Solid acid catalyst as well as preparation method and application thereof

Abstract

The invention provides a solid acid catalyst as well as a preparation method and application thereof, and belongs to the technical field of preparation of solid acid catalysts. The catalyst comprises a carrier, an acidic oxide and an auxiliary agent, the acidic oxide is selected from one or more of tungsten oxide, molybdenum oxide or phosphorus oxide; the auxiliary agent is selected from one or more of lanthanum oxide, cerium oxide, praseodymium oxide, neodymium oxide or europium oxide. The invention also provides a preparation method of the solid acid catalyst. A special surface structure is adopted to stabilize an acid center, inhibit carbon deposition and improve the activity and stability of the catalyst. The prepared catalyst can effectively catalyze waste oil to prepare biodiesel or fatty acid.

Description

Technical Field

[0001] The invention belongs to the technical field of solid acid catalyst preparation, and specifically relates to a solid acid catalyst and a preparation method and application thereof. Background Art

[0002] As a new type of clean fuel, biodiesel is considered a potential alternative to traditional energy. Ester-based biodiesel is mainly prepared by transesterification and esterification. In the process of preparing biodiesel, the current industrial catalyst is mainly a homogeneous catalyst, but the use of homogeneous catalysts will produce a large amount of wastewater, and the catalyst is not easy to separate and recover (S. Debbarma, B. Chetia and A. Bharti, Energy Sources, Part A, 2024, 46, 3964-3978; XJ Zhang, Ind. Crops Prod., 2024, 220, 119144-119162; B. Maleki and SSA Taxh, Renewable Energy, 2024, 224, 120127-120145.), so heterogeneous catalysts are more suitable for industry than homogeneous catalysts. At present, there are also some reports on the research of heterogeneous catalysts for biodiesel preparation, mainly focusing on zeolites (SBLNgomade, CG Fotsop, AKBhonsle, N. Rawat, P. Gupta, R. Singh, IK Tchummegne, RK Singh and N. Atray, Chem. Eng. Res. Des., 2024, 209, 52-66.), supported metal oxides (K. Brindhadevi, PT Kim, A. Chinnathambi, SK Kamarudin and A. Pugazhendhi, Process Saf. Environ. Prot., 2024, 188, 167-176.), ion exchange resins (S. Lee, J. Ha and OL Li, Nanomaterials, 2024, 14, 1313-1327.), heteropoly acids (MK Lam, KTLee and AR Mohamed, Biotechnol. Adv., 2010, 28, 500-518.) etc. Recently, the use of molybdenum-based and tungsten-based solid acid catalysts to synthesize biodiesel has attracted great attention. They show high reactivity and good water resistance and saponification resistance (G. Zhang and W. Xie, Renewable Energy, 2024, 222, 119927-119939;

[0003] C.Chen,L.Cai,L.Zhang,W.Fu,Y.Hong,X.Gao,Y.Jiang,L.Li,X.Yan and G.Wu,Chem.Eng.J.,2020,382,122839-122852;M.Rostamizadeh,M.Oghabi and A. Ghadimi, Res. Chem. Intermed., 2023, 49, 2053-2070; Q. Wang, AHShamsuddin,J.Anal.Appl.Pyrolysis,2022,168,105776-105789; W.Xie and L. Zhao, Energy Convers. Manage., 2014, 79, 34-42; DSLima and OW Perez-Lopez, Renewable Energy, 2019, 136, 828-836; CM Teixeira, R. Fréty, CBM Barbosa, MR Santos, ED Bruce and JGA Paacheco, Catal. Today, 2017, 279, 202-208.). However, these catalysts show good catalytic activity in the transesterification reaction process, but the structural change of the solid catalyst, saponification side reaction and carbon deposition are easy to occur, resulting in poor catalyst stability. Summary of the invention

[0004] The purpose of the present invention is to provide a solid acid catalyst and its preparation method and application. The present invention uses a special surface structure to stabilize the acid center, inhibit carbon deposition and improve the activity and stability of the catalyst. The catalyst prepared by the present invention can effectively catalyze waste oil to prepare biodiesel or fatty acids.

[0005] The present invention first provides a solid acid catalyst, which comprises a carrier, an acidic oxide and an auxiliary agent;

[0006] The acidic oxide is selected from one or more of tungsten oxide, molybdenum oxide or phosphorus oxide;

[0007] The auxiliary agent is selected from one or more of lanthanum oxide, cerium oxide, praseodymium oxide, neodymium oxide or europium oxide.

[0008] Preferably, the carrier is selected from one or more of silicon oxide, titanium oxide or aluminum oxide.

[0009] Preferably, the content of the acidic oxide accounts for 1% to 40% of the total mass of the carrier; the content of the auxiliary agent accounts for 0.5% to 15% of the total mass of the carrier.

[0010] The present invention also provides a method for preparing a solid acid catalyst, comprising:

[0011] Step 1: dissolving one or more of metal molybdenum salt, tungsten salt or phosphate in water to obtain a salt solution, then impregnating the solution on a carrier and drying the solution to obtain a precursor, and calcining the precursor to obtain an intermediate;

[0012] Step 2: impregnating the intermediate obtained in step 1 with a solution of nitrate or chloride containing a rare earth element again, drying it, and calcining it to obtain a solid acid catalyst; the rare earth element is lanthanum, cerium, praseodymium, neodymium or europium.

[0013] Preferably, the molybdenum salt described in step 1 is ammonium heptamolybdate or ammonium molybdate, the tungsten salt is ammonium tungstate, and the phosphate is ammonium phosphate.

[0014] Preferably, the drying temperature in step 1 is 80-150° C., and the drying time is 2 hours to 48 hours.

[0015] Preferably, the calcination temperature in step 1 is 300-1000° C., and the heating rate is 1° C. / min-30° C. / min.

[0016] Preferably, the calcination temperature in step 2 is 400-1000° C., and the heating rate is 1° C. / min-30° C. / min.

[0017] Preferably, the mass ratio of the metal in the metal molybdenum salt, tungsten salt or phosphate to the rare earth element in the nitrate or chloride containing the rare earth element is (1-80):1.

[0018] The present invention also provides the use of the solid acid catalyst in catalyzing waste oil to prepare biodiesel or fatty acid.

[0019] Beneficial effects of the present invention

[0020] The present invention provides a solid acid catalyst and a preparation method and application thereof. The present invention uses a special surface structure to stabilize the acid center, inhibit carbon deposition, and improve the activity and stability of the catalyst. Compared with the prior art, the solid acid catalyst prepared by the present invention, in addition to the Bronsted acid and Lewis acid sites constructed by one or more active species such as molybdenum, tungsten, and phosphorus formed on the surface, also has basic sites constructed by rare earth species, as well as a synergistic effect between special acid sites and basic sites. Compared with conventional solid acid catalysts, its stability is better, especially when treating high-acid-value waste oils and fats containing more free fatty acids, it can show higher reaction activity, better surface resistance to carbon deposition, and better resistance to active center loss, thereby improving the stability of the catalyst. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is the X-ray powder diffraction pattern of the catalyst of Example 1 of the present invention;

[0022] Figure 2 is the X-ray powder diffraction pattern of the catalyst of Example 5 of the present invention;

[0023] Figure 3 is the X-ray photoelectron spectrum of the catalyst of Example 1 of the present invention;

[0024] Figure 4 This is a NH3-TPD temperature desorption test diagram of the catalyst in Example 1 of the present invention;

[0025] Figure 5 This is a NH3-TPD temperature desorption test diagram of the catalyst in Example 5 of the present invention;

[0026] Figure 6 This is the pyridine infrared spectrum of the catalyst of Example 1 of the present invention;

[0027] Figure 7 is the infrared transmission spectrum of the catalyst of Example 1 of the present invention;

[0028] Figure 8 This is a transmission electron microscope photograph of the catalyst of Example 1 of the present invention.

[0029] Fig. 9 This is the gas chromatography test result of the product of producing biodiesel from waste oil and fat in Example 7 of the present invention.

[0030] Fig.10 This is the acid value test result of preparing fatty acids from waste oil and fat using the catalyst in Example 8 of the present invention. DETAILED DESCRIPTION

[0031] The present invention first provides a solid acid catalyst, which comprises a carrier, an acidic oxide and an auxiliary agent; the acidic oxide is selected from one or more of tungsten oxide, molybdenum oxide or phosphorus oxide; the auxiliary agent is selected from one or more of lanthanum oxide, cerium oxide, praseodymium oxide, neodymium oxide or europium oxide.

[0032] According to the present invention, the carrier is preferably selected from one or more of silicon oxide, titanium oxide or aluminum oxide.

[0033] According to the present invention, the content of the acidic oxide accounts for 1% to 40% of the total mass of the carrier; the content of the auxiliary agent accounts for 0.5% to 15% of the total mass of the carrier.

[0034] The present invention also provides a method for preparing a solid acid catalyst, comprising:

[0035] Step 1: dissolve one or more of metal molybdenum salt, tungsten salt or phosphate in water to obtain a salt solution, then impregnate it on a carrier and dry it. The drying temperature is preferably 80-150°C, and the drying time is preferably 2-48 hours to obtain a precursor. After calcining the precursor, an intermediate is obtained. The molybdenum salt is preferably ammonium heptamolybdate or ammonium molybdate, the tungsten salt is preferably ammonium metatungstate, and the phosphate is preferably ammonium phosphate. The calcination temperature is preferably 300-1000°C, and the heating rate is preferably 1°C / min-30°C / min.

[0036] Step 2: impregnating the solution of nitrate or chloride containing rare earth elements into the intermediate obtained in step 1 again and drying it, the drying temperature is preferably 80-150°C, the drying time is preferably 2-48 hours, and calcining, the calcining temperature is preferably 400-1000°C, and the heating rate is preferably 1°C / min-30°C / min, to obtain a solid acid catalyst; the rare earth element is lanthanum, cerium, praseodymium, neodymium or europium, and the solution of nitrate or chloride containing rare earth elements is preferably lanthanum nitrate (hexahydrate) or cerium nitrate (hexahydrate).

[0037] According to the present invention, the mass ratio of the metal in the metal molybdenum salt, tungsten salt or phosphate to the rare earth element in the nitrate or chloride containing the rare earth element is preferably (1-80):1.

[0038] According to the present invention, the impregnation method is preferably continuous impregnation or co-impregnation.

[0039] The present invention also provides the use of the solid acid catalyst in catalyzing waste oil to prepare biodiesel or fatty acid.

[0040] The present invention is described in detail below with reference to specific examples. The raw materials involved in the examples are all commercially available.

[0041] Example 1

[0042] Weigh 0.9g of ammonium heptamolybdate (tetrahydrate) and dissolve it in water, dissolve it completely by ultrasound, stir it evenly, then add it dropwise to 10.0g of silica powder, put it in an oven and dry it at 120°C for 3 hours to obtain precursor 1, grind precursor 1 into powder and spread it in a quartz boat, put it in a muffle furnace, calcine it at 550°C for 3h, the heating rate is 5°C / min, and the intermediate is obtained after natural cooling. Weigh 0.3g of lanthanum nitrate (hexahydrate) and dissolve it in water, dissolve it completely by ultrasound, stir it evenly, add it dropwise to the intermediate, dry it at 120°C for 3 hours to obtain precursor 2, grind precursor 2 into powder and spread it in a quartz boat, put it in a muffle furnace and calcine it at 550°C for 3h, the heating rate is 5°C / min, and after the calcination, cool it naturally to room temperature to obtain MoLaSiO2-1 solid acid catalyst. Figure 1 is the X-ray powder diffraction pattern of the catalyst of Example 1 of the present invention; Figure 1 This indicates that the catalyst prepared by the present invention has very good crystallinity, and its crystalline component is mainly molybdenum trioxide.

[0043] Figure 3 is the X-ray photoelectron spectrum of the catalyst of Example 1 of the present invention; Figure 3 This indicates that the molybdenum component in the catalyst prepared by the present invention exists in the form of pentavalent and hexavalent molybdenum at the same time.

[0044] Figure 4 This is a NH3-TPD temperature desorption test diagram of the catalyst in Example 1 of the present invention; Figure 4 This indicates that there are two different types of acid sites on the surface of the catalyst prepared by the present invention: weak acid sites between 150 and 350°C, and strong acid sites above 400°C.

[0045] Figure 6 This is the pyridine infrared spectrum of the catalyst of Example 1 of the present invention; Figure 6 This indicates that significant Bronsted acid and Lewis acid sites exist on the surface of the catalyst prepared by the present invention.

[0046] Figure 7 is the infrared transmission spectrum of the catalyst of Example 1 of the present invention; Figure 7 illustrate

[0047] Different types of chemical bond vibrations such as O-Si-O, Si-O-Mo, La-O-Mo and the like exist on the surface of the catalyst prepared by the invention.

[0048] Figure 8 This is a transmission electron microscope photo of the catalyst of Example 1 of the present invention; Figure 8 This indicates that the metal components in the catalyst prepared by the present invention have good dispersion and crystallinity.

[0049] Example 2

[0050] Weigh 1.84g of ammonium heptamolybdate (tetrahydrate) and dissolve it in water, dissolve it completely by ultrasound, stir it evenly, then add it dropwise to 10.0g of nano-silicon dioxide, put it in an oven and dry it at 120°C for 3 hours to obtain precursor 1, grind precursor 1 into powder and spread it in a quartz boat, put it in a muffle furnace, calcine it at 450°C for 3h, the heating rate is 5°C / min, and the intermediate is obtained after natural cooling. Weigh 0.3g of lanthanum nitrate (hexahydrate) and dissolve it in water, dissolve it completely by ultrasound, stir it evenly, then add it dropwise to the intermediate, dry it at 120°C for 3 hours to obtain precursor 2, grind precursor 2 into powder and spread it in a quartz boat, put it in a muffle furnace and calcine it at 650°C for 3h, and cool it naturally to room temperature to obtain MoLaSiO2-2 solid acid catalyst.

[0051] Example 3

[0052] Weigh 1.84g of ammonium heptamolybdate (tetrahydrate) and dissolve it in water, dissolve it completely by ultrasonication, stir it evenly, then add it dropwise to 10.0g of nano-silicon dioxide, put it in an oven and dry it at 120°C for 3 hours to obtain precursor 1, grind precursor 1 into powder and spread it in a quartz boat, put it in a muffle furnace, calcine it at 450°C for 3h, the heating rate is 5°C / min, and the intermediate is obtained after natural cooling. Weigh 0.3g of cerium nitrate (hexahydrate) and dissolve it in water, dissolve it completely by ultrasonication, stir it evenly, then add it dropwise to the intermediate, dry it at 120°C for 3 hours to obtain precursor 2, grind precursor 2 into powder and spread it in a quartz boat, put it in a muffle furnace and calcine it at 650°C for 3h, and cool it to room temperature naturally to obtain MoCeSiO2-2 solid acid catalyst.

[0053] Example 4

[0054] Weigh 3g of ammonium metatungstate and dissolve it in water, dissolve it completely by ultrasonication, stir it evenly, then add it dropwise to 10.0g of nano-silicon dioxide, put it in an oven after impregnation and dry it at 120°C for 3 hours to obtain precursor 1, grind precursor 1 into powder and spread it in a quartz boat, put it in a muffle furnace, calcine it at 550°C for 3h, the heating rate is 5°C / min, and the intermediate is obtained after natural cooling. Weigh 0.30g of lanthanum nitrate (hexahydrate) and dissolve it in water, dissolve it completely by ultrasonication, stir it evenly, add it dropwise to the impregnated intermediate, dry it at 120°C for 3 hours to obtain precursor 2, grind precursor 2 into powder and spread it in a quartz boat, put it in a muffle furnace and calcine it at 550°C for 3h, the heating rate is 5°C / min, and after the calcination is completed, cool it naturally to room temperature to obtain WLaSiO2-1 solid acid catalyst.

[0055] Example 5

[0056] Weigh 1.84g of ammonium heptamolybdate (tetrahydrate) and dissolve it in water, weigh 0.3g of ammonium metatungstate and dissolve it in water, ultrasonically dissolve it completely, stir it evenly, then drop it into 10.0g of nano-silicon dioxide, put it into an oven and dry it at 120°C for 3 hours to obtain precursor 1, grind precursor 1 into powder and spread it in a quartz boat, put it into a muffle furnace, calcine it at 450°C for 3h, the heating rate is 5°C / min, and it is naturally cooled to obtain an intermediate. Weigh 0.3g of cerium nitrate (hexahydrate) and dissolve it in water, ultrasonically dissolve it completely, stir it evenly, then drop it into the intermediate, dry it at 120°C for 3 hours to obtain precursor 2, grind precursor 2 into powder and spread it in a quartz boat, put it into a muffle furnace and calcine it at 550°C for 3h, and naturally cool it to room temperature to obtain MoWCeSiO2-1 solid acid catalyst.

[0057] Figure 5 This is a NH3-TPD temperature desorption test diagram of the catalyst in Example 5 of the present invention; Figure 5 This indicates that there are two different types of acid sites on the surface of the catalyst prepared by the present invention, strong and weak, among which the acid sites between 150 and 350°C are more significant.

[0058] Example 6

[0059] Weigh 1.84g of ammonium heptamolybdate (tetrahydrate) and dissolve it in water, weigh 0.5g of ammonium phosphate and dissolve it in water by ultrasonication to completely dissolve it, stir it evenly, then add it dropwise to 10.0g of nano-silicon dioxide, put it in an oven after impregnation and dry it at 120°C for 3 hours to obtain precursor 1, grind precursor 1 into powder and spread it in a quartz boat, put it in a muffle furnace, calcine it at 450°C for 3h, the heating rate is 5°C / min, and it is naturally cooled to obtain an intermediate. Then weigh 0.3g of lanthanum nitrate (hexahydrate) and dissolve it in water, ultrasonication to completely dissolve it, stir it evenly and then add it dropwise to the intermediate, dry it at 120°C for 3 hours to obtain precursor 2, grind precursor 2 into powder and spread it in a quartz boat, put it in a muffle furnace and calcine it at 650°C for 3h, and cool it naturally to room temperature to obtain MoPLaSiO2-2 solid acid catalyst.

[0060] Example 7

[0061] 2.5 g of waste cooking oil, 125 mg of the catalyst in Example 1, and 25 g of methanol were added to a 50 ml autoclave, stirred at 700 rpm and reacted at 155 degrees for 5 hours. Ester biodiesel was obtained by separation. The product was analyzed by gas chromatography internal standard method. The mass yield of ester biodiesel was 87%. Fig. 9 shown.

[0062] Example 8

[0063] 2.5 g of waste cooking oil, 200 mg of the catalyst in Example 5, and 10 ml of deionized water were added to a 50 ml autoclave, stirred at 700 rpm and reacted at 240 degrees for 8 hours. Mixed fatty acids were obtained by separation and purification, and the fatty acid acid value was measured by chemical titration. The fatty acid mass yield was 85%. Fig.10 As shown, Fig.10 b is an enlarged view of the measurement result in 10a.

Claims

1. A solid acid catalyst, characterized in that The catalyst comprises a carrier, an acidic oxide and a promoter; The acidic oxide is selected from one or more of tungsten oxide, molybdenum oxide or phosphorus oxide; The auxiliary agent is selected from one or more of lanthanum oxide, cerium oxide, praseodymium oxide, neodymium oxide or europium oxide.

2. A solid acid catalyst according to claim 1, characterized in that, The carrier is selected from one or more of silicon oxide, titanium oxide or aluminum oxide.

3. A solid acid catalyst according to claim 1, characterized in that, The content of the acidic oxide accounts for 1% to 40% of the total mass of the carrier; the content of the auxiliary agent accounts for 0.5% to 15% of the total mass of the carrier.

4. The method for preparing a solid acid catalyst according to claim 1, characterized in that: include: Step 1: dissolving one or more of metal molybdenum salt, tungsten salt or phosphate in water to obtain a salt solution, then impregnating the solution on a carrier and drying the solution to obtain a precursor, and calcining the precursor to obtain an intermediate; Step 2: impregnating the intermediate obtained in step 1 with a solution of nitrate or chloride containing a rare earth element again, drying it, and calcining it to obtain a solid acid catalyst; the rare earth element is lanthanum, cerium, praseodymium, neodymium or europium.

5. The method for preparing a solid acid catalyst according to claim 4, characterized in that: The molybdenum salt described in step 1 is ammonium heptamolybdate or ammonium molybdate, the tungsten salt is ammonium tungstate, and the phosphate is ammonium phosphate.

6. The method for preparing a solid acid catalyst according to claim 4, characterized in that: The drying temperature in step 1 is 80-150° C., and the drying time is 2 hours to 48 hours.

7. The method for preparing a solid acid catalyst according to claim 4, characterized in that: The calcination temperature in step 1 is 300-1000° C., and the heating rate is 1° C. / min-30° C. / min.

8. The method for preparing a solid acid catalyst according to claim 4, characterized in that: The calcination temperature in step 2 is 400-1000° C., and the heating rate is 1° C. / min-30° C. / min.

9. The method for preparing a solid acid catalyst according to claim 4, characterized in that: The mass ratio of the metal in the metal molybdenum salt, tungsten salt or phosphate to the rare earth element in the nitrate or chloride containing the rare earth element is (1-80):

1.

10. Use of the solid acid catalyst according to claim 1 in catalyzing waste oils and fats to produce biodiesel or fatty acids.

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