(148i) 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