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Method for separation of impurities from hot synthesis gas mixture in preparation of melamine

A technology of melamine and thermal synthesis, which is applied in the direction of separation methods, filtration separation, chemical instruments and methods, and can solve the problems of reduced strength and short life

Inactive Publication Date: 2001-02-14
DSM IP ASSETS BV
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

However, filters made of the above sintered materials lose their strength in the short term due to the formation of nitrides and / or carbonitrides when they come into contact with ammonia and carbon dioxide gases produced during the production of melamine from urea
As a result, these sintered materials have only a short lifespan in the separation of synthetic gas mixtures containing ammonia and carbon dioxide, since these filters have to be replaced frequently

Method used

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Examples

Experimental program
Comparison scheme
Effect test

example 1

[0023] The side draw from the melamine reactor was led directly to a pilot test reactor in which various filter candles with a length of 1 m and a diameter of 6 cm (as shown in Table 1) were carried out at a temperature of 390° C. and a pressure of 7 bar. filter test. Each filter contained 6 filter candles, and 6 experiments were carried out.

[0024] The composition of melamine gas mixture is: NH 3 86% (volume), CO 2 8% (volume), N 2 3% (volume), melamine 3% (volume) and low concentrations of isocyanic acid and cyanide. Use the pressure drop across the filter chamber to determine when one or several of the filter candles have broken. When the pressure drop in the filter chamber is observed, immediately open the filter chamber and check how many filter candles in the filter have been broken. The results of these tests are listed in Table 1 in full.

[0025] test

example 2

[0027] Test samples of the following dimensions were cut from various types of filter candles of the materials listed in Table 2, with a length of 50 mm, a width of 10 mm and a thickness of 6 mm. Each sample weighs approximately 10 grams. The samples were hung in the gathering atmosphere of the 390°C and 450°C temperature exposure furnaces and kept for more than one week. The composition of the gathering atmosphere is NH 3 86% (volume), CO 2 8% (volume), melamine 3% (volume), N 2 3% (volume) and trace amounts of isocyanic acid and cyanamide. Nitriding of the sample resulted in an increase in sample mass and the test sample mass gain was measured in micrograms per square centimeter per hour. Test samples were cut from filter candles made of sintered chromium, solid chromium and stainless steel (AISI 304L). The above results are listed in Table 2.

[0028] Material

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PUM

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Abstract

The invention relates to an improved method for the separation by means of filters of impurities from a hot synthesis gas mixture obtained in the preparation of melamine from urea, involving filters made of sintered, essentially pure chromium, molybdenum, tungsten, or mixtures of these elements.

Description

Background of the invention [0001] 1. field of invention [0002] The present invention relates to an improved method for separating impurities by using a filter in the thermal synthesis gas mixture obtained from the preparation of melamine from urea. The improvement is that the filter contains at least one element selected from chromium, molybdenum and tungsten. [0003] 2. Description of related technologies [0004] When urea is used to prepare melamine, nitrogen-based or carbon-based gases, usually ammonia or carbon dioxide, especially their mixtures, can be obtained. Wherein, under heating and optional high pressure, according to the following reaction equation, the raw material urea is transformed into a hot mixed gas containing melamine, ammonia and carbon dioxide. [0005] <chemistry num="001"> <chem file="95192093_cml001.xml" / > < / chemistry> [0006] Usually the above reaction is carried out in the presence of a catalyst, and the resulting th...

Claims

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Application Information

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Patent Type & Authority Patents(China)
IPC IPC(8): B01D39/20C07D251/60C07D251/62
CPCC07D251/60B01D39/2034B01D39/2044
Inventor J·G·T·范韦克C·G·M·范迪莫斯迪克J·J·G·特伦
Owner DSM IP ASSETS BV