FI98509C - Process for the purification of contaminated alumina by heat treatment - Google Patents

Description

98509 METHOD FOR THE PURIFICATION OF IMPURITY ALUMINUM OXIDE BY HEAT TREATMENT

The invention relates to the purification of impure alumina and to the use of aluminum salts produced by the process as a raw material industrially.

The hydrogen peroxide process uses alumina to regenerate and remove organic by-products formed in the working solution. The porosity of the active alumina allows its use especially for the adsorption of organic compounds used in the anthraquinone process. The impurities are mainly aromatic hydrocarbons. Once the alumina becomes inactive, it is removed from the process and replaced with 15 new oxides. The alumina used contains organic substances that limit its uses. Currently, waste alumina is most often disposed of as waste or stored pending possible recovery.

20 Attempts have been made to regenerate crude alumina in various ways. According to U.S. Pat. No. 3,814,701, organic matter is removed from the alumina used in the anthraquinone working solution by annealing the alumina at 300 to 400 ° C. Organic matter adsorbed on alumina during annealing: 25 burns off. The annealed alumina is alkali treated and • · re-annealed. However, the alumina treated in this way is quite dusty for reuse in the H 2 O 2 process.

According to DE patent application 4,027,159, impure alumina is purified by a method in which the alumina dissolves. mineral acids or lye. The acid-insoluble matter is separated off, the purified alumina is filtered off, dried and finally calcined. There is no detailed explanation in the application of how the various steps can be performed according to the invention. However, alumina dissolved in acids or alkalis and the organic impurities 98509 2 present form a very difficult-to-handle biphasic solution with an organic-like organic gasase. Further processing of such a solution in large volumes is technically almost impossible. In addition, the problem is caused by the health risks of hydrocarbons in the organic phase, which is why the handling of the solution should be controlled and safe.

Prior art techniques aim at alumina regeneration 10 and recovery to the hydrogen peroxide process. Experience has shown, however, that the structure and mechanical strength of oxide granules always deteriorate during regeneration so that they cannot be returned to the process. On the other hand, there are always some harmful organic compounds left in the granules which do not want to be returned to the process, because the regeneration conditions must be rather gentle.

It is an object of the present invention to provide a process for purifying alumina waste from a hydrogen peroxide process from organic matter. The aim of the process according to the invention is to enable the controlled, safe and environmentally friendly purification of contaminated and impure alumina so that the aluminum salts obtained as a product can be used industrially as a raw material.

It is also an object of the process according to the invention to obtain organic compounds of impure purity both for recycling and for use as fuel.

These objects are achieved by a method according to the invention, which is mainly characterized by the features mentioned in the characterizing part of claim 1.

. The invention relates to a new process for purifying crude alumina used in the preparation of hydrogen peroxide to adsorb organic matter.

35: The process according to the invention makes it possible to obtain a highly pure aluminum salt, e.g. aluminum sulphate or aluminum chloride, which is even purer than commercial

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98509 3 available technical products. The aluminum salts produced by the process are well suited for use as a raw material in industry, in particular aluminum salts are suitable for use as water purification and retention chemicals.

By means of the process according to the invention, the organic hydrocarbons in the alumina as an impurity can be utilized as fuel. According to a preferred embodiment, part of the organic hydrocarbons 10 can be dissolved in the solvent during pre-purification and the useful components therein can be returned to the hydrogen peroxide process. Thus, the method can significantly reduce the environmental impact of organic hydrocarbons compared to most other purification methods.

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Porous, active alumina is used to regenerate the working solution in the preparation of hydrogen peroxide by the anthraquinone method. Porous alumina adsorbs from the working solution mainly organic hydrocarbons used as a solvent for anthraquinone, working solution components and other decomposition and oxidation products. Known solvents for the anthraquinone working solution include e.g. secondary alcohols, trialkyl phosphates, alkylbenzenes, triacetylbenzene, alkylcyclohexanones, naphthalenes, xylenes, anilines and quinals. In addition, the working solution may contain many other possible substances used to dissolve the anthraquinone. The inactive and impure alumina removed from the process can be :: • therefore contains varying amounts of different organic matter depending on the hydrogen peroxide manufacturer.

* ♦ · M30 »· · * According to the invention, the crude alumina is annealed at a temperature of t 500-900 ° C, whereby the organic matter as an impurity evaporates or burns. According to the invention, the annealing temperature must be suitably low in order to maintain the solubility of the alumina in the acids, but on the other hand. ·: High enough to remove organic matter as an impurity. Namely, annealing conditions were found to affect the acid solubility of alumina. The solubility in acids was significantly reduced if the alumina was annealed at higher temperatures, for example at 1000 ° C. In addition, the filtration of aluminum salts slowed down and more 5 insoluble precipitates remained than of alumina annealed at lower temperatures.

This is because the crystal structure of the alumina changes during annealing. Evaporation and combustion of harmful organic substances to carbon already takes place at lower temperatures, e.g. 350-450 ° C, however the carbon content is still too high. This is manifested by the gray color of the alumina and the difficulty in separating the aluminum salt after acid leaching. When the temperature is raised, e.g. to 500-900 ° C, the free carbon formed is also allowed to burn to carbon dioxide, which appears as a white color of alumina. In contrast, at higher temperatures, such as 1000 ° C, alumina is increasingly converted to a crystalline form that is less soluble in acids than alumina annealed at lower temperatures. This is considered to cause a deterioration of the dissolution yield with increasing annealing temperature. Changes in crystal shape can be detected by X-ray diffraction.

• · | ·. ·. The annealing time depends on the amount of organic matter to be burned,. 25 temperature and annealing equipment.

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Annealing can be performed in any furnace suitable for annealing. ΓΙΓ Drum and t · · * tubular furnaces have been found to be particularly suitable. It is desirable to equip the furnace with a catalyst or a thermal afterburner.

• · · * ••• 30 Volatile or combustible organic exhaust gases from annealing · «·» · i V ’are burned catalytically or by a thermal afterburner.

The gases can also be led to the combustion furnace for combustion. The method then makes it possible to use the calorific value of the impurities.

* · "· According to one embodiment of the invention, the crude alumina can be prewashed before annealing with an organic hydrocarbon solvent. The washing solvent is any organic hydrocarbon capable of dissolving the impure organic material from alumina. According to a preferred embodiment, the solvent is Shells. commercially available product and containing mainly C 10 -C 11 aromatic hydrocarbons, prewashing can extract organic useful components from the alumina, such as quinones, which can be recycled directly to the hydrogen peroxide process, reducing the amount of organic matter combusted while restoring organic compounds for recycling in the hydrogen peroxide process.

According to the invention, it is desirable that the annealed alumina be finely ground. Namely, it was found that the finer the alumina, the more complete and faster the acid leaching. It is desirable to grind the alumina to a particle size of 100% less than 0.5 mm, preferably 100% less than 0.4 mm. According to another embodiment of the invention 20, the impure granular alumina can be finely ground even before the heat treatment. The choice of grinding time is influenced by the amount of organic matter in the alumina and whether the alumina has been pre-washed before annealing. Namely, grinding becomes more difficult if the organic impurity • ·, ·. g5 is to a considerable extent. On the other hand, ground, easily dusty

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the annealing of alumina is cumbersome, but the organic matter burns more efficiently from ground than from granular oxide.

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Acid leaching involves dissolving powdered alumina in a concentrated acid solution. Any concentrated mineral acid

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V * is suitable for dissolution, however, the preferred acids are sulfuric and hydrochloric acid. The use of sulfuric acid at 50-60% by weight is considered particularly suitable. It is advantageous to intensify the dissolution by heating. To ensure almost complete dissolution of the alumina: ·: 35 it is recommended to heat the mixture to a temperature of about 100-150 ° C while stirring for several hours.

98509 6

After the reaction, the reaction mixture is diluted with water to prevent crystallization of the aluminum salts if a liquid product is desired which can be filtered to separate the insoluble portion. Can also be crystallized directly by cooling to give a solid aluminum salt.

If necessary, the acid-insoluble alumina precipitate can be filtered off or centrifuged off, and the insoluble portion can be returned to the dissolution step.

The filtrate containing the aluminum salt can be used as such as an aqueous solution or crystallized as a solid.

According to an embodiment of the invention, the aqueous phase is purified after filtration to remove any organic residues which may still be present in the aqueous phase. Purification can be performed by activated carbon treatment. It is also possible to use other chemicals, for example flocculation chemicals instead of or in addition to activated carbon. The use of a flocculation chemical makes it possible to bind a finely divided dissolving residue 20 containing insoluble oxide and possibly unburned carbon in such a way that it is easier to separate it from the solution. After filtration of the activated carbon, a • high purity aqueous solution of the aluminum salt can be used as such or supplied as a solid crystal for utilization, for example as a water purification or retention chemical.

* *> «T · · i 9 *

Figure 1 is a block diagram of the various steps of the invention.

, Figure 2 shows the solubility of alumina in sulfuric acid k I (‘*” 30 as a function of annealing temperature.

* «· \ \ * 9

As shown in Figure 1, the crude alumina is annealed at a temperature of 500-900 ° C. It is also possible to prewash the aluminum. ", oxide before annealing with an organic hydrocarbon solvent, 1 l« '·' 35 whereby the organic useful components '·' · extracted in the solvent can be returned to the hydrogen peroxide process. The heat-treated alumina is ground The purified aluminum salt can be used as an aqueous solution or as a solid industry, for example as a water purification or retention chemical.

The invention is described below mainly by means of examples and experiments. The invention is in no way limited to the accompanying examples, but may be modified within the scope of the appended claims.

eXAMPLES

Example 1.

Dissolution directly in sulfuric acid without heat treatment, not according to the invention.

125 g of alumina used in the hydrogen peroxide process was dissolved in 59% aqueous sulfuric acid. The temperature rose to 107 ° C. A tarry layer formed on the walls of the reaction flask, indicating the unsuitability of the reaction product as an aqueous chemical.

Example 2 Dissolution of alumina heat treated at 200 ° C in sulfuric acid-25 ', not according to the invention.

·. ’·. · The crude alumina was heat treated at 200 ° C for two hours. 100 g of treated alumina was dissolved in sulfur. to a mixture of acid (264 g) and water (278 g). 93% of the alumina dissolved in the acid solution. A tar-like layer of impurities formed on the walls 30 of the reaction vessel.

Example 3.

The spent alumina was pre-washed prior to heat treatment with an organic hydrocarbon solvent to recover anthraquinones. order.

The laboratory column (h = 600 mm, d = 40 mm) was packed with spent alumina removed from the anthraquinone process. Alu 98509 8 mine oxide was normally vaporized to recover solvents and quinones. The quinone content of the washed alumina was still 2.0% and the solvent content (trialkyl phosphate) was 2.2%.

The column containing 510 g of alumina was packed with pure Shellsol AB solvent (200 ml).

The temperature was maintained at about 40-50 ° C. Allow to stand for 7 hours. The solvent was removed. The heat treatment was repeated 2 more times. In the first wash, the kilo noni content of alumina decreased by about 80%. In the second treatment, a reduction of 98-100% was achieved. Solvent residues (trialkyl phosphate) were reduced accordingly.

Example 4.

As Example 3, but the alumina wash was performed by circulating the solvent (200 mL, 400 mL, 600 mL) through an alumina mattress (540 g) for 7 hours at a rate of 6.5 L / h at 40-50 ° C. In each of the 3 experiments, the circulating solution was analyzed every hour. With this arrangement, the uptake of quinones tal-20 was accelerated compared to the washing method of Example 3. Equilibrium was reached in less than two hours. The amount of circulating solvent significantly affected the quinone yield. In the last experiment using the highest amount of solvent (600 ml = 3 x free volume of the mattress), a recovery rate of 95% for quinones and a recovery rate of 92% for the solvent (trialkyl phosphate) was achieved.

. ·; . Example 5.

Heat treatment at higher temperatures.

30 Table 1 shows the analytical results of untreated and heat-treated alumina. The heat treatment was performed in an oven with alumina in a crucible (static mattress) using an annealing time of four hours. The impure alumina used in the experiment was reddish brown in color and was 35 '. contained 75.6% alumina and 4.9% organic impurities as carbon (7.4% as hydrocarbon). The results show that 98509 9 of organic matter can be removed from the alumina used at temperatures> 500 ° C. It can also be seen from the results in Table 1 that when the annealing temperature of 400 ° C is used, the hydrocarbon content is still too high, causing problems in the filtration step. When an annealing temperature of> 500 ° C is used, the hydrocarbons have been burned to a minimum at which hydrocarbons considered harmful are no longer present.

Example 6.

Dissolution of heat-treated alumina in acids.

Powdered alumina (135.5 g) heated at 500 ° C for four hours was dissolved in a mixture of 33% hydrochloric acid (579.4 g) and water (136.5 g). Dissolution was continued for about five hours at 150 ° C. The alumina dissolution yield was 95%. Analysis of the polyaluminium chloride formed shows that the salt contains 14% Al 2 O 3, 0.019% Fe and 21% Cl '.

Example 7

The Al-oxide used in the hydrogen peroxide plant was annealed in a continuous 20 ° C rotary kiln at 550 ° C with a delay time of 1.5 hours. The product was almost white and its analysis was: Al 2 O 3 91%, Fe 0.11% and C 0.2%.

The annealed oxide (150 g) was mixed with water (307 g) in a 2 L beaker, heated to 60 ° C, after which 96% sulfuric acid was carefully added over about 15 minutes to the vessel.

• · · [- The temperature then rose to 115—> 130 degrees. When the exothermic I »· ·. · ·. the reaction was over and most of the oxide was dissolved, the temperature of the reaction mixture dropped to 113 ° C (boiling point), where the reaction mixture was maintained until a total time of 3 h had elapsed. A small sample was then taken for analysis and poured onto a sheet to crystallize. The sample was dissolved in water to a 10% solution, the pH of which was measured: 2.8 (commercial Al sulfate 3.2). Dilution water (810 g) was added to the product mixture and the solution Al-j35 sulfate was analyzed: Al 2 O 3 7.8%, free Al 2 O 3 0.02%, SO 4 2 3%, water insoluble 0.06%, phenolic compounds <0.001%,; TOC (= kok.org. carbon) 2.9 mg / l of the clarified solution. The solution yield was over 99%. The solids and turbidity (> 200 NTU) of the product solution were reduced by the addition of 5 mg polyelectrolyte (polyacrylamide) / 1 solution. A completely clear solution with a turbidity of 1.4 NTU and a TOC of 3.6 mg / l was obtained (commercial product 5 at the corresponding concentration of 7.6 mg / l).

Example 8

The spent Al-oxide containing organic matter (137 g) was ground for 20 s on a Schwing mill and annealed in quartz-10 at a layer thickness of 6 mm for 1.5 h. The annealing loss was 21.3%. In (screened through a 250 μιη: η sieve transmittance 99.3%) was slurried in 100 g of 205 g of water, the reaction mixture was heated to 60 ° C and sulfuric acid (96%, 273 g) was added over a period of half an hour the reaction mixture.. The temperature rose to 120 ° C. React for 15 h at boiling point (112 ° C end) followed by dilution with water (1078 g). The reaction mixture was filtered through a 100 ml Millipore filter with a 12 μιη membrane, the precipitate was washed, dried, weighed and analyzed. The precipitate (pH 1.85) was charged with wash water, after which it was diluted to volume and analyzed. The filtrate (200 ml) contained 21 g Al / l and 5.6 mg Fe / l, the precipitate (0.315 g) contained 52% Al. The dissolution yield of aluminum was 96.2% and the Fe of the solution was 0.014% of Al 2 O 3 when it was 0.022% with commercial pure Al 2: 3 sulfate, i.e. the product was 25 purer than commercial sulfate. Figure 2 shows the dependence of the dissolution yield on the annealing temperature. All experiments were performed according to the example above, so they are comparable.

• · <a * · • · a t

Figure 2 graphically depicts the dissolution yield of alumina annealed at various temperatures in sulfuric acid and the annealing temperature. It can be seen from the results that when the alumina is annealed at> 900 ° C, the dissolution yield of alumina decreases below 90%. Less than 90% dissolution yield is no longer considered acceptable. In this case, the slowness of the filtration of the insoluble matter also worsens the situation.

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Claims (13)

Process for the purification of contaminated alumina used for adsorption of organic matter in the preparation of hydrogen peroxide, characterized in that the impure, granular or atomized alumina a) is annealed at a temperature of 500-900 ° C for combustion of organic pollutants b) dissolved in concentrated mineral acid at elevated temperature; c) the acid solution is diluted with water and filtered or centrifuged as necessary to remove undissolved matter; d) and the aqueous solution containing aluminum salts is used as the seed or further treated as a water purifier. or as a retention chemical. 15 Process according to claim 1, characterized in that the crude alumina is pre-washed with an organic hydrocarbon solvent prior to annealing. 20 Process according to claim 2, characterized in that the organic hydrocarbon used in the prewash is suitably a mixture of C10-Cn aromatic hydrocarbons. • · 4. A process according to any of the preceding claims 1-3, characterized in that the crude alumina used in the preparation of hydrogen peroxide with the anthraquinone process contains the most adsorbed organisms adsorbed from the working solution. hydrocarbons. • · * 3 * 0 Process according to claim 1, characterized in that the annealing is preferably carried out at 500-800 ° C, most preferably at 500-650 ° C. Process according to claim 1, characterized in that the mineral acid used in the solution is sulfuric acid or hydrochloric acid. 98509 Process according to claim 1, characterized in that the mineral acid used in the solution is preferably 50-60% by weight sulfuric acid. 5 Process according to claim 1, characterized in that the impure granular alumina is atomized before annealing or after annealing. Process according to claim 1, characterized in that the dissolution in the mineral acid takes place at a temperature of 100-160 ° C. 10. A process according to claim 1, characterized in that the gases released by the annealing are catalytically, thermally combusted by post-combustion or directly directed into the combustion unit's fireplace hearth. 11. A process according to claim 1, characterized in that the solution containing aluminum salts is filtered, as needed, for the removal of undissolved alumina, and the unsolvated portion can be returned to the dissolution phase and the filtrate is treated with active koi for removal of organic residues as needed. and is used either as aqueous solution or in crystallized solid form. '.25 12. A process according to claim 1 or 11, characterized in that flocculating agents are used to facilitate the filtration or centrifugation of the aqueous solution containing aluminum salts. • «: 3-e • · ·: 13. Use of the aluminum salts prepared according to any of the above-mentioned claims 1-12, such as aluminum sulphate or chloride, as a water purification or retention chemical. 35