Gas Chromatographic Analysis of the Composition of Phthalic Anhydride Tail Gas Wash

Abstract In this paper, capillary column gas chromatography is used to determine the content of each component in the tail gas water wash produced by the oxidation of o-xylene to produce phthalic anhydride. The method is simple and fast, and has high accuracy. In the production of tail gas washing liquid to recover maleic anhydride and other phthalic anhydride by-products, it has an important guiding role in the control of process indicators.
Introduction The tail gas water wash produced by the oxidation of o-xylene to produce phthalic anhydride contains many by-products that can be recycled. Among them, the content of maleic acid is the largest and the recovery value is higher. The market price of maleic anhydride is always higher than that of phthalic anhydride. Maleic anhydride valley is called maleic anhydride, which can be used for dilute synthesis; manufacturing of drugs; dye intermediates; polyester resin, alkyd resin, etc. In addition, maleic anhydride can produce fumaric acid (commonly known as fumaric acid) through isomerization under the action of a catalyst. Fumaric acid has a greater demand in the pharmaceutical and food industries. The phthalic anhydride tail gas washing liquid contains citric acid, benzoic acid, phthalic acid, phenyl peptide and other substances in addition to cis and fumaric acid. In the recovery process of maleic anhydride, crystallization and rectification are mainly adopted to remove other components in the washing liquid. Therefore, timely and accurate analysis and determination of the relative content of various substances in the washing liquid is of great significance for the control of process parameters in each production link and improving the quality and yield of maleic anhydride.

1 Experimental part

1.1 Instruments and reagents Hewlett-Packard 5890 gas chromatograph, which is equipped with a hydrogen flame detector (FID) and Hewlett-Packard data processor. The qualitative reagent used is a chromatographic reagent or analytical grade.
1.2 Chromatographic column and chromatographic operating conditions 30 m × 0.32 mm (LD). OV-17 quartz capillary column (manufactured by Dalian Institute of Physical Chemistry). Vaporization chamber temperature: 250 ℃; detector temperature: 300 ℃; capillary column temperature: 150 ℃, constant temperature for 25 minutes; carrier gas: high-purity nitrogen; carrier gas pressure before the column: 0.7 MPa. If there is suspended matter in the phthalic anhydride tail gas washing liquid, you need to use qualitative filter paper for later use.
1.3 The qualitative and quantitative method adopts the standard sample retention time to control the qualitative and the area normalization method to quantify. Use chromatographic reagents or analytical reagents such as fumaric acid, maleic anhydride, citric acid, phthalic anhydride, phthalide, etc., and weigh accurately according to a certain ratio (the ratio should be close to the exhaust gas washing liquid under normal circumstances) Proportion of the content of each substance), fully dissolved in distilled water (the density of the solution should be basically the same as the exhaust water wash) as the standard sample for the determination of F value. Inject samples according to the chromatographic conditions described in 1.2, and a good separation can be obtained. The retention time of the standard samples and the measured F value [1] are shown in Table 1.

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