DE1167811B - Process for the continuous thermal rearrangement of salts of mono- or binuclear aromatic or heterocyclic, aromatically behaving carboxylic acids - Google Patents

Description

Process for the continuous thermal rearrangement of salts or binuclear aromatic or heterocyclic, more aromatic behavior Carboxylic acids It is known that by heating salts of cyclic carboxylic acids Salts of other carboxylic acids can be obtained. Isomerizations can occur here or disproportionations. So z. B. by thermal conversion of the solid Dipotassium salts of phthalic acid, isophthalic acid or benzoic acid and of benzene polycarboxylic acids or the corresponding salts of mixtures of these salts without the aid of solvents Salts of terephthalic acid can be produced in high yield using reaction temperatures of 400 to 4500 C and carbon dioxide pressures of 5 to 30 atm are required. Other cyclic carboxylic acids that can be prepared by this process are z. B.

Dicarboxylic acids of polynuclear aromatic compounds, such as naphthalenedicarboxylic acid, Diphenic acid or heterocyclic carboxylic acids such as pyridine, furan, thiophene and Pyrrole carboxylic acids. Other cyclic compounds that can be found according to the invention Let this process be produced, for. B. those in addition to a carboxyl group contain another salt-binding acidic group, e.g. B. hydroxy acids such as 4-hydroxybenzoic acid and hydroxynaphthoic acids. As is well known, the thermal conversion is like this made that the well predried starting salts when heated to the between about 250 and 4500 C lying reaction temperatures first sinter together, then go back to the solid state or to a hard, stone-like mass caking. To this process technology at high temperature and at the same time Carry out difficult processes economically and continuously under high pressure To be able to, processes have already been developed in which these conversions in a fluidized bed or a reaction furnace with a rotating belt. However, it was particularly difficult to introduce the absolutely dry starting materials in the reaction chamber.

If the starting materials are conveyed in dust form, e.g. B. with the help of double locks, Screws or by conveying with the help of pressurized flowing inert gases or from carbon dioxide in the reaction chamber, blockages often occur, and it comes to contamination within the reaction space, which leads to disturbances and Cause business interruptions. In addition, the one with the powdery product made itself entrained air in the subsequent reaction has a very detrimental effect on the yield noticeable in rearranged carboxylic acids, since even after previous rinsing Carbon dioxide due to the oxygen content retained in the dusty substances a combustion of rearrangeable carboxylic acids to carbon-like decomposition products entry. In addition to reducing the yield, this creates considerable difficulties in the subsequent work-up - the reaction product to the free carboxylic acids caused.

It is also known to first form the starting materials into molded bodies, such as tablets, spheres or cylinders, and then compress the molded body -in to bring in the reaction space. The production of these moldings is, however, at the same time additionally required, which can only be done with moist material, so that drying must also take place. Also, the yield will decrease and the contamination of the reaction products by those adhering to the molded bodies Atmospheric oxygen not avoided even with carbon dioxide purging.

It has now been found that the continuous thermal Rearrangement of salts of mono- or binuclear aromatic or heterocyclic, aromatically behaving carboxylic acids catalytically at elevated pressure in the presence more effective metal compounds the starting materials used in a simpler manner than before with complete exclusion of oxygen in a compact form in the reaction chamber can be introduced when you put the finely powdered solid starting material in a feed tube introduces, in this tube by a reciprocating piston, optionally at a conically indented point, compacted and the thereby obtained Line of product through an intermediate pipe, which has a smaller cross-section than the feed pipe has, with such a high wall friction in the under that for the thermal conversion required pressure standing reaction chamber presses that the product strand from Pressure in the reaction tube is not pressed back.

The new procedure is easier to carry out than the previous ones, the risk of clogging and business interruption is less, and moreover the disadvantageous oxygen is largely excluded from the reaction space than with the known methods.

When the solids are pressed together, the is in contact with the pipe wall, a strong heating. In some cases it is sufficient to put this surface in a condition that it is good Has sliding properties. However, it is more advantageous by heating the Pipe wall at the compression point of the powdery substances and, if necessary in the following intermediate pipe to a temperature at which the starting materials sinter, to form this slidable layer between the pipe wall and the product strand.

The friction of the introduced substances on the pipe wall of the intermediate pipe but must be kept so large that by the pressure present in the reaction space the reaction material to be introduced is not pressed back. The friction is in different Affected by: the size of the grinding surfaces, the type of surface and the compression in the conical part. As the type of surface by the temperature is influenced on the surface, the jacket temperature also has an influence the friction.

The method is explained in more detail with reference to FIG. 1. In a feed pipe 1, which has a conical taper 2 and then merges into the intermediate pipe 3, this part 3 having a narrower cross-section than the feed pipe 1, the starting material fed through the feed hopper 4 is and reciprocating piston 5 pressed together. The trapped gas escapes through the hopper 4 and swirls up the filling material.

The starting material can already be introduced when it is introduced, e.g. in the filling funnel or in the feed pipe 1, are preheated to a temperature below the Sintering temperature of the starting materials. The heater can, for. B. with the help of Heating jacket 6 take place. The conically tapered part 2 and the intermediate pipe 3 are provided with heating jackets 7 and 8.

It is advantageous to subdivide the heating jackets several times so that one can set temperature gradients in the pipe. The powdery one introduced at 4 and optionally preheated starting material is compressed by the piston 5. By choosing the slope in the conical part 2 or by changing the length and / or of the cross section of the intermediate pipe 3, the compression ratio is set.

The slope depends on the difference in the pipe diameter and on the length of the conical part.

Since, however, in the following intermediate pipe, especially with consideration on the required frictional resistance, not arbitrarily high product speeds can be achieved is the ratio of the cross section between the feed tube and intermediate pipe to be selected so that when compressed the starting material to a density which corresponds to the specific weight, the ratio of the diameters 1: 1 to 1.5: 1, whereby the cone angle can be up to 90 °. Preferably be Diameter ratios from 1: 1 to 1.2: 1 and cone angles up to 200 are used. The cone angle is to be understood as the angle that occurs when the cone is extended to a cone at the apex of the cone when cutting through a through the cone axis Plane is formed by the cone shell. The friction of the product strands in the intermediate pipe depends on the size and texture of the grinding surfaces. she can also be regulated by the heating. Because with a given apparatus If the dimensions of the pipes are fixed, you will either start the pressing process regulate via the heating temperature or via the applied pressure. It will be the For the sake of simplicity, the temperature control is preferred.

The friction of the product in the intermediate pipe 3 is always so great held that when the piston 5 goes back, the entire prevailing in the reaction tube 9 Pressure is absorbed by the product strand. It is of course advisable for friction to provide a correspondingly large safety factor so that there are small fluctuations in the supply of the starting materials or in the heating of the conical part and of the intermediate tube due to the pressure in the reaction chamber, the pressed material when decreasing Piston is not pressed back.

It has proven to be advantageous in the heating jacket of the intermediate pipe set a temperature gradient, e.g. B. slightly increasing.

By changing the piston stroke and the number of piston strokes in the unit of time you can change the amount of solids fed in and on this In this way, a dosage of the solids can be brought about. Since the method according to the Invention no mixing of the solids takes place when introducing, can in In view of the low thermal conductivity, even very small amounts of starting material well dosed.

In the rearrangement of dipotassium orthophthalate to dipotassium terephthalate is it z. B. expedient to preheat the starting materials to about 280 to 3200 C, to keep the jacket temperature in the conical part at around 320 to 3700 C and in the Intermediate pipe at 360 to 4200 C. You can move in the intermediate pipe in the direction of flow set rising temperatures of the goods, e.g. B. from about 380 to about 4100 C. If the pressure in the reaction space is kept at about 20 to 25 atm, a compression pressure is established applied at around 170 to 190 at. The pressing pressure depends of course on the friction in the conical part and in the intermediate pipe.

This is largely regulated by the heating temperature.

After the intermediate pipe, the pressed starting material enters the Reaction space. This can be designed in a manner known per se, e.g. as Shaft furnace through which the goods to be relocated simply fall through, or in which they are is implemented in the form of a fluidized bed; you can also use a belt oven, how he z. B. is described in German Patent 1,062,701. In the end it is possible, as in F i g. 2 shown, to be designed as a tube 10, whereby one escapes using a metal frit tube 14 Gases that are formed by side reactions in the thermal rearrangement are removed.

Suitable starting materials for the process are, for example Salts, in particular the potassium or thallium (I) salts of monovalent and polyvalent ones Benzene carboxylic acids, such as benzoic acid, phthalic acid, isophthalic acid, hemimellitic acid, Trimellitic and trimesic acid, mellophanic, prehnitic, pyromellitic and mellitic acid. Mixtures of the salts of benzenecarboxylic acids, e.g. B. those caused by oxidation obtained from dialkylbenzenes, especially crude xylene, with air or nitric acid or in the oxidative degradation of higher ring systems or in the treatment of carbon-containing substances such as graphite, bituminous coal, lignite, peat, wood, lignin, Coal extracts, tar, pitch, coke or asphalt, with nitric acid or air are suitable. Naphthalic acid can also be used as starting acids and diphenic acid into consideration. For the production of hydroxycarboxylic acids one starts from Salts of other than the oxyacids to be obtained, e.g. B. of 2-hydroxynaphthalene-1-carboxylic acids or salicylic acid. Salts of heterocyclic carboxylic acids can also be used use aromatic behavior, e.g. pyridine, quinoline, isoquinoline, thiophene, Furanic and pyrrole carboxylic acids.

The preparation of the potassium or thallium (I) salts of the above Acids can be done in the usual way, e.g. in solvents by neutralization the acids with the hydroxides or carbonates of potassium or thallium or by Fusing of the acids or their anhydrides with the hydroxides, carbonates or oxalates of potassium or thallium. Appropriately one avoids that the manufactured Salts contain excess hydroxide or carbonate, but there is an excess of potassium or thallium carbonate for the subsequent heat treatment of the salts not disadvantageous. Instead of the salts of the starting acid itself, mixtures can also be used from the acids or their anhydrides and the potassium or thallium hydroxides or - Use carbonates, from which the salts are then formed in the subsequent heat treatment form.

Instead of the potassium or thallium salts, mixtures of these can also be used Use with the appropriate sodium salts as starting materials. So are suitable E.g. salt mixtures which, in addition to potassium or thallium salts, contain 0.5 to 60 percent by weight Contain sodium salts. Also mixed salts of the cyclic ones used as starting materials Carboxylic acids that contain sodium and potassium or thallium at the same time can can be used for the rearrangement. The salt mixtures are expediently prepared in the manner described in German Patent 1,014,982.

Suitable catalysts are, for. B. oxides, carbonates or halides of zinc, cadmium or bivalent iron. Organic salts of these metals, e.g. B. of the carboxylic acids used as starting materials are particularly good catalysts.

It has been shown that beneficial effects can be achieved if one the components of the reaction mixture, i.e. starting material and catalyst, if possible mixes together evenly.

The temperatures required for the conversion are in general between 220 and 4500 C, advantageously between 350 and 4500 C, in particular between about 400 and 4400 C. For the rearrangement of the also to be produced according to the invention Hydroxycarboxylic acids, however, are less high temperatures required, so that one even with temperatures of 250 to 3500 C.

It has proven to be particularly advantageous for the rearrangement of salts of such carboxylic acids obtained by oxidation of nitric acid, z. B. in the oxidation product obtained from crude xylene with nitric acid, low Amounts of hydrides or carbides, in particular of potassium or sodium, also to be used. These additives reduce the nitrogenous impurities, in particular the cyclic nitro groups obtained as by-products in the oxidation Carboxylic acids, made much easier.

The heat treatment is carried out at elevated pressure, e.g. B. between 5 and 25 at. The pressures can be reduced by forcing inert gases, in particular by carbon dioxide or nitrogen. The presence of oxygen and also water during the heat treatment is undesirable, since this reduces the yields.

The salts obtained during the rearrangement become those to be obtained Dicarboxylic acids made free by treatment with acids or acid salts. Man works expediently in such a way that one obtained after the heat treatment Salts in solution with an acidic substance that releases the acid, in particular carbon dioxide, advantageously under pressure, treated, the resulting solid-liquid mixture, optionally after separating at least part of the liquid with the carboxylic acids, whose salts have served as starting materials, or with their acidic salts, if appropriate with the addition of a solvent, the liberated dicarboxylic acid is separated off and the remaining liquid phase, optionally together with the mentioned, liquid separated from the mixture before the addition of the carboxylic acid is evaporated and the dry residue is used again for the production of dicarboxylic acids.

The process according to the invention makes it possible to use the starting materials to be introduced into the reaction chamber completely free of oxygen. It has also been shown that when using the reaction material pressed in this way, only slight charring phenomena enter. Furthermore, the use of carbon dioxide protective gas is on the filling side generally no longer required. When working according to FIG. 2 can as a result of the high internal pressure achieved here, also within the reaction chamber the use of carbon dioxide can be dispensed with without decarboxylation and thus a decline in yield occurs.

Example 1 With the aid of a piston press corresponding to FIG. 1, which is hydraulically driven and controlled and has a piston diameter of 134 mm, one promotes the advance of the plunger according to the stroke setting the piston path from a reservoir 4 every hour 260 kg approx. 2600 C preheated, dry dipotassium phthalate (bulk density 0.6 g / cm3) in the conical mouthpiece 2 of the press heated to about 3450 C. in the conical part, the diameter is reduced to 112 mm over a length of 176 mm. The dipotassium phthalate was previously given 2% zinc ions as a catalyst in the form of zinc phthalate mixed in. By a multiple subdivided electric heater 7 and 8, which over a temperature controller is regulated to a pipe jacket temperature of approx. 3500 C, The dipotassium phthalate mixture serving as the starting product for the thermal conversion is then heated so long on until the pipe wall in the area of the conical part 2 to about has reached a jacket temperature of 3450 C to the middle of the intermediate pipe 3. Of the following part of the as a connecting pipe between extrusion press and reaction chamber 9 serving intermediate tube 3 with a diameter of 122 mm and a length of 1000 mm is heated to 3900 C. While it is sufficient at the beginning of the loading is to compress the starting material with a piston pressure of 5 to 10 at, this pressure must be due to the compression of the product strand in the conical part 2 continuously increased until it reaches the specified temperatures in the individual pipe parts about 160 to 180 at and then remains constant.

The dipotassium phthalate mixture is pressed into an endless, deformed pore-free and thus gas-free product strand, which has a specific weight of 1.72, under the influence of the prevailing in the compression organs Maximum temperature from heating and frictional heat only the surface of the starting materials is brought to sintering and thereby receives a sliding, glass-like surface. As soon as the plunger has reached its end position, it is reversed and again brought back to its original position. At the next stroke, it will feed the starting material again to the press mouthpiece. The return path of the piston can be changed so that the Product inlet opening can be regulated herewith and together with the freely selectable time period precise dosing of the product quantity is guaranteed with a piston stroke. By the intermittent back and forth motion of the piston eventually becomes that continuous product strand deformed reaction product via the intermediate tube 3 the carbon dioxide pressure under 21 ast and by means of flue gas to 4350 C reaction temperature heated reaction chamber 9 fed to a reaction belt furnace. The product line breaks after it reaches the end of the intermediate tube within the reaction space has, under the influence of its own weight, into smaller pieces, whereby the product evenly fills the trough formed from the link belt. The level the rearrangement mixture in the reaction chamber is measured with the help of a radioactive level measurement by controlling the hydraulic press (lifting height and number of strokes per minute) constant held. The rearrangement of the dipotassium phthalate mixture takes place in the reaction chamber in a manner known per se at a temperature of 4350 C. The dipotassium terephthalate formed sinters to a slag-like, hard mass and fills the whole Interior of the link belt. From the sluice of the belt furnace after a Stay- time of 60 minutes per hour deducted 254 kg of reaction product. The raw product is worked up on terephthalic acid in a manner known per se.

164 kg of pure terephthalic acid are thereby obtained, corresponding to a yield of 92% of theory.

Example 2 In a device according to FIG the one described in Example 1 differs in that the reaction space does not as a gas-filled link belt reaction furnace, but as a heatable high-pressure reaction tube 10 is designed with a diameter of 70 mm, an hourly 45 kg per 3000 C preheated dipotassium phthalate mixture, the previously 1.50 / 0 cadmium in the form of Cadmium phthalate were mixed in, formed into an endless strand of product. That Reaction tube 10, which here takes on the function of the reaction furnace, is in two Parts 11 and 12 divided, both with the help of a mercury heater 13 on a temperature of 4300 C. The first part of the reaction furnace 11 is provided with a casing 14 made of a gas permeable metal frit material exists and has a gas discharge channel 15, while the flanged to it Part 12 has a conical expansion of the pipe diameter after the pipe end. The product strand conveyed from the piston press into the reaction tube 10 is there further heated to about 430 to 4350 C until the product is then passed through the surface sintering in the tube part 11 finally in the last part of the reaction tube 12 has reached the oven temperature of 4350 C and as light gray, hard and stone-like Mass sintered together leaves the reaction tube. The piston pressure is adhered to the specified temperatures constant at 350 at.

The formed in the pipe part 11 when heated to a temperature of 4300 C. small amount of gas, which mainly consists of decomposition products (benzene, carbon monoxide, Water vapor) of the phthalate molecule is continuously removed with the help of the metal frit insert 14 discharged via the gas discharge channel 15, since when working without gas discharge the gas bubbles trapped in the product under the effect of the high temperature often lead to spontaneous product breakouts and trouble-free implementation is impossible do. The raw terephthalate removed every hour gives, after working up on terephthalic acid, as described in Example 1, 28.4 kg of pure terephthalic acid, corresponding to one Yield of 93.5 ovo of theory.

Example 3 In a device as described in Example 1 a mixture of 178.5 parts of potassium nicotinate is produced every hour with the aid of the piston press and 81 parts of sodium nicotinate, which is intimately with 5.6 parts of cadmium oxide as a catalyst was mixed, at a temperature of 240 to 2600 C to form an endless strand of product deformed and continuously held in a carbon dioxide pressure of below 20 atm and 3600 C. Pressed in reaction belt furnace. After a dwell time of 55 minutes, the sintered together, pyridine-containing reaction product discharged from the reaction chamber via a lock and after dissolving in water, treating with active charcoal and acidification worked up to a p-value of about 1.5 on pyridine-2,5-dicarboxylic acid. You get after drying, 127.5 parts thereof with a melting point of 248 to 2490 C.

The same procedure can be used under the same reaction conditions also other heterocyclic dicarboxylic acids, such as 2,5-thiophenedicarboxylic acid from 2,4-thiophenedicarboxylic acid, 2,5-furandicarboxylic acid from 2,4-furandicarboxylic acid and 2,5-pyrroledicarboxylic acid from 3,4-pyrroledicarboxylic acid, be obtained in a known manner by rearrangement of the corresponding potassium salts.

Example 4 500 parts of a mixture of 500 parts are produced every hour of the dipotassium salt of naphthalene-1,8-dicarboxylic acid and 22 parts of cadmium oxide as a catalyst with the same device as in the example 1 indicated, deformed in an extruder at 3400 C to form an endless strand of product and entered into a reaction furnace which is under 30 atmospheres of carbon dioxide pressure and is kept at a temperature of 4350 ° C.

The one discharged through a lock after a dwell time of 75 minutes gray discolored, together sintered reaction product is after in a known manner Dissolving in water and separating off the catalyst fraction worked up by acidification. 365.5 parts of naphthalene-2,6-dicarboxylic acid are obtained.

Claims (4)

Claims: 1. Process for continuous thermal rearrangement of salts of mono- or binuclear aromatic or heterocyclic, self-aroma; carboxylic acids with increased behavior Catalytically more effective in the presence of pressure Metal compounds, in which the starting materials in compact form in the reaction chamber are introduced, characterized in that the finely powdered solid starting material introduces into a feed pipe, in this pipe by a reciprocating Piston, if necessary at a conically drawn-in point, compressed and the The product obtained in this way passed through an intermediate tube which had a smaller diameter than the feed pipe, with such high wall friction in the under the for the thermal reaction required pressurized reaction space that the product strand is not pressed back by the pressure in the reaction chamber. 2. The method according to claim 1, characterized in that the from the possibly heated to a temperature below the sintering temperature Starting materials obtained product strand in the compression and optionally heated in the intermediate tube on the surface until sintering. 3. The method according to claim 2, characterized in that the conically drawn-in point of the pipe and the intermediate pipe over several heating circuits, which allow a step-by-step heating. 4. The method according to claim 1 to 3, characterized in that one the thermal rearrangement of the starting material, which has been formed into an endless strand of product makes in an elongated reaction space, which is attached to the intermediate tube in directly connected in the same direction and conically widened can be considered Drawn pamphlets: German Patent Nos. 1 028 577, 1 062701.