FUEL SYNTHESIS DEVICE

Abstract

A fuel synthesis device includes: a supplier to supply CO.sub.2 and H.sub.2 gasses; a fuel synthesis catalyst to chemically react the CO.sub.2 and H.sub.2 gasses to synthesize fuel; a gas-liquid separator to liquefy the fuel into liquid and separate the liquid from a gas containing unreacted CO.sub.2 and H.sub.2 gasses, and CH.sub.4 gas as a side product; a return path to return the separated gas to a point between the supplier and the fuel synthesis catalyst; a bypass path to bypass, and merge downstream of, the return path, and to include a CH.sub.4 separator to separate the CH.sub.4 and a CH.sub.4 oxidation catalyst to oxidize the CH.sub.4; and a switching valve to selectively switch between communication with the return path and communication with the bypass path, wherein whether the switching valve communicates with the return path or bypass path is controlled based on the density of CH.sub.4.

Claims

1. A fuel synthesis device comprising: a supplier arranged upstream of a main path and configured to supply CO.sub.2 gas and H.sub.2 gas; a fuel synthesis catalyst located downstream of the supplier and configured to chemically react the CO.sub.2 gas and the H.sub.2 gas to synthesize fuel; a gas-liquid separator arranged downstream of the fuel synthesis catalyst and configured to liquefy the fuel into liquid and separate the liquid from a gas containing the CO.sub.2 gas and the H.sub.2 gas, which have not yet reacted with the fuel synthesis catalyst, and gas of CH.sub.4 as a side product; a return path configured to return the gas separated by the gas-liquid separator to a point in a flow path between the supplier and the fuel synthesis catalyst; a bypass path configured to bypass, and merge downstream of, the return path, and including a CH.sub.4 separator to separate the CH.sub.4 and a CH.sub.4 oxidation catalyst to oxidize the CH.sub.4 separated by the CH.sub.4 separator; a switching valve provided at a junction of the return path and the bypass path and configured to selectively switch between communication with the return path and communication with the bypass path; and a CH.sub.4 density detector arranged in the return path and configured to detect density of CH.sub.4 contained in the gas separated by the gas-liquid separator, wherein whether the switching valve communicates with the return path or the bypass path is controlled based on the density of CH.sub.4 detected by the CH.sub.4 density detector.

2. The fuel synthesis device according to claim 1, wherein the switching valve is controlled to communicate with the bypass path, on the condition that the density of CH.sub.4 detected by the CH.sub.4 density detector becomes equal to or greater than a predetermined value at which synthesis of the fuel is blocked.

3. The fuel synthesis device according to claim 1, wherein the supplier further has a function of supplying O.sub.2 gas, and the fuel synthesis device includes: a calculator configured to calculate an amount of O.sub.2 required for oxidation, based on the density of CH.sub.4 detected by the CH.sub.4 density detector; and an O.sub.2 supplier configured to supply the O.sub.2 gas from the supplier to the CH.sub.4 oxidation catalyst, based on the amount of O.sub.2 calculated by the calculator.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0019] FIG. 1 shows a schematic configuration of a fuel synthesis device according to a present embodiment;

[0020] FIG. 2 is a flowchart of controlling switching between a return path and a bypass path in the fuel synthesis device according to the present embodiment; and

[0021] FIG. 3 illustrates a mechanism of synthesizing fuel in Direct-FT.

DETAILED DESCRIPTION

[0022] Hereinafter, a description is given in detail of a fuel synthesis device 1 according to an embodiment of the present invention, with reference to the drawings as required. Note that the wordings of upstream and upstream side, and downstream and downstream side in the following description respectively represent an upstream side and a downstream side in a flow direction of fluid flowing into a described device. FIG. 1 of the referenced drawings shows a schematic configuration of the fuel synthesis device 1 according to the present embodiment.

[0023] First described are configurations of paths of the fuel synthesis device 1. The fuel synthesis device 1 has a main path 10 through which fuel is synthesized from supplied gas and separated, and a return path 20 through which the gas remaining in a gas phase after the fuel having been separated is returned to an upstream side of a fuel synthesis catalyst 3 in the main path 10. The main path 10 has a piping 11, a piping 12, a piping 13, a piping 14, and a piping 15. Note that the fuel synthesis device 1 has an ECU (Electronic Control Unit) 60 outside these paths. The ECU 60 controls a switching valve V and various other adjustment valves, to be described below, based on a value from a CH.sub.4 density detector 23 arranged in the return path 20. The ECU 60 also controls a compressor 30, a heater 40, an oil-water separator 5, and the like, based on values from various sensors (not shown).

[0024] The fuel synthesis device 1 includes a supplier 2, a fuel synthesis catalyst 3, and a gas-liquid separator 4 on a route of the main path 10, as shown in FIG. 1. The fuel synthesis device 1 includes the fuel synthesis catalyst 3 located downstream of the supplier 2, and the gas-liquid separator 4 located downstream of the fuel synthesis catalyst 3. The fuel synthesis device 1 also includes the oil-water separator 5 on the route of the main path 10 and located downstream of the gas-liquid separator 4.

[0025] The fuel synthesis device 1 also includes the compressor 30 to compress gas and the heater 40 to heat the compressed gas, between the supplier 2 and the fuel synthesis catalyst 3. The compressor 30 and heater 40 are connected to each other via the piping 12 in the main path 10. The compressor 30 compresses the gas to a pressure of 3 MPa. The heater 40 heats the gas to a temperature of 330 to 380° C. Note that the pressure and temperature of the gas can be set as required, based on characteristics of the fuel synthesis catalyst 3 and the like.

[0026] The supplier 2 is connected with the compressor 30 via the piping 11 in the main path 10. The supplier 2 supplies carbon dioxide (CO.sub.2) gas and hydrogen (H.sub.2) gas to the main path 10. The supplier 2 is also connected with a CH.sub.4 oxidation catalyst 52 via a piping 25. The supplier 2 supplies oxygen (O.sub.2) gas to the piping 25.

[0027] The CO.sub.2 gas is supplied from a tank 21 storing CO.sub.2 gas. The ECU 60 controls the supplied amount of the CO.sub.2 gas. Note that the CO.sub.2 gas may be CO.sub.2 in exhaust gas, exhausted from the internal combustion engine of a vehicle such as a car, and/or in atmosphere adsorbed by an adsorbent. In this case, the absorbent may be used as a CO.sub.2 tank with CO.sub.2 desorbed as required.

[0028] H.sub.2 gas may be obtained by electrolyzing water in an electrolysis tank 22, with the water being produced by a fuel cell or the like. H.sub.2 gas obtained in this way may be stored in an H.sub.2 tank (not shown) and supplied from the H.sub.2 tank for use. Alternatively, H.sub.2 gas may be supplied from a separate H.sub.2 cylinder if required. The amount of H.sub.2 gas to be supplied is controlled by the ECU 60. Note that electrolyzing water in the electrolysis tank 22 produces O.sub.2. That is, the supplier 2 has a function of supplying O.sub.2 gas. The fuel synthesis device 1 uses the O.sub.2 gas produced in the supplier 2 for partial oxidation of CH.sub.4.

[0029] The fuel synthesis catalyst 3 is located downstream of the supplier 2 and chemically reacts CO.sub.2 gas and H.sub.2 gas to synthesize fuel. The fuel to be synthesized is a hydrocarbon having five or more carbons (C.sub.5+), for example, particularly gasoline. The fuel synthesis catalyst 3 is arranged in a reaction tube 31 in the main path 10. The reaction tube 31 is connected, on an upstream side thereof, to the piping 13 of the main path 10 and connected, on a downstream side thereof, to the piping 14 of the main path 10. The gas supplied from the upstream side of the fuel synthesis catalyst 3 in the main path 10 contains CO.sub.2 and H.sub.2. In the reaction tube 31, the CO.sub.2 and H.sub.2 undergo a chemical reaction (hydrogenation reaction) in a predetermined ratio. For example, an Na—Fe.sub.3O.sub.4/HZSM-5 catalyst may be used as the fuel synthesis catalyst 3, but is not limited thereto. The Na—Fe.sub.3O.sub.4/HZSM-5 catalyst is assumed to catalyze reverse water gas shift (RWGS) reaction on Fe.sub.3O.sub.4, FT synthesis reaction on Fe.sub.5C.sub.2, and oligomerization, isomerization, and aromatization at acid points on zeolite. When the Na—Fe.sub.3O.sub.4/HZSM-5 catalyst is used, hydrocarbons of C.sub.5 to C.sub.11 are obtained in maximum yield of 78%, with low production of methane (CH.sub.4) and CO.

[0030] Fuel synthesis by the fuel synthesis catalyst 3 is executed by using a known technique. For example, H.sub.2 metered to have a predetermined ratio of CO.sub.2 to H.sub.2 in the reaction tube 31 is supplied from the electrolysis tank 22 or the H.sub.2 tank (not shown) to the piping 11, and the gas in the reaction tube 31 is then compressed and heated by the compressor 30 and heater 40. This causes the aforementioned RWGS reaction, FT synthesis reaction, and oligomerization and other reactions to proceed in the reaction tube 31, under the action of the fuel synthesis catalyst 3, to produce hydrocarbons (gasoline) of C.sub.5 to C.sub.11 as fuel (Equation (4) below).

nCO.sub.2+mH.sub.2.fwdarw.C.sub.nH.sub.2(m−2n)+2nH.sub.2O   (4)

[0031] The gas-liquid separator 4 is located downstream of the fuel synthesis catalyst 3, particularly between the piping 14 and piping 15 in the main path 10, and cools the fuel to a liquid and separates the liquid from the gas containing the CO.sub.2 gas and H.sub.2 gas, which have not been reacted in the fuel synthesis catalyst 3, and CH.sub.4 gas as a side product. The gas-liquid separator 4 cools the synthesis gas containing gasoline by heat exchange and condenses the gas, to separate the above-described unreacted gas (gas phase) from the gasoline-based liquid (liquid phase (hydrocarbons of C.sub.5+)). Alternatively, the gas-liquid separator 4 may separate the synthesis gas through membrane separation, to separate the gasoline-based liquid (liquid phase). The gasoline-based liquid phase, which has been separated by the gas-liquid separator 4, is fed through the piping 15 to the oil-water separator 5. The gas phase separated by the gas-liquid separator 4 contains hydrocarbons of CH.sub.4 and C.sub.2-4 as side products, unreacted CO.sub.2 and H.sub.2, and unrecovered gasoline and water (H.sub.2O). The gas separated as gas phase in the gas-liquid separator 4 is fed through the return path 20 to a point upstream of the fuel synthesis catalyst 3, such as to the compressor 30, and used again for fuel synthesis.

[0032] The oil-water separator 5 separates gasoline and water in the liquid phase from each other, using the difference in boiling points. The oil-water separator 5 heats the liquid phase to 35° C. or more but less than 100° C., for example. This allows for obtaining gasoline evaporated from the liquid phase, which is either left as gas or liquefied and fed to a fuel tank, not shown, through the piping 16. The remaining liquid phase is almost entirely water (H.sub.2O) and is discharged outside through the piping 17. Note that the heating temperature is desirably set such as to 40° C. or more, 50° C. or more, and 60° C. or more, from the viewpoint of evaporating gasoline. Additionally, the heating temperature may be set such as to 90° C. or less, 80° C. or less, and 70° C. or less, from the viewpoint of reducing water contamination. Alternatively, the heating temperature may be set to multiple temperature ranges in consideration of fractional distillation of gasoline.

[0033] In the present embodiment, a bypass path 50 is provided in the return path 20. The bypass path 50 bypasses, and merges downstream of, the return path 20. The bypass path 50 includes, on a route thereof, a CH.sub.4 separator 51 to separate CH.sub.4 and the CH.sub.4 oxidation catalyst 52 to oxidize CH.sub.4 separated by the CH.sub.4 separator 51.

[0034] For example, a molecular sieve may be used as the CH.sub.4 separator 51. The CH.sub.4 transmitting through, and separated by, the CH.sub.4 separator 51 is fed via a piping 53 to the CH.sub.4 oxidation catalyst 52. Note that the gas phase transmitting through, and separated by, the CH.sub.4 separator 51(transmitted gas phase) may contain H.sub.2, and this H.sub.2 is also fed to the CH.sub.4 oxidation catalyst 52, along with CH.sub.4. In contrast, the gas phase which has not transmitted through the CH.sub.4 separator 51 (retained gas phase) may contain hydrocarbons of CO.sub.2 and C.sub.2-4. The hydrocarbons of CO.sub.2 and C.sub.2-4 are fed to the return path 20 via a piping 54. These hydrocarbons of CO.sub.2 and C.sub.2-4 are then fed to a point upstream of the fuel synthesis catalyst 3, such as the compressor 30, and are used again for fuel synthesis.

[0035] The CH.sub.4 oxidation catalyst 52 causes CH.sub.4 to be incompletely com busted at an oxygen density lower than the theoretical oxygen content required for complete combustion. For example, a Pd/Al.sub.2O.sub.3 catalyst may be used as the CH.sub.4 oxidation catalyst 52. The Pd/Al.sub.2O.sub.3 catalyst reacts CH.sub.4 and O.sub.2 in a predetermined ratio under conditions of 400° C., for example, to partially oxidize CH.sub.4 to produce CO and H.sub.2 (Equation (5)).

CH.sub.4+½O.sub.2.fwdarw.CO+2H.sub.2   (5)

[0036] The CO and H.sub.2, produced as above, and the H.sub.2, fed to the CH.sub.4 oxidation catalyst 52 as being unreacted, are fed to the return path 20 via a piping 55. The CO and H.sub.2 are then fed to the point upstream of the fuel synthesis catalyst 3, such as the compressor 30, along with the hydrocarbons of CO.sub.2 and C.sub.2-4, and are used again for fuel synthesis.

[0037] The switching valve V is provided at the junction of the return path 20 and the bypass path 50. The switching valve V selectively switches between communication with the return path 20 and communication with the bypass path 50.

[0038] In the return path 20, a CH.sub.4 density detector 23 is placed between the gas-liquid separator 4 and the switching valve V. The CH.sub.4 density detector 23 detects density of CH.sub.4 contained in the gas separated by the gas-liquid separator 4. The CH.sub.4 density detector 23 can be an HC analyzer or an exhaust gas detector to detect the density of hydrocarbons. The CH.sub.4 density detector 23 outputs density (detected value) of the CH.sub.4 to the ECU 60. The ECU 60 includes a calculator (not shown) to calculate, based on the inputted density of CH.sub.4, an amount of O.sub.2 required for partially oxidizing the CH.sub.4 in the CH.sub.4 oxidation catalyst 52. The calculator is implemented by a CPU (Central Processing Unit, not shown) of the ECU 60 executing a program necessary for the calculation. The ECU 60 then outputs the required amount of O.sub.2 calculated above to a mass flow controller MFC.

[0039] The CH.sub.4 oxidation catalyst 52 is connected with the supplier 2 (particularly the electrolysis tank 22) via the piping 25 as described above. The O.sub.2 generated in the electrolysis tank 22 is fed via the piping 25 to the CH.sub.4 oxidation catalyst 52 (O.sub.2 supplier). The piping 25 is provided with the mass flow controller MFC. The mass flow controller MFC meters mass flow of O.sub.2 for flow rate control. The mass flow controller MFC feeds O.sub.2 to the CH.sub.4 oxidation catalyst 52, while controlling a flow rate of O.sub.2 supplied from the electrolysis tank 22, based on the amount of O.sub.2 calculated by the ECU 60. This allows for suitably executing partial oxidation of CH.sub.4 in the CH.sub.4 oxidation catalyst 52.

[0040] In the present embodiment, whether the switching valve V communicates with the return path 20 or the bypass path 50 is controlled based on the density of CH.sub.4 detected by the CH.sub.4 density detector 23. The ECU 60 controls the switching valve V. In this way, the fuel synthesis device 1 controls the switching valve V based on the density of CH.sub.4 remaining in the device to partially oxidize the CH.sub.4 and returns the gas (CO) produced by oxidation to the point upstream of the fuel synthesis catalyst 3 (between the supplier 2 and the fuel synthesis catalyst 3).

[0041] This allows the fuel synthesis device 1 to use CO as a feedstock in the fuel synthesis catalyst 3, to synthesize fuel (hydrocarbon of C.sub.5+) for sufficiently growing carbon chain. That is, the fuel synthesis device 1 effectively utilizes CH.sub.4 produced as a side product in the fuel synthesis catalyst 3, to synthesize fuel. The fuel synthesis device 1 uses carbon dioxide to synthesize fuel (gasoline), resulted in reducing carbon dioxide and its negative impact on the global environment.

[0042] The fuel synthesis device 1 may cause the switching valve V to communicate with the bypass path 50, on the condition that the density of CH.sub.4 detected by the CH.sub.4 density detector 23 becomes equal to or greater than a predetermined value at which synthesis of the fuel is blocked. The predetermined value may suitably be set in consideration of performance of the fuel synthesis catalyst 3.

[0043] In such an embodiment, the ECU 60 of the fuel synthesis device 1, on the condition that density of the CH.sub.4 remaining in the device increases to become equal to or greater than the predetermined value at which synthesis of the fuel is blocked, causes the switching valve V to be switched to communicate with the bypass path 50 to allow the CH.sub.4 to be partially oxidized, so that the gas (CO) produced by oxidation is returned to the point upstream of the fuel synthesis catalyst 3. Accordingly, the fuel synthesis device 1 uses CO as a feedstock in the fuel synthesis catalyst to synthesize fuel (hydrocarbon of C.sub.5+) for sufficiently growing carbon chain. Note that the ECU 60 in this embodiment, on the condition that the density of the CH.sub.4 is less than the predetermined density, causes the switching valve V to remain unmoved to keep communicating with the return path 20. The switching valve V communicates with the return path 20 at a time of starting operation and during normal operation. The unreacted CO.sub.2 and H.sub.2, CH.sub.4 as a side product, and hydrocarbon of C.sub.2-4 are then fed (returned) to the point upstream of the fuel synthesis catalyst 3, particularly to the compressor 30. In this way, the CH.sub.4 oxidation catalyst 52 is not used to prevent the CH.sub.4 oxidation catalyst 52 from being degraded, so that the life of the CH.sub.4 oxidation catalyst 52 is extended.

[0044] Next, a description is given of a preferable embodiment of controlling switching between the return path 20 and the bypass path 50 in the fuel synthesis device 1 of the present embodiment, with reference to FIG. 2. FIG. 2 is a flowchart of controlling switching between the return path 20 and the bypass path 50 in the fuel synthesis device 1 of the present embodiment.

[0045] The fuel synthesis device 1 starts operation, as shown in FIG. 2. The supplier 2, the compressor 30, the heater 40, the fuel synthesis catalyst 3, the gas-liquid separator 4, and the oil-water separator 5 operates as described above, to produce hydrocarbon of C.sub.5+ as fuel. The fuel synthesis catalyst 3 produces CH.sub.4 as a side product, in association with fuel being produced.

[0046] Then, the CH.sub.4 density detector 23 detects density of CH.sub.4 as a side product, which has been separated by the gas-liquid separator 4, and outputs the density of CH.sub.4 to the ECU 60 (step S1). The ECU 60 determines whether the density of CH.sub.4 detected by the CH.sub.4 density detector 23 is less than the predetermined value, or equal to or greater than the predetermined value (step S2).

[0047] The ECU 60, on the condition that the density of CH.sub.4 has been less than the predetermined value in step S2, causes the switching valve V to remain unmoved to keep communicating with the return path 20 (step S3). In this case, there is no need of supplying O.sub.2 to the CH.sub.4 oxidation catalyst 52, so that the ECU 60 controls the mass flow controller MFC to shut off the flow (step S4). The processing then returns to step S1 so that the fuel synthesis device 1 operates and the CH.sub.4 density detector 23 detects the density of CH.sub.4 as a side product.

[0048] In contrast, the ECU 60, on the condition that the density of CH.sub.4 is equal to or greater than the predetermined value, causes the switching valve V to communicate with the bypass path 50 (step S5). Concurrently in step S2, the ECU 60 causes the calculator to calculate an amount of O.sub.2 required for partially oxidizing CH.sub.4 in the CH.sub.4 oxidation catalyst 52, based on the density of CH.sub.4, and outputs the required amount of O.sub.2 calculated above to the mass flow controller MFC. The ECU 60 then causes the mass flow controller MFC to operate to supply O.sub.2 to the CH.sub.4 oxidation catalyst 52, while controlling the flow rate of O.sub.2 supplied from the electrolysis tank 22, based on the amount of O.sub.2 calculated by the ECU 60 (step S6). Upon the required amount of O.sub.2 having been supplied, the processing returns to step S1 so that the fuel synthesis device 1 operates and the CH.sub.4 density detector 23 detects the density of CH.sub.4 as a side product.

[0049] As described hereinabove, the fuel synthesis device 1 of the present embodiment controls whether the switching valve V communicates with the return path 20 or the bypass path 50, based on the density of CH.sub.4 detected by the CH.sub.4 density detector 23. The fuel synthesis device 1 thus controls the switching valve V based on the density of CH.sub.4, staying in the device, to cause CH.sub.4 to be partially oxidized and return gas (CO) produced by oxidation to the point upstream of the fuel synthesis catalyst 3 (between the supplier 2 and the fuel synthesis catalyst 3). This allows the fuel synthesis device 1 to use CO as a feedstock in the fuel synthesis catalyst 3 to synthesize fuel (hydrocarbon of C.sub.5+) for sufficiently growing carbon chain.

[0050] The present invention is not limited to the above-described embodiment and can be implemented in various embodiments. In addition, said embodiments can be combined to the extent structurally feasible.

LIST OF REFERENCE SIGNS

[0051] 1: fuel synthesis device, 2: supplier, 3: fuel synthesis catalyst, 4: gas-liquid separator, 5: oil-water separator, 10: main path, 11 to 17: piping, 20: return path, 21: tank, 22: electrolysis tank, 23: CH.sub.4 density detector, 25: piping, 30: compressor, 31: reaction tube, 40: heater, 50: bypass path, 51: CH.sub.4 separator, 52: CH.sub.4 oxidation catalyst, 53 to 55: piping, 60: ECU, MFC: mass flow controller, and V: switching valve.