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FINAL TECHNICAL REPORT September 1, 1994 through August 31, 1995

Project Title: PRODUCTION OF LOW-SULFUR BINDER PITCH FROM HIGH-SULFUR ILLINOIS COALS

DOE Cooperative Agreement Number: ICCI Project Number: Principal Investigator: Project Manager:

DE-FC22-92PC92521 (Year 3) 94-1/4.2A-1M Richard A. Knight, Institute of Gas Technology Dan Banerjee, Illinois Clean Coal Institute

ABSTRACT

The objective of this project is to produce electrode binder pitch with sulfur content below 0.6 wt% from high-sulfur Illinois coal mild gasification liquids. Previously, flash thermo cracking (FTC) was used to successfully upgrade the properties of mild gasifi­cation pitch, yielding a suitable blending stock for use as a binder in the production of carbon electrodes for the aluminum industry. However, in pitches from high-sulfur (4%) Illinois coal, the pitch sulfur content (2%) was still higher than preferred.

In this project, two approaches to sulfur reduction were explored in conjunction with FTC: (1) the use of a moderate-sulfur (1.2%) Illinois coal as mild gasification feedstock, and (2) direct biodesulfurization of the liquids from high-sulfur coal prior to FTC. In Case 1, the liquids were produced by mild gasification of IBC-1 09 coal in a bench-scale fluidized-bed reactor, followed by distillation to isolate the crude pitch. . In Case 2, bio­desulfurization with Rhodococcus Rhodochrous IGTS8 biocatalyst was performed on crude pitch obtained from Illinois No.6 coal tests conducted in the IGT MILDGAS PRU in 1990. Pitch upgrading experiments were then conducted in a continuous FTC reactor.

During the year, mild gasification of IBC-109 coal was completed, producing 450 g of coal liquids, which were then distilled to recover 329 g of Case 1 crude pitch. The sulfur content of the crude pitch was 0.67%. Typically, FTC results in further pitch sulfur reduction. In this case, the sulfur content of the FTC-processed pitch increased to 1.27%. FTC also increased the C:H ratio of the pitch from 0.88 to 1.46, QI from 0.0% to 18.9%, TI from 22.8% to 35.7%, and coking value from 24.6% to 58.7%. Biodesulfurization was performed on Case 2 pitch, resulting in sulfur reductions of 13.5% to 24.8%. This treatment was projected to yield a finished pitch with about 1.5% sulfur.

In approach (1), we have not satisfactorily explained why the sulfur content of the pitch from IBC-1 09 coal increased after FTC. This is contrary to prior results with high-sulfur pitch, and further work is needed to explain it. With respect to approach (2), biodesulfurization of crude pitch is marginally effective for high-sulfur coal liquids, but may be applicable for mild gasification pitches from coals in the 1.5-2.0% sulfur range.