Kinetic studies of turpentine isomerization using hydrochloric acid and acetic acid as catalysts

Abstract

Turpentine is a non-wood forest product derived from pine trees. Turpentine oil can be produced from the distillation of pine tree sap (family Pinaceae). The main component of turpentine is α-pinene, and turpentine isomerization may produce various derivative products. The objective of the present study was to investigate the isomerization products of turpentine oil with two acid catalysts: hydrochloric and acetic acid. Here, the influence of acid concentration was investigated by using various concentrations of hydrochloric and acetic acid concentrations between 0.4 to 1 M. Further, the combination of acetic acid and hydrochloric acid as catalyst was also investigated by varying the molar ratio of HCl:Acetic Acid=1 : 0.5 and 1:1. The experiments were carried out in a batch reactor equipped with heater, condenser, and stirrer. The reaction temperatures were maintained at 150^°C and reaction time of 6 h. The resulting products from turpentine isomerization were analyzed using GC-MS. The results showed that the largest isomerization product obtained with HCl and combination of HCl:H.Acetic was trans sabinene hydrate. Additional products that could be detected varied among α-terpinolene, α-terpineol, α-terpinene, γ-terpinene and δ-carene. The experimental data showed that α-pinene conversion as high as 62, 63 and 57% were obtained by using HCl concentrations of 0.4, 0.7 and 1 M, respectively. In addition, the use of HCl:H.Acetic=1 :0.5 and 1:1 gave final conversion of 63 and 61%. The modeling results showed the kinetic model for pinene conversion for both catalysts was \(\frac{dX}{dt}=0.5222\cdot {(1-X)}^{2.5210}{C}_{\mathrm{HCl}}-0.2233\cdot {(1-X)}^{4.5300}{C}_{\mathrm{HAc}}\)