DE19755426A1 - Recovery of natural organic fruit acids, especially oxalic acid from mixture with malic and citric acids - Google Patents

Abstract

Dilute juice is electrodialyzed in four chambers, formed by alternating cationic and anionic exchange membranes, located between anode and cathode. Flow to each chamber is recirculated, with appropriate make-up (5, 6, 11, 12) and off take (7, 8, 9, 10) connections as follows. The anode side chamber (K1) contains fruit acid concentrate with distilled water addition at the inlet; concentrated fruit acid is removed, from which further recovery of fruit acids takes place in conventional manner.

Description

The invention relates to a method for obtaining naturally occurring organic acids (fruit acids), especially oxalic acid, from filtered Plant juices and extracts.

Naturally occurring organic acids such as citric, malic and lactic acid can by fermentation from carbohydrates using Mikroorga nisms and considerable expenditure on equipment.

Oxalic acid is synthesized chemically, with sucrose using Mineral acids with the help of a catalyst (vanadium pentoxide) in oxal acid is converted.

In nature, organic acids are very common, especially in plants, being the type of acid and its concentrations in the different plants differ greatly. There are plants that contain organic acids and achieve biomass yields that are derived from these compounds Press juices or extracts justified.

An important factor is the one that is possible through the cultivation of plants containing fruit acids Use of set-aside areas for the non-food area and use already Existing technologies and technology of the fruit juice industry to process the Raw materials.

In the biotechnological area, electrodialysis is used to process the product Because of their gentle process parameters of fermantatively produced or  ganic acids such as itaconic and citric acids. There are a number of references and property rights.

The European patent EP 0 230 021 "Continuous process for fermentative production of organic acids ", the acids using electro dialysis are separated.

The patent DE 35 42 861 describes a process for the production of apples acid from fermentation broths.

Other known processes have the goal of using salts obtained by fermentation To convert electrodialysis to the free acids, for example itaconic acid (U.S. Patent 3,873,425) and lactic acid (DE-OS 19 57 395).

Then selected acids, such as those obtained during fermentation, are won.

Process for the extraction of acids, which are in the form of mixtures in plant juices and -Extracts from vegetable raw materials are not known. That concerns both the extraction of such acid mixtures and the selective extraction of individual acids from these mixtures.

It was therefore the task of naturally occurring a method for obtaining to develop organic acids from vegetable raw materials.

It has been found that naturally occurring organic acids (fruit acids), in particular oxalic acid, can be obtained from filtered vegetable juices and extracts if the juices (diluate) are subjected to electro-dialysis in at least 4 chambers, which are alternated by anion exchange elements branches and cation exchange membranes are formed, whereby

• - In the chamber (K4) on the cathode side a mineral acid, the concentration tion by supplying concentrated and deriving the diluted mineral acid is kept constant
• - In a middle chamber (K2) the diluate with supply of the diluate and drain the deacidified diluate,
• - A metal salt solution in the chamber (K3) between the acid and diluate circuit while adding distilled water and deriving the concentrated Metal salt solution and
• - In the chamber (K1) on the anode side, the fruit acid concentrate with supply of distilled water and derived from the fruit acid concentrate circu lieren,

from which the fruit acids are then obtained in a manner known per se he follows.

An alternative possibility is that the juices and extracts (diluate) are subjected to an electrodialysis in at least 2 chambers, which are separated by an anion exchange membrane and each delimited by a bipolar membrane, whereby

• - In the chamber (K2) on the cathode side, the diluate with the supply of fresh Diluate and derivation of the deacidified diluate and
• - In the chamber (K1) on the anode side, the fruit acid concentrate with supply of distilled water and derived from the fruit acid concentrate circu lieren,

from which the fruit acids are then obtained in a manner known per se he follows.

In principle, all vegetable raw materials that are suitable for the process Contain fruit acid. However, rhubarb should preferably be used, which has a high oxalic acid content.  

The process is advantageously between 10 and 70 ° C, preferably between 20 and 50 ° C carried out.

The process for the extraction of naturally occurring organic acids enables the fruit acids to be obtained as a mixture. By creating under Different current densities, it is also possible to selectively add the acids win. For example, the oxalic acid can be extracted from the fruit acid mixture high concentration.

For the two-chamber process, it may be important that before electrodialysis divalent metal ions, especially calcium, by means of selective ion exchangers be separated.

The application of the procedure is not to single bicameral or four chamber systems limited. Electrodialysis is used for technical purposes preferably carried out in several chamber systems connected in parallel.

The process can be carried out batchwise as well as continuously be carried out. The continuous variant is preferred. You need changes the constant addition of the input products and in quantitative terms Ratio the deduction of the resulting products. In the discontinuous The supplies and discharges required in continuous operation become a variant omitted.

The process is described by way of example with the aid of FIGS. 1 and 2. Where:

Reference list Fig. 1 (4-chamber process, according to claim 1)

A anion exchange membrane
K cation exchange membrane
K1 chamber with fruit acid concentrate
K2 chamber with diluate
K3 chamber with metal salt solution
K4 chamber with mineral acid
+ Anode
- cathode

1

Concentrate cycle (selected acids)

2nd

Diluate cycle (e.g. rhubarb juice)

3rd

Metal salt cycle

4th

Mineral acid cycle

5

Add diluate

6

Add concentrated mineral acid

7

Concentrate withdrawal for crystallization

8th

Withdrawal of the deacidified diluate

9

Deduction of the metal salts

10th

Deduction of dilute mineral acid

11

Add distilled water

12th

Add distilled water.

Fig. 2 (2-chamber process, according to claim 2)

A anion exchange membrane
AK Bipolar membrane with anion and cation exchange side
K1 chamber with fruit acid concentrate
K2 chamber with diluate
+ Anode
- cathode

1

Concentrate cycle (selected acids)

2nd

Diluate cycle (e.g. rhubarb juice)

3rd

Concentrate deduction for further processing

4th

Withdrawal of the deacidified diluate

5

Add diluate

6

Add distilled water

Fig. 1 shows the possible stack configuration in a 4-chamber cycle. The individual chambers are delimited by cation and anion exchange membranes, viewed from the anode in the sequence cation and anion exchange membrane.

The separated acids ( 1 ) (oxalic acid, malic acid and citric acid) circulate in the chamber K1. In the chamber K2 the diluate ( 2 ), for example the rhubarb juice to be deacidified, circulates in the chamber K3 a solution of metal salts ( 3 ) which are formed during the process and in the chamber K4 the mineral acid ( 4 ) required as proton supplier (e.g. HCl).

The process of deacidification can also be in a repeating sequence of these 4 chambers.  

When the electric field is applied, the acid anions migrate out of the Chamber K2 in chamber K1, while the metal cations in chamber K3 diffuse. The protons of the mineral acid from chamber K4 migrate into the Chamber K1 and form the free organic acids with the acid anions. Due to the different molecular size of the acid anions as well as the under Different pKs values lead to different diffusion speeds that are supported by the application of different current densities can be.

The free acids can therefore be obtained both selectively and as a mixture and concentrated to the solubility limit in order to be fed to a crystallization stage ( 7 ).

The electrodialytic process step can be carried out either continuously or in the Batch operation can be carried out.

The continuous variant requires the addition of diluate ( 5 ) (e.g. non-deacidified rhubarb juice) in the same quantitative proportion to the deduction of the deacidified diluate ( 8 ). Since the charge carriers of the mineral acid cycle migrate into the chambers K1 and K3 as described above, in order to maintain the process it is necessary to keep the concentration of the charge carriers constant. A corresponding volume of dilute mineral acid is removed ( 10 ) and replaced by concentrated mineral acid ( 6 ). The disadvantage of this configuration is the formation of metal salts ( 9 ), which have to be disposed of. To maintain the continuous process, the removed acid concentrate ( 7 ) and metal salt concentrate ( 9 ) volumes can be compensated for via streams ( 11 ) and ( 12 ) by adding distilled water. However, it is advantageous to obtain the free carboxylic acids, since a mineral acid is used as the proton supplier and the formation of the poorly soluble salts (in particular the oxalates) is avoided.

Fig. 2 shows another possible stack configuration with two chambers, chamber K1 viewed from the anode from a bipolar membrane (AK) and an anion exchange membrane (A) and chamber K2 from the anion exchange membrane (A) and a bipolar membrane (AK) be limited.

The juice or extract ( 2 ) to be deacidified circulates in the chamber K2 and the fruit acid concentrate ( 1 ) in the chamber K1. The basics of this process are known per se for fermentor solutions. When an electric field is applied, water splitting occurs in the bipolar membranes (AK) and thus the ions necessary for charge transport are generated and the protons necessary for the formation of free acid.

The acid anions migrate through the anion exchange membrane from the chamber K2 into the chamber K1, form the free acids with the protons from the water splitting, can be concentrated there and fed to the crystallization ( 3 ). If acid concentrate is removed, a corresponding amount of distilled water must be added ( 6 ).

As with the 4-chamber variant, the continuous variant requires the addition of diluate ( 5 ) (e.g. non-deacidified rhubarb juice) in the same quantitative proportion to the removal of the deacidified diluate ( 4 ). The acids can also be obtained as a mixture or selectively, as described above.

With the described method it is possible to use naturally occurring organic Acids from juices and extracts of vegetable raw materials as a mixture or selectively to win almost quantitatively and in good quality.

The practical implementation of the process in both process systems is in the Examples 1 and 2 described.  

example 1 (4-chamber process)

An ultrafiltered rhubarb extract was used for electrodialysis. He was obtained from the entire above-ground material of the plants. The cut off the ultrafiltration membrane was 100,000 daltons.

The electrodialysis was carried out in a row of 10 parallel arranged with 4 chambers each according to Fig. 1 electrodialysis units. The cation and anion exchange membranes were commercially available products based on styrene-divinylbenzene copolymers.
Membrane area: 4.60 dm ²
Distance between the membranes: 1 mm
Membrane thickness: 0.5 mm.

The following solutions were presented at the start of the experiment:

Electrode chambers
Anode rinsing solution - sodium sulfate solution 3%
Cathode rinsing solution - sodium sulfate solution 3%
Mineral acid cycle - hydrochloric acid 0.2 M
Diluate cycle - rhubarb extract
Concentrate cycle - aqua dest.
Metal salt cycle - aqua dest.

Volume of solutions - 5 l.

The electrodialysis was carried out at 30 ° C and a volume flow of 300 l / h per Circulation. It was worked in constant voltage operation, the potential difference was 30 V. The current was between 0.5 and 2 A.

The deacidification of rhubarb extract took 8 hours in total.

The following were determined for the composition of the rhubarb extract:

This achieved a 90% separation of the oxalic acid, whereas only 24% of malic acid and no citric acid separated from the juice were. This demonstrates the possibility of selective separation of the acids.

Example 2 (2-chamber process)

An ultrafiltered rhubarb extract was used for electrodialysis. He was obtained from the entire above-ground material of the plants and before electrodialysis to remove divalent metal ions from a cation subjected to exchange. The cut-off of the ultrafiltration membrane was 100,000 daltons.

The electrodialysis was carried out in a 2-chamber electrodialysis unit as shown in Fig. 2. The anion exchange membranes and bipolar membranes were commercially available products based on styrene-devinylbenzene copolymers.
Effective membrane area: 1 dm ²
Distance between the membranes: 2 mm
Membrane thickness: 0.5 mm.

The following solutions were presented at the start of the experiment:

Electrode chambers
Anode rinsing solution - sodium sulfate solution 3%
Cathode rinsing solution - sodium sulfate solution 3%
Diluate cycle - rhubarb extract
Concentrate cycle - aqua dest.

Volume of solutions - 5 l.

Electrodialysis was carried out at 40 ° C and a volume flow of 100 l / h per circuit run. Work was carried out in constant voltage operation, with the potential differences limit was 30 V. The current was between 3.0 and 7 A.

The deacidification of rhubarb extract took a total of 5 hours.

The composition of the rhubarb extract was determined:

An approx. 63% separation of oxalic acid was achieved with this, whereas only About 23% of the malic acid was separated from the juice and the citric acid does not move at all under the chosen conditions.

Claims (8)

1. A process for the production of naturally occurring organic acids (fruit acids), in particular oxalic acid, from filtered plant juices and extracts, characterized in that these (diluate) are subjected to electrodialysis in at least 4 chambers which are alternately formed by anion exchange membranes and cation exchange membranes be, where

• - In the chamber (K4) on the cathode side, a mineral acid, the concentration of which is kept constant by supplying concentrated and deriving mineral acid,
• - in a middle chamber (K2) the diluate with supply of the diluate and discharge of the deacidified diluate,
• - In the chamber (K3) between the acid and diluate circuit, a metal salt solution with the addition of distilled water and with the derivation of the concentrated metal salt solutions and
• - circulate the fruit acid concentrate in the chamber (K1) on the anode side with the addition of distilled water and with derivation of the fruit acid concentrate,

from which the fruit acids are then obtained in a manner known per se. 2. Process for the production of naturally occurring organic acids (fruit acids), in particular oxalic acid, from filtered plant juices and extracts, characterized in that these (diluate) are subjected to electrodialysis in at least 2 chambers, which are separated by an anion exchanger and each by a bipolar membrane can be limited, whereby

• - In the chamber (K2) on the cathode side, the diluate with the supply of fresh diluate and discharge of the deacidified diluate and
• - circulate the fruit acid concentrate in the chamber (K1) on the anode side with supply of distilled water and with derivation of the concentrated fruit acid concentrate,

from which the fruit acids are then obtained in a manner known per se. 3. Process for the production of naturally occurring organic acids (Fruit acids) according to claim 1 or claim 2, characterized in that rhubarb is used as a vegetable raw material. 4. Process for the extraction of naturally occurring organic acids (Fruit acids) according to one or more of claims 1 to 3, characterized characterized in that the process between 10 and 70 ° C, preferably between 20 to 50 ° C, is carried out. 5. Process for the recovery of naturally occurring organic acids (Fruit acids) according to one or more of claims 1 to 4, characterized characterized in that the fruit acids as a mixture or, in particular by Applying different current densities, selectively obtained. 6. Process for the extraction of naturally occurring organic acids (Fruit acids) according to one or more of claims 2 to 5, characterized characterized in that prior to electrodialysis divalent metal ions, esp special calcium, can be separated using selective ion exchangers. 7. Process for the extraction of naturally occurring organic acids (Fruit acids) according to one or more of claims 1 to 6, characterized characterized in that the electrodialysis in several connected in parallel Chamber systems is carried out. 8. Process for the recovery of naturally occurring organic acids (Fruit acids) according to one or more of claims 1 to 7, characterized characterized in that the electrodialysis in batch mode with the omission of in feeds and discharges listed in claims 1 and 2 is operated.