Fuels From Unconventional Fossil Resources

For the most part, unconventional fossil fuel resources are utilized for the production of conventional fuel products including methane; residual or heating oil; diesel oil, also known as distillate fuel; kerosene; and gasoline. These are defined in subsequent sections. Unconventional fossil fuel resources may also be used to produce unconventional refined fuel products, including syngas, DME (di-methyl ether) methanol, ethanol, and hydrogen.

In the case heavy oil and tar sand, which are essentially forms of petroleum, the refining process is fairly straightforward, though more involved than is the case with light crudes because the initial chemical composition of the feedstock is further from that of the final product. The same basic cracking and hydrotreating procedures are utilized as in a light crude oil refinery, and the design of the refinery is similar. In the case of oil shale, the intermediate extracted from the rock is an oily substance named kerogen which is somewhat further removed from crude petroleum. Consequently, transforming kerogen into diesel, kerosene, and gasoline is best considered as a synfuel process somewhat akin to producing petroleum product analogs from coal or natural gas.

Methane may be more or less directly extracted from deposits of shale gas, tight gas, coal bed methane, the unconventional natural gas resources. Methane hydrates are bit different, involving some minimal processing to convert the methane hydrate or clathrate into pure methane. The recovered methane may be used as is, or may serve as a feedstock for the production of various, synfuels, alcohols, ethers, and complex petrochemicals.

Peat, our final unconventional fossil fuel resource, is partially decomposed plant biomass in the process of evolving into lignite or brown coal. Peat forms over a period of hundreds or thousands of years, and is much closer in chemical composition to forest or agricultural wastes, containing as it does intact cellulose, hemicellulose, and lignin molecules. Peat, which is assumed by the uninformed to reside in a handful of bogs located somewhere in Northern Europe, is, in actuality, one of the more abundant fossil fuel resources, and is found in tropical and temperate zone settings as well as in arctic and sub-arctic regions. Peat’s energy density is low, however, and its moisture content is generally extremely high, and, as is the case with biomass, complex processing procedures are required to produce refined fuels. Today refined fuels are produced from peat only on a pilot basis, though we believe this could change in the future. The advantage of peat is that vast accumulations occur close to the surface of the ground in very restricted areas, making it one of the easiest feedstocks to harvest.

Unconventional Processes for Producing Conventional Fuels

Hydrocarbons, for the most part, are fungible, in other words, any hydrocarbon may be converted into any other. Thus coal and natural gas feedstocks may be converted into methanol, ethanol, DME, distillate fuel, kerosene, gasoline, hydrogen, and various petrochemicals. Incidentally, the same holds true for biomass. Biomass also may be converted into any of these same products, though the precise conversion procedures are somewhat different for biomass as compared to the fossil fuel sources.

Currently, the economics for converting coal, natural gas, and possibly oil shale into such products as distillate fuel, kerosene, gasoline, methanol, and ethanol appear to be generally better than is the case for biomass as a feedstock for the same. Thus the current push to increase the production of ethanol from grains and agricultural wastes may not represent the cheapest manufacturing strategy in the short term or mid term. Coal is probably the preferred feedstock for ethanol on purely economic grounds, though the environmental case for coal is much weaker.

Natural gas is another matter. The world appears to be approaching a peak in the production of conventional natural gas, and natural gas prices are rising even more steeply than petroleum prices. While it is still cheaper to produce methanol, distillate fuel, and gasoline from natural gas than from coal, and certainly from biomass, this may not hold true in the future. Unless vast reserves of unconventional natural gas are brought into production, natural gas will begin to decline in importance as a feedstock.

The Syngas Cornerstone

Most processes for converting coal and natural gas, or biomass for that matter, into liquid fuels involve the initial production of synthesis gas or syngas. Syngas is a mixture of hydrogen and carbon monoxide, generally in a ratio of two atoms of H2 for every one atom of CO. Syngas may be converted into ethanol, methanol, DME, petroleum analogs (synthetic diesel, kerosene, gasoline), and hydrogen by some fairly simple procedures, most of which involve streaming the syngas over specified catalysts under conditions of heat and pressure.

Two of these procedures are of special interest, the Fischer-Tropsch process and the Mobil process. The Fischer-Tropsch process, which normally employs iron-based catalysts, was developed back in the nineteen twenties, and was extensively used by the Germans in World War II to produce diesel and other petroleum analogs for the armed forces after access to Russian and Middle Eastern oil was cut off. Later South Africa used the process to convert coal into petroleum products when faced with an oil embargo.

The process tends to favor the heavier distillates, but can be adjusted to yield higher proportions of kerosene and gasoline. Fischer-Tropsch can utilize natural gas, coal, or biomass for that matter, but the economics are normally best when natural gas is employed because the latter may easily be converted to syngas by steam reforming, that is, mixing methane with superheated steam.

The Mobil process is also catalytic but involves the initial transformation of methane into methanol and then a further catalytic reaction involving the methane. The Mobil process results in approximately 85% of the methane being converted into gasoline, an extraordinarily high conversion efficiency.

The Mobil process has been far less utilized than Fischer Tropsch, and currently only a single Mobile process plant is in operation in New Zealand.

Conventionalizing the Unconventional

What we have discussed in the preceding sections comes largely under the rubric of synfuels, products that are analogs of petroleum fractions, but are derived from other fossil fuel sources. Synfuels, while subject to strong government sponsorship during the oil crises of the nineteen seventies, are only now arousing renewed interest and are just beginning to find a market. China has by the most active synfuels programs underway, largely because its petroleum resources are so limited relative to its needs, and an early success in that great nation could provide tremendous stimulus toward the revival of the synfuels industry. In the meantime we expect development to go forward slowly but steadily here in the United States, particularly in coal rich states such as Montana and Pennsylvania. But because of the extreme expense involved in building production facilities capable of having an impact on world energy markets, the synfuel business must make a convincing case for further funding both to state and federal governments and to private investors, and must succeed in distancing itself from the well publicized failures and false starts of the Carter Administration—a topic discussed elsewhere in this Website. If the synfuel industry cannot argue its own case convincingly in the marketplace and in the political arena, if will have to await further oil shocks and further economic turmoil before the necessity of synfuel needs no argument.