The meaning of acid value
The value tester is used for the determination of the acid value of transformer oil and turbine oil. The acid value refers to the weight (milligrams) of potassium hydroxide required to neutralize the free fatty acid contained in 1 gram of fat, fatty oil or the like.
Unless otherwise specified, according to the weight specified in the table, accurately weigh the test sample, placed in a 250ml Erlenmeyer flask, add ethanol-diethyl ether (1:1) mixture [apply phenolphthalein indicator solution 1.0ml before use) Potassium hydroxide titration solution (0.1 mol/L) was adjusted to 50 ml of slightly pink color, shaken to completely dissolve (if it is not soluble, it can be slowly heated to reflux to dissolve), using potassium hydroxide titration solution (0.lmol/ L) Titration, until the pink color does not fade for 30 seconds. The volume (ml) of the potassium hydroxide titration solution (0.1 mol/L) is taken as A, and the weight (g) of the test sample is W. The acid value (IA) is calculated according to the following formula:
Scope of application
The acid value tester is used for the determination of the acid value of transformer oil and turbine oil.
The acid value tester meets the requirements stipulated in the national standard GB/T 264-83 "Measurement method for acid value of petroleum products".
This standard specifies two methods for determining the acid value of petroleum products, lubricants, biodiesel and biodiesel blended fuel by potentiometric titration.
Method A is suitable for the determination of the acid value of petroleum products and lubricants which are soluble and substantially soluble in a mixed solvent of toluene and anhydrous isopropanol. Method A can determine those acidic components in the sample with a dissociation constant greater than 1×10-9 in water. The very weak acid with a dissociation constant less than 1×10-9 does not interfere, but the salt with a hydrolysis constant greater than 1×10-9 will Will participate in the reaction, the precision of method A is in acid value (in
The KOH meter is established in the range of 0.1 mg/g to 150 mg/g.
Method B is suitable for the determination of the acid value of biodiesel and biodiesel blended fuels with lower acidity and solubility differences.
Note: The acidic components of new or used oils include organic acids, inorganic acids, esters, phenolic compounds, lactones, resins and heavy metal salts, salts of ammonium salts and other weak bases, acid forms of polybasic acids. Salt and certain antioxidants and detergent additives.
This standard can reflect the relative changes under oxidizing conditions during the use of oil without regard to color and other performance changes. Although the titration is carried out under specific conditions, this standard cannot be used to determine the absolute acidity of the oil to predict its performance under use. No correlation has been found between acid value and bearing corrosion.
Note 1: The acid value measured by this standard may be the same as or different from the results measured by GB/T4945 and SH/T0163. There is no attempt in this standard to correlate the results of the measurements with those obtained by other non-titration methods.
Note 2: A few laboratories have observed that when using aqueous or non-aqueous buffer solutions in this standard, there is a certain difference between the results obtained.
Main test method
The acid value refers to the mass of KOH or NaOH consumed per gram of the acid component of the sample.
Analytical method: Accurately weigh the sample 4~10g sample and add it to the toluene-ethanol (2:1) solution, and shake it to dissolve it. For slow-dissolving high polyester samples, dissolve them with acetone or methyl ethyl ketone. Add 3~5 drops of 1% phenolphthalein indicator and titrate with 0.1mol/L NaOH standard solution until the solution appears pink for 15 minutes without discoloration. Also do blank experiment. The calculation method is as follows:
Av=56.1*CNaOH*(Vs-V0)/m
Where: Av - the acid value of the sample (mg NaOH / g);
Vs—the volume (ml) of the NaOH solution consumed by the sample;
V0—the volume (ml) of the NaOH solution consumed by the blank experiment;
m ─ the mass of the sample (g);
CNaOH - concentration of NaOH solution (mol / L).
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