Method for producing ethylene using carbon dioxide

Abstract

A method comprising: (i) providing a gas stream containing more than 1 volume% of carbon dioxide; (ii) providing water; (iii) converting the carbon dioxide and water into an organic intermediate and oxygen gas in the presence of light; (iv) separating the oxygen gas from the organic intermediate; and (v) converting the organic intermediate into ethylene and carbon dioxide after the step of separating the oxygen gas from the organic intermediate.

Description

Technology Field

[0001] This application claims priority to U.S. provisional application serial number 62 / 992,689 filed on March 20, 2020, and U.S. provisional application serial number 63 / 052,664 filed on July 16, 2020.

[0002] Embodiments of the present invention provide a method and system for converting carbon dioxide into ethylene. Background Technology

[0003] Concerns regarding the long-term availability of fossil fuels, coupled with concerns about atmospheric carbon dioxide levels, have spurred the development of biosynthetic methods to produce petroleum-based products through carbon dioxide fixation. Specifically, the photosynthetic process is used to convert carbon dioxide into useful organic compounds that can be used as fuel or organic building blocks for larger organic molecules.

[0004] For example, U.S. Patent No. 7,807,427 describes genetically modified cyanobacteria (to convert carbon dioxide into intermediate products such as glucose and acetic acid) cyanobacteria It teaches the use of photosynthetic organisms such as ). In a subsequent step, methanogenic bacteria are used to convert the intermediate product into methane. The methane can be collected and stored for use as fuel.

[0005] Ethylene is widely known as the most important chemical feedstock in many industries, and various methodologies have been proposed for the biosynthesis of ethylene through carbon dioxide fixation. Pseudomonas syringae ( Pseudomonas syringae ) is known to synthesize ethylene using the TCA cycle intermediate alpha-ketoglutarate in a single-step reaction catalyzed by an ethylene-forming enzyme referred to as "efe". For the purpose of directly generating ethylene from carbon dioxide, U.S. Patent No. 9,309,541 describes Cytecchocystis ( Synechocystis This discloses methods for expressing and overexpressing the efe gene in hosts such as ). In other words, photoautotrophs are modified through biotechnology to convert the products of carbon fixation into ethylene in a single-step reaction. While current research has focused on modifying photoautotrophs to produce ethylene, harvesting ethylene may present challenges. Literature [Eckert et al., E thylene-forming enzyme and bioethylene production As outlined in [BIOTECHNOLOGY FOR BIOFUELS 2014, 7:33], when O2 is co-generated with ethylene in a photosynthetic system, there is a significant safety issue related to the flammability of ethylene in the presence of O2, which requires engineering design to mitigate the risk.

[0006] One or more embodiments of the present invention provide a method comprising: (i) providing a gas stream containing more than 1 volume% of carbon dioxide; (ii) providing water; (iii) converting the carbon dioxide and water into an organic intermediate and oxygen gas in the presence of light; (iv) separating the oxygen gas from the organic intermediate; and (v) converting the organic intermediate into ethylene and carbon dioxide after the step of separating the oxygen gas from the organic intermediate.

[0007] Another embodiment of the present invention provides a system for producing ethylene, comprising: (i) a first bioreactor comprising photosynthetic microorganisms that convert carbon dioxide into an organic intermediate, wherein the first bioreactor has a carbon dioxide inlet and outlet for said organic intermediate; and (ii) a second bioreactor fluidly connected to the first bioreactor and comprising microorganisms that convert said organic intermediate produced in the first bioreactor into ethylene, wherein the second bioreactor has an outlet for a gaseous substance containing ethylene, and the second bioreactor has an outlet for a fluid substance containing an unreacted organic intermediate. Brief explanation of the drawing

[0008] FIG. 1 is a schematic diagram of a system for carrying out an embodiment of the present invention. FIG. 2 is a schematic diagram of a subsystem for delivering carbon dioxide within an embodiment of the present invention. FIG. 3 is a schematic diagram of an alternative system including a second photosynthetic bioreactor for carrying out an embodiment of the present invention. FIG. 4 is a schematic diagram of a system including an oxygen-fuel combustion system for carrying out an embodiment of the present invention. FIG. 5 is a schematic diagram of a system including upstream carbon dioxide purification for carrying out an embodiment of the present invention. FIG. 6 is a schematic diagram of an ethylene purification and compression method applicable to one or more embodiments of the present invention. FIG. 7 is a schematic diagram of an alternative system including carbon dioxide membrane separation for carrying out one or more embodiments of the present invention. FIG. 8 is a schematic diagram of an alternative system comprising a single bioreactor for carrying out an embodiment of the present invention. Specific details for implementing the invention

[0009] Embodiments of the present invention are based, at least in part, on the discovery of a method for biosynthesizing ethylene from carbon dioxide at an industrially significant level. According to embodiments of the present invention, carbon dioxide is first converted into an organic intermediate by photosynthesis, with the production of oxygen gas as a byproduct. Subsequently, the byproduct oxygen gas is separated from the organic intermediate, and then the organic intermediate is biologically converted into ethylene in the notable absence of the byproduct oxygen gas. While current technology associated with ethylene biosynthesis focuses on single-step synthesis, the two-step method of the present invention addresses safety issues associated with the co-production of ethylene and oxygen gas at an industrially significant level. Furthermore, the bioconversion of the organic intermediate to ethylene generates carbon dioxide as a byproduct, which affects overall carbon efficiency. Moreover, since the amount of carbon dioxide in the ethylene product stream is substantial compared to most carbon dioxide input streams (e.g., fuel gas), the carbon dioxide in the ethylene product stream can be a valuable resource if properly managed. Accordingly, embodiments of the present invention provide a solution for managing byproduct carbon dioxide, which includes, but is not limited to, converting carbon dioxide into an organic intermediate by photosynthesis, and which can be recycled back to a step of biologically converting the organic intermediate into ethylene. Furthermore, the step of biologically converting the organic intermediate into ethylene can be efficiently achieved on a commercial scale by using industrial reactors, such as continuous-stirred tank reactors operating in a steady or near steady state, which would lead to incomplete consumption of the organic intermediate, loss of carbon efficiency, and loss of valuable raw materials. Accordingly, embodiments of the present invention provide a solution to these problems by appropriately managing the effluent stream from the reactor where the organic intermediate is converted into ethylene.

[0010] Process and System Overview

[0011] Embodiments of the present invention may be described with reference to FIG. 1, which illustrates a system (20) for converting carbon dioxide into ethylene. The system comprises a first bioreactor (21) followed by a second bioreactor (41). The first bioreactor (21) is fluidly connected directly or indirectly to the second bioreactor (41) through an intermediate-product conduit (31). The second bioreactor (41) is also fluidly connected to the second bioreactor (21) through an intermediate-recirculation conduit (33). A carbon dioxide separator (61) is located downstream of the second bioreactor (41) and is fluidly connected directly or indirectly to the second bioreactor (41) through a conduit (51). The carbon dioxide separator (61) may also be fluidly connected directly or indirectly to the first bioreactor (21) through a carbon dioxide-recirculation conduit (53).

[0012] According to an embodiment of the present invention, the first bioreactor (21) comprises a photosynthetic organism culture (i.e., photosynthetic microorganism) that converts carbon dioxide and water supplied to the bioreactor (21) into an organic intermediate. This conversion is carried out in the presence of light energy supplied to the first bioreactor (21). The synthesis of the organic intermediate is carried out in the presence of an excess of water acting as a reaction medium, and the excess of water acts as a carrier for the intermediate product stream. In one or more embodiments, the organic intermediate is soluble in water. As recognized by a person skilled in the art, the photosynthetic organism culture may be supplied from an inoculation reactor (23) to the bioreactor (21).

[0013] Oxygen gas is generated as a byproduct during the formation of an organic intermediate within the bioreactor (21). According to an aspect of the invention, the oxygen gas is separated from the organic intermediate before introducing the intermediate product stream into the second bioreactor (41). For example, the oxygen gas may be discharged out of the first bioreactor (21) along with other volatile substances within the reactor, such as nitrogen gas.

[0014] The organic intermediate is transferred directly or indirectly from the first reactor (21) to the second bioreactor (41) through the intermediate-product conduit (31) within the intermediate product stream. In one or more embodiments, the intermediate product stream may be filtered as the stream leaves the bioreactor (21). During operation, filtering the intermediate product stream as the stream leaves the bioreactor (21) can prevent the transfer of any medium used to immobilize photosynthetic microorganisms, thereby preventing the microorganisms from moving from the first bioreactor (21) to the second bioreactor (41).

[0015] In addition to or instead of filtering the intermediate product stream as the stream leaves the bioreactor (21), the intermediate-product stream may be filtered and / or sterilized in one or more intermediate units located between the bioreactor (21) and the bioreactor (41). For example, and referring to FIG. 2, an optional sterilization unit (35) may be located between the first bioreactor (21) and the second bioreactor (41). The unit (35) may include a filtration unit. In addition to or instead of the filtration unit, the unit (35) may include a centrifugation unit. Or, in another embodiment, the unit (35) may include a purification unit (e.g., a settling tank) in addition to or instead of filtration or centrifugation. Instead of or in addition to filtration, centrifugation, and / or purification, the unit (35) may include a sterilization unit. For example, the sterilization unit may use UV sterilization, heat, or gamma rays to process an intermediate-product stream that can be performed to prevent the introduction of any living microorganism from the first bioreactor (21) to the second bioreactor (41).

[0016] In one or more embodiments, the second bioreactor (41) comprises an ethylene-producing organism culture (i.e., an ethylene-producing organism) that converts an organic intermediate into ethylene.

[0017] As a person skilled in the art would recognize, several sub-systems can be designed to introduce microbial cultures into each bioreactor. A person skilled in the art can easily design a suitable system to achieve these goals. For example, and referring to the drawings, suitable microorganisms may be supplied to bioreactor (21) and / or bioreactor (41) from an inoculation unit (23), which may also be referred to as an inoculation reactor (23). The inoculation unit (23) may include a separate chamber or vessel for each microorganism, or a separate unit may be provided for each microorganism. Likewise, it may be desirable to remove biomass from one or more of the bioreactors. In one or more embodiments, the system of the present invention may include a biomass digestion unit (25), wherein biomass obtained from one or both of the bioreactors may be removed from any immobilized support medium and removed from the system. During operation, the biomass decomposition unit (25) may be fluidly connected to one or both of the bioreactors (21, 41), or the biomass (optional with immobilized material) may be manually removed from each reactor. In one or more embodiments, the biomass may be converted into nutrients such as amino acids and returned to the bioreactor as a source of nutrients for microorganisms. Alternatively, the biomass may be removed from the system and directed toward other uses, such as fertilizer.

[0018] Carbon dioxide is produced as a byproduct of ethylene synthesis within the bioreactor (41), and ethylene and carbon dioxide are removed from the second bioreactor (41) as a gaseous product stream. A liquid effluent stream also leaves the second bioreactor (41). This liquid effluent stream may contain water and unreacted organic intermediates, and the stream may be sent back to the first bioreactor (21) through the organic intermediate-recirculation conduit (33). As best illustrated in FIG. 2, the liquid effluent stream containing water and unreacted organic intermediates may undergo filtration and / or sterilization in a filtration / sterilization device (37). Since this filtration and / or sterilization may utilize the same type of technology as unit (35), the above discussion regarding unit (35) is incorporated herein. As a person skilled in the art would recognize, it may be useful to prevent ethylene-producing microorganisms from moving into the first bioreactor (21).

[0019] The gaseous product stream leaving the second bioreactor (41) is sent downstream of the second bioreactor (41), either directly or indirectly, through a conduit (51), to a carbon dioxide separator (61), which may also be referred to as a carbon dioxide separation unit (61). Within the separator (61), which may also be referred to as a separator system (61), carbon dioxide is separated from the gaseous product stream and transported by a conduit (53) to provide a concentrated ethylene stream, which may also be referred to as an ethylene-rich stream. This ethylene-rich stream may be sent to a downstream purification and pressurization unit (100), which will be discussed in more detail herein. The separator (61) also produces a concentrated carbon dioxide stream, which may also be referred to as a purified carbon dioxide stream, and this concentrated carbon dioxide stream may be sent back to the first bioreactor (21) through a conduit (55).

[0020] In an alternative embodiment that may be described with reference to FIG. 3, the purified carbon dioxide stream produced by the carbon dioxide separator (61) may be sent through conduit (57) to an intermediate bioreactor (71) (which may also be referred to as a second photosynthetic bioreactor) containing a culture of photosynthetic organisms that convert carbon dioxide into organic intermediates and oxygen gas through photosynthesis. Advantageously, since the carbon dioxide supply stream to the bioreactor (71) is a purified carbon dioxide stream (through the carbon dioxide separator (61)), the gaseous byproduct stream leaving the second photosynthetic bioreactor (71) contains a relatively pure oxygen gas stream that may be sent through conduit (75). A person skilled in the art will recognize that, within the context of the present invention, a relatively pure oxygen stream contains a stream substantially free of nitrogen gas and argon gas, which would otherwise require a complex and expensive process (e.g., air separation technology) to separate nitrogen and argon from oxygen gas. However, the presence of carbon dioxide in the relatively pure oxygen gas stream defined herein is not harmful, and therefore, since carbon dioxide can be more easily separated from the oxygen gas stream, it may be present in the relatively pure oxygen steam unless otherwise noted. In conjunction with the first bioreactor (21), the intermediate bioreactor (71) produces an effluent stream that may contain organic intermediates and water, which can be sent back to the first bioreactor (21) and / or the second bioreactor (41) through the conduit (79). As generally illustrated, this effluent stream may undergo filtration and / or sterilization in the unit (37) as described with reference to FIG. 2.

[0021] As illustrated throughout the drawing, the gas stream exiting the second bioreactor (41) sent through the conduit (51) may optionally undergo one or more treatments or operations before carbon dioxide separation in the unit (61). For example, the stream may be pressurized in a compression unit (43). In addition to pressurization, or instead, the gas stream may optionally undergo a treatment to remove oxygen in an oxygen removal unit (45). Since carbon dioxide may be generated in the oxygen removal unit (45), it may be advantageous to position the oxygen-removal unit (45) upstream of the carbon dioxide separation unit (61) where the carbon dioxide generated in the unit (45) can be removed.

[0022] Another embodiment of the present invention may be described with reference to FIG. 8. As illustrated, the process (120) comprises a single vessel (121), which may also be referred to as an integrated bioreactor (121), instead of the two bioreactors (21, 41) illustrated in relation to the other system described above. During operation, light energy supplied to the bioreactor (121) is controlled in a manner that generates a light cycle and a dark cycle. During operation, photosynthetic microorganisms within the integrated bioreactor (121) convert carbon dioxide into an organic intermediate during the light cycle, and then ethylene-forming microorganisms within the integrated bioreactor (121) convert the organic intermediate into ethylene during the dark cycle. Oxygen gas may be removed from the bioreactor (121) during its production during the light cycle, and ethylene may be removed from the bioreactor (121) during its production during the dark cycle. In accordance with other embodiments, ethylene can be co-generated with carbon dioxide, and ethylene and carbon dioxide can be separated in a downstream process as described above (e.g., in a carbon dioxide scrubber (61)).

[0023] Returning to FIG. 2, the process of the present invention may include conditioning of the carbon dioxide input stream (i.e., conditioning of the stream before providing the stream to the bioreactor (21). In one or more embodiments, the carbon dioxide input stream carried by the conduit (11) may be pressurized in a compressor (13). In one or more embodiments, pressurization of the carbon dioxide input stream (e.g., in the compressor (13)) achieves a pressure sufficient to overcome the opposing forces within the first bioreactor (21) so that the inert gas (e.g. nitrogen) in the input stream can ultimately enter the head space of the reactor. In one or more embodiments, the carbon dioxide input stream is pressurized to a pressure of about 2 to about 20 psig, in another embodiment about 3 to about 18 psig, and in another embodiment about 5 to about 15 psig.

[0024] Additionally, as best illustrated in FIG. 2, the carbon dioxide input stream may be cooled in a quencher (15) before being delivered to the bioreactor (21) through the conduit (17). As recognized by a person skilled in the art, the quencher (15) may include a water-cooled unit comprising a quench water loop (15') which may include one or more heat exchangers for cooling water. In one or more embodiments, the carbon dioxide input stream is cooled to a temperature lower than would otherwise have a detrimental effect on the microbial culture in the bioreactor (21). In one or more embodiments, the carbon dioxide input stream is cooled to a temperature of about 10 to about 80°C, in another embodiment about 20 to about 60°C, and in another embodiment about 30 to about 50°C before being delivered to the bioreactor (21).

[0025] Considering that the carbon dioxide input stream of one or more embodiments may contain a significant amount of water and that at least a portion of the water will be condensed through a cooling cycle in the quencher (15), the water from the quencher (15) may be supplied to a first bioreactor (21) that consumes a significant amount of water. In one or more embodiments, the water used in the quencher (15) and / or the water stream sent to the first bioreactor (21) may be treated with a corrosive agent to adjust the pH of the water. In one or more embodiments, the water used in the quencher (15) and / or the water sent from the quencher (15) to the first bioreactor (21) is adjusted to a pH greater than 5.5, greater than 6.0 in another embodiment, and greater than 6.5 in another embodiment (e.g., in the range of 5.5-8.0 or 6.0-7.5). The corrosive treatment of the water is expected to form carbonates such as sodium carbonate, which is beneficial to the first bioreactor (21) in relation to pH control, as well as providing an additional source of carbon dioxide in the form of sodium carbonate and / or sodium bicarbonate. A person skilled in the art can easily adjust the conditions and / or provide additional components (e.g., hydrochloric acid) to yield a desirable balance between sodium carbonate and sodium bicarbonate. In a particular embodiment, the caustic soda provided to the quench water in the quencher (15) originates from other processes that can be integrated with the practice of the present invention. For example, ethylene purification can produce sodium carbonate that can be used with caustic soda or integrated with the quencher (15).

[0026] In another embodiment, the liquid effluent stream exiting the second bioreactor (41), which can be sent back to the first bioreactor (21) as described in relation to other embodiments, may optionally be sent to the quencher (15). In one or more embodiments, the liquid effluent stream exiting the second bioreactor (41) is first processed at a sterilization station (37) before being sent to the quencher (15).

[0027] Carbon dioxide supply stream for the first bioreactor

[0028] The method of the present invention can advantageously convert carbon dioxide from various gas sources, which may be referred to as carbon dioxide input streams, into a useful intermediate that can be converted into ethylene. In one or more embodiments, carbon dioxide is supplied to the system by a carbon dioxide input stream comprising more than 1% vol, in another embodiment more than 3% vol, in another embodiment more than 5% vol, and in another embodiment more than 10% vol. In one or more embodiments, the carbon dioxide input stream is an exhaust stream of a combustion process (i.e., a flue gas stream) or is derived therefrom. As a person skilled in the art recognizes, the composition of the exhaust stream may vary based on several factors, including the design of the combustion process and the fuel burned in the combustion process. For example, the flue gas stream may be derived from a coal-fired furnace, a gas-fired furnace, a turbine-power generator, and an oxy-fuel combustion process.

[0029] In one or more embodiments, the carbon dioxide input stream may be derived from the exhaust stream of an oxycombustion process, which may also be referred to as oxycombustion. A person skilled in the art recognizes that these processes involve the combustion of fuel (e.g., hydrocarbons) in the substantial absence of nitrogen and argon. For example, these processes may include a combustion process in which substantially pure oxygen (i.e., substantially free of nitrogen and argon gases), or a mixture of pure oxygen and recirculated flue gas, is fed to the combustion process. Consequently, the combustion products are mostly carbon dioxide and water, with substantially little nitrogen byproduct or argon. Advantageously, because the carbon dioxide input stream from the oxycombustion process contains a significant amount of carbon dioxide and is substantially free of nitrogen and oxygen, the gaseous byproduct stream from the photosynthetic bioreactor will contain a substantially high concentration of oxygen gas along with any unreacted carbon dioxide. The gaseous byproduct stream from the photosynthetic bioreactor can be recirculated as fuel to the oxy-fuel combustion unit within the oxy-fuel combustion process, where any unreacted carbon dioxide provides cooling to the oxy-fuel combustion process.

[0030] For example, referring to FIG. 4, an embodiment of the present invention includes a carbon dioxide input stream from a pure oxygen combustion unit (18). As in the previous embodiment, carbon dioxide is converted by photosynthesis into an organic intermediate along with byproduct oxygen gas in the first bioreactor (21). A byproduct oxygen gas stream containing oxygen gas and unreacted carbon dioxide is sent to the pure oxygen combustion unit (18) through a conduit (22). Additionally, although not illustrated, the carbon dioxide input stream from the pure oxygen combustion unit (18) may be cooled and pressurized as described above in relation to other embodiments (e.g., see FIG. 2). The intermediate product produced in the first bioreactor (21) is sent downstream to the second bioreactor (41) in a manner consistent with other embodiments.

[0031] In another embodiment, a relatively pure carbon dioxide stream may be supplied to the first bioreactor (21). The relatively pure carbon dioxide stream may be obtained from several sources and generally comprises such streams containing more than 90 vol%, 95 vol% in another embodiment, and more than 99 vol% of carbon dioxide in another embodiment. As described above, when a relatively pure carbon dioxide stream is used, the method of the present invention produces a relatively pure oxygen gas stream (i.e., substantially free of nitrogen or argon gas) as a byproduct output from the first bioreactor (21). These relatively pure oxygen gas streams can be used in industrial applications, such as the oxychlorination of ethylene, for example.

[0032] In one or more embodiments, a relatively pure carbon dioxide stream is generated as a step of the present invention and used as an input stream. For example, the input stream containing carbon dioxide may be purified and / or concentrated before the stream is introduced into the first bioreactor (21). In one or more embodiments, the carbon dioxide influent stream may be purified, for example, using amine scrubbing and stripping techniques. As in one or more of the prior embodiments, by providing the purified carbon dioxide stream to the first bioreactor, a relatively high-grade oxygen gas stream may be generated as a byproduct stream exiting the first bioreactor. A person skilled in the art will understand that various carbon dioxide removal and separation techniques may be used in addition to or instead of amine scrubbing and stripping techniques for purifying and / or concentrating the carbon dioxide stream. Such techniques include, but are not limited to, membrane separation, solid adsorbents, and the use of other solvent chemicals such as potassium carbonate.

[0033] An exemplary embodiment may be described with reference to FIG. 5, which illustrates a system (50) comprising a first bioreactor (21) that receives a carbon dioxide input stream from a carbon dioxide purification unit (16). It is introduced into the first bioreactor (21) through a conduit (11'). The purification unit (16) produces a purified carbon dioxide stream that is introduced into the first bioreactor (21) through the conduit (11'). Although not illustrated, the carbon dioxide input stream from the combustion unit may be cooled and pressurized as described above in relation to other embodiments (e.g., see FIG. 2). In the bioreactor (21), the carbon dioxide is converted into an organic intermediate through photosynthesis along with byproduct oxygen gas. The byproduct oxygen gas is sent directly or indirectly through a conduit (24) to, for example, an industrial process (26) requiring relatively high purity oxygen. In one or more embodiments, the ethylene produced in the bioreactor (41) may also be sent to the industrial process (26). Although not illustrated in FIG. 5, the ethylene stream from the second bioreactor (41) will be recognized as undergoing downstream processing as described in relation to other embodiments, including but not limited to oxygen gas conversion, carbon dioxide removal (and recirculation to the photosynthetic bioreactor), and ethylene purification.

[0034] Again, in an embodiment in which the photosynthetic bioreactor yields a relatively pure oxygen byproduct stream that can be derived from the use of a relatively pure carbon dioxide stream, the relatively pure oxygen stream can be used in an industrial application. In one or more embodiments, the gas stream exiting the photosynthetic bioreactor may undergo carbon dioxide removal to remove any unreacted carbon dioxide from the oxygen gas stream. Subsequently, the oxygen gas stream can be sent to a desired industrial application. For example, the oxygen gas stream from these embodiments may be sent to an oxychlorination unit, where ethylene reacts with hydrochloric acid in the presence of oxygen gas. In this example, the ethylene may be derived from an ethylene-generating bioreactor. It will be recognized that the ethylene stream from the ethylene-generating bioreactor will undergo carbon dioxide removal and ethylene purification as described in relation to other embodiments.

[0035] carbon dioxide separation

[0036] In one or more embodiments, downstream carbon dioxide separation (e.g., in the carbon dioxide separation unit (61)) may be performed using conventional amine scrubbing / stripping. Various other carbon dioxide separation techniques may be used, including but not limited to solvent separation using potassium carbonate, membrane separation, and solid adsorbent separation.

[0037] As recognized by a person skilled in the art, amine scrubbing and stripping techniques or methods generally involve the absorption of carbon dioxide by an organic amine within a water carrier (i.e., scrubbing), and the subsequent regeneration or release of carbon dioxide from the organic amine (i.e., stripping). These systems and techniques for their use are widely known in the relevant art, as described in U.S. Publications Nos. 2009 / 0038314, 2009 / 0156696, and 2013 / 0244312, which are incorporated herein by reference. Reference may also be made to the literature [Engineering Data Book, Vol. II, Sections 17-26; Gas Processors Suppliers Assoc. (1994)].

[0038] Instead of or in addition to amine scrubbing / stripping, membrane separation technology may be used. As recognized by those skilled in the art, these membranes may comprise polymer or inorganic microporous membranes that allow the passage of carbon dioxide through the permeate. These membranes and the technology of their use are widely known as described in U.S. Publications No. 2008 / 0173179 and 2013 / 0312604, which are incorporated herein by reference. In carrying out the invention in which membrane separation is used instead of amine scrubbing / stripping technology, it may be desirable to move to the permeate stream and thus otherwise be sent to a stationary reactor (i.e., a first bioreactor) and subsequently move to an oxygen stream. In this regard, refer to FIG. 7, which shows an alternative system (20') comprising a membrane separation unit (61') having a permeate stream of carbon dioxide sent downstream through a conduit (73) to an ethylene treatment unit (75'), said system may be adapted to catalytically treat the stream to remove any residual ethylene in the permeate stream (e.g., through catalytic combustion) before the permeate stream is sent back to a bioreactor (21) through a conduit (51').

[0039] Ethylene purification

[0040] As described above, the carbon dioxide separation of the ethylene-containing product stream of the second bioreactor (41) (e.g., within the separator (61)) produces an ethylene-rich stream carried by the conduit (53). This ethylene-rich stream may undergo purification within the subprocess (100), optional compression for subsequent use, and optional transport, which is best described with reference to FIG. 6. In one or more embodiments, the subprocess (100) processes the ethylene-rich steam provided through the conduit (53) using one or more techniques. For example, the ethylene-rich stream may undergo oxygen gas removal in an optional oxygen gas removal unit (101). Within this unit, the residual oxygen gas in the ethylene-rich stream is consumed, for example, by the catalytic combustion of a portion of the ethylene. In one or more embodiments, the subprocess (100) may include abrasives of the ethylene stream in a caustic wash unit (103), which removes any residual carbon dioxide (e.g., reduces the level of carbon dioxide to less than 10 ppm, or less than 5 ppm, or less than 3 ppm). Downstream of the caustic wash unit (103), the ethylene-rich stream may be dehydrated in a dehydration unit (105), which may include a dehydration unit using a molecular sieve. After dehydration, the ethylene-rich stream may be condensed in a condenser (107), which may be cooled by a propylene cooling unit (108). A person skilled in the art will recognize that the order of various purification steps may change according to a number of factors. Additionally, a person skilled in the art will recognize that various steps of the purification process may be performed with the aim of achieving a desired pressure that may be required for use or transport (e.g., through a pipeline). To this end, the ethylene-rich stream may be pressurized before, after, or between two additional purification steps.For example, as illustrated in FIG. 6, the stream can be pressurized in a compression unit (99). Likewise, additional pressurization can be performed in an ethylene product pump (109).

[0041] Photosynthetic microorganisms

[0042] As described above, the first bioreactor contains a photosynthetic organism culture containing one or more types of photosynthetic microorganisms that convert carbon dioxide and water into organic intermediates in the presence of light energy. In various embodiments, the photosynthetic microorganisms may occur naturally. In other embodiments, the photosynthetic microorganisms may be genetically modified for improved production of the desired organic intermediates. In one or more embodiments, the photosynthetic microorganisms used with the first bioreactor may include photosynthetic bacteria such as cyanobacteria. As recognized by a person skilled in the art, photosynthetic bacteria consume carbon dioxide and water in the presence of light to fix carbon. Advantageously, under aerobic conditions, the major products of the metabolic pathway of cyanobacteria are oxygen and organic intermediates, such as sugars. A person skilled in the art will be able to select suitable photosynthetic microorganisms to produce the desired organic intermediates without excessive experimentation.

[0043] In one or more embodiments, the desired organic intermediate comprises sucrose, dextrose, xylose, glucose, fructose, alpha-ketoglutarate, or a mixture thereof.

[0044] Exemplary photosynthetic microorganisms include, but are not limited to, cyanobacteria, algae, and purple bacteria. Useful types of cyanobacteria include photosynthetic prokaryotes that perform oxygen photosynthesis. Cyanobacteria useful for the purposes outlined herein are generally well known in the relevant art. (See, for example, the literature [Donald Bryant, The Molecular Biology of Cyanobacteria, published by Kluwer Academic Publishers (1994)], the full text of which is incorporated herein by reference). A representative example is Synecchococcus ( Synechococcus Cyanobacteria of the genus, for example, Synecchococcus lividus ( Synechococcus lividus ) and Synecchococcus ilongatus ( Synechococcus elongatus ) and Synecchococcus( Synechococcus Cyanobacteria of the genus, for example, Synecchocystis minervae ( Synechocystis minervae ) and necrocystis( Synchocystis ) Includes Sp PCC 6803. In this regard, U.S. Patent No. 427807 is incorporated herein by reference in its entirety. Examples of synthetic microorganisms that may be used include those disclosed in U.S. Patent No. 10,196,627, the entirety of which is incorporated herein by reference. Other examples include microorganisms disclosed in U.S. Patent Nos. 9,914,947 and 9,309,541, the entirety of which is incorporated herein by reference.

[0045] In one or more embodiments, cyanobacteria are genetically modified to express one or more foreign genes encoding one or more enzymes that provide for the enhanced production of a target organic intermediate. In one or more embodiments, the target organic intermediate comprises sucrose, dextrose, xylose, glucose, fructose, and alpha-ketoglutarate. As will be apparent to a person skilled in the art, the specific gene added to the genome of the cyanobacteria (and the enzyme produced) will depend on the specific target organic intermediate.

[0046] In one or more embodiments, the modified photosynthetic microorganism comprises a modified nucleotide sequence that produces an enzyme that forms alpha-ketoglutarate from carbon dioxide. In certain embodiments, this modified photosynthetic microorganism expresses alpha-ketoglutarate permease protein (AKGP) by expressing a non-native AKGP-forming nucleotide sequence. In one or more embodiments, the modified microorganism produces a greater amount of the enzyme than that produced by a control microorganism lacking the modified nucleotide sequence. This amount may be greater than 1% of the amount produced by the control microorganism lacking the modified nucleotide sequence, greater than 50% in other embodiments, and greater than 75% in other embodiments.

[0047] In one or more embodiments, alpha-ketoglutarate (aKG) may be produced by the oxidative decarboxylation of isocitrate by isocitrate dehydrogenase (ICD) or by the oxidative deamination of glutamate by glutamate dehydrogenase (GDH). The target enzyme for cloning and aKG production in cyanobacteria is ICD enzyme: 1.1.1.42, p. fluorescens ( P. FluorescensIt may include the coding sequence of ) ICD (sequence identification number: 1, sequence identification number: 2), ICD enzyme: 1.1.1.42, coding sequence of Synecchococcus ilongatus PCC794 (sequence identification number: 3, sequence identification number: 4), and GDH enzyme: 1.4.1.2, coding sequence of p. fluorescens (sequence identification number: 5, sequence identification number: 6).

[0048] In one or more embodiments, the enzyme for forming alpha-ketoglutarate is selected from isocitrate dehydrogenase (ICD) protein, glutamate dehydrogenase (GDH) protein, or a combination thereof.

[0049] In a specific embodiment, the modified photosynthetic microorganism expresses an ICD having an amino acid sequence that is at least 98%, or at least 95%, or at least 90%, or at least 85% identical to SEQ ID NO: 1 by expressing a modified ICD protein nucleotide sequence that is at least 98%, or at least 95%, or at least 90%, or at least 85% identical to SEQ ID NO: 2. In a specific embodiment, the modified microorganism expresses an ICD having an amino acid sequence that is at least 98%, or at least 95%, or at least 90%, or at least 85% identical to SEQ ID NO: 3 by expressing a modified ICD protein nucleotide sequence that is at least 98%, or at least 95%, or at least 90%, or at least 85% identical to SEQ ID NO: 4. In a specific embodiment, the modified microorganism expresses a modified GDH protein nucleotide sequence having at least 98%, or at least 95%, or at least 90%, or at least 85% identical nucleotide sequence to SEQ ID No. 6, thereby expressing a GDH having at least 98%, or at least 95%, or at least 90%, or at least 85% identical amino acid sequence to SEQ ID No. 5.

[0050] In one or more embodiments, the organic intermediate is sucrose. In some of these embodiments, for example, cyanobacteria (Synecochoccus ilongatus, Cytecchocystis) may be engineered to produce sucrose that acts as a substrate for the growth of ethylene-producing microorganisms. Various methods of engineering Synecochoccus ilongatus PCC 7942 to produce sucrose may include the activation of one gene (cscB) and the deletion of one gene (GlgC).

[0051] In one or more of these embodiments, the modified photosynthetic microorganism expresses a sucrose synthase protein. In one or more embodiments, the sucrose synthase protein has an amino acid sequence that is at least 98%, or at least 95%, or at least 90%, or at least 85% identical to SEQ ID NO: 10 by expressing a modified sucrose synthase protein nucleotide sequence that is at least 98%, or at least 95%, or at least 90%, or at least 85% identical to SEQ ID NO: 9. In one or more of these embodiments, the modified microorganism expresses a sucrose phosphate synthase protein. In one or more embodiments, the sucrose phosphate synthase protein has at least 98%, or at least 95%, or at least 90%, or at least 85% identical amino acid sequence to SEQ ID No. 11 by expressing a modified sucrose phosphate synthase protein nucleotide sequence having at least 98%, or at least 95%, or at least 90%, or at least 85% identical nucleotide sequence to SEQ ID No. 12.

[0052] As used herein, sequence identity is a relationship between two or more amino acid (polypeptide or protein) sequences or two or more nucleic acid (polynucleotide) sequences, as determined by comparing sequences. Sequence identity or similarity is typically compared over the entire length of each sequence. A person skilled in the art recognizes that “identity” refers to the degree of sequence relatedness between amino acid or nucleic acid sequences, as determined in some cases by the match between strings of such sequences. “Similarity” between two amino acid sequences is determined by comparing the amino acid sequence and the conserved amino acid substituents of one polypeptide with the sequence of the second polypeptide. A person skilled in the art can easily calculate “identity” and “similarity” by various known methods. For example, methods for determining identity and similarity are coded in publicly available computer programs, such as BestFit (publicly available from NCBI), BLASTP (Protein Basic Local Alignment Search Tool), BLASTN (Nucleotide Basic Local Alignment Search Tool), FASTA (Altschul, SF et al., J. Mol. Biol. 215:403-410 (1990)), and other sources (BLAST. RTM. Manual, Altschul, S., et al., NCBI NLM NIH Bethesda, Md. 20894). Exemplary parameters for amino acid sequence comparison using EMBOSS are gap open 10.0, gap extend 0.5, and Blosum matrix. Exemplary parameters for nucleic acid sequence comparison using EMBOSS are gap open 10.0 and gap extend 0.5, is the entire DNA matrix (DNA identity matrix).As understood by a person skilled in the art, DNA / protein sequences between different species can be compared to determine sequence homology using online data such as Gene Banks, KEG, BLAST, and Ensemble. A person skilled in the art may also consider so-called "conservative" amino acid substitutions, which refer to the interchangeability of residues having similar side chains. For example, the group of amino acids with aliphatic side chains is glycine, alanine, valine, leucine, and isoleucine; the group of amino acids with aliphatic-hydroxyl side chains is serine and threonine; the group of amino acids with amide-containing side chains is asparagine and glutamine; the group of amino acids with aromatic side chains is phenylalanine, tyrosine, and tryptophan; the group of amino acids with basic side chains is lysine, arginine, and histidine; and the group of amino acids with sulfur-containing side chains is cysteine ​​and methionine. Substitution variants of the amino acid sequence disclosed herein are those in which at least one residue is removed from the disclosed sequence and a different residue is inserted in its place. Preferably, the amino acid change is conservative. Preferred conservative substitutions for each naturally occurring amino acid are as follows: from Ala to ser; from Arg to lys; from Asn to gin or his; from Asp to glu; from Cys to ser or ala; from Gin to asn; from Glu to asp; from Gly to pro; from His to asn or gin; from lie to leu or val; from Leu to ile or val; from Lys to arg; gin or glu; from Met to leu or ile; from Phe to met, leu or tyr; from Ser to thr; from Thr to Ser; from Trp to tyr; from Tyr to trp or phe; and from Val to ile or leu.

[0053] Unless otherwise noted, the terms “adapted” or “codon adapted” refer to “codon optimization” of a polynucleotide as disclosed herein, the sequence of which may be natural or non-natural, or adapted for expression in other microorganisms. Codon optimization adapts the codon usage for the encoded polypeptide to the codon bias of the organism in which the polypeptide is expressed. Codon optimization generally helps to increase the production level of the encoded polypeptide in the host cell.

[0054] In certain embodiments, the modified photosynthetic microorganism comprises a delta-glgc (Aglgc) mutant microorganism lacking the expression of glucose-1-phosphate adenylyltransferase protein. Similarly, cyanobacteria cells lacking the functional ADP-glucose pyrophosphorylase enzyme are known as described in U.S. Patent Nos. 9,309,541 and 9,309,541, the full text of which is incorporated herein by reference.

[0055] ethylene-producing microorganisms

[0056] As described above, the ethylene-producing organism comprises an organism that is naturally produced or genetically modified to produce ethylene by consuming an organic intermediate produced in a photosynthetic bioreactor. In one or more embodiments, the microorganism used with the second bioreactor comprises such a microorganism that expresses or is genetically modified to express the ethylene-forming enzyme (efe) gene. These microorganisms may be referred to herein as fermenting microorganisms. Any microorganism that produces or is modified to produce ethylene, which is widely known in the art and capable of producing ethylene from a target organic intermediate under the described reaction conditions, may be used. In one or more embodiments, the desired microorganism does not produce anything that would otherwise interfere with the method described herein.

[0057] Exemplary efe-forming microorganisms include Pseudomonas syringa, Pseudomonas syringa fib., and Glycinia ( Pseudomonas syringae pv. Glycinia ), and Penicillium digitatum ( Penicillium digitatum ...including ) and all of them naturally express efe. In another embodiment, the microorganism in the second reactor comprises a modified microorganism that expresses or overexpresses an efe gene such as that naturally found in Pseudomonas syringa or Penicillium digitatum. In these embodiments, one or more copies of one or more efe genes are transfected into a host microorganism using any one of numerous methods known in the art to do so. A useful host microorganism is Esterhias coli ( Escherichia coli ) (i. colai( E. Coli )), Saccharomyces cerevisiae( Saccharomyces cerevisiae ), Pseudomonas putida( Pseudomonas putida ), Trichoderma viride ( Trichoderma viride ), and Trichoderma reisei ( Trichoderma reesei It can include ) without restriction.

[0058] In one or more embodiments, the modified microorganism for producing efe may be produced as described in the literature [Wang, JP, et al., "Metabolic engineering for ethylene production by inserting the ethylene-forming enzyme gene (efe) at the 16S rDNA sites of Pseudomonas putida KT2440" Biosource Technology, (2010) 101: 6404-6409], the full text of which is incorporated herein by reference. In these embodiments, the efe gene is derived from P. syringa and P. glycinia ( P. syringae pv. glycinea ) Cloned from ICMP2189 and using double cross-recombination, Pseudomonas pudita ( Pseudomonas pudita) It is inserted into one or more 16S rDNA regions of the KT2440 host.

[0059] As described above, in one or more embodiments, the microorganism producing the efe enzyme will comprise a genetically modified microorganism. In one or more embodiments, the efe-forming microorganism is a modified microorganism containing one or more foreign nucleotide sequences in its DNA that produce efe when expressed. In one or more embodiments, the modified microorganism produces a greater amount of the efe enzyme than that produced by a control microorganism lacking the modified nucleotide sequence. This amount may be more than 5% of the amount produced by the control microorganism lacking the modified nucleotide sequence, more than 50% in other embodiments, and more than 75% in other embodiments. In various embodiments, the genetically modified microorganism will be modified to contain two or more copies of the foreign nucleotide sequence that produces efe when expressed to further improve ethylene production.

[0060] In one or more embodiments, Pseudomonas sabastanoi piv. passeoricola ( Pseudomonas savastanoi pv. Phaseolicola The ) efe protein (GenBank: KPB44727.1, sequence identification number: 8) can be cloned into a pET-30a(+) vector plasmid. The corresponding nucleotide sequence may also be a codon adapted for expression in E. coli (sequence identification number: 7) and may contain a stop codon and a HindIII site following an arbitrary His tag at the C-terminal end. The Ndel site may also be used for cloning at the 5-prime end, where the Ndel site contains an ATG start codon. In various embodiments, E. coli BL21 (DE3) eligible cells may be transformed with the recombinant plasmid.

[0061] In some embodiments, the ampicillin cassette may be activated by the IPTG-inducible promoter (pTrc) in the presence of the Lad gene; and the LacI gene may be regulated by the Laclq promoter (sequence identification number: 13).

[0062] In a specific embodiment, the ethylene-forming recombinant microorganism expresses an efe protein having an amino acid sequence at least 95%, or at least 90%, or at least 80% identical to SEQ ID No. 7 by expressing a non-natural efe protein nucleotide sequence having at least 95%, or at least 90%, or at least 80% identical to SEQ ID No. 8.

[0063] A person skilled in the art recognizes that it may be advantageous to immobilize microorganisms to increase yield and aid in the management of microorganisms within the process (e.g., to help separate microorganisms from a product stream or reaction medium). In one or more embodiments, microorganisms are immobilized on a support medium, such as a high surface area support medium, but is not limited thereto. Useful high surface area support materials may include sponges, fibrous materials, bio-balls, ceramic filters, etc.

[0064] The first bioreactor (photosynthetic bioreactor)

[0065] Referring again to the drawing, the first bioreactor (21) may include a single reaction vessel or may include multiple (i.e., two or more) reaction vessels that can operate in a complementary manner. For example, two or more reactor vessels may operate simultaneously or in succession to promote a desired photosynthetic reaction.

[0066] A person skilled in the art generally recognizes the appropriate conditions that must be maintained in the first bioreactor (21) to sustain microorganisms and promote the desired photosynthetic reaction. In one or more embodiments, water is a reactant and also acts as a reaction medium within the first bioreactor (21).

[0067] In one or more embodiments, the reactor medium in the photosynthetic bioreactor is maintained at a temperature of about 25 to about 70°C, in another embodiment about 35 to about 60°C, and in another embodiment about 40 to about 50°C. In these or other embodiments, the reaction medium in the photosynthetic bioreactor is maintained at a pH of about 5.0 to about 8.5, in another embodiment about 5.5 to about 8.0, and in another embodiment about 6.0 to about 7.0.

[0068] In one or more embodiments, the photosynthetic bioreactor substantially lacks a microorganism that generates or is adapted to generate the efe gene.

[0069] In one or more embodiments, the first bioreactor includes at least one inlet for introducing at least one reactant (e.g., carbon dioxide) into the bioreactor. In these or other embodiments, the first bioreactor includes at least one outlet for removing at least one product or at least one byproduct from the bioreactor. In one or more embodiments, the first bioreactor (21) includes an outlet for gaseous products / byproducts and an outlet for liquid effluent. In one or more embodiments, the bioreactor (21) is a closed system except for the inlet and outlet. In other embodiments, the bioreactor (21) is an open system. In one or more embodiments, the first bioreactor is selected from a continuous stirred tank reactor, a gas lift reactor, a loop reactor, and a fluidized bed reactor. In one or more embodiments, the first bioreactor has a capacity of more than 10,000 gallons, in another embodiment more than 100,000 gallons, and in another embodiment more than 1,000,000 gallons.

[0070] Second bioreactor (ethylene-producing bioreactor)

[0071] Referring again to the drawing, the second bioreactor (41) may include a single reaction vessel or may include multiple (i.e., two or more) reaction vessels that can operate in a complementary manner. For example, two or more reactor vessels may operate simultaneously or in succession to facilitate the desired reaction of converting an intermediate into ethylene.

[0072] A person skilled in the art generally recognizes the appropriate conditions that must be maintained in the second bioreactor to sustain microorganisms and promote the desired ethylene-forming reaction. In one or more embodiments, water acts as the reaction medium in the second reactor.

[0073] In one or more embodiments, the reactor medium in the ethylene-forming bioreactor is maintained at a temperature of about 25 to about 70°C, in another embodiment about 35 to about 60°C, and in another embodiment about 40 to about 50°C. In these or other embodiments, the reaction medium in the ethylene-forming bioreactor is maintained at a pH of about 6.0 to about 9.5, in another embodiment about 6.5 to about 9.0, and in another embodiment about 7.0 to about 8.0.

[0074] In one or more embodiments, the ethylene-forming bioreactor is substantially free of microorganisms that produce or are adapted to produce oxygen. For example, the second bioreactor is free of or substantially free of photosynthetic microorganisms (e.g., microorganisms operating by the Calvin Cycle).

[0075] In one or more embodiments, the ethylene-forming bioreactor is maintained under anaerobic conditions. In one or more embodiments, the ethylene-forming bioreactor is maintained in the substantial absence of light energy.

[0076] In one or more embodiments, the second bioreactor includes at least one inlet for introducing an organic intermediate product stream into the bioreactor. In these or other embodiments, the second bioreactor includes at least one outlet for removing a product (e.g., a gas outlet for ethylene gas) and at least one byproduct from the second bioreactor (e.g., carbon dioxide). In one or more embodiments, the second bioreactor also includes an effluent outlet for removing a liquid effluent (e.g., water and unreacted organic intermediate). In one or more embodiments, the second bioreactor is selected from a continuous stirred tank reactor, a loop reactor, and a fluidized bed reactor. In one or more embodiments, the second bioreactor has a capacity of more than 10,000 gallons, in another embodiment more than 100,000 gallons, and in another embodiment more than 1,000,000 gallons. In one or more embodiments, the second bioreactor is adapted to provide a closed system except for a reactant inlet and a product or byproduct outlet.

[0077] In one or more embodiments, the concentration of microorganisms in the second reactor may be quantified based on the dry cell weight per unit volume of the reactor. For example, in one or more embodiments, the concentration of microorganisms in the second reactor is greater than 10 grams of dry cell weight per liter, greater than 50 grams in another embodiment, and greater than 100 grams in another embodiment.

[0078] Technology for forming recombinant microorganisms

[0079] In certain embodiments, a nucleotide sequence for expressing an intermediate-forming enzyme or for efe is inserted into a microbial expression vector. In various embodiments, the microbial expression vector may include a bacterial vector plasmid, a nucleotide guide for a homologous recombination system, an antibiotic-resistant system, an auxiliary system for protein purification and detection, a CRISPR CAS system, a phage display system, or a combination thereof.

[0080] As described above, in one or more embodiments, multiple copies of the efe expression nucleotide sequence may be inserted into ethylene-forming microorganisms. Similarly, multiple copies of an intermediate enzyme expressing the nucleotide sequence may be inserted into photosynthetic microorganisms. The number of copies of the gene inserted into the vector and / or host genome is referred to herein as the “copy number.” In certain embodiments, the efe expression nucleotide sequence has a copy number greater than 1 in the microbial expression vector, greater than 10 in other embodiments, greater than 100 in other embodiments, and greater than 250 in other embodiments. As is apparent, expressing multiple copies of efe expressing the nucleotide sequence can increase ethylene yield and thus reduce the volume and cost of ethylene production on a commercial scale.

[0081] In certain embodiments, the microbial expression vector comprises at least one microbial expression promoter. As understood by those skilled in the art, the microbial expression promoter is a nucleotide sequence that initiates the transcription of a later, usually adjacent, DNA sequence, and may be constitutive or inducible. In certain embodiments, at least one microbial expression promoter comprises, without limitation, a photosensitized promoter, a chemically sensitive promoter, a temperature-sensitive promoter, a Lac promoter, a T7 promoter, a CspA promoter, a lambda PL promoter, a lambda CL promoter, a serially generating promoter, a psbA promoter, or a combination thereof. In certain embodiments, at least one promoter inducer may be added to the bioreactor or the reaction medium within the bioreactor to control the amount of organic intermediate and / or the amount of ethylene produced. In certain embodiments, the promoter inducer comprises lactose, xylose, IPTG, cold shock, heat shock, or a combination thereof.

[0082] In one or more embodiments, the ICD and GDH genes can be synthesized using gBlocks™ gene fragments cloned into pSyn6 plasmid constructs (pSyn6_ICD and pSyn6_GDH). For cloning into the pSyn6 plasmid, S. ilongatus ( S. elongatus The ICD coding sequence is flanked by the N-terminal HindIII and C-terminal BamHI recognition sites (Sequence Identification No.: 4). Using the plasmid construct, the ICD and GDH genes can be cloned into unmodified S. ilongatus or S. ilongatus Aglgc mutant strains (see Example 2). Transformation can be performed between 1 to 3 copies of the target gene. Cloning of the ICD and GCH genes can be confirmed by PCR and sequencing. aKG synthesis and quantification can be evaluated by SDS-PAGE, Western Blot, and ethylene production assay.

[0083] In one or more embodiments, generating glycogen mutant strains of cyanobacteria will alter the bacterial pathways to produce and secrete higher concentrations of keto acids, such as aKG. Glycogen mutant cyanobacteria can be generated by generating glycogen-deficient strains through mutations in the glgc gene (Aglgc). For example, the ampicillin resistance (AmpR) gene can be synthesized using gBlocks™ and incorporated into a plasmid construct. The plasmid construct can be transformed into wild-type cyanobacteria (e.g., Cytecchocystis, Synechococcus ilongatus 2973, Synechococcus ilongatus 2434). Subsequently, a mutant strain can be generated by replacing a portion of the wild-type glgc gene with the AmpR gene. The Aglgc mutant strain can be identified by PCR and sequencing after being grown in an AmpR-containing medium.

[0084] Maintaining volatile gas levels

[0085] In one or more embodiments, the second reactor contains a safe level of oxygen gas. In particular, the head space of the second reactor and the gas effluent stream of the second reactor contain a safe level of oxygen gas relative to ethylene. As recognized by a person skilled in the art, a commercially acceptable level of oxygen gas in the ethylene stream may be defined by a lower explosion limit (LEL) that takes into account the level of ethylene present. In one or more embodiments, the amount of oxygen in the second reactor (i.e., in the head space of the reactor or in the gas effluent stream) is less than the acceptable LEL, less than 80% of the acceptable LEL in another embodiment, and less than 50% of the acceptable LEL in another embodiment.

[0086] Process characteristics

[0087] As described herein, the method of the present invention is effective in solving safety problems associated with the co-generation of ethylene and oxygen by using a biosynthetic process while converting carbon dioxide into ethylene with high carbon efficiency.

[0088] In one or more embodiments, the method of the present invention generates ethylene at a generation rate greater than 100, greater than 500 in another embodiment, greater than 1000 in another embodiment, greater than 1500 in another embodiment, greater than 2000 in another embodiment, and greater than 2500 μmol / gCDW / hour in another embodiment (where CDW refers to cell dry weight).

[0089] Various modifications and changes that do not depart from the scope and spirit of the present invention will be apparent to those skilled in the art. The present invention is not formally limited to the exemplary embodiments described herein.

Claims

Claim 1 A method for producing ethylene comprising: (i) providing a gas stream containing more than 1 volume% of carbon dioxide; (ii) providing water; (iii) converting the carbon dioxide and water into an organic intermediate of sucrose, dextrose, xylose, glucose, fructose, alpha-ketoglutarate, or a mixture thereof and oxygen gas in the presence of light and photosynthetic microorganisms; (iv) separating the oxygen gas from the organic intermediate; and (v) converting the organic intermediate into ethylene and carbon dioxide through microorganisms after the step (iv) of separating the oxygen gas from the organic intermediate. Claim 2 A method for producing ethylene according to claim 1, wherein the step (v) of converting an organic intermediate into ethylene and carbon dioxide is carried out in the presence of an excess amount of water from the step (ii) of converting carbon dioxide and water into an organic intermediate, wherein (v) the step of converting the organic intermediate into ethylene and carbon dioxide further comprises the step of consuming only a portion of the organic intermediate formed in the step (iii) of converting carbon dioxide and water into an organic intermediate and oxygen gas, and returning the excess water and organic intermediate from the step (v) of converting the organic intermediate into ethylene and carbon dioxide to the step (iii) of converting carbon dioxide and water into an organic intermediate. Claim 3 A method for producing ethylene according to claim 1, wherein the step (iii) of converting carbon dioxide and water into an organic intermediate and oxygen gas is carried out in a first bioreactor containing microorganisms that produce an organic intermediate and oxygen gas from the carbon dioxide in the presence of light energy. Claim 4 A method for producing ethylene according to any one of claims 1 to 3, wherein the gas stream contains more than 3 volume% of carbon dioxide. Claim 5 A method for producing ethylene, wherein, in any one of claims 1 to 3, the step of compressing a flue gas stream from a combustion stage to form a stream containing carbon dioxide is further included. Claim 6 A method for producing ethylene according to any one of claims 1 to 3, wherein the step (iv) of separating oxygen from the organic intermediate produces an organic intermediate-rich stream introduced into the step (v) of converting the organic intermediate into ethylene and carbon dioxide. Claim 7 A method for producing ethylene according to any one of claims 1 to 3, wherein the organic intermediate-rich stream contains less than 30 ppm of oxygen. Claim 8 A method for producing ethylene, wherein, in any one of claims 1 to 3, the step of separating oxygen gas comprises discharging oxygen gas from a first bioreactor. Claim 9 delete Claim 10 A method for producing ethylene according to any one of claims 1 to 3, wherein the step (v) of converting the organic intermediate into ethylene and carbon dioxide is carried out in the substantial absence of light energy. Claim 11 A method for producing ethylene according to claim 1, wherein the ethylene and carbon dioxide formed in step (v) of converting an organic intermediate form a product stream. Claim 12 A method for producing ethylene according to claim 11, further comprising the step of converting oxygen gas in a product stream into carbon dioxide. Claim 13 A method for producing ethylene according to claim 11 or 12, further comprising the step of removing water from a product stream. Claim 14 A method for producing ethylene according to claim 11 or 12, further comprising the step of separating carbon dioxide from a product stream. Claim 15 A method for producing ethylene according to claim 14, wherein the step of separating carbon dioxide from a product stream produces an ethylene-rich stream. Claim 16 A method for producing ethylene according to claim 15, wherein the step of separating carbon dioxide from a product stream generates a carbon dioxide stream, wherein the carbon dioxide stream is introduced into the step (iii) of converting carbon dioxide and water into an organic intermediate and oxygen gas. Claim 17 A method for producing ethylene, wherein, in any one of claims 1 to 3, the step of converting carbon dioxide and water into an organic intermediate and oxygen gas is carried out in a first bioreactor. Claim 18 A method for producing ethylene according to any one of claims 1 to 3, wherein the step of separating oxygen gas from an organic intermediate comprises discharging oxygen gas from an aqueous medium containing an organic intermediate. Claim 19 A method for producing ethylene according to any one of claims 1 to 3, wherein the step of converting the organic intermediate into ethylene and carbon dioxide after the step of separating oxygen gas from the organic intermediate is carried out in a second bioreactor. Claim 20 An ethylene production system comprising: (i) a first bioreactor comprising photosynthetic microorganisms that convert carbon dioxide into an organic intermediate and byproduct oxygen gas, wherein the first bioreactor has a carbon dioxide inlet, a first outlet for the organic intermediate, and a second outlet for the byproduct oxygen gas; and (ii) a second bioreactor fluidly connected to the first bioreactor and comprising microorganisms that convert the organic intermediate produced in the first bioreactor into ethylene, wherein the second bioreactor has an outlet for a gaseous substance containing ethylene, and the second bioreactor has an outlet for a fluid substance containing an unreacted organic intermediate. Claim 21 An ethylene production system according to claim 20, wherein the outlet for the fluid material of the second bioreactor is fluidly connected to the first bioreactor. Claim 22 An ethylene production system according to claim 20, wherein the outlet for the gaseous material of the second bioreactor is fluidly connected to a carbon dioxide separator. Claim 23 An ethylene production system according to claim 22, wherein the carbon dioxide separator includes an outlet for purified carbon dioxide, said outlet for purified carbon dioxide being in fluid communication with a first bioreactor.

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