DE1191359B - Process for the regeneration of activated carbon - Google Patents

Description

Process for the regeneration of activated carbon in industrial production of terephthalic acid through thermal rearrangement of alkali salts, especially potassium salts aromatic carboxylic acids, e.g. B. benzoic acid, phthalic acid or isophthalic acid a temperature of about 330 to 500 ° C in an inert atmosphere, e.g. B. of carbon dioxide with the use of, for example, cadmium or zinc or other metals or Metal compounds are obtained after treatment of the rearrangement product in an aqueous solution Solution with an acid a terephthalic acid of high purity, which is particularly suitable for Production of a fiber- or film-forming polyethylene terephthalate by esterification with ethylene glycol or a derivative and subsequent polycondensation is suitable. However, the crude product obtained in the thermal rearrangement contains a considerable amount of impurities, such as unreacted raw materials, alkali salts of carboxylic acids as a by-product, inorganic salts, e.g. B.

Alkali carbonates, carbonized or charred substances, catalyst and a colored substance whose structure is unknown. These impurities must be completely separated from the terephthalic acid.

While the unreacted raw materials, which are a by-product accumulating alkali salts, inorganic salts, coked or charred substances and Catalyst relatively light due to the differences in their solubilities can be separated from the terephthalic acid in water, the separation of the colored substance of unknown structure more difficult.

If you omit the separation of this dye, then contains the by precipitation with inorganic or organic acids (except terephthalic acid) terephthalic acid obtained from an aqueous solution of the reaction product this colored substance.

If such a contaminated terephthalic acid is now directly with ethylene glycol polycondensed to polyethylene terephthalate, the polycondensate obtained is also considerably colored and practically unusable.

So far, the colored substance was separated with the help of activated charcoal, since cleaning with activated charcoal has the advantage of being simple and effective.

However, in order to obtain a terephthalic acid of such high purity, which is suitable for the direct polycondensation must be a large amount on activated carbon. Recovery of the activated carbon is therefore technical essential.

You can regenerate activated carbon by heating it to 700 to 800QC. However, this method is uneconomical.

It has now been found, surprisingly, that you can use activated carbon, their Adsorption capacity in the purification of an aqueous solution by thermal Rearrangement of alkali salts of benzene carboxylic acids other than terephthalic acid Alkali terephthalate had been lowered, can regenerate if you wash it with water, especially after treatment with an aqueous alkali solution, washes.

An aqueous alkali solution of one concentration is preferably used for this purpose up to 20 percent by weight, in particular from 2 to 10 percent by weight.

Aqueous potassium hydroxide, sodium hydroxide, sodium and potassium carbonate and bicarbonate solutions and aqueous ammonia.

Treatment with the aqueous solution of an alkali and / or Water can be carried out at room temperature; however, it is preferred to reduce the time required for regeneration, either or both Treatments at a temperature above 60 ° C and up to the boiling point of the aqueous Solution or water.

The aqueous solution of the alkali should be at least in such an amount used to submerge all the used activated carbon; the solution can be used repeatedly.

The amount of wash water can be about 20 to 100 times the weight of used activated carbon.

The alkali treatment is about when using a mixing tank Carried out for 3 to 5 hours.

When using a carbon bed, the treatment is carried out for as long as until the released aqueous solution of the alkali becomes essentially colorless. A the same applies to water washing.

If necessary, the alkali treatment and / or water washing can be used repeated two or three times. In this case, there is preferably an alternating one Treatment with alkali and water.

According to the method, both powdered and granular activated carbon can be used Activated carbon can be regenerated.

When using powdered activated carbon, this is preferred in the aqueous solution of the alkali or in water with stirring and mixing during suspended for a reasonable period of time and then separated. Granular activated carbon is preferably made by passing the aqueous solution of the alkali or water through a fixed bed or a fluidized bed is regenerated.

The process according to the invention is illustrated using the examples below explained in more detail.

Example 1 Dipotassium phthalate containing 3.5 mole percent cadmium phthalate was heated to 440 "C in a carbon dioxide atmosphere under a pressure of 10 kg / cma Heated for 1 hour.

Catalyst and coked or charred and other insoluble substances were removed from the resulting solution by filtration. To 501 of the filtrate (which contains 205 g dipotassium terephthalate per liter and an optical density of 3.1, measured at 380 mu, possesses 15 g of powdered activated carbon with a Content of 500 / o water added. The mixture was stirred for 1 hour at 60 "C, then filtered.

The optical density of the filtrate was now 0.53.

250 cm3 of water were added to the used activated carbon The suspension was heated to boiling for 1 hour and the activated carbon was separated off by filtration.

The separated activated charcoal again became 501 of the dipotassium terephthalate The filtrate containing the mixture was added for 1 hour at 60 "C. and then again filtered. The optical density of the filtrate was 0.80.

Was the activated carbon already used again under the same Conditions but applied without regeneration was the optical one Density of the filtrate 1.41.

Example 2 An aqueous solution which, as indicated in Example 1, was obtained from the catalyst and coked matter by filtration freed. To 50 l of the filtrate (with a content of 195 g dipotassium terephthalate Liter and an optical density of 1.2) became 100 g of powdered activated carbon with a content of 500 / o water was added, the mixture was stirred at 60 ° C. for 1 hour and then filtered.

The optical density of the filtrate was 0.082.

The separated activated charcoal was mixed with 400 cm3 of a 50% aqueous Sodium hydroxide solution heated to boiling for 2 hours, then filtered and the filter cake washed with 1500 cm3 of hot water at 70 "C.

The activated carbon thus regenerated became 50 liters of the initial filtrate added, the mixture stirred at 600 ° C. for 1 hour and then filtered. The optical one The density of the filtrate was 0.092.

If the used activated charcoal has been used again under the same conditions, but used without regeneration, the optical density of the filtrate was 0.22.

Example 3 An aqueous solution obtained according to Example 1 was of Catalyst and coked substances are freed by filtration. The filtrate (with a Content of 200 g dipotassium terephthalate per liter and an optical density of 3.8) was from above through a 2 m high fixed bed of granular activated carbon, with a linear Surface speed of 1.8 m per hour passed. The optical densities, which were measured after 10, 20, 30, 40 and 48 hours since the start of the procedure, were 0.14, 0.18, 0.26, 0.31 and 0.34, respectively.

Because the adsorption capacity of the activated carbon decreases over time 48 hours after the start, the treatment was terminated and the active cooling regenerated by first adding a 50% strength aqueous sodium hydroxide solution 700 C from above through the coal bed at a linear surface velocity of 3.6 m per hour for 4 hours and then water at 70 "C with a linear Surface speed of 10m per hour for 10 hours.

A further amount of the dipotassium terephthalate was then added Starting solution through the coal bed at a linear surface velocity from 1.8 m per hour. Those measured after 10, 20, 30 and 40 hours from the start optical densities were 0.16, 0.23, 0.29 and 0.39, respectively.

Example 4 An aqueous solution obtained as in Example 1 was used freed from insoluble substances by filtration. The filtrate was concentrated, until solid dipotassium terephthalate crystallized out. The solid dipotassium terephthalate thus obtained was dissolved in water, a 170/0 aqueous solution with an optical density of 0.060 was obtained.

This aqueous solution was from above through a 2 m high fixed bed made of granular activated carbon at a linear surface speed of 3.6 m directed per hour. Those after 10, 20 and 30 days after the start of the procedure optical densities measured were 0.015, 0.015 and 0.026, respectively. Since the optical If densities were always above 0.020 after up to 30 days, the treatment was started on 33rd day canceled and the activated carbon regenerated by first one 50% sodium hydroxide solution at 70 "C from above through the coal bed at a linear Surface speed of 3.6 m per hour for 4 hours and then water at 70 "C and a linear surface speed of 10 m per hour during 24 hours passed. Then a further amount of the aqueous solution of Dipotassium terephthalate through the carbon bed at a linear surface velocity of 3.6 m per hour. Those measured after 10, 20 and 30 days after the start optical densities were 0.013, 0.018 and 0.021, respectively.

The treatment was interrupted and the regeneration of activated carbon and the decolorization treatment were repeated in the same manner, whereby the following results were obtained: Optical density of the discolored solution Regenerations the activated carbon 10 days 1 20 days 1 30 days 0 0.015 0.015 0.026 1 0.013 0.018 0.021 2 0.018 0.020 0.027 3 0.018 0.028 0.029.

Example 5 An aqueous solution obtained as in Example 1 was used freed from insoluble substances by filtration. The filtrate was concentrated, until solid dipotassium terephthalate crystallized out. The solid dipotassium terephthalate thus obtained was dissolved in water, a 220% strength aqueous solution with an optical density of 0.070 was obtained.

This aqueous solution was from above through a 2 m high fixed bed made of granular activated carbon corresponding to a sieve size of about one hundred and forty-four up to about eight meshes per square centimeter at 30 "C and with a linear surface velocity of 3.6 nu per hour for 30 days.

Then a 50% aqueous sodium hydroxide solution at 90 ° C. was continuous due to the used activated carbon at a linear surface velocity of 3.6 m per hour for 2 hours and finally water at 90 "C with a linear Surface speed of 10 m per hour passed through for 2 hours and the treatment with the aqueous sodium hydroxide solution and water among the same Conditions repeated.

The so regenerated activated carbon was used for the treatment of further Dipotassium terephthalate solution was used in the manner described above.

The decolorization and regeneration of the activated carbon were repeated three times, and the decolorizing effect of the regenerated activated carbon was determined by measuring the optical densities of the treated solution after 10, 20 and 30 days after the start of the process in a manner similar to that given in Example 4. The results are compiled in the table below. Number of optical density of the discolored Regenerations solution the activated carbon treatment time 10 days 1 20 days 1 30 days 0 0.014 0.015 0.021 1 0.015 0.017 0.024 2 0.011 0.016 0.023 3 0.017 0.021 0.027 The results show that the thoroughness of the regeneration over that of Example 4 improves the degree of regeneration and the initial discoloration capacity can be almost completely recovered.

Claims (6)

Claims: 1. Process for the regeneration of activated carbon, the in the purification of an aqueous dialkali terephthalate from the thermal rearrangement of alkali salts of benzene carboxylic acids other than terephthalic acid containing solution had been inactivated, that the Activated charcoal with water, especially after pre-washing with an aqueous alkali solution, washes. 2. The method according to claim 1, characterized in that as aqueous alkali solution alkali hydroxides, carbonates or bicarbonates or aqueous ammonia used. 3. The method according to claim 1 and 2, characterized in that one a maximum of 20 percent by weight, preferably 2 to 10 percent by weight, aqueous Alkali solution used. 4. The method according to claim 1 to 3, characterized in that one the alkali treatment at a temperature between 60 "C and the boiling point of the solution performs. 5. The method according to claim 1, characterized in that the Carries out water washing at a temperature between 60 and 100 "C. 6. The method according to claim 1, characterized in that the Activated charcoal was repeatedly alternated with alkali and water.