Experimental pressure versus temperature isochoric - isoplethic curves for systems related to the supercritical hydrogenation of polybutadiene

MATIAS MENOSSI; PABLO HÉGEL; JUAN M. MILANESIO; AGUSTINA ANDREATTA; ANDRES CIOLINO; LIDIA MARÍA QUINZANI; MARCELO S. ZABALOY

Viña del Mar

Congreso; IV Conferencia Iberoamericana en Fluidos Supercríticos (PROSCIBA 2016); 2016

Linear low densitypolyethylene of low polidispersivity index could be obtained by hydrogenatinglow polidispersivity index polybutadienes (PBs). Such PBs can be synthesizedusing a high-vacuum anionic polymerization technique, as done in the presentwork. In conventional hydrogenation processes, the system always presents, atleast, two fluid phases during the reaction progress. The presence of aninterphase implies lower mass transfer rates. This could be overcome by using asupercritical fluid as reaction medium, so that the hydrogenation processoccurs, in principle, under single fluid phase conditions. To hydrogenate thePB under supercritical conditions, the solvent (or solvent mixture) should beable to simultaneously dissolve the PB, the hydrogen and the reaction products.The high asymmetry of the reactive mixture, which is due to the largedifference in size between the H2 and PB molecules, implies a high immiscibilitylevel in the absence of the supercritical solvent or solvent mixture. Inparticular, the ?PB + solvent mixture? system should be homogeneous at theconditions of temperature, pressure and PB concentration range at which the PBhydrogenation is to be carried out. The purpose of this work is toexperimentally find the conditions under which a number of ?PB + solventmixture? systems, and related subsystems, are homogeneous. In a typicalexperiment, an in-house constant volume cell is loaded with a known amount of aknown composition mixture. Next, the pressure is measured at set temperature,covering the temperature range of interest. Clearly, the measured pressureversus temperature curve is an isopleth (constant overall composition) and itis also an isochor (constant overall density). Slope changes in the curve implychanges in the phase condition. At high enough temperature, the system becomeshomogeneous, and it remains so at higher temperatures. Pressure vs Temperatureisochoric-isoplethic trajectories were measured in this work for a number ofpure solvents, solvent mixtures, and systems made of PB and a solvent mixture.The experiments where performed at varying overall density and varying overallmixture composition. The experimental results here reported will be useful toguide future hydrogenation experiments that will be conducted in batch mode.