DE102016002413A1 - Process for the production of ammonia - Google Patents

Abstract

The invention provides a process for producing ammonia comprising the steps of providing a metal chloride, in particular alkali metal chloride, an electrolytic conversion of the metal chloride, in particular alkali metal chloride in a metal, in particular alkali metal and chlorine (Cl2), a reaction of the metal (M), in particular alkali metal with nitrogen to a metal nitride (MN), in particular alkali metal nitride, a reaction of the metal nitride (MN), in particular alkali metal nitrate with water (H2O) to a metal hydroxide, in particular alkali metal hydroxide and ammonia (NH3) and a displacement of the metal hydroxide (MOH), in particular alkali metal hydroxide with Hydrochloric acid (HCl) for the production of the metal chloride, in particular alkali metal chloride before.

Description

The invention relates to a process for the preparation of ammonia according to claim 1.

Since ammonia is a basis for all industrially produced nitrogen-containing compounds, ranging from fertilizers to explosives range, the processes of its production in industrial everyday life is of great importance. Named after its inventors Fritz Haber and Carl Bosch, the Haber-Bosch process is today the most important method for the large-scale production of ammonia from the elements nitrogen and hydrogen. The required nitrogen is taken from the air, while the hydrogen is removed by the reaction of Methane is obtained from natural gas sources with water vapor.

The hydrogen gas is purified in several steps by separating unwanted impurities from the natural gas, before it can be used for the actually desired ammonia synthesis. Because the Haber-Bosch process requires highly pure hydrogen, the purification of which makes up a large part of the process costs.

The high activation energy of the reaction due to the triple bond of the nitrogen requires, despite the use of catalysts, a process at high pressure (about 250 bar) and high temperature (about 450 ° C). Accordingly, the production of ammonia using the Haber-Bosch process is very energy- and resource-intensive, which is reflected in the fact that ammonia production as of 2008 accounts for around 3% of the world's energy production. An optimization of the reaction conditions has not been able to eliminate this disadvantage. Other disadvantages are the use of natural gas - a fossil raw material - as a raw material for the provision of hydrogen and the associated accumulation of carbon dioxide as a waste and the basic use of hydrogen and the associated risk potential.

In the prior art, to improve the Haber-Bosch process, there are a variety of approaches that deal with improving the catalysts used in the process.

The invention is therefore based on the object to develop an alternative method for ammonia synthesis, which is cost and resource-saving than the Haber-Bosch method.

The invention solves this problem with the features of claim 1.

Accordingly, the invention provides a process for producing ammonia comprising the steps of providing a metal chloride, in particular alkali metal chloride, an electrolytic conversion of the metal chloride, in particular alkali metal chloride to a metal, in particular alkali metal and chlorine (Cl ₂ ), a reaction of the metal (M), in particular alkali metal with nitrogen to a metal nitride (MN), in particular alkali metal nitride, a reaction of the metal nitride (MN), in particular alkali metal nitrate with water (H ₂ O) to a metal hydroxide, in particular alkali metal hydroxide and ammonia (NH ₃ ) and a displacement of the metal hydroxide (MOH ), in particular alkali metal hydroxide with hydrochloric acid (HCl) to produce the metal chloride, in particular alkali metal chloride before.

The inventive method utilizes a reaction of the metal, in particular alkali metal to a metal nitride and its reaction with water to ammonia.

The process according to the invention can advantageously be used economically. In addition, the invention has the advantage of keeping the metal, in particular alkali metal in a closed circuit.

Further advantages emerge from the subclaims.

An embodiment of the method according to the invention is characterized in that the step of the electrolytic conversion is designed as a fused-salt electrolysis.

In the process according to the invention, the step of electrolytic conversion may comprise adding a further metal chloride, in particular further alkali metal chloride, to form a eutectic mixture having a relative to the melting points of the metal chloride, in particular alkali metal chloride and the further metal chloride, in particular further alkali metal chloride lower melting point.

In one embodiment of the process according to the invention, the metal chloride comprises lithium chloride (LiCl). The process according to the invention for the production of ammonia is then preferably based on the recovery of ammonia by means of nitrogen and lithium.

According to the invention, the further metal chloride may comprise potassium chloride (KCl). Advantages then arise with regard to the temperature of the electrolytic conversion by formation of a eutectic mixture. The electrolytic conversion is preferably carried out at 355 ° C with advantage.

In a further process procedure, the ammonia (NH ₃ ) obtained can be used to determine the ammonia yield for a quantitative analysis.

The quantitative analysis involves a distillation process comprising expelling ammonia from an aqueous solution and comprising condensation in a hydrochloric acid solution. The distillation process is preferably a steam distillation.

In another embodiment of the process according to the invention, the condensation, in particular steam distillation, comprises neutralization of the hydrochloric acid, the amount of ammonia being determinable from a difference in the molar amount of hydrochloric acid before and after the steam distillation.

The process according to the invention may preferably be distinguished by a preparation of the metal chloride, in particular alkali metal chloride, and an isolation of the ammonia (NH ₃ ) from an aqueous solution.

In a preferred embodiment of the method according to the invention, the lithium is worked up by additional steps and recycled. As a result, the demand for lithium can be kept low. In this embodiment of the method according to the invention, it is possible to conduct the lithium in a closed circuit. Such a reuse of the lithium advantageously avoids having to add lithium to the process again and again.

In the following the invention will be explained in more detail by means of exemplary embodiments, reference being made to the figures held at different scales and in some cases greatly simplified. Show it:

1 a lithium circuit,

2 a fused-salt electrolysis,

3 a lithium nitride reactor and

4 an illustration of the quantitative ammonia yield.

At an in 1 In the illustrated circuit, lithium is used as the metal in a process for producing ammonia. In a total with the reference numeral 10 provided lithium circuit according to the present invention, lithium is used in various compounds. In a first process step 1 designed as a fused-salt electrolysis, lithium is prepared from a previously prepared lithium chloride (LiCl) in a mixture with potassium chloride (KCl) according to the following reaction equation

electrolysis

• 2LiCl → 2Li + Cl ₂ won. In fused-salt electrolysis, lithium accumulates elementally at a cathode. The lithium is then in the next step 2 under a N ₂ atmosphere as follows 6Li + N ₂ → 2Li ₃ N fumigated with nitrogen. This lithium nitride (Li ₃ N) is obtained, which as in process step 3 in 1 is shown according to the following reaction equation Li ₃ N + 3H ₂ O → NH ₃ + 3LiOH with water (H ₂ O) to ammonia (NH ₃ ) and lithium hydroxide (LiOH). The yield of ammonia can now be determined quantitatively, while the resulting lithium hydroxide with hydrochloric acid (HCl) added - step 4 - to lithium chloride (LiCl). That from step 4 LiOH + HCl → LiCl + H ₂ O According to the invention, lithium chloride obtained can be used again for the fused-salt electrolysis, whereby the cycle is closed.

For the production of lithium nitride elemental lithium is required according to the invention, which is obtained by means of a fused-salt electrolysis of the lithium chloride. In this case, potassium chloride is added to produce a eutectic mixture, which has a much lower melting temperature than pure salts. Thus, the melting point of lithium chloride (LiCl) is 605 ° C, whereas the melting point of potassium chloride is 770 ° C. The potassium is not deposited at the cathode during the electrolysis because it has a lower electrode potential and thus only the desired lithium from the electrolysis results. For the lowest possible energy consumption, the melting point must be set as low as possible. Therefore, according to the invention, proportions by mass of 52% lithium chloride and 48% potassium chloride are used to obtain a eutectic mixture, to lower the melting temperature to a minimum of 352 ° C and to liquefy both components at the same temperature.

As schematically in 2 For this purpose, a V-shaped tube known to the person skilled in the art is illustrated 6 over a Bunsen burner 7 placed. Previously dried in a conventional drying oven in a conventional manner components are in the tube 6 melted in a mass ratio of 52% lithium chloride and 48% potassium chloride. A graphite electrode 8th serves as an anode and as a cathode becomes an iron electrode 9 used. The two electrodes 8th . 9 be in a circuit 11 in a known manner to a DC voltage source 12 connected. The circuit 11 has an ammeter 14 and potentiometers 15 on.

One of the iron electrode 9 assigned thigh 6a of the V-shaped tube 6 is with a sealing foil 16 covered to a filling of an interior 17 of the thigh 6a above a melt 18 to allow from LiCl and KCl. By providing an argon atmosphere in the interior 17 Oxidation of the forming lithium is avoided. For evacuation of resulting chlorine, the in 2 placed arrangement in a chemistry laboratory deduction.

With the controllable via a transformer not shown DC voltage source 12 A voltage of 15 volts is gradually provided after the electrodes 8th . 9 in the melt 18 have been dived. Using the potentiometer 15 we set a current of about 0.5 amps. The melting process takes about 15 minutes, during which time chlorine can be detected with a potassium iodide-starch paper over the graphite electrode. The chlorine oxidizes the iodide ions to elemental iodine, which undergoes a detection reaction with the starch and thereby leads to a blue to brown coloration of the paper.

After sufficient time, the power can be turned off. The lithium, which has collected in the form of a drop at the electrode, can be taken out of the melt. The remaining lithium, which floats on the surface of the melt due to its lower density, can be removed using a combustion tray. The metal is immediately poured into paraffin oil to prevent oxidation in the air. To protect against still liquid lithium, which may splash when immersed, usual protective measures must be taken. Since only a small portion of the lithium metal adheres to the electrode, use of the combustion spoon to increase the yield is advantageous. The resulting lithium is now detected directly on the cathode by moistened phenolphthalein paper. It reacts with the water on the paper to lithium hydroxide, which causes a color change of the indicator.

By using the combustion spoon to remove the liquid lithium fraction, the yield can be approximately doubled in fused-salt electrolysis. In general, however, it can be said that, according to the invention, a yield depends on a running time of the apparatus, since the formation of elemental lithium depends on the flow of electrons. The advantage of carrying out the method according to the invention with an industrial plant is that it is permanently in operation and salt can be added regularly. As a result, only relatively little energy is needed to melt the salt needed. Next, the lithium can be constantly skimmed off. By such a dimensioning, it would also be much easier to remove the metal from the melt free of impurities by potassium chloride.

As in 3 shown, the lithium reacts in a total with the reference numeral 20 provided lithium nitride reactor with nitrogen to lithium nitride. The lithium nitride reacts strongly exothermically with water. The proposed apparatus 20 works on a nitrogen atmosphere where lithium can only react with nitrogen to protect it from unwanted oxidation. To accelerate the reaction, the gas must be heated to a threshold temperature. To 3 is used as a reaction vessel 21 a three-necked flask used. The nitrogen flows through the apparatus 20 while by means of a bubble counter, not shown, the flow velocity can be measured. At the same time, the invention thus prevents air from an environment of the reaction vessel 21 can flow into it. The nitrogen is on the way to a three-necked flask 21 heated. To achieve this, a slow gas flow must be set and a heat transferring or donating surface should be as large as possible. For this purpose, a laboratory cooler is used according to the invention.

According to the invention, at least two Dimroth coolers are used to heat the nitrogen gas 22 connected in series. By cooling spirals 23 the at least two Dimroth coolers 22 the nitrogen flows. The at least two Dimroth coolers 22 are each in a round bottom flask 24 used with standard ground, with an outer, the cooling spiral 23 surrounding space 25 filled with water. The at least two Dimroth coolers 25 stand in a heated water bath 26 ,

The three-necked flask 21 is with the Bunsen burner 27 heated slowly and only slightly. To favor a complete reaction, a surface of lithium pieces to be used is rolled by rolling in paraffin oil 29 enlarged before the lithium 28 in the three-necked flask 21 is given. Preferably, an embossing roll of the lithium pieces can be used to increase their surface area.

The recovered lithium nitride according to the invention is placed in a water-filled and almost closed Erlenmeyer flask. Despite the atypical white color of the sample being lithium nitride, the lithium nitride, in contact with water, unexpectedly violently reacts and hydrolyzes to form lithium hydroxide and ammonia. The solution has a measured by conventional pH meter pH of 14. The solution is an inorganic superbase defined by being a stronger base than sodium hydroxide. Hydrogen formation, which would be due to a reaction of lithium which is not fully lithium nitride-reacted with lithium to form lithium hydroxide and hydrogen, can be precluded by a sample of a nugatory gas. Furthermore, a strong smell of ammonia is heard after the reaction.

Table 1 shows results of two different constructions of the lithium nitride reactor. As can be seen from a comparison of the results, a change of the lithium nitride reactor according to a first construction has led to an improved conversion of the lithium to lithium nitride. Indicated are the amount of lithium metal used, the mass of the sample after the end of the experiment and the resulting conversion of the lithium to lithium nitride in percent. Table 1 Amount of Li Weight sample implementation 1. Construction 0.7 g 0.78 g 18% 2nd construction 0.9 g 1.17 g 45% 0.9 g 1.24 g 57% 0.6 g 0.83 g 59%

There are no losses due to unreacted lithium, since it reacts in water to lithium hydroxide, which is further reacted in the next step in lithium chloride. The yield can be through Melting of the lithium metal can be increased. The disadvantage here is that then used under tension by again cooled lithium nitride standing three-necked flask are cracked and thus are useless.

One of the resulting from the described steps of the method according to the invention sample is used for a reaction of the lithium with water, the theoretical release of ammonia and lithium hydroxide is shown in Table 2. Table 2 Amount of Li ₃ N used amount of H ₂ O. Amount of NH ₃ Amount of LiOH 0.34 g 20 ml 0.17 g 0.7 g

The experiment is carried out once, because no comparative values are needed, since complete conversion of the lithium nitride is to be expected.

The solution of water, ammonia and lithium hydroxide serves as starting material for a next process step. The solution is first heated, whereby the ammonia is expelled and intercepted. The ammonia gas is passed into a Dimroth cooler and collected in condensed form. Hydrochloric acid is added to the remaining solution, whereupon the lithium hydroxide reacts to lithium chloride and is heated without further trapping of the vapor until lithium chloride salt remains as a crystalline solid. The resulting lithium chloride can now be removed from the glass and mortared reused for the electrolysis.

A quantitative evaluation of the ammonia yield is carried out as described below. The concentration of the ammonia collected in the previous step is unknown since steam was also carried along by heating the solution. The ammonia content is determined quantitatively by reference to the method of "Kjeldahl's nitrogen determination". Nitrogen compounds in a sample are allowed to react with sulfuric acid to form ammonium sulfate, which is dissolved in an excess of sulfuric acid. This is neutralized by means of a base such as sodium hydroxide to form ammonia. The process used according to the invention starts at this point, since the ammonia already exists.

As in 4 a steam flow is shown in one of a piston 32 guided pipeline 33 generated, with the water 31 filled pistons 32 over a Bunsen burner 34 is heated. The steam flow is through the pipeline 33 in a part with a sample solution 35 filled Kjeldahl pistons 36 guided. The ammonia will be as in 4 represented by the strong water vapor stream from a part of a sample solution 35 expelled and after condensation with the help of one with an outlet pipe 37 of the Kjeldahl flask 36 connected Liebig cooler 38 in a hydrochloric acid solution 40 known concentration in an Erlenmeyer flask 41 transferred. Once a condensed water vapor has a neutral pH, the distillation can be stopped. The transferred ammonia has a part of the hydrochloric acid 40 neutralized. To determine the amount of residual hydrochloric acid, it is titrated against a sodium hydroxide solution with phenolphthalein as indicator. From a difference in the amount of hydrochloric acid present before and after the steam distillation, the molar amount of the transferred ammonia can then be determined.

In the preparation of the lithium chloride, the lithium hydroxide previously formed is treated with hydrochloric acid and boiled. A residue is weighed. Table 3 Amount of LiOH used amount of HCl Amount of LiCl Solution from Tab. 2 0.7 g 30 ml (1 mol / L) 1.19 g

Test results recorded in Table 3 show that even in this partial step, an almost complete conversion is possible, which is why this experiment is theoretically optimized despite the simple method.

An interception of the ammonia has not been possible with the scale of the sample with the agents used, which is why a quantitative evaluation of the ammonia yield is limited to a blank test on the accuracy of the method used:
The following information on the chemicals used is given:
Sample: 10 ml NH ₃ (0.2 mol / L), original: 100 ml HCl (0.2 mol / L)
Neutralization (slight coloration of the indicator): 18.2 ml NaOH (1 mol / L)
(required molar amount of NaOH for neutralization, molar amounts of the HCl template) n = c x V = 1 mol / L x 18.2 ml = 1 mmol / ml x 18.2 ml = 18.2 mmol 0.2 mmol / ml x 100 ml = 20 mmol (NH ₃ neutralized part of the acid, theoretically NH ₃ neutralized part of the acid) 20 mmol - 18.2 mmol = 1.8 mmol 0.2 mmol / ml x 10 ml = 2 mmol

The results show that the method according to the invention is reliable and its concentrations can be specified precisely in further tests with ammonia solutions of indeterminate composition.

The invention is not limited to the described embodiments, which can be modified in many ways. So instead of the three-necked flask ( 3 ) also a two-necked flask can be used as the reaction vessel, which is immersed immersed in a water bath. This is heated with a hotplate. The piston is filled via the first neck with nitrogen from a compressed gas cylinder, while the air escapes from the second neck. The gas is piped into the flask for a few minutes to drive off the air completely and the lithium is added before it is closed and the gas flow is turned off. Through the water bath, the piston is heated and the reaction started. After about one hour, the experiment can be stopped and the lithium can be assessed.

Instead of rolling the lithium metal can be used according to the invention also a pressing of the lithium metal to thin sheets in order to achieve an enlargement of the surface.

The process according to the invention has been described on the basis of a performance under experimental laboratory conditions. It is understood, however, that the invention may also comprise other measures or equipment that can be used in an industrially applicable process. Accordingly, the agents described herein are analogous to procedural corresponding means for industrial use in chemical process or production technology transferable.

For example, it is also possible to calculate the exact proportions of the reactants of the underlying reactions and to consider them more experimentally in order to minimize losses and to make the production process even more resource-conserving. For example, larger series of tests could be used to improve efficiency. For example, in an industrial plant for fused-salt electrolysis or when using molten lithium for lithium nitride production.

Claims (10)

A process for the preparation of ammonia comprising the steps of - providing a metal chloride, in particular alkali metal chloride, - an electrolytic conversion of the metal chloride, in particular alkali metal chloride in a metal, in particular alkali metal and chlorine (Cl ₂ ), - a reaction of the metal (M), in particular alkali metal with nitrogen to a metal nitride (MN), in particular alkali metal nitride, - a reaction of the metal nitride (MN), in particular alkali metal nitrate with water (H ₂ O) to a metal hydroxide, in particular alkali metal hydroxide and ammonia (NH ₃ ) and - a displacement of the metal hydroxide (MOH ), in particular alkali metal hydroxide with hydrochloric acid (HCl) to produce the metal chloride, in particular alkali metal chloride. A method according to claim 1, characterized in that the step of electrolytic conversion is designed as a fused-salt electrolysis. A method according to claim 1 or 2, characterized in that the step of electrolytic conversion comprises adding a further metal chloride, in particular further alkali metal chloride for formation a eutectic mixture having a lower melting point compared to the melting points of the metal chloride, in particular alkali metal chloride and of the further metal chloride, in particular further alkali metal chloride. Method according to one of claims 1 to 3, characterized in that the metal chloride comprises lithium chloride (LiCl). A method according to claim 3 or 4, characterized in that the further metal chloride comprises potassium chloride (KCl). Method according to one of claims 1 to 5, characterized in that the ammonia (NH ₃ ) is supplied to determine the ammonia yield to a quantitative analysis. Method according to one of claims 1 to 6, characterized in that the quantitative analysis comprises a distillation process with an expulsion of ammonia from an aqueous solution and a condensation in a hydrochloric acid solution. A method according to claim 7, characterized in that the condensation comprises a neutralization of the hydrochloric acid and the amount of ammonia from a difference of the molar amount of hydrochloric acid before and after the steam distillation can be determined. Method according to one of claims 1 to 8, characterized by a preparation of the metal chloride, in particular alkali metal chloride and an isolation of the ammonia (NH ₃ ) from an aqueous solution. Method according to one of claims 1 to 9, characterized in that during the step of the displacement of the metal hydroxide (MOH), in particular alkali metal hydroxide with hydrochloric acid (HCl) obtained metal chloride, in particular alkali metal chloride is provided as metal chloride, in particular alkali metal chloride.

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