Classifications

• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
  • C01F7/00—Compounds of aluminium
  • C01F7/48—Halides, with or without other cations besides aluminium
  • C01F7/56—Chlorides
  • C01F7/58—Preparation of anhydrous aluminium chloride
  • C01F7/60—Preparation of anhydrous aluminium chloride from oxygen-containing aluminium compounds
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2004/00—Particle morphology
  • C01P2004/50—Agglomerated particles

Definitions

• the invention relates to an improved process for the formation of anhydrous aluminum chloride by carbochlorination of alumina in molten salt baths.
• the first type of process illustrated by French patent 1 481 390 describes the carbochlorination of alumina with the production of anhydrous alt-minium chloride.
• anhydrous aluminum chloride is obtained by reaction with alumina in a vortex layer of chlorine and carbon with low ash content, at temperatures between 450 ° C and 600 ° C using the exothermic character. of the reaction:
• anhydrous aluminum chloride in a single stage by reacting chlorine and carbon with alumina in a vortex layer, this process requires that a charcoal is used. low ash content, this should not be more than 1%.
• the particle sizes of the alumina and of the carbon used must be similar and preferably identical, so that no demixing of the bed takes place during the carbon chlorination.
• alumina used is generally of Bayer origin, it is accompanied, as sodium impurity in an oxidized form, which combines, during the carbochlorination reaction in a fluidized bed, forming sodium chloroaluminate a fraction of which is entrained by vapor pressure with the gaseous effluents, while the other fraction remaining in the reactor, causes agglutinations, materials forming the fluidized bed and demixing of said bed.
• the second type of process which relates to the carbochlorination of alumina in molten salt baths, illustrated by French patent 2334625, consists in bringing into contact, in a molten salt bath formed from at least one chloride of alkali metal and / or alkaline earth metal and aluminum chloride, 1- alumina with a source of chlorine in the presence of a reducing agent-non-gaseous, such as carbon, anhydrous aluminum chloride being collected at the outlet of the bath in a gaseous form.
• a reducing agent-non-gaseous such as carbon
• the chlorine intended for the carbochlorination of alumina is then continuously blown into the bath of molten salts in stoichiometric proportion, in which gas diffusers, of known types, such as, for example, quartz rings, have been immersed diffusers causing the formation of a very large number of gaseous bubbles of very small dimensions which come into contact with the elementary grains of alumina and carbon suspended in the bath subjected to agitation.
• gas diffusers of known types, such as, for example, quartz rings
• the process for the production of aluminum chloride by carbochlorination which consists in bringing a source into contact alumina constituted by agglomerates made up by agglutination and a chlorinating agent in the presence of a reducing agent in a bath of molten salts containing at least one alkali and / or alkaline earth halide, is characterized in that the filling of said bath is constituted by said agglomerates in order to ensure a very intimate contact between the gaseous, liquid and solid phases present during the reaction.
• the bath of split salts generally consists of a mixture of at least one alkali and / or alkaline earth halide with aluminum chloride.
• alkali and / or alkaline earth chlorides preferably lithium, sodium, potassium chlorides, as well as calcium, barium and magnesium.
• the molten salt bath also comprises in its melt from 2 to 60 l, but preferably between 10 i and 50% by molar mass of anhydrous aluminum chloride.
• the temperature of the molten salt bath intended for the carbochlorination according to the invention is between its melting point and its boiling point under the conditions of use.
• the Applicant has found that the temperature range practiced was between 450 ° C and 900 ° C, but that the preferred temperature zone was between 600 ° C and 800 ° C.
• the chlorinated agent used in the context of the invention is generally chlorine gas. However, other chlorine sources can also be used such as, for example, CCI 4 , C 2 Cl 6 , etc. or in mixtures.
• the chlorinated agent is introduced into the reaction medium in an amount at least stoichiometric relative to the alumina to be carbochlorinated introduced into the bath.
• the reducing agent used in the context of carbochlorination may be in a gaseous or solid form and in at least an amount stoichiometric with respect to the alumina to be carbonated introduced into the bath.
• the reducing agent When the reducing agent is in a gaseous form, it is constituted by carbon monoxide or dioxalene (C 2 O 3 ) o.
• the anhydrous aluminum chloride obtained is particularly pure, and can be used in the field of catalysis for example, since it is well known that the aluminum chloride obtained by the carbochlorination of alumina under high temperature, by the simultaneous action of chlorine gas and a reducing agent such as carbon (coke, charcoal, etc.) contains a certain quantity of polychlorinated organic compounds such as hexachlorobenzene, hexachlorethane, decachlorobiphenyl, etc., which are formed during the carbochlorination reaction of alumina, and which can reach a significant weight content, ranging up to 1% to 5% of the content of A1Cl 3 .
• Such organic compounds can be of great discomfort in the field of catalysis of organic syntheses and are all the more troublesome as they have physical properties relatively similar to those, anhydrous aluminum chloride in particular, when it s 'is hexachlorobenzene and they are very difficult to separate.
• aluminum chloride by means known in the art, such as for example sublimation.
• this agent is preferably carbon, but may optionally be chosen from other well known reducing agents.
• the reducing agent is carbon, it comes from the usual sources well known to those skilled in the art, that is to say coals, petroleum and their derivatives.
• This reducing agent is used after having optionally undergone a purification treatment as well as a grinding treatment, in such a way that it is in the form of solid particles of small dimensions, for example between 0, 2 and 200 mm, but preferably between 0.5 and 8 mm.
• the source of alumina intended for carbochlorination is introduced into the bath of molten salts, in an elaborate form of agglomerates made up by agglutination.
• the applicant has observed that the introduction, into the bath of molten salts, of alumina in its most usual form, is that is to say in the form of a fine white powder, required the use of gas diffusers of known type immersed in said bath, such as, for example, quartz rings, for the gaseous mixture of chlorination blown continuously in the carbochlorination medium, these diffusers causing the formation of a very large number of gaseous bubbles of very small dimensions which come into contact with the elementary grains of alumina and carbon suspended in the bath subjected to stirring.
• the alumina agglomerates constituting the lining of the bath of molten salts diffusing the gaseous agents introduced are used so as to form a lining containing the whole bath of split salts, that is to say that the total volume occupied by the alumina agglomerates and the bath of split salts is equal to the apparent volume occupied by the agglomerates alone for the same reactor section.
• the Applicant has found that the total volume occupied by the agglomerates of alumina and the bath of molten salts may be greater than the apparent volume occupied by the agglomerates alone, but at most twice the apparent volume occupied by these agglomerates alone, and is, preferably, at most 1.5 times this same apparent volume.
• the alumina intended to be agglomerated for the purpose of carbochlorination according to the invention, is generally hydrargillite or boehmite, hydrated aluminas resulting from the alkaline attack of * bauxite. However, it can also result from the decomposition of aluminum chloride hexahydrate, sulfates, sulfites or hydrated aluminum nitrates, resulting from the acid attack of silico-aluminous ores.
• the various aluminas corresponding to phase transformations can be agglomerated and undergo with the successful chlorination according to the invention.
• the applicant has also found that the specific surface, which these various forms of alumina have, has no harmful influence on the carbochlorination of agglomerated alumina.
• the carbochlorination of alumina agglomerates offering a specific surface of 2 m2 / g is carried out with as good results as those obtained during the carbochlorination of alumina agglomerates to 160 m2 / g .
• Carbochlorination therefore offers practically the same effectiveness, not only with various types of alumina, but also with a mixture of these various types of alumina.
• alumina agglomerates intended to be subjected to the carbochlorination according to the invention, are generally prepared by methods known to those skilled in the art.
• the process consists, as described in French patent n ° 1 190094, of agglomerate with water a dry powder of an intimate mixture of aluminum trihydrate and sodium aluminate, or else to use the mixture obtained by drying an unwashed trihydrate cake, at a temperature between 80 ° C and 150 ° C and grinding said cake after drying.
• the dry powder of the alumina-sodium aluminate mixture is introduced into a granulator, together with an adequate quantity of water.
• the granules obtained have a diameter of, for example, between 4 and 6 mm, and are subjected to a thermal treatment.
• the Applicant has found that the agglomerates which lend themselves best to carbo-chlorination in a bath of molten salts by providing a high hourly yield of aluminum chloride, are those of compact, substantially spherical or cylindrical farms, obtained according to the process described in the French patent n ° 1 077 163. This process consists, first of all, in dehydrating a hydrated alumina, at a temperature between 150 ° C and 600 ° C, under conditions such that the water vapor is eliminated as and as so ⁇ .
• the applicant has noted with interest that it is possible feeding the molten salt bath by means of mixed agglomerates formed of a mixture of alumina and the reducing agent, such as carbon or its derivatives.
• the alumina can be introduced into the molten salt bath in the form, also prepared, of alumina bars produced according to known techniques, from alumina agglomerates or mixed agglomerates of carbon and alumina, bonded, for example, by means of a coking agent or by means of salts entering into the composition of the carbochlorination bath, said bars having the property of disintegrating in the bath of molten salts by releasing the agglomerates of alumina .
• the largest dimension of the alumina agglomerates or of the mixed alumina and reducing agent agglomerates must be between 0.2 and 200 mm, but preferably between 0.5 and 8 mm.
• agglomerates of alumina alone or of alumina and of carbon and its derivatives are well dehydrated and dehydrogenated according to known calcination processes, to avoid, during the carbochlorination, the formation of hydrochloric acid. gaseous, to the detriment of the carbochlorination itself, which would consume a fraction of the chlorinated agent introduced into the reaction medium.
• the lining of the bath constituted by the agglomerates is consumable, it is necessary to ensure a regular supply of the reaction medium with agglomerates, in such a way that they are not only a source of alumina to be carbonated, but also maintenance of the lining so that the total volume occupied by the alumina agglomerates and the bath of molten salts is at most twice the apparent volume occupied by the agglomerates alone and, preferably, at most 1.5 times this same apparent volume.
• the carbochlorination of alumina can be carried out under pressure of reaction gases, thus allowing better diffusion of the gaseous mixture in the bath of molten salts.
• Such a pressurized carbochlorination process makes it possible to increase the conversion yield.
• the carbochlorination bath enriched with AlCl 3 it is vaporized as soon as the composition of the bath allows. It is then entrained by the gaseous effluents.
• the aluminum chloride is separated from this gaseous fraction by any suitable means known to those skilled in the art, such as, for example, by condensation of the vapor of aluminum chloride in a condensation chamber.
• This example which illustrates the prior art, consists in supplying the bath of molten salts, with an alumina under firm powder. It also illustrates the improvement in the quality of the aluminum chloride produced when the reducing agent used is in gaseous form. rather than in solid form.
• a salt bath consisting of a mixture of sodium chloride and aluminum chloride, having the following composition expressed in% of molar mass: Sodium chloride, 50%
• This bath was subjected to external heating in order to cause the melting of the mixture of salts, then it was introduced into an appropriate laboratory reactor previously furnished with quartz rings, with an external diameter of 6 millimeters, so that this packing contains the entire liquid I ⁇ -ba-ki introduced.
• the total height of the bath was approximately 2.5 meters.
• the bath temperature was maintained at 650 ° C.
• Alumina was added in the form of a fine powder having a specific surface of 77 m 2 / g, at a rate of 128 g per liter of bath of split salts, which was dispersed by stirring until the suspension was closed. with the bath. Then, a gaseous mixture of CO and Cl- 2 , of stoichiometric composition, was blown into the molten salt bath, at the rate of 1.36 normal liters per hour and per gram of alumina introduced, using a gas diffuser. allowing intimate contact within the agitated bath, between the alumina grains and the carbochlorination gases dispersed within the molten salt bath. The alumina consumed was replaced progressively.
• a salt bath was prepared, as in Example 1, consisting of a mixture of sodium chloride and aluminum chloride in the proportions indicated above, which was subjected to the melting of its components and introduced into the reactor of Example 1, previously filled with alumina agglomerates, the largest dimension of which was between 2 and 5 millimeters, in such a way that these agglomerates constitute the lining of the reactor and that the total volume occupied by the alumina agglomerates and the molten salt bath is the same as the apparent volume occupied by the agglomerates alone for the same reactor section.
• the total height of the bath was 2.5 meters-s-vifon.
• the temperature of the bath was then maintained at 650 ° C.
• alumina in the form of agglomerates; whose largest grain size was between 2 mm and 5 mm, peimis to improve hourly production by 25% per liter of reactor.
• this example illustrates the beneficial influence of the pressure, established in the enclosure where the carbochlorination takes place, on the yields of transformation of alumina into aluminum chloride .
• the applicant has carried out tests in the abovementioned laboratory reactor, as a function of the pressure prevailing inside said reactor: - for aluminas in powder form and in the form of agglomerates, - for a gas flow rate of carbochlorination of 1.36 normal liters per hour and per gram of alumina introduced.
• the table reveals the importance of the pressure of the carbochlorination gases in the enclosure by the significant increase in the percentages of the hourly production of AlCl 3 per liter of reactor.
• a salt bath was prepared consisting of a mixture of sodium chloride and aluminum chloride having the following composition, expressed in percent of molar mass:
• This bath was subjected to external heating in order to cause the melting of the mixture of salts, then it was introduced into an appropriate laboratory reactor, previously furnished with alumina agglomerates, spherical lime and carbon agglomerates, of which the largest dimensions were between 2 and 5 mm, so that these agglomerates constitute the lining of the reactor and that the total volume occupied by the agglomerates of carbon alumina and the bath of molten salts is the same as the apparent volume occupied by agglomerates alone for the same reactor section.
• the total height of the bath was approximately 1.2 m.
• the bath temperature was maintained at 650 ° C. to this point, 65 standard liters of chlorine gas per hour and per liter of actual salt bath were blown into the split salt bath. The carbon and alumina consumed were replaced progressively.
• the split salt bath was saturated with aluminum chloride, the product thus formed vaporized, was entrained by gaseous effluents and was collected in a condensation chamber at the rate of 260 g / h and per liter of bath. real split salt.
• the preparation of anhydrous aluminum chloride was carried out by carbochlorination in baths of molten salts, alumina and carbon being introduced under the farm with a fine particle size powder. between 10 and 200 microns, while all the other conditions were equal, apart from the fact that the reactor was lined with quartz rings with an external diameter of 6 mm.
• the production of aluminum chloride was only 163 g / hour and per liter of actual bath.
• Example 2 Was prepared, as in Example 1, a salt bath consisting of a mixture of sodium chloride and aluminum chloride in the proportions indicated above, which was subjected to the melting of its components.
• a salt bath was prepared consisting of a mixture of sodium chloride and aluminum chloride having the following composition, expressed in percent of molar mass:
• agglomerates of substantially cylindrical shape, were obtained by coking a paste produced by mixing coal pitch and alumina, at the temperature of T60 ° C. This paste was then thermally treated at a temperature of 900 ° C to give it good reactivity. These agglomerates contain by weight 46% of Al 2 O 3 and 54% of C. Their largest dimension was between 3 mm and 7 mm.
• the total height of the packed bath was 1.2 m and the temperature of the bath was 650 ° C.
• Test 1 total volume equal to the apparent volume occupied by the agglomerates alone.
• Test 2 total volume equal to 1.2 times the apparent volume occupied by agglomerates alone.
• Test 3 total volume equal to 1.5 times the apparent volume occupied by the agglomerates alone.
• this table reveals the possibility of reducing the volume of agglomerates playing the role of filling by keeping hourly productions of AlCl 3 satisfactory, which allows, in the case of a continuous process of carbochlorination, to ensure a circulation of bath without entrainment of agglomerates, thanks to the presence of a bath zone, or a reserve, lacking in packing.
• a salt bath was prepared consisting of a mixture of sodium chloride and aluminum chloride, having the following composition expressed programe in% of molar mass:
• Aluminum chloride ... 50% This bath was subjected to external heating in order to cause the melting of the mixture of salts, then it was introduced into an appropriate laboratory reactor previously filled with alumina agglomerates, the largest dimension was between 2 and 5mm. These agglomerates, of substantially spherical shape, were prepared according to techniques known to those skilled in the art. The total height of the bath was approximately 2.5 m.
• Test 4 total volume equal to the apparent volume occupied by the agglomerates alone ,.
• Test 5 total volume equal to 1.2 times the apparent volume occupied by the agglomerates alone.
• Test 6 total volume equal to 1.5 times the apparent volume occupied by the agglomerates alone.
• the table reveals, in turn, the possibility of reducing the volume of agglomerates playing the role of filling the bath, by giving hourly production of AlCl 3 which is still acceptable.

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• Compounds Of Alkaline-Earth Elements, Aluminum Or Rare-Earth Metals (AREA)

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• 1981
  • 1981-12-23 EP EP81420191A patent/EP0055681B1/fr not_active Expired
  • 1981-12-23 ES ES508315A patent/ES508315A0/es active Granted
  • 1981-12-23 AU AU79364/82A patent/AU545579B2/en not_active Ceased
  • 1981-12-23 WO PCT/FR1981/000169 patent/WO1982002191A1/fr not_active Ceased
  • 1981-12-23 DE DE8181420191T patent/DE3164781D1/de not_active Expired
  • 1981-12-23 JP JP57500220A patent/JPH02293B2/ja not_active Expired - Lifetime
  • 1981-12-23 GR GR66901A patent/GR75129B/el unknown
  • 1981-12-23 BR BR8108935A patent/BR8108935A/pt unknown

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