Method for preparing biodiesel through co-hydrogenation of straw and waste grease

Abstract

The invention discloses a method for preparing biodiesel through co-hydrogenation of straw and waste grease, and belongs to the technical field of chemical industry. The method comprises the following steps: grinding straw, mixing with waste grease, then adding a molybdenum-based oil-soluble catalyst and a vulcanizing agent, and uniformly stirring to form slurry; and mixing the slurry with hydrogen, and carrying out a hydrodeoxygenation reaction in a slurry bed reactor. According to the method, the waste grease is used as a hydrogen donor to be mixed with the straw, so that the waste grease can provide a hydrogen source for the straw while being subjected to hydrogenation conversion into hydrocarbons, liquefaction of the straw is promoted, and the conversion rate of the straw is increased. Compared with single use of waste oil hydrogenation, co-hydrogenation of straw and waste oil improves the stability of a raw material supply chain and reduces the raw material cost.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical industry, and particularly relates to a method for preparing biodiesel by co-hydrogenation of straw and waste oil. Background Art

[0002] As a major agricultural country, China produces nearly 900 million tons of straw annually. Rice, wheat, and corn straw account for the largest share, totaling 76.12%. Therefore, the rational application of straw is extremely important. my country's straw utilization is diversified, with fertilizer utilization being the primary method, with a utilization rate exceeding 60%. However, my country's high-value straw energy utilization started late, resulting in a low level of high-value utilization, and industrial applications have not been fully promoted. Therefore, the development of high-value straw and industrialization technologies will be a key focus of future straw utilization.

[0003] Rapid pyrolysis of straw is a method for producing biodiesel. This involves rapidly heating straw to 400-500°C in an inert atmosphere to produce pyrolysis oil. However, this method produces pyrolysis oil with a high oxygen content and a low heating value (HHV), significantly limiting its application. Therefore, reducing the oxygen content of the resulting bio-oil and increasing its HHV are key challenges in converting straw into fuel.

[0004] One method for reducing the oxygen content of pyrolysis oil is to add hydrogen under a reducing atmosphere. Hydrogen can provide a sufficient hydrogen source for the straw, thereby inhibiting decarbonylation and decarboxylation reactions and promoting hydrodeoxygenation reactions. Simultaneously, adding a hydrogenation catalyst, under the combined action of hydrogen and catalyst, further increases the proportion of hydrodeoxygenation reactions, producing biodiesel with an oxygen content, H / C ratio, and calorific value comparable to fossil fuels. Another way to overcome the low conversion rate of hydrogen-deficient straw is to use a hydrogen donor. A hydrogen donor is a substance that can provide hydrogen radicals to other compounds under appropriate temperature and pressure. After adding a hydrogen donor, the hydrogenation system has two sources of hydrogen: the hydrogen atmosphere and the hydrogen radicals released by the hydrogen donor. Furthermore, the hydrogen donor acts as a solvent, mixing with straw powder to form a suspension, which improves the dispersion of the straw, allowing it to be heated more evenly, reducing the coking rate, and increasing the light oil conversion rate. Summary of the Invention

[0005] The present invention provides a method for preparing biodiesel by co-hydrogenating straw and waste oil, comprising the following steps: The straw is ground and mixed with waste oil, and then a molybdenum-based oil-soluble catalyst and a sulfiding agent are added and stirred evenly to form a slurry; the slurry is then mixed with hydrogen and subjected to a hydrodeoxygenation reaction in a slurry bed reactor.

[0006] In the above-mentioned method for preparing biodiesel, the straw is one or more of wheat straw, corn straw and rice straw.

[0007] In the above-mentioned method for preparing biodiesel, the waste oil is one or more of cottonseed acidified oil, palmitic acidified oil, kitchen waste oil, sewage oil, and frying waste oil.

[0008] In the above-mentioned method for preparing biodiesel, the mesh size of the crushed straw powder is between 100 and 200 meshes.

[0009] In the above-mentioned method for preparing biodiesel, the mass ratio of the straw to the waste oil is (2-5):10.

[0010] In the above-mentioned method for preparing biodiesel, the molybdenum-based oil-soluble catalyst is one or more of molybdenum oleate, molybdenum octoate, and molybdenum cyclohexaneate.

[0011] In the above-mentioned method for preparing biodiesel, the vulcanizing agent is one or more of sulfur powder, polymerized sulfur, and thiourea.

[0012] In the above-mentioned method for preparing biodiesel, the amount of the molybdenum-based oil-soluble catalyst used is: 100-500 μg molybdenum / g slurry, calculated as molybdenum metal content.

[0013] In the above-mentioned method for preparing biodiesel, the amount of the sulfiding agent used is such that the molar ratio of the sulfiding agent to the sulfur in the molybdenum-based oil-soluble catalyst to the molybdenum is 2:1.

[0014] In the above-mentioned method for preparing biodiesel, the volume ratio of hydrogen to slurry is (600-1200):1.

[0015] In the above-mentioned method for preparing biodiesel, the stirring conditions are: stirring at 50-80° C. for 0.5-1 h.

[0016] In the above-mentioned method for preparing biodiesel, the conditions for the hydrodeoxygenation reaction are: reaction temperature 350-400° C., reaction pressure 12-18 MPa, and reaction time 0.5-3 h.

[0017] The beneficial effects of the present invention are: The raw materials used in the present invention are straw and waste oil, which are widely available, low-cost, and can reduce waste pollution. The waste oil can also serve as a hydrogen donor to promote the liquefaction of straw during hydrogenation, thereby improving the straw conversion rate. Compared with using waste oil hydrogenation alone, the co-hydrogenation of straw and waste oil improves the stability of the raw material supply chain. The catalyst selected in the co-hydrogenation process is an oil-soluble molybdenum-based catalyst, which has good dispersibility and high catalytic activity in straw powder and waste oil, and has a good hydrogenation effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1The actual pictures of the biodiesel prepared in Examples 1 to 3 are Example 1, Example 2 and Example 3 from left to right. DETAILED DESCRIPTION

[0019] In the present invention, the waste grease used is widely sourced, including cottonseed oil, palmitic acid oil, waste cooking grease, slop oil, frying oil, etc. from the catering industry, as well as waste refined grease from the food processing industry. Waste grease has a high H / C ratio and can be used as a good hydrogen donor to provide hydrogen for straw conversion. Therefore, using waste grease as a hydrogen donor, after fully mixing with straw and an oil-soluble molybdenum-based catalyst, and then performing hydrodeoxygenation in a slurry bed reactor, straw and waste grease can be simultaneously converted into a light oil product, thereby being an economical and efficient method for producing biodiesel.

[0020] After testing, the basic properties of the waste oil used in the present invention are shown in Table 1 below: Table 1 Basic properties of waste oil and fat Unless otherwise specified, the terms used in the present invention generally have the meanings commonly understood by those of ordinary skill in the art. The present invention will be further described in detail below with reference to specific implementation cases and data. The following examples are intended to illustrate the present invention and are not intended to limit the scope of the present invention in any way.

[0021] Example 1 The preparation steps of biodiesel are as follows: Wheat straw was dried and ground into a 100-mesh powder. The powder was then mixed with cottonseed oil at a mass ratio of 1:4 and added to a mixing tank. 100 μg / g of molybdenum octoate catalyst (based on molybdenum metal content) and thiourea (at a sulfur to molybdenum molar ratio of 2:1) were then added. The mixture was stirred at 50°C for 0.5 h to form a slurry. The slurry was then mixed with hydrogen (hydrogen:oil volume ratio of 1000:1) and introduced into a heating furnace. After heating, the mixture was introduced into a slurry bed reactor from the bottom. Hydrodeoxygenation was carried out at a temperature of 350°C, a pressure of 12 MPa, and a residence time of 3 h. After cooling, the reaction product was centrifuged to obtain a solid product (ash) and a liquid product. The liquid product was then distilled to collect the gasoline and diesel components. The fraction with an initial boiling point of ~180°C was gasoline, and the fraction between 180 and 360°C was diesel.

[0022] The solid product was washed twice with petroleum ether, dried and weighed, and the straw conversion rate after removing the ash was calculated to be 96.46%; the yield of the liquid product was 90.31 wt.%, of which the yield of diesel was 79.29 wt.%.

[0023] Example 2 To prepare biodiesel, the steps are as follows: Corn straw was dried and ground into a 100-mesh powder. This powder was then mixed with palmitic acid oil in a 1:2 mass ratio into a mixing tank. 100 μg / g molybdenum naphthenate catalyst (based on molybdenum metal content) and sulfur powder (at a sulfur to molybdenum molar ratio of 2:1) were then added. The mixture was stirred at 50°C for 1 hour to form a slurry. The slurry was then mixed with hydrogen (hydrogen to oil volume of 1200:1) and introduced into a heating furnace. After heating, the mixture was introduced into the bottom of a slurry-bed reactor. Hydrodeoxygenation was carried out at a temperature of 380°C, a pressure of 18 MPa, and a residence time of 2 hours. After cooling, the reaction product was centrifuged to obtain a solid product (ash) and a liquid product. The liquid product was then distilled to collect the gasoline and diesel components. The fraction with an initial boiling point of ~180°C was gasoline, and the fraction between 180°C and 360°C was diesel.

[0024] The solid product was washed twice with petroleum ether, dried and weighed, and the straw conversion rate after removing the ash was calculated to be 96.21%; the yield of the liquid product was 89.01 wt.%, of which the yield of diesel was 69.48 wt.%.

[0025] Example 3 To prepare biodiesel, the steps are as follows: Wheat straw was dried and ground into a 100-mesh powder. The powder was then mixed with waste cooking oil in a 1:4 mass ratio into a mixing tank. 200 μg / g of molybdenum oleate catalyst (based on molybdenum metal content) and polysulfide (sulfur:molybdenum molar ratio of 2:1) were then added. The mixture was stirred at 80°C for 1 hour to form a slurry. The slurry was then mixed with hydrogen (hydrogen:oil volume 800:1) and introduced into a heating furnace. After heating, the mixture was introduced into the bottom of a slurry-bed reactor for hydrodeoxygenation at a temperature of 350°C, a pressure of 12 MPa, and a residence time of 2 hours. After cooling, the reaction product was centrifuged to obtain a solid product (ash) and a liquid product. The liquid product was then distilled to collect the gasoline and diesel components. The fraction with an initial boiling point of ~180°C was gasoline, and the fraction between 180°C and 360°C was diesel.

[0026] The solid product was washed twice with petroleum ether, dried and weighed, and the straw conversion rate after removing the ash was calculated to be 97.33%; the yield of the liquid product was 89.94 wt.%, of which the yield of diesel was 79.28 wt.%.

[0027] Example 4 To prepare biodiesel, the steps are as follows: Rice straw was dried and ground into a 100-mesh powder. The powder was then mixed with cottonseed oil at a mass ratio of 1:4 and added to a mixing tank. 300 μg / g of molybdenum oleate catalyst (based on molybdenum metal content) and thiourea (at a sulfur to molybdenum molar ratio of 2:1) were then added. The mixture was stirred at 60°C for 0.5 h to form a slurry. The slurry was then mixed with hydrogen (hydrogen to oil volume 1000:1) and introduced into a heating furnace. After heating, the mixture was introduced from the bottom of a slurry-bed reactor. Hydrodeoxygenation was carried out at a temperature of 350°C, a pressure of 15 MPa, and a residence time of 1.5 h. After cooling, the reaction product was centrifuged to obtain a solid product (ash) and a liquid product. The liquid product was then distilled to collect the gasoline and diesel components. The fraction with an initial boiling point of ~180°C was gasoline, and the fraction between 180 and 360°C was diesel.

[0028] The solid product was washed twice with petroleum ether, dried and weighed, and the straw conversion rate after removing the ash was calculated to be 96.22%; the yield of the liquid product was 90.48 wt.%, of which the yield of diesel was 78.39 wt.%.

[0029] Example 5 To prepare biodiesel, the steps are as follows: Wheat straw was dried and ground into a 100-mesh powder. The powder was then mixed with hogwash oil in a 1:5 mass ratio into a mixing tank. 500 μg / g molybdenum naphthenate catalyst (based on molybdenum metal content) and sulfur powder (at a sulfur to molybdenum molar ratio of 2:1) were then added. The mixture was stirred at 50°C for 0.6 h to form a slurry. The slurry was then mixed with hydrogen (hydrogen:oil, volume: 600:1) and introduced into a heating furnace. After heating, the mixture entered the bottom of a slurry-bed reactor for hydrodeoxygenation at a temperature of 380°C, a pressure of 18 MPa, and a residence time of 0.5 h. After cooling, the reaction product was centrifuged to obtain a solid product (ash) and a liquid product. The liquid product was then distilled to collect the gasoline and diesel components. The fraction with an initial boiling point of ~180°C was gasoline, and the fraction between 180 and 360°C was diesel.

[0030] The solid product was washed twice with petroleum ether, dried and weighed, and the straw conversion rate after removing the ash was calculated to be 99.39%; the yield of the liquid product was 91.53 wt.%, of which the yield of diesel was 82.49 wt.%.

[0031] Example 6 To prepare biodiesel, the steps are as follows: Wheat straw was dried and ground into a 100-mesh powder. The powder was then mixed with waste cooking oil in a 1:4 mass ratio in a mixing tank. 300 μg / g of molybdenum oleate catalyst (based on molybdenum metal content) and polysulfide (sulfur:molybdenum molar ratio of 2:1) were added and stirred at 80°C for 1 hour to form a slurry. The slurry was then mixed with hydrogen (hydrogen:oil volume 800:1) and introduced into a heating furnace. After heating, the mixture was introduced from the bottom of a slurry-bed reactor for hydrodeoxygenation at a temperature of 350°C, a pressure of 12 MPa, and a residence time of 1 hour. After cooling, the reaction product was centrifuged to obtain a solid product (ash) and a liquid product. The liquid product was then distilled to collect the gasoline and diesel components. The fraction with an initial boiling point of ~180°C was gasoline, and the fraction between 180 and 360°C was diesel.

[0032] The solid product was washed twice with petroleum ether, dried and weighed, and the straw conversion rate after removing the ash was calculated to be 98.52%; the yield of the liquid product was 90.48 wt.%, of which the yield of diesel was 80.28 wt.%.

[0033] Example 7 To prepare biodiesel, the steps are as follows: Wheat straw was dried and ground into a 100-mesh powder. The powder was then mixed with waste cooking oil in a 1:3 mass ratio in a mixing tank. 500 μg / g molybdenum octoate catalyst (based on molybdenum metal content) and sulfur powder (at a sulfur-to-molybdenum molar ratio of 2:1) were then added. The mixture was stirred at 80°C for 1 hour to form a slurry. The slurry was then mixed with hydrogen (hydrogen:oil volume 800:1) and introduced into a heating furnace. After heating, the mixture entered the bottom of a slurry-bed reactor for hydrodeoxygenation at a temperature of 350°C, a pressure of 12 MPa, and a residence time of 1 hour. After cooling, the reaction product was centrifuged to obtain a solid product (ash) and a liquid product. The liquid product was then distilled to collect the gasoline and diesel components. The fraction with an initial boiling point of ~180°C was gasoline, and the fraction between 180 and 360°C was diesel.

[0034] The solid product was washed twice with petroleum ether, dried and weighed, and the straw conversion rate after removing the ash was calculated to be 98.39%; the yield of the liquid product was 91.23 wt.%, of which the yield of diesel was 75.93 wt.%.

[0035] Example 8 To prepare biodiesel, the steps are as follows: Wheat straw was dried and ground into a 200-mesh powder. The powder was then mixed with waste cooking oil in a 1:3 mass ratio in a mixing tank. 100 μg / g of molybdenum oleate catalyst (based on molybdenum metal content) and thiourea (sulfur to molybdenum molar ratio of 2:1) were then added. The mixture was stirred at 80°C for 1 hour to form a slurry. The slurry was then mixed with hydrogen (hydrogen to oil volume 800:1) and introduced into a heating furnace. After heating, the mixture was introduced from the bottom of a slurry-bed reactor. Hydrodeoxygenation was carried out at a temperature of 350°C, a pressure of 12 MPa, and a residence time of 2.5 hours. After cooling, the reaction product was centrifuged to obtain a solid product (ash) and a liquid product. The liquid product was then distilled to collect the gasoline and diesel components. The fraction with an initial boiling point of ~180°C was gasoline, and the fraction between 180 and 360°C was diesel.

[0036] The solid product was washed twice with petroleum ether, dried and weighed, and the straw conversion rate after removing the ash was calculated to be 95.38%; the yield of the liquid product was 89.67 wt.%, of which the yield of diesel was 74.39 wt.%.

[0037] Example 9 To prepare biodiesel, the steps are as follows: Wheat straw was dried and ground into a 100-mesh powder. The powder was then mixed with waste cooking oil in a 1:4 mass ratio in a mixing tank. 200 μg / g molybdenum naphthenate catalyst (based on molybdenum metal content) and sulfur powder (at a sulfur to molybdenum molar ratio of 2:1) were then added. The mixture was stirred at 80°C for 1 hour to form a slurry. The slurry was then mixed with hydrogen (hydrogen to oil volume: 800:1) and introduced into a heating furnace. After heating, the mixture was introduced from the bottom of a slurry-bed reactor. Hydrodeoxygenation was carried out at a temperature of 350°C, a pressure of 12 MPa, and a residence time of 1 hour. After cooling, the reaction product was centrifuged to obtain a solid product (ash) and a liquid product. The liquid product was then distilled to collect the gasoline and diesel components. The fraction with an initial boiling point of ~180°C was gasoline, and the fraction between 180 and 360°C was diesel.

[0038] The solid product was washed twice with petroleum ether, dried and weighed, and the straw conversion rate after removing the ash was calculated to be 98.37%; the yield of the liquid product was 91.26wt.%, of which the yield of diesel was 80.38wt.%.

[0039] Example 10 To prepare biodiesel, the steps are as follows: Wheat straw was dried and ground into a 100-mesh powder. The powder was then mixed with waste cooking oil in a 1:3 mass ratio in a mixing tank. 400 μg / g of molybdenum naphthenate catalyst (based on molybdenum metal content) and polysulfide (sulfur:molybdenum molar ratio of 2:1) were then added. The mixture was stirred at 80°C for 1 hour to form a slurry. The slurry was then mixed with hydrogen (hydrogen:oil volume 800:1) and introduced into a heating furnace. After heating, the mixture was introduced from the bottom of a slurry-bed reactor. Hydrodeoxygenation was carried out at a temperature of 350°C, a pressure of 12 MPa, and a residence time of 1 hour. After cooling, the reaction product was centrifuged to obtain a solid product (ash) and a liquid product. The liquid product was then distilled to collect the gasoline and diesel components. The fraction with an initial boiling point of ~180°C was gasoline, and the fraction between 180 and 360°C was diesel.

[0040] The solid product was washed twice with petroleum ether, dried and weighed, and the straw conversion rate after removing the ash was calculated to be 98.24%; the yield of the liquid product was 90.73wt.%, of which the yield of diesel was 75.19wt.%.

[0041] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any other manner. Any person skilled in the art may utilize the above-disclosed technical content to modify or modify the present invention into equivalent embodiments. However, any simple modifications, equivalent variations, and modifications to the above embodiments that do not depart from the technical content of the present invention and are based on the technical essence of the present invention remain within the scope of protection of the present invention.

Claims

1. A method for preparing biodiesel by co-hydrogenation of straw and waste oil, characterized in that: The steps include: The straw is ground and mixed with waste oil, and then a molybdenum-based oil-soluble catalyst and a sulfiding agent are added and stirred evenly to form a slurry; the slurry is then mixed with hydrogen and subjected to a hydrodeoxygenation reaction in a slurry bed reactor.

2. The method according to claim 1, characterized in that The straw is one or more of wheat straw, corn straw and rice straw.

3. The method according to claim 1, characterized in that The waste oil is one or more of cottonseed acidified oil, palmitic acidified oil, kitchen waste oil, sewage oil, and frying waste oil.

4. The method according to claim 1, wherein The mass ratio of the straw to the waste oil is (2-5):

10.

5. The method according to claim 1, wherein The molybdenum-based oil-soluble catalyst is one or more of molybdenum oleate, molybdenum octoate, and molybdenum naphthenate.

6. The method according to claim 1, characterized in that The vulcanizing agent is one or more of sulfur powder, polymerized sulfur and thiourea.

7. The method according to claim 1, characterized in that The amount of the molybdenum-based oil-soluble catalyst used is: 100-500 μg molybdenum / g slurry, calculated based on the molybdenum metal content.

8. The method according to claim 1, characterized in that The amount of the vulcanizing agent used is as follows: the molar ratio of the vulcanizing agent to the sulfur and molybdenum in the molybdenum-based oil-soluble catalyst is 2:

1.

9. The method according to claim 1, characterized in that The volume ratio of the hydrogen to the slurry is (600-1200):

1.

10. The method according to claim 1, characterized in that The conditions of the hydrodeoxygenation reaction are: reaction temperature 350-400° C., reaction pressure 12-18 MPa, and reaction time 0.5-3 h.

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