Phase-Change Reversible Absorption of Hydrogen Sulfide by the Superbase 1,5-Diazabicyclo[4.3.0]non-5-ene in Organic Solvents

Abstract

Phase-change absorption has shown a promising application prospect for acid gas capture because only the gas-rich phase needs to be transported to the stripper for recovery, which could drastically reduce the energy consumption of the regeneration process. In this study, the liquid–liquid phase-change behavior of a new recyclable ternary system, composed of 1,5-diazabicyclo[4.3.0]­non-5-ene (DBN)/hexadecane/hexanol, was evaluated for capturing H2S. The absorption adduct was the [DBNH]+[SH]− salt, and the cause of the phase change was attributed to the polarity difference between the upper and lower phases. Furthermore, considering that only the lower phase needed to be heated for regeneration, the gravimetric absorption capacity was calculated to be 0.205 g H2S/g lower phase at 1 bar and 293.15 K. To the best of our knowledge, this is the largest gravimetric absorption capacity for H2S capture obtained to date. Additionally, when the absorption reached equilibrium, DBN, hexanol, and H2S were concentrated in the lower phase, while hexadecane mostly remained in the upper phase. The DBN/hexadecane/hexanol system showed that the benign desulfurization efficiency was nearly 100% under the condition that the molar ratio of H2S gas to DBN is not more than 0.6 mol/mol. The cyclic absorption experiments showed that the H2S gas could be easily released by bubbling N2 at 80 °C, which indicated the low energy requirement for the regeneration of the absorbent.

Exceptionally effective H2S absorption and conversion into thiols in novel superbase protic ionic liquids

“…As shown in Figure 4B, it is noteworthy that all chemical shifts from the protons on the cation [DBNH] + are shifted toward the lower field after the absorption of H 2 S. It is clear that the chemical shifts of the e, b, a, d, and f protons move from 1.64, 1.81, 2.25, 3.11, and 3.18 ppm to 1.90, 2.03, 2.84, 3.37, and 3.60 ppm, respectively. A possible explanation for this phenomenon is that the reaction with H 2 S results in a significant decrease in the electron density around the a, b, e, d, and f atoms 44 . Meanwhile, the chemical shift of h proton was found to move from 3.46 to 3.49 ppm after absorption of H 2 S (Figure S9).…”

“…It can be observed that the conversion of 1a only reaches 32% at 303.2 K catalyzed by TAPhOH (entry 7), which indicates that the tertiary amine group can promote the reaction. Under the same conditions, the DBN‐mediated conversion of 1a can also reach 84% (entry 8), the higher conversion is that DBN interacts with H 2 S gas to form [DBNH] + [SH] − adduct, 44 in which the affinity group SH − is very favorable for ring opening of 1a . These results suggested that the cationic DBN plays a key role for H 2 S absorption and conversion.…”

“…In addition, the active proton of H 2 S can be ionized in the presence of [TAPhO] − which is strongly basic, and [TAPhO] − will strongly interact with H 2 S containing the active proton by forming OH bond. The sharp and intense peak shows at 1612 cm −1 that is caused by the interaction of H 2 S with [DBNH] + 44 . This fact is due to the reason that after H 2 S interacts with [TAPhO] − to form new OH bond, and the active proton of [DBNH] + was excluded along with the formation of DBN and TAPhOH.…”

“…[DBNH] + . 44 This fact is due to the reason that after H 2 S interacts with 3.37, and 3.60 ppm, respectively. A possible explanation for this phenomenon is that the reaction with H 2 S results in a significant decrease in the electron density around the a, b, e, d, and f atoms.…”

New Solvents for CO2 and H2S Removal from Gaseous Streams

“…Only Heldebrant reported that the solution of dimethylethanolamine (DMEA) and hexane could achieve the liquid−liquid phase-change for H 2 S absorption. Recently, Xu and coworkers (2019) [93] studied the phase-change reversible absorption of hydrogen sulfide by the superbase 1,5-Diazabicyclo[4.3.0]non-5-ene (DBN) in organic solvents. This species has the highest gravimetric capacity for CO 2 capture among several amidine bases, according to the literature.…”