Coal liquids yield carbon black feedstock
IVIonsanto process uses steam dehydrogenation Dehydro tozene recycle to atkylalfon
Recycle ethylbenzene
Etliylbenzene
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Fuel gas
Steam
Recycle ethylfeenzene
Toluene
Styrene monomer
Condensate
Flux ell from ethylbenzene distillation Tar
New styrene process cuts annual costs 16% Monsanto has developed a more efficient process to make styrene that should reduce annual operating costs by $500,000, or about 16%, for producers who build new 500 million pound-a-year plants. Lummus Co. is already building such a plant for Forth Chemicals (owned by British Petroleum and Monsanto) at Baglan Bay, in Britain. The process uses standard technology to alkylate benzene with ethylene in the presence of an anhydrous complex. However, it introduces more efficient steam dehydrogenation of ethylbenzene to form styrene. Lummus Co.'s Charles C. King, manager, process sales, indicates that typical steam requirements in today's existing plants are about 6.6 pounds of steam per pound of styrene produced. In the new process, only 4.6 pounds of steam are required, which means a saving of 2 pounds of steam per pound of styrene. Setting the cost of steam at 50 cents per 1000 pounds, Mr. King calculates savings of 0.1 cent per pound or $500,000 for a 500 million pound-a-year plant. These savings, he explains, result from proprietary changes in the temperature, pressure, and geometry of the dehydrogenation reactor. These improvements allow increased conversion per pass of ethylbenzene, lower steam requirements for styrene distillation because of smaller ethylbenzene re-
cycle, greater generation of steam from waste heat recovery, and direct firing of selected reboilers. Incremental. The savings of $500,000 are an incremental step in reducing production costs of styrene. However, they should help keep established producers competitive if and when more oil companies move into styrene production with billion pounda-year plants (C&EN, Sept. 22, page 22). These savings are sizable, too, in relation to today's typical production costs. • Capital investment for a 500 million pound-a-year styrene plant, including alkylation and dehydrogenation units, runs about $13 million. • Raw materials requirements are 435 million pounds of benzene and 155 million pounds of ethylene to make 500 million pounds of styrene at 88% efficiency. Both cost 3 cents a pound; benzene totals $13.1 million and ethylene $4.6 million for a total of $17.8 million. • Operating costs for one year, including utilities, labor, catalyst, and chemicals, run about $3.2 million. For the first year's operations, then, raw material and operating costs add up to $21 million. If the 500 million pounds of styrene produced sell for an average of 7 cents a pound, sales would total $35 million. The difference of $14 million means a plant payout, before taxes, in one year.
Ashland Oil and Refining Co. has unveiled a process for making carbon black feedstock from 'the tar produced by low-temperature carbonization (LTC) of coal. LTC tar is a product of FMC's char oil energy development (COED) project, which aims at converting coal to synthetic crude oil, pipeline gas, and fuel char (C&EN, April 28, page 47). The COED process uses multiple-stage fluidized-bed pyrolysis with increasing stage temperatures to drive off volatile matter at controlled rates and temperatures. It converts a high percentage of the coal to gas and condensable oil products. So far the tarry liquid has not been competitive with crude oil. Research workers have tried many techniques to upgrade this LTC tar, and have produced a variety of useful products, but their processes have been too complex to be economically feasible. Now Ashland chemical engineers Harold N. Hicks, Donald C. Berkebile, and W. Sidney Green have developed procedures to convert LTC tar into carbon black feedstock. They say their procedures are not only technically practicable, but potentially profitable as well. In the Ashland process, the tar is first heated and blended with benzene to reduce viscosity, centrifuged to remove solids, and then azeotropically distilled to remove water. Next, the dry, solids-free tar is subjected to fixedbed catalytic hydrotreatment to remove hetero atoms—oxygen, nitrogen, and sulfur—which would otherwise reduce the yield of carbon black. The hydrotreated tar is then fractionated at 600° F. to produce an overhead cut and a bottoms fraction. This bottoms fraction can be used as carbon black feedstock without further processing. It produces a satisfactory grade of carbon black, but the yield is only about 80% of that of the standard petroleum feedstock, apparently because of incomplete removal of hetero atoms. To achieve the process goal—a bottoms material with 90% by weight carbon content— the Ashland trio gives this fraction a second hydrotreatment. According to Ashland's United Carbon division, performance of this second-pass tar in a pilot-scale carbon black reactor is practically identical to that of the standard feedstock. Also, rubber samples compounded with the LTC carbon black are substantially the same, in elasticity modulus, tensile strength, and abrasion resistance, as those made with carbon black from standard feedstock. SEPT. 29, 1969 C&EN 49
