US2362463A - Process of producing carbon and activating the same, and products thereof - Google Patents

Description

, PRESSURE OF /000 1a Nov..14, 1944. M. BOEHM ETAL 2,362,463.

R. PROCESS OF PRODUCING CARBON AND ACTIVATING THE SAME, AND PRODUCTS THEREOF Filed March 16, 1940 VOLUME E na/mac" (have: (/FUIY D Y N6 Elma/7765 (bnmzsszn (am 197' A? fivssswrs F mama/aim. film Cowm/m/vq flPPRDl/M47ELY '04 7% Wren, 72/: DEV/M6 fa Ca/vsm/vr '02 IVs/4H1 Bel/v4 Favor/v50 In! 4/1 177 I00 '6. (/00; 01m: 5094: IE'PREJENTS Kan/ME 0/ THE Ulla/WED 53/005723) 77M: l .SECOIVDJ 0/ HOLD/N6 (m 5 //v 61/ Hr 7/95 5764M INVENTOR .5 ROBERT M. BOEHM HORACE E. HALL ATTORNEYS .to provide an illustrative Patented Nov. 14, 1944 UNITED STATES PATENT OFFICE GIN. G THE SAME.

PROCESS OF PRODU TIVATING THEREOF Miss, Laurel, Miss.,

CARBON AND AC- AND PRODUCTS I Hall, Laurel, Corporation,

a corporation oil-Delaware Application March 16, 1940, Serial No. 324,442 6 Clain'1s. (or. 252-267) Our invention .relates to carbon and to a carbon base material for carbonizing, and to the Process of manufacture thereof.

Our carbon base material and carbon can be made from hard fibrous vegetable materials such .as wood of trees, or woody material of annual growths such as bamboo, cane, cornstalks, and the like, and nut and seed hulls containing lignocellulose in large proportions, as cottonseed hulls for example. Wood is the preferred material, and its use and treatment will be described in order an understanding of the invention.

With our invention, substantially the whole of the wood is used and there is no need for preliminary digestion and removal of parts thereof as in paper making for example.

Wood has heretofore been used in making car bon, as in the form of compressed briquettes of wood flour or compressed pieces of wood innatural state, but has the objection that swelling takes place particularly and designated herein the carbon base material, does not swell upon being dried. but on the contrary, shrinks in the invention added binders are not needed because our new carbonbase material isself-bonding, or in other words contains bonding materials formed in the course of its production, including su ars, wood tars and the like. With a small moisture content as about -10%. it has substanembodiment affording in carbonizing, etc.,

tially plastic properties and can be compressed without added binder into strong, dense, selfbonded briquettes.

Resort has heretofore sometimes been had to carbonizing materials under pressure in order to make carbon of increased density and hardness. While we could carbonize our new carbon base material under pressure if desired, it is an object of our invention to eliminate need for carbonizing under pressure. There is no need for use of pressure in carbonization and other heat treatments of our carbon base material because the briquettes thereof, not only shrink in drying as stated, but continue toshrink extensively treatments, and yield strong dense hard carbon.

A further object consists in dispensing with need for use of dehydrating agents such as zinc chloride, for example, ."heretofore considered essential for production of high-grade carbon.

A further object consists in theprovision of a novel type of high-grade primary carbon'with on the Rockwell scale and a hardness over a specific gravity over 1.1, and preferably, over 1.2, and roasted and activated, carbon of still higher hardness and specific gravity. The invention also includes other objects which will appear or be pointed out.

'I'hefirst step of carbon manufacture is the making of the intermediate or carbon base material from the wood. In this step, the woodin somewhat subdivided state, preferably wood in the form of chips of approximately 1" maximum dimension, is sublectedto hi h temperature and pressure in presence of moisture, and the temperature. pressure and time of such treatment is so regulated as to convert the ligno-cellulose material to a condition in which it will shrink upon drying and yield good hi h density carbon upon carbonization and subsequent heat treatments This treatment which we shall call thermohydrolvsls is preferably effected with high pressure steam. and steam treatment will be described. When the steam treatment is terminated. the converted material vis subdivided to a stateof finen ss, While the reduction to linene s c n be performed separately, as by grinding aft rtermination of the steam treatment, we nre erablv carry out the steam treatment by sub- ,iectin z the chips to high pressure steam. as for exam le ste m at a pressure of about 300-1200 lbs. per so. in. or hi her. and preferably at about 1000 lbs. nersq. in.

reduce the material to fineness by the disinteg'rating explosive discharge of .the material from the region of high pressure in the gun chamher, which ensues upon the opening up of the outlet from the gun chamber to a region of much lower, preferably atmospheric, pressure.

(Treatment of wood with high temperature and pressure .in also the use 01' steam therefor and for thereafter causing disintegration by explosive discharge of the material is known in the prior art, and same are not claimed herein per se, but only the application thereof to the manufacture of carbon base material and carbon, which is new with us.)

' The finely exploded carbonbase material on dropping from the cyclone, or other separating device into which the discharge from the gun is preferably led, can be collected and used 'without adding water or washing. However, by reason of the wood sometimes containing initially a considerablerproportion of water, asfor example approximately there being more 30%, and or less condensation to water of the steam used for the heat and explosion treatment, the heattreated and disintegrated carbon base material may contain a considerable proportion, as for example 50% of water, in which case partial drying can be resorted to in order to adjust themoisture contentas may-be desir With a given steam pressure, as for example 1000 lbs.- persq. in. and the steam treatment followed by explosive disintegration, the time of steam treatmentrequired for the preparation of a carbon base material having the important properties of shrinking on drying from com pressed state and upon carbonization, etc., heat treatments is to some extent dependent on the water content of the material used and on the nature of the material taken for treatment. This time is less for treatment of bone dry chips than for'wet chips since conversion into steam of water in the chips will take extra time varying with the percentage of water contained in the chips. Hardwood requires longer treatment with steam than materials of annual growth, and pine wood requires somewhat longer steam-treatment than hardwood such as "gumwoodand the like. The treatment oi gumwood, which is a type of hardwood and has an intermediate status from the standpoint of time of steam treatment required to secure the desired properties, will be selected to afford an exemplary disclosure. In a preferred embodiment of the step of preparing the carbon base material as outlined above, fibrous ligno-cellulose material consisting of dry gumwood chips, was subjected to the action of steam at a pressure of 1000 lbs. per sq. in., and corresponding temperature of 285 C., the steam treatmentconsisting of first bringing the steam up to the pressure of 1000 lbs. per sq. in. in 30 seconds after the chips had been introduced into the gun and the gun closed, followed by holding the steam pressure of 1000 lbs. per sq. in. on the chips for 20 seconds. The steam-treatment was then terminated and the steam-treatedmaterial was thoroughly disintegrated by explosive discharge from the region of high steam pressure as above described. The resulting finely divided carbon base material, was substantially devoid of original fiber structure and substantially dough-like in consistency and dark in color. Briquettes made at a pressure'of 10,000 lbs. per sq. in. from the material'so produced and containing about 7% of moisture were found to presence of moisture is known and l shrink about 5% upon drying to constant weight in four hours at C. Good results were obtained by carbonizing this carbon base material, and good activated carbon obtained by roasting and activation of the primary carbon, and. these treatments will be described later.

In making carbon base material good results can be secured by varying the time of holding at full steam pressure, as for exampie when using steam at 1000 lbs. per sq. in., varying the holding time from about 15 seconds to about 300 seconds. Lower steam pressure, such as 800 lbs. per sq. in. and corresponding temperature of 255 C. can be used by taking a longer time for the heat treatment, as about 1-10 minutes, and still lower pressures as down to about 300 lbs. per sq. in. with much longer times as about 15-40 minutes, but with somewhat less desirable results from the standpoint of explosive disintegration. Higher pressures than 1000 lbs. as 1200 lbs. per sq. in. can also be used with shorter times as about 10-200' seconds.

Organic acids as acetic and formic acids are developed in the treatment with high pressure steam, and the carbon base material so produced in any of the ways above described is of low pH, usually below 3.5 pH. The acids appear to attack some parts of the wood fiber. and in any event, with exposure of the wood to steam at a pressure as high as 1000 lbs. per sq. in. for a holding time as long as 20 seconds for example, folllowed by explosion, the resulting carbon base material becomes substantially devoid of original fiber structure.

Sugars and the like may be incorporated with our carbon base material if desired, as heretofore sometimes practiced with other materials for carbonizing. However, with use of a starting material consisting of wood or equivalent lignocellulose material, and which contains hemi-celluloses and the like materials which are at least partially converted to sugar forming materials and sugars in the heat treatment process as above described, the addition of sugars from extraneous sources is ordinarily unnecessary. The sugar forming materials and sugars being freed or formed in situ in our carbon base material in the course of its production, and being retained therein, can perform the same functions in the carbonizing and other heat treatments, as if added from extraneous sources at resultant increased expense. Furthermore the sugars, etc., formed in the carbon base material itself are in a better state of distribution throughout the material than can be obtained by adding sugars from extraneous sources.

' Constituents having bonding properties in addition to the sugars as above referred to, and apparently including wood tars. pentosans, hexosans, and the like materials, are also developed or freed by the steam treatment, and the steamtreated carbon base material is plastic or substantially so, and isself-bonding and so requires'no added binder, although binders could be added if desired. This high self-bonding property of our carbon base material and its property of shrinkage without cracks and strains in drying from compressed state, and further shrinkage without rupture in carbonization and other heat treatments appear to be at least in large part a result of the steam treatment, since briquettes of wood material which have not been given such steam treatment, such as wood flour for example, even when compressed at 50,000 lbs. pressure per sq. in., swell upon drying and yield on carbonization aseasos I i a I 3 only a loosely bonded and crumbly carbon. The shrinkage, and with absence of cracks, and usexplosion treatment following steam treatment is sures, and 01' strains which would develop into also apparently beneficial in that gases and gas such. defects upon carbonization and later heat forming-materials may be eirectively swept out treatment. In pointing out below the extents by the escaping steam. I 5 to which shrinkage or reduction in volume takes We preferably .form the preferably unwashed place upon subjection oi ourcarbon base matecarbon base material into. shapes. For example, rial to various heat-treatments, the volume. or the doughy-material above referred to. with or the dried blocks, pellets or the like before carwithout someadiustment of watercontent to get bonization will e ak n as he basis for comthe most workable consistency, canbeiormed l parison. into ribbons by forcible extrusion through slot- Inthe accompanying dra like apertures, and dried in such ribbonv form, and 01' this specification the per wing forming a part i such extrusion, and .tor extrusion the waterconmaterial containing about 7% 0 good strength and density. 111 8 118 t e carbon asematerial from which In order to secure carbon of highergstrength these q es w re made, dry gumwood chips and density, the steam-treated and subdivided as e e d under 1000.1bssteam p e s e er sq. carbon base material is preferably formed into 111 1 8 111 f ll W ng the bringing up to such shapes of higher density than obtainable by such Pressure, and then plosively discharged. extrusion treatment, as for example it can be As appears from this chart, with steam treat- V2 seconds at 1000 For example, by adjusting the moisture content 05 lbs. per ,sq. in. .thereis substantially no change of the carbon base material prepared asv above in the volume or the briquettes'oi carbon base described to about 5%-10%, which can be accommaterial upon drying as above described. With plished by an expression treatment followed by a shorter time of exposure to such steam treatpartial drying, and then grinding the material inent in'the gun, swellingoi'the resulting. briand cold-compressing it under moderately {high quettes will take place upon drying, u

pensively formed into blocks or briquettes which steam treatment for a period or are of high density approaching the ultimate with the steam pressure. merely density of wood fiber, as'for example, 1.35 ,sp. gr., 1000 lbs. per sq. in. and the charge immediately and extremely hard. In these and other ways, exploded. Briquettes made or crack and rupany desired volume from quite large pieces to ure when carbonized and are not suitable for the small pellets. Cold-compressing of the carbon purposes of our invention.

base material at substantially room temperature 'As the time of sustained exposure 01' the chips is most desirable, as with this treatment, primary 40 to st am in th gun at thi pressure i increased carbon and activated carbon with'higher density bey'ondabout 3% seconds, shrinkage will take and hardness can be made from the resulting place upqn'drying, an th shrlnkag upon drycarbon base briquettes, pellets and the like than jngjncreases and appmgchesgmaximum of about when this material is compressed in heated state 6% mm ab ll nto tea a 10001 l with chips if m be s... has: massages a later Stagewill develop itsmaximum shrinkage on drying The blocks, pellets or other shapes are thorfrom compressed state and'yl-eldgood hard dense oughly dried. When the carbon base material primary and a'cmvate has been prepared by a steam treatment carrled preferred.

After drying our new carbon base material seconds or more with steam at 1000 lbs. pressure I per in" and highly compressed, not only does is carbonized. Ifhe carbonization can be carried ing, as for example about 6% reduction in volabout 4 hours with 1" blocks containing about Fired in y. 01 the Ways above described as Drei- I "7% of moisture, and in this treatment. materials l is believed 1 e unique in that, if d? I other than water which are volatile at this temred. the carbonization can be r p y e ormed perature, as some fur-rural and acetic acid for 1 he ma rial n relativelvl rs p 1 carbon base material is thus dried not only with cracking or-rupturing, "and with practicall the complete absence of swelling but with definite lame esultlngdensitr I! when muchi n r time 7 Carbon made from wood flour briquettes is used in the carbonization treatment. For example, the .carbonization of our carbon base material prepared by a steam treatment of chips at 1000 lbs. per sq. in. for 20 seconds as above described can be satisfactorily effected in three hours.

Carbonization over a period of 12-24 hours is, however, ordinarily preferable, particularly with large blocks, with a gradual heat increase up to about 450 C., care being exercised to prevent too rapid heat increase from exothermic causes. Air is excluded during carbonizing. the preferred atmosphere for this purpose consisting of CO: gas. Other inert gases can be used. A further and very considerable shrinkage of previously dried and shrunk pellets, briquettes and the like made from our carbon base material takes place during carbonization, as a shrinkage to about one-half or somewhat less than onehalf of the volume of the blocks, pellets, etc. in

dry state prior to carbonization. The specific gravity is ordinarily reduced somewhat by the carbonization but this reduction is ordinarily not considerable, as for example a dry pellet of 1.35 sp. gr. may have its gravity reduced to about 1.1-1.26. The primary carbon 50 obtained is strong and hard and free from cracks, fissures and like defects. The apparent density of our primary carbon is approximatel one half the specific gravity, or about 0.55-0.63.

The carbon made from our improved carbon base material produced by sui'ilcient exposure to steam treatment is very hard and resistant to abrasion. The following table shows in the righthand column Rockwell hardness values of our primarycarbons, and in the left-hand column shows thematerials from which the carbon was produced.

Rockwell hardness number compressed at a pressure of 50,000 lbs.

per sq. in 97 Carbon made from gumwood chips converted to carbon base material under steam pressure broughtup to 1000 lbs. per sq. in. and held at such pressure for times in seconds indicated below, and which are both above and below the preferable time, exploded from this pressure, and compressed with about 7% moisture content into briquettes at 10,000 lbs. per sq. in., and their carbonized for 14 hours at temperature to 450 C.:

It has been found that activation can be later carried on to best advantage and the densest activated carbon obtained when theprimary carbon, obtained by carbonization treatment of our carbon base material as just described is' next given a roasting treatment. During roasting some of the residual hydrocarbons are driven off. 7 This can be accomplished without appreciable loss of carbon by passing flue gas through the material,

aseaaca but the oxygen content, if any, of the flue gas should be kept quite low, preferably under 5%. Carbon dioxide or inert gases such as nitrogen can be used. A desirable roasting procedure consists in application of a temperature of 750 C. for approximately 2 hours. Lower temperatures and longer times may be used, as approximately 600 C. for 4 hours. Additional shrinkage goes on during roasting usually to approximately two-fifths of the volume of the blocks, pellets, etc., in dry state prior to carbonization, and takes place without cracking or the like. It is accompanied by some loss of weight caused by reduction in hydrocarbon content. The density is increased by the roasting, as for example pellets which had an apparent density of .55-.63, after carbonlzing, may have this apparent density increased by roasting to about .65-.'13.

The activation is next performed. During activation the remaining hydrocarbons are largely expelled, leaving activated carbon of enormous surface due to pores and capillaries having been emptied of hydrocarbon material.

While activation can be accomplished in various ways, the activation treatment which appears optimum for carbon made from our carbon base material, which has preferably first been roasted, consists of heating, in an atmosphere containing steam, to a temperature of'approximately 850 C.-l000 C. for about 2 hours. In a preferred procedure, during the first hour a volume of superheated steam preferably equal to about one-half the weight of carbon is passed through it. During the second hour the volume of steam can be reduced, as to about one-fourth the weight of the carbon. A rotary kiln is preferably used for activation treatment in ordento get uniform treatment throughout the material. Further shrinkage takes place during activation, bringing the volume down for example to approximately one-third of the volume in dry state prior to carbonization. The loss in density in activation, if any, is very slight, and in the activation treatment as in other heat treatments, a sound product is made free from fissures and cracks. The acidity of the carbon base material disappears in the heat treatments and the pH of the activated carbon for example is approximately 10.7.

The activated carbon so produced, when suitably ground and screened if made in large pieces, or without reduction in size if made in suitably small pellets, is suitable for use in gas masks, for absorption of vapors in industrial plants, and for purifying air in air conditioning systems, and

various other purposes requiring a high-grade activated carbon. By making activated carbon out of small pellets of our carbon base material and with choice of proper size of the pellets, they can be made to shrink to predetermined size in drying, carbonizing, roasting, and activation, and used in gas masks and for solvent recovery for example, directly upon activation, without need for subdivision to smaller sizes. This activated carbon is very low in ash, a typical figure for ash content being 1.5%.

As has been indicated, the steps of steamtreatment and carbonization may overlap to some extent. Also while the steps of drying, carbonizing,-roasting, and activating have been described separately and are preferably so performed, it is not essential that they shall be completely separate in all cases.

Th use of dehydrating agents such as zinc chloride is not required with our invention at any stage, and without their use a dense, hard carbon can be made by our invention which is at least the equal of the best grades of carbon 'produced with use of such agents. Elimination of need for such dehydrating agents is of great. advantage since if used in preparing the carbon they must be washed out of the carbon for most applications, and this requires large quantities of water and subsequent; drying. Dehydrating agents such as zinc chloride quickly destroy the eflectlveness of copper or copper oxide customarily used in gas mask carbon, and if present in carbon to be used for solvent absorption and other commercial purposes they must be eliminated as completely as possible before the carbon can be used. In making our improved carbon no chlorides or equivalent materials need be added at any stage, and consequently no treatment is needed for their elimination, and in these and other ways our invention provides valuable high grade primary and activated carbon, and enables its production in large quantities from sources of material which are readily available, and at low cost.

From th material prepared from wood or equivalent ligno-cellulose material by use of high pressure steam as above described furfural and volatile organic acids may be recovered during drying and carbonization. By-products may also be obtained which are at least in part such as normally secured in connection with the destructive distillation of wood. The expressed liquors contain materials from which products such as furfural, organic acids as acetic and formic acids, sugars and sugar derivatives can be recovered. Still further lay-product recove'ry can be accomplished by condensing the steam used for steamtreatment and explosion of the chips and carrying volatile constituents therefrom.

We claim:

1. Process for producing carbon material comprising the steps of providing a supply of loosely subdivided, fibrous, ligno-cellulose material, subjecting said material to steam at an elevated pressure for a sufiicient time to eliminate substantially all original fiber structure, disintegrating such treated material into a mass of particles, partially drying the mass of particles in such manner and to such extent that the greater proportion of water is removed and most of the water soluble material formed during the heat treatment is retained therein, cold-compressing said particles, drying the material at such temperatures and for such a period of time as to cause material shrinkage and as to avoid any substantial occurrence of cracks and fissures therein on said drying and on further heating, and carbonizing the compressed material in the substantial absence of oxygen.

2. Process for producing carbon material comprising the steps of providing a supply of coarsely subdivided, fibrous, ligno-cellulose material, subjecting said material to steam at an elevated pres sure for a sufllcient time relative to the steam pressure employed to eliminate substantially all original fiber structure, disintegrating the material by explosive discharge from the region of material, subjecting said drying the mass in such manner and to such extent that the greater proportion of water is removed and most of the water soluble material formed during the heat treatment is retained therein, cold compressing a mass of said particles, drying the material at such temperatures and for such a period of time as to cause material shrinkage and as to avoid any substantial occurrence of cracks and fissures therein on said drying and on further heating, and carbonizing the compressed material in the substantial absence of oxygen.

3. Process for producing activated carbon which comprises the steps of providing a supply of coarsely subdivided, fibrous, ligno-cellulose material, subjecting said -material to steam at an elevated pressure for a suflicient time to eliminate substantially all original fiber structure, disintegrating such material into a mass of particles, partially drying the mass of particles in such manner and to such extent that the greater proportion of water is removed and most of the water soluble material formed during the heat treatment is retained therein, cold compressing said particles, drying said compressed material at such temperatures and for such a period of time as to cause material shrinkage and as to avoid any substantial occurrence of cracks and fissures therein on said drying and on further heating, carbonizing the material by subjecting same to carbonizing temperatures in the substantial absence of oxygen, and subjecting the carbonized material to activating conditions.

4. Process for producing activated carbon which comprises the steps of providing a supply of coarsely subdivided, fibrous, ligno-cellulbse material to steam at an elevated pressure for a sufficient time relative to the pressure emloyed to eliminate substantially all original fiber structure, disintegrating the material by explosive discharge from the region of elevated steam pressure to a region of lower as atmospheric pressure to form a mass of particles, said mass being of dough-like consistency, partially drying the mass in such manner and to such extent that the greater proportion of water is removed and most of the formed during the heat treatment is retained therein, cold-compressing a mass of said particles, drying said compressed material at such temperatures and for such a period 01 time as to cause material shrinkage and as to avoid any substantial occurrence of cracks and fissures therein on said drying and on further heating, carbonizing the material by subjecting same to carbonizing temperatures in th substantial absence of oxygen, and subjecting the carbonized material to activating conditions.

5. A carbon material produced by the process defined in claim 1.

6. An activated carbon material produced by the process defined in claim 3.

ROBERT M. BOEHM. HORACE E. HALL.

water soluble material

Images