Activated carbon Adsorption performance of lampblack. Many catering lampblack contains many carcinogens such as aldehydes and polycyclic aromatic hydrocarbons. Generally, biological scrubbing and catalyst are used to purify cooking fume, but complex operating conditions and expensive costs are its main disadvantages. Therefore, there is an urgent need for a simple and easy to use method for the degradation and treatment of soot. Activated carbon has been widely used due to its unique properties. Its good pore structure and high specific surface area are widely used in the waste gas treatment industry.
The activated carbon for oil fume treatment is made from biomass by microwave heating with phosphoric acid as activator. Or prepare adsorbent by pyrolysis and carbonization, and then activate biomass in nitrogen atmosphere and KOH activation. The activated carbon adsorbent can well adsorb hexavalent chromium from aqueous solution.
Preparation and modification of activated carbon for oil fume adsorption
In a typical experimental procedure, agricultural waste biomass is first washed with water and then dried in an oven at 12 ° C for 12 hours. Then, the dried biomass is added to 60% phosphoric acid solution at a weight ratio of 1:3. Place the mixture in a box type resistance furnace to carbonize and activate at 500 ℃ for 2 hours at a heating rate of 10 ℃ per minute. When it is cooled to room temperature, the product is collected and washed with deionized water until the pH of the solution is close to neutral. Then, the product is dried and stored in a sample bag called activated carbon 0.
The modified reagent is a solution prepared from FeSO4 · 7H2O and H2O2, and the pH value of the solution is adjusted to 3. Immerse the activated carbon-0 into the modified reagent and place it overnight at room temperature. Wash the obtained product with deionized water to neutral, dry it in an oven at 50 ℃, and call the corresponding sample activated carbon-1.
Concentration measurement of pollutants in cooking fume
As shown in Figure 1, collect 3 minutes of simulated cooking fume samples at the inlet and outlet of the sampling tube filled with 5g of granular activated carbon. The sampling was repeated 3 times. Take out the granular activated carbon in the sample tube, transfer it to the flask, and wash it with 15mL carbon tetrachloride for 5 minutes with an ultrasonic instrument. Collect the cleaning solution and transfer it to another flask (marked with A). Wash granular activated carbon again with 10mL carbon tetrachloride, collect cleaning solution and transfer it to flask A.
Figure 1: Schematic diagram of experimental equipment for treating cooking fume with biomass, activated carbon 0 and 1.
Results and analysis after experiment
Figure 2 shows the adsorption breakthrough curve of biomass, activated carbon 0 and 1 on cooking fume. The permeation time of biomass, activated carbon 0 and 1 is 0.9, 2.1 and 4.1 hours respectively, which indicates that the action time of activated carbon 1 is longer in the tested materials. Adsorption capacity of biomass, activated carbon 0 and 1 of cooking fume. The adsorption capacity of biomass, activated carbon 0 and 1 of cooking fume is 6.43, 22.58 and 44.04mg/g respectively, which indicates that the adsorption capacity of activated carbon 1 is relatively large. Therefore, activated carbon 1 shows better adsorption performance than activated carbon 0.
GC-MS analysis was carried out to identify the adsorption components of biomass, activated carbon 0 and 1 on cooking fume. It was found that the main components of cooking fume were aldehydes and substituted olefins. We conducted a systematic study on aldehydes and ketones in exhaust gases from eight restaurants, and found that the concentration range of aldehydes and ketones (C1-C9) and the percentage of C1-C3 were higher than 40%. The adsorption analysis shows that activated carbon 1 has a good adsorption capacity for all soot components, which is due to the influence of modified reagents leading to the main chemical adsorption performance. However, the adsorption capacity of activated carbon for aldehyde is better than that for substituted olefins. This is because aldehyde compounds are a kind of volatile organic compounds with strong chemical reactivity, which are easily adsorbed by activated carbon.
In order to further study the adsorption behavior of activated carbon, the morphology and structure of activated carbon were characterized by specific surface area and pore analyzer, SEM and FTIR. Compared with activated carbon 0, the specific surface area and pore volume of activated carbon 1 are reduced and the pore size is slightly increased. This is because part of the porous microstructure of CO2 collapsed due to the oxidation of H2O2 after treatment with modified reagents. Figure 3 shows the SEM image of activated carbon. A large number of substances are adsorbed on the surface or filled in the pores of activated carbon 1 (Figure 3 (c1-c2)), which proves that the specific surface area and pore volume of activated carbon 1 are reduced.
Compared with activated carbon-0, activated carbon-1 has better adsorption capacity, because it is rich in carbonyl and carboxyl groups, and can react with carboxylic acid and alcohol in cooking flue gas to improve the adsorption capacity of activated carbon-1. Moreover, during the preparation of activated carbon-1, some substances such as HO, Fe3+, Fe2+and H2O2 may remain on the surface or inner wall of the pores of activated carbon-1. These substances can oxidize and decompose most of the oil smoke pollutants adsorbed on the surface of activated carbon, thus improving the adsorption capacity of activated carbon.
In order to deal with cooking fume, we successfully developed an activated carbon, which was activated by phosphoric acid, and then modified the prepared reagent, and studied the adsorption performance of cooking fume. The results show that the modified activated carbon has good adsorption effect. The excellent adsorption performance of activated carbon is due to the large amount of carbonyl and carboxyl groups generated on the surface after modification. Based on the similar compatibility principle, the adsorption effect of activated carbon on different types of oil smoke pollutants was analyzed. It is found that the adsorption of strong polar functional groups is far greater than that of weak polar groups. Compared with iron silicate MEL zeolite, activated carbon also shows better performance in the adsorption of cooking fume.
