KR20210072420A - Method for producing bio oil from microalgae using base catalyst - Google Patents

Abstract

The present invention relates to a method of manufacturing a bio-oil, a bio-oil manufactured thereby with improved purity, and a method of manufacturing a bio-diesel, in which the method of manufacturing the bio-oil includes: a first step of preparing a mixture by adding a hydrophobic organic solvent and a base catalyst dissolved in alcohol to microalgae, and stirring the mixture; a second step of separating a hydrophobic organic solvent layer including the bio-oil from the stirred mixture; and a third step of removing the organic solvent from the hydrophobic organic solvent layer including the bio-oil, and the method of manufacturing the bio-diesel includes adding a bio-diesel conversion catalyst to the bio-oil manufactured by the method of manufacturing the bio-oil. Accordingly, a high-purity bio-oil is extracted while reducing inhibition of moisture without a separate drying process, so that simple and economical properties are obtained.

Description

Method for producing bio oil from microalgae using base catalyst

The present invention relates to a method for producing bio-oil from microalgae using a base catalyst, the bio-oil produced by the method, and a method for producing biodiesel using the bio-oil.

Biodiesel is a methyl or ethyl ester compound of fatty acids produced from vegetable oil or animal fat. Compared to conventional diesel, biodiesel can significantly reduce the emission of air pollutants such as carbon monoxide, fine dust, hydrocarbons, and toxic substances, making it suitable as an eco-friendly vehicle fuel. In addition, carbon dioxide emitted from the combustion of biodiesel is absorbed and fixed again by the photosynthetic mechanism of plants, so there is little net emission of carbon dioxide, and thus it is receiving great attention _{worldwide as a carbon dioxide neutral fuel (CO 2 -neutral fuel).}

However, currently biodiesel is mainly produced using vegetable oil extracted from edible crops such as soybeans and rapeseed, which has been criticized for aggravating food shortages in poor countries such as Africa and low-income groups as it causes grain prices to rise. In addition, it is pointed out that extensive rainforests or forests are being developed for the production of raw materials such as palm oil in response to the increasing demand for biodiesel, which rather promotes global warming. Moreover, as Korea imports most of the raw materials for biodiesel (soybean oil or palm oil) from abroad, it is highly likely that the supply and demand and price will depend heavily on external changes similar to petroleum resources.

In order to solve this problem, a technology that uses microalgae as a raw material instead of the existing soybean oil or palm oil is attracting a lot of attention as 'next-generation biodiesel technology'. Microalgae can be grown using water, carbon dioxide and sunlight, and can be cultivated anywhere, including wasteland, coastal areas, and the sea, so they do not compete with existing land crops in terms of land or space. In addition, microalgae accumulate a large amount of oil (up to 70%) in the living body according to the culture conditions, and the oil production per unit area is 50 to 100 times higher than that of conventional edible crops such as soybeans, so it has a very high potential as an alternative biological oil. high. From this, interest in biodiesel production technology based on microalgae, which has very good oil production per unit area compared to terrestrial plants, is growing.

On the other hand, in order to extract the oil from the microalgae, various methods such as a solvent extraction method, a microwave method, a hydrothermal treatment method, an enzyme treatment method, and a compression method can be used. Most of these oil extraction methods involve a mechanism of releasing the oil inside the cell wall by partially disrupting the cell wall of the microalgae, and an organic solvent is generally used to recover the oil existing inside or outside the collapsed cell wall. The application of the solvent extraction method to the dried sample is the most commonly used method and has high efficiency, but has a disadvantage in that the oil extraction rate is inhibited by moisture, so the energy cost for drying the sample is high. In addition, the microwave device has the advantage of shortening the extraction time, but requires initial facility investment. Although the application of hot water extraction for industrial oil production can be considered, it is suitable for the treatment of microalgae with a thin cell wall, but the cell wall is not easily broken for the treatment of species with thick cell walls such as chlorella, so the efficiency is low. Enzymes are still expensive and require reuse after treatment, and the efficiency of the compression method depends on the size of the microalgae. Therefore, for oil extraction for industrial use, it can be applied in the presence of moisture without drying the sample, and by minimizing the installation cost or material cost, a process that can collapse the cell wall and recover the oil with high efficiency without much process or high cost need to develop

Domestic Patent Publication No. 10-2008-0070988 Domestic Patent Publication No. 10-2008-0015758

One object of the present invention is to prepare a mixture by adding a hydrophobic organic solvent and a base catalyst dissolved in alcohol to microalgae, a first step of stirring; a second step of layer-separating the hydrophobic organic solvent layer containing bio-oil in the stirred mixture; and a third step of removing the organic solvent from the hydrophobic organic solvent layer containing the bio-oil.

Another object of the present invention is to provide a bio-oil produced by the above-described bio-oil manufacturing method, characterized in that the purity is improved.

Another object of the present invention is to provide a biodiesel production method comprising the step of adding a biodiesel conversion catalyst to the bio-oil.

This will be described in detail as follows. Meanwhile, each description and embodiment disclosed in the present invention may be applied to each other description and embodiment. That is, all combinations of the various elements disclosed herein fall within the scope of the present invention. In addition, it cannot be considered that the scope of the present invention is limited by the specific descriptions described below.

A first aspect of the present invention is a first step of preparing a mixture by adding a hydrophobic organic solvent and a base catalyst dissolved in alcohol to microalgae and stirring; a second step of layer-separating the hydrophobic organic solvent layer containing bio-oil in the stirred mixture; and a third step of removing the organic solvent from the hydrophobic organic solvent layer containing the bio-oil.

As used herein, the term "microalgae" can be used to rapidly increase in number while dividing very easily through cell division. Although corn or sugarcane, the main raw materials for biofuel, cannot double in production in a short period of time, single-celled microalgae can rapidly divide and multiply several times a day as long as the surrounding environment, such as water temperature and nutrients, is right. have. Microalgae can be grown using water, carbon dioxide and sunlight, and can be cultivated anywhere, including wasteland, coastal areas, and the sea, so they do not compete with existing land crops in terms of land or space. In addition, since microalgae do not require tissues such as stems or roots like general plants, all cells can participate in photosynthesis. Saying that all cells photosynthesize could mean more favorable for biofuel production. That is, when cultivated in the same area, the amount of biofuel obtained from microalgae can be obtained significantly more than biofuel obtained from plants such as corn or soybeans. More specifically, microalgae accumulate a large amount of oil (up to 70%) in the living body depending on the culture conditions, and the oil production per unit area is 50-100 times higher than that of conventional edible crops such as soybeans, so it has potential as an alternative biological oil. This is very high. From this, it can be seen that the oil production per unit area is very superior to that of land plants.

The "bio-oil" of the present invention is obtained from microalgae by solvent extraction, and includes a mechanism for discharging the oil inside the cell wall by disintegrating a part of the cell wall of the microalgae. At this time, a hydrophobic organic solvent is used to recover the oil existing inside or outside the collapsed cell wall. The extracted bio-oil may use some components of oil extracted from microalgae as raw materials for functional cosmetics as well as biodiesel, or may be used as raw materials for pharmaceuticals (FIG. 1). Specifically, astaxanthin, which has an antioxidant effect, can be applied as a raw material for cosmetics, food, pharmaceuticals, nutritional supplements and feed. Omega-3 fatty acids including DHA (docosa hexaenoic acid) and EPA (eicosapentaenoic acid) are also examples of typical oils that can be extracted from microalgae.

The "base catalyst" of the present invention may be used for improving the properties of bio-oil. Most of the microalgal oil has a dark green viscous and low fluidity liquid form, and the content of fatty acid methyl ester is not high during biodiesel conversion. Therefore, in order to increase the fatty acid methyl ester content of microalgal biodiesel, it is necessary to improve the properties of the oil.

In the 'second step' and 'third step' of the present invention, when a hydrophobic organic solvent is used, the bio-oil with improved properties moves to the hydrophobic organic solvent layer, the base catalyst moves to the alcohol layer, and the microalgal debris forms an intermediate layer. Since the layers are separated from each other, the organic solvent layer can be separated and recovered. Centrifugation may be performed in addition to gravity sedimentation to increase the rate of layer separation. When the solvent is removed through the evaporation process of the solvent layer containing the oil, only bio-oil can be finally obtained.

An acid catalyst may be further added to the stirred mixture after the first step of the present invention. In order to improve oil properties, only a base catalyst can be used, but secondary stirring can also be performed with an acid catalyst after the first stirring with the base catalyst. In this process, the green chlorophyll of bio-oil is also removed. The properties of the oil are similar when only the base catalyst is used and when the acid catalyst is used after the base catalyst is used, but the color of the oil is different. In some cases, decolorization is required when biodiesel is applied, so it is possible to remove green color in the solvent extraction process using an acid catalyst. In addition, since chlorophyll in oil interferes with biodiesel conversion, the content of fatty acid methyl esters may increase during biodiesel conversion of oil with reduced chlorophyll.

Specifically, the microalgae are Anacystis nidulans (Anacystis nidulans), Ankistrodesmus (Ankistrodesmus sp.), Biddulpha aurita (Biddulpha aurita), Chetoceros (Chaetoceros sp.), Chiramidomonas apple Chlamydomonas applanata, Chlamydomonas reinhardtii, Chlorella sp., Chlorella ellipsoidea, Chlorella emersonides, Chlorella protothecoides (Chlorella protothecoides) ), Chlorella pyrenoidosa, Chlorella sorokiniana, Chlorella vulgaris, Chlorella minutissima, Chlorella minutissima, Chlorococculittorale, Clotella (Cyclotella cryptica), Dunaliella bardawil, Dunaliella salina, Dunaliella tertiolecta, Dunaliella primolecta, Gymnodinum sp. .), Hamenomonas carterae (Hymenomonas carterae), Isochrysis galbana (Isochrysis galbana), Isochrysis (Isochrysis sp.), Microcystis aeruginosa (Microcystis aeruginosa), Micromonas fusillae ( Micromonas pusilla), Monodus subterraneous, Nanochloris (Nannochloris sp.), Nanochloropsis sp., Nanochloropsis atomus (Nannochloropsis atomus), Nanochloropsis salina, Nanochloropsis oceanica, Navicula pelliculosa, Nitzschia sp., Nitzscia closterium, Nitz Nitzscia palea, Oocystis polymorpha, Ourococcus sp., Oscillatoria rubescens, Pavlova lutheri, Paodactrium triconutum (Phaeodactylum tricornutum), Pycnococcus provasolii, Pyramimonas cordata, Spirulina platensis, Stephanodiscus minutulus, Stichocococcus sp.), Synedra ulna, Scenedesmus obliquus, Skeletonstrum Gracire (Selenastrum gracile), Skeletonoma costalum (Skeletonoma costalum), Tetraselmis chuli (Tetraselmis) chui), Tetraselmis maculata (Tetraselmis maculata), Tetraselmis (Tetraselmis sp.), Tetraselmis suecica (Tetraselmis suecica), Thalassiostra pseudomona (Thalassiostra pseudomona), anabaena (Anabaena sp.). ), Calothrix sp., Chaemisiphon sp., Chroococcidiopsis sp., Cyanothece sp., Cylindrospermum sp., Demo Capella (Dermocarpella sp.), Fisherella (Fischerella sp.), Gloeocapsa (Gloeocapsa sp.), Myxosarcina (Myxosarcina sp.), Nostoc (Nostoc sp.), Oscillatoria (Oscillatoria sp.), Formidium corium (Phormidium) corium), Pleurocapsa sp., Prochlorococcus sp., Pseudanabaena sp., Synechococcus, Synechococcus, Synechococcus (Synechocystis sp.), Toly Potrix ( Tolypothrix sp.), Xenococcus (Xenococcus sp.), but may be a species, but is not limited thereto.

The moisture content of the 'microalgae' of the present invention may be 0.5 to 99 wt% based on the weight of the microalgae. The numerical range may mean a moisture content including both wet microalgae and dry microalgae. In order to remove moisture from the microalgae, the production cost of bio-oil increases due to the additional drying cost. Therefore, it is preferable to extract oil from microalgae in a moist state. In the present invention, by using a mixture of a base catalyst, alcohol, and a hydrophobic organic solvent, high oil extraction rate and oil purity were confirmed not only in dry microalgae but also in bio-oil extraction from wet microalgae.

The "hydrophobic organic solvent" of the present invention may be pentane, hexane, chlorohexane, heptane, benzene, toluene, chloroform, or dimethyl ether, but is not limited thereto.

The "alcohol" of the present invention may be a C1 to C4 alcohol, but is not limited thereto. Specifically, it may be methanol, ethanol, propanol and butanol.

The mixing ratio of the hydrophobic organic solvent: alcohol in the first step of the present invention may be 1:1 (v/v) to 4:1 (v/v). Specifically, the ratio may be 5:5, 6:4, 7:3, 8:2 (v/v). More specifically, it may be a ratio of 7:3 (v/v).

Among the solvents used in the solvent extraction method, the hydrophobic organic solvent shows an appropriate extraction rate in dry microalgae, but in wet microalgae containing water, there is a problem in that it exhibits a low extraction rate due to the inhibitory action of water. In one embodiment of the present invention, it was confirmed that the inhibitory action of moisture was reduced when using not only the hydrophobic organic solvent but also the alcohol mixed solvent, indicating a higher oil extraction rate than when only the hydrophobic organic solvent was used.

The "base catalyst" of the present invention may include sodium hydroxide (NaOH), potassium hydroxide (KOH), lithium hydroxide (LiOH), calcium hydroxide (Ca(OH) ₂ ), and barium hydroxide (Ba(OH) ₂ ). not limited Specifically, it may be sodium hydroxide (NaOH) or potassium hydroxide (KOH).

In addition, the concentration of the base catalyst may be 4 to 100 wt% based on the weight of the microalgae. When the concentration is less than 4 wt% based on the weight of microalgae, there is a problem in that it is difficult to obtain an oil with improved properties due to the low base catalyst concentration. If there is no other inhibitory action, 15 to 20% of the base catalyst compared to the oil content in the microalgae is suitable, but in fact, using the base catalyst in an excess of this is helpful for the reaction. When the base catalyst is higher than 100 wt%, there is a problem that the amount of catalyst contained in the waste liquid increases due to the use of a large amount of catalyst from microalgae.

The "acid catalyst" of the present invention may be added in addition to the base catalyst and may be specifically sulfuric acid, hydrochloric acid, nitric acid, perchloric acid, or hydrobromic acid, but is not limited thereto.

A second aspect of the present invention is to provide a bio-oil produced by the bio-oil manufacturing method of the first aspect, characterized in that the purity is improved.

The term "purity" in the present invention may mean that the total fatty acid content of the extracted oil is measured by gas chromatography and expressed in %. Among the extracted oils, triglycerides, diglycerides, monoglycerides, and free fatty acids belong to the oil component and the rest are unwanted impurities. It cannot be said to be an effective manufacturing method because the physical properties of the oil are not good. Conversely, if the oil extraction rate is low but the purity is very high, there is a problem in that the amount of recovered oil decreases. Therefore, if the fatty acid content is analyzed by gas chromatography, the percentage of these components in the extracted oil can be measured to compare the oil purity compared to the oil extraction rate. The 'oil extraction rate' may refer to a mass percentage of oil recovered after the oil extraction process among the total weight of the oil of the dried microalgae.

In one embodiment of the present invention, when the reaction was performed by adding all of the hydrophobic organic solvent, alcohol and base catalyst, it was confirmed that the purity of the bio-oil was improved to about 95% or more.

A third aspect of the present invention is to provide a method for producing biodiesel, comprising adding a biodiesel conversion catalyst to the biooil of the second aspect.

The bio-oil produced by the bio-oil manufacturing method of the present invention has improved oil purity, so that biodiesel can be efficiently produced. Specifically, after adding a biodiesel conversion catalyst from biooil, biodiesel can be produced through a transesterification/esterification reaction.

By extracting the oil with improved properties compared to the oil extracted by the conventional solvent extraction method in a simple way, bio-oil with improved properties can be obtained, thereby increasing the biodiesel conversion rate. In addition, it is economical because it can increase the biodiesel production yield and contribute to the dissemination of domestic biodiesel by converting a large amount of extracted microalgal oil into biodiesel.

The 'biodiesel conversion catalyst' of the present invention may _{be HZSM-5 as a homogeneous catalyst KOH and sulfuric acid, FeCl 3} , or a heterogeneous solid catalyst, but is not limited thereto. When the purity of the bio-oil is not good, impurities in the microalgal oil reduce the activity of the solid catalyst, thereby exhibiting a very low biodiesel conversion rate. Therefore, it is possible to exhibit a significantly improved conversion rate of biodiesel produced from the bio-oil produced using the base catalyst of the present invention.

In addition, the bio-oil-derived useful material of the second aspect of the present invention may include, but is not limited to, not only biodiesel, but also fuel for transportation, pharmaceuticals, cosmetics, functional foods, feeds, and the like. 1 shows a schematic diagram of a pathway for producing useful substances from microalgae.

According to the present invention, most of the bio-oil extracted from microalgae by the conventional solvent extraction method has a dark green viscous liquid form with little fluidity, and a base catalyst for the problem that the fatty acid methyl ester content is not high during biodiesel conversion. And by adding alcohol, the bio-oil manufacturing method for lowering the impurity content in the bio-oil was completed. The present invention can extract high-purity bio-oil while reducing moisture inhibition without a separate drying process, and thus can be usefully used in various fields as well as simple and economical biodiesel production.

1 is a schematic diagram showing a useful substance production path from microalgae.
2 is a photograph showing the color of bio-oil extracted from microalgae by a solvent extraction method using a catalyst dissolved in hexane of (left) dry microalgae and (right) wet microalgae.
Figure 3 is a photograph showing the color of the oil extracted from the microalgae by the solvent extraction method using the catalyst using the microalgae in order to compare the effect of the type of alcohol and the microalgae oil dissolved in hexane.
4 shows a biodiesel conversion reaction scheme of bio-oil extracted from microalgae.

Hereinafter, the present invention will be described in more detail by way of Examples. However, the following examples are only for illustrating the present invention, and the scope of the present invention is not limited thereto.

Comparative Example 1. Oil extraction by solvent extraction from Nanochloropsis oceanica (oil content about 19.5 wt%)

The oil content relative to the dry weight of the microalgae is about 19.5%, and hexane, using about 200 g/L wet microalgae and dry microalgae containing more than about 35% of omega-3 fatty acids (EPA, eicosapentaenoic acid) in oil, The oil extraction rates were compared using three solvents: hexane: methanol = 7:3 (v/v), chloroform: methanol = 7:3 (v/v). After sufficiently stirring at 1000 rpm for 6 hours, the solvent layer containing oil was recovered, the solvent was evaporated through vacuum evaporation, and the remaining oil was recovered. In order to measure the total fatty acid content of microalgae and extracted microalgal oil, a direct transesterification method (paper: The Journal of Lipid Research, 25, 1391-1396, 1984) was used.

Oil extraction rate (%) Oil purity (%) Oil yield (%) menstruum dry
microalgae wet
microalgae dry
microalgae wet
microalgae dry
microalgae wet
microalgae hexane 26.3 27.5 88.4 87.7 23.2 24.1 Hexane-Methanol (7:3 (v/v)) 92.6 79.7 83.7 72.6 77.5 57.9 Chloroform-methanol (7:3 (v/v)) 114.3 101.7 66.2 67.6 75.7 68.7

The formula for calculating the oil extraction rate is as follows.

(Equation 1)

Oil extraction rate (%) = mass of recovered oil (g) / total mass of oil in microalgae (g) X 100

The oil purity calculation method is to measure the fatty acid content (quantitative analysis of fatty acids between 14 and 24 carbon atoms) by gas chromatography and express it as a percentage.

For the gas chromatography measurement method, 10 mg of each of microalgae and extracted oil is put in a test tube, 2 mL of chloroform-methanol (2:1, v/v) is added, and then mixed with a vortex mixer for 10 minutes and internal standard material Phosphorus heptadecanoic acid-chloroform solution (heptadecanoic acid-chloroform solution) (Sigma-Aldrich, 500 μg/L) 1 mL was added, and methanol 1 mL and sulfuric acid 0.3 mL were added. After mixing for 10 minutes with a vortex mixer, the mixture was reacted for 10 minutes in a 100 ℃ thermostat, and then cooled sufficiently at room temperature. Add 1 mL of distilled water to the cooled test tube, mix with a vortex mixer for 5 minutes, centrifuge in a centrifuge (4,000 RPM, 10 minutes), and extract the lower layer from the layer-separated solution with a syringe, filter through a filter, and add 1 mL to the vial Analyzed by gas chromatography (Agilent 7890). Quantitative analysis of fatty acids was performed using Mix RM3, Mix RM5, GLC50, and GLC70 (Supelco) as external standards.

The oil yield was calculated as follows.

(Equation 2)

Oil yield (%) = Oil extraction rate (%) X Oil purity (%) / 100

As shown in Table 1 above, for the hexane (hydrophobic organic solvent) solvent, both showed low oil extraction rates of about 26% and about 28%, and in the case of hexane or chloroform solvent with methanol added, dry microalgae and wet microalgae Algae showed high extraction rates of about 93% and about 80%, and about 114% and about 102%. The oil purity was similar to that of the hexane-extracted oil compared to the methanol-applied extraction oil, but when comparing the finally calculated oil yield, the hexane oil yield was very low within the range of about 23% to 25%, and when methanol was added It was confirmed that (hexane-methanol and chloroform-methanol) exhibited a significantly higher oil yield than the oil purity by the solvent extraction method using only hexane even in wet conditions.

Example 1. Oil extraction by solvent extraction using catalyst from Nanochloropsis oceanica (oil content about 19.5 wt%, hexane-methanol solvent)

About 200 g/L dry microalgae and about 200 g/L wet microalgae with an oil content of about 19.5 wt% relative to the dry weight of the microalgae, and 35 wt% or more of omega-3 fatty acids (EPA, eicosapentaenoic acid) in oil In the case of adding about 10 wt% of the base catalyst KOH compared to the microalgae in hexane:methanol=7:3 (v/v) solvent using algae, and the base catalyst KOH at about 50 wt%, about 100 wt% compared to the microalgae After the reaction was added, the oil extraction rate when the acid catalyst sulfuric acid was additionally added was compared. After sufficiently stirring at 1000 rpm for 6 hours, the solvent layer containing oil was recovered, the solvent was evaporated through vacuum evaporation, and the remaining oil was recovered. A direct transesterification method was used to measure the total fatty acid content of microalgae and extracted microalgal oil.

It can be seen that the purity of the oil increased by 10% or more when a catalyst was used compared to the case of extraction by a simple solvent extraction method. The use of a catalyst resulted in an increase in oil purity without a decrease in oil extraction rate. In terms of oil yield considering both oil extraction rate and oil purity, it was found that the case of using a base catalyst or a base/acid catalyst in both dry microalgae and wet microalgae had higher oil yield than in the case of no catalyst. The acid value of the extracted oil is about 38 mg KOH / g to 41 mg KOH / g in the simple solvent extraction method, but a tendency to significantly decrease when a catalyst is used is observed in both dry and wet microalgae. The effect of improving physical properties was also confirmed. When the amount of added KOH was increased to 10 wt%, 50 wt%, or 100 wt% compared to microalgae, there was no significant difference in oil properties or extraction rate.

dry microalgae catalyst free KOH
(10 wt%) KOH
(50 wt%)
/sulfuric acid KOH
(100 wt%)
/sulfuric acid Oil extraction rate (%) 92.6 86.8 87.2 89.6 Oil Purity (%) 83.7 100 98.1 95.9 Oil Yield (%) 77.5 86.8 85.5 85.9 Acid number (mg KOH/g) 38.1 13.6 18.7 20.0

wet microalgae catalyst free KOH
(10 wt%) KOH
(50 wt%)
/sulfuric acid KOH
(100 wt%)
/sulfuric acid Oil extraction rate (%) 79.7 80.0 81.3 79.6 Oil Purity (%) 72.6 96.8 98.8 100 Oil Yield (%) 57.9 77.4 80.3 79.6 Acid number (mg KOH/g) 41.4 16.3 21.7 20.9

The acid value may mean the number of mg of potassium hydroxide required to neutralize free fatty acids contained in 1 g of the sample. That is, the acid value measures the amount of free fatty acids in which fatty acids are not bound to glycerol. Refined vegetable oil is in the form of triglycerides and has an acid value of about 0.5 mg KOH/g or less. In waste cooking oil, triglycerides react with heat or air to become rancid and some of them come off in the form of free fatty acids, and the acid value is about 2 to about 10 mg. It is about KOH/g. The low acid value when a base catalyst or base/acid catalyst is added compared to the case without a catalyst may mean that the risk of corrosion of the reactor is reduced due to the high content of triglyceride type oil, which naturally over time It may mean that the generated additional free fatty acid production rate is not relatively high, and it may also mean that the probability of reducing the oil yield or biodiesel yield by causing a saponification reaction with a base catalyst is lowered.

As shown in FIG. 2 , the microalgal oil extracted with a non-catalyst hexane-methanol solvent had a dark green color. During the KOH base catalysis, some of the chlorophyll was removed, giving the dry microalgae a yellow-green color and the wet microalgae green. When the sulfuric acid catalyst was added, the chlorophyll was additionally removed, giving it a color between yellow and brown. The microalgae extracted with the hexane-methanol solvent had little fluidity in the state from which the hexane was removed, but the base-catalyzed or base/acid-catalyzed oil had a fluid liquid form even after the hexane was removed.

Example 2. Oil extraction by a solvent extraction method according to a hexane-alcohol solvent and hexane-methanol mixing ratio using a catalyst from Nanochloropsis oceanica (oil content about 19.5 wt%)

The oil content is about 19.5 wt% relative to the dry weight of the microalgae, and about 200 g/L wet microalgae containing more than 35% of omega-3 fatty acids (EPA, eicosapentaenoic acid) in the oil is used. Hexane: methanol = 7: 3 (v/v) of the methanol solvent was changed to ethanol, propanol, and butanol, and the oil extraction rate when about 10 wt% of the base catalyst KOH was added compared to the microalgae was compared. The results are shown in Table 4.

wet microalgae methanol ethanol propanol butanol Oil extraction rate (%) 81.5 50.7 42.2 36.4

When methanol was used as the hydrophilic solvent, the oil extraction rate was higher than when ethanol, propanol, and butanol were used. It can be seen that this is because the role of reducing the inhibition of water gradually decreased as the number of carbons increased with ethanol, propanol, and butanol.

As shown in FIG. 3 , when extracted with methanol, it appeared light green, when extracted with ethanol, it appeared light green, and when the oil was extracted with propanol and butanol, it was green, indicating that the degree of chlorophyll removal was different depending on the type of alcohol. it can be seen that

In addition, using about 200 g/L wet microalgae, the hexane:methanol ratio was changed to 5:5, 6:4, 7:3, 8:2 (v/v) to give the base catalyst KOH about 10 wt compared to the microalgae % was added to the reaction, and then the oil extraction rate was compared when the acid catalyst sulfuric acid was additionally added. After sufficiently stirring at 1000 rpm for 6 hours, the solvent layer containing oil was recovered, the solvent was evaporated through vacuum evaporation, and the remaining oil was recovered. The results are shown in Table 5.

wet microalgae 5:5 6:4 7:3 8:2 Oil extraction rate (%) 77.9 76.5 81.5 52.0

In the comparison of oil extraction rates according to the hexane: methanol mixing ratio through Table 5, a similar oil extraction rate was shown at 5:5, 6:4, and 7:3 (v/v), and methanol was significantly reduced at 8:2 (v/v). v) showed a low oil extraction rate of about 52%. In order to extract oil while reducing the inhibitory action of water in wet microalgae, it was confirmed that it was significantly advantageous in terms of oil extraction rate to use a hydrophilic solvent methanol in a ratio of more than 20% with hexane and mixing.

Example 3. Biodiesel conversion of oil extracted from Nanochloropsis oceanica by solvent extraction using catalyst

As shown in the conversion reaction scheme of FIG. 4, with respect to the microalgal oil extracted by the hexane-methanol solvent extraction method, as a biodiesel conversion catalyst, KOH and sulfuric acid as a homogeneous catalyst are bio-oil: methanol = 1:1 (w/w). , FeCl ₃ , and HZSM-5 as a heterogeneous solid catalyst was used to carry out the transesterification/esterification reaction. The reaction was sufficiently carried out at 120° C. for 2 hours in a batch reactor.

oil extraction dry catalyst free dry KOH-sulfuric acid biodiesel conversion catalyst KOH H ₂ SO ₄ FeCl ₃ HZSM-5 H ₂ SO ₄ FAME content (%) 73.0 61.1 6.0 3.2 82.5 Recovery (%) 25.2 94.7 98.4 47.9 91.6 Biodiesel Yield (%) 18.4 57.9 5.9 1.5 75.6

(Equation 3)

Recovery (%) = mass of biodiesel recovered after reaction (g) / total mass of biodiesel that can be produced from oil (g) X 100

(Equation 4)

Biodiesel yield (%) = FAME content (%) X recovery (%) / 100

Table 6 is a table comparing the biodiesel recovery rate and yield of the oil extraction method using the dry KOH-sulfuric acid catalyst compared to the dry non-catalyst. After the reaction, fatty acid methyl ester (FAME) content was about 73% and 61% in _{KOH and H 2} SO _{4 , and FeCl 3} and HZSM-5 showed a very low FAME content of less than 10%. . The impurities of the microalgal oil extracted by the solvent extraction method decreased the activity of the solid catalyst, and thus showed a very low biodiesel yield for HZSM-5.

Among the biodiesel catalysts, the KOH catalyst caused a saponification reaction with the fatty acid component contained in the microalgal oil, making it difficult to separate the biodiesel layer, resulting in a low recovery rate of 25%.

_{According to the above results, sulfuric acid (H 2} SO ₄ ) with the highest yield was selected among the biodiesel conversion catalysts of bio-oil extracted without a dry catalyst, and biodiesel yield of bio-oil extracted by solvent extraction using a KOH-sulfuric acid catalyst was analyzed. As a result, when sulfuric acid was used as the transition esterification catalyst, the FAME content was about 83%, and the recovery rate was also high as about 91.6%. Through this, it was confirmed that the physical properties of the microalgal oil were improved due to the solvent extraction method applying the base catalyst and the acid catalyst, contributing to the improvement of the FAME content.

Therefore, it was found that a significantly higher biodiesel yield could be obtained in the base catalyst-acid catalyst solvent extraction method than in the case of no catalyst.

oil extraction Wet Catalyst Wet KOH Wet KOH-sulfuric acid Wet KOH-sulfuric acid dry KOH-sulfuric acid biodiesel
conversion catalyst H ₂ SO ₄ H ₂ SO ₄ H ₂ SO ₄ HZSM-5 H ₂ SO ₄ FAME content (%) 78.1 85.5 84.8 79.1 82.5 Recovery (%) 71.0 94.4 89.5 92.6 91.6 biodiesel
Yield (%) 55.5 80.7 75.9 73.3 75.6

Table 7 is a table comparing biodiesel recovery and yields for microalgal oil extracted from wet microalgae by a hexane-methanol solvent extraction method, and oil extracted by a solvent extraction method by applying a base catalyst and an acid catalyst. Transesterification/esterification reaction was carried out using sulfuric acid, a homogeneous catalyst, and HZSM-5, a heterogeneous solid catalyst, as a biodiesel conversion catalyst under the condition of bio-oil: methanol = 1:1 (v/v). It was fully reacted for 2 hours at 120 degreeC in a batch reactor. The microalgal oil used in HZSM-5 was prepared by sufficiently reacting the base/acid catalyst.

As shown in Table 7, the fatty acid methyl ester (FAME) content after the reaction is only about 78% when the bio-oil extracted by the solvent extraction method without a catalyst is converted to biodiesel when sulfuric acid is used as a biodiesel conversion catalyst. , increased to about 86% and 85% by the solvent extraction method to which the base catalyst was applied. In the case of extraction using only the solvent extraction method, the recovery rate was about 71%, which was 15% or more lower than when using a base/acid catalyst.

In the case of using the solid catalyst HZSM-5 as a biodiesel conversion catalyst, the FAME content was about 79%, and the FAME content was about 3.2% when HZSM-5 was applied to the oil extracted from the dry microalgae in Table 6 only by solvent extraction. When the solvent extraction method applied with a base/acid catalyst was applied to the wet microalgae of No. 7, it was found that the FAME content was significantly increased to about 79.1%.

In addition, compared with dry microalgae, when bio-oil extracted by solvent extraction method applying a base/acid catalyst to wet microalgae was converted to biodiesel, the FAME content was slightly higher, and the recovery rate was also slightly higher, and finally the biodiesel yield As a result of showing better values, it was confirmed that wet microalgae could be converted into biodiesel in excellent yield without a separate drying process.

Therefore, it was found that a significantly higher biodiesel yield could be obtained in the solvent extraction method applying a base catalyst or a base/acid catalyst compared to the case where dry or wet microalgae were extracted only by the solvent extraction method. In addition, microalgal oil having improved physical properties by solvent extraction using a catalyst has the advantage of being environmentally friendly and easy to apply a reusable solid catalyst.

Claims (13)

A first step of preparing a mixture by adding a hydrophobic organic solvent and a base catalyst dissolved in alcohol to the microalgae and stirring; a second step of layer-separating the hydrophobic organic solvent layer containing bio-oil in the stirred mixture; and a third step of removing the organic solvent from the hydrophobic organic solvent layer containing the bio-oil. According to claim 1,
The hydrophobic organic solvent comprises at least one selected from the group consisting of pentane, hexane, chlorohexane, heptane, benzene, toluene, chloroform, and dimethyl ether. According to claim 1,
The alcohol is a C1 to C4 alcohol, the bio-oil manufacturing method. According to claim 1,
The mixing ratio of the hydrophobic organic solvent: alcohol of the first step is 1:1 to 4:1 (v/v), the bio-oil manufacturing method. According to claim 1,
The base catalyst comprises at least one selected from the group consisting of sodium hydroxide, potassium hydroxide, lithium hydroxide, calcium hydroxide, barium hydroxide, bio-oil manufacturing method. According to claim 1,
The concentration of the base catalyst is 4 wt% to 100 wt% based on the weight of the microalgae, the bio-oil manufacturing method. According to claim 1,
The method for producing bio-oil, which can further add an acid catalyst to the stirred mixture after the first step. 8. The method of claim 7,
The acid catalyst comprises at least one selected from the group consisting of sulfuric acid, hydrochloric acid, nitric acid, perchloric acid, and hydrobromic acid. According to claim 1,
The water content of the microalgae is 0.5 wt% to 99 wt% based on the weight of the microalgae, the bio-oil manufacturing method. According to claim 1,
The microalgae concentration is 100 g / L to 400 g / L compared to 1 L of the culture medium, the bio-oil manufacturing method. According to any one of claims 1 to 10, prepared by the method of any one of claims, bio-oil. 12. The method of claim 11,
The bio-oil will have a purity of 95% or more. A method for producing biodiesel comprising the step of adding a biodiesel conversion catalyst to the biooil of claim 11 .

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