JP2000225311A - Carbon monoxide separation method by adsorption - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a carbon monoxide gas separation method using an innovative adsorbent provided with further excellent carbon monoxide gas adsorbing capability. SOLUTION: In a method for removing carbon monoxide from a gas mixture consisting of at least two types of gases including carbon monoxide by bringing the gas mixture into contact with a zeolite, the zeolite to be used is a faujasite type zeolite having practically 1.0 of Si/Al atomic ratio of the skeletal structure and the cations after ion exchange of the zeolite are two or more metals in combination selected from alkali metals, alkaline earth metals, transition metals, and rare earth metals. The adsorption capacity difference (b-a) of the zeolite between (a) the carbon monoxide adsorption capacity at 760 mmHg pressure and 25 deg.C and (b) the carbon monoxide adsorption capacity at 38 mmHg pressure is 17.0 Nml/g or higher and Langmuir constant of the adsorption isotherm at 25 deg.C of the zeolite is 3.3×10-2 mmHg-1 or lower. Carbon monoxide is adsorbed and separated from a gas flow by using such a zeolite.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for adsorbing and removing carbon monoxide from a gas stream. More specifically, the present invention relates to a method for adsorbing and separating carbon monoxide from a H ₂ -containing gas generated from a steam reforming gas such as naphtha, a coke oven off-gas, a converter off-gas, and the like.

[0002]

2. Description of the Related Art Carbon monoxide is harmful because it is contained in flue gas and the like, and it is necessary to remove it. contained in _2-containing gas, removal in the case of recovery and reuse of the H _2, or, it is necessary to reuse adsorption separation.

[0003] As a method for separating carbon monoxide, there are a cryogenic separation method and an absorption method in which CO ₂ is oxidized to CO ₂ with a copper catalyst and the like is absorbed in a hot potassium carbonate solution or the like. Mainstream. Activated carbon and zeolite are used as the adsorbent.

[0004] Purification of H ₂ from H ₂ -containing gas is mainly performed by the pressure swing method (PSA method). One stage of the H ₂ -P
A method of purifying H ₂ by removing carbon monoxide, CO ₂ , H ₂ O, etc. by SA is also performed. However, in order to improve the purification degree of H ₂ , CO ₂ , H ₂ O, etc. are previously activated with activated carbon or the like. After the removal of carbon monoxide, separation of carbon monoxide, nitrogen and H ₂ by zeolite is also performed.

[0005] The zeolite adsorbents used so far are A-type zeolites or Si / Al atomic ratios of 1.2.
5 or more faujasite-type zeolites. However, also in the H ₂ -PSA method, an adsorbent having higher carbon monoxide adsorption performance has been demanded in order to make the apparatus compact and reduce the power consumption.

Japanese Patent Application Laid-Open No. 10-212103 proposes a method for improving the performance of H ₂ -PSA by using lithium ion exchanged X-type zeolite, but further improvement in performance is required. I have.

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for adsorbing and separating carbon monoxide using a novel adsorbent which is more excellent in carbon monoxide adsorption performance.

[0008]

Means for Solving the Problems As a result of diligent studies on the above-mentioned problems, the present inventors have made a mixed gas comprising at least two kinds of components containing at least carbon monoxide into contact with zeolite to convert carbon monoxide into a mixed gas. In the method of removing more, the Si / Al atomic ratio of the zeolite skeleton is substantially 1.
0 is a faujasite type zeolite, wherein the cation after ion exchange of the zeolite is an alkali metal,
A combination of at least two selected from alkaline earth metals, transition metals and rare earths,
The adsorption capacity difference (ba) between the carbon monoxide adsorption capacity (a) of 38 mmHg and the carbon monoxide adsorption capacity (b) of 38 mmHg is 1
By using a zeolite having a characteristic of not less than 7.0 Nml / g and a Langmuir constant of an adsorption isotherm at 25 ° C. of 3.3 × 10 ⁻² mmHg ⁻¹ or less, the separation performance of carbon monoxide is dramatically improved. Was found to be able to be improved, and the present invention was completed.

Hereinafter, the present invention will be described in detail.

The adsorbent used in the present invention has a skeleton of S
It is essential that the faujasite-type zeolite have an i / Al atomic ratio of substantially 1.0. Here, the skeleton Si / Al atomic ratio of the zeolite is 1.0 or more,
It is known that it does not fall below 1.0. Faujasite-type zeolite having a skeleton Si / Al atomic ratio of 1.2
When smaller, the carbon monoxide adsorption capacity increases,
This is presumed to be due to an increase in the number of cation exchange sites having strong carbon monoxide adsorption ability in the faujasite-type zeolite.

On the other hand, in the case of A-type zeolite which is a typical zeolite having an Si / Al atomic ratio of 1.0 other than the faujasite-type zeolite, the zeolite pore volume and pore size are larger than those of the faujasite-type zeolite. Is small, so that sufficient carbon monoxide adsorption capacity and dynamic characteristics cannot be obtained, which is not suitable for the present invention.

Since the separation is carried out by the PSA method in which the pressure is swung, an adsorbent having a large adsorption capacity in the operation pressure range for adsorption and desorption is preferable. For example, the concentration of carbon monoxide in the source gas is 5%, the adsorption pressure is 20 atm, and the desorption pressure is 1
In the case of atm, the carbon monoxide partial pressure in each case is 1 atm
(760 mmHg) and 38 mmHg, and it is preferable that the difference in adsorption capacity in this pressure range is large, and it is necessary that the difference be 17.0 Nml / g or more at 25 ° C. In order to increase the adsorption capacity in the adsorption / desorption pressure range, the shape of the adsorption isotherm is preferably a linear equilibrium type. Further, as the adsorption isotherm approaches the linear equilibrium type, the interaction between zeolite and carbon monoxide becomes weaker, so that desorption can be performed easily. On the other hand, when the adsorption isotherm is of the quadrature equilibrium type (the adsorption capacity is large in the low pressure area), the adsorption capacity in the operating pressure range is small, the interaction between zeolite and carbon monoxide is strong, and the energy required for desorption is high. Too big. The shape of the adsorption isotherm of carbon monoxide (the strength of the interaction between carbon monoxide and zeolite) is determined by the Langmuir constant. This parameter can be obtained by approximating the adsorption isotherm by the Langmuir equation. Is specifically 3.3 × 10 ⁻² mmHg ⁻¹ or less. It is generally known that the adsorption isotherm of carbon monoxide on zeolite can be approximated by the Langmuir equation.

When H ₂ purification is performed by the PSA method, carbon monoxide is the main impurity, but nitrogen is also present as another impurity. Purified H ₂ is often used for catalytic reactions in the petrochemical field, etc., and a trace amount of carbon monoxide remaining in purified H ₂ becomes a catalyst poison, so it is necessary to remove carbon monoxide rather than nitrogen. . For this purpose, a zeolite that selectively adsorbs carbon monoxide is preferable, and more specifically, it is only necessary that the adsorption capacity ratio between carbon monoxide and nitrogen is 1.6 or more.

The exchange cation of the faujasite-type zeolite used in the present invention is preferably an alkali metal ion, an alkaline earth metal ion, a transition metal ion, or a rare earth element ion. To increase the carbon monoxide adsorption capacity or the adsorption selectivity, Li ion, Na ion, K ion, Ca ion,
Sr ions and Ba ions are preferred. It is preferable that two or more kinds of ions selected from these ions coexist as the exchange cation. When the exchange cation contains Li,
A combination of Li, Na and K ions is preferred, and Li
The ion exchange rate is preferably at least 80%, more preferably at least 90%. When most of the exchanged cations are Na, a combination of Na and K ions is suitable, and the Na ion exchange rate is preferably 80% or more, more preferably 90% or more. Ca for exchange cation
Is preferable, a combination of Ca, Na, and K ions is preferable, and the Ca ion exchange rate is preferably 50% or more. Li, Ca, Na or Li, Na, K, C
The combination of a can also be used, and in this case, the Li exchange rate is 80% or more, more preferably 90% or more.

Further, the ion-exchangeable cation of the zeolite is a combination of sodium and potassium,
Assuming that the ion exchange rate of sodium is 80% or more, the above-mentioned adsorption capacity difference (ba) is not as large as that of the lithium ion-exchanged zeolite, but the adsorption capacity ratio of carbon monoxide and nitrogen becomes larger than the above value. 2.5 or more, which is preferable when it is necessary to separate carbon monoxide and nitrogen.

The faujasite-type zeolite used in the present invention can be used in the form of a powder. However, it is often used in the form of pellets, beads or the like because of easy handling.

When a compact is used, an inorganic or organic binder such as clay or silica sol is added to the zeolite powder, and the mixture is extruded, stirred and granulated by rolling. The amount of binder used is usually about 5 to 30% by weight based on the total amount of zeolite, but the smaller the amount of binder added, the better the adsorbent for higher performance. Further, a binderless molded article in which the binder of the molded article is changed to faujasite type zeolite may be used.

In the interior of the compact, between the zeolite crystal particles or between the zeolite crystals and the binder particles,
Although macropores of about 5 to 1 μm are formed, the average pore diameter of the macropores is 0.1 μm or more and the pore volume is 0.2 cc / g in order to reduce the diffusion resistance inside the molded body.
It is preferable that there is the above.

The size of the molded product is preferably as small as possible to obtain a higher-performance adsorbent. However, since the size of the molded product may be reduced and the pressure loss at the time of filling may be increased, it is usually 0. 0.5 mm or more and 3 mm or less;
A range of 5 mm or more and 2 mm or less is more preferable.

The ion exchange method is carried out by a usual method. For example, an alkali metal ion such as sodium or potassium, an alkaline earth metal ion such as calcium, a transition metal ion such as iron,
The target adsorbent can be obtained by ion exchange in the presence of a rare earth ion such as lanthanum, or each ion can be ion-exchanged as a separate solution. As the salts used for ion exchange, salts showing a certain degree of water solubility, such as chlorides, nitrates, hydroxides, carbonates, and sulfates are selected. The concentration of the aqueous solution is not particularly limited, and is usually performed at a concentration of 0.1 mol / liter to 7 mol / liter. However, when a salt having low solubility is used, this is not limited. In addition, the temperature at the time of ion exchange is from a temperature above the freezing point to a temperature below the boiling point, but if the ion exchange reaction is an endothermic reaction, it is efficient to perform the ion exchange at the highest possible temperature. It is imagined. Further, the ion exchange may be performed by subjecting the zeolite powder to ion exchange, or may be performed after the zeolite powder is formed into a molded body. The ion exchange method can be carried out by any of a column flow method and a batch method, and is not particularly limited.

After the ion exchange has been carried out as intended, it is washed with water, warm water or weakly alkaline water or warm water by a usual method, and then dried. Drying is preferably performed at a relatively low temperature, for example, at a temperature of 120 ° C. or less. When the moisture adhering to the surface is sufficiently dried, the powder is molded into the above-mentioned molded body, and when the molding is performed, the powder is activated.

Activation is indispensable for use as an adsorbent for carbon monoxide. Water molecules adsorbed on the zeolite adsorption site are desorbed by heating to be in a state active for carbon monoxide adsorption. Is the purpose. Activation is 350
It is required to be carried out in a temperature range of up to 600 ° C., in particular, under conditions capable of sufficiently expelling water vapor so as not to cause self-destruction by desorbed water vapor. For example, a method of activating by heating under vacuum, a method of activating by heating while sending dehumidified air, or a method of heating zeolite by heating dehumidified air to the above-mentioned activation temperature range to activate the zeolite Is preferably used.

The zeolite used in the method of the present invention is produced by the above-described process,
In a method of removing a carbon monoxide from a mixed gas by contacting a mixed gas comprising at least two components containing at least carbon monoxide with a zeolite, the zeolite has a Si /
A faujasite-type zeolite having an Al atomic ratio of substantially 1.0, wherein the cation after ion exchange of the zeolite is at least two kinds selected from alkali metals, alkaline earth metals, transition metals and rare earths. A combination of carbon monoxide adsorption capacity (a) of 760 mmHg at 25 ° C. and carbon monoxide adsorption capacity (b) of 38 mmHg at 25 ° C. (ba) of 17.0 Nml / g or more; The Langmuir constant of the adsorption isotherm at ℃ is 3.3
Any zeolite having a characteristic of × 10 ⁻² mmHg ⁻¹ or less can be suitably used for the purpose of the present invention.

The mixed gas containing at least carbon monoxide, which is the object of the present invention, is not particularly limited as long as it contains carbon monoxide, but has a weaker adsorbing power on zeolite than carbon monoxide, that is, A higher effect can be exhibited when a gas having a low polarity is contained. Examples of the mixed gas containing at least carbon monoxide include hydrogen, hydrocarbon, nitrogen, oxygen, argon, and the like as components of the gas other than carbon monoxide.

Further, even if a strongly polar gas such as water, ammonia or carbon dioxide coexists in the mixed gas, the amount of the zeolite adsorbent used is increased or decreased in accordance with the content of these gases, whereby the polarity is increased. It is possible to remove by adsorbing to the adsorbent in the order of strength, or to preliminarily remove these gases with a conventional adsorbent or the like as a pretreatment.

The method and conditions for adsorbing and removing carbon monoxide from a gas stream of a mixed gas comprising two or more components containing carbon monoxide are not particularly limited, but a PSA method is usually used. In the PSA method, the adsorbent used in the present invention is packed in a tower, and a mixed gas as a raw material is flowed under appropriate conditions to adsorb carbon monoxide. Then, it is desorbed under appropriate conditions.
The conditions for desorption are not particularly limited. For example,
At the same time as reducing the pressure from the adsorption pressure, purging a purified gas or a gas containing no other carbon monoxide or the like, or removing the carbon monoxide by heating and purging the gas, Regenerate the sorbent. One step
Although it is possible to simultaneously remove carbon monoxide, hydrocarbons, and the like in the raw material gas with a PSA device, ammonia, moisture, and carbon dioxide were previously removed with a PSA device filled with an adsorbent such as activated carbon. Thereafter, carbon monoxide can be removed by the method of the present invention.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

[0028]

EXAMPLES The ion exchange rates and adsorption capacities in the examples were measured by the following methods.

<Ion exchange rate> A sample was dissolved in a 1: 1 mixed solution of hydrofluoric acid and nitric acid, and then diluted with distilled water to a predetermined concentration. Thereafter, the concentration of each metal ion was identified using an ICP measuring device (Optima 3000) manufactured by PerkinElmer, and the equivalent ratio of the ions, for example, in the case of Li ions, was calculated as Li / (Li + Na + K).

<Adsorption Capacity> BELSOR, manufactured by Bell Japan
P 28SA measures the adsorption capacity of carbon monoxide at a temperature of 25 ° C. in the range of 0 to about 800 mmHg,
The carbon monoxide adsorption capacities of 38 mmHg and 760 mmHg were calculated respectively, and the carbon monoxide adsorption capacities in the pressure range were determined from these values. The adsorption capacity is represented by converting the volume of carbon monoxide adsorbed per 1 g of the adsorbent into a standard state at 0 ° C. and 1 atm.

<Adsorption Capacity Ratio of Carbon Monoxide / Nitrogen> The adsorption capacities of carbon monoxide and nitrogen were measured by the above method, and the adsorption capacity ratio was calculated by the following equation.

Adsorption capacity ratio = (760 mmHg carbon monoxide adsorption capacity) / (760 mmHg nitrogen adsorption capacity) Example 1 An X-type zeolite with a low silica ratio and a skeleton having an Si / Al ratio of 1.0 was prepared as follows. The compound was synthesized according to the method disclosed in the public information publication No. 25527. The synthesis method is Al (OH) ₃
Was dissolved in 267 g of a 50% aqueous solution of Na to obtain solution-1. Next, 85% KOH in 1000 g of water
287 g of the pellet was dissolved, Solution-1 was added, and the mixture was cooled to 4 ° C. Further, sodium silicate (Na ₂ O: 9.6%,
(SiO ₂ : 30.9%) 453.25 g to 1131.7
g and diluted with the previous cooling solution. The obtained gel was aged at 36 ° C. for 3 days, and then heated to 70 ° C. for crystallization for 16 hours. The slurry was filtered and washed to obtain zeolite crystals. All peaks confirmed by X-ray diffraction for the obtained zeolite powder were due to faujasite-type zeolite, and no other zeolite peak was found. The chemical composition determined by ICP analysis was such that the Si / Al ratio was 1.0.

The binder component is added at a ratio of about 20 to 100 of zeolite on a dry weight basis,
The resulting zeolite molded body was shaped into a spherical shape having an average particle diameter of 1.6 mm in diameter, and the obtained zeolite molded body was heated with dry hot air at 650 ° C. to sinter the binder.

The obtained zeolite compact was packed in a column, and ion-exchanged by flowing a 1N aqueous solution of LiCl at a temperature of 60 ° C. to obtain 95% of ion-exchangeable cations.
Was ion-exchanged to lithium ion. The remaining ions are
Sodium ions were 3% and potassium ions were 2%.

The ion-exchanged compact was heated with 400 ° C. dry hot air to desorb water and activate. After the activation was completed, the molded zeolite was stored in a metal container in which air was shut off, cooled, and then activated again at 350 ° C. for 2 hours under vacuum in an adsorption capacity measuring device to measure the adsorption capacity. Table 1 shows the results of the test.

Example 2 The same operation as in Example 1 was performed except that the ion exchange rate of lithium was 86%. The remaining ions were 11% sodium ions and 3% potassium ions. Table 1 shows the results of the test.

Example 3 The same operation as in Example 1 was performed except that the solution used for ion exchange was a 1N aqueous NaCl solution. 98% of the ion-exchangeable cations were exchanged for sodium ions, and the remaining ions were potassium ions for 2%. Table 1 shows the results of the test.

Example 4 The same operation as in Example 1 was performed except that the solution used for ion exchange was a 1 mol / L calcium chloride aqueous solution. 80% of the ion-exchangeable cations were ion-exchanged with calcium ions, and the remaining ions were 17% sodium ions and 3% potassium ions. Table 1 shows the results of the test.

Example 5 The same operation as in Example 4 was performed except that the calcium exchange rate was 92%. The remaining ions were 6% sodium ions and 2% potassium ions. Table 1 shows the results of the test.

Comparative Example 1 A commercially available zeolite compact (binderless pellet) (manufactured by Tosoh Corporation) of CaX (the Si / Al ratio of the skeleton is 1.25) was chemically analyzed by ICP to find that the ion exchangeable cation was Of these, 94% were calcium ions, and the remaining ions were 6% sodium ions. This zeolite compact was tested in the same manner as in Example 1. The results are shown in Table 1.

[0041]

[Table 1]

Claims (7)

[Claims] 1. A method for removing carbon monoxide from a mixed gas by contacting a mixed gas comprising at least two types of components containing at least carbon monoxide with zeolite, wherein the Si / Al atomic ratio of the zeolite skeleton is substantially reduced. 1.0, wherein the cation after ion exchange of the zeolite is a combination of two or more kinds selected from alkali metals, alkaline earth metals, transition metals and rare earth metals; The adsorption capacity difference (ba) between the carbon monoxide adsorption capacity (a) at 760 mmHg and the carbon monoxide adsorption capacity (b) at 38 mmHg at 1 ° C. is 17.0 Nm.
A method for adsorbing and separating carbon monoxide from a gas stream using a zeolite having a characteristic of not more than 1 / g and having a Langmuir constant of an adsorption isotherm at 25 ° C. of 3.3 × 10 ⁻² mmHg ⁻¹ or less. . 2. The method for adsorbing and separating carbon monoxide according to claim 1, wherein zeolite having an adsorbing capacity ratio of carbon monoxide to nitrogen of 1.6 or more is used to adsorb and separate carbon monoxide from a gas stream. how to. 3. The method for adsorbing and separating carbon monoxide according to claim 1, wherein the ion-exchangeable cation of zeolite is lithium, sodium, potassium, calcium,
A method for adsorbing and separating carbon monoxide from a gas stream using zeolite, which is a combination of strontium and barium. 4. The method for adsorbing and separating carbon monoxide according to claim 1, wherein the ion-exchangeable cation of the zeolite is a combination of lithium, potassium and sodium, and the ion exchange rate of lithium is 80%. A method for adsorbing and separating carbon monoxide from a gas stream using the above zeolite. 5. The method for adsorbing and separating carbon monoxide according to claim 1, wherein the ion-exchangeable cation of zeolite is a combination of sodium and potassium, and the ion exchange rate of sodium is 80% or more. A method of adsorbing and separating carbon monoxide from a gas stream using a zeolite having an adsorption capacity ratio of carbon monoxide to nitrogen of 2.5 or more. 6. The method for adsorbing and separating carbon monoxide according to any one of claims 1 to 3, wherein the ion-exchangeable cation of the zeolite is a combination of calcium, potassium and sodium, and particularly, the ion exchange rate of calcium is 50%. % Zeolite is used to adsorb and separate carbon monoxide from a gas stream. 7. The method for adsorbing and separating carbon monoxide according to claim 1, wherein the macropores have an average pore diameter of 0.1 μm.
A method for adsorbing and separating carbon monoxide from a gas stream using a zeolite compact having a pore volume of 0.2 cc / g or more.