CA1124702A - Manufacture of activated carbon - Google Patents
Manufacture of activated carbonInfo
- Publication number
- CA1124702A CA1124702A CA324,785A CA324785A CA1124702A CA 1124702 A CA1124702 A CA 1124702A CA 324785 A CA324785 A CA 324785A CA 1124702 A CA1124702 A CA 1124702A
- Authority
- CA
- Canada
- Prior art keywords
- furnace
- suspended
- temperature
- carbonisation
- cloth
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D39/00—Filtering material for liquid or gaseous fluids
- B01D39/08—Filter cloth, i.e. woven, knitted or interlaced material
- B01D39/083—Filter cloth, i.e. woven, knitted or interlaced material of organic material
-
- A—HUMAN NECESSITIES
- A24—TOBACCO; CIGARS; CIGARETTES; SIMULATED SMOKING DEVICES; SMOKERS' REQUISITES
- A24D—CIGARS; CIGARETTES; TOBACCO SMOKE FILTERS; MOUTHPIECES FOR CIGARS OR CIGARETTES; MANUFACTURE OF TOBACCO SMOKE FILTERS OR MOUTHPIECES
- A24D3/00—Tobacco smoke filters, e.g. filter-tips, filtering inserts; Filters specially adapted for simulated smoking devices; Mouthpieces for cigars or cigarettes
- A24D3/06—Use of materials for tobacco smoke filters
- A24D3/16—Use of materials for tobacco smoke filters of inorganic materials
- A24D3/163—Carbon
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D39/00—Filtering material for liquid or gaseous fluids
- B01D39/08—Filter cloth, i.e. woven, knitted or interlaced material
- B01D39/086—Filter cloth, i.e. woven, knitted or interlaced material of inorganic material
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B32/00—Carbon; Compounds thereof
- C01B32/30—Active carbon
- C01B32/312—Preparation
- C01B32/336—Preparation characterised by gaseous activating agents
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B32/00—Carbon; Compounds thereof
- C01B32/30—Active carbon
- C01B32/354—After-treatment
- C01B32/382—Making shaped products, e.g. fibres, spheres, membranes or foam
-
- D—TEXTILES; PAPER
- D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
- D01F—CHEMICAL FEATURES IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS; APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OF CARBON FILAMENTS
- D01F9/00—Artificial filaments or the like of other substances; Manufacture thereof; Apparatus specially adapted for the manufacture of carbon filaments
- D01F9/08—Artificial filaments or the like of other substances; Manufacture thereof; Apparatus specially adapted for the manufacture of carbon filaments of inorganic material
- D01F9/12—Carbon filaments; Apparatus specially adapted for the manufacture thereof
- D01F9/14—Carbon filaments; Apparatus specially adapted for the manufacture thereof by decomposition of organic filaments
- D01F9/16—Carbon filaments; Apparatus specially adapted for the manufacture thereof by decomposition of organic filaments from products of vegetable origin or derivatives thereof, e.g. from cellulose acetate
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2239/00—Aspects relating to filtering material for liquid or gaseous fluids
- B01D2239/04—Additives and treatments of the filtering material
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2239/00—Aspects relating to filtering material for liquid or gaseous fluids
- B01D2239/10—Filtering material manufacturing
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2239/00—Aspects relating to filtering material for liquid or gaseous fluids
- B01D2239/12—Special parameters characterising the filtering material
- B01D2239/1233—Fibre diameter
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2239/00—Aspects relating to filtering material for liquid or gaseous fluids
- B01D2239/12—Special parameters characterising the filtering material
- B01D2239/1291—Other parameters
Landscapes
- Chemical & Material Sciences (AREA)
- Inorganic Chemistry (AREA)
- Engineering & Computer Science (AREA)
- Organic Chemistry (AREA)
- Textile Engineering (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Materials Engineering (AREA)
- General Chemical & Material Sciences (AREA)
- Carbon And Carbon Compounds (AREA)
- Inorganic Fibers (AREA)
- Treatment Of Fiber Materials (AREA)
- Solid-Sorbent Or Filter-Aiding Compositions (AREA)
Abstract
ABSTRACT
Activated carbon is made by pre-treating a fibrous cellulose material with a Lewis acid comprising one or more selected halides, drying and softening the treated material, suspending the material from a frame in a tensionless manner, heating the suspended material in a furnace to effect carbonisation of the cellulosic material in an environment which is substantially non-reactive towards that material, activating the suspended carbonised material at an elevated temperature in an atmosphere comprising an activating gas until the desired degree of activation has been produced, and thereafter cooling the furnace, the furnace having at least one heating element at its base and at least one heating element arranged on or in a side wall, each heating element being spaced apart from the suspended material.
Activated carbon is made by pre-treating a fibrous cellulose material with a Lewis acid comprising one or more selected halides, drying and softening the treated material, suspending the material from a frame in a tensionless manner, heating the suspended material in a furnace to effect carbonisation of the cellulosic material in an environment which is substantially non-reactive towards that material, activating the suspended carbonised material at an elevated temperature in an atmosphere comprising an activating gas until the desired degree of activation has been produced, and thereafter cooling the furnace, the furnace having at least one heating element at its base and at least one heating element arranged on or in a side wall, each heating element being spaced apart from the suspended material.
Description
i~Z~702 This invention relates to the manufacture of activated carbon from a fibrous cellulosic material, more especially to the manufacture of such carbon in the orm of cloth.
According to one previous proposal, activated carbon in cloth form is produced in a continuous manner by pulling a fibrous organic cloth, for example, a cellulosic cloth, upwardly between and spaced from a pair of longitudinally ex-tending heating elements arranged to raise the temperature of the moving cloth to effect carbonisation of the cloth in an inert atmosphere followed by activation of the carbonised cloth. The same previous proposal also comprises treatment of the cloth with certain Lewis acids before carbonisation.
British Patent Specification No. 1 505 095 relates to a batch process in which a length of cellulosic cloth is first treated with one or more Lewis acids, the treated cloth is dried and then softened by means of a breaking machine, and the softened cloth is suspended from a frame in a tensionless manner (that is to say, under no tension except that arising from its own weight) and heated in a furnace in a suitable atmosphere to effect carbonisation followed by activation of the cloth. As described in Specification No. 1 505 095, the heating elements in the furnace are arranged across its base.
The present invention provides a batch process for the manufacture of 2Q activated carbon, which comprises; (a) treating a fibrous cellulosic material by contacting it with at least one Lewis acid selected from the group consisting of halides of zinc, aluminum, calcium, magnesium, iron, barium, ammonium and chromium; (b) drying the treated material; (c) subjecting the dried material to a mechanical softening treatment; (d) suspending the softened material from a frame in a tensionless manner, said frame being positioned within a furnace .;
adapted to effect carbonisation of the cellulosic material, the furnace having at least one heating element at its base and at least one heating element arranged
According to one previous proposal, activated carbon in cloth form is produced in a continuous manner by pulling a fibrous organic cloth, for example, a cellulosic cloth, upwardly between and spaced from a pair of longitudinally ex-tending heating elements arranged to raise the temperature of the moving cloth to effect carbonisation of the cloth in an inert atmosphere followed by activation of the carbonised cloth. The same previous proposal also comprises treatment of the cloth with certain Lewis acids before carbonisation.
British Patent Specification No. 1 505 095 relates to a batch process in which a length of cellulosic cloth is first treated with one or more Lewis acids, the treated cloth is dried and then softened by means of a breaking machine, and the softened cloth is suspended from a frame in a tensionless manner (that is to say, under no tension except that arising from its own weight) and heated in a furnace in a suitable atmosphere to effect carbonisation followed by activation of the cloth. As described in Specification No. 1 505 095, the heating elements in the furnace are arranged across its base.
The present invention provides a batch process for the manufacture of 2Q activated carbon, which comprises; (a) treating a fibrous cellulosic material by contacting it with at least one Lewis acid selected from the group consisting of halides of zinc, aluminum, calcium, magnesium, iron, barium, ammonium and chromium; (b) drying the treated material; (c) subjecting the dried material to a mechanical softening treatment; (d) suspending the softened material from a frame in a tensionless manner, said frame being positioned within a furnace .;
adapted to effect carbonisation of the cellulosic material, the furnace having at least one heating element at its base and at least one heating element arranged
- 2 -.
~ZA70Z
on a side wall, each heating element being spaced apart from the suspended material, whereby said suspending places a plurality of the fibers in the fibrous cellulosic material transverse across the furnace; (e) heating the suspended material in said furnace to effect carbonisation of the cellulosic material; in an environment which is substantially non-reactive towards the material, said heat being directed into the suspended material from a first direction on the side of the suspended material and from a second direction beneath the suspended material; (f) activating the suspended carbonised material in an activating gas until the desired degree of activation has been produced; and (g) thereafter cooling the activated material. The fibrous cellulosic material is preferably a cellulosic cloth.
The process of the invantion is capable of producing activated carbon of surprisingly good quality and in good yield. It is especially surprising that the variation in product quality over the length of the material is acceptably small, whereas it might have been expected that the outer portions of the material suspended in the furnace would be affected by the carbonisation and activation operations to a substantially greater extent than those portions of the fibrous material that are situated towards the interior of the configuration, owing to the relatively close proximity of the lateral heating elements to those outer 2Q portions and to the fact that the inner portions would seem to be shielded from those heating elements by the intervening fibrous material, especially in the case of cloth material.
Also, as compared with the previously proposed continuous process, the process of the invention offers various advantages. Firstly, it is capable of producing activated carbon cloth of ~ z~02 similar quality with higher throughput at sub~tantially lower capital cost.
Secondly, in the proce3s of the invention, the residual acid content of the activated carbon product (for example, hydrochloric acid derived from the use of a chloride as Lewis acid) can be made relatively small. Thus~ in the continuou3 process, re-absorption of, for example, hydrochloric acid in the upper part of the furnace (especially in the region near the outlet ~here the temperature of the cloth may have fallen to 30 C. or so), may result in ~ re~idual acid content of from 2 to 5%, which in turn necessitates a ~pecial washing treatment of the product with water before use~ By contrast, in the process of the present invention, the activated carbon product can be made practically free from acid contamination, that is to say, with a residual acid content of only o.1 to 0.5%, and even less in some cases. Those beneficial results are obtainable by a combination of temperature control and gas purge, arranged to ensure that most of any acid vapour is expelled before cooling the activated carbon product.
Thirdly, utopping-upU the activity of the product, by prolonging the activation stage after testing a sample of the product, i9 a simple operation in the process of the invention, ~ut impossible in the continuous process.
The fibrous cellulosic material may be in the form of a single filament or as staple fibre, but is preferably a cellulosic cloth~
~2~702 The preliminary treatment of the cellulosic material with one or ~ore Lewis acids provides various beneficial effect3 depending primarily on the particular acid or acids used, ~ut also on the treatment time and on ~he proce~ing and drying temperatures employed. The advantage~ obtainable by the Lewis acid treatment include increased carbonisation yield, and increa~ed produ~t strength.
Advantageously, the or each Lewis acid is a br~mide or a chloride, and is preferably a chloride. A preferred treating agent comprise~ a mixture of zinc chloride~ aluminium chloride and ammonium chloride, the preferred concentration of each chloride in aqueous solution being approximately 30 by weight.
In general, the fibrous cellulosic material i8 contacted (for example, by immersion or ~praying) with a solution or di~perqion, more e3pacially aqueous, of the selected LeWiB
ac~d or acid~ The concentration of Lewi~ acid in the -colution or ~i~persion may be in the range o$ from 1 to 30 by weight~ preferably from 2 to 10~ by weight.
~ In the process of the invention, the fibrous cellulosic material is contacted with one or more Lewi9 acid~ before any carbonisation is effected. It is p3~sible, however~ to incorporate a further quantity of a Lewi9 acid with the cellulo~ic material during carbonisation.
Further detail~ ragarding the effect of various Lewi~ acid treatments on carboni3ation may be found~ for example, in Briti~h Patent Specification No. 1 301 101, The treated cellulosi~ mater~al may bo dr~ed at a temperature in the range of from room temperature to t40C or more, a drying temperature towards the upper or lower end of that range being preferred.
Softening of the cellulosic material to remove or reduce the st$ffness resulting from the Lewis aG~d treatment may ~e effected in a variety of ways, for example, by manual w~rking or by drawing the material over a smooth edge. Preferably, however, to produce an activated carbon of high breaking strength, the softening i3 effected using a breaking machine, which may be a pin-stenter or, more e~pecially, the type of machine known in the textile indu~try as a qpiral-roller breaker.
-~ The fibrous cellulosic material i8 su~pended from a frame in a tensionless manner, that is to say, under no ten~ion except that arising from the weight of the material. A~ a ~24~)2 result, substantially full ~hrinkage of the matexial takeq place during the carbonisation and activation operationq. Because the material is suspended so a~ to be able to shrink freely in all direc:tions, no tension is caused by the shrin~age. By contrast, in the previously proposed continuous proces3 referred to herein-before, tension is generated in the warp as the cloth .qhrinks, resulting in weakening of the cloth product.
It is important, however, to avoid undue tension arising from the weight of the fibrous material, especially in the case of cloth. In general, the heig~t of a cloth configuration suqpended from the frame should not exceed.5 metres, and is advantageou-qly not more than 2 metres. A preferred heig~ is 1 metre ~ ~X.
~aturally, the tension produced in suspended cloth by its own weight depends in part on the weight per unit area of the cloth and, advantageously, the maximum tension in suspended cloth (in a vertical direction and excluding regions in the immediate vicinity of points at which the cloth is suspended), is 5 gm per cm length across the top of the suspended configuration, and the - maximum tension preferably does not exceed 4 gm per cm length.
Advantageously,. the weight of a cellulosic cloth before the Lewis acid treatment is in the range of from 20 to 30 mg/cm2.
Typically, the diameter of the fibreQ in the cloth will be in the range of from 5 to 20 ~.
Advantageou~ly, the su~pension frame is attached to the underside of a removable lid of the furnace, and is preferably pivotally mounted under the lid to facilitate hanging of the fibrous cellulosic material.
Preferably, a cellulosic cloth i9 suspended in a spiral configuration, but other configurations may be adopted, ~12~0~ .
for example, a serpent~ne or star-shaped configuration. It will be appreciated that, in texms of proce~s throughput~ it i8 desirable to suspend the cloth in a configuration which allow~ the maxLmum length of cloth to be contained within a given volume. That consideration i~ subject, however, to the turns or folds of cloth being suspended sufficiently far apart to permit adequate heat transfer to the ~hole length of cloth, and adequate access of gas, especially during activation.
Advantageously, the length of a cellulo~ic cloth that is suspended from the frame is in the range of 50 to 150 metres, preferably at least 80 metres, and more especially from 90 to 110 metres.
A cellulosic cloth material may be suspended ~y means of hooks secured to the fxame and pa~sing through an upper edge portion of the cloth. Instead, cloth may be suspended by _ means of clips which engage the upper edge portion~ or may bs folded longitudinally over a ~eries of transverse supporting ra~s In the case ~here cloth i8 ~uspended from hooks or other suspension means acting on an upper edge portion, there will initially be excess cloth hung between adjacent suspansion position~ to allow for shrinkage during the carbonisatîon and activation operations. As a result, the cloth will hang initially in a wave-like form, and adjacent turns or folds may touch in places.
~ ~ . ~ .
li:Z 4702 Advantageously, the distan oe between adjaoent suspension positions along the same fold or turn of a suspended cloth con-figuration does not exceed 15 cm. The minimum distan oe between the suspensian positions of adjacent turns or folds of the suspended cloth may be in the range of from 1 to 5 cm., advantageously from 1 to 3 cm., and preferably from 1.5 to 2.5 cm. The minLmwm preferred spacing of the suspension positions of adjaoent turns or folds de-pends on the height of the suspended configuration ~which corres-ponds to the width of a cloth strip to be processed), and may vary, for example~ from 1 cm. in the case of a 1/2 m. width to 2 cm. for a metre width. The preferred spacings can be exceeded, but there will in general be little or no advantage in so doing to oompensate for the resulting reduced area of cloth that could then be accommD-dated at any one time in a furnaoe of given volume, and for the re-sulting reduoe d throughput.
qhe frame and associated SuSpensiQn means will be arranged to enable the fibrous oellulosic material to be suspended in the de-; sired configuration. A preferred form of frame, for suspending cloth in a spiral, oo~prises a plurality of radial arms (each, say, 0.5 to 1.0 m. in length) each providing a series of discrete suspension posi-tians, some of the arms extending outwardly from cross-pie oes arranged between adjacent radial arms. Advantageously, the number and arrangement of radial arms and of the suspension means thereon is such that the maxim~m spacing between adjaoent suspension positions 1/ .
'1124'702 along the ~ame ~urn of the cloth is 15 cm., and the ~pacing between adjacent su~pension po~itions along the same radial arm is advantageou~ly in the range of from 1 to 5 cm., preferably from 1 to 3 cm., more e~pecially from 1.5 to 2.5 cm. .
The spacing between the top and bottom of the suspended configuration and the top and bottom, respecti~ely, of the furnace may be in the range of from 10 to 20 cm. ~measured prior to shrinkage), more especially about 15 cm. Similarly, the spacing b~twean the lateral heating element~s) and the outside of the suspended configuration may be from 10 to 20 cm.~ more especially 15 cm.
~he ~hape and dimensions of the interior of the furnace will corre~pond generally to the size and shape of the suspended configuration. For example, for cloth suspended in ~he form of a spiral. the interior of the furnace will preferably be -- right-circular cylindrical. Advantageously, the spacing be~een the suspended configuration and the side wall of the furnace i~ substantially constant over the whole periphery o the configuration.
By way of example~ ~he interior dimension~ o~ a cylindrical furnace may be within the following ranges:
~nternal diameter 1.5 to 2.0 m., more especially about 1.8 m., internal height from the furnace base to the under-
~ZA70Z
on a side wall, each heating element being spaced apart from the suspended material, whereby said suspending places a plurality of the fibers in the fibrous cellulosic material transverse across the furnace; (e) heating the suspended material in said furnace to effect carbonisation of the cellulosic material; in an environment which is substantially non-reactive towards the material, said heat being directed into the suspended material from a first direction on the side of the suspended material and from a second direction beneath the suspended material; (f) activating the suspended carbonised material in an activating gas until the desired degree of activation has been produced; and (g) thereafter cooling the activated material. The fibrous cellulosic material is preferably a cellulosic cloth.
The process of the invantion is capable of producing activated carbon of surprisingly good quality and in good yield. It is especially surprising that the variation in product quality over the length of the material is acceptably small, whereas it might have been expected that the outer portions of the material suspended in the furnace would be affected by the carbonisation and activation operations to a substantially greater extent than those portions of the fibrous material that are situated towards the interior of the configuration, owing to the relatively close proximity of the lateral heating elements to those outer 2Q portions and to the fact that the inner portions would seem to be shielded from those heating elements by the intervening fibrous material, especially in the case of cloth material.
Also, as compared with the previously proposed continuous process, the process of the invention offers various advantages. Firstly, it is capable of producing activated carbon cloth of ~ z~02 similar quality with higher throughput at sub~tantially lower capital cost.
Secondly, in the proce3s of the invention, the residual acid content of the activated carbon product (for example, hydrochloric acid derived from the use of a chloride as Lewis acid) can be made relatively small. Thus~ in the continuou3 process, re-absorption of, for example, hydrochloric acid in the upper part of the furnace (especially in the region near the outlet ~here the temperature of the cloth may have fallen to 30 C. or so), may result in ~ re~idual acid content of from 2 to 5%, which in turn necessitates a ~pecial washing treatment of the product with water before use~ By contrast, in the process of the present invention, the activated carbon product can be made practically free from acid contamination, that is to say, with a residual acid content of only o.1 to 0.5%, and even less in some cases. Those beneficial results are obtainable by a combination of temperature control and gas purge, arranged to ensure that most of any acid vapour is expelled before cooling the activated carbon product.
Thirdly, utopping-upU the activity of the product, by prolonging the activation stage after testing a sample of the product, i9 a simple operation in the process of the invention, ~ut impossible in the continuous process.
The fibrous cellulosic material may be in the form of a single filament or as staple fibre, but is preferably a cellulosic cloth~
~2~702 The preliminary treatment of the cellulosic material with one or ~ore Lewis acids provides various beneficial effect3 depending primarily on the particular acid or acids used, ~ut also on the treatment time and on ~he proce~ing and drying temperatures employed. The advantage~ obtainable by the Lewis acid treatment include increased carbonisation yield, and increa~ed produ~t strength.
Advantageously, the or each Lewis acid is a br~mide or a chloride, and is preferably a chloride. A preferred treating agent comprise~ a mixture of zinc chloride~ aluminium chloride and ammonium chloride, the preferred concentration of each chloride in aqueous solution being approximately 30 by weight.
In general, the fibrous cellulosic material i8 contacted (for example, by immersion or ~praying) with a solution or di~perqion, more e3pacially aqueous, of the selected LeWiB
ac~d or acid~ The concentration of Lewi~ acid in the -colution or ~i~persion may be in the range o$ from 1 to 30 by weight~ preferably from 2 to 10~ by weight.
~ In the process of the invention, the fibrous cellulosic material is contacted with one or more Lewi9 acid~ before any carbonisation is effected. It is p3~sible, however~ to incorporate a further quantity of a Lewi9 acid with the cellulo~ic material during carbonisation.
Further detail~ ragarding the effect of various Lewi~ acid treatments on carboni3ation may be found~ for example, in Briti~h Patent Specification No. 1 301 101, The treated cellulosi~ mater~al may bo dr~ed at a temperature in the range of from room temperature to t40C or more, a drying temperature towards the upper or lower end of that range being preferred.
Softening of the cellulosic material to remove or reduce the st$ffness resulting from the Lewis aG~d treatment may ~e effected in a variety of ways, for example, by manual w~rking or by drawing the material over a smooth edge. Preferably, however, to produce an activated carbon of high breaking strength, the softening i3 effected using a breaking machine, which may be a pin-stenter or, more e~pecially, the type of machine known in the textile indu~try as a qpiral-roller breaker.
-~ The fibrous cellulosic material i8 su~pended from a frame in a tensionless manner, that is to say, under no ten~ion except that arising from the weight of the material. A~ a ~24~)2 result, substantially full ~hrinkage of the matexial takeq place during the carbonisation and activation operationq. Because the material is suspended so a~ to be able to shrink freely in all direc:tions, no tension is caused by the shrin~age. By contrast, in the previously proposed continuous proces3 referred to herein-before, tension is generated in the warp as the cloth .qhrinks, resulting in weakening of the cloth product.
It is important, however, to avoid undue tension arising from the weight of the fibrous material, especially in the case of cloth. In general, the heig~t of a cloth configuration suqpended from the frame should not exceed.5 metres, and is advantageou-qly not more than 2 metres. A preferred heig~ is 1 metre ~ ~X.
~aturally, the tension produced in suspended cloth by its own weight depends in part on the weight per unit area of the cloth and, advantageously, the maximum tension in suspended cloth (in a vertical direction and excluding regions in the immediate vicinity of points at which the cloth is suspended), is 5 gm per cm length across the top of the suspended configuration, and the - maximum tension preferably does not exceed 4 gm per cm length.
Advantageously,. the weight of a cellulosic cloth before the Lewis acid treatment is in the range of from 20 to 30 mg/cm2.
Typically, the diameter of the fibreQ in the cloth will be in the range of from 5 to 20 ~.
Advantageou~ly, the su~pension frame is attached to the underside of a removable lid of the furnace, and is preferably pivotally mounted under the lid to facilitate hanging of the fibrous cellulosic material.
Preferably, a cellulosic cloth i9 suspended in a spiral configuration, but other configurations may be adopted, ~12~0~ .
for example, a serpent~ne or star-shaped configuration. It will be appreciated that, in texms of proce~s throughput~ it i8 desirable to suspend the cloth in a configuration which allow~ the maxLmum length of cloth to be contained within a given volume. That consideration i~ subject, however, to the turns or folds of cloth being suspended sufficiently far apart to permit adequate heat transfer to the ~hole length of cloth, and adequate access of gas, especially during activation.
Advantageously, the length of a cellulo~ic cloth that is suspended from the frame is in the range of 50 to 150 metres, preferably at least 80 metres, and more especially from 90 to 110 metres.
A cellulosic cloth material may be suspended ~y means of hooks secured to the fxame and pa~sing through an upper edge portion of the cloth. Instead, cloth may be suspended by _ means of clips which engage the upper edge portion~ or may bs folded longitudinally over a ~eries of transverse supporting ra~s In the case ~here cloth i8 ~uspended from hooks or other suspension means acting on an upper edge portion, there will initially be excess cloth hung between adjacent suspansion position~ to allow for shrinkage during the carbonisatîon and activation operations. As a result, the cloth will hang initially in a wave-like form, and adjacent turns or folds may touch in places.
~ ~ . ~ .
li:Z 4702 Advantageously, the distan oe between adjaoent suspension positions along the same fold or turn of a suspended cloth con-figuration does not exceed 15 cm. The minimum distan oe between the suspensian positions of adjacent turns or folds of the suspended cloth may be in the range of from 1 to 5 cm., advantageously from 1 to 3 cm., and preferably from 1.5 to 2.5 cm. The minLmwm preferred spacing of the suspension positions of adjaoent turns or folds de-pends on the height of the suspended configuration ~which corres-ponds to the width of a cloth strip to be processed), and may vary, for example~ from 1 cm. in the case of a 1/2 m. width to 2 cm. for a metre width. The preferred spacings can be exceeded, but there will in general be little or no advantage in so doing to oompensate for the resulting reduced area of cloth that could then be accommD-dated at any one time in a furnaoe of given volume, and for the re-sulting reduoe d throughput.
qhe frame and associated SuSpensiQn means will be arranged to enable the fibrous oellulosic material to be suspended in the de-; sired configuration. A preferred form of frame, for suspending cloth in a spiral, oo~prises a plurality of radial arms (each, say, 0.5 to 1.0 m. in length) each providing a series of discrete suspension posi-tians, some of the arms extending outwardly from cross-pie oes arranged between adjacent radial arms. Advantageously, the number and arrangement of radial arms and of the suspension means thereon is such that the maxim~m spacing between adjaoent suspension positions 1/ .
'1124'702 along the ~ame ~urn of the cloth is 15 cm., and the ~pacing between adjacent su~pension po~itions along the same radial arm is advantageou~ly in the range of from 1 to 5 cm., preferably from 1 to 3 cm., more e~pecially from 1.5 to 2.5 cm. .
The spacing between the top and bottom of the suspended configuration and the top and bottom, respecti~ely, of the furnace may be in the range of from 10 to 20 cm. ~measured prior to shrinkage), more especially about 15 cm. Similarly, the spacing b~twean the lateral heating element~s) and the outside of the suspended configuration may be from 10 to 20 cm.~ more especially 15 cm.
~he ~hape and dimensions of the interior of the furnace will corre~pond generally to the size and shape of the suspended configuration. For example, for cloth suspended in ~he form of a spiral. the interior of the furnace will preferably be -- right-circular cylindrical. Advantageously, the spacing be~een the suspended configuration and the side wall of the furnace i~ substantially constant over the whole periphery o the configuration.
By way of example~ ~he interior dimension~ o~ a cylindrical furnace may be within the following ranges:
~nternal diameter 1.5 to 2.0 m., more especially about 1.8 m., internal height from the furnace base to the under-
3;de of the frame, 1.0 to 1.5 m., more especially about 1.2 m The diameter of a ~piral cloth con~iguration suspended in '' '~ ' `\ ----O-- , ~;. ' ' '- , .
l`lZ~702 such a furnace may, for exa~ple, ke in the range of fxom -1.1 to 1~7 m., more especially about 1.3 m.
It will be appreciated that the m~xLmum internaI
dimensions of the furnace are governed by the requirement S that there should be adequate heat transfer to the whole suspended configuration.
The or each heating element in or on the ~ide wall of the furnace may comprise a circumferentially extending element, ~nd there i3 preferably a plurality of such elements, say, from 6 to 12, more especially 9 arranged at spaced interval~
up the side wall of the furnace. Instead, there may b~ a plurality of upwardly extending heating element-~ arranged ~n a cixcum~erentially extending array in or on the side wall, each preferably extending substantially vertically. Depending on the effective area of such upwardly extending elements and on the furnace dimensions, a minimum of four elements, _ equally spaced around the furnace circumference, may be ~ufficient in the case of a cylindrical furnace, although preferably the numker of elements is greater.
Advantageously, the heating element(s) are arranged ln or on the side wall of the furnace to maintain a uniform temperature up that wall in the region occupied by the suspended fibrou~ material.
The base of the fuxnace may be provided witk heating elements arranged in the form of a cross (as seen in plan view), or there may be provided a plurality of elemRnts arr~nged .
.
'1,1- .
~247~2 in the form of concentric rings, preferably circular.
The or each heating element may be a gas- or oil-fired burner, or a microwave device, but is preferably an electrical resistance heater. A resistance heater at the side of the furnace may comprise a coiled resistance element, which may be in the form of an open coil or may be wouna on a ceramic core, and may be housed in a suitable sheath of, for example, silica. An electrical resistance heater at the base of the furnace is preferably a spiral-wound resi~tance element with a ceramic core.
~0 The production of activated carbon with small variation in quality over the length of the material is unexpectedly dependent on the provision of heating element~ at the base and at the ~ide of the furnace. ~uch larger variations in product quality would be obtained in a furnace havingbeatipg means only in a side ; 15 wall, or in a furnace having heating means only at the base.
Advantageously~ the~eating elements used in the proce~s of the invention are arranged to transfer heat to the suspended material by direc~ radiation and convection, with no intervening gas distributor means. In particular, the use of a perforated gas distributor plate between the suspended material and a radiant heat source tends to reduce the uniformity of the product.
The furnace may be provided with cooling means, for example, conduits for conducting coolant fluid across the base of the furnace and/or conduits or a cooling jacket arranged up the side wall of the furnace, to facilitate rapid cooling of the activated carbon product and thus increa~ing throughput.
The properties of the activated carbon product are dependent on the rate at which the temperature of the furnace i9 increased in the carbonisation and activation operations. In general, rapid temperature increase has deleterious effects~ Advantageously, t~e rate at which the temperature of the furnace is increased does not exceed 6C per minute in either operation, and preferably does not exceed 4C per minute.
3S It is especially important that the rate of temperature increase during carbonisation (especially up to temperatures .
in the region of 300C. to 350C) should be kept relatively low, ~otherwise the product tends to ke brittle) and preferably it doe~ not exceed 3C per minuteO The rate of temperature increase during activation may ke the same as, or even less than, that during carbonisation, but i8 preferably greater.
Adv~tageously, except during the temparature-holding periods discussed below, the rate of increase of temperature i~ at least 1.5C per minute, to enable the temperature programme to be completed in an economically practicable period.
! In æome cases, the quality of the activated carbon product can be improved by holding the temperature in the furnace within one or more narrow temperature bands for periods that will generally be in the range of from 15 to 60 minutes, preferably from 25 to 35 minute.q.
The or each narrow temperature band may com~rise a ~ range not ex.ceeding 0C, advantageously not exceeding 5 & .
Preferably,. the temperature iq maintained subs~antially ._ con~tant in the or each holding period, but in practice it will be difficult to avoid local temperature variations of up to 5 & or so.
Advantageou~ly, the temperature of the furnace i8 held during carbonisation for a period of at least 15 ml~nutes within a 10C band in the range of from 3~5C to 350C.,the band preferahly extending from 315 & . to 32SC. In addition to or in~tead of a temperature-holding period in the range of from 315 & . to 350C., it may be advantageou~ in some cases .
. .
l~Z4702 .
to hold the te~perature during carbonisation of a period of at lea~t 15 minutes within a 10~ band in the range of from 130& . to 315 & . Such temperature-holding perioa~ assi~t in ensuring that carbonisation is ~ub~tantially complete, and can al~o increase the ~reaking strength of the product, in 80me instances by a~ much as 50%.
The rate and uniformity of activa~ion depends on the temperature of the furnace and on the concentration of the activating gas. In general, it will be necessary to attain a temperature of at least 820C. to effect acti.vation at an acceptable rate, and the temperature i~ preferably raised to at least 870C., more especially at least 900C., ~o ensure uniformity of activation.
m e desirea degree of activity will depend on the intended use of the activated carbon product. For example, an activated carbon for use in a respirator will normally _ need to be more active than a product for use in an air-aonditioning ~ystem.
It will be appreciated that the higher the activit~
of the product (that is to .~ay, the longer the activation t~me and/or the higher the temperature reached during the activation) the lower will b~ the product yield and product strength.
In general, the temperature of the furnace during activation should not exceed 1000C., advantageously does - not exceed 950 & . and, more especially, doe~ not exceed 920 ~ 10C.
-~4-_ .
li2A70Z
In general, the furnace i8 maintained during activation at a temperature within the range of from 870 to 1000C.
for a period of at least 30 minutes before cooling i8 commenced. Preferably, the said period does not exceed 45 minute~.
In determining the length of t~e activating period before cooling ~ commenced, it should be noted that activation will continue to a small extent at the beginning of the cooling operation. ~ormally, however, this effect will be of only minor ~ignificance. ~_ - In the cooling operation, it is desirable in principle to open the furnace at the highest temperature practicable, because the total time required for cooling is thereby minimised. It will normally be possible to open the furnace to atmosphere when the temperature has fallen to 100 C., but it may in some cases be possible ~ open the furnace at a significantly higher temperature, say, 300C. or even higher.
` The maximum temperature at which the furnace can be opened 20 i8 determined primarily by the need to avoid excesAive adsorp-tion of the ambient atmosphere, especially ambient air, (which i8 an exothermic reaction) and the consequent risk of self-ignition.
If the furnace is flu~hed with nitrogen or another inert gas during or before cooling, the risk of excessive adsorption of ambient air on opening the furnace is reduced, which in turn enables the furnace to be opened at correspondingly higher temperatures.
, ., ~ ..... ~. .
li24~702 The following is an example of a pre~erred temperature progr~mme in the case of a cellulo~ic cloth carbo~ised and activated in an atmosphere of carbon dioxide:
(a) 20C. to 130C. at 100C. per hour;
(b~ 130C. to 320C.- at 150C. per hour;
(c) maintain at 320C. for 30 minutes;
(d) 320 & . to 920C. at 200C. per hour (e) Maintain at 920C. for 30 minute~; and (f) cool a~ quickly as possiblè to 100 & . and then open the furnace.
The above programme may b v æ ied in ac~ordance with the general directions given hereinbefore. In particular, there may be an additional temperature-holding period of 30 minute3 b*ween 130C. and 320C.
The atmosphere in the furnace during carbonisation advantageously comprises one or more of nitrogen~ carbon - dioxide, helium, argon or steam. The carbonisation a~mosphere is substantially non-reactive towards the cloth but may, as in the case of carbon dioxide and steam, effect someloxidation of decomposition products~ Preferably, a current of gas i9 pa~sed through the furnace to remove volatile decomposition products formed during carbonisation.
Instead, how ver, the carbonisation can be conducted in a normally sealed vessel, the volatiles being flushed out at intervals or when carbonisation is substantially complete.
Activation may also be conduc~ed und~r sealed conditions.
~ ~, ~12A702 but it i8 advantageou~ to allow at least a proportion of any gas generated ky the activation to pass out of the furnace through suitable outlet means, and there may advantageously be gas flow into and through the furnace during activation.
S The activating gas advantageously comprises carbon dioxide and/or steam, alth~ugh water gas, producer ga~, and other coke-oven by-products may be used to b~ing about the necessary controlled oxidation.
Advantageously~ the carboni~ation and activation operations are conducted under as small positive pressure in relation to atmo~phere (s~y, from 5 to 25 cm~ of water) to assist in preventing lea~age of air into the furnace, but higher pressures are in general disadvantageous to the carbonisation and activation reactions.
Activated carbon produced according to the invention may be used, for example, in respirators, air-conditioning ~ystems~
and for industrial filtration and de-colourisation purposes.
~he activated carbon of the invention also has various medical applications, for examplet in bandages and for de-odorising 2~ purposes. Further, the carbon product can be used in cigarettes for filtration purposes.
One form of furnace and su~pen~ion frame for u~e in the proce~s of the invention will now he describad, by way of example, with reference to the accompanying drawings, in which:
Fig. 1 is a plan view of the frame as seen from below:
Fig. 2 is a plan view of the base of the furnace Fig. 3 is a vertical section through the furnace along the line III-III in Fig. 2;
- li2~702 FigO 4 ~hows, in diagrammatic form, part of the frame showing the arrangement of suspension hoo~s Fig. 5 is a plan view of a length of cloth suspended - from the frame in a spiral configuration: and Fig. 6 shows part of the plan view of Fig. 5 in more detail, including the position of the suspension hoo~s.
Referringfirstly to Fig. 3, a generally cylindrical furnace 1 has a removable lid 2 having a cloth suspension frame 3 pivota;ly mounted on its~underside. A seal 4 (for example, a liquid seai) is provided between the furnace and the lid. The base, wall~ and lid of the furnace are provided with insulation 5.
A plurality of circumferentially extending electrical heating elements 6 is arranged on the side wall of the furnace.
Each element 6 comprises a coiled, core-less resistance element.
The furnace has a gas inlet 7 and an exhaust outlet 8 (which includes a non-return valve), to enable thé gaseous atmosphere and flow rate inside the furnace to be controlled.
Inside the furnace, the exhaust gas conduit comprises a circumferentially extending pipe 8a having apertures at regular intervals to avoid ~low variations.
A conduit 9 for cooling fluid is provided across the base of the furnace.
By way of example, the internal diameter of the furnace ` li24702 may be 72 inches (1.83 m.) and the furnace height measured from the base to the underside o~ ~he frame 3 may be 48 inches t1~22 m.).
Referring to Fig. 2, the base of the furnace is provided with heating elements ~0 arranged in the form of a cross, the heaters 10 being spiral-wound electrical resistance elements with a ceramic support. The cooling conduit 9 has tw~ ~ranches 9a and 9b, having outlet8 11a and 11b, respectively.
Re~erring now to Fig. 1, the suspension frame comprise8 a plurality,of radial arm~ some ~ which (12) extend from the centre of the ~rame and others (13 and 14) extend outwardly from cross-pieces (15 and 16) arranged between adjacent radial arms. Each radial arm is provided with a series of hooks 17 (as shown in Fig. 4), or other suspension means providing a plurality of discrete suspension positions.
As shown in Fig. 5, the length of cloth 18 i.~ suspended ~ from the hooks (or other suspension means) in the form of a spiral. The number and arrangement of the hooks 17 is such that the distance between adjacent suspension positions along the same turn of the spiral does not exceed 15 cm.
The length of cloth in the spiral is, for example, 100 metres and its width (which corresponds to the height o~ the suspended con~iguration) i8 ~ for example, 1 metre.
Initially, to allow for shrinkage during the carbon-isation and activation operations, excess cloth is hung ketween adjacent suspension position~. AS a ~ sult, at least _l g_ . _, .
. . .
11;~702 the upper edge of the cloth will hang initially in a wave-like form, and adjacent turns may touch in some place~ (a9 can ~e seen, for example, at 19 in Fig. 6).
AS also shown in Fig. 6, the spacing between adjacent hooks 17 on the same radial arm is approximately 2.5 cm., that then being the distance between adjacent turns.
In operation, a cellulosic cloth is contacted with one or more Lewi8 acids as hereinbefore specified, dried, softened mechanically, and suspended from hooks 17 on the frame 3 in the form of a spiral (Fig. 5), utilising the pivotal movement of the frame on the furnace lid 2 to facilitate loading.
The lid and frame are then placed in poition in the furnace (Fig. 3). Carbon dioxide is introduced through the inlet 7 to establish, in the steady state, a flow rate of at least 30 litres per minute through the furnace. Exhaust gas (carrying volatile decomposition products during carbonisation) leaves the furnace via the circumferentially extending pipe 8a and outlet 8.
Once the air originally in the furnace has been flushed out ~y the carbon dioxide, the temperature of the furnace i9 raised, for example, through the following programme: , (a) 20C. to 130C. at 100C. per hour, (b) 130C. to 320C, at 150C. per hour:
(c) maintain at 320C~ for 30 minutes:
(d) 320C. to 920C. at 200C. per hour;
(e) maintain at 920C. for 30 minute~: and (~) cool as quickly as pos~ible to 100C. and then open the furnace~
The above program~e may be varied in accordance with the - general directions given hereinbefore. In particular there may be an additional temperature-holding period of 30 minute~
between 130C. and 320C.
The following Example illustrate~ the invention:
1 0 13X~5PLB ~ _ ,, A length of woven viscose rayon, measuring 50 m. x 100 cm., weighing 24 mgjcm2 and hàving a square-form linen weave, was immersed for 2 minutes in a bath containing a solution of 3% by weight each of zinc chloride~ ammonium chloride and aluminium chloride in water.
The treated cloth was dried on a heated air bed under minimum tension and the dried cloth was fed through a ~piral-roller breaker having seven pairs of rollers.
The cloth was then suspended in a spiral configuration in a furnace as described with reference to the accompanying drawings, the total electrical power consumption of the wall ; heaters being the same as that of the base heaters.
After purging for one hour with carbon dioxide, the furnace was taken through the following temperature programme:
(a) 20C~ to 130C. at 100C. per hour;
(b) 130C. to 320C. at 150C. per hour;
(c) maintain at 320C. for 30 minutes;
l~lZ4~C~2 (d) 320C. to 920Co at 200C. per hour, (e) maintain at 920C. for 30 minutes, and (f) cool to t~oc. over 4 hours and then open the furnace.
S ~he resulting activated carbon cloth had shrunk ~o dimensions of 30 m. x 66 cm, To te-qt the adsorption properties of the product, the ~ilicone oil heat of wetting was mea~ured for ~amples taken at variou~ points along the spiral~ and the result~ were a~ follows, the samples being fro~ the centra of the strip width in each ca3e:
SampleHeat of wetting (cals./g.) _ _ Interior of ~piral 14.5 24 m. in (from exterior) 14.1 12 m. in (from exterior) 12.1 Exterior of spiral 12.8 In addition, tests on samples taken at each edge of the strip showed only + 5%.variation across the strip at each of the measuring positions indicated above.
It will be appreci~ted that the results ~how only small variation in product activity along the length of the suspended spiral.
l`lZ~702 such a furnace may, for exa~ple, ke in the range of fxom -1.1 to 1~7 m., more especially about 1.3 m.
It will be appreciated that the m~xLmum internaI
dimensions of the furnace are governed by the requirement S that there should be adequate heat transfer to the whole suspended configuration.
The or each heating element in or on the ~ide wall of the furnace may comprise a circumferentially extending element, ~nd there i3 preferably a plurality of such elements, say, from 6 to 12, more especially 9 arranged at spaced interval~
up the side wall of the furnace. Instead, there may b~ a plurality of upwardly extending heating element-~ arranged ~n a cixcum~erentially extending array in or on the side wall, each preferably extending substantially vertically. Depending on the effective area of such upwardly extending elements and on the furnace dimensions, a minimum of four elements, _ equally spaced around the furnace circumference, may be ~ufficient in the case of a cylindrical furnace, although preferably the numker of elements is greater.
Advantageously, the heating element(s) are arranged ln or on the side wall of the furnace to maintain a uniform temperature up that wall in the region occupied by the suspended fibrou~ material.
The base of the fuxnace may be provided witk heating elements arranged in the form of a cross (as seen in plan view), or there may be provided a plurality of elemRnts arr~nged .
.
'1,1- .
~247~2 in the form of concentric rings, preferably circular.
The or each heating element may be a gas- or oil-fired burner, or a microwave device, but is preferably an electrical resistance heater. A resistance heater at the side of the furnace may comprise a coiled resistance element, which may be in the form of an open coil or may be wouna on a ceramic core, and may be housed in a suitable sheath of, for example, silica. An electrical resistance heater at the base of the furnace is preferably a spiral-wound resi~tance element with a ceramic core.
~0 The production of activated carbon with small variation in quality over the length of the material is unexpectedly dependent on the provision of heating element~ at the base and at the ~ide of the furnace. ~uch larger variations in product quality would be obtained in a furnace havingbeatipg means only in a side ; 15 wall, or in a furnace having heating means only at the base.
Advantageously~ the~eating elements used in the proce~s of the invention are arranged to transfer heat to the suspended material by direc~ radiation and convection, with no intervening gas distributor means. In particular, the use of a perforated gas distributor plate between the suspended material and a radiant heat source tends to reduce the uniformity of the product.
The furnace may be provided with cooling means, for example, conduits for conducting coolant fluid across the base of the furnace and/or conduits or a cooling jacket arranged up the side wall of the furnace, to facilitate rapid cooling of the activated carbon product and thus increa~ing throughput.
The properties of the activated carbon product are dependent on the rate at which the temperature of the furnace i9 increased in the carbonisation and activation operations. In general, rapid temperature increase has deleterious effects~ Advantageously, t~e rate at which the temperature of the furnace is increased does not exceed 6C per minute in either operation, and preferably does not exceed 4C per minute.
3S It is especially important that the rate of temperature increase during carbonisation (especially up to temperatures .
in the region of 300C. to 350C) should be kept relatively low, ~otherwise the product tends to ke brittle) and preferably it doe~ not exceed 3C per minuteO The rate of temperature increase during activation may ke the same as, or even less than, that during carbonisation, but i8 preferably greater.
Adv~tageously, except during the temparature-holding periods discussed below, the rate of increase of temperature i~ at least 1.5C per minute, to enable the temperature programme to be completed in an economically practicable period.
! In æome cases, the quality of the activated carbon product can be improved by holding the temperature in the furnace within one or more narrow temperature bands for periods that will generally be in the range of from 15 to 60 minutes, preferably from 25 to 35 minute.q.
The or each narrow temperature band may com~rise a ~ range not ex.ceeding 0C, advantageously not exceeding 5 & .
Preferably,. the temperature iq maintained subs~antially ._ con~tant in the or each holding period, but in practice it will be difficult to avoid local temperature variations of up to 5 & or so.
Advantageou~ly, the temperature of the furnace i8 held during carbonisation for a period of at least 15 ml~nutes within a 10C band in the range of from 3~5C to 350C.,the band preferahly extending from 315 & . to 32SC. In addition to or in~tead of a temperature-holding period in the range of from 315 & . to 350C., it may be advantageou~ in some cases .
. .
l~Z4702 .
to hold the te~perature during carbonisation of a period of at lea~t 15 minutes within a 10~ band in the range of from 130& . to 315 & . Such temperature-holding perioa~ assi~t in ensuring that carbonisation is ~ub~tantially complete, and can al~o increase the ~reaking strength of the product, in 80me instances by a~ much as 50%.
The rate and uniformity of activa~ion depends on the temperature of the furnace and on the concentration of the activating gas. In general, it will be necessary to attain a temperature of at least 820C. to effect acti.vation at an acceptable rate, and the temperature i~ preferably raised to at least 870C., more especially at least 900C., ~o ensure uniformity of activation.
m e desirea degree of activity will depend on the intended use of the activated carbon product. For example, an activated carbon for use in a respirator will normally _ need to be more active than a product for use in an air-aonditioning ~ystem.
It will be appreciated that the higher the activit~
of the product (that is to .~ay, the longer the activation t~me and/or the higher the temperature reached during the activation) the lower will b~ the product yield and product strength.
In general, the temperature of the furnace during activation should not exceed 1000C., advantageously does - not exceed 950 & . and, more especially, doe~ not exceed 920 ~ 10C.
-~4-_ .
li2A70Z
In general, the furnace i8 maintained during activation at a temperature within the range of from 870 to 1000C.
for a period of at least 30 minutes before cooling i8 commenced. Preferably, the said period does not exceed 45 minute~.
In determining the length of t~e activating period before cooling ~ commenced, it should be noted that activation will continue to a small extent at the beginning of the cooling operation. ~ormally, however, this effect will be of only minor ~ignificance. ~_ - In the cooling operation, it is desirable in principle to open the furnace at the highest temperature practicable, because the total time required for cooling is thereby minimised. It will normally be possible to open the furnace to atmosphere when the temperature has fallen to 100 C., but it may in some cases be possible ~ open the furnace at a significantly higher temperature, say, 300C. or even higher.
` The maximum temperature at which the furnace can be opened 20 i8 determined primarily by the need to avoid excesAive adsorp-tion of the ambient atmosphere, especially ambient air, (which i8 an exothermic reaction) and the consequent risk of self-ignition.
If the furnace is flu~hed with nitrogen or another inert gas during or before cooling, the risk of excessive adsorption of ambient air on opening the furnace is reduced, which in turn enables the furnace to be opened at correspondingly higher temperatures.
, ., ~ ..... ~. .
li24~702 The following is an example of a pre~erred temperature progr~mme in the case of a cellulo~ic cloth carbo~ised and activated in an atmosphere of carbon dioxide:
(a) 20C. to 130C. at 100C. per hour;
(b~ 130C. to 320C.- at 150C. per hour;
(c) maintain at 320C. for 30 minutes;
(d) 320 & . to 920C. at 200C. per hour (e) Maintain at 920C. for 30 minute~; and (f) cool a~ quickly as possiblè to 100 & . and then open the furnace.
The above programme may b v æ ied in ac~ordance with the general directions given hereinbefore. In particular, there may be an additional temperature-holding period of 30 minute3 b*ween 130C. and 320C.
The atmosphere in the furnace during carbonisation advantageously comprises one or more of nitrogen~ carbon - dioxide, helium, argon or steam. The carbonisation a~mosphere is substantially non-reactive towards the cloth but may, as in the case of carbon dioxide and steam, effect someloxidation of decomposition products~ Preferably, a current of gas i9 pa~sed through the furnace to remove volatile decomposition products formed during carbonisation.
Instead, how ver, the carbonisation can be conducted in a normally sealed vessel, the volatiles being flushed out at intervals or when carbonisation is substantially complete.
Activation may also be conduc~ed und~r sealed conditions.
~ ~, ~12A702 but it i8 advantageou~ to allow at least a proportion of any gas generated ky the activation to pass out of the furnace through suitable outlet means, and there may advantageously be gas flow into and through the furnace during activation.
S The activating gas advantageously comprises carbon dioxide and/or steam, alth~ugh water gas, producer ga~, and other coke-oven by-products may be used to b~ing about the necessary controlled oxidation.
Advantageously~ the carboni~ation and activation operations are conducted under as small positive pressure in relation to atmo~phere (s~y, from 5 to 25 cm~ of water) to assist in preventing lea~age of air into the furnace, but higher pressures are in general disadvantageous to the carbonisation and activation reactions.
Activated carbon produced according to the invention may be used, for example, in respirators, air-conditioning ~ystems~
and for industrial filtration and de-colourisation purposes.
~he activated carbon of the invention also has various medical applications, for examplet in bandages and for de-odorising 2~ purposes. Further, the carbon product can be used in cigarettes for filtration purposes.
One form of furnace and su~pen~ion frame for u~e in the proce~s of the invention will now he describad, by way of example, with reference to the accompanying drawings, in which:
Fig. 1 is a plan view of the frame as seen from below:
Fig. 2 is a plan view of the base of the furnace Fig. 3 is a vertical section through the furnace along the line III-III in Fig. 2;
- li2~702 FigO 4 ~hows, in diagrammatic form, part of the frame showing the arrangement of suspension hoo~s Fig. 5 is a plan view of a length of cloth suspended - from the frame in a spiral configuration: and Fig. 6 shows part of the plan view of Fig. 5 in more detail, including the position of the suspension hoo~s.
Referringfirstly to Fig. 3, a generally cylindrical furnace 1 has a removable lid 2 having a cloth suspension frame 3 pivota;ly mounted on its~underside. A seal 4 (for example, a liquid seai) is provided between the furnace and the lid. The base, wall~ and lid of the furnace are provided with insulation 5.
A plurality of circumferentially extending electrical heating elements 6 is arranged on the side wall of the furnace.
Each element 6 comprises a coiled, core-less resistance element.
The furnace has a gas inlet 7 and an exhaust outlet 8 (which includes a non-return valve), to enable thé gaseous atmosphere and flow rate inside the furnace to be controlled.
Inside the furnace, the exhaust gas conduit comprises a circumferentially extending pipe 8a having apertures at regular intervals to avoid ~low variations.
A conduit 9 for cooling fluid is provided across the base of the furnace.
By way of example, the internal diameter of the furnace ` li24702 may be 72 inches (1.83 m.) and the furnace height measured from the base to the underside o~ ~he frame 3 may be 48 inches t1~22 m.).
Referring to Fig. 2, the base of the furnace is provided with heating elements ~0 arranged in the form of a cross, the heaters 10 being spiral-wound electrical resistance elements with a ceramic support. The cooling conduit 9 has tw~ ~ranches 9a and 9b, having outlet8 11a and 11b, respectively.
Re~erring now to Fig. 1, the suspension frame comprise8 a plurality,of radial arm~ some ~ which (12) extend from the centre of the ~rame and others (13 and 14) extend outwardly from cross-pieces (15 and 16) arranged between adjacent radial arms. Each radial arm is provided with a series of hooks 17 (as shown in Fig. 4), or other suspension means providing a plurality of discrete suspension positions.
As shown in Fig. 5, the length of cloth 18 i.~ suspended ~ from the hooks (or other suspension means) in the form of a spiral. The number and arrangement of the hooks 17 is such that the distance between adjacent suspension positions along the same turn of the spiral does not exceed 15 cm.
The length of cloth in the spiral is, for example, 100 metres and its width (which corresponds to the height o~ the suspended con~iguration) i8 ~ for example, 1 metre.
Initially, to allow for shrinkage during the carbon-isation and activation operations, excess cloth is hung ketween adjacent suspension position~. AS a ~ sult, at least _l g_ . _, .
. . .
11;~702 the upper edge of the cloth will hang initially in a wave-like form, and adjacent turns may touch in some place~ (a9 can ~e seen, for example, at 19 in Fig. 6).
AS also shown in Fig. 6, the spacing between adjacent hooks 17 on the same radial arm is approximately 2.5 cm., that then being the distance between adjacent turns.
In operation, a cellulosic cloth is contacted with one or more Lewi8 acids as hereinbefore specified, dried, softened mechanically, and suspended from hooks 17 on the frame 3 in the form of a spiral (Fig. 5), utilising the pivotal movement of the frame on the furnace lid 2 to facilitate loading.
The lid and frame are then placed in poition in the furnace (Fig. 3). Carbon dioxide is introduced through the inlet 7 to establish, in the steady state, a flow rate of at least 30 litres per minute through the furnace. Exhaust gas (carrying volatile decomposition products during carbonisation) leaves the furnace via the circumferentially extending pipe 8a and outlet 8.
Once the air originally in the furnace has been flushed out ~y the carbon dioxide, the temperature of the furnace i9 raised, for example, through the following programme: , (a) 20C. to 130C. at 100C. per hour, (b) 130C. to 320C, at 150C. per hour:
(c) maintain at 320C~ for 30 minutes:
(d) 320C. to 920C. at 200C. per hour;
(e) maintain at 920C. for 30 minute~: and (~) cool as quickly as pos~ible to 100C. and then open the furnace~
The above program~e may be varied in accordance with the - general directions given hereinbefore. In particular there may be an additional temperature-holding period of 30 minute~
between 130C. and 320C.
The following Example illustrate~ the invention:
1 0 13X~5PLB ~ _ ,, A length of woven viscose rayon, measuring 50 m. x 100 cm., weighing 24 mgjcm2 and hàving a square-form linen weave, was immersed for 2 minutes in a bath containing a solution of 3% by weight each of zinc chloride~ ammonium chloride and aluminium chloride in water.
The treated cloth was dried on a heated air bed under minimum tension and the dried cloth was fed through a ~piral-roller breaker having seven pairs of rollers.
The cloth was then suspended in a spiral configuration in a furnace as described with reference to the accompanying drawings, the total electrical power consumption of the wall ; heaters being the same as that of the base heaters.
After purging for one hour with carbon dioxide, the furnace was taken through the following temperature programme:
(a) 20C~ to 130C. at 100C. per hour;
(b) 130C. to 320C. at 150C. per hour;
(c) maintain at 320C. for 30 minutes;
l~lZ4~C~2 (d) 320C. to 920Co at 200C. per hour, (e) maintain at 920C. for 30 minutes, and (f) cool to t~oc. over 4 hours and then open the furnace.
S ~he resulting activated carbon cloth had shrunk ~o dimensions of 30 m. x 66 cm, To te-qt the adsorption properties of the product, the ~ilicone oil heat of wetting was mea~ured for ~amples taken at variou~ points along the spiral~ and the result~ were a~ follows, the samples being fro~ the centra of the strip width in each ca3e:
SampleHeat of wetting (cals./g.) _ _ Interior of ~piral 14.5 24 m. in (from exterior) 14.1 12 m. in (from exterior) 12.1 Exterior of spiral 12.8 In addition, tests on samples taken at each edge of the strip showed only + 5%.variation across the strip at each of the measuring positions indicated above.
It will be appreci~ted that the results ~how only small variation in product activity along the length of the suspended spiral.
Claims (34)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A batch process for the manufacture of activated carbon, which com-prises;
(a) treating a fibrous cellulosic material by contacting it with at least one Lewis acid selected from the group consisting of halides of zinc, aluminum, calcium, magnesium, iron, barium, ammonium and chromium;
(b) drying the treated material;
(c) subjecting the dried material to a mechanical softening treatment;
(d) suspending the softened material from a frame in a tensionless manner, said frame being positioned within a furnace adapted to effect carbonisa-tion of the cellulosic material, the furnace having at least one heating element at its base and at least one heating element arranged on a side wall, each heating element being spaced apart from the suspended material, whereby said suspending places a plurality of the fibers in the fibrous cellulosic material transverse across the furnace;
(e) heating the suspended material in said furnace to effect carbonisa-tion of the cellulosic material; in an environment which is substantially non-reactive towards the material, said heat being directed into the suspended materi-al from a first direction on the side of the suspended material and from a second direction beneath the suspended material;
(f) activating the suspended carbonised material in an activating gas until the desired degree of activation has been produced; and (g) thereafter cooling the activated material.
(a) treating a fibrous cellulosic material by contacting it with at least one Lewis acid selected from the group consisting of halides of zinc, aluminum, calcium, magnesium, iron, barium, ammonium and chromium;
(b) drying the treated material;
(c) subjecting the dried material to a mechanical softening treatment;
(d) suspending the softened material from a frame in a tensionless manner, said frame being positioned within a furnace adapted to effect carbonisa-tion of the cellulosic material, the furnace having at least one heating element at its base and at least one heating element arranged on a side wall, each heating element being spaced apart from the suspended material, whereby said suspending places a plurality of the fibers in the fibrous cellulosic material transverse across the furnace;
(e) heating the suspended material in said furnace to effect carbonisa-tion of the cellulosic material; in an environment which is substantially non-reactive towards the material, said heat being directed into the suspended materi-al from a first direction on the side of the suspended material and from a second direction beneath the suspended material;
(f) activating the suspended carbonised material in an activating gas until the desired degree of activation has been produced; and (g) thereafter cooling the activated material.
2. A process as claimed in Claim 1, wherein the fibrous cellulosic materi-al comprises a cellulosic fabric.
3. A process as claimed in Claim 2, wherein the height of the fabric con-figuration suspended from the frame does not exceed 5 metres.
4. A process as claimed in Claim 3, wherein the said height does not ex-ceed 2 metres.
5. A process as claimed in Claim 2, wherein the fabric is suspended in the form of a spiral.
6. A process as claimed in Claim 2, wherein the distance between suspension points of adjacent turns or folds of the suspended fabric is in the range of from 1 to 5 cm.
7. A process as claimed in Claim 2, wherein the distance between suspension points along each individual turn or fold of the suspended fabric does not exceed 15 cm.
8. A process as claimed in Claim 1, wherein the distance between the sus-pended configuration and the inside of the furnace, measured before any shrinkage of the material has occurred, is in the range of from 10 to 20 cm.
9. A process as claimed in Claim 1, wherein there is a plurality of cir-cumferentially extending heating elements arranged at spaced intervals up the side wall of the furnace.
10. A process as claimed in Claim 1, wherein there is a plurality of up-wardly extending heating elements arranged in a circumferentially extending array in or on the side wall of the furnace.
11. A process as claimed in Claim 1, wherein the heating elements are ar-ranged to maintain a uniform temperature up the side wall of the furnace in the region occupied by the suspended fibrous material.
12. A process as claimed in Claim 1, wherein the base of the furnace is provided with heating elements arranged in the form of a cross (as seen in plan view).
13. A process as claimed in Claim 1, wherein the heating elements are ar-ranged to transfer heat to the suspended material by direct radiation and con-vection.
14. A process as claimed in Claim 1, wherein the rate at which the tempera-ture of the furnace is increased does not exceed 6°C per minute.
15. A process as claimed in Claim 14, wherein the said rate does not exceed 4°C per minute.
16. A process as claimed in Claim 1, wherein the rate at which the tempera-ture of the furnace is increased is at least 1.5°C per minute.
17. A process as claimed in Claim 1, wherein the rate at which the tempera-ture of the furnace is increased during carbonisation of the fibrous cellulosic material does not exceed 3°C per minute.
18. A process as claimed in Claim 1, wherein the rate at which the tempera-ture of the furnace is increased during activation of the fibrous material is greater than the rate of increase during carbonisation of the material.
19. A process as claimed in Claim 1, wherein a temperature of at least 870°C
is established during activation.
is established during activation.
20. A process as claimed in Claim 19, wherein a temperature of at least 900°C is established during activation.
21. A process as claimed in Claim 1, wherein the temperature established during activation does not exceed 1000°C.
22. A process as claimed in Claim 21, wherein the temperature established during activation does not exceed 950°C.
23. A process as claimed in Claim 22, wherein the maximum temperature established during activation is in the range of from 910°C to 930°C.
24. A process as claimed in Claim 1, wherein the temperature of the furnace is held during carbonisation for a period of from 15 to 60 minutes within a 10°C
band in the range of from 315°C to 350°C.
band in the range of from 315°C to 350°C.
25. A process as claimed in Claim 24, wherein the said band extends from 315°C to 325°C.
26. A process as claimed in Claim l, wherein the temperature of the furnace is held during carbonisation for a period of from 15 to 60 minutes within a 10°C
band in the range of from 130°C to 315°C.
band in the range of from 130°C to 315°C.
27. A process as claimed in Claim 1, wherein during activation the furnace is maintained at a temperature within the range of from 870°C to 1000°C for a period of at least 30 minutes before cooling is commenced.
28. A process as claimed in Claim 1, wherein during activation the furnace is maintained at a temperature in the range of from 870° to 1000°C for a period not exceeding 45 minutes before cooling is commenced.
29. A process as claimed in Claim 1, wherein the carbonisation is conducted in an atmosphere comprising at least one inert gas or vapour selected from the group consisting of nitrogen, carbon dioxide, helium, argon or steam.
30. A process as claimed in Claim 1, wherein the atmosphere in the furnace during activation comprises at least one of carbon dioxide and steam.
31. A process as claimed in Claim 1, wherein the carbonisation and activa-tion of the material is conducted under a pressure not exceeding 25 cm. of water.
32. A process as claimed in Claim 1, wherein a current of gas is passed through the furnace during carbonisation to remove volatile decomposition pro-ducts formed during carbonisation of the fabric.
33. A process as claimed in Claim 1, wherein said group of Lewis acids con-sists of chlorides.
34. A process as claimed in Claim 1, wherein the mechanical softening treatment is effected with a textile breaking machine.
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB15940/78 | 1978-04-21 | ||
| GB15940/78A GB1570677A (en) | 1978-04-21 | 1978-04-21 | Manufacture of activated carbon |
| US92592578A | 1978-07-19 | 1978-07-19 | |
| US925,925 | 1978-07-19 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1124702A true CA1124702A (en) | 1982-06-01 |
Family
ID=26251652
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA324,785A Expired CA1124702A (en) | 1978-04-21 | 1979-04-03 | Manufacture of activated carbon |
Country Status (6)
| Country | Link |
|---|---|
| JP (1) | JPS54142194A (en) |
| AU (1) | AU523090B2 (en) |
| CA (1) | CA1124702A (en) |
| DE (1) | DE2915640C2 (en) |
| FR (1) | FR2423443A1 (en) |
| SE (1) | SE7903502L (en) |
Families Citing this family (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3228851A1 (en) * | 1982-08-02 | 1984-02-02 | Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V., 8000 München | Wound dressing |
| DE3302984C2 (en) * | 1983-01-29 | 1986-05-22 | Sorbexx GmbH Gesellschaft für Adsorptionstechnik und Verbundstoffe, 8586 Gefrees | Wound cover material in sheet form |
| FI85133C (en) * | 1990-06-27 | 1992-03-10 | Kemira Oy Saeteri | Process for producing activated carbon from cellulosic matter 1 |
| DE19912153B4 (en) | 1999-03-18 | 2004-08-19 | Carbotex Produktions-Und Veredelungsbetriebe Gmbh | Process for the production of shaped high-performance adsorbents |
| JP2004138097A (en) * | 2002-10-15 | 2004-05-13 | Ishizuka Kenkyusho:Kk | Hydrogen storage medium, and method for manufacturing the same |
| CA2524476A1 (en) * | 2003-05-09 | 2004-11-18 | Mcgill University | Process for the production of activated carbon |
| JP2018008245A (en) * | 2016-07-15 | 2018-01-18 | 株式会社オメガ | Regeneration device of absorbent |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1301101A (en) * | 1969-01-08 | 1972-12-29 | Secr Defence | Improvements in the manufacture of carbon |
| US3847833A (en) * | 1969-01-08 | 1974-11-12 | Secr Defence | Flexible activated carbon fibers manufactured from salt impregnated cellulosic fibers |
| GB1310011A (en) * | 1969-01-08 | 1973-03-14 | Secr Defence | Carbonizing process and an apparatus therefor |
| GB1505095A (en) * | 1976-11-11 | 1978-03-22 | Clairaire Ltd | Process for the manufacture of activated carbon |
-
1979
- 1979-04-03 CA CA324,785A patent/CA1124702A/en not_active Expired
- 1979-04-18 DE DE2915640A patent/DE2915640C2/en not_active Expired
- 1979-04-19 AU AU46229/79A patent/AU523090B2/en not_active Ceased
- 1979-04-19 FR FR7909871A patent/FR2423443A1/en active Granted
- 1979-04-20 SE SE7903502A patent/SE7903502L/en not_active Application Discontinuation
- 1979-04-20 JP JP4889679A patent/JPS54142194A/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| SE7903502L (en) | 1979-10-22 |
| AU523090B2 (en) | 1982-07-08 |
| JPS54142194A (en) | 1979-11-06 |
| DE2915640A1 (en) | 1979-10-31 |
| DE2915640C2 (en) | 1986-02-06 |
| FR2423443A1 (en) | 1979-11-16 |
| AU4622979A (en) | 1979-10-25 |
| FR2423443B1 (en) | 1983-04-22 |
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