Jiashu Liu,Shengnan Zhao,Song Song,Haifeng Cong,Wei Luo,Tong Ding,Ye Tian,Xingang Li
One-step lactide (LD) synthesis from lactic acid (LA) is a promising method for an economically viable polylactic acid (PLA) industry. However, this synthesis is based on a highly water-sensitive esterification reaction, and few studies focus on developing an efficient method to improve its activity by water removal from the reaction environment. Herein, we report a new strategy coupling salt-promoted toluene–water phase separation with heteroazeotropic distillation to enhance water removal to realize highly efficient LD synthesis. Different kinds of chloride salts (LiCl, NaCl, CsCl, MgCl2, and CaCl2) were selected to study their influence on the reaction. The highest yield of LD (84.7%) was obtained when CaCl2 was added, much higher than that of the salt-free reaction (72.3%). Hydrated Ca2+ cations with relatively large charge number and small radius can efficiently reduce the solubility of water in toluene due to their strong electrostatic force to attract more water molecules. Mechanism studies demonstrate that the increased yield of LD after adding CaCl2 was attributed to its significant inhibition of LD hydrolysis resulting from the deep water removal from the toluene solvent.
Song Jinbo,Jing Jieying,Zhang Jinpeng,Xu Yufeng,Li Wen-Ying
Alkaline metal salt-promoted MgO sorbents are effective for CO 2 capture, but they face challenges with decreased CO 2 capture performance and powder elutriation in practical applications, arising due to the loss of pore structures and poor mechanical strength of alkaline metal salt-promoted MgO sorbent powder. Herein, granulation technology was employed to resolve the above problem. The optimized alkaline metal salt-promoted MgO sorbent pellets exhibited a CO 2 capture capacity of 11.46 mmol·g −1 and a mechanical strength of 11.14 MPa. This mechanical strength was nearly three times greater than that of alkaline metal salt-promoted MgO sorbent pellets without granulation promoters. After 20 cycles, CO 2 capture capacity stabilized at 8.71 mmol·g −1 , while mechanical strength was maintained at 8.92 MPa. Through characterization, it was revealed that the pore structure generated by the pyrolysis of the granulation promoters notably increased the specific surface area, leading to high CO 2 capture capacity. Meanwhile, the strengthened mechanical strength of the alkaline metal salt-promoted MgO sorbent pellets was primarily due to the in situ formation of a γ -AlOOH sol-gel cluster skeleton. Thus, this study provides an effective technological pathway to enhance the performance of the alkaline metal salt-promoted MgO sorbent pellets for industrial applications.
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