Investigation on the effect of parametric factors for synthesis of hydrogenated HTPB using a Pd-Zr-activated charcoal catalyst

This paper outlines the synthesis of hydrogenated HTPB (HHTPB) using HTPB polymer as a precursor by catalytic hydrogenation method using iso-propyl alcohol and toluene as the active solvent media. A novel synthesis approach to hydrogenate HTPB has been reported using a catalyst made up of palladium and zirconium as base metals supported on activated charcoal. Experiments were conducted in a 100 mL Inconel reactor with a magnetically driven variable speed impeller. Various parameters like operating temperature, operating pressure, solvent-to-feed ratio, and the concentration of the catalyst were studied by conducting multiple experiments. The composition and microstructure of the in-house synthesized catalyst were characterized using SEM and TEM, XRD, and particle size distribution. HTPB and HHTPB polymers were characterized by NMR, FTIR, and chemical analysis. The results showed that the degree of hydrogenation of HTPB is ~74% under hydrogen environment for the optimized operating parameters and the reactor volume with the chosen operating conditions. Process time is fixed as 6 h. It is observed that the formation of HHTPB was predominantly controlled by both physisorption and chemisorption. After hydrogenation of HTPB, an insignificant change in hydroxyl value was observed, and the HHTPB formed is of vinyl-type functional isomer in most of the cases. A marginal increase in molecular weight was observed after hydrogenation. HTPB and HHTPB were subjected to TG- DSC studies and it was found that the thermal stability of HHTPB marginally increased. Pyrolysis studies using GC-MS indicated that HHTPB resulted in relatively higher straight-chain moieties, indicating that the unsaturation was removed preferentially towards -ane compounds such as alkanes and cyclo-alkanes.