A method for preparing a solid catalyst and a method for producing biodiesel

Abstract

The present invention relates to a preparation method and application of a solid catalyst for producing biodiesel, belonging to the fields of catalytic materials and oleochemical applications. The preparation method comprises the following steps: S1, weighing a certain mass of calcium nitrate and / or hydrated calcium nitrate, zinc nitrate and / or hydrated zinc nitrate, and zirconium nitrate and / or hydrated zirconium nitrate, dissolving them in deionized water to obtain a solution; S2, adding urea to the solution obtained in S1, stirring and then carrying out a hydrothermal reaction, and then drying to obtain a solid; S3, performing high-temperature activation on the solid obtained in S2, and then grinding to obtain a solid catalyst. Among them, the molar ratio range of the raw materials Zn:Ca:Zr in S1 includes (1 to 4):4:4 and 4:4:2. The prepared solid catalyst is an amphoteric solid catalyst with both acid and base dual functions, and has the characteristics of less component loss and a wide adaptability range to the free fatty acid content in the raw material oil.

Description

Technical Field

[0001] The present invention belongs to the fields of catalytic materials and application of oil and fat chemicals, and particularly relates to a method for preparing a solid catalyst and a method for producing biodiesel. Background Art

[0002] Biodiesel is a liquid biofuel produced by transesterification of renewable oils and fats such as animal and vegetable oils, waste cooking oil, and microbial oils with alcohols, and its main component is long-chain fatty acid alkyl esters. It has the characteristics of low combustion pollutant emissions and being renewable, and its physical and chemical properties are similar to those of fossil fuels, and it can be doped with them in a certain proportion for use. It is a green and environment-friendly energy source. Generally speaking, the production of biodiesel mainly involves the transesterification of triglycerides and the esterification of free fatty acids. The production of biodiesel by base-catalyzed transesterification is the most widely used technology in industry. Calcium-based solid bases are typical representatives of transesterification catalysts, which can be obtained from conventional calcium sources such as limestone and dolomite, calcium-containing animal shells such as eggshells and snail shells, and calcium-containing industrial wastes such as carbide slag and paper white mud. However, its active components are prone to loss, resulting in difficult catalyst recovery and difficult reuse of the catalyst; it is sensitive to the composition of free fatty acids in the raw material oil. Especially, waste cooking oil as a raw material often contains a large amount of free fatty acids, and too high content of free fatty acids will reduce the catalytic activity.

[0003] In the prior art, composite oxides and supported alkali metal / alkaline earth metal catalysts are used for biodiesel production. Patent CN 105642267 A discloses an X-Ca-Zn-Al and its preparation method, and a metal composite oxide catalyst with good comprehensive performance that takes into account the advantages of several oxides is prepared by compounding, which is used to catalyze the transesterification reaction of castor oil and methanol, and it is found that its catalytic activity is relatively high and the alkali dissolution loss is very small, and the catalytic effect in an acidic environment is not involved. Patent CN101559359A discloses a preparation method of a CaO-ZrO2-KOH solid base catalyst, and the conversion rate of biodiesel reaches 90%, but its transesterification time is as long as 4-6h, and the time is too long, so there is still a certain distance from industrial application. Summary of the Invention

[0004] Aiming at the deficiencies of the prior art, the present invention provides a method for preparing a solid catalyst and a method for producing biodiesel. The solid catalyst has the characteristics of less component loss and a wide adaptability range to the content of free fatty acids in the raw material oil.

[0005] In order to achieve the above object, the technical solution of the present invention is as follows:

[0006] In the first aspect, a method for preparing a solid catalyst includes the following steps.

[0007] S1. Weigh a certain mass of calcium nitrate and / or hydrated calcium nitrate, zinc nitrate and / or hydrated zinc nitrate, and zirconium nitrate and / or hydrated zirconium nitrate, and dissolve them in deionized water to obtain a solution.

[0008] S2. Add urea to the solution obtained in S1, stir, and then carry out a hydrothermal reaction, and then dry to obtain a solid.

[0009] S3. Subject the solid obtained in S2 to high-temperature activation, and then grind it to obtain a solid catalyst.

[0010] Among them, the molar ratio range of raw materials Zn:Ca:Zr in S1 includes (1-4):4:4 and 4:4:2.

[0011] In S2, the molar ratio of urea to NO3 in the solution — is 2:1, and the hydrothermal reaction conditions are to react at 120 °C for 12 h.

[0012] In S3, transfer the precipitate into a muffle furnace for activation, the activation temperature is 750 °C - 950 °C, and the time is 4 h.

[0013] The obtained solid catalyst can synergistically catalyze the esterification and transesterification reactions.

[0014] In the second aspect, a solid catalyst obtained by the preparation method of the above solid catalyst for producing biodiesel.

[0015] In the third aspect, a method for producing biodiesel, the specific steps are as follows:

[0016] S1. Weigh a certain mass of raw materials, including oil raw materials, methanol, and the above solid catalyst, put them into a magnetic high-pressure reaction kettle, the reaction temperature is 130 - 170 °C, and the reaction time is 1 - 3 h.

[0017] S2. Centrifuge the reaction product in S1 to separate the liquid product and the solid catalyst, let the liquid product stand for stratification, the upper layer is the obtained biodiesel, and the solid catalyst is recovered and reused for the production of biodiesel.

[0018] Among them, the oil raw materials in S1 include one or more of rapeseed oil, soybean oil, corn oil, cottonseed oil, peanut oil, sunflower seed oil, coconut oil, and palm oil.

[0019] Optionally, taking palm oil in woody vegetable oils (specifically palm oil with the CAS number 8002-75-3, abbreviated as palm oil in the present invention) as a typical representative, the molar ratio of methanol to palm oil is 15 - 20, and the addition amount of the catalyst accounts for 5 - 7 wt.% of the mass of palm oil.

[0020] The content of free fatty acids in the reaction raw materials accounts for 0% - 10% of the oil raw materials.

[0021] Fourth aspect, biodiesel produced by the above method for producing biodiesel.

[0022] The beneficial effects of the present invention are as follows:

[0023] 1. The solid catalyst of the present invention is supported by ZrO2, which reduces the loss of active components in the catalyst, enhances its stability, and is easy to recycle and reuse multiple times.

[0024] 2. The solid catalyst of the present invention is modified by Zn to construct a Zn / Ca-Zr catalyst with both acid and base dual functions. This catalyst can broaden the applicable range of the raw material oil in terms of the content of free fatty acids: it can complete the transesterification catalysis in the acidified oil containing free fatty acids while having a certain acid resistance. It can reduce the sensitivity of the catalyst to free fatty acids in the raw material oil and is an amphoteric solid catalyst with both acid and base dual functions.

[0025] 3. The solid catalyst of the present invention can synergistically catalyze the esterification and transesterification reactions of waste oils and fats to produce biodiesel. It meets the requirements of green chemistry and has good industrialization prospects. Brief Description of the Drawings

[0026] The accompanying drawings forming a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments and descriptions thereof of the present invention are used to explain the present invention and do not constitute an improper limitation to the present invention.

[0027] Figure 1 It is the X-ray diffraction pattern in Example 6. Detailed Embodiments

[0028] It should be noted that the following detailed descriptions are all exemplary and are intended to provide further explanations of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs.

[0029] Unless otherwise defined, all professional and scientific terms used herein have the same meaning as familiar to those skilled in the art. The reagents or raw materials used in the present invention can be obtained through conventional channels. Unless otherwise specified, the reagents or raw materials used in the present invention are used in the conventional manner in the art or in accordance with the product instructions. In addition, any methods and materials similar or equivalent to the described content can be applied to the method of the present invention. The preferred implementation methods and materials described herein are only for demonstration purposes.

[0030] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular forms are also intended to include the plural forms. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they specify the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0031] Example 1

[0032] I. Preparation of catalyst

[0033] S1. Weigh 2.83 g of Ca(NO3)2·4H2O, 3.57 g of Zn(NO3)2·6H2O, and 2.58 g of Zr(NO3)4·5H2O and place them in a beaker. Add 40 ml of deionized water and stir to dissolve to obtain a solution, that is, the molar ratio of metal elements Zn:Ca:Zr in the solution = 4:4:2.

[0034] S2. Add 8.65 g of urea to the solution obtained in S1 to ensure that the molar ratio of NO3 — in the active component precursor to urea is 1:2. After stirring with a magnetic stirrer for 1 h, pour it into a hydrothermal reaction kettle and react at a temperature of 120 °C for 12 h. Then place the reacted product in a blast drying oven and dry it for 5 h to obtain a solid.

[0035] S3. Put the solid obtained in S2 into a muffle furnace for high-temperature activation. The activation temperatures are set at 750 °C, 850 °C, and 950 °C respectively, the activation time is 4 h, and the heating rate of the muffle furnace is set at 5 °C / min. Then grind it to obtain a solid catalyst.

[0036] Among them, urea is a precipitant, and the precipitation principle is as follows: Urea dissolved in aqueous solution hydrolyzes into NH3 and CO2 at a certain temperature. CO2 has a very low solubility in acidic solution, so it is released from the solution; while NH3 dissolves in the aqueous solution, making the pH value in the system increase slowly and evenly, thus uniformly generating a precipitate.

[0037] II. Preparation of biodiesel

[0038] S1. According to the alcohol-oil molar ratio of 15:1, weigh 10 g of palm oil, 5.21 g of methanol, and 0.7 g of catalyst (accounting for 7% of the mass of palm oil) and put them into a magnetic high-pressure reaction kettle. Set the stirring speed of the reaction kettle at 500 r / min, the reaction temperature at 130 °C, and the reaction time at 3 h.

[0039] S2. Centrifuge the reaction product in S1 to separate the liquid product and the solid catalyst. Let the liquid product stand for stratification, and the upper layer is the obtained crude biodiesel.

[0040] The upper-layer crude biodiesel was detected by a gas chromatograph, and the yields of biodiesel catalyzed by the solid catalysts prepared under the activation temperatures of 750 °C, 850 °C, and 950 °C were measured to be 74%, 87.9%, and 81.9%, respectively.

[0041] Example 2

[0042] The difference from Example 1 is that when preparing the catalyst, in S1, 2.83 g of Ca(NO3)2·4H2O, 0.89 g of Zn(NO3)2·6H2O, and 5.15 g of Zr(NO3)4·5H2O were weighed as raw materials, that is, the molar ratio of metal elements Zn:Ca:Zr in the solution = 1:4:4.

[0043] In S2, 9.37 g of urea was added to the solution obtained in S1 to ensure that the molar ratio of NO3 — to urea in the active component precursor was still 1:2.

[0044] In S3, the activation temperature was set at 850 °C.

[0045] After preparing the biodiesel, the upper-layer crude biodiesel was detected by a gas chromatograph, and the yield of biodiesel catalyzed by the solid catalyst was measured to be 57.2%.

[0046] Example 3

[0047] The difference from Example 1 is that when preparing the catalyst, in S1, 2.83 g of Ca(NO3)2·4H2O, 1.78 g of Zn(NO3)2·6H2O, and 5.15 g of Zr(NO3)4·5H2O were weighed as raw materials, that is, the molar ratio of metal elements Zn:Ca:Zr in the solution = 2:4:4.

[0048] In S2, 10.09 g of urea was added to the solution obtained in S1 to ensure that the molar ratio of NO3 — to urea in the active component precursor was still 1:2.

[0049] In S3, the activation temperature was set at 850 °C.

[0050] After preparing the biodiesel, the upper-layer crude biodiesel was detected by a gas chromatograph, and the yield of biodiesel catalyzed by the solid catalyst was measured to be 80.9%.

[0051] Example 4

[0052] The difference from Example 1 is as follows: When preparing the catalyst, in S1, 2.83 g of Ca(NO3)2·4H2O, 2.23 g of Zn(NO3)2·6H2O, and 5.15 g of Zr(NO3)4·5H2O are weighed as raw materials, that is, the molar ratio of metal elements Zn:Ca:Zr in the solution = 3:4:4.

[0053] In S2, 10.81 g of urea is added to the solution obtained in S1 to ensure that the molar ratio of NO3 — in the active component precursor to urea is still 1:2.

[0054] In S3, the activation temperature is set at 850 °C.

[0055] After preparing the biodiesel, the upper-layer crude biodiesel is detected by a gas chromatograph, and the yield of biodiesel catalyzed by the solid catalyst is measured to be 87.2%.

[0056] Example 5

[0057] The difference from Example 1 is as follows: When preparing the catalyst, in S1, 2.83 g of Ca(NO3)2·4H2O, 3.57 g of Zn(NO3)2·6H2O, and 5.15 g of Zr(NO3)4·5H2O are weighed as raw materials, that is, the molar ratio of metal elements Zn:Ca:Zr in the solution = 4:4:4.

[0058] In S2, 10.81 g of urea is added to the solution obtained in S1 to ensure that the molar ratio of NO3— in the active component precursor to urea is still 1:2.

[0059] In S3, the activation temperature is set at 850 °C.

[0060] After preparing the biodiesel, the upper-layer crude biodiesel is detected by a gas chromatograph, and the yield of biodiesel catalyzed by the solid catalyst is measured to be 90.5%.

[0061] Example 6

[0062] The catalysts prepared in Examples 1 to 5 are subjected to X-ray diffraction detection, and the obtained X-ray diffraction pattern is as Figure 1 shown.

[0063] The figure shows that as the molar ratio of Zn to Ca increases from 1:4 to 4:4, the diffraction peak of ZnO in the XRD pattern gradually increases. Zn exists in the form of ZnO, Zn 2+It can provide Lewis acidic sites and improve the acid resistance of the catalyst. The Ca and Zr elements in the catalyst mainly form a new crystal phase of CaZrO3 with a perovskite-type structure, indicating a strong interaction between Ca and Zr and improving the stability of the catalyst. At the same time, part of Ca and Zr exist in the form of CaO and ZrO2 oxide phases respectively. CaO provides Lewis basic sites, while ZrO2 also has amphoteric acidity and basicity. For the catalyst with a Zn:Ca:Zr molar ratio of 4:4:2, the content of Zr is relatively limited, and there is almost no ZrO2 phase in the XRD pattern.

[0064] Example 7

[0065] I. The process of preparing the catalyst is the same as that in Example 5 and includes the following steps.

[0066] S1. Weigh 2.83 g of Ca(NO3)2·4H2O, 3.57 g of Zn(NO3)2·6H2O, and 5.15 g of Zr(NO3)4·5H2O and place them in a beaker. Add 40 ml of deionized water and stir to dissolve to obtain a solution, that is, the molar ratio of metal elements Zn:Ca:Zr in the solution = 4:4:4.

[0067] S2. Add 10.81 g of urea to the solution obtained in S1 to ensure that the molar ratio of NO3 — in the active component precursor to urea is 1:2. After stirring with a magnetic stirrer for 1 h, pour it into a hydrothermal reaction kettle and react at a temperature of 120 °C for 12 h. Then place the reaction product in a blast drying oven and dry it for 5 h to obtain a solid.

[0068] S3. Put the solid obtained in S2 into a muffle furnace for high-temperature activation. The activation temperature is set at 850 °C, the activation time is 4 h, and the heating rate of the muffle furnace is set at 5 °C / min. Then grind it to obtain a solid catalyst.

[0069] II. Prepare biodiesel.

[0070] S1. According to an alcohol-to-oil molar ratio of 20:1, weigh 10 g of palm oil, 9.64 g of methanol, and 0.5 g of catalyst (5% of the palm oil mass) and put them into a magnetic high-pressure reaction kettle. Then add oleic acid accounting for 0% (i.e., 0 g), 2% (0.2 g), 5% (0.5 g), 8% (0.8 g), and 10% (1.0 g) of the palm oil weight respectively. Set the stirring speed of the reaction kettle at 500 r / min, the reaction temperature at 170 °C, and the reaction time at 3 h.

[0071] S2. Centrifuge the reaction product in S1 to separate the liquid product and the solid catalyst. Let the liquid product stand for stratification, and the upper layer is the obtained crude biodiesel.

[0072] The crude biodiesel in the upper layer was detected by a gas chromatograph. The biodiesel yields were as follows: when the addition amount was 0%, the yield was 94.9%; when the addition amount was 2%, the yield was 95.5%; when the addition amount was 5%, the yield was 95.1%; when the addition amount was 8%, the yield was 89.4%; when the addition amount was 10%, the yield was 84.7%.

[0073] According to acid-base titration, the esterification conversion rates were 93.3% after adding 5% oleic acid, 92.4% after adding 8% oleic acid, and 92.8% after adding 10% oleic acid.

[0074] The added oleic acid is a fatty acid and is acidic. It can simulate the situation where animal and vegetable oils, waste cooking oil, and microbial oils in the raw materials of biodiesel are acidic due to the presence of a certain amount of free fatty acids. The more oleic acid is added, the stronger the acidity of the raw materials.

[0075] The esterification conversion rate can reflect the degree of completion of the esterification reaction of oleic acid. The higher the ester conversion rate, the higher the activity of the catalyst in catalyzing the esterification reaction. The results of this example show that the prepared catalyst can not only catalyze the transesterification reaction but also the esterification reaction, enabling the catalyst to catalyze the production of biodiesel in an environment containing a certain amount of free fatty acids and having acid resistance.

[0076] Comparative Example 1

[0077] A calcium-based solid base catalyst was used, such as a self-made laboratory steel slag supported calcium oxide catalyst. According to an alcohol-to-oil molar ratio of 9:1, 10 g of palm oil, 3.12 methanol, and 0.7 g of catalyst (7% of the mass of palm oil) were weighed into a 250 mL three-necked flask, and 0% (i.e., 0 g), 2% (0.2 g), 5% (0.5 g), and 8% (0.8 g) of oleic acid based on the weight of palm oil were added respectively. The above flask was placed in an atmospheric pressure microwave chemical synthesis reactor, with a reaction temperature of 70 °C and a reaction time of 3 h.

[0078] The reaction conditions are different from those in Example 7 because the optimal catalytic conditions of the two catalysts are different: in Comparative Example 1, the best catalytic effect can be obtained using these reaction conditions; if the reaction conditions of Example 7 are adopted, it has no practical value.

[0079] The biodiesel yields were as follows: when the addition amount was 0%, the yield was 89%; when the addition amount was 2%, the yield was 63.4%; when the addition amount was 5%, the yield was 58.3%; when the addition amount was 8%, the yield was 42.4%.

[0080] Ordinary calcium-based solid alkalis cannot be used to catalytically prepare biodiesel in an environment with too high free fatty acid content. The reasons are as follows: When CaO catalyzes the transesterification reaction, the fatty acid content is required to be lower than <0.5wt%. The free fatty acids present in waste oils and fats will cause saponification of CaO, poisoning and inactivation, and hinder the transesterification.

[0081] By comparing the results of Example 7 with those of Comparative Example 1, it is shown that: compared with the prior art, the present invention indeed has a better acid resistance effect.

[0082] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A preparation method of a solid catalyst for producing biodiesel, characterized in that, It includes the following steps: S1. Weigh a certain mass of calcium nitrate and / or calcium nitrate hydrate, zinc nitrate and / or zinc nitrate hydrate, zirconium nitrate and / or zirconium nitrate hydrate, and dissolve them in deionized water to obtain a solution; S2. Add urea to the solution obtained in S1, stir and then carry out a hydrothermal reaction, and then dry to obtain a solid; S3. High-temperature activate the solid obtained in S2, and then grind it to obtain a solid catalyst; Among them, the molar ratio of raw materials Zn:Ca:Zr in S1 is any one of 1:4:4, 2:4:4, 3:4:4, 4:4:4; In S2, the hydrothermal reaction conditions are a reaction at 120 °C for 12 h; the molar ratio of urea to NO3 in the solution is 2:1; — ​ In S3, transfer the precipitate into a muffle furnace for activation, the activation temperature is 750°C to 950°C, and the time is 4h.

2. The preparation method of the solid catalyst for producing biodiesel according to claim 1, characterized in that, In S2, the stirring operation is: stir with a magnetic stirrer for 1h; The drying operation is: place the reaction product in a forced-air drying oven and dry for 5h.

3. The preparation method of the solid catalyst for producing biodiesel according to claim 1, characterized in that, In S3, the heating rate of the muffle furnace is set at 5°C / min.

4. The preparation method of the solid catalyst for producing biodiesel according to claim 1, characterized in that, In S3, the activation temperature is set at 850°C.

5. A solid catalyst prepared by the preparation method of the solid catalyst for producing biodiesel according to any one of claims 1 - 4.

6. A method for producing biodiesel using the solid catalyst according to claim 5, characterized in that, The specific steps are as follows: S1. Weigh a certain mass of raw materials, including oil raw materials, methanol, and solid catalyst, put the raw materials into a magnetic high-pressure reaction kettle, the reaction temperature is 130 - 170°C, and the reaction time is 1 - 3h; S2. Centrifuge the reaction product in S1 to separate the liquid product and the solid catalyst, let the liquid product stand for stratification, and the upper layer is the obtained biodiesel; Among them, the oil raw materials in S1 include one or more of rapeseed oil, soybean oil, corn oil, cottonseed oil, peanut oil, sunflower seed oil, coconut oil, palm oil; The reaction raw materials include 0% - 10% of free fatty acids by weight of the oil raw materials.

7. The method for producing biodiesel according to claim 6, characterized in that, The oil raw material in S1 is palm oil with the CAS number 8002 - 75 - 3, the molar ratio of methanol to palm oil with the CAS number 8002 - 75 - 3 is 15:1 - 20:1, and the addition amount of the catalyst accounts for 5 - 7wt.% of the mass of palm oil with the CAS number 8002 - 75 - 3.

8. Biodiesel produced by the method for producing biodiesel according to any one of claims 6 - 7.

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