Production of ammonium salts from carbon dioxide and ammonia in the presence of ionic liquid

Abstract

The invention relates to a method for producing at least one ammonium salt from carbon dioxide and ammonia, the method comprising: (a) a first step of reacting carbon dioxide and ammonia in an ionic liquid, producing at least one ammonium salt, and (b) a second step, taking place at the same time as the previous step, in which the obtained ammonium salt precipitates.

Description

[0001] DESCRIPTION

[0002] PRODUCTION OF AMMONIUM SALTS FROM CARBON DIOXIDE AND AMMONIA IN THE PRESENCE OF IONIC LIQUID

[0003] TECHNICAL SECTOR

[0004] The present invention belongs to the chemical industry sector and, in particular, relates to a process for the production of ammonium salts derived from carbon dioxide, preferably mixtures of carbamate and ammonium carbonates, from a reaction between carbon dioxide and ammonia in the presence of an ionic liquid.

[0005] BACKGROUND OF THE INVENTION

[0006] In recent years, the carbon and nitrogen cycles have become essential for ensuring the atomic recovery of both elements within the framework of resource circularity. Carbon dioxide and ammonia, among others, are two key vectors in the carbon and nitrogen cycles. Capture units or adsorbents exist for both compounds, as well as processes in which they react to produce ammonium carbamate, ammonium carbonate, and / or urea. This latter process is one of the simplest for their retention, as it occurs under ambient conditions in the presence of water or organic solvents.

[0007] International application WO 2020 / 025815 describes a process for producing urea or ammonium carbamate using industrial streams, where it is necessary to regenerate the solvent in which the reaction takes place. On the other hand, US patent 10233089 proposes an integrated system for capturing and converting carbon dioxide and producing energy using an osmotic system based on solutions of ammonium carbamate, carbonate, and / or bicarbonate. However, it does not address the production of ammonium salts based on carbon dioxide without a reaction medium or solvents. Patents US 10695719 and GB 2576511 incorporate nitrogen oxides in the production of ammonium carbamate in aqueous solution, AdBlue®, although the processes described in both documents do not resolve the separation of the reaction medium (water) and the ammonium carbamate.International application WO 2021 / 005588 focuses on the production of ammonium carbamate solutions from salts in aqueous solution, without addressing the separation of the carbamate itself. International application WO 2006 / 121332 combines the production of melamine and ammonium carbamate to concentrate the ammonium carbamate solutions prior to urea production, although it does not achieve complete water separation and requires very high temperatures and pressures.

[0008] The present invention arises as a solution to the above drawbacks, eliminating the need to use high pressures and separation stages after the production of ammonium carbamate, carbonate or bicarbonate.

[0009] DESCRIPTION OF THE INVENTION

[0010] A first object of the invention is a process for obtaining at least one ammonium salt from carbon dioxide and ammonia, characterized in that it comprises:

[0011] (a) a first reaction step between carbon dioxide and ammonia in the presence of at least one ionic liquid, which acts as a catalyst, yielding at least one ammonium salt; and

[0012] (b) a second stage, simultaneous to the first stage, of spontaneous separation, by precipitation, of the ammonium salt obtained in the first stage.

[0013] The claimed process can be carried out in either an open or closed cycle and does not require the addition of any other compounds. Preferably, the process will be carried out continuously.

[0014] In one particular embodiment of the invention, the process includes a preliminary feeding stage to at least one reactor of a first stream comprising carbon dioxide and a second stream comprising ammonia. In one particular embodiment, both compounds can be fed simultaneously in separate streams. Alternatively, both compounds can be fed sequentially, first the CO2 and then the ammonia. In a further embodiment of the invention, the carbon dioxide and ammonia can be fed to the reactor together in a single stream comprising both compounds.

[0015] Likewise, the ionic liquid can be fed continuously or in batches, with the preferred option being to work in semi-continuous mode; that is, to load the ionic liquid into the reactor and operate with the continuous input of carbon dioxide and ammonia.

[0016] Preferably, the molar ratio between carbon dioxide and ammonia can vary from 100:1 to 1:100, preferably from 10:1 to 1:10, more preferably from 1:1 to 1:3, and even more preferably from 1:2. Additionally, the molar ratio between ammonia and ionic liquid can vary, preferably, between 1000:1 and 1:1000, more preferably between 100:1 and 1:100, even more preferably between 10:1 and 1:10, and still more preferably between 5:1 and 1:5.

[0017] The ionic liquid may consist of an organic salt that is liquid under the operating conditions. This organic salt may comprise a cation preferably selected from a group consisting of phosphonium (preferably tetraalkylphosphonium), ammonium (preferably tetraalkylammonium), at least one alkylmethylimidazolium, and at least one alkylmethylpyridinium, as well as any combinations thereof (either dicationic ionic liquids or mixtures of ionic liquids). The alkyl groups of all these cations may incorporate, but are not limited to, chains of between 1 and 16 carbon atoms. In particular, compounds derived from the above, such as alkylmethylimidazolium and alkylmethylpyridinium, in which the alkyl groups have polar substituents, such as alcohols or thiols, and / or unsaturations, may also be used.

[0018] Additionally, the organic salt may comprise an anion preferably selected from a group consisting of at least one halide (preferably iodine, bromide and / or chloride, among others), bis(trifluoromethylsulfonyl)imide, at least one heterocyclic aprotic anion (preferably 2-cyanopyrrole, bromopyrazole, imidazole and / or triazole, among others) and at least one amino acid (preferably methionine, glycine, lysine and / or proline, among others), as well as any combinations thereof (either of dianionic liquids or mixtures of ionic liquids).

[0019] In a particular embodiment where the reaction is carried out using a mixture of ionic liquids or dicationic and / or dianionic ionic liquids, the reaction result will be a mixture of ammonium salts, among which may be salts that precipitate spontaneously, which can be separated simultaneously by precipitation, and other salts that, due to their polar nature, do not precipitate simultaneously. These salts (that do not precipitate simultaneously) can be separated in a subsequent step of the separation process, for example, by extraction with at least one volatile solvent that causes them to precipitate or, alternatively, that promotes the precipitation of the ionic liquid. The claimed process is carried out under mild conditions, preferably defined as a temperature between 0 e C and 300 e C, more preferably between 0 e C and 70 eC, and a preferred pressure between 100 kPa and 10,000 kPa. In any case, there are multiple combinations of pressure and temperature conditions valid for this process, which, without limitation, can range from ambient temperature and atmospheric pressure to high pressures and moderate temperatures. In preferred embodiments of the invention, these temperature and pressure combinations can be, among other examples, 25 e C and 100 kPa, 0 e C and 100 kPa or 50 e C and 200 kPa.

[0020] In a particular embodiment of the invention, the process can be carried out in the absence of water. For this purpose, the process can be performed by applying a vacuum to the ionic liquid contained in the reactor to remove the water present in it or in the reaction medium, preferably at a pressure of between 50 and 1 kPa, more preferably between 20 and 1 kPa, or even more preferably between 5 and 1 kPa. Under these vacuum conditions, operation in the absence of water is achieved. Another alternative for removing water from the ionic liquid and the reaction medium is the use of physical or chemical desiccants. Furthermore, in this particular embodiment where the process is carried out in the absence of water, the reactants (carbon dioxide and ammonia) must be introduced into the reactor dry. This can be achieved by any method of drying these streams, such as by using commercially available adsorbents such as zeolites or silica.It has been shown that, under these conditions of absence of water in catalyst, reaction medium and reagents, a pure ammonium salt, particularly ammonium carbamate, can be obtained.

[0021] Furthermore, the claimed process can be carried out in any reactor that allows operation at variable pressure and temperature, within the temperature and pressure range at which the process takes place. Preferably, the reactor further comprises agitation means to facilitate mixing between the carbon dioxide, ammonia, and ionic liquid, as well as means for controlling pressure and temperature.

[0022] One of the main advantages of the process that is the subject of the invention is that it allows for the integration of CO2 capture and conversion into ammonium salts (preferably ammonium carbamate, carbonate, or bicarbonate). Furthermore, it is a process that can be implemented in any production line or waste treatment facility, given its operational flexibility and minimal requirements, essentially a container with ionic liquid.

[0023] Thus, the main advantages of the claimed procedure are the following:

[0024] It allows the simultaneous synthesis and separation of ammonium salts derived from carbon dioxide;

[0025] It allows operation under very varied conditions of temperature, pressure, carbon dioxide concentration, and ammonia concentration;

[0026] It is universal against a wide variety of ionic liquids with very different densities, viscosities, molecular weights, and polarities; and

[0027] It requires only one process vessel and at least one ionic liquid, which is self-regenerating in each cycle, making its replacement potentially unnecessary.

[0028] BRIEF DESCRIPTION OF THE FIGURE

[0029] • Figure 1. Representation of the effect of the type of ionic liquid on the conversion of ammonia to carbon dioxide-based ammonium salts at 25 e C and 400 kPa.

[0030] PREFERRED EMBODIMENT OF THE INVENTION

[0031] The present invention is based on a process for producing ammonium salts derived from carbon dioxide in the presence of an ionic liquid. One of the main novel aspects of the invention is that it allows for the simultaneous reaction and product separation. Thus, a process for producing ammonium salts derived from carbon dioxide is presented for the first time that does not require catalyst regeneration or subsequent product separation.

[0032] Preferably, the carbon dioxide fed to the process is a gas stream characterized by having a variable concentration of carbon dioxide (preferably at least 0.001 mol%, more preferably at least 10 mol%, and even more preferably at least 99 mol%), although it may also include variable concentrations of other gases such as nitrogen, oxygen, methane, nitrous oxide, sulfur dioxide, or water vapor, among others. Specifically, the gas stream may be fed to the reactor continuously or in batches at any flow rate or volume, preferably continuously. In an alternative embodiment, the carbon dioxide used in the process may be supercritical carbon dioxide.

[0033] Additionally, and preferably, the ammonia can be fed to the reactor in a stream separate from the CO2 stream or together with it, both forms being equally preferred, which demonstrates the flexibility of the process. In one particular embodiment, ammonia, in liquid or gaseous form, at ambient temperature (25 e C) and the reactor can be fed continuously or in batches, preferably continuously.

[0034] Preferably, the pressure of the carbon dioxide and ammonia streams and the ionic liquid stream fed to the reactor shall be at least 100 kPa, more preferably at least 150 kPa, and even more preferably at least 500 kPa. Additionally, preferably, this pressure shall be equal to or less than 10,000 kPa, preferably equal to or less than 7,500 kPa, more preferably equal to or less than 5,000 kPa, even more preferably equal to or less than 3,000 kPa, and even more preferably equal to or less than 1,000 kPa.

[0035] Furthermore, preferably, the temperature of the carbon dioxide and ammonia streams and the liquid stream of the ionic liquid fed to the reactor will be at least 0 e C, preferably at least 15 e C, more preferably at least 20 e C and even more preferably at least 25 eC. Additionally, preferably, said temperature shall be equal to or less than 300 e C, preferably equal to or less than 150 e C, even more preferably equal to or less than 100 e C, even more preferably equal to or less than 70 e C and even more preferably equal to or less than 50 e C.

[0036] Depending on the pressure and temperature of the CO2 and NH3 feed streams, these can be fed in a gaseous state or in a liquid state (in the case of NH3) or under supercritical conditions (in the case of CO2).

[0037] Preferably, the gaseous streams of carbon dioxide and ammonia shall be fed to the reactor at the same temperature and pressure, preferably the same as the temperature and pressure at which the ionic liquid is fed to the reactor (if fed as a separate stream). Preferably, this temperature shall be between 0 e C and 300e C, more preferably between 25 and 150 e C and even more preferably between 25 and 70 e C. In turn, the pressure will preferably be between 100 and 10000 kPa, more preferably between 100 and 5000 kPa and even more preferably between 100 and 3000 kPa.

[0038] In a particular embodiment, the carbon dioxide and ammonia stream and the ionic liquid will be fed to the reactor continuously, either in separate streams or forming a single stream.

[0039] In another specific embodiment, the process is carried out semi-continuously, so that the ionic liquid is contained in the reactor at the start of the first reaction stage. The ionic liquid can act as either a heterogeneous or a homogeneous catalyst.

[0040] The following are illustrative examples that reveal the features and advantages of the invention. However, they should not be interpreted as limiting its scope.

[0041] In the experiments, CO2 and ammonia were supplied with a purity of 99.999%, both expressed as mass percentages. The ionic liquids used were: ethoxymethylimidazolium bis(trifluoromethylsulfonyl)imide (EtOHmimNTf2, with a purity of 99% by mass), hexylmethylimidazolium bis(trifluoromethylsulfonyl)imide (hmimNTf2, with a purity of 99% by mass), and butylmethylimidazolium prolinate (bmimPro, with a purity of 95% by mass). Additionally, the ionic liquid trihexyltetradecylphosphonium 2-cyanopyrrole (P66614CNPyr, with a purity of 95% by mass) was synthesized.

[0042] EXAMPLE 1

[0043] Synthesis of ammonium salts derived from carbon dioxide in ionic liquids. One g of ionic liquid was added to a 50 mL reactor in which two successive charges were carried out: first ammonia (200 kPa, 30 min opening time) and then CO2 (an additional 200 kPa, 30 min opening time). The temperature was ambient (25 ± 1 °C). e C and the final pressure of 500 kPa. The reaction time was set at 8 h, including: i) 30 minutes of ammonia opening, ii) 30 minutes of CO2 opening and i) 7 h of additional reaction time.

[0044] Separation of ammonium salts derived from carbon dioxide and ionic liquids

[0045] After the 8 h of each experiment were completed, the product obtained was observed and it was verified that, in all the ionic liquids studied, the product and the ionic liquid were not miscible, so that the ammonium salt obtained in the process precipitated simultaneously with its formation.

[0046] EXAMPLE 2

[0047] Results - ammonia conversion

[0048] Figure 1 shows the results obtained with the different ionic liquids, showing that all the ionic liquids guarantee a complete conversion of ammonia.

Claims

CLAIMS 1. A process for obtaining at least one ammonium salt from carbon dioxide and ammonia, characterized in that it comprises: (a) a first reaction step between carbon dioxide and ammonia in the presence of at least one ionic liquid, yielding at least one ammonium salt; and (b) a second stage, simultaneous to the first stage, of spontaneous separation, by precipitation, of the ammonium salt obtained in the first stage.

2. A process according to claim 1, wherein said process comprises a step prior to the first reaction step, wherein said prior step comprises feeding at least one reactor a first stream comprising carbon dioxide and a second stream comprising ammonia or, alternatively, a single stream comprising carbon dioxide and ammonia.

3. Method, according to claim 2, wherein a liquid stream comprising at least one ionic liquid is additionally fed to the reactor.

4. Method, according to claim 2, wherein the ionic liquid is contained in the reactor at the start of the first reaction stage.

5. A process according to any one of the preceding claims, wherein the molar ratio between carbon dioxide and ammonia varies from 100:1 to 1:

100.

6. A process according to any one of the preceding claims, wherein the molar ratio between ammonia and ionic liquid varies from 1000:1 to 1:1000.

7. A method according to any one of the preceding claims, wherein the ionic liquid consists of an organic salt.

8. A process according to claim 7, wherein said organic salt comprises a cation selected from a group consisting of phosphonium, ammonium, at least one alkylmethylimidazolium and at least one alkylmethylpyridinium, as well as any combinations thereof.

9. A process according to claim 7 or 8, wherein said organic salt comprises an anion selected from a group consisting of at least one halide, bis(trifluoromethylsulfonyl)imide, at least one heterocyclic aprotic anion, and at least one amino acid, as well as any combinations thereof.

10. A process according to any one of the preceding claims, wherein the first reaction step is carried out using a mixture of ionic liquids or dicationic liquids, dianionic liquids or mixtures of dicationic and dianionic liquids, resulting in a mixture of ammonium salts that are either simultaneously separated by precipitation, or separated in a subsequent separation step by extraction.

11. A process according to any one of the preceding claims, wherein said process is carried out at a temperature between 0 e C and 300 e C already a pressure of between 100 kPa and 10000 kPa.

12. A process according to any one of the preceding claims, wherein the pressure of the gaseous streams of carbon dioxide and ammonia and the liquid stream of the ionic liquid fed to the reactor is at least 100 kPa and equal to or less than 10000 kPa.

13. A method according to any one of the preceding claims, wherein the temperature of the carbon dioxide and ammonia streams and the liquid stream of the ionic liquid fed to the reactor is at least 0 e C and equal to or less than 300 e C.

14. A method, according to any one of the preceding claims, wherein said method is carried out in the absence of water.

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