FR2587994A1 - Removing heterocyclic impurities from poly:cyclic aromatic amine(s) - Google Patents

Abstract

Polycyclic aromatic cpds. are freed from heterocyclic impurities by treating technically pure aromatic cpds. with hydrogen at 230-350 deg. C for 3-5 hours at 25-80 bar in the presence of presulpherised molybdenum, cobalt/molybdenum, nickel/tungsten or nickel/molybdenum catalysts and then with the same catalyst at 300-380 deg. C under an inert gas for 5-10 hours. The aromatic cpds. are pref. dissolved in a 12-16 C satd. aliphatic hydrocarbon as solvent.

Description

Process For obtaining aromatic compounds, free of etherocytes.

 The invention relates to a new process for the purification of multinuclear aromatic compounds, in particular for the elimination of compounds containing sulfur, nitrogen or oxygen. Such aromatic compounds consist of materials contained in the tar and are obtained during the reprocessing of tar oils in different fractions. By subsequent purification steps such as redissolution, dephenolation, de-basification or special recrystallizations, technically pure aromatic products are isolated from these fractions.

However, despite the multiple purification processes, small amounts of heterocycles are still attached even to these pure aromatics, zen as accompanying boiling and crystallization products. Separation of these impurities is only possible at considerable cost, which makes high purity aromatics economically unattractive.

 On the other hand, it is precisely for specific fields of application such as for example the subsequent transformation into di- or tetracarboxylic acid of naphthalene and its use for special polymers, that aromatic products free of d heterocycles containing sulfur, nitrogen or oxygen.

 The object of the invention is therefore to provide a process making it possible to obtain, as simply and as economically as possible, polynuclear aromatic products free of heterocycles.

 This object is achieved by treating technically pure aromatic products on presulfurized catalysts of molybdenum, cobalt / molybdenum, nickel / tung stene, or nickel / molybdenum at a temperature of 230 to 350 ° C. and under a pressure in the field. from 25 to 80 bars (cold pressure) for 3-5 hours with hydrogen, then on the same catalyst at a temperature of 300 to 380-C under inert gas for 5-10 hours and then subjected to a treatment of 'elaboration.

 In an advantageous embodiment of the above process, the aromatic compound is dissolved in a solvent during the reaction.

 In another advantageous embodiment of the above process, a saturated aliphatic hydrocarbon having 12 to 16 C atoms is used as solvent.

 In another advantageous embodiment of the above process, the aromatic compound is pyrene.

By treating petroleum, it is known to remove heterocycles from distillates by hydrogenating them. As catalysts, use is made of molybdenum, cobalt / molybdenum, nickel / molybdenum or nickel / tungsten presulfurized catalysts (Winnacker-Küchler; Chemische Technologie, 4th
EditioR, Vol. 5, Page 112 et seq.).

 It has now been found that when technically pure aromatics having two or more rings are treated with the same catalyst systems by hydrogenation under conditions known per se, the heterocyclic accompanying impurities are also cleaved into easily separable fractions .

 It should however be noted that in this case, up to 40% of the aromatic products are also hydrogenated so that, as reaction product, a mixture is obtained which contains, in addition to the solvent optionally used and decomposition products. heterocycles, aromatics and various hydroaromatics. The separation and in particular the decomposition of these hydroaromatic products into pure products is extremely expensive so that this purification process by hydrogenation known per se is not advantageous for obtaining pure aromatic compounds for economic reasons.

 Surprisingly, however, it has now been found that the hydroaromatic products formed are again dehydrogenated in the reaction mixture respectively on the same catalyst, when the reaction mixture is heated under inert gas or when a jet of inert gas is directed at through the heated reaction mixture. The dehydrogenated reaction mixture thus obtained contains the aromatic products in addition to the easily separable solvent and the reaction products obtained from heterocycles. By the combination of the two reaction stages, namely hydrogenation and dehydrogenation, with subsequent recrystallization or decomposition by distillation , there is thus obtained from an aromatic fraction containing heteroatoms the corresponding aromatic compound free of heteroatoms, in a simple and economical manner.

 Using the process according to the invention, it is possible to obtain aromatic compounds free of heterocycles which contain two or more nuclei in the molecule, such as, for example, naphthalene, anthracene, phenanthrene, chrysene, fluoranthene or pyrene.

These aromatic products are either used in the form of a solvent or in the form of a solution in a solvent. As a solvent, saturated aliphatic hydrocarbons having 12 to 16 C atoms are found to be suitable.

 As catalysts, consideration is mainly given to oxides of CoMo and oxides of NiMo, but also oxides of Mo, CoW and NiW on a support of w-Al 2 O 3. Initially, the respective oxides are presulfurized in a manner known per se, that is to say transformed into the sulfurized form activated in a jet of H2 / H28. The optimal activity of an industrial CoMo catalyst is obtained at presulfurization temperatures between 400 and 530-C.

 To carry out the process, the aromatic compound or its solution with approximately 2 to 5% by weight of the presulphurized catalyst is introduced into an autoclave.

The oxygen present is removed from the gas zone by rinsing with an inert gas. Then, hydrogen is introduced under pressure up to a pressure of 25 to 80 bars (cold pressure) and the complete mixture is heated with occasional or continuous mixing to a temperature of 230 to 350-C and maintained in this temperature range for a period of 3 to 5 hours.

 After cooling, when the reaction is complete, the mixture is relaxed and the reaction mixture is rinsed with inert gas to remove the hydrogen residues and the decomposition products of heterocycles, in particular H2S, NH3 and H20.

 Then, the operating step of dehydrogenation is carried out on the same catalyst by treatment for 5 to 10 hours under inert gas at a temperature of 300 to 380 μl. As the inert gas, noble gases, carbon dioxide or nitrogen can be used.

 The inert gases are either also brought under pressures of 20 to 80 bars on the reaction mixture, or are directed during the treatment in the form of a gas stream through the reaction mixture. When the dehydrogenation is complete, the product obtained is reprocessed in a manner known per se by distillation or crystallization.

 Insofar as the final product obtained still contains hydrogenated aromatic products, these can be completely transformed into the aromatic compound by repeating the dehydrogenation step.

Example
125 g of technically pure pyrene and 3.75 g of presulfurized catalyst (BASF M8-21, NI / Mo on Al203 as support) are introduced into a 500 ml autoclave equipped with a stirrer in 200 ml dodecane (about 90-95%, boiling point 213-216XC). Pyrene contains the following secondary components: dihydropyrene (0.14%), fluoranthene (1.18%), phenanthothiophene (1.50%), brazane and benzofluorene (0.48%) as well as azafluoranthene (0.1%).

 After closing the autoclave, rinse twice with N2 at 50 bars to expel the air. Then, H2 is introduced at 50 bars and heated for 4 hours at a temperature of 320 ° C. After the autoclave has cooled to room temperature, it is relaxed and rinsed twice with N2 at 50 bar with stirring.

N2 is again introduced at 50 bars and the mixture is heated for 8 hours at a temperature of 320 ° C.

 After cooling to room temperature and expansion of the autoclave, the crude product is separated from the solvent by filtration. For the separation of the catalyst, it is introduced into the extraction cartridge of a Soxhlet extraction apparatus and extracted with acetone. The acetone extract is concentrated to approximately 500 ml on a rotary evaporator. The product separates out by crystallization in a freezer. It is separated from the mother liquor by filtration and dried in a vacuum desiccator on Cal2. The product contains, in addition to pyrene, dihydropyrene (5.87%) and fluoranthene (0.04 's).

 Composition of the reaction mixture before the dehydrogenation stage: pyrene (61%), dihydropyrene (26%), more hydrogenated pyrene derivatives (11%), phenanthrothiophene breakdown products, i.e. phenanthrene and hydrogenated phenanthrene derivatives (2 o)

Claims (4)

 î. Process for obtaining polynuclear aromatic compounds free of heterocycles, characterized in that the technically pure aromatic products are treated on presulfurized catalysts of molybdenum, cobalt / molybdenum, nickel / tungsten, or nickel / molybdenum at a temperature from 230 to 350 C and under a pressure in the range of 25 to 80 bars (cold pressure) for -3-5 hours with hydrogen, then on the same catalyst at a temperature of 300 to 380 "C under gas inert for 5-10 hours and then subjected to processing.  2. Method according to claim 1, characterized in that the aromatic compound is dissolved in a solvent during the reaction.  3. Method according to claim 2, characterized in that as a solvent, a saturated aliphatic hydrocarbon having 12 to 16 C atoms is used.  4. Method according to claims 1 to 3, ca acterized in that as aromatic compound is used pyrene.