1. Introduction
The economically sustainable chemical model is an attractive trend to
develop the environmental-friendly chemical industry with high economic
benefits 1. Impurity such as hydrogen sulfide
(H2S) exists diffusely in energy gas and is recognized
as major contaminants that can reduce operation safety. In the related
research of H2S, scholars mainly focus on the removal of
acidic gas by the way of absorption 2-4,
adsorption5,6, and
membrane separation 7,8, etc. However, the utilization
of highly purified H2S separated from the
above-mentioned technology remains to be a tough issue. Conversion of
H2S into value-added organic compounds should be a
promising strategy, which usually requires chemical complexation to
activate H2S over a low energy barrier.
As a kind of novel green solvent, ionic liquids (ILs) have attracted
much attention due to their unique properties (negligible volatility,
high thermal stability, structural variation, and excellent affinity to
acidic gas, etc.). The research of ILs mainly focused on
catalytic
synthesis 9-14, energy 15-17,
solvents 18-22, materials 23-26,
etc. Protic ionic liquids (PILs) are a class of cost-effective ILs for
the removal of acidic gas, which can be easily prepared from simple
materials through the direct neutralization between the corresponding
acid and base. In addition to the application in absorption separation,
PILs can provide
hydrogen
bonding in the process of reaction to activate epoxide27.
After years of in-depth research in the field of H2S
capture by functionalized ILs 2-4,28-30, our group has
started to explore the resource utilization of H2S in a
green medium. We firstly reported the ILs and deep eutectic solvents
(DESs) mediated Claus process with excellent H2S
conversion under ambient conditions 30,31. This
finding pioneered a promising method for the capture and conversion of
H2S through green and sustainable mediums. Subsequently,
Wu et al. reported ILs-formulated solvents to promote Claus reaction32. Additionally,
[Bmim][FeCl4] has been tested as an alternative
medium for the oxidation of H2S to produce sulfur33. Notably, the above H2S conversion
target is bulk chemical sulfur. Recently, we disclosed a kind of
task-specific hydrophobic PILs for the efficient capture and conversion
of H2S into value-added mercaptan acids28. These studies demonstrate that ILs are promising
media for the capture and conversion of H2S.
Except for the conversion of H2S into sulfur or
mercaptan acids, is there some other way to reuse H2S?
As is well known,
H2S
can be activated by the tertiary amine group to split into nucleophilic
SH− group 28. The epoxide is
effortless to be ring-opening in presence of a nucleophilic group
because of its instability. It is believed that H2S can
react with epoxide mediated in tertiary amine-functionalized ILs.
To prove the argument above and screen another H2S
conversion way, we develop a novel, inexpensive, and environmentally
friendly H2S utilization process through the addition of
H2S and epoxide into mercaptan alcohols mediated in
tertiary amine-functionalized PILs without any metal or halogen additive
under mild condition (The chemical structure of PILs are presented inScheme 1 ). The effect of cation and anion, reaction
temperature, water content, and ILs loading were systematically studied.
Moreover, quantum chemistry calculation was utilized to calculate the
barriers of ring-opening reaction. Water extraction was employed to
reuse the catalysts. It is believed that this work could provide a
distinctive insight to convert H2S.
Scheme 1 . Chemical structures of the PILs.