Catalyst for preparing biodiesel and application thereof

Abstract

According to the catalyst for preparing biodiesel and the application of the catalyst, mesoporous silica serves as a carrier, the dispersity and binding force of calcium oxide nanoparticles are enhanced through polydopamine modification, the catalyst is in a dispersed spherical particle shape, and the size of the catalyst is about 300 nm. The polydopamine adopted by the invention has excellent adhesion and abundant functional groups, and can modify the traditional catalyst and improve the performance of the traditional catalyst. Calcium oxide has high alkalinity, and the uniformity and stability of calcium oxide need to be further improved due to the fact that calcium oxide has good transesterification and economical efficiency of calcium oxide are concerned. The mesoporous silica designed by the invention is used as a high-efficiency catalytic carrier, and can provide good dispersity and relatively high specific surface area. Therefore, a high-efficiency, stable and green catalyst is developed by combining the polydopamine, the calcium oxide and the mesoporous silica, and the catalyst has important significance in realizing high-efficiency conversion of the waste grease.

Description

Technical Field

[0001] The invention relates to the field of waste oil conversion and recovery, and in particular to a catalyst for preparing biodiesel and application thereof. Background Art

[0002] The resource utilization of waste oil is a hot research direction in the current biodiesel industry. Traditional catalysts have problems such as low selectivity, easy deactivation, and poor impurity tolerance in the process of waste oil conversion, which limits their practical application.

[0003] For example, in the homogeneous alkaline catalysis method, alkaline catalysts such as NaOH and KOH are used to convert triglycerides into biodiesel and glycerol by-products through an ester exchange reaction in waste oils and fats. However, waste oils and fats usually contain high levels of free fatty acids (FFA), which easily react with alkaline catalysts to form soaps, resulting in catalyst deactivation, difficulty in separation, and reduced yields.

[0004] Or the homogeneous acid catalysis method uses acidic catalysts such as sulfuric acid and hydrochloric acid to catalyze ester exchange and esterification reactions, and at the same time convert free fatty acids into ester substances. The disadvantages are that the catalyst is highly corrosive, has high requirements for equipment, has a long reaction time, and consumes a lot of energy.

[0005] The development of an efficient, stable and green catalyst is of great significance to achieve efficient conversion of waste oils and fats. Summary of the invention

[0006] The present invention aims to solve the problems of low selectivity, low conversion rate and easy deactivation of existing catalysts in converting waste oil into biodiesel, and to provide a catalyst with excellent performance and a synthesis method.

[0007] To achieve the purpose of the present invention, the present invention discloses a catalyst for preparing biodiesel, which uses mesoporous silica as a carrier and enhances the dispersibility and binding force of calcium oxide nanoparticles through polydopamine modification. The catalyst is in the form of dispersed spherical particles with a size of about 300nm.

[0008] Further, its synthesis method is as follows: Step 1: Prepare silica. Add 10 parts, 20 parts and 3 parts of deionized water, ethanol and ammonia water by volume into a three-necked flask and stir evenly. Slowly add 6 parts of tetraethyl orthosilicate by volume while stirring. After the reaction lasts for 5-6 hours, collect the precipitate by centrifugation, wash with distilled water and ethanol, and vacuum dry at 60-70°C for 12-14 hours. The prepared SiO2 is spherical nanoparticles with a size of about 200nm. Step 2: Prepare mesoporous silica, denoted as mSiO2. First, disperse 2-6 grams of SiO2 spherical nanoparticles obtained in step 1 in deionized water and ultrasonically treat for 30-40 minutes; take 2-6 grams of polyvinyl pyrrolidone and dissolve it in 400mL of water. Pour the SiO2 dispersion into the polyvinyl pyrrolidone solution, ultrasonically treat for 30-40 minutes, reflux and stir at 100°C for 3 hours, cool to 25-27°C, and add 20-60mL of 11.25 M NaOH solution for etching; use a UV-visible spectrophotometer to monitor the change in absorbance at 700nm. When the absorbance value drops to 70% of the initial value, react for another half an hour and centrifuge to obtain mesoporous silica. Step 3: Prepare calcium oxide mesoporous silica, denoted as CaO-mSiO2, take 1.5-3.0 grams of CaCl2 and dissolve it in 50 milliliters of deionized water, add 1-2 grams of SiO2, and add 30-60 mL of 1M NaOH solution dropwise while stirring. After the addition is complete, continue stirring for 15 minutes, let it stand, remove the supernatant, dry the precipitate at 80°C, and calcine it in air at 600°C in a rotary tube furnace for 1 hour to obtain CaO-SiO2; Step 4: Prepare polydopamine modified calcium oxide mesoporous silica, denoted as PDA-CaO-mSiO2, add 0.5-1.0 g of CaO-SiO2 into 20-40 mL of Tris-HCl buffer with a pH of 8.5 and a concentration of 0.05 M, then add 1-2 mL of dopamine with a concentration of 2 mg / mL, then gently stir at 28°C for 12 h, centrifuge at 9000 r / min for 5-8 min, wash 3 times with deionized water, and dry at 60-80°C to obtain PDA-CaO-mSiO2.

[0009] Furthermore, the mesoporous silica obtained in step 2 has a regular mesoporous structure and a size of about 200 nm.

[0010] Furthermore, the calcium oxide mesoporous silica obtained in step three exhibits a very uniform spherical morphology, and obvious rough features can be observed on the surface of the spherical particles, with a size of about 300 nm.

[0011] Furthermore, the polydopamine-modified calcium oxide mesoporous silica obtained in step 4 is in the form of uniform spherical particles with a size of about 300 nm.

[0012] The above-mentioned application of the catalyst for preparing biodiesel is applied in the field of biodiesel synthesis catalysis.

[0013] The specific method is as follows: the catalyst described in any one of claims 1 to 5 is ultrasonically dispersed in methanol, and deacidified waste cooking oil is added thereto, wherein the acid value of the waste cooking oil is 1 to 2 mg KOH / g, and the mixture is shaken vigorously to form an emulsion, and then placed in a 70°C oil bath to react for 6 hours, the emulsion is centrifuged to break the emulsion, and the oil phase is dried in an oven at 50°C overnight to remove methanol, thereby obtaining biodiesel.

[0014] The polydopamine used in this patent has excellent adhesion and rich functional groups, and can modify traditional catalysts to improve their performance. Calcium oxide has high alkalinity and has attracted attention for its good transesterification reaction and economy, but its uniformity and stability need to be further improved. The mesoporous silica designed in this patent is an efficient catalytic carrier that can provide good dispersibility and a high specific surface area. Therefore, combining polydopamine, calcium oxide and mesoporous silica to develop an efficient and stable catalyst is of great significance for achieving efficient conversion of waste oils and fats. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The detailed description given as non-limiting examples better explains what the invention consists of and how it can be implemented, and furthermore, refers to the accompanying drawings, in which: Figure 1 This is a photo of SiO2 spherical nanoparticles prepared in step 1 under a scanning electron microscope; Figure 2 This is a photo of the mSiO2 spherical nanoparticles prepared in step 2 under a scanning electron microscope; Figure 3 This is a photo of CaO-mSiO2 obtained in step 3 under a scanning electron microscope; Figure 4 This is a photograph of the uniform spherical particles of PDA-CaO-mSiO2 obtained in step 4 under a scanning electron microscope. DETAILED DESCRIPTION

[0016] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0017] Preparation of catalyst:

[0018] Step 1: Preparation of silicon dioxide (SiO2): Add 50 mL of deionized water, 100 mL of ethanol and 15 mL of ammonia water into a three-necked flask and stir evenly. Slowly add 30 mL of tetraethyl orthosilicate while stirring, and continue the reaction for 5 hours. After the reaction is completed, collect the precipitate by centrifugation, wash with distilled water and ethanol, and dry it in a vacuum at 60°C for 12 hours. Characterization Figure 1 The prepared SiO2 is spherical nanoparticles with a size of about 200nm.

[0019] Step 2: Preparation of mesoporous silica (mSiO2): First disperse 2g of SiO2 nanoparticles in 40mL of deionized water, ultrasonically treat for 30min, and then dissolve 2g of polyvinyl pyrrolidone (PVP) in 400mL of water. Pour the SiO2 dispersion into the PVP solution, ultrasonically treat for 30min, reflux and stir at 100°C for 3h, cool to 27°C, and add 20mL of NaOH solution (11.25M) for etching. Use a UV-visible spectrophotometer to monitor the change in absorbance at 700nm. When the absorbance value drops to 70% of the initial value, react for another half an hour and then centrifuge to obtain mesoporous silica, recorded as mSiO2. Centrifugal washing and drying at 60°C. Characterization as follows Figure 2 The prepared mSiO2 is spherical nanoparticles with a regular mesoporous structure and a size of about 200nm.

[0020] Step 3: Preparation of calcium oxide mesoporous silica (CaO-mSiO2): Take 1.5 g of CaCl2 and dissolve it in 50 ml of deionized water, add 1 g of SiO2, and add 30 mL of 1M NaOH solution dropwise while stirring. After the addition is complete, continue stirring for 15 minutes. After standing, remove the supernatant, dry the precipitate at 80°C, and calcine it in air at 600°C in a rotary tube furnace for 1 hour to obtain CaO-SiO2. Characterization Figure 3 , CaO-mSiO2 exhibits a very uniform spherical morphology, and obvious rough features can be observed on the surface of the spherical particles, with a size of about 300nm.

[0021] Step 4: Preparation of polydopamine modified calcium oxide mesoporous silica (PDA-CaO-mSiO2): Add 0.5 g of CaO-SiO2 to 20 mL of Tris-HCl buffer with a pH of 8.5 and a concentration of 0.05 M, then add 1 mL of dopamine with a concentration of 2 mg / mL, then gently stir at 28°C for 12 h, centrifuge at 9000 r / min for 5-8 min, wash with deionized water 3 times, and dry at 60-80°C to obtain PDA-CaO-mSiO2. Characterization Figure 4 It can be seen that PDA-CaO-mSiO2 is in the form of uniform spherical particles with a size of about 300nm.

[0022] Preparation of biodiesel:

[0023] 0.4 g of PDA-CaO-mSiO2 was ultrasonically dispersed in 7.0 g of methanol, and 20.0 g of deacidified waste cooking oil was added thereto, the acid value of which was 1-2 mg KOH / g. The mixture was shaken vigorously to form an emulsion and then placed in a 70°C oil bath for reaction for 6 hours. The emulsion was centrifuged to break the emulsion, and the oil phase was dried in an oven at 50°C overnight to remove methanol, thereby obtaining biodiesel.

[0024] The above biodiesel preparation was repeated four times, and the biodiesel yield was recorded each time, as shown in the following table.

[0025] Table 1 Catalyst usage times and biodiesel yield frequency 1 2 3 4 Weight of waste cooking oil 20g 20g 20g 20g Biodiesel production 17.14 16.74 16.3 14.98 Biodiesel yield% 85.7 83.7 81.5 74.9 It can be concluded from Table 1 that the microscopic pore structure of PDA-CaO-mSiO2 greatly increases the active area of ​​the catalyst and improves the transesterification performance of waste oils. At the same time, the stability and greenness of the catalyst are also enhanced, and it has good application prospects.

[0026] The above embodiments and illustrations do not limit the product form and style of the present invention. Any appropriate changes and modifications made by ordinary technicians in the relevant technical field should be deemed to be within the patent scope of the present invention.

Claims

1. A catalyst for preparing biodiesel, characterized in that: Mesoporous silica is used as a carrier, and the dispersibility and binding force of calcium oxide are enhanced by polydopamine modification. The catalyst is in the form of dispersed spherical particles with a size of about 300nm.

2. A catalyst for preparing biodiesel as claimed in claim 1, characterized in that: The synthesis method is as follows: Step 1: Prepare silica. Add 10 parts, 20 parts and 3 parts of deionized water, ethanol and ammonia water in a three-necked flask in turn and stir evenly. Slowly add 6 parts of tetraethyl orthosilicate in a dropwise manner while stirring. After the reaction lasts for 5-6 hours, collect the precipitate by centrifugation, wash it with distilled water and ethanol, and vacuum dry it at 60-70°C for 12-14 hours. The prepared SiO2 is spherical nanoparticles with a size of about 200nm. Step 2: Prepare mesoporous silica, denoted as mSiO2. First, disperse 2-6 grams of SiO2 spherical nanoparticles obtained in step 1 in deionized water and ultrasonically treat for 30-40 minutes; take 2-6 grams of polyvinyl pyrrolidone and dissolve it in 400mL of water. Pour the SiO2 dispersion into the polyvinyl pyrrolidone solution, ultrasonically treat for 30-40 minutes, reflux and stir at 100°C for 3 hours, cool to 25-27°C, and add 20-60mL of 11.25 M NaOH solution for etching; use a UV-visible spectrophotometer to monitor the change in absorbance at 700nm. When the absorbance value drops to 70% of the initial value, react for another half an hour and centrifuge to obtain mesoporous silica. Step 3: Prepare calcium oxide mesoporous silica, denoted as CaO-mSiO2, take 1.5-3.0 grams of CaCl2 and dissolve it in 50 milliliters of deionized water, add 1-2 grams of SiO2, and add 30-60 mL of 1M NaOH solution dropwise while stirring. After the addition is complete, continue stirring for 15 minutes, let it stand, remove the supernatant, dry the precipitate at 80°C, and calcine it in air at 600°C in a rotary tube furnace for 1 hour to obtain CaO-SiO2; Step 4: Prepare polydopamine modified calcium oxide mesoporous silica, denoted as PDA-CaO-mSiO2, add 0.5-1.0 g of CaO-SiO2 into 20-40 mL of Tris-HCl buffer with a pH of 8.5 and a concentration of 0.05 M, then add 1-2 mL of dopamine with a concentration of 2 mg / mL, then gently stir at 28°C for 12 h, centrifuge at 9000 r / min for 5-8 min, wash 3 times with deionized water, and dry at 60-80°C to obtain PDA-CaO-mSiO2.

3. A catalyst for preparing biodiesel as claimed in claim 2, characterized in that: The mesoporous silica obtained in step 2 has a regular mesoporous structure and a size of about 200 nm.

4. A catalyst for preparing biodiesel as claimed in claim 2, characterized in that: The calcium oxide mesoporous silica obtained in step 3 exhibits a uniform spherical morphology, and obvious rough features can be observed on the surface of the spherical particles, with a size of about 300 nm.

5. A catalyst for preparing biodiesel as claimed in claim 2, characterized in that: The polydopamine-modified calcium oxide mesoporous silica obtained in step 4 is in the form of uniform spherical particles with a size of about 300 nm.

6. Use of a catalyst for preparing biodiesel according to any one of claims 1 to 5, characterized in that: Used in the field of biodiesel synthesis catalysis.

7. The use of a catalyst for preparing biodiesel as claimed in claim 6, characterized in that: The specific method is as follows: the catalyst described in any one of claims 1 to 5 is ultrasonically dispersed in methanol, and deacidified waste cooking oil is added thereto, wherein the acid value of the waste cooking oil is 1 to 2 mg KOH / g, and the mixture is shaken vigorously to form an emulsion, and then placed in a 70°C oil bath to react for 6 hours, the emulsion is centrifuged to break the emulsion, and the oil phase is dried in an oven at 50°C overnight to remove methanol, thereby obtaining biodiesel.

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