인산 및 수증기 활성화에 의한 대나무 활성탄 제조 및 특성 연구

Preparation and Characterization of Bamboo-based Activated Carbon by Phosphoric Acid and Steam Activation

Abstract

대나무는 지구상에 존재하는 식물 중 적절한 기후와 토양조건에서 생산성이 가장 높고, 성장속도가 가장 빠른 다년생 식물로 알려져 있다. 전통적으로 아시아에서 대나무는 음식, 건축 및 다양한 재료로 활용되고 있다. 바이오매스 자원으로 대나무는 열분해과정을 거쳐 활성탄으로 제조될 수 있다. 본 연구에서는 탄화온도, 활성화 온도, 시간, 수증기의 양, 그리고 인산의 양 등을 변화에 따른 최적의 대나무 활성탄 제조 연구를 수행하였다. 대나무 탄화 후 수증기 활성화를 위해 $700{\sim}900^{\circ}C$의 온도, $0.8{\sim}1.8mL-H_2O\;g-char^{-1}\;h^{-1}$ 수증기 유량 범위에서 1 ~ 3 h 동안 활성화를 진행하였다. 수증기 유량을 $1.4mL-H_2O\;g-char^{-1}\;h^{-1}$으로 2 h 동안 실험한 결과 활성탄 수율과 비표면적은 각각 2.04 ~ 20.59 wt%, $499.17{\sim}1074.04m^2\;g^{-1}$의 값이 나왔다. 대나무와 인산의 질량비를 1:1로 혼합한 후 $700^{\circ}C$에서 유량 $1.4mL-H_2O\;g-char^{-1}\;h^{-1}$ 속도로 2 h 동안 활성화를 진행한 결과 활성탄 수율과 비표면적은 각각 24.67 wt%, $1389.59m^2\;g^{-1}$의 값이 나타냈다. 제조된 대나무 활성탄을 대상으로 메틸렌블루 흡착 실험을 통해 유사 1차, 2차 속도식 모델을 적용하였으며, 화학적 흡착을 의미하는 유사 2차 속도식에 따랐다.

Bamboo is an evergreen perennial plant, and it is known as one of the most productive and fastest-growing plants in the world. It grows quickly in moderate climates with only moderate water and fertilizer. Traditionally in Asia, bamboo is used for building materials, as a food source, and as versatile raw materials. Bamboo as a biomass feedstock can be transformed to prepare activated carbon using the thermal treatment of pyrolysis. The effect of process variables such as carbonization temperature, activation temperature, activation time, the amount of steam, and the mixing ratio of phosphoric acid and bamboo were systematically investigated to optimize the preparation conditions. Steam activation was proceeded after carbonization with a vapor flow rate of $0.8{\sim}1.8mL-H_2O\;g-char^{-1}\;h^{-1}$ and activation time of 1 ~ 3 h at $700{\sim}900^{\circ}C$. Carbon yield and surface area reached 2.04 ~ 20.59 wt% and $499.17{\sim}1074.04m^2\;g^{-1}$, respectively, with a steam flow rate of $1.4mL-H_2O\;g-char^{-1}\;h^{-1}$ for 2 h. Also, the carbon yield and surface area were 24.67 wt% and $1389.59m^2\;g^{-1}$, respectively, when the bamboo and phosphoric acid were mixed in a 1:1 weight ratio ($700^{\circ}C$, 2 h, $1.4mL-H_2O\;g-char^{-1}\;h^{-1}$). The adsorption of methylene blue into the bamboo activated carbon was studied based on pseudo first order and second order kinetics models. The adsorption kinetics were found to follow the pseudo second order model, which is governed by chemisorption.

Figure 1. Schematic diagram of tubular type pyrolysis reactor.

Scheme 1. Experimental procedure of bamboo activated carbon and phosphoric acid mixed bamboo activated carbon, Formation of phosphate esters on cellulose side-chains (T < 450 ℃) and cross-linking and Mechanism of phosphate ester formation by phosphorylation of cellulose (T > 450 ℃) [21].

Figure 2. TG&DTG curves and peak separation of bamboo at heating rates of 10 ℃ min^-1.

Figure 3. SEM image of bamboo activated carbon at 750 ℃, 800 ℃, and 850 ℃; ×500.

Figure 4. Micropore and mesopore distribution using BET analysis of bamboo activated carbon with different steam flow rate.

Figure 5. Micropore and mesopore distribution using BET analysis of bamboo activated carbon with different mixing ratio phosphoric acid.

Figure 6. SEM image of phosphoric acid mixed bamboo activated carbon at 600 ℃, 700 ℃, and 850 ℃; ×500.

Figure 7. FT-IR spectra of carbonization carbon and activated carbon for AC3 (800 ℃, 1.4 mL-H₂O g-char^-1 h^-1, 2 h) and AC-P4 (bamboo : phosphoric acid = 1:1 wt ratio, 700 ℃, 1.4 mL-H₂O g-char^-1 h^-1, 2 h) conditions: 1. AC3 Carbonization carbon, 2. AC3 Activated carbon, 3. AC-P4 Carbonization carbon, 4. AC-P4 Activated carbon.

Figure 8. Weight loss for bamboo activated carbon: (a) AC3 (800 ℃, 1.4 mL-H₂O g-char^-1 h^-1, 2 h) and (b) AC-P4 (bamboo : phosphoric acid = 1:1 wt ratio, 700 ℃, 1.4 mL-H₂O gchar^-1 h^-1, 2 h) at heating rate of 10 ℃min^-1.

Figure 9. Kinetic parameters for methylene blue adsorption on activated carbon at different weight: AC3 (800 ℃, 1.4 mL-H₂O g-char^-1 h^-1, 2 h) and AC-P4 (bamboo : phosphoric acid = 1:1 wt ratio, 700 ℃, 1.4 mL-H₂O g-char^-1 h^-1, 2 h).

Table 1. Characteristics of bamboo: contents of volatile matter, fixed carbon, moisture, ash, elements and higher heating value (HHV)

Table 2. Inorganic compositions of bamboo

Table 3. Characteristics of bamboo activated carbon produced through different activation conditions

Table 4. Effect of the mixing ratio of bamboo and phosphoric acid on drying and carbonization yield

Table 5. Effect of mixing ratio of bamboo and phosphoric acid, activation temperature, and steam flow rate on product yield and characteristics

Table 6. Kinetic parameters for adsorption of methylene blue on activated carbon at different weight; (a) AC3 (800 ℃, 1.4 mL-H₂O g-char^-1 h^-1, 2 h) and (b) AC-P4 (bamboo : phosphoric acid = 1:1 wt ratio, 700 ℃, 1.4 mL-H₂O g-char^-1 h^-1, 2 h)