Date of Award

January 2012

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Chemical Engineering

First Advisor

Wayne Seames

Second Advisor

Steven Benson

Abstract

Current research at the University of North Dakota studies the conversion of crop oils into fuels such as diesel and jet fuel. A by-product of this conversion process is a high molecular weight tar, which can be further processed into carbon products such as carbon black, coke, activated carbon, and carbon fibers. This research focuses on converting the tar into high purity carbon. Currently coal and petroleum tars are used to make carbon products and are important nonrenewable sources to replace by the use of crop oil tars.

Lab-scale experiments have shown that the tars produced during crop oil cracking can be converted into a pure, granulated carbon product. This conversion, known as carbonization, occurs at reasonable conditions and is accomplished by refining the residual tars into high purity carbon through pyrolysis of the tar in an inert atmosphere. Residual tars are converted into carbon, while simultaneously removing and recovering distillates to be recycled back through the system where they can be processed into other fuel and chemical products.

The carbonization of tar was performed through the use of a lab scale coking reactor. The independent variables were coking temperature and either vacuum or atmospheric pressure. Process conditions were sought to optimize the production of solid coke, while simultaneously minimizing the formation of gas products. An overall mass balance for carbonization was calculated. Characterization of the solid coke was performed by carbon content analysis and moisture content/volatile matter/fixed carbon/ash content evolution analysis. Characterization of the liquid phase was performed by liquid analysis for fuel cuts and acid concentration analysis. The gas phase was characterized by gas chromatography.

Carbon products were successfully produced in this research. The coking of heavy, residual tars using a temperature above 460 °C and at atmospheric pressure resulted in the maximum formation of bio-derived coke, while also minimizing the formation of low value gas products. These process conditions produced a little more than 10 wt % coke. The coke contains 92 wt % carbon, with the balance primarily volatile matter. Therefore, calcining the coke may be needed, depending on the applications sought for this coke. The liquid phase contained 91 wt % heavy fuel oil and diesel fuel cuts, and had an acid concentration of between 4.0-6.7 wt % acid. Analysis of the non-condensable gas phase presented a mixture of light hydrocarbons, carbon monoxide, carbon dioxide, and hydrogen. Both the liquid phase and gas phase streams can be recycled back through the process.

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