Study On The Synthesis Of 3,3',4,4'-Biphenyltetracarboxylic Dianhydride By Pd/CNF Catalysis Dehalogenated Coupling Process

With the development of high-technology in our country, requirement of high performance engineering material polyimide is increasing constantly. 3,3',4,4'-biphenyltetracarboxylic dianhydride(s-BPDA)was synthesized as a monomer to improve performance of the polyimide in recent years. At present, there are two mainly methods: dehalogenated coupling process and oxidized coupling process in synthesizing s-BPDA abroad, but only industrialization in Japan. There are few researches on the synthesis of s-BPDA in our country. Although Changchun applied chemicals institute applied for the patent of synthesis, there is not industrial report on the synthesis.The key to producing s-BPDA lied on the synthesis of high pure 4-halogenphthalic anhydride and improvement of activity of Pd catalyst. Because of unique configuration and outstanding physical chemistry character of carbon nanofibers(CNF), which is a new carbon material, is used as catalyst carrier. Compared with activated carbon, Al2O3 and so on, CNF possesses excellent activity and selectivity after carrying noble metal. Pd/CNF was firstly used to substitute traditional Pd/C to improve the activity of catalyst, and resolve the question of low yield in traditional method in this dissertation.This dissertation aimed to produce high-purity s-BPDA which was used to manufacture developed products. Firstly, 4-bromophthalic anhydride was synthesized. Secondly the catalyst for synthesizing s-BPDA was studied. Finally s-BPDA was synthesized by dehalogenated coupling using Pd/CNF catalyst.Firstly, a tradition technology of 4-BPA was optimized by orthogonal design testing and single factorial design testing, the optimum reaction conditions of synthetic 4-BPA were as follows: mole ratio of phthalic anhydride and Br2=1:1.25, amount of water=35mL/mol4-BPA, time of dripping Br2=2h, reaction temperature=72.5℃, reaction time=5.5h, yield of 4-BPA=88.7%. The purity of 4-BPA reached 98.46% by recrystallization and rectification.On basis of catalytic mechanism, preparation and activity appraisal of Pd catalyst, optimal results were obtained over the catalyst prepared by treatment of the activated carbon with 30% HNO3 at 60℃for 4h with reflux in water bath, which exhibited activity 2.3 times higher than that without pretreatment. Selective test of the Pd catalyst's carrier was made, and the experimental results had indicated that the yield of CNF as carrier was 5~6% higher than activated carbon.The effect of amount of Pd/CNF, reaction temperature, amount of NaOH, type and amount of reducing agent, reaction time, amount of acetic anhydride and so on were examined on reaction rule of s-BPDA. The optimum reaction conditions of synthetic s-BPDA were as follows: amount of Pd/CNF=0.0167g/g4-BPA, reaction temperature=95℃, mole ratio of NaOH and 4-BPA=3.5:1, mole ratio of oxammonium hydrochloride and 4-BPA=3.5:1, reaction time=10h, mole ratio of acetic anhydride and 3,3', 4,4'-biphenyltetracarboxylic acid=35:1, 4-BPA conversion=99.8%, yield of s-BPDA=83.2%. At the same time, a recycling purification of s-BPDA was developed. It is that s-BPDA became acid after dissolving in hot water(95℃), and then dehydrated under 220℃.Yield of s-BPDA reached 79.8%, purity of s-BPDA reached 99.6% after three times recyclying purification.