(340c) Utilizing Pyrolysis Secondary Gas-Phase Reactions to Produce Anisotropic Carbons from Non-Graphitizing Feedstocks

Research Interests: Materials and process design for sustainable engineering technologies (including renewable energies and carbon capture technologies), Value-added products from waste materials, Carbon materials

Anisotropic carbon materials are valuable intermediate products that are formed through nematic liquid crystals of planar, large polycyclic aromatic hydrocarbons (PAHs). Due to the organized crystal-like arrangement of the PAHs, anisotropic carbon materials can be subsequently converted to graphitic products through appropriate thermal treatment steps. Intermediate anisotropic carbon materials are traditionally produced from heavy pitch fractions of coal and petroleum coking processes, and these anisotropic carbons are most often used to produce high-modulus carbon fiber or needle coke for production of graphite electrodes.

Anisotropy (or “mesophase”) in carbon materials has been widely studied over the years, and it is well known that mesophase conversion and quality is highly dependent on the chemical properties of the feedstock. Some of the important chemical properties that impact mesophase conversion are aromaticity, heteroatom functional groups, viscosity, and molecular weight. Because these chemical properties critically affect mesophase conversion, some feedstocks are intrinsically more suitable for mesophase conversion than others.

Previous work in our group has shown that feedstocks with chemistry originally not suitable for mesophase conversion (e.g. coal tar from non-coking coals) could be modified to be more suitable for mesophase conversion through the utilization of secondary gas-phase reactions (SGR) during pyrolysis. SGR include cracking reactions to produce smaller molecular fragments, and ring-forming/ring-addition condensation reactions to produce larger aromatic species. SGR occur during pyrolysis of carbon-based feedstocks when pyrolysis temperatures are sufficiently high (i.e. T > 600C) and when the pyrolysis gas-phase intermediates are exposed to these high temperatures for sufficiently long residence times. In this work, we will demonstrate the effect of this approach on various coal feedstocks, as well as on completely non-aromatic-type feedstocks, such as polyethylene and polypropylene.

In this work, the SGR pyrolysis approach is being investigated on coals of varying ranks (Wyoming PRB Wyodak, Utah Sufco, Illinois #6, and West Virginia Flying Eagle), commonly used plastics (low-density polyethylene LDPE, and polypropylene PP), and mixtures of coal with plastic. The intermediate pyrolysis products (i.e. tar products) were analyzed for their chemical functionality through Fourier-transform infrared spectroscopy, and their respective molecular weight distributions were measured through laser desorption ionization mass spectrometry. After converting the tar samples into mesophase products, the samples were then viewed under a polarized microscope to determine their mesophase conversion as well as their optical textures to determine the mesophase qualities.

Our results thus far show that for all coals and also for LDPE, mesophase pitch can be successfully produced through the SGR pyrolysis approach. Substantial mesophase conversion (> 60%) was found at appropriate SGR conditions for Utah Sufco, PRB Wyodak, Flying Eagle, and LDPE pitch samples. Current work includes testing the approach on PP as well as on mixtures of coal and plastic. The results of this work thus far show that the use of secondary gas-phase reactions in pyrolysis may be broadly applied to various carbon feedstocks to improve their ability to produce desirable mesophase carbon intermediates. Ultimately, this approach has the potential to create high-value products, such as high-modulus carbon fiber and graphite electrodes from non-traditional carbon feedstocks.