Other technologies

Traditional extraction technologies including Soxhlet solvent extraction, steam distillation and hydro-distillation have been employed successfully for many applications in the food and pharmaceutical industry. These technologies have drawbacks in that they use toxic, flammable solvents that are in many cases being banned from food use. The techniques typically are time and energy consuming and often require further separation or cleanup. Many other innovative extraction technologies now exist in addition to novel SFE techniques. Some of the notable achievements in extraction technologies include microwave-assisted solvent extraction (MASE) (Priego-Capote et al., 2004; Assad et al., 2004; Hogendoorn et al., 2002; Raman and Gaikar, 2002; Luque and Luque, 2004), ultrasound-assisted extraction (Ruiz-Jimenez and Luque de Castro, 2004), pressurized liquid extraction (PLE) (Boselli et al., 2001), accelerated solvent extraction (ASE) (Richter et al., 1995), microwave-assisted hydro-distillation (MAHD) (Stashenko et al., 2004) and solid-phase microextraction (SPME). SPME is an attractive technique that is solvent-free, and extraction and concentration are combined in a single step (Arthur and Pawliszyn, 1990).

Extraction of specialty biochemical components from biological systems presents a vast array of possible extraction systems; users should consider the appropriate variables necessary for optimization. The first step to narrow down the best possible extraction system is to consider the thermodynamic properties of temperature, pressure, volume and composition relations to determine the solubility of the desired compound in the solvent or mixture of solvents based on polarity, molecular weight and volatility of the solvents and solutes. The solubility may be predicted through engineering analysis using classic EOS or statistical mechanics approaches combined with fugacity relationships (Prausnitz et al., 1999). From the equilibrium analysis set as the reference point, operational curves may be constructed (Treybal, 1981). The next step is to characterize the system in terms of fluidity: whether the system will be gas-liquid, liquidliquid, solid-liquid or solid-fluid; and whether porosity and diffusivity of the solvent into the extraction matrix becomes a rate-limiting factor. With these primary extraction variables defined for the particular system, the final important factors of rapidity, energy savings, cleanliness (purity), environmental impact and ultimately product quality must be considered in the design of the extraction system. As the saying goes, 'time is money', and both short-term and long-term analysis based on the previous design steps to determine both operational and capital cost, with greater emphasis on environmental impact, will ultimately determine which extraction system would yield the greatest return on investment. Table 10.3 shows some general ranges of important system properties such as operating temperature (for labile components) and component volatility on the specific extraction mechanism for component separation. Cleanliness is the extraction purity of the components after separation relative to conventional solvent extraction techniques; this is important in the consideration of further purification steps.

10.5.1 Microwave-assisted solvent extraction (MASE)

MASE has several distinct advantages over most extraction technologies, primarily in reduced extraction times and reduced solvent use. The microwave process disrupts hydrogen bonds from microwave-induced dipole rotation of the molecules and movement of ions which tends to enhance solvent penetration (Hubaib et al., 2003). Hubaib et al. (2003) showed that MASE of lipophilic compounds from Echinacea with methanol-water combinations, when compared with conventional Soxhlet extraction and ultrasonic extraction techniques, resulted in better recovery and reproducibility. MASE has been successfully coupled to steam distillation (MASD) for extraction of essential oils from lavender and resulted in a nearly ten-fold decrease in extraction time with higher recovery, lower energy requirement (ten-fold less), lower solvent use and lower CO2 emissions released during distillation (Chemat et al., 2005). Disadvantages include the high temperatures associated with MASE that affect thermally labile components and also the required presence of water. However, if extraction rates may be accelerated for lipophilic compounds in high-moisture systems (most biological systems), this could work as an advantage to prevent the high energy cost of removal of water before lipid extraction.

Table 10.3 Potential ranges of the physical properties of extraction systems

Extraction method

Table 10.3 Potential ranges of the physical properties of extraction systems

Extraction method

Property

MASE/MAHD

SFE-water

SFE-CÜ2/Ethanol

SFE-CO2

SPME

ASE

HD

Temperature

M-H

M

L-M

L-M

L-H

M-H

M-H

Pressure

L

H

H

H

L-H

M

L

Polarity

L-H

M

L-M

L

L-H

L-H

L-H

Molecular weight

L-M

L-M

L-M

L-M

L-H

L-H

L-H

Volatility

L-H

L-M

L-M

L-M

L-H

L-H

L-H

Fluidity

G Li S

G Li S

G Li S

G Li S

G Li

G Li S

G Li S

Rapidity

M-H

M

M

M-H

M

M-H

L-M

Cleanliness

M-H

M

M

M-H

H

M

L

Solvent use

L

L-M

L-M

L-M

L-M

M

H

Environmental impact

Good

Excellent

Excellent*

Excellent*

Good

Good

Poor

Energy

L-M

M

M

M

L-M

M

M-H

Capital cost

M-H

H

H

H

M

M-H

M

Abbreviations: G, gas; Li, liquid; S, solid; L, low; M, mid-range; H, high.

* Efficient recycling of CO2 is necessary.

Supercritical fluid extraction and other technologies for extraction 245 10.5.2 Solid-phase microextraction (SPME)

Solid-phase microextraction (SPME) coupled to gas chromatography has also become a powerful solvent-free technique for analysis of essential oils (Field et al., 1996; Lagalante and Montgomery, 2003; Deng et al., 2006). Deng et al. (2006) introduced a combined technology of microwave distillation and SPME for rapid analysis of essential volatile oils in Artemisia selengen-sis Turcz.

Going Green For More Cash

Going Green For More Cash

Stop Wasting Resources And Money And Finnally Learn Easy Ideas For Recycling Even If You’ve Tried Everything Before! I Easily Found Easy Solutions For  Recycling Instead Of Buying New And Started Enjoying Savings As Well As Helping The Earth And I'll Show You How YOU Can, Too! Are you sick to death of living with the fact that you feel like you are wasting resources and money?

Get My Free Ebook


Post a comment