Patent Application
20170306825
The present invention relates to a CO2 recovery device of an internal combustion engine, configured to reduce CO2 emitted from an internal combustion engine, including CO2 emitted from an automobile or a diesel engine, and CO2 in the air.
Recently from the viewpoint of reducing global warming, a reduction in the amount of CO2 emitted from internal combustion engines and the amount of CO2 in the air has been demanded.
As one method for reducing CO2 emitted from an internal combustion engine, attempts have been made to improve the fuel consumption of the internal combustion engine and accordingly reduce the amount of CO2 generated. In order to reduce the emission amount of generated CO2, a technique for synthesizing fuel using CO2 emitted from an automobile is disclosed (Patent Literatures 1 and 2).
Patent Literature 1: JP 2010-235736 A
Patent Literature 2: JP 2009-269983 A
Patent Literature 1 describes a system including a CO2-absorbing apparatus and a CO2-releasing apparatus, which is configured to synthesize fuel using recovered CO2 as a raw material. This literature describes a heat supplier as well, and this heat supplier is configured to apply thermal energy to the CO2-releasing apparatus. This literature, however, does not disclose how to supply heat, and a lot of thermal energy will be required to release CO2.
Patent Literature 2 describes a technique of synthesizing methane using CO2 emitted from an engine. In this technique, however, any material is not used to recover CO2. Therefore, the concentration of CO2 during fuel synthesis is low, and the efficiency of fuel synthesis is presumably low.
The present invention aims to provide a CO2 recovery device of an internal combustion engine capable of efficiently recovering CO2 emitted from an internal combustion engine or CO2 in the air, and of efficiently synthesizing methane using CO2.
A CO2 recovery device of an internal combustion engine, includes a CO2 capturing material disposed at a through channel of gas including CO2 to capture CO2 in the gas, and methanation catalyst to let CO2 desorbed from the CO2 capturing material react with H2 obtained from a H2 supply source to generate methane. The CO2 recovery device has a function to raise temperature of the CO2 capturing material using heat generated from the internal combustion engine to desorb CO2.
The present invention enables the recovery of CO2 emitted from an internal combustion engine or CO2 in the air sophisticatedly. Further the present invention enables synthesis of methane using the recovered CO2 as a raw material, and the methane can be used as fuel of the internal combustion engine. Therefore the present invention can reduce the fuel consumption sophisticatedly and can reduce the CO2 emission due to the fuel consumption.
The following describes the present invention in details.
Typically exhaust gas emitted from an inner combustion engine as in an automobile, a diesel engine or the like contains a few % to a few tens % of CO2, and a reduction in the amount of CO2 emitted from such an internal combustion engine can lead to the prevention of global warming. Meanwhile, the air also contains CO2 of about 400 ppm, and a reduction in CO2 in the air also leads to the prevention of global warming.
A further study by the present inventors shows that, in a CO2 recovery device of an internal combustion engine having a CO2 capturing material disposed at a through channel of gas including CO2 to capture CO2 in the gas, and methanation catalyst to let CO2 desorbed from the CO2 capturing material react with H2 obtained from a H2 supply source to generate methane, the CO2 recovery device has a function to raise temperature of the CO2 capturing material using heat generated from the internal combustion engine to desorb CO2, whereby CO2 emitted from the internal combustion engine and CO2 in the air can be recovered efficiently.
The CO2 capturing material used is not limited especially. Examples of the CO2 capturing material include activated charcoal, zeolite and solid oxides. Liquid such as amine solution also can be used for this.
The capturing amount of CO2 by the CO2 capturing material, the capturing temperature and the CO2 desorption temperature can be optimized by changing elements used, their additive amount and an adding method of some materials.
The concentration of CO2 flowing into the CO2 capturing material varies with the type of gas flowing into the CO2 capturing material. When the gas is exhaust gas of an internal combustion engine, the concentration may be up to 10% or more. When the gas is the air, the expected concentration is about 400 ppm. The type of the CO2 capturing material has to be selected, depending on the amount and the concentration of CO2 flowing into the CO2 capturing material.
Two or more of the CO2 capturing material may be disposed, which enables the repetition of the CO2 capturing step and the CO2 desorption step. When the CO2 capturing material is disposed at the through channel of exhaust gas or at the through channel of the air, the capturing ability of the CO2 capturing material to capture CO2 will exceed its limit as the CO2 capturing reaction by the CO2 capturing material continues. In such a case, the through channel for exhaust gas is switched so as to introduce exhaust gas or the air into another CO2 capturing material, whereby CO2 in the exhaust gas or the air can be captured continuously. For the CO2 capturing material that has captured the enough amount of CO2, gas flowing thereto is stopped. Then the temperature of the CO2 capturing material is allowed to rise so as to desorb CO2 from the capturing material. Thereby CO2 can be recovered therefrom.
The temperature of the CO2 capturing material can be raised by using heat emitted from the engine, whereby CO2 can be efficiently desorbed in terms of the energy. For instance, a part of exhaust gas from the engine is extracted and heat of the extracted gas is given to the CO2 absorbing material via a heat medium, whereby the temperature of the CO2 absorbing material can be raised.
Alternatively, the CO2 capturing material may be of a rotary type so as to enable the repetition of the CO2 capturing step and the CO2 desorbing step.
An internal combustion engine of the present invention is not limited especially as long as it generates CO2. For instance, examples of the internal combustion engine include internal combustion engines of a gasoline-powered vehicle, a diesel-powered vehicle, and a natural gas-powered vehicle and internal combustion engines used in a constructing machine, an agricultural machine and a ship. This also includes stationary engines.
Methanation catalyst is not limited especially as long as it enables reaction of CO2 and hydrogen to promote the following methanation reaction.
CO2+4H2→CH4±2H2O
For better performance of methanation, the methanation catalyst includes: a porous carrier made of inorganic compound, and a catalyst active component loaded on the porous carrier, the catalyst active component including at least one type selected from Pt, Pd, Rh, and Ni. The porous carrier includes at least one type selected from Al, Ce, La, Ti and Zr. An oxide having a large specific surface area may be used as the porous carrier of the methanation catalyst, whereby Pt, Pd, Rh or Ni can be dispersed highly and the methanation performance can be increased. Especially an oxide including Al may be used as the porous carrier, whereby high methanation performance can be obtained stably. The specific surface area of the porous carrier of the present invention is preferably in the range of 30 to 800 m2/g, and particularly preferably 50 to 400 m2/g.
Two types or more components selected from Pt, Pd, Rh, and Ni may be included as the catalyst active component.
The total loading amount of Pt, Pd, Rh and Ni as the catalyst active component is preferably 0.0003 molar part to 1.0 molar part in terms of elements relative to 2 molar parts of the porous carrier. If the total loading amount of Pt, Pd, Rh and Ni is less than 0.0003 molar part, its loading effect is not sufficient. If the total loading amount thereof exceeds 1.0 molar part, the specific surface area of the active component itself is lowered, and the cost of catalyst rises.
Herein the term “molar part” refers to the ratio of each component included in terms of the molar number. For instance, when the loading amount of component B is 1 molar part relative to 2 molar parts of component A, this refers to component B being loaded with the ratio of 1 relative to 2 of component A in terms of the molar number, independently of the absolute amount of component A.
Methane obtained through the methanation reaction is introduced into the internal combustion engine as its fuel source, whereby the fuel use of the internal combustion engine can be reduced. A water electrolysis device may be disposed at the internal combustion engine so as to generate hydrogen through electrolysis of water. In this case, water obtained through the methanation reaction can be used as the supply source of water.
A method for generating H2 also is not limited especially. For instance, a tank for hydrogen may be disposed at the internal combustion engine, and H2 may be supplied from the tank to the methanation catalyst. In this case, hydrogen as gas is directly compressed or is liquefied, and H2 in such a state may be put in a tank.
H2 carrier such as ammonia, methanol, organic hydride, or hydrogen storing alloy may be used for the supply source. Since ammonia, methanol, organic hydride, or the like is liquid at normal temperatures, they require a storage tank. However, this enables the conveyance of H2 with lower energy than in the case of conveying H2 itself. Heat is required to extract H2 from these H2 carriers. Similarly to the case of raising the temperature of the CO2 absorbing material, exhaust heat from the engine may be used, and the temperature of the H2 carrier can be raised efficiently.
In another effective configuration, a water electrolysis device may be disposed at the internal combustion engine, and hydrogen can be generated through electrolysis of water. In this case, a method for electrolysis of water is not limited especially as long as H2 is obtained through the following reaction.
2H2O→2H2+O2
Examples of the method for electrolysis of water include an alkaline water electrolysis method and a method using solid polymer. Electricity is required for electrolysis of water. In that case, electricity can be generated by recovering heat of exhaust gas from the internal combustion engine, for example, and the obtained electricity can be used for water electrolysis.
Exhaust gas emitted from an internal combustion engine can be 400° C. or more. Therefore electricity can be efficiently obtained using heat of the exhaust gas. One of the method therefor includes the use of combination of a heat exchanger, an expansion machine and a working medium.
The working medium is fed to the heat exchanger in advance for circulation. When exhaust gas flows into this heat exchanger, the working medium changes from liquid to gas due to the heat of exhaust gas. The working medium changed into gas is sent to the expansion machine, whereby electricity can be generated. Thereafter, the working medium is sent to a condenser, and returns to liquid there. In this way, the working medium is circulated so as to recover heat of the exhaust gas, whereby electricity can be generated. The obtained electricity can be used for water electrolysis.
The working medium used is not limited especially as long as it satisfies the above intended use. Examples of the working medium include ethylene glycol and water.
Exhaust gas subjected to heat recovery may be introduced to a CO2 capturing material. In general the effect of capturing CO2 by the CO2 capturing material increases with exhaust gas at lower temperatures. Therefore the above method for recovery of heat of exhaust gas is effective also for improving the ability of the CO2 capturing material to capture CO2.
As one method for obtaining electricity using heat of the exhaust gas, thermoelectric conversion element may be used. A thermoelectric conversion element may be disposed at the through channel of exhaust gas so that exhaust gas comes in contact with the thermoelectric conversion element. Thereby heat of exhaust gas can be converted into electricity, and the electricity can be obtained. The obtained electricity can be used as electricity for water electrolysis.
The type of the thermoelectric conversion element used is not limited especially. Examples of the thermoelectric conversion element include an element including bismuth and tellurium, an element including lead, and an element including silicon and germanium.
A catalyst may be installed between a heat exchanger or a thermoelectric conversion element and an engine included in the internal combustion engine, and the catalyst has a function of burning at least one type or more of H2, CO and hydrocarbon in exhaust gas. Such catalyst installed can purify H2, CO and hydrocarbon in exhaust gas and can raise the temperature of exhaust gas downstream of the catalyst because of the purifying reaction. Therefore the efficiency of recovering exhaust heat by the heat exchanger or the thermoelectric conversion element can be increased more.
The catalyst is not limited especially as long as it can burn H2, CO and hydrocarbon. For instance, this may be catalyst including at least one type selected from Pt, Pd and Rh as a catalyst active component that is loaded on a porous carrier including alumina.
The air may be fed to the CO2 capturing material, whereby CO2 in the air also can be captured. In this case, the step of recovering CO2 may include the combination of the CO2 capturing step and the CO2 desorbing step. After the CO2 capturing material captures a certain amount of CO2, this CO2 capturing material may be replaced with a new one.
A solid CO2 capturing material and a porous carrier or an active component used as the methanation catalyst may be loaded on a substrate. A suitable substrate is made of cordierite, ceramic including Si—Al—O, or a heat-resisting metal substrate made of stainless steel, which have been used conventionally. When the substrate is used, the loading amount of these materials is preferably 10 g or more and 300 g or less with respect to 1 L of the substrate for improving the ability of capturing CO2 and the ability of methanation. If the amount is 10 g or less, the ability of capturing CO2 and the ability of methanation deteriorate. If the amount is 300 g or more, a problem, such as easy clogging at the through channel of the gas, occurs when the substrate has a honeycomb shape.
The solid CO2 capturing material and the methanation catalyst can be prepared by a physical method such as impregnation, kneading, coprecipitation, sol-gel method, ion-exchange method and evaporation, or by a method using a chemical reaction, for example.
The starting raw materials of the solid CO2 capturing material and the methanation catalyst may include various compounds, such as nitric acid compound, chloride, acetic acid compound, complex compound, hydroxide, carbonate compound and organic compound, metals, and metal oxides. For instance, when two types or more of elements are combined as the catalyst active component, a co-impregnation method may be used using impregnating solution in which the active components exist in the same solution. Thereby the catalyst components can be loaded homogeneously.
The shape of the solid CO2 capturing material and the methanation catalyst can be adjusted appropriately depending on the intended use. For instance, the shape may be a honeycomb shape that is obtained by coating a honeycomb structure made of various substrate materials, such as cordierite, Si—Al—O, SiC, or stainless steel, with the purifying catalyst of the present invention. Other shapes include a pellet shape, a plate shape, a granular shape, and a powder shape. In the case of a honeycomb shape, the substrate is preferably a structure made of cordierite or Si—Al—O.
The following describes examples of the present invention.
In
Next, the obtained CO2 is introduced into methanation catalyst 29. Water from a water tank 27 is electrolyzed by an water electrolysis device 28 to obtain H2. The obtained H2 also is introduced into the methanation catalyst 29. Then CO2 and H2 react at the methanation catalyst 29, whereby gas including CH4 and water can be obtained. This gas is introduced into a condenser 30 to separate water, and CH4 only is obtained. The separated water is returned to the water tank 27, and is reused for water electrolysis. The obtained CH4 is compressed by a compressor 31 and is then stored in a methane storing part 32. CH4 is introduced into the engine 26 as needed, and is used as fuel of the engine.
Such a configuration can reduce the amount of CO2 emitted from the engine and can reduce fuel as well.
The thus obtained electricity is used for water electrolysis by a water electrolysis device 28.
Although not illustrated in
Such a configuration can reduce the amount of electricity used for electrolysis of water.
For instance, when water is electrolyzed by a water electrolysis device using electricity of 2 kW, the amount of H2 obtained will be 15 mol/h. Since the methanation reaction is CO2+4H2→CH4+2H2O, 3.7 mol/h of CO2 can be converted into methane using all of the H2 obtained. That is, 3.7 mol/h of CO2 can be reduced from the exhaust gas, meaning that CO2 emitted from the engine can be reduced by about 4%. Further in this case, 3.7 mol/h of methane can be obtained, and the obtained methane can be used as fuel. Thereby the consumption of the fuel can be reduced by about 6%. That is, CO2 emission can be reduced by about 6%. Accordingly considering both of the recovery of CO2 and the reduction of the fuel, the CO2 emission can be reduced by about 10%. Since the resulting reduction in CO2 emission varies with the amount of H2 obtained, such CO2 emission can be reduced more by increasing the amount of electricity during water electrolysis or by supplying H2 from a H2 tank.
Although not illustrated in
| Number | Date | Country | Kind |
|---|---|---|---|
| 2014-230285 | Nov 2014 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2015/078435 | 10/7/2015 | WO | 00 |
