DE1114790B - Process for the separation and recovery of carbon dioxide from gas mixtures - Google Patents

Description

The invention relates to a method for separating and recovering carbon dioxide from gas mixtures by absorption by means of an alkali solution, the arsenic (III) oxide as activating Contains substance and that includes an absorption stage in which the gas mixture is treated by means of the absorption solution, and a regeneration stage includes, in which the loaded solution with expulsion of carbon dioxide by treatment with desorbing gases or air in the warmth or by heating the solution to boiling temperature is regenerated.

Arsenic (III) oxide also includes that of the alkali salts, namely arsenite and meta-arsenite understood what the arsenic (HI) oxide can form with the alkali contained in the solution, at least the presence of the ion of arsenic acid.

In such a known method, the carbonic acid is driven off using normal pressure is applied and is carried out in a temperature range below the boiling point.

The invention is based on the object of enabling an improvement in the regeneration.

The object is achieved in that, according to the invention, the regeneration is carried out under excess pressure at a temperature which exceeds the boiling point of the solution at atmospheric pressure. By using the method according to the invention, the arsenite solution can be assigned a further property which is of particular importance in its industrial utilization, so that the exhausted solutions can be regenerated even more advantageously and more extensively than was possible with the previous methods. The process according to the invention, which can thus be used particularly well industrially, facilitates the expulsion of CO ₂ both in the conversion of bicarbonate into carbonate and in the conversion of carbonate into arsenite, which is associated with particular difficulties. In fact, using the prior art method, it has been found that the removal of CO _{2 is} very easy when it coincides with the conversion of bicarbonate to carbonate, ie when the ratio of CO ₂ (in moles) to Alkali oxide (in moles) in the solution is equal to or greater than 1; but if the removal of CO ₂ coincides with the conversion of carbonate to arsenite, if the ratio just mentioned falls below 1 or to 0, then the removal of CO ₂ takes place more slowly, so that the regeneration process by boiling at atmospheric pressure with external heat input in a process of deposition

and recovery of carbon dioxide

from gas mixtures

Applicant:
Vetrocoke S. p. A., Turin (Italy)

Representative: Dr.-Ing. H. Fincke, Berlin-Lichterfelde, Dipl.-Ing. H. Bohr and DipL-Ing. S. Staeger,

Munich 5, Müllerstr. 31, patent attorneys

Claimed priority:
Italy of October 22, 1957 (No. 2G43)

Giuseppe Giammarco, Porto Marghera (Italy),
has been named as the inventor

Amount of 50 kg of steam per cubic meter takes place practically below a ratio of CO ₂ : alkali oxide (in moles) of 0.8 to 1.0. This means that the regenerated solution contains at most 20 ^fl / o alkali bound as arsenite and 80% alkali bound as carbonate. The invention is primarily concerned with expelling CO ₂ beyond the limit just mentioned, which causes greater difficulties because boiling at atmospheric pressure for any length of time

no complete removal of CO ₂ from the still full

causes constant arsenite formation.

It should be noted for the sake of completeness that a process is known in which organic absorbent alkaline solutions are used, the

z. B. alkylolamines. The like. Contain the regeneration of these solutions under pressure up to temperatures should be carried out at which undesired decomposition of the absorbent does not yet occur. With the one just mentioned known method, however, is a completely different method, which with the inventive Procedure has practically nothing to do; also is the one dealing with this known method No information can be found in the publication that the regeneration, as in the case of the invention, should be carried out at the boiling point at atmospheric pressure exceeding temperature.

109 708/380

3 4

It has now been found that the apparatus above and under the same conditions to

specified properties of the arsenite solutions and any external influence from boiling the solution

the carbonate activated by arsenic (III) oxide - the temperature of 180 ° C and the

solutions to eliminate excessive pressures explained by various assumptions. The history

can be. It can thus be assumed that 5 of the curve and B shows that regeneration

the acidic character of arsenic (III) oxide, which is obtained by boiling at a temperature of 180 ° C and

chemically contributes to the expulsion of CO ₂ , much more advantageous and appropriate in the case of excess pressure

Temperature increase increases, or that the CO ₂ - precipitates than by boiling at atmospheric pressure. It

Vapor pressures of the arsenite solutions at the boiling point can be seen that the expulsion of CO ₂ at the

temperature are too low below atmospheric pressure, io conversion of bicarbonate to carbonate, i. H. until

in order to a significant expulsion of CO ₂ to the ratio of CO ₂ moles to K ₂ O moles greater than 1

lead, but increases rapidly when the temperature rises, in both cases, i.e. both in the case of curve A.

rise and an appropriate industrial removal is going on as well as curve B _{1 at which}

from CO., allow. Conversion of carbonate into arsenite, i.e. at

Apart from the above assumptions, practically 15 is below 1 values of the above

it has been found that the temperature ratio in the case of curve A is extremely slow

increase caused pressure increase contrary to what has taken place so far, which means that even a prolonged boiling

opinion represented by the professional world, according to which the solution and a very considerable heat

Removal of CO ₂ by lowering the pressure did not in any way cost those regeneration values

generally using vacuum, 20, which in the case of curve B while working

should be facilitated, brings more favorable results. at 180 ° C and overpressure easily and quickly under

With the method according to the invention, further lower heat consumption can be achieved,

associated with the advantage that the expelled CO _{2 based on} the above test results

collected under pressure and in this condition a test facility was built to track the course

can be used as it is by the industry, 25 of the previously known CO ₂ absorption process

ζ. B. required for the production of urea with regeneration by boiling at atmospheric

will. Furthermore, the apparatus for performing pressure with the course of the invention

the regeneration stage is reduced and the force CO ₂ absorption process with regeneration of the

effort to circulate the solution between the exhausted solution by boiling at overpressure

both levels lowered. Finally, the temperature can be comparatively fixed under operating conditions.

temperature can be increased at the absorption stage. place.

The beneficial effect of increasing the regenerative The experimental plant was according to the usual

tion temperature when working under overpressure procedure with regeneration by boiling according to

results from a comparison of the course of FIG. 2 operated. The solution, which CO ₂

Regeneration by expelling CO ₂ once absorbed from 35 in tower 1, in countercurrent to

an arsenite solution preheated by boiling at atmospheric- regenerated solution at 2 and the

pressure and on the other hand supplied from the same arsenite tower 3, in which the solution through

by boiling at overpressure, as regenerated by di-boiling by means of the steam coil 4,

gram is illustrated in Fig. 1. The separated CO ₂ exits at the top at 5 and

An aqueous arsenite solution was used, 40 is recovered. The regenerated solution gives

the 190.7 g / l K ₂ O, 113.1 g / l As ₀ O ₃ and 45.3 g / l dissipate their heat at 2, is continued in the water cooler 6

5-valent _{"arsenic" expressed as As 2} O ₃ and cooled and the absorption tower 1 by the

the pump 7 returns up to a ratio of CO ₂ mol to K _{2 O mol.} In the comparison

of 1.33 is loaded with carbon dioxide. Regeneration tower 3 passed the arsenite tests for one thing

solution was once at atmospheric pressure and 45 times from a tower for working with boiling

on the other hand at overpressure for the purpose of reproducing the at atmospheric pressure according to the known state

Relationship of the regeneration process to the boiling of the technology and on the other hand from a smaller one

point heated. In the course of boiling, coal towers are used for working with boiling at overpressure

Dioxide and water vapor released, which in and a temperature of 180 ° C under re-

a cooler for the purpose of condensing the water 50 extraction of the CO ₂ under pressure according to the invention

be cooled, the amount of the collected according to the method.

Water to that used in the regeneration The towers had the following dimensions.

The amount of steam is in direct proportion. In the case of an absorption tower: diameter 0.4 m, usable height 15 m;

certain amounts of condensed water, and regeneration tower (boiling at atmospheric pressure):

practically at intervals of about 10 per cent. diameter 0.6 m, usable height 15 m (filling volume

The volume of the tested liquid was 4.2 m ^s ) or (boiling at overpressure) diameter

self-examined to the progression of 0.4 m, usable height 6 m (filling volume 0.8 m ³ ).

To determine removal of CO ₂ from the same. The experiments were with one and the same

The results are carried out in the diagram of FIG. 1 again arsenite solution containing 200 g / l K ₂ O and

given, in which the abscissa contained the condensed 60 140 g / l As ₂ O ₃ . The absorption

Amount of water, d. H. the tion supplied to the system has a constant operating pressure of 11 atmospheres

Heat, as a percentage of the examined liquid and a constant supply of 300 Nm ^s / h.

amount and the ordinates as the ratio of CO ₂ gas and 2m ^s / h. Solution adhered to. The rain

MoI to K ₂ O moles of carbon dioxide content ration was carried out once at atmospheric pressure and

specify the solution. 65 on the other hand at 5 atm and 8 atm operating pressure below

Curve A shows the course of the regeneration with a constant steam supply of 100 kg / hour. the

by boiling at atmospheric pressure; the curve B results are in the table below

shows the course of regeneration given in the same.

Regeneration pressure

atu

CO _ä content in the gas
Volume percentage

Inlet

Outlet

CO ₂ content in the regenerated

solution

CO ₂ MoIzU

K ₂ OMoI temperatures ⁰ C

absorption

regeneration
Inlet I outlet

Filling volume

of

Regeneration tower m ³

17.8
17.8
17.8

0.2
0.1
0.05

1.06 0.97 0.93 66
66
66

95
160
170

104
168
180

4.2 0.8 0.8

The above results show that regeneration by boiling at overpressure during operation enables a reduction in the capacity, volume and dimensions of the regeneration temperature and that the regeneration of the solution increases with an increase in the boiling temperature under operating pressure in the regeneration stage with the same heat input. An essential advantage is that the CO ₂ expelled during the regeneration can be collected under a pressure of 5 or 8 atmospheres, so that the effort required by the pump 7 is reduced, which in the borderline case can be designed as a circulating pump.

In the above experiments, CO _{2 was} absorbed at overpressure, but CO _{2 can} also be easily absorbed at atmospheric pressure, so that the regeneration takes place at overpressure in order to achieve the advantages outlined above. Then the circulation pump takes on the new task of compressing the solution from the absorption stage after the regeneration stage.

The invention is in no way limited to the use of the boiling process for the solution under excess pressure in the regeneration stage, but can also be used by processes other than boiling, e.g. B. by treating the exhausted solution to be regenerated by means of various inert gases for desorption or CO ₂ separation, provided that the temperature at the regeneration stage, as prescribed above, is higher than the boiling point of the solution at atmospheric pressure.

Furthermore, the temperature of the absorption stage can advantageously be increased significantly in the process of the invention, since it is known that arsenite solutions have a CO ₂ vapor pressure which is significantly lower than that of z. B. carbonate solutions, from which it follows that CO _{2 can be} expediently deposited even at high temperature. Because the regeneration temperature can be increased by using overpressure during the regeneration, the temperature in the absorption stage can also be increased to values which exceed the boiling point of the solution at atmospheric pressure if the absorption takes place at overpressure. In this context it can be pointed out that no other limit is set than the different temperature between the two stages, such that the CO ₂ bound in the absorption stage is removed in the regeneration stage. For example, the possibility of performing the regeneration at 180 ° C allows gas mixtures to be cleaned at 120 to 130 ° C.

Claims (3)

PATENT CLAIMS: 1. A method for separating and recovering carbon dioxide from gas mixtures by absorption by means of an alkali salt solution containing arsenic (III) oxide as an activating substance, comprising an absorption stage in which the gas mixture is treated by means of the absorption solution, and a regeneration stage in which the loaded solution is regenerated with expulsion of carbon dioxide by treatment with desorbing gases or air in heat or by heating the solution to boiling temperature, characterized in that the regeneration is carried out under excess pressure at a temperature which exceeds the boiling point of the solution at atmospheric pressure. 2. The method according to claim 1, characterized in that the regeneration of the loaded Solution takes place by means of inert gases. 3. The method according to claim 1 and 2, characterized in that the absorption at excess pressure and a temperature exceeding the boiling point of the solution at atmospheric pressure. Considered publications: German Auslegeschriften C 7904 IVa / 12 i (published on September 27, 1956), 1 000 356. 1 sheet of drawings