JPS60150831A - Preparation of carbonaceous adsorbent having fine pores - Google Patents

Abstract

PURPOSE:To prepare a carbonaceous adsorbent having uniform and fine pores by introducing nitro group and sulfonic acid group into microbeads of mesocarbon and heat treating the product at a specified temp. in a nonoxidizing atmosphere. CONSTITUTION:Optically anisotropic microspheres generated in heavy bituminous material heat-treated at ca. 350-500 deg.C are separated from the heavy bituminous material to obtain microbeads of mesocarbon. Nitro and sulfonic acid groups are introduced into the microbeads, then the microbeads are heated at 300-600 deg.C in nonoxidizing atmosphere. Thus, a carbonaceous adsorbent having uniform and fine pore having ca. 4Angstrom pore size is prepd. The adsorbent is useful as a kind of molecular sieve.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides mesocarbon microbeads obtained by separating optically anisotropic small spheres generated in heavy bituminous materials heat-treated at about 350 to 500°C from the bituminous materials. By introducing a nitro group and a sulfonic acid group through a chemical reaction, and then heat-treating this in a non-oxidizing atmosphere at 300 to 600°C, a carbon-based material having approximately uniform micropores of about 4A (angstroms) is produced. The present invention relates to a method for manufacturing an adsorbent.

Activated carbon is an example of a carbon-based adsorbent having a pore size, and is used in a wide variety of industries.

Activated carbon uses plant-based materials such as wood and coconut husk, and heavy bituminous materials such as coal, coal tar pitch, and asphalt as raw materials.
It is manufactured by forming pores using a chemical activation method.

Recently, in order to improve the yield of activated carbon, a method has been developed in which asphalt or polyvinyl alcohol (PVA) is treated with sulfuric acid to become sulfonated, and this is activated after firing.

Activated carbon has a very large surface area of 1000 to 1500 m'/g, but its pore size distribution is wide, so it does not have selective adsorption ability to adsorb only specific components.

Activated carbon with uniform pores is made from polyvinylidene chloride (Saran) and is called carbon sieve because it has molecular sieve-like properties, and is commercially available in 5-pore diameter activated carbon. It is said that there is also a 6A product made from the same raw material. Recently, polyvinyl alcohol (PVA)
) is sulfonated and calcined in an inert gas, the product obtained by high-temperature treatment at 900 to 1000°C has adsorption properties similar to those of the carbon sieve described above, and its pores are smooth.・There is also a report that it is (Ishibashi et al., Fuel Association Journal, Vol. 62, p. 70, 198:11
Year).

As described above, several efforts have been made to develop carbon-based adsorbents with uniform micropores, but the raw materials used are materials such as Saran resin, in which the carbon obtained by firing forms a special skeletal structure. Moreover, there is a problem that the yield of the obtained adsorbent is low because it is a synthetic resin. on the other hand,
The production of adsorbents similar to carbon sieves from sulfonated PVA is thought to be based on an original idea in that the introduced sulfonic acid groups are removed by heat treatment, thereby forming pores. Uniform pore diameters are formed in products fired at about 1000° C., and uniform pores are not formed at firing temperatures below this temperature. Since the introduced sulfonic acid groups are eliminated at temperatures above about 200°C, the pores formed by the elimination of the sulfonic acid groups are not uniform (as the sulfonic acid group shrinks as the firing temperature increases, It is assumed that the pores become smaller as well, and that the pores are made more uniform by firing at around 1000°C.Therefore, the elimination of sulfonic acid groups contributes to pore formation;
This does not directly form uniform pores.

The present inventors have conducted extensive research to directly form uniform pores by removing groups introduced into solid organic substances.As a result of intensive research, we have introduced sulfonic acid groups and nitro groups into mesocarbon microbeads. Subsequently, the inventors discovered that when the t group was removed by introducing it by heat treatment at 250° C. or higher, more uniform pores were formed, and the present invention was accomplished based on this finding.

Mesocarbon microbeads used in the present invention include coal-based heavy bituminous materials such as coal tar and coal tar pitch, by-product tar during naphtha thermal cracking (naphtha tar), by-product tar during fluid catalytic cracking, and distillation of crude oil. When petroleum-based heavy bituminous materials such as residual oil are heat-treated at 350 to 500°C, optically anisotropic spherules (mesophase spherules) formed in the bituminous materials are separated from the bituminous materials as organic solvent insoluble matter. This is what I did.

Mesocarbon on this spherical 1trIJ I Pm1J
Microbeads are mainly composed of fused polycyclic aromatic compounds, and these compounds are arranged in a certain direction to form lamellae (thin layers), and have a structure in which these lamellae are stacked. be. Considering this structure, if the lamellae can be expanded, pores will be formed there, and
It is easily expected that the pores are slit-shaped.

Therefore, as a result of investigating the adsorption characteristics mainly due to gas, it was found that the following adsorption behavior was exhibited. In other words, in the case of mesocarbon microbeads that are still separated from bituminous materials, the amount of nitrogen gas adsorbed at a liquid nitrogen temperature of 77° is extremely small, and the specific surface area calculated from this amount is It is equal to the geometric external surface area calculated from the diameter, but when the adsorbed gas is carbon dioxide and the adsorption temperature is 273', the specific surface area is approximately 110
m”7g, and iodine adsorption at 303° is about 28
The amount of adsorption increases as the adsorption temperature rises to 0r+1'/g. However, at 303, methylene blue, which has a larger molecular diameter than iodine, is hardly adsorbed, indicating that it has selective adsorption ability. The amount of adsorption increases with increasing adsorption temperature, which is not often observed in general adsorbents, but this phenomenon is caused by the fact that while general adsorbents are inorganic, mesocarbon microbeads are organic. Therefore, it can be considered that the coefficient of thermal expansion is large, and as the temperature rises, the lamellae expand, resulting in an increase in the amount of adsorption. From this, it is thought that the expansion of the lamellae leads to an increase in the surface area, so we attempted to expand the lamellae by introducing a functional group.

This is because, as mentioned above, mesocarbon microbeads are mainly composed of aromatic compounds, so functional groups can be easily introduced through ordinary organic reactions, and because they form lamellae, It is presumed that the introduced functional groups will exist between the lamellae. Therefore, as a result of actually performing nitration, Friedel-Crafts reaction as an aromatic nucleus substitution reaction, and chlorination as a reaction on an aromatic nucleus aliphatic side chain, the results as expected were obtained (Fuel Temperature Society Journal, Vol. 55, p. 704, 1976). The adsorption behavior of mesocarbon microbeads into which nitro groups and chlorine have been introduced shows that the amount of adsorption decreases even when adsorbed at low temperatures, but the decrease is much smaller than that of mesocarbon microbeads that remain separated. The temperature dependence of the amount of adsorption became smaller.This phenomenon appears to be because the introduced functional group exists between the lamellae, which inhibits the contraction between the lamellae even at low temperatures.However, in 1947, when carbon dioxide gas The specific surface area that determines the amount of adsorption is approximately 190 m'/g, which is a small value for use as an adsorbent. (Details of the above adsorption behavior can be found in the 6th Carbon Materials Society Abstracts.

See pages 6-9, 1979. ) Therefore, in order to increase the specific surface area, we removed the functional groups introduced into mesocarbon microbeads. This is because new pores are formed due to the detachment of the introduced functional group and the size of the detached functional group (molecule) is the same, so the pores formed are expected to have a uniform size. This is for the purpose of As a result of actually removing the introduced functional groups by heating, the specific surface area is over 400 m''/g and the diameter is approximately 4^
It was found that microbeads that can be used as an adsorbent material having almost uniform pores were obtained, and that the intended purpose could be achieved.

The method of the present invention will be described in detail below.

The raw material mesocarbon microbeads used in the present invention are spheres with a sphere diameter of about 1/Jll+ or more. As described above, in this manufacturing method, mesophase spherules produced in a heavy bituminous material when the material is heat-treated at 350 to 500° C. are separated as an organic solvent-insoluble component. For details, see Special Publication No. 50-39833, Special Publication No. 51-29523,
It is described in Japanese Patent Publication No. 53-9599. In addition,
During heat treatment of bituminous materials, mesofaces do not remain in the spherule stage, but sometimes these spherules coalesce to form mesoface regions, that is, bulk mesofaces. Although this bulk mesophase is not spherical but lumpy, it can also be used as a raw material in the same way as mesocarbon microbeads.

Introducing functional groups into mesocarbon microbeads,
Here, the method for introducing nitro groups and sulfonic acid groups will be described.

Nitration: Add a predetermined amount of mesocarbon microbeads little by little to a mixed acid of 1 mol of concentrated nitric acid and 14 mol of concentrated sulfuric acid, and
After maintaining the temperature in the temperature range of ~60°C for 15 minutes or more while stirring, the mixture is poured into a large amount of water to stop the reaction, filtered, and washed with water. When the reaction temperature is 0℃, it takes more than 30 minutes, and when the reaction temperature is 60℃, it takes 15 minutes.
There was no change in volume increase after a holding time of 1 minute or more, and the reaction was considered to be almost complete.

The increase in weight at this time is 30 to 40% by weight. In addition, no coloring of the filtrate was observed at the above reaction temperature, but at 100°C
It turns brown and an oxidative decomposition reaction occurs with nitric acid. Therefore, it is not preferable to react at too high a temperature.

Sulfonation: Heat concentrated sulfuric acid to about 100°C, add mesocarbon microbeads, and treat for about 60 minutes or more. After treatment, put it in a large amount of water to stop the reaction,
Filter and wash with water. Changes in weight increase due to reaction temperature and holding time are approximately 20% by weight at 50°C for 60 minutes, approximately 26% by weight at 80°C for 60 minutes, and approximately 30% by weight at 100°C for 60 minutes.
Even if the reaction was carried out at 100°C for 180 minutes, the increase in volume remained the same.

Through these reactions, the originally hydrophobic mesocarbon microbeads become hydrophilic.

Nitrated or sulfonated mesocarbon microbeads are heat-treated to form pores. When the weight loss on heating was measured using a thermobalance, weight loss occurred at temperatures above about 200°C. Since this weight loss was not observed in unreacted mesocarbon microbeads, it is thought to be due to elimination of the introduced nitro group or sulfonic acid group. but,
Elimination of these groups is believed to occur gradually, as the weight loss does not occur abruptly at a particular temperature, but increases with increasing temperature. From this result, the heat treatment is at least 200°C, and since it is necessary to eliminate a certain amount of groups, the temperature is at least 250°C, preferably 300°C.
The temperature is above ℃. The maximum temperature is 600°C. 60
At 0°C, the pores formed by the elimination of nitro groups or sulfonic acid groups disappear due to the contraction of carbon.
The specific surface area decreases rapidly. Therefore, the heat treatment temperature range is 300 to 600°C. Further, it is not preferable to perform this treatment in an oxidizing atmosphere because there is a risk of combustion, and it is necessary to perform this treatment in an inert atmosphere.

The specific surface area of the mesocarbon microbeads obtained in this way varies somewhat depending on the heat treatment temperature, but is approximately 35
0 to 450m"7g. This value is only 30 to 50% smaller than that of activated carbon, but the crosstalk such as adsorption is Langmuir type (so-called type 1), and liquids with different molecular sizes The pore diameter calculated from the saturated adsorption amount is about 4A, which is a nearly uniform pore size, so it can be fully expected to have selective adsorption ability. There is no particular difference between the groups, except that the specific surface area becomes slightly smaller when the sulfonic acid group is introduced.

As mentioned above, mesocarbon microbeads are approximately IP
Since it is a fine sphere of m or more, it has a higher packing density than angular powder, and therefore has a characteristic of lower flow resistance. Furthermore, mesocarbon microbeads themselves have caking properties and can be molded. Molding is performed using a mold at room temperature and a molding pressure of 500 to 2000 kg/c++r. Further, after molding, a nitro group or a sulfonic acid group may be introduced, but it is preferable to perform molding and heat treatment after introducing these groups because damage to the molded product can be avoided as much as possible.

Hereinafter, the method of the present invention will be explained in more detail with reference to Examples.

Reference Example Coal tar pitch was placed in quinoline and heated to about 90°C to dissolve and disperse it. Pass this through a glass filter (N
The filtrate was distilled under reduced pressure to remove quinoline, and coal tar pitch containing no free carbon was collected. Approximately 400 g of this coal tar pitch was placed in a glass cylindrical flask with a capacity of 500 ml, and treated at 430° C. for 60 minutes while stirring in a nitrogen gas stream. After embedding this heat-treated pitch in resin and polishing it, observation using a reflective polarizing microscope revealed that there were countless optically anisotropic small spheres (mesoface small spheres) with a diameter of about IPm or more in the optically isotropic pitch. However, a small amount of aggregates of several of these small spheres were also observed.Put this pitch in approximately three times the volume of quinoline, and dissolve by heating to approximately 90°C.

After dispersion and centrifugation to precipitate insoluble components, the soluble components of the supernatant were separated. Fresh quinoline was added to the precipitate, heated again to about 90°C, and then subjected to a centrifugal precipitator. After repeating this operation 5 times to remove soluble components, acetone was added to the precipitate, and filtered through a glass filter (No. 4).
) was filtered. After thorough washing with acetone, the beads were dried to obtain mesocarbon ° microbeads. The yield was 10.6% by weight based on the heat-treated pitch. When the obtained mesocarbon microbeads were observed with a scanning electron microscope, most of them were spherical with a diameter of about 1 ymR, and some were large and had a diameter of about 50 Pm. There was also a small amount of angular pieces.

The mesocarbon microbeads obtained in Reference Examples were nitrated and sulfonated as follows.

Concentrated nitric acid 80nt' and concentrated sulfuric acid 100ml in a nitration 500ml Erlenmeyer flask! Place in ice water or in a water bath heated to 60°C.

10 g of mesocarbon microbeads were gradually added while stirring with a magnetic stirrer. After holding at each temperature for 60 minutes or 180 minutes, the reaction was stopped by placing in ice water for about 1 hour. This was filtered under reduced pressure through a glass filter (No. 4) and thoroughly washed with water. The mesocarbon microbeads on the filter were dried under reduced pressure at EO°C for one day and the weight was measured.

Sulfonation 500mI! Pour 100 mJ of concentrated sulfuric acid into a Erlenmeyer flask.
Heat in an oil bath heated to 50-100°C, gradually add 10 g of mesocarbon microbeads while stirring,
60-18 (held for 1 minute. Immediately after the lapse of time, the ζζ flask was taken out from the oil bath and placed in water of about 11 to stop the reaction. Then, the reaction was stopped using a glass filter (No. 4).
), washed thoroughly with water, and dried under reduced pressure at 80° C. all day and night.

Table 1 shows the weight increase rate according to each reaction condition of nitration and sulfonation.

Since the weight increase in Table 1 is thought to be due to the introduction of nitro groups and sulfonic acid groups, Experiment Nos. 1, 2 and 6, which had a large weight increase rate, were selected and heat treated.

Heat treatment was performed using a tubular furnace, with approximately 2 g of the sample placed in a graphite container and heated to 250 ~ 250 °C at a heating rate of 5 °C/min in a nitrogen gas flow.
It was heated to 1000°C and held at each temperature for 30 minutes. For comparison, the raw material mesocarbon microbeads were also heat-treated in the same manner. Table 2 shows the yield by heat treatment.

Table 2 In order to find out the pore volume of each of the heat-treated products listed in Table 2, the amount of adsorption was measured by a gas adsorption method using carbon dioxide gas, and crosstalk such as adsorption was eliminated. The adsorption temperatures are at 273 and 194.5°. From this adsorption isotherm, the monomolecular layer adsorption amount (Vm) was determined and the specific surface area was calculated using the Marsh equation and Langmuir equation. The results are shown in Tables 3 and 4.

Marsh's formula % formula %) Langmi 11 formula P/V=P/Vm+1/bVm Specific surface area (S) =0.269 crm-VmV: Adsorption amount ('
/ g) pVm: monomolecular layer adsorption amount (rnl
/g) B: Constant T: Adsorption temperature ('K) β: Affinity coefficient P
: Normal impact pressure (adjusted Hg), b: Constant of proportionality σIl: Molecular cross section of carbon dioxide, 1 when 273
8.6^', Po at 17,0 when at 194.5°;
Saturated vapor pressure, 26123+maHg at 27g”K
, when 194.50 is 760+w g Further, from the Duminin equation, the pore volume (■0) calculated from the pore volume (Wo) of the micropore (approximately 30 Å or less) and the monomolecular layer adsorption amount, Also listed in the table.

Dex 2 2"-' formula 1ogW = logWo -
0,434 (H person'/β2) W=M −V / 224
14・p (ρdensity, When 273', ρ=1.
When 081.194.5@, ρ= 1.54cd7g
, M is molecular weight = 44) A' = (2,303RT)" (logPO/P
) L (R is gas constant = 1.987 eal/deg) Pore volume from monomolecular layer adsorption amount V o-M-V m/ 22414 ・p As seen from Table 3, the ratio of the non-heat-treated one Although the surface area is slightly larger than that of the raw mesocarbon/micropeas even if it is converted into a carbonate or sulfonate, it becomes 350 to 430//g by heat treatment at 250 to 600°C, and has a much larger specific surface area. become. The case of Table 4 where the adsorption temperature is low is also false. It is clear that these results are the result of the introduction and removal of nitro groups and sulfonic acid groups. Further, all of the adsorption and other crosstalks in Table 4 are of the Langmuir type (type 1), except for those at a processing temperature of 0. In other words, the amount of adsorption is large in the region of low relative pressure (P/Po) (the amount of adsorption is very small when P/Po is about 0.2 or more, and the correlation coefficient is It matches at 0999 or more.At the processing temperature O, it is type 1, but the correlation coefficient is less than 0.98, and it cannot be sorted out by the Langmuir equation.Approximately 30 by the Dubinin equation.
The pore volume (W o ) of Å or less and the volume (vO) determined from the amount of adsorbed single molecules are almost the same, and it is considered that the pores formed are at least 30 Å or less.

For comparison, the adsorption amount of carbon dioxide was measured using a commercially available carbon sieve (trade name MSC5A) at 194.5°, and the results were summarized using the Langmuir equation, with a specific surface area of 565 m'/g, Wo = 0. .158 m17 g
.

V o = 0.155rn1/g, which indicates that the adsorbent has a larger specific surface area than the adsorbent of the present invention.

In order to determine the shape and size of the pores, the saturated adsorption amount of liquids with different molecular diameters was determined. The adsorption method is the method of Hirata et al. (Chemical Engineering, Vol. 24, p. 572).

(1970), one set consists of two branch glass tubes with an outer diameter of 8 mm and a length of 100 mm. Approximately 1 g of the sample is placed in each tube, and after degassing at 5 x 10 mm Hg at 120 °C, the liquid It was connected to the other one with a branch pipe in it. After leaving this in an air constant temperature bath at 30° C. for 20 days, the weight increase of the sample was measured. The value obtained by dividing this increase by the density of the liquid at 30° C. was defined as the saturated adsorption amount. As a representative example, the samples used were treated at a treatment temperature of 50°C in Experiment Nos. 2 and 6 in Table 2.
It is at 0°C. Table 5 summarizes the molecular diameter, density, and saturated adsorption amount for each type of liquid.

Table 5 As can be seen from this table, the amounts of benzene and methanol adsorbed are large, but the amounts of cyclohexane and carbon tetrachloride are small. This result shows that most of the pores have a pore diameter of about 4^. Furthermore, benzene is a planar molecule, and although its spread is large, the adsorption amount is large, similar to methanol, which indicates that the pores are slit-shaped.

Although the size and shape of the pores cannot be determined strictly from this result, since they are generally slit-shaped with a pore diameter of about 4, it can be used as a kind of molecular sieve.

Patent applicant: Director of the Agency of Industrial Science and Technology Kawa 1) Yoshige Hirobe, Director of the Kyushu Institute of Industrial Science and Technology, Agency of Industrial Science and Technology
Departmental Procedures Amendment (Method) % Formula % 2. Name of invention Method for producing carbon-based adsorbent having micropores 3. Person making the amendment 4. Designated agent

Claims (1)

[Claims] 1. Nitro group in mesocarbon micropeas. The sulfonic acid group is introduced, and then in a non-oxidizing atmosphere, 3
A method for producing a carbon-based adsorbent having fine pores, the method comprising heating at a temperature of 00 to 600°C.