HU190913B - Process for production of water-free aluminium chlorid derivated from acid disclosure of aluminium chlorid hexahydrate - Google Patents

Abstract

The present invention relates to a process for the preparation of anhydrous aluminum chloride from aluminum chloride hexahydrate, which is capable of producing metallic metal by electrolysis, whereas said aluminum chloride hexahydrate is obtained from acidic digestion. According to a preferred embodiment, the aluminum chloride hexahydrate obtained from the acid digestion is crystallized in one operation. -1-

Description

The present invention relates to a process for the preparation of anhydrous aluminum chloride which can be electrolyzed to aluminum and chlorine by thermal decomposition of aluminum chloride hexahydrate [(ACH)] from acid digestion and subsequent chlorination.

It is known in the prior art that, at temperatures between 700 ° C and 750 ° C, anhydrous aluminum chloride can be electrolyzed to aluminum and chlorine with less energy consumption than is required for electrolysis of alumina in a Hali system electrolysis bath. Several methods have been proposed so far to economically produce anhydrous aluminum chloride. In these processes, the aluminum chloride added to the electrolysis baths must be free of moisture. An additional requirement for electrolysis is high purity.

U.S. Patent No. 4,264,569 discloses a process for the preparation of anhydrous aluminum chloride by heating the purified ACH at a temperature of 200 ° C to 450 ° C, followed by further calcination of the dehydrated material with Al ₂ O. ₃ , 700-1000 ° C.

In the processes described in U.S. Patent No. 4,264,569, aluminum is prepared by crystallizing aluminum chloride hexahydrate (ACH) from an aluminum-containing raw material, and then electrolyzing the alumina.

However, the process has the disadvantage that the ACH obtained by digestion with hydrochloric acid contains a large amount of impurities, so it must be washed and / or crystallized before calcination to produce alumina of sufficient purity for electrolysis.

However, the process according to the invention does not require such a purification step, since ACH produced during the digestion of aluminum-containing raw material, which contains impurities of phosphorus or magnesium, can produce alumina of sufficient purity. To date, however, such benefits of ACH from acid digestion have not been recognized.

In the improved process of the present invention, ACH crystals containing from 0.001 to 0.05% by weight of phosphorus or magnesium are prepared from the aluminum-containing raw materials by acid digestion, which can then be converted into aluminum and chlorinated by electrolysis of anhydrous aluminum chloride by partial calcination. The use of the ACH prepared in accordance with the present invention resulted in an unexpected chlorine utilization (high chlorination rate) and allowed us to use either solid or gaseous reducing agent in the preparation of anhydrous aluminum chloride.

The process of the invention comprises the following steps: optionally drying and calcining an aluminum-containing raw material containing a phosphorous or magnesium impurity such as clay to activate the aluminum-containing moiety prior to digestion of the hydrochloric acid, optionally calcining the raw material. with hydrochloric acid to liberate the aluminum-containing portion, i.e. to convert it to soluble aluminum chloride. separating the solid and liquid phases of the resulting slurry in settlers and / or filters, removing the ferric chloride from the lye separated from the solid, and from the resulting lye, precipitating aluminum chloride hexahydrate containing the phosphorous or magnesium impurities; the aluminum chloride hexahydrate crystals are heated at 200-450 ° C to sufficiently dehydrate and the resulting partially calcined ACH is chlorinated in the presence of a reducing agent.

The anhydrous aluminum chloride thus prepared can be electrolysed to decompose into aluminum and chlorine.

In the preferred embodiment, the process is carried out by chlorine blowing.

The clay or other aluminum-containing material is leached with acid, leaving the aluminum-containing portions separated from the waste. Any aluminum-containing ore or material can be used, but the sources we prefer are clay or power plant fly ash. We prefer kaolinite or kaolin. Prior to digestion, the clay can be dried, making it easier to handle and reducing the particle size, and can be activated by calcination, although uncalcified clay can be digested, but the rate of digestion will be much slower. Clay discharged from the container is comminuted or agglomerated as required. Any conventional fuel, including coal powder, can be used for calcination.

If the clay is calcined for a period of 0.1 to 2 hours at 650 ° C to 820 ° C, aluminum can be easily dissolved from the clay with acid. The time required for calcination is determined by the size of the particles to be calcined and the amount of heat delivered to each particle. During calcination, all free or bound water is removed and the organic matter present in the extracted clay is also decomposed.

As regards the essential constituents of the extracted clay, expressed as a percentage by weight: Humidity: 22,0%

Total A1 ₂ O ₃ : 35.0% (measured on dry weight basis)

Discoverable Á1 ₂ O ₃ : 32.2%

Total Fe ₂ O ₃ : 1,15% (dry weight)

Discoverable Fe ₂ O ₃ : 1.08%

Loss on ignition: 11.75% (measured on dry weight)

The material added to the grate furnace system is preheated and dried. After preheating, the dry material was calcined for two hours in a coal-fired rotary drum and cooled on a mobile grate, from which the clay was introduced into the digestion tanks at 30 ° C.

A coal-fired fluidized bed reactor may also be used to calculate the clay. In this case, the wet clay particles are reduced from 30 mm to 5 mm in a double cylindrical mill. The clay is then transferred to a hammer mill where the particle size is reduced to 2 mm. The comminuted product is dried until its moisture content is reduced to 10-15% by weight. The calcining flue gases are dried in a rotary kiln. The partially dried clay is ground to a size of 0.75 mm in an open-loop cylindrical mill and stored.

The clay is in a three-stage fluid bed reactor

190,913 are calcined and preferably heated with powdered carbon. The upper fluid bed is operated at 120 ° C and completely dried clay is added. If necessary, additional heat may be applied to this fluid bed to maintain the drying temperature. The dry clay is calcined on a central coal-fired fluid bed at 650 ° C for one hour and then cooled on a third lower fluid bed while the combustion air is preheated to recover heat. The clay leaves the calcining machine at 480 ° C, which is cooled to 66 ° C with the gases discharged from the dryer.

The digestion process involves dissolving the soluble aluminum-containing moieties from the starting material. Since some contaminants are soluble, a contaminated solution or crude alkali containing aluminum chloride and other contaminating chlorides, with the highest content of ferric chlorides, is removed therefrom. The crude alkali containing the insoluble constituents thus appears as a slurry. During exploration, the following major reactions occur:

(A1 ₂ Oj + 2SiO,) + 6HC1 -2A1C1 ₃ + 3H, 0 + 2SiO,

Fe, O ₃ + 6HCl-2FeCl ₃ + ~ 3H, O

Fe6 + 2HC1 - FeCU + H, O "

The calcined clay is continuously discharged from the reservoir into the first digestion tank, for example by means of a screw screw feeder. At the same time, 10-26% by weight, more particularly 20-26% by weight, of hydrochloric acid is added to the digester. Leaving the final leach tank liquor generally contains ¹ 10 gL excess HCl. It is possible to heat the inlet acid to 60 ° C using graphite heat exchangers as needed. This acid can also be indirectly preheated with steam or 107 ° C outlet slurry. Each excavation line consists of tanks with a mixture.

The total residence time is three hours, during which time you can achieve 92% efficient exploration. Although the exploration operation described above is continuous, it can also be performed in batch mode.

The boiling slurry at 107 ° C, which exits the last digestion tank, is fed to a two-stage vacuum blast chiller. The cooled slurry is then passed to a separator to remove all solids from the aluminum chloride solution for further processing. After cooling, the crude slurry exiting the quick-coolers is generally mixed with a flocculant and fed to one or more settlers operating at 46 ° C. The overflow from the last settler is fed to the first unit of the two filter press units. The filter presses are operated in series to clean the alkali. The operation of the second filter press unit ensures that a clear solution is obtained even in the event of malfunction of the first unit. Characteristic composition of the filtered alkali:

Compound Crowd% AlClj 17.73 FeCl ₃ 0.46 CaCl ₂ 0.06 MgCl ₂ 0.06 Other 0.11 HC1 0.85 MONTH 80.73

Although the iron content of the alkali is given as trivalent iron in the table, about 24% by weight of the iron impurity is in the divalent form. 30% by weight of the solids collected from the bottom of the last settler is pumped to the drum filters. The filter cakes, together with the waste from solution cleaning, are transferred to the waste bin.

The iron impurities present in the divalent form should not be trivalent iron in the solution first during decontamination. In this way, the final product will be iron-free.

During the decontamination, the iron impurity present in the divalent form is first oxidized to the trivalent iron with chlorine gas to remove the iron impurity from the solution by solvent extraction. The oxidation of divalent iron to trivalent with chlorine proceeds as follows:

Fe ⁺⁺ + 0.5 Cl, Fe ^{+ + +} + CL

The chlorine, the last filter press and the container containing the rubber-lined chlorinated mother liquor are injected into a pipeline connecting the alkali. The iron removal is carried out using an organic ion exchange solution and the iron is removed in a three-stage countercurrent mixer. The initial iron content of the alkali, 0.46 wt.%, Was reduced to 34.5 ppm. The required contact time is only a few seconds. The organic ion exchange solution is a mixture of decyl alcohol, petroleum and high molecular weight secondary or tertiary amine. The ion exchange solution contains 2% by volume of amine, 9% by volume of decyl alcohol and 89% by volume of petroleum. This mixture is treated with 20% hydrochloric acid to convert the amine to the amine chloride as this is required for ion exchange. The non-ferrous mother liquor is continuously pumped into the feed tank of the crystallization unit. The iron-containing ion exchange solution can be regenerated.

After separation of the solid and liquid phases of the crude slurry and after de-ionization, it contains 25-35% by weight of aluminum chloride hexahydrate (ACH). There are two methods for producing substantially iron-free crystals, evaporative crystallization and hydrochloric acid-blown crystallization. In the case of evaporation crystallization, the non-ferrous alkali is concentrated by means of a heat exchange and rapid vacuum system. The evaporator is used to increase the concentration of aluminum chloride from 18.7% to 29.0% by weight. This saturated solution enters the crystallizer where it is cooled to 89 ° C suddenly to form crystals of aluminum chloride hexahydrate. By operating the crystallizer continuously, the concentration of crystalline aluminum chloride hexahydrate at the bottom of the crystallizer can be maintained at 33% (v / v). Crystals from 0.75 to 1.5 mm in size are thus obtained.

The ACH crystals are separated from the mother liquor in the crystallizer by vacuum filtration or centrifugation. The crystals are then washed with 35% hydrochloric acid, which has a very low solubility of aluminum chloride, to purify the crystals from the mother liquor adhering to them. The mother liquor separated by centrifugation is divided into two portions and one portion is returned to the crystallization medium.

190,913 wells, while the other portion is fed to a refinery crystallizer to control the level of impurities in the system.

In a more preferred embodiment, crystallization is initiated by gas bubbling, whereby the same ionic effect is utilized to reduce the solubility of ACH in the mother liquor. The iron-free mother liquor is evaporated to saturation using equipment similar to the heat exchanger used in the evaporator crystallization tube rapid vacuum system. By evaporation, the aluminum chloride concentration in the mother liquor is increased from 18.7% to 31%.

Introduce a saturated aluminum chloride solution and hydrochloric acid into the circulation system of the crystallizer operating at 71 ° C to obtain an ACH-supersaturated hydrochloric acid solution. Circulating solutions pass through descending conduits into the lower chamber of the crystallizer, from where they flow upward to the fluidized crystal bed. The supersaturation of the solution decreases with the growth of existing crystal nuclei and the formation of new crystal nuclei.

Starting from a saturated solution of aluminum chloride, the ACH crystallizes at the rate at which the hydrochloric acid dissolves, so that the tested molarity of the solution for chlorine remains practically unchanged until the solubility of aluminum chloride is reduced to 6.5% by weight. In the presence of HCl. The solubility of aluminum chloride can be further reduced to 0.7% by weight in the presence of 35.5% by weight HCl. The rate of hydrochloric acid addition is controlled so that only the desired degree of supersaturation in the solution is achieved.

The crystalline slurry is transferred from the crystallization stages to a separating centrifuge and washed. The washed crystals are converted into activated chloride containing residual chloride in the decomposition or calcining unit. The purified mother liquor from the crystallizer is recycled to the clay. The remaining, uncleaned portion of the material lye is used to produce additional ACH crystals and recycled to the evaporator.

The primary purpose of crystallization of aluminum chloride hexahydrate (ACH) is to separate aluminum chloride from soluble impurities. Although ACH tends to crystallize as a pure compound, other elements present in the solution, such as phosphorus and magnesium, tend to precipitate out of solution or co-crystallize with ACH. However, the presence of magnesium and phosphorus in the product is not harmful according to the practice of the present invention. However, it should be noted that when this acidic digestion process is used to produce alumina as a liner material for the Hali electrolysis baths, this contaminant content is not permitted and a second crystallization step is required which is not required by the practice of the present invention.

So far, the ultimate goal of processing the clay has been to produce alumina that can be added to the Hali electrolysis baths. Consequently, in order to produce high purity alumina, the crystallized ACH was further purified to produce a high purity product. The first crystallized ACH was washed and the wash solution was recycled to the ore digestion. The washed ACH crystals were redissolved in pure hydrochloric acid and then re-crystallized as in the former. Purified by recrystallization. The ACH was dried and calcined at a temperature of 1000 to 1280 ° C to obtain alumina for use in Hali electrolysis baths. The HCl gas released during the calcination of ACH was recycled to the contaminated alkali and was used to leach the ore. The concentrations of the single crystallized as well as recrystallized ACH and, for comparison, Bayer alumina are shown in Table I.

/. spreadsheet

Comparison of once-crystallized and recrystallized ACH and u Buyer alumina concentrations

Polluting Once Again crystallized crystallized ACH ACH · concentrations by weight Bayer- alumina PA 0,024 .0309 0.0001 MgO 0,013 0.0009 0,002 Cr and O, 0,004 0,00024- 0,002 MnO 0.0014 0.0009 0,002 v, _{and s} 0.0005 0.0005 0,002 TiO, 0.0005 0.0005 0,005 STONE 0.0038 0.0009 0,005 NiO 0,005 0,005 0,005 CuO .0,0014 0.0014 0.01 Fe O 0013 0,018 0,015 Sio, 0,004 0,002 0,015 ZnO 00.009 0.0015 0.02 CaO 0,004 0,004 0.04 Na, O 0.0028 0.0014 0.4

Concentrations of ACH contaminants in% by weight are based on A1.0:

Table I shows that calcining the once-crystallized ACH results in higher alumina content of P ₂ O ₅ , MgO and Cr, O 1 than in the Bayer process, which is not allowed in the Hali system electrolysis baths. The content of P, (/ -) is most critical because it is well known that the electrolysis efficiency of the aluminum reduces the current efficiency of the Hali system electrolysis baths by 1% at every 0.01 wt% phosphorus concentration. quality alumina can be produced for Hali electrolysis baths, but recrystallization requires higher investment costs and energy use.

In our studies, it has been discovered that once crystallized ACH can be produced anhydrous aluminum chloride which, although containing phosphorus, is not harmful to the process of electrolysis.

In this process, the crystalline ACH product is calcined, i.e., thermally decomposable into an active aluminum-containing material and a hydrochloric acid-water vapor system at temperatures ranging from 200 ° C to 450 ° C, as described in previous literature. The decomposition reaction is as follows:

Heat + 2A1C1 ₃ · 6H ₂ O-> AljOjd ^ Cl ^ · H ₂ O + solid solid + (9 + 3y - x) H ₂ O + 6 (1 - y) HCl (1) gas

The liberated HCl is collected and recycled to the digestion operation. Once crystallized, ACH can be calcined in a rotary drum furnace, fluid bed or instantaneous calciner.

The partially calcined ACH is chlorinated in the presence of one or more reducing agents by conventional means, that is, the dehydrated material is reacted with the chlorinating agent at a temperature in the range of 350 ° C to 1000 ° C, more particularly 350 ° C to 600 ° C. The reduced chlorination reaction is as follows: Al ₇ O _{3 (} , - _y) Cl _6y · xH, O + CO or CO ₂ + (3 + x - 3y) Ch → 2A ₁ Cl ₃ + 2xHCl + CO or CO ₂ (2)

The equilibrium of the reducing agent (C or CO), oxygen (O _{3 (1 ρ} χΟ) and carbon oxides (CO, CO _{2) in} the above equation is a function of temperature and is not equilibrium at the given temperature. Chlorination of dehydrated ACH according to the present invention may be facilitated by the use of gaseous reducing agents such as carbon monoxide or hydrogen or solid reducing agents such as partially calcined petroleum coke and activated carbon from coal or other feedstocks. may be processed by well-known processes such as Kel-Chlor to recover chlorine.

The anhydrous aluminum chloride produced can be electrolyzed to aluminum and chlorine by known methods, such as the bipolar electrolysis bath described in U.S. Patents 3,755,099 and 4,151,061. The chlorine generated in the electrolysis bath and / or the chlorine recovered from the chlorination during chlorination can preferably be recycled to the chlorinator.

The foregoing examples are intended to further illustrate the invention without, however, limiting its scope.

Example 1 (Comparative)

100 grams of a commercially available American Hoechst ACH were calcined in a rotary drum oven at 400 ° C for two hours. A 15 gram sample of dehydrated ACH was then reduced in chlorine in a 25.4 mm fluid bed reactor using chlorine gas as the chlorinating agent. 3 grams of petroleum coke, partially calcined at 650 ° C, was used as a reducing agent under a flow of nitrogen to a size of less than 0.15 mm - 200 cm ³ · mim '. The procedure was repeated with another sample. The chlorination rates measured were as follows:

Experiment: 0.0004 g AlCl 3 · min ¹ ;

Experiment B: 0.02 g AlCl ₃ .min '.

Example 2 (Comparative)

Commercially available from American Hoechst

CH was dehydrated and chlorinated according to the method of Example 1, except that the diluent was carbon monoxide. From two different identities we obtained the following results:

. experiment: 0.01 g A1Cl, · min;

experiment: 0.01 g AlCl ₃ - min * ¹ .

Example 3

ACH was produced by acid digestion of the present invention and prepared from calcined kaolin clay from Georgia Middle East, two hours at 400 ^c C for5 gódobos furnace. The partially calcined ACH was chlorinated in a 25.4 mm fluid bed reactor at 550 ° C using chlorine gas as the chlorinating agent and petroleum coke as the reducing agent as detailed in Example 1. The following results were obtained from two different experiments:

Experiment 3A: 0.089 g of AlCl · min * ';

Experiment 3B: 0.086 g of AlCl, · min ¹ .

Example 4

Prepared according to Example 3 by acid digestion

ACH was calcined and chlorinated as in Example 3, except that carbon monoxide was used as reducing agent. The results of the two different experiments are as follows:

Experiment 4A: 0.086 g AlCl ¹ · min ¹ ;

Experiment 4B: 0.096 g of A1C1 · min * '.

While the present invention has been illustrated in some detail by way of illustration and examples, it is to be understood that the subject matter of the invention may be subject to certain modifications and modifications, but is not limited to the subject matter of the claims.

As mentioned above, the ACH containing impurities used in the process of the invention can be chlorinated more efficiently than the purified ACH used in the known processes, as shown in the following table:

J_____

Example ACH-source chlorination First isme tel districts (g AICl / min) 0.0004 Second known methods B0,02 A is 0.01 Third according to the invention 8 0.01 0.089 process B, 0.086 4th according to the invention 0.086 process B, 0.096

A patent claim

Claims (1)

A patent claim Process for the preparation of anhydrous aluminum chloride which can be electrolysed to aluminum and chlorine, which comprises leaching an aluminum-containing raw material, preferably clay, optionally after heat treatment, containing a phosphorus or magnesium impurity, and dissolving the aluminum-containing portion the solid was removed from the mixture, and then the ferric chloride was removed from the alkali, and aluminum chloride hexahydrate was crystallized from the thus obtained iron-free base, the crystals from the crystalline slurry were separated and decomposed at 200-450 ° C. , characterized in that aluminum chloride hexahydrate containing from 0.001 to 0.05% by weight of impurities of phosphorus or magnesium 65 crystals were decomposed.