HU188168B - Process for producing fumaroic acid from wash water of outgases produced with oxidation of hydrocarbons - Google Patents

Abstract

Fumaric acid is produced from the wash waters of exhaust gases resulting from hydrocarbon oxidation, which contain maleic acid. The process comprises a thermal pre- treatment of the impure maleic acid solution, with optional concurrent concentration, with transformation of part of the impurities to facilitate their elimination from the final product, subsequent hot filtration, isomerization of the maleic acid to fumaric acid, crystallization according to a pre-set time/temperature chart, removal of the mother liquors by filtration, subsequent dissolution in water or in a fumaric acid solution, decolorization, recrystallization and drying.

Description

The present invention relates to a process for the preparation of fumaric acid by the isomerization of a solution containing maleic acid in the scrubbing water of waste gases from the oxidation of naphthalene or hydrocarbon mixtures containing it.

The process according to the invention provides fumaric acid in good yield and high purity, which is essentially due to a heat treatment prior to the maleic acid isomerization.

U.S. Patent 2,454,387 describes a process for preparing fumaric acid by isomerizing a maleic acid solution. This procedure requires the use of pure maleic acid and the solution should be free of impurities.

U.S. Patent 2,548,680 discloses that fumaric acid is prepared from maleic acid-containing washings from a benzene oxidation plant. This type of wash water contains only readily eliminated impurities and is not suitable for the production of fumaric acid of sufficient purity in the case of naphthalene oxidation plant waste gas washing water. The reason for this is that the scrubbing waters of the naphthalene oxidation plant wastewater generally contain a naphthoquinone impurity which is soluble and remains in the crystals of the fumaric acid produced after being filtered.

According to French Patent No. 2 013 333, pure fumaric acid is prepared by isomerization starting from the scrubbing waters of maleic anhydride production. Again, the starting material contains only easily removable impurities.

Isomerization is also carried out according to German Patent Publication No. 1,948,624 to obtain fumaric acid from an aqueous solution of maleic acid. The composition of the starting material is not defined in this specification; they do not mention the problem caused by impurities that are difficult to remove or how to solve it.

Japanese Patent 74/35324 discloses solvent extraction to remove 1,4-natoquinone impurities, however, a further problem to be solved is to completely remove the solvent used for the extraction from the solution to be isomerized.

Thus, none of the known processes described above have enabled the preparation of fumaric acid of sufficient purity from the scrubbing water of the naphthalene oxidation process.

The most widely used process for the preparation of fumaric acid at present consists in the isomerization of maleic acid to fumaric acid using known catalysts such as thiourea, mercaptan and the like, followed by cyclization of the acid obtained, isolation of the precipitate, dissolution of the precipitate in warm water, with charcoal, such as activated charcoal, decolorize, heat filter, crystallize the fumaric acid precipitate under cooling, isolate the crystalline material and then dry.

Due to the extremely variable nature of the starting materials, the process conditions and the activity of the catalyst, impurities are present in the stock solution. Examples of such materials are quinones, in particular naphthoquinone, benzoic acid, toluic acid, citraconic acid, phthalide, phthalic acid, other aliphatic and aromatic acids, as well as aldehydes, condensed products and polymerized products, as well as inorganic acids and salts. The known processes are not capable of completely, completely removing the above mentioned contaminants, which thus remain in the final product and prevent its use in the chemical industry in general and in pharmaceutical products in particular in nutritional formulations. Fumaric acid may be used in place of citric acid, tartaric acid and / or ascorbic acid, provided that it has a purity that meets strict national standards. From the foregoing it can be seen that the above mentioned contaminants in the final product greatly limit the scope and mode of industrial application of the product.

To solve these problems, we have developed a new industrial process for the production of fumaric acid from the scrubbing waters of industrial waste gases from oxidation plants of naphthalene or hydrocarbon mixtures containing it. The process of the present invention provides a purer product with better chemical and physical properties than known processes. The process of the present invention can purify maleic acid solutions of any concentration and concentrations containing impurities that are difficult to remove and convert them to fumaric acid by maleic isomerization. The fumaric acid thus obtained is isolated by crystallization, then purified and dried.

The process of the present invention is based on the discovery that, if properly heat treated prior to isomerization, naphthoquinone is converted to a high molecular weight compound, thereby precipitating and being readily filtered (e.g., by the addition of a filter aid).

The process of the invention will be better understood from the following detailed description which is given by way of example only and is not to be construed as limiting the invention.

Figure 1 is a block diagram of the preparation of fumaric acid by the process of the invention.

Figure 2 is a time / temperature diagram of settling and cooling and pretreatment according to the invention.

Figure 3 is a time / temperature diagram of the isomerization phase and filtration / washing phase.

Figure 4 is a time / temperature diagram of the solubilization / decolorization phase and the crystalline lake / centrifugation phase.

The process of the present invention will now be described by way of example only. The individual phases described in the example correspond to the operations shown in the block diagram of FIG.

Example

Average initial total waste gas from oxidation of a mixture of 30% o-xylene and 70% naphthalene

188 168 has the following composition after separation of phthalic anhydride:

The composition of the effluent gas: phthalic anhydride 0.5 g / Nm 'maleic anhydride 2.0 g / Nm' sulfuric acid 0.27 g / Nm ^{3 *}

1,4-naphthoquinone 0.1 g / Nm ³ benzoic acid 0.05 g / Nm ³ other by-products 0.01 g / Nm ³

2.93 g / Nm ³

The maleic acid solution obtained after washing the waste gas, i.e. the starting material of the process according to the invention, initially contains the following substances:

maleic acid 25 weight% naphthoquinone 0.65 weight% phthalic acid 2.5 weight% other organic acids 0.7 weight% sulfuric acid 0.2 weight%

Phase 1

The maleic acid solution of the composition described above is pre-treated with heat. This pretreatment consists of heating the solution above 90 ° C. The relationship between pre-treatment temperature and treatment time is shown on the right of Figure 2.

The pretreatment operation may coincide with concentrating the solution to the required concentration. Pretreatment involves the conversion of impurities and thus prevents their presence in the final product. Decolourising carbon or other substances having a similar effect may be added to the solution during the pretreatment phase.

Phase 2

The solution is filtered hot through a suitable press filter, vacuum filter, smooth or rotary filter, continuous or batch filter, then the product is washed as needed and air dried as needed. This gives a purified maleic acid solution.

Phase 3

The maleic acid in the filtered solution is isomerized to fumaric acid which crystallizes under cooling using thiourea catalyst. This phase is clearly illustrated in the block diagram of Fig. 1 with reference to the temperature-time relationship in Fig. 3.

As shown in Figure 3, the isomerization and crystallization process is illustrated by a characteristic time / temperature curve with the highest possible yield (92%). In this way, crystals of a size and shape that contain the smallest amount of impurities and are suitable for further processing are obtained (attached photo).

When working under conditions other than those indicated in the diagram, the resulting end product is of poor quality and the cost of production is increased.

The above diagram shows the most suitable method for industrial production, thus achieving greater efficiency than increasing the isomerization time. This latter method is inappropriate due to the slowness of the reaction.

More specifically, the isomerization cycle includes the following steps: charge-warming reaction (maleic acid isomerization), cooling (fumaric acid crystallization), emptying.

The solution of maleic acid to be isomerized has a volume of 10 m ³ and has the same composition as described previously.

Charging time is 30 minutes; the inlet temperature of the solution to be treated is 30 ° C. The isomerizer is filled, the stirrer is started, and heating begins. When the temperature reaches 70 ° C, the aqueous catalyst solution is added and the entire reaction mixture is stirred continuously. The amount of catalyst, in this case thiourea, is calculated on the volume of the maleic acid solution, regardless of concentration. Generally, 6 kg of catalyst is added to 1 m ^{3 of} maleic acid solution, so 60 kg of catalyst is used per 10 m ^{3 of} starting material.

The catalyst promotes the isomerization reaction of maleic acid to fumaric acid.

Obviously, as the isomerization begins, the rate of increase in temperature of the solution in the isomerizer increases. Heating was continued until the temperature reached 100 ° C. This takes 4 hours.

Heating maleic acid at 100 ° C for 4 hours yields a yield of 92% fumaric acid.

In this phase, the heating serves only to compensate for heat loss from the outside.

The agitator is kept in motion throughout the entire isomerization period.

Cooling (crystallization of fumaric acid) does not require much trouble, it is sufficient to stop the heating, then the solution is cooled and cooled to 25 ° C over 3 hours with constant stirring.

Phase 4

The solution containing the fumaric acid crystals was filtered at a constant temperature (55 ° C) for 30 minutes.

To filter the fumaric acid crystals, use a smooth or rotating, continuous or batch filter *! Filtration is followed by appropriate washing treatment followed by drying with a saturated solution of pure fumaric acid at 25 ° C and then air or other gas drying. Filtration is carried out using rotary filter units or a smooth automatic press filter, possibly basket-type or continuous centrifugation, while washing the product.

The filtration operation is preferably carried out by means of a press filter.

The time / temperature diagram is also very important in this phase, especially to the right of Figure 3

188 168 is a diagram for washing the filter.

As shown in Figure 1, the mother liquors from this operation should be destroyed in a lebontóban ⁵ or biological treatment should be carried out activated sludge treatment plant.

Phase 5

The crude fumaric acid crystals are dissolved in water or at 25 ° C in a saturated fumaric acid solution which may be the mother liquor from the second crystallization.

This phase is also clearly shown in the block diagram of FIG. This operation is controlled by temperature ¹⁵ , which must be between 95 ° C and 98 ° C, but can also be controlled by pressure in order to increase the temperature and, consequently, the solubility of fumaric acid.

Phase 6

The decolorizing carbon was added to the above solution, which was maintained at a temperature of 95 ° C to 98 ° C when working at atmospheric pressure.

The carbon used is commercially available as Anticromos 00, Carboraffin C, Darco s 51.

The mixture was stirred, filtered hot and the filter ³⁰ preS. This phase is illustrated in the last section of Figure 4.

Phase 7

After filtration, the solution is cooled and the fumaric acid is crystallized. The crystalline product is separated by a centrifuge, which may be of the semi-automatic type, with a horizontal axis and automatic discharge. When using such a centrifuge, 5-7% moisture remains.

Phase 8 ⁴⁵

A fluid bed hot air dryer may be used for drying. Of course, any device that removes moisture and traces of impurities that can be removed by air or steam can be used, such as benzoic acid.

The fumaric acid produced by the industrial process described above has the following characteristics:

fumaric acid 99.7% color (5% in alcohol) 0-10 Home moisture 0.2% ash 0.01% iron 2 ppm

For the sake of completeness, the efficiency of each step of the process of the invention is given: isomerization efficiency: 92% conversion of the maleic acid in the stock solution: 94% pure conversion of the crude fumaric acid: 86.5% of the maleic acid.

All the steps of the process of the invention have been described and exemplified, but the example is for reference only and the process of the invention is not limited to that described in the example. The time, amount, temperature and catalyst may be varied within the scope of the process of the invention.

Claims (4)

A process for the preparation of fumaric acid from the scrubbing water of waste gases from the oxidation of naphthalene or hydrocarbons containing naphthalene by isomerisation of a maleic acid-containing solution by heating a solution of maleic acid containing difficult to remove impurities to 70-100 ° C. the solution is then hot-filtered and isomerized to fumaric acid, the resulting fumaric acid is crystallized, the crystals are isolated from the mother liquor by filtration, dissolved in water or fumaric acid solution, and the solution is decolorized and dried. Process according to claim 1, characterized in that the heat pretreatment is carried out at a temperature above 90 ° C. Process according to any one of the preceding claims, characterized in that the maleic acid solution is concentrated during the heat pretreatment phase. Process according to any one of the preceding claims, characterized in that, during the isomerization phase, the solution is heated at 30 ° C to 100 ° C for four hours, maintained at this temperature for four hours, then cooled and crystallized while the temperature was lowered to 25-50 ° C over three hours.