Fixed bed hydrogenation of polystyrene in mixtures of supercritical propane and decahydronaphthalene

The density and viscosity of propane mixed with 66/34 trans/cis -decahydronaphthalene (DHN) were measured over a wide range of temperatures (323.15--423.15K), pressures (2.5--207.9 bar), and compositions (0--65 mol% propane). For conditions giving two phases, the composition of the dense phase was measured in addition to the density and viscosity. The modified Sanchez-Lacombe equation of state (MSLEOS) was used with a single linearly temperature-dependent pseudo-binary interaction parameter to correlate the phase compositions and densities. The mixture viscosities were computed from a free volume model (FVM) by using a single constant binary interaction parameter. Density predictions from the MSLEOS were used as input mixture density values required for the FVM.;The phase equilibria of polystyrene in mixtures of propane (C3) and DHN were determined over a wide range of temperatures and pressures. Cloud points were measured to determine suitable conditions for one fluid phase conditions. The conformational properties of polystyrene in neat DHN and mixtures of C3 and DHN were determined by measuring intrinsic viscosities. Although some collapse of the polymer coil was observed, at 423.16 K and 45 mol% C3 in DHN intrinsic viscosity data still indicated the mixed solvent was better than a theta solvent. At 323.15 K, intrinsic viscosity data indicated a theta composition at approximately 30 mol% C3 in DHN. At 45% C3 in DHN the solvent quality was sensitive to pressure, indicating the presence of a theta pressure.;The heterogeneous catalytic hydrogenation of polystyrene in neat DHN using 5%Pd/SiO2 was studied in a batch stirred tank reactor (STR) and a batch packed bed recycle reactor (PBRR). At sufficiently high hydrogen pressures the rate of disappearance of aromatics was approximately first-order with respect to aromatic ring concentration. The rate hydrogenation of polystyrene in the PBRR was significantly slower than in the STR and excellent agreement was found between calculations of the increased influence of mass transfer resistance on the apparent first-order rate constant in the PBRR and the observed first-order rate constant. Breakthrough curves of polystyrene in neat DHN with an inert packing were also used to confirm the presence of hindered diffusion of polystyrene within the pores of the porous particles.;The addition of C3 as a cosolvent in the hydrogenation reactions carried out in the PBRR resulted in an appreciable increase in the observed first-order rate constant for polystyrene with a number average molecular weight of 232,00. Estimation of the apparent first-order rate constant, due to an increase in the rate of external and internal mass transfer of polystyrene could only partially account for the observed increase in the first-order rate constant. The remaining unaccounted increase in the observed first-order rate constant in the PBRR is believed to be a result of an increase of the conformational rearrangement of polystyrene adsorbed on the Pd crystallite due to the presence of supercritical C3.