WO2007082836A1

WO2007082836A1 - Method for the production of polyhydroxy alkanoates having a smaller alkali metal and alkaline earth metal concentration and greater thermal stability

Info

Publication number: WO2007082836A1
Application number: PCT/EP2007/050271
Authority: WO
Inventors: Peter PREISHUBER-PFLÜGL; Arnold Schneller; Dietrich Scherzer
Original assignee: Basf Se
Priority date: 2006-01-17
Filing date: 2007-01-12
Publication date: 2007-07-26
Also published as: EP1979394A1; CN101370851A; CN101370851B

Abstract

The invention relates to a method for producing polyhydroxy alkanoates from biotechnologically produced raw materials that have a total alkali metal and alkaline earth metal content of less than 150 ppm. The inventive method is characterized in that the biotechnologically produced polyhydroxy alkanoate is first concentrated by extracting the biomass and then treated with aqueous acid. Alternatively, the biotechnologically produced polyhydroxy alkanoate is first coagulated, and the coagulated material is treated with acid and is then separated from the biomass by means of an extracting agent. In another embodiment, the biotechnologically produced polyhydroxy alkanoate is separated from the biomass by means of an extracting agent, and the extracted solution is then treated with aqueous acid. The invention further relates to polyhydroxy alkanoates which can be obtained with the aid of said methods.

Description

METHOD FOR OBTAINING POLYHYDROXYALKANOATES WITH A REDUCED CONTENT OF ALKALI AND ERDALKALIMETALLES AND INCREASED THERMAL STABILITY

description

5 The present invention relates to a process for the preparation of polyhydroxyalkanoates from biotechnologically produced raw materials having a total content of alkali metal and alkaline earth metal of less than 150 ppm.

Polyhydroxyalkanoates can be produced with the help of microorganisms. For example, such biotechnological methods are described in Biopolymer, Wiley-VCH, 2002.

The raw materials produced by bioengineering contain, in addition to the desired polyhydroxyalkanoate, the microorganisms which produce the polyhydroxyalkanoate (biomass or non-polyhydroxyalkanoate mass). The isolation of the polyhydroxyalkanoate from the biomass can be achieved a) by dissolving the biomass or b) by extraction of the polyhydroxyalkanoate in a suitable extraction agent.

For the degradation and dissolution of the biomass (work-up a)), for example, enzymes or chemical processes can be used. In addition, surface-active compounds can be added. A combination of several methods is possible.

EP 0145233 describes the degradation of the biomass by enzymes. 25

WO 94/24302 describes the degradation of the biomass by enzymes and hydrogen peroxide.

No. 5,110,980 describes the degradation of the biomass by hypochlorite, which makes accessible high molecular weight polyhydroxyalkanoates. Different parameters such as temperature, time or pH during treatment with hypochlorite are investigated. Purification of the polyhydroxyalkanoate with dilute acids is not described.

35 Chlorinated compounds can be used as suitable extractants for polyhydroxyalkanoates (method b)). Examples are given in EP 0124309 and the literature cited therein.

Furthermore, cyclic carbonates for the extraction of polyhydroxy-40 alkanoates are described in US 4101533. In WO 2005052175, the extraction of polyhydroxyalkanoates with alcohols is carried out at elevated temperature.

Finally, in DE 19712702, the polyhydroxyalkanoate formed is extracted from the crude gas with boiling acetic acid. The polyhydroxyalkanoate turns brownish by this measure.

A problem of polyhydroxyalkanoates, which are usually prepared by the work-up methods a) or b), is the limited thermal stability. Under thermal stress, the molecular weight of the polymer decreases rapidly, thereby deteriorating the mechanical properties. A relationship between mechanical properties and molecular weight is shown in Polymer Bull. 1994, 33, 355.

The object of the present application was therefore to find cost-effective, process-ready processes that are easy to implement even on an industrial scale, with which it is possible to produce polyhydroxyalkanoates with higher thermal stability.

It has surprisingly been found that polyhydroxyalkanoates having a low total content of alkali metals and alkaline earth metals have better thermal stability. By treating the concentrated polyhydroxyalkanoates, the coagulated crude masses or the extraction solutions with acid, preferably aqueous acid, the abovementioned object can be achieved in a surprisingly simple manner.

The following embodiments are the subject of the present invention:

A process for the preparation of polyhydroxyalkanoates having a total content of alkali metal and alkaline earth metal of less than 150 ppm, characterized in that the biotechnologically produced polyhydroxyalkanoate is first concentrated by dissolving out the biomass and then treated with aqueous acid.

A process for the preparation of polyhydroxyalkanoates having a total content of alkali metal and alkaline earth metal of less than 150 ppm, characterized in that the biotechnologically produced polyhydroxyalkanoate is first coagulated, the coagulated mass is treated with acid and then separated with an extractant from the biomass.

A process for the preparation of polyhydroxyalkanoates having a total content of alkali metal and alkaline earth metal of less than 150 ppm, characterized in that the biotechnologically produced polyhydroxyalkanoate with an extractant from the Biomass is separated and then the extraction solution is treated with acid.

Polyhydroxyalkanoates having alkali metal and alkaline earth metal contents of less than 150 ppm, preferably less than 120 ppm, particularly preferably less than 80 ppm, are obtainable by the process according to the invention.

The treatment with acid can be understood as a washing process. Unlike the method described in DE 19712702, the polyhydroxyalkanoates are not dissolved by the acid in the process according to the invention.

The acids of the present invention include both Lewis acids and Bronsted acids. Lewis defined an acid as a substance which is an electrophilic electron pair acceptor. According to Bronsted, an acid is a compound that can release protons to reactants.

The acid may be present as a solid, liquid or gas. Furthermore, the acid may be present as a solution in an organic solvent or water.

Particularly preferred are aqueous acids. Mineral acids are preferably used in a concentration of 0.001 to 1 mol / l. Carboxylic acids and sulfonic acids are generally used in a concentration of 0.01 to 2 mol / l.

As liquid acids, inorganic or organic acids are used. Preferred acids are sulfuric acid, hydrochloric acid, phosphoric acid, phosphonic acid, nitric acid, nitrous acid, carbonic acid, silicic acid, hypochlorous acid, perchloric acid, amidosulfonic acid, acetic acid, formic acid, propionic acid, sulfonic acid, sulfonic acid, methanesulfonic acid, trifluoromethanesulfonic acid or citric acid.

Preferred gaseous acids are SO 2, SO 3 or CO 2.

The polyhydroxyalkanoate may be present during the treatment in solution, as a slurry, as a melt or as a solid.

The treatment with acid can be carried out continuously or discontinuously.

The treatment with acid can be carried out at temperatures between -100 to + 200 ° C, preferably 0 to 120 ° C, particularly preferably 10 to 60 ° C. As already mentioned above, the temperature in the process according to the invention is chosen so that no appreciable amounts of polyhydroxyalkanoate (<5%) go into solution. The biotechnologically produced polyhydroxyalkanoates can be isolated as described above by dissolving the biomass (method a)). For this purpose, enzymes or chemicals can be used. A combination of both is also possible. The obtained polyhydroxyalkanoate is in the form of water-insoluble granules.

By treatment with an acid, the content of alkali and alkaline earth metals of the polyhydroxyalkanoate granules can be lowered.

The acid is present as aqueous acid in the above-mentioned concentration range.

After treatment with acid, the polymer is removed from the aqueous solution. This can be done for example by filtration, centrifugation, sedimentation or hydrocyclone.

However, as already mentioned, the biotechnologically produced polyhydroxyalkanoate can also be isolated from the biomass by extraction with a suitable solvent (method b)).

The fermentation batch (raw material) can be slurried or coagulated before extraction. Coagulation can be achieved by different factors such as pH, enzymes, detergents or temperature. Several of these influences can also be combined. As an example, caustic and temperature should be mentioned here. The metal content of the resulting polyhydroxyalkanoate can be lowered by treating the coagulated mass with an acid prior to extraction.

In a preferred embodiment, the extraction solution of the polyhydroxyalkanoate is treated with an acid to lower the metal content.

The acid used may be in liquid, solid or gaseous state.

A preferred form is the use of a solid acid. Solid acid is understood in particular to mean ion exchangers. Particular preference is given to the use of ion exchangers with acidic groups such as sulfonic acids, phosphoric acids and carboxylic acids.

The acid can also be used as a solution in a two-phase system. Preference is given to the use of a water-insoluble polyhydroxyalkanoate solvent and an aqueous solution of an acid The acid can be present as a gas. The excess acid can be removed by degassing the polyhydroxyalkanoate solution or by extracting the gaseous acid into a second liquid phase.

A polyhydroxyalkanoate can also be isolated by combining solubilization of the biomass (method a)) and extraction of the polyhydroxyalkanoate (method b)). For this purpose, in a first step, the biomass is brought into solution and the polyhydroxyalkanoate isolated as a solid. Subsequently, the polyhydroxyalkanoate is dissolved to increase the purity.

Both options, the treatment of the batch with acid after the first step or after the second step is suitable for obtaining a polyhydroxyalkanoate with a reduced content of alkali metals and alkaline earth metals.

The polyhydroxyalkanoates can have different structures. Preferably, the homopolymer or copolymer of poly-3-hydroxybutyrate is prepared. As comonomer units, hydroxy-carboxylate units can be incorporated. Preference is given to incorporating hydroxy-3-alkanoates or hydroxy-4-alkanoates. Examples of hydroxy-3-alkanoates are hydroxy-3-valerate, hydroxy-3-hexanoate or other hydroxy-3-alkanoates with longer alkyl side chains.

By blending with another biodegradable polymer, biodegradable materials can be obtained.

Carrying out the experiments:

Poly-3-hydroxybutyrate (PHB crude) was prepared by fermentation of sugar with Alcaligenes eutrophus and then separated from the biomass in two different ways (PHB1 and PHB2). PHB1 was isolated by dissolving the biomass (method a)). The biomass was degraded by addition of basic hypochlorite solution as described in US 51 10980, the PHB1 was centrifuged.

PHB2 was separated into an extraction process (method b)). The polymer was extracted with chloroform as described in EP 0036699. Amberlyst 15 was bought by Aldrich.

Thermal stability was determined by the decrease in melt viscosity over a period of time. The method is described in J. Appl. Polym. See, 1991, 42, 845-850. Comparative Example 1

7 g of PHB1 were stirred in 100 ml of deionized water for one hour at room temperature. Subsequently, PHB1 was washed three times with water, once with ethanol and dried.

PHB1 had a content of alkali and alkaline earth metals of 915 ppm before the washing process, and after the washing process with water a content of alkali and alkaline earth metals of 650 ppm. The nitrogen content before purification was 430 ppm, after purification it was 480 ppm.

The melt viscosity of the polymer of Comparative Example 1 was determined at 180 ° C for a certain period of time. The melt viscosity was 14 Pa s after 10 min and 2 Pa s after 20 min.

Comparative Example 2

7 g of PHB1 were stirred in 100 ml of deionized water after adding 50 ml of 10% sodium hypochlorite solution for half an hour at room temperature. Subsequently, the PHB was washed three times with water, once with ethanol and dried.

The PHB1 had a content of alkaline and alkaline earth metals of 915 ppm before the washing process, after washing with water, a content of alkali and alkaline earth metals of 460 ppm. The nitrogen content before purification was 430 ppm, after 50 ppm.

The melt viscosity of the polymer of Comparative Example 2 was determined at 180 ° C. for a certain period of time. The melt viscosity was 22 Pa s after 10 min and 2 Pa s after 20 min.

Example 3

7 g of PHB1 were stirred in 100 ml of deionized water after adding 0.5 g of 2 molar hydrochloric acid for one hour at room temperature. Subsequently, the PHB was washed three times with water, once with ethanol and dried. PHB1 had a content of alkali and alkaline earth metals of 915 ppm before the washing process, and after the washing process with water a content of alkali and alkaline earth metals of 60 ppm.

The melt viscosity of the polymer from Example 3 was determined at 180 ° C. for a specific period of time. The melt viscosity was 503 Pa.s after 10 minutes and 85 Pa.s after 20 minutes. Example 4

7 g of PHB1 was stirred in 100 ml of deionized water after addition of 0.4 g of concentrated sulfuric acid for one hour at room temperature. Subsequently, the PHB was washed three times with water, once with ethanol and dried.

PHB1 had a content of alkali and alkaline earth metals of 915 ppm before the washing process, and after the washing process with water a content of alkali and alkaline earth metals of 80 ppm. The nitrogen content before purification was 430 ppm, after 480 ppm.

The melt viscosity of the polymer of Example 4 was determined at 180 ° C over a period of time. The melt viscosity was 926 Pa s after 10 min and 140 Pa s after 20 min.

Example 5

7 g of PHB1 were stirred in 100 ml of deionized water after addition of 0.4 g of acetic acid for one hour at room temperature. Subsequently, the PHB was washed three times with water, once with ethanol and dried. PHB1 had a content of alkali and alkaline earth metals of 915 ppm before the washing process, and after the washing process with water a content of alkali and alkaline earth metals of 70 ppm. The nitrogen content before purification was 430 ppm, after 490 ppm.

The melt viscosity of the polymer of Example 5 was determined at 180 ° C over a period of time. The melt viscosity was 1170 Pa.s after 10 minutes and 174 Pa.s after 20 minutes.

Comparative Example 6

PHB2 had an alkali and alkaline earth metal content of 155 ppm before treatment with acid. The nitrogen content was 370 ppm.

The melt viscosity of PHB2 without treatment with acid was determined at 180 ° C over a period of time. The melt viscosity was 950 Pa s after 10 min and 313 Pa s after 20 min.

Example 7

4 g of PHB2 were dissolved in 50 ml of chloroform. The solution was then stirred twice with 3 g Amberlyst 15 each over a period of 7 h. After treatment, Amberlyst 15 was filtered off and the polymer was isolated by precipitation in ether / hexane. Example 7 had a content of alkali and alkaline earth metals of 50 ppm. The nitrogen content was 100 ppm.

The melt viscosity of the polymer of Example 7 was determined at 180 ° C over a period of time. The melt viscosity was 2380 Pa s after 10 min and 805 Pa s after 20 min.

Claims

claims

1. A process for the preparation of polyhydroxyalkanoates having a total content of alkali metal and alkaline earth metal of less than 150 ppm, thereby gekennzeich- net that the biotechnologically produced polyhydroxyalkanoate first by

Removing the biomass concentrated and then treated with aqueous acid.

2. A process for the preparation of polyhydroxyalkanoates having a total content of alkali metal and alkaline earth metal of less than 150 ppm, characterized in that the biotechnologically produced polyhydroxyalkanoate is first coagulated, the coagulated mass is treated with acid and then separated with an extractant from the biomass ,

3. A process for the preparation of polyhydroxyalkanoates having a total content of alkali metal and alkaline earth metal of less than 150 ppm, characterized in that the biotechnologically produced polyhydroxyalkanoate is separated with an extractant from the biomass and then the extraction solution is treated with acid.

4. The method according to claim 3, characterized in that the extraction solution is passed over an acidic ion exchanger.

5. Process according to claims 2 or 3, characterized in that an aqueous acid is used.

6. Process according to claims 1 to 3 or 5, characterized in that a mineral acid, carboxylic acid or sulfonic acid is used as the acid.

7. The method according to claims 2 or 3, characterized in that a gas is used as the acid.

8. The method according to claims 1 to 7, characterized in that a polyhydroxyalkanoate is prepared with a total content of alkali and alkaline earth metal of less than 100 ppm.