Abstract. The atmospheric chemistry of organic nitrogen compounds (ONCs) is of great importance for understanding the formation of carcinogenic nitrosamines, and ONC oxidation products might influence atmospheric aerosol particle formation and growth. Indole is a polyfunctional heterocyclic secondary amine with a global emission quantity almost equivalent to that of trimethylamine, the amine with the highest atmospheric emission. However, the atmospheric chemistry of indole remains unclear. Herein, the reactions of indole with ⚫OH and ⚫Cl, and subsequent reactions of resulting indole radicals with O2 under 200 ppt NO and 50 ppt HO2⚫ conditions, were investigated by a combination of quantum chemical calculations and kinetics modeling. The results indicate that ⚫OH addition is the dominant pathway for the reaction of ⚫OH with indole. However, both ⚫Cl addition and H abstraction are feasible for the corresponding reaction with ⚫Cl. All favorably formed indole radicals further react with O2 to produce peroxy radicals, which mainly react with NO and HO2⚫ to form organonitrates, alkoxy radicals and hydroperoxide products. Therefore, the oxidation mechanism of indole is distinct from that of previously reported amines, which primarily form highly oxidized multifunctional compounds, imines or carcinogenic nitrosamines. In addition, the peroxy radicals from the ⚫OH reaction can form N-(2-formylphenyl)formamide (C8H7NO2), for the first time providing evidence for the chemical identity of the C8H7NO2 mass peak observed in the ⚫OH + indole experiments. More importantly, this study is the first to demonstrate that despite forming radicals by abstracting an H atom at the N site, carcinogenic nitrosamines were not produced in the indole oxidation reaction.

Abstract. The atmospheric chemistry of organic nitrogen compounds (ONCs) is of great importance for understanding the formation of carcinogenic nitrosamines and ONC oxidation products might influence atmospheric aerosol particle formation and growth. Indole is a polyfunctional heterocyclic secondary amine with global emission quantity almost equivalent to that of trimethylamine, the amine with the highest atmospheric emission. However, the atmospheric chemistry of indole remains unclear. Herein, the reactions of indole with ·OH/·Cl, and subsequent reactions of resulting indole-radicals with O2 under 200 ppt NO and 50 ppt HO2· conditions, were investigated by a combination of quantum chemical calculations and kinetics modeling. The results indicate that ·OH addition is dominant pathway for the reaction of ·OH with indole. However, both ·Cl addition and H-abstraction are feasible for the corresponding reaction with ·Cl. All favorably formed indole-radicals further react with O2 to produce peroxy radicals, which mainly react with NO and HO2· to form organonitrates, alkoxy radicals and hydroperoxide products. Therefore, the oxidation mechanism of indole is distinct from that of previously reported amines, which primarily form highly oxidized multifunctional compounds, imines or carcinogenic nitrosamines. In addition, the peroxy radicals from the ·OH reaction can form N-(2-formylphenyl)formamide (C8H7NO2), for the first time providing evidence for the chemical identity of the C8H7NO2 mass peak observed in the ·OH + indole experiments. More importantly, this study is the first to demonstrate despite forming radicals by abstracting an H-atom at the N-site, carcinogenic nitrosamines were not produced in the indole oxidation reaction.

Exploring new solvents for efficient acid gas removal is one of the most attractive topics in industrial gas purification. Herein, using 2-tertiarybutylamino-2-ethoxyethanol as an absorbent in a packed column at atmospheric pressure was examined for selective absorption of H2S from mixed gas streams. In the present work, the acid gas load, H2S absorption selectivity, acid gas removal ratio, amine solution regeneration performance, and corrosion performance were investigated through evaluating experiments absorbing H2S and CO2 by using methyldiethanolamine and 2-tertiarybutylamino-2-ethoxyethanol. The experimental results illustrate that the H2S absorption selective factors were 3.88 and 15.81 by using 40% methyldiethanolamine and 40% 2-tertiarybutylamino-2-ethoxyethanol at 40 °C, respectively, showing that 2-tertiarybutylamino-2-ethoxyethanol is an efficient solvent for selective H2S removal, even better than methyldiethanolamine. Based on the consideration of cost, we added 5% TBEE to 35% MDEA to form a blended aqueous solvent. To our satisfaction, the blended amine solvent obtained a 99.79% H2S removal rate and a 22.68% CO2 co-absorption rate, while using the methyldiethanolamine alone achieved a 98.33% H2S removal rate and a 23.52% CO2 co-absorption rate; the blended solvent showed better H2S absorption efficiency and selectivity. Taken together, this work provides valuable information for a promising alkanolamine for acid gas removal, and the preliminary study has found that the aqueous blend of methyldiethanolamine and 2-tertiarybutylamino-2-ethoxyethanol is an efficient solvent for selective H2S removal, which not only extends the application field for sterically hindered amines, but also opens up new opportunities in blended solvent design.

In this contribution, the mechanism of carbonyl sulfide (COS) absorption by N‐methyldiethanolamine (MDEA) aqueous solution was explored via theoretical computations. Detailed reaction mechanisms were analyzed using density functional theory (DFT) calculations at the B3LYP‐D3 level of theory. In total, four different pathways for COS absorption by MDEA have been considered. The most favorable pathway for the removal of COS is a three‐step mechanism including the hydrolysis, proton transfer, and dissociation of CO2, and hydrolysis is the rate‐determining step. The mechanisms of the COS absorption by different amines were investigated, and the calculated results suggest that the total energy barrier for the COS absorption by MDEA is comparable to that by monoethanolamine (MEA), diethanolamine (DEA), and diisopropylamine (DIPA), indicating the COS absorption by all the four amines are feasible, while MDEA gives a better performance in terms of thermodynamics.

Contamination is a leading cause of corrosion, foaming, and amine-absorption capacity limitation, predominantly foaming. There is currently an urgent need to identify the sources of amine foaming and eliminate them or reduce their impacts. Gas chromatography–mass spectrometry (GC-MS) and a sample pretreatment method were developed to identify and quantify the organic contaminants. Linear hydrocarbons (C12–C22), long-chain carboxylic acids and esters, alcohol ethoxylates, and benzene derivatives were detected, characterized, and quantified in amine solutions. Furthermore, the effects of the contaminant concentrations on foaming behavior were also investigated by adding those contaminants. The results reveal that the main issue of foaming is due to the presence of unsaturated fatty acids and alcohol ethoxylates, even with a small amount of 10 ppm, whereas benzene derivatives like methylpyridine, quinoline, methyl naphthalene, benzyl alcohol, octahydroacridine, and linear hydrocarbons have little effect on amine foaming, even with an amount up to 2000 ppm. Therefore, it is necessary to monitor the existence and content of these surface-active contaminants.