US2162366A - Activation of compressed wood - Google Patents

Description

Patented June 13, 1939 PATENT OFFICE 2,162,366 ACTIVATION OF COMPRESSED WOOD Maurice E. Barker and Robert S. Brown, Edgewood, Md.

no Drawing. Application April 21, 1932, Serial No. 607,901

15 Claims.

(Granted under the act of March 3, 1883, as amended Apr--30, 1928: 3'10 0. G. 757) This invention described herein may be manuiactured and used by or for the Government for Government purposes, without the payment to us of any royalty thereon.

5 Our invention relates to a processfor making charcoal, and more particularly has reference to a method of producing adense, active and highly retentive gas adsorbent charcoal from wood of any kind, which heretofore has been possible only by the use of very dense tropical woods.

We are well aware that there are many processes for producing active charcoal from wood, including among them impregnating the wood with an acid prior to carbonization, the practice of selectively oxidizing wood to increase the adsorption power of wood charcoal, and various methods which treat wood charcoal with steam or air at elevated temperatures. However, all of these processes produce a charcoal from ordinary wood containing many large pores, with a resulting low gas retentive value of the charcoal, although large amounts of gas may be adsorbed at high concentrations.

To overcome this difficulty, the art made use of Q5 the expedient of compressing the carbonaceous material employed into blocks or briquettes to increase its density. Such processes have been limited chiefly to the use of a raw material such as coal or charcoal fines, and have employed a binder for holding together the particles of the material treated. In addition, however, attempts have been made to compress wood fibers or other disintegrated wood products into blocks which have been subsequently carbonized, it being necessary to keep the wood as used in this form under pressure during carbonization.

It will hence be apparent that the major, object of our invention is the provision of a process for the production of a dense, active, and highly re im tentive gas adsorbent charcoal from ordinary Wood.

An equally important object of our invention is to provide a process for the formation of charcoal from wood blocks.

Another object of the invention is the provision of a method for forming charcoal from wood blocks, these being first thoroughly dried and then compressed so as to increase their density prior to their carbonization.

Still another object of our invention is to devise a method of forming a highly active gas adsorbent charcoal from solid wood blocks which have been impregnated with a dehydrating agent, then dried and compressed prior to' carbonization.

55 Yet another object of our invention is the provision of a process for producing an activated charcoal from compressed wood blocks impregnated with a dehydrating agent which includes carbonizing the blocks by heating them in the presence of air and then heating them at higher 5 temperatures in carbondioxide gas containing a little water vapor.

A further object of our invention is the provision of a process for forming activated charcoal from compressed wood blocks impregnated with a. 10 dehydrating agent which includes carbonizing the blocks by heating in the presence of air, then increasing the temperature of the heat treatment while heating in the presence of carbon dioxide with a little water vapor, crushing the blocks so 1 treated and activating the blocks in a stream of preheated carbon dioxide at activation temperatures.

A still further object of our invention is the provision of a process for the formation of dense, 20 active charcoal from compressed wood blocks which have been impregnated with a dehydrating agent and which after carbonization and after activation in a stream of preheated carbon dioxide gas are cooled in a stream of carbon 25 dioxide.

With these and other objects in view, the invention consists in the method to be hereinafter set forth and claimed, with the understanding that the steps. thereof and the treatment of the 80 raw materials employed may be varied, for it is apparent that many changes 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.

Broadly, the invention contemplates the provision of a process for the production of a dense, active, and highly retentive gas adsorbent wood charcoal. One manner of practically effecting the concept of the invention is to impregnate 40 dried wood blocks with a dehydrating agent, then again drying these blocks and finally compressing them so as to increase their density.

' The compressed impregnated blocks are next carbonized by heating in a furnace in the presence of air for a suitable time period, after which they are further heated at temperatures elevated above those employed in the first heat treatment,

6 in an atmosphere of carbon dioxide gas containing a small amount of water vapor.

Our invention also comprehends the crushing of the blocks treated in the manner just noted and the subjecting of he fines so obtained to activation in a stream of preheated carbon dioxide held at activation temperatures. After the acti- 65 vation step, the charcoal particles are cooled in -a stream of carbon dioxide and are then ready for use as adsorbent charcoal.

Before giving a complete description of our invention, it should be noted that in the activation of charcoal a primary charcoal is first formed in which the charcoal substance has a true density of about 1.46 and is without a definite X-ray diffraction pattern. After activation, a good chargas retained at zero partial pressure. Furthermore, the amount of gas retained per unit volume of the charcoal is the ultimatecriterion for a gas I mask charcoal. This use demands a charcoal of high apparent density as well as possessing the desired retentive properties. Our invention makes possible the production of such a charcoal from ordinary wood.

We have found that useful results may be attained by cutting wood into approximately two inch cubes, thoroughly kiln drying, compressing the wood to from ten to twenty thousand pounds per square inch, carbonizing the wood and finally activating by any of the known means. By such a process a dense active charcoal having a high retentive value can be formed.

An even better charcoal may be formed by first drying the two inch cubes of wood, impregnating these wood blocks with zinc chloride or other metallic chlorides, drying at a temperature below 100.C., compressing the blocks to approximately twenty thousand pounds per square inch, carbonizing and activating.

vIn following our preferred process, wood blocks which are approximately two inch cubes, are first kiln dried, after which they are impregnated with a good grade of zinc chloride from a 25% water solution by the full cell process.- The zinc chloride, as will hereinafter appear, acts as a dehydrating agent, and while this compound has been disclosed specifically, it is to be noted that in general any dehydrating agent may be employed. Included among such agents are the metallic salts of strong acids or metallic chlorides. Similarly in some instances, it may be found desirable to use more than one dehydrating agent as well as to vary the concentration of the dehydrating solution. The use of a dehydrating agent to increase the yield of charcoal from wood is old in the industry. Obviously, any change in the dehydrating agent employed. or its concentration, is well within the spirit of the invention and the scope of the appended claims.

Impregnation of the thoroughly dried block having been completed, the impregnated blocks are then kiln dried, for approximately two days, being treated at temperatures Just below 100 C. From the second drying step. just disclosed, the blocks are then compressed for the purpose of increasing the density of the wood. To this end, each block is held in a die, and subjected to a pressure of approximately twenty thousand pounds per square inch.

Other pressures may be employed, for it will be obvious to those skilled in the art that a variation in the pressure employed, while compressing the blocks, will only efl'ect their density. However, we have found that a pressure of approximately twenty thousand pounds per square inch produces satisfactory'results with the size of blocks employed.

The compressed impregnated blocks are now ready for carbonization so as to convert them into primary charcoal, which is subsequently activated. These blocks are first heated in a muiile furnace or other standard furnace in the presence of air at a temperature of 100 C., increasing to 200 C. for twenty-four hours. After this initial heating 'step, the blocks are again heated for about twentyfour hours in carbon dioxide gas containing a little water vapor at a temperature of about 200 C., slowly increasing to 800 C. The blocks are, after the second heating step, cooled out of contact with the air.

Prior to activation, and after the cooling of the compressed blocks, they are crushed so as to pass a six mesh screen and be held on a twelve mesh screen. The granules so obtained are then ready for activation, and to this end are loaded into trays, each tray containing granules to a depth of approximately one inch and are activated for about two hours in a stream of. preheated carbon dioxide at 800 C. to 850 C. Following this process the charcoal does not require washing since the metallic elements which remain are desirable in the final product thus obtained.

It should be observed that in carrying out the process, the raw material employed is in the form of solid wood blocks, which blocks are not disintegrated wood products or wood fibers. While we have had considerable success with wood blocks in the form of two inch cubes which have been compressed under a pressure of from ten to twenty thousand pounds per square inch, it is to be understood that the invention is not limited to this size of block or, as already pointed out, to any particular pressure.

In our process; it may be observed that the zinc chloride acts as a dehydrating agent and changes the wood to charcoal and water in the first part of the carbonization, thereby increasing the weight yield of charcoal. The zinc chloride, during the heating at 700 C. to 750 C. in the presence of carbon dioxide, is broken down to zinc oxide, and the chlorine thereof combines with the hydrocarbons present in the charcoal being treated. At the higher temperatures of 800 C. to 850 0. used, the chlorinated hydrocarbons which have been formed are broken down and given oil, additional hydrocarbons'reduce the zinc oxide, some of the zinc is vaporized, and graphite is formed in exceedingly small particle sizes.

Active charcoal produced by our process using any wood as a raw material has an apparent density of from 0.40 to 0.55. Compared to this should be noted the density of 0.25 to 0.30 for the product obtained by practicing the methods heretofore outlined as used by the prior art.

At the same'time, the gas retentivity of charcoal, prepared in accordance with our invention, is about double that of any charcoal produced from wood by following the teachings of the prior art previously noted.

It will hence be appreciated that by following our process a dense, active and highly retentive gas adsorbent charcoal may be produced from a relatively inexpensive and an abundant raw material, namely, wood. Moreover, in carrying out the process, the substances used in treating the raw material employed are also of an inexpensive nature while the process steps carried out are 01 such simple character that they may be performed with standard apparatus.

While we have'shownand described'the preferred manner of carrying out our invention, we wish it to be understood that we do not confine ourselves to the precise method set forth, byway of illustration, as it is apparent that many changes and variations may be made therein, without departing from the spirit of the invention, or exceeding the scope of the appended claims.

We claim:

1. A process of producing charcoal, includin the steps of impregnating wood blocks in their natural state with a dehydrating agent,.compressing the impregnated blocks under a pressure of 10,000 pounds per square inch or upward, and carbonizing the blocks by heat treatment.

2. A process of producing activated charcoal, including the steps of impregnating wood blocks with a dehydrating agent, compressing the impregnated blocks under a pressure of 10,000

7 pounds per square inch or upward, and carbonizing the blocks by first heating them in air and then heating them in carbon dioxide at temperatures elevated above those first employed.

3. A process of producing activated charcoal including the steps or impregnating wood blocks with a dehydrating agent, compressing the impregnated blocks under a pressure 01' 10,000 pounds per square inch or upward, and carbonizing the blocks by first heating themv in air and then heatingthem in carbon dioxide at temperatures elevated above those first employed, and cooling the blocks out of contact with the air.

4. In a process for forming wood charcoal, the steps of impregnating wood blocks with zinc chloride and then compressing the blocks under a pressure of 20,000 pounds per square inch, prior to oarbonization. l

5. A process for producing a dense primary charcoal suitable for activation to a gas adsorbent material, including the steps of impregnating non-comminuted wood blocks with a dehydrating agent, highly compressing the impregnated blocksto a density 01 1.0 or more, and carbonizing the blocks by heat treatinent.

6. In a process for forming primary wood char-' coal, the steps of impregnating wood blocks with a metallic chloride, and then highly compressing" the blocks to a density of 1.0 or more prior to carbonization.

7. In a process for forming wood charcoal, the steps of impregnating the wood blocks with zinc chloride, and then compressing the blocks under a pressure of approximately 20,000 pounds per square inch and then carbonizing the blocks in two stages, the second stage thereof being at a higher temperature than the first stage.

8. A process for forming dense primary charcoal from wood blocks comprising the steps of kiln-drying the blocks, impregnating the blocks with a dehydrating'agent, redrying the blocks, compressing the impregnated blocks to a density of 1.0 or more, and carbonizing the compressed blocks by heat treatment.

9. The method of forming a primary charcoal 1 from non-comminuted wood blocks comprising the steps of kiln-drying the blocks, impregnating the blocks with a dehydrating agent, redrying the blocks in air at approximately 100 (3., highly compressing the impregnated blocks to a density of 1.0 or more, and carbonizing the compressed blocks by heat treatment.

10. The method of forming activated charcoal from wood blocks comprising the steps of kilndrying the blocks, impregnating the non-comminuated blocks with a dehydrating agent, redrying the blocks in air, compressing the impregnated blocks to a density of 1.0 or more, and carbonizing the compressed blocks by first heating them in air and then heating them in carbon dioxide at temperatures elevated above those first employed.

11. A process of producing activated charcoal, including the steps of impregnating non-comminuted wood blocks with zinc chloride, highly compressing the impregnated blocks to a density of 1.0 or more, carbonizing the blocks by first heating them in air at approximately 100 C., and

then heating them in carbon dloxide at temperatures elevated above those first employed.

12. A process otproducing activated charcoal,

including the steps of impregnating non-comminuted wood blocks with a dehydrating agent,

highly compressing the impregnated blocks to a density of 1.0 or more, and carbonizing the blocks by first heating them in air, then heating them in carbon, dioxide at temperatures elevated above those first employed, and cooling the blocks out of contact with air.

13. A method of forming activated charcoal, comprising the steps of kiln-drying non-comminuted woodblocks, impregnating the blocks with a dehydrating'agent, redrying the blocks in air, highly compressing the impregnated blocks to a density of 1.0 or more, carbonizing the blocks by heating to approximately 200 C. in air, fol--v lowed by{ heating at gradually increasing higher temperatures in carbon dioxide gas, cooling the carbonized material out of contact with air, crushing the carbonized material, activating the crushed particles in a stream 0! preheated carbon dioxide at 800-900 C. for two hours, and cooling the particles out of contact with air. I

14. A process of producing dense primary charcoal which comprises cutting blocks 0! wood, compressing the blocks under a pressure or 10,000

pounds per square inch or upward, and carbonizing the compressed blocks by heat treatment.

15. In a process for forming wood charcoal, the steps or impregnating wood blocks with a metallic chloride, and then compressing the blocks under a pressure of 10,000 to 20,000 pounds per square inch prior to carbonization.

MAURICE E. BARKER. ROBERT 5. BROWN.