A process for preparing a product from a carbon-containing gas stream by microorganisms provided on a plurality of trays

Abstract

The present invention provides a process and apparatus for producing an alcohol product stream from a gas fermentation process. A feed gas stream comprising hydrogen and a carbon oxide is subjected to fermentation to convert at least a portion of the feed gas stream to an alcohol. Fermentation is conducted in a reactor having a plurality of trays.

Description

PROCESS FOR PREPARING A PRODUCTFIELD OF THE INVENTION

[0001] The present invention relates to a process for producing a product, in particular an alcohol. More in particular, the present invention relates to a process for producing a product using gas fermentation in a reactor.BACKGROUND OF THE INVENTION

[0002] Processes for producing a product using a gas fermentation are known in the art.

[0003] As one example, WO2018 / 175481A1 discloses the use of a vacuum distillation vessel to recover products from a fermentation broth. A problem of the use of a vacuum distillation vessel to recover products directly from a fermentation broth is that the viability of the microorganisms present in the fermentation broth may be negatively impacted. Also, as acknowledged in paragraph

[0027] of WO2018 / 175481A1, the use of a vacuum distillation vessel may cause the production of foam which results in a decrease in performance.

[0004] As a further example, US2023 / 0105160A1 discloses an integrated process using gas fermentation to convert CO2 into a product, where low conversion reverse water gas shift is employed to convert CO2 into CO before passing to a gas fermentation bioreactor. As mentioned in paragraph

[0029] , . . target products are recovered from the fermentation broth by continuously removing a portion of the broth from the bioreactor, separating microbial cells from the broth (conveniently by filtration), and recovering one or more target products from the broth”, .. . and “Desired products are removed from gas fermentation process 155 in gas fermentation product stream 158.”.

[0005] In this respect it is noted that paragraph

[0030] of US2023 / 0105160A1 mentions that a 'bioreactor off gas stream’ is produced which contains 'unreacted Ci gases and inert gases.’

[0006] A problem of the know n process according to US2023 / 0105160A1 is that the removal of the actual desired product from the liquid fermentation broth by, for example, filtration may be cumbersome as the microorganisms present in the fermentation broth may block or clog the filters. Other known issues of the removal of the desired product from the liquid fermentation broth are foaming of the broth, operation costs and extra maintenance.

[0007] It is an object of the present invention to solve, minimize or at least reduce one or more of the above problems.

[0008] There is a need to provide an alternative process for producing a product using a gas fermentation process, wherein the product is obtained from the fermenter without the need for filtration or distillation of the fermentation broth.SUMMARY OF THE INVENTION

[0009] According to one aspect of the present invention, there is provided for producing a product, in particular one or more C2+ components, the process at least comprising the steps of: (a) providing a carbon-containing gas stream; (b) subjecting the carbon-containing gas stream provided in step (a) to fermentation in a reactor thereby obtaining at least a first gaseous product stream, wherein the reactor contains a plurality of trays and wherein at least some of the trays are provided with at least one microorganism, preferably for converting Cl components into C2+ components; (c) removing the first gaseous product stream obtained in step (b) from the reactor; (d) optionally cooling the first gaseous product stream removed in step (c) thereby obtaining a gas / liquid product mixture; e) optionally separating the gas / liquid mixture obtained in step (d) in a gas / liquid separator thereby obtaining a second gas product stream and an C2+-enriched liquid stream; and (f) optionally recycling the second gas product stream obtained in step (e) to the reactor.

[0010] According to another aspect of the present invention, there is provided an apparatus suitable for performing the process for producing a product according to any one of the preceding claims 1 -11 , the apparatus at least comprising: a reactor for performing a fermentation reaction, the reactor having at least an inlet for a carbon-containing stream and an outlet for a first gaseous product stream, wherein the reactor contains a plurality of trays and wherein at least some of the trays are provided with at least one microorganism, preferably for converting Cl components into C2+ components; an optional compressor for compressing the first gaseous product stream; an optional heat exchanger for cooling the first gaseous product stream to obtain a gas / liquid product mixture: an optional gas / liquid separator for separating the gas / liquid mixture to obtain a second gas product stream and an C2+-enriched liquid stream; an optional recycle line for recycling the second gas product stream to the reactor.BRIEF DESCRPTION OF THE DRAWINGS

[0011] The process of the present invention will be better understood by referring to the following detailed description of preferred embodiments and the drawings referenced therein, in which:

[0012] Figs. 1 - 4 schematically illustrate embodiments of the present invention;

[0013] Figs. 5 A and 5B schematically illustrate embodiments of tray sections of the embodiments of Figs. 1 - 4; and

[0014] Figs. 6A and 6B schematically illustrate embodiments of tray sections with electrodes.

[0015] For the purpose of this description, same reference numbers refer to same or similar components.DETAILED DESCRIPTION

[0016] The present invention provides a process for producing an alcohol product stream from gas fermentation of a feed gas stream. In particular, the process of the present invention provides a process for more efficiently recovering an alcohol product stream from a gas fermentation. It has surprisingly been found according to the present invention that a target product, specifically an alcohol product, can be obtained in a gas fermentation process w ithout the need of filtration or distillation of the fermentation broth. According to the present invention, a major portion of the target alcohol product is obtained from the reactor in a gas stream produced in the fermentation process, rather than from a liquid stream also containing the fermentation broth. Hence, no complicated liquid / liquid separation of the fermentation broth and target alcohol product is required.

[0017] Furthermore, avoiding vacuum distillation (such as used in. for example, WO2018 / 175481 Al) avoids significant temperature changes in the reactor that would be detrimental to the activity (or viability) of the at least one or more microorganisms on trays of the reactor.

[0018] A further advantage of the process according to the present invention, is that lower product losses in the gas stream (which is usually seen as an ‘off-gas stream’) produced in the fermentation process are achieved. Also, less processing steps and less energy for downstream processing of a liquid stream are required. Furthermore, excess w ater produced in the conversion of feed gas to alcohol product may be removed with the gas stream and then distilled and recycled as needed thereby controlling the water balance in the reactor to reduce the overall water footprint of process.

[0019] A particular advantage of the present invention is that the use of the plurality of trays provides for a larger surface and hence a better dissolution of components such as CO2, CO and H2, without the need for mechanical mixing (which would be detrimental to the microorganisms). Also, the use of the plurality of trays provides for an improved vaporization of the first gaseous product stream (and of potential further gaseous product streams, if any, removed at different levels of the reactor).

[0020] Referring to Fig. 1 illustrating one embodiment of the present invention 1, a carbon-containing gas stream, namely a feed gas stream 10 comprising a carbon oxide and hydrogen, is provided. Carbon oxides include carbon monoxide (CO) and carbon dioxide (CO2). The feed gas stream 10 may be provided as a pressured stream and / or compressed in an optional compressor (not shown) to bring the feed gas stream 10 to a desired pressure. Similarly, the feed gas stream 10 may be cooled or heated to bring it to a desired temperature.

[0021] The feed gas stream 10 may be provided at a pressure, for example, in a range of from 0 - 10 MPaG. An advantage of an elevated pressure is to enhance transfer of carbon oxides and hydrogen to the fermentation broth.

[0022] The feed gas stream 10 comprises carbon oxide and hydrogen. The feed gas stream 10 may have various origins, such as electrolysis, fermentation, water gas shift reaction, natural gas or biogas reforming, etc. Preferably, the feed gas stream 10 contains H2 and at least one of CO and CO2. The feed gas stream 10 may be provided as a mixture of carbon oxide and hydrogen. Alternatively, the feed gas stream 10 may be provided as a separate stream for each component and / or as a supplement of one component. The feed gas stream 10 may further comprise a mixture or separate stream of an inert gas. such as nitrogen. Though not depicted in the drawings for simplicity, it will be understood that the same or different feed gas stream 10 may be introduced through two or more injectors to the reactor 2.

[0023] When CO is present, the feed gas stream 10 preferably comprises 5-40 mol.% CO, more preferably 10-35 mol.% CO. It is further preferred to avoid CO concentrations that would result in a partial pressure of CO exceeding 150 kPa, in order to reduce the risk of CO toxicity to the microorganisms.

[0024] When CO2 is present, the feed gas stream 10 preferably comprises 5-45 mol.% CO2, more preferably 10-30 mol.% CO2.

[0025] The feed gas stream 10 also comprises 10-90 mol.% H2, preferably 10-60 mol.% H2, more preferably 10-40 mol.% H2.

[0026] Preferably, the feed gas stream 10 has a H2 to carbon oxide molar ratio in a range of from 2: 1 to 9: 1, more preferably less than or equal to 6: 1.

[0027] Preferably, the feed gas stream 10 is a syngas-containing stream, i.e. a gas stream comprising at least H2 and CO. Preferably, the syngas -containing stream comprises at least 50 mol.% H2 and CO, more preferably at least 70 mol.% H2 and CO, more preferably at least 80 mol.% H2 and CO combined.

[0028] The feed gas stream 10 is subjected to fermentation in a reactor 2, wherein at least a portion of the feed gas stream 10 is converted to an alcohol by microbial activity. The fermentation broth is provided in a liquid phase fermentation broth. During the conversion of hydrogen and carbon oxide to alcohol, additional water is formed as a byproduct.

[0029] The reactor 2 is provided with a fermentation broth comprising the one or more microorganisms. The fermentation broth may further comprise additional components, such as nutrients (such as Mg2+, Ca2+, NH4+, NOs', CH4N2O, PC>42', SO42', Cl"), trace metals (such as Fe2+, Zn2+, Mn2+, Co2+, Cu2+, MoC>42’, Ni2+) and pH-controlling agents (such as NaOH, KOH, NH4OH. H2SO4, H3PO4, CO2. citric acid, acetic acid, formic acid). One or more of these components may be added continuously or intermittently to the reactor 2, for example, by combining with recycle stream 70.

[0030] Suitable fermentation conditions and microorganisms have for example been mentioned in US2023 / 0105160A1.

[0031] The microorganisms are preferably anaerobic. Examples of suitable microorganisms include, without limitation, microorganisms from the classes Clostridium, Escherichia co / i. Moorella, methylococcus , Acetobacterium, Methylosinus , Ruminococcus , Carboxydothermus, Eubacterium, Butylbacterium, Oxobacter, etc. Preferably, a microorganism from the class Clostridium is used.

[0032] The reactor 2 is provided with a plurality of trays 2A, which are configured to enhance contact between a rising gas stream and a descending fermentation broth wi th suspended microorganisms. The trays 2A may include, for example, perforated plates, bubble cap trays, or valve trays. This configuration promotes efficient gas-liquid mass transfer and microbial access to gaseous substrates.

[0033] Figs. 5A and 5B, illustrating examples of a bubble cap tray and a perforated tray respectively, show a portion A of the reactor 2 of Figs. 1 - 4. The feed gas stream 10 enters the tray 2A from below via gas passages 2B. The gas flow is illustrated by the upward arrows in Figs. 5 A and 5B.

[0034] The fermentation broth flows downwardly through liquid passages 2C and horizontally across the tray 2A, as depicted by the downward arrows in Figs. 5A and 5B. Horizontal flow is guided by weirs, which help maintain a desired liquid level on the tray. As the broth flows, it contacts the rising vapor through the gas passages, facilitating gasliquid mass transfer. After traversing the tray, the liquid collects at the outlet weir and flows into the outlet downcomer, which directs it to the tray below. These configurations ensure uniform gas distribution and effective mixing with the fermentation broth. Consequently, the gas follows a defined path through the tray 2A, enabling efficient mass transfer between the gas and liquid phases.

[0035] Preferably, the fermentation is performed at a temperature of from 5 to 70°C, preferably from 20 to 48°C, depending on the selected microorganism. Microorganisms do not typically survive at temperatures above 48°C, unless they are thermophilic such as Clostridium clariflavum.

[0036] According to a preferred embodiment of the process according to the present invention, the fermentation at the (one or more) highest tray(s) is performed at a temperature of from 5 to 70°C, preferably from 20 to 48°C, more preferably between 35 and 45°C.

[0037] Furthermore, it is preferred that a temperature gradient is maintained across the reactor 2, wherein the temperature at the highest tray 2A of the reactor 2 is at least 5°C warmer than the temperature near a bottom outlet of the reactor 2, preferably at least 10°C, more preferably at least 15 °C.

[0038] The gas pressure to be used in the reactor 2 is not particularly limited and change over the height and / or width of the reactor 2. Preferably, the reactor 2 operates at a maximum gas pressure of 7.5 bara (0.75 MPa (abs)) at the gas inlet (21, 25). Furthermore, it is preferred that the gas pressure at the gas outlet 22 of the reactor 2 is in a range of 0.5- 6.0 bara (0.05 - 0.6 MPa (abs)), more preferably 0.9-1.5 bara (0.09 - 0.15 MPa (abs)).

[0039] According to a preferred embodiment of the present invention, at least some of the trays 2A comprise an electrochemical system, preferably a bio-electrochemical system(BES), more preferably a BES that can in situ convert CO2 into CO and / or generate H2 and / or produce alcohol.

[0040] Figs. 6A and 6B illustrate embodiments where electrodes 2D are integrated into the tray 2A. The electrode 2D may function as a cathode, with an anode integrated into the tray 2A. or vice versa. Alternatively, the electrode 2D may comprise a cathode-anode pair separated by an insulating material or a membrane. The cathode and anode are positioned within the tray 2A such that they are in contact with the liquid traversing the tray 2A. The electrodes are electrically connected to provide a cell potential. (Bio-)electrochemical systems of this type have been described, for example, E. Perona-Vico et al. (‘'Bacteria coated cathodes as an in-situ hydrogen evolving platform for microbial electrosynthesis”. Scientific Reports 10, Article number: 19852 (2020)) and V. Sivalingam et al.(“Integrating syngas fermentation into a single-cell microbial electrosynthesis (MES) reactor”. Catalysts 2021, 11(1), 40).

[0041] An advantage of providing a BES in the tray 2A is that it enables in situ conversion of CO2 into CO and / or in situ generation of H2 within the fermentation broth. This provides readily accessible reducing equivalents for selected microorganisms without relying on gas-liquid mass transfer, thereby accelerating the overall formation of desired fermentation products. Additional advantages may include enhanced redox control within the fermentation environment, improved selectivity towards target products, and the potential to suppress unwanted metabolic pathways or by-product formation.

[0042] In accordance with the present invention, the feed gas 10 and optional recycle gas 50 are injected at higher rate than conventional gas fermentation injection rates with an objective of entraining the produced alcohol to carry it to the gas outlet 22 of the reactor 2. In one embodiment, the feed gas 10 may also include nitrogen to increase the gas volume while not affecting the pH of the fermentation broth. The actual gas injection rate may vary depending on the size and configuration of reactor 2.

[0043] In accordance with the present invention, a major portion of the produced alcohol, preferably C2-C4 alcohols, more preferably C2-C3 alcohols, is carried to the gas outlet 22 of the reactor 2. Preferably, at least 50% of the produced alcohol is carried to the gas outlet 22, more preferably 80%, most preferably 100% of the produced alcohol is carried to the gas outlet 22. This contrasts with conventional gas fermentation processes, where the majority of produced alcohol is recovered from the liquid phase of the fermentation broth. The gaseous product stream 20 comprises the produced alcohol,unconverted carbon oxide(s), unconverted H2, and water vapour. Additionally, the gaseous product stream 20 may contain C2+ aldehydes, alkenes, and / or ketones. If nitrogen is added to the feed gas stream 10, it will also be present in the gaseous product stream 20.

[0044] Preferably, the gaseous product stream 20 removed from the reactor 2 comprises at least 0.50 mol.% C2+ (i.e. compounds containing 2 or more carbon atoms, such as ethanol, ethanal, acetone, acetaldehyde, 1 -propanol, 2-propanol, propanal, etc.). More preferably, the gaseous product stream 20 comprises at least 0.9 mol.% C2+. While there is no strict upper limit for the C2+ content, as high yield as possible is desirable, the gaseous product stream 20 preferably comprises up to 8 mol.% C2+. more preferably up to 10 mol.% C2+.

[0045] In this respect it is noted that paragraph

[0030] of US2023 / 0105160A1 mentions that a bioreactor offgas stream is produced which contains unreacted Cl gases and inert gases. This bioreactor off gas stream is, after compression, passed back to the gas fermentation process. No mention is made in US2023 / 0105160A1 that this bioreactor off gas stream is cooled or contains any C2+. Also, no mention is made in US2023 / 0105160A1 of a separation device to separate liquids from the bioreactor off gas stream.

[0046] Further it is preferred that the gaseous product stream 20 removed from the reactor 2 has a partial pressure of C2+ components in the range of from 9 mbar (900 Pa) to 0.2 bar (20 kPa). Also, the gaseous product stream 20 will be saturated with water vapor, which is formed as a by-product during the conversion of feed gas 10 into alcohol products.

[0047] The gaseous product stream 20 is removed via an outlet 22 located at or near the top of the reactor 2.

[0048] The removed gaseous product stream 20 has a temperature in a range of from 5 to 70°C, preferably greater than or equal to 20°C, more preferably greater than or equal to 30°C, even more preferably greater than or equal to 35°C, and preferably less than or equal to 48°C, more preferably less than or equal to 45°C. The gaseous product stream has a pressure in a range of from 0.5 to 10.0 bara (50 kPa to 1 MPa (abs)), preferably from 1.5 to 7.0 bara (150 to 700 kPa).

[0049] The gaseous product stream 20 is then optionally cooled in heat exchanger 3 to form a gas / liquid product mixture 40. Although the temperature of the gas / liquid product mixture 40 is not particularly limited, it is preferably in the range of from 0 to 40°C, morepreferably from 5 to 25°C. Cooling facilitates condensation of volatile components such as alcohols and water vapor, thereby enabling efficient downstream separation and recovery' of the desired products.

[0050] In one embodiment, as illustrated in Fig. 3, the gaseous product stream 20 is compressed in compressor 9 prior to cooling, for example, to a pressure in the range of from 1.5 to 11.0 bara (150 kPa to 1.1 MPa (abs)). In another embodiment, as illustrated in Fig. 3, the recycle gas stream 50 is compressed in compressor 7 before being mixed with feed gas stream 10. Alternatively, depending on the desired inlet pressure, the pressure of feed gas stream 10, and the pressure of the recycle gas stream 50, compressor 7 may be omitted or positioned dow nstream of the mixing point of gas stream 10 and the recycle gas stream 50.

[0051] When cooling the gaseous product stream 20, w ater produced in the conversion of the feed gas 10 to alcohol is also actively condensed and separated. The w ater balance in reactor 2 can be controlled based on the amount of water that recycled from a downstream distillation section, thereby reducing the overall water footprint of process.

[0052] In an optional, but preferred, embodiment of the process according to the present invention, the gas / liquid product mixture 40 is separated in a gas / liquid separator 4 to obtain a second gas product stream 50 and an alcohol-enriched liquid stream 60. The second gas product stream 50 is depleted in C2+ components.

[0053] Preferably, the separation in the gas / liquid separator 4 is performed at a pressure greater than or equal to 150 mbara (15 kPa(abs)), more preferably greater than or equal to 0.9 mbara (90 Pa (abs)). The pressure is preferably less than or equal to 10 bara (1 MPa (abs)).

[0054] The alcohol-enriched liquid stream 60 may be further processed (such as by distillation, rectification, dehydration, extraction, membranes and adsorption processes) to remove undesired components, increase the concentration of the desired target components, and / or further convert into the desired end product. The composition of the alcohol-enriched liquid stream 60 depends on the composition of the feed gas stream 10, the microorganisms, and the operating conditions in the reactor 2.

[0055] In an optional, but preferred, embodiment of the present invention, the second gas product stream 50 is recycled to the reactor 2. The recycled gas 50 may be injected separately into reactor 2 (as shown in Fig. 2) or combined with the feed gas stream 10 prior to injection (as shown in Fig. 3). In the embodiment of Fig. 2, the second gas productstream 50 is compressed in compressor 5. cooled in second heat exchanger 8 and fed into the reactor 2 as stream 90 via inlet 25.

[0056] According to a preferred embodiment of the process according to the present invention, the process further comprises the step of removing a liquid stream 30 from reactor 2 and recycling it to reactor 2.

[0057] The liquid stream 30 removed from the reactor 2 comprises at least a part of the fermentation broth as used in the reactor 2. By recycling the liquid stream 70, gradients in the reactor 2 are reduced, gas transfer is increased, and undesirable by-products may be removed (not shown). Preferably, the whole fermentation broth including microorganisms is recycled. Those skilled in the art will understand how to design equipment and operating conditions to minimize shear stress on the microorganisms. The liquid stream 30 may, after removal from the reactor 2, be processed before being recycled, for example with pump 6, back to the reactor 2 to inlet 24 as recycle liquid stream 70. Non-limiting examples of further processing steps include supplementation with fresh microorganisms, nutrients, pH- controlling agents. Also, if desired, the temperature of the liquid stream 30 may be cooled or heated, as desired, before being recycled back to the reactor 2 as recycle liquid stream 70. Also, the energy balance of the process and apparatus of the present invention 1 may be optimized by applying heat integration of various streams.

[0058] Referring now to Fig. 4, liquid stream 30 removed from the reactor 2 may optionally be subjected to a second fermentation in fermenter 12. The liquid stream 30 may be processed before being subjected to a second fermentation in fermenter 12. The stream may be processed prior to this second fermentation, as discussed above for the recycle liquid stream 70.

[0059] The second fermentation in the fermenter 12 may use the same microorganism as used in the reactor 2 but preferably employs a different microorganism (a co-culture) than used in the reactor 2 in order to achieve a distinct different chemical conversion.

[0060] The fermenter 12 may comprise trays (and include a BES) like the reactor 2 and may operate under gas-phase or liquid-phase fermentation conditions.

[0061] However, preferably, the fermenter 12 applies liquid phase fermentation (contrary to the gas phase fermentation as applied in the reactor 2). Suitable reactor types include, but are not limited to, CSTR (continuous stirred tank reactor), ICR (immobilized cell reactor). TBR (trickle bed reactor), bubble column, gas-lift reactors, packed bed reactor, membrane bioreactor, and fluidized bed reactor. Suitable fermentation systems tobe used for the liquid phase fermentation have for example been mentioned in the article E.M. de Medeiros et al., “Production of ethanol fuel via syngas fermentation: Optimization of economic performance and energy efficiency”, Chemical Engineering Science: X, Volume 5. 2020, 100056.

[0062] Preferably, the recycle liquid stream 70 is fed into the reactor 2 at a (relatively low) liquid velocity of below 50 m / h, preferably below 10 m / h.

[0063] The person skilled in the art will readily understand that many modifications may be made without departing from the scope of the invention.

Claims

CLAIMS1. A process for producing a product, in particular one or more C2+ components, the process at least comprising the steps of:(a) providing a carbon-containing gas stream;(b) subjecting the carbon-containing gas stream provided in step (a) to fermentation in a reactor thereby obtaining at least a first gaseous product stream, wherein the reactor contains a plurality of trays and wherein at least some of the trays are provided with at least one microorganism, preferably for converting Cl components into C2+ components;(c) removing the first gaseous product stream obtained in step (b) from the reactor;(d) optionally cooling the first gaseous product stream removed in step (c) thereby obtaining a gas / liquid product mixture;(e) optionally separating the gas / liquid mixture obtained in step (d) in a gas / liquid separator thereby obtaining a second gas product stream and an C2+- enriched liquid stream; and(1) optionally recycling the second gas product stream obtained in step (e) to the reactor.

2. The process according to claim 1. wherein the carbon-containing gas stream (10) provided in step (a) is a syngas-containing stream.

3. The process according to claim 1 or 2, wherein the fermentation in step (b) at the highest tray is performed at a temperature of from 5 to 70°C, preferably from 20 to 48°C, more preferably between 35 and 45°C.

4. The process according to any one of the preceding claims, wherein there is a temperature gradient across the reactor and wherein the temperature at the highest tray of the reactor is at least 5°C warmer than the temperature near a bottom outlet of the reactor, preferably at least 10°C, more preferably at least 15°C.

5. The process according to any one of the preceding claims, wherein at least some of the trays comprise an electrochemical system, preferably a bioelectrochemical system, more preferably a bio-electrochemical system for in situ converting CO2 to CO and / or generate H2 and / or produce C2+.

6. The process according to any one of the preceding claims, wherein the first gaseous product stream obtained in step (b) comprises at least 0.50 mol.% C2+.

7. The process according to any one of the preceding claims, wherein the first gaseous product stream obtained in step (b) has a partial C2+ pressure of from 9 mbar to 0.2 bar.

8. The process according to any one of the preceding claims, wherein the first gaseous product stream removed in step (c) is, before being cooled in step (d), compressed.

9. The process according to any one of the preceding claims, wherein the separation in step (e) in the gas / liquid separator is performed at a pressure of above 150 mbara, preferably above 0.9 mbara.

10. The process according to any one of the preceding claims, wherein the process further comprises the steps of:(g) removing a liquid stream from the reactor;(h) subjecting the liquid stream in a second reactor to a second fermentation using a further microorganism, thereby obtaining at least an effluent; and(i) recycling the effluent as obtained in step (h) to the reactor.11 . The process according to claim 10, wherein the effluent as obtained in step (h) is fed into the reactor at a liquid velocity of below 50 m / h, preferably below 10 m / h.

12. An apparatus suitable for performing the process for producing a product according to any one of the preceding claims 1-11, the apparatus at least comprising:- a reactor for performing a fermentation reaction, the reactor having at least an inlet for a carbon-containing stream and an outlet for a first gaseous product stream. wherein the reactor contains a plurality of trays and wherein at least some of the trays are provided with at least one microorganism, preferably for converting Cl components into C2+ components;- an optional compressor for compressing the first gaseous product stream;- an optional heat exchanger for cooling the first gaseous product stream to obtain a gas / liquid product mixture;- an optional gas / liquid separator for separating the gas / liquid mixture to obtain a second gas product stream and an C2+-enriched liquid stream;- an optional recycle line for recycling the second gas product stream to the reactor.

13. The apparatus according to claim 12, wherein at least some of the trays comprise an electrochemical system, preferably a bio-electrochemical system, more preferably a bio-electrochemical system for in situ converting CO2 to CO and / or generate H2 and / or produce C2+.

14. The apparatus according to claim 12 or 13, further comprising:- a second reactor for subjecting the liquid stream to a second fermentation using a further microorganism, thereby obtaining at least an effluent; and - a recycle line for recycling the effluent as obtained in the second reactor to the reactor.

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