CN111624278A

CN111624278A - Method for measuring caprolactam content in rearrangement

Info

Publication number: CN111624278A
Application number: CN202010435018.XA
Authority: CN
Inventors: 陈艳芬; 王飞龙; 吴道斌; 杨立新; 瞿亚平; 刘期敏; 吴望成
Original assignee: Fujian Eversun Technology Co ltd
Current assignee: Fujian Eversun Technology Co ltd
Priority date: 2020-05-21
Filing date: 2020-05-21
Publication date: 2020-09-04

Abstract

The invention discloses a method for measuring caprolactam content in rearrangement, which comprises four steps of instrument preparation, standard solution preparation, sample solution preparation and sample injection analysis, and qualitatively and quantitatively analyzes the caprolactam content in discharged liquid by adopting a standard substance contrast method and an external standard method. The method has simple process and easy operation, eliminates human errors to the maximum extent, and has high accuracy of analysis results; optimizing the process and the device and improving the economic benefit of enterprises.

Description

Method for measuring caprolactam content in rearrangement

Technical Field

The invention belongs to the technical field of chemical substance analysis and detection, and particularly relates to a method for determining caprolactam content in heavy discharge liquid in caprolactam industry by high performance liquid chromatography.

Background

Caprolactam is an important petrochemical product for producing synthetic fibers and engineering plastics, and with the rapid development of economic construction in China, the demand of the market for caprolactam is rapidly increased, but the production capacity in China at present is far from meeting the demand of the market. The technical route for producing caprolactam at home and abroad mainly comprises a benzene method and a toluene method, and the production of caprolactam by the toluene method is a method for producing caprolactam by taking toluene as a raw material, which is developed by Italian St.A. (SNIA) company in 1960.

The prior method for producing caprolactam mostly uses benzene as a raw material, the material is subjected to oximation reaction, cyclohexanone oxime is subjected to Beckmann rearrangement reaction to form a caprolactam sulfuric acid solution, amide oil containing caprolactam, ammonium sulfate and byproducts is generated through neutralization, and the amide oil is separated, extracted and refined to obtain pure caprolactam and ammonium sulfate. The content of caprolactam in the heavy discharge liquid can be accurately determined, so that the acid-oxime ratio and the yield of the amide oil in the heavy discharge liquid can be effectively fed back. However, the sample is strongly acidic, contains a large amount of ammonium sulfate salts, and has a large amount of by-products and complex components. If the conventional gas chromatography is used for analysis, irreversible damage is easily caused to the instrument, and the separation effect is poor. The method uses a liquid chromatography analysis method to analyze caprolactam in the heavy discharge liquid, and obtains good effect.

Disclosure of Invention

The object of the present invention is to provide a method for determining the caprolactam content in rearrangement, which solves the problems mentioned in the background art.

In order to achieve the purpose, the invention provides the following technical scheme:

a method for determining caprolactam content in a rearrangement comprising the steps of:

1) preparing an instrument: a chromatographic column: c18 column, phi 4.6mm x 250 mm; mobile phase: performing low-pressure elution by combining a mobile phase A and a mobile phase B, wherein the mobile phase A is methanol, and the mobile phase B is pure water; flow rate: 1 mL/min; column temperature: 40 ℃; sample introduction amount: 20 mu L of the solution;

2) preparation of a standard solution: respectively weighing 0.2g, 0.4g, 0.6g, 0.8g and 1.3g of caprolactam, dissolving the caprolactam in pure water and diluting the caprolactam in a volumetric flask to obtain 1-5# standard solution;

3) preparing a sample solution: weighing 0.7g-1.4g of heavy liquid discharge sample in a beaker, dissolving, adjusting the pH to be less than 7 by using alkali liquor, transferring the sample into a volumetric flask, and carrying out constant volume to obtain solution C.

4) Sample injection analysis: under the condition of the high performance liquid chromatography, after the baseline of the instrument is stabilized, measuring standard solution and solution C, measuring the standard solution, continuously injecting a plurality of needle standard solutions until the area change of the solution of the two adjacent needle standard solutions is less than 1.5%, then measuring the solution C, injecting the two needle standard solutions after the area change of the solution C injected into the two needles is less than 1.5%, and injecting the solution C in the middle of the injection of the two needle standard solutions after the area change of the two needle standard solutions is less than 1.5%;

5) and (3) calculating: according to the peak-out retention time, qualitative determination of caprolactam in the solution C by using a standard substance contrast method; respectively recording the areas of the marking solution and the solution C in each needle in the step 4), and quantitatively calculating the content of caprolactam in the sample by using an external standard method.

As a further scheme of the invention: the volume ratio of the mobile phase A methanol to the mobile phase B pure water is 1: 4.

As a still further scheme of the invention: the mobile phase and sample were filtered through a corresponding 0.45um microporous membrane before entering the column.

Compared with the prior art, the invention has the beneficial effects that:

1. the method has simple process and easy operation, eliminates human errors to the maximum extent, and has high accuracy of analysis results;

2. optimizing the process and the device and improving the economic benefit of enterprises.

Drawings

FIG. 1 is an analytical spectrum of a standard solution, wherein 12.439min shows a peak of caprolactam;

FIG. 2 is an analytical spectrum of sample solution C, wherein 12.548min shows a peak of caprolactam.

FIG. 3 is a standard curve plot of the results of Table 1 for the standard samples.

Detailed Description

In the description of the present invention, it is to be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", and the like, indicate orientations or positional relationships based on those shown in the drawings, and are used only for convenience in describing the present invention and for simplicity in description, and do not indicate or imply that the referenced devices or elements must have a particular orientation, be constructed and operated in a particular orientation, and thus, are not to be construed as limiting the present invention. Furthermore, the terms "first", "second", etc. are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first," "second," etc. may explicitly or implicitly include one or more of that feature. In the description of the present invention, "a plurality" means two or more unless otherwise specified.

In the description of the present invention, it should be noted that, unless otherwise explicitly specified or limited, the terms "mounted," "connected," and "connected" are to be construed broadly, e.g., as meaning either a fixed connection, a removable connection, or an integral connection; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meaning of the above terms in the present invention can be understood by those of ordinary skill in the art through specific situations.

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Example 1

Referring to FIGS. 1-2, in one embodiment of the present invention, a method for determining caprolactam content in a rearrangement comprises the steps of: 1. preparing an instrument: a chromatographic column: c18 column, phi 4.6mm x 250 mm; mobile phase: performing low-pressure elution by combining a mobile phase A and a mobile phase B, wherein the mobile phase A is methanol, and the mobile phase B is pure water; flow rate: 1 mL/min; column temperature: 40 ℃; sample introduction amount: 20 mu L of the solution;

2. preparation of a standard solution: weighing 0.2g, 0.4g, 0.6g, 0.8g and 1.3g caprolactam respectively, dissolving with pure water and diluting in volumetric flask to obtain 1-5^#A standard solution;

table 1:

the results for the standard samples were plotted as a standard curve, as shown in FIG. 3.

3. Preparing a sample solution: weighing 0.7g-1.4g of heavy liquid discharge sample in a beaker, dissolving, adjusting the pH to be less than 7 by using alkali liquor, transferring the sample into a volumetric flask, and carrying out constant volume to obtain solution C.

In the preparation of the sample solution, the adjustment of the pH value to be less than 7 by using the alkali liquor means that the pH value of the sample is adjusted to be less than 7 by using the alkali liquor, and the pH value of the sample solution is strong acid after the sample is dissolved and cannot be directly measured, so that the sample can be injected only by adjusting the pH value of the sample solution to be close to 7 by using the alkali liquor.

4. Sample injection analysis: under the condition of the high performance liquid chromatography, after the baseline of the instrument is stabilized, measuring the standard solution and the solution C, measuring the standard solution, continuously injecting a plurality of needle standard solutions until the area change of the solution of the two adjacent needle standard solutions is less than 1.5%, then measuring the solution C, injecting the two needle standard solutions after the area change of the solution C injected into the two needles is less than 1.5%, and injecting the solution C in the middle of injecting the two needle standard solutions after the sample injection is finished.

Computing

The caprolactam content is:

in the formula: a. the₁: hexanoyl in the solution of the standard solutionAmine peak area;

A₂: peak area of caprolactam in the sample solution;

m₂: mass g of the heavy liquid;

ω₁: the purity g/l of caprolactam standard sample;

v: sample dilution volume.

Wherein, the chromatogram of the standard solution is shown in figure 1, the chromatogram of the solution C is shown in figure 2, and the mass fraction of caprolactam in the sample is quantitatively calculated by an external standard method. The results are shown in table 2:

table 2:

5. the precision of the method is as follows: are respectively paired with 4^#The standard samples were tested in parallel l0 times with an average retention time of 12.4941min and a relative standard deviation of the retention time of 0.3988%, and the peak areas were recorded and the relative standard deviation of caprolactam determined was calculated to be 0.1199%. The results of the experiment are shown in table 3:

TABLE 3

6. The accuracy of the method: the caprolactam standard recovery rate test is carried out on a rearrangement solution sample with a known concentration, the accuracy of the caprolactam standard recovery rate is expressed by the standard recovery rate, and the test result is shown in table 4:

TABLE 4

And (4) conclusion: the recovery rate of the added standard is 98-101%, which indicates that the accuracy of the method meets the analysis requirement.

Detection limit: under the optimal chromatographic condition of the method, the lowest detection limit of the method is calculated to be 0.01mg/L by using 3 times of limit noise.

It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrative embodiments, and that the present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. Any reference sign in a claim should not be construed as limiting the claim concerned.

Furthermore, it should be understood that although the present description refers to embodiments, not every embodiment may contain only a single embodiment, and such description is for clarity only, and those skilled in the art should integrate the description, and the embodiments may be combined as appropriate to form other embodiments understood by those skilled in the art.

Claims

1. A method for determining caprolactam content in rearrangement is characterized by comprising the following steps:

step 1:

preparing an instrument: a chromatographic column: c18 column, phi 4.6mm x 250 mm;

mobile phase: performing low-pressure elution by combining a mobile phase A and a mobile phase B, wherein the mobile phase A is methanol, and the mobile phase B is pure water; flow rate: 1 mL/min;

column temperature: 40 ℃; sample introduction amount: 20L;

step 2: preparation of a standard solution: respectively weighing 0.2g, 0.4g, 0.6g, 0.8g and 1.3g of caprolactam, dissolving the caprolactam in pure water and diluting the caprolactam in a volumetric flask to obtain 1-5# standard solution;

and step 3: preparing a sample solution: weighing 0.7g-1.4g of heavy-weight liquid discharge sample in a beaker, dissolving, adjusting the pH to be less than 7 by using alkali liquor, transferring the heavy-weight liquid discharge sample into a volumetric flask, and performing constant volume to obtain liquid C;

and 4, step 4: sample injection analysis: under the condition of the high performance liquid chromatography, after the baseline of the instrument is stabilized, measuring standard solution and solution C, measuring the standard solution, continuously injecting a plurality of needle standard solutions until the area change of the solution of the two adjacent needle standard solutions is less than 1.5%, then measuring the solution C, injecting the two needle standard solutions after the area change of the solution C injected into the two needles is less than 1.5%, and injecting the solution C in the middle of the injection of the two needle standard solutions after the area change of the two needle standard solutions is less than 1.5%;

and 5: and (3) calculating: according to the peak-out retention time, qualitative determination of caprolactam in the solution C by using a standard substance contrast method; and (4) respectively recording the areas of the marking solution and the solution C per needle in the step 4, and quantitatively calculating the content of caprolactam in the sample by using an external standard method.

2. The method of claim 1, wherein the volume ratio of the mobile phase A methanol to the mobile phase B pure water solution is 1: 4.

3. The method of claim 1, wherein the mobile phase and the sample are filtered through a 0.45um microporous membrane before entering the chromatographic column.