DE2038765A1 - Process for the separation of carbon dioxide from a mixture of acid-free gases - Google Patents

Description

_o "., _Well . DIPL.-ΙΝβ. M. "OOPt.-l-MVe. OR. D.

HÖGER - LEGAL RIGHTS - GRIESSBACH - HAECKER PATENT LAWYERS IN STUTTGART

A 38 311 m

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August 1, 1970

Mine Safety Appliances Company 201 North Braddock Avenue
Pittsburgh, Pennsylvania 15208 / USA

Process for the separation of carbon dioxide from a mixture of acid-free gases

The invention relates to a method for separating carbon dioxide from a mixture of acid-free gases or from breathable air.

Carbon dioxide must often be obtained from gas mixtures in the production " can be leached out by carbon dioxide itself; it is also present in fire gases when carbon-containing ones are burned Materials contain and absorb the same but also in a variety of other compounds, the main reason being a separation of the carbon dioxide can be seen in the removal of this from a desired product gas .. Auf

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In this way, carbon dioxide is removed from working gases or synthesis gases in a steam-hydrocarbon reforming process • for the production of hydrogen _t ammonia and methanol. Furthermore, it is necessary to remove carbon dioxide from gaseous air-hydrocarbon combustion products in order to generate inert gas atmospheres free of oxygen and carbon dioxide; such inert atmospheres are necessary, for example, for the storage of fruits and other products. In addition, it is necessary to remove the exhaled carbon dioxide from the atmosphere in chambers inhabited by people or other living beings, such as submarines and space capsules.

The invention is based on the object of such a separation of carbon dioxide from other gases to an extraordinarily high degree efficient and quick way to carry out, where the separation is of great effectiveness and where moreover the possibility is to regenerate the separating medium again, and to do so repeatedly.

To solve this problem, the invention is based on a method for separating carbon dioxide from a mixture acid-free gases or breathable air and consists in that the gas mixture through a layer (bed) einr-j weak basic ion exchange resin at a temperature is, in which the carbon dioxide is absorbed by the resin, that then steam in the with a Cinla.3-

BATH ORIGINAL

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layer equipped with an outlet opening is initiated, such that the steam condenses at the inlet and forms a Front pushes condensed vapor in the longitudinal direction through the layer, whereby the sequence does not shift against each other absorbed gas and desorbed or released carbon dioxide are released or flushed out of the layer.

This steam generation process first removes the unabsorbed gases from the resin layer, in contrast to carbon dioxide, which have been retained in the free spaces of the layer and then the desorbed carbon dioxide. Such a regeneration process achieves a higher purity of the carbon dioxide and the carbon dioxide-free gases, so that such a regeneration process is to be regarded as an essential part of the invention.

The process just described is for separating carbon dioxide from gas mixtures that contain air, inert gases such as helium, neon and argon, diatomic gas such as hydrogen, oxygen and nitrogen and other acid-free gases that are not absorbed by the weakly basic ion exchange resin, suitable. Gasr.ischungen, the acidic gases such as _Λ CcLwefeloxyd contained in flue gases can be pretreated to ™ usual way to the acid gas prior to introduction into the carbon dioxide separation process to separate.

Fig. 1 can be partly in section and partly in schematic form Representation of an arrangement for implementing de3 according to the invention Removed from the procedure,

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Pig. 2 shows schematically the condition of the resin layer according to Pig. 1 during a regeneration cycle.

The absorbents are first described below. Generally speaking, weakly basic ion exchange resins are for use as absorbents in accordance with the invention useful. Such resins have primary, secondary and / or tertiary functional amine active groups attached to a polymer matrix are attached. The polymer matrix can usually be a polystyrene, a polystyrene-divinylbenzene copolymer, a phenol-formaldehyde, a polyacrylic acid, a polymethacrylic acid-divinylbenzene mixed polymer JBat or an epoxy type polymer. A large number of these resins are available in the Hai del and can be used for the present Invention may be used, but to varying degrees of utility.

Preferred weakly basic ion exchange resins, which have a particularly high affinity and capacity for carbon dioxide, can be regenerated repeatedly without a substantial loss of their absorption properties therein including those resins in which the active group has a polyamine functionality and at least one contains secondary nitrogen amine. Such materials will be produced by reaction of an addition polymer or a Condition polymer with polyfunctional amines, which a

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have secondary nitrogen amines, such as dietary hygienic triamine, Triethyl tetramine and tetraethylene pentamine. Such preferred resins include polyacrylic acid-polyamine resins, the are made according to the instructions of U.S. Patent 2,582,194 and epoxy-polyamine resins prepared in a conventional manner by reacting an epoxy resin and a polyamine in a solution such as xylene.

Polystyrene-divinylbenzene copolymers of the gel resin type have polyamine functional groups and are especially suitable as absorbents. Resins of this type can get through Reaction of a chloromethyl (chloromethylated) -styrene divinylbenzene copolymer with an amine such as diethylenetriamine, triethyltetramine, tetraethylpentamine and other polyfunctional amines are produced. An equimolar amount or excess of amine for each Chloromethyl group causes a condensation of a chloromethyl group with an amine group as shown by that shown below Reaction using diethylenetriamine shown, shows:

+ HCl

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If the ratio of the amine is 1/2 of the equal molar or equimolar ratio, then the condensation creates an additional cross-linking and mainly one second The amine functionality is favored according to the following equation:

[CH ₂ -CH ₂ -J _x

I. II ♦ 2HCl

CH ₂ -NH-CH ₂ -CH ₂ -InI-CH ₂ -CiI ₂ -NH-CH ₂

The carbon dioxide capacity of this type of resin is relative to the ion exchange capacity and conventional methods of improving ion exchange capacity also improve dynamic carbon dioxide capacity. In order to achieve a suitable porosity, copolymers are preferably used which contain less than about 10 » divinylbenzene, expediently 3 to 5 #. Amberlite IR- 45, a chloromethyl

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polystyrene-divinylbenzene copolymer (choromethylated polystyrene-divinylbenzene copolymer), to which diethylenetriamine is added, is a typical one that can be purchased Resin of the preferred type.

The method according to the invention is explained below with reference to FIG. 1, in which an apparatus for removing exhaled CO ₂ from the air in a closed space for maintaining a breathable atmosphere is shown partially schematically. A layer 2 of a weakly basic ion exchange resin is held between two screens "or grids 4 in a space 6; the space 6 is formed by a housing 8 which contains removable cover parts 10 secured with flanges 12. A layer of a flexible, open Foam having cells enables a change in the layer volume, which is caused by different swellings of the resin as a result of different water content. The space is provided with an air inlet opening 14, an outlet opening 15, a steam inlet opening 16 together with associated valves 20, 22, 24 and 26. Heat switch (Thermal switch) 30 and gas volume meter 32 are connected to suitable switching mechanism to open and close the control valves, as will be shown in more detail below M. A condenser 29 removes water vapor from the vented air when dehumidification is desired, as in FIG maintaining a breathable Atmosphere is the case.

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The absorption cycle is discussed in more detail below. If the valves 24 and 26 are closed and the valves 20 and 22 are open, then carbon dioxide is present Room air is forced through the resin layer by means of a fan 34, the carbon dioxide being absorbed by the resin will. The absorption cycle can be a predetermined one Have duration, depending on the characteristics of the particular apparatus being used, but it may as well as a result of a signal which detects COp in the outlet gases, using conventional gas analyzers and monitoring systems.

The resins which are capable of absorbing carbon dioxide contain absorbed water, and expediently have · over 5 Ί · water content; however, preferably the resin is not wet due to unabsorbed water which would hinder carbon dioxide absorption. Although the capacity of various resins differs somewhat, in general a water content of less than about 30 % represents essentially completely absorbed water. The humidity of the gas which flows through the resin layer can, if necessary, be adjusted to an appropriate one To achieve equilibrium with regard to the water content in the resin. For example, at 24 °, and reaches a gas having a relative humidity of 50 $> an equilibrium state at 5 to 10 wt. # Of water in the resin, while a gas with 90 i "relative humidity in an equilibrium state at 25 to 30 # water content in reaches the resin. In general, a gas with a relative humidity of 75 to 90 # is preferred.

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Carbon dioxide is released from the resin layer or resin bed easily absorbed at normal ambient or room temperatures, but higher or lower temperatures can also be used if so desired. The effectiveness the absorption is somewhat increased at lower temperatures above the freezing point of the water, during the Absorption efficiency essentially at temperatures is reduced by or above 33 ° C. Generally one will may prefer to continue the absorption cycle when appropriate f

Operate at temperatures between 5 and 33 ° C. A temperature setting can be done by disguising the resin layer contained chamber can be achieved for the purpose of cooling or heating, or more simply by adjusting the temperature of the incoming gas.

If the method of the present invention is used to remove carbon dioxide in order to maintain a breathable atmosphere, the inflowing gas will contain about 0.4-0.5% carbon dioxide. At the beginning of the absorption ^{cycle 1} , the gas leaving the resin layer will contain very little carbon dioxide, for example 0.1 $> or less COp; this value depends on the ski cht deep, on the spatial Flußgesehwin- \ velocities of the gases on the particular resin and other, existing even at normal absorption process parameters. When the absorption cycle ^{1 continues} , the gas flowing out will contain a slowly and gradually increasing proportion of carbon dioxide, and if

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the carbon dioxide concentration of the outflowing gas reaches a predetermined value, the absorption cycle is ended. In order to maintain a breathable atmosphere, the absorption cycle is preferably terminated when the effluent gas contains about 0.2 to 0.25% carbon dioxide; at these input and output readings of carbon dioxide concentrations, the resin absorbed 1.75 to 2.25 carbon dioxide Gew.56 · At higher concentrations of carbon dioxide is absorbed, a greater proportion of carbon dioxide, for example, the resin absorbs i at an input concentration of 2 »and a starting concentration of 1.5 # carbon dioxide about 4% by weight of carbon dioxide.

The regeneration cycle is explained in more detail below. According to a feature of the invention, the absorbed carbon dioxide is removed from the resin layer or from the resin bed by introducing steam; if the absorption cycle has taken place at low temperatures, preferably at temperatures below 33 ° C., steam now condenses and the condensed steam is absorbed by the resin and transfers the latent heat of evaporation to the resin. As soon as the steam reaches the absorbent and condenses, a front of condensed steam pushes its length through the layer and dissolves absorbed carbon dioxide and air contained in the free spaces of the layer. Due to the increase in the partial pressure of the carbon dioxide in front of the condensation front, CO ₂ is reabsorbed again, so that the originally

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air contained in the layer faster than the COg is purged.

This regeneration process leads to an effective separation of the deeorbed or released carbon dioxide and the air flushed out as well, as will be explained in more detail below with reference to FIG. Fig. 2 shows schematically the state of a resin layer 36 during regeneration at the moment when the condensation front has reached pos. 38. If at one end of the shift When steam is introduced, it will condense on the cooler resin layer and heat it up. He becomes the same at the same time Displacement of air while the vapor pressure drops on the condensation front. The subsequent steam pressure pushes more steam over the hot, wet surface in contact with the still cooler layer material. The plasma mixture that pushes through the layer consists of steam, resorbed carbon dioxide and air. The EaEpf condenses in the condensation zone 1. The hot carbon dioxide-air mixture that originating from the condensation zone is cooled by the layer in zone 2. The carbon dioxide concentration is in this area is considerably high, so that the high partial pressure causes a very rapid reabsorption of the carbon dioxide by the Resin up to amounts approaching the theoretical capacity of the resin, i.e. up to about 20% by weight of carbon dioxide at a carbon dioxide pressure of 1 atmosphere. The displaced air is not absorbed and gets there in zone 3 and emerges first from the outlet layer opening

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deflate. As soon as the leading edge of zone 2 reaches the end of the bed, which is appropriately done by measuring the displaced gas volume or by determining a temperature rise above 33 C, some CO ₂ also comes out of the bed along with the displaced air. As a result, when the condensation front reaches the rear end of the resin layer, which is appropriately determined by a further rise in temperature, only carbon dioxide is flushed out. A special feature of this regeneration process can be seen in the self-correcting property of the steam flow through the tightly packed layer, whereby channel formation is reduced or practically completely prevented. Whenever there are cold spots in the layer, ■ these spots act as condensation points, with the water serving to increase the pressure drop. This forces the steam to condense at every point, so that the layer has an extremely uniform temperature in any cross-sectional plane.

With reference to Figure 1, the regeneration cycle goes like this make sure that the valve 20 is closed and the regeneration is carried out by opening the valve 24, which one Allowed steam to enter the layer to a predetermined extent, so that the steam, as described above, is progressive condensed through the layer. The one pushed out

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Air emerges first from the resin layer and flows through it the valve 22 and passes through the condenser 29 back into the breathable air circuit.

When the condensation front has advanced through the bed to such an extent that the front end of the reabsorption zone reaches the end of the resin bed, the release and scavenging of carbon dioxide from the bed begins. The valve 22 is closed and the valve 6 is opened in order to let the carbon dioxide into the line 27. The valves can be operated automatically to perform the regeneration cycle in response to a signal generated by the detection of carbon dioxide in the effluent gases. It should prove to be expedient ^{to switch the valves or to put them into operation during the regeneration cycle 1,} taking into account the gas volume counter 32, which closes the valve 26 by means of a suitable relay system and opens the valve 28. This volume counter is set so that it emits a signal when the volume of the purged gas corresponds to the volume of air originally contained in the layer.

The thermal switch or the switch 30 responding at a temperature closes at about 100 ° C or when the The condensation front has arrived and actuates suitable relays that close the steam valve 24 and valve 26, thereby ending the regeneration cycle.

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Depending on whether it was the original intention to produce pure carbon dioxide or to remove carbon dioxide from other gases, the timing of the closing of the valve 22 and the opening of the valve 26 can be adjusted so that either through the valve 22 one of carbon dioxide essentially completely free passage of other gases takes place or that through the valve 26 carbon dioxide, which is essentially completely freed from other gases, flows. In this way, about 85 i of carbon dioxide and other gases are separated cleanly with a purity of 99 + $>>; higher yields are possible if a higher level of impurity is allowed.

The fan 34 is then turned on again and the valves 20 and 22 are opened for the next absorption cycle. The air flowing through the layer quickly cools it down and removes the excess in the resin from the previous one Regeneration cycle used water, which was then taken from the air stream by means of the condenser 29.

The process of regeneration, in which the air and carbon dioxide are separated from one another, is a valuable one and represent an important measure, namely with regard to the fact whether the separation for the production of carbon dioxide or from air or to obtain another non-absorbed gas. For example, in this way it is possible to use Systems in space that serve to support life and in which the distance and loss of the

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remaining air would be very expensive by means of the invention Regeneration process, the separation of the carbon dioxide to be removed or discarded while maintaining and retaining substantially all of the air.

The effectiveness of the method according to the invention can be seen in the following example. During a test run using the in Pig. 1 shown apparatus

0.566 m ⁵ per minute (20 cfm) room air (at 27 ° C) with a content of $ 0.48> carbon dioxide through a layer of Amberlite IR-45 resin with a diameter of 37 cm and a depth of 14 cm at a Weight of approx. 12 kg passed through. After one hour the layer had absorbed _{about 0.227 kg of CO 2.} The outflowing gas contained less than 0.1 f> CO ₂ f for 30 minutes, after which the concentration rose to 0.28 # by the end of one hour. Steam was then admitted to one end of the bed at a flow rate of 4.08 kg / hour (9 ^ / hour). After 7 minutes, the temperature of the thermal switch reached 33 ° C., the reflux of the outflowing air into the room was stopped and the outflow was made through the outlet side 27 intended _{for CO 2;} until this ύ

• χ "

Moment was about 95 i "or 20 dnr of containing in the film! Air emitted without mixing with carbon dioxide. After a further 6 minutes, the temperature of the thermal switch was approx. 100 °, whereby the steam flow was switched off, the valve 27 closed and the absorption

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cycle has started again. The carbon dioxide was practically "completely desorbed and recovered. That excess water remaining in the resin layer was removed after about 5 minutes by the air flowing through it. Such an absorption-regeneration cycle can be performed without any substantial Change in effectiveness for a practically unlimited number of repetitions, and well over 1000 times, to be repeated.

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Claims (6)

Al- A 38 311 m a - fl August 1, 1970 Claims 1. A method for separating carbon dioxide from a mixture of acid-free gases or from breathable air, characterized in that, that the gas mixture through a layer (bed) of a weakly basic ion exchange resin at a Temperature is passed through at which the carbon dioxide is absorbed by the resin, that subsequently Steam is introduced into the layer equipped with an inlet and an outlet opening, in such a way that the Steam condenses at the inlet and a front of condensed steam pushes its length through the layer, whereby the unabsorbed gases and desorbed carbon dioxide are shifted from one another in sequence Layer released or rinsed out. 2. The method according to claim 1, characterized in that the resin has a polyamine puncture with at least one having secondary nitrogen amine. 3. The method according to claim 1 and / or 2, characterized in that the polymeric matrix of the resin is a polystyrene-divinylbenzene copolymer is. 109809/1797 A 38 311 JD 1st Augist 1970 4. The method according to one or more of claims 1 to 3, characterized in that the gas mixture has a temperature between 5 and 33 ° C and a relative humidity between 45 and 90 #. 5. The method according to one or more of claims 1 to 4, for use in an enclosed space, in particular For space capsules and the like, characterized in that breathing air is passed through the resin layer and back into the closed space is introduced that the air passage when reaching a predetermined concentration of the Carbon dioxide content in the outflowing air is interrupted and that released by the introduction of the steam breathable atmosphere is fed back into the closed chamber, while the carbon dioxide carried out is outside the Chamber is eliminated. 6. The method according to one or more of claims 1 to 5, characterized in that the amine component of the resin Diethyl triamine is. 109809/1797