1 Subject Content and Scope of Application
This standard specifies the determination method of saponification equivalent of crude glycerol.
2 Reference standard
GB/T 13216.1—91 Glycerol test method; Sampling method of barreled glycerol
3 Principle
The excess alkali is used to neutralize the acids and esters in saponified glycerol, and the excess alkali is titrated with standard acid solution.
4 Reagent
During the analysis, only analytical reagents and distilled water or relatively pure water are used.
4.1 Sodium hydroxide (GB 629): 0.2 mol/L standard solution.
4.2 Sulfuric acid (GB 625): 0.2mol/L standard solution
4.3 Phenolphthalein (GB 10729): 10g/L ethanol (95%) solution.
5 Instrument
5.1 Conical flask: 500 ml, with grinding glass interface.
5.2 Condenser: Water-cooled, with grinding glass joints to match conical flasks.
5.3 Titrating tube: 50 ml.
6 Sample preparation
The glycerol test samples were prepared and stored according to GB/T 13216.1-91.
7 Test procedure
All tests should be conducted in parallel.
The distillation yield of crude glycerol, weighing about 100 g (weighing up to 0.1 g) and mixing uniformly, was measured in flask (5.1). Add 100 ml carbon dioxide-free hot water and 1 ml phenolphthalein indicator (4.3). If the solution is alkaline, the sulfuric acid standard solution (4.2) is used to adjust to just neutral, and then the titrator (5.3) is used to add 20 ml sodium hydroxide standard solution (4.1). Connect the flask to the condensation tube and heat it to boil for 5 minutes. Cool slightly, rinse the condensation tube with a small amount of water. Remove the flask, seal it with a cork with an alkali lime tube and cool it. Titration with burette (5.3) using standard sulfuric acid solution (4.2). At the same time, 140 ml water was used as blank test instead of sample.
8 Calculation of test results
Saponification Equivalent of Glycerol (X) , expressed in mmol/100g, the calculation formula is as follows.
| X | = | c×（V0-V1） | ×100 …………………（3） |
| m |
V0………Volume of standard sulfuric acid solution used in blank test, mL
V1………Volume of standard sulfuric acid solution used for titration of sample solution, mL
m………Quality of test sample, g
c………Concentration of standard sulfuric acid solution used, mol/L
