Low-ammonia-consumption caprolactam production process

[0038] Example 1

[0039] The crystallization law of the mixed reaction of ammonium sulfate and milk of lime was experimentally investigated in a 2L stirred tank. First, charge 900ml of Ca(OH) with a concentration of 1.1mol/L into the mixing kettle 2 Solution, mechanical stirring, the outer jacket of the reactor is heated and controlled by heat transfer oil, the temperature is controlled at 100 ℃; then, 450ml of (NH) with a concentration of 2.0mol/L 4 ) 2 SO 4 The solution (21.2wt%) was quickly poured into the reactor at one time, the lime milk was kept in excess, and the mixture was uniformly mixed by mechanical stirring. After the reaction started, regular samples were taken to determine the pH value, calcium ion concentration and sulfate ion concentration of the solution, and the crystal form and particle size of the gypsum crystals formed were analyzed at the same time. During the reaction process, 50ml/min of nitrogen gas was blown into the liquid phase, and the generated gas phase was absorbed by the dilute hydrochloric acid solution in the subsequent absorption bottle. The ammonia recovery rate was determined by sampling regularly to detect the concentration of ammonium ions in the absorption bottle. The pH value is measured by a PH meter; the calcium ion concentration is measured by the EDTA complexometric titration method, the sulfate ion concentration is measured by the barium sulfate turbidimetric method; the ammonium ion concentration in the absorption solution is measured by the Nessler's reagent spectrophotometry; the Malvern A laser particle size analyzer measures the particle size of gypsum crystal particles, and an X-ray diffractometer is used to determine the XRD pattern to determine the type of gypsum crystals. After 60 minutes of reaction, the ammonium ion concentration in the tail gas absorption bottle was analyzed. Based on the added ammonium sulfate, the calculated ammonia recovery rate was 99.1 wt%, indicating that the amino group could have been completely recovered. The XRD pattern of calcium sulfate obtained after 60 minutes of reaction is as follows Figure 4 (A) shown. by Figure 4 (A) It can be seen that the crystal form of calcium sulfate obtained is hemihydrate gypsum (CaSO 4 ·0.5H 2 O). The particle size distribution is as Figure 5 As shown in (A), the average particle size is 27.7 µm, and there are a large number of small particle size fine crystal distributions.

[0040] Example 2

[0041] As in Example 1, the crystallization law of the mixing reaction of ammonium sulfate and milk of lime was investigated in a 2L stirred tank. The reaction temperature considered was also 100°C. The difference was the feeding method. Under stirring conditions, the milk of lime was added to sulfuric acid at one time. In ammonium solution. First put 450ml of (NH) with a concentration of 2.0mol/L in a 2L stirred tank 4 ) 2 SO 4 Solution (21.2wt%), then add 900ml Ca(OH) with a concentration of 1.1mol/L 2 The solution was quickly poured into the reactor once, the lime milk was kept in excess, and mechanical stirring was added to keep the mixture uniform, while 50ml/min of nitrogen was bubbled into the liquid phase. After 60 minutes of reaction, sampling and analyzing the ammonium ion concentration in the tail gas absorption bottle, the ammonia recovery rate calculated based on the added ammonium sulfate was 98.5 wt%, indicating that the ammonia was basically recovered completely. The solid is sampled and analyzed, and the particle size is measured by a Malvern particle size analyzer, and the XRD pattern is measured by an X-ray diffractometer. The XRD pattern of calcium sulfate obtained after 60 minutes of reaction is as follows Figure 4 (B) shown. by Figure 4 (B) It can be seen that the crystal form of calcium sulfate obtained is hemihydrate gypsum (CaSO 4 ·0.5H 2 O). The particle size distribution is as Figure 5 As shown in (B), there are a large number of small grain size fine crystal distributions at the same time, and the average grain size is 32.5 μm.

[0042] Example 3

[0043] As in Example 1, the crystallization law of the mixed reaction of ammonium sulfate and lime milk was investigated in a 2L stirred tank. The difference was the reaction temperature and the feeding method. The reaction temperature was 120°C. The ammonium sulfate solution was pumped under stirring conditions. Continuously add to the lime milk. First charge 900ml of Ca(OH) with a concentration of 1.1mol/L in a 2L stirred tank 2 Solution, and then add 450ml of (NH 4 ) 2 SO 4 The solution (21.2wt%) was continuously added to the reactor at a flow rate of 50ml/min. After 9 minutes of adding the ammonium sulfate solution, mechanical stirring was added to keep the mixture uniform, while 50ml/min of nitrogen was bubbled into the liquid phase. The jacket of the reactor is filled with thermal oil for heating and insulation, and the temperature is controlled at 120°C. After 60 minutes of reaction, samples were taken to analyze the ammonium ion concentration in the tail gas absorption bottle, and the ammonia recovery rate calculated based on the added ammonium sulfate was 98.8 wt%, indicating that ammonia was basically completely recovered. For solid sampling analysis, Malvern particle size analyzer was used to determine particle size, and X-ray diffractometer was used to determine XRD pattern. The XRD pattern of calcium sulfate obtained after 60 minutes of reaction is as follows Figure 4 (C) Shown. By Figure 4 (C) It can be seen that the obtained calcium sulfate crystal form is calcium sulfate hemihydrate (CaSO 4 ·0.5H 2 O). The particle size distribution is shown in Fig. 5(C). The average particle size is 28.8 µm, and there are not many fine crystals of small particle size. Compared Figure 5 (C), 5(B) and Figure 5 (A) It can be seen that under the conditions of Example 3, the formation of small particles of hemihydrate gypsum can be effectively reduced, which is beneficial to the subsequent filtration and washing processes.