Completed Research
Direct Liquefaction of Two Subbituminous Coals Using KOH/Methanol
Gun Kositchaiwat, MS, 2013
(Thesis: University of Pittsburgh ETD)
Two subbituminous coals, namely Rosebud and Wyodak-Anderson, were used in the development of a non-catalytic direct coal liquefaction process employing potassium hydroxide (KOH) and methanol (CH3OH) at high temperature. Samples from both coals were obtained from the Penn State Coal Sample Bank and Database, where Rosebud coal is from Rosebud seam, Rosebud County, Montana, USA and Wyodak-Anderson coal is from Wyodak seam, Campbell County, Wyoming, USA.
The experiments were conducted in a one-liter, high-pressure, high-temperature agitated autoclave. The effects of temperature (280, 290 and 300 oC) and coal-KOH-methanol (C:K:M) ratio (2:1:9, 2:3:9 and 3:3:9) on the process gaseous and liquid product yields were investigated at a mixing speed of 1200 rpm. The reactor pressure and temperature were monitored and recorded throughout the experiments. At the completion of each experiment, the liquefaction products were neutralized with hydrochloric acid, washed with water, and filtered. The solid products were then subjected to the sequential selective solvent extraction technique, where n-hexane, toluene, and tetrahydrofuran were used to obtain the yield of solubles in each respective solvent. The n-hexane solubles, n-hexane insolubles/toluene solubles, toluene insolubles/THF solubles and THF insolubles measured were denoted as hexane solubles (HS), toluene solubles (TS), THF solubles (THFS) and THF insolubles (THFI), respectively.
The experimental results indicated that at high temperatures CH3OH and KOH appeared to liquefy Rosebud and Wyodak-Anderson coals; and the effects of temperature on the process yields were found to be strongly dependent on coal type and C:K:M ratio. The highest yield of liquid products was obtained at 300 oC and C:K:M ratio of 2:1:9, the liquid products yield obtained from Rosebud coal was higher than that from Wyodak-Anderson coal. The presence of KOH appeared to favors hydrogen production over liquid hydrocarbons production, leading to a high yield of light hydrocarbons and hydrogen and a low yield of liquid hydrocarbons. Also, the maximum total yield of liquid products obtained in this study was about 50 wt.% which was much lower than that reported by Shabtai and Saito [1] who obtained yield up to 90 wt.% in their base-catalyzed liquefaction process, which highlights the fundamental difference between catalytic and non-catalytic coal liquefaction processes.
1. Shabtai, J. S., Saito, I. "Process for the Low-Temperature Depolymerization of Coal and It's Conversion to a Hydrocarbon Oil" U.S. Patent 4,728,418, 1988.