METHOD FOR PREPARING ORGANIC COMPOUNDS

Abstract

The invention relates to a method for preparing organic compounds with recovery of product liquids, which comprise short-chain and medium length-chain carboxylic acids having a chain length of from 2 to 16 carbon atoms, by anaerobic fermentation of biomass with mixed microorganism cultures with suppression of methane formation and by electrolytic treatment of these product liquids containing the carboxylic acids with a constant or varying oxidation flow for the recovery and isolation of the target compounds.

Claims

1. A method for preparing organic compounds, characterised by anaerobic fermentation of biomass with mixed microorganism cultures at temperatures of from 10 to 100° C. and pH values of from 3.5 to 9.5, wherein the methane formation is suppressed, such that product liquids comprising mixtures of short-chain and medium length-chain carboxylic acids having a chain length of from 2 to 16 carbon atoms are recovered, electrolytic treatment of the product liquid containing the carboxylic acids with a constant or varying oxidation current in order to recover the organic compounds, isolation of the organic compounds.

2. The method according to claim 1, characterised in that for fermentation the biomass is liquid or is brought into contact with a liquid in order to form a fermentation broth and temperatures of from 10 to 100° C. are set, solid fermentation residues are removed as appropriate after fermentation, and the product liquid containing at least 5 g/L of short-chain and medium length-chain carboxylic acids is electrolytically treated, optionally after purification and/or concentration.

3. The method according to claim 1, characterised in that the biomass is selected from at least one of the groups of the energy plants or residual materials and waste products from agriculture and industry, or extracts and processing products therefrom, or algae or yeasts or gas mixtures from biomass gassing or pyrolysis, such as syngas and pyrolysis gas, or silaged biomass or biomass pre-treated by means of other physical, physical-chemical, chemical and/or biological methods.

4. The method according to claim 1, characterised in that the carboxylic acids are in a mixture of branched and/or unbranched mono, hydroxy and/or dicarboxylic acids, preferably carboxylic acids having 4 to 10 carbon atoms.

5. The method according to claim 1, characterised in that the organic compounds comprise, as main products, C.sub.6 to C.sub.18 alkanes which are obtained possibly in mixture with corresponding derivatives, such as ethers, esters, alcohols, etc.

6. The method according to claim 1, characterised in that, for fermentation, (a) mixed culture(s) of acid-forming microorganisms and/or methane-forming inhibitor(s) are/is added.

7. The method according to claim 1, characterised in that, for fermentation, alcohols and/or lactic acid are/is added in order to increase the yield of medium length-chain carboxylic acids.

8. The method according to claim 1, characterised in that separate fermenters are used for hydrolysis/acid formation and acetic acid/methane formation, wherein the product liquid from the first-phase reactor is electrolytically treated.

9. The method according to claim 1, characterised in that the product liquid is treated with bases or acids prior to the electrolytic treatment in order to change the pH value.

10. The method according to claim 1, characterised in that the electrolytic treatment is performed with a varying current flow, wherein the current flow (working current flow) is altered at constant or alternating time intervals to another current flow, or what is known as a pulsed flow (pulse method).

11. The method according to claim 10, characterised in that the anode is periodically subjected to an interruption of the power circuit, whereby phases of current flow (production) and no current flow (non production) alternate with one another, wherein the pulse duration varies between 1 second and 2 days, but is always shorter than the duration of the application of the working current flow.

12. The method according to claim 1, characterised in that the fermentation residues created and/or hydrolysis gas formed are used further, preferably for the production of biogas.

Description

PRACTICAL EXAMPLES

[0054] FIG. 1: sequential execution of microbial acid production and electrochemical acid oxidation; [0055] 1: fermenter, 2: electrochemical reactor, 3: product separation, 4: (organic) product phase

[0056] FIG. 2: in situ execution of microbial acid production and electrochemical acid oxidation. [0057] 1: fermentation with in situ electrochemical reaction, 2: (organic) product phase

[0058] (Note: in FIG. 1 and FIG. 2, the hydrogen development reaction is always illustrated as cathode reaction, see the main text with regard to the use thereof and alternative reduction reactions).

Example 1

[0059] Anaerobic fermentation of corn silage in a percolation method (batch test):

Test Structure (FIG. 3)

[0060] 1 biogas removal [0061] 2 fermenter lid with percolation ring system [0062] 3 pressure compensation line [0063] 4 supported sieve [0064] 5 heating line drain [0065] 6 product harvesting and circulation ring line drain [0066] 7 percolate storage chamber [0067] 8 support pipe for supported sieve [0068] 9 solids fermentation chamber [0069] 10 overflow [0070] 11 double-walled fermenter jacket [0071] 12 heating line feed [0072] 13 circulation ring line feed

[0073] A PVC double-walled reactor divided into two compartments (total volume 45 L) with thermostat temperature control (38° C.) and an integrated sprinkler system was constructed (FIG. 3). A sieve bottom (hole diameter 2 mm) was used to retain solid substrate constituents and thus separated the upper reactor chamber, into which substrate was filled, from the lower part, in which the percolate was caught. Two pipes, which connected the compartments to one another, additionally belonged to the internal fittings of the reactor. One of the pipes served for pressure compensation between the two compartments. The other constituted a drain safeguard pipe, which in the event of a blockage of the sieve bottom prevented an overflow of the percolate in the upper compartment. A pump was used to circulate the percolate from the lower reactor region to the sprinkler apparatus below the reactor lid. A temperature-controlled water bath was used to heat the reactor via the double-walled system.

Execution

[0074] 2 kg.sub.fresh mass of corn silage were mixed with 15 g Mn(OH).sub.2 and filled into the reactor. 5 kg of deionised water were used as a basis for the fermentation broth and were added via the corn silage. Then, 1 kg of inoculum liquid (process liquid from a two-stage biogas facility) was added via the corn silage. The percolate was caught and collected within the reactor beneath the sieve bottom. The reactor was closed and a tightness test was carried out (5 mbar N.sub.2 overpressure).

[0075] Then, the pump was activated and the substrate was sprinkled for 15 min long with the percolate. The percolation by the peristaltic pump then followed in interval operation with a rate of 300 mL/30 min until the end of the test.

Analytics

[0076] The percolate was tested at regular intervals for the qualitative analysis thereof. Percolate samples were removed from the circulation line via a drain port. Prior to the analysis, the samples were centrifuged (Megafuge 16R, Nereus, 10,000×g, 10° C., 10 min) and the pellet was separated from the supernatant. The concentrations of acetic acid, propionic acid, iso-butyric acid, n-butyric acid, iso-valeric acid, n-valeric acid, and n-caproic acid in the percolate were determined by means of gas chromatography (for method details see Example 2).

Results

[0077] FIG. 4 shows the production of all measured organic acids (A) and, shown only in part, of C5 to C6 acids (B), specifically of n- and iso-valeric acid and of n-caproic acid in the course of the process.

[0078] Besides these acids, n-butyric acid and acetic acid were also created in significant amounts, respectively 8990 mg/L and 2620 mg/L. Further acids were formed in small amounts: ≈500 mg/L propionic acid, ≈200 mg/L iso-butyric acid. Heptanoic acid was not detected.

Example 2

[0079] Continuous anaerobic fermentation of biogas waste in a two-phase method (hydrolysis/acid formation separate from acetic acid formation/methane formation)

Test Structure (FIG. 5):

[0080] 1 Sampling port gas chamber 1.sup.st stage [0081] 2 Sampling port gas chamber 2.sup.nd stage [0082] 3 Percolate drain 1.sup.st stage [0083] 4 Recirculation of fermentation residue from the 2.sup.nd into the 1.sup.st stage

[0084] The fermentation of biowaste was carried out in a two-phase reactor consisting of solid fermentation in a percolation method (hydrolysis+acid formation) and a stirred reactor (acetogenesis+methanogenesis). This test was performed as a double test, i.e. there were two two-phase reactor systems completely separated from one another, which here are named reactor systems 1 and 2. The first-phase reactors of systems 1 and 2 each consisted of two sieve bottom reactors coupled to one another as described in Example 1. The second-phase stirred reactors each had a working volume of 11 L and were filled with filling material formed from polyethylene as growth material for microorganisms. These reactors were provided with an overflow. The drains of the methane stages were fed back into the corresponding hydrolysis stages.

Execution

[0085] The sieve bottom reactors were operated as percolation reactors as described in Example 1. Here, approximately 900 mL of the liquid phase of a reactor were pumped into the coupled reactor every half an hour. Approximately 2000 mL were pumped daily into the second-phase reactor from the percolate of the sieve bottom reactors.

[0086] Communal biowaste that had been removed from a composting plant on 26.03.2014 was used as substrate. At the start of the test, the percolation reactors were each loaded with 10.0 kg water, 4.0 kg biowaste, and 2.0 kg inoculum (drain of the hydrolysis stage of a two-stage biogas facility). The reactors were flushed with nitrogen, closed in an airtight manner, and the percolation was started.

[0087] The two sieve bottom reactors were charged twice weekly in alternation with 3.0 kg fresh biowaste. In order to compensate for the volume loss by sample removal, an additional 500 mL water were added every 2 weeks. After each substrate change, the reactors were flushed with nitrogen. The sampling was performed at least twice weekly, in each case on the day following the substrate change.

Analytics

[0088] The pH value of the percolate was measured using a WTW pH 3310 pH electrode. Percolate samples were centrifuged by means of a Heraeus Megafuge 16R (10 min at 10,000×g and 10° C.) and the supernatant was examined by means of GC with regard to the concentrations of organic acids and alcohols (triple determination). For this purpose, 3.00 mL of supernatant were pipetted in each case into a 20 mL Headspace vial, mixed with 1.00 mL of a solution of the internal standard (2-methylbutyric acid; 187 mg/L), 0.50 methanol and also 2.50 mL of diluted sulphuric acid (1:4; (v/v)), and closed in a gas-tight manner. The separation was performed on an Agilent Tech. 7890A GC system on a ZB-FFAP (Phenomenex) column. The quantification was performed on the basis of calibrations and the internal standard. The volume of the formed gas of the hydrolysis stage was detected by means of a Ritter MGC-1 V3.1 PMMA milligas counter. The gas was caught in gas-tight bags made of aluminium PE composite foil. An analysis of the main constituents of the gas by means of GC was performed. For this purpose, 20 mL gas vials were closed in a gas-tight manner and were flushed with argon. In each case 1.00 mL of hydrolysis gas was removed by means of a syringe through a septum in the gas line prior to the MGC and was injected into the vials filled with argon. These samples were separated into the individual gas constituents and detected on a Perkin Elmer Clarus® 580GC on a Hayesep N and a Mole sieve 13×, ASAG column.

Results

[0089] In the example, only the process data from the first-phase reaction are shown.

[0090] FIG. 6: production of unbranched organic acids (A) and, shown only in part, of unbranched C.sub.5 to C.sub.8 acids (B) in the first-phase reactor of the reactor system 2.

[0091] In addition, the concentrations of further acids and alcohols were detected (Table 1).

TABLE-US-00001 TABLE 1 Concentration of further acids and alcohols in the first-phase reactors of the reactor systems 1 and 2 Maximum concentration Acids: formic acid  <15 mg/L iso-butyric acid ≦300 mg/L  iso-valeric acid ≦150 mg/L  iso-caproic acid  ≦25 mg/L lactic acid at the start 4300 or 3850 mg/L, later <1000 mg/L Alcohols: ethanol <1000 mg/L  1-propanol <350 mg/L 2-propanol  <15 mg/L 1-butanol <100 mg/L 2-butanol <100 mg/L

Example 3

[0092] Electrochemical conversion of a carboxylic acid mixture in a batch test

Test Structure

[0093] A mixture of carboxylic acids (see substrate) was set to a pH value of 5.5 using 60% potassium carbonate solution. The tests provided the described carbonate acid solution in 250 mL four-neck round-bottom flasks with 100 mL filling volume. Platinum (Goodfellow, Germany) having a geometric surface of approximately 2.7 cm.sup.2 was used as working electrode. A platinum electrode with approximately 4 cm.sup.2 was used as counter electrode, and an Ag/AgCl (sat. KCl) electrode (0.197 mV vs. SHE, SE10 type Meinsberg) was used as reference electrode. In addition to the electrode terminals, a sampling port and waste air cooling means were connected to the piston. The waste air was cooled by means of a Dimroth cooler, water-cooled to 4° C. A magnetic stirrer (4.5×14.5 mm) was used to continuously mix the solution at 500 rpm.

Execution

[0094] Before the test was started, the dissolved oxygen of the carboxylic acid solution was displaced from the system by a 15-minute nitrogen flushing. The galvanostatically performed electrochemical synthesis lasting for 7 h with a current density (relative to the anode surface) of 130 mA/cm.sup.2 was then started. Both the voltage between working electrode and counter electrode and between working electrode and reference electrode were recorded for control purposes. A sample of the aqueous phase was taken every hour (sample volume 400 μL for pH check and HPLC analytics). At the end of the test, in addition to the HPLC check, the organic phase was also removed and measured by means of GC-MS).

Substrate

[0095] 39 g/L n-butyric acid, 20 g/L n-valeric acid and 9 g/L n-caproic acid in distilled water were used as substrate.

Analytics

[0096] The sample of the aqueous phase was used on the one hand to check the pH value by means of test strips (pH indicator rods 4.0-7.0, non-bleeding, Merck; pH indicator rods 7.5-14 non-bleeding, Merck).

[0097] On the other hand, an HPLC (high performance liquid chromatography) analysis (Shimadzu Corporation) enabled quantification of the content of carboxylic acids and water-soluble primary and secondary alcohols. A Hi-Plex H column (Agilent Technologies) was used for the separation at an oven temperature of 65° C., and a refraction index detector (RID-10A) was used for the detection. 5 mM sulphuric acid in water at a flow rate of 0.6 mL/min was used as mobile solvent. The substances were allocated into corresponding dilutions by their retention time on the basis of previous measurements of standard solutions and were quantified on the basis of the calibration of associated peak areas (R.sup.2=0.99).

[0098] GC-MS analytics (gas chromatography mass spectroscopy: gas chromatograph 7890A with column oven and mass spectrometer 5975 C inert MSD with Triple-Axix Detector Agilent Technologies) served for the qualitative and quantitative determination of alkanes, esters, alcohols and further by-products. The used capillary column (HP-SMS, 30 m length, 0.25 mm diameter and 0.25 μm film thickness, Agilent Technologies) was operated with the carrier gas helium 5.0 with a split of 0.1 mL/min. The measurements started at 35° C. with a holding time of 20 min, then the temperature was raised by 5 K/m in to 200° C. A further temperature rise to 300° C. was achieved with 30 K/m in and was then maintained for 2 min. The obtained peaks were compared with the mass spectral library (NIST 2008 Mass Spectral Library, G1033 A, Revision Jan 2008, 597× MSD, 7000A Triple Quad, Agilent Technologies) and calibrated with standards as necessary. The obtained samples were diluted in acetone 1:100 to 1:1000.

Results

[0099] All used carboxylic acids were broken down and the following conversions were attained up to the end of the test (7 h): 59% n-butyric acid, 80% n-valeric acid, and 89% caproic acid. On the whole, a conversion of 77% of the used carboxylic acids could be achieved. FIG. 7 shows the change of the carboxylic acid concentration in Example 3 over the test time. The standard deviations are based on two identical tests.

[0100] The continuous formation of 1-propanol, 2-propanol, 1-butanol and 2-butanol was able to be detected by means of HPLC analytics. After 7 h of test running time, the following concentrations were provided respectively: 0.97 g/L, 2.77 g/L, 0.38 g/L and 1.86 g/L with a deviation of at most 3% within the test repetitions. It is possible that 1-pentanol and 2-pentanol were also formed in low concentrations below the corresponding detection limits.

[0101] The GC-MS analytics of the organic phases diluted 1:1000 times in acetone showed exclusively representatives of the alkanes: n-heptane, n-octane, n-nonane and n-decane (see bottom of FIG. 8). In the 1:100 times dilution the reaction products stated in Table 2 could also be found. After the alkanes, esters were the second-largest product group, confirmed by alcohol formation during the electrochemical process.

[0102] The pH value of the carboxylic acid solution rose within the first two to three hours to 10.5 and remained for the rest of the test time constantly at 10.5.

[0103] The electron yield, that is to say Coulomb efficiency (CE), of 53% was calculated on the assumption that an individual electron was converted during the oxidation per converted acid molecule, and therefore exclusively the radical formation was considered.

TABLE-US-00002 TABLE 2 Main products of the organic phase from Example 3 with 1:100 times dilution in acetone (basis: GC-MS analytics) Esters Alkanes butyric acid-1-methylethyl hexane ester butyric acid-1- heptane methylpropyl ester butyric acid-1-methylethyl octane ester butyric acid-1- nonane methylbutyl ester valeric acid-1- decane methylpropyl ester hexanoic acid-1- methylethyl ester valeric acid-1-butyl ester valeric acid-2-pentyl ester hexanoic acid-2- methylpropyl ester valeric acid-1-pentyl ester hexanoic acid-3-pentyl ester

[0104] FIG. 8:

[0105] Production separation on the basis of the example of the formation of n-octane from n-valeric acid and also GC-MS chromatogram with 1:1000 dilution of the organic phase in acetone (see analytics for details)

Example 3a

Conversion of Further Carboxylic Acids and Mixtures in a Batch Test

Test Structure

[0106] see Example 3, for possible deviations see Table 3

Substrate:

[0107] see Table 3

Execution

[0108] see Example 3, for possible deviations see Table 3

Analytics

[0109] see Example 3

[0110] Table 3 compares the obtained results of the various test approaches in summary. Here, n-valeric acid was examined in various concentrations and at various current densities relative to the anode surface (Table 3, no. 1-3). By way of supplementation, the electrochemical conversion of iso-valeric acid could be shown (Table 3, no. 4). In addition, a mixture of n-butyric acid and n-valeric acid was tested (Table 3, no. 5-6).

TABLE-US-00003 TABLE 3 Overview of different galvanostatically performed electrochemical tests with various carboxylic acids in analogy to the test structure described in Example 4 (running time: 7 h) Conversion of Starting Current Conversion carboxylic concentration density in 7 h CE acids [mmol/ No Substrate [g/L] [mA/cm.sup.2] [%] [%] (cm.sup.2 h)] Main products organic phase 1 n-valeric acid.sup.#1 105 23 82 0.768 octane dibutyl peroxide valeric acid-1-methylpropyl ester valeric acid-butyl ester 2 n-valeric acid.sup.#1 102 150 60 69 1.939 octane dibutyl peroxide valeric acid-1-methylpropyl ester 3 n-valeric acid 39 130 85 35 0.975 2-hexanone octane dibutyl peroxide valeric acid-1-methylpropyl ester valeric acid-butyl ester valeric acid-pentyl ester 4 iso-valeric acid 41 130 86 37 0.903 ethyl hexane valeric acid-2methylpropyl ester valeric acid-butyl ester 5 n-butyric acid/n- 25/26 100 56/76 50 0.855/1.014 octane valeric acid butyric acid-1-methylpropyl ester valeric acid-1-methylethyl ester dibutyl peroxide valeric acid-propyl ester valeric acid-1-methylpropyl ester valeric acid-butyl ester 6 n-butyric acid/n- 25/26 130 68/85 58 1.149/1.028 heptane valeric acid octane butyric acid-1-methylethyl ester butyric acid-1-methylpropyl ester valeric acid-1-methylethyl ester valeric acid-propyl ester valeric acid-1-methylpropyl ester .sup.#1Tests carried out with a working electrode surface of 2.2 cm.sup.2

Example 4

[0111] Conversion of a pure carboxylic acid in a continuous flow-through reactor

Test Structure

[0112] A mixture of carboxylic acids was set to a pH value of 5.5 using potassium carbonate or potassium hydroxide. The tests were carried out in three different configurations in a flow-through reactor (MicroFlowCell, ElectroCell, Denmark) (see top of FIG. 8 and FIG. 9). A platinised titanium electrode having a geometric surface of 10 cm.sup.2 was used as counter electrode. Either a platinised titanium electrode or a lead electrode with 10 cm.sup.2 was used as counter electrode. A reference electrode Ag/AgCl 3.4 M KCl was integrated in the system.

[0113] The sampling and pH measurements were performed at reservoirs 2 and 5. Depending on the volume flow, a magnetic stirrer was additionally used for continuous mixing of the reaction solution at reservoirs 2 and 5.

FIG. 9 Test Structure

[0114] 1: electrochemical cell; 2, 5: reservoir; 3, 4: pump [0115] top: The electrochemical cell 1 consists of an anode chamber and a cathode chamber separated by a membrane. The two electrolyte solutions are each recirculated through a reservoir; [0116] middle: The electrochemical cell 1 is operated without separation of anode chamber and cathode chamber. The reaction solution is pumped around in a circuit from the reservoir 2 with the aid of the pump 3. [0117] bottom: The electrochemical cell 1 is operated without separation of anode chamber and cathode chamber. The reaction solution is pumped around from the reservoir 2 with the aid of the pump 3, the reaction solution is not constantly recirculated. (Note: A combination of the various configurations is possible depending on requirements.)

Execution

[0118] Prior to the test, the tightness of the electrochemical cell was examined. The electrochemical synthesis was then carried out galvanostatically. The reaction time was 0.5 to 8 h depending on reaction conditions. The reaction volume was 10 mL, and the circuit volume varied depending on the test from 25 to 250 mL. Both the voltages between working electrode and counter electrode and between working electrode and reference electrode were recorded (for details see also Table 4). At the end of the test, in addition to the HPLC check of the aqueous phase, the organic phase was also removed and measured by means of GC-MS. Depending on the test, samples of the aqueous phase were also removed during the reaction for control.

Analytics

[0119] The conversion of the carboxylic acid mixture of the aqueous phase was determined by means of HPLC analysis.

[0120] An HPLC system (Spectrasystem P4000, Finnigan Surveyor RI Plus Detector, Fisher Scientific, Germany) with a Hyper-REZXP Carbohydrate H+8 mm (S/N:026/H/012-227) column was used. The mobile phase consisted of a 5 mM sulphuric acid solution (flow rate: 0.5 mL/min). The column was cooled to 10° C. For the product concentrations, calibration lines in the range from 0.1 to 100 mM were created. The substances were allocated into corresponding dilutions by their retention time on the basis of previous measurements of standard solutions and were quantified on the basis of the calibration of associated peak areas (R.sup.2=0.99).

[0121] The formation of the products in the organic phase was determined after the reaction process by means of GC-MS analytics. A GC/MS system (TraceGC Ultra, DSQII, Thermo Scientific, Germany) with a TRWaxMS column (30 m×0.25 mm ID×0.25 μm film GC Column, Thermo Scientific, Germany) or DB-5 column (30 m×0.25 mm ID×0.25 mm film GC Column, Agilent JW Scientific, United States of America) was used.

Results

[0122]

TABLE-US-00004 TABLE 4 Overview of different galvanostatically performed electrochemical tests with various carboxylic acids in analogy to the test structure described in Example 4 Starting Current Volume Circuit concentration density Test flow volume Conversion CE No. Substrate [g/L] [mA/cm.sup.2] structure [mL/min] [mL] [%] [%] Products 1 n-butyric acid 22 100 B 0.7 50 67 19 hexane (22%) butyric acid-1-methylethyl ester (71%) butyric acid-1-methylpropyl ester (7%) 2 n-butyric acid 88 100 B 0.7 50 52 73 hexane butyric acid-1-methylethyl ester butyric acid-1-methylpropyl ester 3 n-butyric acid 44 150 C 0.7 — 56 23 hexane butyric acid-1-methylethyl ester butyric acid-1-methylpropyl ester 4 n-butyric acid 176 150 C 0.7 — 35 34 hexane butyric acid-1-methylethyl ester butyric acid-1-methylpropyl ester 5 n-butyric acid 176 100 C 0.7 — 24 24 hexane butyric acid-1-methylethyl ester butyric acid-1-methylpropyl ester 6 isovaleric acid 26 100 C 0.7 — 65 18 7 n-valeric acid 51 80 B 4 33 95 58 octane dibutyl peroxide valeric acid-1-methylpropyl ester 1-butanol in the aqueous phase 8 n-valeric acid 102 50 A 100 250 30 53 octane (63%) valeric acid-1-methylpropyl ester 9 n-valeric acid 200 100 B 4 50 83 50 octane (81%) dibutyl peroxide(3%) valeric acid-1-methylpropyl ester (16%) 1-butanol in the aqueous phase