Visualization
experiments using one-dimensional (1-D) porous media
made of Plexiglas and two-dimensional glass porous networks were conducted
to obtain qualitative and quantitative information concerning the
precipitation and crystal growth of CaCO3 under varying
flow and concentration conditions. Supersaturated solutions were prepared
by mixing sodium bicarbonate and calcium chloride solutions before
the pore networks. Nucleation and crystal growth were assumed to occur
within the porous media. Changes in the initial and final solution
composition were monitored. At low initial supersaturation values
(SRinitial), a few crystals were observed within the flow
channels and crystal growth took place exclusively on the newly formed
crystals. As the SRinitial increased, more crystals were
formed along the flow channels and new crystallites were continuously
formed during the course of the experiments. Nucleation and crystal
growth were not uniform. The crystal growth rates depended on the
initial value of SR and flow path inside the medium. Porosity for
the 2-D networks decreased when the SRinitial was high
or when calcite-cemented sand was used as substrate.
This paper reports a versatile microfluidic chip developed for on-chip crystallization of proteins through the dialysis method and in situ X-ray diffraction experiments.
The precipitation
and crystal growth of sparingly soluble salts
are associated with scaling problems in oil and gas extraction processes.
The presence of oleic phases and/or organic solvents added as inhibitors
of the gas hydrates often complicates scale formation problems. The
pore structure of the oil reservoir walls is of particular interest
in the process of scale formation. In the present work the effect
of the presence of n-dodecane in the crystallization
of CaCO3 was investigated. The study was done in simulated
one-dimensional porous media made of Plexiglas, in which supersaturated
solutions of various supersaturation ratios (SRinitial)
with respect to calcite were introduced. The growth of the precipitated
crystals was continuously monitored by optical microscopy and calcium
concentration monitoring. At high SRinitial values, larger
numbers of small size crystals were grown, mainly near the oil–water
interface. The presence of n-dodecane resulted in
the reduction of the induction time preceding the appearance of CaCO3 crystals. The measured precipitation rates of CaCO3 were higher with increasing SRinitial values. The presence
of n-dodecane in the supersaturated solutions, in
the respective two-phase system, favored the stabilization of the
thermodynamically less stable polymorphs of CaCO3 (aragonite,
vaterite). Mapping analysis of the deposits polymorphs using Raman
spectroscopy showed that the precipitation was not homogeneous along
the flow channel at the experimental conditions of the present work.
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