FI111245B - A process for separating ammonia from a gas mixture and using an adsorbent composition for this separation - Google Patents

Abstract

The present invention is a process for ammonia gas separation from gas mixtures by a solid copper (I)-containing adsorbent. The process enables an effective and selective separation of ammonia gas from gas mixtures. Additionally it enables the efficient release of adsorbed ammonia by regeneration as well as the ammonia recovery as a pure gas for reuse. The present invention also comprises the adsorbent composition for use in selective adsorption of ammonia and the manufacturing of the adsorbent.

Description

111245

Method for Separating Ammonia from a Gaseous Mixture and Using the Adsorption Composition in this Separation - Förfarande för separering av ammoniak frän en gasblandning och användning av en adsorbentkomposition för denna separering 5

Engineering

The present invention relates to a process for separating ammonia using an adsorbent benzene composition for efficiently separating and recovering ammonia from a gas mixture of ammonia and at least one other gas, air, nitrogen, carbon dioxide, methane, hydrogen, argon, helium, ethane or propane, and solvent. , commonly known as VOCs, effectively using an adsorbent composition having a high ammonia selectivity and also having high ammonia adsorption capacity and improved regeneration properties.

Background of the Invention

Ammonia (NH3) is widely used in the chemical industry as a raw material for the synthesis of various chemicals, including fertilizers, melamine and urea. Almost all ammonia-based chemical processes also produce ammonia-containing gas mixtures, requiring the separation of ammonia gas from other gases. 20 In addition, ammonia production processes, such as the Haber-Bosch process, produce ammonia-containing gas mixtures which are essential for the separation and recovery of the process because of its competitiveness.

Primarily, ammonia is separated by conventional cryogenic separation, in which the gas mixture is liquefied by cooling and then the resulting liquid mixture is distilled at low temperature, whereby the gas components are obtained separately. However, the cryogenic separation is unsatisfactory because it has the following disadvantages: • · (1) The separation requires a great deal of electrical power.

(2) Complex cooling and heat recovery systems must be used.

(3) Construction costs are high.

30 (4) It is difficult to distinguish between compounds having nearly the same boiling point.

In the alternative, ammonia is also separated from the gas mixtures by wet absorption techniques known to those skilled in the art, for example gas scrubbers. Absorption methods can be irreversible or reversible. If the ammonia gas is absorbed, for example, in an acidic solution which converts the ammonia gas into a soluble ammonia salt in a chemical reaction, the process is typically irreversible and reuse is not possible. There are also reversible absorption-thio methods in which ammonia is absorbed in an aqueous solution or an organic solvent such as polyhydric alcohols and desorbed, e.g. by heating. However, these methods are unsatisfactory because they are difficult to perform, equipment investment costs are high, and absorbent solutions are unstable.

Gas adsorption is a separation process which consists of passing a gas stream through a solid adsorbent layer so that the gas component is adsorbed and the exhaust gas stream from which the component is removed is obtained. The adsorbed gas is then desorbed, that is, regenerated from the solid adsorbent by heating and / or reducing pressure. Generally, adsorption methods can eliminate the disadvantages of cryogenic and absorption separation. However, the separation and recovery of ammonia by adsorption differs from other gas adsorption methods, e.g. nitrogen and oxygen separation from air, since ammonia as a polar molecule is very adsorbed to many conventional adsorbents, e.g. zeolites, alumina and silica gel, and H ', C (II). (II), Ni (II), and Zn (II) ion exchange resins (S. Kamata and M. Tashiro, J. Chem. Soc. Jpn., Ind. Chem. Soc., 73, 1083 Therefore, adsorption isotherms are not advantageous to desorption, and it is difficult to regenerate the adsorbent. In order for such adsorbents to be fully regenerated, the pressure must be very low and / or high. The activated carbons behave differently from other conventional adsorbents. Ammonia adsorption isotherms of activated carbon are almost linear and can therefore be easily regenerated even by depressurising. the ammonia selectivity and adsorption capacity of the carbons are low, especially at low pressures, and the volumes of the adsorption columns should be large. It can be noted that, when performing the separation and recovery of ammonia by adsorption, the problems are associated with poor selectivity, low capacity and regenerability of conventional adsorbents.

Chemical AbstractsT Abstract 127: 163868 describes an adsorbent composition containing a zeolite carrier and CuCa. According to this publication, this adsorbent composition can be used to separate carbon monoxide from a gas mixture. si-35 containing carbon monoxide, hydrogen, nitrogen, methane and carbon dioxide.

3, 111245

Chemical Abstracts Abstract 128: 63550 describes a Cu (I) -activated C adsorbent which is shown to have high selectivity for carbon monoxide. According to this publication, this adsorbent can remove small amounts of CO from the synthesis gas of ammonia.

Only a few attempts have been made to develop an economical, efficient and selective adsorption method for the separation and recovery of ammonia from gas mixtures, based on selective adsorbents. Prior art problems have been solved mainly by various process designs in processes employing conventional ammonia adsorbents. A typical example is U.S. Patent No. 4,537,760 to Adsorption Separation and Recovery of Ammonia Gas for Ammonia Synthesis. Ammonia is adsorbed at high pressures, i.e., above 100 bar, on conventional activated carbon, silica, alumina or zeolite layers. Regeneration is accomplished by contacting said adsorbent directly with a stream of concentrated hot ammonia-containing gases at 150 ° C. The pressure must be high to achieve high adsorbent capacity and the temperature to be high during regeneration to allow sufficient release of ammonia gas.

U.S. Patent No. 4,758,250 discloses ammonia separation processes utilizing anion exchange polymer adsorbents. However, it is generally known that anion exchange polymers are expensive and sensitive to high temperatures. It is therefore impractical and uneconomic to use anion exchange polymers in ammonia adsorption processes.

It is an object of the present invention to provide an ammonia separation process which solves the above problems and uses an adsorbent which has a high ammonia selectivity and capacity but can be easily regenerated further.

Summary of the Invention • ·

According to the invention there is provided a process for separating ammonia from a gas mixture using a solid adsorbent composition containing copper (I), wherein the k-30 pair is mainly in oxidation state I. The method comprises contacting the gas mixture with a solid adsorbent composition prepared as described below. Contacting the gas mixture and the solid adsorbent composition takes place under conditions where ammonia adsorbs onto the surface of the solid adsorbent composition. The gas mixture contains ammonia and at least one other 4,111,445 gases which are air, nitrogen, carbon dioxide, methane, hydrogen, argon, helium, ethane or propane.

According to the present invention, ammonia can be separated and recovered from the off-gases in the manufacture of melamine. There is no need to build a melamine plant in the vicinity of 5 urea plants.

Preferably, the ammonia separation can be accomplished by techniques known to those skilled in the art, such as pressure swing adsorption (PSA) or vacuum swing adsorption (VSA) methods. The gas mixture is passed through one or more adsorbent layers in a series of steps as follows: (1) ammonia is adsorbed from the gas mixture to said adsorbent layer composition, (2) said adsorbent layer is desorbed after adsorption (a) by flushing the adsorbent layer with product, i.e.. and (b) lowering the pressure of the adsorbent layer to recover ammonia; and (3) raising the pressure of the adsorbent layer back to the adsorption pressure by introducing a non-adsorptive or less adsorbent gas into the ad-15 sorbent layer.

The solid adsorbent used in the process of the invention may be prepared by any of three conventional methods. In the first method, an inorganic or organic carrier which is an activated carbon, polymer, amorphous oxide or crystalline substance is impregnated with a solution of a cupric compound. The 20 copper (II) impregnated carriers are then heated at an elevated temperature in an inert, oxidizing or reducing atmosphere. If necessary, the carrier impregnated with copper (II) is reduced after heating in a reducing atmosphere whereby the copper I compound is converted to copper (I). In another method, the solid adsorbent composition may be prepared by heating a solid mixture containing a cuprous or cupric compound and an inorganic or organic carrier and, if necessary, reducing the copper (II) compound to copper (I). In the third process, the solid adsorbent can be prepared by ion exchange between an inorganic or organic carrier and a soluble cuprous solution. The copper (II) -exchanged support is then heated at elevated temperature and, if necessary, reduced to copper (I) form.

The present invention also relates to the use of highly effective and selective and easily regenerable adsorbent compositions containing copper (I) and an organic or inorganic carrier for separating ammonia from a gas mixture. The solid adsorbent compositions can be prepared by three methods. In the first process 35, an inorganic or organic carrier which is an activated carbon, a polymer, an amorphous oxide or a crystalline substance is impregnated with a solution of a cupric compound. The copper (II) impregnated carrier is then heated at elevated temperature under an inert, oxidizing or reducing atmosphere. After heating, the copper (II)-impregnated support is reduced, if necessary, in a reducing gas-5, whereby the copper (II) compound is converted to copper (I). In another method, solid adsorbent compositions may be prepared by heating a solid mixture containing a cupro or cupric compound and an inorganic or organic carrier, and, if necessary, reducing the copper (II) compound to copper (I). In the third process, solid adsorbent compositions can be prepared by ion exchange between an inorganic or organic carrier and a soluble cuprous solution. The copper (II) exchanged carrier is then heated at elevated temperature and, if necessary, reduced to the copper (I) form.

Detailed Description of the Invention

The present invention relates to a process for the selective separation of ammonia from gas mixtures containing ammonia and at least one other ingredient using solid copper (I) -containing adsorbent compositions having a substantially copper oxidation number of 1. The method comprises contacting the gas mixture with a solid, as described below. with an adsorbent composition prepared. Contacting the gas mixture and the solid adsorbent composition occurs under conditions where the ammonia adsorbs to the surface of the solid adsorbent composition. The gas mixture contains ammonia and at least one other gas, which is air, nitrogen, carbon dioxide, methane, hydrogen, argon, helium, ethane or propane.

In its broadest sense, the present invention relates to the use of copper (I) -containing compositions having high selectivity and capacity and being readily regenerable for ammonia separation by adsorption. The adsorbent compositions can be used in pressure sports adsorption (PSA), vacuum sports adsorption (VSA) and temperature sports adsorption (TSA) types. In fact, all of these are methods for separating the desired gas by adsorption from the gas mixture. They do not determine whether a distinction is possible or not. It is determined by the adsorbent. In the PSA process, the desired gas is adsorbed onto the adsorbent surface at high pressure (above 1.013 bar), after which the adsorbed gas is desorbed by reducing the pressure. In the industrial application of the PSA method, several adsorbent packed columns are installed, and each of the adsorption columns repeats 35 sets of pressurization - adsorption - rinsing - pressure reduction to provide continuous separation and recovery of product gas. The VSA process is otherwise 6111245 similar to the PSA process except that the adsorption step can be carried out at a pressure of 1.013 bar or more and the pressure reduction is always performed by purging. In the TSA process, the desired gas is first adsorbed onto the surface of the adsorbent at low temperature, and then the adsorbed gas is desorbed by raising the temperature of the adsorption system. In addition, combinations of the above methods, such as VTSA, PTSA, etc., may be used. In accordance with the present invention, the adsorbent composition may also be used in rotary wheel-type adsorption methods.

The adsorption separation according to the present invention can preferably be performed by the PSA or VSA method. The gas mixture is passed through one or more adsorbent layers in a series of steps as follows: (1) ammonia is adsorbed from the gas mixture to said adsorbent bed composition. (2) desorbing said adsorbent layer after adsorption (a) flushing the adsorbent layer with a product, i. and (b) lowering the pressure of the adsorbent layer to recover the ammonia; and (15) increasing the pressure of the adsorbent layer to the adsorption pressure by introducing a non-adsorbent or less adsorbent gas into the adsorbent layer.

These adsorbent compositions not only have a very high adsorption capacity of ammonia, but are also capable of removing it at very low partial pressures of ammonia. Most of them are capable of lowering the ammonia content of the gas mixture up to or below 10 vol. Ppm.

In the present invention, the form of the adsorbent is not critical. For example, the adsorbent may be granular, spherical or particulate. In addition, the adsorbent may be in any other form than the above, e.g. honeycomb. structurally cured, film-like or mass-like. made by molding or pelleting a 25 pellet of granular, spherical or particulate adsorbent.

As carriers for preparing the adsorbents used in the present invention, a relatively large group of solids can be utilized. However, it is desirable that the surface area of the carrier materials be greater than 100 m2g !. Examples of substances used as carrier in the adsorbent composition include, but are not limited to, natural or synthetic zeolites, silica gel, silica, alumina, activated alumina, silica-alumina gel, porous aluminum phosphate, clay minerals, , such as cation exchange resin, organic-inorganic hybrid composition such as sulfonated grafted polystyrene-silica etc. Preferred zeolites are e.g. A-zeolite, X-zeolite, Y-zeolite, dealumized Y-zeolite, 7111245 omega-zeolite zeolite, mordenite, silicalite and mixtures thereof. Zeolites may have the following cations: NFLf ions, H + ions, Na "ions, K" ions, Ca2 "ions, Mg2 + ions, Cu + ions, Cu2 + ions, Ag + ions, Fe2" ions, Fe'v ions and combinations thereof.

The solid adsorbent composition used in the process of the present invention contains a cuprous compound or a mixture thereof with a carrier as described above. The cuprous compound may be delivered to the carrier by techniques known to those skilled in the art, e.g., impregnation, ion exchange, or thermal dispersion. These procedures are described in detail below.

The starting materials for zeolite, silica-alumina, silica, silica gel, activated alumina, alumina, clay mineral, polymer, hybrid, charcoal and activated carbon are commercially available or can be synthesized by methods well known in the art. in accordance with.

As previously noted, cupro ions are an essential component of the solid adsorbent composition used in accordance with the present invention. The impregnation, thermal dispersion and ion exchange described below can be used to deposit the copper on the support. In the case of ion exchange and impregnation, a water-soluble cuprous compound is typically used because the cuprous compounds are not sufficiently soluble or stable, especially in water. Obviously, if the copper compound is applied to the support 20 by impregnation or ion exchange, then the copper (II) must be reduced in order to obtain copper (I), which is the more desirable form of copper.

Preparation of the adsorbent composition by ion exchange

The term '' ion exchange 'refers to a technique in which metal ions, in this case copper ions in particular, actually replace some or all of the cations of the zeolite, ion-exchange resin or sulfonated grafted polystyrene-silica. The ion exchange can be accomplished by mixing or slurrying the zeolite or ion exchange resin or sulfonated grafted polystyrene silica in an excess of a solution containing soluble copper (II) compound. However, the ion exchange can also be carried out continuously on the column. In either case, the concentration of the solutions will vary with the degree of ion exchange desired, but typically will be from about 0.01 to about 10 M. In some cases, heating may also be advantageous to promote ion exchange.

The ion-exchange adsorbent is dried at a temperature of about 50-120 ° C to remove excess and adsorbed solvent. Alternatively, prior to drying, the ion-exchange adsorbent may be washed with water to remove unbound compounds.

8 111245

After drying, the ion-exchanged adsorbent is heated to a temperature of about 80-800 ° C in an inert, oxidizing or reducing atmosphere and, if necessary, reduced to convert some of the copper (II) to the copper (I) form. The reduction can be carried out with any reducing agent and any reducing atmosphere that will allow this conversion to take place. Examples of oxidizing and inert atmospheres include, but are not limited to, air and nitrogen, respectively. Examples of reducing and reducing atmospheres include, but are not limited to, hydrogen, carbon monoxide and ammonia, nitrogen, helium, argon, or a mixture thereof. The reduction temperature is about 80-500 ° C. For ion exchange resins and sulfonated grafted polystyrene silica, temperatures below 120 ° C are used, and zeolites are used throughout.

The soluble cupric compound may be cupric halide, cupric oxide, cupric carboxylate, basic cupric salt, copper (II) amine complex salt, cupric sulfate and cupric nitrate or a mixture thereof. Preferably, the cupric compound is cupric halide, cupric sulfate or cupric nitrate. The amount of copper in the copper compound of the adsorbent compositions of this invention may be 1-95% by weight.

Preparation of Adsorbent Composition by Solid-Solid, Liquid-Solid, and Vapor Solid

As another method for preparing the adsorbent composition for use in accordance with the present invention, a thermal dispersion may be used. In this case, a mixture containing a copper compound and a carrier as described above is used to prepare the adsorbent mucosa. Preferably, the alloy is prepared simply by mixing the solid powder of the copper compound with the solid support. The mixture may also be; obtained by adding to a solid support a solution or suspension of a copper compound in a suitable solvent and subsequently removing the solvent from the resulting mixture by heating and / or pumping. Many cupro compounds and copper compounds or mixtures thereof can be used as the copper compound. Examples of suitable copper compounds for use in the practice of this invention include, but are not limited to, cupric halides such as cupric chloride, cuprobromide, cuprofluoride and cupric iodide; cupro -: ** oxide; cupro carboxylates such as cupro carbonate, cuproformate and cupro acetate; cupric halides such as cupric chloride, cupric bromide, cupric iodide and cuprifluoride; cupric oxide; cupric carboxylates such as cupric acetate and cupric formate; basic copper salts such as basic copper (II) carbonate, basic copper (II) acetate and basic copper (II) phosphate; and complex salts of copper (II) amine, such as hexamine-copper (II) chloride and cupric sulfate, cupric nitrate, etc. The mixture of compounds is also acceptable. Preferably, the copper compound is cupro or cupric halide or oxide. More preferably, the copper compound is cupric chloride or cupric chloride.

9 111245

A relatively large group of solids can be used as a carrier for preparing adsorbents. However, it is desirable that the carrier materials have a surface area greater than 100 m2 g "1. Examples of carrier materials used in the adsorbent composition include, but are not limited to, natural or synthetic zeolites, silica gel, silica, alumina, activated alumina, silica alumina gel, porous aluminum phosphate, clay minerals, titanium dioxide, charcoal, activated carbon and the like. Preferred zeolites are e.g. A-zeolite, X-zeolite, Y-zeolite, dealuminized Y-zeolite, omega-zeolite, ZSM-zeolite, silicalite and mixtures thereof. The cations contained in the zeolites may be NFty-ions and, H + ions, Na + ions, K ions, Ca2 + ions, Mg2 "ions, Cu ions, Cu2 ions, Ag'ions , Fe 2 "ions, Fe 3+ ions and mixtures thereof.

In the above-described alloy containing the copper compound and the carrier, the amount of copper in the copper compound is preferably from 1 to 200% by weight, more preferably from 5 to 90% by weight.

The above prepared mixture containing the copper compound and the carrier is heated. The heating temperature determines whether the preparation of the adsorbent composition is a solid-solid, liquid-solid or vapor-solid process. If the heating temperature is below the melting point of the copper compound, the preparation is carried out by the solid-solid method. As above, if the heating temperature is below or above the evaporation temperature of the copper compound, the preparation is carried out by the liquid-solid method or the vapor-solid method, respectively. In all cases, the plaintiff remains in solid form. Generally, the heating temperature is above 150 ° C, but lower than the decomposition temperature of the compound. The heating step is preferably carried out at a temperature of about 200-800 ° C. The heating time required is from about 1 minute to about 25 to 100 hours, preferably from about 10 minutes to about 50 hours. During heating, the copper compound and the carrier may be mixed continuously, intermittently, or at all. The mixing can be performed pneumatically or mechanically, e.g. in a rotary oven or drum.

** Generally, heating may be carried out in a suitable reducing atmosphere, such as carbon monoxide, hydrogen, acetylene, ethylene, ammonia, nitrogen, helium, argon, or a mixture thereof. The most preferred reducing atmosphere is carbon monoxide, hydrogen, ethylene.

If the mixture of the copper compound and the carrier consists only of the carrier and the cuprous compounds and their mixtures, heating may be carried out in a suitable inert atmosphere 35 or under vacuum. A suitable inert atmosphere is nitrogen, methane, argon, helium, carbon dioxide or a mixture thereof. The heating of the mixtures containing the copper compound can also be carried out simply in air, in an inert atmosphere or in a vacuum.

If a relatively large proportion of the copper compound in the composition is in cupric form, a separate reduction is required. The reduction of these compositions can be carried out by any known reduction method, e.g., by heating at a temperature above 100 ° C in a reducing atmosphere such as carbon monoxide, hydrogen, acetylene, ethylene, ammonia, nitrogen, helium, argon or a mixture thereof.

Preparation of the adsorbent composition by impregnation Copper can be incorporated into the above carrier by impregnation. It is known to those skilled in the art that '' impregnation '' refers to a technique in which a metal compound, which in the present invention refers to a soluble copper (II) compound, is deposited on the surface of the support and throughout its pore structure. Impregnation can be accomplished by dipping the carrier in an excess of the copper compound solution. Ku-15 chloride, nitrate, acetate or sulfate. Preferably, more accurate control is achieved by a technique known as '' impregnation to incipient wetness '' or '' pore impregnation ''. In this method, the amount of copper (II) solution corresponding to a known total pore volume, or slightly less, is injected onto the support. Impregnation can also be carried out using dispersants such as carboxylic acids and sugars.

When the starting carrier is impregnated with a copper (II) compound, the carrier is usually dried at a temperature of about 50-120 ° C to remove excess and adsorbed solvent. At this stage, the copper (II)-impregnated carrier essentially contains a solid mixture containing the copper (II) compound and the carrier. The dry impregnated support is then heated in an inert or oxidizing atmosphere. The heating temperature is about 80-800 ° C. Preferably, the heating temperature is 200-500 ° C. The time required is about 1-24 hours. Alternatively, heating may be carried out in a suitable reducing atmosphere such as carbon monoxide, hydrogen, acetylene, ethylene, ammonia, or a combination thereof. The most preferred atmosphere of your own is carbon monoxide, hydrogen, ethylene.

After heating, the impregnated copper (II) carrier is reduced to copper if necessary. Any effective reducing agent, hydrogen, ammonia, olefinic hydrocarbons such as butene, propylene and butadiene may be used; alcohols such as propanol, and aldehydes including nitrogen, helium, argon, or a mixture thereof 11111245. Carbon monoxide, hydrogen, ammonia and ethylene are preferably used. The reducing conditions have been found to be specific for the reducing agent. After reduction, the copper (I) adsorbent is generally stripped in nitrogen gas at a temperature of about 100 to about 250 for about 30 minutes to about 12 hours.

The soluble cupric compound may be cupric halide, cupric oxide, cupric carboxylate, basic cupric salt, copper (II) amine complex salt, cuprous sulfate or cupric nitrate, or a mixture thereof. Preferably, the cupric compound is cupric halide, cupric sulfate or cupric nitrate. The amount of copper in the copper compound of the adsorbent compositions prepared by impregnation may be from 1 to 95% by weight.

The following illustrative examples illustrate the process of the present invention and the adsorbent composition used therein, but are not intended to limit the invention.

Example 1 15.4 g of powdered cupric chloride was mixed with 30.0 g of silica gel (medium pore-15 size 60 Å and particle size 0.063-0.2 mm). The mixture was heated at 200 ° C for 19 hours. After cooling, the CuCl / SiO 2 adsorbent composition was milled and compressed into 2x8 mm pellets. They were crushed and particles larger than 0.23 mm were recovered by screening.

Example 2 The adsorption isotherm of the adsorbent composition prepared in Example 1 was measured vol-lummetrically by the pressure-volume method using a glass apparatus (Figure 1).

«10 -, - 1 -, -, - τη 12 111245 9 - - 8 · 7 - 'o> 6 ö ε 5 - 5. · σ 4 - 3 - · 2 · 1« ϊ 0 * -1-1- 1-1-1— 0 20000 40000 60000 80000 100000 Ν Η 3 pressure, Pa NH3 pressure, Pa

Figure 1 adsorption isotherm of CuCl / SiO 2 adsorbent at 25 ° C.

The form of the adsorption isotherm of the CuCl / SiO 2 adsorbent composition is surprisingly advantageous. First, the isotherm is approximately linear, especially at pressures greater than about 30,000 Pa, which allows for easy regeneration of ammonia from the adsorbent composition and use of the adsorbent composition in the separation of high ammonia concentrations. Second, the CuCl / SiO 2 adsorbent composition has a high ammonia capacity, which allows the use of smaller columns in separation processes and thus reduces the investment cost of the processes.

The adsorption isotherms of conventional adsorbents were also measured by the same method as above. They are presented for purposes of comparison only, to illustrate the desirability of the adsorbent compositions used in accordance with the present invention (Figures 2-5). The forms of adsorption isotherms of the zeolites and γ-A AO O. are very advantageous for the adsorption, namely they are irreversible, which means that the regeneration of these adsorbents is difficult, so low vacuum and / or high temperature must be used. Instead, the shape of the activated carbon adsorbent is linear, making regeneration of the adsorbent easy. However, the use of activated carbon for the separation of ammonia is weakened by its lower capacity, flammability and lower mechanical stability compared to the adsorbent composition used in the present invention.

13 111245 10 -, -, -, -, - r- | »- ................................-............... ....... ^ .....> 8 '7 - 7 6 ....... Langmuir-Freundlich σ> u; o

E 5 -E

σ ~ 4 * '3 -

1 -O

o -> - 1-1-1 - * - 0 20000 40000 60000 80000 100000 N H, p re ssure, P a NH3 pressure, Pa

Figure 2 Adsorption isotherm of a commercial 13X zeolite adsorbent at 25 ° C.

> »<• φ * 10 I-1-1-1-1-1-τη 14 111245 9 - 8 ~ ............ * .............. ....

............................

7 - ... · · '' * '«....... Langmuir-Freundlich 6 ϊ o

E 5 -E

cr “4 - 3 * ~ 2 -it 1 - 0 I-1 --- 1 -» - 1-200 20000 40000 60000 80000 100000 NH3 pressure, Pa NH3 pressure, Pa

Figure 3: adsorption isotherm of a commercial 5A zeolite adsorbent at 25 ° C.

1 0 -1 -j-1-1-r ~ 9 - 8 -7 - ^ 5 -o ε 5 - 4. ....... Langmuir-Freundlich 3 - 2 ..............-..............-........ .......... * .................... · - 1 o '0 * -1-1 --- L ---- 1 - * - 0 20000 40000 60000 80000 100000 NH3 pressure, Pa NH3 pressure, Pa

Figure 4 Adsorption isotherm of a commercial γ-AhOrzeolite adsorbent at 25 ° C.

10 -1 -, - 1-1-r- 15 111245 9 -8 -7 - 'σ> 6 o

E 5 -E

& 4 - * '3 - · 2 -. * 1 -.

0 -1-1-1-1-- 0 20000 40000 60000 80000 100000 NH3 pressure, Pa NH3 pressure, Pa

Figure 5: adsorption isotherm of a commercial activated carbon adsorbent at 25 ° C. EXAMPLE 3 The purpose of the following example is to illustrate the advantages of the present invention over a process employing a commercial 5A-zeolite adsorbent. Table 1 shows three consecutive 5A zeolite adsorption-regeneration cycles. An adsorption step 4 of 1/1 adsorption step was performed only to determine the capacity of the adsorbent layer after the regeneration step, Adsorption regeneration period 1 to 4 corresponded to the method whereby a mixture of 10.3% ammonia in air was introduced into the adsorbent layer until the passage of ammonia. The feed was stopped immediately after permeation, and the adsorbent bed was flushed upstream with 100% ammonia gas to remove diluting air from the bed. Finally, the adsorbent layer was regenerated by heating at 125 ° C and evacuating at 11 mbar for 35 minutes by flushing up to 10.8 mL min 1 air flow. Table 1 shows that the adsorption step 1 had a permeation capacity of 3.55 mmol NH 4 "", a total capacity of 7.34 mmol NH 3 g -1 calculated from 100% ammonia feed and the amount of ammonia recovered from regeneration 1 was 84.5%. After the adsorption regeneration period 1, the adsorbent layer was impregnated directly with 100% ammonia gas feed without initially introducing 10.3% ammonia into the column as described above. This was not necessary because the total capacity of the bed is the same in both cases. In the adsorption regeneration cycle 2, regeneration was carried out at 12 mbar for 5 minutes, whereby 43.2% ammonia gas was released. Regeneration step 3 was performed in the same manner as step 1 except that the regeneration time was 5 minutes. The yield of ammonia 5 was 69.2%.

Table 2 shows eight successive adsorption regeneration cycles for the adsorbent composition prepared as described in Example 1. In the Ad sorption step 1, a gas mixture containing 10.3% by volume of ammonia and 89.7% by volume of air was passed through the column. Feeding was terminated after reaching the breakpoint of amo-multiple. The adsorbent layer had a permeation capacity of 2.40 mmol NH. g-1. After the adsorption step, it was regenerated at 10 mbar for 5 minutes to release 25.3% ammonia. In the adsorption step 2 of the adsorption-regeneration period, 10.3% ammonia mixture was fed as in step 1 until passage. Regenerated by heating at 126 ° C and evacuating at 10 mbar with 10.8 ml min-1 purge air flow. Thus, 87.5% of the ammonia was released from the adsor benthic layer. At the beginning of the adsorption step 3, the adsorbent benzoate was impregnated with a 10.3% ammonia gas mixture to the breakpoint, then saturated with 100% ammonia to equilibrium. The total capacity of the CuCl / SiO 2 adsorbent composition was significantly higher than that of 5A zeolite at 100% ammonia feed, i.e.

11.4 mmol NH3 g ”1. In regeneration step 3, the adsorbent layers were evacuated at 10 mbar for 5 minutes and, surprisingly, the yield of ammonia was 70.7% compared to the value of 5A zeolite obtained in the corresponding experiment 43.2%. Reactivation. in steps 4 and 7, combined regeneration was investigated by heating at 125 ° C and evacuating at 10 mbar with 10.8 mL min of flushing air flow. The yields of ammonia in steps 4 and 7 were 92.1% and 99.1%, respectively. These values are significantly higher than the value obtained for the 5A zeolite in the corresponding experiment, i.e.

69.2%. In regeneration step 5, the adsorbent layer was completely purified when heated at 125 ° C and with a high air flow rate. Finally, the size of the floor «. The cone capacity at adsorption step 8 was 11.16 mmol NH3 g-1. This confirms that the adsorbent composition used in accordance with the present invention is stable over several successive adsorption regeneration cycles.

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Table 1 Ammonia capacities of commercial 5A zeolite, treatments of adsorption and regeneration steps, and ammonia yields of regenerations as determined by permeation experiments on an adsorption column (internal diameter 19 mm) containing 10.5 g of adsorbent. Adsorption in layer 1 to layer 5 was fed with a mixture of 10.3% ammonia in air (No grain 43.2 mL min "1 and air flow 378.2 mL min" 1). The layer was then directly saturated at 100 percent ammonia gas supply (NH flow 194.5 mL min'1) Adsorption Steps 2-4 utilized only 100% ammonia feed.

10

Section Treatments Ammonia Capacity ________________________ 1 Adsorption Step 41.6 ° C, 10.3% Permeation, 100% q = 3.55 mmol g "1 to Equilibrium (Permeation) q = 7.34 mmol g" 1 (Total) 1 Regeneration Step 125.0 ° C + 11 mbar + 10.8 rpm oil ”1, R = 84.5% 35 min 2 Adsorption step 39.9 ° C, 100% q = 6.20 mmol g” 1 2 Regeneration step 12 mbar, 5 min R = 43.2% 3 Adsorption step 40.3 ° C, 100% q = 3.17 mmol g ”1 3 Regeneration step 124.3 ° C + 14 mbar + 10.8 ml / min min'1, R = 69 , 2% 5 min • 4 Adsorption step at 40.0 ° C, 100% q = 5.08 mmol g ”1

Table 2 Ammonia capacities of the adsorbent composition prepared as in Example 1, treatments of adsorption and regeneration cycles and ammonia yields to be regenerated. Values are determined on an adsorp-15 thiol column (internal diameter 19 mm) containing 2.9 g of adsorbent by means of permeation experiments. In the adsorption steps 1 and 2, a mixture of 10.3% ammonia in air (NH3 flow 21.7 ml min '1 and air flow 189.7 ml min' 1) was fed to the bed until permeability. Thereafter the feeding was stopped and the layer was regenerated. At the beginning of the adsorption step 3, 10.3% ammonia gas mixture was fed to 20 layers. followed by 100% ammonia (NHavilt 195.2 mL min ') from saturation to equilibrium. In steps 4-8 of adsorption 18111245, the layers were saturated directly to equilibrium with 100% ammonia gas feed.

Section Treatments Ammonia Capacity (g) or Yield (R) 1 Adsorption Step 39.3 ° C, 10.3% Permeation q = 2.40 mmol g "1 (Permeation) 1 Regeneration Step 10 mbar, 5 min R = 25 , 3% 2 Adsorption step 39.5 ° C, 10.3% up to pass q = 0.61 mmol g'1 (pass) 2 Regeneration step 125.9 ° C + 10 mbar + R = 87.5% 10.8 min ™ min "1.5 min 3 Adsorption step 40.1 ° C, 10.3% up to permeability, q = 2.10 mmol g" 11 up to 100% equilibrium (permeability) q = 11.4 mmol g "1 (total) 3 Regeneration step 10 mbar, 5 min R = 70.7% 4 Adsorption step 39.5 ° C, 100% q = 8.32 mmol g "1 4 Regeneration step 126.3 ° C + 10 mbar + R = 92.1% 10.8 mljima min "1.5 min 5 Adsorption step 40.0 ° C, 100% q = 10.84 mmol g" 1 5 Regeneration step 125.0 ° C + high rinse volume R = 100% 6 Adsorption step 39.8 ° C, 100% q = 11.77 mmol g "1 • 6 Regeneration step 11 mbar, 5 min R = 65.7% 7 Adsorption step 39.4 ° C, 100% q = 7.73 mmol g" 1 7 Regeneration step 126.1 ° C + 12 mbar + R = 99.1% for 10.8 ml / min "1, 5 min 8 Adsorption step 40.1 ° C, 100% q - 11.66 mmol g "1" 5 Example 4

According to the invention, ammonia can be separated and recovered by means of adsorbent compositions containing copper (I) from gas mixtures containing ammonia and other gases such as nitrogen, carbon dioxide, hydrogen and methane, in the same manner as in Example 3 from air.

19, 111245

Example 5

Copper (I) -containing adsorbents which work as advantageously as the CuCl / SiO 2 adsorbent of Examples 2 and 3 can be prepared by impregnation, thermal dispersion and ion exchange.

The foregoing general discussion and embodiments are intended to illustrate, not limit, the present invention. Other variations within the spirit and scope of the invention are possible and will be apparent to those skilled in the art.

Claims (9)

111245 A process for separating ammonia from a gas mixture, characterized in that a solid adsorbent composition containing copper (I) is used. Process according to Claim 1, characterized in that said gas mixture contains ammonia and at least one other gas which is air, carbon dioxide, water, nitrogen, hydrogen, argon, helium, methane, ethane or propane. A process according to claim 1 or 2, characterized in that said gas mixture consists essentially of ammonia and other gases released during melamine production. A process for separating ammonia from a gas mixture according to any one of claims 1 to 3, characterized in that the gas mixture is passed through one or more copper (I) -containing adsorbent layers and the process comprises the following steps: 1. ammonia is adsorbed from said gas mixture Said adsorbent layer (s), said adsorbent layer (s) being desorbed after adsorption (a) rinsing said adsorbent layer (s) with a product, and (b) reducing the weight of said adsorbent layer (s), adsorbing pressure by introducing into said adsorbent layer (s) a non-adsorbent or a less adsorbent gas. Use of a solid adsorbent composition comprising an organic or inorganic carrier and copper, mainly in oxidation state I, for separating ammonia from a gas mixture. Use according to claim 5, characterized in that the inorganic carrier is natural or synthetic zeolite, silica gel, silica, alumina, activated alumina, silica-alumina gel, porous aluminum phosphate, clay mineral or titanium dioxide. 111245 Use according to claim 5, characterized in that the organic carrier is an activated carbon, charcoal, ion-exchange resin such as a large-cell cation-exchange resin, a non-functionalized polymer such as polystyrene-divinylbenzene-resin, or a hybrid inorganic composition such as a sulfonated oxy. Use according to any one of claims 5 to 7, characterized in that the adsorbent composition contains a cuprous compound which is cuprohalide, cupric oxide, cupric carboxylate or a mixture thereof. Use according to Claim 8, characterized in that the cuprous compound is 10 cupric chloride.