EP2504302A1

EP2504302A1 - Method for isolating an alkanol from an aqueous biotransformation mixture

Info

Publication number: EP2504302A1
Application number: EP10782283A
Authority: EP
Inventors: Jürgen Däuwel; Michael Breuer; Bernhard Hauer
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 2009-11-24
Filing date: 2010-11-24
Publication date: 2012-10-03
Also published as: CN102712560A; JP2013511498A; WO2011064259A1; US20120285816A1

Abstract

The invention relates to the isolation of an alkanol from an aqueous biotransformation mixture, in that a) a first alkanol phase is obtained by means of distilling out an alkanol-water azeotrope from the aqueous biotransformation mixture and, if the azeotrope is a heteroazeotrope, phase separating the azeotrope and separating out an aqueous phase, b) a second alkanol phase is obtained by (i) liquid/liquid extracting the first alkanol phase using a solvent as an extracting agent, or (ii) azeotropic drying the first alkanol phase in the presence of the solvent as a carrier agent, and c) the second alkanol phase is fractionally distilled, producing a pure alkanol fraction. The biotransformation mixture is obtained, for example, by means of reducing an alkanol in the presence of an alcohol dehydrogenase. The method is adapted to the severe dilution of the products of value in the biotransformation mixture and works without long phase separation times when extracting by means of organic solvents.

Description

The invention relates to a process for isolating an alkanol from an aqueous biotransformation broth.

The so-called "biotransformation" is the biotechnological-chemical synthesis of organic chemical compounds using isolated enzymes or enzymes present in cells known. In the biotransformation, the enzymatic

Conversion of a substrate, i. a non-natural (xenobiotic) compound, into a value product.

The biotransformation is characterized by a high chemo-, regio- and stereospecificity even with complex substrates and mixtures. These benefits have in

Combined with high space-time yields, relatively inexpensive, renewable starting materials and often better environmental performance of the processes meant that the number of biotransformation processes used in industry increased enormously.

The focus for the application of this technology is the production of optically active products.

WO 2006/53713 describes a process for the preparation of (S) -butan-2-ol by reduction of butan-2-one in the presence of an alcohol dehydrogenase (ADH) with a specific polypeptide sequence. Preferably, the enantioselective reduction is carried out with the ADH in the presence of a reducing agent, such as glucose or formate, which regenerates the oxidized in the course of the reduction cofactor. For the regeneration of the coenzyme, a second dehydrogenase, e.g. Glucose dehydrogenase or formate dehydrogenase can be added.

WO 2005/108590 discloses a process for the preparation of optically active alkanols which comprises, in an alkanone-containing medium, an enzyme (E) selected from the classes of dehydrogenases, aldehyde reductases and carbonyl reductases incubated in the presence of reducing equivalents, wherein the reducing equivalents consumed in the course of the reaction are regenerated by reacting a sacrificial alcohol to the corresponding sacrificial ketone with the aid of the enzyme (E).

From the literature, various processes for working up biotransformation products from the culture broth of microorganisms are known. The refurbishment

M / 49266-PCT The procedure must be adapted to certain peculiarities of the biotransformation, in particular the strong dilution of the products of value in the culture broth and / or contamination with cell components. Volatile or steam-volatile compounds can be expelled during the reaction with a stripping gas from the culture broth. Such a method is z. As described in US 2005/089979. However, the method is only suitable in cases in which the starting substrates have no appreciable volatility. In many cases, after completion of the biotransformation, the crude product-containing culture broths are concentrated to dryness and the biotransformation products are then extracted with an organic solvent. In a whole-cell biotransformation, a cell separation step may take place before concentration, for example by means of centrifugation, filtration, etc.

In these methods, the biotransformation product is contaminated by lipophilic cell components to a considerable extent, which makes expensive cleaning operations necessary. The prior art usually employs a thermal cleaning process (distillation) to separate the desired product from the lipophilic cell constituents. For steam-volatile compounds, high rates of loss are sometimes observed in this process.

Alternatively, the biotransformation products are treated with organic solvents, e.g. Ether, extracted from the aqueous culture medium. Usually, an up to tenfold excess of organic solvent has to be added to the aqueous phase.

The problem with extraction is that gelation and slime formation phenomena occur when the organic solvent is added to the culture medium. These sometimes seriously impair the isolation of the biocatalytically produced compounds and drastically affect the yield.

The gel and slime formation in the extraction with organic solvents is due to the presence of emulsifying agents in the cell suspension or in the cell-free culture medium. The presence of emulsifying agents in the extraction reduces the efficiency of the extraction in terms of quantity and purity of the product to be isolated. At the same time, the presence of emulsifying agents leads to the formation of gels or gums that are stable for several weeks or months. As part of these emulsifying agents so called bio emulsifiers have been identified. Although it is known, these bioemulsifiers by the addition of hydrolases

M / 49266-PCT to destroy. However, the hydrolases used for the enzymatic de-emulsification contribute significantly to the complexity and cost of the process.

The object of the invention is therefore to provide a process for isolating alkanols, in particular optically active alkanols, from an aqueous biotransformation broth, which is adapted to the high dilution of the desired products in the biotransformation broth and manages without long Phasenseparationszeiten in the extraction with organic solvents , The object is achieved by a process for isolating an alkanol from an aqueous biotransformation broth which comprises a) obtaining a first alkanol phase by distilling off an alkanol-water azeotrope from the aqueous biotransformation broth and, if the azeotrope is a heteroazeotrope, phase separation of the Azeotrope and separation of an aqueous phase,

b) a second alkanol phase obtained by

(i) liquid / liquid extraction of the first alkanol phase with a solvent as extractant; or

(ii) azeotroping the first alkanol phase in the presence of the solvent as an entrainer, and

c) fractionally distilling the second alkanol phase to obtain a pure alkanol fraction. The first alkanol phase has a first water content, the second alkanol phase has a second water content. The second water content is lower than the first water content. By water content is meant the amount of water, based on the alkanol content. The fractional distillation in step c) can be carried out batchwise or continuously.

In this context, biotransformation is understood to mean the reaction of a substrate which is catalyzed by isolated enzymes or enzyme systems, immobilized enzymes or enzyme systems, crude enzyme extracts, whole cells, quiescent cells and / or disrupted cells. These include fermentations.

The workup process according to the invention takes place after the biotransformation has ended, ie. once a desired conversion (of, for example, 90% or more) is achieved.

The process according to the invention has the advantage that the biotransformation broth does not undergo complex mechanical separation or purification operations.

M / 49266-PCT must be drawn, such as a separation of biomass, for example by centrifugation or filtration. Already in the first step of the process, there is a substantial concentration of the desired product while reducing the volumes which have to be handled in the following steps. For example, the azeotrope of 2-butanol and water has a 2-butanol content of about 72% by weight. The boiling point of the azeotrope is at normal pressure at about 87 ° C, well below the boiling points of water and 2-butanol of about 100 ° C.

The method is basically applicable to the isolation of any biotransformed alkanol which forms an azeotrope with water. The azeotrope may be a homogeneous azeotrope or heteroazeotrope. The alkanols include C 2 -C 8 alkanols, in particular C 4 -C 8 alkanols, whose alkyl chain may be straight-chain or branched and which may be primary, secondary or tertiary alcohols. The alkanol is preferably selected from optically active alkanols, in particular optically active 2-alkanols. Particularly preferred examples are S-2-butanol, S-2-pentanol and S-2-hexanol.

In a first step, an alkanol-water azeotrope is distilled off from the aqueous biotransformation broth. The apparatus implementation of the distillation is possible in various embodiments.

The heating of the biotransformation broth to boiling may be carried out in any heatable vessel, e.g. a stirred tank reactor with heating jacket, or evaporator. By way of apparatus, agitating vessels, falling film, thin layers, forced expansion circulation and other types of evaporators in natural or forced circulation can be used. However, the use of evaporators is less preferred because certain components of the biotransformation broth can result in rapid fouling of the evaporator. In an expedient embodiment, the biotransformation broth is heated directly after completion of the biotransformation in the reaction vessel. The heating rate up to the boiling point is preferably at least 20 K / min. With slower heating, the risk of undesirable side reactions, in particular of racemization in optically active alcohols exist.

The distillation can be carried out as a simple distillation, i. essentially without material exchange between rising vapor and returning condensate, or be designed as a rectification. For the latter, all known types of distillation or rectification columns, e.g. run below.

The distilling off of the alkanol-water azeotrope takes place under suitable conditions of pressure and temperature. If desired, the distillation may be carried out under reduced pressure. In general, working under ambient pressure is preferred because of the lower equipment cost.

M / 49266-PCT The vapor containing the alkanol-water azeotrope is at least partially condensed. Suitable for this purpose are any heat exchangers or condensers which may be air-cooled or water-cooled.

When the alkanol forms a homogeneous azeotrope with water, the first alkanol phase obtained as a condensate can be sent for further work-up. Part of the condensate can be added as reflux to the rectification column. When the alkanol forms a heteroazeotrope with water, the condensate decomposes into an aqueous phase and an organic phase, which can be separated in a suitable phase separation vessel or decanter. The aqueous phase may be returned to the evaporation vessel, e.g. as reflux to the rectification column. In the phase separation, the first alkanol phase is obtained as the organic phase.

The first alkanol phase contains dissolved water due to the solubility of water. Before further purification by distillation, the first alkanol phase must therefore be dried. In one embodiment, the drying of the first alkanol phase is carried out by liquid / liquid extraction with a solvent as the extraction agent. Suitable extractants are solvents in which water has only a very low solubility or is substantially insoluble. The water is due to the presence of the extractant, which reduces the solubility of water in the alkanol to be purified, eliminated and forms a separate phase that can be separated.

For liquid-liquid extraction, it is expedient to proceed in such a way that the first alkanol phase is brought into intimate contact with the solvent and an aqueous phase is separated off by decantation, the second alkanol phase being obtained.

For intensive mixing suitable equipment such. As a stirred tank, centrifugal extractor, countercurrent extractor and the like.

Subsequently, the solvent phase and the aqueous phase are separated from each other. The second alkanol phase obtained as the solvent phase now contains the alkanol dissolved in the solvent with a markedly reduced proportion of water.

Alternatively, the first alkanol phase may be subjected to azeotropic drying in the presence of a solvent as an entraining agent. During azeotropic drying, the dissolved water is removed from the system as a water-solvent azeotrope.

M / 49266-PCT For azeotropic drying, it is expedient to proceed by heating the first alkanol phase in a distillation vessel in the presence of the solvent and removing water as a water-solvent azeotrope, the second alkanol phase remaining in the distillation vessel. The water-solvent azeotrope-containing bromide is distilled off and at least partially condensed, the condensate is separated into an aqueous phase and a solvent phase and the solvent phase is recycled to the distillation vessel.

The solvent suitable as extractant or entraining agent is, for example, aliphatic hydrocarbons, such as pentane, hexane, heptane, cyclohexane, methylcyclohexane; aromatic hydrocarbons, such as benzene, toluene, xylenes; halogenated hydrocarbons, such as dichloromethane, trichloromethane, dichloroethane, chlorobenzene. Aliphatic hydrocarbons, such as in particular n-hexane, are particularly preferred because of their comparative non-toxicity and easy separability from the alkanol.

The second alkanol phase is then fractionally distilled to give a pure alkanol fraction. In fractional distillation, the alkanol is freed from the added solvent, unreacted substrate, residual water, by-products and the like.

The apparatus implementation of the distillation is possible in various embodiments. All known types of distillation or rectification columns are suitable. A "rectification column" comprises separating internals such as slabs, fillers and / or packings. In order to improve the separation efficiency in the column, usually a partial flow of the condensate is returned to the column.

In typical tray columns sieve, bell or valve trays are installed, over which the liquid flows. Through special slots or holes of the steam is passed, so that a bubble layer is formed. On each of these soils, a new evaporation equilibrium sets in.

Packed columns can be filled with differently shaped packings. The associated surface enlargement heat and mass transfer are optimized and thus increases the separation capacity of the column. Typical examples of such fillers are the Raschig ring, Pall ring, Hiflow ring, Intalox saddle, Berl saddle and hedgehog. The packing can be ordered, but also random (as a bed) are introduced into the column. Suitable materials include glass, ceramics, metal and plastics.

M / 49266-PCT Structured packings are a further development of the ordered packing. They have a regularly shaped structure. There are different versions of packages z. B. tissue or sheet metal packages. The material used can be metal, plastic, glass and ceramics. Packing columns have a very low liquid content compared to tray columns. This is often advantageous for rectification because it reduces the risk of thermal decomposition of the substances.

In one embodiment, the second alkanol phase is introduced laterally into a fractionation column, the pure alkanol fraction is withdrawn as a side stream, a fraction boiling lower than the alkanol fraction overhead and a fraction boiling higher than the alkanol fraction in the bottom from.

In another embodiment, the second alkanol phase is distilled discontinuously, successively obtaining a fraction boiling lower than the alkanol fraction, the pure alkanol fraction and a fraction which boils higher than the alkanol fraction.

The fraction boiling lower than the alkanol fraction contains the majority of the solvent used and can advantageously be recycled at least partially as solvent to step b).

The aqueous biotransformation broth used in the process of the invention is obtained by any biotransformation process which converts a substrate to an alkanol. This includes both the fermentative production of alkanols and the enzymatic production of alkanols. In fermentative production, alkanols are produced by the metabolism of fermentable carbon sources by an alkanol-producing microorganism. Enzymatic production (or biotransformation in the narrower sense) is the selective chemical conversion of defined pure substances (educts) into products by enzymes, wherein the enzymes may be present in living, dormant or disrupted cells or may be enriched or isolated. a) Fermentative production of alkanols

The fermentative preparation of alkanols is known per se from the prior art. For example, WO 2008/137403 describes a process for the preparation of 2-butanol by fermentation. Examples of suitable natural or recombinant, pro- or eukaryotic microorganisms for fermentative production are those which, under aerobic or anaerobic conditions, can be used for the fermentative production of the desired Al species.

M / 49266-PCT In particular, bacteria are to be mentioned, which are selected from bacteria of the families Enterobacteriaceae, Pseudomonadaceae, Bacillaceae, Rhizobiaceae, Clostridiaceae, Lactobacillaceae, Streptomycetaceae, Rhodococcaceae, Rhodocyclaceae and Nocardiaceae. Examples of suitable genera include in particular Escherichia, Streptomyces, Clostridium, Corynebacterium and Bacillus.

Suitable fermentation conditions, media, fermenters and the like are determinable by one skilled in the art within the scope of his general knowledge. For this he can, for example, the embodiments in suitable technical literature, such. Rehm et al, Biotechnology, Vol. 3 Bioprocessing, 2nd ed., (Verlag Chemie, Weinheim). Thus, the microorganisms can be cultivated continuously, with and without recycling of the biomass, or batchwise in the batch process (batch culturing) or in the fed batch (feed process) or repeated fed batch process (repetitive feed process). The fermentation can be carried out in stirred fermenters, bubble columns and loop reactors. A summary of known cultivation methods is in the textbook by Chmiel (Bioprozesstechnik 1st Introduction to bioprocess engineering (Gustav Fischer Verlag, Stuttgart, 1991)) or in the textbook of Storhas (bioreactors and peripheral facilities (Vieweg Verlag, Braunschweig / Wiesbaden, 1994)) Find.

For this purpose, a sterile culture medium is prepared which contains the substrate (s) and other additives which are necessary for the growth of the microorganism and product formation, such as carbon and / or nitrogen sources, trace elements and the like, and with a suitable amount of a fresh preculture of the microorganism is inoculated.

The culture medium to be used must suitably satisfy the requirements of the respective strains. Descriptions of culture media of various microorganisms are contained in the Manual of Methods for General Bacteriology of the American Society for Bacteriology (Washington D.C, USA, 1981).

These media which can be used according to the invention usually comprise one or more carbon sources, nitrogen sources, inorganic salts, vitamins and / or trace elements.

Preferred carbon sources are sugars, such as mono-, di- or polysaccharides. Very good sources of carbon are, for example, glucose, fructose, mannose, galactose, ribose, sorbose, ribulose, lactose, maltose, sucrose, raffinose, starch or cellulose. Sugar can also be added to the media via complex compounds such as molasses or other by-products of sugar refining. It may also be advantageous to add mixtures of different carbon sources. Other possible sources of carbon are oils and fats such. Soybean oil, sunflower oil, peanut oil

M / 49266-PCT and coconut fat, fatty acids such as. As palmitic acid, stearic acid or linoleic acid, alcohols such. As glycerol, methanol or ethanol and organic acids such. As acetic acid or lactic acid. Nitrogen sources are usually organic or inorganic nitrogen compounds or materials containing these compounds. Exemplary nitrogen sources include ammonia gas or ammonium salts such as ammonium sulfate, ammonium chloride, ammonium phosphate, ammonium carbonate or ammonium nitrate, nitrates, urea, amino acids or complex nitrogen sources such as corn steep liquor, soybean meal, soy protein, yeast extract, meat extract and others. The nitrogen sources can be used singly or as a mixture.

Inorganic salt compounds which may be included in the media include the chloride, phosphorus or sulfate salts of calcium, magnesium, sodium, cobalt, molybdenum, potassium, manganese, zinc, copper and iron.

As sulfur source inorganic sulfur-containing compounds such as sulfates, sulfites, dithionites, tetrathionates, thiosulfates, sulfides but also organic sulfur compounds, such as mercaptans and thiols can be used.

Phosphoric acid, potassium dihydrogen phosphate or dipotassium hydrogen phosphate or the corresponding sodium-containing salts can be used as the phosphorus source. Chelating agents can be added to the medium to keep the metal ions in solution. Particularly suitable chelating agents include dihydroxyphenols, such as catechol or protocatechuate, or organic acids, such as citric acid.

The fermentation media used usually also contain other growth factors, such as vitamins or growth promoters, which include, for example, biotin, riboflavin, thiamine, folic acid, nicotinic acid, panthothenate and pyridoxine. Growth factors and salts are often derived from complex media components, such as yeast extract, molasses, corn steep liquor, and the like. In addition, suitable precursors can be added to the culture medium. The exact composition of the media compounds will depend heavily on the particular experiment and will be decided on a case by case basis. Information about the media optimization is available from the textbook "Applied Microbiol Physiology, A Practical Approach" (ed. P. M. Rhodes, P. F. Stanbury, IRL Press (1997) pp. 53-73, ISBN 0 19 963577 3). Growth media can also be obtained from commercial suppliers, such as Standard 1 (Merck) or BHI (Brain heart infusion, DIFCO) and the like.

M / 49266-PCT All media components are sterilized either by heat (20 min at 1, 5 bar and 121 ° C) or by sterile filtration. The components can either be sterilized together or, if necessary, sterilized separately. All media components may be present at the beginning of the culture or added randomly or in batches as desired.

The temperature of the culture is usually between 15 ° C and 45 ° C, preferably 25 ° C to 40 ° C and can be kept constant or changed during the experiment. The pH of the medium should be in the range of 5 to 8.5, preferably around 7.0. The pH for cultivation can be controlled during cultivation by addition of basic compounds such as sodium hydroxide, potassium hydroxide, ammonia or ammonia water or acidic compounds such as phosphoric acid or sulfuric acid. To control the development of foam anti-foaming agents, such as. As fatty acid polyglycol, are used. In order to maintain the stability of plasmids, suitable selective substances, such as e.g. As antibiotics, are added. In order to maintain aerobic conditions, oxygen or oxygen-containing gas mixtures, such. B. ambient air, registered in the culture. The temperature of the culture is usually 20 ° C to 45 ° C. The culture is continued until a maximum of the desired product has formed. This goal is usually reached within 10 hours to 160 hours.

Depending on the production strain, fumigation with air, oxygen, carbon dioxide, hydrogen, nitrogen or similar gas mixtures may be required to achieve good yields.

After the fermentation has ended, the fermentation broth containing the alkanol can either be fed directly to the further processing according to the invention. Preferably, however, first biomass, for example, separated by centrifugation or filtration and optionally washed and combined the washing liquid with the alkanol phase.

Before the further processing of the fermentation broth in the process of the invention, the fermentation broth can be pretreated, for example, the biomass of the broth can be separated. Methods of separating the biomass are known to those skilled in the art, e.g. Filtration, sedimentation and flotation. Consequently, the biomass can be separated, for example, with centrifuges, separators, decanters, filters or in flotation apparatus. For complete recovery of the desired product is often recommended washing the biomass, z. B. in the form of a diafiltration. The choice of method is dependent on the biomass fraction in the fermenter broth and the properties of the biomass, as well as the interaction of the biomass

M / 49266-PCT se with the value product. The fermentation broth may in one embodiment be sterilized or pasteurized. b) Enzymatic production of alkanols

The preparation of the alkanol is carried out in preferred embodiments by reduction of an alkanone in the presence of an alcohol dehydrogenase.

In a particularly preferred embodiment, a biotransforming broth containing 2-butanol is obtained by reduction of butan-2-one in the presence of an alcohol dehydrogenase (ADH) (EC 1 .1.1 .1).

Dehydrogenases convert ketones or aldehydes into the corresponding secondary or primary alcohols; In principle, the reaction is reversible. They catalyze the enantioselective hydride transfer to the prochiral C atom of the carbonyl compound.

The hydride ions are derived from cofactors, e.g. NADPH or NADH (reduced nicotinamide adenine dinucleotide phosphate or reduced nicotinamide adenine dinucleotide). Since these are very expensive compounds, they are added only in catalytic amounts of the reaction. The reduced cofactors are usually regenerated during the reaction by a concurrent, second redox reaction.

The ADH is for example selected from dehydrogenases from microorganisms of the genus Clostridium, Streptomyces or Escherichia. The ADH can be used in purified or partially purified form or else in the form of the microorganism itself. Methods for recovering and purifying dehydrogenases from microorganisms are known to those skilled in the art, e.g. from K. Nakamura & T. Matsuda, "Reduction of Ketones" in K. Drauz and H. Waldmann, Enzymes Catalysis in Organic Synthesis 2002, Vol. IM, 991-1032, Wiley-VCH, Weinheim. Recombinant methods for generating dehydrogenases are also known, for example from W. Hummel, K. Abokitse, K. Drauz, C. Rollmann and H. Gröger, Adv. Synth. Catal. 2003, 345, No. 1 + 2, pp. 153-159. Preferably, the reduction is carried out with the ADH in the presence of a suitable cofactor. As cofactors for the reduction of the ketone is usually NADH and / or NADPH. In addition, ADH can be used as cellular systems that inherently contain cofactors or alternative redox mediators are added (A.

Schmidt, F. Hollmann and B. Bühler "Oxidation of Alcohols" in K. Drauz and H. Waldmann, Enzyme Catalysis in Organic Synthesis 2002, Vol III, 991-1032, Wiley-VCH, Weinheim).

M / 49266-PCT In particular, the reaction takes place with simultaneous or delayed regeneration of the cofactor consumed during the reaction. Regeneration can be carried out enzymatically, electrochemically or electroenzymatically in a manner known per se (Biotechnology Progress, 2005, 21, 1992, Biocatalysis and Biotransformation, 2004, 22, 89, Angew Chem Chem Ed Engl., 2001, 40, 169 Biotechnol Bioeng, 2006, 96, 18; Biotechnol Adv., 2007, 25, 369; Angew.Chem Int. Ed Engl., 2008, 47, 2275; Current Opinion in Biotechnology, 2003, 14, 421; Current Opinion in Biotechnology, 2003, 14, 583). The reduction with the ADH preferably takes place in the presence of a suitable reducing agent which regenerates the cofactor oxidized in the course of the reduction. Examples of suitable reducing agents are sugars, in particular hexoses, such as glucose, mannose, fructose, and also formate, phosphite or molecular hydrogen. Depending on the thermodynamic and kinetic conditions of the overall reaction, oxidizable alcohols, in particular ethanol, propanol or inexpensive secondary alcohols such as, for example, / -propanol (so-called sacrificial alcohols) can occur as the final hydride donor of the reaction.

For the oxidation of the reducing agent and concomitantly for the regeneration of the cofactor, a regenerating enzyme may be added, such as a second dehydrogenase, e.g. Glucose dehydrogenase (GDH) (EC 1 .1 .1 .47) when using glucose as reducing agent, formate dehydrogenase (EC 1 .2.1.2 or EC 1 .2.1 .43) when using formate as reducing agent or phosphite dehydrogenase ( EC 1.20.1 .1) when using phosphite as a reducing agent. When using a sacrificial alcohol, ketone reduction and sacrificial alcohol oxidation can often be carried out by the same biocatalyst. The regenerating enzyme can be used as a free or immobilized enzyme or in the form of free or immobilized cells. It can be produced either separately or by coexpression in a (recombinant) dehydrogenase strain.

The aqueous reaction media are preferably buffered solutions which generally have a pH of from 5 to 8, preferably from 6 to 8. In addition to water, the aqueous solvent may also contain at least one water-miscible organic compound, such as isopropanol, n-butanol.

Suitable buffers include, for example, ammonium, alkali or alkaline earth metal phosphate buffer, or carbonate buffer, or TRIS / HCI buffer, used in concentrations of about 10 mM to 0.2 M.

The enzymatic reduction is generally carried out at a reaction temperature below the deactivation temperature of the dehydrogenase used and above

M / 49266-PCT from -10 ° C. It is particularly preferably in the range from 0 to 100 ° C, in particular from 15 to 60 ° C and especially from 20 to 40 ° C, for example at about 30 ° C.

The biotransformation can be carried out in stirred reactors, bubble columns and loop reactors. A detailed overview of the possible designs including stirrer shapes and geometrical designs can be found in "Chmiel: Bioprocessing Technology: Introduction to Bioprocess Engineering, Volume 1". In the process management are typically the following, known in the art or z. B. in "Chmiel, Hammes and Bailey: Biochemical Engineering" variants explained, such as batch, fed-batch, repeated fed-batch or even continuous fermentation with and without recycling of the biomass available. Depending on the production strain, fumigation with air, oxygen, carbon dioxide, hydrogen, nitrogen or appropriate gas mixtures can / must be carried out in order to achieve good yields. The enzymatic reaction can also be carried out in a manner known from the literature, continuously or discontinuously, as described above for the fermentation. The optimum concentrations for substrate, enzymes, reduction equivalents and sacrificial compound "can be readily determined by one skilled in the art.

For example, WO 2006/53713 describes a process for preparing (S) -butan-2-ol by reducing butan-2-one in the presence of an alcohol dehydrogenase (ADH) having a specific polypeptide sequence. The enantioselective reduction is preferably carried out with the ADH in the presence of a reducing agent, such as glucose or formate, which regenerates the cofactor oxidized in the course of the reduction. For the regeneration of the coenzyme, a second dehydrogenase, e.g. Glucose dehydrogenase or formate dehydrogenase.

The butan-2-one is preferably used in a concentration of 0.1 g / l to 500 g / l, more preferably from 1 g / l to 50 g / l in the enzymatic reduction and can be followed continuously or discontinuously ,

For carrying out, for example, the butan-2-one with the ADH, the solvent and optionally the cofactors, optionally present a second dehydrogenase for the regeneration of the cofactor and / or other reducing agents and mix the mixture, z. B. by stirring or shaking. However, it is also possible to immobilize the dehydrogenase (s) in a reactor, for example in a column, and to pass through the reactor a mixture containing the butan-2-one and optionally cofactors and / or cosubstrates. For this purpose, the mixture can be circulated through the reactor until the desired conversion is achieved. In this case, the keto group of butan-2-οη is reduced to an OH group, wherein essentially the (S) -enantiomer of the alcohol is formed. Usually will

M / 49266-PCT the reduction to a conversion of at least 70%, particularly preferably of at least 85% and in particular of at least 95%, based on the butane-2-ηη contained in the mixture. The progress of the reaction, ie the sequential reduction of the ketone, can be monitored by conventional methods such as gas chromatography or high pressure liquid chromatography.

WO 2005/108590 discloses a process for the preparation of optically active alkanols which comprises, in an alkanone-containing medium, an enzyme (E) selected from the classes of dehydrogenases, aldehyde reductases and carbonyl reductases incubated in the presence of reducing equivalents, wherein the reducing equivalents consumed in the course of the reaction are regenerated by reacting a sacrificial alcohol to the corresponding sacrificial ketone with the aid of the enzyme (E). According to the process described in WO 2005/108590, it is possible to produce a biotransformation broth containing S-2-pentanol. c) Immobilization of enzymes or microorganisms

The enzymes used for alkanol production can be used freely or immobilized in the methods described herein.

An immobilized enzyme is an enzyme which is fixed to an inert carrier. Suitable support materials and the enzymes immobilized thereon are known from EP-A-1 149849, EP-A-1 069 183 and DE-OS 100193773 and from the references cited therein. The disclosure of these documents is hereby incorporated by reference in its entirety. Suitable support materials include, for example, clays, clay minerals such as kaolinite, diatomaceous earth, perlite, silica, alumina, sodium carbonate, calcium carbonate, cellulose powder, anion exchange materials, synthetic polymers such as polystyrene, acrylic resins, phenolformaldehyde resins, polyurethanes and polyolefins such as polyethylene and polypropylene. The support materials are usually used to prepare the supported enzymes in a finely divided, particulate form, with porous forms being preferred. The particle size of the carrier material is usually not more than 5 mm, in particular not more than 2 mm (grading curve). Similarly, when using the dehydrogenase as a whole-cell catalyst, a free or immobilized form can be selected. Support materials are e.g. Ca alginate, and carrageenan. Enzymes as well as cells can also be cross-linked directly with glutaraldehyde (cross-linking to CLEAs). Corresponding and further immobilization processes are described, for example, in J. Lalonde and A. Margolin "Immobilization of Enzymes" in K. Drauz and H. Waldmann, Enzyme Catalysis in Organic Synthesis 2002, Vol. III, 991-1032, Wiley-VCH, Weinheim. Further information on biotransformations

M / 49266-PCT NEN and bioreactors for carrying out the process according to the invention are also found, for example, in Rehm et al. (Ed) Biotechology, 2nd Edn, Vol. 3, Chapter 17, VCH, Weinheim.

The invention is further illustrated by the following embodiments. example 1

Enzymatic reduction

In a 16 m ³ vessel, an enzymatic reduction of 2-butanone to S-2-butanol was carried out. To this was added 7000 l of water, 43.5 kg of dipotassium hydrogendophosphate, 34 kg of potassium dihydrogen orthophosphate and 2.4 kg of magnesium chloride hexahydrate. After switching on the stirrer, another 1000 l of water were added and the kettle was heated to 25.degree. After one hour, the pH was controlled. The pH should be 6.3-6.7, to which optionally, depending on the pH, 75% phosphoric acid or 48% potassium hydroxide solution were added.

After adjusting the pH, 901 kg of glucose, 1.3 kg of cofactor NAD were dissolved in water, 500 l of ADH biocatalyst, 400 l of glucose dehydrogenase preparation and 361 kg of 2-butanone were added.

After the end of the addition, the contents of the kettle were stirred at an internal temperature of 25 ° C. for a further 24 hours. The pH was kept at pH 6.3-6.7 by addition of 20% NaOH. When the conversion was 90% or more after 24 h, the reaction was complete, at less than 90% conversion, the reaction solution was stirred for a further 2h at 25 ° C.

Azeotropic distillation

The reaction effluent from the enzymatic reduction was heated in the 16 m ³ stirred tank at atmospheric pressure to about 100 ° C internal temperature. In a one-stage distillation about 400 kg of product-containing upper phase were separated via a phase separator, while the aqueous phase was recycled to the stirred tank. The break-off criterion for this step was the end of the two-phase distillation of the distillate.

After reaching this criterion, in addition about 100 kg of single-phase distillate were distilled off in order to achieve a complete separation of the S-2-butanol from the reaction effluent. The yield in this step was more than 90%. Azeotropic drying + hexane distillation

M / 49266-PCT Four fractions from the azeotropic distillation were combined and azeotroped using n-hexane. For this purpose, about 2000 kg of distillate from the azeotropic distillation were placed in 16 m ³ stirred tank and treated with 1600 kg of n-hexane. The kettle contents were heated at normal pressure to about 60 ° C. In a single-stage distillation, about 600 kg of aqueous lower phase were removed from the cell via the phase separator. The organic upper phase was recycled to the stirred tank. Stop criterion for this step was the end of the two-phase distillate. After reaching this criterion about 1300 kg of the remaining n-hexane were distilled off via the attached column and then cooled to room temperature in the boiler contents. The yield in this step was more than 95%.

pure distillation

The crude S-2-butanol from the azeotropic drying was pure-distilled via a continuous column. The column with a diameter of 50 mm consisted of eight sections, each of which was equipped with 0.5 m structured tissue packing (Sulzer CY). The distillation was carried out at atmospheric pressure. The crude product was fed in liquid at a packing height of 3 m, overhead the lower boiling fractions, such as Hexane, 2-butanone and residual water, distilled off. About swamp coloring, higher boiling components were separated. The pure fraction was withdrawn via a vaporous side take-off at a packing height of 0.5 m. The S-2-butanol was present in a purity of more than 99%, the yield of the continuous purifying distillation was more than 90%. Example 2

Enzymatic reduction

In a 4 l mini-planar reactor, an enzymatic reduction of 2-butanone to S-2-butanol was carried out. To this was added 2600 ml of water, 15 g of dipotassium hydrogen orthophosphate, 1 l of potassium dihydrogen orthophosphate and 1 g of magnesium chloride hexahydrate. After switching on the stirrer, the reactor was heated to 25 ° C. After one hour, the pH was controlled. The pH should be 6.3-6.7, optionally depending on the pH value 75% phosphoric acid or 48% potassium hydroxide solution was added.

After adjusting the pH, 300 g of glucose, 0.5 g of cofactor NAD were dissolved in water, 170 ml of ADH biocatalyst, 130 ml of glucose dehydrogenase preparation and 120 g of 2-butanone were added.

After completion of the addition of the contents of the kettle at an internal temperature of 25 ° C was stirred for a further 24h. The pH was increased by adding 20% NaOH

M / 49266-PCT pH 6.3-6.7. When the conversion was 90% or more after 24 h, the reaction was complete, at less than 90% conversion, the reaction solution was stirred for a further 2h at 25 ° C. Azeotropic distillation

The reaction effluent from the enzymatic reduction was heated in a 41-miniplantreaktor at atmospheric pressure to about 100 ° C internal temperature. In a single-stage distillation, about 140 g of product-containing upper phase were separated off via a phase separator, while the aqueous phase was returned to the reactor. Stop criterion for this step was the end of the two-phase distillate. After reaching this criterion, in addition about 30 g of single-phase distillate were distilled off in order to achieve complete separation of the S-2-butanol from the reaction effluent. The yield in this step was more than 90%.

Hexane extraction

In a 500 ml separating funnel, the hydrous S-2-butanol fraction from the azeotropic distillation was admixed with about 100 ml of n-hexane and extracted at room temperature. After phase separation, about 60 ml of an aqueous lower phase and about 240 ml of an organic upper phase were obtained. The water content of the upper phase was reduced by the hexane extraction to less than 5%. The yield in this step was more than 95%. Hexane distillation + purifying distillation

The organic upper phases from two hexane extractions were combined in a 1 l miniiplantreactor with attached column (packing length about 30 cm, packing 3 mm wire mesh rings) and separated by batch distillation at normal pressure and variable reflux ratio. After a low-boiling fraction consisting of hexane, 2-butanone, S-2-butanol and water, a valuable product fraction having a purity of more than 99% and a yield of more than 90% was isolated. The higher boiling, coloring components remained in the bottom of the reactor.

M / 49266-PCT

Claims

claims

1 . A process for isolating an alkanol from an aqueous biotransformation broth comprising: a) obtaining a first alkanol phase by distilling off an alkanol-water azeotrope from the aqueous biotransformation broth and, if the azeotrope is a heteroazeotrope, phase separation of the azeotrope and separation of one aqueous phase,

b) a second alkanol phase obtained by

c) fractionally distilling the second alkanol phase to obtain a pure alkanol fraction.

2. The method of claim 1, wherein the alkanol is selected from optically active 2-alkanols.

3. The method of claim 2, wherein the alkanol is selected from S-2-butanol, S-2-pentanol and S-2-hexanol.

4. The method according to any one of the preceding claims, wherein the solvent is selected from aliphatic hydrocarbons.

5. The method of claim 4, wherein the solvent is n-hexane.

6. The method according to any one of the preceding claims, wherein for the liquid-liquid extraction, the first alkanol phase intimately brings into contact with the solvent and an aqueous phase is separated to obtain the second alkanol phase.

7. The method according to any one of claims 1 to 5, wherein for the azeotropic drying, the first alkanol phase is heated in a distillation vessel in the presence of the solvent and water recirculated as a water-solvent azeotrope, wherein the second alkanol phase remains in the distillation vessel.

8. The method according to any one of the preceding claims, wherein for the fractional distillation, the second alkanol phase continuously laterally into a Frakti-

M / 49266-PCT onierkolonne introduces the pure alkanol fraction withdrawn as a side stream, a lower than the alkanol fraction boiling off overhead deducted and deducting a higher than the alkanol fraction boiling fraction in the bottom.

A process as claimed in any of claims 1 to 7, wherein the second alkanol phase is fractionally distilled for fractional distillation to give, in succession, a fraction boiling lower than the alkanol fraction, the pure alkanol fraction and a fraction boiling higher than the alkanol fraction wins.

A process according to claim 8 or 9, wherein the fraction boiling lower than the alkanol fraction is at least partly recycled as solvent to step b). 1 1. A method according to any one of the preceding claims wherein the biotransformation broth contains live cells, quiescent cells or digested cells.

A process according to any one of the preceding claims, wherein the biotransformation broth is obtained by reduction of an alkanone in the presence of an alcohol dehydrogenase.

The method of claim 12, wherein the biotransformation broth is obtained by reduction of 2-butanone in the presence of an alcohol dehydrogenase.

M / 49266-PCT