EP0880398A2

EP0880398A2 - Process for separating substances using a suitable membrane

Info

Publication number: EP0880398A2
Application number: EP97903300A
Authority: EP
Inventors: Christian Wandrey; Udo Kragl; Andreas Bommarius; Karlheinz Drauz
Original assignee: Degussa GmbH
Current assignee: Evonik Operations GmbH
Priority date: 1996-02-16
Filing date: 1997-02-17
Publication date: 1998-12-02
Also published as: WO1997029837A3; DE19605683A1; WO1997029837A2

Abstract

In catalytic reactions and reactions requiring synthesis-promoters, it is useful to be able to separate the promoter from the product formed and thus make it available for recycling. One possible way of achieving this separation is by immobilising the synthesis-promoter on special carriers. This, however, often reduces the contact area between the promoter and carrier and thus markedly reduces the reactivity of the promoter or alters its mode of action. The immobilisation process itself may also present problems in terms of working time spent and catalyst loss. If the product and promoter in a catalytic reaction are separated by filtration using a nanofiltration or reverse osmosis membrane, it is possible, even when the weight differences between promoter and product are relatively small and provided that the retension differences are sufficient and the associated recovery rate of the promoter therefore high, to dispense with separation based on immobilisation techniques. The process proposed can be used for separating reaction mixtures for catalytic reactions with the aim of efficiently producing organic synthesis products or optically active organic compounds.

Description

Process for the separation of substances using a suitable membrane

The invention relates to a method for separating substances by means of a suitable membrane according to claims 1 to 8.

Separation processes are an essential part of all (bio) chemical syntheses. For example, the separation of substances is indispensable for the recovery of products that are or have been formed during or after syntheses. It represents an important criterion for the synthesis planning in large-scale productions. In many cases, the separation of intermediate or end products in a required quality decides on the possible synthesis route.

In the case of catalytic reactions or reactions which require synthesis auxiliaries, the separation of these auxiliaries from the product formed can also be important. This is because synthesis aids, such as catalysts in chemical syntheses or cofactors in enzymatic syntheses, are generally very expensive. It is therefore the goal to use the synthesis aids as effectively as possible in order to reduce the costs of syntheses as much as possible. On the one hand, the amounts of auxiliaries to be used for corresponding syntheses are kept as low as possible. On the other hand, there are already various approaches to enable better use of synthesis aids. These include in particular attempts to separate the products formed during the syntheses from the auxiliary in order to achieve reuse of the auxiliary.

The separation of products from the synthesis aid has so far been achieved in various ways. For example, the auxiliaries or catalysts are immobilized on supports, but the contact surfaces between the adjuvant and the support are often greatly reduced, which is attempted to be compensated for by a corresponding increase in the porosity of the support material. That too is

Immobilization process in terms of labor and catalyst loss is not without problems. Furthermore, immobilization often results in a changed mode of action of the auxiliary.

Another way to separate products from

Synthesis aid is made by using membranes. For example, the enzymes used in enzymatic reactions are separated from the remaining reaction solution by membranes. However, such a separation is possible because the molecular weight differences between enzyme or protein and the other reaction participants, such as substrates, products, cocatalyst or cofactor, among others, are usually very large: the molecular weight of enzymes is in a range of 40 000 g / mol, that of the other reaction participants often below 1,000 g / mol. In Figure 1, the retention rate of commercially available membranes (amicon) is plotted against the molar mass. As can be seen from this figure, enzymes in the molecular weight range mentioned can easily be passed through a membrane, such as the YMIO membrane. separate from the other substances with a molecular weight below 1,000 g / mol.

Considering the graph of the membranes with smaller pore sizes, e.g. for the membrane YC05 (nominal separation limit 500 g / mol), one has to state that one should no longer speak of a separation limit. Rather, a mass range is created in which a more or less good retention of the molecules occurs. This tendency can already be seen in the membranes YM1 (nominal separation limit 1 000 g / mol) and YM3 (nominal separation limit 3 000 g / mol). If you try to separate substances whose molecular weight difference relative to the nominal separation limit is relatively small, you will find good retention differences at high nominal separation limits (such as with YM10, YM30, YM100 membranes), while at low nominal separation limits ( as for example with YC05, YM1, YM3 membranes) no or hardly any retention differences are found.

If, for example, the auxiliary or cofactor NAD (P) or NAD (P) H, whose molecular weight is approximately 700 g / mol, is also to be used frequently in enzymatic reactions and is separated from products with a molecular weight, for example, 150 g / mol separation by means of membranes, as shown in FIG. 1, is no longer possible: If a YC05 membrane according to FIG. 1 is used, it would be expected that about 75% of the product would be retained by the membrane and that there would be no effective separation between the cofactor and product . When using a YML membrane according to FIG. 1, the product was not retained; for that would but also a relatively large proportion of the cofactor pass through the membrane and thus there is no effective separation of both substances. This example, given from enzyme-catalyzed reactions, can of course also be applied to other reactions: For example, in chemical catalysis, valuable auxiliaries, including catalysts, are used, the reuse of which is of great importance. But even in these cases the difference in molar mass between the product and the catalyst or auxiliary is often so small that a separation of the substances by means of membranes cannot be expected.

In order to enable separation by filtration anyway, substances to be separated, e.g. Synthesis auxiliaries, enlarged in such a way that their molar mass and steric demands differ by orders of magnitude from those of the other substances or the products formed in order to achieve retention by means of suitable membranes. However, the main disadvantages of such a procedure are - as already mentioned above for the immobilization of the auxiliary substances - high losses of the auxiliary substance, e.g. during the polymer attachment, as well as changed properties: For example, the chemical affinity of the enzyme to the cofactors is often reduced by chemical modification of cofactors, which previously could only be carried out for a small number of cofactors.

It has now surprisingly been found that separation of substances by means of membranes with lower Separation limit also occurs when the

Molecular weight differences between the substances are relatively small. For this purpose, the molar mass of a substance Si should be 70 to 1,000 g / mol, the molar mass of another substance ≤2 300 to 2,000 g / mol, the molar mass difference S2 minus Sι_ 200 to 1,000 g / mol, the quotient (S2 minus Sι_) / S2 0.5 to 0.9 and the retention rate of S2 is at least 75 to 80%. Membranes suitable for the separation process are those which are generally referred to in the trade as nanofiltration or reverse osmosis membranes. A membrane that is optimal for separation can be determined by tests, with manufacturer information on nominal separation limits or salt retention rates only serving as a guide.

The process according to the invention makes it very easy to separate substances with the following molecular weights, the

Retention rate of substance S2 95 up to 100% is:

Molar mass

(g / mol)

Sl S2 S _] _ minus S2 (Si minus S2) / S2

70 300 230 0.767

70 350 280 0.800

70 700 630 0.900

100 550 450 0.818

112200 884400 772200 0.857

130 720 590 0.819

500 1000 500 0.500

500 1500 1000 0, 667

1000 2000 1000 0.500 The process according to the invention is particularly suitable for separating products formed in the presence of a synthesis aid from the synthesis aid. Products obtained from enzyme-catalyzed reactions can thus be separated from cofactors or products obtained from chemical, preferably asymmetrical, chemical catalysis from the catalyst. Particularly in the case of enzyme-catalyzed reactions, products and cofactors such as NAD (P), FAD or PQQ are separated extremely effectively. The process according to the invention thus makes it possible to retain auxiliary substances or to separate products, in particular epoxides, amino acids, alcohols or hydroxy acids, with comparable orders of magnitude but slightly different retentions. Separations can also be carried out in all solvents and under all membrane-compatible conditions. In addition, the auxiliaries can be used without change and therefore do not lose their typical characteristics.

Furthermore, the method can also be used to separate a large number of other substances, e.g. those substances which are listed in Table 1 as examples. Substance 2 is in part non-complexed ligands of a synthesis aid; for substance 1, the conditions according to the invention apply with regard to the molecular weight ranges.

The invention is explained in more detail below with reference to the accompanying drawings and three exemplary embodiments.

REPLACEMENT BUTT (RULE 26) They show schematically for enzymatic catalysis (examples 1 and 2):

Figure 2: a reaction as it was carried out in a membrane reactor. A substrate S is converted into a product P in a reaction catalyzed by enzyme 1. This requires a cofactor, here NADH, which reacts to NAD ⁺ and is regenerated in a second reaction by an enzyme 2 catalyzed reaction (oxidation of formic acid, HCOOH, to CO2).

Figure 3: Use of a nanofiltration (NF) or

Reverse osmosis membrane (RO) in a membrane reactor (1). The feed solution containing substrate, cofactor and HCOOH is fed to the reactor via a pump (3). The NF / RO membrane (2) now retains the enzymes (4) and some of the cofactors, while the unreacted substrate and the product formed, as well as the small proportion of the cofactor, pass through the membrane.

The arrangement shown in Figure 3 was used to produce chiral alcohols and amino acids. The process conditions are listed in the two examples below (Example 1 and Example 2).

Table 2 finally shows the retentions of the substrates or products obtained in the exemplary embodiments and of the catalysts or auxiliaries as a function of the molar mass, concentration and

Dwell time. The retentions measured for some other substances are also given. example 1

In a 10 ml enzyme membrane reactor (EMR) with a reverse osmosis membrane (ROM 365, amafilter) the enzymes were:

Lactobacillus kefir alcohol dehydrogenase: 0.5 U / mL Candida boidinii formate dehydrogenase: 0.5 U / mL

given and as an feed solution with an aqueous solution of pH 7.0

[Acetophenone] = 7 mM

[Magnesium chloride] = 1 mM [NADP +] = 25 μM (corresponds to 5% of the intended concentration in the reactor)

[Sodium formate] = 100 mM

[di-potassium hydrogen phosphate] = 50 mM

With a residence time of 1 h and a reaction temperature of 25 ° C., the conversion with respect to the substrate acetophenone was 75%.

At the start of the reaction, the concentration of the cofactor in the reactor was raised to 0.5 mM by a single addition of the cofactor. The solution fed to the reactor contained only 5% of this cofactor concentration. This means that the retention capacity of the membrane is so high that the small proportion of the permeating cofactor can be replaced by this 5%. This small amount also compensates for the thermal deactivation of the cofactor.

ERSATZBLAH (REGEL26) The number of changes in the cofactor was 204 molp / mol _NAD (75% x 7 mM / 25 μM).

Without the use of the RO membrane, there would be an alternating number of 10.5 molp / mol _{NAJ: ι} (75% x 7 mM / 500 μM). The recycling of the cofactor, which is possible through retention, results in a 20-fold better utilization of the expensive cofactor.

Despite the retention of acetophenone or phenylethanol, no accumulation of these substances was found in the reactor.

Example 2

Amino acid dehydrogenase from Bacillus sp. : 15 U / mL formate dehydrogenase from Candida boidinii; 15 U / mL

given and as an aqueous solution brought to pH 8 with NH3

[Trimethyl pyruvate] = 500 mM [formic acid] = 1.0 M [NAD +] = 0.08 mM (corresponds to 33% of the intended concentration in the reactor)

With a residence time of 4 h and a reaction temperature of 30 ° C., the conversion with respect to the substrate trimethylpyruvate was 95%. At the start of the reaction, the concentration of the cofactor in the reactor was raised to 0.2 mM by a single addition of the cofactor. The solution fed to the reactor contained only 33% of this cofactor concentration. In contrast to Example 1, the reaction conditions for the cofactor are very unfavorable, so that due to the pH value and the temperature, a significantly higher deactivation of the cofactor NAD (H) occurs, which must be compensated for by a correspondingly higher cofactor concentration in the substrate solution. Ie that with a large part of the supplied cofactor quantity, only the deactivated cofactor has to be compensated. Even in this case, a third of the cofactor can still be saved by using the RO membrane.

The number of changes of the cofactor was 7920 molp /

(95% x 500mM / 0.08mM).

Without the use of the RO membrane, there would be one

Alternation number of 2375 molp / mol _NAD (95% x 500 mM /

This results in the possible through retention

Recycling the cofactor is 3.3 times better

Exploiting the expensive cofactor.

In contrast, the retention rate of the substrate trimethyl pyruvate or the product formed was tert. Leucine at only 2%. Example 3

A nanofiltration membrane (Celfa CMF-KX-060, or Membrane Products: MPF 60) is conditioned in a 10 ml EMR (experimental setup corresponds to that of FIG. 2) by rinsing with 1.) acetone and 2.) dichloromethane. Now the weighed-in amount of ligand (ligand of the Jacobsen catalyst, see FIG. 4) dissolved in dichloromethane is flushed in. The solution emerging during the flushing-in process is collected and the ligand concentration is determined photometrically in order to be able to calculate the amount of ligand remaining in the reactor. At a flow rate of 20 ml / h (= residence time of 0.5 h), the emerging solution is collected over a period of 1 hour and the ligand concentration in this permeate is also determined photometrically. This gives the possibility to calculate the permeated amount of ligand per unit of time and to relate it to the amount of ligand remaining in the reactor.

This results in retention of over 97% over a period of 7 dwell times until the experiment is terminated.

The retention of styrene, a possible substrate for enantioselective epoxidation, is determined using the same procedure. A gas chromatographic method was chosen as the analysis.

Retentions of less than 47% are obtained for styrene, although here too there was no accumulation of the substance in the reactor.

REPLACEMENT BLAπ (RULE 26) Table 1

Substrate 2 substrate 1

Name or substance class Molecular weight Name or substance class / (g / mol)

DIOP 498 Olef ine

NORPHOS 463 Olef ine

BINAP 623 olefin

Dendrimers 300-2000 ketones

Sharpless ligands 300-600 olefins

PPPA 429 ketones

X-Pybox 305-318 ketones

Ferrocenylphosphine «660 ketones, aldehydes

Table 2

Claims

claims

1. Process for the separation of substances by means of a suitable membrane, in which the molar mass of a substance S _] _70 to 1,000 g / mol, the molar mass of a further substance S2 300 to 2,000 g / mol, the molar mass difference S ₂ - Si 200 up to 1000 g / mol, the quotient (S ₂ - S _] _) / S2 0.5 to 0.9 and the retention rate of S2 is at least 75%.

2. The method according to claim 1 for the separation of products formed in the presence of a synthesis aid (S2)

<Sχ) from the synthesis aid (S2).

3. The method according to claim 2 for separating products obtained from enzyme-catalyzed reactions (S _] _) from cofactors (S ₂ ).

4. The method according to claim 2 for separating products obtained from chemical catalysis (S] _) from the catalyst (S2) •

5. The method according to claim 4 for the separation of products (Si) obtained from asymmetric chemical catalysis from the catalyst (S2).

6. The method according to any one of claims 2 to 5, characterized in that the product is an epoxide, an amino acid, an alcohol or a -hydroxy acid.

SPARE BLADE (RULE 26)

7. The method according to any one of claims 2 to 6, characterized in that a membrane reactor is used for the reaction and separation.

8. The method according to any one of claims 2 to 7, characterized in that the reaction and separation takes place continuously,