Process Q&A: Methanol and Purification Technology Exchange Edition 20191010

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Determination of methanol color: A visual color comparison is made between the methanol sample and a platinum-cobalt color standard. The result is expressed in platinum-cobalt chromaticity units (the color of a solution containing 2 mg of cobalt chloride hexahydrate and 1 mg of platinum per liter). Instruments and reagents. (1) Colorimetric tube: graduated, with a capacity of 100 mL. (2) Colorimetric tube holder. The bottom is lined with a white background. (3) Hydrochloric acid: C(HCl) = 0.1 mol/L; C(HCl) = 6 mol/L. (4) Preparation of the colorimetric standard solution: Accurately weigh 1.245 g of potassium chloroplatinate (K2PtCl6, analytical grade) and 1.000 g of cobalt chloride (CoCl2·6H2O, analytical grade), with precision to 0.001 g. Dissolve in an appropriate amount of water, add 200 ml of 6 mol/L hydrochloric acid, transfer to a 1000 mL volumetric flask, and dilute to the mark with water. This liquid is a colorimetric standard solution No. 500. Store in a dark place; it is valid for one year. Take 0.0, 0.4, 1.0, 1.4, 2.0, 2.4, 3.0┄┄6.0 mL of the 500-number color standard solution and add it to separate 100 mL colorimetric tubes; then dilute to the mark with 0.1 mol/L hydrochloric acid to obtain the color standard solutions with numbers 0, 2, 5, 7, 10, 12, 15┄┄30. Store in a dark place; it is valid for 15 days. Measurement steps. Take the sample and fill it into a 100 mL colorimetric tube to the mark. Compare it with the colorimetric standard solution under daylight or fluorescent lighting, against a white background, by axial observation, in order to determine the chromaticity number of the methanol sample. Allow difference. The difference between the results of parallel measurements should not exceed 2 notches; the average value is taken as the measurement result.