NZ626283B2 - Management of ethanol concentration during syngas fermentation - Google Patents

Abstract

process for fermentation of syngas is disclosed where syngas is contacted with a medium inoculated with acetogenic bacteria and having a cell density of at least about 0.3 grams per litre. The syngas is fermented to convert CO to ethanol. Cells and medium are removed from the fermentation upon reaching an ethanol concentration of more than about 10 g/L in the fermentation. The removed cells and medium are separated to provide concentrated cells and permeate. Ethanol is separated from the permeate to provide ethanol and a reduced ethanol aqueous stream having less than about 5 weight % alcohol; and the reduced ethanol aqueous stream is provided having less than about 5 weight % alcohol to the fermentation. A ratio of a rate of providing the reduced ethanol aqueous stream to the fermentation to a rate of removing the cells and medium from the fermentation is about 5 to about 15 and an ethanol concentration of more than about 10 g/L is maintained in the fermentation. aching an ethanol concentration of more than about 10 g/L in the fermentation. The removed cells and medium are separated to provide concentrated cells and permeate. Ethanol is separated from the permeate to provide ethanol and a reduced ethanol aqueous stream having less than about 5 weight % alcohol; and the reduced ethanol aqueous stream is provided having less than about 5 weight % alcohol to the fermentation. A ratio of a rate of providing the reduced ethanol aqueous stream to the fermentation to a rate of removing the cells and medium from the fermentation is about 5 to about 15 and an ethanol concentration of more than about 10 g/L is maintained in the fermentation.

Description

MANAGEMENT OF ETHANOL CONCENTRATION DURING SYNGAS FERMENTATION This application claims the benefit of US. Provisional Application No. 61/569,355, which was filed on December 12, 2011, and which is incorporated in its entirety herein by reference.

A process is provided for management of ethanol concentration during syngas fermentation. More specifically, cells and medium are removed from a tor and a reduced ethanol aqueous stream is returned to the fermentor at a rate ive to maintain a desired ethanol concentration.

OUND Anaerobic microorganisms can produce ethanol from carbon monoxide (CO) through fermentation of gaseous substrates. Fermentations using anaerobic rganisms from the genus Clostrz'dz'um produce ethanol and other useful products. For e, U.8. Patent No. 5,173,429 describes Closrridium Zjungdahlz‘i A’I‘CC No. 49587, an anaerobic microorganism that produces ethanol and acetate from synthesis gas. US. Patent No. 5,807,722 describes a method and apparatus for converting waste gases into organic acids and alcohols using Clostridium Uurzgdahlz’i A’I‘CC No. 55380. US. Patent No. 6,136,577 describes a method and apparatus for converting waste gases into ethanol using idz‘um (jungdahlii ATCC No. 55988 and 55989, The CO is ofien provided to the fermentation as part of a gaseous substrate in the form of a syngas. Gasification of carbonaceous als to e producer carbon monoxide and hydrogen is well gas or sis gas or syngas that includes known in the art. Typically, such a gasification s involves 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 2009/154788.

Ethanol concentration ses during fermentation. Certain levels of ethanol become inhibitory and result in reactor failure or decreased productivity.

Processes are needed which are effective for balancing l removal with maintaining desired cell density levels and ethanol productivity.

SUMMARY In a first aspect, the present invention provides a process for tation of syngas comprising: contacting syngas with a medium inoculated with acetogenic bacteria and having a cell density of at least about 0.3 grams per liter; fermenting the syngas to convert CO to ethanol; removing cells, and medium from the fermentation upon ng an ethanol concentration of more than about 10 g/L in the fermentation; separating the removed cells and medium to provide concentrated cells and permeate; separating l from the permeate to provide ethanol and a reduced ethanol aqueous stream having less than about 5 weight % alcohol; and providing the reduced ethanol aqueous stream having less than about 5 weight % alcohol to the fermentation; n a ratio of a rate of providing the reduced ethanol aqueous stream to the fermentation to a rate of removing the cells and medium from the fermentation is about 5 to about 15, wherein an ethanol concentration of more than about 10 g/L is maintained in the fermentation.

A process for fermentation of syngas includes inoculating a medium to provide an inoculated medium having cell density of at least about 0.1 grams per liter. Cells and medium are removed and separated to provide trated cells and permeate. Ethanol is separated from the permeate to provide l and a reduced ethanol aqueous stream. The reduced ethanol aqueous stream is returned to the tation. In an important aspect, a ratio of a rate of providing the reduced ethanol aqueous stream to the tation to a rate of ng the cells and medium from the fermentation is about 0.5 to about 25.

AH26(11346017_1):EOR In another , a process for fermentation of syngas includes inoculating a medium to provide an inoculated medium having cell density of at least about 0.1 grams per liter.

Inoculated medium is contacted with syngas and upon reaching an ethanol concentration of more than about 10 g/L in the fermentation, cells and medium are removed and separated to provide concentrated cells and permeate. A permeate holding tank receives permeate. A distillation column receives permeate from the te holding tank. The distillation column is effective for separating ethanol from the permeate to provide ethanol and a reduced ethanol s stream. The reduced ethanol aqueous stream is returned to the fermentation. In an important aspect, a ratio of a rate of providing the reduced ethanol aqueous stream to the fe1mentation to a rate of removing the cells and medium from the fermentation is about 0.5 to about 25.

In another aspect, a process for tation of syngas includes inoculating a medium to provide an inoculated medium having cell density of at least about 0.1 grams per liter. Cells and medium are removed and separated to provide concentrated cells and permeate. Ethanol is separated from the permeate to provide ethanol and a reduced ethanol aqueous stream. The reduced l aqueous stream is returned to the fermentation. In an ant , a rate of providing the reduced ethanol aqueous stream and a rate of removing the cells and medium is effective for providing a growth factor of 0.01 grams/gram/hour (increase in amount of dry weight of cell in grams/gram of dry weight of parent cell/hour).

In r , a process for fermentation of syngas includes inoculating a medium to provide an inoculated medium having cell density of at least about 0.1 AH26(11346017_1):EOR grams per liter. Inoculated medium is contacted with syngas. A growth factor is measured and an aqueous stream is returned to the tation when the growth factor is less than a critical growth factor.

In another aspect, a s for high productivity fermentation of syngas includes inoculating a medium to provide an inoculated medium having cell y of at least about 0.1 grams per liter. Cells and medium are removed and separated to provide concentrated cells and permeate. Ethanol is separated from the permeate to provide ethanol and a reduced ethanol aqueous stream. The reduced ethanol aqueous stream is returned to the fermentation. In an important aspect, a ratio of a rate of providing the reduced ethanol aqueous stream to the fermentation to a rate of removing the cells and medium from the tation is about 0.5 to about 25. The of at least about 60 g/(L‘day). process is effective for maintaining an STY BRIEF DESCRIPTION OF FIGURES The above and other aspects, features and advantages of several aspects of the s will be more apparent from the following gs.

Figure 1 illustrates a process and system for fermentation of syngas.

Figure 2 shows a process and system for fermentation of syngas that includes a permeate holding tank. for fermentation of syngas that Figure 3 illustrates a s and system includes a heat exchanger. of syngas that includes Figure 4 shows a process and system for fermentation a heat exchanger and C02 er.

Figure that illustrates a process and system for fermentation of syngas includes a vent gas scrubber. ethanol concentration for a Figure 6 shows a graph of growth factor vs. culture of acetogenic bacteria.

Figure 7 shows a graph of growth factor vs. ethanol concentration for a culture of enic ia.

Figure 8 illustrates the effect of aqueous recycle on ethanol concentration and total uptake ofCO and H2.

Corresponding reference characters indicate corresponding components artisans will appreciate that. throughout the several views of the drawings. Skilled 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 elements in the figures may be exaggerated relative to other elements to help to improve understanding of various aspects of the present process and apparatus. Also, common but well—understood elements that are useful or necessary in commercially feasible aspects are often not ed in order to facilitate a less cted View of these various aspects.

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

Upon p and subsequent fermentation there is a need to balance cell and time to remove from medium removal from the fermentor with ed cells to return a reduced permeate, remove ethanol from permeate, and time required balances these ethanol permeate back to the fermentor. The present process and subsequent fermentation. processes to provide a stable startup and acetogenlc Syngas fermentations conducted in bioreactors with medium of CO in syngas bacteria as described herein are effective for providing conversions into ls and other ts. In this aspect, productivity may be expressed as this aspect, the process is STY (space time yield expressed as g ethanol/(L-day). In effective for providing a STY (space time yield) of at least about 10 g/(L'day), at least about 30 g/(L‘day), in another aspect, at least about 60 another aspect, g/(L-day), and in another aspect, at least about 90 g/(L-day). Possible STY values ay) to about 200 g/(L‘clay), in another aspect, about 10 e about about 120 g/(L-day) to about 160 g/(L-day), in another , about 10 g/(L-day) to g/(L'day), in another aspect, about 10 g/(L-day) to about 80 g/(L'day), in another g/(L-day) to about 140 g/(L-day), in another aspect, about 20 aspect, about 20 about 140 g/(L'day) to about 100 g/(L-day), in another aspect, about 40 ay) to ay), and in another aSpect, about 40 g/(lxday) to about 100 g/(L-day).

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 teim “about” modifying any amount refers to the variation in that amount encountered in real world conditions, 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 ion 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 product when modified by “about” includes the variation between s in a multiple experiments in the plant or lab and the variation inherent in the analytical method.

Whether or not modified by “about,” the amounts e equivalents to those also be employed amounts. Any quantity stated herein and modified by “about” can in the present disclosure as the amount not modified by “about”. is the name The term s” or “synthesis gas” means synthesis gas which given to a gas mixture that contains varying amounts of carbon monoxide and of l gas hydrogen. Examples of production methods include steam reforming of coal and in some types of or hydrocarbons to produce hydrogen, the gasification from their use as 2O waste-to-energy gasification facilities. The name comes ammonia or intermediates in creating synthetic natural gas (SNG) and for ing methanol. Syngas is combustible and is often used as a fuel source or as an intermediate for the tion ot'other chemicals.

The term n’tor” es a fermentation device consisting of one or which includes the Continuous more vessels and/or towers or piping arrangements, e Bed Reactor Stirred Tank Reactor (CSTR), Immobilized Cell Reactor (ICR), Gas Lift Fermenter, (TBR), Moving Bed Biofilm Reactor (MBBR), Bubble Column, Static Membrane Reactor such as Hollow Fibre Membrane Bioreactor (HFMBR), Mixer, or other vessel or other device suitable for gas-liquid t. “fermentation on” The terms “fennentation”, fermentation process” or and the like are intended to encompass both the growth phase product conversion of biosynthesis phase of the process. In one aspect, fermentation refers to CO to alcohol.

The term “cell density” means mass of microorganism cells per unit volume of fermentation broth, for example, grams/liter.

The term “cell recycle” refers to separation of microbial cells from a fermentation broth and returning all or part of those separated microbial cells back to the fermentor. Generally, a filtration device is used to accomplish separations.

The term “increasing the efficiency”, ased efficiency” and the like, when used in relation to a fermentation process includes increasing one or more of the rate of growth of microorganisms in the fermentation, the volume or mass of l0 desired product (such as alcohols) produced per volume or mass of substrate (such level of production of the as carbon monoxide) consumed, the rate of production or desired product, and the relative proportion of the desired product produced compared with other by~products of tation.

Smgas Fermentation System Figure l illustrates a process and system for fermentation of syngas. Syngas enters reactor vessel lOO through a syngas inlet 110. Medium and cells and are cell tion filter 200 drawn out through medium outlet 120 and supplied to a filter supply 160 using a medium recirculation pump 150. The cell through tion filter 200 provides concentrated cells and permeate. The reactor vessel 100 receives concentrated cells through cell recycle line 210 and a distillation column 400 es permeate h a permeate supply 250. The distillation reduced ethanol aqueous column 400 provides an ethanol/water azeotrope 440 and a receive the l/water azeotmpe stream 410. A lar sieve/dryer 700 may 440 and provide l product 720. A reboiler 500 receives a portion of the line 430. The reboiler reduced ethanol aqueous stream 410 through a reboiler supply An aqueous stream 500 provides a preheated d ethanol aqueous stream 510. recirculation pump 550 es the reduced ethanol aqueous stream through stream recirculation pump 550 provides the aqueous supply line 420. The aqueous reduced d ethanol aqueous stream back to the reactor vessel 100 through a ethanol aqueous stream supply line 560. the distillation column In another aspect, a fusel oil may be removed from 400 at side draw 450. As used herein, “fusel oil” may include amyl alcohol, propanol, butanol, fatty acids, esters, and mixtures f.

Figure 2 rates another aspect of a process and system for fermentation of syugas. The process and system described in Figure 2 are similar to Figure 1 and the system and process in Figure 2 includes a permeate holding tank 300. in this from filter 200 through , the permeate holding tank 300 receives permeate permeate supply line 220. A distillation column 400 receives te through a permeate supply line 250. Any of the aspects described herein may include a permeate holding tank.

Figure 3 illustrates another aspect of a process and system for fermentation l and of . The process and system described in Figure 3 are similar to Figure 555. In this aspect, the the system and process in Figure 3 includes heat exchanger and permeate from filter heat exchanger receives a reduced ethanol aqueous stream is effective for providing a 200 through supply line 230. The heat exchanger 555 preheated permeate. The distillation column 400 receives the preheated permeate this aspect, heat remaining in the through ted permeate supply line 252. In reduced ethanol aqueous stream may be ed to preheat permeate prior to heat exchanger. distillation. Any of the aspects described herein may include a for fermentation Figure 4 illustrates r aspect of a s and system 4 are similar to Figure l and of syngas. The process and system described in Figure 600. In this , the the system and process in Figure 4 include a C02 stripper C02 er 600 receives permeate and is effective for providing a reduced C02 permeate. Reduced €02 permeate will have a lower level of CO; than prior to have a reduction in (302 of stripping. In this aspect, the reduced 002 permeate will about 10% or more, in another aspect, about 25% or more, in another aspect, about 50% or more, in another aspect, about 75% or more, and in another aspect, about removal. The distillation 90% or more, as compared to the permeate before C02 line 254. column 400 receives d C02 permeate through (302 permeate supply This aspect may include a heat ger 555 as shown and may also include a permeate holding tank, for fermentation Figure 5 illustrates another aspect of a process and system are similar to Figure 1 and of syngas. The process and system described in Figure scrubber 620‘ In this aspect, the system and process in Figure 5 include a vent gas the vent gas scrubber 620 receives the reduced ethanol s stream through a reduced ethanol supply line 560, vent gas through vent gas supply line 640, and distillation column exhaust gas 750. The vent gas scrubber 620 provides a reduced ethanol aqueous stream back the reactor vessel 100 through aqueous supply line 563 and allows vent gas to vent through vent gas exit 650. The vent gas scrubber may be included in any of the aspects bed . In one aspect, the vent gas scrubber ethanol from the tor off~gas. may be effective for removing Syngas Fermentation Process Medium: In accordance with one aspect, the fermentation process is d vessel. The liquid contained in the by addition of a suitable medium to the r nutrient medium or fermentation reactor vessel may include any type of suitable broth. The nutrient medium will include vitamins and minerals effective for permitting growth of the microorganism being used. Some examples of medium itions are described in US. Serial Nos. 61/650,098 and 61/650,093, filed filed July 23, 2001, all of which May 22, 2012, and in US. Patent No. 7,285,402, herein by reference. The medium may be sterilized to remove are incorporated undesirable rganisms and the reactor is inoculated with the d microorganisms, Sterilization may not always be required. bacteria lnoculum: in accordance with the process, a culture of acetogcnic a minimum are inoculated into a reactor to provide an inoculated medium having viable cell density of cell density. As used herein, “minimum cell density” means a at least about 0.2 grams per liter, at least about 0.1 grams per liter, in another aspect, in another , at least about in another aspect, at least about 0.3 grams per liter, liter. The 0.4 grams per liter, and in another aspect, at least about 0.5 grams per liter. In another aspect, minimum cell density will not exceed about l2 grams per seed reactor has a pH of 6.5 or less, the first culture used to inoculate a pro—reactor or about 4.0 to about 4.5. The first in another aspect 4.5 or less, and in another aspect, of about 10 grams culture used to inoculate a reactor has an acetic acid concentration I to about 10 grams per liter, in another per liter or less, in another aspect, about 1 to about 3 grams aspect, about I to about 5 grams per liter, in another aspect, about another aspect, about 2 grams per liter. per liter, and in In one aspect, the microorganisms utilized include acetogenic bacteria.

Examples of useful acetogenic bacteria include those of the genus Ciosafridz‘um, such in WO 2000168407, as strains of Clostrz'a'ium ljungdahlz‘i, including those described RP 117309, US. Patent Nos. 5,173,429, 5,593,886 and 6,368,819, W0 1998/00558 and W0 2002/08438, strains of Clostridz'um autoethanogenum (DSM 10061 and DSM 19630 of DSMZ, Germany) including those bed in WO 17157 and and Clostrz'dium ragsdalez' (P11, ATCC 2) and Alkalibaculum bacchi (CPll, ATCC BAA-1772) including those described respectively in US. Patent No. 7,704,723 and “Biofuels and BiOproducts from Biomass—Generated Synthesis Gas”, Hasan Atiyeh, presented in Oklahoma EPSCoR Annual State Conference, April 29, 2010 and Clostridium carboxidivorans (ATCC PTA—7827) described in US. Patent Application No. 2007/0276447. Other suitable microorganisms includes those of the genus Moorella, including Moorella sp. nces is 1, and those of the genus Carboxya’othermus. Each of these incorporated herein by nce. Mixed cultures of two or more microorganisms may be used.

Some examples of useful bacteria include Acetogerzium kivui, Acetoanaerobium baccki CPll noteme, Acetobacterium woodiz', Alkalz‘baculum (ATCC BAA~1772), Blautia producta, bacterium methylotrop/zicum, Caldarzaerobacter subterraneous, Caldanaerobacter subterraneous pacificus, Carboxydothermus hyclrogenoformans, Clostridt‘um aceticum, Clostridz‘um Clostridium acetobutylicum P262 (DSM 19630 of DSMZ acetobutylicum.

Germany), Clostridium autoethanogenum (DSM 19630 of DSMZ Germany), Clostridium autoethanogenum (DSM 10061 of DSMZ Germany), Closzridium autoethanogenum (DSM 23693 of DSMZ Germany), dium hcmogenum (DSM 24138 of DSMZ Germany), ia'z‘um carboxz‘divorans P7 (ATCC PTA— 7827), Clostridium coskatz'i (ATCC PTA-10522), z'dz'um drakez‘, Closlr'idium ijungdahlii PETC (ATCC 49587), Clostridz’um yungdahlii ERIZ (ATCC 55380), Clostrz‘dium ljungdalzlz'i C~01 (ATCC 55988), Closiridz'um ljungdahiiz’ 0—52 (ATCC 55889), ria’z'um magnum, Clostrz‘dz‘um pasteurianum (DSM 525 of DSMZ Germany), Clostrz‘dium ragsdali P! I (ATCC BAA~622), Closiridium Scatologenes, Clostridium lhermoaceticwn, Clostridium nse, Desulfotomaculum kuznetsovii', Eubacterium m, Geobacter sulfurreducens, Met/zanosarcina acetivorans, Methanosarcina bar/cert, Morrella thermoacetica, Morrella thermoautotrophica, Oxobacter pfermigii, Peptostreptococcus productus, Ruminococcus productus, Thermoanaerobacter kivui, and mixtures thereof. gages: Gasification involves partial combustion of biomass in a restricted supply of oxygen. The resultant gas mainly includes CO and H2. In this aspect, syngas will contain at least about 20 mole % CO, in one aspect, about 20 to about 100 mole % CO, in another aspect, about 30 to about 90 mole % CO, in another aspect, about 40 to about 80 mole % CO, and in r , about 50 to about 70 mole % CO. The syngas will have a CO/CO; ratio of at least about 0.75. Some es of suitable gasiflcation methods and apparatus are provided in US Serial Numbers 61/516,667, 61/516,704 and ,646, all of which were filed on April 6, 2011, and in US. Serial Numbers 13/427,144, 13/427,193 and 33/427,247, all of which were filed on March 22, 2012, and all of which are incorporated herein by reference.

Syngas is introduced into the bioreactor at a rate effective for maintaining a about 0.25 psig, pressure in the bioreactor of at least about 0 psig, in another aspect, in another aspect, about 0.5 psig, in another aspect about 1 psig, and in another aspect, a pressure of about 10 to about 250 psig. In various other , the pressure about 100 psig, about 10 to about 75 may be about 10 to about 200 psig, about 10 to psig, about 10 to about 50 psig, about 10 to about 25 psig, about 20 to about 250 psig, about 20 to about 200 psig, about 20 to about 100 psig, about 20 to abOut 75 psig, about 20 to about 50 psig, about 20 to about 25 psig, about 30 to about 250 psig, about 30 to about 200 psig, about 30 to about 100 psig, about 30 to about 75 psig, about 30 to about 50 psig, about 40 to about 250 psig, about 40 to about 200 psig, about 40 to about 100 psig, about 40 to about 75 psig, about 40 to about 50 psig, about 50 to about 250 psig, about 50 to about 200 psig, about 50 YO about 100 psig, and about 50 to about 75 psig.

In one aspect, in certain size fermentors, syngas is introduced into the gas sparger 110 at a rate of about 10 to about 50 figs/sec, and in another aspect, a rate of about 25 to about 35 its/sec. Pressure is controlled through controlling the rate at which syngas is introduced in combination with controlling the rate at which gas is exhausted from the on vessel. Pressure may be measured in the reactor headspace or at the bottom of the reactor vessel. ion: Startup agitation is set to about 10 to about 30 Hz, in another aspect about 25 Hz, during inoculation. Agitation ramps up to about 35 to about 50 Hz, in another aspect, about 45 Hz, at a ramping rate of about 2 to about 10 Hz every minutes, and in another aspect, about 5 Hz every 10 s.

Cell Recycle: Upon ng an ethanol concentration of more than about 10 g/liter in the fermentation, the process includes removing cells and medium from the fermentor 100. In another aspect, the process includes removing cells and medium l0 when the fermentation reaches and ethanol concentration of more than about 20 gliter, and in r aspect, more than about 30 g/liter. Concentrated cells and medium are provided by separating cells from the medium. Separation of cells from medium may be done using known methods, such as for example a cell separation filter 200. As used herein, “concentrated cells” refers to a stream of cells which has a higher density of cells than prior to separation of medium from the cells. “Penneate” refers to the medium after separation of the cells. In this aspect, the permeate may contain ethanol, All or part of the concentrated cells may be returned to the fermentor 100. In one , cell recycle may be started prior to or immediately upon ation.

In another aspect, cells and medium may be removed upon reaching a cell density of about 0.5 grams per liter or more, in another aspect, about 0.6 grams per liter or more, in another aspect, about 0.7 grams per liter or more, in another aSpeet, about 0.8 grams per liter or more, in another aspect about 0.9 grams per liter or liter or more, in another aspect about 1.5 more, in another aspect about 1.0 grams per grams per liter or more, in r aspect about 2.0 grams per liter or more, in another aspect about 2.5 grams per liter or more, in r aspect about 0.5 to about .0 grams per liter or more, in another aspect about 1.0 to about 4.0 grams per liter about 3.0 grams per liter or more. or more, and in another aspect about 2.0 to The process provides for separation of l from permeate to supply ethanol and a d ethanol aqueous stream. In one aspect, permeate may be transferred to a permeate holding tank 300 and subsequently transferred to a distillation column 400. In one aspect, upon reaching a volume of at least about 1% to about 100% of a total volume of the permeate holding tank, permeate from the holding tank is continuously transferred to a distillation column 400. In another aspect, transfer of permeate to the distillation column may occur once the te holding tank 300 reaches a volume of about 10% of its total volume, in another aspect, at least about 25% of its volume, in another , at least about 50% of its volume, in another aspect, at least about 75% of its volume, and in r aspect, at least about 90% of its volume. The distillation column 400 provides ethanol 450 and a reduced ethanol aqueous stream 4'10. The distillation column can be any distillation column known in art, e.g. a tray column, a packed column. The distillation column lly produces an ethanol~water azeotrope that is further processed using, for example, a molecular sieve to e anhydrous ethanol.

As used herein, “reduced ethanol s ” refers to the aqueous stream after removal of at least a portion of ethanol. The reduced ethanol aqueous stream may include only the reduced ethanol aqueous stream from the distillation column or may include the reduced ethanol aqueous stream from the distillation column in addition to other added medium and/or water. The reduced ethanol In this aspect, a s stream is continuously returned to the reactor vessel 100. ratio of a rate of providing the reduced ethanol aqueous stream to a rate of removing the cells and medium is about 0.5 to about 25, in another aspect, about 0.5 to about 10, in another , about 0.5 to about 5, in r aspect, about 0.5 to about 1, in another aspect, about 1 to about 20, in another , about 5 to about 15, in another aspect, about 5 to about 10, in another aspect, about 4 to about 8, in another aspect, about 5 to about 7, in another aspect, about 5, in another aspect, about 6, and in another aspect, about 7. In this aspect, the reduced ethanol aqueous stream will include less than about 10 weight % alcohol, in another , less than about 5 weight % l, in another aspect, less than about 2.5 weight % alcohol, in another another aspect, less than about 0.5 aspect, less than about 1.0 weight % alcohol, in weight % alcohol, in another aspect, less than about 0.1 weight % alcohol, and in another aspect, less than about 0.01 weight % alcohol.

The reduced ethanol aqueous stream may include acetic acid. In this aspect, liter acetic acid or the reduced ethanol aqueous stream may have about 5.0 grams per acid or less, in another aspect, less, in another aspect, about 2.5 grams per liter acetic about 1.0 grams per liter or less acetic acid, in another aspect, about 0.01 to about .0 grams per liter acetic acid, and in another aspect, about 0.01 to about 0.02 grams acid may per liter acetic acid. The reduced ethanol aqueous stream containing acetic be sent back to the r such that no net acetic acid is produced. An equilibrium is established between ethanol and water in the reactor. As a result, all C0, C02 and Hg fed to the reactor may be converted to ethanol, except for that used for culture maintenance.

In another aspect, the rate of providing the reduced ethanol aqueous stream and a rate of removing the cells and medium from the fermentor may be controlled by utilizing a growth factor ement. As used herein, “growth factor” is the se in amount of cells (in grams, dry weight) per gram of (parent) cells (dry weight) per hour. In this aspect, the rate of providing the reduced ethanol aqueous stream and a rate of removing the cells and medium is effective for ing a growth factor of at least about 0.01 grams/gram/hour, in another , a growth factor of about 0.01 to about i, in another aspect, a growth factor of about 0.01 to about 0.5, in another aspect, a growth factor of about 0.01 to about 0.25, and in r aspect, a growth factor of about 0.01 to about 0.1. As used herein “critical growth factor” refers to a minimum desired growth factor. In one aspect, an example of a minimum desired growth factor is about 0.01, in another aspect, about 0.02, and in another aspect, about 0.03. Growth factor may be determined as follows: Growth (Dry wt of cells in grams at T2) - (Dry wt. of cells'In grams at T1) Factor (Dry wt of cellsIn grams at T1) where T2 is the dry weight of cells in grams measured at 60 minutes after T1 where T1 is the dry weight of cells in grams at selected starting time. critical growth In this aspect, when the growth factor reaches or goes below a of growth factor vs. factor, an aqueous stream is provided to the fermentor. A graph and 7. In this ethanol concentration for idz'um Zjungdahlii is shown in Figures 6 ethanol concentrations may be detrimental or inhibitory for other aspect, lower strains of bacteria. of about 10 g/L or in one , upon reaching an ethanol tration 20 g/L or more, and in another aspect, about 30 g/L or more, in another aspect, about more in the fermentation, cells and medium are removed from the lbrmentation. The cells and medium are separated into ethanol and a reduced l aqueous stream and the reduced ethanol aqueous stream is returned to the fermentation. As further bed, any of the described ethanol concentration levels may be utilized in connection with any of the described recycle ratios, cell densities, growth factors and STY . in another aspect, upon reaching an ethanol concentration of about 10 g/L or more, the ratio of the rate of providing the reduced ethanol stream to the fermentation to the rate of ng cells and medium from the fermentation is l0 about 0.5 to about 25, in another aspect, about 0.5 to about 10, in another aspect, about 0.5 to about 5, in another aspect, about 0.5 to about 1, in another aspect, about i to about 20, in r aspect, about 5 to about 15, in another aSpect, about 5 to about 10, in another aspect, about 4 to about 8, and in another aspect, about 5 to about ’7, in another aspect, about 5, in r aspect, about 6, and in r aspect, about 7. In a similar aspect, upon reaching an ethanol concentration of about 10 g/L or more and a cell density of about 0.5 g/L or more, in another aSpect, about 0.6 g/L or more, in another aspect, about 0.7 g/L or more, in r aspect, about 0.8 g/L or about 1.0 g/L or more, in another aspect, about 0.9 g/L or more, in another aspect, more, in another aspect about 1.5 g/L or more, in another aspect about 2.0 gL or in another aspect about 0.5 to about more, in another aspect about 2.5 g/L or more, .0 g/L, in another aspect about 1.0 to about 4.0 g/L, and in another aspect about 2.0 stream to the to about 3.0 g/L, the ratio of the rate of providing the reduced ethanol fermentation to the rate of removing cells and medium from the tation is about 0.5 to about 25, in another aspect, about 0.5 to about 10, in another aspect, about 0.5 to about 5, in another aspect, about 0.5 to about 1, in another aspect, about 1 to about 20, in another aspect, about 5 to about 15, in another aspect, about 5 to to about 7, about 10, in another aspect, about 4 to about 8, in another aspect, abOut about 7. in another aSpect, about 5, in another aspect, about 6, and in another , The process is effective for providing a growth factor of about 0.01 to about 1, in another , about 0.01 to about 0.5, in another aspect, about 0.01 to about 0.25, and in another aspect about 0.01 to about 0.1. The s is further effective for providing an STY of about 10 g/(L-day) to about 200 g/(L-day), in another aspect, about 10 g/(L-day) to about 160 g/(L'day), in another aspect, about 10 g/(L-day) to about 120 g/(L'day), in another aspect, about 10 g/(L-day) to aborit 80 ay), in another aspect, about 20 g/(L-day) to about 140 g/(L-day), in another aspect, about g/(L-day) to about 100 g/(I..'day), in another aspect, about 40 ay) to about 140 ay), and in another aspect, about 40 g/(L-day) to about 100 g/(L-day).

In r aspect, upon reaching an ethanol concentration of about 20 g/L or the ratio of the rate of providing the reduced ethanol stream to the more, fermentation to the rate of ng cells and medium from the fermentation is abOut 0.5 to about 25, in r aspect, about 0.5 to about 10, in another aspect, about 0.5 to about 5, in another aspect, about 0.5 to about 1, in another aspect, about about 5 1 to to about 20, in r aspect, about 5 to about 15, in another , about 10, in another aspect, about 4 to about 8, and in another aspect, about 5 to another aspect, about 7, in another aspect, about 5, in another aspect, about 6, and in about 7. in a simiiar aspect, upon reaching an ethanol concentration of about 10 g/L in another aspect, about 0.6 g/L or more and a cell density of about 0.5 g/L or more, or more, in another , about 0.8 g/L or or more, in another aspect, about 0.7 g/L 0.9 g/L or more, in another aspect, about 1.0 g/L or more, in another aSpect, about more, in another aspect about 1.5 g/L or more, in another aspect about 2.0 g/L or 2.5 g/L or more, in another aspect about 0.5 to about more, in another aspect abetit in another aspect about 2.0 5.0 g/L, in another aspect about 1.0 to about 4.0 g/L, and the reduced ethanol stream to the to about 3.0 g/L, the ratio of the rate ol‘providing fermentation to the rate of removing cells and medium from the fermentation is , in another aspect, about 0.5 to about 25, in another aspect, about 0.5 to about in another aspect, about about 0.5 to about 5, in r aspect, about 0.5 to about 1, to 1 to about 20, in another aspect, about 5 to about 15, in another aspect, about about 5 to about 7, about 10, in another aspect, about 4 to about 8, in another aspect, r aspect, about 7. in another aspect, about 5, in another aspect, about 6, and in is effective for providing a growth factor of about 0.01 to about The process 1, in another aspect, about 0.01 to about 0.5, in another aspect, about 0.01 to about 0.25, and in another aspect about 0.01 to about 0.1. The process is further effective for another , providing an STY of about 10 g/(L-day) to about 200 g/(L‘day), in about 10 g/(L-day) to about 10 g/(L‘day) to about 160 g/(L-day), in another aspect, about 120 g/(I,*day}, in another aspect, about 10 g/(L-day) to about 80 ML-day), in another aSpeot, about 20 g/(Lday) to about 140 g/(L-day), in another aspect, about g/(L‘day) to about 100 g/(L‘day), in another aspect, about 40 g/(L-day) to about 140 g/(L~day), and in another aspect, about 40 g/(L'day) to about 100 g/(L-day). in another aspect, upon reaching an ethanol tration of about 30 g/L or more, the ratio of the rate of providing the reduced ethanol stream to the fermentation to the rate of removing cells and medium from the fermentation is about 0.5 to about 25, in another aspect, about 0.5 to about 10, in another aspect, about 0.5 to about 5, in another aspect, about 0.5 to about 1, in another aspect, about 1 to about 20, in another aspect, about 5 to about 15, in another aspect, about 5 to about 10, in another aspect, about 4 to about 8, and in another aspect, about 5 to about 7, in another aspect, about 5, in another aspect, about 6, and in another aspect, about 7. In a similar aspect, upon reaching an ethanol concentration of about 10 g/L in another aspect, about 0.6 g/L or more and a coil density of about 0.5 g/L or more, another aspect, about 0.8 g/L or or more, in r , about 0.7 g/L or more, in in another aspect, about 1.0 3/1. or more, in another aspect, about 0.9 g/L or more, more, in another aspect about 1.5 g/L or more, in another aspect about 2.0 g/L or 2.5 g/L, in another aspect about 0.5 to about 5.0 gL, more, in r aspect about about 2.0 to about in another aspect about 1.0 to about 4.0 g/L, and in another aspect 3.0 g/L, the ratio of the rate of providing the reduced ethanol stream to the fermentation to the rate of removing cells and medium from the fermentatiori is about 0.5 to about 25, in another aspect, about 0.5 to about 10, in another aspect, about 0.5 to about 5, in another aspect, about 0.5 to about '1, in another aspect, about 1 to about 20, in another aspect, about 5 to about 15, in another aspect, about 5 to about 7, about 10, in r aspect, about 4 to about 8, in another aspect, about 5 to about 7. in another , about 5, in another aspect, about 6, and in another aspect, The process is effective for ing a growth factor of about 0.01 to about 1, in another aspect, about 0.01 to about 0.5, in another , about 0.01 to about 0.25, and in another aspect about 0.01 to about 0.1. The process is r effective for providing an STY of about 10 ay) to about 200 g/(L'day), in r aspect, about 10 g/(L‘day) to about 160 g/(L-day), in another aspect, about 10 g/(L'day) to about 80 g/(L~day), in about 120 g/(L-day), in r aspect, about 10 g/(L-day) another aspect, about 20 g/(L-dny) to about 140 g/(L-day), in another aspect, about ay) to about 100 g/(L-day), in another aspect, about 40 g/(L-day) to about 140 g/(L-day), and in another aspect, about 40 lay) to about 100 ay).

EXAMPLE Example 1: Effect ofAqueous Recycle on Uptake of 1-12 and CO A fermentation was conducted with Clostrz'dz‘um Liungdahlz‘z‘ at a 60 g/L STY level. A graph of ethanol concentration and total H2 and CO uptake are shown in Figure 8. In this fermentation, water recycle was started once the ethanol concentration exceeded 36.8 g/L. After ng water recycle, l concentration ed to about 28 g/L. Total uptake of Hz and CO reached a maximum at an ethanol tration of about 33.7 g/L and then decreased from about 2.02 mole/min to about 1.85 mole/min when the ethanol concentration exceeded 36 g/L.

Once water recycle was started (about 537“1 hour), ethanol concentration decreased and total H2 and CO uptake increased. Continuing the fermentation without water recycle results in decline in total uptake of total Hz and CO and culture failure.

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

I/WE

Claims (8)

CLAIM :

1. A process for fermentation of syngas sing: contacting syngas with a medium inoculated with acetogenic bacteria and having a cell density of at least about 0.3 grams per liter; fermenting the syngas to convert CO to ethanol; removing cells, and medium from the fermentation upon reaching an ethanol concentration of more than about 10 g/L in the fermentation; separating the removed cells and medium to provide concentrated cells and permeate; separating ethanol from the permeate to provide ethanol and a reduced ethanol aqueous stream having less than about 5 weight % l; and providing the reduced ethanol s stream having less than about 5 weight % alcohol to the fermentation; wherein a ratio of a rate of providing the reduced ethanol aqueous stream to the tation to a rate of removing the cells and medium from the fermentation is about 5 to about 15, wherein an l concentration of more than about 10 g/L is maintained in the fermentation.

2. The process of claim 1 wherein cells and medium are removed upon reaching a cell density of about 0.5 grams per liter or more.

3. The process of claim 1 or claim 2 wherein permeate is transferred to a permeate holding tank.

4. The process of claim 3 wherein permeate is transferred to a distillation . AH26(11346017_1):EOR

5. The process of claim 4 wherein prior to distillation, the permeate is preheated by heat exchange with the d ethanol aqueous stream.

6. The process of any one of claims 1 to 5 wherein the reduced ethanol aqueous stream comprises acetic acid.

7. The process of claim 4 wherein CO2 is removed from the permeate prior to lation.

8. The process of any one of claims 1 to 7 wherein fusel oil is removed from a distillation column at a side draw. INEOS BIO SA Ryan Senaratne Song Liu By the Attorneys for the Applicant SPRUSON & ON Per: AH26(11346017_1):EOR