process yields diesel-like fuel from coal, peat, biomass
TRANSCRIPT
TECHNOLOGY
Process Yields Diesel-Like Fuel From Coal, Peat, Biomass
Chevron researcher using mild oxidation at 50 °C with nitric acid achieves solubilization in alcohol; product burns cleaner than conventional diesel fuel
Oxidatively solubilized coal (OSC) in alcohol has all the characteristics of diesel fuel, says J. Gustav Schulz, in summarizing his research findings over the past few years at the research labs of Gulf Oil, now part of Chevron, in Pittsburgh. Further, the younger the coal, the easier it is to solubilize because of its relatively high aliphatic content. For that reason, peat is an even better feedstock, Schulz told last mon th ' s ACHEMA exhibition and congress held in Frankfurt, West Germany (C&EN, June 24, page 31).
Moreover, where large amounts of biomass are available, that, too, can be processed into diesel fuel, the Chevron senior research associate says. For example, bagasse, left over after sugar is extracted from sugarcane, can be used equally well. This is of potential economic importance to sugar-producing countries that now import their oil products.
In Schulz's process, coal, pulverized to a mesh size of about 10, is slurried with an equal weight of water and heated to about 50 °C. Concentrated nitric acid is added, care being taken that the heat generated is dissipated to prevent the slurry from becoming too hot. When the reaction is completed, excess acid is removed by a simple additional step, details of which Schulz declines to reveal.
Earlier experiments failed, Schulz explains, because the reaction was
carried out at temperatures well over 100 °C. Above 75 °C, decarboxylation occurs, yielding an insoluble product similar in appearance to coal itself. Consequently, it was thought that no reaction had taken place.
Under milder conditions, nitric acid cleaves the large coal molecules at their aliphatic sites, breaking them into units of molecular weight averaging 1000. Some nitration also occurs on the aromatic rings. Most important, free carbox-yl groups, essential for solubility in alcohol, remain intact.
Following the reaction, the coal slurry is dried and extracted with alcohol. Filtration removes mineral ash and partially oxidized coal, which is recycled. Nitrogen oxides evolved during the process may be converted back to nitric acid for reuse.
Solutions of peat-derived OSC in methanol, containing up to 50% by weight of product, closely match conventional diesel fuel in viscosity, lubricity, and cetane value. When burned in a diesel engine, the exhaust gas is essentially smoke-free and low in nitrogen oxides, Schulz claims.
Any improvement in the environmental impact of the fuel should be welcomed by makers and operators of diesel-powered heavy vehicles. These vehicles are coming under increasing public scrutiny because of their noise level and the amount of particulates they emit. In the European Economic Community, for instance, stricter noise standards are due to come into effect in 1990, and in the U.S. an amendment to the Clean Air Act under consideration in Congress would require substantial reductions in diesel particulate emissions by the mid-1990s.
The European action has prompted
Sch ulz: econ omically a t tractive
the setting up of the Quiet Heavy Vehicle 90 project in the U.K. in which makers of diesel engines, components, and vehicles are collaborating in designing engines and vehicles to meet the new noise criteria. Coordinated by Britain's Transport & Road Research Laboratory, QHV 90, as the project is referred to, is the only national program of its kind in Europe on such a scale.
Contributing to noise and smoke is the quality of the diesel fuel itself. This has been worsening because of changes in the catalytic cracking procedures used by refiners. The changes favor output of lighter fractions to meet the greater demand for aviation-grade gasoline. As a result, heavier grades of oil are being used to make diesel fuel. But that change has brought about a reduction of the cetane value (from around the mid-50s to the mid-40s level), together with a trend toward increased specific gravity and viscosity and higher aromatics content.
July 1, 1985 C&EN 23
Technology
Such fuel tends to make a vehicle run more noisily and produce more smoke unless the engine is precisely and frequently tuned.
Alcohol solutions of OSC derived from some varieties of coal haven't performed so well as when the OSC used is made from peat, Schulz admits, mainly because of their relatively high viscosity and poor lubricity. These shortcomings might be overcome, he suggests, by modifying the process parameters so that the molecular weight spectrum of the product would impart the desired viscosity to the solution. Lack of lubricity could be corrected by adding appropriate lubricants.
"Alcohols," Schulz points out, "are an economically attractive alternate to petroleum-derived motor fuels. Their use in diesel engines is particularly attractive in view of the higher energy efficiencies [of these engines] compared to combustion in spark engines."
But to function satisfactorily in a diesel engine, alcohols need an ignition promoter, usually an alkyl nitrate, which adds to their cost. OSC, with its alkyl components, functions as an ignition promoter as well as being a fuel in its own right. And its cost is about half that of methanol, Schulz observes.
"Coal's excellent ignitability, a prerequisite for diesel fuels, resides in its highly reactive aliphatic components," he notes. Others, including Rudolf Diesel himself, have looked at powdered coal to run diesel engines. Some have tried a slurry of coal in water.
"Presence of ash, however, a severe detriment to engine life, remains the obstacle to any practical use of coal as fuel for internal combustion engines," Schulz observes. "Solids handling also presents a major inconvenience. Liquefaction is the obvious solution to these problems. It requires dissection of large coal [molecular] structures into much smaller fragments to provide the basis for liquidity. This also allows removal of solid contaminants."
Some argue that a development program centered on coal as a diesel fuel source might not be warranted, given the weak price and abundance of oil. But this might not always be so. Indeed, Helga
Steeg, executive director of the International Energy Agency, cautions that industrial countries should not be lulled into a sense of false security by current abundant energy supplies. IEA foresees sustained economic growth in the last decade of the century and a decline in oil production in the industrialized world.
During his five decades of scientific research, Paul J. Flory has played a central role in laying the foundations of modern polymer science. On the occasion of his 75th birthday, which he celebrated June 19, more than 100 of his colleagues gathered at Stanford University for an international symposium that paid tribute to Flory and his accom-
Additionally, OSC could have significance for countries that have sizable peat deposits. Schulz also suggests that Brazil, where sugar-derived ethanol is being used to run automobiles, could convert its bagasse waste into OSC for blending with the alcohol and use as diesel fuel. •
plishments. Entitled "Foundations and Challenges of Polymer Science," the symposium brought together a broad range of polymer scientists. Many of them began their careers as graduate students or postdoctoral fellows under Flory, and many others had collaborated with Flory at one time or another. Among the many dist inguished participants were Nobel Laureates Herman F. Mark and Henry Taube.
Flory, who received the Nobel Prize in Chemistry in 1974, is an emeritus professor of chemistry at Stanford, where he maintains an active research program. The symposium was sponsored by Stanford and IBM, with which Flory has long maintained a consulting relationship. The symposium was organized by James E. Mark, chemistry professor at the University of Cincinnati, and Leo Mandelkern, chemistry professor at Florida State University.
The symposium's scientific pre-
Flory with his wife, Emily (left), and holding first edition of his collected works (below), presented to him by FSU's Mandelkern
Symposium celebrates Flory's 75th birthday
24 July 1, 1985 C&EN