A single-atom graphene-like biochar and its application in preparing biodiesel from oil and fat using photothermal catalysis

Abstract

The invention discloses a single-atom graphene-like biochar and its application in preparing biodiesel from oil and fat by photothermal catalysis. A method for preparing a catalyst comprises the following steps: taking a single-atom precursor, dissolving it in a mixed solvent and then adding a graphene-like substance, stirring for 2 to 12 hours, evaporating the mixture at 40 to 100° C., drying the solid obtained above, and pyrolyzing it in a nitrogen flow at 300 to 900° C. for 1 to 9 hours to obtain a single-atom graphene-like photothermal biochar catalyst. The prepared single-atom graphene-like biochar catalyst is used to catalyze oil and fat to prepare biodiesel. When the catalyst dosage is 1 to 7 wt.%, the light intensity is 50 to 300 W, the reaction time is 0.1 to 5 hours, and the molar ratio of oil and fat to methanol is 1:4 to 1:40, the yield of biodiesel is 16.9 to 99.8%.

Description

Technical field:

[0001] The invention relates to a single-atom graphene-like biochar catalyst and application thereof in preparing biodiesel from oil and fat by photothermal catalysis, belonging to the field of heterogeneous catalysis. Background technology:

[0002] The large-scale exploitation and consumption of fossil fuels will bring serious environmental problems and greenhouse effect problems. Therefore, the development of green, environmentally friendly renewable energy to replace the use of fossil fuels is a key strategy to solve energy shortages and environmental problems. Biodiesel is a typical "green energy" with good environmental performance, good engine starting performance, good fuel performance, wide raw material sources, and renewable characteristics. It can not only be used as a fuel, but also as a raw material or intermediate for chemical products, such as industrial solvents, surfactants and lubricants. Vigorously developing biodiesel is of great significance to the sustainable development of the economy, promoting energy substitution, alleviating environmental pressure, and controlling urban air pollution. Biodiesel is usually prepared by using acid or alkali as a catalyst to catalyze the transesterification (esterification) reaction of vegetable oil (such as rapeseed oil, soybean oil, peanut oil, corn oil, cottonseed oil, etc.), animal oil (such as fish oil, lard, tallow, sheep oil, etc.), waste oil or microbial oil with methanol or ethanol to obtain fatty acid methyl ester or ethyl ester. The raw material oil contains a certain amount of free fatty acids, which will saponify with the alkaline catalyst. Therefore, when using the alkaline catalyst, the raw material needs to be pretreated, which increases the production process and production cost. Based on this, it is of great practical significance to develop highly efficient alkali (alkaline earth) metal single-atom catalysts that do not undergo saponification reaction with fatty acids.

[0003] Light and heat are common driving forces in catalytic reactions, because heat drives the reaction rate faster. Therefore, more industrial catalytic production uses heat as the driving force. It is worth noting that high heat energy requires the combustion of more fossil energy, which contradicts the green sustainable development strategy. Light-driven is a green, energy-saving and sustainable driving force, but the light-driven reaction rate is slower than that of heat-driven. In recent years, local photothermal catalysis and interfacial solar heating with high solar energy utilization have rapidly developed into a new research field, which combines the advantages of photocatalysis and heat catalysis. Under solar radiation, photothermal materials (such as graphene-type, graphene-like and carbonaceous materials) can effectively convert solar energy into thermal energy, which is then transmitted to the thin layer of liquid around the material interface, resulting in a direct liquid-gas phase transition. However, there are few reports on the research work on the catalytic preparation of biodiesel from oils and fats using single-atom graphene-like photothermal biochar catalysts. Summary of the invention:

[0004] The purpose of the present invention is to address the problems of high energy consumption, complex production process and easy occurrence of chemical reaction of alkaline catalyst in traditional heat-driven catalytic preparation of biodiesel system.

[0005] Technical solution of the present invention: The present invention uses an impregnation method to load a single-atom precursor on a graphene-like biochar. A certain amount of single-atom precursor is dissolved in a mixed solvent (water / ethanol) and then a certain amount of graphene-like is added. After stirring for 2 to 12 hours, the mixture is evaporated at 40 to 100°C. After the solid obtained above is dried, it is pyrolyzed in a nitrogen flow at 300 to 900°C for 1 to 9 hours to obtain a single-atom graphene-like photothermal biochar catalyst.

[0006] The single-atom precursor includes sodium nitrate, sodium thiosulfate, sodium carbonate, potassium nitrate, potassium sulfate, potassium chloride, potassium hydroxide, potassium oxide, rubidium fluoride, cesium carbonate, cesium fluoride, cesium oxalate, cesium bicarbonate, cesium carbonate, calcium nitrate, calcium chloride, calcium oxalate, calcium carbonate, calcium oxide, strontium nitrate, strontium carbonate, barium nitrate, barium carbonate, barium chloride, magnesium nitrate, magnesium chloride, and magnesium sulfate.

[0007] The single atom (X) includes sodium, potassium, rubidium, cesium, magnesium, calcium, strontium, and barium.

[0008] The volume ratio of the mixed solvent (water / ethanol) is 1:9 to 9:1.

[0009] The mass ratio of the single atom precursor to the graphene-like biochar is 0.01 to 60 wt.%.

[0010] The preparation method of the graphene-like material comprises the following steps: washing the biomass with distilled water, breaking it up, and then freeze-drying it to maintain its original structure; dispersing the biomass into H2O2 / HAc; transferring the suspension into a polytetrafluoroethylene-lined stainless steel autoclave and maintaining it at 60-180°C for 1-10 hours; cooling it to room temperature, centrifuging the suspension and freeze-drying it; placing the prepared sample in a horizontal tube furnace, and heating it from room temperature to 300-900°C at a rate of 2°C / min for 1-6 hours under a nitrogen flow rate; then soaking the obtained carbon in an aqueous solution of HCl to remove excess impurities; neutralizing the residual HCl with deionized water; and finally drying the obtained solid material at 80°C for 8-12 hours.

[0011] The volume ratio of the H2O2 / HAc aqueous solution is 1:9 to 9:1. The solid-liquid ratio of the biomass to the H2O2 / HAc is 1:1 to 1:9. The biomass includes microalgae, plants, animals and waste products thereof.

[0012] The single-atom graphene-like photothermal biochar catalyst is used to catalyze the transesterification (esterification) reaction of caper oil in the preparation of biodiesel.

[0013] A method for preparing biodiesel by catalyzing the transesterification (esterification) reaction of caper oil: the caper oil is converted into biodiesel by a one-pot conversion method.

[0014] A method for preparing biodiesel by catalyzing the transesterification (esterification) reaction of caper oil is specifically as follows: the single-atom graphene photothermal biochar catalyst uses caper oil and methanol as substrates, and the catalyst is added according to 0.005-1g of single-atom graphene / 1g of caper oil, and the reaction is carried out for 0.1-8h under a light intensity of 50-300W, wherein the molar ratio of caper oil to methanol is 1:4-1:40.

[0015] After the catalyst reaction is completed, it is separated from the product, washed with methanol and deionized water respectively, and dried before being used again to catalyze the transesterification (esterification) reaction of caper oil to prepare biodiesel.

[0016] The single-atom graphene-like photothermal biochar catalyst is used to catalyze the transesterification (esterification) reaction of jatropha oil in the preparation of biodiesel.

[0017] A method for preparing biodiesel by catalyzing the transesterification (esterification) reaction of jatropha oil: the jatropha oil is converted into biodiesel by a one-pot conversion method.

[0018] A method for preparing biodiesel by catalyzing the transesterification (esterification) reaction of jatropha oil is specifically as follows: the single-atom graphene photothermal biochar catalyst uses jatropha oil and methanol as substrates, and the catalyst is added according to 0.005-1g of single-atom graphene photothermal biochar / 1g of jatropha oil, and the reaction is carried out at a light intensity of 50-300W for 0.1-8h, wherein the molar ratio of jatropha oil to methanol is 1:4-1:40.

[0019] The principle of preparing single-atom graphene photothermal biochar catalyst in the present invention is as follows: Figure 1 .

[0020] Beneficial effects of the present invention:

[0021] 1. The present invention adopts an impregnation method to load a single-atom precursor on graphene-like biochar and calcines it at 300-900°C to prepare a single-atom graphene-like photothermal biochar catalyst. It successfully overcomes the problems of high energy consumption, complex production process and easy chemical reaction of alkaline catalyst in the traditional heat-driven catalytic preparation of biodiesel.

[0022] 2. The reaction process is simple. The prepared single-atom graphene photothermal biochar is used as a catalyst, and the oils with different acid values ​​are converted into biodiesel in a one-pot method.

[0023] 3. The prepared single-atom graphene photothermal biochar catalyst has good catalytic effect and mild reaction temperature. When the light intensity is 200W, the reaction time is 3h, the catalyst dosage is 4wt.%, and the molar ratio of caper oil to methanol is 20:1, the yield of biodiesel is 97.5%.

[0024] 4. The prepared single-atom graphene photothermal biochar catalyst is a heterogeneous type. After the reaction, the catalyst can be recovered by a simple centrifugation method and used in the next catalytic reaction. After being reused 4 times, the yield of biodiesel can still reach more than 92%, reflecting the strategy of green and sustainable development.

[0025] 5. The present invention solves the problems of high energy consumption, complex production process and easy chemical reaction of alkaline catalyst in the traditional heat-driven catalytic preparation of biodiesel, and improves the safety and economy of the production system. The single-atom graphene photothermal biochar catalyst can realize the efficient conversion of oil into biodiesel within the range of 50-300W light intensity. The used catalyst can be directly reused after centrifugation, washing and drying, realizing the recycling of the single-atom graphene photothermal biochar catalyst. Description of the drawings:

[0026] Figure 1 The schematic diagram of the preparation of single-atom graphene-like photothermal biochar catalyst of the present invention;

[0027] Figure 2 is the hydrogen spectrum of the biodiesel in Example 1;

[0028] Figure 3 This is a graph showing the yield of preparing biodiesel from caper oil using K-single-atom graphene-like photothermal biochar catalyst at different reaction times in Example 1;

[0029] Figure 4 This is a graph showing the yield of preparing biodiesel from caper oil using the Cs-single-atom graphene-like photothermal biochar catalyst at different reaction times;

[0030] Figure 5 This is a graph showing the yield of preparing biodiesel from caper oil using the Ca-single-atom graphene-like photothermal biochar catalyst at different reaction times.

[0031] Figure 6 This is a graph showing the yield of preparing biodiesel from caper oil using Ba-single-atom graphene-like photothermal biochar catalyst at different reaction times.

[0032] Figure 7 This is a graph showing the yield of preparing biodiesel from caper oil using the Mg-single-atom graphene-like photothermal biochar catalyst of Example 1 at different reaction times. Specific implementation method:

[0033] The technical scheme of the present invention is further described in detail below in conjunction with the embodiments, but they are not intended to limit the present invention.

[0034] Example 1

[0035] 1. Preparation of K-atom graphene photothermal biochar catalyst:

[0036] The chlorella was washed with distilled water, crushed, and then freeze-dried to maintain its original structure. 2 g of chlorella was dispersed in a 10 wt.% H2O2 / Hac (H2O2:Hac volume ratio = 1:2) aqueous solution, and then the suspension was transferred to a polytetrafluoroethylene-lined stainless steel autoclave and kept at 120°C for 3 h. After the reaction was completed and cooled to room temperature, the suspension was centrifuged and freeze-dried. The prepared sample was placed in a horizontal tube furnace and heated from room temperature to 700°C at a rate of 2°C / min under a nitrogen (N2) flow rate for 3 h. The obtained carbon was then soaked in an aqueous HCl solution to remove excess impurities, and the residual HCl was neutralized (pH = 7) with deionized water, and finally the obtained solid material was dried at 80°C for 8 to 12 h.

[0037] KNO3 was loaded on graphene-like biochar by impregnation method. 0.01g of single-atom precursor was dissolved in a mixed solvent (water / ethanol) and 0.3g of graphene-like was added. After stirring for 12h, the mixture was evaporated at 80°C. The solid obtained above was dried and pyrolyzed in a nitrogen flow at 800°C for 3h to obtain K-single-atom graphene-like photothermal biochar catalyst.

[0038] 2. Catalyst performance test

[0039] 1g of caper oil, 0.04g of K-monoatom graphene photothermal biochar catalyst and 2.8mL of methanol were added to a 15mL pressure tube, and the pressure tube was placed under a 200W xenon lamp for stirring and reaction for 3h. After the reaction, the mixture in the pressure tube was poured into a centrifuge tube, and the catalyst was separated by centrifugation at 8000rpm, and petroleum ether was added to the centrifuge to extract the product. The product was used for 1 The yield of biodiesel was calculated to be 97.5% by HNMR. 1 The general method for detecting the yield of biodiesel by HNMR is as follows: tetramethylsilane (TMS) is used as the internal standard for quantitative analysis, and deuterated chloroform (CDCl3) is used as the solvent to dissolve the product. 1 In the HNMR spectrum, the difference before and after the reaction is that biodiesel has a new -OCH3 peak at 3.66ppm. At the same time, the triplet peak at 2.30ppm in biodiesel and crude oil remains unchanged, which is the typical peak of -CH2- at the α position. Therefore, the yield of biodiesel can be determined by the peak area of ​​α-CH2 and new -OCH3. The calculation formula for biodiesel is as follows:

[0040] Biodiesel yield (%) = (2A OMe / 3A CH2 )×100%

[0041] Where: A OMe is the proton peak area of ​​-OCH3 at 3.66ppm, A CH2 is the proton peak area of ​​α-CH2 at 2.30 ppm.

[0042] Example 2

[0043] 1. Preparation of Cs-atom graphene-based photothermal biochar catalyst:

[0044] The chlorella was washed with distilled water, crushed, and then freeze-dried to maintain its original structure. 2 g of chlorella was dispersed in a 10 wt.% H2O2 / Hac (H2O2:Hac volume ratio = 1:2) aqueous solution, and then the suspension was transferred to a polytetrafluoroethylene-lined stainless steel autoclave and kept at 180°C for 1 h. After the reaction was completed and cooled to room temperature, the suspension was centrifuged and freeze-dried. The prepared sample was placed in a horizontal tube furnace and heated from room temperature to 900°C at a rate of 2°C / min under a nitrogen (N2) flow rate for 2 h. The obtained carbon was then soaked in an aqueous HCl solution to remove excess impurities, and the residual HCl was neutralized (pH = 7) with deionized water, and finally the obtained solid material was dried at 80°C for 8 to 12 h.

[0045] CsCO3 was loaded on graphene-like biochar by impregnation method. 0.01g of single-atom precursor was dissolved in a mixed solvent (water / ethanol) and 0.3g of graphene-like was added. After stirring for 8h, the mixture was evaporated at 100℃. The solid obtained above was dried and pyrolyzed in a nitrogen flow at 900℃ for 2h to obtain Cs-single-atom graphene-like photothermal biochar catalyst.

[0046] 2. Catalytic performance test

[0047] The catalyst used was the Cs-atom graphene photothermal biochar catalyst prepared in Example 2. When the reaction time was 40 min, the catalyst dosage was 4 wt.%, the molar ratio of methanol to caper oil was 18:1, and the light intensity was 200 W, the yield of biodiesel was 99.8%.

[0048] Example 3

[0049] 1. Preparation of Ca-atom graphene photothermal biochar catalyst:

[0050] The chlorella was washed with distilled water, crushed, and then freeze-dried to maintain its original structure. 2 g of chlorella was dispersed in a 10 wt.% H2O2 / Hac (H2O2:Hac volume ratio = 1:2) aqueous solution, and then the suspension was transferred to a polytetrafluoroethylene-lined stainless steel autoclave and kept at 80°C for 9 h. After the reaction was completed and cooled to room temperature, the suspension was centrifuged and freeze-dried. The prepared sample was placed in a horizontal tube furnace and heated from room temperature to 400°C at a rate of 2°C / min under a nitrogen (N2) flow rate for 6 h. The obtained carbon was then soaked in an aqueous HCl solution to remove excess impurities, and the residual HCl was neutralized (pH = 7) with deionized water, and finally the obtained solid material was dried at 80°C for 8 to 12 h.

[0051] CaCO3 was loaded on graphene-like biochar by impregnation method. 0.01g of single-atom precursor was dissolved in a mixed solvent (water / ethanol) and 0.3g of graphene-like was added. After stirring for 4h, the mixture was evaporated at 60°C. The solid obtained above was dried and pyrolyzed in a nitrogen flow at 600°C for 9h to obtain Ca-single-atom graphene-like photothermal biochar catalyst.

[0052] 2. Catalytic performance test

[0053] The catalyst used was the Ca-atom graphene photothermal biochar catalyst prepared in Example 3. When the reaction time was 3.5 h, the catalyst dosage was 4 wt.%, the molar ratio of methanol to caper oil was 20:1, and the light intensity was 200 W, the yield of biodiesel was 96.8%.

[0054] Example 4

[0055] 1. Preparation of Ba-atom graphene-based photothermal biochar catalyst:

[0056] KNO3 was replaced by BaCO3, and the rest was the same as in Example 1.

[0057] 2. Catalytic performance test

[0058] The catalyst used was the Ba-atom graphene photothermal biochar catalyst prepared in Example 4. When the reaction time was 1.5 h, the catalyst dosage was 4 wt.%, the molar ratio of methanol to caper oil was 18:1, and the light intensity was 200 W, the yield of biodiesel was 98.8%.

[0059] Example 5

[0060] 1. Preparation of Mg-atom graphene photothermal biochar catalyst:

[0061] KNO3 was replaced by MgCl2, and the rest was the same as in Example 1.

[0062] 2. Catalytic performance test

[0063] The catalyst used was the Mg-atom graphene photothermal biochar catalyst prepared in Example 5. When the reaction time was 4 h, the catalyst dosage was 4 wt.%, the molar ratio of methanol to caper oil was 20:1, and the light intensity was 200 W, the yield of biodiesel was 96.4%.

Claims

1. A method for preparing a single-atom graphene photothermal biochar catalyst, characterized in that: The method comprises the following steps: dissolving a single-atom precursor in a mixed solvent and then adding a graphene-like substance, stirring for 2 to 12 hours, evaporating the mixture at 40 to 100° C., drying the solid obtained above, and pyrolyzing it in a nitrogen flow at 300 to 900° C. for 1 to 9 hours to obtain a single-atom graphene-like photothermal biochar catalyst; the preparation method of the graphene-like substance comprises: washing the biomass with distilled water, breaking it up, and then freeze-drying it to maintain its original structure, dispersing the biomass into H2O2 / HAc, and then transferring the suspension to a polytetrafluoroethylene-lined stainless steel autoclave and maintaining it at 60 to 180° C. for 1 to 10 hours, cooling it to room temperature, centrifuging and freeze-drying the suspension, placing the prepared sample in a horizontal tube furnace, and heating it from room temperature to 300 to 900° C. at a rate of 2° C. / min under a nitrogen flow rate for 1 to 6 hours. h, then immersing the obtained carbon in an aqueous solution of HCl to remove excess impurities, neutralizing the residual HCl with deionized water, and finally drying the obtained solid material; the single atom comprises sodium, potassium, rubidium, cesium, magnesium, calcium, strontium or barium; the mass ratio of the single atom precursor to the graphene-like biochar is 0.01~60wt.%.

2. The method for preparing a single-atom graphene photothermal biochar catalyst according to claim 1, characterized in that: The single-atom precursor includes sodium nitrate, sodium thiosulfate, sodium carbonate, potassium nitrate, potassium sulfate, potassium chloride, potassium hydroxide, potassium oxide, rubidium fluoride, cesium carbonate, cesium fluoride, cesium oxalate, cesium bicarbonate, cesium carbonate, calcium nitrate, calcium chloride, calcium oxalate, calcium carbonate, calcium oxide, strontium nitrate, strontium carbonate, barium nitrate, barium carbonate, barium chloride, magnesium nitrate, magnesium chloride or magnesium sulfate.

3. The method for preparing a single-atom graphene-like photothermal biochar catalyst according to claim 1, characterized in that: The volume ratio of the H2O2 / HAc aqueous solution is 1:9~9:

1.

4. The method for preparing a single-atom graphene photothermal biochar catalyst according to claim 1, characterized in that: The mixed solvent is water / ethanol, and the volume ratio of water / ethanol is 1:9-9:

1.

5. Use of the single-atom graphene-like photothermal biochar catalyst prepared by the preparation method according to any one of claims 1 to 4 in catalyzing the transesterification of caper oil to prepare biodiesel.

6. The use according to claim 5, characterized in that: A method for preparing biodiesel by catalyzing the transesterification reaction of caper oil is as follows: the single-atom graphene photothermal biochar catalyst uses caper oil and methanol as substrates, and the catalyst is added according to 0.005-1 g of single-atom graphene / 1 g of caper oil, and the reaction is carried out at a light intensity of 50-300 W for 0.1-8 h, wherein the molar ratio of caper oil to methanol is 1:4-1:

40.

7. Use of the single-atom graphene-like photothermal biochar catalyst prepared by the preparation method according to any one of claims 1 to 4 in catalyzing the transesterification reaction of jatropha oil to prepare biodiesel.

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