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. 2019 Aug 26;9(1):12345.
doi: 10.1038/s41598-019-48832-8.

Synthesis of Methane Hydrate from Ice Powder Accelerated by Doping Ethanol into Methane Gas

Yen-An Chen  1 , Liang-Kai Chu  1 , Che-Kang Chu  1 , Ryo Ohmura  2 , Li-Jen Chen  3   4
Affiliations

Synthesis of Methane Hydrate from Ice Powder Accelerated by Doping Ethanol into Methane Gas

Yen-An Chen et al. Sci Rep. .

Abstract

Clathrate hydrate is considered to be a potential medium for gas storage and transportation. Slow kinetics of hydrate formation is a hindrance to the commercialized process development of such applications. The kinetics of methane hydrate formation from the reaction of ice powder and methane gas doped with/without saturated ethanol vapor at constant pressure of 16.55 ± 0.20 MPa and constant temperature ranging from -15 to -1.0 °C were investigated. The methane hydrate formation can be dramatically accelerated by simply doping ethanol into methane gas with ultralow ethanol concentration (<94 ppm by mole fraction) in the gas phase. For ethanol-doped system 80.1% of ice powder were converted into methane hydrate after a reaction time of 4 h, while only 26.6% of ice powder was converted into methane hydrate after a reaction time of 24 h when pure methane gas was used. Furthermore, this trace amount of ethanol could also substantially suppress the self-preservation effect to enhance the dissociation rate of methane hydrate (operated at 1 atm and temperatures below the ice melting point). In other words, a trace amount of ethanol doped in methane gas can act as a kinetic promoter for both the methane hydrate formation and dissociation.

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Conflict of interest statement

The authors declare no competing interests.

Figures

Figure 1
Figure 1
Variation of temperature, pressure, and flow rate as a function time. (a) Variation of pressure, gas temperature and sample temperature in the reaction vessel as a function time for the system without ethanol. (b) Accumulated volume of gas released from hydrate dissociation in the system with 2 ml ethanol added, but not direct contact with ice powder, as a function of time in the dissociation stage. (c) Accumulated volume of gas released from hydrate dissociation in the system without additive (ethanol) as a function of time in the dissociation stage. Green dashed-dotted line, the sample temperature; brown dashed line, the gas temperature in the reaction vessel; and black solid line, the pressure in the reaction vessel; red line and blue line, accumulated volume of gas released from hydrate dissociation in system, respectively, without and with ethanol added.
Figure 2
Figure 2
Conversion ratio of methane hydrate from ice for reaction time of 24 h at different temperatures. Red triangle, the conversion ratio for the system without ethanol added; and blue square, the conversion ratio for the system with ethanol added. Blue and red dashed lines stand for the average values of the conversion ratio for the system, respectively, with and without ethanol added.
Figure 3
Figure 3
The relation between the mass fraction of gas released in the first hour of the dissociation process and the hydrate conversion ratio. Red filled triangles, the results without ethanol added in the system; blue filled squares, the results with ethanol added in the system; green open triangles, the results without ethanol added but with temperature ramping process to enhance the conversion ratio; violet open squares, the results with temperature ramping process and ethanol injected at one hour before dissociation process.
Figure 4
Figure 4
The conversion ratio of methane hydrate from ice under the condition of a fixed reaction temperature of −2.7 °C at different reaction (formation) times. Blue squares and red triangles stand for the hydrate conversion ratio for the systems, respectively, with and without ethanol added. Solid lines are guides of eyes.
Figure 5
Figure 5
Schematic of the reaction process of methane hydrate conversion from ice in the absence (upper row) and presence (lower row) of ethanol.
Figure 6
Figure 6
Raman spectrum of methane hydrates. (a) Black line indicates the binary ethanol-methane hydrate (sII) that formed by 8.6 wt% ethanol aqueous solution. (b) Blue line indicates methane hydrate (sI) formed by ice seed method with ethanol added but not direct contact to ice powder. (c) Red line indicates methane hydrate (sI) formed by ice seed method without ethanol added.
Figure 7
Figure 7
Schematic setup of the experimental apparatus for modified ice seed method. 1, methane gas cylinder; 2, reservoir vessel; 3, reaction vessel; 4, gas booster; 5, refrigerated circulator; 6, vacuum pump; 7, wet gas flow meter; 8, ethylene glycol aqueous solution bath; 9, high pressure syringe pump.
Figure 8
Figure 8
Photo of the ice powder sample container with its holder.
See this image and copyright information in PMC

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