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BR-112019024244-B1 - HIGH-PRODUCTIVITY METHANE FERMENTATION PROCESSES

BR112019024244B1BR 112019024244 B1BR112019024244 B1BR 112019024244B1BR-112019024244-B1

Abstract

Processes are provided to increase the productivity of fermenters during the metabolic conversion of methane-containing gases to polyhydroxyalkanoate-containing products, which can be used to make, for example, polymeric articles for animal feed or biodegradable products. The processes involve either attenuating the heat generated to develop a population of microorganisms or removing heat during fermentation by removing carbon dioxide.

Inventors

  • ROBERT F. HICKEY
  • MARGARET CATHERINE MORSE
  • ALLISON J. PIEJA

Assignees

  • Mango Materials, Inc

Dates

Publication Date
20260317
Application Date
20180518
Priority Date
20170519

Claims (20)

  1. 1. High-productivity process for the bioconversion of methane into a product containing polyhydroxyalkanoate, characterized by comprising: (a) passing a substrate gas comprising a methane-containing gas and an oxygen-containing gas to a reaction zone for contact under fermentation conditions with an aqueous medium having a population of methanotrophs inside, said medium containing nutrients for the growth of the methanotroph population to provide an aqueous medium rich in methanotrophs, said growth of the methanotroph population also resulting in the co-production of carbon dioxide, water and heat, and removing the unreacted gas from said reaction zone; (b) passage of a methane-containing gas and an oxygen-containing gas into a reaction zone for contact under fermentation conditions with at least a portion of the methanotroph-rich aqueous medium, said medium having a limitation of at least one nutrient required for the growth of the methanotroph population to create nutrient-limited conditions that inhibit the growth of the methanotroph population and cause the production of polyhydroxyalkanoate by the methanotrophs and the co-production of carbon dioxide, water and heat, and removal of unreacted gas from said reaction zone; and (c) separating the polyhydroxyalkanoate-containing methanotrophs from the aqueous medium of step (b), wherein for at least a portion of the duration of each of steps (a) and (b): i. the rate of passage of at least one substrate-containing gas into the reaction zone in each of steps (a) and (b) is under substrate diffusion conditions; ii. in at least one of steps (a) and (b) a portion of the aqueous medium is continuously withdrawn from the reaction zone and contacted with an extraction gas to remove carbon dioxide and provide an aqueous medium poor in carbon dioxide; and iii. passage of at least a portion of the aqueous medium poor in carbon dioxide to the reaction zone of at least one of steps (a) and (b).
  2. 2. Process according to claim 1, characterized in that the substrate gas comprises methane-containing gas.
  3. 3. Process according to claim 2, characterized in that the rate of passage of methane-containing gas to the reaction zone in at least one of steps (a) and (b) is modulated to provide a substantially stable molar concentration of methane in the unreacted gases.
  4. 4. Process according to claim 1, characterized in that the methane-containing feed contains hydrogen sulfide and the aqueous medium absorbs at least a portion of the hydrogen sulfide to provide an unreacted gas stream containing a reduced concentration of hydrogen sulfide.
  5. 5. Process according to claim 1, characterized in that the reaction zone of at least one of steps (a) and (b) is a deep tank, bubble column reaction zone characterized in substantially uniform liquid composition and substantially non-uniform gas composition over the height of the reaction zone, and at least a portion of said substrate-containing gas is introduced into a lower portion of the reaction zone.
  6. 6. Process according to claim 1, characterized in that the rate of juice withdrawal in step (ii) is sufficient to remove an amount of carbon dioxide equivalent to at least 40 percent of the carbon dioxide produced by metabolic activity in the reaction zone.
  7. 7. Process according to claim 6, characterized in that the rate of juice withdrawal in step (ii) is sufficient to remove between 50 and 75 percent of the carbon dioxide produced by metabolic activity in the reaction zone.
  8. 8. Process according to claim 2, characterized in that at least one oxygenated Cl compound is added to the reaction zone of step (a) when the rate of passage of methane-containing gas into the reaction zone is no longer under methane diffusion conditions.
  9. 9. Process according to claim 1, characterized in that the portion of the aqueous medium poor in carbon dioxide passed to the reaction zone of at least one of steps (a) and (b) is cooled.
  10. 10. Process according to claim 1, characterized in that steps (a) and (b) are carried out sequentially in a reactor vessel.
  11. 11. Process according to claim 1, characterized in that each of the steps (a) and (b) is carried out in separate reactor vessels.
  12. 12. Process according to claim 11, characterized in that a portion of the aqueous medium in the reaction zone of step (a) is passed to the reaction zone of step (b).
  13. 13. Process according to claim 11, characterized in that at least two reaction zones of step (b) are provided for each reaction zone of step (a) and a portion of the aqueous medium of step (a) is passed to at least one of the reaction zones of step (b) in a given time to obtain a semi-batch process.
  14. 14. Process according to claim 13, characterized in that the portion passed to one of the reaction zones of step (b) at a given time is between 25 and 95 percent by volume of the aqueous medium in the reaction zone of step (a), and additional aqueous medium is supplied to the reaction zone of step (a) to develop the methanotroph population.
  15. 15. Process according to claim 1, characterized in that the methane-containing gas comprises biogas.
  16. 16. Process according to claim 15, characterized in that the methane-containing gas comprises an anaerobic gas digester.
  17. 17. Process according to claim 15, characterized in that the methane-containing gas comprises at least one of a landfill gas and one of a waste gas derived directly or indirectly from another fermentation process.
  18. 18. Process, according to claim 1, characterized in that the aqueous medium poor in carbon dioxide is subjected to indirect heat exchange with a cooling fluid for further cooling of the aqueous medium poor in carbon dioxide and heating of the cooling fluid.
  19. 19. Process according to claim 18, characterized in that the heated cooling fluid from the indirect heat exchange is passed to a heat pump to provide a superheated fluid.
  20. 20. Process according to claim 19, characterized in that the superheated fluid is used to heat the extraction gas.

Description

[001] This application claims priority over Provisional Application U.S.62/603,181 filed on May 19, 2017. Field of invention [002] This invention relates to high-productivity processes for methane fermentation by methanotrophs. Fundamentals of the Invention [003] Methane fermentation by methanotrophs is well known. There are proposals for growing microorganisms in methane-containing gas to produce polyhydroxyalkanoates (PHAs) or to produce protein with a modulated PHA content, for example, for use as a component of animal feed. Methane is readily available from fossil sources as well as biological sources. Often, the carbon price from methane sources is considerably less expensive than carbon from other sources, such as sugars. The ability to convert methane into useful products through its fermentation by methanotrophs offers the potential for economic advantages. Additionally, since methane-containing gas sources can be renewable sources such as biogas and landfill gas, there are advantages to producing products from rapidly renewable sources. [004] Polyhydroxyalkanoates can be readily biodegraded and are essentially non-toxic. Thus, PHA has been proposed as a substitute for environmentally persistent plastics. Some studies have indicated that the presence of PHA may have beneficial properties in fish feed. Additionally, PHA may also be a useful component of, for example, a formulated and extruded or pressed feed pellet. [005] Products containing polyhydroxyalkanoate have been made through metabolic processes using sugar feedstocks (including sugars themselves and starches, and cellulosic materials that can produce sugars through enzymatic activity). Sugar feedstocks are typically significantly more expensive than methane-containing gases, and thus attention has been directed to methane as a feedstock. There are challenges, however, in producing PHA-containing products from methane-containing gases as the solubility of methane in aqueous media is low and high heat is generated by methanotrophs during the methane bioconversion process. Traditional bioprocesses for producing PHA from methane thus maintain low methanotroph densities in the aqueous broth, which in turn provide low PHA productivity per unit volume of bioreactor. Consequently, commercially available PHAs have been significantly more expensive than conventional petroleum-based polymers and therefore have not achieved widespread commercial acceptance. [006] In general, bioprocesses for the production of PHA-containing products from methane-containing gases comprise the steps of growing a methanotroph population ("balanced cell growth") and then subjecting the methanotrophs to environmental conditions that do not support the growth of the microorganism population but the production of PHA by the methanotrophs ("unbalanced cell growth"). Where PHA is the desired product, PHA is subsequently harvested from the microorganisms. Both methane-containing gas and oxygen-containing gas are supplied to the aqueous broth containing the same methanotrophs for the growth of the methanotroph population and its production of PHA. [007] Consequently, there is a need to produce PHA-containing products from methane-containing gases with higher productivities per unit volume of bioreactor. [008] Advantageously, the preferred processes would achieve higher productivities in an economically attractive way. Summary of the Invention [009] This invention provides bioprocesses for the production of PHA-containing products from methane-containing gases with high productivities. According to this invention, a high density of methanotrophs per unit volume of the bioreactor can be achieved without undue cooling costs associated with the substantial exothermic nature of methane bioconversion. The processes of this invention facilitate desirable high mass transfer rates of methane from the gas phase to the broth or aqueous medium. These high mass transfer rates support high methanotroph densities. However, high mass transfer rates and high methanotroph densities result in greater heat generation and greater carbon dioxide production. The processes of this invention integrate the ability to obtain high methane transfer rates with heat removal to maintain the aqueous medium at temperatures suitable for the bioprocess. [010] In the processes of this invention, a portion of the aqueous medium containing carbon dioxide generated by methanotrophs is removed from the reaction zone and placed in contact with an extraction gas to remove dissolved carbon dioxide from the removed aqueous medium (resulting in "carbon dioxide-poor medium or broth"). At least a portion, and preferably essentially all, of the carbon dioxide-poor medium is passed into the reaction zone where it becomes part of the aqueous medium in the reaction zone. The removal of carbon dioxide from the aqueous medium results in higher mass transfer rates of both methane and oxygen to the aqueous medium in the reaction zone.