System for converting carbon dioxide to a biochemical

Abstract

The invention regards a system for converting a CO2 source to a biochemical, comprising: - a liquid absorbent mixture comprising a CO2 capture agent, - a bioreactor reaction medium comprising microorganisms selected for converting CO2 to a biochemical, - a CO2 selective membrane defined by a feed side and a permeate side, wherein the system is configured for passing the liquid absorbent mixture to the feed side of the CO2 selective membrane to generate CO2 permeation through the membrane, and wherein the permeate side of the CO2 selective membrane is at least in partial contact with the bioreactor reaction medium.

Description

[0001] System for converting carbon dioxide to a biochemical

[0002] Technical field

[0003] The present invention relates to a system for converting a CO2 source to a biochemical such as biomethane and / or biobased acetic acid or acetate, as well as a method for converting a CO2 source to a biochemical.

[0004] Background

[0005] Technologies for reducing greenhouse gas emissions from combustion of e.g. fossil fuels are receiving increasing focus in view of the climate challenges. In the same context, technologies for providing alternatives to combustion of fossil fuels and fossilbased chemicals, such as the platform molecule acetate, are of increasing importance.

[0006] The main anthropogenic greenhouse gas is carbon dioxide (CO2 or CO2), which is for example released as part of the flue gas from combustion plants, such as power plants, biogas plants, petrochemical plants, and refineries. To reduce the CO2 emission into the atmosphere, the carbon may be captured from the flue gas after combustion and before the flue gas is released to the atmosphere.

[0007] The carbon capture (CC) is typically obtained by use of a gas scrubber which is a liquid solvent capable of absorbing or adsorbing CO2 from the gas stream. The captured CO2 may subsequently be separated or stripped from the scrubber as gas, such that pure CO2 gas is formed, and whereby the liquid scrubber solvent is regenerated. The stripped CO2 gas may be transported and stored underground, also referred to as carbon capture and storage (CCS), and / or the stripped CO2 may be recycled and e.g. used as a solvent or fluid (e.g. for beverages, refrigeration, dry cleaning).

[0008] In addition or alternatively, the captured carbon may be converted into a higher value chemical or fuel, e.g. natural gas, methanol, polymers, cement, concrete. Such recycling of captured CO2 is also referred to as carbon capture and utilization (CCU).

[0009] KR 20200085633 discloses a system where CO2 from a biogas plant is captured and converted into higher purity methane (CH4) suitable for the natural gas grid. GB 2540798 discloses use of purified CO2 from a flue gas, as a gaseous feedstock to a methanol bioreactor.

[0010] Summary

[0011] The present disclosure provides a system for converting a carbon dioxide source to a biochemical, such as biomethane (CH4) and / or biobased acetic acid (AcOH) or acetate. The system is capable and particularly suitable and efficient for capturing and converting diluted carbon dioxide sources, such as flue gas streams and / or air streams having low concentrations of carbon dioxide and / or high concentrations of oxygen, and optionally NOx, SOx and particulate matter. Thus, the system provides a way of capitalizing on gas streams which are otherwise difficult to utilize.

[0012] The system allows for a more efficient, flexible, and robust conversion of CO2 due to a CO2 selective membrane, where the membrane feed side is contacted with a liquid absorbent mixture comprising a CO2 capture agent, which facilitates a high CO2 capture capacity or CO2 saturation of the mixture. For example, the CO2 capture capacity of the liquid mixture may be above 0.1 mol / L mixture, which is significantly above the CO2 content of a typical CO2 gas supply. Accordingly, when the membrane permeate side is contacted with a bioreactor reaction medium essentially absent of CO2, the chemical concentration gradient across the membrane may enable efficient CO2 transfer across the membrane. The chemical concentration gradient across the membrane may further be maintained and / or enhanced over time due to the CO2 conversion at the permeate side, e.g. by the microorganisms present in the reaction medium, i.e. due to the microbial CO2 conversion activity or the microorganism CO2 conversion activity. It follows that a system with a CO2 gradient across the membrane, irrespective of the specific type of membrane, the specific liquid absorbent mixture, and the specific type of bioreactor reaction medium and microorganisms, present on the opposite sides of the membrane, may facilitate CO2 transfer across the membrane followed by CO2 conversion.

[0013] It further follows that the efficiency and driving force of the CO2 transfer and conversion may increase with a larger concentration gradient across the membrane, e.g. for liquid absorbent mixtures with higher amounts of CO2 e.g. facilitated by a higher amount of capture agent, and / or for bioreactor reaction mediums with microorganisms with higher CO2 conversion rates or CO2 conversion activity. The system and membrane enable separation of the catalytic active CCh-converting microorganisms present in the bioreactor reaction medium and the liquid absorbent mixture, while still allowing transfer of captured CO2 across the membrane. Thus, the membrane facilitates that liquid absorbent mixtures with CO2 capture agents, which are conventionally known to be toxic to the microorganisms of a bioreactor, specifically when the capture agents are present in concentrations needed for capturing dilute CO2 sources. This is achieved by the capture agent mixtures being in indirect contact with the bioreactor reaction medium via the membrane, since the membrane allows for gasses to diffuse without direct contact between capture agents and microorganisms. Further, the membrane facilitates that the bioreactor may include a more flexible range of microorganisms, including microorganisms that are specifically efficient and / or specifically selective towards e.g. production of specific compounds such as biomethane, acetic acid, or other compounds derived directly or indirectly from captured CO2, as the microorganisms may be selected irrespective of their tolerance to the CO2 capture agents. Moreover, the downstream processing of the obtained biochemicals may be more cost efficient (with regards to process units, energy economy etc.), since the products (e.g. acetate) are a separate phase not contaminated with liquid absorbent mixture and capture agents.

[0014] The system further has the advantage of being self-contained in the sense that the driving mechanisms for the CO2 capturing and the CO2 liberation and conversion may be inherently induced by the liquid absorbent mixture, capture agent and the microorganisms maintaining the CO2 gradient across the membrane. The capture agents may ensure a high CO2 content on the feed side of the membrane, while the microorganisms may ensure a low CO2 content on the permeate side of the membrane due to their CO2 conversion activity.

[0015] A first aspect of the disclosure relates to a system for converting a CO2 source to a biochemical, comprising: a liquid absorbent mixture comprising a CO2 capture agent, a bioreactor reaction medium comprising microorganisms selected for converting CO2 to a biochemical, a CO2 selective membrane defined by a feed side and a permeate side, wherein the system is configured for passing the liquid absorbent mixture to the feed side of the CO2 selective membrane to generate CO2 permeation through the membrane, and wherein the permeate side of the CO2 selective membrane is at least in partial contact with the bioreactor reaction medium.

[0016] Thus, the bioreactor reaction medium comprising microorganisms is present on a permeate side of the CO2 selective membrane, and this implies that the CO2 permeation through the membrane is controllable by the microorganism CO2 conversion activity, such as enhanced by the microbial CO2 conversion activity. It follows that the higher the CO2 conversion activity, the stronger the CO2 gradient across the membrane, and the faster the CO2 permeation.

[0017] A second aspect of the disclosure relates to a method for converting a CO2 source to a biochemical, comprising the steps of: a) providing a liquid absorbent mixture comprising a CO2 capture agent, b) optionally contacting the liquid absorbent mixture with a CO2 source, thereby enriching the liquid absorbent mixture with CO2, c) passing the liquid absorbent mixture to a feed side of a CO2 selective membrane, thereby producing a CO2 permeate and a retentate, d) contacting at least a part of the CO2 permeate with a bioreactor reaction medium comprising microorganisms selected for converting CO2 to a biochemical, e) optionally recycling the retentate as the liquid absorbent mixture in step a.

[0018] For an efficient process, the CO2 permeate may advantageously be contacted with a bioreactor reaction medium by passing the liquid absorbent mixture to the feed side of the CO2 selective membrane, wherein the permeate side of the CO2 selective membrane is at least in partial contact with the bioreactor reaction medium.

[0019] Preferably the system of the first aspect is configured to carry out the method according to the second aspect.

[0020] In addition or alternatively, the method of the second aspect is configured to be carried out in the system according to the first aspect. Description of Drawings

[0021] The invention will in the following be described in greater detail with reference to the accompanying drawings.

[0022] Figure 1 shows embodiments of a system suitable for converting a CO2 source such as a flue gas, from a power plant, where: shows an embodiment where flue gas 6 is passed to a carbon capture reactor 1 including a CO2 absorbent 1.1 , such that the exhaust 1.4 of the carbon capture reactor is a CO2 lean flue gas. The CO2 enriched absorbent 1.2 is then passed to a CO2 desorber 5 stripping the absorbent at elevated temperatures of typically 100-

[0023] 150 °C resulting in stripped CO2 7 for storage / utilization, and regenerated CO2 lean absorbent 1.3 which may be recycled back into the carbon capture reactor 1 . shows an embodiment according to the present disclosure where flue gas 6 is passed to a carbon capture reactor 1 as in Figure 1A. The CO2 enriched absorbent

[0024] 1.2 is then passed into a bioreactor 2 via a membrane 3, preferably a CO2 selective membrane such that CO2 is present within bioreactor, and the CO2 lean absorbent 1.3 may be recycled back into the carbon capture reactor 1. The bioreactor comprises microorganisms 2.1 capable of converting the membrane separated CO2 into a biochemical product, such as methane (CH4) and / or acetic acid (AcOH), which may be recovered at a bioreactor exhaust 2.2. The conversion of the microorganism may advantageously occur at temperatures of 30-85 °C in the presence of a reducing source, such as advantageously green hydrogen.

[0025] Figure 2 shows schematic embodiments of (A) a mixed bioreactor, and (B) a membrane bioreactor according to the present disclosure.

[0026] Figure 3 shows schematic embodiments of four experimental bioreactor setups where

[0027] (A) shows an abiotic setup, (B) a mixed system setup, (C) a positive control setup, and

[0028] (D) a membrane setup according to the present disclosure.

[0029] Figure 4 shows embodiments of (A) an abiotic setup and (B) a membrane setup according to the present disclosure.

[0030] Figure 5 shows data from Example 1 where (A) shows calculated CO2 flux in NmL

[0031] (normal milliliter ) per hour per sguare meter membrane surface area for 3 tested membranes in the abiotic reactor setup, based on the time needed for reducing the pH in the reactor from 10 to 8, and (B) shows the calculated CO2 flux (left y-axis) for a thin silicone tube (0.4 mm VMQ) with a feed of either 100 vol% CO2 in gas phase, or a liguid feed of 1.5 M MDEA saturated with CO2, in the abiotic system. The corresponding CO2 content in mol / L for the two types of feeds is also indicated (right y- axis).

[0032] Figure 6 shows experimental data from Example 2 where the maximum H2 conversion rate (Vmax) in the membrane bioreactor setup D for different membranes are evaluated.

[0033] Figure 7 shows experimental data from Example 2 where (A) shows the relative amount of CO2 converted into either biomethane and / or biobased acetic acid , and (B) shows the amount of H2 consumed.

[0034] Figure 8 shows experimental data from Example 3 where the maximum H2 conversion rate (Vmax) in a mixed system setup as shown in Figure 3B, and a membrane setup as shown in Figure 3D, is measured. For comparison, the maximum H2 conversion rate for a positive control system as shown in Figure 3C is included.

[0035] Figure 9 shows experimental data from Example 3 where the hydrogen (H2) distribution in resulting biochemicals (biomethane CH4, biobased acetic acid AcOH, and others) is measured for a membrane reactor setup with membrane feeds having different MDEA concentrations and saturated CO2 concentrations.

[0036] Figure 10 shows experimental data from Example 4 where (A) shows the measured maximum H2 conversion rate (Vmax), and (B) the distribution of the H2 in resulting biochemicals, when using respectively a synthetic CO2 source (20:80 CO2:N2) and a flue gas source for saturating the membrane feed.

[0037] Figure 11 shows measured gas chromatography-flame ionization (GC-FID) of bioreactor reaction medium in contact with a membrane supplied with a feed of (A) 10 mM, (B) 25 mM, (C) 250 mM capture agent (MDEA). shows schematic embodiments of the bioreactor setups where (A) shows a membrane setup similar to Figure 3D, where a tubular membrane is supplied with a MDEA feed saturated either (left image) a synthetic CO2 source (20:80 CO2:N2), or

[0038] (right image) an industrial flue gas source. (B) shows a cross sectional view across the membrane, showing (upper image) the CO2 transfer across the membrane, and (lower image) the CO2 concentration gradients.

[0039] Figure 13 shows experimental data from Example 4 where (A) shows the measured maximum CO2 conversion rate (rmax), and (B) the distribution of the resulting biochemicals, when using respectively a synthetic CO2 source (20:80 CO2:N2) and a flue gas source for saturating the membrane feed.

[0040] Figure 14 shows experimental data from Example 1 where (A) shows calculated CO2 flux in NmL (normal milliliter) per hour per sguare meter membrane surface area for 4 tested membranes in the abiotic reactor setup, based on the time needed for reducing the pH in the reactor from 10 to 8, and (B) shows the CO2 flux (left y-axis) for a thin silicone tube (0.4 mm VMQ) with a feed of either 150, 600, or 1500 mM MDEA saturated with CO2, in the abiotic or biological membrane system.

[0041] Figure 15 shows experimental data from Example 5, with the measured maximum H2 conversion rates for membrane setups and a positive control using a synthetic CO2 source (20:80 CO2:N2) and a flue gas source for saturating the membrane feed, and bioreactors with pure cultures of either Acetobacterium wieringae or Sporomusa ovata. Figure 16 shows experimental data from Example 6, with the measured maximum H2 conversion rates for biological membrane setups with pure culture of Sporomusa ovata consuming H2 and CO2 under different levels of cysteine.

[0042] Detailed description

[0043] The invention is described below with the help of the accompanying figures. It would be appreciated by the people skilled in the art that the same feature or component of the device are referred with the same reference numeral in different figures. A list of the reference numbers can be found at the end of the detailed description section.

[0044] Bioreactor conversion of carbon dioxide source

[0045] Captured CO2 may be converted into higher value chemicals, such as methane (CH4) suitable for the natural gas grid, and / or acetic acid (CH3COOH, abbreviated as AcOH) or acetate (CHsCCh') which may be used as platform molecules for renewable fuels or other chemicals. For example, acetate may be a precursor for vinyl acetate and acetic anhydride, which are used for emulsion polymers, resins, coatings and textiles. The carbon dioxide conversion may occur within a bioreactor, which is a reactor comprising a biological catalyst, such as biochemical or microbiological catalysts, facilitating the conversion. The resulting product may accordingly be referred to as a biochemical, e.g. biomethane or biobased acetic acid or acetate.

[0046] For example, the bioreactor may be a biomethanation reactor where the biological catalyst is methanogens, selected (i.e. configured or adapted) to be primarily methane producing microorganisms according to the methanation reaction shown in Eguation 1. In addition or alternatively, the bioreactor may be an acetic acid reactor where the microbiological catalyst is selected to primarily produce acetic acid according to the acetogenesis reaction shown in Equation 2.

[0047] Thus, in the presence of selected microorganisms and a source of reducing agents, such as hydrogen, the captured CO2may be converted to a corresponding selected or defined biochemical. In the presence of hydrogen, the process may also be referred to as H2mediated biomethanation or acetogenesis. However, the conversion may also be mediated by other reducing agents than hydrogen, for example reducing equivalents such as formats and / or an electron source, e.g. in the form of a cathode. To improve the energy efficiency of the system, the reducing agent is advantageously green hydrogen produced by electrolysis using renewable electricity.

[0048] Bioreactors are generally not suitable for converting dilute carbon dioxide sources directly, such as flue gas streams and / or air waste streams having low concentrations of carbon dioxide and / or high concentrations of oxygen. For example, methanogens are known to be viable under anaerobic conditions and very low oxygen concentration conditions, such as oxygen concentrations below 3 mg / L, and their productivity may decrease significantly in the presence of oxygen. Typically flue gas streams and air waste streams have CO2contents below 33 vol% and / or oxygen contents above 5 vol%. For example, a flue gas from a natural gas fired power plant typically contain 8- 10 vol% CO2, 18-20 vol% H2O, 2-3 vol% O2, 67-72 vol% N2, whereas a flue gas from a biogas plant typically contain 50-70 vol% CH4, 30-50 vol% CO2, in addition to minor impurities (0-10.000 ppm) of NH3, siloxanes, volatile organic carbons, H2S.

[0049] Thus, in order to apply a dilute CO2source such as flue gas in a bioreactor, the CO2may be concentrated by applying a CO2absorbent solution. A dilute carbon dioxide source may be upconcentrated to an essentially CO2rich fluid (gas and / or liquid), which may then be introduced and converted efficiently in a bioreactor, as sketched in Figure 1A. The flue gas 6 is passed from a power plant to a carbon capture reactor 1 including a CO2absorbent 1.1 , such that the exhaust 1.4 of the carbon capture reactor is a CO2lean flue gas. The CO2enriched absorbent 1.2 is then passed to a CO2 desorber 5 stripping the absorbent at elevated temperatures of typically 100-150 °C resulting in stripped CO2 7 for storage or utilization in a bioreactor, and the regenerated CO2 lean absorbent 1.3 may be recycled back into the carbon capture reactor 1.

[0050] Membrane bioreactor

[0051] A more efficient, flexible, and robust conversion of a carbon dioxide source, including dilute carbon dioxide sources such as flue gas, may be obtained by a system comprising a membrane, such as a membrane bioreactor sketched in Figure 1 B.

[0052] Figure 1 B shows a carbon dioxide source, e.g. a flue gas 6 from a power plant, that is passed to a carbon capture reactor 1 . A carbon capture reactor is generally a reactor configured for capturing CO2 from gas streams by a media within the reactor, e.g. a solid or fluid, which is capable of capturing an amount of carbon dioxide from the gas phase into the media. For example, the media may be a liquid capable of capturing the carbon dioxide by dissolving, adsorbing or absorbing the CO2. A liquid capable of absorbing CO2 may be referred to as a liquid absorbent, a capture liquid, or a liquid gas scrubber.

[0053] The efficiency of a liquid absorbent will depend on the CO2 capture rate and the CO2 capture capacity of the liquid. By the term “CO2 capture capacity” is meant the maximum amount of CO2 that can be absorbed in the liquid, which may also be referred to as the saturated CO2 concentration. It follows that the higher the CO2 capture rate and the higher the CO2 capture capacity, the more efficient the liquid absorbent and the more dilute CO2 sources may be captured.

[0054] Higher CO2 capture rates and higher CO2 capture capacity may be obtained by a liquid absorbent mixture comprising a CO2 capture agent. By the term “CO2 capture agent” is meant a compound that increases the CO2 capture rate (e.g. by bonding and / or shifting equilibrium and / or catalysis), and / or a compound that is promoting the CO2 capture by shifting the equilibrium for the CO2 absorption. Preferably, the liquid absorbent mixture is a solution, where the CO2 capture agent is completely soluble and / or miscible with the liquid.

[0055] Accordingly, liquid absorbents with high CO2 capture capacity, such as capacities above 0.1 mol / L, require mixtures with a capture agent. Further, the higher the concentration of the capture agent, the higher the CO2 capture capacity. It is however known that high concentrations of capture agents may be toxic to the microorganisms of a bioreactor. For comparison, the CO2 content of a typical CO2 gas supply is significantly below 0.1 mol / L, e.g. below 0.05 mol CO2 per liter gas as indicated in Figure 5B.

[0056] The carbon capture reactor 1 in Figure 1B comprises a liquid absorbent mixture 1.1 , advantageously configured by CO2 capture agents to have a high CO2 capture capacity, such that it is suitable for capturing dilute CO2 sources. The CO2 enriched liquid absorbent mixture 1.2 is then passed to the feed side of a CO2 selective membrane 3 having a permeate side in contact with a bioreactor 2, such that the captured CO2 may permeate through the membrane and into the bioreactor. The retentate CO2 lean liquid absorbent mixture 1.3 may be recycled back into the carbon capture reactor 1.

[0057] The bioreactor comprises microorganisms 2.1 capable of converting the permeated CO2 into a biochemical product, e.g. according to Equations 1 and 2, and the biochemical product may be recovered at a bioreactor exhaust 2.2. The conversion reactivity or activity of the microorganisms further provides a driving force for the desorption and transfer of the captured CO2 through the membrane, in addition to the chemical concentration gradient across the membrane facilitated by the liquid absorbents having a high CO2 capture capacity, such as above 0.1 mol / L. Particularly, as further described in Example 1 and related Figures 12B 14B, the conversion reactivity of the microorganisms may generate an advantageous microbial-enhanced CO2 flux across the membrane.

[0058] Since the microbial conversion process (also referred herein to as the conversion of the microorganisms) occurs separately from the liquid absorbent mixture and the capture agents, the system facilitates use of more efficient, more concentrated, and / or toxic liquid absorbent mixtures, such liquid absorbent mixtures configured to a CO2 capture capacity above 0.1 mol / L.

[0059] The advantages of a membrane bioreactor are further illustrated in Figure 2 showing a bioreactor comprising a gaseous headspace with H2, a liquid reaction medium where the microorganisms 2.1 are located, and an interface between the gas phase and liquid phase which is essentially horizontal.

[0060] Figure 2A shows a bioreactor without a membrane, where the liquid absorbent mixture comprising capture agent (MDEA) and enriched with captured CO2 is passed directly into the bioreactor to contact the microorganisms 2.1. Such mixed bioreactors may suffer from low production rates of the biochemicals, since the capture agents are toxic to the microorganisms, as e.g. demonstrated in Example 3 and Figure 8. Further, the produced non-volatile biochemicals (AcOH, such as soluble acetic acid and / or acetate) are in the liquid phase with the liquid absorbent and the capture agent. Thus, a further downstream separation step is required if the acetic acid and / or acetate is to be used.

[0061] Figure 2B shows a bioreactor with a membrane 3 in contact with the liquid reaction medium of the bioreactor. The CO2 enriched liquid absorbent mixture 1.2 is passed to the feed side of the CO2 selective membrane. Since the membrane is essentially only permeable to CO2, the captured CO2 may be desorbed and passed through the membrane as permeate to contact the microorganisms 2.1. Accordingly, the toxic liquid absorbent mixture with capture agents is not brought into contact with the microorganisms, and the recovered non-volatile biochemical (AcOH) will not be contaminated.

[0062] To obtain an efficient and flexible system for CO2 conversion, the system advantageously comprises a liquid absorbent mixture comprising any CO2 capture agents configuring the liquid absorbent mixture to a high CO2 capture capacity, e.g. above 0.1 mol / L. Accordingly, the system is efficient and suitable for capturing dilute CO2 sources, despite the liquid absorbent mixture being toxic to microorganisms.

[0063] In an embodiment of the disclosure, the liquid absorbent mixture is configured to have a CO2 capture capacity above 0.1 mol / L, such as a CO2 capture capacity between 0.2- 0.7 mol / L, more preferably between 0.3-0.6 mol / L, such as 0.4, 0.5, or 0.55 mol / L.

[0064] The liquid absorbent mixture is optionally the reactor liquid present within a carbon capture reactor, which may be a liquid gas scrubber, such as a carbon dioxide scrubber. Accordingly, the liquid absorbent mixture may be the liquid applied in a liquid gas scrubber, e.g. in a carbon dioxide scrubber. For example, the carbon capture reactor liquid may be in fluid connection with a gas scrubber unit, preferably a carbon dioxide scrubber unit. Accordingly, the carbon capture reactor liquid and the liquid in the carbon dioxide scrubber unit are similar. Thus, the system may comprise a carbon capture reactor comprising the liquid absorbent mixture. The liquid absorbent mixture may in addition or alternatively be supplied to the bioreactor system from or via a buffer tank or container in fluid communication with the carbon capture reactor. Alternatively, the gas scrubber unit may be in fluid connection with the carbon capture reactor.

[0065] In an embodiment of the disclosure, the system comprises a carbon capture reactor comprising the liquid absorbent mixture, and wherein the system is configured for passing the liquid absorbent mixture in a forward flow from the carbon capture reactor to the feed side of the CO2 selective membrane. In a further embodiment, the liquid absorbent mixture is a carbon capture reactor liquid, such as a liquid gas scrubber, and preferably is a carbon dioxide scrubber. For example, the carbon capture reactor liquid may be applied in a liquid gas scrubber, such as in a carbon dioxide scrubber.

[0066] Accordingly, the operation of the membrane bioreactor in Figure 1B may include an optional initial step occurring in the carbon capture reactor, where the liquid absorbent mixture is contacted with a CO2 source to enrich the liquid absorbent mixture with CO2, before the liquid absorbent mixture is passed to the feed side of a CO2 selective membrane. The resulting CO2 permeate on the permeate side of the CO2 selective membrane is then contacted with a bioreactor medium in fluid communication with a H2 source, whereby the CO2 is converted to a biochemical by the microorganisms present in the medium.

[0067] Optionally, the retentate is recycled as the liquid absorbent mixture in the carbon capture reactor, and the cycle may be repeated multiple times infinitely, thereby providing a sustainable system.

[0068] Figure 12B shows a schematic cross sectional view across the membrane, where the upper image shows the CO2 transfer across the membrane 3, from the feed side (or retentate) to the permeate side. The membrane feed side is in contact with the capture liquid 1.1 comprising a capture agent (e.g. MDEA) promoting capturing of the CO2 as bicarbonate acid (HCOa'), further described by Equations 3A-C in the section below. The permeate side of the membrane is in contact with the bioreactor reaction medium 2 comprising microorganisms 2.1 capable of converting CO2 to e.g. AcOH or gaseous CH4, as sketched in Figure 12.

[0069] Thus, the capture liquid is present on the feed side of the membrane, and the bioreactor reaction medium is present on the permeate side of the CO2 selective membrane. Due to the CO2 concentration gradient across the membrane (shown in the lower image of Figure 12B), the CO2 flux across the membrane is dominantly going from the feed and retentate side of the membrane (i.e. from the liquid absorbent mixture or capture liquid), through the membrane, and to the permeate side, where the microorganisms are present.

[0070] The chemical concentration gradient across the membrane may be maintained during operation due to the CO2 conversion activity of the microorganisms present in the reaction medium on the permeate side. It follows that a system with a CO2 gradient across the membrane, irrespective of the specific type of membrane, the specific liquid absorbent mixture, and the specific type of bioreactor reaction medium and microorganisms, present on the opposite sides of the membrane, may facilitate CO2 transfer across the membrane followed by CO2 conversion.

[0071] In an embodiment of the disclosure, the bioreactor reaction medium is present on the permeate side of the CO2 selective membrane, such that the CO2 permeation through the membrane is managed or controllable by the microbial CO2 conversion activity

[0072] The efficiency and driving force of the CO2 transfer and conversion may be increased by enhancing the concentration gradient across the membrane, e.g. for liquid absorbent mixtures with higher amounts of CO2 or capture agent, and / or for bioreactor reaction mediums with microorganisms with higher CO2 conversion rates or CO2 conversion activity.

[0073] As further described in Examples 1-6, it is found that CO2 transfer and conversion may be obtained for systems comprising variable membranes, capture liquid feeds with different CO2 loadings, impurities and microbial toxicity, and for bioreactors with variable microbial cultures. It is specifically found that capture liquids that are efficient for capturing CO2 from dilute sources such as flue gas and which are further toxic to microorganisms may be used in the system according to the disclosure. Liquid absorbent mixture

[0074] The system advantageously comprises an efficient liquid absorbent mixture, which is configured to have a high CO2 capture capacity, such that it may be configured for dilute carbon dioxide sources, despite the high capture capacity implying toxicity to microorganisms.

[0075] Efficient liquid absorbent mixtures with high CO2 capture capacity above 0.1 mol / L may be obtained by a high capture agent concentration. Particularly high and controllable CO2 capture capacity is seen for aqueous solutions of the CO2 capture agent in concentrations above 1 mM.

[0076] In an embodiment of the disclosure, the liquid absorbent mixture is an aqueous solution of the CO2 capture agent in a concentration above 1 mM, such as a concentration between 150 mM - 3.5 M, more preferably between 500 mM - 3 M, and most preferably between 1 - 2.5 M, such as 1 M, or 1.5 M.

[0077] A high capture capacity may be obtained for liquid absorbent mixtures configured for capturing the CO2 as bicarbonate and / or carbamate. It is further seen that liquid absorbent mixtures comprising CO2 capture agents configured to promote the CO2 capture by shifting the equilibrium for the CCh-bicarbonate absorption or the equilibrium of the carbamate formation, may show surprisingly high and controllable CO2 capture capacities. Specifically, the CO2 absorption rate may be sufficient for equilibrium based absorption.

[0078] CO2 captured as bicarbonate and / or carbamate further has the advantage of being reversibly captured with sufficient interaction- or bonding strength to allow for equilibrium based desorption or decomposition. The bonding strength of bicarbonate / carbamate allows the CO2 to remain captured during the turbulent flow which may occur during the passage from the carbon capture reactor to the membrane, and simultaneously the strength of interaction allows the CO2 to be extracted, i.e. desorbed by dehydration of the bicarbonate or decomposition of the carbamate, when subjected to a chemical potential gradient, e.g. in proximity of the microorganisms. In an embodiment of the disclosure, the liquid absorbent mixture is configured for capturing CO2 as bicarbonate and / or carbamate. In a further or alternative embodiment, the CO2 capture agent is configured to promote CO2 absorption and / or CO2 desorption via bicarbonate and / or carbamate formation / decomposition.

[0079] An example of a capture agent in aqueous solution configured to capture CO2 as bicarbonate and configured to promote the CO2 capture by shifting the equilibrium, is tertiary amines (R3N or R3N) as shown in Equation 3A. The presence of R3N shifts the equilibrium to the right, compared to Equation 3. An example of a tertiary amine is MDEA, and the equilibrium is shown in Equation 3B.

[0080] (Eq. 3) C02+ H20 H++ HCO3

[0081] (Eq. 3A) C02+ R3N + H2O HCO3 + R3NH +

[0082] (Eq. 3B) C02+ MDEA + H20 HCO3 + MDEAH+

[0083] It is seen that the CO2 capture agent (R3N or MDEA) does not bind directly to the captured CO2, but instead promote the bicarbonate formation. The capture agent may further act as a catalyst and / or buffer for the bicarbonate formation by increasing the reaction rate. Primary and secondary amines are examples of alternative capture agents promoting CO2 capture by bonding e.g. by carbamate. To facilitate a high CO2 capture capacity, including for dilute carbon dioxide sources, the CO2 capture agent may be configured to have a CO2 capture capacity of at least 0.5 mol CO2 per mol capture agent, such as 1 mol CO2 per mol capture agent. It follows that a tertiary amine such as MDEA may have a capture capacity of at least 1 mol CO2 per mol capture agent. It further follows that primary and secondary amines, such as MEA or diamine, may have a capture capacity of at least 0.5 mol CO2 per mol capture agent.

[0084] In an embodiment of the disclosure, the CO2 capture agent is configured to have a CO2 capture capacity of at least 0.5 or 1 mol CO2 per mol capture agent.

[0085] Liquid absorbent mixtures with similar high CO2 capture capacity may be obtained by including CO2 capture agents with similar properties as R3N and MDEA. In an embodiment of the disclosure, the CO2 capture agent is selected from the group of: primary amines, secondary amines, tertiary amines, sterically hindered amines, carbonic anhydrases, hydroxide solutions such as NaOH and / or KOH solutions, and amine blends, such as blends comprising tertiary and primary and / or secondary amines, diamines, and combinations thereof. In a further or alternative embodiment, the CO2 capture agent comprises one or more amine(s) or alkylamine(s), wherein the amines optionally are selected from the group of: primary amines, secondary amines, tertiary amines, tertiary alkanol amines, heterocyclic amines, sterically hindered amines, and combinations thereof.

[0086] Particular efficient liquid absorbent mixtures may be obtained by including CO2 capture agents selected from amines and amine derivatives, despite the amines displaying higher toxicity towards the microorganisms present in the bioreactor. Examples of tertiary amines, such as tertiary alkanol amines include: N-Methyldiethanolamine (MDEA), MDEA derivatives, such as alkyl substituted diethanolamines (e.g. N-Ethyl diethanolamine (EDEA), N-Propyl diethanolamine (PDEA), N-iso-Propyl diethanolamine (iPDEA), N-Butyl diethanolamine (BDEA), N-tert-Butyl diethanolamine (tBDEA)), and alcohol substituted alkyl diethanolamines (e.g. Triethanolamine (TEA)), and N,N-disubstituted alkanolamines (e.g. 2-Dimethylaminoethanol (DMAE), 2- (Diethylamino)ethanol (DEEA), 2-Dipropylaminoethanol (DPEA), 2- (Dibutylamino)ethanol (DBEA), 6-Dimethylamino-1 -hexanol (DMAH), 3-Diethylamino-1- propanol (3DEA1 P)).

[0087] In an embodiment of the disclosure, the CO2 capture agent is selected from the group of: diethanolamine (DEA), monoethanolamine (MEA), methyldiethanolamine (MDEA), diisopropanolamine (DIPA), and aminoethoxyethanol or diglycolamine (DGA), and any combinations thereof. In an alternative and further embodiment, the one or more tertiary alkanol amines are selected from the group of: MDEA, MDEA derivatives, such as alkyl substituted diethanolamines, alcohol substituted alkyl diethanolamines, N,N- disubstituted alkanolamines, and combinations thereof.

[0088] The microorganisms are seen to be particularly intolerant to MDEA, especially in concentrations above 25 mM. However, liquid absorbent mixtures comprising MDEA also show particular high efficiency, and thus provide a particular efficient system. The concentration of the capture agent (e.g. MDEA) in the liquid absorbent mixture present on the feed side of the CO2 selective membrane may be 1.5 M or 2.5 M, and if the capture agents were directly transferred to the bioreactor, this may correspond to a MDEA concentration in the bioreactor reaction medium of 250 mM or 417 mM.

[0089] In an embodiment of the disclosure, the liquid absorbent mixture comprises one or more tertiary alkanol amines in a concentration between 150 mM - 3.5 M, more preferably between 500 mM - 3 M, and most preferably between 1 - 2.5 M, such as 1 M, or 1.5 M.

[0090] CO2 selective membrane

[0091] By the term “CO2 selective membrane” is meant a membrane that allows CO2 molecules to permeate through, while blocking other molecules. The membrane may thus also be referred to as a semi-permeable membrane. Accordingly, the membrane is advantageously configured to have a high CO2 permeance, and a low permeance of other feed components, such as the liquid absorbent and / or the CO2 capture agent. The membrane may be configured for cross-flow filtration of the CO2, as shown in Figure 2B.

[0092] The CO2 selective membrane may be configured for highly selective CO2 permeation. CO2 selective membrane defined by a feed side and a permeate side, wherein the system is configured for passing the liquid absorbent mixture to the feed side of the CO2 selective membrane, facilitating CO2 permeation, and wherein the permeate side of the CO2 selective membrane is at least in partial contact with the bioreactor reaction medium. Accordingly, the passing of the liquid to the feed side and the presence of the bioreactor medium on the permeate side facilitates and / or generates the CO2 permeation through the CO2 selective membrane, and further facilitates that the rate of permeation is controllable or managed, such as enhanced by a high CO2 gradient across the CO2 selective membrane.

[0093] The CO2 selective membrane forms a boundary interface between the liquid absorbent mixture being transferred from e.g. the carbon capture reactor, and the bioreactor reaction medium, as illustrated in Figures 1B and 2B, Accordingly, the membrane may have any geometry providing a boundary comprising two sides, where the first side is a feed side for contacting the liquid absorbent mixture, and the second side is a permeate side for contacting the bioreactor reaction medium. For example, the membrane may be a membrane tube 3.1 defined by a tube wall, where the inner tube wall forms a lumen for the liquid absorbent mixture, and the outer tube wall is in contact with the bioreactor reaction medium, as sketched in Figure 3D. Alternatively, the membrane may be a dead-end tube, or a planar or sheet, as indicated in Figure 2B. The membrane may further comprise multiple membranes, such as tubular membranes with multiple channels and / or a hollow fibre membranes. It also follows that the feed side and permeate side of the membrane may be interchangeable. For example, for a tubular membrane, the tube lumen may define the feed side and / or the permeate side.

[0094] In an embodiment of the disclosure, the CO2 selective membrane has a geometry selected from the group of: planar sheet, curved sheet, tube, tubular with multiple channels, dead-end tube, hollow fibre membranes, and any combinations thereof. In a further embodiment, the CO2 selective membrane is a tube or dead-end tube defined by a tube wall, wherein the tube lumen defines the feed side of the membrane, and the outer surface of the tube defines the permeate side of the membrane. In an alternative embodiment, the CO2 selective membrane is a tube or dead-end tube defined by a tube wall, wherein the tube lumen defines the permeate side of the membrane, and the outer surface of the tube defines the feed side of the membrane.

[0095] The conversion reactivity of the microorganisms provides a driving force for the desorption of the captured CO2 in the liquid absorbent mixture, as well as the transfer of the desorbed CO2 through the membrane. Accordingly, the CO2 flux through the membrane may be increased by increasing reaction activity of the microorganisms. By the term “flux” is meant the rate of flow of an element (e.g. CO2) per unit area. Thus for a CO2 impermeable membrane, the CO2 flux is 0 L / h / m2of the membrane. The flux volume may be given in normal liters (NL), which is the volume at normal conditions 0 °C and 1 bar pressure. The CO2 flux may also be increased by reducing the membrane thickness. To facilitate the manufacture and mechanical stability of a thin membrane, the membrane may comprise a porous mechanical support, e.g. a macro porous layer comprising metal or ceramic materials.

[0096] In an embodiment of the disclosure, the CO2 selective membrane comprises a porous mechanical support. In a further or alternative embodiment, the thickness of the CO2 selective membrane is between 0.05 - 2.5 mm, more preferably between 0.1 - 2 mm, and most preferably between 0.3 - 1.5 mm, such as 0.4 mm or 1 mm. The CO2 flux through a membrane depends on a number of factors, such as for example the membrane thickness and the chemical concentration gradient across the membrane, which is determined by the CO2 concentration in the feed and the reaction activity of the microorganisms. In addition, the flux is determined by the membrane material structure and material porosity. Advantageously, the membrane material is selected such that it is configured to have a high CO2 permeance, and a low permeance of other feed components, such as the liquid absorbent and / or the CO2 capture agent. Suitable membrane materials include polymers, polymer blends, inorganic and polymer-inorganic hybrids. For cost efficiency and manufacture flexibility, the membrane material is advantageously a polymer based material, and may advantageously comprise an elastomeric polymer, such as silicone, for easy handling. Polymer materials having high CO2 flux and / or high CO2 selectivity may include: cellulose acetates (CA), polydimethylsiloxane (PDMS), polyethylene oxide (PEO), polyethylene (PE), polypropylene, polyvinylchloride (PVC), polysulfones (Psf), polyimides (PI), polyamides, polyacetylenes, silicones such as VMQ tubes, and any combinations thereof, and preferably comprises or consists of an elastomeric polymer, such as silicone.

[0097] It is found that the membrane material preferably is hydrophobic, thereby facilitating permeation of nonpolar molecules such as CO2, and preventing polar liquid molecules such as H2O and polar capture agents such as MDEA from passing across the membrane. An example of a hydrophobic membrane material is silicone. By the term “silicone” is a polymer composed of repeating units of siloxane (-R2Si-O-SiR2-, where R is an organic group). Suitable commercially available silicone membranes are for example VMQ tubes. The hydrophobicity of a material may be quantified by the wettability, such as the water contact angle, which may be measured by an optical tensiometer. Silicones may have a water contact angle of between 90-110°, whereas polyethylenes may be less hydrophobic and have a water contact angle of between SOOS0.

[0098] In an embodiment of the disclosure, the CO2 selective membrane comprises or consists of a primarily hydrophobic material. In a further embodiment, the CO2 selective membrane comprises or consists of a material with a water contact angle between 80- 120°, more preferably between 90-115°, and most preferably between 95-110°. In an embodiment of the disclosure, the CO2 selective membrane comprises or consists of one or more polymers, optionally selected from the group of: Cellulose acetates (CA), polydimethylsiloxane (PDMS), polyethylene oxide (PEO), polysulfones (Psf), polyimides (PI), polyamides, polyacetylenes, silicones, such as VMQ tubes, and any combinations thereof. In a further embodiment, the CO2 selective membrane is a VMQ silicone tube.

[0099] The permeate side of the CO2 selective membrane is at least partially in contact with the bioreactor reaction medium, such that the reaction medium is configured for receiving the permeate. To further improve the CO2 conversion efficiency of the system, the membrane permeate side is advantageously essentially completely or to a high degree in contact with the bioreactor reaction medium. A larger contact area between CO2 permeate and bioreactor reaction medium will facilitate a higher efficiency. Thus, advantageously, the membrane has a configuration for increasing the specific contact area. For example a tube shaped membrane, may be linear, coiled, or placed in a meandering pattern. An example of a coiled tube membrane is shown in Figures 4B and 12A. Advantageously, the specific contact area between the permeate side of the CO2 selective membrane and the bioreactor reaction medium is sufficient such that the reaction medium is configured for receiving the permeate efficiently. For example, the specific surface area of the membranes in contact with the bioreactor reaction medium may be between 150-450 m2per m3reaction medium in the reactor.

[0100] In an embodiment of the disclosure, the bioreactor reaction medium is configured for receiving the permeate of the CO2 selective membrane. In a further embodiment, the membrane has a geometric configuration selected from the group of: linear, coil, meander, and any combinations thereof. In a further embodiment, the specific contact area between the permeate side of the CO2 selective membrane and the bioreactor reaction medium is between 150-450 m2 / m3, more preferably between 200-400 m2 / m3, and most preferably between 250-370 m2 / m3, such as 300 m2 / m3.

[0101] Hydrogen source

[0102] The CO2 conversion of the microorganisms typically includes hydrogen (H2 or H2) as a reactant, as indicated by Equations 1 and 2. Thus a hydrogen source may be in fluid communication with the reaction medium. Advantageously, the hydrogen is green hydrogen supplied from a renewable energy device, such as an electrolyzer, i.e. hydrogen that may be sourced from renewable energy e.g. by water electrolysis.

[0103] In an embodiment of the disclosure, the bioreactor comprises a hydrogen source in fluid communication with the bioreactor reaction medium. In a further embodiment, the hydrogen source is a renewable energy device, such as an electrolyzer.

[0104] To further improve the efficiency of the system, and particularly the energy efficiency, the system may advantageously be based on H2 produced from renewable energy, i.e H2 produced by electrolysis, also referred to as green H2. H2 is essentially insoluble in most liquids, including the liquid absorbent mixtures. Thus, to facilitate sufficient supply of hydrogen to the bioreactor reaction medium, the hydrogen is advantageously supplied as a continuous hydrogen flow to the bioreactor, e.g. the hydrogen flow direction in the headspace is advantageously perpendicular or parallel to the interface between the headspace and the reaction medium. to the headspace of the bioreactor. In addition or alternatively, the hydrogen flow may be provided by gas diffusion into the reaction medium.

[0105] In an embodiment of the disclosure, the hydrogen source is a hydrogen flow provided to a headspace of the bioreactor and / or a hydrogen flow provided to the bioreactor reaction medium by gas diffusion. In a further embodiment, the hydrogen flow direction forms an angle to an interface between the headspace and the bioreactor reaction medium of the bioreactor, such as perpendicular or parallel.

[0106] To further facilitate a sufficient supply of both CO2 and H2 to the microorganisms in the bioreactor reaction medium, the permeate side of the CO2 selective membrane may advantageously be placed in parallel with the interface to the headspace of the bioreactor comprising H2. Further, the permeate side of the membrane may be placed immediately subjacent to the interface to the headspace, as indicated in Figures 2B and 3D. The hydrogen may be supplied to the headspace as a hydrogen flow perpendicular or parallel to the interface. Alternatively, a bioreactor without a headspace may be used, and the hydrogen supplied to the reaction medium by gas diffusion, e.g. by bubbling hydrogen gas through the bioreactor reaction medium. In an embodiment of the disclosure, a part of the permeate side of the CO2 selective membrane is placed in parallel with the interface between the headspace and reaction medium of the bioreactor. In a further embodiment, a part of the permeate side of the CO2 selective membrane is placed immediately subjacent to the interface between the headspace and the reaction medium of the bioreactor. In an embodiment of the disclosure, the membrane is a tube located in a plane of the bioreactor that is in parallel with an interface between the headspace and reaction medium of the bioreactor.

[0107] Examples of membrane bioreactors are further described in Examples 1-4 and 5-6.

[0108] CO2 source

[0109] Due to the efficient liquid absorbent mixture with high CO2 capacity, the system is particularly suitable for converting CO2 from dilute carbon dioxide sources directly, such as flue gas streams and / or air waste streams having low concentrations of carbon dioxide and / or high concentrations of oxygen. The liquid absorbent mixture of the system may thus be in fluid communication with the CO2 source, as shown in Figure 1 B where the carbon capture reactor liquid is in fluid communication with the CO2 source.

[0110] In an embodiment of the disclosure, the liquid absorbent mixture within the carbon capture reactor is in fluid communication with a CO2 source. In a further embodiment, the CO2 source is a flue gas stream and / or an air stream.

[0111] The CO2 selective membrane facilitates that the microorganisms in the bioreactor reaction liquid may extract the CO2 as permeate, while preventing contact with components that are toxic to the microorganisms, such as the capture agents and dissolved oxygen. The high CO2 capture capacity of the liquid absorbent mixture further facilitates that CO2 is efficiently captured from even dilute CO2 sources with CO2 contents below 33 vol%, and the resulting enriched CO2 concentration in the liquid absorbent mixture may facilitate a higher driving force and easier extraction of the CO2 by the microorganisms.

[0112] In an embodiment of the disclosure, the CO2 source comprises below 33 vol% CO2, more preferably between 5-25 vol%, and most preferably between 7-23 vol%, such as 15 vol%. In a further or alternative embodiment, the CO2 source comprises above 5 vol% O2, more preferably between 7-25 vol%, such as 10 or 21 vol%.

[0113] An example of a membrane bioreactor with different CO2 sources is further described in Example 4.

[0114] Bioreactor reaction medium

[0115] The bioreactor may be a liquid based bioreactor comprising a gaseous headspace with a H2 source and / or supply, and a liquid reaction medium wherein the microorganisms are viable. Several examples of liquid based bioreactors are known.

[0116] In an embodiment of the disclosure, the bioreactor is selected from the group of: tricklebed gas phase reactors, continuous stirred-tank reactors (CSTR), up-flow anaerobic sludge bed reactors (LIASB), membrane reactors, and bioelectrochemical reactors.

[0117] The type of microorganisms present in the bioreactor will affect the type and amounts of produced biochemical. Advantageously, the microorganisms are selected such that a defined or predefined biochemical is obtained. For example, the microorganisms may be selected such that the CO2 is primarily converted into biomethane and / or biobased acetic acid or acetate. Examples of microorganisms with high selectivity towards producing methane and acetic acid or acetate are methanogens, such as hydrogenotrophic and acetoclastic methanogens, and / or homoacetogens. Suitable homoacetogens for converting CO2 into acetic acid or acetate in the membrane bioreactor include, but is not limited to, Sporomusa ovata and / or Acetobacterium wieringae. To further increase the amount of a predefined biochemical, the bioreactor reaction medium may advantageously comprise a microbial monoculture or a defined mixed culture with a high selectivity for e.g. acetate. However, a microbial monoculture may be more intolerant to oxygen present in the bioreactor reaction medium. To mitigate the adverse effect of oxygen present, the reaction medium may comprise an oxygen scavenger in a sufficient amount, such as 0.3 g / L cysteine or aerobic microorganisms, as further described in Example 6.

[0118] In an embodiment of the disclosure, the reaction medium of the bioreactor comprises microorganisms selected or adapted for converting CO2 and H2 to a predefined biochemical, such as biomethane and / or biobased acetic acid or acetate. In a further embodiment, the reaction medium of the bioreactor comprises methanogens and / or homoacetogens, such as Sporomusa ovata and / or Acetobacterium wieringae.

[0119] In an embodiment of the disclosure, the bioreactor reaction medium comprises a mixed microbial culture, a microbial monoculture, or a defined mixed culture. In an embodiment of the disclosure, the bioreactor reaction medium comprises an oxygen scavenger, such as cysteine, optionally in an amount between 0.005-0.5 g / L, more preferably between 0.01-0.4 g / L, and most preferably between 0.015-0.35 g / L, such as 0.017, 0.1, 0.2, or 0.3 g / L.

[0120] The microorganisms with high selectivity towards methane and / or acetic acid or acetate, may further be specifically intolerant to CO2 capture agents. Particularly, the microorganisms may be intolerant to CO2 capture agents in concentrations above 25 mM, where their conversion rate is reduced at least 50%. For example, the concentration of the capture agent (e.g. MDEA) in the liquid absorbent mixture present on the feed side of the CO2 selective membrane may be 1.5 M or 2.5 M, and if the capture agents were directly transferred to the bioreactor, this may correspond to a MDEA concentration in the bioreactor reaction medium of 250 mM or 417 mM.

[0121] In an embodiment of the disclosure, the reaction medium of the bioreactor comprises microorganisms which are intolerant (i.e. microorganisms configured to be intolerant and hence the bioreactor is configured to comprise microorganisms which are adapted and / or selected to be intolerant), to an aqueous solution of a CO2 capture agent with a concentration above 25 mM, and more preferably above 50 mM. In a further embodiment, the microorganisms are configured to (i.e. adapted and / or selected to) have reduced conversion rate in the presence of the aqueous solution, wherein the rate is reduced at least 50%, more preferably reduced at least 70% or 80%, and most preferably reduced at least 90%, such as 95%, 97%, or 99%.

[0122] During operation, the pH of reaction medium of the bioreactor may decrease due to the presence of increasing amounts of acetic acid / acetate. The pH may affect the viability of the microorganisms. Due to the dependence of pH, the system may be controlled by use of a pH sensor. In addition or alternatively, the system may be controlled by the use of a CO2 sensor. Accordingly, the process may be regulated via the CO2 in the gas, and / or the system may comprise a pH regulator for adjusting the pH of the reaction medium. For example, the medium may include a pH buffer, or the amount of acetic acid / acetate may be maintained constant by liquid circulation.

[0123] In an embodiment of the disclosure, the system comprises a pH regulator for adjusting the pH of the bioreactor reaction medium.

[0124] The energy efficiency and sustainability of the system may be further improved by recycling the membrane retentate to the carbon capture reactor. The system may accordingly be operated continuously without replacement of the liquid absorbent mixture or the carbon capture reactor liquid.

[0125] In an embodiment of the disclosure, the system is configured for passing the retentate of the CO2 selective membrane to the carbon capture reactor, and optionally recycling the retentate as liquid absorbent mixture.

[0126] Reference numbers

[0127] 1 - Carbon capture reactor, e.g. scrubber

[0128] 1.1 - Liquid absorbent mixture

[0129] 1.2 - CO2 rich liquid absorbent mixture

[0130] 1.3 - CO2 lean liquid absorbent mixture

[0131] 1.4 - Carbon capture reactor exhaust

[0132] 2 - Bioreactor

[0133] 2.1 - Microorganisms

[0134] 2.2 - Bioreactor exhaust / effluent, e.g. CH4, AcOH

[0135] 3 - Membrane

[0136] 3.1 - Membrane tube

[0137] 4 - H2 source, e.g. electrolysis unit

[0138] 5 - CO2 desorber, e.g. stripper

[0139] 6 - CO2 source, e.g. flue gas

[0140] 7 - Stripped CO2

[0141] Examples

[0142] The invention is further described by the examples provided below.

[0143] Materials and methods Tests were carried out in five different experimental bioreactor setups, as sketched in Figure 3, showing (A) an abiotic setup, (B) a mixed system biological setup, (C) a positive control biological setup, (D) a biological membrane setup. A negative control setup is included based on (B). The setups are further described below.

[0144] A) Abiotic setup

[0145] The reactor liquid comprised an aqueous 5 mM NaOH solution absent of microorganisms (prepared by dissolving 0.2 g NaOH in 1 L MilliQ water). The abiotic reactor was filled with the NaOH solution, ensuring no headspace to keep all dissolved inorganic carbon (DIG) in the liquid.

[0146] The reactor liquid is contacted with the permeate side of a membrane, where the membrane may be in the form of a tubular wall, as indicated in Figure 3A. Accordingly, the inner lumen of the tube may be provided with a feed, and the outer surface of the tube may be the permeate side of the membrane.

[0147] The reactor was equipped with a modified lid, in which the desired membrane was mounted, ensuring a continuous flow through the membrane. A pH sensor was mounted, to monitor the pH drop as the CO2 would permeate the membrane into the NaOH solution.

[0148] The feed side of the membrane was provided with a CO2 source that was either 100% CO2 gas or a 1 .5 M MDEA solution saturated with CO2, or different MDEA concentrations as specified below. The MDEA solution saturated with CO2 were prepared by a synthetic 20:80 CO2:N2 gas mixture until pH of the solution was stable, indicating full saturation with CO2. MDEA concentrations of around 1.5 M correspond to the industrial standard of most carbon capture reactors.

[0149] Tubular membranes of the following types were tested: Vinyl Methyl (VMQ) silicone tube with a wall thickness of 0.4 or 1 mm purchased from Witeg and Tygon tubes (Tygon A-60-F) with wall thickness 1 mm supplied by Saint Gobain®, polyethylene (PE) and polyvinyl chloride (PVC). The inner diameter for all tubular membranes was 3 mm and the wall thickness 1 mm.

[0150] The different membranes were mounted in the abiotic reactor, ensuring no nicks and free passage through it. The pH measurements were initiated simultaneously with stirring (500 rpm) and either CO2 gas or saturated MDEA was flushed through the membrane. Experiments were conducted until pH in the reactor liquid had decreased below 8.

[0151] B) Mixed system biological setup

[0152] Experiments were conducted in 250 mL borosilicate serum bottles. The liquid volume was kept constant at 24 mL with an inoculum concentration of 8.33 v / v% in 1X phosphate-buffered saline (PBS) solution. Furthermore, 4 mL of saturated MDEA was added in varying concentrations (0.15, 0.60, 1.5 M), resulting in reactors with MDEA concentrations of 25, 100 and 250 mM. The reactor headspace was flushed with 100% H2 (Air Liquide) and pressurized at 1 .8 bar, ensuring an excess amount of H2. Reactors were incubated at 37 °C with 500 rpm stirring.

[0153] C) Positive control biological setup

[0154] The reactor was constructed as in B), but with water instead of MDEA. Furthermore, the reactor headspace was provided with 20:80 CO2:H2 (Air Liquide) and pressurized at 1.8 bar.

[0155] D) Biological membrane setup

[0156] The reactors were constructed as in B), but the MDEA was added to a tubular membrane sealed in both ends, thus separating the capture solution and the microorganisms. Two parameters were varied in the biological membrane setup:

[0157] 1) The thickness of a VMQ silicone membrane (0.4, 1 and 1.5 mm), while keeping the MDEA concentration constant at 250 mmol / L reactor.

[0158] 2) The MDEA concentration (25, 100, 250 mmol / L reactor), while keeping the thickness of the VMQ silicone membrane constant at 0.4 mm.

[0159] The membrane was packed inside the serum bottle, while maximizing the amount of membrane being suspended in the liquid to augment the contact between microorganisms and membrane. Thus, the specific surface area of the membranes in contact with the bioreactor reaction medium was between 150-450 m2per m3reaction medium in the reactor. For example, for respectively a 0.4 mm, 1 mm, and 1.5 mm VMQ membrane the specific surface area may be 276 m2 / m3liquid in reactor, 350 m2 / m3, and 309 m2 / m3. (E) Negative control

[0160] The reactor was constructed as in B), but where the MDEA is flushed with only N2, thereby omitting CO2 as a carbon source.

[0161] Measurements and calculations

[0162] A) Abiotic setup

[0163] For the abiotic setup in Figure 3A and the membrane setup in Figure 3D, the liquid reactor is provided with CO2 as it permeates through the membrane. Accordingly, the maximum supply of CO2 to the liquid reactor may be determined by the CO2 flux across the membrane.

[0164] The CO2 flux across a membrane is evaluated by use of the model by T. Shesh et al. (Journal of Membrane Science (2019), 592, 117389) for the abiotic setup. The amount of total dissolved inorganic carbon in the NaOH solution at both pH 8 and 10 was calculated by equation 4:

[0165] Where Alko is the initial alkalinity of the solution (5 mM), Kw is the ionic product of water (1 O’14), [H+] is determined by pH, and a are the ionization fractions for the various species of dissolved inorganic carbon calculated by pH and the dissociation constants K. Then, the total amount of DIG in the reactor was determined by equation 5:

[0166] (5)nDic = CT* V

[0167] Where CT is the total amount of DIC and V is the volume of the reactor liquid.

[0168] Converting the moles to NmL by equation 6:

[0169] Where R is the gas constant, T is the in the reactor at and P is the pressure in the reactor (1 atm, thus not normalizing it).

[0170] Lastly, the CO2 flux into the reactor was determined (equation 7):

[0171] Where the numerator describes the difference in the volume of dissolved CO2 between pH 10 and 8 [NmL], which is divided with the surface area available for diffusion [m2] and the time needed for pH to drop from 10 to 8 [h].

[0172] B) Biological setup experiments

[0173] The membranes were also proven to supply CO2 to a mixed microbial culture from a mesophilic biogas plant in batch setups (i.e. a mixed mesophilic culture). The microorganisms were able to convert CO2 and H2 into either biomethane or biobased acetic acid by reaction equations 1-2 above. Hydrogen and CO2 can also be transformed into bacterial biomass, thus renewing the microbial catalysts continuously.

[0174] The rate of CO2 conversion is thus related to the rate of H2 conversion. As H2 was supplied to the microbial culture from the headspace, it was possible to follow the H2 consumption by continuous pressure measurements, as the pressure decreases due to microbial activity (MPX4250AP, CASE 867B-04, NPX) with an A / D-converter (MCP3423E / SL, Microchip).

[0175] The resulting pressure profiles resemble inverted sigmoidal curves, and the maximum rate was found by linear regression in the steepest linear area. The pressure data was converted into the hydrogen consumption rate by equation 8, followed by division by the reactor liquid volume, to get the volume-specific rate:

[0176] Where vH2is the rate of H2 conversion, Vheadspace is the reactor headspace, Pexpis the measured pressure, TnOrmai is the normal temperature (273 K), PnOrmai is the normal pressure (1 atm), Texpis the incubation temperature and t is the time. It should be kept in mind that the H2 only can be consumed if CO2 is available to the microorganisms, and thus, the H2 rate can be used as a measure for the CO2 availability from the membrane.

[0177] Furthermore, the H2 conversion rate can be converted into a CO2 conversion rate by combining the fraction of H2 converted into CH4 and acetate, together with the stochiometric relation between H2 and CO2, as given by Equation 1 and 2:

[0178] The formation of methane was evaluated by combining the final pressure with a final gas chromatography measurement (GC-2014, Shimadzu, Japan).

[0179] The formation of acetic acid was analysed by GC-FID (System 7890A, Agilent Technologies, USA) with a HP-IN NOWAX column (Agilent Technologies, USA) with helium as carrier gas.

[0180] For the biological membrane bioreactors (MBR), the presence of MDEA in the reactor liquid was measured by GC-FID equipped with a Zebron ZB-1 MS column (Phenomenex, USA) with helium as carrier gas, to examine whether a true separation of capture solution and microorganisms was achieved. Figure 11 shows measured gas chromatography-flame ionization (GC-FID) of a 10 mM MDEA solution (A) and a bioreactor reaction medium in contact with a membrane supplied with a feed of (B) 150 mM, or (C) 1.5 M capture agent (MDEA). True separation of capture agent (MDEA) and microorganisms was observed.

[0181] Example 1 - Membrane CO2 flux

[0182] To determine the CO2 permeability of the membranes, abiotic experiments were conducted (Figure 3A) and the CO2 flux across the membrane was evaluated by the time for pH to drop from 10 to 8, as described previously.

[0183] Results and conclusions

[0184] Figure 5A shows the calculated CO2 flux in NmL (normal milliliter) per hour per square meter membrane surface area for 3 tested membranes in the abiotic setup, based on the time needed for reducing the pH in the reactor from 10 to 8. The highest flux is seen for the thinner silicone tube (0.4 mm VMQ) showing a CO2 flux around 400 NmL / h / m2. A thicker silicone tube (1 mm VMQ) shows markedly lower CO2 flux around 140 NmL / h / m2. The Tygon tube shows very low flux, and accordingly the Tygon membrane is essentially resistant to CO2 permeation.

[0185] Figure 14A is similar to Figure 5A and shows the calculated CO2 flux in NmL per area, per hour, for comparison of membranes of VMQ, Tygon, PE and PVC. The membranes are tubular with an inner diameter of 3 mm and a wall thickness of 1 mm, and fed with a flow of 100% CO2 gas in the abiotic reactor setup. The silicone tube shows highest flux, whereas the PE and PVC is similar to the Tygon.

[0186] Figure 5B shows the calculated CO2 flux (left y-axis) for a thin silicone tube (0.4 mm VMQ) with a feed of either 100 vol% CO2 in gas phase, or a liquid feed of 1 .5 M M DEA saturated with CO2, in the abiotic system. The corresponding CO2 content in mol / L for the two types of feeds is also indicated (right y-axis).

[0187] In accordance with Figure 5A, the CO2 flux across the membrane for a feed with CO2 gas is around 400 NmL / h / m2. The CO2 content of the gas feed corresponds to around 0.03 mol / L. For the same membrane, the CO2 flux across the membrane is much lower (50 NmL / h / m2) if the membrane is fed with CO2 saturated 1.5 M MDEA, corresponding to a CO2 content of ca. 0.6 mol / L. The low CO2 flux for MDEA despite the high CO2 content indicates that use of MDEA implies that a desorption force or stripping force is needed, such as the microorganisms, to extract the CO2 content from the MDEA, and hereby create a concentration based driving force across the membrane.

[0188] A similar conclusion may be seen from Figure 14B showing the CO2 flux for a thin silicone tube (0.4 mm VMQ) with a feed of either 150, 600, or 1500 mM MDEA saturated with CO2, in the abiotic or membrane system. For both systems, the CO2 flux increased with the MDEA concentration due to the increased CO2 loading. However, for all MDEA concentrations, the CO2 flux is higher in the biological reactors than in the abiotic with biological enhancement factors of 3.2, 2.8, and 3.3. Thus, it is clearly indicated that efficient transfer of CO2 across the membrane implies the presence of microorganisms, and that the CO2 permeation through the membrane is mainly controllable by the conversion reactivity of the microorganisms.

[0189] Example 2 - Bioreactor with different membranes It was evaluated how the membranes would perform in a biological batch reactor, when supplying CO2 to a mixed microbial community. For the bioreactor setups in Figures 3B-D, the provided H2 and CO2 is converted by the microorganisms to biochemicals, such as biomethane or biobased acetic acid. Since both H2 and CO2 are reactants on the microbial processes of methanogenesis and acetogenesis, H2 conversion rates are also related to the amount of converted CO2.

[0190] Results and conclusions

[0191] Figure 6 shows the maximum H2 conversion rate (Vmax) in the membrane bioreactor setup D for different membranes. A similar H2 consumption of around 800 NmL H2 / h / m2 is seen for all types of membranes, despite the expected difference in CO2 flux based on the abiotic experiments with membrane thickness (cf. Example 1). Hence, even though the possible CO2 supply from the VMQ 0.4 mm membrane is higher (flux of around 400 NmL CC>2 / h / m2), the consumption rate of the microorganisms are not correspondingly higher. In contrast, a lower surface-specific H2 consumption is seen for VMQ 0.4 mm, which may be due to more surface area being available in this treatment due to different dimensions of the turbular membranes.

[0192] The data indicates that CO2 transfer across the membrane is not limiting process for the microorganism conversion in the test setup, but instead H2 supply to the microorganisms from the headspace to the liquid interface.

[0193] Figure 7A shows the relative amount of converted CO2 into biomethane or biobased acetic acid and Figure 7B shows the amount of H2 consumed. It is seen that ca. 50 vol% of the CO2 is converted into products for all three types of membranes. It is believed that the threshold is related to acidification of the membrane reactor, which may reduce the activity of the microorganisms. A final pH of ca. 5.2 was seen in all reactors. It is expected that more CO2 could be consumed from the membranes, if the reactors would not have been inhibited by acidification. The production rates and final yields does therefore not represent a maximum of the system, and may be improved by e.g. a pH controlled system.

[0194] Example 3 - Bioreactor with variable MDEA concentrations

[0195] The bioreactor setups in Figure 3B (mixed system biological setup) and 3D (biological membrane setup) is tested with different MDEA concentrations and corresponding different saturated CO2 concentrations. For the membrane setup, the different MDEA concentrations are provided as reactor concentrations (thus being more concentrated in the membrane feed). For the mixed system setup, the different MDEA concentrations are provided as a mixture comprising the microorganisms.

[0196] Results and conclusions

[0197] Figure 8 shows the maximum H2 conversion rate (Vmax) (directly corresponding to the CO2 conversion rate) in a mixed system setup as shown in Figure 3B, and a membrane setup as shown in Figure 3D. For comparison, the maximum H2 conversion rate for a positive control system as shown in Figure 3C is included.

[0198] For the mixed system it is seen that increasing the MDEA concentration results in a dramatic decrease in the H2 conversion rate, and at high MDEA concentrations essentially no H2 consumption by the microorganisms is observed. The reduced H2 consumption reflects the toxicity of the capture agent MDEA, and indicates the reduced degree of biocompatibility.

[0199] The positive control setup indicates a maximum H2 conversion rate for a bioreactor that is not limited by the CO2 supply, since in this case gaseous CO2 is supplied to the headspace. A H2 conversion rate of approximately 220 NmL / h / L culture is measured for the setup.

[0200] For the membrane reactor setup, the H2 conversion rate is seen to increase with increasing MDEA concentration and correspondingly increasing CO2 available. Thus, the consumption rate of the microorganisms increases with the amount of CO2 available, and this indicates that the permeation rate across the membrane is not limiting the microorganisms, and that the microbes are in equilibrium with the membrane. It should also be noted that the microbial toxicity of MDEA is no longer a problem due to separation by the membrane. It is further seen that the activity of the membrane reactors are equal to those of the positive control, indicating that the membrane reactors with captured CO2 can supply CO2 as efficiently as when CO2 is supplied as gaseous CO2. The microorganisms are here thought to be limited by the other reactant (H2) in both methanogenesis and acetogenesis. Figure 9 shows the distribution in resulting biochemicals (biomethane CH4, biobased acetic acid AcOH, and others) a membrane reactor setup with membrane feeds having different MDEA concentrations and saturated CO2 concentrations. It is indicated that for higher CO2 concentrations, the microorganisms will produce a higher fraction of AcOH.

[0201] Example 4 - Bioreactor with membrane feed from flue gas

[0202] The bioreactor setup in Figure 3D (membrane setup) is tested with an MDEA concentration of 1.5 M, resulting in a bioreactor concentration of 250 mM saturated with either a synthetic CO2 source (20:80 CO2:N2), or an industrial flue gas source, comprising 5-10 vol% O2, and minor amounts of NOx, SOx, and particulate matter.

[0203] Results and conclusions

[0204] Figure 10 shows (A) the measured maximum H2 conversion rates, and (B) the distribution in resulting biochemicals, when using respectively a synthetic CO2 source (20:80 CC>2:N2) and a flue gas source for saturating the membrane feed.

[0205] The maximum H2 conversion rate is similar for the two CO2 sources indicating that the microorganisms conversion rate of H2 is not significantly inhibited by the presence of oxygen or other impurities, which may also permeate through the membrane.

[0206] Figure 13 shows similar results as in Figure 10, where Figure 13A shows the CO2 conversion rate and Figure 13B the resulting biochemicals. A decrease in the CO2 conversion rate of ca. 18% is seen, when using flue gas compared to clean synthetic lab gas. Thus, a minor inhibition of the microorganism is indicated possibly due to the presence of oxygen, NOx, and SOx.

[0207] Example 5 - Bioreactor with microbial monoculture

[0208] The bioreactor setup of Example 4 was reproduced with variable microorganisms to demonstrate the flexibility of the system for different microorganisms to generate a sufficient CO2 flux across a membrane, and further to demonstrate that the microorganisms may be configured to generate selected conversion products.

[0209] In the bioreactor (i.e. the 250 mL borosilicate serum bottle), the mixed microbial culture was replaced with a microbial monoculture or pure culture of either: Acetobacterium wieringae and Sporomusa ovata, each cultivated in 50 mL of respectively DSMZ 135 medium and DSMZ 311 medium with all organic carbon sources omitted. The two different species have different CO2 conversion activities, and may further have different tolerances to the presence of oxygen.

[0210] As shown in related Figure 3D and Figure 12A, the tubular membrane was supplied with a MDEA feed (i.e. the liquid absorbent mixture or capture liquid) saturated by either a synthetic CO2 source (20:80 CO2:N2), or an industrial flue gas source, comprising 5-10 vol% O2, and minor amounts of NOx, SOx, and particulate matter, thereby facilitating a CO2 flux across the membrane and into the bioreactor. For comparison, positive controls using a setup as sketched in Figure 3C were included.

[0211] As described earlier, the microorganism conversion of CO2 and H2 into either biomethane and / or biobased acetic acid may be measured via the H2 pressure decrease, and the formation of methane evaluated by gas chromatography measurements, and the formation of acetic acid analysed by GC-FID.

[0212] Results and conclusions

[0213] Figure 15 shows the measured maximum H2 conversion rates for membrane setups and a positive control (abbreviated “Pos Con”), based on bioreactors with pure cultures of either Aceto bacterium wieringae (abbreviated “A. Wieringae”), and Sporomusa ovata (abbreviated “S. ovata”).

[0214] In all setups, a higher H2 conversion activity is seen for Sporomusa ovata.

[0215] It is further indicated that at least similar or even improved conversion rates as for the mixed microbial cultures in Examples 2-4 may be obtained for a pure culture.

[0216] Accordingly, it is indicated that 70-90% of the captured CO2 may be converted using a microbial monoculture.

[0217] Further, similar to Example 4 based on mixed microbial cultures, a decrease in the CO2 conversion rate of ca. 18% is indicated, when using flue gas compared to clean synthetic lab gas.

[0218] The distribution in resulting biochemicals (biomethane CH4, biobased acetic acid AcOH, and others) may be evaluated, and indicates that a higher fraction of AcOH is obtained when using pure cultures. Thus, pure homoacetogenic cultures may be used to maximize the acetate production. Furthermore, no biomethane was formed, which confirm no presence of hydrogenotrophic methanogens.

[0219] Example 6 - Bioreactor with microbial monoculture and cysteine

[0220] Example 5 was repeated with the modification of adding cysteine to the bioreactor as oxygen scavenger. Accordingly, any oxygen being transferred the capture liquid saturated with flue gas, may be removed by the cysteine, such that the microorganisms conversion activity may be maintained. Alternatively or in combination, microbial based oxygen scavengers, such as aerobic microorganism, may be applied. Hence, in an alternative example, the bioreactor comprises a defined mixed culture comprising e.g. anaerobic microorganisms combined with aerobic microorganisms.

[0221] The degree of oxygen removal may depend on the concentration of cysteine. For sufficient oxygen scavenger effect, a cysteine concentration of 0.3 g / L was applied.

[0222] Results and conclusions

[0223] Figure 16 shows the measured maximum H2 conversion rates for the membrane setups and bioreactors including cysteine in two different concentrations, based on capture liquids with different MDEA concentrations (1500 or 500 mM) saturated with flue gas or synthetic CO2. In all cases, a similar conversion rate is observed, indicating that the microorganisms are not affected by the possible presence of oxygen.

[0224] The distribution in resulting biochemicals (biomethane CH4, biobased acetic acid AcOH, and others) may be evaluated, and indicates that the pure homoacetogenic cultures may be used to maximize the acetate production based on flue gas sources, as no methane was detected.

[0225] Items

[0226] The presently disclosed may be described in further detail with reference to the following items.

[0227] 1. A system for converting a CO2 source to a biochemical, comprising: a liquid absorbent mixture comprising a CO2 capture agent, a bioreactor reaction medium comprising microorganisms selected, configured or adapted for converting CO2 to a biochemical, a CO2 selective membrane defined by a feed side and a permeate side, wherein the system is configured for passing the liquid absorbent mixture to the feed side of the CO2 selective membrane to generate CO2 permeation through the membrane, and wherein the permeate side of the CO2 selective membrane is at least in partial contact with the bioreactor reaction medium. The system according to item 1 , wherein the bioreactor reaction medium is present on the permeate side of the CO2 selective membrane, such that the CO2 permeation through the membrane is managed or controllable by the microorganism CO2 conversion activity or the microbial CO2 conversion activity. The system according to any one of the preceding items, comprising a carbon capture reactor comprising the liquid absorbent mixture, and wherein the system is configured for passing the liquid absorbent mixture in a forward flow from the carbon capture reactor to the feed side of the CO2 selective membrane. The system according to any one of the preceding items, wherein the liquid absorbent mixture is a carbon capture reactor liquid, such as a liquid gas scrubber, and preferably is a carbon dioxide scrubber. The system according to any one of the preceding items, wherein the liquid absorbent mixture is configured to have a CO2 capture capacity above 0.1 mol / L, such as a CO2 capture capacity between 0.2-0.7 mol / L, more preferably between 0.3-0.6 mol / L, such as 0.4, 0.5, or 0.55 mol / L. The system according to any one of the preceding items, wherein the liquid absorbent mixture is an aqueous solution of the CO2 capture agent in a concentration above 1 mM, such as a concentration between 150 mM - 3.5 M, more preferably between 500 mM - 3 M, and most preferably between 1 - 2.5 M, such as 1 M, or 1.5 M. The system according to any one of the preceding items, wherein the liquid absorbent mixture is configured for capturing CO2 as bicarbonate and / or carbamate. 8. The system according to any one of the preceding items, wherein the CO2 capture agent is configured to promote CO2 absorption and / or CO2 desorption via bicarbonate and / or carbamate formation / decomposition.

[0228] 9. The system according any one of the preceding items, wherein the CO2 capture agent is configured to have a CO2 capture capacity of at least 0.5 or 1 mol CO2 per mol capture agent.

[0229] 10. The system according to any one of the preceding items, wherein the CO2 capture agent is selected from the group of: primary amines, secondary amines, tertiary amines, sterically hindered amines, carbonic anhydrases, hydroxide solutions such as NaOH and / or KOH solutions, and amine blends, such as blends comprising tertiary and primary and / or secondary amines, diamines, and combinations thereof.

[0230] 11 . The system according to any one of the preceding items, wherein the CO2 capture agent comprises one or more amine(s) or alkylamine(s), wherein the amines optionally are selected from the group of: primary amines, secondary amines, tertiary amines, tertiary alkanol amines, heterocyclic amines, sterically hindered amines, and combinations thereof.

[0231] 12. The system according to any one of the preceding items, wherein the CO2 capture agent is selected from the group of: diethanolamine (DEA), monoethanolamine (MEA), methyldiethanolamine (MDEA), diisopropanolamine (DIPA), and aminoethoxyethanol or diglycolamine (DGA), and any combinations thereof.

[0232] 13. The system according to any one of items 10-12, wherein the one or more tertiary alkanol amines are selected from the group of: MDEA, MDEA derivatives, such as alkyl substituted diethanolamines, alcohol substituted alkyl diethanolamines, N,N-disubstituted alkanolamines, and combinations thereof.

[0233] 14. The system according to item 13, wherein the liquid absorbent mixture comprises one or more tertiary alkanol amines in a concentration between 150 mM - 3.5 M, more preferably between 500 mM - 3 M, and most preferably between 1 - 2.5 M, such as 1 M, or 1.5 M. The system according to any one of the preceding items, wherein the CO2 selective membrane has a geometry selected from the group of: planar sheet, curved sheet, tube, tubular with multiple channels, dead-end tube, hollow fibre membranes, and any combinations thereof. The system according to any one of the preceding items, wherein the CO2 selective membrane is a tube or dead-end tube defined by a tube wall, wherein the tube lumen defines the feed side of the membrane, and the outer surface of the tube defines the permeate side of the membrane. The system according to any one of items 1-15, wherein the CO2 selective membrane is a tube or dead-end tube defined by a tube wall, wherein the tube lumen defines the permeate side of the membrane, and the outer surface of the tube defines the feed side of the membrane. The system according to any one of the preceding items, wherein the CO2 selective membrane comprises a porous mechanical support. The system according to any one of the preceding items, wherein the thickness of the CO2 selective membrane is between 0.05 - 2.5 mm, more preferably between 0.1 - 2 mm, and most preferably between 0.3 - 1.5 mm, such as 0.4 mm or 1 mm. The system according to any one of the preceding items, wherein the CO2 selective membrane comprises or consists of a primarily hydrophobic material. The system according to any one of the preceding items, wherein the CO2 selective membrane comprises or consists of a material with a water contact angle between 80-120°, more preferably between 90-115°, and most preferably between 95-110°. The system according to any one of the preceding items, wherein the CO2 selective membrane comprises or consists of one or more polymers, optionally selected from the group of: cellulose acetates (CA), polydimethylsiloxane (PDMS), polyethylene oxide (PEO), polyethylene (PE), polypropylene, polyvinylchloride (PVC), polysulfones (Psf), polyimides (PI), polyamides, polyacetylenes, silicones, such as VMQ tubes, and any combinations thereof, and preferably comprises or consists of an elastomeric polymer, such as silicone.

[0234] 23. The system according to any one of the preceding items, wherein the bioreactor reaction medium is configured for receiving the permeate of the CO2 selective membrane.

[0235] 24. The system according to any one of the preceding items, wherein the membrane has a geometric configuration selected from the group of: linear, coil, meander, and any combinations thereof.

[0236] 25. The system according to any one of the preceding items, wherein the specific contact area between the permeate side of the CO2 selective membrane and the bioreactor reaction medium is between 150-450 m2 / m3, more preferably between 200-400 m2 / m3, and most preferably between 250-370 m2 / m3, such as 300 m2 / m3.

[0237] 26. The system according to any one of the preceding items, wherein the bioreactor comprises a hydrogen source in fluid communication with the bioreactor reaction medium.

[0238] 27. The system according to item 26, wherein the hydrogen source is a renewable energy device, such as an electrolyzer.

[0239] 28. The system according to any one of items 26-27, wherein the hydrogen source is a hydrogen flow provided to a headspace of the bioreactor and / or a hydrogen flow provided to the bioreactor reaction medium by gas diffusion.

[0240] 29. The system according to item 28, wherein the hydrogen flow direction forms an angle to an interface between the headspace and the bioreactor reaction medium of the bioreactor, such as perpendicular or parallel.

[0241] 30. The system according to any one of the preceding items, wherein the liquid absorbent mixture within the carbon capture reactor is in fluid communication with a CO2 source.

[0242] 31 . The system according to item 30, wherein the CO2 source is a flue gas stream and / or an air stream. 32. The system according to any one of items 30-31 , wherein the CO2 source comprises below 33 vol% CO2, more preferably between 5-25 vol%, and most preferably between 7-23 vol%, such as 15 vol%.

[0243] 33. The system according to any one of items 30-32, wherein the CO2 source comprises above 5 vol% O2, more preferably between 7-25 vol%, such as 10 or 21 vol%.

[0244] 34. The system according to any one of the preceding items, wherein the bioreactor is selected from the group of: trickle-bed gas phase reactors, continuous stirred- tank reactors (CSTR), up-flow anaerobic sludge bed reactors (LIASB), membrane reactors, and bioelectrochemical reactors.

[0245] 35. The system according to any one of the preceding items, wherein the bioreactor reaction medium comprises microorganisms selected and / or adapted for converting CO2 and H2 to a predefined biochemical, such as biomethane and / or biobased acetic acid or acetate.

[0246] 36. The system according to any one of the preceding items, wherein the bioreactor reaction medium comprises methanogens and / or homoacetogens, such as Sporomusa ovata and / or Acetobacterium wieringae.

[0247] 37. The system according to any one of the preceding items, wherein the bioreactor reaction medium comprises a mixed microbial culture, a defined mixed microbial culture or a microbial monoculture.

[0248] 38. The system according to one of the preceding items, wherein the bioreactor reaction medium comprises cysteine, optionally in an amount between 0.005- 0.5 g / L, more preferably between 0.01-0.4 g / L, and most preferably between 0.015-0.35 g / L, such as 0.017, 0.1 , 0.2, or 0.3 g / L.

[0249] 39. The system according to any one of the preceding items, wherein the bioreactor reaction medium comprises microorganisms adapted to be intolerant to an aqueous solution of a CO2 capture agent with a concentration above 25 mM, and more preferably above 50 mM. The system according to item 39, wherein the microorganisms are configured to have reduced conversion rate in the presence of the aqueous solution, wherein the rate is reduced at least 50%, more preferably reduced at least 70% or 80%, and most preferably reduced at least 90%, such as 95%, 97%, or 99%. The system according to any one of the preceding items, comprising a pH regulator for adjusting the pH of the bioreactor reaction medium. The system according to any one of the preceding items, wherein the system is configured for passing the retentate of the CO2 selective membrane to the carbon capture reactor, and optionally recycling the retentate as liquid absorbent mixture. The system according to any one of items 1-42, configured to carry out the method according to any one of items 44-46. A method for converting a CO2 source to a biochemical, comprising the steps of: a) providing a liquid absorbent mixture comprising a CO2 capture agent, b) optionally contacting the liquid absorbent mixture with a CO2 source, thereby enriching the liquid absorbent mixture with CO2, c) passing the liquid absorbent mixture to a feed side of a CO2 selective membrane, thereby producing a CO2 permeate and a retentate, d) contacting at least a part of the CO2 permeate with a bioreactor reaction medium comprising microorganisms selected, configured or adapted for converting CO2 to a biochemical, e) optionally recycling the retentate as the liquid absorbent mixture in step a. The method according to item 44, wherein the CO2 selective membrane in step (c) comprises a permeate side of the CO2 selective membrane being at least in partial contact with the bioreactor reaction medium. The method according to any one of items 44-45, configured to be carried out in the system according to any one of items 1-43.

Claims

Claims1. A system for converting a CO2 source to a biochemical, comprising: a liquid absorbent mixture comprising a CO2 capture agent, a bioreactor reaction medium comprising microorganisms selected for converting CO2 to a biochemical, a CO2 selective membrane defined by a feed side and a permeate side, wherein the system is configured for passing the liquid absorbent mixture to the feed side of the CO2 selective membrane to generate CO2 permeation through the membrane, and wherein the permeate side of the CO2 selective membrane is at least in partial contact with the bioreactor reaction medium.

2. The system according to claim 1 , wherein the bioreactor reaction medium is present on the permeate side of the CO2 selective membrane, such that the CO2 permeation through the membrane is controllable by the microbial CO2 conversion activity.

3. The system according to any one of the preceding claims, comprising a carbon capture reactor comprising the liquid absorbent mixture, and wherein the system is configured for passing the liquid absorbent mixture in a forward flow from the carbon capture reactor to the feed side of the CO2 selective membrane.

4. The system according to any one of the preceding claims, wherein the liquid absorbent mixture is a carbon capture reactor liquid, such as applied in a liquid gas scrubber, and preferably in a carbon dioxide scrubber.

5. The system according to any one of the preceding claims, wherein the liquid absorbent mixture is configured to have a CO2 capture capacity above 0.1 mol / L, such as a CO2 capture capacity between 0.2-0.7 mol / L, more preferably between 0.3-0.6 mol / L, such as 0.4, 0.5, or 0.55 mol / L.

6. The system according to any one of the preceding claims, wherein the liquid absorbent mixture is an aqueous solution of the CO2 capture agent in a concentration above 1 mM, such as a concentration between 150 mM - 3.5 M,more preferably between 500 mM - 3 M, and most preferably between 1 - 2.5 M, such as 1 M, or 1.5 M.

7. The system according any one of the preceding claims, wherein the CO2 capture agent is configured to have a CO2 capture capacity of at least 0.5 or 1 mol CO2 per mol capture agent.

8. The system according to any one of the preceding claims, wherein the CO2 capture agent is selected from the group of: primary amines, secondary amines, tertiary amines, sterically hindered amines, carbonic anhydrases, hydroxide solutions such as NaOH and / or KOH solutions, and amine blends, such as blends comprising tertiary and primary and / or secondary amines, diamines, and combinations thereof.

9. The system according to claim 8, wherein the liquid absorbent mixture comprises one or more tertiary alkanol amines in a concentration between 150 mM - 3.5 M, more preferably between 500 mM - 3 M, and most preferably between 1 - 2.5 M, such as 1 M, or 1.5 M.

10. The system according to any one of the preceding claims, wherein the CO2 selective membrane has a geometry selected from the group of: planar sheet, curved sheet, tube, tubular with multiple channels, dead-end tube, hollow fibre membranes, and any combinations thereof.11 . The system according to any one of the preceding claims, wherein the CO2 selective membrane is a tube or dead-end tube defined by a tube wall, wherein the tube lumen defines the feed side of the membrane, and the outer surface of the tube defines the permeate side of the membrane or wherein the tube lumen defines the permeate side of the membrane, and the outer surface of the tube defines the feed side of the membrane.

12. The system according to any one of the preceding claims, wherein the CO2 selective membrane comprises a porous mechanical support.

13. The system according to any one of the preceding claims, wherein the thickness of the CO2 selective membrane is between 0.05 - 2.5 mm, morepreferably between 0.1 - 2 mm, and most preferably between 0.3 - 1.5 mm, such as 0.4 mm or 1 mm.

14. The system according to any one of the preceding claims, wherein the CO2 selective membrane comprises or consists of a primarily hydrophobic material.

15. The system according to any one of the preceding claims, wherein the CO2 selective membrane comprises or consists of one or more polymers, optionally selected from the group of: cellulose acetates (CA), polydimethylsiloxane (PDMS), polyethylene oxide (PEO), polyethylene (PE), polypropylene, polyvinylchloride (PVC), polysulfones (Psf), polyimides (PI), polyamides, polyacetylenes, silicones, such as VMQ tubes, and any combinations thereof, and preferably comprises or consists of an elastomeric polymer, such as silicone.

16. The system according to any one of the preceding claims, wherein the bioreactor reaction medium is configured for receiving the permeate of the CO2 selective membrane.

17. The system according to any one of the preceding claims, wherein the membrane has a geometric configuration selected from the group of: linear, coil, meander, and any combinations thereof.

18. The system according to any one of the preceding claims, wherein the specific contact area between the permeate side of the CO2 selective membrane and the bioreactor reaction medium is between 150-450 m2 / m3, more preferably between 200-400 m2 / m3, and most preferably between 250-370 m2 / m3, such as 300 m2 / m3.

19. The system according to any one of the preceding claims, wherein the bioreactor comprises a hydrogen source in fluid communication with the bioreactor reaction medium.

20. The system according to claim 19, wherein the hydrogen source is a hydrogen flow provided to a headspace of the bioreactor and / or a hydrogen flow provided to the bioreactor reaction medium by gas diffusion.

21. The system according to any one of the preceding claims, wherein the liquid absorbent mixture within the carbon capture reactor is in fluid communication with a CO2 source.

22. The system according to claim 21, wherein the CO2 source is a flue gas stream and / or an air stream.

23. The system according to any one of the preceding claims, wherein the bioreactor reaction medium comprises microorganisms selected for converting CO2 and H2 to a predefined biochemical, such as biomethane and / or biobased acetic acid or acetate.

24. The system according to any one of the preceding claims, wherein the bioreactor reaction medium comprises methanogens and / or homoacetogens, such as Sporomusa ovata and / or Acetobacterium wieringae.

25. The system according to any one of the preceding claims, wherein the bioreactor reaction medium comprises a mixed microbial culture, a microbial monoculture, or a defined mixed culture.

26. The system according to one of the preceding claims, wherein the bioreactor reaction medium comprises an oxygen scavenger, such as cysteine, optionally in an amount between 0.005-0.5 g / L, more preferably between 0.01-0.4 g / L, and most preferably between 0.015-0.35 g / L, such as 0.017, 0.1, 0.2, or 0.3 g / L.

27. The system according to any one of the preceding claims, comprising a pH regulator for adjusting the pH of the bioreactor reaction medium.

28. The system according to any one of the preceding claims, wherein the system is configured for passing the retentate of the CO2 selective membrane to the carbon capture reactor, and optionally recycling the retentate as liquid absorbent mixture.

29. A method for converting a CO2 source to a biochemical, comprising the steps of: a) providing a liquid absorbent mixture comprising a CO2 capture agent, b) optionally contacting the liquid absorbent mixture with a CO2 source, thereby enriching the liquid absorbent mixture with CO2,c) passing the liquid absorbent mixture to a feed side of a CO2 selective membrane, thereby producing a CO2 permeate and a retentate, d) contacting at least a part of the CO2 permeate with a bioreactor reaction medium comprising microorganisms selected for converting CO2 to a biochemical, e) optionally recycling the retentate as the liquid absorbent mixture in step a.

30. The method according to claim 29, wherein the CO2 selective membrane in step (c) comprises a permeate side of the CO2 selective membrane being at least in partial contact with the bioreactor reaction medium.

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