Screening Stability, Thermochemistry, and Chemical kinetics of 3-Hydroxy butanoic acid as a bi-functional biodiesel additive

Thermo-kinetic aspects of 3-Hydroxybutanoic acid ( 3-HBA ) pyrolysis in the gas phase have been studied computationally in the temperature range 600–1700 K and pressure of 1 bar using the ab initio CBS-QB3 method and M06-2X/cc-pvTZ level with the aid of the Gaussian 09 program and the Kinetic and Statistical Thermodynamical Package (KiSThelP). The degradation mechanism was divided into seventeen pathways: seven complex fissions and ten barrierless reactions. Chemical kinetics simulations of barrier reactions are calculated using transition state theory (TST) and unimolecular Rice-Ramsperger-Kassel-Marcus (RRKM) theories, while the kinetics of barrier reactions are estimated using the accurate classical method. Thermodynamics results indicate six stable conformers within 4 kcal mol − 1 . To confirm the chemical stability of these conformers, the HOMO-LUMOs energy gaps were checked. The estimated chemical kinetics results indicated that TST and RRKM are comparable which gives confidence to our calculations. Branching ratio analysis shows the full dominance of the dehydration reaction R4 at T  ≤ 650 K, with a minor contribution for the simple bond fission R9. At T ≥700 K, R9 became the main decomposition route, with a small contribution from R10 (~ 16% at 1700 K) and R8 (~ 9% at 1700 K) reactions.