US2005102A - Distillation of tar - Google Patents

Description

Filed May 21, 1,931

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DISTILLATION OF TAR Filed May 21, '1931 5 sheets-sheet s Egg. sa

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DISTILLATION OF TAR Filed May 21, 1951 5 Sheets-Sheetv 4 lNvENToR 5. 752141 BY 0 ATTORNEYS Patented June 18, 1935 DlsTlLLArroN oF TAR Stuart Parmelee Miller, Englewood, N. J., as-

signor to The Barrettv Company, New York, N. Y., a corporation of New Jersey Application May 21, 1931, Serial No. 539,019

8 Claims.

This invention relates to new coal tar oils and pitches.- These new products result from the distillation of coal tar in hot coal distillation gases and are formed by processes which prevent or minimize any substantial decomposition of the coal tar constituents. High yields of dis tillate are obtained and correspondingly low yields of pitch are produced. The products are substantially free from the decomposition products present in coal tar distillate and pitches produced by the ordinary distillation methods, particularly those produced on distillation at lower temperatures, and contain the less stable constituents which are decomposed by ordinary methods of distillation, and further these products contain ingredients present in the coal distillation gases employed for the distillation and these ingredients are recovered directly from the gases and incorporated in the products of the distillation.

The new coal tar oils contain higher boiling constituents of the coal tar which are relatively unstable and which are, therefore, decomposed by the usual methods of distillation. They contain oils originally present in vapor form in the coal distillation gases employed for the tar distillation. They are substantially free from pitch constituents. They are substantially free from decomposition products Which result from the ordinary methods of distillation, particularly those produced at lower temperatures. The total distillate from a given coal tar represents a larger percentage of the constituents of the coal tar than is usually contained in total distillate and the oil fractions included in this invention comprise a correspondingly large percentage of distillate. The oils of this invention include distillate resulting from the production of pitch with a melting point of 260 F. and preferably 300 F. or greater and oil fractions including distillate of this range. They are suitable for use as creosote oil and for other uses to which ordinary coal tar distillate is put.

The pitches of this invention contain higher boiling constituents which are decomposed by ordinary distillation processes and are substantially free from decomposition products ordinarily present in coal tar pitches, particularly those produced by distillation processes in which materials are kept at distilling temperatures for a considerable period of time. They represent a lower percentage of the coal tar than does ordinary coal tar pitch. They include ingredients present in the coal distillation gases which are directly recovered during the tar distillation pro-- cess and incorporated in the pitch produced. These directly recovered constituents include inn gredients which are present in the coal distillation gases in the form of a iine suspension or mist known in the art as tar fog.

The oils and pitches of this invention are pro- (cl. 19e-149) duced by the distillation of tar in hot coal distillation gases such ashot coke oven gases or hot gas retort gases. They include pitches of the highest melting point andthe maximum oil yield which can be obtained and pitches of lower melting point in the production of which an oil yield is obtained of lower percentage. They include pitches with a melting point of260 F. or higher and the distillate corresponding to these pitches or fractions thereof or fractions of distillate which include oils of this range. v

1n producing the oils and pitches of this invention coal tar is brought into direct and intimate contact with hot coal distillation gases at or near their maximum temperature as they leave the ovens or retorts. The tar is atomized or sprayed into the hot gases With such volume, in-i tensity and uniformity of spraying that the coke oven gases are immediately cooled from theirI maximum temperature to a materially lower tern-rv perature with simultaneous heating of the tar and repeated distillation thereof and vwith such thorough scrubbing of the hot gases as will free them from all or a greater part of their entrained carbon and pitch particles. The resulting admixed coke oven gases and vaporized oils are continuously withdrawn from the still while at a high temperature and `subsequently cooled to condense the oils therefrom and the pitch produced is also continuously withdrawn from the still.

Coke oven gases, for example, leave the incandescent upper portions of the ovens at a temperature, for example, around 550 to 860 C. or higher, depending upon the construction of the ovens, the coking cycle,` the degree of coking, etc. y Such highly heated gases are at a tempera-ture above that at which coking of pitch will occur but-such coking is practically eliminated in the'present process by subjecting the hot gases as soon asthey enter the still to contact with an excessively large volume of spray of tar which is ata considerably lower temperature and which has adequate capacity for absorbing the heat of the gases as senY sible heat and as latent heat. The eiect of an excessive and intensive showering or spraying of tarinto the gases is to suddenly and rapidly cool the gases to a temperature considerably lower than their initial temperature while'a'tjthe same time rapidly vlout'uniforrnly and'in a `controlled manner heating the tar and distilling vaporizable constituents therefrom. In this way the gases are rapidly cooledto a temperature such; that obv l jectionable coking can be readily `avoided while the 4high temperature'land heat contenty of they highly heated gases is nevertheless employedin a particularly advantageous manner 4for therapid distillation ofthe tar.` y

The gases from horizontall gas retorts leave the retortsat temperatures of 500 to 700 C. or even much higher and are used to advantage lfor the distillation of tar by spraying the tar into the gases in the form of a fine intense spray and in sufficient volume to rapidly cool the gases and thus prevent excessive decomposition'of the tar constituents. Y

The use of such highly heated gases has the further advantage that the gases even after being cooled by distillation of tar may still be at a high temperature, for example, when making 400 F. melting point pitch, around 350 to 400 C. and can be withdrawn from the still at such high temperatures with advantages which will khereinafter be pointed out. The scrubbing of the highly heated gases is so eiectively carried out that the.v

gases themselves are thoroughly cleaned of entrained dust, pitchy material, etc., by the scrubbing operation and the distillate oils subsequently condensed` from the gases are free or substantially so from such pitchy and other extraneous constituents, these constituents being scrubbed from the gases and added to the pitch residue.

The oils and pitches of this invention are ob-v tained by the distillation of tars from various sources such as coke oven tars, gas retort tars, etc. Heavy tars or lighter tars or tarry oils can be distilled to produce the products of this invention. In the case of coke oven tar for example, the tar distilled may be the total tar produced at the coke oven plant or it may be the heavy tar separated in the collector main or the light tar or tarry oil separated in the condensers. The oil yieldvwill not be the same in distillng a light tar as in distillng a total tar since there is more oil present in the former product. In other Words, a light tar may be regarded as a total tar plus distillate oil and the oil yield will correspond to that from a total tar plus this additional amount of oil. In the claims the 'expression obtainable by the distillation of a total tar is not intended to limit the claims to products made by distillng only total tar but is intended to include the corresponding products made by other processes k'such as the distillation of a tarry oil.

'Ihe still in which the oils and pitches of this invention are produced includes means for introducing the hot coal distillation gases as well as means for introducing the tarand for wwithdrawing the pitch and also the admixed gases and vapors from the still. A total condenser or a series of fractional condensers is Aused for cooling the admixed gases and vapors to separate the coal tar oils therefrom. In order to tale advantage of the maximum distillation capacityof the gases the still-may be so located that the gases enter it at a temperature which is not greatly below that at which they leave the individual ovens or retorts. Any moderate drop in temperature of the gases can be compensated for by use of an added quantity of the heated gases. The volume and composition of the gases given off from adjacent coke ovens, for example, vary, the volume of the gases being greater at the beginning of the coking period after the oven is charged and being considerably less near the end of the coking period before the oven is pushed. Adjacent ovens are commonly charged at different times so that, for example, at the time one oven is charged the adjacent oven on one side will be well advanced in the coking period and vthe adjacent oven onv the other side will also be well advanced but `to a diierent extent. Ac-

' cordingly by connecting gasoil-takes from the individual ovens so that as the gases from these enter the still the variations in the amount, composition and temperature of the gases from any vtion capacity and high melting point pitch, it is important to provide the still with heavy insulation and, as well as possible, avoid cooling of the gases after they leave the coke ovens and before they enter the still. Heat losses can be reduced to a minimum by providing the still and connecting pipes with heavy insulation.

The percentages of those ingredients-present in the oils and pitches of this invention which are recovered directly from' the coal distillation gases and incorporated in the'oil and pitch produced are not uniform. Furthermore, they do not vary directly with the melting point of pitch produced or the boiling range of the oil obtained. The per cent of these ingredients directly recovered from the coal distillation gases depends upon the amount of tar distilled in a unit volume of the gases and the vapor and pitch content of these gases. The composition of coal distillation gases moreover varies with the nature of the coal distilled, the type of distillation apparatus employed and the temperature and rate at which the coal is distilled, etc.

i The distillng capacity of a denite amount of the hot gases can be greatly increased, for example, by preheating the tar to remove water from the tar before it enters the still and for this purpose the tar may be heated to a temperature around but preferably somewhat higher than 100 C. The distillation capacity can be still further materially increased by preheating the tar to a higher temperature in order to supply from low temperature sources as much as possible'of the latent and sensible heat required for distillng the oils of low and medium boiling points. For example in producing pitch with a melting point around 400 F. an increase in preheatingof'the tar from lO0 C. to 200 C. before admitting it into the still resulted in an increased capacity of distillation per unit quantity of hot gas of about 40% to produce pitch of the same melting point and the distillation capacity of the gases per thousand cubic feet was increased from about '7.8 gallons of tar to about 10.8 gallons of tar. 'The following examples indicate the distillation capacity of hot gases with tar added at Various temperatures. The tar when preheated to higher temperatures was preheated by the hot enriched gases leaving the still. 'I'he hot gases in each case entered at about 650 C. and the tar used contained about 2% water by volume. The distillation capacity is expressed as gallons of tar per thousand cubic feet of gas (the volume being calculated to standard conditions). Pitch of 400 F. melting point is made in each case: f

In actual operation it has been found that the per cent of tar constituents recovered directly 4THr from the' gases when expressed as per centof the oil produced has `varied at different plants. At one plant when the tar was heated to 200 C. and 400 F. melting pointpitch was produced it was calculated that 4% of the oil obtained Was recovered directly fromv the coal distillation gases and that 5.9%. was recovered when the tar was preheated to 115 C. and 300 F. melting point pitch was produced.' At another plant withy a preheat of 177 C. when 400 F. melting point pitch was produced it was calculated that 6.6% oi' the oil was recovered directly from the gases and that '7.2% of the oil was recovered from the gases when 300 F. melting point pitch was produced and the tar was preheated at88, C. At still another plant when the tar was preheated to 150 C. Aand 350 F. melting point pitch was produced it was calculated that 13.6% of 'the oil was ,recovered directly from the gases. Therefore although the oils and pitches of this invention contain constituents recovered directly from the gases, the percentage of the directly'recovered constituents may vary over a considerable range within the scope of this invention.

As an illustration of the invention lthe products produced at one plant during a period of about a years time may be mentioned. From two million gallons oi coke `oven tar nearly one and one-half million gallons of distillate oil were produced together with pitch having an average melting point of around 380 F. Oil yields from the coke oven tar distilled have been obtained of 75% or more over long periods of time with the production of pitch of melting point around 400 F. or higher. Pitch of 435 and 450 F. melting point has been made over considerable periods of time. The coke oven gases entering the still have been at a temperature around 5504 C. or higher. The temperature of the gases and vapors leaving the still has varied for example between 350 and 400 C. When pitch of 300 F. melting point wasy produced with hot gases at about 550 C. the gases and vapors had an outlet temperature from the still of about 306 C. and the pitch left the still at a temperature of about 328 C., While With pitch of r400 F.fmelting point the gases and vapors left the still at a temperature of about 324 C.and the pitch left the still at a temperature of about 355 C. The still employed was about 20 feet long of rectangular' cross section about 31/2 feet wide and high and with six ovens connected by individual uptake pipes with the still.

It is important in producing the oils and pitches of this invention to provide for a rapid and intensive showering or spraying or atomizing of the tar into the hot gases so that the gases will be brought into immediate, continual and thorough contact with the spray and so that all parts of the still will be thoroughly flushed `with liquid pitch and the walls kept clean from coke deposit. 1t is important that there shall be no local overheating of any portion of the still 'and that to avoid such overheating at all times there shall be in atomized form within the still a sufficient quantity of tar or partially distilled tar to absorb the heat of the hot gases by being itself distilled to pitch of the desired melting point under regulated conditions. It is important to avoid a denciency of pitch or of partially distilled tar on any and all exposed surfaces of the distillation apparatus since such a deciency would result in local over-distillation andV the formation of coke because of the high temperature of the highly heated gases. Over-distillation and the formation of coke produce decomposition products, lower the oil yield and decompose constituents present in the tar which, so far as possible, are obtained in their original form inthe oil and pitch products of this invention. vConsequently in producing i the oils and pitches of this invention all interior surfaces of the distillation apparatus should lbe continuously and intensively supplied and washed with the pitch or partially distilled tar. The same ythorough and abundant scrubbing of the hot gases with the tar or partially distilled tar, which `re sults in the cooling'of the gases and the rapid distillation of the tar, also serves to keep all parts of the still surfaces flushed with partially distilled tar or pitch and prevents local overheating and coking thereon.

This thorough and abundant spraying of the gases with the tar or pitch may be accomplished by suitable mechanical devices of such a character and so located and operated that the tar or partially ldistilled tar will be projected kinto the hot gases and eicient subdivision of the tar accomplished. This is important not only to providea large surface of evaporation and distillation but also to provide suilicient tar in the gas. space of the still to absorb the heat of the hotgases therein, to keep the interior surfaces of the still liushed with the tar or partially distilled tar, to

prevent objectionable coke formation and to adequately wash or scrub the gases to remove pitchy or carbon particles from them.` One satisfactory means for atomizing the tar comprises a horizontal roll or a plurality of rolls or elongated cylinders rotating rapidly and with the cylindrical surface dipping into the tar or pitch at the bottom of the still and rotating at such a ratefthat either directly or indirectly to condense all or most of-the vapors therefrom in a single composite product the heavy constituents remain dissolved in the lighter oilsI and form with the lighter oils an oil suitable for creosote oil. The oils of this invention include oils of wide and also 'narrow boiling range suitable for creosote oil.

The total oil produced by the distillation of tar by a process yielding as much as 75% or,r

more of the tar distilled, can be condensed as a single composite oil and employed for example as creosote oil or the adrnixed gases and vaporscan be fractionally cooled and fractionally condensed and a plurality of oil fractions recovered. A sample of the oil produced at one plant showed a specicgravity at 38 C. of 1.110, only a trace of free carbon, and when subjected to distillation in accordance with the American Society for Testing Materials method No. D-246w 28, showed up to 200 1.1%, up to 210 2.3%, up to 285 8.3%, up to 270 22.4%, up to 315 34.3%, up to 355 48.8% and the per cent of coke residue on thevoil was 1.9%. It will be evident that the distillation can be carried out without the production of the maximum oil yield and the highest melting point pitch, and in this case an unusually high oil yield corresponding to the melting point of the pitch produced will be ob pacitythe yoil yield is only around 44% when the distillation is carried to the point of producing pitch of around 300 F. and coking may begin before pitch of 400 F. melting point kis reached. With other methods of distillation somewhat higher yields of oils can be obtained to 300 F. melting point pitch but pitch as high as 400 F. has been made only with extreme diiiiculty. But by the process described new pitch products with a melting point of 400 F. are produced in a thoroughly successful manner and yields of around '75% or more of distillate are obtained from coke oven tar when distilled to the point of producing pitch of melting point oiy around 400 F. or higher; while with the production of pitch of lower melting point around 300 F. melting point it is possible to produce oil yields representing around two-thirds or more of the tar distilled.

. The invention willbe further described in the accompanying drawings which show apparatus in which the oils and pitches of this invention may be produced by distillation in hot coal distillation gases. The drawings further illustrate in a graphic way the composition of the new oil products and pitches by representing the oil yield obtained on distillation to pitches of diierent melting points in producing the oils and pitches of this invention. v

In the drawings Fig. l is a plan view of a coke oven battery equipped with a still for producing the oilsand pitches ofthis invention.y y

Fig. 2 is an elevation partly in section of th still. f

Fig. 3 is a cross sectionr on the line 3 3 of Fig. y2.

Fig. 4 is an enlarged View partially in section showing one type of fractional condenser.

Fig. 5 is a section on the line 5-5'of Fig. 4. Fig. 6 is a section on the line 6 6 of Fig. 4.

Fig. 7 is a diagrammatic View showing the still and the condensing system of Figs. 1-6.

Fig. 8 is a graph illustrating geometrically the relation of pitch melting point to oil yield of the new pitches and new oils obtained by the distillation of tar in hot coal distillation gases under the carefully regulated conditions by which either theV new pitches or new oils of this invention are produced. The abscissee represent percentage oil yields by volume based on the tar distilled and the ordinates represent pitch melting points in degrees Fahrenheit (air.

bath method).

In Figs. l to 3 part of a coke oven block or battery is indicated conventionally at I and part of the conventional by-product recovery system is illustrated. Individual coke ovens 2 have uptake pipes 3 leading to a collector main 4 common tov a number of the ovens of the battery. The crossover main 5 connects the collector main with the condenser 6 and the gas is then passed through the exhauster 'l to the ammonia absorber, the benzol scrubber, etc. Ordinarily ammonia liquor or ammonia liquor and tar are introduced into the collector main to cool the gases and keep the main flushed. A drain for the tar and ammonia liquor is indicated at 8 leading to the decanter 9 from which the tar isdrawn off into the tar receptacle l0. Two condensers E are provided with means for drawing oi thecooling liquids and light tar into the decanter I I from which the light tar collects in receptacle I2.V v

The apparatus'thus far described which is illustrated only schematically varies somewhat in different coke oven plants and is described merely for purposes ofillustration.

-A still 20 is located 'on the other side oi the coke oven block. rThis still is of rectangular cross-section and is of such a length that four uptake pipes 2I pass upwardly into it from four individual ovens and two additional uptake pipes 22 connectadjacent ovens with'the still. TheY internal uptake pipes 2| have lateral openings into the still and closures 23 operated byy operat-l ing handles 24 for closing the individual uptake pipes during the charging of the coke ovens or when it is desiredto valve ofi any oven from the still.l Clean-out openings 25.. are provided for each of the uptake pipes.

The still and external pipes 22 are shown as provided with heavy insulation to prevent or reduce heat loss and reduction of temperature of the gases entering the still. is provided the gases will enter the still at a temperature not materiallyA below that at which they leave the individual ovens and they will thus tom of which the cooled gases passthrough thel pipe 32 to the gas handling system for the coke oven plant.

The condenser illustrated is a three-stage condenser having two lowercooling sections 33 cooled by a suitable cooling liquid such as water and with an upper cooling section 34 which serves' as a tary preheater and as a preliminarycondenser forthe gases and vapors. heating section has a tar supply pipe 35 leading to the tar coils 36 from which the preheated tar passes through the pipe 3l to the nozzle 38 1ocated in the tower 28 between two packed sections 39 and 40 lledr with broken up material or cylindrical rings e. g. the well known Raschig rings. The upper section 39r serves to reduce entrainment of suspended particles while the lower section 40 serves the same purpose andin addition serves to bring the preheated tar into intimate contact vwith the admixed gases and vapors leaving the still. The preheated tar is thus partially distilled andthe residue collects jat the bottom of the tower 28 in the `collecting section 4I and iiows through the pipe 42 to one end of the still 20. I l

VAt the other end of the still is located a pitch outlet shown asa trap 43 having an adjustable overiiow outlet 46` leading to the troughY 41 which is supplied with a rapidly moving stream of water through a supply pipe 44.A The pitch is granulated by rapid chilling in thewater in the trough which discharges the water and granulated pitch into the receptacle 45. This method of cooling and hanlding the pitch is only one of various methods which can be employed and for certain purposes the pitch can -be cooled without admixture of water to give a solidied pitch product free from water. A y

Within the still Y2l] are located suitable atomizing. or spraying devices for intensively atomizing or spraying the tar and pitch into the gases in such away that all parts of the gases 'in the still are thoroughly scrubbed bythe tar and pitch and so thatalli of the internal Vsurfaces of the still 75 v If heavy insulation The upper tar'Y are intensively flushed by Van excess of the tar or pitch'.` Where internal uptakes are employed the space back of these uptakes'whe're the spray will not reach may be lled with suitablefilling material. kThe mechanical spray devices shown are cylindrical rolls approximately 10 in diameter, three in number indicated at 48, 49 and 50 and driven at vrelatively high speed, for example 900 to 1,000 R. P. M. by motors 5I and 52 located at the ends of the still. AThe middle row 40 is cou-` pled with one of the end rolls and is driven there' with by one of the motors, theY coupling being shown at 53. In order to providebearings 55 for the individual rolls part 'of the still is cut away as indicated at 54. The rolls are so located as to dip into the tar or pitch in the bottom of the still and the adjustable outlet for the pitch enables.

the depth to be regulated. By suchregulation of the depth of the tar or pitch the extent to which the roll 'dips thereinto is governed andthe character of the spray and the intensity may be governed at will by regulation ofthe depth of tar or pitch. A

The production of the oils and pitches of this invention is not limited to processes which involve preheating the tar nor to processes involving the introduction of the tar into the gases'and vapors escaping from the still to effectv partial distillation before it enters the still but such pre heating and partial distillation are vadvantageous and. means for effecting them are shown in the drawings.

The condensing system shown is a fractional or multi-stage condensing system the iirst stage of which is a preheater for the tar in which the tar is preheated by indirect contactk with the hot gases and vapors. Therate of distillationr can be greatly increased by preheating the tar in this way while the gases arev at the same time cooled to condense part of the distillate therefrom.' The admixed gases and vapors are then further cooled in the lower stages of the condenser for example by indirect contact with cooling coilscontaining water. The cooling system shown in Figs. 4 to 7y has a water inlet 60 and a water outlet 6I supplying water to the lower cooling sections 33. Threeoutlets 62, 63 and 64 are provided for the condensate from the respective sections. Two return pipes 65 and 66 each leading to distributing nozzles' 61 and 68 provide for returning the co'ndensate from'the upper section into the'next lower section whereit will blend with the condensate sprayed in such section. By returning the condensate from each of the two upper seci tions to the lower sections the condenser becomes a total condenser where all of the constituents are condensed and collected together to be drawn cir through the bottom outlety 64. The construction of the condenser may vary and that shown in Figs. 4 to 6 is only one of various types of condensers which can be employed. v

The tar supplied yto the-still may Ybe the tarcollected in the by-product system of the same plant and pumped from the tanks I0 and I2 by pumps 56 and 5l through pipe 58 to the still, or tar from another source of supply can be introy duced through pipeA 59.

The following data were collected when pitch of about 400 F. melting point was being produced in a still oi the type shown in the drawings and these data may serve as an example of how the still is operated to produce the oils and pitches of'this invention. Tar was supplied to the preheater at a temperature oi around 63 C. and preheated by indirect contact with hot gases and vapors. to around 221 Vwhile the gases and vapors were cooled from around 293 C. to around 175 C. The tar preheated to 221 C. thenente'red the settling chamber where it was further heated e and distilled by direct contact with the hotgases and vapors therein which were thereby cooled toa temperature of about 293 C. before they went to the preheater.

The intensive scrubbing to which the gases are subjected in tlie'still during the distillation results in effectively cleaning the gases from suspended carbon and pitch particles. As a result when the gases and vapors from the still are subjected to condensation, the oils condensed' are clean oils substantially free from tarry. or pitchy constituents and show 'only traces of so-called free carbon when subjected to the usual benzcl extraction test. I

In representing the pitches of this invention graphically in Fig. 8 the melting pointsA of pitches in degrees Fahrenheit are plotted against the per cent .of

oil which distillation to that melting point yields.

production of the 011s and 2 o The oil'A is the oil actually distilled from the tar and the yield expressed does not include the oil recovered directly from the co'al distillation gases.

Those oils and pitches with a melting point above 260 F. which are produced by distillation in hot coal distillation gases by processes which yield distillate in excess of that expressed by the equation y=2.152-246+7290 where y is the melting point of pitch in degrees Fahrenheit and a: is the per cent of oil yield, are included in this invention and more particularly the invention includes only those oils and pitches sc produced by proc` esses where the ratio of oil yield to pitch is less and approximately that expressed by the equation 30y=11x2l175|38250- The .graph of Fig. 8 shows all three of these curves and on this graph are also plotted the melting points and oilyields actually obtained for pitches as follows:

1 Melting point Oil yield 400 76. 3 400 82. 5 400 79. 0 ev 8l. 4 355 73. 4 300 71. 7 360 66. 7 350. 67. 6 325 68. 6 310 62. 8 295 62. 8 260 60. 1

My co-pending application Serial No. 326,769, iiled December 18, 1928, of which this is in part a continuation, claims method and apparatus yby which the oils and pitches of this invention may be produced. The curve 30y=l12-11`75x138250 of Fig.V 8 includes the pitch of 4400 1.y melting point and oil yield of 75% described in that prior application and other voils and pitches the yield and melting point of which bear this relation to one another. The relation of the oil yield to the melting point of the pitch produced will vary and depends upon the composition of the tar treated, etc. 'I'he new products include the pitches and oils produced by `processes in which the ratio of the oil yield to pitch melting point is as low as that represented by the curve y:2.l5x2246+7290, provided the pitch melting point is not below 260 F. and more particu- F rious characteristics. Thepoils, are clean oils substantially free' from carbon or heavyr pitch constituentsand thefterm, clean in the claims isused-in this sense.. Both the oils and pitches vare substantially free from tar decomposition products, particularly those ordinarily produced by long-continued distillation, and contain con-` stituents of coal tar ordinarily decomposed by the usual processes of distillation and in addition contain ingredients directly recovered from the coal distillationgases in which they are dis-V tilled. .l

In the claims pitch melting point rrefers to melting ,point in Vdegrees Fahrenheit (air bath' method, Journal of YIndustrial and Engineering Chemistry, vol. 10, pages 821, 822) and oil yield refers to'percentage yield by volume based on net dryr tar. f

I claim:

1.. Clean coal tar oils comprising oil condensed directly from coal distillation gases and adistillate oil, the distillate oil being obtainable by the distillation of a total coaltar to pitch with a melting point of at least 260 F. by a process according to which y 'equals between .3125x2- 36.25z+1286 and 2.15x2-246-f-'7290 Where y: pitch melting point and =oil yield, the upper limit of the boiling range of the oils condensed directly from the gases and the oils distilled from the tar beingthe same.

2. Clean coal tar oil fractions consisting of oil condensed directly from coal distillation gases andA a distillate oil, the distillate oil being obtainable by the distillation of a total coke oven tar to pitch with a melting point of at least 260 F. by a process according to'which y equals between .3l252-3625-f-l26 and 215332-24614- 7290 where y=pitch melting point and =oil yield, the upper limit of the boiling range of the oils condensed directly from the gases and the oils distilled' from the tar being the same.

3. Clean coal tar oil fractions consisting of oil condensed directlyfrom coal distillation gases and a distillate oil, the distillate oil being obtainable by the distillation of a total coal tar to rpitch with a melting point of at least 260 F.

by a process according to which 30g equals about hr2-117532+38250 where y=pitch Y melting point and x=oil yield, l, the upper limit of the boiling range of the oils condensed directly from the gases and the oils distilled from the tar being the same. y

4. Clean coal tar oil fractions consisting of oil condensed directlyV from coal distillation' gases and distillate obtainableA by the distillation of a total coke oven tar to pitch Awith a melting point of at least 300 F., by a. process according towhich 'the ratio of the pitch melting point expressed as y and the oil yield expressed as :c lies between .3125x2-36.25:c+ 1286 and 2.15x2-246-i-72v90 where y=pitch melting point and x=oil yield, the boiling point of the lowest boiling of the constituents recovered directlyfrom the gases and the lowest boiling of the` constituents resulting from the distillation being the same..

Y6. Pitch comprising pitch constituents recovn ered directly from coal distillation gases andy pitch yobtainable by the distillation of a total coke oven tar to pitch having r.a melting zpoint of. between about 260 F. and about .400 F. by a process according to which y equals between .3125:c2-36.25:c+1286 and 2.15`ac2-246rr-ff'7290l 111;? 11751'4-38250 where y=pitchmelting point' and =oil yield, the boiling point of the lowest boiling of the constituents recovered directly from the gases, and the vlowest `boiling of )the con-` tituents resulting from the `distillation of the tar being the same.

8L-Pitch consisting of constituents .recovered directly from coal distillation gases and constituents obtainable by'the distillation of a total coke oven tar to pitch with a melting point of at least 300F. by a process according to which thev ratio of the pitch melting point expressed as' y. and the oil yield expressed as :z: lies between y=2'.15:v2-246+7290 and the boiling point of the lowest boiling of the constituents recovered directly from the gasesr and the lowest boiling of the constituents resulting from the distillation of the tar being the same.

, S. P. IVHLLER.

y=.3125:v2-36.25:1J+ 1286,

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