| The upgrading of lignite is one of the important ways of low rank coal utilization. The industrial value of tar and phenolic compounds in the pyrolysis products, especially the low-level phenols (such as phenol, cresol and xylenol) is rather high, and the simple phenols content is considerable. In the dissertation, a series of pyrolysis experiments with Yunnan Zhaotong lignite were conducted in an electricity heated fixed-bed in order to investigate the effect of reaction condition on the yield, composition and distribution of the tar and low-level phenolic compounds. Based on the experiments, the experimental conditions are optimized, and meanwhile the catalyst is used to improve the yield of tar and low-level phenolic compounds. It is realistically significant to broaden the way of coal tar utilization.In the dissertation, directional conversion experiments with the tar and phenolic compounds from lignite and catalytic pyrolysis in the fixed-bed with the thermogravimetric analyzer, gas chromatography and GC-MS analysis were conducted in order to investigate the effect of experiment conditions on the low-level phenolic compounds yield. First, in the fixed-bed pyrolysis, the path of piecewise hydrogenation was proposed to reduce the hydrogen consumption and improve the hydrogenation efficiency. Second, changing the fuel-feeding method and increasing heating rate were adopted to increase the low-level phenolic compounds yield. Finally, in the fast pyrolysis process, combing the hydrogen spillover mechanism and catalytic cracking hydrogenation process, online catalysis was used. Changing the catalyst ratio and catalytic method can affect the contents of tar yield of and the important components (BTX, PCX, simple naphthalene) in different degree.The main research contents and results are as follows.(1) The effect of the reaction conditions with the reaction temperature of200-800℃, carrier gas flow rate of100-400ml/min, residence time of0-30min, heating rate of 5-30℃/min on the yield of tar and phenolic compounds in the lignite pyrolysis process were explored in the fixed-bed taking nitrogen as carrier gas. The tar yield reaches the maximum at the reaction temperature of550℃, residence time of20min, carrier gas flow rate of200ml/min, heating rate of20℃/min. With the increase in the reaction temperature, the total phenolic compounds yield increases first and then decreases, reaching the maximum at the reaction temperature of520℃. The yield of simple phenols increase with the increase in the pyrolysis temperature. The yield of the total phenolic compounds shows the same tendency with that of the tar, reaching the maximum at the residence time of10min. The yields of the simple phenols and the complicated phenolic compounds increase with the increase in the heating rate.(2) The contents of tar and the simple phenolic compounds increase in the process of pyrolysis hydrogenation. In the dissertation, the method of piecewise hydrogenation reaction is applied. Hydrogen was introduced at the reaction temperature of350℃and then stayed for10minutes at the reaction temperature of450℃. The method can reduce the hydrogen consumption and improve the yield of tar and the phenolic compounds.(3) In the fixed-bed, changing the fuel-feeding method and increasing heating rate were adopted to increase the low-level phenolic compounds yield. The effects of the reaction temperature, the carrier gas flow rate and the residence time on the tar and phenolic compounds distribution were explored in the fast pyrolysis reaction. The experimental results reveal that with the increase in the reaction temperature, the tar yield tends to increase first and then decrease, reaching the maximum at the reaction temperature of520℃. The yield of total phenolic compounds has the same variation tendency with that of tar, reaching the maximum at the reaction temperature of540℃. The yield of the simple phenols in the fast pyrolysis is obviously higher than that in the slow pyrolysis.(4) In order to improve hydro-pyrolysis efficiency and enhance the quality of tar, in the fast pyrolysis process, combing the hydrogen spillover mechanism and catalytic cracking hydrogenation process, online catalysis was used to investigate the effects of catalyst contents and catalytic method on the contents of tar and the important components (BTX, low-level of phenols, simple naphthalene). The conversion rate of coal catalytic pyrolysis was investigated by thermogravimetric analyzer, and Ni and Mo are taken as active centers. The experimental results in the fixed-bed demonstrate that the different catalytic impregnation liquid concentration and the placement of the catalysts display different catalytic effects. The effect of post9#catalyst shows the best effect to PCX and BTX, the post3#catalyst improves the simple naphathlene best. The catalytic pyrolysis reaction with self-prepared catalyst is important to improve the hydrogenation efficiently in the catalytic pyrolysis, realize the catalyst separation, recovery and regeneration of coal catalytic pyrolysis, increase the yield of tar components with high value. |
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