Process for degrading one or more hydrocarbon compounds

Abstract

The invention relates to a process for degrading one or more hydrocarbon compounds in an aqueous solution. The one or more hydrocarbons comprise at least one of phenol, methyl phenyl ketone and methyl phenyl methanol. The degradation process is carried out in two or more continuously operating bioelectrochemical cells, thereby defining at least one upstream bioelectrochemical cell and one downstream bioelectrochemical cell, and the applied voltage of each bioelectrochemical cell is different. The bioelectrochemical cell includes a microbial culture. The one or more hydrocarbon compounds are converted at the anode to produce carbon dioxide, protons, and optional degradation products. At the cathode, the carbon dioxide and / or optional degradation products react with the protons to produce methane. A treated aqueous solution having a reduced content of the one or more hydrocarbon compounds is thus obtained.

Description

Technical Field

[0001] The present invention relates to a process for degrading one or more hydrocarbon compounds in an aqueous solution, wherein the one or more hydrocarbons at least include one of phenol, methyl phenyl ketone and methyl phenyl methanol. Background Art

[0002] This aqueous solution can be wastewater from a chemical process. It is known that phenol, methyl phenyl ketone and methyl phenyl carbinol cannot be treated in a specific wastewater treatment process due to their toxicity to the organisms usually present in the anaerobic digestion process. For this reason, this aqueous solution is usually subjected to a so-called wet air oxidation process. This process is very energy-intensive and a more energy-efficient process is needed to replace it.

[0003] Patent GB2262052 describes a process in which an aqueous solution is freeze-concentrated to obtain concentrated waste, salt crystals and an almost pure aquatic product. The disadvantage of this process is that it is still energy-consuming. Another disadvantage is that hydrocarbon compounds, especially phenol, one of methyl phenyl ketone and methyl phenyl carbinol, are not degraded into other compounds. Therefore, the problem of how to deal with these compounds still remains. Summary of the invention

[0004] The objective of the present process is to provide an improved process for the degradation of one or more of phenol, methyl phenyl ketone and methyl phenyl carbinol in aqueous solution with improved energy efficiency and applicability.

[0005] The object is achieved by the following process. A process for degrading one or more hydrocarbon compounds in a feed aqueous solution, wherein the one or more hydrocarbons include at least one of phenol, methyl phenyl ketone and methyl phenyl carbinol, The degradation process is carried out in a bioelectrochemical cell comprising a microbial culture, an anode and a cathode. A battery voltage is applied between the anode and cathode, causing electrons to be transferred from the anode to the cathode. wherein the one or more hydrocarbon compounds are converted at the anode to generate carbon dioxide, protons and optional degradation products, and wherein, at the cathode, carbon dioxide and / or optional degradation products react with protons to form methane, thereby obtaining a treated aqueous solution having a reduced content of the one or more hydrocarbon compounds, and The degradation process is carried out in two or more bioelectrochemical cells connected in series and operated in series, thereby defining at least one upstream bioelectrochemical cell and one downstream bioelectrochemical cell, and the cell voltage applied to each bioelectrochemical cell is different.

[0006] Applicants have discovered that, through this process, phenol, methyl phenyl ketone and methyl phenyl carbinol in an aqueous solution can be continuously degraded into other products. The treated aqueous solution may have a sufficiently low chemical oxygen demand (COD) so that the aqueous solution can be discharged into the environment. In addition, the content of toxic components such as phenol, methyl phenyl ketone and methyl phenyl carbinol can be reduced to a level sufficient to enable the aqueous solution to be successfully further treated in a conventional anaerobic wastewater treatment process to produce methane. The energy required to run this process is significantly less than the prior art process described above, and the undesirable phenol, methyl phenyl ketone and methyl phenyl carbinol can be effectively removed.

[0007] The present invention will be described in detail below.

[0008] The feed aqueous solution includes at least one of phenol, methyl phenyl ketone and methyl phenyl carbinol. The feed aqueous solution may further include methanol, 1-propanol, monopropylene glycol and / or benzaldehyde. The feed aqueous solution may contain non-salt organic matter between 1% and 3.5% by mass and organic salts between 3% and 6% by mass. In addition, it may also contain up to 2% by mass of sodium carbonate and sodium bicarbonate, and / or a small amount of sodium hydroxide.

[0009] The chemical oxygen demand (COD) of the feed aqueous solution may be between 10 g / L and 120 g / L. Applicants have found that lower COD enhances the degradation of compounds. Preferably, the COD is less than 50 g / L, and more preferably, the COD is less than 30 g / L. If the COD of the initial feed aqueous solution is high, it is preferred to reduce the COD by dilution to obtain the above-mentioned preferred COD level. Dilution can be achieved by adding water, preferably tap water. When degradation occurs in a bioelectrochemical cell, the feed aqueous solution can also be diluted by a circulating flow of the process. The circulation can be part of the treated aqueous solution. The circulating flow can be collected in a buffer tank, which receives the circulating flow and the initial feed aqueous solution at the same time. The COD level in the feed aqueous solution required above can be controlled and achieved by increasing or decreasing the circulating flow.

[0010] The pH value of the feed aqueous solution may be between 5 and 10, preferably between 8 and 10.

[0011] The above-mentioned feed aqueous solution is preferably wastewater from a chemical process, such as described in the patent GB2262052 mentioned above.

[0012] The microbial culture is suitably obtained from anaerobically grown cultures. Suitable mixed cultures include electroactive bacteria (e.g. Geobacter species), phenol degrading bacteria (e.g. Desulfovibrio, Acinetobacter species), fermentative bacteria (e.g. Clostridium and Acetobacter species) and methanogens (e.g. Methanobacter species).

[0013] The microbial culture is preferably obtained from an anaerobic system, such as an anaerobic growth culture. Preferably, the anaerobic growth culture is obtained from an existing bioelectrochemical system using hydrocarbons (e.g., phenolic compounds) as feedstock. The mixed culture can be obtained from sludge from an anaerobic bioreactor, such as an anaerobic fermenter (e.g., a fermenter for anaerobic chain extension), an anaerobic digester (e.g., an upflow anaerobic sludge blanket reactor (UASB)); other suitable bioreactors for providing sludge are expanded granular sludge blanket (EGSB), sequencing batch reactor (SBR), continuous stirred tank reactor (CSTR) or anaerobic membrane bioreactor (AnMBR). In this article, the term "sludge" refers to semi-solid flocs or particles containing a mixed microbial culture.

[0014] It was found that the process can operate satisfactorily when started with a mixed microbial culture obtained only from an anaerobic system. To further enhance the biological activity at the anode, aerobic bacteria can be added to the mixed microbial culture. Such aerobic bacteria can be obtained from activated sludge.

[0015] The degradation process occurs in a bioelectrochemical cell comprising a microbial culture, an anode and a cathode. The microbial culture may suitably be present in the form of a combination of a biofilm and a suspension. The suspended microorganisms may be attached to a suspension carrier. The anode will be located in the anode compartment and the cathode will be located in the cathode compartment. The bioelectrochemical cell may be any bioelectrochemical cell in which the anode and cathode are in contact with the feed aqueous solution. Another preferred feature is that protons can be transported unimpeded between the anode and the cathode. A more preferred feature is that the degradation products formed on the anode can be transported unimpeded from the anode to the cathode.

[0016] Therefore, preferably there is no membrane between the anode and cathode compartments. A bioelectrochemical cell without a membrane has advantages because it simplifies the bioelectrochemical cell and the way it is used. For example, no maintenance for membrane fouling is required. If side reactions need to be avoided, such as oxygen reduction reactions at the cathode under microaerobic conditions, a membrane can be provided. The membrane prevents significant amounts of oxygen from reaching the cathode.

[0017] Due to the different electro / chemical reactions at the anode and cathode electrodes, the microbial communities formed at the anode and cathode will also be different. On the anode, there may be more fermentative and heterotrophic bacteria that are electroactive. On the cathode, there may be the above-mentioned hydrogenotrophic methanogens and bacteria that can use electrons to reduce organic compounds.

[0018] The anode can be made of carbon-based and metal-based conductive materials. Suitable carbon-based conductive materials include carbon fibers, graphite felt, graphite rods or granular activated carbon (GAC). Suitable metal-based conductive materials are titanium, for example in the form of titanium mesh and / or titanium plate.

[0019] The cathode may be made of the same carbon-based conductive material as described above for the anode. Suitable carbon-based conductive materials include carbon fibers, graphite felt, graphite rods, or granular activated carbon (GAC).

[0020] The operating temperature of the process is preferably between 10° C. and 35° C. The process can be carried out under pressure. Preferably, the process is carried out under normal pressure or near normal pressure.

[0021] The battery voltage is preferably between 1.0 V and 5.0 V.

[0022] In the cathode or cathode chamber, the process is preferably operated without or with a small amount of molecular oxygen. In the anode or anode chamber, the presence of oxygen will not be detrimental to the desired conversion process and may even enhance the desired conversion. Therefore, it is possible to choose to supply an oxygen-containing gas (such as air) to the anode chamber to increase the oxygen content at the anode.

[0023] The bioelectrochemical cell can be operated as an intermittent reactor or a semi-intermittent reactor, for example, a gaseous oxygen flow is continuously supplied to the anode chamber, and the methane and other gaseous products generated are continuously discharged from the reactor. In this intermittent operation process, the cell voltage can change over time during the intermittent operation process. The cell voltage of the intermittently operated bioelectrochemical cell can be between 1.0 V and 5.0 V, wherein 1.0 V is the lower limit and 5.0 V is the upper limit. During the intermittent operation process, the cell voltage is appropriately reduced from the initial voltage to a lower voltage. It is preferred to control the cell voltage by measuring the conversion rate and / or the amount of methane generated by any one of the compounds present in the feed aqueous solution, and adjusting the cell voltage according to the measured conversion rate and / or the amount of generation. It is preferred to measure the conversion rate of phenol, methyl phenyl ketone and / or methyl phenyl methanol.

[0024] Preferably, the bioelectrochemical cell is operated continuously. In such a continuously operated process, the feed aqueous solution is preferably fed into the cathode chamber. In the continuously operated process, the process is preferably carried out in two or more continuously operated series bioelectrochemical cells, thereby defining at least one upstream bioelectrochemical cell and one downstream bioelectrochemical cell. Preferably, the cell voltage of each bioelectrochemical cell is different. The cell voltage of the bioelectrochemical cells connected in series is between 1.0 V and 5.0 V, wherein 1.0 V is the lower limit and 5.0 V is the upper limit. The voltage of the upstream cell is higher than the voltage of the downstream cell.

[0025] The process was found to be particularly effective in degrading phenol, methyl phenyl ketone and methyl phenyl carbinol. When the feed aqueous solution also contains other hydrocarbon compounds, the process can be used to convert these compounds as well, thereby reducing the chemical oxygen demand (COD) of the aqueous solution. These other hydrocarbon compounds may be compounds that are known to be effectively treated by conventional water treatment technologies, such as anaerobic water treatment processes. These hydrocarbon compounds may be fatty acids, such as acetic acid, propionic acid and butyric acid. These compounds are referred to as easily degradable COD. The applicant has found that the process can be operated so that phenol, methyl phenyl ketone and methyl phenyl carbinol are selectively degraded, thereby obtaining an aqueous solution intermediate containing these easily degradable COD. The aqueous solution intermediate is preferably further treated by a conventional water treatment process (such as an anaerobic water treatment process) to reduce the COD to the required discharge standard level. In this way, more complex processes in bioelectrochemical cells can be designed and operated to mainly degrade difficult-to-treat compounds, while in the most advanced conventional water treatment processes (such as anaerobic water treatment processes), easily degradable COD is converted.

[0026] The present invention will be described below with reference to the accompanying drawings. Figure 1 A schematic connection (3) of the cathode (1) and anode (2) is shown for applying a cell voltage. At the anode (2), compounds such as phenol, methyl phenyl ketone and / or methyl phenyl carbinol (hereinafter referred to as A) are converted in aqueous solution into carbon dioxide, protons and compounds (B) that are more easily degraded in conventional water treatment processes. This conversion process is carried out in the presence of a mixed microbial culture (4). The protons, carbon dioxide and / or compounds (D) are converted into methane and more reduced compounds (E) at the cathode in the presence of a mixed microbial culture (5). The cathode is located in the cathode chamber (6) and the anode is located in the anode chamber (7). The cathode chamber (6) and the anode chamber (7) are essentially the volumes of aqueous solution surrounding the respective cathode (1) and anode (2). These chambers (6, 7) are fluidically connected and there is no barrier between them. Therefore, the boundaries cannot be clearly distinguished.

[0027] Figure 2 Three bioelectrochemical cells (8a, 8b, 8c) connected in series and operating continuously are shown. Each bioelectrochemical cell (8a, 8b, 8c) is equipped with Figure 1The cathode (1) and anode (2) are shown. An upstream bioelectrochemical cell (8a) and a downstream bioelectrochemical cell (8c) are shown. A feed aqueous solution (9) is supplied to the cathode chamber (6) of the upstream bioelectrochemical cell (8a), wherein one or more hydrocarbon compounds include at least phenol, methyl phenyl ketone and methyl phenyl carbinol. An intermediate aqueous solution (10) is discharged from the anode chamber (7) of the upstream bioelectrochemical cell (8a) and supplied to the cathode chamber (6) of the next bioelectrochemical cell (8b) in the series of bioelectrochemical cells (8a, 8b, 8c). In the bioelectrochemical cell (8b), any unconverted phenol, methyl phenyl ketone and methyl phenyl carbinol are converted at its anode (2) and methane is generated at its cathode (2). A second intermediate aqueous solution (11) is discharged from the anode chamber (7) of the bioelectrochemical cell (8b) and supplied to the cathode chamber (6) of the next bioelectrochemical cell (8c) in the series of bioelectrochemical cells (8a, 8b, 8c). In the bioelectrochemical cell (8c), any unconverted phenol, methyl phenyl ketone and methyl phenyl carbinol are converted at its anode (2) and methane is generated at its cathode (2). This process can be repeated in more bioelectrochemical cells (not shown) until the desired reduction in phenol, methyl phenyl ketone and / or methyl phenyl carbinol is achieved. The treated aqueous solution (13) is discharged from the anode chamber (7) of the downstream bioelectrochemical cell (8c). The generated methane (12) is discharged from each bioelectrochemical cell (8a, 8b, 8c). The cell voltage applied in the bioelectrochemical cell (8a) is higher than the cell voltage in the bioelectrochemical cell (8b). The cell voltage applied in the bioelectrochemical cell (8b) is higher than the cell voltage in the bioelectrochemical cell (8c).

[0028] Figure 3 A possible bioelectrochemical cell is shown in a very simplified form, designed as a barrier-free structure. The cell has no obstacles to flow, such as the absence of a membrane.

[0029] Example 1 A bioelectrochemical cell was inoculated with a mixed microbial culture of anaerobic granular sludge from an anaerobic digestion process in Eerbeek, the Netherlands. The feed aqueous solution, which contained detectable amounts of phenol, methyl phenyl ketone, methyl phenyl carbinol, methanol, 1-propanol, 1,2-propylene glycol, and benzaldehyde, had a chemical oxygen demand (COD) of 109 g / L, a pH of 9.5, and a conductivity of 43.2 mS / cm, and was diluted by adding 1.5 times the volume of the aqueous solution of tap water to obtain a diluted aqueous solution with an initial COD of approximately 40 g / L.

[0030] The diluted aqueous solution was added to a sequencing batch bioelectrochemical cell. A cell voltage was applied between the anode and cathode to transfer electrons from the anode to the cathode. The cell voltage between the anode and cathode was maintained at 3 V. After 20 days of operation, the solution was further diluted by adding tap water equal to the volume of the diluted aqueous solution to the bioelectrochemical cell to obtain a further diluted aqueous solution inside the cell.

[0031] Over time, the pH value stabilizes between 8 and 8.5. The reduction of COD in the aqueous solution in the battery is shown in Figure 4 The marker "BES raw-40%-20%" (indicated by the open squares) in the graph shows that only after dilution on the 20th day, a decrease in COD was observed.

[0032] Example 2 The operation of Example 1 was repeated, except that the initial aqueous solution was diluted by adding tap water equivalent to 4 times the volume of the aqueous solution to obtain a diluted aqueous solution with an initial COD of about 25 g / L.

[0033] A gas rich in carbon dioxide is formed at the anode, and a gas rich in methane is formed at the cathode. The reduction in COD of the aqueous solution in the cell is as follows Figure 4 The analysis after 40 days showed that most of the so-called toxic hydrocarbons had been converted. 85% of phenol was converted, 98% of methyl phenyl ketone was converted, and 82% of methyl phenyl carbinol was converted.

[0034] On day 20, the COD of the aqueous solution in the cell was measured after filtering through a 0.2 µm filter membrane. There was no change in COD compared to the unfiltered sample. This result suggests that the COD measured in the aqueous solution is not derived from biomass or other insoluble matter (particle size > 0.2 µm), but rather that soluble organic compounds are believed to be the main contributor to the COD measured in the aqueous solution.

[0035] Comparative test The operation of Example 2 was repeated, except that no potential was applied between the anode and cathode. The results of the measurement of COD of the aqueous solution in the cell are as follows: Figure 4 After the initial reduction, the COD level remained constant at just above 20 g / L.

[0036] Sequential batch experiments have shown that at high COD levels, degradation of hydrocarbon compounds cannot proceed. The degradation process only begins to occur when the initial COD is reduced by dilution. In a continuously operating bioelectrochemical cell (BES), the COD within the cell, as well as the COD around the anode and cathode, will usually be equal to or close to the COD of the continuously discharged treated aqueous solution. For such a continuously operating bioelectrochemical cell (BES), a high COD aqueous solution can be continuously supplied without worrying that degradation of hydrocarbon compounds cannot proceed. Preferably, an aqueous solution is continuously discharged from each cell of two or more continuously operating bioelectrochemical cells and flows into a downstream cell as an intermediate aqueous solution, or is discharged from the most downstream bioelectrochemical cell as a treated aqueous solution, wherein the oxygen demand (COD) of the intermediate aqueous solution or the treated aqueous solution is less than 30 g / L, more preferably less than 25 g / L.

[0037] Cyclic voltammetry is the most widely used electrochemical technique for obtaining qualitative information about electrochemical reactions. It can quickly analyze the redox potential of electroactive substances in aqueous solutions. During the operation of Example 2, cyclic voltammetry analysis of the anode electrode was performed on the 7th day, the 18th day, and the 39th day. The results are shown in Figure 2. Figure 5 As shown. On the 18th day ( Figure 5 An oxidation peak of 1.5 V was found on day 39 ( Figure 5 An oxidation peak at 0.8 V was found (see “b” in Figure 2). However, no oxidation peak was observed on day 7. In this batch experiment, the cyclic voltammetry results of different running days showed that the required optimal potential gradually decreased during the experiment.

[0038] As a conclusion of cyclic voltammetry, when the present process is carried out in two or more bioelectrochemical cells connected in series in a continuous operation, preferably different cell voltages are applied. Even more preferably, the cell voltage of the upstream cell of the bioelectrochemical cells connected in series in a continuous operation is higher than the cell voltage of the downstream cell.

Claims

1. A process for degrading one or more hydrocarbon compounds in a feed aqueous solution, wherein the one or more hydrocarbon compounds include at least one of phenol, methyl phenyl ketone and methyl phenyl carbinol, in, The degradation process takes place in a bioelectrochemical cell consisting of a microbial culture, an anode and a cathode. Applying a battery voltage between the anode and cathode causes electrons to be transferred from the anode to the cathode. The one or more hydrocarbon compounds are converted at the anode to generate carbon dioxide, protons and optional degradation products, and at the cathode, the carbon dioxide and / or the optional degradation products react with the protons to generate methane, thereby obtaining a treated aqueous solution with a reduced content of the one or more hydrocarbon compounds, and The degradation process is carried out in two or more bioelectrochemical cells connected in series and operated in series, thereby defining at least one upstream bioelectrochemical cell and one downstream bioelectrochemical cell, and the cell voltage applied in each bioelectrochemical cell is different.

2. The process according to claim 1, wherein the microbial culture is a mixed microbial culture obtained from an anaerobic growth culture.

3. The process of claim 2, wherein the anaerobically grown culture is derived from sludge from an anaerobic bioreactor.

4. The process according to claim 3, wherein the anaerobic bioreactor is an upflow anaerobic sludge blanket reactor (UASB).

5. The process according to any one of claims 2 to 4, wherein the anaerobically grown culture is from a municipal wastewater treatment plant.

6. The process according to any one of claims 1 to 5, wherein the anode and cathode are in contact with an aqueous solution and protons and optionally degradation products can be transported unimpeded between the anode and cathode.

7. The process according to any one of claims 1 to 6, wherein the pH value of the feed aqueous solution is between 8 and 10.

8. The process of any one of claims 1-7, wherein the cell voltage is between 1.0 V and 5.0 V.

9. The process according to claim 8, wherein the battery voltage is between 1.0 V and 5.0 V, wherein 1.0 V is a lower limit and 5.0 V is an upper limit, and the battery voltage of the upstream battery is higher than the battery voltage of the downstream battery.

10. The process according to any one of claims 1 to 9, wherein the chemical oxygen demand (COD) of the feed aqueous solution is between 50 g / L and 120 g / L.

11. A process according to any one of claims 1 to 10, wherein an aqueous solution is continuously discharged from each cell of two or more continuously operated bioelectrochemical cells connected in series and flows into a downstream cell as an intermediate aqueous solution, or is discharged from the most downstream bioelectrochemical cell as a treated aqueous solution, and the oxygen demand (COD) of the intermediate aqueous solution or the treated aqueous solution is less than 30 g / L.

12. The process according to any one of claims 1 to 11, wherein when the degradation is carried out in the bioelectrochemical cell, the feed aqueous solution is diluted by a recycle stream of the process.

13. The process according to any one of claims 1 to 12, wherein the aqueous feed solution comprises phenol, methyl phenyl ketone and methyl phenyl carbinol.

14. The process of claim 13, wherein the aqueous feed solution further comprises methanol, 1-propanol, monopropylene glycol and / or benzaldehyde.

15. The process of any one of claims 1 to 14, wherein the treated aqueous solution comprises degradation products and the degradation products are converted to methane in a separate anaerobic water treatment process.

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