HK1103759A1 - Biological production of acetic acid from waste gases - Google Patents

Abstract

The method and apparatus for converting the waste gas from petroleum processing, carbon black production, coke production, ammonia production, methanol production and other industrial production into useful product is revealed. The method includes leading the waste gas into one bioreactor, where waste gas is fermented with the anaerobic bacteria into organic acids, alcohols, H2, SCP and organic acid salts, and recovering, separating and purifying the ultimate products of these organic matters.

Description

Biological production of acetic acid from waste gases

The patent application of the invention is a divisional application of an invention patent application with the international application number of PCT/US96/11146, the international application date of which is after PCT international application of 7/1/1996 enters the national stage of China, the application number of 96180363.0 and the name of the invention is 'preparation of acetic acid from waste gas by a biological method'.

The present invention relates to biological processes, microorganisms and apparatus for producing products, feedstocks, intermediates and the like (e.g., organic acids, Single Cell Proteins (SCPs), hydrogen, alcohols and organic acid salts) from waste gas streams of certain industrial processes, and more particularly to processes for achieving such conversions using continuous gas phase substrate fermentation under anaerobic conditions.

A conventional procedure for the preparation of organic acids, alcohols, hydrogen and salts of organic acids is the chemical synthesis of petroleum derived feedstocks. The rapid rise in petroleum costs has generated great interest in the production of these valuable products by fermentation processes using recyclable or waste materials as raw materials. Single cell proteins are produced as a by-product of fermentation and are used as animal feed.

The great amount of atmospheric pollutants and greenhouse gases generated in the traditional industry are also gradually attracting attention. Environmental protection agencies have recently predicted that more than six million tons of carbon monoxide and nearly four million tons of hydrogen are emitted annually by industrial complexes. The major portion of these carbon monoxide and hydrogen is produced by carbon black and coke plants, roughly estimated at about 260 million tons CO and 50 million tons and H₂. Sources of large amounts of carbon monoxide or hydrogen production are also the ammonia industry (125144 tons CO for 1991), petroleum processing (8 tons per 1000 barrels), steel works (152 pounds per ton steel produced)) And kraft pulp of wood (286 pounds per ton of pulp). In 1991, the adipic acid industry produced 40773 tons of carbon monoxide that was burned using the combustion value or white spirit. In many cases, these gases are vented to the atmosphere, creating a heavy pollution load on the environment.

The production of industrial products is generally carried out by the release of waste gases at low pressures and temperatures. Modern technology cannot utilize these dilute gases under such conditions. The separation and recovery of hydrogen and carbon monoxide from these waste gas streams using prior art techniques is costly and impractical.

In view of the foregoing, there is a need for a cost effective and practical method, microorganism and apparatus for utilizing such waste gases to produce products, feedstocks, intermediates and the like, such as organic acids, alcohols, hydrogen and organic acid salts, without the need for chemical synthesis of petroleum derived feedstocks.

Summary of the invention

According to the present invention, products, raw materials, intermediates and the like, such as organic acids, alcohols, hydrogen, single-cell proteins and/or organic acid salts, are produced from waste carbon monoxide, hydrogen and/or carbon dioxide in industrial processes, thereby reducing environmental pollution while saving energy and chemical raw materials.

In accordance with the process exemplified herein, the components of the dilute gas mixture required are introduced into a bioreactor containing one or more cultured anaerobic bacterial strains capable of utilizing the waste gas components to produce the desired compounds by a direct route. The compound is recovered from the liquid phase in one or more vessels using a recovery process suitable for the compound produced. Examples of recovery methods include extraction, distillation or a combination thereof, or other effective recovery methods. The bacteria are recovered from the liquid phase and recycled to avoid their toxicity and to maintain high cell concentrations, thus maximizing the reaction rate. If desired, separation of the cells may be accomplished by centrifugation, membrane ultrafiltration, or other techniques.

It is a primary object of the present invention to provide a process and/or a microorganism for the production of products, intermediates, feedstocks and the like, such as organic acids, hydrogen, single cell proteins, alcohols and/or salts of organic acids, from carbon monoxide, hydrogen and/or carbon dioxide.

It is another object of the present invention to provide methods, microorganisms and apparatus for producing products such as organic acids, alcohols, hydrogen, single cell proteins and or salts from waste gas streams in industrial processes such as petroleum processing, carbon black, coke, ammonia production and methanol production.

It is a further object of the present invention to provide a process for producing acetic acid and/or ethanol from an offgas stream of the same composition as found in carbon black manufacture.

It is another more specific object of the present invention to provide processes, microorganisms and apparatus for converting waste gas streams comprising continuous gaseous substrate fermentation under anaerobic conditions to accomplish the conversion of certain industrial processes to useful products such as organic acids including acetic acid, alcohols, hydrogen, single cell proteins and salts of organic acids.

Other objects and further scope of applicability of the present invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings, wherein like reference numerals denote like parts.

FIG. 1 is a schematic diagram of a process for producing acetic acid from an off-gas.

Figure 2 is a schematic of a process for producing CMA from an off-gas.

FIG. 3 is a schematic of a process for producing ethanol from an off-gas.

FIG. 4 is a schematic representation of a continuous fermentation system according to one embodiment of the present invention.

FIG. 5 is a graphical representation of cell concentration (OD) versus time.

Fig. 6 is a graphical representation of acetic acid (HAC) versus time.

The term "off-gas" or "off-gas stream" as used herein refers to carbon monoxide and hydrogen in which other elements and compounds, including carbon dioxide, nitrogen and methane, are mixed, which are present in gaseous form, typically released or evacuated to the atmosphere either directly or by combustion. Typically, the release occurs at standard stack temperatures and pressures. Thus, the process of the present invention is suitable for converting these atmospheric pollutants into useful products, such as organic acids, alcohols and organic acid salts. These products include, but are not limited to, acetic acid, propionic acid, and butyric acid; methanol, ethanol, propanol, and n-butanol; and salts, such as Calcium Magnesium Acetate (CMA) and potassium acetate (KA).

Anaerobic bacteria known to convert carbon monoxide and water or hydrogen and carbon dioxide to alcohols, acids and acid salts include Acetobacter kivui of Acetobacter genus, A.woodii, Clostridium acetobacter, Butyribacterium methylotrophicum of Butyribacterium genus, butyric acetate of Clostridium acetobacter species, acetic acid formate species, C.kluyveri, thermophilic acetic acid species, thermophilic fiber species, C.thermohydrosulfurifurum, thermophilic saccharolytic species, Eubacterium limosum, C.ljungdahlii PETC of Clostridium genus and Pentosteptococcus productus. Anaerobic bacteria known to produce hydrogen from carbon monoxide and water include rhodospirillum rubrum and pilobacterium gliobatum.

More specifically, such bacteria as Acetogenium kivui, Peptostreptococcus productus, Acetobacter wood, Clostridium thermoaceticum and Eubacterium limosus produce acetate by the following reaction:

4CO+2H₂O→CH₃COOH+2CO₂dG ═ 39 kcal/reaction (1)

It is known that many anaerobic bacteria can also be constructed from H₂And CO₂Acetic acid is produced. These bacterial isolates include species a.kivui, p.productus and acetobacter, which oxidize hydrogen and CO anaerobically according to the following reaction equation₂Using the same typeAcetic acid fermentation:

4H₂+2CO₂→CH₃COOH+2H₂dG-25 kj/reaction (2)

Acetobacter woodoii and Acetoanaerobium noterae were reacted as above with H₂And CO₂Acetate is produced, but in addition to acetate, a. noterae also produces certain propionates and butyrates. Another chemolithotrophic bacterium, Clostridium aceticum, can utilize the glycine decarboxylase pathway from CO₂Producing acetate.

Certain bacteria, such as a.kivui, p.productus and a.woodii, are derived from CO and H₂O or H₂And CO₂Producing acetate. Products gave particularly fast conversion rates and showed high tolerance to CO; however, this bacterium showed an advantage over equation (2) in following equation (1).

In addition to these enumerated bacteria, two strains of the genus Clostridium are isolated which can be separated from CO and H₂O or H₂And CO₂Producing acetic acid or ethanol. One of these is Clostridium ljungdahlii ERI2, which is rod-shaped, gram-positive, a non-thermophilic anaerobic bacterium that gives high acetic acid yields and reacts at low pH, which greatly improves product recovery. Ljungdahlii ERI2 is capable of performing vigorous glucose acetogenic fermentation. It occasionally also sporulates and proceeds predominantly with hexoses or H₂:CO₂The acetic acid production and fermentation. It moves by peripheral flagella. The new c.ljungdahlii strain, designated ERI2, was isolated from a natural source and sent to the American Type Culture Collection (ATCC) at rockwell, maryland, on 8.12.1992, catalog number: 55380.

the "mixed strains" listed above may be used in the preparation of the products of the invention. By mixed strain is meant a mixed culture of two or more anaerobic bacteria. The mixed strain can produce organic acid (such as acetic acid, etc.) or their salts, alcohols, hydrogen, SCP, etc. when used in the process.

During the course of the present study, new anaerobic strains were isolated which were capable of efficient transformation. In addition, varying fermentation conditions can allow certain strains to produce ethanol instead of acetic acid. Depending on the specific strain used, several variables must be considered in forming the product from the off-gas, including nutrient composition and concentration, medium, pressure, temperature, gas flow rate, liquid flow rate, reaction pH, agitation rate (if a continuous fermentation stirred tank reactor is used), inoculation level, maximum substrate (input gas) concentration to avoid inhibition, and maximum product concentration to avoid inhibition.

According to one embodiment of the invention and as shown in FIG. 1, the first step in the transformation process is to prepare a medium (10) to be supplied with anaerobic bacteria. The composition of the nutrient medium will vary depending on the type of anaerobic bacteria used and the desired product. Nutrients are continuously fed to a bioreactor or fermentor (12) which consists of one or more vessels and/or a type of column including a Continuous Stirred Tank Reactor (CSTR), an Immobilized Cell Reactor (ICR), a Trickle Bed Reactor (TBR), a bubble column, an airlift fermentor or other suitable fermentation reactor. A culture of single or mixed anaerobic species for use in a gas conversion process is placed within a bioreactor (12). In CSTRs, TBRs, bubble columns and gas lift fermenters, these bacteria live dispersed in the liquid phase of the reactor, but with ICRs, the bacteria adhere to the media filled inside. The packing medium must provide maximum surface area, high mass transfer rates, low pressure drop, uniform gas and liquid distribution, and must minimize plugging, fouling, nesting, and tube wall channeling. Examples of such dielectric materials are ceramic arc saddle packing, packing rings or other high performance packing.

The waste gas (14) is continuously introduced into the bioreactor (12). The residence time of the gas in the bioreactor (12) is such as to maximise the efficiency of the process. The gas (16) containing the inert unreacted substrate is then discharged. The effluent liquid (18) is passed through a centrifuge, hollow membrane or other filtration device (20) to separate the microorganisms contained therein. These microorganisms (22) are returned to the bioreactor (12) to maintain the high cell concentration (cell recycle) required to produce a faster reaction rate.

The next step in the process is to separate the desired biologically produced product from the filtrate or centrate (24). In the embodiment shown in fig. 1, the filtrate or centrate (24) passes through an extraction chamber (26) where it is contacted with a solvent (28). The solvent (28) should have a high partition coefficient for the desired end product, a high recovery coefficient, low toxicity to humans, low toxicity to bacteria, immiscibility with water, a suitably high boiling point and not form an emulsion with the components of the bioreactor. The partition between the solvent and the aqueous phase will determine the thermodynamic feasibility and the amount of solvent required to remove the final product. Typical solvents include secondary and tertiary amines, tributyl phosphate, ethyl acetate, trioctylphosphine oxide and related compounds dissolved in suitable co-solvents, long chain alcohols, hexane, cyclohexane, chloroform and tetrachloroethylene in suitable solvents.

The nutrients and materials in the aqueous phase (30) are returned to the bioreactor (12) and the solvent/acid/water solution (32) is passed through a distillation column (34) where it is heated to a temperature sufficient to separate the solvent (28) from the water and acid (36). The solvent (28) is passed from the distillation column (34) through a cooling chamber (38) to a temperature optimum for extraction and then returned to the extraction chamber (26) for reuse. The acid and aqueous solution (36) is passed through a final distillation column (40) where the desired final product (42) is separated from the water and withdrawn. The water (44) is recycled for nutrient preparation.

FIG. 2 shows a process for producing the road anti-icing agent Calcium Magnesium Acetate (CMA) (46) from exhaust gas (48). The process is the same as the acetic acid process by solvent extraction of figure 1. I.e. continuous fermentation using the same bacteria, nutrients and process conditions, including the reaction vessel. Also, in this process, cells are recycled using hollow fiber membranes, centrifugation or other filtration devices, all the same. Finally, a process is used in which acetic acid is extracted in an extraction chamber, followed by recycling of the acid-free medium.

After extraction, the process for producing CMA is much different from the acetic acid production process of figure 1. In a CMA process a solvent (50) containing acetic acid and a small amount of water are fed to a reaction vessel (52) to produce CMA. The water content of the solvent stream depends on the solvent used to extract the acetic acid. Further, solvents such as secondary and tertiary amines, tributyl phosphate, ethyl acetate, trioctylphosphine oxide and related compounds dissolved in a suitable co-solvent, long chain alcohols, hexane, cyclohexane, chloroform and tetrachloroethylene, dissolved in a suitable co-solvent, may be used with varying effects. The most suitable reaction vessel (52) for producing CMA is a Continuous Stirred Tank Reactor (CSTR), although other reactors may be used. A mixture of dolomitic lime and magnesia dissolved in water is added to a solvent containing acetic acid and water. A CMA-producing reaction occurs, reaching a saturation or sub-saturation level in aqueous solution.

The CMA, water and solvent (56) are then sent to a settling device (58) to separate the water and solvent phases. The solvent phase (60) is returned to the extraction chamber for recycling. The CMA/water (62) is sent to drying/settling (64) to produce a settled CMA product.

Another product, potassium acetate (KA), can be produced by replacing dolomite lime with caustic potash (or potassium oxide). Because KA is produced as a 50% aqueous solution, drying and settling are not required.

FIG. 3 shows a process for producing ethanol from an off-gas. As shown in FIG. 1, waste gas (66) and nutrients (68) are fed into a reactor (70) containing a microbial culture. The reactor may be of any of the types described above with reference to figure 1. The bacteria used in the ethanol production process must be capable of producing ethanol rather than acetic acid/acetate. Low fermentation pHs of 4.0-5.5 are generally required, while nutrient limitation is imposed. The above-listed bacteria capable of reacting at a low pH level can be used in the ethanol production process.

The off-gas is fed to a reactor containing a culture of bacteria capable of producing ethanol and essential nutrients. The product ethanol was produced in a similar manner to that in figure 1. The cell concentration in the reactor can be increased by recycling (72) of the cells, but this is not required for the process to operate. The filtrate (74) from the cell recycle device, containing the ethanol diluted in the culture medium, is sent to distillation (76) where water (78) and ethanol (80) are separated. 95% ethanol comes out from the top of the distillation column, while water (spent medium) comes out from the bottom of the column. The spent medium is returned to the reactor as a recycle of water. The 95% ethanol is fed to a molecular sieve system (82) to produce anhydrous ethanol (84).

Thus, valuable organic acids, alcohols or salts of organic acids can now be produced according to the invention by fermentation of gaseous substrates, not only reducing the consumption of valuable chemical raw materials, but also removing harmful atmospheric pollutants from many industrial waste gas streams. Previous processes for biologically producing these chemicals have been based on sugar fermentation.

It is desirable in the above process to carry out the process at a pressure above one atmosphere. Preferably at a pressure of up to 30 atmospheres, more preferably up to 20 atmospheres, and most preferably up to 15 atmospheres.

The following specific examples are provided for illustration only and are not to be construed as limiting the invention. Parts and percentages used in the present specification and claims are by volume unless otherwise indicated.

EXAMPLE 1 production of acetic acid from carbon Black off-gas

This example relates to a process for converting an exhaust gas composition of an exhaust gas from a carbon black-producing furnace to acetic acid. The composition of the off-gas is about 13% carbon monoxide, 14% hydrogen and 5% carbon dioxide, with the remaining 68% being mostly nitrogen, with small amounts of oxygen and sulfur compounds. The off-gas is produced as a result of the partial oxidation of the gas or oil by an insufficient amount of air to form amorphous carbon, producing about 1.2 pounds of carbon monoxide per pound of elemental carbon. These waste gases pose a serious problem of atmospheric pollution and are valuable chemical raw material resources which are not recovered at present.

Two routes to acetic acid from carbon black off-gas were investigated in the study of the present process. The direct route is to subject CO to the following equations (1) and (2), respectivelyAnd H₂O or H₂And CO₂Directly converted into acetic acid. The indirect route is the reaction of CO and H by water gas shift₂Conversion of O to H₂And CO₂Then from H₂And CO₂Acetic acid is produced. This indirect approach was found to be a less efficient technical application.

The tested acetic acid-producing bacteria are summarized in Table 1. Of such bacteria that produce acetic acid directly from CO, a. kivui and the newly isolated strain c.ljungdahlii ERI2 are responsible for CO and H₂Exhibit much higher speeds. Further experiments were performed with these two strains of anaerobic bacteria.

The simultaneous use of carbon monoxide and hydrogen has significant advantages for bacteria. This enables the most efficient use of the exhaust gases and the removal of the maximum amount of atmospheric pollutants.

Laboratory scale operation of the above-described process for producing acetic acid

As shown in FIG. 4, a laboratory scale continuous transformation system is illustrated, including a BioFlo IIC fermentor (150) (available from New Brunswick scientific Co., Inc., of Edison, N.J.), according to one embodiment of the present invention. The fermentation tank (150) is equipped with a stirring motor, a pH controller, a foam controller, a thermostat, a dissolved oxygen probe, a feed pump and a 2.5-liter culture vessel. The reaction volume can vary (1.5-2.0 liters). Other variable operating parameters include medium feed rate (dilution rate), gas flow rate (gas residence time), agitation (rpm). The vented or exhausted gas is exhausted from the fermentor (150) through a condenser attached to the hood via a water vapor valve and a sample port.

The broth (152) was recirculated through a cross-flow hollow fiber unit (154) by a peristaltic pump (available from Cole Parmer). The recirculation rate is about 80-100 ml/min. The hollow filament unit (154) has the following characteristics: the surface area was 0.35 square feet, the pore size was 0.2 microns, and the diameter of the lumen was 1 mm. The filtrate (156) is pumped to a storage vessel (158) (raw material storage). The cultured cells are returned to the fermentor along line (155).

A counter-current acetic acid extraction system comprising two staged mixers and a settling tank comprises: first and second mixers (160) and (162) and first and second settling tanks (164) and (166). Filtrate (168) from the storage vessel (158) is pumped to the mixer (160) through a flow rate controller (170). Solvent (172) is pumped from a solvent storage vessel (174) through a flow controller (176) to the mixer (162). Both mixers (160) and (162) are equipped with stirring mechanisms to achieve good mixing of the aqueous and solvent phases. The two-phase mixture from mixers (160) and (162) enters settling tanks (164) and (166), respectively. The phase separation was completed in a settling tank. The aqueous phase (178) from the settling tank (164) is pumped to the mixer (162), the solvent phase (180) from the settling tank (166) is pumped to the separator (182), the aqueous phase (184) from the settling tank (166) is pumped to the raffmate storage tank (186), and the solvent phase (188) from the settling tank (166) is pumped to the mixer (160). The raffinate is recycled to the CSTR (50) along line (190). This recirculation conduit (190) is partially vented at (192) to remove the inhibiting factors.

The solvent (180) containing acetic acid is pumped through preheater (196) to distillation flask (194). The retort (194) is equipped with two thermocouples (196) and (198) to monitor and control the temperature in the liquid and vapor phases. The temperature at which the distillation is heated is determined to maximize the evaporation of acetic acid. Acetic acid vapor was condensed in condenser (100) and collected in bottle (102). The acetic acid-depleted solvent (104) is pumped through cooling coil (106) to solvent reservoir (174).

The laboratory scale operating equipment of the process shown in fig. 4 was set up in the laboratory in order to determine the yield under optimum conditions. The nutrient mixture fed to the bacteria was as follows:

1.80.0 ml of salt consisting of

KH₂PO₄3.00 g/l

K₂HPO₄3.00 g/l

(NH₄)₂SO₄6.00 g/l

NaCl 6.00 g/l

MgSO₄.2H₂O1.25 g/l

2.1.0 g of yeast extract

3.1.0 g trypticase

4.3.0 ml of PFN (pfenning) trace metal solution

FeCl₂.4H₂O1500 mg

ZnSO₄.7H₂O100 mg

MnCl₂.4H₂O30 mg

H₃BO₃300 mg of

CoCl₂.6H₂O200 mg

CuCl₂.H₂O10 mg

NiCl₂.6H₂O20 mg

NaMoO₄.2H₂O30 mg

Na₂SeO₃10 mg of

1000 ml of distilled water

5.10.0 ml vitamin B

Pyridoxal HCl 10 mg

50 mg of riboflavin

Thiamine, HCl 50 mg

50 mg of nicotinic acid

Ca-D-pantothenate 50 mg

Lipoic acid 60 mg

50 mg of p-aminobenzoic acid

Folic acid 20 mg

Biotin 20 mg

Cyanocobalamin 50 mg

1000 ml of distilled water

6.0.5 g cysteine, HCl

7.0.06 g of CaCl₂.2H₂O

8.2.0 g NaHCO₃

9.1.0 ml Resazurin (0.01%)

10.920.0 ml of distilled water

The pH of the nutrient solution was adjusted to 6.6 using a.kivui, and to 4.9 using the new strain c.ljungdahlii ERI 2. It would be advantageous to be able to operate at lower pH conditions in the recovery of acetic acid. Then using 20% CO₂And 80% N₂The mixed gas sparged the solution for 20 minutes, then transferred and autoclaved for 15 minutes in the absence of oxygen.

Numerous experiments were performed both with a continuous stirred reactor (CSTR) and an Immobilized Cell Reactor (ICR). The results are illustrated in the following data.

CSTR experiments were performed with bacterial strains A. kivui and C.ljungdahlii ERI2

A laboratory scale system operated with CSTR and anaerobic bacteria, c.ljungdahlii ERI2 and a.kivui included a New Brunswick Scientific Bioflo IIc fermenter, a hollow silk membrane unit for recycled cells and an extraction and distillation column. The nutrient mixture was fed into the bioreactor at a rate of 3.2 cubic centimeters per minute. The volume of the reactor was 2.5 liters, with a constant liquid level of 1.5 liters being maintained. The liquid is stirred at various speeds, up to 1000 revolutions per minute, and the gas is introduced at a rate of about 500 cubic centimeters per minute. The optimum gas residence time is in the three minute range. The gas feed varies with its uptake by the bacteria as a function of cell density.

Liquid from the bioreactor is passed through the hollow fiber membranes at a rate of 55 to 70 milliliters per minute. The filtrate passing through the hollow fiber membranes was collected at a rate of 1.5 ml per minute. Analysis of this filtrate showed that the acetic acid/acetate concentration at this stage was over 20 grams per liter. Using c.ljungdahlii ERI2 operating at ph4.9, 42% of the product was in the acid form. The acid yield with a.kivui was only 1.4%. The results of different experiments with these two bacteria, including conversion and yield, are summarized in tables 2 and 3.

ICR experiments with the bacterial strain C.ljungdahlii ERI2

An Immobilized Cell Reactor (ICR) comprising a 2 inch outer diameter and 24 inch high glass tube, wrapped with fabric to support cells and Enkamat7020 as an immobilization medium was also used to test the acetic acid production process. When c.ljungdahlii ERI2 was used as the acetogenic anaerobe, 100% of the carbon monoxide and 79% of the hydrogen were converted at a gas residence time of 20 minutes. The concentration of acetic acid in the withdrawn liquid was about 6.0 grams per liter. The ICR findings are summarized in Table 4.

ICR has been attractive on a commercial scale because the cost of energy consumed to operate the reactor is significantly reduced. Proper selection of the encapsulating material, solution phase and pressure may allow yields approaching those of a CSTR.

Recovery of acetic acid

Recovery of acetic acid from the filtrate with various solvents was tested and the results are summarized in table 5. Tributyl phosphate was identified to have both a high partition coefficient and a high boiling point. The solvent and filtrate from the cell separator were mixed in a two-stage extraction process. Alternatively an extraction column may be used. The filtrate was introduced into a 3 liter bottle where it was mixed with the incoming solvent. Extraction is performed well with a ratio of one part solvent to one part filtrate, resulting in high recovery. The combined liquids from the mixer are passed through a 4-liter settling chamber where the solvent/acetic acid mixture is separated as a low density phase from the water and nutrients. The residence time used in the settler was about 15 minutes. The low density phase is extracted and sent to a distillation flask. The raffinate from the first settling tank passes through a second mixer where it is again contacted with solvent and then moved to a second settling chamber. This allows a more complete extraction of acetic acid; when tributyl phosphate is used, the recovery rate increases from 82% to over 96%. The solvent/acetic acid mixture from this settling chamber is returned to the first mixer, while the raffinate of water and organics is returned to the bioreactor.

The distillation unit was a 5-liter bottle with a boiling hood. A conventional distillation column with reflux can be used to recover the acid completely. Because of the high boiling point of tributyl phosphate, almost complete recovery can be achieved in one step. The solvent/acetic acid mixture was heated to 120 c and the acetic acid was collected in the overhead of the condensation coil. In this one-step system, the distillation efficiency reached 70%.

Solvent mixtures were also tried and the partition coefficients of the mixed solvents are summarized in table 6.

Example 2

Recovery of acetic acid from carbon black off-gas

Under high pressure

Operating the system under elevated pressure conditions further enhances mass transfer in the cellular response. Simple batch experiments were performed to test the kinetics of this system. The reaction rate was found to increase linearly with pressure and the effective residence time was reduced accordingly. A further advantage of operating at high pressure is that the reaction volume can also be reduced in a linear manner, i.e. the reactor volume required at 10 atm is one tenth of the reactor volume at 1 atm. FIGS. 5 and 6 show that cell density and acetic acid concentration increase with increasing pressure, respectively. This acetic acid concentration far exceeds the typical batch concentration for a batch reactor at atmospheric pressure.

Example 3

Production of acetic acid from carbon black off-gas using surfactants

The use of surfactants also improves mass transfer. Table 7 shows the results of c.ljungdahlii ERI2 uptake of carbon monoxide with the addition of various commercially available surfactants. In each case, the 100 (%) control value represents the CO uptake in the batch fermentation, while the sample value represents the percentage of the control in the batch fermentation with surfactant added.

TABLE 1 for testing CO, H₂And CO₂Transformed acetogenic bacteria

Bacterial pathways	CO and HWhile consuming
		Direct route
P.productus	Whether or not
		E.limosum	Whether or not
A.noterae	Whether or not
		C.aceticum	Whether or not
C.thermoaceticum	Whether or not
		S.sphaeroides	Whether or not
A.woodii	Is that
		A.kivui	Is that
C.ljungdahlii ERI2	Is that
		Indirect route
R.gelatinosa	Whether or not
		R.rubrum	Whether or not

TABLE 2 summary of the results of the ER12 experiment in a CSTR system with cell recycle

Table 3 summary of a.kivui experimental results in CSTR system with cell recycle

TABLE 4 ICR Performance of Fabric Using ERI2

TABLE 5 study of acetic acid partition coefficient

Solvent(s)	Equilibrium concentration of aqueous acetic acid, g/l	Partition coefficient of acetic acid
			Hexane (C)	6.559	0.0
Decane	5.968	0.08
			Chloroform	5.128	0.09
Kerosene oil	4.648	0.11
			Hexadecane (Hexadecane)	5.866	0.13
Dodecane	4.654	0.13
			Acetic acid dodecyl ester	5.787	0.15
Dibutyl phosphate	4.615	0.18
			Oleyl alcohol	5.114	0.28
Trioctylamine	3.785	0.31
			Undecanol	4.528	0.40
Ethyl acetate	4.550	0.41
			Butyric acid ethyl ester	4.665	0.42
Dexyl alcohol	3.890	0.42
			Octanol (I)	4.358	0.45
Nonoyl alcohol	3.470	0.55
			2-ethyl-1-hexanol	3.308	0.77
3-methylcyclohexanol	2.110	1.26
			Cyclohexanone	2.702	1.66
Phosphoric acid tributyl ester	1.657	2.38

TABLE 6 partition coefficient of mixed solvent

Solvent mixture	Distribution coefficient	Percentage increase
			Oleyl alcohol (10cc)	0.17
Oleyl alcohol (10cc) + Cyc (1cc)	0.31	72
			Oleyl alcohol (10cc) + TBP (1cc)	0.29	61
Oleyl alcohol (10cc) + Cyc (2cc)	0.45	150
			Oleyl alcohol (10cc) + TBP (2cc)	0.42	133
Oleyl alcohol (10cc) + Cyc (3cc)	0.36	100
			Oleyl alcohol (10cc) + TBP (3cc)	0.42	133
Oleyl alcohol (10cc) + Cyc (4cc)	0.35	94
			Oleyl alcohol (10cc) + TBP (4cc)	0.40	122
Oleyl alcohol (10cc) + Cyc (6cc)	0.52	188
			Oleyl alcohol (10cc) + TBP (6cc)	0.65	261
Oleyl alcohol (10cc) + Cyc (7cc)	0.69	283
			Oleyl alcohol (10cc) + TBP (7cc)	0.74	311

TABLE 7 consumption of ERI2 on CO in the presence of surfactant

Example 4

Preparation of CMA from carbon Black off-gas

Will be at N₂Contains CO 14% and H17%₂And 4% CO₂Carbon black off-gas as the main component was sprayed into a 160 liter continuous stirred tank reactor (tank reactor) maintained at 6 atmospheres at 37 ℃ and containing Clostridium Ijungdahlii isolate ER12 (deposited with the ATCC under accession No. 55380). The exhaust gas is produced as a result of the partial oxidation of hydrocarbons with insufficient air to form amorphous carbon, producing about 1.2 pounds of carbon monoxide per pound of elemental carbon. These exhaust gases pose a serious atmospheric pollution problem and also mean that valuable sources of chemical raw materials are not currently being utilized. The gas residence time (defined as the ratio of reactor volume to gas flow rate at standard conditions) was maintained at 0.52 minutes. In 1.05hr^-1Liquid dilution rate (defined as the ratio of liquid flow rate to reactor volume) an aqueous liquid medium containing water, alkaline salts, B-vitamin, nitrogen source and sulfide source is added to the reactor. The reactor was stirred at 322rpm, 37 ℃ and pH 5.03. Under these conditions, the conversion of CO was 83%, H₂The conversion of (a) was 54%. The cell concentration inside the reactor was maintained at 10.5 g/l using a hollow fiber membrane cell recycle device (hollow cell unit). The dilute acetic acid/acetate product stream from the reactor containing 13.2 g/l acetic acid/acetate was fed to a three stage reverse extraction unit and extracted with solvent. The ratio of solvent to feed was 1: 4. The acetic acid content of the acetic acid/acetate product stream was 3.7 grams/liter. In the solvent leaving the extractorThe acid concentration was 16.7 g/l. The water (culture medium) from the extraction unit is recycled back into the fermenter.

Dolomitic lime/MgO was added directly to acetic acid in the solvent phase to form CMA. After the reaction, the saturated CMA solution was dried and allowed to settle to form 1.15 pounds of Ca-containing solution per pound of acetic acid²⁺/Mg²⁺(molar ratio 3/7).

Example 5

Production of acetic acid from carbon black off-gas

Will be at N₂Contains CO 14% and H17%₂And 4% CO₂The carbon black off-gas of (a) was sprayed into a 144 liter trickle bed reactor containing Clostridium Ijungdahlii isocyanate ER12 (deposited with the ATCC under accession number 55380) at 37 c under 1.58 atmospheres. The trickle bed reactor is a packed column with commercially available packing (e.g., packed rings or curved saddle packing) in which liquid and gas contact each other as they flow through the column. In this embodiment, both liquid and gas enter the column from the top in a co-current manner, although counter-current flow (gas entering from the bottom and liquid entering from the top) is also possible. The gas residence time was maintained at 0.46 minutes and the liquid medium dilution rate was 0.57hr^-1. The liquid medium contained the same ingredients as in example 1. Agitation was provided in the reactor by liquid circulation using a circulation rate of 60 gpm. The pH in the reactor was 5.05 during operation. Under these conditions, the conversion of CO was 57%, H₂The conversion of (a) was 58%. The cell concentration inside the reactor was maintained at 13.6 g/l using a hollow fiber device (hollow fiber unit).

A dilute acetic acid/acetate product stream containing 6.4 grams/liter of mixed acetic acid/acetate and 2 grams/liter of acetic acid was fed to a three-stage reverse extraction column. The ratio of solvent to feed was 1: 4. The solvent leaving the extractor had an acetic acid content of 10 g/l. The water (medium) from the extraction unit is returned to the reactor for recycling.

The acetic acid containing solvent is sent to a distillation unit to recover the acid and solvent. A vacuum solvent distillation column and an acetic acid distillation column were used in the separation. The final product produced was glacial acetic acid.

Example 6

Preparation of potassium acetate from carbon black waste gas

The carbon black off gas of example 4 was used to make potassium acetate instead of CMA. All fermentation and solvent extraction conditions remained the same. Caustic potash (potassium oxide) was reacted with acetic acid to produce a 50% potassium acetate solution directly in the solvent phase.

Example 7

SCP preparation from coke oven exhaust gas

Will contain about 6% CO, 2% CO₂、57％H₂、5％N₂And 27% gaseous hydrocarbons were added to a continuously stirred tank reactor with cell recycle as described in example 4 above. The reactor is used to produce products such as dilute acetic acid or ethanol. In addition, the cell concentration in the reactor was 13.6 g/L. These cells (microorganisms) can be collected for use as bacterial single cell proteins for animal feed. The cell-containing purge stream exiting the reactor is sent to a dryer for processing into dried single-cell protein.

Example 8

Production of H from refinery off gas₂

Will contain about 45% CO, 50% H₂And 5% CH₄Is sprayed at 50 ℃ and several inches of water pressure and contains Bacillus smithii isolate ERIH2 (which was deposited at 3.18 days 1993 at the American Type Culture Collection of Rockville, Md., USA, and which received a proof of deposit (No. 55404) in a 1 liter CSTR, the medium in the reactor is 1.0 gram/liter corn steep liquor, CO in the off-gas is converted to CO with water₂And H₂. The exit gas stream contained 3.2% CO, 64.4% H₂、28.8％CO₂And 3.6% CH₄. Removal of CO, CO from gas streams by solvent extraction₂And CH₄。

Example 9

Preparation of other compounds from carbon black exhaust gas

Nitrogen gas containing about 14% CO and 17% H₂And 4% CH₄The carbon black off-gas of (a) was injected into a 1 liter CSTR at 37 c and several inches of water pressure. The culture medium in the reactor is a basic salt mixture containing water, B-vitamins, salts and minerals. Liquid phase products of methanol, propanol, butanol, propionic acid, butyric acid or other desired products are produced in the reactor, either individually or in combination. The system set-up is essentially the same as that used in example 6 after dilution, the product is recovered in a suitable product recovery system, including extraction, distillation or other well-known product recovery techniques. If multiple products are produced, a staged product recovery system is employed.

Accordingly, the present invention provides a highly efficient and improved process for converting waste gases to acids (including organic acids such as acetic acid; alcohols; hydrogen; SCP or salts of organic acids) by which the primary objective is fully achieved. It is anticipated and will be apparent to those skilled in the art from the foregoing description and accompanying drawings that modifications and/or variations can be made to the described examples without departing from the scope of the invention. It is therefore evident that the foregoing description and drawings are illustrative of preferred embodiments only and are not limiting upon the present invention. The true spirit and scope of the present invention is defined by the appended claims.

Claims (2)

1. Bacillus smithii (Bacillus smithii) ERI-H2 deposited at the American type culture Collection under accession number ATCC No. 55404.

2. A method of producing hydrogen gas, the method comprising the steps of:

fermenting an off-gas comprising carbon monoxide in a bioreactor comprising an aqueous nutrient medium and bacillus smithii ERI-H2 deposited at the american type culture collection with accession No. atccno.55404, said bacillus smithii ERI-H2 being capable of producing said hydrogen by anaerobic fermentation of said carbon monoxide; and recovering hydrogen therefrom.