CN114112965A

CN114112965A - Method for detecting trace moisture in isocyanate and application of method in online monitoring

Info

Publication number: CN114112965A
Application number: CN202010891614.9A
Authority: CN
Inventors: 徐丹; 陈良进; 李楠; 王普照; 国欣; 吴雪峰; 张宏科
Original assignee: Wanhua Chemical Group Co Ltd; Wanhua Chemical Ningbo Co Ltd
Current assignee: Wanhua Chemical Group Co Ltd; Wanhua Chemical Ningbo Co Ltd
Priority date: 2020-08-31
Filing date: 2020-08-31
Publication date: 2022-03-01
Anticipated expiration: 2040-08-31
Also published as: CN114112965B

Abstract

The invention provides a method for monitoring trace moisture in isocyanate and application of on-line monitoring, which comprises the following steps: isocyanate and water were passed through a membrane carrying bis (3-amidomorpholinyl) diethyl ether as an isocyanate-reactive catalyst to produce carbon dioxide, and the content of the produced carbon dioxide was measured and converted to the moisture content in the isocyanate. The invention utilizes indirect measurement method, greatly reduces the measurement detection limit of water in isocyanate, can meet the requirement of isocyanate production monitoring on the measurement precision, can monitor whether the production device leaks water in time, and avoids the occurrence of greater safety accidents.

Description

Method for detecting trace moisture in isocyanate and application of method in online monitoring

The technical field is as follows:

the invention belongs to the field of monitoring of isocyanate production quality and production safety, and provides a method for detecting trace moisture in isocyanate and application of online monitoring of the method.

Background art:

isocyanates are important raw materials for polyurethane materials, which are generally produced as follows: firstly, producing amine corresponding to isocyanate, then carrying out phosgenation reaction on the amine and phosgene to generate a crude product containing isocyanate, and carrying out separation means such as rectification, evaporation, recrystallization and the like on the crude product to obtain a pure product.

In the isocyanate production process, the prodromal amine production reaction involves water, which may be brought downstream due to incomplete dehydration; in summer, moisture in the environment may permeate into the device due to improper pipelines, heat exchangers, packaging and the like, and the moisture may react with NCO active groups in isocyanate in production, storage and transportation systems and the like to generate urea substances which are difficult to dissolve in the isocyanate. The accumulation of urea in the reactor causes pipeline blockage, which can cause serious potential safety hazard; on the other hand, after water enters in the packaging, storing and transporting process, due to the low reaction temperature (30-50 ℃), the reaction speed is slow, when the isocyanate product passes through a packaging filter, water does not react in time to generate urea and is filtered and removed, so that the water is brought into a packaging barrel or a tank car to react with the isocyanate slowly, the isocyanate raw material used by a user is turbid, the quality of downstream products is affected, and complaints of customers are caused.

At present, the determination of the moisture in the isocyanate mainly comprises off-line sampling, laboratory chromatography and spectroscopy, the off-line determination consumes a large amount of manpower and material resources, and the time required in the processes of sample feeding and manual analysis is long, so that the quality of the isocyanate at the sampling moment can not be accurately represented; on the other hand, the sample is inevitably contacted with air in the sampling process, and the measurement result is not the real situation of the sample in the humid summer. However, the on-line analysis of moisture in isocyanate at home and abroad has few reports, and as disclosed in the patent publication CN107703096A, the moisture measurement of an isocyanate sample is directly performed by using the characteristic near-infrared absorption wavelength of water and adopting a near-infrared method, but the method has many problems: on one hand, the near infrared model is seriously influenced by the type of an isocyanate sample, the environment temperature and the pressure, the correction coefficients are greatly different under different conditions, and the modeling is complicated; on the other hand, the analysis quantitative limit of the near infrared analyzer to water is generally above 0.005%, and in practice, off-line analysis in a laboratory shows that the water content in a normal isocyanate sample is often lower than the value, so that the monitoring value of the near infrared method to normal isocyanate may greatly fluctuate due to system reasons, causing DCS misinformation and causing unnecessary troubles.

Therefore, it is necessary to perform an on-line analysis of the moisture content of isocyanate in the strand and packaged product in real time and accurately.

The invention content is as follows:

the invention provides a method for monitoring trace moisture in isocyanate and application of on-line monitoring, wherein an indirect measurement method is utilized, the measurement detection limit of water in the isocyanate is greatly reduced, the measurement precision can meet the requirement of isocyanate production monitoring, whether a production device leaks water can be monitored in time, and the occurrence of greater safety accidents is avoided.

In order to achieve the above object, the present invention provides a method for detecting trace moisture in isocyanate, comprising the steps of: passing isocyanate and water through a membrane loaded with an isocyanate active catalyst bis (3-amidomorpholinyl) diethyl ether to generate carbon dioxide, measuring the content of the generated carbon dioxide, and converting the content of the generated carbon dioxide into the moisture content in the isocyanate; the isocyanate active catalyst bis (3-amidomorpholinyl) diethyl ether has the following structural formula:

R₁is catechol ethyl, R₂Is C1-C5 alkyl or phenyl, preferably methyl, ethyl or phenyl.

According to the method provided by the invention, the isocyanate sample is selected from one or more of diphenylmethane diisocyanate, polyphenyl methane polyisocyanate, toluene diisocyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate, hexamethylene diisocyanate and phenyl isocyanate; preferred are diphenylmethane diisocyanate and isomers thereof, including one or more of 4, 4-diphenylmethane diisocyanate, 2, 4-diphenylmethane diisocyanate, and 2, 2-diphenylmethane diisocyanate.

The diphenylmethane diisocyanate and isomers thereof are preferably selected from one or more of 4, 4-diphenylmethane diisocyanate, 2-diphenylmethane diisocyanate.

The isocyanate active catalyst bis (3-amidomorpholinyl) diethyl ether is prepared by preparing precursor bis (3-carboxymorpholinyl) diethyl ether, and then loading the precursor bis (3-carboxymorpholinyl) diethyl ether on a membrane through chloracylation reaction with thionyl chloride and subsequent nitrogen acylation reaction, wherein the precursor bis (3-carboxymorpholinyl) diethyl ether has the following structural formula:

the preparation method of the preposed di (3-carboxyl morpholinyl) diethyl ether comprises the following steps:

(1) weighing 3-carboxyl morpholine in certain mass, and dissolving in a solvent reagent;

(2) adding a catalyst, preferably dropwise adding diethyl ether into 3-carboxymorpholine at a constant speed, and carrying out reflux reaction after the required proportion is reached;

(3) the pure product of the isocyanate active catalyst bis (3-carboxyl morpholinyl) diethyl ether is obtained by separation and purification.

In the preparation of the precursor di (3-carboxymorpholinyl) diethyl ether, the mass ratio of the 3-carboxymorpholine to the diethyl ether is 5-20:1, preferably 8-10: 1.

In the preparation of the precursor di (3-carboxymorpholinyl) diethyl ether, the solvent is one or more of tetrahydrofuran, acetonitrile, N-N-dimethylformamide, N-methylpyrrolidone and cyclohexane, and preferably N-N-dimethylformamide; the mass ratio of the 3-carboxyl morpholine to the solvent is 1:1.5-8, preferably 1: 2-4.

In the preparation of the precursor di (3-carboxymorpholinyl) diethyl ether, the temperature of the reaction system is 60-120 ℃, and the highest temperature is the temperature of a reaction solvent.

In the preparation of the precursor di (3-carboxymorpholinyl) diethyl ether, the catalyst is one or more of hydroxide, halide and carbonate of alkali metal, and is preferably a single type of potassium iodide, potassium bromide and sodium carbonate; the mass ratio of the 3-carboxyl morpholine to the catalyst is 20-80:1, preferably 30-50: 1.

In the preparation of the precursor di (3-carboxymorpholinyl) diethyl ether, the reactant diethyl ether is completely dropped to 100 percent in the reaction process, the dropping speed is 0.5-3 percent/min, preferably 0.7-1.5 percent/min, and the reaction time is 4-8 hours.

In the preparation of the catalyst of the present invention, in the step (3), the separation and purification methods required to be involved are extraction, reduced pressure distillation, atmospheric distillation and recrystallization, and the specific operations are as follows:

(1) carrying out atmospheric distillation or extraction on the liquid phase sample after reaction to remove the solvent; the distillation temperature should be higher than the boiling point of the solvent and not higher than 220 ℃.

(2) Distilling the sample prepared in the step (1) under reduced pressure to remove redundant reaction raw materials and solvents; the reduced pressure distillation conditions are 20-40mmHg, preferably 25-30mmHg, the temperature is 180-230 ℃, preferably 195-205 ℃. (3) And (3) recrystallizing the sample prepared in the step (2) to obtain a pure product. The solvent of choice for recrystallization may be ethyl acetate, acetonitrile or acetone, with acetonitrile being preferred.

The invention provides a preparation method of a supported membrane of an isocyanate active catalyst, which comprises the following steps:

(1) adding thionyl chloride and a catalyst required by the reaction into the put bis (3-carboxymorpholinyl) diethyl ether, wherein the mass ratio of the bis (3-carboxymorpholinyl) diethyl ether to the thionyl chloride is 1:3-20, and preferably 1: 5-8; heating and refluxing, and performing rotary evaporation to remove thionyl chloride to obtain an intermediate bis (3-acyl chloride morpholinyl) diethyl ether, wherein the substance has the following structure;

the catalyst required for the reaction can be any one of amide, tertiary amine and carbonate, and N-N-dimethylformamide is preferred. The mass ratio of bis (3-carboxymorpholinyl) diethyl ether to catalyst is 50-400:1, preferably 80-150: 1. The temperature of the reaction system is 60-120 ℃, and the reaction time is 2-8 h;

(2) washing the basement membrane with a solvent, and naturally airing;

the base membrane can be polyvinylidene fluoride (PVDF) or Polytetrafluoroethylene (PTFE), preferably polyvinylidene fluoride (PVDF); the cleaning solvent can be one or more of methanol, ethanol, acetone and ultrapure water, and is preferably acetone;

(3) after the basement membrane is soaked in a dopamine solution, a polydopamine mesomeric layer is constructed on the surface of the basement membrane;

the dopamine solution is a mixed solution of dopamine, buffer salt and water, and the pH value of the solution is 5-9; wherein the concentration of dopamine in the solution is 5-20mg/mL, the buffer salt can be one or more of phosphate, ammonium salt and organic salt, and preferably any one of potassium dihydrogen phosphate-dipotassium hydrogen phosphate and Tris-HCl. The buffer salt concentration is 30-200mM, preferably 80-150 mM. The soaking time is 12-24h, and the temperature of the soaking system is 30-60 ℃.

(4) And (3) soaking the base film constructing the intermediate conducting layer in the step (3) in a solvent containing intermediate bis (3-acyl chloride morpholinyl) diethyl ether, and finally converting the intermediate bis (3-acyl chloride morpholinyl) diethyl ether into a catalyst bis (3-amide morpholinyl) diethyl ether to be loaded on the base film through nitrogen acylation reaction.

The solvent in the load reaction can be one or more of amide, acetone and cyclohexane, and N-N-dimethylformamide is preferred; the concentration of the bis (amidomorpholinyl) diethyl ether solution is 5-20 mg/mL. The soaking time is 12-24h, and the soaking temperature is 40-80 ℃.

(5) And (4) soaking the membrane loaded with the catalyst bis (3-amidomorpholinyl) diethyl ether in the end-capping reagent to finish end-capping.

The blocking agent may be one or more of an acyl chloride species, preferably acetyl chloride. The end capping reaction time is 6-12 h; the blocking temperature is normal temperature, and the mass ratio of the blocking agent to the catalyst is 300-1000: 1.

The invention also provides an application of the method in online monitoring of trace moisture in isocyanate production, which comprises the following steps:

step one, installing a membrane loaded with an isocyanate active catalyst bis (3-amidomorpholinyl) diethyl ether at the inlet end of an online measurement device;

and secondly, starting a measuring device by controlling measuring equipment, introducing a sample at a position point into a buffer tank through a sample output pipeline arranged in advance when the moisture content of the sample is monitored on line at the position point related to the device, introducing the sample into an on-line measuring device through the buffer tank, regulating the temperature of an isocyanate sample through the buffer tank, then, utilizing a pump to pass the isocyanate sample with a certain mass through a membrane loaded with a catalyst, enabling the isocyanate and trace moisture to react to generate carbon dioxide, measuring the generated carbon dioxide content by using an on-line carbon dioxide measuring instrument, and converting the content into the moisture content in the isocyanate through automatic calculation. According to the method provided by the invention, the moisture online measuring device in the step one comprises a control measuring device, a buffer tank, a sample conveying pump, a reaction device containing a catalyst supported membrane, a measuring gas chamber, a carbon dioxide online measuring instrument and relevant connecting pipelines which are connected through pipelines. The online moisture determination device is connected with a site to be measured through a material pipeline, the material pipeline is firstly connected into a buffer tank, the material in the buffer tank is introduced into a measurement chamber through a delivery pump, after measurement is carried out, a sample is pressed into the lower space of a nested catalyst membrane by a sample pressing piston in the measurement chamber, after reaction occurs, the sample flows out to a measured sample chamber, and finally is introduced into a waste liquid tank; and the gas generated by the reaction enters a measuring gas chamber attached with a carbon dioxide on-line measuring instrument to complete analysis and measurement. The whole moisture online measuring device is positioned in a constant-temperature closed space.

According to the method provided by the invention, the control and measurement equipment in the step two is a controller for starting the system, and the automatic analysis time can be set by the connected external host computer or the system can be forcibly started manually.

The constant temperature value of the online moisture measuring equipment is 50-95 ℃, and preferably 70-80 ℃. The temperature should be kept constant, in a constant range not higher than 1% to 10%, preferably 1% to 2%.

The buffer tank is a closed container which is connected in front of the catalyst supported membrane to stabilize the temperature of the isocyanate sample, so that the temperature of the isocyanate sample pumped into the membrane is consistent with the temperature of the reaction system. The residence time of the isocyanate sample in the buffer tank is 2-10min, preferably 3-5 min.

The adjusting parameters of the sample conveying pump are as follows: when the isocyanate sample is transmitted to the moisture online measuring device, the transmission amount of the isocyanate sample is 30-200g, preferably 50-80 g; the transmembrane pressure is from 30 to 300KPa, preferably from 50 to 100 KPa.

The contact area of the catalyst supported membrane and an isocyanate sample is 20-100cm²Preferably 50-80cm²。

The measurement gas chamber is connected with the catalyst load membrane through a gas pipeline, the isocyanate and the moisture are diffused into the measurement gas chamber through carbon dioxide generated by catalytic reaction of the catalyst, and the content of the carbon dioxide in the gas chamber is measured by a carbon dioxide on-line measuring instrument. The volume of the measuring air chamber is 10-50L, preferably 15-25L;

according to the method provided by the invention, the carbon dioxide on-line measuring instrument can be various types sold on the market meeting the measuring requirements, a non-dispersive mid-infrared light emitting method is preferably selected as the measuring principle, the carbon dioxide has strong absorption to light in a mid-infrared band region of 4.26 mu m, the absorbed energy and the gas content have good linear relation, the absorbed energy is converted by a circuit to obtain the concentration of the carbon dioxide, and then the moisture content in the isocyanate is calculated by the volume of the air chamber and the transmission quantity of the isocyanate.

The carbon dioxide on-line measuring instrument probe is arranged inside the gas chamber to measure the content of carbon dioxide in the gas chamber. The installation position of the probe is 10% -90% of the height of the air chamber, preferably 40% -50%; preferably, the carbon dioxide on-line determinator probe is an immersion type optical fiber probe. More preferably, the immersed carbon dioxide on-line determinator probe is a telescopic probe.

The material of the probe of the carbon dioxide on-line measuring instrument is selected from one or more of stainless steel, hastelloy and ceramic, and 316L stainless steel is preferred according to the property of isocyanate material flow.

According to the method provided by the invention, the chemical reaction involved in the step two and the diffusion of the generated carbon dioxide to the gas chamber take a period of time to achieve the content balance, so that the content of the carbon dioxide in the gas chamber is delayed to be measured after the isocyanate sample completely passes through the membrane, and then the measured isocyanate sample is discharged. The delay time of the carbon dioxide on-line measuring instrument is 0.5-10min, preferably 2-4 min.

According to the method provided by the invention, in the second step, measurement data such as the transmission speed, the transmission time and the measured value of the carbon dioxide on-line measuring instrument of the isocyanate sample are transmitted into the PC host machine through the optical cable, and the host machine calculates the moisture content in the isocyanate sample.

According to the method provided by the invention, in the second step, the host computer automatically converts the measured value of the carbon dioxide into the water content in the isocyanate, and the measured value of the carbon dioxide needs to be corrected and established through a system measurement model which is confirmed in advance and is recorded into an analysis system. According to the method provided by the present invention, preferably, the establishing of the analysis model comprises the following steps: the isocyanate samples of the calibration set were analyzed as described in the present invention to obtain analytical measurements, which were correlated to known levels and an analytical model was established by a multivariate data regression analysis.

In a preferred embodiment, the established analytical model is subjected to a bias test.

In a preferred embodiment, the multivariate data regression analysis method is partial least squares regression.

In a preferred embodiment, the isocyanate sample collected includes both the original sample of the apparatus on-line, tank car, can, and the experimental sample with artificially added moisture.

In a preferred embodiment, the calibration set has a number of isocyanate samples of not less than 20. The water content of the isocyanate sample in the calibration set is 0.0003-0.03 percent, preferably 0.0008-0.016 percent, based on 100 percent of the total weight of the isocyanate sample in the calibration set.

According to the method provided by the invention, preferably, in order to improve the measurement precision of the moisture content of the isocyanate sample, the correlation coefficient (R) of the established analysis model²) The error between the predicted value and the true value is required to be higher than 0.985.

According to the method provided by the invention, the measurement data such as the transmission quantity of the isocyanate sample, the measured value of the carbon dioxide content and the like are transmitted into the PC host machine through the optical cable, and the host machine calculates the moisture content in the isocyanate sample according to the preset moisture content analysis model.

According to the method provided by the invention, preferably, the sample moisture content data of the monitored site is transmitted to a DCS picture of a control room in a wired or wireless mode, and meanwhile, DCS high-limit alarm is set; more preferably, the DCS alarm minimum is 0.008-0.012% moisture content.

By utilizing the method provided by the invention, the moisture content of the isocyanate sample in the system can be monitored in real time at different key sites of the isocyanate production system, wherein the sites need to be monitored are as follows: a heat exchanger end socket at a side line extraction point of the rectifying tower, a pipeline with sample effusion, a buffer tank, a product packaging pipeline and the like.

According to the method provided by the invention, each measuring point can preferably realize continuous monitoring of the moisture of the isocyanate sample at a preset time interval. In a preferred embodiment, the sample measurement and data acquisition interval at the site to be monitored is 10-30 min.

The invention has the positive effects that:

(1) preparing a catalyst for efficiently catalyzing the reaction of isocyanate and water, and loading the catalyst on a membrane; reacting isocyanate permeating the membrane with moisture contained in the isocyanate to generate carbon dioxide through the catalytic effect of the membrane; therefore, the moisture detection with higher detection limit and difficult detection is converted into the carbon dioxide detection which is easy to realize trace analysis, the analysis detection limit is greatly reduced, and the measurement precision is further improved.

(1) Compared with the laboratory offline analysis method, the method eliminates the measurement positive interference caused by the introduction of moisture in the air due to sampling, and the determined sample can flow back to the inside of the device, thereby avoiding a series of problems of occupational health, waste liquid treatment and the like caused by manual sampling and offline analysis of the isocyanate sample.

(2) Compared with the laboratory off-line analysis method, the measurement time is obviously shortened (<10min), which is equivalent to approximately monitoring the product quality condition inside the current device in real time. The production personnel can quickly diagnose and process abnormal conditions according to the online analysis data, and the further leakage of the moisture is avoided to cause larger accidents. Meanwhile, the turbid phenomenon caused by the fact that a large amount of water permeates into the production device of the client shipment material can be avoided, the complaint of the client is reduced, and the manpower and material resources for troubleshooting the specific problems of the device are also reduced. However, the measurement period of the current laboratory method is as long as several hours, and in the time of waiting for the analysis result, production personnel cannot confirm the specific condition of the current device, the production is continued, and the occurrence of production hidden troubles and accidents caused by the long measurement period is avoided by optimizing the analysis method.

Description of the drawings:

the above and other objects, features and advantages of the present invention will become more apparent by describing in more detail exemplary embodiments thereof with reference to the attached drawings, in which like reference numerals generally represent like parts throughout.

FIG. 1 shows a schematic diagram of an apparatus for on-line measurement of moisture in isocyanate.

The indicated reference numerals are explained below:

1: device site, 2: buffer tank, 3: sample pressing piston, 4: sample area to be reacted, 5: catalyst-supported membrane, 6: waste liquid tank, 7: reacted sample region, 8: air chamber, 9: carbon dioxide meter main unit, 10: a carbon dioxide meter probe;

wherein the catalyst-supporting membrane is located at a lower position of the sample region to be reacted. The buffer tank is connected with the to-be-sampled point of the device through a heat preservation pipeline.

FIG. 2 shows the correlation of the true moisture content of an isocyanate sample with the content analyzed by a laboratory instrument.

FIG. 3 shows a plot of the true moisture content of an isocyanate sample versus the amount of carbon dioxide generated after reaction by an on-line analyzer.

FIG. 4 shows a correlation curve between two sets of measurements obtained from isocyanate samples by the laboratory analysis method and the on-line measurement device analysis method, respectively.

The specific implementation mode is as follows:

the technical features and contents of the present invention are described in detail below with reference to specific embodiments. It should be understood, however, that the present invention may be embodied in other specific forms and should not be construed as limited to the specific embodiments set forth herein.

The analysis and test method comprises the following steps:

1. carbon dioxide on-line measurement:

the carbon dioxide on-line measuring instrument is selected from an MCP-200 infrared analyzer of AAI company, a heat-resistant protection device is additionally arranged, and a probe is made of 316L stainless steel.

2. Determination of the Water content in the isocyanate sample by the laboratory test method:

basic principle of analysis of water content in isocyanate samples: at a humidity of<Accurately weighing 75g of isocyanate sample to be measured in 5% environment, transferring the isocyanate sample to a sample area to be reacted of a designed online measuring device, immediately applying 100Kpa pressure by a sample pressing piston to enable the sample to contact a catalytic membrane (a supported catalyst membrane 1) for reaction, wherein the total contact area of the catalytic membrane is 70cm²Transferring all the samples to a reacted sample area after permeation, and after delaying for 4min, determining the concentration of the reaction product carbon dioxide diffused to the gas chamber by a carbon dioxide determinator, wherein the probe is used for measuring 50% of the height of the gas chamber, and the volume of the gas chamber is 20L; the water content in the sample is indirectly determined from the measured value. The specific analysis steps are as follows:

(1) adding isocyanate samples to be detected with the same mass into n groups of 500mL sample bottles, and adding water (calculated as m) with different masses₁、m₂、m₃…m_n) Performing reaction and instrument analysis under the above conditions to determine the corresponding measured value of carbon dioxide concentration in the sample(in terms of S)₁、S₂、S₃…S_n)；

(2) Adding isocyanate samples to be detected with the same mass as that of the samples in the group (1) into 120 mL sample bottle without adding water, directly carrying out reaction and instrument analysis according to the conditions, determining the corresponding measured value of the concentration of carbon dioxide in the samples, and taking the measured value as S₀。

(3) In the amount of water added (m)₁、m₂、m₃…m_n) On the x-axis, corresponding to the increase in measured carbon dioxide concentration (i.e., S)₁-S₀、S₂-S₀、S₃-S₀…S_n-S₀) Determining a slope k, namely a first derivative value of the water addition amount and the measured value of the carbon dioxide concentration, by taking a y axis;

(4) and (3) carrying out reaction and instrument analysis on the isocyanate sample to be detected according to the conditions, wherein the water content n is (S/k)/m, wherein S is the corresponding measured value of the concentration of carbon dioxide in the sample, and m is the adding amount of the sample.

In the above laboratory test methods, the analytical instrument used is selected from:

(1) avance III 400M NMR spectrometer from Bruker, Germany. An Ultrashield 400 magnet and a 5mm Dual (13C, 1H) Dual core probe are configured.

(2) The yield of the precursor bis (3-carboxymorpholinyl) diethyl ether in the examples was determined by liquid chromatography:

agilent 1260 liquid chromatograph, USA, with DAD detector;

a chromatographic column: CAPCELL PAK-C185 μm, 4.6X 250 mm;

gradient elution:

time(min)	methanol (%, v/v)	0.1% of phosphorusAcid (%, v/v)
			0	10	90
7	10	90
			15	80	20
20	10	90
			30(end)	10	90

0.1% phosphoric acid, 1mL phosphoric acid dissolved in 1L ultrapure water

Column temperature: 40 ℃, flow rate: 1.0mL/min, sample size: 30 μ L, UV detector wavelength: 210nm

(3) In the examples, the yield of bis (3-acylmorpholinyl) diethyl ether was quantified by chlorine analyzer: muti EA 5000 element analyzer, a chlorine detector and a liquid sample injector of Analytikjena, Germany, samples are diluted by 500 times with chromatographic grade acetone (without chlorine element), and then are analyzed, and are quantified by a chlorine standard oil sample standard addition method, and finally, the relative content of the di (3-acyl chloride morpholinyl) diethyl ether molecules in the reaction products of the examples is calculated according to the chlorine element content of the samples.

Example 1:

method for the synthesis of isocyanate-reactive catalyst precursor bis (3-carboxymorpholinyl) diethyl ether example 1:

dissolving 400g of 3-carboxymorpholine in 1000g N-N-dimethylformamide, adding the solution into a reactor provided with a thermometer and a reflux condenser tube, controlling the temperature of a reaction system to be 100 ℃, adding 10g of potassium iodide, dripping 40g of dichloroethyl ether into the reactor at the flow rate of 0.4g/min, stirring, refluxing, reacting, and preserving heat for 30min after the dripping is finished. Cooling at normal temperature, separating phases, wherein solid phases are hydrochloride of 3-carboxymorpholine and potassium iodide (which can be recovered and reused after being treated by sodium hydroxide), and a liquid phase is distilled at 160 ℃ under normal pressure to remove a solvent N-N-dimethylformamide; then, under the pressure of 25mmHg, the redundant 3-carboxyl morpholine is removed by reduced pressure distillation at the temperature of 200 ℃, and a crude product can be obtained; the crude product is recrystallized by acetonitrile, and is filtered by suction to obtain the product of bis (3-carboxymorpholinyl) diethyl ether with the yield of 84 percent. The reaction formula is as follows:

¹H NMR(CDCl₃500MHz), 12.39(s,2H),4.43(s,4H),4.03(d, J-12.1 Hz,2H),3.77(d, J-12.1 Hz,2H),3.57-3.61(m,4H),3.34(t, J-11.1 Hz,2H),2.62-2.72(m,4H). Synthesis of isocyanate-reactive catalyst precursor bis (3-carboxymorpholinyl) diethyl ether example 2:

dissolving 400g of 3-carboxymorpholine in 2000g N-methylpyrrolidone, adding the mixture into a reactor provided with a thermometer and a reflux condenser tube, controlling the temperature of a reaction system to be 120 ℃, adding 20g of sodium carbonate, dripping 60g of dichloroethyl ether into the reactor at the flow rate of 0.3g/min, stirring and refluxing for reaction, and keeping the temperature for reaction for 30min after the dripping is finished. Cooling at normal temperature, separating phases, wherein the solid phase is hydrochloride of 3-carboxymorpholine and sodium carbonate (which can be treated by sodium hydroxide and then recycled), and the liquid phase is distilled at 205 ℃ under normal pressure to remove the solvent N-methylpyrrolidone; then, under the pressure of 25mmHg, the redundant 3-carboxyl morpholine is removed by reduced pressure distillation at the temperature of 200 ℃, and a crude product can be obtained; the crude product is recrystallized by acetonitrile, and is filtered by suction to obtain the product of bis (3-carboxymorpholinyl) diethyl ether with the yield of 91 percent.

¹H NMR(CDCl₃,500MHz):12.68(s,2H),4.48(s,4H),4.09(d,J＝12.1Hz,2H) 3.59(d, J ═ 12.1Hz,2H),3.62-3.64(m,4H),3.39(t, J ═ 11.1Hz,2H),2.84-2.90(m,4H), method for the synthesis of isocyanate-reactive catalyst precursor bis (3-carboxymorpholinyl) diethyl ether example 3:

dissolving 400g of 3-carboxymorpholine in 750g of tetrahydrofuran, adding the tetrahydrofuran into a reactor provided with a thermometer and a reflux condenser tube, controlling the temperature of a reaction system to be 60 ℃, adding 6g of potassium bromide, dripping 20g of dichloroethyl ether into the reactor at the flow rate of 0.5g/min, stirring and refluxing for reaction, and preserving heat for reaction for 60min after the dripping is finished. Cooling at normal temperature, separating phases, wherein solid phases are hydrochloride and potassium bromide of 3-carboxymorpholine (which can be treated by sodium hydroxide and then recycled), and liquid phases are distilled at 80 ℃ under normal pressure to remove tetrahydrofuran serving as a solvent; then, under the pressure of 25mmHg, the redundant 3-carboxyl morpholine is removed by reduced pressure distillation at the temperature of 200 ℃, and a crude product can be obtained; the crude product is recrystallized by acetonitrile, and is filtered by suction to obtain the product of bis (3-carboxymorpholinyl) diethyl ether with the yield of 75 percent.

¹H NMR(CDCl₃,500MHz):12.55(s,2H),4.45(s,4H),4.13(d,J＝12.1Hz,2H),3.48(d,J＝12.1Hz,2H),3.68-3.70(m,4H),3.33(t,J＝11.1Hz,2H),2.74-2.81(m,4H).

Example 2:

preparation of a film carrying an isocyanate-reactive catalyst method example 1;

adding 700g of thionyl chloride into 100g of bis (3-carboxymorpholinyl) diethyl ether, then dropwise adding 1g N-N-dimethylformamide, heating and refluxing for 3h at 80 ℃, and removing redundant thionyl chloride and N-N-dimethylformamide by rotary evaporation to obtain the membrane active matrix bis (3-acyl chloride morpholinyl) diethyl ether, wherein the yield is 92%, and the reaction formula is as follows:

¹H NMR(CDCl₃,500MHz):4.44(s,4H),4.09(d,J＝12.1Hz,2H),3.84(d,J＝12.1Hz,2H),3.57-3.61(m,4H),3.23(t,J＝11.1Hz,2H),2.62-2.72(m,4H).

and (3) cleaning the polyvinylidene fluoride membrane (PVDF) by using an acetone solvent, and naturally drying. And (3) soaking the washed membrane material in a dopamine buffer solution (10mg/mL of dopamine, 50mM of Tris and 50mM of HCl aqueous solution) for 18 hours at 50 ℃ to construct a polydopamine mediated layer on the surface of the membrane. Soaking a basement membrane for constructing a polydopamine mediated layer in a 10mg/mL N-N-dimethylformamide solution of bis (3-acyl chloride morpholinyl) diethyl ether at 50 ℃ for 18h to load a catalyst; finally, soaking the membrane loaded with the catalyst in acetyl chloride with the mass of 500 times that of the catalyst for 8 hours at normal temperature to finish end capping to obtain a loaded catalyst membrane 1, wherein the reaction formula is as follows: r represents catechol ethyl.

Preparation of a film carrying an isocyanate-reactive catalyst example 2;

adding 1200g of thionyl chloride into 100g of bis (3-carboxymorpholinyl) diethyl ether, then dropwise adding 0.5g of triethylamine, heating and refluxing for 7h at 65 ℃, removing redundant thionyl chloride and triethylamine through rotary evaporation to obtain the membrane active matrix bis (3-acyl chloride morpholinyl) diethyl ether with the yield of 87%,

¹H NMR(CDCl₃,500MHz):4.35(s,4H),4.08(d,J＝12.1Hz,2H),3.81(d,J＝12.1Hz,2H),3.49-3.57(m,4H),3.28(t,J＝11.1Hz,2H),2.69-2.79(m,4H).

and (3) cleaning the polyvinylidene fluoride membrane (PVDF) by using an acetone solvent, and naturally drying. The washed membrane material was soaked in a dopamine buffer solution (15mg/mL dopamine +150mM dipotassium hydrogen phosphate +10mM potassium dihydrogen phosphate aqueous solution) at 55 ℃ for 12 hours to construct a polydopamine mediated layer on the membrane surface. Soaking a basement membrane for constructing a polydopamine mediated layer in 15mg/mL acetone solution of bis (3-acyl chloride morpholinyl) diethyl ether for 12 hours at 75 ℃ to load a catalyst; finally, soaking the membrane loaded with the catalyst in acetyl chloride with the mass of 500 times that of the catalyst for 6 hours at normal temperature to finish end sealing, thereby obtaining a loaded catalyst membrane 2.

Preparation of isocyanate-supported active catalyst membrane method example 3;

adding 400g of thionyl chloride into 100g of bis (3-carboxymorpholinyl) diethyl ether, then dropwise adding 2g of sodium carbonate, heating and refluxing for 3h at 110 ℃, performing rotary evaporation, and filtering to remove redundant thionyl chloride and sodium carbonate to obtain membrane active matrix bis (3-acyl chloride morpholinyl) diethyl ether with the yield of 94%;

¹H NMR(CDCl₃,500MHz):4.39(s,4H),4.04(d,J＝12.1Hz,2H),3.80(d,J＝12.1Hz,2H),3.52-3.54(m,4H),3.29(t,J＝11.1Hz,2H),2.63-2.74(m,4H).

and (3) cleaning the polyvinylidene fluoride membrane (PVDF) by using an acetone solvent, and naturally drying. The washed membrane material is soaked in a dopamine buffer solution (6mg/mL of dopamine, 40mM of ammonium chloride and 5mM of ammonia water solution) for 24 hours at 35 ℃, and a polydopamine mediated layer is constructed on the surface of the membrane. Soaking a basement membrane for constructing a polydopamine mediated layer in a cyclohexane solution of 5mg/mL bis (3-acyl chloride morpholinyl) diethyl ether for 24 hours at the temperature of 45 ℃ to load a catalyst; finally, soaking the membrane loaded with the catalyst in acetyl chloride with the mass of 500 times that of the catalyst for 12 hours at normal temperature to finish end capping, thus obtaining a loaded catalyst membrane 3.

Example 3:

according to the method provided by the invention, an on-line measuring device is designed, as shown in figure 1, and the following are application examples of the device of the supported membrane catalyst under different preparation methods.

On-line assay device application example 1:

introducing the sample into a buffer tank through a previously determined device site, keeping the temperature at 80 +/-1 ℃ for 5min, metering by a buffer load balance, transferring 75g of a diphenylmethane diisocyanate sample into a sample area to be reacted, immediately applying 100Kpa pressure by a sample pressing piston to enable the sample to contact a catalytic membrane (a loaded catalyst membrane 1) for reaction, wherein the total contact area of the catalytic membrane is 70cm²After all the sample has permeated and transferred to the reacted sample area, and after a further 4min delay, the concentration of the reaction product carbon dioxide diffusing into the gas chamber is determined by a carbon dioxide meter, wherein the probe measures 50% of the height of the gas chamber and the volume of the gas chamber is 20L. The sample in the reacted sample area is transferred to a waste liquid tank, can be treated by waste liquid according to requirements, and can also be returned to the original device site.

On-line assay device application example 2:

introducing the sample into a buffer tank through a previously determined device site, keeping the temperature at 50 +/-1 ℃ for 5min, metering by a buffer load balance, transferring 120g of toluene diisocyanate sample into a sample area to be reacted, immediately applying 200Kpa pressure by a sample pressing piston to enable the sample to contact a catalytic membrane (a supported catalyst membrane 2) for reaction, wherein the total contact area of the catalytic membrane is 90cm²And transferring all the samples to a reacted sample area after permeation, and measuring the concentration of the reaction product carbon dioxide diffused to the gas chamber by a carbon dioxide measuring instrument after delaying for 4min, wherein the height of the probe is 30% of the height of the gas chamber, and the volume of the gas chamber is 30L. The sample in the reacted sample area is transferred to a waste liquid tank, can be treated by waste liquid according to requirements, and can also be returned to the original device site.

On-line assay device application example 3:

introducing the sample into a buffer tank through a previously determined device site, keeping the temperature at 90 +/-3 ℃ for 5min, metering by a buffer load balance, transferring 40g of hexamethylene diisocyanate sample into a sample area to be reacted, immediately applying 50Kpa pressure by a sample pressing piston to enable the sample to contact a catalytic membrane (a supported catalyst membrane 3) for reaction, wherein the total contact area of the catalytic membrane is 40cm²After all the sample has permeated and transferred to the reacted sample area, and after a further 7min delay, the concentration of the reaction product carbon dioxide diffusing into the gas chamber is determined by a carbon dioxide analyzer, wherein the probe measures 70% of the height of the gas chamber and the volume of the gas chamber is 10L. The sample in the reacted sample area is transferred to a waste liquid tank, can be treated by waste liquid according to requirements, and can also be returned to the original device site.

Example 4:

according to the method provided by the invention, in order to obtain the online measurement result of the water content of the isocyanate sample, a result model of the water content of the isocyanate sample and the carbon dioxide content generated by the reaction of the sample in an online measurement device needs to be established, and by taking diphenylmethane diisocyanate (MDI) as an example, the method comprises the following specific steps:

(1) a total of 20 diphenylmethane diisocyanate samples of different positions, different times and different 4,4/2,4 isomeric ratios were collected and analyzed using the laboratory analysis method described aboveAnalyzing the water content in the sample, determining the MDI sample with the lowest water content, artificially adding water with different contents into the sample, wherein the added water content is 0-0.015 percent respectively, and the added water content is distributed in an arithmetic progression to obtain a group of samples with different water contents, and determining the laboratory analysis content of the group of samples by using a laboratory analysis method. The correlation curve of the real moisture content of the sample and the laboratory analysis content is shown in FIG. 2, and the correlation coefficient R²The laboratory analysis results are approximately considered to characterize the true moisture content of the isocyanate sample, 0.9988.

(2) After 20 isocyanate samples with water added in (1) were subjected to reaction by an on-line analyzer, the carbon dioxide content was measured, and all the reaction conditions of the on-line analyzer were kept the same as those of example 1 in example 3.

(3) Correlating the real moisture content of 20 isocyanate samples added with moisture in the step (1) with the content of carbon dioxide generated by reaction after passing through an online analysis device, establishing a quantitative model of the water content of the diphenylmethane diisocyanate sample by using a partial least squares regression method, wherein a correlation curve of the real moisture content of the sample and the content of the carbon dioxide in a reactor is shown in figure 3, and a correlation coefficient R²The modeling results are ideally reliable at 0.9926, so the reactor generated carbon dioxide content can be accurately described as the moisture content of the isocyanate.

(4) Using the established quantitative model, the remaining 19 diphenylmethane diisocyanate samples of (1) were subjected to moisture analysis using an on-line analytical apparatus and compared with the moisture content obtained by the laboratory analytical method of (1), the correlation curve of the two analytical methods is shown in fig. 4, and the correlation coefficient R is²0.9885, the maximum deviation is 0.0005%, and the accuracy of the online analysis value determined by the model can meet the requirements of device production.

Example 5:

the online reactor and the analysis result model related to the

embodiments

3 and 4 are applied to online moisture determination of the MDI product storage tank sample, and the specific steps are as follows:

(1) installing the online reactor described in the embodiment 3 at a specified position corresponding to a specific height of an MDI product feeding pipeline and a storage tank;

(2) the carbon dioxide concentration values collected at each site are transmitted to a PC (personal computer), the PC calculates the water content of the sample by using the data and the analysis result model established in the embodiment 4, the calculation result is transmitted to a DCS (distributed control system) screen of a control room, the test interval is 30min or more, and the measurement can be manually operated.

(3) When the analyzed water content is higher than a set alarm value (the set alarm value is 0.001%), the DCS gives an alarm, an operator needs to switch the high-water-content MDI product into an unqualified product tank in time, and simultaneously immediately checks whether a leakage point exists near the position point until the analysis value is recovered to be normal, and then the DCS can be switched back into a normal product tank.

While various embodiments of the present invention have been described above, it should be understood that the above embodiments are only exemplary and not exclusive, and that various modifications and optimizations of various embodiments may be possible and will be apparent to those skilled in the art.

Claims

1. A method for detecting trace moisture in isocyanate, comprising the steps of: passing isocyanate and water through a membrane loaded with an isocyanate-reactive catalyst bis (3-amidomorpholinyl) diethyl ether to generate carbon dioxide, measuring the content of the generated carbon dioxide, and converting the content into the moisture content in the isocyanate, wherein the isocyanate-reactive catalyst bis (3-amidomorpholinyl) diethyl ether has the following structural formula:

(ii) a Wherein R is₁Is catechol ethyl, R₂Is C1-C5 alkyl or phenyl, preferably methyl, ethyl or phenyl.

2. The method of claim 1, wherein the isocyanate is selected from one or more of diphenylmethane diisocyanate and isomers thereof, polyphenylmethane polyisocyanate, toluene diisocyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate, hexamethylene diisocyanate, phenyl isocyanate; preferably diphenylmethane diisocyanate and isomers thereof; the diphenylmethane diisocyanate and isomers thereof are preferably selected from one or more of 4, 4-diphenylmethane diisocyanate, 2-diphenylmethane diisocyanate.

3. The method as claimed in claim 1, wherein the isocyanate-reactive catalyst bis (3-amidomorpholinyl) diethyl ether is supported on a membrane by preparing a precursor bis (3-carboxymorpholinyl) diethyl ether, and then performing a chlorinoacylation reaction with thionyl chloride and a subsequent nitrogen acylation reaction, wherein the precursor bis (3-carboxymorpholinyl) diethyl ether has the following structural formula:

(1) dissolving 3-carboxyl morpholine in a solvent;

(2) adding a catalyst, adding diethyl ether into 3-carboxymorpholine to obtain a mixture according to a required ratio, and performing reflux reaction;

(3) the bis (3-carboxymorpholinyl) diethyl ether is obtained by separation and purification.

4. A process according to claim 3, characterized in that the mass ratio of 3-carboxymorpholine to diethyl ether is 5-20:1, preferably 8-10: 1; and/or the temperature of the reaction system is 60-120 ℃; and/or dripping diethyl ether into 3-carboxymorpholine at a constant speed, wherein the dripping speed is 0.5-3%/min, preferably 0.7-1.5%/min, and the reaction time is 4-8h, wherein the total dripping speed of the reactant diethyl ether is 100%.

5. The process according to claim 3 or 4, wherein the solvent is one or more of tetrahydrofuran, acetonitrile, N-N-dimethylformamide, N-methylpyrrolidone, cyclohexane, preferably N-N-dimethylformamide; and/or the mass ratio of the 3-carboxyl morpholine to the solvent is 1:1.5-8, preferably 1: 2-4.

6. A process according to any one of claims 3 to 5, wherein the catalyst is one or more of a hydroxide, halide, carbonate of an alkali metal, preferably potassium iodide, potassium bromide or sodium carbonate; the mass ratio of the 3-carboxyl morpholine to the catalyst is 20-80:1, preferably 30-50: 1.

7. A process according to any one of claims 3 to 6, characterized in that the process for the preparation of the isocyanate-reactive catalyst loaded membrane comprises the following steps:

(1) adding thionyl chloride and a catalyst required by the reaction into bis (3-carboxymorpholinyl) diethyl ether, heating and refluxing, and performing rotary evaporation to remove thionyl chloride to obtain an intermediate bis (3-acyl chloride morpholinyl) diethyl ether, wherein the substance has the following structural formula;

(2) washing the basement membrane with a solvent, and naturally airing;

(4) soaking the base film of the intermediate conducting layer constructed in the step (3) in a solvent containing intermediate bis (3-acyl chloride morpholinyl) diethyl ether, and carrying out nitrogen acylation reaction on the intermediate bis (3-acyl chloride morpholinyl) diethyl ether to finally convert the intermediate bis (3-amide morpholinyl) diethyl ether into a catalyst bis (3-amide morpholinyl) diethyl ether and load the catalyst bis (3-amide morpholinyl) diethyl ether on the base film;

(5) and (4) soaking the film loaded with the catalyst bis (3-amidomorpholinyl) diethyl ether in the step (4) in an end-capping agent to finish end-capping.

8. The method of claim 7, wherein: the mass ratio of the di (3-carboxyl morpholinyl) diethyl ether to the thionyl chloride in the step (1) is 1:3-20, preferably 1: 5-8; and/or the catalyst is any one of amide, tertiary amine and carbonate, preferably N-N-dimethylformamide; and/or the mass ratio of the bis (3-carboxymorpholinyl) diethyl ether to the catalyst is 50-400:1, preferably 80-150: 1; and/or the temperature of the reaction system is 60-120 ℃, and the reaction time is 2-8 h.

9. The method according to claim 7 or 8, characterized in that: the dopamine solution in the step (3) is a mixed solution of dopamine, buffer salt and water, and the pH value of the solution is 5-9; preferably, the concentration of dopamine in the solution is 5-20mg/mL, the buffer salt is one or more of phosphate, ammonium salt and organic salt, and preferably any one of potassium dihydrogen phosphate-dipotassium hydrogen phosphate and Tris-HCl; and/or the buffer salt concentration is 30-200mM, preferably 80-150 mM; and/or the soaking time is 12-24h, and the temperature of the soaking system is 30-60 ℃.

10. The method according to any one of claims 7-9, wherein: the solvent in the step (4) is one or more of amide, acetone and cyclohexane, and N-N-dimethylformamide is preferred; the concentration of the di (acyl chloride morpholinyl) diethyl ether solution is 5-20mg/mL, and/or the soaking time is 12-24h, and the soaking temperature is 40-80 ℃.

11. The method according to any one of claims 7-10, wherein: the blocking agent in the step (5) is one or more of acyl chloride substances, preferably acetyl chloride; and/or the blocking reaction time is 6-12h, and/or the mass ratio of the blocking agent to the catalyst is 300-1000: 1.

12. Use of the process according to any one of claims 1 to 11 for on-line monitoring of traces of moisture in isocyanates in the production of isocyanates, characterized in that it comprises the following steps:

and step two, starting a measuring device by controlling the measuring equipment, adjusting the temperature of the isocyanate sample by a buffer tank, allowing the isocyanate sample to pass through a membrane loaded with a catalyst, reacting the isocyanate with trace moisture to generate carbon dioxide, measuring the content of the generated carbon dioxide by using a carbon dioxide on-line measuring instrument, and converting the content of the generated carbon dioxide into the moisture content of the isocyanate.

13. The use of claim 12, wherein the on-line measuring device comprises a control measuring device, a buffer tank, a sample delivery pump, a reaction device containing a catalyst-supported membrane, a measuring gas chamber and an on-line carbon dioxide measuring instrument which are connected by a pipeline; the probe of the carbon dioxide on-line measuring instrument is arranged in the air chamber, and the installation position is 10% -90% of the height of the air chamber, preferably 40% -50%; preferably, the carbon dioxide on-line determinator probe is an immersion type optical fiber probe, and more preferably a telescopic type optical fiber probe.

14. The use according to claim 13, characterized in that the isocyanate sample flows into the buffer tank through the site to be measured, enters the reaction device containing the catalyst supported membrane through the sample delivery pump, the gas generated by the reaction flows into the measurement gas chamber, and the online measurement instrument in the gas chamber collects the data and transmits the measurement data through the optical fiber.

15. Use according to any of claims 12 to 14, wherein in step one, the on-line measuring device is operated at a temperature of 50 to 95 ℃, preferably 70 to 80 ℃; the temperature should be kept constant, the constant range is not higher than 1% -10%, preferably 1% -2%; and/or the volume of the air chamber is 10-50L, preferably 15-25L.

16. The use according to any of claims 12 to 15, wherein in step two, the isocyanate sample is subjected to a membrane reaction, the temperature of the isocyanate sample is adjusted in advance by a buffer tank, so that the temperature of the isocyanate sample is consistent with the temperature of an on-line measuring device, and the buffer time is 2 to 10min, preferably 3 to 5 min.

17. Use according to any of claims 12 to 16, characterized in that in step two, the isocyanate sample is delivered in an amount of 30 to 200g, preferably 80 to 100 g; and/or the sample transmembrane pressure is from 30 to 300KPa, preferably from 50 to 100 KPa; and/or the contact area of the catalyst supported membrane and the isocyanate sample is 20-100cm²Preferably 50-80cm²(ii) a And/or the measurement delay time is 0.5-10min, preferably 2-4 min.

18. The use according to any one of claims 12 to 17, wherein in the second step, the transmission amount, the measured value of the carbon dioxide content, the specific location of the equipment and the measurement time of the isocyanate sample are transmitted to a PC host through an optical cable, the host calculates the moisture content in the isocyanate sample, an analysis model of the measured values of the carbon dioxide content corresponding to isocyanate samples with different moisture contents is established first, and the correspondence relationship is recorded in the host to realize automatic calculation.

19. The use according to claim 18, wherein the establishment of the analytical model comprises the steps of: introducing the isocyanate sample of the correction set into a reactor provided with a membrane containing an isocyanate active catalyst bis (3-amidomorpholinyl) diethyl ether, carrying out online analysis to obtain an analysis measured value, correlating the analysis measured value with the known content of the analysis measured value, and establishing an analysis model by a multivariate data regression analysis method, wherein the multivariate data regression analysis method is preferably a partial least squares regression method; and/or, the number of the isocyanate samples in the calibration set is not less than 20, and the moisture content of the isocyanate samples in the calibration set is preferably 0.0003-0.03% (w/w, the same applies hereinafter), more preferably 0.0008-0.016%, based on 100% of the total weight of the isocyanate samples in the calibration set.

20. The application of claim 19, wherein the sample moisture content data of the monitored site is transmitted to a DCS picture of a control room in a wired or wireless mode through a PC host computer, and a DCS high limit alarm is set; preferably, the DCS alarm minimum value is 0.008-0.012% of moisture content; and/or the sample measurement and data acquisition interval of the site to be monitored is 10-30 min.