The effect of water content and packing on the yield of the essential oil obtained from lemon thyme: offered models

Abstract Essential oil distillation from lemon thyme was studied using steam distillation method. The effects of pre-irrigation and packing material on the yield and essential oil contents were investigated. Both parameters improved the yield and the highest yield values were obtained as 1.737 and 2.213, respectively. The major components carvacrol, p-cymene, thymol and γ-terpinene were detected by GC-MS and carvacrol percent reached to the highest value as 52.58% for 30 ml water and 300 g packing. Dimensionless groups were introduced to explain the dependence of the yield on packing. Four models were offered and applied successfully. The modified Weibull model fits best and the other models converge to the first-order indicating ineffective of resistance constant as a result of the improvement of the yield by the packing material. This result reveals the existence of channel forming and improvement of flow regime. The effect of the pre-irrigation was firstly explained by the swelling mechanism showing that the thyme swelled as relaxation-controlled and increased the yield until a limiting value where a resistance to diffusion occurs after a pre-irrigation value of 40 ml. Temperature has also a contribution on the increase in the yield. Lemon thyme was also characterized by FT-IR and TGA methods.