NZ619557B2 - Process for fermentation of syngas - Google Patents

Abstract

Disclosed herein is a process for fermenting syngas which is effective for decreasing an amount of time needed to inoculate a main reactor. The process includes propagating a culture of acetogenic bacteria in a pre-reactor to provide an inoculum of a minimum viable cell density which is transferred to a main reactor and syngas is fermented in the main reactor. to a main reactor and syngas is fermented in the main reactor.

Description

PROCESS FOR FERMENTATION 0F SYNGAS This application claims the benefit of US. Provisional Application Nos. 61/571,564 and ,565, both filed June 30, 2011 and 61/573,845, filed September 13, 201 1, all of which are incorporated in their entirety herein by reference.

A process is provided for tation of syngas. More specifically, the process includes propagating a e effective for use as an inoculum for a main reactor and fermenting sygnas in the main reactor.

BACKGROUND Anaerobic microorganisms can produce ethanol from carbon monoxide (CO) through fermentation of gaseous substrates. Fermentations using anaerobic microorganisms from the genus Ciostridium produce ethanol and other useful products.

For example, US. Patent No. $373,429 describes Closzfridz’um ljungdahlz'i ATCC No. 49587, an anaerobic microorganism that produces ethanol and acetate from sis gas.

U.S. Patent No. 5,807,722 describes a method and apparatus for converting waste gases into organic acids and alcohols using Clostridium fiungdahlii ATCC No. 55380. US.

Patent No. 577 describes a method and apparatus for ting waste gases into ethanol using Clostridium yungdahlii ATCC No. 55988 and 55989.

The CO is often provided to the fermentation as part of a gaseous substrate in the form of a syngas. ation of carbonaceous materials to produce producer gas or synthesis gas or syngas that es carbon monoxide and hydrogen is weil known in the art. Typically, such a gasification process es a partial oxidation or starved—air oxidation of carbonaceous material in which a sub-stoichiometric amount of oxygen is supplied to the gasification process to promote production of carbon monoxide as described in W0 2009/ 1 54788.

Fermentation processes with acetogenic bacteria may include one or more seed reactors, one or more growth rs and at least one main reactor. Acetogenic bacteria are normally grown to a certain cell density in a seed reactor. The seed reactor is then used to ate a growth fermentor. The growth fermentor will usually be of a larger size than seed reactor. Acetogenic bacteria in the growth reactor are then grown to a desired cell density. The growth reactor may then be used to inoculate another larger growth r or may be used to inoculate a main reactor. The main reactor will be of a larger size than the growth reactor. In view of this process, inoculating a main reactor starting from a seed reactor requires time. Further, if a growth reactor fails, the process needs to be ted, requiring even more time.

A process for ting syngas is provided which is effective for decreasing an amount of time needed to inoculate a main reactor. In this aspect, the total time from inoculation of a seed reactor to inoculation of a main reactor is decreased. The process also provides for faster ts in the event of reactor e.

In a first aspect, the present invention provides a process for fermenting syngas comprising propagating a culture of acetogenic bacteria effective for inoculating a main reactor, the propagating including, i) inoculating a first culture of acetogenic bacteria into a pre-reactor to provide a minimum viable cell density of at least 0.2 grams per liter, ii) g the culture of enic bacteria in the pre-reactor to provide a actor target cell density of at least 5 grams per liter, wherein if: (a) the pre-reactor target cell density multiplied by the pre-reactor volume/a volume of the main reactor; multiplied by; a volume of the pre-reactor/a volume of the pre-reactor which is transferred; is greater than or equal to a minimum viable cell density, transfer a volume of the pre-reactor to the main reactor in an amount effective for ing a minimum viable cell density in the main reactor, or (b) the pre-reactor target cell density multiplied by the pre-reactor volume)/( a volume of the main reactor; multiplied by; a volume of the pre-reactor/a volume of the pre-reactor which is transferred, is less than a minimum viable cell density, transfer a volume of the prereactor to a subsequent pre-reactor in an amount ive for providing a minimum viable cell density in a uent actor, and iii) repeat step ii until a volume of the culture from the pre-reactor is transferred to the main r, wherein the pre-reactor is supplied with syngas.

In a second aspect, the present invention provides fermented syngas ed by the process of the first aspect.

In one aspect, a process for fermenting syngas is provided that includes propagating a culture of acetogenic bacteria effective for inoculating a main reactor. The propagation includes: i) inoculating a first culture of acetogenic bacteria into a pre-reactor to provide a minimum viable cell density, and ii) growing the culture of aeetogenie bacteria in the pre- (11057216_1):MGH reactor to provide a pre-reactor target cell density. Propagation may be further described by the following equations: (a) n, if (the pre-reactor target cell density multiplied by the pre-reactor volume) ÷ (a volume of the main reactor multiplied by (a volume of the ctor ÷ a volume of the pre-reactor which is transferred)) is greater than or equal to a minimum viable cell density, transfer a volume of the pre-reactor to the main reactor in an amount effective for providing a minimum viable cell density in the main reactor, or (b) if (the pre-reactor target cell density multiplied by the pre-reactor volume) ÷ (a volume of the main reactor multiplied by (a volume of the pre-reactor ÷ a volume of the pre-reactor which is transferred)) is less than a minimum viable cell y, transfer a volume of the pre-reactor to a subsequent pre-reactor in an amount effective for providing a minimum viable cell density in the subsequent pre-reactor. Step ii is repeated until a volume of pre-reactor is transferred to the main reactor. Fermentation of syngas is then ted in the main reactor.

In one aspect, a process for fermenting syngas is provided that includes propagating a culture of acetogenic bacteria effective for inoculating a main reactor. The propagation includes: i) inoculating a first e of aeetogenic bacteria into a pre-reactor to provide a m viable cell density, and ii) growing the culture of cnic bacteria in the ctor to provide a pre-reactor target cell density. Propagation may be further described by the following ons: (a) n, if (the pre-reactor target cell density multiplied by the pre-reactor volume) ÷ (a volume of the main reactor multiplied by (a volume of the prereactor + a volume of the pre-reactor which is transferred)) is greater than or equal to a minimum viable cell density, transfer a volume of the pre-reactor (11057216_1):MGH to the main reactor in an amount effective for providing a minimum viable cell density in the main reactor, or (b) if (the pre—reactor target cell density lied by the pre-reactor volume) + (a volume of the main reactor lied by (a volume of the pre~reactor _:— a volume of the pre-reactor which is transferred» is less than a minimum viable cell density, adjusting the volume of the main reactor and transferring a volume of the pre-reactor to the main reactor in an amount effective for providing a minimum viable cell density in the main reactor, and increasing the volume of the main reactor while maintaining a minimum viable cell density. Fermentation of syngas is then conducted in the main reactor. in another aspect, a process is provided for starting a main fer-mentor for fermentation of syngas. The process includes inoculating a first e of acetogenic ia into a seed reactor to provide a minimum initial viable ceil density in the seed reactor of at least about 0.2 grams per liter. The culture of acetogenic bacteria is grown with syngas to provide a cell density in the seed r of at least about 5 grams per liter.

A first growth reactor is inoculated with an inoculum from the seed reactor in an amount effective for providing a cell y in the growth reactor of at Ieast about 0.2 grams per liter. The culture is grown with syngas to provide a cell density in the first growth reactor of at least about 5 grams per liter. A second growth reactor is inoculated with an inoculum from the first growth reactor in an amount effective for providing a cell density in the growth reactor of at Ieast about 0.2 grams per liter. The culture is grown with syngas to provide a cell density in the second growth r of at least about 5 grams per titer. A main fermentor is inoculated with an inoculum from the second growth reactor in an amount effective for providing a cell density in the main reactor of at least about 0.2 grams per liter.

BRIEF DESCRIPTION OF FIGURES The above and other aspects, features and advantages of several aspects of the process will be more apparent from the following figure.

Figure 1 illustrates a s for fermenting syngas. ponding reference characters indicate ponding components throughout the several views of the gs. Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the ts in the figures may be exaggerated relative to other elements to help to improve tanding of various s of the present process and apparatus. Also, common but well—understood elements that are useful or necessary in commercially feasible aspects are often not depicted in order to facilitate a less obstructed view of these various aspects.

DETAILED DESCRIPTION The ing description is not to be taken in a limiting sense, but is made merely for the purpose of describing the general principles of exemplary embodiments. The scope of the invention should be determined with reference to the claims.

A series of one or more pro—reactors is provided which are ive for y providing an inoculum to a main reactor. The one or more actors and main r are operatively connected to allow transfer of culture. Each of the one or more pre-reactors is ated with a minimal viable cell density and is then grown to provide a target cell density for subsequent inoculation. A volume of about 25% to about 75% of any pre- reactor is transferred to a uent reactor. The remaining volume is maintained and can be used for re-inoculation should any subsequent reactor fail.

Definitions Unless otherwise defined, the following terms as used throughout this specification for the present disclosure are defined as follows and can include either the singular or plural forms of definitions below defined: The term “about” ing any amount refers to the variation in that amount encountered in real world conditious, e.g., in the lab, pilot plant, or production facility. For example, an amount of an ingredient or measurement employed in a mixture or quantity when modified by “about” includes the variation and degree of care typically employed in measuring in an experimental condition in production plant or lab. For e, the amount of a component of a t when modified by ” includes the ion between batches in a multiple experiments in the plant or lab and the ion inherent in the analytical method. Whether or not modified by “about,” the amounts include equivalents to those amounts. Any quantity stated herein and modified by “about" can also be employed in the t disclosure as the amount not modified by “about”.

“Carbonaceous al” as used herein refers to carbon rich material such as coal, and petrochemicals. However, in this specification, carbonaceous material includes any carbon material whether in solid, Eiquid, gas, or plasma state. Among the numerous items that can be considered carbonaceous material, the present disclosure contemplates: carbonaceous material, carbonaceous liquid product, carbonaceous industrial liquid recycle, carbonaceous municipal solid waste (MSW or msw), carbonaceous urban waste, carbonaceous agricultural material, carbonaceous forestry material, carbonaceous wood waste, carbonaceous uction material, carbonaceous vegetative material, carbonaceous industrial waste, aceous fermentation waste, carbonaceous petrochemical co products, carbonaceous alcohol production co-products, carbonaceous coal, tires, cs, waste plastic, coke oven tar, fibersoft, lignin, black liquor, polymers, waste polymers, polyethylene terephthalate (PETA), yrene (PS), sewage sludge, animal waste, crop residues, energy crops, forest processing residues, wood processing es, livestock wastes, poultry wastes, food processing residues, fermentative process , ethanol co-products, spent grain, spent microorganisms, or their combinations.

The term “fibersoft” or “Fibersoft” or “fibrosofi” or “fibrousoft” means a type of carbonaceous material that is produced as a result of softening and tration of various substances; in an example carbonaceous material is produced via steam autoclaving of various substances. In another example, the fibersoft can include steam aving of municipal, industrial, commercial, and medical waste resulting in a fibrous mushy material.

The term “municipal solid waste” or “MSW” or “msw” means waste that may include household, commercial, industrial andi’or residual waste.

The term “syngas” or “synthesis gas” means Synthesis gas which is the name given to a gas e that contains varying amounts of carbon monoxide and hydrogen.

Examples of production s include steam reforming of natural gas or hydrocarbons to produce hydrogen, the gasification of coal and in some types of waste—to-energy gasification facilities. The name comes from their use as intermediates in creating synthetic natural gas (SNG) and for producing ammonia or methanol. Syngas comprises use as an intermediate in producing synthetic petroleum for use as a fuel or lubricant via Fischer—Tropsch synthesis and previously the Mobil methanol to gasoline process. Syngas consists ily of en, carbon mon0xide, and some carbon dioxide, and has less than half the energy density (i.e., BTU content) of natural gas. Syngas is combustible and is often used as a fuel source or as an intermediate for the production of other chemicals.

The terms “fermentation”, fermentation process” or “fermentation on” and the like are ed to encompass both the growth phase and t biosynthesis phase of the process. In one aspect, fermentation refers to conversion of CO to alcohol.

PrenReactor Design In accordance with the process, a culture of enic bacteria is inoculated into a pre—reactor to provide a minimum cell density. In this , the pre—reactor may be one or more seed reactors and one or more growth reactors. The seed reactor may have a volume of about 500 liters or less, in another aspect, about 400 liters or less, in another , about 300 liters or less, in r , about 200 liters or less, in another aspect, about 100 liters or less, and in another aspect, about 50 liters or less. Growth reactors may have a volume of about 250,000 liters or less, in another aspect, about 150,000 liters or less, in another aspect, about 100,000 titers or less, in another aspect, about 50,000 liters or less, in another aspect, about l0,000 liters or less, and in another aspect, about 1,000 liters or less, As used herein, “volume” refers to a non—gassed liquid working volume.

The seed reactor may be supplied with syngas, including for example bottled syngas. In this aspect, using a seed reactor having a volume of 500 liters or less allows the seed reactor to be supplied with bottled syngas. The use of bottled syngas may be important if a supply of syngas from a gasification process is not available. Useful syngas compositions are described herein. In one aspect, pre-reactors may be supplied with gas recycled from the main reactor.

Culture in the seed r is grown to a actor target cell density and a volume of the seed reactor is used to inoculate a subsequent pro—reactor having a larger voiume than the seed reactor. In this aspect, the second pre-reactor may be one or more growth reactors. In an ant aspect, the s utilized at least two growth reactors, in another aspect, at least three growth reactors, and in another aspect at least four growth reactors.

One aspect of a process for fermenting syngas is lly illustrated in Figure 1.

In this aspect, the process includes a seed reactor 100, a first growth reactor 200, a second growth reactor 300, and a main reactor 400. Each reactor can be supplied with syngas through a gas supply 500. Nutrients may be ed to each reactor through nutrient supply 600. Each reactor may include an agitator 150 and at least one impeller 250.

Medium from each reactor may be sent to a /heat exchanger 550 and cooled medium may he cycled back to the reactor vessel. Medium from one reactor may be erred to the next reactor through a transfer line 700.

Medium from each reactor may be sent to a recycle filter 350. Concentrated cells 425 may be returned to the reactor vessel and penneate 450 may be sent for further processing. Further processing may include separation of desired product such as for example ethanol, acetic acid and butanol.

Pre-Reactor Operation actor operation allows for a rapid start up for a main r inoculation. In this aspect, the time from inoculation of a first pre-reactor to inoculation of a main reactor is about 20 days or less, in another , about 15 days or less, and in another aspect, about 10 days or less. The s also allows for a more rapid recovery should any of the pre—reactors fail.

In accordance with the process, a e of acetogenic bacteria is inoculated into a pro-reactor or seed reactor to provide a minimum cell density. As used herein, “minimum cell density” means a viable cell density of at least about 0.1 grams per liter, in another aSpect, at least about 0.2 grams per liter, in another aspect, at least about 0.3 grams per liter, in another aspect, at least about 0.4 grams per liter, and in another aSpect, at least about 0.5 grams per liter. The minimum cell density will not exceed about 1.2 grams per liter. In another , the first culture used to inoculate a pre—reactor or seed reactor has a pH of 6.5 or less, in another aspect 4.5 or less, and in another aspect, about 4.0 to about 4.5. The first culture used to inoculate a pre-reactor or seed reactor has an acetic acid concentration of about 10 grams per liter or less, in r aspect, about 1 to about 10 grams per liter, in another aspect, about 1 to about 5 grams per liter, in another aspect, about 1 to about 3 grams per liter, and in another aspect, about 2 grams per liter.

The acetogenic bacteria is grown in the pre—reactor until a target cell density is reached. As used herein, “pie—reactor target cell density” means a viable cell density of at least about 5 grams per liter, in another aspect, at least about 10 grams per liter, in another aspect, at least about 15 grams per liter, and in another aspect, at least about 20 grams per liter. The pie-reactor target cell density will generally not exceed about 50 grams per liter.

In another aspect, the pie—reactor target cell density is about 12 to about 15 grams per liter, and in another aspect, about 20 to about 24 grams per liter.

In one aspect, each subsequent pro-reactor has a larger volume than its preceding actor. In accordance with this process, a volume ratio of the pre-reactor volume transferred to a subsequent pro-reactor or main reactor is about 0.02 to about 0.5, and in another aspect, about 0.02 to about 0.2. In another aspect, about 20 to about 75% of a volume of a pre—reactor is used to ate a subsequent pro-reactor or main r.

Other reactor volumes that may be transferred include about 30 to about 70%, about 40 to about 60%, and about 45 to about 55%. In this aspect, maintaining a volume allows for faster recovery should a subsequent reactor fail. As used herein, “reactor e” refers to a condition where no gas conversions are taking place and cells appear ly dead after microscopic evaluation. In this aspect, once a r failure occurs, the reactor may be re~.. inoculated within 24 hours.

Upon reaching a target cell density in a pro-reactor, uent steps in the process may be described as follows: (pre-reactor target cell density) x (pro-reactor volume) if 2 minimum viable ceil density (volume of ore-reactor) e of main r) x (volume of pro-reactor transferred) then a volume of the pie-reactor is transferred to a main reactor in an amount effective for providing a minimum cell density in the main reactor; or (pro—reactor target cell density) x (pro-reactor volume) _ . if 5 minimum viable cell density (volume of pro-reactor) (volume of main reactor) x (volume of pro-reactor transferred) then a volume of the pre-reactor is transferred to a subsequent pro—reactor in an amount effective for providing a minimum cell density in the main r. This step of erring from one pie—reactor to another may be repeated until transfer to a main reactor. in another aspect, upon reaching a target cell density in a pre‘reactor, subsequent steps in the process may be described as follows: (pre—reactortarget cell density)x(pre-reactor volume) _ _ _ if Z minlmum Viable cell density (voiume of preareactor) (volume of main reactor) x (voiume of actor transferred) then a volume of the pre~reactor is transferred to a main reactor in an amount effective for providing a m cell density in the main reactor; or Viv-ulvluu-l ./ 1v1,uv_ul-lu.uv_. (pro-reactor target cell density) x (pro-reactor volume) if S minimum viable CB" den ' ( OIUHIe 0! main reactor) x (volume of pro—reactor transferred) then a volume of the main reactor may be adjusted and a volume of the pre~reactor may be erred in an amount to provide a minimum viabie ceil density in the main reactor. The volume of the main reactor is then increased over time to a desired voiume while maintaining a minimum viabie cell density.

Each reactor may be ed in a manner effective for maximizing cell growth and maintaining culture health. in one aspect, medium used in each reactor may be the same or different. es of suitable mediums include those described in US. Patent No. 7,285,402, PCT/U82009/001522, and U.S. ional Application Nos. ,899, 61/458,903, and 61/458,976, all flied December 3, 2010, and all of which are incorporated in their entirety herein by reference. Higher concentration levels of one or more vitamins may be used during growth phase.

In one aspect, a seed reactor may be inoculated with about 0.3 to about 0.7 grams of cells per liter. Syngas may be d into the seed reactor at a rate of about 0.5 to about 2.0 liters per minute, in r aspect, about 0.75 to about 1.25 liters per minute.

Initial agitation is conducted at about 10 to about 40% of full agitation power. ion rates may be increased up to full power over an hour. For e, agitation rates may be increased from about 100 to about 1000 rpm for smaller reactors, and the increases may be correspondingly less for larger reactors.

Acetogenic Bacteria In one aspect, the microorganisms utilized include acetogenic bacteria. Examples of useful acetogenic bacteria e those of the genus Clostridium, such as strains of Closzridium Ijungdahlz‘z‘, inciuding those described in W0 2000/68407, EP 117309, U.S.

Patent Nos. 5,173,429, 5,593,886 and 6,368,819, W0 1998/00558 and W0 2002/08438, strains of Clostridium autoerhanogenum (DSM 10061 and DSM 19630 of DSMZ, Germany) including those described in W0 20077117157 and and Clostridium ragsdalez‘ (P1 l, ATCC BAA-622) and baculum bacchz’ (CP1l, ATCC BAA-1772) including those described respectively in U.S. Patent No. 7,704,723 and els and Bioproducts from Biomass-Generated Synthesis Gas”, Hasan Atiyeh, presented in Oklahoma EPSCOR Annual State Conference, April 29, 2010 and idium carboxz'dz'vomns (ATCC PTA-7827) described in US Patent Application No. 2007/0276447. Other suitable microorganisms includes those of the genus Moorella, including Moorella sp. HUCZZ-l, and those of the genus Carboxydothemms. Each of these references is incorporated herein by reference. Mixed cultures of two or more microorganisms may be used.

Some examples of useful bacteria include Acetogenium ktvui, Acetoanaerobtum e, Acetobacterz‘um woodz‘i, Alkalibaculum baccki CPll (ATCC BAA-1772), Blautia producta, Butyrz‘bacterium methylotrophicum, Caldanaerobacter subterraneous, Caldanaerobacter subterraneous pacificus, Carboxydothermus hya’rogenoformans, Clostrz'dt'um aceticum, Clostridium acetobutylicum, Clostrz'dz'um acetobutylicum P262 (DSM 19630 of DSMZ Germany), Clea-Iridium hanogenum (DSM 19630 of DSMZ Germany), Clostridium autoei‘hanogeaum (DSM 10061 of DSMZ y), Clostridium autoethanogenum (DSM 23693 of DSMZ Germany), Clostrz'dz'um hanogenum (DSM 24138 of DSMZ Germany), Clostridium carboxz'dz'vomns P7 (ATCC PTA—7827), Clostrz'dium cos/cairn (ATCC PTA—10522), Clostrtdt'um drakez', Clostridz'um flungdahlit PETC (ATCC , Clostridz'um ljungdahlii ERI2 (ATCC 55380), Clostridium Uungdahlii C—OI (ATCC 55988), Clostridium bungdahlii 0—52 (ATCC 55889), Clostrfdium , idz'um pasteurianum (DSM 525 of DSMZ Germany), Clostridium ragsdali' P11 (ATCC BAA-622), Clostridium scatologenes, Closrridium thermoacetz‘cum, Clostridium ultunense, Desulfotomaculum kuznersovii, Eubacterium limosum, Geobacter suHurreducerzs, Methanosarcina acetz’vorans, Methanosarcma i, la thermoacetica, Morrella thermoautotrophica, Oxobacrer pfennigii, Peptostreptococcus productus, Ruminococcus productus, Thermoanaerobacrer kivm’, and mixtures thereof.

Syngas Syngas may be provided from any know source. In one aspect, syngas may be sourced from gasification of carbonaceous materials. Gasification involves partial tion of biomass in a cted supply of oxygen. The resultant gas mainly includes CO and H2. In this aspect, syngas will contain at least about 10 mole % CO, in one aspect, at least about 20 mole %, in one aspect, about 10 to about 100 mole %, in r aspect, about 20 to about 100 mole % CO, in another aspect, about 30 to about 90 mole “/0 CO, in another aspect, about 40 to about 80 mole % CO, and in another aspect, about 50 to about 70 mole % CO. The syngas will have a CO/COZ molar ratio of at least about 0.75. Some es of suitable gasification methods and apparatus are provided in U.S Serial Numbers 61/516,667, 61/516,704 and 61/516,646, all of which were filed on April 6, 201 1, and all of which are incorporated herein by reference.

In another aspect, syngas utilized for propagating acetogenic bacteria may be substantially CO. As used herein, “substantially CO” means at least about 50 mole % CO, in another , at least about 60 mole % CO, in r aspect, at least about 70 mole % CO, in another aspect, at least about 80 mole % CO, and in another aspect, at least about 90 mole % CO. l0 EXAMPLE I: Start-Up with Two Growth Reactors A seed tor (90 liters) is lated with Clostria’ium ljungdahliz‘. Syngas was fermented untii a cell density of about 12 grams/liter is Obtained. Half of the seed fermentor (about 45 liters) is used to inoculate a first growth reactor to provide a total volume in the first growth reactor of about 1390 liters and a starting cell density of about 0.38 grams per liter. Syngas is fermented for 140 hours from time of ation to provide a cell density of about 12 grams per liter. Culture from the first growth r (about 703 liters) is used to inocuiate a second growth reactor to provide a total volume in the second growth reactor of about 22200 liters and a cell density of about 0.38 grams per liter. Syngas is fermented for 140 hours from time of ation to provide a cell density of about 12 grams per liter. Culture from the second growth reactor (about 12,000 liters) is used to inoculate a main reactor to provide a total volume in the main reactor of about 350,000 to 400,000 liters and a cell density of about 0.40 grams per liter. The total elapsed time from inoculation of the first growth reactor to inoculation of the main reactor is 11.7 days.

EXAMPLE 2: Start-Up with Seed Reactor and One Growth rs A seed fermentor (about 1600 liters) is incoculated with Clostridium ljungdahlii.

Syngas was ted until a cell density of about 12 grams/liter is obtained. Half of the seed fermentor (about 700 liters) is used to inoculate a first growth reactor to provide a total volume in the first growth reactor of about 2250 liters and a starting cell density of about 0.38 grams per liter. Syngas is fermented for 140 hours from time of inoculation to provide a cell density of about 12 grams per liter. Culture from the first growth reactor (about 11,000 ) is used to inoculate a main reactor to provide a total volume in the main reactor of about 350,000 to about 400,000 liters and a cell density of about 0.38 grams per liter. The total elapsed time from inoculation of the first growth reactor to inoculation of the main reactor is 9.2 days.

While the invention herein disclosed has been described by means of specific embodiments, examples and ations thereof, numerous modifications and variations could be made thereto by those skilled in the art Without ing from the scope of the invention set forth in the claims

Claims (9)

1. A process for fermenting syngas sing propagating a culture of acetogenic bacteria effective for inoculating a main reactor, the propagating including, i) inoculating a first culture of acetogenic bacteria into a pre-reactor to provide a minimum viable cell density of at least 0.2 grams per liter, ii) growing the culture of acetogenic bacteria in the pre-reactor to e a pre-reactor target cell density of at least 5 grams per liter, wherein if: (a) the pre-reactor target cell density multiplied by the pre-reactor volume/a volume of the main reactor; lied by; a volume of the pre-reactor/a volume of the pre-reactor which is transferred; is r than or equal to a minimum viable cell density, transfer a volume of the pre-reactor to the main reactor in an amount effective for providing a minimum viable cell density in the main reactor, or (b) the pre-reactor target cell density multiplied by the pre-reactor volume)/( a volume of the main reactor; multiplied by; a volume of the pre-reactor/a volume of the pre-reactor which is transferred, is less than a minimum viable cell density, transfer a volume of the ctor to a subsequent pre-reactor in an amount effective for providing a minimum viable cell density in a subsequent pre-reactor, and iii) repeat step ii until a volume of the culture from the pre-reactor is erred to the main reactor, wherein the actor is supplied with syngas.

2. The process of claim 1 wherein about 25% to about 75% of a volume of a actor is used to inoculate a subsequent pre-reactor or main reactor.

3. The process of claim 1 or claim 2 wherein a volume ratio of the pre-reactor volume transferred to a subsequent pre-reactor volume or main reactor volume is about 0.02 to about 0.5.

4. The process of any one of claims 1 to 3 n the syngas has a CO/CO molar ratio of at least 0.75.

5. The process of any one of claims 1 to 4 wherein the first culture has a pH of 6.5 or less and an acetic acid concentration of 10 grams per liter or less.

6. The process of any one of claims 1 to 5 wherein the syngas has about 20 to about 100 mole% CO.

7. The s of any one of claims 1 to 6 wherein the syngas used for propagating acetogenic bacteria is substantially CO. (11057216_1):MGH

8. The process of any one of claims 1 to 7 wherein the acetogenic bacteria are selected from the group consisting of Acetogenium kivui, Acetoanaerobium noterae, Acetobacterium woodii, Alkalibaculum bacchi CP11 - deposit ATCC BAA-1772, Blautia producta, Butyribacterium otrophicum, Caldanaerobacter subterraneous, Caldanaerobacter subterraneous cus, Carboxydothermus hydrogenoformans, Clostridium um, Clostridium acetobutylicum, Clostridium acetobutylicum P262 - deposit DSM 19630, Clostridium autoethanogenum - deposit DSM 19630,Clostridium autoethanogenum - deposit DSM 10061, Clostridium autoethanogenum - t DSM 23693, Clostridium autoethanogenum - deposit DSM 24138, Clostridium carboxidivorans P7- deposit ATCC PTA-7827, Clostridium coskatii - deposit ATCC PTA- 10522, idium drakei, Clostridium ljungdahlii PETC - deposit ATCC 49587, Clostridium ljungdahlii ER12 - deposit ATCC 55380, Clostridium ljungdahlii C-01 - deposit ATCC 55988, Clostridium ljungdahlii O-52 - deposit ATCC 55889, Clostridium magnum, Clostridium pasteurianum - deposit DSM 525, Clostridium ragsdali PII - deposit ATCC BAA-622, Clostridium scatologenes, Clostridium thermoaceticum, Clostridium ultunense, Desulfotomaculum sovii, Eubacterium limosum, Geobacter sulfurreducens, Methanosarcina orans, Methanosarcina i, la thermoacefica, Morrella thermoautotrophica, Oxobacter pfennigii, Peptostreptococcus productus, Ruminococcus productus, Thermoanaerobacter kivui, and mixtures thereof.

9. Fermented syngas produced by the process of any one of claims 1 to 8. INEOS Bio SA By the eys for the Applicant N & FERGUSON Per: (11057216_1):MGH FIG. 1