Zeolite catalysts enable sustainable production of biodegradable plastic materials

The two most important carbonyl-containing chemicals, methylmethoxyacetic acid and methyl formation, can be directly produced using zeolite-catalyzed carbonylation and DMM imbalances, heterologous catalysts, with 100% selectivity for each process. Methylmethoxyacetate, a DMM carbonylated production, can be easily converted to glycolic acid, methylglycolic acid, and monoethylene glycol.

Glycolic acid and methylglycolic acid are monomers for the production of degradable plastics and polyglycolic acid, and exhibit high tensile strength, impact resistance and excellent barrier properties. Polyglycolic acid may be widely used in daily life, medical fields and industrial production due to increased demand for environmental protection.

DMM carbonylation provides the only non-metal base and zeolite catalyst route for the production of methylmethoxyacetic acid. The uncovering of new zeolite catalysts and deeper recognition of the reaction mechanism plays an important role in the development of DMM carbonylation.

Recently, Dr. Liang Qi and Professor Zhongmin Liu (Dalian Chemical Physics, Chinese Academy of Sciences) have announced the use of the very broad-pore zeolite ZeO-1 in the novel in the carbonylation and de-transparency of DMM. ZEO-1 showed high DMM carbonylation activity, selectivity, stability, and excellent DMM imbalance activity. The results were published in Catalyst Journal.

ZeO-1 showed higher DMM carbonylation selectivity and stability compared to FAU. It was considered the best DMM carbonylation catalyst in the past. Kinetic experiments showed that the rate of MMAC formation exhibits a linear dependence on partial pressure of the peculiar side, but a negative dependence on partial pressure of the DMM.

The rate of MF formation showed a negative dependence on partial CO pressure, but a positive dependence on partial DMM pressure. These features indicate that carbonylation and imbalance in DMM is a competitive reaction for the zeolite ZeO-1, which affects the kinetics of each reaction.

In-situ IR experiments were employed to observe the evolution of reaction intermediates. With the introduction of CO and DMM, ZEO-1 exhibited similar acyl peak positions compared to FAU, indicating that ZEO-1 and FAU exhibited similar surface properties. The density of the carbonylated acyl intermediate (1744 cm-1) is comparable for FAU and ZEO-1, whereas the density of MMAC (1759 cm-1) is much lower for ZeO-1.

The IgA results also showed that N-pentane diffusion was rapidly diffused in ZeO-1. Therefore, it can be speculated that ZeO-1 exhibits better diffusion properties, and MMAC can diffuse faster from ZEO-1 and increase the reaction activity.

The carbonylation and imbalance mechanisms of DMM at various sites in ZEO-1 were proposed based on reaction results, kinetic experiments, and in-existence IR results. The active sites in large cages consisting of 16×16 and 16×12 MRS intersections tended to highly selectively promote DMM carbonylation, whereas those in small cages consisting of 12×12 MRS intersections exhibited high DMM deformation activity.

The equations of motion for the formation of MMAC and MF were also estimated. This study provides a deeper understanding of zeolite-catalyzed DMM carbonylation and contributes to the development of novel and efficient catalysts.