Coal Liquids Refinery

Refinery feedstocks from coal (coal liquids) have not been dealt with elsewhere in this text but descriptions are available from other sources (Speight, 2008, 2011). Once the liquids are produced, the next issue is the means by which these liquids can be refined to produce the necessary fuel products. 

The Bergius process was one of the early processes for the production of liquid fuels from coal. In the process, lignite or subbituminous coal is finely ground and mixed with heavy oil recycled from the process. Catalyst is typically added to the mixture and the mixture is pumped into a reactor. The reaction occurs between 400°C and 500°C under a pressure of hydrogen and produces heavy oil, middle oil, gasoline, and gas  

A number of catalysts have been developed over the years, including catalysts containing tungsten, molybdenum, tin, or nickel. 

The different fractions can be sent to a refinery for further processing to yield synthetic fuel or a fuel blending stock of the desired quality. It has been reported that as much as 97% of the coal carbon can be converted to synthetic fuel but this very much depends on the coal typo, the reactor configuration, and the process parameters. 

However, liquid products from coal are generally different from those produced by petroleum refining, particularly as they can contain substantial amounts of phenols. Therefore, there will always be some question about the place of coal liquids in refining operations. For this reason, there have been some investigations of the characterization and next-step processing of coal liquids. 

---

Figure 11. Economic comparison for petroleum vs. coal liquid refinery...

Cumene (isopropylhenzene), a liquid, is soluble in many organic solvents hut not in water. It is present in low concentrations in light refinery streams (such as reformates) and coal liquids. It may he obtained by distilling (cumene s B.P. is 152.7°C) these fractions. 

Conversion from coal to natural gas. Sasol 1 was designed as a coal-to-liquids facility. A natural gas pipeline was constructed and commissioned in 2004. This allowed the Sasol 1 facility to be converted to a gas-to-liquids plant. Although it implied that the associated coal tar refinery would become redundant, the decision was made by Sasol to keep the coal-to-chemicals units at Sasol 1 in operation by supplying coal pyrolysis products from its larger CTL facility in Secunda. 

Mass spectrometers used to be expensive and complex for routine use as a GC detector. The Ion Trap Detector (ITD, Finnigan) is a low priced mass spectrometer (MS) for capillary chromatography. Three analytical tools - SEC, GC, and ITD - are incorporated into a powerful analytical system for the analysis of complex mixtures such as coal liquids, petroleum crude and various refinery products. The instrumentation and the SEC-GC-MS analysis of a coal liquid are presented in this paper in order to demonstrate the technology. 

The species which are unknown and have not been identified as one of the major chemical lump such as alkanes, phenols and aromatics are lumped together as unidentified. However, the species in this lump include saturated and unsaturated cycloalkanes with or without side chains, which resembles the naphthenes, a petroleum refinery product group. A number of well known species in coal liquid are not mentioned in this lumping scheme. Such as heterocyclic compounds with sulfur, nitrogen or oxygen as the heteroatom, and other heteroatora containing species. Some of these compounds appear with aromatics (e.g. thiophenes, quinolines) and with phenols (e.g. aromatic amines), and most of them are lumped with the unidentified species lump. 

Although the first major use of coal liquids will be as boiler fuels, it is clear that in order to make the largest impact on the U.S. liquid fuel demand, products from direct liquefaction have to be upgraded to quality liquid fuels for both transportation and home heating oil uses. The products coming from the all-distillate coal liquefaction processes such as H-Coal Syncrude, SRC-II and Donor Solvent, along with shale oil production will be candidates for use as refinery feedstock. 

The SRC s used in this study were obtained from the SRC process demonstration unit operated by Southern Services Inc. in Wilsonville, Alabama. Three SRC s were studied and these products were derived from the following coals Illinois No. 6 Burning Star, Illinois No. 6 Monterey, and Wyodak (Amax). The as-received SRC s were wet owing to a water quench and therefore each SRC was dried carefully before sampling and analysis. The vacuum resid was prepared by laboratory vacuum distillation of an atmospheric resid obtained from a commercial refinery source. The identification and source of the coal liquid samples used in this study along with other pertinent information are presented in Table I. 

Nitrogen-containing compounds always pose problems for oil refinery industry via catalyst poisoning (1). Their combustion products also cause great concern in air pollution (2). Due to higher nitrogen content in shale oil and coal liquid (1-2%) than in crude oil (<0.5%), it is essential to lower the nitrogen content in shale oil before any refinery processes are performed. 

Current concepts for refining the products of coal liquefaction processes rely for the most part on the already existing petrolenm refineries, although it must be recognized that the acidity (i.e., phenol content) of the coal liquids and the potential incompatibility of the coal liquids with conventional petroleum (or even heavy oil) feedstocks may pose severe problems within the refinery system (European Chemical News, 1981). 

In terms of liquids from coal that can be integrated into a refinery, this represents the most attractive option and does not threaten to bring on incompatibility problems as can occnr when phenols are present in the coal liquids. 

Note Some applications creating hazardous condilions are petrochemical or fertilizer plants, refineries, coal mines etc., where inflammable gases and volatile liquids are handled, processed and stored. 

The co-processing of coal with heavy crude oil or its heavier fractions is being developed to lower capital requirements for coal hquefaction and to integrate processing of the products of coal conversion into existing petroleum refineries. This development appears to represent the main route by which coal-based liquid fuels will supplement and perhaps someday displace petroleum-based fuels. 

The transportation fuels produced and marketed (Table 18.9)40 met the South African fuel specifications of that time and included some coal-derived liquids (not shown in Figure 18.5). Although the refinery originally produced no jet fuel, it was demonstrated that the hydrogenated kerosene range oligomers from olefin oligomerization over a solid phosphoric acid catalyst met the requirements for jet fuel.38 (Semisynthetic jet fuel was approved in 1999 and fully synthetic jet fuel was approved in 2008 DEFSTAN 91-91/Issue 6). 

In addition to this, solid acid catalysts can also be used in the hydroisomerization cracking of heavy paraffins, or as co-catalysts in Fischer-Tropsch processes. In the first case, it could also be possible to transform inexpensive refinery cuts with a low octane number (heavy paraffins, n-Cg 20) to fuel-grade gasoline (C4-C7) using bifunctional metal/acid catalysts. In the last case, by combining zeolites with platinum-promoted tungstate modified zirconia, hybrid catalysts provide a promising way to obtain clean synthetic liquid fuels from coal or natural gas. 

---