76
3 Gas Hydrates
[72]. In other words, AAs do not work in a gas field that hardly produces oil (liquid
hydrocarbons).
The surface of clathrate hydrate particles is hydrophilic and most likely wet with
a quasi-liquid layer (QLL), as we will see in the next chapter. The presence of a
QLL would give rise to attractive capillary force between clathrate hydrate particles
in a continuous oil phase. Thus, it is necessary to render the surface forces between
clathrate hydrate particles strongly repulsive for these particles to remain dispersed
in an oil phase [77]. A common way to do so is to use amphiphilic molecules like
surfactants whose hydrophilic head groups adsorb to clathrate hydrate particles and
whose hydrophobic tails are exposed to the continuous oil phase. This configuration
provides steric repulsion between surfactant-coated clathrate hydrate particles in the
oil phase [77].
It tuned out that quaternary ammonium surfactants such as tetra-butyl-ammonium
bromide (TBAB) and tetra-pentyl-ammonium bromide (TPAB) are good AAs [72,
78, 79]. In particular, quaternary surfactants with two or three n-butyl, n-pentyl, or
iso-pentyl groups performed especially well as AAs. Unfortunately, these AAs are
toxic and have low biodegradability [72] and a search for an environmentally friendly
alternative has been ongoing.
3.3.4 Anti-freeze Proteins
Anti-freeze proteins prevent ice crystals from forming in fish that live in cold regions
by binding to the surface of ice nuclei. Given the similarities between ice and clathrate
hydrates, some proteins might bind to the surface of clathrate hydrate nuclei and
prevent clathrate hydrate crystals from forming [80–84]. This line of research is
ongoing; however, anti-freeze proteins have generally been found to be precious
and hence expensive, and fairly poor KHIs [72]. Compatibility issues with other
chemicals in pipelines such as scale inhibitors, corrosion inhibitors, or THIs pose
additional challenges to the use of anti-freeze proteins as clathrate hydrate inhibitors.
3.4 Tea Time Break: Similarities of Biological Systems
to the Flow Assurance Challenges of Oil and Natural
Gas Pipelines
Crystal growth is generally undesirable in human bodies (e.g., oxalic acid, bile stone,
gallstone, gout). The mechanism with which such harmful stones form in human
bodies remains unknown [85]. For example, urine is supersaturated with respect to
the components that form gallstones, but gallstones do not form in the bodies of
healthy people [86, 87]. This circumstance is eerily similar to the flow assurance
3 Gas Hydrates
[72]. In other words, AAs do not work in a gas field that hardly produces oil (liquid
hydrocarbons).
The surface of clathrate hydrate particles is hydrophilic and most likely wet with
a quasi-liquid layer (QLL), as we will see in the next chapter. The presence of a
QLL would give rise to attractive capillary force between clathrate hydrate particles
in a continuous oil phase. Thus, it is necessary to render the surface forces between
clathrate hydrate particles strongly repulsive for these particles to remain dispersed
in an oil phase [77]. A common way to do so is to use amphiphilic molecules like
surfactants whose hydrophilic head groups adsorb to clathrate hydrate particles and
whose hydrophobic tails are exposed to the continuous oil phase. This configuration
provides steric repulsion between surfactant-coated clathrate hydrate particles in the
oil phase [77].
It tuned out that quaternary ammonium surfactants such as tetra-butyl-ammonium
bromide (TBAB) and tetra-pentyl-ammonium bromide (TPAB) are good AAs [72,
78, 79]. In particular, quaternary surfactants with two or three n-butyl, n-pentyl, or
iso-pentyl groups performed especially well as AAs. Unfortunately, these AAs are
toxic and have low biodegradability [72] and a search for an environmentally friendly
alternative has been ongoing.
3.3.4 Anti-freeze Proteins
Anti-freeze proteins prevent ice crystals from forming in fish that live in cold regions
by binding to the surface of ice nuclei. Given the similarities between ice and clathrate
hydrates, some proteins might bind to the surface of clathrate hydrate nuclei and
prevent clathrate hydrate crystals from forming [80–84]. This line of research is
ongoing; however, anti-freeze proteins have generally been found to be precious
and hence expensive, and fairly poor KHIs [72]. Compatibility issues with other
chemicals in pipelines such as scale inhibitors, corrosion inhibitors, or THIs pose
additional challenges to the use of anti-freeze proteins as clathrate hydrate inhibitors.
3.4 Tea Time Break: Similarities of Biological Systems
to the Flow Assurance Challenges of Oil and Natural
Gas Pipelines
Crystal growth is generally undesirable in human bodies (e.g., oxalic acid, bile stone,
gallstone, gout). The mechanism with which such harmful stones form in human
bodies remains unknown [85]. For example, urine is supersaturated with respect to
the components that form gallstones, but gallstones do not form in the bodies of
healthy people [86, 87]. This circumstance is eerily similar to the flow assurance