亚临界低温萃取的应用.doc

The 4th International Conference on Biomass Energy Technologies-8th World Bioenergy Symposium (ICBT-WBS 2014)
Subcritical fluid extraction technology and its Application on forestry products

Hua-Min Liua,b, Kun Qib*, Qian Yangb , Linlin Wangb, Peng Hub

aCollege of Food Science and Technology, Henan University of Technology, Zhengzhou, 450001, China
b Henan Province Subcritical Extraction Biological Technology Co., Ltd., Anyang, 455000, China;

*Corresponding author: Kun Qi
Telephone: [phone]
E-mail: 13603720980@
Address correspondence to this author at Henan Province Subcritical Extraction Biological Technology Co., Ltd, Henan Province Development Zone of advanced technology and equipment, Anyang, China 455000

Abstract

Subcritical fluid extraction is performed at lower temperatures and pressures than those employed in supercritical fluid extraction. It is an excellent extraction that has some advantages such as lower operating temperature and pressures, shorter extraction time, environmental compatibility, good selectivity, one step from the extraction to the separation and avoidance of residual solvents. Subcritical fluid extraction based processes are applied to a wide variety of areas, including forestry products, essential oil, special plants and Chinese herbal medicine oil, natural spices, removal of pesticide residues. The subcritical extraction equipment has been very mature and the extraction capability ranged from 1 to 100 T/D. In this paper, the objective was to review the subcritical fluid extraction process and the application of subcritical fluid extraction on forestry products.

Keywords: Subcritical fluid extraction, Forestry products, Equipment

1. Introduction

In the past 20 years, supercritical fluid (SCF) has become popular because of its distinct advantages, including being chemically inert, harmless to humans and animals, non-toxic, nonflammable and environmentally friendly [1]. Unfortunately, supercritical fluid requires a higher temperature or a higher pressure. For example, supercritical water requires a temperature of > 374 °C and a pressure of > 221 bar and is corrosive [2]. Supercritical CO2 extraction often requires a high pressure (up to 30 MPa) for a preferable yield of products such as carotenoids, plant oil, and essential oil. Therefore, supercritical fluid extraction requires high pressures and is expensive, limiting its industrial application.
Subcritical fluid extraction, also called pressurized low-polarity fluid extraction, is an emerging technology based on the use of a certain extraction solvent at a temperature between its boiling point and critical temperature and at a pressure sufficient to keep the solvent in a liquid state [3]. In 1990, Kun Qi’s invention patent <LPG extraction process of oil> (patent number: 90108660.6) represents the birth of this technology. It is an excellent extraction that has numerous advantages such as lower operating temperature and pressures, shorter extraction time, environmental compatibility, good selectivity, one step from the extraction to the separation and avoidance of residual solvents [4,5]. Therefore, the extraction technology is one of the most popular techniques which can overcome the defects of the conventional organic solvent extraction and expeller pressing methods. It can be considered a technological revolution in the extraction industry.
Subcritical fluid extraction based processes are applied to a wide variety of areas, including forestry products, essential oil, special plants and Chinese herbal medicine oil, natural spices, removal of pesticide residues. We have researched and extended subcritical fluid extraction technology about 25 years, and have established 70 production lines in China. Among the 70 production lines, subcritical propane, butane and their mixture extraction equipment have accounted more than 10. The daily processing capacity of single production line is 1-100 ton, and the extraction raw materials include wheat germ, walnuts, grape seed, pepper, marigold, soybeans, cocoa cake, fungus spores, and roses et al.. In this paper, the objective was to review the subcritical fluid extraction process and its application on forestry products.

2. Subcritical extraction solvents

The material, which was gas at room temperature and can liquid at the low pressure, can be used as suitable extraction solvents. The solvents have some advantages such as low investment in production equipment, low production cost, convenient transportation. Table 1 shows some suitable extraction solvents and its physical properties.

Table 1. Physical properties of the suitable subcritical fluid extraction solvents.

Propane
Butane
Dimethylether
Tetrafluoroethane
Ammonia
Formula
C3H8
C4H10
CH3OCH3
CH2FCF3
NH3
Molecular weight
44
58

102
17
Boiling point °C
-42
-0.5
-24.9
-26.2
-33.4
Vapor pressure (MPa, 20°C)
0.83
0.23
0.533
0.6
0.88
Critical temperature (°C)
95.7
152.8
129
101.1
132.3
Critical pressure (MPa)
4.4
3.6
5.32
4.07
11.3
Liquid density (25°C, kg/L)
0.49
0.57
0.66
1.2
0.61
Liquid density (25°C, kg/m3)
20.15
6.18

0.6
Permittivity
1.69
1.78
5.02

16.9
latent heat of vaporization (KJ/kg, 30°C)
329
358
410
216
1369
explosion limit
2.3%-9.5%
1.9%-8.5%
3.5%-27%
Noncombustible
16％～25％
Toxicity LC50(mg/m3)
Slight toxicity
Slight toxicity 680
308000
Non-toxic
1390
Character
Colorless
flavored
Colorless
flavored
Colorless
flavored
Colorless
tasteless
Colorless
pungent odor

Butane and propane were non-polar solvents and have been firstly used in subcritical fluid extraction. Butane, propane, and their mixture were often used as the subcritical fluid mainly because they need lower critical pressures and temperatures, and they have excellent dissolving power for lipophilic compound. Also the solvents are low boiling point, inexpensive, colorless, and clean solvent that leaves very little solvent residue in the product [6]. Chinese Ministry of Health declared that propane and butane have been included in the list of food processing aids at NO. 13 in 2008.
Dimethyl ether can dissolve with many polar and non-polar solvents, and can extracte the polar and non-polar compounds. Dimethyl ether is produced from methanol dehydration reaction, and has many advantages such as low prices, wide sources, and low toxicity. At present, dimethyl ether has been mass produced to instead of liquefied petroleum gas in the world. Meanwhile, dimethyl ether has been widely used as spray in hairspray and miehailing. In recent years, rapid development of production capacity made dimethyl ether be an inexpensive subcritical extraction solvent. However, it has not been included in the list of food aids and limited its legitimate application in food industry. (We are going all out to do the job)
Tetrafluoroethane (R134a) was one of the most widely used low-temperature refrigerants. It is chemically inert, non-flammable, nontoxic and non-ozone destroying [7]. Furthermore, R134a was an ideal alternative to the refrigerant Freon-12 (R12), which was forbidden worldwide because it causes ozone depletion and produces greenhouse effects. Compared to hydrocarbon ether solvents, it was not explosive, which have led to an evaluation of its use as an alternative hydrocarbon ether solvents for subcritical fluid extraction. At present, R134a has not been included in the list of Chinese food aids, and its price was relatively high.
Liquid ammonia was mainly used for production nitrate, urea, and other chemical fertilizers, and could be used as raw material of medicine and pesticide. Large refrigerators are mostly used ammonia as refrigerants. Liquid ammonia was an ideal polar solvent for subcritical extraction, and could be used to extract oligosaccharides, plant polyphenols, alkaloids, flavonoids, biological glycosides, pigments and other water-soluble material composition. Liquid ammonia is mature on the use in industrial, which has many advantages such as low price, wide sources, low toxicity, and 99.9% purity ammonia was the national standard products. Ammonia has been included in the list of food aids and used in food production.

3. Subcritical fluid extraction equipment

Up to now, subcritical extraction equipment has been serialized. The subcritical extraction equipment has been very mature and the extraction capability ranged from 1 to 100 T/D. The equipment of 80T/D extraction capability was the key demonstration plant of the State Economic and Trade Commission. The plant has been operating for 15 years and nearly 100000 tons of raw materials are extracted.

Figure 1. Subcritical fluid extraction equipment (a-100 L laboratory equipment; b-5 L laboratory equipment; c-100T/D production line; d-60T/D production line)

The equipment of subcritical fluid mainly consist of extraction tanks, solvent tanks, mixing tanks, evaporation tanks, rising film evaporators, condensers, compressors, vacuum pumps and auxiliary buffer, filter tank, and other tanks. Container class devices are the second class pressure vessel. Compressor can be used ammonia compressor, liquefied petroleum gas compressor and Freon compressors according to various extraction solvents. The extraction tanks generally consist of 1 to 6 units according to the production capability. Extraction tanks are often vertical tank in early. At present, the extraction process is often conducted in 4-12 m3 horizontal tanks with automatic mixers. The extract is temporarily stored in the mixing tank, and the solvent is separated by evaporation system. Evaporation system generally consisted of a continuous two-liter membrane and one-liter falling film evaporator, and some system also increased one-liter vacuum thin film evaporator. Intermittent evaporation tank is often used for small extraction capability processing. Figure 1 shows the subcritical fluid extraction laboratory equipments and production lines build by Henan Province Subcritical Extraction Biological Technology Co., Ltd..

4. Security of production process and edible

Among subcritical extraction solvents mentioned in this paper, the subcritical extraction solvents have the dangerous of explosive and combustion except R134a, and subcritical solvents have certain pressures. Therefore, it made the production process have some dangerous. Subcritical fluid extraction and NO. 6 solvent extraction plants are all Band one in class A, and the electrical equipments are the same level. Although the explosion ranges of the subcritical solvents mentioned in this paper are wide, the lower explosion limits are higher as compared to NO. 6 solvent. Moreover, gas has smaller density than NO. 6 solvent. For the two points perspective, their security are better than NO. 6 solvent. However, the subcritical fluid extraction often requires a pressure. Therefore, the subcritical solvent extraction equipment should use pressure vessels. Piping, instrumentation, and valves are worked under 0.2 ~ 0.6 MPa. The extraction equipment of butane and propane have lower operation pressures (< 1.6 MPa) as compared to subcritical CO2 and other high-pressure process in chemical industry. Moreover, piping, instrumentation, and valves used in subcritical extraction technology are often worked under 0.6 MPa. Therefore, the securities of industrial applications are mature technology.
Subcritical extraction solvents have been broadly used in food industry, essential oils, health care products, and herbal extraction. Subcritical solvent belong to food additives according to the relevant provisions of the <Health Law> in China. In this section, the food security of subcritical propane and butane extraction has been reviewed as show blow.
(1) FAO Codex regulated that propane and butane can be used for food processing and there are no limit residues. Propane and butane are included in the list of U.S. <Food Chemicals Codes> and mainly used for food propellant, crisp agent, inflatable agent (oxygen blocking agent). In 1983, U.S. Food and Drug Administration has classified the butane and propane as “generally recognized as security” and is no limit on residue in food. In 2000, <Japanese food additive normative standards > seventh edition has added butane and propane in the list of available solvents and there is no limit on its residues in food. European Scientific Committee of Food approved propane and butane can be used in food process and there are also no limits in food. Ireland, New Zealand and other countries have also recognized propane and butane can be used in food processing.
(2) According to <chemical toxicity and regulatory environment Data Sheet>, United States and Germany proposed that the allowed values of propane and hexane in air are 1800 mg/m3 and 180 mg/m3, respectively. This result shows that the propane is safer for humans than hexane. According to < oil extraction technology>, human health limit concentration (load time average) of butane and hexane are 800mg/kg and 50mg/kg, respectively. Therefore, butane is also safer for humans than hexane.
(3) The toxicological tests of butane has been investigated through mice toxicity test, micronucleus test, mice sperm abnormality test, and rats 30d feeding test by Henan Provincial Health and Epidemic Prevention Station and Shandong Provincial Health and Epidemic Prevention Station, Which based on "food safety toxicology evaluation procedures and methods" GB15193-1994. The results show that butane is non-toxic.

5. Application of subcritical fluid extraction

5.1. Application on woody oils and essential oil

Generally, the traditional methods of extraction of plant oil include expeller pressing and organic solvent extraction methods. The yield of oil from the former method is lower. The latter method as the drawback that the oil must be heated to distill it and contains residual solvents, and at the same time the oil is oxidative unstable, and is easily subject to rancidity during the subsequent separation process [8]. Subcritical fluid extraction is one of the most popular techniques which can overcome the defects of the organic solvent extraction, expeller pressing, and supercritical fluid extraction methods.
Paeonia, the only genus in the family Paeoniaceae, comprises Ca. 35 species in three sections of Sect. Moutan, Sect, Onaepia, and Sect. Paeonia. Paeonia is widely distributed in a few provinces of China, such as Shandong, Henan, Anhui, and Shanxi [9]. Various peony species are among the important raw drug materials in traditional Chinese medicine, which was used toward atopic eczema along with for anticoagulant, anti-inflammatory, analgesic, and sedative purposes [10]. The seeds of peony are major byproducts in the peony processing industry, and the seeds contain high concentrations of unbound unsaturated fatty acids, such as lino