Research On Crystallization Process Of 2-nitro-4-acetyl Amino Benzene Methyl Ether

2-amino-4-acetyl amino benzene ether (AMA) is an important intermediate of dye, its production technology is mature, by the raw materials of nitrochlorobenzene via methoxy, reduction, acetylation, nitration, reduction to AMA, but in the nitrification section, on accout of intermediate 2 nitro 4-acetoxy amino benzene ether (NMA) dissolved in sulfuric acid catalyst, the production enterprises took water as solventing-out agent, precipitated the NMA, and diluted sulfuric acid solution was concentrated and recycled. But there were two problems, one is the low concentration of diluted sulfuric acid, resulting in the high energy consumption, another is the precipitated NMA with low purity and fine particle size. The paper carried on study basing on these two problems.Aiming at the problem of low purity of NMA, the paper determined the certain temperature range of (273.15 K-298.15 K), the solubility of NMA in methanol, ethanol, propyl alcohol, isopropanol, n-Butyl alcohol, ethylene glycol, acetone of seven kinds pure solvents and two mixed solvents of (methanol+water), (acetone+water). The experimental result showed that the solubility of NMA in acetone performed largest increase with the rise of temperature, namely, the dissolution of NMA in acetone was most sensitive to temperature changes, the research obtained acetone could be used in cooling crystallization to purify NMA. When temperature was constant, with the concentration of acetone and methanol solution increased respectively from 0 to 40%, the solubility of NMA increased slowly; with the concentration of acetone and methanol solution increased respectively from 40% to 90%, the solubility of NMA increased significantly. For example, under the temperature of 293.15K, with the concentration of acetone solution increased from 0% to 40%, the molar solubility(103xe) increment of NMA was 2.5; with the concentration of acetone solution increased from 40% to 90%, the solubility increment of NMA was 39. In methanol, the difference of increment was smaller. The research obtained that the binary solvent of acetone-water could be used in solventing-out crystallization to purify NMA, and the vast NMA was separated out when the concentration of acetone solution was 40%. Aiming at the problem of fine particle size of NMA, the paper measured the certain temperature range of (278.15 K-298.15 K), the cooling rate range was (6-36) K-h-1, the metastable zone width (MZWs) of NMA in methanol, propyl alcohol and n-Butyl alcohol. The result showed that when the saturation temperature was constant, the MZWs of NMA in three solvents was widened with the increase of cooling rate and when cooling rate was constant, the MZWs of NMA was narrowed with the increase of temperature. The research obtained the max temperature interval of crystallization operation of NMA, to control crystal form of NMA, so as to avoid primary nucleation bringing about the problem of fine particle size of NMA. By the Kubota’s interpretation theoretical model correlating the relationship between the MZWs and cooing rate, the result suggested that nucleation in three solvents were instantaneous with the nucleation order of m less than 3.Aiming at the low concentration of diluted sulfuric acid, the paper determined the certain temperature range of (273.15 K-323.15 K), the solubility of NMA in H2SO4 solution with concentration from 0% to 98%. The experimental results showed that when the temperature was certain, with the concentration of sulfuric acid increased from 0% to 60%, the solubility of NMA increased slowly; with the concentration of sulfuric acid increased from 60% to 98%, the solubility of NMA increased rapidly. For example, under the temperature of 298.15K, with the the concentration of sulfuric acid increased from 0% to 60%, the molar solubility increment of NMA was 5.8; with the concentration of sulfuric acid increased from 60% to 98%, the solubility increment was 259. The research indicated that when the sulfuric acid solution was diluted to 60%, the vast NMA was separated out. Aiming at the problem of high energy consumption of concentrating sulfuric acid, the calculation of energy consumption of vacuum evaporation concentration of sulfuric acid was carried out, which was based on the experimental result and the existing process, the result showed that concentrating from 60% to 93% compared to concentrating from 33% to 93% could save steam consumption by 45%, water by 45%, diluted water by 69%, the enterprise diluted sulfuric acid solution containing a large number of NMA to 60%, in which the content of NMA was 3.5% and compared to the NMA content of 0.3% in 33% sulfuric acid solution, though the specific value was nearly 10 times, the NMA still retained in sulfuric acid solution, and recycled to nitrification section and was continuely used, no waste. This new way will not only save a lot of energy, and brings the economic cost to enterprise, but also save a lot of water resources, which is consistent with the idea of sustainable development.