Background
The carbon aerogel material has excellent performance and has good application potential in novel batteries, environmental protection, biological medical treatment and other national strategic emerging industries. However, the carbon aerogel product has high cost, is difficult to accept in the market and is difficult to industrialize due to expensive raw materials, complex preparation process, long production period, large scale production difficulty and the like.
In recent years, domestic research on carbon aerogel production processes has increased, and mass production has been achieved. In the existing mature production process, resorcinol and formaldehyde are dispersed in an oil phase according to a certain proportion and then polymerized at a certain temperature.
The preparation method of the carbon aerogel disclosed in the Chinese patent application 201611110955.8 comprises the following steps: step one, resorcinol and formaldehyde are used as raw materials, organic amine is used as a catalyst, water is used as a solvent, the mixture is uniformly stirred, and a gel reaction is carried out to obtain an intermediate product; step two, carrying out aging treatment on the obtained intermediate product to obtain organic wet gel; step three, carrying out vacuum pumping and drying treatment on the organic wet gel to obtain organic aerogel; and step four, placing the organic aerogel in a carbonization furnace, heating and carbonizing under the protection of nitrogen, and naturally cooling to room temperature to obtain the carbon aerogel. However, as the price of chemical raw materials rises, the price of resorcinol rises dramatically (10-12 ten thousand yuan/ton in 2020), so that the cost price of the carbon aerogel prepared by resorcinol is higher than that of competitive products, namely super activated carbon, and the market competitiveness is lost.
Phenol is cheap (1 ten thousand yuan/ton in 2020), and can be used as a substitute of resorcinol and polymerized with formaldehyde to obtain a precursor. However, since phenol contains only one hydroxyl group, the ortho-para reaction is far less active than resorcinol, resulting in a slow polymerization rate. In addition, the phenol preparation precursor has the problems of shrinkage, internal structure collapse and low specific surface area after carbonization, and the quality of subsequent products is influenced. In addition, phenol can be dissolved in white oil, so that the problems of insufficient reaction, low yield, difficult separation from the white oil and the like are caused, and the method is not favorable for environmental protection. The above problems restrict the preparation of carbon aerogel precursors from inexpensive phenol instead of expensive resorcinol.
Disclosure of Invention
The invention aims to solve the problems in the prior art and provide a low-cost preparation method of a carbon aerogel precursor, which has the advantages of low raw material price, low production cost, high product performance, safety and environmental protection.
In order to solve the problems, the technical scheme of the invention is as follows: the mixed solution of phenol and formaldehyde is refluxed at high temperature to a critical state to be cured, at the moment, the phenol and the formaldehyde are polymerized into a chain, the reaction rate reaches the fastest speed, and the reaction is stopped by cooling with ice water. The critical reaction solution was cut with an emulsion pump, and the droplets were separated with a white oil containing a surfactant to prevent re-adhesion. And (3) adding the cut granular critical reaction liquid into high-temperature white oil, restarting the reaction, and instantly solidifying the reaction liquid.
The invention relates to a low-cost preparation method of a carbon aerogel precursor, which specifically comprises the following steps:
(1) adding phenol into a formaldehyde aqueous solution, adding a catalyst, and stirring for dissolving to obtain a mixture aqueous solution; the catalyst is one of potassium hydroxide, sodium hydroxide and calcium hydroxide, the molar ratio of the phenol to the formaldehyde is generally controlled within the range of 1 (1.3-3.3), and the range of 1 (1.5-3) is preferred; the stirring and dissolving temperature is controlled to be within the range of 30-60 ℃,
the catalyst can also be organic base triethylamine.
(2) Refluxing the mixture aqueous solution obtained in the step (1) at the temperature of 55-85 ℃ to a critical state to be solidified, then quickly cooling the mixture aqueous solution in ice water, and stopping the reaction process to obtain a precursor aqueous solution with a certain crosslinking degree;
the reflux temperature is preferably controlled within the range of 60-80 ℃, and the reflux time is controlled within 1-8 hours.
(3) Mixing the surfactant and the white oil, stirring and mixing uniformly at room temperature to prepare a white oil mixed solution; the surfactant is span 80 or other surfactants with similar properties.
(4) And naturally cooling 1.8-10.0% of the total amount of the white oil mixed solution for later use, and heating the rest white oil mixed solution to 75-105 ℃.
(5) And (3) respectively feeding the precursor aqueous solution obtained in the step (3) and the cold white oil mixed solution naturally cooled for standby in the step (4) into an emulsification pump to be fully mixed into suspension, wherein the flow ratio of the precursor aqueous solution to the cold white oil mixed solution is generally controlled within the range of (8-50): 1, and preferably (9-15): 1.
(6) The suspension liquid is directly fed into the heated white oil mixed liquid by an emulsification pump and fully reacts with the white oil mixed liquid to obtain precursor white oil slurry; the reaction temperature is controlled within the range of 80-95 ℃, and the reaction time is 10-30 hours.
(7) Performing solid-liquid separation and washing on the precursor white oil slurry to obtain a carbon aerogel precursor; the washing used is any one solvent of methanol, ethanol and dichloromethane, or a mixed solvent of two or three solvents.
Compared with the prior art, the low-cost preparation method of the carbon aerogel precursor has the following beneficial effects:
(1) and the expensive resorcinol is replaced by the cheap phenol, so that the cost is saved.
(2) The phenol and the formaldehyde are pre-reacted for a period of time to have certain polymerization, so that the reaction activity of the phenol is improved, the subsequent reaction can be quickly carried out, the shrinkage and the collapse of a precursor are reduced, the specific surface area of a subsequent carbonized sample is improved, and the product quality is improved.
(3) The pre-reaction ensures that phenol formaldehyde is polymerized, the molecular weight is increased, the phenol formaldehyde is not easy to dissolve in white oil, the reaction is more sufficient, the reaction yield is improved, and the cost is saved.
(4) Almost no phenol enters the white oil after the pre-reaction, and the white oil is easier to recover and more environment-friendly.
Detailed Description
For the purpose of describing the present invention, the low cost preparation of a carbon aerogel precursor of the present invention is described in further detail below with reference to examples. The invention is not limited to the examples.
Example 1:
(1) adding 94.11g of phenol into 121.74g of 37% formaldehyde aqueous solution with the mass concentration of 1:1.5, adding 0.9g of sodium hydroxide, stirring and dissolving, and controlling the stirring and dissolving temperature to be within the range of 30-60 ℃ to obtain a mixture aqueous solution;
(2) refluxing the mixture aqueous solution at 80 ℃ for 7 hours and 15 minutes to a critical state to be cured, then quickly cooling the mixture aqueous solution in ice water, and stopping the reaction process to obtain a precursor aqueous solution with a certain crosslinking degree;
(3) adding 5ml of surfactant span 80 into 500ml of white oil, and uniformly stirring at room temperature to prepare a white oil mixed solution;
(4) naturally cooling 30ml of white oil mixed solution for later use, and heating the rest white oil mixed solution to 95 ℃;
(5) starting an emulsification pump, adjusting the rotating speed to 1000r/min, and controlling the flow ratio of the precursor aqueous solution to the cold white oil mixed solution for standby natural cooling to be 10: 1, fully mixing the two into suspension in an emulsification pump;
(6) the suspension liquid is directly fed into the heated white oil mixed liquid by an emulsification pump and fully reacts with the white oil mixed liquid, and the mixture is continuously kept at 95 ℃ for fully reacting for 10 hours to obtain precursor white oil slurry;
(7) and finally, carrying out solid-liquid separation and washing on the slurry to obtain the carbon aerogel precursor.
Example 2:
(1) adding 94.11g of phenol into 121.74g of 37% formaldehyde aqueous solution with the mass concentration of 1:1.5, adding 0.9g of sodium hydroxide, stirring and dissolving, and controlling the stirring and dissolving temperature to be within the range of 30-60 ℃ to obtain a mixture aqueous solution;
(2) refluxing the mixture aqueous solution at 60 ℃ for 12 hours and 20 minutes to a critical state to be cured, then quickly cooling the mixture in ice water, and stopping the reaction process to obtain a precursor aqueous solution with a certain crosslinking degree;
(3) adding 5ml of surfactant span 80 into 300ml of white oil, and uniformly stirring at room temperature to prepare a white oil mixed solution;
(4) taking 10ml of white oil mixed solution, naturally cooling for later use, and heating the rest white oil mixed solution to 95 ℃;
(5) starting an emulsification pump, adjusting the rotating speed to 1000r/min, and controlling the flow ratio of the precursor aqueous solution to the cold white oil mixed solution for standby natural cooling to be 10: 1, fully mixing the two into suspension in an emulsification pump;
(6) the suspension liquid is directly fed into the heated white oil mixed liquid by an emulsification pump and fully reacts with the white oil mixed liquid, and the white oil mixed liquid is continuously kept at 95 ℃ for full reaction for 12 hours to obtain precursor white oil slurry;
(7) and finally, carrying out solid-liquid separation and washing on the slurry to obtain the carbon aerogel precursor.
Example 3:
(1) adding 47.06g of phenol into 60.87g of 37% formaldehyde aqueous solution with the mass concentration of 1:1.5, adding 0.5g of sodium hydroxide, stirring and dissolving, and controlling the stirring and dissolving temperature to be within the range of 30-60 ℃ to obtain a mixture aqueous solution;
(2) refluxing the mixture aqueous solution for 8 hours and 55 minutes at 70 ℃ to a critical state to be cured, then quickly cooling the mixture aqueous solution in ice water, and stopping the reaction process to obtain a precursor aqueous solution with a certain crosslinking degree;
(3) adding 5ml of surfactant span 80 into 500ml of white oil, and uniformly stirring at room temperature to prepare a white oil mixed solution;
(4) taking 10ml of white oil mixed solution, naturally cooling for later use, and heating the rest white oil mixed solution to 90 ℃;
(5) starting an emulsification pump, adjusting the rotating speed to 1000r/min, and controlling the flow ratio of the precursor aqueous solution to the cold white oil mixed solution for standby natural cooling to be 10: 1, fully mixing the two into suspension in an emulsification pump;
(6) the suspension liquid is directly fed into the heated white oil mixed liquid by an emulsification pump and fully reacts with the white oil mixed liquid, and the mixture is continuously kept at 90 ℃ for fully reacting for 15 hours to obtain precursor white oil slurry;
(7) and finally, carrying out solid-liquid separation and washing on the slurry to obtain the carbon aerogel precursor.
Example 4:
(1) adding 47.06g of phenol into 121.74g of 37% formaldehyde aqueous solution with the mass concentration of 1:3, adding 0.5g of sodium hydroxide, stirring and dissolving, and controlling the stirring and dissolving temperature to be within the range of 30-60 ℃ to obtain a mixture aqueous solution;
(2) refluxing the mixture aqueous solution for 8 hours and 30 minutes at 80 ℃ to a critical state to be cured, then quickly cooling the mixture aqueous solution in ice water, and stopping the reaction process to obtain a precursor aqueous solution with a certain crosslinking degree;
(3) adding 3ml of surfactant span 80 into 300ml of white oil, and uniformly stirring at room temperature to prepare a white oil mixed solution;
(4) naturally cooling 30ml of white oil mixed solution for later use, and heating the rest white oil mixed solution to 80 ℃;
(5) starting an emulsification pump, adjusting the rotating speed to 1000r/min, and controlling the flow ratio of the precursor aqueous solution to the cold white oil mixed solution for standby natural cooling to be 10: 1, fully mixing the two into suspension in an emulsification pump;
(6) the suspension liquid is directly fed into the heated white oil mixed liquid by an emulsification pump and fully reacts with the white oil mixed liquid, and the mixture is continuously kept at 80 ℃ for fully reacting for 24 hours to obtain precursor white oil slurry;
(7) and finally, carrying out solid-liquid separation and washing on the slurry to obtain the carbon aerogel precursor.
Example 5:
(1) adding 47.06g of phenol into 121.74g of 37% formaldehyde aqueous solution with the mass concentration of 1:3, adding 1g of sodium hydroxide, stirring and dissolving, and controlling the stirring and dissolving temperature to be within the range of 30-60 ℃ to obtain a mixture aqueous solution;
(2) refluxing the mixture aqueous solution at 90 ℃ for 6 hours and 25 minutes to a critical state to be cured, then quickly cooling the mixture aqueous solution in ice water, and stopping the reaction process to obtain a precursor aqueous solution with a certain crosslinking degree;
(3) adding 6ml of surfactant span 80 into 600ml of white oil, and uniformly stirring at room temperature to prepare a white oil mixed solution;
(4) naturally cooling 30ml of white oil mixed solution for later use, and heating the rest white oil mixed solution to 90 ℃;
(5) starting an emulsification pump, adjusting the rotating speed to 1000r/min, and controlling the flow ratio of the precursor aqueous solution to the cold white oil mixed solution for standby natural cooling to be 10: 1, fully mixing the two into suspension in an emulsification pump;
(6) the suspension liquid is directly fed into the heated white oil mixed liquid by an emulsification pump and fully reacts with the white oil mixed liquid, and the mixture is continuously kept at 90 ℃ for full reaction for 12 hours to obtain precursor white oil slurry;
(7) and finally, carrying out solid-liquid separation and washing on the slurry to obtain the carbon aerogel precursor.
Example 6:
(1) adding 47.06g of phenol into 81.16g of 37% formaldehyde aqueous solution with the mass concentration of 1:2, adding 0.5g of sodium hydroxide, stirring and dissolving, and controlling the stirring and dissolving temperature to be within the range of 30-60 ℃ to obtain a mixture aqueous solution;
(2) refluxing the mixture aqueous solution at 60 ℃ for 8 hours and 30 minutes to a critical state to be cured, then quickly cooling the mixture aqueous solution in ice water, and stopping the reaction process to obtain a precursor aqueous solution with a certain crosslinking degree;
(3) adding 5ml of surfactant span 80 into 500ml of white oil, and uniformly stirring at room temperature to prepare a white oil mixed solution;
(4) taking 50ml of white oil mixed solution, naturally cooling for later use, and heating the rest white oil mixed solution to 80 ℃;
(5) starting an emulsification pump, adjusting the rotating speed to 1000r/min, and controlling the flow ratio of the precursor aqueous solution to the cold white oil mixed solution for standby natural cooling to be 10: 1, fully mixing the two into suspension in an emulsification pump;
(6) the suspension liquid is directly fed into the heated white oil mixed liquid by an emulsification pump and fully reacts with the white oil mixed liquid, and the mixture is continuously kept at 80 ℃ for fully reacting for 15 hours to obtain precursor white oil slurry;
(7) and finally, carrying out solid-liquid separation and washing on the slurry to obtain the carbon aerogel precursor.
The detection shows that the tap density and the specific surface area of the dried and carbonized precursor prepared in the examples 1 to 6 are as follows:
TABLE 1 comparison of the examples with phenol without reflux, resorcinol yield, carbon tap density, and specific surface area
As can be seen from the above table, the carbon aerogel precursor prepared by the method disclosed by the invention has the advantages of high tap density and greatly improved specific surface area after being dried and carbonized. Can replace resorcinol to prepare a precursor.