DE2519383C3 - Process for the purification and recovery of alkali metal alkylamides from solution - Google Patents

Description

Alkali metal alkylamides in solution in a primary Alkylamine. in particular potassium methylamide in solution with methylamine are used as enrichment catalysts used by deuterium in hydrogen.

However, it has been found that during the course of this deuterium enrichment a slow decomposition, For example, the potassium methylamide catalyst lu a variety of products takes place, in particular xu N.N'-Dimethj'lformamiciln in the form of its chewing saly. The decomposition products must be removed from the catalytic solution during the course of the leaching process removed in order to maintain a satisfactory level of catalysis. For one In economical operation it is essential that the undecomposed part of the catalyst is in a form which is suitable for recovery as a solution of potassium methylamide in methylamine.

It is also known that the addition of other alkali metal methylamides to the potassium methylamide-methylamine catalyst solution, used for the enrichment of deuterium in hydrogen streams offers many advantages. In particular the addition of Lithium methyl amide / u solutions of potassium methyl · »mid in methylamine lead to more advantageous operating conditions and slows down the rate of thermal decomposition of the catalyst solution. the thermal decomposition of the mixed catalyst solution leads to a number of impurities, but especially to the alkali metal salts of Ν, Ν'-dimethylforniamidine. As in the case of potassium methylamide must remove the decomposition products from the catalytic solution during the enrichment process removed to an appropriate degree of catalysis maintain. For economical operation it is essential that the not decomposed Part of the alkali metal methylamides is obtained in a form that is suitable for recovery.

It is from Chemical Refuse 20 (1937), see 236 known that Alkallnielällälkylamide mil Ammöhiak converting to alkali metal amides,

The implementation of Lithiümalkylamid with ammonia is from »Z. ahöfg, U, general Chern. «273, ropes 300 and 301 (1953) known, likewise the conversion of Alkalifhelalianfideri with Alkylammert to Alkalirnetällal · kylamiden from CA-PS 5 52 779 and »H ο u b e η W e y I, Meth, d. org. Chemistry ", Vol. XI / 2, page 184 (1958).

The invention has set itself the task of a

Process for the removal of impurities from and recovery of alkali metal alkylamides To create compounds, regardless of whether they are used individually or in mixture in this way to regenerate catalysts for the above-mentioned deuterium enrichment process. «!.

This object is achieved according to the invention according to the

ίο Claims resolved

In particular, the invention provides a method for the recovery of potassium methylamide in purified Form before, which consists in a) adding ammonia to a solution of potassium methylamide in methylamine and to allow a reaction between the ammonia and the potassium methylamide, thereby Solution contains impurities that do not react with ammonia, b) that obtained in this way Separate potassium amide from the mother liquor, which contains the impurities, c) add the mother liquor distill and d) the distillate, which consists of methylamine, which contains ammonia, with the separated Contact potassium amide and take a reaction between the methylamine and the potassium amide to allow such conditions under which NHj is removed, using a solution of potassium methylamide in methylamine, which is essentially freed from impurities, is obtained. The procedure looks before. rectifying this latter solution in order to also remove the ammonia, d. H. a distillation with a small column to remove the NHj overhead and feed it to the amine of stage a).

The invention also provides a process for the recovery of mixed alkali metal alkylamides (for example a mixture of lithium and potassium methyl amides) in purified form, which consists of a) ammonia in a solution of mixed alkali metal methyl amides' ¹ . in methylamine and to allow a reaction between the ammonia and the mixed alkali metal methylamides, the solution containing impurities which do not react with the ammonia, b) the mixture of alkali metal amides thus obtained is separated from the mother liquor which contains the impurities , c) distilling the mother liquor and d) contacting the distillate consisting of methylamine, which contains ammonia, with the separated mixture of alkali metal amides and allowing a reaction between the methylamine and the mixture of alkali metal amides under conditions under which NHi is removed whereby a solution of the mixed alkali metal methylamides in methylamine is obtained which is essentially free of impurities. The latter solution is rectified in the manner previously described to remove ammonia.

Durth F. Removal of part of the potassium methylamide solution in methylamine, which is used as a kaialytic solution for Implementation of the deuterium enrichment process described above is used, and by ■ The addition of ammonia will reduce the potassium * methylamide as potassium amide according to the following reaction failed:

CH ₃ KHK-fNHj ^

i + KNH4

Rude.

The precipitated potassium amide is separated from the mother liquors by filtration or centrifugation,

which is the potassium salt of N.N'-dimethylformamidine that does not react with ammonia. The mother liquors are evaporated, leaving a residue remains from the decomposition products. The methyl amine distillate, which contains some ammonia, is again supplied to the solid potassium amide under conditions that result in a removal of ammonia favor the reaction temperature, for example by rectification using a suitable fractional distillation column stripping off ammonia, the potassium amide reacts with methylamine to form a solution of potassium methyl amide in Methylamine. This solution can be used to partially refresh the catalyst for the deuterium enrichment process, lost through decomposition can be used.

The procedure is applicable to any alkali metal alkylamides as well as being applicable to mixtures thereof. If ammonia is added to a solution of a mixture of lithium and chewing methylamide in methylamine added, then the present lithium and Kaliu nmethylamide precipitated as lithium amide and potassium amide according to the following equations:

CH ₃ NHK + NH ₃ ^ CH ₃ NH ₂ + KNH ₂ I.

CHjNHLi + NHj - CH ₁ NH ₂ + LiNH ₂ J

The precipitated amides are removed from the mother liquors by filtration or centrifugation, which contain the salts of the decomposition products so that they do not react with ammonia. The mother liquors are evaporated, leaving a residue of the decomposition products. The methylamine distillate. containing ammonia is fed back into the mixture of solid lithium and potassium amides. Under ji Conditions that favor removal of ammonia from the reaction zone, for example by Rectifying using a suitable fractionating distillation column, the alkali metal amides react with methylamine to form a solution of the alkali metal methylamides in methvlamine, which can optionally be used to replace part of the catalyst by decomposition lost. In this way, the undecomposed one becomes Part of the catalytic solution of the 1 decomposition products separated and regenerated in a form that can be used again to carry out the Deuterium exchange process is suitable, namely after the addition of fresh :? Alkali metal methylides in the quantities needed to restore the original mi chen composition are required.

Various alkali metals including mixtures thereof can be used. Of special Those whose alkylamides are catalytically active for an HD exchange in amine systems are of interest. v, Suitable mixtures are described in DE-OS 24 34 016.7. In particular lower alkyl groups can be present in the alkali metal alkylamides, for example methyl, ethyl or propyl.

The invention is explained in more detail below with reference to the drawing. It shows the

Figure is a schematic flow diagram showing a Process for the recovery of an alkali metal alkyl amide, for example potassium methylamide.

According to the figure, a catalytic solution (A) from a deuterium enrichment process, which contains potassium methylamide and its decomposition products, mainly the potassium salt of N.N'Oimethylformamidine, in solution in methylamine, is fed through line 10 to a reaction vessel 12 where it is mixed with an ammonia-rich solution of ammonia in methylamine (H) which is fed to the reaction vessel via line 14. The resulting slurry (B) of the solid potassium amide in a solution of the decomposition products and an excess of ammonia in methylamine are then passed through line 16 to the pressure filter 18, where filtration takes place where it is distilled. A concentrated solution of the decomposition products (E) is drawn off from the reboiler 24 via a line 26. The distillate (F), which consists of a dilute solution of ammonia in methylamine, flows from the top of fractionation column 22 through line 28 and is used to backwash the potassium amide (C) from pressure filter 18. The Ka! Iumamid-Auf. ^The elutriation in the dilute solution of ammonia> r · methylamine that is thereby formed is then introduced into fractionation column 29 through lines 32 and 34. An ammonia-rich distillate (H) is withdrawn from the top of fractionation column 30 and again Reaction vessel 12 is fed through line 14. A solution of essentially pure potassium methylamide in methylamine (G) is withdrawn from reboiler 36 through line 38 and returned to the deuterium enrichment process (not shown).

The process does not require any ammonia supply and can be continuous, semi-continuous or batch-wise be performed.

The amount of ammonia required to precipitate Potassium amide used from the partially decomposed solution is not critical. Any excess ammonia over an equimolar amount, based on the potassium methylamide present, which is suitable for the Eriöhune des Amide precipitation efficiency can be recovered along with the "ammonia, which reacts to form potassium amide, with recovery in the regeneration stage of the proceedings. It is not necessary to use pure ammonia for the precipitation of Add potassium amide. Mixtures of ammonia and methylamine can be used. Of the Use of mixtures of ammonia and methylamine is advantageous in that it is possible. to achieve considerable economic advantages in the regeneration step by having such Mixture is withdrawn from the top of the fractionating column, in which way it is possible will use a simpler fractionation column, wodui ch energy is also saved.

1 to 10 moles of ammonia per mole of potassium methylamide. that is to be recovered can be used but a molar ratio of 2 to 5: 1 is preferred. The molar ratio can be in the way be chosen "that an economic compromise between the loss of valuable Potassium methyl amide in the mother liquor with low ammonia contents and increasing rust, dtr ammonia separation by methylamine the regeneration stage is achieved at high ammonia levels.

The process can be performed at ambient temperatures and under moderate pressures sufficient to keep the methylamine in the liquid phase to keep. Small benefits can be obtained at other temperatures and pressures

is being worked on.

Similarly, a mixture of alkali metal methylamides can be treated; At this Embodiment of the invention (see the figure) contains the catalytic solution (A) from a Deüteriuman * enrichment process, which is treated, a mixture of alkali metal methylamides and their decomposition products, mainly the alkali metal salts of N.N'-dimethylformamidine, in a methylamine solution. This solution is passed through line 10 into a reaction vessel 12, where it is rich in ammonia Solution of ammonia in methylamine (H) is mixed, which the reaction vessel over the Line 14 is supplied. The reaction of the ammonia with the mixture of Alkalimetalimethyiamiden is carried out. The obtained slurry (B) of a mixture of solid alkali metal amides The decomposition products as well as excess ammonia in methylamine are then in a solution fed through the line 16 to the pressure filter 18, where the mixture of alkali metal amides from the solution is separated. The filtrate (D) is fed via line 20 to a fractionating distillation column 22, where it is distilled. A concentrated solution of the Decomposition products (E) are withdrawn from reboiler 24 through line 26. The distillate (F) that consists of a dilute solution of ammonia in methylamine, is from the top of the Fractionation column 22 withdrawn through line 28 and used to convert the mixture of solid alkali metal amides (C) backwash from pressure filter 18. The resulting slurry is put into the fractionation column 29 inserted through lines 32 and 34. An ammonia-rich distillate (H) is produced from the top withdrawn from the fractionation column 30 and fed back to the reaction vessel 12 through line 14. A solution of essentially pure mixed alkali metal dimethyl amides in methylamine (G) is obtained from withdrawn from the reboiler 36 through the line 38 and again the deuterium enrichment process (not shownx).

The process conditions, for example the amounts of ammonia, those with regard to the mixed alkali metal methylamides which are purified should be used, as well as the operating temperatures and pressures, are similar to the process conditions, as described above in connection with the process for the recovery of chewing methylamide have been described in purified form.

The following examples illustrate the invention.

Example I.

The addition of ammonia (108.8 mmol) to a solution of potassium methylamide in methylamine ₍ das

Contains 47.6 mmol potassium methylamide, the precip Lung before 86% of the Kaliümmelhylämids as Käliümamid result.

The addition of ammonia (6.24 mMoj / g solution) too a solution of the potassium salt of NjN'-dimethyl-

formamidine (0.47 mmol / g solution) in methylamine does not result in any precipitation.

The addition of ammonia (92 mmol) to a partially ihermolysikrten solution of potassium methylamide in methylamine, the 27.0 mmol of potassium methylamide and 16.7 mmol of the potassium salt of N.N'-dimethylformamidine has the precipitation of 74% of the Potassium methyl amide as potassium amide result. The solution concentration of the potassium salt of N.N'-dimethylformamidine stays unchanged.

Example 2

The addition of ammonia (1.54 mmol / g of the solution) to a solution of lithium methylamide (0.84 mmol / g of the solution) and potassium methylamide (0.50 mmol / g of the solution) at 25 ° C caused the precipitate result in greater than 98% of the alkali metal methylamides as their amides.

A solution of lithium methyl amide and potassium methyl amide, which is initially lithium methyl amide (0.52 mmol / g of the solution) and potassium methylamide (0.43 mmol / g of the solution) is thermally too decomposed of a mixture containing 031 mmol / g of the solution the salts of the main decomposition product, namely Ν, Ν'-dimethylformamidine, contain ammonia (2.98 mmol / g of the mixture) is added, followed by the mixture over a period of 16 hours is stirred and filtered. The filtrate contains only 0.1 meq / g of the solution methyl amide ions, but always still essentially all of the N, N'-dimethylformamidine (0.29 mmol / g of solution). An alkali metal

Ui ati t-iiiiiiutitiir-

nen (0.01 meq / g of the solution) and potassium ions (031 meq / g of the solution). Analysis of the residue shows that it consists of lithium amide (equivalent to 0 _; 49 meq / g of the starting solution) and potassium amide (equivalent to 0.17 meq / g of the starting solution). The remainder therefore contains essentially all the alkali metals which correspond to the undecomposed methylamides.

'Hierztid'BIatt drawings ii:

Claims (4)

Patent claims: 1. Process for the purification and recovery of alkali metal alkylamides from a solution, characterized in that ammonia is added to the solution to be treated, the obtained alkali metal amide separated from the solution and heated with a primary alkylamine and Releases ammonia 2. The method according to claim 1, characterized in that alkali metal alkyl amide systems whose alkali metal consists of sodium, lithium and / or potassium is recovered 3. The method according to claim 1 and 2, characterized in that there is a starting material Alkyl amide uses a mixture of alkali metals ^{4. Use of the Λ} alkali metal amides purified according to Claims 1 to 3 as catalysts for the enrichment of deuterium in hydrogen.