Surfactants are found to be good candidates in enhancing the rate of hydrate nucleation and growth. Anionic surfactants are the most effective in enhancing the rate of hydrate formation and/or reducing the induction time. Surfactants lower interfacial tension in presence of surfactants, which favorably affects hydrate formation rate by enhancing gas−water contact by efficient diffusion of hydrate forming gases to bulk water. Lower interfacial tension leading to significant change in the hydrate morphology resulting in catastrophic hydrate growth on the walls of the reactor. It has been suggested that this catastrophic growth of hydrates in the presence of surfactants is probably due to continuous availability of water at the interface due to a capillary-driven water supply. Formation of micelles in the presence of surfactants not only enhanced ethane solubility but the micelles themselves acted as nucleating sites for faster hydrate growth.

1. SURFACTANTS IN
PROMOTING GAS
HYDRATE
FORMATION
NAME:- PRERNA BS RAWAT
SAP ID:- 500087879

2. GAS HYDRATES
• Crystalline water based solids physically
resembling ice, gases are trapped inside
"cages" of hydrogen bonded,
frozen water molecules.
• Host molecule is water and guest
molecule is gas or liquid formed under
particular conditions of low temperature
and moderate to high pressure.
• Main reason of gas hydrate existence is
ability of water molecules to form a
lattice structure through
hydrogen bonding under suitable
conditions.
• Lattice structure is thermodynamically
unstable. Inclusion of nonpolar gas
molecules into hydrate structure makes
the structure stabilized; therefore,
hydrates can form at temperatures above
the freezing point of liquid water.
Kumar et al., 2015, Industry and engineering chemistry research

3. PROMOTORS OF GAS HYDRATE FORMATION
• Thermodynamic promoters shift
the three phase boundaries of
gas hydrate, liquid water and
gas, LHV, to the higher
temperature/lower
pressure while kinetic promoters
increase the hydrate formation
rate and normally the gas
uptake.
• In contrast to the
thermodynamic
promoters, kinetic promoters, as
a second type of promoters, do
not have any influence on
equilibrium conditions.
Promoters are special
chemicals which,
being added to water,
enhance the hydrate
formation process.
Depending on their
effects, promoters are
divided into:-
1]Thermodynamic
Promotors
2] Kinetic Promotors

4. SURFACE ACTIVE AGENTS (SURFACTANTS)
• Surfactants are compounds whose molecules contain both
lipophilic and hydrophilic moieties, they are amphiphilic
(exhibit affinity for both polar and nonpolar substances).
Lipophilic and hydrophilic groups characteristic of each
surfactant are property-determining factors.
• Surfactants can diffuse from bulk phase to an interface,
altering the surface or interfacial tension, modifying contact
angle between phases and wettability of solid surfaces, and
thus changing surface charge and surface viscosity. At
suitable concentrations, surfactant molecules in water
aggregate to form various kinds of structures called micelles
with diverse shapes and orientations.
Kumar et al., 2015, Industry and engineering chemistry research
Kumar et al., 2015, Industry
and engineering
chemistry research

5. Gemini Surfactants
• Gemini surfactants are a new and unique class of
surfactants; they are dimeric surfactants having
two hydrophilic head groups and two hydrophobic
tails. The hydrophilic head groups of the
surfactants are linked by a spacer group of varying
length.
• Gemini surfactants not only have lower CMC values
but also show lower surface tension at their
respective CMC values. Gemini surfactants have
also been studied as additives for hydrate
formation.
• The authors have reported enhanced kinetics for
methane hydrate formation in the presence of
these Gemini surfactants.
Kumar et al., 2015, Industry and engineering chemistry research​

6. MECHANISM OF ACTION OF DIFFERENT SURFACE ACTIVE
AGENTS ON GAS HYDRATE FORMATION
• In general it has been observed that surfactants with large hydrophobic
groups and large hydrophilic groups show lower interfacial tension
values than similar surfactants with lower molecular weights and with
the same balance of hydrophilic and lipophilic groups
• When a hydrophilic group is shifted to a more central position in the
chain, the CMC of the surfactant increases, which might have an impact
on the kinetics of hydrate formation and decomposition.
• Out of the three types of surfactants (anionic, cationic, and nonionic)
for CO2 hydrate formation kinetics; Anionic surfactant (SDS) was found
to be most effective in enhancing the rate of hydrate formation as well
as reducing the induction time. Nonionic surfactant (Tween-80) was
found to be better than the cationic surfactant DTACl.
• A few studies have quoted enhanced hydrate growth due to the
formation of micelles in the presence of surfactants. Formation of
micelles not only increases the solubility of hydrocarbon gas in the
aqueous phase but that it also acts as a nucleating site, inducing the
formation of hydrate crystals around the micelle in the bulk water
phase.

7. Krafft Temperature and CMC of Surfactants
• A sharp increase in the solubility of
surfactants occurs above a certain
temperature, which is a characteristic of each
compound. This temperature is termed the
Krafft point. The Krafft point is the minimum
temperature at which micelles can form.
• Nonionic surfactants do not exhibit a Krafft
point; their solubility decreases with
increasing temperature, and these surfactants
may begin to lose their surface active
properties above a transition temperature
referred to as the cloud point.
• A surfactant does not micellize at
temperatures below its Krafft point or below a
certain concentration known as the critical
micelle concentration (CMC).
• At the Krafft point, the solubility of the
surfactant is equal to its CMC.
• The Krafft point for SDS in water under
atmospheric pressure was found to be in the
range of 8−16 °C
Kumar et al., 2015, Industry and engineering chemistry research

8. Effect of Surfactants on Contact Angle, Interfacial
tension and adhesion energy.
Kumar et al., 2015, Industry and engineering chemistry research
• The wettability of a solid surface by a liquid is
determined by the contact angle θ. The contact angle is
measured through the liquid at the point where the
gas−liquid interface meets a solid surface.
• The wettability of a solid surface by a liquid is
determined by the contact angle θ. The contact angle is
measured through the liquid at the point where the
gas−liquid interface meets a solid surface.
• The addition of a surfactant decreases the surface
tension of liquid water, which also means lowering of the
contact angle.
Kumar et al., 2015, Industry and engineering chemistry research

9. Role of Surfactants on the Morphology of Gas Hydrate
Formation
Kumar et al., 2015, Industry and engineering chemistry research
Kumar et al., 2015, Industry and engineering chemistry research

10. Conclusion
• Surfactants are found to be good candidates in enhancing the rate of hydrate nucleation
and growth.
• Anionic surfactants are the most effective in enhancing the rate of hydrate formation
and/or reducing the induction time.
• Surfactants lower interfacial tension in presence of surfactants, which favorably affects
hydrate formation rate by enhancing gas−water contact by efficient diffusion of hydrate
forming gases to bulk water. Lower interfacial tension leading to significant change in the
hydrate morphology resulting in catastrophic hydrate growth on the walls of the reactor.
• It has been suggested that this catastrophic growth of hydrates in the presence of
surfactants is probably due to continuous availability of water at the interface due to a
capillary-driven water supply.
• Formation of micelles in the presence of surfactants not only enhanced ethane solubility
but the micelles themselves acted as nucleating sites for faster hydrate growth.

11. REFERENCES
• Sloan, E. D.; Koh, C. A. Clathrate hydrates of
natural gases, 3rd ed.; CRC Press: New York, USA,
2008
• Kumar A, Bhattacharjee G, Kulkarni B.D, Kumar
R., Role of Surfactants in Promoting Gas Hydrate
Formation; Industry and engineering
chemistry research,2015
• Mandal and Laik.; Effect of the Promoter on Gas
Hydrate Formation and Dissociation; Energy &
Fuels 2008, 22, 2527–2532; 2008