A method for producing a mixed oil and a method for producing biodiesel

Abstract

The present disclosure relates to a method for preparing mixed oil and a method for preparing biodiesel, which comprises: feeding raw oil and saturated monohydric alcohol into a fixed bed reactor in a continuous feeding mode, and reacting with a solid catalyst; the solid catalyst comprises an acidic molecular sieve and an inert binder, the acidic molecular sieve comprises one or more of ZSM-5 molecular sieve with a silicon-aluminum ratio of 100 or more, ZSM-48 molecular sieve with a silicon-aluminum ratio of 100 or more, beta molecular sieve with a silicon-aluminum ratio of 20 or more, X-type molecular sieve with a silicon-aluminum ratio of 1 or more, and NaY molecular sieve with a silicon-aluminum ratio of 2 or more, wherein the silicon-aluminum ratio is the molar ratio of SiO2 to Al2O3 in the acidic molecular sieve; the raw oil comprises glycerol trimethyl ester and fatty acid. The present disclosure packs the solid catalyst in the fixed bed reactor, and feeds the raw oil and saturated monohydric alcohol in a continuous feeding mode, and the product is free of catalyst and has low acid value, which can be directly used for preparing biodiesel, and the operation steps are simple.

Description

Technical Field

[0001] This disclosure relates to a method for preparing a mixed oil and a method for preparing biodiesel. Background Technology

[0002] Energy is a key factor in my country's sustained and stable economic development. my country is poor in oil resources, and since the 21st century, its dependence on imported oil has exceeded 60%. Biomass energy, represented by renewable biodiesel, is an important energy supplement. Biodiesel produced from inexpensive raw materials such as waste animal and vegetable oils, swill, and waste cooking oil is a beneficial research direction. On the one hand, it turns waste into treasure, protecting the environment and public health; on the other hand, it can partially replace fossil fuels, reducing emissions of harmful substances such as sulfur, nitrogen, and aromatic hydrocarbons. Waste cooking oil comes from food waste and liquid waste from kitchen washing, and generally contains high levels of free fatty acids (acid value 20-60 mg KOH / g). Statistics show that my country's annual total oil production exceeds 50 million tons, with waste oil accounting for about 10 million tons. Assuming a collection rate of 30%-50%, 3-5 million tons of oil can be utilized annually. Converting waste oil into clean biodiesel and its derivatives has significant social and economic benefits.

[0003] For high-acid-value swill oil, both domestically and internationally, the current common method is a combination of concentrated sulfuric acid-catalyzed esterification deacidification and alkali-catalyzed transesterification to produce fatty acid methyl esters, as described in CN102533455A. This method suffers from drawbacks such as sulfuric acid wastewater and waste residue discharge, and excessive saponification reactions. Meanwhile, some researchers have utilized the reaction of glycerol with high-acid oils to generate triglycerides, reducing the free fatty acid value to below 1-2 mgKOH / g, followed by a subsequent alkali-catalyzed transesterification reaction. Chinese patents CN105623861B, CN104694256A, and CN111500373A have disclosed glycerol esterification deacidification processes, using a multi-reactor series connection to reduce the acid value to 1.0 mgKOH / g. The catalyst used is calcium glycerol, which is regenerated through processes such as de-alcoholization, sedimentation, and glycerol distillation. This method suffers from the use of homogeneous catalysts and the need for product refining and separation. CN101638609A mentions a supercritical method for preparing biodiesel, in which both esterification and transesterification reactions are carried out at high temperature and high pressure, showing good results for high-acid-value oils with an acid value ranging from 3 to 200 mg KOH / g. The pre-esterification stage is carried out at temperatures above 220°C, with a methanol-to-oil molar ratio of 10, a temperature of 240°C, and a pressure of 9 MPa. Under catalyst-free conditions, the acid value can be reduced to 1.0-2.0 mg KOH / g. No acidic or alkaline catalyst residues are found in the product. Yang Dongyuan et al. [Grains and Oils, 2009, (6) 18-20] proposed using arginine as a catalyst to catalyze the preparation of biodiesel from waste oils under supercritical methanol conditions. However, the operating conditions are harsh, the reaction pressure exceeds 8 MPa, the investment in the reaction equipment is high, and the technical and economic efficiency is poor. Researchers at home and abroad have also used solid acid catalysts to prepare biodiesel. For example, Lan Zhanwei et al. [Petrochemical Applications, 2014, 33(11), 80-83] used MCM-41 as a base and modified with sulfonic acid as a catalyst to carry out transesterification and pre-esterification reactions of high-acid cottonseed oil. The single-pass conversion rate was less than 88%, and the efficiency was low.

[0004] In summary, conventional swill esterification and pre-esterification reactions either employ homogeneous acidic catalysts and batch operations, resulting in catalyst residues in the product, complex subsequent treatment, and high emissions of waste; or they involve reactions under supercritical conditions, high temperature and high pressure operations, which place high demands on the corrosion and pressure resistance of the equipment and result in poor technical and economic efficiency. Summary of the Invention

[0005] The purpose of this disclosure is to provide a method for preparing a mixed oil and a method for preparing biodiesel. The product prepared by this method has no catalyst residue, the operation steps are simple, and the prepared mixed oil has a low acid value, which can be directly used to prepare biodiesel.

[0006] To achieve the above objectives, the first aspect of this disclosure provides a method for preparing mixed oils, the method comprising: feeding raw oils and saturated monohydric alcohols into a fixed-bed reactor in a continuous feeding manner, and reacting them with a solid catalyst;

[0007] The solid catalyst comprises an acidic molecular sieve and an inert binder. The acidic molecular sieve comprises one or more of the following: ZSM-5 molecular sieve with a silica-to-alumina ratio of 100 or more, ZSM-48 molecular sieve with a silica-to-alumina ratio of 100 or more, β molecular sieve with a silica-to-alumina ratio of 20 or more, X-type molecular sieve with a silica-to-alumina ratio of 1 or more, and NaY molecular sieve with a silica-to-alumina ratio of 2 or more. The silica-to-alumina ratio is the molar ratio of SiO2 to Al2O3 in the acidic molecular sieve.

[0008] The raw material oils include trimethyl glycerol and fatty acids.

[0009] Optionally, the acidic molecular sieve includes one or more of the following: ZSM-5 molecular sieve with a silica-to-alumina ratio of 100-200, ZSM-48 molecular sieve with a silica-to-alumina ratio of 100-200, β molecular sieve with a silica-to-alumina ratio of 20-100, X-type molecular sieve with a silica-to-alumina ratio of 1-1.5, and NaY molecular sieve with a silica-to-alumina ratio of 2-30.

[0010] The inert binder includes one or more of boehmite, silica sol, and graphite binders;

[0011] Optionally, the content of the acidic molecular sieve is 75-98% by weight and the content of the inert binder is 2-25% by weight relative to the total weight of the solid catalyst.

[0012] Optionally, the raw material oil includes swill acid extracted from kitchen waste and / or high-acid oil after processing waste kitchen oil;

[0013] The acid value of the raw material oil is 20-200 mg KOH / g;

[0014] The fatty acid content is 10-80% by weight relative to the total weight of the raw oil.

[0015] Optionally, the solid catalyst is spherical with a diameter of 0.5-3.0 mm; or,

[0016] The solid catalyst is in strip shape and has a length of 3-8 mm.

[0017] Optionally, the saturated monohydric alcohol includes one or more of saturated monohydric alcohols having 1-3 carbon atoms, preferably methanol and / or ethanol;

[0018] The fatty acids include one or more of lauric acid, myristic acid, palmitic acid, oleic acid, linoleic acid, and linolenic acid.

[0019] Optionally, the conditions for the contact reaction include: a temperature of 180-280°C and a pressure of 0.5-3.0 MPa;

[0020] Based on the total weight of the raw material oils, the feed mass hourly space velocity is 0.1-1.0 h⁻¹. -1 The weight ratio of the raw material oil to the saturated monohydric alcohol is 3:(1-9).

[0021] Optionally, the method further includes: preheating the raw material oil and the saturated monohydric alcohol before introducing them into the fixed-bed reactor before the contact reaction, wherein the preheating temperature is 160-260°C.

[0022] Optionally, the method further includes: flash evaporating the mixture obtained from the contact reaction to obtain a flash vapor phase and a flash liquid phase containing the mixed oil, condensing the flash vapor phase, and returning the resulting condensate as a supplementary saturated monohydric alcohol to the fixed-bed reactor to continue the contact reaction;

[0023] The flash evaporation conditions include: a temperature of 100-180℃ and a pressure of 10... 4 -10 5 Pa.

[0024] Optionally, the acid value of the mixed oil is less than 2.0 mg KOH / g.

[0025] The second aspect of this disclosure provides a method for preparing biodiesel, the method comprising: preparing a mixed oil using the method described in the first aspect of this disclosure, and subjecting the mixed oil to a transesterification reaction in the presence of an alkaline catalyst.

[0026] Optionally, the alkaline catalyst comprises an organic base and / or an inorganic base;

[0027] Optionally, the alkaline catalyst includes one or more of sodium methoxide, sodium ethoxide, NaOH, KOH, and Ca(OH)2;

[0028] The conditions for the transesterification reaction include: a temperature of 30-80℃ and a retention time of 1-12h.

[0029] Through the above technical solution, this disclosure loads a solid catalyst into a continuous operation reactor and feeds raw oil and saturated monohydric alcohol in a continuous feeding manner to prepare mixed oil. The above method can achieve online water separation without the use of a dehydrating agent and reduce the acid value of the mixed oil. There is no catalyst residue in the product, and no catalyst separation is required after the reaction. The operation steps are simple, and the prepared product has a low acid value and can be directly used to prepare biodiesel. It is especially suitable for the production of biodiesel from waste oil, high-acid oil, and free fatty acids.

[0030] Other features and advantages of this disclosure will be described in detail in the following detailed description section. Detailed Implementation

[0031] The following provides a detailed description of specific embodiments of this disclosure. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of this disclosure.

[0032] The first aspect of this disclosure provides a method for preparing a mixed oil, the method comprising: feeding raw oil and saturated monohydric alcohol into a fixed-bed reactor in a continuous feeding manner, and reacting them with a solid catalyst;

[0033] The solid catalyst comprises an acidic molecular sieve and an inert binder. The acidic molecular sieve comprises one or more of the following: ZSM-5 molecular sieve with a silica-to-alumina ratio of 100 or more, ZSM-48 molecular sieve with a silica-to-alumina ratio of 100 or more, β molecular sieve with a silica-to-alumina ratio of 20 or more, X-type molecular sieve with a silica-to-alumina ratio of 1 or more, and NaY molecular sieve with a silica-to-alumina ratio of 2 or more. The silica-to-alumina ratio is the molar ratio of SiO2 to Al2O3 in the acidic molecular sieve.

[0034] The raw material oils include trimethyl glycerol and fatty acids.

[0035] This disclosure utilizes a solid acid catalyst containing acidic molecular sieves to achieve continuous conversion of fatty acids in feedstock oils into fatty acid esters in a fixed-bed reaction. Simultaneously, transesterification may occur, converting a portion of the trimethylglycerol esters into fatty acid esters. Because homogeneous organic and inorganic acids such as sulfuric acid and benzenesulfonic acid are not used, the product contains no metal or conventional catalyst acid residues, eliminating the need for subsequent alkali neutralization and product washing processes, and preventing the generation of acidic wastewater. The solid catalyst itself is hydrophobic, allowing water to be carried from the catalyst surface into the gas phase during the reaction. This phase equilibrium transfer improves the conversion rate, and a low-acid-value product can be obtained in a single pass, satisfying the requirements for subsequent alkali-catalyzed transesterification reactions. The overall process is highly efficient and environmentally friendly, safe and simple to operate, highly controllable, and adaptable to various feedstocks. Furthermore, the use of a fixed-bed reactor offers higher production efficiency compared to traditional reactors.

[0036] In this disclosure, the raw material oils are mainly derived from waste cooking oils and swill, including, for example, swill acid extracted from swill and / or high-acid oils after processing waste cooking oils; the acid value of the raw material oils is 20-200 mg KOH / g; and the fatty acid content is 10-80% by weight relative to the total weight of the raw material oils. The method of this disclosure can efficiently convert fatty acids in swill and waste cooking oils into fatty acid esters, and can also convert some of the trimethyl glycerols in them into fatty acid esters through transesterification.

[0037] According to one embodiment of this disclosure, the acidic molecular sieve includes one or more of the following: ZSM-5 molecular sieve with a silica-to-alumina ratio of 100-200, ZSM-48 molecular sieve with a silica-to-alumina ratio of 100-200, β molecular sieve with a silica-to-alumina ratio of 20-100, X-type molecular sieve with a silica-to-alumina ratio of 1-1.5, and NaY molecular sieve with a silica-to-alumina ratio of 2-30. For example, the silica-to-alumina ratio of ZSM-5 molecular sieve can be 120 or 200; the silica-to-alumina ratio of ZSM-48 molecular sieve can be 150, 180, or 200.

[0038] According to one embodiment of this disclosure, the type of inert binder is conventional in the art, including one or more of boehmite, silica sol, and graphite binders.

[0039] According to one embodiment of this disclosure, the content of acidic molecular sieve is 75-98% by weight and the content of inert binder is 2-25% by weight relative to the total weight of the solid catalyst.

[0040] According to one embodiment of this disclosure, the solid catalyst can be of any shape. Preferably, the solid catalyst is spherical with a diameter of 0.5-3.0 mm; or, the solid catalyst is strip-shaped with a length of 3-8 mm. The cross-section of the strip-shaped catalyst can be of any shape, such as circular, rectangular, or irregular. The strip-shaped catalyst can be cylindrical with a length of 3-8 mm and a diameter of 1-3 mm.

[0041] According to one embodiment of this disclosure, the solid catalyst is formed in a conventional manner in the art, such as ball forming, extrusion forming or tablet forming, and the specific steps are not described in detail here.

[0042] According to one embodiment of this disclosure, the saturated monohydric alcohol includes one or more of saturated monohydric alcohols having 1-3 carbon atoms, preferably methanol and / or ethanol; the fatty acid includes fatty acids having 12-24 carbon atoms, preferably one or more of lauric acid, myristic acid, palmitic acid, oleic acid, linoleic acid and linolenic acid.

[0043] According to one embodiment of this disclosure, the contact reaction conditions include: a temperature of 180-280°C and a pressure of 0.5-3.0 MPa; and a feed mass hourly space velocity (WHSV) of 0.1-1.0 h⁻¹, based on the total weight of the raw material oils. -1 The weight ratio of raw oil to saturated monohydric alcohol is 3:(1-9); the contact reaction temperature can be any temperature between 180-280℃, such as 200℃, 210℃, 220℃, 240℃, 250℃, etc.; the contact reaction pressure can be any pressure between 0.5-3.0MPa, such as 0.8MPa, 1.0MPa, 1.2MPa, 1.5MPa, 2.5MPa, etc.; the feed mass hourly space velocity can be 0.1-1.0h. -1 Any mass space velocity between these values, for example, could be 0.3h. -1 0.4h -1 0.5h -1 1.0h -1 wait.

[0044] In this disclosure, "feeding the raw material oil and saturated monohydric alcohol into the fixed bed reactor in a continuous feeding manner" can mean feeding the raw material oil and saturated monohydric alcohol into the fixed bed reactor in a continuous feeding manner, or feeding the raw material oil and saturated monohydric alcohol into the fixed bed reactor in a continuous feeding manner after mixing them.

[0045] According to one embodiment of this disclosure, the method further includes: preheating the raw material oil and saturated monohydric alcohol before the contact reaction and then introducing them into a fixed-bed reactor, wherein the preheating temperature is 160-260°C; specifically, the raw material oil and saturated monohydric alcohol can be preheated separately by passing them into heat exchangers, then mixed by a mixer, and then introduced into the fixed-bed reactor.

[0046] According to one embodiment of this disclosure, the method further includes: flash evaporating the mixture obtained from the contact reaction to obtain a flash vapor phase and a flash liquid phase containing the mixed oils; condensing the flash vapor phase; and returning the resulting condensate as a supplementary saturated monohydric alcohol to the fixed-bed reactor for continued contact reaction; the flash evaporation conditions include: a temperature of 100-180°C and a pressure of 10... 4 -10 5 Pa. The above-described flash evaporation treatment can further improve the conversion rate of saturated monohydric alcohols.

[0047] According to one embodiment of this disclosure, the mixed oil comprises trimethyl glycerol and fatty acid esters, and the acid value of the mixed oil is less than 2.0 mg KOH / g.

[0048] The second aspect of this disclosure provides a method for preparing biodiesel, the method comprising: preparing a mixed oil using the method described in the first aspect of this disclosure, and subjecting the mixed oil to a transesterification reaction in the presence of an alkaline catalyst.

[0049] According to one embodiment of this disclosure, the conditions for the transesterification reaction include: a temperature of 30-80°C, a retention time of 1-12 hours, and a pressure typically at atmospheric pressure. The "retention time" refers to the duration of the transesterification reaction in the reactor.

[0050] According to one embodiment of this disclosure, the alkaline catalyst used in the transesterification reaction is conventional in the art, such as an organic base and / or an inorganic base; specifically, it may include one or more of sodium methoxide, sodium ethoxide, NaOH, KOH and Ca(OH)2.

[0051] According to one embodiment of this disclosure, the amount of alkaline catalyst used is 0.5-5.0% by weight relative to the total mass of the mixed oils.

[0052] According to one embodiment of this disclosure, the reactor for the transesterification reaction is conventional in the art, such as a stirred tank reactor or a tubular reactor.

[0053] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way.

[0054] All raw materials used in the examples and comparative examples were obtained commercially and, unless otherwise specified, were of analytical grade.

[0055] The acid value test method is the SH / T 0264 standard method, which involves dissolving the sample in an ethanol-water solution and then titrating the acid amount with KOH.

[0056] Example 1

[0057] NaY molecular sieves with a silica-to-alumina ratio of 2.6 and silica sol as an inert binder were rolled into spheres to obtain spherical catalysts with a diameter of 1.5 mm. The content of NaY molecular sieves was 95% by weight, and the content of the inert binder was 5% by weight relative to the total weight of the catalyst. Raw material oil with an acid value of 120 mg KOH / g and methanol were pumped separately into a heat exchanger and preheated to 200 °C. Then, the mixture was fed into a fixed-bed reactor with an inner diameter of 12 mm. The catalyst loading was 15.0 g, the feed method was top-in, bottom-out, the reaction temperature was 240 °C, the reaction pressure was 1.5 MPa, and the mass hourly space velocity (HHSV) was 0.3 h⁻¹ based on the total weight of the raw material oil. -1The raw material oil and methanol are in a weight ratio of 3:1.8. The mixture is passed through a single-pass reactor and converted to obtain a mixture. This mixture is then subjected to flash evaporation to obtain a flash vapor phase and a flash liquid phase containing the mixed oil. The flash vapor phase is condensed, and the resulting condensate is returned to the fixed-bed reactor as a supplementary saturated monohydric alcohol for further contact reaction. The flash evaporation temperature is 110℃ and the pressure is 10... 4 Pa, the mixed oil after single-pass conversion is divided into upper and lower phases. After mixing, the acid value is titrated and the acid value is 1.35 mg KOH / g;

[0058] Biodiesel was prepared by transesterification of mixed oils in a stirred tank reactor in the presence of KOH catalyst (0.1% of the total mass of oils). The transesterification conditions included a temperature of 40°C, a pressure of atmospheric pressure, and a retention time of 4 hours.

[0059] The raw material oil is derived from swill acid extracted from kitchen waste, which includes trimethyl glycerol and fatty acids. The fatty acid content is 56% by weight, and the fatty acid is palmitic acid.

[0060] Example 2

[0061] ZSM-48 molecular sieve with a silica-to-alumina ratio of 180 was extruded with boehmite as an inert binder to obtain strip-shaped catalysts with diameters of 1.5 mm and 3-6 mm. The content of ZSM-48 molecular sieve was 88% by weight, and the content of inert binder was 12% by weight. Raw material oil with an acid value of 188 mg KOH / g and methanol were pumped separately into a heat exchanger and preheated to 200°C. Then, the mixture was fed into a fixed-bed reactor with an inner diameter of 12 mm. The catalyst loading was 15.0 g, the feed method was top-in, bottom-out, the reaction temperature was 200°C, the reaction pressure was 1.0 MPa, and the mass hourly space velocity (HHSV) was 0.4 h⁻¹ based on the total weight of the raw material oil. -1 The raw material oil and methanol are in a weight ratio of 3:2. The mixture is passed through a single-pass reactor and converted to obtain a mixture. This mixture is then subjected to flash evaporation to obtain a flash vapor phase and a flash liquid phase containing the mixed oil. The flash vapor phase is condensed, and the resulting condensate is returned to the fixed-bed reactor as a supplementary saturated monohydric alcohol for further contact reaction. The flash evaporation temperature is 110℃ and the pressure is 10... 4 Pa, the mixed oil after single-pass conversion is divided into upper and lower phases, with acid values ​​of 1.20 mg KOH / g and 1.65 mg KOH / g, respectively. The main component of the upper layer material is fatty acid methyl ester.

[0062] Biodiesel was prepared by transesterification of mixed oils in a stirred tank reactor in the presence of sodium ethoxide catalyst (0.1% of the total mass of the mixed oils). The transesterification conditions included a temperature of 50°C, a pressure of atmospheric pressure, and a retention time of 3 hours.

[0063] The raw material oil is derived from swill acid extracted from kitchen waste, which includes trimethyl glycerol and fatty acids. The fatty acid content is 85% by weight, and the fatty acid is oleic acid.

[0064] Example 3

[0065] X-type molecular sieves with a silica-to-alumina ratio of 1 and pseudoboehmite as an inert binder were extruded to obtain cylindrical catalysts with a diameter of φ1.5mm × 3mm. The content of X-type molecular sieves was 85% by weight, and the content of inert binder was 15% by weight. Raw material oil with an acid value of 40 mg KOH / g and methanol were pumped separately into a heat exchanger and preheated to 200℃. Then, the mixture was fed into a fixed-bed reactor with an inner diameter of 12mm and a catalyst loading of 15.0g. The feed method was top-in, bottom-out. The reaction temperature was 240℃, the reaction pressure was 1.2 MPa, and the mass hourly space velocity (HHSV) was 0.5 h⁻¹ based on the total weight of the raw material oil. -1 The raw material oil and methanol are in a weight ratio of 3:2.4. The mixture is passed through a single-pass reactor and converted to obtain a mixture. This mixture is then subjected to flash evaporation to obtain a flash vapor phase and a flash liquid phase containing the mixed oil. The flash vapor phase is condensed, and the resulting condensate is returned to the fixed-bed reactor as a supplementary saturated monohydric alcohol for further contact reaction. The flash evaporation temperature is 110℃ and the pressure is 10... 4 Pa, the mixed oil after single-pass conversion is divided into upper and lower phases. After mixing, the acid value is titrated and the acid value is 1.60 mg KOH / g;

[0066] Biodiesel was prepared by transesterification of mixed oils in a tubular reactor in the presence of NaOH catalyst (0.1% of the total mass of oils). The transesterification conditions included a temperature of 60°C, a pressure of atmospheric pressure, and a retention time of 6 hours.

[0067] The raw material oil is derived from swill acid extracted from kitchen waste, which includes trimethyl glycerol and fatty acids. The fatty acid content is 21% by weight, and the fatty acids are a mixture of fatty acids with 16 carbon atoms.

[0068] Example 4

[0069] ZSM-5 molecular sieve with a silica-to-alumina ratio of 200 was mixed with graphite binder as an inert binder and pressed into cylindrical tablets with a diameter of φ5mm × 5mm. The content of ZSM-5 molecular sieve was 97% by weight, and the content of inert binder was 3% by weight. Raw material oil with an acid value of 140 mg KOH / g and methanol were pumped into a heat exchanger using two separate pumps and preheated to 200°C. The mixture was then fed into a fixed-bed reactor with an inner diameter of 12mm. The catalyst loading was 15.0g, the feed method was top-in, bottom-out, the reaction temperature was 250°C, the reaction pressure was 1.0 MPa, and the mass hourly space velocity (HHSV) was 0.5 h⁻¹ based on the total weight of the raw material oil. -1 The raw material oil and methanol are in a weight ratio of 3:1.8. The mixture is passed through a single-pass reactor and converted to obtain a mixture. This mixture is then subjected to flash evaporation to obtain a flash vapor phase and a flash liquid phase containing the mixed oil. The flash vapor phase is condensed, and the resulting condensate is returned to the fixed-bed reactor as a supplementary saturated monohydric alcohol for further contact reaction. The flash evaporation temperature is 110℃ and the pressure is 10... 4 Pa, the mixed oil after single-pass conversion is divided into upper and lower phases. After mixing, the acid value is titrated and the acid value is 1.15 mg KOH / g;

[0070] Biodiesel was prepared by transesterification of mixed oils in a stirred tank reactor in the presence of KOH catalyst (0.1% of the total mass of oils). The transesterification conditions included a temperature of 40°C, a pressure of atmospheric pressure, and a retention time of 10 h.

[0071] The raw material oil is derived from swill acid extracted from kitchen waste, which includes trimethyl glycerol and fatty acids. The fatty acid content is 68% by weight, and the fatty acids are a mixture of fatty acids with 12-14 carbon atoms, mainly palmitic acid.

[0072] Comparative Example 1

[0073] ZNP-type acidic molecular sieves with a silica-to-alumina ratio of 15 were extruded with boehmite as an inert binder to obtain strip-shaped catalysts with a diameter of 2.0 mm and a length of 3-5 mm. The content of ZNP-type acidic molecular sieves was 90% by weight, and the content of inert binder was 10% by weight. Raw material oil with an acid value of 188 mg KOH / g and methanol were pumped separately into a heat exchanger and preheated to 200°C. Then, the mixture was fed into a fixed-bed reactor with an inner diameter of 12 mm and a catalyst loading of 15.0 g. The feed method was top-in, bottom-out. The reaction temperature was 220°C, the reaction pressure was 1.0 MPa, and the mass hourly space velocity (HHSV) was 0.4 h⁻¹, based on the total weight of the raw material oil. -1The raw material oil and methanol are in a weight ratio of 3:2. The mixture is passed through a single-pass reactor and converted to obtain a mixture. This mixture is then subjected to flash evaporation to obtain a flash vapor phase and a flash liquid phase containing the mixed oil. The flash vapor phase is condensed, and the resulting condensate is returned to the fixed-bed reactor as a supplementary saturated monohydric alcohol for further contact reaction. The flash evaporation temperature is 110℃ and the pressure is 10... 4 Pa, the mixed oil after a single-pass conversion is divided into upper and lower phases, with acid values ​​of 30.5 mg KOH / g and 20.1 mg KOH / g, respectively;

[0074] The mixed oils obtained by this catalyst are too acidic and will undergo saponification in the presence of an alkaline catalyst, thus preventing them from directly entering the transesterification process.

[0075] The raw material oil is derived from swill acid extracted from kitchen waste, which includes trimethyl glycerol and fatty acids. The fatty acid content is 85% by weight, and the fatty acids are a mixture of fatty acids with 12-14 carbon atoms, mainly palmitic acid.

[0076] Based on the above data, it can be seen that by using the method disclosed herein, a mixed oil containing trimethyl glycerol and fatty acid esters can be prepared from raw material oils derived from kitchen waste and / or waste cooking oils and saturated monohydric alcohols. The product has a low acid value, which can meet the requirements for subsequent biodiesel production.

[0077] The preferred embodiments of this disclosure have been described in detail above. However, this disclosure is not limited to the specific details of the above embodiments. Within the scope of the technical concept of this disclosure, various simple modifications can be made to the technical solutions of this disclosure, and all such simple modifications fall within the protection scope of this disclosure.

[0078] It should also be noted that the various specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, this disclosure will not describe the various possible combinations separately.

[0079] Furthermore, various different embodiments of this disclosure can be combined in any way, as long as they do not violate the spirit of this disclosure, they should also be regarded as the content disclosed in this disclosure.

Claims

1. A method for preparing a mixed oil, characterized in that, The method includes: feeding raw oil and saturated monohydric alcohol into a fixed-bed reactor in a continuous feeding manner, reacting with a solid catalyst to obtain the mixed oil; The conditions for the contact reaction include: a temperature of 180-280℃ and a pressure of 0.5-3.0 MPa; Based on the total weight of the raw material oils, the feed mass hourly space velocity is 0.1-1.0 h⁻¹. -1 The weight ratio of the raw material oil to the saturated monohydric alcohol is 3:(1-9). The method further includes: flash evaporating the mixture obtained from the contact reaction to obtain a flash vapor phase and a flash liquid phase containing the mixed oil, condensing the flash vapor phase, and returning the resulting condensate as a supplementary saturated monohydric alcohol to the fixed-bed reactor to continue the contact reaction; The solid catalyst comprises an acidic molecular sieve and an inert binder. The acidic molecular sieve is a ZSM-48 molecular sieve with a silicon-to-aluminum ratio of 100 or higher, wherein the silicon-to-aluminum ratio is the molar ratio of SiO2 to Al2O3 in the acidic molecular sieve. The raw material oils include trimethyl glycerol and fatty acids; The solid catalyst is hydrophobic.

2. The preparation method according to claim 1, wherein, The acidic molecular sieve is ZSM-48 molecular sieve with a silica-alumina ratio of 100-200; The inert binder is one or more of boehmite, silica sol, and graphite binder.

3. The preparation method according to claim 1, wherein, The content of the acidic molecular sieve is 75-98% by weight relative to the total weight of the solid catalyst, and the content of the inert binder is 2-25% by weight.

4. The preparation method according to claim 1, wherein, The acid value of the raw material oil is 20-200 mg KOH / g; The fatty acid content is 10-80% by weight relative to the total weight of the raw oil.

5. The preparation method according to claim 1, wherein, The solid catalyst is spherical with a diameter of 0.5-3.0 mm; or, The solid catalyst is in strip shape and has a length of 3-8 mm.

6. The preparation method according to claim 1, wherein, The saturated monohydric alcohol includes one or more of the saturated monohydric alcohols having 1-3 carbon atoms; The fatty acid is one or more of lauric acid, myristic acid, palmitic acid, oleic acid, linoleic acid and linolenic acid.

7. The preparation method according to claim 1, wherein, The saturated monohydric alcohol is methanol and / or ethanol.

8. The preparation method according to claim 1, wherein, The method further includes: before the contact reaction, preheating the raw material oil and the saturated monohydric alcohol before introducing them into the fixed-bed reactor, wherein the preheating temperature is 160-260℃.

9. The preparation method according to claim 1, wherein, The flash evaporation conditions include: a temperature of 100-180℃ and a pressure of 10... 4 -10 5 Pa.

10. The preparation method according to claim 1, wherein, The acid value of the mixed oil is less than 2.0 mg KOH / g.

11. A method for preparing biodiesel, characterized in that, The method includes: preparing a mixed oil using the method described in any one of claims 1-10, and subjecting the mixed oil to transesterification in the presence of an alkaline catalyst.

12. The preparation method according to claim 11, wherein, The alkaline catalyst includes organic bases and / or inorganic bases; The conditions for the transesterification reaction include: a temperature of 30-80℃ and a retention time of 1-12h.

13. The preparation method according to claim 11, wherein, The alkaline catalyst includes one or more of sodium methoxide, sodium ethoxide, NaOH, KOH, and Ca(OH)2.