KR20140000801A - Method of harvesting microalgal biomass using amine-grafted magnetic nanoflocculant - Google Patents

Abstract

The present invention relates to a method for collecting microalgae biomass existing in an aqueous solution with low concentration and, more specifically, to a method for collecting microalgae using amine-magnetic nanoparticles which aggregates the microalgae biomass using the amine based compound-grafted magnetic nanoparticles, collects the microalgae biomass and the nanoparticles which are aggregated using magnetic force, processes the microalgae biomass in a following process after separating the microalgae biomass from the nanoparticles, and reuses the nanoparticles for aggregation. [Reference numerals] (AA,BB) Magnet

Description

Method for harvesting microalgal biomass using amine-grafted magnetic nanoflocculant

The present invention relates to a method for recovering a microalgae biomass (biomass), and more particularly, an amine-magnetic nanocoagulant and a microalgae biocoagulation using the same, which effectively aggregates the microalgal biomass and is easily recovered. The present invention relates to a method for efficiently recovering mass.

Due to concerns about global warming and depletion of fossil fuels, fuel production using biomass is in the spotlight. However, the first generation biofuel produced from grain biomass is not free from the ethical issue of the fuel-only use of food resources, and it is suggested that the effect of GHG reduction in the environmental aspect is not significant. Therefore, attention has been paid to bioenergy production using microalgae, organic waste, and forest resources as non-edible biomass. Among them, microalgae have the advantage of better photosynthetic efficiency than land plants, direct use of carbon dioxide emitted from thermal power plants, and a substantial part of the body is composed of lipids that can be easily converted into fuel.

However, despite the distinct advantages of microalgae as a biofuel raw material, full-scale application has not been made yet. The reason for this is that centrifugation and filtration, which is a method for recovering cells from a conventional biological process, require a long time because of the high process load to be applied to a low concentration of microalgal broth, and a high cost of equipment. .

The microalgae bioenergy process consists of four stages: 1) microalgae cultivation, 2) microalgae recovery, 3) extraction of raw materials including lipids, and 4) fuel conversion. Many have been proposed. Among these, interest in the microalgae recovery method has recently increased. However, even with a highly productive photobioreactor system, the biomass concentration is less than 5 g / L and the algae concentrations that can be obtained in most microalgal cultures are less than 1 g / L. The process cost of is burdened.

On the other hand, microalgae cells, including microalgae, have a negative charge on functional groups such as carboxyl groups present on the cell surface, and thus have a characteristic of maintaining a stable state in an aqueous solution. Therefore, by adding a cationic electrolyte such as alum or a cationic polymer such as chitosan to the microalgal culture, neutralizing the negative charge of the microalgal cells, inducing aggregation and precipitating the aggregate by gravity or supplying microbubbles. Many methods of flotation have been proposed. Such agglomeration-based method has the advantages of simple process configuration, which is suitable for large-capacity processes, but takes a long time to agglomerate, and requires a separate pH control in order to optimize the agglomeration conditions. There is a disadvantage to be consumed. In addition, the flocculant present with the microalgal biomass has also been pointed out the disadvantage that acts as an impurity in the lipid extraction or conversion process of the latter stage.

Japanese Patent Application No. 1998-528813 Republic of Korea Patent Application No. 2000-0024048 Republic of Korea Patent Application 2007-0097738 U.S. Patent Application 2003-703150 U.S. Patent Application No. 2010-924460 WO, PCT-US1997-022649

 Journal of Renewable Sustainable Energy 2010 vol. 2. 012701  Bioresource Technology 2012 vol. 105. 114-119  Bioresource Technology 2012 vol. 110. 496-502  Biotechnology and Bioengineering 2012. doi: 10.1002 / bit.24449

An object of the present invention is to utilize the microalgae as biomass, the concentration of the microalgae is low, takes a long time to aggregate the microalgae, not only need to adjust the pH to optimize the flocculation conditions, but also a flocculant used once To solve the problem that cannot be reused.

The present invention provides an amine-magnetic nanocoagulant capable of shortening the aggregation time, easy recovery of the flocculant and reuse of the flocculant in order to achieve the above object. The present invention also provides a method for efficiently recovering microalgal biomass using the amine-magnetic nanocoagulant.

The amine-magnetic nanocoagulant of the present invention is a magnetic nanoparticle covalently bonded to an amine compound. The magnetic nanoparticles are preferably from 10 nm to 100 nm in diameter, more preferably from 20 nm to 80 nm particles can be used without limitation, iron group metal elements (Fe, Ni, Co), manganese, bismuth (Mn , Bi) and at least one selected from the group consisting of metal oxides or alloy oxides thereof or alloys thereof. In addition, the rare earth elements (La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu), metal elements (Cu, Ag, Au), zinc Or an alloy containing a group element (Zn, Cd, Hg), an aluminum group element (Al, Ga, In, Tl), an alkaline earth metal element (Ca, Sr, Ba, Ra) and a platinum group element (Pt, Pd) Selected alloy oxides are also possible.

The amine compound may be used without limitation an amine compound containing one or more amine groups. It is preferable to select at least one of the amine compounds having the formula (1).

(1)

In the above formula (1)

로 연결되어 고리를 형성할 수 있고, R₄ 및 R₅의 알킬기, 아릴기 또는 아르알킬기는 아미노기, 하이드록시기, 비닐기, 니트로기, 트리C₁-C₃ 알킬실릴기, 트리C₁-C₃알콕시실릴기 및 아미노카보닐기 중에서 선택된 하나 이상의 치환기로 더 치환될 수 있다.
n is an integer from 1 to 3; R ₁ to R ₃ are each independently hydrogen (H), a hydroxy group (-OH), a halide group, a C ₁ -C ₅ alkyl group, or a C ₁ -C ₅ alkoxy group; R ₄ and R ₅ independently of each other, hydrogen (H), C ₁ -C ₇ alkyl group, C ₆ -C ₂₀ aryl group or C ₆ -C ₂₀ arC ₁ -C ₇ alkyl group or wherein R ₄ and R ₅ is

It may be connected to form a ring, and the alkyl group, aryl group or aralkyl group of R ₄ and R ₅ , amino group, hydroxy group, vinyl group, nitro group, triC ₁ -C ₃ alkylsilyl group, triC _1- It may be further substituted with one or more substituents selected from C ₃ alkoxysilyl group and aminocarbonyl group.

Specific and preferred examples of the general formula (1) include (1) (N, N-dimethylaminopropyl) triethoxysilane having the following structural formula {(N, N-Dimethylaminopropyl) trimethoxysilane}, (2) [3- (Diethylamino) propyl] trimethoxysilane {[3- (Diethylamino) propyl] trimethoxy silane}, (3) trimethoxy [3-methylamine] propylsilane {Trimethoxy [3- (methylamino) propyl] silane} , (4) [3- (2-aminoethylamino) propyl] trimethoxysilane {[3- (2-Aminoethylamino) propyl] trimethoxysilane}, (5) N1- (3-trimethoxysilylpropyl) diethylenetri Amine {{N1- (3-Trimethoxysilylpropyl) diethylenetriamine}, (6) (3-aminopropyl) triethoxysilane {(3-Aminopropyl) triethoxysilane}, (7) 3- [bis (2-hydroxyethyl) amino ] Propyl-triethoxysilane {3- [Bis (2-hydroxyethyl) amino] propyl-triethoxysilane}, (8) N- [3- (trimethoxysilyl) propyl] -N '-(4-vinylbenzyl) Ethylenediamine {N- [3- (Trimethoxysilyl) propyl] -N '-(4-vinylbenzyl) ethylenediamine}, (9) triethoxy Tri-3- (2-imidazolin-1-yl) propylsilane {Triethoxy-3- (2-imidazolin-1-yl) propylsilane}, (10) bis [3- (trimethoxysilyl) propyl] amine {Bis [3- (trimethoxysilyl) propyl] amine}, (11) N- [3- (trimethoxysilyl) propyl] aniline {N- [3- (Trimethoxysilyl) propyl] aniline}, (12) 1- [ 3- (trimethoxysilyl) propyl] urea {1- [3- (Trimethoxysilyl) propyl] urea}.

It is preferable that an amine compound is 1-200 weight part with respect to 100 weight part of said magnetic nanoparticles.

A method of preparing an amine-magnetic nanocoagulant includes a first step of preparing magnetic nanoparticles (S01); and a second step (S02) of bonding an amine compound to the surface of the magnetic nanoparticles; . In order to prepare the magnetic nanoparticles of the first step S01, various methods such as coprecipitation, spray pyrolysis, and electroexplosion may be used. One example used in the present invention is a coprecipitation method using ferric chloride aqueous solution and ferric chloride aqueous solution. According to the example step of mixing and stirring the ferric chloride aqueous solution and ferric chloride aqueous solution (S11); Co-precipitation (coproecipitation) by adjusting the pH of the aqueous solution (S12); And recovering the co-precipitated magnetic nanoparticles by washing 3 to 4 times with distilled water and alcohol (S13). Manufacturing methods are included.

Since the method for washing and recovering the precipitate is conventionally well known, a detailed description thereof will be omitted.

The coprecipitation step (S12) is a pH of 7.0 to 12.0 using a basic solution such as NH ₄ OH or NaOH. When the pH is less than 7.0, coprecipitation due to chemical bonding does not occur. The temperature in the coprecipitation step (S12) may be made by heating to room temperature (about 25 ℃) or less than 100 ℃. That is, heating is not limited. The molar ratio of the ferric chloride aqueous solution and the ferric chloride aqueous solution in the step (S11) is preferably 1: 5 to 0.2, the molar ratio of the ferric chloride aqueous solution and ferric chloride aqueous solution affects the size of the magnetic nanoparticles. The preferred size of the magnetic nanoparticles is 10 to 100 nm. When the size of the nanoparticles is smaller than 10 nm, the recovery efficiency of the nanoparticles (coagulant) using magnetic force is lowered, and when the size of the nanoparticles is larger than 100 nm, the amount of the amine compound bonded to the magnetic nanoparticles is decreased, thereby decreasing the aggregation efficiency. , Dispersibility in aqueous solution worsens.

A second step (S02) of combining the magnetic nanoparticles and the amine compound includes the steps of coating the nanoparticles with an amine compound by bonding an amine compound to the surface of the magnetic nanoparticles (S21); And washing the magnetic nanoparticles coated with the amine compound with alcohol to remove the unreacted amine compound remaining on the surface of the nanoparticles (S22). Reference)

The amine-magnetic nanocoagulant (B) of FIG. 1 prepared according to the above method is used to recover microalgal biomass. With respect to 100 parts by weight of the microalgal biomass, the content of the amine-magnetic nanocoagulant is preferably used to be mixed to 20 to 100 parts by weight. This is because when the content of the amine-magnetic nanocoagulant is 20 parts by weight or less, the flocculation effect is insignificant, and when the content of the amine-magnetic nanocoagulant is 100 parts by weight or more, the amount of the flocculant is unnecessarily excessive compared to the flocculation effect.

The microalgal biomass recovery method using the amine-magnetic nanocoagulant of the present invention is a microalgal biomass by mixing and stirring the microalgal culture solution (a) and the amine-magnetic nanocoagulant (b) in a precipitation tank Forming an aggregate (a '+ b) consisting of agglomerates (S2); Agglomerates (a '+ b) consisting of microalgal biomass-coagulants by precipitating the aggregate (a' + b) by magnetic force and removing the supernatant (a-a ') from which the microalgal biomass (a') has been removed. Obtaining (S3); Alkali aqueous solution such as NaOH, KOH, Ca (OH) ₂ , Mg (OH) ₂ or basic solution such as ammonia gas are added to increase the pH of the aggregate (a '+ b), or HCl or H ₂ Adding an acidic solution (d) such as SO ₄ to reduce the pH of the aggregate (a '+ b) to separate the aggregate (a' + b) into microalgal biomass (a ') and flocculant (b) (S4); (S5) precipitating the flocculant (b) separated in the step (S4) by magnetic force; Obtaining a microalgal biomass (a ') suspension of the upper layer (S6); And drying the microalgal biomass (a ') of the suspension. The precipitated coagulant may be reused in step (S2) by adding it to a new microalgae culture. The stirring intensity in the step S2 is preferably such that the flocculant and the microalgae are in sufficient contact with each other. If the pH of the agglomerate (a '+ b) is increased or decreased in the step S4, the electrostatic attraction between the agglutinating agent and the microalgae cells is lost and re-separation occurs. The pH should be adjusted to a range over which the zeta potential of the flocculant (b) has a negative value, and in the case of adding a basic solution, the pH is preferably about 11 to 12. When the pH is lower than 11, the charge of the flocculant (b) may not disappear sufficiently, and when the pH is higher than 12, the re-separation effect is insignificant as compared with the increase in the amount of the basic substance used. The strong agitation process can facilitate the separation between the flocculant and the cells. The microalgal biomass recovery method may be operated in a continuous process by using two settling tanks alternately as needed.

The microalgae that can be recovered by the amine-magnetic nanocoagulant according to the present invention include red tides or tides in lakes or rivers, and examples of preferred biomass are Botryococcus braunii and Chlamydomonas Chlamydomonas. reinhardtii, Chlorella sp., Chlorella ellipsoidea, Chlorella emersonii, Chlorella protothecoides, Chlorella pyrenoidosa, Chlorella pyronoidosa (Chlorella sorokiniana), Chlorella vulgaris, Chlorella minutissima, Dunaliella bardawil, Dunaliella salina, Isocrysis galbana Isochrysis sp., Microcystis aeruginosa, Nannochloris sp., A hot pot or (Anabaena sp.), Or cine Cauchy seutiseu (Synechocystis sp.), But not always limited thereto. The microalgae that can be recovered by the amine-magnetic nanocoagulant of the present invention is a microalgae having a negatively charged property such as carboxyl groups on the cell membrane, thereby binding the amine-magnetic nanocoagulant by interaction with an amine group cation.

The microalgae may be recovered as it is collected without culturing the collected in the sea, rivers, lakes, etc., may be microalgae cultured using a photobiological incubator.

Microalgae recovery method using the amine-magnetic nano-coagulant according to the present invention is capable of efficient and rapid recovery of the microalgae present in a low concentration. In addition, since the amine-magnetic nanocoagulant can be reused, there are no by-products and there is no cost burden of the flocculant.

1 is a view showing a recovery method of microalgae biomass using the amine-magnetic nano-coagulant of the present invention.
2 is a view showing the manufacturing process of the amine-magnetic nanocoagulant.
3 is a graph showing the results of X-ray diffraction analysis of the amine-magnetic nanocoagulant.
4 is a projection electron microscope (TEM) image of the amine-magnetic nanocoagulant.
5 is a graph showing the zeta potential value according to the pH of the amine-magnetic nanocoagulant.
Figure 6 is a photograph showing the degree of aggregation of the microalgae according to the addition of the amine-magnetic nanocoagulant.
7 is a micrograph of the amine-magnetic nanocoagulant-microalgae aggregate.
8 is a photograph of amine-magnetic nanocoagulant and microalgal cells separated.

Hereinafter, the present invention will be described in more detail with reference to examples and comparative examples. It is to be understood by those skilled in the art that these embodiments are merely illustrative of the present invention and that the scope of the present invention is not limited by these embodiments.

Example 1 Preparation of Magnetic Nanoparticles

Magnetic nanoscale ferric trioxide was prepared using ferric chloride (FeCl ₂ · 4H ₂ O) and ferric chloride (FeCl ₃ · 4H ₂ O) solutions.

4.3 g of ferrous chloride and 11.68 g of ferric chloride were mixed with 200 ml of distilled water to prepare an aqueous solution, and the two solutions were mixed and stirred. The mixed aqueous solution was heated at about 85 ° C for 30 minutes while flowing nitrogen, and 28 ml of ammonium hydroxide (NH ₄ OH 28.8%) was mixed and precipitated. The precipitates were washed three times with excess water and alcohol and then recovered with magnets. Iron tetraoxide, which is a magnetic nanoparticle having a size of 10 to 30 nm, was synthesized by the same method as described above.

Example 2. Preparation of Amine-Magnetic Nanocoagulant

An amine-magnetic nano flocculant was prepared using ferric trioxide, which is the magnetic nanoparticles prepared in Example 1.

About 5 g of magnetic nanoparticles of iron tetraoxide were mixed with 200 g of ethanol together with 10 g of aminopropyltriethoxysilane, an amine compound, and mixed at a temperature of 25 ° C. for 12 hours. After the coating of the amine compound, it was washed three times with alcohol and magnetically recovered the amine-magnetic nanocoagulant.

Example 3. Amine-Magnetic Nanocoagulant Characterization

The X-ray diffraction analysis of the amine-magnetic nanocoagulant of Example 2 is shown in Figure 3. It can be seen that the amine-magnetic nano flocculant has a crystal structure of magnetite (Fe ₃ O ₄ ) even after the amine group coating can be easily separated by a magnet.

Looking at the projection electron microscopy (TEM) image of the amine-magnetic nanocoagulant of Example 2 (see FIG. 4), it can be seen that it has a relatively even diameter and a lattice (lattice) to show crystallinity. Can be.

As a result of analyzing the zeta potential change according to the pH of the magnetic nanoparticles of Example 1 and the amine-magnetic nanocoagulant of Example 2 (see FIG. 5), the magnetic nanoparticles showed negative zeta potential values even in weakly acidic solutions. In the case of the amine-magnetic nanocoagulant, the zeta potential value was positive up to pH 10 due to the attached amine group. Given that the pH of the microalgal culture is between 6 and 8, it can be assumed that the amine-magnetic nanocoagulant has a positive charge in the above range, thereby inducing aggregation by attraction with the microalgal cells.

Example 4. Microalgal Aggregation Using Amine-Magnetic Coagulants

Coagulation experiments were carried out on chlorella species (Chlorella sp. KR-1 (KCTC0426BP)) cultured in a photobioreactor. The samples incubated for one week were used for the experiment, and the cell concentration was 1.5 to 1.7 g / L (660 nm absorbance 6.096).

The flocculant prepared in Example 2 was added to 30 ml of the microalgal culture solution and mixed by stirring. Coagulant dose was adjusted to 200 ~ 10,000 ppm relative to the total solution. After mixing, a magnetic force was applied to the bottom of the microalgal broth-coagulant mixture to induce precipitation. Precipitation is completed in 1 ~ 3 minutes after applying magnetic force. In order to evaluate the aggregation efficiency, the absorbance at 660 nm was measured for the supernatant from which the microalgae were removed. As can be seen from <Figure 6> and <Table 1>, the microalgal cells aggregated and precipitated when the coagulant concentration was 500 ppm or more, and the microalgal cells were completely aggregated and precipitated when the concentration of the coagulant was 1000 ppm or more.

TABLE 1 Microalgal flocculation / precipitation effect by addition of amine-magnetic nanocoagulant

Microscopic observation of the microalgal cell aggregates (FIG. 7) shows that coagulants are attached around the cells to form a large floc, which can be easily recovered by magnetic force.

Example 5 Microalgal Biomass-Coagulant Separation

The coagulant prepared in Example 2 was added to 25 ml of microalgal culture (absorbance 5.14 at 660 nm) to a concentration of 1,000 ppm, and stirred and mixed. After mixing, magnetic force was applied to the bottom of the microalgae culture - coagulant mixture to induce sedimentation, and microalgae aggregation was confirmed and redispersed again. NaOH was added to the mixed solution to adjust the pH of the solution to 12, and the mixture was stirred for 1 minute using a high-speed stirrer. After stirring, magnetic force was applied to the bottom of the mixed solution to induce precipitation. After the precipitation was completed, the precipitate and the supernatant were separated by solid-liquid separation. As a result of measuring the absorbance at 660 nm wavelength with respect to the supernatant, it showed a value of 4.86, and as shown in FIG. 8, the supernatant showed the color of the microalgal culture as it is, effectively separating the microalgae and flocculant, respectively It was confirmed that it can recover.

Example 6 Reuse of Amine-Magnetic Coagulants

The reusability was evaluated by attempting flocculation of microalgae biomass using the lower precipitate recovered in Example 5. 25 mL (660 nm absorbance 5.14) of the microalgal culture solution was added to the precipitate recovered in Example 5, followed by stirring and mixing. After mixing, a magnetic force was applied to the lower portion to induce precipitation. As in Example 4, the precipitation was completed after 1 to 3 minutes after the magnetic force was applied, and the absorbance at 660 nm was measured for the supernatant from which the microalgae were removed. Absorbance measurements showed a value of 0.049, indicating that the flocculant still exhibited performance upon reuse.

Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims. It will be understood that the present invention can be changed.

Claims (9)

(1) inducing aggregation of the microalgal biomass using an amine-magnetic nanocoagulant comprising an amine compound and magnetic nanoparticles; And
(2) recovering the aggregates by magnetic force; microalgae biomass recovery method comprising a. The method of claim 1,
A method of recovering microalgae biomass, further comprising separating the microalgae and the amine-magnetic nanocoagulant by adding a basic solution or an acidic solution to the aggregate recovered after the step (2). 3. The method according to claim 1 or 2,
The amine-magnetic nano flocculant recovery method of microalgae biomass, characterized in that precipitated by magnetic force recovered and reused. 3. The method according to claim 1 or 2,
A method for recovering microalgal biomass, characterized in that 20 to 100 parts by weight of the amine-magnetic nanocoagulant is mixed with respect to 100 parts by weight of the microalgal biomass. 3. The method according to claim 1 or 2,
The size of the magnetic nanoparticles is a microalgae biomass recovery method, characterized in that 10 to 100 nm. 3. The method according to claim 1 or 2,
The microalgae are Botryococcus braunii, Chlamydomonas reinhardtii, Chlorella sp., Chlorella ellipsoidea, Chlorella emersonii, Chlorella emersonii. Chlorella protothecoides, Chlorella pyrenoidosa, Chlorella sorokiniana, Chlorella vulgaris, Chlorella minutissima, Dunariella bardawil ), Dunaliella salina, Isochrysis galbana, Isochrysis sp., Microcystis aeruginosa, Nannochloris sp. Microalgae bar, characterized in that at least one selected from the genus Anabaena sp., And Synechocystis sp. A method for recovering five mass. The method of claim 1, wherein the amine compound is a compound consisting of the following general formula (1).

(1)
[In the formula (1), n is an integer of 1 to 3; R _1, to R ₃ are halide groups, C ₁ -C ₅ hydrogen (H), hydroxyl group (-OH), independently of one another An alkyl group or a C ₁ -C ₅ alkoxy group; R ₄ And R ₅ is, independently of each other, hydrogen (H), a C ₁ -C ₇ alkyl group, a C ₆ -C ₂₀ aryl group or a C ₆ -C ₂₀ arC ₁ -C ₇ alkyl group, or wherein R ₄ and R ₅ are

It may be connected to form a ring, and the alkyl group, aryl group or aralkyl group of R ₄ and R ₅ , amino group, hydroxy group, vinyl group, nitro group, triC ₁ -C ₃ alkylsilyl group, triC _1- It may be further substituted with one or more substituents selected from C ₃ alkoxysilyl group and aminocarbonyl group.] 8. The method of claim 7,
The amine compound is
(1) (N, N-dimethylaminopropyl) triethoxysilane;
(2) [3- (diethylamino) propyl] trimethoxysilane;
(3) trimethoxy [3-methylamine] propylsilane;
(4) [3- (2-aminoethylamino) propyl] trimethoxysilane;
(5) N1- (3-trimethoxysilylpropyl) diethylenetriamine;
(6) (3-aminopropyl) triethoxysilane;
(7) 3- [bis (2-hydroxyethyl) amino] propyl-triethoxysilane;
(8) N- [3- (trimethoxysilyl) propyl] -N '-(4-vinylbenzyl) ethylenediamine;
(9) triethoxy-3- (2-imidazoline-1-yl) propylsilane;
(10) bis [3- (trimethoxysilyl) propyl] amine;
(11) N- [3- (trimethoxysilyl) propyl] aniline; And
(12) 1- [3- (trimethoxysilyl) propyl] urea; Method for recovering microalgal biomass, characterized in that at least one selected from. The method of claim 1,
A method for recovering microalgae biomass, characterized in that the content of the amine compound is 1 to 200 parts by weight based on 100 parts by weight of the magnetic nanoparticles.

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