CN102590175B - Raman spectrum superposition-based method for quickly determining content of methanol in methanol gasoline - Google Patents

Abstract

The invention discloses a Raman spectrum superposition-based method for quickly determining the content of methanol in methanol gasoline. The Raman spectrum superposition-based method comprises the following steps of: firstly, measuring a base oil spectrum, a pure methanol spectrum and a methanol gasoline spectrum with known methanol content; secondly, obtaining a spectrum superposing formula according to data and storing base oil and a corresponding spectrum superposition parameter in a spectrum database; and constructing the spectrum database and then estimating the content of the methanol from the methanol gasoline spectrum with the unknown methanol content by using the spectrum superposition formula. The invention provides the spectrum superposition formula from a view of spectrum soft processing as well as the formula-based method for quickly determining the content of the methanol in the methanol gasoline. According to the method, the quantity of samples required to be calibrated can be greatly reduced in the application process, the labor capacity of calibrating works is reduced and the problem that the measurement for low-content methanol is inaccurate or even cannot be measured in the traditional method is overcome; and in addition, the measurement precision of the unknown methanol gasoline prepared from the base oil can also be maintained.

Description

Rapid Determination Method of Methanol Content in Methanol Gasoline Based on Raman Spectroscopy Superposition

technical field

The invention belongs to the field of chemometrics, and relates to a method for measuring spectra of substances in a mixture, in particular to a method for measuring methanol content in methanol gasoline.

Background technique

With the rapid development of my country's economy and the rapid increase of automobile usage, the demand for gasoline in the domestic market has increased rapidly, which has brought enormous pressure to my country's oil supply and environmental protection. The only way to change oil shortage and severe environmental pollution is to reduce dependence on oil and develop green, efficient and clean alternative energy sources. As a substitute for ordinary gasoline, methanol gasoline is a path of "replacing oil with coal", which can directly replace ordinary gasoline. While alleviating the shortage of gasoline supply, it has good environmental protection benefits and is conducive to the sustainable development of the country's ecological economy, Social progress is of great significance.

Methanol gasoline is a mixture of methanol, gasoline and additives. The amount of methanol incorporated is generally 5% to 30%. The one mixed with 15% is the most, which is called M15 methanol gasoline. The calorific value of methanol is about half that of gasoline. Under the premise of not changing the compression ratio of the automobile engine, the methanol content must be fixed within a certain range. If the content is too low, the octane number will be too low and damage the engine; if the content is too high, the calorific value of the fuel will be insufficient, fuel consumption will be increased, and the cost will be increased. At the end of 2009, my country officially promulgated the product standard of high-proportion methanol gasoline for vehicles "Methanol Gasoline for Vehicles (M85)", requiring the content of methanol in methanol gasoline to be about 85%. Shaanxi Province has fully promoted the use of M15 methanol gasoline. In the national standard (M85) and the local standards of various provinces, such as the local standard of Hebei Province "M30 Methanol Gasoline for Vehicles", "Methanol Gasoline Component Oil for Vehicles", the local standard of Shanxi Province DB14/T 92-2002, the local standard of Zhejiang Province Standards such as DB33/T 756.2-2009 have strict requirements on the methanol content in methanol gasoline.

Among the various standards, official methods for measuring methanol content include gas chromatography and fractional distillation. These two methods are accurate in measurement, but the operation is complicated, the detection period is long, and the equipment is complicated, so they are not suitable for on-site detection. At the same time, gas chromatography also requires an internal standard. Therefore, it is necessary to develop a rapid and accurate measurement method for the methanol content in blended gasoline, which is of vital significance for the quality control and inspection of methanol gasoline.

The current rapid detection methods mainly use near-infrared spectroscopy and Raman spectroscopy. This type of method first uses near-infrared or Raman spectrometers to obtain the spectral data of the oil to be tested, and then compares it with the spectra of a large number of training samples (referring to oil samples with known methanol content and corresponding spectra) in the database, and then estimates Methanol content in methanol gasoline. This type of method has fast measurement speed and is easy to use. However, the main problem of these two types of methods is that a large number of training samples with different base oils and different methanol contents need to be collected, so as to ensure the detection accuracy of the methanol content of the oil to be tested. At the same time, due to the molecular absorption characteristics of near-infrared spectroscopy, the measurement results are easily interfered by other alcohols.

Contents of the invention

The object of the present invention is to aim at the deficiencies of the prior art, and provide a method for quickly measuring the methanol content of methanol gasoline based on Raman spectrum superposition, which is simple and effective.

The object of the present invention is achieved by the following technical scheme: a kind of methanol gasoline methanol content rapid assay method based on Raman spectrum linear superposition principle, the method comprises the following steps:

(1) Add methanol to a certain base oil, and configure methanol gasoline with any volume content; the base oil uses a Raman spectrometer to measure the Raman spectra of the base oil, the above-mentioned methanol gasoline and pure methanol; Filtering, fluorescence background removal and other pretreatments; then normalize the saturated hydrocarbon characteristic peaks of the base oil and methanol gasoline spectra to obtain spectrum A and spectrum B; normalize the maximum value of the pure methanol spectrum to obtain spectrum C;

 The base oil refers to methanol-free conventional gasoline mixed with catalytic gasoline, reformed gasoline and MTBE.

(2) Express the spectrum B as the weighted algebraic sum of the base oil spectrum A and the pure methanol spectrum C, and establish the spectral linear superposition formula corresponding to the base oil:

B=k1[(1-m)A]+k2(mC) +E ;

In the formula, m is the volume percentage concentration of methanol in methanol gasoline, E is the spectral measurement error, k1=a, k2=aK, a is a system parameter, K is the relative Raman intensity of methanol in methanol gasoline,

Then use the least square method to get k1 and k2, use K=k2/k1 to get the key parameter K in the spectral linear superposition formula, and finally store the spectrum A and parameter K in the spectral database;

(3) Select different base oils and repeat steps 1 and 2, so that the spectral linear superposition formula corresponding to different base oils can be established, as well as a spectral database containing the spectra of various base oils and their parameter K;

(4) For the oil sample to be tested with unknown base oil type and unknown methanol content, use a Raman spectrometer to measure its spectrum; Oneization, the spectrum D is obtained;

(5) Select different base oil spectra A and their related parameters K from the spectral database, use the spectral superposition formula, D=k3A+k4KC+E, where k3=a(1-m), k4=am using the least squares method Estimate k3 and k4; select the coefficients k3 and k4 with the smallest estimation errors in all cases as the final estimation coefficients, use k3 and k4 to calculate m, and thus obtain the methanol content in the methanol gasoline sample.

The beneficial effect of the present invention is that, the present invention is based on the linear superposition principle of Raman spectrum, and the rapid determination method of the methanol content of methanol gasoline has fast measurement speed, high analysis precision, and the required calibration samples are greatly reduced, which provides a new method for the popularization of methanol gasoline in my country. A convenient means of detection.

Description of drawings

Figure 1 is the base oil spectrum of a refinery;

Figure 2 M20 spectrum of a refinery;

Fig. 3 is pure methanol spectrum;

The base oil spectrum of a refinery after treatment in Fig. 4;

Figure 5 M20 spectrum of a refinery after treatment;

Pure methanol spectrum after Fig. 6 treatment;

Figure 7 Base oil spectrum of a gasoline blending station;

Figure 8 M30 spectrum of a gasoline blending station;

Figure 9 Base oil spectrum of a gasoline blending station after treatment;

Figure 10 Spectrum of M30 of a certain gasoline blending station after processing;

Figure 11 part of the test sample spectrum;

Figure 12 Spectra of some test samples after treatment.

Detailed ways

The present invention is based on the rapid determination method of methanol content in methanol gasoline based on the Raman spectrum linear superposition principle, comprising the following steps:

1. Add methanol to a certain base oil, and configure methanol gasoline with any volume content; use a Raman spectrometer to measure the Raman spectra of the base oil, the above methanol gasoline and pure methanol. Firstly, preprocessing such as smoothing, noise filtering, and fluorescent background removal was performed on the obtained spectrum. Then, the characteristic peaks of saturated hydrocarbons were normalized for the spectra of base oil and methanol gasoline to obtain spectra A and B;

2. Express spectrum B as the weighted algebraic sum of base oil spectrum A and pure methanol spectrum C, and establish the spectral linear superposition formula corresponding to the base oil:

B=k1[(1-m)A]+k2(mC) +E ;

In the formula, m is the volume percentage concentration of methanol in methanol gasoline, E is the spectral measurement error, k1=a, k2=aK, a is a system parameter, K is the relative Raman intensity of methanol in methanol gasoline,

Then use the least squares method to get k1 and k2, use K=k2/k1 to get the key parameter K in the spectral linear superposition formula, and finally store the spectrum A and parameter K in the spectral database.

3. Select different base oils, and repeat steps 1 and 2, so that the spectral linear superposition formulas corresponding to different base oils can be established, as well as a spectral database containing the spectra of various base oils and their parameter K.

4. For the oil sample to be tested with unknown base oil type and unknown methanol content, use a Raman spectrometer to measure its spectrum. First, the spectrum was preprocessed by smoothing, noise filtering, fluorescence background removal, etc., and saturated hydrocarbon normalization was performed to obtain spectrum D.

5. Select different base oil spectra A and its related parameters K from the spectral database, use the spectral superposition formula, D=k3A+k4KC+E, where k3=a(1-m), k4=am is estimated by the least square method Out of k3, k4. Select the coefficients k3 and k4 with the smallest estimation errors in all cases as the final estimation coefficients, use k3 and k4 to calculate m, and thus obtain the methanol content in the methanol gasoline sample.

Below in conjunction with accompanying drawing and example, further illustrate the present invention.

Example 1:

The spectral test conditions of the example are: the central wavelength of the laser is 785nm, the probe is an InPhotonics Raman probe, and the spectrometer uses a QE65000 spectrometer from Ocean Optics of the United States. The integration time of the spectrometer was set to 10 s, and the average was collected 10 times.

1. For the base oil of a refinery, configure methanol gasoline with a methanol content of 20% (denoted as M20). The Raman spectra of base oil, methanol gasoline with known methanol volume content and pure methanol were measured by Raman spectrometer. They are shown in Figure 1, Figure 2, and Figure 3 respectively. Firstly, preprocessing such as smoothing, noise filtering, and fluorescent background removal was performed on the obtained spectrum. Then, the spectra of base oil and methanol gasoline were normalized to the characteristic peaks of saturated hydrocarbons to obtain spectrum A and spectrum B, as shown in Figure 4 and Figure 5, respectively. Carry out maximum normalization to pure methanol spectrum, obtain spectrum C, as shown in Figure 6;

2. Express spectrum B as the weighted algebraic sum of base oil spectrum A and pure methanol spectrum C, and establish the spectral linear superposition formula corresponding to the base oil:

B=k1[(1-m)A]+k2(mC) +E ;

In the formula, m is the volume percentage concentration of methanol in methanol gasoline, E is the spectral measurement error, k1=a, k2=aK, a is a system parameter, K is the relative Raman intensity of methanol in methanol gasoline,

Then use the least squares method to get k1 and k2, and use K=k2/k1 to get the key parameter K=1.333 in the spectral linear superposition formula, and finally store the spectrum A and parameter K in the spectral database.

3. Select the base oil of a gasoline blending station, configure methanol gasoline with a methanol content of 30% (denoted as M30), and repeat steps (1) and (2), where K=1.7932. The Raman spectra of the base oil and M30 of the gasoline blending station are shown in Fig. 7 and Fig. 8 . The treated base oil and M30 spectra are shown in Fig. 9 and Fig. 10 .

In this way, the spectral superposition formula corresponding to different base oils can be established, as well as a spectral database containing various base oils and related parameters K.

4. Use the base oil of a refinery to prepare methanol gasoline with methanol content of 40%, 60%, 80%; use the base oil of a gasoline blending station to prepare methanol content of 0%, 5%, 10%, 15%, 20%, 30% , 40%, 50%, 60%, 70% methanol gasoline. The above methanol gasoline was used as samples to be tested with unknown base oil type and unknown methanol content, and their spectra were measured with a Raman spectrometer. Figure 11 is the spectra of some of the samples. First, the spectrum is preprocessed by smoothing, noise filtering, fluorescence background removal, etc., and saturated hydrocarbons are normalized to obtain the corresponding spectrum D. Figure 12 is the spectrum of some samples.

5. Select different base oil spectra A and its related parameters K from the spectral database, use the spectral superposition formula, D=k3A+k4KC+E, where k3=a(1-m), k4=am is estimated by the least square method Out of k3, k4. Select the coefficients k3 and k4 with the smallest estimation errors in all cases as the final estimation coefficients, use k3 and k4 to calculate m, and thus obtain the methanol content in the methanol gasoline sample. The test results are shown in Table 1 and Table 2:

Table 1: Base oil sample measurements taken from refineries

actual value 40 60 80 Calculated 39.71 57.97 78.08 error 0.29 2.03 1.92

Note: The data in the table is the volume content of methanol in methanol gasoline.

Table 2: Measurement results of base oil samples taken from a gasoline blending station.

actual value 0 5 10 15 20 Calculated 0 5.07 9.02 12.91 19.08 error 0 -0.07 0.98 2.19 0.92 actual value 30 40 50 60 the Calculated 30.00 36.94 48.28 56.68 the error 0 3.16 1.72 3.32 the

Note: The data in the table is the volume content of methanol in methanol gasoline.

Claims (1)

1. a kind of methanol gasoline methanol content fast assay method based on Raman spectrum linear superposition principle, it is characterized in that, the method comprises the following steps: (1) Add methanol to a certain base oil, and configure methanol gasoline with any volume content; use a Raman spectrometer to measure the Raman spectra of the base oil, the above-mentioned methanol gasoline, and pure methanol; firstly, preprocess the obtained spectra, and the Preprocessing includes smoothing, noise filtering, and fluorescence background removal; then, the saturated hydrocarbon characteristic peaks are normalized for the base oil and methanol gasoline spectra to obtain spectra A and B; the maximum value normalization is performed for pure methanol spectra to obtain spectra C; (2) Express the spectrum B as the weighted algebraic sum of the base oil spectrum A and the pure methanol spectrum C, and establish the linear superposition formula of the spectrum corresponding to the base oil: B=k1[(1-m)A]+k2(mC) +E ; In the formula, m is the volume percentage concentration of methanol in methanol gasoline, E is the spectral measurement error, k1=a, k2=aK, a is a system parameter, K is the relative Raman intensity of methanol in methanol gasoline, Then use the least square method to get k1 and k2, use K=k2/k1 to get the key parameter K in the spectral linear superposition formula, and finally store the spectrum A and parameter K in the spectral database; (3) Select different base oils and repeat steps 1 and 2, so that the spectral linear superposition formula corresponding to different base oils can be established, as well as a spectral database containing the spectra of various base oils and their parameter K; (4) For the oil sample to be tested with unknown base oil type and unknown methanol content, use a Raman spectrometer to measure its spectrum; first, preprocess the spectrum, which includes smoothing, noise filtering, and fluorescence background removal, And carry out saturated hydrocarbon normalization, obtain spectrum D; (5) Select different base oil spectra A and their related parameters K from the spectral database, use the spectral superposition formula, D=k3A+k4KC+E, where k3=a(1-m), k4=am using the least squares method Estimate k3 and k4; select the coefficients k3 and k4 with the smallest estimation errors in all cases as the final estimation coefficients, use k3 and k4 to calculate m, and thus obtain the methanol content in the methanol gasoline sample.

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