DE1945859C3 - Process for the preparation of alkali aluminum hydrides - Google Patents

Description

a pressure of 100 to 250 atmospheres.

2. The method according to claim 1, characterized in that for the preparation of sodium, the duration of the implementation of the process aluminum hydride the aluminum in a stoichio- »5 is 24 to 52 hours, of which 6 to 18 hours metric excess of 1 to 5 weight - for synthesis.

Percent, based on the weight of sodium, disadvantages of the known method are also the

begins. Use of organic solvents in

larger quantities (85 to 90%), the need

3. The method according to claim 1, characterized in that the use of bulky equipment is larger draws that one for the production of potassium, capacity with a complicated system Rubidium or cesium aluminum hydride the aluminum of compounds, as well as a low yield of minium in a stoichiometric excess of alkali aluminum hydrides per unit of reaction-3 up to 10 percent by weight, based on the alkali volume.

metals, uses. 35 In addition, the use of organic solutions

medium not harmless due to the high synthesis temperature and the exothermic reaction of the formation of the aluminum hydrides. Due to this condition

there is a potential danger of an explosive

40 Cleavage of solvents by the aluminum hydrides, especially in the production of potassium and cesium aluminum hydrides. The solvent is practically always split by the latter.

The present invention relates to reducing the yield and quality of the drive to the production of alkali aluminum hydrides 45 end products.

of the general formula MAlH ₄ , where M is sodium, Another disadvantage of the known method

Is potassium, rubidium, cesium. The mentioned consists in the need to use 5 to 10% (by weight alkali aluminum hydrides are characterized by one of the alkali metal) of expensive and extremely pyrophoric high heat resistance and fusibility of aluminum alkyls as activators. In and can for the production of other hydride «; as well as the absence of aluminum alkyls, there is practically no formation of alkali aluminum hydrides as reducing agents and catalysts.
Synthesis of preparations of the fine and pltiarma- A major disadvantage of the known method

chemical chemistry can be used. is also the need as a result of heterogeneity

A method is known for producing from the reaction a larger excess of alumi-alkali aluminum hydrides, which consists in that 55 nium (30 to 50% by weight of the alkali metal) to alkali metals such as sodium, potassium, cesium or use, un all the alkali metal in To bind aluminum their hydrides at a temperature of 120 to 150 ⁰ C hydride. The aluminum excess lowers the content of the end product under a hydrogen pressure of 100 to 150 atm in the product obtained with excess previously activated aluminum and makes the separation in the medium of a solvating or inert "or the pure alkali aluminum hydride extremely difficult. The particles suspended in the hydrocarbon in the presence of aluminum liquid phase of the aluminum which has not been heated as activator (see H. Cla se n, reaction cannot be ab-Angew. Chem., 73, 46, 1961; EC Ashby, GJ. The liquid is also not completely cleared by allowing it to stand and centrifuging Brendel, HE Redman, Inorg. Chem., 2, 499. 1963; French patent 1235 689; German 65 Another disadvantage of the known method is patent 44 277; British patent specification 972 076; the relatively low quality of the products obtained according to USA patent specification 3,158,437; Soviet patent - the one-time separation of the phases, publication 168 651). The products mentioned are identified by

3 4

a low content of end product (40 to 70%) frees the molten alkali aluminum hydride

and by a high, pyrophoric property. Except- the surface of the aluminum particles, which is useful

These products cannot do this without a rapid postponement of the reaction beforehand

going cleaning in any reactions below right as well as an almost quantitative implementation of the

Involvement of the alkali aluminum hydrides as a result of the ta 5 alkali metal in alkali aluminum hydride,

These products contain finely dispersed aluminum. According to this page, NaAlH ₄ melts at

minium particles can be used. 186 ° C and 1 atm with partial decomposition (DAN

The aim of the present invention is the AN USSR, 148, 588/1963); KAlH ₄ , RbAlH ₄ , CsAlH ₄

Elimination of the disadvantages mentioned. melt in the range from 280 to 380 ° C only with water

The invention was based on the object, io fabric printing.

one in its technology and apparatus design in the area of the liquid phase is according to the invention

simpler and more economical process for above the melting point of aluminum hydrides

Production of alkali aluminum hydrides with an experimentally an area of extremely intensive absorption

high yield of end products to develop, the tion of the hydrogen base, which after 10 to

for use in various reactions occurs 15 15 minutes abruptly, it has been determined

suitable without prior cleaning. It was also recognized that it is necessary at

This task is the greatest possible hydrogen production of alkali aluminum hydrides of general absorption - ie a certain, for each aluminum formula MAlH ₄ , where M is sodium, potassium, minium hydride characteristic limit pressure - to rubidium or cesium - to rubidium or cesium by conversion one reach 20.

Alkali metal with aluminum and hydrogen in the case of the invention, the optimal para-

elevated temperatures and pressures, thereby solved, for the synthesis of aluminum hydrides in the meter

that you can do the implementation without using a melt:
further dispersing medium at one temperature
above the melting point of the corresponding 35

Alkali aluminum hydride, specifically for production in the production of NaAlH ₄ - / = 200 to

of sodium aluminum hydride at temperatures of 350 °; Pu ₂ ■ = 175 to 300 atm,

200 to 35O ° C and a pressure of 175 to 300 atü in the production of KAlH ₄ , RbAlH «,

or for the production of potassium, rubidium and CsAlH ₄ - / = 250 to 400 °; Ph ₂ = 100 to

Cesium aluminum hydrides at a temperature of 30 250 atm.
250 to 400 ⁰ C and a pressure of 100 to 250 atm
performs.

To manufacture technical products with a The general rule in chemistry that a

high content of end product, which easily up to an increase in temperature the reactants

high degree of purity and to activate thermally 35 and the reaction rate

Use in reactions involving the increase is intended to say nothing about it and does it

Aluminum hydrides are suitable, the reaction is by no means self-evident that above 200 ° C the

Sodium with aluminum and hydrogen purpose- formation of alkali aluminum hydride from simple

moderate with a stoichiometric excess of substances such as alkali metal, aluminum and hydrogen

Aluminum from 1 to 5%, based on the weight 40, must proceed very quickly, with only the disso-

of sodium and the reaction of potassium, rubidium ciative pressure is increased. The field of intense

or cesium with aluminum and hydrogen with hydrogen absorption, when they suddenly jump

an excess of aluminum of 3 to 10%, takes place, as well as that for the formation of the alkali

Based on the weight of the respective aluminum hydride mentioned, the necessary limit pressure would still have to be

Metal carried out. 45 can be found.

The direct reaction of an alkali metal with It must be pointed out that in the

Aluminum and hydrogen is thus a heterogeneous cited patent 63 767 of the office

Process, the process of which through the dense oxide layer for inventions and patents in East Berlin

on the surface of the aluminum particles makes it difficult for the temperature to rise above is, i.e., the process is carried out on the 50 200 ° C in the synthesis of sodium aluminum hydride

The surface of these particulate-forming solids is excluded at all (column 3, lines 16

NaH, Na ₃ AlH ₉ , NaAlH ₄ delayed. until 20).

In accordance with the countered »Inorg. Chem. «2, 499 to 501 (1963) does not contain

Patent specification 63 767 of the office for invention and only no information about the inventively fixed patent system In East Berlin, heterogeneity is posed as the possibility and expediency of work

limit in the reaction to be investigated through in the melt and consequently takes the suggested

specially developed procedures for the activation of procedures not in advance, but also contradicts

Overcome aluminum. the patent 63 767. For example:

The process according to the invention differs from Table V, p. 501, that without from patent 63 767 and any other medium of an organic liquid, the NaAlH,

known publications by the fact that the Hete- dissolves, or without a catalyst a formation of NaAlH,

rogeneity barrier is overcome by not taking place.

Reaction in the temperature range of the liquid phase on p. 501 (left column after Table IV)

the aluminum hydrides is carried out. claims that the response speed is between

65 increases from 150 to 180 °, but so insignificantly that e!

it is not necessary to raise the temperature like this.

M (liquid) + Al (solid) + H _a (gaseous)> MAlH ₄ From Table II, p. 500 it can be seen that with dei

(liquid) (M = Na, K, Rb, Cs). Carrying out the reaction in THF the Umsetzuni

of sodium in _NaAlH4 at temperatures f fs 150 ° C falls. If the reaction is carried out in diglyra (Table III, p. 500), the decrease in the yield, depending on the pressure, is higher than 140 ° C / 70.2 atm, 160 ° C / 140.4 atm and 180 ° C / 351 atm.

As first established according to the invention, vird Sodium, in contrast to the results reported, the reaction in the absence of an organic Solvent intensified strongly over 200 and at relatively low pressures of 175 to 300 atm carried out.

In order to prove the technical progress achieved according to the invention, a comparative one is given below Analysis of the application and the cited patent 63 767 of the Office for Invention and. Patent system given in East Berlin.

Features of the patent specification 63 767 of the Office for Invention and Patents in East Berlin:

a) The process of patent specification 63 767 of the Office for Invention and Patents in East Berlin only relates to the synthesis of NaAlH ₄ through the reaction of the simple substances sodium, aluminum and hydrogen and, in terms of the parameters, cannot be used for the production of aluminum hydrides of potassium, rubidium and cesium.

b) The main idea of the known process is the achievement of a great technical advance compared to the processes known at the time by using activated aluminum, which is produced by grinding with or without additives before or during the synthesis of NaAlH ₄ in specially designed apparatus.

c) The main additive in the activation of aluminum is sand in the amount of 60 to 130% the weight of aluminum. Also other abrasive, preferably natural materials that Oxides containing at least one heavy metal can be used. The grinding time is 8 to 40 hours with or without organic solvent that can dissolve dis aluminum hydride or not. Without sand, the conversion is unstable from 0 to 80% (Examples 1 and 2 of the description).

d) The main means of carrying out the activation of the aluminum are not normal ones Drum mills, but special machines with vibratory mixing (Vibration mixture) z. B. a pear mill that can do without additives (column 4, Line 20).

e) The basic parameters of the process are: / = 50 to 200 ⁰ C, Pn ₂ = 11 to 351 atm, with a preactivation of the aluminum before the actual synthesis of NaAlH ₄ / = 130 to 180 ⁰ C, Pn ₂ = 101 to 351 = 80 to 13O ⁰ C, Pu to 101 atm be atm and upon activation of the aluminum, together with the synthesis / ₂ = 50th

NaAlH ₄ dissolving liquid (tetrahydrofuran). 80% of the volume of the mounds is entered into the autoclave, an equirolar amount: 100% of the aluminum weight of Na and Al and sand; the process is carried out at 100 ^° C. and 76 atm, with a mixture with 900 vibrations per minute in 40 hours. The conversion is calculated according to the concentration of the solution without precipitation of the solid NaAlH ₄ .

ίο Omitting or changing one or more the optimal conditions deteriorate the result progressively. So is sales without that most important additive, namely sand unstable 0 to 80% (example 1 and 2). The preparatory grinding of the

Aluminum (for 8 hours) with sand (100% of the aluminum weight) in toluene and separately from NaH with toluene when synthesized in this medium with 50% aluminum overcapacity at 150 ° C gave 351 atm after 20 hours a conversion of 88%

ao (example 1). An analogous activation, but in tetrahydrofuran in 18 hours with lower parameters of 120 ^° C. and 81 atm, resulted in a conversion of 83% in 2 hours. Ultimately, only NaAlH ₄ was discovered in the product, which was obtained from Na and without solvents

"5 AI, taken with a 400%" excess was and previously activated in a special mill for 15 hours, also in the absence of a thinner was, had been produced (Example 4, quantitative data of the conversion are not included).

30th

g) It is quite obvious that the patent 63 767 of the Office for Invention and Patent system in East Berlin proposed methods of activating the aluminum, which complicated itself and takes a long time and requires special equipment, the process is still through it makes it difficult that by introducing a large amount of dietary fiber: sand (100% of the aluminum weight), Excess aluminum (50% in Example 1 and 400% in Example 4), dispersing agents and other additives, the reaction product is strongly diluted and its removal per Rcaktorvolumeinhei » is decreased.

h) The presence of the large amount of ballast materials in the end product also makes the phase separation after the reaction, the extraction and separation of the pure NaAlH ₄ difficult.

i) The use of organic solvents in the synthesis required for patent 63,767 of the Office for Invention and Patents in East Berlin is preferred (column 4, lines 20 to 23 and 25 to 27) is made more difficult by the secondary reactions of the solvent, which reduce the yield with the aluminum hydride, the pyrophoric admixtures of the decomposition products of the solvent and can become explosive and unregulated when the temperature rises, especially at the production of potassium, rubidium and cesium aluminum hydrides.

f) From the documents of the patent it can be seen, j) In the following table the above mentioned in the optimal variant (90% conversion, wrote the conditions of the synthesis of sodium example 2 of the patent) the activation of the aluminum aluminum hydride NaAlH ₄ According to the patent miniums at the same time with the synthesis is carried out by writing 63 767 of the office for invention and grinding of the reagents in the rocking mixer with patent system in East Berlin and the invention against steel balls in the presence of sand and a superimposed.

Comparative table of conditions for the synthesis of NaAlH ₄

condition According to the Office's patent 63,767 According to the invention No. for inventions and patents in Activation of aluminum - hours East Berlin no I. Entry of sand or other abrasive necessarily 8 to 40 no average absolutely necessary 6 (1 to 130% -> Excess aluminum, % the weight of the aluminum 1 to 10 3 Introduction of a solvent preferably 50, 400 no 4th Synthesis temperature ^{, 0 C} preferably 200 to 350 5 Hydrogen pressure, atm 50 to 200 175 to 300 6th Response time, hours 11 to 351 2 to 3 7th Phase separation after the reaction 2 to 40 no 8th - Hours necessary 1 to 3 Separation of NaAlH ₄ from the no·? 9 Solution, duration, hours is carried out when in use a NaAIH- dissolving solution Extraction of NaAlH ₄ , duration, hours by means of (THF) 1 to 2 the technical product IO the is carried out when in use is for all reactions of a NaAlH ₄ non-dissolving solvent suitable Preparation and regeneration of the solvent (toluene) 2 to 3 no 11th Solvent, time, hours 6 to 12 ° / o NaAlH ₄ in the original product 90 to 95 12th 25 to 70 not pyrophoric safety flammable sludge OlrlilllGI / .G
Pressure is only from 13th potential danger of splitting the Source hydrogen Solvent pressure Ph ₂ and t ° C certainly Total time of the process, hours 2 to 3 14th Special equipment 18 to 56 no 15th necessary to activate the Alu miniums

From the table it can be seen that, according to the invention, a practically small increase in the parameters compared to patent specification 63 767 of the Office for Invention and Patents in East Berlin, namely the temperature to over 200 ° C and up to 35O ⁰ C and The lower limit hydrogen pressure of 175 atm _{ensures the melting of NaAlH 4} , and this in turn not only enables the avoidance of lengthy and extensive operations such as activation of the aluminum, separation of NaAlH ₄ from flammable sludge after the reaction, preparation and regeneration of the solvents, but rather the Process significantly intensified: In a significantly shorter time (2 to 3 hours instead of 18 to 56 hours) a practically pure primary product is obtained which contains 90 to 95% NaAlH ₄ (instead of 25 to 70% according to the patent), which is suitable for use in is suitable for any B.eactions without having to be cleaned. Ordinary autoclaves are used for the reaction. Special devices for activating aluminum are completely superfluous.

In addition, the method according to the invention enables potassium, rubidium and cesium-aluminum hydrides to manufacture.

The special features of the invention:

a) The inventive method relates to a synthesis of alkali metal aluminum hydrides MAlH ₄ - sodium, potassium, rubidium and cesium - by direct reaction of simple substances such as alkali metal, aluminum and hydrogen.

b) The basic idea of the process is to achieve a higher technical level and to intensify the process by carrying out the reaction of the substances mentioned in point 1 in a melt of the alkali metal that is first present, but increasingly disappearing, and of the liquid aluminum hydride that is formed and accumulates, MAlH ₄ (Patent claim 1), with the experimentally determined optimal parameters t and P.

c) The proposed method makes it possible to achieve a practically quantitative conversion of the alkali metals into aluminum hydride, and to obtain technical products in the form of light gray, non-pyrophoric melts mi): a high content of basic MAlH ₄ (90 to 95%), which are suitable for direct use in a wide variety of reactors. It is easy to produce preparations of near purity from these technical products, which are rich in raw materials, by extracting NaAlH with tetrahydrofuran and KAlH ₄ , RbAlH ₄ CsAlH ₄ with diglyme (ethylene glycol dimethyl ester)

d) The synthesis of aluminum hydride takes place according to the process according to the invention in one stage is characterized by the high speed. The main amount of hydrogen is in 10 bi Absorbed by the reaction mixture for 15 minutes. The whole process including the preparations heating to the optimal temperature takes 2 to 3 hours.

nt)

^{ε ΛΤ proceed "eifordert no} or 5 _m ί if S / iTh ^IUinS --n oT *? **"

with a slight 1 to 10% excess to the ^{t M d to be produced}

\/NS

η n _a «

The costs of the alkali aluminum hydrides which are produced by the process ^{according to the invention decrease} due to the exclusion of expensive aluminum alkyls

I _n accordance with the present invention may Alkaüaluminiumhydride metal when using ^v ° "aluminum in amounts are synthesized ^{(weight of} alkali metals up to 10% ^of 5)

g) The procedure in accordance with the designation is, as a result of

S da Tt hoÄ, ", ₅ would take ₁ per unit volume of the finished MAlH

^ f ^{h enables} <

^{the process} according to the invention

free.

h) The process according to the invention is characterized by relative safety, since the pressure in the system is only determined by the initial pressure of the hydrogen and the temperature of the synthesis and the occurrence of any secondary reactions (e.g. the cleavage of the solution, the TZ

uncontrollable increase in pressure are excluded here. '

The alkali metal and powder Ϊ are placed in a rotating stainless steel autoclave Aluminum with a particle size of up to 2 μm with an excess of aluminum of 1 to 10 μm Weight of the alkali metal. Then you lead in de ™ Autoclave hydrogen under a pressure of 100b J 300 atm. With continuous stirring, the Mixture in the autoclave to a temperature dL around 30 to 50C the melting point d-s ieweiligc? Aluminum hydrides, heated. In doing so, there is a rapid drop in the hydrogen pressure, After the pressure reduction is complete, the TenW door is increased by 30 to 100 ° C, the contents of the autoclave at this temperature for 0.5 to 1 hour keep aS Cooled to room temperature and discharged the resulting molten product.

As a result of a relatively small admixture of the excess aluminum, the alkali aluminum hydrides can be from molten products by recrystallization from tetrahydrofuran or dimethyl Separate the diethylene glycol ester.

According to the invention, a high rate of formation of alkali aluminum hydride is achieved the rate of formation of alkali aluminum hydrids in the known processes around the 2 to Exceeds 4 times. As a result, the duration of the synthesis of the alkali aluminum hydride in the invention according to the procedure 8 to IT times ab in the known procedures.

By excluding the organic medium, it is possible to simplify the apparatus considerably and to reduce their volume by about 10 to 1 thing, whereby the Yield of alkali aluminum hydride per unit of reaction volume is increased.

The method according to the invention is also relatively

moderately safe, since during the synthesis the decomposition reaction of the alkali aluminum hydrides takes place Increase in pressure over the through dien inlet pressure of the hydrogen and the temperature certain pressure is also excluded

to operate such products; it's not difficult

iorhe "/ ^^? p"'· ^{Also e} ' ^gnen j ^{e themselves} °! Τ most ^ ^Rt » ^m & ⁿ S ™ use in the

7 "» interesting reactions.
_w T ^Patch f ^{re "understanding the} present invention Tm ^{below fol} ge" ^d e examples of the manufacturing ^ ⁸ ° ^V "iniumhydriden mentioned ^alkali ^^.

·
B e ι s ρ ι e I 1

"™» ⁶ " _K ^{autoclave of 2 l} capacity leads, ο ^" _t ° ⁰ ^ atnum 120 g of aluminum powder with a

t £ T w ™ ^{aluminum by 97} % ^{a and} S ^ibt

^ w "™ ° ^{rUCk V} °" ³ °° ^3tm ^ P ™ _f one scratches with intense agitation

n / T * ^{Tem perature of 220} ° C. After the «^ ^r . ^{ucksenk "n} g ^{W1 [d} ^ e temperature increased to 260 ⁰ C.

t T κ "ί ' ^{5 bC} ' ^{during this temperature period}

Man e ffiS "

m » ^e i ^{alt 235 g greyish white} melt, which contains 96% ^{Na nu} ' ^llaluminin ₁ hydride.

_Ao hvH * ^e ' ⁿ recrystallization from tetra-

_{^η Μ} '° ^{ίΐ1Γ3η e, you rhak} Products Containing ^Natri "maluminiumhydrid of 99.7%.

Example 2

α ^{mtnum and 14} ^ g of aluminum be in erniizt ShTt ° ^{klav rapidly to a} temperature of 220 ⁰ C to obtain thereby a spontaneous temperature ^ei ^ S ^{to chan} gj f ^lu 280 ° C observed. Work is carried out under a ^water resistance of 175 to 300 atm and with stirring for 2 hours. a 5, ^{to the tem} perature of 320 to 35O ⁰ C ^un ° ^scnaltet the system off after 30 minutes. ι ·· ^Cr i ^{alt 275 g} melt, which contains 95% sodium ^alu ™ ⁿ ' ^u ™ hydnd.
^S5 . ^ ^{after the} one-time recrystallization from tetra-

? Ροϊ "" ^ · " ^ma " ^{a product containing / u Nainumalunii} niumhydrid.

B e i η i I l so σ i ^. · P'ei j

-i, valium and 60 g of aluminum heated to wanrend 2 hours at a temperature of 360 ⁰ C bi 9 <n ^hear "" ^ ^{e 'nem water} toffdruck 200

6 * _a i ^u .. ^{erJla 143} E gray melt containing 94% potassium ^alu ™ contains aluminum hydride.

erh-f. ^single recrystallization from jDiglym

ν ν ^m , ^{to a product} with a content of 97% potassium aluminum hydride.

Example 4

4 g of rubidium and 3 g of aluminum are heated within 1.5 hours at a temperature of 350 to 38O ° C with stirring under a hydrogen pressure of 200 atm.

A small bar of rubidium aluminum hydride containing 85% of the base material is obtained.

Example 5

14 g of cesium and 3.0 g of aluminum are heated to a temperature of within 3 hours

38O ° C under a hydrogen pressure of 250 atm while stirring. 17 g of gray melt are obtained which contain 90% cesium aluminum hydride.

After a single recrystallization from diglyme, a product is obtained with a content of 96% Cesium aluminum hydride.

Thus, the process of the present invention is effective in producing alkali aluminum hydride in the speed with which the process is carried out and in the manufacture of high quality products, as well as in the extreme simple apparatus used for the synthesis.

Claims (1)

Disadvantages of the known process are the length of the synthesis, due to the slow patent claims: the formation of alkali aluminum hydride proceeds under the specified process conditions and its multiple stages. 1. Process for the preparation of Alkaiialu- The most important stages of the known process miniumhydriden of the general formula MAlH ₁ , and their duration (in hours) are: where M is sodium !, potassium, rubidium or cesium
is, by reacting an alkali metal with aluminum and hydrogen at increased Te'nperatu io., · · _£ . -, -ren and pressing, thereby identifying activation of aluminum ... 6 ba 12
net that you can carry out the implementation without cleaning and drying ^{the application} another dispersing medium at eifier tem- solvent 6 ms 12 temperature above the melting point jles ent- hydrogenation ο to 18 speaking alkali aluminum urahydride, and although 15 separation of the phases of the reaction for the production of sodium aluminum hydride in an ion mixture after hydrogenation Temperatures from 200 to 350 ⁰ C and a pressure by filtering or centrifuging from 175 to 300 atmospheres or for the production and washing of aluminum alkyls 2 to 4 Potassium, rubidium and cesium aluminum hydride distillation of solvents and those at a temperature of 250 to 400 ⁰ C and »0 their return to the cycle .. 4 to 6