Removal of Carbon Dioxide from Natural Gas by Using Gas Hydration

Natural Gas is a vital component of the world's supply of energy. It is one of the
cleanest, safest, and most useful of all energy sources. Natural gas has many uses,
residentially, commercially and industrially.
Carbon dioxide is a corrosive and non-combustible gas present in natural gas. This
undesired gas must be removed from natural gas to a permissible level. Typical pipeline
quality states that the composition of carbon dioxide in the treated gas stream must not
be more than 2%. In Malaysia, Gas Malaysia set an even more stringent limit where the
level of carbon dioxide is further reduced to 1.83% maximum.
A typical content of 0-8% carbon dioxide can be removed by using commercially
available absorption or membrane method. However, with carbon dioxide content
increased to 50-80% in natural gas produced, the current equipments cannot purify this
much of carbon dioxide effectively. Therefore gas hydration is being studied by
mathematical method and simulation to see the possibility of applying this property of
gases to purify natural gas.
Hydrates are ice-like solids that form when a sufficient amount ofwater and a hydrate
former is present, and there is a right combination of temperature and pressure (hydrate
formation is favored by low temperature and high pressure). Hydrates are notorious for
forming at conditions where a solid would no otherwise be expected.
Methane and carbon dioxide clathrates occur naturally at temperature above freezing
point ofwater (up to 30°C) under pressure of0.1 MPa (~latm) to 100 MPa (~1000atm).
Different types of gases form hydrate at different ranges of temperature and pressure.
Gas hydrate can be converted back to gas and water easily by applying heat to the
hydrate solid. This property can be employed to the separation of carbon dioxide from
natural gas by either capturing carbon dioxide or methane in hydrate form if applicable.

The main objective of this study is to predict the separation of carbon dioxide from
methane using hydration method. The effect of associated parameters such as
temperature and pressure are also included.
PetronasSim 2.55.2, Excel and K-factor methods were used in this work to obtain
hydrate formation temperature and pressure, and phase equilibrium composition. The
results show that: As temperature increases, formation pressure increases; as carbon
content of gas mixture increase, formation pressure decreases; as water/gas ratio
increases, formation pressure increases; At low temperature more carbon dioxide form
hydrate as compared to methane; At low pressure region (associated with low
temperature) the higher the pressure the lower the concentration of carbon dioxide in
vapor phase or the more carbon dioxide form hydrate Temperature, pressure and gas
composition are main parameters governing the formation of gas hydrate; The lower is
the temperature the larger is the difference of concentration of carbon dioxide in hydrate
phase andin vapor phasewhich indicates a better separation;
The study shows that gas hydration has a bright future to be explored further to
transform the theory into designing equipments to separate carbon dioxide from natural
gas.