Zeolite catalyst enables sustainable production of biodegradable plastic materials

Methyl methoxyacetate and methyl formate, two of the most important carbonyl‐containing chemicals, can be produced directly by zeolite‐catalyzed carbonylation and disproportionation of DMM, using a heterogeneous catalyst, and with near 100% selectivity for each process. Methyl methoxyacetate, the DMM carbonylation production, could be easily converted to glycolic acid, methyl glycolate and monoethylene glycol.

Glycolic acid and methyl glycolate are monomers for the production of degradable plastics, polyglycolic acid, which exhibit high tensile strength, impact resistance and excellent barrier properties. Polyglycolic acid could potentially be widely used in daily life, medical field and industrial production due to the increasing demand for environmental protection.

DMM carbonylation provides up to now the only non-metal-based and zeolite-catalyzed route for the production of methyl methoxyacetate. Revealing novel zeolite catalysts and deep recognition of the reaction mechanism play an important role for the development of DMM carbonylation.

Recently, Dr. Liang Qi and professor Zhongmin Liu (Dalian Institute of Chemical Physics, Chinese Academy of Sciences) published the use of the novel extra-large pore zeolite ZEO-1 in DMM carbonylation and disproportionation. ZEO-1 exhibited high DMM carbonylation activity, selectivity, stability and also excellent DMM disproportionation activity. The results were published in the Chinese Journal of Catalysis.

ZEO-1 exhibited higher DMM carbonylation selectivity and stability compared with FAU, which was considered as the best DMM carbonylation catalysts in the past. Kinetics experiments showed that the rate of MMAc formation exhibited a linear dependence on CO partial pressure but negative dependence on DMM partial pressure.

The rate of MF formation showed negative dependence on CO partial pressure but positive dependence on DMM partial pressure. These features indicated that DMM carbonylation and disproportionation are competitive reactions in zeolite ZEO-1 and influence 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 showed similar acyls peaks positions compared with FAU, indicating that ZEO-1 and FAU exhibited similar surface properties. The density of carbonylation acyls intermediate (1744 cm^-1) is comparable for FAU and ZEO-1 but the density of MMAc (1759 cm^-1) is much lower for ZEO-1.

IGA results also showed that n-pentane diffused faster in ZEO-1. Therefore, it could be deduced that ZEO-1 exhibits better diffusion properties and MMAc could diffuse out of ZEO-1 faster, enhancing reaction activity.

DMM carbonylation and disproportionation mechanisms over different sites in ZEO-1 were proposed based on reaction results, kinetics experiments and in-situ IR results at last. Active sites in the large cages comprised of 16×16 and 16×12 MRs intersections tended to promote DMM carbonylation highly selectively, while those in small cages comprised of 12×12 MRs intersections exhibited high DMM disproportionation activity.

The kinetic equations of the formation of MMAc and MF were also deduced. This work provides deep understanding of zeolite catalyzed DMM carbonylation and contributes to the development of novel and efficient catalysts.