Reaction Intensification Study On Synthesis Of Cumene Over Structured Catalysts

Cumene (or isopropylbenzene) is an important starting material for the production of acetone and phenol. This work investigated the transfer and reaction performances and the energy consumptions for the alkylation reaction of benzene with propylene to cumene over structured catalysts using the combination the CFD simulation, Aspen Plus, Pro II, and experimental methods. Furthermore, the relation between geometric parameters and reactor performances (the pressure drop, mass transfer, heat transfer, propylene conversion, cumene selectivity, effectiveness factor, and so on) was identified using CFD models.Firstly, due to high energy consumption brought by high feeding molar ratio of benzene to propylene, an optimized process design has been developed and is presented. First, a side-stream was added to the DIPB distillation column to recover some triisopropylbenzene (TIPB), resulting in a decrease of the energy consumption per product. On the other hand, if the original fixed-bed reactor is replaced by a bubble-point reactor, the total heat duty on condensers and reboilers will decrease by18.5and22.8%, respectively. Then, a fixed-bed catalytic distillation (FCD) column was proposed for producing cumene. The improvement of FCD column was done by carrying out alkylation and transalkylation reactions simultaneously in a single column for producing cumene, with the result that investment of equipment for transalkylation is reduced and the process is simplified. Finally, with the combination of the improved DIPB column and FCD process, the heat duty was found to be the lowest.Secondly, two types of structured catalytic packings (i.e. BH-1and BH-2types) were involved, and the relationship between geometric configuration and performance of pressure drop and mass transfer coefficients for BH-1and BH-2types was identified by means of the combination of experiments and computational fluid dynamics (CFD). The results showed that under the same operating conditions pressure drops for BH-1and BH-2types were significantly lower than those for conventional fixed-bed reactor packed with pellet catalyst particles by one to three orders of magnitude. Two kinds of transition structures were proposed and the calculated results revealed that they were favorable when considering pressure drop and mass transfer coefficient together. Furthermore, it was found that a low ratio of packing height to diameter was favorable for increasing mass transfer coefficient, but leads to increasing pressure drop like common structured packings; a low area ratio of separation to reaction region for BH-1type would increase mass transfer coefficient and decrease pressure drop simultaneously.Thirdly, a three-dimensional (3D) mathematical model was established to determine the optimum operating conditions and to examine the reactor performance when traditional catalyst pellets were replaced with BH structured catalytic packings for benzene alkylation with propylene. It was found that the optimum operating conditions were the reaction temperature of160℃and the molar ratio of benzene to propylene in the feed of4.0. In this work, we also explored the relationship between the geometric configuration and the reactor performance. The momentum transfer (pressure drop), heat transfer (Nu number), mass transfer (Sh number), propylene conversion, cumene selectivity, and effectiveness factor were determined for different geometric configurations, which included changes in the corrugation angle, ratio of the packing height to the diameter, and ratio of the areas of the reaction and open-channel regions. Two new types of transition or wave-like structures (30-45-30°and45-30-45°), which resulted in a higher propylene conversion, cumene selectivity and effectiveness factor, were adopted. Furthermore, the applicability of this new technology for benzene alkylation with propylene was verified in a pilot plant.Finally, the transfer and reaction performances for benzene alkylation with propylene to produce cumene over monolith catalysts were investigated by means of the combination of experiments and computational fluid dynamics (CFDs). A three-dimensional (3D) mathematical model was established to identify the geometric configuration-performance relation so as to provide a comprehensive comparison of momentum transfer (pressure drop), heat transfer (Nu number), mass transfer (Sh number), and reaction performances (i.e. propylene conversion, cumene selectivity, and effectiveness factor) among monolith catalysts with five kinds of channel shapes (i.e. circle, hexagon, square, rectangle, and regular triangle). It was found that monolith catalyst exhibits the lower pressure drop, higher cumene selectivity and higher effectiveness factor; and regular triangle or rectangle channel is optimum when considering pressure drop and cumene selectivity together. Furthermore, the advantages of monolith catalyst can lead to the lowest energy consumption for the whole process.