JPH06104174B2 - Method for adsorption separation of easily adsorbed components from mixed gas - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to a method for separating and recovering an easily adsorbed component from a mixed gas containing the easily adsorbed component.

Technical Background of the Invention and Problems Thereof A large amount of lower hydrocarbons such as ethylene and propylene is contained in the gas by-produced from the fluid catalytic cracking apparatus or the purge gas generated in various processes. Efficient separation and recovery is desired.

Therefore, a desired hydrocarbon is obtained from a mixture containing hydrocarbons,
A method for separating and collecting using an adsorbent has been studied for a long time. The method for separating hydrocarbons using such an adsorbent is generally classified into the following four types depending on the difference in the desorption method of the adsorbed hydrocarbon from the adsorbent.

Heat Regeneration Method (Thermal Swing Method) This method is a method of desorbing and recovering hydrocarbons adsorbed on the adsorbent at low temperature by heating.

However, this method has a serious problem that the separation efficiency is low because it takes a long time to heat or cool the adsorbent.

Pressure Swing Method This method involves adsorbing hydrocarbons at high pressure on an adsorbent and then
When desorbing at a low pressure, the hydrocarbon adsorbed on the adsorbent is reduced to an intermediate pressure between the high pressure and the low pressure to remove at least a part of the desorbed hydrocarbon, and then the hydrocarbon is adsorbed again at the low pressure. It is a method of desorbing and recovering. This method is an iso-sieve method from naphtha to n-
It has been put to practical use as a method for separating paraffin.

However, this method has a problem that the facility cost or the operating cost is increased because a compressor or a vacuum pump is required.

Purge Gas Stripping Method This method is a method of recovering hydrocarbons adsorbed by the adsorbent by desorbing the hydrocarbons from the adsorbent using a purge gas such as nitrogen.

However, this method has a problem that a step such as distillation is required to separate the desorbed hydrocarbon and the purge gas.

Substitution Method This method is a method of desorbing and recovering hydrocarbons from the adsorbent by substituting the hydrocarbons adsorbed on the adsorbent with the adsorbent. This method is a method of using ammonia as a displacing agent when separating and recovering n-paraffin from a hydrocarbon mixture (Ensorb method) or a lower n-paraffin method.
-Method using paraffin (Molex method, TSF method, BP
Law) has been put to practical use.

However, this method cannot be applied when the hydrocarbons to be separated and recovered are lower hydrocarbons such as ethylene and propylene because the separation of the displacing agent and the hydrocarbons is difficult.

In order to separate and collect the easily adsorbed components, which are components easily adsorbed by the adsorbents such as ethylene and lower hydrocarbons represented by propylene, from the mixed gas by using the adsorbent,
Although several methods have been known in the past, all of them have problems such as high equipment cost or operation cost, or separation of the purge gas and the easily adsorbed component.

The present inventors have conducted extensive studies to solve the above problems, and when separating and recovering easily adsorbable components such as ethylene and lower hydrocarbons typified by propylene using a solid adsorbent, solid adsorption is performed. If a hydrophobic adsorbent is used as an agent and the adsorption step is performed by a pressure swing method in a pressure-normal pressure region, and desorption of an adsorbed gas is performed by introducing steam into the adsorbent, it is very efficient and The present invention has been completed by finding that the facility cost and the operating cost are not required.

An object of the present invention is to solve the above problems associated with the prior art, and to obtain a mixed gas containing easily adsorbed components such as lower hydrocarbons typified by ethylene and propylene. The object of the present invention is to provide a method for efficiently separating and recovering easily adsorbed components without incurring facility costs or operating costs.

SUMMARY OF THE INVENTION A method for separating an easily adsorbed component from a mixed gas according to the present invention,
It is configured to include the following steps (a) to (c).

(A) A mixed gas containing an easily adsorbed component is introduced into an adsorption tower which is filled with a hydrophobic adsorbent and kept at 80 to 200 ° C., and brought into contact with the adsorbent under pressure to remove the easily adsorbed component. A step of adsorbing to the adsorbent, (b) depressurizing the adsorbent having the easily adsorbed component adsorbed in the step (a) to a pressure equal to or lower than the pressure in the step (a) to release at least a part of the adsorbed component Step (c) A step of desorbing and recovering the easily adsorbed component still adsorbed by the adsorbent after the step (b) by contacting the adsorbent and steam at a temperature at which steam does not condense.

In the present invention, in separating and recovering the easily adsorbed component from the gas containing the easily adsorbed component such as lower hydrocarbon, a hydrophobic adsorbent is used as the adsorbent, and the adsorbed component adsorbed by the adsorbent is desorbed by steam. Therefore, it is extremely easy to separate the easily adsorbed component from steam, and the easily adsorbed component such as propylene can be efficiently separated and recovered without incurring the facility cost or the operating cost.

DETAILED DESCRIPTION OF THE INVENTION The method for separating easily adsorbed components from a mixed gas according to the present invention will be specifically described below.

In the present invention, the easily adsorbed component is efficiently separated and recovered from the mixed gas containing the easily adsorbed component. Examples of the easily adsorbable components separated in the present invention include lower hydrocarbons having 2 to 5 carbon atoms, such as olefins such as ethylene, propylene and butene, paraffins such as ethane, propane and butane, acetylenes such as acetylene. Is specifically exemplified.

Examples of the gas that coexists with such an easily adsorbable component as a lower hydrocarbon include carbon monoxide, carbon dioxide, hydrogen, nitrogen, argon, helium, oxygen, water, methane and the like. A sulfur compound such as sulfur dioxide or hydrogen sulfide or a nitrogen compound such as ammonia may coexist as long as the amount is small.

Specific examples of the mixed gas containing an easily adsorbed component such as the lower hydrocarbon as described above include a gas by-produced from the fluid catalytic cracking apparatus or a barge gas by-produced from various processes.

In the present invention, the following series of processes (a) to (c) are added to the mixed gas containing the above-mentioned easily adsorbed components, and each step will be described in order. (A) A mixed gas containing an easily adsorbed component is introduced into an adsorption tower which is filled with a hydrophobic adsorbent and kept at a temperature of 80 to 200 ° C., preferably 100 to 200 ° C. and at least 1 kg / cm ² G Preferably 1 to
Contact with the adsorbent under a pressure of 30 Kg / cm ² G,
The easily adsorbed component is adsorbed on the adsorbent.

A hydrophobic adsorbent is used as the adsorbent. The reason why the hydrophobic adsorbent is used in the present invention is that the easily adsorbed component adsorbed to the adsorbent is desorbed by steam in the subsequent step (c), but if the adsorbent is not hydrophobic, the adsorbent is This is because water is strongly adsorbed and a separate step for desorbing this water from the adsorbent is required, which is not preferable.

As the hydrophobic adsorbent, activated carbon, molecular sieving carbon, polystyrene, silicalite, high-silica zeolite whose Si / Al ratio is specified by acid extraction, activated carbon carrying copper chloride or copper oxide, etc. are widely used.

The temperature at the time of adsorption is 80 to 200 ° C, preferably 100 to 200 ° C. Generally, when the adsorption temperature is raised, the easily adsorbed components adsorbed on the adsorbent are decreased, but in the present invention, as described below, the adsorbent is easily adsorbed by contacting the adsorbent and steam at a temperature at which steam does not condense. Since the adsorbed components are desorbed, if the adsorption temperature is lowered,
The steam will condense when it comes into contact with the adsorbent. Therefore, if the adsorption operation is performed in the low temperature region, the adsorbent must be heated before the adsorbent and steam are brought into contact with each other, and this operation requires a long time.

Therefore, in the present invention, the adsorption temperature is set to a higher temperature range than in the past, but there is a negative point that the adsorption capacity of the easily adsorbed component is reduced by performing the adsorption in the high temperature range, but the adsorption having the adsorption capacity in the high temperature range is also performed. If an agent is used, the merit of the whole process is very large, so the above adsorption temperature is adopted.

The above-mentioned adsorption step of the easily adsorbed component is preferably carried out in the adsorption tower with the adsorbent as a fixed bed. The adsorption step is preferably performed by pressurizing the adsorption tower with the mixed gas as the raw material and then flowing the mixed gas as the raw material into the adsorption tower. At that time, it is preferable to carry out the adsorption step until breakthrough of the easily adsorbed component at the outlet of the adsorption tower occurs or shortly before.

Furthermore, between the step (a) and the step (b), an easily adsorbable component such as a lower hydrocarbon gas mainly obtained as a product gas is introduced into the adsorption tower to obtain an adsorbent in the mixed gas component as a raw material. You may insert the process of desorbing (purging) the component hard to adsorb | suck.

(B) Next, the adsorbent on which the easily adsorbed component is adsorbed as described above is preferably added at a pressure other than the pressure in step (a), preferably 5 kg / cm ² G.
-Decompress to a suitable pressure up to atmospheric pressure to release at least a portion of the adsorbed components adsorbed by the adsorbent.

When such step (b) is added, at least a part of the component weakly adsorbed by the adsorbent is released, and the easily adsorbable component is adsorbed to the adsorbent considerably selectively.

The gas released at this time may be released to the outside, but in some cases, it may be introduced into another adsorption tower after completion of step (c) described below, or used for pressure equalization described below. You can also do it.

Further, the depressurizing step can be performed in two steps.

(C) Next, the easily adsorbed component still adsorbed to the adsorbent after the above step (b) is desorbed and recovered by contacting the adsorbent with steam at a temperature at which steam does not condense.

The easily adsorbed component that is still adsorbed by the adsorbent after the step (b) is a component that is easily adsorbed by the adsorbent, and examples of such a component include ethylene, propylene, ethane, propane, etc. Is exemplified. Of these, when activated carbon is used as the adsorbent, propylene is strongly adsorbed on the adsorbent.

The above step (c) is preferably performed at a pressure lower than that of the step (b) and in the range of 5 Kg / cm ² G to atmospheric pressure.
It is carried out at a temperature of 0 ° C., preferably 100 to 200 ° C. The steam is preferably heated to some extent.

By doing so, the easily adsorbed component adsorbed by the adsorbent is desorbed, and a mixed gas mainly composed of the easily adsorbed component and steam is obtained.

The mixed gas thus obtained, which is mainly composed of an easily adsorbed component and steam, is then optionally cooled by a settler or the like, steam is condensed and separated, and a separated gas mainly composed of an easily adsorbed component is obtained. Is obtained.

Thus, it is extremely easy to remove steam from the mixed gas of the easily adsorbed component and steam, and the present invention is
This point has one major feature.

The mixed gas composed of the easily adsorbed component and steam obtained as described above can be used as it is in another process without separating the easily adsorbed component and steam.

When the adsorbent and steam are brought into contact with each other, the heavy components adhering to the pores (pores) of the adsorbent can also be purged. Therefore, even if the suction is repeatedly used, the effect that the suction force does not decrease can be obtained.

The above series of processes can be carried out by using one adsorption tower, but in an actual plant, it is desirable to carry out a combination of two or more, preferably about three.

Here, the continuous operation process using the three adsorption towers A, B and C will be specifically described.

First, Table 1 shows each operation in the A tower, the B tower, and the C tower.

The mixed gas as a raw material is introduced into the A tower for adsorption, and the introduction of the mixed gas is switched from the A tower to the C tower immediately before or just before the breakthrough of the easily adsorbed component as the target substance occurs.

The A tower and the B tower, which has completed the steam purge (described later) and has a lower pressure than the A tower, are connected to equalize the pressure. This pressure equalization may be performed by connecting the upper parts of the towers to each other or by connecting the lower parts of the towers to each other. In some cases, undesired impurities may be adsorbed at the adsorbent bed inlet of the tower A, and pressure equalization on the mixed gas supply side may be preferable for later recovery of adsorbed gas. After equalizing the pressure, the pressure in the tower A is further reduced. The released gas obtained at this time may be mixed with the adsorbed gas for recovery depending on the purpose, or may be recovered in another department such as combustion, and is appropriately selected.
In addition, the depressurizing operation can be omitted if it is mixed with the separated gas desorbed by steam and recovered.

Next, by introducing steam into the tower A, the easily adsorbed component adsorbed by the adsorbent is desorbed and recovered. As the steam, it is preferable to use superheated steam that is less likely to be condensed than saturated steam, and the steam is introduced in the same direction as the supply flow of the mixed gas as the raw material or in the opposite direction. The introduction direction of this steam is appropriately selected in consideration of the circumstances of each process (fluidization tower of adsorption bed).

The desorbed mixture composed mainly of easily adsorbed components and steam is sent to the next separation and recovery section. The process of separating the easily adsorbed component and steam may be performed by various chemical engineering techniques, but for example, a method of cooling and condensing with a condenser to separate water and the easily adsorbed component is preferable.

The tower A after the steam purging is equalized in pressure in the tower C after the adsorption step as described above, and then the mixed gas as the raw material is introduced to raise the pressure to the adsorption step.
Enter the adsorption operation. Hereinafter, the tower B and the tower C are also sequentially operated in the same manner as described above.

In the above example, the column, among others pressure during adsorption is 7 Kg / cm ² G, column internal pressure of the equalizing pressure time is 4 Kg / cm ² G, column internal pressure of vacuum at the time of, 0.5 Kg / cm ² G, and the pressure in the tower at the time of introducing steam is 0.5 kg / cm ² G.

Table 2 shows the composition of the mixed gas, which is the raw material to which such an operation is applied, and the composition of the separated gas obtained by desorption with steam.

Effect of the Invention In the present invention, when separating and recovering the easily adsorbed component from the mixed gas containing the easily adsorbed component, a hydrophobic adsorbent is used as the adsorbent, and the easily adsorbed component adsorbed by the adsorbent is desorbed by steam. Therefore, it is extremely easy to separate the easily adsorbed component and the steam, and the easily adsorbed component such as propylene can be efficiently separated and recovered without incurring the facility cost or the operating cost.

The present invention will be described below with reference to examples, but the present invention is not limited to these examples.

Example 1 Commercially available active edge (lime type, specific surface area 1190 m ² / g) 10 cc (about 3.
5 g) was packed in an adsorption tower, and mixed gas A having a composition shown in Table 3 at 120 ° C., 5 Kg / cm ² G and SV500 was introduced from the upper part of the adsorption tower for adsorption. When the adsorption progressed and propylene passed through the bottom of the adsorption tower, the introduction of the mixed gas was stopped, the pressure control valve at the bottom of the adsorption tower was opened, and the pressure was reduced from 5 Kg / cm ² G to normal pressure. The produced gas was discarded. Next, steam is fed from the top of the adsorption tower 120
The mixture was introduced into the adsorption tower at SV800 at ℃ and atmospheric pressure to desorb the adsorbed gas. Three minutes after the start of desorption, a separated gas containing propylene at 44.4 mol% (total gas amount: 103 cc) was recovered.

Example 2 After the operation of Example 1 was completed, adsorption-decompression-under the same conditions
The desorption was repeated. Two minutes after the start of desorption by steam, a separated gas containing propylene at 42,2 mol% (total gas amount: 98 cc) was recovered.

Further, adsorption, decompression, and desorption were repeated three times under the same conditions, and the recovered amount and propylene concentration 2 minutes after the start of desorption by steam were almost the same as above.

Example 3 After the operation of Example 2 was completed, adsorption-vacuum-desorption was carried out under the same conditions as in Example 1 except that the temperature of the adsorption tower was 150 ° C. The total amount of gas recovered 3 minutes after the start of desorption by steam was 83 cc, and the propylene concentration was 41.9 mol%.

Comparative Example 1 Except that the adsorption step was performed at normal pressure and the depressurization step was omitted,
Adsorption-desorption was performed in the same manner as in Example 1. The total amount of gas recovered by steam is 45cc in 3 minutes after the start of desorption,
The propylene concentration was 37.6 mol%.

Comparative Example 2 Adsorption, decompression, and desorption were repeated in the same manner as in Example 1 except that the molecular sieve 13X10cc (about 5.9 g) was used as the adsorbent and the adsorption tower temperature was 150 ° C. The amount of desorption by steam at the first time was large at 209.5cc, but 2
The desorption amount after the first time was small, and its composition was almost the same as the source gas.

Example 4 Example 1 was repeated except that the temperature of the adsorption tower was 150 ° C. and the mixed gas B having the composition shown in Table 3 was used as the raw material gas.
Adsorption-decompression-desorption was carried out in the same manner as in. The total amount of collected gas was 137 cc and the propylene concentration was 72 mol% in 3 minutes after the start of desorption by steam.

Example 5 Adsorption-decompression-desorption was performed in the same manner as in Example 4 except that 10 cc of molecular sieving carbon was used as the adsorbent. The total amount of recovered gas was 158.1 cc and the propylene concentration was 68.4 mol% in 3 minutes after the start of desorption by steam. Furthermore, under the same conditions, adsorption-decompression-desorption is performed at 9
Repeatedly, the total amount of recovered gas and the propylene concentration were almost the same as above.

Example 6 A commercially available synthetic mordenide molded product (Na type) is treated with an aqueous solution of ammonium chloride to form H type by washing with water and baking, and then treated with hot air containing 10% of steam at 700 ° C. for 3 hours, and further to 12 After repeating the treatment with normal hydrochloric acid at 90 ° C for 20 hours twice, washing with water, fitting and firing to make SiO ₂ / Al ₂ O
₃ ratio 103 high silica mordenite and (HSM) was prepared.
High silica mordenite adsorbent 10cc thus obtained
(About 5.8 g) was packed in an adsorption tower, and adsorption-decompression-desorption was carried out in the same manner as in Example 1. The total amount of collected gas was 26.5 cc and the propylene concentration was 40.5 mol% in 3 minutes after the start of desorption by steam.

Further, adsorption-decompression-desorption was repeated 5 times under the same conditions, but the total amount of recovered gas and the propylene concentration were almost the same as above.

Claims (9)

[Claims] 1. A method for separating an easily adsorbed component from a mixed gas, which comprises the following steps: (a) A mixed gas containing an easily adsorbed component is filled with a hydrophobic adsorbent and is from 80 to 200. A step of introducing the adsorbent into the adsorption tower kept at ℃ and bringing it into contact with the adsorbent under pressure to adsorb the easily adsorbed component to the adsorbent, and (b) adsorption in which the easily adsorbed component is adsorbed in step (a). Depressurizing the agent to a pressure equal to or lower than the pressure in step (a) to release at least a part of the adsorbed component, (c) removing easily adsorbed component still adsorbed on the adsorbent after step (b) , A step of desorbing and collecting the adsorbent and steam by bringing them into contact with each other at a temperature at which steam does not condense. 2. The method according to claim 1, wherein the easily adsorbable component is a lower hydrocarbon. 3. The method according to claim 1, wherein the lower hydrocarbon to be separated is ethylene or propylene. 4. The method according to claim 1, wherein the hydrophobic adsorbent is activated carbon, molecular sieving carbon, polystyrene, silicalite or high silica zeolite. 5. The method according to claim 1, wherein the adsorption tower is maintained at 100 to 200 ° C. 6. The method according to claim 1, wherein step (c) is carried out at a temperature of 100 to 200 ° C. 7. The steps (a), (b) and (c),
The method according to claim 1, which is carried out continuously by using a plurality of adsorption towers. 8. By cooling the separation gas consisting mainly of easily adsorbed components and steam obtained in step (c),
Claim 1 for separating easily adsorbed components and steam
The method described in the section. 9. An easily adsorbed component gas is introduced into an adsorption tower between steps (a) and (b) to desorb a component of a mixed gas component as a raw material which is difficult to be adsorbed by an adsorbent. A method as claimed in claim 1 including the steps.