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This work presents the effect of NaCl and NaClO4on the kinetics of methane enclathration with cyclopentane (CP) and sodium dodecyl sulfate (SDS) in a nonstirred batch reactor. Methane and 1 cm3of CP were charged sequentially to 150 cm3of solutions in a high-pressure vessel and the reaction system was cooled down to 274.6 K with an initial pressure of 7.1 MPa. Hydrates are visually observed within 1 h after the onset of cooling at a SDS concentration range of 0−200 ppm. At the end of a growth period of 2.5 h, the pressure reduces to 6.4 MPa for SDS concentrations below 20 ppm, whereas it decreases to 3.2 MPa for SDS concentrations above 50 ppm without any salts, which is very close to the hydrate equilibrium pressure. With 20 ppm SDS and 1 cm3of CP, the average enclathration rate maximizes at 1.0 mM NaCl or 5.0 mM NaClO4as the salt concentration increases from 0 to 100 mM. However, with 100 ppm SDS, it decreases monotonically with the increased salt concentration. These results not only provide an implication of reducing the SDS dosage (down to 50 ppm or less) in regard to fast enclathration but also further our understanding of the promoting role of surfactants. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents the phase equilibria of quaternary systems containing gas hydrates and proposes a staged-separation scheme based on the thermodynamic data. The phase equilibria of HLLV of quaternary systems are determined by using a high-pressure differential scanning calorimeter (DSC). The equilibrium dissociation pressures are dependent on the vapor composition and they shift to lower values with the increase in the mole fraction. The difference in the dissociation pressures between various fractions vanishes as the temperature approaches the melting point of CP hydrates at 0.1 MPa. The hydrate dissociation enthalpy is independent of vapor compositions and it is over the temperature range. Experimental data are compared to the calculated ones from John–Holder''s three-shell model. The prediction matches well with experimental data. The presence of CP reduces the operation pressure of a hydrate-based capturing process from the pre-combustion stream. Two equilibrium stages of hydrate crystallization and dissociation can enrich in the vapor-phase significantly from 0.4 of mole fraction to 0.98 at 282K. This thermodynamic analysis provides a conceptual design for developing a new process of pre-combustion capture in IGCC plants. [Copyright &y& Elsevier]

The effect of sodium dodecyl sulfate (SDS), cetyl trimethylammonium bromide (CTAB), and fatty alcohol EO/PO derivative (LS54) on unsteady-state CO2absorption in the metastable region of CO2hydrates and CO2enclathration with cyclopentane (CP) was investigated in an unstirred batch reactor. These surfactants have no measurable effect on the mass transfer of CO2across the gas−liquid interface into water. However, they retard CO2enclathration, and this inhibition effect becomes significant at 200 ppm of SDS and 100 ppm of LS54 or CTAB. A layer of clathrate hydrates is visually observed if charging CO2and CP sequentially. Even though this layer cannot be macroscopically detected when swapping the order of CO2and CP charge, the existence of this layer can be inferred from the unchanged pressure profile. This layer prevents CO2from contacting with water and thus delays CO2enclathration. The habit of clathrate hydrates growing along the reactor wall without agitation is discussed based on the magnitude of temperature spikes at the initial stage of the enclathration. [ABSTRACT FROM AUTHOR]