Cerchar Hydrogenates Coal Tar Fraction to Get High Energy Fuels Waste Gas Recycle Hydrogen
« * — Make-Up Hydrogen
Fraction Heat Exchanger
TECHNOLOGY
Coal Holds Jet Fuel Raw Material Potential French develop process to make high energy jet fuels from tar fraction; success could aid world coal industry New high energy fuels have been made from a coal tar fraction high in polycyclic aromatics. The process, developed by France's Coal Research Center (Cerchar), turns out a fuel with a high density, high heat of combustion, low freezing point, and high hydrogen content. These, plus other properties, make it potentially better fuel for supersonic jet planes than those now in use, according to Dr. Maurice Letort, Cerchar's director of scientific and technical studies. Dr. Letort told the 33rd International Congress of Industrial Chemis56
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try, meeting in Bordeaux, France, that raw material for the process is available in large quantities. Also, it is almost constant in quality and can be processed easily to produce the new fuel at an economic price, he adds. Cerchar has already scaled up the process twice and is now running a semicommercial unit to produce the fuel in tonnage quantities. Fuel from Coal. Fuels have been made from coal for more than 30 years but have lost almost all their markets to petroleum-derived products since World War II. Not only has oil be-
come more plentiful and cheaper, and coal more expensive, but catalytic reforming has provided the aromatics usually in short supply in oil. Most gasoline-from-coal plants have now been shut down or converted to other uses. Coal producers around the world have come to accept this loss of their fuel market. But they have not given up hope of developing new markets through research. Thus Cerchar saw that the kerosine base of most current jet fuels would not be the best power source for faster
planes with prodigieus fuel consumption. A material was needed with a lower vapor pressure, higher thermal stability, higher energy per unit weight and per unit volume—in other words, a high energy fuel. It was on this basis, for example, that the alkyl borane Zip fuel program was launched in the U.S. But the boranes did not give as much improvement in performance as expected. Also, they were hard to make, cost too much, and caused secondary problems in use. As a result the field is still wide open. Under Air Force contracts, the search has, since Project Zip days, centered on cyclic hydrocarbons. Monsanto alone, for example, has considered more than 6000. Almost all the most promising are Decalin or bicyclohexyl derivatives. Only from Coal Tar. To make these molecules from crude oil is expensive, Dr. Letort points out. Further, they are only a small fraction of the crude and occur in highly variable amounts. The only sound way to make them, he adds, is to hydrogenate a raw material rich in polycyclic aromatics and poor in long chain paraffins—in other words, a coal tar made from high temperature coking. These coal tars are made up mostly of naphthalene, acenaphthene, and phenanthrene, which have no side chains, or of their derivatives with very short ( C H 3 or C 2 H 5 ) side chains. They contain very little oxygen, nitrogen, or sulfur. And, Dr. Letort adds, from a given coking plant, their chemical composition varies little with time. Since naphthalene itself (used in phthalic anhydride production) is already in short supply in much of Europe, Cerchar starts with a coal tar fraction with the naphthalene already removed. Typical boiling ranges for the methylnaphthalene cut and the phenanthrene cut are from 230° to 300° C. and from 300° to 360° C. These are the standard heavy oils and anthracene oils and are about 2 5 % of the total coal tar. Catalytic Hydrogenation. To avoid catalyst poisoning, Cerchar hydrogenates over sulfur-resistant catalysts, such as a mixture of tungsten and nickel sulfides on alumina, or molybdenum sulfide on activated carbon. Nickel on kieselguhr and Raney nickel also work but are easily poisoned or too expensive. The sulfur-resistant catalysts are well known in Europe for hydrorefining of lignite tars but have
never been used for this sort of hydrogenation, according to Dr. Letort. The hydrogenation works best at about 420° to 430° C , a partial pressure of hydrogen of 200 to 250 atm., and a 300% excess of hydrogen. Space velocity of the reactants ranges up to about 70 lb. per hr. per cu. ft. of catalyst. The reaction occurs in the vapor phase and is strongly exothermic, Dr. Letort says. Heat of reaction, 500 to 600 kcal. per kg., must be removed or diluted to control reaction temperature, so some of the excess hydrogen, unheated, is injected into various levels of the reactor to keep the temperature uniform. The coal tar fraction and some of the hydrogen, preheated and at the proper pressure, enter the top of the reactor. Reaction products go to a separator where the unreacted hydrogen is recovered and recycled. Next step is to separate the hydrogenate from the remaining gases and from an aqueous phase containing dissolved ammonia and hydrogen sulfide. Then, the hydrogenate goes to a stabilization column to eliminate dissolved gaseous hydrocarbons, and it is distilled to give the final product plus a light fraction made up mostly of cyclohexane and methylcyclohexane. The final product contains about 10% hydrocarbons not completely saturated, an amount that, Dr. Letort says, can be tolerated. By using higher hydrogen partial pressure, these can be saturated if necessary. Fuel Properties. Depending on the starting material, fuel made by this process has a specific gravity of 0.87 to 0.92, a hydrogen content of 12 to 13%, calorie content per unit weight of 10,000 to 10,200 cal. per gram, volumetric heat content of 8800 to 9300 cal. per c c , and freezing points well below — 60° C. In all of these starting materials, the combined properties are better than JP-4, JP-5, or JP-6, the jet fuels now in use by civil and military air operations. In other properties, too—thermal stability, vapor pressure, and flame luminosity— they compare well and are often better, Dr. Letort says. In France alone, some 200,000 tons of coal tar fractions suitable for this process are produced per year. Considering that the U.S. uses about 370,000 tons of jet fuel per year, the success of the Cerchar development would give the world's coal industry a much-needed shot in the arm.
New Concept May Yield Larger Space Launch Vehicles Precast propellant pieces encased at launch site could mean rockets 38 ft. in diameter, 150 ft. high Hercules Powder has come up with a new concept for building large solid propellant boosters' for space launch vehicles. Hercules' approach is to stack precast, pie-shaped pieces of propellant on top of a nozzle, then encase the whole structure in a filamentwound glass fiber case bonded by epoxy resins. The propellant pieces can be cast at a plant, then shipped to a launch site for assembly. With this scheme, single-case rockets of any size can be built using known materials and manufacturing techniques, Hercules says. Other concepts of large solid fuel rockets are limited to diameters of 14 ft. or less by restrictions imposed by transportation and heat treating facilities. Hercules demonstrated its new concept at the 16th Annual Meeting of the American Rocket Society in New York City. Hercules has worked up several possible designs. One of these calls for a motor 38 ft. in diameter and 150 ft. high. It contains 10 million lb. of propellant in 108 pieces. Thrust would be 20 million lb. for two minutes, Hercules estimates. The basic building blocks in Hercules' concept are slices that are about 12 ft. along the peripheral arc, 12 ft. long, and 9 ft. from arc to point. Hercules' isn't the only company with ideas for building large solid boosters. United Technology Corp., for example, prefers clustering of small segmented motors. UTC has already test fired its P-l, single-segment motor (250,000 lb. of thrust) and is preparing to test a two-segment unit that's designed to give about 500,000 lb. of thrust. UTC is also studying a fivesegment, 1 million lb. thrust motor. Aerojet-General and Grand Central Rocket are also working with segmented motors. Aerojet's 100-in., four-segment motor, which was fired last August, developed about 500,000 lb. of thrust for 87 sec. Grand Central is working with a 120-in. motor case. Thiokol, in addition to looking at segmented motors, has also worked up a concept centered around a single monolithic motor having a diameter of 28 ft. This would involve building the motor near the launch site. OCT. 2 3, 1961 C & E N
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