ACID/SALT SEPARATION

Abstract

The invention provides a method for preparing a carboxylic acid, which method includes the steps of providing magnesium carboxylate, wherein the carboxylic acid corresponding with the carboxylate has a solubility in water at 20 C. of 80 g/100 g water or less; acidifying the magnesium carboxylate with HCl, thereby obtaining a solution comprising carboxylic acid and magnesium chloride (MgCl2); optionally a concentration step, wherein the solution comprising carboxylic acid and MgCl2 is concentrated; precipitating the carboxylic acid from the solution comprising the carboxylic acid and MgCl2, thereby obtaining a carboxylic acid precipitate and a MgCl2 solution.

Claims

1. Method for the recovery of a carboxylic acid, comprising the steps of: providing an aqueous solution or suspension of magnesium carboxylate, wherein the carboxylic acid corresponding with the carboxylate has a solubility in water at 20 C. of 80 g/100 g water or less; obtaining solid magnesium carboxylate from said solution or suspension and acidifying the magnesium carboxylate with a solution of hydrogen chloride (HCl), thereby obtaining a solution comprising carboxylic acid and magnesium chloride (MgCl.sub.2); optionally a concentration step, wherein the solution comprising carboxylic acid and MgCl.sub.2 is concentrated; and, precipitating carboxylic acid from the solution comprising carboxylic acid and MgCl.sub.2, thereby obtaining a carboxylic acid precipitate and a MgCl.sub.2 solution.

2. Method according to claim 1, wherein the carboxylic acid has a solubility in water at 20 C. that is lower than that of MgCl.sub.2.

3. Method according to claim 1, wherein the carboxylic acid has a solubility in water of less than 30g /100g water.

4. The method of claim 1, wherein the carboxylic acid is selected from the group consisting of adipic acid, itaconic acid, 2,5-furandicarboxylic acid, fumaric acid, oxalic acid, maleic acid, glutaric acid, malonic acid, and fatty acids having more than 10 carbon atoms.

5. The method according to claim 1, wherein: the aqueous solution or aqueous suspension comprises at least 10 wt. % magnesium carboxylate, based on the total weight of the solution or suspension; and, the solution comprising the carboxylic acid and MgCl.sub.2 comprises at least 5 wt. % of magnesium chloride based on the total weight of the solution comprising carboxylic acid.

6. The method according to claim 1, wherein magnesium carboxylate is provided in dissolved form, as part of an aqueous solution or as part of an aqueous suspension obtained in a fermentation process.

7. The method according to claim 6, wherein said magnesium carboxylate is provided in dissolved form as part of an aqueous suspension obtained in a fermentation process by neutralization of carboxylic acid with a magnesium base and wherein, in said aqueous suspension, at least 95 wt. % of said magnesium carboxylate is in dissolved form.

8. The method according to claim 7, wherein said aqueous suspension consists of dissolved magnesium carboxylate and insoluble biomass.

9. The method according to claim 1, wherein said provided aqueous solution or suspension of magnesium carboxylate is concentrated by evaporation to obtain solid magnesium carboxylate.

10. The method according to claim 9, wherein the concentrated solution or suspension of magnesium carboxylate is subjected to solid-liquid separation and the separated solid magnesium carboxylate is acidified.

11. The method according to claim 1, wherein acidifying the magnesium carboxylate and precipitating the carboxylic acid thus formed are conducted in or as one step.

12. The method according to claim 1, wherein the MgCl.sub.2 solution or concentrated MgCl.sub.2 solution is subjected to a second precipitation step to recover at least part of the carboxylic acid remaining in the MgCl.sub.2 solution obtained in the first precipitation step.

13. The method according to claim 12, wherein the second precipitation is conducted by cooling and/or concentrating the MgCl.sub.2 solution.

14. The method according to claim 12, wherein additional MgCl.sub.2 is added to the MgCl.sub.2 solution prior to the second precipitation.

15. The method according to claim 1, wherein the solution comprising the carboxylic acid and MgCl.sub.2 is concentrated to a carboxylic acid concentration that is equal or up to 10 g/L lower than the saturation point of the carboxylic acid.

16. The method according to claim 1, wherein the solution comprising the carboxylic acid and MgCl.sub.2 is concentrated to a carboxylic acid concentration that is equal or up to 5 g/L lower than the saturation point of the carboxylic acid.

17. The method according to claim 1, further comprising: subjecting the MgCl.sub.2 solution to a thermal decomposition step at temperatures of at least 300 C., thereby decomposing the MgCl.sub.2 to magnesium oxide (MgO) and HCl; dissolving the HCl formed in the thermal decomposition step in water, thereby obtaining a HCl solution; and bringing the MgO in contact with water, thereby obtaining Mg(OH).sub.2, which Mg(OH).sub.2 is optionally recycled for use in a fermentation process.

18. The method according to claim 17, wherein thermal decomposition is conducted using a spray roaster.

19. The method according to claim 17, wherein the thermal decomposition is conducted at a pressure of ranging from 0.1-10 bar.

20. The method according to claim 17, wherein the thermal decomposition is conducted at a temperature ranging from 300-450 C.

21. The method according to claim 17, wherein Mg(OH).sub.2 is converted to MgCO.sub.3, which is then used as a neutralizing agent in a fermentation process.

22. The method according to claim 17, wherein thermal decomposition is conducted by spraying the MgCl.sub.2 solution into contact with a stream of hot gas.

Description

EXAMPLE 1

Magnesium Dicarboxylate Preparation

[0066] Magnesium hydroxide was added to a solution of dicarboxylic acid in water and heated up to complete dissolution. Four different carboxylic acids were used: adipic acid, fumaric acid, itaconic acid and 2,5-furandicarboxylic acid. The amounts of each component are given in Table 1. The resulting dicarboxylate solution was meant to resemble a magnesium dicarboxylate solution obtained in a fermentation process. Although a magnesium dicarboxylate solution obtained in a fermentation process generally comprises compounds other than magnesium dicarbooxylate, such as a relatively large amount of impurities, the magnesium dicarboxylate solution prepared for this example was considered to sufficiently resemble a magnesium dicarboxylate solution obtained in a fermentation process to show the proof of principle that the invention works.

TABLE-US-00001 TABLE 1 Magnesium Dicarboxylic Type of dicarboxylic oxide acid water acid [g] [g] [g] Aclipic acid 47 171 767 Fumaric acid 6.4 18.6 1082 Itaconic acid 51 164 745 2,5-furandicarboxylic 2.4 9.5 528 acid

EXAMPLE 2

Dicarboxylic Acid Precipitation

[0067] A certain amount of an aqueous solution of HCl was added to the magnesium dicarboxylate solution from Example 1, as indicated in Table 2. The temperature of the thus obtained mixtures is also given in Table 2. The mixture was cooled to 20 C. and a precipitate was formed. During cooling, samples were taken of the solution for each 101 centigrade. The composition of the samples and the total amount of precipitate formed were determined.

TABLE-US-00002 TABLE 2 Magnesium Dicarboxylate HCl Type of dicarboxylic solution concentration HCl T, o acid [g] [% (g/g)] [g] [ C.] Aclipic acid 985 37 231 80 Fumaric acid 1107 34.4 36 60 Itaconic acid 960 37 249 60 2,5-furandicarboxylic 541 37 12 50 acid

[0068] The samples were taken only from the solution (for sampling, stirrer was stopped some few seconds, and after crystal settling, sample taken from the upper layer). Magnesium and dicarboxylic acid in solution were analyzed and expressed as g/g water. The amount of crystal produced was calculated as difference between the initial dicarboxylic mass and the remaining dicarboxylic mass in solution.

[0069] The results are shown in Table 3-Table 6 for adipic acid, fumaric acid, itaconic acid and 2,5 furandicarboxylic acid respectively.

TABLE-US-00003 TABLE 3 Aclipic Acid Mg Concentration Amount of Temperature concentration in the in the solution precipitate ( C.) solution (wt %) (wt %) formed (g) 81 14.2 2.7 0 70 11.5 2.6 37.1 60 6.1 2.7 104.9 51 3.5 2.8 134.8 40 2 2.7 151.3 30 1.2 2.8 160.0 20 0.7 2.8 165.3

TABLE-US-00004 TABLE 4 Fumaric Acid Mg Amount of Temperature concentration in the concentration in the precipitate ( C.) solution (wt %) solution (mg/kg) formed (g) 60 1.6 3420 0 50 1.1 3450 5.8 39 0.7 3450 10.4 30 0.5 3450 12.6 20 0.5 3470 12.6

TABLE-US-00005 TABLE 5 Itaconic Acid Mg concentration Amount of Temperature concentration in in the precipitate ( C.) the solution (wt %) solution (% [g/g]) formed (g) 60 13.2 2.6 0 50 9.4 2.8 50.7 41 6.0 2.7 92.6 30 4.1 2.8 114.7 20 2.6 2.4 131.5

TABLE-US-00006 TABLE 6 2,5-Furandicarboxylic Amount of Temperature Acid concentration in precipitate ( C.) the solution (%) Mg Conc (wt %) formed (g) 84 0.52 3260 6.6 72 0.19 3350 8.4 62 0.38 3330 7.3 53 0.25 2930 8.0 42 0.33 3420 7.6 32 0.14 3340 8.6 22 0.06 1190 9.1

[0070] These findings correspond to a total recovery of over 97% for adipic acid, 72% for fumaric acid, 80% for itaconic acid and 96% for 2,5-furandicarboxylic acid.

[0071] This example shows that adipic acid, fumaric acid, itaconic acid and 2,5-furandicarboxylic acid can be efficiently obtained using the method of the invention. During precipitation, the majority of the dicarboxylic acid precipitates, while substantially all magnesium ions remain in solution. It can be concluded that acidulation with HCl and subsequent crystallization results in a very efficient separation of the dicarboxylic acids from the magnesium dicarboxylate solution.

EXAMPLE 3

Precipitation of Citric Acid

[0072] In a first experiment with citric acid, 5 g of citric acid was added to a saturated solution of MgCl.sub.2.

[0073] In a second experiment with citric acid, 15 g of citric acid was added to a saturated solution of MgCl.sub.2.

[0074] In a third experiment with citric acid, 5 g of magnesium chloride was added to a saturated solution of citric acid.

[0075] In a fourth experiment with citric acid, 15 g of magnesium chloride was added to a saturated solution of citric acid.

[0076] In all four experiments, a precipitate was formed. The citric acid and Mg content of the precipitate was analysed using HPLC. The results are shown in Table 7.

TABLE-US-00007 TABLE 7 Experiment citric acid (wt. %) Mg (wt. %) MgCl.sub.2 (wt. %)* 1 97.4 0.76 2.99 2 92.7 1.18 4.62 3 93.0 0.14 0.56 4 86.9 0.93 3.65 *The amount of MgCl.sub.2 was calculated based on the Mg concentration found.

[0077] This experiment shows that citric acid can be precipitated from a magnesium chloride solution.

EXAMPLE 4

Preparation of Succinic Acid

[0078] Magnesium hydroxide (99 g) was added to a solution of 200 g succinic acid in 888 g water at room temperature and heated up to complete dissolution (by visual observation). An amount of 333 g aqueous solution of HCl (37 wt. % wt %) was added to the thus prepared magnesium succinate solution. The temperature of the thus obtained mixture was initially 62 C. The mixture was cooled to 20 C. and a precipitate was formed. During cooling, samples were taken of the solution and the precipitate of the mixture at 62, 52, 40, 31 and 20 C. The composition of the samples and the total amount of precipitate formed were determined.

[0079] The samples were taken only from the solution (for sampling, stirrer was stopped some few seconds, and after crystal settling, a sample was taken from the supernatant). Magnesium and succinic acid in solution were analyzed and expressed as g/g water. The amount of crystal produced was calculated as difference between the initial succinic acid mass and the mass of the succinic acid remaining in solution.

[0080] The results are shown in Table 8.

TABLE-US-00008 TABLE 8 Succinic Acid Mg concentration concentration Amount of in the in the succinic Temperature solution solution acid ( C.) (wt. %) (wt. %) formed (g) 62 13.13 2.71 0 52 8.20 1.82 82 40 5.00 3.15 130 31 3.40 3.20 153 20 2.10 3.19 171

[0081] Furthermore, the amount of succinic acid in the 182 g precipitate formed during the cooling step was determined, which was 94,4% corresponding to 172 g. The rest of the precipitate consisted mainly of water (4.4%) and magnesium chloride. These findings correspond to a total recovery of succinic acid of over 85%.

[0082] This example shows that during precipitation, the majority of succinic acid precipitates, while substantially all magnesium ions remain in solution. It can be concluded that acidulation with HCl and subsequent crystallization results in a very efficient separation of succinic acid from the magnesium succinate solution.

EXAMPLE 5

Precipitation after Concentrating:

[0083] To the magnesium succinate solution as prepared in Example 4 an aqueous solution of HCl (37 wt. %) was added, thereby obtaining 500 g solution comprising 2.1 wt. % succinic acid and 12.6 wt. % MgCl.sub.2 (corresponding to a MgCl.sub.2 concentration of 14.8 g per 100 g water). The solution was then concentrated by water evaporation, thereby obtaining 199 g solution comprising 5.3 wt. % succinic acid and 31.7 wt. % magnesium chloride (corresponding to a MgCl.sub.2 concentration of 50.2 g per 100 g water, which is close to the saturation point of MgCl.sub.2 in water, which is 55 g/100 g water at 20 C.). The initial and final values of the solution are summarized in Table 9.

TABLE-US-00009 TABLE 9 MgCl2 ratio to water concentration (wt %) (mass based) mass (g) MgCl.sub.2 Succinic g/100 gH2O initial 500 12.6 2.1 14.8 final 199 31.7 5.3 50.2

[0084] The solution was then cooled from 115 C. to 20 C. Precipitation started at 82 C. and continued until 20 C. The precipitate was separated from the solution by filtration using a standard gravity filter. The composition of the precipitate and the solution is show in Table 10.

TABLE-US-00010 TABLE 10 Content Mg.sup.+2 water succinic (%) Cl.sup. (wt. %) (wt. %) (wt. %) Solution 0.22 25.0 6.6

[0085] The succinic acid present in the filtrate was determined using high-performance liquid chromatography (HPLC) and was 0.22 wt. %. Assuming that all succinic acid not present in the filtrate would be present in the precipitate, the value of 0.22 wt. % would correspond to a succinic acid yield in the precipitate of over 90%.