JPH04171046A - Regeneration of carbon dioxide adsorbent - Google Patents

Abstract

PURPOSE:To recover CO2 absorbing capacity by bringing a carbon dioxide absorbent mainly consisting of magnesium oxide and/or magnesium hydroxide and lowered in its activity into contact with steam under pressure. CONSTITUTION:A CO2 absorbent containing magnesium oxide and/or magnesium hydroxide as a main lowered in its CO2 absorbing capacity is brought into contact with steam under pressure. Whereupon, the crystal size of the CO2 absorbent again becomes small and the average pore size becomes small and the pore volume and specific surface area thereof increase. By this method, CO2 absorbing capacity can be easily and efficiently recovered and regenerated.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for regenerating carbon dioxide (Co) absorbent,
In particular, magnesium oxide (M g O) and/or magnesium hydroxide (Mg
The present invention relates to a method for regenerating a CO2 gas absorbent that easily and efficiently regenerates a CO8 gas absorbent whose main component is (OH)*) and effectively restores CO and gas absorption performance.

[Prior Art] MgO is most suitable as a renewable solid Cow absorbent, and research is being conducted to further improve its Co2 absorption capacity. For example, a C02 absorbent made by blending an alkali metal hydroxide with MgO has been proposed (U
SP3.557,011).

When this CO□ absorbent is used to absorb CO2, the Co2 absorption efficiency decreases over time, and eventually reaches a breakthrough and no longer absorbs CO□. Therefore, it is necessary to regenerate the CO2 absorbent at the time when the CO2 absorption efficiency decreases before reaching breakthrough.

Conventionally, regeneration of the CO□ absorbent has been carried out by bringing a gas such as N8 gas into contact with the CO3 absorbent at high temperature.

[Problem to be solved by the invention] However, in the above conventional regeneration method, sufficient CO8
Absorption performance has not been recovered, and improvements are desired.

Note that USP 3,557,011 requires that the CO1 absorbent be brought into contact with steam before use. Therefore, the temperature of the steam is preferably 120 to 250'C.

Note that the steam used does not need to be pure H20,
HaO and N2. A mixed gas with a gas such as air may be used. In this case, the ratio of H and O in the mixed gas is preferably 115 or more, preferably 1/3 or more.

In addition, if the pressure is less than 2 ata, regeneration cannot be performed effectively,
If the pressure exceeds 15 ata, the pores of the absorbent tend to change.
．． It is preferable to set it to 7 to 15 ata.

Further, the amount of steam used for regeneration is preferably 10 to 60% by weight of HaO relative to the CO2 absorbent.

In carrying out the present invention, for example, steam at a predetermined pressure and temperature may be fed to a column filled with a CO2 absorbent with reduced COa absorption performance.

In addition, in the present invention, the CO□ absorbent is Therefore,
The temperature of the steam is preferably 120 to 250°C.

Note that the steam used does not need to be pure H20 (
H2O and N2. A mixed gas with a gas such as air may be used. In this case, the proportion of HaO in the mixed gas is preferably about 115 or more, preferably about ⅓ or more.

In addition, if the pressure is less than 2 ata, regeneration cannot be performed effectively,
When it exceeds 15 ata, the pores of the absorbent tend to change. Therefore, the pressurization conditions are 2 to 15 ata, and the H,0 partial pressure is 0.
．． It is preferable to set the thickness to 7 to 15 ata.

Further, the amount of steam used for regeneration is preferably 10 to 60% by weight based on H and 0 weight of the COz absorbent.

In carrying out the present invention, for example, steam at a predetermined pressure and temperature may be fed to a column filled with an absorbent for CO□ whose absorption performance has decreased.

In addition, in the present invention, the CO2 absorbent is MgO and/or
or magnesium hydroxide (Mg(OH)1) 50-9
0% by weight, 5 to 30% by weight of a potassium compound, and 5 to 20% by weight of sodium silicate and/or zirconia.

Here, MgO and/or Mg (OH) is CO≧
It acts as the main component of the absorbent.

In addition, as a potassium compound, potassium hydroxide (KO
H), potassium carbonate A (KmCO3), potassium phosphate (KmPO,), etc., and these can be used alone or in combination of two or more. If the content of these potassium compounds is less than 5% by weight, the CO2 absorption capacity will be low (and if it exceeds 30% by weight, the absorbent will have poor formability. Therefore, the content of potassium compounds should be 5% by weight).
~30% by weight.

Sodium silicate and/or zirconia has a content of 5
It is difficult to form an absorbent with no droplets by weight, and 20% by weight
If it exceeds this, the CO2 absorption capacity will decrease. Therefore, the sodium silicate and/or zirconia content is 5 to 20% by weight.

Such a COa absorbent is produced by, for example, dissolving a predetermined amount of a potassium compound in an aqueous solution of sodium silicate (water glass) and/or zirconia sol, and then adding a predetermined amount of MgO to this.
It can be easily produced by adding and/or Mg (OH), kneading, heating and drying the kneaded product to remove water, and then pulverizing and sizing.

Further heat at 350-500℃ to convert Mg (OHI2 to M
It may be converted to gO.

In the present invention, it is preferable to use water glass having a sodium silicate content of about 10 to 50% by weight. In addition to the zirconia sol described above, a suspension of zirconia fine particles or a zirconium compound that can be converted into zirconia by heating can also be used as the zirconia raw material.

[Effect] The details of why the CO2 absorption performance of a CO2 absorbent with reduced CO2 absorption performance is significantly restored by contacting it with steam under pressure are not clear, but according to research conducted by the present inventors. For example, the following can be said.

In other words, CO2 absorption performance has decreased due to long-term use.
When examining the pore distribution etc. of the z-absorbent, it is found that, compared to the CO2 absorbent before use, the pore size distribution is generally larger, the pore volume is smaller, and the specific surface area is also smaller (
Become. In other words, the micropores that contribute to the specific surface area of the CO□ absorbent are significantly reduced, and the specific surface area of the CO2 absorbent becomes small.This decrease in specific surface area causes a decrease in CO2 absorption performance. When examining the microscopic shape of the CO2 absorbent whose performance has deteriorated, the crystals of this CO2 absorbent are clearly larger than those of the CO2 absorbent before use, and crystal growth has occurred. This is considered to be the cause of the decrease in pore volume and specific surface area.

On the other hand, by bringing such a CO2 absorbent into contact with steam under pressure, the effect of reducing the size of the crystals was observed, the pore size distribution returned to the smaller side, and the pore volume and specific surface area increased. do. This restores the CO□ absorption performance. Although this effect can be obtained to some extent even when brought into contact with steam under normal pressure, an even higher effect can be obtained by contacting with steam under pressure.

[Example] The present invention will be described in more detail with reference to Examples below.

In addition, in the following, Cow absorption conditions and normal regeneration conditions are as follows unless otherwise specified. =300℃ Absorbent filling amount: 450cc Gas flow rate: Cot =N* =H* 0=25ONc
c/win total 75ONcc/min Gas composition: Co, = N, = H, 0 = 33.3% m i
n).

Moreover, the CO2 absorbent was manufactured by the method shown below.

Potassium hydroxide is dissolved in 1゛ water glass (sodium silicate content: 30% by weight) of CO, and then Mg(OH)* powder is added thereto for crosstalk. The mixed material is dried at 100°C, then massaged, and then heated to 140-150°C to substantially remove water. 0.50~ by crushing the dry matter and sieving it
Particles with a size of 1 mm are obtained. The particles are filled into an absorption tube and heated to 450° C. to convert Mg (OH) to MgO.

Example I C containing 15% by weight of KOH and 13% by weight of sodium silicate
An O2 absorbent was manufactured, and after absorbing CO, it was regenerated, and a cycle test of absorption and regeneration was conducted. However, the regeneration process was performed under the conditions of No. 1 in Table 1 below between the 8th cycle and the 9th cycle, and the relationship between the number of cycles and breakthrough time is shown in FIG.

From FIG. 1, it is clear that the regeneration treatment (No. 2) according to the present invention significantly recovers the 063 absorption performance of the Co2 absorbent.

Between the 15th cycle and the 16th cycle, NO in Table 1 below
Regeneration processing was performed under 12 conditions.

Table 1 [Effects of the Invention] As detailed above, according to the method for regenerating a Co absorbent of the present invention, a CO8 absorbent whose COz absorption performance has decreased can be easily and efficiently regenerated, and the CO2 absorption performance can be improved. It is believed that significant improvements can be made.

[Brief explanation of drawings]

FIG. 1 is a graph showing the results of Example 1. Agent: Patent attorney Tsuyoshi Shigeno

Claims (1)

[Claims] (1) A method for regenerating a carbon dioxide absorbent, which comprises bringing a carbon dioxide absorbent whose main component is magnesium oxide and/or magnesium hydroxide, which has decreased carbon dioxide absorption performance, into contact with steam under pressure.