CA1036771A - Method for the preparation of carbon moldings and activated carbon moldings therefrom - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A method for the preparation of a porous carbon molding having a low apparent density, the method comprising the steps of thermally mixing a pitch, which has a softening point of 50-350°C, a carbon content of 80-97 wt%, a hydrogen/
carbon ratio of 0.3-2.5 and a nitrobenzene-insoluble fraction of below 60 wt%, with at least one aromatic hydrocarbon having a boiling point of 200°C or higher, forming the mixture into a suitable shape, immersing the formed material in a solvent, in which the pitch is hardly soluble but the aromatic hydrocarbon is easily soluble, for extracting the aromatic hydrocarbon from the formed material and obtaining a porous pitch material, oxidizing the porous pitch material at a temperature from room temperature to 400°C by the use of an oxidizing agent to form an infusible porous pitch material, and calcining the infusible porous material in an inert atmosphere at a temper-ature higher than 600°C to obtain a porous carbon material.
The porous carbon material or the infusible porous material may be activated by means of steam vapour or air to produce an activated carbon material.

Description

This invention re~ates to a nove] method for thc preparation of a carbon material and an activated carbon material, and more particularly to a method for the prepara-tion of a spherical carbon material and a spherical activated carbon material.
In general, activated carbon is widely used, because of its excellent adsorbin~ property, as an agent for removing pollutants from air, water, etc., or purifying water or air.
Activated carbon, when employed in the spherical form, has many advantages. That is, spherical activated carbon can be readily transferred from one place to another due to its rolling property, and can also be easily illed uniformly in or discharged from a container or vessel in practical applications.
Moreover, spherical activated carbon shows low resistance to gas or liguid flow when applied in a packed bed. The sa~e can be also employed even in a fluidized bed with easy handling.
In addition, because of its spherical form, the spherical activa-ted`carbon is hardly fragmented during operation and almost free from abrasion losses which would occur to a significant ZO degree with other shapes.
Activated spherical carbons have many applications other than in activated spherical carbon moldings which have the above-mentioned advantages. For example, in cases where spherical carbon is used for producing a composite material by mixing with a metal (aluminum, copper, tin, etc.) or a synthetic resin (a nylon, polyester, epoxy resin, fluororesin, etc.), the resultant composite material is remarkably improved in resistance to abrasion and surface-lubricating property, as compared with those using known carbon powders or granules, due to high mechanical strengths inherent in the spherical form and due to the uniformly mixing property of the spherical carbon with the metal or resin. Spherical carbon moldings are also 3~"

~03~77~
useful as a filler ln powder paint or as a sta~ting material for producing isotropic graphite.
Spherical carbon moldings have been heretofore produced by mixing powdery carbon or carbon precursor with a binding agent and molding the mixture into a spherical form.
The resultant spherical carbon moldings can be activated in the usual manner to form activated spherical carbon. In the prior molding method using powdered starting materials, however, i~
i8 very difflcult to form fine spherical carbon moldings or actlvated carbon having a diameter of from several ~ to 1 mm.
The use of the powdered materials incurs reductions in oper-ational efficiency and undesirable irregularities in shape.
Accordingly, it is desired to provide a method which is capable of efficiently producing spherical carbon moldings and spherical aetivated carbon of better quality, It is an ob~ect of the present invention to provide a method for the preparation of porous carbon moldings and porous activated carbon moldings having various shapes.
In one particular aspect the present invention provides a method for the preparation of a porous carbon material comprising the steps of thermally mixing a pitch, having a softening point of 50 - 350C, a carbon content of 80 - 97%, a hydrogen/carbon ratio of 0.3 - 2.5, and a nitroben-zene-insoluble fraction of less than 60%,,with at least one aromatic hydrocarbon having a boiling point of at least 20~C, forming the mixture to a desired shape, immersing the formed material in a solvent in which said pitch is hardly soluble but said aromatic hydrocarbon is easily soluble for extracting said aromatic hydrocarbon from the formed material and obtaining a porous pitch material, oxidi~ing the porous,pitch material a~ a temperature between room temperature and 400C to form an infusible porous pitch material, and calcining the infusible B Jl/S~ -2-"` 1036~71 porous pitch material in an inert atmosphere at a temperature of at least 600C.
Other ob~ects and advantages of the invention will become apparent from the following description.
DETAIL~D DESCRIPTION OF THE INVENTION
The pitch useful in the present invention has a softening point of 50-350C, a carbon content of 80-97 wt%, a hydrogen/carbon ratio of 0.3 - 2.5, snd a nitrobenzene-insoluble fraction of less than 60 wt~. In practical applications, it is preferred that the pitch has a softening point o 150-250C, a carbon content of 85 - 97 wt%, a hydrogen/
carbon ratio of 0.35 - 1.0 and a nitroben~ene-insoluble com-ponent of less thant 60 wt%, In addition, the pitch is pre-ferred not to contain elements other than hydrogen and carbon, more particularly, elements such as sulfur, halogens, metals and the like. If contained, such elements are preferably in.an amount of less than 1%. However, this is only a preferred condition and not an essential requirement in this invention.
The starting pitch used in the present invention can be easily 20 obtained, for example, by heat-treating a tar-like substance which is obtained as a by-product in thermal cracking of oils (including crude oils, naphtha, asphalt, heavy oil, light oil~
kerosene oil, and the like) for the production of gaseous hydro-carbons, or a residual oil which is obtained ~ -3-'~3 - - \

l0367n in a petroleum refinery process, and removing low-boiling point components from the thus treated tar-like substance or residual oil by distillation, extraction or like operations.
The pitch may be also obtained by removin~ low-boiling point components of coal tars. The pitch may be also obtained by removing low-boiling point components from a residue which is obtained by thermal cracking of organic polymers (plastics) and the like Thus, various kinds of materials including petroleun~-or coal-base materials can be used as a starting pitch material in the present invention.
~ The aromatic hydrocarbon to be added to the pitch is required to have a boiling point of 200'C or higher and good compatibility with the pitch. When mixed with the pitch the aromatic hydrocarbon causes a lowering of the softening point and viscosity of the pitch to a certain degree so that the mixture can be easily formed into a suitable shape. Examples of the aromatic hydrocarbons useful in the present invention include aromatic hydrocarbons having two or three rings such as naphthal-ene, methylnaphthalene, dimethylnaphthalene, anthracene, phenan-threne, triphenylene, diphenyl, diphenylmethane, diphenylether and the like, and their alkyl derivatives. Though not critical, the ratio of the pitch to the aromatic hydrocarbons is preferred to be within a range 5-50, parts to 100 parts pitch by weight.
The pitch is mixed with the aromatic hydrocarbons under heating conditions to form a fluidized mixture, and the mixture is then formed into a suitable shape by a known method. For example, in order to form the mixture into a spherical shape, it is dis~
persed in a suitable dispersing medium.
The thus formed material, which is composed of the pitch and one or more aromatic hydrocarbons, is then deprived of most of the aromatic hydrocarbon components to produce a porous pitch material. That is, the formed material composed of the sl:

10367 7~ , pitch and aromatic hydrocarbons is immersed in a solvent in which the pitch is hardly soluble but the aromatic hydrocarbons are easily soluble.
Examples of the solvent include an aliphatic hydro-carbon such as butane, pentane, hexane, heptane, or the like;
a mixture mainly composed of aliphatic hydrocarbons such as naphtha, kerosene, or the like; and an aliphatic alcohol such as methanol, ethanol, propanol, butanol or the like. In accord-ance with the method of the present invention, when the formed material composed of the pitch and hydrocarbon is immersed in the above-mentioned solvent, the hydrocarbon can be extracted from the formed material while maintaining the external shape of the material, thus forming a pitch material having porosity resulting from the extraction of the aromatic hydrocarbon. The porosity of the pitch material is advantageous in carrying out the following infusibilizing, carbonizing and activating processes in an efficient manner. That is, since the infusibilizing pro-cess involves a heterogeneous reaction between the solid pitch material and an oxidizable gas or liquid, the porosity of the solid pitch material allows the oxidizable gas or liquid to reach the inside of the pitch material easily for full and complete treatment thereof. Moreover, the release of decomposed gases in the carbonizing process and the diffusion of an activating gas into the inside of the porous pitch material can also be facili-tated in the same manner as in the infusibilizing process.
It will be appreciated that an apparatus by which the formed material composed of the pitch and aromatic hydro-carbon is immersed in the above-mentioned solvent for forming a porous pitch material may be of any known type, and is not re-quired to be of a particular type.
The thus obtained porous pitch material is oxidized by means of an oxidizing agent at a normal temperature to 400C

ca: - S -~0367'71 to obtain an infusible porous pitch material. The oxidizing agent is, for example, a gas such as 2~ 3~ SO3~ NO2 or C12, a mixed gas obtained by diluting any of the above-mentior.ed gases with air or nitrogen, or an oxidizing gas such as air, or an oxidizing liquid such as sulfuric acid, phosphoric acid, nitric acid~a chromic acid aqueous solution or a perman~anic acid aqueous solution. These oxidizing agents may be used singly or in combination.
Preferably, in the infusibilizing step, the pitch ma-terial is initially treated at a temperature lower than the softening point of the pitch, while gradually raising the treat-ing temperature, since the softening point is raised as the in-fusibilizing reaction procèeds, and thus the infusibilizing time is shortened.
The thus treated infusible porous pitch material is then calcined in an inert atmosphere, for example, of nitrogen at a temperature higher than 600C to produce a porous carbon material. The thus produced carbon material or the infusible pitch material is then actlvated by means of steam vapor, or air activated and porous carbon material can be readily obtained.
The activation can be conducted by any known activation method.
Additionally, where the infusible pitch material is subjected to activation, carbonization as well as activation occurs simul-.taneously.
A prominent feature of the carbon material of the present invention is that the carbon material is porous and has a reduced apparent density. Accordingly, the carbon material is considered useful as a starting material in certain cases.
For example, where the carbon material is used in the form of fibre, its surface treatment can be made easier due to its porosity. Such porous fibre is useful as a starting material in the production of a composite material.- Moreover porous carbon ca:

103 ,6771 fibre activated by the use o~ steam vapor has various app;ica-tions.
In addition, the carbon material of the present inven-tion can be formed into any shape including a sphere, plate, rod or the like, and the thus formed carbon material can easily be activated, so that these carbon materials, activated or not, can ind many applications.
The present invention will be particularly illustra-te~ from the following examples, ~hich are shown only by way of explanation, not limitation.
Exàm~le 1 A tar-like material was obtained by spraying for thermal cracking a Seria petroleum in steam vapor of 2000-C for 0.003 seconds of contact time and then rapidly cooling and distil-ling to remove therefrom distillates having a boiling point lower than 350-C (under a vacuum of SmmHg) to obtain a pitch.
75 kg of the thus obtained pitch (having a softening point of 198-C, a carbon content of 95 wt%, a hydrogen/carbon ratio of 0.6 and a nitrobenzene-insoluble fraction of 35 wt%), and 25 kg of naphthalene were introduced into an autoclave equipped with an agitator a`nd having an inner volume of 400 1 and mixed with each other at 160-C. Then, 200 kg. of 0.2% polyvinyl alcohol (having a saponification degree of 86~) aqueous solution was added to the mixture for dispersing the mixture in the solution while agitating the resultant mixture at 150-C for 40 min at 300 r,p.m. The mixture was then cooled to obtain a slurry containing the pitch in the form of spheres. A major part of water was removed from the slurry, to which methanol was passed ~` in an amount six times by weight as great as that of the spheres for removing naphthalene therefrom. The spherical pitch was dried in air and contained less than 1% naphthalene. The spherical pitch was heated in a fluidized bed by means of air at 103677~
from room temperature up to 300C at a heating rate of 25-C/hr, and was maintained at a temperature of 300C ~or 2 hours to obtain infusible pitch spheres. The infusible pitch spheres were heated in an atmosphere of nitrogen up to lOOO-C at a heating rate of 200C/hr, and were maintained at the temper-ature for 1 hour to yield porous carbon spheres having an average particle size of 450~ and an almost true spherical form, Example 2 Th~ infusibilized spherical pitches of Example 1 ~ere activated, i.e., the pitches were heated by the use of a fluidized bed up to 900C at a heating rate of 200-C/hr in an atmosphere of steam vapor and maintained at 900-C for 3 hours, thereby to obtain an activated spherical carbon.
The thus obtained activated spherical carbon had an average particle diameter of 400 ~, an iodine adsorption number of 950 mg/l (when determined at an equilibrium concentra-tion of lg/l), a caramel decoloration rate of 85% (when determined in accordance with the method prescribed in Japanese Industrial Standards K-1470) and a surface area of 1100 m2/g, thus showing high activity.
Example 3 .
A vacuum distillation residual oil obtained from Kafji crude oil was introduced into a container at 410-420-C, into which heating steam vapor at 430-450-C was passed for 2 hours for a heat-treatment and distillation to obtain a pitch residue.
10 kg of the thus obtained pitch (having a softening point of 210-C, a carbon content of 84 wt%, a hydrogen/carbon ratio of 0.75, and a nitrobenzene-insoluble fraction of 27 Wt%~ and

2.5 kg of naphthalene were introduced into an autoclave having an inner volume of 20 l-and equipped with an agitator and mixed with each other at 160-C. The mixture was then dropped into hexane through a nozzle having an inner diameter of 1 mm and provided at the bottom of the autoclave. In this connection, a cylindrical heating tube which had a length of 2 m and was maintained at 140-C was provided perpendicularly to the nozzle for preventing cooling of the mixture dropped As a result, the mixture was formed into spheres having a diameter of about 2 mm~ The spheres were gently agitated in hexane at room temper-ature for 3 hours for removing thererom naphthalene by extrac-tion. Then thè sphères were withdrawn from the hexane and dried to obtain pitch spheres containing only 2.5% of naphthalene.
Thet~us obtained pitch spheres were heated by mèans of heating air up to 300-C at a heating rate of 20-C/hr, and maintained at 300-C for 3 hours to obtain infusible pitch spheres. The pitch spheres were further heated in an atmosphere of nitrogen up to lOOO-C at a heating rate of 200~C/hr, and maintained at the temperature for 1 hour to obtain porous carbon spheres. The carbon had an average particle size of 1.8 mm and an almost true spherical form.
Example 4 , The porous carbon spheres obtained in Example 3 were heated at 450C in air for lO hours to obtain activated porous carbon spheres. The activated carbon spheres had an average particle size of 1.6 mm, an iodine adsorption number of 700 mg/g (when tested at an equilibrium concentration of l g/l), a caramel decoloration rate of 90% (which was determined in accord-ance With the method prescribed in Japanese Industrial Standards R-1470~ and a total surface area of 850 m2/g, thus showing high activity.
Example 5 80 parts by weight of a pitch and 20 parts by weight Qf methylnaphthalene were thermally mixed with each other by the use of a small-scale test spinning machine. The pitch used was a residue obtained by reduced press~lre clistillation of a bottom oil which was produced in the production of ethylcne, and had a so~tening point of 1~0C, a carbon contcnt of 92 wt~, a hydrogen/carbon ratio of 0.84 and a nitrobenzene-insoluble fraction of 2 wt~. The mixture was spun together with an air flow, through a nozzle having a diametex of 0.5 mm at a nozzle temperature of 130~C to form A filament. The filament was immersed in naphtha to remove therefrom methylnaphthalene to obtain a fibrous material composed substantially of the pitch. The fibrous material which was dried contained methylnaphthalene only in an amount less than 1~. The fibrous pitch material was heated by means of a heating air up to 300C at a heating rate of 25-C/hr, and maintained at 300C for 1 hour to obtain an infusible fibrous pitch mat. The resultant fibre was then thermal-ly treated in an atmosphere of nitrogen up to lOOO-C at a heating rate of 300-C/hr and maintained at 1000C for 1 hour to obtain a porous fibrous carbQn material. An average diameter of the single fibre was 15 ~, its mechanical strength 6 ton/cm2 and a modulus of 250 ton/cm2.
Example 6 .
The fibrous carbon material obtained in Example 4 was treated in an atmosphere of steam vapour of 850C for 8 hours to obtain an activated fibrous carbon material. The average diameter of the single fibre was 12 ~, the iodine adsorption number 830 mg/g ~when determined at an equilibrium concentration of lg/l~ caramel decoloration rate of 83% (when determined in accordance with the method prescribed in Japanese Industrial Standards K-14701, and a total surface area of 950 m2/g, thus showing the fibrous activated carbon material had high activity.
Example 7 A tar-like material, which was obtained by thermally cracking Seria crude oil sprayed into steam vapor at 1200-C for a contacting time of 0.005 seconds and rapidly cooling the treated . _ ,, .. .. ... : . .. . , . . .. , _ ... .. .. ... .. . . . .... . .. .. ... ...... ... ... ... .. .. .. . .. .
.. . . . ...

1036~
oil, was thermally treated at 400-C for 3 hours under a normal pressure and a distillate which had a boiling point lower than 380-C under a vacuum of 5 mmHg was removed from the tar-like material to obtain a pitch. 70 parts by weight of the thus obtained pitch (having a softening point of 220-C, a carbon content of ~wt~, a hydrogen/carbon ratio of 0.65 and a nitro-benzene-insoluble fraction of 47 wt~) and 30 parts by weight of phenanthrene were th~rmally mixed with each other at 180-C
and the mixture was introduced to a thickness of 1 cm in a metal mold having a size of S cm x 5 cm x 3 cm and c~oled to form plate-like moldings. The moldings were inunersed in heptane in an amount~5 times as great as the volume of the plate-like moldings while agitating heptane over 20 hours at room temper-ature for extracting phenanthracene from the moldings. The resultant moldings were heated by means of hot air at temper-atures up to 300-C at a heating rate of lO-C/hr, and maintained at 300-C for 5 hours to obtain infusible plate-like pitch moldings. The resultant moldings were thermally treated in an atmosphere of nitrogen by heating up to lOOO-C at a heating rate of SO-C/hr and maintained at lOOO-C for 3 hours to obtain porous plate-like carbon moldings. The moldings had a compres-ion strength of 550 kg/cm , a compression Young's modulus of 4 x 104 kg/cm2, a specific resistance of 0.03 Q cm and a bulk densit~ of 1.7 g/cc.
Ex~ple~8 The infusibleFlate-like pitch moldings obtained in Ex~mple 7 were heated in a mixed gas containing steam vapour and nitrogen in a ratio of 3:7 up to 900-C at a heating rate of 50-C/hr, and maintained at 900-C for 5 hours to give activated porous plate-like carbon moldings. The resultant moldings had an iodine adsorption number of 750 mg/g ~when determined at an equilibrium concentration of lg/l~, a caramel decoloration rate sl:

of 80% (when determined in accordance with the method pre-scribed in Japanese Industrial Standards K-1470) and a total sur~ace area of 950 m2/g, thus showing high activit~.

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Claims (10)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method for the preparation of a porous carbon material comprising the steps of thermally mixing a pitch, having a softening point of 50 - 350°C, a carbon content of 80 - 97%, a hydrogen/carbon ratio of 0.3 - 2.5, and a nitro-benzene-insoluble fraction of less than 60%, with at least one aromatic hydrocarbon having a boiling point of at least 200°C, forming the mixture to a desired shape, immersing the formed material in a solvent in which said pitch is hardly soluble but said aromatic hydrocarbon is easily soluble for extracting said aromatic hydrocarbon from the formed material and obtaining a porous pitch material, oxidizing the porous pitch material at a temperature between room temperature and 400°C to form an infusible porous pitch material, and calcining the infusible porous pitch material in an inert atmosphere at a temperature of at least 600°C.

2. A method according to claim 1, wherein said shape is spherical.

3. A method according to claim 1, wherein said aromatic hydrocarbon is an aromatic hydrocarbon having two or three aromatic rings or a derivative thereof.

4. A method according to claim 3, wherein said aromatic hydrocarbon is selected from the group consisting of naphthalene, methylnaphthalene, dimethylnaphthalene, anthracene, phenanthrene, triphenylene, diphenyl, diphenylmethane, and diphenylether.

5. A method according to claim 1, wherein said solvent is selected from the group consisting of butane, pentane, hexane, heptane, methanol, ethanol, propanol, butanol, naphtha and kerosene.

6. A method according to Claim 1, wherein said oxidation is effected with a gas.

7. A method according to Claim 6, wherein said gas is selected from the group consisting of O2, O3, SO3, NO2, C12 a mixed gas obtained by diluting said gases with air or nitrogen, and air.

8. A method according to Claim 1, wherein said oxidation is effected with a liquid.

9. A method according to Claim 8, wherein said liquid is selected from the group consisting of sulfuric acid, phosphoric acid, nitric acid, a chromic acid aqueous solution, and a permanganic acid aqueous solution.

10. A method according to Claim 1 including the step of activating the calcined porous pitch material by means of steam vapor or air.