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Tuning Behaviors of Methane Inclusion in Isoxazole Clathrate Hydrates
Cha, Minjun,Baek, Seungjun,Lee, Wonhee,Shin, Kyuchul,Lee, Jae W. American Chemical Society 2015 Journal of chemical and engineering data Vol.60 No.2
<P>In this study, the inclusion of methane (CH<SUB>4</SUB>) gas in isoxazole (C<SUB>3</SUB>H<SUB>3</SUB>NO) clathrate hydrates was investigated through spectroscopic observations, such as powder X-ray diffraction (PXRD) and Raman spectroscopy. PXRD patterns of isoxazole clathrate hydrates having two different mole fractions of water were analyzed, and Raman spectroscopy was used to understand the CH<SUB>4</SUB> inclusion behaviors in the hydrate cavities. Raman spectra indicated that CH<SUB>4</SUB> can be captured in both small and large cavities of structure II hydrate in the C<SUB>3</SUB>H<SUB>3</SUB>NO with 34H<SUB>2</SUB>O system, while CH<SUB>4</SUB> can be entrapped in only small cavities of structure II hydrate in the C<SUB>3</SUB>H<SUB>3</SUB>NO with 17H<SUB>2</SUB>O system. The PXRD result showed both clathrate hydrate samples exhibit the same cubic <I>Fd3m</I> structure II hydrate as expected. However, the structure II hydrate in the C<SUB>3</SUB>H<SUB>3</SUB>NO with 34H<SUB>2</SUB>O system includes a small amount of hexagonal ice and structure I CH<SUB>4</SUB> hydrate. The phase equilibrium conditions of the binary (isoxazole + CH<SUB>4</SUB>) clathrate hydrate were also identified through high-pressure micro differential scanning calorimetry (MicroDSC), and the equilibrium temperatures of the binary (isoxazole + CH<SUB>4</SUB>) clathrate hydrate at given pressures are higher than those of the structure I CH<SUB>4</SUB> hydrate.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jceaax/2015/jceaax.2015.60.issue-2/je500568f/production/images/medium/je-2014-00568f_0008.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/je500568f'>ACS Electronic Supporting Info</A></P>
Hydrophobic Particle Effects on Hydrate Crystal Growth at the Water-Oil Interface
Cha, Minjun,Baek, Seungjun,Morris, Jeffrey,Lee, Jae W. Wiley (John WileySons) 2014 Chemistry - An Asian Journal Vol.9 No.1
<P>This study introduced hydrophobic silica nanoparticles (SiNPs) into an interface of aqueous and hydrate-forming oil phases and analyzed the inhibition of hydrate crystal growth after seeding the hydrate slurry. The hydrate inhibition performance was quantitatively identified by micro-differential scanning calorimetry (micro-DSC) experiments. Through the addition of 1.0 wt% of SiNPs into the water-oil interface, the hydrate crystal growth only occurred around the seeding position of cyclopentane (CP) hydrate slurry, and the growth of hydrate crystals was retarded. Upon a further increase in the SiNP concentration up to 2.0 wt%, the SiNP-laden interface completely prevented hydrate growth. We observed a hollow conical shape of hydrate crystals with 0.0 and 1.0 wt% of SiNPs, respectively, but the size and shape of the conical crystals was shrunken at 1.0 wt% of silica nanoparticles. However, the conical shape did not appear with an increased nanoparticle concentration of 2 wt%. These findings can provide insight into hydrate inhibition in oil and gas delivery lines, possibly with nanoparticles.</P>
Cha, Minjun,Lee, Huen,Lee, Jae W. American Chemical Society 2013 JOURNAL OF PHYSICAL CHEMISTRY C - Vol.117 No.45
<P>Two kinds of heterocyclic organic compounds, a five-membered ring with the chemical formula of C<SUB>4</SUB>H<SUB>4</SUB>NH (pyrrole, PRL) and a six-membered ring with the chemical formula of C<SUB>5</SUB>H<SUB>5</SUB>N (pyridine, PRD), are introduced into clathrate hydrate structures as a coguest with methane (CH<SUB>4</SUB>) gas. The results from powder X-ray diffraction of the binary (pyrrole + CH<SUB>4</SUB>) and (pyridine + CH<SUB>4</SUB>) clathrate hydrates showed that the lattice size of the former is smaller than that of the latter but the crystal structure of both binary hydrates is identified as a cubic <I>Fd</I>3<I>m</I> structure II hydrate. Raman spectroscopy also provided the clear evidence of CH<SUB>4</SUB> and each aromatic ring compound occupying in the small and large cavities of structure II hydrates. The thermodynamic behaviors of the two binary systems were compared with those of the pure methane system to identify the role of the two aromatic compounds in the clathrate hydrate system by using high-pressure micro-differential scanning microcalorimetry. It is striking that the two heterocyclic compounds containing a part of hydrate inhibiting functional groups have a promoting effect on the hydrate formation of the methane–water system.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpccck/2013/jpccck.2013.117.issue-45/jp4076564/production/images/medium/jp-2013-076564_0008.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/jp4076564'>ACS Electronic Supporting Info</A></P>
Superoxide Ions Entrapped in Water Cages of Ionic Clathrate Hydrates
Cha, Minjun,Shin, Kyuchul,Kwon, Minchul,Koh, Dong-Yeun,Sung, Boram,Lee, Huen American Chemical Society 2010 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.132 No.11
<P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jacsat/2010/jacsat.2010.132.issue-11/ja1004762/production/images/medium/ja-2010-004762_0005.gif'> <P>In the present work, we first described the stable entrapment of the superoxide ions in γ-irradiated (Me<SUB>4</SUB>NOH + O<SUB>2</SUB>) clathrate hydrate. Owing to peculiar direct guest−guest ionic interaction, the lattice structure of γ-irradiated (Me<SUB>4</SUB>NOH + O<SUB>2</SUB>) clathrate hydrate shows significant change of lattice contraction behavior even at relatively high temperature (120 K). Such findings are expected to provide useful information for a better understanding of unrevealed nature (such as icy nanoreactor concept, ice-based functional material synthesis and lattice tuning by specific ionic guests) of clathrate hydrate fields.</P></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ja1004762'>ACS Electronic Supporting Info</A></P>
Cha, Minjun,Shin, Kyuchul,Lee, Huen,Moudrakovski, Igor L.,Ripmeester, John A.,Seo, Yutaek American Chemical Society 2015 Environmental science & technology Vol.49 No.3
<P>In this study, the kinetics of methane replacement with carbon dioxide and nitrogen gas in methane gas hydrate prepared in porous silica gel matrices has been studied by in situ H-1 and C-13 NMR spectroscopy. The replacement process was monitored by in situ H-1 NMR spectra, where about 42 mol % of the methane in the hydrate cages was replaced in 65 h. Large amounts of free water were not observed during the replacement process, indicating a spontaneous replacement reaction upon exposing methane hydrate to carbon dioxide and nitrogen gas mixture. From in situ C-13 NMR spectra, we confirmed that the replacement ratio was slightly higher in small cages, but due to the composition of structure I hydrate, the amount of methane evolved from the large cages was larger than that of the small cages. Compositional analysis of vapor and hydrate phases was also carried out after the replacement reaction ceased. Notably, the composition changes in hydrate phases after the replacement reaction would be affected by the difference in the chemical potential between the vapor phase and hydrate surface rather than a pore size effect. These results suggest that the replacement technique provides methane recovery as well as stabilization of the resulting carbon dioxide hydrate phase without melting.</P>
Cha, Minjun,Kwon, Minchul,Youn, Yeobum,Shin, Kyuchul,Lee, Huen American Chemical Society 2012 Journal of chemical and engineering data Vol.57 No.4
<P>In this study, we introduce a new structure-II hydrate former, 2-methylpropane-2-peroxol (tert-butyl hydroperoxide, TBHP), and identify the structure and guest distributions through spectroscopic tools including high-resolution powder diffraction (HRPD), C-13 solid-state NMR, and Raman spectroscopy. Here, the (H + L + V) phase equilibrium data of (TBHP + X) hydrates (X = CH4, N-2, and O-2) were measured at (3.3 to 7.56) MPa and (282.2 to 288.5) K for CH4, (4.0 to 8.5) MPa and (271.6 to 277.5) K for N-2, and (4.0 to 8.6) MPa and (273.8 to 279.6) K for O-2. The (TBHP + X) hydrate phase equilibria showed that the addition of TBHP increased the structural stability with lower hydrate dissociation pressures when compared with those of pure CH4, N-2, and O-2 hydrates. However, we noticed that the TBHP did not promote hydrate formation conditions as effectively as tetrahydrofuran.</P>