Influence of Dissolved Metals on N-Nitrosamine Formation under Amine-based CO₂ Capture Conditions

Abstract

As the prime contender for postcombustion CO2 capture technology, amine-based scrubbing has to address the concerns over the formation of potentially carcinogenic N-nitrosamine byproducts from reactions between flue gas NOx and amine solvents. This bench-scale study evaluated the influence of dissolved metals on the potential to form total N-nitrosamines in the solvent within the absorber unit and upon a pressure-cooker treatment that mimics desorber conditions. Among six transition metals tested for the benchmark solvent monoethanolamine (MEA), dissolved Cu promoted total N-nitrosamine formation in the absorber unit at concentrations permitted in drinking water, but not the desorber unit. The Cu effect increased with oxygen concentration. Variation of the amine structural characteristics (amine order, steric hindrance, -OH group substitution and alkyl chain length) indicated that Cu promotes N-nitrosamine formation from primary amines with hydroxyl or carboxyl groups (amino acids), but not from secondary amines, tertiary amines, sterically hindered primary amines, or amines without oxygenated groups. Ethylenediaminetetraacetate (EDTA) suppressed the Cu effect. The results suggested that the catalytic effect of Cu may be associated with the oxidative degradation of primary amines in the absorber unit, a process known to produce a wide spectrum of secondary amine products that are more readily nitrosatable than the pristine primary amines, and that can form stable N-nitrosamines. This study highlighted an intriguing linkage between amine degradation (operational cost) and N-nitrosamine formation (health hazards), all of which are challenges for commercial-scale CO2 capture technology.

Exploiting response surface methodology (RSM) as a novel approach for the optimization of carbon dioxide adsorption by dry sodium hydroxide

“…In this scheme, the flue gas, which is at 40–60 °C, passes through an absorber column and reacts with aqueous amine solutions. The CO 2 ‐loaded amine solution is drained from the absorber and transported to a stripper upon equilibrium, whereby the CO 2 is released at a higher temperature (>100 °C) . Despite being widely employed at the industrial scale, amine‐consumption‐based solvents such as monoethanolamine have their own limitations, such as the high energy required for sorbent regeneration, the potential of solvent degradation, and equipment corrosion .…”

“…Likewise, the separated CO 2 stream from the regeneration column is of high purity. Though the exact percentage is not stated, most adsorption processes deliver a stream with purity higher than 95% . This is pure enough for sequestration.…”

“…The CO 2 -loaded amine solution is drained from the absorber and transported to a stripper upon equilibrium, whereby the CO 2 is released at a higher temperature (>100 C). [11,12] Despite being widely employed at the industrial scale, amine-consumption-based solvents such as monoethanolamine have their own limitations, such as the high energy required for sorbent regeneration, the potential of solvent degradation, and equipment corrosion. [13] Furthermore, evaporation and amine loss to the ambient air is a great risk, as the atmospheric degradation of the amine-based solvents creates an extensive range of byproducts such as aldehydes, amides, nitrosamine, and nitramine, which are harmful to the environment.…”

“…Though the exact percentage is not stated, most adsorption processes deliver a stream with purity higher than 95%. [10][11][12][13][14][15][16][17][18] This is pure enough for sequestration. NaOH has been exploited as a sorbent to capture CO 2 from flue gas streams.…”

Surface tunable magnetic nano-sorbents for carbon dioxide sorption and separation

“…fossil fuel based power plants) has attracted broad consideration and attention from government, industry, and academia. [7][8][9][10][11][12] CCS consists of CO 2 capture and separation followed by compression, transport, and permanent storage in deep oceans and geological reservoirs either in the form of supercritical liquid or solidified carbonates. [5,11,13,14] Given the relative larger energy consumption for CO 2 capture and separation compared to the transport and storage of CO 2 , extensive research has been focused on developing new approaches to reduce the cost for CO 2 sorption and separation.…”