Method for controlling a gas fermentation platform for the improvement of converting carbon dioxide into a product

Abstract

A method and system for controlling a flexible gas fermentation platform to improve the conversion of CO2 to products has been developed, and in particular relates to a control process and system for controlling the ratio of feed gases and maximizing the concentration of inert components in the bioreactor tail gas stream and / or bioreactor headspace. Improved carbon utilization provides the most beneficial ratio of substrate to bioreactor for the fermentation process.

Description

Technical Field

[0001] Cross - reference to Related Applications This application claims the benefit of U.S. Provisional Patent Application No. 63 / 173,243, filed on April 9, 2021; No. 63 / 173,247, filed on April 9, 2021; No. 63 / 173,262, filed on April 9, 2021; No. 63 / 173,338, filed on April 9, 2021; and No. 63 / 282,546, filed on November 23, 2021, the entire contents of each of which are incorporated herein by reference.

[0002] The present disclosure relates to methods and systems for controlling a flexible fermentation platform to improve the conversion of CO2 into products. In particular, the present disclosure relates to continuous control processes and systems for controlling the ratio of feedstock substrate gases and maximizing the concentration of inert components in the outlet gas stream.

Background Art

[0003] Carbon dioxide (CO2) accounts for approximately 76% of the world's greenhouse gas emissions due to human activities, with methane (16%), nitrous oxide (6%), and fluorinated gases (2%) making up the remainder (United States Environmental Protection Agency). Although industrial and forestry operations also emit CO2 into the atmosphere, most of the CO2 comes from burning fossil fuels to generate energy. Reducing greenhouse gas emissions, particularly CO2, is important for halting the progression of global warming and the associated changes in climate and weather.

[0004] It has long been recognized that gases containing carbon dioxide (CO2), carbon monoxide (CO), and / or hydrogen (H2) can be converted into various fuels and chemicals using catalytic processes such as the Fischer-Tropsch process. However, recently, gas fermentation has emerged as an alternative platform for the biological fixation of such gases. Specifically, C1-fixing microorganisms have been demonstrated to convert gases containing CO2, CO, and / or H2, such as industrial waste gas, syngas, or mixtures thereof, into products such as ethanol and 2,3-butanediol. The efficient production of such products can be limited, for example, by slow microbial growth, limited gas uptake, sensitivity to toxins, or the diversion of carbon substrates to undesirable by-products.

[0005] C1 carbon sources can be derived from industrial process by-products such as exhaust gases from combustion engines, CO2 by-product gases from industrial processes (cement production), ammonia production, by-product gases from syngas purification, ethylene production, ethylene oxide production, methanol synthesis), off-gases from fermentation processes (e.g., conversion of sugar to ethanol), biogas, landfill gas, direct air capture, mined CO2 (fossil CO2), or electrolysis, or from waste gases obtained from another source. The C1 carbon source may also be syngas produced by pyrolysis, roasting, or gasification. In other words, waste may be recycled by pyrolysis, reforming, roasting, or gasification to produce syngas that is used as a substrate and / or C1 carbon source.

[0006] In certain embodiments, the industrial process is selected from the manufacture of ferrous metal products such as steel mill manufacturing, non-ferrous metal product manufacturing, petroleum refining, power generation, carbon black production, ammonia production, methanol production, coke production, or any combination thereof. In these embodiments, the substrate and / or C1 carbon source may be captured from the industrial process using any known method before it is released into the atmosphere.

[0007] The C1 carbon source may include synthesis gas obtained by gasification of coal, gasification of refined residues, gasification of biomass, gasification of lignocellulosic materials, gasification of black liquor, gasification of municipal solid waste, gasification of industrial solid waste, gasification of sewage, gasification of sludge from wastewater treatment, reforming of natural gas, reforming of biogas, reforming of landfill gas, or any combination thereof.

[0008] Examples of municipal solid waste include tires, plastics, as well as shoes, apparel, and fibers contained in fabrics. Municipal solid waste may or may not be sorted. Examples of biomass may include lignocellulosic materials and may also include microbial biomass. Lignocellulosic materials may include agricultural waste and forest waste.

[0009] Industrial gas or synthesis gas may require treatment or decomposition suitable for use in a gas fermentation system. A high CO2 content in industrial gas and / or synthesis gas has been shown to negatively affect the benefits of ethanol selectivity in fermentation, resulting in higher production of undesirable co-products such as acetate and 2,3-butanediol.

[0010] Accordingly, there remains a need for control processes and systems for a flexible fermentation platform that can continuously control the ratio of substrate gas provided to the bioreactor of the fermentation platform to maximize the concentration of inert components in the gas outlet stream of the bioreactor. This is particularly advantageous in situations where the initial starting material is CO2. Additionally, in some embodiments, there is a need to convert some of the CO2 present in the synthesis gas or industrial gas to CO prior to introduction into the bioreactor because improved CO content and improved H2:CO ratio have been shown to improve microbial growth and stability. SUMMARY OF THE INVENTION

[0011] The present disclosure relates to a method for continuously controlling the ratio of input gases provided to a bioreactor in a continuous gas fermentation process. The method includes: a) providing a gas fermentation process, including a first gas stream containing H2 from an H2 source, a second gas stream containing CO2 from an industrial process or a syngas process, a conversion zone for converting CO2 to CO having a CO-enriched eluate containing CO and CO2, and at least one bioreactor having at least one C-1 fixing bacterium for gas fermentation in a nutrient solution, wherein the bioreactor has a product stream including at least one product, an outlet gas stream containing H2, CO2, and an inert component, a headspace containing H2, CO2, and an inert component, or both, and the bioreactor is in fluid communication with the CO-enriched eluate, optionally the first gas stream, optionally the second gas stream, or any combination thereof; b) measuring the H2:CO:CO2 molar ratio in the bioreactor outlet gas stream or the bioreactor headspace to provide the measured H2:CO:CO2 molar ratio; c) inputting the measured H2:CO:CO2 molar ratio into a controller to compare the measured H2:CO:CO2 molar ratio with a predetermined H2:CO:CO2 molar ratio; and d) adjusting the flow rate of the first gas stream, the flow rate of the second gas stream, or both, in response to the difference between the measured H2:CO:CO2 molar ratio and the predetermined H2:CO:CO2 molar ratio to maximize the concentration of the inert component in the bioreactor outlet gas stream.The method includes, in a first compressor, compressing at least a portion of the first gas stream, at least a portion of the second gas stream, or any combination thereof to produce a compressed first gas stream, a compressed second gas stream, and / or a combination of the compressed first gas stream and the second gas stream; treating at least a portion of the first gas stream or the compressed first gas stream or both, and at least a portion of the second gas stream or the compressed second gas stream or both, or the combination of the compressed first gas stream and the second gas stream, in a gas treatment zone comprising a gas component removal unit, a gas desulfurization / acid gas removal unit, or both, before passing the second gas stream and optionally the first gas stream through a CO2 to CO conversion zone; and further recirculating an outlet gas stream to the first compressor, the gas treatment zone, a CO2 to CO conversion system, the first gas stream, the second gas stream, or a combination of the first gas stream and the second gas stream. The method may further include combining a stream of CO-enriched eluate with at least a portion of a treated stream, or the first gas stream, or the second gas stream, or a combination of the first gas stream and the second gas stream, or the compressed first gas stream, or the compressed second gas stream, or a combination of the compressed first gas stream and the second gas stream, or any combination thereof.The first gas stream containing H2 may be passed through the bioreactor without passing through the conversion zone from CO2 to CO. The method includes compressing the bioreactor outlet gas stream to produce a compressed bioreactor outlet gas stream, and passing at least a first portion of the compressed bioreactor outlet gas stream, in any order, through a gas desulfurization and / or acid gas removal unit, or a gas component removal unit, or both a gas desulfurization and / or acid gas removal unit and a gas component removal unit to produce a compressed treated bioreactor outlet gas stream, and recycling the compressed treated bioreactor outlet gas stream to combine with the first gas stream, the second gas stream, or a combination thereof, or sending it to a CO2 to CO conversion system, or combining it with a stream of CO-enriched eluate, or any combination thereof, and optionally recycling a second portion of the compressed bioreactor outlet gas stream to combine with a stream of CO-enriched eluate or the bioreactor. The method may further include combining at least a second portion of the first gas stream, at least a second portion of the second gas stream, or a combination thereof with a stream of CO-enriched eluate. The method may further include passing at least a second portion of the first gas stream, at least a second portion of the second gas stream, or a combination thereof through the bioreactor. The method may further include compressing any portion of the first gas stream, the second gas stream, or a combination thereof. The method may further include using a control valve to control the relative amounts of the first portion and the second portion of the compressed outlet gas stream. The method may further include passing at least a portion of the outlet gas stream through a CO2 to CO conversion system of outlet gas selected from a reverse water gas shift unit, a thermal catalytic conversion unit, a partial combustion unit, a plasma conversion unit, a gasification unit, or a reforming unit to produce a stream of CO-enriched eluate and recycling a second stream of CO-enriched eluate to the bioreactor. The stream of CO-enriched eluate may include an H2:CO:CO2 molar ratio of about 5:1:1, about 4.5:1:1, about 4.33:1:1, about 3:1:1, about 2:1:1, about 1:1:1, or about 1:3:1.The CO2-to-CO conversion system may include at least one of a reverse water gas shift unit, a thermal catalytic conversion unit, a partial combustion unit, a reforming unit, or a plasma conversion unit. The product stream may include at least one fermentation product selected from ethanol, acetate, butanol, butyrate, 2,3-butanediol, lactate, butene, butadiene, methyl ethyl ketone, ethylene, acetone, isopropanol, lipid, 3-hydroxypropionate, isoprene, fatty acid, 2-butanol, 1,2-propanediol, hexanol, octanol, or 1-propanol. The hydrogen source may include at least one of a water electrolysis cell, a hydrocarbon reforming source, a hydrogen purification source, a solid biomass gasification source, a solid waste gasification source, a coal gasification source, a hydrocarbon gasification source, a methane pyrolysis source, a refinery tail gas production source, a plasma reforming reactor, a partial oxidation reactor, or any combination thereof. The industrial process or syngas process may be selected from at least one of a sugar-based ethanol production source, a first-generation corn ethanol production source, a second-generation corn ethanol production source, a sugarcane ethanol production source, a sucrose ethanol production source, a sugar beet ethanol production source, a molasses ethanol production source, a wheat ethanol production source, a grain-based ethanol production source, a starch-based ethanol production source, a cellulose-based ethanol production source, and a cement production source, a methanol synthesis source, an olefin production source, a steel production source, an alloy iron production source, a refinery tail gas production source, a secondary combustion gas production source, a biogas production source, a landfill production source, an ethylene oxide production source, a methanol production source, an ammonia production source, a mined CO2 production source, a natural gas treatment production source, a gasification source, an organic waste gasification source, a direct air capture, or any combination thereof. At least one of the C1-fixing bacteria may be selected from Clostridium autoethanogenum, Clostridium ljungdahlii, or Clostridium ragsdalei.

[0012] The present disclosure relates to a system for controlling the ratio of substrate gases provided to a bioreactor in a continuous gas fermentation process, the system comprising: a) a first gas stream containing substrate H2 from an H2 source; b) a second gas stream containing substrate CO2 from an industrial process or a syngas process; c) a conversion zone in fluid communication with the second gas stream and optionally the first gas stream, having an eluate containing CO and CO2, for converting CO2 to CO; d) at least one bioreactor having at least one C-1 fixing bacterium for gas fermentation in a nutrient solution, the bioreactor having a tail gas stream containing H2, CO2, and an inert component, a headspace containing H2, CO2, and an inert component, or both, and the bioreactor being in fluid communication with an eluate containing CO and CO2, optionally the first gas stream, optionally the second gas stream, or any combination thereof; e) a sensor within the bioreactor tail gas stream or within the bioreactor headspace, or both, capable of measuring the H2:CO2 molar ratio or the H2:CO:CO2 molar ratio of the bioreactor tail gas stream or the bioreactor headspace and providing the measured H2:CO2 molar ratio or the measured H2:CO:CO2 molar ratio; f) a controller that receives the measured H2:CO2 molar ratio or the measured H2:CO:CO2 molar ratio, compares the measured H2:CO2 molar ratio to a predetermined H2:CO2 molar ratio, or compares the measured H2:CO:CO2 molar ratio to a predetermined H2:CO:CO2 molar ratio, provides an output to adjust the flow rate of the first gas stream, the flow rate of the second gas stream, or both, in response to the difference between the measured H2:CO2 molar ratio and the predetermined H2:CO2 molar ratio, or in response to the difference between the measured H2:CO:CO2 molar ratio and the predetermined H2:CO:CO2 molar ratio, to maximize the concentration of the inert component in the tail gas stream. The system may further include an output to the operating parameters of the CO2 to CO conversion zone to increase or decrease the relative amount of CO in the eluate containing CO and CO2. The CO2 to CO conversion system may include at least one of a reverse water gas shift process, a CO2 electrolyzer, a thermal catalytic conversion process, a partial combustion process, or a plasma conversion process.The gas fermentation process may further comprise a gas treatment zone in fluid communication with a first gas stream, a second gas stream, an eluate, or any combination thereof. The gas fermentation process may further comprise at least one compressor in fluid communication with a first gas stream, a second gas stream, an eluate, or any combination thereof. The gas fermentation process may further comprise a methane conversion zone in fluid communication with the bioreactor tail gas stream, and the methane reforming zone comprises an eluate conduit in fluid communication with a conversion zone for converting CO2 to CO.

[0013] The present disclosure involves a control process for an integrated process for the production of at least one fermentation product from a gas stream, the control process first comprising providing a gas fermentation process, the gas fermentation process comprising obtaining a first gas stream comprising hydrogen and a second gas stream comprising CO2, passing at least a portion of the first gas stream and at least a portion of the second gas stream through a CO2-to-CO conversion system operating under conditions to produce a CO-enriched outlet stream, fermenting the CO-enriched outlet stream in a bioreactor having a culture of one or more C1-fixing bacteria to produce at least one fermentation product stream and a bioreactor tail gas stream, compressing the bioreactor tail gas stream to produce a compressed bioreactor tail gas stream, passing at least a first portion of the compressed bioreactor tail gas stream, in any order, i) to a gas desulfurization and / or acid gas removal unit, or ii) to a gas component removal unit, or iii) through both a gas desulfurization and / or acid gas removal unit and a gas component removal unit to produce a compressed treated bioreactor tail gas stream, recycling the compressed treated bioreactor tail gas stream to a) combine with the first gas stream, the second gas stream, or a combination thereof, or b) send to the CO2-to-CO conversion system, or c) combine with the CO-enriched outlet stream, or d) any combination thereof, and optionally recycling a second portion of the compressed bioreactor tail gas stream to combine with the CO-enriched outlet stream or the bioreactor, and optionally recycling a second portion of the compressed bioreactor tail gas stream to combine with the CO-enriched outlet stream or the bioreactor.The control process includes measuring data providing the H2:CO2 molar ratio or the H2:CO:CO2 molar ratio in the bioreactor tail gas stream, the bioreactor headspace, or both, to provide at least one measured H2:CO2 molar ratio or H2:CO:CO2 molar ratio; inputting the measured H2:CO2 molar ratio or H2:CO:CO2 molar ratio into a controller to compare the measured H2:CO2 molar ratio or H2:CO:CO2 molar ratio with a predetermined H2:CO2 molar ratio or H2:CO:CO2 molar ratio; and adjusting the flow rate of the first gas stream, the flow rate of the second gas stream, or both, in response to the difference between the measured H2:CO2 molar ratio or H2:CO:CO2 molar ratio and the predetermined H2:CO2 molar ratio or H2:CO:CO2 molar ratio to maximize the concentration of the inert component in the bioreactor tail gas stream, the bioreactor headspace, or both. The inert component may include nitrogen or methane, or both. The target maximum concentration of the inert component in the bioreactor tail gas stream or the bioreactor headspace is from about 70% to about 80% by volume.

[0014] In a gas fermentation process, at least a second portion of the first gas stream, at least a second portion of the second gas stream, or a combination thereof may be combined with the CO enriched outlet stream. Any portion of the first gas stream, the second gas stream, or a combination thereof may be compressed. The relative amounts of the first portion and the second portion of the compressed tail gas stream may be controlled using a control valve. At least a portion of the tail gas stream is passed to a CO2 to CO conversion system for the tail gas selected from a reverse water gas shift unit, a thermal catalytic conversion unit, a partial combustion unit, a plasma conversion unit, a gasification unit, or a reforming unit to produce a stream of CO enriched eluate, and the second stream of CO enriched eluate may be recycled to the bioreactor. The CO enriched outlet stream may contain an H2:CO:CO2 molar ratio of about 5:1:1, about 4.5:1:1, about 4.33:1:1, about 3:1:1, about 2:1:1, about 1:1:1 or about 1:3:1. The CO2 to CO conversion system may include at least one of a reverse water gas shift unit, a thermal catalytic conversion unit, a partial combustion unit, a reforming unit, or a plasma conversion unit. At least one fermentation product may be selected from ethanol, acetate, butanol, butyrate, 2,3-butanediol, lactate, butene, butadiene, methyl ethyl ketone, ethylene, acetone, isopropanol, lipid, 3-hydroxypropionate, isoprene, fatty acid, 2-butanol, 1,2-propanediol, hexanol, octanol, or 1-propanol. The first gas stream containing hydrogen may be produced by a hydrogen production source including at least one of a water electrolysis cell, a hydrocarbon reforming source, a hydrogen purification source, a solid biomass gasification source, a solid waste gasification source, a coal gasification source, a hydrocarbon gasification source, a methane pyrolysis source, a refinery tail gas production source, a plasma reforming reactor, a partial oxidation reactor, or any combination thereof.The second gas stream containing CO2 may be produced by a gas production source including at least one of a sugar-based ethanol production source, a first-generation corn ethanol production source, a second-generation corn ethanol production source, a sugarcane ethanol production source, a sucrose ethanol production source, a sugar beet ethanol production source, a molasses ethanol production source, a wheat ethanol production source, a grain-based ethanol production source, a starch-based ethanol production source, a cellulose-based ethanol production source, and a cement production source, a methanol synthesis source, an olefin production source, a steel production source, an alloy iron production source, a refinery tail gas production source, a secondary combustion gas production source, a biogas production source, a landfill production source, an ethylene oxide production source, a methanol production source, an ammonia production source, a mined CO2 production source, a natural gas treatment production source, a gasification source, an organic waste gasification source, direct air capture, or any combination thereof. At least one of the C1-fixing bacteria may be selected from Clostridium autoethanogenum, Clostridium ljungdahlii, or Clostridium ragsdalei.

[0015] The present disclosure involves a control process for an integrated process for the production of at least one fermentation product from a gas stream, the control process first including providing a gas fermentation process, the gas fermentation process obtaining a first gas stream containing hydrogen and a second gas stream containing CO2, and optionally, in a first compressor, compressing at least a portion of the first gas stream, at least a portion of the second gas stream, or any combination thereof to produce a compressed first gas stream, a compressed second gas stream, and / or a combination of the compressed first gas stream and the second gas stream; i) at least a portion of the first gas stream, or the compressed first gas stream, or both, with at least a portion of the second gas stream, or the compressed second gas stream, or both, or ii) the combination of the compressed first gas stream and the second gas stream, in a gas treatment zone including a gas component removal unit, a gas desulfurization / acid gas removal unit, or both, to produce a treated stream; forming CO in a CO2-to-CO conversion system operating under conditions to convert CO2 in at least a first portion of the treated stream to produce a CO-enriched outlet stream; fermenting the CO-enriched outlet stream in a bioreactor having a culture of one or more C1-fixing bacteria to produce a stream of at least one fermentation product and a bioreactor tail gas stream; and recycling the tail gas stream to the first compressor, the first gas stream, the second gas stream, or a combination of the first gas stream and the second gas stream.The control process includes measuring data providing the H2:CO2 molar ratio or the H2:CO:CO2 molar ratio in the bioreactor tail gas stream, the bioreactor headspace, or both, to provide at least one measured H2:CO2 molar ratio or H2:CO:CO2 molar ratio; inputting the measured H2:CO2 molar ratio or H2:CO:CO2 molar ratio into a controller to compare the measured H2:CO2 molar ratio or H2:CO:CO2 molar ratio with a predetermined H2:CO2 molar ratio or H2:CO:CO2 molar ratio; and adjusting the flow rate of the first gas stream, the flow rate of the second gas stream, or both, in response to the difference between the measured H2:CO2 molar ratio or H2:CO:CO2 molar ratio and the predetermined H2:CO2 molar ratio or H2:CO:CO2 molar ratio to maximize the concentration of the inert component in the bioreactor tail gas stream, the bioreactor headspace, or both. The inert component may include nitrogen or methane, or both. The target maximum concentration of the inert component in the bioreactor tail gas stream or the bioreactor headspace is from about 70% to about 80% by volume.

[0016] In a gas fermentation process, the CO-enriched outlet stream can be combined with at least a portion of the treated stream, or the first gas stream, or the second gas stream, or a combination of the first and second gas streams, or the compressed first gas stream, or the compressed second gas stream, or a combination of the compressed first and second gas streams, or any combination thereof. At least a portion of the tail gas stream can be passed to a CO2-to-CO conversion system for tail gas selected from a reverse water gas shift unit, a thermal catalytic conversion unit, a partial combustion unit, a plasma conversion unit, a gasification unit, or a reforming unit to produce a CO-enriched eluate stream, and the second CO-enriched eluate stream can be recycled to the bioreactor. The CO-enriched outlet stream may further contain hydrogen and CO2 and may have an H2:CO:CO2 molar ratio of about 5:1:1, about 4.5:1:1, about 4.33:1:1, or about 3:1:1, about 2:1:1, about 1:1:1, or about 1:3:1. The CO2-to-CO conversion system can include at least one of a reverse water gas shift unit, a thermal catalytic conversion unit, a partial combustion unit, a reforming unit, or a plasma conversion unit. The gas treatment zone can further include a deoxygenation unit, a catalytic hydrogenation unit, an adsorption unit, a thermal oxidizer, or any combination thereof. At least one fermentation product can be selected from ethanol, acetate, butanol, butyrate, 2,3-butanediol, lactate, butene, butadiene, methyl ethyl ketone, ethylene, acetone, isopropanol, lipid, 3-hydroxypropionate, isoprene, fatty acid, 2-butanol, 1,2-propanediol, hexanol, octanol, or 1-propanol. The first gas stream containing hydrogen may be produced by the hydrogen production source described above, and the second gas stream containing CO2 may be produced by the gas production source described above. At least one of the C1-fixing bacteria can be selected from Clostridium autoethanogenum, Clostridium ljungdahlii, or Clostridium ragsdalei.The CO concentrated outlet stream may contain hydrogen, and the process may further include separating hydrogen from the CO concentrated outlet stream and recycling the separated hydrogen and combining it with the tail gas stream or a compressor. The remaining portion of the CO concentrated outlet stream may be compressed after the separation of hydrogen. The tail gas stream may contain methane, and this process further includes passing a portion of the tail gas stream through a methane conversion unit to produce a methane conversion unit effluent and combining the methane conversion unit effluent with the tail gas stream. A stream containing oxygen may be generated from an oxygen source and passed to the methane conversion unit. A second gas stream containing hydrogen may be passed from a hydrogen source to the bioreactor, a second gas stream containing CO2 from a CO2 source may be passed to the bioreactor, or both. The second gas stream containing hydrogen from the hydrogen source may be passed to the bioreactor or combined with the CO concentrated outlet stream, the second gas stream containing CO2 from the CO2 source may be passed to the bioreactor or combined with the CO concentrated outlet stream, or any combination thereof may be performed. Combining the second gas stream containing hydrogen from the hydrogen source with the CO concentrated outlet stream, or combining the second gas stream containing CO2 from the CO2 source with the CO concentrated outlet stream, or both, may be achieved by mixing in a mixer. The ratio of the second gas stream containing hydrogen from the hydrogen source to the CO concentrated outlet stream entering the bioreactor may be from about 0:1 to about 4:1. The CO2 to CO conversion system may comprise a combustion heater having a burner, and at least a portion of the tail gas stream is recycled at least to the burner of the combustion heater. The CO2 to CO conversion system may include a steam generator for generating steam, or a water knockout unit for generating a water stream, or both. A portion of the CO concentrated outlet stream may be passed through an inoculator reactor, a buffer tank, or both, and passing may be directly through the inoculator reactor, the buffer tank, or both without intervening units.

[0017] The present disclosure involves a method for an integrated process for producing at least one fermentation product from a gas stream, the control process first comprising providing a gas fermentation process, the gas fermentation process comprising obtaining a first gas stream containing hydrogen and a second gas stream containing CO2, passing at least a portion of the second gas stream and optionally at least a portion of the first gas stream through a CO2-to-CO conversion system operating under conditions to produce a CO-enriched outlet stream, passing at least a portion of the first gas stream containing hydrogen and the CO-enriched outlet stream through a bioreactor having a culture of one or more C1-fixing bacteria and fermenting to produce a stream of at least one fermentation product and a bioreactor tail gas stream (the bioreactor optionally having a headspace), compressing the bioreactor tail gas stream to produce a compressed bioreactor tail gas stream, passing at least a first portion of the compressed bioreactor tail gas stream, in any order, through a gas desulfurization and / or acid gas removal unit, or a gas component removal unit, or both a gas desulfurization and / or acid gas removal unit and a gas component removal unit to produce a compressed treated bioreactor tail gas stream, recycling the compressed treated bioreactor tail gas stream to combine with the first gas stream, the second gas stream, or a combination thereof, or passing it through a CO2-to-CO conversion system, or combining it with the CO-enriched outlet stream, or any combination thereof, and optionally recycling a second portion of the compressed bioreactor tail gas stream to combine with the CO-enriched outlet stream or pass it through the bioreactor.The control process includes measuring data providing the H2:CO2 molar ratio or the H2:CO:CO2 molar ratio in the bioreactor tail gas stream, the bioreactor headspace, or both, to provide at least one measured H2:CO2 molar ratio or H2:CO:CO2 molar ratio; inputting the measured H2:CO2 molar ratio or H2:CO:CO2 molar ratio into a controller to compare the measured H2:CO2 molar ratio or H2:CO:CO2 molar ratio with a predetermined H2:CO2 molar ratio or H2:CO:CO2 molar ratio; and adjusting the flow rate of the first gas stream, the flow rate of the second gas stream, or both, in response to the difference between the measured H2:CO2 molar ratio or H2:CO:CO2 molar ratio and the predetermined H2:CO2 molar ratio or H2:CO:CO2 molar ratio to maximize the concentration of inert components in the bioreactor tail gas stream, the bioreactor headspace, or both. The inert component may include nitrogen or methane, or both. The target maximum concentration of the inert component in the bioreactor tail gas stream or the bioreactor headspace is from about 70% to about 80% by volume.

[0018] The present disclosure is also involved in a system for controlling the ratio of substrate gases provided to a bioreactor in a continuous gas fermentation process, the system comprising a first gas stream containing substrate H2 from an H2 source, a second gas stream containing substrate CO2 from an industrial process or a syngas process, a conversion zone in fluid communication with the second gas stream and optionally the first gas stream and having an eluate containing CO and CO2 for the conversion of CO2 to CO, at least one bioreactor having at least one C-1 fixing bacterium for gas fermentation in a nutrient solution, the bioreactor having a tail gas stream containing H2, CO2, and an inert component, a headspace containing H2, CO2, and an inert component, or both, the bioreactor being in fluid communication with an eluate containing CO and CO2, optionally the first gas stream, optionally the second gas stream, or any combination thereof, a sensor within the bioreactor tail gas stream or within the bioreactor headspace, or both, the sensor having the ability to measure the H2:CO2 molar ratio or the H2:CO:CO2 molar ratio of the bioreactor tail gas stream or the bioreactor headspace and provide the measured H2:CO2 molar ratio or the measured H2:CO:CO2 molar ratio, a controller that receives an input of the measured H2:CO2 molar ratio or the measured H2:CO:CO2 molar ratio, compares the measured H2:CO2 molar ratio to a predetermined H2:CO2 molar ratio or compares the measured H2:CO:CO2 molar ratio to a predetermined H2:CO:CO2 molar ratio, provides an output to adjust the flow rate of the first gas stream, the flow rate of the second gas stream, or both, in response to the difference between the measured H2:CO2 molar ratio and the predetermined H2:CO2 molar ratio or in response to the difference between the measured H2:CO:CO2 molar ratio and the predetermined H2:CO:CO2 molar ratio, and is configured to maximize the concentration of the inert component in the tail gas stream. The system may further include an output to the operating parameters of the CO2 to CO conversion zone to increase or decrease the relative amount of CO in the eluate containing CO and CO2. The CO2 to CO conversion system of the overall system may include at least one of a reverse water gas shift process, a CO2 electrolyzer, a thermal catalytic conversion process, a partial combustion process, or a plasma conversion process.The gas fermentation process of the system may further comprise a gas treatment zone in fluid communication with a first gas stream, a second gas stream, an eluate, or any combination thereof.

Brief Description of the Drawings

[0019]

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DETAILED DESCRIPTION OF THE INVENTION

[0020] FIGS. 1-13 further depict optional embodiments where at least a portion of the input stream to the CO2-to-CO conversion system bypasses around the CO2-to-CO conversion system instead of passing through it. The figures further show optional embodiments where at least a portion of the tail gas stream is passed through a second CO2-to-CO conversion system and the resulting effluent is passed to the bioreactor. The figures further show optional embodiments where at least a portion of the first gas stream containing H2 bypasses around the CO2-to-CO conversion system instead of passing through it. The flow scheme including any of the embodiments is controlled according to an embodiment of the present disclosure.

[0021] In a gas fermentation process, the integration of a gas production process that generates CO2, such as an industrial process or a syngas process, with a process for converting CO2 to CO, particularly the reverse water gas shift process, yields substantial benefits. This integration enables the use of CO2 as a feedstock even when a certain amount of CO is required in the fermentation process. By integrating the conversion of CO2 to CO, the feedstock CO2 can be converted to and recycled as CO in an amount suitable for fermentation.

[0022] In certain embodiments, the industrial process is selected from the manufacture of ferrous metal products such as steelmaking, non-ferrous product manufacturing, petroleum refining, power generation, carbon black production, paper and pulp manufacturing, ammonia production, methanol production, coke manufacturing, petrochemical production, carbohydrate fermentation, cement manufacturing, aerobic digestion, anaerobic digestion, catalytic processes, extraction of natural gas, cellulose fermentation, oil extraction, industrial processing of geological reservoirs, treatment of fossil resources such as natural gas, coal and petroleum, landfill operations, or any combination thereof. Examples of specific processing steps within the industrial process include catalyst regeneration, fluid catalytic cracking, and catalyst regeneration. Air separation and direct air capture are other suitable industrial processes. Examples in steel and alloy iron manufacturing include blast furnace gas, basic oxygen furnace gas, coke oven gas, direct reduction of iron furnace top gas, and residual gas from refined iron. Other common examples include combustion exhaust gases from combustion boilers and heaters, such as combustion boilers or heaters burning natural gas, petroleum, or coal, and the exhaust of gas turbines. In these embodiments, the substrate and / or C1 carbon source may be captured from the industrial process using any known method before it is released into the atmosphere.

[0023] The substrate and / or C1 carbon source may be synthesis gas known as syngas, which may be obtained from reforming, partial oxidation, plasma, or gasification processes. Examples of gasification processes include gasification of coal, refinery residues, petroleum coke, biomass, lignocellulosic materials, waste wood, black liquor, municipal solid waste, municipal liquid waste, industrial solid waste, industrial liquid waste, waste fuel, sewage, sewage sludge, sludge from wastewater treatment, landfill gas, biogas, for example, when biogas is added to enhance the gasification of another material, and the like. Examples of reforming processes include steam methane reforming, steam naphtha reforming, natural gas reforming, biogas reforming, landfill gas reforming, coke oven gas reforming, pyrolysis offgas reforming, ethylene production offgas reforming, naphtha reforming, and dry methane reforming. Examples of partial oxidation processes include thermal and catalytic partial oxidation processes, catalytic partial oxidation of natural gas, partial oxidation of hydrocarbons, partial oxidation of biogas, partial oxidation of landfill gas, or partial oxidation of pyrolysis offgas. Examples of municipal solid waste include tires, plastics, waste fuel, as well as fibers contained in shoes, apparel, fabrics, and the like. Municipal solid waste may simply be landfill-type waste, may be sorted, or may not be sorted. Examples of biomass may include lignocellulosic materials and microbial biomass. Lignocellulosic materials may include agricultural waste and forest waste.

[0024] C1 refers to a one-carbon molecule, such as CO, CO2, methane (CH4), or methanol (CH3OH), and the C1 carbon source refers to a one-carbon molecule that functions as a partial or sole carbon source for the microorganisms of the present disclosure. For example, the C1 carbon source may include one or more of CO, CO2, CH4, CH3OH, or formic acid (CH2O2). The C1 carbon source includes one or both of CO and CO2. The substrate is a carbon and / or energy source. Generally, the substrate is gaseous and includes a C1 carbon source, such as CO, CO2, and / or CH4. The substrate may further include other non-carbon components such as H2, N2, or electrons.

[0025] When discussing recirculation in this specification, the description of recirculating or passing a flow through a unit means including a direct and independent introduction of the flow into the unit, or a combination of inputs specific to the unit and the flow.

[0026] The gas production process that generates CO2 is an industrial process or a syngas process, and typically generates industrial gas or syngas having an effective ratio of CO2 by volume. Further, the industrial gas or syngas may contain some amounts of CO and / or CH4. The gas production process that generates CO2 is intended to include any industrial process or syngas process that generates CO2-containing gas as a desired final product or as a by-product in the production of one or more desired final products. Exemplary gas production processes that generate CO2 include sources such as sugar-based ethanol production sources, first-generation corn ethanol production sources, second-generation corn ethanol production sources, sugarcane ethanol production sources, sugarcane ethanol production sources, sugar beet ethanol production sources, molasses ethanol production sources, wheat ethanol production sources, cereal-based ethanol production sources, starch-based ethanol production sources, cellulose-based ethanol production sources, and sources having ethanol production from cement production sources, methanol synthesis sources, olefin production sources, steel production sources, alloy iron production sources, refinery tail gas production sources, secondary combustion gas production sources, biogas production sources, landfill production sources, ethylene oxide production sources, methanol production sources, ammonia production sources, mined CO2 production sources, natural gas treatment production sources, gasification sources, organic waste gasification sources, direct air capture, or any combination thereof. Some examples in steel and alloy iron production sources include blast furnace gas, basic oxygen furnace gas, coke oven gas, direct reduction of iron furnace top gas, electric arc furnace offgas, and residual gas from refined iron. Other common examples include combustion exhaust gases from combustion boilers and combustion heaters such as combustion boilers or heaters burning natural gas, oil, or coal, and exhaust gases from gas turbines.

[0027] Figure 1 depicts an integrated system having a flexible production platform and process for the production of at least one fermentation product from a gas stream according to an embodiment of the present disclosure. The process includes receiving a first gas stream containing hydrogen and a second gas stream containing CO2, and passing the streams through a conversion system for converting CO2 to CO. In Figure 1, the conversion system 125 for converting CO2 to CO is shown as a reverse water gas shift unit. The hydrogen production source 110 generates a first gas stream 120 containing hydrogen. In one embodiment, the hydrogen production source 110 is a water electrolyzer. The water stream 500 is introduced into the hydrogen production source 110 and may receive power from a power source (not shown), for example, 4.78 kwh / Nm 3 and convert water to hydrogen and oxygen according to the following stoichiometric reaction.

[0028]

Number

[0029] Water electrolysis technology is well known and exemplary processes include alkaline water electrolysis, proton exchange membrane (PEM) electrolysis, and solid oxide electrolysis. Suitable electrolyzers include alkaline electrolyzers, PEM electrolyzers, and solid oxide electrolyzers. The oxygen-enriched stream 115 containing oxygen produced as a byproduct of water electrolysis may be used for various purposes. For example, particularly when the gas production source 220 is selected to be a syngas production process including an oxygen-blown gasifier, at least a portion of the oxygen-enriched stream 115 may be introduced into the gas production source 220. Such use of the oxygen-enriched stream 115 reduces the need and associated costs for obtaining oxygen from an external source. As used herein, the term "enriched" means having a higher concentration after a process step compared to before the process step.

[0030] In certain embodiments, the hydrogen production source 110 can be selected from hydrocarbon reforming, hydrogen purification, solid biomass gasification, solid waste gasification, coal gasification, hydrocarbon gasification, methane pyrolysis, refinery tail gas production processes, plasma reforming reactors, partial oxidation reactors, or any combination thereof.

[0031] The gas production source 220 generates a second gas stream 140 containing CO2 from direct air capture, a CO2 generating industrial process, a syngas process, or any combination thereof. The first gas stream 120 containing hydrogen and the second gas stream 140 containing CO2 are passed to the CO2 to CO conversion system 125, either individually or in combination, to generate a CO enriched outlet stream 130. The gas composition of the combination of the first gas stream 120 containing hydrogen and the second gas stream 140 containing CO2 includes an H2:CO2 molar ratio of about 3:1 in one embodiment, about 2.5:1 in another embodiment, and about 3.5:1 in yet another embodiment, and the H2:CO molar ratio may be greater than about 5:1. The CO2 to CO conversion system 125 may be at least one unit selected from a reverse water gas shift unit, a thermal catalytic conversion unit, a partial combustion unit, a reforming unit, or a plasma conversion unit.

[0032] In certain embodiments, the CO2 to CO conversion system 125 is a reverse water gas shift unit. Reverse water gas shift (rWGS) technology is known and is used to produce carbon monoxide from carbon dioxide and hydrogen, with water as a byproduct. The temperature of the rWGS process is the main factor for the shift to occur. The reverse water gas shift unit may include a single stage reaction system or two or more reaction stages. Different stages may be carried out at different temperatures and may use different catalysts.

[0033] In another embodiment, the CO2-to-CO conversion system 125 involves thermal catalytic conversion, which involves using thermal energy as the driving force for the reaction to break the stable atomic and molecular bonds of CO2 and other reactants on the catalyst to produce CO. Since CO2 molecules are thermodynamically and chemically stable, a large amount of energy is required when CO2 is used as a single reactant. Therefore, in order to facilitate the thermodynamic process, other substances such as hydrogen are often used as co-reactants. Many catalysts are known for processes such as metals and metal oxides, as well as nano-sized catalytic metal-organic frameworks. Various carbon materials have been used as carriers for the catalyst.

[0034] In another embodiment, the CO2-to-CO conversion system 125 involves partial combustion, where oxygen supplies at least a portion of the oxidizer requirements for partial oxidation, and the reactant carbon dioxide and water are substantially converted to carbon monoxide and hydrogen.

[0035] In yet another embodiment, the CO2-to-CO conversion system 125 involves plasma conversion, which is a combination of plasma and catalyst, and is also called plasma catalyst. Plasma is an ionized gas composed of electrons, various types of ions, radicals, excited atoms, and molecules, as well as neutral ground-state molecules. The three most common types of plasma in the conversion of CO2 to CO include dielectric barrier discharge (DBD), microwave (MW) plasma, and gliding arc (GA) plasma. The advantages of selecting plasma conversion for the conversion of CO2 to CO include: (i) high process versatility, enabling different types of reactions such as the splitting of pure CO2 and the conversion of CO2 in the presence of a hydrogen source (such as CH4, H2, or H2O); (ii) low investment and operating costs; (iii) no need for rare earth metals; (iv) a convenient modular setting where the plasma reactor scales linearly with the plant output; and (v) the ability to easily combine with various types of renewable energy.

[0036] The figure is described when the CO2-to-CO conversion system 125 is selected to include at least one rWGS unit. The rWGS reaction produces CO and H2O by the reversible hydrogenation of CO2. Due to its chemical stability, CO2 is a relatively non-reactive molecule, and thus the reaction to convert it to the more reactive CO is energy-intensive.

[0037]

Number

[0038] Since the rWGS reaction is endothermic, it is thermodynamically favored by elevated temperatures. Typically, a temperature of about 500 °C is desirable to produce a significant amount of CO. In embodiments using higher temperatures, iron-based catalysts are often considered as one of the most effective active metals for higher temperatures due to their thermal stability and high oxygen mobility. In embodiments using lower temperatures, copper is often considered to be effective due to its enhanced adsorption of reaction intermediates. In some other embodiments, the rWGS catalyst selection includes Fe / Al2O3, Fe-Cu / Al2O3, Fe-Cs / Al2O3, Fe-Cu-Cs / Al2O3, or combinations thereof.

[0039] The CO2-to-CO conversion system 125 generates a CO-enriched outlet stream 130, for example, by utilizing rWGS technology. In some embodiments, the H2:CO molar ratio of the CO-enriched outlet stream 130 may be greater than about 3:1. Based on the stoichiometry of ethanol as a product and a CO2:CO molar ratio of 1:1, the H2:CO:CO2 molar ratio of the CO-enriched outlet stream 130 can be about 5:1:1.

[0040] In some examples, the rWGS reaction operates at a level such that the H2:CO molar ratio in the CO-enriched outlet stream 130 is a predetermined ratio, such as about 3:1 or less. Such CO levels may exceed the CO levels required for gas fermentation. Higher CO conversion than the CO2-to-CO conversion system 125 can result in suboptimal performance. Thus, the size of the CO2-to-CO conversion system 125 is designed to be larger than necessary. Such large systems are expensive. Thus, to avoid such large systems, at least a portion of the first gas stream containing hydrogen is directed to bypass 520 and not passed to the CO2-to-CO conversion system 125. The bypass stream 520 is combined with the CO-enriched outlet stream 130. Thus, the H2:CO ratio of line 130 delivered for fermentation may be adjusted to be greater than the predetermined ratio with an optimally sized CO2-to-CO conversion system 125. Similarly, a portion of the second gas stream 140 containing CO2 may be diverted around the bypass CO2-to-CO conversion system 125 using a second bypass stream 525. In this way, the amount of CO can be controlled without overdesigning the capacity of the CO2-to-CO conversion system 125.

[0041] If ethanol is not the intended fermentation product, the stoichiometry described above will be different. For example, if 2,3-butanediol (2,3-BDO) is the intended fermentation product, the H2:CO:CO2 molar ratio of the CO-enriched outlet stream 130 is about 4.5:1:1 based on the stoichiometry of 2,3-BDO, and the CO2:CO molar ratio is 1:1.

[0042]

Number

[0043] If acetone is the intended fermentation product, the H2:CO:CO2 molar ratio of the CO-enriched outlet stream 130 can be about 4.33:1:1 with a CO2:CO molar ratio of 1:1 based on the stoichiometry of acetone.

[0044]

Number

[0045] When the fermentation product intended is acetate, the H2:CO:CO2 molar ratio of the CO-enriched exit stream 130 can be about 3:1:1 with a CO2:CO molar ratio of 1:1, based on the stoichiometry of acetate.

[0046]

Number

[0047] When the fermentation product intended is sopropyl alcohol, the H2:CO:CO2 molar ratio of the CO-enriched exit stream 130 can be about 5:1:1 with a CO2:CO molar ratio of 1:1, based on the stoichiometry of sopropyl alcohol.

[0048]

Number

[0049] The CO-enriched exit stream 130 is passed to a bioreactor 142 containing a culture of one or more C1-fixing bacteria. The bioreactor 142 may be a fermentation system consisting of one or more vessels and / or towers or piping arrangements. Examples of bioreactors include membrane reactors such as continuous stirred tank reactors (CSTRs), immobilized cell reactors (ICRs), trickle bed reactors (TBRs), bubble columns, gas lift fermenters, static mixers, circulation loop reactors, hollow fiber membrane bioreactors (HFM BRs), or other devices suitable for gas-liquid contact. The bioreactor 142 may include multiple reactors or stages, either in parallel or in series. The bioreactor 142 may be a production reactor in which most of the fermentation product is produced.

[0050] The bioreactor 142 contains a culture of one or more C1-fixing microorganisms having the ability to produce one or more products from a C1 carbon source. "C1" refers to a one-carbon molecule, such as CO or CO2. "C1 carbon source" refers to a one-carbon molecule that functions as a partial or sole carbon source for the microorganism. For example, the C1 carbon source can include one or more of CO, CO2, or CH2O2. In some embodiments, the C1 carbon source can include one or both of CO and CO2. Typically, the C1-fixing microorganism is a C1-fixing bacterium. In one embodiment, the microorganism is derived from the C1-fixing microorganisms identified in Table 1. The microorganisms may be classified based on functional characteristics. For example, the microorganisms can be derived from C1-fixing microorganisms, anaerobic organisms, acetogens, ethanologens, and / or carboxydotrophs. Table 1 provides a representative list of microorganisms and identifies the functional characteristics of the microorganisms.

[0051]

Table 1

[0052] An "anaerobic organism" is a microorganism that does not require oxygen for growth. Anaerobic organisms can exhibit a negative reaction or can die if oxygen is present above a certain threshold. Typically, the microorganism is an anaerobic organism (i.e., anaerobic). In one embodiment, the microorganism is an anaerobic organism identified in Table 1 or is derived therefrom.

[0053] An "acetogen" is a microorganism that produces, or is capable of producing, acetate (or acetic acid) as a product of anaerobic respiration. Typically, acetogens are obligate anaerobic bacteria that use the Wood-Ljungdahl pathway as their major mechanism for energy conservation and for the synthesis of acetyl-CoA-derived products such as acetyl-CoA and acetate (Ragsdale, Biochim Biophys Acta, 1784: 1873-1898, 2008). Acetogens use the acetyl-CoA pathway as a mechanism for (1) the reductive synthesis of acetyl-CoA from CO2, (2) terminal electron acceptance, an energy conservation process, and (3) the fixation (assimilation) of CO2 in the synthesis of cellular carbon (Drake, Acetogenic Prokaryotes, In: The Prokaryotes, 3rd edition, p. 354, New York, N.Y., 2006). All naturally occurring acetogens are C1-fixing, anaerobic, autotrophic, and non-methanotrophic. In one embodiment, the microorganism is an acetogen. In one embodiment, the microorganism is an acetogen identified in Table 1 or derived therefrom.

[0054] More broadly, the microorganism can be derived from any genus or species identified in Table 1. For example, the microorganism may be a member of the genus Clostridium. In one embodiment, the microorganism of the present disclosure is derived from a cluster of Clostridia including the species Clostridium autoethanogenum, Clostridium ljungdahlii, and Clostridium ragsdalei. These species were first reported and characterized by Abrini, Arch Microbiol, 161: 345-351, 1994 (Clostridium autoethanogenum), Tanner, Int J System Bacteriol, 43: 232-236, 1993 (Clostridium ljungdahlii), and Huhnke, WO2008 / 028055 (Clostridium ragsdalei). The microorganism of the present disclosure can also be derived from an isolate or variant of Clostridium autoethanogenum, Clostridium ljungdahlii, or Clostridium ragsdalei. Examples of isolates and variants of Clostridium autoethanogenum include JA1-1 (DSM10061) (Abrini, Arch Microbiol, 161: 345-351, 1994), LBS1560 (DSM19630) (WO 2009 / 064200), and LZ1561 (DSM23693).Examples of Clostridium ljungdahlii isolates and variants include ATCC 49587 (Tanner, Int J Syst Bacteriol, 43: 232-236, 1993), PETCT (DSM13528, ATCC 55383), ERI-2 (ATCC 55380) (U.S. Patent No. 5,593,886), C-01 (ATCC 55988) (U.S. Patent No. 6,368,819), 0-52 (ATCC 55989) (U.S. Patent No. 6,368,819), and OTA-1 (Tirado-Acevedo, Production of bioethanol from synthesis gas using Clostridium ljungdahlii, PhD thesis, North Carolina State University, 2010). Examples of Clostridium ragsdalei isolates and variants include PI 1 (ATCC BAA-622, ATCC PTA-7826) (WO 2008 / 028055).

[0055] The microorganisms of the present disclosure can be cultured to produce one or more products. For example, Clostridium autoethanogenum can produce ethanol (WO 2007 / 117157), acetate (WO 2007 / 117157), butanol (WO 2008 / 115080 and WO 2012 / 053905), butyrate (WO 2008 / 115080), 2,3 - butanediol (WO 2009 / 151342), lactate (WO 2011 / 112103), butene (WO 2012 / 024522), butadiene (WO 2012 / 024522), methyl ethyl ketone (2 - butanone) (WO 2012 / 024522 and WO 2013 / 185123), ethylene (WO 2012 / 026833), acetone (WO 2012 / 115527), isopropanol (WO 2012 / 115527), lipids (WO 2013 / 036147), 3 - hydroxypropionate (3 - HP) (WO 2013 / 180581), isoprene (WO 2013 / 180584), fatty acids (WO 2013 / 191567), 2 - butanol (WO 2013 / 185123), 1,2 - propanediol (WO 2014 / 0369152), and 1 - propanol (WO 2014 / 0369152), or can be engineered to produce them. In addition to one or more target products, the microorganisms of the present disclosure can also produce ethanol, acetate, and / or 2,3 - butanediol. In certain embodiments, the microbial biomass itself can be considered a product.

[0056] The culture is generally maintained in an aqueous medium containing sufficient nutrients, vitamins, and / or minerals to allow for the growth of the microorganisms. The aqueous medium may be an anaerobic microbial medium such as a minimal anaerobic microbial growth medium. Suitable media are known in the art.

[0057] The culture and / or fermentation may desirably be carried out under conditions appropriate for the production of the target product. Typically, the culture / fermentation is carried out under anaerobic conditions. Reaction conditions to be considered include pressure (or partial pressure), temperature, gas flow rate, liquid flow rate, medium pH, medium redox potential, agitation rate (when using a continuous stirred tank reactor), inoculation level, maximum gas substrate concentration to ensure that the gas in the liquid phase is not limiting, and maximum product concentration to avoid product inhibition. Specifically, the introduction rate of the substrate may be controlled to ensure that the concentration of the gas in the liquid phase is not limiting, since the product can be consumed by the culture under gas-limiting conditions.

[0058] Operating the bioreactor at elevated pressure allows an increased rate of gas mass transfer from the gas phase to the liquid phase, thus providing a benefit. Also, since a given gas conversion rate is in part a function of the substrate holding time, the conversion rate defines the volume of the bioreactor required. The use of a pressurization system can significantly reduce the volume of the bioreactor required and, as a result, the capital cost of the culture / fermentation facility. This means that the holding time, defined as the liquid volume in the bioreactor divided by the inlet gas flow rate, can be reduced when the bioreactor is maintained at a pressure elevated above atmospheric pressure. The optimal reaction conditions depend in part on the particular microorganism used. In certain embodiments, the fermentation operates at a pressure higher than atmospheric pressure.

[0059] The target product may be separated from the fermentation broth using any method or combination of methods known in the art, including, for example, fractional distillation, evaporation, pervaporation, gas stripping, phase separation, such as extraction separation including liquid-liquid extraction. In certain embodiments, the target product is recovered from the fermentation broth by first separating the microbial cells from the broth and then separating the target product from the aqueous residue, with a portion of the broth being continuously withdrawn from the bioreactor. Alcohol and / or acetone can be recovered, for example, by distillation. The acid can be recovered, for example, by adsorption on activated carbon. The separated microbial biomass may be recycled to the bioreactor. The solution remaining after the target product has been removed may also be recycled to the bioreactor. Additional nutrients may be added to the recycled solution to replenish the medium before it is returned to the bioreactor.

[0060] The CO enriched outlet stream 130 is introduced into the bioreactor 142 and fermented to produce a tail gas stream 160 that may contain any of the products described above and a stream 150 of the fermentation product. The term tail gas refers to the gases and vapors that are typically released from an industrial process to the atmosphere after all reactors and treatments have been performed. The tail gas stream 160 is ultimately recycled and combined with a second gas stream 140 containing CO2 for introduction into the CO2 to CO conversion system 125. The tail gas stream 160 may contain some CO2 produced, for example, by reaction during fermentation.

[0061]

Number

[0062] Recycling the CO2 present in the tail gas stream 160 from the bioreactor 142 to the CO2 to CO conversion system 125 increases the carbon dioxide recovery efficiency of the overall process. The tail gas stream 160 depleted in CO may contain less than about 5 mol% CO. In some embodiments, the H2:CO2 molar ratio of the tail gas stream 160 is about 3:1 or less.

[0063] The tail gas stream 160 can contain various components that are preferably removed before further processing. In these examples, the tail gas stream 160 removes one or more components to produce a desulfurized and / or acid gas treated tail gas stream 340, which may be combined with a second gas stream 140 containing CO2. One or more components that can be removed from the tail gas stream 160 can include sulfur-containing compounds (including but not limited to hydrogen sulfide (H2S), carbon disulfide, and / or sulfur dioxide), aromatic compounds, alkynes, alkenes, alkanes, olefins, nitrogen compounds, phosphorus-containing compounds, particulate matter, solids, oxygen, oxides, halogenated compounds, silicon-containing compounds, carbonyls, metals, alcohols, esters, ketones, peroxides, aldehydes, ethers, tars, methanethiol, ammonia, diethylamine, triethylamine, acetic acid, methanol, ethanol, propanol, butanol and higher alcohols, naphthalene, or combinations thereof. These components can be removed by conventional removal modules well known in the art, such as hydrolysis modules, acid gas removal modules, deoxygenation modules, catalytic hydrogenation modules, particulate removal modules, chloride removal modules, tar removal modules, and / or hydrogen cyanide removal modules, and combinations thereof. In a specific example, at least one component removed from the tail gas stream includes a sulfur-containing compound such as hydrogen sulfide that can be produced, introduced, and / or concentrated by a fermentation process. Hydrogen sulfide may be a catalyst inhibitor in the system 125 for the conversion of CO2 to CO using rWGS technology and a catalyst.

[0064] The tail gas stream 160 is passed through a gas component removal unit 170. The gas component removal unit 170 removes components other than sulfur-containing compounds or acid gas components. In some embodiments, the component to be removed is water. Since the water gas shift reaction produces water, it is advantageous to limit the amount of water supplied to the water gas shift reactor. Removing water improves the water balance throughout the process. In some embodiments, the component to be removed is a hydrocarbon. The gas component removal unit 170 may include a plurality of sub-modules for removing a plurality of components other than sulfur-containing compounds. In some embodiments, a liquid scrubber is used to remove ethanol, which includes other soluble components and higher alcohols. In these embodiments, the gas component removal unit 170 may operate to capture and recover fermentation products contained in the tail gas stream 160. Volatile organic compounds may also be removed within the gas component removal unit 170. Other components that can be removed by the gas component removal unit 170 include, for example, nitrogen monoxide species such as hydrogen cyanide (HCN), ammonia (NH3), nitrogen oxides (NO x ), in addition to other known enzyme-inhibiting gases such as acetylene (C2H2), ethylene (C2H4), ethane (C2H6), BTEX (benzene, toluene, ethylbenzene, xylene, (BTEX), and / or oxygen (O2).

[0065] The resulting processed tail gas stream 185 is passed to a first compressor 190, where a compressed processed gas stream 200 is generated, which is passed to the gas desulfurization / acid gas removal unit 180. In some embodiments, the compressor 190 is positioned upstream of the gas component removal unit 170 between the bioreactor 142 and the gas component removal unit 170 to compress the tail gas stream 160 before it passes through the gas component removal unit 170. Generally, the compressor 190 operates at a pressure of about 3 Barg to about 10 Barg. The compressed processed tail gas stream 200 is passed through the gas desulfurization / acid gas removal unit 180 to produce a desulfurized and / or acid gas treated tail gas stream 340. Gas desulfurization / acid gas removal unit 180. Sulfur-containing compounds and / or acid gases are removed because they act as inhibitors within the CO2 to CO conversion system 125 using the rWGS technology by suppressing the activity of the rWGS catalyst. Many commercial desulfurization technologies cannot efficiently remove sulfur in the form of COS, but can better handle sulfur in the form of hydrogen sulfide. In one embodiment, the gas desulfurization / acid gas removal unit 180 operates to convert compounds such as carbonyl sulfide COS to hydrogen sulfide H2S by hydrolysis according to the following reaction.

[0066]

Number

[0067] Hydrolysis can be achieved with a metal oxide catalyst or an alumina catalyst to convert COS to H2S. In some embodiments, two or more desulfurization operations, such as an iron sponge followed by a metal oxide catalyst, may be used. In certain other embodiments, the gas desulfurization / acid gas removal unit 180 may remove hydrogen sulfide using a zinc oxide (ZnO) catalyst. In other embodiments, pressure swing adsorption (PSA) is utilized to remove acid gas by adsorption through a suitable adsorbent in a fixed bed contained within a vessel under high pressure. In yet other embodiments, caustic washing is used for gas desulfurization. Caustic washing may include passing the compressed treated tail gas stream 200 through a caustic solution such as NaOH to remove sulfur-containing compounds. The removal of hydrogen sulfide by caustic washing can be represented as follows.

[0068]

Number

[0069] The desulfurized and / or acid gas treated tail gas stream 340 exiting the gas desulfurization / acid gas removal unit 180 may be combined with a second gas stream 140 containing CO2 and recycled to the CO2 to CO conversion system 125. Alternatively, instead of the desulfurized and / or acid gas treated tail gas stream 340 being passed through to be combined with the second gas stream 140 containing CO2, an alternative desulfurized and / or acid gas treated tail gas stream 345 is combined with the first gas stream 120 containing hydrogen.

[0070] A portion of the compressed treated tail gas stream 200 may be passed to the bioreactor 142 instead of being combined with the CO enriched outlet stream 130 and passed to the gas desulfurization / acid gas removal unit 180. Such recycling benefits the growth of microorganisms as they consume sulfur to produce amino acids such as methionine and cysteine. As a result, the sulfur dosing requirement to the bioreactor 142 is reduced by the recycling of sulfur as a portion of the compressed treated tail gas stream 200.

[0071] In an optional embodiment where the gas production source 220 includes the production of biogas, a portion of the second gas stream 140 containing CO2 is passed to an optional biogas reformer 230. Biogas means a gas produced by the anaerobic digestion of organic matter such as manure, sewage sludge, municipal solid waste, biodegradable waste, or any other biodegradable raw material. Biogas mainly consists of methane and carbon dioxide. Generally, in a biogas reformer, steam reforming of CO2 and methane is combined to produce a syngas stream.

[0072]

Number

[0073] With respect to FIG. 1, the flow 240 of the biogas reformer effluent containing CO and H2 produced by the biogas reformer 230 is combined with the CO enriched outlet stream 130 and may operate to improve the H2:CO ratio for many fermentation processes.

[0074] In one embodiment, at least a portion of the tail gas stream 160 passes through an optional second CO2 to CO conversion system 510 which may be a reverse water gas shift unit, a thermal catalytic conversion unit, a partial combustion unit, a plasma conversion unit, a gasification unit, or a reforming unit. The tail gas stream 160 may have low CO but have residual H2 and CO2. By passing at least a portion of the tail gas stream 160 through an optional second CO2 to CO conversion system 510 and recycling the second CO2 to CO conversion system effluent 512 to the bioreactor 142, the H2:CO ratio in the bioreactor 142 can be reduced. Such a reduction in the H2:CO ratio in the bioreactor 142 can benefit the product selectivity and can result in an increase or acceleration of microbial growth. It is noted that the second CO2 to CO conversion system effluent 512 may be recycled to be combined with the stream 130 instead of being passed independently to the bioreactor 142 (not shown).

[0075] In one embodiment, an optional additional stream containing hydrogen 430 generated from hydrogen production source 110 is passed to bioreactor 142 or the CO enriched outlet stream 130, thus bypassing the CO2 to CO conversion system 125. The additional stream containing hydrogen 430 may pass through without intervening processing units. Microbial fermentation of CO in the presence of H2 can result in substantially complete carbon transfer to products such as alcohol, but if sufficient H2 is not present, only a portion of the available CO is converted to products while another portion is converted to CO2 according to the following equation: 6CO + 3H2O → C2H5OH + 4CO2. Thus, providing sufficient hydrogen to bioreactor 142 may be beneficial in some embodiments. By employing a bypass of the additional stream containing hydrogen 430 that is passed to bioreactor 142 or the CO enriched outlet stream 130 without passing through the CO2 to CO conversion system 125, control of the amount of hydrogen directed to the unit is possible at different times during overall process execution. For example, during startup, less hydrogen may be required in the bioreactor including any inoculum, thereby gaining benefit from a feed rich in CO during startup. However, towards the end of operation, less CO may be required in the bioreactor and a larger relative amount of H2 may be used. This can be particularly beneficial during turndown, or during the inoculation stage (the main bioreactor receives less CO than the inoculation bioreactor), or when using a buffer tank. With the bypass, the control can vary the H2:CO ratio of the feed to the CO2 to CO conversion system 125, to the bioreactor 142, or both. With the bypass, it is also possible to control to vary the H2:C (hydrogen:carbon) with respect to the CO2 to CO conversion system 125, the bioreactor 142, or both.

[0076] The use of the CO2-to-CO conversion system 125 and the recirculation of CO2 from the bioreactor 142 through the CO2-to-CO conversion system 125 to provide an environment rich in CO to the bioreactor 142 can be beneficial to the product selectivity for improved products in a gas environment with a high ratio of CO. Such an example is the production of ethanol. Another advantage is that the microbial growth of certain microorganisms having the Wood-Ljungdahl pathway may increase. This is because when these microorganisms consume a higher concentration of CO, the biological water-gas shift of the Wood-Ljungdahl pathway is improved.

[0077] Figure 2 shows an integrated system for the production of at least one fermentation product from a gas stream, according to another embodiment of the present disclosure. A hydrogen production source 110 generates a first gas stream 120 containing hydrogen. A gas production source 220, which can be a direct air capture or an industrial process that generates CO2, generates a second gas stream 140 containing CO2. The first gas stream 120 containing hydrogen and the second gas stream 140 containing CO2 are combined to form a composite feed stream 250, which is passed to a CO2-to-CO conversion system 125. The gas composition in the composite feed stream 250 includes an H2:CO2 molar ratio of about 3:1 in one embodiment, about 2.5:1 in another embodiment, about 3.5:1 in yet another embodiment, and greater than about 5:1 in still another embodiment.

[0078] In one embodiment, the CO2-to-CO conversion system 125 employs rWGS technology. In the CO2-to-CO conversion system 125, CO2 is reacted to produce a CO-enriched outlet stream 130. The molar ratios of the components in the stream are as discussed in FIG. 1. As shown in FIG. 2, in one embodiment, at least a portion of the feed stream 250 is optionally bypassed around the CO2-to-CO conversion system 125 with a bypass stream 520. The bypass stream 520 is combined with the CO-enriched outlet stream 130. The advantages of the bypass stream 520 are as described in FIG. 1. The CO-enriched outlet stream 130 is passed to a bioreactor 142 having a culture of one or more C1-fixing microorganisms. The culture is fermented to produce one or more fermentation products 150 and a tail gas stream 160. The tail gas stream 160 depleted in CO may contain less than about 5 mol% CO. In some embodiments, the H2:CO2 molar ratio of the tail gas stream 160 is about 3:1 or less.

[0079] The tail gas stream 160 is passed to a first compressor 190 to produce a compressed tail gas stream 202. The compressed tail gas stream 202 is recycled for combination with the CO-enriched outlet stream 130. Optionally, a small first purge stream 204 of the tail gas stream 160 or a small second purge stream 206 of the compressed tail gas stream 202 may be removed to control the accumulation of nitrogen, methane, argon, helium, or other inert components.

[0080] As in FIG. 1, in one embodiment, at least a portion of the tail gas stream 160 passes through an optional second CO2-to-CO conversion system 510, and the second CO2-to-CO conversion system eluate 512 is recycled to the bioreactor 142 or the CO-enriched outlet stream. Also as in FIG. 1, the second CO2-to-CO conversion system eluate 512 may be recycled for combination with the stream 130 instead of being passed independently to a bioreactor 142 (not shown).

[0081] Figure 3 shows another embodiment similar to Figure 2, except that the compressed tail gas stream 202 is passed to the gas desulfurization / acid gas removal unit 180, and the resulting desulfurized and / or acid gas treated tail gas stream 340 is passed to the CO2 to CO conversion system 125. The gas compositions in the combined feed streams 250 within the CO enriched outlet stream 130 and within the tail gas stream 160 are as described in Figures 1 and 2. The optional bypass related embodiments are as described in Figure 2.

[0082] Figure 4 shows another embodiment similar to Figures 2 and 3. The tail gas stream 160 is passed to a first compressor 190, and the resulting compressed tail gas stream 202 is passed to an optional control valve 550. The optional control valve 550 is used to control the relative portion of the compressed tail gas stream 202 that is directed to the gas treatment zone 182 or combined with the CO enriched outlet stream 130. The gas treatment zone 182 is shown as including a gas component removal unit 170 and a gas desulfurization / acid gas removal unit 180. However, both units are not required in all embodiments, and the gas treatment zone 182 may include only one of the gas component removal unit 170 or the gas desulfurization / acid gas removal unit 180. Further, the units of the gas treatment zone 182 may be in any order. The treated tail gas stream 185 produced from the gas treatment zone 182 is added to the combined feed stream 250 and passed to the CO2 to CO conversion system 125. The optional control valve 550 may be adjusted to divide the compressed tail gas stream 202 at different rates based on the phase of the fermentation at that time. For example, during the startup fermentation phase, an increase in the CO demand within the bioreactor 142 may be achieved by adjusting the control valve 550 to direct more of the compressed tail gas stream 202 and combining it with the CO enriched outlet stream 130 rather than the gas treatment zone 182. On the other hand, as the fermentation in the bioreactor 142 transitions to the steady state phase, a decrease in the CO demand of the bioreactor 142 may be achieved by adjusting the control valve 550 to reduce the flow rate of the compressed tail gas stream 202 and combining it with the CO enriched outlet stream 130 rather than the gas treatment zone 182. In another example, when the H2 utilization during fermentation is low, e.g., less than 70%, the control valve 550 may be adjusted to direct more of the compressed tail gas stream 202 and combine it with the CO enriched outlet stream 130 rather than the gas treatment zone 182. As shown, the control valve 550 is used to achieve dynamic control of the H2:CO ratio provided to the bioreactor 142 based on the CO and / or H2 requirements during fermentation. The gas composition is described in relation to Figures 2 and 3, and the optional bypass embodiment is as described in Figure 2.

[0083] Figure 5 is similar to Figure 4 with the addition of a second compressor 192. The combined feed stream 250 is passed to the second compressor 192 to produce a compressed combined feed stream 260. The gas composition of the compressed combined feed stream 260 is as described above. The compressed combined feed stream 260 is combined with the treated tail gas stream 185 and passed to the CO2 to CO conversion system 125 to produce a CO enriched outlet stream 130. The gas compositions of the CO enriched outlet stream 120 and the tail gas stream 160 are as described above. Optional control valve 550 and bypass embodiments are as described above.

[0084] FIG. 6 shows an embodiment in which both the composite feed stream 250 and the tail gas stream 160 are passed to the first compressor 190. The first compressor 192 provides a compressed stream 270 that is passed to the gas treatment zone 182. The gas treatment zone is as described above. Of course, some gas treatment modules may be added to or removed from the gas treatment zone 182 based on the actual gas composition. For example, in some embodiments, the compressed stream 270 may contain acetylene (C2H2) that can act as a microbial inhibitor in fermentation. To remove acetylene, a catalytic hydrogenation module can be included in the gas treatment zone 182. Catalytic hydrogenation involves adding hydrogen in the presence of a hydrogenation catalyst, such as those containing nickel, palladium, platinum. The choice of hydrogenation catalyst depends on the specific gas composition and operating conditions of the system. In certain embodiments, alumina-supported palladium (Pd / Al2O3) is used as the catalyst. An example of such a catalyst is BASF™ R0-20 / 47. In other embodiments, the gas composition of the compressed stream 270 may contain benzene, ethylbenzene, toluene, and xylene (BETX) that can inhibit fermentation. Accordingly, a BETX removal module may be added to the gas treatment zone 182. An exemplary BETX removal module may involve the adsorption of BETX components using one or more activated carbon beds. Another exemplary BTEX removal module includes vent gas incineration, which is a thermal oxidation process where the BTEX components are combusted at a temperature above about 650°C. The treated stream 290 is passed to the CO2-to-CO conversion system 125. The gas compositions of the various streams are shown above. The bypass embodiments are as described above.

[0085] Figure 7 is similar to Figure 6, but the first gas stream 120 containing hydrogen may already be pressurized by the hydrogen source 110 and thus need not be passed to the first compressor 190. The first gas stream 120 containing hydrogen may be combined with the second gas stream 140 containing CO2 before, after, or both before and after the gas treatment zone 182 without passing through the first compressor 190. The gas composition in the gas stream 290 before introduction into the CO2-to-CO conversion system 125 includes an H2:CO2 molar ratio of about 3:1 in one embodiment, about 2.5:1 in another embodiment, about 3.5:1 in yet another embodiment, and greater than about 5:1 in yet another embodiment. The gas compositions of the CO enriched outlet stream 130 and the tail gas stream 160 are as described above.

[0086] FIG. 7 also shows an embodiment that cannot be employed, instead of employing a stream containing hydrogen 430 produced from hydrogen production source 110 that is optional and does not pass through the CO2-to-CO conversion system 125, regardless of the pressure provided by hydrogen source 110. The additional stream containing hydrogen 430 may be passed to bioreactor 142 or may be combined with the CO enriched outlet stream 130. Optionally, the stream containing hydrogen 430 produced from hydrogen production source 110 can be compressed to the target pressure. Separating the supply of CO2 from the supply of H2 can increase the control over the amount of hydrogen directed to bioreactor 142 at different times throughout the process implementation. For example, during startup, less hydrogen may be required in the bioreactor, including any inoculum, such that a benefit is obtained from a supply rich in CO during startup. However, towards the end of implementation, less CO may be required in the bioreactor and a greater relative amount of H2 may be used. This can be particularly beneficial during turndown, or during the inoculation stage (the main bioreactor receives less CO than the inoculation bioreactor), or when using a buffer tank. By means of a bypass, the control can vary the H2:CO ratio of the supply to the CO2-to-CO conversion system 125, to the bioreactor 142, or to both. One target H2:CO:CO2 ratio for the bioreactor can be 1:3:1.

[0087] In FIG. 8, a portion of the second gas stream 140 containing CO2 is passed to the first compressor 190, and another portion of the second gas stream 140 containing CO2 is combined with the first gas stream 120 containing hydrogen and passed to the gas treatment zone 182, thereby bypassing the first compressor 190. Some gas production sources 220 may provide oxygen as a component of the second gas stream 140 containing CO2. However, for some microorganisms, oxygen may be a microbial inhibitor, and the oxygen content in the second gas stream 140 containing CO2 may need to be reduced to an acceptable level. In these situations, the gas treatment zone 182 may further include a deoxygenation module. The deoxygenation module may employ a catalytic process in which oxygen is reduced to either CO2 or water. In certain embodiments, the catalyst used in the deoxygenation module contains copper. Examples of such catalysts are BASF PURISTAR™ R 3.15 or BASF CU 0226S. The deoxygenation process is exothermic, and the heat generated can be used within the overall process, such as preheating the gas prior to the endothermic reaction in the CO2-to-CO conversion system 125 including the rWGS technology. The gas compositions of the various streams are as described above. The bypass embodiments are as described above.

[0088] FIG. 9 shows an embodiment in which the CO enriched outlet stream 130 to the CO2 to CO conversion system 125 is passed through a hydrogen separation unit 330 before being passed to the bioreactor 142. The hydrogen separation unit 330 can involve membrane separation technology or pressure swing adsorption technology. When hydrogen is separated from the CO enriched outlet stream 130, the amount of CO in the H2:CO ratio of the hydrogen separation unit eluate 350 increases and this is passed to the bioreactor 142. The separated hydrogen stream 344 produced by the hydrogen separation unit 330 is either separately recycled to the first compressor 190 (not shown) or combined with the tail gas stream 160 and also recycled to the first compressor 190. FIG. 9 shows an embodiment in which the first gas stream 120 containing hydrogen is already at a sufficient pressure and thus bypasses the first compressor 190 and combines with the compressed stream 270 before the gas treatment zone 182. If the first gas stream 120 containing hydrogen is not yet pressurized, at least a portion of the first gas stream 120 containing hydrogen can pass through the first compressor 190. The gas composition of the treated stream 290 before introduction into the CO2 to CO conversion system 125 includes an H2:CO2 molar ratio of about 3:1 in one embodiment, about 2.5:1 in another embodiment, about 3.5:1 in yet another embodiment, and greater than about 5:1 in yet another embodiment. The H2:CO gas composition in the CO enriched outlet stream 130 is as described above. In one embodiment, the gas composition in the hydrogen separation zone eluate 350 includes an H2:CO molar ratio greater than about 1:1 but not exceeding about 5:1 and an H2:CO:CO2 molar ratio of about 5:1:1, where ethanol is the product as described above and further for other products as described above. The gas composition of the tail gas stream 160 is as described above. The bypass embodiment is generally as described above.

[0089] FIG. 10 is similar to FIG. 9 with the addition of a hydrogen separation unit vent compressor 370. When the hydrogen separation unit 330 uses pressure swing adsorption, the hydrogen separation unit vent 350 is often below the pressure required for the bioreactor 142. The hydrogen separation unit vent compressor 370 provides further compression of the hydrogen separation unit vent to achieve the pressure required for introduction into the bioreactor 142. The gas composition in the treated stream 290 before introduction into the CO2 to CO conversion system 125 and at the CO enriched outlet stream 130 is as described above. The gas composition of the hydrogen separation unit vent before introduction into the vent compressor 370 of the hydrogen eluate zone includes an H2:CO molar ratio of greater than about 1:1 but not exceeding about 5:1, and the H2:CO:CO2 molar ratio of the gas stream 365 may be about 5:1:1 for ethanol as a product as described above, and further as described above for other products. The gas composition in the tail gas stream 160 is as described above. The bypass embodiment is as described above.

[0090] Figure 11 is similar to Figure 6, except that the CO enriched outlet stream 130 from the CO2 to CO conversion system 125 further includes methane from the hydrogen source 110 or as a byproduct of the CO2 to CO conversion system 125 that includes the rWGS technology. Over time, methane from either or both of these sources can accumulate in the bioreactor tail gas stream 160. When the methane concentration in the bioreactor tail gas stream 160 increases to a threshold limit, for example, greater than 10 mol% and perhaps greater than 50 mol%, at least a portion of the tail gas stream 160 is passed to the methane conversion unit 400 as the tail gas purge 390. An optional oxygen source 410 can provide a stream 420 containing optional oxygen to the methane conversion unit 400. In some embodiments, the oxygen source 410 of the methane conversion unit 400 can be a water electrolyzer, whereby oxygen is a byproduct. The methane conversion unit 400 produces at least CO2 by the oxidation of methane by the reaction CH4 + 2O2 → CO2 + 2H2O, produces a flow 421 of methane conversion eluate that includes at least CO2 and further comprises CO and H2, which can be combined with the tail gas stream 160 and passed to the first compressor 190. The methane conversion unit 400 can be a methane reforming unit, a methane steam reforming unit, a partial oxidation unit, an autothermal reforming unit, an oxidation unit, a combustion unit, a biogas reforming unit, or a gasification unit. When the methane conversion unit 400 is involved, it involves the steam reforming of methane represented by the following equation:

[0091]

Number

[0092] The stream 420 containing oxygen can also be burned in a heater burner to generate steam or to heat the methane conversion unit. The methane conversion unit can involve autothermal reforming (ATR) that uses oxygen or carbon dioxide as a reactant with methane to form syngas. The reaction can occur in a single reactor where methane is partially oxidized. The reaction can be described by the following equation.

[0093]

Number

[0094] The gas compositions of the treated stream 290 and the CO enriched outlet stream 130 are as described above. The gas composition of the tail gas stream 160 or the tail gas purge 390 typically contains less than about 5 mol% CO. In some embodiments, the H2:CO2 molar ratio of the tail gas stream 160 or the tail gas purge 390 is about 3:1 or less, and the accumulated methane is greater than about 5 mol%. The bypass embodiment is as described above.

[0095] In one embodiment, as described above, an optional additional stream containing hydrogen 430 generated from the hydrogen production source 110 is passed directly to the bioreactor 142. Microbial fermentation of CO in the presence of H2 can result in substantially complete carbon transfer to products such as alcohols, but if sufficient H2 is not present, only a portion of the available CO is converted to products while another portion is converted to CO2 by the following equation: 6CO + 3H2O → C2H5OH + 4CO2. Thus, providing sufficient hydrogen to the bioreactor 142 can be beneficial in some embodiments. In another embodiment, an optional additional stream containing CO2 440 generated from the gas production source 220 is passed directly to the bioreactor 142. Such an arrangement can be beneficial for maintaining the CO2 partial pressure in the CO2 depletion zone of the bioreactor 142.

[0096] FIG. 12 is directed to an embodiment in which the CO2 to CO conversion system 125 is selected to be an rWGS system and additional apparatus of the rWGS system is specifically illustrated. The hydrogen production source 110 and the first gas stream 120, and the gas production source 220 and the second gas stream containing CO2, and the composite feed stream 250 are all as described above. In addition to the gas treatment zone 182 and the treated stream 290, the bioreactor 142, the fermentation product stream 150 and the tail gas stream 160 are as described above.

[0097] The processed stream 290 is introduced into the preheater 560 where it is heated via indirect heat exchange with the rWGS reactor effluent 588 to provide a preheated stream 562. The preheated stream 562 is further passed to an electric heater 564 to produce an electrically heated stream 566 and then further heated in a fired heater 568 to produce a fully heated stream 570. Different heating modes are employed to maximize the available energy to reach the target temperature of the rWGS reactor. The heat of the stream that needs to be cooled is transferred to the stream that needs to be heated, and the combustible components of the waste are burned in a burner to produce a hot stream that requires high temperature.

[0098] The fully heated stream 570 is introduced into an rWGS reactor 571 which can be a single-stage or multi-stage reactor system. In the rWGS reactor 571, at least a portion of the CO2 present in the fully heated stream 570 is converted to CO. Thus, the rWGS reactor effluent 588 is enriched in CO compared to the fully heated stream 570. Since the rWGS reactor effluent is at the temperature of the rWGS reactor 571, it contains available heat that can be used to heat another stream and is thus passed to the preheater 560 for indirect heat exchange with the processed stream 290. The heat-exchanged rWGS reactor effluent 563 is then passed from the preheater 560 to a heat recovery / steam generator 572 to further recover available heat. A cooling water stream 574 is passed to the heat recovery / steam generator 572 to receive the exchange of available heat from the heat-exchanged rWGS reactor effluent 563 and produce a steam stream 576. This can be used elsewhere in the overall process or in another process. The resulting heat-depleted stream 578 is passed to a water knockout unit 580 to produce a stream containing water 584 and a water-depleted stream 582. The steam containing water 584 may be directed to any part of the process or another process that requires water. The water-depleted stream 582 is passed to an air cooler 586 to provide a CO-enriched outlet stream 130.

[0099] The CO enriched outlet stream 130 may be split into portions, with a first portion passed to an optional mixer 590 or, in the absence of an optional mixer 590, passed to the bioreactor 142. An optional second portion of the CO enriched outlet stream 130 may be passed to another unit such as a buffer tank (not shown) or an inoculator reactor which may or may not be part of the bioreactor 142. Having a storage quantity of the CO enriched outlet stream 130 is advantageous for periods when the supply of the gas stream containing CO2 drops. If the hydrogen requirements of the inoculator reactor are lower compared to the bioreactor, it may be advantageous to pass the second portion of the CO enriched outlet stream 130 to the inoculator before adding any additional hydrogen to the CO enriched outlet stream 130. An optional third portion of the CO enriched outlet stream 130 may be recycled to the combustion heater 568 and burned within the burner of the combustion heater 568 to provide heat. This embodiment is particularly advantageous during start-up when the bioreactor 142 is still upstream of the flow for consumption of CO within the CO enriched outlet stream 130.

[0100] In some embodiments, it is advantageous to adjust and control the amount of hydrogen provided to the bioreactor 142 by providing an additional stream containing hydrogen 430 from the hydrogen production source 110 that is passed to the mixer 590. In the mixer 590, the CO enriched outlet stream 130 is mixed with an additional stream 430 containing hydrogen to produce the bioreactor feed stream 592. The ratio of the additional stream 430 containing hydrogen to the CO enriched outlet stream 130 from the hydrogen source is from about 0:1 to about 4:1. The bioreactor feed stream is provided to the bioreactor 142 and the fermentation product stream 150 is produced similar to the bioreactor tail gas stream 160. The bioreactor tail gas stream 160 may be split in part and recycled to different locations within the process. Where the bioreactor tail gas is routed often depends on the current operating state of the process. For example, if the bioreactor 142 is operated in a mode that produces substantial CO2, at least a portion of the bioreactor tail gas 160 may be recycled to the gas treatment zone 182 or the CO to CO2 conversion system 125 for conversion of CO2 to CO. At any point in time, a portion of the bioreactor tail gas 160 may be supplied to the burner of the combustion heater 568 for combustion and heat generation. Using at least a portion of the bioreactor tail gas 160 in this way for combustion is particularly advantageous in embodiments where the bioreactor tail gas 160 contains methane. It is contemplated that biogas from the wastewater treatment system may be combined with the bioreactor tail gas 160 and used for combustion and heat of the combustion heater 568. Further, it is contemplated that biogas from the wastewater treatment system may be recycled or recycled directly to the bioreactor.

[0101] Figure 13 is directed to an embodiment in which a separate hydrogen stream does not pass through the CO to CO2 conversion system but is mixed downstream of the CO to CO2 conversion system to form a feed stream to the bioreactor. The separate hydrogen stream 602 may be obtained from a separate second hydrogen source 600 (not shown) or from the hydrogen source 110. The separate hydrogen stream 602 containing hydrogen may be passed through an optional hydrogen stream gas treatment zone 603 to produce a treated hydrogen stream 604 containing hydrogen. The hydrogen stream gas treatment zone 603 may include a gas component removal unit and / or a gas desulfurization / acid gas removal unit. Both units are not required in all embodiments, and the hydrogen gas treatment zone 603 may include only one of the gas component removal unit or the gas desulfurization / acid gas removal unit. Further, the units within the hydrogen stream gas treatment zone 603 may be in any order. The treated hydrogen gas stream 604 produced from the hydrogen stream gas treatment zone 603 passes through the mixer 590 and is mixed with the treated CO enriched outlet stream 186 to produce a bioreactor feed stream 592.

[0102] The hydrogen production source 110, the first gas stream 120 containing hydrogen, the gas production source 220, the second gas stream 140 containing CO2, and the composite feed stream 250 are all as described above. The gas treatment zone 182 and the treated stream 290, as well as the CO to CO2 conversion system 125, the CO enriched outlet stream 130, the mixer 590, the mixed stream 592, the bioreactor 142, the fermentation product stream 150 and the tail gas stream 160 are as described above, but may have different ratios of H2 and CO2. The second gas treatment zone 183 and the third gas treatment zone 187 are as described for the gas treatment zone 182.

[0103] Referring to the first gas stream 120 containing hydrogen from the hydrogen production source 110 and the second gas stream 140 containing CO2 from the gas production source 220, different ratios of hydrogen and CO2 in the streams are useful in different aspects of the overall process operation. For example, the molar ratio of H2 in the first gas stream 120 containing hydrogen to CO2 in the second gas stream 140 containing CO2 (H2:CO2) can be about 1:1 in one embodiment, about 2:1 in another embodiment, and about 3:1 in yet another embodiment. In an embodiment where the H2:CO2 molar ratio is 1:1, the first gas stream 120 containing hydrogen may have twice the volume of a separate hydrogen stream 602 obtained from a separate second hydrogen source 600. In an embodiment where the H2:CO2 molar ratio is 2:1, the first gas stream 120 containing hydrogen may have half the volume of a separate hydrogen stream 602 obtained from a separate second hydrogen source 600. In an embodiment where the H2:CO2 molar ratio is 3:1, the first gas stream 120 containing hydrogen provides all the hydrogen required and a separate hydrogen stream 602 obtained from a separate second hydrogen source 600 is not used. Effectively, different amounts of hydrogen may bypass the CO to CO2 conversion system 125 through the use of the hydrogen stream 602 / treated hydrogen gas stream 604. In one embodiment, in addition to the hydrogen in the first gas stream 120 containing hydrogen, the sum of the hydrogen in the separate hydrogen stream 602 provides sufficient hydrogen to result in an H2:CO2 molar ratio of 3:1, and the CO2 is measured within the second gas stream 140 containing CO2.

[0104] The tail gas stream 160 may be recycled to the bioreactor 142 or to the CO to CO2 conversion system 125. Optionally, the tail gas stream 160 may pass through a third gas treatment zone 187 to produce a treated tail gas stream 185, which may then pass through the CO to CO2 conversion system 125. The second gas treatment zone 183 may optionally separate a portion of the CO enriched outlet stream 130, which can be recycled to the CO to CO2 conversion system 125 as stream 181.

[0105] Figures 1 - 13 further illustrate elements of the control system of the present disclosure. One or more sensors 117 are used to measure the H2:CO2 molar ratio of the tail gas 160 of the bioreactor 142. As another method, or additionally, one or more sensors 117 are used to measure the H2:CO2 molar ratio of the headspace of the bioreactor 142. The sensor 117 may be an analytical instrument such as a gas chromatograph, a probe, an indicator, or other such measuring device. The measurement value providing the H2:CO2 molar ratio from the sensor 117 is input into the controller 115 using a wireless connection 118 or a wired connection (not shown). The controller may be a feedback loop controller. The controller 115 may be a distributed control system (DCS) type controller. Within the controller 115, the measured data providing the H2:CO2 molar ratio from the sensor 117 is compared with a predetermined H2:CO2 molar ratio. The predetermined H2:CO2 molar ratio is selected by the operator and is based on a number of variables. The predetermined H2:CO2 molar ratio is expected to be different for different operations. The controller 115 then adjusts the flow rates of the first gas stream 140, the second gas stream 120, an additional stream containing hydrogen 430, or any additional stream containing CO2 440 (as shown in FIG. 11), or any combination thereof, in response to the difference between the measured H2:CO2 molar ratio and the predetermined H2:CO2 molar ratio, to maximize the concentration of the inert component in the tail gas stream. The adjustment of the flow rate can be achieved using a flow controller 116 that receives a wireless signal 118 or a wired (not shown) signal from the controller 115. The inert component may be a component that does not participate in the fermentation or participates only in negligible amounts. In this way, the ratio of the gas substrates provided to the bioreactor in the gas fermentation process is controlled. In another embodiment, the sensor 117 may measure data to provide the H2:CO:CO2 molar ratio of the tail gas 160 and / or the bioreactor headspace, and the control process may proceed as described above using the measured H2:CO:CO2 molar ratio and the predetermined H2:CO:CO2 molar ratio.The purpose of the control is to maximize the concentration of nitrogen in the tail gas stream and / or the bioreactor headspace, or for some microorganisms, inert components such as methane. For example, in one embodiment, the target maximum concentration of inert components in the bioreactor tail gas stream or the bioreactor headspace is from about 70% to about 80% by volume.

[0106] Sensor 117 may acquire data continuously or periodically, and the frequency may vary according to different situations such as the performance of the bioreactor, the operating stage of the bioreactor, the situation where a hydrogen source or a C1 source is involved, operating conditions, environmental conditions, and others. Similarly, a predetermined molar ratio may also vary over time. The predetermined or target molar ratio can be adjusted according to situations such as the performance of the bioreactor, the operating stage of the bioreactor, the situation where a hydrogen source or a C1 source is involved, operating conditions, environmental conditions, and the like.

[0107] Similarly, in order to maximize the concentration of inert components in the tail gas stream, the frequency of the controller that operates to adjust the flow rate of one or more streams in response to the difference between the measured molar ratio and the predetermined or target molar ratio can also vary. In situations where the operation fluctuates rapidly, the adjustment needs to be performed frequently, and in steady-state operation, the adjustment may not be performed as frequently.

[0108] Examples of possible analytical instruments include gas chromatographs with various detection modes, as well as gas analyzers such as non-dispersive infrared (NDIR), electrochemical, dew point, and thermal conductivity.

[0109] All references, including the published documents, patent applications, and patents listed in this specification, are incorporated herein by reference as if each reference were individually and specifically indicated to be incorporated by reference. The references cited in this specification are not recognized as part of the common general knowledge in any country's field of endeavor.

[0110] The description of value ranges in this specification is merely intended to serve as an ellipsis for individually referring to each individual value within the range, and each individual value is incorporated into the specification as if it were individually listed herein. For example, unless otherwise indicated, any concentration range, percentage range, ratio range, integer range, size range, or thickness range should be understood to include any integer value within the recited range, and, where appropriate, fractions thereof (such as tenths and hundredths of an integer). Unless otherwise indicated, ratios are molar ratios and percentages are weight-based.

[0111] All methods described herein can be performed in any suitable order, unless otherwise indicated in this specification or unless clearly contrary to the context. Any examples provided herein or the use of exemplary language such as "such as" are merely intended to better clarify the disclosure and do not limit the scope of the disclosure unless otherwise claimed. No language in this specification should be construed as indicating any non-claimed element essential to the practice of the disclosure.

[0112] Preferred embodiments of the present disclosure are described herein. Variations of these embodiments may be apparent to those skilled in the art upon reading the foregoing description, and the adoption of such variations is intended to be within the scope since the present disclosure can be practiced in ways other than those specifically described herein. Accordingly, the present disclosure includes all modifications and equivalents of the subject matter recited in the claims as permitted by applicable law. Further, any combination of the above elements in all possible variations thereof is included by the present disclosure unless otherwise indicated in this specification or unless clearly contrary to the context. It should be noted that the present invention includes the following aspects. [Aspect 1] A method for continuously controlling the ratio of input gases provided to a bioreactor in a continuous gas fermentation process, comprising: a. Providing a gas fermentation process, comprising: i. A first gas stream containing H 2 from an H 2 source; ii. A second gas stream containing CO 2 from an industrial process or a syngas process; iii. A CO conversion zone having a CO-enriched eluate, in fluid communication with the second gas stream and optionally the first gas stream, and containing CO and CO 2 ; 2 iv. At least one bioreactor having at least one C-1 fixing bacterium for gas fermentation in a nutrient solution, the bioreactor having a product stream containing at least one product, an outlet gas stream containing H , CO 2 , and inert components, an H 2 , CO 2 , and inert component-containing headspace, or both, and the bioreactor being in fluid communication with the CO-enriched eluate, optionally the first gas stream, optionally the second gas stream, or any combination thereof; 2 b. Measuring the H :CO:CO 2 molar ratio of the bioreactor outlet gas stream or the bioreactor headspace to provide a measured H 2 :CO:CO 2 molar ratio; 2 c. Inputting the measured H :CO:CO 2 molar ratio into a controller and comparing the measured H 2 :CO:CO 2 molar ratio with a predetermined H 2 :CO:CO 2 molar ratio; 2 d. Adjusting the flow rate of the first gas stream, the flow rate of the second gas stream, or both, in response to the difference between the measured H :CO:CO 2 molar ratio and the predetermined H 2 :CO:CO 2 molar ratio to maximize the concentration of inert components in the bioreactor outlet gas stream. 2 A method as described above. [Aspect 2] The method according to Aspect 1, further comprising: e) Compressing at least a portion of the first gas stream, at least a portion of the second gas stream, or any combination thereof in a first compressor to produce a compressed first gas stream, a compressed second gas stream, and / or a combination of the compressed first gas stream and the second gas stream; f) g) Passing the outlet gas stream through the first compressor, the gas treatment zone, the CO 2 The method according to aspect 1, further comprising recirculating to the conversion system from CO, the first gas stream, the second gas stream, or the combination of the first gas stream and the second gas stream. [Aspect 3] In combination with the stream of the CO-enriched eluate, i. the treated stream, or ii. the first gas stream, or iii. the second gas stream, or iv. the combination of the first gas stream and the second gas stream, or v. the compressed first gas stream, or vi. the compressed second gas stream, or vii. the combination of the compressed first gas stream and the second gas stream, or viii. the method according to aspect 2, comprising at least a portion of any combination thereof. [Aspect 4] The first gas stream containing H 2 is passed to the bioreactor without passing through the conversion zone from CO to CO, and the method comprises 2 e) compressing the bioreactor outlet gas stream to produce a compressed bioreactor outlet gas stream; f) passing at least a first portion of the compressed bioreactor outlet gas stream, in any order, i. through a gas desulfurization and / or acid gas removal unit, or ii. through a gas component removal unit, or iii. through both the gas desulfurization and / or acid gas removal unit and the gas component removal unit to produce a compressed treated bioreactor outlet gas stream; g) recirculating the compressed treated bioreactor outlet gas stream to i. combine with the first gas stream, the second gas stream, or a combination thereof, or ii. pass to a conversion system from CO to CO, or iii. combine with the stream of the CO-enriched eluate, or iv. any combination thereof, and 2 h) optionally, recirculating a second portion of the compressed bioreactor outlet gas stream to combine with the stream of the CO-enriched eluate or the bioreactor. The method according to aspect 1, further comprising. [Aspect 5] The method according to aspect 1, further comprising combining at least a second portion of the first gas stream, at least a second portion of the second gas stream, or a combination thereof with the stream of the CO-enriched eluate. [Aspect 6] The method according to aspect 1, further comprising passing at least a second portion of the first gas stream, at least a second portion of the second gas stream, or a combination thereof through the bioreactor. [Aspect 7] ​ ​ ​ The method according to aspect 1, further comprising compressing any portion of the first gas stream, the second gas stream, or a combination thereof. [Aspect 8] The method according to aspect 1, further comprising using a control valve to control the relative amounts of the first portion of the compressed outlet gas stream and the second portion of the compressed outlet gas stream. [Aspect 9] At least a portion of the outlet gas stream is passed through a CO to CO conversion system selected from a water-gas shift unit, a thermal catalytic conversion unit, a partial combustion unit, a plasma conversion unit, a gasification unit, or a reforming unit to produce a stream of CO-enriched eluate, and further comprising recycling the second stream of CO-enriched eluate to the bioreactor. 2 The method according to aspect 1. [Aspect 10] The stream of CO-enriched eluate has an H 2 :CO:CO 2 molar ratio of about 5:1:1, about 4.5:1:1, about 4.33:1:1, or about 3:1:1, about 2:1:1, about 1:1:1, or about 1:3:1. [Aspect 11] The CO 2 to CO conversion system includes at least one of a water-gas shift unit, a thermal catalytic conversion unit, a partial combustion unit, a reforming unit, or a plasma conversion unit. [Aspect 12] The product stream includes at least one fermentation product selected from ethanol, acetate, butanol, butyrate, 2,3-butanediol, lactate, butene, butadiene, methyl ethyl ketone, ethylene, acetone, isopropanol, lipid, 3-hydroxypropionate, isoprene, fatty acid, 2-butanol, 1,2-propanediol, hexanol, octanol, or 1-propanol. [Aspect 13] The hydrogen source includes at least one of a water electrolysis cell, a hydrocarbon reforming source, a hydrogen purification source, a solid biomass gasification source, a solid waste gasification source, a coal gasification source, a hydrocarbon gasification source, a methane pyrolysis source, a refinery tail gas production source, a plasma reforming reactor, a partial oxidation reactor, or any combination thereof. [Aspect 14] The industrial process or syngas process is selected from a sugar-based ethanol production source, a first-generation corn ethanol production source, a second-generation corn ethanol production source, a sugarcane ethanol production source, a sucrose ethanol production source, a sugar beet ethanol production source, a molasses ethanol production source, a wheat ethanol production source, a grain-based ethanol production source, a starch-based ethanol production source, a cellulose-based ethanol production source, and a cement production source, a methanol synthesis source, an olefin production source, a steel production source, an alloy iron production source, a refinery tail gas production source, a secondary combustion gas production source, a biogas production source, a landfill production source, an ethylene oxide production source, a methanol production source, an ammonia production source, a mined CO 2 production source, a natural gas treatment production source, a gasification source, an organic waste gasification source, direct air capture, or any combination thereof, the method according to embodiment 1. [Embodiment 15] The method according to embodiment 1, wherein at least one C1-fixing bacterium is selected from Clostridium autoethanogenum, Clostridium ljungdahlii, or Clostridium ragsdalei. [Embodiment 16] A system for controlling the ratio of substrate gases provided to a bioreactor in a continuous gas fermentation process, comprising: a. A first gas stream containing substrate H 2 from an H 2source; b. A second gas stream containing substrate CO 2 from an industrial process or syngas process; c. A conversion zone from CO 2 to CO having an eluate containing CO and CO 2 , in fluid communication with the second gas stream and optionally the first gas stream; d. At least one bioreactor having at least one C-1 fixing bacterium for gas fermentation in a nutrient solution, the bioreactor having a tail gas stream containing H 2 , CO 2 , and inert components, a headspace containing H 2 , CO 2 , and inert components, or both, the bioreactor being in fluid communication with the eluate containing CO and CO 2 , optionally the first gas stream, optionally the second gas stream, or any combination thereof; e. A sensor within the bioreactor tail gas stream or within the bioreactor headspace, or both, measuring the H 2 :CO 2 molar ratio or the H 2 :CO:CO 2 molar ratio of the bioreactor tail gas stream or the bioreactor headspace to obtain the measured H 2 :CO 2 molar ratio or measured H 2 :CO:CO 2 a sensor capable of providing a molar ratio, and f. a controller, wherein the measured H 2 :CO 2 molar ratio or the measured H 2 :CO:CO 2 receives an input of the molar ratio and measures the H 2 :CO 2 compares the molar ratio with a predetermined H 2 :CO 2 molar ratio, or measures the H 2 :CO:CO 2 compares the molar ratio with a predetermined H 2 :CO:CO 2 molar ratio, provides an output, and measures the flow rate of the first gas stream, the flow rate of the second gas stream, or both, based on the measured H 2 :CO 2 molar ratio and the predetermined H 2 :CO 2 molar ratio, or measures the H 2 :CO:CO 2 molar ratio and the predetermined H 2 :CO:CO 2 molar ratio difference, and adjusts to maximize the concentration of the inert component in the tail gas stream, a controller configured as such, a system comprising. [Aspect 17] In order to increase or decrease the relative amount of CO in the eluate containing CO and CO 2 , further includes an output to the operating parameters of the conversion zone from CO to CO 2 , the system according to aspect 16. [Aspect 18] The conversion system from CO 2 to CO includes at least one of a reverse water gas shift process, a CO 2 electrolytic cell, a thermal catalytic conversion process, a partial combustion process, or a plasma conversion process, the system according to aspect 16. [Aspect 19] The gas fermentation process further comprises a gas treatment zone in fluid communication with the first gas stream, the second gas stream, the eluate, or any combination thereof, the system according to aspect 16. [Aspect 20] The gas fermentation process further comprises at least one compressor in fluid communication with the first gas stream, the second gas stream, the eluate, or any combination thereof, the system according to aspect 16. [Aspect 21] The gas fermentation process further comprises a methane conversion zone in fluid communication with the bioreactor tail gas stream, and the methane reforming zone comprises an eluate conduit in fluid communication with the conversion zone from CO 2 to CO, the system according to aspect 16.

Claims

1. A method for continuously controlling the ratio of input gases provided to a bioreactor in a continuous gas fermentation process, comprising: a. providing a gas fermentation process, said gas fermentation process comprising: i. a first gas stream containing H ２ from an H ２ source; and ii. a second gas stream containing CO ２ from an industrial process or a synthesis gas process; and iii. a CO2-to-CO conversion zone in fluid communication with said second gas stream, or said second gas stream and said first gas stream, wherein a CO-enriched eluate containing CO and CO ２ is produced in said CO2-to-CO conversion zone, said CO ２ to CO conversion zone; and iv. at least one bioreactor having at least one C-1 fixing bacterium for gas fermentation in a nutrient solution, said bioreactor having a product stream containing at least one product, an outlet gas stream containing H ２ , CO ２ , and inert components, an overhead space containing H ２ , CO ２ , and inert components, or both, said bioreactor being in fluid communication with said CO-enriched eluate, said first gas stream, said second gas stream, or combinations thereof; b. compressing and recycling said outlet gas stream to said CO2-to-CO conversion zone, said first gas stream, said second gas stream, or a combination of said first gas stream and said second gas stream; ２ c. measuring the H ２ :CO:CO ２ molar ratio in said bioreactor outlet gas stream or said bioreactor overhead space to provide a measured H ２ :CO:CO ２ molar ratio; and d. said measured H ２ :CO:CO​ ２ Input the molar ratio into a controller, and the measured H ２ :CO:CO ２ molar ratio to a predetermined H ２ :CO:CO ２ molar ratio and compare them, and e. Adjust the flow rate of the first gas stream, the flow rate of the second gas stream, or both, in response to the difference between the measured H ２ :CO:CO ２ molar ratio and the predetermined H ２ :CO:CO ２ molar ratio to maximize the concentration of inert components in the bioreactor outlet gas stream. A method comprising.

2. Further comprising, in a first compressor, compressing at least a portion of the first gas stream, at least a portion of the second gas stream, or a combination thereof to produce a compressed first gas stream, a compressed second gas stream, and / or a combination of the compressed first gas stream and the second gas stream. The method according to claim 1.

3. Before passing the second gas stream, or the second gas stream and the first gas stream, to the CO ２ conversion zone from CO to CO, i. At least a portion of the first gas stream or the compressed first gas stream or both, and at least a portion of the second gas stream or the compressed second gas stream or both, or ii. The combination of the compressed first gas stream and the second gas stream, Further comprising treating in a gas treatment zone comprising a gas component removal unit, a gas desulfurization / acid gas removal unit, or both. The method according to claim 1 or 2.

4. Before passing it to the bioreactor, passing the CO ２ concentration eluate from the CO conversion zone from CO to CO through a hydrogen separation unit. The method according to claim 1.

5. The method according to claim 1, 2, or 4, further comprising the step of recycling the separated hydrogen stream from the hydrogen separation unit to the first compressor or combining it with the outlet gas stream.

6. The method according to claim 1, further comprising the step of combining at least a portion of the first gas stream, at least a portion of the second gas stream, or a combination thereof with the stream of the CO enriched eluate.

7. The method according to claim 1, further comprising the step of passing at least a portion of the first gas stream, at least a portion of the second gas stream, or a combination thereof through the bioreactor.

8. The method according to claim 1, further comprising the step of compressing a portion of the first gas stream, a portion of the second gas stream, or a combination thereof.

9. At least a portion of the outlet gas stream is passed through a system for converting CO in the outlet gas selected from a reverse water gas shift unit, a thermal catalytic conversion unit, a partial combustion unit, a plasma conversion unit, a gasification unit, or a reforming unit to produce a stream of CO enriched eluate, and further comprising the step of recycling the second stream of CO enriched eluate to the bioreactor. The method according to claim 1. ２ from CO to CO

10. The method according to claim 1, wherein the stream of CO enriched eluate contains an H ２ :CO:CO ２ molar ratio of about 5:1:1, about 4.5:1:1, about 4.33:1:1, or about 3:1:1, about 2:1:1, about 1:1:1, or about 1:3:

1.

11. The CO ２ to CO conversion system includes at least one of a reverse water gas shift unit, a thermal catalytic conversion unit, a partial combustion unit, a reforming unit, or a plasma conversion unit. The method according to claim 1.

12. The method according to claim 1, wherein the product stream comprises at least one fermentation product selected from ethanol, acetate, butanol, butyrate, 2,3 - butanediol, lactate, butene, butadiene, methyl ethyl ketone, ethylene, acetone, isopropanol, lipid, 3 - hydroxypropionate, isoprene, fatty acid, 2 - butanol, 1,2 - propanediol, hexanol, octanol, or 1 - propanol.

13. The method according to claim 1, wherein the hydrogen source comprises at least one of an electrolytic water cell, a hydrocarbon reforming source, a hydrogen purification source, a solid biomass gasification source, a solid waste gasification source, a coal gasification source, a hydrocarbon gasification source, a methane pyrolysis source, a refinery tail gas production source, a plasma reforming reactor, a partial oxidation reactor, or a combination thereof.

14. The industrial process or syngas process is selected from at least one of a sugar - based ethanol production source, a first - generation corn ethanol production source, a second - generation corn ethanol production source, a sugarcane ethanol production source, a sucrose ethanol production source, a sugar beet ethanol production source, a molasses ethanol production source, a wheat ethanol production source, a grain - based ethanol production source, a starch - based ethanol production source, a cellulose - based ethanol production source, and a cement production source, a methanol synthesis source, an olefin production source, a steel production source, an alloy iron production source, a refinery tail gas production source, a secondary combustion gas production source, a biogas production source, a landfill production source, an ethylene oxide production source, a methanol production source, an ammonia production source, a mined CO ２ production source, a natural gas treatment production source, a gasification source, an organic waste gasification source, direct air capture, or a combination thereof, according to claim 1.

15. The method according to claim 1, wherein the at least one C1 - fixing bacterium is selected from Clostridium autoethanogenum, Clostridium ljungdahlii, or Clostridium ragsdalei.

16. A system for controlling the ratio of substrate gas provided to a bioreactor in a continuous gas fermentation process, a. A first gas stream containing substrate H ２ from a source, ２ and, b. A second gas stream containing substrate CO ２ from an industrial process or a syngas process, c. A CO2 to CO conversion zone in fluid communication with the second gas stream, or the second gas stream and the first gas stream, wherein an eluate containing CO and CO ２ is produced in the CO2 to CO conversion zone, the CO ２ to CO conversion zone, d. At least one bioreactor having at least one C-1 fixing bacterium for gas fermentation in a nutrient solution, the bioreactor having a tail gas stream containing H ２ CO ２ and an inert component, a headspace containing H ２ CO ２ and an inert component, or both, the bioreactor being in fluid communication with the eluate containing CO and CO ２ the first gas stream, the second gas stream, or a combination thereof, the bioreactor, e. A compressor for compressing the tail gas stream, the compressor being in fluid communication with the CO ２ to CO conversion zone, the first gas stream, the second gas stream, or a combination of the first gas stream and the second gas stream, f. A sensor within the bioreactor tail gas stream or within the bioreactor headspace, or both, the H ２ :CO ２ molar ratio or the H ２ :CO:CO ２ molar ratio in the bioreactor tail gas stream or the bioreactor headspace is measured to obtain the measured H ２ :CO ２ molar ratio or the measured H ２ :CO:CO ２The sensor capable of providing a molar ratio, g. A controller that receives the measured H ２ :CO ２ molar ratio or the measured H ２ :CO:CO ２ receives the input of the molar ratio, and compares the measured H ２ :CO ２ molar ratio with a predetermined H ２ :CO ２ molar ratio, or compares the measured H ２ :CO:CO ２ molar ratio with a predetermined H ２ :CO:CO ２ molar ratio, provides an output, and adjusts the flow rate of the first gas stream, the flow rate of the second gas stream, or both, in response to the difference between the measured H ２ :CO ２ molar ratio and the predetermined H ２ :CO ２ molar ratio, or adjusts in response to the difference between the measured H ２ :CO:CO ２ molar ratio and the predetermined H ２ :CO:CO ２ molar ratio, and is configured to maximize the concentration of the inert component in the tail gas stream, the controller The system comprising.

17. CO and CO ２ to increase or decrease the relative amount of CO in the eluate containing, the CO ２ The system according to claim 16, further comprising an output to the operating parameters of the conversion zone from CO to CO.

18. The CO ２ to CO conversion system includes at least one of a reverse water gas shift process, a CO ２ electrolytic cell, a thermal catalytic conversion process, a partial combustion process, or a plasma conversion process, the system according to claim 16.

19. The system according to claim 16, wherein the gas fermentation process further comprises a gas treatment zone in fluid communication with the first gas stream, the second gas stream, the eluate, or a combination thereof.

20. The system according to claim 16, wherein the gas fermentation process further comprises at least one compressor in fluid communication with the first gas stream, the second gas stream, the eluate, or a combination thereof.

21. The gas fermentation process further comprises a methane conversion zone in fluid communication with the bioreactor tail gas stream, and the methane reforming zone comprises an eluate conduit in fluid communication with a conversion zone for converting CO ２ to CO. The system according to claim 16.

22. In fluid communication with the CO ２ to CO conversion system, and further comprising a hydrogen separation unit for separating hydrogen from the eluate comprising CO and CO ２ The system according to claim 16.

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