Studies On Optimal Preparation Of Graphite Electrode Based On Lignin And Collagen As Binder And Its Performance

Coal tar pitch, as the waste residue of coking system, is generated from the processing of coal tar vacuum distilling. Considering the carcinogenicity of its main aromatics components, especially benzo[a]pyrene and benzo[a]anthracene, the widespread use of coal tar pitch has been tightly restricted, except no alternatives to the typical binder and impregnant for carbon products manufacturing. Therefore, it is an urgent and meaningful mission to develop novel substitutes for coal tar pitch to reduce its risk of cancer and environmental pollution. Biomass, one of the renewable resources that consiste of organic carbon, has the potential to develop alternatives to petroleum-based products or equivalents. In present work, the practicability of pine softwood lignin and collagen used as coal tar pitch alternatives to prepare novel graphite electrode with high density was studied. By studying the pyrolysis characteristics, the pyrolysis products formation and the interaction of pine softwood lignin and collagen during co-pyrolysis, this paper provides a solid foundation of data and theoretical guidance for the optimal preparation of graphite electrode in industry.The pyrolytic decomposition of pine softwood lignin, collagen and their blends could be described as a three-stage process:dehydration, pyrolysis and carbonization. With the increasing temperature, the lagging effect in heat transfer was more apparent and the final char yield also decreased steady. Moreover for a given fractional conversion, lower pyrolytic temperature occurred was reached for more content of collagen. Apparent activation energies (Ea) computed by the Kissinger, the Weibull, and the Flynn-Wall-Ozawa (FWO) methods showed the same trends. The blends pyrolysis exhibited synergistic presence of collagen, which could help initiate the py-rolysis mass loss reactions at 250～390℃, and participate in the condensation reactions of aro-matic fragments at 390～800℃, leading to less emission of some gaseous products and more preservation of residual char.The char yield and ash content of pine softwood lignin, collagen and their blends indicated that the synergistic effect between pine softwood lignin and collagen had greater influence on char yield than ash content. The ratio of C/H and C/O increased gradually with increase in temperature. On the contrary, the content of bonded OH stretch, the symmetric CH3 stretch and aliphatic CH stretch decreased as the temperature increased. On the basis of element analysis, Fourier transform infrared spectroscopy (FTIR) and scanning electron microscope (SEM), collagen was believed to improve the aromatic index and carbonization degree of the blend system. It was also revealed to construct a carbonized fragile skeleton structure with pine softwood lignin in the form of filling, covering and bridging at the temperature range of 450℃～600℃.For the carbonization of green graphite electrode, lower heating rate should be adopted to improve the properties of carbonized electrode, especially at the temperature of 250℃～500℃. According to the results of fractional factorial experiments and single factor experiments, the response surface methodology was employed for further optimation of the graphite electrode preparation, i.e. pine softwood lignin content 12.961%, collagen content 3.561%, petroleum coke content 27.438%, heating temperature 400℃, pressure 30MPa, the soaking time 2h, and the optimum density of carbonized electrode 1.671g/cm3.The puffing during the baking was mainly caused by the pyrolytic gaseous products, and the resulting crack was largely in horizontal crack, which increased maximum and then decreased with the growing puffing.