TECHNOLOGY
Alkali Metals Upgrade Coal Chemicals NaK alloy and Na desulfurize benzene, BTX mixtures, and naphthalene from coking plants 137TH
ACS NATIONAL
MEETING
Industrial and Engineering Chemistry
Producers of coke oven benzene and other coal chemicals are lining up their sights to take another shot at their biggest competitor—the petroleum industry. Oil companies have the advantage at the moment—demand is high, their product is usually purer than that from coke plants. But two new processes presented at the Cleveland ACS meeting may tip the scales the other way. The two: • A sodium-potassium process to remove thiophene and carbon disulfide from coke oven benzene or benzenetoluene-xylene (BTX) mixtures. • A sodium process to desulfurize coke oven naphthalene. BTX Process. Some of the big steel producers already have the BTX problem fairly well under control with a combination hydrogenation-extraction process, Frank Vancheri of MSA Research told the Division of Industrial and Engineering Chemistry. But
there are many coke plants which do not process enough coal to be able to invest the kind of money needed for the hydrogenation-extraction processes, Mr. Vancheri points out. A potential answer: MSA Research's NaK-based process, now entering the pilot plant stage. The MSA approach should have the best chance for economic success in coking plants which don't put out enough benzene to make the combination process economically attractive, according to Mr. Vancheri and coworker Dr. Oscar Wright. Reason: Investment is low— less than a $25,000 addition to process up to 10,000 gallons a day; other costs —raw material, labor, and utilities—are 0.9 cent per gallon or less, depending on how the process fits in with the existing plant. The NaK process works this way: Acid-washed benzene and NaK (56% K) alloy are fed continuously to a reactor containing 1 to 2% NaK in benzene at reflux. Ratio of NaK added to thiophene in the feed is 1.5:1. Benzene is distilled continuously as the feed is added; holdup time is 15 minutes. Almost all the thiophene is destroyed; the distillate contains only
Batch Process for BTX Treatment
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about 1.5 p.p.m., down from an input level of about 260 p.p.m. There are a couple of other requirements as well, Mr. Vancheri points out. The benzene should be as dry as possible, since using NaK is an expensive way to remove water. The same goes for CSL>. Although NaK removes it, too, standard processing methods, such as distillation, take it out more cheaply. NaK is much better than either sodium or potassium alone, Mr. Vancheri adds. One reason: It is liquid, thus disperses more readily in the reaction mixture than do Na or K alone. So far, seven coal and petrochemical companies are interested in the MSA process, according to Mr. Vancheri. Next step: Build a demonstration plant, pin down process economics and product quality more closely.
137TH
ACS NATIONAL
MEETING
Gas and Fuel Chemistry
Desulfurize Naphthalene. Coke oven naphthalene poses many of the same problems as do benzene and BTX when it comes to desulfurization. Hydrogen ation is a possibility here, too, but only for the big producer who can afford the investment. With an eye out for potential consumers of sodium, Du Pont has come up with a continuous sodium treating process well suited to the needs of the small producer or user—10 million to 50 million pounds per year. Sodium has been used commercially in a few batch operations for a number of years, Dr. Donald A. Swalheim
Dispersed Sodium Rids\ Naphthalene of Sulfur Compounds Desulfurized Naphthalene
Heavier Reforming Feeds Possible Current steam-hydrocarbon reforming catalysts work with light liquids 137TH
Naphthalene
ACS
NATIONAL
MEETING
Gas and Fuel Chemistry
Naphthalene Recovery and Residue Separation
and C. J. Stapf, Jr., of Da Pont told the Division of Gas and Fuel Chemistry in a symposium on coal chemicals. But it had never been developed into a large-scale continuous operation. Such a process, Mr. Stapf says, has commercial importance for naphthalene users—such as producers of phthalic anhydride—as well as for naphthalene makers. The process is based on a fine particle sodium dispersion, since solid sodium doesn't have the needed surface area. Crude naphthalene, with a melting range 74° to 78° C , is the dispersing medium. The impurities, explains Mr. Stapf, act as very effective dispersing agents. Three major steps make up the process: dispersion, reaction, and recovery. In the first step, says Mr. Stapf, liquid sodium is dispersed in crude naphthalene to make a 50-50 mixture. A high-shear dispersion unit does the work, agitating the sodium-naphthalene mixture for five to 10 minutes before it is sent to a holding tank. The dispersion then feeds continuously into the main naphthalene feed stream which enters an evaporator (desulfurization reactor). Design of the evaporator provides an average product holdup time of three hours. The three streams—incoming feed, vaporized naphthalene, and side stream to the recovery evaporator—are adjusted to keep a 50r/r residue-507^ naphthalene mixture in the evaporator. Bottoms from this evapo-
rator go to a second, smaller, recovery evaporator. The second reactor operates on a semicontinuous basis, strips the remaining naphthalene from the 50-50 residue-naphthalene mix. It operates, explains Mr. Stapf, until the residue comes close to filling the vessel. The feed stream is then shut off and the vessel discharged. Residue, fluid at operating temperature, can be drained directly to a tank and sent to an incinerator. However, Mr. Stapf cautions that sodium in the residue should be destroyed before discharge from the evaporator if it is going to a slag pile or other area for disposal. This can be done by reacting it with steam to form NaOH. Dr. Swalheim and Mr. Stapf have worked out the preliminary costs for a 30 million pound-per-year naphthalene plant, figure capital investment for such a plant runs around $100,000. Using 0.5 pound of sodium per 100 pounds of naphthalene, the operating cost of the plant is about 0.37 cent per pound. This is based on desulfurizing 78° C. coke oven naphthalene from a sulfur level of 6000 p.p.m. to a level of 2000 p.p.m. However, says Mr. Stapf, increasing the amount of sodium to 2 pounds per 100 pounds of naphthalene will give an almost completely desulfurized product—less than 50 p.p.m. sulfur. The cost here, using the same facilities, would run about 0.68 cent per pound of desulfurized naphthalene.
The chemical industry in the United States and Europe depends heavily on catalytic steam-hydrocarbon reforming for producing ammonia synthesis gas, high purity hydrogen, and hydrogencarbon monoxide mixtures for chemical synthesis. The feed materials for the reforming process are invariably natural gas or propane. However, areas where these materials are in short supply—Europe, for examplemight find light liquids in the naphtha range more attractive. It's possible to use currently available reforming catalysts with such light liquids, J. C. Yarze and T. E. Lockerbie of M. W. Kellogg told the Division of Gas and Fuel Chemistry. Pilot plant tests with propane and n-heptane, Mr. Yarze says, show that light liquids follow reactions similar to those of conventional feedstocks. Complex Series. The conversion occurs through a complex series of consecutive and competing reactions, Mr. Yarze explains. A series of steps involving cracking, dehydrogenation, and polymerization results in converting feedstock molecules to carbon on the catalyst. Competing against this is a steam reaction which removes carbon deposits from the catalyst. Products from both of these reactions, along with steam, join in a side reaction—the water gas shift. In another side reaction, some of the methane produced is reformed to original feedstock. Pilot plant tests also show that steam-carbon ratio (moles of steam per feedstock carbon atom) increases with increasing molecular weight of the feedstock, according to Mr. Yarze. This ratio is important, he says, since too little steam makes the reformer inoperable because of carbon deposits. However, too excessive a ratio results in high manufacturing costs. Mr. Yarze finds that a minimum ratio of 1.0 is needed for a feedstock with a molecular weight of 10, whereas it's 3.0 for a molecular weight of 100. APRIL
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