The Preparation Of Feedstuff Grade L-Tryptophan

L-tryptophan was one of necessary amino acids wildly used in f eedi ngstuff. In this dissertation, L-tryptophan was prepared through chemical synthesis and enzymatic resolution with low-cost. This study mainly included the following contents: Preparation of indole was conducted through dehydrogenation and cyclization of ethylaniline--byproduct of ch loramphenicol. By using CuAB-1 as catalyst, the conversion of the reaction and selectivity of indole were 100% and over 90% respectively. The half-life of this catalyst was over 200hours. According, to the experiment results, this catalyst possibly has double active centers, one was copper center and the other one was solid-acid center. With ethanolamine as catalyst, indolmetylenehydantoin was prepared by direct condensation of indolealdhyde through Vilsmeirer-Haack reaction and hydantoin that was synthesized under atmospheric pressure. The yield was 85.6%. In the NaOH aqueous solution, indolmetylenehydantoin of the insoluble form with sodium salt and one water for first time. By increasing alkali concentration, the salt could form more easily. In hydrogenation, the reaction rate is inverse proportional to indolmethylenehydan toin concentration, and direct proportional to catalyst concentration and hydrogen pressure respectively. The activation energy for this reaction is 15.92kJ mol-1. DL-tryptophan was prepared by hydrolyzing indolmethylhydantoin. The alkaline hydrolysis of hydantoin is found to be a consecutive first-order reaction. The restrictive step is that N-ca rbamoyI-DL-tryptophan is hydrolyzed into DL-tryptophan, and can be eliminated by increasing reaction temperature and pressure. By a compact consecutive reaction process as hydrogenation-hydrolysis-acylation method, the molar yield of N-acetyl-DL-tryptophan was 80% for indolmethylenehydantoin. L-trypto.phan was prepared by aminoacylase asymmetry hydrolysis. In liquid-state fermentation, aminoacylase of Aspergillusoryzae 3042 was activated by phytaticacid. Through optimizing the culture medium by Plackett-Burman experiment design and response surface methodology analysis, the aminoacylase activity of Aspergillus oryzae 3042 increased 2.26 folds. The mycelium could be reused 4 times.Magnetic separation technology was also studied for recycling Raney-Ni catalyst in the hydrogenation of indolmetylenehydantoin. During twenty-batchhydrogenation, the catalyst was separated and reused by putting with magnetic material. The average yield of IMH was 78%, and the dosage of catalyst fell down to 3% of the original. For the soluble substrates, the immobilized-bed pipe reactor was a good choice.