CH620221A5 - Process for regenerating an alkali-metal-alkylamide-containing system - Google Patents

Description

The present invention relates to a method for regenerating a system containing an alkali metal alkyl amide. Alkali metal alkyl amide systems containing impurities are formed in deuterium enrichment processes where they are used as a catalyst. The regenerated alkali metal alkylamides can again be used as catalysts.

Alkali metal alkyl amides, dissolved in a primary alkyl amine, especially potassium methyl amide in methyl amine, have hitherto been used as catalysts in a deuterium enrichment process in hydrogen.

However, it was discovered that during the deuterium enrichment process, the potassium methylamide catalyst slowly decomposes into a number of products, especially in N, N -dimethylformamidine in the form of its potassium salt. The decomposition products have to be during the exchange process

5

10th

15

20th

25th

30th

35

40

45

50

55

60

65

3rd

620 221

removed from the catalytic solution to maintain some degree of catalysis. It is important for an economical process to recover the undecomposed part of a catalyst in a suitable form, namely as a solution of purified potassium methylamide in methylamine.

It is also known that the addition of further alkali metal methylamides to the potassium methylamide-methylamine catalyst solution has many advantages in the deuterium enrichment process in a hydrogen stream. In particular, the addition of lithium methylamide to solutions of potassium methylamide in methylamine leads to more advantageous process conditions and a reduction in the rate of thermal decomposition of the catalyst solution. The thermal decomposition of the mixed catalyst solution results in a number of impurities, especially alkali metal salts of N, N -dimethylformamidine. As with potassium methylamide, the decomposition products must be removed from the catalyst solution in order to keep the enrichment process at an appropriate level of catalysis. For an economical process, it is important to obtain the undecomposed part of the alkali metal methyl amide in a suitable form for cleaning.

It is an object of the present invention to provide a method for removing contaminants from alkali metal alkyl amides.

Another goal is the purification of alkali metal alkyl amides, whether used alone or in mixtures, to regenerate the active catalyst for the above-mentioned deuterium enrichment process.

It has been found that alkali metal alkylamides react with ammonia to form alkali metal amides, while the alkali metal salts of the thermal decomposition products of alkali metal alkylamides do not react with ammonia. The solubility of alkali metal amides in primary alkylamines, especially in methylamine, differs considerably from the solubility of alkali metal salts of the decomposition products, which is sufficient for separating the undecomposed alkali metal alkylamides from the decomposition products. Since the alkali metal alkyl amides can be easily recovered from the corresponding alkali metal amides, it has been found that alkali metal alkyl amides can be obtained in a purified state and that they are suitable for use as a catalyst in a deuterium enrichment process.

The present invention thus relates to a process for the regeneration of a system containing an alkali metal alkyl amide, which is characterized in that ammonia is added to a solution containing an alkali metal alkyl amide and impurities, which do not react with ammonia, but a reaction between ammonia and the Alkali metal alkyl amide to an alkali metal amide takes place by separating the reaction product thus obtained from the solution and reacting it with a primary alkyl amine under conditions in which ammonia is removed and a solution of the pure alkali metal alkyl amide is formed in the primary alkyl amine used.

In a preferred embodiment of the method according to the invention, the procedure is as follows:

a) adding ammonia to a solution of potassium methylamide in methylamine and reacting ammonia with the potassium methylamide, the impurities not reacting with the ammonia;

b) separation of the potassium amide thus obtained from the mother liquor which contains the impurities;

c) distillation of the mother liquor and d) reacting the distillate, which contains methylamine and ammonia, with the separated potassium amide, wherein methylamine is reacted with potassium amide under conditions such that ammonia is removed, giving a solution of potassium methylamide in methylamine, which essentially is free of the impurities mentioned. As indicated, the process involves rectification of the latter solution to also remove the ammonia, i. H. ammonia is removed at the top by distillation with a small column and returned to the amine in a).

According to the invention, mixed alkali metal methylamides, e.g. B. a mixture of lithium and potassium methylamide, a purified form as follows.

a) adding ammonia to a solution of mixed alkali metal methylamides in methylamine, ammonia reacting with the alkali metal methylamides and the impurities such. B. N, N-dimethylformamidine, do not react with the ammonia;

b) separation of the mixture of alkali metal amides thus obtained from the mother liquor which contains the impurities;

c) distillation of the mother liquor and d) reacting the distillate, which contains the methylamine and ammonia, with the separated mixture of the alkali metal amides under those conditions in which ammonia is removed, a solution of the mixed alkali metal methylamides in methylamine being formed which is essentially free of the impurities mentioned. The latter solution is rectified to remove the ammonia in the manner indicated above.

The preferred procedure is as follows:

When a part of the potassium methylamide solution in methylamine, which is used as a catalyst solution in the deuterium enrichment process mentioned above, is removed and ammonia is added, the potassium methylamide present is precipitated as potassium amide according to the following reaction scheme:

CH3NHK + NH3 CH3NH2 + KNH2 1 (contaminated)

The precipitate of potassium amide is usually separated from the mother liquor, which contains the potassium salt of N, N'-dimethylformamidine, which does not react with ammonia by filtration or centrifugation. The mother liquors can be evaporated to leave a residue of decomposition products and the methylamine distillate, containing some ammonia, is returned to the solid potassium amide. Under conditions that favor removal of ammonia from the reaction zone, e.g. B. rectification using a suitable fractionation-distillation column with ammonia removal, the potassium amide reacts with methylamine, forming a solution of potassium methylamide in the methylamine. This solution can be used in part, if desired, to supplement the decomposition lost catalyst for the deuterium enrichment process.

The process according to the invention can be applied to any alkali metal alkyl amide or mixtures thereof. If e.g. B. If ammonia is added to the solution of a mixture of lithium and potassium methylamides in methylamine, lithium and potassium amide are precipitated according to the following scheme:

s

10th

IS

20th

25th

30th

35

40

45

50

55

60

65

620 221

4th

. . "/ CHsNHK + NH3 ^ CH3NH2 + KNH2 i contaminated ^ Ch3NHLì + NH:> ^ CH3NII2 + LÌNH2 i

The deposited amides are usually separated from the mother liquors, which contain the potassium salt of the decomposition products which do not react with ammonia, by filtration or centrifugation. The mother solutions are e.g. B. evaporated, leaving a residue of decomposition products, and the methylamine distillate containing ammonia can be recycled to the mixture of solid lithium and potassium amides.

Under conditions that favor removal of ammonia from the reaction zone, e.g. B. rectification using a suitable fractionation distillation column, the alkali metal amides react with methylamine, resulting in a solution of the alkali metal methylamides in methylamine, which, if desired, is used to replenish the part of the catalyst lost by decomposition. In this way, the undecomposed part of the catalyst solution is separated from the decomposition products and can be regenerated in a suitable form for reuse in the deuterium exchange process, after addition of fresh alkali metal methylamides in the amounts required to restore the original composition.

Various alkali metals are effective, including mixtures thereof. Of particular interest are those whose alkylamides are catalytically active for H-D exchange in amine systems. Suitable blends are described in U.S. Patent No. 3,995,017. In particular, lower alkyl radicals can be used in the alkali metal alkyl amides, e.g. B. methyl, ethyl or propyl.

The invention will now be described with reference to the accompanying drawing. This provides a schematic flow diagram for a process for the purification of an alkali metal alkyl amide, e.g. B. potassium methylamide.

Herein (A) means a stream of the catalytic solution from a deuterium enrichment process which contains potassium methylamide and its decomposition products, in particular the potassium salt of N, N'-dimethylformamidine, dissolved in methylamine. This solution is passed through line 10 into the reaction vessel 12, where it is mixed with a strong ammonia-containing solution of ammonia in methylamine (H) which reaches the reaction vessel via line 14. The resulting slurry (B) of solid potassium amide in a solution of decomposition products and excess ammonia in methylamine is then passed through line 16 to pressure filter 18 where it is filtered. The filtrate (D) is introduced via line 20 into a fractionation distillation column 22 where it is distilled, and a concentrated solution of the decomposition products (E) is drawn off from the heating apparatus 24 via line 26. Filtered potassium amide leaves the pressure filter 18 through line 3. The distillate (F), consisting of a dilute solution of ammonia in methylamine, leaves the top of the fractionation column 22 via line 28 and is used to wash the solid potassium amide (C) obtained from the pressure filter 18. The resulting slurry of potassium amide in the above-mentioned dilute solution of ammonia in methylamine, which has formed

is fed via line 32 into the fractionator 29. A distillate (H) enriched with ammonia is drawn off from the top of the fractionation column 30 and returned to the reaction vessel 12 via line 14. A solution of essentially pure potassium methylamide in methylamine (G) is drawn off from the heating apparatus 36 via line 38 and returned to the deuterium enrichment process (not shown).

The process is self-sufficient with respect to ammonia and can be carried out continuously, semi-continuously or as a single batch.

The amount of ammonia for precipitating the potassium amide from the partially decomposed solution is not critical. Any excess of ammonia, more than the equimolar amount, based on the potassium amide present, which is used to increase the effectiveness of the amide precipitation, can be recovered in the regeneration stage of the process, together with the ammonia which is converted to potassium amide. It is not necessary to add pure ammonia to precipitate the potassium amide; Mixtures of ammonia and methylamine can also be used. This is even advantageous because significant economic savings are made in the regeneration step by using such a mixture from the top of the fractionation distillation column, which enables the use of a simpler fractionation column and energy savings.

Between 1 and 10 moles of ammonia can be used per mole of potassium methylamide to be obtained, but a molar ratio of 2 to 5: 1 is preferred. The molar ratio can be chosen so that there is an economic balance between the loss of valuable potassium methylamide in the mother liquor with a low ammonia content and increasing costs for the separation of ammonia from methylamine with a high ammonia content in the regeneration stage.

The process can be carried out at ambient temperatures and moderate pressures that keep the methylamine in the liquid phase. Smaller advantages in the process can be achieved by changing temperatures and pressures, which is easily understood by the person skilled in the art.

Mixtures of alkali metal methyl amides can be treated in a similar manner. In this embodiment of the process according to the invention (see drawing), the stream of catalytic solution (A) from the deuterium enrichment process contains a mixture of alkali metal methylamides and their decomposition products, especially the alkali metal salts of N, N'-dimethylformamidine, dissolved in methylamine. This solution is passed through line 10 into the reaction vessel 12, where it is mixed with a solution rich in ammonia in methylamine (H), which reaches the reaction vessel via line 14, the ammonia being able to react with the mixture of the alkali metal methylamides. The resulting slurry (B) of a mixture of solid alkali metal amides in a solution of decomposition products and excess ammonia in methylamine is then fed via line 16 to pressure filter 18, where the mixture of alkali metal amides is separated from the solution. The filtrate (D) is transferred via line 20 to the fractionation-distillation column 22 where it is distilled, and a concentrated solution of the decomposition products (E) is withdrawn from the heater 24 via line 26. The distillate (F), consisting of a dilute solution of ammonia in methylamine, goes via line 28 from the top of the fraction column 22 and is used to wash the mixture of the solid alkali metal amides (C) obtained in the pressure filter 18. The slurry formed is fed into the fractionator 29 via line 34. A distillate (H) enriched with ammonia is drawn off from the top of the fractionation column 30 and returned to the reaction vessel 12 via line 14. A solution of essentially pure mixed alkali metal methylamides in methylamine (G) is drawn off from the heater 36 via line 38 and returned to the deuterium enrichment process (not shown).

s

10th

IS

20th

25th

30th

35

40

45

50

55

60

65

5

The process conditions, such as the amount of ammonia to be used with respect to the mixture of alkali metal methylamides to be purified, the temperatures and pressures are similar to those described above in the process for cleaning potassium methylamide. s

The following examples serve to illustrate the invention and are in no way intended to limit the scope of the invention.

example

By adding ammonia (108.8 mmol) to a solution of potassium methylamide in methylamine containing 47.6 mmol potassium methylamide, a precipitate of 86% of the potassium methylamide is obtained as potassium amide.

No precipitate is obtained by adding ammonia (6.24 mmol / g solution) to a solution of the potassium salt of N, N'-dimethylformamidine (0.47 mmol / g solution) in methylamine.

The addition of ammonia (92 mmoles) to a partially thermolyzed solution of potassium methyl amide in methyl amine containing 27.0 mmoles of potassium methyl amide and 16.7 20 mmoles of potassium salt of N, N'-dimethylformamidine gives a precipitate of 74% of the potassium methyl amide as potassium amide. The solution concentration of the potassium salt of N, N'-dimethylformamidine remained unchanged.

Example 2

By adding ammonia (1.54 mmol / g solution) to

620 221

a solution of lithium methylamide (0.84 mmol / g solution) and potassium methylamide (0.50 mmol / g solution) at 25 ° C gives a precipitate of more than 98% of the alkali metal methylamides in the form of their amides.

A solution of lithium and potassium methyl amide, initially containing 0.52 mmol / g solution of lithium methyl amide and 0.43 mmol / g solution of potassium methyl amide, was thermally decomposed to a mixture containing 0.31 mmol / g solution of the salts of the main decomposition product N, N ' -Dimethylformamidin contained. Ammonia (2.98 mmol / g mixture) was added and the mixture was shaken for 16 hours and then filtered. The filtrate contained only 0.1 mole eq / g solution of the methyl amide ion, but still essentially all of the N, N'-dimethylformamidine (0.29 mmol / g solution). Analysis for alkali metal ions showed traces of lithium ions (0.01 mol eq / g solution) and potassium ions (0.31 mol eq / g solution).

Analysis of the residue showed that it contained lithium amide (equivalent to 0.49 mole / g initial solution) and potassium amide (equivalent to 0.17 mole / g initial solution). The residue thus contained essentially all of the alkali metals which correspond to the undecomposed methylamides.

The filtrate could then be distilled and the distillate reacted with the precipitate containing lithium amide and potassium amide under conditions in which ammonia is removed to give a solution of purified lithium and potassium methyl amides.

B

1 sheet of drawings

Claims (10)

620 221 1. A process for the regeneration of a system containing an alkali metal alkyl amide, characterized in that ammonia is added to a solution containing an alkali metal alkyl amide and impurities, which do not react with ammonia, on the other hand there is a reaction between ammonia and the alkali metal alkyl amide to form an alkali metal amide, that the reaction product thus obtained is separated from the solution and reacted with a primary alkyl amine under conditions in which ammonia is removed and a solution of the pure alkali metal alkyl amide is formed in the primary alkyl amine used. 2. The method according to claim 1, characterized in that that the starting materials are an alkyl amide of a mixture of alkali metals and the products are an alkyl amide of the said mixture of alkali metals in pure form. 2nd PATENT CLAIMS 3. The method according to claim 1, characterized in that one carries out the following steps: a) adding ammonia to a solution of potassium methyl amide in methylamine and reaction of ammonia and the potassium methyl amide, the solution containing impurities which do not react with ammonia; b) separation of the potassium amide thus obtained from the mother liquor which contains the impurities; c) distillation of the mother liquor and d) reaction of the distillate, which contains methylamine and ammonia, with the separated potassium amide, the methylamine reacting with the potassium amide under conditions such that ammonia is removed and a solution of potassium methylamide in methylamine is obtained, which is essentially free of the impurities mentioned. 4. The method according to claim 1, characterized in that you do the following: a) adding ammonia to a solution of mixed alkali metal methyl amides in methylamine and reaction of ammonia and the mixed alkali metal methyl amides, the solution containing impurities which do not react with ammonia; b) separation of the mixture of alkali metal amides thus obtained from the mother liquor which contains the impurities; c) distillation of the mother liquor and d) reaction of the distillate, which contains methylamine and ammonia, with the separated mixture of the alkali metal amides, the methylamine reacting with the mixture of the alkali metal amides under conditions such that ammonia is removed, and a solution the mixed alkali metal methyl amide in methylamine, which is essentially free of the impurities mentioned. 5. The method according to claim 4, characterized in that the starting material is a mixture of lithium and potassium methyl amides and the end product is a mixture of lithium and potassium methyl amides in pure form. 6. The method according to claim 3, characterized in that one carries out the following steps: a) reacting a solution of potassium methylamide and its decomposition products in methylamine in a reaction vessel with an ammonia-enriched solution of ammonia in methylamine until a slurry of potassium amide is formed in a solution of the decomposition products mentioned and excess ammonia in methylamine; b) separation of the potassium amide from the solution by filtration; c) fractional distillation of the filtrate; d) reacting the distillate, which is a dilute solution of ammonia in methylamine, with said potassium amide obtained to give a slurry; e) rectification of this slurry in a fractionation column, a solution of essentially pure potassium methylamide in methylamine and an upper distillate of ammonia with some methylamine being obtained; f) withdrawing an ammonia-enriched solution of ammonia in methylamine from the top of the fractionation column and returning the solution to the reaction vessel; and g) isolating the solution of essentially pure potassium methylamide in methylamine. 7. The method according to claim 4, characterized in that one carries out the following steps: a) reacting a solution of mixed alkali metal methylamides and their decomposition products in methylamine in a reaction vessel with an ammonia-enriched solution of ammonia in methylamine until a slurry of a mixture of solid alkali metal amides is formed in a solution of the decomposition products mentioned and excess ammonia in methylamine ; b) separating the mixture of the alkali metal amides from the solution by filtration; c) fractional distillation of the filtrate; d) reacting the distillate, which is a dilute solution of ammonia in methylamine with said mixture of the alkali metal amides obtained, a slurry being obtained; e) rectification of this slurry in a fractionation column, whereby a solution of essentially pure mixed alkali metal methylamides in methylamide and an upper distillate of ammonia with about methylamine is obtained; f) withdrawing ammonia-enriched solution of ammonia in methylamine from the top of the fractionation column and returning the solution to the reaction vessel; and g) isolating the solution of substantially pure mixed alkali metal methyl amides in methyl amine. 8. The method according to claim 5, characterized in that the molar ratio of ammonia to the mixed lithium and potassium methyl amides is 2: 1 to 5: 1. 9. Use of the pure potassium methylamide obtained in the process according to claim 6 in methylamine as a catalyst in a deuterium enrichment process in hydrogen. 10. Use of the mixed alkali metal methylamides obtained in the process according to claim 7 in methylamine as a catalyst in a deuterium enrichment process in hydrogen.