Gas Hydrates:
Alternative for Natural Gas in Future
ABSTRACT:
Gas Hydrates,
solid compounds between water and small molecules such as methane, are
attracting a great deal of attention, both in public media and as a research
topic. They are noted especially for there capacity for storing gas, ~ 160
volumes at STP for every volume of hydrate in a case of methane.
Gas hydrate, or
more generally, clathrate hydrates are consider to be the archetypal guest -
host system, and are also consider to be models for hydrophobic hydration.
World wide consumption of fuel is increasing day by day and the sources of
natural gas are limited. it is no secret that
the worlds production of
conventional fossil fuel will being to decline some time during next century At
that time some oil companies may go extent and might start referring to gas
hydrates. There is bright future for gas hydrates
INTRODUCTION:
Since a few decades it is known that considerable amounts of natural gas
are stored in naturally occurring gas hydrates fields sub-sea sediments on the
ocean floor and in permafrost regions. Due to finite resources of fossil fuels,
exploration of these gas hydrate fields for recovery of natural gas might be
desirable in the future.
Hydrates were 1st discovered by Humphrey Davy and Michael Faraday in
1811. Lot of work was conducted in France
Hydrates remains curiosity throughout the 19th Century for researchers were mainly interested
in what components form hydrates and what condition of pressure &
temperature.
The large storage potential of gas hydrates makes it attractive to use,
as alternative for natural gas, liquefying or compressing gas.
what
is gas hydrates?
Gas hydrates are ice-like minerals that form naturally at the low
temperature and high pressure in the deep sea and also in permafrost.
Hydrates can be formed in systems of water and small molecules. When the
small molecules are gaseous at ambient conditions we are speaking of gas
hydrates. These small molecules eg. Methane (CH4), Propane (C3H8), Carbon Dioxide (CO2), Nitrogen (N2) but also
Flueroform (CHF3)
are enclosed in cavities formed by the hydrogen bonded water molecules can
exist because of the enclosed molecules in the cavities, i.e. they stabilize
the whole structure. Wouldn't the small molecules be present and the conditions
be suitable (i.e. temp. < 00C) that the framework of hydrogen bonded water
molecules would prefer the conformation of ice, which is not able to
accommodate other molecules as a guest. Water is called 'host' & hydrate
former called 'guest' which enters the lattice and stabilizes it.
types
of gas HYDRATES:-
Hydrates are basically of three types, Type I, Type II & Type H. Each
has different No. of water and gas molecules. The ratio of water molecules to
gas molecules is called hydrate no. The amount of gas actually contained is
called the "Degree of Filling".
Type I:-
§ It is usually smaller molecules.
§ Type I hydrate formers include
1) Methane
2) Ethane
3) Carbon dioxide
4) Hydrogen Sulphide
§ Type I Hydrates are made up of 8
polyhedral cages of water molecules two small dodecahedral cages & six tetra
decahedral cages. These cages can hold only small gas molecules with molecular diameters
not exceeding 5.2 A0.
§ The Hydrate no is 5.75. These hydrates
contain 46 water molecules per 8 gas molecules. Thus we have a theoretical
composition of 8X46 H20. Where X is the guest molecules.
Type II:-
§ It is usually larger molecules.
§ Type II hydrate formers include
1) Propane
2) Isobutane
3) Nitrogen
§ Type II hydrates are made up of 24
polyhedral cages, 16 small dodecahedral & 8 large hexagonal decahedral.
They may contain gases with molecular dimensions from 5.9 to 6.9 A0.
§ These hydrates contain 136 water
molecules per 24 gas molecules. Thus we have a theoretical composition. 24 X
136 H2O.
§ The hydrate no. is 5.67
Type H :-
§ Type H hydrates are formed by larger
molecules but only in the presence of a smaller molecules, such as methane.
§ Type H hydrate formers include
1) 2-Methyl butane
2) Methyl cyclo pentane
3) Methyl Cyclo hexane
4) Cyclooctane
§ Type H hydrates is made up of six
polyhedral cages.
§ These hydrates contains 34 water
molecules per 6 gas molecules. Thus the hydrate no. is 5.67. They have a theoretical
composition X5Y.34H2O, Where X - Large molecule & Y - Small molecule.
formation
of gas HYDRATES:-
Hydrates are formed when -
§ A sufficient amount of water is
present
§ Gas hydrates exists where the water
depths exceed 300 to 500 meters.
§ The right combination of temp. &
Pressure.
§ The hydrate former gases are present.
There are two processes by which hydrates are formed, organic process and
gas venting.
Organic PROCESS:-
Organically most natural gas hydrates is formed from biogenic methane,
excreted by bacteria that eat organic matter that has been died into the ocean.
This type of hydrate is concentrated where there is a rapid accumulation of
organic matter and also where there is accumulation of sediments.
gas venting PROCESS:-
Hydrates are also form when faults permits natural gas or other gases to
migrate from deeper inside the earth's crust of the surface of the seabed at
places with appropriate temperature and pressure levels. Hydrates formed from
venting tend to have many gases mixed, in addition to Methane, along with
minerals and other compounds.
-
Hydrogen Sulphide
forms a hydrate at 10 C and 290 K Pa and Carbon dioxide forms a hydrate at 5 C
and 2230 K Pa.
-
Highly soluble
gases do not form hydrates. E.g. Ammonia & Hydrogen Chloride.
Hydrates
also forms in the pipeline of natural gas. These hydrates formation is
Hazardous for the crude oil industry & natural gas industry.
Hydrates deposits are found all over the world. Hydrates are
also found in gulf of Mexico. The conditions are good for gas hydrates off the
coast of India Andaman
Seas Arctic
including Siberia , the north slope of Alaska
condition
of FORMATION:-
Hydrates are formed when -
§ A sufficient amount of water is
present
§ Gas hydrates exists where the water
depths exceed 300 to 500 meters.
§ The right combination of temp. &
Pressure.
§ The hydrate former gases are present.
There are two processes by which hydrates are formed, organic process and
gas venting.
Organic PROCESS:-
Organically most natural gas hydrates is formed from biogenic methane,
excreted by bacteria that eat organic matter that has been died into the ocean.
This type of hydrate is concentrated where there is a rapid accumulation of
organic matter and also where there is accumulation of sediments.
gas venting PROCESS:-
Hydrates are also form when faults permits natural gas or other gases to
migrate from deeper inside the earth's crust of the surface of the seabed at
places with appropriate temperature and pressure levels. Hydrates formed from
venting tend to have many gases mixed, in addition to Methane, along with
minerals and other compounds.
-
Hydrogen Sulphide
forms a hydrate at 10 C and 290 K Pa and Carbon dioxide forms a hydrate at 5 C
and 2230 K Pa.
-
Highly soluble
gases do not form hydrates. e.g. Ammonia & Hydrogen Chloride.
Hydrates also forms in the pipeline of natural gas. These hydrates
formation is Hazardous for the crude oil industry & natural gas industry.
Hydrates deposit are found all over the world. Hydrates are
also found in gulf of Mexico. The conditions are good for gas hydrates off the
coast of India Andaman
Seas Arctic
including Siberia , the north slope of Alaska
properties
of gas HYDRATES:-
Properties Ice Hydrates
Dielectric
Constant at 273 K 94 58
Isothermal
Young's module at 268 K 9.5 8.4
Poisson's
ratio 0.33 0.33
Bulk
modulus (272 K) 8.8 5.6
Shear
modulus (272 K) 3.9 2.4
Bulk
density (gm/cm3) 0.916 0.912
Thermal
Conductivity at 263 K 2.23 0.49
burning ICE:-
Gas hydrates are ice like inclusion components that are regularly built
and can store large amounts of guest molecules. Albert they look like ice, gas
hydrates can exist at temperature higher than the freezing point of water and
elevated pressure, because of stabilization by the enclosed guest molecules
when these guest molecules are flammable the gas hydrates can be ignited and
you get burning ice.
future
PROSPECTS:-
Hydrate is a gas concentrator; the breakdown of a unit volume of Methane
hydrate at a pressure of one atmosphere produces 160 unit volumes of gas. The
worldwide amount of methane in gas hydrates is considered to contain at least
1x104 gigatons of carbon in very conservative
estimate. This is about twice amount of carbon held in all fossil fuels on
earth.
Gas hydrates are not yet produced in Industry from escaping gas. There is
a formidable obstacle to using hydrates as fuel. When removed from its high
pressure, low temperature environment hydrate decomposes and releases the
hydrocarbon gas contained in it. We don't yet have a way to safely transport
large amounts of hydrate to production facilities on land.
One new approach to the hydrate transportation is to inflate large
bladder like blimps with hydrate in deep sea. Submarines could then too the
hydrates to shallower water where they slowly decomposed to yield fuel &
water.
Perhaps chemical engineers could-design additives to make hydrates more
stable at lower pressure and higher temperature. If they can hydrate might
actually be safer to transport in conventional ships than liquified natural
gas.
effect
of hydrates on CLIMATE:-
Like Carbon dioxide, Methane is a common component of air. Most natural
occurrences of methane in atmosphere appears in such natural sources as swamps
and termites supplemented by agricultural and other man made sources like rice
paddies and Cow dung.
The heat absorbing gases like carbon dioxide and methane have been
identified as green house gases. Methane in the air is 10 times more effective
than carbon dioxide in absorbing the heat from the sun and thus warming the
earth's temperature which could bring about climate change.
Methane bound in hydrates is approximately 3000 times the volume of methane
in the atmosphere. If that were released into atmosphere, bring atmospheric
warming and result in climate change.
Hydrates may melt of either temperature increases or pressure decreases.
If the wide spread melting of hydrates occurs it can bring about climate
change. It might be occur during the earth's glacial periods because as
significant amount of the water ocean freeze and become slandered on land, the
drop in sea level could reduce the pressure on hydrates. The release of methane
might be speeded up.
Conversely during earth's warming cycles, ice melts and sea level rise,
creating more pressure on the sea floor over a wider area. And thus methane becomes
locked up in hydrates. Showing by the glacial cycle.
CONCLUSION:-
World wide consumption of fuels is increasing day by day. And the source
of natural gas is limited. It is no secret that the world's productions of
conventional fossil fuels will begin to decline sometime during the next
century. At that time some oil companies may go extent or might start referring
to gas hydrates. But before that happens the climatic effects of using hydrates
as a fuel must be studied thoroughly and it must be ensured that there are no
effects on the climate clearly. There is a bright future for gas hydrates.
REFERENCES:-
1.
Magazine:
Chemical Engg. World June 2003
2.
Chemistry for
environment Engg. by Sawyer, Parkin.
3.
Environmental
Chemistry by Jain & Jain
4.
www.gashydrates.org.com
5.
www.oceantamu.edu.com
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