Experimental Study On Catalytic Hydrogenation Of MDA To Prepare PACM Containing Lower Trans-trans Isomer

As for the industries of Polyurethane (PU) and Polyamines, bis(para-aminocyclohexyl)methane(PACM) is an important intermediate. In general, PACM could be synthesized by hydrogenating 4,4'-Methylene-dianiline (MDA) with catalyst in high temperature and pressure environment.In term of thermal properties of PACM, its stereo-isomers could be grouped into three categories: trans-trans, cis-trans, cis-cis. The properties and future uses of PACM and its derivatives are determined by the proportions of the three stereo-isomers. And it is difficult to produce pure stereoisomer or the ratio given PACM. In the industry, the products of PACM are named according to the percentage of tans-trans stereo-isomer. For example, the PACM containing 20% trans-trans isomer is named as PACM-20, which is mainly used to prepare the corresponding isocyanate, and analogously, the PACM with 50% trans-trans isomer is called as PACM-50, which is mainly used to prepare alicyclic polyamines.In the last decade, a promising prospect of alicyclic isocyanate, which is transparent and hurtless to the environment, begins to emerge, and the need of PACM-20 turns to be growing. And thus, the methods for steadily synthesizing PACM-20 become the key technology for producing PACM-20. Under this background, the thesis emphasizes on the studies and production of the catalysts which can be used to the catalytic hydrogenation of MDA to prepare PACM-20, and establishes the reliable process for the further industrial production of PACM-20. The detailed content and results were given as following:1. One kind of catalyst was prepared which could be used for the catalytic hydrogenation of MDA to prepare the target PACM-20. This catalyst mainly made up of Ruthenium and Rhodium with proper ratio, and its carrier was y-A12O3.2. The catalyst which was post-processed by LiOH is steadier than that without post-process.3. The most significant factor to the yield was the temperature, and the secondly important factor was the ratio between ruthenium and rhodium. The alteration of pressure and dosage of catalysts had the least effects on the yield.4. The reaction time has a remarkable effect on the content of trans-trans isomer. And prolonging the reaction time could lead to the increase of the content of trans-trans isomer.5. The efficient control of the reaction temperature and time were crucial to prepare the PACM containing low trans-trans isomer.6. The optimal reaction process derived by experiments was listed as following: 180 ,8.0Mpa, 2.5% catalytic dosage which was post-processed by alkali.7. Under the optimized reaction conditions, the improved catalyst could still meet the requirements of preparing PACM-20 after re-use three times and the yield of PACM could still reach 95%-97%.8. The reaction network for synthesizing PACM from MDA was proposed. Moreover, the key steps for control side reactions were pointed out, which could provide guidance for further optimization of the reaction process.