GB2098612A - Production of fumaric acid from wash waters of exhaust gases resulting from hydrocarbon oxidation - 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

SPECIFICATION Production of fumaric acid from wash waters of exhaust gases resulting from hydrocarbon oxidation The present invention relates to the industrial production offumaric acid. The process of the present invention uses as starting material wash waters of exhaust gases from the oxidation of hydrocarbons. At present the most common process for production of fumaric acid involves isomerization of the maleic acid in fumaric acid using known catalysts, for example, thiourea or a mercaptan. The isomerization is followed by crystallization of the acid obtained, separation of the precipitate, dissolution of the precipitate in hot water, decolorization of the solution using agents such as, in particular, carbon, hot filtration, crystallization by cooling, separation of the fumaric acid precipitate, and subsequent drying.

Given the extreme variety of raw materials, process conditions and catalyst activities, impurities are present in the initial solution, for example, quinones (specifically naphthaquinone), benzoic acid, toluic acids, citraconic acids, phthalaldehyde, phthalic acid, other aliphatic and aromatic acids and aldehydes, condensation products and polymerized products, and inorganic acids and salts. Consequently the known processes are not able to totally and completely eliminate all the above-mentioned pollutants, which consequently remain in the final product and prevent its subsequent use in chemistry in general and in pharmaceutical products and foodstuffs in particular.It should be noted, in this regard, that if fumaric acid is pure, it can be used, according to the regulations of several countries that are extremely strict in these matters, to replace the conventional citric acid, tartaric acid and/or ascorbic acid. It is clear and evident that the presence of pollutants as specified above in the final product drastically limits areas and means of industrial use of fumaric acid.

The present invention is based on the discovery of a new industrial process designed to produce fumaric acid from the wash waters of industrial exhaust gases coming from plants that oxidize hydrocarbons, in particular, ortho-xylene, naphthalene and their mixtures, alkylnaphthalenes, benzene, analogous substances to benzene, butane and butylene, or mixtures of these, or from wash water mixes coming from any type of plant oxidizing the aboveindicated hydrocarbons. Such waters contain impure maleic acid. The new process can possibly achieve a product that is more pure and has better chemical and physical characteristics than the product obtainable according to the prior art.In particular the maleic acid solution, no matter how it is obtained and at any concentration, is purified and the maleic acid is isomerized to fumaric acid, which is separated by crystallization, purified and dried.

The present invention can be better understood by the following detailed description, which is given by way of non-limiting example, of a possible method of obtaining fumaric acid according to the invention.

In the accompanying drawings:- Figure 1 shows a block diagram illustrating production of fumaric acid according to the invention; Figure 2 gives time/temperature charts of, respectively, deposit and cooling and subsequent pre-treatment according to the invention; Figure 3 gives time/temperature charts of, respectively, the isomerization phase and the filtration/filter wash phase; Figure 4 gives time/temperature charts of, respectively, dissolution/decolorization phases and crystallization centrifuging phases.

To better understand the object of the invention a possible guideline composition of the starting products is given as follows: The average composition of an exhaust gas from oxidation of a mix of ortho-xylene (30%) and naphthalene (70%), after separation of phthalic anhydride, in grams per cubic metre at standard temperature and pressure (g/N m3) is :- Phthalic anhydride 0.5 Maleic anhydride 2.0 Sulphuric acid 0.27 1,4 napthaquinone 0.1 Benzoic acid 0.05 Other by-products 0.01 Total 2.93 The typical content of a solution of maleic acid is, by weight:- Maleic acid 25% Naphthaquinone 0.65% Phthalic acid 2.5% Other organic acids 0.7% Sulphuric acid 0.2% Basically the process according to the invention consists of the following stages:: Stage 1 The impure maleic acid solution, however obtained, and specifically of the type indicated above, with the presence of the pollutants indicated, is thermally pretreated by heating it to a temperature above 900 in a curve like that shown on the chart in Figure 2. This operation can coincide with concentration of the solution should that be necessary. Pretreatment transforms part of the pollutants so as to prevent them from being present in the final product. Decolorizing carbon or other similar-acting substances can be added during these pretreatment stages.

Stage 2 The product of Stage 1 is filtered hot through a suitable pressure, vacuum, flat, rotary, continuous or interrupted filter with or without washing and with or without air drying.

Stage 3 The maleic acid contained in the filtered solution can now be isomerized into fumaric acid, which is crystallized by cooling. Thiourea is used as a catalyst. This stage is clearly indicated in the block diagram in Figure 1, and can be performed according to the chart given in Figure 3.

The entire isomerization and crystallization operation is performed following a specific time/temperature chart in order to achieve maximum output efficiencies (92%) and to produce crystals with sizes and shapes such that they contain the least possible quantities of impurities and are suitable for further processing operations (see enclosed photograph, Figure 5).

It should be noted that operating under different conditions gives a final product of inferior quality and a higher production cost.

It should also be noted that the chart indicated must be considered as an optimum diagram for industrial production, since even higher output efficiencies than that indicated herein could be obtained by increasing the isomerization time, even though the slowness of the reaction makes this inconvenient.

Stage 4 The fumaric acid crystals are separated from the mother liquor by filtration, using a suitable flat or rotary, continuous or interrupted filter. This filtration, being accompanied by suitable washing treatments using saturated solutions of pure fumaric acid at 250C and drying by air or other gas, can use FRP rotary filter pressure units made by COGEIM, or flat automatic discharge pressure filters made by Seitz and Funda, with basket-type or continuous centrifuges with washing of the panel. In particular the operation can be performed using the so-called "Pressofiltro" manufactured by Comber.

The time/temperature charts are very important in this stage too, and in particular those illustrated at the right-hand side of Figure 3 referring to filtration and suspension washing using the Comber "Pressofiltro".

As shown by the chart in Figure 1, the mother liquors that result from this operation must be destroyed in an incinerator or biologically purified in an active sludge treatment plant.

Stage 5 The raw crystalline fumaric acid is dissolved in water or in 250C saturated fumaric acid solution, these being the mother liquors coming from the second crystallization. This stage is clearly shown in the block diagram in Figure 1. This operation is optimized by properly regulating the temperature, which must be between 95 and 980/min., and, if necessary, by regulating pressure in order to increase the temperature and consequently the solubility of the fumaric acid.

Stage 6 Decolorizing carbon is added to the above solution, maintained at a temperature between 95 and 980C when working at ambient pressure. This carbon can be that known by the trade marks Anticromos 00, Carboraffin C, or Darco S 51.

The mixture is agitated and filtered warm in the "Pressofiltro". This stage is clearly indicated in the left-hand section of Figure 4.

Stage 7 Cooling of the filtered product makes fumaric acid crystallize. It is separated by a centrifuge, which can be of semi-automatic type having horizontal axis and automatic discharge. Use of this type of centrifuge will leave about 5 to 7% residual humidity.

Stage 8 A fluidized-bed hot air drier can be used for drying. Obviously any appliance can be used that eliminates humidity and any traces of impurities such as benzoic acid that can be eliminated by air or steam currents. In particular the process can use the drier known as T.S., manufactured by the S.l.E. Soc. Ital. Essiccatoi of Caleppion (MI).

The fumaric acid obtained using the abovedescribed industrial process has the following characteristics: Fumaricacid 99.7% Colour (5% in alcohol) 0--10 Hazen Humidity 0.2% Ash 0.01% Iron 2 ppm Guideline process output efficiency levels are indicated for the sake of completeness: Isomerization 92% of the maleic efficiency: acid present in the initial solution Purification 94% of the raw efficiency: fumaric acid Total efficiency: 86.5% of the maleic acid

Claims (7)

1. A process for producing fumaric acid from wash waters of exhaust gases resulting from hydrocarbon oxidation, comprising a preliminary thermal pre-treatment of the wash waters, which contain impure maleic acid in solution, to transform at least part of the impurities to enable them to be eliminated from the final product, subsequent hot filtration, isomerization of the maleic acid to fumaric acid, crystallization of the fumaric acid according to a predetermined time/temperature chart, separation from the mother liquors by filtration, subsequent dissolution in water or in a fumaric acid solution, decolorization, recrystallization and drying.

2. A process according to Claim 1 in which the isomerization and thermal pre-treatment stages are combined.

3. A process according to Claim 1 or 2 in which the thermal pre-treatment comprises heating the solution to a temperature in the range 70 to 1000C.

4. A process according to Claim 3 in which the said temperature is above 900 C.

5. A process according to any one of the preceding claims, in which the thermal pre treatment includes simultaneous concentration of the maleic acid in the starting solution.

6. A process according to any one of the preceding claims, in which the isomerization stage is also subject to a time/temperature chart in which the mass of product is heated, in an exponential curve, from 30 to 1 000C over a period of approximately four hours, then maintained at this temperature for approximately four hours, and finally cooled with concomitant crystallization, to about 500C over about three hours.

7. Crystalline fumaric acid of high purity obtained by a process according to any one of the preceding claims.