Transcript terpconnect.umd.edu

Solvent for Absorption of H2S
from Natural Gas
CHBE446
Griffin Jayne
Jay Foreman
Zachary Alford
Mengesteab Adera
Introduction
Introduction
● Choosing a solvent
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Basic solubility rules
Think about ease of recovery
Potential reactions
Low vapor pressure to prevent loss
Natural Gas and its Components
● Primarily CH4, as well as a range of other
larger hydrocarbons.
● Nitrogen
● Carbon Dioxide
● Hydrogen Sulfide
● Oxygen
H2S in Natural Gas
● Why do we care?
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Highly corrosive
● What can we do with it?
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Convert to elemental sulfur (Claus)
● Toxicity
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Highly toxic, comparable to HCN or CO, causes
cellular respiration to cease.
H2S Removal
● Absorption Column
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Gas impurity is absorbed into a
solvent liquid at liquid-gas
phase interfaces
Regenerated through distillation
column to reuse solvent
http://www.sulzer.com/en//media/Media/Images/ProductsAndServices/Separatio
nTechnology/Distillation_and_Absorption/CT_191.jpg?
mw=690
Common Solvents for H2S Removal
● Monoethanolamine
● Diethanolamine
● Dimethylethanolamine
Monoethanolamine(MEA)
Monoethanolamine History
● Precursor ethylene oxide first developed in
the mid 1800s, followed by commercial
production in the 1930s
Monoethanolamine
● Several uses and applications
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Binding agent in dry cleaning and wool treatment
○ “Enhances performance characteristics” in paints
and polishes
○ Textile additive
○ Lubricants
○ Cutting oils
○ Pharmaceuticals
Monoethanolamine as an acidic gas scrubber
● Pros:
○ Particularly useful acidic gas scrubber
■ Weak alkaline gives great affinity for weak acids (CO2,
H2S)
■ Because weak alkaline, capable of regenerating the acid
○ Decently soluble within organic solvents
○ Completely water soluble
●
Cons:
○ Freezes before water (10.5 degrees Celsius)
○ Toxic/corrosive upon touch/inhalation with human skin and thus
has a 2-3 ppm exposure limit across many nations (US, UK,
Japan, Spain, Malaysia)
Di-methyl-ethanol-amine (DMEA)
Dimethylethanolamine(DMEA)
● Has a combined physical and chemical characteristics
of both alcohols and amines
● These properties enable it to be useful intermediates in
the synthesis of various target molecules
Source: http://www.indiamart.com/siddhichem/dimethyl-amino-ethanol.html
Applications
DMEA is widely used in diverse areas such as
● Synthesis of textile auxiliaries and corrosion
inhibitors
● Personal care products
● Pharmaceuticals
● Water treatments
● Natural gas treating (Sweetening)
DMEA
Physical and Chemical properties
● Physical State - clear liquid
● Boiling Point - 133 - 135 0C
● Solubility in Water - soluble (miscible in alcohol and
ether)
● Stability - stable under ordinary conditions
● Odor - ammoniacal
Source: http://www.indiamart.com/siddhichem/dimethyl-amino-ethanol.html
Sweetening
● A process of removing hydrogen sulfide (H2S) from natural gas that
contains significant amount of Sulfur (Sour gas).
● The sour gas runs through a tower containing DMEA solution which
has an affinity to hydrogen sulfur.
Source:http://www.che.com/chementator/A-lower-energy-approach-tonatural-gas-sweetening_7738.html
Sweetening Process Diagram
(Sweet Gas)
H2S
rich
(Sour Gas)
DMEA
Amine rich
Amine lean
Source: http://terpconnect.umd.edu/~nsw/chbe446/H2S/H2SRemoval.pdf
Advantages of using DMEA
● Holds onto hydrogen sulfide without the addition of water
● Nonpolar solvents (Eg:Alkanes) are added to effect the
rapid release of H2S at low temperature.
● Significant energy savings due to low temperature
requirement for regeneration
● Avoiding the need for heating in regeneration will avoid
thermal decomposition and lengthen the lifetime of DMEA
Source: http://www.sciencenewsline.com/articles/2011031213000006.html
Summary
Gas Sweetening
Sour Gas
Fresh Solvent
Sweet Gas
Used Solvent
MEA
DMEA
Which is Better?
Well, it depends...
Do you want to remove CO2?
Yes:
MEA
Much stronger affinity for CO2 than DMEA, so produced gas will contain much
less CO2.
This will result in a shorter reusable life, but could be worthwhile if the
specifications demand as little CO2 as possible.
If Not:
DMEA
Much weaker affinity for CO2 meaning very little will be removed from product
gas.
This results in longer reusable life.
DMEA also removes H2S slightly better than MEA.
Finally, recently emerging techniques allow DMEA to be recycled with much
reduced energy costs.
Conclusion
DMEA is easily the superior solvent.
However, while performing better in almost every category, DMEA is relatively poor at
removing CO2, meaning that in cases where CO2 absorption is absolutely necessary MEA
could prove to be the superior choice.