A method for producing ethylene from carbon dioxide

Abstract

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

Description

Technical Field

[0006]

[0001] This application claims the benefit of U.S. Provisional Patent Application No. 62 / 992,689, filed Mar. 20, 2020, and U.S. Provisional Patent Application No. 63 / 052,664, filed Jul. 16, 2020.

[0002] ​​​​​​​​​​​​​​​​​​​​Pseudomonas syringae is known to synthesize ethylene using alpha-ketoglutarate, an intermediate in the tricarboxylic acid (TCA) cycle, in a one-step reaction catalyzed by an ethylene-forming enzyme called "efe (ethyleneforming enzyme)." With the aim of directly producing ethylene from carbon dioxide, U.S. Patent No. 9,309,541 discloses a method for expressing and overexpressing the efe gene in hosts such as Synechocystis to create strains capable of phototrophically producing ethylene. In other words, bioengineering modifies photoautotrophs so that carbon fixation products are converted to ethylene in a one-step reaction. Current research focuses on modifying photoautotrophs to produce ethylene, but ethylene recovery can be a challenge. As outlined in Eckert et al., Ethylene-forming enzyme and bioethylene production, BIOTECHNOLOGY FOR BIOFUELS 2014, 7:33, when O2 is produced simultaneously with ethylene in the photosynthetic system, there are significant safety concerns regarding the flammability of ethylene in the presence of O2, requiring engineering designs to mitigate the risks. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] U.S. Patent No. 7,807,427 [Patent Document 2] U.S. Patent No. 9,309,541 [Non-patent literature]

[0008] [Non-Patent Document 1] Eckert et al.,Ethylene-forming enzyme and bioethylene production,BIOTECHNOLOGY FOR BIOFUELS 2014,7:33 [Overview of the project] [Means for solving the problem]

[0009] One or more embodiments of the present invention provide a method comprising: (i) providing a gas stream containing more than 1 volume percent of carbon dioxide; (ii) providing water; (iii) converting the carbon dioxide and the water into an organic intermediate and an 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.

[0010] A further embodiment of the present invention provides a system for producing ethylene, the system comprising: (i) a first bioreactor comprising photosynthetic microorganisms that convert carbon dioxide into organic intermediates, the first bioreactor having a carbon dioxide inlet and an outlet for organic intermediates; and (ii) a second bioreactor in fluid communication with the first bioreactor comprising microorganisms that convert organic intermediates produced in the first bioreactor into ethylene, the second bioreactor having an outlet for a gaseous material containing ethylene and an outlet for a fluid material containing unreacted organic intermediates. [Brief explanation of the drawing]

[0011] [Figure 1] This is a schematic diagram of a system for carrying out an embodiment of the present invention.

[0012] [Figure 2] This is a schematic diagram of a subsystem for delivering carbon dioxide in an embodiment of the present invention.

[0013] [Figure 3]Schematic diagram of an alternative system including a second photosynthesis bioreactor for implementing embodiments of the present invention.

[0014] [Figure 4] Schematic diagram of a system including an oxygen-fuel combustion system for implementing embodiments of the present invention.

[0015] [Figure 5] Schematic diagram of a system including upstream carbon dioxide purification for implementing embodiments of the present invention.

[0016] [Figure 6] Schematic diagram of an ethylene purification and compression scheme applicable to one or more embodiments of the present invention.

[0017] [Figure 7] Schematic diagram of an alternative system including carbon dioxide membrane separation for implementing one or more embodiments of the present invention.

[0018] [Figure 8] Schematic diagram of an alternative system including a single bioreactor for implementing embodiments of the present invention.

Embodiments for Carrying Out the Invention

[0019] Embodiments of the present invention are at least partially based on the disclosed method of biosynthesizing ethylene from carbon dioxide at an industrially significant level. According to embodiments of the present invention, carbon dioxide is first photosynthetically converted to an organic intermediate with the production of oxygen gas as a by-product. The by-product oxygen gas is then separated from the organic intermediate, and then the organic intermediate is biologically converted to ethylene in the absence of the by-product oxygen gas. Current techniques related to ethylene biosynthesis focus on one-step synthesis, but the two-step method of the present invention addresses safety concerns related to the simultaneous production of ethylene and oxygen gas at an industrially significant level. Also, the bioconversion of the organic intermediate to ethylene produces carbon dioxide as a by-product, which affects the overall carbon efficiency. Furthermore, the amount of carbon dioxide in the ethylene product stream is much higher than in most carbon dioxide feed streams (e.g., flue gas), and thus, carbon dioxide in the ethylene product stream can be a valuable resource if properly managed. Accordingly, embodiments of the present invention provide a method of managing the by-product carbon dioxide, which includes, but is not limited to, photosynthetically converting carbon dioxide to an organic intermediate, which can be recycled to the step of biologically converting the organic intermediate to ethylene. Still further, the step of biologically converting the organic intermediate to ethylene can be efficiently realized on a commercial scale by using an industrial reactor such as a continuously stirred tank reactor operating in a steady state or near a steady state, the steady state of which affects the incomplete consumption of the organic intermediate, the loss of carbon efficiency, and the loss of valuable raw materials. Accordingly, embodiments of the present invention provide solutions to these problems by properly managing the effluent stream from the reactor in which the organic intermediate is converted to ethylene.

[0020] Overview of the Method and System Embodiments of the present invention can be described with reference to Figure 1, which shows a system 20 for converting carbon dioxide to ethylene. The system includes a first bioreactor 21 and a second bioreactor 41 connected in series thereto. The first bioreactor 21 is in direct or indirect fluid communication with the second bioreactor 41 via an intermediate product conduit 31. The second bioreactor 41 is also in fluid communication with the first bioreactor 21 via an intermediate recirculation conduit 33. A carbon dioxide separator 61 is located downstream of the second bioreactor 41 and is in direct or indirect fluid communication with the second bioreactor 41 via a conduit 51. The carbon dioxide separator 61 may also be in direct or indirect fluid communication with the first bioreactor 21 via a carbon dioxide recirculation conduit 53.

[0021] According to embodiments of the present invention, the first bioreactor 21 includes a photosynthetic organism culture (i.e., photosynthetic microorganisms) that converts carbon dioxide and water supplied to the bioreactor 21 into organic intermediates. This conversion takes place in the presence of light energy supplied to the first bioreactor 21. The synthesis of the organic intermediates takes place in the presence of excess water acting as a reaction medium, which acts as a carrier for the intermediate product flow. In one or more embodiments, the organic intermediates are water-soluble. As those skilled in the art will recognize, the photosynthetic organism culture can be supplied to the bioreactor 21 from an inoculator 23.

[0022] While organic intermediates are formed in the bioreactor 21, oxygen gas is produced as a byproduct. According to an aspect of the present invention, the oxygen gas is separated from the organic intermediates before the intermediate product stream is introduced into the second bioreactor 41. For example, the oxygen gas can be released from the first bioreactor 21 along with other volatile substances, such as nitrogen gas, within the reactor.

[0023] Organic intermediates are transferred directly or indirectly from the first reactor 21 to the second bioreactor 41 via the intermediate product conduit 31 within the intermediate product stream. In one or more embodiments, the intermediate product stream can be filtered as it exits the bioreactor 21. During operation, filtering of the intermediate product stream as it exits the bioreactor 21 can prevent the movement of any medium used to immobilize photosynthetic microorganisms, thereby helping to prevent the movement of microorganisms from the first bioreactor 21 to the second bioreactor 41.

[0024] In addition to filtering the intermediate product stream as the flow exits bioreactor 21, or instead, the intermediate product stream can be filtered and / or sterilized in one or more intermediate units positioned between bioreactor 21 and bioreactor 41. For example, referring to Figure 2, an optional sterilization unit 35 can be positioned between the first bioreactor 21 and the second bioreactor 41. Unit 35 may include a filtration unit. In addition to, or instead of, a filtration unit, unit 35 may include a centrifugation unit. Or, in other embodiments, in addition to, or instead of, filtration or centrifugation, unit 35 may include a purification unit (e.g., a sedimentation tank). In addition to, or instead of, filtration, centrifugation, and / or purification, unit 35 may include a sterilization unit. For example, the intermediate product stream may be treated by a sterilization unit using UV sterilization, heat, or gamma rays, which may be done to prevent the introduction of any live microorganisms from the first bioreactor 21 to the second bioreactor 41.

[0025] In one or more embodiments, the second bioreactor 41 includes an ethylene-producing biological culture (i.e., an ethylene-producing organism) that converts an organic intermediate into ethylene.

[0026] As those skilled in the art will recognize, several subsystems can be designed to introduce microbial cultures into each bioreactor. Those skilled in the art can easily design a suitable system to achieve these objectives. For example, referring to several figures, a suitable group of microorganisms can be supplied to bioreactors 21 and / or bioreactors 41 from an inoculation unit 23, which may also be called an inoculation reactor 23. The inoculation unit 23 may include separate chambers or containers for each microorganism, or separate units may be provided for each microorganism. Furthermore, it may be desirable to remove biomass from one or more bioreactors. In one or more embodiments, the system of the present invention may include a biomass digestion unit 25 that can remove biomass obtained from either or both bioreactors from any immobilization support medium and remove it from the system. During operation, the biomass digestion unit 25 can be in fluid communication with either or both bioreactors 21, 41, or the biomass can be manually removed from each reactor (optionally together with the immobilization material). In one or more embodiments, biomass can be converted into nutrients such as amino acids and returned to the bioreactor as a nutrient source for microorganisms. Alternatively, the biomass can be removed from the system and used for other purposes such as fertilizer.

[0027] Within the bioreactor 41, carbon dioxide is produced as a byproduct of ethylene synthesis, and ethylene and carbon dioxide are removed from the second bioreactor 41 as a gaseous product stream. A liquid effluent also exits the second bioreactor 41. This liquid effluent may contain water and unreacted organic intermediates, and this stream can be returned to the first bioreactor 21 via the organic intermediate recirculation conduit 33. As best shown in Figure 2, the liquid effluent containing water and unreacted organic intermediates can be filtered and / or sterilized in a filtration / sterilization unit 37. This filtration and / or sterilization may utilize the same type of technique as in unit 35, and therefore the above description relating to unit 35 is incorporated hereby incorporated. As those skilled in the art will recognize, it may be useful to ensure that ethylene-producing microorganisms never move to the first bioreactor 21.

[0028] The gaseous product stream exiting the second bioreactor 41 is sent downstream of the second bioreactor 41, either directly or indirectly, via conduit 51, to a carbon dioxide separator 61, which may also be called a carbon dioxide separation unit 61. Within the separator 61, which may also be called a separator system 61, carbon dioxide is separated from the gaseous product stream and provided with a concentrated ethylene stream, which may also be called a concentrated ethylene stream, carried by conduit 53. This concentrated ethylene stream can be sent downstream to a purification and pressurization unit 100, which will be described in more detail herein. The separator 61 also generates a concentrated carbon dioxide stream, which may also be called a purified carbon dioxide stream, and this concentrated carbon dioxide stream can be sent back to the first bioreactor 21 via conduit 55.

[0029] In an alternative embodiment that can be illustrated with reference to Figure 3, the purified carbon dioxide stream produced by the carbon dioxide separator 61 can be delivered via conduit 57 to an intermediate bioreactor 71 (which may be called a second photosynthetic bioreactor 71) containing a photosynthetic biological culture that photosynthetically converts carbon dioxide into organic intermediates and oxygen gas. Advantageously, since the carbon dioxide supply stream to the bioreactor 71 is a purified carbon dioxide stream (via the carbon dioxide separator 61), the gaseous byproduct stream leaving the second photosynthetic bioreactor 71 contains a relatively pure oxygen gas stream, which can be delivered via conduit 75. A relatively pure oxygen stream contains a stream substantially free of nitrogen and argon gases, and those skilled in the art in the context of the present invention will recognize that if nitrogen and argon gases are present, a complex and expensive process (e.g., air separation technique) is required to separate them from the oxygen gas. However, the presence of carbon dioxide in a relatively pure oxygen gas stream as defined herein is not harmful, and therefore, unless otherwise specified, carbon dioxide may be present in a relatively pure oxygen gas stream because it can be more easily separated from the oxygen gas stream. Without conflicting with the first bioreactor 21, the intermediate bioreactor 71 generates an effluent, which may contain organic intermediates and water, and can be returned to the first bioreactor 21 and / or the second bioreactor 41 via the conduit 79. As generally shown, this effluent may be filtered and / or sterilized in unit 37, as described with reference to Figure 2.

[0030] As shown throughout the drawings, the gas flow exiting the second bioreactor 41 and delivered through the conduit 51 can optionally undergo one or more treatments or operations before carbon dioxide separation in unit 61. For example, the flow can be pressurized in a compression unit 43. In addition to pressurization, or instead, the gas flow can optionally be treated for oxygen extraction in an oxygen extraction unit 45. Since carbon dioxide can be produced in the oxygen extraction unit 45, it may be beneficial to place the oxygen extraction unit 45 upstream of the carbon dioxide separation unit 61, from which the carbon dioxide produced in unit 45 can be extracted.

[0031] Still another embodiment of the present invention can be described with reference to Figure 8. As shown, process 120 includes a single vessel 121, which may also be called an integrated bioreactor 121, instead of the two bioreactors 21, 41 shown with respect to the other systems described above. During operation, the light energy supplied to the bioreactor 121 is controlled in such a way that it generates a light cycle and a dark cycle. During operation, photosynthetic microorganisms in the integrated bioreactor 121 convert carbon dioxide into organic intermediates during the light cycle, and then during the dark cycle, ethylene-forming microorganisms in the integrated bioreactor 121 convert the organic intermediates into ethylene during the dark cycle. Oxygen can be extracted from the bioreactor 121 during oxygen production in the light cycle, and ethylene can be extracted from the bioreactor 121 during ethylene production in the dark cycle. Without contradiction to the other embodiments, ethylene may be produced co-produced with carbon dioxide, and ethylene and carbon dioxide can be separated in the downstream processes described above (e.g., in a carbon dioxide scrubber 61).

[0032] Returning to Figure 2, the method of the present invention may include adjusting the carbon dioxide input flow (i.e., adjusting the flow before providing the flow to the bioreactor 21). In one or more embodiments, the carbon dioxide input flow carried by the conduit 11 may be pressurized in a compressor 13. In one or more embodiments, the pressurization of the input flow (e.g., in the compressor 13) is achieved to a pressure sufficient to overcome the opposing forces in the first bioreactor 21, so that the inert gas (e.g., nitrogen) in the carbon dioxide input flow can eventually enter the reactor headspace. In one or more embodiments, the carbon dioxide input flow is pressurized to a pressure of about 2 to about 20 psig, in other embodiments about 3 to about 18 psig, and in other embodiments about 5 to about 15 psig.

[0033] Furthermore, as best shown in Figure 2, the carbon dioxide injection stream can be cooled in a quencher 15 before being delivered to the bioreactor 21 via the conduit 17. As those skilled in the art will recognize, the quencher 15 may include a water cooling unit including a cooling water loop 15', the cooling water loop 15' may include one or more heat exchangers for cooling the water. In one or more embodiments, the carbon dioxide injection stream is cooled to a temperature below which it would have a detrimental effect on the microbial culture in the bioreactor 21. In one or more embodiments, the carbon dioxide injection stream is cooled to a temperature of about 10 to about 80°C, in other embodiments about 20 to about 60°C, and in other embodiments about 30 to about 50°C before being delivered to the bioreactor 21.

[0034] In one or more embodiments, the carbon dioxide input stream may contain a considerable amount of water, at least a portion of which will be condensed in the quencher 15 via a cooling cycle, so that water from the quencher 15 can be supplied to the first bioreactor 21, which consumes a considerable 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 can be treated with a caustic substance 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, in other embodiments to a pH greater than 6.0, and in other embodiments to a pH greater than 6.5 (e.g., in the range of 5.5 to 8.0 or 6.0 to 7.5). The caustic treatment of the water is expected to form carbonates such as sodium carbonate, which not only benefit the first bioreactor 21 in terms of pH control but also provide an additional carbon dioxide source in the form of sodium carbonate and / or sodium bicarbonate. Those skilled in the art can easily adjust the conditions and / or provide additional components (e.g., hydrochloric acid) to obtain a desirable balance between sodium carbonate and sodium bicarbonate. In certain embodiments, the caustic soda supplied to the cooling water in the quencher 15 originates from other processes that can be integrated into embodiments of the present invention. For example, caustic soda can be used in ethylene purification and / or sodium carbonate can be produced in ethylene purification that can be incorporated into the quencher 15.

[0035] In further embodiments, as described in relation to other embodiments, the liquid outflow from the second bioreactor 41 can be sent back to the first bioreactor 21 and optionally to the quencher 15. In one or more embodiments, the liquid outflow from the second bioreactor 41 is first processed at the sterilization station 37 before being sent to the quencher 15.

[0036] Carbon dioxide supply flow to the first bioreactor The method of the present invention can advantageously convert carbon dioxide from various gas sources, which may be called carbon dioxide input streams, into useful intermediates that can be converted to ethylene. In one or more embodiments, carbon dioxide is supplied to the system by a carbon dioxide input stream containing more than 1% by volume, more than 3% by volume in other embodiments, more than 5% by volume in other embodiments, and more than 10% by volume in other embodiments. In one or more embodiments, the carbon dioxide input stream is or is derived from the exhaust stream (i.e., flue gas stream) of a combustion process. As those skilled in the art will recognize, 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 generator, and an oxygen-fueled combustion process.

[0037] In one or more embodiments, the carbon dioxide input stream may originate from the exhaust stream of an oxy-fuel combustion process, also known as oxycombustion. Those skilled in the art will recognize that these methods involve the combustion of a fuel (e.g., hydrocarbons) in the substantially absent presence of nitrogen and argon. For example, these processes may include a combustion process to which substantially pure oxygen (i.e., substantially free of nitrogen and argon gases), or a mixture of pure oxygen and recirculated flue gas, is supplied. As a result, the combustion products are mostly carbon dioxide and water, with substantially little nitrogen by-product or argon. Advantageously, since the carbon dioxide input stream from the oxycombustion process contains a considerable level of carbon dioxide and substantially no nitrogen and oxygen, the gaseous by-product stream from the photosynthetic bioreactor will contain substantially high concentrations of oxygen gas, along with any unreacted carbon dioxide. The gaseous by-product stream from the photosynthetic bioreactor can then be recirculated to an oxycombustion unit as fuel in the oxycombustion process, in which case the oxycombustion process is cooled if any unreacted carbon dioxide remains.

[0038] Referring, for example, to Figure 4, one embodiment of the present invention includes a carbon dioxide input stream from an oxygen combustion unit 18. Similar to the previous embodiment, carbon dioxide is photosynthetically converted into an organic intermediate in the first bioreactor 21, accompanied by the by-product oxygen gas. The oxygen gas stream, containing the by-products including oxygen gas and unreacted carbon dioxide, is sent to the oxygen combustion unit 18 via a conduit 22. Although not shown, the carbon dioxide input stream from the oxygen combustion unit 18 can also be cooled and pressurized as described above with respect to other embodiments (see, for example, Figure 2). The intermediate products generated in the first bioreactor 21 are sent downstream to the second bioreactor 41 in a manner consistent with other embodiments.

[0039] In yet another embodiment, a relatively pure carbon dioxide stream can be supplied to the first bioreactor 21. The relatively pure carbon dioxide stream can be obtained from several sources and generally includes a stream containing more than 90 vol% carbon dioxide, more than 95 vol% in another embodiment, and more than 99 vol% in yet another embodiment. When a relatively pure carbon dioxide stream is used, as described above, the method of the present invention produces a relatively pure (i.e., substantially free of nitrogen or argon gas) oxygen gas stream as a byproduct effluent from the first bioreactor 21. These relatively pure oxygen gas streams can be used for industrial applications, such as the oxychlorination of ethylene.

[0040] In one or more embodiments, a relatively pure carbon dioxide stream is generated as a step of the present invention and used as the feed stream. For example, the feed stream containing carbon dioxide can be purified and / or concentrated before being introduced into the first bioreactor 21. In one or more embodiments, the carbon dioxide feed stream can be purified by, for example, amine scrubbing and stripping techniques. Similar to one or more of the earlier embodiments, a relatively high-grade oxygen gas stream can be generated as a by-product stream exiting the first bioreactor by providing the purified carbon dioxide stream to the first bioreactor. Those skilled in the art will recognize that, in addition to or instead of amine scrubbing and stripping techniques, various carbon dioxide extraction and separation techniques can be used to purify and / or concentrate the carbon dioxide stream. These techniques include, but are not limited to, membrane separation, solid adsorbents, and the use of other solvent chemistry such as potassium carbonate.

[0041] An exemplary embodiment can be described with reference to Figure 5, which shows a system 50 including a first bioreactor 21 that receives a carbon dioxide input stream from a carbon dioxide purification unit 16. The purification unit 16 generates a purified carbon dioxide stream that is introduced into the first bioreactor 21 via a conduit 11'. Although not shown, the carbon dioxide input stream from a combustion unit can be cooled and pressurized as described above with respect to other embodiments (see, for example, Figure 2). In the bioreactor 21, the carbon dioxide is photosynthetically converted into an organic intermediate with the byproduct oxygen gas. The byproduct oxygen gas is delivered directly or indirectly via a conduit 24 to, for example, an industrial process 26 that requires relatively high-purity oxygen. In one or more embodiments, ethylene produced in the bioreactor 41 can also be delivered to the industrial process 26. Although not shown in Figure 5, it will be recognized that the ethylene flow from the second bioreactor 41 undergoes downstream processing, including but not limited to oxygen gas conversion, carbon dioxide extraction (and recirculation to the photosynthetic bioreactor), and ethylene purification, as described in relation to other embodiments.

[0042] Indeed, in embodiments in which a relatively pure oxygen byproduct stream can be obtained from the use of a relatively pure carbon dioxide stream by the photosynthetic bioreactor, the relatively pure oxygen stream can be used for industrial applications. In one or more embodiments, the gas stream exiting the photosynthetic bioreactor can undergo a carbon dioxide removal treatment to remove any unreacted carbon dioxide in the oxygen gas stream. The oxygen gas stream can then be sent to the desired industrial application. For example, the oxygen gas stream from these embodiments can be sent to an oxychlorination unit, where ethylene reacts with hydrochloric acid in the presence of oxygen gas. In this example, the ethylene may originate from an ethylene-producing bioreactor. It will be recognized that the ethylene stream from the ethylene-producing bioreactor undergoes a carbon dioxide removal treatment and ethylene purification, as described in relation to other embodiments.

[0043] Separation of carbon dioxide In one or more embodiments, the separation of carbon dioxide downstream (e.g., in the carbon dioxide separation unit 61) may be performed by conventional amine scrubbing / stripping. Various other carbon dioxide separation techniques can be used, and these include, but are not limited to, solvent separation using potassium carbonate, membrane separation, and solid adsorbent separation.

[0044] As those skilled in the art will recognize, amine scrubbing and stripping techniques or methods generally involve the absorption of carbon dioxide by an organic amine in a water carrier (i.e., scrubbing), followed by the regeneration or release of carbon dioxide from the organic amine (i.e., stripping). These systems and techniques for using them are well known in the art, as described in U.S. Patent Publications No. 2009 / 0038314, No. 2009 / 0156696, and No. 2013 / 0244312, which are incorporated herein by reference. See also Engineering Data Book, Volume II, Sections 17–26, Gas Processors Suppliers Assoc. (1994).

[0045] Membrane separation techniques may be used instead of, or in addition to, amine scrubbing / stripping. As those skilled in the art will recognize, these membranes may include polymer or inorganic microporous membranes through which carbon dioxide can pass. These membranes and techniques for using them are well known, as described in U.S. Patent Application Publications 2008 / 0173179 and 2013 / 0312604, which are incorporated herein by reference. In the implementation of the present invention, when membrane separation is used instead of amine scrubbing / stripping techniques, it may be desirable to remove residual ethylene. Residual ethylene can move into the permeate stream and, if not removed, will be sent back to the stationary reactor (i.e., the first bioreactor) and finally into the oxygen stream. In this regard, referring to Figure 7, an alternative system 20' is shown which includes a membrane separation unit 61' having a permeate flow of carbon dioxide sent downstream to an ethylene treatment unit 75 via a conduit 73, the ethylene treatment unit 75 may be adapted to catalytically treat the flow in order to remove any residual ethylene in the permeate flow (e.g. by catalytic combustion) before the permeate flow is sent back to the bioreactor 21 via the conduit 51'.

[0046] Ethylene purification As described above, carbon dioxide separation (e.g., in separator 61) of the ethylene-containing product stream from the second bioreactor 41 generates a concentrated ethylene stream that is transported by conduit 53. This concentrated ethylene stream can be purified and optionally compressed for later use and optionally transport within subprocess 100, which is best illustrated with reference to Figure 6. In one or more embodiments, in subprocess 100, the concentrated ethylene stream provided via conduit 53 is processed using one or more techniques. For example, the concentrated ethylene stream may undergo oxygen gas extraction treatment in an optionally selected oxygen gas extraction unit 101, where residual oxygen gas in the concentrated ethylene stream is consumed, for example, by catalytic combustion of a portion of the ethylene. In one or more embodiments, subprocess 100 may include polishing of the ethylene stream in a caustic cleaning unit 103 that removes any residual carbon dioxide (e.g., reduces the carbon dioxide level to less than 10 ppm, or less than 5 ppm, or less than 3 ppm). Downstream of the caustic washing unit 103, the ethylene concentrate stream may be dewatered in a dewatering unit 105, which may include a dewatering unit using molecular sieves. After dewatering, the ethylene concentrate stream can be condensed in a condenser 107, which can be cooled by a propylene refrigeration unit 108. Those skilled in the art will recognize that the sequence of various purification steps can be changed depending on several factors. They will also recognize that various steps in the purification process may be performed for the purpose of obtaining a desired pressure that may be required for use or transport (e.g., via pipeline). For this purpose, the ethylene concentrate stream may be pressurized before, after, or between two or more purification steps. For example, as shown in Figure 6, the stream may be pressurized in a compression unit 99. Similarly, further pressurization can be performed in an ethylene product pump 109.

[0047] photosynthetic microorganisms As described above, the first bioreactor contains a photosynthetic biological culture containing one or more photosynthetic microorganisms that convert carbon dioxide and water into organic intermediates in the presence of light energy. In various embodiments, the photosynthetic microorganisms may be of natural origin. In other embodiments, the photosynthetic microorganisms may be genetically modified to improve the production of the desired organic intermediates. In one or more embodiments, the photosynthetic microorganisms utilized in the first bioreactor may include photosynthetic bacteria such as cyanobacteria. As those skilled in the art will recognize, photosynthetic bacteria fix carbon by consuming carbon dioxide and water in the presence of light. Advantageously, the main products of the metabolic pathway of cyanobacteria under aerobic conditions are oxygen and organic intermediates such as sugars. Those skilled in the art will be able to select suitable photosynthetic microorganisms to produce the desired organic intermediates without excessive experimentation.

[0048] In one or more embodiments, the desired organic intermediate includes sucrose, dextrose, xylose, glucose, fructose, alpha-ketoglutaric acid, or a mixture thereof.

[0049] Examples of photosynthetic microorganisms include, but are not limited to, cyanobacteria, algae, and purple bacteria. Useful types of cyanobacteria include photosynthetic prokaryotes that perform oxygen-producing photosynthesis. Cyanobacteria useful for the purposes outlined herein are generally well known in the art. (See, for example, The Molecular Biology of Cyanobacteria by Donald Bryant, published by Kluwer Academic Publishers (1994), whose entire disclosure is incorporated herein by reference). Representative examples include cyanobacteria of the genus Synechococcus, such as Synechococcus lividus and Synechococcus elongatus, and cyanobacteria of the genus Synechocystis, such as Synechocystis minervae and Synchocystis Sp) PCC 6803. In this regard, U.S. Patent No. 7,807,427 is incorporated herein by reference in its entirety. Examples of synthetic microorganisms that can be used include those disclosed in U.S. Patent No. 10,196,627, which is incorporated herein by reference in its entirety. Further examples include the microorganisms disclosed in U.S. Patents No. 9,914,947 and No. 9,309,541, which are incorporated herein by reference in their entirety.

[0050] In one or more embodiments, cyanobacteria are genetically modified to express one or more exogenous genes encoding one or more enzymes that enhance the production of a target organic intermediate. In one or more embodiments, the target organic intermediate includes sucrose, dextrose, xylose, glucose, fructose, and alpha-ketoglutaric acid. As will be apparent to those skilled in the art, the specific genes added to the genome of the cyanobacteria (and the enzymes produced) are determined by the specific target organic intermediate.

[0051] In one or more embodiments, the modified photosynthetic microorganism contains a modified nucleotide sequence that produces an enzyme that forms alpha-ketoglutarate from carbon dioxide. In one embodiment, the modified photosynthetic microorganism expresses AKGP by expressing a non-natural alpha-ketoglutarate permease protein (AKGP) forming nucleotide sequence. In one or more embodiments, the modified microorganism produces a greater amount of 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.

[0052] In one or more embodiments, alpha-ketoglutarate (aKG) can be produced by oxidative decarboxylation of isocitrate by isocitrate dehydrogenase (ICD) or by oxidative deamination of glutamate by glutamate dehydrogenase (GDH). Target enzymes for cloning and aKG production in cyanobacteria may include ICD enzyme: 1.1.1.42, the coding sequence of Pseudomonas fluorescens (P.Fluorescens) ICD (SEQ ID NO: 1, SEQ ID NO: 2), ICD enzyme: 1.1.1.42, the coding sequence of Synechococcus elongatus PCC794 (SEQ ID NO: 3, SEQ ID NO: 4), and GDH enzyme: 1.4.1.2, the coding sequence of P.Fluorescens (SEQ ID NO: 5, SEQ ID NO: 6).

[0053] In one or more embodiments, the enzyme for forming alpha-ketoglutaric acid is selected from isocitrate dehydrogenase (ICD) proteins, glutamate dehydrogenase (GDH) proteins, or a combination thereof.

[0054] In one embodiment, a modified photosynthetic microorganism expresses an ICD protein having an amino acid sequence at least 98%, at least 95%, at least 90%, or at least 85% identical to SEQ ID NO: 1 by expressing a modified ICD protein nucleotide sequence having at least 98%, at least 95%, at least 90%, or at least 85% identical to SEQ ID NO: 2. In another embodiment, a modified photosynthetic microorganism expresses an ICD protein having an amino acid sequence at least 98%, at least 95%, at least 90%, or at least 85% identical to SEQ ID NO: 3 by expressing a modified ICD protein nucleotide sequence having at least 98%, at least 95%, at least 90%, or at least 85% identical to SEQ ID NO: 4. In one embodiment, the modified microorganism expresses a GDH protein having an amino acid sequence that is at least 98%, at least 95%, at least 90%, or at least 85% identical to SEQ ID NO: 5 by expressing a modified GDH protein nucleotide sequence having at least 98%, at least 95%, at least 90%, or at least 85% identical to SEQ ID NO: 6.

[0055] In one or more embodiments, the organic intermediate is sucrose. In some of these embodiments, for example, cyanobacteria (Synechococcus elongatus, Synechocystis) can be manipulated to produce sucrose, which acts as a substrate for the growth of ethylene-producing microorganisms. Various methods of manipulating Synechococcus elongatus PCC7942 to produce sucrose may include activation of one gene (cscB) and deletion of one gene (GlgC).

[0056] In one or more of these embodiments, the modified photosynthetic microorganism expresses sucrose synthase protein. In one or more embodiments, the sucrose synthase protein has an amino acid sequence that is at least 98%, at least 95%, at least 90%, or at least 85% identical to SEQ ID NO: 9 by expressing a modified sucrose synthase protein nucleotide sequence that is at least 98%, at least 95%, at least 90%, or at least 85% identical to SEQ ID NO: 10. In one or more of these embodiments, the modified microorganism expresses sucrose phosphate synthase protein. In one or more embodiments, the sucrose phosphate synthase protein has an amino acid sequence that is at least 98%, at least 95%, at least 90%, or at least 85% identical to SEQ ID NO: 11 by expressing a modified sucrose phosphate synthase protein nucleotide sequence that is at least 98%, at least 95%, at least 90%, or at least 85% identical to SEQ ID NO: 12.

[0057] As used herein, sequence identity refers to the relationship between two or more amino acid (polypeptide or protein) sequences or two or more nucleic acid (polynucleotide) sequences, determined by comparing their sequences. Sequence identity or similarity is generally compared over the entire length of each sequence. Those skilled in the art will recognize that “identity” refers to the degree of sequence relevance between amino acid sequences or nucleic acid sequences, sometimes determined by the consistency between strings of amino acid sequences or nucleic acid sequences. “Similarity” between two amino acid sequences is determined by comparing the amino acid sequence and its conserved amino acid substitutions of one polypeptide with the sequence of another polypeptide. Those skilled in the art can readily calculate “identity” and “similarity” by various known methods. For example, methods for determining identity and similarity are codified in publicly available computer programs such as BestFit, 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)), published by NCBI and other sources (BLAST.RTM.Manual, Altschul, S. et al., NCBI NLM NIH Bethesda, Md.20894), and EMBOSS (European Molecular Biology Open Software Suite). Exemplary parameters for amino acid sequence comparison using EMBOSS are gap open 10.0, gap extend 0.5, and block amino acid substitution matrix (BLOCKS SUBbstitution Matrix: Blosum). Exemplary parameters for nucleic acid sequence comparison using EMBOSS are gap open 10.0, gap extend 0.5, and DNA full matrix (DNA identity matrix). As those skilled in the art will understand, DNA / protein sequences between different species can be compared and sequence homology can be determined using online data such as Genebank, KEG, BLAST, and Ensemble. Those skilled in the art may also take into account so-called "conservative" amino acid substitutions, which refer to the interchangeability of residues with similar side chains. For example, the group of amino acids having aliphatic side chains are glycine, alanine, valine, leucine, and isoleucine; the group of amino acids having aliphatic-hydroxyl side chains are serine and threonine; the group of amino acids having amide-containing side chains are asparagine and glutamine; the group of amino acids having aromatic side chains are phenylalanine, tyrosine, and tryptophan; the group of amino acids having basic side chains are lysine, arginine, and histidine; and the group of amino acids having sulfur-containing side chains are cysteine ​​and methionine. The amino acid substitution variants disclosed herein are obtained by removing at least one residue in the disclosed sequence and inserting a different residue in its place. Preferably, the amino acid changes are conservative. Preferred conservative substitutions for each of the naturally occurring amino acids are as follows: That is, substitutions are made from Ala to ser; Arg to Lys; Asn to gln or his; Asp to glu; Cys to ser or ala; Gln to asn; Glu to asp; Gly to pro; His to asn or gln; Ile to leu or val; Leu to ile or val; Lys to arg, gln or glu; Met to leu or ile; Phe to met, leu or tyr; Ser to thr; Thr to ser; Trp to tyr; Tyr to trp or phe; and Val to ile or leu.

[0058] Unless otherwise specified, the terms “adapted” or “codon adapted” refer to “codon-optimized” polynucleotides disclosed herein, the sequences of which may be natural or non-natural, or adapted to expression in other microorganisms. Codon optimization adapts the codon usage for an 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.

[0059] In one embodiment, the modified photosynthetic microorganisms include delta-glgc (Δglgc) mutant microorganisms lacking expression of glucose-1-phosphate adenylyltransferase protein. Similarly, cyanobacterial cells lacking the functional ADP glucose pyrophosphorylase enzyme are known as described in U.S. Patent No. 9,309,541, and these are incorporated herein by reference in their entirety.

[0060] Ethylene-producing microorganisms As described above, ethylene-producing organisms include organisms that naturally produce ethylene by consuming organic intermediates produced in a photosynthetic bioreactor, or organisms that have been genetically modified to produce ethylene. In one or more embodiments, microorganisms utilized in the second bioreactor include microorganisms that express or have been genetically modified to express an ethylene-forming enzyme (efe) gene. These microorganisms may be referred to herein as efe-forming microorganisms. Microorganisms that produce or have been modified to produce ethylene are well known in the art, and any microorganism capable of producing ethylene from the organic intermediate of interest under the reaction conditions described may be used. In one or more embodiments, the desired microorganism does not produce anything else that, if produced, could interfere with the methods described herein.

[0061] Exemplary efe-forming microorganisms include Pseudomonas syringae, Pseudomonas syringae pv. Glycinia, and Penicillium digitatum, all of which naturally express efe. In other embodiments, the microorganisms in the second reactor include modified microorganisms that express or overexpress efe genes, such as genes naturally found in Pseudomonas syringae or Penicillium digitatum. In these embodiments, the host microorganism is genetically introduced using one or more copies of one or more efe genes using one of many methods known in the art for gene transfer. Useful host microorganisms may include, but are not limited to, Escherichia coli (E. coli), Saccharomyces cerevisiae, Pseudomonas putida, Trichoderma viride, and Trichoderma reesei.

[0062] In one or more embodiments, a modified microorganism for producing efe may be produced as described in Wang, J.P. et al., "Metabolic engineering for ethylene production by inserting the ethylene-forming enzyme gene (efe) at the 16S rDNA sites of Pseudomonas putida KT 2440," Biosource Technology, (2010) 101:6404-6409, the disclosure thereof is incorporated herein by reference in its entirety. In these embodiments, the efe gene is cloned from P. syringae pv. glycinea ICMP2189 and inserted into one or more 16S rDNA sites of the Pseudomonas pudita KT 2440 host using double crossover recombination.

[0063] As described above, in one or more embodiments, the microorganism that produces efe enzyme includes a genetically modified microorganism. In one or more embodiments, the efe-forming microorganism is a modified microorganism that contains in its DNA one or more foreign nucleotide sequences that produce efe when expressed. In one or more embodiments, the modified microorganism produces a greater amount of efe enzyme than that produced by a control microorganism lacking the modified nucleotide sequence. This amount may exceed 5% of the amount produced by the control microorganism lacking the modified nucleotide sequence, exceed 50% in other embodiments, and exceed 75% in other embodiments. In various embodiments, the genetically modified microorganism is modified to contain two or more copies of the foreign nucleotide sequence that produces efe when expressed, further improving ethylene production.

[0064] In one or more embodiments, the polynucleotide encoding the Pseudomonas savastanoi pv.Phaseolicola efe protein (GenBank: KPB 44727.1, SEQ ID NO: 8) can be cloned into a pET-30a(+) vector plasmid. The corresponding nucleotide sequence can also be adapted to be expressed in E. coli (SEQ ID NO: 7) and to include an optional His tag at the C-terminus, followed by a stop codon and a HindIII site. An NdeI site can also be used for cloning at the 5-prime end, in which case the NdeI site includes an ATG start codon. In various embodiments, E. coli BL21(DE3) competent cells can be transformed with the recombinant plasmid.

[0065] In some embodiments, the ampicillin cassette can be activated by an isopropyl thiogalactoside (IPTG)-inducible promoter (pTrc) in the presence of the LacI gene, and the LacI gene can be controlled by the LacIq promoter (SEQ ID NO: 13).

[0066] In one embodiment, a recombinant microorganism that forms ethylene expresses an efe protein having an amino acid sequence that is at least 95%, 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%, at least 90%, or at least 80% identical to SEQ ID NO: 8.

[0067] Those skilled in the art will recognize that immobilizing microorganisms can be beneficial to increase yield and assist in the control of microorganisms within a process (e.g., to help separate microorganisms from the product flow or reaction medium). In one or more embodiments, the microorganisms are immobilized on a support medium, such as a high surface area support medium, but are not limited to these. Useful high surface area support materials may include sponges, fibrous materials, bioballs, ceramic filters, and the like.

[0068] First bioreactor (photosynthetic bioreactor) Referring again to the figure, the first bioreactor 21 may include a single reaction vessel or may include multiple (i.e., two or more) reaction vessels that may be operated complementaryly. For example, two or more reaction vessels may be operated in parallel or in series to promote a desired photosynthetic reaction.

[0069] Those skilled in the art are generally aware of the appropriate conditions to be maintained in the first bioreactor 21 in order to sustain the microorganisms and promote the desired photosynthetic reaction. In one or more embodiments, water acts not only as a reactant but also as a reaction medium within the first bioreactor 21.

[0070] In one or more embodiments, the reactor medium in the photosynthetic bioreactor is maintained at a temperature of approximately 25 to 70°C, in other embodiments approximately 35 to 60°C, and in other embodiments approximately 40 to 50°C. In these or other embodiments, the reaction medium in the photosynthetic bioreactor is maintained at a pH of approximately 5.0 to 8.5, in other embodiments approximately 5.5 to 8.0, and in other embodiments approximately 6.0 to 7.0.

[0071] In one or more embodiments, the photosynthetic bioreactor substantially does not contain microorganisms that produce or are adapted to produce efe genes.

[0072] 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 by-product from the bioreactor. In one or more embodiments, the first bioreactor 21 includes an outlet for gaseous products / by-products 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 greater than 10,000 gallons, greater than 100,000 gallons in other embodiments, and greater than 1,000,000 gallons in other embodiments.

[0073] Second bioreactor (ethylene-producing bioreactor) Referring again to the figure, the second bioreactor 41 may include a single reaction vessel or multiple (i.e., two or more) reaction vessels that may be operated complementaryly. For example, two or more reaction vessels may be operated in parallel or in series to promote a desired reaction that converts an intermediate to ethylene.

[0074] Those skilled in the art are generally aware of the appropriate conditions to be maintained in the second bioreactor in order to sustain the microorganisms and promote the desired ethylene formation reaction. In one or more embodiments, water acts as the reaction medium in the second reactor.

[0075] 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 other embodiments about 35 to about 60°C, and in other embodiments 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 other embodiments about 6.5 to about 9.0, and in other embodiments about 7.0 to about 8.0.

[0076] In one or more embodiments, the ethylene-forming bioreactor substantially does not contain microorganisms that produce oxygen or are adapted to produce oxygen. For example, the second bioreactor does not contain or substantially contains photosynthetic microorganisms (e.g., microorganisms that function by the Calvin cycle).

[0077] 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 a state where light energy is substantially absent.

[0078] 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 (e.g., a gas outlet for ethylene gas) for removing the product and at least one by-product (e.g., carbon dioxide) from the second bioreactor. In one or more embodiments, the second bioreactor also includes an effluent outlet for removing liquid effluent (e.g., water and unreacted organic intermediates). 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 exceeding 10,000 gallons, exceeding 100,000 gallons in other embodiments, and exceeding 1,000,000 gallons in other embodiments. In one or more embodiments, the second bioreactor is adapted to provide a closed system except for the reactant inlet and the product or by-product outlet.

[0079] 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 a dry cell weight of more than 10 grams per liter, more than 50 grams per liter in other embodiments, and more than 100 grams per liter in other embodiments.

[0080] Technology for forming recombinant microorganisms In one embodiment, a nucleotide sequence for expressing an intermediate-forming enzyme or efe is inserted into the 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 resistance system, an auxiliary system for protein purification and detection, a CRISPR-CAS system, a phage display system, or a combination thereof.

[0081] As described above, in one or more embodiments, multiple copies of the efe expression nucleotide sequence may be inserted into an ethylene-forming microorganism. Similarly, multiple copies of the intermediate enzyme expression nucleotide sequence may be inserted into a photosynthetic microorganism. The number of copies of a gene inserted into a vector and / or host genome is referred to herein as the “copy number.” In one embodiment, the efe expression nucleotide sequence has a copy number greater than 1 in the microbial expression vector, greater than 10 in another embodiment, greater than 100 in yet another embodiment, and greater than 250 in yet another embodiment. As is clear, the expression of multiple copies of the efe expression nucleotide sequence can increase ethylene yield, thereby reducing the volume and cost of ethylene production on a commercial scale.

[0082] In some embodiments, the microbial expression vector comprises at least one microbial expression promoter. As will be understood by those skilled in the art, the microbial expression promoter is typically a nucleotide sequence that initiates transcription of an adjacent subsequent DNA sequence, and may be constitutive or inductive. In some embodiments, the at least one microbial expression promoter may include, but are not limited to, a photosensitive promoter, a chemosensitive promoter, a temperature-sensitive promoter, a Lac promoter, a T7 promoter, a CspA promoter, a lambda PL promoter, a lambda CL promoter, a continuous-production promoter, a psbA promoter, or a combination thereof. In some embodiments, at least one promoter inducer may be added to a bioreactor or a reaction medium within a bioreactor to control the amount of organic intermediates and / or the amount of ethylene produced. In some embodiments, the promoter inducer may include lactose, xylose, IPTG, cold shock, heat shock, or a combination thereof.

[0083] In one or more embodiments, the ICD and GDH genes may be synthesized using gBlocks® gene fragments cloned into pSyn6 plasmid constructs (pSyn6_ICD and pSyn6_GDH). For cloning into pSyn6 plasmids, the S. elongatus ICD coding sequence is flanked by the N-terminal HindIII recognition site and the C-terminal BamHI recognition site (SEQ ID NO: 4). Using the plasmid constructs, the ICD and GDH genes can be cloned into unmodified S. elongatus or S. elongatus Δglgc mutants (see Example 2). One to three copies of the target genes may be transformed. Cloning of the ICD and GCH genes can be confirmed by polymerase chain reaction (PCR) and sequencing. The synthesis and quantification of aKG can be evaluated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), Western blotting, and ethylene production assay.

[0084] In one or more embodiments, glycogen mutants of cyanobacteria are created to alter the bacterial pathway, causing them to produce and secrete keto acids such as aKG at higher concentrations. Glycogen mutant cyanobacteria can be created by creating glycogen-deficient strains via mutations in the glgc gene (Δglgc). For example, the ampicillin resistance (AmpR) gene can be synthesized using gBlocks™ and incorporated into a plasmid construct. This plasmid construct can then be used to transform wild-type cyanobacteria (e.g., Synechocystis, Synechococcus elongatus 2973, Synechococcus elongatus 2434). A mutant strain can then be created by replacing a portion of the wild-type glgc gene with the AmpR gene. The Δglgc mutant strain can be identified by PCR and sequencing after growth in AmpR-containing medium.

[0085] Maintaining volatile gas levels In one or more embodiments, the second reactor contains a safe level of oxygen gas. In particular, the headspace of the second reactor and the gaseous outlet flow of the second reactor contain a safe level of oxygen gas for ethylene. As those skilled in the art will recognize, a commercially acceptable level of oxygen gas in an ethylene flow can be defined by the lower explosion limit (LEL) taking into account the level of ethylene present. In one or more embodiments, the amount of oxygen in the second reactor (i.e., in the reactor headspace or gaseous outlet flow) is less than the acceptable LEL, in other embodiments less than 80% of the acceptable LEL, and in other embodiments less than 50% of the acceptable LEL.

[0086] Process characteristics As described herein, the method of the present invention is effective in converting carbon dioxide to ethylene with high carbon efficiency while addressing safety concerns associated with the simultaneous production of ethylene and oxygen, by utilizing a biosynthetic process.

[0087] In one or more embodiments, the method of the present invention produces ethylene at a rate exceeding 100 μmol / gCDW / hour, in other embodiments exceeding 500 μmol / gCDW / hour, in other embodiments exceeding 1000 μmol / gCDW / hour, in other embodiments exceeding 1500 μmol / gCDW / hour, in other embodiments exceeding 2000 μmol / gCDW / hour, and in other embodiments exceeding 2500 μmol / gCDW / hour, where CDW refers to cell dry weight.

[0088] 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 illustrative embodiments described herein.

[0089] Sequence List Sequence ID 1-

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[0090] The following information is a numerical identifier <223> Provided for arrays containing free text under the following conditions. [Table 1]

Claims

1. It is a method, (i) To provide a gas stream containing more than 1% by volume of carbon dioxide, (ii) To provide water, (iii) Converting the carbon dioxide and water into organic intermediates and oxygen gas by photosynthetic microorganisms at 25-70°C in the presence of light, (iv) Separating the oxygen gas from the organic intermediate, (v) After step (iv) of separating the oxygen gas from the organic intermediate, the organic intermediate is converted into ethylene and carbon dioxide by a microorganism that expresses or has been genetically modified to express an ethylene-forming enzyme (efe) gene at 25 to 70°C. Includes, The organic intermediate comprises sucrose, dextrose, xylose, glucose, fructose, alpha-ketoglutaric acid, or a mixture thereof. method.

2. A method according to claim 1, wherein the step (v) of converting the organic intermediate to ethylene and carbon dioxide is carried out in the presence of excess water from the step (iii) of converting carbon dioxide and water to an organic intermediate and oxygen gas, the step (v) of converting the organic intermediate to ethylene and carbon dioxide consumes only a portion of the organic intermediate formed in the step (iii) of converting carbon dioxide and water to an organic intermediate and oxygen gas, and further includes sending back the excess water and the organic intermediate from the step (v) of converting the organic intermediate to ethylene and carbon dioxide to the step (iii) of converting carbon dioxide and water to an organic intermediate and oxygen gas.

3. A method according to claim 1, wherein the step (iii) of converting carbon dioxide and the water into an organic intermediate and oxygen gas is performed in a first bioreactor.

4. The method according to any one of claims 1 to 3, wherein the gas flow contains more than 3 volume percent of carbon dioxide.

5. The method according to any one of claims 1 to 4, further comprising the step of compressing the flue gas flow from the combustion process to form the gas flow containing carbon dioxide.

6. The method according to any one of claims 1 to 5, wherein the step (iv) of separating the oxygen gas from the organic intermediate generates a concentrated stream of the organic intermediate which is introduced into the step (v) of converting the organic intermediate to ethylene and carbon dioxide.

7. The method according to claim 6, wherein the concentrated organic intermediate stream contains less than 30 ppm of oxygen.

8. The method according to claim 3, wherein the step (iv) of separating the oxygen gas from the organic intermediate includes releasing the oxygen gas from the first bioreactor.

9. The method according to any one of claims 1 to 8, wherein the step (v) of converting the organic intermediate to ethylene and carbon dioxide is performed in a second bioreactor.

10. The method according to any one of claims 1 to 9, wherein the step (v) of converting the organic intermediate to ethylene and carbon dioxide is carried out in a state where light energy is substantially absent.

11. The method according to any one of claims 1 to 10, wherein the ethylene and carbon dioxide formed in step (v) of converting the organic intermediate to ethylene and carbon dioxide form a product stream.

12. The method according to claim 11, further comprising the step of converting oxygen gas in the product stream into carbon dioxide.

13. The method according to claim 11 or 12, further comprising the step of extracting water from the product stream.

14. The method according to any one of claims 11 to 13, further comprising the step of separating carbon dioxide from the product stream.

15. The method according to claim 14, wherein the step of separating carbon dioxide from the product stream generates a concentrated ethylene stream.

16. The method according to claim 14 or 15, wherein the step of separating the carbon dioxide from the product stream generates a carbon dioxide stream, and the carbon dioxide stream is introduced into step (iii) of converting carbon dioxide and water into an organic intermediate and oxygen gas.

17. The method according to any one of claims 1 to 16, wherein the step (iv) of separating the oxygen gas from the organic intermediate includes releasing the oxygen gas from an aqueous medium containing the organic intermediate.

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