15 Raman spectra of CHClF2 hydrates formed in 5 wt% NaCl, MgCl2 and NiCl2 brine solutions and pure water···24. 18 Graph of the fitting results of experimental data in the initial formation reaction of CHClF2 hydrate formed in NaCl brine solutions ···31. 22a Comparison of experimental and calculated formation kinetics of CHClF2 hydrates formed in NaCl brine solutions ···38.
22b Comparison of experimental and calculated formation kinetics of CHClF2 hydrates formed in MgCl2 brine solutions ···38. 22c Comparison of experimental and calculated formation kinetics of CHClF2 hydrates formed in NiCl2 brine solutions ···39.
Introduction
Background
- Clathrate Hydrate
- Desalination
- Hydrate-Based Desalination
- CHClF 2
3, the occupancy of the gas hydrate cavities depends on the size of the guest molecules (von Stackelberg, 1949; Ripmeester, et al., 1987). With these improvements in competing technologies such as RO, the installation of MSF plants is on a downward trend (Mezher et al., 2011). The cost of producing one ton of drinking water for HBD is comparable to more mature RO and is significantly lower than MSF (Babu, et al., 2018).
In addition to seawater desalination, HBD technology can be used to separate heavy metals from aqueous solutions, especially in electroplating wastewater treatment (Song et al., 2016). CHClF2 forms sI hydrate and can only be captured in large sI hydrate cages due to the larger size than small sI hydrate cages (Wittstruck et al., 1961).
Purpose
Experimental Section
Materials and Apparatus
After the hydrate formation was complete, the CHClF2 hydrate slowly dissociated by increasing the cell temperature at a rate of 0.1 K/h. The crystal structure of CHClF2 hydrate formed in aqueous solution was identified by a high-resolution synchrotron XRD at beamline 9B of the Pohang Accelerator Laboratory (PAL). Moreover, I observed that with increasing concentration of NiCl2 salt solutions, the equilibrium curves of CHClF2.
14, the crystal structures of the CHClF2 hydrates formed in 5wt% NaCl, MgCl2 and NiCl2 brine solutions and pure water were determined from the high-resolution synchrotron XRD. Lattice parameter and unit cell volume of the CHClF2 hydrates with and without salt are tabulated in table. Raman spectra of the CHClF2 hydrates formed in 5 wt% NaCl, MgCl2 and NiCl2 brine solutions, compared to Raman spectra of CHClF2 hydrates formed in pure water, there were no changes in Raman spectra.
17a, b, c show the experimental results of the kinetics of CHClF2 hydrate formation, which was formed in 0, 5 and 10% by mass solutions of NaCl, MgCl2 and NiCl2, respectively. The amount of CHClF2 gas consumed during hydrate formation was calculated from the pressure-volume-temperature (PVT) relationship of CHClF2. 18 Showing the corresponding results of the experimental data in the initial reaction of the formation of CHClF2 hydrate, which is formed in NaCl brine solutions.
The kinetic parameters for the formation of the CHClF2 hydrate formed in NaCl, MgCl2 and NiCl2 salt solutions are tabulated in Table 5. In summary, I investigated the three-phase equilibria (hydrate-aqueous liquid-vapor) of the CHClF2 hydrate formed in NiCl2 brine solutions . I also observed the crystal structure and guest occupancy behavior of the CHClF2 molecules in the CHClF2 hydrate formed in NaCl, MgCl2 and NiCl2 brine solutions using XRD and Raman spectroscopy measurement.
Experimental Method
- Phase Equilibrium Conditions
- X-ray Diffraction
Raman Spectra
To explore the structural and intramolecular vibrational changes of the CHClF2 hydrates due to the addition of NaCl, MgCl2 and NiCl2, the Raman spectroscopy measurement was performed. In addition, the broad Raman bands around 3000-3500 cm-1 represent the O-H vibration of water molecules in the clathrate structure and the spectral region of 200-350 cm-1. 15 Raman spectra of CHClF2 hydrates formed in 5 wt% NaCl, MgCl2 and NiCl2, saline solutions and pure water.
From the results I confirmed that the NaCl, MgCl2 and NiCl2 do not affect the gas (CHClF2) occupation in the hydrate cages and the crystalline structure of CHClF2 hydrates. The CHClF2 is an asymmetric apex molecule belonging to the point group Cs (Snels & D'Amico, 2001) and intramolecular vibration of CHClF2. In this study, as shown in Fig 16, noticeable difference in the Raman spectra between solid CHClF2 and CHClF2 clathrate hydrates at the same temperature and pressure was observed in the v1 and v4 regions around 3000-3050 cm-1 and 750- 850 cm- 1, resp., which are assigned to CH and C-Cl stretching vibrations of CHClF2 molecules trapped in the clathrate cages.
16 Enlargement of Raman spectra in the v4 and v1 region of CHClF2 trapped in CHClF2 hidrate and solid CHClF2.
Hydrate Formation Kinetics
- Experimental Results
- Kimetic model
In this study, a new kinetic model for the theoretical prediction of the formation kinetics of CHClF2 hydrates was proposed. According to kinetic model for hydrate particle growth proposed by Englezos et al. where n is the moles of CHClF2 consumed during the hydrate formation, f is the fugacity of CHClF2 in the gas phase, feq is the equilibrium fugacity of CHClF2, and kapp is the apparent rate constant of the hydrate formation. To overcome these problems, I proposed a new approach using the transient time-dependent apparent rate constant of hydrate formation.
Assuming that the apparent rate constant is nearly constant during the hydrate growth, the following equation can be easily obtained by integrating Eq. Using n(t) from the experimental data, P(t) from Eq. 6), the apparent rate constant kapp can be calculated as a function of time. The apparent rate constant cap during hydrate formation in the NaCl-salt water solutions is shown in Fig.
The apparent rate constant increases rapidly in the initial period of hydrate growth, up to ∼50 s, in all concentration systems, the NiCl2 and MgCl2 system results were also the same as that. 20 Apparent rate constant as a function of time during the formation of NaCl salt solutions. It means that the apparent rate constants are significantly affected by the salt concentration during the formation of CHClF2.
22a Comparison of experimental and calculated formation kinetics of CHClF2 hydrates formed in NaCl brine solutions. 22b Comparison of experimental and calculated formation kinetics of CHClF2 hydrates formed in MgCl2 brine solutions. 22c Comparison of experimental and calculated formation kinetics of CHClF2 hydrates formed in NiCl2 brine solutions.
CHClF2 hydrate under NaCl brine solution CHClF2 hydrate under MgCl2 brine solution CHClF2 hydrate under NiCl2 brine solution. 23 The relationship between the concentration of the brine solution and the apparent rate constant from formation kinetics at 278 K.
Conclusion
길고 짧은 석사과정이 이 논문으로 끝난다는 것이 믿겨지지 않습니다. 하지만 제가 아무 것도 모르고 이 과정을 성공적으로 마칠 수 있었던 것은 주변 분들의 많은 도움과 격려가 있었기 때문이라고 분명히 알 수 있을 것 같습니다. 석사과정 동안 학문적인 측면뿐만 아니라 삶의 측면에서도 많은 가르침을 주신 윤지호 교수님께 깊은 감사의 말씀을 전하고 싶습니다.
교수님의 지도 덕분에 저는 석사과정 학생으로서 경험할 수 있는 다양하고 멋진 것들을 경험할 수 있었고, 이러한 경험들이 제 인생에 큰 밑거름이 될 것이라 믿어 의심치 않습니다. 학문에 열정을 갖고 계신 교수님을 보면서 연구자의 길이 무엇인지 막연히 알게 되었고, 무엇을 하든 그 열정을 추구하고 싶습니다. 공동 지도교수님으로 항상 격려해 주시는 한국해양과학기술원 김동선 교수님께 감사의 말씀을 전하고 싶습니다.
또한, 논문을 검토해주시고 피드백을 주신 유경근 교수님께 진심으로 감사의 말씀을 전하고 싶습니다. 또한, 매 학기마다 대학원 세미나를 통해 제가 더욱 성장할 수 있도록 도와주신 장원일 교수님, 신성렬 교수님, 임종세 교수님, 정우근 교수님에게도 감사의 말씀을 전하고 싶습니다. 학부 때 교수님들이 가르쳐주신 모든 것 하나하나가 석사 과정에서 내 연구의 생명이자 영혼이 되었다고 생각합니다.
덕분에 힘든 대학원생활을 행복하게 보낼 수 있었습니다. 마지막으로 항상 저를 사랑해주시고 옆에서 지켜봐 주시는 가족들, 아버지, 어머니, 재하 오빠에게 진심으로 감사하다는 말씀 전하고 싶습니다. 앞으로도 저를 믿고 응원해주시길 바라며, 부끄럽지 않은 딸, 언니가 되도록 최선을 다하겠습니다.
