Gas treating solvents used in the separation of CO2 break down as a result of long exposure or repeated use because of side reactions with CO2, malady O2, SO2, dissolved metals and other contaminants. This process is called degradation and products formed as a result of degradation are termed degradation products. Formation of degradation products will eventually result in a loss of capacity and give rise to a number of operating problems including corrosion and foaming. In the case of severe degradation, the solvent will need to be replaced and the degraded solvent must be disposed of in an environmentally acceptable manner. This is why it is highly desirable to prevent or at the very least to minimize solvent degradation.
Although it is well known that amines undergo severe degradation in the presence of O2, this gas is usually not present in a typical natural gas stream. As such, there has been no practical incentive to study amine degradation caused by O2. Therefore, although a number of studies have been carried out on degradation of different solvents due to CO2, very limited information is available on solvent degradation with O2. However, since flue gases contain O2 and the desire to separate CO2 from flue gas streams is gaining momentum, there is an urgent need to develop a better understanding of degradation of gas treating solvents with O2. The main objective of conducting this type of study is to develop an understanding of the mechanism of degradation and use this knowledge to formulate a degradation prevention strategy. Degradation prevention becomes important since it implies that any suitable solvent can be used repeatedly without the economic and operational burden imposed by loss of CO2 removal capacity that occurs as a result of severe degradation. The strategy will be as follows:
- Identifying the degradation products.
- Determining the overall rate of degradation of single and mixed solvents in the presence of CO2 O2, SO2 and dissolved metals.
- Postulating reaction mechanisms for degradation of single and mixed solvents in the presence of CO2 and O2.
- Verifying the reaction mechanisms.
- Formulating degradation prevention strategies for single and mixed solvents.
The degradation prevention strategy will likely include the addition of other components aimed at minimizing degradation. It will also look at the role of the operation of the stripping column and other high temperature sections of a typical CO2 extraction plant in causing degradation. All the strategies developed at bench scale will be tested at pilot plant scale.