A method for the preparation of activated carbon for polar solvent recovery

Abstract

The application provides a preparation method of activated carbon for polar solvent recovery, comprising the following steps: 1) crushing and drying biomass to obtain biomass powder; 2) taking an activating agent, a surfactant and alcohol to configure a mixed solution, uniformly mixing the biomass powder with the mixed solution, then kneading with a vacuum kneader, and then performing extrusion granulation, hardening, first-stage activation, second-stage activation, cooling, washing and drying to obtain the activated carbon for polar solvent recovery; the activating agent is compounded by a phosphorus aphid derivative and a phosphoric acid solution with a mass ratio of 5-10:100. The application takes biomass as a raw material, takes a phosphorus aphid derivative and phosphoric acid as activating agents, and performs two-stage activation, so that the prepared activated carbon has a large specific surface area, rich pore structure and appropriate surface chemical structure, and exhibits excellent adsorption performance on polar organic solvents such as methanol and ethanol.

Description

Technical Field

[0001] The invention belongs to the technical field of activated carbon, and particularly relates to a method for preparing activated carbon for recovering polar solvents. Background Art

[0002] The recycling and utilization of organic solvents not only meets the social need for environmental protection, but also meets the urgent needs of solvent users to reduce production costs and improve market competitiveness.

[0003] Adsorption is a representative recovery technology for separating and concentrating organic solvents. Common methods use the adsorption properties of adsorption materials such as activated carbon, activated carbon fiber, zeolite, molecular sieve, porous clay ore, activated alumina, silica gel and polymer adsorption resin to first adsorb and concentrate the organic solvent onto the adsorption material, and then use temperature, pressure or other methods to desorb the concentrated organic solvent from the adsorption material and then recycle it. The technology has the advantages of a wide range of applications and relatively stable effects.

[0004] Activated carbon is a commonly used hydrophobic adsorbent. Compared with other adsorbent materials, it has the advantages of strong adsorption capacity, good selectivity, strong regeneration and low cost. It has been widely used in the fields of air purification and industrial waste gas treatment. Common activated carbons include charcoal, coal, coconut shell charcoal, etc. For example, patent CN103588200B discloses a method for producing wood coal-based shaped activated carbon, which includes: (1) mixing sawdust and coal powder in proportion, soaking them in phosphoric acid solution, taking them out, placing them in an oil bath, and plasticizing them until the color of the mixture changes from brown to black and becomes relatively sticky, then ending the plasticizing to obtain a plasticized product; (2) quickly transferring the obtained plasticized product to a mold, molding it on a hydraulic press, and placing the pressed carbonaceous precursor molded product in a drying oven for slow constant temperature drying and hardening; (3) carbonizing and activating the prepared shaped carbonaceous precursor in an activation furnace to obtain wood coal-based shaped activated carbon. Patent CN1290606C discloses wood-based automotive activated carbon and its preparation method. The method of the present invention is: mixing wood and a catalyst, and then subjecting the mixture to shaping (granulation), shaping (carbonization), activation, and drying steps to prepare high-performance wood-based shaped activated carbon.

[0005] Activated carbon, composed of graphitized carbon microcrystals and ungraphitized amorphous carbon, is a hydrophobic adsorbent with the ability to selectively adsorb non-polar saturated hydrocarbon compounds. However, the pharmaceutical industry, adhesive tapes, and the chemical industry use large quantities of highly polar solvents such as methanol and ethanol, which are major industrial waste gases. Activated carbon has poor selective adsorption properties for polar solvents like methanol. Therefore, it is necessary to develop an activated carbon with high polar solvent adsorption capabilities to meet the polar solvent recovery needs of pharmaceutical companies, adhesive tapes, and the chemical industry. Summary of the Invention

[0006] In order to solve the technical problem of poor adsorption capacity of activated carbon for polar organic solvents in the prior art, the present invention provides a method for preparing activated carbon for polar solvent recovery. Biomass is used as raw material, and phosphaphenanthrene derivatives and phosphoric acid are used as activators. Through two-stage activation, the activated carbon prepared has a large specific surface area, rich pore structure and appropriate surface chemical structure, so that it exhibits excellent adsorption performance for highly polar organic solvents such as methanol and ethanol.

[0007] In order to achieve the above objectives, the following technical solutions are adopted:

[0008] A method for preparing activated carbon for polar solvent recovery comprises the following steps:

[0009] 1) Grinding and drying the biomass to obtain biomass powder;

[0010] 2) An activator, a surfactant, and an alcohol are prepared into a mixed solution, the biomass powder and the mixed solution are uniformly mixed, and then kneaded using a vacuum kneader. The mixture is then subjected to extrusion granulation, hardening, a first-stage low-temperature activation, a second-stage high-temperature activation, cooling, washing, and drying to obtain activated carbon for polar solvent recovery.

[0011] The activator is prepared by compounding a phosphaphenanthrene derivative and a phosphoric acid solution in a mass ratio of 5-10:100.

[0012] In step 1), the biomass is selected from one or a combination of two or more of coconut shells, apricot shells, palm shells, wood flour, sawdust, wood chips, and wood shavings. The biomass is crushed to 100-150 mesh. The drying step is performed at 100-150°C to a constant weight.

[0013] Step 2) The phosphaphenanthrene derivative is selected from 10-(2,5-dihydroxyphenyl)-10H-9-oxa-10-phosphaphenanthrene-10-oxide (CAS No.: 99208-50-1), [(6-oxo-6H-dibenzo[C,E][1,2]oxaphosphahexacyclo-6-yl)methyl]butanedioic acid (CAS No.: 63562-33-4), 9,10-dihydro-9-oxa-10-phosphaphenanthrene-1 One or a combination of two or more of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-methanol 10-oxide (CAS No.: 35948-26-6), preferably 10-(2,5-dihydroxyphenyl)-10H-9-oxa-10-phosphaphenanthrene-10-oxide (CAS No.: 99208-50-1).

[0014] Furthermore, the concentration of the phosphoric acid solution is 60-80 wt%.

[0015] Furthermore, the surfactant is selected from one or a combination of two or more of alkylphenol polyoxyethylene ether, stearate, sodium alkylbenzene sulfonate, and sodium alkylnaphthalene sulfonate.

[0016] Furthermore, the surfactant is an alkylphenol polyoxyethylene ether, selected from one or a combination of two or more of nonylphenol polyoxyethylene ether, octylphenol polyoxyethylene ether, nonylphenol polyether-3, and nonylphenol polyoxyethylene ether-2, preferably nonylphenol polyoxyethylene ether. The alcohol is selected from one or a combination of two of methanol, ethanol, and isopropanol.

[0017] Furthermore, the mass ratio of the activator, surfactant, alcohol and biomass powder is 105-110:0.05-0.1:10-20:70-90.

[0018] Furthermore, the kneading conditions are kneading at a vacuum degree of -0.01 MPa to -0.1 MPa and 100-180°C for 1-5 hours. The hardening is hardening the granules obtained by granulation at 100-150°C for 1-3 hours. The first stage low-temperature activation is activation at 350-400°C for 10-30 minutes, and the second stage high-temperature activation is activation at 500-600°C for 1-3 hours. The cooling is natural cooling to room temperature. The washing is washing with water to a pH of 5-7. The drying is drying at 100-150°C to constant weight.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] The present invention uses biomass as raw material, phosphaphenanthrene derivatives and phosphoric acid as activators, and through two stages of activation, the prepared activated carbon has a large specific surface area, rich pore structure and appropriate surface chemical structure, so that it exhibits excellent adsorption performance for organic solvents with high polarity such as methanol and ethanol. DETAILED DESCRIPTION

[0021] The present invention will be further described below in conjunction with specific embodiment, but is not limited to the content on the specification sheets. Unless otherwise specified, "parts" described in the embodiments of the present invention are all parts by weight. All reagents used are commercially available reagents in this area.

[0022] Example 1

[0023] 1) Grind the coconut shell into 150 mesh and dry at 100°C to constant weight to obtain coconut shell powder;

[0024] 2) A mixture of 10 parts of 10-(2,5-dihydroxyphenyl)-10H-9-oxa-10-phosphaphenanthrene-10-oxide, 100 parts of a 60wt% phosphoric acid solution, 0.1 parts of nonylphenol polyoxyethylene ether, and 20 parts of ethanol was prepared. 70 parts of coconut shell powder was evenly mixed with the mixture, and then kneaded in a vacuum kneader at a vacuum degree of -0.08 MPa and 150°C for 2 hours. The mixture was then extruded and granulated, hardened at 150°C for 1 hour, activated at a low temperature of 350°C for 30 minutes in the first stage, activated at a high temperature of 500°C for 3 hours in the second stage, cooled naturally to room temperature, washed with water to a pH of 7, and dried at 100°C to constant weight to obtain columnar activated carbon for solvent recovery with a diameter of 3.4 mm and a length of 5.7 mm.

[0025] Example 2

[0026] The rest of the process is the same as in Example 1, except that the amount of 10-(2,5-dihydroxyphenyl)-10H-9-oxa-10-phosphaphenanthrene-10-oxide is 5 parts.

[0027] Example 3

[0028] The rest of the process is the same as in Example 1, except that the amount of 10-(2,5-dihydroxyphenyl)-10H-9-oxa-10-phosphaphenanthrene-10-oxide used is 3 parts.

[0029] Example 4

[0030] The rest of the process is the same as in Example 1, except that the amount of 10-(2,5-dihydroxyphenyl)-10H-9-oxa-10-phosphaphenanthrene-10-oxide used is 12 parts.

[0031] Example 5

[0032] The rest of Example 1 is the same, except that an equal mass of [(6-oxo-6H-dibenzo[C,E][1,2]oxaphosphorin-6-yl)methyl]butanedioic acid is used instead of 10-(2,5-dihydroxyphenyl)-10H-9-oxa-10-phosphaphenanthrene-10-oxide.

[0033] Example 6

[0034] The rest of the process is the same as in Example 1, except that octylphenol polyoxyethylene ether is used in place of nonylphenol polyoxyethylene ether with the same mass.

[0035] Example 7

[0036] The rest of the process is the same as in Example 1, except that calcium stearate of equal mass is used to replace nonylphenol polyoxyethylene ether.

[0037] Example 8

[0038] The rest of the process is the same as in Example 1, except that the amount of ethanol used is 10 parts.

[0039] Example 9

[0040] The rest of Example 1 is the same, except that, in step 2), 5 parts of 10-(2,5-dihydroxyphenyl)-10H-9-oxa-10-phosphaphenanthrene-10-oxide, 100 parts of 80wt% phosphoric acid solution, 0.05 parts of nonylphenol polyoxyethylene ether, and 10 parts of ethanol are prepared into a mixed solution, 90 parts of coconut shell powder are evenly mixed with the mixed solution, and then kneaded with a vacuum kneader at -0.08 MPa and 150°C for 2 hours, followed by extrusion granulation, hardening at 150°C for 1 hour, low-temperature activation at 400°C for 10 minutes in the first stage, high-temperature activation at 500°C for 3 hours in the second stage, naturally cooled to room temperature, washed with water to a pH of 7, and dried at 100°C to constant weight to obtain activated carbon for polar solvent recovery.

[0041] Comparative Example 1

[0042] The rest of the embodiment is the same as in Example 1, except that:

[0043] Step 2) A mixture consisting of 10 parts of 10-(2,5-dihydroxyphenyl)-10H-9-oxa-10-phosphaphenanthrene-10-oxide, 100 parts of a 60wt% phosphoric acid solution, 0.1 parts of nonylphenol polyoxyethylene ether, and 20 parts of ethanol is prepared. 70 parts of coconut shell powder is evenly mixed with the mixture and kneaded in a vacuum kneader at -0.08 MPa and 150°C for 2 hours. The mixture is then extruded into pellets, hardened at 150°C for 1 hour, activated at 500°C for 3 hours, cooled naturally to room temperature, washed with water to a pH of 7, and dried at 100°C to constant weight to obtain activated carbon for polar solvent recovery. This means that only the second stage of high-temperature activation is performed.

[0044] Comparative Example 2

[0045] The rest of the process is the same as in Example 1, except that the activator is 110 parts of a 60 wt % phosphoric acid solution.

[0046] Comparative Example 3

[0047] The rest of the process is the same as in Example 1, except that ethanol is not added.

[0048] The activated carbons prepared in the above examples and comparative examples were subjected to the following performance tests:

[0049] 1. Pore structure characterization: The pore structure specific surface area was measured by NOVA 1000e pore structure specific surface area tester. The sample was degassed at 350℃ for 2h and adsorbed with liquid nitrogen at 77K and relative pressure (P / P0) 10 -6N2 adsorption was carried out in the range of -1, and the specific surface area was calculated by the BET equation.

[0050] 2. Dynamic adsorption test: The test equipment TP-5080 fully automatic multi-purpose adsorption instrument (Tianjin Xianquan Industry and Trade Development Co., Ltd.) was connected to a gas chromatograph. The activated carbon was first dried at 200°C for 2 hours and loaded into a quartz adsorption column. The cylinder was opened and the pressure reducing valve and flow meter were adjusted to a flow rate of 30 mL / min. The mass ratio of methanol or ethanol to nitrogen was 8%, and the pressure was one atmosphere. Nitrogen was blown into the adsorption column at room temperature (15-20°C) through a liquid storage tank. The organic gas concentration at the sampling port was measured every 3 minutes. When the concentration remained unchanged for 30 minutes, the activated carbon adsorption was considered to have reached adsorption equilibrium, and the equilibrium adsorption amount was recorded in mg / g.

[0051] Table 1 Test results

[0052] .

[0053] As can be seen from Table 1, the activated carbon prepared by using the compound of phosphaphenanthrene derivative and phosphoric acid solution as the activator has a large specific surface area and rich pore structure, and exhibits excellent adsorption performance for highly polar organic solvents such as methanol and ethanol.

[0054] It can be seen from the microporosity test results of Examples 1-4 that the change in the relative amount of a tiny phosphaphenanthrene derivative causes a large change in the equilibrium adsorption capacity. It is speculated that the phosphaphenanthrene derivative and the phosphoric acid solution have different chemical structures and properties, and have different penetration and catalytic hydrolysis rates on biomass raw materials, resulting in the pore structure and surface polarity of the activated carbon being greatly affected by the composite ratio of the two. The pore structure formed by the excessively large composite ratio of the two is relatively complex, and the adsorption sites are unevenly distributed, which increases the diffusion resistance, slows down, or even hinders the polar molecules from reaching the adsorption sites; when the composite ratio is too small, the pore size is larger, the surface polarity is smaller, the interaction force is weakened, and the polar solvent is quickly discharged, which is not conducive to adsorption. Therefore, the selection of the composite ratio of phosphaphenanthrene derivatives and phosphoric acid solution needs to be appropriate.

[0055] It can be seen from Example 1 and Comparative Example 2 that if the activator is entirely phosphoric acid, although the specific surface area is large, the surface chemical structure of the activated carbon is not conducive to promoting the adsorption of methanol and ethanol, and the equilibrium adsorption capacity of methanol and ethanol is still low.

[0056] From Example 1, Example 8, and Comparative Example 3, it can be seen that as the amount of ethanol used decreases, the average pore size increases, the microporosity decreases, and the specific surface area decreases. It is speculated that ethanol helps dissolve 10-(2,5-dihydroxyphenyl)-10H-9-oxa-10-phosphaphenanthrene-10-oxide, promoting its more uniform mixing with coconut shell powder and more conducive to penetration.

Claims

1. A method for preparing activated carbon for polar solvent recovery, characterized in that: The steps include: 1) Grinding and drying the biomass to obtain biomass powder; 2) An activator, a surfactant, and an alcohol are prepared into a mixed solution, the biomass powder and the mixed solution are uniformly mixed, and then kneaded using a vacuum kneader. The mixture is then subjected to extrusion granulation, hardening, a first-stage low-temperature activation, a second-stage high-temperature activation, cooling, washing, and drying to obtain activated carbon for polar solvent recovery. The activator is prepared by compounding a phosphaphenanthrene derivative and a phosphoric acid solution in a mass ratio of 5-10:100; the phosphaphenanthrene derivative is selected from one or a combination of two or more of 10-(2,5-dihydroxyphenyl)-10H-9-oxa-10-phosphaphenanthrene-10-oxide, [(6-oxo-6H-dibenzo[C,E][1,2]oxaphosphahexacyclo-6-yl)methyl]succinic acid, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-ethanol 10-oxide, and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-methanol 10-oxide.

2. The method for preparing activated carbon for polar solvent recovery according to claim 1, characterized in that: Step 1) The biomass is selected from one or a combination of two or more of coconut shells, apricot shells, palm shells, wood flour, and wood chips.

3. The method for preparing activated carbon for polar solvent recovery according to claim 1, characterized in that: The pulverizing step is to pulverize the mixture into 100-150 meshes, and the drying step is to dry the mixture at 100-150° C. to a constant weight.

4. The method for preparing activated carbon for polar solvent recovery according to claim 1, characterized in that: Step 2) The phosphaphenanthrene derivative is 10-(2,5-dihydroxyphenyl)-10H-9-oxa-10-phosphaphenanthrene-10-oxide.

5. The method for preparing activated carbon for polar solvent recovery according to claim 1, characterized in that: The concentration of the phosphoric acid solution is 60-80 wt %.

6. The method for preparing activated carbon for polar solvent recovery according to claim 1, characterized in that: The surfactant is selected from one or a combination of two or more of alkylphenol polyoxyethylene ether, stearate, sodium alkylbenzene sulfonate, and sodium alkylnaphthalene sulfonate.

7. The method for preparing activated carbon for polar solvent recovery according to claim 1, characterized in that: The surfactant is an alkylphenol polyoxyethylene ether, selected from one or a combination of two or more of nonylphenol polyoxyethylene ether, octylphenol polyoxyethylene ether, nonylphenol polyether-3, and nonylphenol polyether-2; the alcohol is selected from one or a combination of two of methanol, ethanol, and isopropanol.

8. The method for preparing activated carbon for polar solvent recovery according to claim 7, characterized in that: The surfactant is nonylphenol polyoxyethylene ether.

9. The method for preparing activated carbon for polar solvent recovery according to claim 1, characterized in that: The mass ratio of the activator, surfactant, alcohol and biomass powder is 105-110:0.05-0.1:10-20:70-90.

10. The method for preparing activated carbon for polar solvent recovery according to claim 1, characterized in that: The kneading conditions are: kneading at a vacuum degree of -0.01 MPa to -0.1 MPa and 100-180° C. for 1-5 hours; The hardening is to harden the particles obtained by granulation at 100-150° C. for 1-3 hours.

11. The method for preparing activated carbon for polar solvent recovery according to claim 1, characterized in that: The first stage of low-temperature activation is activation at 350-400° C. for 10-30 minutes, and the second stage of high-temperature activation is activation at 500-600° C. for 1-3 hours.