CN118914165A - Polyurethane reaction process online monitoring method and system - Google Patents

Abstract

The invention relates to the technical field of chemical reaction progress monitoring, and discloses a polyurethane reaction progress online monitoring method and system, wherein the method comprises the following steps: the molar flow or the molar flow rate of isocyanate groups in the reaction process is monitored online through Raman spectrum, so that the online monitoring of the polyurethane reaction process is realized; the Raman characteristic signal wave band of the isocyanate group is any wave band of 1400-1500cm ^‑1 or 2000-4000cm ^‑1. According to the invention, raman spectrum is used as a signal acquisition instrument, the correlation between the spectrum signal and the reaction process is established by a chemometric method based on the analysis result of the reaction kettle or the process pipeline on the molar quantity of the isocyanate groups, and finally, the method for on-line monitoring of the reaction process in the polyurethane synthesis process is realized.

Description

A polyurethane reaction process online monitoring method and system

Technical Field

The invention relates to the technical field of chemical reaction progress monitoring, and in particular to a polyurethane reaction process online monitoring method and system.

Background Art

Polyurethane can be synthesized from diisocyanate monomers, diol monomers and chain extenders. The reaction process of polyurethane is defined as the percentage of the molar amount of isocyanate groups consumed by the polymerization reaction to the initial isocyanate groups at a certain moment in the reaction, which reflects the change in the content of isocyanate groups in the system and also characterizes the extent to which the polyurethane system reaction proceeds. Developing a real-time and accurate online monitoring method for the degree of isocyanate group reaction is of great significance for stabilizing the polymerization production process and controlling product quality.

In the prepolymerization stage, the isocyanate group needs to be added in excess. When the molar amount of the isocyanate group no longer changes, the prepolymerization stage can be considered to be over. In the chain extension stage, the amount of chain extender added needs to be strictly controlled to make the isocyanate group react just right. Therefore, the molar amount of the isocyanate group occupies an important position in the synthesis of polyurethane.

Patent CN112147237A discloses a method for determining the reactivity of isocyanate groups in diisocyanate compounds, comprising: in the presence of a solvent, uniformly mixing the diisocyanate compound with methanol in a container and reacting, and using a gas chromatograph to determine the content changes of different components in the mixture during the reaction; wherein the molar number of the isocyanate group is less than or equal to the molar number of methanol. The method determines the reactivity of isocyanate groups, including the reactivity of isocyanate groups with different steric hindrance effects, the influence of isocyanate groups that have participated in the reaction on the reactivity of unreacted isocyanate groups in the molecule, and the reactivity of isocyanate compounds with isomeric structures, etc. The operation is simple, fast, efficient, and has high measurement accuracy. It determines the reactivity of multiple isocyanate groups, but does not involve the detection of the degree of reaction.

Many works point out methods for determining isocyanate compounds. For example, patent CN109444278A proposes to determine diphenylmethane diisocyanate in adhesives by liquid phase tandem mass spectrometry, and discloses a method for determining diphenylmethane diisocyanate in adhesives, including a hydrolyzate preparation step: adding hydrochloric acid and glacial acetic acid to ionized water, then diluting with water, then adding acetonitrile, mixing evenly, to obtain a hydrolyzate; a water bath step: taking an adhesive, adding a hydrolyzate to the adhesive, heating in a water bath, to obtain an aqueous solution; a determination step: filtering the aqueous solution through a membrane, and then determining it by a liquid phase tandem mass spectrometer. The determination method uses liquid phase tandem mass spectrometry to determine the hydrolysis product of diphenylmethane diisocyanate, and has simple operation, high efficiency, and high accuracy.

Most of the detection methods for isocyanate groups are offline tests. The chemical industry standard "HG/T 2409-2023 Determination of Isocyanate Group Content in Polyurethane Prepolymers" proposes testing through titration and near-infrared spectroscopy. Both methods rely on manual sampling. First, the molar amount of isocyanate groups in the polymer sample is determined, and then converted into the degree of reaction. The titration method generally takes 6-8 hours from sampling to obtaining results, and there is a large time lag. The test results of the degree of reaction cannot be used immediately to guide automated process production, which is not conducive to controlling product quality; near-infrared spectroscopy has high limitations and is easily affected by the chemical structure of the sample, the measurement temperature, and the interaction between the analyzed system and other components, such as catalysts, water content, etc. Fluctuations or contamination of the properties of the measured system will significantly affect the test results. The analysis mode of near-infrared spectroscopy based on data modeling has the risk of gradual drift of model prediction values.

The reaction process of the polyurethane system urgently needs an online and universal detection method to facilitate real-time monitoring of the polymerization process and realize feedback control.

Summary of the invention

In view of the shortcomings of the prior art such as the lack of an online monitoring method for the reaction progress in polyurethane synthesis or the existence of an influence on the reaction process, the present invention provides a method for detecting isocyanate groups by using Raman spectroscopy signals to achieve online monitoring of the polyurethane reaction process. The method has the advantages of good real-time performance, high accuracy, wide applicability, no model calibration, low equipment technical transformation cost, etc., and will not have any influence on the polymerization process.

To achieve the above object, the technical solution adopted by the present invention is:

A method for online monitoring of a polyurethane reaction process comprises the following steps: online monitoring of the molar flow rate or molar flow rate of isocyanate groups during the reaction process by Raman spectroscopy to achieve online monitoring of the polyurethane reaction process; the Raman characteristic signal band of the isocyanate groups is any one of 1400-1500 cm ^-1 or 2000-4000 cm ^-1 .

In the polyurethane reaction process with diisocyanate compounds as monomers in the present invention, since the prepolymerization reaction is an addition prepolymerization reaction of excess diisocyanate monomers and dihydroxy monomers, the product is a prepolymer terminated with diisocyanate groups, and the reaction equation is shown in Formula (5); the prepolymer will further undergo an addition chain extension reaction with the hydroxyl group or amino group of the chain extender, consuming the isocyanate groups to generate a high molecular weight polyurethane product, and the reaction equation is shown in Formula (6).

(5)

(6)

Therefore, during the reaction, the change in the molar amount of isocyanate groups directly reflects the progress of the reaction. The polyurethane reaction progress can be calculated by analyzing and monitoring the molar amount of isocyanate groups in the reactor or process pipeline, thereby achieving the purpose of online monitoring.

At time t, when the polyurethane reaction is intermittent, the relationship between the molar flow rate n(t) _NCO of the isocyanate group and the reaction progress x(t)% is as shown in formula (1):

(1)

Wherein, the unit of reaction progress x(t)% is %, the unit of molar flow rate of isocyanate groups n(t) _NCO is mol, and n(0) _NCO is the initial molar amount of isocyanate groups, in mol;

When the polyurethane reaction is continuous, the relationship between the molar flow rate F(t) _NCO of the isocyanate group and the reaction progress x(t)% is as shown in formula (2):

(2)

Wherein, the unit of reaction progress x(t)% is %, the unit of molar flow rate of isocyanate group F(t) _NCO is mol/min or kmol/h, and F(0) _NCO is the molar amount of isocyanate group fed, in mol/min or kmol/h.

Compared with near-infrared spectroscopy, mid-infrared spectroscopy, ultraviolet spectroscopy and fluorescence spectroscopy, Raman spectroscopy has the advantages of non-destructive and convenient detection of samples, the Raman shift of functional groups has "fingerprint properties", the quantitative analysis model has strong resistance to data drift, and the detection time period can achieve long-distance real-time analysis. In the present invention, it was unexpectedly found that the characteristic signal of the isocyanate group is protruding in the Raman spectrum without overlap, which is very beneficial as a monitoring target value.

When the polyurethane reaction is intermittent, the molar flow rate n(t) _NCO of the isocyanate group and the Raman spectral characteristic signal The relationship is shown in formula (3):

(3)

Where k is the correlation coefficient of Raman spectrum, is the peak area of the Raman characteristic signal band of the isocyanate group at time t.

When the polyurethane reaction is continuous, the relationship between the molar flow rate F(t) _NCO of the isocyanate group and the reaction progress x(t)% is as shown in formula (4):

(4)

Wherein, the unit of reaction progress x(t)% is %, the unit of molar flow rate of isocyanate group F(t) _NCO is mol/min or kmol/h, and F(0) _NCO is the feeding molar flow rate of isocyanate group, the unit is mol/min or kmol/h.

When the polyurethane reaction is intermittent, the online monitoring of the polyurethane reaction process specifically includes the following steps:

Step 1: Establish a standard curve of the Raman spectrum characteristic signal of the isocyanate group and the molar flow rate of the isocyanate group using a diisocyanate compound standard to obtain the molar flow rate n _NCO of the isocyanate group and the Raman spectrum characteristic signal The relationship , k is the correlation coefficient of Raman spectrum;

Step 2, collecting the Raman spectrum in the polyurethane reaction process online in real time, and obtaining the real-time molar flow rate n(t) _NCO of the isocyanate group in the reaction process according to the relationship in step 1;

Step 3: Calculate the polyurethane reaction progress x(t)% based on the real-time molar flow rate of isocyanate groups n(t) _NCO .

Specifically, step 1 includes the steps of:

Step 1-1, preparing a series of concentrations of diisocyanate compound monomer standard products, performing Raman spectroscopy testing, and obtaining Raman spectra of the standard products;

Step 1-2, preprocessing the Raman spectrum of the standard product in step 1-1, including background subtraction, baseline correction and spectrum standardization, to obtain a standardized Raman spectrum of the diisocyanate compound standard product;

Step 1-3, using the colligative property between the characteristic signal of Raman spectrum and the concentration, the characteristic signal of isocyanate group is selected in the band range of 300-4000 cm ^-1 , and the characteristic band of 1400-1500 cm ^-1 or 2000-4000 cm ^-1 is used as the characteristic signal of isocyanate group, and the molar flow rate n _NCO of isocyanate group and the characteristic signal of Raman spectrum are obtained. The relationship , k is the correlation coefficient of Raman spectrum.

Specifically, step 2 includes the steps of:

Step 2-1, using a Raman spectroscopy probe to collect Raman spectroscopy information at time t in the polyurethane reactor in real time;

Step 2-2, preprocessing the Raman spectrum information collected in step 2-1, specifically including: background subtraction, baseline correction and spectrum standardization, obtaining a standardized online Raman spectrum in the reactor, obtaining the peak area of the characteristic signal of the isocyanate group in the range of 1400-1500 cm ^-1 or 2000-4000 cm ^-1 , and the size of the area value is recorded as A(t) _NCO;

Step 3 specifically includes: calculating the polyurethane reaction progress x(t)% according to the peak area A(t) _NCO of the Raman spectrum characteristic signal of the isocyanate group at time t through the stoichiometric relationship of formula (3) and formula (1).

(3)

(1)

Wherein, n(t) _NCO is the molar flow rate of isocyanate groups in the reactor at time t, in mol, and n(0) _NCO is the initial molar amount of isocyanate groups, in mol.

When the polyurethane reaction is continuous, the online monitoring of the polyurethane reaction process specifically includes the following steps:

Step 1: Establish a standard curve of the Raman spectrum characteristic signal of the isocyanate group and the molar flow rate of the isocyanate group using a diisocyanate compound standard to obtain the molar flow rate F(t) _NCO of the isocyanate group and the Raman spectrum characteristic signal The relationship , k is the correlation coefficient of Raman spectrum;

Step 2, collecting the Raman spectrum of the polyurethane continuous reaction process online in real time, and obtaining the real-time molar flow rate F(t) _NCO of the isocyanate group during the reaction process according to the relationship in step 1;

Step 3: Calculate the polyurethane reaction progress x(t)% based on the real-time molar flow rate F(t) _NCO of the isocyanate group.

Specifically, step 1 includes the steps of:

Step 1-1, preparing a series of concentrations of diisocyanate compound monomer standard products, performing Raman spectroscopy testing, and obtaining Raman spectra of the standard products;

Step 1-2, preprocessing the Raman spectrum of the standard product in step 1-1, including background subtraction, baseline correction and spectrum standardization, to obtain a standardized Raman spectrum of the diisocyanate compound standard product;

Step 1-3, using the colligative property between the characteristic signal of Raman spectrum and the concentration, the characteristic signal of isocyanate group is selected in the band range of 300-4000 cm ^-1 , and the characteristic band of 1400-1500 cm ^-1 or 2000-4000 cm ^-1 is used as the characteristic signal of isocyanate group, and the molar flow rate F _NCO of isocyanate group and the characteristic signal of Raman spectrum are obtained. The relationship , k is the correlation coefficient of Raman spectrum.

Specifically, step 2 includes the steps of:

Step 2-1, using a Raman spectrum probe to collect Raman spectrum information at time t in the polyurethane reactor in real time;

Step 2-2, preprocessing the Raman spectrum information collected in step 2-1, specifically including: background subtraction, baseline correction and spectrum standardization, obtaining a standardized online Raman spectrum in the reactor, obtaining the peak area of the characteristic signal of the isocyanate group in the range of 1400-1500 cm ^-1 or 2000-4000 cm ^-1 , and the size of the area value is recorded as A(t) _NCO;

Step 3 specifically includes: calculating the polyurethane reaction progress x(t)% according to the peak area A(t) _NCO of the Raman spectrum characteristic signal of the isocyanate group at time t through the stoichiometric relationship of formula (4) and formula (2).

(4)

(2)

Wherein, F(t) _NCO is the molar flow rate of isocyanate groups in the reactor at time t, in mol/min or kmol/h, and F(0) _NCO is the feed molar flow rate of isocyanate groups, in mol/min or kmol/h.

The polyurethane reaction refers to the reaction of raw materials including diisocyanate compound monomers, dihydroxy compound monomers and chain extenders;

The polyurethane reaction includes two stages: prepolymerization and chain extension. The monitoring method of the present invention is applicable to any time in the two stages.

Preferably, the raw materials for the polyurethane reaction also include a chain extender.

The diisocyanate compound monomer includes aromatic and/or aliphatic diisocyanate compounds.

The diisocyanate compound monomer includes one or more of toluene diisocyanate, 4,4'-diphenylmethane diisocyanate, p-phenylene diisocyanate, naphthalene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, dicyclohexylmethane-4,4'-diisocyanate, tetramethyl meta-xylylene diisocyanate, and trans-1,4-cyclohexyl diisocyanate.

The dihydroxy compound monomer includes one or more of polyethylene adipate, polybutylene adipate, polyε-caprolactone, polycarbonate, polytetramethylene glycol, polyethylene glycol, polyoxypropylene, polyhydroxy-terminated isobutylene, and polyhydroxy-terminated butadiene.

The chain extender includes one or more of 1,4-butanediol, ethylene glycol, propylene glycol, methyl propylene glycol, 3,5-diaminoisobutyl p-chlorobenzoate, 4,4'-diaminodiphenylmethane, and 2,6-diaminopyridine.

The present invention also provides an online monitoring system for the polyurethane reaction process, comprising a polyurethane reactor, a Raman spectrum probe, a Raman spectrometer and a computing device;

A Raman spectrum probe is arranged in the reactor or on the process pipeline to collect Raman spectrum information of the reactants in real time. The signal obtained by the Raman spectrum probe is transmitted to the computing device after being detected by the Raman spectrometer, and the reaction progress of the polyurethane polymerization process is monitored online according to the Raman spectrum characteristic signal of isocyanate; the Raman spectrum characteristic signal of isocyanate is any band in 1400-1500cm ^-1 or 2000-4000cm ^-1 .

At time t, when the polyurethane reaction is intermittent, the relationship between the molar flow rate n(t) _NCO of the isocyanate group and the reaction progress x(t)% is as shown in formula (1):

(1)

Wherein, the unit of reaction progress x(t)% is %, the unit of molar flow rate of isocyanate groups n(t) _NCO is mol, and n(0) _NCO is the initial molar amount of isocyanate groups, in mol;

When the polyurethane reaction is continuous, the relationship between the molar flow rate F(t) _NCO of the isocyanate group and the reaction progress x(t)% is as shown in formula (2):

(2)

Wherein, the unit of reaction progress x(t)% is %, the unit of molar flow rate of isocyanate group F(t) _NCO is mol/min or kmol/h, and F(0) _NCO is the molar amount of isocyanate group fed, in mol/min or kmol/h.

When the polyurethane reaction is intermittent, the online monitoring of the reaction progress of the polyurethane polymerization process according to the Raman spectrum characteristic signal of isocyanate specifically includes:

Step 1: Establish a standard curve of the Raman spectrum characteristic signal of the isocyanate group and the molar flow rate of the isocyanate group using a diisocyanate compound standard to obtain the molar flow rate n _NCO of the isocyanate group and the Raman spectrum characteristic signal The relationship , k is the correlation coefficient of Raman spectrum;

Step 2, collecting the Raman spectrum in the polyurethane reaction process online in real time, and obtaining the real-time molar flow rate n(t) _NCO of the isocyanate group in the reaction process according to the relationship in step 1;

Step 3: Calculate the polyurethane reaction progress x(t)% based on the real-time molar flow rate of isocyanate groups n(t) _NCO .

When the polyurethane reaction is continuous, the online monitoring of the reaction progress of the polyurethane polymerization process according to the Raman spectrum characteristic signal of isocyanate specifically includes:

Step 1: Establish a standard curve of the Raman spectrum characteristic signal of the isocyanate group and the molar flow rate of the isocyanate group using a diisocyanate compound standard to obtain the molar flow rate F(t) _NCO of the isocyanate group and the Raman spectrum characteristic signal The relationship , k is the correlation coefficient of Raman spectrum;

Step 2, collecting the Raman spectrum in the polyurethane reaction process online in real time, and obtaining the real-time molar flow rate F(t) _NCO of the isocyanate group in the reaction process according to the relationship in step 1;

Step 3: Calculate the polyurethane reaction progress x(t)% based on the real-time molar flow rate F(t) _NCO of the isocyanate group.

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

(1) The present invention proposes an online monitoring method for the polyurethane reaction process based on the determination of the molar amount of isocyanate groups in the reactor and process pipeline system. The Raman spectrum is used as a signal acquisition instrument. The internal system of the reactor can be directly detected, and the process pipeline can be analyzed, or a branch line can be added to the process pipeline to indirectly monitor the reaction process in the reaction vessel through the analysis of the process pipeline. Compared with the existing methods, the present invention has the advantages of good real-time performance, high accuracy, wide applicability, only one-time calibration of the online model, and low equipment technical transformation cost. It makes up for the deficiency that there is no real-time detection of the polyurethane reaction process by the molar amount of isocyanate groups at this stage.

(2) The online monitoring method of the present invention has a fast monitoring speed, a short measurement time (≤1 min), a high result accuracy, no direct contact with the reaction system, and only requires a one-time calibration without the need for regular calibration. It is applicable to a wide range of monomers, including online monitoring of the reaction progress of the polyurethane polymerization process of aromatic and/or aliphatic diisocyanates.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is an online monitoring system of a Raman spectrometer in Example 1 and Example 2, 1-computing device; 2-Raman spectrometer; 3-low-noise optical fiber; 4-Raman spectroscopy laser probe; 5-high-transmittance reactor.

FIG. 2 is a standard Raman spectrum of HMDI monomer in Example 1 and Example 2.

FIG. 3 is a comparison of the Raman spectra and infrared spectra of HMDI in Example 1 and Example 2.

FIG. 4 is a standard curve of HMDI in Example 1 and Example 2.

FIG5 is a comparison of the reaction progress data obtained by the online Raman spectrum prediction and the offline H NMR spectrum of the two-step method of “prepolymerization-chain extension” in Example 1.

FIG6 is a comparison of the reaction progress data obtained by the online Raman spectrum prediction of the "one-pot method" in Example 2 and the offline H NMR spectrum.

DETAILED DESCRIPTION

In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with embodiment. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. Those skilled in the art can make modifications or equivalent substitutions based on the understanding of the technical scheme of the present invention without departing from the spirit and scope of the technical scheme of the present invention, and all should be included in the protection scope of the present invention.

The raw materials used in the following specific embodiments are all purchased from the market.

Example 1

In this embodiment, a two-step method of "prepolymerization-chain extension" is used, and a polyurethane reaction progress monitoring system based on isocyanate group molar analysis is used. The Raman spectrum probe is arranged on the inner wall of a high-transmittance low-hydroxyl quartz reactor. The schematic diagram of the structure is shown in FIG1 .

The Raman spectrometer used in this embodiment comes from Hangzhou Paixi Optoelectronics Technology Co., Ltd. It emits a near-infrared laser with a wavelength of 785 nm, is equipped with a 100 μm quartz excitation optical fiber, and has a maximum sampling time interval of 1 min.

The object of this embodiment is an intermittently operated "4,4-dicyclohexylmethane diisocyanate-polycaprolactone diol-1,4-butanediol" type polyurethane system, the raw material monomers are 4,4-dicyclohexylmethane diisocyanate (HMDI, 90%) and polycaprolactone diol (PCL, _Mn = 2000 g/mol), and the chain extender is 1,4-butanediol (BDO, 99%). PCL was vacuum dried at 80 ° C for more than 12 h to remove any trace moisture that may exist. The molten polycaprolactone diol was added to a quartz reactor, heated to 100 ° C under a nitrogen atmosphere, and then HMDI was added to start the prepolymerization reaction. Samples were taken at the set time and the sampling mass was recorded. After the prepolymerization reaction was completed, BDO was added in proportion to carry out the chain extension reaction. The total molar ratio of isocyanate groups and hydroxyl groups was 1:1, and the molar ratio of HMDI, PCL and BDO was 2:1:1.

An online monitoring method for the polyurethane "prepolymerization-chain extension" two-step reaction process based on isocyanate group molar analysis, the specific process includes:

Step 1-1, preparing a series of concentrations of 4,4-dicyclohexylmethane diisocyanate standard products, performing Raman spectroscopy testing, and obtaining Raman spectra of the standard products;

Step 1-2, preprocessing the Raman spectrum of the standard product in step 1-1, including background subtraction, baseline correction and spectrum standardization, to obtain the Raman spectrum of the diisocyanate compound standard product.

In order to eliminate the influence of the CCD pixel current noise, laser power fluctuation and temperature of the spectrometer, the background spectrum needs to be subtracted first. In order to eliminate the influence of the fluorescence background in the spectral signal, baseline correction is required. The baseline correction method using iterative polynomial fitting is used, and the range of baseline correction is 400-1800cm ^-1 . The baseline algorithm is referenced in Wang, T., Dai, LK. Applied Spectroscopy, 2017, 71(6), 1169-1179. The spectrum normalization method is the spectrum maximum normalization method, and the range of the normalization method is 400-1800cm ^-1 .

After spectral preprocessing, the Raman spectrum of pure component HMDI under 785nm wavelength laser can be obtained as shown in Figure 2. Among them, the characteristic peak of the isocyanate group is 1445cm ^-1 (NCO pseudo-antisymmetric stretching vibration), while the characteristic peak of the isocyanate group in the infrared spectrum is very unclear, and there are overlapping peaks, as shown in Figure 3. Therefore, the range of 1400-1500cm ^-1 in the Raman spectrum is selected as the characteristic area of the isocyanate group, and the area value is recorded as A _NCO .

Step 1-3, using the colligative property between the characteristic signal of Raman spectrum and the concentration, the characteristic signal of isocyanate group is selected in the band range of 300-4000cm ^-1 , and the characteristic band of 1400-1500cm ^-1 is used as the characteristic signal of isocyanate group. A standard curve between characteristic signal and content is established by fitting method, and a quantitative analysis model between characteristic signal and molar flow rate of isocyanate group is obtained as shown in FIG4. The quantitative analysis model established in this embodiment is a first-order linear model. The molar flow rate of isocyanate group n _NCO and the characteristic signal of Raman spectrum are obtained. The relationship is shown in formula (3):

(3)

Where k is the correlation coefficient of the Raman spectrum, which is 3.96;

Step 2-1, using a Raman spectroscopy probe to collect Raman spectroscopy information at time t in the polyurethane reactor in real time;

Step 2-2, preprocessing the Raman spectrum information collected in step 2-1, specifically including: background subtraction, baseline correction and spectrum standardization, obtaining the standardized online Raman spectrum in the reactor, obtaining the peak area of the characteristic signal of the isocyanate group in the range of 1400-1500 cm ^-1 , and the size of the area value is recorded as A(t) _NCO .

Step 3, according to the peak area A(t) _NCO of the Raman spectrum characteristic signal of the isocyanate group at time t, the polyurethane reaction progress x(t)% is calculated by sequentially using the stoichiometric relationship of formula (3) and formula (1).

(3)

(1)

Wherein, n(t) _NCO is the molar flow rate of isocyanate groups in the reactor at time t, in mol, and n(0) _NCO is the initial molar amount of isocyanate groups, in mol.

The above-mentioned online monitoring method for the polyurethane reaction process based on the reactor isocyanate molar flow analysis was used to monitor the reaction process of the intermittent polymerization process of "4,4-dicyclohexylmethane diisocyanate-polycaprolactone diol-1,4-butanediol" type polyurethane online. Table 1 shows the monitoring results at some time points. The reaction process of the polyurethane in the reactor can be calculated in real time, the calculation is convenient, and the detection speed is fast.

Table 1 Online monitoring results of the reaction progress of the batch polymerization process in Example 1

Time t/minute Reaction progress/% 0 0 30 19.39 60 34.62 120 50.89 150 64.83 180 77.61

In order to compare the accuracy of the monitoring method of the present invention with the detection method of the prior art, the present invention also carried out isocyanate group molar flow analysis on samples taken at different reaction times according to nuclear magnetic resonance hydrogen spectroscopy (reference Rochery M, Vroman I, Lam T M. Journal of Macromolecular Science, Part A, 2000, 37(3): 259-275.), and calculated the reaction progress according to formula (7). FIG5 shows the comparison of the results of the present invention and nuclear magnetic resonance hydrogen spectroscopy during the reaction process.

(7)

in, , The peak areas of the characteristic peaks at the shifts of 3.77 ppm and 3.40 ppm, respectively, represent the H on the methine connected to -NH-COO- formed after the NCO reaction; , The peak areas of the characteristic peaks at shifts of 3.81 ppm and 3.26 ppm respectively represent the protons on the methyl group to which the unreacted NCO is attached.

The testing process of nuclear magnetic resonance hydrogen spectroscopy is cumbersome, time-consuming, and damaging to the sample, while the method of the present invention is simple and fast. From the comparison of the results in Figure 5, it can be seen that the reaction process of the monitoring calculation of the present invention is not much different from the reaction process of the nuclear magnetic resonance hydrogen spectroscopy test. However, nuclear magnetic resonance hydrogen spectroscopy is affected by the test personnel, sample preparation errors, etc. In comparison, the accuracy of the present invention is higher and the applicability is stronger.

Example 2

In this embodiment, the "one-pot method" is used, and the monomer and the chain extender are added simultaneously before the reaction starts. The polyurethane reaction process monitoring system is based on the molar amount analysis of the isocyanate group. The Raman spectrum probe is set on the inner wall of the high-transmittance low-hydroxyl quartz reactor. The structural schematic diagram is shown in Figure 1.

The Raman spectrometer used in this embodiment comes from Hangzhou Paixi Optoelectronics Technology Co., Ltd. It emits a near-infrared laser with a wavelength of 785 nm, is equipped with a 100 μm quartz excitation optical fiber, and has a maximum sampling time interval of 1 min.

The object of this example is an intermittently operated "4,4-dicyclohexylmethane diisocyanate-polycaprolactone diol-1,4-butanediol" type polyurethane system, the monomers are 4,4-dicyclohexylmethane diisocyanate (HMDI, 90%) and polycaprolactone diol (PCL, _Mn = 2000 g/mol), and the chain extender is 1,4-butanediol (BDO, 99%). PCL was vacuum dried at 80 °C for more than 12 h to remove any trace moisture that may exist. The molten polycaprolactone diol was added to a quartz reactor, heated to 100 °C under a nitrogen atmosphere, and then HMDI and chain extender BDO were added to start a "one-pot" reaction, and samples were taken at the set time and the sample mass was recorded. The total molar ratio of isocyanate groups and hydroxyl groups was 1:1, and the molar ratio of HMDI, PCL, and BDO was 2:1:1.

A method for online monitoring of the polyurethane "one-pot" reaction process based on isocyanate group molar flow analysis, the specific process is the same as that of Example 1, and the obtained reaction process prediction diagram is shown in Figure 5.

In order to compare the accuracy of the monitoring method of the present invention with the detection method of the prior art, the samples taken at different reaction times were also tested for the molar flow of isocyanate groups according to H NMR spectroscopy (reference Rochery M, Vroman I, Lam T M. Journal of Macromolecular Science, Part A, 2000, 37(3): 259-275.), and the reaction progress was calculated according to formula (7). FIG6 shows the comparison of the results of the present invention and H NMR spectroscopy during the reaction.

(7)

in, , The peak areas of the characteristic peaks at the shifts of 3.77 ppm and 3.40 ppm, respectively, represent the H on the methine connected to -NH-COO- formed after the NCO reaction; , The peak areas of the characteristic peaks at shifts of 3.81 ppm and 3.26 ppm, respectively, represent the protons on the methyl group to which the unreacted NCO is attached.

The testing process of nuclear magnetic resonance hydrogen spectroscopy is cumbersome, time-consuming, and damaging to the sample, while the method of the present invention is simple and fast. From the comparison of the results in Figure 6, it can be seen that the reaction process of the monitoring calculation of the present invention is not much different from the reaction process of the nuclear magnetic resonance hydrogen spectroscopy test. However, nuclear magnetic resonance hydrogen spectroscopy is affected by the test personnel, sample preparation errors, etc. In comparison, the accuracy of the present invention is higher and the flexibility is stronger.

Claims (10)

1. The on-line monitoring method for the polyurethane reaction progress is characterized by comprising the following steps: the molar flow or the molar flow rate of isocyanate groups in the reaction process is monitored online through Raman spectrum, so that the online monitoring of the polyurethane reaction process is realized; the Raman characteristic signal wave band of the isocyanate group is any wave band of 1400-1500cm ^-1 or 2000-4000cm ^-1.

2. The online monitoring method of polyurethane reaction progress according to claim 1, wherein at time t, when the polyurethane reaction is intermittent, the relation between the molar flow n (t) _NCO of the isocyanate group and the reaction progress x (t)% is shown as formula (1):

（1）

Wherein the unit of the reaction progress x (t)% is mol, the unit of the molar flow rate n (t) _NCO of the isocyanate group is mol, and n (0) _NCO is the initial molar amount of the isocyanate group, and the unit is mol;

When the polyurethane reaction is continuous, the relationship between the molar flow rate F (t) _NCO of the isocyanate groups and the reaction progress x (t)% is shown in the formula (2):

（2）

Wherein the unit of the reaction progress x (t)% is mol/min or kmol/h of the molar flow rate F (t) _NCO of the isocyanate groups, and F (0) _NCO is the feeding molar quantity of the isocyanate groups, and the unit is mol/min or kmol/h.

3. The method for online monitoring of polyurethane reaction progress according to claim 1, wherein when the polyurethane reaction is intermittent, the molar flow rate n (t) _NCO of the isocyanate group and the raman spectrum characteristic signalThe relation of (2) is shown in the formula (3):

（3）

where k is the correlation coefficient of the Raman spectrum, At the t moment, the peak area of the Raman characteristic signal wave band of the isocyanate group;

When the polyurethane reaction is continuous, the relationship between the molar flow rate F (t) _NCO of the isocyanate groups and the reaction progress x (t)% is as shown in formula (4):

（4）

Wherein the unit of the reaction progress x (t)% is mol/min or kmol/h of the molar flow rate F (t) _NCO of the isocyanate groups, and F (0) _NCO is the feeding molar quantity of the isocyanate groups, and the unit is mol/min or kmol/h.

4. The method for online monitoring of the progress of a polyurethane reaction according to claim 1, wherein when the polyurethane reaction is intermittent, the online monitoring of the progress of the polyurethane reaction specifically comprises the steps of:

Step 1, establishing a standard curve of the Raman spectrum characteristic signal of the isocyanate group and the molar flow of the isocyanate group by using a diisocyanate compound standard substance to obtain the molar flow n _NCO of the isocyanate group and the Raman spectrum characteristic signal Is a relation of (2)K is the correlation coefficient of the Raman spectrum;

Step 2, acquiring Raman spectra in the polyurethane intermittent reaction process in real time on line, and obtaining real-time molar flow n (t) _NCO of isocyanate groups in the reaction process according to the relational expression in the step 1;

Step 3, calculating according to the real-time molar flow n (t) _NCO of the isocyanate groups to obtain polyurethane reaction progress x (t)%;

When the polyurethane reaction is continuous, the online monitoring of the polyurethane reaction process specifically comprises the following steps:

Step 1, establishing a standard curve of the Raman spectrum characteristic signal of the isocyanate group and the molar flow rate of the isocyanate group by using a diisocyanate compound standard substance to obtain the molar flow rate F (t) _NCO of the isocyanate group and the Raman spectrum characteristic signal Is a relation of (2)K is the correlation coefficient of the Raman spectrum;

Step 2, acquiring Raman spectra in the continuous polyurethane reaction process in real time on line, and obtaining the real-time molar flow rate F (t) _NCO of isocyanate groups in the reaction process according to the relational expression in the step 1;

And 3, calculating according to the real-time molar flow rate F (t) _NCO of the isocyanate groups to obtain the polyurethane reaction process x (t)%.

5. The method for on-line monitoring of polyurethane reaction progress according to claim 1, wherein the polyurethane reaction is a reaction performed by raw materials including diisocyanate compound monomers, dihydroxy compound monomers and chain extenders; the polyurethane reaction comprises two stages of prepolymerization and chain extension.

6. The method for on-line monitoring of the progress of polyurethane reaction according to claim 1, wherein said diisocyanate compound monomers comprise aromatic and/or aliphatic diisocyanate compounds.

7. The polyurethane reaction progress online monitoring system is characterized by comprising a polyurethane reactor, a Raman spectrum probe, a Raman spectrometer and computing equipment;

A Raman spectrum probe is arranged in the reactor or on a process pipeline, raman spectrum information of the reactant is acquired in real time, signals obtained by the Raman spectrum probe are transmitted to a computing device after being detected by a Raman spectrometer, and the reaction progress of the polyurethane polymerization process is monitored on line according to the Raman spectrum characteristic signals of isocyanate; the Raman spectrum characteristic signal of isocyanate is any wave band of 1400-1500cm ^-1 or 2000-4000cm ^-1.

8. The online monitoring system for polyurethane reaction progress according to claim 7, wherein at time t, when the polyurethane reaction is batch type, the relation between the molar flow n (t) _NCO of the isocyanate group and the reaction progress x (t)% is as shown in formula (1):

（1）

Wherein the unit of the reaction progress x (t)% is mol, the unit of the molar flow rate n (t) _NCO of the isocyanate group is mol, and n (0) _NCO is the initial molar amount of the isocyanate group, and the unit is mol;

When the polyurethane reaction is continuous, the relationship between the molar flow rate F (t) _NCO of the isocyanate groups and the reaction progress x (t)% is shown in the formula (2):

（2）

Wherein the unit of the reaction progress x (t)% is mol/min or kmol/h of the molar flow rate F (t) _NCO of the isocyanate groups, and F (0) _NCO is the feeding molar quantity of the isocyanate groups, and the unit is mol/min or kmol/h. .

9. The polyurethane reaction progress online monitoring system according to claim 7, wherein when the polyurethane reaction is intermittent, the online monitoring of the reaction progress of the polyurethane polymerization process according to the raman spectrum characteristic signal of isocyanate specifically comprises:

Step 1, establishing a standard curve of the Raman spectrum characteristic signal of the isocyanate group and the molar flow of the isocyanate group by using a diisocyanate compound standard substance to obtain the molar flow n _NCO of the isocyanate group and the Raman spectrum characteristic signal Is a relation of (2)K is the correlation coefficient of the Raman spectrum;

step 2, acquiring Raman spectrum in the polyurethane reaction process in real time on line, and obtaining real-time molar flow n (t) _NCO of isocyanate groups in the reaction process according to the relational expression in the step 1;

And 3, calculating according to the real-time molar flow n (t) _NCO of the isocyanate groups to obtain the polyurethane reaction process x (t)%.

10. The polyurethane reaction progress online monitoring system according to claim 7, wherein when the polyurethane reaction is continuous, the online monitoring of the reaction progress of the polyurethane polymerization process according to the raman spectrum characteristic signal of isocyanate specifically comprises:

Step 1, establishing a standard curve of the Raman spectrum characteristic signal of the isocyanate group and the molar flow rate of the isocyanate group by using a diisocyanate compound standard substance to obtain the molar flow rate F (t) _NCO of the isocyanate group and the Raman spectrum characteristic signal Is a relation of (2)K is the correlation coefficient of the Raman spectrum;

Step 2, acquiring Raman spectra in the polyurethane reaction process in real time on line, and obtaining the real-time molar flow rate F (t) _NCO of isocyanate groups in the reaction process according to the relational expression in the step 1;

And 3, calculating according to the real-time molar flow rate F (t) _NCO of the isocyanate groups to obtain the polyurethane reaction process x (t)%.