NO137277B - PROCEDURES FOR THE EXTRACTION OF ALUMINUM FROM AN ALUMINUM / SILICINE TYPE ALLOY. - Google Patents

Description

This invention relates to a method for recovery

of aluminum from ternary or quaternary alloys containing as main elements aluminium, silicon and titanium respectively, and aluminium, silicon, titanium and iron, where the alloys are reacted with hydrogen and an aluminum alkyl compound in the presence of a catalyst.

It is generally known that organic aluminum and/or aluminum alkyl compounds can be prepared by allowing aluminum to react with an organic aluminum compound and hydrogen or with an olefin and hydrogen in the presence of an organic aluminum compound. See e.g. US Patents 2,787,626, 2,900,402, 2,930,808, 3,000,919, 3,016,396, 3,032,574, 3,207,770, 3,207,772, 3,207,773, 3,207,774, 3,393,215, and 37,505 .

US Patent 3,393,217 describes the preparation of organic aluminum compounds using an aluminum-silicon binary alloy containing more than 13 percent by weight of silicon.

The patent further states that contamination levels of iron, copper

and titanium and magnesium may also be present in the binary alloy. However, these amounts of contamination are quite small, usually approx. 0.1% by weight or less of the aluminum-silicon binary alloy.

US patent 3 39 3 217 further reveals that binary aluminum-silicon alloys with 13-60% by weight of silicon give far greater utilization during the hydrogenalumination than binary aluminum-silicon alloys containing less than 13% by weight of silicon. Extremely poor utilizations or aluminum recoveries are achieved (less than 10%) when the silicon content of the binary alloy is as low as approx. 8 wt% silicon.

US Patent 3,402,190, which relates to a process for producing alkylaluminum compounds using certain activators or catalysts, states that with the use of such catalysts, namely alkoxides of lithium, sodium or potassium, alkylaluminum compounds can be produced from multi-component alloys , such as aluminum-silicon-iron or aluminum-silicon-iron-titanium, and alloys are indicated as having the composition 13-40 wt% silicon, 1-15 wt% iron, 0-10 wt% titanium while the rest consists of aluminium. Small amounts of other metals such as magnesium and calcium can also be introduced into the alloy.

A certain degree of good results have been obtained using these previously known processes, but it has unexpectedly been discovered that sustained or constant outstanding efficiencies can be obtained by reactions involving the use of ternary and quaternary alloys, including aluminum, silicon , titanium, and. aluminium, silicon, titanium and iron, the titanium being present in an amount sufficient to accelerate the hydrogenalumination reaction, but not in an amount sufficient to have a detrimental effect on the amount of aluminum which can be reacted from the alloy.

According to the invention, a method for extracting aluminum from an aluminum/silicon type alloy is provided, by selective reaction of the aluminum content by reaction with hydrogen and a tri-(C2-C4-alkyl)-aluminum compound

. in the presence of a catalyst, for the formation of a liquid alkyl-aluminum compound, and separation of the liquid compound and release of substantially pure aluminum. The procedure is characterized by the fact that

(a) starts from an alloy with a composition of:

33-94% aluminum by weight

5-58 wt% silicon

0.2-4 wt% titanium and

0-5 wt% iron, and

(b) ■■ as a catalyst uses a complex of an alkali metal hydride and a trialkylaluminum compound and/or a dialkylaluminum hydride compound.

Titanium must be present in more than contaminant amounts and in an amount sufficient to accelerate or enhance the hydrogen-alumination reaction. Titanium must also be present in sufficiently small amounts not to have a detrimental effect on the reaction.

In the quaternary alloy, i.e. when iron is present, it is

generally preferable that the amount of titanium exceeds the amount of iron, when the amount of iron is small, however, excellent results are obtained even when the amount of iron exceeds the amount of titanium.

In general, it is preferable that both titanium and iron are

present in such small amounts that precisely this will effectively increase the hydrogen-alumination reaction. The less iron present in the quaternary alloy, the more titanium can be tolerated, and vice versa,

the more iron present in the alloy, the less titanium can be tolerated.

In an unexpected way, the titanium remedies the harmful effect of silicon in a hydrogen-alumination reaction using binary aluminum-silicon alloys as indicated in US Pat.

3-393 217.

The present invention provides a sustained or constant utilization of 90% or more in the hydrogen-alumination reaction. It should be noted that an increase in the yield of the utilization rate of even just 1% is of extremely great importance in practice when large-scale industry uses the method.

When an aluminum alkyl is used as the main reagent, stoichiometric amounts are used. When an olefin is used in the reaction, only catalytic amounts of aluminum alkyl are required.

In the following, a preferred embodiment will be described. The ternary aluminium-silicon-titanium alloy or the quaternary aluminium-silicon/iron/titanium alloy is preferably activated for use by the reaction, as in the case of aluminium, and the activation may be carried out according to any of the known methods proposed when aluminum metal is used,

and which is effected by crushing or cutting the alloy in a hydrocarbon solvent containing a small amount of organic aluminum compound, by injecting the alloy in a molten state into a protective liquid under an inert atmosphere, or by using an activator, such as trialkylaluminium, dialkylaluminum hydride or -halide or the like, or sodium ethoxide, other alkoxy compounds or other suitable activators.

In one embodiment of the invention, shavings or small particles of a ternary or quaternary aluminum alloy, containing as principle elements, aluminium, silicon and titanium or aluminium, silicon, titanium and iron, are brought to react with 1.5 times the theoretical amount of triisobutyl aluminum with hydrogen at a pressure of 105 kg/cm at 120°C for approx. 7 to 15 hours.

In another embodiment of the invention where a more reactive aluminum alkyl is used, such as, for example, triethylaluminium, good results are achieved at a hydrogen pressure of 70 kg/cm at 140°C for approx. 1 to 3 hours.

The ternary or quaternary alloy may contain impurity amounts of copper, magnesium, calcium, zirconium,

vanadium and other elements.

The amount of aluminum that the alloy contains is preferably more than 50% by weight, but may be as low as 3% by weight.

The amount of silicon that the alloy contains can be any amount from approx. 5 to approx. 58% by weight of the alloy.

The amount of titanium in the alloy is at least 0.2% by weight and not more than 4% by weight. A weight % of titanium from 0.6 - 3 is particularly preferable.

The amount of iron in the alloy is preferably as small as possible, but may be from 0 to 5% by weight, and alloys containing less than 4% iron are preferred. A weight% of iron of approx. 1 more

4 is particularly advantageous.

The alloy may be finely divided, or may have any other form, such as e.g. chip-like fragments obtained by using a planer, a lathe or a drill,

or other small particles obtained by simple crushing or cutting.

The trialkyl aluminum compound used as one of the materials used in the present invention is represented

of the general formula RR'AIR", where R, R' and R" are selected from alkyl radicals having 2 to 4 carbon atoms. Preferred alkylaluminum compounds are triethylaluminum, tri-n-propylaluminum, triisobutylaluminum, ethyldipropylaluminum and mixtures thereof.

Catalysts used in the present invention

can be selected from the group of alkali metal hydride complexes with a trialkyl aluminum compound and/or a dialkyl aluminum hydride compound.

A particularly preferred catalyst is sodium alkyl aluminum hydride, e.g. sodium triethylaluminum hydride and sodium diethylaluminum dihydride. Particularly good results have been obtained using a catalyst of the formula NaH.xTEA.yDEAH, where x + y = 5, but can be equal to at least 1 and preferably equal to 3 to 5.

(TEA) is triethyl aluminum and DEAH is diethyl aluminum hydride).

Preferred alkali metals are sodium, potassium and lithium,

but sodium is most preferable. Preferred alkaline earth metals are magnesium and calcium, and calcium is particularly preferred.

Some examples of alkyl groups are ethyl, propyl, isobutyl, n-butyl, sec-butyl, pentyl, hexyl, heptyl, octyl, octadecyl and eicosyl. Alkyl groups with from 2 to 4 carbon atoms are most preferred. ..The complex metal compound catalyst may be prepared or formed in situ or may be added to the hydrogen aluminization reactants.

The reaction temperatures to be used in the production of alkyl aluminum compounds from the ternary or quaternary aluminum alloy are in the range of from 70 to 250°C, preferably from 100 to 180°C. Suitable reaction pressures are in the range of 10 to 300 kg/cm 2 . Under pressures of less than 10 kg/cm 2 , the reaction rate is low, but when pressures of more than 300 kg/cm 2 are used, the reaction apparatus will necessarily become quite complicated and such pressures are therefore not appropriate to use.

In a preferred embodiment of the invention, small particles of a quaternary aluminum alloy with a particle size of approx. 20 to 100 mesh, containing based on weight %, 78 aluminium, 20 silicon, 1 iron and 1 titanium to react with triethylaluminum, ethylene and hydrogen at a pressure of approx. 70 kg/cm^ at 140°C

in a time of approx. 1 hour.

In accordance with the method according to the invention, a metal residue containing a large amount of silicon which has been used in the production of alkyl aluminium, is separated from the reaction mixture, it is used for the production of an alloy of a suitable composition and can then be used again. In such a case, the metal residue can be recycled in the form of silicon containing impurity amounts of iron and titanium by converting the free aluminum present in the alloy into an alkylaluminum compound, or it can be recycled in the form of an alloy or a mixture which contains aluminium, silicon and titanium, with and without iron, by converting only a part of the aluminum present in the alloy.

In order to facilitate the understanding of the invention, a number of design examples will be given in the following.

EXAMPLE A

Two series of alloys were prepared for investigation. 'Both series had varying amounts of silicon from 0 to approx. 50%: Each alloy was prepared by weighing the calculated amount of commercially pure metals into a graphite crucible which was heated in an induction furnace to 1400-1450<C>>C for the series (A) or 1800-1950°C for the series (B ). The molten mixture was stirred with a graphite stirrer and allowed to cool. The resulting ingot was processed with a rasp device to remove graphite from the crucible and then machined on a lathe to remove the end pieces and outer skin.

The alloy ingots were split or comminuted by means of a lathe using a cutting width of about... ©-.09 mm. The turning chips turned out to be somewhat thicker than 0.09 mm, and were smooth on one side and jagged on the other. They were of similar dimensions, approx. 1.6 mm wide, about 3 to 6 mm. long and on average 0.15 to 0.18 mm thick. Two exceptions were samples 1 (A) and 2 (A), which produced larger, thicker chips with an average thickness of approx. 0r23 to 0.33 mm. Alloys with a high silicon content generally produced shorter and more brittle chips. 16 mesh fines were removed from all alloy chips. Samples for pre-examination by hydrogelumination reaction were divided by dividing into four from the main mass sample.

X-ray fluorescence analyzes (XRF) of these alloys are shown in Tables I and II.

Into a 300 ml stirred Magnedrive autoclave manufactured by Auto Engineers, a quantity of the alloy calculated to contain approx. 3.6 g of aluminum and 6.8 ml of a sodium ethyl aluminum hydride solution to give 0.6 wt% sodium based on triisobutylaluminum (TIBA), and 100 ml (79 g) of TIBA. TIBA contained 8% diisobutylaluminum hydride (DIBAH). The TIBA/AI molar ratio was close to 3.0, which represents a 50% excess of TIBA equal to the theoretical amount (for trial no. 8 TIBA/Al = 3.4).

The catalyst solution was prepared from the reaction of sodium with a mixture containing approx. 70% diethylaluminum hydride (DEAH), 30% triethylaluminum (TEA) and the formed aluminum metal were filtered off. According to analysis, it contained 8.1% sodium. The composition of the catalyst is not stoichiometric and is best represented by the general formula NaH.xEt^Al.yEt2AlH

(x + y = 5), but can be equal to at least 1 and preferably equal to 3 to 5).

After the alloy, TIBA and the catalyst had been introduced into the autoclave, it was closed and put under a pressure of approx. 70 kg/cm^ with hydrogen and heated to 120°C with stirring. Then more hydrogen gas was introduced into the autoclave. until the pressure was approx. 105 kg/cm. This pressure and temperature were maintained for 5 hours. The pressure was then increased to 123 kg/cm and the reaction carried out for a further 10 hours. The pressure at the termination time varied from 105 to 123 kg/cm 2. The. total reaction time was 15 hours.

The reaction mixtures were worked up under nitrogen with special care is taken to recover the full amount of solid residue. A stream of benzene from a wash bottle was used to remove solids on the stirrer and to transfer the solids to a medium glass frit Buchner funnel. The residues were washed well with benzene and petroleum ether, vacuum dried, the filter and weighed.

All the foodstuffs, and the residues that were. inhomogenes [especially 1 (A) and 2 (A) ] were freeze-ground in a Spex freeze-mill at -196°C before analysis. This was done to ensure that the samples were homo-mogen .

The amounts of aluminum that reacted in the two series are shown in Tables III and IV.

EXAMPLE B

A series of alloys was prepared to determine the effect of titanium on the utilization rate of aluminium/silicon/titanium alloys. The alloys were prepared in a similar manner to those listed in Series A in Example A.

Nominal compositions of these alloys are shown in Table V.

The hydrogenalumination was carried out using the method indicated in example A. In all cases, 100 ml of TIBA, 3.6 g of aluminum and 0.5 g of sodium as NaH•xTEA•yDEAH were reacted for 7.5 and 15 hours at a pressure of 105 kg/cm 2 hydrogen.

The amounts of aluminum that were brought into reaction are listed in Table VI.

The beneficial effects of titanium in aluminium/silicon ternary and quaternary alloys containing titanium and titanium and iron

EXAMPLE C

For the sake of comparison, binary aluminium/silicon alloys of varying proportions were investigated. The alloys were commercially produced alloy powders blown from a melt in an inert atmosphere by known manufacturers. The composition of the alloys and a sieve analysis of each sample are listed in Table VII.

Hydrogenalumination reactions were carried out using the procedure set forth in Example A using TIBA at 120°C, 105 kg/cm 2 and for 15 hours using a catalyst. The results of these experiments are listed in Table VII.

EXAMPLE D

Another series of alloy powders of different elemental compositions similarly blown from the smelter as in Example C was obtained from the same commercial source. The elemental composition of these samples is listed in Table IX.

The hydrogenalumination reactions were carried out using the method set forth in Example A below

-by TIBA at 120°C, 105 kg/cm^ hydrogen pressure for 15 hours. The results of these tests are listed in the table. X.

EXAMPLE E

A hydrogenalumination reaction was carried out using triethyl aluminum (TEA) as aluminum alkyl and the procedure was as described in Example A. 4 g of the quaternary alloy No. 4 (see Table IX in Example D) was reacted with 87 ml of TEA and 6 ml of the sodium ethylaluminum hydride catalyst at 140°C under 140 kg/cm^ hydrogen pressure for 3 hours. The reaction mixture was worked up as described in example A and gave 1.75 g of solid residue. This residue weight corresponds to 90.4% utilization of the aluminum that was present in the original aluminium/silicon quaternary alloy....

EXAMPLE F

A sample of an aluminum/silicon quaternary alloy was prepared by melting the calculated amounts of commercially pure metals to obtain the intended composition, namely the following weight percentages: 56 Al - 31 Si - 2 Ti - 11 Fe. The molten alloy was cooled. crushed and ground and sieved through a -100 mesh sieve. X-ray fluorescence (XRF) analysis showed that the actual iron content was. 7.9% and the titanium content was 2.2%. 4 g of this alloy was reacted with 87 ml of TEA in the presence of sodium ethyl aluminum hydride catalyst at 140°C under 140 kg/cm<2> hydrogen pressure for 3 hours. The reaction mixture was worked up as described in Example E. Based on the weight of solid residue recovered, the degree of utilization of aluminum in the original quaternary alloy was only

73%. This shows the harmful effect of an excessively high iron content on the degree of utilization of aluminium/silicon alloys in the hydrogen-alumination reaction.

A similar experiment was carried out with an alloy produced in a similar manner and with an intended composition based on wt% of 5 Ti and 4 Fe. The actual composition according to XRF was 4.6% Fe and 5.0% Ti. Reaction of this alloy with TEA, catalyst and hydrogen at 140°C and a pressure of 140 kg/cm<2> for 3 hours gave an amount of solid residue corresponding to 80% utilization of aluminum in the original lsering sample. This result shows -den

combined adverse effect of a high iron content and a high titanium content: on the degree of utilization of quaternary aluminium/silicon alloys, in the hydrogenalumination reaction.

The excellent degree of utilization of ternary and quaternary alloys is clear from examples D and E.

Aluminum which is bound as intermetallic compounds is not reactive and preferably the amount of these intermetallic compounds should be kept as low as possible by keeping the amount of iron and titanium as low as possible.

In the initial step of a thermal decomposition process, aluminum or an aluminum/silicon alloy is converted into a dialkylaluminum hydride-containing liquid phase and a phase of residual solids. The raw aluminum or aluminum/silicon alloy must contain some metallic aluminum that is not firmly bound in the form of an intermetallic compound. Aluminium/sil:sium alloys are particularly preferred as materials to be refined by this method. Aluminum/silicon alloys can be easily produced at low cost with various electrothermal reduction processes and thereby serve as an economical source of purified aluminum metal. Furthermore, the remaining solids formed by the present method will comprise metallic silicon (usually, but not necessarily combined with other common impurities such as iron, titanium and the like). Such residue solids, which can be easily extracted, are of great use and applicability in chemical processes, e.g. in steel production. In addition, the silicon obtained as a by-product of the process is very active, and can thus be brought to react directly with alkyl halides to form alkyl halosilanes. The use of the preferred aluminum/silicon alloys, particularly those containing small amounts of titanium and/or iron, is thus advantageous in that they are an economical source of cheap aluminum and provide, in the present process, useful silicon-containing by-products which are likewise of industrial and economic importance.

The raw or pure aluminum or the aluminium/silicon alloy is preferably used in divided or particulate form, although efficient use can be made of turning chips, chips of another kind, flakes, strips etc.

In carrying out the first stage of the cleavage process, there were two general methods of converting the raw metallic aluminum or aluminium/silicon alloy into the dialkyl aluminum hydride containing liquid phase. One such method involves reacting the aluminum content with suitable amounts of an α-olefin (eg ethylene, propylene, isobutylene, etc.) and hydrogen in the presence of an alkylaluminum catalyst (eg triethylaluminum). In this way, it is possible to convert this aluminum content into a product which in most cases contains the corresponding dialkyl aluminum hydride and trialkyl aluminum compounds. As is known, it is desirable to activate the aluminum in a suitable way so that the initiation of the reaction is facilitated and the reaction time is reduced. These reactions are generally carried out at somewhat elevated temperatures and pressures.

The second and more preferred method of converting the aluminum/silicon alloy into the dialkylaluminum hydride-containing liquid phase involves reacting the raw aluminum with appropriate amounts of trialkylaluminum and hydrogen. This reaction proceeds very easily and, under suitable conditions, quite rapidly, whereby dialkyl aluminum hydride can be formed in good yield. The use of this embodiment of the method further makes it possible to recycle or re-use the trialkylaluminum co-product which is formed in the aluminum producing step.

A preferred embodiment of the cleavage process therefore comprises converting the aluminum-silicon alloy into an alkylaluminum hydride-containing liquid phase and residual solids by allowing the aluminum to react with trialkylaluminum and hydrogen under suitable reaction conditions. Such conditions preferably comprise the use of the aluminium/silicon alloy, activation of the aluminum by known working methods and the use of suitably elevated temperatures and pressure conditions.

The above-mentioned first work step can be modified if desired so that other suitable alkyl aluminum hydride-containing liquid phases are formed. Although it is preferable for the liquid phase to contain a significant amount of dialkylaluminum hydride, this liquid phase may also contain or instead contain other alkylaluminum hydrides. The reaction between the aluminium/silicon alloy, trialkylaluminum and hydrogen can further be carried out in admixture with a tertiary amine, as described above. "In this case the alkylaluminum hydride product or

-products (and trialkylaluminum is almost always also present)

tend to be in the form of alkyl aluminum tertiary amine complex compounds.

Once the above-mentioned alkylaluminum hydride-containing liquid phase and the solids phase are formed, it is quite simple to effect a separation thereof. Filtration, centrifugation and the like will usually be used. The separated liquid phase is then subjected to a thermal decomposition process so that pure aluminium, hydrogen and trialkylaluminum are obtained.

When aluminum/silicon alloys are used as a source of aluminum in the first employed initial working step of the extensive cleavage process, it is not always necessary (although preferred) to introduce a preformed thermal dissociation catalyst into the heating zone to form the purified aluminum metal. Without being bound by theoretical considerations, it should be mentioned that it seems that one or more of the contaminating metals originally present in the aluminium/silicon alloy (perhaps titanium, vanadium or the like), has a tendency to form a thermal dissociation catalyst in situ, and a small amount of this appears to be transferred to the heating zone along with the stream containing the alkylaluminum hydride. With a well-considered selection of a suitable aluminum/silicon alloy, it may therefore prove, with the help of a few pilot tests, to be completely possible to carry out the heating process without introducing a thermal dissociation catalyst into the system. For most practical purposes, however, it is preferable to use such thermal dissociation catalysts in any thermal cracking process, the more so as these added catalysts ensure that aluminum, gaseous hydrogen, and the trialkylaluminum co-product will be formed very rapidly without any appreciable release of free hydrocarbon (e.g. olefin) .

In carrying out the hydrogenalumination reaction to convert the aluminum/silicon alloy into an alkylaluminum hydride-containing product for use in the thermal cleavage reaction, it is desirable, although not essential, to use a relatively small amount of sodium, sodium hydride, or a similar material for to increase system reactivity. Further details regarding such working methods can e.g. found in US patent 3,050,541

Claims (2)

1. Process for the recovery of aluminum from an aluminum/silicon type alloy, by selective reaction of the aluminum content by reaction with hydrogen and a tri-(C^^C^-alkyl) - aluminum compound in the presence of a catalyst, to form a liquid alkyl aluminum compound, and separation of the liquid compound and liberation of substantially pure aluminum, characterized in that one (a) starts from an alloy with a composition of: 33-94% by weight aluminum 5-58% by weight silicon 0.2-4% by weight titanium and 0-5% by weight iron, and (b) as a catalyst uses a complex of an alkali metal hydride and a trialkyl aluminum compound and/or a dialkyl aluminum hydride compound. 2. Method as stated in claim 1, characterized in that the aluminum is released from the liquid alkyl aluminum compound by thermal decomposition.