Lignin is the second largest renewable resource in nature, second only to cellulose, and will be the main source of resources for humanity in the future. Preparation of new materials and chemical industry using lignin as raw materialRaw materials are gradually replacing increasingly depleted resources such as fossilsResources are becoming a new development trend. Lignin is mainly composed of phenylpropane units（C6-C3)A three-dimensional network amorphous polymer formed by the interconnection and irregular coupling of carbon carbon bonds and ether bonds. Its molecular structure contains hydroxyl groups (phenolic hydroxyl and alcohol hydroxyl)）Double bond, Da Pai bond,Carboxylic acid groups, including phenolic hydroxyl and carboxylic acid groups, can ionize in alkaline solutions, and their content determines the solubility of lignin in aqueous solutions. Due to the conversion of ligninMost of the modification reactions are carried out in aqueous medium, so accurately determining the water-soluble functional groups of lignin--The content of phenolic hydroxyl and carboxylic acid groups affects the chemical modification and modification of ligninBasic research is very important.

1 Measurement principle and method

《Journal of Chemical Engineering》第 63 roll First Issue 2012 year 1 moon 《Determination of Phenolic Hydroxyl and Carboxylic Acid Content in Lignin by Water Phase Potentiometric Titration

Content determination: Non aqueous phase potentiometric titration method uses tetrabutylammonium hydroxide standard solution as the titrant, and its specific preparation method is as follows: 10%Tetrabutyl hydroperoxideAmmonium aqueous solution 40g,join 280mlDilute with isopropanol and then sonicate 30minStand still for later use. Accurate weighing 0.03gAdd the sample to the beaker 1-3drop 37%Acidify with concentrated hydrochloric acid, then add accurately weighed 0.05gHydroxybenzoic acid internal standard, added 25mlDissolve the sample and internal standard in dimethylformamide, and then treat with ultrasound30minPrepare for testing. In addition, precise weighing 0.05gHydroxybenzoic acid dissolved in 25mlIn dimethylformamide, add 1-3drop 37%Concentrated hydrochloric acid is used for blank value determination.

2 Experimental apparatus

lGT90potentiometric titrator

lpH Composite electrode

l10ml Burette unit