469481 Carboxylation of Propylene Oxide to Propylene Carbonate in Slurry and Trickle Bed Reactors
Carboxylation of Propylene oxide to Propylene carbonate in slurry and trickle bed reactorS
Pallavi Bobba, Xin Jin, Bala Subramaniam and Raghunath V. Chaudhari
Center for Environmentally Beneficial Catalysis, Department of Chemical & Petroleum Engineering, University of Kansas,
1501 Wakarusa Dr., Lawrence, KS 66047
CO2 is naturally available carbon source and emitted from industrial processes, automobiles and petrochemical refineries. Catalytic conversion of CO2 to value added chemicals provides an alternative green, cheap and sustainable synthesis route for industrial chemicals, otherwise produced using toxic reagents such as phosgene. An important example is the carboxylation of propylene oxide (PO) to propylene carbonate (PC), a key intermediate for dimethyl carbonate and polycarbonates. These cyclic carbonates are widely used as aprotic solvents, antifoaming agents, antifreeze, plasticizers and monomer for various commodity polymers. Several studies are known on synthesis of cyclic carbonates by carboxylation of epoxides employing homogeneous and heterogeneous catalysts. Heterogeneous catalysts consisting of metal oxides, zeolites, polymer supported quaternary onium salts, ion exchange resins, and polymer supported ionic liquids have been studied with the goal of improving catalytic activity and selectivity. However, no efforts have been made to understand the intrinsic kinetics of carboxylation and the related reaction engineering studies. Here, we report an experimental study on (a) intrinsic kinetics of carboxylation of PO to PC using ion exchange resin catalyst in a batch slurry reactor, and (b) modeling of a trickle bed reactor with experimental validation.
The experiments for kinetic studies were carried out in a stirred pressure reactor with 100 cm3 capacity with provisions for control of agitation speed, temperature and sampling of liquids. In these experiments, the CO2 pressure in the reactor was kept constant by continuous supply through a CO2 reservoir using a constant pressure regulator such that the temporal reaction progress was followed from the pressure decrease in the reservoir. At the end of each experiment, liquid products were analyzed for PO and PC to assess the material balance. The effects of catalyst loading, PO concentration, pressure and temperature were studied as shown in Figures 1 and 2. Kinetic analysis of these data will be presented along with discrimination of rate models and estimation of rate parameters.
Figure 1. Effect of Concentration and Catalyst loading on CO2 consumption as a function of time at 368.15K and 1.4 MPa
Figure 2. Effect of Pressure at 368.15K and Temperature at .14 MPa on CO2 consumption.
For trickle bed experiments, a high-pressure trickle bed reactor of 2.5 cm diameter and 10 cm length was used with down flow of gas (pure CO2) and liquid (PO in PC) phase. The effect of gas and liquid velocity, inlet PO concentration and temperature was studied. Steady state conversion and selectivity were observed for different reaction conditions. The analysis of reactant/products was carried out using GC. Typical results showing the effect of liquid velocity on PO conversion are shown in Figure 3. Detailed mathematical model for the trickle bed reactor based on the kinetics determined in the slurry reactor will be presented incorporating the effect of mass transfer and the wetting of catalyst particles.
Figure 3. Conversion as function of liquid velocity at 361.15K at CO2 velocity of 1.867 cm/s and pressure of 0.4 MPa