Thermodynamic and kinetic analysis of gas hydrates for desalination of saturated salinity water

Seo, Seong Deok,Hong, Sang Yeon,Sum, Amadeu K.,Lee, Kun-Hong,Lee, Ju Dong,Lee, Bo Ram Elsevier 2019 CHEMICAL ENGINEERING JOURNAL -LAUSANNE- Vol.370 No.-

<P><B>Abstract</B></P> <P>The shortage of fresh water is among the most serious issues in the world. A representative technology to overcome the problem is desalination, but most conventional methods (RO membrane or thermal distillation) have been focused on the treatment of relatively low salinity water, such as seawater or brackish water. To strengthen water security, in this study, we introduce a possibly economic technology for desalination of high salinity water (over-saturated concentration, in this study, a 30 wt% NaCl system) via gas hydrate formation by coupling LNG waste cold energy. First, the thermodynamic effects of NaCl on CH<SUB>4</SUB> (methane), SF<SUB>6</SUB> (sulfur hexafluoride), and HFC-134a hydrates were investigated. Based on the phase equilibrium of each hydrate, experimental pressures for kinetic experiments were selected under vapor pressure boundaries as follows: 4.5 MPa for CH<SUB>4</SUB>, 0.75 MPa for SF<SUB>6</SUB>, and 0.16 MPa for HFC-134a at 258.15 K (assuming the use of LNG waste cold energy). The results of the formation kinetics on the basis of gas moles consumed for hydrates showed the order CH<SUB>4</SUB> > HFC-134a > SF<SUB>6</SUB>; however, after considering the hydration numbers and structures for each hydrate, surprisingly, the conversion rate of water to gas hydrates showed the order HFC-134a > CH<SUB>4</SUB> > SF<SUB>6</SUB>, even though the experimental pressure condition for HFC-134a was very mild (0.16 MPa) compared to CH<SUB>4</SUB> (4.5 MPa). For this interesting phenomenon, we suggest a possible mechanism through visual observations during hydrate formation. We believe these thermodynamic, kinetic, and morphological results show potential as an alternative desalination technology, especially for saturated salinity water, with lower energy consumption.</P> <P><B>Highlight</B></P> <P> <UL> <LI> Thermodynamics and kinetics of gas hydrates were studied in saturated NaCl system. </LI> <LI> Using LNG waste cold energy was assumed for hydrate formation kinetics experiments. </LI> <LI> HFC-134a hydrates in saturated NaCl system formed at 0.16 MPa and 258.15 K. </LI> <LI> The kinetics of hydrates conversion showed the order HFC-134a > CH<SUB>4</SUB> > SF<SUB>6</SUB>. </LI> <LI> HBD process with HFC-134a is possibly economic in over-saturated salinity system. </LI> </UL> </P>

Gas hydrate formation from high concentration KCl brines at ultra-high pressures

Yue Hu,이건홍,이보람,Amadeu K. Sum 한국공업화학회 2017 Journal of Industrial and Engineering Chemistry Vol.50 No.-

The phase equilibria of methane hydrates were measured in high concentration KCl brines (up tosaturation concentration) at ultra-high pressures (up to 200 MPa). The results show the hydrateequilibrium boundary moves to lower temperature and higher pressure as the KCl concentrationincreased up to the saturation limit and the hydrate equilibrium is unchanged from the saturationconcentration for four-phase equilibrium. From the measurements at the saturation concentration, wealso determine the pressure effect on the solubility of KCl. The kinetic studies reveal hydrates form evenwith salt precipitated and hydrates and salt are competing solid precipitation under saturated conditions.

Quantification of the risk for hydrate formation during cool down in a dispersed oil-water system

곽계훈,이건홍,이보람,Amadeu K. Sum 한국화학공학회 2017 Korean Journal of Chemical Engineering Vol.34 No.7

Gas hydrates are considered a nuisance in the flow assurance of oil and gas production since they can block the flowlines, consequently leading to significant losses in production. Hydrate avoidance has been the traditional approach, but recently, hydrate management is gaining acceptance because the practice of hydrate avoidance has become more and more challenging. For better management of hydrate formation, we investigated the risk of hydrate formation based on the subcooling range in which hydrates form by associating low, medium, and high probability of formation for a gas+oil+water system. The results are based on batch experiments which were performed in an autoclave cell using a mixture gas (CH4 : C3H8=91.9 : 8.1mol%), total liquid volume (200 ml), mineral oil, watercut (30%), and mixing speed (300 rpm). From the measurements of survival curves showing the minimum subcooling required before hydrate can form and hydrate conversion rates for the initial 20 minutes, we developed a risk map for hydrate formation.

Insight into increased stability of methane hydrates at high pressure from phase equilibrium data and molecular structure

Hu, Yue,Lee, Bo Ram,Sum, Amadeu K. Elsevier 2017 Fluid phase equilibria Vol.450 No.-

<P><B>Abstract</B></P> <P>The methane hydrate dissociation conditions are measured at high pressures (up to 200 MPa) to fundamentally understand the hydrate properties. The results show an increased enthalpy of dissociation, from about 53 to 58 kJ/mol, as the hydrate equilibrium pressures transition from low (<80 MPa) to higher pressures (up to 200 MPa), indicating greater stability for the hydrates. Molecular simulations are used to understand and explain the increased stability with increasing pressure, by calculating the enthalpy and molecular structure of the phases.</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Phase equilibrium data of methane hydrates in mixed brine solutions

Hu, Yue,Lee, Bo Ram,Sum, Amadeu K. Elsevier 2017 Journal of natural gas science and engineering Vol.46 No.-

<P><B>Abstract</B></P> <P>Knowing the hydrate phase equilibria in brines is critically important to assess the risk of hydrate formation, especially for conditions involving high salinity and very high pressure, which are becoming more prevalent in oil/gas exploration and production. Hydrate phase equilibria data for mixed salt brines over a wide range of pressure is very limited in the open literature. Inorganic salts are thermodynamic hydrate inhibitors and are commonly present in produced water from oil/gas production. As such, this study reports methane hydrate phase equilibria in brines composed of mixed salts (NaCl, KCl, CaCl<SUB>2</SUB> and MgCl<SUB>2</SUB>) for total salt concentration up to 29.2 wt% and for pressures ranging from 20 to 200 MPa (2900 to 29,000 psia). Data under these conditions are the first reported and they add significant value in furthering knowledge of the phase space for hydrate formation. In addition, these data are used for the development and assessment of models to capture hydrate phase equilibria over a wide range of salt concentrations and pressures. At last, critical factors (such as pressure, salt species, and concentration) that influence the hydrate suppression temperature relative to the uninhibited (salt-free) systems are also investigated.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Methane hydrate phase equilibria in mixed salt brines were measured up to 200 MPa. </LI> <LI> Measured data were compared with predicted results from commonly used tools. </LI> <LI> Data provided information on the hydrate suppression temperature dependence on pressure. </LI> </UL> </P>

Research on Gas Hydrates in Flow Assurance

Bo Ram Lee(이보람),Kun-Hong Lee(이건홍),Amadeu K. Sum 한국신재생에너지학회 2018 한국신재생에너지학회 학술대회논문집 Vol.2018 No.4

Molecular Behavior of SF₆+H₂ Structure II Hydrates

박다혜(Park, Da-Hye),이보람(Lee, Bo Ram),사정훈(Sa, Jeong-Hoon),이건홍(Lee, Kun-Hong),Sum, Amadeu K. 한국신재생에너지학회 2011 한국신재생에너지학회 학술대회논문집 Vol.2011 No.11

Sulfur hexafluoride (SF₆), one of the most potent greenhouse gases, is known as a hydrate former and has been studied at the high pressure up to 1.3 GPa with gas mixtures and with aqueous surfactant. Since we regard SF₆ as a potential promoter molecule that can stabilize hydrate structure more effectively compare to the other promoters, further investigation is required to verify the stabilizing ability of SF₆ in the hydrate structure. However, the insoluble nature of SF₆ in water or gases hinders fine scale analyses. This work discusses the data obtained by using molecular dynamics simulations of structure II (sII) clathrate hydrates containing SF₆ and H₂. The simulations were performed using the TIP4P/Ice model for water molecule and a previously reported SF₆ molecular model (optimized at the pure SF₆ single phase system (Olivet and Vega, 2007)), and a H₂ molecular model (adapted from the THF+H₂ hydrate system (Alavi et al., 2006)). The simulations are performed to observe the stability of SF₆ and H₂ in the sII clathrate hydrate system with varying temperature and pressure conditions and occupancies of SF₆ and H₂, which cannot be easily tuned experimentally. We observe that stability of H2 enclathrated in the hydrate structure more affected by the occupancy of SF₆ molecules and temperature than pressure, which ranges from 1 to 100 bar.

Gas hydrates phase equilibria for structure I and II hydrates with chloride salts at high salt concentrations and up to 200MPa

Hu, Yue,Makogon, Taras Y.,Karanjkar, Prasad,Lee, Kun-Hong,Lee, Bo Ram,Sum, Amadeu K. Elsevier 2018 The Journal of chemical thermodynamics Vol.117 No.-

<P><B>Abstract</B></P> <P>Gas hydrates phase equilibria for structure I and II hydrates with chloride salts (NaCl, CaCl<SUB>2</SUB>, KCl and MgCl<SUB>2</SUB>) were measured at high salt concentrations and up to 200MPa. The measured equilibrium data represent three-phase (Solution – Hydrate – Vapor) or four-phase (Solution – Hydrate – Salt precipitated – Vapor) equilibrium depending on the salt concentration. The hydrate phase boundary with salts was shifted to lower temperatures and higher pressures when the experimental system was below the salt saturation concentration, while the boundaries were unchanged at salt concentrations above saturation, corresponding to quadruple points. The experimental data were compared with hydrate equilibrium predictions calculated by commonly used predictive tools to assess the reliability of these tools for the brines and conditions considered. The comparison demonstrates that predictive tools exhibit large deviation to the measured data, especially at high pressures and high salinity conditions.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Gas hydrates phase equilibria with chloride salts were measured up to 200MPa. </LI> <LI> Predictions deviate from measured data at high salt concentration and high pressure. </LI> <LI> Measured data are valuable to test and improve hydrate predictive tools. </LI> </UL> </P>

Phase Behavior and Raman Spectroscopic Analysis for CH₄ and CH₄/C₃H₈ Hydrates Formed from NaCl Brine and Monoethylene Glycol Mixtures

Kwak, Gye-Hoon,Lee, Kun-Hong,Hong, Sang Yeon,Seo, Seong Deok,Lee, Ju Dong,Lee, Bo Ram,Sum, Amadeu K. American Chemical Society 2018 Journal of chemical and engineering data Vol.63 No.6

<P>We present pure CH<SUB>4</SUB> and CH<SUB>4</SUB>/C<SUB>3</SUB>H<SUB>8</SUB> mixed hydrate phase equilibria formed from a mixture of NaCl (10 wt %) and monoethylene glycol (MEG, 10 and 30 wt %) solutions. As expected for thermodynamic inhibitors, the mixture of salt and glycol causes the hydrate phase equilibrium boundary to shift to lower temperatures and higher pressures, and on increasing the MEG concentration, the hydrate stable region shifted more. The measured experimental data are also compared with a thermodynamic model recently developed, named the Hu-Lee-Sum correlation, showing that the data match well with the predictions. The experimental data were used to calculate the enthalpy of hydrate dissociation. The enthalpies of CH<SUB>4</SUB> hydrates in the mixture of 10 wt % NaCl brine and 10 or 30 wt % MEG were found to be ∼58.7 and 54.63 kJ/mol, respectively, corresponding to structure I hydrates, whereas for the CH<SUB>4</SUB>/C<SUB>3</SUB>H<SUB>8</SUB> (91.98:8.02 mol %) mixed gas system, the enthalpies of dissociation were found to be ∼101.10 kJ/mol (10 wt % NaCl + 10 wt % MEG) and 95.34 kJ/mol (10 wt % NaCl + 30 wt % MEG), confirming the mixed hydrates formed structure II. We also performed Raman analysis for CH<SUB>4</SUB> hydrates and CH<SUB>4</SUB>/C<SUB>3</SUB>H<SUB>8</SUB> mixed hydrates in the NaCl and MEG system and investigated their spectroscopic behavior and hydrate structure.</P> [FIG OMISSION]</BR>

Guest-Guest Interactions and Co-Occupation by Distinct Guests in the Metastable State of Clathrate Hydrates

Lee, Bo Ram,Sa, Jeong-Hoon,Hong, Sang Yeon,Lee, Ju Dong,Lee, Kun-Hong,Seo, Yongwon,Sum, Amadeu K. American Chemical Society 2019 The Journal of Physical Chemistry Part C Vol.123 No.6

<P>The current knowledge of guest-guest interactions and co-occupation in clathrate hydrates is exclusive for the same guests (H<SUB>2</SUB> or N<SUB>2</SUB>) at moderate pressure. Here, we introduce the unusual co-occupation of distinct guests in the metastable state of hydrates. With controlled hydrate fraction, particle size, and intensification of the sintering of SF<SUB>6</SUB> hydrate particles formed from water and SF<SUB>6</SUB> gas as a help gas, we observed an abnormal but unique synchronous behavior in Raman intensities of two guest molecules (SF<SUB>6</SUB> and N<SUB>2</SUB>/H<SUB>2</SUB>) in hydrates consistently and repeatedly; over time, the scattering intensity for the guests (i) increases, (ii) decreases, and (iii) finally reaches the stable level. Without a concentration change of SF<SUB>6</SUB>, this abnormal behavior must arise from the possible changes in the scattering cross section of the molecules, suggesting that N<SUB>2</SUB>/H<SUB>2</SUB> strongly interacts with SF<SUB>6</SUB> in the large cages, resulting in a possible co-occupation during the metastable transition. These observations on the metastability of gas hydrate attest the importance of the sintering effect as a barrier to prevent fast gas diffusion for reaching equilibrium, which could have significant implication in increasing overall gas storage in clathrate hydrates.</P> [FIG OMISSION]</BR>