Dimethylformamide Impurities as Propylene Polymerization Inhibitor

Joaquín Hernández-Fernández; Rafael González-Cuello; Rodrigo Ortega-Toro

doi:10.3390/polym15183806

Dimethylformamide Impurities as Propylene Polymerization Inhibitor

Polymers (Basel). 2023 Sep 18;15(18):3806. doi: 10.3390/polym15183806.

Authors

Joaquín Hernández-Fernández^{1

2

3}, Rafael González-Cuello⁴, Rodrigo Ortega-Toro⁴

Affiliations

¹ Chemistry Program, Department of Natural and Exact Sciences, San Pablo Campus, University of Cartagena, Cartagena 130015, Colombia.
² Chemical Engineering Program, School of Engineering, Universidad Tecnológica de Bolivar, Parque Industrial y Tecnológico Carlos Vélez Pombo, Km 1 Vía Turbaco, Turbaco 130001, Colombia.
³ Department of Natural and Exact Science, Universidad de la Costa, Barranquilla 30300, Colombia.
⁴ Food Packaging and Shelf-Life Research Group (FP&SL), Food Engineering Program, Universidad de Cartagena, Avenida del Consulado St. 30, Cartagena de Indias 130015, Colombia.

Abstract

This research study examined how the use of dimethylformamide (DMF) as an inhibitor affects the propylene polymerization process when using a Ziegler-Natta catalyst. Several experiments were carried out using TiCl₄/MgCl₂ as a catalyst, aluminum trialkyl as a cocatalyst, and different amounts of DMF. Then, we analyzed how DMF influences other aspects of the process, such as catalyst activity, molecular weight, and the number of branches in the polymer chains obtained, using experimental and computational methods. The results revealed that as the DMF/Ti ratio increases, the catalyst activity decreases. From a concentration of 5.11 ppm of DMF, a decrease in catalyst activity was observed, ranging from 45 TM/Kg to 44 TM/Kg. When the DMF concentration was increased to 40.23 ppm, the catalyst activity decreased to 43 TM/Kg, and with 75.32 ppm, it dropped even further to 39 TM/Kg. The highest concentration of DMF evaluated, 89.92 ppm, resulted in a catalyst productivity of 36.5 TM/Kg and lost productivity of 22%. In addition, significant changes in the polymer's melt flow index (MFI) were noted as the DMF concentration increased. When 89.92 ppm of DMF was added, the MFI loss was 75%, indicating a higher flowability of the polymer. In this study, it was found that dimethylformamide (DMF) exhibits a strong affinity for the titanium center of a Ziegler-Natta (ZN) catalyst, with an adsorption energy (E_ad) of approximately -46.157 kcal/mol, indicating a robust interaction. This affinity is significantly higher compared to propylene, which has an E_ad of approximately -5.2 kcal/mol. The study also revealed that the energy gap between the highest occupied molecular orbital (HOMO) of DMF and the lowest unoccupied molecular orbital (SOMO) of the Ziegler-Natta (ZN) catalyst is energetically favorable, with a value of approximately 0.311 eV.

Keywords: N,N-dimethylformamide (DMF); Ziegler–Natta catalyst; catalyst inhibition; density functional theory (DFT); melt flow index (MFI); molecular weight distribution (MW); polypropylene; productivity.

Grants and funding

This research received no external funding.