The bis(imino)pyridyl iron-based ethylene oligomerization catalysts have the advantages of mild reaction conditions, high activity and high selectivity to linear α -olefins. However, barriers, such as high polymer content in the product mixture and large methylaluminoxane (MAO) dosage, are still limitations for the development of these systems at the industrial scale. In this study, new cocatalysts are prepared by the reaction of alkylaluminums with urea and its derivatives, and successfully used to activate iron-based catalysts. It is found that the type and molar ratio of alkylaluminum and urea have significant influence on the performance of the cocatalysts. The activity of the preferred triisobutylaluminum/urea activated systems reaches more than 3.0 × 10 8 g (mol-Fe) −1 h −1 , and the polymer content can be controlled to be less than 2 wt.%. Notably, the catalytic system exhibits good high temperature stability, the activity can still reach 1.0 × 10 8 g (mol-Fe) −1 h −1 even at 120 °C. Further 1 H NMR studies show that alkylaluminum can react with the N H moieties of urea, forming complex alkylaluminum clusters, even aluminoxane-like structures. This study offers a promising family of cocatalysts, making it possible to simultaneously improve their performance and reduce their cost.
Mengbo Zhang,Yirong Feng,Linjin Lou,Haomiao Zhang,Jingdai Wang,Yongrong Yang
We present a flow strategy to characterize reaction enthalpy and showcase the application in synthesis of alkylaluminoxanes from the fast and exothermic alkylaluminum hydrolysis. Our platform mainly encompasses a three-dimensional printed micromixer and a tubular reactor in an adiabatic vacuum box, aided by a thermal imaging camera to record temperature profiles. The temperature increase at steady state is used to calculate the released heat, which is further decoupled to quantify the reaction enthalpy and enthalpy of mixing. We validate the concept with the classic neutralization reaction between sulfuric acid and sodium hydroxide, with less than 2% deviation from theoretical values. In application, we determine the exothermic reaction enthalpy and the endothermic enthalpy of mixing to be −143.13 and +7.66 kJ/mol for triisobutylaluminum hydrolysis and −164.63 and +5.03 kJ/mol for trimethylaluminum hydrolysis, respectively. The presented platform, on the one hand, yields new insights into the microreactor scale-up for alkylaluminoxane synthesis and, on the other hand, can be readily used to measure reaction enthalpies of other reactions.
Yanjiao Xu,Mengbo Zhang,Hengyu Zhong,Shuying Xie,Xuxin Zhu,Haomiao Zhang,Jingdai Wang,Yongrong Yang
We present a 3D-printed stackable miniature membrane reactor to handle gas–liquid-solid reactions effectively and showcase its application in the synthesis of alkylaluminoxanes. The combination of membrane dispersion and microreaction techniques allows for better process control of the ultrafast and highly exothermic reactions of alkylaluminums hydrolysis with pyrophoric reactants. Droplet generation experiments guide the optimization of the reactor structure and operating parameters, highlighting its ability to produce clustered microdroplets with a narrow size distribution and minimal energy consumption. Our visualized reactor design provides insights into the transient characteristics of alkylaluminoxanes formation, improving understanding of the complex chemistries and achieving room-temperature synthesis of highly active methylaluminoxane (MAO) and isobutylaluminoxane (IBAO) for ethylene polymerization. When scaled up, our compact and integrated five-layer stacked reactor demonstrates uniform flow distribution and consistent reaction performance among all layers, achieving an impressive production rate exceeding ten tons/year. Our work demonstrates a versatile membrane microreaction platform for the scalable and inherently safe production of highly reactive materials, offering a promising approach for other challenging chemical synthesis applications.
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