Patent Application
20160199808
The present invention relates to a carbon dioxide capturing material and to a carbon dioxide recovery apparatus using the capturing material.
Global warming due to greenhouse gas emission becomes a worldwide issue. Examples of the greenhouse gas include carbon dioxide (CO2), methane (CH4), and chlorofluorocarbons (CFCs). Among them, CO2 applies greatest impact on global warming, and CO2 emission reduction becomes imperative. Possible solutions to achieve the emission reduction include techniques of chemical absorption, physical absorption, membrane separation, adsorptive separation, and cryogenic separation. These techniques include a CO2 separation/recovery technique using a solid CO2 capturing material.
In a CO2 separation and recovery system using such a CO2 capturing material, a CO2-containing gas is introduced into a capturing material container packed with the CO2 capturing material, and the gas is brought into contact with the CO2 capturing material to capture and remove CO2 from the gas. Thereafter the capturing material is heated, or the internal pressure of the capturing material container is reduced, to desorb and recover CO2 from the capturing material. The CO2 capturing material after the CO2 desorption is cooled, and then used in another CO2 capture and removal process by feeding another portion of the CO2-containing gas.
Patent Literature 1 describes a technique relating to a carbon dioxide capturing material. The technique focuses attention on average pore size and provides a carbon dioxide capturing material for efficiently capturing carbon dioxide. The carbon dioxide capturing material is an oxide containing Ce and at least one element selected from the group consisting of K, Mg, Al, and Pr. The carbon dioxide capturing material contains the at least one element selected from the group consisting of K, Mg, Al, and Pr in a total mole ratio to Ce of 0.01 to 1.00 in terms of elementary metal.
Patent Literature 1: Japanese Patent Application Laid-Open No. 2013-59703
Experimental investigations demonstrated that the carbon dioxide capturing material described in PTL 1 has an initial specific surface area of 100 m2/g or more, but has a specific surface area of about 80 m2/g after firing at 500° C. Specifically, the carbon dioxide capturing material undergoes large reduction in specific surface area upon firing and has room for improvements in heat resistance (thermal stability). In general, a capturing material tends to capture a larger amount of carbon dioxide with an increasing specific surface area.
The present invention has an object to provide a carbon dioxide capturing material that captures a large amount of carbon dioxide, less suffers from decrease in an amount of the captured carbon dioxide, and has excellent heat resistance.
The present invention provides a carbon dioxide capturing material for separating and recovering carbon dioxide from a carbon-dioxide-containing gas. The carbon dioxide capturing material is an oxide containing Ce and Al. The oxide contains Ce in a highest content among metal elements in the oxide and contains Al in a content of 0.01% by mole to 40% by mole.
The present invention provides a carbon dioxide capturing material that captures a large amount of carbon dioxide, less suffers from decrease in the amount of the captured carbon dioxide, and has excellent heat resistance.
The present invention relates to a carbon dioxide capturing material for separating and recovering CO2 from a CO2-containing gas (carbon-dioxide-containing gas) such as a combustion gas. The carbon dioxide capturing material is hereinafter also referred to as a “CO2 capturing material”. In particular, the present invention relates to a technique that increases an amount of the captured CO2. The carbon-dioxide-containing gas herein is typified by a combustion gas having a carbon dioxide concentration of 3% to 18% by volume, but the carbon-dioxide-containing gas for use in the present invention is not limited thereto, and the present invention is also applicable typically to exhaust gases from chemical plants that treat solid reactions typically of calcium carbonate. In this case, the carbon dioxide concentration can possibly be 18% by volume or more. Carbon dioxide is more easily recovered from the gas with an increasing carbon dioxide concentration. The present invention is not limited to carbon-dioxide-containing gases having a carbon dioxide concentration of 3% by volume or more, but is also applicable to gases having a carbon dioxide concentration of less than 3% by volume.
Embodiments of the present invention will be illustrated below. It should be noted, however, that the embodiments and examples as follows are never construed to limit the scope of the present invention.
The CO2 capturing material according to the present invention is an oxide containing Ce and Al. The capturing material (oxide) contains Ce in a highest content among metal elements in the capturing material and contains Al in a content of 0.01% by mole to 40% by mole (0.01% to 40% by mole). It has been verified that the CO2 capturing material having the configuration can capture a larger amount of CO2.
The advantageous effects are obtained probably because (1) Ce and Al form complex oxides to thereby form sites that easily capture CO2; and (2) the capturing material has a larger specific surface area. An oxide containing Al in a content of more than 40% by mole and an oxide containing Al alone capture CO2 in smaller amounts as compared with an oxide containing Ce alone. Even an oxide containing Al in a content of 40% by mole has only to contain Ce in a content of 40% by mole or more in order to contain Ce in a highest content among metal elements. The oxide herein may contain Ce and one or more other elements in highest contents among metal elements in the oxide.
The term “percent (%) by mole” used herein which is a unit indicating the content of a metal element refers to the proportion of the metal element based on the total amount (100% by mole) of all metal elements contained in the CO2 capturing material. Specifically, the term “percent (%) by mole” refers to a value on mole basis determined by dividing the content of the specific metal element by the total content of all metal elements contained in the CO2 capturing material.
The Al content is more preferably 0.01% by mole to 30% by mole (0.01% to 30% by mole) and particularly preferably 5% by mole to 20% by mole (5% to 20% by mole).
The oxide constituting the CO2 capturing material may further contain 0.01% by mole or more of at least one metal element selected from the group consisting of Fe, Cu, V, and Mo, in addition to Ce and Al. The CO2 capturing material captures CO2 in a decreasing amount with an increasing total content of these metal elements, but can capture CO2 in a larger amount as compared with the oxide containing Ce alone (cerium oxide alone). This is because of the presence of Al in the oxide.
Preferred contents of these elements are 10% by mole or less for Fe, 7% by mole or less for Cu, 3% by mole or less for V, and 3% by mole or less for Mo. In case that two or more of these metal elements are contained, the oxide preferably has a composition meeting a condition specified by Expression (1), where Expression (1) is determined by weighting based on the correlation between proportions (contents) of the elements and the decrease in the amount of the captured CO2.
(Fe content)×1.0+(Cu content)×1.3+(V content)×3.3+(Mo content)×3.3≦10 (1)
where the contents in the equation are indicated in mole percent.
Advantageously, the use of the CO2 capturing material according to the present invention allows the use of a low-purity raw material and eliminates or minimizes the need for a purification step for removing impurities. This results in reduction of costs for raw materials and facilities.
Examples of the compound to be used as the raw material to synthetically prepare the CO2 capturing material according to the present invention include, but are not limited to, oxides, nitrates, chlorides, sulfates, carbonates, phosphates, hydroxides, oxalates, acetates, and formates.
The raw material for Ce may also be selected from minerals such as monazite and bastnaesite. The minerals may further contain, in addition to Ce, at least one of lanthanides excluding Ce (La, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu). In case that Ce and at least one of these lanthanide elements are contained, the resulting oxide captures CO2 in a larger amount as compared with an oxide containing Ce alone and has not always to be purified so as to reduce the contents of the lanthanide elements other than Ce. The total content of the lanthanides is typically 0.01% by mole to 50% by mole, and more preferably 0.01% by mole to 30% by mole. The use of the raw material as mentioned above reduces purification cost and still increases the amount of the captured CO2.
Examples of the technique to synthetically prepare the CO2 capturing material according to the present invention include chemical preparation techniques such as impregnation, kneading, coprecipitation, and a sol-gel process; and physical preparation techniques such as vapor deposition. For example, the CO2 capturing material may be prepared by preparing a solution containing cerium nitrate and aluminum nitrate, adding a basic compound to the solution to adjust the pH to 7 to 10, and thereby co-precipitating Ce and Al. The basic compound is exemplified by, but not limited to, aqueous ammonia solution, sodium hydroxide (NaOH), and calcium hydroxide (Ca(OH)2). In this case, aluminum hydroxide (Al(OH)3) forms flocs and thereby causes the synthesized product to be settled at a higher velocity and to be synthesized in a shorter time.
In addition, the carbon dioxide capturing material according to the present invention (e.g., Example 1 mentioned later) may have a specific surface area of 130 m2/g even after firing at 600° C. The carbon dioxide capturing material is accordingly considered to less suffer from decrease or deterioration in the amount of the captured carbon dioxide.
In contrast, the carbon dioxide capturing material described in Example 5 of PTL 1 has a reduced specific surface area of about 80 m2/g after firing at 500° C. Accordingly, this carbon dioxide capturing material is considered to suffer from large decrease in the amount of the captured carbon dioxide.
The firing temperature is higher than an actual regeneration temperature. The firing test, however, is a high-temperature firing test performed as an accelerated test so as to determine, at an early stage, whether a tested carbon dioxide capturing material deteriorates upon repetition of adsorption and regeneration of the carbon dioxide capturing material. In practice, such a capturing material may gradually deteriorate during a long-term use even at a service temperature of about 200° C.
Firing at 600° C. is far severer than firing at 500° C. Assume that a carbon dioxide capturing material has a higher specific surface area after firing at 600° C. as compared with the specific surface area after firing at 500° C. This indicates that the carbon dioxide capturing material is resistant to deterioration, has excellent heat resistance, and is resistant to long-term repeated use.
These demonstrate that the carbon dioxide capturing material according to the present invention has higher heat resistance as compared with the carbon dioxide capturing material described in PTL 1. This advantageous effect is considered to owe to the presence of Al in the oxide, in addition to Ce.
Examples of constituents constituting a CO2 recovery apparatus using the CO2 capturing material according to the present invention include, but are not limited to, a reactor packed with the capturing material; lines that introduce a CO2-containing gas and a heating gas into the reactor; a line that discharges gases from the reactor; a heating device that heats the reactor; devices that increase or decrease the internal pressure of the reactor; a condenser that condenses water vapor in the gas; a container that recovers and contains condensed water from the reactor; and a compressor that compresses the CO2-containing gas.
The CO2 capturing material according to the present invention may be selected from ceria and other materials having a high specific surface area, where the materials include ceria supported on or combined with another material. Examples of the other material include, but are not limited to, silica, alumina, titania, zirconia, zeolite, polymeric materials, activated carbon, molecular organic frameworks (MOFs), and zeolitic imidazolate frameworks (ZIFs). The CO2 capturing material may include a constitutive minimum unit which is a granule, an aggregate of granules, or a composite of them. In case that the carbon dioxide capturing material is formed as a structural component (member), it preferably has such a shape as to offer gas-permeability in order to reduce pressure drop. For example, the carbon dioxide capturing material may be a porous article or a honeycomb article each having a high voidage. The carbon dioxide capturing material may have an external shape of a bulk or a sheet (plate). In this connection, the carbon dioxide capturing material may have a low voidage in order to increase the CO2 purity in the recovered gas. Specifically, when the capturing material has a granular shape and has a low voidage, it disadvantageously suffers from a large pressure drop, but advantageously offers a high CO2 purity in the recovered gas. This is because smaller amounts of gases other than CO2 remain in the voids.
Examples of a method for recovering CO2 using the CO2 recovery apparatus according to the present invention include, but are not limited to, methods for: recovery by temperature swing; recovery by pressure swing; and recovery by pressure and temperature swing. These recovery methods may be selected and determined in consideration of the pressure, CO2 partial pressure, and temperature of the CO2-containing gas. For example, assume that CO2 is recovered from a combustion gas typically from a coal-fired power plant. In this case, CO2 may be recovered typically by a method in which CO2 is captured by the CO2 capturing material and thereby removed from the CO2-containing gas at about 50° C., then the CO2 capturing material is heated up to 150° C. to 200° C. to desorb CO2, and CO2 with an increased purity is thus recovered.
Examples of a technique for heating the CO2 capturing material include, but are not limited to, a technique of bringing a heated heat-transfer medium, such as a gas or liquid, into direct contact with the CO2 capturing material; a technique of passing a heated heat-transfer medium, such as a gas or liquid, typically through a heat-transfer tube to heat the capturing material via thermal conduction through a heat-transfer surface; and a technique of heating the CO2 capturing material by electrical heat generation typically with an electric furnace.
Examples of a technique to reduce the pressure of the atmosphere surrounding the CO2 capturing material include, but are not limited to, a technique of mechanically reducing the pressure of the atmosphere typically with a pump or a compressor; and a technique of condensing water vapor in the atmosphere by cooling. Exemplary techniques for reducing the CO2 partial pressure in the atmosphere surrounding the CO2 capturing material include a technique of passing another gas than CO2, in addition to the above techniques. The gas for use herein is preferably a gas that is easily separable from CO2 and is particularly preferably water vapor (steam). This is because the water vapor is easily condensable by cooling.
The atmosphere surrounding the CO2 capturing material may be pressurized typically by mechanical pressurization typically with a pump or compressor; or by introducing, into the reactor, a gas having a higher pressure as compared with the ambient atmosphere.
When the CO2 capturing material adsorbs other substances such as SOx, NOx, and soot dust, it can possibly capture CO2 in a smaller amount. To eliminate or minimize this and to maintain the CO2 capturing material performance, the concentrations of the SOx, NOx, and soot dust in the CO2-containing gas are preferably reduced. For example, assume that CO2 is recovered from an exhaust gas from a coal-fired power plant. In this case, the CO2 recovery apparatus using the CO2 capturing material may possibly be disposed downstream from a denitrator (NOx remover), a desulfurizer (SOx remover), and a dust collector.
The present invention will be illustrated in further detail with reference to several examples below.
Cerium nitrate hexahydrate (Ce(NO3)3.6H2O), aluminum nitrate nonahydrate (Al(NO3)3.9H2O), iron(III) nitrate nonahydrate (Fe(NO3)3.9H2O), copper(II) nitrate trihydrate (Cu(NO3)2.3H2O), ammonium vanadate (NH4VO3), ammonium molybdate ((NH4)6Mo7O24.4H2O), and 28% by weight aqueous ammonia solution used herein were all reagents of JIS Special Grade supplied by Wako Pure Chemical Industries, Ltd.
In 1080 g of purified water, 26.05 g of cerium nitrate hexahydrate were dissolved with vigorous stirring at room temperature to give an aqueous solution. While being stirred, the aqueous solution was combined with a 28% by weight aqueous ammonia solution added dropwise so as to have a pH of 9.0. After being stirred for 8 hours, the mixture was left stand for one hour, and precipitates were collected via washing and filtration. The collected precipitates were dried in a drying oven at 120° C., fired in an electric furnace at 400° C. in an air atmosphere for one hour, and yielded cerium oxide as a CO2 capturing material.
An oxide was synthetically prepared as a CO2 capturing material by the synthetic preparation procedure of Comparative Example 1, except for using, instead of 26.05 g of cerium nitrate hexahydrate, 23.45 g of cerium nitrate hexahydrate and 2.25 g of aluminum nitrate nonahydrate.
An oxide was synthetically prepared as a CO2 capturing material by the synthetic preparation procedure of Comparative Example 1, except for using, instead of 26.05 g of cerium nitrate hexahydrate, 20.84 g of cerium nitrate hexahydrate and 4.50 g of aluminum nitrate nonahydrate.
An oxide was synthetically prepared as a CO2 capturing material by the synthetic preparation procedure of Comparative Example 1, except for using, instead of 26.05 g of cerium nitrate hexahydrate, 13.03 g of cerium nitrate hexahydrate and 11.25 g of aluminum nitrate nonahydrate.
An aluminum oxide was prepared by firing 5 g of boehmite (Condea Pural-SB1) in an electric furnace at 400° C. in an air atmosphere for one hour and used as a CO2 capturing material.
An oxide was synthetically prepared as a CO2 capturing material by the synthetic preparation procedure of Comparative Example 1, except for using, instead of 26.05 g of cerium nitrate hexahydrate, 23.45 g of cerium nitrate hexahydrate and 2.42 g of iron(III) nitrate nonahydrate.
An oxide was synthetically prepared as a CO2 capturing material by the synthetic preparation procedure of Comparative Example 1, except for using, instead of 26.05 g of cerium nitrate hexahydrate, 23.45 g of cerium nitrate hexahydrate and 1.45 g of copper(II) nitrate trihydrate.
An oxide was synthetically prepared as a CO2 capturing material by the synthetic preparation procedure of Comparative Example 1, except for using, instead of 26.05 g of cerium nitrate hexahydrate, 23.45 g of cerium nitrate hexahydrate and 0.70 g of ammonium vanadate.
An oxide was synthetically prepared as a CO2 capturing material by the synthetic preparation procedure of Comparative Example 1, except for using, instead of 26.05 g of cerium nitrate hexahydrate, 23.45 g of cerium nitrate hexahydrate and 1.06 g of ammonium molybdate.
Measuring Method of Amount of Captured CO2
A tested CO2 capturing material was pelletized using a die having a diameter of 40 mm and a pressing machine at 200 kgf. The pellets were pulverized, and sized and granulated into granules of a size of 0.5 to 1.0 mm using a sieve. An aliquot (1.0 ml) of the granules was measured with a graduated cylinder and placed securely in a quartz glass tubular reactor.
The tubular reactor was placed in an electric furnace. The temperature of the CO2 capturing material was raised up to 400° C. while passing He through the reactor at a flow rate of 150 ml/min, and held at that temperature for one hour to remove impurities and adsorbed gases from the capturing material.
The CO2 capturing material temperature was decreased down to 50° C. by cooling. While keeping the specimen temperature at 50° C. in an electric furnace, the specimen was subjected to a pulsed CO2 capturing test to measure the amount of the captured CO2. A sample gas used herein was a gaseous mixture containing 12% by volume of CO2 and 88% by volume of He. In a pulsed manner, 10 ml of the sample gas were introduced for 2 minutes every 4 minutes, and the CO2 concentration at the tubular reactor outlet was measured by gas chromatography. The pulsed introduction of the sample gas was performed until the CO2 concentration measured at the tubular reactor outlet became saturated. He carrier gas was also used.
It is considered that a CO2 capturing material may capture a larger amount of CO2 as compared with the CO2 capturing material according to Comparative Example 1 when a decrease in the amount of the captured CO2 due to the addition of an element selected from Fe, Cu, V, and Mo is smaller than an increase in the amount of the captured CO2 due to the addition of Al.
(decrease in amount of captured CO2)=(amount of captured CO2 of Comparative Example 1)−(amount of captured CO2 of each comparative example) (2)
In
Assuming that the decrease in the amount of the captured CO2 is proportional to the element content, the decrease in the amount of the captured CO2 of a CO2 capturing material is when the CO2 capturing material contains 1% by mole of any one of the elements: 9 mmol/L per percent by mole of Fe, 14 mmol/L per percent by mole of Cu, 31 mmol/L per percent by mole of V, and 31 mmol/L per percent by mole of Mo. Based on these values, preferred contents of the elements so as to offer a higher amount of the captured CO2 as compared with Comparative Example 1 were estimated. The results are as follows.
The estimated preferred contents are 10% by mole or less for Fe, 7% by mole or less for Cu, 3% by mole or less for V, and 3% by mole or less for Mo. The CO2 capturing material preferably has such a composition that the total of the decreases in the amount of the captured CO2 is 90 mmol/L or less when the CO2 capturing material contains two or more of these metal elements. Specifically, the CO2 capturing material preferably has such a composition as to meet a condition specified by Expression (1).
Exemplary configurations of the CO2 recovery apparatus will be illustrated below.
In
To capture and remove CO2 from the CO2-containing gas, the CO2-containing gas is introduced into the reactor 1, and the gas, from which CO2 has been removed, is discharged to the atmosphere. To desorb CO2 from the CO2 capturing material, water vapor is introduced into the heat-transfer tube 6 to heat the CO2 capturing material to thereby desorb CO2 from the capturing material. Water vapor in the desorbed gases is removed with the condenser 10. Residual gases are introduced into the compressor 13, and compressed and liquefied to give liquefied CO2. The liquefied CO2 is recovered.
The apparatus may have another configuration in which a high-temperature gas is introduced into the reactor to bring the high-temperature gas into contact with the carbon dioxide capturing material to thereby heat the carbon dioxide capturing material. Examples of the gas at a high temperature include, but are not limited to, gases obtained from the air; inert gases such as nitrogen gas; CO2; and water vapor (steam). When it is acceptable that the recovered gases have a low CO2 concentration, the air or nitrogen may be used as the high-temperature gas. When the CO2 concentration has to be higher, CO2 may be used as the high-temperature gas. When the high-temperature gas has to be separated from the desorbed gas, water vapor is preferably used. This is because the water vapor has a low condensation temperature.
In
To capture and remove CO2 from the CO2-containing gas, the CO2-containing gas is introduced into the reactor 1, and gases from which CO2 has been removed are discharged to the atmosphere. To desorb CO2 from the CO2 capturing material, the decompressor 51 reduces the internal pressure of the reactor 1 to desorb CO2 from the CO2 capturing material, water vapor (moisture vapor) is removed from the desorbed gases using the condenser 10, and the residual gases are introduced into the compressor 13 to be compressed and liquefied to give liquefied CO2. The liquefied CO2 is recovered.
The apparatus may further include a pressurization unit (e.g., a compressor) (not shown). The pressurization unit is disposed upstream (in the line 2) from the reactor 1. The pressurization unit increases the internal pressure of the reactor 1. CO2 adsorption is more accelerated with an increasing CO2 partial pressure in the CO2-containing gas. Accordingly, it may be preferred to pass the CO2-containing gas which is pressurized with the pressurization unit through the reactor in some concentrations and/or in some temperature ranges.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2014-026237 | Feb 2014 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2014/077440 | 10/15/2014 | WO | 00 |
