Preparation method of dimer acid with low color, low iron content and low phosphorus content

Abstract

The invention relates to a preparation method of dimer acid with low color, low iron content and low phosphorus content. The preparation method comprises the steps of polymerization, acidification, coordination, water washing, distillation, cooling storage and the like. According to the preparation process, organic carboxylic acid is used as an acidifying agent in the acidifying step, and phosphoric acid is not used; meanwhile, a coordination process is added, and metal ions such as iron ions and the like are removed through a coordination reaction between a coordination agent and the metal ions. Each step adopts a continuous closed process, and connecting pipelines among the steps adopt 316L stainless steel, so that the dimer acid with low color, low iron content and low phosphorus content is finally obtained. The dimer acid is measured by an iron-cobalt colorimeter, has a color of 2-5, and has good color storage stability; the phosphorus content is less than or equal to 1ppm; the iron content is less than or equal to 2ppm, so that the requirement of the market on high-quality dimer acid can be met.

Description

Technical Field

[0001] The invention relates to the technical field of oil and fat chemical industry, and in particular to a preparation technology of dimer acid. Background Art

[0002] Dimer acid, also known as dimer fatty acid, is named for the two carboxylic acid groups in the molecule. It is a viscous, transparent liquid. Its chemical reaction is active, and it has properties such as non-toxicity, high thermal stability, and good fluidity. Combined with its own structural characteristics, dimer acid has become a very important chemical intermediate raw material, which can be used to prepare polyamide resins, coatings, lubricants, fuel additives and many other important fine chemical products.

[0003] The preparation process of dimer acid widely used in industry at present is the kaolin catalysis method. It uses unsaturated fatty acids from a wide range of sources as raw materials, kaolin and lithium carbonate as catalysts, and obtains crude dimer acid through polymerization reaction. Crude dimer acid is obtained by acidification, filtration and other methods to obtain dimer acid with higher purity. Since kaolin is used as a catalyst, metal ions in the kaolin are inevitably brought into the dimer acid, and saponification products are formed under high temperature conditions, which affects the quality of the dimer acid. In order to remove metal ions and reduce saponification products to dimer acid, the traditional method is to add phosphoric acid to the crude dimer acid, and through the acidification process, phosphoric acid and metal ions form phosphate precipitation, and the precipitation is removed by filter pressing. The introduction of phosphoric acid inevitably brings trace phosphate to the dimer acid product. Then, impurities are removed by water washing and centrifugation to obtain dimer acid. In industrial practice, the dimer acid produced in the above manner has low purity, heavy color, and a high content of metal ions and phosphates.

[0004] In recent years, environmental protection requirements have become increasingly stringent, and green and recyclable chemical industrial products have gradually become market demand. Phosphates can destroy the ecological balance, lead to water quality deterioration, and have an indirect negative impact on human health. Many countries and regions are taking measures to reduce phosphate emissions. Moreover, with the expansion of the application field of dimer acid, dimer acid has begun to be used in heavy anti-corrosion coatings such as ships, automobiles, and containers. These fields require dimer acid to have higher purity, lighter color, and lower metal ion content. For example, the trace amount of metal ions such as iron in dimer acid used in heavy anti-corrosion of ships should be less than 2ppm, and the trace amount of phosphorus should be less than 3ppm. Color is also an important indicator for evaluating the quality of dimer acid. During use, dimer acid is often used as an initial raw material, and its color can affect the color and color stability of the final product. At present, domestic dimer acid products generally have the problem of too high color, which cannot meet the market demand for high-quality dimer acid, resulting in long-term dependence on imports of high-quality dimer acid. In short, the current status of domestic dimer acid has seriously restricted the development and application of dimer acid.

[0005] In the prior art, some enterprises have begun to realize some of the above technical problems and have tried to make various technical improvements. For example, CN102010322A discloses a method for preparing a light-colored, low-iron, low-phosphorus dimer acid, which is adjusted by controlling special equipment and parameters: for example, adjusting the steady flow delivery of the gear pump, the steady flow delivery of distilled water, the static mixing of dimer acid and process water, separation by a butterfly centrifuge, vacuum degree, temperature, and evaporation area control in scraper film distillation, vacuum degree, temperature control in short-range molecular distillation, etc., to obtain a light-colored, low-iron, low-phosphorus dimer acid; the dimer acid color (Gardner) is 5-7, the trace iron is controlled at 0.5-2ppm, and the trace phosphorus is controlled at 0.5-7ppm. However, the preparation method has high requirements for the adjustment of equipment and process parameters, and the investment cost of the enterprise for the equipment is increased, and the dimer acid obtained by the preparation method is still high in color. CN101838193A discloses a light-colored low-phosphorus dimer acid production process, which adopts a multi-stage continuous combined molecular distillation technology and a new process of pressurization, cooling, and high-purity water washing, which can increase the purity content of the distilled dimer acid to more than 86%, reduce the phosphorus content to less than 10ppm, and the product color is 7# (iron-cobalt colorimetric). The purity, phosphorus content, and product color of the dimer acid obtained by this process still need to be further improved. CN107141214A discloses a production method of low-phosphorus dimer acid, which is catalyzed by white clay, phosphoric acid acidification to obtain a crude dimer acid, and a metal cation reagent, such as aluminum sulfate, calcium carbonate, etc., is added to react with phosphate to generate a precipitate and filter to remove trace phosphates and other impurities, thereby obtaining a phosphorus content of less than 2ppm and a purity of about 80% dimer acid, but this process will inevitably bring aluminum ions and calcium ions into the dimer acid, thereby increasing the content of metal ions in the dimer acid.

[0006] Therefore, there is still an urgent need to improve the preparation process of dimer acid to solve technical problems such as low purity, excessive phosphate and iron ion residues, and heavy color. Summary of the invention

[0007] The purpose of the present invention is to overcome the technical defects of the above process and provide a method for preparing dimer acid with low color, low iron content and low phosphorus content. The low color is measured by an iron-cobalt colorimeter and is 2-5 colors; the low phosphorus content is a phosphorus content of ≤1ppm; and the low iron content is an iron content of ≤2ppm.

[0008] In order to achieve the above object, the present invention provides a method for preparing dimer acid with low color, low iron content and low phosphorus content, which comprises the following steps:

[0009] 1) Aggregation:

[0010] Add vegetable oleic acid, clay and lithium carbonate into a polymerization reaction kettle, stir and mix thoroughly to carry out polymerization reaction.

[0011] Furthermore, the vegetable oleic acid is selected from one or more of soybean oleic acid, tall oleic acid or cottonseed oleic acid.

[0012] Furthermore, the amount of the white clay added is 6-12% by weight of the vegetable oleic acid, preferably 8-10%, more preferably 8%;

[0013] Furthermore, the amount of lithium carbonate added is 0.2-0.4% by weight of the vegetable oleic acid, preferably 0.3%;

[0014] Furthermore, the above materials are heated to 180-230° C. at 1-5 atmospheres for polymerization reaction for 2-4 hours; more preferably, the above materials are heated to 200-230° C. at 2-3 atmospheres for polymerization reaction for 2-3 hours.

[0015] 2) Acidification:

[0016] The polymerized material flows into the acidification kettle through a pipeline, and an organic carboxylic acid is added to react. The reacted material is filtered or filtered, and the filtrate is collected to obtain a crude dimer acid.

[0017] Further, the acidification reaction temperature of the acidification kettle is 80-180°C, preferably 130-160°C;

[0018] Further, the acidification reaction time is 0.5-5 hours, preferably 1-3 hours;

[0019] Furthermore, the organic carboxylic acid is selected from one or two of the following: acetic acid, oxalic acid; preferably oxalic acid.

[0020] Furthermore, the amount of the organic carboxylic acid added is 0.1-3% by weight of the vegetable oleic acid, and can be selected from 0.2%, 0.5%, 0.8%, 1%, 1.5%, 2%, 2.5%, 3%; preferably 1%-2%, more preferably 1%-1.5%.

[0021] 3) Coordination:

[0022] The crude dimer acid flows into the coordination kettle through a pipeline, and the coordination agent is added, stirred, and reacted.

[0023] Further, the temperature in the kettle is set to 70-120°C, preferably 80-100°C, more preferably 90-95°C;

[0024] Furthermore, the stirring reaction time in the kettle is 2-8 hours, preferably 4-6 hours.

[0025] Further, the complexing agent is selected from one or more of the following: monoethanolamine, diethanolamine, triethanolamine, diethylenetriaminepentaacetic acid, nitrilotriacetic acid;

[0026] Furthermore, the complexing agent is preferably monoethanolamine, diethanolamine and triethanolamine;

[0027] Furthermore, the complexing agent is more preferably a mixture of triethanolamine and nitrilotriacetic acid, and the weight ratio of the two is preferably 1-3:1, more preferably 1:1;

[0028] Furthermore, the amount of the complexing agent added is 0.01-0.3% by weight of the vegetable oleic acid, and can be selected from 0.02%, 0.025%, 0.05%, 0.08%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%; preferably 0.05-0.2%, most preferably 0.1%.

[0029] 4) Washing:

[0030] The coordinated crude dimer acid flows into a water washing kettle through a pipeline for water washing and then centrifugation to remove water.

[0031] Furthermore, the temperature in the water washing kettle is 80-100°C.

[0032] 5) Distillation:

[0033] The washed material is freed of water and low-boiling substances, and then subjected to multi-stage distillation to ultimately obtain a dimer acid with low color, low phosphorus and low iron content.

[0034] Furthermore, the water and low-boiling substances are removed by using a scraper film evaporator. The specific process conditions of the film evaporation are: heating to 100-140°C, at 0.8-1.2 atmospheres, using a scraper film evaporator to continuously degas, dehydrate, and remove low-boiling substances.

[0035] Furthermore, the multi-stage distillation is preferably three-stage, and a three-stage short-path molecular distillation device is used. The specific process steps are as follows:

[0036] The dimer acid from which water and low-boiling substances have been removed is sent to the first-stage short-range molecular distiller through a pipeline, and is distilled and purified under the conditions of a vacuum degree of 10-50Pa and a temperature of 200-240°C to obtain ordinary dimer acid as a heavy phase material and monomer acid as a light phase material.

[0037] The material after the first stage short-range molecular distillation enters the second stage short-range molecular distillation device, and is distilled and purified under the conditions of vacuum degree 10-30Pa and temperature 210-250°C to further remove monomer acid and intermediates.

[0038] The material after the second stage short-range molecular distillation enters the third stage short-range molecular distiller, and is distilled and purified under the conditions of vacuum degree 1-5Pa and temperature 230-270℃ to obtain a light phase of high-purity dimer acid with a content of more than 98.5%, and a heavy phase of polyacid.

[0039] 6) Cooling storage:

[0040] The dimer acid obtained by the above process is cooled to room temperature and flows into a storage tank through a pipeline. It can be stored for 24-36 months without discoloration and has a stable color.

[0041] Furthermore, the polymerization reactor, acidification reactor, coordination reactor, water washing reactor, storage tank and other containers in each step are pre-blown with nitrogen to remove oxygen therein.

[0042] Furthermore, each step adopts a continuous closed process, and the pipelines in each step are made of 316L stainless steel.

[0043] After testing, the color of the obtained dimer acid is measured by an iron-cobalt colorimeter and is 2-5; the phosphorus content is ≤1ppm; and the iron content is ≤2ppm.

[0044] Compared with the prior art, the present invention has the following beneficial effects:

[0045] The present invention adopts organic carboxylic acid as acidulant, instead of traditional phosphoric acid as acidulant, thus avoiding the addition of phosphorus element, thereby reducing the phosphorus content in dimer acid. The present invention adds a coordination process compared with the prior art, through the coordination reaction of the coordination agent and the metal ion, and through the water washing step, the metal ion ligand is removed, thereby reducing the content of metal ions such as iron ions. In the prior art of the preparation process of dimer acid, the pipelines in each step mostly adopt 316 type pipes. The inventor found that although the pipe of this type has good corrosion resistance and heat resistance, it affects the color. After the prepared dimer acid is placed for 24 months, the color will increase. The storage stability of dimer acid is poor, which is not conducive to market sales. The inventor found that the use of 316L stainless steel can keep the color of dimer acid unchanged after being stored in a storage tank for 24-36 months.

[0046] The beneficial effects of the present invention are that the dimer acid obtained by the preparation process is measured by an iron-cobalt colorimeter and has a color of 2-5, and has good color storage stability; the phosphorus content is ≤1ppm; the iron content is ≤2ppm, and the market demand for high-quality dimer acid can be met. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 An example diagram of the dimer acid production process of the present invention. DETAILED DESCRIPTION

[0048] The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention. If no specific techniques or conditions are specified in the examples, the techniques or conditions described in the literature in the field are followed. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased through regular channels. Unless otherwise specified, the experiments or test methods are conventional methods in the field.

[0049] Example 1

[0050] Add 100 kg of cottonseed oil acid, 8 kg of clay and 0.3 kg of lithium carbonate into a polymerization reactor, stir and mix thoroughly, and carry out polymerization reaction at 200°C for 3 hours at 2 atmospheres. The polymerized material flows into the acidification reactor through a pipeline, 1 kg of oxalic acid is added, and the reaction is stirred for 2 hours at 130°C. The reacted material is filtered and the filtrate is collected to obtain crude dimer acid.

[0051] The crude dimer acid flows into the coordination kettle through a pipeline. The temperature in the kettle is set at 95°C. 0.1 kg of the coordination agent monoethanolamine is added while stirring. The coordination reaction is carried out for 4 hours.

[0052] The crude dimer acid after coordination flows into the water washing kettle through the pipeline for water washing and then centrifugal removal of water. The water washing temperature is 90℃.

[0053] The dehydrated material enters the scraper film evaporator through a pipeline, and water and low-boiling substances are continuously removed at 120°C and 0.8 atmospheres; then the material enters the first-stage short-path evaporator for purification and refining, and under the conditions of a vacuum degree of less than 30Pa and a temperature of 220°C, a heavy phase material dimer acid is obtained, and a light phase is a monomer acid; then the material enters the second-stage short-path evaporator for purification and refining, and under the conditions of a vacuum degree of less than 10Pa and a temperature of 230°C, the monomer acid and intermediates are further removed to obtain a heavy phase material of dimer acid; then the material enters the third-stage short-path evaporator for purification and refining, and under the conditions of a vacuum degree of less than 5Pa and a temperature of 250°C, the light phase obtained is dimer acid, and the heavy phase is polydimer acid.

[0054] The dimer acid obtained by the above process is cooled to room temperature and stored in a storage tank via a pipeline.

[0055] Each reaction vessel in the above preparation process is pre-blown with nitrogen in advance. The above preparation process adopts a continuous closed process, and the connecting pipelines between each step are made of 316L stainless steel.

[0056] Example 2

[0057] Add 100kg soybean oleic acid, 8kg white clay and 0.3kg lithium carbonate into the polymerization reactor, stir and mix thoroughly, and carry out polymerization reaction at 2 atmospheres and 210°C for 3 hours. The polymerized material flows into the acidification reactor through a pipeline, 1kg oxalic acid is added, and the reaction is stirred for 2 hours at 130°C. The reacted material is filtered and the filtrate is collected to obtain crude dimer acid.

[0058] The crude dimer acid flows into the coordination kettle through a pipeline. The temperature in the kettle is set at 90°C. 0.15 kg of the coordination agent nitrilotriacetic acid is added. The coordination reaction is carried out for 5 hours while stirring.

[0059] The crude dimer acid after coordination flows into the water washing kettle through the pipeline for water washing and then centrifugal removal of water. The water washing temperature is 90℃.

[0060] The dehydrated material enters the scraper film evaporator through a pipeline, and water and low-boiling substances are continuously removed at 130°C and 0.9 atmospheres; then the material enters the first-stage short-path evaporator for purification and refining, and under the conditions of a vacuum degree of less than 25Pa and a temperature of 230°C, a heavy phase material dimer acid is obtained, and a light phase is a monomer acid; then the material enters the second-stage short-path evaporator for purification and refining, and under the conditions of a vacuum degree of less than 15Pa and a temperature of 230°C, the monomer acid and intermediates are further removed to obtain a heavy phase material of dimer acid; then the material enters the third-stage short-path evaporator for purification and refining, and under the conditions of a vacuum degree of less than 3Pa and a temperature of 250°C, the light phase obtained is dimer acid, and the heavy phase is polydimer acid.

[0061] The dimer acid obtained by the above process is cooled to room temperature and stored in a storage tank via a pipeline.

[0062] Each reaction vessel in the above preparation process is pre-blown with nitrogen in advance. The above preparation process adopts a continuous closed process, and the connecting pipelines between each step are made of 316L stainless steel.

[0063] Example 3

[0064] Add 100 kg of tall oil acid, 10 kg of clay and 0.4 kg of lithium carbonate into a polymerization reactor, stir and mix thoroughly, and carry out polymerization reaction at 3 atmospheres and 230°C for 2.5 hours. The polymerized material flows into the acidification reactor through a pipeline, 1 kg of acetic acid is added, and the reaction is stirred for 3 hours at 110°C. The reacted material is filtered and the filtrate is collected to obtain crude dimer acid.

[0065] The crude dimer acid flows into the coordination kettle through a pipeline. The temperature in the kettle is set to 100° C. 0.15 kg of the coordination agent diethanolamine is added while stirring, and the coordination reaction is carried out for 6 hours.

[0066] The crude dimer acid after coordination flows into the water washing kettle through the pipeline, is washed with water, and then centrifuged to remove water. The water washing temperature is 100℃.

[0067] The dehydrated material enters the scraper film evaporator through a pipeline, and water and low-boiling substances are continuously removed at 130°C and 1 atmosphere; then the material enters the first-stage short-path evaporator for purification and refining, and under the conditions of a vacuum degree of less than 40Pa and a temperature of 240°C, a heavy phase material dimer acid is obtained, and a light phase is a monomer acid; then the material enters the second-stage short-path evaporator for purification and refining, and under the conditions of a vacuum degree of less than 10Pa and a temperature of 230°C, the monomer acid and intermediates are further removed to obtain a heavy phase material of dimer acid; then the material enters the third-stage short-path evaporator for purification and refining, and under the conditions of a vacuum degree of less than 2Pa and a temperature of 250°C, a light phase of dimer acid is obtained, and a heavy phase of polydimer acid is obtained.

[0068] The dimer acid obtained by the above process is cooled to room temperature and stored in a storage tank via a pipeline.

[0069] Each reaction vessel in the above preparation process is pre-blown with nitrogen in advance. The above preparation process adopts a continuous closed process, and the connecting pipelines between each step are made of 316L stainless steel.

[0070] Example 4

[0071] The materials are basically the same as those in Example 1, except that the complexing agent is 0.1 kg of a mixture of triethanolamine and nitrilotriacetic acid in a weight ratio of 1:1.

[0072] Example 5

[0073] The materials are basically the same as those in Example 1, except that the complexing agent is 0.1 kg of a mixture of triethanolamine and nitrilotriacetic acid in a weight ratio of 3:1.

[0074] Example 6

[0075] The materials are basically the same as those in Example 1, except that the complexing agent is 0.12 kg of diethylenetriaminepentaacetic acid.

[0076] Example 7

[0077] The materials are basically the same as those in Example 1, except that the complexing agent is 0.2 kg of triethanolamine.

[0078] Example 8

[0079] The materials are basically the same as those in Example 1, except that the connecting pipes are made of 316 stainless steel.

[0080] Example 9

[0081] The materials are basically the same as those in Example 4, except that the connecting pipes are made of 316 stainless steel.

[0082] Comparative Example 1

[0083] Add 100 kg of cottonseed oil acid, 8 kg of clay and 0.3 kg of lithium carbonate into a polymerization reactor, stir and mix thoroughly, and carry out polymerization reaction at 200°C for 3 hours at 2 atmospheres. The polymerized material flows into the acidification reactor through a pipeline, 2 kg of phosphoric acid is added, and the reaction is stirred for 1.5 hours at 150°C. The reacted material is filtered and the filtrate is collected to obtain crude dimer acid.

[0084] The crude dimer acid flows into the water washing kettle through the pipeline for water washing and then centrifugal removal of water. The water washing temperature is 95℃.

[0085] The dehydrated material enters the evaporator to remove water and low-boiling substances at 110°C and 1 atmosphere. Then it enters the short-path distiller through the pipeline to obtain dimer acid at 230°C and a vacuum degree of 25Pa.

[0086] The dimer acid obtained by the above process is cooled to room temperature and stored in a storage tank via a pipeline.

[0087] Each reaction vessel in the above preparation process is pre-blown with nitrogen in advance. The above preparation process adopts a continuous closed process, and the connecting pipes between each step are made of 316 stainless steel.

[0088] Comparative Example 2

[0089] Add 100 kg of cottonseed oil acid, 8 kg of clay and 0.3 kg of lithium carbonate into a polymerization reactor, stir and mix thoroughly, and carry out polymerization reaction at 200°C for 3 hours at 2 atmospheres. The polymerized material flows into the acidification reactor through a pipeline, 2 kg of phosphoric acid is added, and the reaction is stirred for 1.5 hours at 150°C. The reacted material is filtered and the filtrate is collected to obtain crude dimer acid.

[0090] The crude dimer acid flows into the water washing kettle through the pipeline for water washing and then centrifugal removal of water. The water washing temperature is 90℃.

[0091] The dehydrated material enters the scraper film evaporator through a pipeline, and water and low-boiling substances are continuously removed at 130°C and 1 atmosphere; then the material enters the first-stage short-path evaporator for purification and refining, and under the conditions of a vacuum degree of less than 40Pa and a temperature of 240°C, a heavy phase material dimer acid is obtained, and a light phase is a monomer acid; then the material enters the second-stage short-path evaporator for purification and refining, and under the conditions of a vacuum degree of less than 10Pa and a temperature of 230°C, the monomer acid and intermediates are further removed to obtain a heavy phase material of dimer acid; then the material enters the third-stage short-path evaporator for purification and refining, and under the conditions of a vacuum degree of less than 1Pa and a temperature of 250°C, the light phase obtained is dimer acid, and the heavy phase is polydimer acid.

[0092] The dimer acid obtained by the above process is cooled to room temperature and stored in a storage tank via a pipeline.

[0093] Each reaction vessel in the above preparation process is pre-blown with nitrogen in advance. The above preparation process adopts a continuous closed process, and the connecting pipes between each step are made of 316 stainless steel.

[0094] Comparative Example 3

[0095] The materials are basically the same as those in Comparative Example 2, except that the acidulant phosphoric acid is replaced by oxalic acid.

[0096] The above-mentioned Examples 1-9 and Comparative Examples 1-3 were tested, and the specific testing methods are as follows:

[0097] Detection method:

[0098] Purity test: Use high performance liquid chromatography to measure its purity.

[0099] Color detection: Use an iron-cobalt colorimeter to measure the color of dimer acid. Visually compare the sample with a series of iron-cobalt standard color scale solutions with color value labels to evaluate the color depth, represented by 1-18. The lightest is No. 1 and the darkest is No. 18. Characterize by color number. The dimer acid obtained by the above process is characterized by "initial color".

[0100] Phosphorus content detection: The sample is burned and ashed, then dissolved in hydrochloric acid, and then sodium molybdate and other reagents are added to generate phosphomolybdate. Phosphomolybdate is reduced by the reducing agent ascorbic acid to produce colored complexes such as molybdenum blue. The colorimetric determination is performed at a wavelength of 650nm using a spectrophotometer. The depth of the color is proportional to the phosphorus content in the sample. The phosphorus content in the sample is calculated using the standard phosphorus content curve. The unit of measurement is ppm.

[0101] Iron content detection: The sample is burned and ashed, and then dissolved in hydrochloric acid to make a dilute hydrochloric acid solution. Hydroxylamine hydrochloride is used to reduce iron (III) to iron (II), and iron (II) forms a stable red complex with 1,10-phenanthroline in the pH range of 3 to 9. The absorbance is measured at a wavelength of 510nm using a spectrophotometer. The iron ion content in the sample is calculated using the standard iron content curve. The unit of measurement is ppm.

[0102] Storage stability test: The prepared dimer acid is placed in a storage tank pre-blown with nitrogen and stored in a dark and cool place for 24 months. Its color is measured using an iron-cobalt colorimeter and characterized by a color number. The storage stability is characterized by the "color after 24 months of storage". Compared with the initial color, the less the color change, the better its storage stability.

[0103] The test results are shown in Table 1 Performance Test Table.

[0104] Table 1 Performance test table

[0105] purity Phosphorus content Iron content Initial color Color after 24 months storage Example 1 ≥99％ 0.81 0.9 2 2 Example 2 ≥99％ 0.9 1.2 3 3 Example 3 ≥99％ 0.85 0.9 3 3 Example 4 ≥99％ 0.8 0.5 2 2 Example 5 ≥99％ 0.8 0.6 2 2 Example 6 ≥99％ 0.83 1.2 2 2 Example 7 ≥99％ 0.8 0.8 2 2 Example 8 ≥99％ 0.81 0.9 2 5 Example 9 ≥99％ 0.8 0.5 2 4 Comparative Example 1 ≥80％ 30 18 8 11 Comparative Example 2 ≥98.5％ 25 11 7 10 Comparative Example 3 ≥99％ 1 10 6 8

[0106] From the above test results, it can be seen that the dimer acid obtained by the preparation process of the present invention has a purity of more than 99%, a phosphorus content of less than 1ppm, an iron content of ≤1.2ppm, and an initial color number of ≤3; after storage for 24 months, the color does not change, and the storage stability is good. Its performance indicators are better than the dimer acid prepared in Comparative Examples 1-3.

[0107] Although the embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the claims and their equivalents.

Claims

1. A method for preparing dimer acid with low color, low iron content and low phosphorus content, wherein the low color is measured by an iron-cobalt colorimeter and is 2-5 colors; the low phosphorus content is a phosphorus content ≤ 1 ppm; and the low iron content is an iron content ≤ 2 ppm; It includes the following steps: 1) Polymerization: Add vegetable oleic acid, clay and lithium carbonate into a polymerization reaction kettle, stir and mix thoroughly, and perform polymerization reaction; 2) Acidification: The polymerized material flows into an acidification kettle through a pipeline, an organic carboxylic acid is added to react, the reacted material is filtered or filtered, and the filtrate is collected to obtain a crude dimer acid; 3) Coordination: The crude dimer acid flows into the coordination kettle through the pipeline, and the coordination agent is added, stirred, and reacted; 4) Water washing: The crude dimer acid after coordination flows into the water washing kettle through the pipeline, is washed with water, and then centrifuged to remove water; 5) Distillation: Remove water and low-boiling substances from the washed material, and then perform multi-stage distillation to obtain a dimer acid with low color, low phosphorus and low iron content; 6) Cooling and storage: The dimer acid obtained by the above process is cooled to room temperature and flows into a storage tank through a pipeline for storage.

2. The method for preparing dimer acid according to claim 1, characterized in that: The organic carboxylic acid is selected from one or two of the following: acetic acid and oxalic acid.

3. The method for preparing dimer acid according to claim 2, characterized in that: The organic carboxylic acid is selected from oxalic acid.

4. The method for preparing dimer acid according to claim 1, characterized in that: The added amount of the organic carboxylic acid is 0.1-3% of the weight of the vegetable oleic acid.

5. The method for preparing dimer acid according to claim 1, characterized in that: The complexing agent is selected from one or more of the following: monoethanolamine, diethanolamine, triethanolamine, diethylenetriaminepentaacetic acid, and nitrilotriacetic acid.

6. The method for preparing dimer acid according to claim 5, characterized in that: The complexing agent is selected from one or more of the following: monoethanolamine, diethanolamine and triethanolamine.

7. The method for preparing dimer acid according to claim 5, characterized in that: The complexing agent is a mixture of triethanolamine and nitrilotriacetic acid, and the weight ratio of the two is 1-3:

1.

8. The method for preparing dimer acid according to claim 7, characterized in that: The complexing agent is a mixture of triethanolamine and nitrilotriacetic acid, and the weight ratio of the two is 1:

1.

9. The method for preparing dimer acid according to claim 1, characterized in that: The added amount of the complexing agent is 0.01-0.3% of the weight of the vegetable oleic acid.

10. The method for preparing dimer acid according to claim 1, characterized in that: Each step adopts a continuous closed process, and the pipelines in each step are made of 316L stainless steel.

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