Patent Publication Number: US-2018044702-A1

Title: Method and apparatus for producing organic substances

Description:
FIELD OF THE INVENTION 
     The present invention relates to a method and an apparatus for producing organic substances, and particularly relates to a production method and a production apparatus suitable for producing ethanol from a raw material gas such as a synthetic gas. 
     BACKGROUND OF THE INVENTION 
     Plants that produce ethanol from a raw material gas such as a synthetic gas are well known (refer to Patent Documents 1 to 3). Patent Documents 1 to 3 disclose producing ethanol from a synthetic gas by a fermentation action of a certain type of anaerobic microorganisms. 
     Patent Document 4 discloses producing CO and H 2 O from CO 2  and H 2  by a reverse shift reaction using a reverse shift reaction catalyst (formula (1)): 
       CO 2 +H 2 →CO+H 2 O  (1)
 
     The reverse shift reaction catalyst contains an alkali earth metal carbonates of Ca, Sr or Ba and a complex oxide of Ca, Sr or Ba and Ti, Al, Zr, Fe, W or Mo. A temperature condition for the reverse shift reaction is 700 degrees C. or higher. 
     PRIOR ART DOCUMENTS 
     Patent Documents 
     Patent Document 1: Japanese Patent Application Publication No. 2004-504058 
     Patent Document 2: International Patent Application Publication No. WO2011/087380 
     Patent Document 3: United States Patent Application Publication No. US2013/0065282A1 
     Patent Document 4: Japanese Patent Application Publication No. 2010-194534 
     SUMMARY OF THE INVENTION 
     Problem to be Solved by the Invention 
     According to the knowledge of the inverters, the anaerobic microorganisms mentioned above intake more CO than H 2  and CO 2  for fermentation. Therefore, a generation efficiency of ethanol can be enhanced by subjecting the H 2  and CO 2  in the raw material gas to a reverse shift reaction, and thereby converting CO 2  into CO. On the other hand, in a case of Patent Document 2, an operating cost may be high for the reverse shift reaction because it is required to make a temperature 700 degrees C. or higher. 
     In view of the above, it is an objective of the present invention to make it possible for a raw material gas to perform the reverse shift reaction under low temperature conditions, and thereby reducing the operating cost and enhancing efficiency of generating organic substances such as ethanol. 
     Means for Solving the Problems 
     To solve the problems mentioned above, a method of the present invention provides a method for producing organic substances from a raw material gas containing CO 2  and H 2 , the method including steps of: subjecting the raw material gas to a reverse shift reaction; and generating organic substances from the raw material gas after the reverse shift reaction, wherein: the raw material gas is contacted with a reverse shift reaction catalyst in the subjecting step; the reverse shift reaction catalyst includes a support and a catalyst metal supported by the support; and the catalyst metal includes a transition metal. 
     An apparatus of the present invention provides an organic substance producing apparatus that produces organic substances from a raw material gas containing CO 2  and H 2 , the apparatus including: a reverse shift reactor subjecting the raw material gas to a reverse shift reaction; and an organic substance generator generating the organic substances from the raw material gas after the reverse shift reaction, wherein: the reverse shift reactor includes a reverse shift reaction catalyst contactable with the raw material gas; the reverse shift reaction catalyst includes a support and a catalyst metal supported by the support; and the catalyst metal includes a transition metal. 
     By the reverse shift reaction, the CO 2  in the raw material gas can be converted into CO. By using the reverse shift reaction catalyst, conversion efficiency can be sufficiently enhanced. Moreover, a temperature condition can be set at 150 to 500 degrees C., which is lower than the temperature condition (700 degrees C. or higher) of Patent Document 4 mentioned above. Accordingly, smaller energy is required for the reverse shift reaction, and an operation cost can be reduced. An efficiency of generating organic substances such as ethanol can be enhanced by making the raw material gas CO rich by the reverse shift reaction. 
     The transition metal may be Fe, Sc, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, Ta, W, Re, Os, Ir, Pt, Au or Hg, for example. 
     Preferably, the catalyst metal includes Fe with at least one kind of metal selected from a group of Al, Ga, In, Cu, Ag, Au, Pd, and Mn added thereto. 
     Preferably, the catalyst metal includes Fe with Pd added thereto. 
     By this arrangement, the conversion efficiency of the reverse shift reaction can be further enhanced. 
     Preferably, the support may be composed of at least one selected from a group of SiO 2 , CeO 2 , TiO 2 , Al 2 O 3 , MgO, ZrO 2 , ZSM-5 (zeolite). 
     Preferably, an offgas generated in the generating step is mixed with the raw material gas before the reverse shift reaction. 
     Preferably, the apparatus further includes an offgas passage adapted to send out an offgas from the organic substance generator therethrough, the offgas passage extending to the reverse shift reactor. 
     By this arrangement, CO 2  generated at the time of producing the organic substances can be subjected to the reverse shift reaction, thereby being converted into CO and used for the production of the organic substances. Thus, CO 2  and CO can be used in a cyclic manner. 
     Preferably, the generating step includes a step of culturing microorganisms in a liquid culture medium; and the microorganisms fermentatively generate the organic substances from the raw material gas after the reverse shift reaction. 
     Preferably, the organic substance generator includes a culture tank adapted to culture microorganisms in a liquid culture medium therein; and the microorganisms fermentatively generate the organic substances from the raw material gas after the reverse shift reaction. 
     The efficiency of fermentative generation of the organic substances by the microorganisms can be enhanced by increasing a concentration of CO by the reverse shift reaction. 
     Advantageous Effects of the Invention 
     According to the present invention, the raw material gas can be subjected to the reverse shift reaction under a relatively low temperature condition, and thereby the operation cost can be reduced. By converting CO 2  of the raw material gas into CO by the reverse shift reaction, the efficiency of generating the organic substances such as ethanol can be enhanced. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram schematically showing an organic substance producing system according to a first embodiment of the present invention. 
         FIG. 2  is a block diagram schematically showing an organic substance producing system according to a second embodiment of the present invention. 
     
    
    
     MODE FOR CARRYING OUT THE INVENTION 
     Embodiments of the present invention will be described hereinafter with reference to the drawings. 
     First Embodiment 
       FIG. 1  shows a first embodiment of the present invention. An organic substance producing system  1  includes a raw material gas generator  2  and an organic substance producing apparatus  3 . A raw material gas g 1  is generated at the raw material gas generator  2 . Organic substances (target substances) are generated from the raw material gas g 1  by the organic substance producing apparatus  3 . The raw material gas g 1  is a synthetic gas (syngas). The target substance may be ethanol (C 2 H 5 OH), for example. 
     The raw material gas generator  2  is a waste disposal facility in this embodiment. Wastes may include municipal wastes, tires, biomass, wooden chips and plastic wastes. The waste disposal facility  2  is provided with a melting furnace. In the melting furnace, the wastes are burnt by a highly-concentrated oxygen gas and decomposed at a low-molecular level. Eventually, the raw material gas g 1  (synthetic gas) is generated. 
     The raw material gas g 1  (synthetic gas) may contain CO, H 2  and CO 2  as major constituents. A constituent ratio may be around 30 vol % of CO, around 30 vol % of H 2  and around 30 vol % of CO 2 , but it is not required that the constituent ratio should be as given above. Most of the remaining constituents of the raw material gas g 1  may be N 2 . The raw material gas g 1  may further include minute amount of impure constituents such as H 2 S, O 2  and benzene. 
     As shown in  FIG. 1 , the organic substance producing apparatus  3  includes a gas supply passage  10 , a gas purifier  11 , a reverse shift reactor  12  and an organic substance generator  13 . The gas supply passage  10  extends from the waste disposal facility  2  to the organic substance generator  13 . The gas purifier  11  and the reverse shift reactor  12  are disposed at a point along the gas supply passage  10 . The gas purifier  11  includes a desulfurizing portion, deoxidizing portion and a debenzenizing portion. 
     The reverse shift reactor  12  is disposed at a point of the gas supply passage  10  on a downstream side with respect to the gas purifier  11 . A reverse shirt reaction catalyst  20  is received in the reverse shift reactor  12 . The reverse shift reaction catalyst  20  includes a support  21  and a catalyst metal  22 . The support  21  may be composed of SiO 2 , CeO 2 , TiO 2 , Al 2 O 3 , MgO, ZrO 2  or ZSM-5. In this embodiment, the support  21  is composed of silicon oxide (SiO 2 ). The catalyst metal  22  is supported by the support  21 . The supported catalyst may be prepared by wet impregnation, co-precipitation, Schlenk Line, or the like. 
     The catalyst metal  22  may include a transition metal such as Fe. 
     Preferably, the catalyst metal  22  may include Fe with at least one kind of metal from among Al, Ga, In, Cu, Ag, Au, Pd, and Mn added thereto. One kind of metal may be added or two or more kinds of metal may be added. 
     More preferably, the catalyst metal  22  is composed of Fe with Pd added thereto. 
     A content rate of the catalyst metal  22  in the reverse shift reaction catalyst  20  may be preferably 5 wt % to 50 wt % of the entire reverse shift reaction catalyst  20  and more preferably around 20 wt of the entire reverse shift reaction catalyst  20 . 
     A content rate of added constituents (Al, Ga, In, Cu, Ag, Au, Pd or Mn) in the catalyst metal  22  may be preferably 0.1 wt % to 1.0 wt % of the entire catalyst metal  22  and more preferably around 0.2 wt % of the entire catalyst metal  22 . 
     A heater  12   h  (temperature controller) is disposed in the reverse shift reactor  12 . A temperature of an inside of the reverse shift reactor  12 , and thereby a temperature of the reverse shift reaction catalyst  20  can be controlled to be a desired temperature by the heater  12   h.    
     The organic substance generator  13  is disposed subsequent to the reverse shift reactor  12 . The organic substance generator  13  is provided with a culture tank. A liquid culture medium is stored in the culture tank. Gas-utilizing microorganisms are cultured in the liquid culture medium. Anaerobic bacteria disclosed in the Patent Documents 1 to 3 mentioned above may be used as the gas-utilizing microorganisms, for example. The gas-utilizing microorganisms synthesize ethanol (C 2 H 5 OH), etc. from CO and H 2 , etc. by a fermentative action thereof. 
     A refiner  14  is disposed subsequent to the organic substance generator  13 . The refiner  14  is composed of a distillation tower. 
     An offgas passage  15  extends from the organic substance generator  13 . An offgas purifier  16  is disposed at a point along the offgas passage  15 . The offgas purifier  16  includes a desulfurizing portion and a water eliminating portion. A downstream end of the offgas passage  15  is joined to the gas supply passage  10  at a point between the gas purifier  11  and the reverse shift reactor  12 . 
     Ethanol (organic substance) is generated by the organic substance producing system 1 in the following manner: 
     &lt;Raw Material Gas Generating Step&gt; 
     The raw material gas g 1  is generated by burning wastes at the waste disposal facility  2 . 
     The raw material gas g 1  is introduced to the gas supply passage  10 . 
     &lt;Raw Material Gas Purifying Step&gt; 
     Impure components such as H 2 S, O 2  and benzene in the raw material gas g 1  are removed in the gas purifier  11 . The impure components may be removed by using a catalyst. The impure components may be removed by condensation. Thereby, the raw material gas g 1  is purified. 
     &lt;Reverse Shift Reaction Step&gt; 
     Subsequently, the raw material gas g 1  is introduced to the reverse shift reactor  12 . 
     A temperature of the reverse shift reactor  12  is controlled to be 150 degrees C. to 500 degrees C. by the heater  12   h.    
     A pressure of the reverse shift reactor  12  may be set at 0.8 to 2 atmospheric pressure (gauge pressure), for example. 
     The raw material gas g 1  is contacted with the reverse shift reaction catalyst  20  in the reverse shift reactor  12 . Thereby, at least a portion of CO 2  and H 2  in the raw material gas g 1  is subjected to a reverse shift reaction as expressed in the following formula (1): 
       CO 2 +H 2 →CO+H 2 O  (1)
 
     Accordingly, CO 2  in the raw material gas g 1  can be converted into CO. The raw material gas after the reverse shift reaction is referred to as “raw material gas g 2 ” hereinafter. CO concentration is higher in the raw material gas g 2  than in the raw material gas g 1  before the reverse shift reaction. CO 2  concentration and H 2  concentration are lower in the raw material gas g 2  than in the raw material gas g 1 . 
     By using the reverse shift reaction catalyst  20  having a structure and composition mentioned above as a catalyst, a conversion efficiency of CO 2 →CO can be sufficiently enhanced. The conversion efficiency of 20% or higher can be achieved, for example. 
     By using Fe with a minute amount of Pb added thereto as the catalyst metal  22 , the conversion efficiency can be enhanced to around 50%. 
     Thereby, the CO concentration in the raw material gas g 2  can be made sufficiently high. 
     Moreover, temperature condition of about 150 degrees C. to 500 degrees C. may be sufficient for the reverse shift reaction, which is much lower than the temperature condition (700 degrees C. or higher) in the Patent Document 1 mentioned above. Accordingly, energy required for the heater  12   h  can be reduced, and therefore, an operation cost can be reduced. 
     &lt;Fermentation Step (Organic Substance Generating Step)&gt; 
     The raw material gas g 2  from the reverse shift reactor  12  is introduced into the liquid culture medium in the organic substance generator  13 . Then the gas-utilizing microorganisms in the liquid culture medium take in CO and H 2  in the raw material gas g 2  and perform fermentation, thereby generating the target substance, ethanol. 
     The gas-utilizing microorganisms of this kind perform fermentation taking in more H 2  than CO. Therefore, the efficiency of generating ethanol can be enhanced by making the CO concentration of the raw material gas g 2  high in the reverse shift reaction step. 
     &lt;Refining Step&gt; 
     A portion b 1  of the liquid culture medium in the organic substance generator  13  is taken out and sent out to the refiner  14  composed of a distillation tower. The liquid culture medium b 1  is distilled in the refiner  14 . Thereby, the ethanol (EtOH) can be refined. 
     An amount of the culture medium in the organic substance generator  13  is arranged to be maintained constant by newly replenishing the culture medium to the organic substance generator  13  in an amount corresponding to the sent out amount. 
     &lt;Exhaust Step&gt; 
     CO 2  is generated as a by-product during the fermentation of ethanol mentioned above. Therefore, a large amount of CO 2  is contained in an offgas g 3  from the organic substance generator  13 . Besides CO 2 , the offgas g 3  contains CO, H 2 , etc. of the raw material gas g 2  that were not used for the fermentation. The offgas g 3  is sent to the offgas purifier  16 . Impure components of the offgas g 3  such as H 2 O and a minute amount of H 2 S are removed in the offgas purifier  16 . 
     &lt;Reusing Step&gt; 
     After that, the offgas g 3  is joined to the gas supply passage  10  via the offgas passage  15  and mixed with the raw material gas g 1  in the gas supply passage  10 . Thereby, CO 2  in the offgas g 3  can be provided to the reverse shift reactor  12  together with the raw material gas g 1  for the reverse shift reaction. In short, CO 2  generated in the fermentation step as the by-product can be converted into CO, and the CO can be sent to the organic substance generator  13  as a part of the raw material gas g 2  and can be used for fermentation. Thereby, CO 2  and CO can be used in a cyclic manner in which the CO 2  and CO are repeatedly converted into each other. 
     Other embodiments of the present invention will be described hereinafter. Same reference numerals are used in the drawings to designate parts that correspond to those in foregoing embodiments and description thereof will be omitted. 
     Second Embodiment 
       FIG. 2  shows a second embodiment of the present invention. A raw material gas generator  2 B of an organic substance producing system  1 B according to the second embodiment includes a carbon dioxide generator  4  and a hydrogen generator  5 . The carbon dioxide generator  4  may be a coal power plant, a LNG power plant, a petroleum products manufacturing plant, a cement manufacturing plant, etc. In these plants, CO 2  is generated, but H 2  is hardly generated. 
     The hydrogen generator  5  is disposed at a point along a gas supply passage  10  from the carbon dioxide generator  4 . 
     The hydrogen generator  5  may be a steam reforming plant for natural gas such as methane (CH 4 ). The methane is steam-reformed as expressed in the following formula (2): 
       CH 4 +H 2 O→CO+3H 2    (2)
 
     The reformed gas (CO, H 2 ) is mixed with the CO 2  from the carbon dioxide generator  4 . Thereby, a raw material gas g 1  (synthetic gas) containing CO, H 2  and CO 2  can be obtained. The raw material gas g 1  is supplied to a reverse shift reactor  12  via a gas purifier  11 , and thereby subjected to a reverse shift reaction. Thus, a CO rich raw material gas g 2  can be obtained. Thereby, an efficiency of generation of ethanol in an organic substrate generator  13  can be enhanced. 
     The present invention is not limited to the embodiments described above. Various modifications can be made without departing from the scope and spirit of the invention. 
     For example, the catalyst metal  22  of the reverse shift reaction catalyst  20  may be composed only of Fe, without containing the added constituents. 
     The organic substrate generator  13  may generate ethanol by bringing the raw material gas g 2  into contact with the metal catalyst instead of by microbial fermentation. 
     EXPLANATION OF REFERENCE NUMERALS 
     b 1  culture medium 
     g 1  raw material gas 
     g 2  raw material gas after the reverse shift reaction 
     g 3  offgas 
       1  organic substance producing system 
       2  waste disposal facility (raw material gas generator) 
       2 B raw material gas generator 
       3  organic substance producing apparatus 
       4  carbon dioxide generator 
       5  hydrogen generator 
       10  gas supply passage 
       11  gas purifier 
       12  reverse shift reactor 
       12   h  heater (temperature controller) 
       13  organic substance generator 
       14  refiner 
       15  offgas passage 
       16  offgas purifier 
       20  reverse shift reaction catalyst 
       21  support (silicon oxide substrate) 
       22  catalyst metal