Methane Hydrate Formation
A novel spiral-agitated reactor was
used, the schematic diagram of which is presented in Figure S1, and more
details can be found in our previous
publications24,35. The high-pressure reactor is
composed of a stainless-steel cylinder and a stirring rod, and the
effective volume of the reactor is 581.71 mL. The stirring rod is
equipped with screw blade, the pitch of which is 10 mm (see in Figure
S2). Two windows are set up at the reactor to observe inner hydrate
morphologies. The experimental temperature is acquired by a PT100
temperature transducer (± 0.1 K), while pressure is recorded by a BP801
pressure transducer (± 0.01 MPa). The reactor is supported by a bracket,
so the inclined angle of the spiral-agitated reactor can be adjusted.
All of the above devices are put in a thermostatic chamber. The consumed
methane is measured by a flow totalizer with an uncertainty of 0.01
mL/min, and the flow, pressure and temperature data are logged by a data
acquisition system every second.
Before hydrate formation experiments, the reactor was firstly adjusted
to a set inclined angle, and hydrate formation under three inclined
angles (25°, 35° or 45°) was evaluated in this work. Subsequently, the
reactor was washed with deionized water three times, the stirring was
turned on at a revolving speed of 60 rpm during cleaning, and then the
reactor was flushed with methane three times. 120 mL solution was
injected into the reactor, and the cooling system was turned on to
precool the solution and methane. When the temperature inner the reactor
reached the experimental temperature (275.15 K), methane was fed into
the reactor to a desired pressure, and then the stirring was turned on.
When
the
stirring rod was stuck by formed hydrates, the stirring was turned off,
and hydrate formation continues in a static system. Three trails were
performed at each experimental condition to ensure the repeatability.
Methane storage capacity was defined as the STP volume of methane stored
in per unit volume of hydrates, which can be calculated using Eq. (S1),
and the water-to-hydrate conversion was calculated using a hydration
number of 6.136.