Process for the purification of pentamethylenediamine from lysine whole broth

Abstract

Disclosed herein is a method of preparing pentamethylenediamine (PMDA, also known as cadaverine or 1, 5 pentanediamine), by: contacting a fermentation broth containing pentane-1,5-diaminium 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 a quantity of a precipitated divalent metal salt or salts of the anion or anions; removing precipitated divalent metal salt or salts from the fermentation broth to form a broth comprising less of the divalent metal salt or salts; and removing PMDA from the broth from which precipitated divalent metal salt or salts have been removed.

Description

[0001] PROCESS FOR THE PURIFICATION OF PENTAMETHYLENEDIAMINE FROM LYSINE WHOLE BROTH

[0002] TECHNICAL FIELD

[0003] The invention relates to the preparation of pentane-l,5-diamine, also known as cadaverine or pentamethylenediamine (PMDA), from a lysine fermentation broth in a purity to be suitable for use as a monomer for polymer synthesis.

[0004] BACKGROUND

[0005] The present invention relates to a novel method and system for purifying cadaverine (or 1,5 -pentanediamine or pentamethylene diamine (PMDA)) from a fermentation broth. More specifically, the invention focuses on the purification of PMDA produced from a lysine fermentation broth, where lysine has been converted as previously known to PMDA through the action of lysine decarboxylase. PMDA finds applications in various industries, including the production of sustainable polymeric materials including polyurethanes, polyimides, and polyamides.

[0006] PMDA has gained considerable attention due to its diverse applications and sustainability in production via renewable resources through the microbial fermentation of lysine, a common amino acid. After lysine fermentation, lysine decarboxylase, an enzyme produced by specific microorganisms, catalyzes the conversion of lysine into PMDA. The production of PMDA by fermentation is however accompanied by the formation of various impurities and by-products which represent yield losses as well as complicate the recovery of PMDA in the typically very high purities required for making such sustainable polymeric materials. Particularly problematic is the presence of anions, particularly the major conjugate anion salts of PMDA made by fermentation such as phosphate or sulfate, as well as the presence of carbonate, carboxylic acids and amino acids and other organic contaminants.

[0007] Various approaches 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 some extent, these methods have various drawbacks, such as low yields, high energy consumption, and the use of environmentally harmful solvents or chemicals.

[0008] Hence, there remains a significant need for an improved purification method that overcomes the limitations of existing approaches. The present invention provides a novel and more efficient strategy to purify PMDA from a lysine fermentation broth with (in relation to the known alternative methods) one or more of an improved yield, a reduced production cost and a reduced environmental impact.

[0009] BRIEF SUMMARY

[0010] Described herein is a method of preparing pentamethylenediamine (PMDA), comprising contacting a fermentation broth containing one or more corresponding pentane- 1, 5 -diaminium 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 a quantity of a precipitated divalent metal salt or salts of the anion or anions; removing precipitated divalent metal salt or salts from the fermentation broth to form a broth comprising less of the divalent metal salt or salts; and removing PMDA from the broth from which precipitated divalent metal salt or salts have been removed.

[0011] In certain embodiments, substantially all of the precipitated pentane- 1,5- diaminium salts are removed to provide a desalted broth, from which PMDA freebase is recovered.

[0012] In certain embodiments, the pentane- 1,5 -diaminium salts are primarily sulfate salts.

[0013] In certain embodiments, removing the precipitated divalent metal salt or salts comprises at least one of filtering the broth containing the same over 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 or salt cake fraction with water and filtering the washed salt cake fraction or centrifuging the washed retentate or washed salt cake fraction to obtain a second filtrate fraction or second supernatant fraction and preferably then combining the first and second filtrate or first and second supernatant fractions to form a combined filtrate fraction or combined supernatant mass containing PMDA. It will be understood, incidentally, that the word “fraction” as used herein shall mean simply a part of a whole, whether that part is produced as a discrete part in a batchwise mode of operation or as a continuous partial portion in a continuous mode of operation. In further, preferred embodiments, the method includes further purifying PMDA from the broth from which precipitated divalent metal salt or salts have been removed, by contacting the broth with a strong base type 1 anion exchange resin and obtaining an eluant fraction containing freebase PMDA with less than 20 ppm carboxylate anions and less than 1 ppm each of carbonate, sulfate, phosphate, and chloride anions.

[0014] In further, preferred embodiments further purifying the PMDA includes flash evaporating the eluant fraction to obtain a vapor fraction with higher concentration PMDA than in the eluant fraction and condensing the vapor fraction.

[0015] In still further, preferred embodiments, the method further comprises distilling the condensed vapor fraction to obtain a purified PMDA distillate of at least 99.5% wt / wt purity.

[0016] In one particular embodiment, disclosed herein is a method of preparing PMDA comprising contacting a fermentation broth containing a pentane- 1, 5 -diaminium salt or salts of 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 for a first period of time at a temperature of 25 °C or lower then heating to a temperature greater than 25 °C for a second period of time whereby after the second period of time a solid mass fraction is formed of precipitated divalent metal salt or salts comprised of magnesium or calcium (not typically both being used) with the anion(s) of the pentane- 1,5-diaminium salt or salts ; removing the precipitated divalent metal salts in the solid mass fraction from the fermentation broth by filtration or centrifugation to form a) a broth from which anion(s) of the starting pentane- 1,5- diaminium salt or salts have thus been removed as a first filtrate or first supernatant and b) a retentate 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 or second supernatant fraction; combining the first and second filtrate or supernatants to form a combined broth fraction from which anion(s) of the starting pentane- 1,5 -diaminium salt or salts have thus been removed; contacting the combined broth fraction with a strong base type 1 anion exchange resin to obtain an eluant fraction containing PMDA with less than 20 ppm carboxylate anions and less than 1 ppm of carbonate, sulfate, phosphate, and chloride anions; evaporating the eluant fraction to obtain a concentrated PMDA sample; and distilling the concentrated PMDA sample fraction to obtain a purified PMDA sample having at least 99% purity on a wt / wt basis.

[0017] In certain embodiments of this particular sequence of steps, the contacting with the divalent metal salt and washing the salt cake are done at a temperature of at least 90 °C but less than the boiling temperature of the broth.

[0018] In certain embodiments the evaporation is done in a first evaporation step obtaining a concentrated bottoms fraction and in a second evaporation step obtaining a concentrated vapor fraction from the concentrated bottoms fraction.

[0019] Certain embodiments include wherein the distillation is done in a first distillation step under vacuum pressure obtaining a first PMDA distillate and in a second distillation step under vacuum pressure obtaining a final PMDA distillate

[0020] The best embodiments of the foregoing methods provide a monomer grade PMDA of a purity of at least 99.9%.

[0021] BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 illustrates the critical Ca(OH)2:SO4 mole ratio threshold for effective deionization (de-salting) of the PMDA reaction mixture.

[0023] Figures 2A - 2D show a time course of the percentage of sulfate removed from a PMDA sulfate whole broth using Ca(OH)z according to the present invention at 35 °C (A), 50°C (B), 65°C (C) and 90° C. (D).

[0024] Figures 3A and 3B show the concentrations of primary anions sulfate, phosphate, chloride and total carboxylates over time for a 4L PMDA reaction mixture deionization with Ca(OH)2 at 3:1 mole ratio to sulfate at 90C.

[0025] Figure 4 shows the effect of temperature and wash volume on recovering residual PMDA by washing a salt cake retentate fraction made by Ca(OH)2 precipitation of sulfate from a whole broth according to the present invention.

[0026] Figure 5 shows tables with data obtained from screening anion exchange resins for practices of certain steps of the present invention.

[0027] Figure 6 shows a process flow diagram for a commercial scale production facility designed to implement a particular illustrative embodiment of the invention starting from a fermentation to make lysine, through conversion to PMDA and then applying various measures to recover a purified PMDA product. DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0028] The following description of certain embodiments of a method according to the present invention is meant to be illustrative only of the present invention as more particularly defined by the claims which follow thereafter, and should not be taken as limiting of the present invention as so claimed and as the same would be understood by those of ordinary skill in the art, but as merely descriptive of the core principles underlying the present invention and the solution it provides to the need for improved methods for the recovery of PMDA produced from lysine fermentation broth.

[0029] With this caveat, the following description is particularly concerned with the preparation of purified pentamethylenediamine (PMDA) from a whole broth fermentation media in which the media has been adjusted to an appropriate pH using ammonium sulfate, so the lysine produced therein is in primarily in the form of lysine sulfate. Although the described embodiments use lysine sulfate, it should be noted that the same approach can be taken if the media is pH adjusted using phosphoric acid, forming lysine phosphate.

[0030] In the case of using ammonium sulfate, the majority of the ammonia is used as a nitrogen source for the growing lysine producing biomass. The lysine produced is catalytically decarboxylated using a lysine decarboxylase enzyme from E. coli (CadA) in the presence of pyridoxal-5 -phosphate to produce PMDA. The decarboxylation reaction introduces free carbonate anions into the media that also contains other detectable 1-6 carbon carboxylate anions in the form of formate, lactate, acetate, propionate, butyrate, isobutyrate, and glucarate. The PMDA salts in the broth therefore include sulfate or phosphate as dominant salts along with carbonate salts. In preferred applications of the method of the present disclosure at least 95% and more often at least 98% of the sulfate or phosphate and carboxylate anions are removed using calcium hydroxide precipitation, followed by filtration to form a desalted and, indeed, a substantially desalted broth.

[0031] The desalting step relies on the retrograde solubility of calcium or magnesium salts of sulfate, phosphate and carbonate, which means the water solubility of these salts decreases as temperature increases. The same is true for calcium hydroxide to a lesser extent. Therefore, the desalting step is executed in preferred embodiments by first contacting the fermentation broth with the calcium or magnesium oxide or hydroxide at room temperature (25 °C) or lower, then heating the mixture to an elevated temperature, meaning at a temperature greater than 25 °C up to the boiling point of the fermentation broth. In some embodiments the temperature should be at least 50 °C, in other embodiments the temperature should be at least 70 °C, in exemplary embodiment the temperature is about 90 °C and in preferred embodiments the temperature is from 90 °C up to the boiling point of the broth.

[0032] Although exemplified using calcium hydroxide, the method can be practiced with magnesium or calcium oxide, or hydroxide Residual anions may be removed from the desalted broth in certain embodiments using a type 1 strong base anion exchange resin. In further embodiments, the PMDA freebase solution resulting from the deionization is first concentrated by evaporation at reduced pressure, then flash evaporated overhead as a water: PMDA solution distillate. The product from flash evaporation can then be further concentrated using continuous distillation and then further purified to a polymer grade specification of greater than 99% or even greater than 99.9% purity, using for example high vacuum fractional distillation.

[0033] An overall process flow diagram for an illustrative industrial scale operation for producing PMDA according to the present disclosure is shown in Fig. 6.

[0034] Deionization by Precipitation

[0035] In a typical practice, lysine is produced by fermentation using a lysine producing bacteria such as Corynebacteria glutamicum or E. coli with the addition of ammonium sulfate during the fermentation process. The ammonium is mostly consumed as a source of nitrogen to feed the growing culture and the majority of lysine produced is present as lysine sulfate, though as previously noted, it will be readily understood by one of ordinary skill in the art that lysine phosphate can also be used in conjunction with the method of the present invention if the fermentation were conducted in the presence of phosphate as the dominant anion.

[0036] Moreover, a lysine whole broth can be used without initial removal of biomass by clarification because the first step after the precipitation reaction that forms an insoluble material according to the present invention will be centrifugation or filtration, that will also remove the biomass along with precipitated salts.

[0037] From any of these starting points (i.e., clarified lysine sulfate or lysine phosphate broths or whole lysine sulfate or phosphate broths), PMDA is formed by adding lysine decarboxylase to the fermentation broth to decarboxylate the lysine, forming PMDA as a salt of sulfate or phosphate as the major anions in the fermentation broth. Once the decarboxylation reaction has progressed to >99% conversion, the reaction mixture is optionally heat-treated at 70 °C for 30 min to kill any remaining living organisms. The heat treatment is only necessary if the reaction mixture is going to be held at room temperature for an extended period of time before processing, otherwise the heat treatment can be omitted.

[0038] The first stage of PMDA purification according to an exemplary embodiment of the invention is deionization by calcium hydroxide precipitation. In the work reported in greater detail below to demonstrate the invention, the initial amount of lysine present in the clarified whole broth was 14% wt / wt (0.09589 mol) which was buffered with SO4 (4.5%, 0.046875mol) to pH 7.0.The decarboxylation reaction generates Imole CO2 per mole of lysine. The measured lysine:SO4 mole ratio is roughly 2:1. The CO2 either evolves out of solution or is captured as PMDA-ammonium bicarbonate, PMDA-ammonium carbonate, or free carbonate. Both the sulfate and carbonate act as pH buffers

[0039] Treatment of the clarified whole broth containing PMDA sulfate with Ca(OH)2 solid resulted in an insoluble calcium sulfate species that precipitated out of solution, leaving PMDA free base and water. Treatment of the broth with Ca(OH)2 also produces some calcium-bicarbonate which is water soluble at pH 6.5 - 10.5, along with PMDA free base, and water. As the calcium sulfate precipitates out of solution, however, the pH increases. Above pH 10.5 the calcium bicarbonate changes to the insoluble calcium carbonate species that also precipitates out of solution.

[0040] The form (dihydrate, hemihydrate, or anhydrate) and solubility of calcium sulfate are temperature dependent. Many of the calcium compounds formed by the addition of Ca(OH)2 display retrograde solubility, meaning that higher temperatures during treatment show greater reduction of sulfate because the salts formed by the present invention exhibit reduced solubility at higher temperatures. However, Ca(OH)2 itself also exhibits retrograde solubility that could hamper the reaction, so it is best to add the Ca(OH)2 to the reaction mixture at room temperature or below, then heat to force greater precipitation and filter the mixture while the reaction mixture is still hot. The use of calcium hydroxide itself provides some of the heating because its addition to the broth gives a measurable 5 - 10°C exotherm. Other calcium carboxylate salts formed by the addition of Ca(OH)2 exhibit pH dependency. Calcium-bicarbonate at pH 6.5 - 10.5 is completely soluble while calcium-carbonate at pH >10.5 is nearly insoluble. The other calcium- salts of the 1-6 carbon carboxylate species are present at around 1% wt / wt in the broth show higher, non-retrograde, solubility.

[0041] Multiple experiments were conducted by the inventors focused on time, temperature and mole ratio of Ca(0H)2 to sulfate. Initial proof-of-concept experiments used an economically untenable excess of Ca(0H)2 relative to sulfate while subsequent efforts were focused on reducing the amount of Ca(0H)2 to obtain an economically optimum value. Sulfate was used as the key anionic marker for the amount of calcium hydroxide to add, due to the robustness of the sulfate analysis. As mentioned above, in addition to sulfate, the reaction mixture derived from a lysine whole fermentation broth also contains several other anions including carbonate, phosphate, carboxylate and amino acids.

[0042] Work began with simple DOE factorial experiments to understand main effects and reduce calcium hydroxide. All the factorial experiments show significant (>97 %) reduction in SO4. However, it quickly became apparent the calcium hydroxide to sulfate ratio was the most important factor and revealed a distinct threshold for efficacy. Plotting the data from a total of 64 reactions including: 3 factorial screening DOEs, augmented reaction points (DOE 4&5), and 4 timed reaction sets (35, 50, 65, 90 deg C), the raw data suggested a critical Ca(OH)2:SO4 ratio threshold at 2.5 mol / mol (Fig. 1). Indeed, the experiments revealed that the optimum amount of calcium hydroxide to use is about 2.5 times the calculated amount of sulfate in the broth. The need for excess Ca(OH)2 is more than likely due to the presence of the additional, measured or unmeasured anions in solution.

[0043] With reference now to Figure 2 (graphs A-D), four sets of 6 timed reactions were run at the 10 cubic centimeter scale to observe the rate of sulfate removal and gain better resolution around temperature and time. The PMDA sulfate containing broth was agitated with a stir bar with a 2.5 molar ratio of calcium hydroxide to sulfate for 0 to 4 hours at 35°C, 50°C,65°C, and 90°C.

[0044] The sulfate removal reaction with calcium hydroxide is surprisingly rapid, with the majority (>95%) of the SO4 dropping out of solution in the first 15 minutes at all temperatures investigated. The retrograde solubility of calcium sulfate was apparent in the quicker removal of sulfate at higher temperatures compared to the lower temperature reactions at the same mole ratio. The higher 90-degree Celsius temperature runs, however, showed similar results to the 65 degree Celsius runs in total reduction of SO4, at around 98% (1100 ppm by total weight residual). The higher temperature reactions resulted in less precipitate in the filtrate after CaSO4 removal over time, at ambient temperature. Some differences were observed in the total SO4 reduction between different reaction temperatures over the course of the full 4-hour reaction time. The best results in the timed and factorial experiments were 97 - 98% reduction of SO4 on a mass basis, compared to 100% reduction in the PO4 buffered reactions. This is the direct effect of the disparity in solubilities between calcium sulfate and calcium phosphate. The PMDA and total carboxylic acid concentrations were unaffected during the calcium treatment, staying constant or slightly increasing over time.

[0045] Accordingly, the present teaching in removing sulfate ions from a PMDA sulfate containing broth can be practiced at any temperature from 25°C to the boiling temperature of the media, preferably at temperature of 35°C to boiling, more preferably at 50°C to boiling, still more preferably at 65°C to boiling, and most preferably at 90°C to boiling.

[0046] After Ca(OH)2 treatment of the PMDA containing broth, unidentified solids were observed to continue to precipitate over time at room temperature. This could be the slow interconversion between CafHCCh CaCCh. The extent of the precipitation seems to correlate to the reaction temperature more than the retrograde solubility of calcium sulfate. A lower temperature treatment results in a greater amount of residual Ca and more additional precipitation over time, whereas higher temperature reactions showed lower residual Ca concentration and less, or no additional precipitation. The concentrations of calcium and sulfate were measured by ICP / OES and IC / CD respectively in the supernatant of the samples over time. While the concentration of residual Ca showed some reduction, the SO4 appeared unaffected at all experimental temperatures and times after treatment.

[0047] Screening and optimization experiments above were conducted in the lab at the 20 mL scale. The calcium treatment of the PMDA reaction mixture generated from a lysine sulfate whole broth feedstock was then scaled up multiple times at IL, 4L, and WOOL scales with excellent results. At the 1 or 4L scale, calcium treatment of PMDA reaction mixtures was conducted in a three-neck round bottom flask fitted with a mechanical agitator, thermocouple, and temperature-controlled heating mantle under inert conditions with argon or nitrogen gas displacement of air.

[0048] In one experiment, 4L of unfiltered whole broth lysine sulfate was treated with CadA to form PMDA. The reaction mixture, also unfiltered, was treated by slow addition of solid calcium hydroxide at room temperature up to a mole ratio of 3.08: 1 Ca(OH)2:SO4 , then the temperature was raised to and held at 90°C for 4.5 hrs before the mixture as a whole was then filtered hot through a Buchner funnel containing a Whatman GF / A filter. Sulfate was reduced by about 97% in the first 90 minutes, which was about 15 minutes after the target temperature was reached. Phosphate present in the broth was also reduced by 100% almost immediately while the chloride remained stable. The total carboxylates interestingly appeared to double in concentration (Table 1., Fig 3A-B). This might be the result of base catalyzed protein hydrolysis leading to peptide and amino acid release.

[0049] Table 1

[0050] Table 1 shows the reduction of anionic species in PMDA reaction mixture, at 90C, over time, at the 4L scale.

[0051] In further experiments, two scaled up calcium hydroxide treatments of two separate PMDA reaction mixtures were performed using a 110 gallon, stainless steel, baffled reactor with a 45 deg offset pitch blade turbine agitator with internal steam coil. In each of the two scaled up experiments, a 240 kg PMDA reaction mixture derived by decarboxylation of a whole lysine fermentation broth was treated with 31 kg solid Ca(OH)2, in a 3:1 mokmol ratio to sulfate at room temperature. Then the treated broth was heated to 90 °C and sampled at multiple time points. The heterogeneous slurry was filtered hot through a custom Buchner funnel fitted with a fiber filter and vacuum filtered for ~40 minutes. Table 2

[0052] Table 2 shows that calcium hydroxide treatments of the PMDA reactions showed a >99% reduction in sulfate concentration after filtration and a PMDA yield of 96% on a mass basis.

[0053] A considerable amount of PMDA is trapped in the wet cake after filtration and should preferably be washed out of the cake to achieve a better yield. Provided that the pH of the reaction after calcium addition is >13 the majority of the PMDA should not be chemically bound and consequently able to be recovered simply with hot water wash(es) of the cake. In one lab experiment at the IL scale, roughly 90% by mass of the generated PMDA was recovered in the mother liquor during the first filtration while 10% was still adsorbed on the wet cake. Similar results were observed at the 4 kg and 240 kg scales. A screening experiment in the lab at the 10 g scale was conducted to optimize the cake washing step.

[0054] Wet cake from a IL Ca(OH)2 treatment was used for wash experiments at the 10 g scale, exploring multiple conditions, using a Buchner funnel containing GF / A filter paper. The focus of the experiment was to maximize PMDA yield through optimization of water temperature and weight ratio of water to cake. The water ratio to wet cake by mass was the most significant variable for PMDA recovery, with the best water to weight cake ratio demonstrated being a ratio of 4: 1. Temperature was also a factor, with washing at a temperatures of 80°C being better than at 40°C, which in turn was better than 20°C (Fig. 4). Unfortunately, the higher wash ratio also adds more water to be evaporated downstream, increasing utilities cost. Temperature is a significant variable for PMDA recovery, hotter wash water recovered more yield, and the effect is increased at low wash water to cake weight ratios. In addition to improved PMDA recovery as a consideration, the wash should preferably be hot to take advantage of retrograde solubility to keep calcium sulfate in the solid phase. The roughly 90% recovery of PMDA from cake was improved to 96% - 99% recovery of PMDA total after washing, when the first filtrate containing desalted PMDA was added to the second filtrate being the wash water obtained after filtering the washed cake over the filter.

[0055] Washing efficiency might be improved with the use of either a belt filter or a centrifuge allowing for the reduction in wash water. The wet cake itself is roughly 60% solid and 40% water. Some residual PMDA is left in the cake along with other organic small molecules however the bulk of the dry solid is inorganic calcium salts, including calcium carbonate, calcium sulfate, and calcium hydroxide. Heating the cake to high temperatures to burn any organic material and convert the calcium hydroxide and carbonate into calcium oxide would allow this stream to be recycled all or in part, to be reused as the precipitating salt in the first step of the process.

[0056] Ion Exchange

[0057] The mother liquor and wash filtrates were combined into a single process stream that contains residual anions that should be removed prior to evaporation. Residual sulfate in the 700 - 1500 ppm range and chloride in the 500 - 1000 ppm range are typical inorganic anion concentrations remaining in the combined filtrate, while phosphate is almost always below detection. Organic anions like carboxylates are present in the 3000 - 6000 ppm range with exceptions sometimes as high as 2% w / w. Amino acids and ammonia present at a 2000 - 5000 ppm concentration range are also typical. It is expected, based on current understanding of the chemistry and composition of the stream, that some amount of carbonate or bicarbonate is also present at a significant concentration, however carbonate species are especially difficult to measure accurately, particularly at low levels. Inorganic cations including calcium, potassium, and sodium at the 1000 - 5000 ppm rage total are normally present in the filtrate streams. Ion exchange was investigated for suitability in removing these minor species.

[0058] Ion exchange of carboxylic acids and amino acids using standard ion exchange resins proved challenging. Screening experiments with standard strong base type 1 (strong base) and type 2 (weak base) anion resins gave mixed results. Resin screenings were conducted using a 10 cc HDPE graduated syringe fitted with a Titan 3 5um nylon filter. Resin was added to the syringe, then washed using the plunger with lOcc 18MQ MQwater, 10 cc 5% sodium hydroxide, and then 10 cc water again to ensure that the resin was in the hydroxide form. An aliquot of filtrate product obtained after calcium hydroxide precipitation was added to the top of the resin using a pipette, then passed through the resin using the plunger. The effluent was collected and analyzed by IC for anions. Figure 5 table 1 shows that the type I ion exchange resins sold under the tradenames Dowex 1x8 200-400 mesh Type 1 and Purolite pfa860 were effective at removing most of the sulfate, carboxylate and chloride ions present in the desalted filtrate in one bed volume flow contact with the Type 1 resin. However only the Dowex 1x8 200-400 mesh showed any reduction of carboxylic and amino acids Fig 5 table 2 likely due to the improved kinetics of the smaller resin size (70um) compared to the industrial grade resin size (300um).

[0059] The total desalted filtrate from a 4L scale-up reaction was acquired and contacted with DOWEX 1x8 200-400 type 1 strong base anion exchange resin for a series of break through experiments at 10 cc and 500 cc scales. Breakthrough experiments were conducted in a #25 glass jacketed IX column with a recirculation heater / chiller and 80 sample automated fraction collector. 50cc DOWEX 1x8 was loaded into the column and washed with 500 cc MQH20 at 30°C and 5mL / min flow rate, then regenerated with 500 cc 5% KOH / MQWater at 30°C and lOmL / min flow rate. The resin expands on contact with base from 50cc to roughly 63.9 cc and showed a visible color change from white to orange. The resin was washed again with 1000 cc MQH20 at 30°C and 10 mL / min flow rate. Feed was then introduced to the resin at 5mL / min and fractions were collected at a rate dependent upon the feed flow. The samples were analyzed by IC / CD for anion concentration.

[0060] Flow rate, temperature, and the total number of regenerations were investigated in the column experiments. Temperature in the 30 - 50°C range seemed to make little impact on the resin utility as did flow rate in the 2.5 - 10 mL / min range. For commercial ion exchange applications, 5 - 10 BV / hr are acceptable. In these experiments 2.5 - 10 mL / min for a 50 cc resin bed is equivalent to roughly 3 - 12 BV / hr. Virgin resin never showed SO4 breakthrough, only after regeneration was SO4 visible in the effluent. Also apparent after regeneration was the diminishing capacity for carboxylates, decreasing from roughly 6BV to 3BV over four breakthrough experiments. Chloride was constant regardless.

[0061] As illustrated in Table 3, it was determined the Dowex Type I resin was capable of absorbing most of the carboxylate and chloride and at least 95% of the sulfate ions from about 3.5 to 6 bed volumes of desalted broth filtrate and that this capacity remained even after three rounds of bed regeneration.

[0062] Table 3

[0063] The anion exchange was scaled up to a IL resin bed and used to treat 3.165 kg of combined filtrates of desalted PMDA broth at room temperature, and 2 BV / hr flowrate. A #50 glass, non-jacketed, IX column with dimensions 34.3cm L x 8.28cm D, was charged with l,000cc DOWEX 1x8 200-400, then washed with 6,000cc MQH2O at RT, 40mL / min, 3psi. The resin was then regenerated with 4,000cc 5% NaOH / MQWater at RT, 40mL / min, 5psi. The bed was washed again with 2,000cc MQH2O, RT, 40mL / min, 5psi, then regenerated again with 4,000cc 5% NaOH / MQWater, RT, 40mL / min, 5psi to ensure complete regeneration. The column was washed one last time with 8,000cc MQH20, RT, 40mL / min, 5psi. The PMDA yield was 95%, the SO4 reduction 100%, the carboxylate reduction was 99.6%, and the amino acid + NH4 reduction was 82.8%. The deionized product was used for evaporation experiments.

[0064] Evaporation

[0065] Two evaporation steps are used to concentrate the desalted, fermentation broth comprised of the combined filtrate and wash samples subjected to ion exchange chromatography to deionize the sample. Step one is a simple concentration where the diluted, deionized ion exchange product is dewatered under reduced pressure. The second step is a flash evaporation, in which the concentrated PMDA is taken overhead as a distillate product. The water is removed during the first evaporation under relatively mild conditions at a temperature of 45-49°C and a vacuum pressure of -27 in Hg. Despite the low temp and vacuum and high boiling point of PMDA, some loss is observed in this step, especially towards the end when PMDA becomes more concentrated. In one experiment 9.6 kg of deionized PMDA solution in water was concentrated to 30% in a 120 L evaporator over 21 hours. The concentration in the pot and in the distillate was monitored by GC.

[0066] Table 4 While the concentration of the PMDA in the distillate never got above about

[0067] 3000 ppm, roughly 4% of the total PMDA was lost over the course of this evaporation at -27in Hg at less 50°C. The loss of PMDA at evaporation conditions below its boiling point suggests it has some affinity to water or PMDA entrainment in the distillate. In another evaporation experiment using a similarly configured evaporation system 1184 kg of ion exchange product was concentrated from 4% w / w to 40% w / w PMDA in approximately 144 total hours. The average pressure, reboiler temperature, and flash vessel temperatures were 1.3psia, 93 deg C and 50 deg C, respectively. The average rate of condensate removal was 38 Ibs / hr.

[0068] Table 5

[0069] Table 5 shows the average operation conditions for the concentration by evaporation of a deionized aqueous PMDA reaction mixture by reduced pressure evaporation.

[0070] Near complete deionization is critical to the second evaporation step (PMDA flash evaporation) which may also be called a first distillation step because PMDA is volatilized and recovered in the vapor phase as opposed to being concentrated in the pot. Any anions present in the feed for evaporation are potential salt formers with PMDA rendering it non-volatile and therefore less recoverable by evaporative distillation. Moreover, salt formation can lead to significant solidification in the bottoms of the evaporator compounding the effect and significantly impacting processability and yield. While the bulk of the sulfate, phosphate and carbonate are removed during the calcium hydroxide precipitation step, and considerable amount of sulfate and carbonate anions are removed by the ion exchange step, an unacceptably high amount of organic contaminants still remain and must be polished out of solution along with residual sulfate and carbonate to make polymer grade material

[0071] Pot material recovered from the first dewatering evaporation step described above was transferred to a 20 L Buchi industrial Rotovap. A batch type evaporator is most useful for this step compared to an evaporation system that heats via a pumparound loop through a heat exchanger. Also important is high vacuum to keep pot temperature low in this second evaporation step where the PMDA is recovered as the vapor distillate. Table 6 below shows a time course, temperature, vacuum pressure used to recover PMDA from the vapor phase in this second evaporation step using such a device. Table 6 Solidification of the bottoms occurred in the flask after about 50% of the available PMDA was removed as distillate. The intractable bottoms were re-dissolved with DI water and re-evaporated only to result in the same solidification issue, with diminishing returns of 22% PMDA yield. After two rounds of evaporation the experiment was stopped with a 72% total yield of PMDA at greater than 99% purity. The purity was actually at least 99.9%.

[0072] Comparative evaporator yields at three different scales illustrate the impact of the ion exchange on the yield obtainable from the evaporation flash step is illustrated in Table 7 below. Table 7

[0073] Overall superior yields were realized when the Dowex resin was used in the ion exchange chromatography step because it removed more ions than the other resins resulting in a cleaner PMDA for the subsequent evaporation steps, leading to more volatilization and ultimately more recovery of the PMDA in the final evaporation step. Ion exchange is described in the deionization section above, however the impact of a poor ion exchange is realized in the evaporation section of the process. The Mitsubishi strong base type 1 anion exchange resin PA3O8 has the same chemical functionality as the DOWEX 1x8, the feeds have very similar compositions, and the method of treatment is the same down-flow 2 - 5 BV / hr through a column at ambient temperature and pressure. The results however are strikingly different. The total deionization for the larger diameter resin is measurably sub-par compared to the small particle Dowex resin and this results in a demonstrably better evaporation in both yield and material processability.

[0074] Distillation

[0075] Fractional distillation is the final purification step in the PMDA process. The feed into the final distillation is an aqueous solution of PMDA 50 - 60% weigh 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 the upstream process prior to distillation, however water and minor organic impurities, some with close boiling points to PMDA, remain after the second evaporation. Minor organic impurities include but are not limited to: CO2, ammonia, trimethylamine, monoethanolamine, piperidine, 2,3,4,5-tetrahydropyridine, putrescine, d-valerolactam, a-amino-e-caprolactam, PMDA-mono-acetamide, PMDA-bis- acetamide, and other unknown amine containing compounds. The separation during the final distillation is both of PMDA from water, and of PMDA from amine containing organic impurities.

[0076] Feed to the distillation is a homogeneous, clear colorless solution comprised of water, PMDA and a mixture of minor organic impurities shown in Table 8 below. PMDA boils at a temperature of 180 °C so most of the remaining impurities are separable with adequate distillation column and operating conditions.

[0077] Table 8 The primary end use of PMDA is for polymer applications such as polyurethane or nylon. Both applications require very stringent specifications that make understanding and optimizing the fractional distillation essential to a successful industrial process. In-spec, and close to in-spec, PMDA have been produced according to the present teaching from lab-scale (10 g - 200 g) to the semi-pilot scale (1kg - 5kg) in good yield. Fractional distillation of evaporator flash product has been performed at the lab scale, in standard distillation glassware (e.g. Vigreux) and in a spinning band distillation system. Distillations have also been scaled-up to the multi-kilogram scale. Lab distillations use a single pot still, setup for removal of the water and low-boiling compounds first, followed by fractions of pure PMDA as distillate product, while higher boiling compounds remain in the bottoms as residue. At the pilot scale, distillation equipment utilizes two systems, the first is a continuous still for dewatering and lights removal, followed by a second pot-still used for final purification.

[0078] A few points worth reiterating on fractional distillation of PMDA regardless of the equipment: the atmosphere must remain inert by flushing with N2 or Ar including the final product,; the vacuum must remain high, i.e., less than 50 torr with maintaining an inert atmosphere but ideally less than 10 torr, to reduce the needed pot temperature to preferably below 50 °C, and air leaks need to be avoided, as air leaks can cause carbonate formation in the joints and can lead to occlusions in the distillation system.

[0079] In one experiment a spinning band distillation system was used for distillation of a feed containing 576 g of 64% PMDA in water, which was added to a IL single neck round bottom flask. The system was sealed, and 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 held at 0°C during the initial dewatering stage of the distillation then increased to I0°C during PMDA fraction collection. The vacuum was help constant at 8 - 9 Torr and the heat rate was held constant at 10% output. The reflux ratio was initially 10:1 then reduced during product take-off to 5:1, then finally 2:1. Over the course of roughly 1000 minutes five fractions were collected and analyzed for water using coulometric Karl Fischer, PMDA using GC / FID, and color using Konica Minolta CM-5 colorimeter. One of the samples was of sufficient quality of greater than 99.9% purity for commercial use, imposed by most polymer maker specifications.

[0080] In a second lab-scale distillation in the spinning band system, dewatered material was distilled. 380g of -99% PMDA (~7000ppm water) solution was added to the IL single neck round bottom flask. The system was sealed, and 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 held at 10C during PMDA fraction collection. Vacuum was held constant at 9 - 10 Torr and the heat rate was held constant at 10% output. Reflux ratio was initially 10:1 then reduced during product take-off to 2:1. Over the course of roughly 450min five fractions were collected and analyzed for water using coulometric Karl Fischer, PMDA using GC / FID, and color using Konica Minolta CM-5 colorimeter.

[0081] Figure 6 is a process flow diagram for one embodiment or arrangement of a complete industrial scale PMDA production process according to the present disclosure.

Claims

CLAIMS1. A method of preparing pentamethylenediamine (PMDA) comprising, a. contacting a fermentation broth containing pentane- 1, 5 -diaminium 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 a quantity of a precipitated divalent metal salt or salts of the anion or anions; b. removing precipitated divalent metal salt or salts from the fermentation broth to form a broth comprising less of the divalent metal salt or salts; and c. removing PMDA from the broth from which precipitated divalent metal salt or salts have been removed.

2. The method of claim 1 wherein the pentane- 1,5 -diaminium salt or salts is or are primarily sulfate salts.

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

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

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

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

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

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

9. The method of claim 1 wherein the contacting with the oxide or hydroxide salt of the divalent metal is initially done at a temperature of 25 °C or lower, then involves heated to a temperature greater than 25 °C but less than the boiling point of the fermentation broth.

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

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

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

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

14. A method of preparing pentamethylenediamine (PMDA) comprising, a. contacting a fermentation broth containing a pentane- 1,5-diaminium salt or salts of an anion or 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 for a first period of time at a temperature of 25 °C or lower then heating the mixture to a temperature greater than 25 °C for a second period of time sufficient to form a precipitated divalent metal salt or salts of the anion or anions; b. removing precipitated divalent metal salt or salts from the fermentation broth by filtration or centrifugation to form a broth containing less of the precipitated divalent metal salt or salts as a first, corresponding filtrate fraction or first supernatant fraction and provide a corresponding retentate fraction or salt cake fraction; c. washing the retentate fraction or salt cake fraction with water at a temperature greater than 25 °C ; d. filtering or centrifuging the washed retentate fraction or salt cake fraction to form a second filtrate fraction or second supernatant fraction; e. combining the first and second filtrate fractions or first and second supernatant fractions to form a broth comprising less of the divalent metal salt or salts; f. contacting the broth with a strong base type 1 anion exchange resin to obtain an eluant fraction containing PMDA with less than 20 ppm carboxylate anions and less than 1 ppm of carbonate, sulfate, phosphate, and chloride anions;g. evaporating the eluant fraction to obtain a concentrated PMDA fraction; and h. distilling the concentrated PMDA fraction to obtain a purified PMDA having at least a 99% purity on a wt / wt basis.

15. The method of claim 14 wherein the broth contacting for the second period of time and washing of the retentate fraction or salt cake fraction are both done at a temperature of at least 90 °C but less than the boiling temperature of the broth.

16. The method of claim 14 wherein the distillation of the concentrated PMDA fraction is done in a first distillation step under vacuum pressure obtaining a first PMDA distillate and in a second distillation step under vacuum pressure obtaining a final PMDA distillate from the first PMDA distillate.

Images