Industrial acrylonitrile. Determination of total aldehyde content. Spectrophotometric method (1)

1 Subject content and scope of application

This standard specifies the spectrophotometric method for determining the content of aldehydes in acrylonitrile

This standard is applicable to the determination of the total aldehyde content ( calculated as acetaldehyde ) in acrylonitrile, and the measurement range is 0.

2 Reference standards

GB/T3723 General Safety Rules for Sampling of Industrial Chemical Products

GB/T6678 General Rules for Sampling of Chemical Products

GB/T6680 General rules for sampling of liquid chemical products

GB 6682 Analysis and experiment air water specifications and test methods

GB/T9721 General Rules of Chemical Reagent Molecular Absorption Spectrophotometry (UV and Visible Light Part)

3 Principles of the method

The aldehyde in the sample reacts with 3-methyl-2-benzothiazolone hydrazone (MBTH) to form an azine, and the excess MBTH is oxidized by ferric chloride to a cation, which then reacts with the azine to form a colored cationic dye Measure the absorbance at 628nm

4 Reagents and solutions

Unless otherwise noted, the reagents used are of analytical grade, and the water used is in compliance with the third-grade water specifications specified in GB6682

4.

Weigh out 0.

Note: The full name of MBTH is 3-methyl-2-benzothiazolinone hydrazone; LR grade can also be used

4.

Weigh 8.

4.

It is a 0.

Note: The full name of MEHQ is: 4-mcthoxyphenol (monomethyl ether of hydroquinone)

4.

4.

Inject the cooled formaldehyde-free acrylonitrile (4.

4.

4.
7 Anhydrous sodium sulfate : pure superior grade
.

4.
8 Concentrated hydrochloric acid
.

4.
9 732 resin
.

4.
10 2,4-Dinitrophenylhydrazine
.

4.
11 Preparation of aldehyde-free acrylonitrile:

The following two methods are recommended for selection.
The treated acrylonitrile should be placed in a brown bottle and refrigerated, which can be stored for one week
.

Method A: Take 100 mL of acrylonitrile and place it in a separatory funnel, add 90 mL of water, 10 mL of sodium hydroxide solution (4.
6) and shake for 1 min.
After layering, release the lower layer solution, and then add 10 g of anhydrous sodium sulfate in the separatory funnel ( 4.
7) After shaking, filter out the acrylonitrile layer and distill to collect the middle distillate with a boiling range of 75.
5-79.
5°C
.

Method B: Take 100mL of acrylonitrile, add 1g of 2,4-dinitrophenylhydrazine (4.
10), then add 10g of 732 resin (4.
9) soaked in concentrated hydrochloric acid (4.
8), heat to reflux for 4h, distill and collect 75.
5 ~79.
5°C middle distillate
.