High-pressure hydrogenation of polybutadiene at conditions found from phase transitions of the non-reactive system polybutadiene + n-pentane + dimethyl ether + hydrogen

CIOLINO, ANDRÉS; MENOSSI, MATIÁS; L. M. QUINZANI; MILANESIO, JUAN M.; ZABALOY, MARCELO S.

Nova Friburgo

Congreso; X Congresso Brasileiro de Termodinâmica Aplicada; 2019

Linear low-density polyethylene (LLDPE) with a polydispersity index (PD) close to unity can be obtained by hydrogenating polybutadienes (PBs) with narrow molecular weight distributions. In the conventional hydrogenation of unsaturated heavy compounds, the system presents, at least, two fluid phases during the reaction progress. The fluid-fluid interface reduces the hydrogen mass transfer rate. This could be overcome by using a supercritical solvent o solvent mixture as reaction medium, thus conducting the reaction under single fluid phase conditions. To hydrogenate the PB under fluid homogeneity conditions, the solvent (or solvent mixture) should be able to simultaneously dissolve the PB, the H2 and the reaction products. In particular, the system PB + solvent mixture + H2 should be homogeneous under the temperature, pressure and component concentration conditions at which the hydrogenation reaction is to be carried out. The goals of this work are the following: (a) to obtain new PVT data, at set T, global composition and global density, in a visual constant volume equilibrium cell, for the quaternary system PB + n-pentane (C5) + dimethyl ether (DME) + H2, in the absence of catalysts. (b) to carry out PB hydrogenation experiments in the presence of a catalyst and of a single fluid phase at conditions based on the PVT information gathered in (a). The cell makes possible to observe the number of phases of the system. In a non-reactive experiment, the constant volume cell, whose internal volume is known, is loaded with a known amount of a known composition mixture. Next, the pressure is measured at a set temperature. A temperature range of interest is covered. The measured pressure versus temperature curve is both, isoplethic and isochoric. A slope discontinuity in the curve implies a phase transition. Phase equilibrium results are presented for the non-reactive system, and hydrogenation results are reported for the reactive system. Hydrogenation reactions to 6 hours at high pressures were carried out modifying the molar ratio of double bonds and amount of hydrogen (C=C:H2) between 1:10-1:25. Relative hydrogenation percentages between 73-98% were obtained, decreasing 8 times the reaction time of traditional hydrogenations.