Methyl diethanolamine (MDEA)
One of the basic processes in natural gas processing is the separation of acid gases or gas sweetening. During this process, hydrogen sulfide and carbon dioxide and other acidic gases such as carbonyl sulfide, mercaptans and carbon sulfide are separated from natural gas.
In general, in the natural gas industry, the separation of hydrogen sulfide and carbon dioxide from natural gas during the sweetening process is of great importance. Reasons such as safety and environmental needs due to the high toxicity of hydrogen sulfide and the prevention of corrosion of pipelines and gas transmission, processing and distribution equipment have made the separation of hydrogen sulfide of special importance and necessity compared to the separation of carbon dioxide. Other acidic compounds should be given priority. Reasons why carbon dioxide emissions are important include:
- Prevention of corrosion of pipelines and gas transmission, processing and distribution equipment
- Prevent the reduction of the calorific value of natural gas
Usually the amount of hydrogen sulfide in the processed gas used in the pipeline or for sale should be less than 4 ppmv. In addition, the permissible range of carbon dioxide in the processed gas used in The pipeline is between 1 ppmv to 3 ppmv.
Many factors are effective in choosing the right process for gas sweetening, the most important of which are:
- Combined natural gas composition (especially the amount and type of hydrocarbon components)
- The amount and type of acidic gases in the gas (especially hydrogen sulfide and carbon dioxide)
- The amount of gas flow processed
- Temperature and pressure of available sour gas and sweet gas obtained
- Final specifications for processed gas,
- The amount of solvent loss and consequently compensatory solvent costs
- Utility peripherals required for the process
- The ability of the process to withstand changes in the amount and composition of feed
Figure (1) shows a simple diagram of the gas sweetening process :
Figure (1): Simple diagram of the gas sweetening process
MDEA has many advantages over other conventional amines, including:
- Low energy consumption required for regeneration
- Ability to selectively separate hydrogen sulfide in the presence of carbon dioxide
- Low corrosion
In recent decades, it has been widely used for gas sweetening in the world. But this amine also has an important drawback, and that is the low rate of reaction with carbon dioxide and therefore the low amount of carbon dioxide absorption by this solvent.
To solve this problem and use the benefits of this solvent, in recent years the use of amines based on MDEA, including formulated amines and amino mixtures has been expanded. These amines are added to MDEA, an activator, or an amine of the first or second type. Studies show that about 70% of the world’s liquefied natural gas units that were operational between 2000 and December 2010 have used these amines.