JPH0413288B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention is characterized in that polyvinyl alcohol resin is
50% by weight, 10-40% by weight of melamine resin, and 30-70% by weight of phenolic resin, carbonized or activated.The maximum value of the pore size distribution is in the region with a pore diameter of 10 Å or less. and pore diameter 15~
This invention relates to carbon molecular sieves for air separation having a pore volume of 0.1 g/cm ³ or less within a range of 200 Å. (Prior art) Silica-alumina-based zeolites are widely known as adsorbents with a molecular sieving effect, but in recent years, molecular sieving carbon has also come to be industrially manufactured using various manufacturing methods. It's coming.
These molecular sieves are used for the separation of various hydrocarbons, hydrogen purification, etc., and have particularly attracted attention in recent years as a separating agent for nitrogen and oxygen in the air.
Pressure swing adsorption (PSA) is used in air separation using molecular sieves.
This method is commonly used, and as is already well known, in zeolite, the equilibrium adsorption amount of nitrogen is larger than that of oxygen. Nitrogen and oxygen are separated by taking advantage of the large . As mentioned above, both zeolite and carbon molecular sieves are used as molecular sieves for air separation by taking advantage of their different properties. However, zeolite-based molecular sieves have poor heat resistance and chemical resistance, and are polar It has the disadvantage that it has strong selective adsorption to substances and does not exhibit a molecular sieving effect in the presence of polar substances. On the other hand, molecular sieve carbon is attracting attention as a molecular sieve that has excellent heat resistance and chemical resistance and can be used even in the presence of polar substances, but its industrial manufacturing process is complicated and its ability to separate nitrogen and oxygen is high. There are many problems, such as the desire for a further increase in the number of people. The industrial manufacturing methods for molecular sieve carbon that have been developed so far include:
For example, a method in which synthetic resin raw materials are adsorbed together with a catalyst on pre-manufactured activated carbon with large pores and then carbonized again (Japanese Patent Publication No. 49-37036)
(No. 52-47758), a method in which Saran waste is heated and carbonized at high temperature, then crushed, sintering agent, granulating agent, etc. are added, granulated, and heated and carbonized again (Special Publication No. 52-47758), or pre-produced Examples include a method in which activated carbon is recalcined in an atmosphere containing hydrocarbons and carbon generated by thermal decomposition of hydrocarbons is attached to the pore walls of the activated carbon, but as mentioned above, all of these manufacturing methods involve a number of steps. In addition to being complicated, the current situation is that it is desired to further improve the separation ability when applied to the separation of nitrogen and oxygen, which have an extremely small difference in molecular diameter. In order to improve the air separation ability of carbon molecular sieves, it is necessary to use high-performance carbon molecular sieves with sharp pore size distribution and large adsorption capacity to further increase the adsorption rate difference between nitrogen and oxygen, which have extremely small molecular diameter differences. need to be manufactured. (Problems to be Solved by the Invention) The present inventors have completed the present invention as a result of intensive research in view of the above-mentioned drawbacks of existing molecular sieve carbons. That is, in the present invention, the polyvinyl alcohol resin is
A synthetic resin composite porous body consisting of 10 to 50% by weight of melamine resin, 10 to 40% by weight of melamine resin, and 30 to 70% by weight of phenol resin is carbonized in a temperature range of 500 to 700°C in a non-oxidizing atmosphere, or carbonized. After that, the pore diameter is further activated in an oxidizing atmosphere at a temperature range of 500 to 700°C to the extent that the weight of the carbide decreases within 15% by weight.
The present invention provides a carbon molecular sieve for air separation, which has a maximum value of pore size distribution in the region of 10 Å or less, and has a pore volume of 0.1 cm ³ /g or less in the pore diameter range of 15 to 200 Å. In the present invention, polyvinyl alcohol resin
The polyvinyl alcohol resin used for the synthetic resin composite consisting of 10 to 50% by weight, 10 to 40% by weight of melamine resin, and 30 to 70% by weight of phenolic resin is:
These are polyvinyl alcohol and polyvinyl acetal resins such as polyvinyl formal and polyvinyl benzal obtained by an acetalization reaction of polyvinyl alcohol. Also, what is melamine resin?
It is a melamine-formaldehyde initial condensate and is usually water-soluble. Further, as the phenol resin, a solution-like resol resin or novolac resin can be suitably used. A method for producing a synthetic resin composite from these polyvinyl alcohol resins, melamine resins, and phenol resins involves adding a crosslinking agent and a curing catalyst to polyvinyl alcohol and reacting them to produce polyvinyl acetal resins such as polyvinyl formal and polyvinyl benzal. After that, a predetermined amount of melamine resin or phenolic resin is applied to the resin by means such as impregnation, or after uniformly mixing polyvinyl alcohol and liquid melamine resin or polyvinyl alcohol and liquid phenolic resin, a crosslinking agent and a curing agent are added. Alternatively, after copolymerizing by adding a curing catalyst, the remaining resin is applied, or polyvinyl alcohol, liquid melamine resin,
After uniformly mixing the liquid phenolic resin, a method can be used in which a crosslinking agent and a curing agent or a curing catalyst are added to perform a copolymerization reaction. Crosslinking agents or curing agents used in these reactions,
The following are suitable as curing catalysts. That is, as a crosslinking agent for polyvinyl alcohol, aldehydes such as formaldehyde and benzaldehyde are suitable, and as a catalyst for the acetalization reaction of polyvinyl alcohol and the curing reaction of phenol resin, hydrochloric acid, sulfuric acid, oxalic acid, lactic acid, and para-toluenesulfonic acid are suitable. , maleic acid, malonic acid, etc. are suitable, and as curing agents for melamine resin, inorganic acids such as hydrochloric acid and sulfuric acid, carboxylic acid esters such as dimethyl oxalate, and ethylamine hydrochloride and triethanolamine hydrochloride are suitable. Hydrochlorides of amines, etc. can be used. In addition, starch,
By adding a pore-forming material such as a modified starch, a starch derivative, or a water-soluble metal salt, a synthetic resin composite porous body having continuous macropores in a network structure can be produced. The manufacturing method is described in, for example, Japanese Patent Publication No. 58-54082,
The method disclosed in JP-A-57-51109, JP-A-57-118009, etc. or other known methods may be used. In short, a synthetic resin composite consisting of 10 to 50% by weight of polyvinyl alcohol resin, 10 to 40% by weight of melamine resin, and 30 to 70% by weight of phenolic resin is sufficient, but the composition of this synthetic resin composite is preferably 15 to 40% by weight of polyvinyl alcohol resin, 15 to 30% by weight of melamine resin, and 40 to 65% by weight of phenolic resin, and most preferably 20 to 30% by weight of polyvinyl alcohol resin and 15% by weight of melamine resin. ~25% by weight, phenolic resin
It is 45-60% by weight. The molecular sieve carbon of the present invention is a synthetic resin composite composed of 10 to 50% by weight of polyvinyl alcohol resin, 10 to 40% by weight of melamine resin, and 30 to 70% by weight of phenolic resin, obtained by the method described above. Carbonization in a temperature range of 500 to 700℃ in a non-oxidizing range, or subsequent carbonization in a temperature range of 500 to 700℃ in an oxidizing range, resulting in a weight loss of up to 15% by weight of the carbide. It can be obtained by activating within the range. Although the details of the mechanism of formation of molecular sieve carbon from a synthetic resin composite are not clear, thermal decomposition of the synthetic resin composite progresses from around 200℃ by increasing the temperature at a controlled rate. 300～
This becomes especially noticeable near 500°C, and during this temperature raising process, extremely fine micropores are generated on the surface of the carbide that is the thermal decomposition residue, and these micropores further increase by activation in the temperature range of 500 to 700°C. The pore volume and pore radius of micropores were analyzed using the nitrogen adsorption isotherm and Kelvin equation, which will be described later.The pore diameter was determined using the above analysis method.
The amount of micropores with a diameter of 10 Å or less is usually reduced to 0.01 to 0.01 in terms of pore volume by carbonization in the temperature range of 500 to 700°C.
The pore volume and pore diameter decrease with increasing carbonization temperature in a non-oxidizing atmosphere, and when the carbonization temperature exceeds 700°C ^, it is no longer practical as a molecular sieve carbon. become scarce. Therefore, the carbonization temperature in a non-oxidizing atmosphere for producing carbon molecular sieves is 500-700°C, preferably 530-670°C, more preferably 550-650°C. In addition, the pore diameter of micropores generated by carbonization in a non-oxidizing atmosphere also depends on the heating rate;
There is a tendency for the pore diameter to increase as the temperature increase rate increases. Therefore, in producing molecular sieve carbon, it is preferable that the temperature increase rate be slow. Normally, the temperature increase rate in the temperature range of 200°C or higher is preferably 120°C/hr or less, more preferably 90°C/hr.
The most preferred temperature is below 60°C/hr. The carbide obtained as described above can be used as it is as molecular sieve carbon, but the carbide may be further activated in an oxidizing atmosphere such as a steam atmosphere or a carbon dioxide atmosphere in a temperature range of 500 to 700°C. This makes it possible to significantly increase the number of micropores with a pore diameter of 10 Å or less, thereby significantly improving the molecular sieving ability. However, when the activation temperature exceeds 700℃, the pore diameter of the micropores increases, the maximum value of the pore size distribution shifts to the larger pore size, and the pore volume in the pore diameter region of 15 Å to 200 Å increases, making it difficult to select The molecular sieve effect disappears as the target adsorption properties are lost. Furthermore, if the activation temperature is less than 500°C, the progress of weight loss due to activation is extremely slow and is not practical. Therefore, the activation temperature range of carbide must be in the range of 500 to 700℃, preferably 530 to 670℃.
°C, most preferably 550-650 °C. Furthermore, even when activated in the temperature range of 500 to 700°C, the weight loss due to activation is 15% by weight of the weight of the carbide obtained by carbonization in a non-oxidizing atmosphere.
If the value exceeds 0.05, the pore diameter of the micropores increases and the molecular sieving effect disappears. Therefore, even in the case of activation in the temperature range of 500 to 700°C, the weight loss due to activation must be within 15% by weight of the carbide before activation, preferably within 12% by weight, most preferably 10% by weight or less.
Within % by weight. Now, the pore volume and pore size distribution of adsorbents having fine pores, such as activated carbon and silica gel, are usually determined from adsorption isotherms of nitrogen gas, ethane gas, butane gas, and the like. Most commonly, nitrogen gas is used as the adsorbent gas and helium gas is used as the carrier gas, and the adsorption is performed by cooling the adsorbent to the temperature of liquid nitrogen and determining the relationship between the amount of nitrogen gas adsorbed into the pores of the adsorbent and the nitrogen partial pressure. An isotherm is obtained. The Kelvin equation based on capillary condensation has been proposed as a method for determining pore volume and pore radius from adsorption isotherms, and analysis is generally performed based on this equation. Kelvin equation lnP/P ₀ = -2VγCOSθ/r _K RT... P, saturated vapor pressure P ₀ when adsorbed gas condenses into pores, saturated vapor pressure γ of adsorbed gas in normal state, surface tension V, liquid nitrogen 1 molecular volume R, gas constant T, absolute temperature r _K , pore Kelvin radius The pore Kelvin radius requires correction for adsorption other than capillary condensation, such as Higuchi's monomolecular layer adsorption amount. How to correct only
A correction method based on the Halsey formula is often used.
Strictly speaking, the applicable range of the Kelvin equation based on capillary condensation is said to be approximately 40 Å to 600 Å in pore diameter.
A strict pore radius measurement method that can replace the Kelvin equation has not yet been established, and analysis using the Kelvin equation is often used even in the region of pore diameters of 40 Å or less. In the analysis of pore diameter and pore size distribution in the present invention, the Kelvin equation is applied up to a pore diameter of 10 Å in combination with its commonly used correction method. (Effect of the invention) The molecular sieve effect in molecular sieve carbon is a region in which the pore diameter of the micropores is several angstroms, which is extremely close to the molecular diameter of the adsorbed molecules, and has selective adsorption properties for various substances with different molecular diameters. This is by showing that Therefore, the performance of molecular sieve carbon is determined by the pore size distribution of the micropores, and the pore diameter is usually 10 Å or less, preferably 3 to 5 Å.
Carbon having a sharp pore size distribution within a certain range is most preferred as the molecular sieve carbon. The molecular diameter of nitrogen molecules is 3.0×4.1Å, and the molecular diameter of oxygen molecules is 2.8×
It is 3.9 Å, and the difference in molecular diameter is extremely small.
Therefore, molecular sieve carbon for air separation is required to have an extremely sharp pore size distribution.
The molecular sieve carbon of the present invention meets these demands by finding the optimum composition of the synthetic resin composite and the optimum conditions for carbonization or activation. In addition, pores with a diameter of about 15 to 200 Å do not have a molecular sieving effect and simultaneously adsorb coexisting gases and different solutes in the solution. Therefore, the smaller the amount of pores in the range of pore diameters from 15 to 200 Å, the better the performance of the molecular sieve. Now, the commonly used specific surface area is 1000 to 1500.
m ² /g of activated carbon, the maximum value of the pore size distribution is in the region with a pore diameter of about 15 Å or more;
The pore volume in the 200 Å range is about 0.15-0.25 g/ ^cm3 , but the molecular sieve carbon of the present invention has a pore diameter of 10
The maximum value of the pore size distribution is in the range of 15 to 200 Å, and the pore volume in the pore diameter range of 15 to 200 Å is 0.1 cm ³ /g or less, and has an excellent molecular sieving effect. The smaller the pore volume in the range of pore diameters from 15 to 200 Å, the more preferable it is, preferably 0.07 cm ³ /g or less, most preferably 0.05 cm ³ /g or less. Further, the specific surface area of the molecular sieve carbon of the present invention is not particularly limited, but it is usually 100 to 600 m ² /g for carbonized products and 200 to 800 m 2 /g for activated products.
It is about m ² /g. Furthermore, the molecular sieve carbon of the present invention is a synthetic resin composite having continuous macropores in a network structure by using a known porous material manufacturing method during the production of a synthetic resin composite consisting of a polyvinyl alcohol resin, a melamine resin, and a phenolic resin. It can be made into a porous body. By carbonizing and activating this synthetic resin composite porous body under the conditions of the present invention, a molecular sieve carbon having continuous macropores in a network structure can be obtained. The molecular sieve carbon usually has an apparent density of 0.1 to 0.8 g/cm ³ , a porosity of 50 to 95%, and an average macropore diameter of 1 to 500 μm, preferably an apparent density of 0.20 to 0.7 g/cm ³ and a porosity of 60 to 90. %, the average macropore diameter is 5 to 400 μm, and most preferably the apparent density is 0.25 to 0.6 g/cm ³ , the porosity is 65 to 85%, and the average macropore diameter is 10 to 300 μm. The molecular sieve carbon obtained by the present invention has a sharp pore size distribution and an excellent molecular sieving effect, and is extremely effective in separating nitrogen and oxygen in the air. That is, by using the carbon molecular sieve of the present invention, it is possible to easily separate nitrogen and oxygen even under normal pressure in a relatively low temperature range of about 0°C to -100°C. In addition, nitrogen and oxygen in the air can be separated extremely efficiently using the pressure swing adsorption (PSA) method. This will be explained in detail below using examples. Example 1 500 g of polyvinyl alcohol with a degree of polymerization of 1700 and a degree of saponification of 99% was dispersed in water, and after dissolving by heating, 300 g of potato starch was added and gelatinized. After cooling this to room temperature,
700g of 37wt% formalin and 250g of 50wt% sulfuric acid
was added and mixed uniformly, and the liquid volume was adjusted with an appropriate amount of water to bring the total liquid volume to 10. Pour this mixture into a 250 x 250 mm square mold,
A crosslinking reaction was carried out in warm water at 60°C for 24 hours, followed by washing with water to obtain a polyvinyl formal (PVF) porous body having a network structure. The PVF porous body is 40×40×
After forming into a 250mm square cylinder, solid content concentration is 10-50% by weight.
Melamine resin (Sumitomo Chemical Co., Ltd. product, Sumitex Resin M-3, curing agent Sumitex Resin)
ACX), centrifuged, and then cured at 90℃ for 24 hours, and further water-soluble resol resin with a solid content concentration of 20 to 50% by weight (Showa Kobunshi Co., Ltd. product, BRL-2854)
After being immersed in water, it was cured at 90°C for 24 hours to obtain three types of synthetic resin composite porous bodies having the compositions shown in Table 1. The synthetic resin composite porous body was placed in an electric furnace, heated at a rate of 30°C/hr in a nitrogen atmosphere, and carbonized at 670°C. Table 1 shows the characteristic values of the obtained carbonized product. The pore size distribution and pore volume of each sample were determined from the nitrogen gas adsorption isotherm. The smaller the pore diameter
Although the accuracy of the Kelvin equation decreases, by applying the Kelvin equation up to a pore diameter of 10 Å, it was determined whether the maximum value of the pore size distribution was 10 Å or less. Next, air separation experiments at -50°C were conducted using each sample. In the air adsorption separation experiment, a sample was set in a stainless steel adsorption tower of a flow-through adsorption device with a filling length of 30 mmφ x 500 mm L, and 90% He and dry air were used.
A mixed gas consisting of 10% was flowed at a flow rate of 20 Nml/min, and the change in concentration of the adsorption tower outlet gas over time was measured.
Ratio of outlet gas concentration (C) to inlet gas concentration (Co) C/
A breakthrough curve was created by determining Co. Temperature control of the adsorption tower is carried out by using a combination of liquid nitrogen and a band heater, and a gas chromatograph (TCD detector,
Column; Molecular Sieve 5A) was used.
Figure 1 shows the breakthrough curve measurement results. As can be seen from FIG. 1, separation of nitrogen and oxygen was observed in sample No. 2 manufactured from the synthetic resin composite porous body having the composition range of the present invention, but in sample No. 1 and No. 3, separation of nitrogen and oxygen was observed.
It was found that both nitrogen and oxygen were adsorbed to approximately the same extent, making it impossible to separate the two.

[Table] Example 2 Same as Example 1, polymerization degree 1700, saponification degree
After dissolving 4 kg of 88% polyvinyl alcohol in hot water, 3 kg of wheat flour starch was added to gelatinize. After adding 20 kg of water-soluble resol resin (manufactured by Showa Kobunshi Co., Ltd., BRL-2854) with a solid content concentration of 60% to this solution and stirring thoroughly, further 37% by weight of formalin 7
Kg and 3 Kg of 30% by weight oxalic acid were added and mixed uniformly, and the liquid volume was adjusted with an appropriate amount of water to make the total liquid volume 100. This mixed solution was poured into a 620 x 620 mm square mold and reacted in the same manner as in Example 1 to obtain a PVA/phenol synthetic resin composite porous body. After molding the synthetic resin composite porous body into a 100 x 100 x 500 mm square column,
Melamine resin was applied in the same manner as in Example 1, with 20% by weight of polyvinyl alcohol resin and 20% by weight of melamine resin.
A synthetic resin composite porous body consisting of 60% by weight of phenolic resin was obtained. The synthetic resin composite porous body was placed in an electric furnace, heated to a predetermined temperature at a heating rate of 50° C./hr under a nitrogen atmosphere, and activated for a predetermined time under a steam atmosphere. Table 2 shows the physical property values of the obtained activated product.

[Table] Pressure spink adsorption (PSA) using the above two samples
An attempt was made to separate nitrogen and oxygen from the air using this method. The above sample was molded and inserted into a 30 mmφ x 1200 mmL adsorption tower of a two-column PSA device, and an adsorption separation experiment was conducted under the following operating conditions. That is, the adsorption pressure 4
Kg/cm ² , air flow rate 200Nml/min, adsorption time 1
The two towers were switched alternately with a desorption time of 1 minute and a vacuum pump for forced exhaust during desorption. As a result of analyzing the concentration of the gas at the outlet of the adsorption tower, sample no.
In Material No. 1, the nitrogen concentration was 99.2%, but in Material No. 2, the nitrogen concentration was 79.1%, which was the same as the inlet air composition.

[Brief explanation of drawings]

Figure 1 shows a breakthrough curve in an air adsorption separation test using the synthetic resin composite according to the present invention, where the horizontal axis is time (minutes) and the vertical axis is outlet gas concentration (C) and inlet gas concentration (Co). represents the ratio C/Co.

Claims (1)

[Scope of Claims] 1. A synthetic resin composite consisting of 10 to 50% by weight of polyvinyl alcohol resin, 10 to 40% by weight of melamine resin, and 30 to 70% by weight of phenol resin is heated to 500 to 500% by weight in a non-acid atmosphere. Carbonized in a temperature range of 700°C, or activated after carbonization under an acidic atmosphere in a temperature range of 500 to 700°C to the extent that the weight loss of the carbide is within 15%, with a pore diameter of 10 Å or less. A molecular sieve carbon for air separation, which has a maximum value of pore size distribution and a pore volume of 0.1 cm ³ /g or less in a pore diameter range of 15 to 200 Å. 2 Molecular sieve carbon has an apparent density of 0.1 to 0.8 g/cm ³ ,
The molecular sieve carbon for air separation according to claim 1, which has a porosity of 50 to 90% and a continuous macropore having a network structure of 1 to 500 μm in diameter.