C4’s to MTBE reactor
LPG absorber
Iso C
C
Lean MDEA
Sweet LPG
Demi water
Wash water column
MEROX
Sour LPG
Demi water BD
C
n C
Rich MDEA
Figure 2 Merox-based C3/C4 purification flow diagram
20
30
40
50
MDEA (wt%)
Amines can also impair emulsion behaviour in both the reaction and treating sections. For instance, in sulphu - ric-acid–catalysed alkylation, amines react with the sulphu - ric acid to form sulfonated compounds. Upon neutralisation with caustic, these compounds behave like surfactants, which can cause emulsion stability issues in the alkaline water wash. Similarly, in oxygenate production units such as MTBE/ETBE, amine contamination can accelerate the deactivation of acidic ion exchange resins used as catalysts, ultimately reducing unit performance. Over the years, mon - itoring of the resins consistently showed that amines were among the main causes of accelerated deactivation. Mercaptan removal challenges in gas and LPG Some refineries processing high mercaptan or high sulphur feedstocks may experience elevated SOx emissions even when H₂S removal meets specification. This occurs because MDEA has low reactivity towards mercaptans. Therefore, if the refinery must reduce SOx emissions or produce a cleaner fuel gas, solvent selection must account for mer - captan absorption performance, not just H₂S efficiency. In several cases, high mercaptan concentrations also degrade LPG quality (i.e., copper strip corrosion test), as downstream mercaptan removal units, such as Merox (mer - captan oxidation), may not be designed to handle such ele - vated levels. The situation is even more challenging when mercaptan removal relies solely on amine scrubbing, which is often insufficient under these conditions. Maximising mercaptan removal from LPG in the amine absorption sec - tion remains the most effective strategy even under normal operating conditions. Reducing the mercaptan content in the feed provides energy savings and operational benefits for the Merox unit (see Figure 2 ). In particular, a lower mercaptan level decreases the amount of air required for oxidation, as the necessary air injection rate must be adjusted according to changes in both feed rate and mercaptan concentration. In a few cases, achieving sufficiently low mercaptan levels can even enable the shutdown of the downstream oxidation unit, resulting in significant cost savings for the refinery. Carbonyl sulphide (COS) is generated in cracking pro - cesses and can be partially removed chemically with amines. MDEA has a low tendency to absorb COS. DEA
Figure 1 Solubility of MDEA in LPG
optimise efficiency across multiple performance dimen - sions discussed in this article. MEA (monoethanolamine), DGA (diglycolamine), and DIPA (diisopropanolamine) have largely disappeared from refinery applications because they require high energy and provide less efficient operations compared to MDEA-based systems. Refineries that still rely on these legacy technolo - gies, particularly MEA and DGA, are now very few. Amine system operating issues Many refineries operating MDEA in LPG-containing circuits experience solvent losses. A common mitigation strategy is lowering the amine concentration. While this reduces losses, it also decreases energy efficiency and can reduce absorption capacity (see Figure 1 ). Solvent losses are not only an economic concern; they can also create significant downstream processing issues. When cracked LPG contaminated with amines is routed to units such as those producing isobutene for alkylation feed or methyl tert-butyl ether (MTBE)/ethyl tert-butyl ether (ETBE), several problems may arise. In alkylation units, con - taminants like MDEA or DEA in the olefin feed can react with or dilute the acid catalyst. This leads to increased acid consumption, formation of undesirable byproducts, and, in some cases, higher polymer generation.
COS removal comparison
High
Average
Low
MDEA
DEA
UCARSOL
Figure 3 MDEA and DEA vs Ucarsol
44
PTQ Q4 2026
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