US2066386A - Distillation product - Google Patents

Description

Patented Jan. 5, 1937 Frank H. Bergeim, Lconia, N. J., assignor to The Barrett Company, New York, N. Y., a corporation of New Jersey No Drawing. Application October 3, 1930, 1 Serial No. 486,278

' 3 Claims. (01.198-149) My invention relates to a product obtained from a coal tar derived by the carbonization of coal at low temperatures and to the products obtained by said process. 1

The destructive distillation of coal at low temperatures, that is, at temperatures of about 400 to 600 C. or up to 800 (3., results in the production of coal tars which in many respects are very different from coal tars obtained by the destructive distillation of coal at higher temperatures,

for example at from 1000 to 1200 C., as in the ordinary by-product coke oven practice. Two to three times as much tar is produced by the treatment of coal at low temperatures and the tar contains substantially no solid aromatic compounds and almost no free carbon. Furthermore, the low temperature tars are of'lower specific gravity than the high temperature tars. It is generally considered that the-constituents of low temperature tars differ from those present in tars resulting from the destructive distillation of coal at high temperaturesin that the materials have not been subjected to high temperatures and therefore they have not undergone chemical decomposition and rearrangement to the same extent.

I have discovered that products having novel and valuable characteristics are produced by subjecting the aforementioned low temperature tar to fractional distillation under a vacuum. I have found that the products of vacuum distillation of low temperature tar differ not only from the products of low temperature tar distillation at atmospheric pressure, but also from the products of vacuum distillation of ordinary high temperature tar.

The result of-vacuum distillation of coal tar, whether produced by high temperature or low temperature distillation of coal, is to decrease the degree of decomposition of the products undergoing distillation by reason of the fact that the temperature to which the materials are subjected in effecting their distillation is materially lowered. However, the vacuum distillation of tar originally obtained by the distillation of coal at high temperatures gives no indication of the characteristics of the material which may be obtained by the vacuum distillation of low temperature tars.

-The organiccompounds present in the various fractions obtained by fractional distillation under a vacuum are probably different from those obtained by distillation at atmospheric pressure because of the fact that the tar is not heated to such a high temperature during the distillation operation.

- The principal object of my invention is to provide a new process for treatinglow tempera-= ture tars by means of which new products are obtained.

A further object of my invention is to produce 5 new and valuable coal tar products having char-- acteristics which distinguish them from coal tar products derived by other methods of production.

The term low temperature tar as employed throughout the specification andin the claims refers to the condensate from volatile products derived by the carbonization of coal at temperatures of from about 400 to 600 C. and not in excess of 800 C. as distinguished from high temperature tars produced by the carbonization of coal at from 1000 to 1200" C. as in the usual byproduct coke oven practice.

In accordance with my invention low temperature tar is subjected to fractional distillation .under a vacuum, preferably a high vacuum, for example a vacuum corresponding to an absolute pressure of not over about '75 mm. of mercury. In carrying out my process it is found that as the temperature of distillation under vacuum and the amount of the tar removed as distillate is increased, the differences in the characteristics of the distillate from corresponding fractions obtained by atmospheric distillation become more pronounced. In general,'fractions of the distillate coming over at temperatures above about 200 C. under high vacuum are much more viscous and of higherspecific gravity than corresponding fractions obtained by distillation of low temperature tar at atmospheric pressure. A striking characteristic of the higher boilingproducts obtained by my process is the resinous nathe temperatures at which distillation occurs are considerably lower so that coking of the pitch does not occur so readily and about 80% by volume of the tar can be obtained as distillate. Thus I not only obtain new products by my process but the amount of the tar obtained as valuable distillate is materially increased.

In order that my process may be clearly understood and the products contrasted with those obtained by the distillation of low temperature tars under atmospheric pressure, the following comparison is given. The same tar was used in each case and fractions of about equal percent by volume of the tar were collected in order that the fractions obtained in each instance would correspond as nearly as possible to each other.

Distillation at atmospheric pressure M. 1. of Temp. oi Sp. gr. of oil vapor $33 at 15.5 C.

"" "565 III: fis' 205-3l8 c as o. .970 318-336 c 112; c. 1.035 195 0 1. 059

The boiling point ranges given in the above table and recited throughout the application refer to thermometer-in-vapor temperatures.

pitch residue, after the removal of the first fraction or light oil, were not determined as the distillate amounted to only about 2% of the tar and the residue in each'instance'was fiuid at atmospheric temperature. No fraction corresponding to the resins produced by vacuum distillation was obtainable from the low temperature tar when distilled at atmospheric temperatures because of the formation of coke on further heating.

The viscosity of the middle, heavy and extra heavy oil fractions in the above table when determined with the Engler viscosimeter is as follows:

taken 0 Atm. middle oil 0. 070 25 200 78. 7 Vac. middle oil. 972 25 2i!) 85.0 Atm. heavy oil. 1. 035 40 50 58. Vac. heavy oil l. 061 40 50 254 Atm. extra heavy oil- 1. 059 80 50 29. 0 Vac. extra heavy oil. 1. 091 80 w 171 It will be noted that the specific gravity of the heavy oil and extra heavy oil fractions obtained by distillation under vacuum is considerably greater than that of the corresponding fractions obtained by distillation under atmospheric pressure. The viscosity and resinous characteristics of these fractions are also much greater in the case of the products obtained by vacuum. distillation.

One of the most outstanding characteristics of the'iow temperature tar distillates produced by vacuum distillation is their freedom from or comparatively low content of high boiling crystalline compounds. This property of my new products is in striking contrast with distillates obtained by the vacuum distillation of tars produced-by the distillation of coal at high temperatures. This freedom from crystals characterizing my new products is a highly desirable property forproducts which are to be used as rubber softeners.

The middle and heavy oil fractions obtained by distillation under a high vacuum both contain substantial quantities of tar acids probably of a complex composition. A typical sample of the middle oil fraction has been found to'contain 37% by volume of tar acids and a heavy oil fraction contains 27% by volume of tar acids. Such middle oil fractions containing substantial quantities of tar acids have been found to range in specific gravity from about 0.90 to 1.00 at 15.5 C.

The heavy oil fraction has a specific gravity considerably higher than the corresponding fraction obtained by distillation at atmospheric temperatures. The extra heavy oil fraction is not only of higher specific gravity but is resinous and rubbery in character and will scarcely fiow at room temperature.

The resins produced as a final fraction when vacuum distillation is employed are tough but can be made pliable by warming in the hands. When. so warmed, the resin takes on a rubberlike consistency in that it can be stretched to a considerable extent without breaking. An outstanding feature of the resins produced is their freedom from crystalline substances. This'freedom from crystals is a highly desirable characteristic distinguishing the resins obtained by my process from products obtained from high temperature tars. I have found that this property of my resins renders them particularly suitable as materials to be used as rubber softeners, as specifically disclosed and claimed in my copending application Serial No. 486,279, filed October 3, 1930, now U. S. Patent 2,001,176. The new resins of my invention are also suitable for use in varnishes, lacquers, molded resinous composi-' tion is taken. The specific gravity of the final.

fraction may vary from 1.09 to 1.132 at 15.5 C. or somewhat higher. When-distilling with a vacuum of about 25 mm. of mercury, it has been found that a typical low temperature tar yields about 20% of resinous distillate within a temperature range of 277 to 315 C. This product has a softening point of about 52 C. as determined by the cube-in-water method. When this portion of The fusible nature of the resinous product renders it suitable for use in molded articles either by itself or in combination with other resins,

gums, fillers and similar materials employed in the manufacture of molded products.

The fractions in the above table are taken arbitrarily but it is evident that fewer or a greater number of fractions may be taken and the temperatures at which the successive fractions are collected may be varied as desired. The degree of vacuum to be employed in distilling the low temperature tar also may be varied and will depend largely upon the character of the product desired.

While a preferred method of treating low temperature tar has been described, and a specific example cited, it is not intended that the invention should be limited to the treatment of such materials under the specific conditions disclosed which are merely illustrative of the invention, nor is it considered that the invention is limited to the production of low temperature coal tar fractions collected at the specific temperatures ly less than atmospheric, said distillate being substantially free from high boiling crystalline compounds, said distillate having a specific gravity of about 1.09 to 1.13 at 155 C. and a softening point of from 40 to 60 C.

2. As a new product, a distillate obtained by the condensation of vapors coming off within the range of 275 to 315 C. in the distillation of low temperature coal tar under pressure substantially less than atmospheric, said distillate being sub stantially free from high boiling crystalline compounds, said distillate having a specific gravity of about 1.09 to about 1.13 at 155 C., a softening point of from 40 to 60 C., and said distillate being of a resinous consistency as distinguished from an oily or waxy consistency.

3. As a'new product, a distillate obtained by the condensation of vapors coming off within the range of 275 to 315 C. in the distillation of low temperature coal tar under pressure conditions such that decomposition of the oil content of the tar is minimized, the said distillate having a softening point of from 40 to 60 C., a specific gravity of from about 1.09 to about 1.13 at 155 C.

and said distillate being substantially free of high boiling crystalline compounds, and being of a resinous consistency as distinguished from an oily or waxy consistency.

FRANK H. BERGEIM.