FI98508C - Method for purification of impure alumina by extraction - Google Patents

Description

98508

METHOD FOR PURIFYING PURIFY ALUMINUM OXIDE BY EXTRACTION

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

5

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 new oxide. The alumina used contains organic substances that limit its uses. Currently, landfill-15 mine oxide is most often disposed of as waste or stored pending possible recovery.

Attempts have been made to purify impure alumina in various ways.

According to U.S. Pat. No. 3,814,701, the alumina used in the anthraquinone working solution 20 is stripped of organic matter by annealing the alumina at 300 to 400 ° C. During annealing, the organic matter adsorbed on the alumina burns off. The annealed alumina is alkali treated and re-annealed. However, the alumina thus treated 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 process in which alumina is dissolved in mineral acids or lye. The material insoluble in acids or lye 30 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 present form a biphasic solution which is very difficult to handle, the organic phase of which is tar-like 2 98508 and which is sticky in all places. 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 the regeneration and recovery of alumina in 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. However, since the regeneration conditions must be quite gentle, there will always be some harmful organic compounds left in the granules that are not desired to be returned to the process.

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 as a raw material industrially. It is also an object of the process according to the invention to avoid a rather expensive calcination step. In addition, the aim is to obtain organic compounds as impurities 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.

With the process according to the invention it is possible to obtain a high-purity aluminum salt, e.g. aluminum sulphate or 35 3 98508 aluminum chloride, which are even purer than commercially available 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 are recovered in the solvent and can be recycled to the extraction stage and the part 10 can be recovered as fuel. According to a preferred embodiment, part of the organic hydrocarbons can be dissolved in the solvent during the pre-purification and the useful components therein can be returned to the hydrogen peroxide process.

In this way, the process can significantly reduce the environmental impact of organic hydrocarbons 15 compared to most other purification methods.

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, components of the working solution and other decomposition and oxidation products. Known solvents for the anthraquinone working solution include e.g. secondary alcohols, trialkyl phosphates, alkyl-25-benzenes, triacetylbenzene, alkylcyclohexanones, naphthalenes, xylenes, anilines and quinones. 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 may thus contain varying amounts of different organic matter depending on the hydrogen peroxide manufacturer.

According to one embodiment of the invention, the crude alumina can be pre-washed before the heat treatment with an organic hydrocarbon solvent. The washing solvent is any organic hydrocarbon capable of dissolving the impure organic matter from alumina. According to a preferred embodiment, the solvent is Shellsol AB, which is a commercially available product and which contains mainly C10-Cn aromatic hydrocarbons. The prewash can be used to extract organic useful components from the alumina which can be returned directly to the hydrogen peroxide process. By means of the prewash, it is possible to reduce the amount of organic matter to be burned and at the same time to return the organic compounds for recycling in the hydrogen peroxide process.

According to the invention, it is desirable that the crude alumina be finely ground. Namely, it was found that the finer the alumina, the more completely successful 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.

15

The acid leaching extraction step comprises dissolving the ground alumina in a concentrated acid solution. Any concentrated mineral acid is suitable for dissolution, however, the preferred acids are sulfuric and hydrochloric acid. The use of sulfuric acid at 50-60% by volume is considered particularly suitable. It is advantageous to intensify the dissolution by heating. To ensure almost complete dissolution of the alumina, it is recommended to heat the mixture to a temperature of about 100-150 ° C while stirring for several hours. During dissolution, the organic matter contained in the alumina separates into its own phase on the surface of the aqueous phase. The reaction mixture is diluted with water to prevent crystallization of the aluminum salts. The separation of organic matter is enhanced by extraction with either completely pure or completely reused or partially reused and partially pure organic solvent.

The extraction solvent is any organic hydrocarbon capable of dissolving organic matter from alumina. According to a preferred embodiment, the solvent is Shellsol AB, 35 which is a commercially available product and which contains mainly C10-Cn aromatic hydrocarbons. A particularly preferred solvent is toluene, which can be easily distilled after the separation of the phases from the organic phase and returned to the post-dissolution stage. After the phase separation, the recycled organic solvent returned to the extraction step can be purified and, if necessary, enhanced with pure solvent.

According to the invention, the phases are allowed to separate. The organic phase clarified on the surface mainly contains organic matter in the alumina as an impurity and, in addition, possibly the organic solvents used in the extraction. The organic phase is recycled to the extraction step or recycled. If desired, the solvent returned to the extraction step can be purified, for example by distillation.

The aqueous phase clarified to the bottom is filtered to remove insoluble material. The precipitate is returned to the dissolution step, incinerated together with organic matter or collected as waste. The filtrate containing the aluminum salt can be used as such as an aqueous solution or crystallized as a solid.

According to one embodiment of the invention, the aqueous phase is purified again after filtration to remove any organic residues still present in the aqueous phase. Purification 25 can be performed by activated carbon treatment. It is also possible to use other chemicals, for example flocculation chemicals, in addition to or instead of activated carbon. After the activated carbon treatment, the high purity aqueous solution of the aluminum salt can be used as such or supplied as a solid crystallized • 30 for utilization, for example as a water purification or retention chemical.

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

35 As shown in Figure 1, the crude alumina is ground, then dissolved in an acid. The organic impurities separate into the organic phase. The mixture is diluted with water and the separation of organic impurities is enhanced by extraction using recycled and / or pure organic solvents. After phase separation, the organic phase is passed for incineration or used as a solvent in the extraction step.

5 The aqueous phase is filtered or centrifuged. The material undissolved in the aqueous phase is returned to the leaching step and the filtrate is used as such or subjected to further purification.

The invention is described below mainly by means of examples and experiments 10. The invention is in no way limited to the appended examples but may be modified within the scope of the appended claims.

Examples 15

Grinding and dissolving alumina

The crude alumina from the hydrogen peroxide plant was ground to a particle size of less than 0.35 mm. A Schwing mill was used for grinding and a sieve was used to obtain the desired particle size. Table 1 shows the dissolution results of three different experiments in sulfuric acid. Dissolution of alumina was performed in the same way in all three experiments. To the water in the flask (164 g) was added sulfuric acid, which raised the temperature. to about 70 ° C. Alumina (100 g) was slowly added to the water-sulfuric acid-25 mixture. During the addition, there was apparently no reaction and the temperature did not rise due to the addition of alumina, but the flask had to be heated all the time to prevent the temperature from falling. The temperature was finally raised to 90-110 ° C. The mixture was kept at reflux for 3 h. The mixture was dark brown in color. The resulting mixture was diluted with water. The goal was an 8% solution for alumina.

li 7 98508

Table 1.

Experiment H 2 SO 4 addition Al 2 O 3 addition (100) Reaction Dilution with water No. ____ T, eC ___ amount T at the end time T at the end (pig amount Σ weight theoretical g * C min eC 3 g g Al 2 O 3

pit. X

1,219.2 60__27__92__108 452.3 935 7.8 5 2 "__Il__19 110 110 429.8 913 8.0 3 208.2 76 12 90 110 440.8 913__"

Extraction of organic matter and phase separation

From the diluted solution obtained above, the organic matter was extracted with either Shellsol (Experiment 1) or toluene (Experiments 2 and 3).

The extraction solution was added to a 2 L flask containing the diluted Al 2 (SO 4) 3 solution (Table 2), using toluene, allowing the temperature to drop below 50 ° C before adding the solution to prevent evaporation. Stirring was continued for 1 h. In Experiment 3, distilled toluene obtained from Experiment 2 and the so-called new toluene to compensate for the solution loss in Experiment 2 (Table 2). The sides of the flask had adhered to a brown "organic" "rim" which did not dissolve directly from the mixture in the extraction solution, but had to be "plastered", whereupon dissolution did occur.

After stirring for 1 h, the mixture was poured into a separatory funnel, to which was added the extraction solution used to rinse the flask.

The solutions were mixed in a separatory funnel, after which the phases were allowed to separate. When using Shellsol, the settling time was 1 h, but when using toluene, it had to be settled overnight. The time differences may also be due to the amount of extraction solution used, which when toluene was used was only about a quarter of the amount of 30 Shellsol. After settling, the phases were separated and weighed (Table 2).

8 98508

Taulukko_2 i _____ _ = ^ === ==== 8,

Organic extraction Phase separation

Test - No. No. Amount, g T, Mixture Water- Organic 5 Extraction solution --- “C Σ mass phase n.

Extraction Huuh- Σ- g g 6 S

___test amount ______ 1 Shellsol AB 356.5 100 456.5 70 1392 935.5 456.5 1392 2 Toluene 87 8.7 95.7 45 1009 882.8 104.0 986.8 3 Toluene: from the test 2 77.4 - 77.4 45 - 881.3 109.8 991.1 -new 9.6 8.7 18.3 10 Distillation of the organic phase Experiment 1 (Table 2)

Distillation of Shellsol (C10-Cn aromatic hydrocarbons) was performed in a 1 L round bottom flask heated to 110-120 ° C in an oil bath. Table 3 shows the distillation process, the times used, the temperatures and pressures, and the fractions collected. There was initially 450 g of organic matter to be distilled. 261.8 g of distillate accumulated. The distillate was a perfectly clear, colorless liquid. The loss in distillation was 8.5%.

20 Experiment 2 (Table 2)

Toluene (99.1 g) was distilled in a round bottom flask heated to 111 ° C. At the end, the temperature rose to 116 ° C, at which point the distillation was stopped. Distillate, a clear, colorless liquid, accumulated 78.1 g. 17.9 g of brown distillation waste accumulated. The loss in distillation-25 sa was 3.1%.

Experiment 3 (Table 2)

In Experiment 2, 95.7 g (110 ml) of toluene were added in the extraction step. 78.1 g of distillate were obtained. Loss in distillation 8.3%.

30 9 98508

Table 3. Shellsol distillation in vacuo.

Time T, Pressure Distillate- Distillation- h: min * C mbar t ml waste g Note: _ 0:00 __-__ 450__ 5 2:00 120 450 23 __; __ 2:40 - 400__28 __-_ From distillate 1st fraction: 28 ml- 19.2 g.

Boiling stones were placed in the flask and replacement air was introduced. Manual adjustment of air -> boiling was more even._ 0:00 100 1000 417.9__ 10 2:20 106 120 45 __-__ 3:30 108 79 100__From distillate 2nd fraction: 100 ml-82.4 g, 3:45 - 85 5 __-__ 4:00 -__; __ 319.4 From distillate Fraction 3: 14 ml-7.2 g.

143.54 g was taken from the distillation residue in the flask.

15 172.6 g of 54.5 Z remained in the flask, which was distilled to completion._ 0:00 101 85 __-__ 172.6__ 0:20 104 73 10___ 0:40 102 110 19___ 1:00 106 82 22___ 20 1:20 108 75 34___ 2:00 107 71 63___ 2:40 108 67__88__97.3 Of the distillate Fraction 4: 88 ml-72.9 g 3:10 "66 11___ 3:40 100 72 21___ 25 4:10 106 52 49__66.7 Of the distillate 5 , fraction: 49 ml-28.28 g 0:00 102 83 __: __ 66.7__ 0:30 "75 10___ 1:00 106 54 12___ 3:30 116 81 30___ 30 5:00 120 75 38 36.5 Added 5. to a fraction of 38 ml-28.6 g _____--> 5, fraction fr. 57.4 g_ 0:00 108 60 36 ^ 5__ 1:15 112 45 17 25.2 To fraction 5 was added 10.1 g ______--> 5. fraction total, 67.5 g_ 0:00 106 72 __-__ 25.2__ 1:10 116 44 17 13.4 The distillation was stopped, the distillation residue appeared thick and the steam began to crystallize in the condenser.

Distillate ____ 11 ^ 59 ^ - 5 ^ fraction derivative ^ 79 ^ 06 £ ^ 10 98508 was added to fraction 5.

Treatment of the aqueous phases Separation of insolubles

The insoluble precipitate was separated from the aqueous phase obtained from the extraction step by either filtration or centrifugation.

5

In Experiment 1, the separation of the precipitate was tested by filtration. To about half of the resulting aqueous phase, 400.9 g, was added to improve the filtration with a flocculant, Fennopol K 211, 30 ppm as a 0.1% solution, i.e. 12 ml. Mixing with a Heidolph-10 mixer for 15 sec, speed 450 rpm. Thanks to the addition of Fennopol, a well-landing flock was obtained.

The resulting mixture was filtered on a Biihner 0 0 cm. Whatman GF / A fiberglass paper was used as the paper. The vacuum was aspirated with 15 vacuum pumps, the pressure used was 600 mbar. The resulting filtrate was taken off and the precipitate was washed with warm water (Table 4). The precipitate was dried in an oven at 100 ° C overnight.

Separation of the precipitate by centrifugation proved to be a useful method. Again, a flocculant from Fennopol K 211 was added to the aqueous phase at 30 ppm as a 0.1% solution. Centrifugation was performed with a Heraeus Labofuge T-centrifuge. The rotational speed used was 3000 rpm and the time 20 25 min. After centrifugation, water was poured off the surface.

The water was almost clear, a few light "flakes" floating on the surface. The precipitate was washed with water, filtered through glass fiber paper and dried at 100 ° C (Table 4).

30 Removal of organic from filtrates

Organic residues were removed from the filtrates by treatment with activated carbon. 150 ml of the filtrate and 7.5 g of activated carbon granules (used in the H 2 O 2 plant to purify the wash water) were stirred together with a magnetic stirrer for 1 h. After addition to the activated carbon, the filtrate bubbled vigorously. Filtration with Biihner with fiberglass paper.

Il 11 98508

analysis

All filtrates were analyzed for TOC and for the filtrates of Experiments 1 and 3, Fe and Al (AAS flame).

The fines of Experiments 1 and 3 were analyzed for Fe and Al. Results 5 in Table 4.

Solubility and distribution of aluminum and iron

The amount of sulfuric acid used in the alumina dissolution (Experiment 1: stoichiometric amount and Experiment 3: 95% of the stoichiometric amount) 10 did not affect the solubility of aluminum and iron. In both experiments, 90% of the aluminum was dissolved in the aqueous phase and 98.4% of the iron (Table 5).

Treatment of the aqueous phase and separation of the insoluble Insoluble was separated from the aqueous phase by either filtration or centrifugation. Both separation methods are useful, a clear filtrate is obtained, although the turbidity of the filtrate obtained by centrifugation (22) is about ten times that of the filtrate obtained by filtration (2,4). In contrast, the amount of 20 organic carbon in the filtrate (0.07%) is not affected by the separation method (Table 4).

Activation of the aqueous phase with activated carbon caused the turbidity to drop to 0.15-0.5 and the TOC decreased to 0.004-0.006% (Table; 25 4).

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98508 14

Both Shellsol AB and toluene were used to extract organic impurities from the aqueous phase. Based on TOC analyzes of the aqueous phase, both are useful solvents. Distillation of toluene was easier due to the lower boiling point. Toluene recycling based on the experiments performed does not affect the turbidity of the aqueous phase or the TOC content (Table 4, Experiments 2 and 3).

Claims (14)

15 98508 A process for purifying crude alumina used to adsorb organic matter in the preparation of hydrogen peroxide, characterized in that a) the crude alumina is ground, b) the ground alumina is dissolved in concentrated mineral acid at elevated temperature, and the resulting acid solution is added thereto. an organic solvent for extracting organic impurities, d) separating the organic phase and the aqueous phase, e) filtering or centrifuging the insoluble matter from the aqueous phase containing aluminum salts and using the resulting filtrate as such or as a further water purification or retention chemical, f) using the organic phase Process according to Claim 1, characterized in that the crude alumina is pre-washed with an organic hydrocarbon solvent before grinding. Process according to Claim 2, characterized in that the organic hydrocarbon used in the prewash is preferably a mixture of C 10 -Cu aromatic hydrocarbons. Process according to Claim 1, characterized in that the impure alumina used for the production of hydrogen peroxide by the anthraquinone process contains mainly organic hydrocarbons adsorbed from the working solution. Process according to Claim 1, characterized in that the concentrated mineral acid used for dissolution is sulfuric acid or hydrochloric acid. 16 98508 Process according to Claim 5, characterized in that the concentrated mineral acid used for dissolution is preferably 50 to 60% by weight of sulfuric acid. Process according to Claim 1, characterized in that the crude alumina is ground to a particle size of less than 0.5 mm, preferably less than 0.4 mm. Process according to Claim 1, characterized in that the dissolution in the mineral acid takes place at a temperature of 100 to 160 ° C. Process according to Claim 1, characterized in that the organic solvent used in the extraction step is either recycled and / or pure organic hydrocarbon. Process according to Claim 1 or 9, characterized in that the organic hydrocarbon used in the extraction step is preferably a mixture of C10-Cu aromatic hydrocarbons or toluene. Process according to Claim 1, characterized in that, after the phase separation, part of the organic phase is returned as solvent to the extraction step and part is fed to the incinerator as incinerated ash. Process according to Claim 1, characterized in that the aqueous phase containing aluminum salts is filtered or centrifuged to remove insoluble alumina, which can be returned to the dissolution step, and the filtrate is treated with activated carbon to remove organic residues and used either as an aqueous solution or solid crystallized. Process according to Claim 1 or 12, characterized in that a flocculant 98508 17 is used to facilitate filtration and centrifugation of the aqueous phase containing aluminum salts. Use of aluminum salts prepared by the process according to any one of the preceding claims 1 to 13, such as aluminum sulphate or chloride, as a water purification or retention chemical. 98508 18