Supercritical extraction of crotalaria spectabilis in the cross‐over region

Abstract

Chimowitz and Pennisi (1986) have recently described a novel process for the separation and purification of components from mixtures of solutes in supercritical fluids. Their process was based on operation in the multicomponent temperaturesolubility cross-over region. For a single solute, the cross-over point (~3 y / a T )~ = 0 represents the pressure a t which there is a change in the temperature dependence of the solubility. Below this pressure, solubility is principally dependent on solvent density and a decrease in the temperature leads to an increase in the density and hence the solubility. Above this pressure, solubility is principally dependent on solute sublimation pressure. Raising the temperature leads to an increase in the sublimation pressure and therefore an increase in solubility. In the case of two solutes, each solute exhibits a cross-over point. If these points are a t different pressures, the system temperature may be manipulated a t an intermediate pressure causing one of the solutes to fall out of solution. Chimowitz and Pennisi demonstrated that this effect could be used to separate mixtures of 1,lO-decanediol and benzoic acid using supercritical carbon dioxide. They also recommended a processing scheme for the separation of multicomponent mixtures, but did not study any multicomponent systems experimentally.We have recently studied the extraction of monocrotaline (Schaeffer et al., 1988), a pyrrolizidine alkaloid of chemotherapeutic interest, from the seeds of Crotalaria spectabilis using supercritical carbon dioxide and carbon dioxide-ethanol mixtures. In our study, the crushed seeds of Crotalaria spectabilis were extracted a t temperatures ranging from 308.1 5 to 328.1 5 K and at pressures ranging from 8.86 to 27.41 MPa with carbon dioxide containing up to 10 mol ?6 ethanol. Our results indicated that the single-stage supercritical extraction process could not be used to isolate monocrotaline since the lipid material is always extracted with the monocrotaline. However, if the extract is assumed to consist of two components only-namely, monocrotaline and lipid material, crossover regions a t different pressures could be identified in our work, Figure 1. The present work was, therefore, undertaken to examine the feasibility of isolating pure monocrotaline from a complex extract using cross-over phenomena. It differs from the work of Chimowitz and Pennisi (1986) in that the solute is a multicomponent system consisting of the polar monocrotaline and a series of nonpolar lipids. ExperimentalThe apparatus used in this investigation is shown schematically in Figure 2. It has been described in detail in our previous work (Schaeffer et al., 1988). Pressurized carbon dioxide was filtered, liquified in an ice bath, and fed into an Eldex dual-head metering pump. The cosolvent from a 250 mL graduated cylinder was also filtered and entered the Eldex pump. Both the solvent and cosolvent were pumped to the desired system pressure and fed into an extraction vessel which was packed with alternating layers ...

Influence of Matrix Composition on the Solubility of Hydroxybenzoic Acid Isomers in Supercritical Carbon Dioxide

“…Separation of isomers using retrograde crystallization therefore seems unlikely, although Johnston et al (1987) have identified one candidate system (2,3-and 2,6-dimethylnaphthalene). The technical feasibility of retrograde crystallization has been demonstrated in other nonisomeric systems with varying degrees of success (Kelley and Chimowitz, 1989;Schaeffer et al, 1988). In practice, crossover regions tend to be quite narrow, perhaps less than 20 bar, and are difficult to define because a distinct crossover pressure does not necessarily exist for all temperatures between two isotherms (see Figure 3).…”

Desorption processes: Supercritical fluid regeneration of activated carbon

“…Hence, the values of Kp were nearly constant and varied from 3 to 3.3 as shown also in Figure 4. The pressure at which the effect of temperature on solubility reverses has been termed the crossover point (Chimowitz and Pennisi, 1986;Schaeffer et al 1988). Our results for Kp indicate that a similar crossover pressure exists for desorption and that for ethyl acetate desorbing from activated carbon into C02 this pressure is near 13 MPa.…”

Supercritical CO2 recovery of caffeine from green coffee oil: new experimental solubility data and modeling

“…An increase in the cross over pressure is normally detected in solubility isotherms obtained using supercritical solvents modified with a co-solvent due to the increase in the critical temperature and pressure of the mixed solvent. 26 These authors observed that varying the concentration of ethanol in supercritical CO 2 from 0 to 10% resulted in an increase in the crossover pressure of monocrotaline solubility isotherms from 7.5 to 27.5 MPa.…”