Page 208 - Synthetic Fuels Handbook

194 CHAPTER SIX

However, no similar “dissolution” approach to oil shale conversion is known, because
the chemistry of kerogen is markedly different from the chemistry of coal.
As a first step in developing a direct route, some attempts were made in the 1970s to
isolate kerogen from the oil shale by dissolving away the minerals. Acid treatment to dis-
solve the mineral carbonate followed by fluoride treatment to remove the aluminosilicate
minerals might be considered. Such a scheme will only work if the kerogen is not chemi-
cally bonded to the inorganic matrix. However, if the kerogen is bonded to the inorganic
matrix, the bonding arrangement must be defined for the scheme to be successful.
Opportunities for circumventing the arsenic problem include development of an in-
reactor process for regenerating the catalyst, collecting arsenic in a safe form away from
the catalyst, and development of a catalyst or process where the removed arsenic exits the
reactor in the gas or liquid phase to be scrubbed and confined elsewhere.
Shale oil produced by both above-ground and in situ techniques in the 1970s and 1980s
were rich in organic nitrogen. Nitrogen compounds are catalyst poisons in many common
refinery processes such as fluid catalytic cracking, hydrocracking, isomerization, naphtha
reforming, and alkylation. The standard method for handling nitrogen poisoning is hydrode-
nitrogenation (HDN).
HDN is a well-established high-pressure technology using nickel molybdenum cata-
lysts. It can consume prodigious amounts of hydrogen, typically made by steam reforming
of natural gas, with carbon dioxide as a by-product.
Thus, after a decline of production since 1980 and the current scenarios that face a
petroleum-based economy, the perspectives for oil shale can be viewed with a moderately
positive outlook. This perspective is prompted by the rising demand for liquid fuels, the
rising demand for electricity, as well as the change of price relationships between oil shale
and conventional hydrocarbons.
Experience in Estonia, Brazil, China, Israel, Australia, and Germany has already dem-
onstrated that fuels and a variety of other products can be produced from oil shale at
reasonable, if not competitive, cost. New technologies can raise efficiencies and reduce
air and water pollution to sustainable levels and if innovative approaches are applied to
waste remediation and carbon sequestration, oil shale technology take on a whole new
perspective.
In terms of innovative technologies, both conventional and in situ retorting processes
result in inefficiencies that reduce the volume and quality of the produced shale oil.
Depending on the efficiency of the process, a portion of the kerogen that does not yield
liquid is either deposited as coke on the host mineral matter, or is converted to hydrocarbon
gases. For the purpose of producing shale oil, the optimal process is one that minimizes the
regressive thermal and chemical reactions that form coke and hydrocarbon gases and maxi-
mizes the production of shale oil. Novel and advanced retorting and upgrading processes
seek to modify the processing chemistry to improve recovery and/or create high-value
by-products. Novel processes are being researched and tested in laboratory-scale environ-
ments. Some of these approaches include: lower heating temperatures; higher heating rates;
shorter residence time durations; introducing scavengers such as hydrogen (or hydrogen
transfer/donor agents); and introducing solvents (Baldwin, 2002).
Finally, the development of western oil shale resources will require water for plant
operations, supporting infrastructure, and the associated economic growth in the region.
While some oil shale technologies may require reduced process water requirements, stable
and secure sources of significant volumes of water may still be required for large-scale oil
shale development. The largest demands for water are expected to be for land reclamation
and to support the population and economic growth associated with oil shale activity.
Nevertheless, if a technology can be developed to economically recover oil from oil
shale, the potential is enormous. If the kerogen could be converted to oil, the quantities
would be far beyond all known conventional oil reserves. Unfortunately, the prospects for oil