SE186945C1 - - Google Patents

Description

Inventors: R B Egbert, R Landau and A Saffer Priority as of May 10, 1954 (USA) This invention relates to a process for the preparation of phthalic acids comprising a major proportion of terephthalic acid or a major proportion of isophthalic acid.

Terephthalic acid is a commercially valuable intermediate for the production of polyester-type resins and also for the production of polyester-type textile fibers, such as the polymeric ethylene glycol terephthalate. Isophthalic acid is also a commercially valuable intermediate for the production of polyester type resins.

It is a special problem to produce these acids economically.

The reactions between benzene or toluene and lower olefins in the presence of acid-reacting alkylation catalysts, such as aluminum chloride, to give mixed rings of the various types of substitution products and their isomers. Under equilibrium conditions, the various modifications occur in some cases in approximately equal amounts, and difficulties or high costs associated with their separation are a serious disadvantage from an industrial point of view.

The present invention intends to solve the above problem resp. Avoid the above disadvantages.

The process according to the invention is characterized in that benzene or toluene is alkylated at a temperature of 50 to 110 ° C with an olefin having 2 to 4 carbon atoms in the molecule in a molar ratio of 1.6 to 2.5 moles of olefin per mole of benzene or a molar ratio of 0.8 to 1.5 moles of olefin per mole of toluene and in the presence of aluminum chloride either in a low concentration of, for example, about 0.5% by weight, the pH of the aromatic reactant is a high concentration of, for example, about 2.5% by weight of aluminum chloride, shaved off the aromatic reactant, to form a dialkylbenzene fraction containing a major proportion of meta-isomer, that the dialkylbenzene fraction formed from the alkylation mixture formed by the alkylation reaction , containing a major proportion of terephthalic acid or isophthalic acid, and that single isomeric phthalic acids are separated from the mixture of isomeric phthalic acids.

Oxidations with molecular oxygen of the recovered dialkylbenzene fraction to a mixture of phthalic acids suitably take place in the presence of a heavy metal catalyst.

A modification of the process according to the invention can be characterized in that the monoalkylbenzene and the trialkyl and the higher alkylated benzenes in the carbonate mixture obtained by the alkylation are recycled to the alkylation step and that the molar ratio between olefin and benzenoid compound is controlled sh. that one mole of ph sh sat introduced alkyl group constitutes the equivalent of one mole of olefin.

Orthophthalic acid can be separated from the isomeric mixture of phthalic acids by heating so that it is converted to the phthalic anhydride and, sh. that this at the same time evaporates the Iran mixture. The meta- and paradicarboxylic acids can be separated by conversion to the corresponding dialkyl esters by reaction with a lower alkanol under pressure or in the presence of an acid-reacting catalyst, and these esters can be separated by fractional distillation and optionally converted back to the corresponding acids by hydrolysis with dilution dehydration of acid.

In order to facilitate the understanding of the invention, the following special examples are omitted.

Example 1. In a suitable reaction vessel having a fringe resistant surface (e.g. glass, ceramic, corrosion resistant metal or alloy), equipped with a non-agitator, such as a gas blower or a mechanical agitator, and with heating devices or cooling the contents of the vessel, such as a loop or jacket, an afer river condenser, a gas inlet pipe and optionally an outlet for diverting low boiling material, are charged: 9 parts by weight of aluminum chloride, 1700 parts of benzene (ap or thiophene free), 6.8 parts of isopropyl chloride (or anhydrous chlorine level). 1930 parts of propylene (for example 99% propylene gas) are absorbed therein over a period of about 2.5 hours with stirring, while the temperature is in the range of about 65-100 ° C. print. This temperature can be maintained either by passing cooling water through the indirect heat exchange device or by allowing the mixture to boil and condensate being brought back from there if the temperature tends to rise Mgt, or by passing water vapor through these devices if the temperature tends to drop.

The reaction mass is then cooled to room temperature, for example indirectly with the aid of cooling water, and then poured into about 500 parts of water. Then about 100 parts of about 18% aqueous solution of hydrochloric acid was added, and the resulting mixture was stirred for about a quarter of an hour. The mixture is then allowed to stand, forming two layers. The upper carbonate layer is recovered, washed with about 550 parts of about 10% aqueous sodium hydroxide solution and then with about 800 parts of water and then dried by azeotropic distillation of the water with the lower boiling carbonate present. The carbonate is then fractionated in an efficient column, after which the following analysis is obtained (as a percentage by weight): Hexane O Benzene 8.0 Cumene 11,7 Diisopropylbenzene28.2 Triis, opropylbenzene50.3, Tetraisopropylbenzene1.8 29.9% of the metaisomer and 4.4% of the orthoomer.

This dialkylbenzene fraction is charged into a reaction vessel of the above type together with a small portion of an oxidation catalyst, such as, about 1% by weight of manganese halide, and air or other gaseous oxygen material is introduced, while the mixture is stirred and kept at a temperature of about 160-250 °. C. For example, a reaction medium was added, for example an equal amount by weight of acetic acid (100%).

For example: 125 parts by weight of para-diisopropylbenzene (98% para and 2% meta) 125 parts of acetic acid (100%) 2.0 parts of manganese bromide (MnBr 2) The reaction vessel is filled, about half with the liquid mixture.

Air is fed into the reaction mixture in an amount of 400 liters (measured at atmospheric pressure and at about 27 ° C) per hour, while the reaction mixture is melted at 180 ° C with vigorous stirring for 4 hours, and pressurized at about 21-28 kg / cm 2. This pressure is such that the reaction mixture contains a liquid phase containing lower carbonic acid.

The crude solid terephthalic acid in the mixture is separated by filtration, washed three times with about 100% acetic acid, accustomed to washing with about 100 parts by weight of acetic acid per 40 parts of form, and then washed three times with water using approximately the same amounts. The washings obtained with the attic acid are distilled. The residue can be recycled to the reaction vessel or treated to recover isophthalic acid.

Drainage, the gases from the reaction vessel were passed through two carbon dioxide traps in series, and the liquid collected during the reaction was washed with about two volumes of water to remove waterlogged materials and then added to the above filtrate. The filtrate was then combined with the residue, an Iran attic acid slurry, and the mixture was distilled.

The distillation was continued until the temperature reached 139 ° C at 1-2 mm Hg pressure. The distillation was then continued up to a temperature of 250 ° C at Hg pressure.

The residue remaining in the reaction vessel was resinous and carbonaceous. The destination fractions can be returned to the reaction vessel, for example in the next experiment.

A yield of 52.4% terephthalic acid is obtained in this 4 hour experiment. The filtrate and the liquid residues contain intermediates which can be added to the oxidation step to obtain more terephthalic acid, for example up to about 90% by weight of the portion originally charged to the flask. The reaction can be carried out under pressure, suitably so that the lower acid medium is dissolved in a liquid phase, for example 28 kg / cm 2. The solid dicarboxylic acids are separated by filtration and optionally washed with acetic acid (100%), and then the mixture is separated into its constituents. Any phthalic acid present can be removed by heating, for example up to 200 ° C, to dehydrate it and evaporate the phthalic anhydride formed, which can be recovered by condensation of the anta.

The remaining mixture of isophthalic acid and terephthalic acid can be separated by conversion to the corresponding dimethyl esters by reaction with methanol under elevated pressure or in the presence of dilute aqueous hydrochloric acid, and the esters formed can then be separated by fractional distillation.

After separation, the dimethyl terephthalate and dimentyl isophthalate are useful as such for conversion to polyester material by reaction with suitable polyhydric alcohols, thorn ethylene glycol, glycerol or the like. If the acid is desired, the ester can be hydrolyzed with dilute aqueous hydrochloric acid and the resulting terephthalic or isophthalic acid obtained.

Example 2. The above procedure is followed with the exception that the amount of aluminum chloride is increased about four times and the amount of isopropyl chloride is increased about seven times. The formed carbonate layer leaves on fractionation the following analysis: Hexane 0.3 Benzene 0.7 Cumene 14.4 Diisopropylbenzene 57.7 Triisopropylbenzene 26.9 Tetraisopropylbenzene This layer contains 56% of the methadiisopropylbenzene, together with 40% of the paraisomer and 4% of the ortho isomer.

Upon oxidation as described above, the corresponding dicarboxylic acids are obtained.

It can be seen from the above that by using a very low catalyst concentration to obtain an equilibrated alkylation system it is possible to obtain a dialkylbenzene fraction containing a major part of the paraisomer, and this gives an acid mixture containing a major proportion of terephthalic acid.

On the other hand, if one works with much larger proportions of the catalyst under so-called iron weight ratios, a diisopropylbenzene fraction containing a larger part of the metaisomer is obtained, and upon oxidation it leaves a mixture of aryl dicarboxylic acids containing a larger part of isophthalic acid.

Undesirable or with the above comparable results are obtained with various modifications, as follows: The reaction time may be from 0.1-10 hours, preferably 0.5-4 hours. Higher temperatures are usually associated with shorter times, and the time and temperature are chosen to obtain the desired conversion at the desired throughput speeds. Additional aluminum chloride as a catalyst may be added as needed (for example determined by a soul sample to challenge alkylation reaction with use as catalyst, of a prey of the sludge which is recycled for catalytic activity). The spent catalyst is treated with water containing 15-30% of hydrochloric acid to break up the catalyst complexes, and the resulting hydrocarbon phase is precipitated and reused in the system.

Easily available olefin materials can be anyandas, preferably free from other unsaturated materials. The reaction system may be provided with outlets for diverting low boiling hydrocarbons which do not react within the system. Any acidic monoalkylbenzene or tri- or higher alkylbenzene separated from the hydrocarbon product layer can be returned to the alkylation step. Benzene or toluene rea-. gensen bora be free frail other aromatic compounds, but they may contain some paraffins, which may be separated from the system. Lamply, they have low sulfur content and Oro preferably sulfur-free.

In the reaction with benzene, 1.6 to 2 moles of the olefin reagent are used, preferably 1.8-2.0 moles, and preferably about 1.9 moles. In the reaction with toluene, 0.8 to 1.5 moles of the olefin reagent were used, suitably 0.9 to about 1.2, and preferably about 1.1.

The catalytic material used in the oxidation reaction may be a heavy metal compound, for example a compound of any of the following metals: lead, manganese, jam, nickel, cobalt, chromium, vanadium, copper, mercury. Mixtures thereof may be used and the compounds may be in the form of the oxide, hydroxide, halide or organic salts of the metals or combinations thereof. The organic salts may be salts of one or more of the acids formed in the reaction system or of carboxylic acids, such as acetic acid and the other lower fatty acids, naphthenic acids and the like. These can be prepared on the edge The oxidation can be carried out in the presence of a medium for the carbonate, which medium is relatively indifferent to the oxidation in the system, such as. benzene, or the like, or halogenated aromatic liquid or a lower aliphatic acid or a lower araliphatic acid, such as acetic acid, propionic acid, butyric acid, valeric acid, isosmorphic acid, phenyl acetic acid, beta-ethoxyacetic acid and the like. The solution may contain from about 10 to 90% of the medium, preferably 12-40%. In addition - it may contain an organic peroxide or a material which easily forms such a peroxide in the presence of gaseous oxygen, such as benzoyl peroxide, perbenzoic acid, peracetic acid, acetaldehyde and similar aldehydes having 3-5 carbon atoms in the molecule, acetone and similar ketones containing 4 -6 carbon atoms in the molecule, diethyl ether and similar ethers containing 5-10 carbon atoms in the molecule, hexane, cyclic hexane and similar olefins containing 7-12 carbon atoms in the molecule and the like, or inorganic peroxides. These may be present in a concentration of about 0.05 to about 25% shaved by the weight of the carbonate subjected to oxidation.

The lower olefins used contain from 2-7-4 carbon atoms, but the total amount of alkyl carbon atoms in the dialkyl compound should be from 3 to about 8, preferably with an upper limit of 6, and the children do not contain any tertiary butyl groups. In the case of diethylbenzenes, preparation with the aluminum chloride catalyst gives an approximately equal distribution of the broad isomers.

The Mr esterification using lower alcohol may contain 1-4 carbon atoms and methanol is preferred.

The filtrate of the reaction mixture obtained from the oxidation reaction can be recycled to the oxidation step to obtain higher yields of acids based on dialkylbenzene charged or consumed. Optionally, the filtrate can be treated for the extraction of all dicarboxylic acids and for the removal of water from recirculation.

It is very surprising that the process according to the invention can be carried out in such a simple manner with high conversions while maintaining a substantially theoretical yield of the desired product. This is especially true when considering the complex and expensive methods previously used for the production of terephthalic acid or ice ophthalic acid.

It is clear that variations and modifications may be made in the process described above without departing from the scope of the invention.

Claims (3)

Patent claim: A process for the preparation of phthalic acids comprising a major portion of terephthalic acid or a major portion of isophthalic acid, characterized in that benzene or boluene is alkylated at a temperature of 50 to 110 ° C with an olefin having 2 to 4 carbon atoms in the molecule in a molar ratio of 1 , 6 to 2.5 moles of olefin per mole of benzene or, a molar ratio of 0.8 to 1.5 moles of olefin per mole of toluene and in the presence of aluminum chloride either in a low concentration of, for example, about 0.5% by weight, aromatic reactant, for Mining a dialkylbenzene fraction containing a major portion of paraisomers, or in a high concentration of, for example, about 2.5% by weight of aluminum chloroated on the aromatic reactant, to form a dialkylbenzene fraction containing a major portion of the meta-isomer, from the carbonate mixture formed by the alkylation reaction, that the recovered dialkylbenzene fraction is oxidized to the corresponding the formation of phthalic acids, containing a stone portion of terephthalic acid or isophthalic acid, and that individual isomeric phthalic acids are separated from the Iran mixture of isomeric phthalic acids. Modification of the process according to claim 1, characterized in that the monoalkylbenzene and trialkyl, and the higher alkylated benzenes in the alkylate mixture obtained by the alkylation are recycled to the alkylation step and the molar ratio of olefin to benzenoid compound is regulated so that one alkyl of salt the equivalent of one mole of olefin. 3. A process according to claim 1 or 2, characterized in that orthophthalic acid is separated and recovered from the isomeric mixture of phthalic acids in the form of its anhydride. Request publications: