JP2761471B2 - Nitrogen-selective zeolite adsorbent and nitrogen adsorption process using it - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zeolitic adsorbent for selectively adsorbing nitrogen, which is used in a process for separating nitrogen from air or the like, and a recycle process for nitrogen separation using the adsorbent.

[0002]

BACKGROUND OF THE INVENTION Separation of the two major components of air, nitrogen and oxygen, is an important industrial project that produces hundreds of billions of cubic feet each year. If large amounts of either nitrogen or oxygen components are required, such as oxygen in the steel industry, for example, the cost of using a cryogenic system for their separation has been paid. Oxygen and nitrogen can also be created by a pressure swing adsorption (PSA) process if the required amount of one of the components is reduced. In this PSA process, compressed air is fed through a fixed bed of adsorbent that has preferential adsorption for one of the feed components. An effluent product stream having an increased concentration of non-adsorbed or low-adsorbed components is then obtained. The PSA process has relatively simple equipment and relatively easy maintenance compared to the low-temperature process, but the solution is a problem because the product recovery rate is low and the energy consumption is high. Has become.

[0003] Crystalline zeolitic molecular sieves which selectively adsorb nitrogen, especially nitrogen from air, are known in the art. For example, U.S. Pat. No. 3,409,931 proposes the use of a 4.6 Angstrom type zeolite. U.S. Pat.No.3140932 includes strontium,
The use of zeolite X comprising at least one cation of barium or nickel has been proposed.
U.S. Pat. No. 3,140,933 discusses the advantages of various alkali metal cations of zeolites, including zeolite X. U.S. Pat. No. 4,577,736 includes Zeolite X
Are taught as preferred adsorbents for the adsorption of nitrogen from air. U.S. Patent No. 4,481,018 discloses activation conditions that are substantially free of ionic hydrolysis of the framework and polyvalent cation forms of faujasite. These compositions are particularly suitable for Mg ²⁺ , Ca ²⁺ , S
In the case of r ²⁺ and / or Ba ²⁺ cation form, it is regarded as an excellent adsorbent for separating nitrogen from air. From the value indicating the selectivity N ₂ and O ₂ derived from the study by gas chromatography, Ca ²⁺ in the above U.S. Pat. No. 4,481,018
It teaches that the higher the degree of exchange, the greater the selectivity and capacity of the faujasite adsorbent for the separation of nitrogen from air. The minimum content of calcium disclosed in this patent is 50%, the preferred adsorbent is 80%
Contains more than equivalent calcium cations. As described above, in the prior art, calcium, strontium, and lithium cation are considered to be desirable components of the zeolite adsorbent used for nitrogen separation.
Other cations, such as sodium, have not been found to be desirable.

[0004]

SUMMARY OF THE INVENTION The present invention provides a novel composition of zeolitic adsorbent having excellent selective adsorptivity for nitrogen used in a PSA process using a mixture of oxygen and nitrogen, particularly air. It is an object of the present invention to provide an industrially excellent circulating nitrogen adsorption process using an adsorbent.

[0005]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventor has conducted intensive studies and found that Si / A of zeolite X was used.
The molar ratio of l ₂ are particularly at 2.0 to 2.4, 60-89 Suitable 60-80 equivalent percent Ca ⁺⁺ cations, from 10 to 40 equivalent percent of Na ⁺ cations and 0 equivalent% of K ⁺ cations With ions, Ca ⁺⁺ , Na ⁺ and K ⁺
A zeolite X containing a charge-balanced cation having a total cation equivalent of at least 90% at a temperature of 50 to -20 ° C;
In the separation of air in a pressure swing adsorption process of 5 to 506.5 kPa (0.05 to 5.0 atm), the exchange rate of calcium is surprisingly far greater than that of zeolite X exchanged at a lower or higher exchange rate than this calcium. I found that there is. Further, an adsorption bed containing the above zeolite X as an adsorbent is provided, and at a temperature of -20 ° C to 50 ° C, the pressure in the bed is increased to 13.8 to 506.8 kPa (2 to 73.5 psia), and nitrogen is removed from the zeolite. A mixture of nitrogen and oxygen is pumped into the bed until the adsorbent selectively adsorbs, the unadsorbed oxygen is discharged from the bed at the adsorption pressure, and the adsorbed nitrogen is desorbed and desorbed from the bed The bed pressure should be 101.4-0.7 kPa (14.7-0.1
In the step of reducing the final desorption pressure of psia), a circulating process for separating nitrogen from a mixture of nitrogen and oxygen was carried out to achieve a very industrially superior nitrogen separation method.

According to the present invention, the molar ratio of SiO ₂ / Al ₂ O ₃ is 2.0
2.42.4 framework, and 60-89 equivalents of Ca ⁺⁺ cation, 10-40 equivalents of Na ⁺ cation,
Containing ~ 10% (excluding 0)% K ⁺ cations and Ca
^++, the molar ratio of the zeolite X or SiO ₂ / Al ₂ O ₃ Total cation equivalents of Na ⁺ and K ⁺ is at least 90% 2.0
2.35, a framework comprising 65 to 80 equivalent% of Ca ⁺⁺ cation, and 20 to 35 equivalent% of zeolite X which is a Na ⁺ cation and is substantially free of K ^+. A zeolite adsorbent for selectively adsorbing nitrogen from a mixture of oxygen and nitrogen used in a circulating pressure swing adsorption process, and (a) a skeleton having a SiO ₂ / Al ₂ O ₃ molar ratio of 2.0 to 2.4. And 60-89 equivalent% of the Ca ⁺⁺ cation,
Consists of zeolite X containing 0-40 equivalent% Na ⁺ cations and 0-10% K ⁺ cations and having a total cation equivalent of at least 90% of Ca ⁺⁺ , Na ⁺ and K ^+. A step of providing a zeolitic adsorbent on the adsorption bed,
Increasing to 506.8 kPa (2-73.5 psia) and feeding a mixture of nitrogen and oxygen into the adsorbent bed at a temperature of -20 ° C to 50 ° C until nitrogen is selectively adsorbed on the adsorbent; (c E) discharging the non-adsorbed oxygen as a product from the adsorbent bed at substantially the adsorbent pressure, and (d) desorbing the adsorbed nitrogen and bringing the bed pressure to a final pressure of 101.4-0.7 kPa (14.7-0.1 psia). Discharging nitrogen from the bed by reducing to desorption pressure,
A cyclic process for selectively adsorbing nitrogen from a mixture of oxygen and nitrogen.

[0007]

DETAILED DESCRIPTION OF THE INVENTION nitrogen has a quadrupole moment of 0.31A ³ (quadrupole moment), to react more strongly than oxygen there is only quadrupole moment of about 0.10 A ³ and zeolitic cations Are known. Nitrogen is selectively adsorbed on zeolites from a mixture of nitrogen and oxygen by thermodynamic principles. This selectivity for nitrogen adsorption is the basis for many air separation processes using a fixed bed pressure swing adsorption-desorption cycle. The nature of these zeolitic cations is the most important factor related to the selectivity and adsorption capacity of nitrogen adsorption. It is also known that lithium and calcium as zeolite cations have a particularly strong affinity for nitrogen.

[0008] Calcium exchangers of zeolite X show the effect of increasing calcium content in US Pat.
Reported in Issue 018. The patent states that a calcium cation content of greater than about 80 equivalent% would provide better selectivity and adsorption capacity. The improvement in nitrogen adsorption efficiency is attributed to the fact that the calcium and other polyvalent metal cations of the zeolite X used are in a predominantly dehydrated / dehydrated state. According to these teachings, the higher the content of a particular metal cation, the better the performance of air separation, if the zeolite in the particular metal cation form exhibits excellent adsorptivity for nitrogen. Is a general understanding of those skilled in the art. However, in the case of zeolite X in the form of calcium exchange, peak performance in air separation under constant temperature and pressure conditions cannot be obtained when the calcium content is maximum, and the degree of calcium exchange is 60 to 89 equivalent%, particularly , 65-80 equivalent% is unexpected. Even more surprising is that the effect provided by lowering the calcium exchange level is due to the X ₂ zeolite SiO ₂ / Al ₂
It was found that the O ₃ ratio was between 2.0 and 2.4. From the above, the conventional theory considers that the charge density of the calcium cation was too much emphasized without giving due consideration to other factors. At least for the zeolite X in the calcium exchanged form represented by CaNaX, the nitrogen selectivity and capacity depend on the composition and zeolites of the cation and the temperature and pressure conditions when the adsorbent and nitrogen-containing gas are contacted. It is a complicated function. Thus, the nitrogen selectivity of CaNaX compositions reported in the prior art is often measured by chromatographic techniques at very low nitrogen pressures on the adsorbent.
Since the nitrogen selectivity of CaNaX is sensitive to pressure,
The reported high values of selectivity are not applicable at high pressures. The present invention is based, at least in part, on the finding that, depending on the level of calcium exchange, the nitrogen selectivity of CaNaX may decrease significantly with increasing pressure. In addition, the pressure used in the separation step of an actual, industrial-scale air separation process is considerably higher than the nitrogen pressure as measured by chromatographic techniques. Thus, the selectivity measured by chromatographic methods has little relevance to the adsorption step in an industrial pressure swing adsorption process. In the PSA air separation process, adsorption is a necessary step in the process. An efficient adsorbent must minimize the desorption interval and minimize the nitrogen load during it in order to regenerate the adsorbent with minimal use of vacuum pumps and oxygen products. In other words, in order to achieve an efficient desorption step in the PSA air separation process, the adsorbent needs to desorb or have a low nitrogen affinity at the discharge pressure. The high nitrogen selectivity observed by chromatography suggests that such adsorptive properties have low desorption properties in the PSA process, as the nitrogen pressure by chromatographic measurements is well within the desorption pressure in PSA air separation processes. doing.

Ideally, to effect PSA air separation, the adsorbent should exhibit a low nitrogen affinity at low pressures and a high nitrogen affinity at high pressures. Theoretically, it is not possible to obtain such a nitrogen adsorbent, as has been confirmed in experiments. Thus, the next best are adsorbents whose nitrogen selectivity does not drop sharply with increasing adsorption pressure. In the present invention, Ca
For NaX adsorbents, the decrease in nitrogen affinity with increasing nitrogen pressure is highly dependent on the level of calcium ion exchange. High calcium X, such as 90 equivalent% or more, has a sharp decrease in nitrogen affinity. Ca ⁺⁺ level 60 ~ 8
At 9% CaNaX, the affinity for nitrogen at very low pressures is not very high and does not decrease with increasing pressure. As a result, the operational nitrogen selectivity of moderate calcium exchanged CaNaX may be higher than CaX with higher levels of calcium exchange. More importantly, at the desorption pressure, nitrogen is readily desorbed from moderately ion exchanged CaNaX, making regeneration of the adsorbent much easier. As a result, the overall performance of the particular CaNaX composition used in the present invention is higher than that of CaX with higher levels of ion exchange. The evaluation of a substance as a PSA air separation adsorbent needs to take into account the following three criteria. 1. At the desorption pressure, the residual nitrogen load, which is the nitrogen load, the excellent PSA air adsorbent has a low residual nitrogen load. 2. The nitrogen delta loading, which is the difference between the loading at the adsorption pressure and the loading at the desorption temperature, is high for a good PSA air separation adsorbent. 3. Operational selectivity, defined as the nitrogen delta load divided by the oxygen delta load. In the case of an excellent air adsorbent, the operation selectivity to nitrogen is high.

The temperature at which this process is performed is an important factor in the performance of the adsorbent in air separation. Industrial PSA air separation vessels are usually very large and the process circulation time is short compared to the time required to heat and cool large volumes of adsorbent. Thus, the process circulation is performed under adiabatic or near adiabatic conditions, and CaNa
The heat of adsorption of nitrogen on X zeolite is noteworthy. The heat released by adsorption is forwarded by the feedstock and product gas and is accumulated to form a thermal front. Some of this thermal front may exit the tower with the product gas. The rest of the front is pushed back during the desorption phase of the circulation process. During desorption, kinetic energy is consumed to release nitrogen from the adsorbent. Therefore, the temperature of the nitrogen and the adsorbent decreases. The heat of desorption creates a cold front in the floor, some of which exit the floor with the exhaust gas. The remainder of the cold front is pushed back through the column by the feed gas during the next adsorption step. After many adsorption-desorption cycles, a stable state is created. In the steady state, a part of the floor has a considerably lower temperature than the surrounding area. Therefore, it is necessary to use an adsorbent whose adsorption performance is not significantly impaired by changes in temperature. The present invention is based in part on the finding that although the adsorption performance of zeolite X in a highly calcium-exchanged form is significantly impaired by lowering the temperature, such a decrease is not observed with moderately ion-exchanged CaNaX. Based on knowledge. A moderate decrease in the adsorption temperature also significantly increases the residual nitrogen load and results in a decrease in the nitrogen operation selectivity of X zeolites with high levels of calcium exchange. The present invention also provides that adiabatic desorption can be achieved with CaNa for CaX with high ion exchange levels.
Causes a greater temperature drop than X.

In the PSA air separation process, adsorbent productivity is determined not only by nitrogen delta loading and nitrogen operation selectivity, but also by the length of circulation time. The more the adsorbent can perform its function in a short time, the better the productivity will be. The circulation time is determined by how quickly the adsorbent regenerates and can be used in the next adsorption step. Nitrogen was found to desorb faster from medium exchange level CaNaX than from high exchange level CaX. In short, taking into account the PSA air separation conditions, it was found that CaNaX with a medium calcium exchange level was a better adsorbent than CaX with a high exchange level. The characteristics and specific examples of the present invention are shown in Tables 1 to 5 and graphs in FIGS. In order to obtain this data, the following adsorbent compositions, their production methods and test means were used.

Preparation of Starting Zeolite X Composition The molar ratio of the framework Si / Al ₂ is 2.0, 2.3, respectively.
And 2.5 samples of zeolite X were prepared. Si / Al
₂ The sample with a molar ratio of 2.0 is in Na ⁺ -K ⁺ cation mixed form, for example NaKX 2.0, according to the technique disclosed in GB 1580928, sodium hydroxide, potassium hydroxide, sodium silicate, It was synthesized by a hydrothermal reaction at a temperature of 70 ° C. using aluminum hydroxide and water as reagents. When first crystallized, NaKX 2.0 contained about 25 equivalent% of K ⁺ cations, the remainder being Na ⁺ cations. Almost all K ⁺ cations were removed and exchanged for Na ⁺ cations by complete ion exchange with a NaCl solution. Some of the testing procedures were performed with pure, ie, unbound, zeolite samples, while other tests used bound agglomerates. In the latter case, the binding material is Attapulgite, obtained from Floridin under the trade name Minugel.
It is a type clay. This agglomerate in the form of beads and extruded pellets was produced by methods known in the art.

To produce a partially calcium exchanged sorbent, a batch exchange technique was used. The powdered or agglomerated zeolite was immersed in a calcium chloride solution at 80-95 ° C with stirring. This operation lasted basically 1-2 hours. Calcium exchange levels were controlled by the amount of zeolite and calcium chloride used. To produce high zeolite X fractions with high calcium exchange levels, a repetitive batch exchange technique using large amounts of calcium chloride was used. A column exchange method was used to produce a high exchange mass. The zeolite agglomerate was placed in a heated column and the preheated calcium chloride solution was passed through the column to exchange and flush the exchanged sodium and potassium. The details of this exchange means will be shown in the following embodiments.

[0014]

Example 1 This example describes the preparation and adsorbent properties of a CaNaX composition with a 2.0 Si / Al ₂ framework ratio. These compositions are called CaNaX 2.0.
Samples of CaNaX2.0 were prepared by batch ion exchange of agglomerates combined with NaX2.0 clay in the form of 8 × 12 beads, generally yielding 50 grams of starting material NaX2.0 beads (dry weight), It was added to 0.15 moles of aqueous CaCl ₂ solution 1-2 liters was adjusted to pH 9.0 with Ca (OH) _2. In each case, the exact amount and concentration of the CaCl ₂ solution was chosen in light of the target degree of Ca ⁺⁺ ion exchange to be achieved. If necessary, multiple ion exchange steps were performed to obtain a product with the desired degree of ion exchange. At each batch exchange, the beads containing the zeolite were stirred in the CaCl ₂ solution, the solution was raised from room temperature to 90 ° C., and then stirring was continued for 1 hour. The ion-exchanged beads are collected by filtration using a Buckner funnel.
The mixture was washed with 50 ml of hot water adjusted to pH 9.0 by adding Ca (OH) ₂ . Thereafter, the beads were stirred for 30 minutes in 1 liter of water adjusted to pH 9.0 with Ca (OH) ₂ at 90 ° C., collected by filtration and dried in air. In total, seven samples were prepared, shown below as 1a-1g, and the specific data for the preparation and chemical composition of these products are shown in Tables 1 and 2 below, respectively. All of these clumped beads are 12
It contained a weight percent of clay binder.

[0015]

[Table 1]

[0016]

[Table 2]

[0017]

EXAMPLE 2 Six powder samples of calcium-exchanged NaX with a Si / Al ₂ molar ratio of 2.3 and two bead samples were prepared essentially according to the general procedure described in Example 1. did. The major difference in the means was the temperature of the ion exchanged medium, which was set at 95 ° C. compared to 90 ° C. in Example 1. Tables 1 and 2 show the ion exchange means and chemical compositions of these ion-exchanged products, which are numbered 2a to 2h below.

[0018]

Example 3 As-synthesized sodium zeolite X having a Si / Al ₂ molar ratio of 2.5 was used to ion exchange 8 × 12 beads bound with clay with Ca ⁺⁺ ions. Four samples indicated below with reference numerals 3a to 3d were manufactured. Samples 3a and 3b were ion exchanged using the batch method of Examples 1 and 2, and samples 3c and 3d were
The aqueous solution of CaCl ₂ was ion exchanged using a column method in which it passed through a heated column containing zeolite-containing beads. The ion exchange procedure and chemical composition of the ion exchanged products are shown in Tables 1 and 2, respectively.

[0019]

Example 4 The nitrogen and oxygen isotherms of the activated 1a-1g sample and the NaX 2.0 starting material of Example 1 were determined using Sartorius balance, at 40 ° C., 20 ° C., 0 ° C. and −
Determined at 20 ° C. The sample was activated by heating from room temperature to 510 ° C. in a glass tube over 10 hours in a system equipped with an oil diffusion pump and a liquid nitrogen trap and maintaining the final temperature for 6 hours. At the final stage of this activation means, a pressure of 1.33 × 10 to ⁶ kPa (1 × 10 to ⁵ Torr) was achieved. In measuring the nitrogen and oxygen isotherms, the temperature of each test sample was controlled by placing the sample chamber in a thermostat or tube furnace as needed.
In the range of 0 to 506.7 kPa (0 to 73.5 psia), 13 data
Set points. Exactly 10.7 to 101.4 kPa (1.55 and 14.7 psia) nitrogen loading is calculated by the interpolation method (intrapolatio
The determination was made using n). The difference between these two values is the nitrogen delta load. The oxygen loading at 25.5 kPa (3.7 psia) was also determined by interpolation. 25.5kPa (3.7psia) to 0kP
The nitrogen delta loading obtained from the oxygen delta loading in the range of a (0 psia) nitrogen delta loading shows a so-called operational selectivity. The values indicating the residual load, the delta load, and the operation selectivity are shown in Table 3 below, and are shown in FIGS.
Shown in

[0020]

[Table 3]

[0021]

Embodiment 5 According to the means shown in Embodiment 4, Embodiment 2
NaX numbered 2a to 2h, respectively
The residual nitrogen loading, nitrogen delta loading, and nitrogen operation selectivity of the 2.3 and CaNaX 2.3 samples were determined. Table 4 shows the results. All of these samples were unbound, that is, free of clay and zeolite granules. FIGS. 4, 5 and 6 show the residual loading and operating selectivity as a function of calcium exchange level and adsorption temperature.

[0022]

[Table 4]

[0023]

Embodiment 6 According to the means described in Embodiment 4, N
The aX2.5 and CaNaX2.5 samples 3a, 3b and 3c were tested for residual nitrogen loading, nitrogen delta loading and selectivity for nitrogen operation. Table 5 shows the results. Figures 7, 8 and 9 show the residual loading and operating selectivity as a function of calcium exchange level and adsorption temperature.

[0024]

[Table 5]

[0025]

Example 7 In order to evaluate the desorption time required for the adsorbent in the PSA circulation, the nitrogen desorption rate was measured using Sartorius Balance. The activated adsorbent was first contacted with nitrogen under a pressure of 101.3 kPa (1 atm).
After reaching the adsorption equilibrium, the gas was rapidly evacuated with a vacuum pump. The pump down step was aborted when the pressure dropped to 1.4 kPa (0.2 psia). It took about 10 seconds to reach this pressure. Next, the adsorbent was allowed to reach an equilibrium state, and the weight loss of the adsorbent was continuously observed. The final pressure at the Sartorius balance is related to the adsorption capacity of the adsorbent. For CaNaX with different silica to alumina ratios and different calcium exchange levels, the final pressure ranges from 1.72 to 2.62 kPa (0.25 to 0.38 psia). Since nitrogen has a large heat of desorption, if it is rapidly desorbed under adiabatic conditions, the temperature of the adsorbent will drop sharply. Vacuum desorption within the Sartorius balance is very similar to adiabatic desorption. However, it is very difficult to measure the sample temperature directly within the salitria balance, and therefore the temperature after desorption is determined by measuring the residual load with the nitrogen isotherms of 20 ° C, 0 ° C, and -20 ° C, respectively. Was estimated by comparison.

(A) Nitrogen desorption curve of 1 g sample of Example 1 High calcium exchange level (97%) and Si /
FIG. 1 shows a nitrogen desorption curve of a 1 g sample of zeolite X having an Al ₂ molar ratio of 2.0. To obtain the data, the vacuum-activated sample was first equilibrated in a Sartorius balance using nitrogen under a pressure of 16.3 psia (112.4 kPa). The balance was rapidly reduced to a pressure of 1.38 kPa (0.2 psia) to allow the sample to reach equilibrium, after which the pressure increased to 2.62 kPa (0.38 psia). FIG. 10 also shows that by extrapolation from 10.3 to 2.62 kPa (1.5 to 0.38 psia), at temperatures of 20 ° C., 0 ° C., and −20 ° C.
The equilibrium nitrogen load at a pressure of 2.62 kPa (0.38 psia) is shown. From these data, the zeolite sample is cooled to around 0 ° C. when desorbed in Sartorius balance. (B) Using essentially the same procedure as in (a) above, a nitrogen desorption curve was determined for sample 1d of Example 1 containing 75 equivalent% calcium cations. Figure out these data
See Figure 11. The final nitrogen pressure within the balance is 1.72 kPa (0.2
At 5 psia), the residual loading was around 0.09 mmol / gm. This is also shown in FIG. 11 at a temperature of 20 ° C., 0 ° C., and −20 ° C., respectively, under a pressure of 1.72 kPa (0.25 psia) (by extrapolation from 10.3 kPa (1.5 psia)). From the expected equilibrium nitrogen loading of this sample, the sample is cooled to a temperature of the order of 10 ° C. during desorption. (C) Using the same means as in (a) above, the nitrogen desorption curve of sample 2h of Example 2 containing 97 equivalent% of calcium cation was determined. These data are shown in FIG. Final nitrogen pressure within the balance is 2.55 kPa (0.37 psia)
The residual load was about 0.38 mmol / gm. This is also Figure 1
The equilibrium nitrogen load at a pressure of 2.55 kPa (0.37 psia) and a temperature of 20 ° C., 0 ° C., and −20 ° C., respectively, in the range of 10.34 to 2.55 kPa (1.5 psia to 0.37 psia) as shown in Figure 2. Extrapolated from This sample is cooled to a temperature of the order of 3 ° C. during desorption. (D) Using the same means as in (a) above, a nitrogen desorption curve of 2 g of the sample of Example 2 containing 77 equivalent% of calcium cation was determined. These data are shown in FIG. The final nitrogen means within the balance is 1.93 kPa (0.28 psia)
The residual load was 0.07 mmol / gm. 10.34 to 1.93kPa
(1.5 psia to 0.28 psia) extrapolated from the range of 1.93 kPa (0.28 psia) and 20 ° C., 0
Figure Estimated equilibrium nitrogen loading at -20 ° C and -20 ° C
See Figure 13. From these data, the sample is cooled to a temperature on the order of 5 ° C. during desorption. (E) Using the same means as in (a) above, the nitrogen desorption curve of sample 3d of Example 3 (containing 98 equivalent% calcium cation) was determined. These data are shown in FIG. The final nitrogen pressure in the balance is 2.62 kPa (0.38 psia)
The residual load was about 0.18 mmol / gm. 10.34 ~ 2.62kP
a (1.5-0.38 psia) extrapolated from the range 2.
41 kPa (0.35 psia) pressure and 22 ° C, 30 ° C respectively
FIG. 14 shows the predicted equilibrium nitrogen load at −20 ° C. This sample is cooled to about -13 ° C during desorption. (F) Using the same means as in (a) above, the nitrogen desorption curve of sample 3b of Example 3 containing 77 equivalent% calcium cation was determined. These data are shown in FIG. The final nitrogen pressure in the vanlance was 56.88 kPa (8.25 psia) and the residual load was around 0.06 mmol / gm. This is also Figure 1
As shown in FIG. 5, from a pressure of 2.41 kPa (0.35 psia) and the expected equilibrium nitrogen loading at temperatures of 22 ° C. and 0 ° C., respectively, this sample dropped to a temperature of about 3 ° C. during desorption. . The expected equilibrium load is 10.34 to 1.72 kPa (1.5 psia to 0.2
It was determined by extrapolation from a range of 5 psia). The effectiveness of the adsorbent for air separation is measured by three parameters: nitrogen delta loading, nitrogen operation selectivity, and residual nitrogen loading at the desorption temperature. Taking these parameters into account, the data shown in the tables and figures of the specification, including the following specific observation data, clearly show the superiority of the present invention.

Table 3 shows the desorption data of Clay Bond X2.0. FIG. 1 shows the relationship between the residual nitrogen load and the level of calcium ion exchange. From these data, as the calcium cation level of the zeolite adsorbent increases,
It is clearly shown that the desorption of nitrogen becomes rapidly more difficult, thus increasing the residual load. calcium·
Above 90% levels, the residual nitrogen load becomes very high and product contamination becomes a serious problem. Residual nitrogen levels are also sensitive to temperature. The combination of the 90% calcium level and the operating temperature of 0 ° C. results in unacceptably high levels of residual nitrogen. Since cooling always occurs in the PSA process, these data indicate that calcium exchange of 90% or more can compromise the efficiency of X2.0 in multiple ways. FIG. 2 shows the CaNaX 2.0,10 as a function of calcium level and desorption temperature.
The delta loading of nitrogen in the pressure range of 1.3 to 10.69 kPa (14.7 and 1.55 psia) is shown. Initially, as the calcium content increases, so does the delta loading of nitrogen. When the delta load reaches the broad maximum, it then begins to fall. These data indicate that calcium exchange levels above 90% or below 60% are desirable. FIG. 3 shows the operational selectivity of X2.0 as a function of calcium exchange and temperature. This is a clear example of how temperature overwhelms the effects of cations. At 40 ° C., the nitrogen operation selectivity increases with increasing calcium content. It peaks when the Ca ⁺⁺ exchange level is on the order of 85% and then begins to fall.
At 20 ° C, peak operation selectivity is 60-80 for calcium content
%. If the temperature is below 0 ° C,
NaX2.0 shows higher operation selectivity than CaNaX2.0. −2
At 0 ° C., the nitrogen selectivity of CaNaX2.0 is much lower than NaX2.0. Table 4 shows the adsorption data of the X2.3 sample. FIGS. 4, 5 and 6 show delta loading and operating selectivity data of X2.3 as a function of calcium exchange level and adsorption temperature, respectively. Since these samples do not contain clay, their loading is higher than the corresponding combined samples. The results for the X2.3 samples are almost the same as the results for X2.0. More than 90% of the cations are Ca ⁺⁺
It is clearly undesirable to use a form of X2.3 and a process temperature of 0 ° C. It is desirable to use CaNaX 2.3 with a calcium level of at least 60%, and less than 90%, in order to achieve sufficient process circulation with fairly large temperature amplitudes. Normally, CaNaX2.3
Is less selective than the CaNaX 2.0 adsorbent. Join X
Table 5 shows the adsorption data of 2.5. These data show that the performance of the PSA adsorbent is single, along with the residual loading, delta loading, and operating selectivity shown in relation to the calcium exchange levels shown in FIGS. 7, 8 and 9, respectively. It is clearly shown that it is not determined solely by the structural parameters of. The silica: alumina ratio usually has the same important significance as the calcium level. As the calcium level increases, the nitrogen delta loading of X2.5 increases and the nitrogen manipulation selectivity decreases. This is basically the same as observed for X2.0 and X2.3, but with important differences in detail.
The nitrogen delta loading of CaNaX2.5 in the range of 60-90% is much lower than the corresponding X2.3 and X2.0. It is for these reasons that CaNaX 2.5 is not used in the practice of the present invention.

The data in FIG. 1 shows that as the calcium content in the zeolite increases, the 10.7 kPa (2.55 psia) residual or nitrogen load increases rapidly. The rate of increase is inversely proportional to the adsorption temperature. At 0 ° C,
The residual load of X2.0 with a calcium exchange level of 97% is 0.7
9 mmol / gm, this value is the delta loading (0.74 mmol / g
m) much higher. Therefore, it would be more difficult to produce pure oxygen using a CaX2.0 adsorbent at 0 ° C. At 20 ° C., its residual nitrogen load is 0.39 mmol / gm, which is high, but the sorbent works well with proper process cycles. On the other hand, when the calcium level is 76 equivalent%, the residual nitrogen load is 0.46 mmol / g at 0 ° C.
At m, this value is similar to the value of CaX at 20 ° C. 20
The residual loading of CaNaX 2.0 at 0 ° C is 0.25 mmol / gm.
CaNaX 2.0 (76%) is much more desirable because it can work at 0 ° C. In FIG. 2, the nitrogen delta loading at 0 ° C. is greatest at a calcium content of 75%. At 20 ° C. and 40 ° C., the peak is reached when the calcium content is around 90%. Based on the nitrogen delta load,
A 75% exchanged CaNaX 2.0 is a 97% exchanged CaX2.
It has a distinct advantage over zero. FIG.
At 20.degree. C. and 0.degree. C. show higher operational selectivity than CaNaX 2.0 with 97% exchange of CaNa 2.0 with a calcium exchange level of 76%. Based on these data, CaNaX2.
When 0 is used, setting of process conditions is much more free than when CaX2.0 is used. Referring to the desorption curves in FIG. 10 and FIG.
g [CaX2.0 (97% Ca)] sample 1d
It can be seen that it is six times [CaNaX2.0 (75% Ca)]. These data indicate that highly exchanged zeolites require longer times for regeneration as compared to lower exchange level compositions. Another important point suggested by these data is that after desorption, the highly exchanged material may have a lower temperature compared to the lower exchange level zeolite. Lowering the adsorption temperature causes similar problems as those experienced with zeolites with very high Ca ⁺⁺ exchange levels because they are very inefficient at low temperatures. C
aX 2.3 (97% Ca) nitrogen desorption curve and 2.55 kPa (0.37 psi)
The expected equilibrium adsorption capacity in a) is shown in FIG. CaNaX2.3
The desorption curve for (77% Ca) and the expected equilibrium adsorption capacity at 1.72 kPa (0.25 psia) are shown in FIG. The residual load of CaX2.3 is
0.17 mmol / gm, the expected temperature after desorption is 3 ° C
It is about. The residual loading of CaNaX2.3 is of the order of 0.05 mmol / gm and the expected temperature after desorption is of the order of 9 ° C. Again, 77% exchange X2.3 is a more efficient adsorbent than 97% exchange. The nitrogen desorption curve for CaX2.5 (97% Ca) and the expected equilibrium adsorption capacity at 262 kPa (38 psia) are shown in FIG. Desorption curve of CaNaX2.5 (77% Ca) and 1.
Its expected adsorption capacity at 72 kPa (0.25 psia) is shown in FIG. The residual load of CaX2.5 is about 0.17 mmol / gm,
The temperature after desorption is expected to be around -13 ° C. CaNaX
The equilibrium load of 2.3 is about 0.07 mmol / gm, and the temperature after desorption is expected to be about -3 ° C. CaNaX2.5 is -3
It is surprising that the residual load is almost the same as in the case of ° C. However, this is due to the fact that
Consistent with the fact that the PSA adsorbent is worse compared to X2.0 and CaNaX2.3.

[0029]

The zeolitic adsorbent of the present invention is an adsorbent having extremely excellent nitrogen selective adsorption in the PSA air separation process. When this is used as an adsorbent in a PSA air separation process, it is an industrially extremely useful invention capable of performing extremely efficient nitrogen and oxygen separation.

[Brief description of the drawings]

FIG. 1. CaNaX 2.0 after desorption to 10.7 kPa (1.55 psia) correlating to calcium exchange levels at 40 ° C., 20 ° C., and 0 ° C., respectively (eg, a 2: 1 silica / alumina ratio).
1 shows the nitrogen residual load of X 2 zeolite containing Ca ²⁺ and Na ¹⁺ cations.

FIG. 2. Ca in the range of 14.7 to 1.55 psia correlating to calcium exchange levels at 40 ° C., 20 ° C., and 0 ° C., respectively.
The nitrogen delta load of NaX2.0 is shown.

FIG. 3 shows the nitrogen manipulation selectivity of CaNaX 2.0 correlating to calcium exchange levels at 40 ° C., 20 ° C., and 0 ° C., respectively.

FIG. 4 shows the residual nitrogen loading, delta loading, and operational selectivity of CaNaX2.3 correlated to calcium exchange levels at 40 ° C., 20 ° C., and 0 ° C., respectively.

FIG. 5 shows the residual nitrogen loading, delta loading, and operational selectivity of CaNaX2.3 correlated to calcium exchange levels at 40 ° C., 20 ° C., and 0 ° C., respectively.

FIG. 6 shows the residual nitrogen loading, delta loading, and operational selectivity of CaNaX2.3 correlated to calcium exchange levels at 40 ° C., 20 ° C., and 0 ° C., respectively.

FIG. 7 shows the residual nitrogen loading, delta loading, and operational selectivity of CaNaX2.5 correlated to calcium exchange levels at 40 ° C., 20 ° C., and 0 ° C., respectively.

FIG. 8 shows the residual nitrogen loading, delta loading, and operational selectivity of CaNaX2.5 correlated to calcium exchange levels at 40 ° C., 20 ° C., and 0 ° C., respectively.

FIG. 9 shows the residual nitrogen loading, delta loading, and operational selectivity of CaNaX2.5 correlated to calcium exchange levels at 40 ° C., 20 ° C., and 0 ° C., respectively.

FIG. 10 shows the desorption rate of CaX2.0 (97% Ca) at 22 ° C.

FIG. 11 shows the desorption rate of CaNaX2.0 (75% Ca) at 22 ° C.

FIG. 12 shows the desorption rate of CaX2.3 (97% Ca) at 22 ° C.

FIG. 13 shows the desorption rate of CaNaX2.3 (77% Ca) at 22 ° C.

FIG. 14 shows the desorption rate of CaX2.5 (97% Ca) at 22 ° C.

FIG. 15 shows the desorption rate of CaNaX2.5 (77% Ca) at 22 ° C.

Claims (4)

(57) [Claims] 1. A framework having a SiO ₂ / Al ₂ O ₃ molar ratio of 2.0 to 2.4, and 60 to 89 equivalent% of Ca ⁺⁺ cation and 10 to 40 equivalent% of Na ⁺ cation. And zeolite X containing 0 to 10 (excluding 0)% of K ⁺ cations and having a total cation equivalent of at least 90% of Ca ⁺⁺ , Na ⁺ and K ^+. A zeolitic adsorbent that selectively adsorbs nitrogen from a mixture of oxygen and nitrogen used in a circulating pressure swing adsorption process. 2. The composition according to claim 1, wherein the molar ratio of SiO ₂ / Al ₂ O ₃ is 2.0-2.35,
2. The zeolitic adsorbent according to claim 1, wherein the cation component is 65-80% calcium and 20-35% sodium cation and is substantially free of potassium cation. (3) The molar ratio of SiO ₂ / Al ₂ O ₃ is 2.0 to 2.0.
With a framework of 2.4 and 60-89 equivalent% Ca
⁺⁺ cation, 10-40 equivalent% of Na ⁺ cation, 0-10
% Of a K ⁺ cation and a total cation equivalent of Ca ⁺⁺ , Na ⁺ and K ⁺ of at least 90%.
A framework with an O ₂ / Al ₂ O ₃ molar ratio of 2.0 to 2.35, 65 to 80 equivalent% of Ca ⁺⁺ cations, and 20 to 35 equivalent% of Na ⁺ cations and substantially K ⁺ Providing a zeolitic adsorbent composed of zeolite X not contained in the adsorbent bed, (b) pressure in the bed is 13.8 to 506.8 kPa (2 to 73.5 psia)
And feeding a mixture of nitrogen and oxygen into the adsorbent bed at a temperature of -20 ° C to 50 ° C until nitrogen is selectively adsorbed on the adsorbent, (c) substantially above the adsorption pressure Discharging oxygen not adsorbed from the adsorption bed as a product; (d) desorbing the adsorbed nitrogen and increasing the bed pressure to 101.4.
Discharging the nitrogen from the bed to a final pressure of ~ 0.7 kPa (14.7-0.1 psia), the process comprising selectively adsorbing nitrogen from a mixture of oxygen and nitrogen. 4. The recirculating process according to claim 3, wherein the mixture of oxygen and nitrogen is air.