Title of Invention

"A PROCESS FOR IMPROVING THE YIELD OF PURE PRODUCTS FROM CRUDE ANTHRACENE"

Abstract

A process for improving the yield of pure products from crude anthracene, characterized in that the distillation is carried out m two steps, and that in the first step a fraction from a boiling range of 280 to 320°C at normal pressure is separated as a top product; the bottom of this column is fed carbazole residues, and in a second column this mixture is separated into anthracene and carbazole fractions.

Full Text

The invention relates to a process for improving the yield of pure products from crude anthracene, and more particularly to a continuous distillation process for improving the yield of pure products from crude anthracene. Crude anthracene is a crystal fraction which is obtained by suspension crystallisation of anthracene oil, a boiling fraction of about 300 to 400°C of crude tar refining. Crude anthracene is a mixture of various condensed aromatic compounds. The principal components are phenanthrene, anthracene and carbazole, apart from many other aromatic compounds. Due to the complex composition, this raw material is not used directly in the manufacture of pure products by crystallisation if several ingredients are tc be obtained. From H.--G. Frank, J.W. Stadelhofer, Industrielle Aromaten-chemre [Industrial aromatics chemistry], Springer-Verlag (198'), p. 355/356 it is known for crude anthracene to be subjected to a distillation process. In this way, enrichment of the anthracene of approximately 50% is obtained. Subsequently, reprocessing to pure anthracene with a content exceeding 95% takes place by recrystallisation in polar solvents. A. disadvantage of this process is that the anthracene obtained in this way contains a considerable amount of low-ociling components, in particular diph.enyle.ne oxide, which can have an undesirable effect in certain applications. Due to its origin, the raw material crude anthracene -which is used to obtain, by distillation, the anthracene-and carbazole fractions - contains mainly carbazole as a high-boiling component. For reasons of operational safety, the known distillation bottom cannot be operated free of carbazole, because the column must be operated with a minimum bottom draw-off in order to compensate for heat losses in the bottom pipes and in order to suppress excessive dwell times in the bottom, which lead to carbonisation. It is therefore the object of the invention to avoid the above-mentioned disadvantages. This object is accomplished by a process for improving the yield of pure products from crude anthracene, by carrying out the distillation in two steps, whereby in the first step a fraction from a boiling range of 280 to 320°C at normal pressure is separated as a top product; the bottom is fed carbazole residues from this column and, in a second column, this mixture is separated into anthracene- and carbazole fractions. Accordingly, there is provided a process for improving the yield of pure products from crude anthracene, characterized in that the distillation is carried out in two steps, and that in the first step a fraction from a boiling range of 280 to 320°C at normal pressure is separated as a top product; the bottom of this column is fed carbazole residues, and in a second column this mixture is separated into anthracene and carbazole fractions. The process according to the invention makes it possible to obtain a disphenylene oxide/fluorene fraction, free of anthracene, as a top product in the first distillation step. This fraction can be fed directly into the crystallisation to obtain fluorene. Further advantages arise because the recycling of carbazole contents from crystallisation, back into the distillation, significantly increases the yield of pure carbazole in relation to the use of crude anthracene, because to a large extent, crystallisation losses are collected again through distillation. Furthermore, recycling of crystallisation residues with a high content of carbazole and bottom components leads to an increase in the carbazole. concentration in the feed of the distillation column and to an increased load of the critical distillate part of the column. When observing the minimal bottom draw-off quantity, the distillation bottom can be operated hotter and thus leaner in carbazole. In this way, carbazole losses by way of bottom feed are minimised and the carbazole yield of the process is further improved. According to a preferred embodiment of the invention, part of the bottom of the second distillation column is drained off and fed again into this distillation column. According to a further preferred embodiment, the top fraction containing phenanthrene is removed. According to another preferred embodiment of the process according to the invention, a diphenylene oxide/fluorene fraction, free of anthracene, is obtained as a top product of the first distillation step. Preferably, distillation is carried out: in plate columns. The carbazole residues used according to the invention originate from the carbazole crystallisation, to which the carbazole fraction obtained in the second distillation column is subjected. Apart from approximate 40% by weight of carbazole, these residues predominantly contain high-boiling and thus bottom-forming components. The following is a comparison of the product qualities of the process according to the invention with that of prior art. (Table Removed) These results clearly show the superiority of the process according to the invention. Process flow chart 1 schematically explains the process according to the invention; process flow chart 2 relates to the state of the art. Below, by way of an example, one embodiment of the process according to the invention is described. Molten crude anthracene is fed into the column and at the head of this column a fraction of the boiling range from 280 to 320°C (at normal pressure) is removed. This fraction, free of anthracene can be fed directly into crystallisation for obtaining fluorene. The bottom product of column 1, which has been freed of light-boiling components, together with carbazoie residues, a by-product of obtaining carbazole, is fed into in-line column 2. Furthermore, part of the bottom of column 2 is fed back as feed into column 2. At the head of column 2 a fraction of the boiling range 320 to 335°C (at normal pressure) is removed; the principal constituent part of this fraction is phenanthrene. The anthracene fraction with a boiling range from 335 to 3 4 5°C (at normal pressure) and the carbazole fraction with a boiling range from 345 to 370°C (at normal pressure) are removed as lateral cuts. The high-boiling components as well as a part of the fed-m carbazole are removed during operation, by way of the bottom of column 2. Feeding the carbazole residues into column 2 serves the purpose of increasing the bottom loa¬ding of column 2 with high-boiling components beyond carbazole, and to utilise the carbazole contents of this material stream in obtaining the carbazole fraction. The partial recycling of the bottom of column 2 back into the feed of the column also serves to increase the load of the cist ill ate part of the column. This allows a respective higher loading of the buoyancy part. In this way, the reflux ratio at the top of column 2 can be increased which in turn leads to an increase in efficiency of the column in the buoyancy part. In order to obtain pure products from the fractions of crude-anthracene processing by distillation, the fractions -- in particular the fractions containing fluorene, anthracene and carbazole - are fed to a solvent cry¬stallisation, preferably by using polar solvents. Such solvents are for example dimethylformamide, N-methyl-pyrro-lidone, acetophenone and cyclohexanone. Crystallisation can take place in stirred cooling apparatus in batch operation. Solvent content and cooling end temperatures during crystallisation are set depending on the material properties of the fractions and the desired product purities. In order to separate the pure products from the original solution, it is preferable to use a centrifuge. Ef necessary, the solid material obtained by the centrifugal process can be subjected to in-line drying in order to remove the solvent contents of the pure products. Compositions of pure products according to the invention are those of fluorene, anthracene and carbazole. With the known one-step distillation process, no fluorene fraction was available. Fluorene obtained by solvent crystallisation showed significant anthracene contamination, because it was hardly possible to separate the anthracene by crystallisation. The fluorene-pure products composition obtained according to the invention is low in anthracene and contains at the most approximately 5% by weight, preferably 3% by weight, and in a particularly preferred rrariner less than 2% by weight of anthracene. The composition of pure products containing anthracene contains less than approximate 60 ppm, preferably approximately 1 to 40 ppm, of diphenylene oxide. The composition of pure products containing carbazole contains more than 94 % by weight, preferably more than 9 6% by weight, of carbazole. The following tables show typical compositions of pure products obtained by solvent crystallisation of fractions of crude anthracene processing by distillation according to the invention. Fluorene (Table Removed) Anthracene (Table Removed) Carbazole (Table Removed) Due to the two-step processing by distillation of the crude anthracene, the quality of the composition of pure products in relation to the content of low-boiling components could be significantly improved. Diphenylene oxide is to be regarded as the standard sample of a component for these compounds. Thus a quality of anthracene can be produced from the raw material crude tar which in regard to contamination by low-boiling components, can compete with material from the anthracene synthesis. This considerably improves the fields of application of this product obtained according to the invention. This is particularly the case for use in wood processing for obtaining pulp. Example Feed 2370 1/h of crude anthracene, molten at approximate 2 8 0°C into column 1 which has a diameter of approximate 2 m with at least 20 plates. With a reflux ratio R/D of 50/1 and a top pressure of approximate 12 0 mbar, about 2 60 1/h of fluorene fraction are drawn off at the top of column 1. The bottom product, practically free of diphenylene oxide, is fed into column 2, which has a diameter of 2 m and at least 60 plates, at a rate of approximate 2110 1/h, together with approximate 390 1/h of molten carbazole residues. In addition, approximate 1000 1/h bottom of column 2 are fed back as feed into this column. With a reflux ratio R/D of 2 0/1 and a top product of approximate 300 mbar, at the top of column 2 approximate 320 1/h of phenanthrene fraction are drawn off. Approximate 1070 1/h of anthracene fraction are drawn off at the upper lateral draw-off tray of column 2; and approximate 730 1/h of carbazole fraction at the lower lateral draw-off tray of column 2. The fluorene fraction which is free of anthracene; the phenanthrene fraction; the anthracene fraction which is free of low-boiling components; and the carbazole fraction, are subsequently processed in the known manner by recry-stallisation, so that in the case of anthracene a product with a diphenylene oxide content WE CLAIM:- 1. A process for improving the yield of pure products from crude anthracene, characterized in that the distillation is carried out in two steps, and that in the first step a fraction from a boiling range of 280 to 320°C at normal pressure is separated as a top product; the bottom of this column is fed carbazole residues, and in a second column this mixture is separated into anthracene and carbazole fractions. 2. A process as claimed in claim 1, wherein that part of the bottom of the second column is drained off and fed into the column again. 3. A process as claimed in any one of claims 1 or 2, wherein the top fraction containing phenanthrene is removed. 4. A process as claimed in any one of claims 1 to 3, wherein a diphenylene oxide/fluorene-fraction free of anthracene is removed as a top product of the first distillation column. 5. A process as claimed in any one of claims 1 to 4, wherein the distillation is carried out in plate columns. 6. A process as claimed in any one of claims 1 to 5, wherein the fractions obtained, which contain anthracene, carbazole, phenanthrene and fluorene, are processed to obtain anthracene, carbazole, phenanthrene or fluorene. 7. A process as claimed in claim 6, wherein the fractions obtained, which contain anthracene, carbazole, phenanthrene and fluorene, are processed by solvent crystallisation. 8. A process as claimed in claims 1 to 7, wherein the anthracene obtained in such a way is oxidised to anthraquinone. 9. A process for improving the yield of pure products from crude anthracene substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

Documents:

861-del-1997-abstract.pdf

861-del-1997-claims.pdf

861-del-1997-correspondence-others.pdf

861-del-1997-correspondence-po.pdf

861-del-1997-description (complete).pdf

861-del-1997-drawings.pdf

861-del-1997-form-1.pdf

861-del-1997-form-13.pdf

861-del-1997-form-19.pdf

861-del-1997-form-2.pdf

861-del-1997-form-3.pdf

861-del-1997-form-4.pdf

861-del-1997-form-6.pdf

861-del-1997-pa.pdf

861-del-1997-petition-137.pdf

861-del-1997-petition-138.pdf