Method for synergistically preparing biodiesel from kitchen waste and algae mud

Abstract

The invention discloses a method for synergistically preparing biodiesel from kitchen waste and algae mud, which comprises the following steps: by taking the kitchen waste and the algae mud as raw materials, adding an accelerant, uniformly mixing, carrying out hydrothermal treatment under the conditions that the temperature is 270-330 DEG C and the pressure is 7.0-12.5 MPa, and carrying out solid-liquid separation on the product, sulfonating the solid-phase product and concentrated sulfuric acid at 150-190 DEG C to prepare a solid acid catalyst; and taking a liquid-phase product grease layer, adding methanol and a solid acid catalyst, carrying out esterification and etherification reactions, and carrying out subsequent distillation treatment to obtain the biodiesel. According to the method, collaborative resourceful treatment of the kitchen waste and the algae mud is achieved, energy substances such as biodiesel and hydrothermal carbon are recycled, the added value of products is high, and a new technical approach is provided for low-carbon treatment and energy utilization of organic solid waste.

Description

Technical Field

[0001] This invention belongs to the field of organic solid waste treatment, disposal and resource utilization technology, specifically relating to a method for co-producing biodiesel from kitchen waste and algal sludge. Background Technology

[0002] With the acceleration of urbanization and the rapid improvement of sewage treatment capacity, the production of easily perishable organic solid waste with high water content, such as kitchen waste, sewage sludge, and dehydrated algae sludge from algae-water separation stations, is constantly increasing, but its resource utilization is significantly lagging behind. In 2021, my country's annual production of kitchen waste was nearly 127 million tons, and the annual production of wet sludge reached 55.52 million tons; at the same time, the Dianchi Lake blue-green algae control project alone produced nearly 25,000 tons of dehydrated algae sludge. The algae sludge produced during the algae-water separation process is rich in protein, lipids, and polysaccharides, and its dehydration cost is high and its disposal is difficult. Kitchen waste contains components such as starch, cellulose, protein, oil, and inorganic salts, and is characterized by high water and organic matter content and complex composition. If not properly treated, it is extremely prone to rotting and deterioration, breeding mosquitoes and flies, and emitting foul odors, which not only affects urban environmental sanitation but also causes secondary pollution of water bodies and soil.

[0003] For organic solid waste with high water content, traditional landfill or incineration methods suffer from problems such as large leachate production, large land area requirements, and high treatment costs, while aerobic composting has issues such as long processing cycles and noticeable odors. Meanwhile, the urgent global demand for energy transition has led to increased attention for biodiesel as a clean fuel alternative to fossil diesel. Current biodiesel production mainly relies on waste cooking oil or energy crops. The former faces problems such as unstable raw material supply and high pretreatment costs, while the latter raises ethical controversies regarding competition for land with food crops. To address these challenges, hydrothermal liquefaction technology offers unique advantages: it can directly process biomass with high water content, converting organic matter into bio-oil through hydrolysis, decarboxylation, and recombination reactions under high temperature and pressure. Existing patent CN103710158A uses hydrothermal treatment to separate oil from kitchen waste, producing biodiesel through esterification with short-chain alcohols in a container filled with immobilized lipase. This technology requires the synthesis of bio-enzyme catalysts to promote the esterification reaction, resulting in high biodiesel production costs and limited raw material adaptability. Patent CN105733693A proposes a method for preparing bio-oil using algae and lignocellulosic biomass as raw materials through high-temperature and high-pressure liquefaction in a subcritical / supercritical alcohol-water co-solvent. Byproduct gases, residues, and the aqueous phase can be utilized as resources. However, this technology involves subcritical / supercritical operating conditions, placing extremely high demands on process equipment. Furthermore, the extraction stage uses toxic solvents such as dichloromethane and acetone, potentially posing adverse effects on oil safety and the environmental benefits of the preparation process. Therefore, developing bio-oil preparation technologies tailored to the characteristics of organic solid waste raw materials to achieve efficient, economical conversion and resource utilization is receiving increasing attention. Summary of the Invention

[0004] This invention provides a method for co-producing biodiesel from kitchen waste and algal sludge. Using organic-rich kitchen waste and dehydrated algal sludge as raw materials, a synergistic hydrothermal treatment is performed after adding an accelerator to promote decomposition, oxidation, and polymerization reactions of the organic materials, forming a liquid product containing crude bio-oil and carbon-based solids. The resulting carbon-based solids can be directly recycled. A portion of the carbon-based solids undergoes micro-oxygen magnetization roasting and concentrated sulfuric acid sulfonation treatment to prepare a magnetic solid acid catalyst, which is subsequently added to a mixture of crude bio-oil and methanol to promote esterification and etherification reactions. The carbon-based catalyst powder in the reactor is separated from the liquid oil by magnetic attraction and reused. The liquid oil is then distilled to remove methanol and water from the mixture, yielding biodiesel for recycling.

[0005] The specific implementation steps of this invention are as follows: (1) After crushing the kitchen waste, mix it with dehydrated algae mud, add an accelerator to the mixed slurry, mix well and then perform hydrothermal treatment, and then perform solid-liquid separation to obtain solid products and liquid products containing water and oil. (2) Take a portion of the solid product and calcine it under a micro-oxygen environment. The resulting product is then mixed with concentrated sulfuric acid for sulfonation treatment to prepare a magnetic solid acid catalyst. (3) The liquid product obtained by the above hydrothermal treatment is allowed to stand and separate into layers and the aqueous solution is discarded. Solid acid catalyst and methanol are added to the collected oil layer to carry out esterification and etherification reactions.

[0006] (4) The product obtained from the above reaction is distilled at 100-103 °C to remove methanol and water from the mixture and recover biodiesel.

[0007] Preferably, in step (1), the mass ratio of kitchen waste to dehydrated algae mud is 4:1-10:1, the solid content in the mixed slurry is 8%-15%, and the algae mud is dehydrated algae mud from an algae-water separation station.

[0008] Preferably, the accelerator added in step (1) is ferrous sulfate, ferric chloride and potassium carbonate, and the accelerator is added at 0.8%-1.5% of the dry basis mass of the mixture.

[0009] Preferably, in step (1), the content of potassium carbonate accounts for 15%-30% of the total mass of the accelerator, and the mass ratio of ferrous sulfate to ferric chloride is 1:1-1:3.

[0010] Preferably, in step (1), the hydrothermal reaction temperature is 270-330 ℃, the processing time is 50-90 min, and the pressure is 7.0-12.5 MPa.

[0011] Preferably, in step (2), the oxygen content in the inert gas carrier gas during the magnetization roasting treatment of the carbon-based solid product is 0.2%-0.6%, the roasting temperature is 280-320 ℃, and the heat treatment time is 90-120 min.

[0012] Preferably, in step (2), during the sulfonation treatment, the mass ratio of carbon-based material to concentrated sulfuric acid is 1:5-1:10, the reaction temperature is 150-190 ℃, and the treatment time is 3-6 h.

[0013] Preferably, in step (3), the mass ratio of oil to methanol is 3.5:1 to 7.5:1, and the amount of solid acid catalyst added is 1.0% to 2.5% of the mass of the oil and methanol mixture.

[0014] Preferably, the temperature conditions for the esterification and etherification reactions are 85-110 °C, and the reaction time is 2-5 h.

[0015] Furthermore, in step (3), the esterification and etherification reactions are carried out at a temperature of 90-110 °C and for a reaction time of 3-5 h.

[0016] Compared with the prior art, the present invention has the following beneficial effects: (1) Kitchen waste and dehydrated algae mud were selected as raw materials for hydrothermal treatment, and accelerators were added to adjust the decomposition, oxidation and polymerization reaction process of organic materials to form crude bio-oil and carbon-based solids, thus realizing the efficient synergistic treatment of organic solid waste with high water content.

[0017] (2) The solid products from hydrothermal treatment can be directly recycled. A small portion of the solid products are then processed into magnetic solid acid catalysts through subsequent magnetization roasting and sulfonation to promote the esterification and etherification reactions of crude bio-oil and methanol, effectively improving the quality of biodiesel. The magnetic solid acid catalysts can be separated from the liquid oil by magnetic attraction and reused. The distillation condensate contains methanol and water, which can be further recovered through distillation and reused in the biodiesel synthesis process, effectively reducing the economic operating cost of the organic solid waste energy utilization technology. Attached Figure Description

[0018] Figure 1 Technological routes for the preparation of biodiesel.

[0019] Figure 2 The infrared spectra of the magnetic solid acid catalysts in Examples 1, 2, and 3 of this invention are shown. Detailed Implementation

[0020] The present invention will be further described below with reference to specific embodiments, and detailed implementation methods and operation processes are given. However, the scope of protection of the present invention is not limited to the content described.

[0021] Example 1 Crushed kitchen waste and dehydrated algae sludge were mixed at a mass ratio of 6:1 to obtain a homogeneous slurry with a solid content of 10%. An accelerator was added at 1.2% of the dry weight of the slurry, with potassium carbonate accounting for 23% of the total accelerator mass, and ferrous sulfate and ferric chloride in a mass ratio of 1:2. After mixing, the materials were hydrothermally treated for 70 min at 300 ℃, 11.5 MPa, and 200 rpm. After the reaction, the product was subjected to solid-liquid separation. The obtained solid product was heat-treated in a tubular electric furnace at 300 ℃ for 100 min in an inert carrier gas atmosphere with an oxygen content of 0.4%. The resulting magnetic carbon-based material was mixed with concentrated sulfuric acid at a mass ratio of 1:7 and then transferred to a reaction vessel for sulfonation at 170 ℃ for 5 h to obtain a magnetic solid acid catalyst. The liquid product obtained from hydrothermal treatment was subjected to oil-water separation. The oil layer was collected and mixed with methanol at a mass ratio of 5.5:1. A solid acid catalyst was added at 1.7% of the oil-methanol mixture, and the mixture was subjected to esterification / etherification reaction in a reactor at 105 °C for 2 h. Subsequently, the mixture was distilled at 102 °C to remove methanol and water, and biodiesel was recovered.

[0022] After the above method, the crude oil obtained by hydrothermal treatment has an esterification rate of 65.2% when reacted with methanol, and a biodiesel yield of 36.6%.

[0023] Example 2 Kitchen waste and algal sludge were mixed at a mass ratio of 4:1 to obtain a homogeneous slurry with a solid content of 8%. An accelerator, composed of ferrous sulfate and ferric chloride in a 1:1 ratio and containing 15% potassium carbonate, was added at 0.8% of the slurry's dry weight. The mixture was hydrothermally treated at 330 °C and 12.5 MPa for 50 min, followed by solid-liquid separation. The resulting solid product was heat-treated in an inert carrier gas atmosphere (0.6% oxygen content) in a tubular electric furnace at 320 °C for 90 min. The resulting magnetic carbon-based material was mixed with concentrated sulfuric acid at a mass ratio of 1:10 and then transferred to a reaction vessel for sulfonation at 190 °C for 3 h to obtain a magnetic solid acid catalyst. The liquid product obtained from hydrothermal treatment was subjected to oil-water separation. The oil layer was collected and mixed with methanol at a mass ratio of 7.5:1. A solid acid catalyst was added at 2.5% of the oil-methanol mixture, and the mixture was subjected to esterification / etherification reaction in a reactor at 110 °C for 2 h. Subsequently, the mixture was distilled to remove methanol and water, and biodiesel was recovered. The remaining process conditions, unless otherwise mentioned, were the same as in Example 1.

[0024] After the above method, the crude oil obtained by hydrothermal treatment had an esterification rate of 67.4% when reacted with methanol, and a biodiesel yield of 34.3%.

[0025] Example 3 Kitchen waste and algal sludge were mixed at a mass ratio of 10:1 to obtain a homogeneous slurry with a solid content of 15%. An accelerator, composed of ferrous sulfate and ferric chloride in a 1:3 ratio and containing 30% potassium carbonate, was added at 1.5% of the slurry's dry weight. The mixture was hydrothermally treated at 275 °C and 7.3 MPa for 90 min. The resulting solid product was then heat-treated in a tubular furnace at 280 °C for 120 min in an inert carrier gas atmosphere with an oxygen content of 0.3%. The resulting magnetic carbon-based material was mixed with concentrated sulfuric acid at a mass ratio of 1:5 and transferred to a reactor for sulfonation at 160 °C for 6 h to obtain a magnetic solid acid catalyst. The liquid product obtained from the hydrothermal treatment was subjected to oil-water separation. The oil layer was collected and mixed with methanol at a mass ratio of 3.8:1. A solid acid catalyst was added at 1.2% of the oil-methanol mixture, and the mixture was subjected to esterification / etherification in a reactor at 90 °C for 3.5 h. Subsequently, the mixture was distilled to remove methanol and water, recovering biodiesel. The remaining unmentioned process conditions were the same as in Example 1.

[0026] After the above method, the crude oil obtained by hydrothermal treatment has an esterification rate of 62.3% when reacted with methanol, and a biodiesel yield of 38.8%.

Claims

1. A method for co-producing biodiesel from kitchen waste and algal sludge, characterized in that... Includes the following steps: (1) Mix kitchen waste with algae mud, add an accelerator to the mixed slurry, mix well and then perform hydrothermal treatment, followed by solid-liquid separation to obtain solid products and liquid products containing water and oil. (2) Take a portion of the solid product and subject it to magnetization roasting under micro-oxygen conditions, then mix it with concentrated sulfuric acid for sulfonation treatment to prepare a solid acid catalyst; (3) After hydrothermal treatment, the aqueous phase of the liquid product is discarded, and solid acid catalyst and methanol are added to the collected oil layer to carry out esterification and etherification reactions. (4) The product obtained in step (3) is distilled at 100-103 °C to remove methanol and water from the mixture and obtain biodiesel for recycling.

2. The method according to claim 1, characterized in that... In step (1), the mass ratio of kitchen waste to algae mud is 4:1-10:1, the solid content in the mixed slurry is 8%-15%, and the algae mud is dehydrated algae mud from the algae-water separation station.

3. The method according to claim 1, characterized in that... In step (1), the accelerators are ferrous sulfate, ferric chloride and potassium carbonate, and the amount of accelerator added is 0.8%-1.5% of the dry basis mass of the mixed slurry.

4. The method according to claim 3, characterized in that... Potassium carbonate accounts for 15%-30% of the total mass of the accelerator, and the mass ratio of ferrous sulfate to ferric chloride is 1:1-1:

3.

5. The method according to claim 1, characterized in that... The hydrothermal treatment conditions in step (1) are: reaction temperature of 270-330 ℃, operating pressure of 7.0-12.5 MPa, and treatment time of 50-90 min.

6. The method according to claim 1, characterized in that... In step (2), the oxygen content in the inert carrier gas during the magnetization roasting treatment of the solid product is 0.2%-0.6%, the roasting temperature is 280-320 ℃, and the heat treatment time is 90-120 min.

7. The method according to claim 1, characterized in that... In step (2) sulfonation, the mass ratio of magnetized roasted hydrothermal carbon to concentrated sulfuric acid is 1:5-1:10, the operating temperature is 150-190 ℃, and the reaction time is 3-6 h.

8. The method according to claim 1, characterized in that... In step (3), the mass ratio of collected oil to added methanol is 3.5:1 to 7.5:1, and the amount of solid acid catalyst added is 1.0% to 2.5% of the mass of the oil and methanol mixture.

9. The method according to claim 1, characterized in that... The temperature conditions for the esterification and etherification reactions in step (3) are 85-110 °C and the reaction time is 2-5 h.

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