CN1328425C - Active carbon fiber in hollow morphological structure, and preparation method - Google Patents

Abstract

The invention relates to an activated carbon fiber with a hollow shape structure and a preparation method, wherein the pore size distribution of the mesopores and macropores is 2-90 nm, and the pore size distribution of the mesopores is mainly 2-5 nm. The medical polyacrylonitrile hollow fiber is used as the raw material, soaked in the phosphide-containing solution for pretreatment, and then pre-oxidized, carbonized and activated. The polyacrylonitrile-based activated carbon fiber produced by this method has a high specific surface area, and the mesopore content and the specific surface area of the mesopore in the carbon fiber are high, and have high adsorption capacity for small molecular substances and medium molecular substances. Rate. The method of the invention has simple process, low investment, high adsorption performance, wide application range and good purification effect, and can be applied to fields requiring adsorption purification such as air purification, water purification, organic matter adsorption purification, blood purification and the like.

Description

Activated carbon fiber with hollow morphology and preparation method

technical field

The invention relates to an activated carbon fiber with a hollow shape structure and a preparation method.

Background technique

Activated carbon fiber (ACF) is a carbon adsorption material developed on the basis of carbon fiber. It is made of organic fiber as raw material and activated by high-temperature carbonization. Compared with traditional activated carbon, ACF has the following characteristics: large specific surface area; concentrated pore size distribution; fast adsorption and desorption rate, and can have various processing forms such as felt, cloth, and paper; The adsorption of trace substances is particularly effective, that is, the adsorption efficiency is high at low concentrations. Activated hollow carbon fiber (ACHF) started late and is a new type of adsorption material. Compared with ACF, it is hollow, porous, self-supporting, and the pore size can be controlled by fibrils, carbonization, and activation process conditions. Features, small volume can have a large specific surface area, can be used for adsorption, separation and dialysis of liquid or gas mixture, broaden its application in the fields of catalysis, medicine, electronics and liquid phase adsorption.

In 1999, Chen Lu (patent application number: 97120296.6) reported the method of using solid polyacrylonitrile fiber as raw material to produce activated carbon fiber, but the pre-oxygenated silk was soaked with inorganic salt _NaCO3 , but this method used metal ion-containing Pre-oxygenated silk inevitably contains more metal ions in the final ACF, which limits its application in the fields of medicine and catalysis. In 1997, Zhang Yinzhi (patent application number: 95119030.X) and others reported a method for preparing mesoporous activated carbon fibers using a mixed raw material of resin and carbon material, and the mesoporosity in the prepared mesoporous activated carbon fibers was 50-70% . In 1994, Liu Zhiren (patent application number: 94108414.0) reported the method of using wood-based viscose fiber non-woven fabric or wood-based viscose fiber paper as raw material to prepare highly absorbent activated carbon fibers. In 1997 Zeng Hanmin reported (patent application number: 97108889.6) the method that adopts natural fiber to prepare activated carbon fiber as raw material (as sisal fiber). The various fibers mentioned above are all solid fibers, and the fibers with a solid structure contain fewer pores. When the pre-oxidation, carbonization and activation processes are carried out in the later stage, the permeation of gas is affected, and it is easy to cause "different" structures and properties. skin-core" structure.

Contents of the invention

The object of the present invention is to provide an activated carbon fiber with a hollow morphology.

The object of the present invention is also to provide a method for preparing activated carbon fibers with a hollow morphology.

In the activated carbon fiber with a hollow morphology structure of the present invention, the pore size distribution of the mesopores and macropores is 2-90 nm. In addition to micropores, the pore diameter is composed of mesopores with a diameter of 2-50nm and macropores with a diameter of >50nm-90nm. Among them, the pore size distribution of mesopores is mainly concentrated in the range of 2-5nm, accounting for more than 95% of all mesopores.

The preparation method of the activated carbon fiber with a hollow shape structure of the present invention is obtained by pretreating the polyacrylonitrile hollow fiber with an aqueous solution of phosphide, followed by preoxidation, carbonization and activation.

The specific preparation method is to wash and soak the raw material fibers in distilled water for 1 to 3 days, and change the water every few hours to remove glycerin and other additives on the surface of the fibers, then put them in a centrifuge to dry them, and dry them in the air. Naturally dry in the middle, then dry to constant weight in a desiccator filled with P ₂ O ₅ and weigh; then soak the hollow fiber in a 2-10% by weight (wt) phosphide aqueous solution for 10-120 minutes Carry out pretreatment, take it out and dry it naturally in the air, then place it in a desiccator filled with P ₂ O ₅ to constant weight and weigh it; then put it in an oven at 200-300°C and heat it for 0.5-6 hours The hollow fiber is pre-oxidized; then carbonized, the pre-treated and pre-oxidized hollow fiber is placed in the quartz tube in the tube furnace, the air in the quartz tube is pumped out with a vacuum pump, nitrogen gas is introduced, and the nitrogen gas is protected. Heating at a heating rate of 10°C/min, the carbonization temperature is 500-1000°C, and the carbonization time is 10-110 minutes; after the carbonization is completed, the activation treatment is carried out, and the carbonized hollow fiber continues to be heated in the furnace at 600-1000°C Under the condition of CO ₂ gas for activation, the activation time is 20-100 minutes; when the activation is finished, turn off the CO ₂ gas, use a vacuum pump to remove the CO ₂ gas in the quartz tube, and then inject nitrogen gas, when the nitrogen pressure in the quartz tube is 1 At 1 atmospheric pressure, plug both ends of the quartz tube, turn off the nitrogen gas, and when the temperature in the quartz tube drops to room temperature, take out the hollow fiber, which is the finished product—activated carbon fiber with a hollow shape.

The phosphide described in the above method can be ammonium phosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, phosphoric acid or metaphosphoric acid and the like.

The hollow fiber in the present invention has a hollow structure and adopts the forming method of dry jet wet spinning, so there are more microporous structures inside the obtained fiber, and its cross section is a double-row finger-like hole structure, and the surface of the fiber has Rich holes. This structural characteristic determines that the ACHF prepared in the later stage also has a rich pore structure, so that the BET specific surface area and adsorption rate have been greatly improved, especially for the adsorption rate of medium relative molecular weight substances, such as VB ₁₂ , etc. improve.

The activated carbon fiber with a hollow shape structure of the present invention has more advantages than the solid activated carbon fiber. It is a kind of high adsorption performance for small molecular substances and medium molecular substances, wide application range, good formability and good purification effect. Activated carbon fibers with highly absorbent hollow morphology. Moreover, it is a preparation method with simple process.

Description of drawings

Fig. 1 is a kind of mesopore and macropore pore size distribution of activated carbon fiber with hollow morphology structure;

Fig. 2 is the adsorption isotherm of the activated carbon fiber with hollow morphology structure;

Figure 3 is a diagram of the pore size distribution of mesopores and macropores of different samples of activated carbon fibers with hollow morphology.

In the accompanying drawings, the abscissa of Fig. 1 is the relative pressure, and the ordinate is the adsorption pore volume; the abscissa of Fig. 2 is the pore diameter, and the ordinate is the incremental pore volume; the abscissa of Fig. 3 is the pore diameter, and the ordinate is the incremental pore volume.

Detailed ways

The following examples will help to understand the present invention, but do not limit the content of the present invention.

Example 1

Take 1.5 g of polyacrylonitrile hollow fiber raw material, put it into (NH ₄ ) ₂ HPO ₄ aqueous solution with a concentration of 4% by weight (wt) and soak it for 30 minutes at room temperature, and put it into an oven after being dried naturally in the air. In the air, heat at 230°C for 2 hours, and the pre-oxidation is completed; then put the pre-oxidized fiber into the quartz tube in the tube furnace, heat to 900°C under the protection of nitrogen, and heat at 900°C for 70 minutes, and the carbonization is completed; Then lower the furnace temperature naturally to 800°C, introduce CO ₂ gas, and heat at 800°C for 40 minutes. After the activation is completed, turn off the CO ₂ gas, use a vacuum pump to remove the CO ₂ gas in the quartz tube, and then inject nitrogen gas. When the nitrogen pressure in the tube is 1 atmosphere, seal both ends of the quartz tube and turn off the nitrogen until the temperature in the quartz tube drops to room temperature, then take out the hollow fiber, which is the finished product—activated carbon fiber with a hollow shape.

Example 2

The adsorption rate of above-mentioned activated carbon fiber to small molecular substance (creatinine) and medium molecular substance (VB ₁₂ ) is shown in the following table: Static adsorption in aqueous solution of creatinine and VB ₁₂ at 37°C for 24 hours.

name creatinine VB ₁₂ Adsorption rate(%) 99 84

Example 3

The BET specific surface area and mesopore specific surface area of the above activated carbon fiber are respectively

BET specific surface area (m ² ·g ^-1 ) Mesopore specific surface area (m ² ·g ^-1 ) sample 1422 1234

Example 4

The adsorption isotherms of the above-mentioned activated carbon fibers are shown in Fig. 1. The pore size distribution of mesopores and macropores is shown in Fig. 2.

The test of the above data is to use the automatic adsorption instrument Tristar 3000 of the American Mike Company to adopt the multi-point method, and use nitrogen as the adsorption proton to carry out the adsorption at the liquid nitrogen temperature (77K). The adsorption isotherm obtained from the measurement is calculated by the BET method. (B.C.Lippens et al., J.Cat., 4,319,1985) calculates mesopore specific surface area, calculates mesopore by BJH method (E.P.Barrett et al., J.Amer.Chem.Soc., 73,373,1951) and macropore size distribution.

Example 5

Take 1.5g of polyacrylonitrile hollow fiber raw material and put it into a 4wt% (NH ₄ ) ₂ HP0 ₄ aqueous solution at room temperature and soak for 30 minutes. After drying naturally in the air, put it in an oven. 230°C, heated for 2 hours, the pre-oxidation was completed; then put the pre-oxidized fiber into the quartz tube in the tube furnace, heated to 900°C under the protection of nitrogen, and heated at 900°C for 30 minutes, the carbonization was completed; then the furnace temperature Naturally lower to 800°C, introduce _CO2 gas, heat at 800°C for 40 minutes, after the activation is completed, turn off the _CO2 gas, use a vacuum pump to remove the _CO2 gas in the quartz tube, and then inject nitrogen gas, when the nitrogen pressure in the quartz tube When the pressure is 1 atmosphere, seal both ends of the quartz tube, turn off the nitrogen gas, and when the temperature in the quartz tube drops to room temperature, take out the hollow fiber, which is the finished product—activated carbon fiber with a hollow shape, which is sample A.

Example 6

1.5 g of the raw material of Example 5 was soaked in 4wt% (NH ₄ )H ₂ PO ₄ aqueous solution at room temperature for 30 minutes, and allowed to dry naturally in the air. Preoxidation, carbonization, and activation methods were the same as in Example 5 to obtain sample B.

Embodiment 7:

1.5 g of the raw material of Example 5 was soaked in a 4 wt % (NH ₄ ) ₃ PO ₄ aqueous solution at room temperature for 30 minutes, and allowed to dry naturally in the air. Preoxidation, carbonization, and activation methods were the same as in Example 5 to obtain sample C.

Example 8

1.5 g of the raw material of Example 5 was soaked in a 4 wt % H ₃ PO ₄ aqueous solution at room temperature for 30 minutes, and allowed to dry naturally in the air. Preoxidation, carbonization, and activation methods were the same as in Example 5 to obtain sample D.

Example 9

1.5 g of the raw material of Example 5 was put into a 4 wt % HPO _aqueous solution at room temperature and soaked for 30 minutes, and then dried naturally in the air. Preoxidation, carbonization, and activation methods were the same as in Example 5 to obtain sample E.

Figure 3 is the pore size distribution diagram of the mesopores and macropores of A, B, C, D, E samples.

Listed in the table below is the yield, shrinkage rate, BET specific surface area, mesopore specific surface area, adsorption rate of creatinine and VB ₁₂ of samples A, B, C, D, and E

The test of the above data is to use the automatic adsorption instrument Tristar 3000 of the American Mike Company to adopt the multi-point method, and use nitrogen as the adsorption proton to carry out the adsorption at the liquid nitrogen temperature (77K). The adsorption isotherm obtained from the measurement is calculated by the BET method. (B.C.Lippens et al., J.Cat., 4,319,1985) calculates mesopore specific surface area, calculates mesopore by BJH method (E.P.Barrett et al., J.Amer.Chem.Soc., 73,373,1951) and macropore size distribution.

sample A B C D E Yield/% 39.6 40.3 40 45.2 42.5 Shrinkage/% 52.0 49.3 49.3 49.3 49.3 BET specific surface area/m ² ·g ^-1 766 659 705 451 428 Mesopore specific surface area/m ² ·g ^-1 174 104 93 71 75 Adsorption rate to creatinine/% 93.8 97.3 89.5 89.5 97.6 Adsorption rate to VB ₁₂ /% 97.7 93.4 94.3 94.7 97.2

Claims (5)

1. An activated carbon fiber with a hollow morphological structure, characterized in that it is mainly an activated carbon fiber with a hollow morphological structure of 2 to 5 nm in pore size distribution. 2. a kind of preparation method with the activated carbon fiber of hollow form structure as claimed in claim 1, it is characterized in that the phosphide aqueous solution of 2-10% weight with the medical grade polyacrylonitrile hollow fiber that cleans and dries Soak for 10-120 minutes to pre-treat and dry; then keep at 200-300°C for 0.5-6 hours to pre-oxidize the hollow fiber; carbonize the pre-treated and pre-oxidized hollow fiber under nitrogen protection to Heating at a heating rate of 10°C/min, and carbonization for 10-110 minutes at a carbonization temperature of 500-1000°C; the carbonized hollow fiber continues to be activated with CO ₂ gas at 600-1000°C for 20-100 minutes. 3. The method according to claim 2, characterized in that said phosphide is ammonium phosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, phosphoric acid or metaphosphoric acid. 4. The method according to claim 2, characterized in that the activated carbon fibers in the hollow form after the activation treatment make the reactor down to room temperature and normal pressure under nitrogen protection. 5. The method according to claim 2, characterized in that the cleaned polyacrylonitrile hollow fiber refers to the polyacrylonitrile hollow fiber soaked in distilled water for 1 to 3 days, changing the water continuously, and then dried.

Images