Process for purifying pentamethylenediamine from lysine whole broth

Abstract

Disclosed herein is a process for the preparation of pentamethylenediamine (PMDA, also referred to as cadaverine or 1, 5-pentanediamine) by reacting pentane-1, 3-pentanediamine containing at least one anion selected from the group consisting of carbonate, sulfate and phosphate to form pentamethylenediamine; contacting the fermented broth comprising one or more 1, 5-diammonium salts with an amount of an oxide or hydroxide salt of a divalent metal selected from magnesium and calcium sufficient to form a broth comprising an amount of one or more precipitated divalent metal salts of one or more anions; removing the one or more precipitated divalent metal salts from the fermented broth to form a broth comprising a lesser amount of the one or more divalent metal salts; and removing PMDA from the bouillon from which the one or more precipitated divalent metal salts have been removed.

Description

TECHNICAL FIELD

[0001] The present invention relates to the preparation of pentane-1,5-diamine, also known as cadaverine or pentamethylene diamine (PMDA), from lysine fermentation broth, which is of a purity suitable for use as a monomer for polymer synthesis. BACKGROUND

[0002] The present invention relates to a new method and system for purifying cadaverine (or 1,5-pentanediamine or pentamethylene diamine (PMDA)) from fermentation broth. More specifically, the invention focuses on the purification of PMDA produced from lysine fermentation broth, wherein lysine has been converted to PMDA by the action of lysine decarboxylase as previously known. PMDA has applications in a variety of industries, including the production of sustainable polymer materials, including polyurethanes, polyimides and polyamides.

[0003] PMDA has gained considerable interest due to its diverse applications and sustainability through microbial fermentation of lysine, a common amino acid. Following lysine fermentation, lysine decarboxylase, an enzyme produced by specific microorganisms, catalyzes the conversion of lysine to PMDA. However, the production of PMDA through fermentation is accompanied by the formation of various impurities and by-products, which represent a loss of yield and complicate the recovery of PMDA at the typically very high purity required to manufacture such sustainable polymer materials. Of particular concern is the presence of anions, particularly the major conjugate anion salt of PMDA prepared by fermentation, such as phosphate or sulfate, as well as the presence of carbonate, carboxylic and amino acids and other organic contaminants.

[0004] A variety of methods have been proposed in the prior art to purify PMDA from lysine fermentation broth. These techniques typically involve multiple separation steps, such as extraction, filtration and chromatography. While effective to a certain extent, these methods have various drawbacks, such as low yield, high energy consumption and the use of solvents or chemicals that are harmful to the environment.

[0005] Accordingly, there remains a strong need for improved purification methods that overcome the limitations of existing methods. The present invention provides a new and more efficient strategy for purifying PMDA from lysine fermentation broth, which has one or more of improved yield, reduced production cost and reduced environmental impact relative to known alternative methods. BRIEF SUMMARY

[0006] Described herein is a method of making pentamethylene diamine (PMDA), the method comprising: contacting a fermentation broth containing one or more corresponding pentane-1,5-diammonium salts of at least one anion selected from the group consisting of carbonate, sulfate, and phosphate with an amount of an oxide or hydroxide salt of a divalent metal selected from magnesium and calcium sufficient to form a broth comprising one or more precipitated divalent metal salts of the amount of one or more anions; removing the one or more precipitated divalent metal salts from the fermentation broth to form a broth comprising less of the one or more divalent metal salts; and removing PMDA from the broth that has had the one or more precipitated divalent metal salts removed.

[0007] In certain embodiments, substantially all of the precipitated pentane-1,5-diammonium salts are removed to provide a desalted broth, and PMDA free base is recovered from the desalted broth.

[0008] In certain embodiments, the pentane-1,5-diammonium salts are primarily sulfate salts.

[0009] In certain embodiments, removing the one or more precipitated divalent metal salts comprises at least one of filtering the broth containing the one or more precipitated divalent metal salts on a filter to obtain a retentate salt cake fraction and a first filtrate fraction, or centrifuging the broth to obtain a salt cake fraction and a supernatant. In such embodiments, the first filtrate fraction or supernatant fraction preferably contains less than 1% of the PMDA salt anions originally present in the fermentation broth. In best practices of these embodiments, the method further comprises washing the retentate fraction or salt cake fraction with water, and filtering the washed salt cake fraction or centrifuging the washed retentate fraction or the washed salt cake fraction to obtain a second filtrate fraction or a second supernatant fraction, and then preferably combining the first filtrate fraction and the second filtrate fraction or the first supernatant fraction and the second supernatant fraction to form a combined filtrate fraction or a combined supernatant material containing PMDA. Incidentally, it should be understood that the word "fraction" as used herein should simply mean a portion of the whole, whether that portion is produced as a discrete portion in a batch mode of operation or as a continuous partial portion in a continuous mode of operation.

[0010] In further preferred embodiments, the method comprises further purifying PMDA from the broth that has had the one or more precipitated divalent metal salts removed by contacting the broth with a strong base type 1 anion exchange resin, and obtaining an eluate fraction containing free base PMDA having less than 20 ppm of carboxylate anions, and less than 1 ppm each of carbonate anions, sulfate anions, phosphate anions, and chloride anion.

[0011] In further preferred embodiments, further purifying the PMDA comprises flash evaporation of the eluate fraction to obtain a vapor fraction having a higher concentration of PMDA than the concentration of PMDA of the eluate fraction, and condensing the vapor fraction.

[0012] In still further preferred embodiments, the method further comprises distilling the condensed vapor fraction to obtain a purified PMDA distillate having a purity of at least 99.5% wt / wt.

[0013] In a particular embodiment, disclosed herein is a method of making PMDA, the method comprising: contacting a fermentation broth containing one or more pentane-1,5-diammonium salts having anions selected from the group consisting of carbonate, sulfate, and phosphate, with an amount of an oxide or hydroxide salt of a divalent metal selected from magnesium and calcium at a temperature of 25 °C or less for a first period of time, and then heating to a temperature greater than 25 °C for a second period of time, whereby after the second period of time, a solid material fraction is formed from one or more precipitated divalent metal salts containing magnesium or calcium, typically not both; removing the precipitated divalent metal salts in the solid material fraction from the fermentation broth by filtration or centrifugation to form a) a broth from which one or more anions of the one or more starting pentane-1,5-diammonium salts have thereby been removed as a first filtrate or first supernatant, and b) a retentate fraction or salt cake fraction; washing the salt cake fraction with water at a temperature greater than 25 °C; filtering or centrifuging the washed salt cake fraction to form a second filtrate fraction or second supernatant fraction; combining the first filtrate and the second filtrate or the first supernatant and the second supernatant to form a combined broth fraction from which one or more anions of the one or more starting pentane-1,5-diammonium salts have thereby been removed; contacting the combined broth fraction with a strong base type 1 anion exchange resin to obtain an eluate fraction containing PMDA, the eluate fraction having less than 20 ppm carboxylate anions and less than 1 ppm of carbonate anions, sulfate anions, phosphate anions, and chloride anions; evaporating the eluate fraction to obtain a concentrated PMDA sample; and distilling the concentrated PMDA sample fraction to obtain a purified PMDA sample having a purity of at least 99% by wt / wt.

[0014] In certain embodiments of this particular sequence of steps, the contacting with the divalent metal salt and the washing of the salt cake are performed at a temperature of at least 90 °C but less than the boiling temperature of the broth.

[0015] In certain embodiments, the evaporation is performed in a first evaporation step to obtain a concentrated bottoms fraction, and in a second evaporation step from the concentrated bottoms fraction to obtain a concentrated vapor fraction.

[0016] Certain embodiments include wherein the distillation in the first distillation step is performed under vacuum pressure, obtaining a first PMDA distillate, and the distillation in the second distillation step is performed under vacuum pressure, obtaining a final PMDA distillate.

[0017] The best mode of the foregoing process provides monomeric grade PMDA having a purity of at least 99.9%. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 The critical Ca(OH)2:SO4 molar ratio threshold for efficient deionization (desalination) of PMDA reaction mixtures is illustrated.

[0019] Figure 2 A- Figure 2 D shows the time course of sulfate removal from PMDA sulfate full broth using Ca(OH)2 according to the present application at 35°C (A), 50°C (B), 65°C (C), and 90°C (D).

[0020] Figure 3 A and Figure 3 B shows the concentration of the main anions sulfate, phosphate, chloride, and total carboxylate as a function of time for a 4 L PMDA reaction mixture deionized with Ca(OH)2 at 90°C with a 3: 1 molar ratio to sulfate.

[0021] Figure 4 The effect of temperature and wash volume on the recovery of residual PMDA from the salt cake retentate fraction prepared by washing the Ca(OH)2 precipitated sulfate from the full broth according to the present application is shown.

[0022] Figure 5 A table is shown with data obtained from screening anion exchange resins for use in practicing certain steps of the present application.

[0023] Figure 6 A process flow diagram is shown for a commercial scale production facility designed to implement a particular illustrative embodiment of the present application, starting with the production of lysine from fermentation, through conversion to PMDA, and then applying various measures to recover a purified PMDA product. DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0024] The following description of certain embodiments according to the present application is merely merely intended to be illustrative of the application as defined by the claims that follow thereafter and should not be taken as limiting thereof, and it will be understood by those skilled in the art that this is merely a description of the core principles of the present application and the solution it provides, to meet the need for an improved process for recovering PMDA produced from lysine fermentation broth.

[0025] Under this premise, the following description specifically relates to the preparation of purified pentamethylenediamine (PMDA) from a whole broth fermentation medium, wherein the medium has been adjusted to a suitable pH using ammonium sulfate, so that the lysine produced therein is primarily in the form of lysine sulfate. Although the described embodiment uses lysine sulfate, it should be noted that the same method can be used if the pH of the medium is adjusted using phosphate to form lysine phosphate.

[0026] In the case of ammonium sulfate, most of the ammonia is used as the nitrogen source for the lysine-producing biomass. In the presence of pyridoxal-5-phosphate, the produced lysine is catalytically decarboxylated using lysine decarboxylase (CadA) from *E. coli* to produce PMDA. The decarboxylation reaction introduces free carbonate anions into the culture medium, which also contains other detectable 1-6 carbon carboxylate anions in the form of formate, lactate, acetate, propionate, butyrate, isobutyrate, and gluconic acid diacid. Therefore, the PMDA salt in the broth comprises sulfate or phosphate as the main salt, as well as carbonate. In a preferred application of the method of this disclosure, at least 95% and more usually at least 98% of the sulfate or phosphate anions and carboxylate anions are removed using calcium hydroxide precipitation, followed by filtration to form a desalted and substantially desalted broth.

[0027] The desalination step relies on the reverse solubility of calcium or magnesium salts of sulfate, phosphate, and carbonate, meaning that the water solubility of these salts decreases with increasing temperature. The same is true for calcium hydroxide to a lesser extent. Therefore, in a preferred embodiment, the desalination step is performed by first contacting the fermented broth with the oxides or hydroxides of calcium or magnesium at room temperature (25°C) or lower, and then heating the mixture to an elevated temperature (meaning a temperature greater than 25°C up to the boiling point of the fermented broth). In some embodiments, the temperature should be at least 50°C, in other embodiments at least 70°C, in exemplary embodiments about 90°C, and in a preferred embodiment, the temperature is from 90°C up to the boiling point of the broth.

[0028] Although calcium hydroxide is used as an example, this method can be implemented with magnesium oxide or calcium oxide, or magnesium hydroxide or calcium hydroxide. In some embodiments, a type I strong base anion exchange resin can be used to remove residual anions from the desalted broth. In another embodiment, the free PMDA base solution produced by deionization is first concentrated by evaporation under reduced pressure, followed by flash distillation at the top to a water:PMDA solution distillate. The product from the flash distillation can then be further concentrated using continuous distillation, and then further purified to polymer-grade specifications with a purity greater than 99% or even greater than 99.9% using, for example, high-vacuum fractionation.

[0029] The overall process flow diagram for the illustrative industrial-scale operation of PMDA production, based on this disclosure, is as follows: Figure 6 As shown in the image.

[0030] Deionization by precipitation In typical practice, lysine is produced through fermentation using lysine-producing bacteria, such as Corynebacterium glutamicum (L.). Corynebacteria glutamicum Or Escherichia coli, with ammonium sulfate added during the fermentation process. Ammonium is primarily consumed as a nitrogen source to supply the growing culture, and most of the lysine produced is present as lysine sulfate, although, as previously stated, those skilled in the art will readily understand that lysine phosphate can also be used in conjunction with the method of the present invention if fermentation is carried out in the presence of phosphate as the predominant anion.

[0031] Furthermore, lysine-rich broth can be used without the need for preliminary removal of biomass through clarification, because according to the present invention, the first step after the precipitation reaction that forms insoluble material will be centrifugation or filtration, which will also remove biomass and precipitated salt.

[0032] From any of these starting points (i.e., clarified lysine sulfate or lysine phosphate broth, or whole lysine sulfate or phosphate broth), lysine is decarboxylated by adding lysine decarboxylase to the fermentation broth, forming PMDA, which is a salt of sulfate or phosphate, the major anion in the fermentation broth. Once the decarboxylation reaction has proceeded to >99% conversion, the reaction mixture is optionally heat-treated at 70°C for 30 min to kill any remaining viable organisms. Heat treatment is only necessary if the reaction mixture is to be kept at room temperature for an extended period before processing; otherwise, heat treatment can be omitted.

[0033] The first stage of PMDA purification according to an exemplary embodiment of the invention is deionization via calcium hydroxide precipitation. In the work described below in more detail to demonstrate the invention, the initial amount of lysine present in the clarified whole broth was 14% wt / wt (0.09589 mol), buffered to pH 7.0 with SO4 (4.5%, 0.046875 mol). The decarboxylation reaction produced 1 mole of CO2 per mole of lysine. The measured lysine:SO4 molar ratio was approximately 2:1. CO2 was precipitated from the solution or captured as PMDA-ammonium bicarbonate, PMDA-ammonium carbonate, or free carbonate. Both sulfate and carbonate act as pH buffers.

[0034] Treatment of a clear whole broth containing PMDA sulfate with solid Ca(OH)₂ produces insoluble calcium sulfate, which precipitates out of the solution, leaving behind free PMDA alkali and water. Treatment of the broth with Ca(OH)₂ also produces some water-soluble calcium bicarbonate at pH 6.5–10.5, as well as free PMDA alkali and water. However, as calcium sulfate precipitates out of the solution, the pH increases. Above pH 10.5, calcium bicarbonate transforms into insoluble calcium carbonate, which also precipitates out of the solution.

[0035] The form (dihydrate, hemihydrate, or anhydrous) and solubility of calcium sulfate are temperature-dependent. Many calcium compounds formed by the addition of Ca(OH)₂ exhibit reverse solubility, meaning that higher temperatures during treatment result in a greater reduction in sulfate ions, as the salts formed by this invention exhibit reduced solubility at higher temperatures. However, Ca(OH)₂ itself also exhibits reverse solubility that can hinder the reaction; therefore, it is best to add Ca(OH)₂ to the reaction mixture at room temperature or lower, followed by heating to promote further precipitation, and filtering the mixture while the reaction mixture is still hot. The use of calcium hydroxide itself provides some heating, as its addition to the broth gives a measurable exothermic reaction of 5°C–10°C. Other calcium carboxylate salts formed by the addition of Ca(OH)₂ exhibit pH dependence. Calcium bicarbonate is completely soluble at pH 6.5–10.5, while calcium carbonate is almost insoluble at pH >10.5. Other calcium salts of 1–6-carbon carboxylate compounds are present in the broth at approximately 1% wt / wt, exhibiting even higher non-reverse solubility.

[0036] The inventors conducted several experiments focusing on time, temperature, and the molar ratio of Ca(OH)₂ to sulfate. The initial proof-of-concept experiment used an economically unsustainable excess of Ca(OH)₂ relative to sulfate, while subsequent efforts focused on reducing the amount of Ca(OH)₂ to obtain an economically optimal value. Due to the robustness of sulfate analysis, sulfate was used as a key anion marker for the amount of calcium hydroxide added. As mentioned above, in addition to sulfate, the reaction mixture derived from the lysine-based fully fermented broth also contains several other anions, including carbonate, phosphate, carboxyl, and amino acids.

[0037] The work began with simple DOE factorial experiments to understand the main effects and reduce calcium hydroxide. All factorial experiments showed a significant (>97%) reduction in SO4. However, it quickly became apparent that the calcium hydroxide to sulfate ratio was the most important factor and revealed different efficacy thresholds. Data from a total of 64 reactions were plotted, including: 3 factor-screened DOEs, enhanced reaction sites (DOE 4 & 5), and 4 timed reaction groups (35°C, 50°C, 65°C, 90°C). The raw data indicated that the critical Ca(OH)2:SO4 ratio threshold was 2.5 mol / mol. Figure 1 In fact, experiments have shown that the optimal amount of calcium hydroxide used is approximately 2.5 times the calculated amount of sulfate ions in the broth. The need for excess Ca(OH)₂ is likely due to the presence of other anions in the solution, whether measured or not.

[0038] Now for reference Figure 2 ( Figure 2 A- Figure 2 D) Four groups of six timed reactions were run on a 10 cubic centimeter scale to observe the sulfate removal rate and obtain better resolution regarding temperature and time. The broth containing PMDA sulfate was stirred with a stir bar for 0 to 4 hours at 35°C, 50°C, 65°C, and 90°C with a molar ratio of calcium hydroxide to sulfate of 2.5.

[0039] The sulfate removal reaction using calcium hydroxide was surprisingly rapid, with most (>95%) of the SO4 precipitating from solution within the first 15 minutes at all studied temperatures. The reverse solubility of calcium sulfate was evident in the faster sulfate removal at higher temperatures compared to reactions at the same molar ratio at lower temperatures. However, the higher 90°C run showed similar results in total SO4 reduction as the 65°C run, with a total reduction of approximately 98% (1100 ppm, by weight of residue). At ambient temperature, the higher temperatures resulted in less precipitate in the filtrate after CaSO4 removal over time. Some differences in total SO4 reduction were observed between different reaction temperatures throughout the 4-hour reaction time. The best results in the timed and factorial experiments showed a 97%–98% reduction of SO4 by weight, compared to 100% reduction in the PO4 buffer reaction. This is a direct effect of the difference in solubility between calcium sulfate and calcium phosphate. During calcium treatment, PMDA and total carboxylic acid concentrations remained unaffected, either constant or slightly increasing over time.

[0040] Therefore, the present invention teaches that the removal of sulfate ions from broth containing PMDA sulfate can be carried out at any temperature from 25°C to the boiling temperature of the culture medium, preferably at 35°C to the boiling temperature, more preferably at 50°C to the boiling temperature, still more preferably at 65°C to the boiling temperature, and most preferably at 90°C to the boiling temperature.

[0041] Following Ca(OH)₂ treatment of broth containing PMDA, unidentified solids were observed to continue precipitating over time at room temperature. This is likely due to Ca(HCO₃)₂. Slow interconversions between CaCO3. The degree of precipitation appears to correlate more with reaction temperature than with the reverse solubility of calcium sulfate. Over time, lower temperature treatments result in greater residual Ca and more additional precipitation, while higher temperature reactions show lower residual Ca concentrations and less or no additional precipitation. The concentrations of calcium and sulfate in the sample supernatant over time were measured by ICP / OES and IC / CD, respectively. While the concentration of residual Ca showed some decrease, SO42- appeared to be unaffected at all experimental temperatures and after treatment time.

[0042] The screening and optimization experiments described above were conducted in the laboratory on a 20 mL scale. Then, the calcium treatment of the PMDA reaction mixture from lysine sulfate whole broth was scaled up multiple times to 1 L, 4 L, and 1000 L, yielding excellent results. At the 1 L or 4 L scale, the calcium treatment of the PMDA reaction mixture was carried out in an inert environment with air replaced by argon or nitrogen in a three-necked round-bottom flask equipped with a mechanical stirrer, thermocouple, and temperature-controlled heating mantle.

[0043] In one experiment, 4 L of unfiltered whole broth lysine sulfate was treated with CadA to form PMDA. The also unfiltered reaction mixture was treated by slowly adding solid calcium hydroxide at room temperature until the molar ratio was 3.08:1 Ca(OH)₂:SO₄, then the temperature was raised to 90 °C and maintained at 90 °C for 4.5 hours. The entire mixture was then thermally filtered through a Buchner funnel containing a Whatman GF / A filter. Sulfate decreased by approximately 97% within the first 90 minutes, which was about 15 minutes after reaching the target temperature. Phosphate present in the broth also decreased by almost 100% almost immediately, while chloride remained stable. Interestingly, the total carboxylate concentration showed a doubling (Table 1). Figure 3 A- Figure 3 B). This may be a result of alkaline-catalyzed protein hydrolysis leading to the release of peptides and amino acids.

[0044] Table 1

[0045] Table 1 shows the decrease of anionic substances in the PMDA reaction mixture over time at 90°C on a 4 L scale.

[0046] In another experiment, two separate PMDA reaction mixtures were subjected to two scale-up calcium hydroxide treatments using a 110-gallon stainless steel baffle reactor equipped with a 45-degree offset folded-blade turbine agitator with an internal steam coil. In each of the two scale-up experiments, 240 kg of PMDA reaction mixture obtained from the decarboxylation of a total lysine fermentation broth was treated at room temperature with 31 kg of solid Ca(OH)₂ at a 3:1 mol:mol ratio to sulfate. The treated broth was then heated to 90°C and sampled at multiple time points. The heterogeneous slurry was hot-filtered through a custom-made Buchner funnel fitted with a fiber filter, and vacuum filtration was performed for ~40 minutes.

[0047] Table 2

[0048] Table 2 shows that the calcium hydroxide treatment of the PMDA reaction resulted in a >99% reduction in sulfate concentration after filtration, and the PMDA yield was 96% by mass.

[0049] A significant amount of PMDA is retained in the wet cake after filtration and should preferably be washed off the cake for better yield. As long as the pH of the reaction after calcium addition is >13, most of the PMDA should not be chemically bound and can therefore be easily recovered by washing the cake with hot water. In a 1 L-scale laboratory experiment, approximately 90% by mass of the generated PMDA was recovered in the mother liquor during the first filtration, while 10% remained adsorbed on the wet cake. Similar results were observed at 4 kg and 240 kg scales. Screening experiments were conducted in the laboratory at a 10 g scale to optimize the cake washing procedure.

[0050] Using a Buchner funnel containing GF / A filter paper, wet cake from 1 L of Ca(OH)₂ treatment was used in a 10 g scale washing experiment to explore various conditions. The focus of the experiment was to maximize PMDA yield by optimizing water temperature and the water-to-cake weight ratio. The water-to-wet-cake weight ratio was the most important variable for PMDA recovery, and the optimal water-to-cake weight ratio was found to be 4:1. Temperature was also a factor; washing at 80°C was superior to washing at 40°C, and washing at 40°C was superior to washing at 20°C. Figure 4Unfortunately, a higher wash ratio also adds more water that remains to evaporate downstream, thus increasing facility costs. Temperature is a significant variable in PMDA recovery; hotter wash water recovers more, and the effect is enhanced at lower wash water to cake weight ratios. In addition to improved PMDA recovery, washing should preferably be hot to utilize reverse solubility to retain calcium sulfate in the solid phase. When a first filtrate containing desalted PMDA is added to a second filtrate, which is the wash water obtained after filtering the washed cake on a filter, the approximately 90% recovery of PMDA from the cake after washing is increased to a total PMDA recovery of 96%–99%.

[0051] Using belt filters or centrifuges can improve washing efficiency and allow for reduced wash water usage. The wet cake itself is approximately 60% solids and 40% water. Some residual PMDA remains in the cake along with other small organic molecules; however, the majority of the dry solids are inorganic calcium salts, including calcium carbonate, calcium sulfate, and calcium hydroxide. Heating the cake to a high temperature to burn off any organic material and converting the calcium hydroxide and calcium carbonate into calcium oxide would allow the stream to be recycled, either wholly or partially, for reuse as a precipitate salt in the first step of the process.

[0052] Ion exchange The mother liquor and washing filtrate were combined into a single process stream containing residual anions that should be removed prior to evaporation. Residual sulfate in the range of 700 ppm–1500 ppm and chloride in the range of 500 ppm–1000 ppm are typical inorganic anion concentrations remaining in the combined filtrate, while phosphate is almost always below detectable levels. Organic anions such as carboxylate are present in the range of 3000 ppm–6000 ppm, with exceptions sometimes up to 2% w / w. Amino acids and ammonia are also typical, present in concentrations ranging from 2000 ppm–5000 ppm. Based on the current understanding of the chemistry and composition of the convection, a certain amount of carbonate or bicarbonate is expected to be present in significant concentrations; however, carbonate is particularly difficult to measure accurately, especially at low levels. Inorganic cations, including calcium, potassium, and sodium, are typically present in the filtrate stream in a total range of 1000 ppm–5000 ppm. The applicability of ion exchange in removing these minor substances was investigated.

[0053] Ion exchange of carboxylic acids and amino acids using standard ion exchange resins proved challenging. Screening experiments using standard strong-base type I (strong base) and type II (weak base) anion exchange resins yielded mixed results. Resin screening was performed using a 10 cc HDPE graduated syringe fitted with a Titan 3 5 μm nylon filter. Resin was added to the syringe and then washed with 10 cc 18 MΩ MQ water and 10 cc 5% sodium hydroxide using a plunger, followed by washing with 10 cc water to ensure the resin was in hydroxide form. Aliquots of the filtrate obtained after calcium hydroxide precipitation were added to the top of the resin using a pipette and then passed through the resin using a plunger. The effluent was collected and anions were analyzed by IC50. Figure 5 Table 1 shows that Type I ion exchange resins, sold under the trade names Dowex 1x8 200-400 mesh Type I and Purolite pfa860, effectively remove most of the sulfate, carboxylate, and chloride ions present in the desalination filtrate in a one-bed volumetric flow with Type I resin in contact. However, only Dowex 1x8 200-400 mesh shows any reduction in carboxylic acids and amino acids. Figure 5 Table 2 shows that this may be due to the improved kinetics of the smaller resin size (70 μm) compared to the industrial-grade resin size (300 μm).

[0054] Total desalination filtrate from a 4 L scale-up reaction was obtained and contacted with a DOWEX 1x8 200-400 Type 1 strong base anion exchange resin for a series of breakthrough experiments at 10 cc and 500 cc scales. Breakthrough experiments were performed in a #25 glass-jacketed IX column equipped with a recirculating heater / cooler and an 80-sample automated fraction collector. 50 cc of DOWEX 1x8 was loaded into the column and washed with 500 cc of MQH2O at 30 °C and a flow rate of 5 mL / min, followed by regeneration with 500 cc of 5% KOH / MQ water at 30 °C and a flow rate of 10 mL / min. The resin expanded from 50 cc to approximately 63.9 cc upon contact with the base, exhibiting a visible color change from white to orange. The resin was washed again with 1000 cc of MQH2O at 30 °C and a flow rate of 10 mL / min. Feed was then introduced into the resin at 5 mL / min, and fractions were collected at rates depending on the feed flow rate. The anion concentration of the sample was analyzed by IC / CD.

[0055] Flow rate, temperature, and total number of regenerations were investigated in column experiments. Temperatures in the 30°C–50°C range appeared to have little effect on resin efficiency, as did flow rates in the 2.5 mL / min–10 mL / min range. For commercial ion exchange applications, 5 BV / h–10 BV / h is acceptable. In these experiments, for a 50 cc resin bed, 2.5 mL / min–10 mL / min corresponds to approximately 3 BV / h–12 BV / h. Unused resin permeated from undisplayed SO4, which was only visible in the effluent after regeneration. A significant reduction in carboxylate capacity was also observed after regeneration, decreasing from approximately 6 BV to 3 BV after four permeation experiments. Chloride ion concentrations remained constant regardless.

[0056] As illustrated in Table 3, it was determined that the Dowex Type I resin was able to absorb most of the carboxyl and chloride ions and at least 95% of the sulfate ions from desalted broth filtrate of approximately 3.5 to 6 bed volumes, and this ability was retained even after three-bed regeneration.

[0057] Table 3

[0058] Anion exchange was scaled up to a 1 L resin bed and used to treat the combined filtrate of 3.165 kg of desalted PMDA broth at room temperature and a flow rate of 2 BV / h. 1,000 cc of DOWEX 1x8 200-400 was packed into a #50 glass unjacketed IX column (34.3 cm L × 8.28 cm D) and washed with 6,000 cc of MQH2O at RT, 40 mL / min, and 3 psi. The resin was then regenerated with 4,000 cc of 5% NaOH / MQ water at RT, 40 mL / min. The bed was washed again with 2,000 cc of MQH2O at RT, 40 mL / min, and 5 psi, and then regenerated again with 4,000 cc of 5% NaOH / MQ water at RT, 40 mL / min, and 5 psi to ensure complete regeneration. The column was washed a final time with 8,000 cc MQH2O, RT, 40 mL / min, and 5 psi. The PMDA yield was 95%, SO4 decreased by 100%, carboxylate by 99.6%, and amino acid + NH4 by 82.8%. The deionized product was used for evaporation experiments.

[0059] evaporation Two evaporation steps are used to concentrate a desalted fermented broth containing a combined filtrate and a washed sample, the washed sample being subjected to ion-exchange chromatography to deionize the sample. The first step is simple concentration, where the diluted, deionized ion-exchange product is dehydrated under reduced pressure. The second step is flash evaporation, where the concentrated PMDA is withdrawn as a distillate product from the top.

[0060] Water was removed during the first evaporation under relatively mild conditions, at a temperature of 45-49°C and a vacuum pressure of -27 mm Hg. Despite the low temperature, vacuum, and the high boiling point of PMDA, some loss was observed in this step, particularly towards the end, where PMDA became more concentrated. In one experiment, 9.6 kg of deionized PMDA aqueous solution was concentrated to 30% in a 120 L evaporator over 21 hours. The concentration in the tank and distillate was monitored by GC.

[0061] Table 4

[0062] Although the concentration of PMDA in the distillate never exceeded approximately 3000 ppm, about 4% of the total PMDA was lost during this evaporation process at -27 mm Hg and below 50°C. This loss of PMDA under evaporation conditions below the boiling point of PMDA indicates that PMDA has a certain affinity for water or PMDA entrainment in the distillate.

[0063] In another evaporation experiment using an evaporation system with a similar configuration, 1184 kg of ion-exchange products were concentrated from 4% w / w PMDA to 40% w / w PMDA over a total of approximately 144 hours. The average pressure, reboiler temperature, and flash vessel temperature were 1.3 psia, 93 °C, and 50 °C, respectively. The average rate of condensate removal was 38 lbs / h.

[0064] Table 5

[0065] Table 5 shows the average operating conditions for evaporating and concentrating deionized aqueous PMDA reaction mixtures by vacuum evaporation.

[0066] Near-complete deionization is crucial for the second evaporation step (PMDA flash evaporation), which can also be referred to as the first distillation step because PMDA evaporates and is recovered in the gas phase rather than being concentrated in the tank. Any anions present in the feed used for evaporation are potential salt formations with PMDA, making it non-volatile and therefore difficult to recover by evaporative distillation. Furthermore, salt formation can lead to significant solidification of the evaporator bottoms, complicating the process and significantly impacting processability and yield. Although most of the sulfate, phosphate, and carbonate ions are removed during the calcium hydroxide precipitation step, and a considerable amount of sulfate and carbonate anions are removed by the ion exchange step, an unacceptably large amount of organic contaminants remains, and these must be precipitated from the solution along with the residual sulfate and carbonate ions to prepare polymer-grade materials.

[0067] The tank material recovered from the first dehydration evaporation step described above is transferred to a 20 L industrial rotovap. A batch evaporator is most useful for this step compared to an evaporation system heated via a pump circulation loop through a heat exchanger. Equally important is a high vacuum to maintain a low tank temperature in this second evaporation step, in which PMDA is recovered as a vapor distillate. Table 6 below shows the time, temperature, and vacuum pressure used to recover PMDA from the vapor phase in this second evaporation step using such a device.

[0068] Table 6

[0069] After removing approximately 50% of the usable PMDA as distillate, solidification of the substrate occurred in the flask. Redissolving and reevaporating the difficult-to-treat substrate with DI water resulted in the same solidification problem, with diminishing returns of 22% PMDA yield. After two rounds of evaporation, the experiment was stopped, with an overall PMDA yield of 72% and a purity greater than 99%. The purity was actually at least 99.9%.

[0070] The comparative evaporator yields of three different scales illustrate the effect of ion exchange on the yields obtainable from the evaporation flash evaporation step, as explained in Table 7 below.

[0071] Table 7

[0072] When Dowex resin is used in the ion exchange chromatography step, a superior overall yield is achieved because Dowex resin removes more ions than other resins, resulting in cleaner PMDA for the subsequent evaporation step, leading to more volatilization and ultimately more PMDA recovery in the final evaporation step. Ion exchange has been described in the deionization section above; however, poor ion exchange was achieved in the evaporation section of this process. Mitsubishi strong base type 1 anion exchange resin PA308 has the same chemical properties as DOWEX 1x8, the feed has a very similar composition, and the treatment method is the same downflow through the column at ambient temperature and pressure of 2 BV / h–5 BV / h. However, the results are significantly different. The larger diameter resin exhibits significantly lower overall deionization compared to the smaller particle size of the Dowex resin, resulting in significantly better evaporation in both yield and material processability.

[0073] distillation Fractional distillation is the final purification step in the PMDA process. The feed to the final distillation is an aqueous solution of 50-60 wt% PMDA recovered from the second evaporation step. Major impurities, including inorganic salts (Na, K, Ca, SO4, PO4, Cl), amino acids including residual lysine, and carboxylates, have been removed by upstream processes prior to distillation. However, after the second evaporation, water and trace amounts of organic impurities remain, some of which have boiling points close to those of PMDA. These trace amounts of organic impurities include, but are not limited to: CO2, ammonia, trimethylamine, monoethanolamine, piperidine, 2,3,4,5-tetrahydropyridine, putrescine, d-valerolactam, α-amino-ε-caprolactam, PMDA-monoacetamide, PMDA-diacetamide, and other unknown amine-containing compounds. The separations during the final distillation are the separation of PMDA from water and the separation of PMDA from both amine-containing organic impurities.

[0074] The feed for distillation is a homogeneous, clear, colorless solution containing water, PMDA, and a small amount of organic impurities as shown in Table 8 below. PMDA boils at 180°C, so most of the remaining impurities can be separated using appropriate distillation columns and operating conditions.

[0075] Table 8

[0076] The primary end use of PMDA is in polymer applications, such as polyurethane or nylon. Both of these applications require very stringent specifications, making understanding and optimization of fractionation essential for successful industrial processes. Based on the teachings of the present invention, PMDA meeting or nearing specifications has been produced in good yields from laboratory scale (10 g–200 g) to semi-pilot scale (1 kg–5 kg).

[0077] Fractionation of the flash distillation products has been carried out on a laboratory scale, in standard distillation glassware (e.g., Vigreux), and in a rotary distillation system. Distillation has also been scaled up to the kilogram scale. Laboratory distillation uses a single-bottle still, set up to first remove water and low-boiling compounds, then remove the fraction of pure PMDA as the distillate product, while higher-boiling compounds are retained as residues at the bottom. On a pilot scale, the distillation apparatus utilizes two systems: a first continuous still for dehydration and removal of light matter, followed by a second still for final purification.

[0078] Regarding the fractionation of PMDA, regardless of the equipment, several points are worth reiterating: the atmosphere must be kept inert by purging with N2 or argon (including the final product); the vacuum must be kept high, i.e. less than 50 Torr, while maintaining an inert atmosphere, but ideally less than 10 Torr, to reduce the required pot temperature to preferably below 50°C; and air leakage needs to be avoided, as it can lead to the formation of carbonates in the joints and may cause blockages in the distillation system.

[0079] In one experiment, a feed containing 576 g of 64% PMDA in water was distilled using a rotary belt distillation system and added to a 1 L single-necked round-bottom flask. The system was sealed, and a vacuum was applied through the condenser and cold trap using an Edwards 2-stage rotary vane pump with a J-Kem vacuum controller. The condenser was maintained at 0°C during the initial dehydration phase of distillation, then increased to 10°C during PMDA fraction collection. The vacuum was maintained constant at 8–9 Torr, and the heating rate was maintained constant at 10% output. The reflux ratio was initially 10:1, then decreased to 5:1 during product removal, and finally to 2:1. Over a process of approximately 1000 minutes, five fractions were collected, and water was analyzed using coulombic Karl Fischer titration, PMDA was analyzed using GC / FID, and color was analyzed using a Konica Minolta CM-5 colorimeter. One of the samples had sufficient mass and purity (greater than 99.9%) for commercial use, which is required by the specifications of most polymer manufacturers.

[0080] In a second laboratory-scale distillation in the rotating belt system, the dehydrated material was distilled. 380 g of a ~99% PMDA (~7000 ppm water) solution was added to a 1 L single-necked round-bottom flask. The system was sealed, and a vacuum was applied through the condenser and cold trap using an Edwards 2-stage rotary vane pump with a J-Kem vacuum controller. The condenser was maintained at 10°C during PMDA fraction collection. The vacuum was kept constant at 9–10 Torr, and the heating rate was kept constant at 10% output. The reflux ratio was initially 10:1, then reduced to 2:1 during product removal. Over a process of approximately 450 min, five fractions were collected, and water was analyzed using coulombic Karl Fischer chromatography, PMDA was analyzed using GC / FID, and color was analyzed using a Konica Minolta CM-5 colorimeter.

[0081] Figure 6 This is a process flow diagram of one implementation or layout of a complete industrial-scale PMDA production process based on the contents of this disclosure.

Claims

1. A method for preparing pentamethylenediamine (PMDA), comprising, a. A fermentation broth containing a pentane-1,5-diammonium salt of an anion selected from the group consisting of carbonate, sulfate and phosphate is contacted with an amount of an oxide or hydroxide salt of a divalent metal selected from magnesium and calcium, said amount being sufficient to form a broth containing one or more precipitates of one or more anions. b. Remove one or more precipitated divalent metal salts from the fermented broth to form a broth containing fewer of the one or more divalent metal salts; and c. Removal of PMDA from broths from which one or more precipitates of divalent metal salts have been removed.

2. The method according to claim 1, wherein one or more pentane-1,5-diammonium salts are primarily sulfates.

3. The method according to claim 1, wherein removing one or more precipitated metal salts from the fermented broth comprises at least one of the following: filtering the broth to obtain a osmotic salt cake fraction and a first filtrate fraction, or centrifuging the fermented broth to obtain a salt cake fraction and a first supernatant fraction.

4. The method of claim 3, wherein the first filtrate fraction or the first supernatant fraction contains less than 1% of PMDA salt anions initially present in the fermented broth.

5. The method of claim 3, further comprising washing the leachate fraction or salt cake fraction with water, filtering or centrifuging the washed leachate fraction or washed salt cake fraction to obtain a second filtrate fraction or a second supernatant fraction, and combining the first filtrate fraction and the second filtrate fraction or the first supernatant fraction and the second supernatant fraction to thereby form a combined filtrate fraction or a combined supernatant fraction containing PMDA.

6. The method according to claim 1, wherein removing PMDA from the broth comprises contacting the broth with a strong base type 1 anion exchange resin and obtaining an eluent fraction containing free base PMDA, the eluent fraction having less than 20 ppm by mass of carboxylate anions and less than 1 ppm by mass of carbonate anions, sulfate anions, phosphate anions and chloride anions, respectively.

7. The method of claim 6, further comprising flash evaporating the eluent fraction to obtain a vapor fraction with a PMDA concentration higher than that of the eluent fraction, and condensing the vapor fraction.

8. The method of claim 7, further comprising distilling the condensed vapor fraction to obtain a purified PMDA distillate with a purity of at least 99.5% wt / wt.

9. The method of claim 1, wherein the contact with the oxide or hydroxide salt of the divalent metal is initially carried out at a temperature of 25°C or lower, and then involves heating to a temperature greater than 25°C but below the boiling point of the fermented broth.

10. The method of claim 9, wherein the heating reaches a temperature of at least 50°C.

11. The method of claim 10, wherein the heating reaches a temperature of at least 65°C.

12. The method of claim 11, wherein the heating reaches a temperature of about 90°C.

13. The method of claim 1, wherein the anion is sulfate and the divalent metal salt is calcium hydroxide added relative to the sulfate at a molar ratio of about 2.5:

1.

14. A method for preparing pentamethylenediamine (PMDA), comprising, a. A fermentation broth containing one or more pentane-1,5-diammonium salts of one or more anions selected from the group consisting of carbonate, sulfate and phosphate is contacted with a certain amount of oxides or hydroxides of divalent metals selected from magnesium and calcium at a temperature of 25°C or lower for a first time period, and then the mixture is heated to a temperature above 25°C for a second time period, the second time period being sufficient to form one or more precipitates of the one or more anions of the divalent metal salts; b. Remove one or more precipitated divalent metal salts from the fermented broth by filtration or centrifugation to form a broth containing fewer of the one or more precipitated divalent metal salts as a first corresponding filtrate fraction or a first supernatant fraction, and provide a corresponding osmotic fraction or salt cake fraction. c. Wash the osmotic fraction or salt cake fraction with water at a temperature above 25°C; d. Filter or centrifuge the washed osmotic fraction or salt cake fraction to form a second filtrate fraction or a second supernatant fraction; e. Combine the first filtrate fraction and the second filtrate fraction or the first supernatant fraction and the second supernatant fraction to form a broth containing fewer of one or more divalent metal salts; f. Contact the broth with a strong base type 1 anion exchange resin to obtain an eluent fraction containing PMDA, the eluent fraction having less than 20 ppm of carboxylate anions and less than 1 ppm of carbonate anions, sulfate anions, phosphate anions and chloride anions. g. Evaporate the eluent fraction to obtain a concentrated PMDA fraction; and h. Distill the concentrated PMDA fraction to obtain purified PMDA with a purity of at least 99% by weight.

15. The method of claim 14, wherein the broth contact during the second time period and the washing of the slurry fraction or salt cake fraction are both performed at a temperature of at least 90°C but below the boiling temperature of the broth.

16. The method of claim 14, wherein the distillation of the concentrated PMDA fraction is carried out under vacuum pressure in a first distillation step to obtain a first PMDA distillate, and is carried out under vacuum pressure in a second distillation step to obtain a final PMDA distillate from the first PMDA distillate.

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