon dioxide from the organic phase stream to form a recovered carbon dioxide stream and a carbon dioxide-free organic phase stream.

36. The method of claim 35, wherein at least a portion of the recovered carbon dioxide stream is recycled to provide at least a portion of the carbon dioxide used in second contacting step.

37. The method of claim 36, wherein at least a portion of the carbon dioxide-free organic stream comprising medium-chain fatty acids is recycled to provide at least a portion of the medium-chain fatty acids used in the first contacting step.

38. A method comprising: a first contacting step comprising contacting carboxylic acid salts with mediumchain fatty acids to create a mixture comprising carboxylic acids and medium-chain fatty acid salts; a first separation step comprising separating the carboxylic acids from the mixture; and a second contacting step comprising contacting the remaining mixture with CO2, thereby producing an acidified mixture comprising medium-chain fatty acids.

39. The method of claim 38, further comprising separating the medium-chain fatty acids from the acidified mixture.

40. The method of claim 39, further comprising recycling the medium-chain fatty acids for use in the first contacting step.

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