Clean Technology (청정기술)

The Korean Society of Clean Technology (한국청정기술학회)
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Adsorption Calculation of Oxygen, Nitrogen and Argon in Carbon-Based Adsorbent with Randomly Etched Graphite Pores

무작위 에칭 흑연 기공을 가지는 탄소기반 흡착제에 의한 산소, 질소 및 아르곤의 흡착 계산

  • Seo, Yang Gon (Department of Chemical Engineering/RIGET, Gyeongsang National University)
  • 서양곤 (경상대학교 화학공학과/그린에너지융합연구소)
  • Received : 2018.09.20
  • Accepted : 2018.10.16
  • Published : 2018.12.31
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Abstract

The adsorption equilibria of oxygen, nitrogen and argon on carbonaceous adsorbent with slit-shaped and randomly etched graphite (REG) pores were calculated by molecular simulation method. Reliable models of adsorbents and adsorbates for adsorption equilibria are important for the correct design of industrial adsorptive separation processes. At the smallest physical pore of $5.6{\AA}$, only oxygen molecules were accommodated at the center of the slit-shaped pore, and from $5.9{\AA}$ nitrogen and argon molecules could be accommodated in the pores. Slit pores showed higher adsorption capacity compared with REG pores with same averaged reenterance pore size due to dead volume and inaccessible volume in defected pores. And it was shown the adsorption capacities of oxygen and argon was same in larger pore size. From calculated adsorption isotherms at 298 K it showed that the adsorption capacity ratio of oxygen to nitrogen is increased as pressure is increased.

분자전산 모사 방법에 의하여 슬릿 기공과 무작위 에칭 흑연(randomly etched graphite, REG) 기공을 가지는 탄소계 흡착제에서 산소, 질소 그리고 아르곤에 대한 흡착 평형을 계산 하였다. 흡착량 계산에서 흡착제와 흡착질의 신뢰할 만한 모델은 공업적 흡착 분리 공정의 정확한 설계에 매우 중요하다. $5.6{\AA}$의 가장 작은 물리적 기공 크기에서 오직 산소만이 기공의 중심에 흡착하였으며, $5.9{\AA}$부터 질소와 아르곤이 흡착을 시작하였다. 균일한 표면을 가지는 슬릿기공이 결함 기공의 불용 부피와 접근이 불가능한 부피로 인하여 표면에 이질성을 가지는 REG 기공보다 더 높은 흡착 능력을 보였다. 탄소계 흡착제의 경우 질소보다 산소가 높은 흡착량을 보였으며, 기공이 큰 경우 산소와 아르곤의 흡착량은 동일함을 보였다. 298 K에서 흡착 등온선 계산으로부터 압력이 증가할수록 질소에 대한 산소의 흡착량의 비율이 높아짐을 보였다.

Keywords

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Figure 1. Schematic diagram of a SLIT pore (a) and a modified randomly etched graphite model (b).

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Figure 2. A sketch of the LJ and TraPPE models for argon (a), nitrogen (b) and oxygen (c).

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Figure 3. Singlet distribution for the nitrogen models in three slit-shaped pores (H = 8 (a), 10 (b) and 15 Å (c)) at 273.15 K and 1 bar. Filled circle symbols: 2 LJ site and square symbols: 1 LJ site.

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Figure 4. Schematic diagram of nitrogen molecules adsorbed on graphite wall with slit-shaped pore (H: physical width, w or w': reentrant width, H': accessible width).

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Figure 5. Calculated cumulative and pore size distribution of the slit-shaped pore and REG models. Dashed lines are cumulative distributions.

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Figure 6. Molecule density of nitrogen, oxygen and argon according to physical width of slit pores, and snapshots of oxygen at 77 K and 1 bar. The solid line-segments are drawn between the individual oxygen atoms in snapshots.

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Figure 7. Calculated adsorption isotherms for nitrogen in slit pores. open symbols represent desorption.

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Figure 8. Adsorption isotherms on slit pore and REG models at 298 K: red, nitrogen; blue, oxygen; black, argon; filled circle, slit_H101; open rectangle, REG_A10; open triangle, REG_A20.

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Figure 9. Illustration of the accessible pores in REG pore model.

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Figure 10. Plot of adsorption ratio of oxygen to nitrogen as a function of pressure.

Table 1. Lennard-Jones parameters used in this work

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