Hernández-Fernández Joaquín, González-Cuello Rafael, Ortega-Toro Rodrigo
Chemistry Program, Department of Natural and Exact Sciences, San Pablo Campus, University of Cartagena, Cartagena 130015, Colombia.
Chemical Engineering Program, School of Engineering, Universidad Tecnológica de Bolivar, Parque Industrial y Tecnológico Carlos Vélez Pombo, Km 1 Vía Turbaco, Turbaco 130001, Colombia.
Polymers (Basel). 2023 Sep 18;15(18):3806. doi: 10.3390/polym15183806.
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 TiCl/MgCl 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 () of approximately -46.157 kcal/mol, indicating a robust interaction. This affinity is significantly higher compared to propylene, which has an 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.
本研究考察了在使用齐格勒-纳塔催化剂时，将二甲基甲酰胺（DMF）用作抑制剂对丙烯聚合过程的影响。使用TiCl/MgCl作为催化剂、三烷基铝作为助催化剂以及不同量的DMF进行了若干实验。然后，我们运用实验和计算方法分析了DMF对该过程其他方面的影响，如催化剂活性、分子量以及所得聚合物链中的支链数量。结果表明，随着DMF/Ti比率的增加，催化剂活性降低。从DMF浓度为5.11 ppm开始，观察到催化剂活性下降，从45 TM/Kg降至44 TM/Kg。当DMF浓度增加到40.23 ppm时，催化剂活性降至43 TM/Kg，而在75.32 ppm时，进一步降至39 TM/Kg。所评估的最高DMF浓度89.92 ppm导致催化剂生产率为36.5 TM/Kg，生产率损失22%。此外，随着DMF浓度增加，聚合物的熔体流动指数（MFI）出现显著变化。添加89.92 ppm的DMF时，MFI损失为75%，表明聚合物具有更高的流动性。在本研究中发现，二甲基甲酰胺（DMF）对齐格勒-纳塔（ZN）催化剂的钛中心表现出很强的亲和力，吸附能（）约为-46.157 kcal/mol，表明存在强相互作用。与丙烯相比，这种亲和力明显更高，丙烯的吸附能约为-5.2 kcal/mol。该研究还表明，DMF的最高占据分子轨道（HOMO）与齐格勒-纳塔（ZN）催化剂的最低未占据分子轨道（SOMO）之间的能隙在能量上是有利的，值约为0.311 eV。
