JP7202220B2 - oxygen adsorbent - Google Patents

Description

TECHNICAL FIELD The present invention relates to an oxygen adsorbent, and more particularly to an oxygen adsorbent comprising a perovskite oxide having high adsorption performance over a wide temperature range.

Conventionally, a pressure swing adsorption method (PSA method) is known as one method for separating oxygen from a mixed gas containing oxygen. This PSA method is a method of separating oxygen from a mixed gas containing oxygen by utilizing the fact that the amount of oxygen adsorbed by an oxygen adsorbent depends on the partial pressure of oxygen.

More specifically, in the PSA method, a mixed gas containing oxygen is introduced into an adsorption tower filled with an oxygen adsorbent, and oxygen in the mixed gas is selectively transferred to the oxygen adsorbent under predetermined temperature and pressure conditions. Along with the adsorption, the mixed gas after oxygen has been adsorbed on the adsorbent is discharged from the adsorption tower, and then the pressure in the adsorption tower is reduced to desorb (also referred to as desorption) the oxygen from the oxygen adsorbent. , the oxygen is discharged from the adsorption tower and recovered.

In recent years, it has been proposed that various perovskite-type oxides are useful as oxygen adsorbents in the above-described PSA method (see Patent Document 1).

Specifically, for example, the composition formula La _1-x Sr _x Co _1-y Fe _y O _3-z (wherein x, y and z are 0.05≦x≦1.0 and 0≦y≦ is a number that satisfies 0.95 and z>0, where z indicates the amount of oxygen deficiency.

Furthermore, the composition formula Sr _1-x Ca _x FeO _3-σ (wherein x and σ are numbers satisfying 0.12≦x≦0.40 and 0≦σ≦0.5, respectively, and σ is an oxygen deficiency A less expensive oxygen adsorbent composed of a perovskite-type oxide (hereinafter sometimes referred to as “SCaF”) represented by the following formula has been proposed. It is known that this SCaF does not contain expensive elements such as lanthanum and yet has excellent oxygen adsorption performance (see Patent Document 2).

In the PSA method, such an oxygen adsorbent comprising a perovskite-type oxide is usually formed into a compact such as a pellet, which is packed into an adsorption tower for use. However, when many perovskite-type oxides, including SCaF, are packed in an adsorption tower and heated, they are not heated to the same temperature depending on the position where they are packed in the adsorption tower. The inventors have found that the adsorption performance is significantly reduced in some regions.

JP-A-2005-87941 JP 2017-64673 A

Therefore, the present inventors have made intensive research to solve the above-mentioned problems in the oxygen adsorbent made of SCaF, and as a result, have made SCaF have a certain amount of barium and have high crystallinity perovskite type The inventors have completed the present invention by discovering that oxygen adsorbents made of oxides have substantially constant high oxygen adsorption performance over a wide temperature range. That is, the present invention provides an oxygen adsorbent that exhibits high oxygen adsorption performance almost constantly over a wide temperature range, usually in the range of 500 to 800°C, preferably in the range of 550 to 700°C. With the goal.

According to the present invention, the composition formula (I)
Sr _(1-xy) Ca _{x Bay Fe z O 3-δ}
where x, y and z are respectively 0.1500≦x≦0.3000,
0.0002≤y≤0.0140 and 0.9775≤z≤1.0000
is a number that satisfies the following conditions, δ is the amount of oxygen deficiency, and is composed of a perovskite oxide, and the crystallite size of the (110) plane obtained from X-ray diffraction measurement is 700 Å or more.

The oxygen adsorbent according to the present invention comprises a perovskite-type oxide having the above composition formula (I), that is, strontium calcium barium ferrate, and has a crystallite size of 700 Å or more in the (110) plane obtained from X-ray diffraction measurement results. Since it has high crystallinity, it has almost constant high oxygen adsorption performance over a wide temperature range, usually in the range of 500 to 800°C, preferably in the range of 550 to 700°C.

As an example, a process for measuring the oxygen adsorption amount of the oxygen adsorbent at a temperature of 600° C. is shown. 1 shows a powder X-ray diffraction pattern of an oxygen adsorbent made of a perovskite oxide according to Example 1 of the present invention.

The oxygen adsorbent according to the present invention has a composition formula (I)
Sr _(1-xy) Ca _{x Bay Fe z O 3-δ}
where x, y and z are respectively 0.1500≦x≦0.3000,
0.0002≤y≤0.0140 and 0.9775≤z≤1.0000
is a number that satisfies , δ is the amount of oxygen deficiency, and is composed of a perovskite-type oxide, and the crystallite size of the (110) plane obtained from X-ray diffraction measurement is 700 Å or more.

The oxygen adsorbent according to the present invention has, as a first feature, generally a perovskite-type oxide (strontium ferrate) having an _ABO3 structure having strontium at the A site and iron at the B site. Part of the strontium is replaced by barium as well as calcium. That is, in the SCaF, part of the A-site element strontium is further substituted with barium at a predetermined ratio.

SCaF is a perovskite-type oxide represented by the composition formula SrFeO _3-δ , in which part of the A-site element strontium is replaced with calcium having an ionic radius smaller than that of strontium at a predetermined ratio. Ions are considered to be difficult to diffuse. This is considered to be due to the fact that the perovskite-type oxide has a smaller unit cell (also referred to as a unit lattice or unit cell).

Here, the oxygen adsorbent comprising the perovskite-type oxide represented by the composition formula (I) according to the present invention is the SCaF, in which part of the A-site element strontium is added to calcium, and further at a predetermined ratio Strontium is replaced by barium, which has a larger ionic radius than strontium, and is thought to have a larger unit cell and higher oxygen adsorption performance. However, the present invention is not restricted by any theory.

In the perovskite-type oxide represented by the above composition formula (I), oxygen adsorption performance regardless of temperature when the calcium composition ratio x is less than 0.15 or when x is greater than 0.3000 inferior in

In the perovskite-type oxide represented by the above composition formula (I), when the composition ratio y of barium is less than 0.0002, it does not have high oxygen adsorption performance in a high temperature range of 700° C. or higher. When the composition ratio y of is greater than 0.0140, the oxygen adsorption performance is rather inferior regardless of the temperature.

In the perovskite-type oxide represented by the above compositional formula (I), when the iron composition ratio z is less than 0.9775, the oxygen adsorption performance is inferior regardless of the temperature, while it is greater than 1.0000. Oxygen adsorption performance is poor, especially in a high temperature range of about 700°C or higher.

In general, the physical properties of perovskite-type oxides having an _ABO3 structure are often discussed using the A/B ratio. Therefore, in the oxygen adsorbent Sr _{1-x-y Ca x} Bay Fe _z O _3-δ according to the present invention, the number of moles (composition ratio), i.e., 1/z, which is the A/B ratio, 1/z is
1.0000≤1/z≤1.0230
meet.

According to the present invention, in the oxygen adsorbent comprising the perovskite-type oxide represented by the composition formula (I), the composition ratio x of calcium, the composition ratio y of barium, and the composition ratio z of iron are preferably ,
0.2000≦x≦0.2500,
0.0003≦y≦0.0060 and 0.9775≦z≦0.9950 (i.e., 1.0050≦1/z≦1.0230)
is a number that satisfies
0.2300≦x≦0.2500,
0.0003≦y≦0.0060 and 0.9780≦z≦0.9950 (i.e., 1.0050≦1/z≦1.0225)
is a number that satisfies

Most preferably, in the above, the barium composition ratio y is 0.0003 ≤ y ≤ 0.0050
is a number that satisfies

Furthermore, in the present invention, the oxygen adsorbent comprising the perovskite-type oxide represented by the composition formula (I) has a (110) plane crystallite size of 700 Å or more obtained from X-ray diffraction measurement results. is necessary. When the crystallite size is smaller than 700 Å, the oxygen adsorption performance is low regardless of temperature.

In the perovskite-type oxide represented by the above composition formula (I), δ is the amount of oxygen deficiency, which is determined by stoichiometry and is a number that satisfies 0≦δ<3.

The oxygen adsorbent according to the present invention has substantially constant high oxygen adsorption performance over a wide temperature range, usually in the range of 500 to 800° C., preferably in the range of 550 to 700° C. concentration. , at a temperature of 600 ° C., the oxygen adsorption amount per unit weight (1 g) of the oxygen adsorbent is 10 cm ³ or more, and the oxygen adsorption amount per unit weight of the oxygen adsorbent at temperatures of 550 ° C., 650 ° C. and 700 ° C. is 600 ° C. 70% or more of the oxygen adsorption amount per unit weight of the oxygen adsorbent at °C. Therefore, the total amount of oxygen adsorption per unit weight of the oxygen adsorbent at temperatures of 550°C, 600°C, 650°C and 700°C is 31 cm ³ or more, and preferably 35 cm ³ or more.

In the PSA method, the oxygen adsorbent according to the present invention is a mixed gas containing oxygen at a temperature usually in the range of 500 to 800 ° C., preferably in the range of 550 to 700 ° C., typically oxygen in air. It is used for selective adsorption and subsequent desorption.

The perovskite-type oxide represented by the composition formula (I) according to the present invention can be produced by any of the conventionally known solid-phase method and liquid-phase method. For example, in the case of the solid-phase method, raw materials containing strontium, calcium, barium and iron, such as strontium carbonate, calcium carbonate, barium carbonate and iron oxide, are weighed so as to match the composition formula (I) above, and are dry-processed. Alternatively, after wet-mixing, the mixture is fired and pulverized to obtain a powder. Here, the powder preferably has a particle size of several hundred nanometers to several hundred micrometers. Raw materials containing strontium, calcium, barium and iron are not limited to the above.

The firing temperature is usually preferably in the range of 1000 to 1500°C. When the calcination temperature is too low, the crystallite size of the (110) face of the obtained perovskite-type oxide becomes small, and such a perovskite-type oxide has low oxygen adsorption performance. When the calcination temperature is too high, the specific surface area is lowered and the number of oxygen adsorption/desorption sites is reduced, which is not preferable.

EXAMPLES The present invention will be described more specifically below with reference to examples and comparative examples.

In the following, the X-ray crystal structure analysis of the obtained oxygen adsorbent was performed using an X-ray diffractometer (manufactured by Rigaku Co., Ltd., RINT TTR III, radiation source CuKα, monochromator, tube voltage 50 kV, current 300 mA, long slit PSA200 (Total length: 200 mm, design opening angle: 0.057 degrees), and measurement was performed under the following conditions.

Measurement method: Parallel method (continuous)
Scan speed: 2 degrees/minute Sampling width: 0.02 degrees 2θ: 20 to 80 degrees

The crystallite size was determined by the Scherrer method using integrated powder X-ray analysis software (manufactured by Rigaku Co., Ltd., PDXL-2).

Scherrer constant = 0.940
Standard sample: _SiO2

In addition, the oxygen adsorption amount of the obtained oxygen adsorbent was measured at 550 ° C., 600 ° C., 650 ° C. and 700 ° C. using a differential thermal thermogravimetric simultaneous measurement device (manufactured by Hitachi High-Tech Science Co., Ltd., STA7300). Measured at temperature.

As an example, FIG. 1 shows a process for measuring the oxygen adsorption amount of an oxygen adsorbent at a temperature of 600.degree. That is, the temperature of the oxygen adsorbent was raised to 800° C. under the flow of nitrogen gas in the above measuring apparatus, and was held for 30 minutes. After that, the temperature of the oxygen adsorbent was lowered to 600° C. and held for 30 minutes. After that, the circulating gas was switched to air. Air was circulated for 60 minutes to cause oxygen to be adsorbed on the oxygen adsorbent, and then the circulating gas was returned to nitrogen gas again and held for 60 minutes to desorb oxygen from the oxygen adsorbent. After oxygen was adsorbed on the oxygen adsorbent in this manner, the oxygen adsorption amount a per unit weight of the oxygen adsorbent was calculated from the amount of change in weight of the oxygen adsorbent when it was desorbed.

Then, the gas is switched to air again, held for 60 minutes, then returned to nitrogen gas, held for 60 minutes, and in the same manner as described above, oxygen is adsorbed by the oxygen adsorbent and then desorbed, The oxygen adsorption amount b per unit weight of the oxygen adsorbent was calculated from the weight change amount of the oxygen adsorbent at that time. The average value of the oxygen adsorption amounts a and b per unit weight of the oxygen adsorbent was defined as the oxygen adsorption amount per unit weight of the oxygen adsorbent at a temperature of 600°C.

Example 1
The ratio of each metal element represented by the composition formula Sr _1-xy Ca _x Ba _y Fe _z O _3-δ , that is, 1-xy, x, y and z, to the values shown in Table 1 Each required raw material was weighed and mixed so that

Specifically, strontium carbonate (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) 77.80 g, calcium carbonate (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) 17.39 g, barium carbonate (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) ) and 55.68 g of iron oxide (III) (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) were weighed into a 500 mL capacity resin pot. 225 mL of zirconia beads with a diameter of 1.0 mm and 150 mL of ion-exchanged water were added to the pot, and mixed using a planetary ball mill (manufactured by Fritsch, P-5) at a rotation speed of 210 rpm for 120 minutes, and then the zirconia beads were separated. . The water slurry thus obtained was heated at 110° C. to remove water and obtain a solid. This solid matter was pulverized in a mortar and passed through a sieve with an opening of 500 μm to obtain a raw material mixture as a powder.

The raw material mixture thus obtained was placed in a magnesia crucible, heated in an electric furnace in an air atmosphere at a temperature elevation rate of 200°C/hour from room temperature to 1350°C, held at this temperature for 5 hours, and fired. Thereafter, the mixture was cooled to normal temperature at a temperature-lowering rate of 200° C./hour to obtain strontium-calcium-barium ferrate as a fired product.

An X-ray diffraction measurement was performed on the fired product. As shown in FIG. 2 for its powder X-ray diffraction pattern, it was confirmed that the fired product consisted of a single perovskite oxide phase.

Also, the above X-ray diffraction measurement results were analyzed using an integrated powder X-ray analysis software to determine the crystallite size of the (110) plane diffraction line appearing between 32° and 33° 2θ. Table 1 shows the results.

Furthermore, the oxygen adsorption amount per unit weight at each temperature of 550 ° C., 600 ° C., 650 ° C. and 700 ° C. of the obtained oxygen adsorbent, the total amount of the oxygen adsorption amount per unit weight at each temperature, Table 1 shows the ratio of the oxygen adsorption amount per unit weight at temperatures of 550°C, 650°C and 700°C to the oxygen adsorption amount per unit weight at a temperature of 600°C.

Examples 2-4
Strontium calcium barium ferrate was fired in the same manner as in Example 1 except that strontium carbonate, calcium carbonate, barium carbonate and iron (III) oxide were weighed and mixed so that the composition ratio shown in Table 1 was obtained. obtained as

Along with the crystallite size of the (110) plane of the obtained strontium calcium barium ferrate, the oxygen adsorption amount per unit weight of the obtained oxygen adsorbent at temperatures of 550 ° C., 600 ° C., 650 ° C. and 700 ° C., and each of the above Table 1 shows the total amount of oxygen adsorption per unit weight at temperature and the ratio of the oxygen adsorption amount per unit weight at temperatures of 550°C, 650°C and 700°C to the oxygen adsorption amount per unit weight at a temperature of 600°C. .

Comparative Examples 1-4
Strontium calcium barium ferrate was fired in the same manner as in Example 1, except that strontium carbonate, calcium carbonate, barium carbonate, and iron (III) oxide were weighed and mixed so that the composition ratios shown in Table 1 were obtained. obtained as an object.

Comparative example 5
Strontium carbonate, calcium carbonate, barium carbonate and iron oxide were weighed and mixed so that the composition ratio shown in Table 1 was obtained. Strontium calcium barium was obtained as a fired product.

Per unit weight of the obtained oxygen adsorbent at temperatures of 550 ° C., 600 ° C., 650 ° C. and 700 ° C. and the total amount of oxygen adsorption per unit weight at each temperature, and the oxygen adsorption per unit weight at temperatures of 550 ° C., 650 ° C. and 700 ° C. with respect to the oxygen adsorption amount per unit weight at a temperature of 600 ° C. Amount percentages are shown in Table 1.

Comparative Example 1 shows an oxygen adsorbent made of SCaF, which has a small oxygen adsorption amount at 650 to 700°C. In contrast, all of the oxygen adsorbents according to Examples 1 to 4 according to the present invention have an oxygen adsorption amount per unit weight at 600°C exceeding 10 cm ³ and a unit of oxygen adsorption amount at a temperature of 600°C. The ratio of the oxygen adsorption amount per unit weight at temperatures of 550 ° C., 650 ° C. and 700 ° C. to the oxygen adsorption amount per weight is 70% or more. The total amount of oxygen adsorption per weight is 35 cm ³ or more.

In the oxygen adsorbent according to Comparative Example 2, the composition ratio y of barium in the perovskite-type oxide exceeds the upper limit specified in the present invention. significantly inferior in

All of the oxygen adsorbents according to Comparative Examples 3 to 5 have a barium composition ratio y within the range defined by the present invention. However, in the oxygen adsorbent according to Comparative Example 3, the iron composition ratio z is larger than the upper limit specified by the present invention, and the oxygen adsorption amount in the high temperature range (700° C.) is extremely small.

On the contrary, the oxygen adsorbent according to Comparative Example 4 has an iron composition ratio z smaller than the lower limit specified by the present invention, and is inferior in oxygen adsorption performance in the range of 550 to 700° C. regardless of the temperature.

In the oxygen adsorbent according to Comparative Example 5, both the composition ratio y of barium and the composition ratio z of iron are within the ranges specified by the present invention, but the crystallite size is smaller than the lower limit specified by the present invention. , in the range of 550 to 700° C., the oxygen adsorption performance is inferior regardless of the temperature.

Claims (2)

Composition formula (I)
Sr _(1-xy) Ca _{x Bay Fe z O 3-δ}
where x, y and z are respectively 0.1500≦x≦0.3000,
0.0002≤y≤0.0140 and 0.9775≤z≤1.0000
is a number that satisfies the requirements, δ is the amount of oxygen deficiency, and is made of a perovskite-type oxide, and the crystallite size of the (110) plane obtained from X-ray diffraction measurement is 700 Å or more. 2. The oxygen adsorbent of claim 1, wherein x, y and z are each
0.2000≦x≦0.2500,
0.0003≤y≤0.0060 and 0.9775≤z≤0.9950
Oxygen adsorbent that is a number that satisfies

Images