CN112961053A - Method for preparing branched fatty acid methyl ester by using modified ZSM-5 molecular sieve catalyst - Google Patents
Method for preparing branched fatty acid methyl ester by using modified ZSM-5 molecular sieve catalyst Download PDFInfo
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Abstract
本发明公开了一种由改性ZSM‑5分子筛催化剂制备支链脂肪酸甲酯的方法。该方法包括：将ZSM‑5分子筛母体利用碱性溶液进行改性，再经过离子交换，然后通过离心、洗涤、干燥、煅烧，得到改性ZSM‑5分子筛；将获得的改性ZSM‑5分子筛、直链不饱和脂肪酸烷基酯以及水在高压密闭反应釜中混合进行骨架异构化反应，得到含支链不饱和脂肪酸烷基酯的混合物；再加入钯碳催化剂和甲醇混合进行加氢反应，获得支链脂肪酸甲酯。本发明提供的支链脂肪酸甲酯的制备方法，改性后的ZSM‑5分子筛的催化性能稳定，产率和选择性高，重复利用性能优异，可以降低生产成本，符合绿色化学的发展要求，是一种具有良好工业应用前景的制备方法。
The invention discloses a method for preparing branched-chain fatty acid methyl esters from a modified ZSM-5 molecular sieve catalyst. The method comprises: modifying a ZSM-5 molecular sieve precursor with an alkaline solution, then performing ion exchange, and then performing centrifugation, washing, drying and calcining to obtain a modified ZSM-5 molecular sieve; and modifying the obtained modified ZSM-5 molecular sieve , straight-chain unsaturated fatty acid alkyl esters and water are mixed in a high-pressure closed reactor to carry out skeletal isomerization reaction to obtain a mixture containing branched-chain unsaturated fatty acid alkyl esters; then add palladium-carbon catalyst and methanol to mix for hydrogenation reaction , to obtain branched-chain fatty acid methyl esters. According to the preparation method of branched chain fatty acid methyl ester provided by the invention, the modified ZSM-5 molecular sieve has stable catalytic performance, high yield and selectivity, excellent reusability, can reduce production cost, and meets the development requirements of green chemistry, It is a preparation method with good industrial application prospect.
Description
Technical Field
The invention belongs to the technical field of daily chemicals, cosmetics, lubricating oil base oil, surfactants and the like, and particularly relates to a method for preparing branched fatty acid methyl ester by using a modified ZSM-5 molecular sieve catalyst.
Background
The branched fatty acid methyl ester has the advantages of linear saturated and linear unsaturated fatty acid methyl esters, such as high oxidation stability, excellent low-temperature performance, excellent fluidity and the like, due to the existence of alkyl branched chains. Due to the characteristic generated by the branched chain structure, the branched chain fatty acid methyl ester has incomparable superiority with similar substances, has wide application in the fields of daily chemicals, cosmetics, lubricating oil base oil, surfactants and the like, and can improve the performances of oxidation stability, lubricity, surface activity and the like of products.
Researches find that the catalyst with the Bronsted acid active site and the proper pore channel size can effectively catalyze the linear chain unsaturated fatty acid alkyl ester to carry out skeletal isomerization to prepare the branched chain fatty acid methyl ester, and the catalytic isomerization effect of the catalyst is influenced by the Bronsted acid content, the pore structure distribution and other factors.
At present, a process route taking the branched chain fatty acid methyl ester as a main product does not exist in China, most of products are extracted from by-products for producing dimer acid, and the branched chain fatty acid methyl ester is not in demand due to insufficient capacity and rapid development of the nursing product industry, so that the industrial demand cannot be met. The synthesis of branched fatty acid methyl ester usually takes acid clay as catalyst to catalyze high-purity oleic acid (more than 90%) to react to obtain dimer acid and a small part of branched stearic acid methyl ester, and then the needed product is obtained through separation processes such as molecular distillation and the like. This production route has many drawbacks: firstly, the yield of the branched chain fatty acid methyl ester is low, even if oleic acid with high purity is used as a raw material, the yield of the branched chain fatty acid methyl ester can only reach about 40 percent at most; secondly, the subsequent separation cost is high, and the separated product has dark color, high iodine value and low purity; and thirdly, the acid clay cannot be recycled for many times, the solid catalyst waste is difficult to treat, the cost burden is increased, and the development requirement of green chemistry is not met. In addition, the synthesis of the branched fatty acid methyl ester can also be realized through a Reppe carbonylation reaction and a Koch carbonylation reaction, but the two reactions generate more byproducts, are complicated to separate and purify, can only be explored in a laboratory scale, and are not beneficial to realizing industrial production.
Foglia et al used activated clay to catalytically isomerize high purity oleic acid (98%) with the addition of an auxiliary agent such as H3PO4And CH3SO3H) The results show that the yield of the branched fatty acids reaches 50 percent at the highest under the better reaction condition. Hodgson et al use mordenite to catalyze oleic acid isomerization to prepare branched-chain fatty acid, and research shows that oleic acid (97.4%) reacts for 4h at 275 deg.C, the yield of branched-chain fatty acid is 60%, and SiO in the catalyst is2/Al2O3The influence on the oleic acid isomerization reaction is obvious, and the low Si/Al content is beneficial to improving the conversion rate and the yield of the isomerization reaction. The method uses H-type mordenite as a catalyst and oleic Acid (AR) as a raw material in the Yuan-Qiang, the yield is only 55%, and the acid value, the iodine value and the freezing point of the product are high. Zhang et Al have studied the structure, acidity and Si/Al of H-beta zeolite to the influence of oleic acid or methyl oleate isomerization, the result shows that the catalytic activity of H-beta zeolite is determined by acid site number and the combination amount of acid site and raw material, the smaller the Si/Al, the stronger the acidity of the catalyst, and the better the catalytic isomerization effect of beta zeolite with mesoporous structure, too small or too large pore canal is not conducive to improving the yield of isostearic acid.
The ZSM-5 molecular sieve has wider specific surface area, uniform and regular framework pore size structure and adjustable acid sites and has excellent shape-selective catalytic performance, and researchers gradually develop modification researches on the ZSM-5 molecular sieve and explore a process route for preparing branched fatty acid methyl ester by catalyzing skeletal isomerization of straight-chain unsaturated fatty acid alkyl ester. The modified ZSM-5 molecular sieve catalyst has the following advantages: firstly, the pore channel structure of the ZSM-5 molecular sieve can be regulated and controlled, so that the selectivity of a branched chain product is improved; secondly, the acid active site of the ZSM-5 molecular sieve can be chemically modified, so that the selectivity of the skeletal isomerization reaction is improved or controlled; thirdly, the ZSM-5 molecular sieve has low price, excellent recycling performance and simple and convenient regeneration method, thereby reducing the cost.
However, the research on using the modified ZSM-5 molecular sieve as a catalyst for preparing branched fatty acid methyl ester is less in China, and the challenge of researchers is how to modify the ZSM-5 molecular sieve catalyst to obtain a suitable Bronsted acid active site and a suitable pore structure so as to improve the selectivity and yield of the isomerization reaction.
Disclosure of Invention
In order to overcome the defects and shortcomings of the prior art, the invention aims to provide a modification method of a ZSM-5 molecular sieve catalyst for synthesizing branched fatty acid methyl ester, and a process for establishing an effective branched linear unsaturated fatty acid alkyl ester. The method adopts alkaline solution to modify molecular sieve matrix, so that abundant Bronsted acid active sites and proper pore channel structure are obtained, and further, the selectivity and yield of branched chain fatty acid methyl ester prepared by linear chain unsaturated fatty acid alkyl ester skeleton isomerization are improved.
It is another object of the present invention to provide a method for preparing branched fatty acid methyl esters using natural renewable vegetable oil raw materials such as linear unsaturated fatty acid alkyl esters, and which is environmentally friendly from the viewpoint of excellent recycling properties of ZSM-5 molecular sieve catalysts.
The purpose of the invention is realized by the following scheme:
a method for preparing branched fatty acid methyl ester by using a modified ZSM-5 molecular sieve catalyst comprises the following steps:
(1) mixing the alkaline solution with a ZSM-5 molecular sieve, and then continuously stirring;
(2) separating, washing and drying the solid-liquid mixture obtained after the stirring in the step (1) to obtain the Na-ZSM-5 molecular sieve;
(3) grinding the Na-ZSM-5 molecular sieve in the step (2) into powder, and adding NH4Mixing Cl solution with the Na-ZSM-5 molecular sieve powder, continuously stirring, and centrifugingSeparating and repeating for 2-5 times;
(4) separating, washing, drying and calcining the solid-liquid mixture obtained in the step (3) to obtain a modified ZSM-5 molecular sieve catalyst;
(5) adding the modified ZSM-5 molecular sieve catalyst obtained in the step (4), the linear chain unsaturated fatty acid alkyl ester and water into a high-pressure reaction kettle, uniformly mixing, heating under stirring to enable the mixture to generate a skeletal isomerization reaction, and after the reaction is finished, carrying out suction filtration to separate the modified ZSM-5 molecular sieve to obtain a mixture containing branched chain unsaturated fatty acid methyl ester;
(6) and (3) stirring and mixing the mixture containing the branched chain unsaturated fatty acid methyl ester in the step (5) and a palladium-carbon catalyst in an organic solvent, carrying out hydrogenation reaction with hydrogen, filtering to remove the palladium-carbon catalyst after the reaction is finished, and removing the organic solvent through rotary evaporation to obtain the branched chain fatty acid methyl ester.
Further, the alkaline solution in the step (1) is Na2CO3Solution and NaOH solution; the concentration of the alkaline solution is 0.1-1 mol/L; the mass of the ZSM-5 molecular sieve is 7-10 in volume ratio to the alkaline solution: 70-100 g/ml; the stirring temperature of the mixture is 65-75 ℃; the stirring time is 4-6 h.
Further, the separation in the step (2) is centrifugal separation, the rotating speed of the centrifugal separation is 3000-6000 rpm, and the time of the centrifugal separation is 5-15 minutes/time; the washing is carried out for 3-5 times by using deionized water; the drying temperature is 60-70 ℃, and the drying time is 6-8 h.
Further, said NH in step (3)4The concentration of the Cl solution is 1-2 mol/L; the using amount of the Na-ZSM-5 molecular sieve powder is 7-10 g; mass and NH of the Na-ZSM-5 molecular sieve powder4The volume ratio of the Cl solution is 7-10: 70-100 g/mL; the stirring time is 4-6 h.
Further, the separation in the step (4) is centrifugal separation, the rotating speed of the centrifugal separation is 3000-6000 rpm, and the time of the centrifugal separation is 5-15 minutes/time; the washing is carried out for 3-5 times by using deionized water; the drying temperature is 60-70 ℃, and the drying time is 6-8 h; the calcining is carried out in a muffle furnace, the calcining temperature is 500-600 ℃, and the calcining time is 3-5 h.
Further, the adding amount of the H-ZSM-5 molecular sieve catalyst in the step (5) is 4-8% of the mass of the linear chain unsaturated fatty acid alkyl ester; the addition amount of the water is 1 to 7 percent of the mass of the linear chain unsaturated fatty acid alkyl ester.
Further, the stirring speed in the step (5) is 750-850 revolutions per minute; the temperature of the skeletal isomerization reaction is 220-300 ℃; the skeletal isomerization reaction time is 12-24 h.
Preferably, the linear unsaturated fatty acid alkyl ester in the step (5) is methyl oleate with the purity of 80-95%.
Furthermore, the adding amount of the palladium carbon catalyst in the step (6) is 3-5% of the mass of the mixture containing the branched fatty acid methyl ester.
Further, the organic solvent in the step (6) is methanol.
Further, the stirring speed of the step (6) is 400-500 revolutions per minute; the hydrogen pressure of the hydrogenation reaction is 0.4-0.5 Mpa; the temperature of the hydrogenation reaction is 35-50 ℃; the time of the hydrogenation reaction is 2-4 h.
Further, washing, centrifuging, drying and calcining the modified ZSM-5 molecular sieve separated by suction filtration in the step (5) by using an organic solvent, so that the molecular sieve can be recycled. Further, the organic solvent is absolute ethyl alcohol; washing for 3-5 times by using absolute ethyl alcohol; the rotating speed of the centrifugation is 5000-6000 rpm, and the time of the centrifugation is 5-10 minutes/time; the drying condition is 60-80 ℃, and the drying time is 18-24 h; the calcining is carried out in a muffle furnace, the calcining temperature is 500-600 ℃, and the calcining time is 3-5 h.
Compared with the prior art, the invention has the following advantages:
(1) the invention provides a method for preparing branched chain fatty acid methyl ester by using a modified ZSM-5 molecular sieve catalyst, which is environment-friendly and meets the development requirement of green chemistry except for the catalyst without adding other chemical reagents, and has good application prospect.
(2) The preparation method of the branched chain fatty acid methyl ester provided by the invention has the advantages that the modified ZSM-5 molecular sieve has stable catalytic performance, high yield and selectivity and excellent recycling performance, can reduce the production cost, and is favorable for realizing the application in industrial production.
Drawings
FIG. 1 is a gas chromatogram of the skeletal isomerization of a linear unsaturated fatty acid alkyl ester to produce branched fatty acid methyl esters of example 1;
FIG. 2 is a diagram showing the catalytic performance of the modified ZSM-5 molecular sieve catalyst of examples 1 to 5 in catalyzing the skeletal isomerization of linear unsaturated fatty acid alkyl ester to prepare branched fatty acid methyl ester.
Detailed Description
The following examples and drawings further illustrate the practice of the present invention, but the practice of the present invention is not limited thereto. The products of the illustrative process were analyzed by gas chromatography with a flame ion detector to determine the amount of branched, linear, lactone, dimer, etc. in the process. It should be noted that the following processes, if not described in particular detail, are all realizable or understandable by those skilled in the art with reference to the prior art. The reagents or apparatus used are not indicated to the manufacturer, and are considered to be conventional products available by commercial purchase.
Example 1
A method for preparing branched fatty acid methyl ester by using a modified ZSM-5 molecular sieve catalyst comprises the following steps:
(1) modification of ZSM-5 molecular sieve: weighing 10g of ZSM-5 molecular sieve and 100mL of NaOH solution with the concentration of 0.5mol/L, mixing in a round-bottom flask, and placing the round-bottom flask in an oil bath kettle at 70 ℃ for stirring and refluxing for 4 hours at constant temperature; after the ion exchange is finished, cooling the mixed solution to room temperature, performing centrifugal separation on the mixed solution, washing the mixed solution to be neutral by using deionized water, and then drying the washed solution in an oven at the temperature of 70 ℃ for 6 hours to obtain the Na-ZSM-5 molecular sieve catalyst.
(2) Ion exchange of Na-ZSM-5 molecular sieves: 100mL of NH with the concentration of 1mol/L is measured4Cl solution, mixed with the 10g Na-ZSM-5 molecular sieve described in step (1) in the round-bottomed flask, and the round-bottomed flask was put in an oil bath at 80 deg.CStirring and refluxing for 4h at constant temperature in the pot; after the reaction is finished, cooling the mixed solution to room temperature, performing centrifugal separation on the mixed solution, and repeating the centrifugal separation for three times; and finally, centrifuging, washing, drying and calcining the sample to obtain the modified H-ZSM-5 molecular sieve.
The structural characterization parameters of the modified ZSM-5 molecular sieve catalyst prepared in this example are shown in table 1.
TABLE 1 parameters of the modified ZSM-5 molecular sieve prepared in example 1
(3) Preparation of branched unsaturated fatty acid methyl ester: weighing 3g of the H-ZSM-5 molecular sieve in the step (2), 1.5g of deionized water and 50g of methyl oleate (purity 85%) in a closed high-pressure reaction kettle, and introducing N2The initial pressure is 0.4MPa, the reaction is carried out for 12 hours under the condition of 260 ℃, and the stirring speed is 800 rpm; and after the reaction is finished, cooling the reaction kettle to room temperature, and performing suction filtration to separate the H-ZSM-5 molecular sieve to obtain a mixture containing the branched chain unsaturated fatty acid methyl ester.
(4) Preparation of branched fatty acid methyl ester: taking 5g of the mixture containing the branched chain unsaturated fatty acid methyl ester in the step (3), 0.25g of palladium-carbon catalyst and 50mL of methanol, placing the mixture in a closed high-pressure reaction kettle, and introducing H2The initial pressure is 0.45MPa, the reaction is carried out for 2.5h at the temperature of 40 ℃, and the stirring speed is 450 rpm; and after the reaction is finished, filtering and separating the palladium-carbon catalyst, and distilling under reduced pressure to remove excessive methanol to obtain the branched-chain fatty acid methyl ester.
(5) And (3) product analysis: the linear and branched fatty acid methyl ester content of the product was determined by gas chromatography and calculated to give a conversion of methyl oleate of 89.46% and yield and selectivity of branched fatty acid methyl ester of 74.30% and 83.05%, respectively (see figure 2). The gas chromatogram of the product is shown in FIG. 1; the peak appearance time of the substances in examples 2, 3, 4, 5 and 6 was the same as in example 1, but the peak areas were different, as shown in FIG. 1.
Example 2
A method for preparing branched fatty acid methyl ester by using a modified ZSM-5 molecular sieve catalyst comprises the following steps:
(1) modification of ZSM-5 molecular sieve: weighing 7g of ZSM-5 molecular sieve and 70mL of NaOH solution with the concentration of 1mol/L, mixing in a round-bottom flask, and placing the round-bottom flask in an oil bath kettle at 70 ℃ for stirring and refluxing for 4 hours at constant temperature; after the ion exchange is finished, cooling the mixed solution to room temperature, performing centrifugal separation on the mixed solution, washing the mixed solution to be neutral by using deionized water, and then drying the washed solution in an oven at the temperature of 70 ℃ for 6 hours to obtain the Na-ZSM-5 molecular sieve catalyst.
(2) Ion exchange of Na-ZSM-5 molecular sieves: measuring 70mL of NH with the concentration of 1mol/L4Mixing Cl solution with the 7g of Na-ZSM-5 molecular sieve in the step (2) in the round-bottom flask, and placing the round-bottom flask in an oil bath kettle at the temperature of 80 ℃ to stir and reflux for 4 hours at constant temperature; after the reaction is finished, cooling the mixed solution to room temperature, performing centrifugal separation on the mixed solution, and repeating the centrifugal separation for three times; and finally, centrifuging, washing, drying and calcining the sample to obtain the modified H-ZSM-5 molecular sieve.
(3) Preparation of branched unsaturated fatty acid methyl ester: weighing 3g of the H-ZSM-5 molecular sieve in the step (2), 1.5g of deionized water and 50g of methyl oleate (purity 85%) in a closed high-pressure reaction kettle, and introducing N2The initial pressure is 0.4MPa, the reaction is carried out for 12 hours under the condition of 260 ℃, and the stirring speed is 800 rpm; and after the reaction is finished, cooling the reaction kettle to room temperature, and performing suction filtration to separate the H-ZSM-5 molecular sieve to obtain a mixture containing the branched chain unsaturated fatty acid methyl ester.
(4) Preparation of branched fatty acid methyl ester: taking 5g of the mixture containing the branched chain unsaturated fatty acid methyl ester in the step (3), 0.25g of palladium-carbon catalyst and 50mL of methanol, placing the mixture in a closed high-pressure reaction kettle, and introducing H2The initial pressure is 0.45MPa, the reaction is carried out for 2.5h at the temperature of 40 ℃, and the stirring speed is 450 rpm; and after the reaction is finished, filtering and separating the palladium-carbon catalyst, and distilling under reduced pressure to remove excessive methanol to obtain the branched-chain fatty acid methyl ester.
(5) And (3) product analysis: the linear and branched fatty acid methyl ester content of the product was determined by gas chromatography and calculated to give a conversion of methyl oleate of 84.85% and yield and selectivity of branched fatty acid methyl ester of 69.56% and 81.98%, respectively (see figure 2). The gas chromatogram of the product can be shown in FIG. 1.
Example 3
A method for preparing branched fatty acid methyl ester by using a modified ZSM-5 molecular sieve catalyst comprises the following steps:
(1) modification of ZSM-5 molecular sieve: weighing 10g of ZSM-5 molecular sieve and 100mL of NaOH solution with the concentration of 0.3mol/L, mixing in a round-bottom flask, and placing the round-bottom flask in an oil bath kettle at 70 ℃ for stirring and refluxing for 4 hours at constant temperature; after the ion exchange is finished, cooling the mixed solution to room temperature, performing centrifugal separation on the mixed solution, washing the mixed solution to be neutral by using deionized water, and then drying the washed solution in an oven at the temperature of 70 ℃ for 6 hours to obtain the Na-ZSM-5 molecular sieve catalyst.
(2) Ion exchange of Na-ZSM-5 molecular sieves: measuring 70mL of NH with the concentration of 1mol/L4Mixing Cl solution with the 7g of Na-ZSM-5 molecular sieve in the step (2) in the round-bottom flask, and placing the round-bottom flask in an oil bath kettle at the temperature of 80 ℃ to stir and reflux for 4 hours at constant temperature; after the reaction is finished, cooling the mixed solution to room temperature, performing centrifugal separation on the mixed solution, and repeating the centrifugal separation for three times; and finally, centrifuging, washing, drying and calcining the sample to obtain the modified H-ZSM-5 molecular sieve.
(3) Preparation of branched unsaturated fatty acid methyl ester: weighing 3g of the H-ZSM-5 molecular sieve in the step (2), 1.5g of deionized water and 50g of methyl oleate (purity 85%) in a closed high-pressure reaction kettle, and introducing N2The initial pressure is 0.4MPa, the reaction is carried out for 12 hours under the condition of 260 ℃, and the stirring speed is 800 rpm; and after the reaction is finished, cooling the reaction kettle to room temperature, and performing suction filtration to separate the H-ZSM-5 molecular sieve to obtain a mixture containing the branched chain unsaturated fatty acid methyl ester.
(4) Preparation of branched fatty acid methyl ester: taking 5g of the mixture containing the branched chain unsaturated fatty acid methyl ester in the step (3), 0.25g of palladium-carbon catalyst and 50mL of methanol, placing the mixture in a closed high-pressure reaction kettle, and introducing H2The initial pressure is 0.45MPa, the reaction is carried out for 2.5h at the temperature of 40 ℃, and the stirring speed is 450 rpm; and after the reaction is finished, filtering and separating the palladium-carbon catalyst, and distilling under reduced pressure to remove excessive methanol to obtain the branched-chain fatty acid methyl ester.
(5) And (3) product analysis: the linear and branched fatty acid methyl ester content of the product was determined by gas chromatography and calculated to give a conversion of methyl oleate of 83.96% and yield and selectivity of branched fatty acid methyl ester of 66.19% and 78.83%, respectively (see figure 2). The gas chromatogram of the product can be shown in FIG. 1.
Example 4
A method for preparing branched fatty acid methyl ester by using a modified ZSM-5 molecular sieve catalyst comprises the following steps:
(1) modification of ZSM-5 molecular sieve: weighing 10g of ZSM-5 molecular sieve and 100mL of NaOH solution with the concentration of 0.1mol/L, mixing in a round-bottom flask, and placing the round-bottom flask in an oil bath kettle at 70 ℃ for stirring and refluxing for 4 hours at constant temperature; after the ion exchange is finished, cooling the mixed solution to room temperature, performing centrifugal separation on the mixed solution, washing the mixed solution to be neutral by using deionized water, and then drying the washed solution in an oven at the temperature of 70 ℃ for 6 hours to obtain the Na-ZSM-5 molecular sieve catalyst.
(2) Ion exchange of Na-ZSM-5 molecular sieves: 100mL of NH with the concentration of 1mol/L is measured4Mixing the Cl solution and the 10g of Na-ZSM-5 molecular sieve in the step (2) in the round-bottom flask, and placing the round-bottom flask in an oil bath kettle at the temperature of 80 ℃ to stir and reflux for 4 hours at constant temperature; after the reaction is finished, cooling the mixed solution to room temperature, performing centrifugal separation on the mixed solution, and repeating the centrifugal separation for three times; and finally, centrifuging, washing, drying and calcining the sample to obtain the modified H-ZSM-5 molecular sieve.
(3) Preparation of branched unsaturated fatty acid methyl ester: weighing 3g of the H-ZSM-5 molecular sieve in the step (2), 1.5g of deionized water and 50g of methyl oleate (purity 85%) in a closed high-pressure reaction kettle, and introducing N2The initial pressure is 0.4MPa, the reaction is carried out for 12 hours under the condition of 260 ℃, and the stirring speed is 800 rpm; and after the reaction is finished, cooling the reaction kettle to room temperature, and performing suction filtration to separate the H-ZSM-5 molecular sieve to obtain a mixture containing the branched chain unsaturated fatty acid methyl ester.
(4) Preparation of branched fatty acid methyl ester: taking 5g of the mixture containing the branched chain unsaturated fatty acid methyl ester in the step (3), 0.25g of palladium-carbon catalyst and 50mL of methanol, placing the mixture in a closed high-pressure reaction kettle, and introducing H2The initial pressure is 0.45MPa, the reaction is carried out for 2.5h at the temperature of 40 ℃, and the stirring speed is 450 rpm; and after the reaction is finished, filtering and separating the palladium-carbon catalyst, and distilling under reduced pressure to remove excessive methanol to obtain the branched-chain fatty acid methyl ester.
(5) And (3) product analysis: the linear and branched fatty acid methyl ester content of the product was determined by gas chromatography and calculated to give a conversion of methyl oleate of 67.28% and yield and selectivity of branched fatty acid methyl ester of 45.23% and 67.23%, respectively (see figure 2). The gas chromatogram of the product can be shown in FIG. 1.
Example 5
A method for preparing branched fatty acid methyl esters from unmodified ZSM-5 molecular sieve catalysts, comprising the steps of:
(1) preparation of branched unsaturated fatty acids: 3g of unmodified ZSM-5 molecular sieve, 1.5g of deionized water and 50g of methyl oleate (purity 85%) are weighed and placed in a closed high-pressure reaction kettle, and N is introduced2The initial pressure is 0.4MPa, the reaction is carried out for 12 hours under the condition of 260 ℃, and the stirring speed is 800 rpm; and after the reaction is finished, cooling the reaction kettle to room temperature, and performing suction filtration to separate the ZSM-5 molecular sieve to obtain a mixture containing the branched chain unsaturated fatty acid methyl ester.
(2) Preparation of branched fatty acid methyl ester: taking 5g of the mixture containing the branched chain unsaturated fatty acid methyl ester in the step (1), 0.25g of palladium-carbon catalyst and 50mL of methanol, placing the mixture in a closed high-pressure reaction kettle, and introducing H2The initial pressure is 0.45MPa, the reaction is carried out for 2.5h at the temperature of 40 ℃, and the stirring speed is 450 rpm; and after the reaction is finished, filtering and separating the palladium-carbon catalyst, and distilling under reduced pressure to remove excessive methanol to obtain the branched-chain fatty acid methyl ester.
(3) And (3) product analysis: the linear and branched fatty acid methyl ester content of the product was determined by gas chromatography and calculated to give a conversion of methyl oleate of 58.61% and yield and selectivity of branched fatty acid methyl ester of 35.61% and 61.17%, respectively (see figure 2). The gas chromatogram of the product can be shown in FIG. 1.
Example 6
A method for recycling a modified ZSM-5 molecular sieve catalyst for preparing branched fatty acid methyl ester comprises the following steps:
(1) regeneration of the modified ZSM-5 molecular sieve: washing the H-ZSM-5 molecular sieve separated by suction filtration in the step (3) of the example 1 with absolute ethyl alcohol, performing centrifugal separation, and repeating the steps for 3 times. Drying at 70 ℃ for 20h, and then calcining in a muffle furnace at 500 ℃ for 3h to obtain the regenerated modified ZSM-5 molecular sieve catalyst.
(2) Preparation of branched unsaturated fatty acids: weighing 3g of the regenerated modified ZSM-5 molecular sieve in the step (1), 1.5g of deionized water and 50g of methyl oleate (purity 85%) in a closed high-pressure reaction kettle, and introducing N2The initial pressure is 0.4MPa, the reaction is carried out for 12 hours under the condition of 260 ℃, and the stirring speed is 800 rpm; and after the reaction is finished, cooling the reaction kettle to room temperature, and performing suction filtration to separate the H-ZSM-5 molecular sieve to obtain a mixture containing the branched chain unsaturated fatty acid methyl ester.
(3) Preparation of branched fatty acid methyl ester: taking 5g of the mixture containing the branched chain unsaturated fatty acid methyl ester in the step (2), 0.25g of palladium-carbon catalyst and 50mL of methanol, placing the mixture in a closed high-pressure reaction kettle, and introducing H2The initial pressure is 0.45MPa, the reaction is carried out for 2.5h at the temperature of 40 ℃, and the stirring speed is 450 rpm; and after the reaction is finished, filtering and separating the palladium-carbon catalyst, and distilling under reduced pressure to remove excessive methanol to obtain the branched-chain fatty acid methyl ester.
(4) And (3) product analysis: the content of the linear chain fatty acid methyl ester and the branched chain fatty acid methyl ester in the product is determined by adopting gas chromatography, the conversion rate of the methyl oleate is calculated to be 87.74%, the yield and the selectivity of the branched chain fatty acid methyl ester are respectively 71.34% and 81.32%, and the activity of the catalyst is basically maintained at a higher level. The gas chromatogram of the product can be shown in FIG. 1.
The above-mentioned embodiments are only preferred embodiments of the present invention, and are only used for explaining the present invention, but the embodiments of the present invention are not limited by the above-mentioned embodiments, and it is obvious to those skilled in the art that simplification, decoration, combination and improvement can be made without departing from the principle of the present invention, and these simplification, decoration, combination and improvement also belong to the protection scope of the present invention.
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