Process for removing free fatty acid from waste tea oil by extraction

Abstract

A kind of process for extracting and removing free fatty acid in waste tea oil, comprising the following steps: (1) pretreatment: after waste tea oil is filtered to remove solid impurities, it is stored in dry place for standby use; (2) extraction deacidification: after waste tea oil pretreated in step (1) is mixed with tetrabutylammonium chloride uniformly, it is extracted and deacidified under the condition of ultrasonic heating and stirring, after centrifugal separation, the upper oil phase is taken, which is deacidified tea oil; (3) rotary evaporation treatment: after tetrabutylammonium chloride containing oil mixture obtained after centrifugal separation in step (2) is added with n-hexane, vortex assisted extraction is carried out, centrifugal separation is carried out, the upper n-hexane mixture is taken, after rotary evaporation, neutral oil and n-hexane are obtained respectively. The deacidification rate of deacidified tea oil obtained by the process is high, the total yield of oil is high, the obtained neutral oil is rich in nutrition and stable in quality, the deacidification reaction condition is mild, green and pollution-free, the process is simple, efficient, low in cost and suitable for industrial production.

Description

Technical Field

[0001] This invention relates to a process for extracting and removing free fatty acids, specifically a process for extracting and removing free fatty acids from waste tea oil. Background Technology

[0002] Due to the continuous increase in population, the production of waste cooking oil has grown unprecedentedly. my country generates approximately 20 million tons of waste edible oil annually, and this amount is increasing year by year. Camellia oil, as a major edible oil in my country, generates a huge amount of waste each year. Waste edible camellia oil can replace animal and vegetable oils in the production of biodiesel, turning waste into treasure and significantly reducing raw material costs. However, because waste edible camellia oil contains a large amount of free fatty acids, pigments, and other impurities, its composition is complex. Therefore, pre-deacidification treatment is often required before biodiesel production. Current technologies mostly use alkali refining for deacidification. However, this method has a low yield of neutral oil, and is particularly unsuitable for high-acid-value oils. Furthermore, alkali refining significantly damages the nutrients in the oil, and the wastewater generated from washing also causes environmental pollution. Therefore, it is essential to find a green, environmentally friendly, and energy-efficient deacidification method.

[0003] CN113061486A discloses an enzyme-catalyzed method for removing free fatty acids from oils, which utilizes a multifunctional natural eutectic solvent system constructed with lipase to remove fatty acids from vegetable oils. Although it has high catalytic efficiency, the enzyme reaction conditions, such as temperature, pH, and ionic strength, are difficult to control, making the operation challenging. Furthermore, the enzyme is prone to inactivation, difficult to preserve, and expensive.

[0004] CN111909781A discloses a method for extracting free fatty acids from crude vegetable oil, which utilizes a polyol-based eutectic solvent to remove free fatty acids from the crude vegetable oil. Although the operation is simple, the removal rate of free fatty acids is low, and the extractant cannot be reused.

[0005] CN1458255A discloses a method for separating and purifying unsaturated fatty acids from peanut oil, which uses a molecular distillation apparatus to remove free fatty acids from peanut oil. Although it achieves a high degree of separation, molecular distillation equipment is expensive. The apparatus requires a high vacuum, demanding high-quality sealing materials, and necessitates a suitable distance between the evaporation and condensation surfaces. The equipment is difficult to manufacture, costly, and not easily applicable to conventional industrial production.

[0006] CN101717689A discloses a method for preparing first-grade tea oil by alcohol extraction and deacidification, which utilizes the polar solvent alcohol to extract and deacidify crude tea seed oil. Although it has a high oil yield, the removal effect of free fatty acids is generally poor, and the reaction requires vacuum, high temperature and high pressure, which is time-consuming, complex and difficult to control.

[0007] Therefore, there is an urgent need to develop a process for removing free fatty acids from waste tea oil using eutectic solvent extraction. The resulting deacidified tea oil has a high deacidification rate and a high total oil yield. The resulting neutral oil is rich in nutrients and has stable quality. The deacidification reaction conditions are mild, green, and pollution-free. The process is simple, efficient, and low in cost, making it suitable for industrial production. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to overcome the above-mentioned defects of the prior art and provide a process for extracting and removing free fatty acids from waste tea oil with high deacidification rate, high total oil yield, rich nutrition and stable quality of the obtained neutral oil, mild deacidification reaction conditions, green and pollution-free process, simple and efficient process, low cost, and suitable for industrial production.

[0009] The technical solution adopted by this invention to solve its technical problem is as follows: A process for extracting and removing free fatty acids from waste tea oil, comprising the following steps: (1) Pretreatment: After filtering out solid impurities, the waste tea oil is stored in a dry place for later use; (2) Extraction and deacidification: The waste tea oil pretreated in step (1) is mixed evenly with tetrabutylammonium chloride. Under ultrasonic heating and stirring, the tea oil is extracted and deacidified. After centrifugation, the upper oil phase is taken as the deacidified tea oil. (3) Rotary evaporation treatment: After centrifugation in step (2), n-hexane is added to the lower layer of tetrabutylammonium chloride oil mixture. After vortex-assisted extraction, centrifugation is performed, and the upper layer of n-hexane mixture is taken. After rotary evaporation, neutral oil and n-hexane are obtained respectively.

[0010] Preferably, in step (1), the mass fraction of free fatty acids in the waste tea oil is 1-4%. The waste tea oil used in this invention is derived from waste oil obtained by frying frozen fish for 3-5 minutes after boiling tea oil.

[0011] Preferably, in step (1), the filtration uses a 400-600 mesh filter.

[0012] Preferably, in step (2), the mass ratio of the pretreated waste tea oil to tetrabutylammonium chloride is 1:0.1-0.5. The eutectic solvent tetrabutylammonium chloride used in this invention is a novel solvent. First, it can chemically react with waste tea oil. Tetrabutylammonium chloride is lipophilic and can form stable hydrogen bonds with free fatty acids in waste tea oil, thereby efficiently removing free radicals from the oil. Second, it can be used as an extractant to extract bioactive substances from plant materials, such as polyphenols, polysaccharides, phenolic acids, and other beneficial components. It can also separate and enrich trace components in oils and their byproducts, such as tocopherols. The amount of extractant used will affect the contact area with free fatty acids in tea oil and the mass transfer rate of free fatty acids in the two phases.

[0013] Preferably, in step (2), the ultrasonic power for extraction and deacidification is 300–900 W, the temperature is 25–70 °C, the stirring speed is 400–1200 r / min, and the time is 5–15 min. Suitable extraction and deacidification conditions can ensure that tetrabutylammonium chloride and the free fatty acids in waste tea oil come into full contact, thereby improving the extraction efficiency.

[0014] Preferably, in step (2), the centrifugation speed is 1000-5000 r / min and the time is 10-30 min. Suitable centrifugation conditions can promote the separation of deacidified tea oil and tetrabutylammonium chloride. If the speed is too fast, a small amount of oil will dissolve into the lower liquid phase.

[0015] Preferably, in step (3), the volume-to-mass ratio (mL / g) of the n-hexane to the pretreated waste tea oil is 8–18:100. The n-hexane is beneficial for fully dissolving the residual neutral oil in the tetrabutylammonium chloride oil mixture.

[0016] Preferably, in step (3), the vortex-assisted extraction time is 1 to 8 minutes. The purpose of vortex-assisted extraction is to allow the hexane and the lower layer of tetrabutylammonium chloride oil mixture to be fully mixed and reacted, so as to extract as much neutral oil as possible and reduce oil loss.

[0017] Preferably, in step (3), the centrifugation speed is 1000-4000 r / min and the time is 10-30 min. Suitable centrifugation conditions can promote the complete separation of the upper hexane mixture and the lower tetrabutylammonium chloride.

[0018] Preferably, in step (3), the rotary evaporation temperature is 45-75°C and the time is 20-60 min. The neutral oil is the partially deacidified tea oil lost during extraction and deacidification. If stirring is used, a small amount of oil will dissolve into the lower liquid phase. Since hexane is volatile, rotary evaporation can be used for atmospheric pressure distillation and boiling to distill off the hexane, thereby reducing the loss of neutral oil.

[0019] Preferably, in step (3), the lower layer of tetrabutylammonium chloride, after vortex-assisted extraction and centrifugation, is subjected to vacuum desolventizing treatment and then reused. Vacuum desolventizing treatment can further remove residual oil and solvent from the surface of tetrabutylammonium chloride.

[0020] Preferably, the vacuum desolventizing treatment is performed at a temperature of 60–70°C, a vacuum pressure of -0.08–-0.10 MPa, and a time of 15–25 min.

[0021] The beneficial effects of the process of this invention are as follows: (1) The deacidification process of the present invention uses a low eutectic solvent for deacidification treatment, and the deacidified tea oil obtained has a deacidification rate of up to 97.49% and a total oil yield of up to 92.70%. The free fatty acid content in the deacidified tea oil is as low as 0.11%, and the free fatty acid content in the neutral oil is as low as 0.06%. The neutral oil obtained by the process of the present invention has a light color, clear and transparent luster, rich nutrients, and stable quality. (2) The tetrabutylammonium chloride used in the process of this invention has the characteristics of being stable and not easily volatile, and can be reused after treatment. The deacidification reaction conditions are mild, green and pollution-free. (3) The process of this invention is simple, efficient and low-cost, and suitable for industrial production. Detailed Implementation

[0022] The present invention will be further described below with reference to the embodiments.

[0023] The waste tea oil used in this embodiment of the invention has a free fatty acid content of 3.85%, which is derived from waste oil obtained by frying frozen fish for 4 minutes after boiling the tea oil. Unless otherwise specified, the raw materials or chemical reagents used in this embodiment and comparative example of the invention are obtained through conventional commercial channels.

[0024] In the embodiments and comparative examples of this invention, the free fatty acids in the raw materials and products were detected using the method for determining the acid value of oils before and after deacidification, as specified in the national standard GB 5009.2229-2016 "National Food Safety Standard - Determination of Acid Value in Food".

[0025] Example 1 (1) Pretreatment: After filtering the waste tea oil through a 500-mesh filter to remove solid impurities, store it in a dry place for later use; (2) Extraction and deacidification: 100g of waste tea oil pretreated in step (1) was mixed with 40g, 10g, 30g and 50g of tetrabutylammonium chloride (referred to as Example 1-1 to Example 1-4 respectively) in sequence. Under the conditions of ultrasonic power of 600W, temperature of 55℃ and stirring speed of 1000r / min, the mixture was extracted and deacidified for 10min. After centrifugation at 5000r / min for 20min, the upper oil phase was taken, which is the deacidified tea oil. (3) Rotary evaporation treatment: 10 mL of n-hexane was added to the lower layer of tetrabutylammonium chloride oil mixture obtained after centrifugation in step (2), and after vortex-assisted extraction for 5 min, centrifugation was carried out at 2000 r / min for 20 min. The upper layer of n-hexane mixture was taken and rotary evaporated at 75℃ for 40 min to obtain neutral oil and n-hexane respectively.

[0026] In step (3), the lower layer of tetrabutylammonium chloride, which was separated by centrifugation after vortex-assisted extraction, was subjected to vacuum desolvation treatment at 65℃ and -0.09MPa for 20 minutes and then reused.

[0027] In Example 1 of this invention, after treating waste tea oil with different amounts of extractant, the total removal rate of free fatty acids in the deacidified tea oil and neutral oil (calculated by formula = 1 - (mass of deacidified tea oil g * free fatty acid content of deacidified tea oil % + mass of neutral oil g * free fatty acid content of neutral oil %) / (100g * 3.85%) * 100%, the same below) and the total yield of deacidified tea oil and neutral oil (calculated by formula = (mass of deacidified tea oil g + mass of neutral oil g) / 100g * 100%, the same below) are shown in Table 1.

[0028] Table 1. Total removal rate of free fatty acids and total oil yield after treating waste tea oil in Example 1 of this invention.

[0029] As shown in Table 1, the amount of tetrabutylammonium chloride used as an extractant affects its contact area with free fatty acids in tea oil and the mass transfer rate of free fatty acids in the two phases.

[0030] Example 2 (1) Pretreatment: After filtering the waste tea oil through a 500-mesh filter to remove solid impurities, store it in a dry place for later use; (2) Extraction and deacidification: 100g of waste tea oil pretreated in step (1) was mixed evenly with 40g of tetrabutylammonium chloride. Under the conditions of ultrasonic power of 600W, temperature of 25℃, 40℃, 55℃ and 70℃ respectively (referred to as Example 2-1 to Example 2-4 respectively), and stirring speed of 400r / min, the mixture was extracted and deacidified for 5min. After centrifugation at 2000r / min for 20min, the upper oil phase was taken, which is the deacidified tea oil. (3) Rotary evaporation treatment: 12 mL of n-hexane was added to the lower layer of tetrabutylammonium chloride oil mixture obtained after centrifugation in step (2). After vortex-assisted extraction for 5 min, centrifugation was carried out at 1500 r / min for 30 min. The upper layer of n-hexane mixture was taken and evaporated at 75℃ for 40 min to obtain neutral oil and n-hexane respectively.

[0031] In step (3), the lower layer of tetrabutylammonium chloride, which was separated by centrifugation after vortex-assisted extraction, was subjected to vacuum desolvation treatment at 65℃ and -0.09MPa for 20 minutes and then reused.

[0032] Table 2 shows the total removal rate of free fatty acids and the total yield of deacidified tea oil and neutral oil obtained after treating waste tea oil at different extraction temperatures in Example 2 of this invention.

[0033] Table 2. Total removal rate of free fatty acids and total oil yield after treating waste tea oil in Example 2 of this invention.

[0034] As shown in Table 2, since the extractant tetrabutylammonium chloride is solid at room temperature, it is difficult to form a uniform and transparent liquid eutectic solvent phase with free fatty acids at lower temperatures. Appropriately increasing the temperature helps tetrabutylammonium chloride form hydrogen bonds with free fatty acids, and at the same time can reduce the viscosity of tea oil and increase the mass transfer rate of free fatty acids in the two phases. However, if the temperature is too high, it will cause the triglycerides in tea oil to decompose into free fatty acids, which will increase the acid value.

[0035] Example 3 (1) Pretreatment: After filtering the waste tea oil through a 500-mesh filter to remove solid impurities, store it in a dry place for later use; (2) Extraction and deacidification: 100g of waste tea oil pretreated in step (1) was mixed evenly with 30g of tetrabutylammonium chloride. Under the conditions of ultrasonic power of 600W, temperature of 55℃ and stirring speed of 800r / min, the tea oil was extracted and deacidified for 5min, 7.5min, 10min and 15min respectively (referred to as Example 3-1 to Example 3-4 respectively). After centrifugation for 20min at a speed of 2000r / min, the upper oil phase was taken, which is the deacidified tea oil. (3) Rotary evaporation treatment: 14 mL of n-hexane was added to the lower layer of tetrabutylammonium chloride oil mixture obtained after centrifugation in step (2). After vortex-assisted extraction for 5 min, centrifugation was carried out at 1500 r / min for 20 min. The upper layer of n-hexane mixture was taken and evaporated at 75℃ for 40 min to obtain neutral oil and n-hexane respectively.

[0036] In step (3), the lower layer of tetrabutylammonium chloride, which was separated by centrifugation after vortex-assisted extraction, was subjected to vacuum desolvation treatment at 65℃ and -0.09MPa for 20 minutes and then reused.

[0037] Table 3 shows the total removal rate of free fatty acids and the total yield of deacidified tea oil and neutral oil obtained after treating waste tea oil at different extraction times in Example 3 of this invention.

[0038] Table 3. Total removal rate of free fatty acids and total oil yield after treating waste tea oil in Example 3 of this invention.

[0039] As shown in Table 3, an appropriate extraction time is conducive to achieving extraction equilibrium, thereby improving the total removal rate of free fatty acids and the total oil yield. If the extraction time is too short, it will not be conducive to achieving extraction equilibrium, while if the extraction time is too long, it will increase production costs.

[0040] Example 4 (1) Pretreatment: After filtering the waste tea oil through a 500-mesh filter to remove solid impurities, store it in a dry place for later use; (2) Extraction and deacidification: 100g of waste tea oil pretreated in step (1) was mixed evenly with 50g of tetrabutylammonium chloride. Under the conditions of ultrasonic power of 600W, temperature of 70℃, and stirring speed of 400r / min, 800r / min, 1000r / min and 1200r / min respectively (referred to as Example 4-1 to Example 4-4 respectively), the mixture was extracted and deacidified for 10min. After centrifugation at 2000r / min for 20min, the upper oil phase was taken, which is the deacidified tea oil. (3) Rotary evaporation treatment: 16 mL of n-hexane was added to the lower layer of tetrabutylammonium chloride oil mixture obtained after centrifugation in step (2). After vortex-assisted extraction for 5 min, centrifugation was carried out at 2000 r / min for 30 min. The upper layer of n-hexane mixture was taken and evaporated at 75℃ for 40 min to obtain neutral oil and n-hexane respectively.

[0041] In step (3), the lower layer of tetrabutylammonium chloride, which was separated by centrifugation after vortex-assisted extraction, was subjected to vacuum desolvation treatment at 65℃ and -0.09MPa for 20 minutes and then reused.

[0042] The total removal rate of free fatty acids and the total yield of deacidified tea oil and neutral oil obtained after treating waste tea oil at different extraction stirring speeds in Example 4 of this invention are shown in Table 4.

[0043] Table 4. Total removal rate of free fatty acids and total oil yield after treating waste tea oil in Example 4 of this invention.

[0044] As shown in Table 4, a suitable stirring speed can allow tetrabutylammonium chloride to fully contact the free fatty acids in waste tea oil, thereby improving the extraction efficiency.

[0045] In summary, in the process of this invention, the amount of extractant, extraction temperature, extraction time, and stirring speed are important factors affecting the deacidification effect of tea oil. Under suitable conditions, these factors help to obtain a high removal rate of free fatty acids and a high yield of waste tea oil.

[0046] Comparative Example 1 100 g of crude tea oil with an acid value of 105.35 mg / g was weighed and added to a mixed solution of 88% ethanol at a ratio of 1:2.5. The mixture was stirred thoroughly at 60°C using a constant-temperature magnetic stirrer. The mixture was then poured into a separatory funnel and allowed to stand for 40 min. When a clear separation of the upper and lower layers (ethanol and oil) appeared, the lower oil phase was collected and the extraction was repeated twice. After extraction, both phases were evaporated separately using a vacuum rotary evaporator to recover the ethanol. Under these optimal conditions, the acid value of the deacidified tea oil was 12.81 mg / g, and the deacidification rate was 87.84%.

[0047] In this comparative example, the removal rate of free fatty acids from tea oil was 87.84%, which is lower than that in the embodiment of the present invention. Furthermore, the price of the extractant ethanol mixture solution is expensive, the concentration of the ethanol solution recovered after deacidification is reduced, and it is difficult to reuse.

Claims

1. A process for extracting and removing free fatty acids from waste tea oil, characterized in that, Includes the following steps: (1) Pretreatment: After filtering out solid impurities, the waste tea oil is stored in a dry place for later use; (2) Extraction and deacidification: The waste tea oil pretreated in step (1) is mixed evenly with tetrabutylammonium chloride. Under ultrasonic heating and stirring conditions, extraction and deacidification are performed. After centrifugation, the upper oil phase is taken as the deacidified tea oil. The mass ratio of the pretreated waste tea oil to tetrabutylammonium chloride is 1:0.1 to 0.

5. The ultrasonic power of the extraction and deacidification is 300 to 900 W, the temperature is 25 to 70 °C, the stirring speed is 400 to 1200 r / min, and the time is 5 to 15 min. (3) Rotary evaporation treatment: After centrifugation in step (2), n-hexane is added to the lower layer of tetrabutylammonium chloride oil mixture. After vortex-assisted extraction, centrifugation is performed, and the upper layer of n-hexane mixture is taken. After rotary evaporation, neutral oil and n-hexane are obtained respectively.

2. The process for extracting and removing free fatty acids from waste tea oil according to claim 1, characterized in that: In step (1), the mass fraction of free fatty acids in the waste tea oil is 1-4%; the filtration uses a 400-600 mesh filter.

3. The process for extracting and removing free fatty acids from waste tea oil according to claim 1 or 2, characterized in that: In step (2), the centrifugation speed is 1000-5000 r / min and the time is 10-30 min.

4. The process for extracting and removing free fatty acids from waste tea oil according to claim 1 or 2, characterized in that: In step (3), the volume-to-mass ratio of n-hexane to pretreated waste tea oil is 8-18:100 (mL / g); the vortex-assisted extraction time is 1-8 min; the centrifugation speed is 1000-4000 r / min and the time is 10-30 min; the rotary evaporation temperature is 45-75℃ and the time is 20-60 min.

5. The process for extracting and removing free fatty acids from waste tea oil according to claim 3, characterized in that: In step (3), the volume-to-mass ratio of n-hexane to pretreated waste tea oil is 8-18:100 (mL / g); the vortex-assisted extraction time is 1-8 min; the centrifugation speed is 1000-4000 r / min and the time is 10-30 min; the rotary evaporation temperature is 45-75℃ and the time is 20-60 min.

6. The process for extracting and removing free fatty acids from waste tea oil according to claim 1 or 2, characterized in that: In step (3), the lower layer of tetrabutylammonium chloride, which is separated by centrifugation after vortex-assisted extraction, is reused after vacuum desolventizing treatment; the temperature of the vacuum desolventizing treatment is 60-70℃, the vacuum pressure is -0.08--0.10MPa, and the time is 15-25min.

7. The process for extracting and removing free fatty acids from waste tea oil according to claim 3, characterized in that: In step (3), the lower layer of tetrabutylammonium chloride, which is separated by centrifugation after vortex-assisted extraction, is reused after vacuum desolventizing treatment; the temperature of the vacuum desolventizing treatment is 60-70℃, the vacuum pressure is -0.08--0.10MPa, and the time is 15-25min.

8. The process for extracting and removing free fatty acids from waste tea oil according to claim 4, characterized in that: In step (3), the lower layer of tetrabutylammonium chloride, which is separated by centrifugation after vortex-assisted extraction, is reused after vacuum desolventizing treatment; the temperature of the vacuum desolventizing treatment is 60-70℃, the vacuum pressure is -0.08--0.10MPa, and the time is 15-25min.

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