US1933579A - Preparation of charcoal from coal - Google Patents

Description

Patented Nov. 7, 1933 1,933,579 PREPARATION or CHARCOAL FROM co AL Maurice E. Barker, Edgewood, Md.

No Drawing. Application April 4,1932 Serial N0. 603,214

3 Claims.

(Granted under the act of March 3, 1883, as amended April 30, 1928; 370 0. G. 757) This invention described herein may be manufactured and usedby or for the Government for Government purposes, without the payment to me of any royalty thereon.

My invention relates to a process for forming primary charcoal and more especially has reference to a. process by which charcoal of this type may be obtained from coal.

This application is a continuation in part of application Serial No. 504,205, filed December 22, 1930.

Heretofore, great difiiculty has been encountered in obtaining primary charcoal from coal inasmuch as relatively high temperatures must be employed to carbonize the coal. This difficulty is due to the fact that the volatile portion of carbonaceous material, such as coal, when heated at temperatures above 500 C. breaks down into gas carbon which glazes the whole interior of the charcoal'particle. Such a granule is valueless as an adsorbent and can not be activated, at least up to the present, by any process.

It will hence be apparent that the major object of my invention is the provision of a process for the preparation of primary charcoal from carbonaceous material. I

An equally important object of my invention is the provision of a process whereby primary charcoal may be obtained from coal, the coal being heated to relatively high temperatures in the various steps of the process.

Another object of my invention is the provision of a process for the formation of primary charcoal from coal, the coal being heated at high temperatures and so treated that substantially no gas carbon is formed.

Still another object of my invention is the provision of a method for obtaining charcoal from coal, whereby the coal is distilled in a vacuum and is then oxidized by air while being heated.

Yet another object of the invention is to provide a process for the formation of primary charcoal from coal, the coal in the carbonizing step of the process being heat treated at relatively high temperatures in an atmosphere of a gas mixture containing a low oxygen content.

A further object of my invention is the provision of a method for preparing primary charcoal suitable for activation from a coal by successively vacuum distilling, air oxidizing, and carbonizing in a stream of a gas mixture containing a small percentage of oxygen.

r A still further object of the invention is the provision of a process whereby primary charcoal may be successfully formed from a non-coking coal of the anthracite, semi-anthracite, or semibituminous grades, the coal having a low ash content, which ash is fusible only at very high temperatures.

With these and other objects in view. which may be incident to my improvements, the invention consists in the method to be herein set forth and claimed, with the understanding that the several necessary steps comprising the invention may be accomplished in any order found most suitable for carrying the same into practical effect, without departing from the spirit of the invention and the scope of the appended claims.

The invention comprehends the provision of a process for the production of primary charcoal from coal. One method of practically efiecting the concept of the invention is the selection of a non-coking anthracite, semi-anthracite, or semibituminous coal as the raw material. The coal selected as the raw material should have a low ash content, which ash is non-fusible at high temperatures.

Briefly, the process first involves the steps of sorting, crushing to suitable sizes, and resorting the coal selected as the raw material, after which the coal is vacuum distilled. From the vacuum treatment, the coal is subjected to an oxidizing step in a suitable heater while an air current is passed over the particles being treated and on completion of this step is then allowed to stand for some time. The coal having been distilled and oxidized is then carbonized in an atmosphere containing a low percentage of oxygen, and at temperatures above. 500 C. Aftercarbonization of the coal, primary charcoal is obtained and this substance may be activated by the process disclosed in application Serial No. 504,205, or by any other process desired.

Before fully describing my invention, it should be noted that a primary charcoal may be defined as a charcoal which will adsorb less than 20% by weight of saturated carbon tetrachloride vapor at 25 C., while an active or activated charcoal will adsorb more than this weight of gas under the same conditions. As will appear, charcoal of this nature may be produced by following the method to be hereinafter outlined.

To. be observed is the fact that when coal is heatedat' temperatures above 500 C. gas carbon is formed and it is to the end of preventing the formation of this undesired substance while making use of an'inexpensive and vast supply of raw material that my invention is designed.

My investigation has shown that the volatile portion of coal readily adds oxygen, and when I this oxidized coal is heated at carbonizing temperatures under suitable conditions a porous mass remains which is free of gas carbon and which is readily activated by any of the standard processes, such as those employing the use of steam, carbon dioxide, or sulfur dioxide. Furthermore, I have found that the presence of a fusible ash in the coal likewise glazes the interior of the coal granule and effectively prevents subsequent activation.

Considering the type of grade of coal which is employed, it should be observed that coals can be divided into groups based upon many classifications. Anthracite is the densest and hardest of coals. Below anthracite are semi-anthracite and semi-bituminous, then bituminous coal, lignite and peat. Further, some coals swell on heating and are termed coking coals. Those that do not swell are termed non-coking coals.

When a coking coal is first slowly'oxidized at a temperature below the ignition temperature, the coal may subsequently be heated with very little swelling. However, in this case the charcoal remaining is brittle and easily shattered. A noncoking coal, on the other hand, when so treated yields a hard dense residue that has the necessary cohesion for use as a granular adsorbent. I therefore prefer to use a non-coking anthracite, semi-anthracite, or semi-bituminous coal having an ash content of less than 10%, which ash is non-fusible at 1000 C. as the raw material- A volatile content, as determined by the standard coking test, of at least 10% is desirable.

Bearing in mind the foregoing discussion, a non-coking coal having a non-fusible ash content of less than 10% and a volatile content of 10% or more, is selected as the raw material. This coal is sorted by any suitable machinery to remove slate and other earthy particles, after which it is crushed to such a size that the particles will pass a standard six mesh screen and be held on a 14 mesh screen. While crushing to this size has been described, it should be observed that if desired, coarser or finer particles may be employed without departing from the spirit of the invention or the scope of the appended claims. For example, in some instances, it may be found desirable to so crush the particles that they pass a six mesh screen and are retained on a ten mesh screen.

After the crushing and screening, the coal particles may again be sorted by machinery or-by any other means for the purpose 'of removing any slate or other undesired substances and materials remaining with them.

The coal particles are now ready for the distillation step in the process and to this end the granules are charged into any suitable apparatus and vacuum distilled at a temperature of about 300 C. for a period of approximately four hours. By this distillation, water and loosely held hydrocarbons are removed from the particles with the result that a more or less porous granule is formed.

From the distillation step, the coal granules are fed into a suitable heater in thin layers, not over one inch deep, and heated for a period of from 12 to 24 hours in-a gentle current of air at a temperature of approxmately 200 C. slowly increasing to approximately 400 C. While tempera-' tures of from 200 to 400 C. have been disclosed, it shouldbe noted that during this step, care should be taken at all times to hold the temperature of the coal below its ignition point. Some variation in the temperatures given may of gen for example) or by removing some of its concourse be expected, depending upon the class or grade of coal used. This treatment is for the purpose of causing the addition of oxygen to the hydrocarbons in the coal to the end of obtaining a porous mass, free from gas carbon, which may be readily activated.

Prior to carbonization and just after the oxidation of the granules, they are allowed to stand for'a period of about a week. By such an expedient further air oxidation of the coal occurs.

After the oxidation of the coal granules, this material is ready for carbonizing which may be carried'out in any suitable Mn, a tunnel kiln, of any standard design being preferred. In such an apparatus, the coal is heated gradually from a temperature of 500 C. to about 800 C. for a period of from 6 to 24 hours. During this heating, a slight vacuum may be maintained in the carbonization apparatus or preferably a gaseous mixture containing a low percentage of oxygen 9: may be passed through the kiln at a slight positLve pressure for the purpose of washing out the gases given up by the coal. A

In application Serial No. 504,205, there is disclosed a method for producing activated charcoal from a mixture of charcoal fines (primary charcoal) and wood flour, which mixture is treated with a sugar solution and a dehydrating fireproofing agent. This mixture is formed into briquettes and then subjected to a number of steps of heat treatment to activate the carbon content of the briquettes. In this application and specifically limited to the activation of charcoal fines brique'tted in this manner and subsequently subjected to heat treatment, in certain of the heating steps, a flue gas containing a'low percentage of free oxygen is passed through the heating apparatus at a slight positive pressure. Such a gas mixture is preferred in the carbonization step disclosed in this application.

The gas mixture preferred, besides oxygen, may contain nitrogen and carbon dioxide as well as other atmospheric gases, in each instance, care being taken that the free oxygen content of the mixture is less than 5% Not only does this treatment serve to remove the gases formed from the coal, but a preliminary activation takes place. By the use of such a mixture, it will be appreciated that an inexpensive method for removing the gases given up by the coal is provided inasmuch as in general any flue gas may be employed for this purpose. Moreover, the composition of a flue gas may be readily varied to meet any requirements by adding to its constituents (nitrostituents (oxygen for example).

Carbonization having been completed, the residue obtained therefrom, which residue is primary charcoal, is now ready for activation. This may be carried out by any standard activation process or if desired by bilquetting the charcoal fines and treating by the method disclosed in application 'Serial No. 504,205.

It will be appreciated from the foregoing description that I have provided a process for forming primary charcoal which allows the utilization of a vast and inexpensive supply of raw material, namely, coal. Moreover, by following the steps of the process heretofore outlined, carbonization of coal may be accomplished without the formation of gas carbon. It may also be observed that the method outlined is simple and inexpensive to carry out, standard apparatus being employed in all the steps.

While I have shown and described the preferred embodiment o! my invention, I wish it to be understood that I do not confine myself to the precise details set forth, as it is apparent that many changes and variations may be made therein by those skilled in' the art without departing from the spirit of the invention or exceeding the scope of the appended claims.

I claim:

1. A'method of forming adsorbent charcoal from non-coking coal or the anthracite, semianthracite, and semi-bituminous grades comprising the steps of sorting andcrushing the coal, distilling the granules obtained from crushing in partial vacuum at a temperature of approximately 300 C. until substantially all water and loosely held hydrocarbo'ns are removed, oxidizing the crushed particles by heating while passing an air current over the same, and carbonizing the particles by heating while passing a .flue gas mixture containing less than 5% tree oxygen thereover.

2. A method of forming adsorbent charcoal from non-coking coal of the anthracite, semianthracite, and semi-bituminous grades comprising the stepsot sorting and crushing thecoal, distilling the granules obtained from crushing in vacuum at a temperature of approximately 300 C. for four hours, oxidizing the coal particles by heating at slowly rising temperatures or from about 200 to 400 C. tor 24 hours while passing an air current over the same and then carbonizing thecoal particles by heating while passing a gas mlxturejcontaining less than 5% free oxygen thereover.

3. A method of forming adsorbent charcoal Irom non-coking coal otthe anthracite, semi- .anthracite,-and semi-bituminous grades com-x lzs.