US2070961A - Process of treating tar and pitch - Google Patents

Description

Patented Feb- 16, 1937 UNITED STATES PROCESS OF TREATING TAB. AND PITCH Charles S. Reeve, Leonia, N. J assignor to The Barrett Company, New York, N. Y., a corporation of New Jersey No Drawing. Application July 18, 1930, Serial 13 Claims. (01. 196-46) My invention relates to the treatment of tars and pitches such as coal and water-gas tars and pitches, and particularly to methods of treating such materials to give desired characteristics to the final product.

In the manufacture of road materials, roofing pitches, and other similar products, a material relatively high in free carbon (material insoluble in benzol) has generally been preferred on account of its low susceptibility to changes in temperature, that is, the relatively slight tendency of the material to change in consistency with changes in temperature. To obtain the desired free carbon content and low susceptibility to changes in temperature heretofore has necessitated the use of tars which inherently or initially have a high free carbon content, such as those produced in horizontal retorts and commonly termed gashouse tars. The supply of these tars has been rapidly diminished due to new methods of gas production. In an effort to find a substitute therefor, I have discovered that by heating materials containing a low amount of free carbon such as coke-oven tar, water-gas tar, low free carbon pitches, and other similar materials which are not adapted for use in most methods of road and roof construction, under pressure and at a sufficiently high temperature, the free carbon content can be materially increased and a product having the desired physical and chemical properties can be obtained. I have found that the rate at which free carbon is produced on heating tar and pitch increases very materially if the temperature of the treatment is above about 650 F. and is comparatively rapid when the material is heated to temperatures in the neighborhood of 700 F. to 800 F. or higher. Such temperatures are attainable without loss of volatile constituents desired to be retained in the material in practicing my invention by heating the material under pressure as by treating the material in an autoclave or under pressure of the gases and vapors produced during the heating of the tar or pitch.

It is well known that when tars or pitches are heated to high temperatures they undergo decomposition with an increase in the free carbon content to some extent. However, the increase in free carbon which takes place in an ordinary distillation process is accompanied by a great increase in the viscosity and melting point of the residue tending toward the formation of coke. Therefore, the residues from distillation operations which contain substantial amounts of free carbon are often unsuitable for use as roadbuilding materials or roofing compositions.

Although my invention is particularly adapted to the treatment of tars and pitches containing a low amount of free carbon, that is initially below about 10%, I have found that the invention is also applicable to the treatment of materials containing a relatively large amount of free carbon in order further to increase the amount of free carbon therein.

The principal objects of my invention are to decrease the susceptibility of tars, pitches and similar bituminous materials to changes in temperature and to produce a bituminous product of high free carbon content characterized by low susceptibility to changes in temperature from low free carbon bitumens.

These and other objects and features of my invention will appear from the following description thereof in which I refer to preferred methods of treatment which have been found to be particularly applicable to the treatment of certain bituminous materials, some of which have a low amount of free carbon, whereas others initially contain a relatively large amount of free carbon. However, the invention is not limited to the specific examples to which I shall refer as illustrative of the invention.

In treating bituminous materials in accordance with my invention, the material is heated under pressure to a high temperature preferably above about 650 F., with or without agitation, for a sufficient length of time to bring aboutthe desired changes in characteristics and composition of the material. In some instances the tar or pitch may first be heated to distill off a certain amount of the volatile constituents of the tar or pitch and thereafter subjected to treatment under pressure to increase the free carbon content.

In order to heat the material to the desired high 4 temperature without loss of volatile constituents desired to be retained therein, the heating is carried out under pressure of the volatile constituents of the material. The temperature to which the material is heated, the length of time of treatment and the amount of pressure employed are subject to variation in treating different materials and in obtaining different end products. The resulting product may be mixed or cut back with a certain amount of light oil, preferably the distillate from the initial treatment thereof, or the product may be distilled to obtain a residue having the desired physical and chemical properties. It may be desirable for certain purposes to add some of the treated material having a high free carbon content to other materials such as low free carbon tar or pitch which has not been so treated. The products so produced will be found to be useful for all those purposes for which high free carbon bitumens with low susceptibility to temperature change are demanded.

I have carried out the process in many different ways, the following being typical of the treatment given various materials:

Example I.-Light water-gas tar was distilled to remove 25% by volume of the volatile constituents thereof, a vapor temperature of 460 F. being reached during distillation. The residue remaining after distillation had a free carbon content of 0.7% and an Engler viscosity of 60 sec. cc. at 100 C.). This residue was introduced into a closed vessel and heated for five hours at a temperature of 747 F. and at an average pressure of pounds per square inch. The pressure was maintained by allowing the pressure in the vessel created by the production of fixed gases and volatile constituents to reach pounds per square inch and then allowing the gases and vapors to escape until the pressure was reduced to 110 pounds per square inch. The volatile material vented was largely fixed gases, although a certain amount of condensable material was collected. The resulting product after heating was homogeneous and slightly heavier in consistency than the original tar. This product had an Engler viscosity of 90 sec. (100 cc. at 100 C.), and a free carbon content of 16.1%. The resulting product was distilled until the material remaining had a melting point of 106 F. and a free carbon content of 18.9%. During this distillation 17% by volume of the heated product was removed as distillate. The material thus produced is well suited for road construction, or it may be further distilled if desired for the manufacture of a satisfactory roofing material.

Example II.The operation was carried out with relatively heavy water-gas tar containing 1.9% free carbon and having an Engler viscosity of 82 sec. (100 cc. at 40 C.). 25% of the volatile matter was distilled off. The residue had a free carbon content of 5.7%. This residue was heated for five hours at 740 to 750 F. under pressures varying from 100 to 103 pounds per square inch, the excess gases being allowed to escape continuously during the heating operation. The resulting product was found to be homogeneous and had a free carbon content above 18%, a melting point of 97 F. and an Engler viscosity of 393 sec. (100 cc. at 100 C.). This product was distilled until the material remaining had a melting point of 107 F. and a free carbon content of 18.2%.

In each of the foregoing examples the material was heated by direct heat and without agitation.

Example III.-In another instance pitch containing 16% free carbon and having a melting point of 108 F. was heated for nine hours at an average temperature of about 752 F. and at an average pressure of about 90 pounds per square inch. The resulting product had a free carbon content of 54.8% and a melting point of 274 F. This offers an excellent base for fluxing with a heavy coal tar distillate or distilled tar for the production of a high carbon road material, roofing pitch or rubber softener.

Ernample I V.-In afurther instance the starting material was a coal tar pitch having a free carbon content of 15.7% and a melting point of F. The material was slowly heated, to a temperature of about 752 F. and maintained at about that temperature for a period of six and one-half hours, at an average pressure of about 70 pounds per square inch. The resulting product had a melting point of 172 F. and a free carbon content of 25.6%.

The process in Examples III and IV was carried out with an air bath heating arrangement and the material was agitated during the period of heating.

As indicated by the examples cited, the increase in free carbon content effected by treating tars and pitches in accordance with my process is very material. Even in the case of pitches initially containing substantial amounts of free carbon as in Examples III and IV above, an increase in the free carbon content of 50% or more over that initially present in the bitumen has been obtained.

The products obtained from the reactions described are suitable for use for numerous purposes either directly or in combination with other materials such as tars or pitches having much lower free carbon content. For certain purposes the products may be distilled, although this is not necessary in the production of some materials. In some instances the product after being heated is mixed with lighter bituminous materials. These materials may be obtained from a preliminary distillation of the material treated or they may be the condensible products from the volatile materials vented during the heating operation, but other bituminous materials may be employed if preferred. In a few cases I have found that the product after heating contains granular material or has separated into layers having different consistencies. This can be avoided to a great extent by agitation and the granular effect can be destroyed by mixing or stirring the product on a steam bath. The granular product is not gritty and the granular appearance largely disappears when it is subjected to suitable mechanical treatment, as for example in a rubber compounding mill.

I prefer to carry out the process at temperatures above 650 F. and ranging from about 700 F. to about 820 F. I have treated materials initially containing free carbon in amounts ranging from about of 1% to over 20%, and ranging in melting point from about 90 F. to 150 F. The pressures employed in carrying out the process have varied over a wide range and have been as high as 120 lbs. per square inch gage pressure. The materials treated have included water-gas tar and pitch, coke oven tar and pitch, high boiling tar distillates, and numerous special types of pitch. In general the materials adapted to be treated in accordance with my invention are those tars and pitches produced in coal gasification processes such as coal tar and pitch, water gas tar and pitch, etc. as distinguished from petroleum or mineral oil derivatives. The expression tars and pitches used throughout the specification and claims is intended to include all such materials. The materials have been heated continuously for periods of from three to nine hours and have also been heated in repeated stages of from one-half to four hours, being allowed to cool between successive heating operations. The examples cited and the range of materials, temperatures and pressures mentioned above do not indicate the limiting factors for the process, but are given as illustrative and to emphasize the fact that the process is applicable to a wide range of materials "described or to the ranges of temperature, pressure and other factors affecting 'the reaction which have been mentioned except as defined by the claims.

l. The method of treating water-gas tar which comprises distilling off about 25% by volume of the tar, collecting the distillate, heating the residue for about five hours at a temperature of about 750 F. and under a pressure of about pounds per square inch without substantial distillation thereof, and distilling off constituents of the product so obtained until the material remaining has a melting point of over 100 F.

2. The method for treating tars and pitches produced in coal gasification processes to increase the free carbon content thereof which comprises heating the material under a pressure between about 15 and pounds per square inch at a high temperature without substantial distillation thereof so that the free carbon content of the material is substantially increased, and under conditions so as to retain in the product a substantial amount of volatile matter and to avoid coking of the material.

3. The method for treating tars and pitches produced in coal gasification processes to increase the free carbon content thereof which comprises heating the material under superatmospheric pressure at a temperature above about 650 F. Without substantial distillation thereof so that the free carbon content of the material is substantially increased, and under conditions so as to retain in the product a substantial amount of volatile matter and to avoid coking of the material.

4. The method for treating tars and pitches produced in coal gasification processes to increase the free carbon content thereof which comprises heating the material at temperatures between about 750 F. and 820 F. and under pressure of its vapors without substantial distillation thereof sothat the free carbon content of the material is substantially increased, and under conditions so as to retain in the product a substantial amount of volatile matter and to avoid coking of the material.

5. The method for treating tars and pitches produced in coal gasification processes to increase the free carbon content thereof which comprises heating the material under superatmospheric pressure in a closed vessel and maintaining the material under substantially constant pressure by removing fixed gases without substantial amounts of vapors from the vessel during the treatment so that the free carbon content of the material is substantially increased, and under conditions so as to retain in the product a substantial amount of volatile matter and to avoid coking of the material.

6. The method for treating tars and pitches produced in coal gasification processes to increase the free carbon content thereof which comprises distilling off a portion of the volatile constituents of th' material', heatingthe residue under superatmospheric pressure at a high temperature without substantial distillation thereofso that the free carbon content of the material is substantially increased, and under conditions so as to retain in the product a substantial amount of volatile matter and to avoid coking of the material.

"7'."' Ihe method for treating tars and pitches produced in coal gasification processes to increase the free carbon content thereof which comprises heating the material under superatmospheric pressure a plurality of times to a temperature above about 250 allowing the material to cool :between successive heating operations maintain- 'ingitlie material at substantially that temperature' for an aggregateperiod of several hours to form in the material substantially increased amounts of free carbon, and under conditions so as to retain in the product a substantial amount of volatile matter and to avoid coking of the material.

8. The method for treating tars and pitches produced in coal gasification processes to increase the free carbon content thereof which comprises distilling oiT a portion of the volatile constituents of the material, collecting the distillate, heating the residue at a high temperature without substantial distillation thereof so that the free carbon content of the material is substantially increased, and under conditions so as to retain in the product a substantial amount of volatile matter and to avoid coking of the material, and mixing the resulting product with distillate obtained from the material.

9. The method for treating tars and pitches produced in coal gasification processes to increase the free carbon content thereof which comprises heating the material under superatmospheric pressure at a high temperature for over one hour Without substantial distillation thereof to form in the material substantially increased amounts of free carbon, and under conditions so as to retain in the product a substantial amount of volatile matter and to avoid coking of the material, and thereafter distilling off constituents of the product so obtained.

10. The method for treating tars and pitches produced in coal gasification processes to increase the free carbon content thereof which comprises heating the material under superatmospheric pressure at a temperature between 700 F. and 820 F. for a period of several hours to form in the material substantially increased amounts of free carbon, and under conditions so as to retain in the product a substantial amount of volatile matter and to avoid coking of the material, and distilling off constituents of the product so obtained until the material remaining has a melting point of over about 100 F.

11. The method for treating tars and pitches produced in coal gasification processes to increase the free carbon content thereof which comprises distilling ofi a portion of the volatile constituents of the material, collecting the distillate, heating the residue from the distillation operation under a pressure between 15 and 120 pounds per square inch at a temperature between about 700 and 820 F., without substantial distillation thereof so that the free carbon content of the material is substantially increased, and under conditions so as to retain in the product a substantial amount of volatile matter and. to avoid coking of the material, and

mixing at least a portion of the distillate with the resulting product. v

12. The method of producing pitch products of predetermined free carbon content, which comprises heating tars and pitches of the class; coke oven tar, water gas tar, coal tar, gashouse tars and pitches obtained from such tars at elevated temperatures and under superatmospheric pressure without substantial distillation thereof to a point where the desired amount of free carbon formation takes place but not beyond a point where pitch not capable of being cut back with liquid tar products is formed to produce a pitch having a substantially increased amount of free carbon as compared with the amount in the tars and pitches initially heated.

13. The method oi. producing pitch products of predetermined free carbon content, which comprises heating tars and pitches of the class;

CHARLES S. REEVE.