Carboxylic acid recovery from magnesium carboxylate mixture

Abstract

The invention is directed to a method for recovering carboyxlic acid from an magnesium carboxylate containing aqueous mixture, including the steps of: contacting the aqueous mixture with an acidic ion exchanger, thereby forming a carboxylic acid mixture and an ion exchanger loaded with magnesium ions; contacting the ion exchanger loaded with magnesium ions with a hydrochloric acid solution, thereby forming a magnesium chloride solution; and thermally decomposing the magnesium chloride solution at a temperature of at least 300 C., thereby forming magnesium oxide (MgO) and hydrogen chloride (HCl).

Claims

1. A method for recovering carboyxlic acid, comprising the steps of fermenting a carbohydrate source by means of a microorganism in a fermentation broth to form a carboxylic acid and neutralising at least part of the carboxylic acid by addition of a magnesium base thereby forming a fermentation medium comprising a magnesium carboxylate salt, subjecting the fermentation medium to a step wherein solid matter is removed to form an aqueous mixture, contacting the aqueous mixture with an acidic ion exchanger, thereby forming a carboxylic acid mixture and an ion exchanger loaded with magnesium ions; and contacting the ion exchanger loaded with magnesium ions with a hydrochloric acid solution, thereby forming a magnesium chloride solution; and thermally decomposing the magnesium chloride solution at a temperature of at least 300 C., thereby forming magnesium oxide (MgO) and hydrogen chloride (HCl).

2. The method according to claim 1, further comprising dissolving the HCl in water, thereby obtaining a HCl solution; and bringing the MgO in contact with water, thereby obtaining Mg(OH).sub.2.

3. The method according to claim 2, wherein the HCl solution is recycled for use in contacting the ion exchanger loaded with magnesium ions.

4. The method according to claim 1, wherein MgO and/or Mg(OH).sub.2 is recycled for use in a fermentation process.

5. The method according to claim 1, wherein at least part of the carboxylic acid mixture is fed back to the aqueous mixture.

6. The method according to claim 1, wherein the ion exchanger loaded with magnesium ions is washed with water before contacting it with the hydrochloric acid solution.

7. The method according to claim 1, wherein the acidic ion exchanger is strongly acidic and comprises one or more sulphonic acid and/or phosphonic acid groups.

8. The method according to claim 1, wherein the acidic ion exchanger is a solid acidic ion exchanger.

9. The method according to claim 1, wherein the ion exchange step is conducted in an ion exchange column.

10. The method according to claim 1, wherein the ion exchange step is conducted in a fluidized bed or a simulated moving bed of polymeric ion exchange resin beads.

11. The method according to claim 1, wherein the acidic ion exchanger is a liquid acidic ion exchanger.

12. The method according to claim 11, wherein the acidic ion exchanger is an organic compound comprising one or more sulphonic acid and/or phosphonic acid groups, wherein the acidic ion exchanger is optionally dissolved in a hydrophobic solvent.

13. The method according to claim 1, wherein the carboxylic acid is selected from the group consisting of lactic acid, succinic acid, propionic acid, 3-hydroxypropionic acid, hydroxybutyric acid, citric acid, fumaric acid, itaconic acid, adipic acid, acrylic acid, levulinic acid, maleic acid, terephthalic acid, 2,5-furandicarboxylic acid, lactylic acids and fatty acids.

14. The method according to claim 1, wherein at least 99 wt. % of the aqueous mixture is in liquid or dissolved form, based on the total weight of the aqueous mixture.

15. The method according to claim 1, wherein contacting the aqueous mixture with the acidic cation exchanger is conducted at a temperature of at least 40 C.

Description

EXAMPLE 1

Ion Exchange of Magnesium Lactate to Lactic Acid on Strong Cation Exchange Resin

(1) A magnesium lactate feed solution was prepared by adding 8 g of magnesium lactate dihydrate to 92 g water and mixing to complete dissolution. The thus prepared feed solution comprised 6.8 wt % of magnesium lactate in water. The solution was heated to 20 C.

(2) Although magnesium carboxylate solutions obtained in a fermentation process typically comprise additional compounds (in particular impurities such as sugars, protein and/or biomass), the feed solution prepared in this example is considered to sufficiently resemble such solutions for the proof of principle shown in this Example to apply to feed solutions obtained in a fermentation process as well.

(3) 50 ml of Amberlite FPC23 H resin was put in the glass column. The column was heated to 20 C. Resin was washed with 3 bed volumes of water. The water flow was then stopped and 6.8 wt % of magnesium lactate solution was pumped through the column with the flow of 0.83 ml/min. The pH of the feed solution was determined to be pH 6.2. The first product sample was taken after 50 min. The sample had a pH 2 and the magnesium content measured by atomic adsorption spectrometry below the detection limit of 5 ppm, indicating that the ion exchanger had exchanged H.sup.+ ions for magnesium ions. The concentration of lactate ions remained constant at 7.1 wt %.

(4) This example shows simultaneous removal of magnesium ions and acidulation of magnesium lactate to lactic acid by cation exchange resin, resulting in an ion exchanger loaded with magnesium ions and an aqueous lactic acid solution.

EXAMPLE 2

Formation of Magnesium Chloride Solution

(5) The magnesium ion loaded Amberlite FPC23 H resin used in Example 1 was washed with 3 BV of water to remove any residual magnesium lactate and lactic acid.

(6) Then 108 g of 37 wt % hydrochloric acid was mixed with 692 g of water resulting in 5 wt % hydrochloric acid solution. This solution was pumped through the column with flow of 1.7 ml/min. Every 30 min product samples were taken and pH of the sample and magnesium content was measured. After 60 min pH of the taken sample was 0.30 and magnesium content was 9070 ppm. After 90 min the product sample had a pH value of 0.15 and magnesium content of 3910 ppm.

(7) This example shows that magnesium is recovered from strong cation exchange resin in the form of a magnesium chloride solution. The magnesium chloride solution had a high purity. No lactic acid or lactate was detected and decomposable salts that may decrease the efficiency of the thermal decomposition step were expected to be removed by the washing step.

EXAMPLE 3

Ion Exchange of Magnesium Lactate to Lactic Acid on Liquid Ion Exchanger

(8) A magnesium lactate feed solution was prepared by adding 7.4 g of magnesium lactate dihydrate to 15.2 g water. The prepared feed solution comprised 28 wt % of magnesium lactate slurry in water. Solution was prepared at 20 C.

(9) Although magnesium carboxylate solutions obtained in a fermentation process typically comprise additional compounds (in particular impurities such as sugars, protein and/or biomass), the feed solution prepared in this example is considered to sufficiently resemble such solutions for the proof of principle shown in this Example to apply to feed solutions obtained in a fermentation process as well.

(10) The liquid ion exchanger was prepared by adding 25 g of dinonylnaphthalenesulfonic acid to 25 g of heptane and mixing till complete dissolution. The liquid ion exchanger thus comprised 50 wt % of dinonylnaphthalenesulfonic acid.

(11) The liquid ion exchanger (50 g) was mixed with 22.6 g of 28 wt % magnesium lactate slurry at 20 C. and mixed for 2 hours. The thus obtained solution was transferred to a separation funnel where two phases were observed: an aqueous phase and an organic phase. Using the separation funnel, 7.8 g of aqueous phase was separated off. The aqueous phase had a pH of 1.8 and contained 17 wt % of lactic acid, indicating that the ion exchanger had exchanged H.sup.+ ions for magnesium ions and that the lactic acid formed in this process was present in the aqueous phase.

(12) Then, 10 g of fresh water was added to the organic layer in the separation funnel, after which the funnel was shaken and phases were again separated. 10.6 g of aqueous phase was separated. This aqueous phase had a pH of 1.93 and contained 7.5 wt % of lactic acid.

(13) In this experiment, the magnesium content was decreased from 3.36 wt. % in the magnesium carboxylate solution to 2280 ppm in the aqueous phase after ion exchange.

(14) Thus, the example shows simultaneous removal of magnesium ions and acidulation of magnesium lactate to lactic acid by a cation liquid ion exchanger.

EXAMPLE 4

Regeneration of Liquid Ion Exchanger

(15) An amount of 20 g hydrochloric acid solution (20 wt % in water) was added to 60.6 g of the organic phase obtained after the phase separations in Example 3. The mixture was stirred for 50 min at 20 C. Afterwards, the mixture was transferred to a separation funnel. Two phases were observed: an organic layer and an aqueous layer. The aqueous layer was separated and the magnesium content was analyzed using atomic adsorption spectrometry. The layer comprised 8100 ppm of magnesium, indicating that an aqueous magnesium chloride solution was formed.

(16) This example shows that magnesium can be recovered from liquid ion exchanger in the form of a magnesium chloride solution by exchanging hydrogen ions present in hydrochloric acid with magnesium ions present in the cation liquid exchanger.

EXAMPLE 5

Ion Exchange of Magnesium Succinate to Succinic Acid Using a Strong Cation Exchange Resin

(17) A magnesium succinate feed solution was prepared by adding 151.3 g of magnesium succinate tetra hydrate to 848.7 g water and mixing to complete dissolution. The thus prepared feed solution comprised 10 wt % of magnesium succinate in water. The solution was heated to 60 C.

(18) Although magnesium carboxylate solutions obtained in a fermentation process typically comprise additional compounds (in particular impurities such as sugars, protein and/or biomass), the feed solution prepared in this example is considered to sufficiently resemble such solutions for the proof of principle shown in this Example to apply to feed solutions obtained in a fermentation process as well.

(19) A glass column of 100 ml was filled with beads of a strongly acidic cation exchange resin comprising sulfonate groups (available under the name Amberlite FPC23 H). The column was heated to 60 C. The resin was washed with 3 bed volumes (BV) of water. The water flow was then stopped and 10 wt % of magnesium succinate solution was pumped through the column with a flow of 3.5 ml/min. The pH of the feed solution was determined to be pH 7. Every 20 minutes, a product sample was taken and its pH value was measured. Also, its magnesium content was measured by atomic adsorption spectrometry. The product sample taken after 20 min had a pH value of 2.2 and a magnesium content below the detection limit of 5 ppm, indicating that the ion exchanger had exchanged H.sup.+ ions for magnesium ions. The concentration of succinate remained constant at 8.2 wt %.

(20) This example thus shows simultaneous removal of magnesium ions and acidulation of magnesium succinate to succinic acid by an acidic cation exchange resin, resulting in an ion exchanger loaded with magnesium ions and an aqueous succinic acid solution.

EXAMPLE 6

Formation of Magnesium Chloride Solution

(21) The magnesium ion loaded Amberlite FPC23 H resin used in Example 5 was washed with 3 bed volumes (BV), corresponding to 100 ml of water, to remove any residual magnesium succinate and succinic acid, as well as any decomposable salts (such as NaCl, KCl and CaCl.sub.2) if present.

(22) Then 108 g of 37 wt % hydrochloric acid was mixed with 692 g of water resulting in 5 wt % hydrochloric acid solution. This solution was pumped through the column with flow of 3.5 ml/min. Every 20 min product sample was taken, pH value of the sample and magnesium content was measured. After 20 min pH of the product sample was 6.8 and magnesium content was 4600 ppm. After 40 min the product sample had a pH of 0.38 and magnesium content of 12300 ppm. No succinic acid or succinate could be detected in the samples (detection limit<0.1 wt. %).

(23) This example shows that magnesium is recovered from strong cation exchange resin in the form of a magnesium chloride solution. The magnesium chloride solution had a high purity. No succinic acid or succinate was detected and decomposable salts that may decrease the efficiency of the thermal decomposition step were expected to be removed by the washing step.