Liquid ammonia content

This post was last edited by Hakusano Aku on 2018-4-25 at 22:06. Original link: Determination of the residue content of liquid anhydrous ammonia – Gravimetric method – **Standard of the People’s Republic of China _Wenhua Longjiang_ Sina Blog http://blog.sina.com.cn/s/blog_15cf454420102x9at.html. Determination of the residue content of liquid anhydrous ammonia – Gravimetric method – **Standard of the People’s Republic of China. Liquefied anhydrous ammonia – Determination of residue content – Gravimetric method. UDC 661.518:543.06; GB 8570.3–88 replaces GB 536–65. This standard is equivalent to the international standard ISO 4276–78 “Anhydrous ammonia for industrial use – Determination of evaporative residues – Gravimetric method”. This standard specifies the determination of the residue content of anhydrous liquid ammonia (liquid ammonia) by gravimetric method. This standard applies to products with a residue content of 0.02% (m/m) or higher, and serves as the adjudicative method for determining residue content. Note: If the residue content is below the lower limit of the testing method specified in this standard, it shall be reported as ＜0.02%(m/m). 1 Reference standards: GB 601 – Methods for preparing standard solutions of chemical reagents; GB 8570.1 – Anhydrous ammonia in liquid form – Sampling of laboratory samples. 2 Principle: At room temperature, the liquid ammonia sample is evaporated, and the residue resulting from this evaporation is weighed. In the presence of an indicator, sulfuric acid standard solution is used to react with the ammonia present in the residue. The amount of ammonia is determined, and by subtracting this value from the mass of the residue, the content of the remaining substances can be calculated. 3 Reagents and Solutions: In analysis, unless otherwise specified, only analytically pure reagents, distilled water, or water of equivalent purity shall be used. 3.1 Refrigerant: a mixture of solid carbon dioxide (dry ice) and industrial alcohol, with a cooling temperature of –35°C to –40°C. 3.2 Sulfuric acid (GB 625－77): approximately 10% (m/m) solution. 3.3 Sulfuric acid (GB 625－77): A standard solution with c (1/2 H2SO4) = 0.1 mol/L (equivalent to 1 N), prepared and standardized in accordance with GB 601. 3.4 Methyl red (HG 3-958-76): a 1 g/L solution in 95% (V/V) ethanol. 4 Instruments: Standard laboratory instruments and: 4.1 Sample sampling device (see figure). 4.1.1 Glass test tube: With a total volume of approximately 150 ml, marked at 100 ml; equipped with a standard ground glass joint No. 29 along with a corresponding external standard ground glass stopper, such that one tube is connected to the three-way piston 3, while the other tube is connected in series with two 1000 ml conical flasks A and B. Thus, in the assembled instrument, the test tube can be connected to two three-way pistons 3 and 4, which in turn are connected to the liquid ammonia sampling cylinder and the two conical flasks A and B. The glass piston is lubricated with silicone grease (3.5), or it can be made of polytetrafluoroethylene instead. 4.1.2 Dewar flask: Used to hold test tubes (4.1.1); once the test tubes are placed inside, their markings can be seen clearly. 5 Sampling: Laboratory samples shall be taken in accordance with the provisions of G 8750.1. 6 Operating Procedures 6.1 Sampling Weigh the mass of conical flasks A and B, each equipped with a connecting tube starting from point 5 of the self-connection (see figure), by adding approximately 500 ml of sulfuric acid solution (3.2) and 2 drops of methyl red solution (3.4) to them; the measurement should be accurate to 0.1 g. Weigh the mass of the test tube with stopper (4.1.1) (to an accuracy of 0.0001 g). Immerse the test tube into the cryogen (3.1) in the Dewar flask (4.1.2) to three-quarters of its depth. Remove the stopper and connect flasks A and B. Rotate piston 3 to seal the test tube, with ends 1 and 2 open to the atmosphere. Connect one end of the rubber tube to the sampling cylinder containing the laboratory sample, carefully open cylinder valve A, and allow ammonia to slowly escape into the atmosphere until both ends 1 and 2 are well cooled and ammonia droplets appear. Rotate piston 4 so that end 6 faces the atmosphere ； At this point, piston 3 is immediately rotated to seal one end and connect the other end to the test tube. Immediately rotate piston 4 to connect the test tube with the two conical flasks and seal end 6. As a result, liquid ammonia is collected in the test tube, while ammonia gas is absorbed by the sulfuric acid solution (3.2) in the two conical flasks. When the liquid ammonia in the test tube reaches the 100 ml mark, immediately rotate piston 4 to expose the test tube to the atmosphere and isolate the conical flask; at the same time, rotate piston 3 to seal the test tube, allowing the ammonia gas to escape into the atmosphere through both ends. Thereafter, close sampling cylinder valve A and remove the cylinder. After sampling, flasks A and B, which contain the connection tubes at the self-connection point 5, were immediately removed. Once they had cooled to room temperature, they were weighed with an accuracy of 0.1 g. 6.2 Measurement: The test tube (4.1.1) containing the sample is removed from the Dewar flask (4.1.2), and ammonia is allowed to evaporate slowly from both ends at room temperature, until a residue at the bottom of the test tube is formed consisting of ammonia water, oil, and other substances that do not volatilize at room temperature. After the test tube and evaporation residues have reached room temperature, a slow stream of dry air (about 100 L/h) is passed over them for 30 seconds. Seal the test tube, wipe its outer wall clean with a clean dry cloth, and then weigh it to an accuracy of 0.0001 g. Add 50 ml of water and 2 drops of methyl red solution (3.4) to a test tube, stir well, and titrate with standard sulfuric acid solution (3.3) until the solution changes from yellow to pale red. 7 Results: 7.1 The residue content X, expressed as a mass percentage, is calculated using equation (1): Determination of the residue content of anhydrous liquid ammonia – Methods of gravimetry – **Standard of the People’s Republic of China ………………………………………(1) Where: m0 – mass of the sample, in g ； m1 – mass of the empty stoppered test tube, g ； m2 – Mass of test tube with stopper and evaporated residues, g ； m3 – Mass of ammonia in the evaporation residues, in g. After determination by titration, it is calculated using equation (2): Determination of the content of anhydrous ammonia residues in liquids – Gravimetric method – **Standard of the People’s Republic of China …………………………………(2) Where: V1 is the volume of the standard sulfuric acid solution used for titration (3.3), in ml. Note: If the concentration of the sulfuric acid standard solution used is not exactly the same as that specified in this standard, corresponding corrections should be made. 7.2 Allowable error 7.2.1 The arithmetic mean of the results of two parallel measurements shall be taken as the measurement result. 7.2.2 Absolute allowable difference for parallel test results: Residue content, % – Absolute allowable difference, % ≤0.1 ≤0.02 ＞0.1 ≤0.04 Additional note: This standard is under the jurisdiction of the Shanghai Research Institute of Chemical Industry, Ministry of Chemical Industry. This standard was drafted by the Shanghai Research Institute of Chemical Industry under the Ministry of Chemical Industry and Wujing Chemical Plant. The main drafters of this standard are Yin Yongkang, Jin Zhigen, Yao Bingsheng, Liu Miaode, and Zhang Wenwei. The pH range for the color change of methyl red is from 4.4 (red) to 6.2 (yellow). According to these standards, when the solution changes color, for 0.1 mol/L sulfuric acid AN, you can use 0.1 mol/L sulfuric acid AN and add a drop of ammonia solution to achieve the yellow color. To 0.1 mol/L sulfuric acid an, add another drop of 0.1 mol/L sulfuric acid to mark the red color.