US1742258A - Discontinuous distillation of tars - Google Patents

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DISCONTINUOUS DISTILLAT ION OF TARS Filed novfzs, 192s Patented Jan. 7,1930 p v UNITED STATES PATENT OFFICE LEOPOLD F IBEPJLIN-DLHLEM, GERMANY DISCONTINUOUS DISTI LLATION or TABS Application filed November 26, 1923, Serial No. 677,187, and in Germany December 20, 1922.

The present invention refers to the distiltar is gradually vapourizedso destructive dislation of tars, especially coal-tars but also tillation is as far as possible obviated and other tars and has the object, to obtain the the vapours are directly and immediately final distillates, ready for the market, difractionated or dephlegmated, the condensed rectly from the tars. portions or fractions being returned to the 50 Hitherto the process generally used has tars which are being distilled. The vapours consisted in distilling the coal tars to obfrom the tar are in my process conducted ditain four fractions (the so called raw fracrectly and without previous condensation tions) (1) the light oil, passing over up to into a highly eflicient dephlegmating or frac- 150 degrees centrigrade, (2) the middle oil, tionating column and are here gradually and 55 boiling between 150 and 200 degrees centifractionally condensed, the substances of difgrade, (3) the heavy oil, boiling between 200 ferent boiling points being separated from and 310 degrees centigrade, (4) the anthraeach other as completely as possible. This is cene oil or green oil, boiling between 300 effected by forcing the vapours throughsepand 400 degrees centigrade, the residue in arate chambers placed above each other and 60 the retort constituting the pitch. Each of connected by pipes for the passage of the the four fractions was then subjected to vapours and having pipes for the return careful fractional distillation, a suitable flow of the condensed liquid, a certain porfractionating column being employed in ortion of the vapours being condensed in each der to effect complete separation. By this chamber, the vapours being forced to go 65 fractional distillation several products were. through the liquid in each. respective chamobtained, as raw benzol, oarbolic oil, crude her. The separation of the substances acnaphthalene, washing oils, motor fuel oils, cording to their different boiling points is impregnating oils, 'anthracene oils, crude effected by cooling the vapours and forcing anthracene etc., which were either directly the vapours through the fractionally con- 7 sold or from which certain products as credensed liquids so gradually that it is possols, phenols, pyridine, pure naphthalene, sible to secure fractions of sharp boiling acenaphthene, anthracene, carbazol were points as required for the market. This is manufactured. Tars of the other sources, effected practically b' arranging the column as from brown coalwere also separated into with a certain num erof fractionati'ng or 75 several raw fractions which were then furdephlegmating chambers and conducting the ther fractionated. This process had the disdistillation and cooling so that the desired advantage, that itwas necessary to first 'preseparation according to the boiling point pare raw fractions by condensation and'then occurs. The vapours are led into a device subject these to one or more fractional diswhich is essentially a dephlegmator or frac- 80 tillation which process is expensive because tionating column having a series of perforof the large consumption of fuel, in the sep- 'ated plates provided with overflow tubes. arate stills etc. By the separation of the Such an apparatus per se is well known and tars into raw fractions the several chemically is made in many different forms. The less quite different substances, as phenols, bases, volatile constiuents of the vapours are suc- 85 hydrocarbons etc. went into the various fraccessively cooled or condensed in the" succestions and not into a single raw fraction, sive-chambers, the more volatile constituents whichrendered their preparation in a pure passing upwardly and the condensed liquids state Very-difiicult and caused losses. passing downwardly into the distillation The present process consists in that the still. 96

In the drawing I diagrammatically show three forms of, apparatus suitable for carrying out my method. In Fig. l the still 1 is heated by means of a heater 2 and communicates with the dephlegmator or frac tionating column 5 at the top of which I provide the inclined pipe 3 which communicates with the coolin deviceor condenser The horizontal plates 6 divide the column into several successive chambers. Each plate 6 has a vertical pipe 7 provided with a dome 8, and it also has one or more overflow pipes 9 to fix the height of the liquid layer therein. The ascending vapours are caused to bubble through the layers of liquid on each plate 6 since the bottom of each dome 8 is below the layer of liquid on its respective plate 6.

Fig. 2 shows a modification of the well known form of dephlegmator or fractionatin column above mentioned in which the wel known Raschig rings are provided.

Fig. 3 shows another form of dephlegmator in which horizontally arranged sieves are provided in the dephlegmator column 12. The openings in these sieves are so fine that while the vapours can bubble through them, the condensed layers of liquid do not flow backward until they have reached a certain height upon each of the said sieves.

The operation of the device shown in Fig. 1, for example, is as follows The tar in the still 1 is first heated to the temperature'at which the first fraction can pass into the outlet tube 3. A certain amount of the constituents having higher boiling points are vapourized and these are successively condensed on the plates 6 so that the bottom plate 6 has the largest amount of constituents of high boiling point condensed thereon. Hence, the vapours passing into the condenser 4 represent the refined product or fraction having the lowest boiling point. After the passage of the first fraction through the condenser 4 has stopped, the temperature to which the contents of the still 1 is heated is increased to the boiling point of the second desired fraction, and this temperature is maintained until no more vapour is evolved. While the second purified fraction is being condensed, more of the constituents having higher boiling points are deposited in the form of liquid layers upon the plates 6. In this manner, the volatile constituents of the tar are separated with a minimum consumption of fuel into sharply defined fractions having the desirable properties above mentioned.

Whereas the phenols, cresols and xylenols in the usual distillation of coal tar enter into all fractions, according to the present invention the said compounds are sharply confined to the earbolic oil or naphthalene oil fraction.

The carbolic oil and the washing-oil fraction obtained accordin to the present process are free from nap thalene. The latter is only found in the naphthalene fraction of narrow boiling points. The crude naphthalene obtained therefrom has the quality of a redistilled product of the old process. One obtain 50% more of naphthalene from the tar than according to the present process.

Practically the whole quantity of phenol, cresols and pyridine are in the carbolic oil and in the naphthalene oil fraction. The oil drained oil from the naphthalene fractioncan be used immediately for the manufacture of'carbolic acid without redistillation. After the naphthalene fraction distillates go over which are sharply distinguished from the naphthalene fraction and allow an acenaphthene to crystallize of 94% purity and higher which is after mechanical separation from the oil suitable for the market. The following fraction allows fluorene of purity to crystallize, which will be converted into pure fluorene by a single crystallization, whereas hitherto fluorene could be obtained from coal tar only by complicated and expensive chemical processes. Here after one obtains the anthracene fraction sharply distinguished by its clearing point (the point of temperature at.

which the mixture becomes a thoroughly clear liquid) the solid substances therein containing anthracene and carbazol in the proportion of about 14:2 and give after simple crystallization from benzol hydrocarbons an anthracene of about 90% purity. Associated with this is chiefly phenanthrene, which remains as residue from the distilled hydrocarbons and is a crude phenanthrene with about above purity. It may be purified by crystallization from alcohol. Finally one obtains a carbazol fraction giving after solidification a solid mixture of about 17 parts carbazol and 25 parts anthracene, from which the carbazol may be separated by dissolving the mixture in hydrocarbons and may be purified by crystallization from organic bases, mixtures of bases and hydrocarbons or by means of the potash melting process.

Distilled tar has already been continuously distilled by conducting the vapours of single raw fractions, for instance those from the light oil fraction or from the middle oil fraction into separated fractionating columns. The purpose of the use of the fractionating columns in the said known process is to divide the raw distillates from the various stills into two fractions. In the known processes, there is no return of the reflux condensates from the column into the retort. In the present process however the vapours leaving the tar distilling still are conducted immediately and directly, Without being divided orseparated into raw fractions, into a very eflicient fractionating column in which they are fractionated. By this proceeding I obtain the new and surprising result of preventing the various compounds from the tars "being condensed in all fractions. They are sharply separated in individual fractions and one ob tains a prompt and immediate sharp separation from eachother.

The present process may be applied for distilling tars of all sorts and kinds, not only to coal tars, but also to tars from brown coal,

shale etc. -The fractions from brown coal tar according to the present process are for instance crude solar oil, benzene, parafiine oils, parafline mass, fat oils.

The present process is carried out by distilling' the raw tar from an ordinary distilation still intoa highly efficient fractionating column. If raw coal tar is distilled in an ordinary distillation still having arranged directly on the top thereof a'bell column With about 40 chambers or a sieve column of the same effect or a column filled with so called The process of the boiling of the several fractions was the following:

solidifying point of the pitch 7 8 degrees centigrade.

The constituents of the fractions according Raschig rings the following products are 010- to the present process are: tained:

a 4 Naphtha- Washing Carbolic Oil gg; ii f l g i e iiei til Naphthalene fraction 18.9 Washino il 8,1 Specific gravity 0. 985 1.025 1. 03s 1. 093 Anthragene oil." 14.75- Vat 53%; 19,1374; z Pitch 5. L. 0 3% 2% 9% By crystallization of the naphthalene and Progress of the 9 0 of the Several o draining off the oil carbolic oil 6.5%, is ob fractlons w the fOuOWmg 3 tained as Well as15.6% .of naphthalene suit- 7 able for direct pressing, the yield of the other cairblolic fi f g 33222? @323- products being the above quoted. On the 01 other hand there is obtained by distillation Beginning from the still, the same as in the above quoted example, but Without immediate fraction- T; ating of the vapours and therefore Without use of a fractionating column the following results: 110

. i i Per cent Water 0. 3 Crude light oil 0. 2 Crude middle oil 12.7 Crude heavy oil -Q 10. 3 Pitch 52. 2 Loss O. 6

The constituents of the raw fractions obv v I tained Without fractionating 'of the vapours q y g P011113 of the Pltch 59 degrees and Without the use of a fractionating column centlgrade- Whereas 1n the ordinary distillation by first condensingthe vapours from the still no frac- Light Middle Heavy Anthw tionating is obtained and the several fraco 011 oil oil cene oil tions are present in each dlstlllate, the present invention gives a sharp separation of the ve wv at 15 f several fractions Which are sharply distingrees centigradenrnv; 0.992 p 1.022 1.048 1.106 w 1 0 o. 5% Traces. Traces. guished from each other, the fractions boilmg $3 ,23 i 8;; 3; 8%; it; Within very narrow limits. The intervals of the boiling points in each fraction are in the (products of the invention no more than 20 egrees centigrade, whereas the intervals in the ordinary distillates are to 100 degrees centigrade. In the products of the present invention the separation of the naphthalene and of the acids is especially remarkable.

A further improvement in the process consists in that I distill the raw tar according to the above described process with immediate fractional separation of the vapours andthe fractions condensed are chosen so that I obtain after the carbolic oil fraction, fractions containing chiefly the various solid hydrocarbons which fractions are further divided by crystallization. These crystals are separated from the liquid constituents, whereupon the solid thus obtained hydrocarbons are vaourized gradually in a still, thetemperature eing gradually increased and the vapours are immediately and directly fractionated while constantly reconducting the reflux condensation products into the tar in the still subjected to distillation. The fractionating column of the first distillation is arranged to obtain substantially a naphthalene fraction having boiling points between 190. to 220 degrees centigrade, afterwards an acenaphthene fraction'having a boiling point of about 240 to 280 degrees centi grade, then a fiourene fraction having a boilm point of about 27 5 to 295 degrees centigrade, then a phenanthrene fraction having a boiling point of about 290 to 345 degrees centigrade, and finally an an thracene fraction of a' boiling point of about 315 to 350 degrees centigrade. The said fractions are separated and cooled to ordinary temperature or below, until the solid hydrocarbons are separated, a certain portion of each fraction remaining fluid. The said liquid oils are separated mechanically from the solid hydrocarbons, for instance by allowing them to drop off from the crystals or by centrifuging the mixture. The said solid hydrocarbons are then brought to a still and gradually vaporized, the vapours being directly and immediately fractionated or dephlegmated in a highly efiicient fractionating column as described above for the raw tars. The vapours are led immediately and directly to a highly efiicient fractionating column, so the vapours are condensed gradually and progressively, so that the rising vapours go through the condensates formed and the conden sates are returning to the distilling still.

The raw naphthalene separated from the naphthalene fraction alluded to is heated in a distilling column gradually to 210-218 derees centigrade and the vapours are directy and immediately subjected-to a highly efficient fractionating. I obtain a first fraction of a boiling point of about 180 to 210 degrees centigrade and adistillate or fraction solidifying at cooling to about ordinary temperature, having a melting point about 78.5 to 79 degrees centigrade, resembling in its proper ties nearly completely to the commercial pressed crude naphthalene, manufactured hitherto by pressing in heated presses and draining off the liquid, a very tedious and expensive operation.

The yield of the present process calculated on the same weight of raw naphthalene is higher than in the hitherto common method.

The crude acenaphthene fraction is cooled and the crude acenaphthene solidified after cooling to ordinary temperature or below is separated from the oily portions. The said crude is vaporized gradually in a still by heating to 270 to 280 degrees centigrade and the vapours fractionated immediately and directly. I obtain an acenaphthene of about 99% purity.

The solid fluorene separated from the fluorene fraction is vapourized gradually by heating in a still to about 285 to 295 degrees centigrade. The vapours are led immediately and directly to a highly efiicient fractionating column, where an immediate and direct eflicient fractionating is effected. I obtain nearly pure iluorene and as second fraction afterwards condensed fromthe vapours diphenylendioxide of high percentage.

The solid hydrocarbons from the phenanthrene fraction, separated from the liquid portions of the fraction, are vapourized by heating in a still to about 320 to 335 degrees centigrade. The vapours are immediately and directly led to a highly efficient fractionating column and here directly and immediately subjected to a highly efficient fractionating. v

I obtain a phenanthrene of about purity and even higher, especially free of anthracene and carbazol, which may be freed from by constituents by crystallization from hydrocarbons, especially aromatic.

The crude anthracene, obtained from the anthracene fraction alluded to above after cooling and mechanical separation from the oily constituents is vapourized by heating gradually in a still and the vapours are led immediately and directly into a highly efiicient fractionating column, where immediately and directly an eflicient fractionating is effected. I obtain a very pure anthracene which may be crystallized from benzolhydrocarbons or a mixture of benzolhydrocarbons and aromatic bases, as aniline or, and its homologues, or pyridine or, and its homologues.

The other fractions which may be obtained besides crude anthracene as its residues from the distillation may be treated in the same manner as hereinbefore' described by vapourizing and immediate and direct eflicient fractionating. I obtain a fluoranthene fraction of the melting point from 7 0 to 80 degrees centigrade and boiling point 350 to 37 5 degrees centigrade which gives after cooling crude fiuoranthene containing 40% and more fluoranthene. The second fraction is a pyrene fraction of the boiling point of 380 to .410 degrees centigrade, giving by cooling solids,

consisting of about pyrene, For obtaining fluoranthene and pyrene from the solid one may extract it with carbon disulphide, whereby fluorantheno and pyrene are dissolved.

The process may be carried out at ordinary atmospheric or diminished pressure.

I claim 1. The process for obtaining solid hydrocarbonsfrom raw coal tar containing them consisting in evaporating those parts of the raw coal tar which distill below the boiling point of the lowest boiling solid hydrocarbon contained in the raw coal tar and then heating the said tar gradually to substantially the boiling point of the solid hydrocarbon of the lowest boiling point to generate its vapours, fractionating the vapours immediately, ef-

fecting a gradual condensing and revaporizing of the vapours so often that the vapours essentially contain the entire quantity of the respective lowest boiling solid hydrocarbon contained in the said tar, reconducting continuously the total reflux from thefractionating operation into the said raw tar to be distilled, leading away the vapours containing essentially one single solid hydrocarbon cooling the said vapours separating the solid hydrocarbon from the constituents remainedliquid in the cooling process, heating the separated solid hydrocarbon, fractionating again the vapours effecting a gradual condensing and revaporizin g of the vapours reconducting continuously the total reflux from the frac-' tionating operation into the said raw tar to be distilled, leading away the vapours and cooling the said vapours.

2. The process for obtaining phenanthrene of high purity from raw coal tar containing it, which consists in treating the tar according to claim 1, and after having led away the vapours boiling between 275295 degrees centigrade heating the said tar further to generate vapours boiling between 290-345 degrees centigrade fractionating said vapours, effecting a gradual condensing and revaporizing of the vapours so often that they contain all phenanthrene present in the raw coal tar reconducting continuously the total reflux from the fractionating operation into the raw coal tar to be distilled leading away the vapours essentially containing all phenanthrone, cooling the said vapours to solidify the phenanthrene, separating" the phenanthrene from the liquid constituents, heating the separated phenanthreneto about 320- 335 degrees centigrade, fractionating the said vapours immediately effecting a gradual condensing and revaporizing of the vapours, reconducting continuously the total reflux 1 from the fractionating operation into the raw coal tar to be distilled leading away the un-' condensed vapours and cooling the said vapours.

of crude coal tar which comprises heating the crude coal tar to vaporize therefrom a fraction, and intensively fractionating the vapors evolved in order to obtain this fraction in vapor form of-largely homogeneous chemical character having a narrow boiling point range.

4. A process as set forth in claim 3 in which liquid is formed during the fractionating operation and is returnedto the tar undergoing treatment.

5. The process of discontinuous distillation of crude coal tar which comprises heating the crude coal tar to vaporize at least a fraction thereof, and intensively fractionating the vapors evolved in order to obtain this fraction in vapor form of largely homogeneous chemical character having a narrow boiling point range and returning any liquid formed during the fractionating operation to the tar undergoing heat treatment.

6. A process as set forth in claim 3 in which the temperatureof the crude coal tar is in 3. The process of discontinuous distillation successively increasing boiling point, the boilmg point increment being not greater than the said tar to vaporize at least a portion thereof and intensively fra'ctionating the evolved vapors, raising the distillation temperature ofthe crude coal tar to' vaporize portions of successively increasing boiling points and fractionating the evolved vapors in order to separate from the crude coal tar a naphthalene fraction, an'acenaphthene fraction, a tluoren fraction, a phenanthrene fraction, an anthracene fraction, a fluoranthene fraction and a pyrene fraction of largely homogeneous chemical character having a narrow boiling point range.

1.0. The process of discontinuous distillation of crude coal tar which comprises heating the said tar to vaporize at least a portion thereof and intensively fractionating the evolved vapors, raising the distillation temperature of the crude coal tar to vaporize portions of successively increasing boiling oints and fractionating the evolved vapors in order to separate from the crude coal tar a naphthalene fraction, an acenaphthene 1o fraction, a fluoren fraction, a phenathrene fraction, an anthracene fraction, a fiuoranthene fraction and a pyrene fraction each of such fractions being of'largely homogeneous chemical character having a narrow boiling point range, separately heating each such fraction to vaporize at least a portion thereof, fractionating the vapors evolved in order to obtain therefrom a fraction of narrower boiling point range than that of the fraction from which it was derived.

11. The process of discontinuous distillation of crude coal tar which comprises heating the said tar to vaporize at least a portion thereof and intensively fractionating the 5 evolved vapors, raising the distillation temperature of the crude coal tar to vaporize portions of successively increasing boiling points and fractionating the evolved vapors in order to separate from the crude coal tar fracac tions having the following boiling point ranges: 190-220 (1, 2&0-280 0., 275-295 (1., a phenanthrene fraction, 315350 0., a fluoranthene fraction, and a pyrene fraction.

In testimony whereof I hereunto afiix my signature.

LEOPOLD KAHL.

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