Determination method for hydroxyl value of vegetable oil-based and its derivative-based polyols

Abstract

The present invention belongs to the technical field of the determination of hydroxyl value of polyols, and particularly relates to a method for determining the hydroxyl value of vegetable oil-based and its derivative-based polyols. In the method for determining the hydroxyl value of vegetable oil-based and its derivative-based polyols of the present invention, the unopened epoxy bonds in the polyol sample to be measured are completely destroyed by epoxy value determination, and the change value of the hydroxyl value caused by the epoxy bond part during the determination of the hydroxyl value of the sample by the acylation method is calculated according to the epoxy value, and this part of the hydroxyl group change value is deducted from the total hydroxyl value measured from the ring-opened sample of the polyol, so as to effectively eliminate the influence of the epoxy bond on the test result of the hydroxyl value of the sample, and significantly improve the accuracy of the determination of the hydroxyl value of the vegetable oil-based polyol sample. Moreover, the determination method of the present invention is more environmentally friendly, has a wide hydroxyl value determination range and high accuracy, and has good popularization and application prospects in the production process improvement and product quality control of vegetable oil-based and its derivative-based polyols.

Description

Technical Field

[0001] The present invention belongs to the technical field of the determination of hydroxyl value of polyols, and particularly relates to a method for determining the hydroxyl value of vegetable oil-based and its derivative-based polyols. Background Art

[0002] Vegetable oil-based and its derivative-based polyols are obtained by chemical or biological modification using vegetable oils or vegetable oil derivatives as raw materials, and have been widely used in the polyurethane industry, lubricants, surfactants, polymer materials and other fields. In recent years, due to the changes in the international situation leading to fluctuations in crude oil prices and the increasing tightness of petrochemical resources, the supply pressure in the global petroleum market has increased, and vegetable oil-based polyols and vegetable oil derivative-based polyols as renewable resources have gradually become the research focus.

[0003] The preparation of vegetable oil-based and its derivative-based polyols includes ozonation, epoxidation-hydroxylation, hydroformylation, transesterification, ammonolysis, etc. These preparation methods have their own advantages and disadvantages, and the properties of the vegetable oil-based and its derivative-based polyols produced are also different. Among them, the epoxidation-hydroxylation method is the most studied and widely used at home and abroad. For the vegetable oil-based and its derivative-based polyols prepared by the epoxidation-hydroxylation method, due to different ring-opening conditions, there is often a problem of coexistence of epoxy groups and hydroxyl groups. The properties of vegetable oil-based and its derivative-based polyols are closely related to the number of hydroxyl groups and the degree of side reactions occurring during the preparation process. Hydroxyl is an important functional group in vegetable oil-based polyols, and the hydroxyl content and its distribution largely determine the activity and application properties of vegetable oil-based and its derivative-based polyol products. Therefore, the determination of hydroxyl value is an important basis for manufacturers to control the production and product quality of polyol products.

[0004] For the determination of hydroxyl value in vegetable oil-based and its derivative-based polyols, the existing determination methods mainly include chemical acylation method, bromination method, periodic acid oxidation method, coupling method, active hydrogenation method, etc., and the chemical acylation method recommended by ASTM standard (D1957-86) and AOAC standard (956.32) is the most common. The hydroxyl value determined by the chemical acylation method recommended by the above standards is expressed as the milligrams of potassium hydroxide equivalent to the hydroxyl content per gram of the sample. The determination principle is that under reflux conditions, the hydroxyl groups react with acetic anhydride dissolved in pyridine for acylation reaction, and the excess acetic anhydride is titrated with a potassium hydroxide-ethanol standard solution to obtain the hydroxyl value of the sample.

[0005] However, when using the above chemical acylation method to determine the actual hydroxyl value of vegetable oil-based and its derivative-based polyols, through multiple experiments and verifications, the present invention found that the epoxy bonds existing in vegetable oil-based polyols will react with anhydrides to varying degrees under different acylation conditions, thus having varying degrees of influence on the determination results of hydroxyl value. As a result, the measured hydroxyl value is not accurate, and the problem of inaccurate determination of hydroxyl value occurs. Moreover, due to the occurrence of side reactions during the preparation process of opening the hydroxyl group ring, the theoretical hydroxyl value of the prepared vegetable oil-based polyol product cannot be effectively calculated and speculated based on the change in epoxy value before and after the ring opening of the raw material epoxidized vegetable oil, resulting in the inability to effectively evaluate the quality of the polyol product. In addition, the standard chemical acylation method usually uses pyridine with strong toxicity as a solvent, which will produce new turbid substances during the determination process of the hydroxyl value of vegetable oil-based polyols, thus affecting the judgment of the titration end point. And the existing standard acylation method has a limited range for determining hydroxyl value, usually within 1000 mgKOH / g, which limits its further application in the industry.

[0006] Therefore, developing a new method that is environmentally friendly, accurate, has a wide range of applicable hydroxyl values, and can effectively realize the determination of the hydroxyl value of vegetable oil-based and its derivative-based polyols is of great significance for evaluating the preparation process and service performance of related products of vegetable oil-based and its derivative-based polyols. Summary of the Invention

[0007] In order to overcome the deficiencies of the prior art, the purpose of the present invention is to provide a method for determining the hydroxyl value of vegetable oil-based and its derivative-based polyols, which is non-toxic, environmentally friendly, has a wide range for determining hydroxyl value, and can accurately determine the hydroxyl value of vegetable oil-based and its derivative-based polyols.

[0008] The purpose of the technical solution of the present invention is mainly achieved by adopting the following technical solutions:

[0009] A method for determining the hydroxyl value of vegetable oil-based and its derivative-based polyols, comprising the following steps:

[0010] (1) Subject the polyol sample to be measured to ring-opening treatment to completely destroy the epoxy bonds in the sample, and determine the epoxy value of the sample; the polyol sample is a vegetable oil-based polyol sample and / or a vegetable oil derivative-based polyol sample;

[0011] (2) Extract the sample after the epoxy value determination in step (1) with a solvent, and then remove the solvent to obtain the ring-opened sample of the polyol;

[0012] (3) Mix the ring-opening sample of the polyol with an acylating agent for an acylation reaction, and then perform chemical titration with a standard alkali solution to determine the total hydroxyl value of the ring-opening sample of the polyol; then, using the total hydroxyl value and the change value of the hydroxyl value caused by the epoxy groups in the sample calculated from the epoxy value, calculate the difference between the total hydroxyl value and the change value of the hydroxyl value, and the obtained difference is the actual hydroxyl value of the polyol sample to be measured;

[0013] Among them, in step (3), the acylating agent is an acetic acid - acetic anhydride mixed solution; in the acetic acid - acetic anhydride mixed solution, the volume ratio of acetic acid to acetic anhydride is 1∶(2 - 6).

[0014] Preferably, in step (1), the polyol sample is prepared by an epoxidation - hydroxylation method. The present invention does not make special limitations on the testable polyol objects. Vegetable oil - based polyols or vegetable oil derivative - based polyol products prepared by the epoxidation - hydroxylation method often have the problem of co - existence of epoxy groups and hydroxyl groups, so they are all applicable to the detection method of the present invention.

[0015] More preferably, the vegetable oil - based polyol sample is selected from one or more of soybean oil - based polyol, rapeseed oil - based polyol, sunflower seed oil - based polyol, Canola oil - based polyol, castor oil - based polyol, linseed oil - based polyol, rice bran oil - based polyol; the vegetable oil derivative - based polyol sample is selected from one or more of free fatty acid - based polyol, fatty acid methyl ester - based polyol, fatty acid ethyl ester - based polyol, monoglyceride - based polyol, diglyceride - based polyol, triglyceride - based polyol.

[0016] Preferably, in step (1), the hydroxyl value range of the polyol sample to be measured is ≤1827 mgKOH / g. After experimental verification by the present invention, it is found that using the determination method of the present invention, the maximum value of hydroxyl value determination can reach 1827 mgKOH / g, and the test range is significantly larger than the test ranges of the existing ASTM standard (D1957 - 86) and AOAC standard (956.32) recommended chemical acylation methods, which is more conducive to the accurate determination of polyol samples with extremely high hydroxyl values.

[0017] Furthermore, the ring - opening treatment is carried out with a hydrochloric acid - acetone solution; the epoxy value is determined according to Method A in Standard GB / T1677 - 2008.

[0018] Furthermore, in step (2), the number of extractions is 2 - 4 times; the solvent is ether or ethyl acetate; after extraction, it also includes a step of removing water with a desiccant; the solvent is removed by vacuum distillation.

[0019] In step (3), the acylation reaction is carried out under thermal reflux conditions; the time of the acylation reaction is 2 - 3 h.

[0020] Further, in step (3), the alkali standard solution is a potassium hydroxide standard solution. The solvent used for the potassium hydroxide standard solution is ethanol.

[0021] In step (3), the specific steps for determining the total hydroxyl value of the sample are as follows: Mix the ring-opening sample of the polyol with an acylating agent for acylation reaction, then add water and continue the reaction. After the reaction, cool it, and titrate it to the end point with a potassium hydroxide standard solution. Record the volume of the potassium hydroxide standard solution consumed by the ring-opening sample of the polyol during acylation; at the same time, conduct a blank test with only the acylating agent added, and record the volume of the potassium hydroxide standard solution consumed during the blank test of acylation; take another ring-opening sample of the polyol, conduct an acidity titration with a potassium hydroxide standard solution, and conduct a blank test at the same time to obtain the volume of the potassium hydroxide standard solution consumed by the ring-opening sample of the polyol during acidity determination; finally, calculate the total hydroxyl value of the ring-opening sample of the polyol according to the calculation formula for determining the hydroxyl value by the acylation method.

[0022] Preferably, in step (3), the dosage ratio of the ring-opening sample of the polyol to the acylating agent is (0.06 - 0.8) g∶(3.5 - 10) mL; the concentration of the potassium hydroxide standard solution is 0.001 mol / mL; the concentration of the potassium hydroxide standard solution used in the acylation titration and the acidity titration is the same; during acidity determination, the mass of the ring-opening sample of the polyol used is 9 - 11 g.

[0023] Further preferably, the specific process for obtaining the volume of the potassium hydroxide standard solution consumed by the ring-opening sample of the polyol during acidity determination is as follows: Weigh the ring-opening sample of the polyol, add acetic acid and an indicator, and then titrate it to the end point with a potassium hydroxide standard solution to obtain the volume of the potassium hydroxide standard solution consumed by the ring-opening sample of the polyol and acetic acid in total; at the same time, conduct a blank test without adding the ring-opening sample of the polyol to obtain the volume of the potassium hydroxide standard solution consumed by acetic acid; calculate the difference between the volume of the potassium hydroxide standard solution consumed by the ring-opening sample of the polyol and acetic acid in total and the volume of the potassium hydroxide standard solution consumed by acetic acid during the blank test, which is the volume of the potassium hydroxide standard solution consumed by the ring-opening sample of the polyol during acidity determination.

[0024] The present invention does not specifically limit the determination process of the epoxy value, and it can be carried out with reference to Method A in GB / T 1677 - 2008. As a further preferred solution, in step (1), the calculation formula for the epoxy value is:

[0025]

[0026] Wherein, X0 is the epoxy value, in %; 16 is a constant, being the molar mass of oxygen, in g / mol; v0 is the volume of the sodium hydroxide standard solution consumed in the blank test during the determination of the epoxy value of the polyol sample, in mL; v1 is the volume of the sodium hydroxide standard solution consumed by the polyol sample during the acidity determination, in mL; v2 is the volume of the sodium hydroxide standard solution consumed by the polyol sample during the epoxy value determination, in mL; C N is the concentration of the sodium hydroxide standard solution, in mol / mL; m1 is the mass of the polyol sample during the epoxy value determination, in g; m2 is the mass of the polyol sample during the acidity determination, in g.

[0027] Preferably, the concentration of the sodium hydroxide standard solution is 1.5×10 -4 mol / mL.

[0028] Furthermore, in step (3), the calculation formula for the total hydroxyl value is:

[0029]

[0030] Wherein, X 总 is the total hydroxyl value, in mgKOH / g; 56.1 is a constant, representing the molar mass of potassium hydroxide, in g / mol; v'0 is the volume of the potassium hydroxide standard solution consumed in the blank test for acylation, in mL; v3 is the volume of the potassium hydroxide standard solution consumed by the ring-opening sample of the polyol during the acidity determination, in mL; v4 is the volume of the potassium hydroxide standard solution consumed by the ring-opening sample of the polyol during acylation, in mL; C K is the concentration of the potassium hydroxide standard solution, in mol / mL; m3 is the mass of the ring-opening sample of the polyol reacting with the acylating agent, in g; m4 is the mass of the ring-opening sample of the polyol during the acidity determination, in g.

[0031] Even further, in step (3), the actual hydroxyl value of the polyol sample is calculated through the following formula:

[0032]

[0033] Wherein, X is the actual hydroxyl value of the polyol sample, in mgKOH / g; X 总 is the total hydroxyl value, in mgKOH / g; X0 is the epoxy value, in %; 56.1 is a constant, referring to the molar mass of potassium hydroxide, in g / mol; 16 is a constant, being the molar mass of oxygen, in g / mol; is the change value of the hydroxyl value caused by the epoxy bonds in the sample calculated from the epoxy value.

[0034] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0035] The method for determining the hydroxyl value of the vegetable oil-based and derivative-based polyols of the present invention is a new method for determining the hydroxyl value that is non-toxic, has a wide range of hydroxyl value determination, and has accurate determination results. Among them, the present invention has found for the first time in practical applications that the epoxy bond of the vegetable oil-based polyol will have a greater impact on the determination result of the hydroxyl value. The hydroxyl value of the vegetable oil-based polyol currently measured by conventional methods is not accurate and cannot represent the true content of hydroxyl groups in the product. If the influence of the epoxy bond is not eliminated, the accurate determination of the hydroxyl value cannot be achieved at all. Therefore, when determining the hydroxyl value of the vegetable oil-based and derivative-based polyols, the present invention first completely destroys the unopened epoxy bond in the sample by epoxy value determination, and calculates the hydroxyl value change value caused by the epoxy bond part of the sample when the hydroxyl value of the sample is determined by the acylation method according to the epoxy value, and deducts the partial hydroxyl change value from the total hydroxyl value measured by the open-loop sample of the polyol, thereby effectively eliminating the influence of the epoxy bond on the test result, and significantly improving the accuracy of the determination of the hydroxyl value of the vegetable oil-based polyol.

[0036] Furthermore, the present invention uses acetic acid instead of toxic pyridine as a solvent on the basis of the original chemical acylation method, and effectively uses acetic acid for the determination of the hydroxyl value of plant oil-based and derivative-based polyols, mainly based on the following three reasons: ① After the excess acetic anhydride reacts with the hydroxyl group, the excess acetic anhydride is hydrolyzed into acetic acid by adding water, and then the alkaline solution can be used for direct neutralization titration, without distinguishing whether the acid comes from the acetic acid hydrolyzed from the anhydride or the acetic acid as a solvent, and the amount of potassium hydroxide standard solution used to deduct the excess anhydride and the solvent acetic acid can be calculated together. That is, using acetic acid as a solvent can simplify the subsequent calculation process of the hydroxyl value. ② Acetic acid is a common solvent in daily life. Compared with pyridine, it is basically non-toxic, low-priced, and more environmentally friendly and economical. ③ The present invention uses acetic acid as a solvent, and participates in the acylation reaction together with acetic anhydride, which can effectively broaden the determination range of the hydroxyl value. This is because: the acylation reaction between the hydroxyl group and acetic anhydride is a reversible reaction, and the substrate ratio, that is, the ratio of the acylating agent to the hydroxyl value, has a great influence on the determination result. However, in the existing standard acylation method using pyridine as solvent, if the hydroxyl value of the sample to be measured is too large, the ratio of the acylating agent to the hydroxyl value will become smaller, which will lead to incomplete reaction and inaccurate measurement results. Therefore, in order to make the hydroxyl group completely acylated, the hydroxyl value of the sample in the standard acylation method cannot be too large, and the measurement range of the hydroxyl value is also narrow, usually within 1000mgKOH / g. The present invention uses acetic acid as a solvent, which can participate in the acylation reaction together with acetic anhydride. Since the present invention uses acetic acid and acetic anhydride to acylate with the hydroxyl value, the degree of acylation can be greatly improved, so the hydroxyl value of the polyol sample to be measured can be effectively widened, up to 1827mgKOH / g, which can better meet the measurement requirements of polyol samples with high hydroxyl values.

[0037] In summary, the method for determining the hydroxyl value of vegetable oil-based and its derivative-based polyols provided by the present invention is more environmentally friendly, has a wide hydroxyl value determination range and high accuracy, and has good popularization and application prospects in the improvement of the production process of vegetable oil-based and its derivative-based polyols and product quality control. Detailed Embodiments

[0038] The technical solutions of the present invention will be further described below in conjunction with specific examples. It should be understood that the following examples are only for further clarifying the present invention and not for limiting the present invention. Unless otherwise specified, the reagents used in the following examples can be obtained from commercial channels.

[0039] Among them, the epoxidized soybean oil used in the following examples was purchased from Shanghai Macklin Biochemical Co., Ltd., and its epoxy value was measured to be 6.23% by method A of GB / T 1677-2008. The potassium hydroxide standard solution used in the following examples was a potassium hydroxide-ethanol standard solution; the sodium hydroxide standard solution was a sodium hydroxide-water standard solution.

[0040] It should be noted that since the vegetable oil-based polyol product prepared by the epoxidation-hydroxylation method is not a standard product, the corresponding theoretical hydroxyl value and epoxy value cannot be accurately known, and the test accuracy of the present invention cannot be effectively verified. Therefore, in the following examples, the present invention uses 2,3-butanediol, which also contains two adjacent secondary alcohols, as a substitute for the hydroxyl part in the vegetable oil-based polyol (containing multiple groups of two adjacent secondary alcohols), and at the same time uses epoxidized soybean oil as a substitute for the epoxy bond. Since 2,3-butanediol and epoxidized soybean oil are pure products and their theoretical hydroxyl values and epoxy values are known, they can be used to verify the accuracy of the method of the present invention in determining the hydroxyl value.

[0041] Specifically, in the embodiments of the present invention, a composite of epoxidized soybean oil and 2,3-butanediol mixed in different proportions is used as the polyol sample to be measured, so as to truly simulate the composition of the vegetable oil-based polyol sample containing both epoxy bonds and hydroxyl groups, and to evaluate the accuracy of the method of the present invention. Since the theoretical values of the composites of epoxidized soybean oil and 2,3-butanediol mixed in different proportions involved in the examples are known, the accuracy of the method of the present invention in measuring the hydroxyl value of vegetable oil-based polyols can be effectively verified.

[0042] In other embodiments, those skilled in the art can use the testing method of the present invention to directly measure real vegetable oil-based polyol samples and / or vegetable oil derivative-based polyol samples prepared by the epoxidation-hydroxylation method, and it can achieve quite accurate hydroxyl value testing. Of course, in different embodiments, the vegetable oil-based polyol samples can be selected from one or more of soybean oil-based polyols, rapeseed oil-based polyols, sunflower seed oil-based polyols, Canola oil-based polyols, castor oil-based polyols, linseed oil-based polyols, rice bran oil-based polyols. The vegetable oil derivative-based polyol samples can be selected from one or more of free fatty acid-based polyols, fatty acid methyl ester-based polyols, fatty acid ethyl ester-based polyols, monoglyceride-based polyols, diglyceride-based polyols, triglyceride-based polyols. The selection of the above test objects will not affect the accuracy of the hydroxyl value determination by the testing method of the present invention, so none of them depart from the protection scope of the present invention.

[0043] Example 1

[0044] In the method for determining the hydroxyl value of the vegetable oil-based and its derivative-based polyols in this example, a mixture of epoxidized soybean oil and 2,3-butanediol (9:1, m / m) is used as the test object to simulate the vegetable oil-based polyol sample, and the testing method includes the following steps:

[0045] (1) According to Method A of GB / T 1677-2008, the mixture of epoxidized soybean oil and 2,3-butanediol (9:1, m / m) is subjected to ring-opening treatment to completely destroy the epoxy bonds in the sample, and the epoxy value of the sample is determined. The specific operation is as follows: Accurately weigh 0.5 g of the mixture sample of epoxidized soybean oil and 2,3-butanediol (accurate to 0.0001 g), place it in a 250 mL stoppered ground glass conical flask, accurately add 20 mL of hydrochloric acid-acetone solution (1:40, v / v), tightly stopper, shake well and place in the dark, and let it stand for 30 min. Add 5 drops of mixed indicator (0.1% cresol red and 0.1% thymol blue), and titrate with 1.5×10 -4 mol / mL sodium hydroxide standard titration solution until it turns purple-blue. At the same time, perform a blank test.

[0046] Acidity determination: Accurately add 9 g of the mixture sample of epoxidized soybean oil and 2,3-butanediol (accurate to 0.0001 g), place it in a 250 mL stoppered ground glass conical flask, accurately add 50 mL of ether-isopropanol solution (1:1, v / v), add 5 drops of phenolphthalein indicator, and titrate with 1.5×10 -4 mol / mL sodium hydroxide standard titration solution until it turns faintly red, and when there is no obvious fading within 15 s, it is the titration end point. At the same time, perform a blank test.

[0047] The calculation formula for the epoxy value is:

[0048]

[0049] In the formula, X0 is the epoxy value, in %; 16 is a constant, which is the molar mass of oxygen, in g / mol; v0 is the volume of the sodium hydroxide standard solution consumed in the blank test during the determination of the epoxy value of the sample, in mL; v1 is the volume of the sodium hydroxide standard solution consumed by the sample during the acidity determination, in mL; v2 is the volume of the sodium hydroxide standard solution consumed by the sample during the epoxy value determination, in mL; C N is the concentration of the sodium hydroxide standard solution, in mol / mL; m1 is the mass of the sample during the epoxy value determination, in g; m2 is the mass of the polyol sample during the acidity determination, in g.

[0050] (2) Extract the reaction solution after the epoxy value determination in step (1) three times with 50, 30, and 20 mL of diethyl ether in sequence to obtain an ether solution of the ring-opened soybean oil-based polyol. Then add anhydrous sodium sulfate to remove trace water, and remove the diethyl ether under reduced pressure at 35 °C to obtain a ring-opened sample;

[0051] (3) Take 0.1 g of the ring-opened sample obtained in step (2), mix it with 5 mL of an acylating agent acetic acid-acetic anhydride mixed solution (the mixing ratio of acetic acid and acetic anhydride is 1:4, v / v) in a 250 mL conical flask and mix well. After adding a magnetic stir bar, reflux and condense in a magnetic stirrer in a boiling water bath for 2 h. Then add 10 mL of distilled water from the upper end of the condenser and continue heating for 10 min. After heating, cool to room temperature under reflux and condensation conditions. Then measure 25 mL of n-butanol, add half of its volume of n-butanol from the upper end of the condenser to wash the acetic acid condensed on the inner wall of the condenser, then remove the condenser, and wash the inner wall of the conical flask and the interface with the remaining n-butanol. After washing, add 1 mL of phenolphthalein indicator, and titrate with a 0.001 mol / mL potassium hydroxide-ethanol standard solution until a faint pink end point appears, and record the volume of the potassium hydroxide standard solution consumed by the ring-opened sample during acylation; at the same time, conduct a blank test with only the acylating agent added, and record the volume of the potassium hydroxide standard solution consumed during the acylation blank test.

[0052] Weigh another 9 g of the ring-opened sample obtained in step (2) (accurate to 0.001 g) and place it in a conical flask, add 10 mL of acetic acid, shake well slowly, add 1 mL of phenolphthalein indicator, and titrate with a 0.001 mol / mL potassium hydroxide-ethanol standard solution until a faint pink end point appears, and record the volume of the potassium hydroxide standard solution consumed by the ring-opened sample and acetic acid together; at the same time, conduct a blank test without adding the ring-opened sample to obtain the volume of the potassium hydroxide standard solution consumed by acetic acid; calculate the difference between the two volumes recorded above, which is the volume of the potassium hydroxide standard solution consumed by the ring-opened sample during the acidity determination.

[0053] Further, according to the calculation formula for determining the hydroxyl value by the acylation method, the total hydroxyl value of the ring-opening sample of the polyol is calculated. The calculation formula for the total hydroxyl value is as follows:

[0054]

[0055] In the formula, X 总 is the total hydroxyl value, in units of mgKOH / g; 56.1 is a constant, representing the molar mass of potassium hydroxide, in units of g / mol; v'0 is the volume of the potassium hydroxide standard solution consumed in the blank test for acylation, in units of mL; v3 is the volume of the potassium hydroxide standard solution consumed by the ring-opening sample during acidity determination, in units of mL; v4 is the volume of the potassium hydroxide standard solution consumed by the ring-opening sample during acylation, in units of mL; C K is the concentration of the potassium hydroxide standard solution, in units of mol / mL; m3 is the mass of the ring-opening sample reacting with the acylating agent, in units of g; m4 is the mass of the ring-opening sample during acidity determination, in units of g.

[0056] Finally, using the total hydroxyl value and the change value of the hydroxyl value caused by the epoxy groups in the sample calculated from the epoxy value, the difference between the total hydroxyl value and the change value of the hydroxyl value is calculated, and the obtained difference is the actual hydroxyl value of the polyol sample to be measured. The actual hydroxyl value is calculated by the following formula:

[0057]

[0058] In the formula, X is the actual hydroxyl value of the sample to be measured, in units of mgKOH / g; X 总 is the total hydroxyl value, in units of mgKOH / g; X0 is the epoxy value, in units of %; 56.1 is a constant, representing the molar mass of potassium hydroxide, in units of g / mol; 16 is a constant, being the molar mass of oxygen, in units of g / mol; is the change value of the hydroxyl value caused by the epoxy groups in the sample calculated from the epoxy value.

[0059] Example 2

[0060] In the method for determining the hydroxyl value of the vegetable oil-based and its derivative-based polyols in this example, a mixture of epoxy soybean oil and 2,3-butanediol (7:3, m / m) is used as the test object to simulate the vegetable oil-based polyol sample. The test method is the same as that in Example 1 except for the composition of the test object.

[0061] Example 3

[0062] In the method for determining the hydroxyl value of the vegetable oil-based and its derivative-based polyols in this example, a mixture of epoxy soybean oil and 2,3-butanediol (5:5, m / m) is used as the test object to simulate the vegetable oil-based polyol sample. The test method is the same as that in Example 1 except for the composition of the test object.

[0063] Example 4

[0064] For the method for measuring the hydroxyl value of the vegetable oil-based and its derivative-based polyols in this example, a mixture of epoxidized soybean oil and 2,3-butanediol (3:7, m / m) was used as the test object to simulate the vegetable oil-based polyol sample. Except for the different composition of the test object, the test method was the same as that in Example 1.

[0065] Example 5

[0066] For the method for measuring the hydroxyl value of the vegetable oil-based and its derivative-based polyols in this example, a mixture of epoxidized soybean oil and 2,3-butanediol (1:9, m / m) was used as the test object to simulate the vegetable oil-based polyol sample. Except for the different composition of the test object, the test method was the same as that in Example 1.

[0067] Example 6

[0068] For the method for measuring the hydroxyl value of the vegetable oil-based and its derivative-based polyols in this example, pure epoxidized soybean oil was used as the test object. Except for the different composition of the test object, the test method was the same as that in Example 1.

[0069] Example 7

[0070] For the method for measuring the hydroxyl value of the vegetable oil-based and its derivative-based polyols in this example, pure 2,3-butanediol was used as the test object. Except for the different test object, the test method was the same as that in Example 1.

[0071] Comparative Example 1

[0072] The method for measuring the hydroxyl value in this comparative example was basically the same as that in Example 7. The only difference between the two was that in step (3), the acylating agent was an acetic acid-acetic anhydride mixed solution, and the mixing ratio of acetic acid and acetic anhydride was 3:2, v / v; the reflux condensation time was 1 h.

[0073] Comparative Example 2

[0074] The method for measuring the hydroxyl value in this comparative example was basically the same as that in Example 7. The only difference between the two was that in step (3), the acylating agent was an acetic acid-acetic anhydride mixed solution, and the mixing ratio of acetic acid and acetic anhydride was 3:2, v / v; the reflux condensation time was 1.5 h.

[0075] Comparative Example 3

[0076] The method for measuring the hydroxyl value in this comparative example was basically the same as that in Example 7. The only difference between the two was that in step (3), the acylating agent was an acetic acid-acetic anhydride mixed solution, and the mixing ratio of acetic acid and acetic anhydride was 3:3, v / v; the reflux condensation time was 1 h.

[0077] Comparative Example 4

[0078] The hydroxyl value determination method of this comparative example is basically the same as that of Example 7, and the only difference between the two is that in step (3), the acylating agent is an acetic acid-acetic anhydride mixed solution, and the mixing ratio of acetic acid and acetic anhydride is 3:4, v / v; the reflux condensation time is 1 h.

[0079] Comparative Example 5

[0080] The hydroxyl value determination method of this comparative example is basically the same as that of Example 7, and the only difference between the two is that in step (3), the acylating agent is an acetic acid-acetic anhydride mixed solution, and the mixing ratio of acetic acid and acetic anhydride is 3:5, v / v; the reflux condensation time is 1 h.

[0081] Comparative Example 6

[0082] The hydroxyl value determination method of this comparative example refers to the ASTM standard (D1957-86) acylation method, and the specific steps are as follows: Place 2 g of epoxidized soybean oil and 5 mL of a pyridine-acetic anhydride mixed solution (3:1, v / v) in a 250 mL conical flask and mix well. After adding a magnetic stir bar, reflux and condense in a magnetic stirrer in a boiling water bath for 1 h. Add 10 mL of distilled water from the upper end of the condenser and continue heating for 10 min, and then cool to room temperature under reflux and condensation conditions. Measure 25 mL of n-butanol, add about half of it from the upper end of the condenser tube to rinse the acetic acid and pyridine condensed on the inner wall of the condenser tube, then remove the condenser tube, and use the remaining n-butanol to wash the bottle wall and the interface downwards. Add 1 mL of phenolphthalein indicator, and titrate with 0.5 mol / L potassium hydroxide-ethanol standard solution until a light red end point appears; at the same time, perform a blank test. Weigh 9 g of epoxidized soybean oil into a conical flask, add 10 mL of pyridine neutralized to neutral with 0.5 mol / L potassium hydroxide-ethanol standard solution, shake well slowly, add 1 mL of phenolphthalein indicator, and titrate with 0.5 mol / L potassium hydroxide-ethanol standard solution until a light red end point appears; at the same time, perform a blank test.

[0083] Test Example 1

[0084] The hydroxyl value results obtained by testing Examples 1 to 7 of the present invention and Comparative Examples 1 to 6 are uniformly characterized, and the test results are expressed as the average value of at least two results. The results are shown in Tables 1 and 2.

[0085] Table 1 Epoxy value, total hydroxyl value and relative deviation obtained by measuring Examples 1 to 7 and Comparative Examples 1 to 6

[0086]

[0087] Table 2 Actual hydroxyl value and relative deviation obtained by measuring Examples 1 to 7 and Comparative Examples 1 to 6

[0088]

[0089]

[0090] As can be seen from the results of Table 1 and Table 2, within the range of the mass ratio of epoxidized soybean oil to 2,3-butanediol from 10:0 to 0:10 in the present invention, when the ratio of acetic acid to acetic anhydride in the acylating agent used is 1∶(2 - 6), the relative deviation value of the hydroxyl value measured is between -3.11% and 0.36%. While in Comparative Examples 1 - 5, when the ratio of acetic acid to acetic anhydride in the acylating agent is 3∶(2 - 5), the relative deviation of the hydroxyl group is as high as -35.84% to -14.74%. It can be seen that by using the hydroxyl value determination method of the present invention and effectively controlling the ratio of the acylating agent, the deviation between the measured hydroxyl value and the theoretical value can be effectively reduced, and the accuracy of the hydroxyl value determination can be significantly improved.

[0091] Furthermore, it can be seen from Example 7 that since the 2,3-butanediol sample does not contain epoxy bonds, it is found in the experiment that whether directly acylating it for hydroxyl value determination or using the method of first ring-opening and then acylating for hydroxyl value determination of the present invention, the obtained hydroxyl value determination results are the same.

[0092] From Example 6 in combination with Comparative Example 6, the epoxy value of the epoxidized soybean oil sample is 6.23%. When directly acylating the epoxy bond of the epoxidized soybean oil for hydroxyl value determination and first ring-opening and then acylating for hydroxyl value determination, the results of the hydroxyl values measured by the two methods are very different. The deviation of the hydroxyl value measured by the hydroxyl value determination method of the present invention is only 7.29 mgKOH / g, while the deviation of the hydroxyl value measured by the ASTM D1957-86 method is as high as 224.48 mgKOH / g. It can be seen that compared with the existing standard acylating method, the present invention can effectively improve the accuracy of the hydroxyl value determination and has incomparable technical advantages.

[0093] Test Example 2

[0094] This test example determines the hydroxyl value range of the test method of the present invention. The specific test groups and test results are as follows:

[0095] Experimental Group 1: 0.1 g of 2,3-butanediol and 5 mL of acetic acid-acetic anhydride mixed solution (3:2, v / v) were placed in a 250 mL conical flask and mixed evenly. After adding a magnetic stir bar, it was refluxed and condensed in a magnetic stirrer in a boiling water bath for 2.5 h. 10 mL of distilled water was added from the upper end of the condenser and heating was continued for 10 min, then it was cooled to room temperature under reflux and condensation conditions. 25 mL of n-butanol was measured, and half of it was added from the upper end of the condenser to wash the condensed acetic acid on the inner wall of the condenser. Then the condenser was removed, and the remaining n-butanol was used to wash the bottle wall and the interface. 1 mL of phenolphthalein indicator was added, and it was titrated with 0.001 mol / mL potassium hydroxide-ethanol standard solution until a light pink endpoint appeared; at the same time, a blank test was conducted. 9 g of 2,3-butanediol sample (accurate to 0.0001 g) was weighed and placed in a conical flask, 10 mL of acetic acid was added, shaken gently, 1 mL of phenolphthalein indicator was added, and it was titrated with 0.001 mol / mL potassium hydroxide-ethanol standard solution until a light pink endpoint appeared; at the same time, a blank test was conducted, and the hydroxyl value of the sample was calculated.

[0096] Experimental Group 2: 0.1 g of 2,3-butanediol and 5 mL of acetic acid-acetic anhydride mixed solution (3:3, v / v) were placed in a 250 mL conical flask and mixed evenly. After adding a magnetic stir bar, it was refluxed and condensed in a magnetic stirrer in a boiling water bath for 1.5 h. 10 mL of distilled water was added from the upper end of the condenser and heating was continued for 10 min, then it was cooled to room temperature under reflux and condensation conditions. 25 mL of n-butanol was measured, and half of it was added from the upper end of the condenser to wash the condensed acetic acid on the inner wall of the condenser. Then the condenser was removed, and the remaining n-butanol was used to wash the bottle wall and the interface. 1 mL of phenolphthalein indicator was added, and it was titrated with 0.001 mol / mL potassium hydroxide-ethanol standard solution until a light pink endpoint appeared; at the same time, a blank test was conducted. 9 g of 2,3-butanediol sample (accurate to 0.0001 g) was weighed and placed in a conical flask, 10 mL of acetic acid was added, shaken gently, 1 mL of phenolphthalein indicator was added, and it was titrated with 0.001 mol / mL potassium hydroxide-ethanol standard solution until a light pink endpoint appeared; at the same time, a blank test was conducted, and the hydroxyl value of the sample was calculated.

[0097] Experimental Group 3: 0.1 g of 2,3-butanediol and 5 mL of acetic acid-acetic anhydride mixed solution (3:4, v / v) were placed in a 250 mL conical flask and mixed evenly. After adding a magnetic stir bar, it was refluxed and condensed in a magnetic stirrer in a boiling water bath for 1.5 h. 10 mL of distilled water was added from the upper end of the condenser and heating was continued for 10 min, then it was cooled to room temperature under reflux and condensation conditions. 25 mL of n-butanol was measured, and half of it was added from the upper end of the condenser to rinse the condensed acetic acid on the inner wall of the condenser. Then the condenser was removed, and the remaining n-butanol was used to wash the bottle wall and the interface. 1 mL of phenolphthalein indicator was added, and it was titrated with 0.001 mol / mL potassium hydroxide-ethanol standard solution until a light pink end point appeared; at the same time, a blank test was carried out. 9 g of 2,3-butanediol sample (accurate to 0.0001 g) was weighed and placed in a conical flask, 10 mL of acetic acid was added, shaken gently, 1 mL of phenolphthalein indicator was added, and it was titrated with 0.001 mol / mL potassium hydroxide-ethanol standard solution until a light pink end point appeared; at the same time, a blank test was carried out, and the hydroxyl value of the sample was calculated.

[0098] Experimental Group 4: 0.1 g of 2,3-butanediol and 5 mL of acetic acid-acetic anhydride mixed solution (3:5, v / v) were placed in a 250 mL conical flask and mixed evenly. After adding a magnetic stir bar, it was refluxed and condensed in a magnetic stirrer in a boiling water bath for 1.5 h. 10 mL of distilled water was added from the upper end of the condenser and heating was continued for 10 min, then it was cooled to room temperature under reflux and condensation conditions. 25 mL of n-butanol was measured, and half of it was added from the upper end of the condenser to rinse the condensed acetic acid on the inner wall of the condenser. Then the condenser was removed, and the remaining n-butanol was used to wash the bottle wall and the interface. 1 mL of phenolphthalein indicator was added, and it was titrated with 0.001 mol / mL potassium hydroxide-ethanol standard solution until a light pink end point appeared; at the same time, a blank test was carried out. 9 g of 2,3-butanediol sample (accurate to 0.0001 g) was weighed and placed in a conical flask, 10 mL of acetic acid was added, shaken gently, 1 mL of phenolphthalein indicator was added, and it was titrated with 0.001 mol / mL potassium hydroxide-ethanol standard solution until a light pink end point appeared; at the same time, a blank test was carried out, and the hydroxyl value of the sample was calculated.

[0099] Experimental group 5: 0.1 g of 2,3-butanediol and 5 mL of acetic acid-acetic anhydride mixed solution (3:6, v / v) were placed in a 250 mL conical flask and mixed evenly. After adding a magnetic stir bar, it was refluxed and condensed in a magnetic stirrer in a boiling water bath for 1 h. 10 mL of distilled water was added from the upper end of the condenser and heating was continued for 10 min, and then it was cooled to room temperature under reflux and condensation conditions. 25 mL of n-butanol was measured, and half of it was added from the upper end of the condenser to rinse the condensed acetic acid on the inner wall of the condenser. Then the condenser was removed, and the remaining n-butanol was used to clean the bottle wall and the interface. 1 mL of phenolphthalein indicator was added, and it was titrated with 0.001 mol / mL potassium hydroxide-ethanol standard solution until a faint pink endpoint appeared; at the same time, a blank test was carried out. 9 g of 2,3-butanediol sample (accurate to 0.0001 g) was weighed and placed in a conical flask, 10 mL of acetic acid was added, shaken gently, 1 mL of phenolphthalein indicator was added, and it was titrated with 0.001 mol / mL potassium hydroxide-ethanol standard solution until a faint pink endpoint appeared; at the same time, a blank test was carried out, and the hydroxyl value of the sample was calculated.

[0100] Experimental group 6: 0.1 g of 2,3-butanediol and 5 mL of acetic acid-acetic anhydride mixed solution (3:2, v / v) were placed in a 250 mL conical flask and mixed evenly. After adding a magnetic stir bar, it was refluxed and condensed in a magnetic stirrer in a boiling water bath for 2 h. 10 mL of distilled water was added from the upper end of the condenser and heating was continued for 10 min, and then it was cooled to room temperature under reflux and condensation conditions. 25 mL of n-butanol was measured, and half of it was added from the upper end of the condenser to rinse the condensed acetic acid on the inner wall of the condenser. Then the condenser was removed, and the remaining n-butanol was used to clean the bottle wall and the interface. 1 mL of phenolphthalein indicator was added, and it was titrated with 0.001 mol / mL potassium hydroxide-ethanol standard solution until a faint pink endpoint appeared; at the same time, a blank test was carried out. 9 g of 2,3-butanediol sample (accurate to 0.0001 g) was weighed and placed in a conical flask, 10 mL of acetic acid was added, shaken gently, 1 mL of phenolphthalein indicator was added, and it was titrated with 0.001 mol / mL potassium hydroxide-ethanol standard solution until a faint pink endpoint appeared; at the same time, a blank test was carried out, and the hydroxyl value of the sample was calculated.

[0101] Experimental group 7: 0.5 g of methanol and 5 mL of acetic acid - acetic anhydride mixed solution (3:2, v / v) were placed in a 250 mL conical flask and mixed evenly. After adding a magnetic stir bar, it was refluxed and condensed in a magnetic stirrer in a boiling water bath for 2.5 h. 10 mL of distilled water was added from the upper end of the condenser and heating was continued for 10 min, then it was cooled to room temperature under reflux condensation conditions. 25 mL of n-butanol was measured, and half of it was added from the upper end of the condenser to rinse the condensed acetic acid on the inner wall of the condenser. Then the condenser was removed, and the remaining n-butanol was used to clean the bottle wall and the interface. 1 mL of phenolphthalein indicator was added, and it was titrated with 0.001 mol / mL potassium hydroxide - ethanol standard solution until a light pink end point appeared; at the same time, a blank test was carried out. 9 g of methanol sample (accurate to 0.0001 g) was weighed and placed in a conical flask, 10 mL of acetic acid was added, shaken gently, 1 mL of phenolphthalein indicator was added, and it was titrated with 0.001 mol / mL potassium hydroxide - ethanol standard solution until a light pink end point appeared; at the same time, a blank test was carried out, and the hydroxyl value of the sample was calculated.

[0102] Experimental group 8: 0.5 g of n-butanol and 5 mL of acetic acid - acetic anhydride mixed solution (3:2, v / v) were placed in a 250 mL conical flask and mixed evenly. After adding a magnetic stir bar, it was refluxed and condensed in a magnetic stirrer in a boiling water bath for 1.5 h. 10 mL of distilled water was added from the upper end of the condenser and heating was continued for 10 min, then it was cooled to room temperature under reflux condensation conditions. 25 mL of n-butanol was measured, and half of it was added from the upper end of the condenser to rinse the condensed acetic acid on the inner wall of the condenser. Then the condenser was removed, and the remaining n-butanol was used to clean the bottle wall and the interface. 1 mL of phenolphthalein indicator was added, and it was titrated with 0.001 mol / mL potassium hydroxide - ethanol standard solution until a light pink end point appeared; at the same time, a blank test was carried out. 9 g of n-butanol sample (accurate to 0.0001 g) was weighed and placed in a conical flask, 10 mL of acetic acid was added, shaken gently, 1 mL of phenolphthalein indicator was added, and it was titrated with 0.001 mol / mL potassium hydroxide - ethanol standard solution until a light pink end point appeared; at the same time, a blank test was carried out, and the hydroxyl value of the sample was calculated.

[0103] Test group 9: 0.5 g of isopropanol and 5 mL of acetic acid - acetic anhydride mixed solution (3:2, v / v) were placed in a 250 mL conical flask and mixed well. After adding a magnetic stir bar, the mixture was refluxed and condensed in a magnetic stirrer in a boiling water bath for 2.5 h. 10 mL of distilled water was added from the upper end of the condenser and heating was continued for 10 min, then it was cooled to room temperature under reflux and condensation conditions. 25 mL of n-butanol was measured, and half of it was added from the upper end of the condenser to rinse the condensed acetic acid on the inner wall of the condenser. Then the condenser was removed, and the remaining n-butanol was used to wash the bottle wall and the interface. 1 mL of phenolphthalein indicator was added, and it was titrated with 0.001 mol / mL potassium hydroxide - ethanol standard solution until a faint pink endpoint appeared; at the same time, a blank test was conducted. 9 g of isopropanol sample (accurate to 0.0001 g) was weighed and placed in a conical flask, 10 mL of acetic acid was added, shaken well slowly, 1 mL of phenolphthalein indicator was added, and it was titrated with 0.001 mol / mL potassium hydroxide - ethanol standard solution until a faint pink endpoint appeared; at the same time, a blank test was conducted, and the hydroxyl value of the sample was calculated.

[0104] Test group 10: 0.1 g of tert-butanol and 5 mL of acetic acid - acetic anhydride mixed solution (3:10, v / v) were placed in a 250 mL conical flask and mixed well. After adding a magnetic stir bar, the mixture was refluxed and condensed in a magnetic stirrer in a boiling water bath for 2 h. 10 mL of distilled water was added from the upper end of the condenser and heating was continued for 10 min, then it was cooled to room temperature under reflux and condensation conditions. 25 mL of n-butanol was measured, and half of it was added from the upper end of the condenser to rinse the condensed acetic acid on the inner wall of the condenser. Then the condenser was removed, and the remaining n-butanol was used to wash the bottle wall and the interface. 1 mL of phenolphthalein indicator was added, and it was titrated with 0.001 mol / mL potassium hydroxide - ethanol standard solution until a faint pink endpoint appeared; at the same time, a blank test was conducted. 9 g of tert-butanol sample (accurate to 0.0001 g) was weighed and placed in a conical flask, 10 mL of acetic acid was added, shaken well slowly, 1 mL of phenolphthalein indicator was added, and it was titrated with 0.001 mol / mL potassium hydroxide - ethanol standard solution until a faint pink endpoint appeared; at the same time, a blank test was conducted, and the hydroxyl value of the sample was calculated.

[0105] Test Group 11: 0.1 g of ethylene glycol and 5 mL of acetic acid - acetic anhydride mixed solution (3:3, v / v) were placed in a 250 mL conical flask and mixed evenly. After adding a magnetic stir bar, it was refluxed and condensed in a magnetic stirrer in a boiling water bath for 1.5 h. 10 mL of distilled water was added from the upper end of the condenser and heating was continued for 10 min, then it was cooled to room temperature under reflux and condensation conditions. 25 mL of n-butanol was measured, and half of it was added from the upper end of the condenser to wash the condensed acetic acid on the inner wall of the condenser. Then the condenser was removed, and the remaining n-butanol was used to wash the bottle wall and the interface. 1 mL of phenolphthalein indicator was added, and it was titrated with 0.001 mol / mL potassium hydroxide - ethanol standard solution until a faint pink endpoint appeared; at the same time, a blank test was conducted. 9 g of ethylene glycol sample (accurate to 0.0001 g) was weighed and placed in a conical flask, 10 mL of acetic acid was added, shaken slowly, 1 mL of phenolphthalein indicator was added, and it was titrated with 0.001 mol / mL potassium hydroxide - ethanol standard solution until a faint pink endpoint appeared; at the same time, a blank test was conducted, and the hydroxyl value of the sample was calculated.

[0106] Test Group 12: 0.1 g of glycerol and 5 mL of acetic acid - acetic anhydride mixed solution (3:6, v / v) were placed in a 250 mL conical flask and mixed evenly. After adding a magnetic stir bar, it was refluxed and condensed in a magnetic stirrer in a boiling water bath for 2 h. 10 mL of distilled water was added from the upper end of the condenser and heating was continued for 10 min, then it was cooled to room temperature under reflux and condensation conditions. 25 mL of n-butanol was measured, and half of it was added from the upper end of the condenser to wash the condensed acetic acid on the inner wall of the condenser. Then the condenser was removed, and the remaining n-butanol was used to wash the bottle wall and the interface. 1 mL of phenolphthalein indicator was added, and it was titrated with 0.001 mol / mL potassium hydroxide - ethanol standard solution until a faint pink endpoint appeared; at the same time, a blank test was conducted. 9 g of glycerol sample (accurate to 0.0001 g) was weighed and placed in a conical flask, 10 mL of acetic acid was added, shaken slowly, 1 mL of phenolphthalein indicator was added, and it was titrated with 0.001 mol / mL potassium hydroxide - ethanol standard solution until a faint pink endpoint appeared; at the same time, a blank test was conducted, and the hydroxyl value of the sample was calculated.

[0107] The hydroxyl value results calculated for each of the above test groups are shown in Table 3.

[0108] Table 3 Hydroxyl values and their deviations of each test group

[0109]

[0110] As can be seen from the results in Table 3, for the test method of the present invention, the maximum value of the measured hydroxyl value can reach 1827 mg KOH / g, and the relative deviation value of the hydroxyl value is small. Therefore, the present invention can at least accurately measure the hydroxyl value of polyol samples within the range of 1827 mg KOH / g hydroxyl value, and the hydroxyl value measurement range is significantly better than the existing methods for acylating and measuring hydroxyl values.

[0111] In summary, the method for determining the hydroxyl value of vegetable oil-based and its derivative-based polyols provided by the present invention is more environmentally friendly, has a wide range of hydroxyl value determination and high accuracy, and has good prospects for popularization and application in the improvement of the production process and product quality control of vegetable oil-based and its derivative-based polyols.

Claims

1. A method for determining the hydroxyl value of a vegetable oil-based and its derivative-based polyol, characterized in that, It includes the following steps: (1) Subject the polyol sample to be measured to a ring-opening treatment to completely destroy the epoxy bonds in the sample, and measure the epoxy value of the sample; the polyol sample is a vegetable oil-based polyol sample and / or a vegetable oil derivative-based polyol sample; (2) Extract the sample after epoxy value measurement in step (1) with a solvent, and then remove the solvent to obtain a ring-opened sample of the polyol; (3) Mix the ring-opened sample of the polyol with an acylating agent for an acylation reaction, and then perform a chemical titration with a standard alkali solution to measure the total hydroxyl value of the ring-opened sample of the polyol; then, use the total hydroxyl value and the change value of the hydroxyl value caused by the epoxy bonds in the sample calculated from the epoxy value to calculate the difference between the total hydroxyl value and the change value of the hydroxyl value, and the obtained difference is the actual hydroxyl value of the polyol sample to be measured; Among them, in step (1), the ring-opening treatment is carried out with a hydrochloric acid-acetone solution; in step (3), the acylating agent is an acetic acid-acetic anhydride mixed solution; in the acetic acid-acetic anhydride mixed solution, the volume ratio of acetic acid to acetic anhydride is 1∶(2 - 6).

2. The method for determining the hydroxyl value of the vegetable oil-based and its derivative-based polyols according to claim 1, characterized in that, In step (1), the polyol sample is prepared by an epoxidation-hydroxylation method; the vegetable oil-based polyol sample is selected from one or more of soybean oil-based polyol, rapeseed oil-based polyol, sunflower seed oil-based polyol, Canola oil-based polyol, castor oil-based polyol, linseed oil-based polyol, rice bran oil-based polyol; the vegetable oil derivative-based polyol sample is selected from one or more of free fatty acid-based polyol, fatty acid methyl ester-based polyol, fatty acid ethyl ester-based polyol, monoglyceride-based polyol, diglyceride-based polyol, triglyceride-based polyol.

3. The method for determining the hydroxyl value of the vegetable oil-based and its derivative-based polyols according to claim 1, wherein, In step (1), the hydroxyl value range of the polyol sample to be measured is ≤1827mgKOH / g; the epoxy value is measured according to method A in standard GB / T1677-2008.

4. The method for determining the hydroxyl value of the vegetable oil-based and its derivative-based polyols according to claim 1, characterized in that, In step (2), the number of extractions is 2 - 4 times; the solvent is ether or ethyl acetate; after extraction, it also includes a step of removing water with a desiccant; the removal of the solvent is by vacuum distillation to remove the solvent.

5. The method for determining the hydroxyl value of a vegetable oil-based and its derivative-based polyol according to claim 1, characterized in that, In step (3), the acylation reaction is carried out under thermal reflux conditions; the time of the acylation reaction is 2 - 3h.

6. The method for determining the hydroxyl value of a vegetable oil-based and its derivative-based polyol according to claim 1, characterized in that, In step (3), the standard alkali solution is a potassium hydroxide standard solution; the specific steps for measuring the total hydroxyl value of the sample are: mix the ring-opened sample of the polyol with the acylating agent for an acylation reaction, then add water to continue the reaction, cool after the reaction, titrate to the end point with a potassium hydroxide standard solution, and record the volume of the potassium hydroxide standard solution consumed by the ring-opened sample of the polyol during acylation; at the same time, perform a blank test with only the acylating agent added, and record the volume of the potassium hydroxide standard solution consumed during the blank test of acylation; Take another ring-opened sample of the polyol, perform an acidity titration with a potassium hydroxide standard solution, and perform a blank test at the same time to obtain the volume of the potassium hydroxide standard solution consumed by the ring-opened sample of the polyol during acidity measurement; Finally, calculate the total hydroxyl value of the ring-opened sample of the polyol according to the calculation formula for measuring the hydroxyl value by the acylation method.

7. The method for determining the hydroxyl value of a vegetable oil-based and its derivative-based polyol according to claim 6, characterized in that, In step (3), the dosage ratio of the ring-opening sample of polyol to the acylating agent is (0.06 - 0.8) g∶(3.5 - 10) mL; the concentration of the potassium hydroxide standard solution is 0.001 mol / mL; the concentration of the potassium hydroxide standard solution used in the acylation titration and the acidity titration is the same; when determining the acidity, the mass of the ring-opening sample of polyol used is 9 - 11 g.

8. The method for determining the hydroxyl value of a vegetable oil-based and its derivative-based polyol according to claim 6 or 7, characterized in that, The specific process for obtaining the volume of the potassium hydroxide standard solution consumed by the ring-opening sample of polyol during the acidity determination is as follows: Weigh the ring-opening sample of polyol, add acetic acid and an indicator, and then titrate with the potassium hydroxide standard solution to the end point to obtain the volume of the potassium hydroxide standard solution consumed by the ring-opening sample of polyol and acetic acid in total; at the same time, conduct a blank test without adding the ring-opening sample of polyol to obtain the volume of the potassium hydroxide standard solution consumed by acetic acid; calculate the difference between the volume of the potassium hydroxide standard solution consumed by the ring-opening sample of polyol and acetic acid in total and the volume of the potassium hydroxide standard solution consumed by acetic acid during the blank test, which is the volume of the potassium hydroxide standard solution consumed by the ring-opening sample of polyol during the acidity determination.

9. The method for determining the hydroxyl value of a vegetable oil-based and its derivative-based polyol according to any one of claims 1 to 7, characterized in that, In step (1), the calculation formula for the epoxy value is: Wherein, X0 is the epoxy value, unit %; 16 is a constant, which is the molar mass of oxygen, unit g / mol; v0 is the volume of the sodium hydroxide standard solution consumed in the blank test during the determination of the epoxy value of the polyol sample, unit mL; v1 is the volume of the sodium hydroxide standard solution consumed by the polyol sample during the acidity determination, unit mL; v2 is the volume of the sodium hydroxide standard solution consumed by the polyol sample during the epoxy value determination, unit mL; C N is the concentration of the sodium hydroxide standard solution, unit mol / mL; m1 is the mass of the polyol sample during the epoxy value determination, unit g; m2 is the mass of the polyol sample during the acidity determination, unit g; In step (3), the calculation formula for the total hydroxyl value is: where X 总 is the total hydroxyl value, in mgKOH / g; 56.1 is a constant, representing the molar mass of potassium hydroxide, with the unit g / mol; v'0 is the volume of the potassium hydroxide standard solution consumed in the blank test of acylation, with the unit mL; v3 is the volume of the potassium hydroxide standard solution consumed by the ring-opening sample of polyol during acidity determination, with the unit mL; v4 is the volume of the potassium hydroxide standard solution consumed by the ring-opening sample of polyol during acylation, with the unit mL; C K is the concentration of the potassium hydroxide standard solution, with the unit mol / mL; m3 is the mass of the ring-opening sample of polyol reacting with the acylating agent, with the unit g; m4 is the mass of the ring-opening sample of polyol during acidity determination, with the unit g.

10. The method for determining the hydroxyl value of the vegetable oil-based and its derivative-based polyols according to claim 9, characterized in that, In step (3), the actual hydroxyl value of the polyol sample is calculated through the following formula: Wherein, X is the actual hydroxyl value of the polyol sample, in units of mgKOH / g; X 总 is the total hydroxyl value, in units of mgKOH / g; X0 is the epoxy value, in units of %; 56.1 is a constant, referring to the molar mass of potassium hydroxide, with the unit of g / mol; 16 is a constant, being the molar mass of oxygen, with the unit of g / mol; is the change value of hydroxyl value caused by epoxy bonds in the sample calculated from the epoxy value.

Images