纯镍表面结焦形貌及其影响因素研究

系统研究了丙烯裂解过程中纯镍表面的结焦形貌及其影响因素，结果表明，纯镍表面的沉积焦炭有三种形貌，分别为纤维状、颗粒状和膜状、。纤维状焦炭在800℃左右形成，需要基底金属镍的参与，预氧化后的镍表面显著加剧这种焦炭的沉积，提高结焦温度或延长结焦时间，结焦机制发生转变，焦炭形貌也逐渐转变为颗粒状。颗粒状焦炭形成于气相反应，与基底金属镍无关，膜状焦炭形成于结焦切期，溶解．析出机制及表面直接形核、生长机制均对其形有贡献，抑制纤维状焦炭的形成有益于减轻镍表面总的结焦程度。

STUDY ON SURFACE COKINGMORPHOLOGY OFPURE NICKEL AND ITS CORRELATIVE FACTORS

Surface coking morphology of pure nickel and its correlative factors were investigated systematically. Results reveal that the coke deposited on surface of pure nickel includes the filamentary coke, the particle-like coke, and the film-like coke. Deposition of the filamentary coke happens at approximate 800℃ and is closely dependent on the nickel substrate. Pre-oxidation markedly aggravates the deposition of the filamentary coke on surface of pure nickel. Either raising the coking temperature or prolonging the coking time results in change of the coking mechanism, and the deposited coke tends to show a particle-like morphology. Since the particle-like coke is derived from a series of gas-phase reactions, it bears no relation to the nickel substrate naturally. The film-like coke is only deposited at the initial coking stage. Both the dissolution/precipitation mechanism and the direct nucleation/growth mechanism may make a contribution to development of the film-like coke. Restraining the formation of the filamentary coke can be beneficial to alleviate the totally coking degree on the nickel surface.