Solubilities and relative distributions of key components of spearmint oil in sub/supercritical carbon dioxide

Abstract

IV ABSTRACT in this work, solubilities and reîative distribution of the key components of two essential oils (origanum oil and spearmint oil) in sub and supercritical carbon dioxide were investigated at various temperatures and pressures in a stainless-steel high-pressure equilibrium celi. The work could be summarized in three experimental parts. in the first part, the ternary system of benzene/toluene/CO2 was used to test the experimental set-up. A satisfactory sampling system and sampling procedure, which eliminated possibility of entrainment in the gas-phase samples, were developed. in the second set of experiments, origanum-oil/CO2 system was used to estimate the necessary time for the system to reach thermodynamic equilibrium in the high-pressure celi. The minimum necessary equilibration time was found to be approximately 60 minutes. in the third set of experiments, temperature and pressure effects on the solubilities and the reîative equilibrium distribution of the key components of spearmint oil in sub and supercritical carbon dioxide were studied. Samples of the dense gas phase were analyzed using a capillary gas chromatograph and the key components of the essential oils were identified via GC/MS analyses. Eight key components of the origanum oil and twelve key components of the spearmint oil were selected to represent the origanum and spearmint oils. These key components of the essential oils were grouped as monoterpene hydrocarbons and sesquiterpene hydrocarbons and constituted the bulk of essential oils.vıı Sonuçlar nane yağının yoğun CO^deki çözünürlüğünün yalnızca CO^in çözücü gücüne (CO2 yoğunluğu) bağlı olmadığını, belirleyici bileşenlerin fizikokimyasal (buhar basıncı, polarite, molekül ağırlığı) özelliklerine de bağlı olduğunu göstermiştir. Kritik basınçtan oldukça düşük basınçlarda (20-40 atm), esansiyel yağ bileşenlerinin buhar basınçlarının etkisinin çözücü güç (çözücü yoğunluğu) etkisinden daha önemli olduğu görülmüştür. Bu nedenle alçak basınçlarda göreceli olarak daha yüksek buhar basınçlarına sahip olan monoterpen hidrokarbonlarının göreceli dağılım katsayıları daha alçak buhar basınçlarına sahip olan seskiterpenlerinkinden daha büyüktür. Orta yükseklikteki basınçlarda ise (50-80 atm), nane yağının monoterpen ve seskiterpen hidrokarbonları yoğun COfde eşit olarak çözünürlük göstermektedirler. Yüksek basınçlarda ise (80-1 10 atm), çözücü güç etkisi bileşenlerin buhar basınçlarının etkisinden daha önemli olmakta ve C02'in seskiterpen hidrokarbonlarına olan seçiciliği daha yüksek olmaktadır. Kekik yağı ile 95 atm ve 50, 55 ve 60 °C sıcaklıklarda yapılan deneylerde anahtar bileşenlerin kritiküstü CO^deki göreceli dağılımlarında ters sıcaklık etkisi belirlenmiştir. Özellikle monoterpen hidrokarbonlarının göreceli dağılım katsayılarının artan sıcaklık ile azaldığı görülmüştür. Esansiyel yağların kalitelerinin artan monoterpen hidrokarbon oranlan ile düştüğü genel kabulü göz önüne alındığında bu çalışmanın sonuçlan önem kazanmaktadır. Bu çalışma bulgulan temelinde süperkritik akışkanlar ile sürdürülecek terpenden anndırma işlemlerinin düşük sıcaklıklarda ters etki alanının dışında, yüksek sıcaklıklarda ise ters etki alanında yapılmasının gerektiğine işaret edilmektedir.

IV ABSTRACT in this work, solubilities and reîative distribution of the key components of two essential oils (origanum oil and spearmint oil) in sub and supercritical carbon dioxide were investigated at various temperatures and pressures in a stainless-steel high-pressure equilibrium celi. The work could be summarized in three experimental parts. in the first part, the ternary system of benzene/toluene/CO2 was used to test the experimental set-up. A satisfactory sampling system and sampling procedure, which eliminated possibility of entrainment in the gas-phase samples, were developed. in the second set of experiments, origanum-oil/CO2 system was used to estimate the necessary time for the system to reach thermodynamic equilibrium in the high-pressure celi. The minimum necessary equilibration time was found to be approximately 60 minutes. in the third set of experiments, temperature and pressure effects on the solubilities and the reîative equilibrium distribution of the key components of spearmint oil in sub and supercritical carbon dioxide were studied. Samples of the dense gas phase were analyzed using a capillary gas chromatograph and the key components of the essential oils were identified via GC/MS analyses. Eight key components of the origanum oil and twelve key components of the spearmint oil were selected to represent the origanum and spearmint oils. These key components of the essential oils were grouped as monoterpene hydrocarbons and sesquiterpene hydrocarbons and constituted the bulk of essential oils.V Resuits show that the solubility behavior of the spearmint oil in dense CÛ2 depends not only on solvent power of CC>2 (density of CC>2) but also on the physicochemical properties (vapor pressure, polarity, molecular weight) of the key components. At pressures far below the critical pressure (20-40 atm) vapor-pressure effect of the essential-oil components dominates the solvent-power (solvent-density) effect. Therefore, at low pressures, the retative distribution coefficients of the monoterpene hydrocarbons (which have comparably higher vapor pressures) are greater than that of the sesquiterpene hydrocarbons (which have lower vapor pressures). At intermediate pressures (50-80 atm) both the monoterpene and the sesquiterpene fractions of the spearmint oil are equally soluble in dense CO2- At elevated pressures (80-110 atm), however, solvent-density effects dominate the vapor-pressure effects, and supercritical CC>2 exhibits higher selectivities for the sesquiterpene hydrocarbons. Experiments performed with the origanum oil at 95 atm and at three different temperature levels (50-55-60 °C) reveal a retrograde temperature effect on relative distribution of the key components in supercritical CX>2- Especially the relative distribution coefficient of the monoterpene hydrocarbons decreases with increasing temperature. Based on the accepted fact that the quality of essential oüs decreases with increasing fraction of the monoterpene hydrocarbons, the findings of this study are important. On the basis of this work it can be concluded that supercritical-fluid-aided deterpenation operations should be carried out at lower temperatures outside the retrograde region, whereas at higher temperatures within the retrograde regjon.