Direct liquefaction of low-rank coal. Quarterly technical progress report, April 1, 1995--June 30, 1995 Page: 4 of 13
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DIRECT LIQUEFACTION OF LOW-RANK COAL
Direct liquefaction research at the Energy & Environmental Research Center (EERC) has,
for a number of years, concentrated on developing a direct liquefaction process specifically for
low-rank coals (LRCs) through the use of hydrogen-donating solvents and solvents similar to coal-
derived liquids, the water-gas shift reaction, and lower-severity reaction conditions. The
underlying assumption of all of the research was that advantage could be taken of the reactivity and
specific qualities of LRCs to produce a tetrahydrofuran (THF)-soluble material that might be easier
to upgrade than the soluble residuum produced during direct liquefaction of high-rank coals. A
multistep approach was taken to produce the THF-soluble material, consisting of 1) preconversion
treatment to prepare the coal for solubilization, 2) solubilization of the coal in the solvent, and
3) polishing to complete solubilization of the remaining material. The product of these three steps
can then be upgraded during a traditional hydrogenation step.
To provide a preliminary comparison between the EERC process and existing direct
liquefaction processes, product slurry produced during solubilization (Step 2) and polishing (Step
3) steps (for example, without the Step 1 pretreatment) was catalytically hydrotreated to
equilibrium based upon hydrogen uptake. The hydrotreatment was performed in this manner to
define the practical upper limit of the product's hydrotreatability. The results were positive, and
further tests were performed incorporating the pretreatment step (Step 1). Steps 1 through 3
(pretreatment, solubilization, and polishing) were performed in an integrated fashion. The
products were catalytically hydrotreated to demonstrate the maximum hydrotreatability of the
solubilized slurry and to provide products that could be compared to the products of existing
The results of the EERC's research indicated that additional studies to more fully develop
this process were justified. Two areas were targeted for further research: 1) determination of the
recyclability of the solvent used during solubilization and 2) determination of the minimum severity
required for hydrotreatment of the liquid product. This project addresses these two areas.
2.0 GOALS AND OBJECTIVES
The project goals are to determine the recyclability of the solvent used during solubilization
and to determine the minimum hydrotreatment severity required to upgrade the liquid product of
the multistep EERC process.
The project will be performed as two tasks. The first task will consist of ten recycle tests.
Lignite will be solubilized through the pretreatment, solubilization, and polishing steps. The
product of these three steps will be combined with a vehicle solvent, and the resulting stream will
be distilled to remove water, solubilization solvent, and oxygenated light coal-derived liquids. The
overheads will be further distilled to separate the water and light oil streams. The light oil will
then be recycled for use as the solubilization solvent in the next test sequence. The analyses of the
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Hetland, M.D. Direct liquefaction of low-rank coal. Quarterly technical progress report, April 1, 1995--June 30, 1995, report, July 1, 1995; Grand Forks, North Dakota. (digital.library.unt.edu/ark:/67531/metadc618539/m1/4/: accessed April 23, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.