JPH08178842A - Method for analyzing constituent concentration of dihydric alcohol - Google Patents

Abstract

PURPOSE: To realize an on-line short time analysis of the constituent concentration of dihydric alcohol by measuring the absorbance at least one wavelength in a specified region for a plurality of reference samples of dihydric alcohol having known different constituent concentrations using a near infrared spectroscopic analyzer. CONSTITUTION: (a). The absorbance is measured at least one wavelength in the band of 800-2500nm using a near infrared spectroscopic analyzer. (b). Statistic processing including multiple regression analysis or partial least square analysis is then performed according to a calibration equation representative of the relationship of constituent components of dihydric alcohol including the absorbance as an independent variable based on the known constituent components of dihydric alcohol of each sample and the absorbance of the sample determined in step (a). The offset constants and the weighting constants for the variables in the equation are then determined to establish a calibration equation for determining the constituent components of dihydric alcohol based on the absorbance measured by the analyzer thus determining the constituent components of dihydric alcohol.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for analyzing the concentration of a dihydric alcohol component, more specifically, phenols, dihydric alcohols and alkaline earth metal oxides or hydroxides, The dihydric alcohol in the reaction product and intermediate product obtained by reacting sulfur as necessary,
For example, the present invention relates to a method for analyzing the component concentrations of ethylene glycol, propylene glycol, trimethylene glycol and the like.

[0002]

2. Description of the Related Art Analyzing the concentration of dihydric alcohols, such as ethylene glycol, in the above-mentioned reaction products and intermediate products controls the production process of those reaction products and intermediate products in the actual production site. It is always necessary to do this. For example, in the method for producing an overbased sulfurized alkaline earth metal phenate-type detergent described in JP-A-3-26793, measuring the component concentration of ethylene glycol in the reaction product and the intermediate product is It occupies an extremely important position in producing a basic sulfurized alkaline earth metal phenate type detergent. The method for producing the overbased alkaline earth sulfide metal phenate-type detergent disclosed in the above publication is
Phenols, dihydric alcohols and alkaline earth metal oxides or hydroxides with sulfur added are reacted to simultaneously carry out metal addition and sulfidation of phenols (first reaction), followed by carbon disulfide treatment. In the method for producing an overbased sulfurized alkaline earth metal phenate-type detergent consisting of performing (second reaction), metal addition and sulfurization are performed under pressure / sealing conditions. Hereinafter, ethylene glycol will be described as an example of the dihydric alcohol.

In the above-mentioned detergent manufacturing process, analysis of the ethylene glycol component concentration is necessary to analyze the ethylene glycol component concentration in the intermediate product after the completion of the first reaction step. That is, in the second reaction step, the intermediate product obtained in the first reaction is distilled to remove at least a part of the product water in the intermediate product or all the product water and at least a part of the unreacted dihydric alcohol. It will take place after distilling off.
The ethylene glycol component concentration analysis is a process of distilling the intermediate product obtained in the first reaction step, and the progress of the distillation process is controlled by measuring the ethylene glycol component concentration in the distillation residue. Then, it is performed in order to determine the time to shift to the second reaction step. It is also necessary to measure the concentration of ethylene glycol component in the reaction product obtained in the second reaction step.

As another example, Japanese Patent Laid-Open No. 64-2935.
The necessity of analysis of the component concentration of ethylene glycol will be explained with reference to the method for producing a sulfurized mixture of an alkaline earth metal salt of hydroxyalkylbenzoic acid and alkylphenol disclosed in Japanese Patent Publication No. This production method comprises: a phenol, an ethylene glycol, and a reaction raw material mixture comprising an oxide or hydroxide of an alkaline earth metal having a gram equivalent ratio to the phenol of 0.99 or less, or a mixture thereof. And then distilling off ethylene glycol until the amount becomes 0.6 mol or less per mol of water and the alkaline earth metal reagent, carbon dioxide is reacted with the obtained distillation residue, and the obtained product is treated with alkali. It is characterized by reacting 0.1 to 4 mol of elemental sulfur per mol of the earth metal reagent. Even in the case of this production method, in order to control the progress of the distillation step, it is necessary to analyze the concentration of the dihydric alcohol, that is, ethylene glycol, in the distillation residue.

In any of the above-mentioned manufacturing processes, it is necessary to promptly confirm the end point of distillation at which the ethylene glycol component concentration in the distillation residue becomes constant by distillation. Otherwise, in the next reaction step, it is not possible to produce high quality products, for example high quality additives by the above two methods. One of the most troublesome problems in this field, especially for commercial operators, has been to know when the constituent concentrations of ethylene glycol in the distillation residue have reached practically useful concentrations.

By the way, conventionally, gas chromatographic methods have been used to analyze the concentration of ethylene glycol components. In the gas chromatographic method, a sample is injected into a separation column and is carried by an eluting inert gas such as helium until it reaches the final end of the separation column. , A heat conduction detector or other detector, and based on that, the ethylene glycol component concentration is calculated.

[0007]

However, in the gas chromatographic method, analysis takes a long time, so that the feedback of the analysis value is delayed, and therefore, for example, the above-mentioned overbased sulfurized alkaline earth metal phenate type detergent is not used. It is technically difficult to adopt the gas chromatograph method as an online analysis method with a fast response in order to control the process of the manufacturing apparatus. Therefore, an object of the present invention is to provide a method for analyzing the component concentration of a dihydric alcohol, such as ethylene glycol, which requires a short time for analysis and enables on-line analysis.

[0008]

Means for Solving the Problems After trying various analytical methods, the present inventor focused on near-infrared spectroscopy and studied its application. Near infrared ray (800 nm to 2500 n
m, or light having a wave number of 12500 cm ^{-1 to} 4000 cm ^-1 ) is irradiated to the substance, absorption specific to the substance is observed at a specific wavelength. This absorbed near-infrared light is the overtone and binding sound of the standard vibration of the molecule of the substance, and the near-infrared spectroscopic analysis method measures the absorbance at the specific wavelength, and by performing predetermined data processing, It is a method of calculating the component concentration of the substance. Near-infrared spectroscopy is a method for measuring the composition and properties of hydrocarbon mixtures in recent years.
Experimental attempts have been made to analyze the composition of paraffins, olefins and aromatics or to measure the octane number of gasoline.

However, near infrared spectroscopy has not yet been attempted for the component analysis of complex composition mixtures such as intermediates in the additive manufacturing process, especially for the concentration analysis of dihydric alcohols such as ethylene glycol. Not reported. It is an extremely complicated mixture consisting of various components as an intermediate in the additive manufacturing process, and the composition ratio of ethylene glycol and other mixtures differs from sample to sample. It was thought to be very difficult to do.

The present inventors have studied the application of near-infrared spectroscopic analysis and found that the near-infrared spectroscopic analysis can be applied to the analysis of the component concentration of ethylene glycol in the above-mentioned intermediate product and reaction product. It was verified as follows. First,
As the first step, samples 1 to 6 in which the concentration of ethylene glycol component was gradually decreased were prepared. All of the samples were obtained from the bottom residue of the distillation pot where the intermediate product obtained in the first reaction step of the above-mentioned overbased sulfurized alkaline earth metal phenate type detergent was subjected to simple distillation. Therefore, the compositions of Samples 1 to 6 are different from each other in the ethylene glycol component concentration, the solvent component concentration, the alkylphenol component concentration, and the particle concentration. A predetermined amount of toluene was added to this, and the mixture was stirred, and then subjected to a centrifugal separator to remove particles, and a sample was prepared. Then, the optical density (hereinafter, abbreviated as "absorbance") was measured in the wavelength region of 800 to 2500 nm, and the results shown in FIG. 1 were obtained. In FIG. 1, the horizontal axis represents the wavelength of near infrared rays and the vertical axis represents the absorbance, showing the relationship between absorbance and wavelength.

As the second step, a mathematical function was obtained for the absorbance vs. wavelength relationship shown in FIG. As examples of mathematical functions, the relationship between the absorbance vs. wavelength itself shown in FIG. 1, the function of the primary differential value versus the wavelength obtained by first-derivating the absorbance vs. wavelength relationship with wavelength,
There is a function of the second derivative of the second derivative versus the wavelength, and further a function of the higher derivative versus the wavelength. FIG. 2 shows a functional relationship between the second derivative value and the wavelength obtained by second-derivating the absorbance-wavelength relationship of six samples, Samples 1 to 6, which have different ethylene glycol component concentrations, at a wavelength interval of 2 nm. hand,
When expanded, it can be seen that the order of the concentration of ethylene glycol components in the sample (shading of the concentration) corresponds to the order of the second derivative of the absorbance of the sample (the magnitude of the second derivative).

FIG. 3 shows the functional relationship between the second derivative of the absorbance of one sample and the wavelength (thick line), and 10 for ethylene glycol.
It is a graph which contrasted the 2nd derivative value of the light absorbency of 0% sample, and the functional relationship (thin line) of wavelength, and was piled up and shown on the same drawing. As can be seen from FIG. 3, there is a correlation between the sample sample and the 100% ethylene glycol sample in the specific wavelength range regarding the absorption of CH ₂ overtones, 3rd overtones, and OH overtones peculiar to ethylene glycol. And the wavelength range is a characteristic wavelength that can be used to measure the concentration of the ethylene glycol component. From FIG. 2 and FIG. 3, 800-2500 nm
It can be seen that the ethylene glycol component in the sample can be identified and the concentration of the component can be detected by using the characteristic wavelength within the wavelength region of.

The concentration of ethylene glycol in Samples 1 to 6 was measured by a gas chromatograph method.
FIG. 4, in which the horizontal axis represents wavelength and the vertical axis represents correlation coefficient, shows the correlation between the concentration of ethylene glycol component of Samples 1 to 6 and the second derivative of the absorbance versus wavelength relationship. FIG. 4 is a graph showing that the closer the correlation coefficient is to 1.00 or −1.00, the better the correlation between the absorbance of ethylene glycol with the wavelength and the second derivative absorbance of the sample,
The correlation coefficient shows a value close to 1.00 or -1.00 in many wavelength regions.

From these correlated wavelength ranges, three wavelength ranges centered around arbitrary 1784 nm, 1844 nm and 2312 nm are selected, and then the absorbance vs. wavelength of the three wavelength ranges selected for each sample. Seeking a relationship,
The function value (second derivative value) of the second derivative function obtained by second derivative of the absorbance vs. wavelength is 1784 nm, 1844 nm, 2
It was determined for each of the three wavelengths of 312 nm. With respect to the calibration equation of the ethylene glycol component concentration in which the second-order differential functions in the three wavelength regions are independent variables, the second-order derivative value of each sample obtained for each wavelength,
Based on the analysis value of the component concentration of ethylene glycol by the gas chromatographic method, one of the statistical processing including the multiple regression analysis method and the partial least squares analysis method is performed, and the offset constant of the calibration equation and the independent variable A weighting constant was determined, and a calibration equation was established to calculate the ethylene glycol component concentration based on the absorbance measured by a near infrared spectrophotometer.

Then, again by a near infrared spectrophotometer,
Sample 1 showing the relationship between the absorbance and wavelength of the three selected wavelength ranges
From the above, the second derivative of the absorbance vs. wavelength relationship at the selected wavelength was determined in the same manner as described above, and the component concentration of ethylene glycol was calculated by the calibration equation.

FIG. 5 shows samples 1 to 6 calculated by the obtained calibration equation by performing the statistical processing by the multiple regression analysis method to obtain the calibration equation.
3 shows the comparison between the analysis value of the component concentration of ethylene glycol and the analysis value of the component concentration of ethylene glycol of Samples 1 to 6 by gas chromatography. Figure 5
As can be seen, the analytical values obtained by both analytical methods are correlated with a correlation coefficient of 0.9996, and the calibration equation obtained by the multiple regression analytical method was used to measure the concentration of ethylene glycol. I know that you can do it. Therefore, the absorbance-wavelength relationship in a specific wavelength region is obtained for a plurality of samples with mutually different ethylene glycol component concentrations, and multiple regression analysis is performed from the second-order differential value at the specific wavelength of the ethylene glycol component concentration and the absorbance-wavelength relationship. If the calibration equation is obtained in advance by the method, the component concentration of ethylene glycol in the sample can be obtained from the calibration equation created in advance in the subsequent measurement.

Instead of the multiple regression analysis method, statistical processing by the partial least squares analysis method can be performed. FIG. 6 shows a calibration equation obtained by performing statistical processing by the partial least squares method, the analysis values of the component concentrations of ethylene glycol of Samples 1 to 6 calculated by the obtained calibration equation, and Sample 1 by the gas chromatograph method. 7 shows the comparison with the analysis values of the component concentrations of ethylene glycol of Nos. 6 to 6. As can be seen from FIG. 6, the analytical values obtained by both analytical methods are correlated with a correlation coefficient of 0.9996, and the calibration equation obtained by the partial least squares method is for measuring the concentration of ethylene glycol. It can be used for. Therefore, the absorbance-wavelength relationship in a specific wavelength range is obtained for a plurality of samples with known different ethylene glycol component concentrations, and the partial minimum two If the calibration equation is obtained in advance by the multiplication method, the component concentration of ethylene glycol in the sample can be obtained from the previously prepared calibration equation in the subsequent measurement.

Based on the above experiments, the method for analyzing the component concentration of the dihydric alcohol according to the present invention is carried out by using phenols, dihydric alcohols and alkaline earth metal oxides or alkaline earth metal hydroxides, and if necessary. In the method for analyzing the component concentration of a dihydric alcohol in a reaction product and an intermediate product obtained by reacting sulfur with sulfur, (1) a plurality of standards having different known component concentrations of a dihydric alcohol For each of the samples, (a) the near infrared spectrophotometer was used to measure the absorbance at at least one wavelength in the 800-2500 nm band, and (b) the component concentration of the dihydric alcohol with absorbance as the independent variable. For a calibration equation consisting of a function, multiple regression analysis was performed based on the known component concentration of the dihydric alcohol in each sample and the absorbance of each sample determined in step (a). Method or partial statistical analysis including partial least squares analysis is performed to determine the offset constant of the calibration equation and the weighting constant for the independent variable, based on the absorbance measured by the near infrared spectrophotometer. Establishing a calibration equation to calculate the component concentration of the dihydric alcohol, (2) then, using a near infrared spectrophotometer, perform the above step (a) on the measurement sample, and further based on the absorbance measurement value. It is characterized in that the concentration of the dihydric alcohol component of the measurement sample is calculated according to the calibration equation.

Further, a more preferable method for analyzing the component concentration of the dihydric alcohol according to the present invention is to use phenols, dihydric alcohols and alkaline earth metal oxides or alkaline earth metal hydroxides, and if necessary, A method for analyzing the component concentration of a dihydric alcohol in a reaction product and an intermediate product obtained by reacting sulfur, comprising: (1) a plurality of reference samples having different known dihydric alcohol component concentrations. (A) using a near-infrared spectrophotometer for each of the above, determining the absorbance versus wavelength relationship in at least one wavelength region of the 800-2500 nm band,
(B) Select one of a function obtained by first-order differentiating the absorbance vs. wavelength relationship in each wavelength region by wavelength, a second-order differentiated function, and a higher-order differentiated function, and (c) specify in each wavelength region. Each wavelength is selected, (d) the function value of the selected function is calculated for the specific wavelength, and (e) step (b)
Based on the known component concentration of the dihydric alcohol in each sample and the function value of each sample obtained in step (d), with respect to the calibration equation consisting of the function of the component concentration of the dihydric alcohol whose independent variable is the function selected in By performing any of the statistical processing including the multiple regression analysis method and the partial least squares analysis method, the offset constant of the calibration equation and the weight constant for the independent variable are determined,
A calibration equation was established to calculate the component concentration of the dihydric alcohol based on the absorbance measured by the near-infrared spectrophotometer, and (2) the near-infrared spectrophotometer was then used to perform the above steps for the measurement sample ( It is characterized in that a) and (d) are carried out and the concentration of the dihydric alcohol component in the measurement sample is calculated according to the calibration equation based on the obtained function value.

The method of the present invention can be applied to the analysis of samples having a wide range of component concentrations of dihydric alcohols such as ethylene glycol. The lower limit of measurement is about 0.1% and the upper limit is 100%. % Mass concentration. The specifications of the near-infrared spectrophotometer used in the method of the present invention are not particularly limited, and commercially available products can be used. The wavelength to be used is a wavelength or wavelength range in which the absorbance changes maximally in response to changes in the ethylene glycol component concentration in the 800 to 2500 nm band. From the viewpoint of measurement accuracy, for example, around 1784 nm, around 1844 nm,
It is preferable to use the wavelength range around 2312 nm. That is, in order to improve the measurement accuracy, a wavelength region (for example, around 1784 nm) having the largest absolute value of the correlation coefficient of the correlation equation for a single wavelength is first selected in the measurement wavelength region. After that, the wavelength range that maximizes the correlation coefficient (for example, around 1844 nm and around 2312 nm) is sequentially selected. In the present invention, the plurality of reference samples of known ethylene glycol component concentration used for obtaining the calibration equation are preferably close to the sample for which the ethylene glycol component concentration needs to be measured from the viewpoint of analytical accuracy. It is preferably a composition. The concentration of ethylene glycol component is determined by gas chromatography.

In the present invention, the calibration equation is expressed by the following equation (1). c = K ₀ + K ₁ * r ₁ + K ₂ * r ₂ + ... + K _n * r _n (1) where K ₀ : offset constant K _n : absorbance at wavelength λ _n or mathematics of absorbance versus wavelength weight constant r _n for objective function values: wavelength mathematical function value of absorbance or absorbance versus wavelength relationship lambda _n C: the component concentration (mass% or weight%), the calibration equation, than the function of the absorbance as a variable It is preferable to use a mathematical function of the relationship between absorbance and wavelength as a variable from the viewpoint of analysis accuracy because disturbance can be removed, and in particular, the first derivative or the second derivative depending on the wavelength of the absorbance wavelength relationship is most preferable. Similarly, higher order differentials can be used, but noise tends to be emphasized as the order becomes higher, and conversely the tendency becomes worse. The statistical processing including the multiple regression analysis method and the partial least squares analysis method used in the method of the present invention are both known statistical methods,
It is not particularly peculiar to the method of the present invention.

When the viscosity of the measurement sample is high, it is desirable to prepare a measurement sample having a low viscosity by diluting with a suitable solvent such as toluene. Further, when solid or quasi-solid particles are suspended in the sample, it is desirable to prepare a measurement sample in which particles are separated in advance by a particle separator such as a centrifugal separator. By preparing the sample in this way,
The viscosity of the measurement sample is reduced, and the subsequent analysis operation for quantifying the ethylene glycol concentration by the near-infrared spectroscopic analysis method is simplified, and the analysis accuracy can be improved. In particular, the reaction product and intermediate product obtained in the above-mentioned manufacturing process of the overbased alkaline earth metal phenate detergent are:
The viscosities are high and the temperatures at which they flow are above about 120 ° C. Therefore, filling the sample cells with the measurement samples obtained from them requires heating the samples to about 140 ° C. or diluting with a solvent for easy handling. When using on-line analysis at the production site or immersion probes, the heating method is easier, but for laboratory analysis it is easier to dilute with solvent. As the solvent, a commonly used solvent such as toluene or n-hexane can be used. When the sample is measured without diluting it with a solvent, the heated sample is filled in the reflective cell of the near-infrared analyzer or is directly connected to the manufacturing process line to collect the sample for measurement.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in more detail with reference to embodiments. Analysis Example 1 A model NIRS6500 manufactured by NIRS Systems was prepared as a near-infrared spectrophotometer and calibrated in advance according to the method of the present invention. 17 as the wavelength used
84nm, 1844nm, selects the 2312Nm, calibration equation, C = 9.814-26.914r ₁ -25.055r ₂
+ 1.580r is _3. Here, C: ethylene glycol wt% r ₁ : second derivative of absorbance at wavelength of 1784 nm r ₂ : second derivative of absorbance at wavelength of 1844 nm r ₃ : second derivative of absorbance at wavelength of 2312 nm . Then, in the step of producing the overbased sulfurized alkaline earth metal phenate-type detergent by the above-mentioned production method, the intermediate product obtained in the first reaction is subjected to simple distillation to remove residual light fraction such as ethylene glycol. Samples 1 to 6 were collected from the residue of the bottom of the simple distillation still. The sample is
The distillation time has passed in the order of Nos. 1 to 6, and therefore the residual ethylene glycol is low. Collect 5 g of each sample in a 50 ml beaker and
Toluene is added to dissolve the sample and the total volume is 25 ml.
Samples 1 to 6 were prepared. When the sample contained particles, the particles were removed by centrifugation.

By using a calibrated near-infrared spectrophotometer, 800 to 800 for prepared measurement samples 1 to 6.
The absorbance-wavelength relationship at 2500 nm is determined, and the wavelength 1784
The analytical values (mass%) of the ethylene glycol component concentration in the measurement sample were obtained as shown in Table 1 according to the calibration equation based on the second derivative values at nm, 1844 nm, and 2312 nm. Moreover, the component concentration of ethylene glycol was measured by the gas chromatographic method for the same measurement sample, and the measured values are also shown in Table 1.

[Table 1]

Analytical Example 2 Samples obtained from another batch of simple distillation residual oil were sampled, and measurement samples 7 to 10 were prepared in the same manner as in Analytical Example 1. Then, the concentration of ethylene glycol in the measurement sample was measured by the method of the present invention and the gas chromatograph method, and the results shown in Table 1 were obtained.

Analytical Example 3 Samples were taken from still another batch of simple distillation residual oil, and measurement samples 11 to 14 were prepared in the same manner as in Analytical Example 1. Then, the concentration of ethylene glycol in the measurement sample was measured by the method of the present invention and the gas chromatograph method.
The results shown in are obtained.

Analytical Example 4 The same as Analytical Example 1 except that the sample taken from the residue of the simple distillation pot was used as it was as a measurement sample without being diluted with a solvent, and the viscosity was reduced by heating. Measurement samples 15 to 21 were prepared by measuring the concentration of ethylene glycol component in the measurement samples, and the results shown in Table 2 were obtained.

[Table 2]

As is clear from the results shown in Tables 1 and 2, the analysis results of the measurement samples 1 to 14 correlate with the gas chromatographic method with a correlation coefficient of 0.996, and the analysis accuracy is 5% or less. there were. The time required for the analysis was about 10 minutes, and the processing time was remarkably shortened as compared with the gas chromatographic method. Therefore, the method of the present invention comprises a concentration of ethylene glycol in a reaction product and an intermediate product obtained by reacting phenols, ethylene glycol, an alkaline earth metal oxide or hydroxide, and optionally sulfur. It can be said that it has been proved that it is extremely useful as a method for analyzing, and is particularly applicable to real-time online analysis at the production site.

[0029]

According to the method of the present invention, after the calibration equation is established in advance by the procedure specified in the method of the present invention, the near infrared absorption of the sample is measured using the near infrared spectrophotometer, and the absorbance is measured. By calculating the component concentration of ethylene glycol in the sample according to the calibration equation based on the function value at the specific wavelength of the mathematical function specified for the relationship with respect to wavelength, phenols, ethylene glycol and alkaline earth metal oxides or water are calculated. It is possible to easily analyze the component concentration of ethylene glycol in the reaction product and intermediate product obtained by reacting the oxide and, if necessary, sulfur. By using the method of the present invention, the component concentration of ethylene glycol in a sample can be accurately and easily analyzed in a short time, so that it can be applied to real-time online analysis at a production site, thereby appropriately controlling the production process. You can

[Brief description of drawings]

FIG. 1 is a near-infrared region spectrum of six samples having different ethylene glycol component concentrations.

FIG. 2 shows the spectrum in the near infrared region in FIG.
It is a graph of the secondary differential value with respect to wavelength of the absorbance of each sample versus wavelength.

FIG. 3 is a diagram showing one of the graphs of the second-order differential value versus wavelength of the absorbance shown in FIG. 2 and the second-order derivative value of absorbance of ethylene glycol in the near infrared region versus wavelength.

FIG. 4 is a graph showing the correlation between the measured value of the ethylene glycol component concentration measured by a gas chromatograph method and the measured value of the ethylene glycol component concentration obtained from the second derivative of the absorbance with respect to the wavelength. .

FIG. 5 is a graph showing a comparison of the ethylene glycol component concentrations obtained by gas chromatography and near infrared spectroscopy (statistical processing by multiple regression analysis).

FIG. 6 is a graph showing a comparison of ethylene glycol component concentrations obtained by gas chromatography and near infrared spectroscopy (statistical processing by partial least squares analysis).

Claims (2)

[Claims] 1. A phenol, a dihydric alcohol, an alkaline earth metal oxide or an alkaline earth metal hydroxide, and, if necessary, a reaction product obtained by reacting sulfur and a divalent in an intermediate product. In the method for analyzing the component concentration of alcohol, (1) for each of a plurality of reference samples having different known component concentrations of dihydric alcohol, (a) using a near-infrared spectrophotometer, Absorbance of at least one wavelength in the 800-2500 nm band is measured, and (b) a calibration equation composed of a function of the component concentration of the dihydric alcohol having the absorbance as an independent variable, and the known component concentration of the dihydric alcohol of each sample, Based on the absorbance of each sample obtained in step (a), either statistical processing including multiple regression analysis method and partial least squares analysis method is performed to Establishing a calibration equation for determining the offset constant and the weighting constant for the independent variable of the libration equation and calculating the component concentration of the dihydric alcohol based on the absorbance measured by the near-infrared spectrophotometer, (2) Using the near-infrared spectrophotometer, the above step (a) is performed on the measurement sample, and the concentration of the dihydric alcohol component of the measurement sample is calculated according to the calibration equation based on the measured absorbance value. Analytical method for concentration of polyhydric alcohol components. 2. A phenol, a dihydric alcohol, an alkaline earth metal oxide or an alkaline earth metal hydroxide, and a divalent compound in a reaction product and an intermediate product obtained by reacting sulfur, if necessary. In the method for analyzing the component concentration of alcohol, (1) for each of a plurality of reference samples having different known component concentrations of dihydric alcohol, (a) using a near-infrared spectrophotometer, The absorbance vs. wavelength relationship is determined in at least one wavelength region of 800 to 2500 nm band,
(B) Select one of a function obtained by first-order differentiating the absorbance vs. wavelength relationship in each wavelength region by wavelength, a second-order differentiated function, and a higher-order differentiated function, and (c) specify in each wavelength region. Each wavelength is selected, (d) the function value of the selected function is calculated for the specific wavelength, and (e) step (b)
Based on the known component concentration of the dihydric alcohol in each sample and the function value of each sample obtained in step (d), with respect to the calibration equation consisting of the function of the component concentration of the dihydric alcohol whose independent variable is the function selected in By performing any of the statistical processing including the multiple regression analysis method and the partial least squares analysis method, the offset constant of the calibration equation and the weight constant for the independent variable are determined,
A calibration equation was established to calculate the component concentration of the dihydric alcohol based on the absorbance measured by the near-infrared spectrophotometer, and (2) the near-infrared spectrophotometer was then used to perform the above steps for the measurement sample ( A method for analyzing the component concentration of a dihydric alcohol, which comprises performing a) and (d), and further calculating the concentration of the dihydric alcohol component of the measurement sample according to a calibration equation based on the obtained function value.