Method for green recovery of high-concentration acetic acid from organic solid waste anaerobic fermentation liquor

Abstract

The application discloses a new method for green recovery of high-concentration acetic acid from organic solid waste anaerobic fermentation liquid, and belongs to the technical field of environmental protection.The application mainly removes volatile fatty acids other than acetic acid in the organic solid waste anaerobic fermentation liquid by using a combination of extractants, retains the acetic acid in the water phase, and then obtains liquid chemicals containing high-concentration acetic acid through evaporation and concentration.Compared with the traditional extraction method, the application has the advantages of green environmental protection, low cost, high selectivity and the like.

Description

Technical Field

[0001] This invention belongs to the field of environmental protection technology, specifically relating to a method for recovering high-concentration acetic acid products from anaerobic fermentation liquid of organic solid waste. Background Technology

[0002] Organic solid waste, such as kitchen waste and sewage sludge, is generated in daily life and production. It is characterized by high organic matter content and easy decomposition, and conventional treatment methods include sanitary landfill, composting, and incineration. Anaerobic fermentation, which converts organic solid waste into liquid chemicals such as acetic acid, is considered a promising approach. However, the separation and purification of high-concentration acetic acid from anaerobic fermentation broth remains a bottleneck limiting the large-scale production and application of bio-based acetic acid.

[0003] Existing methods for separating and purifying acetic acid mainly include solvent extraction, adsorption, and membrane processes. Solvent extraction, using solvents such as fatty amines and phosphine as extractants, can almost completely extract volatile fatty acids into the organic phase, but it has low selectivity for acetic acid and cannot separate acetic acid from volatile fatty acids such as propionic acid and butyric acid produced during fermentation. Adsorption, using amine-functionalized resins as adsorbents, has some selectivity, but the elution and regeneration processes require large amounts of chemical reagents, resulting in high costs. Membrane processes offer higher selectivity than the previous two methods, but the high cost of membranes, as well as operating and maintenance costs, limits their application.

[0004] To date, there have been no research reports on the effective separation of volatile fatty acids such as acetic acid and propionic acid using solvent extraction. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention proposes a method for separating and recovering acetic acid from mixed volatile fatty acids in anaerobic fermentation broth using solvent extraction. Unlike conventional solvent extraction methods, this method retains acetic acid in the aqueous phase rather than extracting it into the organic phase. Instead, it extracts and removes volatile fatty acids such as propionic acid from the aqueous phase, thereby achieving the separation of acetic acid and propionic acid. Acetic acid is then concentrated by evaporation. The natural solvent used in this method has the advantages of being environmentally friendly, sustainable, and low-cost, while the mixed solvent extraction process exhibits high selectivity for acetic acid.

[0006] The technical solution of the present invention is as follows:

[0007] A method for recovering acetic acid from anaerobic fermentation broth of organic solid waste, the method comprising the following steps:

[0008] (1) Separate the organic solid waste anaerobic fermentation liquid into solid and liquid phases, collect the aqueous phase, and obtain the fermentation liquid after solid-liquid separation treatment;

[0009] (2) Separate the fermentation broth after solid-liquid separation treatment obtained in step (1) through a microfiltration membrane to remove the bacterial cells and obtain the fermentation broth after microfiltration membrane treatment;

[0010] (3) Add an appropriate amount of inorganic acid to the fermentation broth after microfiltration membrane treatment obtained in step (2) to adjust the pH to 2.0-3.0;

[0011] (4) Mix the liquid in step (3) that has been adjusted to acidity with the composite extractant to allow the volatile fatty acids and the extractant to undergo an extraction reaction, thereby obtaining an aqueous phase and an organic phase;

[0012] (5) Centrifuge the mixture of aqueous phase and organic phase obtained in step (4) to separate the aqueous phase and organic phase, and obtain the aqueous phase after centrifugation.

[0013] (6) Add an appropriate amount of inorganic alkali to the aqueous phase after centrifugation obtained in step (5) to adjust the pH to 8.0-9.0, and separate it through a microfiltration membrane to remove the protein and obtain the fermentation broth after microfiltration membrane treatment.

[0014] (7) The fermentation broth obtained in step (6) after microfiltration membrane treatment is evaporated and concentrated. When it is evaporated to a certain volume, an appropriate amount of inorganic acid is added, centrifuged, and the supernatant is collected to obtain a liquid chemical containing a high concentration of acetic acid.

[0015] In one embodiment of the present invention, in step (1), the anaerobic fermentation liquid of organic solid waste includes, but is not limited to, anaerobic fermentation liquid of organic solid waste such as catering waste, kitchen waste, feces, and animal solid waste.

[0016] In one embodiment of the present invention, in step (1), the anaerobic fermentation liquid of organic solid waste contains volatile fatty acids such as acetic acid as the main fermentation products.

[0017] In one embodiment of the present invention, the acetic acid concentration in the anaerobic fermentation liquid of organic solid waste in step (1) is between 6000 mg / L and 16000 mg / L.

[0018] In one embodiment of the present invention, in step (1), the solid-liquid separation can be any of centrifugal separation or pressure filtration / filtration separation.

[0019] In one embodiment of the present invention, in step (2), the pore size of the microfiltration membrane is 0.22 μm, 0.30 μm, or 0.45 μm.

[0020] In one embodiment of the present invention, in step (3), the inorganic acid used is one or more of hydrochloric acid, sulfuric acid, nitric acid or phosphoric acid, and the concentration of the inorganic acid is 0.1 to 1 mol / L.

[0021] In one embodiment of the present invention, in step (4), the composite extractant used is a mixture of n-octanol, sunflower seed oil and ethyl acetate; wherein the volume ratio of n-octanol, sunflower seed oil and ethyl acetate is (1-5):(1-5):5.

[0022] In one embodiment of the present invention, in step (4), the extraction process distributes volatile fatty acids other than acetic acid to the organic phase, while acetic acid remains in the aqueous phase.

[0023] In one embodiment of the present invention, in step (4), the amount of composite extractant added is 1 / 20 to 1 / 5 of the volume of the liquid to be extracted.

[0024] In one embodiment of the present invention, in step (4), the extraction time is 12 to 24 hours.

[0025] In one embodiment of the present invention, in step (5), the centrifugation speed is 4500-12000 rpm and the centrifugation time is 5-10 minutes.

[0026] In one embodiment of the present invention, in step (6), the inorganic base used is either sodium hydroxide or potassium hydroxide, with a concentration of 0.1 to 1 mol / L.

[0027] In one embodiment of the present invention, in step (6), the pore size of the microfiltration membrane is 0.22 μm, 0.30 μm, or 0.45 μm.

[0028] In one embodiment of the present invention, in step (7), the steam temperature during evaporation and concentration is 100-108°C.

[0029] In one embodiment of the present invention, step (7) refers to evaporating to a certain volume, which means concentrating to 1 / 40 to 1 / 20 of the original liquid.

[0030] In one embodiment of the present invention, in step (7), the inorganic acid used is one or more of concentrated hydrochloric acid and concentrated sulfuric acid, wherein the mass fraction of concentrated hydrochloric acid is 18-36% and the mass fraction of concentrated sulfuric acid is 49-98%.

[0031] This invention provides the application of the above method in anaerobic fermentation of organic solid waste.

[0032] The beneficial effects of this invention are:

[0033] (1) This invention proposes a new method for efficient separation and recovery of acetic acid from anaerobic fermentation liquid of organic solid waste. The method removes volatile fatty acids such as propionic acid by solvent extraction and increases the concentration of acetic acid by evaporation, thereby obtaining acetic acid liquid chemical with a certain purity and concentration.

[0034] (2) The present invention is simple to operate, low in cost, and the chemical reagents used are relatively environmentally friendly. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the process for recovering high-concentration acetic acid from anaerobic fermentation broth of organic solid waste. Detailed Implementation

[0036] The following examples provide a more detailed explanation of the invention. It should be understood that the examples given below are only for illustrative purposes and do not encompass all the contents of the invention.

[0037] Example 1

[0038] The initial anaerobic fermentation liquid of a certain food waste treatment project has carboxylic acids as its main components, namely acetic acid, propionic acid and butyric acid, and contains impurities such as bacteria and proteins. The concentration of acetic acid is 6881.0 mg / L, the concentration of propionic acid is 2115.7 mg / L, and the concentration of butyric acid is 2331.8 mg / L.

[0039] (1) The anaerobic fermentation liquid of kitchen waste was centrifuged at 4500 rpm for 10 min to separate the solid, liquid and oil in the fermentation liquid. The middle layer of fermentation liquid was collected to obtain the fermentation liquid after centrifugation.

[0040] (2) The centrifuged fermentation broth was passed through a microfiltration membrane with a pore size of 0.45 μm to remove the bacterial cells, and the microfiltration membrane-treated fermentation broth was obtained.

[0041] (3) Add an appropriate amount of 1mol / L hydrochloric acid to the fermentation broth after microfiltration membrane treatment to adjust the pH to 3.0;

[0042] (4) A composite extractant consisting of n-octanol, ethyl acetate, and sunflower seed oil in a volume ratio of 5:5:5 was used to perform a first-stage shaking extraction on the volatile fatty acids in the liquid after pH adjustment in step (3) at a ratio (O / A) of 3:40. After 24 hours of extraction, the concentration of acetic acid in the aqueous phase was 6782.5 mg / L, the concentration of propionic acid was 1503.4 mg / L, and the concentration of butyric acid was 1855.2 mg / L. Among them, the removal rate of valeric acid was 94.21%.

[0043] (5) Centrifuge the mixture of aqueous phase and organic phase at 4500 rpm for 10 min to separate the aqueous phase and organic phase, and obtain the aqueous phase after centrifugation.

[0044] (6) Add an appropriate amount of 3 mol / L sodium hydroxide to the aqueous phase after centrifugation to adjust the pH to 8.0, and remove the protein by passing it through an ultrafiltration membrane with a pore size of 0.22 μm to obtain the fermentation broth after ultrafiltration membrane treatment.

[0045] (7) The fermentation broth after ultrafiltration membrane treatment was evaporated and concentrated at a steam temperature of 100℃. When the volume was reduced to 1 / 20 of the initial volume, 500 μL of concentrated hydrochloric acid with a mass fraction of 36% was added and centrifuged. The supernatant was collected. The final concentrate had an acetic acid concentration of 139472 mg / L, a propionic acid concentration of 24253.0 mg / L, and a butyric acid concentration of 14167.4 mg / L. Acetic acid accounted for 78.3% of the volatile fatty acids.

[0046] Example 2

[0047] The anaerobic fermentation liquid in the later stage of a certain food waste treatment project has carboxylic acids as its main components, which are acetic acid, propionic acid and butyric acid. It also contains impurities such as bacteria and proteins. The concentration of acetic acid is 12181.86 mg / L, the concentration of propionic acid is 4159.9 mg / L and the concentration of butyric acid is 3052.3 mg / L.

[0048] (1) The anaerobic fermentation liquid of kitchen waste was centrifuged at 12,000 rpm for 5 minutes to separate the solid, liquid and oil in the fermentation liquid. The middle layer of fermentation liquid was collected to obtain the centrifuged fermentation liquid.

[0049] (2) The centrifuged fermentation broth was passed through a microfiltration membrane with a pore size of 0.22 μm to remove the bacterial cells and obtain the microfiltration membrane-treated fermentation broth.

[0050] (3) Add an appropriate amount of 0.1 mol / L hydrochloric acid to the fermentation broth after microfiltration membrane treatment to adjust the pH to 2.0;

[0051] (4) A composite extractant consisting of n-octanol, ethyl acetate, and sunflower seed oil in a volume ratio of 1:5:5 was used to perform a first-stage shaking extraction on the volatile fatty acids in the liquid after pH adjustment in step (3) at a ratio (O / A) of 1:5. After 24 hours of extraction, the concentration of acetic acid in the aqueous phase was 8043.8 mg / L, the concentration of propionic acid was 1983.0 mg / L, the concentration of butyric acid was 1308.4 mg / L, and the removal rate of valeric acid was 93.19%.

[0052] (5) Centrifuge the mixture of aqueous phase and organic phase at 12000 rpm for 5 min to separate the aqueous phase and organic phase, and obtain the aqueous phase after centrifugation.

[0053] (6) Add an appropriate amount of sodium hydroxide to the aqueous phase after centrifugation to adjust the pH to 9.0, and remove the protein by passing it through an ultrafiltration membrane with a pore size of 0.22 μm to obtain the fermentation broth after ultrafiltration membrane treatment;

[0054] (7) The fermentation broth after ultrafiltration membrane treatment was evaporated and concentrated at a steam temperature of 108°C. When the volume was reduced to 1 / 40 of the initial volume, 500 μL of 98% concentrated sulfuric acid was added and centrifuged. The supernatant was collected. The final concentrate had an acetic acid concentration of 315059.2 mg / L, a propionic acid concentration of 28251.2 mg / L, and a butyric acid concentration of 13942.9 mg / L. Acetic acid accounted for 88.2% of the volatile fatty acids.

[0055] Example 3

[0056] An anaerobic fermentation broth for producing acetic acid from activated sludge has the following fermentation products: carboxylic acids, mainly acetic acid, propionic acid, and butyric acid, and also contain impurities such as bacteria and proteins. The concentrations of acetic acid, propionic acid, and butyric acid are 15450.25 mg / L, 8063.24 mg / L, and 4750.27 mg / L, respectively.

[0057] (1) The anaerobic fermentation liquid of kitchen waste was centrifuged at 6000 rpm for 5 min to separate the solid, liquid and oil in the fermentation liquid. The middle layer of fermentation liquid was collected to obtain the centrifuged fermentation liquid.

[0058] (2) The centrifuged fermentation broth was passed through a microfiltration membrane with a pore size of 0.30 μm to remove the bacterial cells, and the microfiltration membrane-treated fermentation broth was obtained.

[0059] (3) Add an appropriate amount of 1mol / L hydrochloric acid to the fermentation broth after microfiltration membrane treatment to adjust the pH to 2.0;

[0060] (4) A composite extractant consisting of n-octanol, ethyl acetate, and sunflower seed oil in a volume ratio of 5:1:5 was used to perform a first-stage shaking extraction on the volatile fatty acids in the liquid after pH adjustment in step (3) at a ratio (O / A) of 1:20. After 12 hours of extraction, the concentration of acetic acid in the aqueous phase was 9208.35 mg / L, the concentration of propionic acid was 4934.70 mg / L, the concentration of butyric acid was 2308.63 mg / L, and the removal rate of valeric acid was 97.07%.

[0061] (5) Centrifuge the mixture of aqueous phase and organic phase at 6000 rpm for 5 min to separate the aqueous phase and organic phase, and obtain the aqueous phase after centrifugation.

[0062] (6) Add an appropriate amount of sodium hydroxide to the aqueous phase after centrifugation to adjust the pH to 9.0, and remove the protein by passing it through an ultrafiltration membrane with a pore size of 0.30 μm to obtain the fermentation broth after ultrafiltration membrane treatment;

[0063] (7) The fermentation broth after ultrafiltration membrane treatment was evaporated and concentrated at a steam temperature of 108°C. When the volume was reduced to 1 / 20 of the initial volume, 500 μL of concentrated hydrochloric acid with a mass fraction of 18% was added and centrifuged. The supernatant was collected. The final concentrate had an acetic acid concentration of 180559.4 mg / L, a propionic acid concentration of 33248.26 mg / L, and a butyric acid concentration of 6823.83 mg / L. Acetic acid accounted for 81.8% of the volatile fatty acids.

[0064] Comparative Example 1

[0065] The extractants used in the extraction steps were n-octanol, sunflower oil, and ethyl acetate, with the remaining operating parameters and steps the same as in Example 1. The extraction rates of n-octanol for acetic acid and propionic acid were 29.39% and 22.41%, respectively, showing little difference in selectivity for acetic acid and propionic acid. The extraction rates of ethyl acetate and sunflower oil for butyric acid were 54.05% and 52.46%, respectively, and for valeric acid were 74.15% and 59.68%, respectively, failing to separate acetic acid from butyric acid and valeric acid. The results indicate that these three solvents, when used as single extractants, cannot achieve highly selective separation of acetic acid and other volatile fatty acids.

[0066] Comparative Example 2

[0067] The extraction solvents used in the extraction steps were a mixture of n-octanol and ethyl acetate (volume ratio 1:1), a mixture of sunflower seed oil and ethyl acetate (volume ratio 1:1), and a mixture of n-octanol and sunflower seed oil (volume ratio 1:1), with the remaining operating parameters and steps being the same as in Example 1. The n-octanol and ethyl acetate mixture (volume ratio 1:1) showed high extraction rates for butyric acid and valeric acid, at 86.25% and 97.07%, respectively; however, the extraction rates for acetic acid and propionic acid were only 17.00% and 57.26%, respectively, showing little selectivity and insufficient for achieving high selective separation of acetic acid and other volatile fatty acids. The sunflower seed oil and ethyl acetate mixture (volume ratio 1:1) only achieved extraction rates of 68.50% and 72.06% for butyric acid and valeric acid, respectively, failing to effectively separate acetic acid from butyric acid and valeric acid. Similarly, the extraction rates of butyric acid and valeric acid by a mixed solvent of n-octanol and sunflower seed oil (volume ratio 1:1) were only 74.41% and 74.52%, respectively, which could not effectively separate acetic acid from butyric acid and valeric acid.

[0068] By comparing the extraction effects of the composite extractant prepared by mixing n-octanol, ethyl acetate, and sunflower seed oil in a volume ratio of 5:5:5 in Example 1 with the composite extractants prepared by mixing a single solvent or two solvents in a volume ratio of 1:1 in Comparative Examples 1 and 2, it was found that the composite extractant prepared by mixing n-octanol, ethyl acetate, and sunflower seed oil has a higher selectivity than that prepared by a single solvent or other combinations.

[0069] Although the present invention has been described in detail through the preferred embodiments above, it should be understood that the above description should not be considered as a limitation of the present invention. Various modifications and substitutions to the present invention will be apparent to those skilled in the art after reading the above description. Therefore, the scope of protection of the present invention should be defined by the appended claims.

Claims

1. A method for recovering acetic acid from anaerobic fermentation broth of organic solid waste, characterized in that, The method includes the following steps: (1) Separate the organic solid waste anaerobic fermentation liquid into solid and liquid phases, collect the aqueous phase, and obtain the fermentation liquid after solid-liquid separation treatment; (2) Separate the fermentation broth after solid-liquid separation treatment obtained in step (1) through a microfiltration membrane to remove the bacterial cells and obtain the fermentation broth after microfiltration membrane treatment; (3) Add an appropriate amount of inorganic acid to the fermentation broth after microfiltration membrane treatment obtained in step (2) to adjust the pH to 2.0-3.0; (4) Mix the liquid in step (3) that has been adjusted to acidity with the composite extractant to allow the volatile fatty acids and the extractant to undergo an extraction reaction, thereby obtaining an aqueous phase and an organic phase; (5) Centrifuge the mixture of aqueous phase and organic phase obtained in step (4) to separate the aqueous phase and organic phase, and obtain the aqueous phase after centrifugation. (6) Add an appropriate amount of inorganic alkali to the aqueous phase after centrifugation obtained in step (5) to adjust the pH to 8.0-9.0, and separate it through a microfiltration membrane to remove the protein and obtain the fermentation broth after microfiltration membrane treatment. (7) The fermentation broth obtained after microfiltration membrane treatment in step (6) is evaporated and concentrated. When it is evaporated to a certain volume, an appropriate amount of inorganic acid is added and centrifuged. The supernatant is collected to obtain a liquid chemical containing a high concentration of acetic acid. In step (4), the composite extractant is a mixture of n-octanol, sunflower seed oil and ethyl acetate; The anaerobic fermentation liquid of the organic solid waste includes catering waste; the acetic acid concentration in the anaerobic fermentation liquid of the organic solid waste is between 6000 mg / L and 16000 mg / L; The volume ratio of n-octanol, sunflower seed oil, and ethyl acetate is (1-5):(1-5):5; The amount of the composite extractant added is 1 / 20 to 1 / 5 of the volume of the liquid to be extracted.

2. The method according to claim 1, characterized in that, The pore size of the microfiltration membrane mentioned in step (2) and step (6) is 0.22 μm, 0.30 μm, or 0.45 μm.

3. The method according to claim 1, characterized in that, In step (3), the inorganic acid used is one or more of hydrochloric acid, sulfuric acid, nitric acid or phosphoric acid, and the concentration of the inorganic acid is 0.1 to 1 mol / L; in step (6), the inorganic base used is one of sodium hydroxide or potassium hydroxide, and the concentration is 0.1 to 1 mol / L.

4. The method according to claim 1, characterized in that, In step (4), the extraction time is 12 to 24 hours.

5. The method according to claim 1, characterized in that, In step (7), evaporating to a certain volume means concentrating to 1 / 40 to 1 / 20 of the original liquid.

6. The method according to any one of claims 1 to 5, characterized in that, In step (7), the inorganic acid used is one or more of concentrated hydrochloric acid and concentrated sulfuric acid, with the mass fraction of concentrated hydrochloric acid being 18-36% and the mass fraction of concentrated sulfuric acid being 49-98%.

7. The application of the method according to any one of claims 1 to 6 in anaerobic fermentation of organic solid waste.

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