CN114574288B - Method for converting high acid value algae oil by molecular sieve in-situ growth two-dimensional ultrathin nanosheets - Google Patents

Method for converting high acid value algae oil by molecular sieve in-situ growth two-dimensional ultrathin nanosheets Download PDF

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CN114574288B
CN114574288B CN202210154031.7A CN202210154031A CN114574288B CN 114574288 B CN114574288 B CN 114574288B CN 202210154031 A CN202210154031 A CN 202210154031A CN 114574288 B CN114574288 B CN 114574288B
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mixed solution
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molecular sieve
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dimethylformamide
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CN114574288A (en
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程军
郭浩
杨卫娟
刘建忠
周俊虎
岑可法
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Zhejiang University ZJU
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    • C—CHEMISTRY; METALLURGY
    • C11—ANIMAL OR VEGETABLE OILS, FATS, FATTY SUBSTANCES OR WAXES; FATTY ACIDS THEREFROM; DETERGENTS; CANDLES
    • C11C—FATTY ACIDS FROM FATS, OILS OR WAXES; CANDLES; FATS, OILS OR FATTY ACIDS BY CHEMICAL MODIFICATION OF FATS, OILS, OR FATTY ACIDS OBTAINED THEREFROM
    • C11C3/00—Fats, oils, or fatty acids by chemical modification of fats, oils, or fatty acids obtained therefrom
    • C11C3/003—Fats, oils, or fatty acids by chemical modification of fats, oils, or fatty acids obtained therefrom by esterification of fatty acids with alcohols
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J31/00—Catalysts comprising hydrides, coordination complexes or organic compounds
    • B01J31/16—Catalysts comprising hydrides, coordination complexes or organic compounds containing coordination complexes
    • B01J31/18—Catalysts comprising hydrides, coordination complexes or organic compounds containing coordination complexes containing nitrogen, phosphorus, arsenic or antimony as complexing atoms, e.g. in pyridine ligands, or in resonance therewith, e.g. in isocyanide ligands C=N-R or as complexed central atoms
    • B01J31/1805—Catalysts comprising hydrides, coordination complexes or organic compounds containing coordination complexes containing nitrogen, phosphorus, arsenic or antimony as complexing atoms, e.g. in pyridine ligands, or in resonance therewith, e.g. in isocyanide ligands C=N-R or as complexed central atoms the ligands containing nitrogen
    • B01J31/181—Cyclic ligands, including e.g. non-condensed polycyclic ligands, comprising at least one complexing nitrogen atom as ring member, e.g. pyridine
    • B01J31/1815—Cyclic ligands, including e.g. non-condensed polycyclic ligands, comprising at least one complexing nitrogen atom as ring member, e.g. pyridine with more than one complexing nitrogen atom, e.g. bipyridyl, 2-aminopyridine
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10L—FUELS NOT OTHERWISE PROVIDED FOR; NATURAL GAS; SYNTHETIC NATURAL GAS OBTAINED BY PROCESSES NOT COVERED BY SUBCLASSES C10G, C10K; LIQUEFIED PETROLEUM GAS; ADDING MATERIALS TO FUELS OR FIRES TO REDUCE SMOKE OR UNDESIRABLE DEPOSITS OR TO FACILITATE SOOT REMOVAL; FIRELIGHTERS
    • C10L1/00—Liquid carbonaceous fuels
    • C10L1/02—Liquid carbonaceous fuels essentially based on components consisting of carbon, hydrogen, and oxygen only
    • C—CHEMISTRY; METALLURGY
    • C11—ANIMAL OR VEGETABLE OILS, FATS, FATTY SUBSTANCES OR WAXES; FATTY ACIDS THEREFROM; DETERGENTS; CANDLES
    • C11C—FATTY ACIDS FROM FATS, OILS OR WAXES; CANDLES; FATS, OILS OR FATTY ACIDS BY CHEMICAL MODIFICATION OF FATS, OILS, OR FATTY ACIDS OBTAINED THEREFROM
    • C11C3/00—Fats, oils, or fatty acids by chemical modification of fats, oils, or fatty acids obtained therefrom
    • C11C3/04—Fats, oils, or fatty acids by chemical modification of fats, oils, or fatty acids obtained therefrom by esterification of fats or fatty oils
    • C—CHEMISTRY; METALLURGY
    • C11—ANIMAL OR VEGETABLE OILS, FATS, FATTY SUBSTANCES OR WAXES; FATTY ACIDS THEREFROM; DETERGENTS; CANDLES
    • C11C—FATTY ACIDS FROM FATS, OILS OR WAXES; CANDLES; FATS, OILS OR FATTY ACIDS BY CHEMICAL MODIFICATION OF FATS, OILS, OR FATTY ACIDS OBTAINED THEREFROM
    • C11C3/00—Fats, oils, or fatty acids by chemical modification of fats, oils, or fatty acids obtained therefrom
    • C11C3/04—Fats, oils, or fatty acids by chemical modification of fats, oils, or fatty acids obtained therefrom by esterification of fats or fatty oils
    • C11C3/10—Ester interchange
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J2231/00—Catalytic reactions performed with catalysts classified in B01J31/00
    • B01J2231/40—Substitution reactions at carbon centres, e.g. C-C or C-X, i.e. carbon-hetero atom, cross-coupling, C-H activation or ring-opening reactions
    • B01J2231/49—Esterification or transesterification
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J2531/00—Additional information regarding catalytic systems classified in B01J31/00
    • B01J2531/80—Complexes comprising metals of Group VIII as the central metal
    • B01J2531/84—Metals of the iron group
    • B01J2531/845—Cobalt
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E50/00—Technologies for the production of fuel of non-fossil origin
    • Y02E50/10—Biofuels, e.g. bio-diesel
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P30/00—Technologies relating to oil refining and petrochemical industry
    • Y02P30/20—Technologies relating to oil refining and petrochemical industry using bio-feedstock

Abstract

The invention relates to biomass energy utilization technology, and aims to provide a method for converting high acid value algae oil by growing two-dimensional ultrathin nanosheets in situ by using a molecular sieve. Comprising the following steps: 2-methylimidazole is dissolved in a 5N, N-dimethylformamide-water mixed solution; adding a mesoporous Y-type molecular sieve and performing ultrasonic treatment to obtain a mixed solution A; dissolving cobalt nitrate hexahydrate in an N, N-dimethylformamide-water mixed solution to obtain a solution B; uniformly mixing the solution B with the mixed solution A for full reaction, separating solids, cleaning and drying to obtain a catalyst; mixing the catalyst with microalgae oil, adding methanol at a molar ratio of alcohol to oil of 10:1, and reacting at 160deg.C for 2 hr to obtain product oil containing fatty acid methyl ester as main component. The catalyst provided by the invention realizes in-situ uniform growth of two-dimensional ultrathin nanosheets, and avoids stacking of sheets while realizing nanoscale thickness, so that the catalytic conversion efficiency of the microalgae grease with high acid value is greatly improved, and the catalyst has higher stability in recycling.

Description

Method for converting high acid value algae oil by molecular sieve in-situ growth two-dimensional ultrathin nanosheets
Technical Field
The invention relates to biomass energy utilization technology, in particular to a method for converting high acid value algae oil by in-situ growth of two-dimensional ultrathin nanosheets by using a molecular sieve.
Background
The microalgae has the advantages of high photosynthetic efficiency, high growth speed, high lipid content (up to 30-75 wt.%), no cultivated land occupation and the like, and can replace the traditional animal and vegetable oil to be an important raw material for edible oil or biodiesel. Microalgae can decompose during harvest and storage to produce large amounts of free fatty acids. The acid value is generally greater than 20mg KOH g -1 The oil and fat raw material of (2) is defined as having a high acid value, and therefore has an acid value of more than 20mg KOH g -1 The algae oil of (2) is regarded as high acid value microalgae oil. Due toFree fatty acids deactivate conventional basic catalysts by saponification and present problems for the purification of biodiesel products, so that acid-base bifunctional catalysts must be studied to utilize such fats and oils. In order to produce biodiesel using high acid value microalgae greases, a complex two-step process is generally required: the first step is to esterify free fatty acid with acid catalyst to reduce the acid value of grease, and the second step is to transesterify triglyceride with base catalyst to obtain biodiesel.
The acid-base double-function heterogeneous catalyst with both acid sites and alkaline sites can simultaneously convert free fatty acid and triglyceride into biodiesel, and has wide application prospect in industry. The surface of the cobalt-based organic metal framework (ZIF-67) is distributed with rich acid and alkali sites, and the sites are attributed to coordination unsaturated Co-N x (x<4) And an uncoordinated N site. However, the traditional ZIF-67 is of a dodecahedron microporous structure, the pore diameter of the ZIF-67 restricts the diffusion of large-size grease molecules, so that esterification and transesterification reactions only can occur on the surface of crystals, and the conversion efficiency of catalyzing microalgae grease with high acid value to produce biodiesel needs to be improved. Therefore, the dodecahedron structure is converted into a two-dimensional ultrathin nano sheet structure so as to increase the contact opportunity of ZIF-67 active sites and grease molecules, and the catalyst is a technical key for realizing efficient recycling of the catalyst for preparing biodiesel by converting algae oil.
Wan et al add sodium dodecyl sulfate in ZIF-67 synthetic process to prevent ZIF-67 from vertical growth, thus obtain two-dimensional ZIF-67 nanosheets with thickness of about 20nm, but the structure is still microporous, which is unfavorable for the diffusion reaction of grease molecules. Huang et al formed ultra-thin two-dimensional ZIF-67 nanoplatelets with a thickness of 4.5nm by adding a large amount of NaCl to the methanol of the ZIF-67 synthesis solution, which allowed the reaction solvent to grow only in the NaCl crystal gap, but the nanoplatelets were easily stacked, prevented the reactants from contacting the active site, and the synthesis process was complicated.
Therefore, if a bifunctional catalyst with a novel structure can be provided, the two-dimensional nano-sheets can be better dispersed to expose more active sites, and the conversion efficiency of catalyzing the microalgae grease with high acid value can be effectively promoted.
Disclosure of Invention
The invention aims to solve the technical problem of overcoming the defects in the prior art and providing a method for converting high acid value algae oil by growing two-dimensional ultrathin nanosheets in situ by using a molecular sieve.
In order to solve the technical problems, the invention adopts the following solutions:
the method for converting the two-dimensional ultrathin nanosheets into the high acid value algae oil by the molecular sieve in-situ growth comprises the following steps:
(1) 1.312 to 13.12g of 2-methylimidazole is taken and dissolved in 50 to 500mL of N, N-dimethylformamide-water mixed solution; adding 0.5-5 g of mesoporous Y-type molecular sieve into the solution, and carrying out ultrasonic treatment to obtain a mixed solution A; (mesoporous Y-type molecular sieves, although insoluble in solution, do not affect the adsorption and in situ growth of Co ions and 2-methylimidazole on the molecular sieve surface because they are soluble.)
(2) 1.164-11.64 g of cobalt nitrate hexahydrate is taken and dissolved in 50-500 mL of N, N-dimethylformamide-water mixed solution, and solution B is obtained after ultrasonic treatment;
(3) Pouring the solution B into the mixed solution A, uniformly mixing, and then transferring the mixed solution B into a microwave synthesis kettle for full reaction for 2 hours; after the reaction is finished, centrifugally separating solids, washing with deionized water and drying to obtain a catalyst with a mesoporous Y-type molecular sieve surface in-situ grown two-dimensional ultrathin ZIF-67 nanosheets;
(4) Mixing the obtained catalyst with microalgae grease according to a mass ratio of 1:25, and then adding the mixture into a polytetrafluoroethylene sealed reaction kettle;
(5) Testing specific components of the microalgae grease, and carrying out normalization treatment according to the molecular weight and the content of each component to obtain the average molecular weight of the microalgae grease; then adding methanol into the reaction kettle according to the molar ratio of alcohol to oil of 10:1, and reacting for 2 hours at the constant temperature of 160 ℃ to obtain the product oil with the main component of fatty acid methyl ester.
In a preferred embodiment of the present invention, the volume ratio of N, N-dimethylformamide to water in the N, N-dimethylformamide-water mixed solution is 1:2.
As a preferable scheme of the invention, the ultrasonic treatment time is 30min, the power intensity is 0.5W/mL, and the frequency is 20kHz.
As a preferable scheme of the invention, the power of the microwave synthesis kettle is 500W, and the reaction temperature is 90 ℃.
As a preferable scheme of the invention, the deionized water is washed for 3 times.
As a preferable mode of the invention, the acid value of the microalgae grease is in the range of 34-68 mg KOH g -1 。
As a preferable scheme of the invention, the main component of the product oil is fatty acid methyl ester with a carbon chain length of C14-C22.
Based on the conversion method of the high acid value algae oil, the invention further provides a preparation method of the catalyst for in-situ growth of the two-dimensional ultrathin ZIF-67 nanosheets on the surface of the mesoporous Y-type molecular sieve.
Description of the inventive principles:
1. the prepared bifunctional catalyst product has the following structural characteristics: two-dimensional ultrathin ZIF-67 nanosheets are grown on the surface of the mesoporous Y-type molecular sieve in situ to form a scaly structure, and Co-Nx with unsaturated coordination of acidic sites and N basic sites without coordination are distributed outside the scaly structure. Thus, the dual function catalyst of the present invention comprises an internal Y-type molecular sieve structure
Figure BDA0003511738110000031
The acid sites and the external two-dimensional ultrathin nano-sheet structure provide Lewis acid-base sites (unsaturated coordinated Co-Nx and uncomplexed N), so that the synergistic effect of three active sites can be exerted, and the conversion of the high acid value microalgae grease is promoted.
The traditional bifunctional catalyst has single active site, and is difficult to efficiently convert the microalgae grease with high acid value. The invention can obtain conversion efficiency far exceeding that of the existing catalyst by utilizing the synergistic catalysis of three active sites. There is no disclosure of the mechanism of the cobalt Co ion of Lewis acid and the uncomplexed N basic site in catalytic esterification and transesterification reactions.
2. The invention is made ofIn the preparation process, co ions in the N, N-dimethylformamide-water mixed solution can be adsorbed on hydroxyl groups on the surface of the Y-type mesoporous molecular sieve, and the Co ions are used as sites for in-situ growth of ZIF-67. The interfacial effect of the N, N-dimethylformamide-water mixed solution can limit the transverse growth of ZIF-67 particles, so that ultrathin nano sheets adsorbed on the surface of the Y-type mesoporous molecular sieve are formed. The thickness of the two-dimensional ultrathin nano-sheet prepared by synthesis is about 4nm, and the two-dimensional ultrathin nano-sheet is uniformly distributed. The Y-type mesoporous molecular sieve is uniformly distributed and not stacked under the fixation effect, so that more active sites are exposed, and the phenomenon that the traditional two-dimensional ultrathin nano-sheets are easily stacked to further obstruct the contact of reactants and the active sites is avoided. At the same time, the Y-type mesoporous molecular sieve is self-contained
Figure BDA0003511738110000032
The acidic sites can promote the conversion of free fatty acids in the grease, and the conversion efficiency is synergistically improved.
3. The catalyst for in-situ growth of two-dimensional ultrathin ZIF-67 nanosheets on the surface of the mesoporous Y-type molecular sieve is characterized in that a two-dimensional ultrathin nanosheet structure is additionally arranged on the surface of the mesoporous Y-type molecular sieve. The mesoporous Y-type molecular sieve is distributed with a certain amount of
Figure BDA0003511738110000033
The acidic sites can catalyze the esterification reaction of free fatty acid, and the mesoporous structure can promote the diffusion of large-size grease molecules (about 1.3 nm) so as to fully utilize the active sites inside the catalyst. The single Y-type molecular sieve can not completely convert microalgae grease, so that the two-dimensional ultrathin ZIF-67 nanosheets are synthesized and supported on the surface of the molecular sieve, the nanosheets can be uniformly dispersed and not stacked, and the synergistic catalytic effect of the two nanosheets can be exerted.
4. In the catalytic decomposition process of microalgae grease, carbonyl oxygen O of free fatty acid is preferentially adsorbed on cobalt Co ions of Lewis acid of the catalyst. The strong interaction between Co and O atoms results in electron migration from fatty acids to Co-N x The site, activates the carbonyl carbon into a carbonium ion. Upon nucleophilic attack by methanol, a tetrahedral intermediate is formed, which breaks downWater molecules and fatty acid methyl esters. Co-N 4 The adsorption energy of the fatty acid molecules at the site is-0.271 eV, and Co-N 3 And Co-N 2 The adsorption energy of the fatty acid molecules at the sites was-0.344 eV and-1.003 eV, respectively. This is illustrated with Co-N 4 Fatty acids are more readily adsorbed on Co-N than on Co-N 2 Further activation at the site forms a carbocation. At the same time, the surface of the Y-type mesoporous molecular sieve
Figure BDA0003511738110000034
The acid sites also release free protons which attack the carbonyl oxygen of the fatty acid to form a carbonium ion which in turn facilitates the esterification reaction. The transesterification reaction occurs at the uncomplexed N basic site, and methanol adsorbs at the basic sites pyrrole N and pyridine N (the 2-methylimidazole contains pyrrole N and pyridine N sites, which form a Co-N coordination bond if coordinated to Co ions, and which form methoxy anions in the form of free pyrrole N and pyridine N sites if not coordinated at structural defects or at the end of the backbone). The methoxy anions then react with the carbonyl groups of the triglycerides to form tetrahedral intermediates, which rapidly decompose to the fatty acid methyl esters of the product oil.
Compared with the prior art, the invention has the beneficial effects that:
1. the invention prepares the heterogeneous catalyst by in-situ growth of two-dimensional ultrathin ZIF-67 nanosheets on the surface of the mesoporous Y-type molecular sieve, avoids the problems of equipment corrosion, environmental pollution and the like caused by difficult recovery of the homogeneous acid-base catalyst, and provides a green and efficient novel method for preparing biodiesel by converting microalgae grease.
2. Compared with the two-dimensional ultrathin ZIF-67 nanosheets reported in the prior document, the two-dimensional ultrathin ZIF-67 nanosheets grown on the mesoporous Y-type molecular sieve surface in situ catalyst prepared by the invention realize the in situ uniform growth of the two-dimensional ultrathin nanosheets, and avoid stacking of sheets while realizing nanoscale thickness, so that the catalytic conversion efficiency of the high acid value microalgae grease is as high as 97.5-98.5%.
3. The catalyst has good stability after being recycled, the conversion efficiency of the fresh catalyst is 95.5-96.5% after the catalyst is regenerated, and the recycling service life of the catalyst is more than or equal to 2000 hours.
Drawings
FIG. 1 is a process flow diagram of the present invention.
Fig. 2 is an electron micrograph of a scale-like structure bifunctional catalyst of two-dimensional ultrathin nanosheets obtained by the present invention.
Detailed Description
The preparation process of the microalgae grease belongs to the prior art and is sold by commercial products. The invention relates to the catalytic conversion of microalgae grease only, but not to the preparation process of the microalgae grease. Any microalgae lipid prepared by the prior art can be used in the invention. The microalgae grease used in the embodiments of the invention is obtained by drying and grinding nannochloropsis produced by the company Limited for culturing the sea-melted microalgae in a smoke table, extracting with a mixed solution of chloroform and methanol, and the acid value range is 34-68 mg KOH g -1 。
The invention is described in further detail below with reference to the drawings and the detailed description. The examples will allow a person skilled in the art to more fully understand the invention and are not intended to limit it in any way.
Example 1
1.312g of 2-methylimidazole was dissolved in 50mL of a solvent (N, N-dimethylformamide: water volume ratio=1:2). Dissolving 0.5g of mesoporous Y-type molecular sieve in the solution, and performing ultrasonic treatment for 30min (the power intensity is 0.5W/mL, and the frequency is 20 kHz) to obtain a mixed solution A. 1.164g of cobalt nitrate hexahydrate was dissolved in 50mL of a solvent (N, N-dimethylformamide: water=1:2), and sonicated under the same conditions for 30 minutes to obtain a solution B. The solution B was slowly poured into the mixture A and reacted in a microwave synthesis kettle for 2 hours (the microwave synthesis power was 500W and the temperature was 90 ℃). And after the full reaction, carrying out centrifugal treatment, filtering out solids, washing the solids with deionized water for 3 times, and then drying the solids to obtain the catalyst for in-situ growth of the two-dimensional ultrathin ZIF-67 nanosheets on the surface of the mesoporous Y-type molecular sieve.
2g of the catalyst obtained above was taken together with 50g of a high acid value (34 mg KOH g -1 ) Mixing microalgae oil and fat, placing into polytetrafluoroethylene sealed reaction kettle, adding 25mL of methanol (alcohol-oil molar ratio 10:1) The reaction time at 160℃was 2h.
The catalyst has high acid value microalgae grease catalytic conversion efficiency up to 97.5% tested according to the method described in paper Phosphotungstic acid-modified zeolite imidazolate framework (ZIF-67) as an acid-base bifunctional heterogeneous catalyst for biodiesel production from microalgal lipids. After the catalyst is regenerated according to the method described in the paper, the catalyst can be recycled to reach 95.5% of the conversion efficiency of the fresh catalyst, and the recycling service life of the catalyst can reach more than or equal to 2000 hours.
Example 2
13.12g of 2-methylimidazole are taken and dissolved in 500mL of solvent (N, N-dimethylformamide: water volume ratio=1:2). 5g of mesoporous Y-type molecular sieve is dissolved in the solution, and the solution is subjected to ultrasonic treatment for 30min (the power intensity is 0.5W/mL, and the frequency is 20 kHz) to obtain a mixed solution A. 11.64g of cobalt nitrate hexahydrate was dissolved in 500mL of a solvent (N, N-dimethylformamide: water=1:2), and subjected to ultrasonic treatment under the same conditions for 30 minutes to obtain a solution B. The solution B was slowly poured into the mixture A and reacted in a microwave synthesis kettle for 2 hours (the microwave synthesis power was 500W and the temperature was 90 ℃). And after the full reaction, carrying out centrifugal treatment, filtering out solids, washing the solids with deionized water for 3 times, and then drying the solids to obtain the catalyst for in-situ growth of the two-dimensional ultrathin ZIF-67 nanosheets on the surface of the mesoporous Y-type molecular sieve.
20g of the catalyst obtained above was taken together with 500g of a high acid value (52 mg KOH g -1 ) Mixing microalgae grease, placing the mixture in a polytetrafluoroethylene-sealed reaction kettle, and adding 250mL of methanol (the molar ratio of the alcohol to the oil is 10:1), wherein the reaction temperature is 160 ℃ and the reaction time is 2 hours.
The catalyst has high acid value microalgae grease catalytic conversion efficiency up to 98% tested according to the method described in paper Phosphotungstic acid-modified zeolite imidazolate framework (ZIF-67) as an acid-base bifunctional heterogeneous catalyst for biodiesel production from microalgal lipids. After the catalyst is regenerated according to the method described in the paper, the catalyst can be recycled to 96% of the conversion efficiency of the fresh catalyst, and the recycling service life of the catalyst can be more than or equal to 2000 hours.
Example 3
6.56g of 2-methylimidazole was dissolved in 250mL of a solvent (N, N-dimethylformamide: water volume ratio=1:2). 2.5g of mesoporous Y-type molecular sieve is dissolved in the solution, and the solution is subjected to ultrasonic treatment for 30min (the power intensity is 0.5W/mL, and the frequency is 20 kHz) to obtain a mixed solution A. 5.82g of cobalt nitrate hexahydrate was dissolved in 250mL of a solvent (N, N-dimethylformamide: water=1:2), and sonicated under the same conditions for 30 minutes to obtain a solution B. The solution B was slowly poured into the mixture A and reacted in a microwave synthesis kettle for 2 hours (the microwave synthesis power was 500W and the temperature was 90 ℃). And after the full reaction, carrying out centrifugal treatment, filtering out solids, washing the solids with deionized water for 3 times, and then drying the solids to obtain the catalyst for in-situ growth of the two-dimensional ultrathin ZIF-67 nanosheets on the surface of the mesoporous Y-type molecular sieve.
10g of the catalyst obtained above was mixed with 250g of a high acid value (68 mg KOH g -1 ) Mixing microalgae grease, placing the mixture in a polytetrafluoroethylene-sealed reaction kettle, and adding 125mL of methanol (the molar ratio of the alcohol to the oil is 10:1), wherein the reaction temperature is 160 ℃ and the reaction time is 2 hours.
The catalyst has high acid value microalgae grease catalytic conversion efficiency up to 98.5% tested according to the method described in paper Phosphotungstic acid-modified zeolite imidazolate framework (ZIF-67) as an acid-base bifunctional heterogeneous catalyst for biodiesel production from microalgal lipids. After the catalyst is regenerated according to the method described in the paper, the catalyst can be recycled to 96.5% of the conversion efficiency of the fresh catalyst, and the recycling service life of the catalyst can be more than or equal to 2000 hours.
Comparative example 1
The two-dimensional ZIF-67 nanosheets are prepared by the ZIF-67 synthesis process of Wan et al described in Facet engineering in metal organic frameworks to improve their electrochemical activity for water oxidation paper and are used as a bifunctional catalyst for the catalytic decomposition reaction of microalgae grease. The raw material amount and the reaction conditions in the reaction process are referred to in example 1 of the present invention.
The catalyst was tested and regenerated in the same manner as in example 1 to give a high acid value microalgae oil catalytic conversion efficiency of 83.1%, and after regeneration, the catalyst was recycled to a fresh catalyst conversion efficiency of 73.2%, and the catalyst had a cycle life of 900 hours.
Comparative example 2
Referring to In situ synthesis of ultrathin metal-organic framework nanosheets:a new method for 2D metal-based nanoporous carbon electrocatalysts, the ZIF-67 synthesis process of Huang et al is described to prepare ultrathin two-dimensional ZIF-67 nanosheets, and the nanosheets are used as bifunctional catalysts for catalytic decomposition reaction of microalgae grease. The raw material amount and the reaction conditions in the reaction process are referred to in example 1 of the present invention.
The catalyst was tested and regenerated in the same manner as in example 1 to give a high acid value microalgae oil catalytic conversion efficiency of 87.4%, and after regeneration, the catalyst was recycled to a fresh catalyst conversion efficiency of 83.3%, and the catalyst had a cycle life of 1200 hours.
According to the data of the embodiment and the data of the comparative example, the scale-shaped structure synthesized by the invention ensures that the two-dimensional ultrathin nano-sheets are uniformly distributed and not stacked through the fixing action of the Y-shaped mesoporous molecular sieve, thereby exposing more active sites and avoiding the phenomenon that the traditional two-dimensional ultrathin nano-sheets are easily stacked to further obstruct the contact of reactants and the active sites. At the same time, the internal Y-shaped molecular sieve structure provides
Figure BDA0003511738110000061
The acid site and the external two-dimensional ultrathin nano-sheet structure provide Lewis acid-base sites, so that the synergistic effect of three active sites can be exerted, and the conversion of the high acid value microalgae grease is promoted. Therefore, the synthetic catalyst has higher catalytic conversion efficiency and more stable cycle performance.
Finally, it should be noted that the above list is only specific embodiments of the present invention. Obviously, the invention is not limited to the above embodiments, but many variations are possible. All modifications directly derived or suggested to one skilled in the art from the present disclosure should be considered as being within the scope of the present invention.

Claims (8)

1. The method for converting the two-dimensional ultrathin nanosheets into the high acid value algae oil by molecular sieve in-situ growth is characterized by comprising the following steps of:
(1) 1.312-13.12 g of 2-methylimidazole is taken and dissolved in 50-500 mL of N, N-dimethylformamide-water mixed solution; adding 0.5-5 g of mesoporous Y-type molecular sieve into the solution, and carrying out ultrasonic treatment to obtain a mixed solution A;
(2) 1.164-11.64 g of cobalt nitrate hexahydrate is taken and dissolved in 50-500 mL of N, N-dimethylformamide-water mixed solution, and solution B is obtained after ultrasonic treatment;
(3) Pouring the solution B into the mixed solution A, uniformly mixing, and then transferring the mixed solution B into a microwave synthesis kettle for full reaction for 2 hours; after the reaction is finished, centrifugally separating solids, washing with deionized water and drying to obtain a catalyst with a mesoporous Y-type molecular sieve surface in-situ grown two-dimensional ultrathin ZIF-67 nanosheets;
(4) Mixing the obtained catalyst with algae oil at a mass ratio of 1:25, and adding into a polytetrafluoroethylene sealed reaction kettle;
(5) Testing specific components of the algae oil, and carrying out normalization treatment according to the molecular weight and the content of each component to obtain the average molecular weight value of the algae oil; then adding methanol into the reaction kettle according to the molar ratio of alcohol to oil of 10:1, and reacting for 2 hours at the constant temperature of 160 ℃ to obtain the product oil with the main component of fatty acid methyl ester.
2. The method of claim 1, wherein the volume ratio of N, N-dimethylformamide to water in the N, N-dimethylformamide-water mixed solution is 1:2.
3. The method of claim 1, wherein the sonication is performed for 30 minutes at a power intensity of 0.5W/mL and a frequency of 20kHz.
4. The method of claim 1, wherein the microwave synthesis tank has a power of 500W and a reaction temperature of 90 ℃.
5. The method of claim 1, wherein the deionized water is washed 3 times.
6. The method of claim 1, wherein the algae oil has an acid value ranging from 34 to 68mg KOH g -1 。
7. The method of claim 1, wherein the main component of the product oil is fatty acid methyl esters having carbon chain lengths of C14 to C22.
8. The preparation method of the two-dimensional ultrathin ZIF-67 nanosheet catalyst for in-situ growth on the surface of the mesoporous Y-type molecular sieve is characterized by comprising the following steps of:
(1) 1.312-13.12 g of 2-methylimidazole is taken and dissolved in 50-500 mL of N, N-dimethylformamide-water mixed solution; adding 0.5-5 g of mesoporous Y-type molecular sieve into the solution, and carrying out ultrasonic treatment to obtain a mixed solution A;
(2) 1.164-11.64 g of cobalt nitrate hexahydrate is taken and dissolved in 50-500 mL of N, N-dimethylformamide-water mixed solution, and solution B is obtained after ultrasonic treatment;
(3) Pouring the solution B into the mixed solution A, uniformly mixing, and then transferring the mixed solution B into a microwave synthesis kettle for full reaction for 2 hours; and after the reaction is finished, centrifugally separating solids, washing with deionized water, and drying to obtain the catalyst with the mesoporous Y-type molecular sieve surface in-situ grown two-dimensional ultrathin ZIF-67 nanosheets.
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