Towards the hydrogenation of polybutadiene within a single reactive phase

J. M. MILANESIO; P. E. HEGEL; A. CIOLINO; L. M. QUINZANI; L. J. ROVETTO; M. S. ZABALOY

Eindhoven

Simposio; European Symposium on Applied Thermodynamics; 2014

Polybutadiene (PB) is an amorphous homopolymer produced from 1,3-butadiene polymerization. Depending on the catalyst and the solvent used in the polymerization reaction, the relative amount of double bond configurations (cis 1-4, trans 1-4 and vinyl 1-2) can be controlled, and, therefore, the PB physical properties. The complete hydrogenation of PB yields a copolymer of ethylene and 1-butene (hPB) which highly resembles the structure of linear low-density (LLD) polyethylene (PE) (LLDPE) [1]. Furthermore, PB may be synthesized using the anionic polymerization technique that makes possible to obtain polymers of very narrow molecular weight distribution (MW/MN < ∼1.1). Consequently, the hydrogenation of PBs obtained by anionic polymerization could produce LLDPEs of narrow molecular weight distribution. Milanesio et al. [2,3] measured high pressure liquid-liquid phase equilibrium data (also known as ?cloud points?) in binary, ternary and one quaternary system related to the potential hydrogenation of PB in a single reactive phase. These data suggest that the use of a solvent mixture made of a light polar solvent, e.g., DME, and a heavier non polar solvent, e.g., C5, should be a convenient choice to carry out the single-fluid-phase supercritical hydrogenation of PB at relatively moderate conditions. This solvent mixture tends to solubilize the reactive polymer, its reaction product (i.e. the LLDPE) and intermediate species. The solvent mixture should have a solvent ratio close to 1:1 (DME/C5, weight basis) and the polymer mass fraction in the reactive mixture should be about 3 wt% [2, 3]. At these conditions, the pressure needed to have a single phase for the mixture containing the unsaturated reactive polymer and the saturated product is about 300 bar, in the 30 to 200 oC temperature range, if the hydrogen is absent. In this work, the conditions suggested in references [2, 3] were tested for the hydrogenation of PB in an experimental setup specially designed and built for this project. The effect of a number of variables, such as reaction time, presence of catalyst and initial concentration of hydrogen in the reactive mixture, was studied. The phase behavior during the evolution of the reactive process was also investigated.