(58e) Production of Coal-Based Fuels and Value-Added Products: Processes Reacting Coal and Coal Liquids with Petroleum Refining Solvents

BACKGROUND: Because of the recent rise in petroleum prices, alternative hydrocarbon resources are being sought to produce fuel and value-added materials. Much of the focus recently has been on gasification coupled with Fischer-Tropsch synthesis; however, liquid fuels made from processes such as these may not easily produce ring compounds (aromatic and naphthenic) that may be necessary to improve some fuel properties (thermal stability and lubricity) and to produce value-added chemicals. Researchers at The Pennsylvania State University Energy Institute have been involved in research involving several processes that utilize coal, coal-based materials, and by-product biomass in existing refining facilities. One of our major projects is the production of thermally stable jet fuel from coal using unique processing to take advantage of the existing structures in the coal. We have been focusing on three processes: 1) coal tar/refinery solvent blending and hydrotreatment, 2) co-coking of coal/refinery solvents, and 3) coal extraction using refinery solvents. The following briefly discusses the progress of each project and where we plan to go in the future. COAL TAR/REFINERY SOLVENT BLENDING: The overall objective of this project is to examine the characteristics and quality of all of the fuel streams and to determine the effect those materials would have on other unit operations in the refinery. Using coal tar as one of the feedstocks will impact the quantity and quality of the other refinery products, such as gasoline, diesel fuel, and fuel oil. This project is currently being done at the pilot scale, through Intertek PARC, in order to obtain larger quantities of fuel. Refined chemical oil (RCO), a coal tar by-product from metallurgical coke production, was blended with light cycle oil (LCO) from United Refinery, in a 1:1 ratio. The feeds were hydrotreated in the first stage to remove sulfur and nitrogen, then hydrogenated in a second stage to saturate the ring compounds, with fractionation taking place at various stages. The main variation in the process has been the location of the fractionation units, either before hydrotreatment, after the first stage, or after the second stage. When fractionating the product after both hydrotreatments, the co-processed material yields a product distribution of 6% gasoline, 80% jet fuel, 10% diesel and 4% fuel oil. The fuels produced are being tested in real systems. The jet fuel fraction contains mainly two-ring hydroaromatics and cycloalkanes. The jet fuel produced from this process was successfully tested by the Air Force in a helicopter engine and exceeded most specifications for current jet fuel. The gasoline and diesel fractions were analyzed and tested in internal combustion engines. For the gasoline cut, the prominent coal-derived species were methylcyclohexane, decalin, and tetralin (only a small amount of tetralin was detected), which lowered the octane number compared to gasoline, but for the most part did not affect the overall gasoline pool when blended in. For the diesel cut, the prominent coal-derived species were fluorene, phenanthrene, and their hydrogenated derivatives. Blends of up to 5% of these compounds with a base diesel fuel did not alter the properties significantly. Co-processed fuel oil was similar to No. 5 and No. 6 fuel oil, with less sulfur and nitrogen; however, the trace metals in the co-processed fuel oil were more similar to coal than to petroleum. Work continues on the improvement of catalysts that would be utilized for these processes. The focus for desulfurization and denitrogenation catalysts has been on adsorption catalysts (to remove heavy sulfur and nitrogen compounds) and unsupported dispersed Ni/Mo and Co/Mo hydrodesulfurization catalysts. Work continues on catalysts for saturation of ring compounds and for the production of high-value aromatic compounds. Future work will focus on testing fuels generated from variations in the hydrotreatment process. It is expected that larger scale demonstration tests will be done to produce larger quantities of jet fuel for continued testing in aircraft engines and to provide necessary data for complete economic evaluation. CO-COKING COAL/DECANT OIL: The focus of the second project is to blend coal/decant oil to feed into a delayed coker, to produce a high quality carbon material and produce liquids that could produce thermally stable jet fuel. The Energy Institute has a unique lab-scale co-coking unit that allows introduction of coal into the coking process. Addition of coal into petroleum refining streams may yield benefits from the development of carbon products with different properties than typically generated from residua alone. Although this work has been directed at producing a carbon product suitable for the anode or graphite electrode markets, there are other developing markets that may be attainable, i.e., substitute for blast furnace or for solid carbon-based direct reduction processes. Consequently, the objective of this part of the refinery integration research program is to investigate whether coal introduced into the delayed coker can result in carbon materials of higher value along with providing useful liquid streams for liquid fuels and binder pitch. When using a feed of 4:1 United Refining decant oil to ultra-clean Pittsburgh seam coal, conditions of ~465°C and 25 psig, the products are ~30% coke, 3% gas, and 67% liquid (by weight). Characterization of the materials in this process is in progress. Coke produced using ultra-clean coal proved to be of high quality for anode use, but iron and silica content in the carbon did not meet anode specifications. Future work includes extraction of coal with decant oil in order to feed an ashless material to meet the mineral specifications for anodes and electrodes. EXTRACTION OF COAL USING REFINERY SOLVENTS: One of the main limitations to the coal tar blending is the availability of RCO; metallurgical coke plants are being slowly being shut down in the US for environmental reasons. We are currently developing a process that is capable of extraction of coal using LCO, the advantage being that once the extraction takes place, no separation of the liquids is necessary and can be fed directly into a hydrotreater. When using a 10:1 ratio of LCO and Pittsburgh coal in a stirred autoclave at 350 °C, ~ 50% extraction yield was obtained. In a lab-scale multistage reactor, the yield increased to ~70%. We are currently scaling up the process and engineering the reactor for separation of solids and liquids while heated. Once this is achieved, we will focus on reducing the solvent needed to do the extraction and developing a multi-stage reactor, which will allow production of a 1:1 LCO/coal liquid for further hydrotreatment. We also plan to investigate the use of other by-product solvents. SUMMARY: Liquid fuels produced directly from coal and coal tar by-products utilize the inherent structures in coal. The advantages to utilizing refining solvents/coal/coal tar and processes that exist within a refinery to produce particular fuels and value-added materials are (1) implementation could be much faster than projected for commercial gasification in the US and (2) production of fuels and carbon materials with specific uses that F-T liquids may not be suitable for. ACKNOWLEDGEMENTS: Financial support was provided by the US Department of Energy under grant no. DE-FC26-03NT41828. The authors would also like to acknowledge the contributions of Dr. Leslie R. Rudnick as for his past participation in the work on this project. We would also like to acknowledge several researchers and technicians involved in this work, including Ron Wincek, Glenn Decker, Brad Maben, Vince Zello, Ron Wasco, and the late Dr. David Clifford.