Román-Ramírez Luis A, McKeown Paul, Jones Matthew D, Wood Joseph
School of Chemical Engineering, University of Birmingham, Edgbaston, Birmingham B15 2TT, U.K.
Department of Chemistry, University of Bath, Claverton Down, Bath BA2 7AY, U.K.
ACS Omega. 2020 Mar 4;5(10):5556-5564. doi: 10.1021/acsomega.0c00291. eCollection 2020 Mar 17.
The kinetics of the transesterification of polylactic acid (PLA) with methanol to form methyl lactate catalyzed by Zn(II) complexes was studied experimentally and numerically. The complexes, Zn( ) and Zn( ), were synthesized from ethylenediamine and propylenediamine Schiff bases, respectively. The temperature range covered was 313.2-383.2 K. An increase in the reaction rate with the increase in temperature was observed for the Zn( )-catalyzed reaction. The temperature relationship of the rate coefficients can be explained by a linear Arrhenius dependency with constant activation energy. The kinetics of Zn( ), on the other hand, is only explained by non-Arrhenius kinetics with convex variable activation energy, resulting in faster methyl lactate production rates at 323.2 and 343.2 K. The formation of a new catalyst species, likely through reaction with protic reagents, appears to promote the formation of intermediate complexes, resulting in the nonlinear behavior. Stirring speed induced the stability of the intermediate complexes. Contrary to Zn( ), Zn( ) was susceptible to the presence of air/moisture in solution. The kinetic parameters were obtained by fitting the experimental data to the mass and energy balance of a consecutive second step reversible reaction taking place in a jacketed stirred batch reactor. For the case of Zn( ), the activation energy was fitted to a four-parameter equation. The kinetic parameters presented in this work are valuable for the design of processes involving the chemical recycling of PLA into green solvents.
实验和数值研究了锌（II）配合物催化聚乳酸（PLA）与甲醇酯交换生成乳酸甲酯的动力学。这些配合物，即Zn( )和Zn( )，分别由乙二胺和丙二胺席夫碱合成。研究的温度范围为313.2 - 383.2 K。对于Zn( )催化的反应，观察到反应速率随温度升高而增加。速率系数与温度的关系可用具有恒定活化能的线性阿伦尼乌斯依赖关系来解释。另一方面，Zn( )的动力学仅能用具有凸形可变活化能的非阿伦尼乌斯动力学来解释，这导致在323.2 K和343.2 K时乳酸甲酯的生成速率更快。一种新的催化剂物种的形成，可能是通过与质子试剂反应，似乎促进了中间配合物的形成，从而导致非线性行为。搅拌速度影响中间配合物的稳定性。与Zn( )相反，Zn( )在溶液中易受空气/水分的影响。通过将实验数据拟合到夹套搅拌间歇反应器中发生的连续第二步可逆反应的质量和能量平衡来获得动力学参数。对于Zn( )的情况，活化能拟合到一个四参数方程。这项工作中给出的动力学参数对于涉及将PLA化学循环转化为绿色溶剂的工艺设计具有重要价值。
