Production safety of oil extraction with #4 solvent and its products safety
Qi Kun, Wang Ruiyuan
(1.Henan Anyang Mantianxue Protein Co., Ltd., 455000 Henan Anyang, China;
2. China National Association of Grain Sector / CCOA, 100053 Beijing, China)
Abstract: The characteristics of 4# solvent, oil extraction technology, oil production safety and food safety with 4# solvent were discussed. The main component in 4# solvent is liquefied butane. Compared with the oil extraction technology by6# solvent, the technology by 4#solvent has some benefits such as little toxic, lower energy consumption and less residual solvent etc. Multi - stage countercurrent extraction technology with 4# solvent is ripe, and has been applied in practice. Many international organizations and developed countries have generally recognized the safety of propane and butane in the application in food processing, but the quality standards of propane and butane as food adjuncts have not been established. Our country should issue the standards as soon as possible.
Key words: 4# solvent; oils; extraction; liquefied butane; liquefied propane; food safety; production safety
4# solvent is a mixture of pure liquefied butane and liquefied propane, like 6# solvent from oil refining process. 4# solvent used in oil extraction for 17 years, have been established throughout the country more than 20 sets of leaching equipment, used for leaching of dozens of lipid production. For more than 10 years, through the practice of the production safety, draw lessons from the relevant safety standards and liquefied petroleum gas industry combining with the characteristics of this process, establishing a set of effective system of production safety. We hereby engage with the 4# solvent leaching grease technology and give a brief introduction of product safety, for peer reference.
1. 4# solvent properties
The main components of the 4# solvent for liquefied butane (four carbon hydrocarbon, C4), its name is put forward relatively to the 6# solvent given priority to hexane (six carbon hydrocarbons C6).
In practice, 4# solvent is consist of butane (C4) and propane (C3), table 1 lists the physical and chemical properties of propane, butane, and lists the main components of the 6# solvent hexane part of the data. Table 2 is currently used in the production of the main components of propane and butane solvent which is the test result of the national standards of material research center.
Table 1 and 2 shows C3 and C4 is high purity solvents that consist of 4# solvent. In the oil refining fractionation process, methane, ethane (boiling point 88.3℃)is difficult to liquefaction and seldom exists in C3 and C4 fractions, pentane C5 (boiling point 36.1 ℃) above the composition is not easy to gasification, when C3 and C4 fractionation in the liquid phase, and rarely enter propane and butane fractions, so as to ensure the purity of the 4# solvent.
In practice, propane and butane can be used either with different mixing proportion, and also be used alone, if use pure propane solvent (boiling point 47.1 ℃), mixed oil and meal desolventizing temperature can be lower, the material of heat sensitive material is safer, residual solvent will under 1 mg/kg or even not detected.
Pure liquefied propane and butane are slightly lower than the price of 6# solvent that can be transported by train and bus tanker.
Table1, Solvent physicochemical property
Index Propane Butane Hexane
Color and transparency colorless and transparent colorless and transparent colorless and transparent
Odour odourless odourless odourless
Average molecular weight 44 58 86
Dielectric constant 1.69 1.78 1.89
Liquid ratio (g/cm3) 0.484 0.568 0.652
Boiling point (℃) -47.1 -0.5 68.7
Vapor pressure (MPa, 30 ℃) 1.09 0.32 0.027
Upper and lower explosion (%) 2.1 ～9.5 1.8 ～9.1 1.1 ～7.5
Flash point (℃) - 104.4 - 60 - 22.8
Spontaneous combustion point (℃) 466 405 260
Risk 3.52 4.06 5.82
Table2, the composition and content of the solvent used in the production(%)
Composition Propane solvent Butane solvent
Methane 0.0044 0.058
Ethane 0.55 0.058
Propane 99.4 3.8
n-butane 0.031 59.0
iso-pentane 0.0003 0.0005
n-pentane 0.0006 0.0003
n-hexane 0.0008 0.0006
butane 0 0.24
2. 4# solvent oil leaching process
2.1 The introduction of tank group type oil extraction process
4# solvent leaching process is under the pressure of 0.2 ~ 0.6 MPa, leaching equipment is pressure vessel.
After material entering extractor, close the feed valve and take out the empty gas cans, pumping mixed oil with other leaching tank countercurrent extraction, the leaching time and frequency is determined by leaching materials’ characteristics. Reaching the desired residual oil, start meal desolventizing. Open the unicom valve of the leaching tank with compressor while desolventizing. Solvent in pulp after gasification by compressor, compression after liquefaction flows into the solvent tank. After desolventizing, the meal discharged from the leaching tank to finished meal, and leaching tank into the next cycle. Mixed oil steamed in the evaporation system, when evaporation by compressor, solvent gasification in mixed oil and pump out by compressor, pressure shrink after liquefied into the solvent flow tank, crude oil to refining workshop.
Continuous leaching process have feasible scheme and will carry out after funds workable.
2.2 Characteristics of extraction process
(1) The material do not need to intense heat in leaching process, desolventizing temperature as room temperature, ensure the meal and oil in the invariance of the thermal sensitive material.
(2) Steam consumption is very low in the leaching process. 6# solvent leaching, not only heat the meal and oil to above 100 ℃ respectively, and the corresponding solvent evaporation for gas condensate down again ultimately, that consume a large amount of heat. In this process the meal and oil in the same temperature and feed temperature, solvent evaporation heat most provided by the liquefaction of solvent release heat, low heat consumption.
(3) Low residual solvent, low solvent toxicity. The production of this product residue solvent are below 10 mg/kg, if necessary, you can easily reach below 1 mg/kg, (cooking oil specified in the national standard under 10 mg/kg is not detected). In terms of solvent toxicity, according to the grade of toxicology, hexane as the low poison, butane, propane as slightly toxic, its LC50 value is: butane 680 g/m3, hexane 120 ~ 150 g/m3.It is visible that butane inhalation toxicity is four or five times lower than hexane.
2.3 The application of extraction process
Now more than a dozen provinces in the country had established more than 20 extraction workshop using 4# solvent applied in walnut, marigold, microbial oil, beans, cocoa butter and many other products. Our company has large-scale processing products are: soybean, wheat germ (10000 t/d) (3, 000 t/d), lutein (2,500 t/d), chili red element (3, 000 t/a), grape seed (2,000 t/a), roses, ganoderma lucidum spore, sweet basil, walnut and so many kinds of raw materials and products with good efficiency.
3. Production safety of 4# solvent oil extraction process
In accordance with the requirements of the national ‘Code for Fire Protection Design of Buildings’, both 4# and 6# solvent extraction workshop are A class level of explosion-proof workshop, the fire prevention space and explosion venting area are basically the same. Compared with 6# solvent, 4# solvent the upper and lower explosion range is big, the lower explosive limit is higher, gas proportion is little and difficult to gather explosive gas, for the explosion risk of solvent escape, 4# solvent is safe. But 4# solvents are working under pressure, high requirements for equipment and workers, and once leak, it will bring great latent risks. So 4# solvent extraction equipment are mostly pressure vessel, pipes, instruments and valves are working under the pressure of 0.2 ~ 0.6MPa. But compared with supercritical carbon dioxide extraction with 30 ~ 50MPa work pressure, and chemical industry with middle-high pressure, 4# solvent only work within the range of low pressure (below 1.6MPa is low pressure), industrial application security is based on mature technology and equipment.
4. Edible safety of 4# solvent oil extraction process
Due to 4# solvent extraction mainly used in food processing, according to the "health law" the relevant provisions, 4# solvent belongs to food additives, it has high demands for its edible security. So we made investigation and study on the edible safety of 4# solvent extraction product.
(1) In the United Nations food and agriculture organization of the codex alimentarius, propane and butane can be used in food processing, and no limited residue; In the United States Food chemicals codex, propane and butane mainly used as food propellant, degeneration agent, filling agent (oxygen blocking agent); In 1983 the Us Food and Drug Administration put propane and butane as "general think security" item, no residue limits; In 2000, the seventh edition of the Japanese food additive standards, propane and butane are among the available solvent, the residues in food has no limits; As early as March 24, 1999 European food science committee approved propane is used for food, and no residue limits; In addition, Irish, New Zealand and other countries accept propane and butane used in food processing.
But in addition to the food chemicals codex defined several technical index for propane and butane, other codes and standards only approve to use without specific technical index.
(2) In order to comprehensive search about propane and butane standard in foreign countries, I have commissioned national standard pavilion novelty search foreign standards of liquefied propane and butane used as food additives, by the end of October 2006, checked the ISO, IEC, the United States, Britain, Japan, Germany, France and so on more than 30 countries standards of the country and the United States more than 400 industry, carried on the novelty retrieval, novelty conclusion: only in the Us Food and Drug Administration saying propane and butane can be used in the food processing, but no standards of propane and butane used as food additives.
(3) Refer to the toxicity of chemicals and regulations handbook of environmental data, the regulations and Germany recommended values are: in a professional environment in the air of permissible exposure limits of propane 1,800 mg/m3, n-hexane 180 mg/m3, it is visible that propane is 10 times higher safety than hexane to human body. Check the oil leaching technology, human body health limiting concentration (load time average values), n-butane for 800 mg/kg, n-hexane for 50 mg/kg, it is visible that butane toxicity to human body is 16 times smaller than hexane.
(4) The health epidemic prevention station of Henan and Shandong province carried out toxicology test on 4# solvent respectively, test according to the food safety toxicology evaluation procedure and method of GB 15193-1994 in mice with acute toxicity test, Ames test, bone marrow micronucleus test and mouse sperm malformation test, 30 d of rats by gastric feeding test 6 project is researched, the conclusion is non-toxic.
5. Conclusion
It is widely recognized by international organizations and developed countries that butane and propane in the applications of food security, but no standards. It has important significance to make standards in our country for butane and propane as food additives as soon as possible. 4# solvent toxicity is less than 6 solvent, low residue solvent in oil and meal and small energy consumption. It is feasible to instead of 6# solvent within a certain range in extraction process.
