A method for increasing the yield of biodiesel

Abstract

The present application provides a method for improving the yield of biodiesel, comprising: contacting and reacting low-acid-value oil and fat with monohydric alcohol in the presence of metal oxide or sulfide catalyst, characterized in that carboxylic acid or high-acid-value oil and fat is additionally added. The method of the present application can effectively solve the problem of low activity of various metal oxide or metal sulfide catalysts when used for preparing biodiesel from low-acid-value oil raw materials, expand the application range of oxide or sulfide catalysts, obtain high-yield biodiesel at lower temperature and pressure, and greatly reduce the investment in devices since the reaction is carried out at low pressure.

Description

Technical Field

[0001] This invention relates to a method for preparing biodiesel by reacting oils and monohydric alcohols. Background Technology

[0002] Biodiesel can be produced through transesterification of oils and fats with monohydric alcohols. The reaction products include monoalkyl fatty acid esters (i.e., biodiesel), as well as monoglycerides, diglycerides, glycerol, and unreacted alcohols and oils (i.e., triglycerides). Existing biodiesel preparation methods can be categorized into acid-catalyzed methods, base-catalyzed methods, enzyme-catalyzed methods, and supercritical methods.

[0003] CN1473907A uses by-products from vegetable oil refining and recycled edible oil as raw materials. The catalyst is a compound of inorganic or organic acids such as sulfuric acid, hydrochloric acid, p-toluenesulfonic acid, dodecylbenzenesulfonic acid, and naphthalenesulfonic acid. Production involves acidification to remove impurities, continuous dehydration, esterification, separation, and vacuum distillation. Continuous vacuum dehydration is carried out at a pressure of 0.08-0.09 MPa and a temperature of 60-95℃, dehydrating to a water content below 0.2%. In the esterification step, the catalyst addition is 1-3%, the esterification temperature is 60-80℃, and the reaction time is 6 hours. After the reaction, the product is first neutralized to remove the catalyst, then separated to remove water. The dehydrated product is then subjected to vacuum distillation to obtain biodiesel. However, the acid-catalyzed reaction is slow and produces a large amount of waste acid, polluting the environment.

[0004] The method disclosed in DE3444893 uses an acid catalyst, atmospheric pressure, and 50-120°C to esterify free fatty acids with alcohols, pre-esterifying the oil before proceeding with transesterification under an alkali metal catalyst. However, the remaining acid catalyst needs to be neutralized by the alkali, increasing the amount of alkali metal catalyst required. Pre-esterification lengthens the processing time, significantly increases equipment investment and energy consumption. Furthermore, the alkali catalyst needs to be removed from the product, generating substantial wastewater and making glycerol recovery difficult.

[0005] In the method disclosed in US5713965A, fatty acid methyl esters, i.e. diesel engine fuel, are prepared by reacting oils and alcohols with hexane as a solvent in the presence of lipase.

[0006] The method disclosed in CN1472280A uses fatty acid esters as acyl acceptors to catalyze the transesterification reaction of biological organisms to produce biodiesel in the presence of enzymes. The drawbacks of using enzyme catalysts are: long reaction time, low efficiency, high cost, and easy deactivation in high-purity methanol.

[0007] JP9905431 discloses a method for preparing fatty acid esters by reacting oils and fats with a monohydric alcohol. The method includes reacting methanol with oils and fats to obtain fatty acid esters. Under the conditions of 270-280°C and 11-12 MPa, the fatty acid methyl ester production rate is 55-60%.

[0008] As can be seen from the above, even with continuous medium- and high-pressure methods, the yield of fatty acid esters remains low without the addition of a catalyst. Catalytic methods, on the other hand, mostly use two types of catalysts: acids such as sulfuric acid and hydrochloric acid, and bases such as KOH, NaOH, and NaOR. Both types of catalysts are completely dissolved in the reaction system during the reaction, making it difficult to separate the product from the catalyst, resulting in significant post-treatment waste emissions and severe corrosion and pollution during application. Summary of the Invention

[0009] To overcome the above-mentioned defects, this invention proposes a method to improve biodiesel yield. This method can significantly improve the reactivity of low-acid-value feedstock oils and obtain a high biodiesel yield.

[0010] Experiments revealed that when low-acid-value oils undergo transesterification and esterification reactions with monohydric alcohols, the biodiesel yield is low under relatively low temperature and pressure if only a small amount of fatty acids, or only a small amount of oxides or sulfides, are added as catalysts. However, the biodiesel yield significantly increases when a small amount of fatty acids or high-acid-value oils are added simultaneously with a small amount of oxides or sulfides. For a few specific metal oxides or sulfides, the yield increase far exceeds expectations. The yield increase when fatty acids and metal oxides or sulfides are added simultaneously is much greater than the sum of the yield increases when fatty acids and metal oxides or sulfides are added separately.

[0011] The method for improving biodiesel yield provided by the present invention includes: reacting low-acid-value feedstock oil with a monohydric alcohol in the presence of a metal oxide or sulfide catalyst, wherein a carboxylic acid or high-acid-value oil is also added.

[0012] The metal oxide is selected from at least one oxide of Group IIB, IVB, VIB, VIIB, VIII, IIIA, IVA and rare earth metals, preferably oxides of zinc, titanium, zirconium, molybdenum, tungsten, manganese, iron, aluminum, lead and lanthanum, and more preferably at least one of zinc oxide, manganese oxide and lead oxide.

[0013] The metal sulfide is selected from one or more sulfides of group VIB, VIIB, VIII, IB and IIB metals, preferably at least one of zinc, copper, iron, nickel, molybdenum, tungsten and manganese sulfides, and more preferably at least one of iron sulfide, copper sulfide and manganese sulfide.

[0014] The catalyst is added in an amount of 0.01-5 wt% of the weight of the raw oil, preferably 0.1-5 wt%, and more preferably 0.1-2.5 wt%. The catalyst can be added to the oil or to a monohydric alcohol.

[0015] The term "oils and fats," as used in the terms "low-acid-value oils" and "high-acid-value oils," has a generally known meaning in this field. It is a general term for oils and fats, with fatty acid triglycerides as their main component. Generally, substances that are liquid at room temperature are called oils, while those that are solid or semi-solid at room temperature are called fats (or simply fats). The term "oils and fats" includes vegetable oils and animal oils, as well as oilseeds derived from microorganisms, algae, and even crude oil, waste oils, and spoiled oils. Crude oil refers to oils that are unrefined or whose refined oil does not meet product standards. Refining processes include, but are not limited to, degumming, alkali refining, dephosphorization, decolorization, and deodorization. Oils and fats may also contain a certain amount of unsaponifiable matter. Examples of vegetable oils include, but are not limited to, soybean oil, rapeseed oil, peanut oil, sunflower seed oil, palm oil, coconut oil, and substances containing fatty groups from the fruits, stems, leaves, branches, and roots of various other crops and wild plants (including wood pulp oil produced during papermaking). Examples of animal fats include, but are not limited to, lard, tallow, mutton tallow, and fish oil. A mixture of two or more types of oils can be used.

[0016] The low-acid-value oil can be refined oil or unrefined oil, with an acid value of less than 10 mg KOH / g, more preferably less than 3 mg KOH / g, for example, 0.5-2 mg KOH / g.

[0017] The carboxylic acid mentioned can be C1-C 24 Saturated or unsaturated carboxylic acids, preferably C 12 -C 18 The fatty acid may have one or more double bonds, preferably one double bond. Examples of fatty acids include, but are not limited to, tetracosanoic acid, docosanoic acid, eicosanoic acid, nonadecanoic acid, stearic acid, heptadecanoic acid, palmitic acid, pentadecanoic acid, myristic acid, tridecanoic acid, lauric acid, undecanoic acid, decanoic acid, docosahexaenoic acid, arachidonic acid, oleic acid, linolenic acid, linoleic acid, undecanoic acid, etc. Oleic acid and palmitic acid are particularly preferred.

[0018] The high-acid-value oils mentioned can be crude oil or waste oil, etc. The acid value of high-acid-value oils is 5-200 mgKOH / g, preferably 40-180 mgKOH / g. High-acid-value oils can belong to the same category or different categories as low-acid-value oils.

[0019] The weight ratio of low-acid-value oils to high-acid-value oils or carboxylic acids is 1:0.02-2, preferably 1:0.05-1, and more preferably 1:0.1-0.5.

[0020] In this invention, the monohydric alcohol can be a monohydric alcohol with 1-6 carbon atoms, and can be a saturated alcohol or an unsaturated alcohol. Preferably, the monohydric alcohol is at least one selected from methanol, ethanol, propanol, allyl alcohol, butanol, and pentanol, and more preferably methanol and / or ethanol. The propanol can be n-propanol and / or isopropanol, the butanol can be n-butanol and / or isomers of n-butanol, and the pentanol can be n-pentanol and / or isomers of n-pentanol.

[0021] According to the method of the present invention, the mass ratio of alcohol to oil in the reaction can be 1:0.04-1, preferably 1:0.1-1, more preferably 1:0.1-0.5. Increasing the mass ratio of alcohol to oil within the above range is beneficial to increasing the reaction yield.

[0022] The method of the present invention can achieve high yields at relatively low temperatures, with a preferred reaction temperature of 100-200°C, and more preferably 120-180°C. Within the above range, increasing the reaction temperature is advantageous for improving the reaction yield.

[0023] The method according to the present invention can significantly reduce the reaction pressure to 0.1-3 MPa, preferably 0.1-2 MPa, and more preferably 0.2-1.6 MPa, thereby enabling the reaction to proceed at low pressure. Similarly, increasing the reaction pressure within the above range is beneficial for improving the reaction yield.

[0024] According to the method of the present invention, the reaction time can be 0.1-10 hours, preferably 0.4-4 hours. Extending the reaction time within the above range is advantageous for improving the reaction yield.

[0025] The contact reaction can be carried out in a reactor known to those skilled in the art that is capable of producing biodiesel and meets the aforementioned temperature and pressure ranges. The reactor can be a tubular reactor or a batch reactor (such as an autoclave).

[0026] When using a batch reactor, it is preferable to have a stirring device, which is more conducive to improving the yield of biodiesel. In the contact reaction of oils, monohydric alcohols, and oil derivatives, the oils, monohydric alcohols, and oil derivatives can be supplied to the reactor individually or mixed together.

[0027] When using a tubular reactor, the oil and monohydric alcohol can be supplied to the reactor separately or premixed before being supplied. Preferably, the liquid hourly space velocity is controlled at 0.1-20 h⁻¹. -1 More preferably 1-5h -1Before being fed into the reactor, the material can be preheated using a preheater or fed directly into the reactor. If a preheater is used, the oil and monohydric alcohol can be preheated separately or mixed and preheated together. In a tubular reactor, the oil and monohydric alcohol preferably enter the reactor from the bottom, while the crude reaction product flows out from the top.

[0028] The method for separating biodiesel includes: distilling monohydric alcohol from the crude reaction product, separating a mixed ester phase (containing fatty acid esters, monoglycerides, diglycerides, and unreacted triglycerides) from glycerol, and distilling the mixed ester phase and glycerol separately to obtain high-purity fatty acid esters and glycerol.

[0029] The method of this invention can effectively solve the problem of low activity of various metal oxide or metal sulfide catalysts when used to prepare biodiesel from low acid value oil feedstocks, thus expanding the application range of oxide or sulfide catalysts, enabling high-yield biodiesel to be obtained at lower temperatures and pressures, and the reaction is carried out at low pressure, which can significantly reduce equipment investment. Detailed Implementation

[0030] The invention is further illustrated by the following examples, but the invention is not limited thereto.

[0031] In this embodiment, the biodiesel yield is obtained by distillation, and the biodiesel yield is calculated as follows: biodiesel / (biodiesel + residue in the reactor) × 100%.

[0032] Comparative Example 1

[0033] 100g of vegetable oil (acid value 1mgKOH / g) and methanol (methanol-to-oil mass ratio 0.17) were added to an autoclave. The reaction was carried out for 2 hours at 140℃, 0.7MPa, and a stirring speed of 200 rpm. The crude product was distilled, and methanol was removed at <150℃. The methanol was recovered and reused. The remaining material was separated into a glycerol phase, and the resulting mixed ester phase was subjected to vacuum distillation to obtain biodiesel with a yield of <5%. This indicates that low-acid-value oils have very low reactivity under low temperature and low pressure.

[0034] Comparative Example 2

[0035] The raw materials and reaction conditions were the same as in Comparative Example 1, except that 19g of oleic acid was added to the reaction, resulting in a biodiesel yield of 22.8%. This indicates that under low temperature and low pressure, even with only fatty acids added to low-acid-value oilseeds for reaction, the biodiesel yield remains low.

[0036] Comparative Example 3

[0037] The raw materials and reaction conditions were the same as in Comparative Example 1, except that 0.6% zinc oxide by weight of the oil was added. The reaction of Example 1 was repeated, and the biodiesel yield was 18.9%. This indicates that under low temperature and low pressure, even with only zinc oxide added to react with low-acid-value oil, the biodiesel yield is still low.

[0038] Example 1

[0039] The raw materials and reaction conditions were the same as those in Comparative Example 1. The difference was that 0.6% zinc oxide by weight of the oil was added, and 19g of oleic acid was also added for the reaction. After the reaction, the crude product was distilled to recover methanol. The remaining material was separated into glycerol phase and the resulting mixed ester phase was subjected to vacuum distillation. The high-purity fatty acid methyl ester obtained was biodiesel, and the biodiesel yield was 95.8%.

[0040] A comparison of Example 1 with Comparative Examples 1, 2, and 3 shows that in Example 1, the simultaneous addition of zinc oxide and oleic acid significantly increased the reaction yield, exceeding the combined yield increases when oleic acid and zinc oxide were added separately. Oleic acid and zinc oxide exhibit an unexpected synergistic effect.

[0041] Example 2

[0042] 100g of vegetable oil (acid value 0.7mgKOH / g) and methanol were added to a high-pressure reactor at a methanol-to-oil mass ratio of 0.17:1. 0.9% by weight of MnO2 was added as a catalyst, along with 15g of oleic acid. The reaction was carried out at a high-pressure reactor temperature of 140℃, a pressure of 0.7MPa, and a stirring speed of 200 rpm for 3.5 hours. The crude product was distilled to remove excess methanol at a temperature below 150℃ at the bottom of the reactor. The methanol was recovered and reused. The remaining material was separated into a glycerol phase, and the resulting mixed ester phase was subjected to vacuum distillation to obtain biodiesel with a yield of 93.8%.

[0043] Example 3

[0044] The raw materials and reaction conditions were the same as in Example 1, except that 19g of oleic acid was replaced with 18.5g of high-acid-value oil (acid value 129mgKOH / g). After the reaction, the crude product was distilled to recover methanol. The remaining material was separated into a glycerol phase, and the resulting mixed ester phase was subjected to vacuum distillation. The yield of biodiesel was 86.7%.

[0045] Comparative Example 4

[0046] 100g of vegetable oil (acid value 1mgKOH / g) and methanol were added to a high-pressure reactor at a methanol-to-oil mass ratio of 0.17:1. 1.5% CuO by weight of the oil was added as a catalyst, along with 19g of oleic acid. The reaction was carried out for 3.5 hours at a high-pressure reactor temperature of 150℃, a pressure of 1MPa, and a stirring speed of 200 rpm. The crude product was distilled to remove excess methanol at a temperature below 150℃ at the bottom of the reactor. The methanol was recovered and reused. The remaining material was separated into a glycerol phase, and the resulting mixed ester phase was subjected to vacuum distillation. The biodiesel yield was 23.7%.

[0047] Comparative Example 5

[0048] 100g of vegetable oil (acid value 0.7mgKOH / g) and methanol were added to a high-pressure reactor at a methanol-to-oil mass ratio of 0.17:1. 0.9% CeO2 by weight of the oil was added as a catalyst, along with 15g of oleic acid. The reaction was carried out for 3.5 hours at a high-pressure reactor temperature of 140℃, a pressure of 0.7MPa, and a stirring speed of 200 rpm. The crude product was then distilled to remove excess methanol at a temperature below 150℃ at the bottom of the reactor. The methanol was recovered and reused. The remaining material was separated into a glycerol phase, and the resulting mixed ester phase was subjected to vacuum distillation to obtain biodiesel with a yield of 39.5%.

[0049] Comparative Example 6

[0050] 100g of soybean oil (acid value 1mgKOH / g) and methanol were added to a high-pressure reactor at a methanol-to-oil mass ratio of 0.17:1. 0.6% SnO by weight of the oil was added as a catalyst, along with 19g of oleic acid. The reaction was carried out for 3.5 hours at a high-pressure reactor temperature of 140℃, a pressure of 0.7MPa, and a stirring speed of 200 rpm. The crude product was distilled to remove excess methanol at a temperature below 150℃ at the bottom of the reactor. The methanol was recovered and reused. The remaining material was separated into a glycerol phase, and the resulting mixed ester phase was subjected to vacuum distillation to obtain biodiesel with a yield of 44.7%.

[0051] If 19g of oleic acid is not added, and other conditions are the same as in Comparative Example 6, the yield of biodiesel is 79.7%. For SnO, the yield decreases when fatty acids are added to low-acid-value feedstocks.

[0052] Comparative Example 7

[0053] 100g of soybean oil (acid value 1mgKOH / g) and methanol were added to a high-pressure reactor at a methanol-to-oil mass ratio of 0.17:1. 0.6% SnO2 by weight of the oil was added as a catalyst, along with 19g of oleic acid. The reaction was carried out for 3.5 hours at a high-pressure reactor temperature of 140℃, a pressure of 0.7MPa, and a stirring speed of 200 rpm. The crude product was then distilled to remove excess methanol at a temperature below 150℃ at the bottom of the reactor. The methanol was recovered and reused. The remaining material was separated into a glycerol phase, and the resulting mixed ester phase was subjected to vacuum distillation to obtain biodiesel with a yield of 26.4%.

[0054] If 19g of oleic acid is not added, and other conditions are the same as in Comparative Example 7, the yield of biodiesel is 77%. For SnO2, adding fatty acids to low-acid-value feedstock actually reduces the yield.

[0055] A comparison of Examples 1 and 2 with Comparative Examples 4, 5, 6, and 7 shows that the yields vary greatly depending on the oxides added. Even with higher reaction temperatures and pressures, and an increased amount of oxide added, the product yield in Comparative Example 4 remained low.

[0056] Comparative Example 8

[0057] 100g of vegetable oil (acid value 1.2mgKOH / g) and methanol were added to a high-pressure reactor at a methanol-to-oil mass ratio of 0.30:1. 25g of palmitic acid was also added. The reaction was carried out at 180℃, 1.7MPa, and 600 rpm for 3.5 hours. The crude product was distilled, and excess methanol was removed at a temperature below 150℃ at the bottom of the reactor. The methanol was recovered and reused. After separating the glycerol phase from the remaining material, the resulting mixed ester phase was subjected to vacuum distillation, yielding biodiesel with a yield of 37.3%. This indicates that even with increased reaction temperature and pressure, adding only a relatively large amount of carboxylic acid to low-acid-value oil does not result in a very low biodiesel yield.

[0058] Comparative Example 9

[0059] The raw materials and reaction conditions were the same as in Comparative Example 1, except that 0.6% FeS by weight of the oil was added. The reaction was repeated in Comparative Example 1, and the biodiesel yield was 18.1%. This indicates that adding only FeS to low-acid-value oils results in a lower biodiesel yield.

[0060] Example 4

[0061] The raw materials and reaction conditions were the same as those in Comparative Example 1. The difference was that 0.6% FeS by weight of the oil was added, and 19g of oleic acid was also added for the reaction. After the reaction, the crude product was distilled to recover methanol. The remaining material was separated into glycerol phase, and the resulting mixed ester phase was subjected to vacuum distillation. The high-purity fatty acid methyl ester obtained was biodiesel, and the biodiesel yield was 96.1%.

[0062] As can be seen from the comparison between Example 4 and Comparative Examples 1, 2 and 9, the reaction yield was greatly improved after the simultaneous addition of iron sulfide and oleic acid in Example 4. The increase in yield was much greater than the sum of the increases when the two were added separately. Oleic acid and sulfide have an unexpected synergistic effect.

[0063] Example 5

[0064] 100g of vegetable oil (acid value 0.7mgKOH / g) and methanol were added to a high-pressure reactor at a methanol-to-oil mass ratio of 0.16:1. 0.6% MnS by weight of the oil was added as a catalyst, along with 15g of oleic acid. The reaction was carried out at 140℃, 0.7MPa, and 200 rpm for 3.5 hours. The crude product was distilled to remove excess methanol at a temperature below 150℃ at the bottom of the reactor. The methanol was recovered and reused. The remaining material was separated into a glycerol phase, and the resulting mixed ester phase was subjected to vacuum distillation to obtain biodiesel with a yield of 89.3%.

[0065] Comparative Example 10

[0066] Using the same raw materials as in Example 5, 100g of vegetable oil and methanol were added together to a high-pressure reactor at a methanol-to-oil mass ratio of 0.30:1. 1.7% of the oil weight of MoS2 was added as a catalyst, along with 15g of oleic acid. The reaction was carried out at 160°C, 1.2 MPa, and 600 rpm for 3.5 hours. The crude product was distilled to remove excess methanol at a temperature below 150°C at the bottom of the reactor. The methanol was recovered and reused. The remaining material was separated into a glycerol phase, and the resulting mixed ester phase was subjected to vacuum distillation to obtain biodiesel with a yield of 42.1%.

[0067] The comparison of Examples 4, 5, and Comparative Example 10 shows that the yield varies greatly depending on the addition of different sulfides. Even with higher temperatures, pressures, increased MoS2 addition, enhanced stirring, and longer reaction times, the product yield in Comparative Example 10 remained low.

Claims

1. A method for increasing the yield of biodiesel from low-acid-value oils, comprising: In the presence of a metal oxide catalyst, a low-acid-value oil is brought into contact with a monohydric alcohol for reaction. The reaction is characterized by the addition of a carboxylic acid, wherein the metal oxide is selected from manganese dioxide, the carboxylic acid is selected from oleic acid, the low-acid-value oil has an acid value below 3 mg KOH / g, the weight ratio of the low-acid-value oil to the carboxylic acid is 1:0.02-2, the reaction temperature is 100-180℃, and the reaction pressure is 0.2-1.6 MPa.

2. The method according to claim 1, wherein, The amount of catalyst added is 0.01-5 wt% of the weight of the raw oil.

3. The method according to claim 1, wherein, The amount of catalyst added is 0.1-2.5 wt% of the weight of the raw oil.

4. The method according to claim 1, wherein, The acid value of the low acid value oil is 0.5-2 mg KOH / g.

5. The method according to claim 1, wherein, The weight ratio of low-acid-value oils to carboxylic acids is 1:0.1-0.

5.

6. The method according to claim 1, wherein, The mass ratio of alcohol to oil in the reaction is 0.04-1:

1.

7. The method according to claim 1, wherein, The mass ratio of alcohol to oil in the reaction is 0.1-0.5:

1.

8. The method according to claim 1, wherein, The reaction temperature is 120-180℃.

9. The method according to claim 1, wherein, The reaction time is 0.1-10 hours.

10. The method according to claim 1, wherein, The reaction time is 0.4-4 hours.