JP2013111535A - Hydrocarbon adsorption agent and hydrocarbon adsorbent - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hydrocarbon adsorption agent and a hydrocarbon adsorbent, which are capable of sufficiently adsorbing and retaining a large amount of hydrocarbon.SOLUTION: The hydrocarbon adsorption agent includes a zeolite crystal skeleton of an aluminosilicate. The hydrocarbon adsorbent comprises the hydrocarbon adsorption agent supported by a porous carrier. In the hydrocarbon adsorption agent, at least a portion of aluminum in the zeolite crystal skeleton is substituted with boron, and an alkali metal ion is present in at least a portion of an ion exchange site within the zeolite crystal skeleton.

Description

  The present invention relates to a hydrocarbon adsorbent having a zeolite crystal skeleton and a hydrocarbon adsorbent using the hydrocarbon adsorbent.

  The exhaust gas discharged from an internal combustion engine such as an automobile contains hydrocarbons (HC) and the like. In order to purify this hydrocarbon and the like, an exhaust gas purification catalyst comprising a three-way catalyst such as platinum (Pt), palladium (Pd), and rhodium (Rh) is used. However, immediately after the start of the internal combustion engine, the HC concentration in the exhaust gas is high, and the exhaust gas purification catalyst has not reached a temperature sufficient to exhibit purification activity, so that hydrocarbons are discharged without being purified. . In view of this, a technique has been developed in which HC is adsorbed and held in a hydrocarbon adsorbent made of zeolite at a low temperature immediately after the internal combustion engine is started to reduce HC immediately after the start.

As such a hydrocarbon adsorbent, a part or all of Al of the aluminosilicate is replaced with Fe, and the molar ratio of SiO ₂ / Al ₂ O ₃ is _twice the molar ratio of SiO ₂ / Fe ₂ O _3. A hydrocarbon adsorbent having a SiO ₂ / Al ₂ O ₃ molar ratio of 80 or more and a SiO ₂ / Fe ₂ O ₃ molar ratio of 40 or more has been developed (see Patent Document 1).
Further, an adsorbent for hydrocarbons comprising a zeolite having an absolute value of oxygen charge of 0.210 or more and a SiO ₂ / Al ₂ O ₃ molar ratio of 30 or more determined from an average or principle of Sanderson's electronegativity. Has been developed (see Patent Document 2)

JP-A-9-99207 Japanese Patent Laid-Open No. 2003-126669

However, conventional hydrocarbon adsorbents have insufficient adsorbing power for hydrocarbons and cannot sufficiently adsorb and hold hydrocarbons. For this reason, hydrocarbons may pass through the hydrocarbon adsorbent and be discharged at a low temperature.
Therefore, development of a hydrocarbon adsorbent capable of sufficiently adsorbing and holding a larger amount of hydrocarbon is desired.

  The present invention has been made in view of such a background, and intends to provide a hydrocarbon adsorbent and a hydrocarbon adsorbent capable of sufficiently adsorbing and holding a large amount of hydrocarbons.

One aspect of the present invention is a hydrocarbon adsorbent having an aluminosilicate zeolite crystal framework,
A hydrocarbon characterized in that at least a part of aluminum in the zeolite crystal skeleton is substituted with boron, and an alkali metal ion is present in at least a part of ion exchange sites in the zeolite crystal skeleton. In the adsorbent (Claim 1).

  Another aspect of the present invention is a hydrocarbon adsorbent comprising the above-mentioned hydrocarbon adsorbent supported on a porous carrier (claim 4).

  In the hydrocarbon adsorbent, at least a part of aluminum in the zeolite crystal skeleton is substituted with boron. Furthermore, alkali metal ions are present in at least a part of the ion exchange sites in the zeolite crystal skeleton. Therefore, the hydrocarbon adsorbent exhibits an excellent adsorptive power for hydrocarbons and can sufficiently adsorb and hold a large amount of hydrocarbons.

  Specifically, when at least a part of the aluminum (Al) site is substituted with boron (B) in the zeolite crystal skeleton, the basicity can be increased more than when Al is substituted with Fe or the like. . Therefore, the adsorption power with respect to hydrocarbons can be increased. Furthermore, the zeolite crystal skeleton in which at least a part of aluminum (Al) sites is substituted with boron (B) is made basic by synergistically effectively by allowing an alkali metal ion to exist in at least a part of the ion exchange sites. Can be further increased. As a result, the adsorption power for hydrocarbons can be further increased.

  Next, the hydrocarbon adsorbent is formed by supporting the hydrocarbon adsorbent on a porous carrier. Therefore, the hydrocarbon adsorbent can sufficiently adsorb and hold a large amount of hydrocarbons by utilizing the excellent adsorption power of the hydrocarbon adsorbent.

Explanatory drawing (a) which shows arrangement | sequence of the structural element in the general zeolite crystal skeleton in Example 1, (b) explanatory drawing which shows arrangement | sequence of the structural element in the zeolite crystal skeleton of hydrocarbon adsorbent (sample E1) Explanatory drawing which shows the toluene desorption peak temperature of the hydrocarbon adsorbent (Sample E1, Sample C1, and Sample C2) in Example 1. Explanatory drawing which shows the toluene adsorption amount per unit surface area of the hydrocarbon adsorbent (Sample E1, Sample C1, and Sample C2) in Example 1. FIG. 3 is an explanatory view showing the entire hydrocarbon adsorbent in Example 2. FIG. 4 is an explanatory view showing a cross-sectional configuration of a hydrocarbon adsorbent in Example 2. FIG. 4 is an explanatory diagram showing an arrangement example in an exhaust gas flow path between a hydrocarbon adsorbent and an exhaust gas purification catalyst body in Example 2.

Next, a preferred embodiment of the present invention will be described.
In the hydrocarbon adsorbent, at least a part of Al in the zeolite crystal skeleton of the aluminosilicate is substituted with B. In the hydrocarbon adsorbent, a part of Al in the zeolite crystal skeleton may be substituted by B, but all of Al may be substituted by B.

In the hydrocarbon adsorbent, the molar ratio of Si / B in the zeolite crystal skeleton is preferably 10 or more and 50 or less (Claim 2).
When the Si / B molar ratio is less than 10, the crystal structure of the zeolite tends to collapse, and the hydrothermal stability of the hydrocarbon adsorbent may be impaired. On the other hand, when it exceeds 50, there exists a possibility that the adsorption power improvement effect with respect to the hydrocarbon by the above-mentioned B substitution may become small.

In the zeolite crystal skeleton, alkali metal ions are present at least at a part of the ion exchange sites.
A typical zeolite containing SiO ₂ and Al ₂ O ₃ has a bond of Si—O—Al, and O in this bond is negatively charged. Therefore, a cation such as a hydrogen ion is bonded to O, and the site to which this cation is bonded is called an ion exchange site. In the above hydrocarbon adsorbent, at least a part of aluminum is substituted with boron, but in this case as well, since O in the bond of Si—O—B is negatively charged, an ion exchange site exists.
In a general zeolite, the cation is a hydrogen ion, but in the hydrocarbon adsorbent, an alkali metal ion is present at the ion exchange site as described above.

The alkali metal ion is preferably at least one of Li ion, Na ion, K ion, Rb ion, and Cs ion. More preferably, at least one of K ion, Rb ion, and Cs ion is good.
In this case, the adsorptive power of the hydrocarbon adsorbent for hydrocarbons can be further improved.

The zeolite crystal skeleton is preferably MFI type or BEA type.
In this case, the hydrocarbon adsorbent can exhibit excellent adsorption retention performance even for relatively small hydrocarbons.

Moreover, the said hydrocarbon adsorbent can be arrange | positioned, for example in an exhaust gas flow path, and can be used in order to adsorb | suck the hydrocarbon contained in exhaust gas. In this case, it is possible to make full use of the function and effect of the hydrocarbon adsorbent that can sufficiently adsorb and hold a large amount of hydrocarbons.
Moreover, the said hydrocarbon adsorbent can be arrange | positioned and used for the upstream of the exhaust gas purification catalyst which consists of a three way catalyst etc. in an exhaust gas flow path.

Next, the hydrocarbon adsorbent is formed by supporting the hydrocarbon adsorbent on a porous carrier.
As the porous carrier, for example, a porous honeycomb structure made of cordierite, aluminum titanate, SiC, titania or the like can be used.
The hydrocarbon adsorbent can be used in the exhaust gas flow path, for example, arranged upstream of the exhaust gas purification catalyst body in which a three-way catalyst is supported on a porous carrier.

Example 1
Next, examples of the hydrocarbon adsorbent will be described.
The hydrocarbon adsorbent of this example (sample E1) has an aluminosilicate zeolite crystal skeleton.
A general zeolite crystal skeleton is constituted by a network structure of Si atoms, Al atoms, and O atoms (see FIG. 1A). In the hydrocarbon adsorbent of this example (sample E1), zeolite is used. At least a part of aluminum in the crystal skeleton is substituted with boron (see FIG. 1B). 1A and 1B show a part of the zeolite crystal skeleton. In addition, cations are present at ion exchange sites in the zeolite crystal skeleton. In a general zeolite crystal skeleton, H ⁺ is present as a cation (X ⁺ ) (see FIG. 1A). In the hydrocarbon adsorbent (sample E1) of this example, a cation (X ⁺ ), An alkali metal ion is present (see FIG. 1B).

In this example, a hydrocarbon adsorbent (sample E1) in which all of aluminum in the MFI-type zeolite crystal skeleton is substituted with boron and Cs ⁺ exists at the ion exchange site is prepared.
Specifically, first, silica (SiO ₂ ), boric acid (B (OH) ₃ ), tetrapropylammonium hydroxide (TPAOH), and ultrapure water (H ₂ O) in a molar ratio, SiO ₂ : B (OH) ₃ : TPAOH: H ₂ O = 1: 0.084: 0.1: 34 The mixture was mixed and stirred at room temperature for 1 hour. The obtained mixed aqueous solution was put into a Teflon (registered trademark) pressure-resistant container having an internal volume of 100 mL and allowed to stand at a temperature of 155 ° C. for 120 hours, and zeolite was synthesized by a hydrothermal method.

Next, the obtained solid was filtered and thoroughly washed with ultrapure water. Then, it was dried at a temperature of 100 ° C. for 12 hours, and further baked in the atmosphere at a temperature of 500 ° C. for 6 hours. By this calcination, all of the aluminum in the MFI-type zeolite crystal skeleton was replaced with boron, and a zeolite in which H ⁺ ions were present at the ion exchange site was obtained. This is designated as Sample C2. Sample C2 was subjected to ICP-AES analysis using an inductively coupled plasma emission spectrometer (ICP-AES apparatus, “Optima 4300DV” manufactured by PerkinElmer Co., Ltd.). The Si / B ratio (molar ratio) was determined to be Si / B. = 12.

  Next, ion exchange was performed by adding 1 g of sample C2 to 1M aqueous cesium chloride solution and stirring at a temperature of 70 ° C. for 6 hours. The obtained solid was filtered and thoroughly washed with ultrapure water. Then, it was dried at a temperature of 100 ° C. for 12 hours, and further fired in the air at a temperature of 500 ° C. for 6 hours. In this way, a hydrocarbon adsorbent (sample E1) was obtained.

  In this example, a sample for comparison with the sample E1 (sample C1) was prepared. Sample C1 was prepared by calcining H + type MFI zeolite (“HSZ-840HOA” manufactured by Tosoh Corporation) with Si / Al = 18.5 (molar ratio) at a temperature of 500 ° C. for 6 hours. .

As described above, a hydrocarbon adsorbent having three types of zeolite frameworks, sample E1, sample C1, and sample C2, was obtained.
Sample E1 is a hydrocarbon adsorbent in which all of the aluminum in the MFI-type zeolite crystal skeleton is substituted with boron and Cs ions are present at the ion exchange site. Sample E1 has a skeletal structure in which X ⁺ in FIG. 1 (b) is Cs ⁺ .
Sample C1 is a hydrocarbon adsorbent having an MFI type zeolite crystal skeleton. Sample C1 has a skeleton structure X ⁺ is H ⁺ in Fig. 1 (a).
Sample C2 is a hydrocarbon adsorbent in which all of the aluminum in the MFI-type zeolite crystal skeleton is substituted with boron, and H ions are present at the ion exchange site. Sample C2 has a skeletal structure in which X ⁺ in FIG. 1 (b) is H ⁺ .

Next, the desorption peak temperature and the amount of adsorption when hydrocarbon (toluene) was adsorbed to the sample E1, sample C1, and sample C2 were measured. The measurement was performed using a temperature programmed temperature rising catalyst analyzer (“BEL-CAT” manufactured by Nippon Bell Co., Ltd.).
Specifically, first, 0.1 g of each powder sample (sample E1, sample C1, and sample C2) was raised to a temperature of 400 ° C. at a temperature rising rate of 20 ° C./min under a He gas flow at a flow rate of 50 mL / min. After preheating and holding at a temperature of 400 ° C. for 20 minutes, a pretreatment for lowering the temperature to 50 ° C. was performed. Next, while maintaining the temperature at 50 ° C., a toluene mixed gas (toluene: 5% by volume, He: balance) was passed through each sample at a flow rate of 50 mL / min for 15 minutes to adsorb toluene. Subsequently, He gas with a flow rate of 50 mL / min was circulated through each sample until toluene was not observed in the mass spectrometer. Thereafter, each sample was heated to a temperature of 400 ° C. at a heating rate of 10 ° C./min under a flow of He gas at a flow rate of 30 mL / min and held at a temperature of 400 ° C. for 15 minutes to desorb the adsorbed toluene. I let you. The components desorbed from each sample as the temperature rises were qualitatively and quantified with a mass spectrometer ("BEL-Mass" manufactured by Nippon Bell Co., Ltd.), and the temperature at which the desorption amount of toluene is maximized. (Toluene desorption peak temperature (° C.)) was measured, and the result is shown in FIG.
Further, the amount of toluene adsorbed on each sample was determined by measuring the amount of toluene desorbed by mass spectrometry.

Moreover, the specific surface area of each sample was measured using the automatic specific surface area analyzer ("BELSORP-miniII" by Nippon Bell Co., Ltd.).
Specifically, first, 0.2 g of each sample was heated to a temperature of 300 ° C. at a heating rate of 10 ° C./min while exhausting using an exhaust pretreatment device (“BELPREP-vac II” manufactured by Nippon Bell Co., Ltd.). The temperature was raised, and a pretreatment was performed at this temperature of 300 ° C. for 1 hour. For each sample after pretreatment, nitrogen adsorption measurement was performed in the vicinity of the boiling point of liquid nitrogen (77K), and the specific surface area of each sample was calculated by the multipoint BET method. And the toluene adsorption amount (micromol / m < ² >) per unit specific surface area of each sample was computed by remove | dividing the toluene adsorption amount measured by the above-mentioned mass spectrometry by the value of the specific surface area obtained here. The result is shown in FIG.

As is known from FIG. 2, the hydrocarbon adsorbent of sample E1 in which aluminum in the zeolite crystal skeleton is substituted with boron and alkali metal ions (Cs ⁺ ) are present at the ion exchange site is SiO ₂ and The toluene desorption peak temperature is higher than that of the sample C1 having a normal zeolite crystal skeleton made of Al ₂ O ₃ . Further, the sample E1 has a higher toluene desorption peak temperature than the sample C2 in which the aluminum in the zeolite crystal skeleton is substituted with boron and the hydrogen ion (H ⁺ ) is present at the ion exchange site. ing. Therefore, it can be seen that the sample E1 can adsorb and hold hydrocarbons with sufficiently excellent adsorption power.
Further, as can be seen from FIG. 3, it can be seen that the sample E1 can adsorb a larger amount of toluene than the samples C1 and C2.

  Thus, according to this example, the hydrocarbon adsorbent in which the aluminum in the zeolite crystal skeleton is replaced with boron and the alkali metal ions are present at the ion exchange site is sufficiently adsorbed and retained. I understand that I can do it.

(Example 2)
This example is an example of a hydrocarbon adsorbent formed by supporting a hydrocarbon adsorbent on a porous carrier.
As shown in FIGS. 4 and 5, the hydrocarbon adsorbent 1 of this example includes, as a porous carrier 2, an outer skin 20, cell walls 21 arranged in a polygonal lattice shape inside the outer skin 20, and the cell walls 21. And a porous honeycomb structure having a large number of cells 22 divided into two.

As shown in FIGS. 4 and 5, the porous carrier 2 has a substantially cylindrical shape. The porous carrier 2 includes a cylindrical outer skin 20 and cell walls 21 arranged in a substantially quadrangular lattice shape in the outer skin 20. A large number of cells 22 formed by being partitioned by the cell walls 21 are formed so as to extend in the axial direction from one end face 28 to the other end face 29 of the cylindrical porous carrier 2.
The porous carrier 2 is a porous body made of cordierite, and pores (not shown) are formed in the cell walls 21.

In the hydrocarbon adsorbent 1 of this example, as shown in FIGS. 4 and 5, the hydrocarbon adsorption layer 3 containing a hydrocarbon adsorbent is formed on the cell wall 21 of the porous carrier 2.
The hydrocarbon adsorption layer 3 includes a support layer (not shown) in which alumina particles are aggregated and a hydrocarbon adsorbent (not shown) supported on the support layer. Further, the porous adsorption layer 3 is formed on the cell wall 21 and is also filled in the pores of the cell wall 21. As the hydrocarbon adsorbent, the sample E1 of Example 1 is supported.

Next, the manufacturing method of the hydrocarbon adsorbent of this example will be described.
First, a honeycomb structure made of cordierite is prepared as a porous carrier.
Specifically, first, talc, silica, kaolin, alumina, aluminum hydroxide and the like were mixed so as to have a cordierite composition. And the binder and water were added and kneaded with respect to mixed powder, and plasticity was adjusted. Thereafter, the kneaded product was molded by an extruder to obtain a honeycomb molded body having a cylindrical shape as a whole and a square cell shape.
Next, the honeycomb formed body was dried until moisture was sufficiently removed, and then fired. Thereby, a porous carrier having a honeycomb structure was obtained.

Next, a hydrocarbon adsorption layer was formed on the cell wall of the porous carrier.
Specifically, first, sample E1 prepared in Example 1 and alumina sol were mixed with water to obtain a slurry. Next, a porous carrier having a honeycomb structure was immersed in this slurry and pulled up, and then excess slurry in the cells of the porous carrier was removed by an air flow. And after drying a porous support | carrier, it baked at the temperature of 400 degreeC for 1 hour.
In this way, a hydrocarbon adsorbent was obtained in which a hydrocarbon adsorption layer containing a hydrocarbon adsorbent was formed on the surface of the cell wall of the porous carrier. In this example, alumina sol is used as the inorganic binder, but silica sol or yttria sol can be used instead of alumina sol.

In the hydrocarbon adsorbent 1 of this example, a hydrocarbon adsorbing layer 3 containing a hydrocarbon adsorbent (sample E1) is supported on a porous carrier 2 (see FIGS. 4 and 5). As the hydrocarbon adsorbent, the sample E1 of Example 1 in which at least part of aluminum in the zeolite crystal skeleton is substituted with boron and alkali metal ions are present in at least part of the ion exchange site is employed. ing.
Therefore, the hydrocarbon adsorbent can sufficiently adsorb and hold a large amount of hydrocarbons by making use of the excellent adsorption power for hydrocarbons shown by the sample E1.

Further, as shown in FIG. 6, the hydrocarbon adsorbent 1 can be used in the exhaust gas flow path 6 by being arranged upstream of the exhaust gas purification catalyst body 5 in which a three-way catalyst such as a noble metal is supported on a porous carrier. . Thereby, for example, when the temperature is lower than the activation temperature of the three-way catalyst, the hydrocarbon adsorbent 1 arranged on the upstream side can adsorb hydrocarbons, and when the temperature becomes higher than the activation temperature, the exhaust gas arranged on the downstream side The exhaust gas can be purified by the purification catalyst body 5. Therefore, it becomes possible to more reliably prevent the hydrocarbons contained in the exhaust gas from being discharged.
The exhaust gas purification catalyst body 5 can have the same configuration as that of the hydrocarbon adsorbent 1, for example, except that a three-way catalyst is used instead of the hydrocarbon adsorbent. Further, FIG. 6 shows an example in which the hydrocarbon adsorbent 1 and the exhaust gas purification catalyst body 5 are arranged side by side and arranged with almost no gap therebetween, but the gap between the two is sufficiently increased. You can also.

DESCRIPTION OF SYMBOLS 1 Hydrocarbon adsorbent 2 Porous support 21 Cell wall 22 Cell 3 Hydrocarbon adsorption layer

Claims (4)

A hydrocarbon adsorbent having a zeolite crystal framework of aluminosilicate,
A hydrocarbon characterized in that at least a part of aluminum in the zeolite crystal skeleton is substituted with boron, and an alkali metal ion is present in at least a part of ion exchange sites in the zeolite crystal skeleton. Adsorbent.   The hydrocarbon adsorbent according to claim 1, wherein the molar ratio of Si / B in the zeolite crystal skeleton is 10 or more and 50 or less.   The hydrocarbon adsorbent according to claim 1 or 2, wherein the zeolite crystal skeleton is of MFI type or BEA type.   The hydrocarbon adsorbent formed by carrying the hydrocarbon adsorbent according to any one of claims 1 to 3 on a porous carrier.

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