CN108203712B - Method for catalytically synthesizing ethyl caproate by modified silicon oxide loaded immobilized enzyme - Google Patents
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Abstract
The invention relates to the field of ethyl caproate synthesis, and particularly discloses a method for synthesizing ethyl caproate by catalysis of a modified silicon oxide-loaded immobilized enzyme, which comprises the following steps: (1) preparing pure silicon oxide material; (2) modifying pure silicon oxide material; (3) preparing an immobilized enzyme; (4) and (3) catalyzing and synthesizing ethyl caproate by using the prepared immobilized enzyme. The method for synthesizing the ethyl caproate has the advantages of good catalytic performance of enzyme, high product yield, mild reaction conditions and low production cost.
Description
Technical Field
The invention relates to the field of ethyl caproate synthesis, in particular to a method for synthesizing ethyl caproate by catalysis of a modified silicon oxide-loaded immobilized enzyme.
Background
An enzyme is a high molecular substance with a biocatalytic function, and in a catalytic reaction system of the enzyme, a reactant is generally called a substrate, and the substrate reacts under catalysis of the enzyme to generate a product. Like inorganic catalysts, enzymes do not affect the chemical equilibrium of the reaction, but accelerate the reaction rate by reducing the activation energy of the reaction, but compared with inorganic catalysts, the catalytic conditions of enzymes are milder, and the catalytic efficiency is higher.
In the reaction process, the catalytic activity of the enzyme is easily influenced by the environment of the reaction system, such as temperature, pH value, substrate concentration and the like, the stability of the enzyme is difficult to control, the enzyme is easy to aggregate into a mass during catalysis, the reaction rate is not easy to improve, and the enzyme immobilization provides an idea of avoiding enzyme aggregation, enabling the enzyme to be uniformly distributed in the reaction system and improving the stability of the enzyme. After the enzyme is immobilized, the surface area of the enzyme contacted with a substrate is increased, the diffusion effect and the thermodynamic stability of the enzyme in an organic solvent can be improved to a certain extent, the activity and the selectivity of the enzyme can be regulated and controlled, and the enzyme recovery and continuous production are facilitated. The immobilized enzyme is prepared by immobilizing enzyme in a special phase, so that the immobilized enzyme is separated from the whole phase, but can still carry out molecular exchange with a substrate, and can not only have the catalytic property of the enzyme, but also have the advantages of recovery and repeated use of common chemical catalysts and the like the immobilized catalysts of common chemical reactions.
At present, the enzyme immobilization technology is widely applied in the industries of food industry, fine chemical industry, medicine and the like, and has made a certain progress in the aspect of wastewater treatment. The enzyme immobilization technology is used for producing chemical products, the conditions are mild, three wastes are not generated, and the method is environment-friendly. Therefore, the development of a new enzyme immobilization method and a new immobilization material or modification of various known carriers has been a hot spot of enzyme immobilization research.
Ethyl hexanoate is an important flavor and is widely used in the food industry. Currently, the industrial synthesis method of ethyl caproate is to directly esterify and synthesize the ethyl caproate by taking caproic acid and ethanol as raw materials and taking sulfuric acid as a catalyst. The use of sulfuric acid as a catalyst has the following disadvantages: (1) under the condition of esterification reaction, sulfuric acid has esterification, dehydration and oxidation effects at the same time, so a series of side reactions can occur, and by-products generated by the side reactions bring difficulty to the refining of products and the recovery of raw materials; (2) the post-treatment of the reaction product needs alkali neutralization and water washing to remove sulfuric acid used as a catalyst, so that the process is complex, the product and unreacted raw materials are lost, a large amount of waste liquid is generated, and the environment is polluted; (3) due to the severe corrosiveness of sulfuric acid, equipment has to be periodically renewed despite the use of enamel reactors and advanced stainless steel coffins, thereby increasing production costs. Therefore, the search for a cleaner and more efficient catalyst for producing the ethyl caproate is of great significance for improving the yield of the ethyl caproate and reducing the production cost.
Disclosure of Invention
The invention aims to provide a method for catalytically synthesizing ethyl caproate by using a modified silicon oxide-loaded immobilized enzyme, and the method for producing ethyl caproate has the advantages of good catalytic performance of the enzyme, high product yield, mild reaction conditions and low production cost.
In order to achieve the purpose, the basic scheme of the invention is as follows: a method for catalytically synthesizing ethyl caproate by using an immobilized enzyme loaded by modified silicon oxide comprises the following steps:
(1) preparing pure silicon oxide material;
(2) modifying a pure silicon oxide material: dissolving magnesium salt in deionized water to obtain a magnesium salt solution, mixing the magnesium salt solution and a pure silicon oxide material in equal volume to form a mixed solution, putting the mixed solution into a rotary evaporator, performing reduced pressure evaporation to obtain wet powder, putting the wet powder into a vacuum drying oven, drying to obtain dry powder, putting the dry powder into a muffle furnace, and calcining to obtain a magnesium oxide modified silicon oxide carrier material;
(3) preparing an immobilized enzyme: adding the magnesia modified silica carrier material obtained in the step (2) into an enzyme solution, stirring, filtering to obtain an enzyme-containing filtrate and filter residue, washing the filter residue with the enzyme-containing filtrate, washing the filter residue with a buffer solution, and drying the filter residue after washing to obtain the immobilized enzyme;
(4) synthesis of ethyl caproate: adding caproic acid, ethanol and immobilized enzyme into an organic solvent, stirring to form a reaction system, wherein the mass ratio of the caproic acid to the ethanol is 1:1-3, the caproic acid concentration is 0.2-1mol/L, the immobilized enzyme dosage is 30-80mg/ml, the stirring speed is 90-500r/min, and after stirring, placing the reaction system in a water bath at 36-37.5 ℃ for reaction to synthesize ethyl caproate.
The prepared pure silicon oxide material is modified by magnesium oxide, and during modification, a magnesium salt solution and the pure silicon oxide are mixed in equal volume, so that the magnesium salt solution is fully immersed in a pore channel of the pure silicon oxide. And then removing moisture contained in the magnesium salt by drying the silicon oxide impregnated with the magnesium salt solution by distillation and vacuum drying to obtain dried silicon oxide impregnated with the magnesium salt, putting the dried silicon oxide impregnated with the magnesium salt into a muffle furnace for calcination, gradually heating the magnesium salt to decompose magnesium oxide in the calcination process, and finally precipitating the magnesium oxide decomposed from the magnesium salt to be attached in pore channels of the silicon oxide. When the rotary evaporator is used for removing the moisture in the magnesium salt under the reduced pressure condition, the moisture is efficiently evaporated at the temperature lower than the normal-pressure boiling point, so that the magnesium salt dissolved in water is effectively prevented from being aggregated in the nanometer pore channel of the silicon oxide, and the obtained magnesium oxide is in a bulk aggregation state, namely, the uniform distribution of magnesium nitrate in the nanometer pore channel of the silicon oxide is facilitated, and the finally obtained magnesium oxide is also in a uniform distribution state. Experiments show that compared with an unmodified pure silicon oxide carrier material, the magnesium oxide modified silicon oxide carrier material can improve the catalytic performance of the corresponding immobilized enzyme by 50%.
Adding the magnesia modified silica carrier material into an enzyme solution, and carrying out stirring, filtering and flushing operations to successfully immobilize free enzyme on the magnesia modified silica carrier material so as to obtain the immobilized enzyme catalyst, wherein the operation is simple and convenient. When ethyl caproate is synthesized, caproic acid and ethanol are used as raw materials, the immobilized enzyme prepared in the step (3) is used as a catalyst, and the chemical equation of the reaction is as follows:
compared with the traditional synthetic route which adopts concentrated sulfuric acid as a catalyst, the immobilized enzyme is used for catalyzing the esterification reaction of caproic acid and ethanol, the reaction condition is milder, the catalysis efficiency is higher, no by-product is generated, the method is environment-friendly, and the quality of ethyl caproate products is higher. Compared with immobilized enzyme taking pure silicon oxide material as a carrier, when the immobilized enzyme taking the magnesium oxide modified silicon oxide material as the carrier catalyzes the esterification reaction of caproic acid and ethanol to synthesize ethyl caproate, the conversion rate of caproic acid can be improved by 50%. The method uses immobilized enzyme loaded by the magnesia modified silica carrier material to catalyze and synthesize ethyl caproate, and can obviously improve the catalytic reaction efficiency.
Further, the method for preparing the pure silicon oxide material in the step (1) comprises the following steps: a. adding a block type nonionic surfactant P123 into hydrochloric acid with the concentration of 0.4mol/L, and stirring to obtain a clear solution; b. standing the clear solution in 35-36 deg.C water bath for 0.5-1 hr, adding ethyl orthosilicate, stirring at 35-36 deg.C for 20-24 hr, and refluxing for hydrolysis to obtain hydrolysis mixture; c. carrying out heat treatment on the hydrolysis mixture, wherein during the heat treatment, the hydrolysis mixture is placed in a water bath with the temperature of 100-105 ℃ and stands for 40-48 h; d. filtering the hydrolyzed mixture after the heat treatment to obtain a white solid, washing the white solid, carrying out vacuum drying on the washed white solid, and calcining the white solid in a muffle furnace after the drying is finished to obtain the pure silicon oxide material.
Further, in the step (1), the dosage of the hydrochloric acid is 30-50ml, the dosage of the block nonionic surfactant P123 is 1-2g, and the dosage of the tetraethoxysilane is 2-4 g; in the step d, the calcination temperature is 500-600 ℃, and the calcination time is 3-5 h; the obtained pure silicon oxide material has a pore diameter of 7.8nm and a specific surface area of 990cm2g-1Pore volume of 1.5cm3g-1. The obtained pure silicon oxide material has a good three-dimensional network structure and a large specific surface area, and is suitable for being used as an immobilized carrier of enzyme.
Further, the magnesium salt in the step (2) is magnesium nitrate, and the dosage of the magnesium salt is 0.05-0.1 g; the dosage of the deionized water is 3-6ml, and the dosage of the pure silicon oxide material is 0.2-0.7 g; the drying temperature is 40-60 ℃, and the drying time is 40-48 h; the calcination temperature is 500-600 ℃, and the calcination time is 3-5 h.
Magnesium nitrate is adopted as the magnesium salt, and the magnesium nitrate can be completely decomposed into magnesium oxide solid and nitric oxide gas products at the calcining temperature of 500-600 ℃. The magnesia modified silica carrier material prepared by adopting the conditions has the advantages that the magnesia can be uniformly distributed in the pore channels of the silica material, so that the magnesia modified silica material can still keep the characteristics of large specific surface area, large pore volume and regular pore channel structure of the pure silica material after loading free enzyme.
Further, in the step (3), the concentration of the enzyme solution is 5g/L, the dosage of the enzyme solution is 80-100ml, and the dosage of the magnesia modified silica carrier material is 0.2-0.7 g.
Further, the preparation method of the enzyme solution comprises the following steps: adding dry enzyme powder into a buffer solution, stirring, and taking supernatant to prepare the enzyme solution, wherein the dry enzyme powder is lipase dry enzyme powder. The buffer solution can adjust the pH value of the enzyme environment and avoid enzyme inactivation.
Further, the buffer was a phosphate-citrate buffer with a pH of 4.06.
The immobilized enzyme catalyst prepared by the conditions has the aperture of 5.7nm and the specific surface area of 520cm2g-1Pore volume of 0.8cm3g-1The characteristics of large specific surface area, large pore volume and regular pore channel structure of the pure silicon oxide material are still maintained.
Further, in the step (4), the organic solvent is anhydrous cyclohexane, the using amount of the anhydrous cyclohexane is 1-3ml, and the time of the synthesis reaction of the ethyl hexanoate is 20-24 h.
Drawings
FIG. 1 is a scanning electron micrograph (a) of a pure silica support material used in example 1 and comparative example, a scanning electron micrograph (b) of an immobilized enzyme supported by a silica support in comparative example, and a scanning electron micrograph (c) of an immobilized enzyme supported by a 5wt% magnesia-modified silica support in example 1.
FIG. 2 is a transmission electron micrograph (a) of a pure silica support material used in example 1 and comparative example, a transmission electron micrograph (b) of an immobilized enzyme supported by a silica support in comparative example, and a transmission electron micrograph (c) of an immobilized enzyme supported by a 5wt% magnesia-modified silica support in example 1.
FIG. 3 is a nitrogen adsorption-desorption curve of the pure silica support material (a) used in example 1 and comparative example, the immobilized enzyme (b) supported on the silica support in comparative example, the immobilized enzyme (c) supported on the silica support modified with 5% by weight of magnesium oxide in example 1.
FIG. 4 is a pore size distribution curve of the pure silica support material (a) used in example 1 and comparative example, the immobilized enzyme (b) supported on the silica support in comparative example, and the immobilized enzyme (c) supported on the silica support modified with 5% by weight of magnesium oxide in example 1.
FIG. 5 is a UV-visible diffuse reflectance spectrum of a pure silica support material used in example 1 and a comparative example, a 5wt% magnesia-modified silica support material used in example 1, a dry enzyme powder used in example 1 and a comparative example, a silica support-supported immobilized enzyme used in a comparative example, and a 5wt% magnesia-modified silica support-supported immobilized enzyme used in example 1.
FIG. 6 is a graph showing the comparison of the catalytic activities of the immobilized enzyme supported on a silica carrier in the comparative example and the immobilized enzyme supported on a 5wt% magnesia-modified silica carrier in example 1 for catalyzing the esterification reaction of hexanoic acid and ethanol.
Detailed Description
The following is further detailed by the specific embodiments:
hexanoic acid, ethanol, anhydrous cyclohexane, Tetraethylorthosilicate (TEOS), magnesium nitrate (Mg (NO) mentioned in the examples below3)2) Are all analytical pure reagents; p123 is a triblock copolymer, which is fully called polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer, is a block nonionic surfactant, and the above reagents are all from Aldrich company; the concentration of hydrochloric acid is 0.4mol/L, and the hydrochloric acid comes from Chengdu Kelong chemical reagent factories; the dry enzyme powder is lipase dry enzyme powder, is from Shenzhen Luweikang bioengineering Limited company, and has enzyme activity of 100000U/g determined by olive oil emulsification method in national standard (GB/T23535-; the pH value of the phosphoric acid-citric acid buffer solution is 4.06, and analytically pure citric acid and NaH are adopted2PO4•2H2O and Na2HPO4•12H2And preparing an O reagent from a Chengdu Kelong chemical reagent factory.
The following describes in detail a method for catalytically synthesizing ethyl hexanoate by using a modified silica-supported immobilized enzyme, taking example 1 as an example, and other examples are shown in table 1, and the parts not shown are the same as those in example 1.
Example 1
A method for catalytically synthesizing ethyl caproate by using an immobilized enzyme loaded by modified silicon oxide comprises the following steps:
firstly, preparing pure silicon oxide material, the method is as follows:
(1) adding 1.23g P123 to 40ml hydrochloric acid, and stirring to obtain a clear solution;
(2) equilibrating the resulting clear solution in a 35 ℃ water bath for 0.5 hour;
(3) adding 2.8g of TEOS into the balanced solution, and stirring, refluxing and hydrolyzing for 24 hours at 35 ℃;
(4) treating the resulting hydrolysis mixture at 105 ℃ for 48 hours;
(5) filtering the mixed solution after the water heat treatment to obtain white solid, and washing the filtered white solid by using deionized water;
(6) and (3) drying the washed white solid in vacuum at room temperature, and then calcining the white solid in a muffle furnace at 550 ℃ for 4 hours to obtain the pure silicon oxide material.
FIG. 1 is a scanning electron microscope image of the obtained pure silicon oxide material, and it can be seen from FIG. 1 that the particles of the material have uniform morphology and are all in a long strip shape, and the length of the particles in the long axis direction exceeds 10 micrometers. Fig. 2 is a transmission electron microscope image of the obtained pure silicon oxide material, and the parallel arrangement of the nano-pores of the obtained pure silicon oxide material can be clearly identified from fig. 2. FIGS. 3 and 4 are a nitrogen adsorption-desorption curve and a pore size distribution curve of the obtained pure silica material, respectively, and it can be seen from FIGS. 3 and 4 that the silica material has typical adsorption characteristics and a very concentrated pore size distribution of a mesoporous material, and the obtained pure silica material has a pore size of 7.8nm and a specific surface area of 990cm2g-1Pore volume of 1.5cm3g-1。
Secondly, preparing a 5wt% magnesia modified silica support material by the following method:
(1) 0.092g Mg (NO)3)2Dissolving in 5ml deionized water to obtain Mg (NO)3)2Mixing the water solution with 0.5g of pure silicon oxide material to prepare a mixture;
(2) evaporating the water of the mixture in a rotary evaporator, wherein the temperature is not higher than 60 ℃ when the water is evaporated, and simultaneously reducing the air pressure in the evaporator by using a circulating water pump to extract air;
(3) treating the solid evaporated by the rotary evaporator in a vacuum drying oven at 50 ℃ for 2 days;
(4) and (4) calcining the substance treated in the step (3) at 550 ℃ for 4 hours to obtain white powder, wherein the white powder is the 5wt% of magnesia modified silica carrier material.
Thirdly, preparing the immobilized enzyme by taking the 5wt% magnesia modified silica material as a carrier, wherein the method comprises the following steps:
(1) weighing a certain amount of dry enzyme powder, adding a phosphoric acid-citric acid buffer solution with the pH value of 4.06, wherein the ratio of the dry enzyme powder to the buffer solution is 5g/L, stirring for 1 hour, standing for 2 hours, and taking the supernatant fluid, namely the enzyme solution.
(2) 0.5g of a 5% by weight magnesia-modified silica support material was weighed into a beaker containing 100ml of the enzyme solution, stirred for 1.5 hours and filtered.
(3) Repeatedly washing the filtrate with enzyme-containing filtrate for 3-4 times.
(4) The filtrate was washed with 200mL of a pH 4.06 phosphate-citrate buffer to remove the weak lipase adsorbed on the surface of the carrier, and then filtered again.
(5) And (4) sucking the filtered immobilized enzyme catalyst by using filter paper, and storing the immobilized enzyme catalyst in a refrigerator at 4 ℃.
Fig. 1 is a scanning electron microscope image of the obtained immobilized enzyme supported by the 5wt% magnesia-modified silica support material, fig. 2 is a transmission electron microscope image of the obtained immobilized enzyme supported by the 5wt% magnesia-modified silica support material, and fig. 3 and fig. 4 are a nitrogen adsorption-desorption curve and a pore size distribution curve, respectively, of the obtained immobilized enzyme supported by the 5wt% magnesia-modified silica support material. It can be seen from the above several figures that the obtained immobilized enzyme catalyst supported by 5wt% of magnesia-modified silica carrier material has well maintained the pore size structure of pure silica carrier material, and the obtained immobilized enzyme catalyst supported by 5wt% of magnesia-modified silica carrier material has a pore size of 5.7nm and a specific surface area of 520cm2g-1Pore volume of 0.8cm3g-1。
Fourthly, synthesizing ethyl caproate by catalyzing immobilized enzyme loaded by the magnesium oxide modified silicon oxide carrier with the weight percent of 5 percent, wherein the method comprises the following steps:
(1) in 2ml of anhydrous cyclohexane solvent, according to the proportion that the dosage of the immobilized enzyme is 50mg/ml, the concentration of the caproic acid is 0.3mol/L and the acid-alcohol ratio is 1:1.8, the immobilized enzyme catalyst, the caproic acid and the ethanol are added and stirred and mixed to prepare a reaction system, and the stirring speed is 100 r/min.
(2) The reaction system was placed in a 37 ℃ water bath to start the reaction, with a reaction time of 24 hours.
TABLE 1
| Test group parameters | Example 1 | Example 2 | Example 3 |
| Hydrochloric acid (ml) | 40.0 | 30.0 | 50.0 |
| P123（g） | 1.23 | 1.00 | 2.00 |
| TEOS（g） | 2.80 | 2.00 | 4.00 |
| Mg(NO3)2（g） | 0.092 | 0.05 | 0.10 |
| Pure silicon oxide material (g) | 0.50 | 0.20 | 0.70 |
| Modified silica support material (g) | 0.50 | 0.20 | 0.70 |
| Immobilized enzyme (mg/ml) | 50.0 | 30.0 | 80.0 |
Comparative example
The difference between the comparative example and the above example is that the preparation of the immobilized enzyme takes pure silicon oxide material as a carrier, and the preparation method is as follows:
(1) weighing a certain amount of dry enzyme powder, adding a phosphoric acid-citric acid buffer solution with the pH value of 4.06, and stirring to obtain an enzyme solution with the concentration of 5 g/L.
(2) 0.5g of pure silica material was weighed into a beaker containing 100ml of enzyme solution, stirred for 1.5 hours and then filtered. The preparation method of the pure silicon oxide material was identical to that described in example 1.
(3) Repeatedly washing the filtrate with enzyme-containing filtrate for 3-4 times.
(4) The filtrate was washed with 200mL of a pH 4.06 phosphate-citrate buffer to remove the weak lipase adsorbed on the surface of the carrier, and then post-filtered again.
(5) And (3) sucking the filtered immobilized enzyme catalyst by using filter paper, and storing the immobilized enzyme catalyst in a refrigerator at 4 ℃.
Fig. 1 is a scanning electron micrograph of the obtained silica carrier-supported immobilized enzyme, fig. 2 is a transmission electron micrograph of the obtained silica carrier-supported immobilized enzyme, and fig. 3 and 4 are a nitrogen adsorption-desorption curve and a pore diameter distribution curve, respectively, of the obtained silica carrier-supported immobilized enzyme. It can be seen from the above several figures that the obtained silica carrier-supported immobilized enzyme catalyst well maintains the pore structure of the carrier material.
Performance analysis
The immobilized enzyme prepared in example 1 was extracted and tested for its esterification reaction catalyzing caproic acid and ethanol, and compared with the immobilized enzyme prepared in comparative example for its esterification reaction catalyzing caproic acid and ethanol, the following results were obtained:
FIG. 5 is a UV-VIS diffuse reflectance spectrum of a pure silica support material and a dry enzyme powder used in example 1 and a comparative example, a 5wt% magnesia-modified silica support material in example 1, a silica support-supported immobilized enzyme catalyst in a comparative example, and a 5wt% magnesia-modified silica support-supported immobilized enzyme catalyst in example 1. It can be seen that the spectrum of the pure silica support material shows no absorption peak in the whole wavelength range, the 5wt% magnesia-modified silica support material in example 1 can recognize an absorption edge in the region less than 200nm, and the spectrum of the dry enzyme powder has an obvious absorption peak at the wavelength of 276 nm; a strong absorption edge is present at wavelengths close to 200 nm. The spectra of the immobilized enzyme supported on the silica carrier in the comparative example and the immobilized enzyme supported on the 5wt% magnesia-modified silica carrier in example 1 both showed characteristics that were very consistent with the spectrum of the free enzyme, also having a distinct absorption peak at 276nm and a strong absorption edge near 200nm, indicating that the free enzyme had been successfully immobilized on the silica carrier in the comparative example and the 5wt% magnesia-modified silica carrier in example 1, respectively, to obtain the corresponding immobilized enzyme catalysts, through the above-described preparation processes.
It can be seen from fig. 6 that the immobilized enzyme supported on the silica carrier in the comparative example catalyzes the esterification reaction of hexanoic acid and ethanol with an hexanoic acid conversion rate of 60%, whereas the immobilized enzyme supported on the silica carrier modified with 5wt% of magnesium oxide in example 1 catalyzes the esterification reaction of hexanoic acid and ethanol with an hexanoic acid conversion rate of 90%. Therefore, compared with the immobilized enzyme loaded by the silica carrier, the catalytic performance of the immobilized enzyme loaded by the 5wt% of the magnesia modified silica carrier is improved by 50%, which shows that the catalytic reaction efficiency can be obviously improved by using the immobilized enzyme loaded by the magnesia modified silica carrier material to catalytically synthesize ethyl hexanoate.
The foregoing is merely an example of the present invention and common general knowledge of known specific structures and features of the embodiments is not described herein in any greater detail. It should be noted that, for those skilled in the art, without departing from the structure of the present invention, several changes and modifications can be made, which should also be regarded as the protection scope of the present invention, and these will not affect the effect of the implementation of the present invention and the practicability of the patent.
Claims (8)
1. A method for catalytically synthesizing ethyl caproate by using an immobilized enzyme loaded by modified silicon oxide is characterized by comprising the following steps:
(1) preparing pure silicon oxide material;
(2) modifying a pure silicon oxide material: dissolving magnesium salt in deionized water to obtain a magnesium salt solution, mixing the magnesium salt solution and a pure silicon oxide material in equal volume to form a mixed solution, putting the mixed solution into a rotary evaporator, performing reduced pressure evaporation to obtain wet powder, putting the wet powder into a vacuum drying oven, drying to obtain dry powder, putting the dry powder into a muffle furnace, and calcining to obtain a magnesium oxide modified silicon oxide carrier material;
(3) preparation of immobilized lipase: adding the magnesia modified silica carrier material obtained in the step (2) into an enzyme solution, stirring, filtering to obtain an enzyme-containing filtrate and filter residue, washing the filter residue with the enzyme-containing filtrate, washing the filter residue with a buffer solution, and drying the filter residue after washing to obtain immobilized lipase;
(4) synthesis of ethyl caproate: adding caproic acid, ethanol and immobilized lipase into an organic solvent, stirring to form a reaction system, wherein the mass ratio of the caproic acid to the ethanol is 1:1-3, the concentration of the caproic acid is 0.2-1mol/L, the dosage of the immobilized lipase is 30-80mg/ml, the stirring speed is 90-500r/min, and after stirring, placing the reaction system in a water bath at 36-37.5 ℃ for reaction to synthesize ethyl caproate.
2. The method for catalytically synthesizing ethyl hexanoate by using the modified silica-supported immobilized enzyme according to claim 1, wherein the method comprises the following steps: the method for preparing the pure silicon oxide material in the step (1) comprises the following steps: a. adding a block type nonionic surfactant P123 into hydrochloric acid with the concentration of 0.4mol/L, and stirring to obtain a clear solution; b. standing the clear solution in 35-36 deg.C water bath for 0.5-1 hr, adding ethyl orthosilicate, stirring at 35-36 deg.C for 20-24 hr, and refluxing for hydrolysis to obtain hydrolysis mixture; c. carrying out heat treatment on the hydrolysis mixture, wherein during the heat treatment, the hydrolysis mixture is placed in a water bath with the temperature of 100-105 ℃ and stands for 40-48 h; d. filtering the hydrolyzed mixture after the heat treatment to obtain a white solid, washing the white solid, carrying out vacuum drying on the washed white solid, and calcining the white solid in a muffle furnace after the drying is finished to obtain the pure silicon oxide material.
3. The method for catalytically synthesizing ethyl hexanoate by using the modified silica-supported immobilized enzyme according to claim 2, wherein the method comprises the following steps: the dosage of the hydrochloric acid is 30-50ml, the dosage of the block type nonionic surfactant P123 is 1-2g, and the dosage of the tetraethoxysilane is 2-4 g; in the step d, the calcination temperature is 500-600 ℃, and the calcination time is 3-5 h; the obtained pure silicon oxide material has a pore diameter of 7.8nm and a specific surface area of 990cm2g-1Pore volume of 1.5cm3g-1。
4. The method for catalytically synthesizing ethyl hexanoate by using the modified silica-supported immobilized enzyme according to claim 1, wherein the method comprises the following steps: in the step (2), the magnesium salt is magnesium nitrate, and the dosage of the magnesium salt is 0.05-0.1 g; the dosage of the deionized water is 3-6ml, and the dosage of the pure silicon oxide material is 0.2-0.7 g; the drying temperature is 40-60 ℃, and the drying time is 40-48 h; the calcination temperature is 500-600 ℃, and the calcination time is 3-5 h.
5. The method for catalytically synthesizing ethyl hexanoate by using the modified silica-supported immobilized enzyme according to claim 1, wherein the method comprises the following steps: in the step (3), the concentration of the enzyme solution is 5g/L, the dosage of the enzyme solution is 80-100ml, and the dosage of the magnesia modified silica carrier material is 0.2-0.7 g.
6. The method for catalytically synthesizing ethyl hexanoate by using the modified silica-supported immobilized enzyme according to claim 5, wherein the method comprises the following steps: the preparation method of the enzyme solution comprises the following steps: adding dry enzyme powder into a buffer solution, stirring, and taking supernatant to prepare the enzyme solution, wherein the dry enzyme powder is lipase dry enzyme powder.
7. The method for catalytically synthesizing ethyl hexanoate by using the modified silica-supported immobilized enzyme according to claim 1 or 6, wherein the method comprises the following steps: the buffer was a phosphate-citrate buffer at pH 4.06.
8. The method for catalytically synthesizing ethyl hexanoate by using the modified silica-supported immobilized enzyme according to claim 1, wherein the method comprises the following steps: in the step (4), the organic solvent is anhydrous cyclohexane, the dosage of the anhydrous cyclohexane is 1-3ml, and the time of the ethyl caproate synthesis reaction is 20-24 h.
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| 《SBA-15固定化脂肪酶催化合成棕榈酸乙酯的研究》;李洋;《中国优秀硕士学位论文全文数据库 医药卫生科技辑》;20141015(第10期);第16和24页 * |
| 《Transesterification of vegetable oil to biodiesel over MgO-functionalized mesoporous catalysts》;Li Eugena等;《ENERGY & FUELS》;20081231;第22卷(第1期);摘要、第146页左栏最后一段第2.2.3节 * |
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