Ju Dong Lee

Gas hydrates: A cleaner source of energy and opportunity for innovative technologies

The global energy system is characterized by a gradual de-carbonization and move to cleaner burning technologies: from wood to coal to oil and to natural gas. A final destination characterized by the term“hydrogen economy” is desired. Gas hydrate found in the earth’s crust is considered a source of natural gas that is essentially 100% methane (CH4) gas. Natural gas hydrate estimates worldwide range from 10,000 to 40,000 trillion cubic meters (TCM). Efforts are underway to exploit this resource. These methane hydrates in the earth’s crust also have the potential to be a significant factor in global climate change. Moreover, gas hydrates offer opportunities for the development of innovative technologies (separation of CO2 from CO2/N2 and CO2/H2 mixtures, CO2 sequestration, natural gas transportation and storage and H2 storage). In this work we assess the progress towards exploitation of gas hydrates as a resource for methane (cleaner energy) and summarize the state of the art with respect to the role of gas hydrates in the development of innovative technologies.

Synergistic Hydrate Inhibition of Monoethylene Glycol with Poly(vinylcaprolactam) in Thermodynamically Underinhibited System

This study investigates the hydrate inhibition performance of monoethylene glycol (MEG) with poly(vinylcaprolactam) (PVCap) for retarding the hydrate onset as well as preventing the agglomeration of hydrate particles. A high-pressure autoclave was used to determine the hydrate onset time, subcooling temperature, hydrate fraction in the liquid phase, and torque changes during hydrate formation in pure water, 0.2 wt % PVCap solution, and 20 and 30 wt % MEG solutions. In comparison to water with no inhibitors, the addition of PVCap delays the hydrate onset time but cannot reduce the hydrate fraction, leading to a sharp increase in torque. The 20 and 30 wt % MEG solutions also delay the hydrate onset time slightly and reduce the hydrate fraction to 0.15. The addition of 0.2 wt % PVCap to the 20 wt % MEG solution, however, delays the hydrate onset time substantially, and the hydrate fraction was less than 0.19. The torque changes were negligible during the hydrate formation, suggesting the homogeneous dispersion of hydrate particles in the liquid phase. The well-dispersed hydrate particles do not agglomerate or deposit under stirring. Moreover, when 0.2 wt % PVCap was added to the 30 wt % MEG solution, no hydrate formation was observed for at least 24 h. These results suggest that mixing of MEG with a small amount of PVCap in underinhibited conditions will induce the synergistic inhibition of hydrate by delaying the hydrate onset time as well as preventing the agglomeration and deposition of hydrate particles. Decreasing the hydrate fraction in the liquid phase might be the reason for negligible torque changes during the hydrate formation in the 0.2 wt % PVCap and 20 wt % MEG solution. Simple structure II was confirmed by in situ Raman spectroscopy for the synergistic inhibition system, while coexisting structures I and II are observed in 0.2 wt % PVCap solution.

Inhibition of methane and natural gas hydrate formation by altering the structure of water with amino acids.

Natural gas hydrates are solid hydrogen-bonded water crystals containing small molecular gases. The amount of natural gas stored as hydrates in permafrost and ocean sediments is twice that of all other fossil fuels combined. However, hydrate blockages also hinder oil/gas pipeline transportation, and, despite their huge potential as energy sources, our insufficient understanding of hydrates has limited their extraction. Here, we report how the presence of amino acids in water induces changes in its structure and thus interrupts the formation of methane and natural gas hydrates. The perturbation of the structure of water by amino acids and the resulting selective inhibition of hydrate cage formation were observed directly. A strong correlation was found between the inhibition efficiencies of amino acids and their physicochemical properties, which demonstrates the importance of their direct interactions with water and the resulting dissolution environment. The inhibition of methane and natural gas hydrate formation by amino acids has the potential to be highly beneficial in practical applications such as hydrate exploitation, oil/gas transportation, and flow assurance. Further, the interactions between amino acids and water are essential to the equilibria and dynamics of many physical, chemical, biological, and environmental processes.

Pure SF6 and SF6-N2 mixture gas hydrates equilibrium and kinetic characteristics.

Sulfur hexafluoride (SF6), whether pure or mixed with inexpensive inert gas, has been widely used in a variety of industrial processes, but it is one of the most potent greenhouse gases. For this reason, it is necessary to separate and/or collect it from waste gas streams. In this study, we investigated the pure SF6 and SF6-N2 mixture gas hydrates formation equilibrium aswell asthe gas separation efficiency in the hydrate process. The equilibrium pressure of SF6-N2 mixture gas was higher than that of pure SF6 gas. Phase equilibrium data of SF6-N2 mixture gas was similar to SF6 rather than N2. The kinetics of SF6-N2 mixture gas was controlled by the amount of SF6 at the initial gas composition as well as N2 gas incorporation into the S-cage of structure-II hydrate preformed by the SF6 gas. Raman analysis confirmed the N2 gas incorporation into the S-cage of structure-II hydrate. The compositions in the hydrate phase were found to be 71, 79, 80, and 81% of SF6 when the feed gas compositions were 40, 65, 70, and 73% of SF6, respectively. The present study provides basic information for the separation and purification of SF6 from mixed SF6 gas containing inert gases.

Surfactant effects on SF6 hydrate formation

Sulfur hexafluoride (SF(6)) has been widely used in a variety of industrial processes, but it is one of the most potent greenhouse gases. For this reason, it is necessary to separate or collect it from waste gas streams. One separation method is through hydrate crystal formation. In this study, SF(6) hydrate was formed in aqueous surfactant solutions of 0.00, 0.01, 0.05, 0.15 and 0.20 wt% to investigate the effects of surfactants on the hydrate formation rates. Three surfactants, Tween 20 (Tween), sodium dodecyl sulfate (SDS) and linear alkyl benzene sulfonate (LABS), were tested in a semi-batch stirred vessel at the constant temperature and pressures of 276.2 K and 0.78 MPa, respectively. All surfactants showed kinetic promoter behavior for SF(6) hydrate formation. It was also found that SF(6) hydrate formation proceeded in two stages with the second stage being the most rapid. In situ Raman spectroscopy analysis revealed that the increased gas consumption rate with the addition of surfactant was possibly due to the increased gas filling rate in the hydrate cavity.

Synthesis of Nanosized TiO2-Ag-SiO2 Sols by Modified Sol-Gel Method and their Application for Methane Hydrate Formation

Nanosized TiO2-Ag-SiO2 sols were prepared with modified sol-gel method using reduction agent. The physical properties of the prepared particles were investigated by TEM, XRD and FT-IR. The titanium tetraisopropoxide (TTIP, 98% Aldrich), teraethylorthosilicate (TEOS, 98% Aldrich) and silver nitrate were used as precursors of titania, silica and silver, respectively. Sodium citrate tribasic dihydrate (C6H5Na3.2H2O, Aldrich) was used as a reduction agent. This paper presents the effect of nanosized TiO2-Ag-SiO2 sols on the formation of methane hydrate in a semi-batch vessel. The micrographs of TEM showed that the TiO2-Ag-SiO2 particles possessed a spherical morphology with a narrow size distribution. The crystallite size of particles decreased with an increasing the SiO2 content. In addition, the water solution with 1.0 wt% of TiO2-Ag-SiO2 particles acted as promoter for methane hydrate formation.

Effects of Organic Additives on the Residual Stress of Ni and Ni Alloys Electrodeposited from the Sulfamate Bath

The residual stress in the deposits of Ni and Ni alloys was estimated from the deflection of one side deposited test strips (Specialty testing & Development Co.). 2,6-Naphthalene- disodiumsulfate (2,6-NDS) and 1,3,6-Naphthalenetrisodiumsulfate (1,3,6-NTS) were adopted instead of saccharin and , among the three additives, the lowest residual stress was obtained with 1,3,6-NTS. However, to adjust compressive stress, certain quantity of amine additives such as MEA (Monoethanolamine), DEA (Diethanolamine) and TEA(Triethanolamine) were added stepwise to the bath containing 1,3,6-NTS while electrodepositon proceeded. Effects on reducing residual stress was in order of MEA<DEA<TEA, which seemed to have a connection with lone pair and basicity of the nitrogen attached to the amine additives. The highest Vickers hardness was attained with the Ni-Co alloy deposit from the Ni-Co(Ni:80g/L-Co:4.8g/L) bath and the cobalt content of the deposit was 28.4%(wt./wt.). Properties and cobalt content of the deposits were evaluated and analyzed with SEM, XRD, EDS and ICP respectively.

Pre-Combustion Capture of Carbon Dioxide Using Principles of Gas Hydrate Formation

The emission of carbon dioxide from the burning of fossil fuels has been identified as a major contributor to green house emissions and subsequent global warming and climate changes. For these reasons, it is necessary to separate and recover CO gas. A new process based on gas hydrate crystallization is proposed for the CO separation/recovery of the gas mixture. In this study, gas hydrate from CO /H gas mixtures was formed in a semi-batch stirred vessel at a constant pressure and temperature. This mixture is of interest to CO separation and recovery in Integrated Coal Gasification (IGCC) plants. The impact of tetrahydrofuran (THF) on hydrate formation from the CO /H was observed. The addition of THF not only reduced the equilibrium formation conditions significantly but also helped ease the formation of hydrates. This study illustrates the concept and provides the basic operations of the separation/recovery of CO (pre-combustion capture) from a fuel gas (CO /H ) mixture.

Crystallization kinetics for carbon dioxide gas hydrate in fixed bed and stirred tank reactor

The phase change from germ nuclei to growth nuclei and subsequent volume transformation in a crystallization process was modeled by Avrami equations. The phase change during the hydrate formation was fitted with the classical Avrami model by utilizing gas uptake data. The idea is to understand the difference in growth behavior of hydrate crystals when in small pores compared to a stirred tank reactor which does not pose any physical restrictions to hydrate growth. The parameters n and k of the Avrami equation were determined explicitly for CO2 hydrate formation.

Effects of Surfactant on SF 6 Gas Hydrate Formation Rate

본 연구에 사용된 실험장치는 Fig. 1과 같이 구성되어있다. 반응기(R)는 SUS 316 재질을 사용하여 충분한 고압에 견디며, 온도와 압력 조절이 가능하도록 설계하였고, 또한, 용기 내부 관찰이 용이하도록 2석영창을 앞뒤로 설치하였다. 모든 반응은 정압반응으로 물속에 용해되거나 하이드레이트 형성으로 인해 소모된 가스의 공급을 위해 actuator를 이용하여 가스를 공급하였고, 정밀도를 높이기 위해 actuator와 반응기 사이에 needle valve를 설치하였다. 온도는 수면높이가 일정하게 유지되는 일수식 수조에 반응기가 완전히 잠기게 하여 수온의 조절을 통해 제어하도록 설계하였다. 온도를 단시간에 제어할 수 있도록 두 개의 항온조를 -구성하였으며, 밸브 및배관시스템으로 연결되고 그 사이를 냉매가 직접 순환하게 하였다. 이 수조의 외벽은 투명한 아크릴로 만들어 외부로부터 육안 및 현미경을 통한 관찰이 가능하도록 하였다. 온도는 총 4개의 구리-콘스탄탄 열전대(Omega, ±0.10K)를 설치하였으며, 반응기 내부 기체부분과 액체부분 그리고 나머지 두 개는 수조의 온도 측정을 위해 3. 사용하였다. 효율적인 교반을 위해 용기의 내부에 자석 젓개(magnetic bar)를 설치하고 수조의 1)하부에서 자력으로구동하여 하이드레이트 형성을 유도하였다. 또한 자석 젓개로 인해 형성되는 소용돌이 형성 방해 및 기-액 계면에 형성된 하이드레이트 입자의 원활한 섞임을 유도하기위해 3개의 대라와 수평바로 이루어진 방해판(baffle)을설치하였다.실험에 하이드레이트 형성촉진제로 사용된 첨가제인Tween 20(계면활성제)은 Aldrich사 제품으로 density가1.105인 시약을 사용하여 하이드레이트 형성 실험을 수행하였다 실험 절차로는 먼저 반응기 내부의 습기와 먼지를 완전히 제거하고 반응기를 조립한 뒤, 약 100cc의pure water 또는 촉진제(promoter) 합성용액을 반응기에주입하였다. 또한 SF