Application of Rotating Packed Bed (RPB) Reactor in Production of MDA

Weiqi Hua^{1* ,} Jiangsheng Ding¹, Jian-Feng Chen²

 

1. R&D Center, Yantai Wanhua Polyureathanes Co. Ltd., Yantai, Shangndong 264003, P.R.China

2. Research Center of the Ministry of Education for High Gravity Engineering and Technology, College ofChemical Engineering, Beijing University of Chemical Technology, Beijing 100029, P.R. China 

MDA (Methylene diphenyl "Cdiamine) is the precursor of MDI (Methylene diphenyl -diisocyanate). Its production involves condensation of aniline with formaldehyde in the presence of hydrochloric acid to give oligomeric di- and polyamines that are phosgenated without further need of purification. A mixture of polymeric methylenephenylamines is prepared by condensing aniline with formaldehyde in the presence of HCl . The reaction usually is run with an excess of aniline at atmospheric pressure with condensation reactions The destination products are poly-amine which has normally yield level at ~96 %.

  

  And there are series of by-products such as N-methyl-phenyliamines, phenyli-acridines etc.. Because those by-products will react with phosgene to form ¡°acidities¡± and ¡°hydrolysable chlorides¡± in further phosgeantion process that will seriously degrade the application performance of MDI for polyurethanes synthesis, the way to depress those harmful components level is crucial to improve the product quality in the industry. It is known that the above reaction is controlled by the micromixing. At present industrial operation, either agitator or jet mixer is used to mix very active formaldehyde with the mixture of polyamines and aniline. The reactants mixtures standard viscosity range is about 40 to 80 centipoises, which inhibit the disperse and micromixing since the flow is always in transition state. To avoid any formaldehyde surplus in reaction system, the aldehyde feed will be usually divided into several streams and blended with large amine recycling loops sequentially to dilute as well as cool down system, which leads to high energy consumption and complexity of the whole process.     . The rotating packed bed (RPB) is a novel reactor that utilizes centrifugal acceleration to tremendously intensify the micromixing and mass-transfer processes, However, so far the industrial application for reaction process using RPB is still very few. Here, at the first time we  reported our pilot plant trial results using RPB reactor in the production of aniline/ formaldehyde condensation. We choose the traditional stirrer tank reactor as comparison.

In the Rotating Packed Bed (RPB), the rate of micromixing between liquid- liquid is 1-3 orders of magnitude large than that in a conventional reaction vessel. From the pilot trial result, we found, that the key index by-product level decreases near 5 folds than that in one stirring mixer, while the way of three stirring in series only can reduce the key impurity N-methyl-phenyliamine by 42.3% . This is contributed by the feature of RPB with greater dissipation rate and shorter characteristic micromixing time (around 0.1ms). Based on the pilot trial results, we believe that RPB reactor can be the novel choice for the system where requires intensive dispersion and mixing with relative high viscosity, and also its compact and easy for scaling up and operation nature will provide a ideal platform for the liquid (or gas)-liquid condensation and polymerization processes.

 

Acknowledgement

This work was supported by the National Hi-Tech R&D Project (863 Project), No.2006AA030203