Page 202 - Synthetic Fuels Handbook

188 CHAPTER SIX

TABLE 6.7 Properties of Oil-Shale Distillates Compared with Benchmark Crude Oils
API %Sulfur

OTA reported oil-shale distillates properties * 19.4–28.4 0.59–0.92
Shell ICP oil-shale distillate † 34 0.8
Oil tech oil-shale distillate ‡ 30 no report
West Texas intermediate crude oil § 40 0.30
NYMEX deliverable grade sweet crude oil specification ¶ 37–42 <0.42
Alaska north slope crude oil § 29–29.5 1.10
* OTA, An Assessment of Oil Shale Technologies, Table 19, 1980.
† Energy Washington Week, “Shell Successfully Tests Pilot of New In Situ Oil Shale Technology,” Oct. 12, 2005.
‡ Jack Savage, Testimony Before the Subcommittee on Energy and Mineral Resources, June 23, 2005.
§ Platt’s Oil Guide to Specifications, 1999.
¶ NYMEX, Exchange Rulebook, Light “Sweet” Crude Oil Futures Contract.
Source: Andrews, A.: “Oil Shale: History, Incentives, and Policy,” Specialist, Industrial Engineering and
Infrastructure Policy Resources, Science, and Industry Division, Congressional Research Service, the Library of
Congress, Washington, D.C., 2006.

with the inorganic aggregate, the nitrogen content is beneficial. If not removed, the arsenic
and iron in shale oil would poison and foul the supported catalysts used in hydrotreating.
Blending shale oil products with corresponding crude oil products, using shale oil frac-
tions obtained from a very mildly hydrogen treated shale oil, yields kerosene and diesel
fuel of satisfactory properties. Hydroprocessing shale oil products, either alone or in a
blend with the corresponding crude oil fractions, is therefore necessary. The severity of the
hydroprocessing has to be adjusted according to the particular property of the feed and the
required level of the stability of the product.
Gasoline from shale oil usually contains a high percentage of aromatic and naphthenic
compounds that are not affected by the various treatment processes. The olefin content,
although reduced in most cases by refining processes, will still remain significant. It is
assumed that diolefins and the higher unsaturated constituents will be removed from the
gasoline product by appropriate treatment processes. The same should be true, although to
a lesser extent, for nitrogen- and sulfur-containing constituents.
The sulfur content of raw shale oil gasoline may be rather high due to the high sulfur
content of the shale oil itself and the frequently even distribution of the sulfur compounds
in the various shale oil fractions. Not only the concentration but also the type of the sulfur
compounds is of an importance when studying their effect on the gum-formation tendency
of the gasoline containing them.
Sulfides (R-S-R), disulfides (R-S-S-R), and mercaptans (R-SH) are, among the other
sulfur compounds, the major contributors to the gum formation in gasoline. Sweetening
processes for converting mercaptans to disulfides should therefore not be used for shale oil
gasoline; sulfur extraction processes are preferred.
Catalytic hydrodesulfurization processes are not a good solution for the removal of
sulfur constituents from gasoline when high proportions of unsaturated constituents are
present. A significant amount of the hydrogen would be used for hydrogenation of the
unsaturated components. However, when hydrogenation of the unsaturated hydrocarbons
is desirable, catalytic hydrogenation processes would be effective.
Gasoline derived from shale oil contains varying amounts of oxygen compounds. The
presence of oxygen in a product, in which free radicals form easily, is a cause for con-
cern. Free hydroxy radicals are generated and the polymerization chain reaction is quickly
brought to its propagation stage. Unless effective means are provided for the termination
of the polymerization process, the propagation stage may well lead to an uncontrollable
generation of oxygen bearing free radicals leading to gum and other polymeric products.