Fig. 8 Study on the reuse of PILs-XSS catalyst. The reaction conditions
were as follows: catalyst PILs-XSS dosage 2.5 wt %, CO2pressure 1.5 MPa, reaction temperature 100 °C, reaction time 4 h,
methanol / PO molar ratio 3: 1, and ester exchange catalyst
Na2CO3 dosage 3 wt %.
3.4 Effect of Na2CO3 on conversion
For transesterification catalysts, the strength of the alkali determines
the efficiency of transesterification, but too strong an alkali will
lead to side reactions. For example, strong alkalis such as NaOH and KOH
cannot be used as transesterification catalysts in this study. They are
not only easily contaminated by CO2, but also can
directly react with methanol. Catalysts with relatively strong basicity
can only be used. Sodium methoxide is a strong base and does not react
with CO2 and methanol. The basicity is much stronger
than that of Na2CO3. Under the same
conditions, the transesterification catalyst is replaced by sodium
methoxide. The yield of DMC does not increase, but the conversion of PO
is reduced to 86.7 %. In this regard, we carried out the corresponding
research. After comparing several common transesterification catalysts,
we found that carbonate had a certain promoting effect on
CO2 and propylene oxide.
4. Conclusions
In summary, PILs-XSS/Na2CO3 has been
used as a catalyst for the one-pot synthesis of DMC from methanol,
propylene oxide, and carbon dioxide. The catalyst is synthesized by
suspension polymerization. The polymerization ionic liquid catalyst
PILs-XSS has a certain pore size, specific surface area, and certain
heat resistance by characterization.
The optimal reaction conditions were as follows: the dosage of PILs-XSS
was 2.5 wt %, the CO2 pressure was 1.5 MPa, the
reaction temperature was 100 °C, the reaction time was 4 h, the molar
ratio of methanol to propylene oxide (PO) was 3: 1, and the dosage of
cocatalyst Na2CO3 was 3 wt %. Under the
optimum conditions, the conversion of PO was up to 98.8 % and the yield
of DMC reached 53.7 %. In addition, the combined catalyst
PILs-Na2CO3 was easily recovered by
filtration in the reaction system. After five times of repeated use, the
activity and the shape of the catalyst were almost unchanged, which
meant that the catalyst had amazing mechanical strength. It has a
spherical shape and good repeatability, which is a special breakthrough
for the continuous production of DMC. This catalyst(PILs-XSS) is a
very promising catalyst in for CO2 development.