Experimental and computational study of the initial decomposition of gamma-valerolactone

The thermal decomposition of gamma-valerolactone (GVL) diluted 1:10 mol/mol in nitrogen was studied experimentally in a tubular flow reactor. Variation of the temperature from 873 K to 1073 K for a residence time of approximately 400 ms at 0.17 MPa covered the complete GVL conversion range from 1% to 98%. Comprehensive 2D MS analysis of the effluent revealed that the main products observed at temperatures below 1000 K are CO, CO2, C4-olefins and 4-pentenoic acid. Initially, GVL is consumed predominantly through isomerization to 4-pentenoic acid, although minor contributions of bimolecular decomposition channels cannot be ruled out. CBS-QB3 level characterization of the C5H8O2 potential energy surface reveals the existence of a low energy barrier for ring-opening to 4-pentenoic acid. The weak CC bond between C2 and C3 in 4-pentenoic acid allows formation of radicals that further convert gamma-valerolactone or 4-pentenoic acid. The 4-pentenoic acid yield increases steadily with rising temperature before a sharp decrease around 1010 K. The latter can be explained by radical chemistry taking over at high temperatures.