PROCESS FOR THE BIOLOGICAL PRODUCTION OF HYDROGEN AND/OR METHANE BY ABSORPTION AND BIOLOGICAL CONVERSION OF CARBON DIOXIDE

Abstract

A process for the biological production of hydrogen and/or methane by absorption and biological conversion of carbon dioxide, includes the steps of being performed by co-culture of one or more hydrogen-producing bacteria in at least one first reactor, and one or more acetogenic bacteria in at least one second reactor, and/or one or more methanogenic microorganisms in at least one third reactor.

Claims

1-14. (canceled)

15. A process for the biological production of hydrogen and/or methane by absorption and biological conversion of carbon dioxide, said process including the following steps: (i) introducing carbon dioxide in at least one first reactor containing up to 95% by volume of a first culture medium comprising one or more hydrogen-producing bacteria and keeping under continuous stirring in anaerobic conditions until a stationary phase of the growth of the one or more hydrogen-producing bacteria is achieved, obtaining a first fermented culture medium and a gaseous mixture of hydrogen and residual carbon dioxide, wherein the one or more hydrogen-producing bacteria are selected from the group consisting of Clostridium beijerinckii, Clostridium butyricum, Clostridium bifermentans, Clostridium sporogenes, Rhodobacter sphaeroides, Rhodobacter capsulatus, Enterobacter cloacae, Thermotoga neapolitana and Hungateiclostridium thermocellum; (ii) optionally separating the hydrogen from the gaseous mixture of hydrogen and residual carbon dioxide obtained in step (i); (iii) introducing the gaseous mixture of hydrogen and residual carbon dioxide obtained in step (i) in at least one of: a) at least one second reactor comprising up to 95% by volume of a second culture medium which comprises one or more acetogenic bacteria and keeping under continuous stirring in anaerobic conditions, obtaining a second fermented culture medium and hydrogen, and b) at least one third reactor comprising up to 95% by volume of a third culture medium comprising one or more methanogenic microorganisms and keeping under continuous stirring in anaerobic conditions, obtaining a third fermented culture medium and a gaseous mixture comprising methane, or introducing the residual carbon dioxide separated from the hydrogen in step (ii) in the at least one second reactor which comprises up to 95% by volume of a second culture medium comprising one or more acetogenic bacteria and keeping under continuous stirring in anaerobic conditions, obtaining a second fermented culture medium; wherein the one or more acetogenic bacteria are selected from the group consisting of Acetoanaerobium noterae, Acetoanaerobium pronyense, Acetoanaerobium sticklandii, Acetobacterium carbinolicum, Moorella thermoacetica, Butyribacterium methylotrophicum, Eubacterium limosum, Moorella thermoautotrophica, Desulfosporosinus orientis, and Blautia producta; and the one or more methanogenic microorganisms are selected from the group consisting of Methanolacinia paynteri, Methanothermobacter wolfeii, Methanothermobacter thermautotrophicus, Methanothermobacter marburgensis, Methanosarcina barkeri, Methanosarcina mazei, Methanobacterium bryantii, Methanothermobacter tenebrarum, and Methanosarcina thermophila.

16. The process according to claim 15, wherein in step (i) the operating temperature and pressure of the at least one first reactor are respectively lower than 40° C. and lower than 250 kPa.

17. The process according to claim 15, wherein in step (iii) the operating temperature and pressure of the at least one second reactor are respectively lower than 39° C. and lower than 250 kPa.

18. The process according to claim 15, wherein in step (iii) the operating temperature and pressure of the at least one third reactor are respectively lower than 75° C. and lower than 500 kPa.

19. The process according to claim 15, wherein after reaching the stationary growth phase of the one or more hydrogen-producing bacteria step (i) includes the following steps: (i.a) drawing the gaseous mixture of hydrogen and residual carbon dioxide from the head space of the at least one first reactor; (i.b) unloading from the at least one first reactor a volume of the first fermented culture medium until a concentration of the one or more hydrogen-producing bacteria in the first fermented culture medium of no less than 2 g/l is reached; (i.c) loading inside the at least one first reactor a quantity by volume of the first culture medium that is equal to the volume of the first fermented culture medium unloaded in step (i.b); and (i.d) restarting the growth of the one or more hydrogen-producing bacteria until the stationary growth phase of the one or more hydrogen-producing bacteria is reached and repeating steps (i.a) to (i.c).

20. The process according to claim 19, further comprising the step of (i.b′) separating the first fermented culture medium unloaded in step (i.b) into a liquid component and a solid component.

21. The process according to claim 15, wherein the gaseous mixture of hydrogen and residual carbon dioxide obtained in step (i) is drawn from the first reactor and stored in one or more accumulation tanks.

22. The process according to claim 15, wherein in step (iii) the gaseous mixture of hydrogen and residual carbon dioxide obtained in step (i) is introduced in at least one between the at least one second reactor and the at least one third reactor.

23. The process according to claim 15, including the step of (ii) separating the hydrogen from the gaseous mixture of hydrogen and residual carbon dioxide obtained in step (i), wherein in step (iii) the residual carbon dioxide separated from the hydrogen in step (ii) is introduced in the at least one second reactor.

24. The process according to claim 15, wherein in step (iii) the introduction of the gaseous mixture of hydrogen and residual carbon dioxide in at least one between the at least one second reactor and the at least one third reactor occurs, preferably continuously, by injecting the gaseous mixture into the second culture medium and/or into the third culture medium.

25. The process according to claim 15, further including the step of: (iv) introducing the gaseous mixture comprising methane obtained in step (iii) in at least one additional second reactor which comprises up to 95% by volume of a culture medium which comprises one or more acetogenic bacteria and keeping under continuous stirring in anaerobic conditions, obtaining a fermented culture medium and methane, wherein the one or more acetogenic bacteria are selected from the group consisting of the acetogenic bacteria.

26. The process according to claim 25, wherein in step (iv) the operating pressure and temperature of the at least one additional second reactor are respectively lower than 39° C. and lower than 250 kPa.

27. The process according to claim 15, further including the step of separating the second fermented culture medium and/or the third fermented culture medium into a liquid component and a solid component.

28. The process according to claim 15, further including the step of introducing in the at least one second reactor and/or in the at least one third reactor carbon dioxide that originates from sources which are external with respect to the one that originates from step (i).

Description

DETAILED DESCRIPTION OF THE DISCLOSURE

[0031] Further characteristics and advantages of the disclosure will become better apparent from the following detailed description.

[0032] The process according to the disclosure seeks to contribute to the reduction of the concentration of carbon dioxide in the atmosphere, while producing hydrogen and/or methane, i.e., important energy resources, by means of a co-culture of specific bacteria and microorganisms that allows to achieve high levels of production efficiency.

[0033] For the production of hydrogen, the process according to the disclosure uses one or more of the following hydrogen-producing bacteria, preferably, but not exclusively the strains identified in brackets by respective deposit numbers:

[0034] Clostridium beijerinckii (ATCC No. 25752 and ATCC No. 17778), Clostridium butyricum (ATCC No. 860 and ATCC No. 19398), Clostridium bifermentans (ATCC No. 19299, NCTC No. 1340 and NCTC No. 8780), Clostridium sporogenes (ATCC No. 3584 and ATCC No. 19494), Rhodobacter sphaeroides (ATCC No. 17023), Rhodobacter capsulatus (ATCC No. 11166), Enterobacter cloacae (IIT-BT No. 08), Thermotoga neapolitana (ATCC No. 49049) and Hungateiclostridium thermocellum (ATCC No. 27405).

[0035] For the absorption of carbon dioxide, the process according to the disclosure uses instead one or more of the following acetogenic bacteria, preferably, but not exclusively, the strains identified in brackets by respective deposit numbers:

[0036] Acetoanaerobium noterae (ATCC No. 35199), Acetoanaerobium pronyense (DSM No. 27512), Acetoanaerobium sticklandii (DSM No. 519), Acetobacterium carbinolicum (DSM No. 2925), Moorella thermoacetica (ATCC No. 39073, ATCC No. 49707 and ATCC No. 35608), Butyribacterium methylotrophicum (DSM No. 3468 and ATCC No. 33266), Eubacterium limosum (ATCC No. 8486), Moorella thermoautotrophica (ATCC No. 33924), Desulfosporosinus orientis (DSM No. 765) and Blautia producta (ATCC No. 27340).

[0037] Said acetogenic bacteria culture can also be used for the absorption of carbon dioxide present in gaseous mixtures that originate from other industrial processes.

[0038] For the production of methane, the process according to the disclosure uses one or more of the following methanogenic microorganisms, preferably, but not exclusively, the strains identified in brackets by the respective deposit numbers:

[0039] Methanolacinia paynteri (DSM No. 2545), Methanothermobacter wolfeii (ATCC No. 43096), Methanothermobacter thermautotrophicus (DSM No. 3720 and ATCC No. 29096), Methanothermobacter marburgensis (DSM No. 2133), Methanosarcina barkeri (ATCC No. 43569), Methanosarcina mazei (ATCC No. 43573), Methanobacterium bryantii (ATCC No. 33272), Methanothermobacter tenebrarum (DSM No. 23052) and Methanosarcina thermophila (DSM No. 2980).

[0040] In each of the reactors used in the process of the present disclosure, a quantity up to 95% of the total volume of each reactor of culture medium is added with the nutritional components required for the one or more bacteria and microorganisms belonging to the groups described above.

[0041] The nutritional components suitable for the above cited bacteria and microorganisms are those known to the person skilled in the art; for example the hydrogen producing bacteria can be grown in: Reinforced clostridial medium (RCM), Rhodospirillaceae medium available on the German Collection of Microorganisms and Cells (DSMZ)—catalogue number DSMZ 27, Nutrient agar available on the German Collection of Microorganisms and Cells (DSMZ)—catalogue number DSMZ 1; acetogenic bacteria can be grown in: Nutrient agar available on the German Collection of Microorganisms and Cells (DSMZ)—catalogue number DSMZ 1, Thermotoga TF(C) medium—available on the German Collection of Microorganisms and Cells (DSMZ)—catalogue number DSMZ 613, Clostridium noterae medium available on the America Type Culture Collection (ATCC)—catalogue number ATCC 1344, Moorella medium available on the German Collection of Microorganisms and Cells (DSMZ)—catalogue number DSMZ 60, Modified chopped meat medium available on the America Type Culture Collection (ATCC)—catalogue number ATCC 1490, Desulfovibrio (Postgate) medium available on the German Collection of Microorganisms and Cells (DSMZ)—catalogue number DSMZ 63; methanogenic microorganisms can be grown in: Modified chopped meat medium available on the America Type Culture Collection (ATCC)—catalogue number ATCC 1490, Methanosarcina barkeri medium available on the German Collection of Microorganisms and Cells (DSMZ)—catalogue number DSMZ 120a., Methanogenium medium available on the German Collection of Microorganisms and Cells (DSMZ)—catalogue number DSMZ 141.

[0042] In each reactor, the fermentation continues by appropriately controlling temperature, the pH, and the supply of nutrients and microelements, as known to the person skilled in the art.

[0043] Step (i) of the process starts with the introduction of carbon dioxide in the head space of the at least one first reactor.

[0044] In the process according to the present disclosure, in fact, carbon dioxide (CO.sub.2) is used as raw material. Therefore, gaseous emissions that are rich in carbon dioxide but also include other gaseous components must undergo pretreatment before being dispatched to absorption and/or biological conversion according to the process described herein. The pretreatment, necessary to separate the carbon dioxide from any other gaseous components and to purify it from the presence of any pollutants, can be performed by using various known technologies for capturing CO.sub.2 such as, by way of non-limiting example, membrane separation, so-called pressure swing adsorption, and washing with amines.

[0045] Preferably, in step (i) the operating temperature and pressure of the at least one first reactor are respectively lower than 40° C. and lower than 250 kPa (2.5 bar).

[0046] Optionally, the process according to the disclosure can comprise the step ii) of separating the hydrogen from the gaseous mixture of hydrogen and residual carbon dioxide obtained in step (i) by using known technologies suitable for this purpose.

[0047] Step (iii) of the process starts with the introduction of the gaseous mixture of hydrogen and residual carbon dioxide obtained in step (i) in the at least one second reactor and/or in the at least one third reactor.

[0048] Preferably, in step (iii) the operating temperature and pressure of the at least one second reactor are respectively lower than 39° C. and lower than 250 kPa (2.5 bar).

[0049] Preferably, in step (iii) the operating temperature and pressure of the at least one third reactor are respectively lower than 75° C. and lower than 500 kPa (5.0 bar).

[0050] In a preferred embodiment of the process according to the disclosure, after reaching the stationary growth phase of the one or more hydrogen-producing bacteria, step (i) comprises the additional steps of: [0051] (i.a) drawing the gaseous mixture of hydrogen and residual carbon dioxide from the head space of the at least one first reactor; [0052] (i.b) unloading from the at least one first reactor a volume of the first fermented culture medium until a concentration of the one or more hydrogen-producing bacteria in the first fermented culture medium of no less than 2 g/l is reached; [0053] (i.c) loading inside the at least one first reactor a quantity by volume of the first culture medium that is equal to the volume of the first fermented culture medium unloaded in step (i.b); [0054] (i.d) restarting the growth of the one or more hydrogen-producing bacteria until the stationary growth phase of the one or more hydrogen-producing bacteria is reached and repeating steps (i.a) to (i.c).

[0055] Within the scope of this embodiment, the process of the disclosure preferably further comprises the step (i.b′) of separating the first fermented culture medium unloaded in step (i.b) into a liquid component and a solid component.

[0056] Separation of the liquid component from the solid component is performed by unloading the fermented culture medium into an adapted separation device, such as for example a decanter centrifuge. Said fermented culture medium may be used for the extraction of organic acids to be used in the food, agricultural and/or pharmaceutical sector. The solid component is constituted by bacteria which can be used in the food, agricultural and/or pharmaceutical sector or as nutrients for subsequent fermentations. From the liquid component it is instead possible to recover water to be reused for the preparation of culture media.

[0057] Optionally, the gaseous mixture of hydrogen and residual carbon dioxide obtained in step (i) is drawn from the first reactor and stored in one or more accumulation tanks.

[0058] In one embodiment of the process according to the disclosure, in step (iii) the gaseous mixture of hydrogen and residual carbon dioxide obtained in step (i) is introduced in at least one between the at least one second reactor and the at least one third reactor.

[0059] Preferably, in step (iii) the introduction of the gaseous mixture of hydrogen and residual carbon dioxide in at least one between the at least one second reactor and the at least one third reactor occurs, preferably continuously, by injecting the gaseous mixture into the second culture medium and/or into the third culture medium.

[0060] In another embodiment, the process according to the disclosure comprises the step of (ii) separating the hydrogen from the gaseous mixture of hydrogen and residual carbon dioxide obtained in step (i), wherein in step (iii) the residual carbon dioxide separated from the hydrogen in step (ii) is introduced in the at least one second reactor. Preferably, the hydrogen separated from the residual carbon dioxide in step (ii) is introduced in one or more accumulation tanks.

[0061] Unlike what occurs for the at least one first reactor of step (i), the unloading of the fermented medium from the at least one second and/or at least one third reactor of step (iii) is not correlated with the growth cycles of the bacteria and microorganisms, but rather with the need to keep constant the volume of culture medium within the at least one reactor used in step (iii).

[0062] The fermented culture medium of the at least one second reactor of step (iii) may be unloaded into a suitable device for separating the liquid component from the solid component, such as for example a decanter centrifuge. Said fermented culture medium may be used for the extraction of organic acids and/or minerals to be used in industry and/or in the food and/or pharmaceutical sector. From the liquid component it is instead possible to recover water to be reused for the preparation of culture media.

[0063] The solid component is constituted by bacteria that can be used in the agricultural sector or as nutrients for subsequent fermentations.

[0064] In the process according to the present disclosure, the production of methane (“methanization”) occurs by the action of methanogenic microorganisms, which use CO.sub.2 and produce methane according to the following reaction:

4H.sub.2+CO.sub.2--->CH.sub.4+2H.sub.2O; i.e.,

4H.sub.2+HCO.sup.−+H.sup.+--->CH.sub.4+3H.sub.2O

[0065] Methanogenic microorganisms are able to perform this reaction by coupling the oxidation of molecular hydrogen (H.sub.2) with the reduction of CO.sub.2 (final electron acceptor) with reoxidation of NAD by virtue of the continuous removal of said H.sub.2. The absorption of CO.sub.2 by methanogenic microorganisms in the at least one third reactor is limited to use in the methanogenesis reaction according to the above cited reaction. In the process of methanogenesis according to the disclosure, the hydrogen needed by the methanogenic microorganisms is produced in the at least one first reactor and the gaseous mixture of hydrogen and carbon dioxide obtained in step (i) is conveyed into the at least one third reactor directly, or after a step of storage in accumulation tanks.

[0066] The gaseous mixture, which comprises methane produced at the end of the methanization step, is in turn drawn from the head space of the at least one third reactor, optionally in a continuous mode, and further purified or stored in one or more accumulation tanks.

[0067] The process according to the disclosure, therefore, allows to obtain hydrogen and/or methane depending on whether in step iii) the gaseous mixture obtained in step i) is introduced only in the at least one second reactor which comprises acetogenic bacteria, only in the at least one third reactor which comprises methanogenic microorganisms, or in both.

[0068] When the mixture of hydrogen and residual carbon dioxide is introduced, by injection into the culture medium directly or after storage, a gaseous mixture comprising methane is produced in the at least one third reactor assigned to methanization.

[0069] The fermented culture medium of the at least one third reactor of step (iii) may be unloaded into a suitable device for separating the liquid component from the solid component, such as for example a decanter centrifuge. The solid component is constituted by microorganisms to be used in the agricultural sector or as nutrients for subsequent fermentations. From the liquid component it is instead possible to recover water to be reused for the preparation of the culture media.

[0070] The process according to the disclosure allows furthermore to purify the methane from the gaseous mixture obtained from the at least one reactor assigned to methanization.

[0071] In a preferred embodiment, the process according to the disclosure further comprises the step of:

[0072] (iv) introducing the gaseous mixture comprising methane obtained in step (iii) in at least one additional second reactor which comprises up to 95% by volume of a culture medium which comprises one or more acetogenic bacteria and keeping under continuous stirring in anaerobic conditions, obtaining a fermented culture medium and methane, wherein the one or more acetogenic bacteria are selected from the group consisting of the acetogenic bacteria described above.

[0073] Preferably, in said step (iv) the operating temperature and pressure of the at least one additional second reactor are respectively lower than 39° C. and lower than 250 kPa (2.5 bar).

[0074] In one embodiment, the process according to the disclosure further comprises the step of introducing in the at least one second reactor and/or in the at least one third reactor carbon dioxide that originates from sources which are external with respect to the one that originates from step (i), preferably in continuous mode by injecting the carbon dioxide into the culture media.

[0075] Advantageously, the process according to the disclosure, unlike other processes such as for example the symbiotic process described in EP2016/077771, does not limit the introduction of carbon dioxide into the process to only the quantities necessary for conversion into methane, but also allows its absorption, increasing the potential of the process according to the disclosure to contribute to the reduction of the concentration of carbon dioxide in the atmosphere.

[0076] The carbon dioxide, in fact, is introduced in a virtuous process of circular economy which allows to transform a problem of global importance into resources, i.e., hydrogen and methane of biological origin, produced with the utmost respect for environmental sustainability and with reduced energy consumption.

[0077] The disclosures in Italian Patent Application No. 102020000013006 from which this application claims priority are incorporated herein by reference.