Production of Mesophase Pitch from Coal for Carbon Fiber Production

摘要

In the last few decades, significant research has been done on coal pyrolysis products and coal tar pitch (CTP) upgrading to mesophase CTP, but these are usually investigated independently. Coal pyrolysis has primarily been studied to understand what types of products evolve under different reaction conditions, or to modify conditions such that coal tar/oil yields are maximized or minimized. CTP upgrading to mesophase has almost always been investigated using a commercially-provided CTP from a coking process. In light of recent trends in decreased use of coal for energy generation, many investigators are searching for ways to create alternative, high-value products from this plentiful resource, such as carbon fiber. It is comparatively easy to make carbon fiber from a commercially-provided, refined CTP compared to a non-coking, lower rank coal. In this work, we are interested in achieving the ability to create quality carbon fiber from traditionally non-coking coals, and we will present our efforts to connect the two processes of coal pyrolysis with coal tar upgrading to mesophase CTP. We will focus on what characteristics and conditions may be necessary during coal pyrolysis to create a coal tar suitable for creating mesophase CTP, and subsequently for high-quality carbon fiber production. In this work, we performed pyrolysis and coal tar upgrading on Utah Sufco coal. The coal pyrolysis was performed in a two-stage reactor, where the primary tar was evolved in the first part of the reactor, and then the tar vapor was further heated in the second stage to induce secondary gas-phase reactions. We looked at the effect of gas-phase secondary reaction residence time on the coal tar composition and characteristics, and used several analytical techniques to infer what properties are needed to create mesophase CTP. The techniques used included matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS), thermogravimetric analysis (TGA), Fourier-transform infrared spectroscopy (FT-IR), and nuclear magnetic resonance spectroscopy (NMR). The coal tar was upgraded to mesophase CTP in a small sparging reactor, and the mesophase content was observed by polarized microscopy. The samples created were compared against a commercial CTP, which has been shown by our co-investigators at the University of Kentucky to be a very effective feedstock for spinning carbon fibers.