Introduction
Natural and refinery gases typically contain acid gases in concentrations ranging from a few parts per million to tens of volume percent The major acid gases are hydrogen sulfide (H2S) and carbon dioxide (CO2).
Because of the corrosivity of acid gases in the presence of water , the toxicity of H2S, and the lack of heating value of CO2, the gases must be purified prior to use. Aqueous solutions of alkanolamines react reversibly with acid gases and therefore are widely used to remove them.
The alkanolamines of primary significance include monoethanolamine (MEA), diethanolamine (DEA), methyldiethanolamine (MDEA) , di-2-propanolamine (DIPA), and diglycolamine (DGA). Although the acid gasamine reactions are reversible, irreversible reactions may also occur, resulting in products from which the amines are not easily recovered. This phenomenon is called amine degradation. Partially degraded DEA solutions usually contain ydroxyethyl oxazolidone (HEOD) , bis (hydroxyethy ) piperazine (BHEP), and tris-(hydroxyethyl) ethtlendiamine (THEED), together with small oncentrations of higher boiling compounds.
In addition to impurities resulting from acid gas induced amine degradation, industrial amine solutions frequently contain other contaminants such as suspended solids, dissolved hydrocarbons, sodium and chloride ions, iron sulfide, foaming agents and foam suppressants, corrosion inhibitors, and heat stable salts.
The latter are formed as a result of amine protonation by acids stronger than CO2 and H2S. The accumulation of contaminants in amine solutions creates major operational problems including foaming, fouling , corrosion , a reduction in active amine content, and an increase in solution viscosity.
To maintain process efficiency , the circulating amine solutions must be partially or completely replaced with fresh amines. The chemical and physical nature of the contaminants makes the development of purification schemes inherently difficult. Several techniques for the purification of degraded DEA solutions have been proposed and/or patented .
Most of them deal only with the removal of heat stable salts. Some preliminary work has also been reported on recovering DEA by reversing the degradation reactions. The purification technique, which has been the most successful so far, is distillation. Description
The contaminated amine feed solution is contacted and mixed thoroughly with the hot inert liquid in the distillation column in which the amine, water, and some of the volatile
degradation products are heated under vacuum conditions.
The feed/inter liquid ratio and temperature of the distillation column are set so that a portion of the inter liquid is also volatilized .
The entire solids content of the feed solution is precipitated in the distillation column.
The vapor leaving the column is condensed and enters the separator column.
The inert liquid and degradation products are separated from the amine and leave the distillation column at the bottom, whereas DEA, water , and small amounts of the inert compound pass overhead.
Since the solubility of the inert liquid in the amine solution is very small at the condenser temperature, it is easily separated.
The inert liquid is then recalculated.
These major process modifications lead, in principle, to a high degree of amine recovery and purity. Application Alkanolamines regeneration from contaminants specially degradation products. Removal of a part of heat stable salts from amines. Using regenerated amine in gas treating units. Decreasing of corrosion rate. Decreasing of foaming and plugging. Increasing of acid gases absorption .
Economics
Regeneration of amines and its reusing , corrosion rate decreasing , increasing of gas treating value causes increasing of incomes and decreasing of costs. Other
Saving of contaminants amines create difficult for environmental |
